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Hougland, James L. "Ghrelin octanoylation by ghrelin O-acyltransferase: Unique protein biochemistry underlying metabolic signaling." Biochemical Society Transactions 47, no. 1 (2019): 169–78. http://dx.doi.org/10.1042/bst20180436.
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Abstract Ghrelin is a small peptide hormone that requires a unique post-translational modification, serine octanoylation, to bind and activate the GHS-R1a receptor. Ghrelin signaling is implicated in a variety of neurological and physiological processes, but is most well known for its roles in controlling hunger and metabolic regulation. Ghrelin octanoylation is catalyzed by ghrelin O-acyltransferase (GOAT), a member of the membrane-bound O-acyltransferase (MBOAT) enzyme family. From the status of ghrelin as the only substrate for GOAT in the human genome to the source and requirement for the octanoyl acyl donor, the ghrelin–GOAT system is defined by multiple unique aspects within both protein biochemistry and endocrinology. In this review, we examine recent advances in our understanding of the interactions and mechanisms leading to ghrelin modification by GOAT, discuss the potential sources for the octanoyl acyl donor required for ghrelin's activation, and summarize the current landscape of molecules targeting ghrelin octanoylation through GOAT inhibition.
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Holliday, Nicholas D., Birgitte Holst, Elena A. Rodionova, Thue W. Schwartz, and Helen M. Cox. "Importance of Constitutive Activity and Arrestin-Independent Mechanisms for Intracellular Trafficking of the Ghrelin Receptor." Molecular Endocrinology 21, no. 12 (2007): 3100–3112. http://dx.doi.org/10.1210/me.2007-0254.
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Abstract The ghrelin receptor (GhrelinR) and its related orphan GPR39 each display constitutive signaling, but only GhrelinRs undergo basal internalization. Here we investigate these differences by considering the roles of the C tail receptor domains for constitutive internalization and activity. Furthermore the interaction between phosphorylated receptors and β-arrestin adaptor proteins has been examined. Replacement of the FLAG-tagged GhrelinR C tail with the equivalent GPR39 domain (GhR-39 chimera) preserved Gq signaling. However in contrast to the GhrelinR, GhR-39 receptors exhibited no basal and substantially decreased agonist-induced internalization in transiently transfected HEK293 cells. Internalized GhrelinR and GhR-39 were predominantly localized to recycling compartments, identified with transferrin and the monomeric G proteins Rab5 and Rab11. Both the inverse agonist [d-Arg1, d-Phe5, d-Trp7,9, Leu11] substance P and a naturally occurring mutant GhrelinR (A204E) with eliminated constitutive activity inhibited basal GhrelinR internalization. Surprisingly, we found that noninternalizing GPR39 was highly phosphorylated and that basal and agonist-induced phosphorylation of the GhR-39 chimera was elevated compared with GhrelinRs. Moreover, basal GhrelinR endocytosis occurred without significant phosphorylation, and it was not prevented by cotransfection of a dominant-negative β-arrestin1(319–418) fragment or by expression in β-arrestin1/2 double-knockout mouse embryonic fibroblasts. In contrast, agonist-stimulated GhrelinRs recruited the clathrin adaptor green fluorescent protein-tagged β-arrestin2 to endosomes, coincident with increased receptor phosphorylation. Thus, GhrelinR internalization to recycling compartments depends on C-terminal motifs and constitutive activity, but the high levels of GPR39 phosphorylation, and of the GhR-39 chimera, are not sufficient to drive endocytosis. In addition, basal GhrelinR internalization occurs independently of β-arrestins.
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Holst, Birgitte, Erik Brandt, Anders Bach, Anders Heding, and Thue W. Schwartz. "Nonpeptide and Peptide Growth Hormone Secretagogues Act Both as Ghrelin Receptor Agonist and as Positive or Negative Allosteric Modulators of Ghrelin Signaling." Molecular Endocrinology 19, no. 9 (2005): 2400–2411. http://dx.doi.org/10.1210/me.2005-0059.
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Abstract Two nonpeptide (L692,429 and MK-677) and two peptide [GH-releasing peptide (GHRP)-6 and ghrelin] agonists were compared in binding and in signal transduction assays: calcium mobilization, inositol phosphate turnover, cAMP-responsive element (CRE), and serum-responsive element (SRE) controlled transcription, as well as arrestin mobilization. MK-677 acted as a simple agonist having an affinity of 6.5 nm and activated all signal transduction systems with similar high potency (0.2–1.4 nm). L-692,429 also displayed a very similar potency in all signaling assays (25–60 nm) but competed with a 1000-fold lower apparent affinity for ghrelin binding and surprisingly acted as a positive allosteric receptor modulator by increasing ghrelin’s potency 4- to 10-fold. In contrast, the potency of GHRP-6 varied 600-fold (0.1–61 nm) depending on the signal transduction assay, and it acted as a negative allosteric modulator of ghrelin signaling. Unexpectedly, the maximal signaling efficacy for ghrelin was increased above what was observed with the hormone itself during coadministration with the nonendogenous agonists. It is concluded that agonists for the ghrelin receptor vary both in respect of their intrinsic agonist properties and in their ability to modulate ghrelin signaling. A receptor model is presented wherein ghrelin normally only activates one receptor subunit in a dimer and where the smaller nonendogenous agonists bind in the other subunit to act both as coagonists and as either neutral (MK-677), positive (L-692,429), or negative (GHRP-6) modulators of ghrelin function. It is suggested that an optimal drug candidate could be an agonist that also is a positive modulator of ghrelin signaling.
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Heldsinger, Andrea, Gintautas Grabauskas, Xiaoyin Wu, et al. "Ghrelin Induces Leptin Resistance by Activation of Suppressor of Cytokine Signaling 3 Expression in Male Rats: Implications in Satiety Regulation." Endocrinology 155, no. 10 (2014): 3956–69. http://dx.doi.org/10.1210/en.2013-2095.
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Abstract The anorexigenic adipocyte-derived hormone leptin and the orexigenic hormone ghrelin act in opposition to regulate feeding behavior via the vagal afferent pathways. The mechanisms by which ghrelin exerts its inhibitory effects on leptin are unknown. We hypothesized that ghrelin activates the exchange protein activated by cAMP (Epac), inducing increased SOCS3 expression, which negatively affects leptin signal transduction and neuronal firing in nodose ganglia (NG) neurons. We showed that 91 ± 3% of leptin receptor (LRb) –bearing neurons contained ghrelin receptors (GHS-R1a) and that ghrelin significantly inhibited leptin-stimulated STAT3 phosphorylation in rat NG neurons. Studies of the signaling cascades used by ghrelin showed that ghrelin caused a significant increase in Epac and suppressor of cytokine signaling 3 (SOCS3) expression in cultured rat NG neurons. Transient transfection of cultured NG neurons to silence SOCS3 and Epac genes reversed the inhibitory effects of ghrelin on leptin-stimulated STAT3 phosphorylation. Patch-clamp studies and recordings of single neuronal discharges of vagal primary afferent neurons showed that ghrelin markedly inhibited leptin-stimulated neuronal firing, an action abolished by silencing SOCS3 expression in NG. Plasma ghrelin levels increased significantly during fasting. This was accompanied by enhanced SOCS3 expression in the NG and prevented by treatment with a ghrelin antagonist. Feeding studies showed that silencing SOCS3 expression in the NG reduced food intake evoked by endogenous leptin. We conclude that ghrelin exerts its inhibitory effects on leptin-stimulated neuronal firing by increasing SOCS3 expression. The SOCS3 signaling pathway plays a pivotal role in ghrelin's inhibitory effect on STAT3 phosphorylation, neuronal firing, and feeding behavior.
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Wu, Chia-Shan, Jiyeon Noh, Ellie Tuchaai, et al. "SUPPRESSION OF GHRELIN SIGNALING EXACERBATES ULCERATIVE COLITIS IN OLDER MICE." Innovation in Aging 3, Supplement_1 (2019): S87. http://dx.doi.org/10.1093/geroni/igz038.334.
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Abstract The aging process is characterized by increased chronic low-grade inflammation, aka inflamm-aging, which offend is accompanied by ‘leaky gut’ syndrome. Inflamm-aging is a highly significant risk factor for both morbidity and mortality in the older adult population (>65 years of age). In addition, there is a growing prevalence of inflammatory bowel disease (IBD), a chronic inflammatory condition of the gastrointestinal tract in the older adult population. The pathogenesis of late-onset IBD is suggested to be more complex compared with younger IBD patients; the causes determining the age of IBD onset remain unexplained. Ghrelin is a 28-amino-acid peptide hormone mainly produced by X/A-like cells of the stomach, with well-characterized functions in growth hormone secretion, food intake, adiposity and insulin resistance. Ghrelin’s biological relevant receptor is Growth Hormone Secretagogue Receptor (GHS-R). Ghrelin and ghrelin mimetics have been considered viable candidates for treating cachexia, sarcopenia, and gastrointestinal disorders. As expected, we observed that the expression of tight junction proteins in colon mucosal layer decreases with age. When challenged with dextran sulfate sodium (DSS) to induce experimental ulcerative colitis, 18-months old male C57BL/6 mice exhibited exacerbated disease activity scores compared to young male mice (5-months), showing worsened pathology such as rectal bleeding and difficulty in defecation. DSS-induced colitis was exacerbated in both ghrelin-deficient (Ghrl-/-) and ghrelin receptor-deficient (Ghsr-/-) mice. Together, these data suggest endogenous ghrelin signaling contributes to susceptibility to colitis, and ghrelin signaling pathway may present a novel target for prevention and treatment of leaky gut syndrome in aging.
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Lin, Tsung-Chieh, Yuan-Ming Yeh, Wen-Lang Fan, et al. "Ghrelin Upregulates Oncogenic Aurora A to Promote Renal Cell Carcinoma Invasion." Cancers 11, no. 3 (2019): 303. http://dx.doi.org/10.3390/cancers11030303.
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Ghrelin is a peptide hormone, originally identified from the stomach, that functions as an endogenous ligand of the growth hormone secretagogue receptor (GHSR) and promotes growth hormone (GH) release and food intake. Increasing reports point out ghrelin’s role in cancer progression. We previously characterized ghrelin’s prognostic significance in the clear cell subtype of renal cell carcinoma (ccRCC), and its pro-metastatic ability via Snail-dependent cell migration. However, ghrelin’s activity in promoting cell invasion remains obscure. In this study, an Ingenuity Pathway Analysis (IPA)-based investigation of differentially expressed genes in Cancer Cell Line Encyclopedia (CCLE) dataset indicated the potential association of Aurora A with ghrelin in ccRCC metastasis. In addition, a significant correlation between ghrelin and Aurora A expression level in 15 ccRCC cell line was confirmed by variant probes. ccRCC patients with high ghrelin and Aurora A status were clinically associated with poor outcome. We further observed that ghrelin upregulated Aurora A at the protein and RNA levels and that ghrelin-induced ccRCC in vitro invasion and in vivo metastasis occurred in an Aurora A-dependent manner. Furthermore, MMP1, 2, 9 and 10 expressions are associated with poor outcome. In particular, MMP10 is significantly upregulated and required for the ghrelin-Aurora A axis to promote ccRCC invasion. The results of this study indicated a novel signaling mechanism in ccRCC metastasis.
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Madison, Lisa D., Jarrad M. Scarlett, Peter Levasseur, et al. "Prostacyclin signaling regulates circulating ghrelin during acute inflammation." Journal of Endocrinology 196, no. 2 (2007): 263–73. http://dx.doi.org/10.1677/joe-07-0478.
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Ghrelin is an octanoylated 28 amino acid peptide predominantly secreted by the stomach, and has potent stimulatory effects on appetite. Several laboratories, including our own, have demonstrated that ghrelin levels fall in states of acute inflammation brought about by injection of bacterial lipopolysaccharide (LPS). We now demonstrate that the decrease in circulating ghrelin is not due to a decrease in ghrelin gene expression, but is instead likely to be due to an acute decrease in ghrelin secretion. Furthermore, we have found that the change in circulating ghrelin during acute inflammation required a prostaglandin second messenger, but did not require the synthesis of nitric oxide. Interestingly, i.v. injection of prostaglandin E2 failed to decrease circulating ghrelin levels, whereas prostacyclin decreased circulating ghrelin to a similar extent as did LPS. We also provide anatomical evidence for the mechanism of the regulation of ghrelin by inflammation. We demonstrate that the type 1 interleukin-1β (IL-1β) receptor is expressed within the gastric mucosa, but is not expressed by ghrelin cells. The prostacyclin receptor was also expressed in the gastric mucosa, and the majority of ghrelin-producing cells were found to co-express this receptor. Mice with genetic deletion of the type 1 IL-1 receptor do not suppress circulating ghrelin levels with LPS administration. Collectively, these data support a model in which the mechanism of inflammation induced decreases in ghrelin are due to the action of IL-1β on cells within the gastric mucosa that in turn produce prostacyclin as a second messenger. These data provide further support for the potential role of ghrelin as a therapeutic agent in acute and chronic inflammatory diseases.
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Xu, Geyang, Yin Li, Wenjiao An, et al. "Gastric Mammalian Target of Rapamycin Signaling Regulates Ghrelin Production and Food Intake." Endocrinology 150, no. 8 (2009): 3637–44. http://dx.doi.org/10.1210/en.2009-0372.
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Ghrelin, a gastric hormone, provides a hunger signal to the central nervous system to stimulate food intake. Mammalian target of rapamycin (mTOR) is an intracellular fuel sensor critical for cellular energy homeostasis. Here we showed the reciprocal relationship of gastric mTOR signaling and ghrelin during changes in energy status. mTOR activity was down-regulated, whereas gastric preproghrelin and circulating ghrelin were increased by fasting. In db/db mice, gastric mTOR signaling was enhanced, whereas gastric preproghrelin and circulating ghrelin were decreased. Inhibition of the gastric mTOR signaling by rapamycin stimulated the expression of gastric preproghrelin and ghrelin mRNA and increased plasma ghrelin in both wild-type and db/db mice. Activation of the gastric mTOR signaling by l-leucine decreased the expression of gastric preproghrelin and the level of plasma ghrelin. Overexpression of mTOR attenuated ghrelin promoter activity, whereas inhibition of mTOR activity by overexpression of TSC1 or TSC2 increased its activity. Ghrelin receptor antagonist d-Lys-3-GH-releasing peptide-6 abolished the rapamycin-induced increment in food intake despite that plasma ghrelin remained elevated. mTOR is therefore a gastric fuel sensor whose activity is linked to the regulation of energy intake through ghrelin.
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Suzuki, Hajime, Akihiro Asakawa, Namiko Kawamura, Takakazu Yagi, and Akio Inui. "Hesperidin Potentiates Ghrelin Signaling." Recent Patents on Food, Nutrition & Agriculture 6, no. 1 (2014): 60–63. http://dx.doi.org/10.2174/2212798406666140825120623.
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Gluck, Elizabeth F., Natalie Stephens, and Steven J. Swoap. "Peripheral ghrelin deepens torpor bouts in mice through the arcuate nucleus neuropeptide Y signaling pathway." American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 291, no. 5 (2006): R1303—R1309. http://dx.doi.org/10.1152/ajpregu.00232.2006.
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Many small mammals have the ability to enter torpor, characterized by a controlled drop in body temperature (Tb). We hypothesized that ghrelin would modulate torpor bouts, because torpor is induced by fasting in mice coincident with elevated circulating ghrelin. Female National Institutes of Health (NIH) Swiss mice were implanted with a Tb telemeter and housed at an ambient temperature (Ta) of 18°C. On fasting, all mice entered a bout of torpor (minimum Tb: 23.8 ± 2.0°C). Peripheral ghrelin administration (100 μg) during fasting significantly deepened the bout of torpor (Tb minimum: 19.4 ± 0.5°C). When the arcuate nucleus (ARC) of the hypothalamus, a ghrelin receptor-rich region of the brain, was chemically ablated with monosodium glutamate (MSG), fasted mice failed to enter torpor (minimum Tb = 31.6 ± 0.6°C). Furthermore, ghrelin administration had no effect on the Tb minimum of ARC-ablated mice (31.8 ± 0.8°C). Two major pathways that regulate food intake reside in the ARC, the anorexigenic α-melanocyte stimulating hormone (α-MSH) pathway and the orexigenic neuropeptide Y (NPY) signaling pathway. Both Ay mice, which have the α-MSH pathway blocked, and Npy −/− mice exhibited shallow, aborted torpor bouts in response to fasting (Tb minimum: 29.1 ± 0.6°C and 29.9 ± 1.2°C, respectively). Ghrelin deepened torpor in Ay mice (Tb minimum: 22.8 ± 1.3°C), but had no effect in Npy −/− mice (Tb minimum: 29.5 ± 0.8°C). Collectively, these data suggest that ghrelin's actions on torpor are mediated via NPY neurons within the ARC.
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Egecioglu, Emil, Mikael Bjursell, Anna Ljungberg, et al. "Growth hormone receptor deficiency results in blunted ghrelin feeding response, obesity, and hypolipidemia in mice." American Journal of Physiology-Endocrinology and Metabolism 290, no. 2 (2006): E317—E325. http://dx.doi.org/10.1152/ajpendo.00181.2005.
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We have previously shown that growth hormone (GH) overexpression in the brain increased food intake, accompanied with increased hypothalamic agouti-related protein (AgRP) expression. Ghrelin, which stimulates both appetite and GH secretion, was injected intracerebroventricularly to GHR−/− and littermate control (+/+) mice to determine whether ghrelin's acute effects on appetite are dependent on GHR signaling. GHR−/− mice were also analyzed with respect to serum levels of lipoproteins, apolipoprotein (apo)B, leptin, glucose, and insulin as well as body composition. Central injection of ghrelin into the third dorsal ventricle increased food consumption in +/+ mice, whereas no change was observed in GHR−/− mice. After ghrelin injection, AgRP mRNA expression in the hypothalamus was higher in +/+ littermates than in GHR−/− mice, indicating a possible importance of AgRP in the GHR-mediated effect of ghrelin. Compared with controls, GHR−/− mice had increased food intake, leptin levels, and total and intra-abdominal fat mass per body weight and deceased lean mass. Moreover, serum levels of triglycerides, LDL and HDL cholesterol, and apoB, as well as glucose and insulin levels were lower in the GHR−/− mice. In summary, ghrelin's acute central action to increase food intake requires functionally intact GHR signaling. Long-term GHR deficiency in mice is associated with high plasma leptin levels, obesity, and increased food intake but a marked decrease in all lipoprotein fractions.
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Hosoda, Hiroshi. "Effect of Ghrelin on the Cardiovascular System." Biology 11, no. 8 (2022): 1190. http://dx.doi.org/10.3390/biology11081190.
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Ghrelin, an n-octanoyl-modified 28-amino-acid-peptide, was first discovered in the human and rat stomach as an endogenous ligand for the growth hormone secretagogue receptor (GHS-R). Ghrelin-GHS-R1a signaling regulates feeding behavior and energy balance, promotes vascular activity and angiogenesis, improves arrhythmia and heart failure, and also protects against cardiovascular disease by suppressing cardiac remodeling after myocardial infarction. Ghrelin’s cardiovascular protective effects are mediated by the suppression of sympathetic activity; activation of parasympathetic activity; alleviation of vascular endothelial dysfunction; and regulation of inflammation, apoptosis, and autophagy. The physiological functions of ghrelin should be clarified to determine its pharmacological potential as a cardiovascular medication.
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Liao, Pengzhi, Dan Yang, Duan Liu, and Yuehong Zheng. "GLP-1 and Ghrelin Attenuate High Glucose/High Lipid-Induced Apoptosis and Senescence of Human Microvascular Endothelial Cells." Cellular Physiology and Biochemistry 44, no. 5 (2017): 1842–55. http://dx.doi.org/10.1159/000485820.
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Background/Aims: GLP-1 and ghrelin are common appetite-regulating hormones. Both have multiple functions beyond metabolic regulation. However, the effects of GLP-1 and ghrelin on endothelial biology are not fully understood. Here, we investigate the roles of GLP-1 and ghrelin in microvascular endothelial apoptosis and senescence. Methods: Human microvascular endothelial cells (HMECs) were exposed to high glucose/high lipid (HG/HL) conditions and treated with GLP-1 or ghrelin. Cellular apoptosis, senescence, and mitochondrial function were measured. In addition, the MAPK and Akt signaling pathways were examined. Results: Both GLP-1 and ghrelin treatment decreased the number of TUNEL-positive cells and inhibited caspase-3 and PARP cleavage and mitochondrial dysfunction in HG/HL-exposed HMECs. GLP-1, but not ghrelin decreased the number of β-galactosidase (β-gal)-positive cells. Furthermore, GLP-1 and ghrelin inhibited ERK1/2, JNK1/2, and p38 signaling. GLP-1 suppressed Akt signaling, but ghrelin had no effect. Moreover, JNK1/2 and p38 inhibitors, but not ERK1/2 and Akt inhibitors, decreased the number of TUNEL-positive cells. Additionally, only the Akt inhibitor decreased the number of β-gal-positive cells. Conclusion: These results demonstrate that GLP-1 and ghrelin inhibit mitochondrial dysfunction under HG/HL conditions, and suppress endothelial apoptosis via inhibiting JNK1/2 and p38 signaling; moreover, GLP-1 alleviates endothelial senescence via inactivating Akt signaling.
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Sustkova-Fiserova, Magdalena, Chrysostomos Charalambous, Anna Khryakova, Alina Certilina, Marek Lapka, and Romana Šlamberová. "The Role of Ghrelin/GHS-R1A Signaling in Nonalcohol Drug Addictions." International Journal of Molecular Sciences 23, no. 2 (2022): 761. http://dx.doi.org/10.3390/ijms23020761.
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Drug addiction causes constant serious health, social, and economic burden within the human society. The current drug dependence pharmacotherapies, particularly relapse prevention, remain limited, unsatisfactory, unreliable for opioids and tobacco, and even symptomatic for stimulants and cannabinoids, thus, new more effective treatment strategies are researched. The antagonism of the growth hormone secretagogue receptor type A (GHS-R1A) has been recently proposed as a novel alcohol addiction treatment strategy, and it has been intensively studied in experimental models of other addictive drugs, such as nicotine, stimulants, opioids and cannabinoids. The role of ghrelin signaling in these drugs effects has also been investigated. The present review aims to provide a comprehensive overview of preclinical and clinical studies focused on ghrelin’s/GHS-R1A possible involvement in these nonalcohol addictive drugs reinforcing effects and addiction. Although the investigation is still in its early stage, majority of the existing reviewed experimental results from rodents with the addition of few human studies, that searched correlations between the genetic variations of the ghrelin signaling or the ghrelin blood content with the addictive drugs effects, have indicated the importance of the ghrelin’s/GHS-R1As involvement in the nonalcohol abused drugs pro-addictive effects. Further research is necessary to elucidate the exact involved mechanisms and to verify the future potential utilization and safety of the GHS-R1A antagonism use for these drug addiction therapies, particularly for reducing the risk of relapse.
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Rogers, Nicole H., Heidi Walsh, Oscar Alvarez-Garcia, et al. "Metabolic Benefit of Chronic Caloric Restriction and Activation of Hypothalamic AGRP/NPY Neurons in Male Mice Is Independent of Ghrelin." Endocrinology 157, no. 4 (2016): 1430–42. http://dx.doi.org/10.1210/en.2015-1745.
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Abstract Aging is associated with attenuated ghrelin signaling. During aging, chronic caloric restriction (CR) produces health benefits accompanied by enhanced ghrelin production. Ghrelin receptor (GH secretagogue receptor 1a) agonists administered to aging rodents and humans restore the young adult phenotype; therefore, we tested the hypothesis that the metabolic benefits of CR are mediated by endogenous ghrelin. Three month-old male mice lacking ghrelin (Ghrelin−/−) or ghrelin receptor (Ghsr−/−), and their wild-type (WT) littermates were randomly assigned to 2 groups: ad libitum (AL) fed and CR, where 40% food restriction was introduced gradually to allow Ghrelin−/− and Ghsr−/− mice to metabolically adapt and avoid severe hypoglycemia. Twelve months later, plasma ghrelin, metabolic parameters, ambulatory activity, hypothalamic and liver gene expression, as well as body composition were measured. CR increased plasma ghrelin and des-acyl ghrelin concentrations in WT and Ghsr−/− mice. CR of WT, Ghsr−/−, and Ghrelin−/− mice markedly improved metabolic flexibility, enhanced ambulatory activity, and reduced adiposity. Inactivation of Ghrelin or Ghsr had no effect on AL food intake or food anticipatory behavior. In contrast to the widely held belief that endogenous ghrelin regulates food intake, CR increased expression of hypothalamic Agrp and Npy, with reduced expression of Pomc across genotypes. In the AL context, ablation of ghrelin signaling markedly inhibited liver steatosis, which correlated with reduced Pparγ expression and enhanced Irs2 expression. Although CR and administration of GH secretagogue receptor 1a agonists both benefit the aging phenotype, we conclude the benefits of chronic CR are a consequence of enhanced metabolic flexibility independent of endogenous ghrelin or des-acyl ghrelin signaling.
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Skibicka, Karolina P., Rozita H. Shirazi, Caroline Hansson, and Suzanne L. Dickson. "Ghrelin Interacts with Neuropeptide Y Y1 and Opioid Receptors to Increase Food Reward." Endocrinology 153, no. 3 (2012): 1194–205. http://dx.doi.org/10.1210/en.2011-1606.
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Ghrelin, a stomach-derived hormone, is an orexigenic peptide that was recently shown to potently increase food reward behavior. The neurochemical circuitry that links ghrelin to the mesolimbic system and food reward behavior remains unclear. Here we examined the contribution of neuropeptide Y (NPY) and opioids to ghrelin's effects on food motivation and intake. Both systems have well-established links to the mesolimbic ventral tegmental area (VTA) and reward/motivation control. NPY mediates the effect of ghrelin on food intake via activation of NPY-Y1 receptor (NPY-Y1R); their connection with respect to motivated behavior is unexplored. The role of opioids in any aspect of ghrelin's action on food-oriented behaviors is unknown. Rats were trained in a progressive ratio sucrose-induced operant schedule to measure food reward/motivation behavior. Chow intake was measured immediately after the operant test. In separate experiments, we explored the suppressive effects of a selective NPY-Y1R antagonist or opioid receptor antagonist naltrexone, injected either intracerebroventricularly or intra-VTA, on ghrelin-induced food reward behavior. The ventricular ghrelin-induced increase in sucrose-motivated behavior and chow intake were completely blocked by intracerebroventricular pretreatment with either an NPY-Y1R antagonist or naltrexone. The intra-VTA ghrelin-induced sucrose-motivated behavior was blocked only by intra-VTA naltrexone. In contrast, the intra-VTA ghrelin-stimulated chow intake was attenuated only by intra-VTA NPY-Y1 blockade. Finally, ghrelin infusion was associated with an elevated VTA μ-opioid receptor expression. Thus, we identify central NPY and opioid signaling as the necessary mediators of food intake and reward effects of ghrelin and localize these interactions to the mesolimbic VTA.
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McGovern-Gooch, Kayleigh R., Trevor Rodrigues, Joseph E. Darling, Michelle A. Sieburg, Alfonso Abizaid, and James L. Hougland. "Ghrelin Octanoylation Is Completely Stabilized in Biological Samples by Alkyl Fluorophosphonates." Endocrinology 157, no. 11 (2016): 4330–38. http://dx.doi.org/10.1210/en.2016-1657.
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Ghrelin is a peptide hormone involved in multiple physiological processes related to energy homeostasis. This hormone features a unique posttranslational serine octanoylation modification catalyzed by the enzyme ghrelin O-acyltransferase, with serine octanoylation essential for ghrelin to bind and activate its cognate receptor. Ghrelin deacylation rapidly occurs in circulation, with both ghrelin and desacyl ghrelin playing important roles in biological signaling. Understanding the regulation and physiological impact of ghrelin signaling requires the ability to rapidly protect ghrelin from deacylation in biological samples such as blood serum or cell lysates to preserve the relative concentrations of ghrelin and desacyl ghrelin. In in vitro ghrelin O-acyltransferase activity assays using insect microsomal protein fractions and mammalian cell lysate and blood serum, we demonstrate that alkyl fluorophosphonate treatment provides rapid, complete, and long-lasting protection of ghrelin acylation against serine ester hydrolysis without interference in enzyme assay or ELISA analysis. Our results support alkyl fluorophosphonate treatment as a general tool for stabilizing ghrelin and improving measurement of ghrelin and desacyl ghrelin concentrations in biochemical and clinical investigations and suggest current estimates for active ghrelin concentration and the ghrelin to desacyl ghrelin ratio in circulation may underestimate in vivo conditions.
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Amitani, Marie, Haruka Amitani, Kai-Chun Cheng, et al. "The Role of Ghrelin and Ghrelin Signaling in Aging." International Journal of Molecular Sciences 18, no. 7 (2017): 1511. http://dx.doi.org/10.3390/ijms18071511.
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Buckinx, An, Yana Van Den Herrewegen, Anouk Pierre, et al. "Differential Effects of a Full and Biased Ghrelin Receptor Agonist in a Mouse Kindling Model." International Journal of Molecular Sciences 20, no. 10 (2019): 2480. http://dx.doi.org/10.3390/ijms20102480.
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The ghrelin system has received substantial recognition as a potential target for novel anti-seizure drugs. Ghrelin receptor (ghrelin-R) signaling is complex, involving Gαq/11, Gαi/o, Gα12/13, and β-arrestin pathways. In this study, we aimed to deepen our understanding regarding signaling pathways downstream the ghrelin-R responsible for mediating anticonvulsive effects in a kindling model. Mice were administered the proconvulsive dopamine 1 receptor-agonist, SKF81297, to gradually induce a kindled state. Prior to every SKF81297 injection, mice were treated with a ghrelin-R full agonist (JMV-1843), a Gαq and Gα12 biased ligand unable to recruit β-arrestin (YIL781), a ghrelin-R antagonist (JMV-2959), or saline. Mice treated with JMV-1843 had fewer and less severe seizures compared to saline-treated controls, while mice treated with YIL781 experienced longer and more severe seizures. JMV-2959 treatment did not lead to differences in seizure severity and number. Altogether, these results indicate that the Gαq or Gα12 signaling pathways are not responsible for mediating JMV-1843′s anticonvulsive effects and suggest a possible involvement of β-arrestin signaling in the anticonvulsive effects mediated by ghrelin-R modulation.
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Bagnasco, Michela, Pushpa S. Kalra, and Satya P. Kalra. "Ghrelin and Leptin Pulse Discharge in Fed and Fasted Rats." Endocrinology 143, no. 2 (2002): 726–29. http://dx.doi.org/10.1210/endo.143.2.8743.
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Abstract Ghrelin stimulates and leptin inhibits appetite by modulating neuropeptide Y (NPY) signaling in the hypothalamus. Analysis of plasma ghrelin and leptin by sensitive radioimmunoassays showed that the two peripheral hormones are secreted in pulsatile fashion in rats consuming ad libitum rat chow. Fasting augmented all parameters of ghrelin pulsatile secretion and diminished leptin secretion by selectively attenuating the pulse amplitude; concomitantly it produced synchrony in ghrelin and leptin pulse discharge. These studies imply that a synchronous leptin restraint and ghrelin stimulus on NPYergic signaling may underlie robust appetitive drive.
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Chung, Hyunju, Endan Li, Yumi Kim, Sehee Kim, and Seungjoon Park. "Multiple signaling pathways mediate ghrelin-induced proliferation of hippocampal neural stem cells." Journal of Endocrinology 218, no. 1 (2013): 49–59. http://dx.doi.org/10.1530/joe-13-0045.
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Ghrelin, an endogenous ligand for the GH secretagogue receptor (GHS-R) receptor 1a (GHS-R1a), has been implicated in several physiologic processes involving the hippocampus. The aim of this study was to investigate the molecular mechanisms of ghrelin-stimulated neurogenesis using cultured adult rat hippocampal neural stem cells (NSCs). The expression of GHS-R1a was detected in hippocampal NSCs, as assessed by western blot analysis and immunocytochemistry. Ghrelin treatment increased the proliferation of cultured hippocampal NSCs assessed by BrdU incorporation. The exposure of cells to the receptor-specific antagonist d-Lys-3-GHRP-6 abolished the proliferative effect of ghrelin. By contrast, ghrelin showed no significant effect on cell differentiation. The expression of GHS-R1a was significantly increased by ghrelin treatment. The analysis of signaling pathways showed that ghrelin caused rapid activation of ERK1/2 and Akt, which were blocked by the GHS-R1a antagonist. In addition, ghrelin stimulated the phosphorylation of Akt downstream effectors, such as glycogen synthase kinase (GSK)-3β, mammalian target of rapamycin (mTOR), and p70S6K. The activation of STAT3 was also caused by ghrelin treatment. Furthermore, pretreatment of cells with specific inhibitors of MEK/ERK1/2, phosphatidylinositol-3-kinase (PI3K)/Akt, mTOR, and Jak2/STAT3 attenuated ghrelin-induced cell proliferation. Taken together, our results support a role for ghrelin in adult hippocampal neurogenesis and suggest the involvement of the ERK1/2, PI3K/Akt, and STAT3 signaling pathways in the mediation of the actions of ghrelin on neurogenesis. Our data also suggest that PI3K/Akt-mediated inactivation of GSK-3β and activation of mTOR/p70S6K contribute to the proliferative effect of ghrelin.
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Gong, Zhi, Makoto Yoshimura, Sayaka Aizawa, et al. "G protein-coupled receptor 120 signaling regulates ghrelin secretion in vivo and in vitro." American Journal of Physiology-Endocrinology and Metabolism 306, no. 1 (2014): E28—E35. http://dx.doi.org/10.1152/ajpendo.00306.2013.
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Ghrelin, an endogenous ligand for the growth hormone secretagogue receptor, is produced predominantly in the stomach. It has been reported that endogenous ghrelin levels are increased by fasting and decreased immediately after feeding and that fasting-induced ghrelin release is controlled by the sympathetic nervous system. However, the mechanisms of plasma ghrelin decrement after feeding are poorly understood. Here, we studied the control of ghrelin secretion using ghrelin-producing cell lines and found that these cells express high levels of mRNA encoding G-protein coupled receptor 120 (GPR120). Addition of GW-9508 (a GPR120 chemical agonist) and α-linolenic acid (a natural ligand for GPR120) inhibited the secretion of ghrelin by ∼50 and 70%, respectively. However, the expression levels of preproghrelin and ghrelin O-acyltransferase (GOAT) mRNAs were not influenced by GW-9508. In contrast, the expression levels of prohormone convertase 1 were decreased significantly by GW-9508 incubation. Moreover, we observed that the inhibitory effect of GW-9508 on ghrelin secretion was blocked by a small interfering RNA (siRNA) targeting the sequence of GPR120. Furthermore, pretreatment with GW-9508 blocked the effect of the norepinephrine (NE)-induced ghrelin elevation in ghrelin cell lines. In addition, we showed that GW-9508 inhibited ghrelin secretion via extracellular signal-regulated kinase activity in ghrelin cell lines. Finally, we found that GW-9508 decreased plasma ghrelin levels in mice. These results suggest that the decrease of ghrelin secretion after feeding is induced partially by long-chain fatty acids that act directly on gastric GPR120-expressing ghrelin cells.
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Naznin, Farhana, Koji Toshinai, T. M. Zaved Waise, Tadashi Okada, Hideyuki Sakoda, and Masamitsu Nakazato. "Restoration of metabolic inflammation-related ghrelin resistance by weight loss." Journal of Molecular Endocrinology 60, no. 2 (2018): 109–18. http://dx.doi.org/10.1530/jme-17-0192.
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High-fat diet (HFD)-induced metabolic inflammation in the central and peripheral organs contributes to the pathogenesis of obesity. Long-term HFD blunts signaling by ghrelin, a gastric-derived orexigenic peptide, in the vagal afferent nerve via a mechanism involving in situ activation of inflammation. This study was undertaken to investigate whether ghrelin resistance is associated with progressive development of metabolic inflammation. In mice, ghrelin’s orexigenic activity was abolished 2–4 weeks after the commencement of HFD (60% of energy from fat), consistent with the timing of accumulation and activation of macrophages and microglia in the nodose ganglion and hypothalamus. Calorie-restricted weight loss after 12-week HFD feeding restored ghrelin responsiveness and alleviated the upregulation of macrophage/microglia activation markers and inflammatory cytokines. HSP72, a chaperone protein, was upregulated in the hypothalamus of HFD-fed mice, potentially contributing to prevention of irreversible neuron damage. These results demonstrate that ghrelin resistance is reversible following reversal of the HFD-induced inflammation and obesity phenotypes.
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Nahata, Miwa, Shuichi Muto, Nobuhiko Oridate, et al. "Impaired ghrelin signaling is associated with gastrointestinal dysmotility in rats with gastroesophageal reflux disease." American Journal of Physiology-Gastrointestinal and Liver Physiology 303, no. 1 (2012): G42—G53. http://dx.doi.org/10.1152/ajpgi.00462.2011.
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Gastroesophageal reflux disease (GERD) is often associated with decreased upper gastrointestinal motility, and ghrelin is an appetite-stimulating hormone known to increase gastrointestinal motility. We investigated whether ghrelin signaling is impaired in rats with GERD and studied its involvement in upper gastrointestinal motility. GERD was induced surgically in Wistar rats. Rats were injected intravenously with ghrelin (3 nmol/rat), after which gastric emptying, food intake, gastroduodenal motility, and growth hormone (GH) release were investigated. Furthermore, plasma ghrelin levels and the expression of ghrelin-related genes in the stomach and hypothalamus were examined. In addition, we administered ghrelin to GERD rats treated with rikkunshito, a Kampo medicine, and examined its effects on gastroduodenal motility. GERD rats showed a considerable decrease in gastric emptying, food intake, and antral motility. Ghrelin administration significantly increased gastric emptying, food intake, and antral and duodenal motility in sham-operated rats, but not in GERD rats. The effect of ghrelin on GH release was also attenuated in GERD rats, which had significantly increased plasma ghrelin levels and expression of orexigenic neuropeptide Y/agouti-related peptide mRNA in the hypothalamus. The number of ghrelin-positive cells in the gastric body decreased in GERD rats, but the expression of gastric preproghrelin and GH secretagogue receptor mRNA was not affected. However, when ghrelin was exogenously administered to GERD rats treated with rikkunshito, a significant increase in antral motility was observed. These results suggest that gastrointestinal dysmotility is associated with impaired ghrelin signaling in GERD rats and that rikkunshito restores gastrointestinal motility by improving the ghrelin response.
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Katare, Rajesh, Shruti Rawal, Pujika Emani Munasinghe, et al. "Ghrelin Promotes Functional Angiogenesis in a Mouse Model of Critical Limb Ischemia Through Activation of Proangiogenic MicroRNAs." Endocrinology 157, no. 2 (2015): 432–45. http://dx.doi.org/10.1210/en.2015-1799.
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Abstract Current therapeutic strategies for the treatment of critical limb ischemia (CLI) have only limited success. Recent in vitro evidence in the literature, using cell lines, proposes that the peptide hormone ghrelin may have angiogenic properties. In this study, we aim to investigate if ghrelin could promote postischemic angiogenesis in a mouse model of CLI and, further, identify the mechanistic pathway(s) that underpin ghrelin's proangiogenic properties. CLI was induced in male CD1 mice by femoral artery ligation. Animals were then randomized to receive either vehicle or acylated ghrelin (150 μg/kg sc) for 14 consecutive days. Subsequently, synchrotron radiation microangiography was used to assess hindlimb perfusion. Subsequent tissue samples were collected for molecular and histological analysis. Ghrelin treatment markedly improved limb perfusion by promoting the generation of new capillaries and arterioles (internal diameter less than 50 μm) within the ischemic hindlimb that were both structurally and functionally normal; evident by robust endothelium-dependent vasodilatory responses to acetylcholine. Molecular analysis revealed that ghrelin's angiogenic properties were linked to activation of prosurvival Akt/vascular endothelial growth factor/Bcl-2 signaling cascade, thus reducing the apoptotic cell death and subsequent fibrosis. Further, ghrelin treatment activated proangiogenic (miR-126 and miR-132) and antifibrotic (miR-30a) microRNAs (miRs) while inhibiting antiangiogenic (miR-92a and miR-206) miRs. Importantly, in vitro knockdown of key proangiogenic miRs (miR-126 and miR-132) inhibited the angiogenic potential of ghrelin. These results therefore suggest that clinical use of ghrelin for the early treatment of CLI may be a promising and potent inducer of reparative vascularization through modulation of key molecular factors.
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Ma, Liangxiao, Hong Tang, Yue Yin, et al. "HDAC5-mTORC1 Interaction in Differential Regulation of Ghrelin and Nucleobindin 2 (NUCB2)/Nesfatin-1." Molecular Endocrinology 29, no. 11 (2015): 1571–80. http://dx.doi.org/10.1210/me.2015-1184.
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Abstract Sodium valporate (VPA), a broad-spectrum inhibitor of histone deacetylases (HDACs), increased ghrelin whereas decreased nesfatin-1 in mice fed normal chow diet or high-fat diet. Alterations in ghrelin and nucleobindin 2/nesfatin-1 were mediated by HDAC5 but not HDAC4. Activation of mTORC1 significantly attenuated the effect of VPA on ghrelin and nesfatin-1 levels. HDAC5 coimmunoprecipitated with raptor. Inhibition of HDAC5 by VPA, trichostatin A, or siHDAC5 markedly increased acetylation of raptor Lys840 and subsequent phosphorylation of raptor Ser792, resulting in suppression of mTORC1 signaling. A raptor mutant lacking the Lys840 acetylation site showed a decrement in phosphorylation of raptor Ser792 and subsequent increase in mTORC1 signaling. These alterations were associated with reciprocal changes in ghrelin and nucleobindin 2/nesfatin-1 expression. These findings reveal HDAC5-mTORC1 signaling as a novel mechanism in the differential regulation of gastric ghrelin and nesfatin-1.
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Li, Danjie, Shaojian Li, Qinling Pan, et al. "Gastric Mammalian Target of Rapamycin Signaling Contributes to Inhibition of Ghrelin Expression Induced by Roux-En-Y Gastric Bypass." Cellular Physiology and Biochemistry 51, no. 2 (2018): 664–80. http://dx.doi.org/10.1159/000495325.
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Background/Aims: Roux-en-Y Gastric Bypass, RYGB, is the most effective strategy to control body weight in morbid obesity. RYGB leads to rapid improvement of glycemic status and weight loss, which are largely attributed to the alteration of gastrointestinal hormones including ghrelin. The current study examined potential mechanisms of altered ghrelin synthesis after RYGB. Methods: Gastric mammalian target of rapamycin (mTOR) signaling, ghrelin synthesis and secretion were determined in lean or obese male mice with or without RYGB operation, as well as in obese patients pre- and post-RYGB surgery. Ghrelin expression and mTOR signaling were investigated by western blotting and immunohistochemistry. Ghrelin mRNA levels were detected by real-time PCR. Plasma ghrelin was measured by enzyme immunoassay. Results: mTOR activity in the gastric fundus was significantly lower than in the forestomachs. Both of them were decreased after 24h fasting. A significant negative correlation was found between gastric levels of phospho-S6 (phospho-S6 ribosomal protein) and proghrelin during changes of energy status. mTOR activity was activated, whereas ghrelin expression was inhibited by Roux-en-Y Gastric Bypass in both rodents and human beings. Increment of ghrelin synthesis and decline of mTOR signaling induced by rapamycin were significantly reversed by RYGB in both lean and obese mice. Administration of Ad-S6K1 (adenovirus-mediated p70 ribosomal protein subunit 6 kinase 1) from tail vein suppressed the expression of ghrelin in RYGB-operated mice relative to control animals. Conclusion: mTOR is therefore a gastric fuel sensor whose activity is linked to the regulation of ghrelin after Roux-en-Y Gastric Bypass.
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Wang, Qin, Ming Zheng, Yue Yin та Weizhen Zhang. "Ghrelin Stimulates Hepatocyte Proliferation via Regulating Cell Cycle Through GSK3β/Β-Catenin Signaling Pathway". Cellular Physiology and Biochemistry 50, № 5 (2018): 1698–710. http://dx.doi.org/10.1159/000494789.
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Background/Aims: Obesity is associated with a reduction in ghrelin, a 28 aa gastric hormone. Whether reduced ghrelin contributes to the impaired proliferation of hepatocytes associated with obesity-related steatosis remains largely unknown. Here we examined the effects of ghrelin on the proliferation of hepatocytes derived from lean and obese mice. Methods: AML 12 cells or hepatocytes isolated from mice fed normal chow diet (NCD) or high fat diet (HFD) were used. Effects of ghrelin on hepatocyte proliferation were detected with CCK8 assay and EdU staining. Cell cycle was analyzed by flow cytometry. Levels of proliferation markers was examined by Western blot. Results: Growth hormone secretagogue receptor 1a (GHS-R1a) mRNA and protein were present in hepatocytes. Levels of GHS-R1a were increased upon ghrelin treatment. Ghrelin significantly increased hepatocyte proliferation measured by Cell Counting Kit-8(CCK8) assay and EdU staining in a dose- and time-dependent manner. Proportion of cells in S phase was markedly increased upon treatment with ghrelin. Ghrelin significantly increased levels of proliferating cell nuclear antigen (PCNA) and cyclin D1, while reducing p27 in hepatocytes from mice fed NCD or HFD. Deletion of GHS-R1a completely abolished the effects of ghrelin in cultured hepatocytes. Ghrelin stimulated the phosphorylation of glycogen synthase kinase 3 beta (GSK3β), leading to subsequent increase of nuclear β-catenin in hepatocytes derived from lean and obese mice. This effect was dependent on the GHS-R1a. Conclusion: Ghrelin activates GHS-R1a to stimulate hepatocyte proliferation via GSK3/β-catenin signaling pathway.
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Holst, Birgitte, Adam Cygankiewicz, Tine Halkjær Jensen, Michael Ankersen, and Thue W. Schwartz. "High Constitutive Signaling of the Ghrelin Receptor—Identification of a Potent Inverse Agonist." Molecular Endocrinology 17, no. 11 (2003): 2201–10. http://dx.doi.org/10.1210/me.2003-0069.
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Abstract Ghrelin is a GH-releasing peptide that also has an important role as an orexigenic hormone-stimulating food intake. By measuring inositol phosphate turnover or by using a reporter assay for transcriptional activity controlled by cAMP-responsive elements, the ghrelin receptor showed strong, ligand-independent signaling in transfected COS-7 or human embryonic kidney 293 cells. Ghrelin and a number of the known nonpeptide GH secretagogues acted as agonists stimulating inositol phosphate turnover further. In contrast, the low potency ghrelin antagonist, [D-Arg1,D-Phe5,D-Trp7,9,Leu11]-substance P was surprisingly found to be a high potency (EC50 = 5.2 nm) full inverse agonist as it decreased the constitutive signaling of the ghrelin receptor down to that observed in untransfected cells. The homologous motilin receptor functioned as a negative control as it did not display any sign of constitutive activity; however, upon agonist stimulation the motilin receptor signaled as strongly as the unstimulated ghrelin receptor. It is concluded that the ghrelin receptor is highly constitutively active and that this activity could be of physiological importance in its role as a regulator of both GH secretion and appetite control. It is suggested that inverse agonists for the ghrelin receptor could be particularly interesting for the treatment of obesity.
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Naznin, Farhana, Koji Toshinai, T. M. Zaved Waise, et al. "Diet-induced obesity causes peripheral and central ghrelin resistance by promoting inflammation." Journal of Endocrinology 226, no. 1 (2015): 81–92. http://dx.doi.org/10.1530/joe-15-0139.
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Ghrelin, a stomach-derived orexigenic peptide, transmits starvation signals to the hypothalamus via the vagus afferent nerve. Peripheral administration of ghrelin does not induce food intake in high fat diet (HFD)-induced obese mice. We investigated whether this ghrelin resistance was caused by dysfunction of the vagus afferent pathway. Administration (s.c.) of ghrelin did not induce food intake, suppression of oxygen consumption, electrical activity of the vagal afferent nerve, phosphorylation of ERK2 and AMP-activated protein kinase alpha in the nodose ganglion, or Fos expression in hypothalamic arcuate nucleus of mice fed a HFD for 12 weeks. Administration of anti-ghrelin IgG did not induce suppression of food intake in HFD-fed mice. Expression levels of ghrelin receptor mRNA in the nodose ganglion and hypothalamus of HFD-fed mice were reduced. Inflammatory responses, including upregulation of macrophage/microglia markers and inflammatory cytokines, occurred in the nodose ganglion and hypothalamus of HFD-fed mice. A HFD blunted ghrelin signaling in the nodose ganglion via a mechanism involvingin situactivation of inflammation. These results indicate that ghrelin resistance in the obese state may be caused by dysregulation of ghrelin signaling via the vagal afferent.
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Zhang, Chengshuo, Le Li, Bochao Zhao, et al. "Ghrelin Protects against Dexamethasone-Induced INS-1 Cell Apoptosis via ERK and p38MAPK Signaling." International Journal of Endocrinology 2016 (2016): 1–11. http://dx.doi.org/10.1155/2016/4513051.
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Glucocorticoid excess induces apoptosis of islet cells, which may result in diabetes. In this study, we investigated the protective effect of ghrelin on dexamethasone-induced INS-1 cell apoptosis. Our data showed that ghrelin (0.1 μM) inhibited dexamethasone-induced (0.1 μM) apoptosis of INS-1 cells and facilitated cell proliferation. Moreover, ghrelin upregulated Bcl-2 expression, downregulated Bax expression, and decreased caspase-3 activity. The protective effect of ghrelin against dexamethasone-induced INS-1 cell apoptosis was mediated via growth hormone secretagogue receptor 1a. Further studies revealed that ghrelin increased ERK activation and decreased p38MAPK expression after dexamethasone treatment. Ghrelin-mediated protection of dexamethasone-induced apoptosis of INS-1 cells was attenuated using the ERK inhibitor U0126 (10 μM), and cell viability increased using the p38MAPK inhibitor SB203580 (10 μM). In conclusion, ghrelin could protect against dexamethasone-induced INS-1 cell apoptosis, at least partially via GHS-R1a and the signaling pathway of ERK and p38MAPK.
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Currie, Paul J., Aaisha Mirza, Rebecca Fuld, Diana Park, and Joseph R. Vasselli. "Ghrelin is an orexigenic and metabolic signaling peptide in the arcuate and paraventricular nuclei." American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 289, no. 2 (2005): R353—R358. http://dx.doi.org/10.1152/ajpregu.00756.2004.
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Ghrelin is a 28-amino acid acylated peptide and is the endogenous ligand for the growth hormone secretagogue receptor (GHS-R). The GHS-R is expressed in hypothalamic nuclei, including the arcuate nucleus (Arc) where it is colocalized with neuropeptide Y (NPY) neurons. In the present study, we examined the effects of ghrelin on feeding and energy substrate utilization (respiratory quotient; RQ) following direct injections into either the arcuate or the paraventricular nucleus (PVN) of the hypothalamus. Ghrelin was administered at the beginning of the dark cycle at doses of 15–60 pmol to male and female rats. In feeding studies, food intake was measured 2 and 4 h postinjection. Separate groups of rats were injected with ghrelin, and the RQ (V̇co2/V̇o2) was measured using an open circuit calorimeter over a 4-h period. Both Arc and PVN injections of ghrelin increased food intake in male and female rats. Ghrelin also increased RQ, reflecting a shift in energy substrate utilization in favor of carbohydrate oxidation. Because these effects are similar to those observed after PVN injection of NPY, we then assessed the impact of coinjecting ghrelin with NPY into the PVN. When rats were pretreated with very low doses of ghrelin (2.5–10 pmol), NPY's (50 pmol) effects on eating and RQ were potentiated. Overall, these data are in agreement with evidence suggesting that ghrelin functions as a gut-brain endocrine hormone implicated in the regulation of food intake and energy metabolism. Our findings are also consistent with a possible interactive role of hypothalamic ghrelin and NPY systems.
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Ma, Xiaojun, Yuezhen Lin, Ligen Lin, et al. "Ablation of ghrelin receptor in leptin-deficient ob/ob mice has paradoxical effects on glucose homeostasis when compared with ablation of ghrelin in ob/ob mice." American Journal of Physiology-Endocrinology and Metabolism 303, no. 3 (2012): E422—E431. http://dx.doi.org/10.1152/ajpendo.00576.2011.
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The orexigenic hormone ghrelin is important in diabetes because it has an inhibitory effect on insulin secretion. Ghrelin ablation in leptin-deficient ob/ob ( Ghrelin−/−: ob/ ob) mice increases insulin secretion and improves hyperglycemia. The physiologically relevant ghrelin receptor is the growth hormone secretagogue receptor (GHS-R), and GHS-R antagonists are thought to be an effective strategy for treating diabetes. However, since some of ghrelin's effects are independent of GHS-R, we have utilized genetic approaches to determine whether ghrelin's effect on insulin secretion is mediated through GHS-R and whether GHS-R antagonism indeed inhibits insulin secretion. We investigated the effects of GHS-R on glucose homeostasis in Ghsr-ablated ob/ ob mice ( Ghsr−/−: ob/ ob). Ghsr ablation did not rescue the hyperphagia, obesity, or insulin resistance of ob/ ob mice. Surprisingly, Ghsr ablation worsened the hyperglycemia, decreased insulin, and impaired glucose tolerance. Consistently, Ghsr ablation in ob/ ob mice upregulated negative β-cell regulators (such as UCP-2, SREBP-1c, ChREBP, and MIF-1) and downregulated positive β-cell regulators (such as HIF-1α, FGF-21, and PDX-1) in whole pancreas; this suggests that Ghsr ablation impairs pancreatic β-cell function in leptin deficiency. Of note, Ghsr ablation in ob/ ob mice did not affect the islet size; the average islet size of Ghsr−/−: ob/ ob mice is similar to that of ob/ ob mice. In summary, because Ghsr ablation in leptin deficiency impairs insulin secretion and worsens hyperglycemia, this suggests that GHS-R antagonists may actually aggravate diabetes under certain conditions. The paradoxical effects of ghrelin ablation and Ghsr ablation in ob/ob mice highlight the complexity of the ghrelin-signaling pathway.
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Overduin, Joost, Dianne P. Figlewicz, Jennifer Bennett-Jay, Sepideh Kittleson, and David E. Cummings. "Ghrelin increases the motivation to eat, but does not alter food palatability." American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 303, no. 3 (2012): R259—R269. http://dx.doi.org/10.1152/ajpregu.00488.2011.
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Homeostatic eating cannot explain overconsumption of food and pathological weight gain. A more likely factor promoting excessive eating is food reward and its representation in the central nervous system (CNS). The anorectic hormones leptin and insulin reduce food reward and inhibit related CNS reward pathways. Conversely, the orexigenic gastrointestinal hormone ghrelin activates both homeostatic and reward-related neurocircuits. The current studies were conducted to identify in rats the effects of intracerebroventricular ghrelin infusions on two distinct aspects of food reward: hedonic valuation (i.e., “liking”) and the motivation to self-administer (i.e., “wanting”) food. To assess hedonic valuation of liquid food, lick motor patterns were recorded using lickometry. Although ghrelin administration increased energy intake, it did not alter the avidity of licking (initial lick rates or lick-cluster size). Several positive-control conditions ruled out lick-rate ceiling effects. Similarly, when the liquid diet was hedonically devalued with quinine supplementation, ghrelin failed to reverse the quinine-associated reduction of energy intake and avidity of licking. The effects of ghrelin on rats' motivation to eat were assessed using lever pressing to self-administer food in a progressive-ratio paradigm. Ghrelin markedly increased motivation to eat, to levels comparable to or greater than those seen following 24 h of food deprivation. Pretreatment with the dopamine D1 receptor antagonist SCH-23390 eliminated ghrelin-induced increases in lever pressing, without compromising generalized licking motor control, indicating a role for D1 signaling in ghrelin's motivational feeding effects. These results indicate that ghrelin increases the motivation to eat via D1 receptor-dependent mechanisms, without affecting perceived food palatability.
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Lee, Junho. "Ghrelin stimulates cell proliferation in T cells (109.22)." Journal of Immunology 186, no. 1_Supplement (2011): 109.22. http://dx.doi.org/10.4049/jimmunol.186.supp.109.22.
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Abstract Ghrelin is a 28 amino acid acylated peptide, which is produced and secreted by X/A-like enteroendocrine cells of the stomach. We have recently demonstrated that ghrelin is expressed by various immune cells including T- and B-lymphocytes, monocytes and neutrophils. These immune cells have also been shown to express the ghrelin receptor, namely the growth hormone secretagogue receptor (GHS-R). In the present study, we have investigated the effects of ghrelin on T cell proliferation and its signaling through its cell surface receptor. We have found that ghrelin induces a modest increase in the proliferation of murine CD4+ T cells and T-cell lines. Western blot experiments have demonstrated that GHS-R ligation activates the external receptor activated kinases (ERK1/2) and Akt signaling pathways in a dose-dependent fashion. Moreover, we have also revealed the involvement of the PKC pathway in the phosphorylation of ERK1/2. The pro-proliferative effects of ghrelin through ERK1/2 appears to be mediated through the regulation of the expression of cell cycle proteins, cyclin D1, CDK4, cyclin E and CDK2 as well as Rb. Together, these data suggest that ghrelin promotes the cell proliferation of T cell via the activation of the PKC, PI-3-K, Akt and Erk1/2 signaling pathways and that this GHS-R signal appears to be essential but not sufficient for cell cycle progression.
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Koyama, Hiroyuki, Hiroshi Iwakura, Katsuko Dote, et al. "Comprehensive Profiling of GPCR Expression in Ghrelin-Producing Cells." Endocrinology 157, no. 2 (2015): 692–704. http://dx.doi.org/10.1210/en.2015-1784.
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Abstract To determine the comprehensive G protein-coupled receptor (GPCR) expression profile in ghrelin-producing cells and to elucidate the role of GPCR-mediated signaling in the regulation of ghrelin secretion, we determined GPCR expression profiles by RNA sequencing in the ghrelin-producing cell line MGN3-1 and analyzed the effects of ligands for highly expressed receptors on intracellular signaling and ghrelin secretion. Expression of selected GPCRs was confirmed in fluorescence-activated cell-sorted fluorescently tagged ghrelin-producing cells from ghrelin-promoter CreERT2/Rosa-CAG-LSL-ZsGreen1 mice. Expression levels of GPCRs previously suggested to regulate ghrelin secretion including adrenergic-β1 receptor, GPR81, oxytocin receptor, GPR120, and somatostatin receptor 2 were high in MGN3-1 cells. Consistent with previous reports, isoproterenol and oxytocin stimulated the Gs and Gq pathways, respectively, whereas lactate, palmitate, and somatostatin stimulated the Gi pathway, confirming the reliability of current assays. Among other highly expressed GPCRs, prostaglandin E receptor 4 agonist prostaglandin E2 significantly stimulated the Gs pathway and ghrelin secretion. Muscarine, the canonical agonist of cholinergic receptor muscarinic 4, stimulated both the Gq and Gi pathways. Although muscarine treatment alone did not affect ghrelin secretion, it did suppress forskolin-induced ghrelin secretion, suggesting that the cholinergic pathway may play a role in counterbalancing the stimulation of ghrelin by Gs (eg, by adrenaline). In addition, GPR142 ligand tryptophan stimulated ghrelin secretion. In conclusion, we determined the comprehensive expression profile of GPCRs in ghrelin-producing cells and identified two novel ghrelin regulators, prostaglandin E2 and tryptophan. These results will lead to a greater understanding of the physiology of ghrelin and facilitate the development of ghrelin-modulating drugs.
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Xu, Xiangbin, Bong Sook Jhun, Chang Hoon Ha, and Zheng-Gen Jin. "Molecular Mechanisms of Ghrelin-Mediated Endothelial Nitric Oxide Synthase Activation." Endocrinology 149, no. 8 (2008): 4183–92. http://dx.doi.org/10.1210/en.2008-0255.
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Metabolic syndrome accelerates the atherosclerotic process, and the earliest event of which is endothelial dysfunction. Ghrelin, a newly discovered gastric peptide, improves endothelial function and inhibits proatherogenic changes. In particular, low ghrelin concentration has been associated with several features of metabolic syndrome, including obesity, insulin resistance, and high blood pressure. However, the molecular mechanisms underlying ghrelin vascular actions remain largely unclear. Here, we showed that ghrelin activated endothelial nitric oxide (NO) synthase (eNOS) in cultured endothelial cells (ECs) and in intact vessels. Specifically, ghrelin rapidly induced phosphorylation of eNOS on an activation site and production of NO in human umbilical vein ECs and bovine aortic ECs. The eNOS phosphorylation was also observed in mouse aortas ex vivo perfused with ghrelin and in aortic tissues isolated from mice injected with ghrelin. Mechanistically, ghrelin stimulated AMP-activated protein kinase (AMPK) and Akt activation in cultured ECs and intact vessels. Inhibiting AMPK and Akt with their pharmacological inhibitors, small interference RNA and adenoviruses carried dominant-negative mutants, markedly attenuated ghrelin-induced eNOS activation, and NO production. Furthermore, ghrelin receptor/Gq protein/calcium-dependent pathway mediates activation of AMPK, Akt, and eNOS, and calmodulin-dependent kinase kinase is a potential convergent point to regulate Akt and AMPK activation in ghrelin signaling. Importantly, eNOS activation is critical for ghrelin inhibition of vascular inflammation. Together, both in vitro and in vivo data demonstrate a new role of ghrelin signaling for eNOS activation, and highlight the therapeutic potential for ghrelin to correct endothelial dysfunction associated with atherosclerotic vascular diseases and metabolic syndrome.
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Petersen, Pia Steen, David P. D. Woldbye, Andreas Nygaard Madsen, et al. "In Vivo Characterization of High Basal Signaling from the Ghrelin Receptor." Endocrinology 150, no. 11 (2009): 4920–30. http://dx.doi.org/10.1210/en.2008-1638.
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The receptor for the orexigenic peptide, ghrelin, is one of the most constitutively active 7TM receptors known, as demonstrated under in vitro conditions. Change in expression of a constitutively active receptor is associated with change in signaling independent of the endogenous ligand. In the following study, we found that the expression of the ghrelin receptor in the hypothalamus was up-regulated approximately 2-fold in rats both during 48-h fasting and by streptozotocin-induced hyperphagia. In a separate experiment, to probe for the effect of the high basal signaling of the ghrelin receptor in vivo, we used intracerebroventricular administration by osmotic pumps of a peptide [D-Arg1, D-Phe5, D-Trp7,9, Leu11]-substance P. This peptide selectively displays inverse agonism at the ghrelin receptor as compared with an inactive control peptide with just a single amino acid substitution. Food intake and body weight were significantly decreased in the group of rats treated with the inverse agonist, as compared with the groups treated with the control peptide or the vehicle. In the hypothalamus, the expression of neuropeptide Y and uncoupling protein 2 was decreased by the inverse agonist. In a hypothalamic cell line that endogenously expresses the ghrelin receptor, we observed high basal activity of the cAMP response element binding protein, an important signaling transduction pathway for appetite regulation. The activation was further increased by ghrelin administration and decreased by administration of the inverse agonist. It is suggested that the high constitutive signaling activity is important for the in vivo function of the ghrelin receptor in the control of food intake and body weight.
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Wang, Jun, Lin He, Bahetiyaer Huwatibieke, et al. "Ghrelin Stimulates Endothelial Cells Angiogenesis through Extracellular Regulated Protein Kinases (ERK) Signaling Pathway." International Journal of Molecular Sciences 19, no. 9 (2018): 2530. http://dx.doi.org/10.3390/ijms19092530.
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Adipose tissue is hyper-vascularized. Vessels in adipose tissue not only supply nutrients and oxygen to nourish adipocytes, but also provide cytokines that regulate mass and function of adipose tissue. Understanding the fundamental mechanisms how vessels modulate adipocyte functions would provide new therapeutic options for treatment of metabolic disease and obesity. In recent years, researches about ghrelin are focused on glucose and lipid metabolism, but its effect on vascular function remains uncharacterized. In the present study, ghrelin receptor gene deletion mice (Ghsr−/− mice) were used to study ghrelin-regulated vascular metabolism in white adipose tissue. Ghsr−/− mice demonstrated lower food intake, lower body weight, and resistance to high-fat diet-induced obesity. The number of vessels in white adipose tissue was decreased in Ghsr−/− mice when compared with wild type mice fed with high-fat diet. To further define ghrelin effects in vitro, we used endothelial progenitor cells from wild type and Ghsr−/− mice as well as human umbilical vein endothelial cells in our experiments. We found that ghrelin stimulated endothelial cells angiogenesis and migration through the MEK-ERK signaling pathway. [d-Lys3]-GHRP-6 and PD98059 could reverse the effects of ghrelin on endothelial cells. Our study indicates that ghrelin activates its receptor on endothelial cells to promote angiogenesis and migration via a mechanism involving the extracellular regulated protein kinases (ERK) signaling pathway.
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Mineev, V. N., T. M. Lalaeva, and A. A. Lebedeva. "Ghrelin signaling pathway in bronchial asthma." Russian Pulmonology 26, no. 1 (2016): 92–97. http://dx.doi.org/10.18093/0869-0189-2016-26-1-92-97.
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Howell, Erin, Hannah Baumgartner, Lia Zallar, Joaquín Selva, Liv Engel, and Paul Currie. "Glucagon-Like Peptide-1 (GLP-1) and 5-Hydroxytryptamine 2c (5-HT2c) Receptor Agonists in the Ventral Tegmental Area (VTA) Inhibit Ghrelin-Stimulated Appetitive Reward." International Journal of Molecular Sciences 20, no. 4 (2019): 889. http://dx.doi.org/10.3390/ijms20040889.
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Current literature indicates that the orexigenic peptide ghrelin increases appetitive motivation via signaling in the mesolimbic reward system. Another gastric peptide, glucagon-like peptide-1 (GLP-1), and the neurotransmitter 5-hydroxytryptamine (5-HT), are both known to suppress operant responding for food by acting on key mesolimbic nuclei, including the ventral tegmental area (VTA). In order to investigate the interaction effects of ghrelin, GLP-1, and 5-HT within the VTA, we measured operant responding for sucrose pellets after the administration of ghrelin, the GLP-1 receptor agonist exendin-4 (Ex-4), and the 5-HT2c receptor agonist Ro60-0175 in male Sprague-Dawley rats. Following training on a progressive ratio 3 (PR3) schedule, animals were first injected with ghrelin into the VTA at doses of 3 to 300 pmol. In subsequent testing, separate rats were administered intraperitoneal (IP) Ex-4 (0.1–1.0 µg/kg) or VTA Ex-4 (0.01–0.1 µg) paired with 300 pmol ghrelin. In a final group of rats, the 5-HT2c agonist Ro60-0175 was injected IP (0.25–1.0 mg/kg) or into the VTA (1.5–3.0 µg), and under both conditions paired with 300 pmol ghrelin delivered into the VTA. Our results indicated that ghrelin administration increased operant responding for food reward and that this effect was attenuated by IP and VTA Ex-4 pretreatment as well as pre-administration of IP or VTA Ro60-0175. These data provide compelling evidence that mesolimbic GLP-1 and serotonergic circuitry interact with the ghrelinergic system to suppress ghrelin’s effects on the mediation of food reinforcement.
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Schalla, Martha, and Andreas Stengel. "The Role of Ghrelin in Anorexia Nervosa." International Journal of Molecular Sciences 19, no. 7 (2018): 2117. http://dx.doi.org/10.3390/ijms19072117.
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Ghrelin, a 28-amino acid peptide hormone expressed in X/A-like endocrine cells of the stomach, is the only known peripherally produced and centrally acting peptide that stimulates food intake and therefore attracted a lot of attention with one major focus on the treatment of conditions where an increased energy intake or body weight gain is desired. Anorexia nervosa is an eating disorder characterized by a pronounced reduction of body weight, a disturbed body image and hormonal alterations. Ghrelin signaling has been thoroughly investigated under conditions of anorexia nervosa. The present review will highlight these alterations of ghrelin in anorexia and discuss possible treatment strategies targeting ghrelin signaling. Lastly, gaps in knowledge will be mentioned to foster future research.
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Wang, Chia-Hao, Ching-Yu Tseng, Wei-Li Hsu, and Jason T. C. Tzen. "Establishment of a Cell Line Stably Expressing the Growth Hormone Secretagogue Receptor to Identify Crocin as a Ghrelin Agonist." Biomolecules 12, no. 12 (2022): 1813. http://dx.doi.org/10.3390/biom12121813.
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The growth hormone secretagogue receptor-1a (GHSR1a) is the endogenous receptor for ghrelin. Activation of GHSR1a participates in many physiological processes including energy homeostasis and eating behavior. Due to its transitory half-life, the efficacy of ghrelin treatment in patients is restricted; hence the development of new adjuvant therapy is an urgent need. This study aimed to establish a cell line stably expressing GHSR1a, which could be employed to screen potential ghrelin agonists from natural compounds. First, by means of lentiviral transduction, the genome of a human HEK293T cell was modified, and a cell platform stably overexpressing GHSR1a was successfully established. In this platform, GHSR1a was expressed as a fusion protein tagged with mCherry, which allowed the monitoring of the dynamic cellular distribution of GHSR1a by fluorescent microscopy. Subsequently, the authenticity of the GHSR1a mediated signaling was further characterized by using ghrelin and teaghrelin, two molecules known to stimulate GHSR1a. The results indicated that both ghrelin and teaghrelin readily activated GHSR1a mediated signaling pathways, presumably via increasing phosphorylation levels of ERK. The specific GHSR1a signaling was further validated by using SP-analog, an antagonist of GHSR1a as well as using a cell model with the knockdown expression of GHSR1a. Molecular modeling predicted that crocin might be a potential ghrelin agonist, and this prediction was further confirmed by the established platform.
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Rouault, Alix A. J., Luciana K. Rosselli-Murai, Ciria C. Hernandez, Luis E. Gimenez, Gregory G. Tall, and Julien A. Sebag. "The GPCR accessory protein MRAP2 regulates both biased signaling and constitutive activity of the ghrelin receptor GHSR1a." Science Signaling 13, no. 613 (2020): eaax4569. http://dx.doi.org/10.1126/scisignal.aax4569.
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Ghrelin is a hormone secreted by the stomach during fasting periods and acts through its receptor, the growth hormone secretagogue 1a (GHSR1a), to promote food intake and prevent hypoglycemia. As such, GHSR1a is an important regulator of energy and glucose homeostasis and a target for the treatment of obesity. Here, we showed that the accessory protein MRAP2 altered GHSR1a signaling by inhibiting its constitutive activity, as well as by enhancing its G protein–dependent signaling and blocking the recruitment and signaling of β-arrestin in response to ghrelin. In addition, the effects of MRAP2 on the Gαq and β-arrestin pathways were independent and involved distinct regions of MRAP2. These findings may have implications for the regulation of ghrelin function in vivo and the role of MRAP2 in energy homeostasis. They also show that accessory proteins can bias signaling downstream of GPCRs in response to their endogenous agonist.
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Taherkhani, Shokoufeh, Fatemeh Moradi, Masoumeh Hosseini, Mohsen Alipour, and Hadi Feizi. "Homeobox B4 gene expression is upregulated by ghrelin through PI3-kinase signaling pathway in rat’s bone marrow stromal cells." Endocrine Regulations 53, no. 2 (2019): 65–70. http://dx.doi.org/10.2478/enr-2019-0008.
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AbstractObjective. Ghrelin, a 28 amino acid peptide, has diverse physiological roles. Phosphatidylino-sitol-bisphosphate 3-kinase (PI3K) and mitogen-activated protein kinase (MAPK) are involved in some of the recognized actions of ghrelin. It has been shown that ghrelin upregulates HOXB4 gene expression but the real mechanism of this effect is not clear.Methods. Rat bone marrow stromal cells (BMSCs) were cultured in DMEM. BMSCs were treated with ghrelin (100 μM) for 48 h. Real-time PCR for HOXB4 was performed from Control (untreated BMSCs), BG (BMSCs treated with 100 µM ghrelin), PD (BMSCs treated with 10 µM PD98059, a potent inhibitor of mitogen-activated protein kinase, and 100 µM ghrelin), LY (BM-SCs treated with 10 µM LY294002, a strong inhibitor of phosphoinositide 3-kinase, and 100 µM ghrelin) and SY (BMSCs treated with 10 µM LY294002 plus 10 µM PD98059, and 100 µM ghrelin) groups. Relative gene expression changes were determined using Relative expression software tool 9 (REST 9).Results. HOXB4 gene has been overexpressed in ghrelin-treated BMSCs (p<0.05). PI3K inhi-bition by LY294002 significantly downregulated the ghrelin-induced overexpression of HOXB4 (p<0.05).Conclusion. We can conclude that ghrelin, through PI3K/Akt pathway, may improve BMSC transplantation potency by reducing its apoptosis. Moreover, upregulating HOXB4 in BMSC and its possible differentiation to HSCs might in the future open the doors to new treatment for hematologic disorders. Therefore, activating the PI3K/Akt pathway, instead of using a non-specific inducer, could be the principal point to increase the efficiency of BMSC-based cell therapies in the future.
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Zheng, Haichong, Wenjie Liang, Wanmei He та ін. "Ghrelin attenuates sepsis-induced acute lung injury by inhibiting the NF-κB, iNOS, and Akt signaling in alveolar macrophages". American Journal of Physiology-Lung Cellular and Molecular Physiology 317, № 3 (2019): L381—L391. http://dx.doi.org/10.1152/ajplung.00253.2018.
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Ghrelin has proven to be protective against sepsis-induced acute lung injury (ALI) via anti-inflammatory effects. However, its mechanisms remain poorly understood. Alveolar macrophages (AMs) play a key role in mediating inflammatory responses during sepsis-induced ALI by secretion of cytokines and chemokines. This study was undertaken to investigate whether ghrelin suppresses inflammatory effects of AMs and therefore may help to attenuate sepsis-induced ALI. A sepsis model in rats was achieved using cecal ligation and puncture. Ghrelin treatment markedly improved histopathological changes in the lungs and reduced pulmonary inflammation in septic rats. NF-κB translocation and p-Akt and inducible nitric oxide synthase (iNOS) activities in AMs from septic rats were suppressed by ghrelin. In vitro data indicated that ghrelin decreased the levels of LPS-induced IL-1β, TNF-α, and IL-6, NF-κB translocation, and iNOS and Akt activities of AMs. Furthermore, the NF-κB/iNOS pathway or Akt signaling was positively correlated with LPS-induced inflammatory production of AMs in vitro. In conclusion, ghrelin exerts a protective role against sepsis-induced ALI probably by reducing the production of inflammatory cytokines from AMs via inhibition of the NF-κB/iNOS pathway or Akt signaling.
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Wagner, Clemens, S. Roy Caplan, and Gloria S. Tannenbaum. "Interactions of ghrelin signaling pathways with the GH neuroendocrine axis: a new and experimentally tested model." Journal of Molecular Endocrinology 43, no. 3 (2009): 105–19. http://dx.doi.org/10.1677/jme-09-0023.
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Growth hormone (GH) is secreted in a pulsatile fashion from the pituitary gland into the circulation. Release is governed by two hypothalamic neuropeptides, growth hormone-releasing hormone (GHRH) and somatostatin (SRIF), resulting in secretion episodes with a periodicity of 3.3 h in the male rat. Ghrelin is an additional recently identified potent GH-secretagogue. However, its in vivo interactions with the GH neuroendocrine axis remain to be elucidated. Moreover, two different sites of ghrelin synthesis are involved, the stomach and the hypothalamus. We used our previously developed core model of GH oscillations and added the sites of ghrelin action at the pituitary and in the hypothalamus. With this extended model, we simulated the effects of central and peripheral ghrelin injections, monitored the GH profile and compared it with existing experimental results. Systemically administered ghrelin elicits a GH pulse independent of SRIF, but only in the presence of GHRH. The peripheral ghrelin signal is mediated to the brain via the vagus nerve, where it augments the release of GHRH and stimulates the secretion of neuropeptide-Y (NPY). By contrast, centrally administered ghrelin initiates a GH pulse by increasing the GHRH level and by antagonizing the SRIF block at the pituitary. In addition, NPY neurons are activated, which trigger a delayed SRIF surge. The major novel features of the present model are a) the role played by NPY, and b) the dissimilar functions of ghrelin in the hypothalamus and at the pituitary. Furthermore, the predictions of the model were experimentally examined and confirmed.
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Jiang, Hong, Lorena Betancourt, and Roy G. Smith. "Ghrelin Amplifies Dopamine Signaling by Cross Talk Involving Formation of Growth Hormone Secretagogue Receptor/Dopamine Receptor Subtype 1 Heterodimers." Molecular Endocrinology 20, no. 8 (2006): 1772–85. http://dx.doi.org/10.1210/me.2005-0084.
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Abstract Our objective is to determine the neuromodulatory role of ghrelin in the brain. To identify neurons that express the ghrelin receptor [GH secretagogue receptor (GHS-R)], we generated GHS-R-IRES-tauGFP mice by gene targeting. Neurons expressing the GHS-R exhibit green fluorescence and are clearly evident in the hypothalamus, hippocampus, cortex, and midbrain. Using immunohistochemistry in combination with green fluorescent protein fluorescence, we identified neurons that coexpress the dopamine receptor subtype 1 (D1R) and GHS-R. The potential physiological relevance of coexpression of these two receptors and the direct effect of ghrelin on dopamine signaling was investigated in vitro. Activation of GHS-R by ghrelin amplifies dopamine/D1R-induced cAMP accumulation. Intriguingly, amplification involves a switch in G protein coupling of the GHS-R from Gα11/q to Gαi/o by a mechanism consistent with agonist-dependent formation of GHS-R/D1R heterodimers. Most importantly, these results indicate that ghrelin has the potential to amplify dopamine signaling selectively in neurons that coexpress D1R and GHS-R.
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Iantorno, Micaela, Hui Chen, Jeong-a. Kim, et al. "Ghrelin has novel vascular actions that mimic PI 3-kinase-dependent actions of insulin to stimulate production of NO from endothelial cells." American Journal of Physiology-Endocrinology and Metabolism 292, no. 3 (2007): E756—E764. http://dx.doi.org/10.1152/ajpendo.00570.2006.
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Ghrelin is an orexigenic peptide hormone secreted by the stomach. In patients with metabolic syndrome and low ghrelin levels, intra-arterial ghrelin administration acutely improves their endothelial dysfunction. Therefore, we hypothesized that ghrelin activates endothelial nitric oxide synthase (eNOS) in vascular endothelium, resulting in increased production of nitric oxide (NO) using signaling pathways shared in common with the insulin receptor. Similar to insulin, ghrelin acutely stimulated increased production of NO in bovine aortic endothelial cells (BAEC) in primary culture (assessed using NO-specific fluorescent dye 4,5-diaminofluorescein) in a time- and dose-dependent manner. Production of NO in response to ghrelin (100 nM, 10 min) in human aortic endothelial cells was blocked by pretreatment of cells with NG-nitro-l-arginine methyl ester (nitric oxide synthase inhibitor), wortmannin [phosphatidylinositol (PI) 3-kinase inhibitor], or (d-Lys3)-GHRP-6 (selective antagonist of ghrelin receptor GHSR-1a), as well as by knockdown of GHSR-1a using small-interfering (si) RNA (but not by mitogen/extracellular signal-regulated kinase inhibitor PD-98059). Moreover, ghrelin stimulated increased phosphorylation of Akt (Ser473) and eNOS (Akt phosphorylation site Ser1179) that was inhibitable by knockdown of GHSR-1a using siRNA or by pretreatment of cells with wortmannin but not with PD-98059. Ghrelin also stimulated phosphorylation of mitogen-activated protein (MAP) kinase in BAEC. However, unlike insulin, ghrelin did not stimulate MAP kinase-dependent secretion of the vasoconstrictor endothelin-1 from BAEC. We conclude that ghrelin has novel vascular actions to acutely stimulate production of NO in endothelium using a signaling pathway that involves GHSR-1a, PI 3-kinase, Akt, and eNOS. Our findings may be relevant to developing novel therapeutic strategies to treat diabetes and related diseases characterized by reciprocal relationships between endothelial dysfunction and insulin resistance.
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Zhang, Xue, Zihan Zeng, Yaning Liu, and Dan Liu. "Emerging Relevance of Ghrelin in Programmed Cell Death and Its Application in Diseases." International Journal of Molecular Sciences 24, no. 24 (2023): 17254. http://dx.doi.org/10.3390/ijms242417254.
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Ghrelin, comprising 28 amino acids, was initially discovered as a hormone that promotes growth hormones. The original focus was on the effects of ghrelin on controlling hunger and satiation. As the research further develops, the research scope of ghrelin has expanded to a wide range of systems and diseases. Nevertheless, the specific mechanisms remain incompletely understood. In recent years, substantial studies have demonstrated that ghrelin has anti-inflammatory, antioxidant, antiapoptotic, and other effects, which could affect the signaling pathways of various kinds of programmed cell death (PCD) in treating diseases. However, the regulatory mechanisms underlying the function of ghrelin in different kinds of PCD have not been thoroughly illuminated. This review describes the relationship between ghrelin and four kinds of PCD (apoptosis, necroptosis, autophagy, and pyroptosis) and then introduces the clinical applications based on the different features of ghrelin.