Gotowa bibliografia na temat „SIRT2-KO mice”

Abstract Background Activation of mitogen-activated protein kinase phosphatase-1 (MKP-1), a dual-specificity protein phosphatase, regulates mitogen-activated protein kinase signaling. C-Jun N-terminal kinase (JNK) and p38 are activated in cisplatin-induced renal injury. However, the change of MKP-1 expression in cisplatin-induced renal injury and the regulatory effect of sirtuin 2 (SIRT2), a nicotinamide adenine dinucleotide–dependent deacetylase, on MKP-1 remains unknown. Methods To address these issues, we used constitutional Sirt2 knockout (KO) mice, transgenic (TG) mice with increased expression of SIRT2 specifically in proximal tubular epithelial cellsand wild-type (WT) mice. Cisplatin nephrotoxicity was induced by intraperitoneal injection of cisplatin. Results MKP-1 expression in the kidney was decreased after cisplatin treatment. Cisplatin-induced downregulation of MKP-1 was reversed in Sirt2 KO mice kidney and further decreased in Sirt2 TG mice kidney. We observed similar phenomenon with SIRT2-knockdown or SIRT2-overexpressed tubular epithelial cells. Phosphorylation of p38 and JNK, a downstream signal pathway of MKP-1, increased in WT mice kidney following treatment with cisplatin. A decrease in SIRT2 suppressed cisplatin-induced phosphorylation of p38 and JNK in kidney and tubular epithelial cells. Overexpression of SIRT2 further increased phosphorylation of p38 and JNK in kidney and tubular epithelial cells. Acetylation of MKP-1 was significantly increased in SIRT2-knockdown cells and decreased in SIRT2-overexpressed cells after cisplatin stimulation. Sirt2 KO mice and Sirt2 TG mice showed amelioration and aggravation of renal injury, apoptosis, necroptosis and inflammation induced by cisplatin. Conclusion Our data show that SIRT2 is associated with cisplatin-induced renal injury through regulation of MKP-1 expression.

Nonalcoholic fatty liver disease (NAFLD), a condition strongly associated with obesity and insulin resistance, is characterized by hepatic lipid accumulation and activation of the endoplasmic reticulum (ER) stress response. The sirtuin 2 (SIRT2) protein deacetylase is emerging as a new player in metabolic homeostasis, but its role in the development of hepatic steatosis and its link with ER stress activation remains unknown. SIRT2-knockout (SIRT2-KO) and wild-type mice were fed either a control or a high-fat diet (HFD) for 4 weeks. Genetic manipulation of SIRT2 levels was performed in human hepatic cells. Although apparently normal under a control diet, SIRT2-KO mice showed accelerated body weight gain and adiposity on a HFD, accompanied by severe insulin resistance. Importantly, SIRT2-KO mice exhibited worsened hepatic steatosis independently from diet, consistent with upregulated gene expression of lipogenic enzymes and increased expression of ER stress markers. Exposure of hepatic cells to palmitate induced lipid accumulation, increased ER stress, and decreased SIRT2 expression. Moreover, SIRT2-silenced cells showed enhanced lipid accumulation and ER stress activation under basal conditions, whereas SIRT2 overexpression abrogated palmitate-induced lipid deposition and ER stress activation. Our findings reveal a role for SIRT2 in the regulation of hepatic lipid homeostasis, potentially through the ER stress response, suggesting that SIRT2 activation might constitute a therapeutic strategy against obesity and its metabolic complications.

Non-alcoholic fatty liver disease (NAFLD), characterized by excessive lipid accumulation in hepatocytes, is an increasing global healthcare burden. Sirtuin 2 (SIRT2) functions as a preventive molecule for NAFLD with incompletely clarified regulatory mechanisms. Metabolic changes and gut microbiota imbalance are critical to the pathogenesis of NAFLD. However, their association with SIRT2 in NAFLD progression is still unknown. Here, we report that SIRT2 knockout (KO) mice are susceptible to HFCS (high-fat/high-cholesterol/high-sucrose)-induced obesity and hepatic steatosis accompanied with an aggravated metabolic profile, which indicates SIRT2 deficiency promotes NAFLD-NASH (nonalcoholic steatohepatitis) progression. Under palmitic acid (PA), cholesterol (CHO), and high glucose (Glu) conditions, SIRT2 deficiency promotes lipid deposition and inflammation in cultured cells. Mechanically, SIRT2 deficiency induces serum metabolites alteration including upregulation of L-proline and downregulation of phosphatidylcholines (PC), lysophosphatidylcholine (LPC), and epinephrine. Furthermore, SIRT2 deficiency promotes gut microbiota dysbiosis. The microbiota composition clustered distinctly in SIRT2 KO mice with decreased Bacteroides and Eubacterium, and increased Acetatifactor. In clinical patients, SIRT2 is downregulated in the NALFD patients compared with healthy controls, and is associated with exacerbated progression of normal liver status to NAFLD to NASH in clinical patients. In conclusion, SIRT2 deficiency accelerates HFCS-induced NAFLD-NASH progression by inducing alteration of gut microbiota and changes of metabolites.

Introduction: Sirtuins are NAD+ dependent deacetylases and critical regulators of energy metabolism and response to oxidative stress. Sirtuin2 (SIRT2) is a cytoplasmic member of the sirtuin family, and has been shown to regulate cellular iron homeostasis through deacetylation of nuclear factor erythroid-derived 2-related factor 2 (NRF2). However, whether SIRT2-NRF2 pathway is involved in the development of heart failure remains unknown. Methods and results: To investigate the functional role of SIRT2 in the response to cardiac stress, SIRT2 knockout (KO) mice and their littermate controls were subjected to pressure overload by transverse aortic constriction (TAC). SIRT2 KO had normal appearance and cardiovascular parameters at baseline. However, in response to TAC, Sirt2 -/- mice displayed resistance to the pathological hypertrophic response, whereas wild type (WT) mice developed cardiac hypertrophy and heart failure. In addition, SIRT2 KO mice displayed less cardiac damage after /reperfusion injury. SIRT2 knockdown in neonatal rat cardiomyocytes (NRCM) reduced reactive oxygen species (ROS) production and cell death after H2O2 treatment. Since cellular oxidative stress is one of major contributor of cardiac dysfunction caused by both I/R injury and pressure overload, we examined whether NRF2 is associated with SIRT2-mediated cardiac response to oxidative stress. Levels of NRF2 was upregulated in NRCM with SIRT2 knockdown and treated with H2O2 compared to wild type (WT) cells. Moreover, NRF2 is translocated into the nucleus and its anti-oxidant target proteins are upregulated in NRCM with SIRT2 knockdown. SIRT2 was also found to bind and deacetylate NRF2 directly as determined by co-immunoprecipitation studies. This led to a reduction of its nuclear translocation and transcriptional activity. Finally, knockdown of both SIRT2 and NRF2 diminished the effects of SIRT2 knockdown on ROS production and cellular damage. Conclusion: These results indicate that SIRT2 contributes to pressure overload and I/R injury induced heart impairment in mice, and promotes oxidative stress injury in cardiomyocytes via deacetylating NRF2 and altering its activity.

Over the last century the major causes of human deaths and ailments has shifted from acute infectious diseases to chronic aging related disorders like cancer and type-2 diabetes. The aging process is a universal property of most organisms, accompanied by a subtle, progressive, and often irreversible decline of physiological and reproductive functions resulting in an increased vulnerability to environmental challenge and a growing risk of disease and death. In molecular terms, it can be understood as a decline of the homeostatic mechanisms that ensure the function of cells, tissues, organs, and organ systems. However, caloric restriction (CR), i.e. reduced intake of food has been shown to ameliorate the effects of aging to some extent. One of the ways through CR slows down aging is by activating a group of enzymes known as Sirtuins, are a family of NAD+ dependant Class III histone deacetylases, which were first characterized in yeast. In S. cerevisiae, overexpression of Sir2, the founding member of the family, was shown to extend the replicative lifespan, while its depletion decreased lifespan. In mammals, there are seven orthologues of Sir2 (SIRT1-7) with a conserved catalytic domain. They differ in their enzymatic activity, subcellular localisation and therefore their binding partners and target molecules. SIRT1, 6 and 7 are localized in nucleus, SIRT3, 4 and 5 are mitochondrial sirtuins. SIRT2, which is mostly cytoplasmic but translocate to the nucleus during G2/M transition phase in cell cycle, has a NAD+-dependent deacetylase activity along with Mono-ADP-Ribosyl transferase activity. SIRT2 regulates microtubule dynamics of the cell by acetylation at K40 residue of tubulin. Although, generally deemed to be a tumour suppressor as it regulates cell cycle progression, it was observed to be upregulated in some cancers. One of the major targets of SIRT2 are FoxO family of transcription factors, which are involved in regulation of processes as varied as cell death, adipocyte differentiation and autophagy. By deacetylating them, SIRT2 can regulate their activity, stability and sub-cellular localization. However, the role of SIRT2 in cardiac diseases, oxidative stress response and regulation of insulin resistance is unknown. In this work, we studied the role of SIRT2 in cardiac hypertrophy, cell death and glucose homeostasis. PART 1: Role of SIRT2 in cardiac hypertrophy To find out if SIRT2 plays a role in cardiac hypertrophy, we treated mice with Isoproterenol, a well-accepted model of pathological hypertrophy. We found SIRT2 protein levels to be significantly downregulated in Isoproterenol-treated mice hearts as compared to the controls. In vitro experiments with primary cardiomyocytes yielded the same results. SIRT2 knockout mice spontaneously developed age dependent cardiac hypertrophy and fibrosis. We found that SIRT2 binds to and deacetylates the transcription factor NFATc2. NFATc2 activation is a well-known modulator of cardiac fetal-programme and cardiac hypertrophy. SIRT2 deficiency leads to hyperacetylation of NFATc2, while acetylation enhances nuclear localization of NFATc2. Further, we have demonstrated that GSK3 activity is markedly reduced in Sirt2 knockout mice, a hallmark of hypertrophic hearts. It has been shown that cardiac specific GSK3 overexpression ameliorates cardiac hypertrophy. We found GSK3 activity increased by SIRT2 mediated deacetylation of Lys246 and Lys183 of GSK3α and GSK3β respectively. Interestingly, reduced GSK activity in SIRT2-deficient mice was independent of inhibitory phosphorylation at Ser9. Moreover, GSK3 is required for the anti-hypertrophic function of SIRT2. PART 2: Role of SIRT2 in regulating oxidative stress-induced cell death Our body is continually exposed to variety of exogenous or endogenous stresses. Chronic stresses can disrupt nearly every system in our body and can eventually lead to serious life-threatening illnesses such as heart attacks, kidney disease and cancer. Sirtuins are known to regulate cell death. SIRT1 increases cell survival, by modulating activity of p53 and FOXO3 deacetylation mediated degradation. SIRT3 decreases cell death by improving mitochondrial function. However, role of SIRT2 in cell death is not well understood. In this study we found that SIRT2-depleted cells are resistant to oxidative stress and show enhanced survival. Similarly, SIRT2-KO mice showed enhanced resistance to acetaminophen-induced hepatocyte cell death. Mechanistically, acetylation of JNK at K153 by p300 acetyl transferase reduced JNK phosphorylation and activity, whereas deacetylation of JNK by SIRT2 promoted its phosphorylation as well its activity. Our molecular simulation and biological assays demonstrated that acetylation of JNK at K153 impairs ATP binding, hence reduces its activity. Our results indicate that deacetylation of JNK by SIRT2 promotes oxidative stress-induced cell death. PART 3: Understanding the role of SIRT2 in glucose homeostasis Glucose is one of the major sources of energy for human body, hence regulation of glucose is tightly regulated. Skeletal muscles play a key role in glucose homeostasis. Skeletal muscles comprise around 40-50% of the total body mass in humans and around 80% of glucose in the body is utilized by skeletal muscles. Impaired glucose uptake by muscle cells leads to insulin resistance. SIRT2 improves glucose uptake in hepatocytes through deacetylation of glucokinase regulatory protein (GKRP) or SIRT2 mediated phosphoenolpyruvate carboxy kinase (PEPCK) deacetylation, thus modulating gluconeogenesis in liver. However, role of SIRT2 in glucose homeostasis in muscle tissue is not well studied. Upon induction of high fat diet (HFD) mediated insulin resistance, SIRT2 levels were increased in skeletal muscle of mice. We found SIRT2-KO mice to be highly resistant to HFD induced insulin resistance as revealed by markedly higher glucose clearance rate. Mechanistically, SIRT2 mediated deacetylation of IRS1 was found to promote the inhibitory phosphorylation of IRS1 at Ser307 through activate JNK, which is associated with impaired insulin signalling. We found that SIRT2 overexpression reduced the insulin-stimulated membrane localization of GLUT4 transporter. Our results further suggest that inhibition of SIRT2 reverses the palmitate-induced reduction in cellular glucose uptake and promotes glucose uptake in insulin resistant myotubes and therefore ameliorates the effects of insulin resistance. In the present work, we have elucidated the role of SIRT2 cardiac myocytes, hepatocytes and skeletal myotubes. We believe that modulation of SIRT2 activity could be a potential therapeutic strategy to treat diseases related to aging