Academic literature on the topic 'Luteotropic factors'

The aims of this study were to examine the effect of luteotropic and luteolytic factors on the mRNA and protein expression of the coactivators HAT: histone acetyltransferase p300 (P300), cyclic adenosine monophosphate response element-binding protein (CREB), and steroid receptor coactivator-1 (SRC-1) and the corepressor: nuclear receptor corepressor-2 (NCOR-2) in bovine luteal cells on days 6–10 and 16–20. HAT and HDAC activities were also measured. The obtained results showed that luteotropic and luteolytic factors influence changes in the mRNA and protein levels of the coregulators of PGRs. However, they did not affect the activity of related HAT and HDAC, respectively. Therefore, it is possible that these factors, through changes in the expression of nuclear receptor coactivators and corepressors, may affect the functioning of the nuclear receptors, including PGRs, in the bovine CL.

The corpus luteum is an endocrine gland that synthesizes the steroid hormone progesterone. luteinizing hormone (LH) is a key luteotropic hormone that stimulates ovulation, luteal development, progesterone biosynthesis, and maintenance of the corpus luteum. Luteotropic and luteolytic factors precisely regulate luteal structure and function; yet, despite recent scientific progress within the past few years, the exact mechanisms remain largely unknown. In the present review, we summarize the recent progress towards understanding cellular changes induced by LH in steroidogenic luteal cells. Herein, we will focus on the effects of LH on inter-organelle communication and steroid biosynthesis, and how LH regulates key protein kinases (i.e., AMPK and MTOR) responsible for controlling steroidogenesis and autophagy in luteal cells.

The aim of the present study was to examine the effects of luteotropic and luteolytic factors on the mRNA and protein levels of progesterone receptor isoforms A (PGRA) and B (PGRB) in the bovine endometrium. Endometrial slices from Days 6–10 and 17–20 of the oestrous cycle were treated with LH (100 ng mL–1), oestradiol (E2; 1 × 10–8 M), prostaglandin (PG) E2 (1 × 10–6 M) and PGF2α (1 × 10–6 M) and the nitric oxide donor NONOate (1 × 10–4 M); these treatments lasted for 6 h for mRNA expression analysis and 24 h for protein expression analysis. On Days 6–10 of the oestrous cycle PGRAB (PGRAB; the entire PGRA mRNA sequence is common to the PGRB mRNA sequence) mRNA expression in endometrial slices was enhanced by E2 treatment (P < 0.001), whereas PGRB mRNA expression was increased by LH (P < 0.001), E2 (P < 0.05) and NONOate (P < 0.05) treatment. On Days 17–20, PGRAB mRNA expression increased after E2 (P < 0.001) and PGE2 (P < 0.05) treatment; PGRB mRNA expression was increased by PGE2 (P < 0.05) and PGF2α (P < 0.01) treatment, but decreased by LH (P < 0.05). On Days 6–10 protein levels of PGRA were stimulated by E2 (P < 0.01), whereas PGRB protein levels were increased by LH (P < 0.05) and E2 (P < 0.05). On Days 17–20 of the oestrous cycle, PGRA protein levels were enhanced by E2 (P < 0.05) and PGF2α (P < 0.05), whereas PGRB protein levels were stimulated by PGE2 (P < 0.05) and PGF2α (P < 0.001). These data suggest that luteotropic and luteolytic factors affect PGRA and PGRB mRNA and protein levels, and this may regulate the effects of progesterone on endometrial cells.

Although LH is essential for survival and function of the corpus luteum (CL) in higher primates, luteolysis occurs during nonfertile cycles without a discernible decrease in circulating LH levels. Using genome-wide expression analysis, several experiments were performed to examine the processes of luteolysis and rescue of luteal function in monkeys. Induced luteolysis with GnRH receptor antagonist (Cetrorelix) resulted in differential regulation of 3949 genes, whereas replacement with exogenous LH (Cetrorelix plus LH) led to regulation of 4434 genes (1563 down-regulation and 2871 up-regulation). A model system for prostaglandin (PG) F2α-induced luteolysis in the monkey was standardized and demonstrated that PGF2α regulated expression of 2290 genes in the CL. Analysis of the LH-regulated luteal transcriptome revealed that 120 genes were regulated in an antagonistic fashion by PGF2α. Based on the microarray data, 25 genes were selected for validation by real-time RT-PCR analysis, and expression of these genes was also examined in the CL throughout the luteal phase and from monkeys treated with human chorionic gonadotropin (hCG) to mimic early pregnancy. The results indicated changes in expression of genes favorable to PGF2α action during the late to very late luteal phase, and expressions of many of these genes were regulated in an opposite manner by exogenous hCG treatment. Collectively, the findings suggest that curtailment of expression of downstream LH-target genes possibly through PGF2α action on the CL is among the mechanisms underlying cross talk between the luteotropic and luteolytic signaling pathways that result in the cessation of luteal function, but hCG is likely to abrogate the PGF2α-responsive gene expression changes resulting in luteal rescue crucial for the maintenance of early pregnancy. Results of genome-wide analyses suggest that curtailment of expression of LH target-genes through PGF2α action in corpus luteum involves cross talk between luteotropic and luteolytic signaling pathways.

The survivability and opportunity of successful development of an embryo are influenced directly or indirectly by factors controlling uterine microenvironment. Out of all factors, hormones such as prostaglandins (PGs) released during the preimplantation period influence molecular interactions involved in maintenance of pregnancy through reciprocal interactions between the conceptus and endometrium. PGs are important regulators of female reproductive functions, namely, ovulation, uterine receptivity, implantation, and parturition. Among different classes of PGs, prostaglandin F2α (PGF2α) and prostaglandin E2 (PGE2) are main prostanoids produced by human and bovine endometrium for successful growth and development of the posthatching blastocyst. In ruminants, PGF2α produced by endometrium is the major luteolytic agent, whereas PGE2 has luteoprotective and antiluteolytic properties. Therefore, the development and maintenance of the corpus luteum (CL), as well as establishment of pregnancy, depend on the balance of luteolytic PGF2α and luteotropic PGE2. In this review, we discussed the expression and function of genes which predominantly regulate the synthesis and their secretion of PGF2α and PGES, namely, PGFS (AKR1B5/AKR1C3), PGES, PGFR, and COX-2.

The Corpus luteum (CL) is a dynamic endocrine structure that develops in the ovary from the remnants of the ovulated follicle and plays a critical role in the control of estrous/menstrual cycle as well as in establishment and maintenance of pregnancy. Its main function is to secrete a steroid hormone progesterone (P4). During non-fertile reproductive cycles, CL undergoes regression but its life span gets extended during fertile cycles including pseudopregnant condition. The growth and function of CL are regulated by luteotropic and luteolytic factors. The luteotropic factors mainly include prolactin, luteinizing hormone (LH), P4 and growth hormone, whereas the luteolytic factors include oxytocin and prostaglandin F2α (PGF2α). LH plays a critical role in the growth and maintenance of CL function in pregnant rats. However, it appears that the effects of LH on CL vary with the stage of pregnancy. Accordingly, it has been observed that LH functions as a luteotropic factor during the first half of pregnancy, but during the second half of pregnancy its luteolytic effects may predominate. While the luteotropic role of LH in several species has been widely accepted and extensively investigated, its luteolytic role has received scant attention. In this work, studies have been carried out to examine the luteolytic actions of LH with a view to elucidate the molecular mechanism/s involved in the initiation of LH-mediated luteolysis in pregnant rats. It has been reported by others that administration of repeated injections of LH leads to initiation of luteolytic events during late pregnancy. In the current studies, the same method has been standardized to initiate luteolysis and to examine the mechanism/s by which repeated administration of LH causes luteolytic effects. Two stages of pregnancy were chosen for the studies; late stage (gestation day 19 to 20) and mid stage (gestation day 8 to 10) of pregnancy. Stocco and co-workers have reported initiation of functional luteolysis upon repeated LH administration during the late stage of pregnancy. The results from the current study suggest that repeated LH administration exerts luteolytic effects both during late and mid stages of pregnancy. However, it was observed the luteolytic effects of repeated LH administration were more pronounced during late stage of pregnancy since both functional and structural luteolysis were seen. On the other hand, expression of markers of only functional luteolysis increased during the mid stage of pregnancy. Studies were carried out to delineate the mechanism by which repeated LH administration mediates its luteolytic effects. Based on previous studies and the data obtained from high throughput microarray analysis, the involvement of cAMP/PKA/CREB pathway, MAP kinase family of serine/threonine kinases, β-arrestins and prostaglandin signaling in the initiation of LH-mediated luteolysis were chosen for further analysis. It was observed that the repeated administration of LH desensitized the cAMP/PKA/CREB pathway. Activation of the cAMP/PKA/CREB pathway through forskolin treatment in desensitized primary culture of luteal tissue prevented the initiation of luteolytic events during both the stages of pregnancy. Of the MAP kinases examined, protein levels of pp38 kinase decreased significantly in rats receiving multiple injections of LH during the late stage of pregnancy. The physiological relevance of the down regulation of pp38 MAP kinase requires further investigation. To further analyse the role of β-arrestins during the process of luteolysis, two approaches were employed. In the first approach, a β-arrestin biased agonist, dg-CG was utilised to increase the endogenous levels of β-arrestin 1 whereas in the second approach, endogenous β-arrestin 1 levels were depleted through siRNA approach. It was observed that the increased expression of β-arrestin 1 had no effect on markers of luteolysis upon dg-CG administration during late stage of pregnancy suggesting that increased expression of β-arrestin 1 alone is not enough to initiate the process of luteolysis. On the other hand, depletion of β-arrestin 1 by siRNA approach resulted in inhibition of the luteolytic events during both stages of pregnancy. Remarkably, the inhibitory effect of β-arrestin 1 depletion was more pronounced during the mid pregnancy stage. Further, the results indicated that late pregnancy stage was more responsive to PGF2α signaling. To confirm the participation of endogenous PGF2α during luteolysis induced by repeated LH administration, production of prostaglandins was inhibited by employing diclofenac (DIC) a prostaglandin biosynthesis inhibitor. After confirming inhibition of the genes associated with PGF2α synthesis by DIC treatment, multiple LH injections were administered to DIC treated rats to examine luteolytic effects of LH in the absence of endogenous PGF2α signaling. It was observed the repeated administration of LH caused only functional luteolysis in the absence of endogenous PGF2α signaling. Overall the results from the present studies suggest that luteolysis is a complex process and relies on different pathways during different stages of pregnancy examined. Desensitization of the cAMP/PKA/CREB appears to initiate the process of luteolysis during both the stages of pregnancy. However, during the late stage of pregnancy PGF2α though important, plays a limited role. A positive correlation between expression of β-arrestin 1 and markers of luteolysis was observed during both the stages of pregnancy

The main goal of this research plan was to elucidate regulatory mechanisms controlling the development, function of the bovine corpus luteum (CL). The CL contains two different sterodigenic cell types and therefore it was necessary to obtain pure cell population. A system was developed in which granulosa and theca interna cells, isolated from a preovulatory follicle, acquired characteristics typical of large (LL) and small (SL) luteal cells, respectively, as judged by several biochemical and morphological criteria. Experiments were conducted to determine the effects of granulosa cells removal on subsequent CL function, the results obtained support the concept that granulosa cells make a substaintial contribution to the output of progesterone by the cyclic CL but may have a limited role in determining the functional lifespan of the CL. This experimental model was also used to better understand the contribution of follicular granulosa cells to subsequent luteal SCC mRNA expression. The mitochondrial cytochrome side-chain cleavage enzyme (SCC), which converts cholesterol to pregnenolone, is the first and rate-limiting enzyme of the steroidogenic pathway. Experiments were conducted to characterize the gene expression of P450scc in bovine CL. Levels of P450scc mRNA were higher during mid-luteal phase than in either the early or late luteal phases. PGF 2a injection decreased luteal P450scc mRNA in a time-dependent manner; levels were significantly reduced by 2h after treatment. CLs obtained from heifers on day 8 of the estrous cycle which had granulosa cells removed had a 45% reduction in the levels of mRNA for SCC enzymes as well as a 78% reduction in the numbers of LL cells. To characterize SCC expression in each steroidogenic cell type we utilized pure cell populations. Upon luteinization, LL expressed 2-3 fold higher amounts of both SCC enzymes mRNAs than SL. Moreover, eight days after stimulant removal, LL retained their P4 production capacity, expressed P450scc mRNA and contained this protein. In our attempts to establish the in vitro luteinization model, we had to select the prevulatory and pre-gonadotropin surge follicles. The ratio of estradiol:P4 which is often used was unreliable since P4 levels are high in atretic follicles and also in preovulatory post-gonadotropin follicles. We have therefore examined whether oxytocin (OT) levels in follicular fluids could enhance our ability to correctly and easily define follicular status. Based on E2 and OT concentrations in follicular fluids we could more accurately identify follicles that are preovulatory and post gonadotropin surge. Next we studied OT biosynthesis in granulosa cells, cells which were incubated with forskolin contained stores of the precursor indicating that forskolin (which mimics gonadotropin action) is an effective stimulator of OT biosynthesis and release. While studying in vitro luteinization, we noticed that IGF-I induced effects were not identical to those induced by insulin despite the fact that megadoses of insulin were used. This was the first indication that the cells may secrete IGF binding protein(s) which regonize IGFs and not insulin. In a detailed study involving several techniques, we characterized the species of IGF binding proteins secreted by luteal cells. The effects of exogenous polyunsaturated fatty acids and arachidonic acid on the production of P4 and prostanoids by dispersed bovine luteal cells was examined. The addition of eicosapentaenoic acid and arachidonic acid resulted in a dose-dependent reduction in basal and LH-stimulated biosynthesis of P4 and PGI2 and an increase in production of PGF 2a and 5-HETE production. Indomethacin, an inhibitor of arachidonic acid metabolism via the production of 5-HETE was unaffected. Results of these experiments suggest that the inhibitory effect of arachidonic acid on the biosynthesis of luteal P4 is due to either a direct action of arachidonic acid, or its conversion to 5-HETE via the lipoxgenase pathway of metabolism. The detailed and important information gained by the two labs elucidated the mode of action of factors crucially important to the function of the bovine CL. The data indicate that follicular granulosa cells make a major contribution to numbers of large luteal cells, OT and basal P4 production, as well as the content of cytochrome P450 scc. Granulosa-derived large luteal cells have distinct features: when luteinized, the cell no longer possesses LH receptors, its cAMP response is diminished yet P4 synthesis is sustained. This may imply that maintenance of P4 (even in the absence of a Luteotropic signal) during critical periods such as pregnancy recognition, is dependent on the proper luteinization and function of the large luteal cell.