Luteal Cells

Ovarian hyperstimulation syndrome (OHSS) is one of the most serious and iatrogenic complications that can occur during in vitro fertilization treatment. Although the pathogenesis of OHSS is not fully understood, vascular endothelial growth factor (VEGF) has been recognized as an important mediator of the development of OHSS. Transforming growth factor-beta-1 (TGF-β1) is known to regulate various ovarian functions. However, whether VEGF can be regulated by TGF-β1 in human granulosa cells has not been determined. In addition, the role of TGF-β1 in the pathogenesis of OHSS remains unknown. In the present study, we demonstrate that TGF-β1 stimulates VEGF expression in and secretion from both immortalized human granulosa-lutein (hGL) cells and primary hGL cells. Our results demonstrate that the SMAD2/3, ERK1/2, and p38 MAPK signaling pathways are involved in TGF-β1-induced VEGF expression and secretion. Using a mouse OHSS model, we show that the expression levels of TGF-β1 and VEGF are increased in the ovaries of OHSS mice. Blocking TGF-β1 signaling inhibits the development of OHSS by attenuating VEGF expression. Moreover, clinical results reveal that the protein levels of TGF-β1 and VEGF are increased in the follicular fluid of patients with OHSS, and that the levels of these two proteins in the follicular fluid are positively correlated. The results of this study help to elucidate the mechanisms by which VEGF expression is regulated in hGL cells, which could lead to the development of alternative therapeutic approaches for treating OHSS.

The corpus luteum is a small gland of great importance because its proper functioning determines not only the appropriate course of the estrous/menstrual cycle and embryo implantation, but also the subsequent maintenance of pregnancy. Among the well-known regulators of luteal tissue functions, increasing attention is focused on the role of neuropeptides and adipose tissue hormones-adipokines. Growing evidence points to the expression of these factors in the corpus luteum of women and different animal species, and their involvement in corpus luteum formation, endocrine function, angiogenesis, cells proliferation, apoptosis, and finally, regression. In the present review, we summarize the current knowledge about the expression and role of adipokines, such as adiponectin, leptin, apelin, vaspin, visfatin, chemerin, and neuropeptides like ghrelin, orexins, kisspeptin, and phoenixin in the physiological regulation of the corpus luteum function, as well as their potential involvement in pathologies affecting the luteal cells that disrupt the estrous cycle.

Steroidogenic acute regulatory protein (StAR) mediates the rate-limiting step in ovarian steroidogenesis and progesterone (P4) synthesis. Melatonin and its receptors are expressed in human granulosa cells, and have been shown to influence basal P4 production. However, previous studies addressing the regulation of StAR expression by melatonin and its impact on P4 secretion yielded contradictory results. Here, we demonstrate that melatonin upregulates StAR expression in primary cultures of human granulosa-lutein (hGL) cells obtained from women undergoing in vitro fertilization (IVF). Using pharmacological inhibitors, we show that the stimulatory effect of melatonin on StAR expression is mediated via both MT1 and MT2 melatonin receptors. Melatonin exposure activates the PI3K/AKT signaling pathway and its inhibition attenuates the stimulatory effect of melatonin on StAR expression. Moreover, siRNA-mediated knockdown of StAR abolishes melatonin-induced P4 production. Importantly, clinical analyses demonstrate that melatonin levels in human follicular fluid are positively correlated with P4 levels in serum. By illustrating the potential physiological role of melatonin in the regulation of StAR expression and P4 production in hGL cells, our results may serve to improve current strategies used to treat clinical infertility.

BackgroundProgesterone production by the corpus luteum is essential for embryo implantation and early pregnancy maintenance and is acutely stimulated by luteinizing hormone (LH). While LH signaling through protein kinase A (PKA) is well established, downstream regulatory networks that constrain or shape luteal steroidogenesis remain incompletely defined. Here, we identify a previously unrecognized role for the Hippo signaling pathway in regulating luteal progesterone production.MethodsUsing primary bovine luteal cells isolated from corpora lutea, we examined the relationship between LH/PKA signaling and Hippo signaling pathway activity. Expression, phosphorylation, and subcellular localization of Hippo pathway components were assessed by immunoblotting and nuclear fractionation. Progesterone production was quantified by ELISA. LH-induced transcriptional responses were analyzed using upstream regulator prediction from RNA sequencing. Functional roles of YAP1 and TAZ were evaluated using adenoviral overexpression of constitutively active mutants and siRNA-mediated knockdown.ResultsHippo pathway components were enriched in luteal cells relative to follicular precursors. LH rapidly increased phosphorylation and cytoplasmic sequestration of YAP1 and TAZ in small luteal cells through PKA. Pharmacologic inhibition of LATS1/2 did not alter LH-stimulated progesterone production, suggesting that LH-induced steroidogenesis is not limited by LATS-dependent regulation of YAP1/TAZ. Sustained activation of YAP1 or TAZ suppressed LH-induced progesterone synthesis, whereas depletion of either factor enhanced progesterone output. Consistently, RNA-seq analysis identified YAP1/TAZ, and TEAD transcription factors as inhibited upstream regulators following LH stimulation in small luteal cells.ConclusionsOur findings support a model in which LH, via PKA and activation of Hippo signaling promotes progesterone synthesis by restraining YAP1/TAZ transcriptional activity in small luteal cells. This work identifies Hippo signaling as an unrecognized regulatory layer in luteal steroidogenesis and highlights YAP1/TAZ as potential therapeutic target for luteal insufficiency and infertility.