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Orexins are neuropeptides that express primarily in the hypothalamus and are produced in two isoforms, orexin A and orexin B. There are two kinds of G protein coupled receptors, orexin type 1 (OX1R) and type 2 (OX2R) receptors. Orexin has been reported to have key roles on sleep-wake regulation and feeding behavior in the central nervous system, whereas its receptors are also expressed in peripheral tissues including the endocrine organs, and orexin affects the regulation of the endocrine system. In our previous experiments, we have revealed the impact of orexins on anterior pituitary functions. For instance, we reported that orexin A plays an inhibitory role in prolactin production through the suppression of endogenous bone morphogenetic protein (BMP) activity in rat pituitary lactotrope GH3 cells. It was also reported that orexin A enhances pro-opiomelanocortin (POMC) transcription by upregulating corticotropin-releasing hormone (CRH) receptor signaling and by downregulating BMP-Smad signaling in mouse corticotope AtT20 cells. However, the effects of orexin on the endocrine function regarding gonadotrope cells remain unclear. We have recently uncovered that core clock genes and BMPs have mutual effects on luteinizing hormone (LH) expression in a phase-dependent manner by mouse gonadotrope LβT2 cells. In the present study, we investigated the effect of orexin on pituitary gonadotropin expression using LβT2 cells, which express OX1R and OX2R, by focusing on the functional involvement of BMP system and clock genes. It was revealed that orexin A stimulation increased LHβ and FSHβ mRNA expression in a concentration-responsive manner in the absence of GnRH, and interestingly, GnRH co-treatment further upregulated LHβ mRNA expression in LβT2 cells. Regarding the interrelationships between the signalings of orexin and BMPs, it was also revealed that orexin A pretreatment enhanced the BMP receptor signaling detected as the Smad1/5/9 phosphorylation, indicating that orexin enables to upregulate the BMP actions in LβT2 cells. In our previous studies, we reported that several BMP ligands such as BMP-6, -7 and 15 expressed in LβT2 cells can promote gonadotropin transcription, in which BMP-6 regulates GnRH-stimulated LH expression by modulating the sensitivity to somatostatin analogs. Based on the present results, it was implied that endogenous orexin can be functionally involved in the underlying mechanisms of gonadotropin expression. Collectively, orexin enhances gonadotropin expression by regulating BMP signaling in gonadotrope cells. Here, we will also discuss functional involvement of clock genes in the regulatory system of gonadotropin secretion induced by orexin and BMPs. Presentation: No date and time listed

Leptin and ghrelin are the two major hormones which regulate food intake and energy balance. They have also been reported to have pleiotropic functions, including the modulation of ovarian function via the hypothalamic-pituitary-ovarian system or in a direct manner to the ovaries. Blood leptin levels increase over the menstrual cycle and peak at the time of the luteinizing hormone (LH) surge. Leptin secreted from adipocytes acts on the hypothalamus and pituitary gland to stimulate the secretion of GnRH and gonadotropins. In the ovaries, high levels of leptin inhibit follicle-stimulating hormone (FSH)-induced steroid secretion and follicular development. Ghrelin, secreted by the stomach, has been reported to modulate GnRH secretion in the hypothalamus and to affect FSH and LH secretion, as well as steroidogenesis in the ovaries. Knockout of these hormones leads to impaired fertility. However, the mechanism of the direct effects of leptin and ghrelin on the ovaries has not been well elucidated. In the present study, we investigated the effects of leptin and ghrelin on the ovarian steroidogenesis using primary culture of rat granulosa cells, by focusing on the ovarian bone morphogenetic protein (BMP) system, which plays an important role in follicular development and steroidogenesis and acts as a luteinizing inhibitor. The results showed that treatment with leptin (1 to 300 ng/mL) did not affect either estradiol (E2) or progesterone (P4) production, but enhanced FSH-induced P4 production at low concentrations (10 ng/mL). On the other hand, treatment with ghrelin (1 to 300 nM) did not affect E2 and P4 production, but enhanced FSH-induced P4 production in a concentration-responsive manner. The mRNA levels of the follicular steroid synthases (StAR, P450scc, 3βHSD, 20αHSD) were examined. Leptin treatment enhanced 3βHSD mRNA levels. Both leptin treatment and ghrelin treatment decreased FSH-induced 20αHSD mRNA levels. However, both treatments decreased FSH-induced cAMP production. In addition, leptin treatment tended to suppress the transcriptional activity of Id-1 induced by BMP-6. Collectively, these results indicate that both leptin and ghrelin enhance FSH-induced P4 production by suppressing BMP signaling in rat granulosa cells. It was thus suggested that leptin and ghrelin which regulate food intake and energy balance can also act as endogenous regulators for the modulation of P4 synthesis and luteinizing process by ovarian follicles. Presentation: No date and time listed

Roles of Clock genes and the bone morphogenetic protein (BMP) system in the regulation of gonadotropin secretion by gonadotropin-releasing hormone (GnRH) were investigated using mouse gonadotropin L beta T2 cells. It was found that luteinizing hormone (LH)beta mRNA expression level in L beta T2 cells changed gradually over time, with LH beta expression being suppressed in the early phase up to 12 h and then elevated in the late phase 24 h after GnRH stimulation. In addition, the mRNA expression levels of Clock genes, including Bmal1, Clock, Per2, and Cry1, also showed temporal changes mimicking the pattern of LH beta expression in the presence and absence of GnRH. Notably, the expression levels of Bmal1 and Clock showed strong positive correlations with LH beta mRNA expression levels. Moreover, a functional link of the ERK signaling of mitogen-activated protein kinases (MAPKs) in the suppression of LH beta mRNA expression, as well as Bmal1 and Clock mRNA expression by GnRH at the early phase, was revealed. Inhibition of Bmal1 and Clock expression using siRNA was involved in the reduction in LH beta mRNA levels in the late phase 24 h after GnRH stimulation. Furthermore, in the presence of BMP-6 and -7, late-phase Bmal1 and LH beta mRNA expression after GnRH stimulation was significantly attenuated. Collectively, the results indicated that LH expression in gonadotrope cells exhibits Bmal1/Clock-dependent fluctuations under the influence of GnRH and that the fluctuations are regulated by ERK and BMPs in the early and late stages, respectively, in a phase-dependent manner after GnRH stimulation.

A functional link between clock gene expression and ovarian steroidogenesis was studied using human granulosa KGN cells. Similarities between changes in the mRNA and protein expression levels of Bmal1 and Clock and those of Per2 and Cry1 were found in KGN cells after treatment with forskolin. Among the interrelationships between the expression levels of clock and steroidogenic factors, Clock mRNA had a strongly positive correlation with P450arom and a negative correlation with 3βHSD. Knockdown of Clock gene by siRNA resulted in a significant reduction of estradiol production by inhibiting P450arom expression, while it induced a significant increase of progesterone production by upregulating 3βHSD in KGN cells treated with forskolin. Moreover, BMP-7 had an enhancing effect on the expression of Clock mRNA and protein in KGN cells. Thus, the expression levels of Clock, being upregulated by forskolin and BMP-7, were functionally linked to estradiol production and progesterone suppression by human granulosa cells.

Functional interactions between the levels of clock gene expression and adrenal steroidogenesis were studied in human adrenocortical H295R cells. Fluctuations of Bmal1, Clock, Per2 and Cry1 mRNA levels were found in H295R cells treated with forskolin (FSK) in a serum-free condition. The changes of clock gene expression levels were diverged, with Clock mRNA level being significantly higher than Cry1 and Per2 mRNA levels after 12-h stimulation with FSK. After FSK induction, mRNA levels of StAR and CYP11B2 were highest at 12 hours and CYP17 mRNA level reached a peak at 6 hours, but HSD3B1 mRNA level was transiently decreased at 3 hours. The expression levels of Clock mRNA showed a significant positive correlation with StAR among the interrelationships between mRNA levels of key steroidogenic factors and clock genes. Knockdown of Clock gene by siRNA led to a significant reduction of FSK-induced expression of StAR and CYP17 after 12-h treatment with FSK. BMP-6 and activin, which modulate adrenal steroidogenesis, had inhibitory effects on Clock mRNA expression, whereas treatment with follistatin, a binding protein of activin, increased Clock mRNA levels in the presence of FSK, suggesting an endogenous function of activin in regulation of Clock mRNA expression. Collectively, the results indicated that changes of Clock mRNA expression, being upregulated by FSK and suppressed by BMP-6 and activin, were tightly linked to StAR expression by human adrenocortical cells.

We previously reported that the expression levels of Clock gene are linked to the expression levels of steroidogenetic enzymes in human granulosa cells (EJ 2019). However, the downstream molecules of the Clock gene actions in the regulation of ovarian steroidogenesis have yet to be elucidated. In the present study, we investigated the roles of the transcription factors, NR5A1 (also known as SF-1) and NR5A2 (LRH-1), which play key roles in the reproductive function as well as steroidogenesis by focusing on the functional link between Clock gene and bone morphogenetic protein (BMP) signaling using human granulosa KGN cells. First of all, we examined the effects of BMPs/growth differentiation factor (GDF) on forskolin (FSK)-induced steroidogenesis. As a result, FSK-induced mRNA levels of StAR and P450scc, but not P450arom, were potently suppressed by treatments with BMP-6, -9, -15 and GDF-9. The expression levels of NR5A1 and NR5A2 mRNA were also upregulated by FSK treatment, while the BMP-target gene Id-1 mRNA levels were stimulated by the treatment with BMPs. Of interest, treatments with BMPs/GDF increased FSK-induced NR5A1 mRNA levels but suppressed FSK-induced NR5A2 mRNA levels by granulosa cells. The expression levels of NR5A1 mRNA were positively correlated with the changes of P450arom and 3βHSD mRNA, whereas the expression levels of NR5A2 mRNA were correlated with that of StAR and P450scc mRNA. In addition, the expression levels of NR5A1 and NR5A2 mRNAs were positively correlated with the levels of Clock mRNA. In particular, Clock mRNA levels showed highly positive correlation with the levels of NR5A2 mRNA compared with NR5A1 mRNA. Of note, Id-1 mRNA levels were positively correlated with the levels of NR5A1 mRNA, but negatively correlated with that of NR5A2 mRNA. Furthermore, the inhibition of Clock gene expression by siRNA attenuated the expression levels of NR5A1 and NR5A2 mRNA, resulting in decreased mRNA levels of StAR and P450arom in the presence of FSK. Thus, the present results suggested a novel mechanism by which Clock expression is functionally linked to the expression of NR5A1 and NR5A2, the latter of which is further regulated by BMP signaling by granulosa cells. The interaction among Clock, NR5A1/NR5A2 and BMPs may be involved in the fine tuning of steroidogenesis by ovarian follicles.

Aldosterone (Aldo) is involved in various cardiovascular diseases such as hypertension and heart failure. Aldo levels are known to be increased in patients with polycystic ovary syndrome, and expression of the mineralocorticoid receptor (MR) has also been detected in the ovary. However, the effect of Aldo on reproductive function has yet to be elucidated. Here, we examined the effects of Aldo on follicular steroidogenesis using primary culture of rat granulosa cells by focusing on the ovarian bone morphogenetic protein (BMP) system acting as a luteinizing inhibitor. We found that Aldo treatment increased FSH-induced progesterone production in a concentration-responsive manner. Consistent with the effects on steroidogenesis, Aldo increased mRNA levels of progesterogenic factor and enzymes including StAR and P450scc, whereas Aldo failed to change FSH-induced estradiol and cAMP synthesis or P450arom expression by granulosa cells. Progesterone production and StAR expression induced by FSH and Aldo were reversed by co-treatment with spironolactone, suggesting the involvement of geonomic MR action. Aldo treatment attenuated Smad1/5/9 phosphorylation and Id1 transcription induced by BMP-6. Furthermore, Aldo enhanced the expression of inhibitory Smad6 in the presence of BMP-6. In addition, BMP-6 downregulated MR expression, while Aldo modulated the mRNA levels of endogenous BMP-6 and BMP type-II receptors, indicating the existence of a feedback loop between the BMP system and MR in granulosa cells. Collectively, the results indicated that Aldo predominantly enhances FSH-induced progesterone production by inhibiting BMP-Smad signaling, suggesting a novel role of Aldo in ovarian steroidogenesis and a functional link between MR and BMP pathways in granulosa cells.

The functional role of the transcription factors NR5A1 and NR5A2 and their interaction with Clock gene and bone morphogenetic proteins (BMPs) were investigated in human granulosa KGN cells. Treatment with BMP-15 and GDF-9 suppressed forskolin (FSK)-induced steroidogenesis as shown by the mRNA expression levels of StAR and P450scc but not the mRNA expression level of P450arom. Of interest, treatment with BMP-15 and GDF-9 also suppressed FSK-induced NR5A2 mRNA expression. Treatment with BMP-15 suppressed NR5A2 mRNA and protein expression but increased Clock mRNA and protein expression levels by granulosa cells. The mRNA expression levels of NR5A1, but not those of NR5A2, were positively correlated with the levels of Clock mRNA, while the mRNA levels of Id-1, the target gene of BMP signaling, were positively correlated with those of NR5A1 but not with those of NR5A2. It was also demonstrated that the mRNA expression levels of NR5A1 were positively correlated with those of P450arom and 3βHSD, whereas the mRNA expression level of NR5A2 was correlated with those of StAR and P450scc. Furthermore, inhibition of Clock gene expression by siRNA attenuated the expression of NR5A1, and the mRNA levels of Clock gene were significantly correlated with those of NR5A1. Collectively, the results suggested a novel mechanism by which Clock gene expression induced by BMP-15 is functionally linked to the expression of NR5A1, whereas NR5A2 expression is suppressed by BMP-15 in granulosa cells. The interaction between Clock NR5A1/NR5A2 and BMP-15 is likely to be involved in the fine-tuning of steroidogenesis by ovarian granulosa cells.