Crosstalk between FSH and relaxin at the end of the proliferative stage of rat Sertoli cells.

Follicle-stimulating hormone (FSH) stimulates the proliferation of immature Sertoli cells through the activation of PI3K/AKT/mTORC1 and MEK/ERK1/2 pathways. Mature Sertoli cells stop proliferating and respond to FSH by stimulating cAMP production. To gain insight into possible mechanisms involved in this switch as well as the impact of paracrine factors that stimulate cell proliferation, we analyzed the effects of FSH and relaxin on intracellular signaling pathways involved with proliferation and differentiation in Sertoli cells from 15-day-old rats, which are close to the transition between the two stages. FSH stimulated 3H-thymidine incorporation and cyclin D1 expression, changes associated with proliferation. In contrast, FSH inhibited AKT and ERK1/2 phosphorylation, activated cAMP production and induced changes in several cell cycle genes that were compatible with differentiation. Relaxin also stimulated 3H-thymidine incorporation but increased phosphorylation of ERK1/2 and AKT. When both hormones were added simultaneously, relaxin attenuated FSH-mediated inhibition of ERK1/2 and AKT phosphorylation and FSH-mediated activation of cAMP production. FSH but not relaxin increased CREB phosphorylation, and relaxin but not FSH shifted NF-κB expression from the cytoplasm to the nucleus. Relaxin did not inhibit the effects of FSH on inhibin α and Bcl2 expression. We propose that at this time of Sertoli cell development, FSH starts to direct cells to differentiation through activation of cAMP/CREB and inhibition of ERK1/2 and AKT pathways. Relaxin counteracts FSH signaling through the inhibition of cAMP and activation of ERK1/2, AKT and NF-κB, but does not block the differentiation process triggered by FSH.

Relaxin and Sertoli cell proliferation.

Immature Sertoli cells proliferate and several factors affect their number, including the follicle stimulating hormone (FSH), testosterone, estradiol and several paracrine growth factors. Using a primary culture of Sertoli cells isolated from 15-day old Wistar rats we have shown that relaxin stimulates Sertoli cell proliferation through the activation of MEK/ERK1/2 and PI3K/AKT pathways. In contrast, FSH inhibited both ERK1/2 and AKT phosphorylation. Furthermore, FSH strongly increased cAMP production, whereas relaxin inhibited basal cAMP production. Our results indicate that in rat Sertoli cells from 15-day old rats relaxin and FSH affect the same signaling pathways in opposite directions. Interplay between both hormones may be important to control the proliferation and differentiation of Sertoli cells.

Effects of relaxin in a co-culture of Sertoli and germ cells.

Spermatogenesis is controlled by FSH, testosterone and paracrine factors produced by Sertoli cells. The knockout of relaxin decreases sperm maturation in mice. Studies from our laboratory have shown that relaxin and its receptor RXFP1 are expressed in rat Sertoli cells, and exogenous relaxin stimulates Sertoli cell proliferation. Relaxin receptors are also detected in the rat germ cells at specific stages of development. Relaxin could therefore affect spermatogenesis either indirectly, by stimulating Sertoli cell proliferation, or directly, by affecting germ cells. The aim of the present study was to explore a role of relaxin at specific stages of spermatogenesis using a co-culture of rat Sertoli and germ cells. Relaxin seems to increase the number of pre-meiotic and meiotic cells.

17Beta-estradiol signaling and regulation of proliferation and apoptosis of rat Sertoli cells.

The aim of the present study was to investigate the intracellular signaling events downstream of the classical estrogen receptors (ESRs) and G protein-coupled estrogen receptor 1 (GPER) involved in regulation of proliferation and apoptosis of rat Sertoli cells, in which we have previously described ESR1, ESR2, and GPER. ESRs play a role in Sertoli cell proliferation, and GPER, but not ESRs, plays a role modulating gene expression involved with apoptosis. The present study shows that 17beta-estradiol (E2) and the GPER-selective agonist G-1 rapidly activate phosphatidylinositol 3-kinase (PIK3)/serine threonine protein kinase (AKT) and cyclic AMP response element-binding (CREB) phosphorylation. E2 and the ESR1-selective agonist 4,4',4″-(4-propyl-(1H)-pyrazole-1,3,5-triyl)trisphenol (PPT) increase the expression of cyclin D1 (CCND1), whereas the ESR2-selective agonist 2,3-bis(4-hydroxyphenyl)-propionitrile (DPN) and G-1 do not change the expression of this protein, suggesting that ESR1 is the upstream receptor regulating Sertoli cell proliferation. E2- or PPT-ESR1, through activation of epidermal growth factor receptor (EGFR)/mitogen-activated protein kinase 3/1 (MAPK3/1) and PIK3 pathways, induces upregulation of CCND1. KG-501, the compound that disrupts the phospho-CREB/CREB binding protein (CBP) complex, does not change E2- or PPT-ESR1-mediated CCND1 expression, suggesting that phospho-CREB/cyclic AMP response element/CBP is not involved in the expression of this protein. E2- or G-1-GPER, through activation of EGFR/MAPK3/1 and PIK3 pathways, may be involved in the upregulation of antiapoptotic proteins BCL2 and BCL2L2. E2- or G-1-GPER/EGFR/MAPK3/1/phospho-CREB decreases BAX expression. Taken together, these results show a differential effect of E2-GPER on the CREB-mediated transcription of proapoptotic and antiapoptotic genes of the same BCL2 gene family. ESR1 and GPER can mediate the rapid E2 actions in the Sertoli cells, which in turn can modulate nuclear transcriptional events important for Sertoli cell function and maintenance of normal testis development and homeostasis. Our findings are important to clarify the role of estrogen in a critical period of testicular development, and to direct further studies, which may contribute to better understanding of the causes of male infertility.

Estrogen and its receptors in efferent ductules and epididymis.

Estrogens play key roles in the development and maintenance of male reproductive function and fertility. In this review, we briefly describe the localization and function of estrogen receptors ESR1 and ESR2 (also known as ERα and ERß, respectively) and the expression of G protein-coupled estrogen receptor-1 (GPER, formerly known as GPR30) in efferent ductules and epididymis. The efferent ductules present the highest levels of ESR1 and ESR2 in the male reproductive system, and represent a major target of estrogen action. In efferent ductules, ESR1 has a crucial role in the regulation of fluid reabsorption, and in the epididymis the receptor helps to maintain fluid osmolality and pH. ESR1 expression in the epididymal epithelium shows considerable variation among species, but differences in laboratory techniques may also contribute to this variation. Here we report that Esr1 mRNA and protein are higher in corpus than in other regions of the rat epididymis. The mRNA level for Gper was also higher in corpus. Although ESR1 is expressed constitutively in efferent ductules and down-regulated by estrogen, in the epididymis, both testosterone (T) and estradiol (E2) may regulate its expression. T and E2 are, respectively, higher and lower in the corpus than in the initial segment/caput and cauda regions. It is important to determine the expression of GPER, ESR1, androgen receptor, and their respective cofactors in specific cell types of this tissue, as well as the intracellular signaling pathways involved in efferent ductules and epididymis. These studies will help to explain the consequences of exposures to environmental endocrine disruptors and provide potential targets for the development of a male contraceptive.

Alpha1-adrenoceptors trigger the snake venom production cycle in secretory cells by activating phosphatidylinositol 4,5-bisphosphate hydrolysis and ERK signaling pathway.

Loss of venom from the venom gland after biting or manual extraction leads to morphological changes in venom secreting cells and the start of a cycle of production of new venom. We have previously shown that stimulation of both alpha- and beta-adrenoceptors in the secretory cells of the venom gland is essential for the onset of the venom production cycle in Bothrops jararaca. We investigated the signaling pathway by which the alpha-adrenoceptor initiates the venom production cycle. Our results show that the alpha(1)-adrenoceptor subtype is present in venom gland of the snake. In quiescent cells, stimulation of alpha(1)-adrenoceptor with phenylephrine increased the total inositol phosphate concentration, and this effect was blocked by the phospholipase C inhibitor U73122. Phenylephrine mobilized Ca(2+) from thapsigargin-sensitive stores and increased protein kinase C activity. In addition, alpha(1)-adrenoceptor stimulation increased the activity of ERK 1/2, partially via protein kinase C. Using RT-PCR approach we obtained a partial sequence of a snake alpha(1)-adrenoceptor (260 bp) with higher identity with alpha(1D) and alpha(1B)-adrenoceptors from different species. These results suggest that alpha(1)-adrenoceptors in the venom secreting cells are probably coupled to a G(q) protein and trigger the venom production cycle by activating the phosphatidylinositol 4,5-bisphosphate and ERK signaling pathway.

Relaxin family peptide receptors Rxfp1 and Rxfp2: mapping of the mRNA and protein distribution in the reproductive tract of the male rat.

BACKGROUND: Relaxin is the endogenous ligand of the G-protein coupled receptor RXFP1, previously known as LGR7. In humans relaxin can also activate, but with lower affinity, the closely related receptor for the insulin-like peptide from Leydig cells, RXFP2, previously known as LGR8. The lack of relaxin impairs male fertility but the precise distribution and the function of relaxin receptors in the male reproductive tract is not known. We investigated the distribution of Rxfp1 and Rxfp2 in the reproductive tract of the male rat and the function of relaxin in the vas deferens, a tissue with high expression of both receptors. METHODS: The presence of mRNA for Rxfp1 and Rxfp2 was investigated in testes, cultured Sertoli cells, epididymis, vas deferens, seminal vesicle, prostate, and spermatozoa by RT-PCR and Southern blot. Protein expression in the testis, vas deferens, primary culture of Sertoli cells, and spermatozoa was assessed by immunohistochemistry and immunofluorescence. The role of relaxin in the vas deferens was evaluated by contractility studies and radioimmunoassay of cAMP production. The effect of relaxin on mRNA levels for metalloproteinase-7 was measured by Northern blot. RESULTS: Transcripts for Rxfp1 and Rxfp2 were present in almost all parts of the male reproductive tract, with high levels in testis and vas deferens. Both receptors were immunolocalized in late stage germ cells but not in mature spermatozoa, although mRNAs for both receptors were also present in mature spermatozoa. Rxfp1 but not Rxfp2 was detected in cultured Sertoli cells. Strong immunostaining for Rxfp1 and Rxfp2 was seen in muscular and epithelial layers of the vas deferens and in arteriolar walls. Relaxin did not affect contractility and cyclic AMP production of the vas deferens, but increased the levels of mRNA for metalloproteinase-7. CONCLUSION: Rxfp1 and Rxfp2 are widely and similarly distributed throughout the male reproductive tract. Our results suggest that Rxfp1 on spermatids and Sertoli cells may be important in spermatogenesis. Relaxin in the vas deferens does not affect contractility, but may affect vascular compliance and collagen and matrix remodeling.