Fibroblast growth factor 9 stimulates steroidogenesis in postnatal Leydig cells

Clinical and gonadal transcriptome analysis of 38,XX disorder of sex development pigs†

Pigs serve as a robust animal model for the study of human diseases, notably in the context of disorders of sex development (DSD). This study aims to investigate the phenotypic characteristics and molecular mechanisms underlying the reproductive and developmental abnormalities of 38,XX ovotestis-DSD (OT-DSD) and 38,XX testis-DSD (T-DSD) in pigs. Clinical and transcriptome sequencing analyses were performed on DSD and normal female pigs. Cytogenetic and SRY analyses confirmed that OT/T-DSD pigs exhibited a 38,XX karyotype and lacked the SRY gene. The DSD pigs had higher levels of follicle-stimulating hormone, luteinizing hormone, and progesterone, but lower testosterone levels when compared with normal male pigs. The reproductive organs of OT/T-DSD pigs exhibit abnormal development, displaying both male and female characteristics, with an absence of germ cells in the seminiferous tubules. Sex determination and development-related differentially expressed genes shared between DSD pigs were identified in the gonads, including WT1, DKK1, CTNNB1, WTN9B, SHOC, PTPN11, NRG1, and NXK3-1. DKK1 is proposed as a candidate gene for investigating the regulatory mechanisms underlying gonadal phenotypic differences between OT-DSD and T-DSD pigs. Consequently, our findings provide insights into the molecular pathogenesis of DSD pigs and present an animal model for studying into DSD in humans.

Comparative transcriptomics analysis of testicular miRNA from indicine and taurine cattle

Numerous studies have shown that several microRNAs (miRNAs) are specifically expressed in testis, play an essential role in regulating testicular spermatogenesis. Hainan and Mongolian cattle are two representative Chinese native cattle breeds representing Bos indicus (indicine cattle) and Bos taurus (taurine cattle), respectively, which are distributed in hot Hainan and cold Inner Mongolia province. To study the functional differences of miRNA in spermatogenesis between indicine and taurine cattle, six mature testes samples from indicine cattle (n = 3) and taurine cattle (n = 3) were collected, respectively. We detected miRNA expression using small RNA sequencing technology following bioinformatic analysis. A total of 578 known miRNAs and 132 novel miRNAs were detected in the six libraries. Among the 710 miRNAs, 564 miRNAs were expressed in both indicine and taurine cattle, 73 miRNAs were found solely in indicine cattle and 73 miRNAs were found solely in taurine cattle. After further analysis, among the miRNAs were identified in both indicine and taurine cattle, 184 miRNAs were differentially expressed (|log2 fold change| ≥ 1 and corrected p-value <0.05). Among the miRNAs that were only expressed in indicine cattle, 10 miRNAs were differentially expressed, whereas, among the miRNAs that were only expressed in taurine cattle, six miRNAs were differentially expressed. The enrichment analysis result showed that predicted target genes of a total of 200 differentially expressed miRNAs were enriched on some testicular spermatogenesis-related Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways, especially mitogen-activated protein kinase (MAPK) signaling pathway. These findings identify miRNAs as key factors to regulate spermatogenesis in both indicine and taurine cattle, which may also be helpful for improving cattle reproductive performance in future studies.

LMO2 upregulation due to AR deactivation in cancer-associated fibroblasts induces non-cell-autonomous growth of prostate cancer after androgen deprivation

The androgen receptor (AR) is expressed in prostate fibroblasts in addition to normal prostate epithelial cells and prostate cancer (PCa) cells. Moreover, AR activation in fibroblasts dramatically influences prostate cancer (PCa) cell behavior. Androgen deprivation leads to deregulation of AR downstream target genes in both fibroblasts and PCa cells. Here, we identified LIM domain only 2 (LMO2) as an AR target gene in prostate fibroblasts using ChIP-seq and revealed that LMO2 can be repressed directly by AR through binding to androgen response elements (AREs), which results in LMO2 overexpression after AR deactivation due to normal prostate fibroblasts to cancer-associated fibroblasts (CAFs) transformation or androgen deprivation therapy. Next, we investigated the mechanisms of LMO2 overexpression in fibroblasts and the role of this event in non-cell-autonomous promotion of PCa cells growth in the androgen-independent manner through paracrine release of IL-11 and FGF-9. Collectively, our data suggest that AR deactivation deregulates LMO2 expression in prostate fibroblasts, which induces castration resistance in PCa cells non-cell-autonomously through IL-11 and FGF-9.

Cytoarchitectural improvement in Leydig cells of diabetic rats after treatment with aqueous and ethanol extracts of Dracaena arborea (Dracaenaceae)

BACKGROUND AND AIM

Recent studies have demonstrated the androgenic effects of Dracaena arborea in castrated and diabetic rats, but the cytoarchitectural mechanism at the level of Leydig cells (LCs) justifying this improvement in androgens production in diabetic rats has never been examined. We investigated the effects of aqueous and ethanol extracts of D. arborea on diabetes-induced cytoarchitectural impairments of LCs in rats.

EXPERIMENTAL PROCEDURE

Besides a normal group, 4 groups of diabetic rats were treated orally with Millipore water (10 ml/kg, diabetic), sildenafil citrate (1.44 mg/kg), aqueous (500 mg/kg) and ethanol (100 mg/kg) extracts of D. arborea for 21 days. On day 22, rats were sacrificed and the testes were removed and prepared for electron microscopic analyses of LCs ultrastructure.

RESULTS AND CONCLUSION

The ultrastructure of LCs in control rats was normal, while that in diabetic rats exhibited large heterochromatization in the nuclei, reduced amount of smooth endoplasmic reticulum with no lipid droplets in the cytoplasm, many autophagosomes and degenerated mitochondria containing lots of electron dense granules in the matrix. Interestingly, treatment with D. arborea especially its aqueous extract (500 mg/kg) alleviated these impairments, characterized by a rarification of heterochromatization in the nuclei coupled to an increase and the presence in the cytoplasm of prominent smooth endoplasmic reticulum and a reduction of electron dense granules in the matrix of mitochondria. These alleviating properties of D. arborea on LCs ultrastructure of diabetic rats could explain its androgenic potential. These results are useful for the management of patients suffering from diabetes-induced hypogonadism.

Anti-Cancer Effect of Cordycepin on FGF9-Induced Testicular Tumorigenesis

Cordycepin, a bioactive constituent from the fungus Cordyceps sinensis, could inhibit cancer cell proliferation and promote cell death via induction of cell cycle arrest, apoptosis and autophagy. Our novel finding from microarray analysis of cordycepin-treated MA-10 mouse Leydig tumor cells is that cordycepin down-regulated the mRNA levels of FGF9, FGF18, FGFR2 and FGFR3 genes in MA-10 cells. Meanwhile, the IPA-MAP pathway prediction result showed that cordycepin inhibited MA-10 cell proliferation by suppressing FGFs/FGFRs pathways. The in vitro study further revealed that cordycepin decreased FGF9-induced MA-10 cell proliferation by inhibiting the expressions of p-ERK1/2, p-Rb and E2F1, and subsequently reducing the expressions of cyclins and CDKs. In addition, a mouse allograft model was performed by intratumoral injection of FGF9 and/or intraperitoneal injection of cordycepin to MA-10-tumor bearing C57BL/6J mice. Results showed that FGF9-induced tumor growth in cordycepin-treated mice was significantly smaller than that in a PBS-treated control group. Furthermore, cordycepin decreased FGF9-induced FGFR1-4 protein expressions in vitro and in vivo. In summary, cordycepin inhibited FGF9-induced testicular tumor growth by suppressing the ERK1/2, Rb/E2F1, cell cycle pathways, and the expressions of FGFR1-4 proteins, suggesting that cordycepin can be used as a novel anticancer drug for testicular cancers.

Linoleic acid promotes testosterone production by activating Leydig cell GPR120/ ERK pathway and restores BPA-impaired testicular toxicity

Bisphenol A (BPA) [2,2-bis(4-hydroxyphenyl) propane] has attracted increasing attention over the past few decades as an endocrine-disrupting chemicals that causes low testosterone levels. Linoleic acid (LA) is an essential fatty acid and GPR120 agonist. Herein, we are the first to report that LA induces the expression of GPR120 in mouse Leydig cells to directly promote testosterone production. In addition, we demonstrated that the activated GPR120 / ERK signaling pathway was involved in upregulating the expression of 3β-HSD and StAR for testosterone production by stimulation of LA. Interestingly, although BPA failed to affect GPR120 expression, LA restored the testosterone levels decreased by BPA in Leydig cells in vitro. Furthermore, the in vivo restoration of testosterone levels and testicular structure was also observed in BPA-impaired mice fed LA. As a result, the sperm functions of BPA-impaired mice returned to normal levels. At the same time, the damaged blood-testis barrier and infertility were also resolved by LA. Our study indicates a novel and safe strategy that utilizes LA to repair reproductive damage caused by low testosterone levels through activating the GPR120/ERK pathway in Leydig cells.

FGF9 is a downstream target of SRY and sufficient to determine male sex fate in ex vivo XX gonad culture

Fibroblast growth factor 9 (FGF9) is an autocrine/paracrine growth factor that plays critical roles in embryonic and organ developments and is involved in diverse physiological events. Loss of function of FGF9 exhibits male-to-female sex reversal in the transgenic mouse model and gain of FGF9 copy number was found in human 46, XX sex reversal patient with disorders of sex development. These results suggested that FGF9 plays a vital role in male sex development. Nevertheless, how FGF9/Fgf9 expression is regulated during testis determination remains unclear. In this study, we demonstrated that human and mouse SRY bind to -833 to -821 of human FGF9 and -1010 to -998 of mouse Fgf9, respectively, and control FGF9/Fgf9 mRNA expression. Interestingly, we showed that mouse SRY cooperates with SF1 to regulate Fgf9 expression, whereas human SRY-mediated FGF9 expression is SF1 independent. Furthermore, using an ex vivo gonadal culture system, we showed that FGF9 expression is sufficient to switch cell fate from female to male sex development in 12-16 tail somite XX mouse gonads. Taken together, our findings provide evidence to support the SRY-dependent, fate-determining role of FGF9 in male sex development.

Long non-coding RNA LOC105611671 modulates fibroblast growth factor 9 (FGF9) expression by targeting oar-miR-26a to promote testosterone biosynthesis in Hu sheep

Fibroblast growth factors (FGFs) play crucial roles in early gonadal development and germ cell maturation of mammals; FGF9 is involved in mammalian testis steroidogenesis. However, the upstream regulators of FGF9 in ovine testosterone biosynthesis remain unknown. Long non-coding RNAs (lncRNAs) are crucial regulators of multiple biological functions that act by altering gene expression. In the present study, we analysed the role of LOC105611671, a lncRNA upstream of FGF9, in Hu sheep steroidogenesis. We found that LOC105611671 expression increased significantly in Hu sheep testes during sexual maturation (P&lt;0.05). Moreover, levels of FGF9 and testosterone were decreased by LOC105611671 knockdown in Hu sheep Leydig cells (LCs). Results of transient transfection and luciferase assays revealed that FGF9 is a functional target gene of oar-miR-26a in ovine LCs. Further functional validation experiments revealed that LOC105611671 regulates testosterone biosynthesis by targeting oar-miR-26a. Overall, the present study describes the expression profile of LOC105611671 during sexual maturation and demonstrates that LOC105611671 modulates FGF9 expression by targeting oar-miR-26a to promote testis steroidogenesis in Hu sheep. Our research provides a new theoretical basis for genetic and molecular research on testosterone biosynthesis in sheep.

Abnormal Expression of Fgf9 during the Development of the Anorectum in Rat Embryos with Anorectal Malformations

The study objective was to investigate the role of fibroblast growth factor 9 (Fgf9) in normal and anorectal malformation (ARM) embryos during the development of the anorectum. Fgf9 expression was assayed in both normal rat embryos and embryos with ARM induced by exposure to ethylenethiourea (ETU) on embryonic day 10 (E10). Fgf9 expression was assayed by immunohistochemical staining, Western blotting, and real-time quantitative polymerase chain reaction (qRT-PCR). Immunohistochemical staining revealed spatiotemporal changes in Fgf9 expression between E13 and E16. Fgf9-positive cells predominated in the mesenchyme of the cloaca on E13 and E14 and at the fusion site of the urorectal septum and cloacal membrane, rectal epithelium, and anal membrane on E15. Fgf9-positive cells were obviously decreased after the anal membrane ruptured on E16. Fgf9-positive staining was significantly decreased in embryos with ARM compared with normal embryos from E13 to E15. The results of Western blots and qRT-PCR were consistent, with significantly increased Fgf9 expression in the hindgut and rectum of normal embryos than in embryos with ARM from E13 to E15. However, there was no difference between the two groups on E16. These results suggested that the anorectal embryogenesis might depend on the induction of Fgf9 signal. The expression of Fgf9 was downregulated in ETU-induced ARM embryos, which might be related to the development of ARM.

Brain-derived neurotrophic factor: A steroidogenic regulator of Leydig cells

The brain-derived neurotrophic factor (BDNF) was first recognized for its roles in the peripheral and central nervous systems, and its complex functions on mammalian organs have been extended constantly. However, to date, little is known about its effects on the male reproductive system, including the steroidogenesis of mammals. The purpose of this study was to elucidate the effects of BDNF on testosterone generation of Leydig cells and the underlying mechanisms. We found that BDNF-induced proliferation of TM3 Leydig cells via upregulation of proliferating cell nuclear antigen ( Pcna) and promoted testosterone generation as a result of upregulation of steroidogenic acute regulatory protein ( Star), 3b-hydroxysteroid dehydrogenase ( Hsd3b1), and cytochrome P450 side-chain cleavage enzyme ( Cyp11a1) both in primary Leydig cells and TM3 Leydig cells, which were all attenuated in Bdnf knockdown TM3 Leydig cells. Furthermore, the possible mechanism of testosterone synthesis was explored in TM3 Leydig cells. The results showed that BDNF enhanced extracellular signal-regulated protein kinases 1 and 2 (ERK1/2) phosphorylation, and the effect was disrupted by Bdnf deletion. Moreover, PD98059, a potent selective inhibitor of ERK1/2 activation, compromised BDNF-induced testosterone generation and upregulation of Star, Hsd3b1, and Cyp11a1. The Bdnf knockdown assay, on the other hand, indicated the autocrine effect of BDNF on steroidogenesis in TM3 Leydig cells. On the basis of these results, we concluded that BDNF, acting as an autocrine factor, induced testosterone generation as a result of the upregulation of Star, Hsd3b1, and Cyp11a1 via stimulation of the ERK1/2 pathway.

FGF9/FGFR2 increase cell proliferation by activating ERK1/2, Rb/E2F1, and cell cycle pathways in mouse Leydig tumor cells

Fibroblast growth factor 9 (FGF9) promotes cancer progression; however, its role in cell proliferation related to tumorigenesis remains elusive. We investigated how FGF9 affected MA‐10 mouse Leydig tumor cell proliferation and found that FGF9 significantly induced cell proliferation by activating ERK1/2 and retinoblastoma (Rb) phosphorylations within 15 minutes. Subsequently, the expressions of E2F1 and the cell cycle regulators: cyclin D1, cyclin E1 and cyclin‐dependent kinase 4 (CDK4) in G₁ phase and cyclin A1, CDK2 and CDK1 in S‐G₂/M phases were increased at 12 hours after FGF9 treatment; and cyclin B1 in G₂/M phases were induced at 24 hours after FGF9 stimulation, whereas the phosphorylations of p53, p21 and p27 were not affected by FGF9. Moreover, FGF9‐induced effects were inhibited by MEK inhibitor PD98059, indicating FGF9 activated the Rb/E2F pathway to accelerate MA‐10 cell proliferation by activating ERK1/2. Immunoprecipitation assay and ChIP‐quantitative PCR results showed that FGF9‐induced Rb phosphorylation led to the dissociation of Rb‐E2F1 complexes and thereby enhanced the transactivations of E2F1 target genes, Cyclin D1, Cyclin E1 and Cyclin A1. Silencing of FGF receptor 2 (FGFR2) using lentiviral shRNA inhibited FGF9‐induced ERK1/2 phosphorylation and cell proliferation, indicating that FGFR2 is the obligate receptor for FGF9 to bind and activate the signaling pathway in MA‐10 cells. Furthermore, in a severe combined immunodeficiency mouse xenograft model, FGF9 significantly promoted MA‐10 tumor growth, a consequence of increased cell proliferation and decreased apoptosis. Conclusively, FGF9 interacts with FGFR2 to activate ERK1/2, Rb/E2F1 and cell cycle pathways to induce MA‐10 cell proliferation in vitro and tumor growth in vivo.

Differential expression of microRNAs in luteinising hormone-treated mouse TM3 Leydig cells

Testosterone is primarily produced by Leydig cells of the mammalian male gonads. The cellular functions of Leydig cells are regulated by the hypothalamus-pituitary-gonad axis, whereas the microRNA (miRNA) changes of LH-treated Leydig cells are unknown. Mouse TM3 Leydig cells were treated with LH, and deep sequencing showed that 29 miRNAs were significantly different between two groups (fold change of >1.5 or <0.5, p < .05), of which 27 were upregulated and two were downregulated. The differential expression of miR-29b-3p, miR-378b, miR-193b and miR-3695 was confirmed by quantitative real-time polymerase chain reaction. Bioinformatic analysis revealed that miRNAs regulated a large number of genes with different functions. Pathway analysis indicated that miRNAs were involved in the Wingless and INT-1, adenosine 5'-monophosphate-activated protein kinase, NF-kappa B and Toll-like receptor signalling pathways. Results showed that miRNAs might be involved in the regulation of LH to Leydig cells.

A role of KIT receptor signaling for proliferation and differentiation of rat stem Leydig cells in vitro

In the testis, KIT ligand (KITL, also called stem cell factor) is expressed by Sertoli cells and its receptor (c-kit, KIT) is expressed by spermatogonia and Leydig cells. Although KITL-KIT signaling is critical for the spermatogenesis, its roles in Leydig cell development during puberty are not clear. In the present study, we investigated effects of KITL on stem Leydig cell proliferation and differentiation. Using an in vitro culture system of seminiferous tubules from Leydig cell-depleted testis, we found that KITL increased the proliferation activity of putative stem Leydig cells at higher concentration (10 and 100 ng/ml). Low concentration (1 ng/ml) of KITL significantly induced the differentiation of stem Leydig cells via increasing the expression level of steroidogenic acute regulatory protein (Star). In contrast, higher concentration (100 ng/ml) of KITL inhibited the differentiation of stem Leydig cells via inhibiting the steroidogenic enzyme (Cyp11a1, Cyp17a1, and Hsd17b3) expression levels. We cultured rat progenitor Leydig cells with KITL for 48 h and did not find any influence of KITL on the proliferation and androgen production of these cells. In conclusion, KITL is a growth factor that regulates the development of the stem Leydig cell.

Fibroblast growth factor 9 (FGF9) regulation of cyclin D1 and cyclin-dependent kinase-4 in ovarian granulosa and theca cells of cattle

To determine the mechanism by which fibroblast growth factor 9 (FGF9) alters granulosa (GC) and theca (TC) cell proliferation, cell cycle proteins that regulate progression through G1 phase of the cell cycle, cyclin D1 (CCND1) and cyclin-dependent kinase-4 (CDK4; CCND1's catalytic partner), were evaluated. Ovaries were obtained from a local abattoir, GC were harvested from small (1-5 mm) and large (8-22 mm) follicles, and TC were harvested from large follicles. GC and TC were plated in medium containing 10% fetal calf serum followed by various treatments in serum-free medium. Treatment with 30 ng/mL of either FGF9 or IGF1 significantly increased GC numbers and when combined, synergized to further increase GC numbers by threefold. Abundance of CCND1 and CDK4 mRNA in TC and GC were quantified via real-time PCR. Alone and in combination with IGF1, FGF9 significantly increased CCND1 mRNA expression in both GC and TC. Western blotting revealed that CCND1 protein levels were increased by FGF9 in TC after 6 h and 12 h of treatment, but CDK4 protein was not affected. A mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK) pathway inhibitor, U0126, significantly reduced FGF9-induced CCND1 mRNA expression to basal levels. For the first time we show that CCND1 mRNA expression is increased by FGF9 in bovine TC and GC, and that FGF9 likely uses the MAPK pathway to induce CCND1 mRNA production in bovine TC.

Annexin A5 regulates Leydig cell testosterone production via ERK1/2 pathway

This study was to investigate the effect of annexin A5 on testosterone secretion from primary rat Leydig cells and the underlying mechanisms. Isolated rat Leydig cells were treated with annexin A5. Testosterone production was detected by chemiluminescence assay. The protein and mRNA of Steroidogenic acute regulatory (StAR), P450scc, 3β-hydroxysteroid dehydrogenase (3β-HSD), 17β-hydroxysteroid dehydrogenase (17β-HSD), and 17α-hydroxylase were examined by Western blotting and semi-quantitative RT-PCR, respectively. Annexin A5 significantly stimulated testosterone secretion from rat Leydig cells in dose- and time-dependent manners and increased mRNA and protein expression of StAR, P450scc, 3β-HSD, and 17β-HSD but not 17α-hydroxylase. Annexin A5 knockdown by siRNA significantly decreased the level of testosterone and protein expression of P450scc, 3β-HSD, and 17β-HSD. The significant activation of ERK1/2 signaling was observed at 5, 10, and 30 min after annexin A5 treatment. After the pretreatment of Leydig cells with ERK inhibitor PD98059 (50 μmol l⁻¹) for 20 min, the effects of annexin A5 on promoting testosterone secretion and increasing the expression of P450scc, 3β-HSD, and 17β-HSD were completely abrogated (P < 0.05). Thus, ERK1/2 signaling is involved in the roles of annexin A5 in mediating testosterone production and the expression of P450scc, 3β-HSD, and 17β-HSD in Leydig cells.

The expression profiles of fibroblast growth factor 9 and its receptors in developing mice testes

An expressional lack of fibroblast growth factor 9 (FGF9) would cause male-to-female sex reversal in the mouse, implying the essential role of FGF9 in testicular organogenesis and maturation. However, the temporal expression of FGF9 and its receptors during testicular development remains elusive. In this study, immunohistochemistry was used to identify the localization of FGF9 and its receptors at different embryonic and postnatal stages in mice testes. Results showed that FGF9 continuously expressed in the testis during development. FGF9 had highest expression in the interstitial region at 17-18 d post coitum (dpc) and in the spermatocytes, spermatids and Leydig cell on postnatal days (pnd) 35-65. Regarding receptor expression, FGFR1 and FGFR4 were evenly expressed in the whole testis during the embryonic and postnatal stages. However, FGFR2 and FGFR3 were widely expressed during the embryonic testis development with higher FGFR2 expression in seminiferous tubules at 16-18 dpc and higher FGFR3 expression in interstitial region at 17-18 dpc. In postnatal stage, FGFR2 extensively expressed with higher expression at spermatids and Leydig cells on 35-65 pnd and FGFR3 widely expressed in the whole testis. Taken together, these results strongly suggest that FGF9 is correlated with the temporal expression profiles of FGFR2 and FGFR3 and possibly associated with testis development.

Origin and Differentiation of Androgen-Producing Cells in the Gonads

Sexual reproduction is dependent on the activity of androgenic steroid hormones to promote gonadal development and gametogenesis. Leydig cells of the testis and theca cells of the ovary are critical cell types in the gonadal interstitium that carry out steroidogenesis and provide key androgens for reproductive organ function. In this chapter, we will discuss important aspects of interstitial androgenic cell development in the gonad, including: the potential cellular origins of interstitial steroidogenic cells and their progenitors; the molecular mechanisms involved in Leydig cell specification and differentiation (including Sertoli-cell-derived signaling pathways and Leydig-cell-related transcription factors and nuclear receptors); the interactions of Leydig cells with other cell types in the adult testis, such as Sertoli cells, germ cells, peritubular myoid cells, macrophages, and vascular endothelial cells; the process of steroidogenesis and its systemic regulation; and a brief discussion of the development of theca cells in the ovary relative to Leydig cells in the testis. Finally, we will describe the dynamics of steroidogenic cells in seasonal breeders and highlight unique aspects of steroidogenesis in diverse vertebrate species. Understanding the cellular origins of interstitial steroidogenic cells and the pathways directing their specification and differentiation has implications for the study of multiple aspects of development and will help us gain insights into the etiology of reproductive system birth defects and infertility.

Molecular regulation of steroidogenesis in endocrine Leydig cells

Steroid hormones regulate essential physiological processes and inadequate levels are associated with various pathological conditions. Consequently, the process of steroid hormone biosynthesis is finely regulated. In the testis, the main steroidogenic cells are the Leydig cells. There are two distinct populations of Leydig cells that arise during development: fetal and adult Leydig cells. Fetal Leydig cells are responsible for masculinizing the male urogenital tract and inducing testis descent. These cells atrophy shortly after birth and do not contribute to the adult Leydig cell population. Adult Leydig cells derive from undifferentiated precursors present after birth and become fully steroidogenic at puberty. The differentiation of both Leydig cell populations is controlled by locally produced paracrine factors and by endocrine hormones. In fully differentially and steroidogenically active Leydig cells, androgen production and hormone-responsiveness involve various signaling pathways and downstream transcription factors. This review article focuses on recent developments regarding the origin and function of Leydig cells, the regulation of their differentiation by signaling molecules, hormones, and structural changes, the signaling pathways, kinases, and transcription factors involved in their differentiation and in mediating LH-responsiveness, as well as the fine-tuning mechanisms that ensure adequate production steroid hormones.

Fibroblast growth factor 9 activates akt and MAPK pathways to stimulate steroidogenesis in mouse leydig cells

Fibroblast growth factor 9 (FGF9) is a multifunctional polypeptide belonging to the FGF family and has functions related to bone formation, lens-fiber differentiation, nerve development, gap-junction formation and sex determination. In a previous study, we demonstrated that FGF9 stimulates the production of testosterone in mouse Leydig cells. In the present study, we used both primary mouse Leydig cells and MA-10 mouse Leydig tumor cells to further investigate the molecular mechanism of FGF9-stimulated steroidogenesis. Results showed that FGF9 significantly activated steroidogenesis in both mouse primary and tumor Leydig cells (p<0.05). Furthermore, FGF9 significantly induced the expression of phospho-Akt at 0.5 and 24 hr, phospho-JNK at 0.25, 0.5, and 24 hr, phospho-p38 at 0.5 hr, and phospho-ERK1/2 from 0.25 to 24 hr in primary Leydig cells (p<0.05). Also, FGF9 significantly up-regulated the expression of phospho-Akt at 3 hr, phospho-JNK at 0.25 hr, and phospho-ERK1/2 at 1 and 3 hr in MA-10 cells (p<0.05). Using specific inhibitors of Akt, JNK, p38, and ERK1/2, we further demonstrated that the inhibitors of Akt and ERK1/2 significantly suppressed the stimulatory effect of FGF9 on steroidogenesis in mouse Leydig cells. In conclusion, FGF9 specifically activated the Akt and ERK1/2 in normal mouse Leydig cells and the Akt, JNK and ERK1/2 in MA-10 mouse Leydig tumor cells to stimulate steroidogenesis.

Effects of fibroblast growth factor 9 on steroidogenesis and control of FGFR2IIIc mRNA in porcine granulosa cells

The objectives of this study were to investigate the effects of fibroblast growth factor 9 (FGF9) on hormone-stimulated porcine granulosa cell proliferation and steroid production and to further elucidate the hormonal and developmental control of FGFR2IIIc gene expression in granulosa cells. Porcine ovaries were collected from a local slaughterhouse and granulosa cells were collected from small to medium (1 to 5 mm) follicles for 5 in vitro studies that were conducted. Cells were cultured for 48 h in 5% fetal calf serum plus 5% porcine serum and then treated with various combinations of FSH, IGF-I, FGF9, Sonic hedgehog (SHH), cortisol, PGE2, and/or wingless-type mouse mammary tumor virus integration site family member 5A (WNT5A) in serum-free medium for an additional 24 or 48 h. Medium was collected for analysis of steroid concentration via RIA, or RNA was collected for gene expression analysis of FGFR2IIIc via quantitative reverse transcription PCR. Fibroblast growth factor 9 stimulated (P < 0.05) IGF-I-induced estradiol production in the presence of FSH and testosterone. However, FGF9 had inconsistent effects on progesterone production, stimulating progesterone production in the presence of FSH and testosterone but inhibiting progesterone production in the presence of IGF-I, FSH, and testosterone. Cell numbers were increased (P < 0.05) by FGF9 in the presence of IGF-I and FSH but not in the presence of FSH and absence of IGF-I. For FGFR2IIIc mRNA studies, granulosa cells were treated with FSH, IGF-I, FGF9, SHH, cortisol, PGE2, or WNT5A. Follicle-stimulating hormone alone had no effect (P > 0.10) whereas IGF-I increased (P < 0.05) FGFR2IIIc mRNA abundance. Cortisol, PGE2, SHH, and WNT5A had no effect (P > 0.10) on FGFR2IIIc gene expression whereas FGF9 in the presence of FSH and IGF-I inhibited (P < 0.05) FGFR2IIIc gene expression. In an in vivo study, granulosa cells from large (7 to 14 mm) follicles had greater (P < 0.05) abundance of FGFR2IIIc mRNA than small (1 to 3 mm) or medium (4 to 6 mm) follicles. In conclusion, IGF-I-induced FGFR2IIIc mRNA may be a mechanism for increased responses to FGF9 in FSH plus IGF-I-treated granulosa cells. Fibroblast growth factor 9 and IGF-I may work together as amplifiers of follicular growth and granulosa cell differentiation by stimulating estradiol production and concomitantly stimulating granulosa cell growth in pigs.

Overexpression of FGF9 in colon cancer cells is mediated by hypoxia-induced translational activation

Human fibroblast growth factor 9 (FGF9) is a potent mitogen involved in many physiological processes. Although FGF9 messenger RNA (mRNA) is ubiquitously expressed in embryos, FGF9 protein expression is generally low and restricted to a few adult organs. Aberrant expression of FGF9 usually results in human malignancies including cancers, but the mechanism remains largely unknown. Here, we report that FGF9 protein, but not mRNA, was increased in hypoxia. Two sequence elements, the upstream open reading frame (uORF) and the internal ribosome entry site (IRES), were identified in the 5' UTR of FGF9 mRNA. Functional assays indicated that FGF9 protein synthesis was normally controlled by uORF-mediated translational repression, which kept the protein at a low level, but was upregulated in response to hypoxia through a switch to IRES-dependent translational control. Our data demonstrate that FGF9 IRES functions as a cellular switch to turn FGF9 protein synthesis ‘on’ during hypoxia, a likely mechanism underlying FGF9 overexpression in cancer cells. Finally, we provide evidence to show that hypoxia-induced translational activation promotes FGF9 protein expression in colon cancer cells. Altogether, this dynamic working model may provide a new direction in anti-tumor therapies and cancer intervention.

RiboTag analysis of actively translated mRNAs in Sertoli and Leydig cells in vivo

Male spermatogenesis is a complex biological process that is regulated by hormonal signals from the hypothalamus (GnRH), the pituitary gonadotropins (LH and FSH) and the testis (androgens, inhibin). The two key somatic cell types of the testis, Leydig and Sertoli cells, respond to gonadotropins and androgens and regulate the development and maturation of fertilization competent spermatozoa. Although progress has been made in the identification of specific transcripts that are translated in Sertoli and Leydig cells and their response to hormones, efforts to expand these studies have been restricted by technical hurdles. In order to address this problem we have applied an in vivo ribosome tagging strategy (RiboTag) that allows a detailed and physiologically relevant characterization of the "translatome" (polysome-associated mRNAs) of Leydig or Sertoli cells in vivo. Our analysis identified all previously characterized Leydig and Sertoli cell-specific markers and identified in a comprehensive manner novel markers of Leydig and Sertoli cells; the translational response of these two cell types to gonadotropins or testosterone was also investigated. Modulation of a small subset of Sertoli cell genes occurred after FSH and testosterone stimulation. However, Leydig cells responded robustly to gonadotropin deprivation and LH restoration with acute changes in polysome-associated mRNAs. These studies identified the transcription factors that are induced by LH stimulation, uncovered novel potential regulators of LH signaling and steroidogenesis, and demonstrate the effects of LH on the translational machinery in vivo in the Leydig cell.

Sex-biased expression of sex-differentiating genes FOXL2 and FGF9 in American alligators, alligator Mississippiensis

Across amniotes, sex-determining mechanisms exhibit great variation, yet the genes that govern sexual differentiation are largely conserved. Studies of evolution of sex-determining and sex-differentiating genes require an exhaustive characterization of functions of those genes such as FOXL2 and FGF9. FOXL2 is associated with ovarian development, and FGF9 is known to play a role in testicular organogenesis in mammals and other amniotes. As a step toward characterization of the evolutionary history of sexual development, we measured expression of FOXL2 and FGF9 across 3 developmental stages and 8 juvenile tissue types in male and female American alligators, Alligator mississippiensis. We report surprisingly high expression of FOXL2 before the stage of embryonic development when sex is determined in response to temperature, and sustained and variable expression of FGF9 in juvenile male, but not female tissue types. Novel characterization of gene expression in reptiles with temperature-dependent sex determination such as American alligators may inform the evolution of sex-determining and sex-differentiating gene networks, as they suggest alternative functions from which the genes may have been exapted. Future functional profiling of sex-differentiating genes should similarly follow other genes and other species to enable a broad comparison across sex-determining mechanisms.

Assuring safety without animal testing: the case for the human testis in vitro

From 15 to 17 June 2011, a dedicated workshop was held on the subject of in vitro models for mammalian spermatogenesis and their applications in toxicological hazard and risk assessment. The workshop was sponsored by the Dutch ASAT initiative (Assuring Safety without Animal Testing), which aims at promoting innovative approaches toward toxicological hazard and risk assessment on the basis of human and in vitro data, and replacement of animal studies. Participants addressed the state of the art regarding human and animal evidence for compound mediated testicular toxicity, reviewed existing alternative assay models, and brainstormed about future approaches, specifically considering tissue engineering. The workshop recognized the specific complexity of testicular function exemplified by dedicated cell types with distinct functionalities, as well as different cell compartments in terms of microenvironment and extracellular matrix components. This complexity hampers quick results in the realm of alternative models. Nevertheless, progress has been achieved in recent years, and innovative approaches in tissue engineering may open new avenues for mimicking testicular function in vitro. Although feasible, significant investment is deemed essential to be able to bring new ideas into practice in the laboratory. For the advancement of in vitro testicular toxicity testing, one of the most sensitive end points in regulatory reproductive toxicity testing, such an investment is highly desirable.

Expression and effect of fibroblast growth factor 9 in bovine theca cells

Fibroblast growth factor 9 (FGF9) protein affects granulosa cell (GC) function but is mostly localized to theca cell (TC) and stromal cell of rat ovaries. The objectives of this study were to determine the 1) effects of FGF9 on TC steroidogenesis, gene expression, and cell proliferation; 2) mechanism of action of FGF9 on TCs; and 3) hormonal control of FGF9 mRNA expression in TCs. Bovine ovaries were collected from a local slaughterhouse and TCs were collected from large (8-22 mm) follicles and treated with various hormones in serum-free medium for 24 or 48 h. FGF9 caused a dose-dependent inhibition (P<0·05) of LH- and LH+IGF1-induced androstenedione and progesterone production. Also, FGF9 inhibited (P<0·05) LH+IGF1-induced expression of LHCGR, CYP11A1, and CYP17A1 mRNA (via real-time RT-PCR) in TCs. FGF9 had no effect (P>0·10) on STAR mRNA abundance. Furthermore, FGF9 inhibited dibutyryl cAMP-induced progesterone and androstenedione production in LH+IGF1-treated TCs. By contrast, FGF9 increased (P<0·05) the number of bovine TCs. Abundance of FGF9 mRNA in GCs and TCs was several-fold greater (P<0·05) in small (1-5 mm) vs large follicles. Tumor necrosis factor α and WNT5A increased (P<0·05) abundance of FGF9 mRNA in TCs. In summary, expression of FGF9 mRNA in TCs is developmentally and hormonally regulated. FGF9 may act as an autocrine regulator of ovarian function in cattle by slowing TC differentiation via inhibiting LH+IGF1 action via decreasing gonadotropin receptors and the cAMP signaling cascade while stimulating proliferation of TCs.

Involvement of FGF9/16/20 subfamily in female germ cell development of the Nile tilapia, Oreochromis niloticus

Fibroblast growth factors (FGFs) have been proved to participate in a wide variety of processes, including growth, differentiation, cell proliferation, migration, sex determination and sex differentiation. The roles of FGF9/16/20 subfamily members in the gonadal development of teleost fish have not yet been reported. Three FGFs (16, 20a and 20b) of the FGF9/16/20 subfamily were cloned from the Nile tilapia by RT-PCR and RACE. Phylogenetic, bioinformatic and syntenic analyses demonstrated that these cloned FGFs are genuine FGF16, 20a and 20b. Our analyses further supported the non-existence of FGF9 ortholog and the existence of two FGF20 paralogs in teleost genomes. Tissue distribution analysis by RT-PCR demonstrated that FGF16 was expressed in a wide range of tissues including the testis and ovary, FGF20b in the brain, pituitary, intestine and ovary, but not in the testis, while FGF20a in the brain, pituitary and spleen, but not in the gonad. These results were consistent with the Northern blot analysis. The expression profiles of FGF16 and FGF20b during normal and sex reversed gonadal development were investigated by real-time PCR. Both showed much higher expression in the XX ovary and 17 beta-estradiol induced XY ovary compared with the XY testis and fadrozole and tamoxifen induced XX testis, with the highest in both sexes at 120 dah. Strong signals of FGF16 and FGF20b were detected in phase II oocytes by in situ hybridization. These data suggest that FGF9/16/20 subfamily is involved in the early oocyte development of the female.

Effects of fibroblast growth factor 9 (FGF9) on steroidogenesis and gene expression and control of FGF9 mRNA in bovine granulosa cells

Gene expression of fibroblast growth factor-9 (FGF9) is decreased in granulosa cells (GC) of cystic follicles compared with normal dominant follicles in cattle. The objectives of this study were to investigate the effects of FGF9 on GC steroidogenesis, gene expression, and cell proliferation and to determine the hormonal control of GC FGF9 production. GC were collected from small (1-5 mm) and large (8-22 mm) bovine follicles and treated in vitro with various hormones in serum-free medium for 24 or 48 h. In small- and large-follicle GC, FGF9 inhibited (P < 0.05) IGF-I-, dibutyryl cAMP-, and forskolin-induced progesterone and estradiol production. In contrast, FGF9 increased (P < 0.05) GC numbers induced by IGF-I and 10% fetal calf serum. FGF9 inhibited (P < 0.05) FSHR and CYP11A1 mRNA abundance in small- and large-follicle GC but had no effect (P > 0.10) on CYP19A1 or StAR mRNA. In the presence of a 3β-hydroxysteroid dehydrogenase inhibitor, trilostane, FGF9 also decreased (P < 0.05) pregnenolone production. IGF-I inhibited (P < 0.05) whereas estradiol and FSH had no effect (P > 0.10) on FGF9 mRNA abundance. TNFα and wingless-type mouse mammary tumor virus integration site family member-3A decreased (P < 0.05) whereas T(4) and sonic hedgehog increased (P < 0.05) FGF9 mRNA abundance in control and IGF-I-treated GC. Thus, GC FGF9 gene expression is hormonally regulated, and FGF9 may act as an autocrine regulator of ovarian function by slowing follicular differentiation via inhibiting IGF-I action, gonadotropin receptors, the cAMP signaling cascade, and steroid synthesis while stimulating GC proliferation in cattle.

The Effect of Cordycepin on Steroidogenesis and Apoptosis in MA-10 Mouse Leydig Tumor Cells

Cordycepin is a natural pure compound extracted from Cordyceps sinensis (CS). We have demonstrated that CS stimulates steroidogenesis in primary mouse Leydig cell and activates apoptosis in MA-10 mouse Leydig tumor cells. It is highly possible that cordycepin is the main component in CS modulating Leydig cell functions. Thus, our aim was to investigate the steroidogenic and apoptotic effects with potential mechanism of cordycepin on MA-10 mouse Leydig tumor cells. Results showed that cordycepin significantly stimulated progesterone production in dose- and time-dependent manners. Adenosine receptor (AR) subtype agonists were further used to treat MA-10 cells, showing that A₁, A _2A , A _2B , and A₃, AR agonists could stimulate progesterone production. However, StAR promoter activity and protein expression remained of no difference among all cordycepin treatments, suggesting that cordycepin might activate AR, but not stimulated StAR protein to regulate MA-10 cell steroidogenesis. Meanwhile, cordycepin could also induce apoptotic cell death in MA-10 cells. Moreover, four AR subtype agonists induced cell death in a dose-dependent manner, and four AR subtype antagonists could all rescue cell death under cordycepin treatment in MA-10 cells. In conclusion, cordycepin could activate adenosine subtype receptors and simultaneously induce steroidogenesis and apoptosis in MA-10 mouse Leydig tumor cells.

FUBP3 interacts with FGF9 3' microsatellite and positively regulates FGF9 translation

A TG microsatellite in the 3'-untranslated region (UTR) of FGF9 mRNA has previously been shown to modulate FGF9 expression. In the present study, we investigate the possible interacting protein that binds to FGF9 3'-UTR UG-repeat and study the mechanism underlying this protein-RNA interaction. We first applied RNA pull-down assays and LC-MS analysis to identify proteins associated with this repetitive sequence. Among the identified proteins, FUBP3 specifically bound to the synthetic (UG)(15) oligoribonucleotide as shown by supershift in RNA-EMSA experiments. The endogenous FGF9 protein was upregulated in response to transient overexpression and downregulated after knockdown of FUBP3 in HEK293 cells. As the relative levels of FGF9 mRNA were similar in these two conditions, and the depletion of FUBP3 had no effect on the turn-over rate of FGF9 mRNA, these data suggested that FUBP3 regulates FGF9 expression at the post-transcriptional level. Further examination using ribosome complex pull-down assay showed overexpression of FUBP3 promotes FGF9 expression. In contrast, polyribosome-associated FGF9 mRNA decreased significantly in FUBP3-knockdown HEK293 cells. Finally, reporter assay suggested a synergistic effect of the (UG)-motif with FUBP3 to fine-tune the expression of FGF9. Altogether, results from this study showed the novel RNA-binding property of FUBP3 and the interaction between FUBP3 and FGF9 3'-UTR UG-repeat promoting FGF9 mRNA translation.

The role of specific mitogen-activated protein kinase signaling cascades in the regulation of steroidogenesis

Mitogen-activated protein kinases (MAPKs) comprise a family of serine/threonine kinases that are activated by a large variety of extracellular stimuli and play integral roles in controlling many cellular processes, from the cell surface to the nucleus. The MAPK family includes four distinct MAPK cascades, that is, extracellular signal-regulated kinase 1/2 (ERK1/2), p38 MAPK, c-Jun N-terminal kinase or stress-activated protein kinase, and ERK5. These MAPKs are essentially operated through three-tiered consecutive phosphorylation events catalyzed by a MAPK kinase kinase, a MAPK kinase, and a MAPK. MAPKs lie in protein kinase cascades. The MAPK signaling pathways have been demonstrated to be associated with events regulating the expression of the steroidogenic acute regulatory protein (StAR) and steroidogenesis in steroidogenic tissues. However, it has become clear that the regulation of MAPK-dependent StAR expression and steroid synthesis is a complex process and is context dependent. This paper summarizes the current level of understanding concerning the roles of the MAPK signaling cascades in the regulation of StAR expression and steroidogenesis in different steroidogenic cell models.

AUF1 p42 isoform selectively controls both steady-state and PGE2-induced FGF9 mRNA decay

Fibroblast growth factor 9 (FGF9) is an autocrine/paracrine growth factor that plays vital roles in many physiologic processes including embryonic development. Aberrant expression of FGF9 causes human diseases and thus it highlights the importance of controlling FGF9 expression; however, the mechanism responsible for regulation of FGF9 expression is largely unknown. Here, we show the crucial role of an AU-rich element (ARE) in FGF9 3′-untranslated region (UTR) on controlling FGF9 expression. Our data demonstrated that AUF1 binds to this ARE to regulate FGF9 mRNA stability. Overexpression of each isoform of AUF1 (p37, p40, p42 and p45) showed that only the p42 isoform reduced the steady-state FGF9 mRNA. Also, knockdown of p42^AUF1 prolonged the half-life of FGF9 mRNA. The induction of FGF9 mRNA in prostaglandin (PG) E₂-treated human endometrial stromal cells was accompanied with declined cytoplasmic AUF1. Nevertheless, ablation of AUF1 led to sustained elevation of FGF9 expression in these cells. Our study demonstrated that p42^AUF1 regulates both steady-state and PGE₂-induced FGF9 mRNA stability through ARE-mediated mRNA degradation. Since almost half of the FGF family members are ARE-containing genes, our findings also suggest that ARE-mediated mRNA decay is a common pathway to control FGFs expression, and it represents a novel RNA regulon to coordinate FGFs homeostasis in various physiological conditions.

The interplay between bioactive sphingolipids and steroid hormones

Steroid hormones regulate various physiological processes including development, reproduction, and metabolism. These regulatory molecules are synthesized from cholesterol in endocrine organs - such as the adrenal glands and gonads - via a multi-step enzymatic process that is catalyzed by the cytochrome P450 superfamily of monooxygenases and hydroxysteroid dehydrogenases. Steroidogenesis is induced by trophic peptide hormones primarily via the activation of a cAMP/protein kinase A (PKA)-dependent pathway. However, other signaling molecules, including cytokines and growth factors, control the steroid hormone biosynthetic pathway. More recently, sphingolipids, including ceramide, sphingosine-1-phosphate, and sphingosine, have been found to modulate steroid hormone secretion at multiple levels. In this review, we provide a brief overview of the mechanisms by which sphingolipids regulate steroidogenesis. In addition, we discuss how steroid hormones control sphingolipid metabolism. Finally, we outline evidence supporting the emerging role of bioactive sphingolipids in various nuclear processes and discuss a role for nuclear sphingolipid metabolism in the control of gene transcription.