TGF-beta1 system in Leydig cells. Part I: effect of hCG and progesterone

The Fate of Leydig Cells in Men with Spermatogenic Failure

The steroidogenic cells in the testicle, Leydig cells, located in the interstitial compartment, play a vital role in male reproductive tract development, maintenance of proper spermatogenesis, and overall male reproductive function. Therefore, their dysfunction can lead to all sorts of testicular pathologies. Spermatogenesis failure, manifested as azoospermia, is often associated with defective Leydig cell activity. Spermatogenic failure is the most severe form of male infertility, caused by disorders of the testicular parenchyma or testicular hormone imbalance. This review covers current progress in knowledge on Leydig cells origin, structure, and function, and focuses on recent advances in understanding how Leydig cells contribute to the impairment of spermatogenesis.

Mifepristone Treatment Promotes Testicular Leydig Cell Tumor Progression in Transgenic Mice

Simple Summary

Recently, the antiprogestin activity of selective progesterone receptor (PR) modulator mifepristone (MF) has proven unsuccessful as a potential anti-cancer agent in various clinical trials. Herein, we analyzed the effects of MF treatment on Leydig cell tumor (LCT) progression in a transgenic mouse model (inhibin-α promoter-driven SV40 T-antigen), as well as on the proliferation of two Leydig tumor cell lines. MF significantly stimulated the proliferation of LCT in vitro. Similarly, a 1-mo MF or P4 treatment stimulated LCT tumor growth in vivo. Only the abundant membrane Pgrmc1 expression was found in LCTs, but no other classical Pgr or nonclassical membrane PRs. Functional analysis showed that PGRMC1 is required for MF and P4 to stimulate the proliferation and invasiveness of LCTs. Our findings provide novel information that the use of MF as an anti-cancer agent should be considered with caution due to its potential PGRMC1 tumor-promoting pathway activation in cancers.

Abstract

The selective progesterone receptor modulator mifepristone (MF) may act as a potent antiproliferative agent in different steroid-dependent cancers due to its strong antagonistic effect on the nuclear progesterone receptor (PGR). Hereby, we analyzed the effects of MF treatment on Leydig cell tumor (LCT) progression in a transgenic mouse model (inhibin-α promoter-driven SV40 T-antigen), as well as on LCT (BLTK-1 and mLTC-1) cell proliferation. MF significantly stimulated the proliferation of LCT in vitro. Similarly, a 1-mo MF or P4 treatment stimulated LCT tumor growth in vivo. Traceable/absent classical Pgr or nonclassical membrane PRs α, β, γ and Pgrmc2, but abundant membrane Pgrmc1 expression, was found in LCTs. MF did not activate glucocorticoid or androgen receptors in LCTs. Functional analysis showed that PGRMC1 is required for MF and P4 to stimulate the proliferation and invasiveness of LCTs. Accordingly, MF and P4 induced PGRMC1 translocation into the nucleus and thereby stimulated the release of TGFβ1 in LCT cells. MF and P4 treatments upregulated Tgfbr1, Tgfbr2, and Alk1 expression and stimulated TGFβ1 release in LCT cells. Our findings provide novel mechanistic insights into the action of MF as a membrane PR agonist that promotes LCT growth through PGRMC1 and the alternative TGFβ1 signaling pathway.

TGFB1 represses the expression of SF1 and LRH1 to inhibit E2 production in rat LCs

Leydig cells (LCs) in the adult testis have been identified as the major sites of oestrogen production, which is crucial for mammalian germ cell differentiation. Our previous work showed that transforming growth factor beta 1 (TGFB1) inhibits estradiol (E₂) secretion via down-regulating Cyp19 gene expression in mature rat LCs. However, the mechanism remains unclear. In the present study, the effects of TGFB1 on the expression levels of steroidogenic factor 1 (SF1), liver receptor homolog 1 (LRH1), cAMP response element-binding protein (CREB) and cAMP responsive element modulator (CREM) were evaluated both in primary cultured LCs and in rat testis. The involvement of TGFB1 signalling in the regulation of SF1 and LRH1 expression was then validated by applying the inhibitor of the TGFB type 1 receptor (TGFBR1) SB431542. Moreover, the expression of CYP19 in testicular LCs was investigated and the production of E₂ in testicular interstitial fluid (TIF) was measured. The results showed that TGFB1 especially down-regulated the expression levels of SF1 and LRH1 both in primary cultured LCs and in rat testis. The down-regulations of TGFB1 in the production of E₂ in TIF and the expression of CYP19 in testicular LCs were also observed in vivo These inhibitory effects could be reversed by TGFBR1 inhibitor SB431542. Our findings suggest that TGFB1 may act through the canonical signalling pathway involving ALK5 to restrain SF1 and LRH1 accumulation and eventually attenuate Cyp19 transcription and oestrogen production in LCs.

Endogenous inhibins regulate steroidogenesis in mouse TM3 Leydig cells by altering SMAD2 signalling

This study tested the hypothesis that inhibins act in an autocrine manner on Leydig cells using a pre-pubertal Leydig cell line, TM3, as a model of immature Leydig cells. The expression of Inha, Inhba, and Inhbb in TM3 cells was determined by RT-PCR and the production of the inhibin-alpha subunit was confirmed by western blot. Knockdown of Inha expression resulted in significant decreases in the expression of Leydig cell markers Cyp17a1, Cyp11a1, Nr5a1, and Insl3. Western blot showed that activin A, TGFβ1 and TGFβ2 activated SMAD2, and that knockdown of Inha expression in TM3 cells enhanced both activin A- and TGFβ-induced SMAD2 activation. SB431542, a chemical inhibitor of the TGFβ/activin type I receptors, blocked ligand-induced SMAD2 activation and the downregulation of Cyp17a1 expression. Our findings demonstrate that TGFβs and activin A negatively regulate steroidogenic gene expression in TM3 cells via ALK4/5 and SMAD2 and endogenous inhibins can counter this regulation.

CD90 and CD105 expression in the mouse ovary and testis at different stages of postnatal development

CD90 (i.e., THY1) and CD105 (i.e., endoglin) are glycoproteins known as mesenchymal stem cell markers that are expressed in various cell types including male and female gonadal cells. We aimed to determine ovarian and testicular expression of CD90 and CD105 in various cell types during postnatal development in mice. The present study was carried out on male (C57BL/6) and female (Balb/C) mice during critical stages of gonadal development. Immunohistochemical localization of CD90 and CD105 was determined in the ovaries obtained at postnatal days (PND) -1, -7, -21 and -60 and in the testes obtained at PND6, -8, -16, -20, -29, -32 and -88. The relative expression of CD90 and CD105 was evaluated by ImageJ software and data were analyzed by analysis of variance. The relative expression of CD90 and CD105 varied during postnatal development and increased significantly in the adult ovary (PND60) and testis (PND88) compared to the early postnatal gonads. In the ovaries, the expression of CD90 was significantly higher in somatic cells in comparison to germ cell compartments. In the testis, CD90 expression was greater in germ cells and Sertoli cells compared to other cell types. Expression of CD105 was higher in germ cells than somatic cells of both the ovary and testis. In addition to different expression of CD90 and CD105 during various developmental stages, also their altered expression in particular cell types suggests specific roles of these glycoproteins in physiological processes of mouse gonads.

Transforming growth factor-β1 signaling represses testicular steroidogenesis through cross-talk with orphan nuclear receptor Nur77

Transforming growth factor- β1 (TGF-β1) has been reported to inhibit luteinizing hormone (LH) mediated-steroidogenesis in testicular Leydig cells. However, the mechanism by which TGF-β1 controls the steroidogenesis in Leydig cells is not well understood. Here, we investigated the possibility that TGF-β1 represses steroidogenesis through cross-talk with the orphan nuclear receptor Nur77. Nur77, which is induced by LH/cAMP signaling, is one of major transcription factors that regulate the expression of steroidogenic genes in Leydig cells. TGF-β1 signaling inhibited cAMP-induced testosterone production and the expression of steroidogenic genes such as P450c17, StAR and 3β-HSD in mouse Leydig cells. Further, TGF-β1/ALK5 signaling repressed cAMP-induced and Nur77-activated promoter activity of steroidogenic genes. In addition, TGF-β1/ALK5-activated Smad3 repressed Nur77 transactivation of steroidogenic gene promoters by interfering with Nur77 binding to DNA. In primary Leydig cells isolated from Tgfbr2^flox/flox Cyp17iCre mice, TGF-β1-mediated repression of cAMP-induced steroidogenic gene expression was significantly less than that in primary Leydig cells from Tgfbr2^flox/flox mice. Taken together, these results suggest that TGF-β1/ALK5/Smad3 signaling represses the expression of steroidogenic genes via the suppression of Nur77 transactivation in testicular Leydig cells. These findings may provide a molecular mechanism involved in the TGF-β1-mediated repression of testicular steroidogenesis.

Functional role of progestin and the progesterone receptor in the suppression of spermatogenesis in rodents

Synthetic progestins such as levonorgestrel (LNG) are used in combination with testosterone (T) in male contraceptive clinical trials to suppress gonadotropins secretion, but whether progestins have additional direct effects on the testis are not known. This study aimed to examine the effect of a potent progestin, (LNG), alone or in combination with testosterone (T) on spermatogenesis in adult rats, and to evaluate the functional role of the progesterone receptors (PRs) in the testis. In comparison with a low dose of LNG treatment in adult rats for 4 weeks, T and T + LNG treatment decreased testicular sperm count to 64.1 and 40.2% of control levels respectively. LNG induced germ cell apoptosis at stages I-IV and XII-XIV; T increased apoptosis at stages VII-VIII; LNG + T treatment induced greater germ cell apoptosis at a wider range of seminiferous epithelial stages. RT-PCR and Western Blots showed that PR was present in testes and up-regulated during suppression of spermatogenesis induced by testicular hormonal deprivation. PR knockout (PRKO) mice had larger testes, greater sperm production, increased numbers of Sertoli and Leydig cells. Suppression of gonadotropin and intratesticular T by GnRH-antagonist treatment induced PR promoter driven LacZ expression in Leydig cells of PRKO mice. This suggests that GnRH-antagonist treatment while inducing germ cell apoptosis also up-regulates PR. We conclude that (i) LNG + T induced greater suppression of spermatogenesis through increase in germ cell apoptosis involving a wider range of seminiferous epithelial stages than either treatment alone, (ii) up-regulation of PR was associated with inhibition of spermatogenesis, (iii) PR knockout mice showed increased sperm production suggesting that testicular PR activated events play a physiological and pharmacological inhibitory role in the testis. These data support the hypothesis that in addition to its known suppressive effects on gonadotropins, progestins may have direct inhibitory actions on the testis.

Involvement of KLF14 and egr-1 in the TGF-beta1 action on Leydig cell proliferation

Transforming growth factor β1 (TGF-β1) is a pleiotropic cytokine that modulates cell homeostasis. In Leydig cells, TGF-β1 exerts stimulatory and inhibitory effect depending on the type I receptor involved in the signaling pathway. The aim of the present work was to study the signaling mechanisms and the intermediates involved in the action of TGF-β1 on TM3 Leydig cell proliferation in the presence or absence of progesterone. The MTT assay showed that the presence of progesterone in the culture media lead to a proliferative effect that was blocked by Ru 486, an inhibitor of progesterone receptor; and ALK-5 did not participate in this effect. TGF-β1 (1 ng/ml) increased the expression of p15 (an inhibitor of cell cycle) in TM3 Leydig cells, and this effect was blocked by progesterone (1μM). The expression of PCNA presented a higher increase in the cell cultured with TGF-β1 plus progesterone than in cells cultured only with TGF-β1. Progesterone induced the gene expression of endoglin, a cofactor of TGF-β1 receptor that leads to a stimulatory signaling pathway, despite of the absence of progesterone response element in endoglin gene. In addition, the presence of progesterone induced the gene expression of egr-1 and also KLF14, indicating that this steroid channels the signaling pathway into a non-canonical mechanism. In conclusion, these findings suggest that the proliferative action of TGF-β1 involves endoglin. This co-receptor might be induced by KLF14 which is probably activated by progesterone.

Influence of the photoperiod on TGF-β1 and p15 expression in hamster Leydig cells

Adult hamsters exposed to short photoperiods show a marked atrophy of their internal reproductive organs, including a reduction in size, though not number of Leydig cells. Transforming growth factor-β1 (TGF-β1) is involved in the regulation of growth and proliferation of different cell types. The aim of the present study was to examine the influence of photoperiod on the protein and gene expression of TGF-β1 and its receptors as well as gene expression of p15. The effect of TGF-β1 on the expression of p15 in purified Leydig cells from regressed and non-regressed hamster testes was also tested. Protein and gene expression of TGF-β1 was detected in both regressed and non-regressed testes. In contrast to the activin receptor-like kinase 1 (ALK-1), the TGF-β1, the activin receptor-like kinase 5 (ALK-5) and the co-receptor endoglin all showed a greater basal expression in regressed than non-regressed hamster testes. Melatonin induced the TGF-β1 mRNA expression in purified Leydig cells from non-regressed testes. The p15 mRNA level was greater in regressed than non-regressed testes. A high dose of TGF-β1 during a short incubation period increased the p15 mRNA level in Leydig cells from non-regressed testes. ALK-5 and mitogen-activated protein kinase (MAPK) p38 might have played a role in this process. In regressed hamster testes, the p15 mRNA level increased due to a low dose of TGF-β1 after short incubation periods and to a high dose after longer incubation periods; in both instances, ALK-5, ERK 1/2 and p38 were involved. Collectively, these results suggest that the alterations in p15 expression, mediated by MAPK, are involved in the shift between the active and inactive states in hamster Leydig cells.

Expression of the TGF-beta1 system in human testicular pathologies

BACKGROUND

In non-obstructive azoospermia, histological patterns of Sertoli cell-only Syndrome (SCO) and hypospermatogenesis (H) are commonly found. In these pathologies, Leydig cell hyperplasia (LCH) is detected in some patients. Since TGF-β1 is involved in cellular proliferation/development, the aim of this work was to analyze the expression of TGF-β1, its receptors TGFBRII, TGFBRI (ALK-1 and ALK-5), and the co-receptor endoglin in human biopsies from patients with idiopathic infertility.

METHODS

Specific immunostaining of TGF-β1, its receptors TGFBRII, TGFBRI (ALK-1 and ALK-5), co-receptor endoglin and Smads proteins, were carried out in testicular biopsies from normal and infertile men with SCO or H. Gene expression of TGF-β1 system were made in biopsies from infertile patients with semi-quantitative and quantitative PCR.

RESULTS

Immunohistochemical studies revealed that TGF-β1 and its specific receptors are present in Leydig cells in biopsies from normal tissue or patients with SCO or H with or without LCH. Smad proteins, which are involved in TGF-β1 signaling, are also detected in both their phosphorylated (activated) and dephosphorylated form in all samples TGF-β1, ALK-1 and endoglin gene expression are stronger in human biopsies with LCH than in those with SCO or H. Neither TGFBRII nor ALK-5 gene expression showed significant differences between pathologies. A significant correlation between ALK-1 and endoglin expression was observed.

CONCLUSIONS

In conclusion, the high levels of mRNA and protein expression of the TGF-β1 system in patients with LCH, particularly ALK1 and its correlation with endoglin, suggest that these proteins acting in concert might be, at least in part, committed actors in the Leydig cell hyperplasia.

TGF-beta1 system in Leydig cells. Part II: TGF-beta1 and progesterone, through Smad1/5, are involved in the hyperplasia/hypertrophy of Leydig cells

Several reports indicate that transforming growth factor beta1 (TGF-beta1) participates in the regulation of cell cycle progression. In this work, we analyzed the in vitro effect of TGF-beta1 on Leydig cell proliferation markers and the in vivo effect of this cytokine in Leydig cell hyperplasia/hypertrophy. The in vitro effect of TGF-beta1 (1 ng/ml) plus progesterone (10(-6) M) on purified Leydig cells from 3 week-old mice increased the immunocytochemically detected PCNA and stimulated the phosphorylation of Smad 1/5. Progesterone (10(-6) M) in the presence or absence of TGF-beta1 diminished the ratio Bax/Bcl-2. Morphometric testicular studies of mice treated with progesterone (s.c.) plus TGF-beta1 (intratesticular), showed an increase in interstitial volume and a decrease in tubular volume. Furthermore, the cytoplasmic volume of Leydig cells showed an increment in this experimental group with a diminution in nuclear volume. Thus, it turned out that the administration of progesterone and TGF-beta1 augmented the volume of Leydig cells. These results indicate a clear effect of TGF-beta1 in the hypertrophy/hyperplasia of Leydig cells.