Leydig cell re-generation and expression of cell signaling molecules in the germ cell-free testis

Testicular niche repair after gonadotoxic treatments: Current knowledge and future directions

The testicular niche, which includes the germ cells, somatic cells, and extracellular matrix, plays a crucial role in maintaining the proper functions of the testis. Gonadotoxic treatments, such as chemotherapy and radiation therapy, have significantly improved the survival rates of cancer patients but have also been shown to have adverse effects on the testicular microenvironment. Therefore, repairing the testicular niche after gonadotoxic treatments is essential to restore its function. In recent years, several approaches, such as stem cell transplantation, gene therapy, growth factor therapy, and pharmacological interventions have been proposed as potential therapeutic strategies to repair the testicular niche. This comprehensive review aims to provide an overview of the current understanding of testis damage and repair mechanisms. We will cover a range of topics, including the mechanism of gonadotoxic action, repair mechanisms, and treatment approaches. Overall, this review highlights the importance of repairing the testicular niche after gonadotoxic treatments and identifies potential avenues for future research to improve the outcomes for cancer survivors.

Effect of cadmium on the regulatory mechanism of steroidogenic pathway of Leydig cells during spermatogenesis

Cadmium is a male reproductive toxicant that interacts with a variety of pathogenetic mechanisms. However, the effect of cadmium on the regulatory mechanism of the steroidogenic pathway of Leydig cells during spermatogenesis is still ambiguous. Light microscopy, Western blot, immunohistochemistry, immunofluorescence, and quantitative polymerase chain reaction were performed to study the regulatory mechanism of the steroidogenic pathway of Leydig cells during spermatogenesis. The results indicated that in the control group, Leydig cells showed dynamic immunoreactivity and immunosignaling action with a strong positive significant secretion of 3β-hydroxysteroid hydrogenase (3β-HSD) in the interstitial compartment of the testis. Leydig cells showed a high active regulator mechanism of the steroidogenic pathway with increased the proteins and genes expression level of steroidogenic acute regulatory protein (STAR), cytochrome P450 cholesterol (CYP11A1), cytochrome P450 cholesterol (CYP17A1), 3β-hydroxysteroid hydrogenase (3β-HSD) 17β-hydroxysteroid hydrogenase (17β-HSD), and androgen receptor (AR) that maintained the healthy and vigorous progressive motile spermatozoa. However, on treatment with cadmium, Leydig cells were irregularly dispersed in the interstitial compartment of the testis. Leydig cells showed reduced immunoreactivity and immunosignaling of 3β-HSD protein. Meanwhile, cadmium impaired the regulatory mechanism of the steroidogenic process of the Leydig cells with reduced protein and gene expression levels of STAR, CYP11A1, CYP17A1, 3β-HSD, 17β-HSD, and AR in the testis. Additionally, treatment with cadmium impaired the serum LH, FSH, and testosterone levels in blood as compared to control. This study explores the hazardous effect of cadmium on the regulatory mechanism of the steroidogenic pathway of Leydig cells during spermatogenesis.

Leukemia inhibitory factor-receptor signalling negatively regulates gonadotrophin-stimulated testosterone production in mouse Leydig Cells

Testicular Leydig cells (LCs) are the principal source of circulating testosterone in males. LC steroidogenesis maintains sexual function, fertility and general health, and is influenced by various paracrine factors. The leukemia inhibitory factor receptor (LIFR) is expressed in the testis and activated by different ligands, including leukemia inhibitory factor (LIF), produced by peritubular myoid cells. LIF can modulate LC testosterone production in vitro under certain circumstances, but the role of consolidated signalling through LIFR in adult LC function in vivo has not been established. We used a conditional Lifr allele in combination with adenoviral vectors expressing Cre-recombinase to generate an acute model of LC Lifr-KO in the adult mouse testis, and showed that LC Lifr is not required for short term LC survival or basal steroidogenesis. However, LIFR-signalling negatively regulates steroidogenic enzyme expression and maximal gonadotrophin-stimulated testosterone biosynthesis, expanding our understanding of the intricate regulation of LC steroidogenic function.

Expression of the NSE,SP,NFH and DβH in normal and cryptorchid testes of Bactrian camel

Neuroendocrine substances play essential roles in regulating the normal physiological functions of testicles. The purpose of this study is to explore the localization and effects of four neuroendocrine markers (NSE, SP, NFH and DβH) in normal and cryptorchid testes of Bactrian camels using western blotting, transmission electron microscopy, immunohistochemistry, and immunofluorescence methods. The results showed that cryptorchidism caused a reduction in layers of spermatogenic epithelium and decreased glycogen positivity in the basement membrane. The ultrastructure revealed that macrophages were always found around the Leydig cells, crowded with swelling mitochondria in cryptorchidism. Expression of NSE in the Leydig cells of cryptorchidism was significantly weakened compared to that in the normal group(p<0.01). We found that SP was always distributed along the nerve fibers in normal testes and was expressed in the Leydig cells of cryptorchidism. However, expression of NFH in the cryptorchidic tissue was strongly positive in the spermatogenic epithelium, with limited expression in Leydig cells and no expression in peritubular myoid cells. Therefore, the expression of DβH in the Sertoli cells was comparatively strong in both the normal and cryptorchidism groups. NFH and DβH expression was significantly increased in the cryptorchidism group compared with the normal group (p<0.01). These findings indicated that the underdeveloped seminiferous epithelium and pathological changes in cryptorchid tissue in Bactrian camels were potentially related to a disorder in glycoprotein metabolism. Our results suggest that NSE and SP could help judge the pathological changes of cryptorchidism. The present study provides the first evidence at the protein level for the existence of NFH and DβH in Sertoli and Leydig cells in Bactrian camel cryptorchidism and provides a more in-depth understanding of neuroendocrine regulation is crucial for animal cryptorchidism.

Comparative transcriptome analysis reveals potential testosterone function-related regulatory genes/pathways of Leydig cells in immature and mature buffalo (Bubalus bubalis) testes

Leydig cells (LCs) are testosterone-generating endocrine cells that are located outside the seminiferous tubules in the testis, and testosterone is fundamental for retaining spermatogenesis and male fertility. In buffalo, adult Leydig cells (ALCs) are developed by immature Leydig cells (ILCs) in the postnatal testes. However, the genes/pathways associated to the regulation of testosterone secretion function during the development of postnatal LCs remains comprehensively unidentified. The present study comparatively analyzed the transcriptome profiles of ILC and ALC in buffalo with significant differences in testosterone secretion. Differentially expressed genes (DEGs) analysis identified 972 and 1,091 annotated genes that were significantly up- and down-regulated in buffalo ALC. Functional enrichment analysis showed that cAMP signaling being the most significantly enriched pathway, and testosterone synthesis and lipid transport-related genes/pathways were upregulated in ALC. Furthermore, gene set enrichment analysis (GSEA) shows that cAMP signaling and steroid hormone biosynthesis were activated in ALC, demonstrating that cAMP signaling may serve as a positive regulatory pathway in the maintenance of testosterone function during postnatal development of LCs. Protein-protein interaction (PPI) networks analysis highlighted that ADCY8, ADCY2, POMC, CHRM2, SST, PTGER3, SSTR2, SSTR1, NPY1R, and HTR1D as hub genes in the cAMP signaling pathway. In conclusion, this study identified key genes and pathways associated in the regulation of testosterone secretion function during the ILC-ALC transition in buffalo based on bioinformatics analysis, and these key genes might be deeply involved in cAMP generation to influencing testosterone levels in LCs. The results suggest that ALCs might increase testosterone levels by enhancing cAMP production than ILCs. Our data will enhance the understanding of developmental mechanism studies related to testosterone function and provide preliminary evidence for molecular mechanisms of LCs regulating spermatogenesis.

Advances in stem cell research for the treatment of primary hypogonadism

In Leydig cell dysfunction, cells respond weakly to stimulation by pituitary luteinizing hormone, and, therefore, produce less testosterone, leading to primary hypogonadism. The most widely used treatment for primary hypogonadism is testosterone replacement therapy (TRT). However, TRT causes infertility and has been associated with other adverse effects, such as causing erythrocytosis and gynaecomastia, worsening obstructive sleep apnoea and increasing cardiovascular morbidity and mortality risks. Stem-cell-based therapy that re-establishes testosterone-producing cell lineages in the body has, therefore, become a promising prospect for treating primary hypogonadism. Over the past two decades, substantial advances have been made in the identification of Leydig cell sources for use in transplantation surgery, including the artificial induction of Leydig-like cells from different types of stem cells, for example, stem Leydig cells, mesenchymal stem cells, and pluripotent stem cells (PSCs). PSC-derived Leydig-like cells have already provided a powerful in vitro model to study the molecular mechanisms underlying Leydig cell differentiation and could be used to treat men with primary hypogonadism in a more specific and personalized approach.

Deficiency in insulin-like growth factors signalling in mouse Leydig cells increase conversion of testosterone to estradiol because of feminization

AIM

A growing body of evidence pointed correlation between insulin-resistance, testosterone level and infertility, but there is scarce information about mechanisms. The aim of this study was to identify the possible mechanism linking the insulin-resistance with testosterone-producing-Leydig-cells functionality.

METHODS

We applied in vivo and in vitro approaches. The in vivo model of functional genomics is represented by INSR/IGF1R-deficient-testosterone-producing Leydig cells obtained from the prepubertal (P21) and adult (P80) male mice with insulin + IGF1-receptors deletion in steroidogenic cells (Insr/Igf1r-DKO). The in vitro model of INSR/IGF1R-deficient-cell was mimicked by blockade of insulin/IGF1-receptors on the primary culture of P21 and P80 Leydig cells.

RESULTS

Leydig-cell-specific-insulin-resistance induce the development of estrogenic characteristics of progenitor Leydig cells in prepubertal mice and mature Leydig cells in adult mice, followed with a dramatic reduction of androgen phenotype. Level of androgens in serum, testes and Leydig cells decrease as a consequence of the dramatic reduction of steroidogenic capacity and activity as well as all functional markers of Leydig cell. Oppositely, the markers for female-steroidogenic-cell differentiation and function increase. The physiological significances are the higher level of testosterone-to-estradiol-conversion in double-knock-out-mice of both ages and few spermatozoa in adults. Intriguingly, the transcription of pro-male sexual differentiation markers Sry/Sox9 increased in P21-Leydig-cells, questioning the current view about the antagonistic genetic programs underlying gonadal sex determination.

CONCLUSION

The results provide new molecular mechanisms leading to the development of the female phenotype in Leydig cells from Insr/Igf1r-DKO mice and could help to better understand the correlation between insulin resistance, testosterone and male (in)fertility.

Phthalate inhibits Leydig cell differentiation and promotes adipocyte differentiation

Studies have shown that phthalates are capable of affecting the development and functions of male reproductive system. The effect of phthalates on Leydig cell functions is well documented. However, little is known about their potential effects on the functions of stem Leydig cells (SLC). In the present study, we have examined the effects of mono-(2-ethylhexyl) phthalate (MEHP) on SLC functions in vitro by culturing seminiferous tubules and isolated SLCs. The results indicate that MEHP can significantly inhibit the proliferation and differentiation of SLCs in both the organ and cell culture systems. Interestingly, the minimal effective concentration that is able to affect SLC function was lower in the tubule culture system (1 μM) than in the isolated cells (10 μM), suggesting a possible involvement of the niche cells. Also, MEHP appeared to affect both the efficiency of SLCs to form Leydig cells and a selected group of Leydig cell-specific genes, including Lhcgr, Scarb1, Hsd3b1, Cyp17a1, Star, Srd5a1, Akr1c14, Insl3, Hao2 and Pah. Since SLCs are multipotent, we also tested the effect of MEHP on the differentiation of SLCs to adipocytes. Though MEHP by itself can not specify SLCs into adipocyte lineage, it indeed significantly increased the adipogenic activity of SLCs if used with an adipocyte inducing medium by up-regulation of multiple adipogenic-related genes, including Pparg and Cebpa. Overall, the results indicate that MEHP inhibits SLCs differentiating into Leydig lineage while stimulates the differentiating potential of SLCs to adipocytes.

A Novel Antigonadotropic Role of Thyroid Stimulating Hormone on Leydig Cell-Derived Mouse Leydig Tumor Cells-1 Line

Subclinical hypothyroid men characterized by a rise in only thyroid stimulating hormone (TSH) levels and normal thyroid hormone levels showed a fall in their serum progesterone and testosterone levels. This suggested a role of TSH in regulating Leydig cell steroidogenesis. Therefore, we investigated the direct role of TSH on steroid production and secretion using a mouse Leydig tumour cell line, MLTC-1. MLTC-1 cells were treated with different doses of TSH isolated from porcine pituitary as well as recombinant TSH. Steroid secretion was measured by radioimmunoassay. The mRNA levels of steroidogenic enzymes were quantitated by real time PCR whereas the corresponding protein levels were determined by Western blot. In MLTC-1 cells, pituitary TSH as well as recombinant TSH inhibited progesterone and testosterone secretion in a dose dependent manner. The inhibitory action of TSH on steroid secretion was unique and not mimicked by other anterior pituitary hormones including FSH and ACTH. Recombinant TSH showed no effect on StAR and CYP11A1, the enzymes catalysing the non-steroidogenic and steroidogenic rate-limiting steps of steroid synthesis respectively. Recombinant TSH was shown to inhibit steroidogenesis in MLTC-1 cells by inhibiting the 3β hydroxy steroid dehydrogenase mRNA and protein levels, the enzyme that catalyses the conversion of pregnenolone to progesterone. This inhibitory effect of TSH is probably direct as both mRNA and protein of the TSH receptor were shown to be present in the MLTC-1 cells.

Human Adipose-derived Pericytes Display Steroidogenic Lineage Potential in Vitro and Influence Leydig Cell Regeneration in Vivo in Rats

Exogenous androgen replacement is used to treat symptoms associated with low testosterone in males. However, adverse cardiovascular risk and negative fertility impacts impel development of alternative approaches to restore/maintain Leydig cell (LC) androgen production. Stem Leydig cell (SLC) transplantation shows promise in this regard however, practicality of SLC isolation/transplantation impede clinical translation. Multipotent human adipose-derived perivascular stem cells (hAd-PSCs) represent an attractive extragonadal stem cell source for regenerative therapies in the testis but their therapeutic potential in this context is unexplored. We asked whether hAd-PSCs could be converted into Leydig-like cells and determined their capacity to promote regeneration in LC-ablated rat testes. Exposure of hAd-PSCs to differentiation-inducing factors in vitro upregulated steroidogenic genes but did not fully induce LC differentiation. In vivo, no difference in LC-regeneration was noted between Sham and hAd-PSC-transplanted rats. Interestingly, Cyp17a1 expression increased in hAd-PSC-transplanted testes compared to intact vehicle controls and the luteinising hormone/testosterone ratio returned to Vehicle control levels which was not the case in EDS + Sham animals. Notably, hAd-PSCs were undetectable one-month after transplantation suggesting this effect is likely mediated via paracrine mechanisms during the initial stages of regeneration; either directly by interacting with regenerating LCs, or through indirect interactions with trophic macrophages.

Trimethyltin (TMT) Reduces Testosterone Production in Adult Leydig Cells in Rats

Trimethyltin (TMT) is widely used as a plastic heat stabilizer and can cause severe toxicity. Here, the effects of TMT on testosterone production by adult Leydig cells and the related mechanisms of action were investigated. Eighteen adult male Sprague Dawley rats (56 days old) were randomly divided into 3 groups and given intraperitoneal injection of TMT for 21 consecutive days at the doses of 0 (vehicle control), 5, or 10 mg/kg/d. After treatment, trunk blood was collected for hormonal analysis. In addition, related gene and protein expression in testes was detected. At 10 mg/kg, TMT significantly reduced serum testosterone levels but increased serum luteinizing and follicle-stimulating hormone levels. The messenger RNA and protein levels of luteinizing hormone/chorionic gonadotropin receptor, steroidogenic acute regulatory protein, cytochrome P450 17-hydroxylase/17,20-lyase, follicle-stimulating hormone receptor, and SRY box 9 were significantly lower in the TMT-treated testes than in controls. Immunohistochemical study showed that TMT decreased adult Leydig cell number. In conclusion, these findings indicate that TMT reduced adult Leydig cell testosterone production in vivo by directly downregulating the expression of steroidogenic enzymes and decreasing adult Leydig cell number in the testis.

Fibroblast growth factor homologous factor 1 stimulates Leydig cell regeneration from stem cells in male rats

Fibroblast growth factor homologous factor 1 (FHF1) is an intracellular protein that does not bind to cell surface fibroblast growth factor receptor. Here, we report that FHF1 is abundantly present in Leydig cells with up‐regulation during its development. Adult male Sprague Dawley rats were intraperitoneally injected with 75 mg/kg ethane dimethane sulphonate (EDS) to ablate Leydig cells to initiate their regeneration. Then, rats daily received intratesticular injection of FHF1 (0, 10 and 100 ng/testis) from post‐EDS day 14 for 14 days. FHF1 increased serum testosterone levels without affecting the levels of luteinizing hormone and follicle‐stimulating hormone. FHF1 increased the cell number staining with HSD11B1, a biomarker for Leydig cells at the advanced stage, without affecting the cell number staining with CYP11A1, a biomarker for all Leydig cells. FHF1 did not affect PCNA‐labelling index in Leydig cells. FHF1 increased Leydig cell mRNA (Lhcgr, Scarb1, Star, Cyp11a1, Hsd3b1, Cyp17a1, Hsd17b3, Insl3, Nr5a1 and Hsd11b1) and their protein levels in vivo. FHF1 increased preadipocyte biomarker Dlk1 mRNA level and decreased fully differentiated adipocyte biomarker (Fabp4 and Lpl) mRNA and their protein levels. In conclusion, FHF1 promotes Leydig cell regeneration from stem cells while inhibiting the differentiation of preadipocyte/stem cells into adipocytes in EDS‐treated testis.

Androgen receptor expression is required to ensure development of adult Leydig cells and to prevent development of steroidogenic cells with adrenal characteristics in the mouse testis

Background

The interstitium of the mouse testis contains Leydig cells and a small number of steroidogenic cells with adrenal characteristics which may be derived from the fetal adrenal during development or may be a normal subset of the developing fetal Leydig cells. Currently it is not known what regulates development and/or proliferation of this sub-population of steroidogenic cells in the mouse testis. Androgen receptors (AR) are essential for normal testicular function and in this study we have examined the role of the AR in regulating interstitial cell development.

Results

Using a mouse model which lacks gonadotropins and AR (hpg.ARKO), stimulation of luteinising hormone receptors in vivo with human chorionic gonadotropin (hCG) caused a marked increase in adrenal cell transcripts/protein in a group of testicular interstitial cells. hCG also induced testicular transcripts associated with basic steroidogenic function in these mice but had no effect on adult Leydig cell-specific transcript levels. In hpg mice with functional AR, treatment with hCG induced Leydig cell-specific function and had no effect on adrenal transcript levels. Examination of mice with cell-specific AR deletion and knockdown of AR in a mouse Leydig cell line suggests that AR in the Leydig cells are likely to regulate these effects.

Conclusions

This study shows that in the mouse the androgen receptor is required both to prevent development of testicular cells with adrenal characteristics and to ensure development of an adult Leydig cell phenotype.

Electronic supplementary material

The online version of this article (10.1186/s12861-019-0189-5) contains supplementary material, which is available to authorized users.

Effects of spermatogenic cycle on Stem Leydig cell proliferation and differentiation

We reported previously that stem Leydig cells (SLC) on the surfaces of rat testicular seminiferous tubules are able to differentiate into Leydig cells. The proliferation and differentiation of SLCs seem likely to be regulated by niche cells, including nearby germ and Sertoli cells. Due to the cyclical nature of spermatogenesis, we hypothesized that the changes in the germ cell composition of the seminiferous tubules as spermatogenesis proceeds may affect tubule-associated SLC functions. To test this hypothesis, we compared the ability of SLCs associated with tubules at different stages of the cycle to differentiate into Leydig cells in vitro. SLCs associated with stages IX-XI were more active in proliferation and differentiation than SLCs associated with stages VII-VIII. However, when the SLCs were isolated from each of the two groups of tubules and cultured in vitro, no differences were seen in their ability to proliferate or differentiate. These results suggested that the stage-dependent local factors, not the SLCs themselves, explain the stage-dependent differences in SLC function. TGFB, produced in stage-specific fashion by Sertoli cells, is among the factors shown in previous studies to affect SLC function in vitro. When TGFB inhibitors were included in the cultures of stages IX-XI and VII-VIII tubules, stage-dependent differences in SLC development were reduced, suggesting that TGFB may be among the paracrine factors involved in the stage-dependent differences in SLC function. Taken together, the findings suggest that there is dynamic interaction between SLCs and germ/Sertoli cells within the seminiferous tubules that may affect SLC proliferation and differentiation.

Dibutyltin Dichloride Retards Leydig Cell Developmental Regeneration in Adult Rat Testis

Dibutyltin dichloride (DBTCl), widely used as plastic stabilizer, can cause comprehensive toxicity. The present study aims to investigate the effects of DBTCl on rat Leydig cell developmental regeneration and characterize the related mechanism. Adult male Sprague Dawley rats were randomly divided into four groups and gavaged with saline (control) or 5, 10, or 20 mg/kg/day of DBTCl consecutively for 10 days. At the end of the DBTCl treatment, all rats received a single intraperitoneal injection (i.p.,) of 75 mg/kg ethane dimethane sulfonate (EDS) to eliminate all the adult Leydig cells and to induce Leydig cell developmental regeneration. Leydig cell developmental regeneration was evaluated by measuring the levels of serum testosterone, luteinizing hormone, and follicle-stimulating hormone on days 7, 35, and 56 post-EDS. Leydig cell gene and protein expression levels, as well as cell morphology and cell counts were also carried out on day 56 post-EDS. The present study found that DBTCl significantly reduced serum testosterone levels on days 35 and 56 post-EDS, but increased serum luteinizing hormone (LH) and follicle-stimulating hormone (FSH) levels on day 56 at ≥ 5 mg/kg/day. The mRNA and protein levels of Leydig (Lhcgr, Scarb1, Star, Cyp11a1, Hsd17b3, and Hsd11b1) and Sertoli cells (Fshr, Amh, and Sox9) were significantly downregulated in the DBTCl-treated testes compared to the control. Immunohistochemical staining showed that DBTCl-treatment caused fewer regenerated Leydig cells and impaired Sertoli cell development and function in the testis on day 56 post-EDS. In conclusion, the present study demonstrates that DBTCl retards rat Leydig cell developmental regeneration by downregulating steroidogenesis-related enzymes at the gene and protein levels, inhibiting Leydig cell proliferation and impairing Sertoli cell function and development.

Dose-response effects of light at night on the reproductive physiology of great tits (Parus major): Integrating morphological analyses with candidate gene expression

Artificial light at night (ALAN) is increasingly recognized as a potential threat to wildlife and ecosystem health. Among the ecological effects of ALAN, changes in reproductive timing are frequently reported, but the mechanisms underlying this relationship are still poorly understood. Here, we experimentally investigated these mechanisms by assessing dose‐dependent photoperiodic responses to ALAN in the great tit (Parus major). We individually exposed photosensitive male birds to one of three nocturnal light levels (0.5, 1.5, and 5 lux), or to a dark control. Subsequent histological and molecular analyses on their testes indicated a dose‐dependent reproductive response to ALAN. Specifically, different stages of gonadal growth were activated after exposure to different levels of light at night. mRNA transcript levels of genes linked to the development of germ cells (stra8 and spo11) were increased under 0.5 lux compared to the dark control. The 0.5 and 1.5 lux groups showed slight increases in testis size and transcript levels associated with steroid synthesis (lhr and hsd3b1) and spermatogenesis (fshr, wt1, sox9, and cldn11), although spermatogenesis was not detected in histological analysis. In contrast, all birds under 5 lux had 10 to 30 times larger testes than birds in all other groups, with a parallel strong increase in mRNA transcript levels and clear signs of spermatogenesis. Across treatments, the volume of the testes was generally a good predictor of testicular transcript levels. Overall, our findings indicate that even small changes in nocturnal light intensity can increase, or decrease, effects on the reproductive physiology of wild organisms.

Probing GATA factor function in mouse Leydig cells via testicular injection of adenoviral vectors

Testicular Leydig cells produce androgens essential for proper male reproductive development and fertility. Here, we describe a new Leydig cell ablation model based on Cre/Lox recombination of mouse Gata4 and Gata6, two genes implicated in the transcriptional regulation of steroidogenesis. The testicular interstitium of adult Gata4flox/flox ; Gata6flox/flox mice was injected with adenoviral vectors encoding Cre + GFP (Ad-Cre-IRES-GFP) or GFP alone (Ad-GFP). The vectors efficiently and selectively transduced Leydig cells, as evidenced by GFP reporter expression. Three days after Ad-Cre-IRES-GFP injection, expression of androgen biosynthetic genes (Hsd3b1, Cyp17a1 and Hsd17b3) was reduced, whereas expression of another Leydig cell marker, Insl3, was unchanged. Six days after Ad-Cre-IRES-GFP treatment, the testicular interstitium was devoid of Leydig cells, and there was a concomitant loss of all Leydig cell markers. Chromatin condensation, nuclear fragmentation, mitochondrial swelling, and other ultrastructural changes were evident in the degenerating Leydig cells. Liquid chromatography-tandem mass spectrometry demonstrated reduced levels of androstenedione and testosterone in testes from mice injected with Ad-Cre-IRES-GFP. Late effects of treatment included testicular atrophy, infertility and the accumulation of lymphoid cells in the testicular interstitium. We conclude that adenoviral-mediated gene delivery is an expeditious way to probe Leydig cell function in vivo Our findings reinforce the notion that GATA factors are key regulators of steroidogenesis and testicular somatic cell survival.Free Finnish abstract: A Finnish translation of this abstract is freely available at http://www.reproduction-online.org/content/154/4/455/suppl/DC2.

A brief exposure to cadmium impairs Leydig cell regeneration in the adult rat testis

Cadmium is an endocrine disruptor, impairing male reproduction. The objective of this study is to investigate whether cadmium affects rat Leydig cell regeneration and to dissect the underlying mechanism. Adult male Sprague-Dawley rats received a single intraperitoneal injection (i.p.) of 0, 0.5 or 1.0 mg/kg of cadmium chloride, followed by ethane dimethane sulfonate (EDS) treatment to eliminate adult Leydig cells 20 days later. Compared to control (0 dose), cadmium treatment reduced serum testosterone levels by days 21, 35, and 56 after EDS treatment. Serum luteinizing hormone (LH) levels were also affected by day 56, the only time point examined. There were fewer regenerated Leydig cells in the cadmium-treated testis on days 35 and 56 after EDS treatment. Further studies demonstrated that the mRNA or protein levels of Leydig (Lhcgr, Scarb1, Star, Cyp11a1, Hsd3b1, Cyp17a1, Hsd17b3, and Hsd11b1), non-Leydig (Fshr and Dhh), and gonadotroph (Lhb) cells were also significantly lower in cadmium-treated animals. Since LH and desert hedgehog (DHH) are critical factors for Leydig cell differentiation, our result demonstrated that the lower doses of cadmium exposure, even briefly, may permanently damage Leydig cell regeneration.

Leydig cell stem cells: Identification, proliferation and differentiation

Adult Leydig cells develop from undifferentiated mesenchymal-like stem cells (stem Leydig cells, SLCs) present in the interstitial compartment of the early postnatal testis. Putative SLCs also have been identified in peritubular and perivascular locations of the adult testis. The latter cells, which normally are quiescent, are capable of regenerating new Leydig cells upon the loss of the adult cells. Recent studies have identified several protein markers to identify these cells, including nestin, PDGFRα, COUP-TFII, CD51 and CD90. We have shown that the proliferation of the SLCs is stimulated by DHH, FGF2, PDGFBB, activin and PDGFAA. Suppression of proliferation occurred with TGFβ, androgen and PKA signaling. The differentiation of the SLCs into testosterone-producing Leydig cells was found to be regulated positively by DHH (Desert hedgehog), lithium-induced signaling and activin; and negatively by TGFβ, PDGFBB, FGF2, Notch and Wnt signaling. DHH, by itself, was found to induce SLC differentiation into LH-responsive steroidogenic cells, suggesting that DHH plays a critical role in the commitment of SLC into the Leydig lineage. These studies, taken together, address the function and regulation of low turnover stem cells in a complex, adult organ, and also have potential application to the treatment of androgen deficiency.

Leukemia inhibitory factor stimulates steroidogenesis of rat immature Leydig cells via increasing the expression of steroidogenic acute regulatory protein

Leukemia inhibitory factor (LIF) has many physiological roles. However, its effects on Leydig cell development are still unclear. Rat immature and adult Leydig cells were cultured with different concentrations of LIF alone or in combination with luteinizing hormone (LH) for 24 h. LIF (1 and 10 ng/ml) significantly increased androgen production in immature Leydig cells, but had no effects on testosterone production in adult Leydig cells. Further studies revealed that LIF dose-dependently increased Star and Hsd17b3 expression levels in immature Leydig cells. Gene microarray revealed that the upregulation of anti-oxidative genes and Star might contribute to LIF-induced androgen production. In conclusion, LIF has stimulatory effects on androgen production in rat immature Leydig cells.

Transplantation of alginate-encapsulated seminiferous tubules and interstitial tissue into adult rats: Leydig stem cell differentiation in vivo?

In vivo and in vitro studies were conducted to determine whether testosterone-producing Leydig cells are able to develop from cells associated with rat seminiferous tubules, interstitium, or both. Adult rat seminiferous tubules and interstitium were isolated, encapsulated separately in alginate, and implanted subcutaneously into castrated rats. With implanted tubules, serum testosterone increased through two months. Tubules removed from the implanted rats and incubated with LH produced testosterone, and cells on the tubule surfaces expressed steroidogenic enzymes. With implanted interstitial tissue, serum levels of testosterone remained undetectable. However, co-culture of interstitium plus tubules in vitro resulted in the formation of Leydig cells by both compartments. These results indicate that seminiferous tubules contain both cellular and paracrine factors necessary for the differentiation of Leydig cells, and that the interstitial compartment contains precursor cells capable of forming testosterone-producing Leydig cells but requires stimulation by paracrine factors from the seminiferous tubules to do so.

Stem cell therapy for the treatment of Leydig cell dysfunction in primary hypogonadism

The production of testosterone occurs within the Leydig cells of the testes. When production fails at this level from either congenital, acquired, or systemic disorders, the result is primary hypogonadism. While numerous testosterone formulations have been developed, none are yet fully capable of replicating the physiological patterns of testosterone secretion. Multiple stem cell therapies to restore androgenic function of the testes are under investigation. Leydig cells derived from bone marrow, adipose tissue, umbilical cord, and the testes have shown promise for future therapy for primary hypogonadism. In particular, the discovery and utilization of a group of progenitor stem cells within the testes, known as stem Leydig cells (SLCs), has led not only to a better understanding of testicular development, but of treatment as well. When combining this with an understanding of the mechanisms that lead to Leydig cell dysfunction, researchers and physicians will be able to develop stem cell therapies that target the specific step in the steroidogenic process that is deficient. The current preclinical studies highlight the complex nature of regenerating this steroidogenic process and the problems remain unresolved. In summary, there appears to be two current directions for stem cell therapy in male primary hypogonadism. The first method involves differentiating adult Leydig cells from stem cells of various origins from bone marrow, adipose, or embryonic sources. The second method involves isolating, identifying, and transplanting stem Leydig cells into testicular tissue. Theoretically, in-vivo re-activation of SLCs in men with primary hypogonadism due to age would be another alternative method to treat hypogonadism while eliminating the need for transplantation.

Identification and characterization of Xenopus tropicalis common progenitors of Sertoli and peritubular myoid cell lineages

The origin of somatic cell lineages during testicular development is controversial in mammals. Employing basal amphibian tetrapod Xenopus tropicalis we established a cell culture derived from testes of juvenile male. Expression analysis showed transcription of some pluripotency genes and Sertoli cell, peritubular myoid cell and mesenchymal cell markers. Transcription of germline-specific genes was downregulated. Immunocytochemistry revealed that a majority of cells express vimentin and co-express Sox9 and smooth muscle α-actin (Sma), indicating the existence of a common progenitor of Sertoli and peritubular myoid cell lineages. Microinjection of transgenic, red fluorescent protein (RFP)-positive somatic testicular cells into the peritoneal cavity of X. tropicalis tadpoles resulted in cell deposits in heart, pronephros and intestine, and later in a strong proliferation and formation of cell-to-cell net growing through the tadpole body. Immunohistochemistry analysis of transplanted tadpoles showed a strong expression of vimentin in RFP-positive cells. No co-localization of Sox9 and Sma signals was observed during the first three weeks indicating their dedifferentiation to migratory-active mesenchymal cells recently described in human testicular biopsies.

Summary: We identified cells co-expressing differentiation markers of Sertoli and peritubular myoid cell lineages in X. tropicalis through the establishment and characterization of cell culture derived from juvenile testis.

Leydig cells contribute to the inhibition of spermatogonial differentiation after irradiation of the rat

Irradiation with 6 Gy produces a complete block of spermatogonial differentiation in LBNF1 rats that would be permanent without treatment. Subsequent suppression of gonadotropins and testosterone (T) restores differentiation to the spermatocyte stage; however, this process requires 6 weeks. We evaluated the role of Leydig cells (LCs) in maintenance of the block in spermatogonial differentiation after exposure to radiation by specifically eliminating functional LCs with ethane dimethane sulfonate (EDS). EDS (but not another alkylating agent), given at 10 weeks after irradiation, induced spermatogonial differentiation in 24% of seminiferous tubules 2 weeks later. However, differentiation became blocked again at 4 weeks as LCs recovered. When EDS was followed by treatment with GnRH antagonist and flutamide, sustained spermatogonial differentiation was induced in >70% of tubules within 2 weeks. When EDS was followed by GnRH antagonist plus exogenous T, which also inhibits LC recovery but restores follicle stimulating hormone (FSH) levels, the spermatogonial differentiation was again rapid but transient. These results confirm that the factors that block spermatogonial differentiation are indirectly regulated by T, and probably FSH, and that adult and possibly immature LCs contribute to the production of such inhibitory factors. We tested whether insulin-like 3 (INSL3), a LC-produced protein whose expression correlated with the block in spermatogonial differentiation, was indeed responsible for the block by injecting synthetic INSL3 into the testes and knocking down its expression in vivo with siRNA. Neither treatment had any effect on spermatogonial differentiation. The Leydig cell products that contribute to the inhibition of spermatogonial differentiation in irradiated rats remain to be elucidated.

Regulation of seminiferous tubule-associated stem Leydig cells in adult rat testes

Testicular Leydig cells are the primary source of testosterone in males. Adult Leydig cells have been shown to arise from stem cells present in the neonatal testis. Once established, adult Leydig cells turn over only slowly during adult life, but when these cells are eliminated experimentally from the adult testis, new Leydig cells rapidly reappear. As in the neonatal testis, stem cells in the adult testis are presumed to be the source of the new Leydig cells. As yet, the mechanisms involved in regulating the proliferation and differentiation of these stem cells remain unknown. We developed a unique in vitro system of cultured seminiferous tubules to assess the ability of factors from the seminiferous tubules to regulate the proliferation of the tubule-associated stem cells, and their subsequent entry into the Leydig cell lineage. The proliferation of the stem Leydig cells was stimulated by paracrine factors including Desert hedgehog (DHH), basic fibroblast growth factor (FGF2), platelet-derived growth factor (PDGF), and activin. Suppression of proliferation occurred with transforming growth factor β (TGF-β). The differentiation of the stem cells was regulated positively by DHH, lithium- induced signaling, and activin, and negatively by TGF-β, PDGFBB, and FGF2. DHH functioned as a commitment factor, inducing the transition of stem cells to the progenitor stage and thus into the Leydig cell lineage. Additionally, CD90 (Thy1) was found to be a unique stem cell surface marker that was used to obtain purified stem cells by flow cytometry.

Alterations of gene profiles in Leydig-cell-regenerating adult rat testis after ethane dimethane sulfonate-treatment

Only occupying about 1%–5% of total testicular cells, the adult Leydig cell (ALC) is a unique endocrine cell that produces androgens. Rat Leydig cells regenerate after these cells in the testis are eliminated with ethane dimethane sulfonate (EDS). In this study, we have characterized Leydig cell regeneration and messenger ribonucleic acids (mRNA) profiles of EDS treated rat testes. Serum testosterone, testicular gene profiling and some steroidogenesis-related proteins were analyzed at 7, 21, 35 and 90 days after EDS treatment. Testicular testosterone levels declined to undetectable levels until 7 days after treatment and then started to recover. Seven days after treatment, 81 mRNAs were down-regulated greater than or equal to two-fold, with 48 becoming undetectable. These genes increased their expression 21 days and completely returned to normal levels 90 days after treatment. The undetectable genes include steroidogenic pathway proteins: steroidogenic acute regulatory protein, Scarb1, Cyp11a1, Cyp17a1, Hsd3b1, Cyp1b1 and Cyp2a1. Seven days after treatment, there were 89 mRNAs up-regulated two-fold or more including Pkib. These up-regulated mRNAs returned to normal 90 days after treatment. Cyp2a1 did not start to recover until 35 days after treatment, indicating that this gene is only expressed in ALCs not in the precursor cells. Quantitative polymerase chain reaction, western blotting and semi-quantitative immunohistochemical staining using tissue array confirmed the changes of several randomly picked genes and their proteins.

Cell-specific ablation in the testis: what have we learned?

Testicular development and function is the culmination of a complex process of autocrine, paracrine and endocrine interactions between multiple cell types. Dissecting this has classically involved the use of systemic treatments to perturb endocrine function, or more recently, transgenic models to knockout individual genes. However, targeting genes one at a time does not capture the more wide‐ranging role of each cell type in its entirety. An often overlooked, but extremely powerful approach to elucidate cellular function is the use of cell ablation strategies, specifically removing one cellular population and examining the resultant impacts on development and function. Cell ablation studies reveal a more holistic overview of cell–cell interactions. This not only identifies important roles for the ablated cell type, which warrant further downstream study, but also, and importantly, reveals functions within the tissue that occur completely independently of the ablated cell type. To date, cell ablation studies in the testis have specifically removed germ cells, Leydig cells, macrophages and recently Sertoli cells. These studies have provided great leaps in understanding not possible via other approaches; as such, cell ablation represents an essential component in the researchers’ tool‐kit, and should be viewed as a complement to the more mainstream approaches to advancing our understanding of testis biology. In this review, we summarise the cell ablation models used in the testis, and discuss what each of these have taught us about testis development and function.

The proteasome inhibitor bortezomib induces testicular toxicity by upregulation of oxidative stress, AMP-activated protein kinase (AMPK) activation and deregulation of germ cell development in adult murine testis

Understanding how chemotherapeutic agents mediate testicular toxicity is crucial in light of compelling evidence that male infertility, one of the severe late side effects of intensive cancer treatment, occurs more often than they are expected to. Previous study demonstrated that bortezomib (BTZ), a 26S proteasome inhibitor used to treat refractory multiple myeloma (MM), exerts deleterious impacts on spermatogenesis in pubertal mice via unknown mechanisms. Here, we showed that intermittent treatment with BTZ resulted in fertility impairment in adult mice, evidenced by testicular atrophy, desquamation of immature germ cells and reduced caudal sperm storage. These deleterious effects may originate from the elevated apoptosis in distinct germ cells during the acute phase and the subsequent disruption of Sertoli-germ cell anchoring junctions (AJs) during the late recovery. Mechanistically, balance between AMP-activated protein kinase (AMPK) activation and Akt/ERK pathway appeared to be indispensable for AJ integrity during the late testicular recovery. Of particular interest, the upregulated testicular apoptosis and the following disturbance of Sertoli-germ cell interaction may both stem from the excessive oxidative stress elicited by BTZ exposure. We also provided the in vitro evidence that AMPK-dependent mechanisms counteract follicle-stimulating hormone (FSH) proliferative effects in BTZ-exposed Sertoli cells. Collectively, BTZ appeared to efficiently prevent germ cells from normal development via multiple mechanisms in adult mice. Employment of antioxidants and/or AMPK inhibitor may represent an attractive strategy of fertility preservation in male MM patients exposed to conventional BTZ therapy and warrants further investigation.

Regeneration of Leydig cells in ectopically autografted adult mouse testes

Ectopic autografting of testis tissue is a promising approach for studying testicular development, male germline preservation and restoration of male fertility. In this study, we examined the fate of various testicular cells in adult mouse testes following ectopic autografting at 1, 2, 4 and 8 weeks post grafting. Histological examination showed no evidence of re-establishment of spermatogenesis in autografts, and progressive degeneration of seminiferous tubules was detected. Expression of germ cell-specific proteins such as POU5F1, DAZL, TNP1, TNP2, PRM1 and PRM2 revealed that, although proliferating and differentiating spermatogenic germ cells such as spermatogonia, spermatocytes and spermatids could survive in autografts until 4 weeks, only terminally differentiated germ cells such as sperm persisted in autografts until 8 weeks. The presence of Sertoli and peritubular myoid cells, as indicated by expression of WT1 and ACTA2 proteins, respectively, was evident in the autografts until 8 weeks. Interestingly, seminal vesicle weight and serum testosterone level were restored in autografted mice by 8 weeks post grafting. The expression of Leydig cell-specific proteins such as CYP11A1, HSD3B2 and LHCGR showed revival of Leydig cell (LC) populations in autografts over time since grafting. Elevated expression of PDGFRA, LIF, DHH and NEFH in autografts indicated de novo regeneration of LC populations. Autografted adult testis can be used as a model for investigating Leydig cell regeneration, steroidogenesis and regulation of the intrinsic factors involved in Leydig cell development. The success of this rodent model can have therapeutic applications for adult human males undergoing sterilizing cancer therapy.

Sertoli cells maintain Leydig cell number and peritubular myoid cell activity in the adult mouse testis

The Sertoli cells are critical regulators of testis differentiation and development. In the adult, however, their known function is restricted largely to maintenance of spermatogenesis. To determine whether the Sertoli cells regulate other aspects of adult testis biology we have used a novel transgenic mouse model in which Amh-Cre induces expression of the receptor for Diphtheria toxin (iDTR) specifically within Sertoli cells. This causes controlled, cell-specific and acute ablation of the Sertoli cell population in the adult animal following Diphtheria toxin injection. Results show that Sertoli cell ablation leads to rapid loss of all germ cell populations. In addition, adult Leydig cell numbers decline by 75% with the remaining cells concentrated around the rete and in the sub-capsular region. In the absence of Sertoli cells, peritubular myoid cell activity is reduced but the cells retain an ability to exclude immune cells from the seminiferous tubules. These data demonstrate that, in addition to support of spermatogenesis, Sertoli cells are required in the adult testis both for retention of the normal adult Leydig cell population and for support of normal peritubular myoid cell function. This has implications for our understanding of male reproductive disorders and wider androgen-related conditions affecting male health.

Sertoli cells control peritubular myoid cell fate and support adult Leydig cell development in the prepubertal testis

Sertoli cells (SCs) regulate testicular fate in the differentiating gonad and are the main regulators of spermatogenesis in the adult testis; however, their role during the intervening period of testis development, in particular during adult Leydig cell (ALC) differentiation and function, remains largely unknown. To examine SC function during fetal and prepubertal development we generated two transgenic mouse models that permit controlled, cell-specific ablation of SCs in pre- and postnatal life. Results show that SCs are required: (1) to maintain the differentiated phenotype of peritubular myoid cells (PTMCs) in prepubertal life; (2) to maintain the ALC progenitor population in the postnatal testis; and (3) for development of normal ALC numbers. Furthermore, our data show that fetal LCs function independently from SC, germ cell or PTMC support in the prepubertal testis. Together, these findings reveal that SCs remain essential regulators of testis development long after the period of sex determination. These findings have significant implications for our understanding of male reproductive disorders and wider androgen-related conditions affecting male health.

Human testicular peritubular cells host putative stem Leydig cells with steroidogenic capacity

AIM

We aim to examine the steroidogenic phenotype and the differentiation potential of human testicular peritubular cells (HTPCs) and to explore their possible relationship to the adult Leydig cell lineage.

BACKGROUND

The cells of the adult Leydig cell lineage may reside in the peritubular compartment of the testis. This suggestion is supported by the facts that the rodent peritubular cells can be differentiated toward this lineage and that cAMP enhances their steroidogenic potential.

METHODS

Human testicular biopsies, and derived HTPCs, were analyzed by immunohistochemistry, RT-PCR, and Western blotting. After stimulation by forskolin or platelet-derived growth factor-BB, quantitative RT-PCR was used to compare the levels of mRNAs encoding proteins involved in steroidogenesis and steroid production was analyzed by liquid chromatography and tandem mass spectrometry.

RESULTS

Immunohistochemical analysis revealed that the peritubular cells that form the outer part of the tubular wall express platelet derived growth factor receptor-α. Furthermore, the pluripotency markers (POU domain class 5 transcription factor 1, GATA-binding protein 4), stem Leydig cell markers (platelet derived growth factor receptor-A, leukemia inhibitory factor receptor), and mRNAs encoding proteins involved in steroidogenesis (nuclear receptor subfamily 5, group A, member 1; steroidogenic acute regulatory protein; CYP11A1; CYP17A1; 3β-hydroxysteroid dehydrogenase) were expressed by the HTPCs. Stimulation with forskolin increased the expression of the steroidogenic markers, which was accompanied by the production of pregnenolone and progesterone by HTPCs in vitro. Treatment with platelet-derived growth factor-BB induced expression of steroidogenic acute regulatory protein.

CONCLUSIONS

Our results indicate that the tubular wall of the human testis is a reservoir for cells of the adult Leydig cell lineage and that the steroidogenic potential of these cells can be activated in culture.

Regulation of the proliferation and differentiation of Leydig stem cells in the adult testis

We reported previously that stem cells associated with adult rat testis seminiferous tubules are able to give rise to differentiated Leydig cells in vitro. The regulatory mechanisms by which they do so, however, are uncertain. Herein, we hypothesized that the proliferation and differentiation of Leydig cell stem cells (stem Leydig cells, SLCs) depend upon locally produced factors from the seminiferous tubules. Microarray analysis revealed that platelet-derived growth factor receptor alpha (PDGFRalpha) is up-regulated and PDGFRbeta is down-regulated with postnatal differentiation of SLCs. This suggested that their ligands, PDGF-AA and PDGF-BB, respectively, might have important roles in SLC proliferation and differentiation. To test this, we developed a unique in vitro culture system in which SLCs proliferate on the surfaces of cultured seminiferous tubules largely during Week 1 of culture and their progeny subsequently differentiate to testosterone-forming Leydig cells during Weeks 2 through 4. Using this system, seminiferous tubules from adult rat testes were cultured with PDGF-AA or PDGF-BB for up to 4 wk. Both ligands stimulated SLC proliferation during the first week of culture, with PDGF-BB significantly more potent than PDGF-AA. Furthermore, PDGF-AA had a stimulatory effect on SLC differentiation from Weeks 2 through 4 of culture. In contrast, PDGF-BB, which stimulated cell proliferation during Week 1, had a significant inhibitory effect on differentiation during Weeks 2 through 4. These findings, made possible by the development of the seminiferous tubule culture system, reveal distinct roles by locally produced PDGFs in SLC regulation.

Identification of Leydig cell-specific mRNA transcripts in the adult rat testis

The adult population of Leydig cells acts to secrete testosterone which is essential for reproductive health and fertility in the adult male. However, other physiological functions of these cells are uncertain, and to address this issue a cell ablation model has been used to identify Leydig cell-specific mRNA transcripts. Ethane dimethane sulphonate (EDS) was synthesised by a novel process and was used to ablate Leydig cells in adult male rats previously treated with butane dimethane sulphonate (busulphan) to delete the germ cell population. Levels of mRNA transcripts were measured in the testis using microarrays 1, 3, 5, 8 and 12 days after EDS injection. During this period, there was a significant change in the levels of 2200 different transcripts with a marked decline in the levels of canonical Leydig cell transcripts, such as Cyp11a1, Cyp17a1 and Insl3. A total of 95 transcripts showed a similar decline in expression after EDS treatment, suggesting that they have a Leydig cell-specific origin. Analysis of selected transcripts confirmed that they were expressed specifically in Leydig cells and showed that most had a late onset of expression during adult Leydig cell development. Apart from transcripts encoding components of the steroidogenic apparatus, the most common predicted function of translated proteins was endogenous and xenotoxicant metabolism. In addition, a number of transcripts encode acute-phase proteins involved in reduction of oxidative stress. Results show that, in addition to androgen secretion, Leydig cells may have a critical role to play in protecting the testis from damage caused by toxicants or stress.

Comparison of cell types in the rat Leydig cell lineage after ethane dimethanesulfonate treatment

The objective of this study was to purify cells in the Leydig cell lineage following regeneration after ethane dimethanesulfonate (EDS) treatment and compare their steroidogenic capacity. Regenerated progenitor (RPLCs), immature (RILCs), and adult Leydig cells (RALCs) were isolated from testes 21, 28 and 56 days after EDS treatment respectively. Production rates for androgens including androsterone and 5α-androstane-17β, 3α-diol (DIOL), testosterone and androstenedione were measured in RPLCs, RILCs and RALCs in media after 3-h in vitro culture with 100 ng/ml LH. Steady-state mRNA levels of steroidogenic enzymes and their activities were measured in freshly isolated cells. Compared to adult Leydig cells (ALCs) isolated from normal 90-day-old rat testes, which primarily produce testosterone (69.73%), RPLCs and RILCs primarily produced androsterone (70.21%) and DIOL (69.79%) respectively. Leydig cells isolated from testes 56 days post-EDS showed equivalent capacity of steroidogenesis to ALCs and primarily produced testosterone (72.90%). RPLCs had cholesterol side-chain cleavage enzyme, 3β-hydroxysteroid dehydrogenase 1 and 17α-hydroxylase but had almost no detectable 17β-hydroxysteroid dehydrogenase 3 and 11β-hydroxysteroid dehydrogenase 1 activities, while RILCs had increased 17β-hydroxysteroid dehydrogenase 3 and 11β-hydroxysteroid dehydrogenase 1 activities. Because RPLCs and RILCs had higher 5α-reductase 1 and 3α-hydroxysteroid dehydrogenase activities they produced mainly 5α-reduced androgens. Real-time PCR confirmed the similar trends for the expressions of these steroidogenic enzymes. In conclusion, the purified RPLCs, RILCs and RALCs are similar to those of their counterparts during rat pubertal development.

Inhibin B response to testicular toxicants hexachlorophene, ethane dimethane sulfonate, di-(n-butyl)-phthalate, nitrofurazone, DL-ethionine, 17-alpha ethinylestradiol, 2,5-hexanedione, or carbendazim following short-term dosing in male rats

BACKGROUND

Inhibin B is a heterodimer glycoprotein that downregulates follicle-stimulating hormone and is produced predominantly by Sertoli cells. The potential correlation between changes in plasma Inhibin B and Sertoli cell toxicity was evaluated in male rats administered testicular toxicants in eight studies. Inhibin B fluctuations over 24 hr were also measured.

METHODS

Adult rats were administered one of eight testicular toxicants for 1 to 29 days. The toxicants were DL-ethionine, dibutyl phthalate, nitrofurazone, 2,5-hexanedione, 17-alpha ethinylestradiol, ethane dimethane sulfonate, hexachlorophene, and carbendazim. In a separate study plasma was collected throughout a 24-hr period via an automatic blood sampler.

RESULTS

Histomorphologic testicular findings included seminiferous tubule degeneration, round and elongate spermatid degeneration/necrosis, seminiferous tubule vacuolation, aspermatogenesis, and interstitial cell degeneration. There was a varying response of plasma Inhibin B levels to seminiferous tubule toxicity, with three studies showing high correlation, three studies with a response only at a certain time or dose, and two studies with no Inhibin B changes. In a receiver operating characteristics exclusion model analysis, where treated samples without histopathology were excluded, Inhibin B showed a sensitivity of 70% at 90% specificity in studies targeting seminiferous tubule toxicity.

CONCLUSION

Decreases in Inhibin B correlated with Sertoli cell toxicity in the majority of studies evaluated, demonstrating the value of Inhibin B as a potential biomarker of testicular toxicity. There was no correlation between decreases in Inhibin B and interstitial cell degeneration. In addition, a pattern of Inhibin B secretion could not be identified over 24 hr.

In vivo evidence for the crucial role of SF1 in steroid-producing cells of the testis, ovary and adrenal gland

Adrenal and gonadal steroids are essential for life and reproduction. The orphan nuclear receptor SF1 (NR5A1) has been shown to regulate the expression of enzymes involved in steroid production in vitro. However, the in vivo role of this transcription factor in steroidogenesis has not been elucidated. In this study, we have generated steroidogenic-specific Cre-expressing mice to lineage mark and delete Sf1 in differentiated steroid-producing cells of the testis, the ovary and the adrenal gland. Our data show that SF1 is a regulator of the expression of steroidogenic genes in all three organs. In addition, Sf1 deletion leads to a radical change in cell morphology and loss of identity. Surprisingly, sexual development and reproduction in mutant animals were not compromised owing, in part, to the presence of a small proportion of SF1-positive cells. In contrast to the testis and ovary, the mutant adult adrenal gland showed a lack of Sf1-deleted cells and our studies suggest that steroidogenic adrenal cells during foetal stages require Sf1 to give rise to the adult adrenal population. This study is the first to show the in vivo requirements of SF1 in steroidogenesis and provides novel data on the cellular consequences of the loss of this protein specifically within steroid-producing cells.

Sertoli cell-specific expression of metastasis-associated protein 2 (MTA2) is required for transcriptional regulation of the follicle-stimulating hormone receptor (FSHR) gene during spermatogenesis

BACKGROUND

Desensitization of FSH response by down-regulation of FSHR transcription is critical for FSH action.

RESULTS

Chromatin modifier MTA2 participates in the down-regulation of FSHR transcription.

CONCLUSION

The FSH/Ar/MTA2 cascade may serve as an indispensable negative feedback mechanism to modulate FSH transduction events in Sertoli cells.

SIGNIFICANCE

Our findings provide new insights into mechanisms by which FSH is deregulated in male infertile patients. The effect of follicle-stimulating hormone (FSH) on spermatogenesis is modulated at a fundamental level by controlling the number of competent receptors present at the surface of Sertoli cells (SCs). One underlying mechanism is the down-regulation of the expression levels of the FSH receptor (FSHR) gene after exposure to FSH. Here we report that metastasis-associated protein 2 (MTA2), a component of histone deacetylase and nucleosome-remodeling complexes, as a gene product induced directly by testosterone or indirectly by FSH, is exclusively expressed in SCs. Stimulation of SCs with FSH is accompanied by up-regulation of MTA2 expression and enhancement of deacetylase activity. This effect requires the integrity of functional androgen receptor. Furthermore, MTA2 is a potent corepressor of FSHR transcription, because it can recruit histone deacetylase-1 onto the FSHR promoter and participates in the down-regulation of FSHR expression upon FSH treatment. Abolishment of endogenous MTA2 by siRNA treatment disrupted the desensitization of the FSH response and thereafter impaired the FSH-dependent secretory function of SCs. From a clinical standpoint, deregulated expression of MTA2 in SCs of human pathological testes negatively correlates to the deregulated level of serum FSH. Overall, our present results provide the first evidence that the FSH/androgen receptor/MTA2 cascade may serve as an indispensable negative feedback mechanism to modulate the transduction events of SCs in response to FSH. These data also underscore an unexpected reproductive facet of MTA2, which may operate as a novel integrator linking synergistic actions of FSH and androgen signaling in SCs.

Stem Leydig cells: from fetal to aged animals

Leydig cells are the testosterone-producing cells of the testis. The adult Leydig cell (ALC) population ultimately develops from undifferentiated mesenchymal-like stem cells present in the interstitial compartment of the neonatal testis. Distinct stages of ALC development have been identified and characterized. These include stem Leydig cells (SLCs), progenitor Leydig cells, immature Leydig cells, and ALCs. This review describes our current understanding of the SLCs in the fetal, prenatal, peripubertal, adult, and aged rat testis, as well as recent studies of the differentiation of steroidogenic cells from the stem cells of other organs.

Sertoli cell androgen receptor DNA binding domain is essential for the completion of spermatogenesis

We examined the biological importance of Sertoli cell androgen receptor (AR) genomic interaction, using a Cre-loxP approach to selectively disrupt the AR DNA-binding domain (AR-DBD). Sertoli cell (SC)-specific transgenic Abpa or AMH promoters targeted Cre-mediated inframe excision of mouse Ar exon-3, encoding the AR-DBD second zinc-finger (ZF2), generating SC-specific mutant AR(DeltaZF2) lines designated Abp.SCAR(DeltaZF2) and AMH.SCAR(DeltaZF2), respectively. Both SCAR(DeltaZF2) lines produced infertile males exhibiting spermatogenic arrest, despite normal SC numbers and immunolocalized SC nuclear AR. Adult homozygous TgCre((+/+)) SCAR(DeltaZF2) or double-TgCre((+/-)) Abp/AMH.SCAR(DeltaZF2) males displayed equivalent small testes 30% of normal size, representing maximal Cre-loxP-disruption of Sertoli AR function. Hemizygous TgCre((+/-)) vs. homozygous TgCre((+/+)) Abp.SCAR(DeltaZF2) testes were larger (47% normal size) with more postmeiotic development, indicating dose-dependent Cre-mediated disruption of SC-specific AR-DBD activity. SCAR(DeltaZF2) males exhibited adult Leydig cell hypertrophy but normal serum testosterone levels. Sertoli cell-specific Rhox5 and Spinlw1 transcription, regulated by divergent or classical androgen-response elements, respectively, were both decreased in postnatal SCAR(DeltaZF2) vs. control testes, demonstrating SC-specific AR-DBD function as early as postnatal d 5. However, Rhox5 expression declined dose-dependently, whereas Spinlw1 expression increased, in adult TgCre((+/-)) and TgCre((+/+)) SCAR(DeltaZF2) testes, revealing differential temporal control for distinct AR-regulated transcripts. Androgen-repressed Ngfr was not up-regulated in SCAR(DeltaZF2) testes, suggesting maintenance of a nonclassical mechanism independent of AR-DBD. Thus, our unique SCAR(DeltaZF2) paradigm provided dose-dependent Cre-mediated disruption of testicular development and gene expression revealing that the AR-DBD is essential for SC function and postmeiotic spermatogenesis. Nongenomic or AR-DBD-independent pathways appear secondary or play no major independent role in SC function.