Is the adult Sertoli cell terminally differentiated?

Reprograming skin fibroblasts into Sertoli cells: a patient-specific tool to understand effects of genetic variants on gonadal development

BACKGROUND

Disorders/differences of sex development (DSD) are congenital conditions in which the development of chromosomal, gonadal, or anatomical sex is atypical. With overlapping phenotypes and multiple genes involved, poor diagnostic yields are achieved for many of these conditions. The current DSD diagnostic regimen can be augmented by investigating transcriptome/proteome in vivo, but it is hampered by the unavailability of affected gonadal tissue at the relevant developmental stage. We try to mitigate this limitation by reprogramming readily available skin tissue-derived dermal fibroblasts into Sertoli cells (SC), which could then be deployed for different diagnostic strategies. SCs form the target cell type of choice because they act like an organizing center of embryonic gonadal development and many DSD arise when these developmental processes go awry.

METHODS

We employed a computational predictive algorithm for cell conversions called Mogrify to predict the transcription factors (TFs) required for direct reprogramming of human dermal fibroblasts into SCs. We established trans-differentiation culture conditions where stable transgenic expression of these TFs was achieved in 46, XY adult dermal fibroblasts using lentiviral vectors. The resulting Sertoli like cells (SLCs) were validated for SC phenotype using several approaches.

RESULTS

SLCs exhibited Sertoli-like morphological and cellular properties as revealed by morphometry and xCelligence cell behavior assays. They also showed Sertoli-specific expression of molecular markers such as SOX9, PTGDS, BMP4, or DMRT1 as revealed by IF imaging, RNAseq and qPCR. The SLC transcriptome shared about two thirds of its differentially expressed genes with a human adult SC transcriptome and expressed markers typical of embryonic SCs. Notably, SLCs lacked expression of most markers of other gonadal cell types such as Leydig, germ, peritubular myoid or granulosa cells.

CONCLUSIONS

The trans-differentiation method was applied to a variety of commercially available 46, XY fibroblasts derived from patients with DSD and to a 46, XX cell line. The DSD SLCs displayed altered levels of trans-differentiation in comparison to normal 46, XY-derived SLCs, thus showcasing the robustness of this new trans-differentiation model. Future applications could include using the SLCs to improve definitive diagnosis of DSD in patients with variants of unknown significance.

Diffusion-weighted magnetic resonance imaging and magnetic resonance spectroscopy for non-invasive characterization of azoospermia: A prospective comparative single-center study

BACKGROUND

Azoospermia affects about 15% of childless males. The differential diagnosis between subtypes of azoospermia is the initial step in its management.

OBJECTIVES

To investigate the role of diffusion-weighted magnetic resonance imaging and proton magnetic resonance spectroscopy in distinguishing obstructive azoospermia from non-obstructive azoospermia and predicting sperm retrieval together with histological alterations in men with non-obstructive azoospermia.

MATERIALS AND METHODS

This prospective comparative study involved 60 men with obstructive azoospermia (group A) and 60 men with non-obstructive azoospermia (group B). Scrotal proton magnetic resonance spectroscopy and diffusion-weighted magnetic resonance imaging were conducted for all participants to respectively evaluate testicular metabolites and normalized apparent diffusion coefficient 1 week before sperm retrieval.

RESULTS

Apparent diffusion coefficient was significantly higher in group B as compared to group A (0.47 ± 0.11 vs. 0.29 ± 0.05; and 0.46 ± 0.14 vs. 0.28 ± 0.02) for the right and left testis, respectively. Conversely, testicular choline and lipids were significantly higher in group A as compared to group B. Normalized apparent diffusion coefficient, choline, and lipids at cut-off levels of 0.353, 0.31, and 0.725 could differentiate between obstructive azoospermia and non-obstructive azoospermia (area under the curve = 0.963; confidence interval = 0.939-0.986, area under the curve = 0.985; confidence interval = 0.974-0.997, and area under the curve = 0.970; confidence interval = 0.940-0.999, respectively). Regarding the prediction of sperm retrieval in the non-obstructive azoospermia group, choline levels had the highest area under the curve (0.923), and its cut-off level was 0.195. The normalized apparent diffusion coefficient was significantly lower in men with positive sperm retrieval as compared to men with unsuccessful retrieval. Finally, it was revealed that all magnetic resonance imaging parameters except creatine could independently predict testicular histology in men with non-obstructive azoospermia. The highest prediction was 95% in normal spermatogenesis, and the least prediction was 40% in spermatid arrest. Regression analysis was used to detect final predictors and extrapolate an equation that could be used to predict testicular pathology CONCLUSIONS: Normalized apparent diffusion coefficient and proton magnetic resonance spectroscopy are helpful in differentiating obstructive azoospermia from non-obstructive azoospermia and predicting sperm retrieval and related histological alterations in men with non-obstructive azoospermia.

Identification of follicle-stimulating hormone-responsive genes in Sertoli cells during early postnatal mouse testis development

BACKGROUND

In the mouse testis, Sertoli cells rapidly divide during a narrow window of time pre-pubertally and differentiate thereafter. The number of Sertoli cells determines the testis size and germ cell-carrying capacity. Follicle-stimulating hormone (FSH) binds its cognate FSH-receptors expressed on Sertoli cells and acts as a mitogen to regulate their proliferation. Fshb-/- mutant adult male mice have reduced Sertoli cell number and testis size and reduced sperm number and motility. However, FSH-responsive genes in early postnatal mouse Sertoli cells are unknown.

OBJECTIVES

To identify FSH-responsive genes in early postnatal mouse Sertoli cells.

MATERIALS AND METHODS

A fluorescence-activated cell sorting method was developed to rapidly purify Sertoli cells from control and Fshb-/- mice carrying a Sox9 GfpKI allele. These pure Sertoli cells were used for large-scale gene expression analyses.

RESULTS

We show that mouse Sertoli cells rarely divide beyond postnatal day 7. Our in vivo BrdU labeling studies indicate loss of FSH results in a 30% reduction in Sertoli cell proliferation in mice at 5 days of age. Flowsorted GFP+ Sertoli cells with maximal Fshr expression were 97%-98% pure and mostly devoid of Leydig and germ cells as assessed by Taqman qPCR quantification of gene expression and immunolabeling of the corresponding cell-specific markers. Large-scale gene expression analysis identified several differentially regulated genes in flow-sorted GFP+ Sertoli cells obtained from testis of control and Fshb-/- mice at 5 days of age. The top 25 networks identified by pathway analysis include those related to the cell cycle, cell survival and most importantly, carbohydrate and lipid metabolism and molecular transport.

DISCUSSION

Several of the FSH-responsive genes identified in this study could serve as useful markers for Sertoli cell proliferation in normal physiology, toxicant-induced Sertoli cell/testis injury, and other pathological conditions.

CONCLUSION

Our studies reveal that FSH-regulates macromolecular metabolism and molecular transport networks of genes in early postnatal Sertoli cells most likely in preparation for establishment of functional associations with germ cells to successfully coordinate spermatogenesis.

Impact of Chronic Multi-Generational Exposure to an Environmentally Relevant Atrazine Concentration on Testicular Development and Function in Mice

A common herbicide, atrazine, is associated with poor health. Atrazine acts as an endocrine disruptor at supra-environmental levels. Little research, however, has been conducted regarding chronic exposure to environmental atrazine concentrations across generations. This study utilized comprehensive endpoint measures to investigate the effects of chronic exposure to a conservative atrazine concentration (0.02 ng/mL), measured in Australian waterways, on male mice fertility across two generations. Mice were exposed through the maternal line, from the pre-conception period and through the F1 and F2 generations until three or six months of age. Atrazine did not impact sperm function, testicular morphology nor germ cell parameters but did alter the expression of steroidogenic genes in the F1, down-regulating the expression of Cyp17a1 (Cytochrome P450 family 17, subfamily A member 1; p = 0.0008) and Ddx4 (DEAD-box helicase 4; p = 0.007), and up-regulating the expression of Star (Steroidogenic acute regulatory protein; p = 0.017). In the F2, atrazine induced up-regulation in the expression of Star (p = 0.016). The current study demonstrates that chronic exposure to an environmentally relevant atrazine concentration perturbs testicular steroid-associated gene expression that varies across generations. Future studies through the paternal and combined parental lineages should be undertaken to further elucidate the multigenerational effects of atrazine on male fertility.

Impact of endocrine disrupting chemicals and pharmaceuticals on Sertoli cell development and functions

Sertoli cells play essential roles in male reproduction, from supporting fetal testis development to nurturing male germ cells from fetal life to adulthood. Dysregulating Sertoli cell functions can have lifelong adverse effects by jeopardizing early processes such as testis organogenesis, and long-lasting processes such as spermatogenesis. Exposure to endocrine disrupting chemicals (EDCs) is recognized as contributing to the rising incidence of male reproductive disorders and decreasing sperm counts and quality in humans. Some drugs also act as endocrine disruptors by exerting off-target effects on endocrine tissues. However, the mechanisms of toxicity of these compounds on male reproduction at doses compatible with human exposure are still not fully resolved, especially in the case of mixtures, which remain understudied. This review presents first an overview of the mechanisms regulating Sertoli cell development, maintenance, and functions, and then surveys what is known on the impact of EDCs and drugs on immature Sertoli cells, including individual compounds and mixtures, and pinpointing at knowledge gaps. Performing more studies on the impact of mixtures of EDCs and drugs at all ages is crucial to fully understand the adverse outcomes these chemicals may induce on the reproductive system.

Single-cell RNA sequencing uncovers dynamic roadmap and cell-cell communication during buffalo spermatogenesis

Spermatogenesis carries the task of precise intergenerational transmission of genetic information from the paternal genome and involves complex developmental processes regulated by the testicular microenvironment. Studies performed mainly in mouse models have established the theoretical basis for spermatogenesis, yet the wide interspecies differences preclude direct translation of the findings, and farm animal studies are progressing slowly. More than 32,000 cells from prepubertal (3-month-old) and pubertal (24-month-old) buffalo testes were analyzed by using single-cell RNA sequencing (scRNA-seq), and dynamic gene expression roadmaps of germ and somatic cell development were generated. In addition to identifying the dynamic processes of sequential cell fate transitions, the global cell-cell communication essential to maintain regular spermatogenesis in the buffalo testicular microenvironment was uncovered. The findings provide the theoretical basis for establishing buffalo germline stem cells in vitro or culturing organoids and facilitating the expansion of superior livestock breeding.

Cellular Modifications in Spermatogenesis during Seasonal Testicular Regression: An Update Review in Mammals

Simple Summary

The most common form of reproduction in mammals is seasonal reproduction. This ensures that offspring are born at the most suitable time for survival, due to the abundance of food and the optimal temperatures for early postnatal development. In males, one way to achieve this is to decrease or lose fertility over a given period. This loss is associated with a greater or lesser degree of spermatogenesis modification that affects both germ and Sertoli cells. This paper reviews the different cellular mechanisms that have been postulated in recent years to explain how the activity of the seminiferous epithelium decreases during the non-reproductive period.

Abstract

Testicular regression occurs during the non-breeding season in many mammals. This affects spermatogenesis, resulting in decreased or arrested activity. Both lead to a decrease or cessation in sperm production. In recent years, the cellular mechanisms that lead to infertility in males in non-reproductive periods have been studied in very different species of mammals. At the start of the present century, the main mechanism involved was considered as an increase in the apoptotic activity of germ cells during the regression period. The loss of spermatogonia and spermatocytes causes not only a decrease in spermatogenesis, but an arrest of the seminiferous epithelium activity at the end of regression. Recently, in some mammal species, it was found that apoptosis is the usual mechanism involved in epithelium activity arrest, although it is firstly atrophied by massive desquamation of the germ cells that are released from their binding with the Sertoli cells, and which are shed into the lumen of the seminiferous tubule. In other species, it has been shown that not only germ cell apoptosis, but also Sertoli cell apoptosis, including decreased proliferative activity, spermatophagy or autophagy, are involved in testicular regression. Furthermore, the most recent studies indicate that there are multiple patterns of seminiferous epithelium regression in seasonally breeding animals, which may not only be used by different species, but also by the same ones to reproduce in the best conditions, ensuring their survival. In conclusion, at this time, it is not possible to consider the existence of a paradigmatic cellular mechanism in the involution of the seminiferous epithelium applicable to all male mammals with seasonal reproduction, rather the existence of several mechanisms which participate to a greater or lesser extent in each of the species that have been studied to date.

Small-Molecule-Driven Direct Reprogramming of Fibroblasts into Functional Sertoli-Like Cells as a Model for Male Reproductive Toxicology

Sertoli cells (SCs) are vital to providing morphological and nutritional support for spermatogenesis. Defects in SCs often lead to infertility. SCs transplantation is a promising potential strategy to compensate for SC dysfunction. However, isolation of SCs from testes is impractical due to obvious and ethical limitations. Here, a molecular cocktail is identified comprising of pan-BET family inhibitor (I-BET151), retinoic acid, and riluzole that enables the efficient conversion of fibroblasts into functional Sertoli-like cells (CiSCs). The gene expression profiles of CiSCs resemble those of mature SCs and exhibit functional properties such as the formation of testicular seminiferous tubules, engulfment of apoptotic sperms, supporting the survival of germ cells, and suppressing proliferation of primary lymphocytes in vitro. Moreover, CiSCs are sensitive to toxic substances, making them an alternative model to study the deleterious effects of toxicants on SCs. The study provides an efficient approach to reprogram fibroblasts into functional SCs by using pure chemical compounds.

Retinoblastoma-E2F Transcription Factor Interplay Is Essential for Testicular Development and Male Fertility

The retinoblastoma (RB) protein family members (pRB, p107 and p130) are key regulators of cell cycle progression, but also play crucial roles in apoptosis, and stem cell self-renewal and differentiation. RB proteins exert their effects through binding to E2F transcription factors, which are essential developmental and physiological regulators of tissue and organ homeostasis. According to the canonical view, phosphorylation of RB results in release of E2Fs and induction of genes needed for progress of the cell cycle. However, there are eight members in the E2F transcription factor family with both activator (E2F1-3a) and repressor (E2F3b-E2F8) roles, highlighting the functional diversity of RB-E2F pathway. In this review article we summarize the data showing that RB-E2F interaction is a key cell-autonomous mechanism responsible for establishment and maintenance of lifelong male fertility. We also review the expression pattern of RB proteins and E2F transcription factors in the testis and male germ cells. The available evidence supports that RB and E2F family members are widely and dynamically expressed in the testis, and they are known to have versatile roles during spermatogenesis. Knowledge of the function and significance of RB-E2F interplay for testicular development and spermatogenesis comes primarily from gene knock-out (KO) studies. Several studies conducted in Sertoli cell-specific pRB-KO mice have demonstrated that pRB-mediated inhibition of E2F3 is essential for Sertoli cell functional maturation and cell cycle exit, highlighting that RB-E2F interaction in Sertoli cells is paramount to male fertility. Similarly, ablation of either pRB or E2F1 in the germline results in progressive testicular atrophy due to germline stem cell (GSC) depletion, emphasizing the importance of proper RB-E2F interplay for germline maintenance and lifelong sperm production. In summary, while balanced RB-E2F interplay is essential for cell-autonomous maintenance of GSCs and, the pRB-E2F3 system in Sertoli cells is critical for providing GSC niche thus laying the basis for spermatogenesis.

SIRT 3 was involved in Lycium barbarum seed oil protection testis from oxidative stress: in vitro and in vivo analyses

CONTEXT

Lycium barbarum L. (Solanaceae) seed oil (LBSO) exerts LBSO exerts protective effects in the testis in vivo and in vitro via upregulating SIRT3.

OBJECTIVE

This study evaluates the effects and mechanism of LBSO in the d-galactose (d-gal)-induced ageing testis.

MATERIALS AND METHODS

Male Sprague Dawley (SD) rats (n = 30, 8-week-old) were randomly divided into three groups: LBSO group (n = 10) where rats received subcutaneous injection of d-gal at 125 mg/kg/day for 8 weeks and intragastric administration of LBSO at 1000 mg/kg/day for 4 weeks, ageing model group (n = 10) received 8-week-sunbcutaneous injection of d-gal, and control group (n = 10) with same administration of normal saline. Lentivirus had established TM4 cells with SIRT3 overexpression or silencing before LBSO intervened in vitro.

RESULTS

Treatment with LBSO, the levels of INHB and testosterone both increased, compared to ageing model. In vitro, we found the ED₅₀ of LBSO was 86.72 ± 1.49 and when the concentration of LBSO at 100 μg/mL to intervene TM4 cells, the number of cells increased from 8120 ± 676.2 to 15251 ± 1119, and the expression of SIRT3, HO-1, and SOD upregulated. However, HO-1 and SOD were dysregulated by silencing SIRT3. On the other hand, the expression of AMPK and PGC-1α upregulated as an effect of SIRT3 overexpression by lentivirus, meanwhile the same increasing trend of that being found in cells treated with LBSO, compared to control group.

DISCUSSION AND CONCLUSIONS

LBSO alleviated oxidative stress in d-gal-induced sub-acutely ageing testis and TM4 cells by suppressing the oxidative stress to mitochondria via SIRT3/AMPK/PGC-1α.

Effects of deoxynivalenol exposure at peripuberty over testicles of rats: structural and functional alterations

Deoxynivalenol (DON) is related to reduced reproductive performance in males and females in several species. Children and adolescents showed a high risk of exposure to DON, however, no study has evaluated reproductive effects of DON at puberty. The present study aimed to evaluate the effects of DON at peripuberty on the testicles of pubertal rats. To achieve this, 10 Wistar rats (28 days old) were fed for 28 days with a DON-contaminated diet (9.4 mg/kg) or a control diet. After the experimental period, rats (56 days old) were euthanised and the following evaluations were performed in the testicles: dynamics of spermatogenesis, tubular morphometry, number of Sertoli cells and Leydig cells, analysis of caspase-3 expression, and the index of cell proliferation using the nucleolus organising regions (NOR) method. Ingestion of DON-contaminated diet induced a significant reduction in the number of Sertoli and Leydig cells and the number of seminiferous tubules in stage XIV. A significant increase in the number of NORs in seminiferous tubules in stage I-VI was observed in animals receiving the DON diet. No significant difference was noted in tubular morphometry or caspase-3 expression. Taken together, our results unravelled that the peripubertal exposure to DON compromised the testicular structure of pubertal rats, changing the dynamics of spermatogenesis.

Deoxynivalenol and Zearalenone: Different Mycotoxins with Different Toxic Effects in the Sertoli Cells of Equus asinus

(1) Background: Deoxynivalenol (DON) and zearalenone (ZEA) are type B trichothecene mycotoxins that exert serious toxic effects on the reproduction of domestic animals. However, there is little information about the toxicity of mycotoxins on testis development in Equus asinus. This study investigated the biological effects of DON and ZEA exposure on Sertoli cells (SCs) of Equus asinus; (2) Methods: We administered 10 μM and 30 μM DON and ZEA to cells cultured in vitro; (3) Results: The results showed that 10 μM DON exposure remarkably changed pyroptosis-associated genes and that 30 μM ZEA exposure changed inflammation-associated genes in SCs. The mRNA expression of cancer-promoting genes was remarkably upregulated in the cells exposed to DON or 30 μM ZEA; in particular, DON and ZEA remarkably disturbed the expression of androgen and oestrogen secretion-related genes. Furthermore, quantitative RT-PCR, Western blot, and immunofluorescence analyses verified the different expression patterns of related genes in DON- and ZEA-exposed SCs; (4) Conclusions: Collectively, these results illustrated the impact of exposure to different toxins and concrete toxicity on the mRNA expression of SCs from Equus asinus in vitro.

MicroRNA-125a-5p modulates the proliferation and apoptosis of TM4 Sertoli cells by targeting RAB3D and regulating the PI3K/AKT signaling pathway

Sertoli cells are cells that provide protection and nutrition for developing sperm. Each stage of sperm development occurs on the surface of Sertoli cells. MicroRNA (MiR)-125a-5p is involved in male reproduction. The current research aimed to probe the role of miR-125a-5p in Sertoli cell function. Functionally, miR-125a-5p knockdown facilitated Sertoli cell proliferation, while miR-125a-5p overexpression suppressed Sertoli cell proliferation, as evidenced by 5-ethynyl-20-deoxyuridine incorporation assay. Additionally, miR-125a-5p knockdown inhibited Sertoli cell apoptosis, while miR-125a-5p upregulation facilitated Sertoli cell apoptosis, as evidenced by flow cytometry analysis. Computationally, we identified four predicted mRNA targets of miR-125a-5p. Based on the results of luciferase reporter assay, miR-125a-5p was confirmed to bind to the predicted sequence in the Ras-related protein Rab-3D (RAB3D) 3'UTR. Rescue experiments showed that miR-125a-5p suppressed the proliferative ability of TM4 Sertoli cells and facilitated their apoptosis by targeting RAB3D. Finally, our data confirmed that miR-125a-5p and RAB3D modulated activation of the PI3K/AKT pathway. In conclusion, our data showed that miR-125a-5p regulated Sertoli cell proliferation and apoptosis by targeting RAB3D and regulating the PI3K/AKT pathway.

Review of Sertoli cell dysfunction caused by COVID-19 that could affect male fertility

Spermatogenesis is a complex and elaborate differentiation process and is vital for male fertility. Sertoli cells play a major role in fertility and induce spermatogenesis by protecting, nourishing, and supporting germ cells. It has been speculated that severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) could directly affect the male reproductive system, and therefore heredity and fertility. The similarity of SARS-CoV-2 to SARS-CoV could confirm this hypothesis because both viruses use angiotensin-converting enzyme (ACE2) as the receptor to enter human cells. ACE2 is expressed by Sertoli cells and other testicular cells, therefore COVID-19 has the potential to impair fertility by destroying Sertoli cells. This hypothesis should be evaluated and confirmed by monitoring fertility in patients with COVID-19.

Sertoli Cells Possess Immunomodulatory Properties and the Ability of Mitochondrial Transfer Similar to Mesenchymal Stromal Cells

It is becoming increasingly evident that selecting an optimal source of mesenchymal stromal cells (MSCs) is crucial for the successful outcome of MSC-based therapies. During the search for cells with potent regenerative properties, Sertoli cells (SCs) have been proven to modulate immune response in both in vitro and in vivo models. Based on morphological properties and expression of surface markers, it has been suggested that SCs could be a kind of MSCs, however, this hypothesis has not been fully confirmed. Therefore, we compared several parameters of MSCs and SCs, with the aim to evaluate the therapeutic potential of SCs in regenerative medicine. We showed that SCs successfully underwent osteogenic, chondrogenic and adipogenic differentiation and determined the expression profile of canonical MSC markers on the SC surface. Besides, SCs rescued T helper (Th) cells from undergoing apoptosis, promoted the anti-inflammatory phenotype of these cells, but did not regulate Th cell proliferation. MSCs impaired the Th17-mediated response; on the other hand, SCs suppressed the inflammatory polarisation in general. SCs induced M2 macrophage polarisation more effectively than MSCs. For the first time, we demonstrated here the ability of SCs to transfer mitochondria to immune cells. Our results indicate that SCs are a type of MSCs and modulate the reactivity of the immune system. Therefore, we suggest that SCs are promising candidates for application in regenerative medicine due to their anti-inflammatory and protective effects, especially in the therapies for diseases associated with testicular tissue inflammation.

Regulation of Cell Types Within Testicular Organoids

Organoids are 3-dimensional (3D) structures grown in vitro that emulate the cytoarchitecture and functions of true organs. Therefore, testicular organoids arise as an important model for research on male reproductive biology. These organoids can be generated from different sources of testicular cells, but most studies to date have used immature primary cells for this purpose. The complexity of the mammalian testicular cytoarchitecture and regulation poses a challenge for working with testicular organoids, because, ideally, these 3D models should mimic the organization observed in vivo. In this review, we explore the characteristics of the most important cell types present in the testicular organoid models reported to date and discuss how different factors influence the regulation of these cells inside the organoids and their outcomes. Factors such as the developmental or maturational stage of the Sertoli cells, for example, influence organoid generation and structure, which affect the use of these 3D models for research. Spermatogonial stem cells have been a focus recently, especially in regard to male fertility preservation. The regulation of the spermatogonial stem cell niche inside testicular organoids is discussed in the present review, as this research area may be positively affected by recent progress in organoid generation and tissue engineering. Therefore, the testicular organoid approach is a very promising model for male reproductive biology research, but more studies and improvements are necessary to achieve its full potential.

Metabolic Requirements for Spermatogonial Stem Cell Establishment and Maintenance In Vivo and In Vitro

The spermatogonial stem cell (SSC) is a unique adult stem cell that requires tight physiological regulation during development and adulthood. As the foundation of spermatogenesis, SSCs are a potential tool for the treatment of infertility. Understanding the factors that are necessary for lifelong maintenance of a SSC pool in vivo is essential for successful in vitro expansion and safe downstream clinical usage. This review focused on the current knowledge of prepubertal testicular development and germ cell metabolism in different species, and implications for translational medicine. The significance of metabolism for cell biology, stem cell integrity, and fate decisions is discussed in general and in the context of SSC in vivo maintenance, differentiation, and in vitro expansion.

The role of estrogen receptors in rat Sertoli cells at different stages of development

The aim of the study was to investigate the effects of estrogen receptors (ESR1 and ESR2) on the expression of the proteins involved with proliferation (CCND1) and differentiation (CDKN1B and CTNNB) of Sertoli cells from rat in different stages of development. ESR1-selective agonist PPT, but not ESR2-selective agonist DPN, increased CCND1 expression in Sertoli cells from 5- and 15-day old rats. PPT did not have any effect on CCND1 expression in Sertoli cells from 20- and 30-day-old rats. DPN, but not PPT, increased CDKN1B expression in Sertoli cells from 15-, 20-, 30-day-old rats. DPN did not have any effect on Sertoli cells from 5-day-old rats. 17β-estradiol (E2) and PPT enhanced the [Methyl-³H] thymidine incorporation in Sertoli cells from 15-day-old rats, whereas the treatment did not have any effect in 20-day-old rats. E2 and DPN, but not PPT, increased non-phosphorylated CTNNB expression in Sertoli cells from 20-day-old rats. This upregulation was blocked by ESR2-selective antagonist PHTPP. The activation of ESR1 and ESR2, respectively, plays a role in the proliferation and differentiation of Sertoli cells in a critical period of testicular development. Furthermore, in Sertoli cells from 20-day-old rats, upregulation of non-phosphorylated CTNNB by E2/ESR2, via c-SRC/ERK1/2 and PI3K/AKT, may play a role in the interaction between Sertoli cells and/or in cell-germ cell adhesion and/or in the stabilization and accumulation of CTNNB in the cytosol. CTNNB could be translocated to the nucleus and modulate the transcriptional activity of specific target genes. The present study reinforces the important role of estrogen in normal testis development.

Regional difference in semen quality of young men: a review on the implication of environmental and lifestyle factors during fetal life and adulthood

The prevalence of low semen quality and the incidence of testicular cancer have been steadily increasing over the past decades in different parts of the World. Although these conditions may have a genetic or epigenetic origin, there is growing evidence that multiple environmental and lifestyle factors can act alone or in combination to induce adverse effects. Exposure to these factors may occur as early as during fetal life, via the mother, and directly throughout adulthood after full spermatogenic capacity is reached. This review aims at providing an overview of past and current trends in semen quality and its relevance to fertility as well as a barometer of men’s general health. The focus will be on recent epidemiological studies of young men from the general population highlighting geographic variations in Europe. The impact of some lifestyle and environmental factors will be discussed with their role in both fetal life and adulthood. These factors include smoking, alcohol consumption, psychological stress, exposure to electromagnetic radiation, and Endocrine Disrupting Chemicals (EDCs). Finally, the challenges in investigating the influence of environmental factors on semen quality in a fast changing world are presented.

BRG1 Is Dispensable for Sertoli Cell Development and Functions in Mice

Sertoli cells are somatic supporting cells in spermatogenic niche and play critical roles in germ cell development, but it is yet to be understood how epigenetic modifiers regulate Sertoli cell development and contribution to spermatogenesis. BRG1 (Brahma related gene 1) is a catalytic subunit of the mammalian SWI/SNF chromatin remodeling complex and participates in transcriptional regulation. The present study aimed to define the functions of BRG1 in mouse Sertoli cells during mouse spermatogenesis. We found that BRG1 protein was localized in the nuclei of both Sertoli cells and germ cells in seminiferous tubules. We further examined the requirement of BRG1 in Sertoli cell development using a Brg1 conditional knockout mouse model and two Amh-Cre mouse strains to specifically delete Brg1 gene from Sertoli cells. We found that the Amh-Cre mice from Jackson Laboratory had inefficient recombinase activities in Sertoli cells, while the other Amh-Cre strain from the European Mouse Mutant Archive achieved complete Brg1 deletion in Sertoli cells. Nevertheless, the conditional knockout of Brg1 from Sertoli cells by neither of Amh-Cre strains led to any detectable abnormalities in the development of either Sertoli cells or germ cells, suggesting that BRG1-SWI/SNF complex is dispensable to the functions of Sertoli cells in spermatogenesis.

The Sertoli cell: what can we learn from different vertebrate models?

Besides having medical applications, comparative studies on reproductive biology are very useful, providing, for instance, essential knowledge for basic, conservation and biotechnological research. In order to maintain the reproductive potential and the survival of all vertebrate species, both sperm and steroid production need to occur inside the testis. From the approximately fifty thousand vertebrate species still alive, very few species are already investigated; however, our knowledge regarding Sertoli cell biology is quite good. In this regard, it is already known that since testis differentiation the Sertoli cells are the somatic cells in charge of supporting and orchestrating germ cells during development and full spermatogenesis in adult animals. In the present review, we highlight key aspects related to Sertoli cell biology in vertebrates and show that this key testis somatic cell presents huge and intrinsic plasticity, particularly when cystic (fish and amphibians) and non-cystic (reptiles, birds and mammals) spermatogenesis is compared. In particular, we briefly discuss the main aspects related to Sertoli cells functions, interactions with germ cells, Sertoli cells proliferation and efficiency, as well as those regarding spermatogonial stem cell niche regulation, which are crucial aspects responsible for the magnitude of sperm production. Most importantly, we show that we could greatly benefit from investigations using different vertebrate experimental models, mainly now that there is a big concern regarding the decline in human sperm counts caused by a multitude of factors.

Loss of Cx43 in Murine Sertoli Cells Leads to Altered Prepubertal Sertoli Cell Maturation and Impairment of the Mitosis-Meiosis Switch

Male factor infertility is a problem in today’s society but many underlying causes are still unknown. The generation of a conditional Sertoli cell (SC)-specific connexin 43 (Cx43) knockout mouse line (SCCx43KO) has provided a translational model. Expression of the gap junction protein Cx43 between adjacent SCs as well as between SCs and germ cells (GCs) is known to be essential for the initiation and maintenance of spermatogenesis in different species and men. Adult SCCx43KO males show altered spermatogenesis and are infertile. Thus, the present study aims to identify molecular mechanisms leading to testicular alterations in prepubertal SCCx43KO mice. Transcriptome analysis of 8-, 10- and 12-day-old mice was performed by next-generation sequencing (NGS). Additionally, candidate genes were examined by qRT-PCR and immunohistochemistry. NGS revealed many significantly differentially expressed genes in the SCCx43KO mice. For example, GC-specific genes were mostly downregulated and found to be involved in meiosis and spermatogonial differentiation (e.g., Dmrtb1, Sohlh1). In contrast, SC-specific genes implicated in SC maturation and proliferation were mostly upregulated (e.g., Amh, Fshr). In conclusion, Cx43 in SCs appears to be required for normal progression of the first wave of spermatogenesis, especially for the mitosis-meiosis switch, and also for the regulation of prepubertal SC maturation.

Primary Sertoli Cell Cultures From Adult Mice Have Different Properties Compared With Those Derived From 20-Day-Old Animals

Cultures of Sertoli cells isolated from 20-day-old mice are widely used in research as substitutes for adult Sertoli cell cultures. This practice is based on the fact that Sertoli cells cease to proliferate and become mature in vivo by 16 to 20 days after birth. However, it is important to verify whether cultured Sertoli cells derived from 20-day-old mice do not proliferate ex vivo and whether they have the same properties as cultured adult Sertoli cells. Herein we described an isolation/culture method of Sertoli cells from 10-week-old adult mice with > 90% purity. Properties of these cultured adult Sertoli cells were then compared with those of cultured Sertoli cells derived from 20-day-old mice (also > 90% purity). By cell counting, bromo-2-deoxyuridine incorporation, and metaphase plate detection, we demonstrated that only adult Sertoli cells did not proliferate throughout 12 culture days. In contrast, Sertoli cells derived from 20-day-old mice still proliferated until Day 10 in culture. The morphology and profiles of intracellular lipidomics and spent medium proteomics of the 2 cultures were also different. Cultured adult Sertoli cells were larger in size and contained higher levels of triacylglycerols, cholesteryl esters, and seminolipid, and the proteins in their spent medium were mainly engaged in cellular metabolism. In contrast, proteins involved in cell division, including anti-Mullerian hormone, cell division cycle protein 42 (CDC42), and collagen isoforms, were at higher levels in Sertoli cell cultures derived from 20-day-old mice. Therefore, cultured Sertoli cells derived from 10-week-old mice, rather than those from 20-day-old animals, should be used for studies on properties of adult Sertoli cells.

Retinoblastoma protein represses E2F3 to maintain Sertoli cell quiescence in mouse testis

Maintenance of the differentiated state and cell cycle exit in adult Sertoli cells depends on tumor suppressor retinoblastoma protein (RB, also known as RB1). We have previously shown that RB interacts with transcription factor E2F3 in the mouse testis. Here, we investigated how E2f3 contributes to adult Sertoli cell proliferation in a mouse model of Sertoli cell-specific knockout of Rb by crossing these mice with an E2f3 knockout mouse line. In the presence of intact RB, E2f3 was redundant in Sertoli cells. However, in the absence of RB, E2f3 is a key driver for cell cycle re-entry and loss of function in adult Sertoli cells. Knockout of E2f3 in Sertoli cells rescued the breakdown of Sertoli cell function associated with Rb loss, prevented proliferation of adult Sertoli cells and restored fertility of the mice. In summary, our results show that RB-mediated repression of E2F3 is critical for the maintenance of cell cycle exit and terminal differentiation in adult mouse Sertoli cells.

High-energy diet enhances spermatogenic function and increases sperm midpiece length in fallow deer (Dama dama) yearlings

Nutrition is a major factor involved in the sexual development of livestock ruminants. In the male, a high-energy diet enhances the reproductive function, but its effects on the underlying processes such as spermatogenic efficiency are not yet defined. Moreover, the possible changes in sperm size due to a supplemented diet remain poorly investigated. The main goal of this study was to evaluate whether a high-energy diet affects the spermatogenic activity, epididymal sperm parameters (concentration, morphology, morphometry and acrosome integrity) and blood testosterone levels in fallow deer yearlings. For this purpose, 32 fallow deer were allocated into two groups according to their diet: control (pasture) and experimental (pasture and barley grain) groups. Fallow deer from the experimental group showed a significant increase in the Sertoli cell function and sperm midpiece length, together with a higher testicular mass, sperm concentration and percentage of normal spermatozoa than the control group (p < 0.05). We also found a tendency for higher blood testosterone levels in the animals fed with barley grain (p = 0.116). The better sperm quality found in the experimental group may be related to their higher efficiency of Sertoli cells and to an earlier onset of puberty. The results of the present work elucidate the mechanisms by which dietary supplementation enhances the male sexual development and might be useful for better practices of livestock management in seasonal breeders.

A Human Gonadal Cell Model From Induced Pluripotent Stem Cells

Sertoli cells are main players in the male gonads development and their study may shed light on 46,XY disorders of sex development (DSD). Mature primary Sertoli cells are incapable of proliferating in prolonged in vitro cultures and the available Sertoli cell models have several limitations since they derive from mouse or human cancer tissues. We differentiated human fibroblasts (HFs)-derived induced pluripotent stem cells into Sertoli-like cells (SLC) and, in order to characterize this new Sertoli cell model, we performed gene expression analyses by NextGeneration Sequencing techniques. This approach revealed that our putative SLC have reduced expression of pluripotency markers and expressed Sertoli cell markers such as SRY-Related HMG-Box 9 (SOX9), vimentin (VIM), and claudin-11 (CLDN-11). More in detail, the transcriptional profile analysis suggested that these cells are in an early stage of Sertoli cells maturation. Harnessing the power of induced pluripotent stem cells, we were able to generate SLC that show genetic and functional similarities to human Sertoli cells (HSerCs). SLC could become an excellent source of patient-specific Sertoli cells that could be of paramount benefit for both basic research and personalized medicine in sex development and reproductive medicine.

A combination of insulin-like growth factor I (IGF-I) and FSH promotes proliferation of prepubertal bovine Sertoli cells isolated and cultured in vitro

Beef and dairy bull calves fed a low-nutrition diet during early life had decreased concentrations of circulating insulin-like growth factor I (IGF-I), delayed increases in testosterone, smaller testes and delayed puberty compared with those fed high-nutrition diets. Although IGF-1 has important roles in Sertoli cell function in rats and mice, this has not been well documented in bulls. The objectives of this study were to: (1) isolate Sertoli cells from bull calves at 8 weeks of age, (2) culture them in vitro and (3) determine the effects of IGF-I, FSH and a combination of both hormones on cell proliferation. For Sertoli cell isolation, minced testicular tissues were treated with collagenase followed by trypsin and hyaluronidase to digest seminiferous tubules and release Sertoli cells. In this study, Sertoli cells were successfully isolated from 8-week-old Holstein bull calves (n=4) and these cells were cultured for up to 8 days. A combination of IGF-I and FSH increased proliferation (~18%) and therefore cell number (1.5-fold) of prepubertal bovine Sertoli cells in culture, providing clear evidence that IGF-I has a similar role in bovine Sertoli cells as reported in rodents.

Suppression of Sertoli cell tumour development during the first wave of spermatogenesis in inhibin α-deficient mice

A dynamic partnership between follicle-stimulating hormone (FSH) and activin is required for normal Sertoli cell development and fertility. Disruptions to this partnership trigger Sertoli cells to deviate from their normal developmental pathway, as observed in inhibin α-knockout (Inha-KO) mice, which feature Sertoli cell tumours in adulthood. Here, we identified the developmental windows by which adult Sertoli cell tumourigenesis is most FSH sensitive. FSH was suppressed for 7 days in Inha-KO mice and wild-type littermates during the 1st, 2nd or 4th week after birth and culled in the 5th week to assess the effect on adult Sertoli cell development. Tumour growth was profoundly reduced in adult Inha-KO mice in response to FSH suppression during Weeks 1 and 2, but not Week 4. Proliferative Sertoli cells were markedly reduced in adult Inha-KO mice following FSH suppression during Weeks 1, 2 or 4, resulting in levels similar to those in wild-type mice, with greatest effect observed at the 2 week time point. Apoptotic Sertoli cells increased in adult Inha-KO mice after FSH suppression during Week 4. In conclusion, acute FSH suppression during the 1st or 2nd week after birth in Inha-KO mice profoundly suppresses Sertoli cell tumour progression, probably by inhibiting proliferation in the adult, with early postnatal Sertoli cells being most sensitive to FSH action.

The ubiquitous isoform of Na/K-ATPase (ATP1A1) regulates junctional proteins, connexin 43 and claudin 11 via Src-EGFR-ERK1/2-CREB pathway in rat Sertoli cells

Interaction of Na/K-ATPase with its ligand ouabain has been implicated in the regulation of various biological processes. The objective was to investigate roles of Na/K-ATPase isoforms in formation and function of junctional complexes in Sertoli cells. Primary cultures of Sertoli cells were obtained by enzymatic digestion of 20-day-old rat testes and grown on Matrigel-coated dishes for 7 days. Sertoli cells predominantly expressed the ubiquitous isoform of Na/K-ATPase (ATP1A1), confirmed by immunoblotting, PCR, immunofluorescence, and mass spectrometry. Treatment of Sertoli cells with 50 nM ouabain increased transepithelial electrical resistance (TER) and expression of claudin 11 (tight junctions) and connexin 43 (gap junctions), whereas 1 mM ouabain had opposite effects. Involvement of Src-EGFR-ERK1/2-CREB pathway in ouabain-mediated expression of claudin 11 and connexin 43 was evaluated. Incubation of Sertoli cells with 50 nM ouabain increased content of p-Src, p-EGFR, p-ERK1/2, and p-CREB; in contrast, 1 mM ouabain decreased phosphorylation of these signaling molecules. Preincubation of Sertoli cells with inhibitors of Src and MAPK pathways inhibited ouabain-induced effects on these signaling molecules, TER, and expression of claudin 11 and connexin 43. In conclusion, we inferred that ATP1A1 regulated Sertoli cell tight junctions and gap junctions through the Src-EGFR-ERK1/2-CREB pathway. Ouabain is an endogenous steroid; therefore, its interaction with ATP1A1 may be a critical signaling mechanism for the regulation of Sertoli cell function and male fertility.

Cholesterol: A Gatekeeper of Male Fertility?

Cholesterol is essential for mammalian cell functions and integrity. It is an important structural component maintaining the permeability and fluidity of the cell membrane. The balance between synthesis and catabolism of cholesterol should be tightly regulated to ensure normal cellular processes. Male reproductive function has been demonstrated to be dependent on cholesterol homeostasis. Here we review data highlighting the impacts of cholesterol homeostasis on male fertility and the molecular mechanisms implicated through the signaling pathways of some nuclear receptors.

Testicular growth and development in puberty

PURPOSE OF REVIEW

To describe pubertal testicular growth in humans, changes in testicular cell populations that result in testicular growth, and the role of testosterone and gonadotrophins follicle-stimulating hormone (FSH) and luteinizing hormone (LH) in testicular growth. When human data were not available, studies in nonhuman primates and/or rodents were used as surrogates.

RECENT FINDINGS

Testicular growth in puberty follows a sigmoidal growth curve, with a large variation in timing of testicular growth and adult testicular volume. Testicular growth early in puberty is due to increase in Sertoli cell number and length of seminiferous tubules, whereas the largest and fastest growth results from the increase in the diameter of the seminiferous tubules first due to spermatogonial proliferation and then due to the expansion of meiotic and haploid germ cells. FSH stimulates Sertoli cell and spermatogonial proliferation, whereas LH/testosterone is mandatory to complete spermatogenesis. However, FSH and LH/testosterone work in synergy and are both needed for normal spermatogenesis.

SUMMARY

Testicular growth during puberty is rapid, and mostly due to germ cell expansion and growth in seminiferous tubule diameter triggered by androgens. Pre-treatment with FSH before the induction of puberty may improve the treatment of hypogonadotropic hypogonadism, but remains to be proven.

BMP6 Regulates Proliferation and Apoptosis of Human Sertoli Cells Via Smad2/3 and Cyclin D1 Pathway and DACH1 and TFAP2A Activation

Sertoli cells are essential for regulating normal spermatogenesis. However, the mechanisms underlying human Sertoli cell development remain largely elusive. Here we examined the function and signaling pathways of BMP6 in regulating human Sertoli cells. RT-PCR, immunocytochemistry and Western blots revealed that BMP6 and its multiple receptors were expressed in human Sertoli cells. CCK-8 and EDU assays showed that BMP6 promoted the proliferation of Sertoli cells. Conversely, BMP6 siRNAs inhibited the division of these cells. Annexin V/PI assay indicated that BMP6 reduced the apoptosis in human Sertoli cells, whereas BMP6 knockdown assumed reverse effects. BMP6 enhanced the expression levels of ZO1, SCF, GDNF and AR in human Sertoli cells, and ELISA assay showed an increase of SCF by BMP6 and a reduction by BMP6 siRNAs. Notably, Smad2/3 phosphorylation and cyclin D1 were enhanced by BMP6 and decreased by BMP6 siRNAs in human Sertoli cells. The levels of DACH1 and TFAP2A were increased by BMP6 and reduced by BMP6 siRNAs, and the growth of human Sertoli cells was inhibited by these siRNAs. Collectively, these results suggest that BMP6 regulates the proliferation and apoptosis of human Sertoli cells via activating the Smad2/3/cyclin D1 and DACH1 and TFAP2A pathway.

Neonatal testicular cell transplantation restores murine spermatogenesis damaged in the course of herpes simplex virus-induced orchitis

Genital tract infection and inflammation may affect male fertility, causing germ and Sertoli cell loss. We determined if testicular cell transplantation is effective at repairing testicular injury induced by herpes simplex virus (HSV) orchitis. ROSA26 mice were used as donors and the recipients were C57BL/6 mice after HSV testicular inoculation; some of the recipients were treated with the antiviral drug acyclovir (ACV). ACV reduced the amount of HSV antigen in testes on Day 3 after transplantation and enhanced the efficacy of transplantation at Day 30. In recipient testes, donor Sertoli cells formed new seminiferous tubules; significantly more new tubules were observed in the testes of ACV-treated mice compared with mice not treated with ACV (17.8% vs 3.6%). Over half (50.4%) of new tubules in ACV-treated testes contained germ cells and round spermatids were detected in 14.2% of new tubules compared with 15.9% and 5.3% in testes not treated with ACV, respectively. At Day 150 the seminiferous epithelium was completely recovered in some donor tubules and elongated spermatids were observed inside it. Thus, our findings reveal the effectiveness of the combination of antiviral therapy with neonatal testis-cell transplantation for the restoration of spermatogenesis damaged by viral infection.

Differences and similarities between extremely severe oligozoospermia and cryptozoospermia in intracytoplasmic sperm injection

Patients with extremely severe oligozoospermia (ESO) and cryptozoospermia (CO) are suitable using intracytoplasmic sperm injection (ICSI) as an infertility treatment. However, some andrologists are confused to distinguish ESO and CO in clinic diagnose. This study was designed for the first time to evaluate and compare patients with ESO and CO to determine whether these are useful clinical distinctions. A total of 270 infertile men in our center were classified into four groups as Group nonobstruction azoospermia (NOA, n = 44), Group ESO (n = 78), Group CO (n = 40), and Group obstruction azoospermia (OA, n = 108). Comparisons of the volume of bilateral testes, the level of follicle stimulating hormone (FSH) and inhibin B were obtained in four groups. Then comparisons of fertilization rates, cleavage rate, and excellent embryos rate were obtained when couples performed ICSI. All indexes (volume of bilateral testis, level of FSH and inhibin B) in Groups ESO and CO were no difference, while Groups OA versus NOA, OA versus ESO, and OA versus CO were significant differences (P < 0.05). The rates of fertilization were no differences in Groups ESO and CO while Groups OA versus ESO, OA versus CO were significant differences (P < 0.05). Therefore, the spermatogenic functions in patients with CO and ESO were similar, better than NOA but worse than OA. However, it would be helpful to evaluate their spermatogenesis using testicular biopsies, especially accompanied azoospermia in clinical practice.

Male reproductive toxicity of CrVI: In-utero exposure to CrVI at the critical window of testis differentiation represses the expression of Sertoli cell tight junction proteins and hormone receptors in adult F1 progeny rats

The effect of gestational exposure to CrVI (occupational/environmental pollutant and target to Sertoli cells(SC)) was tested in a rat model during the testicular differentiation from the bipotential gonad may interrupt spermatogenesis by disrupting SC tight junctions(TJ) and it's proteins and hormone receptors. Pregnant Wistar rats were exposed to 50/100/200ppm CrVI through drinking water during embryonic days 9-14. On Postnatal day 120, testes were subjected to ion exchange chromatographic analysis and revealed increased level of CrIII in SCs and germ cells, serum and testicular interstitial fluid(TIF). Microscopic analyses showed seminiferous tubules atrophy and disruption of SC TJ, which also recorded decreased testosterone in TIF. mRNA and Protein expression analyses attested decreased level of Fshr, Ar, occludin and claudin-11 in SCs. Immunofluorescent detection revealed weak signal of TJ proteins. Taken together, we concluded that gestational exposure to CrVI interferes with the expression of SC TJ proteins due to attenuated expression of hormone receptors.

A link between hypothyroidism, obesity and male reproduction

Hypothyroidism is a condition in which the serum levels of thyroid hormones are below that necessary to carry out physiological functions in the body. Hypothyroidism is related to obesity as an increase in body weight gain is seen in hypothyroid patients. Moreover, an inverse correlation between free thyroxine values and body mass index has been reported. Leptin, a polypeptide hormone produced by adipocytes, was originally thought to be an antiobesity hormone due its anorexic effects on hypothalamic appetite regulation. However, nowadays it is known that leptin conveys information about the nutritional status to the brain being considered a crucial endocrine factor for regulating several physiological processes including reproduction. Since the identification of thyroid hormone and leptin receptors on the testes, these hormones are being recognized as having important roles in male reproductive functions. A clear link exists among thyroid hormones, leptin and reproduction. Both hormones can negatively affect spermatogenesis and consequently may cause male infertility. The World Health Organization (WHO) estimates the overall prevalence of primary infertility ranging from 8 to 15%. The fact that 30% of couples' inability to conceive is related to a male factor and that the longer hypothyroidism persisted, the greater the damage to the testes, strongly suggest that more studies attempting to clarify both hormones actions directly in the testes need to be conducted specially in cases of congenital hypothyroidism. Therefore, the goal of this review is to highlight the relationship of such hormones in the reproductive system.

Clinical Applications of Gonadotropins in the Male

The pituitary gonadotropins, luteinizing hormone (LH), and follicle-stimulating hormone (FSH) play a pivotal role in reproduction. The synthesis and secretion of gonadotropins are regulated by complex interactions among several endocrine, paracrine, and autocrine factors of diverse chemical structure. In men, LH regulates the synthesis of androgens by the Leydig cells, whereas FSH promotes Sertoli cell function and thereby influences spermatogenesis. Gonadotropins are complex molecules composed of two subunits, the α- and β-subunit, that are noncovalently associated. Gonadotropins are decorated with glycans that regulate several functions of the protein including folding, heterodimerization, stability, transport, conformational maturation, efficiency of heterodimer secretion, metabolic fate, interaction with their cognate receptor, and selective activation of signaling pathways. A number of congenital and acquired abnormalities lead to gonadotropin deficiency and hypogonadotropic hypogonadism, a condition amenable to treatment with exogenous gonadotropins. Several natural and recombinant preparations of gonadotropins are currently available for therapeutic purposes. The difference between natural and the currently available recombinant preparations (which are massively produced in Chinese hamster ovary cells for commercial purposes) mainly lies in the abundance of some of the carbohydrates that conform the complex glycans attached to the protein core. Whereas administration of exogenous gonadotropins in patients with isolated congenital hypogonadotropic hypogonadism is a well recognized therapeutic approach, their role in treating men with normogonadotropic idiopathic infertility is still controversial. This chapter concentrates on the main structural and functional features of the gonadotropin hormones and how basic concepts have been translated into the clinical arena to guide therapy for gonadotropin deficit in males.

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

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

Sertoli cells are capable of proliferation into adulthood in the transition region between the seminiferous tubules and the rete testis in Wistar rats

Sertoli cells (SCs) play a crucial role in testis differentiation, development and function, determining the magnitude of sperm production in sexually mature animals. For over 40 years, it has been considered that these key testis somatic cells stop dividing during early pre-pubertal phase, between around 10 to 20 days after birth respectively in mice and rats, being after that under physiological conditions a stable and terminally differentiated population. However, evidences from the literature are challenging this dogma. In the present study, using several important functional markers (Ki-67, BrdU, p27, GATA-4, Androgen Receptor), we investigated the SC differentiation status in 36 days old and adult Wistar rats, focusing mainly in the transition region (TR) between the seminiferous tubules (ST) and the rete testis. Our results showed that SCs in TR remain undifferentiated for a longer period and, although at a lesser degree, even in adult rats proliferating SCs were observed in this region. Therefore, these findings suggest that, different from the other ST regions investigated, SCs residing in the TR exhibit a distinct functional phenotype. These undifferentiated SCs may compose a subpopulation of SC progenitors that reside in a specific microenvironment capable of growing the ST length if needed from this particular testis region. Moreover, our findings demonstrate an important aspect of testis function in mammals and opens new venues for other experimental approaches to the investigation of SC physiology, spermatogenesis progression and testis growth. Besides that, the TR may represent an important site for pathophysiological investigations and cellular interactions in the testis.

Regulation of the blood-testis barrier

The purpose of this review is to describe the endocrine and local testicular factors that contribute to the regulation of the blood-testis barrier (BTB), using information gained from in vivo and in vitro models of BTB formation during/after puberty, and from the maintenance of BTB function during adulthood. In vivo the BTB, in part comprised of tight junctions between adjacent somatic Sertoli cells, compartmentalizes meiotic spermatocytes and post-meiotic spermatids away from the vasculature, and therefore prevents autoantibody production by the immune system against these immunogenic germ cells. This adluminal compartment also features a unique biochemical milieu required for the completion of germ cell development. During the normal process of spermatogenesis, earlier germ cells continually cross into the adluminal compartment, but the regulatory mechanisms and changes in junctional proteins that allow this translocation step without causing a 'leak' remain poorly understood. Recent data describing the roles of FSH and androgen on the regulation of Sertoli cell tight junctions and tight junction proteins will be discussed, followed by an examination of the role of paracrine factors, including members of the TGFβ superfamily (TGFβ3, activin A) and retinoid signalling, as potential mediators of junction assembly and disassembly during the translocation process.

The Sertoli cell: one hundred fifty years of beauty and plasticity

It has been one and a half centuries since Enrico Sertoli published the seminal discovery of the testicular 'nurse cell', not only a key cell in the testis, but indeed one of the most amazing cells in the vertebrate body. In this review, we begin by examining the three phases of morphological research that have occurred in the study of Sertoli cells, because microscopic anatomy was essentially the only scientific discipline available for about the first 75 years after the discovery. Biochemistry and molecular biology then changed all of biological sciences, including our understanding of the functions of Sertoli cells. Immunology and stem cell biology were not even topics of science in 1865, but they have now become major issues in our appreciation of Sertoli cell's role in spermatogenesis. We end with the universal importance and plasticity of function by comparing Sertoli cells in fish, amphibians, and mammals. In these various classes of vertebrates, Sertoli cells have quite different modes of proliferation and epithelial maintenance, cystic vs. tubular formation, yet accomplish essentially the same function but in strikingly different ways.

Biology of the Sertoli Cell in the Fetal, Pubertal, and Adult Mammalian Testis

A healthy man typically produces between 50 × 10(6) and 200 × 10(6) spermatozoa per day by spermatogenesis; in the absence of Sertoli cells in the male gonad, this individual would be infertile. In the adult testis, Sertoli cells are sustentacular cells that support germ cell development by secreting proteins and other important biomolecules that are essential for germ cell survival and maturation, establishing the blood-testis barrier, and facilitating spermatozoa detachment at spermiation. In the fetal testis, on the other hand, pre-Sertoli cells form the testis cords, the future seminiferous tubules. However, the role of pre-Sertoli cells in this process is much less clear than the function of Sertoli cells in the adult testis. Within this framework, we provide an overview of the biology of the fetal, pubertal, and adult Sertoli cell, highlighting relevant cell biology studies that have expanded our understanding of mammalian spermatogenesis.

TGF-β superfamily signaling in testis formation and early male germline development

The TGF-β ligand superfamily contains at least 40 members, many of which are produced and act within the mammalian testis to facilitate formation of sperm. Their progressive expression at key stages and in specific cell types determines the fertility of adult males, influencing testis development and controlling germline differentiation. BMPs are essential for the interactive instructions between multiple cell types in the early embryo that drive initial specification of gamete precursors. In the nascent foetal testis, several ligands including Nodal, TGF-βs, Activins and BMPs, serve as key masculinizing switches by regulating male germline pluripotency, somatic and germline proliferation, and testicular vascularization and architecture. In postnatal life, local production of these factors determine adult testis size by regulating Sertoli cell multiplication and differentiation, in addition to specifying germline differentiation and multiplication. Because TGF-β superfamily signaling is integral to testis formation, it affects processes that underlie testicular pathologies, including testicular cancer, and its potential to contribute to subfertility is beginning to be understood.

Deletion of the tyrosine phosphatase Shp2 in Sertoli cells causes infertility in mice

The male’s ability to reproduce is completely dependent on Sertoli cells. However, the mechanisms governing the functional integrity of Sertoli cells have remained largely unexplored. Here, we demonstrate that deletion of Shp2 in Sertoli cells results in infertility in mice. In Shp2 knockout mice (SCSKO), a normal population of Sertoli cells was observed, but the blood-testis barrier (BTB) was not formed. Shp2 ablation initiated the untimely and excessive differentiation of spermatogonial stem cells (SSCs) by disturbing the expression of paracrine factors. As a consequence, the process of spermatogenesis was disrupted, and the germ cells were depleted. Furthermore, Shp2 deletion impaired the cell junctions of the primary Sertoli cells and failed to support the clonal formation of SSCs co-cultured with SCSKO Sertoli cells. As expected, Shp2 restoration largely restores the cell junctions of the primary Sertoli cells and the clonal formation of SSCs. To identify the underlying mechanism, we further demonstrated that the absence of Shp2 suppressed Erk phosphorylation, and thus, the expression of follicle-stimulating hormone (FSH)- and testosterone-induced target genes. These results collectively suggest that Shp2 is a critical signaling protein that is required to maintain Sertoli cell function and could serve as a novel target for male infertility therapies.

Androgen Receptor Coactivator ARID4B Is Required for the Function of Sertoli Cells in Spermatogenesis

Defects in spermatogenesis, a process that produces spermatozoa inside seminiferous tubules of the testis, result in male infertility. Spermatogenic progression is highly dependent on a microenvironment provided by Sertoli cells, the only somatic cells and epithelium of seminiferous tubules. However, genes that regulate such an important activity of Sertoli cells are poorly understood. Here, we found that AT-rich interactive domain 4B (ARID4B), is essential for the function of Sertoli cells to regulate spermatogenesis. Specifically, we generated Sertoli cell-specific Arid4b knockout (Arid4bSCKO) mice, and showed that the Arid4bSCKO male mice were completely infertile with impaired testis development and significantly reduced testis size. Importantly, severe structural defects accompanied by loss of germ cells and Sertoli cell-only phenotype were found in many seminiferous tubules of the Arid4bSCKO testes. In addition, maturation of Sertoli cells was significantly delayed in the Arid4bSCKO mice, associated with delayed onset of spermatogenesis. Spermatogenic progression was also defective, showing an arrest at the round spermatid stage in the Arid4bSCKO testes. Interestingly, we showed that ARID4B functions as a "coactivator" of androgen receptor and is required for optimal transcriptional activation of reproductive homeobox 5, an androgen receptor target gene specifically expressed in Sertoli cells and critical for spermatogenesis. Together, our study identified ARID4B to be a key regulator of Sertoli cell function important for male germ cell development.

Relaxin affects cell organization and early and late stages of spermatogenesis in a coculture of rat testicular cells

Relaxin and its receptor RXFP1 are co-expressed in Sertoli cells, and relaxin can stimulate proliferation of Sertoli cells. In this study, we investigated a role of relaxin in spermatogenesis, using a short-term culture of testicular cells of the rat that allowed differentiation of spermatogonia to spermatids. Sertoli, germ, and peritubular myoid cells were the predominant cell types in the culture. Sertoli and germ cells expressed RXFP1. Cultures were incubated without (control) or with 0.5% fetal bovine serum (FBS) or 100 ng/mL H2 relaxin (RLN) for 2 days. Cell organization, number, and differentiation were analyzed after 2 (D2), 5 (D5) or 8 (D8) days of culturing. Although the proportion of germ cells decayed from D2 to D5, the relative contribution of HC, 1C, 2C, and 4C germ cell populations remained constant in the control group during the whole culture. RLN did not affect the proportion of germ cell populations compared with control, but increased gene and/or protein expression of the undifferentiated and differentiated spermatogonia markers PLZF and c-KIT, and of the post-meiotic marker Odf2 in D5. RLN favored organization of cells in tubule-like structures, the arrangement of myoid cells around the tubules, arrangement of c-KIT-positive spermatogonia at the basal region of the tubules, and expression of the cell junction protein β-catenin close to the plasma membrane region. Knockdown of relaxin with small interfering RNA (siRNA) reduced expression of β-catenin at the cell junctions, and shifted its expression to the nucleus. We propose that relaxin may affect spermatogenesis by modulating spermatogonial self renewal and favoring cell contact.