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

Changes in local mineral homeostasis facilitate the formation of benign and malignant testicular microcalcifications

Testicular microcalcifications consist of hydroxyapatite and have been associated with an increased risk of testicular germ cell tumors (TGCTs) but are also found in benign cases such as loss-of-function variants in the phosphate transporter SLC34A2. Here, we show that fibroblast growth factor 23 (FGF23), a regulator of phosphate homeostasis, is expressed in testicular germ cell neoplasia in situ (GCNIS), embryonal carcinoma (EC), and human embryonic stem cells. FGF23 is not glycosylated in TGCTs and therefore cleaved into a C-terminal fragment which competitively antagonizes full-length FGF23. Here, Fgf23 knockout mice presented with marked calcifications in the epididymis, spermatogenic arrest, and focally germ cells expressing the osteoblast marker Osteocalcin (gene name: Bglap, protein name). Moreover, the frequent testicular microcalcifications in mice with no functional androgen receptor and lack of circulating gonadotropins are associated with lower Slc34a2 and higher Bglap/Slc34a1 (protein name: NPT2a) expression compared with wild-type mice. In accordance, human testicular specimens with microcalcifications also have lower SLC34A2 and a subpopulation of germ cells express phosphate transporter NPT2a, Osteocalcin, and RUNX2 highlighting aberrant local phosphate handling and expression of bone-specific proteins. Mineral disturbance in vitro using calcium or phosphate treatment induced deposition of calcium phosphate in a spermatogonial cell line and this effect was fully rescued by the mineralization inhibitor pyrophosphate. In conclusion, testicular microcalcifications arise secondary to local alterations in mineral homeostasis, which in combination with impaired Sertoli cell function and reduced levels of mineralization inhibitors due to high alkaline phosphatase activity in GCNIS and TGCTs facilitate osteogenic-like differentiation of testicular cells and deposition of hydroxyapatite.

Tetrabromobisphenol S (TBBPS) exposure induced the testicular aging through NLRP3-mediated inflammatory signaling pathway in vitro and in vivo

Tetrabromobisphenol A (TBBPA) is an extensively employed Brominated flame retardant (BFR), but studies have shown that it has a range of toxicities, and it has been banned from use at present. Tetrabromobisphenol S (TBBPS) is increasingly used in industrial production as a substitute for TBBPA. However, up to now, the toxicity and molecular mechanism of TBBPS in the reproductive system have not been fully revealed. Therefore, we investigated the effects of TBBPS on testicular. In vitro, GC-1 cells and TM4 cells were used as models to perform an array of biochemical tests, and the toxicological impacts of TBBPS on testicular cells were evaluated. It was found that TBBPS could induce testicular cells senescence. Additionally, p16, p21, and p53 expression were also increased after TBBPS treatment. TBBPS also induced oxidative stress and inflammation response. Mechanistic studies have revealed that TBBPS causes mitochondrial damage, which leads to mitochondrial ds-DNA leakage into the cytoplasm, the NLRP3 inflammasome was then activated, in turn leading to inflammatory and senescence responses in testicular cells. In vivo, we found that TBBPS caused testicular tissue aging and inflammatory responses by detecting a series of molecular markers. In summary, the current study demonstrates that TBBPS can induce aging damage and inflammatory responses in testis, and this study lays a foundation for further exploring the reproductive toxicity of TBBPS.

Single-cell sequencing in non-obstructive azoospermia: insights from primary and re-analysis studies

Non-obstructive azoospermia (NOA) constitutes one of the most severe forms of male infertility. Recent advancements in single-cell sequencing have significantly contributed to understanding the molecular landscape of NOA in human testicular tissues, elucidating the factors that underpin spermatogenic dysfunction. This technology has improved our understanding of the condition at a cellular level. Concurrently, bioinformatics developments have facilitated the re-analysis of publicly available single-cell datasets, offering novel insights into the disorder. Nevertheless, a comprehensive review integrating primary and re-analysis studies of single-cell sequencing in NOA is lacking. This review systematically evaluates 10 primary studies reporting original single-cell sequencing data of human NOA testicular samples and 22 secondary studies that re-analyzed these published data. We explore single-cell sequencing applications in germ cells, Sertoli cells, and Leydig cells, offering a comprehensive overview of molecular insights into spermatogenic dysfunction. Our review highlights novel findings in secondary studies, including the roles of transcriptional regulators, RNA transcription, endocrine disruptors, and microtubular cytoskeleton, thereby bridging primary studies and re-analysis studies. Additionally, we discussed future research directions and the challenges of translating single-cell research findings into clinical applications. In summary, single-cell sequencing offers a high-resolution, single-cell perspective of NOA testicular tissue, paving the way for innovative therapeutic strategies in male infertility.

Transcriptomic dynamics and cell-to-cell communication during the transition of prospermatogonia to spermatogonia revealed at single-cell resolution

BACKGROUND

Spermatogonia are essential for the continual production of sperm and regeneration of the entire spermatogenic lineage after injury. In mammals, spermatogonia are formed in the neonatal testis from prospermatogonia (also termed gonocytes), which are established from primordial germ cells during fetal development. Currently, the molecular regulation of the prospermatogonial to spermatogonia transition is not fully understood.

RESULTS

In this study, we examined the gene expression patterns of prospermatogonia, spermatogonia and testicular somatic cells at 4 different stages, including embryonic day (E) 12.5, E17.5 and postnatal days (P) 1 and 6, using single-cell RNA sequencing (scRNA-seq). We identified 5 different molecular states in the prospermogonial population and revealed gene expression dynamics in corresponding testicular somatic cells. Specifically, we found that prospermatogonia mainly receive signals, while Leydig cells and peritubular myoid cells are the mediators for transmitting signals, indicating their potential roles in regulating the development and differentiation of prospermatogonia. Transcription regulon analyses revealed the involvement of basic helix-loop-helix (bHLH) transcription factors in directing prospermogonial fate decisions. We then disrupted this transcription network by ectopic expression of inhibitor of differentiation 2 (Id2), which is a negative regulator of bHLH transcription factors. The overexpression of Id2 in prospermatogonia caused severe defects in the progression of prospermatogonia to spermatogonia.

CONCLUSION

Together, these findings provide a crucial dataset for dissecting key genes that direct the establishment of the foundational spermatogonial pool and the fate transitions of different somatic cell lineages in the testis during fetal and neonatal periods of development.

Extracellular Vesicles in the Aging Male Reproductive System: Progresses and Perspectives

Extracellular vesicles (EVs) serve as crucial mediators of intercellular communication in spermatogenesis, steroidogenesis, and age-related pathophysiological processes within the male reproductive system. These EVs exhibit promising prospects for disease diagnosis and therapeutic administration. This review explores the impact of advanced paternal age on male fertility and testosterone decline, shedding light on the underlying mechanisms. It highlights the decline in semen quality, DNA damage, and alterations in sperm miRNA profiles associated with aging. The interplay between oxidative stress and antioxidants crucially regulates male reproductive aging. Currently, most studies focus on Sertoli cell-derived EVs, while understanding of Leydig cell-derived vesicles remains limited. Multi-omics integration will enhance the understanding of male reproductive aging and guide personalized interventions, revealing potential biomarkers and targets in the future.

Effects of periodontal disease on the reproductive performance and offspring of Wistar rats

BACKGROUND

Periodontitis can induce systemic inflammation, and it may affect the testicles and male reproductive performance. This study investigated the effects of periodontitis on the testicles, reproductive performance, and offspring development in male rats.

METHODS

Male Wistar rats were induced with periodontitis by ligating their first molars. After 14 days of inducing periodontal lesions, the animals were observed for an additional 54 days, corresponding to a complete cycle of spermatogenesis. Rats from the periodontitis group (GP, n = 12) and the control group (GC, n = 12) were paired with healthy females (n = 48) for 10 days, equivalent to 2 estrous cycles. Post-mating, the males underwent microtomographic, histological, and reproductive parameter assessments.

RESULTS

Microtomographic analysis revealed higher porosity around the first molar in GP (26 ± 6%) and greater distance between the amelocemental junction and the alveolar bone (1.37 [1.12-1.90] mm), indicative of bone resorption. GP also exhibited significant decreases in final body weight, reduced Sertoli and Leydig cell counts, and lowered testosterone levels compared to GC. Significant morphological alterations in sperm tails were observed in GP compared to GC.

CONCLUSIONS

Periodontitis adversely affected reproductive performance, evoking, and offspring development in male rats. These findings highlight the systemic impacts of periodontal disease on male reproductive health in an animal model.

PLAIN LANGUAGE SUMMARY

Our study investigated how periodontitis can affect male reproductive health in rats and offspring development. We induced periodontitis in male rats and, after a full cycle of sperm production, these rats were mated with healthy females. We observed that the rats with periodontitis had worse reproductive performance compared to the control group without periodontitis. Additionally, the offspring of the rats with periodontitis showed signs of compromised intrauterine development and a higher incidence of congenital malformations. These results highlight that the inflammation caused by periodontitis can have adverse effects beyond the mouth, significantly impacting male reproductive health and offspring development. These findings suggest the need for further research into the clinical implications of periodontitis on reproductive health.

The role of Sertoli cell-derived miR-143-3p in male fertility declines with age

As delayed parenthood becomes more prevalent, understanding age-related testosterone decline and its impact on male fertility has gained importance. However, molecular mechanisms concerning testicular aging remain largely undiscovered. Our study highlights that miR-143-3p, present in aging Sertoli cells (SCs), is loaded into extracellular vesicles (EVs), affecting Leydig cells (LCs) and germ cells, thus disrupting testicular tissue homeostasis and spermatogenesis. Intriguingly, in SCs, transforming growth factor-β signaling promotes miR-143 precursors transcription, increasing mature miR-143-3p levels. This inhibits Smurf2, activating Smad2, and further enhancing miR-143-3p accumulation. EVs transporting miR-143-3p, originating from SCs, contribute to the age-related decline of testosterone and male fertility by targeting the luteinizing hormone receptor and retinoic acid receptor. Diminishing endogenous miR-143-3p in SCs postpones testis aging, preserving and prolonging male fertility. Thus, our study identified miR-143-3p as a key regulator of testicular function and fertility, revealing miR-143-3p as a potential therapeutic target for male abnormal sexual and reproductive function.

Age-related testosterone decline: mechanisms and intervention strategies

Contemporary societies exhibit delayed reproductive age and increased life expectancy. While the male reproductive system demonstrates relatively delayed aging compared to that of females, increasing age substantially impacts its function. A characteristic manifestation is age-induced testosterone decline. Testosterone, a crucial male sex hormone, plays pivotal roles in spermatogenesis and sexual function, and contributes significantly to metabolism, psychology, and cardiovascular health. Aging exerts profound effects on the hypothalamic-pituitary-gonadal axis and Leydig cells, precipitating testosterone reduction, which adversely affects male health. Exogenous testosterone supplementation can partially ameliorate age-related testosterone deficiency; however, its long-term safety remains contentious. Preserving endogenous testosterone production capacity during the aging process warrants further investigation as a potential intervention strategy.

Low protein uptake during peripuberty impairs the testis, epididymis, and spermatozoa in pubertal and adult Wistar rats

Protein malnutrition during critical periods poses significant risks to reproductive health. Thus, this study aims to evaluate the immediate and delayed effects of a 30-day low-protein diet on the postnatal development of the male reproductive system. For so, male rats were fed a protein-deficient diet from postnatal day 30-60, followed by evaluations of testis, epididymis, and spermatozoa both at the end of the diet and after a 60-day recovery period. Testicular and epididymal weight was lowered in pubertal animals. Several histological alterations were found in the testis, such as acidophilic cells and vacuoles in the seminiferous epithelium, and sperm production was compromised. In the epididymis, the luminal compartment was diminished, and the stroma was enlarged both in the caput and cauda; in the cauda, the epithelial compartment was enlarged; the transit time of spermatozoa through this organ was diminished. Testosterone production was lowered. Spermatozoa's motility, mitochondrial activation, and acrosomal integrity were impaired, and several alterations in morphology were observed. After the recovery period, testicular and epididymal weight was restored. Tissue remodulation was observed in the epididymis, but the spermatozoa's transit time in this organ was not altered. Sperm and testosterone production, spermatozoa motility, mitochondrial activation, and acrosomal integrity were also restored. However, testicular histological alterations and spermatic morphological abnormalities were maintained in protein-restricted animals. Protein restriction during peripuberty impairs the reproductive maturation of pubertal Wistar rats, impairing testicular and epididymal function, with lasting effects even after dietary correction.

Photobiomodulation Improves Histological Parameters of Testis and Spermatogenesis in Adult Mice Exposed to Scrotal Hyperthermia in the Prepubertal Phase

Introduction: Heat stress is one of the environmental causes of damage to the testis, whose effects are less known before puberty. The aim of the present study was to investigate the impact of photobiomodulation (PBM) on the testis of prepubertal mice subjected to hyperthermia. Methods: Twenty-four three-week-old prepubertal male mice were allocated to the following groups: I) control, II) scrotal hyperthermia (Hyp), and III) Hyp+PBM (n=8/each group). In order to induce hyperthermia, the scrotum was placed in water at 43 °C for 20 minutes every other day for a total duration of 10 days. In the Hyp+PBM group, after hyperthermia induction, the testis of the mice was subjected to laser irradiation at a wavelength of 890 nm (0.03 J/cm2 for 30 seconds) for 35 days. After the mice were sacrificed, the testis and epididymis were removed for testing. Results: Compared with those of the Hyp group, the sperm parameters of the laser irradiation group improved notably. In addition, histological examinations revealed that the final number of testis cells and the volume of tissue in the Hyp+PBM group were dramatically greater than those in the Hyp group. The analysis of molecular data revealed an increase in the expression of mitotic genes and testosterone levels and a decrease in the formation of reactive oxygen species (ROS) and the expression of the apoptotic gene in the testis subjected to PBM. Conclusion: Based on the present findings, laser therapy can reduce complications caused by scrotal hyperthermia during prepuberty and ameliorate spermatogenesis during puberty.

Mouse testicular macrophages can independently produce testosterone and are regulated by Cebpb

BACKGROUND

Testicular macrophages (TM) have long been recognized for their role in immune response within the testicular environment. However, their involvement in steroid hormone synthesis, particularly testosterone, has not been fully elucidated. This study aims to explore the capability of TM to synthesize and secrete testosterone de novo and to investigate the regulatory mechanisms involved.

RESULTS

Transcriptomic analysis revealed significant expression of Cyp11a1, Cyp17a1, Hsd3b1, and Hsd17b3 in TM, which are key enzymes in the testosterone synthesis pathway. qPCR analysis and immunofluorescence validation confirmed the autonomous capability of TM to synthesize testosterone. Ablation of TM in mice resulted in decreased physiological testosterone levels, underscoring the significance of TM in maintaining testicular testosterone levels. Additionally, the study also demonstrated that Cebpb regulates the expression of these crucial genes, thereby modulating testosterone synthesis.

CONCLUSIONS

This research establishes that TM possess the autonomous capacity to synthesize and secrete testosterone, contributing significantly to testicular testosterone levels. The transcription factor Cebpb plays a crucial role in this process by regulating the expression of key genes involved in testosterone synthesis.

Heat stress upregulates arachidonic acid to trigger autophagy in sertoli cells via dysfunctional mitochondrial respiratory chain function

As a key factor in determining testis size and sperm number, sertoli cells (SCs) play a crucial role in male infertility. Heat stress (HS) reduces SCs counts, negatively impacting nutrient transport and supply to germ cells, and leading to spermatogenesis failure in humans and animals. However, how HS affects the number of SCs remains unclear. We hypothesized that changes in SC metabolism contribute to the adverse effects of HS. In this study, we first observed an upregulation of arachidonic acid (AA), an unsaturated fatty acid after HS exposure by LC-MS/MS metabolome detection. By increasing ROS levels, expression of KEAP1 and NRF2 proteins as well as LC3 and LAMP2, 100 µM AA induced autophagy in SCs by activating oxidative stress (OS). We observed adverse effects of AA on mitochondria under HS with a decrease of mitochondrial number and an increase of mitochondrial membrane potential (MMP). We also found that AA alternated the oxygen transport and absorption function of mitochondria by increasing glycolysis flux and decreasing oxygen consumption rate as well as the expression of mitochondrial electron transport chain (ETC) proteins Complex I, II, V. However, pretreatment with 5 mM NAC (ROS inhibitor) and 2 µM Rotenone (mitochondrial ETC inhibitor) reversed the autophagy induced by AA. In summary, AA modulates autophagy in SCs during HS by disrupting mitochondrial ETC function, inferring that the release of AA is a switch-like response, and providing insight into the underlying mechanism of high temperatures causing male infertility.

Joint Analysis of Genome-wide DNA Methylation and Transcription Sequencing Identifies the Role of BAX Gene in Heat Stress-Induced-Sertoli Cells Apoptosis

The problem of male infertility is a global health crisis and poses a serious threat to the well-being of families. Under heat stress (HS), the reduction of Sertoli cells (SCs) inhibits energy transport and nutrient supply to germ cells, leading to spermatogenesis failure. DNA methylation of genes is a central epigenetic regulatory mechanism in mammalian reproduction. However, it remains unclear how DNA methylation regulates gene expression in heat-stressed SCs. In this study, we investigated whether the decrease in SC levels during HS could be related to epigenetic DNA modifications. The cells exposed to HS showed changes in differential methylation cytosines and regions (DMCs/DMRs) and differential expression genes (DEGs), but not in global DNA methylations. One of the most important biological processes affected by HS is cell apoptosis induced by the intrinsic apoptotic signaling pathway (GO: 2,001,244, P < 0.05) by enrichment in the Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG). The joint analysis showed that several gene expressions in RNA-seq and WGBS overlapped and the shortlisted genes BAX, HSPH1, HSF1B, and BAG were strongly correlated with stress response and apoptosis. Methylation-specific PCR (MSP) and flow cytometry (FCM) analyzes showed that reduced promoter methylation and enhanced gene expression of BAX with a consequence of apoptosis. The activity of BAX, as well as an increase in its expression, is likely to result in a reduction of SCs population which could further impair ATP supply and adversely affect membrane integrity. These findings provide novel insights into the molecular mechanisms through which stressors cause male reproductive dysfunction and a new molecular etiology of male infertility.

Targeting dysregulated phago-/auto-lysosomes in Sertoli cells to ameliorate late-onset hypogonadism

Age-related changes in testicular function can impact health and well-being. The mechanisms underlying age-related testicular dysfunction, such as late-onset hypogonadism (LOH), remain incompletely understood. Using single-cell RNA sequencing on human testes with LOH, we delineated Sertoli cells (SCs) as pivotal metabolic coordinators within the testicular microenvironment. In particular, lysosomal acidity probing revealed compromised degradative capacity in aged SCs, hindering autophagy and phagocytic flux. Consequently, SCs accumulated metabolites, including cholesterol, and have increased inflammatory gene expression; thus, we termed these cells as phago-/auto-lysosomal deregulated SCs. Exposure to a high-fat diet-induced phago-/auto-lysosomal dysregulated-like SCs, recapitulating LOH features in mice. Notably, efferent ductular injection and systemic TRPML1 agonist administration restored lysosomal function, normalizing testosterone deficiency and associated abnormalities in high-fat diet-induced LOH mice. Our findings underscore the central role of SCs in testis aging, presenting a promising therapeutic avenue for LOH.

Loss of NR5A1 in mouse Sertoli cells after sex determination changes cellular identity and induces cell death by anoikis

To investigate the role of the nuclear receptor NR5A1 in the testis after sex determination, we analyzed mice lacking NR5A1 in Sertoli cells (SCs) from embryonic day (E) 13.5 onwards. Ablation of Nr5a1 impaired the expression of genes characteristic of SC identity (e.g. Sox9 and Amh), caused SC death from E14.5 onwards through a Trp53-independent mechanism related to anoikis, and induced disorganization of the testis cords. Together, these effects caused germ cells to enter meiosis and die. Single-cell RNA-sequencing experiments revealed that NR5A1-deficient SCs changed their molecular identity: some acquired a 'pre-granulosa-like' cell identity, whereas other reverted to a 'supporting progenitor-like' cell identity, most of them being 'intersex' because they expressed both testicular and ovarian genes. Fetal Leydig cells (LCs) did not display significant changes, indicating that SCs are not required beyond E14.5 for their emergence or maintenance. In contrast, adult LCs were absent from postnatal testes. In addition, adult mutant males displayed persistence of Müllerian duct derivatives, decreased anogenital distance and reduced penis length, which could be explained by the loss of AMH and testosterone synthesis due to SC failure.

Single-cell transcriptome analysis of the germ cells and somatic cells during mitotic quiescence stage in goats

The mitotic quiescence of prospermatogonia is the event known to occur during genesis of the male germline and is tied to the development of the spermatogenic lineage. The regulatory mechanisms and the functional importance of this process have been demonstrated in mice; however, regulation of this process in human and domestic animal is still largely unknown. In this study, we employed single-cell RNA sequencing to identify transcriptional signatures of prospermatogonia and major somatic cell types in testes of goats at E85, E105, and E125. We identified both common and specific Gene Ontology categories, transcription factor regulatory networks, and cell-cell interactions in cell types from goat testis. We also analyzed the transcriptional dynamic changes in prospermatogonia, Sertoli cells, Leydig cells, and interstitial cells. Our datasets provide a useful resource for the study of domestic animal germline development.

Sertoli cell-enriched proteins in mouse and human testicular interstitial fluid

Sertoli cells support the development of sperm and the function of various somatic cells in the interstitium between the tubules. Sertoli cells regulate the function of the testicular vasculature and the development and function of the Leydig cells that produce testosterone for fertility and virility. However, the Sertoli cell-derived factors that regulate these cells are largely unknown. To define potential mechanisms by which Sertoli cells could support testicular somatic cell function, we aimed to identify Sertoli cell-enriched proteins in the testicular interstitial fluid (TIF) between the tubules. We previously resolved the proteome of TIF in mice and humans and have shown it to be a rich source of seminiferous tubule-derived proteins. In the current study, we designed bioinformatic strategies to interrogate relevant proteomic and genomic datasets to identify Sertoli cell-enriched proteins in mouse and human TIF. We analysed proteins in mouse TIF that were significantly reduced after one week of acute Sertoli cell ablation in vivo and validated which of these are likely to arise primarily from Sertoli cells based on relevant mouse testis RNASeq datasets. We used a different, but complementary, approach to identify Sertoli cell-enriched proteins in human TIF, taking advantage of high-quality human testis genomic, proteomic and immunohistochemical datasets. We identified a total of 47 and 40 Sertoli cell-enriched proteins in mouse and human TIF, respectively, including 15 proteins that are conserved in both species. Proteins with potential roles in angiogenesis, the regulation of Leydig cells or steroidogenesis, and immune cell regulation were identified. The data suggests that some of these proteins are secreted, but that Sertoli cells also deposit specific proteins into TIF via the release of extracellular vesicles. In conclusion, we have identified novel Sertoli cell-enriched proteins in TIF that are candidates for regulating somatic cell-cell communication and testis function.

Pancreatic lipase-related protein 2 is selectively expressed by peritubular myoid cells in the murine testis and sustains long-term spermatogenesis

Spermatogenesis is a complicated process of germ cell differentiation that occurs within the seminiferous tubule in the testis. Peritubular myoid cells (PTMCs) produce major components of the basement membrane that separates and ensures the structural integrity of seminiferous tubules. These cells secrete niche factors to promote spermatogonial stem cell (SSC) maintenance and mediate androgen signals to direct spermatid development. However, the regulatory mechanisms underlying the identity and function of PTMCs have not been fully elucidated. In the present study, we showed that the expression of pancreatic lipase-related protein 2 (Pnliprp2) was restricted in PTMCs in the testis and that its genetic ablation caused age-dependent defects in spermatogenesis. The fertility of Pnliprp2 knockout animals (Pnliprp2-/-) was normal at a young age but declined sharply beginning at 9 months. Pnliprp2 deletion impaired the homeostasis of undifferentiated spermatogonia and severely disrupted the development and function of spermatids. Integrated analyses of single-cell RNA-seq and metabolomics data revealed that glyceride metabolism was changed in PTMCs from Pnliprp2-/- mice. Further analysis found that 60 metabolites were altered in the sperm of the Pnliprp2-/- animals; notably, lipid metabolism was significantly dysregulated. Collectively, these results revealed that Pnliprp2 was exclusively expressed in PTMCs in the testis and played a novel role in supporting continual spermatogenesis in mice. The outcomes of these findings highlight the function of lipid metabolism in reproduction and provide new insights into the regulation of PTMCs in mammals.

Altered transcriptomic and metabolomic profiles of testicular interstitial fluid during aging in mice

The testicular interstitial fluid (TIF) that bathes seminiferous tubules and testicular interstitial cells is the main microenvironment of the testis and involved in crosstalk between testicular cells. TIF also provides a new mean to investigate dysfunctional states of testis such as spermatogenic disorder and aging. In this study, we performed integrative omics analysis on the exosomal transcriptomics and liquid chromatography-tandem mass spectrometry (LC-MS/MS) based non-targeted metabolomics in TIF by comparison between 21-month-old and 3-month-old male mice. A total of 1627 genes were identified as aging-related differently expressed genes (DEGs) in mouse TIF exosomes, with 1139 downregulated and 488 upregulated. Functional and pathway analysis revealed that the DEGs were associated with oxidative stress, carbon metabolism, and systemic lupus erythematosus. By comparing the DEGs with the Aging Atlas Database, we screened out key aging-related genes functioning as oxidative stress regulators, and their expression pattern in human testis with age was confirmed by immunohistochemistry results in the Human Protein Atlas database. In addition, the metabolomic analysis identified mild differences between young and old groups with 28 downregulated differently expressed metabolites (DEMs) and 6 upregulated DEMs, in the negative ion mode, including decreased level of several antioxidant metabolites. The KEGG analysis demonstrated that 10 pathways were upregulated, while the pyrimidine metabolism pathway was downregulated in the aged mice TIF. Taken together, this study highlighted the prominent role of oxidative stress that contributed to the aging microenvironment in the TIF, and brought comprehensive transcriptomic and metabolomic perspectives for understanding the mechanism underlying the testicular aging.

The emerging role of extracellular vesicles in the testis

Extracellular vesicles (EVs) are nano-sized membrane-bounded particles, released by all cells and capable of transporting bioactive cargoes, proteins, lipids, and nucleic acids, to regulate a variety of biological functions. Seminal plasma is enriched in EVs, and extensive evidence has revealed the role of EVs (e.g. prostasomes and epididymosomes) in the male genital tract. Recently, EVs released from testicular cells have been isolated and identified, and some new insights have been generated on their role in maintaining normal spermatogenesis and steroidogenesis in the testis. In the seminiferous tubules, Sertoli cell-derived EVs can promote the differentiation of spermatogonial stem cells (SSCs), and EVs secreted from undifferentiated A spermatogonia can inhibit the proliferation of SSCs. In the testicular interstitium, EVs have been identified in endothelial cells, macrophages, telocytes, and Leydig cells, although their roles are still elusive. Testicular EVs can also pass through the blood-testis barrier and mediate inter-compartment communication between the seminiferous tubules and the interstitium. Immature Sertoli cell-derived EVs can promote survival and suppress the steroidogenesis of Leydig cells. Exosomes isolated from macrophages can protect spermatogonia from radiation-induced injury. In addition to their role in intercellular communication, testicular EVs may also participate in the removal of aberrant proteins and the delivery of antigens for immune tolerance. EVs released from testicular cells can be detected in seminal plasma, which makes them potential biomarkers reflecting testicular function and disease status. The testicular EVs in seminal plasma may also affect the female reproductive tract to facilitate conception and may even affect early embryogenesis through modulating sperm RNA. EVs represent a new type of intercellular messenger in the testis. A detailed understanding of the role of testicular EV may contribute to the discovery of new mechanisms causing male infertility and enable the development of new diagnostic and therapeutic strategies for the treatment of infertile men.

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.

Ldha-Dependent Metabolic Programs in Sertoli Cells Regulate Spermiogenesis in Mouse Testis

Sertoli cells play indispensable roles in spermatogenesis by providing the advanced germ cells with structural, nutritional, and regulatory support. Lactate is regarded as an essential Sertoli-cell-derived energy metabolite that nurses various types of spermatogenic cells; however, this assumption has not been tested using genetic approaches. Here, we have reported that the depletion of lactate production in Sertoli cells by conditionally deleting lactate dehydrogenase A (Ldha) greatly affected spermatogenesis. Ldha deletion in Sertoli cells significantly reduced the lactate production and resulted in severe defects in spermatogenesis. Spermatogonia and spermatocytes did not show even mild impairments, but the spermiogenesis of Ldha conditional knockout males was severely disrupted. Further analysis revealed that 2456 metabolites were altered in the sperm of the knockout animals, and specifically, lipid metabolism was dysregulated, including choline, oleic acid, and myristic acid. Surprisingly, choline supplementation completely rescued the spermiogenesis disorder that was caused by the loss of Ldha activities. Collectively, these data have demonstrated that the interruption of Sertoli-cell-derived lactate impacted sperm development through a choline-mediated mechanism. The outcomes of these findings have revealed a novel function of lactate in spermatogenesis and have therapeutic applications in treating human infertility.

The potential of sertoli cells (SCs) derived exosomes and its therapeutic efficacy in male reproductive disorders

In the male reproductive system, seminiferous tubules in testis are lined by a complex stratified epithelium containing two distinct populations of cells, spermatogenic cells that develop into spermatozoa, and sertoli cells (SCs) that mainly support and nourish spermatogenic cell lineage as well as exerting powerful effect on men reproductive capacity. Different varieties of proteins, hormones, exosomes and growth factors are secreted by SCs. There are different kinds of junctions found between SCs called BTB. It was elucidated that complete absence of BTB or its dysfunction leads to infertility. To promote spermatogenesis, crosstalk of SCs with spermatogenic cells plays an important role. The ability of SCs to support germ cell productivity and development is related to its various products carrying out several functions. Exosomes (EXOs) are one of the main EVs with 30-100 nm size generating from endocytic pathway. They are produced in different parts of male reproductive system including epididymis, prostate and SCs. The most prominent characteristics of SC-based exosomes is considered mutual interaction of sertoli cells with spermatogonial stem cells and Leydig cells mainly through establishment of intercellular communication. Exosomes have gotten a lot of interest because of their role in pathobiological processes and as a cell free therapy which led to developing multiple exosome isolation methods based on different principles. Transmission of nucleic acids, proteins, and growth factors via SC-based exosomes and exosomal miRNAs are proved to have potential to be valuable biomarkers in male reproductive disease. Among testicular abnormalities, non-obstructive azoospermia and testicular cancer have been more contributed with SCs performance. The identification of key proteins and miRNAs involved in the signaling pathways related with spermatogenesis, can serve as diagnostic and regenerative targets in male infertility.

The solute carrier family 7 member 11 (SLC7A11) is regulated by LH/androgen and required for cystine/glutathione homeostasis in mouse Sertoli cells

Luteinizing hormone (LH) stimulates testosterone production from Leydig cells. Both LH and testosterone play important roles in spermatogenesis and male fertility. To identify LH - and testosterone - responsive transporter genes that play key roles in spermatogenesis, we performed large-scale gene expression analyses on testes obtained from adult control and Lhb knockout mice. We found a significant reduction in cystine/glutamate transporter encoding Slc7a11 mRNA in testes of Lhb null mice. We observed that Slc7a11/SLC7A11 expression was initiated pre-pubertally and developmentally regulated in mouse testis. Immunolocalization studies confirmed that SLC7A11 was mostly expressed in Sertoli cells in testes of control and germ cell-deficient mice. Western blot analyses indicated that SLC7A11 was significantly reduced in testes of mutant mice lacking either LH or androgen receptor selectively in Sertoli cells. Genetic and pharmacological rescue of Lhb knockout mice restored the testicular expression of Slc7a11 comparable to that observed in controls. Additionally, Slc7a11 mRNA was significantly suppressed upon Sertoli cell/testicular damage induced in mice by cadmium treatment. Knockdown of Slc7a11 in vitro in TM4 Sertoli cells or treatment of mice with sulfasalazine, a SLC7A11 inhibitor caused a significant reduction in intracellular cysteine and glutathione levels but glutamate content remained unchanged as determined by metabolomic analysis. Knockdown of Slc7a11 resulted in compensatory upregulation of other glutamate transporters belonging to the Slc1a family presumably to maintain intracellular glutamate levels. Collectively, our studies identified that SLC7A11 is an LH/testosterone-regulated transporter that is required for cysteine/glutathione but not glutamate homeostasis in mouse Sertoli cells.

Perfluorooctane sulfonate induces suppression of testosterone biosynthesis via Sertoli cell-derived exosomal/miR-9-3p downregulating StAR expression in Leydig cells

Perfluorooctane sulfonate (PFOS) is associated with male reproductive disorder, but the related mechanisms are still unclear. In this study, we used in vivo and in vitro models to explore the role of Sertoli cell-derived exosomes (SC-Exo)/miR-9-3p/StAR signaling pathway on PFOS-induced suppression of testosterone biosynthesis. Forty male ICR mice were orally administrated PFOS (0.5-10 mg/kg/bw) for 4 weeks. Bodyweight, organ index, sperm count, reproductive hormones were evaluated. Primary Sertoli cells and Leydig cells were used to delineate the molecular mechanisms that mediate the effects of PFOS on testosterone biosynthesis. Our results demonstrated that PFOS dose-dependently induced a decrease in sperm count, low levels of testosterone, and damage in testicular interstitium morphology. In vitro models, PFOS significantly increased miR-9-3p levels in Sertoli cells and SC-Exo, accompanied by a decrease in testosterone secretion and StAR expression in Leydig cells when Leydig cells were exposed to SC-Exo. Meanwhile, inhibition of SC-Exo or miR-9-3p by their inhibitors significantly rescued PFOS-induced decreases in testosterone secretion and the mRNA and protein expression of the StAR gene in Leydig cells. In summary, the present study highlights the role of the SC-Exo/miR-9-3p/StAR signaling pathway in PFOS-induced suppression of testosterone biosynthesis, advancing our understanding of molecular mechanisms for PFOS-induced male reproductive disorders.

Effects of postnatal exposure to tetrabromobisphenol A on testis development in mice and early key events

Whether or not tetrabromobisphenol A (TBBPA) has reproductive developmental toxicity remains controversial. Here, we evaluated the effects of postnatal TBBPA exposure of dams (before weaning) and pups through drinking water (15, 150, 1500 ng/mL) on testis development in mice. On postnatal day (PND) 56, we found that TBBPA exerted little effects on testis weight, anogenital distance, sperm parameters, and the serum testosterone level, but resulted in dose-dependent reductions in the seminiferous tubule area coupled with decreased Sertoli cells and spermatogonia and the number of stage VII-VIII seminiferous tubules, and cytoskeleton damage in Sertoli cells, along with down-regulated expression of marker genes for Sertoli cells, spermatogonia and spermatocyte. Further study revealed that the reduced tubule area coupled decreased Sertoli cell and germ cell numbers and marker gene expression also occurred in TBBPA-treated testes on PND 7, along with reduced cell proliferation and disordered arrangement of Sertoli cell nuclei. On PND 15, most of these testicular alterations were still observed in TBBPA-treated males, and cytoskeleton damage in Sertoli cells became observable. All observations convincingly demonstrate that postnatal exposure to TBBPA disturbed testis development in early life and ultimately caused adverse outcomes in adult testes, and that cell proliferation inhibition, the reduction in the seminiferous tubule area coupled decreased Sertoli cell and germ cell numbers and marker gene expression, and cytoskeleton damage in Sertoli cells, are early events contributing to adverse outcomes in adult testes. Our study improves the understanding of reproductive developmental toxicity of TBBPA, highlighting its risk for human health.

Updates in Sertoli Cell-Mediated Signaling During Spermatogenesis and Advances in Restoring Sertoli Cell Function

Since their initial description by Enrico Sertoli in 1865, Sertoli cells have continued to enchant testis biologists. Testis size and germ cell carrying capacity are intimately tied to Sertoli cell number and function. One critical Sertoli cell function is signaling from Sertoli cells to germ cells as part of regulation of the spermatogenic cycle. Sertoli cell signals can be endocrine or paracrine in nature. Here we review recent advances in understanding the interplay of Sertoli cell endocrine and paracrine signals that regulate germ cell state. Although these findings have long-term implications for treating male infertility, recent breakthroughs in Sertoli cell transplantation have more immediate implications. We summarize the surge of advances in Sertoli cell ablation and transplantation, both of which are wedded to a growing understanding of the unique Sertoli cell niche in the transitional zone of the testis.

The Rete Testis: Development and Role in Testis Function

Abstract

The rete testis connects seminiferous tubules in which germ cells develop to the efferent ducts and the epididymis, where gametes mature and gain mobility. Several recent studies have thoroughly explored the morphogenesis of this structure in mice during embryonic and postnatal periods. A part of the rete testis has been shown to derive from the precursors of gonad somatic cells before sex determination. The other part forms from embryonal Sertoli cells of testis cords adjacent to the mesonephros. The transformation of Sertoli cells into rete testis cells is apparently not limited to the embryonic stage of development and continues during postnatal testis development. Recently, it was found that the rete testis participates in the formation and maintenance of specialized Sertoli cells in terminal segments of seminiferous tubules, transitional zones. Current views suggest that the transitional zones of the seminiferous tubules may represent a niche for spermatogonial stem cells, the site of the prolonged proliferation of Sertoli cells in the pubertal and postpubertal periods of testis development, and also could be a generator of spermatogenic waves. To sum up, the rete testis transports gametes from the testis to the epididymis, maintains pressure within seminiferous tubules, regulates the composition of the testicular fluid, and impacts the spermatogenic process itself.

Boosting effect of testosterone on GDNF expression in Sertoli cell line (TM4); comparison between TM3 cells-produced and exogenous testosterone

The Glial cell-derived neurotrophic factor (Gdnf) and testosterone induce the spermatogonial stem cells (SSCs) self-renewal and spermatogenesis, respectively. In present study the stimulating role of testosterone on Sertoli cells to produce Gdnf, and the possible effect of Gdnf on Gfrα1 and c-RET expressions were investigated. The TM4 cells (line Sertoli cells) were co-cultured with [0.1, 0.2 and 0.4 (ng/ml)] of exogenous and TM3 (line Leydig cells)-produced testosterones, and consequently the TM4-produced Gdnf concentration was evaluated. Next, the SSCs were co-cultured with the TM-4 derived media (endogenous Gdnf) and exogenous Gdnf [0.1, 0.2, and 0.4 ng/ml)]. The 0.1 and 0.2 ng/ml endogenous and 3 concentrations of exogenous testosterone up-regulated the Gdnf expression versus non-treated Sertoli cells. The TM4-produced and exogenous Gdnfs, in all concentrations, up-regulated the receptors expression. In conclusion, the testosterone, solely, stimulates the Gdnf synthesis and the Gdnf, individually, amplifies its receptor's expression at mRNA and protein levels.

Genetic Regulation of Avian Testis Development

As in other vertebrates, avian testes are the site of spermatogenesis and androgen production. The paired testes of birds differentiate during embryogenesis, first marked by the development of pre-Sertoli cells in the gonadal primordium and their condensation into seminiferous cords. Germ cells become enclosed in these cords and enter mitotic arrest, while steroidogenic Leydig cells subsequently differentiate around the cords. This review describes our current understanding of avian testis development at the cell biology and genetic levels. Most of this knowledge has come from studies on the chicken embryo, though other species are increasingly being examined. In chicken, testis development is governed by the Z-chromosome-linked DMRT1 gene, which directly or indirectly activates the male factors, HEMGN, SOX9 and AMH. Recent single cell RNA-seq has defined cell lineage specification during chicken testis development, while comparative studies point to deep conservation of avian testis formation. Lastly, we identify areas of future research on the genetics of avian testis development.

PAX2 + Mesenchymal Origin of Gonadal Supporting Cells Is Conserved in Birds

During embryonic gonadal development, the supporting cell lineage is the first cell type to differentiate, giving rise to Sertoli cells in the testis and pre-granulosa cells in the ovary. These cells are thought to direct other gonadal cell lineages down the testis or ovarian pathways, including the germline. Recent research has shown that, in contrast to mouse, chicken gonadal supporting cells derive from a PAX2/OSR1/DMRT1/WNT4 positive mesenchymal cell population. These cells colonize the undifferentiated genital ridge during early gonadogenesis, around the time that germ cells migrate into the gonad. During the process of somatic gonadal sex differentiation, PAX2 expression is down-regulated in embryonic chicken gonads just prior to up-regulation of testis- and ovary-specific markers and prior to germ cell differentiation. Most research on avian gonadal development has focused on the chicken model, and related species from the Galloanserae clade. There is a lack of knowledge on gonadal sex differentiation in other avian lineages. Comparative analysis in birds is required to fully understand the mechanisms of avian sex determination and gonadal differentiation. Here we report the first comparative molecular characterization of gonadal supporting cell differentiation in birds from each of the three main clades, Galloanserae (chicken and quail), Neoaves (zebra finch) and Palaeognathe (emu). Our analysis reveals conservation of PAX2+ expression and a mesenchymal origin of supporting cells in each clade. Moreover, down-regulation of PAX2 expression precisely defines the onset of gonadal sex differentiation in each species. Altogether, these results indicate that gonadal morphogenesis is conserved among the major bird clades.

Sperm proteins and cancer-testis antigens are released by the seminiferous tubules in mice and men

Sperm develop from puberty in the seminiferous tubules, inside the blood-testis barrier to prevent their recognition as "non-self" by the immune system, and it is widely assumed that human sperm-specific proteins cannot access the circulatory or immune systems. Sperm-specific proteins aberrantly expressed in cancer, known as cancer-testis antigens (CTAs), are often pursued as cancer biomarkers and therapeutic targets based on the assumption they are neoantigens absent from the circulation in healthy men. Here, we identify a wide range of germ cell-derived and sperm-specific proteins, including multiple CTAs, that are selectively deposited by the Sertoli cells of the adult mouse and human seminiferous tubules into testicular interstitial fluid (TIF) that is "outside" the blood-testis barrier. From TIF, the proteins can access the circulatory- and immune systems. Disruption of spermatogenesis decreases the abundance of these proteins in mouse TIF, and a sperm-specific CTA is significantly decreased in TIF from infertile men, suggesting that exposure of certain CTAs to the immune system could depend on fertility status. The results provide a rationale for the development of blood-based tests useful in the management of male infertility and indicate CTA candidates for cancer immunotherapy and biomarker development that could show sex-specific and male-fertility-related responses.

Sertoli cells as key drivers of testis function

Sertoli cells are the orchestrators of spermatogenesis; they support fetal germ cell commitment to the male pathway and are essential for germ cell development, from maintenance of the spermatogonial stem cell niche and spermatogonial populations, through meiosis and spermiogeneis and to the final release of mature spermatids during spermiation. However, Sertoli cells are also emerging as key regulators of other testis somatic cells, including supporting peritubular myoid cell development in the pre-pubertal testis and supporting the function of the testicular vasculature and in contributing to testicular immune privilege. Sertoli cells also have a major role in regulating androgen production within the testis, by specifying interstitial cells to a steroidogenic fate, contributing to androgen production in the fetal testis, and supporting fetal and adult Leydig cell development and function. Here, we provide an overview of the specific roles for Sertoli cells in the testis and highlight how these cells are key drivers of testicular sperm output, and of adult testis size and optimal function of other testicular somatic cells, including the steroidogenic Leydig cells.

Overexpression of p75NTR in Human Seminoma: A New Biomarker?

Several studies have demonstrated that the p75NTR low-affinity receptor of Nerve Growth Factor (NGF), is produced in abnormally large amounts in several human cancer types. However, the role of p75NTR varies substantially depending on cell context, so that a dual role of this receptor protein in tumor cell survival and invasion, as well as cell death, has been supported in recent studies. Herein we explored for the first time the expression of p75NTR in human specimens (nr = 40) from testicular germ cell tumors (TGCTs), mostly seminomas. Nuclear overexpression of p75NTR was detected by immunohistochemistry in seminoma tissue as compared to normal tissue, whereas neither NGF nor its high-affinity TrkA receptor was detected. An increased nuclear staining of phospho-JNK, belonging to the p75NTR signaling pathway and its pro-apoptotic target gene, p53, was concomitantly observed. Interestingly, our analysis revealed that decreased expression frequency of p75NTR, p-JNK and p53 was related to staging progression, thus suggesting that p75NTR may represent a specific marker for seminoma and staging in TGCTs.

TCF21+ mesenchymal cells contribute to testis somatic cell development, homeostasis, and regeneration in mice

Testicular development and function rely on interactions between somatic cells and the germline, but similar to other organs, regenerative capacity declines in aging and disease. Whether the adult testis maintains a reserve progenitor population remains uncertain. Here, we characterize a recently identified mouse testis interstitial population expressing the transcription factor Tcf21. We found that TCF21lin cells are bipotential somatic progenitors present in fetal testis and ovary, maintain adult testis homeostasis during aging, and act as potential reserve somatic progenitors following injury. In vitro, TCF21lin cells are multipotent mesenchymal progenitors which form multiple somatic lineages including Leydig and myoid cells. Additionally, TCF21+ cells resemble resident fibroblast populations reported in other organs having roles in tissue homeostasis, fibrosis, and regeneration. Our findings reveal that the testis, like other organs, maintains multipotent mesenchymal progenitors that can be potentially leveraged in development of future therapies for hypoandrogenism and/or infertility.

Sertoli cell-derived exosome-mediated transfer of miR-145-5p inhibits Leydig cell steroidogenesis by targeting steroidogenic factor 1

In the mammalian testis, two distinct populations of Sertoli cells (SCs), the immature SCs (ISCs) and adult SCs (ASCs), play significant roles in regulating the development and function of Leydig cells. However, the effect of different SC types on the function of Leydig cells is poorly understood. Here, our study showed that miR-145-5p expression was significantly different in SCs at different stages, with the highest expression observed in ISCs. Exosomes mediate the transfer of miR-145-5p from ISCs to Leydig cells. Overexpression of miR-145-5p in Leydig cells significantly downregulated steroidogenic gene expression and inhibited testosterone synthesis. Additionally, miR-145-5p functioned by directly targeted steroidogenic factor-1 (Sf-1) and downregulated the expression of SF-1, which further downregulated the expression of steroidogenic genes, induced accumulation of lipid droplets, and eventually suppressed testosterone production. These findings demonstrate that SC-derived miR-145-5p plays a significant role in regulating the functions of Leydig cells and may therefore serve as a diagnostic biomarker for male hypogonadism developmental abnormalities during puberty.

Anatomy, Endocrine Regulation, and Embryonic Development of the Rete Testis

Reproduction in males requires the transfer of spermatozoa from testis tubules via the rete system to the efferent ductules, epididymis, and vas deferens. The rete therefore forms an essential bridging system between the testis and excurrent ducts. Yet the embryonic origin and molecular regulation of rete testis development is poorly understood. This review examines the anatomy, endocrine control, and development of the mammalian rete testis, focusing on recent findings on its molecular regulation, identifying gaps in our knowledge, and identifying areas for future research. The rete testis develops in close association with Sertoli cells of the seminiferous cords, although unique molecular markers are sparce. Most recently, modern molecular approaches such as global RNA-seq have revealed the transcriptional signature of rete cell precursors, pointing to at least a partial common origin with Sertoli cells. In the mouse, genes involved in Sertoli cell development or maintenance, such as Sox9, Wt1, Sf1, and Dmrt1, are also expressed in cells of the rete system. Rete progenitor cells also express unique markers, such as Pax8, E-cadherin, and keratin 8. These must directly or indirectly regulate the physical joining of testis tubules to the efferent duct system and confer other physiological functions of the rete. The application of technologies such as single-cell RNA-seq will clarify the origin and developmental trajectory of this essential component of the male reproductive tract.

Age-related changes in human Leydig cell status

STUDY QUESTION

What are the consequences of ageing on human Leydig cell number and hormonal function?

SUMMARY ANSWER

Leydig cell number significantly decreases in parallel with INSL3 expression and Sertoli cell number in aged men, yet the in vitro Leydig cell androgenic potential does not appear to be compromised by advancing age.

WHAT IS KNOWN ALREADY

There is extensive evidence that ageing is accompanied by decline in serum testosterone levels, a general involution of testis morphology and reduced spermatogenic function. A few studies have previously addressed single features of the human aged testis phenotype one at a time, but mostly in tissue from patients with prostate cancer.

STUDY DESIGN, SIZE, DURATION

This comprehensive study examined testis morphology, Leydig cell and Sertoli cell number, steroidogenic enzyme expression, INSL3 expression and androgen secretion by testicular fragments in vitro. The majority of these endpoints were concomitantly evaluated in the same individuals that all displayed complete spermatogenesis.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Testis biopsies were obtained from 15 heart beating organ donors (age range: 19-85 years) and 24 patients (age range: 19-45 years) with complete spermatogenesis. Leydig cells and Sertoli cells were counted following identification by immunohistochemical staining of specific cell markers. Gene expression analysis of INSL3 and steroidogenic enzymes was carried out by qRT-PCR. Secretion of 17-OH-progesterone, dehydroepiandrosterone, androstenedione and testosterone by in vitro cultured testis fragments was measured by LC-MS/MS. All endpoints were analysed in relation to age.

MAIN RESULTS AND THE ROLE OF CHANCE

Increasing age was negatively associated with Leydig cell number (R = -0.49; P < 0.01) and concomitantly with the Sertoli cell population size (R= -0.55; P < 0.001). A positive correlation (R = 0.57; P < 0.001) between Sertoli cell and Leydig cell numbers was detected at all ages, indicating that somatic cell attrition is a relevant cellular manifestation of human testis status during ageing. INSL3 mRNA expression (R= -0.52; P < 0.05) changed in parallel with Leydig cell number and age. Importantly, steroidogenic capacity of Leydig cells in cultured testis tissue fragments from young and old donors did not differ. Consistently, age did not influence the mRNA expression of steroidogenic enzymes. The described changes in Leydig cell phenotype with ageing are strengthened by the fact that the different age-related effects were mostly evaluated in tissue from the same men.

LIMITATIONS, REASONS FOR CAUTION

In vitro androgen production analysis could not be correlated with in vivo hormone values of the organ donors. In addition, the number of samples was relatively small and there was scarce information about the concomitant presence of potential confounding variables.

WIDER IMPLICATIONS OF THE FINDINGS

This study provides a novel insight into the effects of ageing on human Leydig cell status. The correlation between Leydig cell number and Sertoli cell number at any age implies a connection between these two cell types, which may be of particular relevance in understanding male reproductive disorders in the elderly. However aged Leydig cells do not lose their in vitro ability to produce androgens. Our data have implications in the understanding of the physiological role and regulation of intratesticular sex steroid levels during the complex process of ageing in humans.

STUDY FUNDING/COMPETING INTEREST(S)

This work was supported by grants from Prin 2010 and 2017. The authors have no conflicts of interest.

TRIAL REGISTRATION NUMBER

N/A.

Heat stress response of somatic cells in the testis

The testis is a temperature-sensitive organ that needs to be maintained 2-7 °C below core body temperature to ensure the production of normal sperm. Failure to maintain testicular temperature in mammals impairs spermatogenesis and leads to low sperm counts, poor sperm motility and abnormal sperm morphology in the ejaculate. This review discusses the recent knowledge on the response of testicular somatic cells to heat stress and, specifically, regarding the relevant contributions of heat, germ cell depletion and inflammatory reactions on the functions of Sertoli and Leydig cells. It also outlines mechanisms of testicular thermoregulation, as well as the thermogenic factors that impact testicular function.

Prenatal exposure to hexavalent chromium disrupts testicular steroidogenic pathway in peripubertal F1 rats

We have reported sub-fertility in F1 progeny rats with gestational exposure to hexavalent chromium [Cr(VI)], which had disrupted Sertoli cell (SC) structure and function, and decreased testosterone (T). However, the underlying mechanism for reduced T remains to be understood. We tested the hypothesis "transient prenatal exposure to Cr(VI) affects testicular steroidogenesis by altering hormone receptors and steroidogenic enzyme proteins in Leydig cells (LCs)." Pregnant Wistar rats were given drinking water containing 50, 100, and 200 mg/L potassium dichromate during gestational days 9-14, encompassing fetal differentiation window of the testis from the bipotential gonad. F1 male rats were euthanized on postnatal day 60 (peripubertal rats with adult-type LCs alone). Results showed that prenatal exposure to Cr(VI): (i) increased accumulation of Cr(III) in the testis of F1 rats; (ii) increased serum levels of luteinizing and follicle stimulating hormones (LH and FSH), and 17β estradiol, and decreased prolactin and T; (iii) decreased steroidogenic acute regulatory protein, cytochrome P450 11A1, cytochrome P450 17A1, 3β- and 17β-hydroxysteroid dehydrogenases, cytochrome P450 aromatase and 5α reductase proteins, (iv) decreased specific activities of 3β and 17β hydroxysteroid dehydrogenases; (v) decreased receptors of LH, androgen and estrogen in LCs; (vi) decreased 5α reductase and receptor proteins of FSH, androgen, and estrogen in SCs. The current study concludes that prenatal exposure to Cr(VI) disrupts testicular steroidogenesis in F1 progeny by repressing hormone receptors and key proteins of the steroidogenic pathway in LCs and SCs.

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.

Gonadal Sex Differentiation: Supporting Versus Steroidogenic Cell Lineage Specification in Mammals and Birds

The gonads of vertebrate embryos are unique among organs because they have a developmental choice; ovary or testis formation. Given the importance of proper gonad formation for sexual development and reproduction, considerable research has been conducted over the years to elucidate the genetic and cellular mechanisms of gonad formation and sexual differentiation. While the molecular trigger for gonadal sex differentiation into ovary of testis can vary among vertebrates, from egg temperature to sex-chromosome linked master genes, the downstream molecular pathways are largely conserved. The cell biology of gonadal formation and differentiation has long thought to also be conserved. However, recent discoveries point to divergent mechanisms of gonad formation, at least among birds and mammals. In this mini-review, we provide an overview of cell lineage allocation during gonadal sex differentiation in the mouse model, focusing on the key supporting and steroidogenic cells and drawing on recent insights provided by single cell RNA-sequencing. We compare this data with emerging information in the chicken model. We highlight surprising differences in cell lineage specification between species and identify gaps in our current understanding of the cell biology underlying gonadogenesis.

Testis and blood-testis barrier in Covid-19 infestation: role of angiotensin-converting enzyme 2 in male infertility

Severe acute respiratory syndrome coronavirus 2 (SARS- CoV-2) that causes COVID-19 infections penetrates body cells by binding to angiotensin-converting enzyme-2 (ACE2) receptors. Evidence shows that SARS-CoV-2 can also affect the urogenital tract. Hence, it should be given serious attention when treating COVID-19-infected male patients of reproductive age group. Other viruses like HIV, mumps, papilloma and Epstein-Barr can induce viral orchitis, germ cell apoptosis, inflammation and germ cell destruction with attending infertility and tumors. The blood-testis barrier (BTB) and blood-epididymis barrier (BEB) are essential physical barricades in the male reproductive tract located between the blood vessel and seminiferous tubules in the testes. Despite the significant role of these barriers in male reproductive function, studies have shown that a wide range of viruses can still penetrate the barriers and induce testicular dysfunctions. Therefore, this mini-review highlights the role of ACE2 receptors in promoting SARS-CoV-2-induced blood-testis/epididymal barrier infiltration and testicular dysfunction.

Fertility Preservation in Childhood Cancer: Endocrine Activity in Prepubertal Human Testis Xenografts Exposed to a Pubertal Hormone Environment

Simple Summary

Substantial strides have been made in treating childhood cancers; however, as a result of chemotherapy and radiotherapy, young males experience long-term side effects, including impaired fertility. Whilst prepubertal testicular tissue can be cryopreserved prior to gonadotoxic treatments, it remains to be determined how to generate mature gametes from the immature human testis tissue. Development of immature germ cells into sperm is a complex process, which is supported by mature Sertoli cells and testosterone produced from Leydig cells. We used an established testicular xenotransplantation model to investigate the effect of puberty hormones, known as gonadotrophins, on functional maturation of the spermatogonial stem cell (SSC) niche. Limited testosterone production and partial maturation of Sertoli cells occurred in prepubertal testis grafts, suggesting that longer periods of grafting and/or identification of additional factors are required to develop testicular transplantation as a model for fertility preservation in male survivors of childhood cancer.

Abstract

Survivors of childhood cancer are at risk for long-term treatment-induced health sequelae, including gonadotoxicity and iatrogenic infertility. At present, for prepubertal boys there are no viable clinical options to preserve future reproductive potential. We investigated the effect of a pubertal induction regimen with gonadotrophins on prepubertal human testis xenograft development. Human testis tissue was obtained from patients with cancer and non-malignant haematological disorders (n = 6; aged 1–14 years) who underwent testis tissue cryopreservation for fertility preservation. Fresh and frozen-thawed testis fragments were transplanted subcutaneously or intratesticularly into immunocompromised mice. Graft-bearing mice received injections of vehicle or exogenous gonadotrophins, human chorionic gonadotrophin (hCG, 20 IU), and follicle-stimulating hormone (FSH, 12.5 IU) three times a week for 12 weeks. The gross morphology of vehicle and gonadotrophin-exposed grafts was similar for both transplantation sites. Exposure of prepubertal human testis tissue xenografts to exogenous gonadotrophins resulted in limited endocrine function of grafts, as demonstrated by the occasional expression of the steroidogenic cholesterol side-chain cleavage enzyme (CYP11A1). Plasma testosterone concentrations (0.13 vs. 0.25 ng/mL; p = 0.594) and seminal vesicle weights (10.02 vs. 13.93 mg; p = 0.431) in gonadotrophin-exposed recipient mice were comparable to vehicle-exposed controls. Regardless of the transplantation site and treatment, initiation and maintenance of androgen receptor (AR) expression were observed in Sertoli cells, indicating commitment towards a more differentiated status. However, neither exogenous gonadotrophins (in castrated host mice) nor endogenous testosterone (in intact host mice) were sufficient to repress the expression of markers associated with immature Sertoli cells, such as anti-Müllerian hormone (AMH) and Ki67, or to induce the redistribution of junctional proteins (connexin 43, CX43; claudin 11, CLDN11) to areas adjacent to the basement membrane. Spermatogonia did not progress developmentally but remained the most advanced germ cell type in testis xenografts. Overall, these findings demonstrate that exogenous gonadotrophins promote partial activation and maturation of the somatic environment in prepubertal testis xenografts. However, alternative hormone regimens or additional factors for pubertal induction are required to complete the functional maturation of the spermatogonial stem cell (SSC) niche.

E4 Transcription Factor 1 (E4F1) Regulates Sertoli Cell Proliferation and Fertility in Mice

Simple Summary

Male fertility relies on the generation of functional sperm in seminiferous tubules of the testis. In mammals, Sertoli cells are the only somatic cells that directly interact with spermatogenic cells. Compelling evidences suggest that the number of Sertoli cells determines testis size and sperm output, however, molecular mechanisms regulating Sertoli cell proliferation and maturation are not well-understood. Using a Sertoli cell specific loss-of-function approach, here we showed that transcription factor E4F1 played an important role in murine Sertoli cell proliferation. Compared with their littermate control, E4f1 conditional knockout male mice sired a significantly low number of pups. E4f1 deletion resulted in reduced Sertoli cell number and testis size. Further analyses revealed that E4f1 deletion affected Sertoli cell proliferation in the neonatal testis and caused an increase in apoptosis of spermatogenic cells without affecting normal development of spermatogonia, meiotic and post-meiotic germ cells. These findings have shed new light on molecular controlling of spermatogenesis in mice and a similar mechanism likely exists in other animals.

Abstract

In the mammalian testes, Sertoli cells are the only somatic cells in the seminiferous tubules that provide structural, nutritional and regulatory support for developing spermatogenic cells. Sertoli cells only proliferate during the fetal and neonatal periods and enter a quiescent state after puberty. Functional evidences suggest that the size of Sertoli cell population determines sperm production and fertility. However, factors that direct Sertoli cell proliferation and maturation are not fully understood. Transcription factor E4F1 is a multifunctional protein that serves essential roles in cell fate decisions and because it interacts with pRB, a master regulator of Sertoli cell function, we hypothesized that E4F1 may have a functional role in Sertoli cells. E4f1 mRNA was present in murine testis and immunohistochemical staining confirmed that E4F1 was enriched in mature Sertoli cells. We generated a conditional knockout mouse model using Amh-cre and E4f1^flox/flox lines to study E4F1 fucntion in Sertoli cells and the results showed that E4f1 deletion caused a significant reduction in testis size and fertility. Further analyses revealed that meiosis progression and spermiogenesis were normal, however, Sertoli cell proliferation was impaired and germ cell apoptosis was elevated in the testis of E4f1 conditional knockout mice. On the basis of these findings, we concluded that E4F1 was expressed in murine Sertoli cells and served important functions in regulating Sertoli cell proliferation and fertility.

Function and transcriptomic dynamics of Sertoli cells during prospermatogonia development in mouse testis

In mammals, spermatogonial stem cells (SSCs) arise from a subpopulation of prospermatogonia during neonatal testis development. Currently, molecular mechanisms directing the prospermatogonia to spermatogonial transition are not well understood. In the study, we found that reducing Sertoli cells number by Amh-cre mediated expression of diphtheria toxin (AC;DTA) in murine fetal testis caused defects in prospermatogonia fate decisions. Histological and immunohistochemical analyses confirmed that Sertoli cells loss occurred at embryonic day (E) 14.5. Prospermatogonia maintained mitotic arrest at E16.5 in control animals, in contrast, 13.4% of germ cells in AC;DTA testis reentered cell cycle and expressed gH2A.X and Sycp3, indicating the commitment to meiosis. After birth, the number of prospermatogonia resuming mitosis was significantly affected by Sertoli cell loss in AC;DTA animals. Lastly, we isolated primary Sertoli cells using a Sertoli cell specific GFP reporter line and showed dynamics of Sertoli cell transcriptomes at E12.5, E13.5, E16.5 and P1. By further analysis, we revealed unique gene expression patterns and potential candidate genes regulating Sertoli cell development and likely mediating interactions between Sertoli cells, prospermatogonia and other testicular cells.

Applying Single-Cell Analysis to Gonadogenesis and DSDs (Disorders/Differences of Sex Development)

The gonads are unique among the body's organs in having a developmental choice: testis or ovary formation. Gonadal sex differentiation involves common progenitor cells that form either Sertoli and Leydig cells in the testis or granulosa and thecal cells in the ovary. Single-cell analysis is now shedding new light on how these cell lineages are specified and how they interact with the germline. Such studies are also providing new information on gonadal maturation, ageing and the somatic-germ cell niche. Furthermore, they have the potential to improve our understanding and diagnosis of Disorders/Differences of Sex Development (DSDs). DSDs occur when chromosomal, gonadal or anatomical sex are atypical. Despite major advances in recent years, most cases of DSD still cannot be explained at the molecular level. This presents a major pediatric concern. The emergence of single-cell genomics and transcriptomics now presents a novel avenue for DSD analysis, for both diagnosis and for understanding the molecular genetic etiology. Such -omics datasets have the potential to enhance our understanding of the cellular origins and pathogenesis of DSDs, as well as infertility and gonadal diseases such as cancer.

Fetal Leydig cells in buffalo testis: Light and electron microscopic study

The present study was conducted on testis of 20 buffalo fetuses ranging from 2.5 cm to 20 cm curved crown rump length (CVRL). The tissues were processed for light and transmission electron microscopic study. The intertubular tissue was filled with primitive mesenchymal cells, developing Leydig cells and blood vessels. At 7.5 cm CVRL, some of the interstitial mesenchymal cells started developing into foetal Leydig cells and were androgen positive. These cells were characterized by their polygonal shape, eosinophilic cytoplasm and darkly stained spherical nucleus with prominent nucleoli at 9.5 cm CVRL. At 15.5 cm CVRL, the fetal Leydig cells were present in groups around the interstitial blood vessels, which increased in number and size at 20 cm CVRL and decreased afterwards. By TEM, three types of Leydig cells were observed at 14.5 cm CVRL as stem Leydig cells (Leydig cell A), progenitor Leydig cells (Leydig cell B) and immature Leydig cells (Leydig cell C). Leydig cell A had elongated nucleus with a very thin rim of cytoplasm. Leydig cell B had oval nucleus with comparatively larger amount of cytoplasm. Leydig cell C had adult Leydig cell like features and had round to oval nucleus with lager amount of cytoplasm. The cytoplasm of these cells contained mitochondria with elongated cristae, Golgi apparatus and very few lipid inclusions. The number and size of Leydig cells increased during early prenatal life.

Formation of organotypic testicular organoids in microwell culture†

Three-dimensional (3D) organoids can serve as an in vitro platform to study cell-cell interactions, tissue development, and toxicology. Development of organoids with tissue architecture similar to testis in vivo has remained a challenge. Here, we present a microwell aggregation approach to establish multicellular 3D testicular organoids from pig, mouse, macaque, and human. The organoids consist of germ cells, Sertoli cells, Leydig cells, and peritubular myoid cells forming a distinct seminiferous epithelium and interstitial compartment separated by a basement membrane. Sertoli cells in the organoids express tight junction proteins claudin 11 and occludin. Germ cells in organoids showed an attenuated response to retinoic acid compared to germ cells in 2D culture indicating that the tissue architecture of the organoid modulates response to retinoic acid similar to in vivo. Germ cells maintaining physiological cell-cell interactions in organoids also had lower levels of autophagy indicating lower levels of cellular stress. When organoids were treated with mono(2-ethylhexyl) phthalate (MEHP), levels of germ cell autophagy increased in a dose-dependent manner, indicating the utility of the organoids for toxicity screening. Ablation of primary cilia on testicular somatic cells inhibited the formation of organoids demonstrating an application to screen for factors affecting testicular morphogenesis. Organoids can be generated from cryopreserved testis cells and preserved by vitrification. Taken together, the testicular organoid system recapitulates the 3D organization of the mammalian testis and provides an in vitro platform for studying germ cell function, testicular development, and drug toxicity in a cellular context representative of the testis in vivo.