Adult sertoli cells are not terminally differentiated in the Djungarian hamster: effect of FSH on proliferation and junction protein organization

A dynamic transcriptional cell atlas of testes development after birth in Hu sheep

BACKGROUND

Testes development is a fundamental process in sexual development and reproduction. The testes undergo dramatic structural changes during development, including the proliferation and differentiation of somatic cells such as Sertoli cells, Leydig cells, and myoid cells, as well as the maturation of spermatogonia. However, little is known about the onset of spermatogenesis and cell proliferation and maturation in the spermatogonial niche in large animals.

RESULTS

We used single-cell RNA sequencing (scRNA-seq) to profile nearly 100,000 cells from Hu sheep testes across seven developmental stages (birth, prepuberty, puberty, and adulthood). We constructed single-cell transcriptomic atlases and identified distinct spermatogonial subtypes, revealing dynamic gene expression patterns during spermatogenesis. Notably, we observed that two distinct Sertoli cell states converge into a mature population during puberty. Additionally, we identified a common prepubertal progenitor for Leydig and myoid cells, with Leydig cells transitioning through progenitor and immature stages before reaching maturity.

CONCLUSIONS

Our study provides a comprehensive atlas of Hu sheep testes development, revealing key insights into the dynamic changes and regulatory mechanisms of spermatogenesis and somatic cell maturation from birth to adulthood. These findings offer new perspectives on testicular development in large mammals and support future research on reproductive biology and breeding strategies.

The Terminal Segment of the Seminiferous Tubule: The Current Discovery of Its Morphofunctional Importance in Mammals

The morphophysiology of intratesticular sperm pathways in mammals, including humans, is poorly understood. The seminiferous tubule is continuous with the straight tubule; however, its final portion-the terminal segment (TS)-has a different tissue composition. This paper reviews the most important histological results from mammal studies from the last decades of the 20th century, including the different nomenclatures given to the TS. The TS presents a loss of spermatogenesis and is lined mainly with modified Sertoli cells. There is no unanimity among authors when it comes to naming and defining TS. In the last ten years, studies on rats and mice have highlighted the importance of this testicular zone, proposing that there is a high proliferation of modified Sertoli cells with an undifferentiated cellular profile associated with stem spermatogonia. In hamsters, an immunohistochemical study showed the existence of heterogeneity between these cells, and the surrounding interstitium presents numerous Leydig cells that are ultrastructurally different from those of the rest of the testis rest. In conclusion, we have only just begun to understand the tissue biology of TS. Emerging research is very promising; it can potentially modify our current knowledge of testicular biology and be very useful in promoting the advancement of male fertility restoration therapies in andrology.

Thyroxine regulates pig Sertoli cell line proliferation and maturation through the IKK/NFκB and p38 MAPK signaling pathways

The aim of this study was to investigate the signaling pathways involved in the proliferation and differentiation of pig Sertoli cells (SCs) mediated by thyroid hormone (T3) to provide a theoretical and practical basis for enhancing pig semen production. The effects of different concentrations of T3 on the proliferation of pig SCs were evaluated using the CCK8 assay. The impact of T3 on the proliferation and differentiation of pig SCs was further examined using RNA-seq, qPCR, and Western Blotting techniques. Additionally, the involvement of the p38 MAPK and NFκB pathways in mediating the effects of T3 on SCs proliferation and differentiation was investigated. Our findings revealed a strong correlation between the dosage of T3 and the inhibition of pig SCs proliferation and promotion of maturation. T3 regulated the activation state of the NFκB signaling pathway by upregulating IKKα, downregulating IKKβ, and promoting IκB phosphorylation. Furthermore, T3 facilitated SCs maturation by upregulating AR and FSHR expression while downregulating KRT-18. In conclusion, T3 inhibits pig SCs proliferation and promote pig SCs maturation through the IKK/NFκB and p38 MAPK pathways. These findings provide valuable insights into the mechanisms by which T3 influences the proliferation and maturation of pig SCs.

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.

Connexin43 represents an important regulator for Sertoli cell morphology, Sertoli cell nuclear ultrastructure, and Sertoli cell maturation

The Sertoli cell (SC)-specific knockout (KO) of connexin43 (Cx43) was shown to be an effector of multiple histological changes in tubular morphology, resulting in germ cell loss through to a Sertoli-cell-only (SCO) phenotype and vacuolated seminiferous tubules containing SC-clusters. Our present study focused on the effects of Cx43 loss on SC ultrastructure. Using serial block-face scanning electron microscopy (SBF-SEM), we could confirm previous results. Ultrastructural analysis of Sertoli cell nuclei (SCN) revealed that these appear in clusters with a phenotype resembling immature/proliferating SCs in KO mice. Surprisingly, SCs of fertile wild type (WT) mice contained SCN with a predominantly smooth surface instead of deep indentations of the nuclear envelope, suggesting that these indentations do not correlate with germ cell support or spermatogenesis. SBF-SEM facilitated the precise examination of clustered SCs. Even if the exact maturation state of mutant SCs remained unclear, our study could detect indications of cellular senescence as well as immaturity, emphasising that Cx43 affects SC maturation. Moreover, Sudan III staining and transmission electron microscopy (TEM) demonstrated an altered lipid metabolism in SCs of Cx43 deficient mice.

Follicle-stimulating hormone regulates Notch signalling in the seminiferous epithelium of continuously and seasonally breeding rodents

CONTEXT

Juxtacrine (contact-dependent) communication between the cells of seminiferous epithelium mediated by Notch signalling is of importance for the proper course of spermatogenesis in mammals.

AIMS

The present study was designed to evaluate the role of follicle-stimulating hormone (FSH) in the regulation of Notch signalling in rodent seminiferous epithelium.

METHODS

We explored the effects (1) of pharmacological inhibition of the hypothalamus-pituitary-gonadal (HPG) axis and FSH replacement in pubertal rats, and (2) of photoinhibition of HPG axis followed by FSH substitution in seasonally breeding rodents, bank voles, on Notch pathway activity. Experiments on isolated rat Sertoli cells exposed to FSH were also performed. Gene and protein expressions of Notch pathway components were analysed using RT-qPCR, western blot and immunohistochemistry/immunofluorescence.

KEY RESULTS

Distribution patterns of Notch pathway proteins in bank vole and rat seminiferous epithelium were comparable; however, levels of activated Notch1 and Notch3, hairy/enhancer of split 1 (HES1) and hairy/enhancer of split-related with YRPW motif 1 (HEY1) in bank voles were dependent on the length of the photoperiod. In response to FSH similar changes in these proteins were found in both species, indicating that FSH is a negative regulator of Notch pathway activity in seminiferous epithelium.

CONCLUSIONS

Our results support a common mechanism of FSH action on Notch pathway during onset and recrudescence of spermatogenesis in rodents.

IMPLICATIONS

Interaction between FSH signalling and Notch pathway in Sertoli cells may be involved in spermatogenic activity changes of the testes occurring during puberty or photoperiod shift in continuously and seasonally breeding rodents, respectively.

Proliferation, apoptosis, and number of Sertoli cells in the Syrian hamster during recrudescence after exposure to short photoperiod†‡

The Sertoli cell (Sc) has been described as a quiescent cell once the animal has reached sexual maturity. Syrian hamster is an animal that displays testicular regression due to short photoperiod, during which process germ cells and Sc are removed through apoptosis. The aim of this work was to investigate histochemically whether the spontaneous testicular recrudescence processes after exposure to a short photoperiod lead to an increase in Sc proliferative activity in order to restore the normal population. Three spontaneous recrudescence groups were established: initial (IR), advanced (AR), and total (TR) recrudescence, which were compared with animal undergoing the regression process (mild: MRg, strong: SRg, and total: TRg) and animals in long photoperiod (Controls). Histological sections were submitted to histochemical techniques for detecting apoptotic and proliferative Sc with bright-field and fluorescence microscopy. For each group, the proliferative Sc index (PScI) and apoptotic Sc index (AScI), and the total number of Sc were obtained. The results revealed the existence of Vimentin+/TUNEL+ as well as Vimentin+/PCNA+ cells. The PScI was significantly higher in TRg and IR than in the other groups. The AScI was only significantly higher in MRg and SRg with respect to the other groups. The total number of Sc increased among TRg, IR, and AR, reaching values similar to those of the Controls. In conclusion, the increase in Sc proliferation from final regression and recrudescence, accompanied by a similar rate of apoptosis to the Control group, is the cause of the restoration of the Sc population during spontaneous recrudescence.

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.

Structural and Functional Characterization of a Testicular Long Non-coding RNA (4930463O16Rik) Identified in the Meiotic Arrest of the Mouse Topaz1 -/- Testes

Spermatogenesis involves coordinated processes, including meiosis, to produce functional gametes. We previously reported Topaz1 as a germ cell-specific gene highly conserved in vertebrates. Topaz1 knockout males are sterile with testes that lack haploid germ cells because of meiotic arrest after prophase I. To better characterize Topaz1^–/– testes, we used RNA-sequencing analyses at two different developmental stages (P16 and P18). The absence of TOPAZ1 disturbed the expression of genes involved in microtubule and/or cilium mobility, biological processes required for spermatogenesis. Moreover, a quarter of P18 dysregulated genes are long non-coding RNAs (lncRNAs), and three of them are testis-specific and located in spermatocytes, their expression starting between P11 and P15. The suppression of one of them, 4939463O16Rik, did not alter fertility although sperm parameters were disturbed and sperm concentration fell. The transcriptome of P18-4939463O16Rik^–/– testes was altered and the molecular pathways affected included microtubule-based processes, the regulation of cilium movement and spermatogenesis. The absence of TOPAZ1 protein or 4930463O16Rik produced the same enrichment clusters in mutant testes despite a contrasted phenotype on male fertility. In conclusion, although Topaz1 is essential for the meiosis in male germ cells and regulate the expression of numerous lncRNAs, these studies have identified a Topaz1 regulated lncRNA (4930463O16Rik) that is key for both sperm production and motility.

Immunodistribution of RFamide-related peptide-3 (RFRP-3) during the seminiferous epithelium cycle in a desert rodent Psammomys obesus

The Sand rat, Psammomys obesus, living northwest of the Algerian Sahara, presents a seasonal reproductive cycle. The purposes of this study were firstly to determine the stages of seminiferous epithelium cycle (SEC) by histological and morphometric analysis and secondly to investigate, for the first time, the testicular expression of RFamide-related peptide-3 (RFRP-3) during the SEC by immunohistochemistry. The results showed that the SEC consists of 14 stages according to the tubular morphology method. RFRP-3 was observed in both testicular compartments: the tubular and the interstitial. Leydig cells exhibited the highest RFRP-3 signal (30.73 % ± 4.80) compared to Sertoli cells (13-15 %). In the germline, RFRP-3 was detected during the late prophase I of meiosis in late pachytene, diplotene and metaphasic spermatocytes I. In addition, only round and triangular spermatids were positive during spermiogenesis. Referring to the SEC, it was found that the increased staining of RFRP-3 in spermatocytes I coincided with late pachytene of XI and XII stages (16.90 % ± 0.69 and 16.61 % ± 0.28, respectively). In spermatids, the labeling decreased in the triangular ones at stage IX (8.04 % ± 0.42). These results suggest the involvement of RFRP-3 in the control of SEC in P. obesus.

Discrete Hedgehog Factor Expression and Action in the Developing Phallus

Hypospadias is a failure of urethral closure within the penis occurring in 1 in 125 boys at birth and is increasing in frequency. While paracrine hedgehog signalling is implicated in the process of urethral closure, how these factors act on a tissue level to execute closure itself is unknown. This study aimed to understand the role of different hedgehog signalling members in urethral closure. The tammar wallaby (Macropus eugenii) provides a unique system to understand urethral closure as it allows direct treatment of developing offspring because mothers give birth to young before urethral closure begins. Wallaby pouch young were treated with vehicle or oestradiol (known to induce hypospadias in males) and samples subjected to RNAseq for differential expression and gene ontology analyses. Localisation of Sonic Hedgehog (SHH) and Indian Hedgehog (IHH), as well as the transcription factor SOX9, were assessed in normal phallus tissue using immunofluorescence. Normal tissue culture explants were treated with SHH or IHH and analysed for AR, ESR1, PTCH1, GLI2, SOX9, IHH and SHH expression by qPCR. Gene ontology analysis showed enrichment for bone differentiation terms in male samples compared with either female samples or males treated with oestradiol. Expression of SHH and IHH localised to specific tissue areas during development, akin to their compartmentalised expression in developing bone. Treatment of phallus explants with SHH or IHH induced factor-specific expression of genes associated with bone differentiation. This reveals a potential developmental interaction involved in urethral closure that mimics bone differentiation and incorporates discrete hedgehog activity within the developing phallus and phallic urethra.

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.

Thyroid hormone (T3) is involved in inhibiting the proliferation of newborn calf Sertoli cells via the PI3K/Akt signaling pathway in vitro

The experiment was designed to study the effects of Thyroid hormone (T₃) on the proliferation and differentiation of newborn calf Sertoli cells (SCs) to provide a theoretical and practical basis for increased testicular semen production. In this experiment, the cck8 method was used to detect the effects of different concentrations of T₃ on the proliferation rate of newborn calf SCs. qPCR and Western Blot methods were used to explore the effects of T3 on the proliferation and differentiation of calves SCs and whether T₃ through Wnt/β-catenin and PI3K/Akt pathways can regulate the proliferation and differentiation of SCs. We found that dosage (T₃) and time correlated with proliferation inhibition of SC. T₃ inhibited the proliferation of SC by down-regulating cyclinD1, upregulating p21Cip, p27Kip1, and other cell-cycle factors. By up-regulating AR and down-regulating KRT-18, T3 promoted the maturated differentiation of SC. T₃ could not affect the expression of β-catenin in SC of newborn calf, indicating that T₃ may not regulate SCs proliferation through the Wnt pathway. T3 also negatively regulated the gene expression and protein levels of some genes in the PI3K/Akt signaling pathway. We concluded that T₃ inhibited newborn calf SCs proliferation through the PI3K/Akt signaling pathway and possibly promoted their differentiation.

Estradiol and reproduction in the South American toad Rhinella arenarum (Amphibian, Anura)

Rhinella arenarum is a South American toad with wide geographic distribution. Testes of this toad produce high amount of androgens during the non reproductive season and shift steroid synthesis from androgens to 5α-pregnanedione during the breeding. In addition, plasma estradiol (E₂) in males of this species shows seasonal variations but, since testes of R. arenarum do not express aromatase, the source of plasma E₂ remained unknown for several years. However, the Bidder's organ (BO), a structure located at one pole of each testis, is proposed to be the main source of E₂ in male's toads since it expresses several steroidogenic enzymes and is able to produce E₂ from endogenous substrates throughout the year. In addition, there were significant correlations between plasma E₂ and total activity of BO aromatase, and between plasma E₂ and the amount of hormone produced by the BO in vitro. In the toad, apoptosis induced by in vitro treatment with E₂ was mostly detected in spermatocytes during the breeding and in spermatids during the post-reproductive season, suggesting that this steroid has an important role in controlling spermatogenesis. However, in vitro treatment with E₂ had no effect on proliferation. This evidence suggests that the mechanism of action of E₂ on amphibian spermatogenesis is complex and more studies are necessary to fully understand the role of estrogens regulating the balance between cellular proliferation and apoptosis. In addition, in R. arenarum in vitro studies suggested that E₂ has no effect on CypP450c17 protein levels or enzymatic activity, while it reduces 3β-hydroxysteroid dehydrogenase/isomerase (3β-HSD/I) activity during the post reproductive season. As well, E₂ regulates FSHβ mRNA expression all over the year suggesting a down regulation process carried out by this steroid. The effect on LHβ mRNA is dual, since during the reproductive season estradiol increases the expression of LHβ mRNA while in the non-reproductive season it has no effect. In conclusion, the effect of E₂ on gonadotropins and testicular function is complex, not clearly understood and probably varies depending on the species. The aim of the current article is to review evidence on reproductive endocrinology and on the role of estradiol regulating reproduction in amphibians, with emphasis on the South American species Rhinella arenarum.

Postnatal testis development in the collared peccary (Tayassu tajacu), with emphasis on spermatogonial stem cells markers and niche

Collared peccaries (Tayassu tajacu) present a unique testis cytoarchitecture, where Leydig cells (LC) are mainly located in cords around the seminiferous tubules (ST) lobes. This peculiar arrangement is very useful to better investigate and understand the role of LC in spermatogonial stem cells (SSCs) biology and niche. Recent studies from our laboratory using adult peccaries have shown that the undifferentiated type A spermatogonia (A_und or SSCs) are preferentially located in ST regions adjacent to the intertubular compartment without LC. Following these studies, our aims were to investigate the collared peccary postnatal testis development, from birth to adulthood, with emphasis on the establishment of LC cytoarchitecture and the SSCs niche. Our findings demonstrated that the unique LC cytoarchitecture is already present in the neonate peccary's testis, indicating that this arrangement is established during fetal development. Based on the most advanced germ cell type present at each time period evaluated, puberty (the first sperm release in the ST lumen) in this species was reached at around one year of age, being preceded by high levels of estradiol and testosterone and the end of Sertoli cell proliferation. Almost all gonocytes and SSCs expressed Nanos1, Nanos2 and GFRA1. The analysis of SSCs preferential location indicated that the establishment of SSCs niche is coincident with the occurrence of puberty. Taken together, our findings reinforced and extended the importance of the collared peccary as an animal model to investigate testis function in mammals, particularly the aspects related to testis organogenesis and the SSCs biology and niche.

Seasonal variation in sperm freezability associated with changes in testicular germinal epithelium in domestic (Ovis aries) and wild (Ovis musimon) sheep

The aim of this study was to examine ovine sperm cryoresistance during the rutting season (RS) and its association with sperm head area and seminiferous epithelium proliferation. Small ruminants show fluctuating testosterone levels throughout the year, which could interfere with spermatogenesis and sperm cryopreservation. Ejaculates, testicular biopsies and blood were collected during the middle and at the end of the RS (Middle-RS vs End-RS) during periods of high and low testosterone levels in Merino and Mouflon rams. Fresh and frozen–thawed sperm quality, sperm morphometry, seminiferous tubule morphometry and testicular proliferation markers (proliferating cell nuclear antigen, proliferation marker protein Ki-67 and transcription factor GATA-4) were evaluated. Post-thaw sperm viability was higher in the End-RS group in both Merino (69.9±8.2 vs 41.6±7.3%; P=0.020) and Mouflon rams (40.9±3.3 vs 24.2±5.0%; P=0.008). Mouflons had larger sperm head area at the End-RS (38.3±0.2 vs 34.3±0.1µm2; P=0.029), whereas there was no difference between Merino groups (35.7±0.5 vs 34.8±1.0µm2). Seminiferous tubule morphometry and proliferation markers showed higher levels of germinal epithelium proliferation in the Middle-RS of both species. In conclusion, sperm freezability is affected during the RS in domestic and wild rams, which could be correlated with changes that occur during spermatogenesis, since there is an effect of season on cell proliferation in the testis.

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.

Loss of connexin43 in murine Sertoli cells and its effect on blood-testis barrier formation and dynamics

Connexin43 (Cx43) is the predominant testicular gap junction protein and in cases of impaired spermatogenesis, Cx43 expression has been shown to be altered in several mammals. Amongst other functions, Cx43 is supposed to regulate junction formation of the blood-testis barrier (BTB). The aim of the present study was to investigate the expression pattern of different tight junction (TJ) proteins of the murine BTB using SC-specific Cx43 knockout mice (SCCx43KO). Adult homozygous male SCCx43KO mice (SCCx43KO-/-) predominantly show an arrest of spermatogenesis and SC-only tubules that might have been caused by an altered BTB assembly, composition or regulation. TJ molecules claudin-3, -5 and -11 were examined in adult wild type (WT) and SCCx43KO-/- mice using immunohistochemistry (IHC) and quantitative real-time PCR (qRT-PCR). In this context, investigation of single tubules with residual spermatogenesis in SCCx43KO-/- mice was particularly interesting to identify a potential Cx43-independent influence of germ cells (GC) on BTB composition and dynamics. In tubules without residual spermatogenesis, a diffuse cytoplasmic distribution pattern for claudin-11 protein could be demonstrated in mutant mice. Nevertheless, claudin-11 seems to form functional TJ. Claudin-3 and -5 could not be detected immunohistochemically in the seminiferous epithelium of those tubules. Correspondingly, claudin-3 and -5 mRNA expression was decreased, providing evidence of generally impaired BTB dynamics in adult KO mice. Observations of tubules with residual spermatogenesis suggested a Cx43-independent regulation of TJ proteins by GC populations. To determine initial BTB formation in peripubertal SCCx43KO-/- mice, immunohistochemical staining and qRT-PCR of claudin-11 were carried out in adolescent SCCx43KO-/- and WT mice. Additionally, BTB integrity was functionally analysed using a hypertonic glucose fixative. These analyses revealed that SCCx43KO-/- mice formed an intact BTB during puberty in the same time period as WT mice, which however seemed to be accelerated.

Identification of Proliferative and Apoptotic Sertoli Cells Using Fluorescence and Confocal Microscopy

Sertoli cells, the testicular somatic cells of the seminiferous epithelium, are vital for the survival of the epithelium. They undergo proliferation and apoptosis during fetal, neonatal, and prepubertal development. Apoptosis is increased in certain situations such as exposure to many substances, for example, toxics, or short photoperiod in the non-breeding season of some mammals. Therefore, it has always been considered that Sertoli cells that reach adulthood are quiescent cells, that is to say, nonproliferative, do not die, are terminally differentiated, and whose numbers remain constant. Recently, a degree of both proliferation and apoptosis has been observed in normal adult conditions, suggesting that consideration of this cell as quiescent may be subject to change. All this make it necessary to use histochemical techniques to demonstrate whether Sertoli cells are undergoing proliferation or apoptosis in histological sections and to allow the qualitative and quantitative study of these. In this chapter, we present two double-staining techniques that can be used for identifying Sertoli cells in proliferation or apoptosis by fluorescence microscopy. In both, the Sertoli cells are identified by an immunohistochemistry for vimentin followed by an immunohistochemistry for PCNA or a TUNEL histochemistry.

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.

Claudin-11 and occludin are major contributors to Sertoli cell tight junction function, in vitro

The Sertoli cell tight junction (TJ) is the key component of the blood-testis barrier, where it sequesters developing germ cells undergoing spermatogenesis within the seminiferous tubules. Hormonally regulated claudin-11 is a critical transmembrane protein involved in barrier function and its murine knockout results in infertility. We aimed to assess quantitatively the significance of the contribution of claudin-11 to TJ function, in vitro, using siRNA-mediated gene silencing. We also conducted an analysis of the contribution of occludin, another intrinsic transmembrane protein of the TJ. Silencing of claudin-11 and/or occludin was conducted using siRNA in an immature rat Sertoli cell culture model. Transepithelial electrical resistance was used to assess quantitatively TJ function throughout the culture. Two days after siRNA treatment, cells were fixed for immunocytochemical localization of junction proteins or lyzed for RT-PCR assessment of mRNA expression. Silencing of claudin-11, occludin, or both resulted in significant decreases in TJ function of 55% (P < 0.01), 51% (P < 0.01), and 62% (P < 0.01), respectively. Data were concomitant with significant decreases in mRNA expression and marked reductions in the localization of targeted proteins to the Sertoli cell TJ. We provide quantitative evidence that claudin-11 contributes significantly (P < 0.01) to Sertoli cell TJ function in vitro. Interestingly, occludin, which is hormonally regulated but not implicated in infertility until late adulthood, is also a significant (P < 0.01) contributor to barrier function. Our data are consistent with in vivo studies that clearly demonstrate a role for these proteins in maintaining normal TJ barrier structure and function.

Only a small population of adult Sertoli cells actively proliferates in culture

Adult mammalian Sertoli cells (SCs) have been considered to be quiescent terminal differentiated cells for many years, but recently, proliferation of adult SCs was demonstrated in vitro and in vivo. We further examined mouse SC behavior in culture and found that there are two populations of adult SCs. The first population is SCs from seminiferous tubules that hardly proliferate in vitro. The second population is small and consists of SCs with atypical nuclear morphology from the terminal segments of seminiferous tubules, a transitional zone (TZ). TZ SCs multiply in culture and form colonies, display mixture of mature and immature SC characteristics, and generate cord-like structures in a collagen matrix. The specific features of TZ SCs are ACTA2 expression in vitro and DMRT1 low levels in vivo and in vitro. Although the in vivo function of TZ SCs still remains unclear, this finding has significant implications for our understanding of SC differentiation and functioning in adult mammals.

Beneficial role of ascorbic and folic acids antioxidants against thyroxin-induced testicular dysfunction in hyperthyroid rats

Thyroid hormones play a fundamental role in the regulation of metabolism of almost all mammalian tissue including the reproductive system. Hyperthyroidism in early life may cause delayed sexual maturation, although physical development is normal and skeletal growth may be accelerated. Hyperthyroidism after puberty influences reproductive functions and increases testosterone level. The aim of this work is to study the effect of induced hyperthyroidism by L-thyroxine sodium administration on the testis of rats and to evaluate the ameliorating role of different antioxidants as ascorbic acid and folic acid on the hyperthyroid state via the assessment of different biochemical markers, histopathological and immunochemical sections. DNA analysis of the D1 deiodinase was performed to determine genetic mutation due to hyperthyroidism. The results showed partially disrupted in the measured biochemical parameters and spermatogenesis in hyperthyroid rats. Post-administration of both folic and ascorbic acids together in hyperthyroid rats showed the best ameliorating effects on the thyroid hormones, testosterone, testicular GGT and ALP, and all oxidative stress markers. There is no genetic mutations that occurred in D1 deiodinase due to hyperthyroidism. These findings were indicated by the proliferating cell nuclear antigen (PCNA) studies of testes.

NODAL secreted by male germ cells regulates the proliferation and function of human Sertoli cells from obstructive azoospermia and nonobstructive azoospermia patients

This study was designed to explore the regulatory effects of male germ cell secreting factor NODAL on Sertoli cell fate decisions from obstructive azoospermia (OA) and nonobstructive azoospermia (NOA) patients. Human Sertoli cells and male germ cells were isolated using two-step enzymatic digestion and SATPUT from testes of azoospermia patients. Expression of NODAL and its multiple receptors in human Sertoli cells and male germ cells were characterized by reverse transcription-polymerase chain reaction (RT-PCR) and immunochemistry. Human recombinant NODAL and its receptor inhibitor SB431542 were employed to probe their effect on the proliferation of Sertoli cells using the CCK-8 assay. Quantitative PCR and Western blots were utilized to assess the expression of Sertoli cell functional genes and proteins. NODAL was found to be expressed in male germ cells but not in Sertoli cells, whereas its receptors ALK4, ALK7, and ACTR-IIB were detected in Sertoli cells and germ cells, suggesting that NODAL plays a regulatory role in Sertoli cells and germ cells via a paracrine and autocrine pathway, respectively. Human recombinant NODAL could promote the proliferation of human Sertoli cells. The expression of cell cycle regulators, including CYCLIN A, CYCLIN D1 and CYCLIN E, was not remarkably affected by NODAL signaling. NODAL enhanced the expression of essential growth factors, including GDNF, SCF, and BMP4, whereas SB431542 decreased their levels. There was not homogeneity of genes changes by NODAL treatment in Sertoli cells from OA and Sertoli cell-only syndrome (SCO) patients. Collectively, this study demonstrates that NODAL produced by human male germ cells regulates proliferation and numerous gene expression of Sertoli cells.

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.

DNA repair kinetics in SCID mice Sertoli cells and DNA-PKcs-deficient mouse embryonic fibroblasts

Noncycling and terminally differentiated (TD) cells display differences in radiosensitivity and DNA damage response. Unlike other TD cells, Sertoli cells express a mixture of proliferation inducers and inhibitors in vivo and can reenter the cell cycle. Being in a G₁-like cell cycle stage, TD Sertoli cells are expected to repair DSBs by the error-prone nonhomologous end-joining pathway (NHEJ). Recently, we have provided evidence for the involvement of Ku-dependent NHEJ in protecting testis cells from DNA damage as indicated by persistent foci of the DNA double-strand break (DSB) repair proteins phospho-H2AX, 53BP1, and phospho-ATM in TD Sertoli cells of Ku70-deficient mice. Here, we analyzed the kinetics of 53BP1 foci induction and decay up to 12 h after 0.5 Gy gamma irradiation in DNA-PKcs-deficient (Prkdc ^scid ) and wild-type Sertoli cells. In nonirradiated mice and Prkdc ^scid Sertoli cells displayed persistent DSBs foci in around 12 % of cells and a fivefold increase in numbers of these DSB DNA damage-related foci relative to the wild type. In irradiated mice, Prkdc ^scid Sertoli cells showed elevated levels of DSB-indicating foci in 82 % of cells 12 h after ionizing radiation (IR) exposure, relative to 52 % of irradiated wild-type Sertoli cells. These data indicate that Sertoli cells respond to and repair IR-induced DSBs in vivo, with repair kinetics being slow in the wild type and inefficient in Prkdc ^scid . Applying the same dose of IR to Prdkc ^-/- and Ku ^-/- mouse embryonic fibroblast (MEF) cells revealed a delayed induction of 53BP1 DSB-indicating foci 5 min post-IR in Prdkc ^-/- cells. Inefficient DSB repair was evident 7 h post-IR in DNA-PKcs-deficient cells, but not in Ku ^-/- MEFs. Our data show that quiescent Sertoli cells repair genotoxic DSBs by DNA-PKcs-dependent NEHJ in vivo with a slower kinetics relative to somatic DNA-PKcs-deficient cells in vitro, while DNA-PKcs deficiency caused inefficient DSB repair at later time points post-IR in both conditions. These observations suggest that DNA-PKcs contributes to the fast and slow repair of DSBs by NHEJ.

Immunolocalisation of aromatase regulators liver kinase B1, phosphorylated AMP-activated protein kinase and cAMP response element-binding protein-regulated transcription co-activators in the human testis

Although oestrogens are essential for spermatogenesis and their biosynthesis is dependent on aromatase expression, the molecular mechanism of aromatase regulation is poorly understood. Our laboratory has demonstrated that liver kinase B1 (LKB1) is a negative regulator of aromatase in the breast by phosphorylating AMP-activated protein kinase (AMPK) and inhibiting the nuclear translocation of the cAMP response element-binding protein-regulated transcription co-activator (CRTC) 2. The aim of this study was to determine the location of testis-associated proteins in the LKB1-CRTC pathway. Aromatase, LKB1, phosphorylated AMPK (pAMPK) and CRTC1-3 were examined by selected immunofluorescent antibodies in testis samples from a prepubertal boy and three fertile men. Aromatase, pAMPK and LKB1 proteins were present in the seminiferous epithelium and interstitium of the testis and were expressed in a differential and developmental manner in particular cell types. The expression pattern of LKB1 was similar to that of pAMPK and inversely related to aromatase expression. CRTC1 and CRTC3 were localised in the seminiferous epithelium, whereas CRTC2 was barely detectable in testis. These results lead to the conclusion that LKB1 is involved in the molecular pathway that underpins aromatase regulation in the testis via CRTC1 and CRTC3 and may be important for the oestrogen-mediated development of germ cells.

Gonadotropin suppression in men leads to a reduction in claudin-11 at the Sertoli cell tight junction

STUDY QUESTION

Are Sertoli cell tight junctions (TJs) disrupted in men undergoing hormonal contraception?

SUMMARY ANSWER

Localization of the key Sertoli cell TJ protein, claudin-11, was markedly disrupted by 8 weeks of gonadotropin suppression, the degree of which was related to the extent of adluminal germ cell suppression.

WHAT IS KNOWN ALREADY

Sertoli cell TJs are vital components of the blood-testis barrier (BTB) that sequester developing adluminal meiotic germ cells and spermatids from the vascular compartment. Claudin-11 knockout mice are infertile; additionally claudin-11 is spatially disrupted in chronically gonadotropin-suppressed rats coincident with a loss of BTB function, and claudin-11 is disorganized in various human testicular disorders. These data support the Sertoli cell TJ as a potential site of hormonal contraceptive action.

STUDY DESIGN, SIZE, DURATION

BTB proteins were assessed by immunohistochemistry (n = 16 samples) and mRNA (n = 18 samples) expression levels in available archived testis tissue from a previous study of 22 men who had undergone 8 weeks of gonadotropin suppression and for whom meiotic and post-meiotic germ cell numbers were available. The gonadotropin suppression regimens were (i) testosterone enanthate (TE) plus the GnRH antagonist, acyline (A); (ii) TE + the progestin, levonorgestrel, (LNG); (iii) TE + LNG + A or (iv) TE + LNG + the 5α-reductase inhibitor, dutasteride (D). A control group consisted of seven additional men, with three archived samples available for this study.

PARTICIPANTS/MATERIALS, SETTINGS, METHODS

Immunohistochemical localization of claudin-11 (TJ) and other junctional type markers [ZO-1 (cytoplasmic plaque), β-catenin (adherens junction), connexin-43 (gap junction), vinculin (ectoplasmic specialization) and β-actin (cytoskeleton)] and quantitative PCR was conducted using matched frozen testis tissue.

MAIN RESULTS AND THE ROLE OF CHANCE

Claudin-11 formed a continuous staining pattern at the BTB in control men. Regardless of gonadotropin suppression treatment, claudin-11 localization was markedly disrupted and was broadly associated with the extent of meiotic/post-meiotic germ cell suppression; claudin-11 staining was (i) punctate (i.e. 'spotty' appearance) at the basal aspect of tubules when the average numbers of adluminal germ cells were <15% of control, (ii) presented as short fragments with cytoplasmic extensions when numbers were 15-25% of control or (iii) remained continuous when numbers were >40% of control. Changes in localization of connexin-43 and vinculin were also observed (smaller effects than for claudin-11) but ZO-1, β-catenin and β-actin did not differ, compared with control.

LIMITATIONS, REASONS FOR CAUTION

Claudin-11 was the only Sertoli cell TJ protein investigated, but it is considered to be the most pivotal of constituent proteins given its known implication in infertility and BTB function. We were limited to testis samples which had been gonadotropin-suppressed for 8 weeks, shorter than the 74-day spermatogenic wave, which may account for the heterogeneity in claudin-11 and germ cell response observed among the men. Longer suppression (12-24 weeks) is known to suppress germ cells further and claudin-11 disruption may be more uniform, although we could not access such samples.

WIDER IMPLICATIONS OF THE FINDINGS

These findings are important for our understanding of the sites of action of male hormonal contraception, because they suggest that BTB function could be ablated following long-term hormone suppression treatment.

STUDY FUNDING/COMPETING INTERESTS

National Health and Medical Research Council (Australia) Program Grants 241000 and 494802; Research Fellowship 1022327 (to R.I.M.) and the Victorian Government's Operational Infrastructure Support Program. None of the authors have any conflicts to disclose.

TRIAL REGISTRATION NUMBER

Not applicable.

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.

Peroxisome Proliferator-activated Receptor-D (PPARD) Coordinates Mouse Spermatogenesis by Modulating Extracellular Signal-regulated Kinase (ERK)-dependent Signaling

Ppard(-/-) mice exhibit smaller litter size compared with Ppard(+/+) mice. To determine whether peroxisome proliferator-activated receptor-D (PPARD) could possibly influence this phenotype, the role of PPARD in testicular biology was examined. Atrophic testes and testicular degeneration were observed in Ppard(-/-) mice compared with Ppard(+/+) mice, indicating that PPARD modulates spermatogenesis. Higher expression of p27 and decreased expression of proliferating cellular nuclear antigen in Sertoli cells were observed in Ppard(+/+) mice as compared with Ppard(-/-) mice, and these were associated with decreased Sertoli cell number in Ppard(+/+) mice. Cyclin D1 and cyclin D2 expression was lower in Ppard(+/+) as compared with Ppard(-/-) mice. Ligand activation of PPARD inhibited proliferation of a mouse Sertoli cell line, TM4, and an inverse agonist of PPARD (DG172) rescued this effect. Temporal inhibition of extracellular signal-regulated kinase (ERK) activation by PPARD in the testis was observed in Ppard(+/+) mice and was associated with decreased serum follicle-stimulating hormone and higher claudin-11 expression along the blood-testis barrier. PPARD-dependent ERK activation also altered expression of claudin-11, p27, cyclin D1, and cyclin D2 in TM4 cells, causing inhibition of cell proliferation, maturation, and formation of tight junctions in Sertoli cells, thus confirming a requirement for PPARD in accurate Sertoli cell function. Combined, these results reveal for the first time that PPARD regulates spermatogenesis by modulating the function of Sertoli cells during early testis development.

Long-term culture and significant expansion of human Sertoli cells whilst maintaining stable global phenotype and AKT and SMAD1/5 activation

BACKGROUND

Sertoli cells play key roles in regulating spermatogenesis and testis development by providing structural and nutritional supports. Recent studies demonstrate that Sertoli cells can be converted into functional neural stem cells. Adult Sertoli cells have previously been considered the terminally differentiated cells with a fixed and unmodifiable population after puberty. However, this concept has been challenged. Since the number of adult human Sertoli cells is limited, it is essential to culture these cells for a long period and expand them to obtain sufficient cells for their basic research and clinic applications. Nevertheless, the studies on human Sertoli cells are restricted, because it is difficult to get access to human testis tissues.

RESULTS

Here we isolated adult human Sertoli cells with a high purity and viability from obstructive azoospermia patients with normal spermatogenesis. Adult human Sertoli cells were cultured with DMEM/F12 and fetal bovine serum for 2 months, and they could be expanded with a 59,049-fold increase of cell numbers. Morphology, phenotypic characteristics, and the signaling pathways of adult human Sertoli cells from different passages were compared. Significantly, adult human Sertoli cells assumed similar morphological features, stable global gene expression profiles and numerous proteins, and activation of AKT and SMAD1/5 during long-period culture.

CONCLUSIONS

This study demonstrates that adult human Sertoli cells can be cultured for a long period and expanded with remarkable increase of cell numbers whilst maintaining their primary morphology, phenotype and signaling pathways. This study could provide adequate human Sertoli cells for reproductive and regenerative medicine.

Research resource: the dynamic transcriptional profile of sertoli cells during the progression of spermatogenesis

Sertoli cells (SCs), the only somatic cells within seminiferous tubules, associate intimately with developing germ cells. They not only provide physical and nutritional support but also secrete factors essential to the complex developmental processes of germ cell proliferation and differentiation. The SC transcriptome must therefore adapt rapidly during the different stages of spermatogenesis. We report comprehensive genome-wide expression profiles of pure populations of SCs isolated at 5 distinct stages of the first wave of mouse spermatogenesis, using RNA sequencing technology. We were able to reconstruct about 13 901 high-confidence, nonredundant coding and noncoding transcripts, characterized by complex alternative splicing patterns with more than 45% comprising novel isoforms of known genes. Interestingly, roughly one-fifth (2939) of these genes exhibited a dynamic expression profile reflecting the evolving role of SCs during the progression of spermatogenesis, with stage-specific expression of genes involved in biological processes such as cell cycle regulation, metabolism and energy production, retinoic acid synthesis, and blood-testis barrier biogenesis. Finally, regulatory network analysis identified the transcription factors endothelial PAS domain-containing protein 1 (EPAS1/Hif2α), aryl hydrocarbon receptor nuclear translocator (ARNT/Hif1β), and signal transducer and activator of transcription 1 (STAT1) as potential master regulators driving the SC transcriptional program. Our results highlight the plastic transcriptional landscape of SCs during the progression of spermatogenesis and provide valuable resources to better understand SC function and spermatogenesis and its related disorders, such as male infertility.

Nutrition affects Sertoli cell function but not Sertoli cell numbers in sexually mature male sheep

We tested whether the reversible effects of nutrition on spermatogenesis in sexually mature sheep were mediated by Sertoli cells. Rams were fed with diets designed to achieve a 10% increase (High), no change (Maintenance) or a 10% decrease (Low) in body mass after 65 days. At the end of treatment, testes were lighter in the Low than the High group (PP<0.05) in the expression of seven Sertoli cell-specific genes. Under-nutrition appeared to reverse cellular differentiation leading to disruption of tight-junction morphology. In conclusion, in sexually mature sheep, reversible reductions in testis mass and spermatogenesis caused by under-nutrition were associated with impairment of basic aspects of Sertoli cell function but not with changes in the number of Sertoli cells.

A survey of Sertoli cell differentiation in men after gonadotropin suppression and in testicular cancer

It is widely held that the somatic cell population that is responsible for sperm development and output (Sertoli cells) is terminally differentiated and unmodifiable in adults. It is postulated, with little evidence, that Sertoli cells are not terminally differentiated in some phenotypes of infertility and testicular cancer. This study sought to compare markers of Sertoli cell differentiation in normospermic men, oligospermic men (undergoing gonadotropin suppression) and testicular carcinoma in situ (CIS) and seminoma samples. Confocal microscopy was used to assess the expression of markers of proliferation (PCNA and Ki67) and functional differentiation (androgen receptor). As additional markers of differentiation, the organization of Sertoli cell tight junction and associated proteins were assessed in specimens with carcinoma in situ. In normal men, Sertoli cells exhibited a differentiated phenotype (i.e., PCNA and Ki67 negative, androgen 40 receptor positive). However, after long-term gonadotropin suppression, 1.7 ± 0.6% of Sertoli cells exhibited PCNA reactivity associated with a diminished immunoreactivity in androgen receptor, suggesting an undifferentiated phenotype. Ki67-positive Sertoli cells were also observed. PCNA-positive Sertoli cells were never observed in tubules with carcinoma in situ, and only rarely observed adjacent to seminoma. Tight junction protein localization (claudin 11, JAM-A and ZO-1) was altered in CIS, with a reduction in JAM-A reactivity in Sertoli cells from tubules with CIS and the emergence of strong JAM-A reactivity in seminoma. These findings indicate that adult human Sertoli cells exhibit characteristics of an undifferentiated state in oligospermic men and patients with CIS and seminoma in the presence of germ cell neoplasia.

Long-term culture and analysis of cashmere goat Sertoli cells

Sertoli cells have important functions in the testis for spermatogenesis. Thus, Sertoli cell culture systems have been established in many animals, such as rat, mouse, human, dog, cow, and pig, but a goat culture has not been reported. This study describes the isolation and culture of Sertoli cells from 3- to 4-month-old cashmere goat (Capra hircus) testes. These proliferative cells were expanded for 20 passages and repeatedly cryopreserved in vitro, in contrast to previous study in human, of which maintain steady growth for up to seven passages and only passages 1 to 5 could be refrozen. The microstructure and ultrastructure of the culture were typical of Sertoli cells, bearing irregular nuclei and a cytoplasm that was rich in smooth and rough endoplasmic reticulum, mitochondria, Golgi, lysosomes, lipid drops, and glycogenosomes. By immunofluorescence analysis, the all cells expressed SRY-related HMG box gene 9 (Sox9). Growth curves and 5-bromo-2'-deoxyuridine (BrdU) incorporation were used to analyze the proliferation of the cultured cells. With increasing passage times, the proliferation of the Sertoli cells declined, but the transcription of glial cell-derived neurotrophic factor (GDNF), stem cell factor (SCF), and β1-integrin was constant. By flow cytometry, the cells retained the ability to proliferate after 5 yr of cryopreservation. Thus, cashmere goat Sertoli cells have significant proliferative potential in vitro, expressing germ cell regulatory factors and have important applications in studying Sertoli cell-germ cell interactions, spermatogenesis, reproductive toxicology, and male infertility.

Toxoplasma gondii decreases the reproductive fitness in mice

Toxoplasma gondii is a common protozoan parasite that infects warm-blooded animals throughout the world, including mice and humans. During infection, both, the parasite and the host, utilize various mechanisms to maximize their own reproductive success. Mice and humans are both the intermediate hosts for Toxoplasma gondii, which forms specialized vacuoles containing reproductive cysts in the formers' tissue. As half of the human population is infected, developing a disease called toxoplasmosis, along with an ever-growing number of couples suffering with idiopathic infertility, it is therefore surprising that there is a lack of research on how Toxoplasma gondii can alter reproductive parameters. In this study, a detailed histometric screening of the testicular function along with the levels of the pituitary luteinizing hormone (LH) were analysed in infected mice. Data on relative testis and epididymis weight, and sperm count were also collected. Based on the results obtained, the level of LH in the urine of Toxoplasma gondii infected mice was lower compared to the control. In direct correlation with the hormone level, testicular function and sperm production was also significantly lower in Toxoplasma gondii positive group using sperm count and histometric analysis as a marker. Not only were the number of leptotene primary spermatocytes and spermatids lowered, but the number of Sertoli cells and the tubule diameter were elevated. In parallel, a pilot epigenetic study on global testicular methylation, and specific methylation of Crem, Creb1 and Hspa1genes essential for successfully ongoing spermatogenesis was performed. Global methylation was elevated in Toxoplasma infected mice, and differences in the DNA methylation of selected genes were detected between the Toxoplasma positive and control group. These findings demonstrate a direct relation between Toxoplasma gondii infection and the decrease of male reproductive fitness in mice, which may contribute to an increase of idiopathic infertility in humans.

Effect of pyrimethamine treatment on male rat testicular cell population development

Pyrimethamine (PYR) is a drug used in the treatment of newborn with congenital Toxoplasmosis. Even when PYR is highly specific against parasites, it may provoke neutropenia in the patients apart from other affectations, conditions that usually justify its suspension. Moreover, medication against congenital toxoplasmosis coincides with the proliferation stage of Sertoli and germ cells. Although, there are several reports on the effect of this drug on mature testes, records of its effects on the testes of young individuals yet in the process of growth are still lacking. This work was aimed to study the effects of in vivo administration of PYR in the first 21 days of life of male rat pups by evaluating their testicular alterations and its long-term sequels on fertility. Through the determination of the levels of seminiferous epithelium maturity, apoptotic index and cell proliferation index at 7, 14, 35 and 90 days post-natal using immunocytochemical studies. The fertility of the treated rats was evaluated at 90 days. PYR-treated animals were found to undergo some kind of delays in seminiferous epithelium maturity, decreased cell proliferation index and an increase in apoptosis when compared with the control (p < 0.05). Epididymal sperm counts were also affected (p < 0.05). The application of folic acid (FA) in newborns treated with PYR decreased the severity of the problem (p < 0.05). This study provides strong evidence that the effect of PYR on testicular development is specific. It reinforces the importance of FA application in neonates treated with PYR to prevent the effect of the later on spermatogenesis.

The death of sertoli cells and the capacity to phagocytize elongated spermatids during testicular regression due to short photoperiod in Syrian hamster (Mesocricetus auratus)

In the Syrian hamster (Mesocricetus auratus), an animal that displays testicular regression due to short photoperiod, germ cells are removed by apoptosis during this process and the apoptotic remains are phagocytized by Sertoli cells. The aim of this work was to investigate morphologically whether the testicular regression process due to short photoperiod leads to the apoptosis of Sertoli cells, and whether, during testicular regression, the elongated spermatids are eliminated through phagocytosis by Sertoli cells. To this end, we studied testis sections during testicular regression in Syrian hamster subjected to short photoperiod by means of several morphological techniques using conventional light microscopy (hematoxylin and eosin [H&E], semi-thin section vimentin, immunohistochemistry, SBA lectin, and TUNEL staining), fluorescence microscopy, and transmission electron microscopy (TEM). H&E and semi-thin sections identified Sertoli cells with a degenerated morphology. Greater portion of Sertoli cells that were positive for TUNEL staining were observed especially during the mild regression (MR) and strong regression (SR) phases. In addition, TEM identified the characteristic apoptotic changes in the nucleus and cytoplasm of Sertoli cells. Moreover, during testicular regression and using light microscopy, some elongated spermatids were seen in basal position next to the Sertoli cell nucleus. This Sertoli phagocytic activity was higher in MR and SR phases. TEM confirmed this to be the result of the phagocytic activity of Sertoli cells. In conclusion, during testicular regression in Syrian hamster due to short photoperiod, when germ cells are known to be lost through apoptosis, there is morphological evidences that Sertoli cells are also lost through apoptosis, while some elongated spermatids are phagocytized and eliminated by the Sertoli cells.

Environmental toxicants perturb human Sertoli cell adhesive function via changes in F-actin organization mediated by actin regulatory proteins

STUDY QUESTION

Can human Sertoli cells cultured in vitro and that have formed an epithelium be used as a model to monitor toxicant-induced junction disruption and to better understand the mechanism(s) by which toxicants disrupt cell adhesion at the Sertoli cell blood-testis barrier (BTB)?

SUMMARY ANSWER

Our findings illustrate that human Sertoli cells cultured in vitro serve as a reliable system to monitor the impact of environmental toxicants on the BTB function.

WHAT IS KNOWN ALREADY

Suspicions of a declining trend in semen quality and a concomitant increase in exposures to environmental toxicants over the past decades reveal the need of an in vitro system that efficiently and reliably monitors the impact of toxicants on male reproductive function. Furthermore, studies in rodents have confirmed that environmental toxicants impede Sertoli cell BTB function in vitro and in vivo.

STUDY DESIGN, SIZE AND DURATION

We examined the effects of two environmental toxicants: cadmium chloride (0.5-20 µM) and bisphenol A (0.4-200 µM) on human Sertoli cell function. Cultured Sertoli cells from three men were used in this study, which spanned an 18-month period.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Human Sertoli cells from three subjects were cultured in F12/DMEM containing 5% fetal bovine serum. Changes in protein expression were monitored by immunoblotting using specific antibodies. Immunofluorescence analyses were used to assess changes in the distribution of adhesion proteins, F-actin and actin regulatory proteins following exposure to two toxicants: cadmium chloride and bisphenol A (BPA).

MAIN RESULTS AND THE ROLE OF CHANCE

Human Sertoli cells were sensitive to cadmium and BPA toxicity. Changes in the localization of cell adhesion proteins were mediated by an alteration of the actin-based cytoskeleton. This alteration of F-actin network in Sertoli cells as manifested by truncation and depolymerization of actin microfilaments at the Sertoli cell BTB was caused by mislocalization of actin filament barbed end capping and bundling protein Eps8, and branched actin polymerization protein Arp3. Besides impeding actin dynamics, endocytic vesicle-mediated trafficking and the proper localization of actin regulatory proteins c-Src and annexin II in Sertoli cells were also affected. Results of statistical analysis demonstrate that these findings were not obtained by chance.

LIMITATIONS, REASONS FOR CAUTION

(i) This study was done in vitro and might not extrapolate to the in vivo state, (ii) conclusions are based on the use of Sertoli cell samples from three men and (iii) it is uncertain if the concentrations of toxicants used in the experiments are reached in vivo.

WIDER IMPLICATIONS OF THE FINDINGS

Human Sertoli cells cultured in vitro provide a robust model to monitor environmental toxicant-mediated disruption of Sertoli cell BTB function and to study the mechanism(s) of toxicant-induced testicular dysfunction.