Androgens regulate the permeability of the blood-testis barrier

Mechanistic target of rapamycin (mTOR) pathway in Sertoli cells regulates age-dependent changes in sperm DNA methylation

Over the past several decades, a trend toward delayed childbirth has led to increases in parental age at the time of conception. Sperm epigenome undergoes age-dependent changes increasing risks of adverse conditions in offspring conceived by fathers of advanced age. The mechanism(s) linking paternal age with epigenetic changes in sperm remain unknown. The sperm epigenome is shaped in a compartment protected by the blood-testes barrier (BTB) known to deteriorate with age. Permeability of the BTB is regulated by the balance of two mTOR complexes in Sertoli cells where mTOR complex 1 (mTORC1) promotes the opening of the BTB and mTOR complex 2 (mTORC2) promotes its integrity. We hypothesized that this balance is also responsible for age-dependent changes in the sperm epigenome. To test this hypothesis, we analyzed reproductive outcomes, including sperm DNA methylation in transgenic mice with Sertoli cell-specific suppression of mTORC1 (Rptor KO) or mTORC2 (Rictor KO). mTORC2 suppression accelerated aging of the sperm DNA methylome and resulted in a reproductive phenotype concordant with older age, including decreased testes weight and sperm counts, and increased percent of morphologically abnormal spermatozoa and mitochondrial DNA copy number. Suppression of mTORC1 resulted in the shift of DNA methylome in sperm opposite to the shift associated with physiological aging - sperm DNA methylome rejuvenation and mild changes in sperm parameters. These results demonstrate for the first time that the balance of mTOR complexes in Sertoli cells regulates the rate of sperm epigenetic aging. Thus, mTOR pathway in Sertoli cells may be used as a novel target of therapeutic interventions to rejuvenate the sperm epigenome in advanced-age fathers.

Contribution of the seminal microbiome to paternal programming

The field of Developmental Origins of Health and Disease has primarily focused on maternal programming of offspring health. However, emerging evidence suggests that paternal factors, including the seminal microbiome, could potentially play important roles in shaping the developmental trajectory and long-term offspring health outcomes. Historically, the microbes present in the semen were regarded as inherently pathogenic agents. However, this dogma has recently been challenged by the discovery of a diverse commensal microbial community within the semen of healthy males. In addition, recent studies suggest that the transmission of semen-associated microbes into the female reproductive tract during mating has potentials to not only influence female fertility and embryo development but could also contribute to paternal programming in the offspring. In this review, we summarize the current knowledge on the seminal microbiota in both humans and animals followed by discussing their potential involvement in paternal programming of offspring health. We also propose and discuss potential mechanisms through which paternal influences are transmitted to offspring via the seminal microbiome. Overall, this review provides insights into the seminal microbiome-based paternal programing, which will expand our understanding of the potential paternal programming mechanisms which are currently focused primarily on the epigenetic modifications, oxidative stresses, and cytokines.

The effects of fine particulate matter on the blood-testis barrier and its potential mechanisms

With the rapid expansion of industrial scale, an increasing number of fine particulate matter (PM2.5) has bringing health concerns. Although exposure to PM2.5 has been clearly associated with male reproductive toxicity, the exact mechanisms are still unclear. Recent studies demonstrated that exposure to PM2.5 can disturb spermatogenesis through destroying the blood-testis barrier (BTB), consisting of different junction types, containing tight junctions (TJs), gap junctions (GJs), ectoplasmic specialization (ES) and desmosomes. The BTB is one of the tightest blood-tissue barriers among mammals, which isolating germ cells from hazardous substances and immune cell infiltration during spermatogenesis. Therefore, once the BTB is destroyed, hazardous substances and immune cells will enter seminiferous tubule and cause adversely reproductive effects. In addition, PM2.5 also has shown to cause cells and tissues injury via inducing autophagy, inflammation, sex hormones disorder, and oxidative stress. However, the exact mechanisms of the disruption of the BTB, induced by PM2.5, are still unclear. It is suggested that more research is required to identify the potential mechanisms. In this review, we aim to understand the adverse effects on the BTB after exposure to PM2.5 and explore its potential mechanisms, which provides novel insight into accounting for PM2.5-induced BTB injury.

Acute murine-betacoronavirus infection impairs testicular steroidogenesis and the quality of sperm production

Although several testicular alterations promoted by coronavirus infection have been demonstrated, the extent, causes, and players of testicular pathogenesis are not totally understood. The present study aimed to investigate the short-term effects on male fertility of intranasally administered murine hepatitis virus strain 3 (MHV-3), a member of the genus Betacoronavirus, which causes a severe systemic acute infection. This mouse model might be used as a in vivo prototype for investigating the impact of betacoronavirus on the endocrine and exocrine testicular functions with the advantage to be performed in a biosafety level 2 condition. Herein, we performed virological, histopathological, and molecular studies regarding the testicular spermatogenesis and the spermatic quality analyses in an MHV-3-infected C57BL/6 mice. The main outcomes showed that MHV-3 infects mouse testis and induces a testicular inflammatory state, impairing the steroidogenic pathway. The infection led to several alterations in the testicular parenchyma, such as: seminiferous epithelium sloughing, retention of residual bodies, germ cell apoptosis, alterations in intercellular junction proteins, and worse spermatogenic parameters. Moreover, the levels of plasmatic testosterone as well as the quality of sperm production reduced. Therefore, the present data suggest that the viral/inflammatory impairment of the steroidogenic pathway and the consequent imbalance of androgen levels is critical in testicular pathology, disturbing the SC barrier function and the germ cell differentiation. Our study is important for comprehending the effects of beta coronavirus infections on testis function in order to develop treatments that could prevent virus-mediated male infertility.

Hormone Regulation in Testicular Development and Function

The testes serve as the primary source of androgens and the site of spermatogenesis, with their development and function governed by hormonal actions via endocrine and paracrine pathways. Male fertility hinges on the availability of testosterone, a cornerstone of spermatogenesis, while follicle-stimulating hormone (FSH) signaling is indispensable for the proliferation, differentiation, and proper functioning of Sertoli and germ cells. This review covers the research on how androgens, FSH, and other hormones support processes crucial for male fertility in the testis and reproductive tract. These hormones are regulated by the hypothalamic-pituitary-gonad (HPG) axis, which is either quiescent or activated at different stages of the life course, and the regulation of the axis is crucial for the development and normal function of the male reproductive system. Hormonal imbalances, whether due to genetic predispositions or environmental influences, leading to hypogonadism or hypergonadism, can precipitate reproductive disorders. Investigating the regulatory network and molecular mechanisms involved in testicular development and spermatogenesis is instrumental in developing new therapeutic methods, drugs, and male hormonal contraceptives.

Interaction between Chromodomain Y-like Protein and Androgen Receptor Signaling in Sertoli Cells Accounts for Spermatogenesis

Spermatogenesis is a highly regulated process dependent on androgen receptor (AR) signaling in Sertoli cells. However, the pathogenic mechanisms of spermatogenic failure, by which loss of AR impairs downstream target genes to affect Sertoli cell function, remain incompletely understood. By using microarray analysis, we identified several AR-regulated genes involved in the maturation of spermatogenesis, including chromodomain Y-like protein (CDYL) and transition proteins 1 (TNP-1), that were significantly decreased in ARKO mouse testes. AR and CDYL were found to co-localize and interact in Sertoli cells. The AR-CDYL complex bound to the promoter regions of TNP1 and modulated their transcriptional activity. CDYL acts as a co-regulator of AR transactivation, and its expression is decreased in the Sertoli cells of human testes from patients with azoospermia. The androgen receptor-chromodomain Y-like protein axis plays a crucial role in regulating a network of genes essential for spermatogenesis in Sertoli cells. Disruption of this AR-CDYL regulatory axis may contribute to spermatogenic failure. These findings provide insights into novel molecular mechanisms targeting the AR-CDYL signaling pathway, which may have implications for developing new therapeutic strategies for male infertility.

Effect of Metformin on Sertoli Cell Fatty Acid Metabolism and Blood-Testis Barrier Formation

Sertoli cells (SCs) are essential to maintaining germ cell development. Metformin, the main pharmacologic treatment for pediatric type 2 diabetes, is administered to children during SC maturation. The present study aimed to analyze whether metformin affects SC energy metabolism and blood-testis barrier (BTB) integrity. Primary SC cultures were used for the in vitro studies. In vivo effects were studied in Sprague-Dawley rats treated with 200 mg/kg metformin from Pnd14 to Pnd30. Metformin decreased fatty acid oxidation and increased 3-hydroxybutyrate production in vitro. Moreover, it decreased the transepithelial electrical resistance across the monolayer and induced ZO-1 redistribution, suggesting an alteration of cell junctions. In vivo, a mild but significant increase in BTB permeability and ZO-1 expression was observed in the metformin group, without changes in testicular histology and meiosis progression. Additionally, adult rats that received metformin treatment during the juvenile period showed no alteration in BTB permeability or daily sperm production. In conclusion, metformin exposure may affect BTB permeability in juvenile rats, but this seems not to influence spermatogenesis progression. Considering the results obtained in adult animals, it is possible to speculate that metformin treatment during the juvenile period does not affect testicular function in adulthood.

Association of urinary and seminal plasma vanadium concentrations with semen quality: A repeated-measures study of 1135 healthy men

Although animal studies have shown the reproductive toxicity of vanadium, less is known about its effects on semen quality in humans. Among 1135 healthy men who were screened as potential semen donors, we investigated the relationships of semen quality with urinary and seminal plasma vanadium levels via inductively coupled plasma-mass spectrometry (ICP-MS). Spearman rank correlation tests and linear regression models were used to assess the correlations between average urinary and within-individual pooled seminal plasma vanadium concentrations (n = 1135). We utilized linear mixed-effects models to evaluate the associations of urinary and seminal plasma vanadium levels (n = 1135) with repeated sperm quality parameters (n = 5576). Seminal plasma vanadium concentrations were not significantly correlated with urinary vanadium concentrations (r = 0.03). After adjusting for possible confounders, we observed inverse relationships of within-individual pooled seminal plasma vanadium levels with total count, semen volume, and sperm concentration (all P values for trend < 0.05). Specifically, subjects in the highest (vs. lowest) tertile of seminal plasma vanadium concentrations had - 11.3% (-16.4%, -5.9%), - 11.1% (-19.1%, -2.4%), and - 20.9% (-29.0%, -11.8%) lower sperm volume, concentration, and total count, respectively; moreover, urinary vanadium levels appeared to be negatively associated with sperm motility. These relationships showed monotonically decreasing dose-response patterns in the restricted cubic spline analyses. Our results demonstrated a poor correlation between urinary and seminal plasma levels of vanadium, and elevated vanadium concentrations in urine and seminal plasma may be adversely related to male semen quality.

The mitochondrial protease PARL is required for spermatogenesis

Mitochondrial function plays an important role in the maintenance of male fertility. However, the mechanisms underlying mitochondrial defect-related infertility remain mostly unclear. Here we show that a deficiency of PARL (Parl-/-), a mitochondrial protease, causes complete arrest of spermatogenesis during meiosis I. PARL deficiency led to severe downregulation of proteins of respiratory chain complex IV in testes that did not occur in other tested organs, causing a deficit in complex IV activity and ATP production. Furthermore, Parl-/- testes showed an almost complete loss of HSD17B3, a protein of the sER responsible for the last step in testosterone synthesis. While testosterone production appeared to be restored by overexpression of HSD17B12, loss of the canonical testosterone synthesis led to an upregulation of luteinizing hormone (LH) and of LH-regulated responses. These results suggest an important impact of the downstream regulation of mitochondrial defects that manifest in a cell-type-specific manner and extend beyond mitochondria.

The association between levels of samarium, hafnium, tungsten and rhenium in seminal plasma and the risk of idiopathic oligo-astheno-teratozoospermia in men of childbearing age

Oligo-astheno-teratozoospermia (OAT) is a global public health problem, which affects 30% men of childbearing age. Meanwhile, with the rapid development of industry and economy, the contents of rare earth elements (REEs) in the environment are increasing. However, little is known about the associations between REEs levels and OAT risk. To evaluate the associations between the levels of four REEs (samarium (Sm), hafnium (Hf), tungsten (W), rhenium (Re)) in seminal plasma and OAT risk, from October 2021 to November 2022, semen samples from 924 men of childbearing age (460 controls and 464 cases) were collected from the reproductive center of the First Affiliated Hospital of Anhui Medical University. Inductively coupled plasma-mass spectrometry (ICP-MS) was used to measure the levels of Sm, Hf, Re and W in seminal plasma. Bayesian kernel machine regression (BKMR) was conducted to explore the joint effects of levels of four REEs in seminal plasma on the risk of OAT and select the one exerting a major role; generalized linear regression models (GLM) with log link function were employed to investigate the association of every REE level in seminal plasma and OAT risk; sankey diagram and linear regression models were utilized to describe the associations between the levels of four REEs and the indexes of sperm quality. The levels of four REEs in seminal plasma were higher in the case group than levels in the control group (pSm = 0.011, pHf = 0.040, pW = 0.062, pRe = 0.001, respectively). In BKMR analysis, the OAT risk increased when the overall levels of four REEs were higher than their 55th percentile compared to all of them at their 50th percentile, and Re level played a major role in the association. Additionally, Re level in seminal plasma was positively associated with  the OAT risk in the single element model after adjustment of covariates (medium vs. low: OR (95% CI) = 1.55 (1.10, 2.18); high vs. low: OR (95% CI) = 1.69 (1.18, 2.42)). Lastly, the sankey diagram and linear regression models revealed that Sm level was negatively associated with the PR%, total sperm count and total progressively motile sperm count; Hf level was negatively associated with the PR%; W and Re levels were negatively associated with the PR% and total motility, and Re level was positively associated with abnormal morphology rate. Men of childbearing age with OAT had higher levels of Sm, Hf and Re in seminal plasma than those in the control group. An increasing trend for the OAT risk was observed with an increase in mixture levels of Sm, Hf, W and Re, and Re exposure level played a major role in the association whether in BKMR model or single element model. Additionally, the levels of these four REEs were negatively associated with the indexes of sperm quality.

Mono-(2-ethylhexyl) phthalate (MEHP) reversibly disrupts the blood-testis barrier (BTB) in pubertal rats

The blood-testis barrier (BTB) is constituted by tight junctions between adjacent Sertoli cells (SC) that create a specialized adluminal microenvironment to foster the development of spermatocytes and spermatids. The BTB is a well-studied target of numerous environmental toxicants, including di-(2-ethylhexyl) phthalate (DEHP), a compound widely used in various consumer products. MEHP is the active toxic metabolite of DEHP that has long been recognized in postnatal rodents to disrupt SC function. This study evaluates the impact of MEHP on the integrity of the BTB in both pubertal and adult rats and the signal transduction pathways known to be involved in the disruption of the BTB. Treatment of prepubertal rats with 700 mg/kg MEHP for 24 hours functionally disrupted the BTB integrity. A similar treatment of adult rats with MEHP did not disrupt the integrity of the BTB. The observed disruption of the BTB integrity in the MEHP-treated prepubertal rats occurred concomitantly with a decreased expression and mislocalization of both the ZO1 and occludin tight junction-associated proteins, as well as sloughing of spermatocytes and spermatids. At this same time, MEHP treatment induced a transient surge of p44/42 mitogen-activated protein kinase (MAPK) pathway. Interestingly, after a recovery period of 5 weeks, the BTB recovered and was functionally intact. This is the first report to indicate that acute MEHP exposure of prepubertal rats, but not adult rats, disrupts the functional integrity of the BTB and that this effect on the BTB is reversible.

Comparative effects of finasteride and minoxidil on the male reproductive organs: A systematic review of in vitro and in vivo evidence

Finasteride and minoxidil are medicaments commonly prescribed for treating benign prostatic hyperplasia (BPA), hypertension, and/or androgenetic alopecia (AGA). The mechanism of action of finasteride is based on the interference in androgenic pathways, which may lead to fertility-related disorders in men. Minoxidil, however, can act in multiple ways, and there is no consensus that its use can adversely affect male fertility. Since finasteride and minoxidil could be risk factors for male fertility, we aimed to compare their impact on the two reproductive organs testis and epididymis of adult murine models, besides testis/epididymis-related cells, and describe the mechanism of action involved. For such, we used the PRISMA guideline. We included 31 original studies from a structured search on PubMed/MEDLINE, Scopus, and Web of Science databases. For in vivo studies, the bias analysis and the quality of the studies were assessed as described by SYRCLE (Systematic Review Centre for Laboratory Animal Experimentation). We concluded that finasteride and minoxidil act as hormone disruptors, causing oxidative stress and morphological changes mainly in the testis. Our results also revealed that finasteride treatment could be more harmful to male reproductive health because it was more associated with reproductive injuries, including damage to the epididymis, erectile dysfunction, decreased libido, and reduced semen volume. Thus, this study contributes to the global understanding of the mechanisms by which medicaments used for alopecia might lead to male reproductive disorders. We hope that our critical analysis expedites clinical research and reduces methodological bias. The registration number on the Prospero platform is CRD42022313347.

Comparing the adult and pre-pubertal testis: Metabolic transitions and the change in the spermatogonial stem cell metabolic microenvironment

BACKGROUND

Survivors of childhood cancer often suffer from infertility. While sperm cryopreservation is not feasible before puberty, the patient's own spermatogonial stem cells could serve as a germ cell reservoir, enabling these patients to father their own children in adulthood through the isolation, in vitro expansion, and subsequent transplantation of spermatogonial stem cells. However, this approach requires large numbers of stem cells, and methods for successfully propagating spermatogonial stem cells in the laboratory are yet to be established for higher mammals and humans. The improvement of spermatogonial stem cell culture requires deeper understanding of their metabolic requirements and the mechanisms that regulate metabolic homeostasis.

AIM

This review gives a summary on our knowledge of spermatogonial stem cell metabolism during maintenance and differentiation and highlights the potential influence of Sertoli cell and stem cell niche maturation on spermatogonial stem cell metabolic requirements during development.

RESULTS AND CONCLUSIONS

Fetal human spermatogonial stem cell precursors, or gonocytes, migrate into the seminiferous cords and supposedly mature to adult stem cells within the first year of human development. However, the spermatogonial stem cell niche does not fully differentiate until puberty, when Sertoli cells dramatically rearrange the architecture and microenvironment within the seminiferous epithelium. Consequently, pre-pubertal and adult spermatogonial stem cells experience two distinct niche environments potentially affecting spermatogonial stem cell metabolism and maturation. Indeed, the metabolic requirements of mouse primordial germ cells and pig gonocytes are distinct from their adult counterparts, and novel single-cell RNA sequencing analysis of human and porcine spermatogonial stem cells during development confirms this metabolic transition. Knowledge of the metabolic requirements and their changes and regulation during spermatogonial stem cell maturation is necessary to implement laboratory-based techniques and enable clinical use of spermatogonial stem cells. Based on the advancement in our understanding of germline metabolism circuits and maturation events of niche cells within the testis, we propose a new definition of spermatogonial stem cell maturation and its amendment in the light of metabolic change.

The long noncoding RNA CIRBIL is a regulator of steroidogenesis in mice

Infertility affects roughly 8-12 % of couples worldwide, and in above 50 % of couples, male factors are the primary or contributing cause. Many long noncoding RNAs (lncRNAs) are detected in the testis, but their functions are not well understood. CIRBIL was 862 nucleotides in length and was found to be localized mostly in the cytosol of Leydig cell, a small portion was positioned inside the seminiferous tubules. Loss of CIRBIL in mice resulted in male subfertility, characterized by smaller testis and increased germ cell apoptosis. Deletion of CIRBIL significant decreased the number of sperm and impaired the integrity of sperm head and tail. In CIRBIL KO mice, testosterone levels in serum and expression of testosterone biosynthesis genes (STAR and 3β-HSD) were both reduced. Gene Ontology (GO) term and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway were primarily enriched in steroid synthesis process in CIRBIL-binding proteins. Protein-protein (PPI) interaction networks revealed that both cis- and trans-regulated target genes of CIRBIL were associated with testosterone synthesis. Collectively, our results strongly suggest that CIRBIL is a regulator of steroid hormone synthesis.

Hormone measurements and histomorphological observations in male Bactrian camels

The aim of this study was to investigate the effect of age on the hypothalamic-pituitary-gonadal (HPG) axis hormones and to determine the morphological changes of the testis. The Bactrian camels were divided into two groups based on their ages. The results showed that the testicular weight was significantly heavier in adult male camels than in pubertal male camels (P < 0.05). There were also significant differences between testicular length, testicular width, and testicular volume (P < 0.05). In the testes of both pubertal and adult male camels, Sertoli cells, spermatogonia, spermatocytes, round spermatids, and elongated spermatids were observed. Adult male camels had more Sertoli cells (P < 0.01) and elongated spermatids (P < 0.05). The concentrations of testosterone, follicle-stimulating hormone (FSH), and luteinizing hormone (LH) were higher in the plasma and testes of adult camels than in pubertal camels (P < 0.05). E2 concentrations were lower in adult camels than in pubertal camels (P < 0.05). The testosterone levels in testicular tissue were higher than in blood plasma in both adult and pubertal stage (P < 0.05). In conclusion, these findings provide supportive knowledge and show the significant differences in terms of testicular volume, testicular hormone concentrations, and testicular morphology between different developmental stages in Bactrian camels.

What do we know about blood-testis barrier? current understanding of its structure and physiology

Blood-testis barrier (BTB) creates a particular compartment in the seminiferous epithelium. Contacting Sertoli cell-Sertoli cell plasma membranes possess specialized junction proteins which present a complex dynamic of formation and dismantling. Thus, these specialized structures facilitate germ cell movement across the BTB. Junctions are constantly rearranged during spermatogenesis while the BTB preserves its barrier function. Imaging methods are essential to studying the dynamic of this sophisticated structure in order to understand its functional morphology. Isolated Sertoli cell cultures cannot represent the multiple interactions of the seminiferous epithelium and in situ studies became a fundamental approach to analyze BTB dynamics. In this review, we discuss the contributions of high-resolution microscopy studies to enlarge the body of morphofunctional data to understand the biology of the BTB as a dynamic structure. The first morphological evidence of the BTB was based on a fine structure of the junctions, which was resolved with Transmission Electron Microscopy. The use of conventional Fluorescent Light Microscopy to examine labelled molecules emerged as a fundamental technique for elucidating the precise protein localization at the BTB. Then laser-scanning confocal microscopy allowed the study of three-dimensional structures and complexes at the seminiferous epithelium. Several junction proteins, like the transmembrane, scaffold and signaling proteins, were identified in the testis using traditional animal models. BTB morphology was analyzed in different physiological conditions as the spermatocyte movement during meiosis, testis development, and seasonal spermatogenesis, but also structural elements, proteins, and BTB permeability were studied. Under pathological, pharmacological, or pollutant/toxic conditions, there are significant studies that provide high-resolution images which help to understand the dynamic of the BTB. Notwithstanding the advances, further research using new technologies is required to gain information on the BTB. Super-resolution light microscopy is needed to provide new research with high-quality images of targeted molecules at a nanometer-scale resolution. Finally, we highlight research areas that warrant future studies, pinpointing new microscopy approaches and helping to improve our ability to understand this barrier complexity.

Melatonin regulates dihydrotestosterone formation via its membrane receptor in the epididymal epithelial cells of sheep

Both melatonin and androgen, which affect sperm fertility, are the important factors in epididymis of male animal. In the present study, we confirmed that melatonin regulates the formation of dihydrotestosterone (DHT) in sheep epididymides. Here, we investigated the localization and the expression levels of melatonin keys synthases AANAT and HIOMT, membrane receptors MT1 and MT2, and nuclear receptor RORα in sheep epididymides and testes. We also cultured epididymal epithelial cells and treated them with different concentrations of melatonin (10^-11-10^-7 M) and luzindole (10^-5 M) and 4P-PDOT (10^-5 M) to investigate whether melatonin is involved in the regulation of DHT formation and whether these effects are mediated through its receptor pathways. The results showed that AANAT, HIOMT, MT1, MT2, and RORα were differentially expressed between sheep epididymides and testes. In addition, melatonin is involved in mediating the formation of DHT in epididymal epithelial cells, and its influence on DHT is at least partially regulated by the melatonin receptor pathway. Our findings showed that melatonin regulates the functions of the testes and epididymides through an autocrine mechanism and regulates the formation of androgen in sheep epididymides via the receptor pathway. These results provide a basis for further exploring the regulatory mechanisms of melatonin in animal reproduction.

TNFα stimulates the proliferation of immature Sertoli cells by attenuating UPS-degradation of cyclin D1 and leads to the delay of BTB maturation in pubertal rats

BACKGROUNDS

The Sertoli cell that plays a vital role during spermatogenesis is a known target of physiological and pathological factors affecting testicular development. Tumor necrosis factor alpha (TNFα) participates in the blood-testis barrier reconstruction, cell apoptosis, and inflammatory response by recognizing receptors on Sertoli cell. TNFα has also been shown to induce the proliferation of immature Sertoli cell in vitro, yet the mechanism still remains unclarified.

OBJECTIVES

This study was designed to investigate the effect of TNFα on blood-testis barrier development during puberty and the underlying mechanisms of TNFα-induced immature Sertoli cell proliferation.

MATERIALS AND METHODS

Immature male Sprague-Dawley rats of postnatal day 12 were intraperitoneally injected with TNFα. Biotin-labeled method was used to detect permeability of the developing blood-testis barrier after TNFα treatment, and the distribution of occludin and junctional adhesion molecule-A (JAM-A) were detected by immunofluorescence. Sertoli cells isolated from Sprague-Dawley rats of postnatal day 10 were cultured in vitro and treated with TNFα. Cell proliferation rate was reflected by Cell Counting Kit-8 (CCK-8) and 5-ethynyl-2'-deoxyuridine (EdU) assay. Immunoblot and quantitative polymerase chain reaction were used to detect the expression of proliferating cell nuclear antigen, Fbxo4, and cyclin D1. Immunoprecipitation was used to detect the ubiquitination of cyclin D1 and the interaction between Fbxo4 and cyclin D1. Ammonium pyrrolidinedithiocarbamate (PDTC) was applied to detect the effect of nuclear factor kappaB (NFκB) activity inhibition on TNFα-induced Sertoli cell proliferation. The adenoviral recombinant plasmid containing rat Fbxo4 gene was constructed to investigate the effect of Fbxo4 overexpression on Sertoli cell proliferation promoted by TNFα.

RESULTS

The in vivo experiment revealed a significant delay of blood-testis barrier maturation in pubertal rats caused by exogenous TNFα. TNFα (10 ng/ml) treatment in vitro was found to promote the proliferation of immature Sertoli cells, accompanied with increased NFκB activity and cyclin D1 protein level. The level of Fbxo4 and ubiquitination of cyclin D1 were decreased after TNFα treatment. Inhibitor of NFκB or overexpression of Fbxo4 could both reverse the TNFα-induced proliferation of immature Sertoli cells, meanwhile restore the ubiquitin-proteasome system-dependent degradation of cyclin D1. Overexpression of Fbxo4 could not affect the activation of NFκB caused by TNFα.

CONCLUSION

These results indicate that TNFα inhibits the ubiquitination and degradation of cyclin D1 through the NFκB pathway, thereby promoting the proliferation of immature Sertoli cell in vitro and inducing the delay of blood-testis barrier maturation in pubertal rats.

Zika Virus Infection Damages the Testes in Pubertal Common Squirrel Monkeys (Saimiri collinsi)

During the Zika virus (ZIKV) outbreak and after evidence of its sexual transmission was obtained, concerns arose about the impact of the adverse effects of ZIKV infection on human fertility. In this study, we evaluated the clinical-laboratory aspects and testicular histopathological patterns of pubertal squirrel monkeys (Saimiri collinsi) infected with ZIKV, analyzing the effects at different stages of infection. The susceptibility of S. collinsi to ZIKV infection was confirmed by laboratory tests, which detected viremia (mean 1.63 × 106 RNA copies/µL) and IgM antibody induction. Reduced fecal testosterone levels, severe testicular atrophy and prolonged orchitis were observed throughout the experiment by ultrasound. At 21 dpi, testicular damage associated with ZIKV was confirmed by histopathological and immunohistochemical (IHC) analyses. Tubular retraction, the degeneration and necrosis of somatic and germ cells in the seminiferous tubules, the proliferation of interstitial cells and an inflammatory infiltrate were observed. ZIKV antigen was identified in the same cells where tissue injuries were observed. In conclusion, squirrel monkeys were found to be susceptible to the Asian variant of ZIKV, and this model enabled the identification of multifocal lesions in the seminiferous tubules of the infected group evaluated. These findings may suggest an impact of ZIKV infection on male fertility.

hnRNPH1 establishes Sertoli-germ cell crosstalk through cooperation with PTBP1 and AR, and is essential for male fertility in mice

Spermatogenesis depends on the crosstalk of Sertoli cells (SCs) and germ cells. However, the gene regulatory network establishing the communications between SCs and germ cells remains unclear. Here, we report that heterogeneous nuclear ribonucleoprotein H1 (hnRNPH1) in SCs is essential for the establishment of crosstalk between SCs and germ cells. Conditional knockout of hnRNPH1 in mouse SCs leads to compromised blood-testis barrier function, delayed meiotic progression, increased germ cell apoptosis, sloughing of germ cells and, eventually, infertility of mice. Mechanistically, we discovered that hnRNPH1 could interact with the splicing regulator PTBP1 in SCs to regulate the pre-mRNA alternative splicing of the target genes functionally related to cell adhesion. Interestingly, we also found hnRNPH1 could cooperate with the androgen receptor, one of the SC-specific transcription factors, to modulate the transcription level of a group of genes associated with the cell-cell junction and EGFR pathway by directly binding to the gene promoters. Collectively, our findings reveal a crucial role for hnRNPH1 in SCs during spermatogenesis and uncover a potential molecular regulatory network involving hnRNPH1 in establishing Sertoli-germ cell crosstalk.

The abundance and localization of claudin-1 and -5 in the adult tomcats (Felis catus) testis, tubules rectus, rete testis, efferent ductules, and epididymis

Tight junctions (TJ) are the anatomical component of blood-testis (BTB) and blood-epididymis (BEB) barriers and contain many proteins, including claudins. The presence of claudins in domestic cat testis and epididymis has not been previously described. This study aimed to determine whether claudin-1 and claudin-5 participate in the structure of BTB and BEB and whether their amounts differ between the testis and epididymal segments of adult cats, using Western blotting (WB) and immunohistochemistry. WB results demonstrated that claudin-1 was significantly lower in the testis than in all epididymal segments and higher in the corpus epididymis than in the cauda, while claudin-5 in the testis was significantly lower than in the caput and corpus. Claudin-1 was absent at the Sertoli-Sertoli junctions, while claudin-5 was detected at the level of the BTB during stages I and VIII. Both claudins were observed in the pachytene spermatocytes and the developing acrosome of the round and elongating spermatids. Claudin-5 was also detected in the cytoplasm of some spermatogonia, Sertoli cells, and late spermatid acrosome. In the epididymal segments, both claudins were localized to the area of the tight junctions and along the entire length of the lateral plasma membranes of adjacent principal cells and between principal and basal cells. These results may indicate that in the domestic cat, claudin-1 and -5 participate as both tight junction proteins and adhesion molecules in the BEB's structure, claudin 5 is a component of the BTB, and both proteins may be involved in postmeiotic germ cell development, especially acrosome development.

Global warming and testis function: A challenging crosstalk in an equally challenging environmental scenario

Environmental pollution, accounting for both chemical and physical factors, is a major matter of concern due to its health consequences in both humans and animals. The release of greenhouse gases with the consequent increase in environmental temperature is acknowledged to have a major impact on the health of both animals and humans, in current and future generations. A large amount of evidence reports detrimental effects of acute heat stress on testis function, particularly on the spermatogenetic and steroidogenetic process, in both animal and human models, wich is largely related to the testis placement within the scrotal sac and outside the abdomen, warranting an overall scrotal temperature of 2°C-4°C lower than the core body temperature. This review will provide a thorough evaluation of environmental temperature's effect on testicular function. In particular, basic concepts of body thermoregulation will be discussed together with available data about the association between testis damage and heat stress exposure. In addition, the possible association between global warming and the secular decline of testis function will be critically evaluated in light of the available epidemiological studies.

Polystyrene microplastics induce apoptosis in chicken testis via crosstalk between NF-κB and Nrf2 pathways

Microplastics (MPs) are a new type of pollutants that are widespread in nature, and their toxic effects on humans or animals are receiving attention. Birds are in a higher ecological niche in nature, and MPs may have potential bioaccumulation and biomagnification risks to birds. The mechanisms underlying the reproductive toxicity of MPs to birds are mainly unknown. To study the reproductive toxicity of MPs to birds, we randomly divided chickens into six groups and exposed polystyrene microplastics (PS-MPs) through drinking water (0, 1, and 100 mg/L) for 28 and 42 days. We found that PS-MPs caused testicular inflammatory infiltration and interstitial hemorrhage, resulting in testicular tissue damage; the expression of Claudin3 and Occludin in the blood-testis barrier (BTB) decreased and may damage the integrity of the BTB. PS-MPs exposure inhibited the expression of the Nrf2-Keap1 pathway, which in turn reduced HO-1 and NQO1, simultaneous GSH and T-AOC were also reduced, resulting in an imbalance of the redox system; in addition, the NF-κB signaling pathway was activated, increasing the expression of TNF-α, COX-2 and iNOS. Under redox system imbalance and inflammatory stress, exposure to PS-MPs led to decreased expression of Bcl-2 and increased Bax, cytc, caspase-8, and caspase-3, etc., activating apoptosis, and ultimately causing testicular damage. These results suggested that PS-MPs exposure led to an imbalance of the redox system and an inflammatory response, inducing both endogenous and exogenous apoptosis, resulting in testicular tissue damage. Our study provides a theoretical basis for reproductive injury mechanisms in chicken.

Perfluorooctanoic acid alternatives hexafluoropropylene oxides exert male reproductive toxicity by disrupting blood-testis barrier

As alternatives to perfluorooctanoic acid (PFOA), hexafluoropropylene oxide (HFPO) homologues, including hexafluoropropylene oxide dimer acid (HFPO-DA), hexafluoropropylene oxide trimer acid (HFPO-TA), and hexafluoropropylene oxide tetramer acid (HFPO-TeA), have attracted widespread attention recently due to their environmental ubiquity and high potential for bioaccumulation and toxicity. In the present study, a set of in vivo mouse and in vitro mouse testicular Sertoli TM4 cell experiments were employed to explore the male reproductive toxicity and underlying mechanisms of HFPO homologues on blood-testis barrier. Tissue and permeability analyses of mice testes after 28-day treatment with 5 mg/kg/day HFPO-DA or PFOA, or 0.05 mg/kg/day HFPO-TA or HFPO-TeA indicated that there was an increase in the degradation of TJ protein occludin in mice with a disrupted blood-testis barrier (BTB). Following exposure to 100 μM HFPO-DA, HFPO-TA or 10 μM PFOA, HFPO-TeA, transepithelial electrical resistance measurements of TM4 cells also indicated BTB disruption. Additionally, as a result of the exposure, matrix metalloproteinase-9 expression was enhanced through activation of p38 MAPK, which promoted the degradation of occludin. On the whole, the results indicated HFPO homologues and PFOA induced BTB disruption through upregulation of p-p38/p38 MAPK/MMP-9 pathway, which promoted the degradation of TJ protein occludin and caused the disruption of TJ.

Quercetin Abates Aluminum Trioxide Nanoparticles and Lead Acetate Induced Altered Sperm Quality, Testicular Oxidative Damage, and Sexual Hormones Disruption in Male Rats

This study examined the effects of exposure to lead acetate (PbAc) and/or aluminum trioxide nanoparticles (Al2O3NPs) on testicular function. Additionally, the probable reproprotective effects of quercetin (QTN) against Al2O3NPs and PbAc co-exposure in male Sprague Dawely rats were assessed. Al2O3NPs (100 mg/kg b.wt.), PbAc (50 mg/kg b.wt.), and QTN (20 mg/kg b.wt.) were orally administered for 60 days. Then, spermiogram, histopathological examinations of the testis and accessory glands, and immunohistochemical detection of androgen receptors (AR) and tumor necrotic factor alpha (TNF-α) were achieved. Moreover, serum levels of male sex hormones and testicular levels of antioxidant indices were estimated. The results showed that Al2O3NPs and/or PbAc caused significant sperm abnormalities, testicular oxidative stress, and histopathological changes. Furthermore, serum testosterone, LH, and FSH levels significantly decreased, while estradiol levels significantly increased. The Al2O3NPs and/or PbAc co-exposed group had more obvious disturbances. Furthermore, QTN co-administration significantly reversed the Al2O3NPs and PbAc-induced testicular histopathological alterations, reduced antioxidant defenses, and altered AR and TNF-α immune expression in testicular tissues. Conclusively, Al2O3NPs and/or PbAc evoked testicular dysfunction by inducing oxidative injury and inflammation. However, QTN oral dosing effectively mitigated the negative effects of Al2O3NPs and PbAc by suppressing oxidative stress and inflammation and improving the antioxidant defense system.

Tight Junctions, the Key Factor in Virus-Related Disease

Tight junctions (TJs) are highly specialized membrane structural domains that hold cells together and form a continuous intercellular barrier in epithelial cells. TJs regulate paracellular permeability and participate in various cellular signaling pathways. As physical barriers, TJs can block viral entry into host cells; however, viruses use a variety of strategies to circumvent this barrier to facilitate their infection. This paper summarizes how viruses evade various barriers during infection by regulating the expression of TJs to facilitate their own entry into the organism causing infection, which will help to develop drugs targeting TJs to contain virus-related disease.

Sertoli cell survival and barrier function are regulated by miR-181c/d-Pafah1b1 axis during mammalian spermatogenesis

Sertoli cells contribute to the formation of the blood-testis barrier (BTB), which is necessary for normal spermatogenesis. Recently, microRNAs (miRNAs) have emerged as posttranscriptional regulatory elements in BTB function during spermatogenesis. Our previous study has shown that miR-181c or miR-181d (miR-181c/d) is highly expressed in testes from boars at 60 days old compared with at 180 days old. Herein, we found that overexpression of miR-181c/d via miR-181c/d mimics in murine Sertoli cells (SCs) or through injecting miR-181c/d-overexpressing lentivirus in murine testes perturbs BTB function by altering BTB-associated protein distribution at the Sertoli cell-cell interface and F-actin organization, but this in vivo perturbation disappears approximately 6 weeks after the final treatment. We also found that miR-181c/d represses Sertoli cell proliferation and promotes its apoptosis. Moreover, miR-181c/d regulates Sertoli cell survival and barrier function by targeting platelet-activating factor acetylhydrolase 1b regulatory subunit 1 (Pafah1b1) gene. Furthermore, miR-181c/d suppresses PAFAH1B1 expression, reduces the complex of PAFAH1B1 with IQ motif-containing GTPase activating protein 1, and inhibits CDC42/PAK1/LIMK1/Cofilin pathway which is required for F-actin stabilization. In total, our results reveal the regulatory axis of miR-181c/d-Pafah1b1 in cell survival and barrier function of Sertoli cells and provide additional insights into miRNA functions in mammalian spermatogenesis.

Bibliometric and visual analysis of blood-testis barrier research

Background: Extensive research on the blood-testis barrier has been undertaken in recent years. However, no systematic bibliometric study has been conducted on this subject. Our research aimed to identify the hotspots and frontiers of blood-testis barrier research and to serve as a guide for future scientific research and decision-making in the field.

Methods: Studies on the blood-testis barrier were found in the Web of Science Core Collection. VOSviewer, CiteSpace, and Microsoft Excel were used to conduct the bibliometric and visual analyses.

Results: We found 942 blood-testis barrier studies published in English between 1992 and 2022. The number of annual publications and citations increased significantly between 2011 and 2022, notably in the United States. China and the United States, the US Population Council, Endocrinology, and Cheng C. Yan were the most productive countries, institution, journal, and author, respectively. The study keywords indicated that blood-testis barrier research involves a variety of compositional features (tight junctions, cytoskeleton, adherens junctions), cell types (Sertoli cells, germ cells, Leydig cells, stem cells), reproductive toxicity (cadmium, nanoparticles, bisphenol-a), and relevant mechanisms (spermatogenesis, apoptosis, oxidative stress, dynamics, inflammation, immune privilege).

Conclusion: The composition and molecular processes of the blood-testis barrier as well as the blood-testis barrier in male infertility patients are the primary research hotspots in this field. In addition, future research will likely focus on treatment and the development of novel medications that target signal pathways in oxidative stress and apoptosis to preserve the blood-testis barrier. Further studies must extend to clinical diagnosis and therapy.

Gut microbiota supports male reproduction via nutrition, immunity, and signaling

Gut microbiota (GM) is a major component of the gastrointestinal tract. Growing evidence suggests that it has various effects on many distal organs including the male reproductive system in mammals. GM and testis form the gut-testis axis involving the production of key molecules through microbial metabolism or de novo synthesis. These molecules have nutrition, immunity, and hormone-related functions and promote the male reproductive system via the circulatory system. GM helps maintain the integral structure of testes and regulates testicular immunity to protect the spermatogenic environment. Factors damaging GM negatively impact male reproductive function, however, the related mechanism is unknown. Also, the correlation between GM and testis remains to be yet investigated. This review discusses the complex influence of GM on the male reproductive system highlighting the impact on male fertility.

Transcriptomic Analysis of Testicular Gene Expression in a Dog Model of Experimentally Induced Cryptorchidism

Cryptorchidism, a condition in which testes fail to descend from the abdomen into the scrotum, is a risk factor for infertility and germ cell cancer. Normally, tight junctions between adjacent Sertoli cells in the testes form a blood–testes barrier that regulates spermatogenesis; however, the effect of cryptorchidism on tight junctions is not well-understood. We established a model of heat-induced testicular damage in dogs using surgical cryptorchidism. We sequenced RNA to investigate whether certain transcripts are expressed at higher rates in heat-damaged versus normally descended testes. Claudins, cell adhesion molecules, were relatively highly expressed in cryptorchid testes: claudins 2, 3, 5, 11, and 18 were significantly increased in cryptorchid testes and reduced by orchiopexy. SOX9-positive Sertoli cells were present in the seminiferous tubules in both cryptorchid and control testes. Using real-time PCR and Western blot analysis to compare Sertoli cells cultured at 34 °C and 37 °C, we found that Sertoli cell claudins 2, 3, 5, 11, and 18 were significantly increased at 37 °C; however, accumulation was higher in the G0/G1 phase in Sertoli cells cultured at 34 °C. These results indicate that testicular hyperthermia caused by cryptorchidism affects claudin expression, regulated germ cell death, and the proliferation of Sertoli cells.

Junctional complexes of the blood-testis barrier in the Japanese quail (Coturnix Coturnix japonica)

This study investigated the developmental changes in the adherens junctions, gap junctions, as well as tight junctions forming the blood-testis barrier (BTB) in Japanese quail (Coturnix Coturnix japonica) testis. Testicular tissue from pre-pubertal, pubertal, adult, and aged Japanese quail were examined by immunohistochemistry and transmission electron microscopy (TEM). The tight junction proteins claudin-3, claudin-11, occludin and zonula occludens-1 (ZO-1), were generally localised in the cytoplasm of Sertoli cells, spermatogonia, and spermatocytes of pre-pubertal, pubertal, some adult birds. The adherens junction protein E-cadherin had a similar distribution pattern. During pre-pubertal development, the gap junction protein connexin-43 (Cx43) was only localised between Leydig cells in the testicular interstitium. However, TEM revealed the presence of gap junctions between cells of the seminiferous epithelium as early as the pre-pubertal stage. Furthermore, TEM confirmed the presence of tight and adherens junctions in the seminiferous epithelia of all age groups. The findings of this study document age-related differences in the immunolocalisation and intensity of the junctional proteins and the ultrastructure of the junctional complexes forming the BTB in quail testes. Additionally, the junctional complexes forming the BTB in the Japanese quail are well established prior to puberty. This study provides baseline information for the future evaluation of pathological changes in the BTB of avian species at different developmental stages.

Understanding and managing the suppression of spermatogenesis caused by testosterone replacement therapy (TRT) and anabolic–androgenic steroids (AAS)

Use of testosterone replacement therapy (TRT) and anabolic–androgenic steroids (AAS) has increased over the last 20 years, coinciding with an increase in men presenting with infertility and hypogonadism. Both agents have a detrimental effect on spermatogenesis and pose a clinical challenge in the setting of hypogonadism and infertility. Adding to this challenge is the paucity of data describing recovery of spermatogenesis on stopping such agents. The unwanted systemic side effects of these agents have driven the development of novel agents such as selective androgen receptor modulators (SARMs). Data showing natural recovery of spermatogenesis following cessation of TRT are limited to observational studies. Largely, these have shown spontaneous recovery of spermatogenesis after cessation. Contemporary literature suggests the time frame for this recovery is highly variable and dependent on several factors including baseline testicular function, duration of drug use and age at cessation. In some men, drug cessation alone may not achieve spontaneous recovery, necessitating hormonal stimulation with selective oestrogen receptor modulators (SERMs)/gonadotropin therapy or even the need for assisted reproductive techniques. However, there are limited prospective randomized data on the role of hormonal stimulation in this clinical setting. The use of hormonal stimulation with agents such as gonadotropins, SERMs, aromatase inhibitors and assisted reproductive techniques should form part of the counselling process in this cohort of hypogonadal infertile men. Moreover, counselling men regarding the detrimental effects of TRT/AAS on fertility is very important, as is the need for robust randomized studies assessing the long-term effects of novel agents such as SARMs and the true efficacy of gonadotropins in promoting recovery of spermatogenesis.

Exposed and Sequestered Antigens in Testes and Their Protection by Regulatory T Cell-Dependent Systemic Tolerance

Continuous exposure of tissue antigen (Ag) to the autoantigen-specific regulatory T cells (Treg) is required to maintain Treg-dependent systemic tolerance. Thus, testis autoantigens, previously considered as sequestered, may not be protected by systemic tolerance. We now document that the complete testis antigen sequestration is not valid. The haploid sperm Ag lactate dehydrogenase 3 (LDH3) is continuously exposed and not sequestered. It enters the residual body (RB) to egress from the seminiferous tubules and interact with circulating antibody (Ab). Some LDH3 also remains inside the sperm cytoplasmic droplets (CD). Treg-depletion in the DEREG mice that express diphtheria toxin receptor on the Foxp3 promoter results in spontaneous experimental autoimmune orchitis (EAO) and Ab to LDH3. Unlike the wild-type male mice, mice deficient in LDH3 (wild-type female or LDH3 NULL males) respond vigorously to LDH3 immunization. However, partial Treg depletion elevated the wild-type male LDH3 responses to the level of normal females. In contrast to LDH3, zonadhesin (ZAN) in the sperm acrosome displays properties of a sequestered Ag. However, when ZAN and other sperm Ag are exposed by vasectomy, they rapidly induce testis Ag-specific tolerance, which is terminated by partial Treg-depletion, leading to bilateral EAO and ZAN Ab response. We conclude that some testis/sperm Ag are normally exposed because of the unique testicular anatomy and physiology. The exposed Ag: 1) maintain normal Treg-dependent systemic tolerance, and 2) are pathogenic and serve as target Ag to initiate EAO. Unexpectedly, the sequestered Ags, normally non-tolerogenic, can orchestrate de novo Treg-dependent, systemic tolerance when exposed in vasectomy.

Understanding the Underlying Molecular Mechanisms of Meiotic Arrest during In Vitro Spermatogenesis in Rat Prepubertal Testicular Tissue

In vitro spermatogenesis appears to be a promising approach to restore the fertility of childhood cancer survivors. The rat model has proven to be challenging, since germ cell maturation is arrested in organotypic cultures. Here, we report that, despite a meiotic entry, abnormal synaptonemal complexes were found in spermatocytes, and in vitro matured rat prepubertal testicular tissues displayed an immature phenotype. RNA-sequencing analyses highlighted up to 600 differentially expressed genes between in vitro and in vivo conditions, including genes involved in blood-testis barrier (BTB) formation and steroidogenesis. BTB integrity, the expression of two steroidogenic enzymes, and androgen receptors were indeed altered in vitro. Moreover, most of the top 10 predicted upstream regulators of deregulated genes were involved in inflammatory processes or immune cell recruitment. However, none of the three anti-inflammatory molecules tested in this study promoted meiotic progression. By analysing for the first time in vitro matured rat prepubertal testicular tissues at the molecular level, we uncovered the deregulation of several genes and revealed that defective BTB function, altered steroidogenic pathway, and probably inflammation, could be at the origin of meiotic arrest.

The Role of Testosterone in Spermatogenesis: Lessons From Proteome Profiling of Human Spermatozoa in Testosterone Deficiency

Testosterone is essential to maintain qualitative spermatogenesis. Nonetheless, no studies have been yet performed in humans to analyze the testosterone-mediated expression of sperm proteins and their importance in reproduction. Thus, this study aimed to identify sperm protein alterations in male hypogonadism using proteomic profiling. We have performed a comparative proteomic analysis comparing sperm from fertile controls (a pool of 5 normogonadic normozoospermic fertile men) versus sperm from patients with secondary hypogonadism (a pool of 5 oligozoospermic hypogonadic patients due to isolated LH deficiency). Sperm protein composition was analyzed, after peptide labelling with Isobaric Tags, via liquid chromatography followed by tandem mass spectrometry (LC-MS/MS) on an LTQ Velos-Orbitrap mass spectrometer. LC-MS/MS data were analyzed using Proteome Discoverer. Criteria used to accept protein identification included a false discovery rate (FDR) of 1% and at least 1 peptide match per protein. Up to 986 proteins were identified and, of those, 43 proteins were differentially expressed: 32 proteins were under-expressed and 11 were over-expressed in the pool of hypogonadic patients compared to the controls. Bioinformatic analyses were performed using UniProt Knowledgebase, and the Gene Ontology Consortium database based on PANTHER. Notably, 13 of these 43 differentially expressed proteins have been previously reported to be related to sperm function and spermatogenesis. Western blot analyses for A-Kinase Anchoring Protein 3 (AKAP3) and the Prolactin Inducible Protein (PIP) were used to confirm the proteomics data. In summary, a high-resolution mass spectrometry-based proteomic approach was used for the first time to describe alterations of the sperm proteome in secondary male hypogonadism. Some of the differential sperm proteins described in this study, which include Prosaposin, SMOC-1, SERPINA5, SPANXB1, GSG1, ELSPBP1, fibronectin, 5-oxoprolinase, AKAP3, AKAP4, HYDIN, ROPN1B, ß-Microseminoprotein and Protein S100-A8, could represent new targets for the design of infertility treatments due to androgen deficiency.

The Role of ZIP9 and Androgen Receptor in the Establishment of Tight Junctions between Adult Rat Sertoli Cells

The blood-testis barrier (BTB) is formed from tight junctions (TJs) between Sertoli cells. This dynamic structure, which establishes an immune-privileged environment protecting haploid germ cells formed in puberty from cells of the innate immune system, protects male fertility. Testosterone produced in Leydig cells is one of the main regulators of TJ protein expression and BTB dynamics. Nevertheless, although it has been assumed that testosterone effects on TJs and BTB are mediated through the classical androgen receptor (AR), newer results call the importance of this receptor into question. ZIP9, a recently identified androgen receptor of plasma membranes, mediates testosterone effects that promote the expression of TJ proteins and TJ formation in a rat Sertoli cell line that lacks the classical AR. Although these findings suggest that ZIP9 mediates these testosterone effects, participation of the classical AR in these events cannot be excluded. Here we used immortalized adult rat Sertoli cells that express both ZIP9 and AR and addressed the involvement of these receptors in the stimulation of TJ protein expression and TJ formation in response to testosterone and to the androgenic peptide IAPG that acts via ZIP9. We find that both testosterone and IAPG trigger the so-called non-classical signaling pathway of testosterone and stimulate the expression of TJ-associated proteins and TJ formation. Silencing classical AR expression had no effect on the responses, whereas silencing of ZIP9 expression completely blocked them. Our results demonstrate that ZIP9 is the sole androgen receptor involved in the regulation of TJ protein expression and TJ formation at the BTB.

Differential expression and localization of tight junction proteins in the goat epididymis

The blood-epididymis barrier (BEB) forms a unique microenvironment that is crucial for the maturation, protection, transport, and storage of spermatozoa in the epididymis. To characterize the function of tight junctions (TJs), which are constitutive components of the BEB, we determined the expression and localization of TJ proteins such as zonula occludens (ZO)-1, 2, and 3, occludin, and claudin3 (Cldn3) during postnatal development in the goat epididymis. To assess the expression patterns of TJ proteins in immature (3 months of age) and mature (14 months of age) goat epididymides, two different experimental methods were used including immunofluorescence labeling and western blotting. We show that, ZO-1, 2, and 3, and occludin, were strictly expressed and localized to the TJs of the goat epididymis, whereas Cldn3 was present in basolateral membranes as well as TJs. All TJ proteins examined were more highly expressed in the immature epididymis compared to levels in mature tissue. In conclusion, our study indicates that at least five TJ proteins, namely ZO-1, ZO-2, ZO-3, occludin, and Cldn3, are present in TJs, and the expression strength and pattern of TJ proteins tend to be age dependent in the goat epididymis. Together, these data suggest that the distinct expression patterns of TJ proteins are essential for regulating components of the luminal contents in the epididymal epithelium and for forming adequate luminal conditions that are necessary for the maturation, protection, transport, and storage of spermatozoa in the goat epididymis.

Chronic exposure to polystyrene microplastics induced male reproductive toxicity and decreased testosterone levels via the LH-mediated LHR/cAMP/PKA/StAR pathway

Background

Microplastics (MPs), which are smaller in size and difficult to degrade, can be easily ingested by marine life and enter mammals through the food chain. Our previous study demonstrated that following acute exposure to MPs, the serum testosterone content reduced and sperm quality declined, resulting in male reproductive dysfunction in mice. However, the toxic effect of long-term exposure to MPs at environmental exposure levels on the reproductive system of mammals remains unclear.

Results

In vivo, mice were given drinking water containing 100 μg/L and 1000 μg/L polystyrene MPs (PS-MPs) with particle sizes of 0.5 μm, 4 μm, and 10 μm for 180 consecutive days. We observed alterations in testicular morphology and reductions in testosterone, LH and FSH contents in serum. In addition, the viability of sperm was declined and the rate of sperm abnormality was increased following exposure to PS-MPs. The expression of steroidogenic enzymes and StAR was downregulated in testis tissues. In vitro, we used primary Leydig cells to explore the underlying mechanism of the decrease in testosterone induced by PS-MPs. First, we discovered that PS-MPs attached to and became internalized by Leydig cells. And then we found that the contents of testosterone in the supernatant declined. Meanwhile, LHR, steroidogenic enzymes and StAR were downregulated with concentration-dependent on PS-MPs. We also confirmed that PS-MPs decreased StAR expression by inhibiting activation of the AC/cAMP/PKA pathway. Moreover, the overexpression of LHR alleviated the reduction in StAR and steroidogenic enzymes levels, and finally alleviated the reduction in testosterone induced by PS-MPs.

Conclusions

PS-MPs exposure resulted in alterations in testicular histology, abnormal spermatogenesis, and interference of serum hormone secretion in mice. PS-MPs induced a reduction in testosterone level through downregulation of the LH-mediated LHR/cAMP/PKA/StAR pathway. In summary, our study showed that chronic exposure to PS-MPs resulted in toxicity of male reproduction under environmental exposure levels, and these potential risks may ring alarm bells of public health.

Graphical abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12989-022-00453-2.

Silica nanoparticles cause spermatogenesis dysfunction in mice via inducing cell cycle arrest and apoptosis

The widespread use of silica nanoparticles (SiNPs) has increased the risk of human exposure, which raised concerns about their adverse effects on human health, especially the reproductive system. Previous studies have shown that SiNPs could cause damage to reproductive organs, but the specific mechanism is still unclear. In this study, to investigate the underlying mechanism of male reproductive toxicity induced by SiNPs, 40 male mice at the age of 8 weeks were divided into two groups and then intraperitoneally injected with vehicle control or 10 mg/kg SiNPs per day for one week. The results showed that SiNPs could damage testicular structure, perturb spermatogenesis and reduce serum testosterone levels, leading to a decrease in sperm quality and quantity. In addition, the ROS level in the testis of exposed mice was significantly increased, followed by imbalance of the oxidative redox status. Further study revealed that exposure to SiNPs led to cell cycle arrest and apoptosis, as shown by downregulation of the expression of positive cell cycle regulators and the activation of TNF-α/TNFR Ⅰ-mediated apoptotic pathway. The results demonstrated that SiNPs could cause testicles injure via inducing oxidative stress and DNA damage which led to cell cycle arrest and apoptosis, and thereby resulting in spermatogenic dysfunction.

Dihydrotestosterone through blockade of TGF-β/Smad signaling mediates the anti-fibrosis effect under hypoxia in canine Sertoli cells

The hypoxic microenvironment of cryptorchidism is an important factor to induce the impairment of the structure and function of Sertoli cells and thus lead to spermatogenesis loss or tumorigenesis. Dihydrotestosterone (DHT), as a potent nonaromatizable 5α-reduced androgen, has both positive and negative effect on pathological fibrosis process. However, it is still unknown whether DHT can regulate hypoxia-induced fibrosis of Sertoli cells. Herein, in this study, we evaluate the DHT level, two 5α-reductase isoforms, 5α-red1 and 5α-red2, as well as HIF-1α expression pattern in canine cryptorchidism and contralateral normal testis. Results showed that the abdominal testes presented low DHT levels and 5α-red1 and 5α-red2 expression, while significantly higher HIF-1α expression and ECM production compared with the scrotum. Moreover, we established a hypoxia-induced fibrosis model in canine Sertoli cells induced by cobalt chloride (CoCl₂), and found that DHT inhibited the fibrosis of Sertoli cells in a dose-dependent manner. Meanwhile, DHT interfered with the TGF-β signaling by reducing the expression of TGF-βRI and TGF-βRII and inhibiting the expression and phosphorylation of Smad2 and Smad3, while flutamide (androgen receptor inhibitor) inhibited these effects of DHT. Furthermore, use of LY2109761 (TGF-β receptor type I/II inhibitor) to interfere with the TGF-β/Smad pathway showed a similar effect with DHT suppression of the fibrosis in Sertoli cells. Our research data demonstrated that cryptorchidism is located in a hypoxic and DHT deficiency microenvironment. Moreover, supplementing DHT can alleviate the fibrosis process of Sertoli cells caused by hypoxia, which is associated with AR regulating the inhibition of TGF-β/Smad signaling.

What Does Androgen Receptor Signaling Pathway in Sertoli Cells During Normal Spermatogenesis Tell Us?

Androgen receptor signaling pathway is necessary to complete spermatogenesis in testes. Difference between androgen binding location in Sertoli cell classifies androgen receptor signaling pathway into classical signaling pathway and non-classical signaling pathway. As the only somatic cell type in seminiferous tubule, Sertoli cells are under androgen receptor signaling pathway regulation via androgen receptor located in cytoplasm and plasma membrane. Androgen receptor signaling pathway is able to regulate biological processes in Sertoli cells as well as germ cells surrounded between Sertoli cells. Our review will summarize the major discoveries of androgen receptor signaling pathway in Sertoli cells and the paracrine action on germ cells. Androgen receptor signaling pathway regulates Sertoli cell proliferation and maturation, as well as maintain the integrity of blood-testis barrier formed between Sertoli cells. Also, Spermatogonia stem cells achieve a balance between self-renewal and differentiation under androgen receptor signaling regulation. Meiotic and post-meiotic processes including Sertoli cell - Spermatid attachment and Spermatid development are guaranteed by androgen receptor signaling until the final sperm release. This review also includes one disease related to androgen receptor signaling dysfunction named as androgen insensitivity syndrome. As a step further ahead, this review may be conducive to develop therapies which can cure impaired androgen receptor signaling in Sertoli cells.

Tetrapeptides Modelled to the Androgen Binding Site of ZIP9 Stimulate Expression of Tight Junction Proteins and Tight Junction Formation in Sertoli Cells

Androgens stimulate the expression of tight junction (TJ) proteins and the formation of the blood-testis barrier (BTB). Interactions of testosterone with the zinc transporter ZIP9 stimulate the expression of TJ-forming proteins and promote TJ formation in Sertoli cells. In order to investigate androgenic effects mediated by ZIP9 but not by the nuclear androgen receptor (AR), the effects of three tetrapeptides fitting the androgen binding site of ZIP9 were compared with those induced by testosterone in a Sertoli cell line expressing ZIP9 but not the AR. Three tetrapeptides and testosterone displaced testosterone-BSA-FITC from the surface of 93RS2 cells and stimulated the non-classical testosterone signaling pathway that includes the activation of Erk1/2 kinases and transcription factors CREB and ATF-1. The expression of the TJ-associated proteins ZO-1 and claudin-5 was triggered as was the re-distribution of claudin-1 from the cytosol to the membrane and nucleus. Furthermore, TJ formation was stimulated, indicated by increased transepithelial electrical resistance. Silencing ZIP9 expression by siRNA prevented all of these responses. These results are consistent with an alternative pathway for testosterone action at the BTB that does not involve the nuclear AR and highlight the significant role of ZIP9 as a cell-surface androgen receptor that stimulates TJ formation.

Differential Effects of Viral Nucleic Acid Sensor Signaling Pathways on Testicular Sertoli and Leydig Cells

The human testis can be infected by a large number of RNA and DNA viruses. While various RNA virus infections may induce orchitis and impair testicular functions, DNA virus infection rarely affects the testis. Mechanisms underlying the differential effects of RNA and DNA viral infections on the testis remain unclear. In the current study, we therefore examined the effects of viral RNA and DNA sensor signaling pathways on mouse Sertoli cells (SC) and Leydig cells (LC). The local injection of viral RNA analogue polyinosinic-polycytidylic acid [poly(I:C)] into the testis markedly disrupted spermatogenesis, whereas the injection of the herpes simplex virus (HSV) DNA analogue HSV60 did not affect spermatogenesis. Poly(I:C) dramatically induced the expression of the proinflammatory cytokines tumor necrosis factor α (TNF-α) and interleukin 6 in SC and LC through Toll-like receptor 3 and interferon β promoter stimulator 1 signaling pathways, impairing the integrity of the blood-testis barrier and testosterone synthesis. Poly(I:C)-induced TNF-α production thus plays a critical role in the impairment of cell functions. In contrast, HSV60 predominantly induced the expression of type 1 interferons and antiviral proteins via the DNA sensor signaling pathway, which did not affect testicular cell functions. Accordingly, the Zika virus induced high levels of TNF-α in SC and LC and impaired their respective cellular functions, whereas Herpes simplex virus type 2 principally induced antiviral responses and did not impair such functions. These results provide insights into the mechanisms by which RNA viral infections impair testicular functions.

Cdc42 activity in Sertoli cells is essential for maintenance of spermatogenesis

Sertoli cells are highly polarized testicular supporting cells that simultaneously nurture multiple stages of germ cells during spermatogenesis. Proper localization of polarity protein complexes within Sertoli cells, including those responsible for blood-testis barrier formation, is vital for spermatogenesis. However, the mechanisms and developmental timing that underlie Sertoli cell polarity are poorly understood. We investigate this aspect of testicular function by conditionally deleting Cdc42, encoding a Rho GTPase involved in regulating cell polarity, specifically in Sertoli cells. Sertoli Cdc42 deletion leads to increased apoptosis and disrupted polarity of juvenile and adult testes but does not affect fetal and postnatal testicular development. The onset of the first wave of spermatogenesis occurs normally, but it fails to progress past round spermatid stages, and by young adulthood, conditional knockout males exhibit a complete loss of spermatogenic cells. These findings demonstrate that Cdc42 is essential for Sertoli cell polarity and for maintaining steady-state sperm production.

Sertoli cells of the testicular seminiferous tubule must be highly polarized to simultaneously sustain multiple stages of germ cells during spermatogenesis. Heinrich et al. use a Sertoli-specific conditional deletion mouse model to address the roles of CDC42-mediated apicobasal cell polarity in promoting testis development and spermatogenesis.

Kpna6 deficiency causes infertility in male mice by disrupting spermatogenesis

Spermatogenesis is driven by an ordered series of events, which rely on trafficking of specific proteins between nucleus and cytoplasm. The karyopherin α family of proteins mediates movement of specific cargo proteins when bound to karyopherin β. Karyopherin α genes have distinct expression patterns in mouse testis, implying they may have unique roles during mammalian spermatogenesis. Here, we use a loss-of-function approach to determine specifically the role of Kpna6 in spermatogenesis and male fertility. We show that ablation of Kpna6 in male mice leads to infertility and has multiple cumulative effects on both germ cells and Sertoli cells. Kpna6-deficient mice exhibit impaired Sertoli cell function, including loss of Sertoli cells and a compromised nuclear localization of the androgen receptor. Furthermore, our data demonstrate devastating defects on spermiogenesis, including incomplete sperm maturation and a massive reduction in sperm number, accompanied by disturbed histone-protamine exchange, differential localization of the transcriptional regulator BRWD1 and altered expression of RFX2 target genes. Our work uncovers an essential role of Kpna6 in spermatogenesis and, hence, in male fertility.

Summary: Two different mouse models delineate the morphological and functional impact of Kpna6 on spermatogenesis and Sertoli cell function and show that this protein is crucial for fertility in male mice.

UXT in Sertoli cells is required for blood-testis barrier integrity†

Spermatogenesis is a complex process that establishes male fertility and involves proper communication between the germline (spermatozoa) and the somatic tissue (Sertoli cells). Many factors that are important for spermatozoa production are also required for Sertoli cell function. Recently, we showed that the transcriptional cofactor ubiquitously expressed transcript (UXT) encodes a protein that is essential in germ cells for spermatogenesis and fertility. However, the role of UXT within Sertoli cells and how it affects Sertoli cell function was still unclear. Here we describe a novel role for UXT in the Sertoli cell's ability to support spermatogenesis. We find that the conditional deletion of Uxt in Sertoli cells results in smaller testis size and weight, which coincided with a loss of germ cells in a subset of seminiferous tubules. In addition, the deletion of Uxt has no impact on Sertoli cell abundance or maturity, as they express markers of mature Sertoli cells. Gene expression analysis reveals that the deletion of Uxt in Sertoli cells reduces the transcription of genes involved in the tight junctions of the blood-testis barrier (BTB). Furthermore, tracer experiments and electron microscopy reveal that the BTB is permeable in UXT KO animals. These findings broaden our understanding of UXT's role in Sertoli cells and its contribution to the structural integrity of the BTB.

Activation of C-C motif chemokine receptor 2 modulates testicular macrophages number, steroidogenesis, and spermatogenesis progression

The monocyte chemoattractant protein 1 (MCP-1) belongs to the CC chemokine family and acts in the recruitment of C-C motif chemokine receptor 2 (CCR2)-positive immune cell types to inflammation sites. In testis, the MCP-1/CCR2 axis has been associated with the macrophage population's functional regulation, which presents significant functions supporting germ cell development. In this context, herein, we aimed to investigate the role of the chemokine receptor CCR2 in mice testicular environment and its impact on male sperm production. Using adult transgenic mice strain that had the CCR2 gene replaced by a red fluorescent protein gene, we showed a stage-dependent expression of CCR2 in type B spermatogonia and early primary spermatocytes. Several parameters related to sperm production were reduced in the absence of CCR2 protein, such as Sertoli cell efficiency, meiotic index, and overall yield of spermatogenesis. Daily sperm production decreased by almost 40%, and several damages in the seminiferous tubules were observed. Significant reduction in the expression of important genes related to the Sertoli cell function (Cnx43, Vim, Ocln, Spna2) and meiosis initiation (Stra8, Pcna, Prdm9, Msh5) occurred in comparison to controls. Also, the number of macrophages significantly decreased in the absence of CCR2 protein, along with a disturbance in Leydig cell steroidogenic activity. In summary, our results show that the non-activation of the MCP-1/CCR2 axis disturbs the testicular homeostasis, interfering in macrophage population, meiosis initiation, blood-testis barrier function, and androgen synthesis, leading to the malfunction of seminiferous tubules, decreased testosterone levels, defective sperm production, and lower fertility index.

Molecular characterization and functional analysis of cyp11a and cyp11b in black rockfish (Sebastes schlegelii)

The cyp11 includes cyp11a and cyp11b in most mammals and teleosts, encoded cholesterol side chain lyase and 11β-hydroxylase, respectively. It is essential in steroid hormone synthesis. However, studies on the regulation of cyp11 are limited, especially in teleosts. In this study, the molecular characterization and function of cyp11a and cyp11b of black rockfish was investigated. Both of them showed high homology with other teleost counterparts by phylogenetic analysis. The expression of cyp11a and cyp11b exhibited a clear sexually dimorphic pattern, with a higher expression level in testis than that of in ovaries. During the different developmental stages (40 dpf, 80 dpf, 190 dpf, 360 dpf, 720 dpf), the expression of cyp11a was earlier than cyp11b. In situ hybridization results showed that cyp11a and cyp11b were mainly expressed in oogonia and oocytes of the ovary. They were located in spermatogonia and interstitial compartment in the 1.5-year-old gonads, and spermatocytesgonia and the peritubular myoid cell of the testis in the 2.5-year-old gonads. To explore the distinct roles of cyp11a and cyp11b in gonads, oestrogen and androgens were used to stimulate the primary testicular and ovarian cells. The expressions of cyp11a and cyp11b were tested under different dose of 17α-methyltestosterone (17α-MT) and 17β-estradiol (E2). The results showed cyp11a was significantly increased at 10^-6  mol ml^-1 of 17α-MT and 10^-8  mol ml^-1 of E2 in ovary and 10^-10  mol ml^-1 of 17α-MT and E2 in testis, while cyp11b was significantly decreased after 17α-MT and E2 treatment. These results indicated that cyp11a and cyp11b were likely to have different functions, and also implied they might play an important roles in the differentiation of gonads and the synthesis of steroids in black rockfish.

Heat Stress and Pulsed Unfocused Ultrasound: The Viability of these Physical Approaches for Drug Delivery into Testicular Seminiferous Tubules

AIM

To investigate the application of Scrotal Heat Stress (SHS) and Pulsed Unfocused Ultrasound (PuFUS) to explore Blood-Testis Barrier (BTB) permeability in adult mice.

BACKGROUND

The BTB provides a stable microenvironment and a unique immune barrier for spermatogenesis. Meanwhile, it blocks macromolecular substances access, including therapeutic agents and antibodies, thereby it decreases the therapeutic or immunocontraception effects.

OBJECTIVES

To determine the viability of these physical approaches in delivering macromolecular substances into seminiferous tubules.

MATERIALS & METHODS

Mice were subjected to receive single SHS intervention at 39°C, 41°C, or 43°C for 30 min. Whereas, mice received the PuFUS intervention at 1.75w/cm2, 1.25w/cm2, and 2.5w/cm2 for 2 min, 5 min, and 10 min, respectively. The Biotin and macromolecular substances (IgG, IgM, and exosomes) were separately injected into the testicular interstitium at different times following SHS or PuFUS interventions, to observe their penetration through BTB into seminiferous tubules.

RESULTS

As detected by Biotin tracer, the BTB opening started from day-2 following the SHS and lasted for more than three days, whereas the BTB opening started from 1.5h following PuFUS and lasted up to 24h. Apparent penetration of IgG, IgM, and exosomes into seminiferous tubules was observed after five days of the SHS at 43°C, but none at 39°C, or any conditions tested with PuFUS.

CONCLUSION

The current results indicate that SHS at 43°C comparatively has the potential for delivering macromolecular substances into seminiferous tubules, whereas the PuFUS could be a novel, quick, and mild approach to open the BTB. These strategies might be useful for targeted drug delivery into testicular seminiferous tubules. However, further studies are warranted to validate our findings.