Testicular connexin 43, a precocious molecular target for the effect of environmental toxicants on male fertility

Bta-miR-149-3p suppresses inflammatory response in bovine Sertoli cells exposed to microcystin-leucine arginine (MC-LR) through TLR4/NF-kB signaling pathway

This study explored the regulatory role of bta-miR-149-3p in the inflammatory response induced by microcystin-leucine arginine (MC-LR) exposure in bovine Sertoli cells. The research endeavored to enhance the comprehension of the epigenetic mechanisms underlying MC-LR-induced cytotoxicity in Sertoli cells and establish a foundation for mitigating these effects in vitro. In this study, we elucidated the regulatory mechanism of bta-miR-149-3p in the MC-LR-induced inflammatory response by verifying the target gene of bta-miR-149-3p through luciferase assays and treating the cells with a bta-miR-149-3p inhibitor for 24 h. The results demonstrate that nuclear factor κB (NF-κB) acts as a downstream target gene of bta-miR-149-3p, which inhibits the MC-LR-induced inflammatory response in bovine Sertoli cells. This inhibition occurs by regulating the downregulation of tight junction constitutive proteins of the blood-testis barrier (BTB) through the suppression of the TLR-4/NF-κB signaling pathway (p < 0.05) and the up-regulation of the adhesion junction protein β-catenin (p < 0.05). Notably, MC-LR exposure resulted in the up-regulation (p < 0.05) of inflammatory cytokines (IL-6, IL-1β, and NLRP3) and the down-regulation (p < 0.05) of BTB tight junction constitutive proteins (ZO-1, Occludin) in Sertoli cells. Furthermore, the BTB constitutive protein ZO-1 exhibited significant down-regulation in Sertoli cells pretreated with the bta-miR-149-3p inhibitor compared to controls (p < 0.05), while Occludin showed no significant difference from CTNNB1 (p > 0.05). In summary, our findings suggest that bta-miR-149-3p suppresses the MC-LR-induced inflammatory response and alterations in the expression of BTB proteins in bovine Sertoli cells by inhibiting the TLR-4/NF-κB signaling pathway.

Effects of a Sertoli cell-specific knockout of Connexin43 on maturation and proliferation of postnatal Sertoli cells

Adult male Sertoli cell-specific Connexin43 knockout mice (SCCx43KO) exhibit higher Sertoli cell (SC) numbers per seminiferous tubule compared to their wild type (WT) littermates. Thus, deletion of this testicular gap junction protein seems to affect the proliferative potential and differentiation of "younger" SC. Although SC have so far mostly been characterised as postmitotic cells that cease to divide and become an adult, terminally differentiated cell population at around puberty, there is rising evidence that there exist exceptions from this for a very long time accepted paradigm. Aim of this study was to investigate postnatal SC development and to figure out underlying causes for observed higher SC numbers in adult KO mice. Therefore, the amount of SC mitotic figures was compared, resulting in slightly more and prolonged detection of SC mitotic figures in KO mice compared to WT. SC counting per tubular cross section revealed significantly different time curves, and comparing proliferation rates using Bromodesoxyuridine and Sox9 showed higher proliferation rates in 8-day old KO mice. SC proliferation was further investigated by Ki67 immunohistochemistry. SC in KO mice displayed a delayed initiation of cell-cycle-inhibitor p27Kip1 synthesis and prolonged synthesis of the phosphorylated tumour suppressor pRb and proliferation marker Ki67. Thus, the higher SC numbers in adult male SCCx43KO mice may arise due to two different reasons: Firstly, in prepubertal KO mice, the proliferation rate of SC was higher. Secondly, there were differences in their ability to cease proliferation as shown by the delayed initiation of p27Kip1 synthesis and the prolonged production of phosphorylated pRb and Ki67. Immunohistochemical results indicating a prolonged period of SC proliferation in SCCx43KO were confirmed by detection of proliferating SC in 17-days-old KO mice. In conclusion, deletion of the testicular gap junction protein Cx43 might prevent normal SC maturation and might even alter also the proliferation potential of adult SC.

Bisphenols as promoters of the dysregulation of cellular junction proteins of the blood-testis barrier in experimental animals: A systematic review of the literature

Daily, people are exposed to chemicals and environmental compounds such as bisphenols (BPs). These substances are present in more than 80% of human fluids. Human exposure to BPs is associated with male reproductive health disorders. Some of the main targets of BPs are intercellular junction proteins of the blood-testis barrier (BTB) in Sertoli cells because BPs alter the expression or induce aberrant localization of these proteins. In this systematic review, we explore the effects of BP exposure on the expression of BTB junction proteins and the characteristics of in vivo studies to identify potential gaps and priorities for future research. To this end, we conducted a systematic review of articles. Thirteen studies met our inclusion criteria. In most studies, animals treated with bisphenol-A (BPA) showed decreased occludin expression at all tested doses. However, bisphenol-AF treatment did not alter occludin expression. Cx43, ZO-1, β-catenin, nectin-3, cortactin, paladin, and claudin-11 expression also decreased in some tested doses of BP, while N-cadherin and FAK expression increased. BP treatment did not alter the expression of α and γ catenin, E-cadherin, JAM-A, and Arp 3. However, the expression of all these proteins was altered when BPA was administered to neonatal rodents in microgram doses. The results show significant heterogeneity between studies. Thus, it is necessary to perform more research to characterize the changes in BTB protein expression induced by BPs in animals to highlight future research directions that can inform the evaluation of risk of toxicity in humans.

Exposure to manganese during sertoli cell formation and proliferation disturbs early testicular development in rats

Manganese (Mn) is a metal and important micronutrient. However, exposure to supraphysiological levels of Mn, which occur through fungicides, atmospheric emissions, drainages, and spills, has been related to health risks, including morphometric changes in the male reproductive organs and impairment on gametogenesis and sperm quality, impacting the fertile ability of adult animals. Despite the relevance of the fetal/perinatal period for toxicological studies on Mn, previous data only deal with the physical and neurological development of the offspring, without mentioning their reproductive development. The present study investigated whether exposure to Mn during fetal/perinatal phase, specifically during the period of formation and proliferation of Sertoli cells, impairs the reproductive development of male offspring in early postnatal life. Therefore, pregnant Wistar rats were randomly distributed into 3 experimental groups: Ctl (received saline solution), Mn-9 (received 9 mg/kg of MnCl2), and Mn-90 (received 90 mg/kg of MnCl2). The female rats received the experimental treatment by gavage from gestational day 13 to lactational day 15, i.e., postnatal day (PND) 15 of the pups. Oxidative damage to the genetic material of germ and Sertoli cells, together with a decrease in connexin 43 immunolabeling were observed in the testis of male pups evaluated at PND 15. In addition, an increase in the seminiferous tubules presenting slight epithelium vacuolization and cells with eosinophilic cytoplasm were observed, without apparent epididymal changes. In conclusion, it was demonstrated that Mn perturbed the initial testicular development by altering Sertoli cell integrity through oxidative insult, which may compromise the spermatogenesis in the long-term.

Adverse effects of microcystins on sperm: A systematic review

Eutrophication of water bodies can lead to cyanobacterial blooms, with the resultant release of microcystins (MCs), posing a threat to the ecosystem and human health. MCs are environmental toxins with male reproductive toxicity. However, there is a dearth of reviews focusing on sperm or spermatogenesis. In this paper, studies on sperm toxicity caused by MCs in recent 20 years were collected and summarized, aiming at revealing the toxic effects and potential mechanisms of MCs on sperm. Based on the previous findings, MCs can decline sperm quality and count, and cause malformation in vertebrates and invertebrates. The reason might be that MCs cause indirect damage to sperm through impairing the structure and function of the testis. The mechanisms of MCs-induced sperm toxicity mainly result from alterations in genetic material, abnormalities in the structure and function of sperm. The epigenetic modifications such as miRNA and piRNA were also involved in MC-LR-induced sperm damage. In conclusion, MCs exposure is harmful to sperm, but its direct effects and mechanisms on sperm are still not known, which remains a significant research direction. Our review will provide a basis for the protection of male reproductive health damage caused by microcystins.

Bisphenol A damages testicular junctional proteins transgenerationally in mice

Testicular junctions are pivotal to male fertility and regulated by constituent proteins. Increasing evidence suggests that environmental chemicals, including bisphenol A (BPA), may impact these proteins, but whether the impacts persist for generations is not yet known. Here, we investigate the effect of BPA (a ubiquitous endocrine-disrupting chemical) on testis and sperm functions and whether the effects are transferred to subsequent generations. Male mice (F0) were exposed to corn oil (Control) or 5 or 50 mg BPA/kg body weight/day from 6 to 12 weeks of age. The F0 were mated with wild-type females to produce the first filial (F1) generation. F2 and F3 were produced using similar procedures. Our results showed that BPA doses decreased the levels of some junctional proteins partly via binding with estrogen receptors (ERα and Erβ), upregulation of p-ERK1/2, P85, p-JNK and activation of p38 mitogen-activated protein kinase signaling. Consequently, testicular histological abnormalities, disrupted spermatogenesis, decreased sperm count, and inability to fertilize eggs were observed in mice exposed to BPA. These effects were transferred to successive generations (F2), partly through DNA methylation, but mostly alleviated in F3 males. Our findings suggest that paternal exposure to chemicals promoting alteration of testicular junctional proteins and its transgenerational inheritance is a key component of the origin of male reproductive health problems.

Mechanisms of SARS-CoV-2 and Male Infertility: Could Connexin and Pannexin Play a Role?

The impact of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) on male infertility has lately received significant attention. SARS-CoV-2, the virus that causes coronavirus disease (COVID-19) in humans, has been shown to impose adverse effects on both the structural components and function of the testis, which potentially impact spermatogenesis. These adverse effects are partially explained by fever, systemic inflammation, oxidative stress, and an increased immune response leading to impaired blood-testis barrier. It has been well established that efficient cellular communication via gap junctions or functional channels is required for tissue homeostasis. Connexins and pannexins are two protein families that mediate autocrine and paracrine signaling between the cells and the extracellular environment. These channel-forming proteins have been shown to play a role in coordinating cellular communication in the testis and epididymis. Despite their role in maintaining a proper male reproductive milieu, their function is disrupted under pathological conditions. The involvement of these channels has been well documented in several physiological and pathological conditions and their designated function in infectious diseases. However, their role in COVID-19 and their meaningful contribution to male infertility remains to be elucidated. Therefore, this review highlights the multivariate pathophysiological mechanisms of SARS-CoV-2 involvement in male reproduction. It also aims to shed light on the role of connexin and pannexin channels in disease progression, emphasizing their unexplored role and regulation of SARS-CoV-2 pathophysiology. Finally, we hypothesize the possible involvement of connexins and pannexins in SARS-CoV-2 inducing male infertility to assist future research ideas targeting therapeutic approaches.

Endocrine-disrupting chemicals affect sertoli TM4 cell functionality through dysregulation of gap junctional intercellular communication in vitro

The frequencies of adverse outcomes associated with male reproductive health, including infertility and testicular cancer, are increasing. These adverse trends are partially attributed to increased exposure to environmental agents such as endocrine-disrupting chemicals (EDCs). This study addresses effects on EDCs on adjacent prepubertal Sertoli TM4 cells, specifically on 1) testicular gap junctional intercellular communication (GJIC), one of the hallmarks of non-genotoxic carcinogenicity, 2) GJIC building blocks connexins (Cx), and 3) mitogen-activated protein kinases MAPKs. We selected eight representatives of EDCs: bisphenol A and organochlorine chemicals such as pesticides dichlorodiphenyltrichloroethane, lindane, methoxychlor, and vinclozolin, industrial chemical 2,2',4,4',5,5'-hexachlorobiphenyl, and components of personal care products, triclocarban and triclosan. EDCs rapidly dysregulated GJIC in Sertoli TM4 cells mainly via MAPK p38 and/or Erk1/2/pathways by the intermediate hyper- or de-phosphorylation of Cx43 (Ser368, Ser282) and translocalization of Cx43 from the plasma membrane, suggesting disturbed intracellular trafficking of Cx43 protein. Surprisingly, EDCs did not rapidly activate MAPK Erk1/2 or p38; on the contrary, TCC and TCS decreased their activity (phosphorylation). Our results indicate that EDCs might disrupt testicular homeostasis and development via testicular GJIC, junctional and non-junctional functions of Cx43 and MAPK-signalling pathways in Sertoli cells.

Effects of bisphenols on Blood-Testis Barrier protein expression in vitro: A systematic review and meta-analysis

Bisphenols are a group of environmental endocrine-disrupting chemicals that produce alterations in the expression of intercellular junction proteins of the Blood-Testis Barrier (BTB) involved in spermatogenesis. The association between bisphenol exposure and BTB protein expression is controversial. Therefore, we performed this systematic review and meta-analysis to clarify bisphenol effects on Sertoli cell BTB protein expression in vitro. The Standardized Mean Difference (SMD) with a 95 % confidence interval (95 % CI) was used to evaluate the association between alterations in the BTB protein expression and bisphenol exposure in vitro. Six articles were included in the meta-analysis. Bisphenol-A (BPA) exposure at 200 μM was associated with significant decrease in BTB protein expression (SMD = -2.70, 95 %CI: -3.59, -1.80, p het = 0.46, p = <0.00001). In the moderate (40-50 μM) and low dose (<25 μM), no significant associations were obtained. We also found a non-monotonic dose-response curve of bisphenol effect in ZO-1 protein expression; low and high doses presented a significant decrease compared to control, while moderate dose presented no change. The current temporary Tolerable Daily Intake (tTDI) of BPA is 4 μg/kg bw/day. The 5-25 μM doses of BPA are equivalent to ∼1-5 mg/kg bw, respectively. Although the low dose group (<25 μM) assessed doses below the previous NOAEL value, these doses are above the current tTDI. Thus, it is necessary to conduct more studies with lower bisphenol concentrations to avoid underestimating the potential adverse effects of bisphenols at doses below tTDI.

Environmental Factors-Induced Oxidative Stress: Hormonal and Molecular Pathway Disruptions in Hypogonadism and Erectile Dysfunction

Hypogonadism is an endocrine disorder characterized by inadequate serum testosterone production by the Leydig cells of the testis. It is triggered by alterations in the hypothalamic–pituitary–gonadal axis. Erectile dysfunction (ED) is another common disorder in men that involves an alteration in erectile response–organic, relational, or psychological. The incidence of hypogonadism and ED is common in men aged over 40 years. Hypogonadism (including late-onset hypogonadism) and ED may be linked to several environmental factors-induced oxidative stresses. The factors mainly include exposure to pesticides, radiation, air pollution, heavy metals and other endocrine-disrupting chemicals. These environmental risk factors may induce oxidative stress and lead to hormonal dysfunctions. To better understand the subject, the study used many keywords, including “hypogonadism”, “late-onset hypogonadism”, “testosterone”, “erectile dysfunction”, “reactive oxygen species”, “oxidative stress”, and “environmental pollution” in major online databases, such as SCOPUS and PUBMED to extract relevant scientific information. Based on these parameters, this review summarizes a comprehensive insight into the important environmental issues that may have a direct or indirect association with hypogonadism and ED in men. The study concludes that environmental factors-induced oxidative stress may cause infertility in men. The hypothesis and outcomes were reviewed critically, and the mechanistic approaches are applied through oxidant-sensitive pathways. This study also provides reccomendations on future therapeutic interventions and protective measures against such adverse environmental factors-induced hypogonadism and ED.

Intratesticular Peptidyl Prolyl Isomerase 1 Protein Delivery Using Cationic Lipid-Coated Fibroin Nanoparticle Complexes Rescues Male Infertility in Mice

Male infertility is a multifactorial condition. Unexplained male infertility is often caused by spermatogenesis dysfunction. Knockout of Pin1, an important regulator of cell proliferation and differentiation, produces male infertility phenotypes such as testicular immaturity and azoospermia with spermatogonia depletion and blood-testis barrier (BTB) dysfunction. Gene therapy has been clinically considered for the treatment of male infertility, but it is not preferred because of the risks of adverse effects in germ cells. Direct intracellular protein delivery using nanoparticles is considered an effective alternative to gene therapy; however, in vivo testicular protein delivery remains a pressing challenge. Here, we investigated the direct intracellular protein delivery strategy using a fibroin nanoparticle-encapsulated cationic lipid complex (Fibroplex) to restore intratesticular PIN1. Local intratesticular delivery of PIN1 via Fibroplex in Pin1 knockout testes produced fertile mice, achieving recovery from the infertile phenotypes. Mechanistically, PIN1-loaded Fibroplex was successfully delivered into testicular cells, including spermatogonial cells and Sertoli cells, and the sustained release of PIN1 restored the gene expression required for the proliferation of spermatogonial cells and BTB integrity in Pin1 knockout testes. Collectively, testicular PIN1 protein delivery using Fibroplex might be an effective strategy for treating male infertility.

Nigral and ventral tegmental area lesioning induces testicular and sperm morphological abnormalities in a rotenone model of Parkinson's disease

Although sexual health is affected by Parkinson's disease (PD), the effect on testicular health and/or sperm quality is not well discussed. After 21 days of rotenone lesioning, we observed dopaminergic neuronal degeneration in the substantia nigra and hypothalamus. There were minimal SPACA-1-expressing epididymal spermatozoa with morphological abnormalities, scanty luminal spermatozoa and reduced testicular spermatids and post-meiotic germ cells indicating hypospermatogenesis. Occludin-expressing sertoli cells were dispersed over a wide area indicating compromised blood-testes barrier. Activated caspase-3 expression was intense while immunoreactivity of spermatogenic-enhancing SRY and GADD45 g was weak. Although serum follicle stimulating hormone level was not affected, the lesion was associated with reduced serum testosterone level, testicular oxidative damage and inhibition of acetylcholinesterase activity, even when rotenone was not detected in the testes. Together, dopaminergic lesions may mediate testicular and sperm abnormalities via the brain-hypothalamic-testicular circuit independent of the pituitary, thereby establishing a causal link between Parkinsonism and reproductive dysfunction.

Endocrine-disrupting chemicals rapidly affect intercellular signaling in Leydig cells

A decline in male fertility possibly caused by environmental contaminants, namely endocrine-disrupting chemicals (EDCs), is a topic of public concern and scientific interest. This study addresses a specific role of testicular gap junctional intercellular communication (GJIC) between adjacent prepubertal Leydig cells in endocrine disruption and male reproductive toxicity. Organochlorine pesticides (lindane, methoxychlor, DDT), industrial chemicals (PCB153, bisphenol A, nonylphenol and octylphenol) as well as personal care product components (triclosan, triclocarban) rapidly dysregulated GJIC in murine Leydig TM3 cells. The selected GJIC-inhibiting EDCs (methoxychlor, triclosan, triclocarban, lindane, DDT) caused the immediate GJIC disruption by the relocation of gap junctional protein connexin 43 (Cx43) from the plasma membrane and the alternation of Cx43 phosphorylation pattern (Ser368, Ser279, Ser282) of its full-length and two N-truncated isoforms. After more prolonged exposure (24 h), EDCs decreased steady-state levels of full-length Cx43 protein and its two N-truncated isoforms, and eventually (triclosan, triclocarban) also tight junction protein Tjp-1. The disturbance of GJIC was accompanied by altered activity of mitogen-activated protein kinases MAPK-Erk1/2 and MAPK-p38, and a decrease in stimulated progesterone production. Our results indicate that EDCs might disrupt testicular homeostasis and development via disruption of testicular GJIC, a dysregulation of junctional and non-junctional functions of Cx43, activation of MAPKs, and disruption of an early stage of steroidogenesis in prepubertal Leydig cells. These critical disturbances of Leydig cell development and functions during a prepubertal period might be contributing to impaired male reproduction health later on.

Cell membrane-related toxic responses and disruption of intercellular communication in PCB mechanisms of toxicity: A review

An understanding of polychlorinated biphenyl (PCB) congener-specific effects on cell membrane and intercellular communication is important within the studies of PCB absorption, organ-related PCB accumulation and exertion of toxic responses. Toxic potential of PCBs is linked to various deleterious effects on human health, including neurotoxicity, immunotoxicity, reproductive toxicity and genotoxicity and, recently in 2016 International Agency for Research on Cancer (IARC) has upgraded the classification of PCBs to Group 1 "Carcinogenic to humans." Proposed mechanisms of aforementioned PCBs adverse effects at cellular membrane level are: (i) downregulation of gap junction intercellular communication and/or connexins; (ii) compromised membrane integrity; and (iii) altered tight junction barrier function. This study, based on an extensive literature survey, shows the progress in scientific research of each of these three levels with the aim of pointing out the earliest toxic events of PCBs, which can result in serious cell/tissue/organ damage.

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

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

Protective effects of betaine on diabetic induced disruption of the male mice blood-testis barrier by regulating oxidative stress-mediated p38 MAPK pathways

BACKGROUND

Blood-testis barrier (BTB) impairments is one of the major secondary complications of diabetes. Betaine (BET) is the important active ingredients isolated from Lycium barbarum, which exhibits numerous pharmacological activities such as antioxidant, anti-diabetic, and anti-inflammatory effects. This study aimed to establish whether BET contributes to the recovery from BTB dysfunction in streptozotocin (STZ) induced diabetic mice.

METHODS

BET (200, 400, 800 mg/kg) was orally administered to diabetic mice for 8 weeks. Testis tissues were collected for histopathological and biochemical analysis, the reproductive organ weight was estimated. Antioxidant enzyme activity and BTB associated protein expressions were determined with their corresponding assay kits and western blot analysis. The results revealed that BET significantly improved the weight of the reproductive organs and testicular morphology in diabetic mice. Furthermore, reactive oxygen species (ROS) and malondialdehyde (MDA) levels were significantly reduced, and the activities of superoxide dismutase (SOD), catalase (CAT), and glutathione (GSH), markedly increased in the testicular tissue after SAL treatment. In addition, our data also showed a marked down-regulated the expressions of p38 MAPK phosphorylation and up-regulation the protein expressions of ZO-1, Occludin, Claudin-11, N-cadherin, and Connexin-43 after BET administration compared with the diabetic group. In conclusion, these results demonstrated that BET exerts protective effects on diabetes-induced BTB dysfunction, which may be through regulating oxidative stress-mediated p38 MAPK pathways.

Gaps and barriers: Gap junctions as a channel of communication between the soma and the germline

Gap junctions, expressed in most tissues of the body, allow for the cytoplasmic coupling of adjacent cells and promote tissue cooperation. Gap junctions connect also the soma and the germline in many animals, and transmit somatic signals that are crucial for germline maturation and integrity. In this review, we examine the involvement of gap junctions in the relay of information between the soma and the germline, and ask whether such communication could have consequences for the progeny. While the influence of parental experiences on descendants is of great interest, the possibility that gap junctions participate in the transmission of information across generations is largely unexplored.

Icariin attenuate microcystin-LR-induced gap junction injury in Sertoli cells through suppression of Akt pathways

Microcystin-leucine-arginine (MC-LR) can cause male reproductive disorder. However, the underlying mechanism are not yet entirely elucidated. In this study, we aimed to investigated the effects of MC-LR on the integrity of blood-testis barrier (BTB) and the related molecular mechanisms. Both in vivo and in vitro experiments revealed that MC-LR caused disruption of BTB and gap junctions between Sertoli cells respectively, which was paralleled by the alteration of connexin43 (Cx43). Our data demonstrated that MC-LR decreased gap junction intercellular communication (GJIC) and impaired Cx43 expression by activating the phosphatidylinositol 3-kinase/Akt cascades. In addition, a possible protective effect of Icariin (ICA), a flavonoid isolated from Chinese medicinal herb, against MC-LR toxicity was investigated. The ICA prevented the degradation of GJIC and impairment of Cx43 induced by MC-LR via suppressing the Akt pathway. Together, our results confirmed that the expression of Cx43 induced by MC-LR was regulated in vivo and in vitro, which was involved in the destruction of BTB. Additionally, ICA seems to be able to mitigate the MC-LR toxic effects.

Immunolocalization of DMRTB1 in human testis with normal and impaired spermatogenesis

BACKGROUND

The transcription factor DMRTB1 plays a pivotal role in coordinating the transition between mitosis and meiosis in murine germ cells. No reliable data are available for human testis.

OBJECTIVES

The present study aims to examine the testicular expression pattern of DMRTB1 in men showing normal and impaired spermatogenesis.

MATERIALS AND METHODS

Immunohistochemistry was performed using 54 human testicular biopsy specimens and a commercial rabbit polyclonal anti-DMRTB1 primary antibody. RT-PCR complemented immunohistochemistry. To further characterize immunopositive cells and possible co-localization, the proliferation marker Ki-67, the tumor marker PLAP, and an anti-DMRT1 antibody were used.

RESULTS

In men with normal spermatogenesis, a strong immunoreactivity was detectable in a subset of spermatogonia (38.34 ± 2.14%). Some spermatocytes showed a weak immunostaining. Adjacent Sertoli cells were immunonegative. Compared with a hematoxylin and eosin overview staining, these immunopositive cells were almost exclusively identified as A_pale and B spermatogonia and primary spermatocytes in (pre-)leptotene, zygotene, and pachytene stages. In patients with spermatogenic arrest at spermatogonial level, an altered staining pattern was found. No immunoreactivity was detected in Sertoli cells in Sertoli cell-only syndrome. In germ cell neoplasia in situ (GCNIS) tubules, except for a few (0.4 ± 0.03%), pre-invasive tumor cells were immunonegative. Seminoma cells showed no immunostaining.

DISCUSSION

According to previous findings in mice, it seems reasonable that DMRTB1 is expressed in these normal germ cell populations. Moreover, altered staining pattern in spermatogenic arrest at spermatogonial stage suggests a correlation with mitosis and transformation into B spermatogonia. The absence of DMRTB1 in GCNIS cells and tumor cells might be associated with uncontrolled neoplastic cell proliferation and progression into invasive germ cell tumors. Further research is required to elucidate, for example, the role of DMRTB1 in the malignant transformation of human germ cells.

CONCLUSION

Our data indicate a relevant role for DMRTB1 regarding the entry of spermatogonia into meiosis in men.

Pharmacological inhibition of TLR4/NF-κB with TLR4-IN-C34 attenuated microcystin-leucine arginine toxicity in bovine Sertoli cells

This study investigated the pharmacological inhibition of the toll-like receptor 4 (TLR4) genes as a measure to attenuate microcystin-LR (MC-LR) reproductive toxicity. Bovine Sertoli cells were pretreated with TLR4-IN-C34 (C34) for 1 hour. Thereafter the pretreated and non-pretreated Sertoli cells were cultured in medium containing 10% heat-activated fetal bovine serum + 80 μg/L MC-LR for 24 hours to assess the ability of TLR4-IN-C34 to attenuate the toxic effects of MC-LR. The results showed that TLR4-IN-C34 inhibited MC-LR-induced mitochondria membrane damage, mitophagy and downregulation of blood-testis barrier constituent proteins via TLR4/nuclear factor-kappaB and mitochondria-mediated apoptosis signaling pathway blockage. The downregulation of the mitochondria electron transport chain, energy production and DNA replication related genes (mt-ND2, COX-1, COX-2, ACAT, mtTFA) and upregulation of inflammatory cytokines (interleukin [IL]-6, tumor necrosis factor-α, IL-1β, interferon-γ, IL-4, IL-10, IL-13 and transforming growth factor β1) were modulated by TLR4-IN-C34. Taken together, we conclude that TLR4-IN-C34 inhibits MC-LR-related disruption of mitochondria membrane, mitophagy and downregulation of blood-testis barrier proteins of the bovine Sertoli cell via cytochrome c release and TLR4 signaling blockage.

Polycyclic Aromatic Hydrocarbons and Endocrine Disruption: Role of Testicular Gap Junctional Intercellular Communication and Connexins

Ambient air pollution and smoking are well-documented risk factors for male infertility. Prevalent air pollutants and cigarette smoke components, polycyclic aromatic hydrocarbons (PAHs), are environmental and occupational toxicants that act as chemicals disrupting endocrine regulation and reproductive potential in males. Testicular gap junctional intercellular communication (GJIC) is critical for normal development and function of testicular tissue, thus we assessed GJIC as a process potentially targeted by PAHs in testes. Lower MW PAHs with a bay or bay-like region rapidly dysregulated GJIC in Leydig TM3 cells by relocalization of major testicular gap junctional protein connexin 43 (Cx43) from plasma membrane to cytoplasm. This was associated with colocalization between Cx43 and ubiquitin in intracellular compartments, but without any effect on Cx43 degradation rate or steady-state Cx43 mRNA levels. A longer exposure to active PAHs decreased steady-state levels of full-length Cx43 protein and its 2 N-truncated isoforms. Inhibition of GJIC by PAHs, similarly to a prototypic GJIC-inhibitor TPA, was mediated via the MAP kinase-Erk1/2 and PKC pathways. Polycyclic aromatic hydrocarbon-induced GJIC dysregulation in testes was cell-type-specific because neither PAH dysregulated GJIC in Sertoli TM4 cells, despite PAHs were rapidly taken up by both Leydig TM3 as well as Sertoli TM4 cells. Because TPA effectively dysregulated GJIC in both testicular cell types, a unique regulator of GJIC targeted by PAHs might exist in Leydig TM3 cells. Our results indicate that PAHs could be a potential etiological agent contributing to reproductive dysfunctions in males through an impairment of testicular GJIC and junctional and/or nonjunctional functions of Cx43.

Molecular Mechanisms and Signaling Pathways Involved in Sertoli Cell Proliferation

Sertoli cells are somatic cells present in seminiferous tubules which have essential roles in regulating spermatogenesis. Considering that each Sertoli cell is able to support a limited number of germ cells, the final number of Sertoli cells reached during the proliferative period determines sperm production capacity. Only immature Sertoli cells, which have not established the blood-testis barrier, proliferate. A number of hormonal cues regulate Sertoli cell proliferation. Among them, FSH, the insulin family of growth factors, activin, and cytokines action must be highlighted. It has been demonstrated that cAMP/PKA, ERK1/2, PI3K/Akt, and mTORC1/p70SK6 pathways are the main signal transduction pathways involved in Sertoli cell proliferation. Additionally, c-Myc and hypoxia inducible factor are transcription factors which participate in the induction by FSH of various genes of relevance in cell cycle progression. Cessation of proliferation is a pre-requisite to Sertoli cell maturation accompanied by the establishment of the blood-testis barrier. With respect to this barrier, the participation of androgens, estrogens, thyroid hormones, retinoic acid and opioids has been reported. Additionally, two central enzymes that are involved in sensing cell energy status have been associated with the suppression of Sertoli cell proliferation, namely AMPK and Sirtuin 1 (SIRT1). Among the molecular mechanisms involved in the cessation of proliferation and in the maturation of Sertoli cells, it is worth mentioning the up-regulation of the cell cycle inhibitors p21Cip1, p27Kip, and p19INK4, and of the gap junction protein connexin 43. A decrease in Sertoli cell proliferation due to administration of certain therapeutic drugs and exposure to xenobiotic agents before puberty has been experimentally demonstrated. This review focuses on the hormones, locally produced factors, signal transduction pathways, and molecular mechanisms controlling Sertoli cell proliferation and maturation. The comprehension of how the final number of Sertoli cells in adulthood is established constitutes a pre-requisite to understand the underlying causes responsible for the progressive decrease in sperm production that has been observed during the last 50 years in humans.

Sodium Selenite inhibits mitophagy, downregulation and mislocalization of blood-testis barrier proteins of bovine Sertoli cell exposed to microcystin-leucine arginine (MC-LR) via TLR4/NF-kB and mitochondrial signaling pathways blockage

This study was conducted to investigate the ameliorative effect of selenium on microcystin-LR induced toxicity in bovine Sertoli cells. Bovine Sertoli cells were pretreated with selenium (Na₂SeO₃) for 24 h after which selenium pretreated and non-pretreated Sertoli cells were cultured in medium containing 10% heat activated fetal bovine serum FBS+ 80 µg/L MC-LR to assess its ameliorative effect on MC-LR toxicity. The results show that selenium pretreatment inhibited the MC-LR induced mitophagy, downregulation and mislocalization of blood-testis barrier constituent proteins in bovine Sertoli cells via NF-kB and cytochrome c release blockage. The observed downregulation of electron transport chain (ETC) related genes (mt-ND2, COX-1, COX-2) and upregulation of inflammatory cytokines (IL-6, TNF-α, IL-1β, IFN-γ, IL-4, IL-10, 1 L-13, TGFβ1) in non-pretreated cells exposed to MC-LR were ameliorated in selenium pretreated cells. There was no significant difference (P > 0.05) in the protein levels of blood-testis barrier constituent proteins (ZO-1, occludin, connexin-43, CTNNB1, N-cadherin) and mitochondria related genes (mt-ND2, COX-1, COX-2, ACAT1, mtTFA) of selenium pretreated Sertoli cell compared to the control. Taken together, we conclude that selenium inhibits MC-LR caused Mitophagy, downregulation and mislocalization of blood-testis barrier proteins of bovine Sertoli cell via mitochondrial and TLR4/NF-kB signaling pathways blockage.

Influence of warming and reanimation conditions on seminiferous tubule morphology, mitochondrial activity, and cell composition of vitrified testicular tissues in the domestic cat model

Understanding critical roles of warming and reanimation is critical to improve the survival of vitrified testicular tissue in domestic cats. The objective was to study structural and functional properties of testicular tissues from prepubertal domestic cats after standard vitrification followed by two warming protocols (directly at 37°C or with a 5-second pre-exposure to 50°C) and three reanimation time points (immediately, 24 h and 5 days post-warming). In Experiment 1, tissues were evaluated for histo-morphology and mitochondrial activity immediately or 24 h after warming protocols. In Experiment 2, cell viability, DNA fragmentation, and germ cell composition were assessed immediately, 24 h, or 5 days after optimal warming. Preservation of seminiferous tubule structure was better using warming at 50°C for five seconds, and survival of somatic as well as germinal cells was higher compared to direct warming at 37°C for one minute. Short term in vitro culture (for reanimation) also proved that cellular composition and functionality were better preserved when warmed for a short time at 50°C. Collective data showed that short warming at 50°C led to better quality of seminiferous tubule structure and cell composition after vitrification and short-term culture. In addition, data suggest clear directions to further understand and optimize testicular tissue survival after fertility preservation procedures.

Perinatal exposure to 2,2',4'4' -Tetrabromodiphenyl ether induces testicular toxicity in adult rats

Since 1965, polybrominated diphenyl ethers (PBDEs) have been used internationally as flame-retardant additives. PBDEs were recently withdrawn from commerce in North America and Europe due to their environmental persistence, bioaccumulative properties and endocrine-disrupting effects. Generations exposed perinatally to the highest environmental doses of PBDE account for one-fifth of the total United States population. While, toxicity of PBDE for the male reproductive system has been demonstrated in several human and animal studies, the long-lasting effects of perinatal exposures on male reproduction are still poorly understood. In this study, pregnant Wistar rats were exposed to 0.2mg/kg 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) from gestation day 8 until postnatal day 21. Male reproductive outcomes were analyzed on postnatal day 120 in offspring. Exposed animals had significantly smaller testes, displayed decreased sperm production per testis weight, had significantly increased percentage of morphologically abnormal spermatozoa, and showed an increase in spermatozoa head size. Perinatal BDE-47 exposure led to significant changes in testes transcriptome, including suppression of genes essential for spermatogenesis and activation of immune response genes. In particular, we observed a 4-fold average decrease in expression of protamine and transition protein genes in testes, suggesting that histone-protamine exchange may be dysregulated during spermatogenesis, resulting in an aberrant sperm epigenome. The possibility of long-lasting effects of developmental PBDE exposures calls for additional studies to build a foundation for the development of preventive and protective interventions against the environmentally-induced decline in fertility.

Signaling pathways regulating blood-tissue barriers - Lesson from the testis

Signaling pathways that regulate blood-tissue barriers are important for studying the biology of various blood-tissue barriers. This information, if deciphered and better understood, will provide better therapeutic management of diseases particularly in organs that are sealed by the corresponding blood-tissue barriers from systemic circulation, such as the brain and the testis. These barriers block the access of antibiotics and/or chemotherapeutical agents across the corresponding barriers. Studies in the last decade using the blood-testis barrier (BTB) in rats have demonstrated the presence of several signaling pathways that are crucial to modulate BTB function. Herein, we critically evaluate these findings and provide hypothetical models regarding the underlying mechanisms by which these signaling molecules/pathways modulate BTB dynamics. This information should be carefully evaluated to examine their applicability in other tissue barriers which shall benefit future functional studies in the field. This article is part of a Special Issue entitled: Gap Junction Proteins edited by Jean Claude Herve.

Perfluorooctanesulfonate (PFOS)-induced Sertoli cell injury through a disruption of F-actin and microtubule organization is mediated by Akt1/2

PFOS (perfluorooctanesulfonate, or perfluorooctane sulfonic acid) is an anthropogenic fluorosurfactant widely used in consumer products. While its use in Europe, Canada and the U.S. has been banned due to its human toxicity, it continues to be used in China and other developing countries as a global pollutant. Herein, using an in vitro model of Sertoli cell blood-testis barrier (BTB), PFOS was found to induce Sertoli cell injury by perturbing actin cytoskeleton through changes in the spatial expression of actin regulatory proteins. Specifically, PFOS caused mis-localization of Arp3 (actin-related protein 3, a branched actin polymerization protein) and palladin (an actin bundling protein). These disruptive changes thus led to a dis-organization of F-actin across Sertoli cell cytosol, causing truncation of actin microfilament, thereby failing to support the Sertoli cell morphology and adhesion protein complexes (e.g., occludin-ZO-1, CAR-ZO-1, and N-cadherin-ß-catenin), through a down-regulation of p-Akt1-S473 and p-Akt2-S474. The use of SC79, an Akt1/2 activator, was found to block the PFOS-induced Sertoli cell injury by rescuing the PFOS-induced F-actin dis-organization. These findings thus illustrate PFOS exerts its disruptive effects on Sertoli cell function downstream through Akt1/2. As such, PFOS-induced male reproductive dysfunction can possibly be managed through an intervention on Akt1/2 expression.

Effect of dibutyl phthalate on expression of connexin 43 and testosterone production of leydig cells in adult rats

To investigate the adverse effect of dibutyl phthalate (DBP) on Leydig cells and its mechanism related to gap junction, Leydig cells isolated from adult rats were treated with 0.1% dimethylsulfoxide (DMSO), 50mg/L DBP, 50mg/L DBP+10μM prostaglandin E2 (PGE2) and 40μM flutamide respectively. Radioimmunoassay, semi-quantitative RT-PCR, immunofluorescence and Western blot were applied to determine the expression of testosterone and Connexin 43 (Cx43) in Leydig cells. The expression of testosterone and Cx43 were both decreased in DBP group (P<0.05). While Cx43 was up-regulated after administered to PGE2, there was no significant change in testosterone. However, testosterone was down-regulated with a significant decrease of Cx43 in flutamide group. The results indicated that the inhibitory effect of DBP on testosterone production was not through the down-regulation of Cx43. On the contrary, the change of testosterone can influence the expression of Cx43 in Leydig cells.

Rescue of perfluorooctanesulfonate (PFOS)-mediated Sertoli cell injury by overexpression of gap junction protein connexin 43

Perfluorooctanesulfonate (PFOS) is an environmental toxicant used in developing countries, including China, as a stain repellent for clothing, carpets and draperies, but it has been banned in the U.S. and Canada since the late 2000s. PFOS perturbed the Sertoli cell tight junction (TJ)-permeability barrier, causing disruption of actin microfilaments in cell cytosol, perturbing the localization of cell junction proteins (e.g., occluden-ZO-1, N-cadherin-ß-catenin). These changes destabilized Sertoli cell blood-testis barrier (BTB) integrity. These findings suggest that human exposure to PFOS might induce BTB dysfunction and infertility. Interestingly, PFOS-induced Sertoli cell injury associated with a down-regulation of the gap junction (GJ) protein connexin43 (Cx43). We next investigated if overexpression of Cx43 in Sertoli cells could rescue the PFOS-induced cell injury. Indeed, overexpression of Cx43 in Sertoli cells with an established TJ-barrier blocked the disruption in PFOS-induced GJ-intercellular communication, resulting in the re-organization of actin microfilaments, which rendered them similar to those in control cells. Furthermore, cell adhesion proteins that utilized F-actin for attachment became properly distributed at the cell-cell interface, resealing the disrupted TJ-barrier. In summary, Cx43 is a good target that might be used to manage PFOS-induced reproductive dysfunction.

Effects of Fatty Acids on Intracellular [Ca2+], Mitochondrial Uncoupling and Apoptosis in Rat Pachytene Spermatocytes and Round Spermatids

The aim of this work was to explore the ability of free arachidonic acid, palmitic acid and the unsaturated fatty acids oleic acid and docosahexaenoic acid to modify calcium homeostasis and mitochondrial function in rat pachytene spermatocytes and round spermatids. In contrast to palmitic acid, unsaturated fatty acids produced significant increases in intracellular calcium concentrations ([Ca²⁺]_i) in both cell types. Increases were fatty acid specific, dose-dependent and different for each cell type. The arachidonic acid effects on [Ca²⁺]_i were higher in spermatids than in spermatocytes and persisted when residual extracellular Ca²⁺ was chelated by EGTA, indicating that the increase in [Ca²⁺]_i originated from release of intracellular calcium stores. At the concentrations required for these increases, unsaturated fatty acids produced no significant changes in the plasma membrane potential of or non-specific permeability in spermatogenic cells. For the case of arachidonic acid, the [Ca²⁺]_i increases were not caused by its metabolic conversion to eicosanoids or anandamide; thus we attribute this effect to the fatty acid itself. As estimated with fluorescent probes, unsaturated fatty acids did not affect the intracellular pH but were able to induce a progressive decrease in the mitochondrial membrane potential. The association of this decrease with reduced reactive oxygen species (ROS) production strongly suggests that unsaturated fatty acids induced mitochondrial uncoupling. This effect was stronger in spermatids than in spermatocytes. As a late event, arachidonic acid induced caspase 3 activation in a dose-dependent manner both in the absence and presence of external Ca²⁺. The concurrent but differential effects of unsaturated fatty acids on [Ca²⁺]_i and mitochondrial functions are additional manifestations of the metabolic changes that germ cells undergo during their differentiation.

Mammalian target of rapamycin complex (mTOR) pathway modulates blood-testis barrier (BTB) function through F-actin organization and gap junction

mTOR (mammalian target of rapamycin) is one of the most important signaling molecules in mammalian cells which regulates an array of cellular events, ranging from cell metabolism to cell proliferation. Based on the association of mTOR with the core component proteins, such as Raptor or Rictor, mTOR can become the mTORC1 (mammalian target of rapamycin complex 1) or mTORC2, respectively. Studies have shown that during the epithelial cycle of spermatogenesis, mTORC1 promotes remodeling and restructuring of the blood-testis barrier (BTB) in vitro and in vivo, making the Sertoli cell tight junction (TJ)-permeability barrier "leaky"; whereas mTORC2 promotes BTB integrity, making the Sertoli cell TJ-barrier "tighter". These contrasting effects, coupled with the spatiotemporal expression of the core signaling proteins at the BTB that confer the respective functions of mTORC1 vs. mTORC2 thus provide a unique mechanism to modulate BTB dynamics, allowing or disallowing the transport of biomolecules and also preleptotene spermatocytes across the immunological barrier. More importantly, studies have shown that these changes to BTB dynamics conferred by mTORC1 and mTORC2 are mediated by changes in the organization of the actin microfilament networks at the BTB, and involve gap junction (GJ) intercellular communication. Since GJ has recently been shown to be crucial to reboot spermatogenesis and meiosis following toxicant-induced aspermatogenesis, these findings thus provide new insightful information regarding the integration of mTOR and GJ to regulate spermatogenesis.

Roles of connexins in testis development and spermatogenesis

The development and differentiation of cells involved in spermatogenesis requires highly regulated and coordinated interactions between cells. Intercellular communication, particularly via connexin43 (Cx43) gap junctions, plays a critical role in the development of germ cells during fetal development and during spermatogenesis in the adult. Loss of Cx43 in the fetus results in a decreased number of germ cells, while the loss of Cx43 in the adult Sertoli cells results in complete inhibition of spermatogenesis. Connexins 26, 32, 33, 36, 45, 46 and 50 have also been localized to specific compartments of the testis in various mammals. Loss of Cx46 is associated with an increase in germ cell apoptosis and loss of the integrity of the blood-testis barrier, while loss of other connexins appears to have more subtle effects within the seminiferous tubule. Outside the seminiferous tubule, the interstitial Leydig cells express connexins 36 and 45 along with Cx43; deletion of the latter connexin did not reveal it to be crucial for steroidogenesis or for the development and differentiation of Leydig cells. In contrast, loss of Cx43 from Sertoli cells results in Leydig cell hyperplasia, suggesting important cross-talk between Sertoli and Leydig cells. In the epididymis connexins 26, 30.3, Cx31.1, 32, and 43 have been identified and differentiation of the epithelium is associated with dramatic changes in their expression. Decreased expression of Cx43 results in decreased sperm motility, a function acquired by spermatozoa during epididymal transit. Clearly, intercellular gap junctional communication within the testis and epididymis represents a critical aspect of male reproductive function and fertility. The implications of this mode of intercellular communication for male fertility remains a poorly understood but important facet of male reproduction.

Connexin 43 reboots meiosis and reseals blood-testis barrier following toxicant-mediated aspermatogenesis and barrier disruption

Earlier studies have shown that rats treated with an acute dose of 1-(2,4-dichlorobenzyl)-1H-indazole-3-carbohydrazide (adjudin, a male contraceptive under development) causes permanent infertility due to irreversible blood-testis barrier (BTB) disruption even though the population of undifferentiated spermatogonia remains similar to normal rat testes, because spermatogonia fail to differentiate into spermatocytes to enter meiosis. Since other studies have illustrated the significance of connexin 43 (Cx43)-based gap junction in maintaining the homeostasis of BTB in the rat testis and the phenotypes of Sertoli cell-conditional Cx43 knockout mice share many of the similarities of the adjudin-treated rats, we sought to examine if overexpression of Cx43 in these adjudin-treated rats would reseal the disrupted BTB and reinitiate spermatogenesis. A full-length Cx43 cloned into mammalian expression vector pCI-neo was used to transfect testes of adjudin-treated ratsversusempty vector. It was found that overexpression of Cx43 indeed resealed the Sertoli cell tight junction-permeability barrier based on a functionalin vivoassay in tubules displaying signs of meiosis as noted by the presence of round spermatids. Thus, these findings suggest that overexpression of Cx43 reinitiated spermatogenesis at least through the steps of meiosis to generate round spermatids in testes of rats treated with an acute dose of adjudin that led to aspermatogenesis. It was also noted that the round spermatids underwent eventual degeneration with the formation of multinucleated cells following Cx43 overexpression due to the failure of spermiogenesis because no elongating/elongated spermatids were detected in any of the tubules examined. The mechanism by which overexpression of Cx43 reboots meiosis and rescues BTB function was also examined. In summary, overexpression of Cx43 in the testis with aspermatogenesis reboots meiosis and reseals toxicant-induced BTB disruption, even though it fails to support round spermatids to enter spermiogenesis.-Li, N., Mruk, D. D., Mok, K.-W., Li, M. W. M., Wong, C. K. C., Lee, W. M., Han, D., Silvestrini, B., Cheng, C. Y. Connexin 43 reboots meiosis and reseals blood-testis barrier following toxicant-mediated aspermatogenesis and barrier disruption.

Blood-testis barrier and Sertoli cell function: lessons from SCCx43KO mice

The gap junction protein connexin43 (CX43) plays a vital role in mammalian spermatogenesis by allowing for direct cytoplasmic communication between neighbouring testicular cells. In addition, different publications suggest that CX43 in Sertoli cells (SC) might be important for blood-testis barrier (BTB) formation and BTB homeostasis. Thus, through the use of the Cre-LoxP recombination system, a transgenic mouse line was developed in which only SC are deficient of the gap junction protein, alpha 1 (Gja1) gene. Gja1 codes for the protein CX43. This transgenic mouse line has been commonly defined as the SC specific CX43 knockout (SCCx43KO) mouse line. Within the seminiferous tubule, SC aid in spermatogenesis by nurturing germ cells and help them to proliferate and mature. Owing to the absence of CX43 within the SC, homozygous KO mice are infertile, have reduced testis size, and mainly exhibit spermatogenesis arrest at the level of spermatogonia, seminiferous tubules containing only SC (SC-only syndrome) and intratubular SC-clusters. Although the SC specific KO of CX43 does not seem to have an adverse effect on BTB integrity, CX43 influences BTB composition as the expression pattern of different BTB proteins (like OCCLUDIN, β-CATENIN, N-CADHERIN, and CLAUDIN11) is altered in mutant males. The supposed roles of CX43 in dynamic BTB regulation, BTB assembly and/or disassembly and its possible interaction with other junctional proteins composing this unique barrier are discussed. Data collectively indicate that CX43 might represent an important regulator of dynamic BTB formation, composition and function.

Blood-testis barrier and spermatogenesis: lessons from genetically-modified mice

The blood-testis barrier (BTB) is found between adjacent Sertoli cells in the testis where it creates a unique microenvironment for the development and maturation of meiotic and postmeiotic germ cells in seminiferous tubes. It is a compound proteinous structure, composed of several types of cell junctions including tight junctions (TJs), adhesion junctions and gap junctions (GJs). Some of the junctional proteins function as structural proteins of BTB and some have regulatory roles. The deletion or functional silencing of genes encoding these proteins may disrupt the BTB, which may cause immunological or other damages to meiotic and postmeiotic cells and ultimately lead to spermatogenic arrest and infertility. In this review, we will summarize the findings on the BTB structure and function from genetically-modified mouse models and discuss the future perspectives.

Sertoli cells are the target of environmental toxicants in the testis - a mechanistic and therapeutic insight

INTRODUCTION

Sertoli cells support germ cell development in the testis via an elaborate network of cell junctions that confers structural, communicating, and signaling support. However, Sertoli cell junctions and cytoskeletons are the target of environmental toxicants. Because germ cells rely on Sertoli cells for the provision of structural/functional/nutritional support, exposure of males to toxicants leads to germ cell exfoliation due to Sertoli cell injuries. Interestingly, the molecular mechanism(s) by which toxicants induce cytoskeletal disruption that leads to germ cell exfoliation is unclear, until recent years, which are discussed herein. This information can possibly be used to therapeutically manage toxicant-induced infertility/subfertility in human males.

AREAS COVERED

In this review, we provide a brief update on the use of Sertoli cell system developed for rodents and humans in vitro, which can be deployed in any research laboratory with minimal upfront setup costs. These systems can be used to collect reliable data applicable to studies in vivo. We also discuss the latest findings on the mechanisms by which toxicants induce Sertoli cell injury, in particular cytoskeletal disruption. We also identify candidate molecules that are likely targets of toxicants.

EXPERT OPINION

We provide two hypothetical models delineating the mechanism by which toxicants induce germ cell exfoliation and blood-testis barrier disruption. We also discuss molecules that are the targets of toxicants as therapeutic candidates.

Toxicants target cell junctions in the testis: Insights from the indazole-carboxylic acid model

There are numerous types of junctions in the seminiferous epithelium which are integrated with, and critically dependent on the Sertoli cell cytoskeleton. These include the basal tight junctions between Sertoli cells that form the main component of the blood–testis barrier, the basal ectoplasmic specializations (basal ES) and basal tubulobulbar complexes (basal TBC) between Sertoli cells; as well as apical ES and apical TBC between Sertoli cells and the developing spermatids that orchestrate spermiogenesis and spermiation. These junctions, namely TJ, ES, and TBC interact with actin microfilament-based cytoskeleton, which together with the desmosomal junctions that interact with the intermediate filament-based cytoskeleton plus the highly polarized microtubule-based cytoskeleton are working in concert to move spermatocytes and spermatids between the basal and luminal aspect of the seminiferous epithelium. In short, these various junctions are structurally complexed with the actin- and microtubule-based cytoskeleton or intermediate filaments of the Sertoli cell. Studies have shown toxicants (e.g., cadmium, bisphenol A (BPA), perfluorooctanesulfonate (PFOS), phthalates, and glycerol), and some male contraceptives under development (e.g., adjudin, gamendazole), exert their effects, at least in part, by targeting cell junctions in the testis. The disruption of Sertoli–Sertoli cell and Sertoli–germ cell junctions, results in the loss of germ cells from the seminiferous epithelium. Adjudin, a potential male contraceptive under investigation in our laboratory, produces loss of spermatids from the seminiferous tubules through disruption of the Sertoli cell spermatid junctions and disruption of the Sertoli cell cytoskeleton. The molecular and structural changes associated with adjudin administration are described, to provide an example of the profile of changes caused by disturbance of Sertoli-germ cell and also Sertoli cell-cell junctions.

Ezrin is an actin binding protein that regulates sertoli cell and spermatid adhesion during spermatogenesis

During spermatogenesis, the transport of spermatids and the release of sperms at spermiation and the remodeling of the blood-testis barrier (BTB) in the seminiferous epithelium of rat testes require rapid reorganization of the actin-based cytoskeleton. However, the mechanism(s) and the regulatory molecule(s) remain unexplored. Herein we report findings that unfold the functional significance of ezrin in the organization of the testis-specific adherens junction at the spermatid-Sertoli cell interface called apical ectoplasmic specialization (ES) in the adluminal compartment and the Sertoli cell-cell interface known as basal ES at the BTB. Ezrin is expressed at the basal ES/BTB in all stages, except from late VIII to IX, of the epithelial cycle. Its knockdown by RNA interference (RNAi) in vitro perturbs the Sertoli cell tight junction-permeability barrier via a disruption of the actin microfilaments in Sertoli cells, which in turn impeded basal ES protein (eg, N-cadherin) distribution, perturbing the BTB function. These findings were confirmed by a knockdown study in vivo. However, the expression of ezrin at the apical ES is restricted to stage VIII of the cycle and limited only between step 19 spermatids and Sertoli cells. A knockdown of ezrin in vivo by RNAi was found to impede spermatid transport, causing defects in spermiation in which spermatids were embedded deep inside the epithelium, and associated with a loss of spermatid polarity. Also, ezrin was associated with residual bodies and phagosomes, and its knockdown by RNAi in the testis also impeded the transport of residual bodies/phagosomes from the apical to the basal compartment. In summary, ezrin is involved in regulating actin microfilament organization at the ES in rat testes.

Thyroid hormone function in the rat testis

Thyroid hormones are emerging regulators of testicular function since Sertoli, germ, and Leydig cells are found to express thyroid hormone receptors (TRs). These testicular cells also express deiodinases, which are capable of converting the pro-hormone T4 to the active thyroid hormone T3, or inactivating T3 or T4 to a non-biologically active form. Furthermore, thyroid hormone transporters are also found in the testis. Thus, the testis is equipped with the transporters and the enzymes necessary to maintain the optimal level of thyroid hormone in the seminiferous epithelium, as well as the specific TRs to execute thyroid hormone action in response to different stages of the epithelial cycle of spermatogenesis. Studies using genetic models and/or goitrogens (e.g., propylthiouracil) have illustrated a tight physiological relationship between thyroid hormone and testicular function, in particular, Sertoli cell differentiation status, mitotic activity, gap junction function, and blood-testis barrier assembly. These findings are briefly summarized and discussed herein.

Perfluorooctanesulfonate (PFOS) perturbs male rat Sertoli cell blood-testis barrier function by affecting F-actin organization via p-FAK-Tyr(407): an in vitro study

Environmental toxicants such as perfluorooctanesulfonate (PFOS) have been implicated in male reproductive dysfunction, including reduced sperm count and semen quality, in humans. However, the underlying mechanism(s) remains unknown. Herein PFOS at 10-20 μM (∼5-10 μg/mL) was found to be more potent than bisphenol A (100 μM) in perturbing the blood-testis barrier (BTB) function by disrupting the Sertoli cell tight junction-permeability barrier without detectable cytotoxicity. We also delineated the underlying molecular mechanism by which PFOS perturbed Sertoli cell BTB function using an in vitro model that mimics the BTB in vivo. First, PFOS perturbed F-actin organization in Sertoli cells, causing truncation of actin filaments at the BTB. Thus, the actin-based cytoskeleton was no longer capable of supporting the distribution and/or localization of actin-regulatory and adhesion proteins at the cell-cell interface necessary to maintain BTB integrity. Second, PFOS was found to perturb inter-Sertoli cell gap junction (GJ) communication based on a dye-transfer assay by down-regulating the expression of connexin-43, a GJ integral membrane protein. Third, phosphorylated focal adhesion kinase (FAK)-Tyr(407) was found to protect the BTB from the destructive effects of PFOS as shown in a study via an overexpression of an FAK Y407E phosphomimetic mutant. Also, transfection of Sertoli cells with an FAK-specific microRNA, miR-135b, to knock down the expression of phosphorylated FAK-Tyr(407) was found to worsen PFOS-mediated Sertoli cell tight junction disruption. In summary, PFOS-induced BTB disruption is mediated by down-regulating phosphorylated FAK-Tyr(407) and connexin-43, which in turn perturbed F-actin organization and GJ-based intercellular communication, leading to mislocalization of actin-regulatory and adhesion proteins at the BTB.

Sertoli cell is a potential target for perfluorooctane sulfonate-induced reproductive dysfunction in male mice

Perfluorooctane sulfonate (PFOS) is associated with male reproductive disorders, but its targets and mechanisms are poorly understood. We used in vitro and in vivo models to explore the roles of Sertoli cells and the blood-testis barrier (BTB) in PFOS-induced male reproductive dysfunction. First, we used primary Sertoli cell to estimate PFOS-induced cytotoxicity, junction proteins expression, and the changes of barrier function. ICR mice were then administered PFOS (0.25-50mg/kg/day) for 4 weeks. Sperm count, ultrastructure and permeability of the Sertoli cell-based BTB, and testicular PFOS were estimated. Furthermore, the expression and localization of proteins related to junctions between Sertoli cells and mitogen-activated protein kinase (MAPK) signaling pathway were evaluated. Apparent decreases in sperm count were found. PFOS significantly increased vacuolization in Sertoli cells in seminiferous tubules and BTB ultrastructural disassembly, which subsequently increased BTB permeability and testicular PFOS levels, which was confirmed by in vitro results that PFOS decreased transepithelial electrical resistance between Sertoli cells. Additionally, PFOS decreased the expression of junction proteins in Sertoli cells, which was further confirmed by in vivo results that PFOS decreased or dislocated junction proteins (i.e., ZO-1, occludin, claudin-11, and connexin-43) and increased proteins related to the MAPK signaling pathway (i.e., Erk and p38), whereas basal ectoplasmic specialization proteins did not change. The results were confirmed by SB203580, a p38 MAPK selective inhibitor. Sertoli cells appear to be a new cellular target for PFOS. Together with disruption of BTB integrity and function, these cells play an important role in PFOS-induced male reproductive toxicity.

SOX8 regulates permeability of the blood-testes barrier that affects adult male fertility in the mouse

Sertoli cells provide nutritional and physical support to germ cells during spermatogenesis. Sox8 encodes a member of the high mobility group of transcription factors closely related to Sox9 and Sox10. Sertoli cells express SOX8 protein, and its elimination results in an age-dependent dysregulation of spermatogenesis, causing adult male infertility. Among the claudin genes with altered expression in the Sox8(-/-) testes, was claudin-3, which is required for the regulation and maintenance of the blood-testes barrier (BTB). Because the BTB is critical in restricting small molecules in the luminal compartment of the seminiferous tubules, the aim of this study was to analyze the level of tight junction proteins (claudin-3, claudin-11, and occludin) and BTB permeability in Sox8(-/-) adult testes. The acetylation level of alpha-tubulin and microtubule organization was also evaluated because microtubules are critical in maintaining the microenvironment of the seminiferous epithelium. Western blot analysis shows that claudin-3 protein is decreased in Sox8(-/-) testes. Chromatin immunoprecipitation confirmed that SOX8 binds at the promoter region of claudin-3. Claudin-3 was localized to the Sertoli cell tight junctions of wild-type testes and significantly decreased in the Sox8(-/-) testes. The use of biotin tracers showed increased BTB permeability in the Sox8(-/-) adult testes. Electron microscopy analysis showed that microtubule structures were destabilized in the Sox8(-/-) testes. These results suggest that Sox8 is essential in Sertoli cells for germ cell differentiation, partly by controlling the microenvironment of the seminiferous epithelium.