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

The Regulatory Effects of JAK2/STAT3 on Spermatogenesis and the Redox Keap1/Nrf2 Axis in an Animal Model of Testicular Ischemia Reperfusion Injury

The male reproductive system requires the pleiotropic activity of JAK/STAT to maintain its function, especially spermatogenesis. The study aims to investigate the effect of JAK2 signaling on the expression of the Keap1/Nrf2 axis, spermatogenesis, and the Sertoli cells (Sc) junctions in an animal model of testicular ischemia reperfusion injury (tIRI). Testes subjected to tIRI exhibited increased JAK2/STAT3 activity associated with spermatogenic arrest and reduced expression of the Sc junctions. In addition, there was an increased protein expression of Keap1 and decreased Nrf2., which was coupled with the downregulation of gene expression of antioxidant enzymes. Reduced SOD and CAT activities were accompanied by increased lipid peroxidation and protein carbonylation during tIRI. Increased caspase 9 activity and Bax/Bcl2 ratio indicated initiation of apoptosis. Inhibition of JAK2 activity by AG490 maintained the integrity of spermatogenesis and SC junctions, normalized the expression of the Keap1/Nrf2 axis and its downstream antioxidant enzymes, and prevented germ cell apoptosis. The results further emphasized the regulatory role of JAK2/STAT3 on spermatogenesis, Keap1/Nrf2 signaling, and maintenance of the testicular redox balance to combat testicular dysfunction and male infertility.

Analysis of connexin 43, connexin 45 and N-cadherin in the human sertoli cell line FS1 and the human seminoma-like cell line TCam-2 in comparison with human testicular biopsies

BACKGROUND

Germ cell tumors are relatively common in young men. They derive from a non-invasive precursor, called germ cell neoplasia in situ, but the exact pathogenesis is still unknown. Thus, further understanding provides the basis for diagnostics, prognostics and therapy and is therefore paramount. A recently developed cell culture model consisting of human FS1 Sertoli cells and human TCam-2 seminoma-like cells offers new opportunities for research on seminoma. Since junctional proteins within the seminiferous epithelium are involved in cell organization, differentiation and proliferation, they represent interesting candidates for investigations on intercellular adhesion and communication in context with neoplastic progression.

METHODS

FS1 and TCam-2 cells were characterized regarding gap-junction-related connexin 43 (Cx43) and connexin 45 (Cx45), and adherens-junction-related N-cadherin using microarray, PCR, Western blot, immunocytochemistry and immunofluorescence. Results were compared to human testicular biopsies at different stages of seminoma development via immunohistochemistry to confirm the cell lines' representativeness. Furthermore, dye-transfer measurements were performed to investigate functional cell coupling.

RESULTS

Cx43, Cx45 and N-cadherin mRNA and protein were generally detectable in both cell lines via qualitative RT-PCR and Western blot. Immunocytochemistry and immunofluorescence revealed a mainly membrane-associated expression of N-cadherin in both cell lines, but gene expression values were higher in FS1 cells. Cx43 expression was also membrane-associated in FS1 cells but barely detectable in TCam-2 cells. Accordingly, a high gene expression value of Cx43 was measured for FS1 and a low value for TCam-2 cells. Cx45 was primary located in the cytoplasm of FS1 and TCam-2 cells and revealed similar low to medium gene expression values in both cell lines. Overall, results were comparable with corresponding biopsies. Additionally, both FS1 and TCam-2 cells showed dye diffusion into neighboring cells.

CONCLUSION

The junctional proteins Cx43, Cx45 and N-cadherin are expressed in FS1 and TCam-2 cells at mRNA and/or protein level in different amounts and localizations, and cells of both lines are functionally coupled among each other. Concerning the expression of these junctional proteins, FS1 and TCam-2 cells are largely representative for Sertoli and seminoma cells, respectively. Thus, these results provide the basis for further coculture experiments evaluating the role of junctional proteins in context with seminoma progression.

Arachidonic acid impairs the function of the blood-testis barrier via triggering mitochondrial complex-ROS-P38 MAPK axis in hyperthermal Sertoli cells

The death of Sertoli cells (SCs) under condition of heat stress (HS) affects spermatogenesis and is associated with impaired function of the blood-testis barrier (BTB). The fatty acid arachidonic acid (AA) is essential for the maintenance of cellular function. However, excessive release of AA during HS may adversely affect the reproductive function. The molecular mechanisms through which AA modulates the BTB in SCs are unclear. In this study, we found that 100 µM AA damaged testicular morphology and accelerated SC apoptosis during HS, reducing the stability of tight junction proteins (TJPs), shown by measurement of the levels of Claudin 11, 5, Occludin, and trans-epithelial electrical resistance (TEER). It was also found that AA adversely affected TJPs by increasing the accumulation of reactive oxygen species (ROS) and malondialdehyde (MDA), activating p38 mitogen-activated protein kinases (P38 MAPK) and reducing mitochondria DNA (mtDNA) and the expression of mitochondrial complexes I and III. In contrast, pretreatment with SB203508 (a P38 MAPK inhibitor), Rotenone (an inhibitor of complex I) and Antimycin A1 (an inhibitor of complex III) reversed TJPs degradation induced by AA. Interestingly, pretreatment of cells with 10 µM Baicalein, a 12/15 lipoxygenase (12/15-LOX) -dependent inhibitor of AA production, protected against AA-induced TJPs degradation, restored mitochondrial function, and reduced apoptosis. These results suggested an intriguing link between the induction of TJPs degradation induced by AA overload and mitochondrial antioxidant function during HS, which was found to be regulated by the mitochondrial complex-ROS-P38 MAPK axis.

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

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

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

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

Action and Interaction between Retinoic Acid Signaling and Blood–Testis Barrier Function in the Spermatogenesis Cycle

Spermatogenesis is a complex process occurring in mammalian testes, and constant sperm production depends on the exact regulation of the microenvironment in the testes. Many studies have indicated the crucial role of blood–testis barrier (BTB) junctions and retinoic acid (RA) signaling in the spermatogenesis process. The BTB consists of junctions between adjacent Sertoli cells, comprised mainly of tight junctions and gap junctions. In vitamin A-deficient mice, halted spermatogenesis could be rebooted by RA or vitamin A administration, indicating that RA is absolutely required for spermatogenesis. Accordingly, this manuscript will review and discuss how RA and the BTB regulate spermatogenesis and the interaction between RA signaling and BTB function.

Connexin43 in Germ Cells Seems to Be Dispensable for Murine Spermatogenesis

Testicular Connexin43 (Cx43) connects adjacent Sertoli cells (SC) and SC to germ cells (GC) in the seminiferous epithelium and plays a crucial role in spermatogenesis. However, the distinction whether this results from impaired inter-SC communication or between GC and SC is not possible, so far. Thus, the question arises, whether a GC-specific Cx43 KO has similar effects on spermatogenesis as it is general or SC-specific KO. Using the Cre/loxP recombinase system, two conditional KO mouse lines lacking Cx43 in premeiotic (pGCCx43KO) or meiotic GC (mGCCx43KO) were generated. It was demonstrated by qRT-PCR that Cx43 mRNA was significantly decreased in adult pGCCx43KO mice, while it was also reduced in mGCCx43KO mice, yet not statistically significant. Body and testis weights, testicular histology, tubular diameter, numbers of intratubular cells and Cx43 protein synthesis and localization did not show any significant differences in semi-quantitative Western blot analysis and immunohistochemistry comparing adult male KO and WT mice of both mouse lines. Male KO mice were fertile. These results indicate that Cx43 in spermatogonia/spermatids does not seem to be essential for successful termination of spermatogenesis and fertility as it is known for Cx43 in somatic SC, but SC-GC communication might rather occur via heterotypic GJ channels.

Blood-Testis Barrier and Sperm Delayed in the Cauda Epididymis of the Reproductively Regressed Syrian Hamsters

The Syrian (golden) hamsters are seasonal breeders whose reproductive functions are active in summer and inactive in winter. In experimental facility mimicking winter climate, short photoperiod (SP) induces gonadal regression. The blood-testis barrier (BTB) of the sexually involuted animals have been reported to be permeable, allowing developing germ cells to be engulfed or sloughed off the epithelium of the seminiferous tubules. The expressions of genes related to the tight junction composing of BTB were investigated in the reproductive active and inactive testes. Claudin-11, occludin, and junctional adhesion molecule (JAM) were definitely expressed in the active testes but not discernably detected in the inactive testes. And spermatozoa (sperm) were observed in the whole lengths of epididymides in the active testes. They were witnessed in only cauda region of the epididymides but not in caput and corpus regions in animals with the inactive testes. The results imply that the disorganization of BTB is associated with the testicular regression. The developing germ cells are swallowed into the Sertoli cells or travel into the lumen, as supported by the presence of the sperm delayed in the last region of the epididymis. These outcomes suggest that both apoptosis and desquamation are the processes that eliminate the germ cells during the regressing stage in the Syrian hamsters.

The role of different compounds on the integrity of blood-testis barrier: A concise review based on in vitro and in vivo studies

Sertoli cells are "nurturing cells'' in the seminiferous tubules of the testis which have essential roles in the development, proliferation and differentiation of germ cells. These cells also divide the seminiferous epithelium into a basal and an adluminal compartment and establish the blood-testis barrier (BTB). BTB shields haploid germ cells from recognition by the innate immune system. Moreover, after translocation of germ cells into the adluminal compartment their nutritional source is separated from the circulatory system being only supplied by the Sertoli cells. The integrity of BTB is influenced by several organic/ organometallic, hormonal and inflammatory substances. Moreover, several environmental contaminants such as BPA have hazardous effects on the integrity of BTB. In the current review, we summarize the results of studies that assessed the impact of these agents on the integrity of BTB. These studies have implications in understanding the molecular mechanism of male infertility and also in the male contraception.

Suppression of Connexin 43 Leads to Strial Vascular Hyper-Permeability, Decrease in Endocochlear Potential, and Mild Hearing Loss

Objective: Connexin 43 (Cx43) is a protein constituent of gap junctions (GJs) in various barrier cells, especially astrocytes and microglia of the blood-brain-barrier (BBB), where it plays an important role in intercellular communication and regulation of the barrier. Despite the importance of Cx43 in other blood barriers, not much attention has been paid to expression and function of Cx43 in the blood-labyrinth-barrier (BLB) of the stria vascularis in the cochlea. Methods: We used multiple research approaches, including immunocytochemical staining, patch-clamp dye loading technique, real-time quantitative reverse transcription (RT)-PCR, western blot, measurement of endocochlear potential (EP) with an electrode through the scala media, and auditory brainstem response to test hearing function. Results: We found Cx43 expressed in vascular endothelial cells (ECs) and perivascular resident macrophages (PVMs) in the stria vascularis of adult C57BL/6 mouse cochleae. In particular, we found Cx43 expressed in foot processes of PVMs at points of contact with the endothelium. Consistent with Cx43 expression in vivo, we also found Cx43 expressed in EC-EC and EC-PVM interfaces in a co-cultured cell line model. Using a patch-clamp dye loading technique, we demonstrated that Alexa Fluor® 568 dye injected into PVMs diffuses to connected neighboring ECs. The functional coupling between the ECs and PVMs is blocked by 18α-Glycyrrhetinic acid (18α-GA), a GJ blocker. Suppression of Cx43 with small interfering RNA (siRNA) in vivo significantly elevated hearing threshold and caused the EP to drop and the blood barrier to become more permeable. In further study, using in vitro primary EC cell line models, we demonstrated that suppression of Cx43 disrupts intercellular tight junctions (TJs) in the EC monolayer and increases endothelial monolayer permeability. Conculsion: Taken together, these findings underscore the importance of Cx43 expression in the normal ear for maintaining BLB integrity, normal EP, and hearing function.

Establishment and functional characterization of a murine primary Sertoli cell line deficient of connexin43

The Sertoli cell (SC) specific connexin43 (Cx43) knockout (SCCx43KO) mouse line is ideal to gain insight into the mechanistic gap junction formation in SC and the seminiferous epithelium. A method for developing primary SC cultures from these mice was established, validated and successfully characterized via polymerase chain reaction, immunohistochemistry, immunofluorescence (IF), and Western blots (WB). It was evident that both knockout (KO) and wild-type (WT) primary cell cultures were similar in morphology. These highly pure SC cultures were subjected to cell proliferation assays indicating no notable proliferation in cultures of both genotypes. Measurements of cell monolayer integrity indicated significant increases in transepithelial electrical resistance and consequently in tight junction expression of the KO cultures. Using semi-quantitative WB and IF, tight junction protein claudin-11 was analyzed. These results support a role for Cx43 in regulating blood-testis barrier (BTB) function, composition, and dynamics in vitro. Thus, the SC deficient Cx43 cell cultures may provide a valuable in vitro tool for a better understanding of the mechanistic role of Cx43 in spermatogenesis and BTB assembly.

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.

Expression of claudin-11 in canine prepubertal testes, and in canine adult testes showing normal spermatogenesis, impaired spermatogenesis, or testicular neoplasia

The blood-testis barrier (BTB) consists of different cell-to-cell connections, including tight junction proteins like claudin-11 (CLDN11). For dogs, only limited data is published dealing with these proteins in general. Therefore, their physiological relevance, their postnatal expression, and their distribution pattern in pathological conditions, e.g. in altered spermatogenesis and testicular neoplasia were assessed. Canine testes from routine castrations, and those sent in for diagnostic purposes were investigated. Based on morphological evaluation, the dogs and testes were divided into groups: (1) dogs with normal spermatogenesis, (2) four months old prepubertal dogs, (3) intratubular seminoma, (4) diffuse seminoma, (5) Sertoli cell tumours (SCT), (6) Leydig cell tumours (LCT), and (7) dogs with impaired spermatogenesis (e.g. mixed atrophy). In order to examine possible alterations of the BTB components, immunohistochemistry (IHC) and immunofluorescence using a commercial antibody against CLDN11 was performed. Sertoli cell (SC) nuclei (SOX9) and peritubular myoid cells (smooth-muscle-actin, SMA) were also assessed using IHC. Additionally, semi-quantitative Western-blot (WB) and RT-PCR analyses of CLDN11 were conducted. In tubules with normal spermatogenesis, IHC of CLDN11 revealed a basolateral staining at BTB localisation. In prepubertal cords, CLDN11 was diffusely expressed along the cytoplasmic extensions of SCs supposing that the BTB was neither built up nor functional, yet. A shift from weakly expressed CLDN11 between/in residual SCs in intratubular seminoma to only small CLDN11 immunopositive stained spots in the cytoplasm of remaining SOX9-positive SCs in diffuse seminoma was detectable. Reduction or even loss of CLDN11 expression in diffuse seminoma was confirmed using RT-PCR and WB analyses, thus indicating that in seminoma, CLDN11 was downregulated at transcriptional level and completely lost its sealing function. Basal SCs in SCT still showed a CLDN11/SOX9 co-localisation, suggesting that luminal neoplastic SCs undergo de-differentiation during tumour progression. In LCT, no CLDN11 was detectable. Dogs with mixed atrophy showed an upregulation of CLDN11 in tubules with spermatogenic arrest on mRNA and protein level, leading to the conclusion that within these tubules regulatory mechanisms lost their equilibrium. For the first time, the spatial expression of CLDN11 in prepubertal canine testis, impaired spermatogenesis, intratubular seminoma and its absence in diffuse seminoma and LCT was shown. Since altered CLDN11 levels could be part of adaptive mechanisms to modify BTB integrity, further functional investigations to characterize the canine BTB need to be conducted.

The effects of flutamide on cell-cell junctions in the testis, epididymis, and prostate

In this review, we summarize recent findings on the effect of the anti-androgen flutamide on cell-cell junctions in the male reproductive system. We outline developmental aspects of flutamide action on the testis, epididymis, and prostate, and describe changes in junction protein expression and organization of junctional complexes in the adult boar following prenatal and postnatal exposure. We also discuss findings on the mechanisms by which flutamide induces alterations in cell-cell junctions in reproductive tissues of adult males, with special emphasis on cytoplasmic effects. Based on the results from in vivo and in vitro studies in the rat, we propose that flutamide affects the expression of junction proteins and junction complex structure not only by inhibiting androgen receptor activity, but equally important by modulating protein kinase-dependent signaling in testicular cells. Additionally, results from studies on prostate cancer cell lines point to a role for the cellular molecular outfit in response to flutamide.