Maturational changes in connexin 43 expression in the seminiferous tubules may depend on thyroid hormone action

CRISRP/Cas9-mediated knockout of Mct8 reveals a functional involvement of Mct8 in testis and sperm development in a rat

Thyroid hormone (TH) has long been believed to play a minor role in male reproduction. However, evidences from experimental model of thyrotoxicosis or hypothyroidism suggests its role in spermatogenesis. Cellular action of TH requires membrane transport via specific transporters such as monocarboxylate transporter 8 (MCT8). SLC16A2 (encodes for MCT8) inactivating mutation in humans can lead to Allan-Herndon Dudley-syndrome, a X-linked psychomotor and growth retardation. These patients present cryptorchidism which suggests a role of MCT8 during spermatogenesis. In this study, we found that Mct8 is highly expressed during early postnatal development and decreases its expression in the adulthood of testis of wild-type male rats. Histological analysis revealed that spermatogonia largely lacks MCT8 expression while spermatocytes and maturing spermatids highly express MCT8. To further understand the role of Mct8 during spermatogenesis, we generated Slc16a2 (encodes MCT8) knockout rats using CRISPR/Cas9. Serum THs (T3 and T4) level were significantly altered in Slc16a2 knockout rats when compared to wild-type littermates during early to late postnatal development. Unlike Slc16a2 knockout mice, Slc16a2 knockout rats showed growth delay during early to late postnatal development. In adult Slc16a2 knockout rats, we observed reduced sperm motility and viability. Collectively, our data unveil a functional involvement of MCT8 in spermatogenesis, underscoring the importance of TH signaling and action during spermatogenesis.

Role of non-classical effects of testosterone and epitestosterone on AMH balance and testicular development parameters

Testosterone (T) and its 17-α epimer, epitestosterone (EpiT), are described as having non-classical effects in addition to their classical androgen actions via the intracellular androgen receptor (iAR). The actions of these androgens play an essential role in triggering factors that shift Sertoli cells from the proliferation phase to the maturation phase. This process is essential for successful spermatogenesis and normal fertility. The aim of this work was to investigate the difference between T and EpiT effects in normal and in chemically castrated Wistar rats. We also tested the effects of these hormones when the iAR-dependent pathways were inhibited by the antiandrogen flutamide. Rats were chemically castrated on postnatal day (pnd) 5 using EDS, a cytotoxic agent that promotes apoptosis of Leydig cells, reducing androgen levels. Then, animals received replacement with T or EpiT and were treated or not with flutamide from pnd 6 to pnd 13 or 20 and were euthanized on pnd 14 and 21. Animals treated with EpiT and flutamide had lower body weight overall. Epididymis weight was also reduced in animals treated with EpiT and flutamide. Flutamide per se reduced epididymis weight at both ages (pnd 14 and 21). Testicular weight and the testicular/body weight ratio were reduced in EDS animals, and flutamide further reduced this weight in animals which received T replacement. EDS administration reduced mRNA levels of both AMH (anti-Müllerian hormone) and its receptor, AMHR2, at pnd 14. In the testes of flutamide-treated animals, EpiT reduced AMH, and both T and EpiT replacement diminished AMHR2 mRNA expression also on pnd 14. EDS decreased iAR expression, and androgen replacement did not change this effect on pnd 21. In rats receiving flutamide, only those also receiving T and EpiT replacement exhibited decreased iAR expression. An increase in connexin 43 expression was observed in animals treated with EpiT without flutamide, whereas in rats treated with flutamide, both hormones were ineffective to increase connexin 43 expression reduced by EDS. Our results suggest that EpiT has an antiandrogen effect on androgen-sensitive tissues such as the epididymis. Nonetheless, the effects of T and EpiT on testicular development parameters are similar. Both hormones may act through their iAR-independent non-classical pathway, regulating AMH and AMHR2, as well as iAR expression.

In vitro formation of the blood-testis barrier during long-term organotypic culture of human prepubertal tissue: comparison with a large cohort of pre/peripubertal boys

STUDY QUESTION

How does the formation of the blood-testis barrier (BTB), as reflected by the expression of connexin 43 and claudin 11 proteins during the pubertal transition period, take place in vitro compared to samples from a large cohort of pre/peripubertal boys?

SUMMARY ANSWER

The BTB connexin 43 and claudin 11 expression patterns appeared to be partially achieved in organotypic culture when compared to that in samples from 71 pre/peripubertal patients.

WHAT IS KNOWN ALREADY

Although alterations in the protein expression patterns of the BTB, whose main components are connexin 43 and claudin 11, are known to be associated with impaired spermatogenesis in mice and adult men, there is a lack of knowledge on its formation in pre-peripubertal human tissue both in vitro and in vivo. Moreover, despite Sertoli cell (SC) maturation during long-term organotypic culture of immature testicular tissue (ITT), initiation of spermatogenesis has not yet been achieved.

STUDY DESIGN, SIZE, DURATION

Histological sections from 71 pre-peripubertal patients were evaluated for the formation of the BTB acting as in vivo controls according to age, SC maturation, clinical signs of puberty and germ cell differentiation. Testicular tissue fragments retrieved from three prepubertal boys were cultured in a long-term organotypic system to analyze the BTB formation and expression pattern in correlation with SC maturation.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Testicular histological sections from 71 patients aged 0-16 years who underwent a biopsy between 2005 and 2014 to preserve their fertility before gonadotoxic treatment were examined. Immunohistochemistry (IHC) results for connexin 43 and claudin 11 as BTB markers, using a semi-quantitative score for their expression, and for Anti-Mullerian hormone (AMH), as SC maturation marker, were analyzed. Germ cell differentiation was evaluated on Hematoxylin-Eosin sections. Tanner stages at the time of biopsy were recorded from medical files. A longitudinal analysis of connexin 43, claudin 11 and AMH expressions on immunohistological sections of organotypic cultured testicular tissue from three prepubertal boys who underwent a biopsy for fertility preservation was performed. Immunostaining was evaluated at culture Days 0, 1, 3, 10, 16, 27, 32, 53, 64 and 139 for two different types of culture media.

MAIN RESULTS AND THE ROLE OF CHANCE

Immunohistochemical control sections showed progressive maturation of SCs, as shown by the decrease in AMH expression, with increasing age (P ≤ 0.01) and the AMH expression was negatively correlated with the expression of connexin 43 and claudin 11 (P ≤ 0.01 for both proteins). Androgen receptor (AR) expression increased with age (P ≤ 0.01) and was significantly correlated with the expression of connexin 43 (P = 0.002) and claudin 11 (P = 0.03). A statistical correlation was also found between the reduction of AMH expression and both the advancement of Tanner stages (P ≤ 0.01) and the differentiation of germ cells (P ≤ 0.01). Furthermore, positive correlations between BTB formation (using connexin 43 and claudin 11 expression) and age (P ≤ 0.01 for both the proteins), higher Tanner stages (P ≤ 0.001 and P ≤ 0.01 for connexin 43 and claudin 11, respectively), and presence of more advanced germ cells (P ≤ 0.001 for both proteins) were observed. In the subanalysis on organotypic cultured ITT, where a significant decrease in AMH expression as a marker of SC maturation was already reported, we showed the onset of expression of connexin 43 at Day 16 (P ≤ 0.001) and a constant expression of claudin 11 from Days 0 to 139, for all three patients, without differences between the two types of culture media.

LARGE SCALE DATA

N/A.

LIMITATIONS REASONS FOR CAUTION

Accessibility of prepubertal human testicular tissue is a major limiting factor to the analysis of cultured tissue samples from a wide number of patients, as would be needed to assess the in vitro development of the BTB according to the age. The impossibility of performing longitudinal studies on in vivo BTB formation in the same patient prevents a comparison of the time needed to achieve effective BTB formation and protein expression patterns in vivo and in vitro.

WIDER IMPLICATIONS OF THE FINDINGS

To the best of our knowledge, this is the first report describing the expression of two BTB proteins in samples from a cohort of prepubertal and peripubertal boys, for the in vivo pattern, and in cultured ITT from a few prepubertal boys, for the in vitro evaluation. Since the formation of this barrier is essential for spermatogenesis and because little is known about its protein expression patterns and development in humans, a deeper understanding of the testicular microenvironment is essential to improve ITT in vitro culture conditions. The final aim is to restore fertility by acheiving in vitro differentiation of spermatogonial stem cells, using cryopreserved ITT collected before gonadotoxic therapies.

STUDY FUNDING AND COMPETING INTEREST(S)

Funding was received from Fonds National de la Recherche Scientifique de Belgique (Grant Télevie Nos. 7.4554.14F and 7.6511.16) and Fondation Salus Sanguinis. No conflict of interest has to be disclosed.

Thyroid Hormone Deiodination and Action in the Gonads

Alterations in thyroid hormone (TH) status during developmental or adult age are associated with abnormal gonadal development and function in human and animal models. In the developing testis, aberrant levels of TH action lead to disruptions in cell proliferation and differentiation, ultimately influencing testicular size, spermatogenesis, steroidogenesis and male fertility. Recent work is increasingly identifying the systems and signaling pathways in gonadal cells that are affected by TH, as well as delineating the major factors that determine TH signaling in gonadal tissue. The TH receptor alpha, the monocarboxylate transporter 8 and the type 3 deiodinase appear to be major contributors to the timely regulation of TH action in the developing testis.

Connexin 43 expression in the testes during postnatal development of finasteride-treated male rat offspring

INTRODUCTION

Hormone-dependent events that occur throughout the first wave of spermatogenesis, such as cellular communication within seminiferous epithelium during early postnatal testis maturation, are important for adult male fertility. Any changes in the T/DHT ratio in male progeny born from females fertilized by finasteride-treated male rats can result in impairment of testicular physiology. The aim of the study was to verify whether finasteride has a transgenerational effect on the expression of connexin 43 (Cx43), a gap junction protein in testes of the F1 generation.

MATERIAL AND METHODS

The subjects of the study were 7, 14, 21/22, 28, and 90-day-old Wistar male rats born by females fertilized by finasteride-treated rats (F1:Fin). The offspring born by untreated rats were used as controls (F1:Control). Connexin 43 was evaluated in the seminiferous epithelium by immunohistochemistry, and in the testis homogenates by Western blot and qRT-PCR. The Cx43 mRNA and protein expression was correlated with intratesticular levels of T and DHT by Spearman's rank correlation coefficient.

RESULTS

We observed a difference in the Cx43 expression in the testis of male rats born by female rats fertilized by finasteride-treated male rats, as compared to the control on following PND (7, 22 and 28 PND, p < 0.001; 14 PND, p < 0.01); and a strong, positive correlation between Cx43 with DHT was only in the F1:Fin group (mRNA: rs = +0.51, p = 0.004; protein: rs = +0.54, p = 0.002).

CONCLUSIONS

Finasteride treatment of male adult rats may cause changes in the communication between the testicular cells of their offspring, leading to a defective course of spermatogenesis.

Neonatal exposure to T3 disrupts male reproductive functions by altering redox homeostasis in immature testis of rats

T3 is the active hormone, produced by peripheral deiodination of thyroxine. Exposure to excess thyroid hormones leads to hypermetabolic state and thus generates oxidative stress which seems to be involved in hyperthyroidism-induced testicular pathophysiology. We investigated the effects of T3 administration on the testis during development throughout sexual maturation in rats. Male pups were divided into two groups. T3 group was administered 80 µg/kg body weight intraperitoneal T3 injections daily for 21 days from the 1st postnatal day, while the control group was administered saline intraperitoneal injections. The pups were sacrificed at pnd 10, 20 and 30. T3 treatment resulted in a significant decrease in body weight at all ages tested and an increase in testis weight during the treatment period. The treatment produced imbalance in their testicular redox status, reflected by a significant increase in the amount of thiobarbituric acid-reactive substances and protein carbonyl content in the testicular homogenates of 20-day-old rats. We observed a significant increase in antioxidant system activities γ-glutamyl transferase, glucose-6-phosphate dehydrogenase, catalase and superoxide dismutase, reduced glutathione content and lactate dehydrogenase activity. Histological examination showed altered seminiferous tubules, degenerated germ cells and decreased height of the germinal epithelium. Chronic neonatal exposure to T3 resulted in redox state alterations which contribute to testicular impairment.

Tissue Engineering to Improve Immature Testicular Tissue and Cell Transplantation Outcomes: One Step Closer to Fertility Restoration for Prepubertal Boys Exposed to Gonadotoxic Treatments

Despite their important contribution to the cure of both oncological and benign diseases, gonadotoxic therapies present the risk of a severe impairment of fertility. Sperm cryopreservation is not an option to preserve prepubertal boys’ reproductive potential, as their seminiferous tubules only contain spermatogonial stem cells (as diploid precursors of spermatozoa). Cryobanking of human immature testicular tissue (ITT) prior to gonadotoxic therapies is an accepted practice. Evaluation of cryopreserved ITT using xenotransplantation in nude mice showed the survival of a limited proportion of spermatogonia and their ability to proliferate and initiate differentiation. However, complete spermatogenesis could not be achieved in the mouse model. Loss of germ cells after ITT grafting points to the need to optimize the transplantation technique. Tissue engineering, a new branch of science that aims at improving cellular environment using scaffolds and molecules administration, might be an approach for further progress. In this review, after summarizing the lessons learned from human prepubertal testicular germ cells or tissue xenotransplantation experiments, we will focus on the benefits that might be gathered using bioengineering techniques to enhance transplantation outcomes by optimizing early tissue graft revascularization, protecting cells from toxic insults linked to ischemic injury and exploring strategies to promote cellular differentiation.