Tubular Fluid Secretion in the Seminiferous Epithelium: Ion Transporters and Aquaporins in Sertoli Cells

The interactome of cystic fibrosis transmembrane conductance regulator and its role in male fertility: A critical review

The cystic fibrosis transmembrane conductance regulator (CFTR) is a cyclic adenosine monophosphate (cAMP)-regulated chloride and bicarbonate ion channel found in many human cells. Its unique biochemical characteristics and role as a member of the adenosine triphosphate (ATP)-binding cassette transporters superfamily are pivotal for the transport of several substrates across cellular membranes. CFTR is known to interact, physically and functionally, with several other cellular proteins. Hence, its properties are essential for moving various substances across cell membranes and ensuring correct cell functioning. Genetic mutations or environmental factors may disrupt CFTR's function resulting in different possible phenotypes due to gene variations that affect not only CFTR's function, localization, and processing within cells, but also those of its interactors. This has been reported as an underlying cause of various diseases, including cystic fibrosis. The severe clinical implications of cystic fibrosis have driven intense research into the role of CFTR in lung function but its significance to fertility, particularly in men, has been comparatively understudied. However, ongoing and more recent research into CFTR and its interacting proteins in the testis or specific testicular cells is beginning to shed light on this field. Herein, we provide a comprehensive and up-to-date overview of the CFTR, its interactome, and its crucial role in male reproduction, highlighting recent discoveries and advancements in understanding the molecular mechanisms involved. The comprehension of these complex interactions may pave the way for potential therapeutic approaches to improve fertility of men suffering from alterations in the function of CFTR.

A Step Forward in Understanding the Expression of Classical Aquaporins in the Male Reproductive Tract: Study Findings in Cattle (Bos taurus)

Aquaporins (AQPs), also known as water channels, appear to be particularly promising in maintaining male reproductive potential. Therefore, this study aimed to determine the presence of classical AQPs in the bovine (Bos taurus) reproductive system and analyze changes in their expression with age using immunohistochemistry and Western blotting. Of the six classical AQPs, AQP0, AQP1, AQP4, AQP5 and AQP6 were detected, while AQP2 was absent. In the testis, AQP0 was visible in Leydig cells in selected animals, while AQP1 was found in myoid cells surrounding the seminiferous tubules of mature individuals. This characteristic expression patterns of AQP0, limited only to certain bulls, is difficult to explain unequivocally. It is possible that AQP0 expression in cattle is subject to individual variability or changes in response to specific physiological conditions. In the caput and corpus epididymis, AQP0 showed weak expression in epithelial cells of immature animals and stronger expression in basal and principal cells of reproductive bulls. In all animals, AQP1 was present on the apical surface of epithelial cells in the initial segment of the caput epididymis. AQP4, AQP5 and AQP6 were identified in principal and basal cells along the entire epididymis of reproductive bulls. The abundance of AQP4 and AQP6 increased from the caput to the cauda epididymis with the growth and development of the animals. In all males, AQP4, AQP5 and AQP6 were observed in epithelial cells of the vas deferens, and their expression in this section increased with age. In conclusion, the abundance and distribution of the classical AQPs in various cell types and parts of the male reproductive system indicate their crucial role in maintaining water homeostasis, which is essential for normal reproductive function in cattle.

pH Homeodynamics and Male Fertility: A Coordinated Regulation of Acid-Based Balance during Sperm Journey to Fertilization

pH homeostasis is crucial for spermatogenesis, sperm maturation, sperm physiological function, and fertilization in mammals. HCO3- and H+ are the most significant factors involved in regulating pH homeostasis in the male reproductive system. Multiple pH-regulating transporters and ion channels localize in the testis, epididymis, and spermatozoa, such as HCO3- transporters (solute carrier family 4 and solute carrier family 26 transporters), carbonic anhydrases, and H+-transport channels and enzymes (e.g., Na+-H+ exchangers, monocarboxylate transporters, H+-ATPases, and voltage-gated proton channels). Hormone-mediated signals impose an influence on the production of some HCO3- or H+ transporters, such as NBCe1, SLC4A2, MCT4, etc. Additionally, ion channels including sperm-specific cationic channels for Ca2+ (CatSper) and K+ (SLO3) are directly or indirectly regulated by pH, exerting specific actions on spermatozoa. The slightly alkaline testicular pH is conducive to spermatogenesis, whereas the epididymis's low HCO3- concentration and acidic lumen are favorable for sperm maturation and storage. Spermatozoa pH increases substantially after being fused with seminal fluid to enhance motility. In the female reproductive tract, sperm are subjected to increasing concentrations of HCO3- in the uterine and fallopian tube, causing a rise in the intracellular pH (pHi) of spermatozoa, leading to hyperpolarization of sperm plasma membranes, capacitation, hyperactivation, acrosome reaction, and ultimately fertilization. The physiological regulation initiated by SLC26A3, SLC26A8, NHA1, sNHE, and CFTR localized in sperm is proven for certain to be involved in male fertility. This review intends to present the key factors and characteristics of pHi regulation in the testes, efferent duct, epididymis, seminal fluid, and female reproductive tract, as well as the associated mechanisms during the sperm journey to fertilization, proposing insights into outstanding subjects and future research trends.

Predictions from a mathematical approach to model ionic signaling for rapid responses of Sertoli cells exhibit similarities to pharmacological approaches

Sertoli cells are essential for the male reproduction system as they provide morphological support and nutrients for germ cells to guarantee ongoing spermatogenesis. The aim of this work was to predict the electrical properties at the plasma membrane that trigger Sertoli cell rapid responses by involving ionic channels. The rapid responses of Sertoli cells in culture were monitored using patch clamp electrical measurement and compared to data obtained using pharmacological tools (from intact seminiferous tubules). A mathematical model was used to define the roles of potassium channels and the ATP-dependent Na+/K+pump in these responses. Mathematical data verification was also performed to determine the resting and hormonal stimulated membrane potentials of Sertoli cells in the intact seminiferous tubules and of Sertoli cells in culture (patch clamp measurements). The prediction of these data based on mathematical modeling demonstrated, for the first time, the involvement of potassium channels and the activation of Na+/K+pump in the hyperpolarization of Sertoli cells and their consequent rapid responses. Moreover, the mathematical analysis showing the involvement of ionic balance in the rapid responses of these cells to hormones, such as follicle-stimulating hormone, is consistent with previous reports obtained using pharmacological techniques in Sertoli cells. Thus, the validation of such data is reliable and represents a first step in the proposition for a mathematical model to predict rapid responses of Sertoli cells to hormonal stimuli.

A small secreted protein NICOL regulates lumicrine-mediated sperm maturation and male fertility

The mammalian spermatozoa produced in the testis require functional maturation in the epididymis for their full competence. Epididymal sperm maturation is regulated by lumicrine signalling pathways in which testis-derived secreted signals relocate to the epididymis lumen and promote functional differentiation. However, the detailed mechanisms of lumicrine regulation are unclear. Herein, we demonstrate that a small secreted protein, NELL2-interacting cofactor for lumicrine signalling (NICOL), plays a crucial role in lumicrine signalling in mice. NICOL is expressed in male reproductive organs, including the testis, and forms a complex with the testis-secreted protein NELL2, which is transported transluminally from the testis to the epididymis. Males lacking Nicol are sterile due to impaired NELL2-mediated lumicrine signalling, leading to defective epididymal differentiation and deficient sperm maturation but can be restored by NICOL expression in testicular germ cells. Our results demonstrate how lumicrine signalling regulates epididymal function for successful sperm maturation and male fertility.

Environmentally relevant perinatal exposure to DBP accelerated spermatogenesis by promoting the glycolipid metabolism of Sertoli cells in male offspring mice

Since Sertoli cells (SCs) play an essential role in providing energy for spermatogenesis, the present study aimed to investigate the effects of maternal exposure to plasticizer Dibutyl phthalate (DBP) on the onset of spermatogenesis in male offspring through the metabolism pathway as well as the underlying molecular mechanism. Here, pregnant mice were treated with 0 (control), 50, 250, or 500 mg/kg/day DBP in 1 mL/kg corn oil administered daily by oral gavage from gestation day (GD) 12.5 to parturition. The in vivo results showed that 50 mg/kg/day DBP exposure could promote the expression of glucose metabolism-related proteins (GLUT3, LDHA, and MCT4) in the testis of 22 days male offspring. The in vitro results demonstrated that 0.1 mM monobutyl phthalate (MBP, the active metabolite of DBP) promoted the lactate production, glucose consumption, and glycolytic flux of immature SCs, which was paralleled by the upregulated expression of glucose metabolism-related proteins (GLUT1, GLUT3, LDHA, and MCT4). On the other hand, DBP/MBP increased fatty acid (FA) uptake, FA β-oxidation, and ATP production by promoting the expression of CD36 in immature SCs, which might accelerate the maturity of SCs to support the onset of spermatogenesis. Therefore, our findings provided a new perspective on glycolipid metabolism to explain prenatal DBP exposure leading to earlier onset of spermatogenesis in male offspring mice.

Mitochondrial carbonic anhydrase VA and VB: properties and roles in health and disease

Carbonic anhydrase V (CA V), a mitochondrial enzyme, was first isolated from guinea-pig liver and subsequently identified in mice and humans. Later, studies revealed that the mouse genome contains two mitochondrial CA sequences, named Car5A and Car5B. The CA VA enzyme is most highly expressed in the liver, whereas CA VB shows a broad tissue distribution. Car5A knockout mice demonstrated a predominant role for CA VA in ammonia detoxification, whereas the roles of CA VB in ureagenesis and gluconeogenesis were evident only in the absence of CA VA. Previous studies have suggested that CA VA is mainly involved in the provision of HCO₃ ^- for biosynthetic processes. In children, mutations in the CA5A gene led to reduced CA activity, and the enzyme was sensitive to increased temperature. The metabolic profiles of these children showed a reduced supply of HCO₃ ^- to the enzymes that take part in intermediary metabolism: carbamoylphosphate synthetase, pyruvate carboxylase, propionyl-CoA carboxylase and 3-methylcrotonyl-CoA carboxylase. Although the role of CA VB is still poorly understood, a recent study reported that it plays an essential role in human Sertoli cells, which sustain spermatogenesis. Metabolic disease associated with CA VA appears to be more common than other inborn errors of metabolism and responds well to treatment with N-carbamyl-l-glutamate. Therefore, early identification of hyperammonaemia will allow specific treatment with N-carbamyl-l-glutamate and prevent neurological sequelae. Carbonic anhydrase VA deficiency should therefore be considered a treatable condition in the differential diagnosis of hyperammonaemia in neonates and young children.

Tissue hydraulics in reproduction

The development of functional eggs and sperm are critical processes in mammalian development as they ensure successful reproduction and species propagation. While past studies have identified important genes that regulate these processes, the roles of luminal flow and fluid stress in reproductive biology remain less well understood. Here, we discuss recent evidence that support the diverse functions of luminal fluid in oogenesis, spermatogenesis and embryogenesis. We also review emerging techniques that allow for precise quantification and perturbation of tissue hydraulics in female and male reproductive systems, and propose new questions and approaches in this field. We hope this review will provide a useful resource to inspire future research in tissue hydraulics in reproductive biology and diseases.

Do follicle-stimulating hormone receptor polymorphisms in infertile men influence intracytoplasmic sperm injection outcomes? A prospective cohort study

The follicle-stimulating hormone (FSH) and its receptor regulate the quantity and quality of spermatozoa production. Several studies have analyzed the effect of single nucleotide polymorphisms (SNPs) in exon 10 of the FSH receptor (FSHR) on basic semen parameters without yet reaching a firm consensus. The aim of this study was to evaluate the effect of p.Thr307Ala and p.Asn680Ser polymorphisms in exon 10 of the FSHR gene, in infertile men, on intracytoplasmic sperm injection (ICSI) outcomes. This study was conducted between March 2019 and February 2020 on infertile couples undergoing ICSI at Al Hadi Laboratory and Medical Center, Lebanon. Couples with severe infertility factors that may impair gametogenesis/embryogenesis (e.g. advanced maternal age, premature ovarian failure, underwent gonadotoxic treatments, etc.) were excluded from the study. Semen and blood samples were collected from infertile men on the day of oocyte collection. Infertile men (n = 173) were screened for FSHR variants using polymerase chain reaction-restriction fragment length polymorphism. Moreover, fertilization rates, embryo quality, and pregnancy outcomes were evaluated. Higher sperm concentrations were found in the p.Thr307Ala group than the p.Thr307Thr (P < 0.01) and p.Ala307Ala (P < 0.05) groups. Furthermore, fertilization rate was significantly lower in the p.Ala307Ala genotype than in the p.Thr307Thr genotype (P < 0.05). We showed that FSHR variants in infertile men undergoing ICSI could affect sperm concentration, motility, and fertilization rates. Therefore, it will be important to confirm these results in further studies using a larger sample size.

miR-1285-3p targets TPI1 to regulate the glycolysis metabolism signaling pathway of Tibetan sheep Sertoli cells

Glycolysis in Sertoli cells (SCs) can provide energy substrates for the development of spermatogenic cells. Triose phosphate isomerase 1 (TPI1) is one of the key catalytic enzymes involved in glycolysis. However, the biological function of TPI1 in SCs and its role in glycolytic metabolic pathways are poorly understood. On the basis of a previous research, we isolated primary SCs from Tibetan sheep, and overexpressed TPI1 gene to determine its effect on the proliferation, glycolysis, and apoptosis of SCs. Secondly, we investigated the relationship between TPI1 and miR-1285-3p, and whether miR-1285-3p regulates the proliferation and apoptosis of SCs, and participates in glycolysis by targeting TPI1. Results showed that overexpression of TPI1 increased the proliferation rate and decreased apoptosis of SCs. In addition, overexpression of TPI1 altered glycolysis and metabolism signaling pathways and significantly increased amount of the final product lactic acid. Further analysis showed that miR-1285-3p inhibited TPI1 by directly targeting its 3’untranslated region. Overexpression of miR-1285-3p suppressed the proliferation of SCs, and this effect was partially reversed by restoration of TPI1 expression. In summary, this study shows that the miR-1285-3p/TPI1 axis regulates glycolysis in SCs. These findings add to our understanding on the regulation of spermatogenesis in sheep and other mammals.

House feeding pattern increased male yak fertility by improving gut microbiota and serum metabolites

Yaks usually live in an extremely harsh natural environment resulting in low reproductive performance, so the production of yak cannot meet local demand in China. In order to solve this problem, the experiment aims to explore the effect of different feeding modes on the semen quality of male yaks, so as to provide a theoretical basis for improving the yield of yaks in Tibet. We used the combined analysis of metabolomics and microbial sequencing to explore the underlying mechanisms that affect the differences in semen quality between the house feeding (HF) system and the free range (FR). The results showed that the sperm motility (P < 0.001) and sperm concentration (P < 0.05) in the HF group were significantly higher than the FR group, and the abnormal sperm rate (P < 0.01) in HF was significantly lower compared to FR. House feeding modes increased some beneficial materials in blood and testis especially some antioxidants, unsaturated fatty acids, and amino acids. House feeding group increased some gut microbiota at genus level namely Rikenellaceae, Bacteroides, Prevotellaceae_UCG-004, Bacteroidales_RF16, and Alloprevotella, DgA-11. It was interesting that blood metabolites, testicular metabolites, and fecal microbiota were well-correlated with sperm parameters. Meanwhile, the blood metabolites and testicular metabolites were well-correlated with microbes. The result indicated that the HF model was beneficial for yak semen quality by improving the gut microbiota and blood metabolism to increase yak fertility.

Alginate oligosaccharides increase boar semen quality by affecting gut microbiota and metabolites in blood and sperm

Alginate oligosaccharides (AOS), natural polymers from brown seaweeds (such as Laminaria japonica, Undaria pinnatifida, and Sargassum fusiforme), have been reported to possess many beneficial advantages for health. In the current study, after 9 weeks of dietary supplementation, AOS 10 mg/kg group (AOS 10) group increased boar sperm motility from 87.8% to 93.5%, p < 0.05. Moreover, AOS10 increased the relative abundances of Bifidobacterium, Coprococcus, Butyricicoccus (1.3–2.3-fold; p < 0.05) to increase the beneficial blood and sperm metabolites (1.2–1.6-fold; p < 0.05), and important sperm proteins such as gelsolin, Zn-alpha2 glycoprotein, Cation Channel Sperm-Associated Protein, outer dense fiber of sperm tails, etc. (1.5–2.2-fold; p < 0.05). AOS had a long-term beneficial advantage on boar semen quality by the increase in semen volume (175 vs. 160 ml/ejaculation, p < 0.05). AOS may be used as dietary additives for improving semen quality.

Electrophysiology of Human Gametes: A Systematic Review

PURPOSE

Oocytes and spermatozoa are electrogenic cells with the ability to respond to electrical stimuli and modulate their electrical properties accordingly. Determination of the ionic events during the gamete maturation helps to design suitable culture media for gametes in assisted reproductive technology (ART). The present systematic review focuses on the electrophysiology of human gametes during different stages of maturation and also during fertilization.

MATERIALS AND METHODS

The reports published in the English language between January 2000 and July 2021 were extracted from various electronic scientific databases following the PRISMA checklist using specific MeSH keywords.

RESULTS

Subsequent to the screening process with defined inclusion and exclusion criteria, 60 articles have been included in this review. Among them, 11 articles were directly related to the electrophysiology of human oocytes and 49 physiology department to the electrophysiology of human spermatozoa.

CONCLUSIONS

Gametes generate electrical currents by ionic exchange, particularly Na+, K+, Cl-, H+, Zn2+, Cu2+, Se2+, Mg2+, HCO3-, and Ca2+ through specific ion channels in different stages of gamete maturation. The ionic concentrations, pH, and other physicochemical variables are modulated during the gametogenesis, maturation, activation, and the fertilization process following gamete function and metabolism. The electrical properties of human gametes change during different stages of maturation. Although it is demonstrated that the electrical properties are significant regulators of cell signaling and are fundamental to gamete maturation and fertilization, their exact roles in these processes are still poorly understood. Further research is required to unveil the intricate electrophysiological processes of human gamete maturation.

Differential Expressions of Aquaporin Subtypes in the Adult Mouse Testis

Many efforts have been made to study the expression of aquaporins (AQP) in the mammalian reproductive system, but there are not enough data available regarding their localized expression to fully understand their specific roles in male reproduction. The present study investigated the expression and localization patterns of different AQP subtypes in the adult mouse testes and testicular spermatozoa using an immunofluorescence assay. All the studied AQPs were expressed in the testes and revealed subtype-specific patterns in the intensity and localization depending on the cell types of the testes. AQP7 was the most abundant and intensive AQP subtype in the seminiferous tubules, expressing in Leydig cells and Sertoli cells as well as all stages of germ cells, especially the spermatids and testicular spermatozoa. The expression pattern of AQP3 was similar to that of AQP7, but with higher expression in the basal and lower adluminal compartments rather than the upper adluminalcompartment. AQP8 expression was limited to the spermatogonia and Leydig cells whereas AQP9 expression was exclusive to tails of the testicular spermatozoa and elongated spermatids. Taken together, the abundance and distribution of the AQPs across the different cell types in the testes indicating to their relavance in spermatogenesis, as well as in sperm maturation, transition, and function.

Perfusion in Organ-on-Chip Models and Its Applicability to the Replication of Spermatogenesis In Vitro

Organ/organoid-on-a-chip (OoC) technologies aim to replicate aspects of the in vivo environment in vitro, at the scale of microns. Mimicking the spatial in vivo structure is important and can provide a deeper understanding of the cell-cell interactions and the mechanisms that lead to normal/abnormal function of a given organ. It is also important for disease models and drug/toxin testing. Incorporating active fluid flow in chip models enables many more possibilities. Active flow can provide physical cues, improve intercellular communication, and allow for the dynamic control of the environment, by enabling the efficient introduction of biological factors, drugs, or toxins. All of this is in addition to the fundamental role of flow in supplying nutrition and removing waste metabolites. This review presents an overview of the different types of fluid flow and how they are incorporated in various OoC models. The review then describes various methods and techniques of incorporating perfusion networks into OoC models, including self-assembly, bioprinting techniques, and utilizing sacrificial gels. The second part of the review focuses on the replication of spermatogenesis in vitro; the complex process whereby spermatogonial stem cells differentiate into mature sperm. A general overview is given of the various approaches that have been used. The few studies that incorporated microfluidics or vasculature are also described. Finally, a future perspective is given on elements from perfusion-based models that are currently used in models of other organs and can be applied to the field of in vitro spermatogenesis. For example, adopting tubular blood vessel models to mimic the morphology of the seminiferous tubules and incorporating vasculature in testis-on-a-chip models. Improving these models would improve our understanding of the process of spermatogenesis. It may also potentially provide novel therapeutic strategies for pre-pubertal cancer patients who need aggressive chemotherapy that can render them sterile, as well asfor a subset of non-obstructive azoospermic patients with maturation arrest, whose testes do not produce sperm but still contain some of the progenitor cells.

Aquaporins: New markers for male (in)fertility in livestock and poultry?

Improving the methods utilized to facilitate reproduction is associated with a constant need to search for new factors that not only significantly affect reproductive processes, but also create new possibilities when assessing male reproductive potential. Aquaporins (AQPs) belong to a family of small (28-30 kDa) proteins that facilitate the transport of water and other small molecules. There have been 13 AQPs (AQP0-AQP12) discovered in mammals, and these proteins are present in a wide range of cell types. Almost all AQPs, except AQP6 and AQP12 are present in the male reproductive organs and sperm of mammals and birds. Increasing evidence suggests that these proteins are involved in a number of processes responsible for the optimal functioning of the male reproductive system. This review presents the current state of knowledge regarding the abundance and distribution of AQPs in the male reproductive organs and sperm of various livestock and poultry species, including buffalo, cattle, sheep, horses, pigs, turkeys and goose. Furthermore, the possible physiological and pathophysiological significance of AQPs in male reproduction, as well as hormonal regulation of quantities are discussed. It can be concluded from the studies analyzed in this paper that abundance patterns of AQPs may be considered in the future as specific and universal biomarkers of male fertility and infertility in animal husbandry.

Lycium barbarum Polysaccharide Ameliorates Heat-Stress-Induced Impairment of Primary Sertoli Cells and the Blood-Testis Barrier in Rat via Androgen Receptor and Akt Phosphorylation

Male infertility induced by heat stress has been attracting more and more attention. Heat stress not only causes apoptosis of spermatocytes but also has adverse effects on Sertoli cells, further damaging spermatogenesis. Lycium barbarum polysaccharide (LBP) is the main bioactive component of Lycium barbarum, which has a protective effect on male reproduction, but its mechanism is still unclear. In this study, our results proved that LBP blocked the inhibitory effect on the proliferation activity of Sertoli cells after heat stress, reversed the dedifferentiation of Sertoli cells induced by heat stress, and ameliorated the structural integrity of the blood-testis barrier. In addition, it increased the expression of the androgen receptor and activated Akt signaling pathway to resist heat-stress-induced injury of Sertoli cells.

Development and function of smooth muscle cells is modulated by Hic1 in mouse testis

In mammalian testis, contractile peritubular myoid cells (PMCs) regulate the transport of sperm and luminal fluid, while secreting growth factors and extracellular matrix proteins to support the spermatogonial stem cell niche. However, little is known about the role of testicular smooth muscle cells during postnatal testicular development. Here we report age-dependent expression of hypermethylated in cancer 1 (Hic1; also known as ZBTB29) in testicular smooth muscle cells, including PMCs and vascular smooth muscle cells, in the mouse. Postnatal deletion of Hic1 in smooth muscle cells led to their increased proliferation and resulted in dilatation of seminiferous tubules, with increased numbers of PMCs. These seminiferous tubules contained fewer Sertoli cells and more spermatogonia, and fibronectin was not detected in their basement membrane. The expression levels of genes encoding smooth muscle contractile proteins, Acta2 and Cnn1, were downregulated in the smooth muscle cells lacking Hic1, and the seminiferous tubules appeared to have reduced contractility. These data imply a role for Hic1 in determining the size of seminiferous tubules by regulating postnatal smooth muscle cell proliferation, subsequently affecting spermatogenesis in adulthood.

CFTR regulation of aquaporin-mediated water transport

The cystic fibrosis transmembrane conductance regulator (CFTR) is an anion channel responsible for the direct transport of bicarbonate and chloride. CFTR-dependent ionic transport is crucial for pH regulation and fluid homeodynamics among epithelial surfaces. Particularly, CFTR performs an essential role in the male reproductive tract, which requires a tight regulation of water and electrolytes in order to produce healthy spermatozoa. The absence or malfunction of CFTR results in cystic fibrosis, the most common lethal disease among Caucasians, that is characterized by an impaired fluid and ionic homeostasis in the whole organism. Due to the wide expression and importance of CFTR, the male reproductive tract is highly affected by cystic fibrosis, resulting in male infertility. Although CFTR is not permeable to water, this protein acts as a regulator of other protein channels, such as aquaporins. In fact, CFTR acts as a molecular partner of aquaporins in epithelial cells, regulating fluid homeodynamics. Herein, up-to-date data concerning the regulation of aquaporin-mediated water transport by CFTR will be discussed, highlighting the role of both channels in the male reproductive tract.

Alginate oligosaccharides improve germ cell development and testicular microenvironment to rescue busulfan disrupted spermatogenesis

Rationale: Busulfan is currently an indispensable anti-cancer drug, particularly for children, but the side effects on male reproduction are so serious that critical drug management is needed to minimize any negative impact. Meanwhile, alginate oligosaccharides (AOS) are natural products with many consequent advantages, that have attracted a great deal of pharmaceutical attention. In the current investigation, we performed single-cell RNA sequencing on murine testes treated with busulfan and/or AOS to define the mitigating effects of AOS on spermatogenesis at the single cell level.

Methods: Testicular cells (in vivo) were examined by single cell RNA sequencing analysis, histopathological analysis, immunofluorescence staining, and Western blotting. Testes samples (ex vivo) underwent RNA sequencing analysis. Blood and testicular metabolomes were determined by liquid chromatography-mass spectrometry (LC/MS).

Results: We found that AOS increased murine sperm concentration and motility, and rescued busulfan disrupted spermatogenesis through improving (i) the proportion of germ cells, (ii) gene expression important for spermatogenesis, and (iii) transcriptional factors in vivo. Furthermore, AOS promoted the ex vivo expression of genes important for spermatogenesis. Finally, our results showed that AOS improved blood and testis metabolomes as well as the gut microbiota to support the recovery of spermatogenesis.

Conclusions: AOS could be used to improve fertility in patients undergoing chemotherapy and to combat other factors that induce infertility in humans.

New insights into the role of mTORC1 in male fertility in zebrafish

Mechanistic target of rapamycin complex 1 (mTORC1) plays crucial roles in male fertility. In mammals, deregulation of mTORC1 led to disordered spermatogonia proliferation and spermatogenesis, which eventually caused infertility in males. However, its roles in male fertility of non-mammalian species remain unclarified. In the present study, it was found that treatment of rapamycin, an mTORC1 inhibitor, resulted in infertility with decreased milt production and sperm motility in zebrafish. However, it is surprising to find that spermatogenesis was normal in these fish. All types of germ cells were found and the proliferation of spermatogonia and spermatocyte were normal. These results suggested that maturation of sperm may be impaired in males treated with rapamycin. Increased apoptosis was found surrounding the lumen containing spermatozoa, implicating a loss of Sertoli cells in testes treated with rapamycin. Moreover, LH/hCG mediated up-regulation of steroidogenic genes was abolished. The expression of npr and ar induced by LH/hCG was also blocked, which further suppressed the signaling of progestin and androgen. Collectively, mTORC1 maintains male fertility via different mechanisms in fish and mammals. mTORC1 is dispensable for spermatogenesis in zebrafish, but possibly supports the maintenance of Sertoli cells and mediates the signaling of hormones, which are crucial for sperm maturation.

pH and male fertility: making sense on pH homeodynamics throughout the male reproductive tract

In the male reproductive tract, ionic equilibrium is essential to maintain normal spermatozoa production and, hence, the reproductive potential. Among the several ions, HCO3- and H+ have a central role, mainly due to their role on pH homeostasis. In the male reproductive tract, the major players in pH regulation and homeodynamics are carbonic anhydrases (CAs), HCO3- membrane transporters (solute carrier 4-SLC4 and solute carrier 26-SLC26 family transporters), Na+-H+ exchangers (NHEs), monocarboxylate transporters (MCTs) and voltage-gated proton channels (Hv1). CAs and these membrane transporters are widely distributed throughout the male reproductive tract, where they play essential roles in the ionic balance of tubular fluids. CAs are the enzymes responsible for the production of HCO3- which is then transported by membrane transporters to ensure the maturation, storage, and capacitation of the spermatozoa. The transport of H+ is carried out by NHEs, Hv1, and MCTs and is essential for the electrochemical balance and for the maintenance of the pH within the physiological limits along the male reproductive tract. Alterations in HCO3- production and transport of ions have been associated with some male reproductive dysfunctions. Herein, we present an up-to-date review on the distribution and role of the main intervenient on pH homeodynamics in the fluids throughout the male reproductive tract. In addition, we discuss their relevance for the establishment of the male reproductive potential.

Aquaporin 11 is related to cryotolerance and fertilising ability of frozen-thawed bull spermatozoa

Aquaporins (AQPs) are channel proteins involved in the transport of water and solutes across biological membranes. In the present study we identified and localised aquaporin 11 (AQP11) in bull spermatozoa and investigated the relationship between the relative AQP11 content, sperm cryotolerance and the fertilising ability of frozen-thawed semen. Bull ejaculates were classified into two groups of good and poor freezability and assessed through immunofluorescence and immunoblotting analyses before and after cryopreservation. AQP11 was localised throughout the entire tail and along the sperm head. These findings were confirmed through immunoblotting, which showed a specific band of approximately 50 kDa corresponding to AQP11. The relative amount of AQP11 was significantly (P<0.05) higher in both fresh and frozen-thawed spermatozoa from bull ejaculates with good freezability compared with those with poorer freezability. In addition, in vitro oocyte penetration rates and non-return rates 56 days after AI were correlated with the relative AQP11 content in fresh spermatozoa. In conclusion, AQP11 is present in the head and tail of bull spermatozoa and its relative amount in fresh and frozen-thawed spermatozoa is related to the resilience of the spermatozoa to withstand cryopreservation and the fertilising ability of frozen-thawed spermatozoa. Further research is needed to elucidate the actual role of sperm AQP11 in bovine fertility.

Cellular distribution of aquaporins in testes of normal and cryptorchid dogs: A preliminary study on dynamic roles

Fluid regulation within the male gonad is an important process for promoting sperm differentiation and maturation. Aquaporins (AQPs) are a family of thirteen integral membrane proteins involved in these processes. The expression of several genes of AQPs occurs in the male reproductive tract of humans and other animal species, although there are few studies on domestic animals. In this study, the localization of AQP7, AQP8, and AQP9 as well as the abundances of protein and mRNA transcripts were examined in normal and cryptorchid dog testes. There was immunohistochemical localization of AQP7, AQP8, and AQP9 in both the tubular and interstitial compartments of the normal and retained testes and crytorchid dogs, albeit there was an obvious difference in cellular localization with the testes from the cryptorchid dogs. These results were supported by western blotting and real-time RT-PCR analyses, there was a lesser AQP7 and greater AQP9 abundance of protein and mRNA transcripts in the cryptorchid testis. These findings indicate combined testicular functions of AQPs in cell volume regulation. In addition, with the cryptorchid condition characterized there was a different cellular distribution of AQPs supporting the thought that early detection is important for controlling possible side effects of cyptorchidism, such as pre-neoplastic and carcinogenic outcomes.

Carbonic anhydrases are involved in mitochondrial biogenesis and control the production of lactate by human Sertoli cells

The process that allows cells to control their pH and bicarbonate levels is essential for ionic and metabolic equilibrium. Carbonic anhydrases (CAs) catalyse the conversion of CO₂ to HCO 3 - and H⁺ and are thus essential for this process. Herein, we inhibited CAs with acetazolamide - ACT and SLC-0111 - to study their involvement in the metabolism, mitochondrial potential, mitochondrial biogenesis and lipid metabolism of human Sertoli cells (hSCs), obtained from biopsies from men with conserved spermatogenesis. We were able to identify three isoforms of CAs, one mitochondrial isoform (CA VB) and two cell membrane-bound isoforms (CA IX and CA XII) in hSCs. When assessing the expression of markers for mitochondrial biogenesis, we observed a decrease in HIF-1α, SIRT1, PGC1α and NRF-1 mRNAs after all CAs were inhibited, resulting in decreased mitochondrial DNA copy numbers. This was followed by an increased production of lactate and alanine in the same conditions. In addition, consumption of glucose was maintained after inhibition of all CAs in hSCs. These results indicate a reduced conversion of pyruvate to acetyl-coA, possibly due to decreased mitochondrial function, caused by CA inhibition in hSCs. Inhibition of CAs also caused alterations in lipid metabolism, since we detected an increased expression of hormone-sensitive lipase (HSL) in hSCs. Our results suggest that CAs are essential for mitochondrial biogenesis, glucose and lipid metabolism in hSCs. This is the first report showing that CAs play an essential role in hSC metabolic dynamics, being involved in mitochondrial biogenesis and controlling lactate production.

The ubiquitous isoform of Na/K-ATPase (ATP1A1) regulates junctional proteins, connexin 43 and claudin 11 via Src-EGFR-ERK1/2-CREB pathway in rat Sertoli cells

Interaction of Na/K-ATPase with its ligand ouabain has been implicated in the regulation of various biological processes. The objective was to investigate roles of Na/K-ATPase isoforms in formation and function of junctional complexes in Sertoli cells. Primary cultures of Sertoli cells were obtained by enzymatic digestion of 20-day-old rat testes and grown on Matrigel-coated dishes for 7 days. Sertoli cells predominantly expressed the ubiquitous isoform of Na/K-ATPase (ATP1A1), confirmed by immunoblotting, PCR, immunofluorescence, and mass spectrometry. Treatment of Sertoli cells with 50 nM ouabain increased transepithelial electrical resistance (TER) and expression of claudin 11 (tight junctions) and connexin 43 (gap junctions), whereas 1 mM ouabain had opposite effects. Involvement of Src-EGFR-ERK1/2-CREB pathway in ouabain-mediated expression of claudin 11 and connexin 43 was evaluated. Incubation of Sertoli cells with 50 nM ouabain increased content of p-Src, p-EGFR, p-ERK1/2, and p-CREB; in contrast, 1 mM ouabain decreased phosphorylation of these signaling molecules. Preincubation of Sertoli cells with inhibitors of Src and MAPK pathways inhibited ouabain-induced effects on these signaling molecules, TER, and expression of claudin 11 and connexin 43. In conclusion, we inferred that ATP1A1 regulated Sertoli cell tight junctions and gap junctions through the Src-EGFR-ERK1/2-CREB pathway. Ouabain is an endogenous steroid; therefore, its interaction with ATP1A1 may be a critical signaling mechanism for the regulation of Sertoli cell function and male fertility.

ADAMTS1 and ADAMTS5 metalloproteases produced by Sertoli cells: a potential diagnostic marker in azoospermia

In this study, our aim was to detect protein levels of A Disintegrin and Metalloproteinase with Thrombospondin Motifs 1 and 5 (ADAMTS1 and ADAMTS5) proteases and to examine the effect of in vitro FSH supplementation on protease production in cultured Sertoli cells. The expression of metalloproteases, ADAMTS1, and ADAMTS5 were investigated in Sertoli cell cultures as well as in ejaculate of azoospermic men which then were compared with ejaculates of the fertile control group. A total of 15 azoospermic men, diagnosed as obstructive (OA, n = 5) and nonobstructive (NOA, n = 10) azoospermia were included in the study. ADAMTS1, ADAMTS5 and FSH receptors (FSHR) were found to be expressed 2.56, 2.10, and 2.66-fold less in Sertoli cells of NOA patients, than those of OA (p < 0.05). After rFSH was added onto Sertoli cell cultures of NOA patients, their expression did not increase significantly and did not reach to levels of control group. Evaluation of ejaculates revealed that the expression of ADAMTS1 and ADAMTS5 were insignificantly 1.03 and 1.1-fold higher in OA group (p > 0.05), respectively; however, in the NOA group, their expression were 1.70 and 1.96-fold lower, respectively, when compared with the fertile control group (p < 0.05) which was statistically significant. As a conclusion, the present study has revealed that insufficiency of ADAMTS1 and ADAMTS5 expression in Sertoli cells may have an important role in the etiology of male infertility. As expected due to low FSHR expression, rFSH response is impaired in NOA patients with relatively low ADAMTS expression response; therefore, such patients might hardly benefit from rFSH treatment. Further studies with larger cohorts may reveal ADAMTSs' potential use as a predictive marker for positive sperm retrieval in azoospermic patients who are scheduled to undergo testicular sperm extraction. Abbreviations: ADAM: A Disintegrin and Metalloproteinase; ADAMTS1 and ADAMTS5: A Disintegrin and Metalloproteinase with 10 Thrombospondin Motifs 1 and 5; ADAMTS: A Disintegrin and Metalloproteinase with Thrombospondin; ABP: androgen binding protein; CAMs: cell adhesion molecules; ECM: extracellular matrix; FSH: follicle stimulating hormone; FSHR: FSH receptors; HRP: horseradish peroxidase; MMP: matrix metalloproteinases; MP: metalloproteinases; NOA: nonobstructive azoospermia; OA: obstructive azoospermia; TIMP-1: tissue inhibitor of metalloproteinase-1.

In Vivo Genetic Manipulation of Spermatogonial Stem Cells and Their Microenvironment by Adeno-Associated Viruses

Adeno-associated virus (AAV) penetrates the blood-brain barrier, but it is unknown whether AAV penetrates other tight junctions. Genetic manipulation of testis has been hampered by the basement membrane of seminiferous tubules and the blood-testis barrier (BTB), which forms between Sertoli cells and divides the tubules into basal and adluminal compartments. Here, we demonstrate in vivo genetic manipulation of spermatogonial stem cells (SSCs) and their microenvironment via AAV1/9. AAV1/9 microinjected into the seminiferous tubules penetrated both the basement membrane and BTB, thereby transducing not only Sertoli cells and SSCs but also peritubular cells and Leydig cells. Moreover, when congenitally infertile Kitl^Sl/Kitl^Sl-d mouse testes with defective Sertoli cells received Kitl-expressing AAVs, spermatogenesis regenerated and offspring were produced. None of the offspring contained the AAV genome. Thus, AAV1/9 allows efficient germline and niche manipulation by penetrating the BTB and basement membrane, providing a promising strategy for the development of gene therapies for reproductive defects.

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AAVs penetrate the blood-testis barrier and infect SSCs and their environment

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AAVs also penetrate the basement membrane of the seminiferous tubules

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AAVs could rescue spermatogenesis in congenitally infertile Kitl^Sl/Kitl^Sl-d mice

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Offspring did not carry transgenes after microinsemination

Acute effect of bisphenol A: Signaling pathways on calcium influx in immature rat testes

We investigated the acute effect of low concentrations of BPA on calcium influx and the mechanism of action of BPA in this rapid response in the rat testis. BPA increased calcium influx at 1 pM and 1 nM at 300 s of incubation, in a similar manner to that of estradiol. At 1 pM, BPA stimulated calcium influx independently of classical estrogen receptors, consistent with a G-protein coupled receptor. This effect also involves the modulation of ionic channels, such as K⁺, TRPV1 and Cl^- channels. Furthermore, BPA is able to modulate calcium from intracellular storages by inhibiting SERCA and activating IP₃ receptor/Ca²⁺ channels at the endoplasmic reticulum and activate kinase proteins, such as PKA and PKC. The rapid responses of BPA on calcium influx could, in turn, trigger a cross talk by MEK and p38^MAPK activation and also mediate genomic responses.

Localization of epithelial sodium channel (ENaC) and CFTR in the germinal epithelium of the testis, Sertoli cells, and spermatozoa

Spermatogenesis starts within the seminiferous tubules of the testis by mitotic division of spermatogonia that produces spermatocytes. Meiotic division of these spermatocytes produces haploid spermatids that differentiate into spermatozoa. In this study, we examined the expression of ENaC and CFTR (a Cl^- channel) in rat testicular sections using confocal microscopic immunofluorescence. The structural integrity of the seminiferous tubule sections was verified by precise phalloidin staining of the actin fibers located abundantly at both basal and adluminal tight junctions. The acrosome forming regions in the round spermatids were stained using an FITC coupled lectin (wheat germ agglutinin). In all phases of the germ cells (spermatogonia, spermatocytes, and spermatids) ENaC was localized in cytoplasmic pools. Prior to spermiation, ENaC immunofluorescence appeared along the tails of the spermatids. In spermatozoa isolated from the epididymis, ENaC was localized at the acrosome and a central region of the sperm flagellum. The mature sperm are transcriptionally silent. Hence, we suggest that ENaC subunits in cytoplasmic pools in germ cells serve as the source of ENaC subunits located along the tail of spermatozoa. The locations of ENaC is compatible with a possible role in the acrosomal reaction and sperm mobility. In contrast to ENaC, CFTR immunofluorescence was most strongly observed specifically within the Sertoli cell nuclei. Based on the nuclear localization of CFTR we suggest that, in addition to its role as an ion channel, CFTR may have an independent role in gene regulation within the nuclei.

Hormone induced differential transcriptome analysis of Sertoli cells during postnatal maturation of rat testes

Sertoli cells (Sc) are unique somatic cells of testis that are the target of both FSH and testosterone (T) and regulate spermatogenesis. Although Sc of neonatal rat testes are exposed to high levels of FSH and T, robust differentiation of spermatogonial cells becomes conspicuous only after 11-days of postnatal age. We have demonstrated earlier that a developmental switch in terms of hormonal responsiveness occurs in rat Sc at around 12 days of postnatal age during the rapid transition of spermatogonia A to B. Therefore, such “functional maturation” of Sc, during pubertal development becomes prerequisite for the onset of spermatogenesis. However, a conspicuous difference in robust hormone (both T and FSH) induced gene expression during the different phases of Sc maturation restricts our understanding about molecular events necessary for the spermatogenic onset and maintenance. Here, using microarray technology, we for the first time have compared the differential transcriptional profile of Sc isolated and cultured from immature (5 days old), maturing (12 days old) and mature (60 days old) rat testes. Our data revealed that immature Sc express genes involved in cellular growth, metabolism, chemokines, cell division, MAPK and Wnt pathways, while mature Sc are more specialized expressing genes involved in glucose metabolism, phagocytosis, insulin signaling and cytoskeleton structuring. Taken together, this differential transcriptome data provide an important resource to reveal the molecular network of Sc maturation which is necessary to govern male germ cell differentiation, hence, will improve our current understanding of the etiology of some forms of idiopathic male infertility.

The endoplasmic reticulum, calcium signaling and junction turnover in Sertoli cells

The endoplasmic reticulum (ER) forms a continuous network throughout morphologically differentiated Sertoli cells. It is an integral component of intercellular adhesion junctions in this cell type, as well as forming membrane contact sites with the plasma membrane and intracellular organelles. One of the major functions of the ER in cells generally is maintaining calcium homeostasis and generating calcium signals. In this review, we discuss what is currently known about the overall pattern of distribution of the ER in Sertoli cells and the location of calcium regulatory machinery in the various subdomains of the organelle. Current data are consistent with the hypothesis that calcium signaling by the ER of Sertoli cells may play a significant role in events related to junction remodeling that occur in the seminiferous epithelium during spermatogenesis.

Molecular cloning and expression analysis of the aqp1aa gene in half-smooth tongue sole (Cynoglossus semilaevis)

Aquaporin 1 (AQP1) is a member of the transmembrane water channel family of proteins with special structural features, and two AQP1 paralogous genes (aqp1aa and aqp1ab) are reported in teleosts. In the present study, the aqp1aa gene of half-smooth tongue sole (Cynoglossus semilaevis) was cloned and characterized. The full-length cDNA of aqp1aa is 1411 bp with a 786 bp open reading frame encoding a 261-amino acid putative protein with a characteristic structure consisting of 6 membrane-spanning α-helical domains and two highly conserved asparagine—proline—alanine motifs. Real-time quantitative PCR revealed that aqp1aa mRNA is expressed predominantly in the testis of males and pseudo-males, while its expression is low in the ovary and lowest in doublesex and mab-3-related transcription factor 1(DMRT1) knock out fish and triploid males. In situ hybridization indicated that aqp1aa mRNA is expressed mainly in the germ cells of males and pseudo-males, especially in spermatozoa and spermatids. These results suggest that the aqp1aa may play a role in spermatogenesis of C. semilaevis.

Mammalian target of rapamycin (mTOR): a central regulator of male fertility?

Mammalian target of rapamycin (mTOR) is a central regulator of cellular metabolic phenotype and is involved in virtually all aspects of cellular function. It integrates not only nutrient and energy-sensing pathways but also actin cytoskeleton organization, in response to environmental cues including growth factors and cellular energy levels. These events are pivotal for spermatogenesis and determine the reproductive potential of males. Yet, the molecular mechanisms by which mTOR signaling acts in male reproductive system remain a matter of debate. Here, we review the current knowledge on physiological and molecular events mediated by mTOR in testis and testicular cells. In recent years, mTOR inhibition has been explored as a prime strategy to develop novel therapeutic approaches to treat cancer, cardiovascular disease, autoimmunity, and metabolic disorders. However, the physiological consequences of mTOR dysregulation and inhibition to male reproductive potential are still not fully understood. Compelling evidence suggests that mTOR is an arising regulator of male fertility and better understanding of this atypical protein kinase coordinated action in testis will provide insightful information concerning its biological significance in other tissues/organs. We also discuss why a new generation of mTOR inhibitors aiming to be used in clinical practice may also need to include an integrative view on the effects in male reproductive system.

Targeted deletion of the Kv6.4 subunit causes male sterility due to disturbed spermiogenesis

Electrically silent voltage-gated potassium (KvS) channel subunits (i.e. Kv5–Kv6 and Kv8–Kv9) do not form functional homotetrameric Kv channels, but co-assemble with Kv2 subunits, generating functional heterotetrameric Kv2­–KvS channel complexes in which the KvS subunits modulate the Kv2 channel properties. Several KvS subunits are expressed in testis tissue but knowledge about their contribution to testis physiology is lacking. Here, we report that the targeted deletion of Kv6.4 in a transgenic mouse model (Kcng4–/–) causes male sterility as offspring from homozygous females were only obtained after mating with wild-type (WT) or heterozygous males. Semen quality analysis revealed that the sterility of the homozygous males was caused by a severe reduction in total sperm-cell count and the absence of motile spermatozoa in the semen. Furthermore, spermatozoa of homozygous mice showed an abnormal morphology characterised by a smaller head and a shorter tail compared with WT spermatozoa. Comparison of WT and Kcng4–/– testicular tissue indicated that this inability to produce (normal) spermatozoa was due to disturbed spermiogenesis. These results suggest that Kv6.4 subunits are involved in the regulation of the late stages of spermatogenesis, which makes them a potentially interesting pharmacological target for the development of non-hormonal male contraceptives.

Obesogens and male fertility

In the last decades, several studies evidenced a decrease in male fertility in developed countries. Although the aetiology of this trend in male reproductive health remains a matter of debate, environmental compounds that predispose to weight gain, namely obesogens, are appointed as contributors because of their action as endocrine disruptors. Obesogens favour adipogenesis by an imbalance of metabolic processes and can be found virtually everywhere. These compounds easily accumulate in tissues with high lipid content. Obesogens change the functioning of male reproductive axis, and, consequently, the testicular physiology and metabolism that are pivotal for spermatogenesis. The disruption of these tightly regulated metabolic pathways leads to adverse reproductive outcomes. Notably, adverse effects of obesogens may also promote disturbances in the metabolic performance of the following generations, through epigenetic modifications passed by male gametes. Thus, unveiling the molecular pathways by which obesogens induce toxicity that may end up in epigenetic modifications is imperative. Otherwise, a transgenerational susceptibility to metabolic diseases may be favoured. We present an up-to-date overview of the impact of obesogens on testicular physiology, with a particular focus on testicular metabolism. We also address the effects of obesogens on male reproductive parameters and the subsequent consequences for male fertility.

Ghrelin acts as energy status sensor of male reproduction by modulating Sertoli cells glycolytic metabolism and mitochondrial bioenergetics

Ghrelin is a growth hormone-releasing peptide that has been suggested to interfere with spermatogenesis, though the underling mechanisms remain unknown. We studied the effect of ghrelin in human Sertoli cells (hSCs) metabolic phenotype. For that, hSCs were exposed to increasing concentrations of ghrelin (20, 100 and 500 pM) mimicking the levels reported in obese, normal weight, and severely undernourished individuals. The metabolite production/consumption was determined. The protein levels of key glycolysis-related transporters and enzymes were assessed. The lactate dehydrogenase (LDH) activity was measured. Mitochondrial complexes protein levels and mitochondria membrane potential were also measured. We showed that hSCs express the growth hormone secretagogue receptor. At the concentration present in the plasma of normal weight men, ghrelin caused a decrease of glucose consumption and mitochondrial membrane potential in hSCs, though LDH activity and lactate production remained unchanged, illustrating an alteration of glycolytic flux efficiency. Exposure of hSCs to levels of ghrelin found in the plasma of severely undernourished individuals decreased pyruvate consumption and mitochondrial complex III protein expression. All concentrations of ghrelin decreased alanine and acetate production by hSCs. Notably, the effects of ghrelin levels found in severely undernourished individuals were more pronounced in hSCs metabolic phenotype highlighting the importance of a proper eating behavior to maintain male reproductive potential. In conclusion, ghrelin acts as an energy status sensor for hSCs in a dose-dependent manner, showing an inverse association with the production of lactate, thus controlling the nutritional support of spermatogenesis.

Hepatocyte and Sertoli Cell Aquaporins, Recent Advances and Research Trends

Aquaporins (AQPs) are proteinaceous channels widespread in nature where they allow facilitated permeation of water and uncharged through cellular membranes. AQPs play a number of important roles in both health and disease. This review focuses on the most recent advances and research trends regarding the expression and modulation, as well as physiological and pathophysiological functions of AQPs in hepatocytes and Sertoli cells (SCs). Besides their involvement in bile formation, hepatocyte AQPs are involved in maintaining energy balance acting in hepatic gluconeogenesis and lipid metabolism, and in critical processes such as ammonia detoxification and mitochondrial output of hydrogen peroxide. Roles are played in clinical disorders including fatty liver disease, diabetes, obesity, cholestasis, hepatic cirrhosis and hepatocarcinoma. In the seminiferous tubules, particularly in SCs, AQPs are also widely expressed and seem to be implicated in the various stages of spermatogenesis. Like in hepatocytes, AQPs may be involved in maintaining energy homeostasis in these cells and have a major role in the metabolic cooperation established in the testicular tissue. Altogether, this information represents the mainstay of current and future investigation in an expanding field.

The Sertoli cell: one hundred fifty years of beauty and plasticity

It has been one and a half centuries since Enrico Sertoli published the seminal discovery of the testicular 'nurse cell', not only a key cell in the testis, but indeed one of the most amazing cells in the vertebrate body. In this review, we begin by examining the three phases of morphological research that have occurred in the study of Sertoli cells, because microscopic anatomy was essentially the only scientific discipline available for about the first 75 years after the discovery. Biochemistry and molecular biology then changed all of biological sciences, including our understanding of the functions of Sertoli cells. Immunology and stem cell biology were not even topics of science in 1865, but they have now become major issues in our appreciation of Sertoli cell's role in spermatogenesis. We end with the universal importance and plasticity of function by comparing Sertoli cells in fish, amphibians, and mammals. In these various classes of vertebrates, Sertoli cells have quite different modes of proliferation and epithelial maintenance, cystic vs. tubular formation, yet accomplish essentially the same function but in strikingly different ways.

Smad2/3 Upregulates the Expression of Vimentin and Affects Its Distribution in DBP-Exposed Sertoli Cells

Sertoli cells (SCs) in the testes provide physical and nutritional support to germ cells. The vimentin cytoskeleton in SCs is disrupted by dibutyl phthalate (DBP), which leads to SCs dysfunction. In a previous study, we found that peroxisome proliferator-activated receptor alpha (PPARα) influenced the distribution of vimentin by affecting its phosphorylation in DBP-exposed SCs. In the present study, we investigated the role of Smad2/3 in regulating the expression of vimentin in DBP-exposed SCs. We hypothesized that Smad2/3 affects the distribution of vimentin by regulating its expression and that there is cross talk between Smad2/3 and PPARα. The real-time PCR and ChIP-qPCR results showed that SB431542 (an inhibitor of Smad2/3) could significantly attenuate the expression of vimentin induced by DBP in SCs. Phosphorylated and soluble vimentin were both downregulated by SB431542 pretreatment. WY14643 (an agonist of PPARα) pretreatment stimulated, while GW6471 (an antagonist of PPARα) inhibited, the activity of Smad2/3; SB431542 pretreatment also inhibited the activity of PPARα, but it did not rescue the DBP-induced collapse in vimentin. Our results suggest that, in addition to promoting the phosphorylation of vimentin, DBP also stimulates the expression of vimentin by activating Smad2/3 in SCs and thereby induces irregular vimentin distribution.

Mammalian target of rapamycin controls glucose consumption and redox balance in human Sertoli cells

OBJECTIVE

To study the role of mammalian target of rapamycin (mTOR) in the regulation of human Sertoli cell (hSC) metabolism, mitochondrial activity, and oxidative stress.

DESIGN

Experimental study.

SETTING

University research center and private assisted reproductive technology centers.

PATIENT(S)

Six men with anejaculation (psychological, vascular, neurologic) and conserved spermatogenesis.

INTERVENTION(S)

Testicular biopsies were used from patients under treatment for recovery of male gametes. Primary hSCs cultures were established from each biopsy and divided into a control group and one treated with rapamycin, the inhibitor of mTOR, for 24 hours.

MAIN OUTCOME MEASURE(S)

Cytotoxicity of hSCs to rapamycin was evaluated by sulforhodamine B assay. The glycolytic profile of hSCs was assessed by proton nuclear magnetic resonance and by studying protein expression of key glycolysis-related transporters and enzymes. Expression of mitochondrial complexes and citrate synthase activity were determined. Protein carbonylation, nitration, lipid peroxidation, and sulfhydryl protein group contents were quantified. The mTOR signaling pathway was studied.

RESULT(S)

Rapamycin increased glucose consumption by hSCs, maintaining lactate production. Alanine production by rapamycin-exposed hSCs was affected, resulting in an unbalanced intracellular redox state. Rapamycin-exposed hSCs had decreased expression of mitochondrial complex III and increased lipid peroxidation, whereas other oxidative stress markers were unaltered. Treatment of hSCs with rapamycin down-regulated phospho-mTOR (Ser-2448) levels, illustrating an effective partial inhibition of mTORC1. Protein levels of downstream signaling molecule p-4E-BP1 were not altered, suggesting that during treatment it became rephosphorylated.

CONCLUSION(S)

We show that mTOR regulates the nutritional support of spermatogenesis by hSCs and redox balance in these cells.

Gonadotropin-Activated Androgen-Dependent and Independent Pathways Regulate Aquaporin Expression during Teleost (Sparus aurata) Spermatogenesis

The mediation of fluid homeostasis by multiple classes of aquaporins has been suggested to be essential during spermatogenesis and spermiation. In the marine teleost gilthead seabream (Sparus aurata), seven distinct aquaporins, Aqp0a, -1aa, -1ab, -7, -8b, -9b and -10b, are differentially expressed in the somatic and germ cell lineages of the spermiating testis, but the endocrine regulation of these channels during germ cell development is unknown. In this study, we investigated the in vivo developmental expression of aquaporins in the seabream testis together with plasma androgen concentrations. We then examined the in vitro regulatory effects of recombinant piscine gonadotropins, follicle-stimulating (rFsh) and luteinizing (rLh) hormones, and sex steroids on aquaporin mRNA levels during the spermatogenic cycle. During the resting phase, when plasma levels of androgens were low, the testis exclusively contained proliferating spermatogonia expressing Aqp1ab, whereas Aqp10b and -9b were localized in Sertoli and Leydig cells, respectively. At the onset of spermatogenesis and during spermiation, the increase of androgen plasma levels correlated with the additional appearance of Aqp0a and -7 in Sertoli cells, Aqp0a in spermatogonia and spermatocytes, Aqp1ab, -7 and -10b from spermatogonia to spermatozoa, and Aqp1aa and -8b in spermatids and spermatozoa. Short-term in vitro incubation of testis explants indicated that most aquaporins in Sertoli cells and early germ cells were upregulated by rFsh and/or rLh through androgen-dependent pathways, although Aqp1ab in proliferating spermatogonia was also activated by estrogens. However, expression of Aqp9b in Leydig cells, and of Aqp1aa and -7 in spermatocytes and spermatids, was also directly stimulated by rLh. These results reveal a complex gonadotropic control of aquaporin expression during seabream germ cell development, apparently involving both androgen-dependent and independent pathways, which may assure the fine tuning of aquaporin-mediated fluid secretion and absorption mechanisms in the seabream testis.

Hallmarks of therapeutic management of the cystic fibrosis functional landscape

The cystic fibrosis (CF) transmembrane conductance regulator (CFTR) protein does not operate in isolation, rather in a dynamic network of interacting components that impact its synthesis, folding, stability, intracellular location and function, referred to herein as the 'CFTR Functional Landscape (CFFL)'. For the prominent F508del mutation, many of these interactors are deeply connected to a protein fold management system, the proteostasis network (PN). However, CF encompasses an additional 2000 CFTR variants distributed along its entire coding sequence (referred to as CFTR2), and each variant contributes a differential liability to PN management of CFTR and to a protein 'social network' (SN) that directs the probability of the (patho)physiologic events that impact ion transport in each cell, tissue and patient in health and disease. Recognition of the importance of the PN and SN in driving the unique patient CFFL leading to disease highlights the importance of precision medicine in therapeutic management of disease progression. We take the view herein that it is not CFTR, rather the PN/SN, and their impact on the CFFL, that are the key physiologic forces driving onset and clinical progression of CF. We posit that a deep understanding of each patients PN/SN gained by merging genomic, proteomic (mass spectrometry (MS)), and high-content microscopy (HCM) technologies in the context of novel network learning algorithms will lead to a paradigm shift in CF clinical management. This should allow for generation of new classes of patient specific PN/SN directed therapeutics for personalized management of the CFFL in the clinic.

The IP3 R Binding Protein Released With Inositol 1,4,5-Trisphosphate Is Expressed in Rodent Reproductive Tissue and Spermatozoa

Besides its capacity to inhibit the 1,4,5-trisphosphate (IP3) receptor, the regulatory protein IRBIT (IP3 receptor binding protein released with IP3) is also able to control the activity of numerous ion channels and electrolyte transporters and thereby creates an optimal electrolyte composition of various biological fluids. Since a reliable execution of spermatogenesis and sperm maturation critically depends on the establishment of an adequate microenvironment, the expression of IRBIT in male reproductive tissue was examined using immunohistochemical approaches combined with biochemical fractionation methods. The present study documents that IRBIT is expressed in Leydig and Sertoli cells. In addition, pronounced IRBIT expression was detected in sperm precursors during early stages of spermatogenesis as well as in spermatozoa. Analyzing tissue sections of rodent epididymides, IRBIT was found to co-localize with the proton pumping V-ATPase and the cystic fibrosis transmembrane conductance regulator (CFTR) at the apical surface of narrow and clear cells. A similar co-localization of IRBIT with CFTR was also observed for Sertoli cells and developing germ cells. Remarkably, assaying caudal sperm in immunogold electron microscopy, IRBIT was found to localize to the acrosomal cap and the flagellum as well as to the sperm nucleus; moreover, a prominent oligomerization was observed for spermatozoa. The pronounced occurrence of IRBIT in the male reproductive system and mature spermatozoa indicates a potential role for IRBIT in establishing the essential luminal environment for a faithful execution of spermatogenesis and epididymal sperm maturation, and suggest a participation of IRBIT during maturation steps after ejaculation and/or the final fertilization process.

Aquaporin biology of spermatogenesis and sperm physiology in mammals and teleosts

Fluid homeostasis is recognized as a critical factor during the development, maturation, and function of vertebrate male germ cells. These processes have been associated with the presence of multiple members of the aquaporin superfamily of water and solute channels in different cell types along the reproductive tract as well as in spermatozoa. We present a comparative analysis of the existing knowledge of aquaporin biology in the male reproductive tissues of mammals and teleosts. Current data suggest that in both vertebrate groups, aquaporins may have similar functions during differentiation of spermatozoa in the germinal epithelium, in the concentration and maturation of sperm in the testicular ducts, and in the regulation of osmotically induced volume changes in ejaculated spermatozoa. Recent studies have also provided insight into the possible function of aquaporins beyond water transport, such as in signaling pathways during spermatogenesis or the sensing of cell swelling and mitochondrial peroxide transport in activated sperm. However, an understanding of the specific physiological functions of the various aquaporins during germ cell development and sperm motility, as well as the molecular mechanisms involved, remains elusive. Novel experimental approaches need to be developed to elucidate these processes and to dissect the regulatory intracellular pathways implicated, which will greatly help to uncover the molecular basis of sperm physiology and male fertility in vertebrates.

Androgen receptor roles in spermatogenesis and infertility

Androgens such as testosterone are steroid hormones essential for normal male reproductive development and function. Mutations of androgen receptors (AR) are often found in patients with disorders of male reproductive development, and milder mutations may be responsible for some cases of male infertility. Androgens exert their action through AR and its signalling in the testis is essential for spermatogenesis. AR is not expressed in the developing germ cell lineage so is thought to exert its effects through testicular Sertoli and peri-tubular myoid (PTM) cells. AR signalling in spermatogenesis has been investigated in rodent models where testosterone levels are chemically supressed or models with transgenic disruption of AR. These models have pinpointed the steps of spermatogenesis that require AR signalling, specifically maintenance of spermatogonial numbers, blood-testis barrier integrity, completion of meiosis, adhesion of spermatids and spermiation, together these studies detail the essential nature of androgens in the promotion of male fertility.