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

Putative adverse outcome pathways of the male reproductive toxicity derived from toxicological studies of perfluoroalkyl acids

Adverse outcome pathway (AOP) as a conceptual framework is a powerful tool in the field of toxicology to connect seemingly discrete events at different levels of biological organizations into an organized pathway from molecular interactions to whole organism toxicity. Based on numerous toxicological studies, eight AOPs for reproductive toxicity have been endorsed by the Organization for Economic Co-operation and Development (OECD) Task Force on Hazard Assessment. We have conducted a literature survey on the mechanistic studies on male reproductive toxicity of perfluoroalkyl acids (PFAAs), a class of global environmental contaminants with high persistence, bioaccumulation and toxicity. Using the AOP development strategy, five new AOPs for male reproductive toxicity were proposed here, namely (1) changes in membrane permeability leading to reduced sperm motility, (2) disruption of mitochondrial function leading to sperm apoptosis, (3) decreased gonadotropin-releasing hormone (GnRH) expression in hypothalamus leading to reduced testosterone production in male rats, (4) activation of the p38 signaling pathway leading to disruption of BTB in mice, (5) inhibition of p-FAK-Tyr407 activity leading to the destruction of BTB. The molecular initiating events in the proposed AOPs are different from those in the endorsed AOPs, which are either receptor activation or enzyme inhibition. Although some of the AOPs are still incomplete, they can serve as a building block upon which full AOPs can be developed and applied to not only PFAAs but also other chemical toxicants with male reproductive toxicity.

The traditional Chinese medicine Qiangjing tablet prevents blood-testis barrier injury induced by CdCl2 through the PI3K/Akt/Rictor signaling pathway

OBJECTIVE

Environmental contaminants such as cadmium (Cd) may have a deleterious impact on sperm and reduce male fertility by compromising the blood-testis barrier (BTB). Hence, the effects of the traditional Chinese medicine Qiangjing tablet (QJP) on sperm quality and BTB alterations induced by Cd in mouse testes were examined.

METHODS

Adult KM mice challenged with Cd chloride were examined, QJP was administered to mice as an oral drug by gavage, and the experiments lasted 2 weeks. Testicular and epididymal weights, sperm quality, anti-sperm antibodies (AsAb), hormone levels, and histology were evaluated. Changes in the levels of N-cadherin, occludin, ZO-1, claudin-11, F-actin, and β-tubulin and their mRNAs were evaluated. The effects of QJP on the PI3K/Akt/Rictor pathway were evaluated.

RESULTS

CdCl₂ decreased reproductive organ weight, sperm quality, and testosterone (T) levels; increased AsAb, follicle-stimulating hormone (FSH), and luteinizing hormone (LH) levels; induced structural damage in testicles with BTB disruption; increased BTB permeability; and decreased N-cadherin, occludin, ZO-1, claudin-11, F-actin, and β-tubulin expression. After treatment, QJP blocked the effects of Cd on reproductive organ weight, sperm quality, and T; mitigated germinal epithelium compartment alterations; decreased AsAb, FSH, and LH levels; and preserved BTB ultrastructure and function. In addition, QJP induced increases in N-cadherin, occludin, ZO-1, claudin-11, F-actin, and β-tubulin levels and the expression of their mRNAs through the PI3K/Akt/Rictor pathway. After the application of JRAB2011, the levels of a specific mTORC2 suppressor, Rictor, and the BTB-protective effect of QJP were greatly reduced.

CONCLUSIONS

We demonstrated the effect of QJP against Cd-induced damage to the BTB, and the results indicate that QJP may play a significant role in opposing the effects of Cd through the PI3K/Akt/Rictor pathway.

Perfluorooctane Sulfonic Acid Disrupts Protective Tight Junction Proteins via Protein Kinase D in Airway Epithelial Cells

Perfluorooctane sulfonic acid (PFOS) is a long chain per- and polyfluoroalklyl substance (PFAS) that has been used in aqueous film-forming foams. Emerging epidemiological evidence indicates that PFOS may be associated with chronic lung diseases such as asthma and analysis of human tissues demonstrates that the lungs carry a significant body burden of PFOS. Deficits in barrier function are a major risk factor for asthma. Thus, we hypothesized that PFOS exposure will lead to impaired epithelial barrier function through dysregulated tight junctions. Hence, we assessed the impact of PFOS on epithelial barrier integrity. Bronchial epithelial cells (16HBE) were grown on collagen-coated transwells and treated to 5-25 μM PFOS, and assessed for changes in barrier function and tight junction proteins. Rescue experiments were performed using the protein kinase D (PKD) inhibitor, CID755673. PFOS treatment reduced transepithelial electrical resistance (TEER) and increased 4 kDa FITC-dextran flux. Additionally, PFOS significantly decreased protein levels and the tight junction organization rate of occludin and zonula occludens 1. Increased phosphorylation (Ser744/Ser748) of PKD was observed 3 h following PFOS treatment. Pretreatment with the PKD inhibitor attenuated PFOS-mediated changes in TEER and FITC-dextran flux and restored occludin protein levels. In conclusion, PFOS causes loss of airway barrier integrity and the disruption of tight junctions in bronchial epithelial cells, which was partly attenuated through the inhibition of PKD. These findings demonstrate that PFOS is capable of disrupting airway barrier function, a potentially driving factor underlying associations between PFOS and respiratory diseases such as asthma.

The PI3K/AKT signaling pathway: How does it regulate development of Sertoli cells and spermatogenic cells?

The PI3K/AKT signaling pathway is one of the most crucial regulatory mechanisms in animal cells, which can mainly regulate proliferation, survival and anti-apoptosis in cell lines. In the seminiferous epithelium, most studies were concentrated on the role of PI3K/AKT signaling in immature Sertoli cells (SCs) and spermatogonia stem cells (SSCs). PI3K/AKT signaling can facilitate the proliferation and anti-apoptosis of immature Sertoli cells and spermatogenic cells. Besides, in mature Sertoli cells, this pathway can disintegrate the structure of the blood-testis barrier (BTB) via regulatory protein synthesis and the cytoskeleton of Sertoli cells. All of these effects can directly and indirectly maintain and promote spermatogenesis in male testis.

Perfluorooctane sulfonate induces suppression of testosterone biosynthesis via Sertoli cell-derived exosomal/miR-9-3p downregulating StAR expression in Leydig cells

Perfluorooctane sulfonate (PFOS) is associated with male reproductive disorder, but the related mechanisms are still unclear. In this study, we used in vivo and in vitro models to explore the role of Sertoli cell-derived exosomes (SC-Exo)/miR-9-3p/StAR signaling pathway on PFOS-induced suppression of testosterone biosynthesis. Forty male ICR mice were orally administrated PFOS (0.5-10 mg/kg/bw) for 4 weeks. Bodyweight, organ index, sperm count, reproductive hormones were evaluated. Primary Sertoli cells and Leydig cells were used to delineate the molecular mechanisms that mediate the effects of PFOS on testosterone biosynthesis. Our results demonstrated that PFOS dose-dependently induced a decrease in sperm count, low levels of testosterone, and damage in testicular interstitium morphology. In vitro models, PFOS significantly increased miR-9-3p levels in Sertoli cells and SC-Exo, accompanied by a decrease in testosterone secretion and StAR expression in Leydig cells when Leydig cells were exposed to SC-Exo. Meanwhile, inhibition of SC-Exo or miR-9-3p by their inhibitors significantly rescued PFOS-induced decreases in testosterone secretion and the mRNA and protein expression of the StAR gene in Leydig cells. In summary, the present study highlights the role of the SC-Exo/miR-9-3p/StAR signaling pathway in PFOS-induced suppression of testosterone biosynthesis, advancing our understanding of molecular mechanisms for PFOS-induced male reproductive disorders.

Icariin attenuates perfluorooctane sulfonate-induced testicular toxicity by alleviating Sertoli cell injury and downregulating the p38MAPK/MMP9 pathway

Perfluorooctane sulfonate (PFOS) is widely recognized as causing Sertoli cell injury and testicular toxicity in males. Icariin is a flavonoid from Epimedium, which effectively improves spermatogenesis disturbance induced by several factors in clinic. However, it is unclear whether icariin improves PFOS-induced testicular toxicity. In vivo, fifty-two male mice were randomly separated into four groups: normal control group, model group, and low and high doses of icariin-treated groups, with 13 mice in each group. Except for the normal control group, the mice in the model group and icariin-treated groups were administered PFOS (10 mg kg-1) by gavage daily for 28 consecutive days, and concurrently treated with a diet containing different doses of icariin (0, 5 or 20 mg kg-1). In vitro, TM4 cells were treated with 150 μM PFOS to induce Sertoli cell injury, and were then utilized for icariin treatment. Our results demonstrated that icariin attenuated PFOS-induced testicular toxicity by increasing the testicular, epididymal and seminal vesicle weights, epididymal and seminal vesicle indices, sperm parameters, and seminiferous epithelium height. In addition, icariin improved the PFOS-induced blood-testis barrier (BTB) disruption by alleviating the Sertoli cell junctional injury, but without affecting Sertoli cell numbers in the testis of mice. Moreover, icariin increased the expression levels of tight junction proteins (ZO-1, Occludin and Claudin-11) and gap junction proteins (CX43 and p-CX43), and decreased the expression levels of p-p38MAPK and matrix metalloproteinase 9 (MMP9) both in vivo and in vitro. Furthermore, alleviation of the Sertoli cell injury by icariin exerted similar effects as SB203580 (an inhibitor of p38MAPK) in TM4 cells. This study revealed that icariin effectively reduces PFOS-induced testicular toxicity by alleviating the Sertoli cell injury and downregulating the p38MAPK/MMP9 pathway, indicating that icariin may be an attractive dietary supplement for the intervention of PFOS-induced testicular dysfunction.

Pachypodol attenuates Perfluorooctane sulphonate-induced testicular damage by reducing oxidative stress

Perfluorooctane sulfonate (PFOS) is an endocrine disruptor chemical (EDC) with potentially adverse effects on the male reproductive system. Pachypodol (5,4'-dihydroxy-3,7,3'-trimethoxyflavone) is a promising flavonoid isolated from Pogostemon cablin (Blanco) Benth that shows a broad range of pharmacological properties. However, the potential curative effects of pachypodol on testicular toxicity are not available until now. Therefore, this research was proposed to examine the efficiency of pachypodol against PFOS-induced testicular toxicity in adult male rats. The experiments were conducted on Sprague-Dawley rats (n = 48), which were equally distributed into four groups: control, PFOS (20 mg/kg), PFOS + Pachypodol (20 mg/kg + 10 mg/kg respectively), and Pachypodol (10 mg/kg). After 56 days of treatment, testes were excised by slaughtering rats, weighed, and stored till further analysis. The estimated parameters include biochemical markers, spermatogenic indices, hormonal and histopathological profiles. PFOS exposure disturbed the biochemical profile by altering the antioxidant/oxidant balance. For instance, it decreased the activities of catalase (CAT), superoxide dismutase (SOD), glutathione peroxidase (GPx), and glutathione reductase (GSR) while increasing the concentration of reactive oxygen species (ROS) and level of thiobarbituric acid reactive substances (TBARS). PFOS intoxication also led to a notable decline in viability, motility, epididymal sperm count, and the number of HOS coiled-tail sperms, whereas the higher level of abnormality in the head, mid-piece, and tail of sperms were observed. Besides, it lowered luteinizing hormone (LH), follicle-stimulating hormone (FSH), and plasma testosterone. In addition, PFOS exposure led to histopathological damages in testicles. However, pachypodol treatment potently alleviated all the illustrated impairments in testes. Conclusively, our results demonstrate the promising free-radical scavenging activity of pachypodol, a novel phytochemical, against the PFOS-instigated testicular dysfunctions.

Cell-Cell Interaction-Mediated Signaling in the Testis Induces Reproductive Dysfunction—Lesson from the Toxicant/Pharmaceutical Models

Emerging evidence has shown that cell-cell interactions between testicular cells, in particular at the Sertoli cell-cell and Sertoli-germ cell interface, are crucial to support spermatogenesis. The unique ultrastructures that support cell-cell interactions in the testis are the basal ES (ectoplasmic specialization) and the apical ES. The basal ES is found between adjacent Sertoli cells near the basement membrane that also constitute the blood-testis barrier (BTB). The apical ES is restrictively expressed at the Sertoli-spermatid contact site in the apical (adluminal) compartment of the seminiferous epithelium. These ultrastructures are present in both rodent and human testes, but the majority of studies found in the literature were done in rodent testes. As such, our discussion herein, unless otherwise specified, is focused on studies in testes of adult rats. Studies have shown that the testicular cell-cell interactions crucial to support spermatogenesis are mediated through distinctive signaling proteins and pathways, most notably involving FAK, Akt1/2 and Cdc42 GTPase. Thus, manipulation of some of these signaling proteins, such as FAK, through the use of phosphomimetic mutants for overexpression in Sertoli cell epithelium in vitro or in the testis in vivo, making FAK either constitutively active or inactive, we can modify the outcome of spermatogenesis. For instance, using the toxicant-induced Sertoli cell or testis injury in rats as study models, we can either block or rescue toxicant-induced infertility through overexpression of p-FAK-Y397 or p-FAK-Y407 (and their mutants), including the use of specific activator(s) of the involved signaling proteins against pAkt1/2. These findings thus illustrate that a potential therapeutic approach can be developed to manage toxicant-induced male reproductive dysfunction. In this review, we critically evaluate these recent findings, highlighting the direction for future investigations by bringing the laboratory-based research through a translation path to clinical investigations.

Titanium dioxide nanoparticles perturb the blood-testis barrier via disruption of actin-based cell adhesive function

As one of the most commonly used nanoparticles, titanium dioxide nanoparticles (TiO₂-NPs) are widely used as coating reagents in cosmetics, medicine and other industries. The increasing risk of exposure to TiO₂-NPs raises concerns about their safety. In this study, we investigated the mechanism by which TiO₂-NPs cross the blood-testis barrier (BTB). TM-4 cells were selected as an in vitro Sertoli cell model of BTB. Cell viability, cell morphological changes, apoptosis, oxidative damage, and the expression levels of actin regulatory and tight junction (TJ) proteins were assessed in TM-4 cells treated with 3-nm and 24-nm TiO₂-NPs. Cells treated with 3-nm TiO₂-NPs exhibited increased cytotoxicity and decreased Annexin II expression, whereas cells treated with 24-nm TiO₂-NPs exhibited increased Arp 3 and c-Src expression. Both TiO₂-NPs induced significant oxidative stress, decreased the expression of TJ proteins (occludin, ZO-1 and claudin 5), damaged the TJ structure, and exhibited enlarged gaps between TM-4 cells. Our results indicated that both TiO₂-NPs crossed the BTB by disrupting actin-based adhesive junctions of TM-4 cells; however, apoptosis was not observed. Our results provide new insights into how TiO₂-NPs cross the BTB.

Perfluorooctane sulfonate affects mouse oocyte maturation in vitro by promoting oxidative stress and apoptosis induced bymitochondrial dysfunction

Perfluorooctane sulphonate (PFOS), as a surfactant, is widely applied in the agricultural production activities and has become a potential menace to human health. The mechanism of its effect on the maturation of mammalian oocytes is unclear. This study explored the toxic effect of PFOS on mouse oocyte maturation in vitro. The results revealed that PFOS under a concentration of 600 μM could significantly reduce the polar body extrusion rate (PBE) of mouse oocytes and cause symmetrical cell division. Further experiments showed that PFOS resulted in the abnormal cytoskeleton of the oocytes, causing the abnormal spindles and misplaced chromosomes, as well as the impaired dynamics of actin. Moreover, PFOS exposure inhibited the process of oocyte meiosis, which reflected in the slower spindle migration and continuous activation of spindle assembly checkpoint (SAC), then ultimately increased the probability of aneuploidy. Most importantly, PFOS exposure reduced the quality of oocytes, specifically by disrupting the function of mitochondria, inducing cell oxidative stress, and triggering early apoptosis. Furthermore, the level of methylation of histones is additionally influenced. In summary, our findings showed that PFOS exposure interfered with the maturation of mouse oocytes through affecting cytoskeletal dynamics, meiotic progression, oocyte quality, and histone modifications.

Busulfan impairs blood-testis barrier and spermatogenesis by increasing noncollagenous 1 domain peptide via matrix metalloproteinase 9

BACKGROUNDS

Sterility induced by anti-cancer treatments has caused significant concern, yet the mechanism and treatment exploration are little for male infertility after cancer therapy. Busulfan, the antineoplastic that was widely applied before bone marrow transplantation, was known to induce male reproductive disorder.

OBJECTIVES

To investigate the effect of busulfan on blood-testis barrier function in adult rats and determine whether noncollagenous 1 domain peptide, the biologically active fragment proteolyzed from the collagen α3 chain (IV) by matrix metalloproteinase 9, was involved during this process.

MATERIALS AND METHODS

Adult male rats were treated with one-dose or double-dose of busulfan (10 mg/kg) before euthanized at day 35. Blood-testis barrier integrity assay, HE staining, immunofluorescence, and Western blot were used to validate the effect of busulfan on blood-testis barrier permeability and spermatogenesis. JNJ0966 was applied to specifically inhibit the matrix metalloproteinase 9 activity. The polymerization activity of F-actin/G-actin and microtubule/tubulin in the testis were assessed by using commercial kits.

RESULTS

A noteworthy blood-testis barrier injury and significant up-regulation of matrix metalloproteinase 9 activity and noncollagenous 1 level after a single-dose busulfan (10 mg/kg) treatment in adult rat testis were revealed. The application of JNJ0966 was found to decrease noncollagenous 1 level and rescue the busulfan-induced blood-testis barrier injury including the mis-localization of junction proteins across the seminiferous epithelium, by recovering the organization and polymerization of both F-actin and microtubule. The busulfan-induced spermatogenesis impairment was also improved by JNJ0966.

CONCLUSION

These findings thus demonstrate that the elevation in matrix metalloproteinase 9 and noncollagenous 1 might participate in busulfan-induced blood-testis barrier disruption in adult male rats. As such, busulfan-induced male infertility could possibly be managed through interventions on noncollagenous 1 production.

Folpet induces mitochondrial dysfunction and ROS-mediated apoptosis in mouse Sertoli cells

Folpet is a phthalimide type of fungicide and has been used to control several crop diseases. Although it has adverse effects on the gastrointestinal tract, its mechanism and toxic effects on testis have not been demonstrated. In the present study, we elucidated the cytotoxic effect of folpet on the mouse Sertoli cell line, TM4. Our results revealed that folpet suppressed viability and proliferative capacity of TM4 cells and further inhibited 3D spheroid formation. Moreover, folpet impeded appropriate cell cycle progression and induced apoptotic cell death in TM4 cells. It disrupted the electrochemical gradient of mitochondria and calcium homeostasis in TM4 cells. Furthermore, endoplasmic reticulum stress-related proteins were activated in folpet-treated TM4 cells, and relative reactive oxygen species (ROS) production was also increased. N-acetylcysteine (NAC) treatment reinstated the folpet-induced ROS generation in TM4 cells. Additionally, NAC restored the proliferative capacity and reduced the apoptotic cells in folpet-treated TM4 cells. Collectively, we demonstrated that folpet causes ROS-mediated apoptotic cell death with mitochondrial dysfunction and calcium dysregulation in TM4 cells.

Effects of endocrine disruptors on fetal testis development, male puberty, and transition age

PURPOSE

Endocrine disruptors (EDs) are exogenous substances able to impair endocrine system; consequently, they may cause numerous adverse effects. Over the last years, particular focus has been given to their harmful effects on reproductive system, but very little is known, especially in males. The aim of this review is to discuss the detrimental effects of EDs exposure on fetal testis development, male puberty, and transition age.

METHODS

A search for the existing literature focusing on the impact of EDs on fetal testis development, male puberty, andrological parameters (anogenital distance, penile length, and testicular volume), and testicular cancer with particular regard to pubertal age provided the most current information available for this review. Human evidence-based reports were given priority over animal and in vitro experimental results. Given the paucity of available articles on this subject, all resources were given careful consideration.

RESULTS

Information about the consequences associated with EDs exposure in the current literature is limited and often conflicting, due to the scarcity of human studies and their heterogeneity.

CONCLUSIONS

We conclude that current evidence does not clarify the impact of EDs on human male reproductive health, although severe harmful effects had been reported in animals. Despite controversial results, overall conclusion points toward a positive association between exposure to EDs and reproductive system damage. Further long-term studies performed on wide number of subjects are necessary in order to identify damaging compounds and remove them from the environment.

Perfluoroalkyl Chemicals and Male Reproductive Health: Do PFOA and PFOS Increase Risk for Male Infertility?

Poly- and perfluoroalkyl substances (PFAS) are manmade synthetic chemicals which have been in existence for over 70 years. Though they are currently being phased out, their persistence in the environment is widespread. There is increasing evidence linking PFAS exposure to health effects, an issue of concern since PFAS such as perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) bioaccumulate in humans, with a half-life of years. Many epidemiological studies suggest that, worldwide, semen quality has decreased over the past several decades. One of the most worrying effects of PFOS and PFOA is their associations with lower testosterone levels, similar to clinical observations in infertile men. This review thus focuses on PFOS/PFOA-associated effects on male reproductive health. The sources of PFAS in drinking water are listed. The current epidemiological studies linking increased exposure to PFAS with lowered testosterone and semen quality, and evidence from rodent studies supporting their function as endocrine disruptors on the reproductive system, exhibiting non-monotonic dose responses, are noted. Finally, their mechanisms of action and possible toxic effects on the Leydig, Sertoli, and germ cells are discussed. Future research efforts must consider utilizing better human model systems for exposure, using more accurate PFAS exposure susceptibility windows, and improvements in statistical modeling of data to account for the endocrine disruptor properties of PFAS.

Bisphenol S perturbs Sertoli cell junctions in male rats via alterations in cytoskeletal organization mediated by an imbalance between mTORC1 and mTORC2

Bisphenol S (BPS) is now used as an alternative of bisphenol A (BPA), but has been implicated in male reproductive dysfunction-including diminished sperm number and quality and altered hormonal concentrations. However, the mechanisms of action subserving these effects remains unclear. In the present study, BPS at doses of 50 mg/kg bw and 100 mg/kg bw caused defects in the integrity of the blood-testis barrier (BTB) and apical ectoplasmic specialization (ES), and we also delineated an underlying molecular mechanism of action. BPS induced F-actin and α-tubulin disorganization in seminiferous tubules, which in turn led to the truncation of actin filaments and microtubules. Additionally, BPS was found to perturb the expression of the actin-binding proteins Arp3 and Eps8, which are critical for the organization of the actin filaments. mTORC1 and mTORC2 manifest opposing roles in Sertoli cell junctional function, and we demonstrated that mTORC1/rpS6/Akt/MMP9 signaling was increased and that mTORC2/rictor activity was also attenuated. In summary, we showed that BPS-induced disruption of the BTB and apical ES perturbed normal spermatogenic function that was mediated by mTORC1 and mTORC2. The imbalance in mTORC1 and mTORC2, in turn, altered the expression of actin-binding proteins, resulting in the impairment of F-actin and MT organization, and inhibited the expression of junctional proteins at the BTB and apical ES.

The Non-hormonal Male Contraceptive Adjudin Exerts its Effects via MAPs and Signaling Proteins mTORC1/rpS6 and FAK-Y407

Adjudin, 1-(2,4-dichlorobenzyl)-1H-indazole-3-carbohydrazide (formerly called AF-2364), is a nonhormonal male contraceptive, since it effectively induces reversible male infertility without perturbing the serum concentrations of follicle stimulating hormone (FSH), testosterone, and inhibin B based on studies in rats and rabbits. Adjudin was shown to exert its effects preferentially by perturbing the testis-specific actin-rich adherens junction (AJ) at the Sertoli-spermatid interface known as apical ectoplasmic specialization (apical ES), thereby effectively inducing spermatid exfoliation. Adjudin did not perturb germ cell development nor germ cell function. Also, it had no effects on Sertoli cell-cell AJ called basal ectoplasmic specialization (basal ES), which, together with tight junction constitute the blood-testis barrier (BTB), unless an acute dose of adjudin was used. Adjudin also did not perturb the population of spermatogonial stem cells nor Sertoli cells in the testis. However, the downstream signaling protein(s) utilized by adjudin to induce transient male infertility remains unexplored. Herein, using adult rats treated with adjudin and monitored changes in the phenotypes across the seminiferous epithelium between 6 and 96 h in parallel with the steady-state protein levels of an array of signaling and cytoskeletal regulatory proteins, recently shown to be involved in apical ES, basal ES and BTB function. It was shown that adjudin exerts its contraceptive effects through changes in microtubule associated proteins (MAPs) and signaling proteins mTORC1/rpS6 and p-FAK-Y407. These findings are important to not only study adjudin-mediated male infertility but also the biology of spermatogenesis.

Assessment of the Emerging Threat Posed by Perfluoroalkyl and Polyfluoroalkyl Substances to Male Reproduction in Humans

Per-fluoroalkyl and polyfluoroalkyl substances (PFAS) are a diverse group of synthetic fluorinated chemicals used widely in industry and consumer products. Due to their extensive use and chemical stability, PFAS are ubiquitous environmental contaminants and as such, form an emerging risk factor for male reproductive health. The long half-lives of PFAS is of particular concern as the propensity to accumulate in biological systems prolong the time taken for excretion, taking years in many cases. Accordingly, there is mounting evidence supporting a negative association between PFAS exposure and an array of human health conditions. However, inconsistencies among epidemiological and experimental findings have hindered the ability to definitively link negative reproductive outcomes to specific PFAS exposure. This situation highlights the requirement for further investigation and the identification of reliable biological models that can inform health risks, allowing sensitive assessment of the spectrum of effects of PFAS exposure on humans. Here, we review the literature on the biological effects of PFAS exposure, with a specific focus on male reproduction, owing to its utility as a sentinel marker of general health. Indeed, male infertility has increasingly been shown to serve as an early indicator of a range of co-morbidities such as coronary, inflammatory, and metabolic diseases. It follows that adverse associations have been established between PFAS exposure and the incidence of testicular dysfunction, including pathologies such as testicular cancer and a reduction in semen quality. We also give consideration to the mechanisms that render the male reproductive tract vulnerable to PFAS mediated damage, and discuss novel remediation strategies to mitigate the negative impact of PFAS contamination and/or to ameliorate the PFAS load of exposed individuals.

Testis Toxicants: Lesson from Traditional Chinese Medicine (TCM)

The testis is one of the organs in the mammalian body that is sensitive to toxicants. Accumulating evidence has shown that human exposure to toxic ingredients in Traditional Chinese Medicine (TCM), such as triptolide, gossypol, cannabidol, piperine, α-solanine, matrine, aristolochic acid, and emodin, lead to testis injury and reproductive dysfunction. The most obvious phenotype is reduced sperm counts due to defects in spermatogenesis. Studies have also shown that Sertoli cells in the seminiferous tubule, the functional unit of the testis that supports spermatogenesis, are the cell type that is most sensitive to the disruptive effects of toxicants. Since Sertoli cells are the "mother cells" that nurture germ cell development, Sertoli cell injury thus leads to failure in germ cell development in the seminiferous epithelium. Mounting evidence has shown that the Sertoli cell cytoskeletons, mitochondria function, Leydig cells steroidogenesis pathways and sperm ion channels are some of the prime targets of toxicants from TCM. We carefully evaluate recent findings in this area of research herein, and to provide a summary of these findings, including some insightful information regarding the underlying molecular basis of toxicant-induced testis injury that impede spermatogenesis.

Signaling Proteins That Regulate Spermatogenesis Are the Emerging Target of Toxicant-Induced Male Reproductive Dysfunction

There is emerging evidence that environmental toxicants, in particular endocrine disrupting chemicals (EDCs) such as cadmium and perfluorooctanesulfonate (PFOS), induce Sertoli cell and testis injury, thereby perturbing spermatogenesis in humans, rodents and also widelife. Recent studies have shown that cadmium (e.g., cadmium chloride, CdCl₂) and PFOS exert their disruptive effects through putative signaling proteins and signaling cascade similar to other pharmaceuticals, such as the non-hormonal male contraceptive drug adjudin. More important, these signaling proteins were also shown to be involved in modulating testis function based on studies in rodents. Collectively, these findings suggest that toxicants are using similar mechanisms that used to support spermatogenesis under physiological conditions to perturb Sertoli and testis function. These observations are physiologically significant, since a manipulation on the expression of these signaling proteins can possibly be used to manage the toxicant-induced male reproductive dysfunction. In this review, we highlight some of these findings and critically evaluate the possibility of using this approach to manage toxicant-induced defects in spermatrogenesis based on recent studies in animal models.

Microtubule-associated proteins (MAPs) in microtubule cytoskeletal dynamics and spermatogenesis

The microtubule (MT) cytoskeleton in Sertoli cells, a crucial cellular structure in the seminiferous epithelium of adult mammalian testes that supports spermatogenesis, was studied morphologically decades ago. However, its biology, in particular the involving regulatory biomolecules and the underlying mechanism(s) in modulating MT dynamics, are only beginning to be revealed in recent years. This lack of studies in delineating the biology of MT cytoskeletal dynamics undermines other studies in the field, in particular the plausible therapeutic treatment and management of male infertility and fertility since studies have shown that the MT cytoskeleton is one of the prime targets of toxicants. Interestingly, much of the information regarding the function of actin-, MT- and intermediate filament-based cytoskeletons come from studies using toxicant models including some genetic models. During the past several years, there have been some advances in studying the biology of MT cytoskeleton in the testis, and many of these studies were based on the use of pharmaceutical/toxicant models. In this review, we summarize the results of these findings, illustrating the importance of toxicant/pharmaceutical models in unravelling the biology of MT dynamics, in particular the role of microtubule-associated proteins (MAPs), a family of regulatory proteins that modulate MT dynamics but also actin- and intermediate filament-based cytoskeletons. We also provide a timely hypothetical model which can serve as a guide to design functional experiments to study how the MT cytoskeleton is regulated during spermatogenesis through the use of toxicants and/or pharmaceutical agents.

Perfluorooctane Sulfonate (PFOS) and Perfluorohexane Sulfonate (PFHxS) Alters Protein Phosphorylation, Increase ROS Levels and DNA Fragmentation during In Vitro Capacitation of Boar Spermatozoa

Simple Summary

Perfluorinated compounds are synthetic chemicals, with a wide variety of applications like firefighting foams, food packaging, additives in paper and fabrics to avoid dyes. Perfluorooctane sulfonate and perfluorohexane sulfonate are globally distributed, and contaminates air, water, food, and dust, have toxic effects and bioaccumulate. Significant levels of these compounds have found in blood serum, breast milk, and semen of occupationally exposed and unexposed people, as well as in blood serum and organs of the domestic, farm, and wild animals. The present study seeks to analyze the toxic effects and possible alterations caused by the presence of these compounds in boar sperm during the in vitro capacitation, due to their toxicity, worldwide distribution, and lack of information in spermatozoa physiology during pre-fertilization processes.

Abstract

Perfluorooctane sulfonate (PFOS) and perfluorohexane sulfonate (PFHxS) are toxic and bioaccumulative, included in the Stockholm Convention’s list as persistent organic pollutants. Due to their toxicity, worldwide distribution, and lack of information in spermatozoa physiology during pre-fertilization processes, the present study seeks to analyze the toxic effects and possible alterations caused by the presence of these compounds in boar sperm during the in vitro capacitation. The spermatozoa capacitation was performed in supplemented TALP-Hepes media and mean lethal concentration values of 460.55 μM for PFOS, and 1930.60 μM for PFHxS were obtained. Results by chlortetracycline staining showed that intracellular Ca²⁺ patterns bound to membrane proteins were scarcely affected by PFOS. The spontaneous acrosome reaction determined by FITC-PNA was significantly reduced by PFOS and slightly increased by PFHxS. Both toxic compounds significantly alter the normal capacitation process from 30 min of exposure. An increase in ROS production was observed by flow cytometry and considerable DNA fragmentation by the comet assay. The immunocytochemistry showed a decrease of tyrosine phosphorylation in proteins of the equatorial and acrosomal zone of the spermatozoa head. In conclusion, PFOS and PFHxS have toxic effects on the sperm, causing mortality and altering vital parameters for proper sperm capacitation.

NC1-Peptide From Collagen α3 (IV) Chains in the Basement Membrane of Testes Regulates Spermatogenesis via p-FAK-Y407

The blood-testis barrier (BTB) in the testis is an important ultrastructure to support spermatogenesis. This blood-tissue barrier undergoes remodeling at late stage VII to early stage IX of the epithelial cycle to support the transport of preleptotene spermatocytes across the BTB to prepare for meiosis I/II at the apical compartment through a mechanism that remains to be delineated. Studies have shown that NC1-peptide-derived collagen α3 (IV) chain in the basement membrane is a bioactive peptide that induces BTB remodeling. It also promotes the release of fully developed spermatids into the tubule lumen. Thus, this endogenously produced peptide coordinates these 2 cellular events across the seminiferous epithelium. Using an NC1-peptide complementary deoxyribonucleic acid (cDNA) construct to transfect adult rat testes for overexpression, NC1-peptide was found to effectively induce germ cell exfoliation and BTB remodeling, which was associated with a surge and activation of p-rpS6, the downstream signaling protein of mTORC1 and the concomitant downregulation of p-FAK-Y407 in the testis. In order to define the functional relationship between p-rpS6 and p-FAK-Y407 signaling to confer the ability of NC1-peptide to regulate testis function, a phosphomimetic (and thus constitutively active) mutant of p-FAK-Y407 (p-FAK-Y407E-MT) was used for its co-transfection, utilizing Sertoli cells cultured in vitro with a functional tight junction (TJ) barrier that mimicked the BTB in vivo. Overexpression of p-FAK-Y407E-MT blocked the effects of NC1-peptide to perturb Sertoli cell BTB function by promoting F-actin and microtubule cytoskeleton function, and downregulated the NC1-peptide-mediated induction of p-rpS6 activation. In brief, NC1-peptide is an important endogenously produced biomolecule that regulates BTB dynamics.

Microtubule Cytoskeleton and Spermatogenesis-Lesson From Studies of Toxicant Models

Studies have shown that mammalian testes, in particular the Sertoli cells, are highly susceptible to exposure of environmental toxicants, such as cadmium, perfluorooctanesulfonate, phthalates, 2,5-hexanedione and bisphenol A. However, important studies conducted by reproductive toxicologists and/or biologists in the past have been treated as toxicology reports per se. Yet, many of these studies provided important mechanistic insights on the toxicant-induced testis injury and reproductive dysfunction, relevant to the biology of the testis and spermatogenesis. Furthermore, recent studies have shown that findings obtained from toxicant models are exceedingly helpful tools to unravel the biology of testis function in particular spermatogenesis, including specific cellular events associated with spermatid transport to support spermiogenesis and spermiation. In this review, we critically evaluate some recent data, focusing primarily on the molecular structure and role of microtubules in cellular function, illustrating the importance of toxicant models to unravel the biology of microtubule cytoskeleton in supporting spermatogenesis, well beyond information on toxicology. These findings have opened up some potential areas of research which should be carefully evaluated in the years to come.

Cdc42 is involved in NC1 peptide-regulated BTB dynamics through actin and microtubule cytoskeletal reorganization

Noncollagenous domain 1 (NC1)-peptide is a biologically active peptide derived from the C-terminal region of collagen α3(IV) chain, a structural constituent protein at the basement membrane in the rat testis, likely via proteolytic cleavage of matrix metalloproteinase 9. Studies have shown that this NC1 peptide regulates testis function by inducing Sertoli cell blood-testis barrier (BTB) remodeling and is also capable of inducing elongate spermatid exfoliation through its disruptive effects on the organization of actin- and microtubule (MT)-based cytoskeletons at these cell adhesion sites. However, the underlying molecular mechanism remains unknown. NC1 peptide was found to exert its biologic effects through an activation of small GTPase cell division control protein 42 homolog (Cdc42) because cooverexpression of the dominant negative mutant of Cdc42 [namely, Cdc42-T17N (via a single mutation of amino acid residue 17 from the N terminus from Thr to Asn by site-directed mutagenesis, making it constitutively inactive)] and NC1 peptide was able to block the NC1 peptide-induced Sertoli cell tight junction-permeability barrier disruption. Their cooverexpression also blocked the NC1 peptide-induced misdistribution of BTB-associated proteins at the cell-cell interface and also disruptive cytoskeletal organization of F-actin and MTs through changes in spatial expression of the corresponding actin and MT regulatory proteins. Interestingly, NC1 peptide was also found to induce an up-regulation of phosphorylated (p)-ribosomal protein S6 (rpS6) (namely, p-rpS6-S235/S236) and a concomitant down-regulation of p-Akt1/2 (namely, p-Akt1-S473 and p-Akt2-S474), but these changes could not be blocked by overexpression of Cdc42-T17N. More importantly, NC1 peptide-induced Cdc42 activation was effectively blocked by treatment of Sertoli cell epithelium with a p-Akt1/2 activator SC79, which is also capable of blocking NC1 peptide-induced down-regulation of p-Akt1-S473 and p-Akt2/S474, but not p-rpS6-S235/S236 up-regulation. In summary, these findings illustrate that Cdc42 is working downstream of the mammalian target of rapamycin complex 1/rpS6/Akt1/2 signaling pathway to support NC1 peptide-mediated effects on Sertoli cell function in the testis using the rat as an animal model.-Su, W., Cheng, C. Y. Cdc42 is involved in NC1 peptide-regulated BTB dynamics through actin and microtubule cytoskeletal reorganization.

Aucubin, a natural iridoid glucoside, attenuates oxidative stress-induced testis injury by inhibiting JNK and CHOP activation via Nrf2 up-regulation

BACKGROUND

Eucommia ulmoides has been used for many years as a successful strategy to treat male infertility. Aucubin (AU) is the active ingredient extracted from Eucommia ulmoides. However, its protective action and exact mechanism on testicular injury is not yet known.

PURPOSE

Here, the protective effect and the mechanism of action of AU on testis damage under oxidative stress was investigated in vivo and in vitro.

METHODS

As regard the in vivo experiment, male mice were divided into five groups and testicular injury model was established by Triptolide (TP) (120 μg/kg) intraperitoneal injection for two weeks. Animals in the treatment group were pretreated with an intraperitoneal injection of AU at different doses (5, 10 and 20 mg/kg) for 1 h and subsequently treated with TP (120 μg/kg). At the end of the experimental period, the testis was collected for biochemical and histological examination. As regard the in vitro experiment, Sertoli cells (SCs) were used to investigate the protective effect and mechanism of action of AU against disruption of the blood-testis-barrier (BTB) and apoptosis induced by TP via apoptosis detection, western blot, immunofluorescence analysis, and siRNA transient transfection.

RESULTS

TP-treated animals showed testicular atrophy, BTB disruption, increased ROS levels and spermatogenic dysfunction. Pre-administration of AU resulted in a significant protection on keeping a normal testicular weight, sperm morphology, BTB integrity, and a normal level of oxidative stress markers and antioxidants. Furthermore, AU prevented apoptosis through an effective inhibition of PERK/CHOP and JNK dependent apoptosis pathway, as well as protected the integrity of BTB by up-regulating the expression of tight junction proteins (ZO-1, Occludin, Claudin-11) and gap junction protein (Cx43). The mechanistic study revealed that AU significantly triggered Nrf2 translocation, thus increasing nuclear Nrf2 accumulation and then induced antioxidant enzymes expression in the testis and SCs. Furthermore, Nrf2 silencing unsuccessfully reversed the increased CHOP and p-JNK expression induced by TP, abolishing the protective effect of AU.

CONCLUSION

These results indicate that AU might be considered as a potential protective agent against testicular injury.

CAMSAP2 Is a Microtubule Minus-End Targeting Protein That Regulates BTB Dynamics Through Cytoskeletal Organization

During spermatogenesis, microtubule (MT) cytoskeleton in Sertoli cells confers blood-testis barrier (BTB) function, but the regulators and mechanisms that modulate MT dynamics remain unexplored. In this study, we examined the role of calmodulin-regulated spectrin-associated protein (CAMSAP)2 (a member of the CAMSAP/Patronin protein family), and a minus-end targeting protein (-TIP) that binds to the minus-end (i.e., slow-growing end) of polarized MTs involved in determining MT length, in Sertoli cell function. CAMSAP2 was found to localize at discrete sites across the Sertoli cell cytosol, different from end-binding protein 1 (a microtubule plus-end tracking protein that binds to the plus-end of MTs), and colocalized with MTs. CAMSAP2 displayed a stage-specific expression pattern, appearing as tracklike structures across the seminiferous epithelium in adult rat testes that lay perpendicular to the basement membrane. CAMSAP2 knockdown by RNA interference was found to promote Sertoli cell tight junction (TJ) barrier function, illustrating its role in inducing TJ remodeling under physiological conditions. To further examine the regulatory role of CAMSAP2 in BTB dynamics, we used a perfluorooctanesulfonate (PFOS)-induced Sertoli cell injury model for investigations. CAMSAP2 knockdown blocked PFOS-induced Sertoli cell injury by promoting proper distribution of BTB-associated proteins at the cell-cell interface. This effect was mediated by the ability of CAMSAP2 knockdown to block PFOS-induced disruptive organization of MTs, but also F-actin, across cell cytosol through changes in cellular distribution/localization of MT- and actin-regulatory proteins. In summary, CAMSAP2 is a regulator of MT and actin dynamics in Sertoli cells to support BTB dynamics and spermatogenesis.

Mechanistic Insights into PFOS-Mediated Sertoli Cell Injury

Studies have proven that per- and polyfluoroalkyl substances are harmful to humans, most notably perfluorooctanesulfonate (PFOS). PFOS induces rapid disorganization of actin- and microtubule (MT)-based cytoskeletons in primary cultures of rodent and human Sertoli cells, perturbing Sertoli cell gap junction communication, thereby prohibiting Sertoli cells from maintaining cellular homeostasis in the seminiferous epithelium to support spermatogenesis. PFOS perturbs several signaling proteins/pathways, such as FAK and mTORC1/rpS6/Akt1/2. The use of either an activator of Akt1/2 or overexpression of a phosphomimetic (and constitutively active) mutant of FAK or connexin 43 has demonstrated that such treatment blocks PFOS-induced Sertoli cell injury by preventing actin- and MT-based cytoskeletal disorganization. These findings thus illustrate an approach to manage PFOS-induced reproductive dysfunction.

Fluorochloridone perturbs blood-testis barrier/Sertoli cell barrier function through Arp3-mediated F-actin disruption

There are reports of fluorochloridone (FLC)-induced male reproductive toxicity, but the underlying toxicological mechanisms remain unknown. In this study, we looked at how FLC exposure affected the integrity of the blood-testis barrier (BTB) and the Sertoli cell barrier and studied the molecular mechanisms. Male rats received gavage administration of FLC (30 mg/kg/d) for 14 consecutive days with sample collection at the 7th and 14th day; and primary cultured Sertoli cells were treated with 0-10 μM FLC in vitro for 24 h. Our in vivo findings revealed that FLC exposure caused time-dependent testicular injuries, sperm quality decrease as well as adverse changes in BTB integrity, F-actin organization, and expressions of claudin-11 and Arp3. In Sertoli cells isolated from FLC-treated rat testis, Sertoli cell barrier tightness was increased. In Sertoli cells in vitro exposed to FLC, abnormal changes in the barrier permeability were also observed, and the protein expressions of occludin, claudin-11, ZO-1, connexin-43, and Arp3 were significantly decreased in a dose- and time-dependent manner. Furthermore, the FLC-induced adverse changes in Sertoli cell barrier and F-actin were partly alleviated by the induction of Arp3 overexpression. In conclusion, our findings revealed that FLC perturbed BTB/Sertoli cell barrier function through Arp3-mediated F-actin disorganization.

Vitamin E and vitamin C attenuate Di-(2-ethylhexyl) phthalate-induced blood-testis barrier disruption by p38 MAPK in immature SD rats

As an environmental endocrine disruptor, Di-(2-ethylhexyl) phthalate (DEHP) affects blood-testis barrier (BTB)-associated proteins expression, which compromises BTB integrity and causes infertility. Notably, DEHP-induced testicular toxicity is related to oxidative stress, but the specific mechanism remains unclear. Therefore, we sought to investigate this mechanism and determine whether vitamin C and vitamin E administration would attenuate the BTB impairment induced by DEHP in vivo and by Mono-(2-Ethylhexyl) Phthalate (MEHP) in vitro, respectively. HE staining and EM found that DEHP exposure led to spermatogenesis dysfunction and BTB disruption, respectively. The Western blot and immunofluorescence results showed that DEHP exposure caused BTB impairment through oxidative stress-mediated p38 mitogen-activated protein kinase (MAPK) signaling pathway. Furthermore, Vitamin E and vitamin C could alleviate the oxidative stress, block DEHP-induced spermatogenesis dysfunction and BTB disruption by inhibiting p38 MAPK signaling pathway. In summary, vitamin E and vitamin C are good candidates for the treatment of DEHP-induced male infertility.