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

Wan HT, Mruk DD, Li SY, Mok KW, Lee WM, Wong CK, Cheng CY. p-FAK-Tyr 397 regulates spermatid adhesion in the rat testis via its effects on F-actin organization at the ectoplasmic specialization. Am J Physiol Endocrinol Metab 305: E687-E699, 2013. First published July 23, 2013; doi:10.1152/ajpendo.00254.2013.-During spermatogenesis, the molecular mechanism that confers spermatid adhesion to the Sertoli cell at the apical ectoplasmic specialization (apical ES), a testis-specific F-actin-rich adherens junction, in the rat testis remains elusive. Herein, the activated form of focal adhesion kinase (FAK), p-FAK-Tyr 397 , a component of the apical ES that was expressed predominantly and stage specifically in stage VII-early stage VIII tubules, was found to be a crucial apical ES regulator. Using an FAK-Y397E phosphomimetic mutant cloned in a mammalian expression vector for its transfection vs. FAK and vector alone in adult rat testes in vivo, its overexpression was found to cause defects in spermiation. These defects in spermiation were manifested by entrapment of spermatids in the seminiferous epithelium in late stage VIII-X tubules and were mediated by a disruption on the spatiotemporal expression and/or mislocalization of actin regulatory protein actin-related protein 3, which induces branched actin polymerization, epidermal growth factor receptor pathway substrate 8 (an actin barbed end capping and bundling protein), and palladin (an actin cross-linking and bundling protein). This thus perturbed changes of F-actin organization at the apical ES to facilitate spermiation, which also led to a concomitant alteration in the distribution and upregulation of adhesion proteins nectin-2 and nectin-3 at the apical ES. As such, nectin-2 and -3 remained at the apical ES to anchor step 19 spermatids on to the epithelium, delaying spermiation. These findings illustrate a mechanistic pathway mediated by p-FAK-Tyr 397 that regulates spermatid adhesion at the apical ES in vivo. spermatogenesis; focal adhesion kinase; focal adhesion kinase mutant; adherens junction; actin filament bundles; testis IN THE RAT TESTIS, step 1 spermatids derived from secondary spermatocytes via meiosis undergo extensive morphological changes during spermiogenesis (8,10,20). Besides changes in cell shape via 19 steps in which round spermatids (step 1) transform into elongated spermatids (step 19), step 1 spermatids residing in the adluminal compartment but near the basal compartment and adjacent to the basement membrane must traverse back-and-forth the seminiferous epithelium during the epithelial cycle of spermatogenesis (8,19,22). As such, fully developed spermatids (i.e., spermatozoa) can be lined up at the luminal edge of the tubule lumen at late stage VIII of the epithelial cycle for spermiation (10,20,24). During spermiogenesis, a testis-specific adherens junction (AJ) appears at the Sertoli-spermatid (step 8) interface at stage VIII of the cycle known as apical ectoplasmic specialization (apical ES) (6, 27, 32). Once apical ES forms, it replaces d...

Introduction Exposure to endocrine disrupting chemicals (EDCs) has recently been linked to declining fertility in men in both developed and developing countries. Since many EDCs possess intrinsic estrogenic or androgenic activities, thus, the gonad is one of the major targets of EDCs. Areas covered For the past 2 decades, studies found in the literature regarding the disruptive effects of these EDCs on reproductive function in human males and also rodents were mostly focused on oxidative stress-induced germ cell apoptosis, disruption of steroidogenesis, abnormal sperm production and disruption of spermatogenesis in particular cell adhesion function and the blood–testis-barrier (BTB) function. Herein, we highlight recent findings in the field illustrating testis-specific proteins are also targets of EDCs. Expert opinion This information should be helpful in developing better therapeutic approach to manage ECD-induced reproductive toxicity. This information is also helpful to identify potential targets for male contraceptive development.