Scrotal heat stress causes a transient alteration in tight junctions and induction of TGF-β expression

Abstract

Specialized junctions, which occur at sites of Sertoli-Sertoli and Sertoli-germ cell contact of seminiferous epithelium, play pivotal roles in spermatogenesis. Slight increase in scrotal temperature can induce oligospermia or azoospermia via increasing germ cell apoptosis. In this study, we demonstrated that the expression of tight junction (TJ) components, such as occludin, claudin-3 and zonula occludens-1 (ZO-1), was reduced 24-48h after a single mild scrotal heat exposure (43°C for 30min), whereas mRNA levels of claudin-11 were increased. Moreover, the protein localization of occludin and ZO-1 was lost from the blood-testis barrier (BTB) site, whereas claudin-11 immunostaining became diffuse and cytoplasmic 2days following heat exposure. Electron microscopic analysis showed that 2days after the heat treatment, the intercellular space between the two adjacent Sertoli cells was expanded, coupled with defragmentation of actin bundles and the endoplasmic reticulum. In addition, the TJ permeability increased significantly 2days after the heat exposure and recovered approximately 10days later. Heat-induced reversible BTB disruption was associated with a transient induction of transforming growth factor (TGF)-β2, -3 and p38 mitogen-activated protein kinase activation. However, the TGF-β antagonist only partially prevented the heat-induced BTB disruption. In conclusion, the expression of TJ-associated molecules and BTB were reversibly perturbed after mild testicular hyperthermia, and the induction of TGF-β expression may be partially involved in heat-induced BTB damage.

Molecular basis of cryptorchidism-induced infertility

“…However, the observed heat-induced BTB disruption was partially prevented by administration of a TGF-β antagonist to the testes, concomitant with the heat stress [23]. Furthermore, induction of TGF-β and activation of p38 MAPK after heat treatment were detected in the heat-treated testes, as shown in Figure 7, indicating that TGF-β might be one of the regulators involved in the heat-induced TJ disruption.…”

“…We observed a reversible increase in testicular TGF-β3 after heat treatment, which could be involved in the downregulating of TJ-associated proteins and disruption of the BTB [23]. Additionally, p38 mitogen-activated protein kinase (MAPK) signaling pathways were activated in association with the induction of TGF-β3, indicating that the heat-induced increase in TGF-β3 might be involved in regulating BTB dynamics via the p38 MAPK pathway.…”

“…Additionally, p38 mitogen-activated protein kinase (MAPK) signaling pathways were activated in association with the induction of TGF-β3, indicating that the heat-induced increase in TGF-β3 might be involved in regulating BTB dynamics via the p38 MAPK pathway. Activation of the ERK signaling pathway coincided with the induction of TGF-β3 after heat treatment [23], implying perturbation of not only TJs, but also AJs between Sertoli and germ cells. The primary disruption of TJs could lead to secondary loss of cell adhesion function at the site of AJs [24].…”

Regulation of spermatogonial stem cell self-renewal and spermatocyte meiosis by Sertoli cell signaling

“…Our previous studies demonstrated that temporal heat stress in the testes resulted in a dramatic reduction in the expression of upstream factors, such as androgen receptor (AR), Wilms' tumor gene 1 (WT1), and liver receptor homolog 1 (LHR1) in monkey , Guo et al 2007, Chen et al 2008, rat (Guo et al 2007), and mouse (Cai et al 2011); however, these effects were reversible. The reversible dedifferentiation of Sertoli cells is followed by a temporary reversible disruption of the blood-testis barrier (BTB), which leads to dramatic germ cell apoptosis in the testis .…”

The Onset of Heat-Induced Testicular Calcification in Mice

“…5,13 Testicular hyperthermia is also reported to disrupt the BTB. 14,15 The molecular mechanisms responsible for the degenerative changes in heat-induced testicular dysfunction remain largely unknown.…”