TGFβs Modulate Permeability of the Blood-Epididymis Barrier in an In Vitro Model

The blood-epididymis barrier (BEB) is formed by epithelial tight junctions mediating selective permeability of the epididymal epithelium. Defective barrier function can disturb the balance of the epididymal milieu, which may result in infertility. The stroma of the epididymis contains high amounts of cytokines of the TGF beta family of unknown function. We screened possible effects of all three TGF beta isoforms on paracellular tightness in a BEB in vitro model based on the strongly polarized mouse epididymal epithelial MEPC5 cells in the transwell system. In this model we found a robust transepithelial electrical resistance (TER) of about 840 Omega x cm(2). Effects on the paracellular permeability were evaluated by two methods, TER and FITC-Dextran-based tracer diffusion assays. Both assays add up to corresponding results indicating a time-dependent disturbance of the BEB differentially for the three TGF beta isoforms (TGF beta 3>TGF beta 1>TGF beta 2) in a TGF beta-recetor-1 kinase- and Smad-dependent manner. The tight junction protein claudin-1 was found to be reduced by the treatment with TGF beta s, whereas occludin was not influenced. Epididymal epithelial cells are predominantly responsive to TGF beta s from the basolateral side, suggesting that TGF beta may have an impact on the epididymal epithelium from the stroma in vivo. Our data show for the first time that TGF beta s decrease paracellular tightness in epididymal epithelial cells, thus establishing a novel mechanism of regulation of BEB permeability, which is elementary for sperm maturation and male fertility.