The inter-Sertoli tight junction permeability barrier is regulated by the interplay of protein phosphatases and kinases: An in vitro study

The timely opening and closing of inter-Sertoli cell tight junctions in the rat testis are essential cellular events in the completion of spermatogene sis. They permit the passage of preleptotene and leptotene spermatocytes to cross the blood-testis barrier from the basal compartment to the adluminal compartment of the seminiferous epithelium so that these cells can continu e their further development into spermatids. However, the mechanism by whic h these events is regulated remains a mystery in male reproductive physiolo gy. As part of our long-term goal of understanding the biology of this even t and its regulation, transepithelial electrical resistance (TER) across th e Sertoli cell epithelia when inter-Sertoli tight junctions were being asse mbled in vitro was quantified to assess the effects of different inhibitors of phosphatases and kinases on the inter-Sertoli tight junction permeabili ty barrier. It was shown that inhibitors of protein tyrosine phosphatases ( PTPi) and inhibitors of protein Ser/Thr phosphatases (PPi) could perturb th e assembly and maintenance of the inter-Sertoli tight junction permeability barrier. Moreover, the inhibitory effects of PTPi were abolished by pretre ating Sertoli cells with protein tyrosine kinase inhibitor (PTKi), which il lustrates the specificity of the PTPi treatment. A cyclic adenosine monopho sphate-dependent protein kinase A (PKA) activator and inhibitors of calcium -diacylglycerol-dependent protein kinase C (PKC) can also perturb the inter -Sertoli tight junction permeability barrier, which suggests that opening a nd closing of the inter-Sertoli tight junctions during spermatogenesis is l ikely regulated, at least in part, by the PKA/PKC pathways. Needless to say , these results illustrate that the interplay of protein kinases and phosph atases, which regulate the intracellular phosphoprotein content of Sertoli cells possibly via PKA and PKC signal transduction pathways, plays a crucia l role in modulating the assembly and maintenance of inter-Sertoli tight ju nctions in the testis.