rpS6 regulates blood-testis barrier dynamics via its effects on MMP-9 mediated by Akt signaling

Abstract

mTORC1 is an emerging regulator of blood-tissue barrier (BTB) utilizing rpS6 as the downstream signaling molecule. To explore the role of rpS6 in BTB function, a constitutively active rpS6 phosphomimetic mutant was constructed and overexpressed in Sertoli cells cultured in vitro that mimicked the BTB in vivo. Using this phosphomimetic mutant, p-rpS6 was shown to disrupt the IGF-1/insulin signaling, thereby abolishing the Akt phosphorylation which led to an induction of MMP-9. This increase in MMP-9 secretion perturbed the Sertoli cell tight junction (TJ)-permeability barrier via a down-regulation of TJ-proteins at the BTB mediated by proteolysis. These findings were confirmed by the use of a specific MMP-9 inhibitor which blocked the rpS6 mutant-induced TJ-permeability barrier disruption. Additionally, the use of RNAi for Akt silencing was able to mimic the results rpS6 mutant overexpression in Sertoli cells, further confirming this p-rpS6-Akt-MMP-9 signaling pathway. In short, these data support a new concept on mTORC1-mediated BTB regulation, plausibly applicable to other blood-tissue barriers.