Degenerin and TrpC6 channels in renal vascular mechanosesnsor signaling and protection against injury.

ABSTRACT Mechanosensing is a process inherent to nearly all cell types, including vascular smooth muscle (VSM) cells where pressure-induced vascular stretch initiates a mechano-dependent vasoconstriction. This response, termed pressure-induced constriction, occurs in numerous organs including the kidney and serves at least two functions: control of local blood flow and prevention of transmission of damaging high systemic pressures to delicate microvessels. A loss of the pressure-induced constriction response increases susceptibility to vascular injury in organs, including the kidney where a loss of this response accelerates progression of chronic kidney disease. Despite the importance of the pressure-induced constriction response, molecular mechanism(s) underlying its initiation remain unclear. We have shown that members of epithelial Na+ channel (ENaC)/degenerin family of ion channels (bENaC and ASIC2) are required for renal afferent arteriolar pressure- induced constriction. The role of other family members, including gENaC, is unknown. TrpC6 has been suggested to contribute to vascular mechanosignaling in cerebral arteries. However, its role in pressure-induced constriction in renal afferent arterioles is unknown. We recently found that b and gENaC and ASIC2 form functional, mechanoactivated channels when expressed in Xenopus oocytes. Our proposed studies address the hypothesis that b/gENaC-ASIC2 channels and TrpC6 have different roles in VSM cell mechano-signaling in renal afferent atherioles. Specifically, b/gENaC-ASIC2 channels mediate mechano-receptor currents, whereas TrpC6 channels contribute to signal amplification. In Specific Aim 1, we will use the Xenopus oocyte expression system to define the functional characteristics of b/gENaC-ASIC2 channels, and determine the mechanistic roles of b and gENaC, ASIC2 and TrpC6 in mechano-receptor currents and post-mechano-receptor Ca2+ signaling in renal afferent VSM cells. In Specific Aim 2, we will determine the contributions of b and gENaC, ASIC2 and TrpC6 to pressure- induced constriction in renal afferent arterioles. In Specific Aim 3, we will determine if VSM-specific loss of expression of ENaC subunits, ASIC2 or TrpC6 contributes to renal injury in the setting of hypertension. In summary, our proposed studies will determine the mechanistic roles of b/gENaC-ASIC2 and TrpC6 channels in mechanical signaling and in protecting against kidney injury.