βENaC and ASIC2 associate in VSMCs to mediate pressure-induced constriction in the renal afferent arteriole.

In independent studies, our laboratory has shown the importance of the degenerin proteins β-epithelial Na+ channel (βENaC) and acid-sensing ion channel 2 (ASIC2) in pressure-induced constriction (PIC) in renal interlobar arteries. Most, but not all, of the PIC response is abolished in mice lacking normal levels of βENaC or in ASIC2-null mice, indicating that the functions of βENaC and ASIC2 cannot fully compensate for the loss of the other. Degenerin proteins are known to associate and form heteromeric channels in expression systems, but whether they interact biochemically and functionally in vascular smooth muscle cells is unknown. We hypothesized that βENaC and ASIC2 interact to mediate PIC responses in renal vessels. To address this possibility, we 1) used biochemical approaches to show that βENaC associates into high-molecular-weight complexes and immunoprecipitants with ASIC2 in vascular smooth muscle cells and then 2) examined PIC in renal afferent arterioles in mice lacking normal levels of βENaC (βENaCm/m) or/and ASIC2 (ASIC2-/-) using the isolated afferent arteriole-attached glomerulus preparation. We found that the sensitivity of the PIC response (slope of the relationship between intraluminal pressure and percent myogenic tone) decreased to 26%, 27%, and -8% of wild-type controls in ASIC2-/-, βENaCm/m, and ASIC2-/-/βENaCm/m groups, respectively, suggesting that the PIC response was totally abolished in mice deficient in both ASIC2 and βENaC. Surprisingly, we found that resting internal diameters were 20-30% lower (60 mmHg, Ca2+ free) in ASIC2-/-/βENaCm/m (11.3 ± 0.5 µm) mice compared with control (14.4 ± 0.6 µm, P = 0.0007, independent two-tailed t test) or singly modified (15.7 ± 1.0 to 16.3 ± 1.1 µm) mice, suggesting compensatory vasoconstriction or remodeling. We then examined mean arterial blood pressure (MAP) using radiotelemetry and glomerular injury using histological examination of renal sections. We found that 24-h MAP was mildly elevated (+8 mmHg) in ASIC2-/-/βENaCm/m mice versus wild-type controls and the glomerular injury score was modestly increased by 38%. These findings demonstrate that myogenic constriction in afferent arterioles is dependent on normal expression of βENaC and ASIC2 and that mice lacking normal levels of ASIC2 and βENaC have mild renal injury and increased MAP.NEW & NOTEWORTHY Transmission of systemic blood pressure to delicate renal microvessels is a primary determinant of vascular injury in chronic kidney disease progression to end-stage renal disease. Here, we identified two degenerin family members, with an evolutionary link to mechanosensing, that interact biochemically and functionally to regulate systemic blood pressure and renal injury. Thus, degenerin proteins may serve as a target for the development of therapies to prevent or delay renal disease progression.