Kidney-Specific CAP1/Prss8-Deficient Mice Maintain ENaC-Mediated Sodium Balance through an Aldosterone Independent Pathway.

The serine protease prostasin (CAP1/Prss8, channel-activating protease-1) is a confirmed in vitro and in vivo activator of the epithelial sodium channel ENaC. To test whether proteolytic activity or CAP1/Prss8 abundance itself are required for ENaC activation in the kidney, we studied animals either hetero- or homozygous mutant at serine 238 (S238A; Prss8 cat/+ and Prss8 cat/cat ), and renal tubule-specific CAP1/Prss8 knockout (Prss8 PaxLC1 ) mice. When exposed to varying Na + -containing diets, no changes in Na + and K + handling and only minor changes in the expression of Na + and K + transporting protein were found in both models. Similarly, the α- or γENaC subunit cleavage pattern did not differ from control mice. On standard and low Na + diet, Prss8 cat/+ and Prss8 cat/cat mice exhibited standard plasma aldosterone levels and unchanged amiloride-sensitive rectal potential difference indicating adapted ENaC activity. Upon Na + deprivation, mice lacking the renal CAP1/Prss8 expression (Prss8 PaxLC1 ) exhibit significantly decreased plasma aldosterone and lower K + levels but compensate by showing significantly higher plasma renin activity. Our data clearly demonstrated that the catalytic activity of CAP1/Prss8 is dispensable for proteolytic ENaC activation. CAP1/Prss8-deficiency uncoupled ENaC activation from its aldosterone dependence, but Na + homeostasis is maintained through alternative pathways.