Plasma kallikrein activates the epithelial sodium channel in?vitro but is not essential for volume retention in nephrotic mice

摘要

Abstract Aim Recent work has demonstrated that activation of the epithelial sodium channel ( EN aC) by aberrantly filtered serine proteases causes sodium retention in nephrotic syndrome. The aim of this study was to elucidate a potential role of plasma kallikrein ( PKLK ) as a candidate serine protease in this context. Methods We analysed PKLK in the urine of patients with chronic kidney disease ( CKD , n?=?171) and investigated its ability to activate human EN aC expressed in Xenopus laevis oocytes. Moreover, we studied sodium retention in PKLK ‐deficient mice ( klkb1 ?/? ) with experimental nephrotic syndrome induced by doxorubicin injection. Results In patients with CKD , we found that PKLK is excreted in the urine up to a concentration of 2?μg?mL ?1 which was correlated with albuminuria ( r ?=?.71) and overhydration as assessed by bioimpedance spectroscopy ( r ?=?.44). PKLK increased EN aC‐mediated whole‐cell currents, which was associated with the appearance of a 67?kDa γ‐ EN aC cleavage product at the cell surface consistent with proteolytic activation. Mutating a putative prostasin cleavage site in γ‐ EN aC prevented channel stimulation by PKLK . In a mouse model for nephrotic syndrome, active PKLK was present in nephrotic urine of klkb1 +/+ but not of klkb1 ?/? mice. However, klkb1 ?/? mice were not protected from EN aC activation and sodium retention compared to nephrotic klkb1 +/+ mice. Conclusion Plasma kallikrein is detected in the urine of proteinuric patients and mice and activates EN aC in?vitro involving the putative prostasin cleavage site. However, PKLK is not essential for volume retention in nephrotic mice.