Dietary electrolyte-driven responses in the renal WNK kinase pathway in vivo

WNK1 and WNK4 are unusual serine/threonine kinases with atypical positioning of the catalytic active-site lysine (WNK: With-No-K[lysine]). Mutations in these WNK kinase genes can cause familial hyperkalemic hypertension (FHHt), an autosomal dominant, hypertensive, hyperkalemic disorder, implicating this novel WNK pathway in normal regulation of BP and electrolyte balance. Full-length (WNK1-L) and short (WNK1-S) kinase-deficient WNK1 isoforms previously have been identified. Importantly, WNK1-S is overwhelmingly predominant in kidney. Recent Xenopus oocyte studies implicate WNK4 in inhibition of both thiazide-sensitive co-transporter-mediated Na+ reabsorption and K+ secretion via renal outer medullary K+ channel and now suggest that WNK4 is inhibited by WNK1-L, itself inhibited by WNK1-S. This study examined WNK pathway gene expression in mouse kidney and its regulation in vivo. Expression of WNK1-S and WNK4 is strongest in distal tubule, dropping sharply in collecting duct and with WNK4 also expressed in thick ascending limb and the macula densa. These nephron segments that express WNK1-S and WNK4 mRNA have major influence on long-term NaCl reabsorption, BP, K+, and acid-base balance, processes that all are disrupted in FHHt. In vivo, this novel WNK pathway responds with significant upregulation of WNK1-S and WNK4 with high K+ intake and reduction in WNK1-S on chronic lowering of K+ or Na+ intake. A two-compartment distal nephron model explains these in vivo findings and the pathophysiology of FHHt well, with WNK and classic aldosterone pathways responding to drivers from K+ balance, extracellular volume, and aldosterone and cross-talk through distal Na+ delivery regulating electrolyte balance and BP.