Pathophysiological roles of WNK kinases in the kidney.

Since the discovery of mutations in the WNK1 and WNK4 genes in pseudohypoaldosteronism type II (PHAII), the pathophysiological role of WNK kinases in hypertension and renal ion transport has been a hot topic for investigation. Analyses from a mouse model carrying the same mutation as seen in PHAII patients, reveal a new signal cascade in the kidney that regulates NaCl and K balance in the body. WNK kinases phosphorylate and activate oxidative stress responsive kinase 1 (OSR1) and STE20-like proline and alanine-rich kinase (SPAK), and OSR1 and SPAK phosphorylate and activate the thiazide-sensitive Na-Cl cotransporter (NCC). Furthermore, this cascade is regulated by aldosterone, indicating that WNK-OSR1/SPAK-NCC cooperates with this system including the epithelial Na channel (ENaC) to conserve NaCl. With regard to K excretion, however, both systems work in opposite directions whereby PHAII and Liddle syndrome show hyperkalemia and hypokalemia, respectively. Thus, the identification of such aldosterone effecters other than ENaC, will reveal a novel regulatory mechanism of K excretion in the distal nephron, and also provides basic evidence for the therapeutic use of thiazide in various clinical situations.