SPAK Deficiency Corrects Pseudohypoaldosteronism II Caused by WNK4 Mutation

Stimulation of the OSR1 (Oxidative stress-responsive kinase-1)/SPAK [STE20 (sterile 20)/SPS1-related proline/alanine-rich kinase]-NCC (Na+-Cl− cotransporter) signaling cascade plays an important role in the WNK [With-No-Lysine (K)] kinase 4 D561A knock-in mouse model of pseudohypoaldosteronism type II (PHA II) characterized by salt-sensitive hypertension and hyperkalemia. The aim of this study was to investigate the respective roles of Osr1 and Spak in the pathogenesis of PHA II in vivo. Wnk4D561A/+ mice were crossed with kidney tubule-specific (KSP) Osr1 knockout (KSP-Osr1−/−) and Spak knockout (Spak−/−) mice. Blood pressure, plasma and urine biochemistries, and the relevant protein expression in the kidneys were examined. Wnk4D561A/+, KSP-Osr1−/−, and Spak−/− mice recapitulated the phenotypes of PHA II, Bartter-like syndrome, and Gitelman syndrome, respectively. Wnk4D561A/+.KSP-Osr1−/− remained phenotypically PHA II while Wnk4D561A/+.Spak−/− mice became normotensive and lacked the PHA II phenotype. Phosphorylated Spak and Ncc were similarly increased in both Wnk4D561A/+ and Wnk4D561A/+.KSP-Osr1−/− mice while phosphorylated Ncc normalized in Wnk4D561A/+.Spak−/− mice. Furthermore, Wnk4D561A/+.KSP-Osr1−/− mice exhibited exaggerated salt excretion in response to thiazide diuretics while Wnk4D561A/+.Spak−/− mice exhibited normal responses. Wnk4D561A/+.Spak−/−.KSP-Osr1−/− triple mutant mice had low blood pressure and diminished phosphorylated Ncc. Both SPAK and OSR1 are important in the maintenance of blood pressure but activation of SPAK-NCC plays the dominant role in PHA II. SPAK may be a therapeutic target for disorders with salt-sensitive hypertension related to WNK4 activation.