The sodium/proton exchanger NHA2 regulates blood pressure through a WNK4-NCC dependent pathway in the kidney

NHA2 is sodium/hydrogen exchanger that was associated with arterial
hypertension in humans, but the role of NHA2 in kidney function and blood
pressure homeostasis is currently unknown. Here we show that NHA2
localizes almost exclusively to distal convoluted tubules in the kidney.
NHA2 knock-out mice displayed reduced blood pressure, normocalcemic
hypocalciuria and an attenuated response to the thiazide diuretic
hydrochlorothiazide. Phosphorylation of the thiazide-sensitive
sodium/chloride cotransporter NCC and its upstream activating kinase
Ste20/SPS1-related proline/alaninerich kinase (SPAK), as well as the
abundance of with no lysine [K] kinase 4 (WNK4), were significantly
reduced in kidneys of NHA2 knock-out mice. In vitro experiments
recapitulated these findings and revealed increased WNK4 ubiquitylation
and enhanced proteasomal WNK4 degradation upon loss of NHA2. The effect of
NHA2 on WNK4 stability was Kelch-like 3 (KLHL3)-dependent. More
specifically, loss of NHA2 selectively attenuated KLHL3 phosphorylation
and the physiologically important PKAand PKC-mediated decrease of WNK4
degradation was blunted upon loss of NHA2. Phenotype analysis of NHA2/NCC
double knock-out mice supported the notion that NHA2 affects blood
pressure homeostasis by an intrarenal and NCC-dependent mechanism. In
summary, our data reveal NHA2 as a critical component of the WNK4-NCC
pathway and hence as a novel regulator of blood pressure homeostasis in
the kidney.