Dietary salt modulates the sodium chloride cotransporter expression likely through an aldosterone-mediated WNK4-ERK1/2 signaling pathway.

WNK is a serine/threonine kinase. Mutation in WNK1 or WNK4 kinase results in pseudohypoaldosteronism type II (PHA II) featuring hypertension, hyperkalemia and metabolic acidosis. Sodium chloride cotransporter (NCC) is known to be regulated by phosphorylation and trafficking. Dietary salt and hormonal stimulation, such as aldosterone, also affect the regulation of NCC. We have previously reported that WNK4 inhibits NCC protein expression. To determine whether dietary salt affects NCC abundance through WNK4-mediated mechanism, we investigated the effects of dietary salt change with or without aldosterone infusion (1 mg/kg/day) on NCC and WNK4 expression in rats. We found that high-salt (HS, 4% NaCl) diet significantly inhibits NCC mRNA expression and protein abundance while enhancing WNK4 mRNA and protein expression, whereas low-salt (LS, 0.07% NaCl) diet increases NCC mRNA expression and protein abundance while reducing WNK4 expression. We also found that aldosterone infusion in HS-fed rats increases NCC mRNA expression and protein abundance, but decreases WNK4 expression. Administration with spironolactone (0.1 g/kg/day) in LS-fed rats decreases NCC mRNA expression and protein abundance while increasing WNK4 expression. We further showed that ERK1/2 phosphorylation was increased in HS-fed rats, but decreased in LS-fed rats. In HEK293 cells, over-expressed WNK4 increases ERK1/2 phosphorylation, whereas knockdown of WNK4 expression decreases ERK1/2 phosphorylation. Aldosterone treatment for 3 h decreases ERK1/2 phosphorylation. These data suggest that dietary salt change affects NCC protein abundance in an aldosterone-dependent mechanism likely via the WNK4-ERK1/2-mediated pathway.