WNK1/HSN2 mediates neurite outgrowth and differentiation via a OSR1/GSK3β-LHX8 pathway

With no lysine kinase 1 (WNK1) phosphorylates and activates STE20/SPS1-related proline-alanine-rich protein kinase (SPAK) and oxidative stress responsive kinase 1 (OSR1) to regulate ion homeostasis in the kidney. Mutations in WNK1 result in dysregulation of the WNK1-SPAK/OSR1 pathway and cause pseudohypoaldosteronism type II (PHAII), a form of hypertension. WNK1 is also involved in the autosomal recessive neuropathy, hereditary sensory and autonomic neuropathy type II (HSANII). Mutations in a neural-specific splice variant of WNK1 (HSN2) cause HSANII. However, the mechanisms underlying HSN2 regulation in neurons and effects of HSN2 mutants remain unclear. Here, we found that HSN2 regulated neurite outgrowth through OSR1 activation and glycogen synthase kinase 3β (GSK3β). Moreover, HSN2-OSR1 and HSN2-GSK3β signalling induced expression of LIM homeobox 8 (Lhx8), which is a key regulator of cholinergic neural function. The HSN2-OSR1/GSK3β-LHX8 pathway is therefore important for neurite outgrowth. Consistently, HSN2 mutants reported in HSANII patients suppressed SPAK and OSR1 activation and LHX8 induction. Interestingly, HSN2 mutants also suppressed neurite outgrowth by preventing interaction of between wild-type HSN2 and GSK3β. These results indicate that HSN2 mutants cause dysregulation of neurite outgrowth via GSK3β in the HSN2 and/or WNK1 pathways.