KS-WNK1 is required for full activation of WNK4-SPAK-NCC pathway during low potassium intake
Authors: Bahena-Lopez Jessica , Vergara Laura , Ibargüen Paulina , Garcia Janeth , Gutierrez Miguel , Vazquez Norma , Murillo Adrian , Carbajal Hector , Castañeda Maria , Ellison David , Chavez Maria , Gamba Gerardo 
Published: May 2023

KS-WNK1 is a shorter isoform of WNK1, exclusively expressed in the kidney. Although it holds no kinase activity, it has been shown that stimulates NCC via WNK4-SPAK pathway (AJP 2018), its presence is required to form WNK bodies in the distal convoluted tubule (Mol Biol Cell 2018) and its expression during normal-K+ diet is negligible, but increased under low potassium diet (AJP 2021). In wildlife, mammalians are exposed to cycles of no food and thus no K+ intake for days, followed by an acute and vast meal and thus high K+ intake in a few hours. In the present work we designed an strategy to mimic K+ intake changes in wildlife to properly analyze KS-WNK1-NCC pathway.We analyzed the plasma K+, urinary electrolytes and NCC-SPAK-WNK4-KS-WNK1 expression in kidney proteins by immunoblot of C57bl/6 (WT) and KS-WNK1-KO (KSKO) mice exposed to 10 days of zero K+ diet (0KD) or normal K+ diet (NKD) and corresponding groups followed by high K+ ingestion (HKD) (5%) for 12 or 24 hours.No difference was observed in plasma K+, Na+ or K+ urinary excretion or NCC, SPAK and WNK4 phosphorylation between WT and KSKO mice exposed to NKD and followed by 12 or 24 h of HKD. Furthermore, plasma K+ did not increase at 12 or 24h in either genotype. In contrast, after 10 days of 0KD, KSKO mice exhibited lower plasma K+, lower NCC and SPAK phosphorylation and higher Na+ and K+ excretion than WT mice (p<0.05). Interestingly, WNK4 phosphorylation in S64 was only present in WT mice. KS-WNK1 expression was only observed in WT after 0KD. Plasma K+ increased in mice at 12 and 24h of HKD, but KSKO mice had higher plasma K+ than WT mice, which in addition exhibited a slower increase in K+ and Na+ excretion than the KSKO mice at 12 and 24 h after HKD, suggesting that KS-WNK1 prevents Na+ and K+ loss after a HKD challenge only if mice were previously exposed to 0KD.Our data show no difference between WT and KSKO in groups kept under NKD and exposed to 12 or 24 h of HKD challenge. Moreover, KS-WNK1 was not expressed during NKD. In contrast, in mice kept under 0KD, WNK4 phosphorylation at S64 occurred only in WT and upregulation of SPAK-NCC pathways was higher than in KS-KO mice. Additionally, at 12 and 24 h of HKD, down-regulation of NCC was also more effective in WT than in KSKO mice. Therefore, our data show that KS-WNK1 is not present and has no role in mice under NKD, but it is up-regulated during 0KD and plays a role in modulating the WNK4-SPAK-NCC pathway to properly respond to extreme changes in potassium. During 0KD, maximun WNK4 activation was only achieved in the presence of KS-WNK1, suggesting that indeed, KS-WNK1/WNK4 heterodimers ocurrs in vivo. This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.