KS‐WNK1 Expands the Dynamic Range of NCC Regulation by Dietary Potassium

Dietary K+ deficiency activates the Na‐Cl cotransporter (NCC) of the renal distal convoluted tubule (DCT) through enhanced phosphorylation. NCC phosphorylation is regulated by the serine‐threonine kinases WNK1 and WNK4 and the downstream kinase SPAK. During dietary K+ loading and restriction, the WNK‐SPAK pathway condenses into large membraneless cytosolic signaling puncta, termed “WNK bodies” (MBoC 2017). These foci only appear during dietary [K+] imbalance and require KS‐WNK1, a truncated WNK1 isoform that is highly expressed in the DCT. The role of KS‐WNK1 and WNK bodies in NCC regulation during physiological shifts in [K+] remains unclear: early studies reported that KS‐WNK1 suppresses NCC activity, while more recent data suggest that it can function as an NCC activator. To analyze the role of KS‐WNK1 in NCC regulation in vivo, we assessed NCC phosphoactivation (pNCC) at T53, T58, and S71 by immunoblot and IF microscopy in WT and KS‐WNK1 KO mice across a wide range of plasma [K+]. WT and KS‐WNK1 KO mice were treated with low K+ (LK), control, or high K+ (HK) diets for 10d. We also treated a group of HK animals with amiloride (2 mg/kg/d × 7d) to induce frank hyperkalemia. This allowed us to study the effects of KS‐WNK1 on pNCC over a range of plasma [K+] from 2 to 9 mmol/L. In K+ restricted WT mice, pNCC was increased relative to WT mice on control diets, a finding that was associated with the formation of 1–2 μm subnuclear WNK bodies that contained WNK1, WNK4, and SPAK. LK diet‐treated KS‐WNK1 KO mice lacked WNK bodies and exhibited reduced pNCC relative to plasma K+‐matched WT LK diet‐treated mice, suggesting that KS‐WNK1 stimulates NCC during hypokalemia. During K+ loading in WT mice, pNCC was reduced relative to WT mice on control diets; this finding was associated with the formation of 0.5 μm subapical WNK bodies that were absent in HK diet‐treated KS‐WNK1 KO mice. In contrast to the LK dietary condition, however, HK KS‐WNK1 KO mice exhibited increased pNCC relative to plasma K+‐matched WT HK mice, suggesting an inhibitory role for KS‐WNK1 during hyperkalemia. Since KS‐WNK1 amplifies NCC phosphorylation during hypokalemia and attenuates NCC during hyperkalemia, these findings suggest that KS‐WNK1 augments the responsiveness of the WNK‐SPAK pathway to a given change in extracellular [K+], converting small changes in plasma [K+] to large effects on NCC phosphorylation status. These observations, which are likely WNK body dependent, provide insight into the role of KS‐WNK1 in the potassium stress response and potentially resolve conflicting data regarding the role of KS‐WNK1 in NCC regulation. Support or Funding Information NIH T32DK061296, R01DK098145Relationship between pNCC and plasma [K+] in WT and KS‐WNK1 KO miceThis abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .