WNK4 kinase is a physiological intracellular chloride sensor

Area of Science:

• Physiology
• Molecular Biology
• Nephrology

Background:

• With-no-lysine (WNK) kinases are crucial regulators of the renal sodium-chloride cotransporter (NCC).
• Gain-of-function mutations in WNK1 and WNK4 cause pseudohypoaldosteronism type II (PHAII), a hypertensive and hyperkalemic disease.
• Chloride ions (Cl-) inhibit WNK kinase activity by binding to a hydrophobic pocket, a mechanism potentially involved in physiological NCC regulation.

Purpose of the Study:

• To investigate whether WNK4 functions as an intracellular chloride sensor in vivo.
• To elucidate the role of chloride sensing by WNK4 in the physiological regulation of NCC and blood pressure.

Main Methods:

• Generation of knockin mice with a chloride-insensitive WNK4 mutant.
• Phenotypic analysis of knockin mice, including blood pressure, plasma potassium, and NCC activity.
• Assessment of NCC activity in response to dietary potassium restriction, norepinephrine administration, and potassium loading in wild-type and knockin mice.

Main Results:

• WNK4 knockin mice exhibited hypertension, hyperkalemia, and hyperactive NCC, mirroring PHAII.
• Dietary potassium restriction increased NCC activity in wild-type mice but not in knockin mice.
• Potassium loading inactivated NCC in wild-type mice, while WNK4 knockin mice showed no response.

Conclusions:

• WNK4 functions as a physiological intracellular chloride sensor.
• Chloride regulation of WNK4 is a key mechanism underlying the control of NCC by extracellular potassium.
• This chloride-sensing role of WNK4 is critical for maintaining sodium and potassium homeostasis and blood pressure.