Phosphorylation regulates NCC stability and transporter activity in vivo

Area of Science:

• Nephrology
• Molecular Biology
• Genetics

Background:

• Gitelman syndrome (GS) is linked to mutations in the thiazide-sensitive sodium chloride cotransporter (NCC).
• A specific T60M mutation in NCC disrupts its phosphorylation by SPAK/OSR1 kinases, altering transporter activity in vitro.
• The in vivo physiological impact of NCC phosphorylation defects remains incompletely understood.

Purpose of the Study:

• To investigate the in vivo physiological consequences of impaired NCC phosphorylation using a novel knock-in mouse model.
• To elucidate the role of SPAK-mediated NCC phosphorylation in regulating NCC stability, localization, and function.
• To assess the impact of the T60M NCC mutation on Gitelman syndrome and related hypertensive disorders.

Main Methods:

• Generated and characterized Ncc T58M knock-in mice (equivalent to human T60M mutation).
• Analyzed NCC protein levels, phosphorylation status, and localization in mouse kidneys and MDCK cells.
• Assessed thiazide diuretic response, urine NCC excretion in patients, and performed genetic crosses with a pseudohypoaldosteronism type II model.

Main Results:

• Ncc(T58M/T58M) mice recapitulated Gitelman syndrome features, including blunted thiazide response and reduced total/phosphorylated NCC protein levels.
• T58M NCC exhibited altered localization to the cytosol instead of the apical membrane, leading to increased distal tubule volume.
• Impaired NCC phosphorylation reduced protein expression and membrane stability, and diminished urinary NCC excretion in GS patients with homozygous T60M mutations.

Conclusions:

• SPAK-mediated phosphorylation of NCC at T60 is crucial for regulating NCC protein stability and function.
• Defective NCC phosphorylation at T60 underlies the pathophysiology of Gitelman syndrome.
• This defect corrects the hypertensive phenotype in a model of pseudohypoaldosteronism type II, suggesting therapeutic potential.