Glycogen synthase kinase 3α regulates urine concentrating mechanism in mice.

In mammals, glycogen synthase kinase (GSK)3 comprises GSK3α and GSK3ß isoforms. GSK3ß has been shown to play a role in the ability of kidneys to concentrate urine by regulating vasopressin-mediated water permeability of collecting ducts, whereas the role of GSK3α has yet to be discerned. To investigate the role of GSK3α in urine concentration, we compared GSK3α knockout (GSK3αKO) mice with wild-type (WT) littermates. Under normal conditions, GSK3αKO mice had higher water intake and urine output. GSK3αKO mice also showed reduced urine osmolality and aquaporin-2 levels but higher urinary vasopressin. When water deprived, they failed to concentrate their urine to the same level as WT littermates. The addition of 1-desamino-8-d-arginine vasopressin to isolated inner medullary collecting ducts increased the cAMP response in WT mice, but this response was reduced in GSK3αKO mice, suggesting reduced responsiveness to vasopressin. Gene silencing of GSK3α in mpkCCD cells also reduced forskolin-induced aquaporin-2 expression. When treated with LiCl, an isoform nonselective inhibitor of GSK3 and known inducer of polyuria, WT mice developed significant polyuria within 6 days. However, in GSK3αKO mice, the polyuric response was markedly reduced. This study demonstrates, for the first time, that GSK3α could play a crucial role in renal urine concentration and suggest that GSK3α might be one of the initial targets of Li(+) in LiCl-induced nephrogenic diabetes insipidus.

Specific deletion of glycogen synthase kinase-3ß in the renal proximal tubule protects against acute nephrotoxic injury in mice.

Renal proximal tubular damage and repair are hallmarks of acute kidney injury. As glycogen synthase kinase-3ß (GSK3ß) is an important cellular regulator of survival and proliferation, we determined its role during injury and recovery of proximal tubules in a mercuric chloride-induced nephrotoxic model of acute kidney injury. Renal proximal tubule-specific GSK3ß knockout mice exposed to mercuric chloride had improved survival and renal function compared to wild-type mice. Apoptosis, measured by TUNEL staining, Bax activation, and caspase 3 cleavage, was reduced in the knockout mice. The restoration of renal structure, function, and cell proliferation was also accelerated in the GSK3ß knockout mice. This enhanced repair, evidenced by increased Ki-67 and BRDU staining, along with increased cyclin D1 and c-myc levels, was recapitulated by treatment of wild-type mice with the small-molecule GSK3 inhibitor TDZD-8 following injury. This confirmed that hastened repair in the knockout mice was not merely due to lower initial injury levels. Thus, inhibition of GSK3ß prior to nephrotoxic insult protects from renal injury. Such treatment after acute kidney injury may accelerate repair and regeneration.