Renal proximal tubular damage and repair are hallmarks of acute kidney injury. Because glycogen synthase kinase-3β (GSK-3β) 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 GSK-3β 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 were all reduced in the knockout mice. The restoration of renal structure, function, and cell proliferation was also accelerated in the GSK-3β 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 GSK-3 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 GSK-3β prior to nephrotoxic insult protects from renal injury. Such treatment after acute kidney injury may accelerate repair and regeneration.

In mammals, glycogen synthase kinase (GSK)3 comprises GSK3␣ and GSK3␤ isoforms. GSK3␤ 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 GSK3␣ has yet to be discerned. To investigate the role of GSK3␣ in urine concentration, we compared GSK3␣ knockout (GSK3␣KO) mice with wild-type (WT) littermates. Under normal conditions, GSK3␣KO mice had higher water intake and urine output. GSK3␣KO 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 GSK3␣KO mice, suggesting reduced responsiveness to vasopressin. Gene silencing of GSK3␣ 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 GSK3␣KO mice, the polyuric response was markedly reduced. This study demonstrates, for the first time, that GSK3␣ could play a crucial role in renal urine concentration and suggest that GSK3␣ might be one of the initial targets of Li ϩ in LiCl-induced nephrogenic diabetes insipidus.glycogen synthase kinase 3␣; glycogen synthase kinase 3␤; urine concentration; vasopressin; lithium REGULATION OF WATER HOMEOSTASIS is a critical function of the kidneys. When arginine vasopressin (AVP) binds to its V2 receptors on principal cells of renal collecting ducts, it leads to activation of adenylate cyclase, which triggers an elevation of cAMP. cAMP-mediated activation of PKA leads to increased trafficking of aquaporin (AQP)2 to the apical membrane, resulting in water reabsorption from the tubular fluid and the production of concentrated urine (1,27,47). Recent studies have demonstrated that the glycogen synthase kinase (GSK)3 family of serine/threonine protein kinases plays an important role in renal urine concentration (34). This concept originated from the observation that Li ϩ , a common treatment for bipolar disorders that causes an AVP-insensitive form of urinary concentrating defect, is also an effective inhibitor of GSK3 (10,30,32,37,40,42,49).The mammalian GSK3 isoforms, GSK3␣ and GSK3␤, were thought to be redundant in their function because they share 98% sequence identity in their catalytic domains (17). Moreover, deletion of all four alleles of GSK3␣ and GSK3␤ was required to significantly increase ␤-catenin, a substrate negatively regulated by GSK3, suggesting that the isoforms could compensate for each other (7). However, recent studies have also shown that GSK3 isoforms could have unique functions. For example, in Drosophila carrying a mutation in ZW3/ Shaggy, the fly ortholog of mammalian GSK3, GSK3␤ rescued the frizzled phenotype more e...