Glycogen synthase kinase 3α regulates urine concentrating mechanism in mice

Abstract

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...

Glycogen Synthase Kinase-3 Modulates Hyperosmotic-Induced Urea Transporter A1 Relocation in the Inner Medullary Collecting Duct Cells

“…In this study, we disclosed an apparent dosage-dependency of the stimulatory effect on the Li concentration and explored that the redistribution of UT-A1 already occurs at 25 m M LiCl. More recently, reports showed that the GSK3β isoform knockout mice had decreased ability to concentrate urine [11], while GSK3α knockout mice showed an increased urine output and a reduced urine osmolality under basal condition [10]. In this study, we found hypertonic stimulation could inhibit the activity of GSK3.…”

“…Previous studies have shown that GSK3 plays an important role in diabetic nephropathy [7], polycystic kidney disease [8], and proliferative renal diseases [9]. Although it has been reported that GSK3 is involved in concentrating urine by regulating vasopressin-induced AQP2 expression and translocation to the plasma membrane [4,10,11], it is unclear whether GSK3 is also involved in hypertonicity-induced UT-A1 reorganization.…”

Role of adenylyl cyclase 6 in the development of lithium-induced nephrogenic diabetes insipidus

“…GSK3β is suggested to be important for modulating AC activity, cAMP generation, and AVP sensitivity in the CD (18). However, GSK3α knockout mice, despite having impaired AVP-induced cAMP responses in CDs, are only mildly resistant to the onset of Li-NDI (48). Similarly, in the current study, although we saw clear inhibition of GSK3 activity (as evidenced by increased phosphorylation at an inhibitory site) following Li + administration, the developed Li-NDI must be cAMP independent.…”

GSK3: A Kinase Balancing Promotion and Resolution of Inflammation

“…GSK3α KO mice were viable, fertile, had normal body mass [133], and no obvious skeletal defects [134], but showed increased water uptake and urine production [135], enhanced sensitivity towards insulin and glucose, reduced fat mass, and increased hepatic glycogen levels [133]. In an alternative GSK3α KO model, mice were also viable but characterized by higher body weight, heavier organs (especially brain, heart, and testis), male infertility, and slightly reduced lifespan [136].…”