Hypertension-Linked Mutation in the Adducin α-Subunit Leads to Higher AP2-μ2 Phosphorylation and Impaired Na ⁺ ,K ⁺ -ATPase Trafficking in Response to GPCR Signals and Intracellular Sodium

Abstract

Abstract-␣-Adducin polymorphism in humans is associated with abnormal renal sodium handling and high blood pressure. The mechanisms by which mutations in adducin affect the renal set point for sodium excretion are not known. Decreases in Na ϩ ,K ϩ -ATPase activity attributable to endocytosis of active units in renal tubule cells by dopamine regulates sodium excretion during high-salt diet. Milan rats carrying the hypertensive adducin phenotype have a higher renal tubule Na ϩ ,K ϩ -ATPase activity, and their Na ϩ ,K ϩ -ATPase molecules do not undergo endocytosis in response to dopamine as do those of the normotensive strain. Dopamine fails to promote the interaction between adaptins and the Na ϩ ,K ϩ -ATPase because of adaptin-2 subunit hyperphosphorylation. Expression of the hypertensive rat or human variant of adducin into normal renal epithelial cells recreates the hypertensive phenotype with higher Na ϩ ,K ϩ -ATPase activity, 2-subunit hyperphosphorylation, and impaired Na ϩ ,K ϩ -ATPase endocytosis. Thus, increased renal Na ϩ ,K ϩ -ATPase activity and altered sodium reabsorption in certain forms of hypertension could be attributed to a mutant form of adducin that impairs the dynamic regulation of renal Na ϩ ,K ϩ -ATPase endocytosis in response to natriuretic signals. Key Words: high blood pressure Ⅲ sodium retention Ⅲ protein trafficking Ⅲ cytoskeleton Ⅲ endocytosis S pontaneous mutations in ␣-adducin gene favor renal sodium retention and the development of high blood pressure in humans and rodents. 1 The estimated frequency of the mutated allele fluctuates among 8% in African Americans, 15% to 20% in whites, and 50% in Japanese individuals. The resulting phenotype is similar in rats and humans despite species differences in the mutation sites (human G460W/ S586C; rats F316Y). These polymorphisms affect the pressure natriuresis curve, the lithium clearance (an indicator of proximal tubule [PCT] sodium transport), 2 and the chronic blood pressure response to diuretics. 3,4 Recent studies further substantiate the role of adducin in human hypertension and the associated renal or cardiac alterations. 5,6 Many of these findings have been obtained in low-renin hypertensive patients, 7 in whom renal Na ϩ retention is a particularly important pathogenetic factor, or in patients carrying the gene variants known to affect renal Na ϩ handling. 8 At the cellular level, adducin plays an active role in cytoskeleton organization by regulating actin dynamics. 9 The mutated hypertensive variant of the adducin ␣-subunit increases the rate of actin polymerization and bundling in a cell-free system compared with the wild-type variant. 10 In cultured renal cells stably transfected with the mutated ␣-adducin, the actin cytoskeleton network appears thicker and Na ϩ ,K ϩ -ATPase activity is higher than in cells transfected with the wild-type variant. 10 In renal epithelial cells, the Na ϩ ,K ϩ -ATPase is located at the basolateral membrane domain and is critical for vectorial sodium transport. Its regulation by catecholamines cont...

The α-Adducin Gene Is Associated With Macrovascular Complications and Mortality in Patients With Type 2 Diabetes

“…The results of these studies are in line with our finding that type 2 diabetic patients with the homozygous T-allele and with hypertension had a higher risk of mortality than the GG carriers. Considering the low frequency of the TT genotype (4.3%), however, the number of events among the TT genotype is low (range [7][8][9][10][11][12][13][14][15][16][17][18][19], while the association we find is very consistent over different risk factors. More importantly, our study shows that treatment of type 2 diabetes may prevent ADD1-induced mortality in diabetic patients.…”

“…A possible mechanism by which the ADD1 gene is involved in hypertension and atherosclerosis in type 2 diabetic patients is through the Na ϩ -K ϩ pump. A higher Na ϩ -K ϩ pump activity and an impaired Na ϩ -K ϩ pump endocytosis in renal tubular cells is present in carriers of the T-allele (16). In addition, a significant increase in the urinary excretion of nitric oxide (NO) metabolites was observed in carriers of the T-allele (17), which may contribute to abnormal renal sodium handling (18).…”

Pharmacogenomics and Pharmacogenetics of Hypertension

“…Studies on the dynamics of the endocytotic processes in transfected cells have provided an interpretation for the increased cellular expression and activity of the Na-K pump caused by the expression of the ␣-adducin mutants (23). Cells that are transfected with either the human or the rat hypertensive ␣-adducin compared with cells that are transfected with the wild-type variant show a higher Na-K pump activity and an impaired Na-K pump endocytosis in basal conditions (23) as well as in response to natriuretic signals such as dopamine. Deficient endocytosis of the Na-K pump therefore might be an important factor contributing to the increased renal tubular reabsorption observed in humans (24,25), carrying the mutated adducin variant.…”

Arterial properties in relation to genetic variation in α-adducin and the renin–angiotensin system in a White population

“…Mutation of the a-adducin gene (ADD1) entails increased Na þ ,K þ -ATPase activity 1,2 and increased renal tubular sodium reabsorption. 3 Variation in the Na þ ,K þ -ATPase activity and in the intracellular Na þ concentration might influence the sodium-dependent transmembranous Ca þ 2 transport in vascular smooth muscle cells.…”

“…7 Experimental studies in fibroblasts from 51 subjects and in transfected cell models showed higher membrane-bound ACE activity in cells carrying the ADD1 Trp allele. 7 In view of the aforementioned evidence, [1][2][3][4][5][6][7] we hypothesized that arterial properties might be related not only to interactions of ADD1 with ACE, but also to interactions of ADD1 with other genes encoding various components of the renin-angiotensin system. We therefore genotyped Flemish Study on Environment, Genes and Health Outcomes participants for the angiotensinogen (AGT) C-532T and G-6A promoter polymorphisms as well as for the intronic A1166C polymorphism in the angiotensin II type-1 receptor gene (AT1R).…”