Enhanced phosphorylation of Na+–Cl− co-transporter in experimental metabolic syndrome: role of insulin

Abstract

We investigated the activity of thiazide-sensitive sodium-chloride cotransporter (NCC) in experimental metabolic syndrome (MS) and the role of insulin in NCC activation. Renal responses to NCC inhibitor hydrochlorothiazide (HCTZ), as a measure of NCC activity in vivo were studied in 12-week old Zucker obese rats (ZO), a model of MS, and in lean control animals (ZL), together with renal NCC expression, and molecular markers of NCC activity, such as localization and phosphorylation. Effects of insulin were further studied in mammalian cell lines with inducible and endogenous expression of this molecule. ZO rats displayed marked hyperinsulinemia, but no differences in plasma aldosterone as compared to ZL. In ZO, natriuretic and diuretic responses to NCC inhibition with HCTZ were enhanced compared with ZL, and associated with a decrease in blood pressure (BP). ZO rats displayed enhanced Thr53 NCC phosphorylation and predominant membrane localization of both total and phosphorylated NCC, together with a different profile in expression of SPAK isoforms, and lower expression of WNK4. In vitro, insulin induced NCC phosphorylation, which was blocked by PI3 kinase inhibitor. Insulin-induced reduction in WNK4 expression was also observed, but delayed compared with the time course of NCC phosphorylation. In summary, we report increased NCC activity in hyperinsulinemic rodents in conjunction with SPAK expression profile consistent with NCC activation and reduced WNK4 as well as an ability of insulin to induce NCC stimulatory phosphorylation in vitro. Together, these findings indicate that hyperinsulinemia is an important driving force of NCC activity in MS with possible consequences for BP regulation.

Alternatively spliced proline-rich cassettes link WNK1 to aldosterone action

“…Furthermore, emerging data indicate that, like aldosterone, insulin and vasopressin also trigger SPAK/OSR1-mediated NCC phosphorylation (7,38). Since changes in WNK1 protein abundance are directly linked to SPAK and OSR1 activity, our findings suggest that aldosterone, insulin, and vasopressin could all potentially leverage the interaction between NEDD4-2 and WNK1 as a means to activate NCC.…”

“…Several hormones that regulate renal tubular salt reabsorption and blood pressure -including aldosterone, angiotensin II, insulin, and vasopressin -activate NCC and/or NKCC2 (5)(6)(7)(8). Although each of these hormones act via their own sets of receptors and signaling pathways, they all trigger downstream SPAK/OSR1 phosphorylation as a precursor to cation-chloride cotransporter activation.…”

The sodium chloride cotransporter SLC12A3: new roles in sodium, potassium, and blood pressure regulation

“…Similarly, chronic metabolic acidosis also increases aldosterone and therefore NCC [26]. Why other hormones such as insulin [13,57,108,109], vasopressin [83,91,104], estrogen [125], and norepinephrine [82] regulate NCC is less clearly defined ( Table 1), but warrants further study given the role of these hormones in normal physiology and human diseases such as diabetes mellitus, obesity, and hypertension.…”

Distal Convoluted Tubule

“…Several clinically relevant hormones stimulate salt reabsorption in the distal nephron by increasing NCC activity, and in each of these cases, SPAK and/or OSR1 seem to be involved. These hormones include aldosterone (56,57), angiotensin II (58,59), insulin (60,61), and vasopressin (62,63). All of these hormones have been shown to increase the abundance of phosphorylated active NCC and, in some cases, have also been shown to increase NCC abundance or stimulate the movement of NCC from intracellular vesicles to the luminal membrane (64)(65)(66).…”