Silencing regulator of G protein signaling-2 (RGS-2) increases angiotensin II signaling: insights into hypertension from findings in Bartter's/Gitelman's syndromes.

Objective: Regulator of G-protein signaling (RGS)-2 is a regulator of angiotensin II (Ang II) signaling. In Bartter's syndrome/Gitelman's syndrome (BS/GS), we have demonstrated increased RGS-2 levels and blunted Ang II signaling which contribute to their reduced vasomotor tone and remodeling. The present study investigates the effect of silencing RGS-2 in fibroblasts from six BS/GS patients on intracellular Ca2+ (CaI2+) mobilization and extracellular signal-regulated kinase (ERK) 1/2 phosphorylation, established Ang II-mediated responses.

Methods: Fibroblasts were RGS-2 silenced by transfecting chemically synthesized small interfering RNA. Silencing efficiency and Ang II-induced ERK 1/2 phosphorylation were evaluated by western blot and Ang II-induced Cai2+ using Fura-2 AM.

Results: RGS-2 expression in not silenced BS/GS fibroblasts from patients is increased compared with healthy controls [0.34 +/- 0.02 vs. 0.19 +/- 0.01 densitometric units (d.u.), P = 0.0005]. Silencing RGS-2 in BS/GS patients was achieved to the level of controls. Ang II-induced Cai2+ release and ERK 1/2 phosphorylation were reduced in not silenced cells from BG/GS patients compared with controls (112.16 +/- 13.2 vs. 130.33 +/- 13.64 mmol/l, P = 0.011 and 0.64 +/- 0.08 vs. 0.91 +/- 0.03 mmol/l, P < 0.006, respectively). Silencing RGS-2 in BS/GS patients increased Ang II-induced Cai2+ release and ERK 1/2 phosphorylation in silenced cells compared with not silenced cells [59.3 +/- 10.8 (peak-basal) vs. 40.5 +/- 14.1 nmol/l, P = 0.017 and 0.84 +/- 0.06 vs. 0.64 +/- 0.08 nmol/l, P < 0.03, respectively], whereas they were not different compared with controls (60.1 +/- 4.3 and 0.91 +/- 0.03 nmol/l). Integrating the Cai2+ response over time showed increased Cai2+ area under the curve (AUC) of BS/GS silenced cells compared with that of not silenced cells (P = 0.013).

Conclusion: This is the first report of silencing RGS-2 effect on Ang II signaling in a human clinical condition of altered vascular tone regulation and remodeling and establishes RGS-2 as a key regulatory element of Ang II signaling in humans.