Abstract 815: Adrenal Beta-arrestin 1 Mediates Angiotensin II-induced Aldosterone Production In Vitro And In Vivo
Aldosterone is one of the elevated hormones with detrimental effects in chronic heart failure (HF). It is produced and secreted by the adrenocortical zona glomerulosa cells in response to angiotensin II (AngII) activation of AngII type 1A receptors (AT1ARs). AT1ARs are G-protein coupled receptors (GPCRs) that also signal through G-protein-independent pathways. The scaffolding actions of β-arrestin-1 and -2 (βarr1 and -2), originally discovered as co-factors of GPCR kinases (GRKs) in termination of GPCR signaling, promote this G-protein-independent signaling of AT1ARs. Herein, we hypothesized that adrenal βarr1 mediates, at least in part, AT1AR signaling to aldosterone production/secretion and we tested this in vitro, in the human adrenocortical zona glomerulosa cell line H295R, and, in vivo, via adenoviral-mediated gene transfer of βarr1, GRK2, or the GRK2 inhibitor peptide βARKct in the adrenal glands of normal rats. At one week post-infection, βarr1 overexpression (Adβarr1) led to a significant increase in plasma aldosterone levels (536 ± 50 pg/ml), as measured by ELISA, versus control AdGFP (Green Fluorescent Protein)-infected rats (235 ± 40 pg/ml, p<0.01, n = 5). GRK2 overexpression slightly but significantly increased plasma aldosterone, whereas βARKct expression had no effect. In H295R cells, βarr1 transfection markedly increased AngII-induced aldosterone production, compared to control GFP-transfected cells, and this was completely abolished in cells overexpressing a dominant negative βarr1 mutant (V53D DN). Accordingly, at the signaling level, AngII-induced extracellular signal-regulated kinase (ERK) activation was augmented in βarr1-transfected cells, compared to GFP-transfected cells, accompanied by transcriptionally-mediated upregulation of the rate-limiting enzyme in steroid biosynthesis StAR (Steroidogenic Acute Regulator). All these effects were abolished in V53D DN-transfected cells. Studies are under way in HF rats aiming at modulation of aldosterone levels in HF by manipulating adrenal βarr1 activity. In conclusion, adrenal βarr1 appears to promote physiological signaling of AngII to aldosterone biosynthesis in vitro, and physiological aldosterone production in vivo, independently of GRK activity.