The renin-angiotensin system hormone angiotensin II (AngII) is a critical regulator of a number of pathophysiological processes, including regulation of normal blood pressure and normal growth/survival of cells in blood vessels. The type 1 receptor (AT1R) activation is a critical prerequisite for all AngII-mediated pathophysiological processes, and consequently inhibition of the hormone functions by AT1R-blockers (ARBs) is widely used to treat a wide spectrum of cardiovascular diseases. Three sequential signals are activated when AngII binds to AT1R. First, the G protein Gq/11-PLC cascade initiates calcium mobilization leading to muscle contraction or electrolyte/water flux. Second, GRK2/3 recruited to AngII-bound AT1R phosphorylates C- terminal Ser/Thr residues which bind ?-arrestin1/2 and promote internalization. The AT1R continues to signal in endosomes causing long-term changes in gene transcription and protein synthesis. When the AT1R activation becomes chronic, disease states such as vascular, renal and cardiac hypertrophy, aortic aneurism (AA), and vascular fibrosis become prevalent. Genetic and pharmacological studies have shown that chronic G-protein signaling by AT1R increases risk for tissue inflammation, oxidative damage and cell death. Nearly two decades ago we designed an analog of AngII, [Sar1,Ile4,Ile8]AngII (SII-AngII) which did not stimulate G protein signaling, but effectively promoted internalization and intracellular ERK1/2 signaling. We have now developed several high-affinity AT1R ligands that inhibit G-protein dependent AT1R signals and enhance phosphorylation and internalization of AT1R associated with ?-arrestin. Within cells, ERK1/2 associate with ?-arrestin-bound to AT1R leading to ERK1/2 activation restricted to the cytoplasm. This mode of signaling has attained significance due to potential long-term benefits for cardiovascular homeostasis and an innovative opportunity for new treatment modalities. However, the molecular mechanism of these novel AT1R ligands and their in vivo efficacy in vascular disease models remains unclear. Our short-term objective is to test the hypothesis that signals modulated by ?-arrestin-biased AT1R ligands inhibit G-protein activation and will protect aorta prone to AngII-induced damage in vivo.
Our specific aims are:
Aim 1. Determine the efficacy of ?- arrestin-biased AT1R ligands to protect vessels during aortic aneurism (AA) pathogenesis.
Aim 2. Evaluate genetic factors that influence AT1R/?-arrestin-biased signaling.
Aim 3. Delineate the molecular mechanism of coupling of AT1R to ?-arrestin in vascular cells. These proposed studies will advance our knowledge of AT1R signaling and may provide insights into new approaches for preventing tissue/organ hypertrophy and fibrosis. Our long-term goal is to delineate mechanisms of ?-arrestin-mediated signaling of AT1R as well as to develop non-peptide AT1R-selective biased ligands for therapy.
Aortic aneurysm (AA) which occurs in the wall of the aorta is largely asymptomatic with increased risk of rupture and high mortality. We will evaluate the efficacy of AT1R-mediated scaffold signal activation in preventing inflammation, oxidative-damage and fibrosis in a mouse model of AA. We hope to demonstrate inhibition of AA in conjunction with elimination of side effects from long term treatment with ARBs.
