Angiotensin II-mediated Signaling in Astrocytes: Role of Beta-arrestins

Grant Winners

Dean

Abstract

Hypertension is the major risk factor that plays a crucial role in damaging vital organs leading to cardiovascular diseases. It has been demonstrated that the brain renin-angiotensin system (RAS) plays a central role in the development and establishment of the hypertensive state. Although there are a number of biologically active peptides produced by this system, it is appreciated that angiotensin II (Ang II) is the major peptide produced. Although the effects of Ang II are mediated by its interaction with two receptors, it is the Ang type 1 receptor (AT1R), a G-protein coupled receptor (GPCR), that is the primary receptor mediating the cardiovascular effects of the peptide. These AT1R-mediated effects are regulated by the cytosolic proteins beta-arrestin1 and 2. Recently, it was demonstrated that beta-arrestins, in addition to their classical role in regulation of GPCRs, can initiate signaling cascades independently of G protein activation. The involvement of beta-arrestins in AT1R-mediated signaling has been demonstrated to have pharmacological and pathophysiological implications.

In this study, we use brainstem astrocytes as a model in vitro system to determine the role of beta-arrestins in Ang II-induced signaling in the hypertensive versus normotensive state as the importance of beta-arrestins in the central nervous system (CNS) is unclear. We will determine the expression levels of beta-arrestins in both models to see if there is a difference in the hypertensive condition and study the existence of modulating effects of Ang II on the expression levels of beta-arrestins in both rat models. The involvement of beta-arrestins in Ang II-mediated mitogen activated protein (MAP) kinases activation, and Ang II regulation of AGT synthesis will also be investigated. Finally, we will investigate if the involvement of beta-arrestins is different in the hypertensive versus normotensive state. We will utilize real time PCR to analyze gene expression, western blotting and ELISA to analyze and quantify protein samples, and siRNA technique to knock-down beta-arrestin 1 and 2 genes. One-way ANOVA will be employed to determine any significance differences among samples. A Bonferroni t-test will be employed to determine significance differences between a single treatment and the control sample. Findings from these studies will be important in establishing the importance of beta-arrestins in Ang II-mediated effects in the brain and may provide targets to design agents for the treatment of hypertension and other cardiovascular diseases.