Abstract 550: Rac Up-Regulates Angiotensin II Type 1 Receptors through ROS and NF-κB-Dependent Interleukin-1β Production in Rat Cardiac Fibroblasts
Various factors including angiotensin (Ang) II type 1 receptor regulate cardiac remodeling. One of features of remodeling is the excess production of extracellular matrix from cardiac fibroblasts. Up-regulation of angiotensin (Ang) II type 1 receptor (AT1R) enhances the ability of fibroblast to produce extracellular matrix. However, the mechanism responsible for up-regulation of AT1R is still unknown. Here, we demonstrate that a small GTP-binding protein Rac regulates the expression of AT1R. During the study analyzing the effects of Pertussis toxin (PTX) treatment on AT1R function in rat neonatal cardiac fibroblasts, we have found that PTX treatment enhanced the intracellular Ca2+ concentration ([Ca2+]i) by Ang II stimulation. Microarray analysis of mRNAs from PTX-treated or untreated cells revealed that PTX treatment enhances the induction of interleukin (IL)-1β among cytokines. The addition of anti-IL-1β antibody inhibited PTX-treated enhancement of [Ca2+]i by Ang II stimulation. The PTX-induced increases in IL-1β mRNA required nuclear factor (NF)-κ B activation that was completely suppressed by dominant negative (DN)-Rac and DN-p47phox. Treatment with PTX for short term resulted in activation and membrane translocation of Rac, and enhancement of reactive oxygen species (ROS) production. The PTX-induced ROS production, degradation of IκBα, and increase in expression of AT1R were completely suppressed by DN-Rac, suggesting that Rac up-regulates AT1R through NADPH oxidase-mediated ROS production and NF-κB activation in cardiac fibroblasts. As IL-1β treatment also increased AT1R expression and enhances Ang II-stimulated [Ca2+]i through a Rac-dependent pathway. These results suggest that PTX treatment produces IL-1β through Rac-ROS-NF-κB pathway, and the produced IL-1β participates in AT1R up-regulation in rat cardiac fibroblasts.