Abstract 16855: β-arrestins Regulate Mitochondrial Oxidative Stress and Collagen Synthesis in Adult Human Cardiac Fibroblasts
Oxidative stress in cardiac fibroblasts (CF) promotes transformation to myofibroblasts and collagen synthesis which can lead to myocardial fibrosis, a precursor to heart failure (HF). NADPH oxidase 4 (Nox4) is a major source of cardiac reactive oxygen species (ROS), however, mechanisms of Nox4 regulation are unclear. β-arrestins are scaffold proteins which signal in G protein-dependent and independent manners including ERK activation. We hypothesize that β-arrestins can regulate oxidative stress in CF in a Nox4-dependent manner and increase collagen synthesis in the setting of HF. CF were isolated from normal (control) and failing (HF) adult human left ventricles. Mitochondrial oxidative stress, measured by MitoSOX staining, is increased 2-fold in HF versus control CF. Nox4 expression is upregulated > 4 fold in HF. Knockdown of Nox4 in both control and HF CF resulted in a significant inhibition of mitochondrial ROS. siRNA-mediated Nox4 knockdown in failing CF lead to a > 30% decrease in both basal and TGF-β stimulated collagen synthesis. CF β-arrestin1 and 2 expression are increased 2-3 fold in HF versus control. Knockdown of β-arrestin1 or 2 in failing CF decreased ROS by 40% and Nox4 expression by more than 50%. Overexpression of β-arrestin1 or 2 in normal CF increased Nox4 expression and ROS production 2-fold. These increases in oxidative stress were inhibited by pre-treatment with the Nox-inhibitor, apocynin, or ERK-inhibitor, PD 98059. Upregulation of Nox4 appears to be a primary mechanism for the increase in ROS production in failing human CF, which stimulates collagen deposition. β-arrestin expression is also upregulated in failing CF and appears to play an important and novel role in the regulation of mitochondrial ROS production via Nox4. The specific mechanism for this effect is potentially ERK mediated and requires further investigation. Targeted inhibition of β-arrestins in CF may decrease oxidative stress as well as pathological cardiac fibrosis and adverse remodeling.
- © 2013 by American Heart Association, Inc.