Abstract 251: Mitochondrial Calcium Uniporter Regulates Proliferative Activity of Cardiac Fibroblasts Under Angiotensin II Stimulation

Abstract

Introduction: Cardiac fibrosis persists in patients with heart failure (HF) even during treatment with conventional HF therapies designed to control volume/pressure overload and restore cardiomyocyte function. This suggests a critical need to develop novel and effective anti-fibrotic therapies specifically targeting cardiac fibroblasts (CFs). CFs contribute to pathophysiological remodeling such as cardiac fibrosis after cardiac injury and/or during repair in response to various profibrotic stimuli in vivo such as angiotensin II (Ang II). Oxidative stress promotes pathological CF proliferation, but the detailed molecular mechanisms linking mitochondria and CF proliferation remain unclear. Hypothesis: Ang II stimulation promotes mitochondrial ROS (mROS) generation via mitochondrial Ca 2+ (mCa 2+ ) uptake, which subsequently activates mROS-dependent proliferative signaling in CFs. Methods: In CFs isolated from rat hearts, mCa 2+ uptake, mROS levels and mitochondrial morphology were measured using confocal microscopy with a mitochondria-targeted Ca 2+ biosensor mtRCamp1h, a mitochondrial superoxide-sensitive dye MitoSOX, and mitochondria-targeted GFP, respectively.. Results: Ang II (≥1 μM) stimulation induces Ca 2+ release from the endoplasmic reticulum (ER) followed by increased mCa 2+ , mROS, and mitochondrial fragmentation. In addition, Ang II activates ERK1/2- and p38-mediated proliferative pathways, which was inhibited by pretreatment with losartan, an Ang II receptor antagonist. Overexpression of a dominant-negative mCa 2+ uniporter (MCU) with pore domain mutations abolished Ang II-mediated mCa 2+ uptake and mROS generation, and prevented the activation of proliferative pathways. Pretreatment with a mitochondria-targeted antioxidant, mitoTEMPO, also significantly inhibited Ang II-mediated activation of the proliferative pathways without affecting ER-Ca 2+ release or mCa 2+ -uptake. Conclusion: The mROS generation via mCa 2+ accumulation and mitochondrial fragmentation resulting from Ang II stimulation activates mROS-dependent proliferative signaling pathways in CFs. The MCU-dependent mROS generation may serve as an important molecular switch for CF proliferation during cardiac stress.