Abstract 116: A Novel Mediator of Heart Failure Development and Progression- Role of Manganese Superoxide Dismutase

Abstract

Manganese Superoxide Dismutase (MnSOD), an antioxidant enzyme that catalyzes the conversion of superoxide radicals (O 2 •- ) in mitochondria. Constitutive activation mitochondrial reactive oxygen species (ROS) has been implicated in both the pathogenesis and the progression of cardiovascular disease. Absence of SOD2 (gene that encodes MnSOD) is found to be embryonic lethal in animal models due to impairment of mitochondrial function, most noticeably in the heart. In our earlier investigation, we have shown that the MnSOD mimetic, MnTnBuOE-2-PyP 5+ distributes 3-fold more in mitochondria than in cytosol. The exceptional ability of MnTnBuOE-2-PyP 5+ to dismute O 2 •- parallels its ability to reduce ONOO– and CO3–. Based on our earlier reports, we have generated mice that specifically lack MnSOD in cardiomyocytes (Myh6-SOD2 Δ ). These mice showed early mortality ~4 months due to cardiac mitochondrial dysfunction. Oxidative phosphorylation (OXPHOS) in mitochondria is the predominant mode for O 2 consumption in cells, and the mitochondria are the primary source of ROS in cells due to leaked electrons. FACS analyses using Mito-Tracker Green indicated that the mass of mitochondria per cell was slightly decreased in the Myh6-SOD2 Δ to the wild type. We then examined OXPHOS levels in Myh6-SOD2 Δ v.s. Wild type using a Seahorse XF analyzer. The rate of oxygen consumption per cells was significantly lower in Myh6-SOD2 Δ cardiomyocytes than that in wild type. The most noticeable difference in the O 2 consumption was found in the presence of FCCP (H + ionophore / uncoupler). FCCP is an inner membrane pore opener which resets the proton gradient between the mitochondrial matrix and the interspace, resulting in continuous transport of protons and consuming O 2 at the maximum potential. Remarkably, while the FCCP treatment increased O 2 consumption in wild type, the treatment showed no effect on the O 2 consumption in the Myh6-SOD2 Δ cardiomyocytes. The result indicated that the low basal OXPHOS activity in Myh6-SOD2 Δ was due to unusually low OXPHOS potential. We examined glycolysis in these cells by measuring extracellular acidification (ECAR) and the pattern exactly opposite to that of oxygen consumption rate (OCR) was observed for glycolysis rates between Myh6-SOD2 Δ and Wild type.