Abstract 357: Manganese Superoxide Dismutase: a Novel Mediator of Heart Failure Development and Progression

Abstract

Manganese Superoxide Dismutase (MnSOD), an antioxidant enzyme that catalyzes the conversion of superoxide radicals (O₂•-) 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-PyP⁵⁺ distributes 3-fold more in mitochondria than in cytosol. The exceptional ability of MnTnBuOE-2-PyP⁵⁺ to dismute O₂•- parallels its ability to reduce ONOO– and CO3–. Based on our earlier reports, we have generated mice that specifically lack MnSOD in cardiomyocytes (Mhy6-SOD2^Δ). These mice showed early mortality ~4 months due to cardiac mitochondrial dysfunction. Oxidative phosphorylation (OXPHOS) in mitochondria is the predominant mode for O₂ 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 Mhy6-SOD2^Δ to the wild type. We then examined OXPHOS levels in Mhy6-SOD2^Δ v.s. wild type using a Seahorse XF analyzer. The rate of oxygen consumption per cells was signi[[Unable to Display Character: fi]]cantly lower in Mhy6-SOD2^Δ cardiomyocytes than that in wild type. The most noticeable difference in the O₂ 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 O₂ at the maximum potential. Remarkably, while the FCCP treatment increased O₂ consumption in wild type, the treatment showed no effect on the O₂ consumption in the Mhy6-SOD2^Δ cardiomyocytes. The result indicated that the low basal OXPHOS activity in Mhy6-SOD2^Δ was due to unusually low OXPHOS potential. We examined glycolysis in these cells by measuring extracellular acidi[[Unable to Display Character: fi]]cation (ECAR) and the pattern exactly opposite to that of oxygen consumption rate (OCR) was observed for glycolysis rates between Mhy6-SOD2^Δ and wild type.