Loss of caveolin-1 alters cardiac mitochondrial function and increases susceptibility to stress

Abstract

Introduction: Cardiovascular disease (CVD) is the leading cause of morbidity and mortality in the United States. Caveolae, membrane micro-domains enriched in cholesterol, glycosphingolipids, sphingomyelin and the protein caveolin, are critical to ischemic tolerance. We have previously described a specific role for caveolin-3 (Cav-3) in cardiac protection via regulation of mitochondrial function; however, little is known about the role of caveolin-1 (Cav-1) in cardiac mitochondrial bioenergetics. We hypothesized that Cav-1 is crucial in maintaining healthy cardiac mitochondria. Material and Methods: We performed a series of experiments to assess the role of Cav-1 upon mitochondrial functionality, comparing heart tissues and isolated mitochondria from wildtype (WT) and global Cav-1 knock-out (KO) mice. Percoll-purified WT mitochondria were immunogold labeled and imaged by TEM to localize Cav-1 protein to specific mitochondrial membranes. Furthermore, oxygen consumption was evaluated in isolated papillary muscle fibers by high-resolution respirometry using Oroboros O2k oxygraph. Superoxide free radical production was investigated by electron paramagnetic resonance imaging (EPR) using the spin probe DEPMPO in isolated mitochondria. Results: Immunogold labeling showed Cav-1 localization to outer and inner mitochondrial membranes. In Cav-1 KO mice relative oxygen flux was slightly increased in the presence of complex I substrates and ADP. Furthermore, in Cav-1 KO mice, cytochrome c response (a marker for outer mitochondrial damage) was significantly correlated to total complex I & II respiration (malate, pyruvate, glutamate, ADP, and succinate) with increased respiration at higher cytochrome c responses, indicating potential outer mitochondrial membrane damage. ROS was decreased in Cav-1 KO mice during state IV respiration with complex I & II substrates measured by EPR suggesting overall decreased mitochondrial function. Conclusion: Cav-1 may be a critical regulator of cardiac mitochondrial function. Cav-1 may therefore be a viable therapeutic target to alter cardiac mitochondrial bioenergetics.