UC San Diego SearchMenu
2017 Research Showcase
SB Abstracts
Abstract Title : 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 wild type (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.
Advisor : JU CHEN
Abstract Title : Function of BAG3
Abstract : The central question to be addressed by my research project is how Bcl-2-associated athanogene 3 (BAG3), a member of a conserved family of cyto-protective molecular co-chaperones interact and stabilize small heat shock proteins. Cardiomyocytes have developed a multilayer protein quality control (PQC) system to maintain protein homeostasis and cardiac function. BAG3 is one of the important co-chaperones that help stabilize nascent polypeptide chain and refold aberrant proteins. BAG3 knockout leads to growth retardation and development of dilated cardiomyopathy in mice. The BAG domain of BAG3 binds to nucleotide binding domain (NBD) of the ATP-dependent chaperone HSP70. HSP70 is heat shock protein that helps fold nascent and misfolded proteins. It has been identified that the heterozygous p.Pro209Leu (P209L) mutation in humans causes severe muscular dystrophy and cardiomyopathy. However, the molecular pathomechanism how this mutation leads to disease is not known. The P209 residue resides in the IPV motif of BAG3. The IPV domains in BAG3 are a conserved amino acid sequence made up of Isoleucine, Proline, and Valine and have been shown to bind small heat shock protein (sHSP) such as HSPB8. sHPSs are ATP independent chaperone proteins that prevent aggregation of misfolded proteins. We hypothesize the P209L mutation impairs the interaction between BAG3 and sHSPs, resulting in cardiomyopathy. In this project, I will use biochemical methods to test how P209L missense mutation change the BAG3 binding affinity to HSPB8. I also will use BAG3 P209L knock-in mouse model to study the consequences of BAG3 P209L mutation at the organismal level.