Abstract 765: Oxidative Stress is Involved in Reduced Cardiac Contractile Performance of PPARalpha−/− Mice
The peroxisome proliferator-activated receptor alpha (PPARa) plays a critical role in the regulation of cardiac beta-oxidation. Its down-regulation during cardiac hypertrophy may contribute to the progressive deterioration of cardiac function. Cellular mechanisms linking PPARa deficiency to cardiac contractile dysfunction remain unknown. We assessed the hypothesis that PPARa−/− mice (KO, n=20) exhibited reduced cardiac performance and that oxidative damage of the myofibrillar apparatus contributed to contractile abnormalities. Age-matched wild type (WT, n=20) mice were used as controls. Left ventricular (LV) echocardiography, ex vivo papillary muscle assays and in vitro motility assays were used to assess global, intrinsic ventricular muscle performance and myosin mechanical properties respectively, in KO and WT mice. Three-nitrotyrosine (3-NT) formation and HNE protein-adducts, both markers of oxidative damage, were analyzed by Western blotting and immunolabelling. Radical scavenging capacity was analyzed by measuring protein levels and activities of catalase, glutathione peroxidase and mitochondrial and cytosolic superoxide dismutases (MnSOD and Cu/ZnSOD). Data are means +/− SEM, n=5 at least per group. Compared to WT, KO had 16% lower LV fractional shortening (p<0.05). Maximum shortening velocity and isometric tension were respectively 3.5- and 2-fold lower in KO than in WT. Myosin-based velocities were lower in KO than in WT (1.7+/−0.1 vs 1.3+/−0.2 microm/s, p<0.05) with no changes in the amount of alpha- and beta-myosin heavy chain (MHC). KO exhibited increased 3-NT staining compared to WT cardiomyocytes. MHC was identified by Western blot as the main nitrosylated protein and 3-NT MHC was 2-fold higher in KO (p<0.05). HNE-protein adduct, a marker of lipid peroxidation was 3-fold higher in KO than in WT. MnSOD (6.3+/−0.4 vs 8.6+/−0.5 A.U) and activity (3.2+/−0.2 vs 6.9+/−0.4 U/mg) were reduced in KO (each p<0.05). Expression and activities of Cu/Zn SOD, catalase, and glutathione peroxidase did not differ between groups. In conclusion, our data showed that lack of PPARa was associated with cardiac dysfunction and identified oxidative damage of myosin as a potential link between PPARa lack and cardiac dysfunction.