Conditional PPARγ Knockout From Cardiomyocytes Of Adult Mice Induces Cardiac Dysfunction And Hypertrophy

Objective:Peroxisome proliferator-activated receptors (PPARs) are key nuclear receptors with three subtypes (α,δand y), which differentially regulate transcriptional activities of proteins involved in lipid and glucose metabolisms. It is well documented that PPARαandδregulate largely overlapping genes involved in lipid and glucose metabolisms with distinctive patterns. However, the role of PPARy regulating lipid and glucose metabolisms in the heart remains relatively unclear. In this project, we are going to study the influence to energy metabolism and cardiac function in conditional PPARy knockout from cardiomyocyte.Method:In this study, we assessed a Tamoxifen inducible PPARy knockout line (TMPG), which was bred by crossing the a-MyHC driven Mer-Cre-Mer (MCM) transgenic line with the floxed PPARy line. Cardiomyocyte-restricted PPARy knockout was achieved in adult mice with 5-day treatment of Tamoxifen (IP). Quantitative real time PCR (QPCR) and Western blot studies confirmed that cardiomyocyte PPARy mRNA and protein were largely eliminated in the TMPG mice. Quantitative real time PCR (QPCR) and Western blot studies detect the transcription and protein level change of lipid uptake and oxidation gene. We measured cardiac construction and fuction through echocardiography, cardiac lipid content and cardiac metabolism through isolated working heart. We also examined pathological alteration.Result:QPCR revealed that transcript expression of SOD1 and SOD2 were respectively decreased by about 67 and 23% in TMPG hearts compared with TMCM controls. Moreover, transcript levels of important proteins in fatty acid uptake and oxidation, such as CD36, heart type-fatty acid binding protein (H-FABP), and carnitine palmitoyltransferase I (CPT-I) were also respectively reduced by about 65,30 and 50%in RNA samples extracted from left ventricles of TMPG compared with that of TMCM mice. Western blot showed that the protein level of CD36, H-FABP, carnitine palmitoyltransferase II (CPT II) were correspondingly decreased in TMPG hearts. As a result, myocardial total phospholipid and total triglyceride contents were decreased about 7% and 50% in TMPG relative to TMCM hearts, respectively. Induced cardiomyocyte-restricted PPARy knockout in adult mice for 2 weeks led to modest cardiac hypertrophy with increased heart weight to body weight ratio, and induced cardiomyocyte-restricted PPARy knockout in adult mice for 3 months led to even more severe cardiac hypertrophy with increased IVSs, IVSd and heart weight to body weight ratio. The result of isolated working heart indicated decrease of cardiac lipid metabolism and cardiac dysfunction, but glucose metabolism was no markedly change.Conclusion:Tamoxifen induced, cardiomyocyte-restricted PPARy knockout in adult hearts leads to decreased expression of SOD1 and SOD2, correspondingly suppresses oxyradical scavenging capacity,and decreases expression of key protein involved in lipid metabolism, consequently leads to attenuated of fatty acid metabolism, myocardial lipid content in heart, modest cardiac hypertrophy and cardiac dysfunction. These results indicate that PPARy is an essential transcription factor in controlling gene expression of fatty acid uptake, fatty acid oxidation and endogenous anti-oxidants, governing cardiac energy metabolism and function.