High-fat feeding in cardiomyocyte-restricted PPARδ knockout mice leads to cardiac overexpression of lipid metabolic genes but fails to rescue cardiac phenotypes

Peroxisome proliferator-activated receptor δ (PPARδ) is an essential determinant of basal myocardial fatty acid oxidation (FAO) and bioenergetics. We wished to determine whether increased lipid loading affects the PPARδ deficient heart in transcriptional regulation of FAO and in the development of cardiac pathology. Cardiomyocyte-restricted PPARδ knockout (CR-PPARδ−/−) and control (α-MyHC-Cre) mice were subjected to 48 h of fasting and to a long-term maintenance on a (28 weeks) high-fat diet (HFD). The expression of key FAO proteins in heart was examined. Serum lipid profiles, cardiac pathology, and changes of various transduction signaling pathways were also examined. Mice subjected to fasting exhibited upregulated transcript expression of FAO genes in the CR-PPARδ−/− hearts. Moreover, long-term HFD in CR-PPARδ−/− mice induced a strikingly greater transcriptional response. After HFD, genes encoding key FAO enzymes were expressed remarkably more in CR-PPARδ−/− hearts than in those of control mice. Despite the marked rise of FAO gene expression, corresponding protein expression remained low in the CR-PPARδ−/− heart, accompanied by abnormalities in sarcomere structures and mitochondria that were similar to those of CR-PPARδ−/− hearts with regular chow feeding. The CR-PPARδ−/− mice displayed increased expression of PPARγ co-activator-1α (PGC-1α) and PPARα in the heart with deactivated Akt and p42/44 MAPK signaling in response to HFD. We conclude that PPARδ is an essential determinant of myocardial FAO. Increased lipid intake activates cardiac expression of FAO genes via PPARα/PGC-1α pathway, albeit it is not sufficient to improve cardiac pathology due to PPARδ deficiency.