Cardiac-specific LRP6 knockout induces lipid accumulation through Drp1/CPT1b pathway in adult mice

We recently reported low-density lipoprotein receptor-related protein 6 (LRP6) decreased in dilated cardiomyopathy hearts, and cardiac-specific knockout mice displayed lethal heart failure through activation of dynamin-related protein 1 (Drp1). We also observed lipid accumulation in LRP6 deficiency hearts, but the detailed molecular mechanisms are unclear. Here, we detected fatty acids components in LRP6 deficiency hearts and explored the potential molecular mechanisms. Fatty acid analysis by GC-FID/MS revealed cardiac-specific LRP6 knockout induced the higher level of total fatty acids and some medium-long-chain fatty acids (C16:0, C18:1n9 and C18:2n6) than in control hearts. Carnitine palmitoyltransferase 1b (CPT1b), a rate-limiting enzyme of mitochondrial β-oxidation in adult heart, was sharply decreased in LRP6 deficiency hearts, coincident with the activation of Drp1. Drp1 inhibitor greatly improved cardiac dysfunction and attenuated the increase in total fatty acids and fatty acids C16:0, C18:1n9 in LRP6 deficiency hearts. It also greatly inhibited the decrease in the cardiac expression of CPT1b and the transcriptional factors CCCTC-binding factor (CTCF) and c-Myc induced by cardiac-specific LRP6 knockout in mice. C-Myc but not CTCF was identified to regulate CPT1b expression and lipid accumulation in cardiomyocytes in vitro. The present study indicated cardiac-specific LRP6 knockout induced lipid accumulation by Drp1/CPT1b pathway in adult mice, and c-Myc is involved in the process. It suggests that LRP6 regulates fatty acid metabolism in adult heart.