Introduction The transition from cardiac hypertrophy to heart failure is characterized by metabolic changes, particularly downregulation of fatty acid metabolism in favor of increased glucose utilization. It has been shown that reduced fatty acid metabolism leads to an energy deficit and thus likely represents a maladaptive process that further promotes the development of heart failure.  

Purpose Carnitine palmitoyltransferase 1B (CPT1B) catalyzes the rate-limiting step of the carnitine shuttle and is an essential enzyme for fatty acid oxidation. Previous studies have shown down-regulation of CPT1B activity in various heart failure models, indicating an important role for this enzyme in metabolic remodeling. Furthermore, in a murine heart failure model heterozygous CPT1B knockout resulted in deterioration of cardiac function. Therefore, we hypothesize that CPT1B overexpression in heart failure could be a new therapeutic approach in heart failure.

Methods We overexpressed CPT1B in neonatal rat cardiomyocytes (NRVCMs) by transduction with targeted adeno-associated virus serotype 6 (AAV6-CMV-MLC1500-CPT1B); an AAV6-Luciferase virus served as control. Phenylephrine was applied to induce cellular hypertrophy. Mitochondrial potential was monitored by loading cardiomyocytes with membrane-potential-dependent dye tetramethylrhodamine ethyl ester and visualizing them by confocal microscopy. Mitochondrial ROS production was monitored using MitoSOX fluorescence measurements. Next, we induced myocardial hypertrophy and heart failure in 12-week-old mice by performing transverse aortic constriction (TAC). Cardiac CPT1B overexpression in vivo was achieved by transduction with targeted adeno-associated virus serotype 9 (AAV9-CMV-MLC1500-CPT1B) 2 weeks prior to TAC. AAV9-Luciferase treated mice served as controls. Left ventricular (LV) function was monitored by echocardiography. Induction of the fetal gene programme and profibrotic gene expression in the LV were measured by real time qPCR. Fibrosis deposition in the LV was determined by Masson’s trichrome staining, cell size was determined by staining with wheat germ agglutinin.

Results Overexpression of CPT1B in NRVCM significantly attenuated phenylephrine-induced hypertrophy and induction of the fetal gene program.  Furthermore, CPT1B overexpression resulted in a normalization of oxidative stress, as indicated by a decrease of mitochondrial reactive oxidative species, and a significant increase in mitochondrial membrane potential. In mice, AAV-mediated cardiomyocyte specific overexpression of CPT1B prior to TAC attenuated LV systolic dysfunction, cardiac hypertrophy, induction of the fetal gene program, cardiac fibrosis, and cardiac profibrotic gene expression.

Conclusion AAV-mediated cardiac CPT1B overexpression results in amelioration of cardiac dysfunction in mice subjected to transverse aortic constriction and may thus represent a promising novel treatment option for heart failure.