Abstract Body:
Background: Metabolic remodeling is a hallmark of the failing heart. Oncometabolic stress during cancer increases the activity and abundance of the ATP-dependent citrate lyase (ACL, Acly), which promotes histone acetylation and cardiac adaptation. ACL is critical for the de novo synthesis of lipids, but how these metabolic alterations contribute to cardiac structural and functional changes remains unclear.
Methods: We utilized MyH6-Cas9 mice (male and female) and CRISPR/Cas9 gene editing to generate a cardiac-specific Acly knockdown (AclyKD) mouse model. To assess how the loss of Acly impacts cardiac energy substrate metabolism, we conducted positron emission tomography in vivo and ex vivo stable isotope tracer labelling using working heart preparation. We conducted a multi-omics analysis using RNA-sequencing and mass spectrometry-based metabolomics. Experimental data were integrated into computational modelling using the metabolic network CardioNet to identify significantly dysregulated metabolic processes at a systems level.
Results: Loss of ACL expression causes a left-ventricular cardiomyopathy by histology and echocardiography. FDG-PET/CT imaging in male and female mice demonstrated an increased glucose uptake and utilization in AclyKD mice, suggesting a substrate switch from fatty acid oxidation towards glucose. These findings were corroborated by stable isotope tracing, demonstrating that AclyKD suppresses fatty acid oxidation while enhancing lipid remodelling. AclyKD also reduced the efflux of glucose-derived citrate from the mitochondria into the cytosol, confirming that citrate is required for reductive metabolism in the heart. Computational flux analysis and integrative multi-omics analysis indicate that ACL activity supports lipid biosynthesis in the heart. Blocking mitochondrial isocitrate dehydrogenase or alpha-ketoglutarate dehydrogenase sensitized cardiomyocytes to ACL inhibition, and overexpressing cytosolic isocitrate dehydrogenase was sufficient to prevent citrate accumulation.
Conclusions: Our work demonstrates a previously undescribed function of ACL as a regulator of cardiac energy substrate metabolism and lipid modulation.