Metabolic and Transcriptional Alterations in the Early Stages of Cardiac Fuel Switch Hint at Novel mTOR-mediated Regulation of Hypertrophy [Agilent Expression]

1. Background- Long-chain acyl-CoA synthetases (ACSL) catalyze the conversion of long-chain fatty acids (FA) to fatty acyl-CoAs. Cardiac-specific ACSL1 knockout results in a shift towards glycolysis that promotes mTORC1-mediated ventricular hypertrophy. We used unbiased metabolomics and gene expression analyses to examine the early effects of genetic inactivation of FA oxidation on cardiac metabolism and function. 2. Methods and Results- Compared to WT hearts, global cardiac transcriptional analysis revealed differential expression of 245 genes in Acsl1H-/- hearts 2 weeks after Acsl1 ablation. Comparison of the 2- and 10-week transcriptional responses uncovered 139 genes whose expression was uniquely changed upon short-term cardiac inactivation of ACSL1. In particular, partial ACSL1 ablation led to the distinct upregulation of fibrosis genes, a phenomenon not observed after complete ACSL1 knockout. Metabolomic analysis identified 65 metabolites altered in hearts displaying partially reduced ACSL activity, whereas rapamycin treatment normalized the cardiac metabolomic fingerprint. Chronic mTOR inhibition via rapamycin treatment revealed novel mTORC1 targets involved in fibrosis, amino acid catabolism, and mitochondrial transport and metabolism. 3. Conclusions- Short-term cardiac-specific ACSL1 inactivation (Acsl1H-/-) resulted in metabolic and transcriptional derangements distinct from those observed upon complete ACSL1 knockout, leading to the identification of novel mTORC1 targets that regulate cardiac hypertrophy development, and suggesting heart-specific mTOR signaling that occurs during the early stages of substrate switching. Moreover, the rate of increased glucose use correlated negatively with hypertrophy development, strongly suggesting that hearts do not become hypertrophied if they can compensate or switch faster from FA to glucose use. Two-condition experiment, cadiac gene expression of Acsl1H-/- vs Acsl1flox/flox mice 2 weeks or 10 weeks after tamoxifen treatment. Biological replicates: 3-4 per condition.