Abstract
Mitochondrial lipid overload in skeletal muscle contributes to insulin resistance, and strategies limiting this lipid pressure improve glucose homeostasis; however, comprehensive cellular adaptations that occur in response to such an intervention have not been reported. Herein, mice with skeletal muscle-specific deletion of carnitine palmitoyltransferase 1b (Cpt1bM-/-), which limits mitochondrial lipid entry, were fed a moderate fat (25%) diet, and samples were subjected to a multimodal analysis merging transcriptomics, proteomics, and nontargeted metabolomics to characterize the coordinated multilevel cellular responses that occur when mitochondrial lipid burden is mitigated. Limiting mitochondrial fat entry predictably improves glucose homeostasis; however, remodeling of glucose metabolism pathways pales compared with adaptations in amino acid and lipid metabolism pathways, shifts in nucleotide metabolites, and biogenesis of mitochondria and peroxisomes. Despite impaired fat utilization, Cpt1bM-/- mice have increased acetyl-CoA (14-fold) and NADH (2-fold), indicating metabolic shifts yield sufficient precursors to meet energy demand; however, this does not translate to enhance energy status as Cpt1bM-/- mice have low ATP and high AMP levels, signifying energy deficit. Comparative analysis of transcriptomic data with disease-associated gene-sets not only predicted reduced risk of glucose metabolism disorders but was also consistent with lower risk for hepatic steatosis, cardiac hypertrophy, and premature death. Collectively, these results suggest induction of metabolic inefficiency under conditions of energy surfeit likely contributes to improvements in metabolic health when mitochondrial lipid burden is mitigated. Moreover, the breadth of disease states to which mechanisms induced by muscle-specific Cpt1b inhibition may mediate health benefits could be more extensive than previously predicted.
Highlights
Mitochondrial lipid overload in skeletal muscle contributes to insulin resistance, and strategies limiting this lipid pressure improve glucose homeostasis; comprehensive cellular adaptations that occur in response to such an intervention have not been reported
To further identify metabolites that were key contributors to the top principal components explaining the difference between Cpt1bfl/fl versus Cpt1bMϪ/Ϫ mice, we generated a variable-loading heatmap for the first 10 principal components that explains 95% of the variance within the dataset, and we further annotated it with the log ratio and false discovery rates of the metabolites (Fig. 1E)
Results confirmed the extensive remodeling of these pathways, with the most pronounced adaptations being observed in amino acid and lipid metabolism pathways, whereas shifts in glucose metabolism were modest
Summary
Mitochondrial lipid overload in skeletal muscle contributes to insulin resistance, and strategies limiting this lipid pressure improve glucose homeostasis; comprehensive cellular adaptations that occur in response to such an intervention have not been reported. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health. Comparative analysis of transcriptomic data with diseaseassociated gene-sets predicted reduced risk of glucose metabolism disorders but was consistent with lower risk for hepatic steatosis, cardiac hypertrophy, and premature death. These results suggest induction of metabolic inefficiency under conditions of energy surfeit likely contributes to improvements in metabolic health when mitochondrial lipid burden is mitigated. The breadth of disease states to which mechanisms induced by muscle-specific Cpt1b inhibition may mediate health benefits could be more extensive than previously predicted
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