Metabolomics and Proteomics to Understand Fuel Use in Rat Model of High and Low Exercise Capacity.

Abstract

In humans, exercise capacity strongly associates with morbidity, mortality, and disease-risk. Maximal exercise capacity is a heritable trait, and rats selectively bred for high and low exercise capacity mimic phenotypes observed in humans: high capacity running rats (HCR) have lower metabolic-disease risk and increased longevity compared to low capacity running rats (LCR). In prior in vitro studies HCR skeletal muscle was shown to have higher fatty acid (FA) oxidizing capacity than LCR. We hypothesized that HCR would have enhanced FA utilization during in vivo exercise. In this study we use metabolomics and proteomics approaches to test this hypothesis and to explore metabolic differences between HCR and LCR during an increasing-intensity treadmill protocol (speed increasing 1 m/min every 2 min). Using indirect calorimetry, we found that during exercise HCR maintain high FA utilization, while LCR primarily utilize carbohydrates. Skeletal muscle and plasma were collected at rest, at 10 min of exercise (near exhaustion for LCR), and at 45 min of exercise (near exhaustion for HCR). Metabolite profiles showed HCR have increased muscle long-chain acyl-carnitines from rest to 10 min of exercise, indicating increased FA entry into the mitochondria of HCR. In contrast, LCR showed accumulation of short- and medium-chain muscle acylcarnitines from rest to 10 min of exercise, indicating inefficient substrate metabolism. We quantified muscle mitochondrial proteins and protein post-translational modifications (phosphorylation and acetylation) at rest and at 10 min of exercise. At rest, HCR have greater expression of enzymes within FA and branched-chain amino acid (BCAA) metabolic pathways than LCR. Compared to LCR, HCR have lower mitochondrial protein acetylation at rest and show protein deacetylation with 10 min of exercise, specifically in oxidative phosphorylation, citric acid cycle, FA and BCAA metabolic pathways. Consistent with a functional role of increased protein expression and lower protein acetylation within the BCAA pathway, HCR have greater BCAA metabolism during 10 min of exercise as measured by flux of intraperitoneally injected U-13C15N valine into catabolic intermediates. This study suggests enhanced FA and BCAA metabolism supports high running capacity and provides evidence for FA and BCAA pathway protein expression and acetylation in mediating enhanced fuel utilization.