microRNA-1 Regulates Metabolic Flexibility by Programming Adult Skeletal Muscle Pyruvate Metabolism

Metabolic flexibility refers to the ability of a tissue to adjust cellular fuel choice in response to conditional changes in metabolic demand and activity. A loss of metabolic flexibility is now recognized as a defining feature of various diseases and cellular dysfunction. In this study, using an inducible, skeletal muscle-specific knockout (KO) mouse, we found microRNA-1 (miR-1), the most abundant microRNA (miRNA) in skeletal muscle, was necessary to maintain whole-body metabolic flexibility. This was demonstrated by a loss of diurnal oscillations in whole-body respiratory exchange ratio and higher fasting blood glucose in miR-1 KO mice. Argonaute 2 enhanced crosslinking and immunoprecipitation sequencing (AGO2 eCLIP-seq) and RNA-seq analyses identified, for the first time, bona fide miR-1 target genes in adult skeletal muscle that regulated pyruvate metabolism. Comprehensive bioenergetic phenotyping combined with skeletal muscle proteomics and metabolomics showed that miR-1 was necessary to maintain metabolic flexibility by regulating pyruvate metabolism through mechanisms including the alternative splicing of pyruvate kinase (Pkm). The loss of metabolic flexibility in the miR-1 KO mouse was rescued by pharmacological inhibition of the miR-1 target, monocarboxylate transporter 4 (MCT4), which redirects glycolytic carbon flux toward oxidation. The maintenance of metabolic flexibility by miR-1 was necessary for sustained endurance activity in mice and in C. elegans. The physiological down-regulation of miR-1 in response to a hypertrophic stimulus in both humans and mice caused a similar metabolic reprogramming necessary for muscle cell growth. Taken together, these data identify a novel post-transcriptional mechanism of whole-body metabolism regulation mediated by a tissue-specific miRNA. Overall design: At 4 months of age, HSA-MCM; miR-1-1f/f; miR-1-2f/f (HSA-miR-1) were treated with Vehicle (V, 15% ethanol in sunflower seed oil, n=4 female mice) or tamoxifen- to induce knockout (KO) of miR-1 (T, 2 mg/day, n=4 female mice) for 5 days. After an 8-week washout, total RNA was isolated from gastrocnemius muscles from V and T-treated (KO) for bulk RNA-sequencing.