Aerobic Training Alleviates Muscle Atrophy by Promoting the Proliferation of Skeletal Muscle Satellite Cells in Myotonic Dystrophy Type 1 by Inhibiting Glycolysis via the Upregulation of MBNL1.

Background: Skeletal muscle atrophy in myotonic dystrophy type 1 (DM1) is caused by abnormal skeletal muscle satellite cell (SSC) proliferation due to increased glycolysis, which impairs muscle regeneration. In DM1, RNA foci sequester muscleblind-like protein 1 (MBNL1) in the nucleus, inhibiting its role in regulating SSC proliferation. Aerobic training reduces glycolysis and increases SSC proliferation and muscle fiber volume. This study aimed to investigate whether aerobic training prevents muscle atrophy in DM1 through the regulation of glycolysis via MBNL1.

Methods: In this study, we used the HSALR transgenic mice (DM1 mice model) to investigate the effects of aerobic training on skeletal muscle atrophy and its molecular mechanisms. HSALR mice were subjected to 4 weeks of aerobic training. After aerobic training, hindlimb grip, and myofiber mean cross-sectional area (CSA) detected by haematoxylin and eosin (HE) staining were performed. In DM1 primary SSCs, cell proliferation was assessed using Pax7 and MyoD immunofluorescence and CCK-8 assays, RNA foci were detected by RNA fluorescence in situ hybridization, and total MBNL1 expression was measured by western blot. We also used lentivirus to knock down MBNL1 in DM1 primary SSCs and performed RNA sequencing and extracellular acidification rate (ECAR). Furthermore, glycolysis detected by ECAR and oxygen consumption rate (OCR) assays were performed in WT, Sedentary, and Training group SSCs. Glycolysis was inhibited with shikonin, a glycolysis inhibitor, and the proliferation of DM1 SSCs was subsequently evaluated. Finally, we engineered an adeno-associated virus specifically targeting MBNL1 to knock down MBNL1 in DM1 mice. Subsequently, we assessed hindlimb grip strength and CSA in vivo, as well as the glycolytic capacity and proliferative capacity of DM1 SSCs in vitro.

Results: Aerobic training increased hindlimb grip strength and the average myofiber CSA in DM1 mice. Additionally, aerobic training reduced RNA foci, upregulated MBNL1, and promoted SSC proliferation. Gene-set enrichment analysis (GSEA) indicated that glycolytic processes were enriched following the knockdown of MBNL1. Furthermore, ECAR showed glycolysis was enhanced after the knockdown of MBNL1. Aerobic training reduced elevated glycolysis in DM1 mice and primary SSCs. Treatment with shikonin promoted DM1 SSC proliferation. However, MBNL1 knockdown was shown to abolish the reduced glycolysis and increased proliferation capability of SSCs due to aerobic training.

Conclusion: Taken together, aerobic training suppresses glycolysis in SSCs via the upregulation of MBNL1, thereby enhancing SSC proliferation and alleviating muscle atrophy.