Partial Knockout Of Skeletal Muscle Dynamin-Related Protein 1 Modulates Mitochondrial Quality Control Proteins After Exercise

Exercise remodels mitochondria in all processes of mitochondrial quality control (fission, fusion and mitophagy). Dynamin-Related Protein 1 (Drp1) is the main regulator for mitochondrial fission. Recent studies have reported that Drp1 was upregulated in skeletal muscle following exercise and was associated with mitochondrial adaptations to exercise. However, the role of Drp1 in exercise-induced mitochondrial remodeling is not fully elucidated. PURPOSE: To determine the role of a partial knockout of muscle specific Drp1 on regulatory proteins of mitochondrial quality control in mice post exercise. METHODS: 13-week-old C57Bl/6 J male and female wildtype (WT) and tamoxifen-induced skeletal muscle-specific Drp1 partial knockout (mDrp1+/-) mice were used for this study. Mice were randomly assigned to either sedentary (SED) or exercise (EX) group (n = 4-6/group). Exercise protocol included treadmill running (5% grade) at 15 m/min for 90 minutes. Blood lactate was measured using a lactate meter. Gastrocnemius muscle tissues were collected 3 hours post exercise for immunoblotting. Two-way (Gene x EX) ANOVA was used to test statistical differences. RESULTS: Although not statistically significant, post exercise blood lactate concentration was 53% higher in mDrp1+/- mice than WT mice (P = 0.164). Drp1 (Ser616 and Ser637) phosphorylation and Mitofusin 2 (MFN2) protein expression were increased after exercise regardless of their genotype (main effect of exercise, P = 0.086, 0.021 and 0.005, respectively). Interestingly, the increases of Drp1 (Ser616 and Ser637) phosphorylation after exercise were compromised in mDrp1+/- mice compared to WT mice (11% vs. 27% and 26% vs. 65%, respectively). Similarly, mitochondrial fission factor (MFF), an adaptor protein of Drp1, displayed differential responses to exercise in mDrp1+/- and WT mice (-11% vs. 9%). The ratio of LC3BII:I, a marker of autophagy, was significantly elevated following exercise in skeletal muscles from both WT and mDrp1+/- mice (main effect of exercise, P = 0.025), but the magnitude was greater in mDrp1+/- mice when compared to WT mice (57% vs. 14%). CONCLUSION: Our data suggest that Drp1 may play an important role in mitochondria remodeling, specifically in regulating mitochondrial fission activation and autophagosome formation in response to exercise. This study was supported by the National Institute of Health (R15DK131512).