Effects of Partial Ablation of Skeletal Muscle Drp1 on Mitochondrial Quality Control Proteins Following Exercise

Dynamin-related protein 1 (Drp1) is a key regulator of mitochondrial fission and plays an essential role in skeletal muscle homeostasis. Recent studies reported that skeletal muscle Drp1 phosphorylation was upregulated following acute exercise and inhibiting Drp1 resulted in reduced exercise capacity in mice, suggesting Drp1 may play an important role in regulating mitochondrial remodeling following exercise. Objective: To determine the effects of partial ablation of skeletal muscle Drp1 on mitochondrial quality control markers following an acute bout of exercise. Hypothesis: Partial ablation of skeletal muscle Drp1 would decrease Drp1 phosphorylation, resulting in upregulation of mitophagy and autophagy markers following exercise compared to wildtype mice. Methods: C57Bl/6J male and female wildtype (WT) and tamoxifen-induced skeletal muscle-specific Drp1 partial knockout (mDrp1 +/- ) mice either stayed sedentary (SED) or were subjected to an acute bout of exercise (treadmill running (5% grade) at 15 m/min) for 90 minutes. Skeletal muscle tissues were collected from either immediately (EX) or 3 hours (EX+3h) post exercise (n=6-10/group) for immunoblotting. Results: Partial ablation of Drp1 resulted in reduced Drp1 Ser616 and Ser637 phosphorylation, Mitochondrial Fission Factor (MFF) protein content, MFF Ser146 phosphorylation, and Parkin protein content (mitophagy marker), regardless of exercise (genotype main effect, p<0.05). In contrast, partial ablation of Drp1 enhanced Parkin Ser65 phosphorylation regardless of exercise (genotype main effect, p<0.05). With regards to exercise response, Drp1 Ser616 and Ser637 phosphorylation was increased in both WT and mDrp1 +/- mice immediately post exercise (exercise main effect, p<0.05 and P=0.054, respectively), but remained lower in mDrp1 +/- mice compared to WT. Strikingly, Parkin expression was decreased in mDrp1 +/- /EX+3h compared to mDrp1 +/- /SED (-21.1%), while increased in WT/EX+3h compared to WT/SED (10.4%). In mitochondrial enriched fractions, Drp1 was increased by 26.7% immediately post exercise in WT mice, while decreased by -39.1% in mDrp1 +/- mice, compared to their sedentary counterparts. LC3BII protein was increased following exercise (exercise main effect, p<0.05). Although not significant, LC3BII was increased by 35.9% in WT mice, while was only increased by 16.9% in mDrp1 +/- mice immediately post exercise. Similarly, mitochondrial LAMP1 was increased in WT/EX+3h (6.9%) compared to WT/SED, while it was decreased in mDrp1 +/- /EX+3h (-15.4%) compared to mDrp1 +/- /SED. Conclusion: Our data suggest that partial ablation of skeletal muscle Drp1 reduces mitochondrial fission and Parkin-mediated mitophagy machinery, which may compromise the activation of mitophagy in skeletal muscle following exercise. This study was supported by the National Institute of Health (R15DK131512) and UMass Boston Undergraduate Research Funds. This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.