Inhibiting Mitochondrial Fission Protein Drp1 Enhances Mitochondrial Structure, Attenuates Lipid Peroxidation, and Improves Muscle Strength in D2-mdx Mice
Authors: Rosen H. Grace , Berger Nicolas , Hodge Shantel , Fujishiro Atsutaro , Lourie Jared , Kapadia Vrusti , Zou Kai 
Published: May 2024

Duchenne Muscular Dystrophy (DMD) is the most severe muscular dystrophy manifested by progressive muscle wasting and weakness. Mitochondrial dysfunction and reactive oxygen species (ROS) accumulation are early pathological features of DMD and precede myopathy. A fine balance of mitochondrial dynamics (fission and fusion) is crucial to maintain mitochondrial function and skeletal muscle health. We recently reported excessive activation of Dynamin-Related Protein 1 (Drp1)-mediated mitochondrial fission in two animal models of DMD. Mitochondrial fission inhibitor‐1 (Mdivi‐1) is an effective pharmacological inhibitor of Drp1-mediated mitochondrial fission and has been shown benefits in numerous diseases. The objective of the study was to test whether Mdivi-1 could improve skeletal muscle mitochondrial structure, function and muscle strength in D2- mdx mouse model of DMD. Methods: 9-10-week-old male D2- mdx mice were treated with either Mdivi-1 (I.P., 40 mg/kg BW, mdx/Mdivi-1) or vehicle (2%DMSO in PBS, mdx/VEH) for 5 weeks. D2-wildtype mice treated with vehicle (WT/VEH) were used as the control (n=8/group). Muscle strength was measured using a grip strength meter. Mitochondria were isolated from quad muscles collected 24 hours after the last injection to measure mitochondrial respiration. Transmission Electron Microscopy was used to image mitochondrial structure. Gastrocnemius muscles were collected for immunoblot analysis. Results: Grip strength was significantly lower in muscles from D2- mdx mice compared to WT controls (P = 0.01) but was improved in mdx+Mdivi-1 mice (P = 0.05). Mitochondrial fission protein markers, Drp1(Ser616) phosphorylation and Fis1 were markedly higher in skeletal muscles from mdx/VEH than WT/VEH (P= 0.009 and 0.001) but were attenuated in mdx/Mdivi-1 mice (P = 0.041 and 0.1), indicating a rebalance of mitochondrial dynamics. This rebalance subsequently led to improvement in skeletal muscle mitochondrial structure in mdx/Mdivi-1 mice, with evidence of lower numbers of damaged mitochondria and reduced circularity (P = 0.005 and 0.038). Although not statistically significant, ADP and FCCP-stimulated mitochondrial respiration were enhanced by 93.8% and 92.4% in mdx+Mdivi-1 mice compared to mdx/VEH. In addition, lipid peroxidation marker, 4-HNE was significantly higher in mdx/VEH group in comparison to WT/VEH group (P = <0.0001), but was attenuated in mdx/Mdivi-1 mice (P = 0.08). Conclusion: These data demonstrate that inhibition of Drp1-mediated mitochondrial fission is effective in improving muscular strength in D2- mdx mice, which is at least partly due to enhanced mitochondrial dynamics, structure and attenuated lipid peroxidation. Mdivi-1 may be a viable treatment for DMD. National Institute of Health (R15DK131512). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.