The Role Of Mitochondrial Dysfunction And Redox Disturbances After Non-invasive Anterior Cruciate Ligament Injury

Anterior cruciate ligament (ACL) injury results in protracted quadriceps atrophy, however the mechanisms that drive atrophic pathways remain undefined. Mounting evidence has revealed that mitochondrial dysfunction and redox disturbances are causal events in the initiation of muscle atrophy, yet the extent to which mitochondria damage play a key role in quadriceps muscle atrophy after ACL injury has yet to be explored. PURPOSE: Using a pre-clinical animal model of ACL injury, a time course study was performed to investigate the role of mitochondria and Reactive Oxygen Species (ROS) after injury. METHODS: 48 Long Evans rats (n=8 per group; 4m/4f) underwent non-invasive rupture of the right ACL and were euthanized at 1, 3, 7, 14, 28, 56 days post-injury. 8 rats (4m/4f) served as healthy controls (HC). Respiration was measured by high-resolution respirometry in permeabilized muscle fibers from the right vastus lateralis (VL). ROS production was determined using Amplex Red assays. VL weight was normalized to total body mass for measuring muscle mass loss. One-way ANOVAs with Bonferroni post-hoc were used to determine differences between groups (P < 0.05). RESULTS: Reductions in complex I + II state 3 respiration were observed at 7 and 56 days post-injury (HC: 33.92 ± 4.26 pmol·s·mg; 7D: 15.95 ± 1.38 pmol·s·mg; 56D: 18.80 ± 2.15 pmol·s·mg; F = 5.99, P = 0.002 and P = 0.015 respectively). State 4 respiration did not differ between groups (P > 0.05). Respiratory Control Ratio (RCR), defined as respiration in state 3 divided by respiration in state 4, significantly decreased 7 through 56 days post-injury (HC: 4.00 ± 0.13; 7D: 1.54 ± 0.16; 56D: 1.82 ± 0.20; F = 13.29, P = 0.001 and P = 0.001 respectively) along with increased mitochondrial ROS production 7 through 56 days post-injury (HC: 10.16 ± 0.41 pmol·s·mg; 7D: 12.23 ± 0.54 pmol·s·mg; 56D: 26.83 ± 0.54 pmol·s·mg; F = 178.05, P = 0.001 and P = 0.001 respectively). VL atrophy was observed at 7 and 14 days post-injury (HC: 3.52 ± 0.08 mg·g; 7D: 3.14 ± 0.07 mg·g; 14D: 3.18 ± 0.07 mg·g; F = 5.06, P = 0.013 and P = 0.044 respectively). CONCLUSION: Mitochondria are an important source of muscular ROS production after ACL injury. Mitochondrial dysfunction and redox disturbances contribute to ACL injury-induced quadriceps atrophy. Funding Source: NIH grant K01AR071503