The Role of Mitophagy in Quadriceps Atrophy after Non‐Invasive Anterior Cruciate Ligament Injury

Many patients that suffer from anterior cruciate ligament (ACL) injury have persistent quadriceps atrophy even after considerable rehabilitation. Our previous finding has revealed that mitochondrial dysfunction and redox disturbances are causal events in the initiation of muscle atrophy and central to maintenance of a healthy mitochondria is the removal of damaged mitochondria through mitophagy. However, the extent to which mitophagy play a key role in quadriceps muscle atrophy after ACL injury has yet to be explored. If mitophagy is found to play a central role in directing muscle atrophy after ACL injury than it may be an attractive therapeutic target.Using a pre-clinical non-invasive ACL injury model, our objective was to use a time course study to investigate the potential role of mitophagy in quadriceps muscle atrophy after ACL injury.48 Long Evans rats (n=8 per group; 4m/4f) underwent non-invasive rupture of the right ACL and were euthanized at 7, 14, 28, 56 days post-injury. 8 rats (4m/4f) served as healthy controls (HC). Mitophagy-related cellular components of the vastus lateralis were analyzed by Western Blot analysis. One-way ANOVAs with LSD post-hoc were used to determine differences between groups (P < 0.05).Dynamin-related protein 1 (DRP1), a protein regulating mitochondrial fission, was increased significantly at 56 days post-injury [HC: n=8; 1.294 ± 0.364, 56D: n=7; 2.093 ± 1.519 (A.U), P<0.05]. Lysosomes are the terminal step in mitophagy and one of the lysosomal markers, Lysosomal-associated membrane protein 1 (LAMP-1) expression was significantly elevated at 56 days post-injury [HC: n=8; 1.270 ± 0.840, 56D: n=8; 2.266 ± 1.137 (A.U), P<0.05]. Upstream autophagy marker, Beclin-1 expression was also significantly increased at 56 days post-injury (HC: n=8; 1.117 ± 0.339, 56D: n=6; 2.158 ± 1.274, P<0.05).Collectively, these results imply that long-term ACL injury dysregulates mitochondrial quality control including key mitophagy markers, which contributes to ACL injury-induced quadriceps atrophy. Therefore, targeting mitophagy may be the one of the potential therapeutic interventions to prevent muscle atrophy in patients with an ACL injury.