Mitoprotective therapy prevents rapid, strain-dependent mitochondrial dysfunction after articular cartilage injury.

Post-traumatic osteoarthritis (PTOA) involves the mechanical and biological deterioration of articular cartilage that occurs following joint injury. PTOA is a growing problem in healthcare due to the lack of effective therapies combined with an aging population with high activity levels. Recently, acute mitochondrial dysfunction and altered cellular respiration have been associated with cartilage degeneration after injury. This finding is particularly important because recently-developed mitoprotective drugs, including SS-peptides, can preserve mitochondrial structure and function after acute injury in other tissues. It is not known, however, if cartilage injury induces rapid structural changes in mitochondria, to what degree mitochondrial dysfunction in cartilage depends on the mechanics of injury, or the time frame over which such dysfunction develops. Similarly, it is unknown if SS peptide treatment can preserve mitochondrial structure and function after cartilage injury. Here, we combined fast-camera elastography, longitudinal fluorescence assays, and computer vision techniques to track the fates of thousands of individual cells. Our results show that impact induces mechanically-dependent mitochondrial depolarization within a few minutes after injury. Electron microscopy revealed that impact induces rapid structural changes in mitochondria that are related to reduced mitochondrial function, namely fission and loss of cristae structure. We found that SS-peptide treatment prior to impact protects mitochondrial structure and preserves mitochondrial function at levels comparable to that of unimpacted control samples. Overall, this study reveals the vital role of mitochondria in mediating cartilage's peracute (within minutes) response to traumatic injury and demonstrates mitoprotection as a promising therapeutic strategy for injury-induced cartilage damage. This article is protected by copyright. All rights reserved.