Synovial Fluid Mitochondrial DNA Concentration Reflects the Degree of Cartilage Damage After Naturally Occurring Articular Injury

Posttraumatic osteoarthritis (PTOA) is a debilitating sequela to joint injury with no current therapeutics that can slow its progression. Early intervention, prior to the development of degenerative joint changes, has the potential for greater therapeutic success but requires early detection of joint injury. In other tissue types, trauma is associated with the extracellular release of mitochondrial DNA (mtDNA), which serves as a mitochondria-specific Damage Associated Molecular Pattern (mDAMP) to perpetuate inflammation. We demonstrated that chondrocytes release mtDNA following cellular stress and that mtDNA is increased in equine synovial fluid following experimental and naturally occurring mechanical injury to the joint surface. Moreover, we found a strong correlation between the degree of cartilage damage and mtDNA concentration. Finally, impact-induced mtDNA release was mitigated by mitoprotective treatment. These data suggest synovial fluid mtDNA may represent a sensitive marker of early articular injury, prior to the onset of changes on standard diagnostic imaging modalities. One Sentence Summary Synovial fluid mitochondrial DNA increases after articular injury, is associated with the degree of cartilage damage, and is mitigated by mitoprotective treatment. ### Competing Interest Statement The authors have declared no competing interest.