Reprogramming of Mitochondrial Respiratory Chain Complex by Targeting SIRT3-COX4I2 Axis Attenuates Osteoarthritis Progression.

Mitochondrial homeostasis is of great importance for cartilage integrity and associated with the progression of osteoarthritis (OA); however, the underlying mechanisms are unknown. This study aims to investigate the role of mitochondrial deacetylation reaction and investigate the mechanistic relationship OA development. Silent mating type information regulation 2 homolog 3 (SIRT3) expression has a negative correlation with the severity of OA in both human arthritic cartilage and mice inflammatory chondrocytes. Global SIRT3 deletion accelerates pathological phenotype in post-traumatic OA mice, as evidenced by cartilage extracellular matrix collapse, osteophyte formation, and synovial macrophage M1 polarization. Mechanistically, SIRT3 prevents OA progression by targeting and deacetylating cytochrome c oxidase subunit 4 isoform 2 (COX4I2) to maintain mitochondrial homeostasis at the post-translational level. The activation of SIRT3 by honokiol restores cartilage metabolic equilibrium and protects mice from the development of post-traumatic OA. Collectively, the loss of mitochondrial SIRT3 is essential for the development of OA, whereas SIRT3-mediated proteins deacetylation of COX4I2 rescues OA-impaired mitochondrial respiratory chain functions to improve the OA phenotype. Herein, the induction of SIRT3 provides a novel therapeutic candidate for OA treatment.