Mitochondrial DNA released from pyroptotic synovial macrophages via DDIT3-mediated mitophagy aggravates...

Emerging evidence has shown that inflammatory synovial macrophage and anabolism-impaired chondrocytes play essential roles in osteoarthritis (OA). The present work aims at uncovering the pathogenic mechanism of how the damage-associated molecular patterns (DAMPs) released from inflammatory synovial macrophage promote extracellular matrix (ECM) degradation of chondrocytes and developing feasible strategies to counter its detrimental effects.

We identified pyroptosis of synovial macrophages in the synovium of OA human and mouse. The effect and mechanism of mitochondrial DNA (mtDNA) released from pyroptotic synovial macrophage in ECM degradation of chondrocytes and cartilage degeneration was further explored in cellular and animal models. Finally, the ameliorative effect of folic acid-modified poly (lactic-co-glycolic acid) (PLGA) nanoparticles in OA was elucidated by in vivo experiments.

Mitochondrial dysfunction in synovial macrophages leads to the release of mtDNA into the cytoplasm, which promotes macrophage pyroptosis, thereby facilitating extracellular release of mtDNA and creating an inflammatory microenvironment unfavorable to cartilage in OA. DDIT3 deficiency inhibits mtROS production by enhancing PINK1/Parkin-dependent mitophagy, which constraining the mtDNA release into the cytoplasm. The decreased cytosolic mtDNA, in turn, dampens macrophage pyroptosis. In vivo, DDIT3 deficiency significantly alleviates synovial inflammation and cartilage degeneration in OA progression, and targeting inhibition of macrophage pyroptosis by folic acid-modified PLGA nanoparticles mimics the protective effects of DDIT3 deficiency against OA progression.

Our findings identified the pathological role of mtDNA released from pyroptotic synovial macrophages through DDIT3-mediated mitophagy in OA, and demonstrated the efficacy of using folic acid-modified PLGA nanoparticles as a delivery for OA treatment.

This study highlights the pivotal role of mtDNA released from pyroptotic synovial macrophages through DDIT3-mediated mitophagy in OA. Targeting inhibition of macrophage pyroptosis by folic acid-modified PLGA nanoparticles might serve as a potential therapeutic target for alleviating cartilage degeneration in OA.