Inflammatory macrophage-derived extracellular vesicles trigger the non-canonical pyroptosis pathway in chondrocytes leading to cartilage catabolism and degeneration in osteoarthritis

The severity of osteoarthritis (OA) and cartilage degeneration are highly correlated with the development of synovitis, which is mediated by the activity of inflammatory macrophages. A better understanding of intercellular communication between inflammatory macrophages and chondrocytes should aid in the discovery of novel therapeutic targets. Here, we explored the pathological role of inflammatory macrophage-extracellular vesicles (EVs) in cartilage degeneration. Macrophages were stimulated by treatment with bacterial lipopolysaccharides to mimic the state of inflammatory macrophages and the resulting EVs (M-LPS EVs) were harvested for chondrocyte stimulation and intraarticular injection in a mouse model. This stimulation resulted in increased catabolism of chondrocytes and cartilage degeneration. Consistently, RNA-seq analyses of stimulated chondrocytes indicated that upregulated genes are mainly categorized into apoptotic process and TNF-signaling pathway which suggests the induction of apoptotic process. These chondrocytes exhibited a significant elevation in the expression of pyroptosis-related molecules that were correlated with the expression of chondrocyte catabolic factors. The disruption of caspase-11 significantly alleviated pyroptotic and catabolic processes in stimulated chondrocytes and the pathological changes in collagenase-induced OA model. Our results provide a new insight into the pathological mechanisms of OA and suggest that non-canonical pyroptosis signaling in chondrocytes represents an attractive therapeutic target for future treatment. Overall design: RNA-seq for mouse chondrocytes stimulated with extracellular vesicles derived from inflammatory macrophage