NDP52 deficiency accelerates chondrocyte degeneration through promoting pathogenic mitochondrial ROS via reverse electron transport.

Abstract

NDP52, a constituent of the selective autophagy receptors (SARs), was recognized for its involvement in facilitating substrate degradation via autophagic bridging. However, its autonomous function apart from autophagy remained largely unexplored. Here, we reported that NDP52 was down-regulated in degenerated chondrocytes. Besides, NDP52 deficiency promoted the extracellular matrix (ECM) degradation, inflammation, cell apoptosis and senescence via its autophagy-independent functions. The absence of NDP52 disrupted the flow of electron respiration chains and led to the production of intracellular mitochondrial reactive oxygen species (mtROS). Subsequent mechanistic investigations revealed that the downregulation of NDP52 upregulated the expression levels of mitochondrial complex Ⅰ by modulating MTIF3 expression, leading to reverse electron transport (RET) and mtROS production. Our research highlights the significance of NDP52 in facilitating chondrocyte degeneration and osteoarthritis, and provides insights into the distinctive mechanism by which autophagy receptors NDP52 induce intracellular mitochondrial ROS dysregulation via non-canonical pathways.