HECTD1‐Mediated Ubiquitination and Degradation of Rubicon Regulates Autophagy and Osteoarthritis Pathogenesis

Objective Osteoarthritis (OA) is one of the most common degenerative joint diseases and is associated with autophagy suppression. However, the molecular mechanism of autophagy regulation in the context of OA is not fully understood. In this study, we sought to determine the role that HECTD1 plays in the pathogenesis of OA. Methods We used RNA sequencing analysis to explore the differential expression of E3 ubiquitin ligase genes in healthy human cartilage and human cartilage affected by OA. Using surgery‐ and aging‐induced OA mouse models, we comprehensively analyzed the function of the screened gene Hectd1 in the development of OA; furthermore, we dissected the mechanism by which HECTD1 regulates autophagy and OA progression using a combination of molecular biologic, cell biologic, and biochemical approaches. Results HECTD1 was significantly down‐regulated in human OA cartilage samples compared to healthy cartilage samples. Overexpression of HECTD1 in mouse joints alleviated OA pathogenesis, whereas conditional depletion of Hectd1 in cartilage samples aggravated surgery‐ and aging‐induced OA pathogenesis. Mechanistically, HECTD1 bound to Rubicon and ubiquitinated Rubicon at lysine residue 534, which targets Rubicon for proteasomal degradation. More importantly, HECTD1‐mediated Rubicon degradation regulated chondrocyte autophagy, leading to mitigation of stress‐induced chondrocyte death and the subsequent progression of OA. Conclusion HECTD1 plays a crucial role in the pathogenesis of OA, in that HECTD1 regulates chondrocyte autophagy by ubiquitinating and targeting Rubicon for proteasomal degradation.