Inflammation Inhibits HECTD1-Mediated AURKA Ubiquitination to Cause Extracellular Matrix Degradation in Osteoarthritis via Enhancing Cap-Dependent mRNA Translation of ADAMTS12.

Osteoarthritis (OA) is a common joint disease, and chondrocyte extracellular matrix (ECM) degradation was closely associated with its progression. This study investigated the regulatory mechanisms of ECM degradation during OA development. A rat model of OA was established by anterior cruciate ligament transection (ACL-T) and interleukin-1 beta (IL-1β)-stimulated rat chondrocytes were used to simulate OA in vitro. Cartilage damage was evaluated by hematoxylin-eosin (HE) and safranin O-fast green staining. The ECM content in chondrocytes was assessed by alcian blue staining. Real-time quantitative PCR (RT-qPCR), Western Blotting, immunohistochemical staining, and immunofluorescent staining were adopted to analyze associated molecule expression. Molecular mechanisms were elucidated by Co-immunoprecipitation (Co-IP) and GST pull-down assay. We found that Aurora kinase A (AURKA), p-eukaryotic translation initiation factor 4E (eIF4E), and ADAM metallopeptidase with thrombospondin type 1 motif 12 (ADAMTS12) levels were elevated in the human and rat cartilage tissues of OA, as well as IL-1β-exposed chondrocytes. AURKA inhibition restrained ECM degradation to relieve OA via down-regulation of ADAMTS12. AURKA overexpression phosphorylated eIF4E, which promoted cap-dependent translation of ADAMTS12. Moreover, DNA methyltransferase 1 (DNMT1)-mediated methylation down-regulated HECT domain E3 ubiquitin protein ligase 1 (HECTD1) in the OA model and consequently enhanced AURKA expression via inhibiting its ubiquitination. HECTD1 knockdown or ubiquitination repression intensified ECM degradation in IL-1β-stimulated chondrocytes. Taken together, low expression of HECTD1 repressed AURKA ubiquitination to elevate AURKA protein level and subsequently facilitated eIF4E-mediated cap-dependent translation of ADAMTS12, thus resulting in ECM degradation during OA progression.