BACKGROUND: The circadian clock maintains homeostasis in peripheral tissues, including articular cartilage. Cartilage as a highly mechanical loaded tissue experiences diurnal rhythmic mechanical loading activity/rest cycle patterns, which gives external time cue on chondrocytes. Given the cartilage clock driven by loading patterns, we hypothesize that abnormal mechanical loading, a major risk factor for osteoarthritis (OA), can disrupt the cartilage clock, further contributing to OA progression.
METHODS: We used both noninvasivemechanical loading system and PER2Luc reporter mice forbioluminescence recording. RNA sequencing was performed in mouse primary chondrocytes treated with 1.0 MPa static compression, and identified core clock molecule REV-ERBα, which was confirmed in human and murine OA cartilage samples. Chondrocytes were treated withsmall interfering RNA (si-), and adeno-associated virus carrying-specific short hairpin RNA (AAV-sh) was injected intra-articularly in mice to knock down. Relevant signaling pathways regulating REV-ERBα were analyzed by RNA sequencing data. Intraperitoneal injection of SR8278, a specific REV-ERBα antagonist, was performed in mice after mechanical overloading for OA treatment. in vivo ex vivo Rev-erbα Rev-erbα Rev-erbα Rev-erbα Rev-erbα
RESULTS: Excessive mechanical loading disrupted the circadian rhythm of articular cartilage. The core clock molecule REV-ERBα was increased in OA cartilage and knockdown ofalleviated compression-induced chondrocyte dysfunction. Inhibition of MAPK-MYC pathway by U0126 or SB203580 attenuated compression-induced REV-ERBα up-regulation and cartilage clock disruption. Finally, pharmacological inhibition of REV-ERBα expression by SR8278 restored cartilage clock upon abnormal loading and mitigated OA progression. Rev-erbα
CONCLUSIONS: REV-ERBα is a key factor in the association between mechanical overloading-induced circadian disruption and OA pathology. This study illustrates the essential mechanism of impaired circadian rhythm under overloading and provides a possibly impactful therapeutic approach for the treatment of OA.
THE TRANSLATIONAL POTENTIAL OF THIS ARTICLE: Inhibition REV-ERBα expression by clock-based therapeutic drug SR8278 or MAPK-MYC pathway inhibitors could ameliorate mechanical overloading-induced circadian disruption of cartilage and OA degeneration, indicating a clinical conversion potential for OA treatment.
