Background: It remains unclear whether hypoxic conditions affect apoptosis and contribute to degradation of cartilaginous tissues in osteoarthritis (OA) lesions. In this study, we hypothesized that hypoxic conditions induced the accumulation of hypoxia-inducible factor (HIF) and activated apoptosis to contribute to OA cartilage degeneration in vivo.
Methods: Malocclusion stress was applied for 2 weeks, 4 weeks and 8 weeks to induce an OA-like lesion animal model (OD) in rats. Histological analysis was performed by H&E staining and safranin O/fast green staining. The expression levels of protein in condylar cartilage were examined by immunostaining to evaluate cartilage degeneration.
Results: We found apparent histological phenotypes associated with degeneration in the occlusion disorder stress (OD) group. The OD group at 4 weeks and 8 weeks had obviously reduced expression of Acan and Col II in cartilage. In contrast, the OD groups had higher levels of Col X, ADAMTS5 and MMP13 in the condylar cartilage than the control group. Moreover, the OD group cartilage had prominent degenerative changes with reduced levels of HIF1α and increased levels of HIF2α and the apoptosis factor Caspase3 in condylar cartilage at 8 weeks.
Occlusion disorder stress results in cartilage degeneration. HIF1α and HIF2α are involved in temporomandibular joint (TMJ) cartilage homeostasis by regulating chondrocyte apoptosis, which contributes to TMJ cartilage degeneration.
Conclusion: Thus, abnormal hypoxic conditions inducing opposite expression patterns of HIF1α and HIF2α could be involved in the pathogenesis of condylar cartilage degeneration. HIF2α may provide a potential negative feedback mechanism for HIF1α during cartilage damage.