Analysis of DNA methylation in chondrocytes in rats with knee osteoarthritis

Knee osteoarthritis (KOA) is a degenerative knee disease commonly found in the ageing population. DNA methylation works with histone acetylation to participate in aging. Alterations of DNA methylation may involve the joint chondrocyte degeneration in KOA. The aim of this study is to detect DNA methylation changes in chondrocytes of rats with KOA. The rat KOA model was established with the Hulth method (n = 10), while rats receiving sham operation served as the control (n = 10). At 16 weeks after modeling, the knee joint tissue was collected from half of the rats in each group for Micro-CT scanning, Haematoxylin& Eosin (HE) staining, ABH/OG staining, immunohistochemistry for Bax, Bcl-2 and Fas, and TUNNEL staining. Meanwhile, the articular cartilage was collected from the other half to detect promoter methylation in target genes with the MethylTarget approach. Micro-CT scanning, HE staining, ABH/OG staining, immunohistochemistry, and TUNNEL staining all showed more severe cartilage injury in the KOA group than in the control group, indicating successful establishment of KOA model. The methylation rate in the KOA group was significantly decreased for C/ebpα-2 (within a CpG island -452 bp to the initiation codon on chromosome 1 91,363,511), Cdk2 (within a CpG island -55 bp to the initiation codon on chromosome 7 3,132,362), Bak1 (within a CpG island 6452 bp to the initiation codon on chromosome 20 5,622,277), and Fas (within a CpG island on the entire chromosome 1 gene), compared with the sham group (P = 0.005, 0.008, 0.022 and 0.027, respectively). The chondrocyte apoptosis and significantly reduced methylation levels of C/ebpα-2, Cdk2, Bak1, and Fas may participate in the pathogenesis of KOA. However, the exact mechanisms remain to be determined.