Genome-wide promoter methylation analysis of human osteoarthritis

Osteoarthritis (OA) is a chronic disease of the joint characterized by a progressive degradation of articular cartilage and subchondral bone. In healthy tissue, specialized cells called chondrocytes are regulating a balanced cartilage catabolism and anabolism. By contrast osteoarthritic joints are characterized by a dramatic increase of cartilage catabolism, due to changes of gene expression patterns within chondrocytes. To identify potential epigenetic differences regulating this process a genome-wide methylation screening of paired unaffected and osteoarthritic knee cartilage samples was performed. Therefore samples of macroscopic arthritic and non-arthritic cartilage areas of the femoral condyle of five female patients were collected and DNA isolation was performed. For being able to investigate methylation changes on a genome-wide scale using only limited amounts of DNA a specific amplification protocol for mainly methylated DNA has been established, based on combinations of different methylation-sensitive and –independent restriction digestions. The amplified DNA was then labeled and hybridized onto Agilent “Human Promoter Whole Genome” microarrays. A random variance t-test for paired (per patient) samples was performed, identifying 1214 differentially methylated genetic targets between arthritic and non-arthritic samples. The biological relevance of these genes was then further investigated via Gene Ontology (GO) and KEGG pathway analysis. DNA isolated of paired arthritic and non-arthritic knee cartilage samples of five different female osteoarthritis patients (10 samples) was methylation-specifically amplified using combinations of methylation-sensitive and -insensitive restriction enzymes. Amplicons were dye labeled (Cy3) and hybridized onto 2x244k Agilent Human Promoter microarrays.