Epigenetics in Musculoskeletal Disease

Epigenetics refers to heritable and potentially reversible changes in gene expression that occur without any change to the underlying DNA sequence. It is the molecular interface through which the environment, ageing and mechanical loading influence how cells behave, and that makes it directly relevant to musculoskeletal disease. There are three principal mechanisms: DNA methylation, in which methyl groups, typically at promoter CpG islands, generally silence a gene; histone modification, such as acetylation and methylation of histone tails, which open or close chromatin and thereby permit or block transcription; and non-coding RNAs, particularly microRNAs and long non-coding RNAs, which regulate gene expression after transcription. These mechanisms are implicated across musculoskeletal disease. In osteoarthritis, epigenetic dysregulation drives an abnormal chondrocyte phenotype and mesenchymal stem cell senescence, and MSC-derived exosomes carrying regulatory microRNAs are being explored to promote cartilage repair. Epigenetic dysregulation also contributes to osteoporosis through the osteoblast-osteoclast balance and to bone and soft-tissue tumours through silencing of tumour-suppressor genes. A particularly interesting development is the epigenetic clock, an estimate of biological age from DNA-methylation patterns, which is associated with degenerative musculoskeletal disease such as chronic low-back-pain severity and tissue-specific ageing in osteoarthritic cartilage. Because epigenetic changes are reversible, they are attractive as biomarkers and as drug targets, and they underpin regenerative strategies - though I would emphasise these applications are still largely investigational rather than routine practice.