microRNA in Chondrogenesis, Cartilage and Osteoarthritis

Osteoarthritis (OA) is a multifactorial disease, typified by the loss of articular cartilage, with a strong genetic component. Current work, even with genome-wide association studies, has failed to identify the genes that describe the full genetic susceptibility to the disease. This is likely due to low penetrance polymorphisms in the population overall however, epigenetic mechanisms have been proposed to contribute to the heritability of the disease. Such epigenetic events that may play a role in OA progression and the gene expression changes observed in diseased cartilage have been identified by several studies. Epigenetic mechanisms include DNA methylation, histone modifications, and microRNAs which together, enable the cell to respond to environmental cues but when aberrant can be associated with a number of pathological conditions, including OA. In this review, we focus on microRNA, firstly on the identification and characterisation of those important for chondrogenesis then focussing on their disregulation in the disease. Although research on microRNAs in OA is in its infancy they merely represent the ‘tip of the non-coding RNA iceberg’. Future work, although initially focussed on microRNA, will undoubtedly expand to include the role of other such RNAs in skeletal development and disease.