Epigenetic and miRNA Expression Changes in People with Pain: A Systematic Review.

Accumulating evidence suggests that epigenetic mechanisms may hold great potential in the field of pain. We systematically reviewed the literature exploring epigenetic mechanisms in people with pain. Four databases have been interrogated: MEDLINE, The Cochrane Central Register of Controlled Trial, Scopus, and Web of Science, following PRISMA guidelines in conducting study selection and assessment. Thirty-seven studies were included. Studies explored epigenetics in conditions such as fibromyalgia, CRPS, neuropathies, or osteoarthritis. Research focussed on genome-wide and gene-specific DNA methylation, and miRNA expression. Bioinformatics analyses exploring miRNA-associated molecular pathways were also performed. Several genes already known for their role in pain (BDNF, HDAC4, PRKG1, IL-17, TNFRSF13B, etc.), and several miRNAs linked to inflammatory regulation, nociceptive signalling and protein kinases functions have been found to differ significantly between people with chronic pain and healthy controls. Although the studies included were cross-sectional in nature, and no conclusion on causal links between epigenetic changes and pain could be drawn, we summarised the large amount of data available in literature on the topic, highlighting results that have been replicated by independent investigations. The field of pain epigenetics appears very exciting and has all the potential to lead to remarkable scientific advances. However, high-quality, well-powered, longitudinal studies are warranted. PERSPECTIVE: Though more high-quality research is needed, available research exploring epigenetic mechanisms or miRNAs in people with pain shows that genes regulating synaptic plasticity and excitability, protein kinases, and elements of the immune system might hold great potential in understanding the pathophysiology of different conditions.