CpG methylation levels in HPA axis genes predict chronic pain outcomes following trauma exposure.

Chronic posttraumatic musculoskeletal pain (CPTP) is a common outcome of traumatic stress exposure. Biological factors that influence the development of CPTP are poorly understood, though current evidence indicates that the hypothalamic-pituitary-adrenal (HPA) axis plays a critical role in its development. Little is known about molecular mechanisms underlying this association, including epigenetic mechanisms. Here, we assessed whether peritraumatic DNA methylation levels at 248 CpG sites in HPA axis genes (FKBP5, NR3C1, CRH, CRHR1, CRHR2, CRHBP, POMC) predict CPTP and whether identified CPTP-associated methylation levels influence expression of those genes. Using participant samples and data collected from trauma survivors enrolled into longitudinal cohort studies (n=290), we used linear mixed modeling to assess the relationship between peritraumatic blood-based CpG methylation levels and CPTP. 66 (27%) of the 248 CpG sites assessed in these models statistically significantly predicted CPTP, with the three most significantly associated CpG sites originating from the POMC gene region (i.e. cg22900229 [β=0.124, p<0.001], cg16302441 [β=0.443, p<0.001], cg01926269 [β=0.130, p<0.001]). Among the genes analyzed, both POMC (z=2.36, p=0.018) and CRHBP (z=4.89, p<0.001) were enriched in CpG sites significantly associated with CPTP. Further, POMC expression was inversely correlated with methylation levels in a CPTP-dependent manner (six-month NRS<4: r=-0.59, p<0.001; six-month NRS≥4: r=-0.18, p=0.2312). Our results suggest that methylation of HPA axis genes including POMC and CRHBP predict risk for and may contribute to vulnerability to CPTP. Perspective Peritraumatic blood levels of CpG methylation sites in HPA axis genes, particularly CpG sites in the POMC gene, predict chronic posttraumatic musculoskeletal pain (CPTP) development. This data substantially advances our understanding of epigenetic predictors and potential mediators of CPTP, a highly common, morbid, and hard-to-treat form of chronic pain.