Role of DNA methylation during recovery from spinal cord injury with and without β₂-adrenergic receptor agonism

Daily treatment with the FDA-approved β₂-adrenergic receptor agonist formoterol beginning 8 h after severe spinal cord injury (SCI) induces mitochondrial biogenesis and improves recovery in mice. We observed decreased DNA methyltransferase (DNMT) expression, global DNA methylation and methylation of the mitochondrial genes PGC-1α and NDUFS1 in the injury site of formoterol-treated mice 1 DPI, but this effect was lost by 7 DPI. To investigate the role of DNA methylation on recovery post-SCI, injured mice were treated daily with formoterol or vehicle, plus the DNMT inhibitor decitabine (DAC) on days 7–9. While DAC had no apparent effect on formoterol-induced recovery, mice treated with vehicle plus DAC exhibited increased BMS scores compared to vehicle alone beginning 15 DPI, reaching a degree of functional recovery similar to that of formoterol-treated mice by 21 DPI. Furthermore, DAC treatment increased injury site mitochondrial protein expression in vehicle-treated mice to levels comparable to that of formoterol-treated mice. The effect of DNMT inhibition on pain response with and without formoterol was assessed following moderate SCI. While all injured mice not treated with DAC displayed thermal hyperalgesia by 21 DPI, mice treated with formoterol exhibited decreased thermal hyperalgesia compared to vehicle-treated mice by 35 DPI. Injured mice treated with DAC, regardless of formoterol treatment, did not demonstrate thermal hyperalgesia at any time point assessed. Although these data do not suggest enhanced formoterol-induced recovery with DNMT inhibition, our findings indicate the importance of DNA methylation post-SCI and support both DNMT inhibition and formoterol as potential therapeutic avenues.