Expression of the opioid peptide genes proopiomelanocortin (Pomc), proenkephalin (Penk), and prodynorphin (Pdyn), in immune cells plays a key role in endogenous pain control. In a rat model of painful unilateral paw inflammation, we isolated cells from popliteal lymph nodes and evaluated the role of C(p)G island C5-methylation on the transcriptional activation of those genes. Using methylated DNA immunoprecipitation, we sorted gDNA into methylated (me) and non-me fractions and then determined the C(p)G island methylation status of each fraction via quantitative Real Time-PCR (qRT-PCR). In silico analysis by MethPrimer software identified one C(p)G island in Pdyn and three each in Pomc and Penk. No substantial changes in C5-methylation of any gene were observed. In conclusion, the C(p)G island methylation status does not seem to be a key regulator of opioid gene activation in immune cells during peripheral tissue inflammation.
