Hypomethylation of nerve growth factor (NGF) promotes binding of C/EBP alpha and contributes to inflammatory hyperalgesia in rats

Background Chronic pain usually accompanied by tissue damage and inflammation. However, the pathogenesis of chronic pain remains unclear. Methods We investigated the role of nerve growth factor (NGF) in chronic inflammatory pain induced by complete Freund's adjuvant (CFA), explored the methylation status of CpG islands in the promoter region of the NGF gene, and clarified the function and mechanism of C/EBP alpha-NGF signaling pathway from epigenetic perspective in the chronic inflammatory pain model. Results CFA induced significant hyperalgesia and continuous upregulation of NGF mRNA and protein levels in the L4-6 dorsal root ganglions (DRGs) in rats. Hypomethylation of CpG islands occurred in the NGF gene promoter region after CFA treatment. At the same time, the miR-29b expression level was significantly increased, while the DNA methyltransferase 3b (DNMT3b) level reduced significantly. Moreover, CFA treatment promoted binding of C/EBP alpha to the NGF gene promoter region and C/EBP alpha siRNA treatment obviously decreased expression of NGF levels and also alleviate inflammatory hyperalgesia significantly in rats. Conclusion Collectively, the results indicated that CFA leads to the upregulation of miR-29b level, which represses the expression of DNMT3b, enhances the demethylation of the NGF gene promoter region, and promotes the binding of C/EBP alpha with the NGF gene promoter, thus results in the upregulation of NGF gene expression and maintenance of chronic inflammatory pain.