NRSF regulation of OPRM1 through histone acetylation.

The Neuron Restrictive Silencer Factor (NRSF) is a master transcriptional regulator of neuronal differentiation. Dysregulation of NRSF in neurons contributes to multiple neurological disorder. Following peripheral nerve injury, NRSF is upregulated and has been implicated in the establishment and maintenance of neuropathic pain. While the molecular and genetic changes in nerves occur during neuropathic pain are numerous and complex, a key downstream consequence of NRSF activation is repression of the mu-opioid receptor gene (OPRM1), a critical mediator of nociception and opioid responsiveness. NRSF controls repression of gene expression through recruitment of histone deacetylases (HDACs) to target genes. Here, we demonstrate that pharmacological inhibition of HDACs with valproic acid (VPA) is able to de-repress expression of OPRM1 in iPSC-derived neurons. To produce more targeted epigenetic changes to specific genomic loci, we further employed a CRISPR based epigenetic editing strategy using dCas9 fused to the histone acetyltransferase p300. Targeted acetylation of the OPRM1 gene promoter region with dCas9-p300 upregulated OPRM1 gene expression. Restoring OPRM1 expression in neurons is able to alter its responsiveness to mu-opioid receptor agonist, as evidenced by changes in calcium signaling. This study demonstrated targeted epigenetic acetylation with dCas9-p300 is a powerful strategy to reverse NRSF-medicated gene repression and restore opioid receptor function, highlighting a potential therapeutic avenue for neuropathic pain.