Nociceptor HDAC4 regulates inflammatory pain

Transcriptional alterations are characteristic of persistent pain states but the key regulators remain elusive. Using a conditional knockout (cKO) strategy in mice we sought to determine whether loss of the transcriptional co-repressor histone deacetylase four (HDAC4) would have implications for sensory neuron transcription and nociception. HDAC4 was found to be largely dispensable for transcriptional regulation of naïve sensory neurons but was required for transcriptional responses after injury, with Calca and Trpv1 expression consistently downregulated in HDAC4 cKO compared to littermate controls (0.2-0.44 fold). This downregulation corresponded to reduced sensitivity to capsaicin in vitro (76% +/- 4.4% wildtype capsaicin responders vs 56.9% +/- 4.7% cKO responders) and to reduced thermal hypersensitivity in the complete Freund’s adjuvant model of inflammatory pain (1.3-1.4 fold improvement). These data indicate that HDAC4 is a novel inflammatory pain mediator and may be a good therapeutic target, capable of orchestrating the regulation of multiple downstream effectors. Total RNA was extracted from HDAC4 cKO and HDAC4 fl/fl naïve adult lumbar dorsal root ganglia (n=3/group). mRNA expression was compared using Affymetrix Mouse Gene Arrays (Mouse Gene 2.0ST) run on a GeneChip Fluidics Station 450. Chips were scanned on an Affymetrix GeneChip Scanner.