Abstract
Chronic constriction injury of the sciatic nerve in rats causes peripheral neuropathy leading to pain-like behaviors commonly seen in humans. Neuropathy is a leading cause of neuropathic pain, which involves a complex cellular and molecular response in the peripheral nervous system with interactions between neurons, glia, and infiltrating immune cells. In this study, we utilize a nonsteroidal anti-inflammatory drug -loaded nanoemulsion to deliver the cyclooxygenase-2 inhibitor, Celecoxib, directly to circulating monocytes following nerve injury, which provides long-lasting pain relief. However, it is not fully understood how cyclooxygenase-2 inhibition in a macrophage traveling to the site of injury impacts gene expression in the dorsal root ganglia. To elucidate aspects of the molecular mechanisms underlying pain-like behavior in chronic constriction injury, as well as subsequent pain relief with treatment, we employ RNAseq transcriptome profiling of the dorsal root ganglia associated with the injured sciatic nerve in rats. Using high throughput RNA sequencing in this way provides insight into the molecular mechanisms involved in this neuroinflammatory response. We compare the transcriptome from the dorsal root ganglias of the following study groups: chronic constriction injury animals administered with cyclooxygenase-2 inhibiting celecoxib-loaded nanoemulsion, chronic constriction injury animals administered with vehicle treatment, a drug-free nanoemulsion, and a group of naïve, unoperated and untreated rats. The results show an extensive differential expression of 115 genes. Using the protein annotation through evolutionary relationship classification system, we have revealed pain-related signaling pathways and underlying biological mechanisms involved in the neuroinflammatory response. Quantitative polymerase chain reaction validation confirms expression changes for several genes. This study shows that by directly inhibiting cyclooxygenase-2 activity in infiltrating macrophages at the injured sciatic nerve, there is an associated change in the transcriptome in the cell bodies of the dorsal root ganglia.