Neuropathic pain resulting from chronic inflammation and injury to the nervous system is particularly difficult to treat with the currently available drg armamentarium and is a highly problematic unsolved clinical problem. Development of a novel treatment for neuropathic pain is highly significant. Many signaling molecules are likely to partake in the manifestation of neuropathic pain. The Sigma 1 receptor (S1R) is a two-transmembrane mostly endoplasmic reticulum resident protein with many roles in fundamental cellular processes. One of the most robust phenotypes described for the S1R knockout mice is the suppression of neuropathic pain. Intrathecal administration of S1R antagonists mirrors this anti-neuropathic phenotype of the knockout indicating the importance of a spinal segmental level expression of S1R in mediating neuropathic pain. Based on the focused expression of S1R in the ventral horn in the spinal cord proper, we believe S1R in the dorsal root ganglion (DRG) is the key anatomical site of action. We propose a novel concept of the S1R as a master regulator of pronocicptive protein trafficking in the DRG as a mechanism underlying the anti- neuropathic phenotype observed in mice with pharmacological or genetic inhibition of this protein. Preliminary data documents protein:protein interaction between S1R and several pronociceptive proteins including the substance P receptor (NK1R), muscarinic M1 receptor (M1R), and the NR1 subunit of the NMDA receptor all sharing the ability to increase intracellular calcium signaling. Co-expression of S1R increases the plasma membrane expression of NK1R in these cells with a consequent increase in intracellular calcium signaling. We will test the highly innovative working hypothesis that: S1R protein upregulation and modulation of NK1R, M1R, and NMDAR in the dorsal root ganglion (DRG) mediates neuropathic pain. The proposal incorporates state-of-art techniques including a selective in vivo transduction and knockdown of S1R in the DRG by adenoassociated virus 2/8, extensive use of co-immunoprecipitation and novel molecular constructs to decipher the protein domains responsible for the interaction between S1R and the client proteins, and finally examines a gene therapy for neuropathic pain targeting S1R interaction with client proteins.
Neuropathic pain is an unsolved clinical problem extracting tremendous societal resources and causing unimaginable suffering to the afflicted patients. This study examines a potential role of sigma 1 receptor as a master regulator of pronociceptive protein trafficking in the dorsal root ganglion. Extensive biochemical experiments will be followed by a novel in vivo gene therapy in rats targeting the interaction of S1R with pronociceptive proteins.