Molecular probing for the mechanism of neuropathic pain

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DESCRIPTION (provided by applicant): The long-term goal of the proposed R21 project is to elucidate a pathological mechanism underlying peripheral neuropathic pain. It has been postulated that constitutive changes occur in primary sensory neurons leading to abnormal peripheral accumulation of the tetrodotoxin-resistant sodium channel Nav1.8, with a resulting induction of neuropathy symptoms such as allodynia, hyperalgesia, and dysesthesia. It is puzzling, however, that the NaV1.8 mRNA level has alternately been reported to be reduced, unchanged, or slightly increased in the somata of these neurons. The Pi's group recently observed that NaV1.8 mRNA is significantly increased in the rat sciatic nerve after sciatic nerve entrapment (SNE) injury but not spinal nerve ligation (SNL) injury. This suggests that selective manipulation of sensory neuron gene expression may offer a unique opportunity for differential investigations of neuropathic pathogenesis. This application proposes to develop a novel non-invasive gene transfer to sensory neurons using a biocompatible cationized gelatin (CG) vector complexed with plasmid DMA. Subcutaneous CG/DNA complex injection to the glabrous hindpaw should result in peripheral uptake and retrograde transport to the dorsal root ganglion (DRG) via the sciatic nerve. Preliminary studies achieved reporter gene expression in the L4/L5 DRG. Aim 1 is a technology development project which will establish the spatiotemporal kinetics of CG/DNA neural gene transfer. Plasmid expression of small interfering RNA (siRNA) will also be established in this model. Aim 2 will explore the mechanistic hypothesis that the net increase of NaV1.8 mRNA in the peripheral sciatic nerve contributes, in part, to the pathogenesis of neuropathic pain. The rat SNE model will be examined for the spatial distribution of NaV1.8 mRNA in the DRG and sciatic nerve. NaV1.8-targeted siRNA will be applied to study effects of NaV1.8 suppression on neuropathic pain behavior. The outcome of this project will provide a novel entry point for future investigations of, and a putative therapeutic modality for neuropathic pain.