Small Interfering RNA-mediated Selective Knockdown of Postsynaptic Density Protein 95 Reverses Mechanical Allodynia in Neuropathic Pain Rats

  Objective  Postsynaptic density protein 95 (PSD-95) gene specific siRNAs were introduced in vitro or in vivo to determine its succedent influence on neuropathic pain relief, neuron viability and postsynaptic calcium/calmodulin-dependent protein kinase Ⅱ (CaMKII) phosphorylation.

  Methods  siRNAs of rat PSD-95 gene were synthesized for in vitro transfection into NG108-15 neuronal cells. The siRNA to PSD-95, or a mismatch RNA, was mixed with the transfection reagent, i-FectTM (vehicle), and delivered as repeated daily bolus doses (2 μg) via implanted intrathecal catheter to the lumbar spinal cord of rats which received chronic constriction injury (CCI) of sciatic nerve. Both mechanical allodynia and thermal hyperalgesia were measured on the post-operative day 3 and 7. PSD95 gene silenced NG108-15 cells were further stimulated by glutamate, with either the cell viability or the expression and phosphorylation of CaMKIIα to be assayed.

  Results  The siRNAs suppressed PSD-95 gene expression level by 91.5% under the appropriate condition in vitro. High level glutamate induced neurotoxicity, which was partially eliminated by PSD-95 gene silencing. Glutamate also induced the postsynaptic expression and phosphorylation of CaMKIIα. PSD-95 siRNA injected intrathecally in normal rats lowered the expression level of PSD-95 mRNA at cornu dorsale medullae spinalis by 38% (P < 0.05) but had no remarkable effect on the pain threshold. Intrathecal injection of PSD-95 siRNA remarkably alleviated neuropathic pain.

  Conclusions  PSD-95 gene plays an important role in the development of neuropathic pain. Intrathecal injection of PSD-95 siRNA can remarkably alleviate mechanical and thermal hyperalgesia. PSD-95 siRNA may be a promising gene therapy for neuropathic pain.