Down-Regulation of Glial Fibrillary Acidic Protein and Vimentin by RNA Interference Improves Acute Urinary Dysfunction Associated with Spinal Cord Injury in Rats

In spinal cord injury, glial scarring, a result of overexpressed intermediate filament (IF) proteins including glial fibrillary acidic protein (GFAP) and vimentin, is one of the largest obstacles in axonal regeneration. We postulated that specific suppression of IF proteins in the injured CNS might inhibit the excessive reactivity of astrocytes and thereby suppress glial scarring. siRNAs targeting GFAP and vimentin were transfected separately into C6 glioma cells and rat hippocampal astrocytes. These siRNAs suppressed both biphasic elements of each IF proteins: the ordinarily expressed elements having slow turnover and the immediately inducible elements stimulated by tumor necrosis factor-alpha (TNF-alpha). Moreover, adenovirus vectors expressing GFAP or vimentin siRNAs suppressed the proliferation of C6 glioma cells on days 3-9 after infection. Finally, each siRNA mixed with atelocollagen was applied together to the contused thoracic spines of spinal cord injury (SCI) model rats. The introduction of GFAP and vimentin siRNAs prevented the overexpression of IF proteins in the injured lesion (namely, in the white matter surrounding the long tract where the lateral funiculus exists and in the gray matter near the anterior horn neurons). Furthermore, the starting date of spontaneous voiding was significantly accelerated by application of GFAP and vimentin siRNAs. The inhibition of undesirable glial activity surrounding micturition-related pathways improved acute urinary dysfunction due to neurogenic bladder. In conclusion, the down-regulation of IF proteins by RNAi suppresses the overproliferation of reactive astrocytes and thereby might be an effective treatment for spinal cord injury.