SiRNA in MSCs-Derived Exosomes Silences Ctgf Gene for Corticospinal Axon Regeneration and Locomotor Recovery in Spinal Cord Injury Rats

Abstract As RNA interference (RNAi) received solicitous attention by many for its promising performance in gene therapy recently, and how to obtain a choice small interfering RNA (siRNA) vector has become a moot point at this moment. Exosomes (Exo) show advantages of long survival time in vivo, high transmission efficiency and easy penetration across the blood-brain/spinal cord barrier, renowned as excellent carriers of bioactive substances. Previous studies have confirmed the detrimental effect of connective tissue growth factor (CTGF) on axonal regeneration after spinal cord injury (SCI) via stimulating the unrestricted growth of glial scars. In this study, we applied mesenchymal stem cells (MSCs)-derived Exo as the delivery of synthesized siRNA, which were extracted from rat bone marrow. We constructed exosome-siRNA (Exo-siRNA) that could specifically silence Ctgf gene in the injury sites by electroporation. During the administration, we injected Exo-siRNAs into the tail vein of SCI rats, and their distribution and accumulation in the spinal cord were visualized by in vivo fluorescence imaging. Relevant in vivo and in vitro experiments in this study showed that Exo-siRNA not only effectively inhibited the expressions of Ctgf gene and glial scar formation related proteins, such as GFAP, vimentin fibronectin and laminin, in the injured spinal cord segments, but quenched inflammation, and thwarted neuronal apoptosis and reactive astrocytes and glial scar formation. Besides, it significantly up-regulated several neurotrophic factors and anti-inflammatory factors (e.g., TGF-β1), acting as a facilitator of axon regeneration of nerve-injured motor neurons. Thus, the motor function of SCI rats were remarkably promoted. In conclusion, this study has combined the thoroughness of gene therapy and the excellent drug-loading characteristics of Exo for the precise treatment of SCI, which will shed new light on the drug-loading field of Exo.