In-vitro and in-vivo evidence supporting the therapeutic effect of extracellular vesicles derived from mesenchymal stem cells in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease characterized by the selective death of motoneurons (MNs). Despite significant progress the precise pathological mechanisms of MN death remain largely obscure. ALS is also defined a non-cell-autonomous disease, due to the contribution of glial cells that acquire an aberrant reactive phenotype and secrete neurotoxic factors toward MN. At present there is no effective cure for ALS. We previously demonstrated that a single intravenous administration of mesenchymal stem cells (MSCs), prolonged survival probability and ameliorated pathological features, including gliosis and neuroinflammation, in the SOD1G93A mouse model of ALS [1]. We postulated that the beneficial effect of MSCs could be mediated by the paracrine activity of extracellular vesicles (EVs) secreted by MSCs that transfer to target cells their shuttled microRNAs [2]. To confirm this hypothesis we studied in-vitro the activity of MSCs-derived EVs on astrocytes isolated from the spinal cord of symptomatic SOD1G93A mice and human astrocytes (iAstrocytes) differentiated from inducible neural progenitor cells (iNPCs) of ALS patients. The results of our experiments demonstrated that the overexpression of glial activation markers such as GFAP, vimentin and S100β in SOD1G93A astrocytes, was reduced by 24h exposure to MSC-derived EVs. We obtained the same effects concerning pro-inflammatory factors such as TNF-α, IL-1β, IL-6 and CCL2, that were highly expressed in SOD1G93A astrocytes, and which secretion was significantly reduced in astrocytes treated with EVs. In human iAstrocytes, exposure to EVs increased the expression of the Nrf2 anti-oxidant factor and resulted in reduced accumulation of reactive oxygen species. Most importantly, the neurotoxicity of mouse and human ALS astrocytes co-cultured with MNs were significantly reduced when astrocytes where exposed to MSCs-derived EVs. Interestingly, the transfection with synthetic mimics of miRNAs, found upregulated in MSCs, reverted the reactive phenotype of SOD1G93A ALS astrocytes and upregulated the Nrf2 antioxidant pathway in human iAstrocytes [3]. As a subsequent translational application, we planned to test the efficacy of chronic intranasal administration of MSC-derived EVs in SOD1G93A ALS mice by performing a comprehensive panel of in vivo functional studies, as well as ex vivo histological and molecular analyses. Preliminary data are confirming that MSC-derived EVs administration indeed significantly slowdown the progression of the disease and increased the life span in ALS mice. Overall our data pave the way for the application of MSCs-derived EVs or even EV-mimicking synthetic particles as an highly innovative and promising therapeutic strategy for ALS cure.