microRNAs shuttled by extracellular vesicles derived from mesenchymal stem cells revert glial activation and neurotoxicity in in-vitro models of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease characterized by the selective death of motoneurons (MNs). 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 administration of mesenchymal stem cells (MSCs), prolonged survival probability and ameliorated pathological features in the SOD1G93A mouse model of ALS. We postulated that the beneficial effect of MSCs could be mediated by the paracrine activity of extracellular vesicles (EVs) secreted by MSCs. To demonstrated this hypotesis 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 overexpression of astroglial activation markers such as GFAP, vimentin and S100β, was reduced by 24h exposure to EVs, in SOD1G93A astrocytes. We obtained the same effects concerning the pro-inflammatory factors 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 towards MNs were significantly reduced, in co-culture, when astrocytes where previously exposed to MSCs-derived EVs. Interestingly, the transfection with synthetic mimics of miRNAs, found to be upregulated in MSCs, reverted the reactive phenotype and upregulated the Nrf2 antioxidant pathway in ALS astrocytes cultured from SOD1G93A mice and human iAstrocytes, respectvely. Overall, MSCs-derived EVs can modulate astrocyte activation and their toxicity towards MNs, by releasing anti-inflammatory and anti-oxidant EV-shuttled miRNAs, thus representing a new promising therapeutic strategy in ALS.