Extracellular Vesicles from Mesenchymal Stem Cells reduce Aβ plaque burden in early stages of Alzheimer's disease

Object Bone marrow mesenchymal stem cells (MSC), due to their strong protective and anti-inflammatory abilities, are widely investigated in the context of several diseases for their possible therapeutic role, based on the release of a highly proactive secretome composed of soluble factors and Extracellular Vesicles (EVs). MSC-EVs, in particular, convey many of the beneficial features of parental cells, including direct and indirect β-amyloid degrading-activities, immunoregulatory and neurotrophic abilities. Therefore EVs represent an extremely attractive tool for therapeutic purposes in neurodegenerative diseases, including Alzheimer’s disease (AD). We examined the therapeutic potential of intracerebrally injected MSC-EVs into the neocortex of APP/PS1 mice at 3 and 5 months of age, a time window in which the cognitive behavioral phenotype is not yet detectable or just starts to appear. Materials Primary cultures of Bone Marrow-derived MSC (up to P12 passage), APPswe/PS1dE9 (APP/PS1) AD mice. Methods MSC were stimulated by serum-deprivation for 3 hrs and supernatant was submitted to differential ultracentrifugation to collect EVs (including exosomes and microvesicles pools), which were characterized by Nanoparticle tracking, cryo-EM, flow cytometry and Western blot analysis. APP/PS1 mice, 3 and 5 months old, were injected intracortically with 4 uL of BM-MSC-derived EV suspension, corresponding to 22.4 ug of total proteins. Brain sections of mice treated or not with EVs were immunohistochemically stained for Abeta1-42 peptide (6-E10 antibody). Smi31 and 32 antibodies recognizing Neurofilaments were used for staining dystrophic neurites around Abeta1-42 plaques stained by Thioflavin-T. Results Intracerebral injection of MSC-EVs into the neocortex of APP/PS1 mice at 3 and 5 months of age reduced Abeta1-42 plaques burden one month later compared to same-age untreated mice. At 3 months, when plaques have just started to form, treatment conferred a preventive significance. In addition, following treatment with MSC-EVs, a reduction in dystrophic neurites could been measured. This decrease resulted significantly different in 6 month-old AD mice. Neprilysin, a metal-membrane endopeptidase able to degrade Abeta1-42, was detected on MSC-derived EV lysates. Discussion We demonstrate that MSC-EVs are effective in reducing the Aβ plaque burden and the amount of dystrophic neurites, in both cortex and hippocampus. The presence of Neprilysin on MSC-EVs opens the possibility of a direct β-amyloid degrading-action as a possible mechanisms of action. Conclusions Our results indicate a potential role for MSC-EVs already at early stages of AD, suggesting the possibility to intervene before overt clinical manifestations.