Anales RANF

P.55 MICROGLIA VERSUS MACROPHAGE EFFECTS ON OLIGODENDROCYTE PRECURSOR CELLS: ROLE OF EXTRACELLULAR VESICLES Scaroni Federica 1 , Lombardi Marta 2 , Bonfanti Elisabetta 3 , Gabrielli Martina 1 , Filipello Fabia 2 , Fumagalli Marta 3 , Verderio Claudia 1,2 1 CNR Institute of Neuroscience, Milan, Italy 2 IRCCS Humanitas, Rozzano, Milan, Italy 3 Dept of Pharmacol and Biomolec Sciences, Università degli Studi di Milano, Italy. Neuroinflammation plays a central role in multiple sclerosis (MS) by impairing remyelination and causing neuronal injury. Brain resident microglia (MG) and infiltrating macrophages (MP) are among the main effector cells of the inflammatory response associated to MS (Mallucci et al, 2015; Verderio et al, 2012). They contribute to MS onset and outcome, including secondary progressive phases, but also to the restorative phase of the disease (Rawji et al, 2013). However, it is still unclear whether all inflammatory myeloid cells are detrimental in the disease (Cao et al, 2013) and the possibility exists that the inflammatory activity of brain resident MG and peripheral MP may be distinct in MS, as reported in other brain diseases (Dibaj et al, 2011). Recent data of the laboratory show that both inflammatory and proregenerative MG, through the secretion of extracellular vesicles (EVs) i) attract oligodendrocyte precursor cells (OPCs) in primary cultures, the glial cell type able to generate myelinating oligodendrocytes ii) favor OPC differentiation towards mature myelinating cells and ii) enhance myelin deposition in oligodendrocytes-DGR neuron co-cultures. To compare the action of MP and MG on oligodendrocytes I explored the action of EVs shed from pro-inflammatory MP or pro-regenerative MP on the migration and the differentiation of oligodendrocyte precursor cells (OPC). OPC migration was assessed by a classical transwell-based chemokinesis assay. Quantification of migrating OPCs revealed that MP-derived EVs never attract OPCs, independent of the phenotype of donor MP. Specifically, EVs released by pro- inflammatory MP tend to limit OPC migration, albeit the difference didn’t reach a significant difference. Sphingosine phosphate (S1P), a known chemoattractant agent, was used as positive control. Immunocytochemistry analysis for the marker of mature oligodendrocytes MBP revealed that MP-EVs were not able to promote OPC differentiation as compared to MG-derived EVs. In particular, EVs released by pro-inflammatory MP significantly inhibited in vitro OPC maturation into myelin forming cells. Collectively these results indicate that infiltrating macrophages, rather than resident microglia, may be responsible for block of OPC maturation and remyelination failure in the progressive phase of MS.