Anales RANF

S19-01 DETRIMENTAL AND PROTECTIVE ACTION OF MICROGLIAL EXTRACELLULAR VESICLES ON MYELIN LESIONS: ASTROCYTE INVOLVEMENT IN REMYELINATION FAILURE Marta Lombardi 1-2 , Roberta Parolisi 3 , Federica Scaroni 2 , Elisabetta Bonfanti 4 , Alice Gualerzi 5 , Martina Gabrielli 2 , Nicole Kerlero de Rosbo 6 , Antonio Uccelli 6-7 , Paola Giussani 8 , Paola Viani 8 , Cecilia Garlanda 9 , Maria P. Abbracchio 4 , Linda Chaabane 10 , Annalisa Buffo 3 , Marta Fumagalli 4 , Claudia Verderio 2* 1 IRCCS Humanitas, via Manzoni 56, 20089 Rozzano, Italy; CNR Institute of Neuroscience, via Vanvitelli 32, 20129 Milan, Italy; 3 Department of Neuroscience Rita Levi-Montalcini and Neuroscience Institute Cavalieri Ottolenghi, University of Turin, Regione Gonzole 10, 10043 Orbassano, Italy; 4 Department of Excellence: Department of Pharmacological and Biomolecular Sciences (DiSFeB), University of Milan, via Balzaretti 9, 20133 Milan, Italy; 5 IRCCS Fondazione Don Carlo Gnocchi, via Capecelatro 66, 20148 Milan, Italy; 6 Department of Neurology, Rehabilitation, Ophthalmology, Genetics, Maternal and Child Health (DINOGMI), University of Genoa, Largo Paolo Daneo 3, 16132 Genoa, Italy; 7 IRCCS Ospedale Policlinico San Martino, Largo Rosanna Benzi 10, 16132 Genoa, Italy; 8 Department of Biotechnology and Translational Medicine, University of Milan, 20090 Segrate, Italy; 9 Humanitas University, via Manzoni 56, 20089 Rozzano, Italy; 10 Institute of Experimental Neurology (INSPE), San Raffaele Scientific Institute, Via Olgettina Milano 58, 20132 Milan, Italy. Microglia are highly plastic immune cells which exist in a continuum of activation states. By shaping the function of oligodendrocyte precursor cells (OPCs), the brain cells which differentiate to myelin-forming cells, microglia participate in both myelin injury and remyelination during multiple sclerosis. However, the mode(s) of action of microglia in supporting or inhibiting myelin repair is still largely unclear. Here, we analysed the effects of extracellular vesicles (EVs) produced in vitro by either pro- inflammatory or pro-regenerative microglia on OPCs at demyelinated lesions caused by lysolecithin injection in the mouse corpus callosum. Immunolabelling for myelin proteins and electron microscopy showed that EVs released by pro-inflammatory microglia blocked remyelination, whereas EVs produced by microglia co-cultured with immunosuppressive mesenchymal stem cells promoted OPC recruitment and myelin repair. The molecular mechanisms responsible for the harmful and beneficial EV actions were dissected in primary OPC cultures. By exposing OPCs, cultured either alone or with astrocytes, to inflammatory EVs, we observed a blockade of OPC maturation only in the presence of astrocytes, implicating these cells in remyelination failure. Biochemical fractionation revealed that astrocytes are converted into harmful cells by the inflammatory EV cargo, as indicated by immunohistochemical and qPCR analyses, while surface lipid components of EVs promote OPC migration and/or differentiation, linking EV lipids to myelin repair. Despite the lipid species enhancing OPC maturation still remains to be fully defined, we provided the first demonstration that vesicular sphingosine 1 phosphate stimulates OPC migration, the first fundamental step in myelin repair. From this study, microglial EVs emerge as multimodal and multitarget signaling mediators able to influence both OPCs and astrocytes around myelin lesions, which may be exploited to develop novel approaches for myelin repair not only in multiple sclerosis but also in neurological and neuropsychiatric diseases characterized by demyelination.