title: Bone marrow mesenchymal stromal cells drive protective M2 microglia polarization after brain trauma.
abstract: Microglia/macrophages (M) are major contributors to postinjury inflammation, but they may also promote brain repair in response to specific environmental signals that drive classic (M1) or alternative (M2) polarization. We investigated the activation and functional changes of M in mice with traumatic brain injuries and receiving intracerebroventricular human bone marrow mesenchymal stromal cells (MSCs) or saline infusion. MSCs upregulated Ym1 and Arginase-1 mRNA (p < 0.001), two M2 markers of protective M polarization, at 3 and 7 d postinjury, and increased the number of Ym1(+) cells at 7 d postinjury (p < 0.05). MSCs reduced the presence of the lysosomal activity marker CD68 on the membrane surface of CD11b-positive M (p < 0.05), indicating reduced phagocytosis. MSC-mediated induction of the M2 phenotype in M was associated with early and persistent recovery of neurological functions evaluated up to 35 days postinjury (p < 0.01) and reparative changes of the lesioned microenvironment. In vitro, MSCs directly counteracted the proinflammatory response of primary murine microglia stimulated by tumor necrosis factor-α + interleukin 17 or by tumor necrosis factor-α + interferon-γ and induced M2 proregenerative traits, as indicated by the downregulation of inducible nitric oxide synthase and upregulation of Ym1 and CD206 mRNA (p < 0.01). In conclusion, we found evidence that MSCs can drive the M transcriptional environment and induce the acquisition of an early, persistent M2-beneficial phenotype both in vivo and in vitro. Increased Ym1 expression together with reduced in vivo phagocytosis suggests M selection by MSCs towards the M2a subpopulation, which is involved in growth stimulation and tissue repair.
authors: Department of Neuroscience, IRCCS, Istituto di Ricerche Farmacologiche Mario Negri, 20156, Milan, Italy.
authors: Elisa R
authors: ER
authors: Zanier
authors: Francesca
authors: F
authors: Pischiutta
authors: Loredana
authors: L
authors: Riganti
authors: Federica
authors: F
authors: Marchesi
authors: Elena
authors: E
authors: Turola
authors: Stefano
authors: S
authors: Fumagalli
authors: Carlo
authors: C
authors: Perego
authors: Emanuela
authors: E
authors: Parotto
authors: Paola
authors: P
authors: Vinci
authors: Pietro
authors: P
authors: Veglianese
authors: Giovanna
authors: G
authors: D'Amico
authors: Claudia
authors: C
authors: Verderio
authors: Maria-Grazia
authors: MG
authors: De Simoni
mesh_terms: D000818:Animals; D001921:Brain / Q000378:metabolism*; D001930:Brain Injuries / Q000378:metabolism* / Q000628:therapy*; D016764:Cell Polarity; D002478:Cells, Cultured; D016207:Cytokines / Q000378:metabolism; D006801:Humans; D007276:Injections, Intraventricular; D036341:Intercellular Signaling Peptides and Proteins / Q000378:metabolism; D008264:Macrophages / Q000378:metabolism; D008297:Male; D045164:Mesenchymal Stem Cell Transplantation; D059630:Mesenchymal Stem Cells / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D017628:Microglia / Q000378:metabolism*; D009043:Motor Activity; D012333:RNA, Messenger / Q000378:metabolism
chemical_list: D016207:Cytokines; D036341:Intercellular Signaling Peptides and Proteins; D012333:RNA, Messenger