title: Activated microglia inhibit axonal growth through RGMa.
abstract: By causing damage to neural networks, spinal cord injuries (SCI) often result in severe motor and sensory dysfunction. Functional recovery requires axonal regrowth and regeneration of neural network, processes that are quite limited in the adult central nervous system (CNS). Previous work has shown that SCI lesions contain an accumulation of activated microglia, which can have multiple pathophysiological influences. Here, we show that activated microglia inhibit axonal growth via repulsive guidance molecule a (RGMa). We found that microglia activated by lipopolysaccharide (LPS) inhibited neurite outgrowth and induced growth cone collapse of cortical neurons in vitro--a pattern that was only observed when there was direct contact between microglia and neurons. After microglia were activated by LPS, they increased expression of RGMa; however, treatment with RGMa-neutralizing antibodies or transfection of RGMa siRNA attenuated the inhibitory effects of microglia on axonal outgrowth. Furthermore, minocycline, an inhibitor of microglial activation, attenuated the effects of microglia and RGMa expression. Finally, we examined whether these in vitro patterns could also be observed in vivo. Indeed, in a mouse SCI model, minocycline treatment reduced the accumulation of microglia and decreased RGMa expression after SCI, leading to reduced dieback in injured corticospinal tracts. These results suggest that activated microglia play a major role in inhibiting axon regeneration via RGMa in the injured CNS.
authors.affiliation: Department of Molecular Neuroscience, Graduate School of Medicine, Osaka University, Osaka, Japan.
authors.forename: Mari
authors.initials: M
authors.lastname: Kitayama
authors.forename: Masaki
authors.initials: M
authors.lastname: Ueno
authors.forename: Toru
authors.initials: T
authors.lastname: Itakura
authors.forename: Toshihide
authors.initials: T
authors.lastname: Yamashita
mesh_terms: D000818:Animals; D001369:Axons / Q000187:drug effects / Q000378:metabolism*; D002450:Cell Communication / Q000187:drug effects; D015536:Down-Regulation / Q000187:drug effects; D058851:GPI-Linked Proteins / Q000378:metabolism; D020439:Growth Cones / Q000187:drug effects / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D017628:Microglia / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism*; D008911:Minocycline / Q000494:pharmacology; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D012038:Regeneration / Q000187:drug effects
chemical_list: D058851:GPI-Linked Proteins; D009419:Nerve Tissue Proteins; C483496:Rgma protein, mouse; D008911:Minocycline