In vitro neuronal and glial differentiation from embryonic or adult neural precursor cells are differently affected by chronic or acute activation of microglia.
The contribution of microglia to the modulation of neurogenesis under pathological conditions is unclear. Both pro- and anti-neurogenic effects have been reported, likely reflecting the complexity of microglial activation process. We previously demonstrated that prolonged (72 hr) in vitro exposure to lipopolysaccharide (LPS) endows microglia with a potentially neuroprotective phenotype, here referred as to "chronic". In the present study we further characterized the chronic phenotype and investigated whether it might differently regulate the properties of embryonic and adult neural precursor cells (NPC) with respect to the "acute" phenotype acquired following a single (24 hr) LPS stimulation. We show that the LPS-dependent induction of the proinflammatory cytokines interleukin (IL)-1 alpha, IL-1 beta, IL-6, and tumor necrosis factor (TNF)-alpha was strongly reduced after chronic stimulation of microglia, as compared with acute stimulation. Conversely, the synthesis of the anti-inflammatory cytokine IL-10 and the immunomodulatory prostaglandin E2 (PGE2) was still elevated or further increased, after chronic LPS exposure, as revealed by real time PCR and ELISA techniques. Acutely activated microglia, or their conditioned medium, reduced NPC survival, prevented neuronal differentiation and strongly increased glial differentiation, likely through the release of proinflammatory cytokines, whereas chronically activated microglia were permissive to neuronal differentiation and cell survival, and still supported glial differentiation. Our data suggest that, in a chronically altered environment, persistently activated microglia can display protective functions that favor rather than hinder brain repair processes.
Cacci
Emanuele
E
Department of Cell and Developmental Biology, La Sapienza University, Piazzale Aldo Moro 5, 00185, Rome, Italy.
Ajmone-Cat
Maria Antonietta
MA
Anelli
Tonino
T
Biagioni
Stefano
S
Minghetti
Luisa
L
D053687:Adult Stem Cells / Q000187:drug effects / Q000502:physiology*; D000704:Analysis of Variance; D000818:Animals; D000831:Animals, Newborn; D002454:Cell Differentiation / Q000187:drug effects / Q000502:physiology*; D049109:Cell Proliferation; D002478:Cells, Cultured; D002540:Cerebral Cortex / Q000166:cytology; D018920:Coculture Techniques; D017077:Culture Media, Conditioned / Q000494:pharmacology; D016207:Cytokines / Q000378:metabolism; D015232:Dinoprostone / Q000378:metabolism; D004622:Embryo, Mammalian; D053595:Embryonic Stem Cells / Q000187:drug effects / Q000502:physiology*; D005786:Gene Expression Regulation / Q000187:drug effects; D020287:In Situ Nick-End Labeling; D036341:Intercellular Signaling Peptides and Proteins / Q000494:pharmacology; D008070:Lipopolysaccharides / Q000494:pharmacology; D017628:Microglia / Q000187:drug effects / Q000378:metabolism*; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D009569:Nitric Oxide / Q000378:metabolism; D051381:Rats
D017077:Culture Media, Conditioned; D016207:Cytokines; D036341:Intercellular Signaling Peptides and Proteins; D008070:Lipopolysaccharides; D009569:Nitric Oxide; D015232:Dinoprostone