title: Microglia-derived TNFα induces apoptosis in neural precursor cells via transcriptional activation of the Bcl-2 family member Puma.
abstract: Neuroinflammation is a common feature of acute neurological conditions such as stroke and spinal cord injury, as well as neurodegenerative conditions such as Parkinson's disease, Alzheimer's disease, and amyotrophic lateral sclerosis. Previous studies have demonstrated that acute neuroinflammation can adversely affect the survival of neural precursor cells (NPCs) and thereby limit the capacity for regeneration and repair. However, the mechanisms by which neuroinflammatory processes induce NPC death remain unclear. Microglia are key mediators of neuroinflammation and when activated to induce a pro-inflammatory state produce a number of factors that could affect NPC survival. Importantly, in the present study we demonstrate that tumor necrosis factor α (TNFα) produced by lipopolysaccharide-activated microglia is necessary and sufficient to trigger apoptosis in mouse NPCs in vitro. Furthermore, we demonstrate that microglia-derived TNFα induces NPC apoptosis via a mitochondrial pathway regulated by the Bcl-2 family protein Bax. BH3-only proteins are known to play a key role in regulating Bax activation and we demonstrate that microglia-derived TNFα induces the expression of the BH3-only family member Puma in NPCs via an NF-κB-dependent mechanism. Specifically, we show that NF-κB is activated in NPCs treated with conditioned media from activated microglia and that Puma induction and NPC apoptosis is blocked by the NF-κB inhibitor BAY-117082. Importantly, we have determined that NPC apoptosis induced by activated microglia-derived TNFα is attenuated in Puma-deficient NPCs, indicating that Puma induction is required for NPC death. Consistent with this, we demonstrate that Puma-deficient NPCs exhibit an ∼13-fold increase in survival as compared with wild-type NPCs following transplantation into the inflammatory environment of the injured spinal cord in vivo. In summary, we have identified a key signaling pathway that regulates neuroinflammation induced apoptosis in NPCs in vitro and in vivo that could be targeted to promote regeneration and repair in diverse neurological conditions.
authors.affiliation: Robarts Research Institute, University of Western Ontario, London, ON, Canada.
authors.forename: J
authors.initials: J
authors.lastname: Guadagno
authors.forename: X
authors.initials: X
authors.lastname: Xu
authors.forename: M
authors.initials: M
authors.lastname: Karajgikar
authors.forename: A
authors.initials: A
authors.lastname: Brown
authors.forename: S P
authors.initials: SP
authors.lastname: Cregan
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D051017:Apoptosis Regulatory Proteins / Q000172:deficiency / Q000235:genetics*; D017077:Culture Media, Conditioned / Q000494:pharmacology; D007249:Inflammation / Q000378:metabolism / Q000473:pathology; D008070:Lipopolysaccharides / Q000494:pharmacology; D051379:Mice; D018345:Mice, Knockout; D017628:Microglia / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism / Q000473:pathology; D016328:NF-kappa B / Q000235:genetics / Q000378:metabolism; D058953:Neural Stem Cells / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology / Q000637:transplantation; D009570:Nitriles / Q000494:pharmacology; D015398:Signal Transduction / Q000187:drug effects; D013116:Spinal Cord / Q000187:drug effects / Q000378:metabolism / Q000473:pathology; D013119:Spinal Cord Injuries / Q000378:metabolism / Q000473:pathology; D013450:Sulfones / Q000494:pharmacology; D015533:Transcriptional Activation / Q000187:drug effects*; D014409:Tumor Necrosis Factor-alpha / Q000096:biosynthesis / Q000494:pharmacology*; D025521:Tumor Suppressor Proteins / Q000172:deficiency / Q000235:genetics*; D051028:bcl-2-Associated X Protein / Q000172:deficiency / Q000235:genetics
chemical_list: C434003:3-(4-methylphenylsulfonyl)-2-propenenitrile; D051017:Apoptosis Regulatory Proteins; C494827:Bax protein, mouse; D017077:Culture Media, Conditioned; D008070:Lipopolysaccharides; D016328:NF-kappa B; D009570:Nitriles; C488588:PUMA protein, mouse; D013450:Sulfones; D014409:Tumor Necrosis Factor-alpha; D025521:Tumor Suppressor Proteins; D051028:bcl-2-Associated X Protein