title: Formyl-methionyl-leucyl-phenylalanine-induced dopaminergic neurotoxicity via microglial activation: a mediator between peripheral infection and neurodegeneration?
abstract: BACKGROUND
  Parkinson disease (PD), a chronic neurodegenerative disease, has been proposed to be a multifactorial disorder resulting from a combination of environmental mechanisms (chemical, infectious, and traumatic), aging, and genetic deficits. Microglial activation is important in the pathogenesis of PD.
  
  
  OBJECTIVE
  We investigated dopaminergic (DA) neurotoxicity and the underlying mechanisms of formyl-methionyl-leucyl-phenylalanine (fMLP), a bacteria-derived peptide, in relation to PD.
  
  
  METHODS
  We measured DA neurotoxicity using a DA uptake assay and immunocytochemical staining (ICC) in primary mesencephalic cultures from rodents. Microglial activation was observed via ICC, flow cytometry, and superoxide measurement.
  
  
  RESULTS
  fMLP can cause selective DA neuronal loss at concentrations as low as 10(-13) M. Further, fMLP (10(-13) M) led to a significant reduction in DA uptake capacity in neuron/glia (N/G) cultures, but not in microglia-depleted cultures, indicating an indispensable role of microglia in fMLP-induced neurotoxicity. Using ICC of a specific microglial marker, OX42, we observed morphologic changes in activated microglia after fMLP treatment. Microglial activation after fMLP treatment was confirmed by flow cytometry analysis of major histocompatibility antigen class II expression on a microglia HAPI cell line. Mechanistic studies revealed that fMLP (10(-13) M)-induced increase in the production of extracellular superoxide from microglia is critical in mediating fMLP-elicited neurotoxicity. Pharmacologic inhibition of NADPH oxidase (PHOX) with diphenylene-iodonium or apocynin abolished the DA neurotoxicity of fMLP. N/G cultures from PHOX-deficient (gp91PHOX-/ -) mice were also insensitive to fMLP-induced DA neurotoxicity.
  
  
  CONCLUSIONS
  fMLP (10(-13) M) induces DA neurotoxicity through activation of microglial PHOX and subsequent production of superoxide, suggesting a role of fMLP in the central nervous system inflammatory process.
authors.affiliation: Neuropharmacology Section, Laboratory of Pharmacology and Chemistry, National Institute of Environmental Health Sciences, National Institutes of Health, Department of Health and Human Services, Research Triangle Park, NC 27709, USA.
authors.forename: Xi
authors.initials: X
authors.lastname: Gao
authors.forename: Xiaoming
authors.initials: X
authors.lastname: Hu
authors.forename: Li
authors.initials: L
authors.lastname: Qian
authors.forename: Sufen
authors.initials: S
authors.lastname: Yang
authors.forename: Wei
authors.initials: W
authors.lastname: Zhang
authors.forename: Dan
authors.initials: D
authors.lastname: Zhang
authors.forename: Xuefei
authors.initials: X
authors.lastname: Wu
authors.forename: Alison
authors.initials: A
authors.lastname: Fraser
authors.forename: Belinda
authors.initials: B
authors.lastname: Wilson
authors.forename: Patrick M
authors.initials: PM
authors.lastname: Flood
authors.forename: Michelle
authors.initials: M
authors.lastname: Block
authors.forename: Jau-Shyong
authors.initials: JS
authors.lastname: Hong
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D002494:Central Nervous System Infections / Q000209:etiology* / Q000378:metabolism / Q000473:pathology; D004298:Dopamine / Q000378:metabolism*; D004789:Enzyme Activation; D005260:Female; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D017628:Microglia / Q000187:drug effects* / Q000201:enzymology / Q000378:metabolism; D009240:N-Formylmethionine Leucyl-Phenylalanine / Q000633:toxicity*; D019255:NADPH Oxidases / Q000378:metabolism; D019636:Neurodegenerative Diseases / Q000139:chemically induced* / Q000378:metabolism / Q000473:pathology; D009474:Neurons / Q000187:drug effects / Q000378:metabolism; D018384:Oxidative Stress; D010300:Parkinson Disease / Q000209:etiology*; D011247:Pregnancy; D051381:Rats; D011916:Rats, Inbred F344
chemical_list: D009240:N-Formylmethionine Leucyl-Phenylalanine; D019255:NADPH Oxidases; D004298:Dopamine