Formyl-methionyl-leucyl-phenylalanine-induced dopaminergic neurotoxicity via microglial activation: a mediator between peripheral infection and neurodegeneration?
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.
Gao
Xi
X
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.
Hu
Xiaoming
X
Qian
Li
L
Yang
Sufen
S
Zhang
Wei
W
Zhang
Dan
D
Wu
Xuefei
X
Fraser
Alison
A
Wilson
Belinda
B
Flood
Patrick M
PM
Block
Michelle
M
Hong
Jau-Shyong
JS
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
D009240:N-Formylmethionine Leucyl-Phenylalanine; D019255:NADPH Oxidases; D004298:Dopamine