Fractalkine cleavage from neuronal membranes represents an acute event in the inflammatory response to excitotoxic brain damage.
Fractalkine is a recently identified chemokine that exhibits cell adhesion and chemoattractive properties. It represents a unique member of the chemokine superfamily because it is located predominantly in the brain in which it is expressed constitutively on specific subsets of neurons. To elucidate the possible role of neuronally expressed fractalkine in the inflammatory response to neuronal injury, we have analyzed the regulation of fractalkine mRNA expression and protein cleavage under conditions of neurotoxicity. We observed that mRNA encoding fractalkine is unaffected by experimental ischemic stroke (permanent middle cerebral artery occlusion) in the rat. Similarly, in vitro, levels of fractalkine mRNA were unaffected by ensuing excitotoxicity. However, when analyzed at the protein level, we found that fractalkine is rapidly cleaved from cultured neurons in response to an excitotoxic stimulus. More specifically, fractalkine cleavage preceded actual neuronal death by 2-3 hr, and, when evaluated functionally, fractalkine represented the principal chemokine released from the neurons into the culture medium upon an excitotoxic stimulus to promote chemotaxis of primary microglial and monocytic cells. We further demonstrate that cleavage of neuron-derived, chemoattractive fractalkine can be prevented by inhibition of matrix metalloproteases. These data strongly suggest that dynamic proteolytic cleavage of fractalkine from neuronal membranes in response to a neurotoxic insult, and subsequent chemoattraction of reactive immune cells, may represent an early event in the inflammatory response to neuronal injury.
Chapman
G A
GA
Department of Neuroscience Research, SmithKline Beecham Pharmaceuticals, Harlow, Essex, CM19 5AW, United Kingdom. gayle_chapman-1@sbphrd.com
Moores
K
K
Harrison
D
D
Campbell
C A
CA
Stewart
B R
BR
Strijbos
P J
PJ
D000818:Animals; D000831:Animals, Newborn; D001921:Brain / Q000098:blood supply / Q000187:drug effects / Q000503:physiopathology; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism*; D002478:Cells, Cultured; D054428:Chemokine CX3CL1; D020523:Chemokines, CX3C / Q000235:genetics / Q000378:metabolism* / Q000494:pharmacology; D002633:Chemotaxis / Q000187:drug effects / Q000502:physiology; D017077:Culture Media, Conditioned / Q000032:analysis / Q000378:metabolism; D004195:Disease Models, Animal; D004660:Encephalitis / Q000209:etiology / Q000378:metabolism*; D004730:Endothelium, Vascular / Q000166:cytology / Q000378:metabolism; D018698:Glutamic Acid / Q000633:toxicity; D020244:Infarction, Middle Cerebral Artery / Q000150:complications / Q000378:metabolism*; D007375:Interleukin-1 / Q000235:genetics / Q000378:metabolism; D061965:Matrix Metalloproteinase Inhibitors; D020782:Matrix Metalloproteinases / Q000378:metabolism; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism* / Q000494:pharmacology; D017628:Microglia / Q000166:cytology / Q000187:drug effects; D009000:Monocytes / Q000166:cytology / Q000187:drug effects; D009474:Neurons / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D010649:Phenylalanine / Q000031:analogs & derivatives* / Q000494:pharmacology; D011480:Protease Inhibitors / Q000494:pharmacology; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D013876:Thiophenes / Q000494:pharmacology; D014162:Transfection; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology
D054428:Chemokine CX3CL1; D020523:Chemokines, CX3C; D017077:Culture Media, Conditioned; C515540:Cx3cl1 protein, rat; D007375:Interleukin-1; D061965:Matrix Metalloproteinase Inhibitors; D008565:Membrane Proteins; D011480:Protease Inhibitors; D012333:RNA, Messenger; D013876:Thiophenes; D014409:Tumor Necrosis Factor-alpha; D018698:Glutamic Acid; D010649:Phenylalanine; C080985:batimastat; D020782:Matrix Metalloproteinases