Interactions between chemokines: regulation of fractalkine/CX3CL1 homeostasis by SDF/CXCL12 in cortical neurons.
The soluble form of the chemokine fractalkine/CX(3)CL1 regulates microglia activation in the central nervous system (CNS), ultimately affecting neuronal survival. This study aims to determine whether CXCL12, another chemokine constitutively expressed in the CNS (known as stromal cell-derived factor 1; SDF-1), regulates cleavage of fractalkine from neurons. To this end, ELISA was used to measure protein levels of soluble fractalkine in the medium of rat neuronal cultures exposed to SDF-1. Gene arrays, quantitative RT-PCR, and Western blot were used to measure overall fractalkine expression in neurons. The data show that the rate of fractalkine shedding in healthy cultures positively correlates with in vitro differentiation and survival. In analogy to non-neuronal cells, metalloproteinases (ADAM10/17) are involved in cleavage of neuronal fractalkine as indicated by studies with pharmacologic inhibitors. Moreover, treatment of the neuronal cultures with SDF-1 stimulates expression of the inducible metalloproteinase ADAM17 and increases soluble fractalkine content in culture medium. The effect of SDF-1 is blocked by an inhibitor of both ADAM10 and -17, but only partially affected by a more specific inhibitor of ADAM10. In addition, SDF-1 also up-regulates expression of the fractalkine gene. Conversely, exposure of neurons to an excitotoxic stimulus (i.e. NMDA) inhibits alpha-secretase activity and markedly diminishes soluble fractalkine levels, leading to cell death. These results, along with previous findings on the neuroprotective role of both SDF-1 and fractalkine, suggest that this novel interaction between the two chemokines may contribute to in vivo regulation of neuronal survival by modulating microglial neurotoxic properties.
Cook
Anna
A
Departments of Pharmacology and Physiology, Drexel University College of Medicine, Philadelphia, Pennsylvania 19102, USA.
Hippensteel
Randi
R
Shimizu
Saori
S
Nicolai
Jaclyn
J
Fatatis
Alessandro
A
Meucci
Olimpia
O
D051722:ADAM Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism; D000072197:ADAM10 Protein; D000072198:ADAM17 Protein; D053829:Amyloid Precursor Protein Secretases / Q000037:antagonists & inhibitors / Q000378:metabolism; D000818:Animals; D015153:Blotting, Western; D002478:Cells, Cultured; D002540:Cerebral Cortex / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D054428:Chemokine CX3CL1 / Q000235:genetics / Q000378:metabolism*; D054377:Chemokine CXCL12 / Q000235:genetics / Q000378:metabolism*; D004622:Embryo, Mammalian / Q000166:cytology / Q000378:metabolism; D004797:Enzyme-Linked Immunosorbent Assay; D006706:Homeostasis; D016202:N-Methylaspartate / Q000494:pharmacology; D009457:Neuroglia / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D009474:Neurons / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D051381:Rats; D020133:Reverse Transcriptase Polymerase Chain Reaction
D054428:Chemokine CX3CL1; D054377:Chemokine CXCL12; C515540:Cx3cl1 protein, rat; D012333:RNA, Messenger; D016202:N-Methylaspartate; D053829:Amyloid Precursor Protein Secretases; D051722:ADAM Proteins; D000072197:ADAM10 Protein; C542371:ADAM10 protein, rat; D000072198:ADAM17 Protein; C000606464:Adam17 protein, rat