Chemokine fractalkine/CX3CL1 negatively modulates active glutamatergic synapses in rat hippocampal neurons.
We examined the effects of the chemokine fractalkine (CX3CL1) on EPSCs evoked by electrical stimulation of Schaffer collaterals in patch-clamped CA1 pyramidal neurons from rat hippocampal slices. Acute application of CX3CL1 caused a sustained reduction of EPSC amplitude, with partial recovery after washout. CX3CL1-induced EPSC depression is postsynaptic in nature, because paired-pulse ratio was maintained, amplitude distribution of spontaneous excitatory postsynaptic currents shifted to lower values, and whole-cell current responses to AMPA were reversibly inhibited. EPSC depression by CX3CL1 is mediated by CX3CL1 receptor (CX3CR1), because CX3CL1 was unable to influence EPSC amplitude in CA1 pyramidal neurons from CX3CR1 knock-out mice. CX3CL1-induced depression of both EPSC and AMPA current was not observed in the absence of afferent fiber stimulation or AMPA receptor activation, respectively, indicating the requirement of sustained receptor activity for its development. Findings obtained from hippocampal slices, cultured hippocampal neurons, and transfected human embryonic kidney cells indicate that a Ca2+-, cAMP-, and phosphatase-dependent process is likely to modulate CX3CL1 effects because of the following: (1) CX3CL1-induced depression was antagonized by intracellular BAPTA, 8Br-cAMP, phosphatase inhibitors, and pertussis toxin (PTX); (2) CX3CL1 inhibited forskolin-induced cAMP formation sensitive to PTX; and (3) CX3CL1 inhibited forskolin-induced Ser845 GluR1 phosphorylation, which was sensitive to PTX and dependent on Ca2+ and phosphatase activity. Together, these findings indicate that CX3CL1 negatively modulates AMPA receptor function at active glutamatergic synapses through cell-signaling pathways by influencing the balance between kinase and phosphatase activity.
Ragozzino
Davide
D
Istituto Pasteur-Fondazione Cenci Bolognetti and Dipartimento di Fisiologia Umana e Farmacologia, Università La Sapienza, Centro di Eccellenza BEMM, 00185 Roma, Italy. davide.ragozzino@uniroma1.it
Di Angelantonio
Silvia
S
Trettel
Flavia
F
Bertollini
Cristina
C
Maggi
Laura
L
Gross
Cornelius
C
Charo
Israel F
IF
Limatola
Cristina
C
Eusebi
Fabrizio
F
D000818:Animals; D000073883:CX3C Chemokine Receptor 1; D002460:Cell Line; D002478:Cells, Cultured; D054428:Chemokine CX3CL1; D020523:Chemokines, CX3C / Q000235:genetics / Q000378:metabolism* / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D018698:Glutamic Acid / Q000378:metabolism*; D006801:Humans; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism* / Q000494:pharmacology; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D017208:Rats, Wistar; D019707:Receptors, Chemokine / Q000235:genetics / Q000378:metabolism; D013569:Synapses / Q000187:drug effects / Q000378:metabolism*
D000073883:CX3C Chemokine Receptor 1; C515538:CX3CL1 protein, human; D054428:Chemokine CX3CL1; D020523:Chemokines, CX3C; C515539:Cx3cl1 protein, mouse; C515540:Cx3cl1 protein, rat; C471885:Cx3cr1 protein, mouse; D004791:Enzyme Inhibitors; D008565:Membrane Proteins; D019707:Receptors, Chemokine; D018698:Glutamic Acid