Protein kinase A-mediated synapsin I phosphorylation is a central modulator of Ca2+-dependent synaptic activity.
Protein kinase A (PKA) modulates several steps of synaptic transmission. However, the identification of the mediators of these effects is as yet incomplete. Synapsins are synaptic vesicle (SV)-associated phosphoproteins that represent the major presynaptic targets of PKA. We show that, in hippocampal neurons, cAMP-dependent pathways affect SV exocytosis and that this effect is primarily brought about through synapsin I phosphorylation. Phosphorylation by PKA, by promoting dissociation of synapsin I from SVs, enhances the rate of SV exocytosis on stimulation. This effect becomes relevant when neurons are challenged with sustained stimulation, because it appears to counteract synaptic depression and accelerate recovery from depression by fostering the supply of SVs from the reserve pool to the readily releasable pool. In contrast, synapsin phosphorylation appears to be dispensable for the effects of cAMP on the frequency and amplitude of spontaneous synaptic currents and on the amplitude of evoked synaptic currents. The modulation of depolarization-evoked SV exocytosis by PKA phosphorylation of synapsin I is primarily caused by calmodulin (CaM)-dependent activation of cAMP pathways rather than by direct activation of CaM kinases. These data define a hierarchical crosstalk between cAMP- and CaM-dependent cascades and point to synapsin as a major effector of PKA in the modulation of activity-dependent SV exocytosis.
Menegon
Andrea
A
San Raffaele Scientific Institute and Vita-Salute University, 20132 Milan, Italy.
Bonanomi
Dario
D
Albertinazzi
Chiara
C
Lotti
Francesco
F
Ferrari
Giuliana
G
Kao
Hung-Teh
HT
Benfenati
Fabio
F
Baldelli
Pietro
P
Valtorta
Flavia
F
D000704:Analysis of Variance; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D017868:Cyclic AMP-Dependent Protein Kinases / Q000502:physiology*; D004347:Drug Interactions; D004558:Electric Stimulation / Q000379:methods; D004622:Embryo, Mammalian; D004789:Enzyme Activation / Q000502:physiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005455:Fluorescent Antibody Technique / Q000379:methods; D006624:Hippocampus / Q000166:cytology; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology / Q000528:radiation effects; D051379:Mice; D018345:Mice, Knockout; D009474:Neurons / Q000166:cytology* / Q000187:drug effects / Q000502:physiology; D018408:Patch-Clamp Techniques / Q000379:methods; D010766:Phosphorylation / Q000187:drug effects / Q000528:radiation effects; D011189:Potassium Chloride / Q000494:pharmacology; D011726:Pyridinium Compounds / Q000378:metabolism; D000644:Quaternary Ammonium Compounds / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D013569:Synapses / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects; D016704:Synapsins / Q000172:deficiency / Q000378:metabolism*; D013572:Synaptic Vesicles / Q000187:drug effects / Q000502:physiology; D014162:Transfection / Q000379:methods
D004791:Enzyme Inhibitors; C092350:FM 4-64; D011726:Pyridinium Compounds; D000644:Quaternary Ammonium Compounds; D016704:Synapsins; D011189:Potassium Chloride; D017868:Cyclic AMP-Dependent Protein Kinases; D002118:Calcium