CaMKII phosphorylates collapsin response mediator protein 2 and modulates axonal damage during glutamate excitotoxicity.
Intracellular calcium influx through NMDA receptors triggers a cascade of deleterious signaling events which lead to neuronal death in neurological conditions such as stroke. However, it is not clear as to the molecular mechanism underlying early damage response from axons and dendrites which are important in maintaining a network essential for the survival of neurons. Here, we examined changes of axons treated with glutamate and showed the appearance of betaIII-tubulin positive varicosities on axons before the appearance of neuronal death. Dizocilpine blocked the occurrence of varicosities on axons suggesting that these microstructures were mediated by NMDA receptor activities. Despite early increased expression of pCaMKII and pMAPK after just 10 min of glutamate treatment, only inhibitors to Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) and calpain prevented the occurrence of axonal varicosities. In contrast, inhibitors to Rho kinase, mitogen-activated protein kinase and phosphoinositide 3-kinase were not effective, nor were they able to rescue neurons from death, suggesting CaMKII and calpain are important in axon survival. Activated CaMKII directly phosphorylates collapsin response mediator protein (CRMP) 2 which is independent of calpain-mediated cleavage of CRMP2. Over-expression of CRMP2, but not the phosphorylation-resistant mutant CRMP2-T555A, increased axonal resistance to glutamate toxicity with reduced numbers of varicosities. The levels of both pCRMP2 and pCaMKII were also increased robustly within early time points in ischemic brains and which correlated with the appearance of axonal varicosities in the ischemic neurons. Collectively, these studies demonstrated an important role for CaMKII in modulating the integrity of axons through CRMP2 during excitotoxicity-induced neuronal death.
Hou
Sheng T
ST
Experimental NeuroTherapeutics Laboratory, Institute for Biological Sciences, National Research Council Canada, Ottawa, Ontario, Canada. sheng.hou@nrc-cnrc.gc.ca
Jiang
Susan X
SX
Aylsworth
Amy
A
Ferguson
Graeme
G
Slinn
Jacqueline
J
Hu
Houwen
H
Leung
Thomas
T
Kappler
Joachim
J
Kaibuchi
Kozo
K
D000818:Animals; D001369:Axons / Q000187:drug effects*; D001921:Brain / Q000378:metabolism / Q000473:pathology; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2 / Q000378:metabolism*; D016923:Cell Death / Q000187:drug effects; D002478:Cells, Cultured; D002540:Cerebral Cortex / Q000166:cytology; D004195:Disease Models, Animal; D016291:Dizocilpine Maleate / Q000494:pharmacology; D004622:Embryo, Mammalian; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D018698:Glutamic Acid / Q000494:pharmacology*; D049452:Green Fluorescent Proteins / Q000235:genetics; D020244:Infarction, Middle Cerebral Artery / Q000473:pathology; D036341:Intercellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D009154:Mutation / Q000235:genetics; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism*; D009474:Neurons / Q000166:cytology* / Q000187:drug effects; D010766:Phosphorylation / Q000187:drug effects; D040121:Semaphorin-3A / Q000494:pharmacology; D015398:Signal Transduction / Q000187:drug effects; D014162:Transfection / Q000379:methods; D014404:Tubulin / Q000378:metabolism
D004791:Enzyme Inhibitors; D018691:Excitatory Amino Acid Antagonists; D036341:Intercellular Signaling Peptides and Proteins; D009419:Nerve Tissue Proteins; D040121:Semaphorin-3A; D014404:Tubulin; C095114:collapsin response mediator protein-2; C485184:enhanced green fluorescent protein; D049452:Green Fluorescent Proteins; D018698:Glutamic Acid; D016291:Dizocilpine Maleate; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2