The Ca2+/Calmodulin(CaM)-dependent protein kinase II (CaMKII) is activated by Ca2+/CaM, but becomes partially autonomous (Ca2+-independent) upon autophosphorylation at T286. This hallmark feature of CaMKII regulation provides a form of molecular memory and is indeed important in long-term potentiation (LTP) of excitatory synapse strength and memory formation. However, emerging evidence supports a direct role in information processing, while storage of synaptic information may instead be mediated by regulated interaction of CaMKII with the NMDA receptor (NMDAR) complex. These and other CaMKII regulation mechanisms are discussed here in the context of the kinase structure and their impact on post-synaptic functions. Recent findings also implicate CaMKII in long-term depression (LTD), as well as functional roles at inhibitory synapses, lending renewed emphasis on better understanding the spatio-temporal control of CaMKII regulation.

In the CA1 region of the rat hippocampus, long-term potentiation (LTP) requires the activation of NMDA receptors (NMDARs) and leads to an enhancement of AMPA receptor (AMPAR) function. In neonatal hippocampus, this increase in synaptic strength seems to be mediated by delivery of AMPARs to the synapse. Here we studied changes in surface expression of native AMPA and NMDA receptors following induction of LTP in the adult rat brain. In contrast to early postnatal rats, we find that LTP in the adult rat does not alter membrane association of AMPARs. Instead, LTP leads to rapid surface expression of NMDARs in a PKC- and Src-family-dependent manner. The present study suggests a developmental shift in the LTP-dependent trafficking of AMPA receptors. Moreover, our results indicate that insertion of NMDA receptors may be a key step in regulating synaptic plasticity.

SUMMARY Traditionally, hippocampal long-term potentiation (LTP) of synaptic strength requires Ca2+/calmodulin(CaM)-dependent protein kinase II (CaMKII) and other kinases, while long-term depression (LTD) requires phosphatases. Here we found that LTD also requires CaMKII and its phospho-T286-induced “autonomous” (Ca2+-independent) activity. However, while LTP is known to induce phosphorylation of the AMPA-type glutamate receptor (AMPAR) subunit GluA1 at S831, LTD instead induced CaMKII-mediated phosphorylation at S567, a site known to reduce synaptic GluA1 localization. GluA1 S831 phosphorylation by “autonomous” CaMKII was further stimulated by Ca2+/CaM, as expected for traditional substrates. By contrast, GluA1 S567 represents a distinct substrate-class that is unaffected by such stimulation. This differential regulation caused GluA1 S831 to be favored by LTP-type stimuli (strong but brief), while GluA1 S567 was favored by LTD-type stimuli (weak but prolonged). Thus, requirement of autonomous CaMKII in opposing forms of plasticity involves distinct substrate classes that are differentially regulated to enable stimulus-dependent substrate-site preference.

Ca 2؉ /calmodulin (CaM)-dependent protein kinase II (CaMKII) is a major mediator of physiological glutamate signaling involved in higher brain functions. Here, we show CaMKII involvement in pathological glutamate signaling relevant in stroke. The novel inhibitor tatCN21 was neuroprotective even when added hours after glutamate insults. By contrast, the "traditional" inhibitor KN93 attenuated excitotoxicity only when present during the insult. Both inhibitors efficiently blocked Ca 2؉ /CaM-stimulated CaMKII activity, CaMKII interaction with NR2B and aggregation of CaMKII holoenzymes. However, only tatCN21 but not KN93 blocked the Ca 2؉ -independent "autonomous" activity generated by Thr-286 autophosphorylation, the hallmark feature of CaMKII regulation. Mutational analysis further validated autonomous CaMKII activity as the drug target crucial for post-insult neuroprotection. Overexpression of CaMKII wild type but not the autonomy-deficient T286A mutant significantly increased glutamate-induced neuronal death. Maybe most importantly, tatCN21 also significantly reduced infarct size in a mouse stroke model (middle cerebral arterial occlusion) when injected (1 mg/kg intravenously) 1 h after onset of arterial occlusion. Together, these data demonstrate that inhibition of autonomous CaMKII activity provides a promising therapeutic avenue for post-insult neuro-protection after stroke.Glutamate is the most abundant excitatory neurotransmitter in the mammalian brain. However, excessive glutamate release causes Ca 2ϩ -dependent excitotoxic neuronal death in pathological situations such as focal cerebral ischemia (stroke) (for review see Refs. 1-4). Most glutamate receptors are involved in excitotoxicity, but especially important are the Ca 2ϩ -permeable ionotropic receptors such as the NMDA 4 -type glutamate receptor (NMDAR) (5-8). Extensive attempts to develop a stroke therapy by targeting glutamate receptors have resulted in disappointment (for review see Refs. 9, 10), suggesting that alternative strategies will be necessary. Currently, the only approved pharmacological treatment of stroke patients is hemolytic therapy with tissue plasminogen activator. However, less than 2% of patients actually receive tissue plasminogen activator. Although tissue plasminogen activator is effective in stroke caused by blood clots, it is actually contraindicated in hemorrhagic stroke, and diagnostic evaluation pushes most patients beyond the therapeutically effective time window (11-13).The Ca 2ϩ /calmodulin (Ca 2ϩ /CaM)-dependent protein kinase II (CaMKII) is a major physiological downstream target of glutamate-induced Ca 2ϩ signaling (for review see Refs. 14 -17) and was examined in this study for involvement in pathological excitotoxic glutamate signaling. CaMKII is highly expressed in brain where it participates in NMDAR-dependent long term potentiation and learning and memory (14 -17). CaMKII forms multimeric holoenzymes, and each kinase subunit is activated separately by Ca 2ϩ /CaM. An inter-subunit autophosphorylation at Thr-286 ...

Ca2ϩ /calmodulin (CaM)-dependent protein kinase II (CaMKII) "autonomy" (T286-autophosphorylation-induced Ca 2ϩ -independent activity) is required for long-term potentiation (LTP) and for learning and memory, as demonstrated by CaMKII T286A mutant mice. The Ͼ20-year-old hypothesis that CaMKII stimulation is required for LTP induction, while CaMKII autonomy is required for LTP maintenance was recently supported using the cell-penetrating fusion-peptide inhibitor antCN27. However, we demonstrate here that ant/ penetratin fusion to CN27 compromised CaMKII-selectivity, by enhancing a previously unnoticed direct binding of CaM to ant/ penetratin. In contrast to antCN27, the improved cell-penetrating inhibitor tatCN21 (5 M) showed neither CaM binding nor inhibition of basal synaptic transmission. In vitro, tatCN21 inhibited stimulated and autonomous CaMKII activity with equal potency. In rat hippocampal slices, tatCN21 inhibited LTP induction, but not LTP maintenance. Correspondingly, tatCN21 also inhibited learning, but not memory storage or retrieval in a mouse in vivo model. Thus, CaMKII autonomy provides a short-term molecular memory that is important in the signal computation leading to memory formation, but is not required as long-term memory store.

The Ca2+/calmodulin-dependent protein kinase II (CaMKII) assembles into large 12-meric holoenzymes, which is thought to enable regulatory processes required for synaptic plasticity underlying learning, memory and cognition. Here we used single particle electron microscopy (EM) to determine a pseudoatomic model of the CaMKIIα holoenzyme in an extended and activation-competent conformation. The holoenzyme is organized by a rigid central hub complex, while positioning of the kinase domains is highly flexible, revealing dynamic holoenzymes ranging from 15–35 nm in diameter. While most kinase domains are ordered independently, ∼20% appear to form dimers and <3% are consistent with a compact conformation. An additional level of plasticity is revealed by a small fraction of bona-fide 14-mers (<4%) that may enable subunit exchange. Biochemical and cellular FRET studies confirm that the extended state of CaMKIIα resolved by EM is the predominant form of the holoenzyme, even under molecular crowding conditions.

Background: Ca 2ϩ -independent autonomous CaMKII activity and nitric oxide (NO) signaling regulate neuronal function and death. Results: NO generated autonomous CaMKII activity by Ca 2ϩ /CaM-dependent S-nitrosylation, and CaMKII inhibition protected from NO-induced neuronal cell death. Conclusion: NO-mediated regulation of CaMKII contributes to its pathological functions. Significance: S-Nitrosylation is a novel path to CaMKII autonomy that connects Ca 2ϩ -and NO signaling.

These molecular consequences are consistent with the alterations in plasticity and memory caused by sNS at the synaptic level. Our data demonstrate the cognitive impact of sNS and associate memory deficits with specific alterations in glutamatergic synaptic function.