LTP expression mediated by autonomous activity of GluN2B-bound CaMKII.

Learning and memory are thought to require the induction and maintenance of long-term potentiation (LTP) of synaptic strength. LTP induction requires the Ca/calmodulin-dependent protein kinase II (CaMKII) but for structural rather than enzymatic functions. We show that the relevant structural function is regulated by CaMKII binding to the NMDA-type glutamate receptor subunit GluN2B.

Induction of LTP mechanisms in dually innervated dendritic spines.

Dendritic spines are the postsynaptic compartments of excitatory synapses, however, a substantial subset of spines additionally receives inhibitory input. In such dually innervated spines (DiSs), excitatory long-term potentiation (LTP) mechanisms are suppressed, but can be enabled by blocking tonic inhibitory GABA receptor signaling. Here we show that LTP mechanisms at DiSs are also enabled by two other excitatory LTP stimuli.

LTP induction by structural rather than enzymatic functions of CaMKII.

Learning and memory are thought to require hippocampal long-term potentiation (LTP), and one of the few central dogmas of molecular neuroscience that has stood undisputed for more than three decades is that LTP induction requires enzymatic activity of the Ca/calmodulin-dependent protein kinase II (CaMKII). However, as we delineate here, the experimental evidence is surprisingly far from conclusive. All previous interventions inhibiting enzymatic CaMKII activity and LTP also interfere with structural CaMKII roles, in particular binding to the NMDA-type glutamate receptor subunit GluN2B.

Distinct synaptic pools of DAPK1 differentially regulate activity-dependent synaptic CaMKII accumulation.

The death-associated protein kinase 1 (DAPK1) regulates the synaptic movement of the Ca/calmodulin (CaM)-dependent protein kinase II (CaMKII). Synaptic CaMKII accumulation is mediated via binding to the NMDA-receptor subunit GluN2B and is required for long-term potentiation (LTP). By contrast, long-term depression (LTD) instead requires specific suppression of this movement, which is mediated by competitive DAPK1 binding to GluN2B.

Short-term CaMKII inhibition with tatCN19o does not erase pre-formed memory in mice and is neuroprotective in pigs.

The Ca/calmodulin-dependent protein kinase II (CaMKII) is a central regulator of learning and memory, which poses a problem for targeting it therapeutically. Indeed, our study supports prior conclusions that long-term interference with CaMKII signaling can erase pre-formed memories. By contrast, short-term pharmacological CaMKII inhibition with the neuroprotective peptide tatCN19o interfered with learning in mice only mildly and transiently (for less than 1 h) and did not at all reverse pre-formed memories.

Short-term CaMKII inhibition with tatCN19o does not erase pre-formed memory and is neuroprotective in non-rodents.

The Ca /calmodulin-dependent protein kinase II (CaMKII) is a central regulator of learning and memory, which poses a problem for targeting it therapeutically. Indeed, our study supports prior conclusions that long-term interference with CaMKII signaling can erase pre-formed memories. By contrast, short-term pharmacological CaMKII inhibition with tatCN19o interfered with learning in mice only mildly and transiently (for less than 1 h) and did not at all reverse pre-formed memories.

Aβ-induced synaptic impairments require CaMKII activity that is stimulated by indirect signaling events.

Aβ bears homology to the CaMKII regulatory domain, and peptides derived from this domain can bind and disrupt the CaMKII holoenzyme, suggesting that Aβ could have a similar effect. Notably, Aβ impairs the synaptic CaMKII accumulation that is mediated by GluN2B binding, which requires CaMKII assembly into holoenzymes. Furthermore, this Aβ-induced impairment is prevented by CaMKII inhibitors that should also inhibit the putative direct Aβ binding.

GluN2B S1303 phosphorylation by CaMKII or DAPK1: no indication for involvement in ischemia or LTP.

Binding of two different CaM kinases, CaMKII and DAPK1, to the NMDA-type glutamate receptor (NMDAR) subunit GluN2B near S1303 has been implicated in excitotoxic/ischemic neuronal cell death. The GluN2B mutation (L1298A, R1300Q) is neuroprotective but abolishes only CaMKII but not DAPK1 binding. However, both kinases can additionally phosphorylate GluN2B S1303.

CaMKIIα knockout protects from ischemic neuronal cell death after resuscitation from cardiac arrest.

CaMKIIα plays a dual role in synaptic plasticity, as it can mediate synaptic changes in opposing directions. We hypothesized that CaMKIIα plays a similar dual role also in neuronal cell death and survival. Indeed, the CaMKII inhibitor tatCN21 is neuroprotective when added during or after excitotoxic/ischemic insults, but was described to cause sensitization when applied long-term prior to such insult.

Young DAPK1 knockout mice have altered presynaptic function.

The death-associated protein kinase 1 (DAPK1) has recently been shown to have a physiological function in long-term depression (LTD) of glutamatergic synapses: acute inhibition of DAPK1 blocked the LTD that is normally seen at the hippocampal CA1 synapse in young mice, and a pharmacogenetic combination approach showed that this specifically required DAPK1-mediated suppression of postsynaptic Ca/calmodulin-dependent protein kinase II binding to the NMDA-type glutamate receptor (NMDAR) subunit GluN2B during LTD stimuli. Surprisingly, we found here that genetic deletion of DAPK1 (in DAPK1 mice) did not reduce LTD. Paired pulse facilitation experiments indicated a presynaptic compensation mechanism: in contrast to wild-type mice, LTD stimuli in DAPK1 mice decreased presynaptic release probability.

The CaMKII K42M and K42R mutations are equivalent in suppressing kinase activity and targeting.

CaMKII is an important mediator of forms of synaptic plasticity that are thought to underly learning and memory. The CaMKII mutants K42M and K42R have been used interchangeably as research tools, although some reported phenotypic differences suggest that they may differ in the extent to which they impair ATP binding. Here, we directly compared the two mutations at the high ATP concentrations that exist within cells (~4 mM).