Activity-Dependent Stabilization of Nascent Dendritic Spines Requires Nonenzymatic CaMKIIα α Function

The outgrowth and stabilization of nascent dendritic spines are crucial processes underlying learning and memory. Most new spines retract shortly after growth; only a small subset is stabilized and integrated into the new circuit connections that support learning. New spine stabilization has been shown to rely upon activity-dependent molecular mechanisms that also contribute to long-term potentiation (LTP) of synaptic strength. Indeed, disruption of the activity-dependent targeting of the kinase CaMKII alpha alpha to the GluN2B subunit of the NMDA-type glutamate receptor disrupts both LTP and activity-dependent stabilization of new spines. Yet it is not known which of CaMKII alpha's alpha 's many enzymatic and structural functions are important for new spine stabilization. Here, we used two-photon imaging and photolysis of caged glutamate to monitor the activity-dependent stabilization of new dendritic spines on hippocampal CA1 neurons from mice of both sexes in conditions where CaMKII alpha alpha functional and structural interactions were altered. Surprisingly, we found that inhibiting CaMKII alpha alpha kinase activity either genetically or pharmacologically did not impair activity-dependent new spine stabilization. In contrast, shRNA knockdown of CaMKII alpha alpha abolished activity-dependent new spine stabilization, which was rescued by co-expressing shRNA-resistant full-length CaMKII alpha, alpha , but not by a truncated monomeric CaMKII alpha. alpha . Notably, overexpression of phospho-mimetic CaMKII alpha-T286D, alpha-T286D, which exhibits activity-independent targeting to GluN2B, enhanced basal new spine survivorship in the absence of additional glutamatergic stimulation, even when kinase activity was disrupted. Together, our results support a model in which nascent dendritic spine stabilization requires structural and scaffolding interactions mediated by dodecameric CaMKII alpha alpha that are independent of its enzymatic activities.