Activity-dependent stabilization of nascent dendritic spines requires non-enzymatic CaMKIIα function

Abstract

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 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 CaMKIIs 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 functional and structural interactions were altered. Surprisingly, we found that inhibiting CaMKII kinase activity either genetically or pharmacologically did not impair activity-dependent new spine stabilization. In contrast, shRNA knock-down of CaMKII abolished activity-dependent new spine stabilization, which was rescued by co-expressing shRNA-resistant CaMKII. Notably, overexpression of phospho-mimetic CaMKII-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 suggest that nascent dendritic spine stabilization requires structural and scaffolding interactions mediated by CaMKII that are independent of its enzymatic activities. SIGNIFICANCE STATEMENTThe stabilization of nascent dendritic spines is thought to support lasting memory of learned experiences. Here, we show that scaffolding and structural interactions, but not the enzymatic activities, of the kinase CaMKII are required for activity-dependent new spine stabilization. This study furthers our understanding of the cellular and molecular processes that facilitate learning and memory in the mammalian brain. Understanding the cellular and molecular mechanisms of learning and memory is crucial for our ability to develop therapeutics for memory impairments associated with neurological and neurodegenerative disorders.