Heparan Sulfates Regulate Axonal Excitability and Context Generalization through Ca2+/Calmodulin-Dependent Protein Kinase II

Abstract

Our previous studies demonstrated that enzymatic removal of highly sulfated heparan sulfates with heparinase 1 impaired axonal excitability and reduced expression of ankyrin G at the axon initial segments in the CA1 region of the hippocampus ex vivo, impaired context discrimination in vivo, and increased Ca2+/calmodulin-dependent protein kinase II (CaMKII) activity in vitro. Here, we show that in vivo delivery of heparinase 1 in the CA1 region of the hippocampus elevated autophosphorylation of CaMKII 24 h after injection in mice. Patch clamp recording in CA1 neurons revealed no significant heparinase effects on the amplitude or frequency of miniature excitatory and inhibitory postsynaptic currents, while the threshold for action potential generation was increased and fewer spikes were generated in response to current injection. Delivery of heparinase on the next day after contextual fear conditioning induced context overgeneralization 24 h after injection. Co-administration of heparinase with the CaMKII inhibitor (autocamtide-2-related inhibitory peptide) rescued neuronal excitability and expression of ankyrin G at the axon initial segment. It also restored context discrimination, suggesting the key role of CaMKII in neuronal signaling downstream of heparan sulfate proteoglycans and highlighting a link between impaired CA1 pyramidal cell excitability and context generalization during recall of contextual memories.

Neurocan regulates axon initial segment organization and neuronal activity in cultured cortical neurons

“…For instance, digestion of chondroitin sulfates with chondroitinase ABC (chABC) modulates the excitability of parvalbumin-expressing interneurons (Dityatev et al, 2007; Hayani et al, 2018). In contrast, the digestion of heparan sulphates with heparinase reduces the excitability of excitatory neurons and downregulates AnkG at the AIS (Minge et al, 2017) in a calcium/calmodulin kinase II (CaMKII)-dependent manner (Song et al, 2023). Knockdown of Bcan in PV+ interneurons reduced their excitability via modifying clustering of potassium channels (Favuzzi et al, 2017).…”