11 / 2021-07-08 14:22:32

Inhibition of calcium/calmodulin-dependent protein kinase II results in hyperexcitability by increasing NaV1.2 expression and its interaction with CaM

calmodulin; calcium/calmodulin dependent kinase II; epilepsy; Nav1.2 channel; hyperexcitability

Epilepsy is a set of chronic brain diseases characterized by neuronal hyperexcitability. Dysfunction of calcium/calmodulin (CaM)-dependent kinase II (CaMKII) has been shown to involve in epilepsy. However, the exact mechanism underlying CaMKII inhibition in epilepsy remains to be fully elucidated. Additionally, the relationship between Ca²⁺/CaM/CaMKII and voltage-gated sodium (Na_V) channel, a vital antiepileptic drug target, is unknown. In this study, KN93, a prototypical CaMKII inhibitor, was applied to investigate the role of CaMKII inactivation in epilepsy. First, more seizure-like events were observed in response to CaMKII inhibition via EEG in both Wistar and tremor (TRM) rats, an animal model of genetic epilepsy. Meanwhile, CaMKII inhibition enhanced the persistent, slow inactivating sodium current (I_NaP) and hyperexcitability in cultured hippocampal neurons. Likewise, CaMKII inhibition resulted in the potentiation in neuronal activity in induced pluripotent stem cell (iPSC)-derived cortical neurons. In addition, the expression level of Na_V1.2 channel subtype were increased in hippocampus of both Wistar and TRM rats, in cultured hippocampal neurons as well as in iPSC-derived cortical neurons following CaMKII inhibition. Furthermore, elevated association of Na_V1.2 with CaM were also detected in in vivo and in vitro experiments. Intriguingly, a peptide that antagonized CaM binding to Na_V1.2 IQ (ACNp) rescued the hyperexcitability induced by CaMKII inhibition in in vivo and in vitro experiments. Altogether, our data illustrate that CaMKII inhibition by KN93 leads to hyperexcitability through increasing the expression of Na_V1.2 and its association with CaM, thereby providing a novel mechanism for neuronal hyperexcitability.