LGI1 downregulation increases neuronal circuit excitability.

OBJECTIVE:Leucine-rich glioma-inactivated 1 (LGI1) is a secreted transsynaptic protein that interacts presynaptically with Kv1.1 potassium channels and a disintegrin and metalloprotease (ADAM) protein 23, and postsynaptically influences α-amino-3-hydroxy-5-methylisoxazole-4-propionate receptors through a direct link with the ADAM22 cell adhesion protein. Haploinsufficiency of LGI1 or autoantibodies directed against LGI1 are associated with human epilepsy, generating the hypothesis that a subacute reduction of LGI1 is sufficient to increase network excitability. METHODS:We tested this hypothesis in ex vivo hippocampal slices and in neuronal cultures, by subacutely reducing LGI1 expression with shRNA. RESULTS:Injection of shRNA-LGI1 in the hippocampus increased dentate granule cell excitability and low-frequency facilitation of mossy fibers to CA3 pyramidal cell neurotransmission. Application of the Kv1 family blocker, α-dendrotoxin, occluded this effect, implicating the involvement of Kv1.1. This subacute reduction of LGI1 was also sufficient to increase neuronal network activity in neuronal primary culture. SIGNIFICANCE:These results indicate that a subacute reduction in LGI1 potentiates neuronal excitability and short-term synaptic plasticity, and increases neuronal network excitability, opening new avenues for the treatment of limbic encephalitis and temporal lobe epilepsies.

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