EFFECTS OF CHRONIC CANNABINOID SIGNALING ON SYNAPTIC ORGANIZER LGI1 ABUNDANCE AND DISTRIBUTION

Despite widespread use of delta-9-tetrahydrocannabinol (THC)-containing cannabis products, knowledge of their sustained impact on cellular processes in the brain is limited. Identifying novel effectors dysregulated by chronic cannabinoid signaling is therefore critical to understanding their long-term effects and gaining insight into the endocannabinoid system. We identified reduced abundance of the synaptic glycoprotein Leucine-rich, Glioma Inactivated 1 (LGI1) following chronic treatment with THC in rat primary neuron cultures. Like cannabinoid signaling, LGI1 affects presynaptic excitability through interaction with voltage-gated potassium channels, whereby activity-induced exocytosis of LGI1 prolongs potassium efflux. Notably, LGI1’s reported molecular weight varies, possibly indicating the existence of functional variants. With western blotting, we identified a ~60 kDa LGI1 variant to be less abundant following chronic THC treatment, while two ~64 kDa variants remained stable. Using biotin labeling, we showed that only the smaller form was localized on the cell surface and was enriched in the microsomal fraction. However, contrasting with previous literature, incubating the lysate with the glycosidase PNGase F revealed that neither form was glycosylated. When probing with a different anti-LGI1 antibody, we again did not detect glycosylation, but the absence of the ~60 kDa variant in the microsomal fraction and lack of THC-induced change in abundance, suggesting that LGI1 exists in two distinctly regulated ~60 kDa populations. Next, we will characterize downstream signaling responsible for loss of this LGI1 variant and its functional consequence. This work suggests a novel way cannabinoid signaling may regulate synaptic activity and highlights the need for additional characterization of LGI1.