Olfactomedin-3 Enhances Seizure Activity by Interacting With AMPA Receptors in Epilepsy Models.

Shirong Tang,Changyin Yu,Tiancheng Wang,Ping Xu,Yi Guo,Junwei Zeng,Zhong Luo,Dongxu Li,Yuemei Luo,Zucai Xu,Yongsu Zheng,Xiaogang Zhang

doi:10.3389/fcell.2020.00722

Abstract

Background: OLFM3 (olfactomedin-3) is a member of the olfactomedin domain family, which has been found to stimulate the formation and adhesion of tight cell connections and to regulate cytoskeleton formation and cell migration. Differences in the gene coding for OLFM3 have been found between patients with epilepsy and controls. However, the exact role of OLFM3 in epilepsy has not been thoroughly investigated.Methods: Biochemical methods were used to assess OLFM3 expression and localization in the cortex of patients with temporal lobe epilepsy and in the hippocampus and cortex of epileptic mice. Electrophysiological recordings were used to measure the role of OLFM3 in regulating hippocampal excitability in a model of magnesium-free-induced seizure in vitro. Behavioral experiments were performed in a pentylenetetrazol (PTZ)-induced seizure model, and electroencephalograms (EEGs) were recorded in the chronic phase of the kainic acid (KA)-induced epilepsy model in vivo. OLFM3 and its interaction with AMPAR (α-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid receptor) subunits were analyzed by co-immunoprecipitation.Results: The expression of OLFM3 was increased in the cortex of patients with temporal lobe epilepsy and in the hippocampus and cortex of epileptic mice compared with controls. Interestingly, lentivirus-mediated overexpression of OLFM3 in the hippocampus increased the susceptibility of mice to PTZ-induced seizures, and OLFM3 knockdown had the opposite effect. OLFM3 affected AMPAR currents in a brain-slice model of epileptiform activity induced by Mg2+-free medium. We found that OLFM3 co-immunoprecipitation with GluA1 and GluA2. Furthermore, downregulation or overexpression of OLFM3 in the hippocampus affected the membrane expression of GluA1 and GluA2 in epileptic mice.Conclusion: These findings reveal that OLFM3 may enhance seizure activity by interacting with GluA1 and GluA2, potentially indicating a molecular mechanism for new therapeutic strategies.

Highlights

Epilepsy is a common chronic neurological disease, and temporal lobe epilepsy (TLE) is one of the most common types of epilepsy in adult patients (Hauser et al, 1993; Jobst and Cascino, 2015)
The expression of OLFM3 was increased in the cortex of patients with temporal lobe epilepsy and in the hippocampus and cortex of epileptic mice compared with controls
OLFM3 affected α-amino-3-hydroxy5-methyl-4-isoxazole-propionic acid receptor (AMPAR) currents in a brain-slice model of epileptiform activity induced by Mg2+-free medium

Summary

Introduction

Epilepsy is a common chronic neurological disease, and temporal lobe epilepsy (TLE) is one of the most common types of epilepsy in adult patients (Hauser et al, 1993; Jobst and Cascino, 2015). OLFM3 has been found to be a neuronal expression protein that can stimulate the formation and adhesion of tight cell connections and regulate cytoskeleton formation and cell migration (Anholt, 2014). The concentration of the AMPA receptor subunits GluA1 and GluA2 has been shown to be significantly reduced in hippocampal synaptosomes in the postsynaptic density of a kainic acid (KA)-based rat model of chronic TLE These changes in synaptic AMPAR subunits may contribute to further aggravation of the excitotoxic vulnerability of neurons and have significant implications for hippocampal cognition (Egbenya et al, 2018). OLFM3 (olfactomedin-3) is a member of the olfactomedin domain family, which has been found to stimulate the formation and adhesion of tight cell connections and to regulate cytoskeleton formation and cell migration. The exact role of OLFM3 in epilepsy has not been thoroughly investigated

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Discussion

Conclusion