The Downregulation of Truncated TrkB Receptors Modulated by MicroRNA-185 Activates Full-Length TrkB Signaling and Suppresses the Epileptiform Discharges in Cultured Hippocampal Neurons.

Abstract

Epilepsy is a common neurological disorder characterised by occurrence of spontaneous recurrent epileptiform discharges (SREDs) in neurons. The cellular mechanisms that underlie epilepsy are known to be regulated by brain-derived neurotrophic factor. However, some studies show that tropomyosin-related kinase B (TrkB), which is the receptor for BDNF, plays an important role in the pathophysiology of epilepsy. Our previous research revealed that truncated TrkB receptors are upregulated in a rat hippocampal neuronal model of SREDs. In contrast, full-length TrkB receptors are downregulated. Furthermore, the activation of full-length TrkB signaling is suppressed by the overexpression of truncated TrkB. In this study, to regulate the expression of truncated TrkB receptor and full-length TrkB signaling, rno-miR-185-3p was transduced into the SREDs model. Then, the changes in the activity of L-type voltage-gated calcium channels (VGCCs) and in epileptiform discharges were investigated. Transduction of rno-miR-185-3p downregulated the expression of truncated TrkB and dramatically activated full-length TrkB signaling in the model. Next, we found that the activation of full-length TrkB signaling decreased the maximal Ca2+ current density in the model, delayed the steady-state activation and accelerated the inactivation of L-type VGCCs. Finally, the epileptiform discharges in the model could be impaired. Based on the above results, we suggest that the activation of full-length TrkB signaling may suppress the properties of L-type VGCCs, and thus ameliorate the epileptiform discharges in the model. The activation of full-length TrkB signaling may affect the inhibition of epilepsy. This provides a rationale for the activation of full-length TrkB signaling in preventive therapies.