Protective Effects of Bexarotene against Amyloid-β<sub>25-35</sub>-Induced Dysfunction in Hippocampal Neurons through the Insulin Signaling Pathway

Background: Bexarotene, a retinoid X receptor agonist, has been shown to reverse neurodegeneration in mouse models of Alzheimer's disease (AD), accompanied by a decreased level of amyloid-β (Aβ), which is a hallmark of AD. However, the mechanism underlying this therapeutic effect may involve enhancing the sensitivity to insulin. Objective: This study was to test the hypothesis that bexarotene would protect against Aβ_25-35-induced dysfunction through the insulin signaling pathway. Methods: Using a whole-cell patch clamp technique, the excitability and voltage-gated potassium currents of hippocampal neurons were examined in four groups of cells (control, Aβ, Aβ + bexarotene and bexarotene). Results: It was found that insulin increased the excitability of neurons. Bexarotene could enhance this effect and reverse the Aβ_25-35-induced decrease in the firing rate of the action potential (AP). In addition, the properties of the single AP (sAP) and voltage-gated outward K⁺ currents were recorded, which finally showed similar changes to those in the firing frequency. Conclusion: The effects of bexarotene on Aβ-impaired excitability and sAP duration were mainly associated with K⁺ channels through insulin signaling pathway, which may be an additional mechanism underlying the protective effect of bexarotene on AD.