NPD1 Enhances Autophagy and Reduces Hyperphosphorylated Tau and Amyloid-β42 by Inhibiting GSK3β Activation in N2a/APP695swe Cells

Abstract

Background: The most prevalent kind of dementia, Alzheimer’s disease (AD), is a neurodegenerative disease. Previous research has shown that glycogen synthase kinase-3β (GSK-3β) is involved in the etiology and progression of AD, including amyloid-β (Aβ), phosphorylated tau, and mitochondrial dysfunction. NPD1 has been shown to serve a neuroprotective function in AD, although the mechanism is unclear. Objective: The effects of NPD1 on Aβ expression levels, tau protein phosphorylation, apoptosis ratio, autophagy activity, and GSK-3β activity in N2a/APP695swe cells (AD cell model) were studied, as well as the mechanism behind such effects. Methods: N2a/APP695swe cells were treated with NPD1, SB216763, or wortmannin as an AD cell model. The associated proteins of hyperphosphorylated tau and autophagy, as well as the activation of GSK3β, were detected using western blot and RT-PCR. Flow cytometry was utilized to analyze apoptosis and ELISA was employed to observe Aβ42. Images of autophagy in cells are captured using transmission electron microscopy. Results: In N2a/APP695swe cells, NPD1 decreased Aβ42 and hyperphosphorylated tau while suppressing cell death. NPD1 also promoted autophagy while suppressing GSK-3β activation in N2a/APP695swe cells. The outcome of inhibiting GSK-3β is comparable to that of NPD1 therapy. However, after activating GSK-3β, the opposite experimental results were achieved. Conclusion: NPD1 might minimize cell apoptosis, downregulate Aβ expression, control tau hyperphosphorylation, and enhance autophagy activity in AD cell models to promote neuronal survival. NPD1’s neuroprotective effects may be mediated via decreasing GSK-3β.