IRE1α-XBP1 Affects the Mitochondrial Function of Aβ25-35-Treated SH-SY5Y Cells by Regulating Mitochondria-Associated Endoplasmic Reticulum Membranes

Background: Neurotoxicity induced by the amyloid beta (A beta) peptide is one of the most important pathological mechanisms of Alzheimer's disease (AD). Activation of the adaptive IRE1 alpha-XBP1 pathway contributes to the pathogenesis of AD, making it a potential target for AD therapeutics. However, the mechanism of IRE1 alpha-XBP1 pathway involvement in AD is unclear. We, therefore, investigated the effect of the IRE1 alpha-XBP1 axis in an in vitro AD model and explored its potential mechanism. Methods: The human neuroblastoma cell line, SH-SY5Y, was used. Cells were treated with A beta 25-35, with or without 4 mu 8c, an inhibitor of IRE1 alpha. Cells were collected and analyzed by Western blotting, quantitative real-time PCR, electron microscopy, fluorescence microscopy, calcium imaging, and other biochemical assays. Results: A beta-exposed SH-SY5Y cells showed an increased expression of XBP1s and p-IRE1 alpha. 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and calcium imaging analysis showed that the IRE1 alpha inhibitor, 4 mu 8c, reduced A beta-induced cytotoxicity. Increased levels of ATP, restoration of mitochondrial membrane potential, and decreased production of mitochondrial reactive oxygen species after A beta treatment in the presence of 4 mu 8c showed that inhibiting the IRE1 alpha-XBP1 axis effectively mitigated A beta-induced mitochondrial dysfunction in SH-SY5Y cells. Furthermore, A beta treatment increased the expression and interaction of IP3R, Grp75, and vdac1 and led to an increased endoplasmic reticulum (ER)-mitochondria association, malfunction of mitochondria-associated ER-membranes (MAMs), and mitochondrial dysfunction. These deficits were rescued by inhibiting the IRE1 alpha-XBP1 axis. Conclusion: These findings demonstrate that A beta peptide induces the activation of the IRE1 alpha-XBP1 axis, which may aggravate cytotoxicity and mitochondrial impairment in SH-SY5Y cells by targeting MAMs. Inhibition of the IRE1 alpha-XBP1 axis provides the protection against A beta-induced injury in SH-SY5Y cells and may, therefore, be a new treatment strategy.