Upregulation of miR-34a by Inhibition of IRE1α Has Protective Effect against Aβ-Induced Injury in SH-SY5Y Cells by Targeting Caspase-2

BACKGROUND: Neurotoxicity induced by the amyloid-β (Aβ) peptide is one of the most important pathological mechanisms of Alzheimer's disease (AD). Based on accumulating evidence in AD research, both endoplasmic reticulum stress (ER stress) and alterations in the microRNA (miRNA) network contribute to the pathogenesis of the disease, making them potential therapeutic targets for AD. The present study was performed to investigate whether miR-34a and the inositol-requiring enzyme 1 (IRE1) are involved in the regulation of Aβ-induced cytotoxicity. METHODS: Human neuroblastoma SH-SY5Y cells were treated with Aβ1-40. Cell viability was assessed by the MTT assay. The integrity of the plasma membrane was assessed by LDH release. The expression levels of XBP1s, IRE1α, p-IRE1α, and Caspase-2 were detected by Western blot analysis. Spliced-XBP1 mRNA and miR-34a were detected by reverse transcription- (RT-) PCR and quantitative real-time PCR, respectively. Caspase-2 activity was measured using the Caspase-2 cellular activity assay kit. The IRE1 inhibitor (STF-083010) was used to determine the role of IRE1α on miR-34a expression. SH-SY5Y cells were transfected with miR-34a mimics to assess the role of miR-34a on the activation of Caspase-2 and the viability of Aβ-exposed SH-SY5Y cells. RESULTS: We showed that Aβ caused concentration- and duration-dependent death of SH-SY5Y cells. The expression levels of XBP1s, p-IRE1α, and Caspase-2 were increased, along with a corresponding decrease in the miR-34a levels in Aβ-exposed SH-SY5Y cells. The IRE1 inhibitor (STF-083010) upregulated the expression of miR-34a and suppressed the activation of Caspase-2, effectively alleviating the Aβ-induced death of SH-SY5Y cells. Transfection studies show that miR-34a mimics inhibit the expression of Caspase-2 and restore the viability of Aβ-exposed SH-SY5Y cells. CONCLUSION: Aβ peptide induced downregulation of miR-34a through the activation of IRE1α, which may induce cytotoxicity by targeting Caspase-2. Upregulation of miR-34a by inhibition of IRE1α has protective effects against Aβ-induced injury in SH-SY5Y cells.