Aβ monomers protect lens epithelial cells against oxidative stress by upregulating CDC25B

Our previous studies showed high beta-amyloid (A beta) expression levels in the nuclei of the lens epithelial cells (LECs) of healthy subjects and revealed that A beta monomers could protect LECs from oxidative damage. Here, we further explored the mechanism by which A beta monomers act as transcription factors to regulate the oxidative stress of LECs through high-throughput studies. First, we compared the A beta-binding sites in the lens epithelia (LE) of agerelated cataract patients with those in the LE of healthy donors via chromatin immunoprecipitation-sequencing (ChIP-seq), and we identified comparable numbers (1648 and 1445, respectively) of A beta peaks. Then, the KEGG tool was used for gene function enrichment analysis of these genes, which were more highly enriched in healthy LE. Combining the literature review with these KEGG analysis results, in the current study, we chose four target genes related to oxidative stress, namely, CDC25B, SOS2, CTNNA1 and Cox6a1. Then, ChIP-PCR assays, dualluciferase reporter assays, real-time PCR and Western blotting were performed to validate the regulatory effects of A beta on these targets. Our data suggested that A beta monomers could upregulate the mRNA and protein expression levels of CDC25B in LECs. We also confirmed that A beta monomers could activate the Akt/Nrf2 pathway in a CDC25B-dependent manner by knockdown experiments in cultured LECs. Furthermore, we performed functional verification of the CDC25B-mediated protective effects of A beta monomers against oxidative stress. We observed that A beta monomers significantly improved the antioxidant capacity (the GSH level, SOD activity and total antioxidant capacity) and decreased the oxidative stress (the ROS and MDA levels) of LECs, while CDC25B knockdown decreased the antioxidant effects of A beta, disrupting redox homeostasis. Therefore, we propose that A beta monomers activate the Akt/Nrf2 pathway by upregulating CDC25B expression, increase various downstream antioxidant enzyme levels, maintain peroxidation-antioxidant homeostasis in LECs, and prevent the cell damage caused by oxidative stress.