Epigenetics of Neurotoxicity Caused by Lead: Interplay of miR-137 and EZH2 Contributes to the Genome-Wide Redistribution of H3K27me3 Underlying the Pb-Dependent Memory Deficits

Abstract

Background: Lead (Pb) is an environmental neurotoxicant which threatens human health, especially the cognitive memory in children. While its molecular basis is multifactorial, growing evidence implicates epigenetic modifications in the Pb-mediated memory deficits. Methods: We utilized molecular biology techniques, luciferase assay, miRNA profiling and quantification, immunoblots, co-immunoprecipitation, Chromatin immunoprecipitation (CHIP), lentivirus (LV)-based overexpression, Golgi-staining, and behavioral tests to access the roles of H3K27me3 and EZH2 (enhancer of zeste homolog 2) in lead-induced cognitive declines. Findings: Here we found that Pb exposure diminished H3K27me3 levels in vivo through suppressing EZH2 expression at early developmental stages. Notably, intervention of EZH2 in Pb-exposed rats efficiently rescued the H3K27me3 profile and repaired the spatial memory deficits. Furthermore, miR-137 and EZH2 constitute mutually inhibitory loop to regulate the H3K27me3 level, and this feedback regulation could be specifically activated by Pb exposure. Considering molecular events relayed by H3K27me3, ChIP-chip studies revealed that Pb could reshape the genomewide distribution of H3K27me3, including in the Wnt9b and 6 loci. Interestingly, Wnt9b and Wnt6 were regulated by the opposite modifications of H3K4me3 and H3K27me3 in Pb-exposed neurons. Rescue trials further validated the contribution of Wnt9b to Pb-induced neuronal impairments. Interpretation: Our results provided that a new epigenetic pathway, namely miR-137-EZH2-H3K27me3-targets, was suggested to mediate Pbdependent memory impairment, suggesting that a further step towards understanding the molecular basis of lead neurotoxicity. Funding Statement: This work was supported by the National Key Basic Research Program of China (No. 2018YFC1602201, 2018YFC1602204, 2012CB525003)，the National Science Foundation of China (No. 81773475, 21477031, 31401671) , the Key Laboratory of Xin'an Medicine Ministry of Education, Anhui University of Chinese Medicine (No. 2018xayx01) and the Fundamental Research Funds for the Central Universities (PA2017GDQT0018). Declaration of Interests: The authors declare that they have no conflict of interest. Ethics Approval Statement: All animal procedures were carried out in accordance with National Institute of Health Guide for the Care and Use of Laboratory Animals and were approved by the Institutional Animal Care and Use Committee of Hefei University of Technology, China.