Synergistic suppression of BDNF via epigenetic mechanism deteriorating learning and memory impairment caused by Mn and Pb co-exposure

Abstract

Microglia, the resident immune cells of the central nervous system (CNS), play a dual role in neurotoxicity by releasing the NLR Family Pyrin Domain Containing 3 (NLRP3) inflammasome and brain-derived neurotrophic factor (BDNF) in response to environmental stress. Suppression of BDNF is implicated in learning and memory impairment induced by exposure to manganese (Mn) or lead (Pb) individually. Methyl CpG Binding Protein 2 (MeCp2) and its phosphorylation status are related to BDNF suppression. Protein phosphatase2A (PP2A), a member of the serine/threonine phosphatases family, dephosphorylates substrates based on the methylation state of its catalytic C subunit (PP2Ac). However, the specific impairment patterns and molecular mechanisms resulting from co-exposure to Mn and Pb remain unclear. Therefore, the purpose of this study was to explore the effects of Mn and Pb exposure, alone and in combination, on inducing neurotoxicity in the hippocampus of mice and BV2 cells, and to determine whether simultaneous exposure to both metals exacerbate their toxicity. Our findings reveal that co-exposure to Mn and Pb leads to severe learning and memory impairment in mice, which correlates with the accumulation of metals in the hippocampus and synergistic suppression of BDNF. This suppression is accompanied by up-regulation of the epigenetic repressor MeCp2 and its phosphorylation status, as well as demethylation of PP2Ac. Furthermore, inhibition of PP2Ac demethylation using ABL127, an inhibitor for its protein phosphatase methylesterase1 (PME1), or knockdown of MeCp2 via siRNA transfection in vitro effectively increases BDNF expression and mitigates BV2 cell damage induced by Mn and Pb co-exposure. We also observe abnormal activation of microglia characterized by enhanced release of the NLRP3 inflammasome, Casepase-1 and pro-inflammatory cytokines IL-1β, in the hippocampus of mice and BV2 cells. In summary, our experiments demonstrate that simultaneous exposure to Mn and Pb results in more severe hippocampus-dependent learning and memory impairment, which is attributed to epigenetic suppression of BDNF mediated by PP2A regulation. Microglia palys a double-edge function in central neuron system. Abnormal activation of microglia by metals exposure contributes to inflammation cytokines aggregation and brain-derived neurotrophic factor（BDNF）inhibition. Pb and Mn preferentiall accumulate in hippocampus and target to microglia.Furthermore, the demethylation of PP2Ac is upregulated via unbalanced expression of LCMT-1 and PME-1 then results in blocking the activity of PP2A enzyme，which increases the expression of MeCp2 and pMeCp2–421 to susppress BDNF transcription.Strategies of PME-1 inhibitor ABL-127 supplementary and silencing MeCp2 by transfect siRNA restore the decline of BDNF, highlight the mechanism of PP2A related to BDNF suppression via MeCp2 in Mn and Pb exposure contexture • Co-exposure of Mn and Pb caused learning and memory impairment through accumulation of Mn and Pb, activation of NLRP3 inflammasome, released of caspase-1 and IL-1β, and inhibition of BDNF of mice. • The expression of BDNF was regulated by epigenetic factor MeCp2/pMeCp2–421, while downregulating MeCp2 expression via siRNA reversed BNDF expression . • Declining PP2Ac demethylation by ABL-127 rescues the decreased BDNF through repressing MeCp2 and its phosphorylation.

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