Methylmercury (MeHg) causes neuronal death through different pathways. Particularly, we found that in cortical neurons it increased the expression of Repressor Element-1 Silencing Transcription Factor (REST), Histone Deacetylase (HDAC)4, Specificity Protein (Sp)1, Sp4 and reduced the levels of Brain-Derived Neurotrophic Factor (BDNF). Herein, in rat cortical neurons we investigated whether microRNA (miR)206 can modulate MeHg-induced cell death by regulating REST/HDAC4/Sp1/Sp4/BDNF axis. MeHg (1µM) reduced miR206 expression after both 12 and 24 hours and miR206 transfection prevented MeHg-induced neuronal death. Furthermore, miR206 reverted MeHg-induced REST and Sp4 increase and BDNF reduction at gene and protein level, and reverted HDAC4 protein increase, but not HDAC4 mRNA up-regulation. Moreover, since no miR206 seed sequences were identified in the 3'-untranslated regions (3'-UTR) of REST and SP4, we investigated the role of JunD, that presents a consensus motif on REST, Sp4 and BDNF promoters. Indeed, MeHg increased JunD mRNA and protein levels, and JunD knockdown counteracted MeHg-induced REST, Sp4 increase, but not BDNF reduction. Furthermore, we identified a miR206 binding site in the 3'-UTR of JunD mRNA (miR206/JunD) and mutagenesis of miR206/JunD site reverted JunD luciferase activity reduction induced by miR206. Finally, miR206 prevented MeHg-increased JunD binding to REST and Sp4 promoters, and MeHg-reduced BDNF expression was determined by the increase of HDAC4 binding on BDNF promoter IV. Collectively, these results suggest that miR206 down-regulation induced by MeHg exposure determines an up-regulation of HDAC4, that in turn down-regulated BDNF, and the activation of JunD that, by binding REST and Sp4 gene promoters, increased their expression.

The miR206-JunD circuit mediates the neurotoxic effect of methylmercury in cortical neurons

Guida, Natascia;Valsecchi, Valeria;Laudati, Giusy;Serani, Angelo;Mascolo, Luigi;Molinaro, Pasquale;Montuori, Paolo;Di Renzo, Gianfranco;Formisano, Luigi
2018

Abstract

Methylmercury (MeHg) causes neuronal death through different pathways. Particularly, we found that in cortical neurons it increased the expression of Repressor Element-1 Silencing Transcription Factor (REST), Histone Deacetylase (HDAC)4, Specificity Protein (Sp)1, Sp4 and reduced the levels of Brain-Derived Neurotrophic Factor (BDNF). Herein, in rat cortical neurons we investigated whether microRNA (miR)206 can modulate MeHg-induced cell death by regulating REST/HDAC4/Sp1/Sp4/BDNF axis. MeHg (1µM) reduced miR206 expression after both 12 and 24 hours and miR206 transfection prevented MeHg-induced neuronal death. Furthermore, miR206 reverted MeHg-induced REST and Sp4 increase and BDNF reduction at gene and protein level, and reverted HDAC4 protein increase, but not HDAC4 mRNA up-regulation. Moreover, since no miR206 seed sequences were identified in the 3'-untranslated regions (3'-UTR) of REST and SP4, we investigated the role of JunD, that presents a consensus motif on REST, Sp4 and BDNF promoters. Indeed, MeHg increased JunD mRNA and protein levels, and JunD knockdown counteracted MeHg-induced REST, Sp4 increase, but not BDNF reduction. Furthermore, we identified a miR206 binding site in the 3'-UTR of JunD mRNA (miR206/JunD) and mutagenesis of miR206/JunD site reverted JunD luciferase activity reduction induced by miR206. Finally, miR206 prevented MeHg-increased JunD binding to REST and Sp4 promoters, and MeHg-reduced BDNF expression was determined by the increase of HDAC4 binding on BDNF promoter IV. Collectively, these results suggest that miR206 down-regulation induced by MeHg exposure determines an up-regulation of HDAC4, that in turn down-regulated BDNF, and the activation of JunD that, by binding REST and Sp4 gene promoters, increased their expression.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11588/707600
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