Exposure to a low concentration of methylmercury in neural differentiation downregulates NR4A1 expression with altered epigenetic modifications and inhibits neuronal spike activity in vitro

Suzuna Go; Haruka Masuda; Mizuki Tsuru; Masatoshi Inden; Isao Hozumi; Hisaka Kurita

doi:10.1016/j.toxlet.2022.12.010

Exposure to a low concentration of methylmercury in neural differentiation downregulates NR4A1 expression with altered epigenetic modifications and inhibits neuronal spike activity in vitro

Toxicol Lett. 2023 Feb 1:374:68-76. doi: 10.1016/j.toxlet.2022.12.010. Epub 2022 Dec 21.

Authors

Suzuna Go¹, Haruka Masuda¹, Mizuki Tsuru¹, Masatoshi Inden¹, Isao Hozumi², Hisaka Kurita³

Affiliations

¹ Laboratory of Medical Therapeutics and Molecular Therapeutics, Department Biomedical Pharmaceutics, Gifu Pharmaceutical University, 1-25-4 Daigaku-nishi, Gifu city, Gifu, 501-1196, Japan.
² Laboratory of Medical Therapeutics and Molecular Therapeutics, Department Biomedical Pharmaceutics, Gifu Pharmaceutical University, 1-25-4 Daigaku-nishi, Gifu city, Gifu, 501-1196, Japan. Electronic address: hozumi@gifu-pu.ac.jp.
³ Laboratory of Medical Therapeutics and Molecular Therapeutics, Department Biomedical Pharmaceutics, Gifu Pharmaceutical University, 1-25-4 Daigaku-nishi, Gifu city, Gifu, 501-1196, Japan. Electronic address: kurita@gifu-pu.ac.jp.

PMID: 36565944
DOI: 10.1016/j.toxlet.2022.12.010

Abstract

Methylmercury (MeHg) is a well-known developmental neurotoxin. Our previous research showed that the inhibition of neurite extension by exposure to a low level of MeHg (1 nM) was attributed to the decrease of acetylation of histone H3 and the increase of DNA methylation. However, the target molecules responsible for the neurological dysfunctions caused by MeHg exposure have not been identified. This study focused on a nuclear receptor subfamily 4 group A member 1 (NR4A1), which is reported to be related to synaptic plasticity and neurite extension. LUHMES cells, which are derived from human fetal brain, were treated with 0.1 and 1 nM MeHg beginning at two days of differentiation and continued for 6 consecutive days. The present study showed that exposure to a 1 nM MeHg during neural differentiation inhibited neuronal spike activity and neurite extension. Furthermore, MeHg exposure increased DNA methylation, and altered histone modifications for transcriptional repression in the NR4A1 promoter region to decrease the levels of NR4A1 expression. In addition, MeHg exposure inhibited the mobilization of cAMP response element-binding protein (CREB) and CREB binding protein (CBP) in the NR4A1 promoter region. These results suggest that MeHg inhibits the recruitment of the CREB-CBP complex to the NR4A1 promoter region and impairs neuronal functions associated with NR4A1 repression via a decrease in acetylation of histone H3 lysine 14 levels. Conclusively, this study demonstrated that MeHg exposure during neuronal differentiation could induce neurological dysfunctions even at a low concentration in vitro. These dysfunctions could be associated with the transcriptional repression of NR4A1 by the dissociation of CREB and CBP from the NR4A1 promoter region due to the alterations of epigenetic modifications.

Keywords: DNA methylation; Epigenetics; Histone modification; Methylmercury; Neuronal spike activity; Nuclear receptor subfamily 4 group A member 1.

MeSH terms

Cell Differentiation
Epigenesis, Genetic
Histones* / metabolism
Humans
Methylmercury Compounds* / toxicity
Neurons / metabolism
Nuclear Receptor Subfamily 4, Group A, Member 1 / genetics
Nuclear Receptor Subfamily 4, Group A, Member 1 / metabolism

Substances

Histones
Methylmercury Compounds
NR4A1 protein, human
Nuclear Receptor Subfamily 4, Group A, Member 1