Abstract
Exposure to high concentrations of methylmercury (MeHg), as in the case of Minamata disease, is no longer a problem in Japan. There is concern about the effects of exposure of low concentrations of MeHg to the fetus via pregnant women due to ingestion of seafood in which MeHg has accumulated through bioaccumulation. However, the toxic mechanism of MeHg on neuronal differentiation is unknown. Therefore, we investigated the effects of MeHg on neuronal function and epigenetic changes in genes related to neuronal function. LUHMES cells were differentiated and exposed to MeHg (0, 0.1, 1 nM) for 68 days starting from day 2 of neuronal differentiation (D2). Gene expression levels, protein expression levels, and DNA methylation were determined on D10. Neural spike activity was also measured by Maestro MEA system on D4, D10, and D16. Exposure to MeHg 1 nM increased DNA methylation, inhibited neurite outgrowth, and suppressed neuronal spiking. DNMT1 protein level was increased by MeHg 1 nM exposure. DNMT1 methylation, which is involved in DNMT1 degradation, was decreased by MeHg. Furthermore, gene and protein expression levels of SET７，SET８，and LSD1, which regulate DNMT1 methylation, were not significantly different after exposure to 1 nM MeHg. These results suggest that exposure to low concentrations of MeHg during neuronal differentiation suppresses neurite outgrowth via DNA methylation by elevating DNMT1, and that MeHg-induced reduction of DNMT1 methylation may be responsible for the elevated DNMT1.
