Folic Acid Overconsupmtion Leads to Decreased Gene Expression in Neuronal Cells

Folic acid (FA) is a member of the B vitamin family that is found in green foods like brussels sprouts, broccoli and spinach. It is essential to protecting the body from disease by helping to produce and maintain healthy cells. It is it also used to help treat anemia and prevent potential birth defects in pregnant women.

Because of it’s positive health effects, FA has been the subject of many gene expression studies—particularly the potential negative outcomes of overconsumption.

Researchers from the University of South Carolina sought to determine the effect that high levels of folic acid can have on gene expression. Using a type of human neuroblastoma cell called SHSY5Y, they examined the ways that histone methylation and other epigenetic modifications can alter gene activity in chromatin modifying enzymes and dendritic spine densities.

Histone methylation is an epigenetic process that can play a large role in gene expression. Typically, DNA methylation is directly connected to a silencing of gene expression, but methylation to certain specific histone residues can have the same effect.

In this study, the research team treated the SHSY5Y cells with a 2x dose of folic acid for 48 hours and compared those with an untreated control group.

Histone proteins were isolated from 3 control samples and 3 FA treated samples using the EpiQuik Histone Extraction Kit, followed by a Bradford assay to quantify the histone content.

The team then used the EpiQuik Histone H3 Modification Multiplex Assay Kit (Colorimetric) to measure the amount of H3 histone modified in the 2x FA treated versus the control SHSY5Y cells.

In the 2x FA treated cells, the team discovered that there was a significant decrease in expression of MECP2 and MBD2 (as shown in figure 1 below)—two genes that play a crucial role in mammalian development.

Relative Abundance for DNMT, MECP2, MTHFR and other genes.

Fig. 1. A. Relative abundance for DNMT1 mRNA expression. B. Relative abundance for MECP2 mRNA expression. C. Relative abundance for MTHFR mRNA expression. D. Relative abundance of each gene grouping tested in the epigenetic chromatin modifying enzymes arrays. Groups tested were HMT, HMT activity enzymes, HATs, HDACs, DNMTs, DNA/histone demethylases , histone phosphorylases, and histone ubiquitinases.

Though the study was primarily focused on histones, the researchers also measured the effects that an abundance of FA had on DNA methylation and histone acetylation.

They used the MethylFlash Global DNA Methylation (5-mC) ELISA Kit to quantify global DNA methylation levels in the samples and did find a decrease in DNA methylation levels in the cells treated with 2x FA. In addition, the 2x FA treated cells also demonstrated decreased levels of H3K4me1, H3K4me3, H3K9Ac.

Fig. 2: DNA methylation and histone H3 levels

Fig. 2. A. DNA methylation in SHSY5Y cells as determined by 5-mc ELISA assay. B. Percentage of H3 modified with a particular methylation mark. C. Percentage of H3 modified with a particular acetylation mark. D. Percentage of H3 modified with a particular phosphorylation mark.

They also counted the dendritic spines in the treated cells and found a dramatic increase. This is particularly significant, because dendritic spines help transmit signals to the cell body, and abnormally high amounts of dendritic spines are present in intellectual disorders like Fragile X syndrome.

FA is a common and important vitamin, but not much is known about the side effects of overconsumption. Further research is needed to determine if the findings in this study can have a negative effect on human health.

Source
Sayed, Rahaf Al, et al. (2019) “A 2x Folic Acid Treatment Affects Epigenetics and Dendritic Spine Densities in SHSY5Y Cells.” , Biochemistry and Biophysics Reports, 20.

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