Folate Deficiency and Supplementation Result in DNA Methylation Defects in Sperm.

Abstract

Folate is a nutrient that is essential for cell proliferation and involved in the biosynthesis of nucleotides and S-adenosylmethionine (SAM). SAM is the methyl donor for numerous cellular biochemical reactions including DNA methylation, an important epigenetic modification implicated in the control of gene expression, genomic imprinting and normal fertility. Although folate supplementation is used as a treatment for human male infertility, little is known about the effects of low or high dietary folate concentrations on sperm DNA methylation patterns. Our goal was to use a mouse model to examine the effects of folic acid deficiency and supplementation on epigenetic patterns in male germ cells. Male Balb/c strain mice were fed, from weaning age (day 21) to one year of age, either a control diet containing an adequate amount of folic acid (2 mg/kg diet), a 7X low folic acid diet (0.3 mg/kg diet) or a 20X high folic acid diet (40 mg/kg diet). The mice were sacrificed at 12 months and reproductive organs (testes, epididymides and seminal vesicles) collected and weighed. Sperm were collected from the cauda epididymides and genomic DNA extracted. Restriction landmark genomic scanning (RLGS) was used to assess genome-wide levels and patterns of DNA methylation (n=4 samples/group). Although weight gain and reproductive organ weights were not affected by the folate deficiency or supplementation, for both treatment groups, RLGS demonstrated evidence of epigenetic abnormalities in sperm. Mice in the folic acid supplemented group exhibited six consistent changes in their methylation profiles, all of which were hypermethylation. Interestingly, among the 14 loci showing methylation alterations in all of the folic acid deficient mice, 10 were hypermethylated and four were hypomethylated. The loci with altered methylation are in the process of being identified using a virtual RLGS profile. Together, the results indicate that DNA methylation patterns in mouse sperm can be altered by long term exposure to both low and high dietary folate. (Supported by CIHR) (poster)