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Paternal MTHFR deficiency leads to reproductive decline across generations in association with hypomethylation of young retrotransposons

ABSTRACT: 5, 10-Methylenetetrahydrofolate reductase (MTHFR) is a crucial enzyme in the folate metabolic pathway with a key role in generating methyl groups. As MTHFR deficiency impacts male fertility and sperm DNA methylation, there is the potential for epimutations to be passed to the next generation. Here, we assessed whether the impact of MTHFR deficiency on testis morphology and sperm DNA methylation is exacerbated across generations. While MTHFR deficiency in F1 fathers has only minor effects on sperm counts and testis weights and histology, F2 generation sons show further deterioration in reproductive parameters. Extensive loss of DNA methylation is observed in both F1 and F2 sperm, with >80% of sites shared between generations, suggestive of regions consistently susceptible to MTHFR deficiency. These regions are generally methylated during late prenatal germ cell development and are enriched in young retrotransposons. As retrotransposons are resistant to reprogramming of DNA methylation in prenatal germ cells, their hypomethylated state in the sperm of F1 males could contribute to the worsening reproductive phenotype observed in F2 MTHFR- deficient males, findings compatible with the intergenerational passage of epimutations.

ORGANISM(S): Mus musculus

PROVIDER: GSE166586 | GEO | 2021/06/28

REPOSITORIES: GEO

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Project description:Background: DNA methylation (DNAme) erasure and reacquisition occurs during prenatal male germ cell development; some further remodelling takes place after birth during spermatogenesis. Environmental insults during germline epigenetic reprogramming may affect DNAme, presenting a potential mechanism for transmission of environmental exposures across multiple generations. Objectives: We investigated how germ cell DNAme is impacted by lifetime exposures to diets containing either low or high, clinically relevant, levels of the methyl donor folic acid and whether resulting DNAme alterations were inherited in germ cells of male offspring of subsequent generations. Materials and Methods: Female mice were placed on a 7-fold folic acid deficient (7FD) and 10- or 20-fold supplemented (10FS and 20FS) diets before and during pregnancy. Resulting F1 litters were weaned on the respective diets. F2 and F3 males received control diets. Genome-wide DNAme was assessed in F1 spermatogonia, and in F1, F2 and F3 sperm. Results: In F1 germ cells, a greater number of differentially methylated cytosines (DMCs) was observed in spermatogonia as compared with F1 sperm for all folic acid diets. DMCs were lower in number in F2 versus F1 sperm, while an unexpected increase was found in F3 sperm. DMCs were predominantly hypomethylated, with genes in neurodevelopmental pathways commonly affected in F1, F2 and F3 male germ cells. While no DMCs were found to be inherited inter- or transgenerationally, we observed over-representation of repetitive elements, particularly young LINEs. Discussion and Conclusion: These results suggest that the prenatal window is the time most susceptible to folate-induced alterations in sperm DNAme in male germ cells. Altered methylation of specific sites in F1 sperm was not present in later generations. However, the finding of hypomethylated young LINE1 elements in sperm from F1 to F3 males provides insight into potential mechanisms of epigenetic inheritance of the effects of folate deficiency and supplementation.

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Paternal MTHFR deficiency leads to reproductive decline across generations in association with hypomethylation of young retrotransposons

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