Paternal MTHFR deficiency leads to hypomethylation of young retrotransposons and reproductive decline across two successive generations

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 in mouse. Although 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 embryonic germ cell development and are enriched in young retrotransposons. As retrotransposons are resistant to reprogramming of DNA methylation in embryonic germ cells, their hypomethylated state in the sperm of F1 males could contribute to the worsening reproductive phenotype observed in F2 MTHFR-deficient males, compatible with the intergenerational passage of epimutations.

Automated summary

Research has shown that MTHFR deficiency has minimal effects on sperm counts and testis morphology in F1 fathers, but leads to further deterioration in reproductive parameters in F2 generation sons. Extensive loss of DNA methylation is observed in both F1 and F2 sperm, with >80% of sites shared between generations, indicating consistent susceptibility to MTHFR deficiency. This suggests that the hypomethylation of retrotransposons in F1 males' sperm may contribute to the worsening reproductive phenotype observed in F2 MTHFR-deficient males, supporting the intergenerational passage of epimutations.