Impact of mothers' early life exposure to low or high folate on progeny outcome and DNA methylation patterns

The dynamic patterning of DNA and histone methylation during oocyte development presents a potentially susceptible time for epigenetic disruption due to early life environmental exposure of future mothers. We investigated whether maternal exposure to folic acid deficient (FD) and supplemented (FS) diets starting in utero could affect oocytes and cause adverse developmental and epigenetic effects in next generation progeny. Female BALB/c mice (F0) were placed on one of four amino acid defined diets for 4 weeks before pregnancy and throughout pregnancy and lactation: folic acid control (rodent daily recommended intake or DRI; Ctrl), 7-fold folic acid deficient (7FD), 10-fold folic acid supplemented (10FS) or 20-fold folic acid supplemented (20FS) diets. F1 female pups were weaned onto Ctrl diets, mated to produce the F2 generation, and the F2 offspring were examined at E18.5 for developmental and epigenetic abnormalities. Resorption was increased and litter sizes decreased amongst F2 E18.5 day litters in the 20FS group. Increases in abnormal embryo outcomes were observed in all three FD and FS groups. Subtle genome-wide DNA methylation alterations were found in the placentas and brains of F2 offspring in the 7D, 10FS and 20FS groups; in contrast, global and imprinted gene methylation were not affected. The findings show that early life female environmental exposures to both low and high folate prior to oocyte maturation can compromise oocyte quality, adversely affecting offspring of the next generation, in part by altering DNA methylation patterns. Overall design: Eight-week old BALB/c female mice (F0) were exposed for 4 weeks to folic acid control (FCD; 2mg/kg), folic acid deficient (7FD; 0.3mg/kg), 10-fold folic acid supplemented (10FS; 20mg/kg) or a 20-fold folic acid supplemented (20FS; 40mg/kg) diets. Following these 4 weeks, they were then mated to BALB/c male mice on regular chow diets. Throughout mating, gestation and lactation, the females were fed their respective diets and the F1 female offspring were then weaned at postnatal day 20 onto FCD. At 8-10 weeks of age, F1 females, representative of 10 Ctrl, 11 FD, 10 10FS, and 9 20FS different original F0 litters per diet group, were mated with 10 week old male BALB/c mice fed regular mouse chow. Throughout mating and gestation, the F1 females were fed the FCD (2mg/kg). Embryonic tissues from E18.5 embryos were collected (placenta and cortex), flash frozen and kept at -80oC until use for DNA methylation analyses (i.e. RRBS)