Genetic and maternal effects on valproic acid teratogenesis in C57BL/6J and DBA/2J mice

Abstract

Valproic acid (VPA) is used worldwide to treat epilepsy, migraine headaches, and bipolar disorder. However, VPA is teratogenic and in utero exposure can lead to congenital malformations. Using inbred C57BL/6J (B6) and DBA/2J (D2) mice, we asked whether genetic variation could play a role in susceptibility to VPA teratogenesis. Whereas B6 fetuses were more susceptible than D2 fetuses to digit and vertebral malformations, D2 fetuses were more susceptible to rib malformations. In a reciprocal cross between B6 and D2, genetically identical F1 mice carried in a B6 mother had a greater percentage of vertebral malformations following prenatal VPA exposure than F1 mice carried in a D2 mother. This reciprocal F1 difference is known as a maternal effect and shows that maternal genotype/uterine environment is an important mediator of VPA teratogenecity. VPA is a histone deacetylase inhibitor, and it is possible that the differential teratogenesis in B6 and D2 is because of strain differences in histone acetylation. We observed strain differences in acetylation of histones H3 and H4 in both embryo and placenta following in utero VPA exposure, but additional studies are needed to determine the significance of these changes in mediating teratogenesis. Our results provide additional support that genetic factors, both maternal and fetal, play a role in VPA teratogenesis. Lines of mice derived from B6 and D2 will be a useful model for elucidating the genetic architecture underlying susceptibility to VPA teratogenesis.

FIG. 1.

Western blot for H3ac in embryo following in utero exposure to VPA or ethanol. There were no differences in H3 among treatments or between strains, so band densities for each sample were normalized to H3. Results are presented as the percent change from maltose-treated controls. Asterisk indicates a significant increase compared with maltose control, p < 0.01.

FIG. 2.

Western blot for acetylated histone H4 (H4ac) in embryo following in utero exposure to VPA or ethanol. There were no differences in H4 among treatments or between strains, so band densities for each sample were normalized to H4. Results are presented as the percent change from maltose-treated controls. Asterisks indicate a significant increase compared with maltose controls, *p < 0.01; **p < 0.05.

FIG. 3.

Western blot for H3ac in placenta. Band densities for H3ac were normalized to H3 for each sample, and results are presented as the percent change from maltose-treated controls. Asterisks indicate a significant increase, *p < 0.01; **p < 0.05.

FIG. 4.

Western blot for H4ac in placenta. Band densities for H4ac were normalized to H4 for each sample, and results are presented as the percent change from maltose-treated controls. Asterisk indicates a significant increase, p < 0.01.