Prenatal exposure to allergen, DNA methylation, and allergy in grandoffspring mice

Asthma in parents is associated with increased risk of asthma in children, with maternal asthma more strongly associated with risk compared to paternal (1). This pattern suggests that maternal exposures, particularly during gestation, may alter developmental programming, leading to molecular, physiologic, and metabolic adaptations in the offspring (1, 2). For example, prenatal allergen exposure may ‘prime’ T-helper (Th) cells toward a more proallergic Th2 phenotype (3). Previous studies of prenatal exposures on the development of allergy have been mixed, with exposures linked to both increased (4) and decreased (5) allergy in the offspring, likely due to differing effects of dose, timing of exposure during gestation, and other methodological variations. An emerging paradigm is that epigenetic regulation of genes important to Th gene transcription and cytokine production may be responsible for the development of allergy (6). Cell systems have shown that site-specific CpG methylation of Th gene promoters can steer differentiation toward the Th2 phenotype (7, 8). In particular, the CpG−53 of the interferon (IFN)-γ promoter was shown to undergo rapid methylation during Th2 polarization that blocked ATF2-c/Jun and CREB transcription factor binding (7). More limited in vivo studies have been conducted. In one study, our group showed that combined exposure to diesel exhaust particles and allergen in mice altered methylation patterns at CpG sites in the IFN-γ and IL-4 promoters that correlated with changes in immunoglobulin (Ig) E production (9). Epigenetic regulation also may explain partially the heritability of asthma (2). A gestational diet high in folic acid, a methyl donor for methylation reactions, induced allergic airway inflammation in offspring mice (F1) in association with hypermethylation of RUNX3, a T-cell regulator (10). Differences in levels of global DNA methylation among dendritic cells, and in their antigen-presenting activity, derived from offspring mice also were associated with the presence or absence of an asthma-like phenotype in the mother (11). Epidemiologic studies additionally have demonstrated associations between prenatal exposures, including tobacco smoke and polycyclic aromatic hydrocarbons (PAH), with differential methylation patterns in several asthma candidate genes and symptoms in children (12, 13). Also, prenatal smoking, determined using retrospective questionnaire, was associated with greater asthma risk in the grandchildren (14). Others have suggested that the timing of exposure during gestation may be important, with folic acid supplementation either during the first trimester or during late pregnancy being associated with asthma-related symptoms in young children in separate studies (15, 16). We hypothesized that allergen exposure during gestation may alter the allergic phenotype through multiple generations of mice and that such changes would be associated with DNA methylation of Th genes. We also hypothesized that these associations may vary depending on the timing of prenatal exposure. Given our previous report that prenatal Aspergillus fumigatus (A. fumigatus) administration combined with diesel exhaust particles was associated with reduced IgE in sensitized offspring (F1) (17), here we exposed female mice (F0) to multiple doses of A. fumigatus during the early or late period of gestation and determined the effects on IgE, airway eosinophilia, and Th gene IFN-γ and IL-4 promoter methylation in the lungs of their grandoffspring (F2).