Maternal genistein alters coat color and protects [A.sup.vy] mouse offspring from obesity by modifying the fetal epigenome.(Research)

Genistein, the major phytoestrogen in soy, is linked to diminished female reproductive performance and to cancer chemoprevention and decreased adipose deposition. Dietary genistein may also play a role in the decreased incidence of cancer in Asians compared with Westerners, as well as increased cancer incidence in Asians immigrating to the United States. Here, we report that maternal dietary genistein supplementation of mice during gestation, at levels comparable with humans consuming high-soy diets, shifted the coat color of heterozygous viable yellow agouti ([A.sup.vy]/a) offspring toward pseudoagouti. This marked phenotypic change was significantly associated with increased methylation of six cytosine-guanine sites in a retrotransposon upstream of the transcription start site of the Agouti gene. The extent of this DNA methylation was similar in endodermal, mesodermal, and ectodermal tissues, indicating that genistein acts during early embryonic development. Moreover, this genistein-induced hypermethylation persisted into adulthood, decreasing ectopic Agouti expression and protecting offspring from obesity. Thus, we provide the first evidence that in utero dietary genistein affects gene expression and alters susceptibility to obesity in adulthood by permanently altering the epigenome. Key words: developmental origins of adult disease, DNA methylation, epigenetics, viable yellow agouti ([A.sup.vy]) mouse. doi:10.1289/ehp.8700 available via http://dx.doi.org/ [Online 26 January 2006]

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Developmental plasticity occurs when environmental influences affect cellular pathways during gestation, enabling a single genotype to produce a broad range of adult phenotypes (Bateson et al. 2004). Specifically, the developmental origins hypothesis postulates that nutrition and other environmental factors during prenatal and early postnatal development influence developmental plasticity and alter susceptibility to adult cardiovascular disease, type 2 diabetes, and obesity (Barker 1997, 2004). Moreover, persistent epigenetic adaptations that occur early in development in response to maternal nutrition and the environment are associated with increased susceptibility to cancer and other adult-onset chronic diseases (Cooney et al. 2002; Li et al. 2003; Waterland and Jirtle 2004).

Methylation of cytosines in cytosine--guanine (CpG) dinucleotides represents a critical epigenetic DNA modification affecting gene expression and cellular function (Bird 2002). Transposable elements, the promoter regions of housekeeping genes, and cis-acting regulatory elements of imprinted genes are three key epigenetic susceptibility targets containing CpG sites that are normally methylated, unmethylated, and differentially methylated, respectively. Therefore, environmental factors that affect DNA methylation patterning during development can potentially influence adult phenotype via alterations in CpG methylation at epigenetically labile regions in the genome.

The epigenome is likely to be most vulnerable to environmental factors during embryogenesis because the DNA synthetic rate is high, and the elaborate DNA methylation patterning required for normal tissue development is established during this period. Therefore, when evaluating the effects of environmental influences on the epigenome, not only the dose but also the developmental timing must be considered. For example, dietary methyl donor intake in adulthood is not associated with risk of breast cancer among African-American women (Zhu et al. 2003). Nevertheless, it remains possible that epigenetic modifications caused by the nutritional environment of the embryo, fetus, and neonate are involved in the etiology of this adult disease.

Isoflavones represent a class of phytoestrogens present in soy and soy products that are active in multiple biologic systems, including estrogen-receptor--and non-estrogen-receptor-mediated signaling pathways (Lamartiniere et al. 2002; Valachovicova et al. 2004). Genistein, the major isoflavone in soy, exhibits mixed estrogen agonist and antagonist properties (Price and Fenwick 1985), inhibits tyrosine kinase (Akiyama et al. 1987), and scavenges free radicals (Wei et al. 1993), depending on timing, dose, and the tissue examined. A diet rich in soy, such as a typical Asian or Western vegetarian diet, contains as much as 1.4 mg genistein/kg body weight per day (Coward et al. 1993), whereas infants fed soy formula consume almost five times as much genistein (Setchell et al. 1997). Genistein is linked to reduced female reproductive health (Nagaos et al. 2001) but also to breast and prostate cancer chemoprevention (Lamartiniere et al. 2002) and decreased adipose deposition (Naaz et al. 2003). Thus, dietary genistein may help explain the difference in cancer incidence between Westerners and Asian populations with high soy intake (Lee et al. 1991; Peeters et al. 2003; Ziegler et al. 1993).

Despite a growing body of toxicologic and mechanistic literature on the effects of genistein and other phytoestrogens, the long-term health consequences of developmental and early exposure remain largely unknown (Badger et al. 2002). Limited evidence suggests that exposure to phytoestrogens postnatally alters the epigenome (Day et al. 2002; Lyn-Cook et al. 1995). Neonatal exposure to high doses of the phytoestrogens equol and coumestrol is correlated with hypermethylation of a protooncogene in the rat pancreas (Lyn-Cook et al. 1995). More recently, a study employing methylation arrays suggests that adult dietary genistein induces gene hypermethylation in the …