Epigenomics, gestational programming and risk of metabolic syndrome

Epigenetic mechanisms are emerging as mediators linking early environmental exposures during pregnancy with programmed changes in gene expression that alter offspring growth and development. There is irrefutable evidence from human and animal studies that nutrient and environmental agent exposures (for example, endocrine disruptors) during pregnancy may affect fetal/newborn development resulting in offspring obesity and obesity-associated metabolic abnormalities (metabolic syndrome). This concept of 'gestational programming' is associated with alterations to the epigenome (nongenomic) rather than changes in the DNA sequence (genomic). Epigenetic alterations induced by suboptimal maternal nutrition/endocrine factors include DNA methylation, histone modifications, chromatin remodeling and/or regulatory feedback by microRNAs, all of which have the ability to modulate gene expression and promote the metabolic syndrome phenotype. Recent studies have shown tissue-specific transcriptome patterns and phenotypes not only in the exposed individual, but also in subsequent progeny. Notably, the transmission of gestational programming effects to subsequent generations occurs in the absence of continued adverse environmental exposures, thus propagating the cycle of obesity and metabolic syndrome. This phenomenon may be attributed to an extrinsic process resulting from the maternal phenotype and the associated nutrient alterations occurring within each pregnancy. In addition, epigenetic inheritance may occur through somatic cells or through the germ line involving both maternal and paternal lineages. Since epigenetic gene modifications may be reversible, understanding how epigenetic mechanisms contribute to transgenerational transmission of obesity and metabolic dysfunction is crucial for the development of novel early detection and prevention strategies for programmed metabolic syndrome. In this review we discuss the evidence in human and animal studies for the role of epigenomic mechanisms in the transgenerational transmission of programmed obesity and metabolic syndrome.