2012 Study Abstracts
This review focuses on how environmental factors through epigenetics modify disease risk and health outcomes. Major epigenetic events, such as histone modifications, DNA methylation, and microRNA expression, are described. The function of dose, duration, composition, and window of exposure in remodeling the individual’s epigenetic terrain and disease susceptibility are addressed. The ideas of lifelong editing of early-life epigenetic memories, transgenerational effects through germline transmission, and the potential role of hydroxylmethylation of cytosine in developmental reprogramming are discussed. Finally, the epigenetic effects of several major classes of environmental factors are reviewed in the context of pathogenesis of disease. These include endocrine disruptors, tobacco smoke, polycyclic aromatic hydrocarbons, infectious pathogens, particulate matter, diesel exhaust particles, dust mites, fungi, heavy metals, and other indoor and outdoor pollutants. We conclude that the summation of epigenetic modifications induced by multiple environmental exposures, accumulated over time, represented as broad or narrow, acute or chronic, developmental or lifelong, may provide a more precise assessment of risk and consequences. Future investigations may focus on their use as readouts or biomarkers of the totality of past exposure for the prediction of future disease risk and the prescription of effective countermeasures.
Implications of Lifelong Editing of Early-Life Epigenetic Memories
The concept of continued editing of early-life epigenetic markings or memories during adult life has been proposed on the basis of evidence from limited experimental studies. Exposure of mice to diethylstilbestrol (DES, a xenoestrogen) or genistein (a phytoestrogen) during the perinatal period induced specific epigenetic markings in their uteri. However, some of these epigenetic markings (hypomethylation of Nsbp1) remained “hidden” during prepuberty life and appeared in adulthood only in the exposed intact females but not in their ovariectomized counterparts, suggesting that adult exposure to ovarian steroids may cause these markings to “surface.” Coincidentally, the prevalence of uterine cancer was higher in neonatally exposed intact mice, but not in mice ovariectormized before puberty.
Epigenetic Factors Shown to Trigger Epigenetic Events and Affect Disease States
Exposure to EDCs during early developmental periods is a major health concern because it can cause persistent changes in gene expression through epigenetic reprogramming in somatic cells, as well as germ-line cells, and subsequently promote transgenerational inheritance. The xenoestrogen DES was widely used in cattle and other livestock industries and is still an EDC in many populations. Early-life exposure of mice to DES increases risk of uterine cancer that is accompanied by demethylation of an estrogen-responsive gene, lactoferrin, in the mouse uterus. In utero exposure of mice to DES triggered hypermethylation of the homeobox A10 with attended uterine hyperplasia and neoplasia in later life. A more recent report documented hypermethylation of nucleosome binding protein 1 (Nsbp1 or Hmgn5) as a hidden uterine epigenetic mark after neonatal DES exposure that only appeared upon sexual maturation of the exposed mice but failed to manifest if the animals were ovarietomized before puberty. Of significant interest is the transgenerational effect of developmental exposure of mice to DES that promoted c-fos expression, hypomethylation of specific exon CpGs, and increased susceptibility to tumorigenesis in the F2 generation. These experimental data support the hypothesis that epigenetic reprogramming is responsible for the devastating consequences observed in the offspring of women who took DES during pregnancy. The DES effects include female genital abnormalities, vaginal cancer, and male urogenital disorders. The adverse effects may be reverberating in the grandchildren of these women.
- Full study (free access) : Environmental Epigenetics and Its Implication on Disease Risk and Health Outcomes, ILAR Journal, NCBI PubMed PMC4021822, 2012 Dec.
- Featured image by h heyerlein.