Epigenetics

The term epigenetics, first coined by Conrad Waddington (University of Edinburgh), can be defined as an alteration in gene activity that is mitotically stable in the absence of a change in DNA sequence.

Extensive cytological, gene expression and molecular profiling studies have culminated into the present view of epigenetics as an combination of mechanisms that functionally organize the genome in the nucleus, regulate gene expression, propagate cell identity and govern transcriptional responses to external stimuli. Reprogramming of epigenetic states can be induced by environmental exposures such as malnutrition, tobacco smoke, air pollutants, metals, organic chemicals etc., particularly during key periods of development. Thus, epigenetic changes may represent a major pathway by which environmental factors influence disease risk within individuals and across generations. Direct evidence for this important link is emerging from epigenetic profiling but the primary mechanisms are still unclear.

Exposure to environmental factors such as tobacco smoke, chemicals, air pollutants and malnutrition can adversely affect human health. One mechanism for environmental sensing, which needs more investigation, acts through alterations in chemical tags that normally exist on our DNA. These are termed ‘epigenetic marks’ and can act as a ‘barcode’ of DNA function by indicating if genes are in an active or silent state. Alteration and reprogramming of epigenetic marks by environmental triggers can act both as a read out of changes in gene expression and may also directly affect gene function, with downstream effects on the way cells and tissues work. This may promote disease susceptibility, for example resulting in an increase in cancer incidence, or influence chronological processes such as ageing.

In order to increase our knowledge of how the science of epigenetics could have an impact on reproductive toxicology, a solid understanding of the biology and variation of the epigenome is essential to better assess concerns about possible adverse health effects related to epigenetic changes. In particular, little is known about which epigenetic alterations are part of normal variability and which could be considered adverse, hence posing a health risk. To obtain a better insight into the current state of the art of epigenetics and to discuss its potential applications in reproductive toxicology, ECETOC organised a workshop with expert participants in the field of epigenetics as well as reproductive toxicological risk assessment.