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Draft August 3rd 2016Paolo Vineis (1), Aristotelis Chatziioannou (2), Vincent Cunliffe (3)
Conflicts of interest: None declared 2
AbstractExposure to environmental stressors, toxicants and nutrient deficiencies can affect DNA in a number of ways. While some exposures cause damage and alter the structure of DNA, there is increasing evidence that the same or other environmental exposures, including those experienced during fetal development in utero, can cause epigenetic effects which modulate DNA function and gene expression. Some epigenetic changes to DNA that affect gene transcription are at least partially reversible (i.e. they can be enzymatically reversed after cessation of exposure to environmental agents), but some epigenetic modifications seem to persist even for decades. To explain the effects of early life experiences (such as famine and other exposures to stressors) on the long-term persistence of specific patterns of epigenetic modifications, such as DNA methylation, we propose an analogy with immune memory. We propose that an epigenetic memory can be established and maintained in self-renewing stem cell compartments. We suggest that the observations on early life effects on adult diseases and the persistence of methylation changes in smokers support our hypothesis, for which a mechanistic basis, however, needs to be further clarified. We outline a new model based on methylation changes. Though these changes seem to be mainly adaptive, they are also implicated in the pathogenesis and onset of diseases, depending on individual genotypic background and/or types of subsequent exposures. Elucidating the relationships between the adaptive and maladaptive consequences of the epigenetic modifications that result from complex environmental exposures is a major challenge for current and future research in epigenetics.