Identifying the effects of environmental exposures on human health is a our major objective. In environmental health, the recognition that exposures could produce DNA mutations represented a major landmark for risk assessment and prevention.[1] Consequently, chemical agents have been categorized according to their capability to alter the DNA sequence. Such information has been fundamental to determine environmental risks and shape current regulatory efforts for exposure reduction.[2] Recent evidence suggests that the molecular influence of the environment may extend well beyond the interaction with the DNA sequence.[3, 4]

The main molecular mechanisms we have focused our investigations on, are shortly described below:  

Epigenetic mechanisms
The current field of epigenetics includes a number of mechanisms, including DNA methylation, histone modification, and microRNAs.[5, 6] DNA methylation is a covalent modification, heritable by somatic cells after cell division. 5-methyl-cytosine (5MeC) represents 2-5% of all cytosines in mammalian genomes and is found primarily on CpG dinucleotides.[7]  DNA methylation is involved in regulating many cellular processes, including chromatin structure and remodeling, X-chromosome inactivation, genomic imprinting, chromosome stability, and gene transcription.[8, 9] Generally, gene promoter hypermethylation is associated with decreased expression of the gene. [10]
Histones are globular proteins that undergo posttranslational modifications that alter their interaction with the DNA and other nuclear proteins.[11] H3 and H4 histones have long tails protruding from the nucleosome, which can be covalently modified by acetylation, methylation, ubiquitination, phosphorylation, sumoylation, citrullination, and ADP-ribosylation, and thus influence chromatin structure and gene expression.
microRNAs (miRNA) are single-stranded RNAs of 21-23 nucleotides in length that are transcribed from DNA but not translated into proteins (non-coding RNAs); Mature miRNAs are partially complementary to one or more messenger RNA (mRNA) molecules. miRNA main function is to down-regulate gene expression by interfering with mRNA functions.[12, 13] Some environmental factors have been linked to aberrant changes in epigenetic pathways both in experimental and epidemiological studies. In addition, epigenetic mechanisms may mediate specific mechanisms of toxicity and responses to certain chemicals. Whereas mechanisms of action of some of these agents are understood, for others the mode of action remains to be completely elucidated.[14]  Because these epigenetic changes are small, potentially cumulative, and they may develop over time, it may be difficult to establish the cause-effect relationships among environmental factors, epigenetic changes and diseases.

Plasma microvesicles
Microvesicles are spherical structures limited by a lipid bilayer that can be generated by cells and secreted into the extracellular space. There are various types of secreted membrane microvesicles that have distinct structural and biochemical properties depending on their intracellular site of origin, and these features probably affect their function. Microparticles originating from platelets, endothelial cells and monocytes have been most extensively studied.[15] Platelet microparticles were originally studied because of their procoagulant activity [15] and recent studies have investigated their involvement in the pathophysiology of vascular disorders.[15] They could also participate in a defensive shedding of complement attack complexes[16] or in deployment of immunomodulating activities.[17]  Moreover, microvesicles are released from cell membranes by triggers such as endotoxin encounter, hypoxia or oxidative stress conditions, cytokines release, thrombin production [18] and could be one of the means used by tissues to adapt to these changes.[19] Microvesicle membranes are enriched in molecules characteristic of their parent cell and express adhesion molecules on their surface (i.e., ICAM1), which could favor their capture by recipient cells. The fate of microvesicles after binding the surface of recipient cells is not known but recent evidence suggests that they might fuse with recipient cell membranes and deliver their content directly into the cytoplasm of the recipient cells. It has been suggested that microvesicles, after internalization within target cells through surface-expressed ligands, may transfer microRNAs (miRNAs) [20, 21] enabling intercellular and inter-organ communication in the body.[21] Moreover, miRNA expression in circulating microvesicles has been detected also in plasma of normal subjects and a predictive role of peripheral blood miRNA signatures in human disease has been also hypothesized.[21]  

Telomere length
Telomeres are repetitive sequence nucleotides (TTAGGG)n that together with specialized proteins form a proper cap at the ends of linear chromosomes [22]. They have multiple functions in preserving chromosomes stability, protecting chromosomes from nucleolitic degradation and preventing chromosomal end fusion [23]. With shortening telomeres initiated to lose their capping function resulting in sister chromatid fusion and prolonged breakage/fusion/bridge cycles associated with many of types of rearrangements typically of cancer cells [24]. Significant telomeres shortening can lead to telomere dysfunction which, in turn, can be directly implicated in chromosomal instability [25]. Telomere length depends on telomerase activity, a ribonucleoprotein enzyme that elongates telomeric DNA [26], on shelterin complex (TERF1, TERF2, TIN2, hRAP1, TPP1, POT1) that influence telomere function by the formation of a protective cap against degradation and inappropriate DNA repair, avoiding end to end fusion, and by the regulation of telomerase activity [27], on numerous telomere associated proteins, including proteins involved in DNA repair  and helicases [28-31].  In somatic cells, telomeres shorten with each cell division [32], eventually leading to cell senescence when become critically short [33].  

Mitochondrial copy number
Mitochondria are both the major intracellular source and primary target of ROS, which are generated under normal conditions as by-products of aerobic metabolism in animal and human cells [34]. Each human and animal cell contains between several hundred and > 1,000 mitochondria, each carrying 2^10 copies of mitochondrial DNA (mtDNA) [35]. MtDNA copy number (mtDNAcn) is positively correlated with the number and size of mitochondria [36]. Compared with nuclear DNA, mtDNA has diminished protective histones and DNA repair capacity and is therefore particularly susceptible to ROS-induced damage. Cells challenged with ROS have been shown to synthesize more copies of their mtDNA and to increase their mitochondrial abundance to compensate for damage and meet the increased respiratory demand required for ROS clearance [36]. Conversely, ROS are also generated from the increased mitochondria and can, in turn, cause additional oxidative damage to mitochondria and other intracellular constituents, including DNA, RNA, proteins, and lipids.   

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