The impact of environmental contaminants on human DNA methylation variability: the Italian case of Bussi sul Tirino

DNA methylation (DNAm) is an epigenetic mechanism that regulates gene expression and contributes to biological plasticity. An extensive scientific literature has demonstrated the potential of contaminants to alter DNAm profiles, resulting in impacts on human biology and health, especially in terms of reproductive health, biological ageing and neurological diseases. This thesis focuses on a case study of national relevance: the Site of National Interest (SIN) of Bussi sul Tirino (Abruzzo, Italy), an area contaminated by the illegal disposal of industrial waste in soil and groundwater. The central hypothesis is that long-term exposure to pollutants may influence DNAm variability and the health of local residents. To test this hypothesis, buccal swabs were collected from 61 individuals, divided into two groups according to level of exposure. In a subgroup of 33 individuals, DNAm and genetic variation were assessed using Illumina MethylationEPIC (850k) and HumanOmniExpress (720k) arrays, respectively. In addition, DNAm levels of three repetitive elements (LINE-1, Alu, rDNA) were measured in all 61 samples by bisulfite sequencing. Two age- and sex-adjusted linear models revealed 622 CpGs with differential DNAm levels (DMPs) between the two groups associated with different biological pathways and 1,138 CpGs with differential variability and convergence to similar DNAm values in the high-exposure group. The meQTL analysis conducted on the 622 DMPs indicated that these differences were not genetically driven, implicating environmental exposure as the main factor. There were no significant differences between the two groups in the number of epimutations, epigenetic lesions, and epigenetic aging. However, the hypomethylation of LINE-1 found in the high-exposure group suggested a possible role of pollutants in conferring genomic instability and contributing to the onset of certain diseases. Finally, the thesis presents two preliminary studies on DNA for tracking contaminants in groundwater and the role of genetic variability in detoxification from atmospheric contaminants, respectively.