Histone Methylation in Nickel-Smelting Industrial Workers

Nickel is an essential trace metal naturally found in the environment. It is also common in occupational settings, where it associates with various levels of both occupational and nonoccupational exposure In vitro studies have shown that nickel exposure can lead to intracellular accumulation of Ni2+, which has been associated with global decreases in DNA methylation, increases in chromatin condensation, reductions in H3K9me2, and elevated levels of H3K4me3. Histone modifications play an important role in modulating chromatin structure and gene expression. For example, tri-methylation of histone H3k4 has been found to be associated with transcriptional activation, and tri-methylation of H3k27 has been found to be associated with transcriptional repression. Aberrant histone modifications have been found to be associated with various human diseases, including cancer. The purpose of this work was to identify biomarkers for populations with occupational nickel exposure and to examine the relationship between histone methylation and nickel exposure. This may provide a scientific indicator of early health impairment and facilitate exploration of the molecular mechanism underlying cancer pathogenesis. One hundred and forty subjects with occupational exposure to Ni and 140 referents were recruited. H3K4 and H3K27 trimethylation levels were measured in subjects' blood cells. H3K4me3 levels were found to be higher in nickel smelting workers (47.24±20.85) than in office workers (22.65±8.81; P = 0.000), while the opposite was found for levels of H3K27me3(nickel smelting workers, 13.88± 4.23; office workers, 20.67± 5.96; P = 0.000). H3K4me3 was positively (r = 0.267, P = 0.001) and H3K27 was negatively (r = -0.684, P = 0.000) associated with age and length of service in smelting workers. This study indicated that occupational exposure to Ni is associated with alterations in levels of histone modification.