The Intensity of Blood Lymphocyte Apoptosis in Chronically Exposed Individuals with Obligate Forms of Precancerous Conditions.

We studied the apoptotic death of peripheral blood lymphocytes in individuals chronically exposed to radiation with a history of obligate forms of precancerous conditions. The study included 242 subjects chronically exposed to low-intensity radiation in the range of low and medium doses (mean dose of irradiation of the red bone marrow 555±39 mGy). Of these, 121 subjects had obligate forms of precancerous conditions. In irradiated individuals with obligate forms of precancers, a statistically significant increase in the frequency of apoptosis of peripheral blood lymphocytes at an early and late stages was revealed. Correlation analysis revealed no dependence of the apoptotic death of peripheral blood lymphocytes on the dose of red bone marrow irradiation.

[Methylation Status of Apoptosis Genes and Intensity of Apoptotic Death of Peripheral Blood Lymphocytes in Persons Chronically Exposed to Radiation].

Methylation of the CpG islands of gene promoter regions is the most common epigenetic modification involved in the regulation of gene expression. A number of studies have shown that ionizing radiation can cause both hyper- and hypomethylation of DNA. Aberrant methylation affects cellular processes and can lead to the development of various pathological states. In the literature, there are few studies on the methylation status of human DNA a long time after radiation exposure. Here, the methylation level of CpG islands of the promoter regions of apoptosis genes (BCL2, ATM, MDM2, CDKN1A, STAT3, and NFKB1), and also its influence on apoptosis of peripheral blood lymphocytes in chronically exposed persons were studied. Residents of the South Ural region who were chronically exposed to radiation (after discharges of radioactive wastes into the Techa river by the "Mayak Production Association" in 1949-1956) were included in the study. It was established that the proportion of individuals with hypermethylated BCL2 gene promoter among the exposed people was statistically significantly higher than in the control group. The percentage of methylation of the ATM gene promoter weakly positively correlated with dose and age characteristics. Differences in the frequency of lymphocyte apoptosis in exposed individuals with a hypo- or hypermethylated ATM gene promoter were also established. The data indicate that, in the long-term, after chronic low intensity radiation exposure at low and medium doses, epigenetic modifications of the genome occur, which are manifested as changes in methylation of promoter regions of BCL2 and ATM genes.

Transcriptional activity of repair, apoptosis and cell cycle genes (TP53, MDM2, ATM, BAX, BCL-2, CDKN1A, OGG1, XPC, PADI4, MAPK8, NF-KB1, STAT3, GATA3) in chronically exposed persons with different intensity of apoptosis of peripheral blood lymphocytes.

Transcriptional activity of genes involved in maintaining genetic homeostasis (genes for repair, cell cycle and apoptosis: TP53, MDM2, ATM, BAX, BCL-2, CDKN1A, OGG1, XPC, PADI4, MAPK8, NF-KB1, STAT3, GATA3) was studied in chronically exposed persons with an increased intensity of early and late stages of apoptosis and necrosis of peripheral blood lymphocytes. The object of this study was peripheral blood mononuclear cells obtained from 132 chronically exposed residents of the Techa riverside villages. The mean accumulated dose to red bone marrow was 426.4 ± 48.2 mGy (1.3-2930.0 mGy), to thymus and peripheral immune organs, 58.9 ± 7.9 mGy (0.1-489.0 mGy). The study was performed more than 60 years after the onset of exposure, the average age of exposed persons was 68 ± 0.6 years (55-86 years). The study of apoptotic and necrotic death of peripheral blood lymphocytes was based on the presence of phosphatidylserine on the cell membrane surface, as well as on its permeability for DNA-intercalating dye. Evaluation of the relative content of mRNA genes for repair, cell cycle, and apoptosis was carried out using real-time PCR. An increased relative content of PADI4 gene mRNA was registered in the group of chronically exposed persons with the increased intensity of early apoptosis (p = 0.006). Modulation of the relative content of mRNA of the TP53 (p = 0.013) and BCL-2 (p = 0.021) genes was detected in the group of chronically exposed individuals with the increased intensity of the late stage of apoptosis. A statistically signif icant increase in the transcriptional activity of the TP53 gene was observed in the group of chronically exposed persons with the increased intensity of peripheral blood lymphocyte necrosis in the long-term period (p = 0.015). In the course of the study it was noted that exposed people with increased intensity of apoptosis, f irst of all, demonstrate changes in the transcriptional activity of apoptotic genes. These data are consistent with current views on the activation of programmed cell death.