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Section 1. Biology
Abdugafurova Dilnoza Gulyamovna, researcher, Institute of Biophysics and Biochemistry at the National University of Uzbekistan, Tashkent E-mail. [email protected] Kadirova Dilbar Abdullayevna, doctor of biological sciences, professor, Institute of Biophysics and Biochemistry at the National University of Uzbekistan, Tashkent E-mail. [email protected]
STRUCTURAL AND FUNCTIONAL CHROMATIN DISTURBANCES IN THE THYROID CELLS IN THE AGING PROCESS
Abstract: Chromosomal instability during aging leads to the appearance of a large number of cells with various quantitative and structural disorders that occur during chromosomal aberrations. The purpose of subsequent cytogenetic analysis experiments is to study chromosomal aberrations that occur in the cells of the thyroid gland during aging. In the study of cytogenetic, mutational and molecular genetic disorders in most cases, it was found that their frequency increases with age.
Keywords: Age, genome, chromatin, thyroid gland, chromosomal aberrations.
Introduction. The aging of the organism is a multifaceted The aim of the study was to study the frequency and
process, it affects the tissue and cellular levels. This process spectrum of spontaneous chromosomal aberrations in the is controlled by the genome and environmental conditions, where the hereditary program of each organism is implemented [1, 26-34]. The mechanisms of aging are manifested in many types of disorders occurring at the molecular level. Aging includes a number of processes that reduce the organism's resistance [2, 27-32]. It is known that the number of chromosomal aberrations is used as a marker DNA damage in aging organisms. Somatic mutations can arise due to the accumulation of steady aberrations and underlie age-related pathology, including malignant tumors [3, 341-349]. An effective method for assessing the influence of environmental factors on the human organism is a cytogenetic analysis of peripheral blood lymphocytes, which allows to determine the level of chromosomal abnormalities in somatic cells [4, 229-231]. The spontaneous level of chromosomal aberrations in human lymphocytes can vary depending on external and internal factors: organism metabolism, hormonal balance, changing during life [5, 21-29; 6, 125-163; 7, 368]. Many scientific studies indicate that with increasing age, spontaneous levels of chromosomal aberrations in human lymphocytes may increase, which is potentially dangerous for health in terms of the development of cancer pathology [8, 80-85; 9, 277-278; 10, 253-258].
peripheral blood of lymphocytes of conditionally healthy volunteers of different ages with and without diseases of the thyroid gland.
Material and methods. The material of the cytogenetic study was the lymphocytes of the peripheral blood of the young, middle, senior and elderly (7 people in each age group) age. Blood lymphocytes were cultured according to standard methods [11, 23]. Cytogenetic analysis was performed under a microscope at magnification x1000. The entire spectrum of chromosome aberrations was taken into account according to the international nomenclature [12, 140]. The preparations were stained with 4% solution Romanovsky-Giemsa. The analysis was carried out in the metaphase stage.
Results and discussion. Cellular aging is accompanied by various chromosomal changes: a violation of the number of chromosomes, intragroup variations in the number of chromosomes, structural changes in chromosomes, the appearance of marker chromosome aberrations. Cell aging may be associated with the appearance of spontaneous chromosomal aberrations. Chromosomal instability during aging leads to the appearance of a large number of cells with various quantitative and structural disorders that occur during chromosomal
Section 1. Biology
aberrations. The purpose of subsequent cytogenetic analysis experiments is to study chromosomal aberrations that occur in the cells of the thyroid gland during aging. In the study of cytogenetic, mutational and molecular genetic disorders in most cases, it was found that their frequency increases with age. This concerned chromosomal aberrations, micronuclei, aneuploidy, loss of telomeric repeats, mutations. Structural aberrations of chromosomes are related to the type of genetic abnormalities that undoubtedly contribute to the multifactorial process of aging. Unstable chromosomal aberrations - dicentrics, rings, fragments - lead to cell death, stable - translocations, insertions are known to accompany oncogenesis, and can also affect vital cell functions [3, 341-349]. Based on the results obtained, we concluded that with age the thyroid gland does not undergo any special changes. Analysis of the results showed that the average group frequency of chromosome aberrations significantly increased with an increase in the age of the examined individuals from 19 to 70 years. Comparing the obtained results with literary sources, the following can be noted. According to Polish researchers who used G-differential staining of metaphase chromosomes of peripheral blood lymphocytes of healthy volunteers aged from 21 to 78, an increase in all types of chromosomal aberrations with increasing age was shown [13, 763-772].
However, the presence of one or another pathology of the thyroid gland, perhaps, accelerates the aging process. To confirm the obtained data, we performed a cytogenetic analysis of chromosomal aberrations at the metaphase stage of mitosis of peripheral blood lymphocytes in young people (19 years and 25 years) and elderly people (54, 69 and 75 years). It should be noted that the elderly were with thyroid pathology: 54 years and 79 years with diffuse toxic goiter and 75 years with a nodal eu-thyroid goiter. In these cultures, we studied the level ofspontane-ous chromosomal aberrations in peripheral blood lymphocyte
cells. The figure shows that at least 100 metaphases with a good chromosome spread were analyzed for each culture. In patients aged 54, the total number of metaphases studied was 123 cells, among which there is 1 cell with one microfragment (0.8%); in patients aged 79, the total number of metaphases studied was 111 cells and one cell with a paired fragment (0.9%). In a 75-year old patient with a nodal euthyroid goiter, the total number of metaphases studied was 156 cells, of which 3 (1.92%) are aberrant cells with paired fragments. The aberrant cells in this patient exceed the number of aberrant cells in the control (19 years and 25 years). We carried out a cytogenetic analysis of the chromosomes of the cells of peripheral blood lymphocytes of elderly people without thyroid gland pathology (59-75 years). Cytogenetic analysis of chromosomes of cells of peripheral blood lymphocytes at the age of 75 years without thyroid gland revealed single asymmetric translocations of chromosomes (Fig. 1). Chromatid translocations represent the exchange between chromosomes and chromatid exchanges within the chromosomes. The figure shows that in this patient cytogenetic analysis revealed the presence of chromatid asymmetric translocation. Chromatid asymmetric translocations lead to the appearance of chromatid dicentric and fragments and lead to cell death.
Cytogenetic analysis of chromosomes of peripheral blood lymphocytes of patients aged 75 years with papillary adenocarcinoma revealed the presence of chromatid breaks and deletions. Based on our data, we concluded that chromosomal aberrations (translocations, fragments, rings, inversions) can lead to aging of the organism and age-related diseases. Cy-togenetic analysis of peripheral blood lymphocytes of this patient also revealed the presence of gaps, single and paired fragments. It is known that the localization of the gap in the chromosome may indicate the place of the former gap or the junction of fragments. Gaps are unrealized, potential damage that does not go through the repair process.
Figure 1. Asymmetric chromatid translocations detected in patients aged 75 years
The resulting fragments devoid of centromeres during asymmetric translocations usually fall into the plasma and lyse, which upsets the gene balance, and such cells die. In this chapter, we also conducted a study of the age dynamics of
the frequency of stable chromosomal aberrations in the elderly in normal conditions and in papillary adenocarcinoma. Structural aberrations of chromosomes are considered as the most likely events associated with cell malignancy. This fact
is confirmed by the fact that the vast majority of tumors are characterized by chromosomal rearrangements; many carcinogens induce structural chromosome aberrations; mutations in the genes responsible for DNA repair, for the suppression of oncogenes, for control of the cell cycle increase both the frequency of tumors and the frequency of chromosomal breakdowns. It is known that in old age the likelihood of tumor development increases, therefore, the analysis of the age dynamics of chromosomal aberrations can contribute to an understanding of the mechanisms of carcinogenesis and aging. In the lymphocytes of the peripheral blood of elderly people (age 70, 75 years) without thyroid gland pathology, an age-related increase in the level of chromosomal aberrations in the form of deletions and translocations.
Cellular aging is accompanied by various chromosomal changes: a violation of the number of chromosomes, intra-group variations in the number of chromosomes, structural changes in the chromosomes, the appearance of marker chro-
mosomes - aberrations. Cell aging may be associated with the appearance of spontaneous chromosomal aberrations. Chromosomal instability during aging leads to the appearance of a large number of cells with various quantitative and structural disorders that occur during chromosomal aberrations. Aging can be defined as the increasing likelihood of degenerative diseases (cancer, autoimmune diseases, cardiovascular pathology) and death. Structural aberrations of chromosomes are related to the type of genetic disorders that undoubtedly contribute to a multifactorial process. We performed a cytogenetic analysis of chromosomal aberrations at the metaphase stage of mitosis of peripheral blood lymphocytes in young people (18 years and 24 years) and elderly people (54, 59 and 75 years). It has been established that with a nodal euthyroid goiter in a patient at the age of 75 years, small chromosomal aberrations are observed. It was shown that in patients aged 75 years without thyroid gland, isolated asymmetric translocations of chromosomes were observed.
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