The role of polymorphism and expression level of cytokine network genes in forming the molecular-genetic basis of predisposition to essential hypertension

The dissertation is devoted to the study of the molecular-genetic basis of predisposition to essential hypertension (EH), with an emphasis on the polymorphism and expression level of cytokine network genes. The work was carried out on a sample of EH patients and control individuals from the Tatar population residing in the Republic of Bashkortostan, which determines its population-specific orientation. The study includes an assessment of intracardiac hemodynamics and left ventricular myocardial remodeling, genotyping for polymorphic markers of the genes of interleukins, tumor necrosis factor alpha, lymphotoxin, interleukin-1 receptor antagonist, angiotensinogen, and endothelial nitric oxide synthase, as well as an analysis of associations of genotype combinations with risk factors and cardiovascular complications.

A separate place in the work is occupied by a comparative analysis of the expression profile of cytokine and cytokine receptor genes in peripheral blood cells using real-time reverse transcription — polymerase chain reaction. The obtained data are aimed at identifying genetic markers of the risk of EH and its complications, as well as at substantiating approaches to medical-genetic counseling and the prevention of cardiovascular pathology.

Relevance of the problem. Arterial hypertension (AH) remains one of the main risk factors for the development of severe cardiovascular complications, such as stroke and myocardial infarction — the leading causes of mortality in the modern world.

Essential, or primary, hypertension (EH), or hypertensive disease, is a multifactorial disease in the occurrence of which genetic predisposition plays an important role. It is generally accepted that blood pressure (BP) is a quantitative trait controlled by множеством генов [many genes], the expression of which varies depending on environmental factors [196]. Although the general concept of the role of genetic factors in the etiopathogenesis of EH is sufficiently well substantiated, many unclear issues remain regarding the contribution of specific genes. The majority of studies are devoted to a limited set of genes that encode proteins regulating vascular tone, endothelial function, mineral metabolism, and lipid metabolism and transport in the vascular bed. Relatively recently, the question of the participation of cytokine cascade genes in the development of EH has begun to be studied.

Cytokines are key mediators of intercellular interactions, including in the inflammatory process. Endothelial cells and leukocytes are capable of producing and responding to a wide range of pro- and anti-inflammatory cytokines. Inflammation is the main pathophysiological substrate of cardiovascular diseases [184]. Increased expression of inflammatory mediators by the endothelium underlies atherosclerotic damage to the vascular wall [125]. Endothelial dysfunction, along with impaired blood coagulation and hypercholesterolemia, leads to impaired vascular tone. At the same time, it is known that the cytokine network functions in close association with the renin-angiotensin system and endothelial relaxation factors, in particular nitric oxide. All this makes it possible to assign a significant role to cytokines in the pathogenesis of EH. Of particular interest is the study of the expression profile of cytokine network genes in peripheral blood leukocytes of EH patients, the results of which open new possibilities for analyzing the role of the transcriptome of blood cells in the etiopathogenesis of EH.

However, in EH, as in the case of other multifactorial diseases, knowledge of the gene product alone and of the effect of the polymorphism of this gene on the functional properties of the protein is insufficient. The final effect of a gene largely depends on its immediate environment and on the properties of the system in which it functions. This, in turn, largely depends on individual characteristics and environmental conditions. Therefore, the same set of genes may have different functional significance in different populations. In this regard, it is relevant to elucidate the role of the polymorphism of a number of candidate genes, risk factors, and certain clinical features in the development of EH in the Tatar population living on the territory of the Republic of Bashkortostan.

In accordance with the above, the aim of the present investigation was to study the role of the polymorphism and the level of expression of cytokine genes in determining the risk of essential hypertension and their interrelation with the parameters of intracardiac hemodynamics and left ventricular myocardial remodeling in patients with essential hypertension.

To achieve this aim, the following tasks were set: 1. To assess the state of intracardiac hemodynamics and the character of left ventricular myocardial remodeling in patients with essential hypertension depending on the presence of complications.

2. To conduct an analysis of associations with essential hypertension of allelic variants of the genes of interleukin 1 beta (IL1B, -511 T/C), tumor necrosis factor alpha (TNFA, -308A/G), lymphotoxin (LTA, -252A/G), interleukin 6 (IL6, -572G/C), interleukin 10 (IL10, -627C/A), interleukin 12 (IL12B, 1159A/C), interleukin 1 receptor antagonist (IL1RN, VNTR polymorphism), angiotensinogen (AGT, -174T/M), and endothelial nitric oxide synthase (NOS3, VNTR polymorphism in intron 4).

3. To establish the relationship of the polymorphism of the listed genes with risk factors and cardiovascular complications of essential hypertension.

4. To conduct an analysis of associations of allelic variants of candidate genes with left ventricular hypertrophy in patients with essential hypertension.

5. To assess the degree of risk of development of essential hypertension and cardiovascular complications in connection with combinations of genotypes of candidate genes.

6. To conduct a comparative analysis of the expression profiles of cytokine and cytokine receptor genes in peripheral blood cells of patients with essential hypertension and individuals of the control group.

Scientific novelty of the work. The features of left ventricular myocardial remodeling in EH patients have been established depending on the presence of complications. For the first time, an analysis of the associations of polymorphisms of the genes IL10, IL6, IL12B, IL1B, IL1RN, TNFA, LTA with the risk of EH has been carried out and markers of the risk of EH have been identified. For the first time, an association has been shown of combinations of genotypes of polymorphic variants of the genes IL1B, IL6, and IL12B with cardiovascular complications of EH (myocardial infarction and stroke). An association of left ventricular hypertrophy with the VNTR polymorphism of the NOS3 gene has been established in EH patients. On the basis of a study of the expression profile of 84 cytokine genes in peripheral blood cells of EH patients and individuals of the control group, differences in the expression level of 21 genes were revealed. For the first time, in EH patients, an increase in the transcriptional activity of the genes CCL16, CCL17, CCL18, CCL19, CCL23, CCL8, CCR6, CCR8, CX3CR1, CXCL1, CXCL13, ICEBERG, IL13, IL17C, IL1F10, IL1F6, ILF9, SPP1, CD40LG, XCR1 and a decrease in the transcriptional activity of the CCL2 gene in peripheral blood cells have been discovered.

Practical significance. The expediency of conducting genotyping for the polymorphic variants -627C/A of the IL10 gene and -511T/C of the IL1B gene for assessing the risk of development of essential hypertension, as well as genotyping for the polymorphic variants of the genes IL1B, IL-6, IL-10, IL-12B, and TNFA for assessing the risk of development of cardiovascular complications of essential hypertension, has been substantiated. The results of the work are used in the development of recommendations for medical-genetic counseling on EH with the aim of primary and secondary prevention of cardiovascular pathology. The materials of the study can be used in the educational-methodological process at medical and biological faculties, as well as in courses of postgraduate education of cardiologists, therapists, and general practitioners.

Propositions put forward for defense.

1. The development of essential hypertension is characterized by the formation of concentric variants of left ventricular myocardial remodeling. In patients with essential hypertension who have suffered MI, eccentric hypertrophy, including with left ventricular dilatation, is observed more often.

2. The genetic markers of the risk of essential hypertension are allelic variants of the genes IL1B, IL10, IL1RN, IL12B, and AGT.

3. The risk of development of cardiovascular complications of essential hypertension (stroke) is associated with polymorphic variants of the genes IL1B, IL-6, IL-10, IL-12B, and TNFA.

4. The VNTR polymorphism in intron 4 of the endothelial nitric oxide synthase gene (NOS3) is associated with left ventricular hypertrophy in patients with essential hypertension.

5. In peripheral blood cells of patients with essential hypertension, the transcriptional activity of a number of cytokine genes, especially chemokines, is altered in comparison with the control group.