2.1.2. Association of the VEGF Gene SNVs with Changes in the “Angiogenic Switch” Stroke and Functional Resources in Athletes
gene encoding the homonymic protein plays a key role in the regulation of vasculogenesis and angiogenesis. It was identified, isolated, and cloned more than 25 years ago 
. It is localized on chromosome 6p21.1 ().
Figure 1. Localization of the VEGF gene on chromosome 6p21.1.
There are several related genes, including VEGF-B
but the greatest attention is paid to VEGF-A
because of its key role in the regulation of angiogenesis, in both physiological and pathological homeostasis. All isoforms of the VEGF protein have specific receptors. They have different affinities for the different receptors and can bind to them. VEGF-B overrides the activity of VEGF-A by activating VEGFR-1. VEGF-C and VEGF-D can be angiogenic factors. In this case, they are activated via the VEGFR-2 and VEGFR-3 receptors. Furthermore, these factors can be lymphangiogenic (mainly VEGF-D) and are activated through the VEGFR-3 receptor. The absolute and relative levels of expression of VEGFR-2 and VEGFR-3 in the endothelium can influence the nature of the effect of growth factors VEGF-C/D—angiogenic or lymphangiogenic effects. VEGF
expression is stimulated by a variety of proangiogenic factors, including hypoxia-induced factor (HIF), epidermal (EGF), and fibroblast (FGF) growth factors. In addition, the blood pH, the partial pressure, and the O2
concentration in the inhaled air affect the VEGF level. Although VEGF primarily targets endothelial cells, it has been shown to have multiple effects on additional cell types. Primarily, VEGF-mediated pathogenic effects are caused by its effect on vascular permeability and neoangiogenesis (neovascularization) 
The severity of expression of genes encoding the process of angiogenesis is reported to be associated with the intensity of physical activity 
. This confirms the point of view, according to which the change in the “angiogenic switch” stroke is a marker of athletes’ physical performance. Among the studied single nucleotide variants (SNVs) of VEGF
, SNVs in the promoter (regulatory) region are of particular interest. For example, the replacement of cytosine with guanine at position −634 (−634 G/C; rs2010963) increases the activity of the gene and, accordingly, determines individual differences in the level of its expression 
Akhmetov et al. 
investigated the frequency distribution of VEGF-A alleles in athletes involved in cyclic sports and in a control group of subjects not involved in sports. The authors also evaluated the association of the studied SNV rs2010963
(−634 G/C) genotypes of VEGF
with the aerobic performance of athletes and the control group. The frequency of the C allele in the control group was 25.3% in women and 23.6% in men (p
≤ 0.05). The distribution of genotypes in the control group was as follows: GG—57.6%; GC—35.8%; CC—6.6%. The frequency of the C allele was statistically significantly higher in the group of athletes than in the control group (29.2% versus 24.5%, respectively; p
= 0.0026). The distribution of genotypes among athletes was as follows: GG—50.6%; GC—40.4%; CC—9%. Analysis of the distribution of alleles in men and women did not reveal statistically significant differences in both groups (p
≥ 0.05). A higher frequency of the C allele was found in long-distance runners compared to athletes in other sports. This indicates that the C allele can be a genetic predictor of the development and endurance manifestation in athletes.
Considering that SNVs of the VEGF
gene promoter can alter the expression of the VEGF
gene and the level of the VEGF-A protein in tissues, Prior et al. 
suggested that SNVs −2578/−1154/−634 in the promoter region of the VEGF
gene are associated with the expression of VEGF
in human myoblasts and maximal oxygen consumption (MOC) before and after aerobic exercise. The authors analyzed the effect of the VEGF
promoter region haplotype −2578/−1154/−634 on the VEGF
expression using the luciferase reporter assay in cultured human myoblasts. In a study with exposure to hypoxia, it was found that haplotypes CGG and AGG showed the lowest hypoxic induction (1.5 and 2.0 times, respectively), while haplotypes AAG and CGC showed the highest hypoxic induction of the VEGF
gene expression (3.1 and 3.2 times, respectively). According to the authors, the results obtained demonstrated the potential functional effect of SNVs −2578, −1154, and −634 as follows: the combination of G-alleles (AGG and CGG haplotypes) leads to a decrease in the VEGF
gene expression in cultured human myoblasts compared to the AAG and CGC haplotypes; the presence of A or C alleles in −2578 SNV (the first position in the haplotype) did not statistically significantly affect the expression of the VEGF
gene. The data obtained showed that the influence of these haplotypes corresponded to the dominant/recessive genetic model, given that only subjects with two copies of AGG or CGG haplotypes showed low BMD. Subjects with ≥1 copy of AAG or CGC haplotypes showed higher BMD values. As none of these three SNVs has been found at any particular transcription factor binding site identified to date, the exact mechanism of the effects of the VEGF −2578/−1154/−634 haplotype on the VEGF
gene expression remains unknown. It is possible that these SNVs disrupt binding sites for transcription factors that are not yet identified or affect interactions between transcription factors. For example, the hypoxia response element (HRE) in the promoter region of the VEGF
gene (5′-position from −2012 to −2005) requires interaction with the upstream protein activator−1 (5′-position from −2166 to −2160) and the downstream protein activator −2α (5′-position from −1117 to −1110), which lie within the test sequence in the promoter region. The authors suggested that SNVs −1154 and/or −634 might somehow influence these interactions 
Studies conducted by Arsic et al. 
used immunohistochemical analysis to show that in intact muscle fibers neither VEGFR-1 nor VEGFR-2 is expressed. In contrast, damage to muscle fibers led to a marked increase in the presence of these receptors. In particular, both receptors were strongly expressed by elongated cells surrounding the newly formed fibers, which could be identified by the presence of a central nucleus resembling the appearance of activated satellite cells at the edge of regenerating fibers. Expression was detected early after injury and persisted until later stages of the regenerative process. In addition, highly expressed VEGFR-2 was found on the surface of mature muscle fibers in the early recovery period after injury. Most strikingly, overexpression of PlGF, a VEGFR-1 agonist, did not promote muscle regeneration after injury, even at very high doses of the vector. These results clearly indicate that VEGFR-2 is a major mediator of VEGF action on myogenic cells.
Currently, at least two signaling pathways are known that are important for muscle regeneration. The first pathway is the activation of VEGFR-2 in endothelial cells, namely, PI3K/Akt. The second is kinase pathways that lead to increased expression and activity of the MyoD protein. Activation of Akt signaling in muscle cells is important for the suppression of apoptosis during differentiation and growth of myofibrils 
. Interestingly, insulin growth factor-1, a powerful promoter of muscle regeneration that stimulates muscle differentiation through Akt, also increases VEGF synthesis in cells, indirectly suggesting the involvement of VEGF in the regeneration process 
. Accordingly, muscle fibers transduced with active Akt also produce increased levels of VEGF and show signs of muscle hypertrophy. Thus, the SNV rs2010963 (−634 G/C) of the VEGF
gene is associated with the physical performance of athletes and plays a key role in sports selection. The role of other studied SNVs needs to be clarified. The results of these studies are of both fundamental and applied importance as they contribute to a better understanding of the molecular adaptation mechanisms of the cerebrovascular and cardiovascular systems to aerobic loads as well as facilitate the choice of optimal sports specialization and type of professional training of athletes.