The blunted vascular endothelial growth factor-A (VEGF-A) response to high-altitude hypoxia and genetic variants in the promoter region of the VEGFA gene in Sherpa highlanders

Abstract

Background: Sherpa highlanders demonstrate extraordinary tolerance to hypoxia at high altitudes, which may be achieved by mechanisms promoting microcirculatory blood flow and capillary density at high altitudes for restoring oxygen supply to tissues. Vascular endothelial growth factors (VEGFs) are important signaling proteins involved in vasculogenesis and angiogenesis which are stimulated by hypoxia. We hypothesize that the VEGF-A, the major member of the VEGF family, and the gene encoding VEGF-A (VEGFA) play a part in the adaptation to high-altitude hypoxia in Sherpa highlanders.

Methods: Fifty-one Sherpa highlanders in Namche Bazaar village at a high altitude of 3,440 meters (m) above sea level and 76 non-Sherpa lowlanders in Kathmandu city at 1,300 m in Nepal were recruited for the study. Venous blood was sampled to obtain plasma and extract DNA from each subject. The plasma VEGF-A concentrations were measured and five single-nucleotide polymorphisms (SNPs, rs699947, rs833061, rs1570360, rs2010963, and rs3025039) in the VEGFA were genotyped. The VEGF-A levels and allelic frequencies of the SNPs were compared between the two populations.

Results: A significant difference in oxygen saturation (SpO₂) was observed between the two ethnic groups locating at different elevations (93.7 ± 0.2% in Sherpas at 3,440 m vs. 96.7 ± 0.2% in non-Sherpas at 1,300 m, P < 0.05). The plasma VEGF-A concentration in the Sherpas at high altitude was on the same level as that in the non-Sherpas at low altitude (262.8 ± 17.9 pg/ml vs. 266.8 ± 21.8 pg/ml, P = 0.88). This result suggested that the plasma VEGF-A concentration in Sherpa highlanders was stable despite a high-altitude hypoxic stimulus and that therefore the Sherpas exhibited a phenotype of blunted response to hypoxic stress. Moreover, the allele frequencies of the SNPs rs699947, rs833061, and rs2010963 in the promoter region of the VEGFA were different between the Sherpa highlanders and non-Sherpa lowlanders (corrected P values = 3.30 ×10^-5, 4.95 ×10^-4, and 1.19 ×10^-7, respectively).

Conclusions: Sherpa highlanders exhibited a blunted VEGF-A response to hypoxia at high altitudes, which was speculated to be associated with the distinctive genetic variations of the SNPs and haplotype in the promoter region of VEGFA in Sherpa highlanders.

Keywords: Genetic adaptation; High altitude; Hypoxia; Sherpa highlanders; Vascular endothelial growth factor.