Correlation Between EGLN1 Single Nucleotide Polymorphism(SNP) And Brain Volume In Native Tibetans

Background:For those people who have been living in high altitude,they have to encounter stresses include hypoxia,hypobaric,aridity,coldness,ultraviolet radiation and among them hypoxia has the great impact on physiology and cognition.The effects of hypoxia on physiology are mainly manifested in higher concentration hemoglobin,higher pulmonary arterial pressure,shortness of breath and fatigue,etc.The effects of hypoxia on cognition are hypomnesia,unsteady emotion and delayed response.However,Tibetans have the best adaptation to high altitude after 25,000 years of natural selection which has been proved is genetic.Previous studies have identified EGLN1 and EPAS1 as hotspot genes for the adaptation of Tibetans to high altitude.The loci of EGLN1 and EPAS1 are both hypoxia-inducible factors(HIFs),not only are they involved in vascular endothelial growth factor(VEGF),erythropoiesis(EPO)and glycolysis,but they can also regulate the neurons to adapt to the hypoxic environment.The brain,as the center of the nervous system,have lifelong resilience to regulate physical mechanism to adapt the changes of environmental physiological.A lot of studies have demonstrated that genes could change the brain structure and function such as the total volume of the brain,the volume of gray matter and white matter in the region,the thickness of the cortex,and the integrity of white matter,etc.,all of them could be inherited in other words.All in all,after millennia of natural selection,the Tibetan population have gained structural and functional changes of the brain genetically.Purpose:The purpose of the present study was to investigate the correlation between EGLN1 and high-altitude adaptation in the Tibetan plateau.To further explore whether there is a correlation between EGLN1 gene polymorphism in Tibetan population and brain morphological adaptation,and the specific brain region associated with it.According to the frequency distribution of SNP genotype of EGLN1 gene,the differences in brain structures of different genotypes were compared.Materials and methods:1.Participants:One-hundred and thirty-two healthy Tibetan Chinese participants(male-to-female ratio of 1:1,mean age = 19.86±1.03 years)were recruited.All native Tibetans lived in Tibetan Plateau at altitude of 3600?4400m.The participants and their grandparents had lived in high-altitude for their whole life and never lived in lowlands.All participants were not related by blood,and their ancestors were all Tibetans.We selected 65 students from Xiamen University,all of whom were from Han ethnic group and had never been in high-altitude.The genders,age and education degree of Tibetan and Han were matched.2.Methods:MRI scans were performed with a Tim Trio 3 T scanner(Siemens,Erlangen,Germany)at the MR Imaging Center in People's Hospital of Tibet Autonomous Region,Tibet Autonomous Region,China.Siemens engineers guarantee the quality of 2 machines.High-resolution 3D T1-weighted brain volume(BRAVO)MRI sequence was acquired in each participant by using a T1-weighted magnetization-prepared rapid acquisition of gradient each sequence with the following parameters:TR = 5 ms,TE = 2.98 ms,flip angle ? 0°FOV = 240 mm ×256 mm,voxel size = 1×1×1 mm3,and 176 slices.MRI data were analyzed with atlas-based FreeSurfer software(version 5.1.0)image analysis suite(http://surfer.nmr.mgh.harvard.edu/).The cortical surface was constructed through an automated procedure,involving segmentation of the white matter,classification of the gray/white matter boundary,inflation of the folded surface,and automatic correction of topological defects(Dale et al.,1999;Fischl and Dale,2000).After the initial surface model had been constructed,measures of cortical surface area were calculated by computing the area of each triangle of a standardized tessellation.Before MRI scanning and genotyping,Tibetan participants underwent physical and physiological examinations in People's Hospital of Tibet Autonomous Region.Hematological measurements were tested using a hematology analyzer(Sysmex XE-2100,TOA Medical Electronics,Kobe,Japan).After blood sample collected,all genotyping was conducted by Beijing Genomics Institute.The whole genotyping was conducted using the MassARRAY platform(Sequenom,USA).A single SNP correlation analysis,the linkage disequilibrium(LD)analysis and haplotype analysis were employed to analyze the differences in genotype and allele in each locus between Tibetan and Han.To evaluate the difference of the degree of linkage disequilibrium between SNPs locus and their overall shape.Results1:43 SNPs were selected from EGLN1.11 of them failed to meet the needs.The rest 32 SNPs in EGLN1 had significant difference in allelic frequency between Han and Tibetan(p<0.05).2.All 32 chi-square test significance SNPs in EGLN1 were divided into three different pairwise linkage disequilibrium blocks.There were 9 haplotypes having chi-square test significance between Tibetan and Han in three pairwise linkage disequilibrium blocks,with p<0.05.The occurrence frequency of 4 haplotypes in the Tibetan are significantly higher than that of Han.3.The results showed that,regions associated with the EGLN1 gene were the left superior frontal,left parietal,right rostral middle frontal,right pericalcarine and the right lateral precuneus.Conclusion:1.Among 43 SNPs selected from EGLN1,32 SNPs were satisfied with statistical analysis,and they emerged as having chi-square test significance,with p<0.05.It indicated that the 32 SNP sites were related to high-altitude adaptation.2.In the EGLN1 gene,32 SNPs associated with high-altitude adaptation were located in three different modules.SNPs in different modules were related to different brain regions.SNPs in the same module were basically related to the same brain region.3.The regions associated with adaptive SNP in EGLN1 were important regions and visual cortex of the brain's default mode network(DMN).It shows that DMN and visual cortex may play an important role in Tibetan high-altitude adaptation.