Correlation Study Between MtDNA Polymorphisms And Susceptibility To High Altitude Essential Hypertension In Chinese Tajik Population

Mitochondrion is the main place of the energy and metabolism in the cells.The mitochondrial respiratory electron transfer chain plays an important role in the energy and metabolism of the mitochondrion.Meanwhile,the mitochondrial electron transfer disorder will affect the oxidative phosphorylation process and energy metabolism of the mitochondrial respiration,which would result in a series of diseases related by mitochondrion.Mitochondrial DNA(mtDNA)was the main genetic materials of the maternal inheritance,and it regulated structural and function of the mitochondrion together with nuclear gene.MtDNA polymorphisms include single nucleotide polymorphism(SNP),mtDNA haplotype,mtDNA haplogroup,copy number variant(CNV)and so on.At present,the association of mitochondrial DNA polymorphism with high altitude adaptation and various high altitude diseases has been found.The high altitude environment is featured by low temperature and hypoxia,people permanently lived in high altitude often have a good adaptation to the high altitude environment,while the people who have a poor adaptation to high altitude will be prone to have high altitude diseases.Mitochondrion,as the main structure of cell energy metabolism and hypoxia adaptation,has a great influence on high altitude adaptation and high altitude disease due to its changes in structure and function.The Chinese Tajik population is mainly distributed in Tashkurgan County,Kashi region of Xinjiang,east of the Pamir Plateau.They have lived in high altitude for thousands of years,and the total number of population is only more than fifty thousands.A survey on the prevalence of hypertension in Chinese Tajik population over 50 years of age showed that the prevalence rate of hypertension was 39.2%,which caused serious harm to the health of Tajik population.Through whole genome resequencing,the genetic characteristics of Chinese Tajik population and the genetic adaptation to high altitude can be more deeply understood.Thus,providing corresponding guidance and help for the prevention and treatment of high altitude disease are significant to Chinese Tajik population.There have been many reports of essential hypertension and mtDNA polymorphisms,some studies in recent years have found that the mtDNA mutations are associated with the essential hypertension,e.g.,mt15927G→A and mt7492C→T are pathogenic mt-tRNA mutations in hypertension,the combination of the mt16189T→C mutation and a 9-BP(CCCCCTCTA)deletion,mtDNA haplotype combination of mt4401 G and mt5821 A are both associated with essential hypertension in a family study.There is an association between mt-tRNAIle mutation 4263A→G and the maternally inherited hypertension,but there have been no studies in the correlation study of mtDNA polymorphisms and susceptibility to high altitude essential hypertension(HAEH).The high altitude hypoxia environment has a great influence on the structure and function of mitochondrion.The study on the relationship between mtDNA polymorphisms and HAEH can reveal its genetic susceptibility factors and find out its related molecular mechanism.In this paper,the genetic susceptibility factors of HAEH in Chinese Tajik population were analyzed,and the genetic and molecular mechanisms inside were discussed.Research methodsSection One1.Collected whole blood samples,53 cases of HAEH and 46 cases of normal blood pressure from Chinese Tajik population,lived in Tashkurgan county of Kashgar region of Xinjiang,China,and the relevant clinical basic information was also collected.The samples were transported to Army military Medical University by anticoagulant cryopreservation.The whole blood DNA was extracted for the related genetic study.2.Selected a healthy adult male,named as T153.The high throughput second generation sequencing technique was used to analyze the variation of nuclear genome data in whole blood DNA samples,then screened out the single nucleotide variant(SNV),CNV associated with high altitude adaptation.Section Two1.Designed the primers of amplification and sequencing,then amplified and sequenced the mitochondrial genome of whole DNA samples.2.Analyzed the mtDNA sequencing data of the 53 cases of HAEH group and 46 cases of control group,then found out the mtDNA haplogroup and SNPs with statistical difference and the genetic susceptibility related to HAEH.Section ThreeIn order to find out the molecular basis of M316 T mutation in mitochondrial cytochrome B(MTCYB)and susceptibility to HAEH,bioinformatics software was used to analyze and predict the structure of MTCYB protein at all levels.Experimental resultsSection OneThe results of whole genome resequencing of T153 found out some SNV and CNV related to high altitude adaptation.The SNVs related with high altitude adaptation of T153 were different with the Tibetans,Ethiopians and Andes population,and there may be other high altitude genetic adaptations exist.The CNVs of gene DAZ are all decreased in T153,indicating that there may be an important factor in the lower hormone level of the Chinese Tajik male population.Section TwoMtDNA subhaplogroup U4 b was found to be a susceptible factor for HAEH in Chinese Tajik population,and the mtDNA mutation of 15693T→C was found to be a risk factor for HAEH,which resulted in a missense mutation of the 316 th amino acid in MTCYB changed from methionine(Met)to threonine(Thr),then may affect the structure and function of mitochondrion,this may be the main molecular mechanism inside.Section ThreeThe M316 T mutation of MTCYB resulted in a new protein kinase C phosphorylation site,which increased the Vmax value and Km value of the corresponding phosphorylation reaction,then changed the structure and function of MTCYB protein caused by the M316 T mutation,and they may be an important factor in the dysfunction of the mitochondrial respiratory electron transfer chain,indicating that there may be the molecular mechanism of MTCYB(M316T)prone to HAEH in Chinese Tajik population.Conclusions1.The genetic adaptation mechanism of T153 was not related to the population of Tibetans,Ethiopians or Andes.The changed of the copy number of the DAZ gene may be a factor in the lower hormone level of the Chinese Tajik male population.2.MtDNA subhaplogroup U4 b was a genetic susceptibility factor for HAEH in Chinese Tajik population.3.The mtDNA mutation of 15693T→C resulted in a missense mutation of methionine(Met)/ threonine(Thr)in the 316 th amino acids of MTCYB,which resulted in a new Protein kinase C(PKC)phosphorylation binding site of MTCYB protein,which affected the structure and function of mitochondrial COX Ⅲ and led to abnormal energy and metabolism of mitochondrion.We speculate that it may be a molecular mechanism of genetic susceptibility to HAEH.