The Initial Research About The Relationship Between Mitochondrial Genome And High Altitude Acclimatization And Adaptation

Oxygen utilization is one of the central links of hypoxia adaptation in high altitude. Mitochondria house is the final biochemical steps in the production of reducing equivalents that react at the terminal oxidizes of the respiratory chain with molecular oxygen, and thus have been proved to be a reactive organelle in hypoxia. Morphological and functional changes of mitochondria and impairment of mitochondrial DNA (mtDNA) were also been found in acute hypoxia, which could be partially repaired as hypoxia prolonged. Indeed, ultrastructural data obtained from rat and human tissues exposed to hypobaric hypoxia revealed significant mitochondrial morphological changes, namely considerable swelling and cristae degeneration. The mitochondrial function changes are the most important mechanism for high altitude acclimatization and adaptation. Whether the mitochondrial function changes related to the mitochondrial related genes expression changes, mtDNA sequence and copy number variation need us to study.The native Tibetan had lived the longest on the Tibetan plateau, with more consummate ability of transporting and using oxygen, hence they have the better ability to adaptation hypoxia environment than other nations. There was little report about the mitochondrial mechanism of hypoxia adaptation in the high altitude native Tibetan fetuses, to our knowledge. The placentas of native Tibetan and the high-altitude Han (ha-Han) were collected, after the total RNA extraction; the finally synthesized cDNAs were hybridized to mitochondrial array to find the different expression genes between them. Then, the Cox17,DCTN2 and KDR were chosen at random from the different expression genes to further verify the array results using the SYBR Green real-time PCR.Pikas originated in Asia and are small lagomorphs native to cold climates. The plateau pika, Ochotona curzoniae is a keystone species on the Qinghai-Tibet Plateau and an ideal animal model for hypoxic adaptation studies. Altered mitochondrial function, especially cytochrome c oxidase activity, is an important factor in modulation of energy generation and expenditure during cold and hypoxia adaptation. In this study, we determined the complete nucleotide sequence of the O. curzoniae mitochondrial genome.Tibetans are considered the best adapted to the high altitude environment. Mitochondrion is one of the central links of oxygen consumption and mtDNA variation may play a role in high altitude adaptation. In addition, alleles at several polymorphic sites in mtDNA define some common haplogroups, and some of these haplogroups have been implicated in the risk of developing several diseases. The relationship between the mitochondrial haplogroup/hapotype and high altitude adaptation in Tibetan or HAPE susceptibility were studied in this study.Then the relationship between the mtDNA copy number variation and high altitude acclimatization / adaptation in the animals or human was studied in this studied.The main results of our study were listed as follow:1. By a standard of≥1.5 or≤0.67, there were 24 different expressed genes between the native Tibetan and the ha-Han placentas, including 3 up-regulated genes and 21 down-regulated genes. These genes were related to energy metabolism, signal transduction, cell proliferation, electron transport, cell adhesion, nucleotide-excision repair. The array results of Cox17, DCTN2 and KDR were further verified by the real-time RT-PCR.2. The plateau pika mitochondrial DNA is 17,131 bp long and encodes the complete set of 37 proteins typical for vertebrates. Phylogenetic analysis based on concatenated heavy-strand encoded protein-coding genes revealed that pikas are closer to rabbit and hare than to rat.3. The mitochondrial haplogroup D4 frequency was low in Tibetan (P=0.001 VS la-Han, OR=0.166, 95% CI=0.048-0.567; P=0.009 VS ha-Han OR=0.232, 95% CI=0.069-0.778). The characteristic haplotype nt3010G-nt3970C was the significantly higher in Tibetan than the La-Han (P=0.000) and Ha-Han (P=0.001).4. The frequency of haplogroup D4 was lower in the HAPE patients (P=0.033, OR=0.555, 95%CI: 0.327-0.942) than in the controls, however the haplogroup B was higher in the HAPE patients (P=0.013, OR=2.118, 95%CI: 1.194-3.756) than in the controls. The allele nt13497G was significantly higher in the HAPEs (P=0.012) than in the controls among haplogroup R9. The haplotype nt3970C-nt13497G was the higher in the HAPE patients (P=0.000) as compared with the controls also.5. The mtDNA copy numbers in the control SD rats were lower than plateau pika (P<0.005) and SD rat (4500 m, 30 d) (P<0.005).6. The mtDNA copy numbers in the la-Han were lower than ha-Hans (P<0.05). Moreover, the mtDNA copy numbers in the HAPE patients were lower than that of la-Hans (P<0.005), ha-Han (P<0.005) and native Tibetan (P<0.005).The conclusion as suggested in our study was followed:1. The altered mitochondrial related genes in the native Tibetan placentas may have a role in the high altitude adaptation through changing the activity of COX.2. The rabbit or hare would be a good control animal for pikas in cold and hypoxia adaptation studies. Fifteen novel mitochondrial DNA-encoded amino acid changes were identified in the pikas, including three in the subunits of cytochrome c oxidase.3. The mtDNA nucleotides sites (2706, 7028, 8860, 11719, 15326) were totally different from rCRS, 48 SNPs were with the frequency over 5% from the 26 whole mtDNA sequences analysis. These findings provided new insights into the characteristics of Han Chinese mitochondrial genetic diversity.4. The mitochondrial haplogroup D4 is negative associated with high altitude adaptation in Tibetan; however haplotype nt3010G-nt3970C was the significantly good to high altitude adaptation in Tibetan. Our findings suggest that Tibetans process unique mitochondrial variations which may be genetic background associated with high altitude adaptation.5. The haplogroup D4 was the protection factor to HAPE susceptibility, however haplogroup B, allele nt13497G and haplotype nt3970C-nt13497G were the risk factors to HAPE susceptibility, which could contribute to defining the role of the mitochondrial genome in HAPE pathogenesis. 6. The mtDNA copy number increased during the hypoxia acclimatization, but it decreased in the samples that had hypoxia adaptation. In the HAPE patients, the mtDNA copy number was low, which could contribute to define the role of the mitochondrial genome in HAPE pathogenesis.