Effect Of Myoglobin In Cardiac And Skeletal Muscle Adaptation To Hypoxia In Tibetan Antelope (Pantholops Hodgsonni)

Tibetan antelope (Pantholops hodgsonni) belongs to the Bovidae family ofArtiodactyla order and Pantholops genus. It mainly distributed in Qinghai-Tibetanplateau and Xinjiang Autonomous region in China, as well as in India at elevationfrom3250-5500meters, espically in4500-5500meters unmanned area is morecommon,such as alpine meadow, alpine steppe and alpine desert, with strong abilityof high cold resistance and anti anoxia,it is the best animal model to study themechanism of high altitude hypoxia.Myoglobin is a cytoplasmic hemoglobin whichmainly expressed in cardiac myocytes and oxidative skeletal muscle, it’s mainfunction is reversibly binds O2and facilitate O2transport from cytoplasm tomitochondria to restore and transport oxygen. Research studies have shown that underthe same partial pressure of oxygen, its oxygen affinity is6-fold than that ofhemoglobin. Therefore, as one of carrier of oxygen proteins, it plays an important rolein utilizing oxygen on organism. As a native mammal that has been living for manythousands of generation at high altitude and successfully adapted to chronic hypoxia.Tibetan antelope can continuous run70-100km at speed up to60km per hour, itindicate that the myoglobin play special role of oxygen transfer. In order to reveal theeffect and mechanism of myoglobin in cardiac and skeletal muscle adaptation tohypoxia in Tibetan antelope, the full-length cDNA sequence of the myoglobin genewas cloned and analyzed by RACE method.Compared differential expression ofmyoglobin from mRNA and protein levels in cardiac and skeletal muscles amongTibetan antelope, Tibetan sheep and low altitude sheep. the content of myoglobin andlactic acid (LD), the activity of lactate dehydrogenase (LDH) and malatedehydrogenase (MDH) in cardiac and skeletal muscles among three animals weredetected and analyzed by spectrophotometer, and LDH isozyme spectrum amongthree kinds of animal were further analyzed.Our results showed the full length cDNA sequence of the myoglobin was1154bpand comprised a465bp ORF, a111bp5’UTR and a578bp3’UTR. And the ORF inTibetan antelope encodes154amino acids. The sequence has been submitted toGenBank with the accession number JN561790. Sequence analysis showed that the coding region of the myoglobin gene of Tibetan antelope shared more than98%similarity with that of O. aries and B. Taurus, with other mammals (including Bosgrunniens, S. scrofa, H. sapiens, Ochotona curzoniae, M. musculu, R. norvegicus andGallus gallus) was about97%-71%. The amino acid sequence of myoglobin ofTibetan antelope was98%similarity with that of O. aries, B. Taurus and Bosgrunniens, and with other other mammals was about89%-72%. It indicated that themyoglobin gene of Tibetan antelope was highly conservative.The predicted secondarystructure included eight α helices, and comparing the sequence of Tibetan antelopemyoglobin with the sheep sequence, variations were observed at codons21(GGTâ†'GAT) and78(GAAâ†'AAG), which cause changes in the corresponding aminoacids,the changes are Glyâ†'Asp and Gluâ†'Lys, respectively. However, these twoamino acid substitutions are unlikely to cause structural changes because they arelocated far from the heme binding pocket, as revealed by the3D structure of Tibetanantelope myoglobin elaborated by homology modeling. Real-time PCR and westernblot results showed that the expression of myoglobin in Tibetan antelope cardiac andskeletal muscles was significantly higher than expression in plain sheep. And thecontent of myoglobin in skeletal muscle of Tibetan antelope significantly higher thanthat of Tibetan sheep and low altitude sheep. These results indicated that the increasedexpression of myoglobin in cardiac and skeletal muscles could improve the ability ofTibetan antelope to obtain and store more oxygen under hypoxic conditions. As aresult, the cardiac and skeletal muscles could supply enough oxygen for Tibetanantelope living in a hypoxic environment. The determination results of indexes ofenergy metabolism was found the content of LD and the activity of LDH in cardiacand skeletal muscle of Tibetan antelope were significantly lower than that of tibetansheep and low altitude sheep, activity of MDH and the ratio of MDH/LDH weresignificantly higher than that of tibetan sheep and low altitude sheep, it may be thehigh content of Mb in cardiac and skeletal muscle of Tibetan antelope, an adequatesupply of oxygen to muscle cells inhibit the synthesis of LDH. And muscle cellsmainly through aerobic metabolism for energy to meet the demand for oxygen. Itprovides useful information for our understanding and further study of the importantrole of myoglobin in the Tibetan antelope’s adaptation to high altitude hypoxia.