Abstract：Heme oxygenase 2 (HMOX2) is a constitutive subfamily member of heme oxygenase family, and HMOX2 plays an important role in the metabolic regulation of hypoxia stress. This study was to investigate the role of HMOX2 in the adaptation mechanism to high altitude hypoxia, the HMOX2 gene CDS of Tibetan sheep (Ovis aries) was cloned, reverse transcription PCR (RT-PCR), bioinformatics analysis and the comparative analysis of the blood-gas between Tibetan sheep and Hu sheep (control) was carried out. Quantitative real-time PCR (qRT-PCR) was used to analyze the expression differences of HMOX2 gene in different tissues of Tibetan sheep and Hu sheep. The results showed that the CDS region of Tibetan sheep HMOX2 gene (GenBank No. MH358397) was 1 005 bp in length and encoded 344 amino acids, forming a transmembrane hydrophilic non-secreted protein. The results showed that there were 3 mutations in HMOX2 gene, which were G485C, T486G and A500T, respectively, but there were two mutations in G485C and T486G compared with Hu sheep, which did cause 162th cysteine acid into serine, and A500T mutation caused 167th glutamine acid into leucine. The deduced amino acid sequence of Tibetan sheep HMOX2 shared 99%, 99%,99% ,97%, 97%, 84% and 80% identities with those of Ovis aries, Capra hircu, Pantholops, Bos indicus, Bos taurus, Sus scrofa, Homo sapiens. The results of blood-gas analysis showed that the P(O2), P(CO2), HCO3- and SpO2 of Tibetan sheep were significantly lower than Hu sheep (P＜0.01); HGB and HCT of Tibetan sheep were significantly higher than those of Hu sheep (P＜0.01); qRT-PCR results showed that HMOX2 mRNA were expressed in the different organizations, the expression of gene was detected in Tibetan sheep and Hu sheep. The expressions in the lung and heart were significant different (P＜0.01), and the expression in liver, skeletal muscle and fat of Tibetan sheep were significantly higher than the Hu sheep (P＜0.05). The correlation between HMOX2 gene expression and hemoglobin content in Tibetan sheep and Hu sheep showed that there was a significant positive correlation between HMOX2 gene expression and hemoglobin with a correlation coefficient of 0.535 (P＜0.05). There was a significant negative correlation between gene expression and hemoglobin, with a correlation coefficient of -0.097 (P＞0.05). Thus, hypoxia-specific expression of HMOX2 gene can regulate the metabolism of hemoglobin downstream of the hypoxia metabolism pathway, thereby weakening the damage of cells caused by hypoxia stress. This study results provide basic data for the molecular mechanism of Tibetan sheep's adaptation to hypoxia.
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