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ENVIRONMENTAL, EXERCISE AND RESPIRATORY PHYSIOLOGY

Diversities in hepatic HIF-1, IGF-I/IGFBP-1, LDH/ICD, and their mRNA expressions induced by CoCl₂ in Qinghai-Tibetan plateau mammals and sea level mice

¹Division of Neurobiology and Physiology, College of Life Sciences, Zhejiang University (Yuquan Campus), Hangzhou, China; and ²Northwest Plateau Institute of Biology, The Chinese Academy of Sciences, Xining, China

Submitted 7 June 2006 ; accepted in final form 12 September 2006

Ochotona curzoniae and Microtus oeconomus are the native mammals living on the Qinghai-Tibetan-Plateau of China. The molecular mechanisms of their acclimatization to the Plateau-hypoxia remain unclear. Expressions of hepatic hypoxia-inducible factor (HIF)-1, insulin-like growth factor-I (IGF-I)/IGF binding protein (BP)-1(IGFBP-1; including genes), and key metabolic enzymatic genes [lactate dehydrogenase (LDH)-A/isocitrate dehydrogenase (ICD)] are compared in Qinghai-Tibetan-Plateau mammals and sea-level mice after injection of CoCl₂ (20, 40, or 60 mg/kg) and normobaric hypoxia (16.0% O₂, 10.8% O₂, and 8.0% O₂) for 6 h, tested by histochemistry, Western blot analysis, ELISA, and RT-PCR. Major results are CoCl₂ markedly increased 1) HIF-1 only in mice, 2) hepatic and circulatory IGF-I in M. oeconomus, 3) hepatic IGFBP-1 in mice and O. curzoniae, and 4) LDH-A but reduced ICD mRNA in mice (CoCl₂ 20 mg/kg) but were unchanged in the Tibetan mammals. Normobaric hypoxia markedly 1) increased HIF-1 and LDH-A mRNA in mice and M. oeconomus (8.0% O₂) not in O. curzoniae, and 2) reduced ICD mRNA in mice and M. oeconomus (8.0% O₂) not in O. curzoniae. Results suggest that 1) HIF-1 responsiveness to hypoxia is distinct in lowland mice and plateau mammals, reflecting a diverse tolerance of the three species to hypoxia; 2) CoCl₂ induces diversities in HIF-1, IGF-I/IGFBP-1 protein or genes in mice, M. oeconomus, and O. curzoniae. In contrast, HIF-1 mediates IGFBP-1 transcription only in mice and in M. oeconomus (subjected to severe hypoxia); 3) differences in IGF-I/IGFBP-1 expressions induced by CoCl₂ reflect significant diversities in hormone regulation and cell protection from damage; and 4) activation of anaerobic glycolysis and reduction of Krebs cycle represents strategies of lowland-animals vs. the stable metabolic homeostasis of plateau-acclimatized mammals.

hypoxia-inducible factor; insulin-like growth factor; lactate dehydrogenase-A; Tibetan mammal; cobalt chloride; hypoxia