Tibetans have adapted to the chronic hypoxia of high altitude and display a distinctive suite of physiologic adaptations, including augmented hypoxic ventilatory response and resistance to pulmonary hypertension. Genome-wide studies have consistently identified compelling genetic signatures of natural selection in two genes of the Hypoxia Inducible Factor pathway, PHD2 and HIF2A. The product of the former induces the degradation of the product of the latter. Key issues regarding Tibetan PHD2 are whether it is a gain-of-function or loss-of-function allele, and how it might contribute to high-altitude adaptation. Tibetan PHD2 possesses two amino acid changes, D4E and C127S. We previously showed that in vitro, Tibetan PHD2 is defective in its interaction with p23, a cochaperone of the HSP90 pathway, and we proposed that Tibetan PHD2 is a loss-of-function allele. Here, we report that additional PHD2 mutations at or near Asp-4 or Cys-127 impair interaction with p23 in vitro. We find that mice with the Tibetan Phd2 allele display augmented hypoxic ventilatory response, supporting this loss-of-function proposal. This is phenocopied by mice with a mutation in p23 that abrogates the PHD2:p23 interaction. Hif2a haploinsufficiency, but not the Tibetan Phd2 allele, ameliorates hypoxia-induced increases in right ventricular systolic pressure. The Tibetan Phd2 allele is not associated with hemoglobin levels in mice. We propose that Tibetans possess genetic alterations that both activate and inhibit selective outputs of the HIF pathway to facilitate successful adaptation to the chronic hypoxia of high altitude.
|Number of pages
|Proceedings of the National Academy of Sciences of the United States of America
|Early online date
|15 May 2020
|Published (in print/issue) - 2 Jun 2020
Bibliographical noteFunding Information:
We thank Dr. Tobias Raabe of the University of Pennsylvania Perelman School of Medicine Gene Targeting facility for performing the ES cell electroporation. We thank Dr. Jean Richa of the University of Pennsylvania Perelman School of Medicine Transgenic and Chimeric Mouse Facility for injecting targeted ES cells into blastocysts to generate the Phd2 Tib mice and for injecting Crispr reagents into oocytes to generate the p23 AA and Fkbp38 AA mice. This facility is supported by the Institute for Diabetes, Obesity, and Metabolism; the Center for Molecular Studies in Digestive and Liver Diseases; and the Abramson Cancer Center. We thank Dr. Jorge Henao-Mejia for advice on preparation of Crispr reagents for injection into oocytes. We thank Dr. Celeste Simon and Dr. Brian Keith for providing the Hif2a +/- mice, for helpful discussions, and for valuable feedback on the manuscript. We thank Dr. Xingxu Huang and Dr. Akitsu Hotta for gifts of pUC57-sgRNA and pHL-EF1a-SphcCas9-iP-A, respectively. We thank Dr. David Roth and Dr. Mark Tykocinski for their support. We thank the Penn Center for Molecular Studies in Digestive and Liver Diseases for providing the Hepa 1-6 cells. This work was supported by NIH grants R33-HL120751 (F.S.L.) and R01-DK104796 (F.S.L.). W.G. was supported by the Scientific Research Training Program for Young Talents (Union Hospital, Tongji Medical College, Huazhong University of Science and Technology).
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- High-altitude adaptation