Hypoxia-inducible factor–2 (HIF-2) regulates hepatic erythropoietin in vivo
Erinn B. Rankin, … , Brian Keith, Volker H. Haase
Erinn B. Rankin, … , Brian Keith, Volker H. Haase
Published April 2, 2007
Citation Information: J Clin Invest. 2007;117(4):1068-1077. https://doi.org/10.1172/JCI30117.
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Research Article

Hypoxia-inducible factor–2 (HIF-2) regulates hepatic erythropoietin in vivo

Abstract

Erythropoiesis is critically dependent on erythropoietin (EPO), a glycoprotein hormone that is regulated by hypoxia-inducible factor (HIF). Hepatocytes are the primary source of extrarenal EPO in the adult and express HIF-1 and HIF-2, whose roles in the hypoxic induction of EPO remain controversial. In order to define the role of HIF-1 and HIF-2 in the regulation of hepatic EPO expression, we have generated mice with conditional inactivation of Hif-1α and/or Hif-2α (Epas1) in hepatocytes. We have previously shown that inactivation of the von Hippel–Lindau tumor suppressor pVHL, which targets both HIFs for proteasomal degradation, results in increased hepatic Epo production and polycythemia independent of Hif-1α. Here we show that conditional inactivation of Hif-2α in pVHL-deficient mice suppressed hepatic Epo and the development of polycythemia. Furthermore, we found that physiological Epo expression in infant livers required Hif-2α but not Hif-1α and that the hypoxic induction of liver Epo in anemic adults was Hif-2α dependent. Since other Hif target genes such phosphoglycerate kinase 1 (Pgk) were Hif-1α dependent, we provide genetic evidence that HIF-1 and HIF-2 have distinct roles in the regulation of hypoxia-inducible genes and that EPO is preferentially regulated by HIF-2 in the liver.

Authors

Erinn B. Rankin, Mangatt P. Biju, Qingdu Liu, Travis L. Unger, Jennifer Rha, Randall S. Johnson, M. Celeste Simon, Brian Keith, Volker H. Haase

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Figure 1

Generation of mice deficient for Vhlh, Vhlh/Hif-1α, Vhlh/Hif-2α, and Vhlh/ Hif-1α/Hif-2α in the liver.

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Generation of mice deficient for Vhlh, Vhlh/Hif-1α, Vhlh/Hif-2α, and Vhl...
(A) Genomic maps of the Vhlh (2-lox), Hif-1α (2-lox), and Hif-2α (2-lox) conditional alleles. Numbered boxes represent exons targeted for deletion. The locations of LoxP sites and primers used to amplify the conditional allele (2-lox), recombined allele (1-lox), and WT allele are shown with gray triangles and arrows, respectively. N, NcoI; E, EcoR1; P, PstI. (B) Genomic PCR analysis of DNA isolated from the tail (T) and liver (L) of PEPCK-Cre mutant mice. (C) Genomic PCR analysis of DNA isolated from the tail and liver of 4-week-old albumin-Cre mutant mice. Note that mice were bred in a mixed genetic background. Occasionally 2 different Hif-2α WT alleles were detected by genomic PCR analysis, suggesting a polymorphism in the amplified region. (D) Western blot analysis of nuclear protein isolated from livers of the following albumin-Cre mutant littermates: lane 1, -Vhlh haploinsufficient for Hif-1α; lane 2, -Vhlh/Hif-1α haploinsufficient for Hif-2α; lane 3, -Vhlh/Hif-2α; lane 4, -Vhlh/Hif-1α/Hif-2α; lane 5, -Vhlh/Arnt; and lane 6, Cre-negative mice. Note that the recombination efficiency of the Hif-1α conditional allele is best determined by comparing Cre-negative control mice to Vhlh/Hif-1α/Hif-2α mutant mice due to the presence of nonrecombined inflammatory cells in albumin-Vhlh/Hif-1α mutant mice.