Hypoxia-inducible factor–2 (HIF-2) regulates hepatic erythropoietin in vivo
Erinn B. Rankin, Mangatt P. Biju, Qingdu Liu, Travis L. Unger, Jennifer Rha, Randall S. Johnson, M. Celeste Simon, Brian Keith, Volker H. Haase
Erinn B. Rankin, Mangatt P. Biju, Qingdu Liu, Travis L. Unger, Jennifer Rha, Randall S. Johnson, M. Celeste Simon, Brian Keith, Volker H. Haase
View: Text | PDF
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

×

Figure 1

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

Options: View larger image (or click on image) Download as PowerPoint
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.