A Knock-in Mouse Model of Human PHD2 Gene-associated Erythrocytosis Establishes a Haploinsufficiency Mechanism

Arsenault, Patrick R.; Pei, Fei; Lee, Rebecca; Kerestes, Heddy; Percy, Melanie J.; Keith, Brian; Simon, M. Celeste; Lappin, Terence; Khurana, Tejvir S.; Lee, Frank S.

doi:10.1074/jbc.m113.482364

Cited by 48 publications

(64 citation statements)

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“…Those authors then proposed a model involving the differential regulation of NICD transactivation activity depending on oxygen levels, where HIF-2␣ stabilization represses Notch signaling in mild hypoxia, whereas HIF-1␣ competes with HIF-2␣ for NICD binding in severe hypoxia, thus leading to the upregulation of Notch signaling (44). Moreover, acute global deletion of Hif-p4h-2 led to increased spleen weight and extramedullary hematopoiesis, which were restored by concurrent HIF-2␣ deletion (45). These data (44,45) are in line with our in vivo results with regard to the stabilization of splenic HIF-2␣ regulating extramedullary hematopoiesis and the concomitant downregulation of Notch signaling.…”

Section: Discussionmentioning

confidence: 99%

Notch Downregulation and Extramedullary Erythrocytosis in Hypoxia-Inducible Factor Prolyl 4-Hydroxylase 2-Deficient Mice

Myllymäki

Määttä

Dimova

et al. 2017

Molecular and Cellular Biology

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Erythrocytosis is driven mainly by erythropoietin, which is regulated by hypoxia-inducible factor (HIF). Mutations in HIF prolyl 4-hydroxylase 2 (HIF-P4H-2) (PHD2/EGLN1), the major downregulator of HIF␣ subunits, are found in familiar erythrocytosis, and large-spectrum conditional inactivation of HIF-P4H-2 in mice leads to severe erythrocytosis. Although bone marrow is the primary site for erythropoiesis, spleen remains capable of extramedullary erythropoiesis. We studied HIF-P4H-2-deficient (Hifp4h-2 gt/gt ) mice, which show slightly induced erythropoiesis upon aging despite nonincreased erythropoietin levels, and identified spleen as the site of extramedullary erythropoiesis. Splenic hematopoietic stem cells (HSCs) of these mice exhibited increased erythroid burst-forming unit (BFU-E) growth, and the mice were protected against anemia. HIF-1␣ and HIF-2␣ were stabilized in the spleens, while the Notch ligand genes Jag1, Jag2, and Dll1 and target Hes1 became downregulated upon aging HIF-2␣ dependently. Inhibition of Notch signaling in wild-type spleen HSCs phenocopied the increased BFU-E growth. HIF␣ stabilization can thus mediate non-erythropoietin-driven splenic erythropoiesis via altered Notch signaling.KEYWORDS erythrocytosis, hypoxia, hypoxia-inducible factor prolyl-4-hydroxylase 2, spleen E rythrocytosis, defined as an absolute increase in red cell mass, is associated with increased hematocrit and hemoglobin values. Erythropoietin (EPO) stimulates erythropoiesis by binding to the EPO receptor (EPOR) on hematopoietic progenitors to promote erythroid differentiation, survival, and proliferation (1, 2). Classically, erythrocytosis is classified as either primary, caused by intrinsic defects in erythroid progenitor cells in the presence of normal or low serum EPO levels, or secondary. The causes of primary erythrocytosis include mutations in the Janus kinase 2 (JAK2) and EPOR genes, which can lead to EPO-independent proliferation of erythroid precursors or hypersensitivity to EPO (3). Secondary erythrocytosis is due to defects in the oxygen-sensing pathway, including mutations in the genes for hypoxia-inducible factor (HIF) prolyl 4-hydroxylase 2 (HIF-P4H-2/PHD2/EGLN1), HIF-2␣, and von Hippel Lindau (VHL) protein, and impaired oxygen delivery or tissue hypoxia, all associated with the activation of the EPO pathway and elevated serum EPO levels (3-5).During human development, the bone marrow becomes a functional site for hematopoiesis in the fetus at 4 to 5 months, whereas in mice, bone marrow hematopoiesis becomes active after birth (6). To supply oxygen for the needs of the developing fetus, nonmarrow tissues, such as the spleen and liver, serve as sites of extramedullary

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Section: Discussionmentioning

confidence: 99%

Notch Downregulation and Extramedullary Erythrocytosis in Hypoxia-Inducible Factor Prolyl 4-Hydroxylase 2-Deficient Mice

Myllymäki

Määttä

Dimova

et al. 2017

Molecular and Cellular Biology

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“…The following considerations might mitigate against this. First, patients with heterozygous LOF PHD2 mutations do not typically present with pulmonary hypertension, nor do the mice with the heterozygous LOF knockin (P294R) mutation at the Phd2 locus (Lee and Percy 2011;Arsenault et al 2013). This might be contrasted with humans and mice with GOF mutations in the HIF2A gene, in which heterozygosity is sufficient to induce pulmonary hypertension (Gale et al 2008;Tan et al 2013).…”

Section: Tibetan Adaptation To High Altitude and Genetic Analysesmentioning

confidence: 99%

“…Fourth, PHD2 is deployed in a tissue-specific manner, and the presence of two other PHD paralogs with potentially redundant activity with PHD2 will undoubtedly modulate the impact of PHD2 LOF or GOF. For example, loss of murine Phd2 alone in the Epo-producing cells of the kidney, hematopoietic precursors, cardiomyocytes, or hepatocytes is sufficient to produce a phenotype (erythrocytosis in the first two cases, cardiomyopathy in the third case, and activation of Hif-1a in the last), indicating that the other two PHD paralogs cannot suppress Hif-a to normal levels in these tissues (Table 2; Minamishima et al 2008;Takeda et al 2008;Moslehi et al 2010;Arsenault et al 2013;Taniguchi et al 2013). On the other hand, studies also indicate that loss of Phd2 alone in the liver or in osteoblasts does not produce erythrocytosis, whereas concurrent loss of Phd1 and Phd3 does, indicating that all three Phd paralogs contribute to normal Hif-2a suppression in these tissues Rankin et al 2012;Duan et al 2014).…”

Section: Tibetan Adaptation To High Altitude and Genetic Analysesmentioning

confidence: 99%

Human high-altitude adaptation: forward genetics meets the HIF pathway

2014

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Humans have adapted to the chronic hypoxia of high altitude in several locations, and recent genome-wide studies have indicated a genetic basis. In some populations, genetic signatures have been identified in the hypoxia-inducible factor (HIF) pathway, which orchestrates the transcriptional response to hypoxia. In Tibetans, they have been found in the HIF2A (EPAS1) gene, which encodes for HIF-2α, and the prolyl hydroxylase domain protein 2 (PHD2, also known as EGLN1) gene, which encodes for one of its key regulators, PHD2. High-altitude adaptation may be due to multiple genes that act in concert with one another. Unraveling their mechanism of action can offer new therapeutic approaches toward treating common human diseases characterized by chronic hypoxia.

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“…Western Blotting-The sources of antibodies to p23, FKBP38, Flag tag, HA tag, and mouse Hif-1␣, as well as the procedure for Western blotting, have been described (19,29). Rabbit mAb D31E11 to PHD2 was obtained from Cell Signaling Technology.…”

Section: Mouse Embryonic Fibroblast (Mef) Generation-phd2mentioning

confidence: 99%

Defective Tibetan PHD2 Binding to p23 Links High Altitude Adaption to Altered Oxygen Sensing

Song

Arsenault

et al. 2014

Journal of Biological Chemistry

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A Knock-in Mouse Model of Human PHD2 Gene-associated Erythrocytosis Establishes a Haploinsufficiency Mechanism

Abstract: Background: Studies of humans have identified missense mutations in the PHD2 gene associated with erythrocytosis. Results: Mice bearing a heterozygous disease-associated Phd2 mutation display erythrocytosis equivalent in degree to that observed in Phd2 ϩ/Ϫ mice.

Cited by 48 publications

References 50 publications

Notch Downregulation and Extramedullary Erythrocytosis in Hypoxia-Inducible Factor Prolyl 4-Hydroxylase 2-Deficient Mice

Notch Downregulation and Extramedullary Erythrocytosis in Hypoxia-Inducible Factor Prolyl 4-Hydroxylase 2-Deficient Mice

Human high-altitude adaptation: forward genetics meets the HIF pathway

Defective Tibetan PHD2 Binding to p23 Links High Altitude Adaption to Altered Oxygen Sensing

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