Acute postnatal ablation of Hif-2 α results in anemia

Abstract

Adaptive transcriptional responses to oxygen deprivation (hypoxia) are mediated by the hypoxia-inducible factors (HIFs), heterodimeric transcription factors composed of two basic helix-loop-helix-PAS family proteins. The transcriptional activity of HIF is determined by the hypoxic stabilization of the HIF-␣ proteins. HIF-1␣ and HIF-2␣ exhibit high sequence homology but have different mRNA expression patterns; HIF-1␣ is expressed ubiquitously whereas HIF-2␣ expression is more restricted to certain tissues, e.g., the endothelium, lung, brain, and neural crest derivatives. Germ-line deletion of either HIF subunit is embryonic lethal with unique features suggesting important roles for both HIF-␣ isoforms. Global deletion of Hif-2␣ results in distinct phenotypes depending on the mouse strain used for the mutation, clearly demonstrating an important role for HIF-2␣ in mouse development. The function of HIF-2␣ in adult life, however, remains incompletely understood. In this study, we describe the generation of a conditional murine Hif-2␣ allele and the effect of its acute postnatal ablation. Under very stringent conditions, we ablate Hif-2␣ after birth and compare the effect of acute global deletion of Hif-2␣ and Hif-1␣. Our results demonstrate that HIF-2␣ plays a critical role in adult erythropoiesis, with acute deletion leading to anemia. Furthermore, although HIF-1␣ was first purified and cloned based on its affinity for the human erythropoietin (EPO) 3 enhancer hypoxia response element (HRE) and regulates Epo expression during mouse embryogenesis, HIF-2␣ is the critical ␣ isoform regulating Epo under physiologic and stress conditions in adults.Epo ͉ hypoxia-inducible factor ͉ hypoxia ͉ red blood cell H ypoxia-inducible factors (HIFs), members of the basic helix-loop-helix (bHLH)-PAS family of transcription factors, are master regulators of oxygen (O 2 ) homeostasis and stimulate genes important for angiogenesis, erythropoiesis and glucose metabolism (1-3). HIFs are heterodimeric factors consisting of ␣ (HIF-1␣, -2␣, and -3␣) and ␤ subunits [HIF-1␤ or ARNT (arylhydrocarbon-receptor nuclear translocator)].

Targeting Astrocytes for Stroke Therapy

“…[85][86][87][88] Recent reports suggest that another HIF family member, HIF-2, is the major inducer of EPO in hypoxia. 39,89 Not only does EPO production by astrocytes have local effects, but ablation of HIF-2 function selectively in astrocytes causes anemia during hypoxia-ischemia, demonstrating the importance of astrocyte EPO production for erythropoiesis. 90 Several studies suggest a neuroprotective role for EPO (FIG.…”

Hypoxia and the HIF system in kidney disease

“…Recent analysis of HIF-2α knockdown mice revealed that EPO gene expression was significantly affected, in parallel with HIF-2α expression [12]. Conditional knockout of HIF-2α after birth demonstrated that HIF-2α plays a critical role in adult erythropoiesis [13]. In addition, studies using mice with conditional knockout of HIF-1α and/or HIF-2α in hepatocytes revealed that the hypoxic induction of liver EPO in anemic mice was also HIF-2α dependent [14].…”

Carrot and stick: HIF-α engages c-Myc in hypoxic adaptation

“…[42][43][44][45][46][47] At the molecular level, several HIF-2a preferentially regulated genes have been identified, including CCND1, EPO, POU5F1, TGFA, and VEGFA (encoding cyclin D1, erythropoietin, octamer-binding transcription factor 4, transforming growth factor a, vascular endothelial growth factor A, respectively). 46,48,49 However, how HIF-2a specifically targets these genes remains unclear, although the involvement of ETS transcription factors in HIF-2a target gene selection has been suggested.…”