[104], [105] and [106] In a mixed genetic background, check details HIF-2 knockout mice survived into adulthood, but developed hepatic steatosis, skeletal myopathy and cardiac hypertrophy, which

was associated with mitochondrial dysfunction and defects in reactive oxygen species (ROS) scavenging. 107 Furthermore, HIF-2 knockout mice were pancytopenic and displayed a hypocellular bone marrow. 108 Further analysis revealed that anemia in these mice did not result from a cell-autonomous defect in erythroid precursor maturation, but was due to inadequate renal EPO production, indicating that HIF-2 was indispensable for systemic EPO homoeostasis in adults. 70 In a different model, Morita and colleagues showed that local EPO production in the retina was also HIF-2-dependent, 69 suggesting a more general role for HIF-2 in the control of EPO regulation. While these mouse models demonstrated that EPO production in adults was HIF-2-dependent, developmental studies highlighted the importance of HIF-1 in

the regulation of erythropoiesis during embryonic development. HIF-1-deficient embryos were characterized by a reduction in myeloid multi-lineage cells and committed erythroid progenitors at E9.5. This was associated with decreased Epo mRNA levels in the embryo proper but not in the yolk sac, while EpoR mRNA was decreased in both tissues. 54 The most compelling support for the notion that HIF-2 is the main regulator of adult EPO synthesis comes from conditional knockout studies in mice. Utilization of a tamoxifen-inducible, ubiquitously

expressed Cre-recombinase transgene permitted a direct see more comparison of the effects of HIF-1 and HIF-2 inactivation on erythropoiesis. Acute postnatal Palbociclib ic50 global ablation of HIF-2α, but not of HIF-1α, resulted in anemia, which, similar to HIF-2α germ line inactivation, was responsive to treatment with recombinant EPO.71 While stimulation of renal EPO production in response to hemolysis (phenylhydrazine treatment) was blunted in HIF-2α-ablated mice, postnatal deletion of HIF-1α did not have any notable effect on erythropoiesis, which suggested that HIF-1 does not play a significant role in the regulation of systemic EPO homeostasis at baseline or in response to acute anemia.71 Our laboratory has generated cell type-specific knockout mice to investigate the differences between HIF-1 and HIF-2 in the regulation of renal and hepatic EPO synthesis. Inactivation of HIF-2α in the kidney completely ablated the renal EPO response in mice subjected to normobaric hypoxia (10% O2 for 10 days), phlebotomy-induced anemic hypoxia, or treatment with a HIF activating compound.24 Cell type-specific inactivation of the VHL-E3 ubiquitin ligase in hepatocytes resulted in HIF-2-, but not in HIF-1-dependent erythrocytosis, while pharmacological PHD inhibition caused a HIF-2-dependent increase in liver Epo mRNA levels.