HIF-1α is a protective factor in conditional PHD2-deficient mice suffering from severe HIF-2α–induced excessive erythropoiesis

Abstract

Erythropoiesis must be tightly balanced to guarantee adequate oxygen delivery to all tissues in the body. This process relies predominantly on the hormone erythropoietin (EPO) and its transcription factor hypoxia inducible factor (HIF). Accumulating evidence suggests that oxygen-sensitive prolyl hydroxylases (PHDs) are important regulators of this entire system. Here, we describe a novel mouse line with conditional PHD2 inactivation (cKO P2) in renal EPO producing cells, neurons, and astrocytes that displayed excessive erythrocytosis because of severe overproduction of EPO, exclusively driven by HIF-2␣. In contrast, HIF-1␣ served as a protective factor, ensuring survival of cKO P2 mice with HCT values up to 86%. Using different genetic approaches, we show that simultaneous inactivation of PHD2 and HIF-1␣ resulted in a drastic PHD3 reduction with consequent overexpression of HIF-2␣-related genes, neurodegeneration, and lethality. Taken together, our results demonstrate for the first time that conditional loss of PHD2 in mice leads to HIF-2␣-dependent erythrocytosis, whereas HIF-1␣ protects these mice, providing a platform for developing new treatments of EPO-related disorders, such as anemia. (Blood.

HIF prolyl hydroxylase 2 (PHD2) is a critical regulator of hematopoietic stem cell maintenance during steady-state and stress

“…The CD68:cre mouse line and detailed characterization of the CD68:cre-PHD2 f/f (cKO) line were shown in a recent report from our research group. 16 All mice used in this report were born in a normal Mendelian manner. Mouse strains were backcrossed to C57BL/6 at least 9 times.…”

“…To conditionally ablate PHD2 in the hematopoietic system, we combined the PHD2 floxed line with the recently described CD68: cre line to obtain cKO mice. 16 Next to a subset of epithelial cells and erythropoietin-producing cells in kidney and brain, PHD2 is also significantly reduced in the entire BM in this cKO strain. However, no significant decrease of PHD2 was seen in endothelial cells, fibroblasts, or lysates of several nonhematopoietic organs.…”

“…In the present study, we use a recently reported mouse line in which PHD2 is conditionally ablated in the entire hematopoietic system, including the HSC compartment. 16 Under physiological conditions, this leads to increased SMAD7-related proliferation of multipotent progenitors (MPP) in a HIF1a-dependent manner. Moreover, during severe stress, loss of PHD2 leads to self-renewal of HSCs and early MPPs.…”

Sirtuins and their interactions with transcription factors and poly(ADP-ribose) polymerases

“…The significance of this discrepancy has not been extensively tested, but invertebrate data suggest engagement of HIFs in the modulation of ageing rates. Moreover, HIFs' transactivation targets include genes with known neuroprotective products, although it has been suggested that these TFs might play either protective or detrimental roles [54,86,140,223].…”

IGF2: an endocrine hormone to improve islet transplant survival

“…Mechanistically, IGF2 upregulates VEGF by increasing the expression of hypoxia-inducible factor-1a (HIF1a), a master regulator of cellular and systemic homeostatic response to hypoxia. Interestingly, HIF1a itself has been shown to play a protective role in various experimental settings of apoptosis, including islet transplantation (Kim & Kim 2005, Czibik et al 2009, Franke et al 2013, Stokes et al 2013. To our knowledge, there have been no studies aiming to identify whether a synergistic role of IGF2 with HIF1a exists in the context of islet transplant survival; Cell signalling pathways activated in the pancreatic islets following pro-inflammatory cytokine exposure.…”