Prolyl-4-hydroxylase 2 and 3 coregulate murine erythropoietin in brain pericytes

Abstract

A classic response to systemic hypoxia is the increased production of red blood cells due to hypoxia-inducible factor (HIF)-mediated induction of erythropoietin (EPO). EPO is a glycoprotein hormone that is essential for normal erythropoiesis and is predominantly synthesized by peritubular renal interstitial fibroblast-like cells, which express cellular markers characteristic of neuronal cells and pericytes. To investigate whether the ability to synthesize EPO is a general functional feature of pericytes, we used conditional gene targeting to examine the von Hippel-Lindau/prolyl-4-hydroxylase domain (PHD)/HIF axis in cell-expressing neural glial antigen 2, a known molecular marker of pericytes in multiple organs. We found that pericytes in the brain synthesized EPO in mice with genetic HIF activation and were capable of responding to systemic hypoxia with the induction of Epo. Using high-resolution multiplex in situ hybridization, we determined that brain pericytes represent an important cellular source of Epo in the hypoxic brain (up to 70% of all Epo-expressing cells). We furthermore determined that Epo transcription in brain pericytes was HIF-2 dependent and cocontrolled by PHD2 and PHD3, oxygen- and 2-oxoglutarate-dependent prolyl-4-hydroxylases that regulate HIF activity. In summary, our studies provide experimental evidence that pericytes in the brain have the ability to function as oxygen sensors and respond to hypoxia with EPO synthesis. Our findings furthermore suggest that the ability to synthesize EPO may represent a functional feature of pericytes in the brain and kidney.

Loss of PHD3 in myeloid cells dampens the inflammatory response and fibrosis after hind-limb ischemia

“…A compensatory mechanism by PHD3, which limits the HIF response as a consequence of a PHD2 knockout has been described in several cell and animal models. 21 , 28 , 29 , 30 This might explain why some phenotypes induced by a PHD2 knockout are more severe in combination with knocking out PHD3. A singular knockout of PHD3 alone, however, seems to reveal the PHD3 isoform-specific functions and might explain, why the phenotype observed in the PHD3 −/− compared to the WT mice are seen just in the ischemic legs in situ or under simulated ischemic conditions in vitro .…”

HIF‐prolyl hydroxylases as therapeutic targets in erythropoiesis and iron metabolism

“…Our laboratory has recently shown that renal EPC are derived from forkhead box D1‐expressing stroma, which surrounds the cap mesenchyme during kidney development and gives rise to essentially all nonendothelial renal interstitial cells including pericytes and perivascular fibroblasts, mesangial cells, and vascular smooth muscle cells. Interestingly, the ability to produce EPO is shared between brain and renal pericytes, which are both of neural crest origin . PHD2 is the main prolyl hydroxylase that controls HIF activity under normoxic conditions.…”

“…Interestingly, the ability to produce EPO is shared between brain and renal pericytes, which are both of neural crest origin. 38,40 PHD2 is the main prolyl hydroxylase that controls HIF activity under normoxic conditions. Its genetic inactivation in renal interstitial cells results in HIF-2 activation and EPO production in 40% of cortical and outer medullary renal interstitial cells leading to severe polycythemia.…”

Hypoxia-Inducible Factor Prolyl 4-Hydroxylases and Metabolism

“…HIF-P4H-2 (PHD2/EglN1) is the most abundant isoenzyme and the major one regulating HIFstability. In kidney, inactivation of HIF-P4H-2 was sufficient to induce EPO expression while in brain pericytes and hepatocytes it required simultaneous inactivation of HIF-P4Hs 2 and 3 or all HIF-P4Hs, respectively [57,108]. FIH (magenta), which shares the same reaction mechanism and cofactors with HIF-P4Hs but is less dependent on oxygen, hydroxylates an asparagine residue in HIF1/2α.…”