Protective Effects of Hif2 Inhibitor PT-2385 on a Neurological Disorder Induced by Deficiency of Irp2

Abstract

Iron regulatory protein 2 (IRP2) deficiency in mice and humans causes microcytic anemia and neurodegeneration due to functional cellular iron depletion. Our previous in vitro data have demonstrated that Irp2 depletion upregulates hypoxia-inducible factor subunits Hif1α and Hif2α expression; inhibition of Hif2α rescues Irp2 ablation-induced mitochondrial dysfunction; and inhibition of Hif1α suppresses the overdose production of lactic acid derived from actively aerobic glycolysis. We wonder whether Hif1α and Hif2α are also elevated in vivo and play a similar role in neurological disorder of Irp2–/– mice. In this study, we confirmed the upregulation of Hif2α, not Hif1α, in tissues, particularly in the central nervous system including the mainly affected cerebellum and spinal cord of Irp2–/– mice. Consistent with this observation, inhibition of Hif2α by PT-2385, not Hif1α by PX-478, prevented neurodegenerative symptoms, which were proved by Purkinje cell arrangement from the shrunken and irregular to the full and regular array. PT-2385 treatment did not only modulate mitochondrial morphology and quality in vivo but also suppressed glycolysis. Consequently, the shift of energy metabolism from glycolysis to oxidative phosphorylation (OXPHOS) was reversed. Our results indicate that Irp2 depletion-induced Hif2α is, in vivo, in charge of the switch between OXPHOS and glycolysis, suggesting that, for the first time to our knowledge, Hif2α is a clinically potential target in the treatment of IRP2 deficiency-induced neurodegenerative syndrome.

Stimulation of Hepatic Ferritinophagy Mitigates Irp2 Depletion-Induced Anemia

“…The results showed that Fe-S cluster synthesis-related proteins Fxn and Iscu and mitochondrial complex I- and II-related subunits Ndufs1 and Sdhb more or less decreased, but significantly, in Irp2 KO mice, except complex III subunit Uqcrfs1. However, the changed proteins recovered after PT–2385 administration ( Figure 2 C, quantified in Figure 2 D), further in favor of the notion that Irp2 KO-induced upregulation of Hif2 negatively modulates the mitochondrial OXPHOS [ 18 , 19 ].…”

“…It is known that Hif2 mediates the transcriptional activation of erythropoietin ( EPO ), a gene encoding a master hormone regulator of erythropoiesis, by binding 5’ hypoxia-responsive element (HRE), thereby contributing to the changes in tissue oxygen concentration for adaptive adjustment [ 23 ]. Our previous study [ 19 ] and others [ 11 ] have found that deletion of Irp2 in mice increases Hif2α, leading to increased EPO, but this increase may be ineffective due to limited iron content in hematopoietic tissues. We wonder whether the improvement in anemia results from the increased iron availability when Hif2 is inhibited by PT–2385.…”

“…Irp2 homozygous global knockout ( Irp2 KO) mice and WT mice in the C57BL/6J background were generated in our previous study [ 19 ]. Briefly, the Irp2 KO and WT mice used in the experiment were the descendants of Irp2 heterozygous knockout mice purchased from MMRRC at UC Davis (cat.…”

“…The iron content of tissues was detected by ferrozine assays, as previously described [ 19 ]. Briefly, 11 μL of concentrated HCl (11.6 M) was added to 50 μL of tissue sample lysate or serum (250 μg total protein).…”

“…Hif2, but not Hif1, suppresses mitochondrial Fe-S biosynthesis and OXPHOS in Irp2 -deficient cells [ 18 ]. These results have been confirmed in Irp2 knockout mice, showing that an increase in Hif2α switches energy metabolism from OXPHOS to glycolysis, and the inhibition of Hif2 by PT–2385, a selective Hif2 inhibitor, may alleviate the neurological disorder by improving mitochondrial function [ 19 ], which is accomplished by an increase of Fe-S biogenesis [ 18 , 19 ].…”