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Upregulation of COX4-2 via HIF-1α stabilization in COX4-1 deficiency

ABSTRACT: Cytochrome-c-oxidase (COX) subunit 4 (COX4) plays important roles in the function, assembly and regulation of COX (mitochondrial respiratory complex 4), the terminal electron acceptor of the oxidative phosphorylation (OXPHOS) system. The principal COX4 isoform, COX4-1, is expressed in all tissues, whereas COX4-2 is mainly expressed in the lungs, or under hypoxia and other stress conditions. We have previously described a patient with a COX4-1 defect with a relatively mild clinical presentation compared to other primary COX deficiencies, and hypothesized that this could be the result of compensatory upregulation of COX4-2. To this end, COX4-1 was downregulated using a stable expression of COX4I1-targeting shRNAs in human foreskin fibroblasts (HFF), to mirror and compare it to the primary patient's cells. COX4-1, COX4-2 and HIF-1α were detected by immunocytochemistry. The mRNA transcripts of both COX4 isoforms and HIF-1 target genes were carried out by RT-qPCR. COX activity and OXPHOS function were measured by enzymatic and oxygen consumption assays, respectively. Pathways were analyzed by CEL-Seq2 and by RT-qPCR.

ORGANISM(S): Homo sapiens

PROVIDER: GSE166429 | GEO | 2021/02/21

REPOSITORIES: GEO

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Project description:Retinopathy of prematurity (ROP) is the most common cause of childhood blindness worldwide and is caused by oxygen therapy necessary to prevent mortality after premature birth. We have previously demonstrated the efficacy of systemic hypoxia inducible factor (HIF) stabilization through HIF prolyl hydroxylase inhibition (HIF PHi) in protecting retinal vasculature from oxygen toxicity in a mouse model of ROP or oxygen induced retinopathy (OIR). We definitively demonstrated that hepatic HIF-1 can be activated to confer this protection using systemic dimethyloxalylglycine (DMOG) to prevent HIF-1α degradation. In this study we compare Roxadustat, a small molecule stabilizer of HIF-1 currently in phase 3 clinical trials for increasing erythropoiesis in adult patients with chronic kidney disease, to DMOG. We demonstrate that Roxadustat induces vascular protection during hyperoxia to induce the coordinated sequential growth of retinal vasculature with a 3-fold reduction in oxygen induced capillary loss (p-=0.001). In order to define the molecular mechanism of protection, we further compared the transcriptome of both liver and retina after systemic treatment with Roxadustat or DMOG. Similar gene expression profiles were identified in liver but very different effects on transcription were found in retinal tissues because Roxadustat, in contrast to DMOG, directly targets retina, confirmed by western blot and by rescue of the hepatic HIF-1 KO, two criteria that DMOG treatment is unable to fulfill. Systems pharmacologic analysis demonstrates that Roxadustat induces typical HIF regulated genes critical to aerobic glycolysis in liver and retinal tissues whereas DMOG, acting through either secreted hepatokines or by influence of systemic DMOG, downregulates cell adhesion/extracellular matrix interaction pathways while increasing expression of histone cluster genes. Stratification of liver transcriptomes to secreted gene products again shows close consensus of hepatic genes induced by both small molecules, and includes upregulation of a plethora of angiogenic proteins such as plasminogen activator inhibitor (PAI-1), erythropoietin (EPO), and orosomucosoid 2 (ORM2). Secondary validation of these transcripts by serum ELISA confirms secretion of EPO and PAI-1 into blood from liver. These findings definitively demonstrate that HIF stabilization can prevent OIR by two pathways: direct retinal HIF stabilization and induction of aerobic glycolysis or indirect, hepatic HIF-1 stabilization and increased serum angiokines. Systems pharmacology analysis therefore explains why intermittent, low dosage of small molecule HIF stabilizers creates a profound protective phenotype, because both pathways can take advantage of cytoprotection induced by the liver and by retina synergistically. These data provide a rationale for considering low dose, intermittent systemic administration of Roxadustat, currently in phase 3 trials in adults with chronic kidney disease, to eradicate ROP in children.

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Upregulation of COX4-2 via HIF-1α stabilization in COX4-1 deficiency

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