Molecular Characterization and Response of Prolyl Hydroxylase Domain (PHD) Genes to Hypoxia Stress in Hypophthalmichthys molitrix

As an economically and ecologically important freshwater fish, silver carp (Hypophthalmichthys molitrix) is sensitive to low oxygen tension. Prolyl hydroxylase domain (PHD) proteins are critical regulators of adaptive responses to hypoxia for their function of regulating the hypoxia inducible factor-1 alpha subunit (HIF-1α) stability via hydroxylation reaction. In the present study, three PHD genes were cloned from H. molitrix by rapid amplification of cDNA ends (RACE). The total length of HmPHD1, HmPHD2, and HmPHD3 were 2981, 1954, and 1847 base pair (bp), and contained 1449, 1080, and 738 bp open reading frames (ORFs) that encoded 482, 359, and 245 amino acids (aa), respectively. Amino acid sequence analysis showed that HmPHD1, HmPHD2, and HmPHD3 had the conserved prolyl 4-hydroxylase alpha subunit homolog domains at their C-termini. Meanwhile, the evaluation of phylogeny revealed PHD2 and PHD3 of H. molitrix were more closely related as they belonged to sister clades, whereas the clade of PHD1 was relatively distant from these two. The transcripts of PHD genes are ubiquitously distributed in H. molitrix tissues, with the highest expressional level of HmPHD1 and HmPHD3 in liver, and HmPHD2 in muscle. After acute hypoxic treatment for 0.5 h, PHD genes of H. molitrix were induced mainly in liver and brain, and different from HmPHD1 and HmPHD2, the expression of HmPHD3 showed no overt tissue specificity. Furthermore, under continued hypoxic condition, PHD genes exhibited an obviously rapid but gradually attenuated response from 3 h to 24 h, and upon reoxygenation, the transcriptional expression of PHD genes showed a decreasing trend in most of the tissues. These results indicate that the PHD genes of H. molitrix are involved in the early response to hypoxic stress, and they show tissue-specific transcript expression when performing physiological regulation functions. This study is of great relevance for advancing our understanding of how PHD genes are regulated when addressing the hypoxic challenge and provides a reference for the subsequent research of the molecular mechanisms underlying hypoxia adaptation in silver carp.

Impact of Hypoxia-Inducible Factor Prolyl Hydroxylase Inhibitor on Renal Function in Patient with Heart Failure

Hypoxia-inducible factor prolyl hydroxylase (HIF-PH) inhibitor is a recently introduced oral agent to treat renal anemia, but its clinical implications on renal functioning in patients with heart failure remains unknown. We studied an 81-year-old man with heart failure with mildly reduced ejection fraction, chronic kidney disease, and renal anemia. The seven-month HIF-PH inhibitor daprodustat treatment improved the hemoglobin level from 7.4 g/dL to 11.8 g/dL and estimated glomerular filtration ratio from 24 mL/min/1.73 m2 to 35 mL/min/1.73 m2 without any complications, including thromboembolic events. HIF-PH inhibitor might be a promising therapeutic tool to improve renal anemia and renal function in patients with heart failure, although large-scale studies are warranted to validate our findings.

Impact of Hypoxia-Inducible Factor Prolyl Hydroxylase Inhibitor on Heart Failure with Preserved Ejection Fraction

Hypoxia-inducible factor prolyl hydroxylase (HIF-PH) inhibitor is a recently introduced oral medication to treat renal anemia, but its clinical implication in patients with heart failure, particularly heart failure with preserved ejection fraction (HFpEF), remains unknown. We had a 91-year-old woman with HFpEF who was admitted to our institute to treat her worsening heart failure. She initiated HIF-PH inhibitor daprodustat to treat her renal anemia (hemoglobin 8.8 g/dL and estimated glomerular filtration ratio 15.6 mL/min/1.73 m2). Following a 6-month treatment with daprodustat, hemoglobin increased up to 10.4 g/dL, left ventricular mass index decreased from 107 g/m2 to 88 g/m2, and plasma B-type natriuretic peptide decreased from 276 pg/mL to 122 pg/mL, despite doses of other medications remaining unchanged. HIF-PH inhibitors might be a promising tool to ameliorate renal anemia and facilitate cardiac reverse remodeling in patients with HFpEF.

Oxygen-sensing mechanisms in development and tissue repair

ABSTRACT Under normoxia, hypoxia inducible factor (HIF) α subunits are hydroxylated by PHDs (prolyl hydroxylase domain proteins) and subsequently undergo polyubiquitylation and degradation. Normal embryogenesis occurs under hypoxia, which suppresses PHD activities and allows HIFα to stabilize and regulate development. In this Primer, we explain molecular mechanisms of the oxygen-sensing pathway, summarize HIF-regulated downstream events, discuss loss-of-function phenotypes primarily in mouse development, and highlight clinical relevance to angiogenesis and tissue repair.

Hypoxia-Inducible Factor Stabilizers in End Stage Kidney Disease: “Can the Promise Be Kept?”

Anemia is a common complication of chronic kidney disease (CKD). The prevalence of anemia in CKD strongly increases as the estimated Glomerular Filtration Rate (eGFR) decreases. The pathophysiology of anemia in CKD is complex. The main causes are erythropoietin (EPO) deficiency and functional iron deficiency (FID). The administration of injectable preparations of recombinant erythropoiesis-stimulating agents (ESAs), especially epoetin and darbepoetin, coupled with oral or intravenous(iv) iron supplementation, is the current treatment for anemia in CKD for both dialysis and non-dialysis patients. This approach reduces patients’ dependence on transfusion, ensuring the achievement of optimal hemoglobin target levels. However, there is still no evidence that treating anemia with ESAs can significantly reduce the risk of cardiovascular events. Meanwhile, iv iron supplementation causes an increased risk of allergic reactions, gastrointestinal side effects, infection, and cardiovascular events. Currently, there are no studies defining the best strategy for using ESAs to minimize possible risks. One class of agents under evaluation, known as prolyl hydroxylase inhibitors (PHIs), acts to stabilize hypoxia-inducible factor (HIF) by inhibiting prolyl hydroxylase (PH) enzymes. Several randomized controlled trials showed that HIF-PHIs are almost comparable to ESAs. In the era of personalized medicine, it is possible to envisage and investigate specific contexts of the application of HIF stabilizers based on the individual risk profile and mechanism of action.

Repurposing Combination Therapy of Voacamine With Vincristine for Downregulation of Hypoxia-Inducible Factor-1α/Fatty Acid Synthase Co-axis and Prolyl Hydroxylase-2 Activation in ER+ Mammary Neoplasia

Graphical AbstractMechanism of VOA and VIN to inhibit fatty acid synthesis in DMBA-induced mammary gland carcinoma of albino Wistar rats. Hypoxia-activated HIF-1α enhances lactate acidosis in the tumor microenvironment, and dysregulated pH in the tumor microenvironment activates SREBP-1c and FASN expression to speed up the fatty acid synthesis required for plasma membrane synthesis in rapidly proliferating cells. VOA- and VIN-activated PHD-2 enhanced the proteolytic degradation of HIF, thus inhibiting fatty acid synthesis. HIF-1α, hypoxia-inducible factor-1α; SREBP-1c, sterol regulatory element-binding protein-1c; FASN, fatty acid synthesis; PHD-2, prolyl hydroxylase-2.