Detrimental Roles of Hypoxia-Inducible Factor-1α in Severe Hypoxic Brain Diseases

Hypoxia stabilizes hypoxia-inducible factors (HIFs), facilitating adaptation to hypoxic conditions. Appropriate hypoxia is pivotal for neurovascular regeneration and immune cell mobilization. However, in central nervous system (CNS) injury, prolonged and severe hypoxia harms the brain by triggering neurovascular inflammation, oxidative stress, glial activation, vascular damage, mitochondrial dysfunction, and cell death. Diminished hypoxia in the brain improves cognitive function in individuals with CNS injuries. This review discusses the current evidence regarding the contribution of severe hypoxia to CNS injuries, with an emphasis on HIF-1α-mediated pathways. During severe hypoxia in the CNS, HIF-1α facilitates inflammasome formation, mitochondrial dysfunction, and cell death. This review presents the molecular mechanisms by which HIF-1α is involved in the pathogenesis of CNS injuries, such as stroke, traumatic brain injury, and Alzheimer's disease. Deciphering the molecular mechanisms of HIF-1α will contribute to the development of therapeutic strategies for severe hypoxic brain diseases.

Hypoxia, hypoxia-inducible factors and inflammatory bowel diseases

Adequate oxygen supply is essential for maintaining the body's normal physiological function. In chronic inflammatory conditions such as inflammatory bowel disease (IBD), insufficient oxygen reaching the intestine triggers the regulatory system in response to environmental changes. However, the pathogenesis of IBD is still under investigation. Recent research has highlighted the significant role of hypoxia in IBD, particularly the involvement of hypoxia-inducible factors (HIF) and their regulatory mechanisms, making them promising therapeutic targets for IBD. This review will delve into the role of hypoxia, HIF, and the associated hypoxia-inflammatory microenvironment in the context of IBD. Potential interventions for addressing these challenging gastrointestinal inflammatory diseases will also be discussed within this framework.

Roles of β-Cell Hypoxia in the Progression of Type 2 Diabetes

Type 2 diabetes is a chronic disease marked by hyperglycemia; impaired insulin secretion by pancreatic β-cells is a hallmark of this disease. Recent studies have shown that hypoxia occurs in the β-cells of patients with type 2 diabetes and hypoxia, in turn, contributes to the insulin secretion defect and β-cell loss through various mechanisms, including the activation of hypoxia-inducible factors, induction of transcriptional repressors, and activation of AMP-activated protein kinase. This review focuses on advances in our understanding of the contribution of β-cell hypoxia to the development of β-cell dysfunction in type 2 diabetes. A better understanding of β-cell hypoxia might be useful in the development of new strategies for treating type 2 diabetes.

Deficiency of factor-inhibiting HIF creates a tumor-promoting immune microenvironment

Hypoxia signaling influences tumor development through both cell-intrinsic and -extrinsic pathways. Inhibiting hypoxia-inducible factor (HIF) function has recently been approved as a cancer treatment strategy. Hence, it is important to understand how regulators of HIF may affect tumor growth under physiological conditions. Here we report that in aging mice factor-inhibiting HIF (FIH), one of the most studied negative regulators of HIF, is a haploinsufficient suppressor of spontaneous B cell lymphomas, particular pulmonary B cell lymphomas. FIH deficiency alters immune composition in aged mice and creates a tumor-supportive immune environment demonstrated in syngeneic mouse tumor models. Mechanistically, FIH-defective myeloid cells acquire tumor-supportive properties in response to signals secreted by cancer cells or produced in the tumor microenvironment with enhanced arginase expression and cytokine-directed migration. Together, these data demonstrate that under physiological conditions, FIH plays a key role in maintaining immune homeostasis and can suppress tumorigenesis through a cell-extrinsic pathway.

Hypoxia-based critical gene biomarkers as prognostic reporters for gastric adenocarcinoma

BACKGROUND

Gastric cancer is the most common malignant tumour of the digestive system, yet there is a lack of reported prognostic biomarkers for STAD patients.

METHODS

Transcriptomic expression data of STAD from GEO database, single cell sequencing data from OMIX gastric cancer database. Conservative molecular typing of gastric cancer was constructed using non-negative matrix factorization (NMF). The abundance of 28 immune cells in the tumour samples was assessed using ssGSEA. The R package "oncoPredict" was used to predict chemotherapy response. TIDE website for immunotherapy response prediction. Finally, single cell analysis was performed to clarify the specific type annotation of STAD cells and to analysis their spatial expression.

RESULTS

Hypoxia-score demonstrated excellent prognostic discrimination in TCGA gastric cancer samples. Among multiple deconvolution-based algorithms for immune infiltration, Hypoxia-score presented a general immunosuppressive efficacy across multiple datasets, as evidenced by a broad negative correlation with immune cell infiltration. By the likelihood that each group may have specific drug sensitivity to multiple chemotherapeutic and targeted agents. Results showed that high-risk scoring patients were more sensitive to Staurosporine, Sabutoclax, and AZD8055, while low-risk patients were more sensitive to Bortezomib, Dactinomycin, Docetaxel, Daporinad, Sepantronium, and bromide. In the immunotherapy cohort, the Hypoxia-score presented the ability to discriminate for immunotherapy efficacy. The distribution of Hypoxia-score in single-cell descending space was calculated using AddModuleScore and was found to be distributed across the various cell types annotated in the single-cell analysis. It is suggested that various cells in the tumour microenvironment are involved in hypoxia gene set processes to varying degrees.

CONCLUSION

The Hypoxia-score proves to be a valuable tool for assessing the prognosis of gastric cancer patients and guiding drug treatments, providing significant guidance for clinical diagnosis and treatment in the context of gastric cancer.

Gum Arabic-Derived Hydroxyproline-Rich Peptides Stimulate Intestinal Nonheme Iron Absorption via HIF2α-Dependent Upregulation of Iron Transport Proteins

The stimulation of host iron absorption is a promising antianemia strategy adjunctive/alternative to iron intervention. Here, gum arabic (GA) containing 3.14 ± 0.56% hydroxyproline-rich protein with repetitive X-(Pro/Hyp)n motifs was found to increase iron reduction, uptake, and transport to upregulate duodenal cytochrome b (Dcytb), divalent metal transporter 1 (DMT1), ferroportin, and hephaestin to inhibit hypoxia-inducible factor (HIF) prolyl hydroxylase (PHD) and to stabilize HIF2α in polarized Caco-2 cell monolayers in a dose-dependent manner, and this was dependent on its protein fraction, rather than the polysaccharide fraction. Three abundant GA-derived hydroxyproline-containing dipeptides of Hyp-Hyp, Pro-Hyp, and Ser-Hyp were detected by liquid chromatography-mass spectrometry in the lysates of polarized Caco-2 cell monolayers at the maximum levels of  0.167 ± 0.021, 0.134 ± 0.017, and 0.089 ± 0.015 μg/mg of protein, respectively, and showed desirable docking affinity energy values of -7.53, - 7.91, and -7.39 kcal/mol, respectively, against human PHD3. GA-derived peptides also acutely increased duodenal HIF2α stability and Dcytb, DMT1, ferroportin, and hephaestin transcription in rats (P < 0.05). Overall, GA-derived hydroxyproline-rich peptides stimulated intestinal iron absorption via PHD inhibition, HIF2α stabilization, and subsequent upregulation of iron transport proteins.

The HIF-1α and mTOR Pathways Amplify Heterotopic Ossification

Fibrodysplasia ossificans progressiva (FOP; MIM# 135100) is an ultra-rare congenital disorder caused by gain-of-function point mutations in the Activin receptor A type I (ACVR1, also known as ALK2) gene. FOP is characterized by episodic heterotopic ossification (HO) in skeletal muscles, tendons, ligaments, or other soft tissues that progressively causes irreversible loss of mobility. FOP mutations cause mild ligand-independent constitutive activation as well as ligand-dependent bone morphogenetic protein (BMP) pathway hypersensitivity of mutant ACVR1. BMP signaling is also a key pathway for mediating acquired HO. However, HO is a highly complex biological process involving multiple interacting signaling pathways. Among them, the hypoxia-inducible factor (HIF) and mechanistic target of rapamycin (mTOR) pathways are intimately involved in both genetic and acquired HO formation. HIF-1α inhibition or mTOR inhibition reduces HO formation in mouse models of FOP or acquired HO in part by de-amplifying the BMP pathway signaling. Here, we review the recent progress on the mechanisms of the HIF-1α and mTOR pathways in the amplification of HO lesions and discuss the future directions and strategies to translate the targeting of HIF-1α and the mTOR pathways into clinical interventions for FOP and other forms of HO.

Kidney Fibrosis and Oxidative Stress: From Molecular Pathways to New Pharmacological Opportunities

Kidney fibrosis, diffused into the interstitium, vessels, and glomerulus, is the main pathologic feature associated with loss of renal function and chronic kidney disease (CKD). Fibrosis may be triggered in kidney diseases by different genetic and molecular insults. However, several studies have shown that fibrosis can be linked to oxidative stress and mitochondrial dysfunction in CKD. In this review, we will focus on three pathways that link oxidative stress and kidney fibrosis, namely: (i) hyperglycemia and mitochondrial energy imbalance, (ii) the mineralocorticoid signaling pathway, and (iii) the hypoxia-inducible factor (HIF) pathway. We selected these pathways because they are targeted by available medications capable of reducing kidney fibrosis, such as sodium-glucose cotransporter-2 (SGLT2) inhibitors, non-steroidal mineralocorticoid receptor antagonists (MRAs), and HIF-1alpha-prolyl hydroxylase inhibitors. These drugs have shown a reduction in oxidative stress in the kidney and a reduced collagen deposition across different CKD subtypes. However, there is still a long and winding road to a clear understanding of the anti-fibrotic effects of these compounds in humans, due to the inherent practical and ethical difficulties in obtaining sequential kidney biopsies and the lack of specific fibrosis biomarkers measurable in easily accessible matrices like urine. In this narrative review, we will describe these three pathways, their interconnections, and their link to and activity in oxidative stress and kidney fibrosis.

Pharmacodynamic effects of molidustat on erythropoiesis in healthy cats

BACKGROUND

Inhibition of hypoxia-inducible factor prolyl hydroxylase (HIF-PH) stimulates erythropoiesis in rats, dogs, monkeys, and humans.

HYPOTHESIS/OBJECTIVE

Determine if molidustat, a novel HIF-PH inhibitor, stimulates erythropoiesis in healthy cats.

ANIMALS

Seventeen healthy adult laboratory cats.

METHODS

Randomized, placebo-controlled study. Cats were treated PO once daily with suspensions of 0 (Group 1; n = 6), 5 (Group 2; n = 6), or 10 (Group 3; n = 5) mg/kg of molidustat. Effects on red blood cell parameters, reticulocyte indices and plasma erythropoietin (EPO) concentrations were evaluated. Molidustat treatment was stopped when hematocrit (HCT) exceeded 60%.

RESULTS

Compared to placebo, a significant increase in mean HCT was evident starting on Day 14 (Group 2:54.4% vs 40.3%, P < .001, 95% confidence interval [CI] for the difference [8.95-19.28]; Group 3:61.2% vs 40.3%, P < .001, 95% CI [15.48-26.43]) and remained significantly higher for the entire treatment period. In molidustat-treated groups, HCT exceeded 60% on Day 21 (Group 2) and Day 14 (Group 3). Mean HCT in molidustat-treated cats returned to within the reference range (29%-45%) after Day 56 and was numerically comparable to placebo from Day 70 onwards. Red blood cell count and hemoglobin concentrations followed a similar pattern as HCT. Mean EPO concentrations significantly increased after molidustat administration on all assessment days. Molidustat treatments were well tolerated.

CONCLUSIONS AND CLINICAL IMPORTANCE

Marked erythropoietic effects were identified after daily administration of molidustat to healthy cats and additional studies are warranted to evaluate the effects in anemic cats.

Hypoxia-inducible factors activator, roxadustat, increases pulmonary vascular resistance in rats

Activators of hypoxia inducible factors (HIFs), such as roxadustat, are promising agents for anemia treatment. However, since HIFs are also involved in the regulation of the pulmonary circulation, we hypothesized that roxadustat increases pulmonary vascular resistance and vasoconstrictor reactivity. Using isolated, cell-free solution perfused rat lungs, we found perfusion pressure-flow curves to be shifted to higher pressures by 2 weeks of roxadustat treatment (10 mg/kg every other day), although not as much as by chronic hypoxic exposure. Vasoconstrictor reactivity to angiotensin II and acute hypoxic challenges was not altered by roxadustat. Since roxadustat may inhibit angiotensin-converting enzyme 2 (ACE2), we also tested a purported ACE2 activator, diminazene aceturate (DIZE, 0.1 mM). It produced paradoxical, unexplained pulmonary vasoconstriction. We conclude that the risk of serious pulmonary hypertension is not high when roxadustat is given for 14 days, but monitoring is advisable.

Hypoxia-inducible factor stabilisation-related lncRNAs in retinopathy of prematurity

Long non-coding RNAs (lncRNAs) play an important role in the response to many diseases. The previous study reported the transcriptomes of mice that were cured of oxygen-induced retinopathy (OIR, retinopathy of prematurity (ROP) model) by hypoxia-inducible factor (HIF) stabilisation via HIF prolyl hydroxylase inhibition using the isoquinolone Roxadustat or the 2-oxoglutarateanalog dimethyloxalylglycine (DMOG). However, there is little understanding of how those genes are regulated. In the present study, 6918 known lncRNAs and 3654 novel lncRNAs were obtained, and a series of differentially expressed lncRNAs (DELncRNAs) were also identified. By cis- and trans-regulation analyses, the target genes of DELncRNAs were predicted. Functional analysis demonstrated that multiple genes were involved in the MAPK signalling pathway, adipocytokine signalling pathway was regulated by the DELncRNAs. By HIF-pathway analysis, two lncRNAs Gm12758 and Gm15283 were found that can regulate the HIF-pathway by targeting the Vegfa, Pgk1, Pfkl, Eno1, Eno1b and Aldoa genes. In conclusion, the present study provided a series of lncRNAs for further understanding and protecting the extremely premature infant from oxygen toxicity.

Lactate produced by alveolar type II cells suppresses inflammatory alveolar macrophages in acute lung injury

Alveolar inflammation is a hallmark of acute lung injury (ALI), and its clinical correlate is acute respiratory distress syndrome-and it is as a result of interactions between alveolar type II cells (ATII) and alveolar macrophages (AM). In the setting of acute injury, the microenvironment of the intra-alveolar space is determined in part by metabolites and cytokines and is known to shape the AM phenotype. In response to ALI, increased glycolysis is observed in AT II cells, mediated by the transcription factor hypoxia-inducible factor (HIF) 1α, which has been shown to decrease inflammation. We hypothesized that in acute lung injury, lactate, the end product of glycolysis, produced by ATII cells shifts AMs toward an anti-inflammatory phenotype, thus mitigating ALI. We found that local intratracheal delivery of lactate improved ALI in two different mouse models. Lactate shifted cytokine expression of murine AMs toward increased IL-10, while decreasing IL-1 and IL-6 expression. Mice with ATII-specific deletion of Hif1a and mice treated with an inhibitor of lactate dehydrogenase displayed exacerbated ALI and increased inflammation with decreased levels of lactate in the bronchoalveolar lavage fluid; however, all those parameters improved with intratracheal lactate. When exposed to LPS (to recapitulate an inflammatory stimulus as it occurs in ALI), human primary AMs co-cultured with alveolar epithelial cells had reduced inflammatory responses. Taken together, these studies reveal an innate protective pathway, in which lactate produced by ATII cells shifts AMs toward an anti-inflammatory phenotype and dampens excessive inflammation in ALI.

Remote ischemic preconditioning and hypoxia-induced biomarkers in acute myocardial infarction: study on a porcine model

Objectives. Remote ischemic preconditioning (RIPC) mitigates acute myocardial infarction (AMI). We hypothesized that RIPC reduces the size and severity of AMI and explored molecular mechanisms behind this phenomenon. Design. In two series of experiments, piglets underwent 60 min of the circumflex coronary artery occlusion, resulting in AMI. Piglets were randomly assigned into the RIPC groups (n = 7 + 7) and the control groups (n = 7 + 7). The RIPC groups underwent four 5-min hind limb ischemia-reperfusion cycles before AMI. In series I, the protective efficacy of RIPC was investigated by using biomarkers and echocardiography with a follow-up of 24 h. In series II, the heart of each piglet was harvested for TTC-staining to measure infarct size. Muscle biopsies were collected from the hind limb to explore molecular mechanisms of RIPC using qPCR and Western blot analysis. Results. The levels of CK-MBm (p = 0.032) and TnI (p = 0.007) were lower in the RIPC group. Left ventricular ejection fraction in the RIPC group was greater at the end of the follow-up. The myocardial infarct size in the RIPC group was smaller (p = 0.033). Western blot indicated HIF1α stabilization in the skeletal muscle of the RIPC group. PCR analyses showed upregulation of the HIF target mRNAs for glucose transporter (GLUT1), glucose transporter 4 (GLUT4), phosphofructokinase 1 (PFK1), glyceraldehyde 3-phosphate dehydrogenase (GAPDH), enolase 1 (ENO1), lactate dehydrogenase (LDHA) and endothelial nitric oxidate synthase (eNOS). Conclusions. Biochemical, physiologic, and histologic evidence confirms that RIPC decreases the size of AMI. The HIF pathway is likely involved in the mechanism of the RIPC.

Chronic intermittent hypoxia-induced cardiovascular and renal dysfunction: from adaptation to maladaptation

Chronic intermittent hypoxia (CIH) is the dominant pathological feature of human obstructive sleep apnoea (OSA), which is highly prevalent and associated with cardiovascular and renal diseases. CIH causes hypertension, centred on sympathetic nervous overactivity, which persists following removal of the CIH stimulus. Molecular mechanisms contributing to CIH-induced hypertension have been carefully delineated. However, there is a dearth of knowledge on the efficacy of interventions to ameliorate high blood pressure in established disease. CIH causes endothelial dysfunction, aberrant structural remodelling of vessels and accelerates atherosclerotic processes. Pro-inflammatory and pro-oxidant pathways converge on disrupted nitric oxide signalling driving vascular dysfunction. In addition, CIH has adverse effects on the myocardium, manifesting atrial fibrillation, and cardiac remodelling progressing to contractile dysfunction. Sympatho-vagal imbalance, oxidative stress, inflammation, dysregulated HIF-1α transcriptional responses and resultant pro-apoptotic ER stress, calcium dysregulation, and mitochondrial dysfunction conspire to drive myocardial injury and failure. CIH elaborates direct and indirect effects in the kidney that initially contribute to the development of hypertension and later to chronic kidney disease. CIH-induced morphological damage of the kidney is dependent on TLR4/NF-κB/NLRP3/caspase-1 inflammasome activation and associated pyroptosis. Emerging potential therapies related to the gut-kidney axis and blockade of aryl hydrocarbon receptors (AhR) are promising. Cardiorenal outcomes in response to intermittent hypoxia present along a continuum from adaptation to maladaptation and are dependent on the intensity and duration of exposure to intermittent hypoxia. This heterogeneity of OSA is relevant to therapeutic treatment options and we argue the need for better stratification of OSA phenotypes.

Anaemia in CKD - treatment standard

Anaemia is one of the most common complications of chronic kidney disease (CKD), having a significant impact on quality-of-life, and is also associated with a number of adverse clinical outcomes. Its pathogenesis is multifactorial, caused largely by an inadequate production of erythropoietin from the diseased kidneys, with iron deficiency, inflammation, shortened red cell lifespan, and enhanced blood loss also being contributory factors. The management of this condition was transformed in the late-1980's by the advent of recombinant human erythropoietin (epoetin) manufactured in Chinese hamster ovary cells, and treatment paradigms have developed over the last three decades, largely focusing on a combination of epoetin or its analogues (erythropoiesis-stimulating agents; ESAs) along with iron supplementation, often administered intravenously due to increased hepcidin levels limiting iron absorption from the gut. Indeed, in patients with early CKD and iron deficiency, iron per se may be sufficient to improve the anaemia, delaying the need for ESA therapy. Other causes of anaemia should be excluded and corrected (if possible) before resorting to treatment with ESAs and iron. More recently, the HIF-prolyl hydroxylase inhibitors have entered the therapeutic arena; these are orally-active agents that upregulate endogenous erythropoietin production as well as a number of iron-regulatory genes which may also enhance erythropoiesis. The latter drugs are highly efficacious, and may have advantages in inflammatory conditions causing resistance to conventional ESA therapy, but concerns exist regarding their safety, particularly in the longer term. This article reviews the current standards of treatment, as well as recent novel developments in the management of anaemia in CKD.

SUMOylation indirectly suppresses activity of the HIF-1α pathway in intestinal epithelial cells

The hypoxia-inducible factor (HIF) is a master regulator of the cellular transcriptional response to hypoxia. While the oxygen-sensitive regulation of HIF-1α subunit stability via the ubiquitin-proteasome pathway has been well described, less is known about how other oxygen-independent post-translational modifications impact the HIF pathway. SUMOylation, the attachment of SUMO (small ubiquitin-like modifier) proteins to a target protein, regulates the HIF pathway, although the impact of SUMO on HIF activity remains controversial. Here, we examined the effects of SUMOylation on the expression pattern of HIF-1α in response to pan-hydroxylase inhibitor dimethyloxalylglycine (DMOG) in intestinal epithelial cells. We evaluated the effects of SUMO-1, SUMO-2, and SUMO-3 overexpression and inhibition of SUMOylation using a novel selective inhibitor of the SUMO pathway, TAK-981, on the sensitivity of HIF-1α in Caco-2 intestinal epithelial cells. Our findings demonstrate that treatment with TAK-981 decreases global SUMO-1 and SUMO-2/3 modification and enhances HIF-1α protein levels, whereas SUMO-1 and SUMO-2/3 overexpression results in decreased HIF-1α protein levels in response to DMOG. Reporter assay analysis demonstrates reduced HIF-1α transcriptional activity in cells overexpressing SUMO-1 and SUMO-2/3, whereas pretreatment with TAK-981 increased HIF-1α transcriptional activity in response to DMOG. In addition, HIF-1α nuclear accumulation was decreased in cells overexpressing SUMO-1. Importantly, we showed that HIF-1α is not directly SUMOylated, but that SUMOylation affects HIF-1α stability and activity indirectly. Taken together, our results indicate that SUMOylation indirectly suppresses HIF-1α protein stability, transcriptional activity, and nuclear accumulation in intestinal epithelial cells.

Hypoxia-inducible Factor-1α Suppresses the Innate Immune Response in Cultured Human Proximal Tubular Cells

BACKGROUND/AIM

Retinoic acid-inducible gene (RIG)-I like receptors (RLRs) are expressed on renal proximal tubular epithelial cells (RPTECs) in viral nephropathy, indicating the presence of RLR-mediated innate immune responses in RPTECs. Hypoxia is also known to affect innate immunity. This study investigated the effects of hypoxia, and hypoxia-inducible factor (HIF) on innate immunity in RPTECs.

MATERIALS AND METHODS

Primary human RPTECs were cultured under normoxic or hypoxic conditions and treated with a synthetic analog of double-stranded RNA (polyIC). The expression levels of RIG-I and MDA5, as RLRs, and IFNβ, IL6, and TNFα, as inflammatory mediators were evaluated using quantitative reverse transcription-polymerase chain reaction, western blotting, and lactate dehydrogenase activity (LDH) assays. To further investigate the role of hypoxia, a small interfering RNA was used to knockdown HIF1α.

RESULTS

Under normoxic conditions, polyIC increased RIG-I, MDA5, and IFNβ mRNA expression in RPTECs by, 9.4±0.4-, 10.8±0.5-, and 4.0±0.1-fold, respectively, compared to control, and by 5.4±0.1-, 7.4±0.1-, and 2.4±0.3-fold, respectively, under hypoxic conditions, the rate of increase was lower than that under normoxic conditions (p<0.01). Protein expression showed a similar trend. Under hypoxic conditions, polyIC treatment with HIF1α knockdown in RPTECs increased RIG-I, MDA5, and IFNβ mRNA expression by 3.1±0.5-, 2.9±0.4-, and 6.1±0.4-fold, respectively, and cytotoxicity, demonstrated by LDH assay, was increased compared to that without knockdown (all p<0.01).

CONCLUSION

Hypoxia suppresses polyIC-induced RLRs mediated innate immune responses in RPTECs via HIF1α.

TRPM2-L Participates in the Interleukin-6 Pathway to Enhance Tumor Growth in Prostate Cancer by Hypoxia-Inducible Factor-1α

Interleukin-6 (IL-6) can promote cell proliferation in prostate cancer (PCa). Full-length transient receptor potential melastatin 2 (TRPM2-L) is highly expressed in PCa. However, the association between IL-6 and TRPM2-L in PCa is unclear. Here, human PCa cell lines, PC-3 and DU-145, were treated with 10 μg/mL tocilizumab, an IL-6 receptor (IL-6R) inhibitor, and the TRPM2-L protein expression in cells was significantly decreased. Cells were stably transfected with TRPM2 short-interfering RNA (siRNA) and cell survival clearly declined. Recombinant IL-6 treatment weakened the effects of TRPM2-siRNA on cell survival. TRPM2-L binds directly to IL-6R in PC-3 and DU-145 cells. The protein expression of hypoxia-inducible factor-1α was suppressed by reduction with TRPM2-L in PC-3 and DU-145 cells. Human umbilical vein endothelial cells (HUVECs) were indirectly cocultured with PCa cells, and the invasion and angiogenic activity of HUVECs were enhanced after coculture with PCa cells. However, TRPM2-L reduction in PCa cells significantly decreased the invasion and angiogenic activity of HUVECs compared to the control coculture. In vivo, xenograft tumors were induced using PC-3 cells. Tocilizumab treatment or TRPM2-L reduction clearly suppressed tumor growth. Meanwhile, the injection of mouse recombinant IL-6 weakened the antitumor effects of TRPM2-L reduction. These data demonstrate that the IL-6/TRPM2-L axis in PCa tumor growth is important, and interference of the IL-6/TRPM2-L axis may be a novel approach for PCa therapy.

Persistence and expansion of hypoxia detected by pimonidazole adduct immunostaining during progression of diabetic nephropathy in diabetic mice

Hypoxia and oxidative stress are considered to be underlying factors in the deterioration of renal function and pathogenesis in acute kidney injury (AKI) and chronic kidney disease, including diabetic nephropathy (DN). However, the long-term role of hypoxia in DN is unknown. Here, we investigated the distribution, severity, and time course of hypoxia during DN development in our well-established severely diabetic transgenic (Tg) DN mouse model that mimics human DN up to 80 wk of age, using pimonidazole adduct immunohistochemistry. The relationship between pimonidazole adduct distribution and hypoxia-inducible factor (HIF) expression was also examined. We found 1) persistent pimonidazole immunostaining mainly in the outer zone of the outer medulla, extending into the inner zone, 2) significant expansion of area and intensity up to 40 wk of age, and 3) characteristic subcellular localization mainly at apical sites in vesicular form by laser scanning microscopy of thin slices. The distribution of pimonidazole adducts was different from that of HIF reported previously, indicating that hypoxia does not directly contribute to persistent abnormal HIF expression. These results suggest that pimonidazole adducts produced under low [Formula: see text] conditions are sustained by a mechanism distinct from direct ischemia. We propose that in the long course of DN development, persistent hyperfiltration and hyperexcretion of glucose, albumin, and water increase metabolism and energy expenditure in the tubules, and such chronic stimulation leads to relative ischemia and local hypoxia, which may contribute in part to the loss of nephrons.NEW & NOTEWORTHY This study provides new insights into hypoxia during the long course of diabetic nephropathy development. Hypoxia was persistently localized only in limited areas and its distribution differed significantly from that of hypoxia-inducible factors. These findings suggests that in the long course of diabetic nephropathy development, increased energy requirements and limited blood supply may lead to relative ischemia and induction of local and persistent hypoxia, which may contribute in part to the loss of nephrons.

Unlocking the potential of ultra-high dose fractionated radiation for effective treatment of glioblastoma

Background

Conventional radiation therapy for glioblastoma (GBM) has limited efficacy. Regenerative medicine brings hope for repairing damaged tissue, opening opportunities for elevating the maximum acceptable radiation dose. In this study, we explored the effect of ultra-high dose fractionated radiation on brain injury and tumor responses in immunocompetent mice. We also evaluated the role of the HIF-1α under radiation.

Methods

Naïve and hypoxia-inducible factor-1 alpha (HIF-1α)+/- heterozygous mice received a fractionated daily dose of 20 Gy for three or five consecutive days. Magnetic resonance imaging (MRI) and histology were performed to assess brain injury post-radiation. The 2×105 human GBM1 luciferase-expressing cells were transplanted with tolerance induction protocol. Fractionated radiotherapy was performed during the exponential phase of tumor growth. BLI, MRI, and immunohistochemistry staining were performed to evaluate tumor growth dynamics and radiotherapy responses. Additionally, animal lifespan was recorded.

Results

Fractionated radiation of 5×20 Gy induced severe brain damage, starting 3 weeks after radiation. All animals from this group died within 12 weeks. In contrast, later onset and less severe brain injury were observed starting 12 weeks after radiation of 3×20 Gy. It resulted in complete GBM eradication and survival of all treated animals. Furthermore, HIF-1α+/- mice exhibited more obvious vascular damage 63 weeks after fractionated radiation of 3×20 Gy.

Conclusion

Ultra-high dose fractionated 3×20 Gy radiation can eradicate the GBM cells at the cost of only mild brain injury. The HIF-1α gene is a promising target for ameliorating vascular impairment post-radiation, encouraging the implementation of neurorestorative strategies.

Oxygen-sensing pathways and the pulmonary circulation

The unique property of the pulmonary circulation to constrict in response to hypoxia, rather than dilate, brings advantages in both health and disease. Hypoxic pulmonary vasoconstriction (HPV) acts to optimise ventilation-perfusion matching - this is important clinically both in focal disease (such as pneumonia) and in one-lung ventilation during anaesthesia for thoracic surgery. However, during global hypoxia such as that encountered at high altitude, generalised pulmonary vasoconstriction can lead to pulmonary hypertension. There is now a growing body of evidence that links the hypoxia-inducible factor (HIF) pathway and pulmonary vascular tone - in both acute and chronic settings. Genetic and pharmacological alterations to all key components of this pathway (VHL - von Hippel-Lindau ubiquitin E3 ligase; PHD2 - prolyl hydroxylase domain protein 2; HIF1 and HIF2) have clear effects on the pulmonary circulation, particularly in hypoxia. Furthermore, knowledge of the molecular biology of the prolyl hydroxylase enzymes has led to an extensive and ongoing body of research into the importance of iron in both HPV and pulmonary hypertension. This review will explore these relationships in more detail and discuss future avenues of research.

In vivo optical imaging of tumor stromal cells with hypoxia-inducible factor activity

Tumors contain various stromal cells, such as immune cells, endothelial cells, and fibroblasts, which contribute to the development of a tumor-specific microenvironment characterized by hypoxia and inflammation, and are associated with malignant progression. In this study, we investigated the activity of intratumoral hypoxia-inducible factor (HIF), which functions as a master regulator of the cellular response to hypoxia and inflammation. We constructed the HIF activity-monitoring reporter gene hypoxia-response element-Venus-Akaluc (HVA) that expresses the green fluorescent protein Venus and modified firefly luciferase Akaluc in a HIF activity-dependent manner, and created transgenic mice harboring HVA transgene (HVA-Tg). In HVA-Tg, HIF-active cells can be visualized using AkaBLI, an ultra-sensitive in vivo bioluminescence imaging technology that produces an intense near-infrared light upon reaction of Akaluc with the D-luciferin analog AkaLumine-HCl. By orthotopic transplantation of E0771, a mouse triple negative breast cancer cell line without a reporter gene, into HVA-Tg, we succeeded in noninvasively monitoring bioluminescence signals from HIF-active stromal cells as early as 8 days after transplantation. The HIF-active stromal cells initially clustered locally and then spread throughout the tumors with growth. Immunohistochemistry and flow cytometry analyses revealed that CD11b+ F4/80+ macrophages were the predominant HIF-active stromal cells in E0771 tumors. These results indicate that HVA-Tg is a useful tool for spatiotemporal analysis of HIF-active tumor stromal cells, facilitating investigation of the roles of HIF-active tumor stromal cells in tumor growth and malignant progression.

The Emerging Role of Hypoxic Training for the Equine Athlete

This paper provides a comprehensive discussion on the physiological impacts of hypoxic training, its benefits to endurance performance, and a rationale for utilizing it to improve performance in the equine athlete. All exercise-induced training adaptations are governed by genetics. Exercise prescriptions can be tailored to elicit the desired physiological adaptations. Although the application of hypoxic stimuli on its own is not ideal to promote favorable molecular responses, exercise training under hypoxic conditions provides an optimal environment for maximizing physiological adaptations to enhance endurance performance. The combination of exercise training and hypoxia increases the activity of the hypoxia-inducible factor (HIF) pathway compared to training under normoxic conditions. Hypoxia-inducible factor-1 alpha (HIF-1α) is known as a master regulator of the expression of genes since over 100 genes are responsive to HIF-1α. For instance, HIF-1-inducible genes include those critical to erythropoiesis, angiogenesis, glucose metabolism, mitochondrial biogenesis, and glucose transport, all of which are intergral in physiological adaptations for endurance performance. Further, hypoxic training could conceivably have a role in equine rehabilitation when high-impact training is contraindicated but a quality training stimulus is desired. This is achievable through purpose-built equine motorized treadmills inside commercial hypoxic chambers.

Dznep, a histone modification inhibitor, inhibits HIF1α binding to TIMP2 gene and suppresses TIMP2 expression under hypoxia

Epidemiological studies have shown that patients who recovered from acute kidney injury (AKI) may subsequently develop chronic kidney disease (CKD). AKI is primarily caused by renal hypoxia, and it causes epigenetic alterations, known as hypoxic memory. 3-Deazaneplanocin A (Dznep), an inhibitor of histone modification, suppresses renal fibrosis and the expression of tissue inhibitor of metalloproteinases-2 (TIMP2), a profibrotic factor, in mouse ischemia-reperfusion models. The current study investigated the epigenetic regulation of TIMP2 in human kidney 2 (HK-2) cells. The expression of TIMP2 was upregulated in HK-2 cells under hypoxic conditions and was suppressed by Dznep. ChIP-qPCR showed that Dznep reduced the amount of H3K4me3 at the promoter region of the TIMP2 gene under hypoxic condition. Formaldehyde-assisted isolation of regulatory elements-qPCR of the TIMP2 gene showed that Dznep reduced open chromatin area. In addition, based on ChIP-qPCR of hypoxia-inducible factor 1 alpha (HIF1α), Dznep inhibited the binding of HIF1α to the TIMP2 gene under hypoxic conditions. The reporter assays for the binding region of HIF1α showed enhanced transcriptional activity by hypoxia. Dznep suppresses the expression of TIMP2 under hypoxic conditions by inhibiting the binding of HIF1α to the TIMP2 gene.

Chronic environmental hypoxia attenuates innate immunity activation and renal injury in two CKD models

Tissue hypoxia has been pointed out as a major pathogenic factor in chronic kidney disease (CKD). However, epidemiological and experimental evidence inconsistent with this notion has been described. We have previously reported that chronic exposure to low ambient Po2 promoted no renal injury in normal rats and in rats with 5/6 renal ablation (Nx) unexpectedly attenuated renal injury. In the present study, we investigated whether chronic exposure to low ambient Po2 would also be renoprotective in two additional models of CKD: adenine (ADE) excess and chronic nitric oxide (NO) inhibition. In both models, normobaric ambient hypoxia attenuated the development of renal injury and inflammation. In addition, renal hypoxia limited the activation of NF-κB and NOD-like receptor family pyrin domain containing 3 inflammasome cascades as well as oxidative stress and intrarenal infiltration by angiotensin II-positive cells. Renal activation of hypoxia-inducible factor (HIF)-2α, along with other adaptive mechanisms to hypoxia, may have contributed to these renoprotective effects. The present findings may contribute to unravel the pathogenesis of CKD and to the development of innovative strategies to arrest its progression.NEW & NOTEWORTHY Hypoxia is regarded as a major pathogenic factor in chronic kidney disease (CKD). In disagreement with this view, we show here that sustained exposure to low ambient Po2 lessened kidney injury and inflammation in two CKD models: adenine (ADE) excess and chronic nitric oxide (NO) inhibition. Together with our previous findings in the remnant kidney, these observations indicate that local changes elicited by hypoxia may exert renoprotection in CKD, raising the prospect of novel therapeutic strategies for this disease.

Effect of Diosmin on Selected Parameters of Oxygen Homeostasis

Chronic venous disease (CVD) is a condition characterized by functional disturbances in the microcirculation of the superficial and deep veins, affecting up to 30% of the global population. Diosmin, a phlebotropic drug, is commonly used in the treatment of CVD, and its beneficial effects have been described in numerous clinical studies. However, the precise molecular mechanism underlying the activity of diosmin is not yet fully understood. Therefore, the objective of our study was to investigate whether diosmin has an impact on oxygen management, as cardiovascular diseases are often associated with hypoxia. In our study, patients were administered a daily dosage of 2 × 600 mg of diosmin for 3 months, and we evaluated several factors associated with oxygen management, angiogenesis, and inflammation using biochemical assays. Our findings indicate that diosmin reduced the levels of fibroblast growth factors (FGF) and vascular endothelial growth factor (VEGF-C), while increasing endostatin and angiostatin levels, suggesting a potential influence on angiogenesis regulation. Furthermore, diosmin exhibited anti-inflammatory properties by suppressing the levels of tumor necrosis factor-alpha (TNF-α), interleukin 1-beta (IL-1β), and interleukin 6 (IL-6), while promoting the production of interleukin 12 (IL-12). Additionally, diosmin significantly decreased the levels of hypoxia-inducible factor (HIF), anion gap (AG), and lactate, indicating its potential influence on the hypoxia-inducible factor pathway. These findings suggest that diosmin may play a crucial role in modulating oxygen management and inflammation in the context of chronic venous disease.

Pathways of Hypoxia-Inducible Factor (HIF) in the Orchestration of Uterine Fibroids Development

Uterine fibroids (UF) are common benign tumors in women. The course of UF is associated with troubling symptoms and the development of infertility and pregnancy pathology. Surgical treatment even implies hysterectomy, while pharmacological interventions are modestly effective. Classically, hypoxic metabolism is considered a hallmark of malignant tumor. However, the role of hypoxia-induced factor (HIF) is significant in benign tumors as well. Herein, we briefly review the basic biology of HIF-family proteins, outlining their possible roles in UF. Apart from theoretical justifications, we summarized 15 studies reporting increased expression of HIFs and downstream factors in UF samples. Altogether, data suggest that increased expression of the HIF-protein and altered expression of its dependent genes are presumed to be the factors leading to UF development. Thus, even without being a malignant tumor, UF is characterized by the strong involvement of HIF. This novel insight may give rise to further research in the direction of finding new prognostic markers and effective medicines against UF.

Hypoxia-Inducible Factor-Prolyl Hydroxylase Inhibitor Improves Leukocyte Energy Metabolism in Hereditary Hemorrhagic Telangiectasia

The interplay between hypoxia-inducible factors (HIFs) and transforming growth factor beta (TGF-β) is critical for both inflammation and angiogenesis. In hereditary hemorrhagic telangiectasia (HHT), we have previously observed that impairment of the TGF-β pathway is associated with downregulation of HIF-1α. HIF-1α accumulation is mandatory in situations of altered energy demand, such as during infection or hypoxia, by adjusting cell metabolism. Leukocytes undergo a HIF-1α-dependent switch from aerobic mitochondrial respiration to anaerobic glycolysis (glycolytic switch) after stimulation and during differentiation. We postulate that the decreased HIF-1α accumulation in HHT leads to a clinically observed immunodeficiency in these patients. Examination of HIF-1α and its target genes in freshly isolated peripheral blood mononuclear cells (PBMCs) from HHT patients revealed decreased gene expression and protein levels of HIF-1α and HIF-1α-regulated glycolytic enzymes. Treatment of these cells with the HIF-prolyl hydroxylase inhibitor, Roxadustat, rescued their ability to accumulate HIF-1α protein. Functional analysis of metabolic flux using a Seahorse FX extracellular flux analyzer showed that the extracellular acidification rate (indicator of glycolytic turnover) after Roxadustat treatment was comparable to non-HHT controls, while oxygen consumption (indicator of mitochondrial respiration) was slightly reduced. HIF stabilization may be a potential therapeutic target in HHT patients suffering from infections.

Effects of pharmacological delay with roxadustat on multi-territory perforator flap survival in rats

Roxadustat (FG-4592) is a specific hypoxia-inducible factor (HIF) prolyl hydroxylase inhibitor. We investigated the effects of FG-4592 pretreatment on survival and second choke vessels of multi-territory perforator flaps in rats. In total, 72 rats were divided into two groups (n = 36 each): the experimental (FG-4592) group and the control group. FG-4592 was administered orally as a single dose of 60 mg/kg every other day; the first drug solution was administered to the animals 7 days before the surgical procedure. On postoperative day 7, the surviving flap area was calculated. At 12 h post-surgery, in the second choke zone in the flaps, macrovascular hinges were compared by angiography and imaging, and microvascular changes were assessed by histology. Laser Doppler imaging was used to evaluate flap perfusion at the second choke zone at 12 h and 7 days after surgery. At 7 days after surgery, the flap survival area and perfusion were significantly greater in rats given FG-4592 compared with controls. At 12 h after surgery, the diameter of macrovascular and microvascular vessels, nitric oxide content, perfusion, and the protein levels of HIF-1α and inducible nitric oxide synthase were also significantly greater in FG-4592-treated rats than controls. In conclusion, pretreatment with roxadustat may improve initial flap survival and dilate the second choke zone vessels in a multi-territory perforator flap.

MYC overrides HIF-1α to regulate proliferating primary cell metabolism in hypoxia

Hypoxia requires metabolic adaptations to sustain energetically demanding cellular activities. While the metabolic consequences of hypoxia have been studied extensively in cancer cell models, comparatively little is known about how primary cell metabolism responds to hypoxia. Thus, we developed metabolic flux models for human lung fibroblast and pulmonary artery smooth muscle cells proliferating in hypoxia. Unexpectedly, we found that hypoxia decreased glycolysis despite activation of hypoxia-inducible factor 1α (HIF-1α) and increased glycolytic enzyme expression. While HIF-1α activation in normoxia by prolyl hydroxylase (PHD) inhibition did increase glycolysis, hypoxia blocked this effect. Multi-omic profiling revealed distinct molecular responses to hypoxia and PHD inhibition, and suggested a critical role for MYC in modulating HIF-1α responses to hypoxia. Consistent with this hypothesis, MYC knockdown in hypoxia increased glycolysis and MYC over-expression in normoxia decreased glycolysis stimulated by PHD inhibition. These data suggest that MYC signaling in hypoxia uncouples an increase in HIF-dependent glycolytic gene transcription from glycolytic flux.

High-Altitude Andean H194R HIF2A Allele Is a Hypomorphic Allele

For over 10,000 years, Andeans have resided at high altitude where the partial pressure of oxygen challenges human survival. Recent studies have provided evidence for positive selection acting in Andeans on the HIF2A (also known as EPAS1) locus, which encodes for a central transcription factor of the hypoxia-inducible factor pathway. However, the precise mechanism by which this allele might lead to altitude-adaptive phenotypes, if any, is unknown. By analyzing whole genome sequencing data from 46 high-coverage Peruvian Andean genomes, we confirm evidence for positive selection acting on HIF2A and a unique pattern of variation surrounding the Andean-specific single nucleotide variant (SNV), rs570553380, which encodes for an H194R amino acid substitution in HIF-2α. Genotyping the Andean-associated SNV rs570553380 in a group of 299 Peruvian Andeans from Cerro de Pasco, Peru (4,338 m), reveals a positive association with increased fraction of exhaled nitric oxide, a marker of nitric oxide biosynthesis. In vitro assays show that the H194R mutation impairs binding of HIF-2α to its heterodimeric partner, aryl hydrocarbon receptor nuclear translocator. A knockin mouse model bearing the H194R mutation in the Hif2a gene displays decreased levels of hypoxia-induced pulmonary Endothelin-1 transcripts and protection against hypoxia-induced pulmonary hypertension. We conclude the Andean H194R HIF2A allele is a hypomorphic (partial loss of function) allele.

Targeting HIF-1 for prostate cancer: a synthesis of preclinical evidence

INTRODUCTION

Hypoxia-inducible factor (HIF) mediates multiple intracellular processes that drive cellular metabolism and induce proliferation. Dysregulated HIF expression is associated with oncogenic cellular transformation. Moreover, high HIF levels correlate with tumor aggressiveness and chemoresistance, indicating the vital effect of HIF-1α on tumorigenicity. Currently, widespread in-vitro and in-vivo research is focusing on targeting HIF with drugs that have already been approved for use by the FDA, such as belzutifan, in renal cell carcinoma. HIF inhibition is mostly associated with tumor size reduction; however, drug toxicity remains a challenge.

AREA COVERED

In this review, we focus on the potential of targeting HIF in prostate cancer (PC) and summarize the scientific background of HIF activity in PC. This finding emphasizes the rationale for using HIF as a therapeutic target in this malignancy. We have listed known HIF inhibitors that are being investigated in preclinical studies and their potential as anticancer drugs for PC.

EXPERT OPINION

Although HIF-targeting agents have been investigated for over a decade, their use in therapy-resistant cancers remains relevant and should be explored further. In addition, the use of naturally occurring HIF inhibitors should be considered as an add-on therapy for the currently used regimens.

Safety Endpoints With Vadadustat Versus Darbepoetin Alfa in Patients With NonDialysis-Dependent CKD: A Post Hoc Regional Analysis of the PRO2TECT Randomized Clinical Trial of ESA-Treated Patients

Rationale & Objective

In the PRO₂TECT trials, vadadustat was found to be noninferior to darbepoetin alfa in hematologic efficacy but not for major adverse cardiovascular events (MACE; all-cause death or nonfatal myocardial infarction or stroke) in patients with non-dialysis-dependent chronic kidney disease (NDD-CKD). We investigated the regional differences in MACE in the PRO₂TECT trials.

Study Design

Phase 3, global, open-label, randomized, active-controlled clinical trial.

Setting & Participants

A total of 1,725 erythropoiesis-stimulating agent (ESA)-treated patients with anemia and NDD-CKD.

Intervention

1:1 randomization to receive vadadustat or darbepoetin alfa.

Outcomes

The primary safety end point was the time to first MACE.

Results

At baseline, patients in Europe (n=444) were primarily treated with darbepoetin alfa, showed higher proportions on low ESA doses (<90 U/kg/wk epoetin alfa equivalents) with a hemoglobin concentration of ≥10 g/dL compared with patients in the US (n=665) and non-US/non-Europe (n=614) regions. The MACE rates per 100 person-years in the 3 vadadustat groups across regions were 14.5 in the US, 11.6 in Europe, and 10.0 in the non-US/non-Europe groups, whereas event rates in the darbepoetin alfa group were considerably lower in Europe than in the US and non-US/non-Europe groups (6.7 vs 13.3 and 10.5, respectively). The overall hazard ratio for MACE for vadadustat vs darbepoetin alpha was 1.16; 95% CI, 0.93-1.45, but varied by geographical region, with a greater hazard ratio seen in Europe (US, 1.07; 95% CI, 0.78-1.46; Europe, 2.05; 95% CI, 1.24-3.39; non-US/non-Europe, 0.91; 95% CI, 0.60-1.37); interaction between study treatment and geographical region, P = 0.07). In Europe, ESA rescue was associated with a higher risk of MACE in both groups.

Limitations

Several analyses are exploratory.

Conclusions

In this trial, there was a low risk of MACE in the darbepoetin alfa group in Europe. Patients in Europe were generally on low doses of ESA, with hemoglobin already within target range. The low risk of MACE may have been related to a limited need to switch and titrate darbepoetin alfa compared with the non-US/non-Europe group.

Funding

Akebia Therapeutics, Inc.

Trial Registration

ClinicalTrials.gov identifier: NCT02680574.

Safety Endpoints With Vadadustat Versus Darbepoetin Alfa in Patients With Non-Dialysis-Dependent CKD: A Post Hoc Regional Analysis of the PRO2TECT Randomized Clinical Trial of ESA-Naïve Patients

Rationale & Objective

Prespecified analyses of the PRO₂TECT trials comparing the safety of the oral hypoxia-inducible factor prolyl hydroxylase inhibitor vadadustat with darbepoetin alfa in patients with non-dialysis-dependent chronic kidney disease (NDD-CKD) found no difference in major adverse cardiovascular events (MACE; death from any cause or nonfatal myocardial infarction or stroke) among US patients and a higher risk among patients treated with vadadustat outside the United States. We investigated regional differences in MACE in the PRO₂TECT trial that enrolled 1,751 patients previously untreated with erythropoiesis-stimulating agents.

Study Design

Phase 3, global, open-label, randomized, active-controlled clinical trial.

Setting and Participants

Erythropoiesis-stimulating agent-untreated patients with anemia and NDD-CKD.

Intervention

Eligible patients were randomized 1:1 to receive vadadustat or darbepoetin alfa.

Outcomes

The primary safety end point was time to first MACE. Secondary safety end points included time to first expanded MACE (MACE plus hospitalization for heart failure or thromboembolic event, excluding vascular access thrombosis).

Results

In the non-US/non-Europe region, there was a higher proportion of patients with baseline estimated glomerular filtration rate (eGFR) level of ≤10 mL/min/1.73 m² in the vadadustat group [96 (34.7%)] than in the darbepoetin alfa group [66 (24.0%)]. In this region, there were 21 excess MACEs reported in the vadadustat group [78 events (n=276)] versus the darbepoetin alfa [57 events (n=275)], including 13 excess noncardiovascular deaths, largely from kidney failure. Noncardiovascular deaths were concentrated in Brazil and South Africa, which enrolled higher proportions of patients with an eGFR of ≤10 mL/min/1.73 m² and who may not have had access to dialysis.

Limitations

Different regional treatment patterns of patients with NDD-CKD.

Conclusions

The higher MACE rate in the non-US/non-Europe vadadustat group may have been partly because of imbalances in the baseline eGFR level in countries where dialysis was not uniformly available resulting in many kidney-related deaths.

Understanding human aging and the fundamental cell signaling link in age-related diseases: the middle-aging hypovascularity hypoxia hypothesis

Aging-related hypoxia, oxidative stress, and inflammation pathophysiology are closely associated with human age-related carcinogenesis and chronic diseases. However, the connection between hypoxia and hormonal cell signaling pathways is unclear, but such human age-related comorbid diseases do coincide with the middle-aging period of declining sex hormonal signaling. This scoping review evaluates the relevant interdisciplinary evidence to assess the systems biology of function, regulation, and homeostasis in order to discern and decipher the etiology of the connection between hypoxia and hormonal signaling in human age-related comorbid diseases. The hypothesis charts the accumulating evidence to support the development of a hypoxic milieu and oxidative stress-inflammation pathophysiology in middle-aged individuals, as well as the induction of amyloidosis, autophagy, and epithelial-to-mesenchymal transition in aging-related degeneration. Taken together, this new approach and strategy can provide the clarity of concepts and patterns to determine the causes of declining vascularity hemodynamics (blood flow) and physiological oxygenation perfusion (oxygen bioavailability) in relation to oxygen homeostasis and vascularity that cause hypoxia (hypovascularity hypoxia). The middle-aging hypovascularity hypoxia hypothesis could provide the mechanistic interface connecting the endocrine, nitric oxide, and oxygen homeostasis signaling that is closely linked to the progressive conditions of degenerative hypertrophy, atrophy, fibrosis, and neoplasm. An in-depth understanding of these intrinsic biological processes of the developing middle-aged hypoxia could provide potential new strategies for time-dependent therapies in maintaining healthspan for healthy lifestyle aging, medical cost savings, and health system sustainability.

Angiogenesis and Hepatocellular Carcinoma: From Molecular Mechanisms to Systemic Therapies

Hepatocellular carcinoma (HCC) is the most common primary liver malignancy. The hypervascular nature of the majority of HCCs and the peculiar vascular derangement occurring during liver carcinogenesis underscore the importance of angiogenesis in the development and progression of these tumors. Indeed, several angiogenic molecular pathways have been identified as deregulated in HCC. The hypervascular nature and the peculiar vascularization of HCC, as well as deregulated angiogenic pathways, represent major therapeutic targets. To a large extent, intra-arterial locoregional treatments (transarterial-(chemo)embolization) rely on tumor ischemia caused by embolization of tumor feeding arteries, even though this may represent the "primum movens" of tumor recurrence through the activation of neoangiogenesis. Considering systemic therapies, the currently available tyrosine kinase inhibitors (sorafenib, regorafenib, cabozantinib and lenvatinib) and monoclonal antibodies (ramucirumab and bevacizumab, in combination with the anti-PD-L1, atezolizumab) primarily target, among others, angiogenic pathways. Considering the importance of angiogenesis in the pathogenesis and treatment of liver cancer, in this paper, we aim to review the role of angiogenesis in HCC, addressing the molecular mechanisms, available antiangiogenic therapies and prognostic biomarkers in patients receiving these treatments.

Hypoxia induces polycystin-1 expression in the renal epithelium

Mutations in polycystin-1 which is encoded by the PKD1 gene are the main causes for the development of autosomal dominant polycystic kidney disease. However, only little is known about the physiological function of polycystin-1 and even less about the regulation of its expression. Here, we show that expression of PKD1 is induced by hypoxia and compounds that stabilize the hypoxia-inducible transcription factor (HIF) 1α in primary human tubular epithelial cells. Knockdown of HIF subunits confirms HIF-1α-dependent regulation of polycystin-1 expression. Furthermore, HIF ChIP-seq reveals that HIF interacts with a regulatory DNA element within the PKD1 gene in renal tubule-derived cells. HIF-dependent expression of polycystin-1 can also be demonstrated in vivo in kidneys of mice treated with substances that stabilize HIF. Polycystin-1 and HIF-1α have been shown to promote epithelial branching during kidney development. In line with these findings, we show that expression of polycystin-1 within mouse embryonic ureteric bud branches is regulated by HIF. Our finding links expression of one of the main regulators of accurate renal development with the hypoxia signalling pathway and provides additional insight into the pathophysiology of polycystic kidney disease.

The Role of HIF-1α in Bone Regeneration: A New Direction and Challenge in Bone Tissue Engineering

The process of repairing significant bone defects requires the recruitment of a considerable number of cells for osteogenesis-related activities, which implies the consumption of a substantial amount of oxygen and nutrients. Therefore, the limited supply of nutrients and oxygen at the defect site is a vital constraint that affects the regenerative effect, which is closely related to the degree of a well-established vascular network. Hypoxia-inducible factor (HIF-1α), which is an essential transcription factor activated in hypoxic environments, plays a vital role in vascular network construction. HIF-1α, which plays a central role in regulating cartilage and bone formation, induces vascular invasion and differentiation of osteoprogenitor cells to promote and maintain extracellular matrix production by mediating the adaptive response of cells to changes in oxygen levels. However, the application of HIF-1α in bone tissue engineering is still controversial. As such, clarifying the function of HIF-1α in regulating the bone regeneration process is one of the urgent issues that need to be addressed. This review provides insight into the mechanisms of HIF-1α action in bone regeneration and related recent advances. It also describes current strategies for applying hypoxia induction and hypoxia mimicry in bone tissue engineering, providing theoretical support for the use of HIF-1α in establishing a novel and feasible bone repair strategy in clinical settings.

Therapeutics of managing reduced red cell mass associated with chronic kidney disease - Is there a case for earlier intervention?

Reduced red cell mass is a poor prognostic indicator in chronic kidney disease (CKD) patients. Whilst overt anaemia impacts on the quality of life of patients with CKD, lowered red cell mass may also compromise oxygen delivery to proximal tubular cells and contribute to progressive kidney injury. Epidemiological data from cats with CKD support this hypothesis although controlled interventional studies involving drugs that raise red cell mass in trials designed to test this hypothesis are lacking in both human and veterinary medicine. Recombinant analogues of erythropoietin (EPO) are currently standard of care for human CKD patients where low red cell mass impacts on their quality of life. Resistance to EPO is encountered in 20% to 40% of patients treated, probably due to functional iron deficiency, reflecting the difficulties of managing iron deficiency associated with the chronic inflammation of CKD. Similar issues are likely faced in managing anaemia in feline CKD although published data on the use of human EPO analogues are limited as such treatment in cats risks antibody formation resulting in red cell aplasia and transfusion dependency and so is reserved for late stage cases only. This article reviews the recent alternative therapeutic approach to increase red cell mass using HIF-prolyl hydroxylase inhibitors and explains their mode of action and theoretical advantages over EPO analogues in the context of iron metabolism. The results of human clinical trials and the potential benefit of adopting this approach in feline CKD patients are discussed.

Epicatechin gallate promotes vascularization in co-culture of human osteoblasts and outgrowth endothelial cells

Prevascularization is crucial for the survival of tissue-engineered bone and further bone repair/regeneration. Since epicatechin gallate (ECG), the most abundant flavanol in green tea, shows potential beneficial effects on endothelial cells and bone cells, we decided to investigate whether it promotes vascularization/angiogenesis and osteogenesis using a co-culture system containing human primary osteoblasts (POBs) and outgrowth endothelial cells (OECs). We found that treatment with ECG (1) significantly enhanced microvessel formation in co-culture of POB and OECs, (2) improved cell viability/proliferation and the angiogenic/osteogenic capacities of OEC/POBs, (3) significantly increased the levels of E-selectin, IL-6, TNF-α, IFN-γ, VEGF, and PDGF-BB in co-cultures of POB and OEC, and (4) upregulated HIF-1α, HIF-2α, NF-κB, iNOS, GLUT1, VEGF, and Ang1/2 but downregulated PHD1 in monocultures of OEC or POB. Our findings demonstrate that ECG promotes angiogenesis and osteogenesis (probably via HIF signaling) in co-cultures of OECs and POBs. ECG thus has potential applications in the promotion of angiogenesis/vascularization in many tissue constructs including those of bone.

High prevalence of peripheral and carotid artery disease in patients with interstitial lung diseases

Background: Interstitial lung diseases (ILD) are a heterogenous group of diseases, which have pulmonary fibrosis, restrictive lung disease, and decreased diffusion capacity as a common final path. Premature death frequently results not from ILD itself but from comorbidities. Peripheral artery disease (PAD) is a common comorbid disease in different chronic lung diseases. The focus of the present study is to clarify the prevalence of PAD in ILD. Patients and methods: A total of 97 patients with ILD and 30 controls were included in the study. Patients with ILD were subdivided into two groups according to the progression of pulmonary fibrosis: progressive fibrosing and non-progressive fibrosing ILD (PF-ILD and nPF-ILD, respectively). All participants underwent standard angiological and pneumological diagnostic procedures including six-minute walking test, measurement of ankle-brachial-index, and colour-coded duplex sonography. Results: We observed no relevant differences in the baseline characteristics except age. Both, PF-ILD and nPF-ILD patients, presented with a highly increased incidence of atherosclerotic lesions compared to the control group (p<0.001). PAD was present in all patients with PF-ILD and in 73% of patients with nPF-ILD. These results were confirmed by age-adjusted regression analyses. Conclusions: The present results indicate that ILD is an independent risk factor for atherosclerosis. Patients with PF-ILD are more severely affected than nPF-ILD patients with age as a confounding variable. Atherogenesis in ILD may be mediated by increased cardiovascular risk, systemic inflammation and chronic hypoxemia.

Hypoxia-Inducible Factor 2 Alpha (HIF2α) Inhibitors: Targeting Genetically Driven Tumor Hypoxia

Tumors driven by deficiency of the VHL gene product, which is involved in degradation of the hypoxia-inducible factor subunit 2 alpha (HIF2α), are natural candidates for targeted inhibition of this pathway. Belzutifan, a highly specific and well-tolerated HIF2α inhibitor, recently received FDA approval for the treatment of nonmetastatic renal cell carcinomas, pancreatic neuroendocrine tumors, and central nervous system hemangioblastomas from patients with von Hippel-Lindau disease, who carry VHL germline mutations. Such approval is a milestone in oncology; however, the full potential, and limitations, of HIF2α inhibition in the clinic are just starting to be explored. Here we briefly recapitulate the molecular rationale for HIF2α blockade in tumors and review available preclinical and clinical data, elaborating on mutations that might be particularly sensitive to this approach. We also outline some emerging mechanisms of intrinsic and acquired resistance to HIF2α inhibitors, including acquired mutations of the gatekeeper pocket of HIF2α and its interacting partner ARNT. Lastly, we propose that the high efficacy of belzutifan observed in tumors with genetically driven hypoxia caused by VHL mutations suggests that a focus on other mutations that similarly lead to HIF2α stabilization, such as those occurring in neuroendocrine tumors with disruptions in the tricarboxylic acid cycle (SDHA/B/C/D, FH, MDH2, IDH2), HIF hydroxylases (EGLN/PHDs), and the HIF2α-encoding gene, EPAS1, are warranted.

Structural Characterization of Hypoxia Inducible Factor α-Prolyl Hydroxylase Domain 2 Interaction through MD Simulations

The Prolyl Hydroxylases (PHDs) are an enzymatic family that regulates cell oxygen-sensing. PHDs hydroxylate hypoxia-inducible transcription factors α (HIFs-α) driving their proteasomal degradation. Hypoxia inhibits PHDs activity, inducing HIFs-α stabilization and cell adaptation to hypoxia. As a hallmark of cancer, hypoxia promotes neo-angiogenesis and cell proliferation. PHD isoforms are thought to have a variable impact on tumor progression. All isoforms hydroxylate HIF-α (HIF-1,2,3α) with different affinities. However, what determines these differences and how they pair with tumor growth is poorly understood. Here, molecular dynamics simulations were used to characterize the PHD2 binding properties in complexes with HIF-1α and HIF-2α. In parallel, conservation analysis and binding free energy calculations were performed to better understand PHD2 substrate affinity. Our data suggest a direct association between the PHD2 C-terminus and HIF-2α that is not observed in the PHD2/HIF-1α complex. Furthermore, our results indicate that phosphorylation of a PHD2 residue, Thr405, causes a variation in binding energy, despite the fact that this PTM has only a limited structural impact on PHD2/HIFs-α complexes. Collectively, our findings suggest that the PHD2 C-terminus may act as a molecular regulator of PHD's activity.

Hypoxia in Skin Cancer: Molecular Basis and Clinical Implications

Skin cancer is one of the most prevalent cancers in the Caucasian population. In the United States, it is estimated that at least one in five people will develop skin cancer in their lifetime, leading to significant morbidity and a healthcare burden. Skin cancer mainly arises from cells in the epidermal layer of the skin, where oxygen is scarce. There are three main types of skin cancer: malignant melanoma, basal cell carcinoma, and squamous cell carcinoma. Accumulating evidence has revealed a critical role for hypoxia in the development and progression of these dermatologic malignancies. In this review, we discuss the role of hypoxia in treating and reconstructing skin cancers. We will summarize the molecular basis of hypoxia signaling pathways in relation to the major genetic variations of skin cancer.

Roxadustat, a HIF-PHD inhibitor with exploitable potential on diabetes-related complications

Diabetes mellitus (DM) is a group of metabolic diseases caused by absolute or relative deficiency of insulin secretion and characterized by chronic hyperglycemia. Its complications affect almost every tissue of the body, usually leading to blindness, renal failure, amputation, etc. and in the final stage, it mostly develops into cardiac failure, which is the main reason why diabetes mellitus manifests itself as a high clinical lethality. The pathogenesis of diabetes mellitus and its complications involves various pathological processes including excessive production of mitochondrial reactive oxygen species (ROS) and metabolic imbalance. Hypoxia-inducible Factor (HIF) signaling pathway plays an important role in both of the above processes. Roxadustat is an activator of Hypoxia-inducible Factor-1α, which increases the transcriptional activity of Hypoxia-inducible Factor-1α by inhibiting hypoxia-inducible factor prolyl hydroxylase (HIF-PHD). Roxadustat showed regulatory effects on maintaining metabolic stability in the hypoxic state of the body by activating many downstream signaling pathways such as vascular endothelial growth factor (VEGF), glucose transporter protein-1 (GLUT1), lactate dehydrogenase (LDHA), etc. This review summarizes the current research findings of roxadustat on the diseases of cardiomyopathy, nephropathy, retinal damage and impaired wound healing, which also occur at different stages of diabetes and greatly contribute to the damage caused by diabetes to the organism. We attempts to uncover a more comprehensive picture of the therapeutic effects of roxadustat, and inform its expanding research about diabetic complications treatment.

Roles of hypoxia-inducible factor in hepatocellular carcinoma under local ablation therapies

Hepatocellular carcinoma (HCC) is one of the most common digestive malignancies. HCC It ranges as the fifth most common cause of cancer mortality worldwide. While The prognosis of metastatic or advanced HCC is still quite poor. Recently, locoregional treatment, especially local ablation therapies, plays an important role in the treatment of HCC. Radiofrequency ablation (RFA) and high-intensity focused ultrasound (HIFU) ablation are the most common-used methods effective and feasible for treating HCC. However, the molecular mechanisms underlying the actions of ablation in the treatments for HCC and the HCC recurrence after ablation still are poorly understood. Hypoxia-inducible factor (HIF), the key gene switch for adaptive responses to hypoxia, has been found to play an essential role in the rapid aggressive recurrence of HCC after ablation treatment. In this review, we summarized the current evidence of the roles of HIF in the treatment of HCC with ablation. Fifteen relevant studies were included and further analyzed. Among them, three clinical studies suggested that HIF-1α might serve as a crucial role in the RAF treatment of HCC or the local recurrence of HCC after RFA. The remainder included experimental studies demonstrated that HIF-1, 2α might target the different molecules (e.g., BNIP3, CA-IX, and arginase-1) and signaling cascades (e.g., VEGFA/EphA2 pathway), constituting a complex network that promoted HCC invasion and metastasis after ablation. Currently, the inhibitors of HIF have been developed, providing important proof of targeting HIF for the prevention of HCC recurrence after IRFA and HIFU ablation. Further confirmation by prospective clinical and in-depth experimental studies is still warranted to illustrate the effects of HIF in HCC recurrence followed ablation treatment in the future.

Chronic Treatment with Aβ42 with a Toxic Conformer and LPS Induces Inflammatory Responses in BV-2 Microglia with Dysregulation of Hypoxia-Inducible Factor Expression

Amyloid β (Aβ) plays a key role in the pathology of Alzheimer's disease (AD) and is toxic owing to its ability to aggregate into oligomers and fibrils. Aβ has high aggregative ability and potent toxicity due to the "toxic turn" at positions 22 and 23. Furthermore, APP knock-in mice producing E22P-Aβ with the toxic turn exhibited AD-related phenotypes such as cognitive impairment, Aβ plaque accumulation, and tau hyperphosphorylation. In these mice, it is suggested that the activation of neuroinflammation and dysregulation of hypoxia-inducible factor (HIF) expression in the hippocampus contribute to the pathogenesis of AD-related phenotype. However, it remains unclear which cells are responsible for the dysregulation of HIF expression and the neuroinflammation which was induced by E22P-Aβ with the toxic turn. Here, we investigated the effects of chronic treatment with E22P-Aβ42 and lipopolysaccharides (LPS) on the inflammatory response in BV-2 microglia. Chronic treatment with E22P-Aβ42 and LPS increased nitric oxide production and the expression of interleukin-6 (IL-6), whereas it reduced the expression of HIF-1α and HIF-3α in BV-2 microglia. The reduction of HIF-1α caused by E22P-Aβ42 and LPS was milder than that caused by LPS. Furthermore, chronic treatment with E22P-Aβ42 and LPS increased the nuclear translocation of nuclear factor-kappaB (NF-κB). E22P-Aβ42 could enhance the inflammatory response of microglia with abnormal HIF signaling and contribute to the progression of AD pathology.

HIF-1α accumulation in response to transient hypoglycemia may worsen diabetic eye disease

Tight glycemic control (TGC), the cornerstone of diabetic management, reduces the incidence and progression of diabetic microvascular disease. However, TGC can also lead to transient episodes of hypoglycemia, which have been associated with adverse outcomes in patients with diabetes. Here, we demonstrate that low glucose levels result in hypoxia-inducible factor (HIF)-1-dependent expression of the glucose transporter, Glut1, in retinal cells. Enhanced nuclear accumulation of HIF-1α was independent of its canonical post-translational stabilization but instead dependent on stimulation of its translation and nuclear localization. In the presence of hypoxia, this physiologic response to low glucose resulted in a marked increase in the secretion of the HIF-dependent vasoactive mediators that promote diabetic retinopathy. Our results provide a molecular explanation for how early glucose control, as well as glycemic variability (i.e., oscillating serum glucose levels), contributes to diabetic eye disease. These observations have important implications for optimizing glucose management in patients with diabetes.

Crosstalk between microwave ablation and ferroptosis: The next hot topic?

Microwave ablation has been one form of thermal ablation in treatments for many tumors, which can locally control unresectable tumors. Ferroptosis is iron-dependent cell death caused by the cumulative reactive oxygen species and lipid peroxidation products. Recently, increasing evidence has shown that ferroptosis might play a vital role in MWA-induced tumor suppression. In this article, we briefly illustrate the concept of ferroptosis, the related signal pathways and inducers, the basic principle of microwave ablation in killing tumors, and the key molecules released after microwave ablation. Then, we describe the cross-talking molecules between microwave ablation and ferroptosis, and discussed the potential mechanism of microwave ablation-induced ferroptosis. This review explores the therapeutic target of ferroptosis in enhancing the systemic antitumor effect after microwave ablation, providing theoretical support in combinational microwave ablation with pro-ferroptosis therapy.