Physiological Hypoxia Research Articles

Psychophysiological Responses of Pilots in Hypoxia Training at 7000 and 7500 m.

INTRODUCTION: We compared the physiological responses, psychomotor performances, and hypoxia symptoms between 7000 m and 7500 m (23,000 and 24,600 ft) exposure to develop a safer hypoxia training protocol.METHODS: In altitude chamber, 66 male pilots were exposed to 7000 and 7500 m. Heart rate and arterial oxygen saturation were continuously monitored. Psychomotor performance was assessed using the computational task. The hypoxic symptoms were investigated by a questionnaire.RESULTS: The mean duration time of hypoxia was 323.0 56.5 s at 7000 m and 218.2 63.3 s at 7500 m. The 6-min hypoxia training was completed by 57.6% of the pilots and 6.1% of the pilots at 7000 m and at 7500 m, respectively. There were no significant differences in pilots heart rates and psychomotor performance between the two exposures. The Spo₂ response at 7500 m was slightly severer than that at 7000 m. During the 7000 m exposure, pilots experienced almost the same symptoms and similar frequency order as those during the 7500 m exposure.CONCLUSIONS: There were concordant symptoms, psychomotor performance, and very similar physiological responses between 7000 m and 7500 m during hypoxia training. The results indicated that 7000-m hypoxia awareness training might be an alternative to 7500-m hypoxia training with lower DCS risk and longer experience time.Wen D, Tu L, Wang G, Gu Z, Shi W, Liu X. Psychophysiological responses of pilots in hypoxia training at 7000 and 7500 m. Aerosp Med Hum Perform. 2020; 91(10):785789.

Nesting and fate of transplanted stem cells in hypoxic/ischemic injured tissues: The role of HIF1α/sirtuins and downstream molecular interactions.

The nesting mechanisms and programming for the fate of implanted stem cells in the damaged tissue have been critical issues in designing and achieving cell therapies. The fracture site can induce senescence or apoptosis based on the surrounding harsh conditions, hypoxia, and oxidative stress (OS). Respiration deficiency, disruption in energy metabolism, and consequently OS induction change the biophysical, biochemical, and cellular components of the native tissue. Additionally, the homeostatic molecular players and cell signaling might be changed. Despite all aforementioned issues, in the native stem cell niche, physiological hypoxia is not toxic; rather, it is vitally required for homing, self-renewal, and differentiation. Hence, the key macromolecular players involved in the support of stem cell survival and re-adaptation to a new dysfunctional niche must be understood for managing the cell therapy outcome. Hypoxia-inducible factor 1-alpha is the master transcriptional regulator, involved in the cell response to hypoxia and the adaptation of stem cells to a new niche. This protein is regulated by interaction with sirtuins. Sirtuins are highly conserved NAD+-dependent enzymes that monitor the cellular energy status and modulate gene transcription, genome stability, and energy metabolism in response to environmental signals to modulate the homing and fate of stem cells. Herein, new insights into the nesting of stem cells in hypoxic-ischemic injured tissues were provided and their programming in a new dysfunctional niche along with the involved complex macromolecular players were critically discussed.

In vivo survival strategies for cellular adaptation to hypoxia: HIF1α-dependent suppression of mitochondrial oxygen consumption and decrease of intracellular hypoxia are critical for survival of hypoxic chondrocytes.

Hypoxia occurs not only in pathological conditions like cancer and ischemia and in a variety of physiological settings in the adult organism, but also during normal embryonic development. In the inner portion of the fetal growth plate, which is an avascular tissue originating from mesenchymal progenitor cells, chondrocytes experience physiological hypoxia. Hypoxia-Inducible Transcription Factor-1α (HIF1α), a crucial mediator of cellular adaptation to hypoxia, is an essential survival factor for fetal growth plate chondrocytes. This brief review summarizes our current understanding of the survival function of HIF1α during endochondral bone development.

HYPOXIA AND REPRODUCTIVE HEALTH: The presence and role of hypoxia in the endometrium.

The endometrium is a multicellular tissue that is exquisitely responsive to the ovarian hormones. The local mechanisms of endometrial regulation to ensure optimal function are less well characterised. Transient physiological hypoxia has been proposed as a critical regulator of endometrial function. Herein, we review the literature on hypoxia in the non-pregnant endometrium. We discuss the pros and cons of animal models, human laboratory studies and novel in vivo imaging for the study of endometrial hypoxia. These research tools provide mounting evidence of a transient hypoxic episode in the menstrual endometrium and suggest that endometrial hypoxia may be present at the time of implantation. This local hypoxia may modify the inflammatory environment, influence vascular remodelling and modulate endometrial proliferation to optimise endometrial function. Finally, we review current knowledge of the impact of this hypoxia on endometrial pathologies, with a focus on abnormal uterine bleeding. Throughout the manuscript areas for future research are highlighted with the aim of concentrating research efforts to maximise future benefits for women and society.

Hypoxia and hypoxia mimetics differentially modulate histone post-translational modifications

ABSTRACT Post-translational modifications (PTMs) to the tails of the core histone proteins are critically involved in epigenetic regulation. Hypoxia affects histone modifications by altering the activities of histone-modifying enzymes and the levels of hypoxia-inducible factor (HIF) isoforms. Synthetic hypoxia mimetics promote a similar response, but how accurately the hypoxia mimetics replicate the effects of limited oxygen availability on the levels of histone PTMs is uncertain. Here we report studies on the profiling of the global changes to PTMs on intact histones in response to hypoxia/hypoxia-related stresses using liquid chromatography-mass spectrometry (LC-MS). We demonstrate that intact protein LC-MS profiling is a relatively simple and robust method for investigating potential effects of drugs on histone modifications. The results provide insights into the profiles of PTMs associated with hypoxia and inform on the extent to which hypoxia and hypoxia mimetics cause similar changes to histones. These findings imply chemically-induced hypoxia does not completely replicate the substantial effects of physiological hypoxia on histone PTMs, highlighting that caution should be used in interpreting data from their use.

Ion-regulation, acid/base-balance, kidney function, and effects of hypoxia in coho salmon, Oncorhynchus kisutch, after long-term acclimation to different salinities

Land-based salmon farming in closed containment recirculation aquaculture systems (RAS) is an emerging industry with the potential for reducing disease prevalence, improving production efficiency, and reducing environmental impacts compared with open net-pen aquaculture. Salinity and oxygen levels are environmental factors that have significant impacts on the physiology of fishes and possibly influence the production efficiency of fishes in aquaculture. These parameters are particularly relevant for fish production in RAS, where most water parameters can be manipulated and tightly controlled. While much is known about the specific mechanisms associated with the acute transfer between FW and SW and the reverse, little is known about the effects of long-term acclimation on ion- and acid/base-regulation, especially at intermediate salinities. We measured gas-exchange, ion-regulation, acid/base balance, and renal function in coho salmon (Oncorhynchus kisutch Walbaum, 1792) acclimated to four salinities (2.5, 5.0, 10, and 30 ppt) for over a year in RAS and investigated how animals prioritize these functions when faced with 24 h exposure to hypoxia (PO2 = 63 mmHg = 8.4 kPa = 3.76–4.48 mg l−1). We show that fish that were long-term acclimated to 30 ppt had substantially higher plasma osmolality and [Na+] than fish acclimated to lower salinities. These changes were associated with a marked reduction in blood pH at 30 ppt relative to 2.5 ppt, and we discuss a possible thermodynamic link between salinity acclimation and acid/base regulation. Further, we show that hypoxia exposure results in changes in plasma osmolality by over 80 mOsm kg−1, but only in 30 ppt water, demonstrating a salinity-dependent trade-off between gas exchange and osmoregulation. This study provides insight into the physiological state and hypoxia sensitivity of market sized salmon reared under industry-relevant conditions in RAS.

Erythrocyte adaptive metabolic reprogramming under physiological and pathological hypoxia.

The erythrocyte is the most abundant cell type in our body, acting as both a carrier/deliverer and sensor of oxygen (O2). Erythrocyte O2 delivery capacity is finely regulated by sophisticated metabolic control. In recent years, unbiased and robust human metabolomics screening and mouse genetic studies have advanced erythroid research revealing the differential role of erythrocyte hypoxic metabolic reprogramming in normal individuals at high altitudes and patients facing hypoxia, such as sickle cell disease (SCD) and chronic kidney disease (CKD). Here we summarize recent progress and highlight potential therapeutic possibilities. Initial studies showed that elevated soluble CD73 (sCD73, converts AMP to adenosine) results in increased circulating adenosine that activates the A2B adenosine receptor (ADORA2B). Signaling through this axis is co-operatively strengthened by erythrocyte-specific synthesis of sphingosine-1-phosphate (S1P). Ultimately, these mechanisms promote the generation of 2,3-bisphosphoglycerate (2,3-BPG), an erythrocyte-specific allosteric modulator that decreases haemoglobin--O2-binding affinity, and thus, induces deoxygenated sickle Hb (deoxyHbS), deoxyHbS polymerization, sickling, chronic inflammation and tissue damage in SCD. Similar to SCD, plasma adenosine and erythrocyte S1P are elevated in humans ascending to high altitude. At high altitude, these two metabolites are beneficial to induce erythrocyte metabolic reprogramming and the synthesis of 2,3-BPG, and thus, increase O2 delivery to counteract hypoxic tissue damage. Follow-up studies showed that erythrocyte equilibrative nucleoside transporter 1 (eENT1) is a key purinergic cellular component controlling plasma adenosine in humans at high altitude and mice under hypoxia and underlies the quicker and higher elevation of plasma adenosine upon re-ascent because of prior hypoxia-induced degradation of eENT1. More recent studies demonstrated the beneficial role of erythrocyte ADORA2B-mediated 2,3-BPG production in CKD. Taken together, these findings revealed the differential role of erythrocyte hypoxic metabolic reprogramming in normal humans at high altitude and patients with CKD vs. SCD patients and immediately suggest differential and precision therapies to counteract hypoxia among these groups.

The state of erythrocytopoiesis in dogs in physical and emotional load

In our studies, we examined the indices of erythrocytopoiesis in service dogs for physical activity. The studies were conducted on 1.5−2 years old Belgian Shepherd (Malinois) dogs whoperformed exercises from the international Mondioring program, which included physical andemotional training to train dogs for the Armed Forces, Border Troops and National Police. Blood was collected from animals before training (at rest) and after the training process (lasting 2 hours). It was found that 62.5% of animals showed a tendency to increase the total number of erythrocytes and their populations −"old" and "mature". Such changes in dogs during exercise are indicative of more intense maturation of “young” erythrocytes in the peripheral blood, elimination of “mature” cells from the depot, increased resistance to the membrane of their membranes, and intensifi cation of the processes of erythrocyte attachment and delivery. With regard to hemoglobin content in the blood and hematocrit, these fi gures in 75.0% of dogs after exercise tended to increase. However, red blood indices (MCH and MCV) tended to decrease, indicating an increase in the erythrocyte adaptation processes to physiological hypoxia during exercise and the appearance of a large number of unsaturated microcytic forms of erythrocytes in the bloodstream in particular. In the study of the ferumotransferrincomplex, it should be noted that in 87.5% of the animals, the amount of ferum, TIBC and transferrin levels increased, which are related to the release into the bloodstream of the reserve reserves of the ferrum for hemoglobin formation and adequate ability of hepatocytes to synthesize during transplantation. Key words: dogs, physical activity, erythrocytes, hemoglobin, hematocrit, acid resistance of erythrocytes, ferrum, transferrin, ferumotransferin complex.

The Autophagy Gene ATG9A as a HIF Target Essential for Intestinal Epithelial Barrier Function

A pathological hallmark of mucosal diseases such as inflammatory bowel disease (IBD) is disruption of the intestinal epithelium, a selectively permeable barrier that acts to absorb nutrients and water while simultaneously guarding against pathogens and environmental threats. The intestinal epithelium exists in a metabolic state of low oxygen tension termed “physiologic hypoxia” that is essential for its proper function as an absorptive and barrier organ. An important factor in maintaining hypoxic epithelial homeostasis is the transcription factor family HIF, which is stabilized in hypoxic conditions and mediates epithelial homeostatic response to low oxygen tensions. To identify HIF transcriptional targets in epithelia, chromatin immunoprecipitation (ChIP) was performed in Caco‐2 intestinal epithelial cells (IECs) using HIF‐1α and HIF‐2α specific polyclonal antibodies. ChIP‐enriched DNA was hybridized to a custom promoter microarray (termed ChIP‐chip) comprising a genome‐wide set of predicted transcription start site (TSS) flanking sequences at 50‐bp resolution. This unbiased approach identified autophagy as one of the major HIF‐1 targeted pathways. Binding of HIF‐1 to ATG9A, the only transmembrane autophagy protein, was significantly enriched by exposure of IEC to hypoxia. Validation of the ChIP‐chip revealed prominent induction of ATG9A mRNA and protein. Likewise, using luciferase promoter assays, we identified a functional hypoxia response element upstream of the TSS. Hypoxia‐mediated induction of ATG9A was lost in cells lacking HIF‐1. Strikingly, we found that lentiviral‐mediated knockdown of ATG9A in IECs prevents epithelial barrier formation and results in mislocalization of multiple junctional proteins. Extensions of these findings showed that ATG9A knockdown cells have intrinsic differences in junctional protein expression, suggesting that ATG9A is essential for multiple steps of epithelial junction biogenesis. Our findings have novel applicability for inflammatory disorders that involve a compromised epithelial barrier, such as IBD, and suggest that targeting ATG9A may be a rational strategy for future therapeutic intervention.

Lactate stimulates central respiratory motor output in bullfrogs, Lithobates catesbeianus

Ventilation must constantly change to meet varying metabolic and acid‐base regulation needs of the organism. Although O2 and CO2/pH sensors have received much attention for the chemical control of breathing, metabolites such as lactate and ATP have recently been shown to play important roles in both the hypoxic and hypercapnic ventilatory responses of vertebrates. In mammals and fish, lactate anions increase ventilation through peripheral mechanisms, but the actions of lactate in the central respiratory network of any vertebrate species remain unclear. Anuran amphibians (frogs and toads) accumulate large amounts of lactate in the brain during periods of high respiratory drive, suggesting that lactate may act at central sites to stimulate breathing. For example, hypoxia increases brain lactate which may contribute to elevated ventilation following physiological hypoxia caused by breath‐holding. Furthermore, anurans perform mainly anaerobic exercise, leading to large lactate loads in the blood that may get delivered to the brain through transporters present in the blood‐brain barrier. Thus, we tested the hypothesis that lactate stimulates output from the central respiratory network in amphibians. To test this hypothesis, we measured respiratory‐related cranial nerve X (CNX) and hypoglossal nerve (SNII) activity in isolated brainstem‐spinal cord preparations from the American bullfrog, Lithobates catesbeianus, in response to sodium lactate (lac−; n=8). The brainstem‐spinal cord preparation is advantageous because we can assess the actions of lac− on rhythm generating and motor functions of the respiratory network independent of peripheral feedback. Lac− failed to increase frequency of the respiratory rhythm and amplitude of CNX output. However, we identified a striking dose‐dependent increase in amplitude of respiratory‐related SNII output in each preparation, indicating enhanced motor neuron firing and/or recruitment by lac− (P=0.008; Friedman test; 0.5 mM= 33±11, 2 mM= 56±19, 4 mM= 89±29 % increase above baseline). To control for slight increases in [Na+], osmolality, extracellular pH, and time during exposure to sodium lactate, we superfused a separate group of preparations with 0.5, 2, and 4 mM sodium bicarbonate (HCO3−; n=4). HCO3− did not increase the motor amplitude of either SNII or CNX (P>0.9; Friedman test). Thus, lactate anions lead to increased respiratory motor output of SNII, which may enhance activation of buccal floor musculature during periods of high respiratory demand such as hypoxia and exercise. Overall, this work directly implicates lactate anions in the control of central motor networks that regulate breathing in vertebrates.Support or Funding InformationThis work was funded by start‐up funds provided by UNC‐Greensboro to JS.

Microbiota‐derived Purines Support Intestinal Proliferation and Mucus Barrier Integrity

The gastrointestinal mucosa forms a dynamic physical and biochemical barrier to isolate the host immune system from potentially pathogenic microorganisms. A dysfunctional barrier allows bacterial contact with and translocation across the epithelium. Recent studies have appreciated that epithelial barrier formation and maintenance is energetically demanding, yet the colonic epithelium exists in a rather energetically‐depleted state of physiological hypoxia. Moreover, the intestinal mucosa is short lived, undergoing turnover every 3 – 5 days, incurring a substantial need for nucleotide genesis to preserve the epithelial cell population and provide ATP for energy balance. In the present work, we demonstrate that large quantities of purines are made and released by the gut microbiota and that such microbiota‐derived purines (MDP) are available to the intestinal mucosa. Through a series of experiments in which MDP production was depleted by antibiotic treatment, and purines reconstituted by supplementation and colonization with purine‐producing bacteria, the contribution of MDP to colonic proliferation and energetics during DSS‐induced colitis was delineated. Through HPLC‐based metabolite analyses, exogenously supplied purines showed incorporation into the murine colonic purine metabolite pool, were utilized for nucleotide genesis, and promoted energy balance. Immunofluorescent and metabolite analyses revealed that DSS‐insulted colon tissue lacking MDP substrates were proliferatively stunted, with notable energetic and endoplasmic reticulum (ER) stress, to the detriment of mucus barrier integrity. Upon purine reconstitution, the energetic state of the tissue was improved and ER stress alleviated, with concomitant reclamation of proliferative capacity and mucus barrier sterility. Together, this work establishes MDP as a critical substrate for colonic tissue metabolism and facilitates mucosal homeostasis and inflammatory resolution.Support or Funding InformationThis work was supported by NIH grants F32DK122741, DK1047893, DK50189, DK095491, DK103712 and by the Veterans Administration Merit Award BX002182.

Hypoxia is a key mechanism for regulating inflammation in ulcerative colitis

Intestinal bowel diseases (IBD), including ulcerative colitis (UC), is the group of difficult to diagnose widespread among the population diseases. Pathogenesis of the disease is associated with a complex interaction of the genetic factors, the environment, the microbiome and the unpredicted reaction of the immune system, and the existing treatment methods are not effective enough. It is known, that hypoxia plays a key role in both system and local inflammatory reactions, mainly due to microcirculatory disorders and disseminated intravascular coagulation. Therefore a lot of studies have demonstrated that severity of any inflammatory diseases, including Crohn's disease (CD) and UC depends on hypoxia resistance. In this review we discussed microcirculation of blood and physiological hypoxia in the intestine, the role of hypoxia-inducible factors in the development of IBD and UC, as well as their influence on the severity of the inflammatory process. Authors described the protective effect of various PHD inhibitors and its benefits and disadvantages, so as new approaches of searching of very specific low molecular weight substanses as drugs for the control of IBD and UC.

Effect of Placental Growth Factor on Trophoblast-Endothelial Cell Interactions In Vitro.

Placental growth factor (PlGF) is an important angiogenic factor which has an emerging role in the clinical management of suspected preeclampsia. The role of PlGF in normal placental development is not completely understood and it is uncertain whether PlGF influences trophoblast and endothelial cell interactions central to uterine spiral artery remodelling, especially in variable oxygen conditions. A two-cell model of endovascular invasion was used. Tissue culture plates were coated with Matrigel™, on which fluorescent-labelled uterine microvascular endothelial cells (1 × 105/well) and HTR8/SVNeo cells were co-cultured (1 × 105/well) for 20h. Co-cultures were treated with recombinant human PlGF (rhPlGF) (10 or 100ng/mL) and incubated at either 21% O2 or 2% O2. Images were captured by fluorescence microscopy and analysed using ImageJ (n = 7). Data was analysed using SPSSv24. Treatment with rhPlGF did not improve integration in co-cultures irrespective of oxygen conditions but increased proliferation in 2% O2 of both trophoblast and endothelial cells. Expression of angiogenic factors VEGF, sFLT-1, PlGF and CXCL12 in both co-cultures and in isolated trophoblast cells was not altered by rhPlGF treatment. Expression of TLR-3 mRNA in co-cultures was increased by rhPlGF 100ng/mL at 21% O2 (p = 0.03). PlGF contributes to trophoblast and endothelial cell proliferation in the setting of physiological hypoxia but does not influence trophoblast and endothelial cell interactions in an in vitro model of spiral artery remodelling. Upregulation of TLR-3 expression in co-cultures may indicate a role for PlGF in the placental inflammatory response.

Hypoxia and Innate Immunity: Keeping Up with the HIFsters.

Recent years have witnessed an emergence of interest in understanding metabolic changes associated with immune responses, termed immunometabolism. As oxygen is central to all aerobic metabolism, hypoxia is now recognized to contribute fundamentally to inflammatory and immune responses. Studies from a number of groups have implicated a prominent role for oxygen metabolism and hypoxia in innate immunity of healthy tissue (physiologic hypoxia) and during active inflammation (inflammatory hypoxia). This inflammatory hypoxia emanates from a combination of recruited inflammatory cells (e.g., neutrophils, eosinophils, and monocytes), high rates of oxidative metabolism, and the activation of multiple oxygen-consuming enzymes during inflammation. These localized shifts toward hypoxia have identified a prominent role for the transcription factor hypoxia-inducible factor (HIF) in the regulation of innate immunity. Such studies have provided new and enlightening insight into our basic understanding of immune mechanisms, and extensions of these findings have identified potential therapeutic targets. In this review, we summarize recent literature around the topic of innate immunity and mucosal hypoxia with a focus on transcriptional responses mediated by HIF.

Iron and Sphingolipids as Common Players of (Mal)Adaptation to Hypoxia in Pulmonary Diseases.

Hypoxia, or lack of oxygen, can occur in both physiological (high altitude) and pathological conditions (respiratory diseases). In this narrative review, we introduce high altitude pulmonary edema (HAPE), acute respiratory distress syndrome (ARDS), Chronic Obstructive Pulmonary Disease (COPD), and Cystic Fibrosis (CF) as examples of maladaptation to hypoxia, and highlight some of the potential mechanisms influencing the prognosis of the affected patients. Among the specific pathways modulated in response to hypoxia, iron metabolism has been widely explored in recent years. Recent evidence emphasizes hepcidin as highly involved in the compensatory response to hypoxia in healthy subjects. A less investigated field in the adaptation to hypoxia is the sphingolipid (SPL) metabolism, especially through Ceramide and sphingosine 1 phosphate. Both individually and in concert, iron and SPL are active players of the (mal)adaptation to physiological hypoxia, which can result in the pathological HAPE. Our aim is to identify some pathways and/or markers involved in the physiological adaptation to low atmospheric pressures (high altitudes) that could be involved in pathological adaptation to hypoxia as it occurs in pulmonary inflammatory diseases. Hepcidin, Cer, S1P, and their interplay in hypoxia are raising growing interest both as prognostic factors and therapeutical targets.

Pregnant mice submitted to Surgical Embryo Euthanasia (SEE) induce loss of expression of inducible nitric oxide synthase isoform and NO concentration in the maternal-fetal interface

The well-succeeded pregnancy in humans and rodents is the consequence of close interaction between maternal and fetal cells with intervening of cytokines and chemical mediators. In this process a pregnant uterus subset NK cells - uterine Natural Killer cells (uNK cells) play a pivotal modulatory role under the influence of local physiological hypoxia and other alterations. The aim of the present work was to evaluate the expression and commitment of induced form of nitric oxide synthase (iNOS) and NO concentration in the homeostasis of pregnant uterus. It was used normal pregnant mice on gd 10th and those submitted to surgical intervention to induce mechanical lesion in the embryos (SEE). Uterine samples were collected at 0.5, 1, 2 and 6 h after embryo lesion and processed for paraffin embedding and tissue homogenate. The samples destinate for paraffin embedding was performed the Dolichos biflorus (DBA) lectin cytochemistry and anti-iNOS immunocytochemistry. The samples destinate to tissue homogenates were processed for SDS-PAGE and Western-blot using anti-iNOS and evaluate of NO concentration. The embryo-injured uterine segments showed hyperemia and hemorrhage at mesometrial region in which the DBA lectin reaction showed altered uNK cells suggesting the degranulation. Positive reaction with anti-iNOS was seen on uNK cells, trophoblast giant cells, endometrial stromal and decidual cells and smooth muscle cells in the normal pregnant uterus, but 1 and 2 h after embryo lesion, the iNOS labeling decreased or was absent only in uNK cells. The same results was obtained with NO concentration. These results confirm the unique constitutive expression of iNOS in the pregnant mice uterus, being the uNK cells the only one responsive against stress of embryo failure, besides showing that excessive NO produced by quick activation of uNK-iNOS should affect the local vascular permeability.

Vascular Changes in the Retina and Choroid of Patients With EPAS1 Gain-of-Function Mutation Syndrome

Patients with the EPAS1 gain-of-function mutation syndrome (or Pacak-Zhuang syndrome) present with multiple paragangliomas or pheochromocytomas, duodenal somatostatinoma, polycythemia, headaches, and sometimes diminished visual acuity at an early age. The characteristic phenotype and known genetic cause of the syndrome provide an opportunity to study the role of hypoxia-inducible factor 2α (HIF-2α) in oxygen sensing, development in regions of physiologic hypoxia, and other pathological processes. To describe the ocular lesions in EPAS1 gain-of-function mutation syndrome and to establish whether early-onset diminished visual acuity is developmental or associated with long-term physiologic sequelae of the syndrome. This clinical case series with a transgenic murine model study was conducted from July 2013 to June 2019. Participants were 3 patients referred by their primary care physicians to the National Institutes of Health for evaluation of recurrent and metastatic paragangliomas or pheochromocytomas accompanied by polycythemia. The syndrome and somatic mosaicism in patients were confirmed by the identification of gain-of-function mutations in the EPAS1 gene in resected tumors and other tissues. Ocular findings in patients with EPAS1 gain-of-function mutation syndrome. A total of 3 patients (mean [SD] age, 29 [6.2] years) with confirmed ocular abnormalities were included in the study. Increased contrast accumulation at the posterior aspect of the globe was seen bilaterally on magnetic resonance imaging scans in all patients. Ophthalmoscopy images demonstrated fibrosis overlying the optic disc, tortuous and dilated retinal vessels, and retinal pigment epithelium changes. Optic disc edema and retinal exudates were also seen. Fluorescein angiography images showed leakage of dye from postcapillary venules surrounding the optic disc and highlighted aberrant retinal vascular patterns. Enhanced-depth imaging optical coherence tomography images showed substantial thickening of the choroid and dilation of choroidal vessels. The ocular features of the syndrome were confirmed with a transgenic model of mice with gain-of-function Epas1A529V mutation. In this case series, HIF-2α and hypoxia signaling was found to have a role in vessel development within the choroid and retina, indicating that the marked permanent choroidal thickening and tortuous and dilated veins seen in the choroid and retina in patients with EPAS1 gain-of-function mutation syndrome were suggestive of the persistence of venous elements within the developing mesenchyme. These findings may explain other eye and vascular abnormalities whose pathogenesis remains unclear.

Resolution metabolomes activated by hypoxic environment.

Targeting hypoxia-sensitive pathways in immune cells is of interest in treating diseases. Here, we demonstrate that physiologic hypoxia (1% O2), as encountered in bone marrow and spleen, accelerates human M2 macrophage efferocytosis of apoptotic-neutrophils and senescent erythrocytes via lipolysis-dependent biosynthesis of specialized pro-resolving mediators (SPMs), i.e. resolvins, protectins, maresins and lipoxin. SPM-production was enhanced via hypoxia in M2 macrophages interacting with neutrophils and erythrocytes enabling structural elucidation of a novel eicosapentaenoic acid (EPA)-derived resolvin, resolvin E4 (RvE4) that stimulates efferocytosis of senescent erythrocytes and more potently than aspirin in mouse hemorrhagic exudates. In hypoxia, glycolysis inhibition enhanced neutrophil RvE4-SPM biosynthesis. Human macrophage-erythrocyte co-incubations in physiologic hypoxia produced RvE4-SPM from erythrocyte stores of omega-3 fatty acids. These results indicate that hypoxic environments, including bone marrow and spleen as well as sites of inflammation, activate SPM-biosynthetic circuits that in turn stimulate resolution and clearance of senescent erythrocytes and apoptotic neutrophils.

Nitric oxide formation in the metabolism of nitrates in the oral cavity

Nowadays, nitric oxide is recognized as a regulator of important vascular and metabolic functions. Nitric oxide is formed in the endothelium by converting essential amino acid L-arginine to L-citrulline with the participation of constitutional endothelial nitric oxide synthase. In addition to endogenous pathway of formation, dietary nitrate contributes to the nitric oxide generation through the successive stages (NO 3 -NO 2 -NO) mediated by salivary glands and bacteria of the oral cavity. Purpose of the research – to demonstrate modern scientific data focused on a role of salivary glands and bacteria in nitrates metabolism and maintenance of nitric oxide homeostasis. Results of the studies show that in the oral cavity, there are synanthropic facultative anaerobic bacteria which possess nitrate reductase enzymes and reduce nitrates to nitrites. In the acidic environment of the stomach, nitrites undergo non-enzymatic disproportionation, followed by the formation of nitric oxide and other nitrogen compounds which are involved in the regulation of important biological functions. Dietary nitrites and nitrates can be rapidly absorbed from the upper gastrointestinal tract into the systemic bloodstream and serve as effective donors of nitric oxide in a case of physiological hypoxia. This mechanism of nitric oxide formation is called “enterosalivary nitrate-nitrite-nitric oxide pathway”. The review presents a cardioprotective effect of regular consumption of dietary nitrate-rich products. Diagnostic markers of nitric oxide metabolism in the oral fluid are shown. Comclusions. Based on the scientific data, it was concluded that dietary nitrate and bacteria of the oral cavity play a significant role in the synthesis of NO by enzymatic conversion. Regular intake of dietary nitrate-rich products is able to provide a systemic and local vasodilating effect through enterosalivary pathway and conversion of nitrite to nitric oxide.

Hypoxia Induces Macrophage tnfa Expression via Cyclooxygenase and Prostaglandin E2 in vivo.

Macrophage phenotypes are poorly characterized in disease systems in vivo. Appropriate macrophage activation requires complex coordination of local microenvironmental cues and cytokine signaling. If the molecular mechanisms underpinning macrophage activation were better understood, macrophages could be pharmacologically tuned during disease situations. Here, using zebrafish tnfa:GFP transgenic lines as in vivo readouts, we show that physiological hypoxia and stabilization of Hif-1α promotes macrophage tnfa expression. We demonstrate a new mechanism of Hif-1α-induced macrophage tnfa expression via a cyclooxygenase/prostaglandin E2 axis. These findings uncover a macrophage HIF/COX/TNF axis that links microenvironmental cues to macrophage phenotype, with important implications during inflammation, infection, and cancer, where hypoxia is a common microenvironmental feature and where cyclooxygenase and TNF are major mechanistic players.