Alterations In Oxygen Tension Research Articles

Hypoxia-Inducible Factor 1 and Preeclampsia: A New Perspective.

Preeclampsia (PE) is a serious and distinct type of pregnancy-induced hypertension, with an incidence of 2-8% worldwide. PE is defined as pregnancy-related hypertension with proteinuria and peripheral edema after 20weeks of gestation. Hypoxic placenta triggers the release of inflammatory and humoral substances into maternal circulation, leading to induction of oxidative stress, lipid peroxidation, endothelial dysfunction, and peripheral vasoconstriction. The objective of the present narrative review was to find the association between PE and hypoxia-inducible factor 1 (HIF-1) in pregnant women from a new perspective. HIF-1 is the key transcription factor that regulates cellular responses to hypoxia and low oxygen tension. HIF-1α is involved in the differentiation and growth of the placenta mainly in the first and second trimesters. During normal gestation, HIF-1α responds to the alterations in oxygen tension, cytokine, and angiogenic factors release. HIF-1α is considered a key biomarker of placental function and vascularization during pregnancy. HIF-1α plays a crucial role in the pathogenesis of PE through activation of anti-angiogenic and inhibition of proangiogenic factors. As well, HIF-1α increases the expression of the p38MAPK and NLRP3 inflammasomes, which promote placental inflammation and dysfunction. HIF-1α acts as a potential link between inflammatory signaling pathways and the development of PE.

433 Maternal hyperoxia and its effect on the ductus venosus

The ductus venosus(DV) Doppler waveform is a valuable tool in the assessment of any fetal condition that may affect forward cardiac function. We sought to investigate the effects of maternal hyperoxygenation(MH) on the DV Doppler in the third trimester. Forty-six women with a singleton pregnancy ≥31 weeks’ gestational age(GA) were prospectively recruited.The DV Doppler was obtained at the isthmus, near its origin from the umbilical vein in a mid-sagittal view. A Doppler assessment of the umbilical artery (UA) was also performed. Doppler measurements were taken at baseline and following MH for 10minutes.Measurements of mean systolic, diastolic and ‘a’ wave velocities as well as pulsatility index for veins (PIV), preload index (PLI) and peak velocity index for veins (PVIV) ratios were obtained. Satisfactory DV Doppler recordings were obtained from 59% of participants.Qualitative assessment of the DV waveform confirmed a positive ‘a’ wave in all fetuses. DV mean systolic, diastolic and ‘a’ wave velocities increased following MH.The DV Doppler ratios including PIV, PLI and PVIV did not change in response to MH (Table 1).There were no changes in the resistance of the UA in response to MH. The DV responds to MH. Due to the increase in systole,diastole, and atrial contraction contemporaneously, the ratios between these elements were unchanged. As gestation advances the PIV and a-wave-related ratios decrease owing to a decrease in utero-placental resistance and an increase in cardiac compliance and contractility. We have demonstrated no change in the utero-placental resistance indices, therefore the most likely explanation is a constriction of the DV, suggesting that the DV is responsive to alterations in oxygen tension in the fetal blood.The decrease in the DV calibre in response to MH infers that the size of the DV is directly responsible for the shunting of umbilical venous blood away from the hepatic circulation.These findings warrant further investigation in relation to the effect of MH on myocardial function particularly in the context of congenital cardiac disease.

OLEOTHORAX: INCIDENTAL FINDING AND RELIC OF THE PAST

SESSION TITLE: Medical Student/Resident Chest Infections Posters SESSION TYPE: Med Student/Res Case Rep Postr PRESENTED ON: October 18-21, 2020 INTRODUCTION: Preceding the advent of effective antimicrobial regimens, “collapse therapy” was the mainstay of treatment for tuberculosis. This therapy became obsolete after the discovery of potent multi-drug regimens in the 1950s. However, collapse therapy represents an important historical treatment that was lifesaving to many patients in the 1930s and 1940s. CASE PRESENTATION: A 97-year-old female presented to the emergency department with acute onset dyspnea, worsening over several days. She was tachycardic to 163 bpm. Physical examination revealed right hemithoracic basilar crackles and poor air movement over the entire left hemithorax. EKG revealed multi-focal atrial tachycardia. Troponins were negative, however pro-BNP was elevated at 2950 ng/L. Chest radiography revealed left hemithoracic mass-like opacification with calcific margins. Chest computed tomography confirmed a well-circumscribed, peripherally calcified left hemithoracic mass. Contents of the mass were heterogeneous with areas measuring -60 HU, suggestive of lipoid material. Right-sided pleural effusion was also noted. She disclosed that she had been diagnosed with tuberculosis in her twenties and spent 5 months in a sanatorium prior to undergoing surgery. She denied post-operative complications. Her dyspnea resolved with diuresis and rate control. She was discharged home in improved condition. DISCUSSION: Collapse therapy was thought to provide the lung with much-needed rest and promote healing. In reality, alterations in oxygen tension created an unfavorable environment for the obligate aerobe. Plomage thoracoplasty was a form of collapse therapy in which apicolysis was achieved through insertion of inert materials, called plombe, usually into the extrapleural space. Materials used included paraffin wax, lucite spheres, gauze, sponges and mineral or vegetable oil. Oleothorax refers specifically to plomage utilizing mineral or vegetable oil. The intra-operative mortality of this historic therapy was 10%. Successful sputum conversion rates ranged from 61-93%. Immediate complications included infection and failure to heal. Long term complications include fistulization with surrounding structures, erosion of major vessels and malignancy. Oil plombe was intended to be aspirated after sputum conversion, usually after 24 to 48 months. However, some patients were lost to follow up after release from sanatoriums. CONCLUSIONS: As patients who underwent collapse therapy continue to age, familiarity with these therapies will diminish. Importantly, extensively drug resistant (XDR) tuberculosis may herald the return of surgical treatment for tuberculosis. Thus, we encourage awareness of the historic treatments for tuberculosis and its future therapeutic potential. Reference #1: Murray JF, Schraufnagel DE, Hopewell PC. Treatment of Tuberculosis. A Historical Perspective. Annals of the American Thoracic Society. 2015;12(12):1749-1759. doi:10.1513/annalsats.201509-632ps. Reference #2: Weissberg D, Weissberg D. Late Complications of Collapse Therapy for Pulmonary Tuberculosis. Chest. 2001;120(3):847-851. doi:10.1378/chest.120.3.847. Reference #3: Kolkailah AA, Fugar S, Rey-Mendoza J, Campagnoli T, Fakhran S. Revisiting the evolution of tuberculosis therapy: historical reflections in the modern era. Oxford Medical Case Reports. 2018;2018(9). doi:10.1093/omcr/omy055. DISCLOSURES: No relevant relationships by Victoria Andarcia, source=Web Response No relevant relationships by Joe Harb, source=Web Response No relevant relationships by Joseph Henain, source=Web Response No relevant relationships by Anneka Hutton, source=Web Response No relevant relationships by Navneet Kaur, source=Web Response

Tailoring bacterial cellulose structure through CRISPR interference-mediated downregulation of galU in Komagataeibacter xylinus CGMCC 2955.

Diverse applications of bacterial cellulose (BC) have different requirements in terms of its structural characteristics. culturing Komagataeibacter xylinus CGMCC 2955, BC structure changes with alterations in oxygen tension. Here, the K. xylinus CGMCC 2955 transcriptome was analyzed under different oxygen tensions. Transcriptome and genome analysis indicated that BC structure is related to the rate of BC synthesis and cell growth, and galU is an essential gene that controls the carbon metabolic flux between the BC synthesis pathway and the pentose phosphate (PP) pathway. The CRISPR interference (CRISPRi) system was utilized in K. xylinus CGMCC 2955 to control the expression levels of galU. By overexpressing galU and interfering with different sites of galU sequences using CRISPRi, we obtained strains with varying expression levels of galU (3.20-3014.84%). By testing the characteristics of BC, we found that the porosity of BC (range: 62.99-90.66%) was negative with galU expression levels. However, the crystallinity of BC (range: 56.25-85.99%) was positive with galU expression levels; galU expression levels in engineered strains were lower than those in the control strains. Herein, we propose a new method for regulating the structure of BC to provide a theoretical basis for its application in different fields.

The impact of preterm adversity on cardiorespiratory function.

What is the topic of this review? We review the influence of prematurity on the cardiorespiratory system and examine the common sequel of alterations in oxygen tension, and immune activation in preterm infants. What advances does it highlight? The review highlights neonatal animal models of intermittent hypoxia, hyperoxia and infection that contribute to our understanding of the effect of stress on neurodevelopment and cardiorespiratory homeostasis. We also focus on some of the important physiological pathways that have a modulatory role on the cardiorespiratory system in early life. Preterm birth is one of the leading causes of neonatal mortality. Babies that survive early-life stress associated with immaturity have significant prevailing short- and long-term morbidities. Oxygen dysregulation in the first few days and weeks after birth is a primary concern as the cardiorespiratory system slowly adjusts to extrauterine life. Infants exposed to rapid alterations in oxygen tension, including exposures to hypoxia and hyperoxia, have altered redox balance and active immune signalling, leading to altered stress responses that impinge on neurodevelopment and cardiorespiratory homeostasis. In this review, we explore the clinical challenges posed by preterm birth, followed by an examination of the literature on animal models of oxygen dysregulation and immune activation in the context of early-life stress.

Abstract 5034: Time-lapse analysis of drug response and invasive capacity using patient-derived CRC microfluidic 3D cancer models under oxygen-controlled conditions

Abstract The development of relevant, reliable, human-derived, and cost-effective cellular models is a present need to bring precision medicine to fruition and to accelerate drug discovery. 3D cultures show robust genomic stability and tissue-specific gene expression with high fidelity to their tissue of origin, making them ideal for preserving healthy and cancer tissue molecular and morphological traits. Our objective is to expand the number of relevant human cancer models available and implement methods that allow cellular response quantification of 3D cultures. We sought to establish and implement 3D cell-based assays suitable for detection of known molecular biomarkers in cancer using spherical cancer models (multicellular tumor spheroids and tissue-derived tumor spheres). We validate our procedures by detecting colorectal cancer (CRC) biomarkers both in patient-derived cultures and cell-lines (HCT116, HT29, LS174T). We expanded the study's scope to the analysis of specific CRC transcriptional and proteomic signatures in 3D. To this end, we employ primary cultures derived from CRC patients, and cell lines. Our methodology takes advantage of multiplex antibody microarrays to detect proteomic levels of 10 metalloproteinases of which MMP-13 and MMP- 9, as well as of surface proteins known to be involved in colorectal cancer invasion. Alterations in oxygen tension are milestones in tumor progression, and low oxygen tension (hypoxia) has been demonstrated in CRC. The Hypoxia Inducible Factor (HIF) transcription factor family is central to the response to hypoxic stress and is correlated with CRC carcinogenesis, invasion, VEGF expression, and poorer diagnosis. To increase the relevance of our model we use low oxygen conditions (3-5% physioxia conditions), and atmospheric oxygen levels (normoxia conditions) finding relevant differences at the proteomic, transcriptional and miRNA levels (also verified by qRT-PCR). We test the spherical cancer models on microfluidics chip and assess their vessel invasion capacity in normoxia and hypoxia, finding a correlation between hypoxia stress response and augmented invasiveness. Additionally, we test cellular responses to standard drugs and vasculature invasive capacity by time-lapse microscopy on-chip. We design, develop and validate cellular assays for human cancer 3D culture generation, long-term maintenance and analysis. We analyze and quantify cellular responses to cytotoxic drugs, image and quantify invasion in fluidic chambers, determine levels of apoptosis, cell proliferation. We demonstrate that a combination of controllable assays can successfully be used for identification of biomarker expression and compound screening in preclinical studies. 3D models are, therefore, a cost-effective in vitro model capable of recapitulating reliably physiological responses. Citation Format: Dora Sabino, Isabelle Fixe, Alexandra Foucher, Eric Mennesson, Nadia Normand. Time-lapse analysis of drug response and invasive capacity using patient-derived CRC microfluidic 3D cancer models under oxygen-controlled conditions [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 5034.

Hypoxia and metabolic adaptation of cancer cells.

Low oxygen tension (hypoxia) is a pervasive physiological and pathophysiological stimulus that metazoan organisms have contended with since they evolved from their single-celled ancestors. The effect of hypoxia on a tissue can be either positive or negative, depending on the severity, duration and context. Over the long-term, hypoxia is not usually consistent with normal function and so multicellular organisms have had to evolve both systemic and cellular responses to hypoxia. Our reliance on oxygen for efficient adenosine triphosphate (ATP) generation has meant that the cellular metabolic network is particularly sensitive to alterations in oxygen tension. Metabolic changes in response to hypoxia are elicited through both direct mechanisms, such as the reduction in ATP generation by oxidative phosphorylation or inhibition of fatty-acid desaturation, and indirect mechanisms including changes in isozyme expression through hypoxia-responsive transcription factor activity. Significant regions of cancers often grow in hypoxic conditions owing to the lack of a functional vasculature. As hypoxic tumour areas contain some of the most malignant cells, it is important that we understand the role metabolism has in keeping these cells alive. This review will outline our current understanding of many of the hypoxia-induced changes in cancer cell metabolism, how they are affected by other genetic defects often present in cancers, and how these metabolic alterations support the malignant hypoxic phenotype.

CEACAM1 confers resistance toward oxygen-induced vessel damage in a mouse model of retinopathy of prematurity.

To determine a functional role for the carcinoembryonic antigen-related cell-adhesion molecule 1 (CEACAM1) in retinal neovascularization in a mouse model of oxygen-induced retinopathy (OIR). In a 21/75/21% OIR mouse model, retinal neovascularization was compared in wild-type and CEACAM1-deficient mice. Animals were housed under normoxic conditions until postnatal day 7, followed by exposure to 75% oxygen for 5 days, and further housing under normoxic conditions. Retinal vascular anatomy, vaso-obliteration, neovascularization, and tuft formation were characterized and quantified in retinal flat-mounts from untreated mice and from experimental mice during and at different time points after exposure to high oxygen levels. The vascular network was stained with fluorescently labeled isolectin B4. Mice deficient in CEACAM1 did not present any apparent abnormalities in their postnatal retinal vascular development under normoxic housing conditions. However, after hyperoxia and under relative hypoxic conditions, retinal neovascularization and tuft formation were aggravated in the mutant. Congruently, revascularization and vessel maturation were delayed in CEACAM1-deficient mice whereas in wild-type mice, tuft regression and vascular remodeling occurred efficiently after exposure to high oxygen levels. Our report describes a functional role for CEACAM1 in retinal neovascularization in a mouse model of OIR. This is the first study demonstrating that CEACAM1 enhances vascular remodeling and tuft regression by increasing endothelial resistance to alterations in oxygen tension, thus accelerating vascular recovery after systemic hypoxia.

High-resolution genome-wide mapping of HIF-binding sites by ChIP-seq

AbstractHypoxia-inducible factor (HIF) regulates the major transcriptional cascade central to the response of all mammalian cells to alterations in oxygen tension. Expression arrays indicate that many hundreds of genes are regulated by this pathway, controlling diverse processes that in turn orchestrate both oxygen delivery and utilization. However, the extent to which HIF exerts direct versus indirect control over gene expression together with the factors dictating the range of HIF-regulated genes remains unclear. Using chromatin immunoprecipitation linked to high throughput sequencing, we identify HIF-binding sites across the genome, independently of gene architecture. Using gene set enrichment analysis, we demonstrate robust associations with the regulation of gene expression by HIF, indicating that these sites operate over long genomic intervals. Analysis of HIF-binding motifs demonstrates sequence preferences outside of the core RCGTG-binding motif but does not reveal any additional absolute sequence requirements. Across the entire genome, only a small proportion of these potential binding sites are bound by HIF, although occupancy of potential sites was enhanced approximately 20-fold at normoxic DNAse1 hypersensitivity sites (irrespective of distance from promoters), suggesting that epigenetic regulation of chromatin may have an important role in defining the response to hypoxia.

The role of hypoxia and HIF-dependent signalling events in rheumatoid arthritis

An adequate supply of oxygen and nutrients is essential for survival and metabolism of cells, and consequentially for normal homeostasis. Alterations in tissue oxygen tension have been postulated to contribute to a number of pathologies, including rheumatoid arthritis (RA), in which the characteristic synovial expansion is thought to outstrip the oxygen supply, leading to areas of synovial hypoxia and hypoperfusion. Indeed, the idea of a therapeutic modality aimed at 'starving' tissue of blood vessels was born from the concept that blood vessel formation (angiogenesis) is central to efficient delivery of oxygen to cells and tissues, and has underpinned the development of anti-angiogenic therapies for a range of cancers. An important and well characterized 'master regulator' of the adaptive response to alterations in oxygen tension is hypoxia-inducible factor (HIF), which is exquisitely sensitive to changes in oxygen tension. Activation of the HIF transcription factor signalling cascade leads to extensive changes in gene expression, which allow cells, tissues and organisms to adapt to reduced oxygenation. One of the best characterized hypoxia-responsive genes is the angiogenic stimulus vascular endothelial growth factor, expression of which is dramatically upregulated by hypoxia in many cells types, including RA synovial membrane cells. This leads to an apparent paradox, with the abundant synovial vasculature (which might be expected to restore oxygen levels to normal) occurring nonetheless together with regions of synovial hypoxia. It has been shown in a number of studies that vascular endothelial growth factor blockade is effective in animal models of arthritis; these findings suggest that hypoxia may activate the angiogenic cascade, thereby contributing to RA development. Recent data also suggest that, as well as activating angiogenesis, hypoxia may regulate many other features that are important in RA, such as cell trafficking and matrix degradation. An understanding of the biology of the HIF transcription family may eventually lead to the development of therapies that are aimed at interfering with this key signalling pathway, and hence to modulation of hypoxia-dependent pathologies such as RA.

Regulation of Photosystem Synthesis in Rhodobacter capsulatus

Control of the synthesis of the purple bacterial photosystem has been an active area of research for many decades. The period of the 1960s involved physiological characterization of photosystem synthesis under different growth conditions. In the 1970s Barry Marrs and coworkers developed genetic tools that were used to define and map genes needed for synthesis of photopigments. The 1980s was a period of cloning and physical mapping of photosynthesis genes onto the chromosome, the demonstration that regulation of photosystem synthesis involved transcriptional control of gene expression, and sequence analysis of photosynthesis genes. The 1990s was a period of the discovery and characterization of regulatory genes that control synthesis of the photosystem in response to alterations in oxygen tension and light intensity. Although several photosynthetic organisms are mentioned for comparison and contrast, the focus of this minireview is on Rhodobacter capsulatus.

Polymorphonuclear leucocyte (PMN)-derived inflammatory cytokines--regulation by oxygen tension and extracellular matrix.

The kinetics of IL-8, tumour necrosis factor-alpha (TNF-alpha) and IL-1 beta release by PMN adhered to fibronectin, laminin or plastic for 24 h in response to continuous stimulation with lipopolysaccharide (LPS; 50 ng/ml), N-formyl-Met-Leu-Phe (fMLP; 100 mM), or phorbol myristate acetate (PMA; 10 ng/ml), was investigated under altered oxygen tension conditions. Cell supernatants were sampled for cytokine content every 6 h and measured by ELISA. IL-8 was the most abundant cytokine, produced in a range of up to 5.4 ng/ml; TNF-alpha and IL-1 beta were produced in a range of up to 1 ng/ml. During normoxia, LPS was the most potent stimulus, inducing the release of each cytokine, while fMLP showed a less pronounced effect on IL-8 and IL-1 beta production and markedly inhibited TNF-alpha production. PMA markedly suppressed IL-8 and IL-1 beta release and failed to induce any release of TNF-alpha. Hypoxia had an overall inhibitory effect on cytokine release except for PMA-induced IL-1 beta release, and hypoxia/reoxygenation had a significant up-regulating effect except for a further inhibition of fMLP-induced release of TNF-alpha. Integrinmatrix protein ligation differentiated both spontaneous and externally induced cytokine release and its sensitivity to alteration in oxygen tension. Thus the process of PMN elaboration of inflammatory cytokines is controlled on multiple levels of signal transduction, differentiated by integrin-extracellular matrix interactions, and is sensitive to alterations in microenvironmental oxygen tension.

AppA Is a Blue Light Photoreceptor that Antirepresses Photosynthesis Gene Expression in Rhodobacter sphaeroides

Photosynthetic bacteria regulate photosystem synthesis in response to alterations in oxygen tension and light intensity. In this study we show that the PpsR repressor from Rhodobacter sphaeroides binds to DNA in a redox-dependent manner through the formation/breakage of an intramolecular disulfide bond. We also demonstrate that PpsR is antagonized by the flavin-containing antirepressor, AppA, that is capable of breaking the disulfide bond in oxidized PpsR as well as forming a stable AppA-PpsR 2 antirepressor-repressor complex. Blue light excitation of AppA induces a photocycle that is characterized by a long-lived red-shifted absorbance of the flavin. Light-excited AppA was found to be incapable of forming the AppA-PpsR 2 antirepressor complex. These results establish AppA as a transcription factor that controls both redox and blue light repression of photosystem gene expression by mediating DNA binding activity of PpsR.

Analysis of the puc operon promoter from Rhodobacter capsulatus.

Expression of the Rhodobacter capsulatus puc operon, which codes for structural polypeptides of the light-harvesting-II peripheral antenna complex, is highly regulated in response to alterations in oxygen tension and light intensity. To obtain an understanding of the puc promoter region we report the high-resolution 5' mapping of the puc mRNA transcriptional start site and DNA sequence analysis of the puc upstream regulatory sequence (pucURS). A sigma70-type promoter sequence was identified (pucP1) which has a high degree of sequence similarity with carotenoid and bacteriochlorophyll biosynthesis promoters. Inspection of the DNA sequence also indicated the presence of two CrtJ and four integration host factor (IHF) binding sites. Transcriptional fusions of the pucURS fused to lacZ also confirmed that puc promoter activity is regulated by the transcriptional regulators IHF, CrtJ, and RegA. Gel retardation analysis using cell extracts indicates that mutations in IHF and RegA disrupt protein binding to DNA fragments containing the pucURS.

DNA binding characteristics of CrtJ. A redox-responding repressor of bacteriochlorophyll, carotenoid, and light harvesting-II gene expression in Rhodobacter capsulatus.

Previous genetic analysis indicated that the photosynthesis gene cluster from Rhodobacter capsulatus coded for the transcription factor, CrtJ, that is responsible for aerobic repression of bacteriochlorophyll, carotenoid, and light harvesting-II gene expression. In this study, we have heterologously overexpressed and purified CrtJ to homogeneity and shown by gel mobility shift assays that CrtJ is biologically active. DNase I footprint analysis confirms molecular genetic studies by showing that CrtJ binds to conserved palindromic sequences that overlap the -10 and -35 promoter regions of the bchC operon. Graphs of the percentage of DNA bound versus protein concentration show sigmoidal curves, which is highly indicative of cooperative binding of CrtJ to the two palindromic sites. A binding constant for interaction of CrtJ with the palindrome that spans the -10 region was calculated to be 4.8 x 10(-9) M, whereas affinity for the palindrome that spans the -35 region was found to be 2.9 x 10(-9) M. Binding of CrtJ to the bchC promoter region was also found to be redox-sensitive, with CrtJ exhibiting a 4.5-fold higher binding affinity under oxidizing versus reducing conditions.

Altered Oxygen Tension Modulates Cytokine-Induced Signal Transduction in Polymorphonuclear Leukocytes: Regulation of the GPLCPathway

The purpose of these studies was to examine the sensitivity of the PIP2–PLC-transducing pathway (GPLC) and its relationship to the respiratory burst in human polymorphonuclear leukocytes (PMN) stimulated by IL-8, TNF-α, or IL-1β during sequential changes in buffer oxygen tension from normoxia (pO2= 180–200 mm Hg), to hypoxia (pO2< 30 mm Hg) and then reoxygenation (pO2> 140 mm Hg). Our specific hypothesis was that altered oxygen tensions would regulate the GPLCpathway in human PMN. GPLCactivity was assayed by investigating phospholipase C activity by measuring inositol phosphates and diacylglycerol (DAG) formation. Respiratory burst activity was assayed as O−2production and NADPH oxidase activation in intact PMN and in a cell-free system, respectively, and correlated separately to both early and late DAG production. At 1 min, DAG formation during normoxia was decreased by IL-8 plus fibronectin while hypoxia had no regulatory effect on control of DAG formation by any of the cytokines. In contrast to early DAG formation, hypoxia significantly downregulated late DAG formation induced by buffer without fibronectin, IL-8 plus fibronectin, and IL-1β with or without fibronectin. Hypoxia/reoxygenation in and of itself significantly increased DAG formation vs levels seen in the presence or absence of IL-8, TNF-α, or IL-1β with or without fibronectin. Changes in early DAG production during the alterations in oxygen tension correlated best with corresponding changes in O−2production in intact cells, whereas late DAG production correlated best with NADPH oxidase activation assayed in the cell-free system. Thus, changes in oxygen tension can directly modulate the extent of the PMN response to stimulation by IL-8, TNF-α, or IL-1β and the GPLC-receptor pathway is particularly regulated by physiologically relevant periods of hypoxia/reoxygenation.

Regulation of erythropoietin gene expression.

The study of erythropoietin gene expression provides a paradigm for understanding gene regulation in response to hypoxia. The sensor for detecting alterations in oxygen tension appears to be a heme protein. Ongoing transcription and protein synthesis are necessary for hypoxic induction of erythropoietin messenger RNA. In the past few years, considerable progress has been made in the identification and characterization of cis-acting elements and trans-acting factors that contribute to erythropoietin gene expression. The erythropoietin promoter and 3' enhancer function synergistically in response to hypoxia. Whereas hypoxia-inducible factor 1 specifically binds to the 3' enhancer conferring hypoxic induction, hepatic nuclear factor 4 interacts with the promoter as well as the 3' enhancer for stimulus- and tissue-specific induction of the erythropoietin gene. In addition, a segment in the 3' untranslated region contributes to the relatively rapid turnover of erythropoietin messenger RNA.

Temporal correlation between intrauterine oxygen tension and endometrial H4-lactic dehydrogenase in the guinea pig.

Ambient oxygen tension can alter carbohydrate metabolism of uterine tissue in vitro by modifying the relative proportions of “H” and “M” subunits of lactic dehydrogenase: low oxygen tension favors production of M-LDH wheras elevated pO2 stimulates H-LDH synthesis (Dawson, Goodfriend and Kaplan, 1964). Previous studies have demonstrated that, in the rat, the luminal surface of the uterus is normally exposed in vivo to alterations in oxygen tension during the estrous cycle (Mitchell and Yochim, 1968a) and pregnancy (Yochim and Mitchell, 1968). Since O2 tension modifies lactic dehydrogenase isozyme distribution, it was hyposthesized (Yochim and Mitchell, 1968) and subsequently substantiated (Yochim, 1975) that increased intrauterine pO2 favors the synthesis of H4-LDH in the endometrium and results in increased oxidative metabolism. Thus, in the rat, the concentration of oxygen to which the endometrium is exposed appears to exert a marked effect on LDH isozyme activity. Subsequently, cyclic alterations in intrauterine oxygen tension have also been observed in the guinea pig (Garris and Mitchell, 1979). The following study was therefore undertaken to determine if the relative proportion of H-LDH present in the endometrium of the guinea pig also correlates with changes in intrauterine oxygen tension.

Oxygen tension alterations in the intervertebral disc as a response to changes in the arterial blood.

Measurements of oxygen tension in the canine lumbar intervertebral disc, by the use of a polarographic oxygen electrode, were performed. The oxygen tension in the arterial blood was changed by regulating the oxygen concentration in the inspired air. The alterations in oxygen tension in the nucleus pulposus, as a function of distance to the vertebral endplate were determined. The response times registered in the disc matrix were relatively short (within five min.), which implies an efficient solute transport from the vertebral blood pool underneath the hyaline cartilage into the avascular intervertebral disc.

Microvascular pressure distribution and responses of pulmonary allografts and cheek pouch arterioles in the hamster to oxygen.

Despite extensive investigations of the pulmonary circulation using both in vitro and in vitro preparations, few direct microcirculatory studies have been made. Consequently, the mechanisms involved in the response of the pulmonary microvasculature to changes in oxygen tension remain unclear. The present study represents the first direct observation of the responses in pulmonary microvessels to alterations in oxygen tension. Neonatal lung tissue was transplanted into the hamster cheek pouch using a chamber technique. Both tissues were characterized with respect to their microvascular pressure profile and vascular response to hypoxia. The results showed the two tissues to be remarkably different. Small pulmonary and cheek pouch arterioles exhibited opposite responses to changes in oxygen environment; hypoxia elicited a constriction of pulmonary arterioles, but a dilation of cheek pouch arterioles. Pulmonary capillary pressure, although comparable to that measured in the intact lung (13 mm Hg), was substantially lower than cheek pouch capillary pressure, which was within the range of that described for several systemic vascular beds. The microcirculatory effects of oxygen on both tissues were confined to the arteriolar segments. The characteristics of this pulmonary microcirculation are such that it is a unique model for further physiological and pharmacological studies.