Adrenomedullin gene expression is developmentally regulated and induced by hypoxia in rat ventricular cardiac myocytes

Exposure to normobaric hypoxia shapes the acute inflammatory response in human whole blood cells in vivo

Cells of the immune defence, especially leukocytes, often have to perform their function in tissue areas that are characterized by oxygen deficiency, so-called hypoxia. Physiological hypoxia significantly affects leukocyte function and controls the innate and adaptive immune response mainly through transcriptional gene regulation via the hypoxia-inducible factors (HIFs). Multiple pathogens including components of bacteria, such as lipopolysaccharides (LPS) trigger the activation of leukocytes. HIF pathway activation enables immune cells to adapt to both hypoxic environments in physiological and inflammatory settings and modulates immune cell responses through metabolism changes and crosstalk with other immune-relevant signalling pathways. To study the mutual influence of both processes in vivo, we used a human endotoxemia model, challenging participants with an intravenous LPS injection post or prior to a 4-h stay in a hypoxic chamber with normobaric hypoxia of 10.5% oxygen. We analysed changes in gene expression in whole blood cells and determined inflammatory markers to unveil the crosstalk between both processes. Our investigations showed differentially altered gene expression patterns of HIF and target genes upon in vivo treatment with LPS and hypoxia. Further, we found evidence for effects of hypoxic priming upon inflammation in combination with immunomodulatory effects in whole blood cells in vivo. Our work elucidates the complex interplay of hypoxic and inflammatory HIF regulation in human immune cells and offers new perspectives for further clinical research.

Regulation of cells of the arterial wall by hypoxia and its role in the development of atherosclerosis

The cell's response to hypoxia depends on stabilization of the hypoxia-inducible factor 1 complex and transactivation of nuclear factor kappa-B (NF-κB). HIF target gene transcription in cells resident to atherosclerotic lesions adjoins a complex interplay of cytokines and mediators of inflammation affecting cholesterol uptake, migration, and inflammation. Maladaptive activation of the HIF-pathway and transactivation of nuclear factor kappa-B causes monocytes to invade early atherosclerotic lesions, maintaining inflammation and aggravating a low-oxygen environment. Meanwhile HIF-dependent upregulation of the ATP-binding cassette transporter ABCA1 causes attenuation of cholesterol efflux and ultimately macrophages becoming foam cells. Hypoxia facilitates neovascularization by upregulation of vascular endothelial growth factor (VEGF) secreted by endothelial cells and vascular smooth muscle cells lining the arterial wall destabilizing the plaque. HIF-knockout animal models and inhibitor studies were able to show beneficial effects on atherogenesis by counteracting the HIF-pathway in the cell wall. In this review the authors elaborate on the up-to-date literature on regulation of cells of the arterial wall through activation of HIF-1α and its effect on atherosclerotic plaque formation.

Plasma Adrenomedullin, Allelic Variations in the ADM Gene, and Risk for Lower-Limb Amputation in People With Type 2 Diabetes

OBJECTIVE

Patients with diabetes have an increased risk for lower-limb amputation (LLA), but biomarkers to assess risk of LLA are lacking. Adrenomedullin (ADM) is a vasodilator peptide that also plays a role in fluid and electrolyte homeostasis in the kidney, increasing natriuresis and diuresis. ADM was shown to be associated with cardiovascular and renal events in diabetes, but it was not investigated in terms of LLA risk. We investigated the hypothesis that ADM is associated with LLA in people with type 2 diabetes.

RESEARCH DESIGN AND METHODS

We studied 4,375 participants in the DIABHYCAR and SURDIAGENE cohorts (men, 68%; mean 66 years of age; mean duration of diabetes 12 years; and median follow-up 5.3 years). Plasma midregional proadrenomedullin (MR-proADM; a surrogate for ADM) was measured by immunofluorescence. Five single nucleotide polymorphisms (SNPs) in the ADM gene region were genotyped.

RESULTS

LLA requirement during follow-up by increasing tertiles of plasma MR-proADM distribution was 1.0% (tertile 1 [T1]), 2.3% (T2), and 4.4% (T3) (P < 0.0001). In Cox multivariate analysis, the adjusted hazard ratio (95% CI) for LLA was 4.40 (2.30-8.88) (P < 0.0001) for T3 versus T1. Moreover, MR-proADM significantly improved indices for risk stratification of LLA. Four SNPs were associated with plasma MR-proADM concentration at baseline and with LLA during follow-up. Alleles associated with higher MR-proADM were associated with increased LLA risk.

CONCLUSIONS

We observed associations of plasma MR-proADM with LLA and of ADM SNPs with plasma MR-proADM and with LLA in people with type 2 diabetes. This pattern of Mendelian randomization supports the causality of the association of ADM with LLA.

Oocyte-specific disruption of adrenomedullin 2 gene enhances ovarian follicle growth after superovulation

BACKGROUND

Adrenomedullin 2 (ADM2), adrenomedullin (ADM), and calcitonin gene-related peptides (α- and β-CGRPs) signal through heterodimeric calcitonin receptor-like receptor/receptor activity-modifying protein 1, 2 and 3 (CLR/RAMP1, 2 and 3) complexes. These peptides are important regulators of neurotransmission, vasotone, cardiovascular development, and metabolic homeostasis. In rodents, ADM is essential for regulating embryo implantation, fetal-placental development, and hemodynamic adaptation during pregnancy. On the other hand, ADM2 was shown to affect vascular lumen enlargement, and cumulus cell-oocyte complex (COC) communication in rodent and bovine ovarian follicles. To investigate whether oocyte-derived ADM2 plays a physiological role in regulating ovarian folliculogenesis, we generated mice with oocyte-specific disruption of the Adm2 gene using a LoxP-flanked Adm2 transgene (Adm2 loxP/loxP) and crossed them with Zp3-Cre mice which carry a zona pellucida 3 (Zp3) promoter-Cre recombinase transgene.

RESULTS

While heterozygous Adm2 +/-/Zp3-Cre and homozygous Adm2 -/-/Zp3-Cre mice were fertile, Adm2 disruption in oocytes significantly increased the number of ovulated oocytes following a superovulation treatment. Oocyte-specific Adm2 disruption also significantly impaired the developmental capacity of fertilized eggs and decreased the size of the corpus luteum following superovulation, perhaps due to a reduction of ovarian cyclin D2-associated signaling.

CONCLUSIONS

The disruption of intrafollicular ADM2 signaling leads to follicular dysfunction. These data suggested that oocyte-derived ADM2 plays a facilitative role in the regulation of hormonal response and follicle growth independent of the closely related ADM and CGRP peptides, albeit in a subtle manner.

Toxicity of the iron siderophore mycobactin J in mouse macrophages: Evidence for a hypoxia response

Mycobacterium tuberculosis, the causative agent of tuberculosis, is an obligate intracellular pathogen that lives within the phagosome of macrophages. Here we demonstrate that the siderophore mycobactin J, produced by the closely related intracellular pathogen Mycobacterium paratuberculosis, is toxic to murine macrophage cells. Its median lethal dose, 10 μM, is lower than that of the iron chelators desferrioxamine B and TrenCAM, an enterobactin analog. To determine the source of this toxicity, we conducted microarray, ELISA, and metabolite profiling experiments. The primary response is hypoxia-like, which implies iron starvation as the underlying cause of the toxicity. This observation is consistent with our recent finding that mycobactin J is a stronger iron chelator than had been inferred from previous studies. Mycobactin J is known to partition into cell membranes and hydrophobic organelles indicating that enhanced membrane penetration is also a likely factor. Thus, mycobactin J is shown to be toxic, eliciting a hypoxia-like response under physiological conditions.

Hypoxia Inducible Factors as Central Players in the Pathogenesis and Pathophysiology of Cardiovascular Diseases

Cardiovascular (CV) diseases are the major cause of death in industrialized countries. The main function of the CV system is to deliver nutrients and oxygen to all tissues. During most CV pathologies, oxygen and nutrient delivery is decreased or completely halted. Several mechanisms, including increased oxygen transport and delivery, as well as increased blood flow are triggered to compensate for the hypoxic state. If the compensatory mechanisms fail to sufficiently correct the hypoxia, irreversible damage can occur. Thus, hypoxia plays a central role in the pathogenesis and pathophysiology of CV diseases. Hypoxia inducible factors (HIFs) orchestrate the gene transcription for hundreds of proteins involved in erythropoiesis, glucose transport, angiogenesis, glycolytic metabolism, reactive oxygen species (ROS) handling, cell proliferation and survival, among others. The overall regulation of the expression of HIF-dependent genes depends on the severity, duration, and location of hypoxia. In the present review, common CV diseases were selected to illustrate that HIFs, and proteins derived directly or indirectly from their stabilization and activation, are related to the development and perpetuation of hypoxia in these pathologies. We further classify CV diseases into acute and chronic hypoxic states to better understand the temporal relevance of HIFs in the pathogenesis, disease progression and clinical outcomes of these diseases. We conclude that HIFs and their derived factors are fundamental in the genesis and progression of CV diseases. Understanding these mechanisms will lead to more effective treatment strategies leading to reduced morbidity and mortality.

Hypoxia-Inducible Factor (HIF): Fuel for Cancer Progression

Hypoxia is an integral part of the tumor microenvironment, caused primarily due to rapidly multiplying tumor cells and a lack of proper blood supply. Among the major hypoxic pathways, HIF-1 transcription factor activation is one of the widely investigated pathways in the hypoxic tumor microenvironment (TME). HIF-1 is known to activate several adaptive reactions in response to oxygen deficiency in tumor cells. HIF-1 has two subunits, HIF-1β (constitutive) and HIF-1α (inducible). The HIF-1α expression is largely regulated via various cytokines (through PI3K-ACT-mTOR signals), which involves the cascading of several growth factors and oncogenic cascades. These events lead to the loss of cellular tumor suppressant activity through changes in the level of oxygen via oxygen-dependent and oxygen-independent pathways. The significant and crucial role of HIF in cancer progression and its underlying mechanisms have gained much attention lately among the translational researchers in the fields of cancer and biological sciences, which have enabled them to correlate these mechanisms with various other disease modalities. In the present review, we have summarized the key findings related to the role of HIF in the progression of tumors.

The influence of hypoxia on the cardiac transcriptomes of two estuarine species - C. variegatus and F. grandis

Increased nutrient loading has led to eutrophication of coastal shelf waters which has resulted in increased prevalence of persistent hypoxic zones - areas in which the dissolved oxygen content of the water drops below 2 mg/L. The northern Gulf of Mexico, fed primarily by the Mississippi River watershed, undergoes annual establishment of one of the largest hypoxic zones in the world. Exposure to hypoxia can induce physiological impacts in fish cardiac systems that include bradycardia, changes in stroke volume, and altered cardiovascular vessel development. While these impacts have been addressed at the functional level, there is little information regarding the molecular basis for these changes. This study used transcriptomic analysis techniques to interrogate the effects of hypoxia exposure on the developing cardiovascular system in newly hatched larvae of two estuarine species that occupy the same ecological niche - the sheepshead minnow (Cyprinodon variegatus) and the Gulf killifish (Fundulus grandis). Results suggest that while differential gene expression is largely distinct between the two species, downstream impacts on pathways and functional responses such as reduced cardiac hypertrophy, modulation of blood pressure, and increased incidence of apoptosis appear to be conserved. Further, differences in the magnitude of these conserved responses may suggest that the length of embryonic development could impart a level of resiliency to hypoxic perturbation in early life stage fish.

Altered expression of ADM and ADM2 by hypoxia regulates migration of trophoblast and HLA-G expression†

Preeclampsia (PE) is a placental disorder caused by endothelial dysfunction via trophoblast inadequate invasion activity. Adrenomedullin (ADM) and ADM2 are multifunctional peptides that can support vascular activity and placental growth. However, correlation between ADMs and trophoblast functions is currently unclear. The objective of this study was to analyze changes in expression of ADMs in placenta and HTR-8/SVneo trophoblast cells under hypoxia and their effects on invasion activity of trophoblast cells and expression of HLA-G. In placental tissues of PE, expression levels of ADM and HLA-G were significantly increased (P < 0.05) whereas expression of ADM2 was decreased compared to that in normal term placenta. Under hypoxia, expression levels of ADM, ADM2, and HLA-G and invasion ability of trophoblast cells were increased in hypoxia-inducible factor-1 (HIF-1α)- dependent manner (P < 0.05). Treatment with ADMs agonists reduced HIF-1α activity whereas enhanced invasion ability under hypoxia. However, they were not changed after cotreatment of ADMs and HIF-1α inhibitor, YC-1, although expression levels of invasion-related genes MMP2, MMP9, and Rac1 were altered (P < 0.05). ADMs also increased HLA-G expression under normoxia whereasADM2 or cotreatment of ADMs under hypoxia attenuated HLA-G expression (P < 0.05). Our findings demonstrate that altered expression of ADMs plays a critical role in placental physiology, especially in trophoblast invasion and immune-modulation under hypoxia.

Adrenomedullin - Current perspective on a peptide hormone with significant therapeutic potential

The peptide hormone adrenomedullin (ADM) consists of 52 amino acids and plays a pivotal role in the regulation of many physiological processes, particularly those of the cardiovascular and lymphatic system. Like calcitonin (CT), calcitonin gene-related peptide (CGRP), intermedin (IMD) and amylin (AMY), it belongs to the CT/CGRP family of peptide hormones, which despite their low little sequence identity share certain characteristic structural features as well as a complex multicomponent receptor system. ADM, IMD and CGRP exert their biological effects by activation of the calcitonin receptor-like receptor (CLR) as a complex with one of three receptor activity-modifying proteins (RAMP), which alter the ligand affinity. Selectivity within the receptor system is largely mediated by the amidated C-terminus of the peptide hormones, which bind to the extracellular domains of the receptors. This enables their N-terminus consisting of a disulfide-bonded ring structure and a helical segment to bind within the transmembrane region and to induce an active receptor confirmation. ADM is expressed in a variety of tissues in the human body and is fundamentally involved in multitude biological processes. Thus, it is of interest as a diagnostic marker and a promising candidate for therapeutic interventions. In order to fully exploit the potential of ADM, it is necessary to improve its pharmacological profile by increasing the metabolic stability and, ideally, creating receptor subtype-selective analogs. While several successful attempts to prolong the half-life of ADM were recently reported, improving or even retaining receptor selectivity remains challenging.

Development of chimeric and bifunctional antagonists for CLR/RAMP receptors

CGRP, adrenomedullin (ADM), and adrenomedullin 2 (ADM2) family peptides are important neuropeptides and hormones for the regulation of neurotransmission, vasotone, cardiovascular morphogenesis, vascular integrity, and feto‒placental development. These peptides signal through CLR/RAMP1, 2 and 3 receptor complexes. CLR/RAMP1, or CGRP receptor, antagonists have been developed for the treatment of migraine headache and osteoarthritis pain; whereas CLR/RAMP2, or ADM receptor, antagonists are being developed for the treatment of tumor growth/metastasis. Based on the finding that an acylated chimeric ADM/ADM2 analog potently stimulates CLR/RAMP1 and 2 signaling, we hypothesized that the binding domain of this analog could have potent inhibitory activity on CLR/RAMP receptors. Consistent with this hypothesis, we showed that acylated truncated ADM/ADM2 analogs of 27–31 residues exhibit potent antagonistic activity toward CLR/RAMP1 and 2. On the other hand, nonacylated analogs have minimal activity. Further truncation at the junctional region of these chimeric analogs led to the generation of CLR/RAMP1-selective antagonists. A 17-amino-acid analog (Antagonist 2–4) showed 100-fold selectivity for CLR/RAMP1 and was >100-fold more potent than the classic CGRP receptor antagonist CGRP8-37. In addition, we showed (1) a lysine residue in the Antagonist 2–4 is important for enhancing the antagonistic activity, (2) an analog consisted of an ADM sequence motif and a 12-amino-acid binding domain of CGRP exhibits potent CLR/RAMP1-inhibitory activity, and (3) a chimeric analog consisted of a somatostatin analog and an ADM antagonist exhibits dual activities on somatostatin and CLR/RAMP receptors. Because the blockage of CLR/RAMP signaling prevents migraine pain and suppresses tumor growth/metastasis, further studies of these analogs, which presumably have better access to the tumor microenvironment and nerve endings at the trigeminal ganglion and synovial joints as compared to antibody-based therapies, may lead to the development of better anti-CGRP therapy and alternative antiangiogenesis therapy. Likewise, the use of bifunctional somatostatin-ADM antagonist analogs could be a promising strategy for the treatment of high-grade neuroendocrine tumors by targeting an antiangiogenesis agent to the neuroendocrine tumor microenvironment.

Adrenomedullin as a Protein with Multifunctional Behavior and Effects in Various Organs and Tissues

In literature, it has been reported that adrenomedullin, which is generally thought to have vasodilator, natriuretic and diuretic effects, is synthesized in almost all body, especially CNS, vascular muscles and endothelium, heart, liver, lung, kidney, gastric mocosa, intestinal endothelium and various blood cells. It has been found that the possible effects of adrenomedullin can be demonstrated directly or indirectly by means of active mediators, neuropeptides, enzymes and hormones. It is also suggested that it regulates the endocrine system by affecting the hypothalamic-pituitary axis. It increases in heart failure, acute coronary syndromes, hypertensive conditions, cerebrovascular accessory, chronic renal failure and periodontitis and decreases in peptic ulcer and intestinal diseases. However, it is still not clear whether increase/decrease in adrenomedullin level is a cause of a disease or is a result of damage due to an illness. This peptide, which could be thought to multifunctional, should be considered as a molecule with genetic coding that may have different effects on different tissues and conditions. For all these reasons, we aimed to review the multifonctional behavior of adrenomedullin in the light of the current literature to pioneer new hypotheses and discuss possible mechanisms.

Adrenomedullin: Continuing to explore cardioprotection

Adrenomedullin (AM), a peptide isolated from an extract of human pheochromocytoma, comprises 52 amino acids with an intramolecular disulfide bond and amidation at the carboxy-terminus. AM is present in various tissues and organs in rodents and humans, including the heart. The peptide concentration increases with cardiac hypertrophy, acute myocardial infarction, and overt heart failure in the plasma and the myocardium. The principal function of AM in the cardiovascular system is the regulation of the vascular tone by vasodilation and natriuresis via cyclic adenosine monophosphate-dependent or -independent mechanism. In addition, AM may possess unique properties that inhibit aldosterone secretion, oxidative stress, apoptosis, and stimulation of angiogenesis, resulting in the protection of the structure and function of the heart. The AM receptor comprises a complex between calcitonin receptor-like receptor (CLR) and receptor activity-modifying protein (RAMP) 2 or 3, and the AM-CLR/RAMP2 system is essential for heart development during embryogenesis. Small-scale clinical trials have proven the efficacy and safety of recombinant AM peptide therapy for heart failure. Gene delivery and a modified AM peptide that prolongs the half-life of the native peptide could be an innovative method to improve the efficacy and benefit of AM in clinical settings. In this review, we focus on the pathophysiological roles of AM and its receptor system in the heart and describe the advances in AM and proAM-derived peptides as diagnostic biomarkers as well as the therapeutic application of AM and modified AM for cardioprotection.

Prognostic value of plasma MR-proADM vs NT-proBNP for heart failure in people with type 2 diabetes: the SURDIAGENE prospective study

AIMS/HYPOTHESIS

N-terminal pro-B-type natriuretic peptide (NT-proBNP) is the gold standard prognostic biomarker for diagnosis and occurrence of heart failure. Here, we compared its prognostic value for the occurrence of congestive heart failure with that of plasma mid-region pro-adrenomedullin (MR-proADM), a surrogate for adrenomedullin, a vasoactive peptide with vasodilator and natriuretic properties, in people with type 2 diabetes.

METHODS

Plasma MR-proADM concentration was measured in baseline samples of a hospital-based cohort of consecutively recruited participants with type 2 diabetes. Our primary endpoint was heart failure requiring hospitalisation.

RESULTS

We included 1438 participants (age 65 ± 11 years; 604 women and 834 men). Hospitalisation for heart failure occurred during follow-up (median 64 months) in 206 participants; the incidence rate of heart failure was 2.5 (95% CI 2.2, 2.9) per 100 person-years. Plasma concentrations of MR-proADM and NT-proBNP were significantly associated with heart failure in a Cox multivariable analysis model when adjusted for age, diabetes duration, history of coronary heart disease, proteinuria and baseline eGFR (_adjHR [95%CI] 1.83 [1.51, 2.21] and 2.20 [1.86, 2.61], respectively, per 1 SD log₁₀ increment, both p < 0.001). MR-proADM contributed significant supplementary information to the prognosis of heart failure when we considered the clinical risk factors (integrated discrimination improvement [IDI, mean ± SEM] 0.021 ± 0.007, p = 0.001) (Table 3). Inclusion of NT-proBNP in the multivariable model including MR-proADM contributed significant complementary information on prediction of heart failure (IDI [mean ± SEM] 0.028 ± 0.008, p < 0.001). By contrast, MR-proADM did not contribute supplementary information on prediction of heart failure in a model including NT-proBNP (IDI [mean ± SEM] 0.003 ± 0.003, p = 0.27), with similar results for heart failure with reduced ejection fraction and preserved ejection fraction.

CONCLUSIONS/INTERPRETATION

MR-proADM is a prognostic biomarker for heart failure in people with type 2 diabetes but gives no significant complementary information on prediction of heart failure compared with NT-proBNP.

Adrenomedullin surges are linked to acute episodes of the systemic capillary leak syndrome (Clarkson disease)

BACKGROUND

Systemic Capillary Leak Syndrome (SCLS) is an extremely rare and life-threatening vascular disorder of unknown etiology. SCLS is characterized by abrupt and transient episodes of hypotensive shock and edema due to plasma leakage into peripheral tissues. The disorder has garnered attention recently because its initial presentation resembles more common vascular disorders including systemic anaphylaxis, sepsis, and acute infections with the Ebola/Marburg family of filoviruses. Although approximately 70-85% of patients with SCLS have a concurrent monoclonal gammopathy of unknown significance (MGUS), any contribution of the paraprotein to acute flares is unknown.

PROCEDURE

To identify circulating factors that might trigger acute SCLS crises, we profiled transcriptomes of paired peripheral blood mononuclear cell fractions obtained from patients during acute attacks and convalescent intervals by microarray.

RESULTS

This study uncovered 61 genes that were significantly up- or downregulated more than 2.5-fold in acute samples relative to respective baselines. One of the most upregulated genes was ADM, which encodes the vasoactive peptide adrenomedullin. A stable ADM protein surrogate (pro-ADM) was markedly elevated in SCLS acute sera compared to remission samples or sera from healthy controls. Monocytes and endothelial cells (ECs) from SCLS subjects expressed significantly more ADM in response to proinflammatory stimuli compared to healthy control cells. Application of ADM to ECs elicited protective effects on vascular barrier function, suggesting a feedback protective mechanism in SCLS.

CONCLUSIONS

Since ADM has established hypotensive effects, differentiating between these dual actions of ADM is crucial for therapeutic applications aimed at more common diseases associated with increased ADM levels.

Hematopoietic Stem Cell Niche in Health and Disease

Regulation of stem cells in adult tissues is a key determinant of how well an organism can respond to the stresses of physiological challenge and disease. This is particularly true of the hematopoietic system, where demands on host defenses can call for an acute increase in cell production. Hematopoietic stem cells receive the regulatory signals for cell production in adult mammals in the bone marrow, a tissue with higher-order architectural and functional organization than previously appreciated. Here, we review the data defining particular structural components and heterologous cells in the bone marrow that participate in hematopoietic stem cell function. Further, we explore the case for stromal-hematopoietic cell interactions contributing to neoplastic myeloid disease. As the hematopoietic regulatory networks in the bone marrow are revealed, it is anticipated that strategies will emerge for how to enhance or inhibit production of specific blood cells. In that way, the control of hematopoiesis will enter the domain of therapies to modulate broad aspects of hematopoiesis, both normal and malignant.

Transcription factor HIF1A: downstream targets, associated pathways, polymorphic hypoxia response element (HRE) sites, and initiative for standardization of reporting in scientific literature

Hypoxia-inducible factor-1α (HIF-1α) has crucial role in adapting cells to hypoxia through expression regulation of many genes. Identification of HIF-1α target genes (HIF-1α-TGs) is important for understanding the adapting mechanism. The aim of the present study was to collect known HIF-1α-TGs and identify their associated pathways. Targets and associated genomics data were retrieved using PubMed, WoS ( http://apps.webofknowledge.com/ ), HGNC ( http://www.genenames.org/ ), NCBI ( http://www.ncbi.nlm.nih.gov/ ), Ensemblv.84 ( http://www.ensembl.org/index.html ), DAVID Bioinformatics Resources ( https://david.ncifcrf.gov /), and Disease Ontology database ( http://disease-ontology.org/ ). From 51 papers, we collected 98 HIF-1α TGs found to be associated with 20 pathways, including metabolism of carbohydrates and pathways in cancer. Reanalysis of genomic coordinates of published HREs (hypoxia response elements) revealed six polymorphisms within HRE sites (HRE-SNPs): ABCG2, ACE, CA9, and CP. Due to large heterogeneity of results presentation in scientific literature, we also propose a first step towards reporting standardization of HIF-1α-target interactions consisting of ten relevant data types. Suggested minimal checklist for reporting will enable faster development of a complete catalog of HIF-1α-TGs, data sharing, bioinformatics analyses, and setting novel more targeted hypotheses. The proposed format for data standardization is not yet complete but presents a baseline for further optimization of the protocol with additional details, for example, regarding the experimental validation.

Regulation of endothelial and epithelial barrier functions by peptide hormones of the adrenomedullin family

The correct regulation of tissue barriers is of utmost importance for health. Barrier dysfunction accompanies inflammatory disorders and, if not controlled properly, can contribute to the development of chronic diseases. Tissue barriers are formed by monolayers of epithelial cells that separate organs from their environment, and endothelial cells that cover the vasculature, thus separating the blood stream from underlying tissues. Cells within the monolayers are connected by intercellular junctions that are linked by adaptor molecules to the cytoskeleton, and the regulation of these interactions is critical for the maintenance of tissue barriers. Many endogenous and exogenous molecules are known to regulate barrier functions in both ways. Proinflammatory cytokines weaken the barrier, whereas anti-inflammatory mediators stabilize barriers. Adrenomedullin (ADM) and intermedin (IMD) are endogenous peptide hormones of the same family that are produced and secreted by many cell types during physiologic and pathologic conditions. They activate certain G-protein-coupled receptor complexes to regulate many cellular processes such as cytokine production, actin dynamics and junction stability. In this review, we summarize current knowledge about the barrier-stabilizing effects of ADM and IMD in health and disease.

Role of neuropeptides in cardiomyopathies

The role of neuropeptides in cardiomyopathy-associated heart failure has been garnering more attention. Several neuropeptides--Neuropeptide Y (NPY), vasoactive intestinal peptide (VIP), calcitonin gene related peptide (CGRP), substance P (SP) and their receptors have been studied in the various types of cardiomyopathies. The data indicate associations with the strength of the association varying depending on the kind of neuropeptide and the nature of the cardiomyopathy--diabetic, ischemic, inflammatory, stress-induced or restrictive cardiomyopathy. Several neuropeptides appear to alter regulation of genes involved in heart failure. Demonstration of an association is an essential first step in proving causality or establishing a role for a factor in a disease. Understanding the complexity of neuropeptide function should be helpful in establishing new or optimal therapeutic strategies for the treatment of heart failure in cardiomyopathies.

Potentiated adrenomedullin-induced vasorelaxation during hypoxia in organ cultured porcine coronary arteries

This study describes the effect of variable oxygen supply on relaxing responses induced by α-calcitonin gene-related peptide (CGRP) and adrenomedullin (AM) on isolated pig coronary arteries in vitro. Organ culture during normoxia (21% of O₂) and hypoxia (5% of O₂) induced a significant leftward shift of the AM concentration-response curves compared with fresh vessels altering the pEC₅₀ values from 6.9 ± 0.04 to 8.0 ± 0.04, whereas the potency (pEC₅₀) of αCGRP was attenuated from 8.8 ± 0.04 to 7.6 ± 0.04. AM₂₂₋₅₂ exerted significant antagonistic effect on AM-induced vasorelaxation in hypoxic and normoxic conditions (apparent pK(B) = 6.8-7.2), whereas no antagonistic effect was observed in fresh and hyperoxic (95%) organ cultured vessels. The antagonistic effect exerted by αCGRP₈₋₃₇ (10⁻⁶·⁵-10⁻⁵·⁵ M) on αCGRP-induced vasodilatation in fresh vessels (derived from Schild plot pA₂ = 7.4 ± 0.1) was unaltered during organ culture. The antagonistic effect exerted by αCGRP₈₋₃₇ (10⁻⁶ M) on AM-induced vasorelaxation in fresh vessels (apparent pK(B) = 7.4 ± 0.1) was absent during hypoxic organ culture. The receptor activity-modifying proteins 1 (RAMP1)/calcitonin-like receptor (CLR) messenger RNA ratio was reduced and RAMP2/CLR messenger RNA ratio was increased during hypoxic and normoxic organ culture compared with fresh vessels. Hypoxic organ culture for 24-72 hours potentiated the AM-induced vasorelaxation through an AM₂₂₋₅₂-sensitive receptor but attenuated the vasorelaxant effect of CGRP through the CGRP receptors. This could possibly be explained by relatively decreased levels of RAMP1, thus favoring RAMP2 + CLR complex (=AM receptor) formation during hypoxic organ culture.

The heart as an endocrine organ

The concept of the heart as an endocrine organ arises from the observation that the atrial cardiomyocytes in the mammalian heart display a phenotype that is partly that of endocrine cells. Investigations carried out between 1971 and 1983 characterised, by virtue of its natriuretic properties, a polypeptide referred to atrial natriuretic factor (ANF). Another polypeptide isolated from brain in 1988, brain natriuretic peptide (BNP), was subsequently characterised as a second hormone produced by the mammalian heart atria. These peptides were associated with the maintenance of extracellular fluid volume and blood pressure. Later work demonstrated a plethora of other properties for ANF and BNP, now designated cardiac natriuretic peptides (cNPs). In addition to the cNPs, other polypeptide hormones are expressed in the heart that likely act upon the myocardium in a paracrine or autocrine fashion. These include the C-type natriuretic peptide, adrenomedullin, proadrenomedullin N-terminal peptide and endothelin-1. Expression and secretion of ANF and BNP are increased in various cardiovascular pathologies and their levels in blood are used in the diagnosis and prognosis of cardiovascular disease. In addition, therapeutic uses for these peptides or related substances have been found. In all, the discovery of the endocrine heart provided a shift from the classical functional paradigm of the heart that regarded this organ solely as a blood pump to one that regards this organ as self-regulating its workload humorally and that also influences the function of several other organs that control cardiovascular function.

Tubular von Hippel-Lindau knockout protects against rhabdomyolysis-induced AKI

Renal hypoxia occurs in AKI of various etiologies, but adaptation to hypoxia, mediated by hypoxia-inducible factor (HIF), is incomplete in these conditions. Preconditional HIF activation protects against renal ischemia-reperfusion injury, yet the mechanisms involved are largely unknown, and HIF-mediated renoprotection has not been examined in other causes of AKI. Here, we show that selective activation of HIF in renal tubules, through Pax8-rtTA-based inducible knockout of von Hippel-Lindau protein (VHL-KO), protects from rhabdomyolysis-induced AKI. In this model, HIF activation correlated inversely with tubular injury. Specifically, VHL deletion attenuated the increased levels of serum creatinine/urea, caspase-3 protein, and tubular necrosis induced by rhabdomyolysis in wild-type mice. Moreover, HIF activation in nephron segments at risk for injury occurred only in VHL-KO animals. At day 1 after rhabdomyolysis, when tubular injury may be reversible, the HIF-mediated renoprotection in VHL-KO mice was associated with activated glycolysis, cellular glucose uptake and utilization, autophagy, vasodilation, and proton removal, as demonstrated by quantitative PCR, pathway enrichment analysis, and immunohistochemistry. In conclusion, a HIF-mediated shift toward improved energy supply may protect against acute tubular injury in various forms of AKI.

Hypoxia-inducible factor 1 and cardiovascular disease

Cardiac function is required for blood circulation and systemic oxygen delivery. However, the heart has intrinsic oxygen demands that must be met to maintain effective contractility. Hypoxia-inducible factor 1 (HIF-1) is a transcription factor that functions as a master regulator of oxygen homeostasis in all metazoan species. HIF-1 controls oxygen delivery, by regulating angiogenesis and vascular remodeling, and oxygen utilization, by regulating glucose metabolism and redox homeostasis. Analysis of animal models suggests that by activation of these homeostatic mechanisms, HIF-1 plays a critical protective role in the pathophysiology of ischemic heart disease and pressure-overload heart failure.

Regulation of HIF-1α activity by overexpression of thioredoxin is independent of thioredoxin reductase status

Under hypoxic conditions, cells activate a transcriptional response mainly driven by hypoxia-inducible factors (HIFs). HIF-1α stabilization and activity are known to be regulated by thioredoxin 1 (Txn1), but how the thioredoxin system regulates the hypoxic response is unknown. By examining the effects of Txn1 overexpression on HIF-1α function in HeLa, HT-29, MCF-7 and EMT6 cell lines, we found that this oxidoreductase did not stabilize HIF-1α, yet could increase its activity. These effects were dependent on the redox function of Txn1. However, Txn1 deficiency did not affect HIF-1α hypoxic-stabilization and activity, and overexpression of thioredoxin reductase 1 (TR1), the natural Txn1 reductase, had no influence on HIF-1α activity. Moreover, overexpression of Txn1 in TR1 deficient HeLa and EMT6 cells was still able to increase HIF-1α hypoxic activity. These results indicate that Txn1 is not essential for HIF-1α hypoxic stabilization or activity, that its overexpression can increase HIF-1α hypoxic activity, and that this effect is observed regardless of TR1 status. Thus, regulation of HIF-1α by the thioredoxin system depends on the specific levels of this system's major components.

Hypoxia-inducible factor-1 (HIF-1): a potential target for intervention in ocular neovascular diseases

Constant oxygen supply is essential for proper tissue development, homeostasis and function of all eukaryotic organisms. Cellular response to reduced oxygen levels is mediated by the transcriptional regulator hypoxia-inducible factor-1 (HIF-1). It is a heterodimeric complex protein consisting of an oxygen dependent subunit (HIF-1α) and a constitutively expressed nuclear subunit (HIF-1β). In normoxic conditions, de novo synthesized cytoplasmic HIF-1α is degraded by 26S proteasome. Under hypoxic conditions, HIF-1α is stabilized, binds with HIF-1β and activates transcription of various target genes. These genes play a key role in regulating angiogenesis, cell survival, proliferation, chemotherapy, radiation resistance, invasion, metastasis, genetic instability, immortalization, immune evasion, metabolism and stem cell maintenance. This review highlights the importance of hypoxia signaling in development and progression of various vision threatening pathologies such as diabetic retinopathy, retinopathy of prematurity, age-related macular degeneration and glaucoma. Further, various inhibitors of HIF-1 pathway that may have a viable potential in the treatment of oxygen-dependent ocular diseases are also discussed.

The oncogene HER2/neu (ERBB2) requires the hypoxia-inducible factor HIF-1 for mammary tumor growth and anoikis resistance

ERBB2, a receptor tyrosine kinase amplified in breast cancer, is a well established regulator of tumor growth in vivo and anoikis resistance leading to disruption of architecture in three-dimensional mammary epithelial acinar structures in vitro. ERBB2 promotes anoikis resistance by maintaining signaling pathways and by rescuing metabolic defects and thus inhibiting accumulation of deleterious reactive oxygen species. Recent evidence suggests that hypoxia, via hypoxia-inducible factors (HIFs), can inhibit anoikis; thus, we hypothesized that HIF-1 may play a role in ERBB2-mediated anoikis resistance and oncogenesis. Indeed, tumors isolated from MMTV-Neu mice contain elevated HIF-1α levels and tumor cells created from MMTV-Neu mice harboring deletion of Hif1α alleles reduced primary tumor growth in vivo. ERBB2 overexpressing cancer cells stabilize HIF under normoxic conditions and require HIF-1 for ERBB2-mediated anchorage-independence, three-dimensional culture growth and anoikis resistance. HIF-1 reduction in ERBB2 cells was associated with induction of the pro-anoikis protein BIM and decreased ERK and AKT signaling during cell detachment. ERBB2-mediated inhibition of metabolic defects, including decreased reactive oxygen species generation in suspension, required HIF-1 expression that was critical for ERBB2-mediated oncogenesis. Gene expression profiling of hypoxic three-dimensional acinar structures identified a number of genes elevated in response to hypoxia that are known ERBB2 targets, suggesting that hypoxic conditions and ERBB2 overexpression share both phenotypic and genetic components via HIF-1 regulation. Thus, our data demonstrate that ERBB2 requires HIF-1 for tumor growth and suggest that HIF is a major downstream regulator of ERBB2 that protects cells from anoikis and metabolic stress caused by decreased matrix adhesion.

Hypoxia-induced arterial differentiation requires adrenomedullin and notch signaling

Hypoxia (low oxygen) and Notch signaling are 2 important regulators of vascular development, but how they interact in controlling the choice between arterial and venous fates for endothelial cells during vasculogenesis is less well understood. In this report, we show that hypoxia and Notch signaling intersect in promotion of arterial differentiation. Hypoxia upregulated expression of the Notch ligand Dll4 and increased Notch signaling in a process requiring the vasoactive hormone adrenomedullin. Notch signaling also upregulated Dll4 expression, leading to a positive feedback loop sustaining Dll4 expression and Notch signaling. In addition, hypoxia-mediated upregulation of the arterial marker genes Depp, connexin40 (Gja5), Cxcr4, and Hey1 required Notch signaling. In conclusion, the data reveal an intricate interaction between hypoxia and Notch signaling in the control of endothelial cell differentiation, including a hypoxia/adrenomedullin/Dll4 axis that initiates Notch signaling and a requirement for Notch signaling to effectuate hypoxia-mediated induction of the arterial differentiation program.

Adrenomedullin and pregnancy: perspectives from animal models to humans

A healthy pregnancy requires strict coordination of genetic, physiologic and environmental factors. The relatively common incidence of infertility and pregnancy complications has resulted in increased interest in understanding the mechanisms that underlie normal versus abnormal pregnancy. The peptide hormone adrenomedullin (AM) has recently been the focus of some exciting breakthroughs in the pregnancy field. Supported by mechanistic studies in genetic animal models, there continues to be a growing body of evidence demonstrating the importance of AM protein levels in a variety of human pregnancy complications. With more extensive mechanistic studies and improved consistency in clinical measurements of AM, there is great potential for the development of AM as a clinically-relevant biomarker in pregnancy and pregnancy complications.

HIF-independent regulation of thioredoxin reductase 1 contributes to the high levels of reactive oxygen species induced by hypoxia

Cellular adaptation to hypoxic conditions mainly involves transcriptional changes in which hypoxia inducible factors (HIFs) play a critical role. Under hypoxic conditions, HIF protein is stabilized due to inhibition of the activity of prolyl hydroxylases (EGLNs). Because the reaction carried out by these enzymes uses oxygen as a co-substrate it is generally accepted that the hypoxic inhibition of EGLNs is due to the reduction in oxygen levels. However, several studies have reported that hypoxic generation of mitochondrial reactive oxygen species (ROS) is required for HIF stabilization. Here, we show that hypoxia downregulates thioredoxin reductase 1 (TR1) mRNA and protein levels. This hypoxic TR1 regulation is HIF independent, as HIF stabilization by EGLNs inhibitors does not affect TR1 expression and HIF deficiency does not block TR1 hypoxic-regulation, and it has an effect on TR1 function, as hypoxic conditions also reduce TR1 activity. We found that, when cultured under hypoxic conditions, TR1 deficient cells showed a larger accumulation of ROS compared to control cells, whereas TR1 over-expression was able to block the hypoxic generation of ROS. Furthermore, the changes in ROS levels observed in TR1 deficient or TR1 over-expressing cells did not affect HIF stabilization or function. These results indicate that hypoxic TR1 down-regulation is important in maintaining high levels of ROS under hypoxic conditions and that HIF stabilization and activity do not require hypoxic generation of ROS.

Midregional Proadrenomedullin for Prediction of Cardiovascular Events in Coronary Artery Disease: Results from the AtheroGene Study

BACKGROUND

Midregional proadrenomedullin (MR-proADM) is a newly identified prognostic marker in heart failure. We evaluated the prognostic impact of MR-proADM in a cohort of patients with symptomatic coronary artery disease according to their clinical presentation.

METHODS

We measured baseline MR-proADM concentrations in 2240 individuals from the prospective AtheroGene study and evaluated the prognostic impact on future fatal and nonfatal cardiovascular events during a follow-up period of 3.6 (1.6) years.

RESULTS

The sample comprised 1355 individuals with stable angina pectoris (SAP) and 885 with acute coronary syndrome (ACS). A cardiovascular event occurred in 192 people. Individuals presenting with SAP had only slightly lower plasma MR-proADM concentrations than those with ACS (0.53 vs 0.55 nmol/L, P = 0.006). MR-proADM showed a moderate association with age, serum N-terminal pro–B-type natriuretic peptide (NT-proBNP), glomerular filtration rate, serum C-reactive protein, hypertension, diabetes, and prevalent multivessel disease (all P &lt; 0.0005). Individuals suffering from a cardiovascular event had higher MR-proADM concentrations at baseline in both groups (SAP 0.63 vs 0.53 nmol/L and ACS 0.65 nmol/L vs 0.55 nmol/L, both P &lt; 0.0005). Cox regression analysis incorporating various variables of cardiovascular risk and NT-proBNP revealed a hazard ratio of 1.4 (95% CI 1.2–1.6; P &lt; 0.0005) per increment of MR-proADM by 1SD. In risk models for secondary prevention, MR-proADM provided information comparable to that of NT-proBNP.

CONCLUSIONS

MR-proADM is an independent predictor for future cardiovascular events in patients with symptomatic coronary artery disease, providing information comparable to NT-proBNP for secondary risk stratification.

Adrenomedullin interacts with VEGF in endometrial cancer and has varied modulation in tumours of different grades

OBJECTIVE

Endometrial cancer, in developed countries, is the most common malignancy of the female genital tract. Surgery and radiotherapy are successful in many patients but systemic and recurrent diseases have no consistently effective treatments, and for high grade advanced disease the prognosis is poor. The study investigated characteristics of adrenomedullin in endometrial cancer to assist in identifying targets for developing treatments.

METHODS

Endometrial samples of women with and without cancer, and the Ishikawa cell line were used to investigate adrenomedullin mRNA regulation, peptide expression, adrenomedullin secretion and effects of adrenomedullin on VEGF secretion.

RESULTS

Expression of adrenomedullin mRNA was upregulated compared to that in healthy post-menopausal endometria. Adrenomedullin secretion was increased by cobalt chloride in this study. Secretion was reduced by the naturally-occurring compounds, (-)-epigallocatechin gallate (EGCG) and 3,4',5-trihydroxystilbene (resveratrol), which we have previously demonstrated to also suppress VEGF secretion in endometrial tumour tissue. We noted, for the first time, that adrenomedullin enhanced VEGF secretion from tumour cells.

CONCLUSIONS

Increased adrenomedullin expression may result in amplifying both tumorigenic and angiogenic activities. A substantial impact on growth of tumours may result in vivo as a consequence of the synergism between adrenomedullin and VEGF. Adrenomedullin, which has altered cellular characteristics in tumour compared to healthy tissue, offers an understudied target with potential to modify endometrial cancer behaviour, complementing other treatments.

Many mechanisms mediating mobilization: an alliterative review

PURPOSE OF REVIEW

Blood cell production is maintained by hematopoietic stem cells (HSCs) that reside in specialized niches within bone marrow. Treatment with granulocyte-colony stimulating factor (G-CSF) causes HSC egress from bone marrow niches and trafficking to the peripheral blood, a process termed 'mobilization'. Although the mobilization phenomenon has been known for some time and is utilized clinically to acquire HSC for transplant, the mechanisms mediating HSC release are not completely understood. We discuss recent advances and controversies in defining the mechanisms responsible for G-CSF-induced mobilization.

RECENT FINDINGS

New reports define a role for resident monocytes/macrophages in maintaining niche cells, which is diminished after G-CSF treatment, suggesting a new mechanism for mobilization. Although osteoblasts have been reported to be a primary component of the HSC niche, new results suggest a unique niche composed of innervated mesenchymal stem cells. Modulating bioactive lipid signaling also facilitates mobilization, and may define a future therapeutic strategy.

SUMMARY

Hematopoietic mobilization by G-CSF is primarily mediated by alterations to the bone marrow niche by both direct and indirect mechanisms, rather than directly altering HSC function. Further understanding of the processes mediating mobilization will advance our understanding on the cellular and molecular components of the HSC niche.

Identification of hypoxia-induced genes in human SGBS adipocytes by microarray analysis

Hypoxia in adipose tissue is suggested to be involved in the development of a chronic mild inflammation, which in obesity can further lead to insulin resistance. The effect of hypoxia on gene expression in adipocytes appears to play a central role in this inflammatory response observed in obesity. However, the global impact of hypoxia on transcriptional changes in human adipocytes is unclear. Therefore, we compared gene expression profiles of human Simpson-Golabi-Behmel syndrome (SGBS) adipocytes under normoxic or hypoxic conditions to detect hypoxia-responsive genes in adipocytes by using whole human genome microarrays. Microarray analysis showed more than 500 significantly differentially regulated mRNAs after incubation of the cells under low oxygen levels. To gain further insight into the biological processes, hypoxia-regulated genes after 16 hours of hypoxia were classified according to their function. We identified an enrichment of genes involved in important biological processes such as glycolysis, response to hypoxia, regulation of cellular component movement, response to nutrient levels, regulation of cell migration, and transcription regulator activity. Real-time PCR confirmed eight genes to be consistently upregulated in response to 3, 6 and 16 hours of hypoxia. For adipocytes the hypoxia-induced regulation of these genes is shown here for the first time. Moreover in six of these eight genes we identified HIF response elements in the proximal promoters, specific for the HIF transcription factor family members HIF1A and HIF2A. In the present study, we demonstrated that hypoxia has an extensive effect on gene expression of SGBS adipocytes. In addition, the identified hypoxia-regulated genes are likely involved in the regulation of obesity, the incidence of type 2 diabetes, and the metabolic syndrome.

The expression and regulation of adrenomedullin in the human endometrium: a candidate for endometrial repair

After menstruation, the endometrium has a remarkable capacity for repair, but the factors involved remain undefined. We hypothesize adrenomedullin (AM) plays a role in this process. Premenstrually progesterone levels decline, stimulating prostaglandin (PG) synthesis, vasoconstriction, and hypoxia. This study aimed to determine 1) AM expression throughout the menstrual (M) cycle and 2) its regulation by PG and hypoxia. Human endometrial biopsies (n = 51) were collected with ethical approval and consent. AM mRNA expression was examined by quantitative RT-PCR and was found to be selectively elevated in endometrium from the menstrual (M) phase (P < 0.001). AM immunohistochemical staining was maximal in M and proliferative (P) endometrium. Culture of secretory, but not P, explants with 100 nm PGF(2α) or hypoxia (0.5% O2) increased AM mRNA (P < 0.05). P explants were induced to increase AM expression using in vitro progesterone withdrawal but required the presence of hypoxia (P < 0.05). Short hairpin sequences against hypoxia-inducible factor-1α (HIF-1α) inhibited AM hypoxic up-regulation but did not alter PGF(2α)-induced expression. The AM receptor was immunolocalized to endothelial cells in both lymphatic and blood vessels. Conditioned medium from PGF(2α)-treated cells increased endothelial cell proliferation and branching (P < 0.05). This was abolished by AM receptor antagonists. In conclusion, AM is elevated at the time of endometrial repair and induces both angiogenesis and lymphangiogenesis by stimulating endothelial cell proliferation and tube formation. In the human endometrium, AM expression is up-regulated by two mechanisms: a HIF-1α-mediated hypoxic induction and a HIF-1α-independent PGF(2α) pathway. These physiological mechanisms may provide novel therapeutic targets for disorders such as heavy menstrual bleeding.

Acute mountain sickness, inflammation, and permeability: new insights from a blood biomarker study

The pathophysiology of acute mountain sickness (AMS) is unknown. One hypothesis is that hypoxia induces biochemical changes that disrupt the blood-brain barrier (BBB) and, subsequently, lead to the development of cerebral edema and the defining symptoms of AMS. This study explores the relationship between AMS and biomarkers thought to protect against or contribute to BBB disruption. Twenty healthy volunteers participated in a series of hypobaric hypoxia trials distinguished by pretreatment with placebo, acetazolamide (250 mg), or dexamethasone (4 mg), administered using a randomized, double-blind, placebo-controlled, crossover design. Each trial included peripheral blood sampling and AMS assessment before (-15 and 0 h) and during (0.5, 4, and 9 h) a 10-h hypoxic exposure (barometric pressure = 425 mmHg). Anti-inflammatory and/or anti-permeability [interleukin (IL)-1 receptor agonist (IL-1RA), heat shock protein (HSP)-70, and adrenomedullin], proinflammatory (IL-6, IL-8, IL-2, IL-1β, and substance P), angiogenic, or chemotactic biomarkers (macrophage inflammatory protein-1β, VEGF, TNF-α, monocyte chemotactic protein-1, and matrix metalloproteinase-9) were assessed. AMS-resistant subjects had higher IL-1RA (4 and 9 h and overall), HSP-70 (0 h and overall), and adrenomedullin (overall) compared with AMS-susceptible subjects. Acetazolamide raised IL-1RA and HSP-70 compared with placebo in AMS-susceptible subjects. Dexamethasone also increased HSP-70 and adrenomedullin in AMS-susceptible subjects. Macrophage inflammatory protein-1β was higher in AMS-susceptible than AMS-resistant subjects after 4 h of hypoxia; dexamethasone minimized this difference. Other biomarkers were unrelated to AMS. Resistance to AMS was accompanied by a marked anti-inflammatory and/or anti-permeability response that may have prevented downstream pathophysiological events leading to AMS. Conversely, AMS susceptibility does not appear to be related to an exaggerated inflammatory response.

Mobilization of hematopoietic stem cells from the bone marrow niche to the blood compartment

The vast majority of hematopoietic stem cells (HSCs) reside in specialized niches within the bone marrow during steady state, maintaining lifelong blood cell production. A small number of HSCs normally traffic throughout the body; however, exogenous stimuli can enhance their release from the niche and entry into the peripheral circulation. This process, termed mobilization, has become the primary means to acquire a stem cell graft for hematopoietic transplant at most transplant centers. Currently, the preferred method of HSC mobilization for subsequent transplantation is treatment of the donor with granulocyte colony-stimulating factor. The mobilizing effect of granulocyte colony-stimulating factor is not completely understood, but recent studies suggest that its capacity to mobilize HSCs, at least in part, is a consequence of alterations to the hematopoietic niche. The present article reviews some of the key mechanisms mediating HSC mobilization, highlighting recent advances and controversies in the field.

Anti-inflammatory actions of adrenomedullin through fine tuning of HIF stabilization

In intact mucosal tissues, epithelial cells are anatomically positioned in proximity to a number of subepithelial cell types, including endothelia. A number of recent studies have suggested that imbalances between energy supply and demand can result in "inflammatory hypoxia." Given these associations, we hypothesized that endothelial-derived, hypoxia-inducible mediators might influence epithelial function. Guided by cDNA microarray analysis of human microvascular endothelial cells (HMEC-1 line) subjected to hypoxia (pO(2) 20 torr, 8 h), we identified adrenomedullin (ADM) as a prominent hypoxia-inducible factor (HIF) that acts on epithelial cells through cell surface receptors. We assessed the functional ability for exogenous ADM to signal in human intestinal Caco2 cells in vitro by demonstrating a dose-dependent induction of Erk1/2phosphorylation. Further analysis revealed that ADM deneddylates cullin-2 (Cul2), whose action has been demonstrated to control the activity of HIF. Caco2 cells stably expressing a hypoxic response element (HRE)-driven luciferase promoter confirmed that ADM activates the HIF signaling pathway. Extensions of these studies revealed an increase in canonical HIF-1-dependent genes following stimulation with ADM. To define physiological relevance, we investigated the effect of ADM in a DSS model of murine colitis. Administration of ADM resulted in reduced inflammatory indices and less severe histological inflammation compared to vehicle controls. Analysis of tissue and serum cytokines showed a marked and significant inhibition of colitis-associated TNF-α, IL-1β, and KC. Analysis of circulating ADM demonstrated an increase in serum ADM in murine models of colitis. Taken together, these results identify ADM as an endogenously generated vascular mediator that functions as a mucosal protective factor through fine tuning of HIF activity.

Hypoxia. 3. Hypoxia and neurotransmitter synthesis

Central and peripheral neurons as well as neuroendocrine cells express a variety of neurotransmitters/modulators that play critical roles in regulation of physiological systems. The synthesis of several neurotransmitters/modulators is regulated by O(2)-requiring rate-limiting enzymes. Consequently, hypoxia resulting from perturbations in O(2) homeostasis can affect neuronal functions by altering neurotransmitter synthesis. Two broad categories of hypoxia are frequently encountered: continuous hypoxia (CH) and intermittent hypoxia (IH). CH is often seen during high altitude sojourns, whereas IH is experienced in sleep-disordered breathing with recurrent apneas (i.e., brief, repetitive cessations of breathing). This article presents what is currently known on the effects of both forms of hypoxia on neurotransmitter levels and neurotransmitter synthesizing enzymes in the central and peripheral nervous systems.