Role of hypoxia in the evolution and development of the cardiovascular system

Dietary Selenium Insufficiency Induces Cardiac Inflammatory Injury in Chicks

BACKGROUND

Laying hens undergo intensive metabolism and are vulnerable to cardiac insults. Previous research demonstrated overt heart disorders of broiler chickens induced by dietary Se deficiency.

OBJECTIVES

This study aimed to reveal effects and mechanism of dietary Se insufficiency on cardiac injuries of egg-type chicks in their early life.

METHODS

White Leghorn chicks (0-d-old, female) were fed a corn-soy, Se-insufficient basal diet (BD, 0.05 mg Se/kg; n = 11) or the BD supplemented with 0.3 mg Se/kg (as sodium selenite; n = 8) for 35 d. Cardiac tissues were collected at the end of study for histology and to determine its relationship with heart Se contents, selenoprotein expression profiles, antioxidant and inflammatory status, and the Toll-like receptor 4/extracellular signal-regulated kinases/p38 map kinase/c-Jun N-terminal kinase (TLR4/ERK/P38/JNK) pathway.

RESULTS

Compared with those fed 0.35 mg Se/kg, chicks fed BD had significantly lower body weights and average daily gain, and 28% lower heart Se, and developed cardiac mononuclear inflammatory cell infiltration, along with elevated (P < 0.05) serum concentrations of creatine kinase, aldolase, and interleukin-1 (IL-1). The BD decreased (P < 0.05) body weight and heart glutathione contents and expression of selenoproteins but increased (P < 0.05) heart concentrations of malondialdehyde and reactive oxygen species. These changes were associated with increased (P < 0.05) mRNA and/or protein concentrations of cyclooxygenases, lipoxygenase-12, cytokines (IL-1β), nuclear factor (NF) κB subunit, chemokines, and receptors (CCL20, CXCR1, and CXCLI2) and increased (P < 0.1) TLR4/ERK /P38/JNK in the heart of Se-insufficient chicks.

CONCLUSIONS

Dietary Se insufficiency induces infiltration of mononuclear inflammatory cells in the heart of egg-type chicks. This cardiac injury was mediated by decreased functional expressions of selenoproteins, which resulted in apparent elevated oxidative stress and subsequent activations of the TLR4 pathway and NF κB.

Redox mechanisms of environmental toxicants on male reproductive function

Humans and wildlife, including domesticated animals, are exposed to a myriad of environmental contaminants that are derived from various human activities, including agricultural, household, cosmetic, pharmaceutical, and industrial products. Excessive exposure to pesticides, heavy metals, and phthalates consequently causes the overproduction of reactive oxygen species. The equilibrium between reactive oxygen species and the antioxidant system is preserved to maintain cellular redox homeostasis. Mitochondria play a key role in cellular function and cell survival. Mitochondria are vulnerable to damage that can be provoked by environmental exposures. Once the mitochondrial metabolism is damaged, it interferes with energy metabolism and eventually causes the overproduction of free radicals. Furthermore, it also perceives inflammation signals to generate an inflammatory response, which is involved in pathophysiological mechanisms. A depleted antioxidant system provokes oxidative stress that triggers inflammation and regulates epigenetic function and apoptotic events. Apart from that, these chemicals influence steroidogenesis, deteriorate sperm quality, and damage male reproductive organs. It is strongly believed that redox signaling molecules are the key regulators that mediate reproductive toxicity. This review article aims to spotlight the redox toxicology of environmental chemicals on male reproduction function and its fertility prognosis. Furthermore, we shed light on the influence of redox signaling and metabolism in modulating the response of environmental toxins to reproductive function. Additionally, we emphasize the supporting evidence from diverse cellular and animal studies.

Association between aluminum and iron exposure in maternal blood and umbilical cord blood and congenital heart defects in children

Background

Congenital heart disease (CHDs) is the major cause of mortality from birth defects, affecting up to 1% of live births worldwide. However, the relationship between aluminum (Al) and iron (Fe) levels and the risk of CHDs has yielded inconsistent results.

Methods

We conducted a pair-matched case-control study that included 97 CHDs and 194 non-CHDs to investigate the association and interaction between Al/Fe exposure and the risk of CHDs in a birth cohort study in Lanzhou, China.

Results

Higher concentrations of cord blood Al were associated with a greater risk of total CHDs (aOR = 2.826, 95% CI [1.009-7.266]) and isolated CHDs (aOR = 10.713, 95% CI [1.017-112.851]) compared to the lowest Al level. Both in maternal blood and cord blood, a significant dose-effect was observed between Al level and total CHDs (Ptrend < 0.05), but a similar pattern was not observed for Fe. High Al in addition to high Fe appeared to elicit a stronger association with CHDs than both lowest tertile of Al and Fe level in umbilical cord blood, particularly for multiple CHDs, septal defects and patent ductus arteriosus.

Conclusions

Our study suggests that exposure to Al during pregnancy (≥2,408 μg/L) is significantly associated with an increased risk of CHDs in offspring, especially septal defects, and that high levels of Al and Fe are strongly correlated with fetal heart development. Further research is needed to understand the underlying mechanisms.

Dietary Inflammatory Index during Pregnancy and Congenital Heart Defects

The relationship between diet-related inflammation during pregnancy and congenital heart defects (CHD) is unclear. This study attempted to investigate the association between the dietary inflammation index (DII) during pregnancy, reflecting the overall inflammatory potential of the maternal diet, and CHD in Northwest China. A case-control study with 474 cases and 948 controls was performed in Xi'an City, China. Eligible women awaiting delivery were recruited, and their dietary and other information during pregnancy was collected. Logistic regression models were applied to estimate the risk of CHD in association with DII. The maternal DII ranged from -1.36 to 5.73 in cases, and 0.43 to 5.63 in controls. Pregnant women with per 1 higher DII score were at 31% higher risk of fetal CHD (OR = 1.31, 95%CI = 1.14-1.51), and the adjusted OR (95%CI) comparing the pro-inflammatory diet group with the anti-inflammatory diet group was 2.04 (1.42-2.92). The inverse association of maternal DII score with CHD risk was consistent across various subgroups of maternal characteristics. Maternal DII in pregnancy had good predictive value for CHD in offspring, with the areas under the receiver operating characteristic curve higher than 0.7. These findings suggested that avoiding a pro-inflammatory diet in pregnancy should be emphasized in the prevention of CHD.

The Association of Folic Acid, Iron Nutrition during Pregnancy and Congenital Heart Disease in Northwestern China: A Matched Case-Control Study

Background: The purpose of this study was to investigate the relationship between folic acid and iron nutrition during pregnancy and congenital heart disease (CHD) in the offspring. Methods: Conditional logistic regression models and nonlinear mixed-effects models were used to analyze the effects of folic acid and iron nutrition during pregnancy on CHD in offspring. Results: After adjusting for confounders, folic acid or iron supplementation during pregnancy reduced the risk for fetal CHD (OR = 0.60 (0.45, 0.82) or 0.36 (0.27, 0.48)). Similarly, dietary iron intake during pregnancy (≥29 mg/d) was associated with a reduced risk of fetal CHD (OR = 0.64 (0.46, 0.88)). Additionally, compared with women who only supplemented folic acid (OR = 0.59 (0.41, 0.84)) or iron (OR = 0.32 (0.16, 0.60)), women who supplemented both folic acid and iron had lower risk for newborns with CHD (OR = 0.22 (0.15, 0.34)). Similarly, compared with women who only supplemented folic acid (OR = 0.59 (0.41, 0.84)) or higher dietary iron intake (≥29 mg/d) (OR = 0.60 (0.33, 1.09)), women who supplemented both folic acid and higher dietary iron intake (≥29 mg/d) had lower risk for the newborn with CHD (OR = 0.41 (0.28, 0.62)). The combined effects were significant in the multiplication model (OR = 0.35 (0.26, 0.48) or 0.66 (0.50, 0.85)) but not in the additive model. Conclusions: Our study found that folic acid and iron nutrition during pregnancy were associated with a reduced risk of CHD in the offspring and confirmed a statistically significant multiplicative interaction between folic acid and iron nutrition on the reduced risk of CHD in offspring.

Dietary Quality during Pregnancy and Congenital Heart Defects

Limited studies on maternal dietary quality indices and congenital heart defects (CHD) are available. This study aimed to explore the relationship between dietary quality in pregnancy and CHD among the Chinese population. A case-control study was performed in Northwest China, and 474 cases and 948 controls were included. Eligible women waiting for delivery were interviewed to recall diets and other information during pregnancy. Dietary quality was assessed by the Global Diet Quality Score (GDQS) and Mediterranean Diet Score (MDS). Logistic regression models were adopted to evaluate the associations of dietary quality scores with CHD. Pregnant women with higher scores of GDQS and MDS were at a lower risk of fetal CHD, and the adjusted ORs comparing the extreme quartiles were 0.26 (95%CI: 0.16−0.42; Ptrend < 0.001) and 0.53 (95%CI: 0.34−0.83; Ptrend = 0.007), respectively. The inverse associations of GDQS and MDS with CHD appeared to be stronger among women with lower education levels or in rural areas. Maternal GDQS and MDS had good predictive values for fetal CHD, with the areas under the receiver operating characteristic curves close to 0.8. Efforts to improve maternal dietary quality need to be strengthened to decrease the prevalence of CHD among the Chinese population.

Plant glucose transporter structure and function

The carbohydrate D-glucose is the main source of energy in living organisms. In contrast to animals, as well as most fungi, bacteria, and archaea, plants are capable to synthesize a surplus of sugars characterizing them as autothrophic organisms. Thus, plants are de facto the source of all food on earth, either directly or indirectly via feed to livestock. Glucose is stored as polymeric glucan, in animals as glycogen and in plants as starch. Despite serving a general source for metabolic energy and energy storage, glucose is the main building block for cellulose synthesis and represents the metabolic starting point of carboxylate- and amino acid synthesis. Finally yet importantly, glucose functions as signalling molecule conveying the plant metabolic status for adjustment of growth, development, and survival. Therefore, cell-to-cell and long-distance transport of photoassimilates/sugars throughout the plant body require the fine-tuned activity of sugar transporters facilitating the transport across membranes. The functional plant counterparts of the animal sodium/glucose transporters (SGLTs) are represented by the proton-coupled sugar transport proteins (STPs) of the plant monosaccharide transporter(-like) family (MST). In the framework of this special issue on “Glucose Transporters in Health and Disease,” this review gives an overview of the function and structure of plant STPs in comparison to the respective knowledge obtained with the animal Na⁺-coupled glucose transporters (SGLTs).

The Redox Theory of Development

Significance: The geological record shows that as atmospheric O2 levels increased, it concomitantly coincided with the evolution of metazoans. More complex, higher organisms contain a more cysteine-rich proteome, potentially as a means to regulate homeostatic responses in a more O2-rich environment. Regulation of redox-sensitive processes to control development is likely to be evolutionarily conserved. Recent Advances: During early embryonic development, the conceptus is exposed to varying levels of O2. Oxygen and redox-sensitive elements can be regulated to promote normal development, defined as changes to cellular mass, morphology, biochemistry, and function, suggesting that O2 is a developmental morphogen. During periods of O2 fluctuation, embryos are "reprogrammed," on the genomic and metabolic levels. Reprogramming imparts changes to particular redox couples (nodes) that would support specific post-translational modifications (PTMs), targeting the cysteine proteome to regulate protein function and development. Critical Issues: Major developmental events such as stem cell expansion, proliferation, differentiation, migration, and cell fate decisions are controlled through oxidative PTMs of cysteine-based redox nodes. As such, timely coordinated redox regulation of these events yields normal developmental outcomes and viable species reproduction. Disruption of normal redox signaling can produce adverse developmental outcomes. Future Directions: Furthering our understanding of the redox-sensitive processes/pathways, the nature of the regulatory PTMs involved in development and periods of activation/sensitivity to specific developmental pathways would greatly support the theory of redox regulation of development, and would also provide rationale and direction to more fully comprehend poor developmental outcomes, such as dysmorphogenesis, functional deficits, and preterm embryonic death.

Maternal dietary diversity during pregnancy and congenital heart defects: a case-control study

BACKGROUND/OBJECTIVES

Maternal diet is critical to fetal development. This study aimed to explore the association between maternal dietary diversity during pregnancy and congenital heart defects (CHD) in Chinese population.

METHODS

A hospital-based case-control study was conducted including 474 cases and 948 controls in Northwest China. We recruited eligible women waiting for delivery in the hospital and gathered their diets during the whole pregnancy by a validated food frequency questionnaire. According to the FAO Minimum Dietary Diversity for Women (MDD-W) guideline, the participants were categorized into "inadequate dietary diversity score (DDS)" (DDS < 5) and "adequate DDS" (DDS ≥ 5) groups. The association between dietary diversity and CHD was estimated using the mixed logistic regression models.

RESULTS

Case mothers had a lower DDS during pregnancy than the controls (P < 0.001). The proportions of women consuming all the ten defined food groups were lower in the inadequate DDS group than in the adequate DDS group among both cases and controls (all P < 0.001). The prevalence of inadequate micronutrient intake was higher in the inadequate DDS group than in the adequate DDS group among both cases and controls (all P < 0.05). Women in the adequate DDS group had reduced risks of having fetuses with total CHD (OR = 0.62, 95% CI = 0.45-0.84) and ventricular septal defects (OR = 0.58, 95% CI = 0.38-0.88).

CONCLUSIONS

Adequate DDS during pregnancy might be associated with a lower risk of CHD in offspring. Efforts to promote dietary diversity during pregnancy need to be strengthened to reduce the prevalence of CHD in Chinese population.

Acute vs. Chronic vs. Cyclic Hypoxia: Their Differential Dynamics, Molecular Mechanisms, and Effects on Tumor Progression

Hypoxia has been shown to increase the aggressiveness and severity of tumor progression. Along with chronic and acute hypoxic regions, solid tumors contain regions of cycling hypoxia (also called intermittent hypoxia or IH). Cyclic hypoxia is mimicked in vitro and in vivo by periodic exposure to cycles of hypoxia and reoxygenation (H-R cycles). Compared to chronic hypoxia, cyclic hypoxia has been shown to augment various hallmarks of cancer to a greater extent: angiogenesis, immune evasion, metastasis, survival etc. Cycling hypoxia has also been shown to be the major contributing factor in increasing the risk of cancer in obstructive sleep apnea (OSA) patients. Here, we first compare and contrast the effects of acute, chronic and intermittent hypoxia in terms of molecular pathways activated and the cellular processes affected. We highlight the underlying complexity of these differential effects and emphasize the need to investigate various combinations of factors impacting cellular adaptation to hypoxia: total duration of hypoxia, concentration of oxygen (O2), and the presence of and frequency of H-R cycles. Finally, we summarize the effects of cycling hypoxia on various hallmarks of cancer highlighting their dependence on the abovementioned factors. We conclude with a call for an integrative and rigorous analysis of the effects of varying extents and durations of hypoxia on cells, including tools such as mechanism-based mathematical modelling and microfluidic setups.

Oxygen and lack of oxygen in fetal and placental development, feto-placental coupling, and congenital heart defects

Low oxygen concentration (hypoxia) is part of normal embryonic development, yet the situation is complex. Oxygen (O₂ ) is a janus gas with low levels signaling through hypoxia-inducible transcription factor (HIF) that are required for development of fetal and placental vasculature and fetal red blood cells. This results in coupling of fetus and mother around midgestation as a functional feto-placental unit (FPU) for O₂ transport, which is required for continued growth and development of the fetus. Defects in these processes may leave the developing fetus vulnerable to O₂ deprivation or other stressors during this critical midgestational transition when common septal and conotruncal heart defects (CHDs) are likely to arise. Recent human epidemiological and case-control studies support an association between placental dysfunction, manifest as early onset pre-eclampsia (PE) and increased serum bio-markers, and CHD. Animal studies support this association, in particular those using gene inactivation in the mouse. Sophisticated methods for gene inactivation, cell fate mapping, and a quantitative bio-reporter of O₂ concentration support the premise that hypoxic stress at critical stages of development leads to CHD. The secondary heart field contributing to the cardiac outlet is a key target, with activation of the un-folded protein response and abrogation of FGF signaling or precocious activation of a cardiomyocyte transcriptional program for differentiation, suggested as mechanisms. These studies provide a strong foundation for further study of feto-placental coupling and hypoxic stress in the genesis of human CHD.

The Different Routes to Metastasis via Hypoxia-Regulated Programs

Hypoxia is linked to metastasis; however, how it affects metastatic progression is not clear due to limited consensus in the literature. We posit that this lack of consensus is due to hypoxia being studied using different approaches, such as in vitro, primary tumor, or metastasis assays in an isolated manner. Here, we review the pros and cons of in vitro hypoxia assays, highlight in vivo studies that inform on physiological hypoxia, and review the evidence that primary tumor hypoxia might influence the fate of disseminated tumor cells (DTCs) in secondary organs. Our analysis suggests that consensus can be reached by using in vivo methods of study, which also allow better modeling of how hypoxia affects DTC fate and metastasis.

Coronary arterial vasculature in the pathophysiology of hypertrophic cardiomyopathy

Alterations in the coronary vascular system are likely associated with a mismatch between energy demand and energy supply and critical in triggering the cascade of events that leads to symptomatic hypertrophic cardiomyopathy. Targeting the early events, particularly vascular remodeling, may be a key approach to developing effective treatments. Improvement in our understanding of hypertrophic cardiomyopathy began with the results of early biophysical studies, proceeded to genetic analyses pinpointing the mutational origin, and now pertains to imaging of the metabolic and flow-related consequences of such mutations. Microvascular dysfunction has been an ongoing hot topic in the imaging of genetic cardiomyopathies marked by its histologically significant remodeling and has proven to be a powerful asset in determining prognosis for these patients as well as enlightening scientists on a potential pathophysiological cascade that may begin early during the developmental process. Here, we discuss questions that continue to remain on the mechanistic processes leading to microvascular dysfunction, its correlation to the morphological changes in the vessels, and its contribution to disease progression.

Oxygen Regulation in Development: Lessons from Embryogenesis towards Tissue Engineering

Oxygen is a vital source of energy necessary to sustain and complete embryonic development. Not only is oxygen the driving force for many cellular functions and metabolism, but it is also involved in regulating stem cell fate, morphogenesis, and organogenesis. Low oxygen levels are the naturally preferred microenvironment for most processes during early development and mainly drive proliferation. Later on, more oxygen and also nutrients are needed for organogenesis and morphogenesis. Therefore, it is critical to maintain oxygen levels within a narrow range as required during development. Modulating oxygen tensions is performed via oxygen homeostasis mainly through the function of hypoxia-inducible factors. Through the function of these factors, oxygen levels are sensed and regulated in different tissues, starting from their embryonic state to adult development. To be able to mimic this process in a tissue engineering setting, it is important to understand the role and levels of oxygen in each developmental stage, from embryonic stem cell differentiation to organogenesis and morphogenesis. Taking lessons from native tissue microenvironments, researchers have explored approaches to control oxygen tensions such as hemoglobin-based, perfluorocarbon-based, and oxygen-generating biomaterials, within synthetic tissue engineering scaffolds and organoids, with the aim of overcoming insufficient or nonuniform oxygen levels and nutrient supply.

Restoration of cardiac function after anaemia-induced heart failure in zebrafish

AIMS

New therapeutic approaches are needed to fight against the growing epidemic of heart failure. Unlike mammals, zebrafish possess the incredible ability to regenerate cardiac tissue after acute trauma such as apical resection. Yet, the ability of zebrafish to recover after a chronic stress leading to heart failure has not been reported. The aim of this study was to test whether zebrafish can recover a normal cardiac function after anaemia-induced heart failure.

METHODS AND RESULTS

Eight- to ten-month-old zebrafish were treated with phenylhydrazine hydrochloride, an anaemia inducer, to generate heart failure. Treatment was stopped after 5 weeks and fish were followed-up for 3 weeks. Assessment of ventricular function by ultrasound at the end of the treatment revealed an increase in ventricle diameter (+47%) and a decrease in heart rate (-36%) and fractional shortening (-30%). A decrease in swim capacity was also observed (-31%). Tissue staining showed a thickening of the ventricular wall (5-fold), cell apoptosis and proliferation but no fibrosis. Expression of foetal genes, angiogenic factor and inflammation markers was increased, and β-adrenergic receptor-1 was decreased. Three weeks after phenylhydrazine hydrochloride withdrawal, all parameters returned to baseline and the fish recovered a normal cardiac function, tissue morphology and gene expression.

CONCLUSIONS

Zebrafish are able to completely recover from anaemia-induced heart failure. This model represents a unique opportunity to investigate the mechanisms of cardiac repair and may lead to the discovery of novel therapeutic targets of heart failure.

Hypoxic conditioning in blood vessels and smooth muscle tissues: effects on function, mechanisms, and unknowns

Hypoxic preconditioning, the protective effect of brief, intermittent hypoxic or ischemic episodes on subsequent more severe hypoxic episodes, has been known for 30 yr from studies on cardiac muscle. The concept of hypoxic preconditioning has expanded; excitingly, organs beyond the heart, including the brain, liver, and kidney, also benefit. Preconditioning of vascular and visceral smooth muscles has received less attention despite their obvious importance to health. In addition, there has been no attempt to synthesize the literature in this field. Therefore, in addition to overviewing the current understanding of hypoxic conditioning, in the present review, we consider the role of blood vessels in conditioning and explore evidence for conditioning in other smooth muscles. Where possible, we have distinguished effects on myocytes from other cell types in the visceral organs. We found evidence of a pivotal role for blood vessels in conditioning and for conditioning in other smooth muscle, including the bladder, vascular myocytes, and gastrointestinal tract, and a novel response in the uterus of a hypoxic-induced force increase, which helps maintain contractions during labor. To date, however, there are insufficient data to provide a comprehensive or unifying mechanism for smooth muscles or visceral organs and the effects of conditioning on their function. This also means that no firm conclusions can be drawn as to how differences between smooth muscles in metabolic and contractile activity may contribute to conditioning. Therefore, we have suggested what may be general mechanisms of conditioning occurring in all smooth muscles and tabulated tissue-specific mechanistic findings and suggested ideas for further progress.

Inactivation of maternal Hif-1α at mid-pregnancy causes placental defects and deficits in oxygen delivery to the fetal organs under hypoxic stress

A critical transition occurs near mid-gestation of mammalian pregnancy. Prior to this transition, low concentrations of oxygen (hypoxia) signaling through Hypoxia Inducible Factor (HIF) functions as a morphogen for the placenta and fetal organs. Subsequently, functional coupling of the placenta and fetal cardiovascular system for oxygen (O₂) transport is required to support the continued growth and development of the fetus. Here we tested the hypothesis that Hif-1α is required in maternal cells for placental morphogenesis and function. We used Tamoxifen-inducible Cre-Lox to inactivate Hif-1α in maternal tissues at E8.5 (MATcKO), and used ODD-Luciferase as a reporter of hypoxia in placenta and fetal tissues. MATcKO of Hif-1α reduced the number of uterine natural killer (uNK) cells and Tpbpa-positve trophoblast cells in the maternal decidua at E13.5 -15.5. There were dynamic changes in all three layers of E13.5-15.5 MATcKO placenta. Of note was the under-development of the labyrinth at E15.5 associated with reduced Ki67 and increased TUNEL staining consistent with reduced cell proliferation and increased apoptosis. Labyrinth defects were particularly evident in placentas connected to effectively HIF-1α heterozygous null embryos. MATcKO had no effect on basal ODD-Luciferase activity in fetal organs (heart, liver, brain) at any stage, but at E13.5-15.5 resulted in enhanced induction of the ODD-Luciferase hypoxia reporter when the dam's inspired O₂ was reduced to 8% for 4 hours. MATcKO also slowed the growth after E13.5 of fetuses that were effectively heterozygous for Hif-1α, with most being non-viable at E15.5. The hearts of these E15.5 fetuses were abnormal with reduction in size, thickened epicardium and mesenchymal septum. We conclude that maternal HIF-1α is required for placentation including recruitment of uNK and trophoblast cells into the maternal decidua and other trophoblast cell behaviors. The placental defects render the fetus vulnerable to O₂ deprivation after mid-gestation.

Hypoxia paradoxically inhibits the angiogenic response of isolated vessel explants while inducing overexpression of vascular endothelial growth factor

This study was designed to investigate how changes in O2 levels affected angiogenesis in vascular organ culture. Although hypoxia is a potent inducer of angiogenesis, aortic rings cultured in collagen paradoxically failed to produce an angiogenic response in 1-4 % O2. Additionally, aortic neovessels preformed in atmospheric O2 lost pericytes and regressed at a faster rate than control when exposed to hypoxia. Aortic explants remained viable in hypoxia and produced an angiogenic response when returned to atmospheric O2. Hypoxic aortic rings were unresponsive to VEGF, while increased oxygenation of the system dose-dependently enhanced VEGF-induced angiogenesis. Hypoxia-induced refractoriness to angiogenic stimulation was not restricted to the aorta because similar results were obtained with vena cava explants or isolated endothelial cells. Unlike endothelial cells, aorta-derived mural cells were unaffected by hypoxia. Hypoxia downregulated expression in aortic explants of key signaling molecules including VEGFR2, NRP1 and Prkc-beta while upregulating expression of VEGFR1. Medium conditioned by hypoxic cultures exhibited angiostatic and anti-VEGF activities likely mediated by sVEGFr1. Hypoxia reduced expression of VEGFR1 and VEGFR2 in endothelial cells while upregulating VEGFR1 in macrophages and VEGF in both macrophages and mural cells. Thus, changes in O2 levels profoundly affect the endothelial response to angiogenic stimuli. These results suggest that hypoxia-induced angiogenesis is fine-tuned by complex regulatory mechanisms involving not only production of angiogenic factors including VEGF but also differential regulation of VEGFR expression in different cell types and production of inhibitors of VEGF function such as sVEGFR1.

HIF hydroxylase pathways in cardiovascular physiology and medicine

Hypoxia inducible factors (HIFs) are α/β heterodimeric transcription factors that direct multiple cellular and systemic responses in response to changes in oxygen availability. The oxygen sensitive signal is generated by a series of iron and 2-oxoglutarate-dependent dioxygenases that catalyze post-translational hydroxylation of specific prolyl and asparaginyl residues in HIFα subunits and thereby promote their destruction and inactivation in the presence of oxygen. In hypoxia, these processes are suppressed allowing HIF to activate a massive transcriptional cascade. Elucidation of these pathways has opened several new fields of cardiovascular research. Here, we review the role of HIF hydroxylase pathways in cardiac development and in cardiovascular control. We also consider the current status, opportunities, and challenges of therapeutic modulation of HIF hydroxylases in the therapy of cardiovascular disease.

Evolution and physiology of neural oxygen sensing

Major evolutionary trends in animal physiology have been heavily influenced by atmospheric O2 levels. Amongst other important factors, the increase in atmospheric O2 which occurred in the Pre-Cambrian and the development of aerobic respiration beckoned the evolution of animal organ systems that were dedicated to the absorption and transportation of O2, e.g., the respiratory and cardiovascular systems of vertebrates. Global variations of O2 levels in post-Cambrian periods have also been correlated with evolutionary changes in animal physiology, especially cardiorespiratory function. Oxygen transportation systems are, in our view, ultimately controlled by the brain related mechanisms, which senses changes in O2 availability and regulates autonomic and respiratory responses that ensure the survival of the organism in the face of hypoxic challenges. In vertebrates, the major sensorial system for oxygen sensing and responding to hypoxia is the peripheral chemoreflex neuronal pathways, which includes the oxygen chemosensitive glomus cells and several brainstem regions involved in the autonomic regulation of the cardiovascular system and respiratory control. In this review we discuss the concept that regulating O2 homeostasis was one of the primordial roles of the nervous system. We also review the physiology of the peripheral chemoreflex, focusing on the integrative repercussions of chemoreflex activation and the evolutionary importance of this system, which is essential for the survival of complex organisms such as vertebrates. The contribution of hypoxia and peripheral chemoreflex for the development of diseases associated to the cardiovascular and respiratory systems is also discussed in an evolutionary context.

Vulnerability of the developing heart to oxygen deprivation as a cause of congenital heart defects

Background

The heart develops under reduced and varying oxygen concentrations, yet there is little understanding of oxygen metabolism in the normal and mal‐development of the heart. Here we used a novel reagent, the ODD‐Luc hypoxia reporter mouse (oxygen degradation domain, ODD) of Hif‐1α fused to Luciferase (Luc), to assay the activity of the oxygen sensor, prolyl hydroxylase, and oxygen reserve, in the developing heart. We tested the role of hypoxia‐dependent responses in heart development by targeted inactivation of Hif‐1α.

Methods and Results

ODD‐Luciferase activity was 14‐fold higher in mouse embryonic day 10.5 (E10.5) versus adult heart and liver tissue lysates. ODD‐Luc activity decreased in 2 stages, the first corresponding with the formation of a functional cardiovascular system for oxygen delivery at E15.5, and the second after birth consistent with complete oxygenation of the blood and tissues. Reduction of maternal inspired oxygen to 8% for 4 hours caused minimal induction of luciferase activity in the maternal tissues but robust induction in the embryonic tissues in proportion to the basal activity, indicating a lack of oxygen reserve, and corresponding induction of a hypoxia‐dependent gene program. Bioluminescent imaging of intact embryos demonstrated highest activity in the outflow portion of the E13.5 heart. Hif‐1α inactivation or prolonged hypoxia caused outflow and septation defects only when targeted to this specific developmental window.

Conclusions

Low oxygen concentrations and lack of oxygen reserve during a critical phase of heart organogenesis may provide a basis for vulnerability to the development of common septation and conotruncal heart defects.

Time-lapse imaging of cell cycle dynamics during development in living cardiomyocyte

Mammalian cardiomyocytes withdraw from the cell cycle shortly after birth, although it remains unclear how cardiomyocyte cell cycles behave during development. Compared to conventional immunohistochemistry in static observation, time-lapse imaging can reveal comprehensive data in hard-to-understand biological phenomenon. However, there are no reports of an established protocol of successful time-lapse imaging in mammalian heart. Thus, it is valuable to establish a time-lapse imaging system to enable the observation of cell cycle dynamics in living murine cardiomyocytes. This study sought to establish time-lapse imaging of murine heart to study cardiomyocyte cell cycle behavior. The Fucci (fluorescent ubiquitination-based cell cycle indicator) system can effectively label individual G1, S/G2/M, and G1/S-transition phase nuclei red, green and yellow, respectively, in living mammalian cells, and could therefore be useful to visualize the real-time cell cycle transitions in living murine heart. To establish a similar system for time-lapse imaging of murine heart, we first developed an ex vivo culture system, with the culture conditions determined in terms of sample state, serum concentration, and oxygen concentration. The optimal condition (slice culture, oxygen concentration 20%, serum concentration 10%) successfully mimicked physiological cardiomyocyte proliferation in vivo. Time-lapse imaging of cardiac slices from E11.5, E14.5, E18.5, and P1 Fucci-expressing transgenic mice revealed an elongated S/G2/M phase in cardiomyocytes during development. Our time-lapse imaging of murine heart revealed a gradual elongation of the S/G2/M phase during development in living cardiomyocytes.

Cobalt chloride pretreatment promotes cardiac differentiation of human embryonic stem cells under atmospheric oxygen level

Our previous study demonstrated the direct involvement of the HIF-1α subunit in the promotion of cardiac differentiation of murine embryonic stem cells (ESCs). We report the use of cobalt chloride to induce HIF-1α stabilization in human ESCs to promote cardiac differentiation. Treatment of undifferentiated hES2 human ESCs with 50 μM cobalt chloride markedly increased protein levels of the HIF-1α subunit, and was associated with increased expression of early cardiac specific transcription factors and cardiotrophic factors including NK2.5, vascular endothelial growth factor, and cardiotrophin-1. When pretreated cells were subjected to cardiac differentiation, a notable increase in the occurrence of beating embryoid bodies and sarcomeric actinin-positive cells was observed, along with increased expression of the cardiac-specific markers, MHC-A, MHC-B, and MLC2V. Electrophysiological study revealed increased atrial- and nodal-like cells in the cobalt chloride-pretreated group. Confocal calcium imaging analysis indicated that the maximum upstroke and decay velocities were significantly increased in both noncaffeine and caffeine-induced calcium transient in cardiomyocytes derived from the cobalt chloride-pretreated cells, suggesting these cells were functionally more mature. In conclusion, our study demonstrated that cobalt chloride pretreatment of hES2 human ESCs promotes cardiac differentiation and the maturation of calcium homeostasis of cardiomyocytes derived from ESCs.

Bioenergetics, mitochondria, and cardiac myocyte differentiation

Cardiac metabolism is finely tuned, and disruption of myocardial bioenergetics can be clinically devastating. Many cardiomyopathies that present early in life are due to disruption of the maturation of these metabolic pathways. However, this bioenergetic maturation begins well before birth, when the embryonic heart is first beginning to beat, and continues into the mature animal. Thus, the changes in energy production seen after birth are actually part of a continuum that coincides with the structural and functional changes that occur as the cardiac myocyte differentiates and the heart undergoes morphogenesis. Therefore, although bioenergetics and mitochondrial biology have not been studied in great detail in the developing heart, bioenergetic maturation should be considered an important component of normal myocyte differentiation.Although events occurring after birth will be discussed, this review will focus on the changes in bioenergetics and mitochondrial biology that coincide with myocyte differentiation and cardiac morphogenesis. The relationship of these changes to the etiology and presentation of cardiomyopathies will be used as a starting point for this discussion. Then, after reviewing cardiac development and mitochondrial biology, the published data on bioenergetics and mitochondrial structure and function in the developing heart will be presented. Finally, the case will be made that mitochondria may be critical regulators of cardiac myocyte differentiation and cardiac development.

Connecting vascular and nervous system development: angiogenesis and the blood-brain barrier

The vascular and nervous systems share a common necessity of circuit formation to coordinate nutrient and information transfer, respectively. Shared developmental principles have evolved to orchestrate the formation of both the vascular and the nervous systems. This evolution is highlighted by the identification of specific guidance cues that direct both systems to their target tissues. In addition to sharing cellular and molecular signaling events during development, the vascular and nervous systems also form an intricate interface within the central nervous system called the neurovascular unit. Understanding how the neurovascular unit develops and functions, and more specifically how the blood-brain barrier within this unit is established, is of utmost importance. We explore the history, recent discoveries, and unanswered questions surrounding the relationship between the vascular and nervous systems with a focus on developmental signaling cues that guide network formation and establish the interface between these two systems.

Hypoxia and fetal heart development

Fetal hearts show a remarkable ability to develop under hypoxic conditions. The metabolic flexibility of fetal hearts allows sustained development under low oxygen conditions. In fact, hypoxia is critical for proper myocardial formation. Particularly, hypoxia inducible factor 1 (HIF-1) and vascular endothelial growth factor play central roles in hypoxia-dependent signaling in fetal heart formation, impacting embryonic outflow track remodeling and coronary vessel growth. Although HIF is not the only gene involved in adaptation to hypoxia, its role places it as a central figure in orchestrating events needed for adaptation to hypoxic stress. Although "normal" hypoxia (lower oxygen tension in the fetus as compared with the adult) is essential in heart formation, further abnormal hypoxia in utero adversely affects cardiogenesis. Prenatal hypoxia alters myocardial structure and causes a decline in cardiac performance. Not only are the effects of hypoxia apparent during the perinatal period, but prolonged hypoxia in utero also causes fetal programming of abnormality in the heart's development. The altered expression pattern of cardioprotective genes such as protein kinase c epsilon, heat shock protein 70, and endothelial nitric oxide synthase, likely predispose the developing heart to increased vulnerability to ischemia and reperfusion injury later in life. The events underlying the long-term changes in gene expression are not clear, but likely involve variation in epigenetic regulation.

Formation of cardiovascular tubes in invertebrates and vertebrates

The cardiovascular system developed early in evolution and is pivotal for the transport of oxygen, nutrients, and waste products within the organism. It is composed of hollow tubular structures and has a high level of complexity in vertebrates. This complexity is, at least in part, due to the endothelial cell lining of vertebrate blood vessels. However, vascular lumen formation by endothelial cells is still controversially discussed. For example, it has been suggested that the lumen mainly forms via coalescence of large intracellular vacuoles generated by pinocytosis. Alternatively, it was proposed that the vascular lumen initiates extracellularly between adjacent apical endothelial cell surfaces. Here we discuss invertebrate and vertebrate cardiovascular lumen formation and highlight the possible modes of blood vessel formation. Finally, we point to the importance of a better understanding of vascular lumen formation for treating human pathologies, including cancer and coronary heart disease.

Pathogenic peptide deviations support a model of adaptive evolution of chordate cardiac performance by troponin mutations

In cardiac muscle, the troponin (cTn) complex is a key regulator of myofilament calcium sensitivity because it serves as a molecular switch required for translating myocyte calcium fluxes into sarcomeric contraction and relaxation. Studies of several species suggest that ectotherm chordates have myofilaments with heightened calcium responsiveness. However, genetic polymorphisms in cTn that cause increased myofilament sensitivity to activating calcium in mammals result in cardiac disease including arrhythmias, diastolic dysfunction, and increased susceptibility to sudden cardiac death. We hypothesized that specific residue modifications in the regulatory arm of troponin I (TnI) were critical in mediating the observed decrease in myofilament calcium sensitivity within the mammalian taxa. We performed large-scale phylogenetic analysis, atomic resolution molecular dynamics simulations and modeling, and computational alanine scanning. This study provides evidence that a His to Ala substitution within mammalian cardiac TnI (cTnI) reduced the thermodynamic potential at the interface between cTnI and cardiac TnC (cTnC) in the calcium-saturated state by disrupting a strong intermolecular electrostatic interaction. This key residue modification reduced myofilament calcium sensitivity by making cTnI molecularly untethered from cTnC. To meet the requirements for refined mammalian adult cardiac performance, we propose that compensatory evolutionary pressures favored mutations that enhanced the relaxation properties of cTn by decreasing its sensitivity to activating calcium.

The role of hypoxia in development of the Mammalian embryo

Hypoxia inducible factor (HIF) is a transcription factor that acts in low-oxygen conditions. The cellular response to HIF activation is transcriptional upregulation of a large group of genes. Some target genes promote anaerobic metabolism to reduce oxygen consumption, while others "alleviate" hypoxia by acting non-cell-autonomously to extend and modify the surrounding vasculature. Although hypoxia is often thought of as being a pathological phenomenon, the mammalian embryo in fact develops in a low-oxygen environment, and in this context HIF has additional responsibilities. This review describes how low oxygen and HIF affect gene expression, cell behavior, and ultimately morphogenesis of the embryo and placenta.

Development of cardiac form and function in ectothermic sauropsids

Evolutionary morphologists and physiologists have long recognized the phylogenetic significance of the ectothermic sauropsids. Sauropids have been classically considered to bridge between early tetrapods, ectotherms, and the evolution of endotherms. This transition has been associated with many modifications in cardiovascular form and function, which have changed dramatically during the course of vertebrate evolution. Most cardiovascular studies have focused upon adults, leaving the development of this critical system largely unexplored. In this essay, we attempt a synthesis of sauropsid cardiovascular development based on the limited literature and indicate fertile regions for future studies. Early morphological cardiovascular development, i.e., the basic formation of the tube heart and the major pulmonary and systemic vessels, is similar across tetrapods. Subsequent cardiac chamber development, however, varies considerably between developing chelonians, squamates, crocodilians, and birds, reflected in the diversity of adult ventricular structure across these taxa. The details of how these differences in morphology develop, including the molecular regulation of cardiac and vascular growth and differentiation, are still poorly understood. In terms of the functional maturation of the cardiovascular system, reflected in physiological mechanisms for regulating heart rate and cardiac output, recent work has illustrated that changes during ontogeny in parameters such as heart rate and arterial blood pressure are somewhat species-dependent. However, there are commonalities, such as a beta-adrenergic receptor tone on the embryonic heart appearing prior to 60% of development. Differential gross morphological responses to environmental stressors (oxygen, hydration, temperature) have been investigated interspecifically, revealing that cardiac development is relatively plastic, especially, with respect to change in heart growth. Collectively, the data assembled here reflects the current limited morphological and physiological understanding of cardiovascular development in sauropsids and identifies key areas for future studies of this diverse vertebrate lineage.

Behavioral recovery from acute hypoxia is reliant on leptin

Individuals affected by hypoxia experience a variety of immune-associated sickness symptoms including malaise, fatigue, lethargy and loss of interest in the physical and social environment. Recently, we demonstrated that the interleukin (IL)-1beta arm of the neuroimmune system was critical to the sickness symptoms caused by hypoxia, and that IL-1 receptor antagonist (IL-1RA), IL-1beta's endogenous inhibitor, was critical to promoting sickness recovery. Here, we report that leptin is key to recovery from hypoxia because it dramatically augmented IL-1RA production in mice. We found that hypoxia increased leptin in white adipose tissue (WAT) which in turn, caused a marked rise in serum IL-1RA. Interestingly, in-vitro, leptin was a more potent inducer of IL-RA, in macrophages, than hypoxia. In leptin receptor defective (db/db) and leptin deficient (ob/ob) mice, sickness recovery from hypoxia was delayed 3-fold. Importantly, in ob/ob mice, leptin administration completely reversed this delayed recovery and induced a marked increase in serum IL-1RA. Finally, leptin administration to normal mice reduced hypoxia recovery time by 1/3 and dramatically increased WAT and serum IL-1RA. Leptin did not alter recovery from hypoxia in IL-1RA knock out mice. These results show that by enhancing IL-1RA production leptin promoted sickness recovery from hypoxia.

Wound healing essentials: let there be oxygen

The state of wound oxygenation is a key determinant of healing outcomes. From a diagnostic standpoint, measurements of wound oxygenation are commonly used to guide treatment planning such as amputation decision. In preventive applications, optimizing wound perfusion and providing supplemental O(2) in the perioperative period reduces the incidence of postoperative infections. Correction of wound pO(2) may, by itself, trigger some healing responses. Importantly, approaches to correct wound pO(2) favorably influence outcomes of other therapies such as responsiveness to growth factors and acceptance of grafts. Chronic ischemic wounds are essentially hypoxic. Primarily based on the tumor literature, hypoxia is generally viewed as being angiogenic. This is true with the condition that hypoxia be acute and mild to modest in magnitude. Extreme near-anoxic hypoxia, as commonly noted in problem wounds, is not compatible with tissue repair. Adequate wound tissue oxygenation is required but may not be sufficient to favorably influence healing outcomes. Success in wound care may be improved by a personalized health care approach. The key lies in our ability to specifically identify the key limitations of a given wound and in developing a multifaceted strategy to specifically address those limitations. In considering approaches to oxygenate the wound tissue it is important to recognize that both too little as well as too much may impede the healing process. Oxygen dosing based on the specific need of a wound therefore seems prudent. Therapeutic approaches targeting the oxygen sensing and redox signaling pathways are promising.

The developing embryonic cardiac outflow tract is highly sensitive to oxidant stress

This study tested the hypothesis that the remodeling of the cardiac outflow tract (OFT) may represent a developmental window of vulnerability to reactive oxygen species (ROS). Chick embryos were exposed in ovo or ex ovo to increasing concentrations of the stable oxidant hydrogen peroxide (H2O2). As assessed by trypan blue staining, H2O2 induced cell injury in the stage 25-30 OFT at concentrations as low as 1 nM. Higher concentrations were required to induce cell injury in the ventricular and atrial myocardium. Using DCFDA as an indicator of oxidant stress, H2O2 also induced a greater fluorescent signal in the OFT myocardium. H2O2 at these low concentrations also induced Caspase activity, indicative of activation of the pathway of PCD. Interestingly, the induction of Caspase-3 activity was predominately in the OFT cushion mesenchymal cells. Thus, the developing OFT is particularly sensitive to ROS-mediated injury, suggesting that ROS could play a role in the development of congenital defects of the cardiac OFT.

Analysis of the retinal gene expression profile after hypoxic preconditioning identifies candidate genes for neuroprotection

Background

Retinal degeneration is a main cause of blindness in humans. Neuroprotective therapies may be used to rescue retinal cells and preserve vision. Hypoxic preconditioning stabilizes the transcription factor HIF-1α in the retina and strongly protects photoreceptors in an animal model of light-induced retinal degeneration. To address the molecular mechanisms of the protection, we analyzed the transcriptome of the hypoxic retina using microarrays and real-time PCR.

Results

Hypoxic exposure induced a marked alteration in the retinal transcriptome with significantly different expression levels of 431 genes immediately after hypoxic exposure. The normal expression profile was restored within 16 hours of reoxygenation. Among the differentially regulated genes, several candidates for neuroprotection were identified like metallothionein-1 and -2, the HIF-1 target gene adrenomedullin and the gene encoding the antioxidative and cytoprotective enzyme paraoxonase 1 which was previously not known to be a hypoxia responsive gene in the retina. The strongly upregulated cyclin dependent kinase inhibitor p21 was excluded from being essential for neuroprotection.

Conclusion

Our data suggest that neuroprotection after hypoxic preconditioning is the result of the differential expression of a multitude of genes which may act in concert to protect visual cells against a toxic insult.

Hypoxia: life on the edge

Hypoxia and its corollaries pose both negative and positive pressures to multicellular eukaryotes. Evolutionarily, life developed under hypoxia, and the building blocks were established under conditions close to anaerobiosis; therefore, reason exists to expect that certain biologic processes may perform preferentially under hypoxia. Evolving evidence suggests that by providing an environment of reduced oxidative stress, hypoxia may help preserve the biologic functions of some cells and prevent senescence. Hypoxia provides essential signals for development, trimming redundant tissue by inducing apoptosis and driving the growth and development of oxygen and nutrient delivery systems, as well as those for waste management. The pathologic consequences of hypoxia and ischemia, including acidosis and oxidative stress associated with hypoxia-reoxygenation, form the basis of most of the major diseases confronting humans, including heart disease, cancer, and age-related degenerative conditions. The 11 articles in the forum touch on multiple aspects of hypoxia, in particular, signaling responses, adaptations, and diseases that result from imbalance and fluctuations of supply and demand. Although we have developed elaborate processes to combat hypoxia and oxidative damage, it is clear that oxygen and our environment still control us, perhaps even more than they did our unicellular ancestors 2 billion years ago.