Hypoxia induces angiogenic factors in brain microvascular endothelial cells

SARS-CoV-2 Infection to Premature Neuronal Aging and Neurodegenerative Diseases: Is there any Connection with Hypoxia?

The pandemic of coronavirus disease-2019 (COVID-19), caused by SARS-CoV-2, has become a global concern as it leads to a spectrum of mild to severe symptoms and increases death tolls around the world. Severe COVID-19 results in acute respiratory distress syndrome, hypoxia, and multi- organ dysfunction. However, the long-term effects of post-COVID-19 infection are still unknown. Based on the emerging evidence, there is a high possibility that COVID-19 infection accelerates premature neuronal aging and increases the risk of age-related neurodegenerative diseases in mild to severely infected patients during the post-COVID period. Several studies correlate COVID-19 infection with neuronal effects, though the mechanism through which they contribute to the aggravation of neuroinflammation and neurodegeneration is still under investigation. SARS-CoV-2 predominantly targets pulmonary tissues and interferes with gas exchange, leading to systemic hypoxia. The neurons in the brain require a constant supply of oxygen for their proper functioning, suggesting that they are more vulnerable to any alteration in oxygen saturation level that results in neuronal injury with or without neuroinflammation. We hypothesize that hypoxia is one of the major clinical manifestations of severe SARS-CoV-2 infection; it directly or indirectly contributes to premature neuronal aging, neuroinflammation, and neurodegeneration by altering the expression of various genes responsible for the survival of the cells. This review focuses on the interplay between COVID-19 infection, hypoxia, premature neuronal aging, and neurodegenerative diseases and provides a novel insight into the molecular mechanisms of neurodegeneration.

PKCε activator protects hippocampal microvascular disruption and memory defect in 3×Tg-Alzheimer's disease mice with cerebral microinfarcts

Background

Current evidence suggests that microvessel disease is involved in Alzheimer's disease (AD). Cerebrovascular disease correlates with cardiovascular disease and is complicated in ≈40% of AD patients. The protein kinase C (PKC) ε activator DCPLA can stimulate human antigen (Hu) R that prevents degradation and promotes the translation of mitochondrial Mn-superoxide dismutase (MnSOD) and vascular endothelial growth factor-A (VEGF) mRNAs.

Methods

To induce brain microinfarcts, we injected triple transgenic (3×Tg) and wild-type (WT) control mice with microbeads (20 μm caliber) into common carotid arteries, with or without the DCPLA-ME (methyl-ester) for 2 weeks. After water maze training, mice at 16 months old were examined for confocal immunohistochemistry at a single cell or microvessel level in the hippocampal CA1 area, important for spatial memory storage, and in the dorsal hippocampus by western blots.

Results

In 3×Tg mice without cerebral microinfarcts, an accelerating age-related increase in (mild) oxidative stress and hypoxia inducible factor (HIF)-1α, but a reduction in VEGF, mitochondrial transcription factor A (TFAM), and MnSOD were associated with capillary loss. The change was less pronounced in arterioles. However, in 3×Tg mice with cerebral microinfarcts, increasing arteriolar diameter and their wall cells were related with the strong oxidative DNA damage 8-hydroxy-2'-deoxyguanosine (8-OHdG), apoptosis (cleaved caspase 3), and sustained hypoxia (increased HIF-1α and VEGF/PKCε/extracellular signal regulated kinase or ERK pathway). Microocclusion enhanced the loss of the synaptic marker spinophilin, astrocytic number, and astrocyte-vascular coupling areas and demyelination of axons. DCPLA-ME prevented spatial memory defect; strong oxidative stress-related apoptosis; sustained hypoxia (by reducing HIF-1α and VEGF); and exaggerated cell repair in arteriolar walls, pericapillary space dilation, neuro-glial-vascular disruption, and demyelination.

Conclusion

In conclusion, in 3×Tg mice with cerebral microinfarcts, sustained hypoxia (increased HIF-1α and VEGF signals) is dominant with arteriolar wall thickening, and DCPLA has a protective effect on sustained hypoxia.

Brain Endothelial Cells Activate Neuroinflammatory Pathways in Response to Early Cerebral Small Vessel Disease (CSVD) Patients' Plasma

The pathogenesis of cerebral small vessel disease (CSVD) is largely unknown. Endothelial disfunction has been suggested as the turning point in CSVD development. In this study, we tested the effect of plasma from CSVD patients on human cerebral microvascular endothelial cells with the aim of describing the pattern of endothelial activation. Plasma samples from three groups of young subjects have been tested: PTs (subjects affected by early stage CSVD); CTRLs (control subjects without abnormalities at MRI scanning); BDs (blood donors). Human Brain Endothelial Cells 5i (HBEC5i) were treated with plasma and total RNA was extracted. RNAs were pooled to reduce gene expression-based variability and NGS analysis was performed. Differentially expressed genes were highlighted comparing PTs, CTRLs and BDs with HBEC5i untreated cells. No significantly altered pathway was evaluated in BD-related treatment. Regulation of p38 MAPK cascade (GO:1900744) was the only pathway altered in CTRL-related treatment. Indeed, 36 different biological processes turned out to be deregulated after PT treatment of HBEC5i, i.e., the cytokine-mediated signaling pathway (GO:0019221). Endothelial cells activate inflammatory pathways in response to stimuli from CSVD patients' plasma, suggesting the pathogenetic role of neuroinflammation from the early asymptomatic phases of cerebrovascular disease.

Neuronal GPR81 regulates developmental brain angiogenesis and promotes brain recovery after a hypoxic ischemic insult

Perinatal hypoxic/ischemic (HI) brain injury is a major clinical problem with devastating neurodevelopmental outcomes in neonates. During HI brain injury, dysregulated factor production contributes to microvascular impairment. Glycolysis-derived lactate accumulated during ischemia has been proposed to protect against ischemic injury, but its mechanism of action is poorly understood. Herein, we hypothesize that lactate via its G-protein coupled receptor (GPR81) controls postnatal brain angiogenesis and plays a protective role after HI injury. We show that GPR81 is predominantly expressed in neurons of the cerebral cortex and hippocampus. GPR81-null mice displayed a delay in cerebral microvascular development linked to reduced levels of various major angiogenic factors and augmented expression of anti-angiogenic Thrombospondin-1 (TSP-1) in comparison to their WT littermates. Coherently, lactate stimulation induced an increase in growth factors (VEGF, Ang1 and 2, PDGF) and reduced TSP-1 expression in neurons, which contributed to accelerating angiogenesis. HI injury in GPR81-null animals curtailed vascular density and consequently increased infarct size compared to changes seen in WT mice; conversely intracerebroventricular lactate injection increased vascular density and diminished infarct size in WT but not in GPR81-null mice. Collectively, we show that lactate acting via GPR81 participates in developmental brain angiogenesis, and attenuates HI injury by restoring compromised microvasculature.

Glucose and Serum Deprivation Led to Altered Proliferation, Differentiation Potential and AMPK Activation in Stem Cells from Human Deciduous Tooth

Stem cell therapy is an evolving treatment strategy in regenerative medicine. Recent studies report stem cells from human exfoliated deciduous teeth could complement the traditional mesenchymal stem cell sources. Stem cells from human exfoliated deciduous teeth exhibit mesenchymal characteristics with multilineage differentiation potential. Mesenchymal stem cells are widely investigated for cell therapy and disease modeling. Although many research are being conducted to address the challenges of mesenchymal stem cell therapy in clinics, most of the studies are still in infancy. Host cell microenvironment is one of the major factors affecting the homing of transplanted stem cell and understanding the factors affecting the fate of stem cells of prime important. In this study we aimed to understand the effects of serum deprivation in stem cells derived from human deciduous tooth. Our study aimed to understand the morphological, transcriptional, cell cycle and stemness based changes of stem cells in nutrient deprived medium. Our results suggest that stem cells in nutrient deprived media undergo low proliferation, high apoptosis and changed the differentiation potential of the stem cells. Serum deprived mesenchymal stem cells exhibited enhanced chondrogenic differentiation potential and reduced osteogenic differentiation potential. Moreover, the activation of key metabolic sensor AMP-activated kinase (AMPK) leads to activation of transcription factors such as FOXO3, which leads to an S phase quiescence. Serum deprivation also enhanced the expression of stemness related genes Sox2 and c-Myc.

Targeting Endothelin in Alzheimer's Disease: A Promising Therapeutic Approach

Endothelin is a chemical mediator that helps in maintaining balance within the blood-brain barrier by regulating the levels of toxicants and molecules which pass through the brain, suggesting that a rise in its production determines Alzheimer's disease. The inequity in the amyloid β occurs due to a problem in its clearance from the brain initiating the production of reactive oxygen species and superoxide that activates a cascade wherein the release of inflammatory mediators and various enzymes like endothelin-converting enzymes take place. Furthermore, the cascade increases the levels of endothelin in the brain from endothelial cells. Endothelin levels are upregulated, which can be regulated by modulating the action of endothelin-converting enzymes and endothelin receptors. Hence, endothelin paves a pathway in the treatment of Alzheimer's disease. In this article, we have covered various mechanisms and preclinical studies that support and direct endothelin involvement in the progression of Alzheimer's disease by using various search tools such as PubMed, Science Direct, and Medline. Conclusive outcome data were extracted that all together defy contrivance pathways, potential drugs, endothelin receptors, and endothelin enzymes in our article giving profound importance to target endothelin for prevention and treatment of Alzheimer's disease.

Human Cerebral Perfusion, Oxygen Consumption, and Lactate Production in Response to Hypoxic Exposure

Exposure to moderate hypoxia in humans leads to cerebral lactate production, which occurs even when the cerebral metabolic rate of oxygen (CMRO2) is unaffected. We searched for the mechanism of this lactate production by testing the hypothesis of upregulation of cerebral glycolysis mediated by hypoxic sensing. Describing the pathways counteracting brain hypoxia could help us understand brain diseases associated with hypoxia. A total of 65 subjects participated in this study: 30 subjects were exposed to poikilocapnic hypoxia, 14 were exposed to isocapnic hypoxia, and 21 were exposed to carbon monoxide (CO). Using this setup, we examined whether lactate production reacts to an overall reduction in arterial oxygen concentration or solely to reduced arterial oxygen partial pressure. We measured cerebral blood flow (CBF), CMRO2, and lactate concentrations by magnetic resonance imaging and spectroscopy. CBF increased (P < 10-4), whereas the CMRO2 remained unaffected (P > 0.076) in all groups, as expected. Lactate increased in groups inhaling hypoxic air (poikilocapnic hypoxia: $0.0136\ \frac{\mathrm{mmol}/\mathrm{L}}{\Delta{\mathrm{S}}_{\mathrm{a}}{\mathrm{O}}_2}$, P < 10-6; isocapnic hypoxia: $0.0142\ \frac{\mathrm{mmol}/\mathrm{L}}{\Delta{\mathrm{S}}_{\mathrm{a}}{\mathrm{O}}_2}$, P = 0.003) but was unaffected by CO (P = 0.36). Lactate production was not associated with reduced CMRO2. These results point toward a mechanism of lactate production by upregulation of glycolysis mediated by sensing a reduced arterial oxygen pressure. The released lactate may act as a signaling molecule engaged in vasodilation.

MiR-126-HMGB1-HIF-1 Axis Regulates Endothelial Cell Inflammation during Exposure to Hypoxia-Acidosis

Crosstalk between molecular regulators miR-126, hypoxia-inducible factor 1-alpha (HIF-1-α), and high-mobility group box-1 (HMGB1) contributes to the regulation of inflammation and angiogenesis in multiple physiological and pathophysiological settings. Here, we present evidence of an overriding role for miR-126 in the regulation of HMGB1 and its downstream proinflammatory effectors in endothelial cells subjected to hypoxia with concurrent acidosis (H/A). Methods. Primary mouse endothelial cells (PMEC) were exposed to hypoxia or H/A to simulate short or chronic low-flow ischemia, respectively. RT-qPCR quantified mRNA transcripts, and proteins were measured by western blot. ROS were quantified by fluorogenic ELISA and luciferase reporter assays employed to confirm an active miR-126 target in the HMGB1 3'UTR. Results. Enhanced expression of miR-126 in PMECs cultured under neutral hypoxia was suppressed under H/A, whereas the HMGB1 expression increased sequentially under both conditions. Enhanced expression of HMGB1 and downstream inflammation markers was blocked by the premiR-126 overexpression and optimized by antagomiR. Compared with neutral hypoxia, H/A suppressed the HIF-1α expression independently of miR-126. The results show that HMGB1 and downstream effectors are optimally induced by H/A relative to neutral hypoxia via crosstalk between hypoxia signaling, miR-126, and HIF-1α, whereas B-cell lymphoma 2(Bcl2), a HIF-1α, and miR-126 regulated gene expressed optimally under neutral hypoxia. Conclusion. Inflammatory responses of ECs to H/A are dynamically regulated by the combined actions of hypoxia, miR-126, and HIF-1α on the master regulator HMGB1. The findings may be relevant to vascular diseases including atherosclerotic occlusion and interiors of plaque where coexisting hypoxia and acidosis promote inflammation as a defining etiology.

Hypoxia and its preconditioning on cardiac and vascular remodelling in experimental animals

Since oxygen (O₂) is indispensable for mammalian life, every cell in the body is endowed with mechanisms to detect and to respond to changes in the O₂ levels in the microenvironment. The heart and the brain are the two most vital, life-supporting organs requiring a continuous supply of O₂ to sustain their high metabolic rate. On being challenged with hypoxia, maintenance of O₂ supply to these organs even at the cost of others becomes a priority. This review describes the cardiovascular, skeletal muscle vascular, pulmonary vascular and cerebrovascular remodelling in face of chronic mild hypoxia exposure and the underlying mechanisms, with special reference to the role of oxidative stress, hypoxia signalling, autonomic nervous mechanisms. The significance of the normalized wall index (NWI) in assessing the remodelling of the vessels particularly of the intramyocardial coronary artery has been underscored. The review also highlights the basic concepts of hypoxic preconditioning and the subsequent protection of the brain against an acute ischemic insult in preclinical studies hinting towards its possible therapeutic potential in the management of ischemic stroke.

Perfluorocarbon as an adjuvant for tumor anti-angiogenic therapy: Relevance to hypoxia and HIF-1

Lack of vascularization results in increased demand for oxygen and creates a defined feature of the tumor microenvironment known as tumor hypoxia. It is well established that in response to hypoxia, hypoxia-inducible factor-1 α (HIF-1α) is induced which is an important factor in angiogenesis, invasion and metastasis. In turn, HIF-1α regulates the expression of angiogenic factors, such as vascular endothelial growth factor (VEGF). Ascribed to abnormal characteristics of tumor angiogenic networks, antiangiogenic therapy approaches can even worsen the hypoxic condition and can create cancer cells with stemness features. Hence oxygen delivery via perfluorocarbon (PFC) to hypoxic sites seems to result in unstable HIF expression and consequent inactivation of angiogenesis cascade and metastasis and therefore, inhibition of cancer cells stemness.

Three-dimensional induced pluripotent stem-cell models of human brain angiogenesis

During brain development, chemical cues released by developing neurons, cellular signaling with pericytes, and mechanical cues within the brain extracellular matrix (ECM) promote angiogenesis of brain microvascular endothelial cells (BMECs). Angiogenesis is also associated with diseases of the brain due to pathological chemical, cellular, and mechanical signaling. Existing in vitro and in vivo models of brain angiogenesis have key limitations. Here, we develop a high-throughput in vitro blood-brain barrier (BBB) bead assay of brain angiogenesis utilizing 150 μm diameter beads coated with induced pluripotent stem-cell (iPSC)-derived human BMECs (dhBMECs). After embedding the beads within a 3D matrix, we introduce various chemical cues and extracellular matrix components to explore their effects on angiogenic behavior. Based on the results from the bead assay, we generate a multi-scale model of the human cerebrovasculature within perfusable three-dimensional tissue-engineered blood-brain barrier microvessels. A sprouting phenotype is optimized in confluent monolayers of dhBMECs using chemical treatment with vascular endothelial growth factor (VEGF) and wnt ligands, and the inclusion of pro-angiogenic ECM components. As a proof-of-principle that the bead angiogenesis assay can be applied to study pathological angiogenesis, we show that oxidative stress can exert concentration-dependent effects on angiogenesis. Finally, we demonstrate the formation of a hierarchical microvascular model of the human blood-brain barrier displaying key structural hallmarks. We develop two in vitro models of brain angiogenesis: the BBB bead assay and the tissue-engineered BBB microvessel model. These platforms provide a tool kit for studies of physiological and pathological brain angiogenesis, with key advantages over existing two-dimensional models.

MALAT1 affects hypoxia-induced vascular endothelial cell injury and autophagy by regulating miR-19b-3p/HIF-1α axis

Cardiovascular disease has become the leading cause of death in the world. Metastasis-associated lung adenocarcinoma transcript 1 (MALAT1) plays an important role in cardiovascular disease, such as stroke. However, the role of MALAT1 in hypoxia (HYP)-induced vascular endothelial cells (VECs) remains unclear. In the present study, HYP-treated human umbilical vein endothelial cells (HUVECs) were utilized to simulate HYP-induced VEC injury. It was found that after HYP treatment, the levels of MALAT1 and hypoxia-induced factor-1 (HIF-1α) in HUVECs were upregulated, while the level of miR-19b-3p was downregulated. Knockdown of MALAT1 with siRNA significantly reduced the HIF-1α level induced by HYP. In addition, MALAT1 knockdown inhibited HYP-induced HUVECs apoptosis, autophagy and inflammation. The overexpression of HIF-1α overcame the effect of MALAT1 knockdown. Mechanism analysis showed that MALAT1-targeted miR-19b-3p and then regulated downstream HIF-1α. MALAT1 knockdown increased the level of miR-19b-3p in cells, and increased miR-19b-3p further inhibited the expression of HIF-1α, thereby reducing the HYP-induced HUVECs apoptosis, autophagy and inflammation. Taken together, these results suggest that MALAT1 may be a potential target for mitigating HYP-induced endothelial cell injury.

Roles of the hypoximir microRNA-424/322 in acute hypoxia and hypoxia-induced pulmonary vascular leakage

Acute mountain sickness (AMS) occurs in up to 25% of unacclimatized persons who ascend to 3000 m and can result in high-altitude pulmonary edema (HAPE). MicroRNAs (miRs) can regulate gene expression at the post-transcriptional level. Hypoxia selectively disrupts endothelial tight junction complexes through a hypoxia-inducible factor-1α (HIF-1α)-dependent mechanism. Though increased HIF-1α expression is associated with adaptation and protection from AMS development in the early stage of hypoxia, a downstream effector of HIF-1α, VEGF, can induce overzealous endothelial barrier dysfunction, increase vascular permeability, and ultimately result in HAPE and high-altitude cerebral edema. We hypothesized that the fine-tuning of downstream effectors by miRs is paramount for the preservation of endothelial barrier integrity and the prevention of vascular leakage. We found that several miRs were up-regulated in healthy volunteers who were subjected to a 3100-m height. By reviewing the literature and using online bioinformatics prediction software, we specifically selected miR-424 for further investigation because it can modulate both HIF-1α and VEGF. Hypoxia-induced miR-424 overexpression is HIF-1α dependent, and miR-424 stabilized HIF-1α, decreased VEGF expression, and promoted vascular endothelial cadherin phosphorylation. In addition, hypoxia resulted in endothelial barrier dysfunction with increased permeability; miR-424 thus attenuated hypoxia-induced endothelial cell senescence and apoptosis. miR-322 knockout mice were susceptible to hypoxia-induced pulmonary vascular leakage. miR-322 mimics improved hypoxia-induced pulmonary vascular leakage in vivo. We conclude that several miRs were up-regulated in healthy adult volunteers subjected to hypobaric hypoxemia. miR-424/322 could modulate the HIF-1α-VEGF axis and prevent hypoxia-induced pulmonary vascular leakage under hypoxic conditions.-Tsai, S.-H., Huang, P.-H., Tsai, H.-Y., Hsu, Y.-J., Chen, Y.-W., Wang, J.-C., Chen, Y.-H., Lin, S.-J. Roles of the hypoximir microRNA-424/322 in acute hypoxia and hypoxia-induced pulmonary vascular leakage.

Current paradigms and new perspectives on fetal hypoxia: implications for fetal brain development in late gestation

The availability of oxygen to the fetus is limited by the route taken by oxygen from the atmosphere to fetal tissues, aided or diminished by pregnancy-associated changes in maternal physiology and, ultimately, a function of atmospheric pressure and composition of the mother's inspired gas. Much of our understanding of the fetal physiological response to hypoxia comes from experiments designed to elucidate the cardiovascular and endocrine responses to transient hypoxia. Complementing this work is equally impactful research into the origins of intrauterine growth restriction in which animal models designed to restrict the transfer of oxygen from the maternal to the fetal circulation were used. A common assumption has been that outcomes measured after a period of hypoxia are related to cellular deprivation of oxygen and reoxygenation: an assumption based on a focus on what we can see "under the streetlights." Recent studies demonstrate that availability of oxygen may not tell the whole story. Transient hypoxia in the fetal sheep stimulates transcriptomics responses that mirror inflammation. This response is accompanied by the appearance of bacteria in the fetal brain and other tissues, likely resulting from a hypoxia-stimulated release of bacteria from the placenta. The appearance of bacteria in the fetus after transient hypoxia complements the recent discovery of bacterial DNA in the normal human placenta and in the tissues of fetal sheep. An understanding of the mechanism of the physiological, cellular, and molecular responses to hypoxia requires an appreciation of stimuli other than cellular oxygen deprivation: stimuli that we would have never known about without looking "between the streetlights," illuminating direct responses to the manipulated variables.

Ketamine Reduces Inflammation Pathways in the Hypothalamus and Hippocampus Following Transient Hypoxia in the Late-Gestation Fetal Sheep

The physiological response to hypoxia in the fetus has been extensively studied with regard to redistribution of fetal combined ventricular output and sparing of oxygen delivery to fetal brain and heart. Previously, we have shown that the fetal brain is capable of mounting changes in gene expression that are consistent with tissue inflammation. The present study was designed to use transcriptomics and systems biology modeling to test the hypothesis that ketamine reduces or prevents the upregulation of inflammation-related pathways in hypothalamus and hippocampus after transient hypoxic hypoxia. Chronically catheterized fetal sheep (122 ± 5 days gestation) were subjected to 30 min hypoxia (relative reduction in P_aO₂∼50%) caused by infusion of nitrogen into the inspired gas of the pregnant ewe. RNA was isolated from fetal hypothalamus and hippocampus collected 24 h after hypoxia, and was analyzed for gene expression using the Agilent 15.5 k ovine microarray. Ketamine, injected 10 min prior to hypoxia, reduced the cerebral immune response activation to the hypoxia in both brain regions. Genes both upregulated by hypoxia and downregulated by ketamine after hypoxia were significantly associated with gene ontology terms and KEGG pathways that are, themselves, associated with the tissue response to exposure to bacteria. We conclude that the results are consistent with interruption of the cellular response to bacteria by ketamine.

The effect of hypoxia on ZEB1 expression in a mimetic system of the blood-brain barrier

The blood-brain barrier consists of a tightly sealed monolayer of endothelial cells being vital in maintaining a stable intracerebral microenvironment. The barrier is receptive to leakage upon exposure to environmental factors, like hypoxia, and its disruption has been suggested as a constituent in the pathophysiology of both neurological and psychiatric disorders. The schizophrenia associated ZEB1 gene encodes a transcription factor susceptible to transcriptional control by a hypoxia induced factor, HIF1A, known to be implicated in blood-brain barrier dysfunction. However, whether ZEB1 is also implicated in maintaining blood-brain barrier integrity upon hypoxia is unknown. Here we assessed Hif1a, Zo1 and Zeb1 mRNA expression and ZO1 protein abundancy in a mimetic system of the in vivo blood-brain barrier comprising mouse brain endothelial cells subjected to the norm- and proven hypoxic conditions. Despite that, Hif1a mRNA expression was significantly increased, clearly indicating that the oxygen-deprived environment introduced a hypoxia response in the cells, we found no hypoxia-induced changes in neither ZO1 abundancy nor in the expression of Zo1 and Zeb1 mRNA. However, independent of hypoxia status, we found that Zeb1 and Zo1 mRNA expression is highly correlated. Further studies are warranted that investigate the implication of the ZEB1/ZO1 axis in blood-brain barrier maintenance under different physiological conditions.

Kidney, heart and brain: three organs targeted by ageing and glycation

Advanced glycation end-product (AGE) is the generic term for a heterogeneous group of derivatives arising from a non-enzymatic reaction between reducing sugars and proteins. In recent years, evidence has accumulated that incriminates AGEs in pathogenic processes associated with both chronic hyperglycaemia and age-related diseases. Regardless of their exogenous or endogenous origin, the accumulation of AGEs and their derivatives could promote accelerated ageing by leading to protein modifications and activating several inflammatory signalling pathways via AGE-specific receptors. However, it remains to be demonstrated whether preventing the accumulation of AGEs and their effects is an important therapeutic option for successful ageing. The present review gives an overview of the current knowledge on the pathogenic role of AGEs by focusing on three AGE target organs: kidney, heart and brain. For each of these organs we concentrate on an age-related disease, each of which is a major public health issue: chronic kidney disease, heart dysfunction and neurodegenerative diseases. Even though strong connections have been highlighted between glycation and age-related pathogenesis, causal links still need to be validated. In each case, we report evidence and uncertainties suggested by animal or epidemiological studies on the possible link between pathogenesis and glycation in a chronic hyperglycaemic state, in the absence of diabetes, and with exogenous AGEs alone. Finally, we present some promising anti-AGE strategies that are currently being studied.

Increased Lung Ischemia-Reperfusion Injury in Aquaporin 1-Null Mice Is Mediated via Decreased Hypoxia-Inducible Factor 2α Stability

Aquaporin (AQP) 1, a water channel protein expressed widely in vascular endothelia, has been shown to regulate cell migration, angiogenesis, and organ regeneration. Even though its role in the pathogenesis of lung ischemia-reperfusion (IR) injury has been defined, the functional role of AQP1 during long-term IR resolution remains to be clarified. Here, we found that AQP1 expression was increased at late time points (7-14 d) after IR and colocalized with endothelial cell (EC) marker CD31. Compared with IR in wild-type mice, IR in Aqp1(-/-) mice had significantly enhanced leukocyte infiltration, collagen deposition, and microvascular permeability, as well as inhibited angiogenic factor expression. AQP1 knockdown repressed hypoxia-inducible factor (HIF)-2α protein stability. HIF-2α overexpression rescued the angiogenic factor expression in pulmonary microvascular ECs with AQP1 knockdown exposed to hypoxia-reoxygenation. Furthermore, AQP1 knockdown suppressed cellular viability and capillary tube formation, and enhanced permeability in pulmonary microvascular ECs, which were partly rescued by HIF-2α overexpression. Thus, this study demonstrates that AQP1 deficiency delays long-term IR resolution, partly through repressing angiogenesis mediated by destabilizing HIF-2α. These results suggest that AQP1 participates in long-term IR resolution, at least in part by promoting angiogenesis.

RETRACTED: Protective effects of total flavonoids in Caragana against hypoxia/reoxygenation-induced injury in human brain microvascular endothelial cells

This article has been retracted: please see Elsevier Policy on Article Withdrawal (http://www.elsevier.com/locate/withdrawalpolicy). This article has been retracted at the request of the Editor-in-Chief. An Expression of Concern for this article was previously published while an investigation was conducted (see related editorial: https://doi.org/10.1016/j.biopha.2022.113812). This retraction notice supersedes the Expression of Concern published earlier. Concern was raised about the reliability of the Transwell assay images shown in Figure 4A, which appear to contain similar features to those found in other publications, as detailed here: https://pubpeer.com/publications/FE1B7461C358F48E6838BF1622C291; and here: https://docs.google.com/spreadsheets/d/1r0MyIYpagBc58BRF9c3luWNlCX8VUvUuPyYYXzxWvgY/edit#gid=262337249. An additional suspected image duplication within Figure 5A was also identified. The journal requested the corresponding author comment on these concerns and provide the associated raw data. The authors did not respond to this request and therefore the Editor-in-Chief decided to retract the article.

Precision medicine of aneurysmal subarachnoid hemorrhage, vasospasm and delayed cerebral ischemia

INTRODUCTION

Precision medicine provides individualized treatment of diseases through leveraging patient-to-patient variation. Aneurysmal subarachnoid hemorrhage carries tremendous morbidity and mortality with cerebral vasospasm and delayed cerebral ischemia proving devastating and unpredictable. Lack of treatment measures for these conditions could be improved through precision medicine. Areas covered: Discussed are the pathophysiology of CV and DCI, treatment guidelines, and evidence for precision medicine used for prediction and prevention of poor outcomes following aSAH. A PubMed search was performed using keywords cerebral vasospasm or delayed cerebral ischemia and either biomarkers, precision medicine, metabolomics, proteomics, or genomics. Over 200 peer-reviewed articles were evaluated. The studies presented cover biomarkers identified as predictive markers or therapeutic targets following aSAH. Expert commentary: The biomarkers reviewed here correlate with CV, DCI, and neurologic outcomes after aSAH. Though practical use in clinical management of aSAH is not well established, using these biomarkers as predictive tools or therapeutic targets demonstrates the potential of precision medicine.

Angiographic Structural Differentiation between Native Arteriogenesis and Therapeutic Synangiosis in Intracranial Arterial Steno-Occlusive Disease

BACKGROUND AND PURPOSE

Encephaloduroarteriosynangiosis has been shown to generate collateral vessels from the extracranial-to-intracranial circulation in patients with Moyamoya disease and intracranial arterial steno-occlusive disease. The mechanisms involved are not well-understood. We hypothesized that angiogenesis is the leading mechanism forming collaterals after encephaloduroarteriosynangiosis because there are no pre-existing connections. Angiogenesis-generated collaterals should exhibit higher architectural complexity compared with innate collaterals.

MATERIALS AND METHODS

Pre- and postoperative digital subtraction angiograms were analyzed in patients enrolled in a prospective trial of encephaloduroarteriosynangiosis surgery. Branching angioscore, tortuosity index, and local connected fractal dimension were compared between innate and postoperative collaterals.

RESULTS

One hundred one angiograms (50 preoperative, 51 postoperative) were analyzed from 44 patients (22 with intracranial atherosclerosis and 22 with Moyamoya disease). There was a significantly higher median branching angioscore (13 versus 4, P < .001) and a lower median tortuosity index (1.08 versus 1.76, P < .001) in the encephaloduroarteriosynangiosis collaterals compared with innate collaterals. Higher mean local fractal dimension peaks (1.28 ± 0.1 versus 1.16 ± 0.11, P < .001) were observed in the encephaloduroarteriosynangiosis collaterals compared with innate collaterals for both intracranial atherosclerosis (P < .001) and Moyamoya disease (P < .001) groups. The observed increase in high connectivity was greater in the intracranial atherosclerosis group compared with patients with Moyamoya disease (P = .01).

CONCLUSIONS

The higher median branching angioscore and local connected fractal dimension, along with the lower median tortuosity index of encephaloduroarteriosynangiosis collaterals, are consistent with the greater complexity observed in the process of sprouting and splitting associated with angiogenesis.

Tuning graft- and host-derived vascularization in modular tissue constructs: a potential role of HIF1 activation

A better understanding of the factors governing the vascularization of engineered tissues is crucial for their advancement as therapeutic platforms. Here, we studied the effect of implant volume and cell densities on the in vivo vascularization of modular engineered tissue constructs. Sub-millimeter collagen modules containing adipose-derived mesenchymal stromal cells (adMSC) and enveloped by human umbilical vein endothelial cells (HUVEC) were subcutaneously implanted in severe-combined immunodeficient mice with a beige-mutation (SCID-bg) mice. Implant volume and cell density was varied relative to a base case, defined as a 0.01 mL implant containing 1.5×10(7) adMSC/mL and 3.9×10(6) HUVEC/mL. At 7 and 14 days post-transplantation, the constructs were harvested for immunohistochemical analysis of total (CD31(+)) and graft-derived (UEA1(+)) vessel formation, hypoxia-inducible factor 1-alpha (HIF1α) expression, infiltration of host-derived leukocytes (CD45), and macrophages (F4/80). Implant volume and cell density affected the relative contributions of host- versus graft-derived vascularization, highlighting that different mechanisms underlie the two processes. Graft-derived vessel formation was most rapid and robust in implants with high HIF1α expression, namely large volume implants and implants with high adMSC and HUVEC density (p<0.01 compared to base case at day 7). Many HIF1α(+) cells were vessel-lining HUVEC, suggesting that HIF1 activation may be key to vessel assembly in the graft. Host vessel ingrowth, however, dominated the vascularization of small volume implants (of high and low adMSC density alike), which showed low HIF1α expression at day 7. Host vessels were sustained to day 14 when adMSC density alone was increased, presumably due to increased paracrine secretions. This study points to a potential role of HIF1 activation in the vascularization of tissue constructs, which may be harnessed to engineer robust vessels for therapeutic applications.

In vitro modeling of the neurovascular environment by coculturing adult human brain endothelial cells with human neural stem cells

Brain and vascular cells form a functionally integrated signalling network that is known as the neurovascular unit (NVU). The signalling (autocrine, paracrine and juxtacrine) between different elements of this unit, especially in humans, is difficult to disentangle in vivo. Developing representative in vitro models is therefore essential to better understand the cellular interactions that govern the neurovascular environment. We here describe a novel approach to assay these cellular interactions by combining a human adult cerebral microvascular endothelial cell line (hCMEC/D3) with a fetal ganglionic eminence-derived neural stem cell (hNSC) line. These cell lines provide abundant homogeneous populations of cells to produce a consistently reproducible in vitro model of endothelial morphogenesis and the ensuing NVU. Vasculature-like structures (VLS) interspersed with patches of differentiating neural cells only occurred when hNSCs were seeded onto a differentiated endothelium. These VLS emerged within 3 days of coculture and by day 6 were stabilizing. After 7 days of coculture, neuronal differentiation of hNSCs was increased 3-fold, but had no significant effect on astrocyte or oligodendrocyte differentiation. ZO1, a marker of adherens and tight junctions, was highly expressed in both undifferentiated and differentiated endothelial cells, but the adherens junction markers CD31 and VE-cadherin were significantly reduced in coculture by approximately 20%. A basement membrane, consisting of laminin, vitronectin, and collagen I and IV, separated the VLS from neural patches. This simple assay can assist in elucidating the cellular and molecular signaling involved in the formation of VLS, as well as the enhancement of neuronal differentiation through endothelial signaling.

Hypoxia selectively disrupts brain microvascular endothelial tight junction complexes through a hypoxia-inducible factor-1 (HIF-1) dependent mechanism

The blood-brain barrier (BBB) constitutes a critical barrier for the maintenance of central nervous system homeostasis. Brain microvascular endothelial cells line the vessel walls and express tight junction (TJ) complexes that restrict paracellular passage across the BBB, thereby fulfilling a crucial role in ensuring brain function. Hypoxia, an impaired O(2) delivery, is known to cause BBB dysfunction but the mechanisms that drive this disruption remain unclear. This study discloses the relevance of the master regulator of the hypoxic response, hypoxia-inducible factor-1 (HIF-1), in hypoxia-induced barrier disruption using the rat brain endothelial cell line RBE4. Hypoxic exposure rapidly induced stabilization of the HIF-1 oxygen-dependent alpha subunit (HIF-1α) concomitantly with BBB impairment and TJ disruption mainly through delocalization and increased tyrosine phosphorylation of TJ proteins. Similar observations were obtained by normoxic stabilization of HIF-1α using CoCl(2), deferoxamine, and dimethyloxalylglycine underlining the involvement of HIF-1 in barrier dysfunction particularly via TJ alterations. In agreement inhibition of HIF-1 stabilization by 2-methoxyestradiol and YC-1 improved barrier function in hypoxic cells. Overall our data suggests that activation of HIF-1-mediated signaling disrupts TJ resulting in increased BBB permeability.

Glycation: the angiogenic paradox in aging and age-related disorders and diseases

Angiogenesis is generally a quiescent process which, however, may be modified by different physiological and pathological conditions. The "angiogenic paradox" has been described in diabetes because this disease impairs the angiogenic response in a manner that differs depending on the organs involved and disease evolution. Aging is also associated with pro- and antiangiogenic processes. Glycation, the post-translational modification of proteins, increases with aging and the progression of diabetes. The effect of glycation on angiogenesis depends on the type of glycated proteins and cells involved. This complex link could be responsible for the "angiogenic paradox" in aging and age-related disorders and diseases. Using diabetes as a model, the present work has attempted to review the age-related angiogenic paradox, in particular the effects of glycation on angiogenesis during aging.

Adjusting the compass: new insights into the role of angiogenesis in Alzheimer's disease

Growing evidence suggests that vascular perturbation plays a critical role in the pathogenesis of Alzheimer’s disease (AD). It appears to be a common feature in addition to the classic pathological hallmarks of amyloid beta (Aβ) plaques and neurofibrillary. Moreover, the accumulation of Aβ in the cerebral vasculature is closely associated with cognitive decline, and disruption of the blood–brain barrier (BBB) has been shown to coincide with the onset of cognitive impairment. Although it was originally hypothesized that the accumulation of Aβ and the subsequent disruption of the BBB were due to the impaired clearance of Aβ from the brain, a body of data now suggests an alternative hypothesis for vascular dysfunction in AD that amyloidogenesis promotes extensive neoangiogenesis leading to increased vascular permeability and subsequent hypervascularization. In this review, we discuss the role Aβ plays in angiogenesis of the neurovasculature and BBB and how it may contribute to the pathogenesis of AD. These studies suggest that interventions that directly or indirectly affect angiogenesis could have beneficial effects on amyloid and other pathways in AD.

Circulating microparticles from obstructive sleep apnea syndrome patients induce endothelin-mediated angiogenesis

Microparticles are deemed true biomarkers and vectors of biological information between cells. Depending on their origin, the composition of microparticles varies and the subsequent message transported by them, such as proteins, mRNA, or miRNA, can differ. In obstructive sleep apnea syndrome (OSAS), circulating microparticles are associated with endothelial dysfunction by reducing endothelial-derived nitric oxide production. Here, we have analyzed the potential role of circulating microparticles from OSAS patients on the regulation of angiogenesis and the involved pathway. VEGF content carried by circulating microparticles from OSAS patients was increased when compared with microparticles from non-OSAS patients. Circulating microparticles from OSAS patients induced an increase of angiogenesis that was abolished in the presence of the antagonist of endothelin-1 receptor type B. In addition, endothelin-1 secretion was increased in human endothelial cells treated by OSAS microparticles. We highlight that circulating microparticles from OSAS patients can modify the secretome of endothelial cells leading to angiogenesis.

Activating glucocorticoid receptor-ERK signaling pathway contributes to ginsenoside Rg1 protection against β-amyloid peptide-induced human endothelial cells apoptosis

The deposition of β-amyloid (Aβ) in neurons and vascular cells of the brain has been characterized in Alzheimer's disease. Ginsenoside Rg1 (Rg1) is an active components in Panax ginseng, a famous traditional Chinese medicines recorded in Compendium of Materia Medica. Present study attempted to evaluate the potential mechanisms of Aβ-mediated insult and the protective effects of Rg1 on human endothelial cells. Rg1 attenuated the Aβ25-35-associated mitochondrial apoptotic events, accompanied by inhibiting HIF-1α expression followed by intracellular reactive nitrogen species generation, and protein nitrotyrosination. These protective effects were abolished by glucocorticoid receptor (GR) antagonist RU486 or p-ERK inhibitor U0126 rather than estrogen receptor α antagonist ICI 82,780. Taken together, our results suggested that Rg1 protected against Aβ25-35-induced apoptosis at least in part by two complementary GR-dependent ERK phosphorylation pathways: (1) down-regulating HIF-1α initiated protein nitrotyrosination, and (2) inhibiting mitochondrial apoptotic cascades. These data provided a novel insight to the mechanisms of Rg1protective effects on Aβ25-35-induced endothelial cells apoptosis, suggesting that GR-ERK signaling pathway might play an important role in it.

Chronic asthma results in cognitive dysfunction in immature mice

Asthma is the most common chronic childhood illness today. However, little attention is paid for the impacts of chronic asthma-induced hypoxia on cognitive function in children. The present study used immature mice to establish ovalbumin-induced chronic asthma model, and found that chronic asthma impaired learning and memory ability in Morris Water Maze test. Further study revealed that chronic asthma destroyed synaptic structure, impaired long-term potentiation (LTP) maintaining in the CA1 region of mouse hippocampal slices. We found that intermittent hypoxia during chronic asthma resulted in down-regulation of c-fos, Arc and neurogenesis, which was responsible for the impairment of learning and memory in immature mice. Moreover, our results showed that budesonide treatment alone was inadequate for attenuating chronic asthma-induced cognitive impairment. Therefore, our findings indicate that chronic asthma might result in cognitive dysfunction in children, and more attention should be paid for chronic asthma-induced brain damage in the clinical therapy.

Vascular endothelin receptor type B: structure, function and dysregulation in vascular disease

Endothelin-1 (ET-1) is a major regulator of vascular function, acting via both endothelin receptor type A (ET(A)R) and type B (ET(B)R). Although the role of ET(A)R in vascular smooth muscle (VSM) contraction has been studied, little is known about ET(B)R. ET(B)R is a G-protein coupled receptor with a molecular mass of ~50 kDa and 442 amino acids arranged in seven transmembrane domains. Alternative splice variants of ET(B)R and heterodimerization and cross-talk with ET(A)R may affect the receptor function. ET(B)R has been identified in numerous blood vessels with substantial effects in the systemic, renal, pulmonary, coronary and cerebral circulation. ET(B)R in the endothelium mediates the release of relaxing factors such as nitric oxide, prostacyclin and endothelium-derived hyperpolarizing factor, and could also play a role in ET-1 clearance. ET(B)R in VSM mediates increases in [Ca(2+)](i), protein kinase C, mitogen-activated protein kinase and other pathways of VSM contraction and cell growth. ET-1/ET(A)R signaling has been associated with salt-sensitive hypertension (HTN) and pulmonary arterial hypertension (PAH), and ET(A)R antagonists have shown some benefits in these conditions. In search for other pathogenetic factors and more effective approaches, the role of alterations in endothelial ET(B)R and VSM ET(B)R in vascular dysfunction, and the potential benefits of modulators of ET(B)R in treatment of HTN and PAH are being examined. Combined ET(A)R/ET(B)R antagonists could be more efficacious in the management of conditions involving upregulation of ET(A)R and ET(B)R in VSM. Combined ET(A)R antagonist with ET(B)R agonist may need to be evaluated in conditions associated with decreased endothelial ET(B)R expression/activity.