Mechanisms of hypoxic signal transduction regulated by reactive nitrogen species

Comparative Molecular and Biological Characteristic of the Systemic Inflammatory Response in Adult and Old Male Wistar Rats with Different Resistance to Hypoxia

Morphological, molecular, and biological features of the systemic inflammatory response induced by LPS administration were assessed in adult and old male Wistar rats with high and low resistance to hypoxia. In 6 h after LPS administration, mRNA expression levels of Hif1a, Vegf, Nfkb, and level of IL-1β protein in old rats were higher than in adult rats regardless of hypoxia tolerance. The morphometric study showed that the number of neutrophils in the interalveolar septa of the lungs was significantly higher in low-resistant adult and old rats 6 h after LPS administration. Thus, in old male Wistar rats, systemic inflammatory response is more pronounced than in adult rats and depends on the initial tolerance to hypoxia, which should be considered when developing new approaches to the therapy of systemic inflammatory response in individuals of different ages.

Adaptive Responses to Hypoxia and/or Hyperoxia in Humans

Significance: Oxygen is indispensable for aerobic life, but its utilization exposes cells and tissues to oxidative stress; thus, tight regulation of cellular, tissue, and systemic oxygen concentrations is crucial. Here, we review the current understanding of how the human organism (mal-)adapts to low (hypoxia) and high (hyperoxia) oxygen levels and how these adaptations may be harnessed as therapeutic or performance enhancing strategies at the systemic level. Recent Advances: Hyperbaric oxygen therapy is already a cornerstone of modern medicine, and the application of mild hypoxia, that is, hypoxia conditioning (HC), to strengthen the resilience of organs or the whole body to severe hypoxic insults is an important preparation for high-altitude sojourns or to protect the cardiovascular system from hypoxic/ischemic damage. Many other applications of adaptations to hypo- and/or hyperoxia are only just emerging. HC-sometimes in combination with hyperoxic interventions-is gaining traction for the treatment of chronic diseases, including numerous neurological disorders, and for performance enhancement. Critical Issues: The dose- and intensity-dependent effects of varying oxygen concentrations render hypoxia- and/or hyperoxia-based interventions potentially highly beneficial, yet hazardous, although the risks versus benefits are as yet ill-defined. Future Directions: The field of low and high oxygen conditioning is expanding rapidly, and novel applications are increasingly recognized, for example, the modulation of aging processes, mood disorders, or metabolic diseases. To advance hypoxia/hyperoxia conditioning to clinical applications, more research on the effects of the intensity, duration, and frequency of altered oxygen concentrations, as well as on individual vulnerabilities to such interventions, is paramount. Antioxid. Redox Signal. 37, 887-912.

Identification of a 6-RBP gene signature for a comprehensive analysis of glioma and ischemic stroke: Cognitive impairment and aging-related hypoxic stress

There is mounting evidence that ischemic cerebral infarction contributes to vascular cognitive impairment and dementia in elderly. Ischemic stroke and glioma are two majorly fatal diseases worldwide, which promote each other's development based on some common underlying mechanisms. As a post-transcriptional regulatory protein, RNA-binding protein is important in the development of a tumor and ischemic stroke (IS). The purpose of this study was to search for a group of RNA-binding protein (RBP) gene markers related to the prognosis of glioma and the occurrence of IS, and elucidate their underlying mechanisms in glioma and IS. First, a 6-RBP (POLR2F, DYNC1H1, SMAD9, TRIM21, BRCA1, and ERI1) gene signature (RBPS) showing an independent overall survival prognostic prediction was identified using the transcriptome data from TCGA-glioma cohort (n = 677); following which, it was independently verified in the CGGA-glioma cohort (n = 970). A nomogram, including RBPS, 1p19q codeletion, radiotherapy, chemotherapy, grade, and age, was established to predict the overall survival of patients with glioma, convenient for further clinical transformation. In addition, an automatic machine learning classification model based on radiomics features from MRI was developed to stratify according to the RBPS risk. The RBPS was associated with immunosuppression, energy metabolism, and tumor growth of gliomas. Subsequently, the six RBP genes from blood samples showed good classification performance for IS diagnosis (AUC = 0.95, 95% CI: 0.902–0.997). The RBPS was associated with hypoxic responses, angiogenesis, and increased coagulation in IS. Upregulation of SMAD9 was associated with dementia, while downregulation of POLR2F was associated with aging-related hypoxic stress. Irf5/Trim21 in microglia and Taf7/Trim21 in pericytes from the mouse cerebral cortex were identified as RBPS-related molecules in each cell type under hypoxic conditions. The RBPS is expected to serve as a novel biomarker for studying the common mechanisms underlying glioma and IS.

Relevance of angiogenesis in autoimmune testis inflammation

Experimental autoimmune orchitis (EAO) is a useful model to study organ-specific autoimmunity and chronic testicular inflammation. This model reflects testicular pathological changes reported in immunological infertility in men. Progression of EAO in rodents is associated with a significantly increased percentage of testicular endothelial cells and interstitial testicular blood vessels, indicating an ongoing angiogenic process. Vascular endothelial growth factor A (VEGFA), the main regulator of physiological and pathological angiogenesis, can stimulate endothelial cell proliferation, chemotaxis and vascular permeability. The aim of this study was to explore the role of VEGFA in the pathogenesis of testicular inflammation. Our results found VEGFA expression in Leydig cells, endothelial cells and macrophages in testis of rats with autoimmune orchitis. VEGFA level was significantly higher in testicular fluid and serum of rats at the end of the immunization period, preceding testicular damage. VEGF receptor (VEGFR) 1 is expressed mainly in testicular endothelial cells, whereas VEGFR2 was detected in germ cells and vascular smooth muscle cells. Both receptors were expressed in testicular interstitial cells. VEGFR2 increased after the immunization period in the testicular interstitium and VEGFR1 was downregulated in EAO testis. In-vivo-specific VEGFA inhibition by Bevacizumab prevented the increase in blood vessel number and reduced EAO incidence and severity. Our results unveil relevance of VEGFA-VEGFR axis during orchitis development, suggesting that VEGFA might be an early marker of testicular inflammation and Bevacizumab a therapeutic tool for treatment of testicular inflammation associated with subfertility and infertility.

The interrelationship between cerebral ischemic stroke and glioma: a comprehensive study of recent reports

Glioma and cerebral ischemic stroke are two major events that lead to patient death worldwide. Although these conditions have different physiological incidences, ~10% of ischemic stroke patients develop cerebral cancer, especially glioma, in the postischemic stages. Additionally, the high proliferation, venous thrombosis and hypercoagulability of the glioma mass increase the significant risk of thromboembolism, including ischemic stroke. Surprisingly, these events share several common pathways, viz. hypoxia, cerebral inflammation, angiogenesis, etc., but the proper mechanism behind this co-occurrence has yet to be discovered. The hypercoagulability and presence of the D-dimer level in stroke are different in cancer patients than in the noncancerous population. Other factors such as atherosclerosis and coagulopathy involved in the pathogenesis of stroke are partially responsible for cancer, and the reverse is also partially true. Based on clinical and neurosurgical experience, the neuronal structures and functions in the brain and spine are observed to change after a progressive attack of ischemia that leads to hypoxia and atrophy. The major population of cancer cells cannot survive in an adverse ischemic environment that excludes cancer stem cells (CSCs). Cancer cells in stroke patients have already metastasized, but early-stage cancer patients also suffer stroke for multiple reasons. Therefore, stroke is an early manifestation of cancer. Stroke and cancer share many factors that result in an increased risk of stroke in cancer patients, and vice-versa. The intricate mechanisms for stroke with and without cancer are different. This review summarizes the current clinical reports, pathophysiology, probable causes of co-occurrence, prognoses, and treatment possibilities.

High mobility group box 1 (HMGB1) acts as an "alarmin" to promote acute myeloid leukaemia progression

High mobility group box 1 (HMGB1) is a non-histone protein localised in the cell nucleus, where it interacts with DNA and promotes nuclear transcription events. HMGB1 levels are elevated during acute myeloid leukaemia (AML) progression followed by participation of this protein in triggering signalling events in target cells as a pro-inflammatory stimulus. This mechanism was hypothesised to be employed as a survival pathway by malignant blood cells and our aims were therefore to test this hypothesis experimentally. Here we report that HMGB1 triggers the release of tumour necrosis factor alpha (TNF-α) by primary human AML cells. TNF-α induces interleukin 1 beta (IL-1β) production by healthy leukocytes, leading to IL-1β-induced secretion of stem cell factor (SCF) by competent cells (for example endothelial cells). These results were verified in mouse bone marrow and primary human AML blood plasma samples. In addition, HMGB1 was found to induce secretion of angiogenic vascular endothelial growth factor (VEGF) and this process was dependent on the immune receptor Tim-3. We therefore conclude that HMGB1 is critical for AML progression as a ligand of Tim-3 and other immune receptors thus supporting survival/proliferation of AML cells and possibly the process of angiogenesis.

Ameliorative effect of trimetazidine on cisplatin-induced hepatotoxicity in rats

This study was designed to evaluate the protective effects of trimetazidine (TMZ) against cisplatin (CP) induced liver damage in rats. Animals were distributed among 4 groups as follows: control group; TMZ group (20 mg/kg body mass, per oral), which was treated for 10 days; CP group (6 mg/kg, by intraperitoneal injection), which received a single injection; and the CP + TMZ group (20 mg/kg, per oral), which received TMZ 4 days before and 6 days after CP injection. The extent of hepatic damage was studied by assessing biochemical parameters and histopathological evaluation of the extracted liver tissue. The results revealed that liver enzymes were markedly elevated after injection of CP, as evident from significant increases in the serum levels of alanine transaminase (AST), alanine aminotransferase (ALT), gamma glutamyl transferase (γ-GT), and lactate dehydrogenase (LDH), as well as marked changes to the liver architecture, with a significant decrease in serum levels of albumin. There were also marked changes to the antioxidant defense system, as indicated by significant decreases in total antioxidants and hepatic levels of reduced glutathione (GSH) and superoxide dismutase (SOD), together with a significant increase in lipid peroxidation. However, there was a significant increase in the activity of hepatic nuclear factor kappa B (NF-κB) as well as hepatic Bax protein expression. We conclude that TMZ protects against CP-induced liver damage through scavenging free radicals and anti-inflammatory and antiapoptotic effects, as well as through reducing NF-κB activation.

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.

Small molecule signaling agents: the integrated chemistry and biochemistry of nitrogen oxides, oxides of carbon, dioxygen, hydrogen sulfide, and their derived species

Several small molecule species formally known primarily as toxic gases have, over the past 20 years, been shown to be endogenously generated signaling molecules. The biological signaling associated with the small molecules NO, CO, H₂S (and the nonendogenously generated O₂), and their derived species have become a topic of extreme interest. It has become increasingly clear that these small molecule signaling agents form an integrated signaling web that affects/regulates numerous physiological processes. The chemical interactions between these species and each other or biological targets is an important factor in their roles as signaling agents. Thus, a fundamental understanding of the chemistry of these molecules is essential to understanding their biological/physiological utility. This review focuses on this chemistry and attempts to establish the chemical basis for their signaling functions.

Hypoxia-inducible factor 1 as one of the "signaling drivers" of Toll-like receptor-dependent and allergic inflammation

Hypoxia-inducible factor 1 (HIF-1) is a heterodimeric transcription complex which plays a crucial role in cellular adaptation to low oxygen availability. In the last years there has been increasing evidence about the role of this factor in inflammatory/innate immune reactions. It has also been found to contribute to different types of allergic inflammation. In this review the current knowledge about the accumulation and role of HIF-1 in Toll-like receptor-mediated and allergic inflammation is summarized. Differential biochemical mechanisms employed to stabilize the protein in different cases are discussed.

Primers on molecular pathways: lipopolysaccharide signaling - potential role in pancreatitis and pancreatic cancer

The innate immune system recognizes the presence of bacterial pathogens through the expression of a family of membrane receptors known as Toll-like receptors (TLRs). Lipopolysaccharide (LPS) is specifically recognized by TLR4. Recognition of microbial components by TLRs initiates signal transduction pathways, which triggers expression of genes. These gene products control innate immune responses and further instruct development of antigen-specific acquired immunity. TLR signaling pathways are finely regulated by TIR domain-containing adaptors, such as MyD88, TIRAP/Mal, TRIF and TRAM. LPS can act not only on immune cells but also on some types of epithelial cells including cancer cells and promote its transformed phenotype. Specifically, LPS can activate NF-kappaB signaling in pancreatic cancer cells, thus connecting inflammation with cancer progression. The TLR4 signaling pathway may offer a useful therapeutic target for patients with pancreatitis or pancreatic cancer associated with inflammation.

Apoptosis signal-regulating kinase 1 (ASK1) and HIF-1alpha protein are essential factors for nitric oxide-dependent accumulation of p53 in THP-1 human myeloid macrophages

Nitric oxide (NO) is a reactive secondary mediator, which has been found to participate in cell cycle regulation and apoptosis in myeloid macrophages, the key effectors of inflammatory and innate immune responses. However, the molecular mechanisms of nitric oxide-induced death of myeloid macrophages are not well understood. In this study we have found that NO derived from S-nitrosoglutathione (GSNO) activates ASK1 in THP-1 human myeloid macrophages in a concentration and time-dependent manner. It also induces accumulation of HIF-1alpha protein in a concentration-dependent manner, which peaks at 4 h of exposure to 1 mM GSNO. GSNO does not affect the level of HIF-1alpha mRNA as detected by the RT-PCR. In addition, GSNO was found to induce accumulation of p53 in normal but not HIF-1alpha knockdown THP-1 cells, where expression of this protein was silenced by specific siRNA. It has also been found that GSNO-mediated accumulation of p53 depends on activation of ASK1 since no GSNO-induced p53 stabilisation was observed in THP-1 cells transfected with dominant-negative form of this kinase. However, in both HIF-1alpha knockdown THP-1 cells and those transfected with the dominant-negative form of ASK1, GSNO was able to induce cell death as detected by the MTS cell viability assay leading to an increase in release of LDH.

Plasma and placental nitric oxide levels in women with and without pre-eclampsia living at different altitudes

OBJECTIVE

To investigate the nitric oxide (NO) levels in the plasma and the placentas of pregnant women with pre-eclampsia and women without pre-eclampsia, and to determine the effect of high or low altitude of residence.

METHODS

NO was determined by chemoluminescence and group comparisons were performed.

RESULTS

Women with pre-eclampsia (n=63) had higher plasma NO levels (38.6+/-17.44 vs 30.6+/-12.44 micromol/L, P=0.004) and higher placental NO levels (38.5+/-17.0 vs 24.3+/-7.16 ng/mg protein, P<0.05) compared with women without pre-eclampsia. A similar trend was found when comparisons were made according to altitude of residence. NO levels were significantly higher in the plasma of pre-eclamptic women living at sea level (41.11+/-18.78 vs 28.96+/-9.57 micromol/L, P=0.003), and in the placentas of women living at high altitude (39.51+/-16.98 vs 21.91+/-6.64 ng/mg protein, P<0.0001).

CONCLUSION

Women with pre-eclampsia had higher plasma and placental NO levels and the differences were associated with altitude of residence.

Lessons in hypoxic adaptation from high-altitude populations

An increase in hemoglobin level is seen in virtually all lowlanders who move to or train at altitude; however, studies of high-altitude native populations illustrate that this response is not necessary for successful long-term residence. Indigenous populations living at the same altitude have differences not only in hemoglobin level but also in other traits like oxygen saturation. Support for a genetic causation for differences in features of oxygen transport, namely hemoglobin levels and oxygen saturation, is derived from kindred studies among the highlander populations. Indeed, evidence from Tibet suggests that inferred genes for high oxygen saturation are associated with higher offspring survival. It may be that signaling molecules like nitric oxide and transcription factors such as hypoxia-inducible factor could act as an upstream regulator for highlander traits. However, the preponderance of data suggests that it is unlikely that one process or even a common set of processes is responsible for successful biologic adaptation shown in all three resident high-altitude populations. Future studies will require the ability to identify combinations of genetic variants with outcomes including expression levels, appropriate phenotypes, and functional responses.

Modeling the neurovascular niche: murine strain differences mimic the range of responses to chronic hypoxia in the premature newborn

Preterm birth results in significant cognitive and motor disabilities, but recent evidence suggests that there is variable recovery over time. One possibility that may explain this variable recovery entails variable neurogenic responses in the subventricular zone (SVZ) following the period of chronic hypoxia experienced by these neonates. In this report, we have characterized the responses to chronic hypoxia of two mouse strains that represent a wide range of susceptibility to chronic hypoxia. We determined that C57BL/6 pups and neural progenitor cells (NPCs) derived from them exhibit a blunted response to hypoxic insult compared with CD-1 pups and NPCs. Specifically, C57BL/6 pups and NPCs exhibited blunted in vivo and in vitro proliferative and increased apoptotic responses to hypoxic insult. Additionally, C57BL/6 NPCs exhibited lower baseline levels and hypoxia-induced levels of selected transcription factors, growth factors, and receptors (including HIF-1alpha, PHD2, BDNF, VEGF, SDF-1, TrkB, Nrp-1, CXCR4, and NO) that determine, in part, the responsiveness to chronic hypoxic insult compared with CD-1 pups and NPCs, providing insight into this important and timely problem in perinatology.

Nitric oxide donor, (+/-)-S-nitroso-N-acetylpenicillamine, stabilizes transactive hypoxia-inducible factor-1alpha by inhibiting von Hippel-Lindau recruitment and asparagine hydroxylation

We have confirmed that the NO donor (+/-)-S-nitroso-N-acetylpenicillamine (SNAP) stabilizes the transactive form of hypoxia-inducible factor-1alpha (HIF-1alpha), leading to the induction of HIF-1alpha target genes such as vascular endothelial growth factor and carbonic anhydrase 9. Activation of HIF-1alpha should require inhibition of the dual system that keeps it inactive. One is ubiquitination, which is triggered by hydroxylation of HIF-1alpha-proline and the subsequent binding of E3 ubiquitin ligase, the von Hippel Lindau (VHL) protein. The other is hydroxylation of HIF-1alpha-asparagine, which reduces the affinity of HIF-1alpha for its coactivator, cAMP responsive element binding protein/p300. We examined the effects of the NO donor SNAP on proline and asparagine hydroxylation of HIF-1alpha peptides by measuring the activities of the corresponding enzymes, HIF-1alpha-specific proline hydroxylase 2 (PHD2) and the HIF-1alpha-specific asparagine hydroxylase, designated factor inhibiting HIF-1alpha (FIH-1), respectively. We found that the SNAP did not prevent PHD2 from hydroxylating the proline of HIF-1alpha. Instead, it blocked the interaction between VHL and the proline-hydroxylated HIF-1alpha, but only when the reducing agents Fe(II) and vitamin C were limiting. The fact that the absence of cysteine 520 of HIF-1alpha abolishes its responsiveness to SNAP suggests that this residue mediates the inhibition by SNAP of the interaction between VHL and HIF-1alpha, presumably by S-nitrosylation of HIF-1alpha. Un-like PHD2, asparagine hydroxylation by FIH-1 was directly inhibited by SNAP, but again only when reducing agents were limiting. Substitution of cysteine 800 of HIF-1alpha with alanine failed to reverse the inhibitory effects of SNAP on asparagine hydroxylation, implying that FIH-1, not its substrate HIF-1alpha, is inhibited by SNAP.

PI3 kinase and direct S-nitrosation are involved in down-regulation of apoptosis signal-regulating kinase 1 during LPS-induced Toll-like receptor 4 signalling

Toll-like receptor 4 (TLR4) is the human pattern recognition receptor that detects lipopolysaccharide (LPS) shared by Gram-negative bacteria. TLR4 is expressed in different cell types including myeloid cells, the key effectors of innate immune reactions. Apoptosis signal-regulating kinase 1 (ASK1), the upstream kinase of MAP kinase-dependent apoptotic pathway has recently been found to be selectively required for p38 MAP kinase activation/cytokine production during TLR4 signalling. However, the activity of this enzyme has to be down-regulated to protect the cells against apoptosis. In the present study we have found that inhibition of PI3 kinase by LY294002 in THP-1 cells exposed to LPS attenuated down-regulation of ASK1 activity followed by programmed cell death. In addition, nitric oxide produced in response to exposure of THP-1 cells to LPS was found to S-nitrosate and therefore, down-regulate ASK1 activity.

LPS-induced Toll-like receptor 4 signalling triggers cross-talk of apoptosis signal-regulating kinase 1 (ASK1) and HIF-1alpha protein

Toll-like receptor 4 (TLR4) is required for recognition of lipopolysaccharide (LPS) of Gram-negative bacteria and induction of the innate immune response to them. Nevertheless, the involvement of some crucial pathways in TLR4 signalling is poorly understood. Here, we report that LPS-induced TLR4 signalling triggers cross talk of HIF-1alpha and ASK1 in THP-1 human myeloid monocytic leukaemia cells. Both pathways are activated via redox-dependent mechanism associated with tyrosine kinase/phospholipase C-1gamma-mediated activation of protein kinase C alpha/beta, which are known to activate NADPH oxidase and the production of reactive oxygen species that activate both HIF-1alpha and ASK1. ASK1 contributes to the stabilisation of HIF-1alpha, most likely via activation of p38 MAP kinase.