Rac1 activity is required for the activation of hypoxia-inducible factor 1

PICK1 modulates glycolysis and angiogenesis of hypoxic endothelial cells by regulating iron homeostasis

Iron accumulation, which is controlled by transferrin receptor 1 (TfR1), modulates hypoxia-inducible factor-1α (HIF-1α) activation and angiogenesis of hypoxic endothelial cells. The study examined the role of protein interacting with C-kinase 1 (PICK1), a scaffold protein containing PDZ domain, in regulating glycolysis and angiogenesis of hypoxic vascular endothelial cells through its potential effect on TfR1, which features a supersecondary structure that interacts with the PDZ domain. Iron chelator deferoxamine and TfR1 siRNA were employed to assess the impact of iron accumulation on angiogenesis, while the effects of PICK1 siRNA and overexpressing lentivirus on TfR1-mediated iron accumulation were also investigated in hypoxic human umbilical vein vascular endothelial cells (HUVECs). The study found that 72-h hypoxia impaired the proliferation, migration, and tube formation of HUVECs, and reduced the upregulation of vascular endothelial growth factor, HIF-1α, 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase 3, and PICK1, while increasing the expression of TfR1 as compared to 24-h hypoxia. Administration of deferoxamine or TfR1 siRNA reversed these effects and led to increased glycolysis, ATP content, and phosphofructokinase activity, along with increased PICK1 expression. PICK1 overexpression improved glycolysis, enhanced angiogenic capacity, and attenuated TfR1 protein upregulation in hypoxic HUVECs, with higher expression of angiogenic markers, which could be significantly reversed by the PDZ domain inhibitor. PICK1 knockdown exerted opposite effects. The study concluded that PICK1 modulated intracellular iron homeostasis, thereby promoting glycolysis and angiogenesis of HUVECs in response to prolonged hypoxia, at least in part, by regulating TfR1 expression.

Pangenome obtained by long-read sequencing of 11 genomes reveal hidden functional structural variants in pigs

Long-read sequencing (LRS) facilitates both the genome assembly and the discovery of structural variants (SVs). Here, we built a graph-based pig pangenome by incorporating 11 LRS genomes with an average of 94.01% BUSCO completeness score, revealing 206-Mb novel sequences. We discovered 183,352 nonredundant SVs (63% novel), representing 12.12% of the reference genome. By genotyping SVs in an additional 196 short-read sequencing samples, we identified thousands of population stratified SVs. Particularly, we detected 7,568 Tibetan specific SVs, some of which demonstrate significant population differentiation between Tibetan and low-altitude pigs, which might be associated with the high-altitude hypoxia adaptation in Tibetan pigs. Further integrating functional genomic data, the most promising candidate genes within the SVs that might contribute to the high-altitude hypoxia adaptation were discovered. Overall, our study generates a benchmark pangenome resource for illustrating the important roles of SVs in adaptive evolution, domestication, and genetic improvement of agronomic traits in pigs.

ROS elevate HIF-1α phosphorylation for insect lifespan through the CK2-MKP3-p38 pathway

Diapause in insects is akin to dauer in Caenorhabditis elegans and hibernation in vertebrates, characterized by metabolic depression and lifespan extension. Previous studies have shown that reactive oxygen species (ROS) and hypoxia-inducible factor-1α (HIF-1α) in brains of diapause-destined pupae are more abundant than those in nondiapause-destined pupae in Helicoverpa armigera, but the ROS regulating HIF-1α activity remain unknown. Here, we showed that high ROS levels in brains of diapause-destined pupae resulted in low casein kinase 2 (CK2) activity and that downregulation of CK2 caused low expression of mitogen-activated protein kinase phosphatase 3 (MKP3), which is an inhibitor of p-p38. Thus, high p-p38 levels accumulate to improve HIF-1α activity via activating HIF-1α phosphorylation at the S732 residue to regulate insect diapause. This is the first report showing that a new pathway, ROS-CK2-MKP3-p38, regulates HIF-1α activity for lifespan in insects.

Clinical Significance of Combined Epithelial-Mesenchymal Transition Markers Expression and Role of Rac1 in Hepatocellular Carcinoma

Epithelial-mesenchymal transition (EMT) has been implicated in cancer progression, invasion, and metastasis. We aimed to evaluate the correlations between clinicopathological characteristics and EMT markers in patients with hepatocellular carcinoma (HCC) who underwent surgical resection and to identify the key regulator in EMT process. Fresh-frozen HCC tissues and adjacent nontumor liver tissues from 30 patients who underwent surgical resection were provided by the Gachon University Gil Medical Center Bio Bank. Human HCC cell lines, Hep3B, SNU449, and Huh7 cells were transfected with Rac1 siRNA and exposed to hypoxic conditions. The combined EMT markers expression (down-expression of E-cadherin and overexpression of p21-activated kinases 1 (PAK1)/Snail) by Western blot in HCC tissues when compared to adjacent nontumor liver tissues was significantly associated with macrovascular invasion (p = 0.021), microvascular invasion (p = 0.001), large tumor size (p = 0.021), and advanced tumor stage (p = 0.015). Patients with combined EMT markers expression showed early recurrence and poor overall survival. In vitro studies showed that Rac1 knockdown decreased the expression of EMT markers including PAK1 and Snail in hypoxia-induced Hep3B cells and suppressed the migration and invasion of hypoxia-induced HCC cells. Rac1 may be a potential therapeutic target for inhibition of EMT process through the inhibition of PAK1 and Snail in HCC.

Hypoxia mimetics restore bone biomineralisation in hyperglycaemic environments

Diabetic patients have an increased risk of fracture and an increased occurrence of impaired fracture healing. Diabetic and hyperglycaemic conditions have been shown to impair the cellular response to hypoxia, via an inhibited hypoxia inducible factor (HIF)-1α pathway. We investigated, using an in vitro hyperglycaemia bone tissue engineering model (and a multidisciplinary bone characterisation approach), the differing effects of glucose levels, hypoxia and chemicals known to stabilise HIF-1α (CoCl2 and DMOG) on bone formation. Hypoxia (1% O2) inhibited bone nodule formation and resulted in discrete biomineralisation as opposed to the mineralised extracellular collagen fibres found in normoxia (20% O2). Unlike hypoxia, the use of hypoxia mimetics did not prevent nodule formation in normal glucose level. Hyperglycaemic conditions (25 mM and 50 mM glucose) inhibited biomineralisation. Interestingly, both hypoxia mimetics (CoCl2 and DMOG) partly restored hyperglycaemia inhibited bone nodule formation. These results highlight the difference in osteoblast responses between hypoxia mimetics and actual hypoxia and suggests a role of HIF-1α stabilisation in bone biomineralisation that extends that of promoting neovascularisation, or other system effects associated with hypoxia and bone regeneration in vivo. This study demonstrates that targeting the HIF pathway may represent a promising strategy for bone regeneration in diabetic patients.

Growth and mechanobiology of the tendon-bone enthesis

Tendons are cable-like connective tissues that transfer both active and passive forces generated by skeletal muscle to bone. In the mature skeleton, the tendon-bone enthesis is an interfacial zone of transitional tissue located between two mechanically dissimilar tissues: compliant, fibrous tendon to rigid, dense mineralized bone. In this review, we focus on emerging areas in enthesis development related to its structure, function, and mechanobiology, as well as highlight established and emerging signaling pathways and physiological processes that influence the formation and adaptation of this important transitional tissue.

Discovery of the signal pathways and major bioactive compounds responsible for the anti-hypoxia effect of Chinese cordyceps

ETHNOPHARMACOLOGICAL RELEVANCE

Hypoxia will cause an increase in the rate of fatigue and aging. Chinese cordyceps, a parasitic Thitarodes insect-Ophiocordyceps sinensis fungus complex in the Qinghai-Tibet Plateau, has long been used to ameliorate human conditions associated with aging and senescence, it is principally applied to treat fatigue, night sweating and other symptoms related to aging, and it may play the anti-aging and anti-fatigue effect by improving the body's hypoxia tolerance.

AIMS OF THE STUDY

The present study investigated the anti-hypoxia activity of Chinese cordyceps and explore the main corresponding signal pathways and bioactive compounds.

MATERIALS AND METHODS

In this study, network pharmacology analysis, molecular docking, cell and whole pharmacodynamic experiments were hired to study the major signal pathways and the bioactive compounds of Chinese cordyceps for anti-hypoxia activity.

RESULTS

17 pathways which Chinese cordyceps acted on seemed to be related to the anti-hypoxia effect, and "VEGF signal pathway" was one of the most important pathway. Chinese cordyceps improved the survival rate and regulated the targets related VEGF signal pathway of H9C2 cells under hypoxia, and also had significant anti-hypoxia effects to mice. Chorioallantoic membrane model experiment showed that Chinese cordyceps and the main constituents of (9Z,12Z)-octadeca-9,12-dienoic acid and cerevisterol had significant angiogenic activity in hypoxia condition.

CONCLUSION

Based on the results of network pharmacology and molecular docking analysis, cell and whole pharmacodynamic experiments, promoting angiogenesis by regulating VEGF signal pathway might be one of the mechanisms of anti-hypoxia effect of Chinese cordyceps, (9Z, 12Z)-octadeca-9,12-dienoic acid and cerevisterol were considered as the major anti-hypoxia bioactive compounds in Chinese cordyceps.

Optimizing metastatic-cascade-dependent Rac1 targeting in breast cancer: Guidance using optical window intravital FRET imaging

Assessing drug response within live native tissue provides increased fidelity with regards to optimizing efficacy while minimizing off-target effects. Here, using longitudinal intravital imaging of a Rac1-Förster resonance energy transfer (FRET) biosensor mouse coupled with in vivo photoswitching to track intratumoral movement, we help guide treatment scheduling in a live breast cancer setting to impair metastatic progression. We uncover altered Rac1 activity at the center versus invasive border of tumors and demonstrate enhanced Rac1 activity of cells in close proximity to live tumor vasculature using optical window imaging. We further reveal that Rac1 inhibition can enhance tumor cell vulnerability to fluid-flow-induced shear stress and therefore improves overall anti-metastatic response to therapy during transit to secondary sites such as the lung. Collectively, this study demonstrates the utility of single-cell intravital imaging in vivo to demonstrate that Rac1 inhibition can reduce tumor progression and metastases in an autochthonous setting to improve overall survival.

HACE1 blocks HIF1α accumulation under hypoxia in a RAC1 dependent manner

Uncovering the mechanisms that underpin how tumor cells adapt to microenvironmental stress is essential to better understand cancer progression. The HACE1 (HECT domain and ankyrin repeat-containing E3 ubiquitin-protein ligase) gene is a tumor suppressor that inhibits the growth, invasive capacity, and metastasis of cancer cells. However, the direct regulatory pathways whereby HACE1 confers this tumor-suppressive effect remain to be fully elucidated. In this report, we establish a link between HACE1 and the major stress factor, hypoxia-inducible factor 1 alpha (HIF1α). We find that HACE1 blocks the accumulation of HIF1α during cellular hypoxia through decreased protein stability. This property is dependent on HACE1 E3 ligase activity and loss of Ras-related C3 botulinum toxin substrate 1 (RAC1), an established target of HACE1 mediated ubiquitinylation and degradation. In vivo, genetic deletion of Rac1 reversed the increased HIF1α expression observed in Hace1^-/- mice in murine KRas^G12D-driven lung tumors. An inverse relationship was observed between HACE1 and HIF1α levels in tumors compared to patient-matched normal kidney tissues, highlighting the potential pathophysiological significance of our findings. Together, our data uncover a previously unrecognized function for the HACE1 tumor suppressor in blocking HIF1α accumulation under hypoxia in a RAC1-dependent manner.

Rac1 repression reverses chemoresistance by targeting tumor metabolism

Tumor metabolism is exemplified by the increased rate of glucose utilization, a biochemical signature of cancer cells. The enhanced glucose hydrolysis enabled by the augmentation of glycolytic flux and the pentose phosphate pathway (PPP) plays a pivotal role in the growth and survival of neoplastic cells. In a recent report, it has been shown that in human breast cancer the GTP binding protein, Rac1 enables resistance to therapy, particularly against the DNA-damaging therapeutics. Significantly, the findings demonstrate that Rac1-dependent chemoresistance involves the upregulation of glycolytic flux as well as PPP. Using multiple approaches, the study demonstrates that disruption of Rac1 activity sensitizes cancer cells to DNA-damaging agents. More importantly, the data uncover a previously unknown PPP regulatory role of Rac1 in breast cancer. Finally, the authors also show the effectiveness and the feasibility of in vivo targeting of Rac1 to enhance the chemosensitivity of breast cancer. This elegant report provokes scientific curiosity to expand our understanding of the intricacies of the role and regulation of Rac1 in cancer.

Apoptosis signal-regulating kinase 1 inhibition in in vivo and in vitro models of pulmonary hypertension

Pulmonary arterial hypertension, group 1 of the pulmonary hypertension disease family, involves pulmonary vascular remodelling, right ventricular dysfunction and cardiac failure. Oxidative stress, through activation of mitogen-activated protein kinases is implicated in these changes. Inhibition of apoptosis signal-regulating kinase 1, an apical mitogen-activated protein kinase, prevented pulmonary arterial hypertension developing in rodent models. Here, we investigate apoptosis signal-regulating kinase 1 in pulmonary arterial hypertension by examining the impact that its inhibition has on the molecular and cellular signalling in established disease. Apoptosis signal-regulating kinase 1 inhibition was investigated in in vivo pulmonary arterial hypertension and in vitro pulmonary hypertension models. In the in vivo model, male Sprague Dawley rats received a single subcutaneous injection of Sugen SU5416 (20 mg/kg) prior to two weeks of hypobaric hypoxia (380 mmHg) followed by three weeks normoxia (Sugen/hypoxic), then animals were either maintained for three weeks on control chow or one containing apoptosis signal-regulating kinase 1 inhibitor (100 mg/kg/day). Cardiovascular measurements were carried out. In the in vitro model, primary cultures of rat pulmonary artery fibroblasts and rat pulmonary artery smooth muscle cells were maintained in hypoxia (5% O₂) and investigated for proliferation, migration and molecular signalling in the presence or absence of apoptosis signal-regulating kinase 1 inhibitor. Sugen/hypoxic animals displayed significant pulmonary arterial hypertension compared to normoxic controls at eight weeks. Apoptosis signal-regulating kinase 1 inhibitor decreased right ventricular systolic pressure to control levels and reduced muscularised vessels in lung tissue. Apoptosis signal-regulating kinase 1 inhibition was found to prevent hypoxia-induced proliferation, migration and cytokine release in rat pulmonary artery fibroblasts and also prevented rat pulmonary artery fibroblast-induced rat pulmonary artery smooth muscle cell migration and proliferation. Apoptosis signal-regulating kinase 1 inhibition reversed pulmonary arterial hypertension in the Sugen/hypoxic rat model. These effects may be a result of intrinsic changes in the signalling of adventitial fibroblast.

Sphingolipids in Obesity and Correlated Co-Morbidities: The Contribution of Gender, Age and Environment

This paper reviews our present knowledge on the contribution of ceramide (Cer), sphingomyelin (SM), dihydroceramide (DhCer) and sphingosine-1-phosphate (S1P) in obesity and related co-morbidities. Specifically, in this paper, we address the role of acyl chain composition in bodily fluids for monitoring obesity in males and females, in aging persons and in situations of environmental hypoxia adaptation. After a brief introduction on sphingolipid synthesis and compartmentalization, the node of detection methods has been critically revised as the node of the use of animal models. The latter do not recapitulate the human condition, making it difficult to compare levels of sphingolipids found in animal tissues and human bodily fluids, and thus, to find definitive conclusions. In human subjects, the search for putative biomarkers has to be performed on easily accessible material, such as serum. The serum “sphingolipidome” profile indicates that attention should be focused on specific acyl chains associated with obesity, per se, since total Cer and SM levels coupled with dyslipidemia and vitamin D deficiency can be confounding factors. Furthermore, exposure to hypoxia indicates a relationship between dyslipidemia, obesity, oxygen level and aerobic/anaerobic metabolism, thus, opening new research avenues in the role of sphingolipids.

De novo assembly of a Tibetan genome and identification of novel structural variants associated with high-altitude adaptation

Structural variants (SVs) may play important roles in human adaptation to extreme environments such as high altitude but have been under-investigated. Here, combining long-read sequencing with multiple scaffolding techniques, we assembled a high-quality Tibetan genome (ZF1), with a contig N50 length of 24.57 mega-base pairs (Mb) and a scaffold N50 length of 58.80 Mb. The ZF1 assembly filled 80 remaining N-gaps (0.25 Mb in total length) in the reference human genome (GRCh38). Markedly, we detected 17 900 SVs, among which the ZF1-specific SVs are enriched in GTPase activity that is required for activation of the hypoxic pathway. Further population analysis uncovered a 163-bp intronic deletion in the MKL1 gene showing large divergence between highland Tibetans and lowland Han Chinese. This deletion is significantly associated with lower systolic pulmonary arterial pressure, one of the key adaptive physiological traits in Tibetans. Moreover, with the use of the high-quality de novo assembly, we observed a much higher rate of genome-wide archaic hominid (Altai Neanderthal and Denisovan) shared non-reference sequences in ZF1 (1.32%–1.53%) compared to other East Asian genomes (0.70%–0.98%), reflecting a unique genomic composition of Tibetans. One such archaic hominid shared sequence—a 662-bp intronic insertion in the SCUBE2 gene—is enriched and associated with better lung function (the FEV1/FVC ratio) in Tibetans. Collectively, we generated the first high-resolution Tibetan reference genome, and the identified SVs may serve as valuable resources for future evolutionary and medical studies.

Tendinosis develops from age- and oxygen tension-dependent modulation of Rac1 activity

Age‐related tendon degeneration (tendinosis) is characterized by a phenotypic change in which tenocytes display characteristics of fibrochondrocytes and mineralized fibrochondrocytes. As tendon degeneration has been noted in vivo in areas of decreased tendon vascularity, we hypothesized that hypoxia is responsible for the development of the tendinosis phenotype, and that these effects are more pronounced in aged tenocytes. Hypoxic (1% O₂) culture of aged, tendinotic, and young human tenocytes resulted in a mineralized fibrochondrocyte phenotype in aged tenocytes, and a fibrochondrocyte phenotype in young and tendinotic tenocytes. Investigation of the molecular mechanism responsible for this phenotype change revealed that the fibrochondrocyte phenotype in aged tenocytes occurs with decreased Rac1 activity in response to hypoxia. In young hypoxic tenocytes, however, the fibrochondrocyte phenotype occurs with concomitant decreased Rac1 activity coupled with increased RhoA activity. Using pharmacologic and adenoviral manipulation, we confirmed that these hypoxic effects on the tenocyte phenotype are linked directly to the activity of RhoA/Rac1 GTPase in in vitro human cell culture and tendon explants. These results demonstrate that hypoxia drives tenocyte phenotypic changes, and provide a molecular insight into the development of human tendinosis that occurs with aging.

miR-31-5p Is a LIPUS-Mechanosensitive MicroRNA that Targets HIF-1α Signaling and Cytoskeletal Proteins

The roles of low-intensity pulsed ultrasound (LIPUS) and microRNAs (miRNAs) on hMSCs commitments have already been investigated; however, the effects of the application of their co-treatments in an in vitro cell model are still unknown. Our previous studies demonstrated that (i) LIPUS modulated hMSCs cytoskeletal organization and (ii) miRNA-675-5p have a role in HIF-1α signaling modulation during hMSCs osteoblast commitment. We investigated for the first time the role of LIPUS as promoter tool for miRNA expression. Thanks to bioinformatic analysis, we identified miR-31-5p as a LIPUS-induced miRNA and investigated its role through in vitro studies of gain and loss of function. Results highlighted that LIPUS stimulation induced a hypoxia adaptive cell response, which determines a reorganization of cell membrane and cytoskeleton proteins. MiR-31-5p gain and loss of function studies, demonstrated as miR-31-5p overexpression, were able to induce hypoxic and cytoskeletal responses. Moreover, the co-treatments LIPUS and miR-31-5p inhibitor abolished the hypoxic responses including angiogenesis and the expression of Rho family proteins. MiR-31-5p was identified as a LIPUS-mechanosensitive miRNAs and may be considered a new therapeutic option to promote or abolish hypoxic response and cytoskeletal organization on hMSCs during the bone regeneration process.

Hypoxia-inducible factor 1α protects peripheral sensory neurons from diabetic peripheral neuropathy by suppressing accumulation of reactive oxygen species

Diabetic peripheral neuropathy (DPN) is one of the most common diabetic complications. Mechanisms underlying nerve damage and sensory loss following metabolic dysfunction remain largely unclear. Recently, hyperglycemia-induced mitochondrial dysfunction and the generation of reactive oxygen species (ROS) have gained attention as possible mechanisms of organ damage in diabetes. Hypoxia-inducible factor 1 (HIF1α) is a key transcription factor activated by hypoxia, hyperglycemia, nitric oxide as well as ROS, suggesting a fundamental role in DPN susceptibility. We analyzed regulation of HIF1α in response to prolonged hyperglycemia. Genetically modified mutant mice, which conditionally lack HIF1α in peripheral sensory neurons (SNS-HIF1α^-/-), were analyzed longitudinally up to 6 months in the streptozotocin (STZ) model of type1 diabetes. Behavioral measurements of sensitivity to thermal and mechanical stimuli, quantitative morphological analyses of intraepidermal nerve fiber density, measurements of ROS, ROS-induced cyclic GMP-dependent protein kinase 1α (PKG1α), and levels of vascular endothelial growth factor (VEGF) in sensory neurons in vivo were undertaken over several months post-STZ injections to delineate the role of HIF1α in DPN. Longitudinal behavioral and morphological analyses at 5, 13, and 24 weeks post-STZ treatment revealed that SNS-HIF1α^-/- developed stronger hyperglycemia-evoked losses of peripheral nociceptive sensory axons associated with stronger losses of mechano- and heat sensation with a faster onset than HIF1α^fl/fl mice. Mechanistically, these histomorphologic, behavioral, and biochemical differences were associated with a significantly higher level of STZ-induced production of ROS and ROS-induced PKG1α dimerization in sensory neurons of SNS-HIF1α^-/- mice as compared with HIF1α^fl/fl. We found that prolonged hyperglycemia induced VEGF expression in the sciatic nerve which is impaired in SNS-HIF1α mice. Our results indicate that HIF1α is as an upstream modulator of ROS in peripheral sensory neurons and exerts a protective function in suppressing hyperglycemia-induced nerve damage by limiting ROS levels and by inducing expression of VEGF which may promote peripheral nerve survival. Our data suggested that HIF1α stabilization may be thus a new strategy target for limiting sensory loss, a debilitating late complication of diabetes. KEY MESSAGES: • Impaired hypoxia-inducible factor 1α (HIF1α) signaling leads to early onset of STZ-induced loss of sensation in mice. • STZ-induced loss of sensation in HIF1α mutant mice is associated with loss of sensory nerve fiber in skin. • Activation of HIF1α signaling in diabetic mice protects the sensory neurons by limiting ROS formation generated due to mitochondrial dysfunction and by inducing VEGF expression.

Chronic asthma-induced behavioral and hippocampal neuronal morphological changes are concurrent with BDNF, cofilin1 and Cdc42/RhoA alterations in immature mice

INTRODUCTION

Recent studies have found that persistent hypoxia caused by chronic asthma, especially during childhood, affects the development and function of the brain, but the mechanism is unclear. In the present study, BDNF and its signal pathway was investigated in mediating chronic asthma induced-neuronal changes that lead to behavior alterations.

METHODS

The chronic asthma model was induced by sensitization with ovalbumin for more than 9 weeks in immature mice. Morris water maze test (MWMT), open field test (OFT) and elevated plus maze test (EPMT) were used to conduct behavioral evaluation. Neuronal morphology in hippocampal CA1, CA3 and DG was assessed using ImageJ's Sholl plugin and RESCONSTRUCT software. BDNF signaling pathway related molecules was determined by Western blotting.

RESULTS

Chronic asthma does affect the behavioral performances of immature mice evaluated in MWMT, OFT, and EPMT. The analysis by three-dimensional reconstruction software found that following the behavioral alteration of asthmatic mice, dendritic changes also occurred in hippocampal neurons, including shortened dendrite length, significantly reduced number of dendritic branches, decreased density of dendritic spines, and reduced percentage of functional dendritic spine types. At the same time, by immunofluorescence and western blotting, we also found that alterations in dendritic morphology were consistent with activation of cofilin1 and changes in BDNF-Cdc42/RhoA levels. Some of the changes mentioned above can be alleviated by intranasal administration of budesonide.

CONCLUSION

Our data suggest that response similar to nicotine withdrawal or/and hypoxia induced by childhood chronic asthma enhances the BDNF-Cdc42/RhoA signaling pathway and activates cofilin1, leading to the remodeling of actin, causing the loss of dendritic spines and atrophy of dendrites, eventually resulting in behavioral alterations.

Neuronal Rho GTPase Rac1 elimination confers neuroprotection in a mouse model of permanent ischemic stroke

The Rho GTPase Rac1 is a multifunctional protein involved in distinct pathways ranging from development to pathology. The aim of the present study was to unravel the contribution of neuronal Rac1 in regulating the response to brain injury induced by permanent focal cerebral ischemia (pMCAO). Our results show that pMCAO significantly increased total Rac1 levels in wild type mice, mainly through rising nuclear Rac1, while a reduction in Rac1 activation was observed. Such changes preceded cell death induced by excitotoxic stress. Pharmacological inhibition of Rac1 in primary neuronal cortical cells prevented the increase in oxidative stress induced after overactivation of glutamate receptors. However, this was not sufficient to prevent the associated neuronal cell death. In contrast, RNAi-mediated knock down of Rac1 in primary cortical neurons prevented cell death elicited by glutamate excitotoxicity and decreased the activity of NADPH oxidase. To test whether in vivo down regulation of neuronal Rac1 was neuroprotective after pMCAO, we used tamoxifen-inducible neuron-specific conditional Rac1-knockout mice. We observed a significant 50% decrease in brain infarct volume of knockout mice and a concomitant increase in HIF-1α expression compared to littermate control mice, demonstrating that ablation of Rac1 in neurons is neuroprotective. Transmission electron microscopy performed in the ischemic brain showed that lysosomes in the infarct of Rac1- knockout mice were preserved at similar levels to those of non-infarcted tissue, while littermate mice displayed a decrease in the number of lysosomes, further corroborating the notion that Rac1 ablation in neurons is neuroprotective. Our results demonstrate that Rac1 plays important roles in the ischemic pathological cascade and that modulation of its levels is of therapeutic interest.

[The cellular and molecular mechanisms of angiogenesis regulation in the brain]

This review presents the data on cellular and molecular mechanisms of angiogenesis regulation linked to the vascular epithelium. According to current conceptions, activated endothelial cells and their predecessors (progenitor cells) are involved in the regulation of angiogenesis. These cells synthesize angiogenic molecules differing by the chemical structure and mechanism of biological effect and allowing a direct or indirect control over each stage of angiogenesis. Both the excess and insufficient angiogenesis can lead to fast and irreversible changes in nervous tissue under certain conditions. For this reason, the balance in the system of molecular stimulators and inhibitors of angiogenesis is especially important for brain function. Without adequate reperfusion of an affected brain area the post-stroke neuroreparation, which can be provided with timely stimulation of angiogenesis, is unattainable and the intensification of this process in tumors, on the contrary, has adverse consequences. Growth of a tumor and its metastatic spread are substantially associated with an increase in the level of tumor tissue vascularization, and blocking angiogenesis is often the only productive way to limit the growth of a tumor. However our knowledge of mechanisms of angiogenesis regulation in the brain on the cellular and molecular level in physiological and pathological conditions is still insufficient, and, therefore, the influence of angiogenic factors on tissue targets do not always cause the expected effects.

Paving the Rho in cancer metastasis: Rho GTPases and beyond

Malignant carcinomas are often characterized by metastasis, the movement of carcinoma cells from a primary site to colonize distant organs. For metastasis to occur, carcinoma cells first must adopt a pro-migratory phenotype and move through the surrounding stroma towards a blood or lymphatic vessel. Currently, there are very limited possibilities to target these processes therapeutically. The family of Rho GTPases is an ubiquitously expressed division of GTP-binding proteins involved in the regulation of cytoskeletal dynamics and intracellular signaling. The best characterized members of the Rho family GTPases are RhoA, Rac1 and Cdc42. Abnormalities in Rho GTPase function have major consequences for cancer progression. Rho GTPase activation is driven by cell surface receptors that activate GTP exchange factors (GEFs) and GTPase-activating proteins (GAPs). In this review, we summarize our current knowledge on Rho GTPase function in the regulation of metastasis. We will focus on key discoveries in the regulation of epithelial-mesenchymal-transition (EMT), cell-cell junctions, formation of membrane protrusions, plasticity of cell migration and adaptation to a hypoxic environment. In addition, we will emphasize on crosstalk between Rho GTPase family members and other important oncogenic pathways, such as cyclic AMP-mediated signaling, canonical Wnt/β-catenin, Yes-associated protein (YAP) and hypoxia inducible factor 1α (Hif1α) and provide an overview of the advancements and challenges in developing pharmacological tools to target Rho GTPase and the aforementioned crosstalk in the context of cancer therapeutics.

Small G protein Rac GTPases regulate the maintenance of glioblastoma stem-like cells in vitro and in vivo

Glioblastoma is the most common and aggressive malignant brain tumor in adults. The existence of glioblastoma stem cells (GSCs) or stem-like cells (stemloids) may account for its invasiveness and high recurrence. Rac proteins belong to the Rho small GTPase subfamily which regulates cell movement, proliferation, and survival. To investigate whether Rac proteins can serve as therapeutic targets for glioblastoma, especially for GSCs or stemloids, we examined the potential roles of Rac1, Rac2 and Rac3 on the properties of tumorspheres derived from glioblastoma cell lines. Tumorspheres are thought to be glioblastoma stem-like cells. We showed that Rac proteins promote the STAT3 and ERK activation and enhance cell proliferation and colony formation of glioblastoma stem-like cells. Knockdown of Rac proteins reduces the expression of GSC markers, such as CD133 and Sox2. The in vivo effects of Rac proteins in glioblastoma were further studied in zebrafish and in the mouse xenotransplantation model. Knocking-down Rac proteins abolished the angiogenesis effect induced by the injected tumorspheres in zebrafish model. In the CD133+-U373-tumorsphere xenotransplanted mouse model, suppression of Rac proteins decreased the incidence of tumor formation and inhibited the tumor growth. Moreover, knockdown of Rac proteins reduced the sphere forming efficiency of cells derived from these tumors. In conclusion, not only Rac1 but also Rac2 and 3 are important for glioblastoma tumorigenesis and can serve as the potential therapeutic targets against glioblastoma and its stem-like cells.

Implications of Hypoxia in Breast Cancer Metastasis to Bone

Most solid tumors contain regions of hypoxia in which increased cell proliferation promotes increased oxygen consumption and the condition is further exacerbated as cancer cells become localized far from a functional blood vessel, further decreasing the oxygen supply. An important mechanism that promotes cell adaptation to hypoxic conditions is the expression of hypoxia-inducible factors (HIFs). Hypoxia-inducible factors transcriptionally regulate many genes involved in the invasion and metastasis of breast cancer cells. Patients, whose primary tumor biopsies show high HIF expression levels, have a greater risk of metastasis. The current review will highlight the potential role of hypoxia in breast cancer metastasis to the bone by considering the regulation of many steps in the metastatic process that include invasion, migration, margination and extravasation, as well as homing signals and regulation of the bone microenvironment.

S1P prophylaxis mitigates acute hypobaric hypoxia-induced molecular, biochemical, and metabolic disturbances: A preclinical report

Sphingosine-1-phosphate (S1P) is emerging to have hypoxic preconditioning potential in various preclinical studies. The study aims to evaluate the preclinical preconditioning efficacy of exogenously administered S1P against acute hypobaric hypoxia (HH)-induced pathological disturbances. Male Sprague Dawley rats (200 ± 20 g) were preconditioned with 1, 10, and 100 μg/kg body weight (b.w.) S1P (i.v.) for three consecutive days. On the third day, S1P preconditioned animals, along with hypoxia control animals, were exposed to HH equivalent to 7,620 m (280 mm Hg) for 6 h. Postexposure status of cardiac energy production, circulatory vasoactive mediators, pulmonary and cerebral oxidative damage, and inflammation were assessed. HH exposure led to cardiac energy deficit indicated by low ATP levels and pronounced AMPK activation levels, raised circulatory levels of brain natriuretic peptide and endothelin-1 with respect to total nitrate (NOx), redox imbalance, inflammation, and alterations in NOx levels in the pulmonary and cerebral tissues. These pathological precursors have been routinely reported to be coincident with high-altitude diseases. Preconditioning with S1P, especially 1 µg/kg b.w. dose, was seen to reverse the manifestation of these pathological disturbances. The protective efficacy could be attributed, at least in part, to enhanced activity of cardioprotective protein kinase C and activation of small GTPase Rac1, which led to further induction of hypoxia-adaptive molecular mediators: hypoxia-inducible factor (HIF)-1α and Hsp70. This is a first such report, to the best of our knowledge, elucidating the mechanism of exogenous S1P-mediated HIF-1α/Hsp70 induction. Conclusively, systemic preconditioning with 1 μg/kg b.w. S1P in rats protects against acute HH-induced pathological disturbances. © 2016 IUBMB Life 68(5):365-375, 2016.

Hypoxia-Inducible Factors (HIFs) and Phosphorylation: Impact on Stability, Localization, and Transactivity

The hypoxia-inducible factor α-subunits (HIFα) are key transcription factors in the mammalian response to oxygen deficiency. The HIFα regulation in response to hypoxia occurs primarily on the level of protein stability due to posttranslational hydroxylation and proteasomal degradation. However, HIF α-subunits also respond to various growth factors, hormones, or cytokines under normoxia indicating involvement of different kinase pathways in their regulation. Because these proteins participate in angiogenesis, glycolysis, programmed cell death, cancer, and ischemia, HIFα regulating kinases are attractive therapeutic targets. Although numerous kinases were reported to regulate HIFα indirectly, direct phosphorylation of HIFα affects HIFα stability, nuclear localization, and transactivity. Herein, we review the role of phosphorylation-dependent HIFα regulation with emphasis on protein stability, subcellular localization, and transactivation.

The immunological effect of hyaluronan in tumor angiogenesis

The relationship between the immune system and angiogenesis has been described in several contexts, both in physiological and pathological conditions, as pregnancy and cancer. In fact, different types of immune cells, such as myeloid, macrophages and denditric cells, are able to modulate tumor neovascularization. On the other hand, tumor microenvironment also includes extracellular matrix components like hyaluronan, which has a deregulated synthesis in different tumors. Hyaluronan is a glycosaminoglycan, normally present in the extracellular matrix of tissues in continuous remodeling (embryogenesis or wound healing processes) and acts as an important modulator of cell behavior by different mechanisms, including angiogenesis. In this review, we discuss hyaluronan as a modulator of tumor angiogenesis, focusing in intracellular signaling mediated by its receptors expressed on different immune cells. Recent observations suggest that the immune system is an important component in tumoural angiogenesis. Therefore, immune modulation could have an impact in anti-angiogenic therapy as a new therapeutic strategy, which in turn might improve effectiveness of treatment in cancer patients.

A macrophage-dominant PI3K isoform controls hypoxia-induced HIF1α and HIF2α stability and tumor growth, angiogenesis, and metastasis

Tumor growth, progression, and response to the hypoxic tumor microenvironment involve the action of hypoxia-inducible transcription factors, HIF1 and HIF2. HIF is a heterodimeric transcription factor containing an inducible HIFα subunit and a constitutively expressed HIFβ subunit. The signaling pathways operational in macrophages regulating hypoxia-induced HIFα stabilization remain the subject of intense investigation. Here, it was discovered that the PTEN/PI3K/AKT signaling axis controls hypoxia-induced HIF1α (HIF1A) and HIF2α (EPAS1) stability in macrophages. Using genetic mouse models and pan-PI3K as well as isoform-specific inhibitors, inhibition of the PI3K/AKT pathway blocked the accumulation of HIFα protein and its primary transcriptional target VEGF in response to hypoxia. Moreover, blocking the PI3K/AKT signaling axis promoted the hypoxic degradation of HIFα via the 26S proteasome. Mechanistically, a macrophage-dominant PI3K isoform (p110γ) directed tumor growth, angiogenesis, metastasis, and the HIFα/VEGF axis. Moreover, a pan-PI3K inhibitor (SF1126) blocked tumor-induced angiogenesis and inhibited VEGF and other proangiogenic factors secreted by macrophages. These data define a novel molecular mechanism by which PTEN/PI3K/AKT regulates the proteasome-dependent stability of HIFα under hypoxic conditions, a signaling pathway in macrophages that controls tumor-induced angiogenesis and metastasis.

IMPLICATIONS

This study indicates that PI3K inhibitors are excellent candidates for the treatment of cancers where macrophages promote tumor progression.

MAPK14/p38α-dependent modulation of glucose metabolism affects ROS levels and autophagy during starvation

Increased glycolytic flux is a common feature of many cancer cells, which have adapted their metabolism to maximize glucose incorporation and catabolism to generate ATP and substrates for biosynthetic reactions. Indeed, glycolysis allows a rapid production of ATP and provides metabolic intermediates required for cancer cells growth. Moreover, it makes cancer cells less sensitive to fluctuations of oxygen tension, a condition usually occurring in a newly established tumor environment. Here, we provide evidence for a dual role of MAPK14 in driving a rearrangement of glucose metabolism that contributes to limiting reactive oxygen species (ROS) production and autophagy activation in condition of nutrient deprivation. We demonstrate that MAPK14 is phosphoactivated during nutrient deprivation and affects glucose metabolism at 2 different levels: on the one hand, it increases SLC2A3 mRNA and protein levels, resulting in a higher incorporation of glucose within the cell. This event involves the MAPK14-mediated enhancement of HIF1A protein stability. On the other hand, MAPK14 mediates a metabolic shift from glycolysis to the pentose phosphate pathway (PPP) through the modulation of PFKFB3 (6-phosphofructo-2-kinase/fructose 2,6-bisphosphatase 3) degradation by the proteasome. This event requires the presence of 2 distinct degradation sequences, KEN box and DSG motif Ser273, which are recognized by 2 different E3 ligase complexes. The mutation of either motif increases PFKFB3 resistance to starvation-induced degradation. The MAPK14-driven metabolic reprogramming sustains the production of NADPH, an important cofactor for many reduction reactions and for the maintenance of the proper intracellular redox environment, resulting in reduced levels of ROS. The final effect is a reduced activation of autophagy and an increased resistance to nutrient deprivation.

Mitigation of oxygen-induced retinopathy in α2β1 integrin-deficient mice

PURPOSE

The α2β1 integrin plays an important but complex role in angiogenesis and vasculopathies. Published GWAS studies established a correlation between genetic polymorphisms of the α2β1 integrin gene and incidence of diabetic retinopathy. Recent studies indicated that α2-null mice demonstrate superior vascularization in both the wound and diabetic microenvironments. The goal of this study was to determine whether the vasculoprotective effects of α2-integrin deficiency extended to the retina, using the oxygen-induced retinopathy (OIR) model for retinopathy of prematurity (ROP).

METHODS

In the OIR model, wild-type (WT) and α2-null mice were exposed to 75% oxygen for 5 days (postnatal day [P] 7 to P12) and subsequently returned to room air for 6 days (P12-P18). Retinas were collected at postnatal day 7, day 13, and day 18 and examined via hematoxylin and eosin and Lectin staining. Retinas were analyzed for retinal vascular area, neovascularization, VEGF expression, and Müller cell activation. Primary Müller cell cultures from WT and α2-null mice were isolated and analyzed for hypoxia-induced VEGF-A expression.

RESULTS

In the retina, the α2β1 integrin was minimally expressed in endothelial cells and strongly expressed in activated Müller cells. Isolated α2-null primary Müller cells demonstrated decreased hypoxia-induced VEGF-A expression. In the OIR model, α2-null mice displayed reduced hyperoxia-induced vaso-attenuation, reduced pathological retinal neovascularization, and decreased VEGF expression as compared to WT counterparts.

CONCLUSIONS

Our data suggest that the α2β1 integrin contributes to the pathogenesis of retinopathy. We describe a newly identified role for α2β1 integrin in mediating hypoxia-induced Müller cell VEGF-A production.

Rho GTPases modulate malignant transformation of tumor cells

Rho GTPases are involved in the acquisition of all the hallmarks of cancer, which comprise 6 biological capabilities acquired during the development of human tumors. The hallmarks include proliferative signaling, evading growth suppressors, resisting cell death, enabling replicative immortality, inducing angiogenesis, and activating invasion and metastasis programs, as defined by Hanahan and Weinberg. (1) Controlling these hallmarks are genome instability and inflammation. Emerging hallmarks are reprogramming of energy metabolism and evading immune destruction. To give a different view to the readers, we will not be focusing on invasion, metastasis, or cytoskeletal remodeling, but we will review here how Rho GTPases contribute to other hallmarks of cancer with a special emphasis on malignant transformation.

Hypoxia and the modulation of the actin cytoskeleton - emerging interrelations

Recent progress in understanding the influence of hypoxia on cell function has revealed new information about the interrelationship between the actin cytoskeleton and hypoxia; nevertheless, details remain cloudy. The dynamic regulation of the actin cytoskeleton during hypoxia is complex, varies in different cells and tissues, and also depends on the mode of hypoxia. Several molecular players and pathways are emerging that contribute to the modulation of the actin cytoskeleton and that affect the large repertoire of actin-binding proteins in hypoxia. This review describes and discusses the accumulated knowledge about actin cytoskeleton dynamics in hypoxia, placing special emphasis on the Rho family of small guanosine triphosphatases (Rho GTPases). Given that RhoA, Rac and Cdc42 are very well characterized, the review is focused on these family members of Rho GTPases. Notably, in several cell types and tissues, hypoxia, presumably via Rho GTPase signaling, induces actin rearrangement and actin stress fiber assembly, which is a prevalent modulation of the actin cytoskeleton in hypoxia.

Rho GTPases in the regulation of pulmonary vascular barrier function

Pulmonary endothelial permeability is an important determinant of vascular adaptation to changes in oxygen tension, blood pressure, levels of growth factors or inflammatory cytokines. The Ras homologous (Rho) family of guanosine triphosphate phosphatases (Rho GTPases), key regulators of the actin cytoskeleton, regulate endothelial barrier function in response to a variety of environmental factors and signalling agents via the reorganization of the actin cytoskeleton, changes in receptor trafficking or the phosphorylation of junctional proteins. This review provides a brief summary of recent knowledge on Rho-GTPase-mediated effects on pulmonary endothelial barrier function and focuses in particular on their role in pulmonary vascular disorders, including pulmonary hypertension, chronic obstructive pulmonary disease, acute lung injury and acute respiratory distress syndrome.

Pin1, a new player in the fate of HIF-1α degradation: an hypothetical mechanism inside vascular damage as Alzheimer's disease risk factor

Aetiology of neurodegenerative mechanisms underlying Alzheimer’s disease (AD) are still under elucidation. The contribution of cerebrovascular deficiencies (such as cerebral ischemia/stroke) has been strongly endorsed in recent years. Reduction of blood supply leading to hypoxic condition is known to activate cellular responses mainly controlled by hypoxia-inducible transcription factor-1 (HIF-1). Thus alterations of oxygen responsive HIF-1α subunit in the central nervous system may contribute to the cognitive decline, especially influencing mechanisms associated to amyloid precursor protein (APP) amyloidogenic metabolism. Although HIF-1α protein level is known to be regulated by von Hippel-Lindau (VHL) ubiquitin-proteasome system, it has been recently suggested that glycogen synthase kinase-3β (Gsk-3β) promotes a VHL-independent HIF-1α degradation. Here we provide evidences that in rat primary hippocampal cell cultures, HIF-1α degradation might be mediated by a synergic action of Gsk-3β and peptidyl-prolyl cis/trans isomerase (Pin1). In post-ischemic conditions, such as those mimicked with oxygen glucose deprivation (OGD), HIF-1α protein level increases remaining unexpectedly high for long time after normal condition restoration jointly with the increase of lactate dehydrogenase (LDH) and β-secretase 1 (BACE1) protein expression (70 and 140% respectively). Interestingly the Pin1 activity decreases about 40–60% and Pin1^S16 inhibitory phosphorylation significantly increases, indicating that Pin1 binding to its substrate and enzymatic activity are reduced by treatment. Co-immunoprecipitation experiments demonstrate that HIF-1α/Pin1 in normoxia are associated, and that in presence of specific Pin1 and Gsk-3β inhibitors their interaction is reduced in parallel to an increase of HIF-1α protein level. Thus we suggest that in post-OGD neurons the high level of HIF-1α might be due to Pin1 binding ability and activity reduction which affects HIF-1α degradation: an event that may highlight the relevance of ischemia/HIF-1α as a risk factor in AD pathogenesis.

HIF-1α activation results in actin cytoskeleton reorganization and modulation of Rac-1 signaling in endothelial cells

BACKGROUND

Hypoxia is a major driving force in vascularization and vascular remodeling. Pharmacological inhibition of prolyl hydroxylases (PHDs) leads to an oxygen-independent and long-lasting activation of hypoxia-inducible factors (HIFs). Whereas effects of HIF-stabilization on transcriptional responses have been thoroughly investigated in endothelial cells, the molecular details of cytoskeletal changes elicited by PHD-inhibition remain largely unknown. To investigate this important aspect of PHD-inhibition, we used a spheroid-on-matrix cell culture model.

RESULTS

Microvascular endothelial cells (glEND.2) were organized into spheroids. Migration of cells from the spheroids was quantified and analyzed by immunocytochemistry. The PHD inhibitor dimethyloxalyl glycine (DMOG) induced F-actin stress fiber formation in migrating cells, but only weakly affected microvascular endothelial cells firmly attached in a monolayer. Compared to control spheroids, the residual spheroids were larger upon PHD inhibition and contained more cells with tight VE-cadherin positive cell-cell contacts. Morphological alterations were dependent on stabilization of HIF-1α and not HIF-2α as shown in cells with stable knockdown of HIF-α isoforms. DMOG-treated endothelial cells exhibited a reduction of immunoreactive Rac-1 at the migrating front, concomitant with a diminished Rac-1 activity, whereas total Rac-1 protein remained unchanged. Two chemically distinct Rac-1 inhibitors mimicked the effects of DMOG in terms of F-actin fiber formation and orientation, as well as stabilization of residual spheroids. Furthermore, phosphorylation of p21-activated kinase PAK downstream of Rac-1 was reduced by DMOG in a HIF-1α-dependent manner. Stabilization of cell-cell contacts associated with decreased Rac-1 activity was also confirmed in human umbilical vein endothelial cells.

CONCLUSIONS

Our data demonstrates that PHD inhibition induces HIF-1α-dependent cytoskeletal remodeling in endothelial cells, which is mediated essentially by a reduction in Rac-1 signaling.

Decorin inhibits angiogenic potential of choroid-retinal endothelial cells by downregulating hypoxia-induced Met, Rac1, HIF-1α and VEGF expression in cocultured retinal pigment epithelial cells

Choroidal neovascularization (CNV) is one of the most common causes of severe vision loss. Decorin, a multiple receptor tyrosine kinase inhibitor, has been recently shown to play an important regulatory role in angiogenic response. This study aims to investigate whether the overexpression of decorin in retinal pigment epithelial (RPE) cells under hypoxia alters the in vitro angiogenic ability of cocultured choroid-retinal endothelial cells and to explore the possible mechanisms involved. Human RPE cells (ARPE-19) were subjected to hypoxia with or without decorin pretreatment, and RNA interference technique was used to knock down the Met gene in ARPE-19 cells. Cell viability was determined using the Cell Counting Kit-8 assay. Expression of Met, Rac1 and hypoxia-inducible factor-1 alpha (HIF-1α) was evaluated by western blot and quantitative real-time polymerase chain reaction (qRT-PCR). Vascular endothelial growth factor (VEGF) expression was evaluated by enzyme-linked immunosorbent assay (ELISA) and qRT-PCR. We then constructed a recombinant lentiviral vector carrying the decorin gene to transduce ARPE-19 cells. The overexpression of decorin in transduced RPE cells was confirmed by qRT-PCR and western blot. The transduced RPE cells were then cocultured with rhesus macaque choroid-retinal endothelial cells (RF/6A) in a transwell coculture system to observe the effects of decorin overexpression in ARPE-19 cells on the proliferation, migration and tube formation of RF/6A cells. In response to hypoxia, the VEGF concentrations in the culture supernatants increased greatly at 24 and 48 h, and this effect was inhibited significantly and nearly equally in the presence of 50-200 nM decorin. Decorin pretreatment before hypoxia exposure effectively reduced the hypoxia-induced expression of Met, Rac1, HIF-1α and VEGF in ARPE-19 cells. Transfection of small interfering RNA against Met to ARPE-19 cells also resulted in significant downregulation of Rac1, HIF-1α and VEGF under hypoxia, and this effect was similar to that noted with decorin pretreatment alone or with their combination. Results from the coculture system showed that the overexpression of decorin in ARPE-19 cells significantly inhibited the proliferation, migration and tube formation of RF/6A cells. These results indicate that Met pathway activation plays an important role in the upregulation of VEGF in RPE cells under hypoxia. Decorin may interfere with angiogenesis by downregulating hypoxia-induced Met, Rac1, HIF-1α and VEGF expression in RPE cells, which suggests a potential strategy for the inhibition of CNV.

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

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

MgcRacGAP, a cytoskeleton regulator, inhibits HIF-1 transcriptional activity by blocking its dimerization

Hypoxia inducible factor-1 (HIF-1), a dimeric transcription factor of the bHLH-PAS family, is comprised of HIF-1α, which is inducible by hypoxia and ARNT or HIF-1β, which is constitutively expressed. HIF-1 is involved in cellular homeostasis under hypoxia, in development and in several diseases affected by oxygen availability, particularly cancer. Since its expression is positively correlated with poor outcome prognosis for cancer patients, HIF-1 is a target for pharmaceutical therapy. We have previously shown that male germ cell Rac GTPase activating protein (MgcRacGAP), a regulator of Rho proteins which are principally involved in cytoskeletal organization, binds to HIF-1α and inhibits its transcriptional activity. In this work, we have explored the mechanism of the MgcRacGAP-mediated HIF-1 inactivation. We show that the Myo domain of MgcRacGAP, which is both necessary and sufficient for HIF-1 repression, binds to the PAS-B domain of HIF-1α. Furthermore MgcRacGAP competes with ARNT for binding to the HIF-1α PAS-B domain, as shown by in vitro binding pull down assays. In mammalian cells, ARNT overexpression can overcome the MgcRacGAP-mediated inhibition and MgcRacGAP binding to HIF-1α in vivo inhibits its dimerization with ARNT. We additionally present results indicating that MgcRacGAP binding to HIF-1α is specific, since it does not affect the transcriptional activity of HIF-2, a close evolutionary relative of HIF-1 also involved in hypoxia regulation and cancer. Our results reveal a new mechanism for HIF-1 transcriptional activity regulation, suggest a novel hypoxia-cytoskeleton link and provide new tools for selective HIF-1 inhibition.

Expression of Rac1, HIF-1α, and VEGF in gastric carcinoma: correlation with angiogenesis and prognosis

BACKGROUND

The aim of this study was to investigate the relationship between the expression of hypoxia-inducible factor-1α (HIF-1α), Ras-related C3 botulinum toxin substrate 1 (Rac1), and vascular endothelial growth factor (VEGF), as well as their correlation with angiogenesis and prognosis in gastric carcinoma.

MATERIAL AND METHODS

The expression of Rac1, HIF-1α, VEGF, and CD34 (described in terms of microvessel density, MVD) was determined by immunohistochemical staining of tissues from 60 radically resected gastric cancer specimens.

RESULTS

The proportion of specimens expressing Rac1, HIF-1α, and VEGF was 37/60 (61.7%), 35/60 (58.3%), and 40/60 (66.7%), respectively. The levels of Rac1, HIF-1α, and VEGF expression were significantly correlated with Lauren's classification, lymph node metastasis, and pathologic staging (p < 0.05). There were positive correlations between MVD and the expression of Rac1, HIF-1α, and VEGF. The mean survival time and 5-year survival rate in cases with positive Rac1, HIF-1α, and VEGF expression and MVD ≥ 26.3 were significantly shorter than those with negative Rac1, HIF-1α, and VEGF expression and MVD < 26.3.

CONCLUSION

Rac1, HIF-1α, and VEGF play an important role in tumor invasion and metastasis, especially in tumor angiogenesis. Thus, testing the expression of Rac1, HIF-1α, and VEGF may be a useful index for treatment and prognosis.

The possible mechanisms underlying the impairment of HIF-1α pathway signaling in hyperglycemia and the beneficial effects of certain therapies

Hypoxia-inducible factor 1 alpha (HIF-1α), an essential transcription factor which mediates the adaptation of cells to low oxygen tensions, is regulated precisely by hypoxia and hyperglycemia, which are major determinants of the chronic complications associated with diabetes. The process of HIF-1α stabilization by hypoxia is clear; however, the mechanisms underlying the potential deleterious effect of hyperglycemia on HIF-1α are still controversial, despite reports of a variety of studies demonstrating the existence of this phenomenon. In fact, HIF-1α and glucose can sometimes influence each other: HIF-1α induces the expression of glycolytic enzymes and glucose metabolism affects HIF-1α accumulation in some cells. Although hyperglycemia upregulates HIF-1α signaling in some specific cell types, we emphasize the inhibition of HIF-1α by high glucose in this review. With regard to the mechanisms of HIF-1α impairment, the role of methylglyoxal in impairment of HIF-1α stabilization and transactivation ability and the negative effect of reactive oxygen species (ROS) on HIF-1α are discussed. Other explanations for the inhibition of HIF-1α by high glucose exist: the increased sensitivity of HIF-1α to Von Hippel-Lindau (VHL) machinery, the role of osmolarity and proteasome activity, and the participation of several molecules. This review aims to summarize several important developments regarding these mechanisms and to discuss potentially effective therapeutic techniques (antioxidants eicosapentaenoic acid (EPA) and metallothioneins (MTs), pharmaceuticals cobalt chloride (CoCl2), dimethyloxalylglycine (DMOG), desferrioxamine (DFO) and gene transfer of constitutively active forms of HIF-1α) and their mechanisms of action for intervention in the chronic complications in diabetes.

Lack of bcr and abr promotes hypoxia-induced pulmonary hypertension in mice

BACKGROUND

Bcr and Abr are GTPase activating proteins that specifically downregulate activity of the small GTPase Rac in restricted cell types in vivo. Rac1 is expressed in smooth muscle cells, a critical cell type involved in the pathogenesis of pulmonary hypertension. The molecular mechanisms that underlie hypoxia-associated pulmonary hypertension are not well-defined.

METHODOLOGY/PRINCIPAL FINDINGS

Bcr and abr null mutant mice were compared to wild type controls for the development of pulmonary hypertension after exposure to hypoxia. Also, pulmonary arterial smooth muscle cells from those mice were cultured in hypoxia and examined for proliferation, p38 activation and IL-6 production. Mice lacking Bcr or Abr exposed to hypoxia developed increased right ventricular pressure, hypertrophy and pulmonary vascular remodeling. Perivascular leukocyte infiltration in the lungs was increased, and under hypoxia bcr-/- and abr-/- macrophages generated more reactive oxygen species. Consistent with a contribution of inflammation and oxidative stress in pulmonary hypertension-associated vascular damage, Bcr and Abr-deficient animals showed elevated endothelial leakage after hypoxia exposure. Hypoxia-treated pulmonary arterial smooth muscle cells from Bcr- or Abr-deficient mice also proliferated faster than those of wild type mice. Moreover, activated Rac1, phosphorylated p38 and interleukin 6 were increased in these cells in the absence of Bcr or Abr. Inhibition of Rac1 activation with Z62954982, a novel Rac inhibitor, decreased proliferation, p38 phosphorylation and IL-6 levels in pulmonary arterial smooth muscle cells exposed to hypoxia.

CONCLUSIONS

Bcr and Abr play a critical role in down-regulating hypoxia-induced pulmonary hypertension by deactivating Rac1 and, through this, reducing both oxidative stress generated by leukocytes as well as p38 phosphorylation, IL-6 production and proliferation of pulmonary arterial smooth muscle cells.

NADPH oxidases as a source of oxidative stress and molecular target in ischemia/reperfusion injury

Ischemia/reperfusion injury (IRI) is crucial in the pathology of major cardiovascular diseases, such as stroke and myocardial infarction. Paradoxically, both the lack of oxygen during ischemia and the replenishment of oxygen during reperfusion can cause tissue injury. Clinical outcome is also determined by a third, post-reperfusion phase characterized by tissue remodeling and adaptation. Increased levels of reactive oxygen species (ROS) have been suggested to be key players in all three phases. As a second paradox, ROS seem to play a double-edged role in IRI, with both detrimental and beneficial effects. These Janus-faced effects of ROS may be linked to the different sources of ROS or to the different types of ROS that exist and may also depend on the phase of IRI. With respect to therapeutic implications, an untargeted application of antioxidants may not differentiate between detrimental and beneficial ROS, which might explain why this approach is clinically ineffective in lowering cardiovascular mortality. Under some conditions, antioxidants even appear to be harmful. In this review, we discuss recent breakthroughs regarding a more targeted and promising approach to therapeutically modulate ROS in IRI. We will focus on NADPH oxidases and their catalytic subunits, NOX, as they represent the only known enzyme family with the sole function to produce ROS. Similar to ROS, NADPH oxidases may play a dual role as different NOX isoforms may mediate detrimental or protective processes. Unraveling the precise sequence of events, i.e., determining which role the individual NOX isoforms play in the various phases of IRI, may provide the crucial molecular and mechanistic understanding to finally effectively target oxidative stress.

Hyaluronic acid promotes angiogenesis by inducing RHAMM-TGFβ receptor interaction via CD44-PKCδ

Hyaluronic acid (HA) has been shown to promote angiogenesis. However, the mechanism behind this effect remains largely unknown. Therefore, in this study, the mechanism of HA-induced angiogenesis was examined. CD44 and PKCδ were shown to be necessary for induction of the receptor for HA-mediated cell motility (RHAMM), a HA-binding protein. RHAMM was necessary for HA-promoted cellular invasion and endothelial cell tube formation. Cytokine arrays showed that HA induced the expression of plasminogen activator-inhibitor-1 (PAI), a downstream target of TGFβ receptor signaling. The induction of PAI-1 was dependent on CD44 and PKCδ. HA also induced an interaction between RHAMM and TGFβ receptor I, and induction of PAI-1 was dependent on RHAMM and TGFβ receptor I. Histone deacetylase 3 (HDAC3), which is decreased by HA via rac1, reduced induction of plasminogen activator inhibitor-1 (PAI-1) by HA. ERK, which interacts with RHAMM, was necessary for induction of PAI-1 by HA. Snail, a downstream target of TGFβ signaling, was also necessary for induction of PAI-1. The down regulation of PAI-1 prevented HA from enhancing endothelial cell tube formation and from inducing expression of angiogenic factors, such as ICAM-1, VCAM-1 and MMP-2. HDAC3 also exerted reduced expression of MMP-2. In this study, we provide a novel mechanism of HA-promoted angiogenesis, which involved RHAMM-TGFβRI signaling necessary for induction of PAI-1.

Role of RhoB in the regulation of pulmonary endothelial and smooth muscle cell responses to hypoxia

RATIONALE

RhoA and Rho kinase contribute to pulmonary vasoconstriction and vascular remodeling in pulmonary hypertension. RhoB, a protein homologous to RhoA and activated by hypoxia, regulates neoplastic growth and vasoconstriction but its role in the regulation of pulmonary vascular function is not known.

OBJECTIVE

To determine the role of RhoB in pulmonary endothelial and smooth muscle cell responses to hypoxia and in pulmonary vascular remodeling in chronic hypoxia-induced pulmonary hypertension.

METHODS AND RESULTS

Hypoxia increased expression and activity of RhoB in human pulmonary artery endothelial and smooth muscle cells, coincidental with activation of RhoA. Hypoxia or adenoviral overexpression of constitutively activated RhoB increased actomyosin contractility, induced endothelial permeability, and promoted cell growth; dominant negative RhoB or manumycin, a farnesyltransferase inhibitor that targets the vascular function of RhoB, inhibited the effects of hypoxia. Coordinated activation of RhoA and RhoB maximized the hypoxia-induced stress fiber formation caused by RhoB/mammalian homolog of Drosophila diaphanous-induced actin polymerization and RhoA/Rho kinase-induced phosphorylation of myosin light chain on Ser19. Notably, RhoB was specifically required for hypoxia-induced factor-1α stabilization and for hypoxia- and platelet-derived growth factor-induced cell proliferation and migration. RhoB deficiency in mice markedly attenuated development of chronic hypoxia-induced pulmonary hypertension, despite compensatory expression of RhoA in the lung.

CONCLUSIONS

RhoB mediates adaptational changes to acute hypoxia in the vasculature, but its continual activation by chronic hypoxia can accentuate vascular remodeling to promote development of pulmonary hypertension. RhoB is a potential target for novel approaches (eg, farnesyltransferase inhibitors) aimed at regulating pulmonary vascular tone and structure.

Activation of TRPC6 channels is essential for lung ischaemia-reperfusion induced oedema in mice

Lung ischaemia–reperfusion-induced oedema (LIRE) is a life-threatening condition that causes pulmonary oedema induced by endothelial dysfunction. Here we show that lungs from mice lacking nicotinamide adenine dinucleotide phosphate (NADPH) oxidase (Nox2^y/−) or the classical transient receptor potential channel 6 (TRPC6^−/−) are protected from LIR-induced oedema (LIRE). Generation of chimeric mice by bone marrow cell transplantation and endothelial-specific Nox2 deletion showed that endothelial Nox2, but not leukocytic Nox2 or TRPC6, are responsible for LIRE. Lung endothelial cells from Nox2- or TRPC6-deficient mice showed attenuated ischaemia-induced Ca²⁺ influx, cellular shape changes and impaired barrier function. Production of reactive oxygen species was completely abolished in Nox2^y/− cells. A novel mechanistic model comprising endothelial Nox2-derived production of superoxide, activation of phospholipase C-γ, inhibition of diacylglycerol (DAG) kinase, DAG-mediated activation of TRPC6 and ensuing LIRE is supported by pharmacological and molecular evidence. This mechanism highlights novel pharmacological targets for the treatment of LIRE.

The signalling cascade involved in lung ischaemia–reperfusion-induced oedema is poorly understood. Using knockout mice, Weissmann et al. propose a model in which reactive oxygen species production by endothelial NOX2 leads to phospholipase C-γ activation, DAG kinase inhibition and subsequent TRPC6 activation.

Fentanyl activates hypoxia-inducible factor 1 in neuronal SH-SY5Y cells and mice under non-hypoxic conditions in a μ-opioid receptor-dependent manner

Hypoxia-inducible factor 1 (HIF-1) is the main transcription factor responsible for hypoxia-induced gene expression. Perioperative drugs including anesthetics have been reported to affect HIF-1 activity. However, the effect of fentanyl on HIF-1 activity is not well documented. In this study, we investigated the effect of fentanyl and other opioids on HIF-1 activity in human SH-SY5Y neuroblastoma cells, hepatoma Hep3B cells, lung adenocarcinoma A549 cells and mice. Cells were exposed to fentanyl, and HIF-1 protein expression was examined by Western blot analysis using anti-HIF-1α and β antibodies. HIF-1-dependent gene expression was investigated by semi-quantitative real-time reverse transcriptase (RT)-PCR (qRT-PCR) and luciferase assay. Furthermore, fentanyl was administered intraperitoneally and HIF-1-dependent gene expression was investigated by qRT-PCR in the brains and kidneys of mice. A 10-μM concentration of fentanyl and other opioids, including 1 μM morphine and 4 μM remifentanil, induced HIF-1α protein expression and HIF-1 target gene expression in an opioid receptor-dependent manner in SH-SY5Y cells with activity peaking at 24h. Fentanyl did not augment HIF-1α expression during hypoxia-induced induction. HIF-1α stabilization assays and experiments with cycloheximide revealed that fentanyl increased translation from HIF-1α mRNA but did not stabilize the HIF-1α protein. Furthermore, fentanyl induced HIF-1 target gene expression in the brains of mice but not in their kidneys in a naloxone-sensitive manner. In this report, we describe for the first time that fentanyl, both in vitro and in vivo, induces HIF-1 activation under non-hypoxic conditions, leading to increases in expression of genes associated with adaptation to hypoxia.

Hypoxia-inducible factor in thyroid carcinoma

Intratumoural hypoxia (low oxygen tension) is associated with aggressive disease and poor prognosis. Hypoxia-inducible factor-1 is a transcription factor activated by hypoxia that regulates the expression of genes that promote tumour cell survival, progression, metastasis, and resistance to chemo/radiotherapy. In addition to hypoxia, HIF-1 can be activated by growth factor-signalling pathways such as the mitogen-activated protein kinases- (MAPK-) and phosphatidylinositol-3-OH kinases- (PI3K-) signalling cascades. Mutations in these pathways are common in thyroid carcinoma and lead to enhanced HIF-1 expression and activity. Here, we summarise current data that highlights the potential role of both hypoxia and MAPK/PI3K-induced HIF-1 signalling in thyroid carcinoma progression, metastatic characteristics, and the potential role of HIF-1 in thyroid carcinoma response to radiotherapy. Direct or indirect targeting of HIF-1 using an MAPK or PI3K inhibitor in combination with radiotherapy may be a new potential therapeutic target to improve the therapeutic response of thyroid carcinoma to radiotherapy and reduce metastatic burden.