Angiopoietin-1-induced angiogenesis is modulated by endothelial NADPH oxidase

Antioxidant Defenses, Oxidative Stress Responses, and Apoptosis Modulation in Spontaneous Abortion: An Immunohistochemistry Analysis of First-Trimester Chorionic Villi

Oxidative stress (OS) and apoptosis are critical factors in placental development and function. Their interplay influences trophoblast proliferation, differentiation, and invasion, as well as vascular development. An imbalance between these processes can lead to pregnancy-related disorders such as preeclampsia, intrauterine growth restriction, and even spontaneous abortion. Our study seeks to elucidate the associations between preventive antioxidant/protective OS response factors-glutathione (GSH), MutT Homolog 1 (MTH1), and apoptotic regulation modulators-tumor protein p53 and B-cell lymphoma (Bcl-2) transcripts, in the context of spontaneous abortion (30 samples) versus elective termination of pregnancy (20 samples), using immunohistochemistry (IHC) to determine their proteomic expression in chorionic villi within abortive fetal placenta tissue samples. Herein, comparative statistical analyses revealed that both OS response factors, GSH and MTH1, were significantly under-expressed in spontaneous abortion cases as compared to elective. Conversely, for apoptotic regulators, p53 expression was significantly higher in spontaneous abortion cases, whereas Bcl-2 expression was significantly lower in spontaneous abortion cases. These findings suggest that a strong pro-apoptotic signal is prevalent within spontaneous abortion samples, alongside reduced anti-apoptotic protection, depleted antioxidant defenses and compromised oxidative DNA damage prevention/repair, as compared to elective abortion controls. Herein, our hypothesis that OS and apoptosis are closely linked processes contributing to placental dysfunction and spontaneous abortion was thus seemingly corroborated. Our results further highlight the importance of maintaining redox homeostasis and apoptotic regulation for a successful pregnancy. Understanding the mechanisms underlying this interplay is essential for developing potential therapies to manage OS, promote placentation, and avoid unwanted apoptosis, ultimately improving pregnancy outcomes. Antioxidant supplementation, modulation of p53 activity, and the enhancement of DNA repair mechanisms may represent potential approaches to mitigate OS and apoptosis in the placenta. Further research is needed to explore these strategies and their efficacy in preventing spontaneous abortion.

Characteristics of Inflammatory and Normal Endothelial Exosomes on Endothelial Function and the Development of Hypertension

Endothelial dysfunction is associated with the development of hypertension. We hypothesize that inflammatory and normal endothelial exosomes play their roles by mediating endothelial function, and they induce endothelial angiogenesis through different signaling pathways. Endothelial cell-derived exosomes were isolated from the human umbilical vein endothelial cells (HUVECs) treated with (TExo) or without (CExo) tumor necrosis factor (TNF)-α. We monitored dermal microcirculation profiles in spontaneously hypertensive rats (SHRs) and WKY rats using a laser Doppler imager and a laser Doppler perfusion and temperature monitor. Tube formation, levels of angiogenesis-related proteins in HUVEC-conditioned media, and reactive oxygen species (ROS) levels were assessed following TNF-α, CExo, or TExo treatments. Western blot analysis was conducted to examine signaling proteins associated with inflammation and ROS. The results showed increased blood perfusion and the mean amplitude of endothelial oscillator in SHRs following CExo administration. TNF-α, CExo, and TExo treatments promoted endothelial tube formation and elevated levels of angiogenic factors and ROS. TExo significantly increased phosphorylation levels of STAT3, p38, and level of NF-κB, while decreasing phosphorylation levels of JNK and Erk (P < 0.01 or P < 0.05). CExo significantly increased STAT3 phosphorylation and reduced JNK and Erk phosphorylation (all P < 0.01). In conclusion, TNF-α and TExo induce inflammatory and pathological angiogenesis via the NF-κB pathway, while CExo exhibits a physiologically pro-angiogenic effect on endothelial cells. Increased ROS, interplaying with inflammatory signals, contribute to exosome-mediated alterations of endothelial function, thereby playing a role in the development of hypertension.

p53 Acetylation Exerts Critical Roles in Pressure Overload-Induced Coronary Microvascular Dysfunction and Heart Failure in Mice

BACKGROUND

Coronary microvascular dysfunction (CMD) has been shown to contribute to cardiac hypertrophy and heart failure (HF) with preserved ejection fraction. At this point, there are no proven treatments for CMD.

METHODS

We have shown that histone acetylation may play a critical role in the regulation of CMD. By using a mouse model that replaces lysine with arginine at residues K98, K117, K161, and K162R of p53 (p534KR), preventing acetylation at these sites, we test the hypothesis that acetylation-deficient p534KR could improve CMD and prevent the progression of hypertensive cardiac hypertrophy and HF. Wild-type and p534KR mice were subjected to pressure overload by transverse aortic constriction to induce cardiac hypertrophy and HF.

RESULTS

Echocardiography measurements revealed improved cardiac function together with a reduction of apoptosis and fibrosis in p534KR mice. Importantly, myocardial capillary density and coronary flow reserve were significantly improved in p534KR mice. Moreover, p534KR upregulated the expression of cardiac glycolytic enzymes and Gluts (glucose transporters), as well as the level of fructose-2,6-biphosphate; increased PFK-1 (phosphofructokinase 1) activity; and attenuated cardiac hypertrophy. These changes were accompanied by increased expression of HIF-1α (hypoxia-inducible factor-1α) and proangiogenic growth factors. Additionally, the levels of SERCA-2 were significantly upregulated in sham p534KR mice, as well as in p534KR mice after transverse aortic constriction. In vitro, p534KR significantly improved endothelial cell glycolytic function and mitochondrial respiration and enhanced endothelial cell proliferation and angiogenesis. Similarly, acetylation-deficient p534KR significantly improved coronary flow reserve and rescued cardiac dysfunction in SIRT3 (sirtuin 3) knockout mice.

CONCLUSIONS

Our data reveal the importance of p53 acetylation in coronary microvascular function, cardiac function, and remodeling and may provide a promising approach to improve hypertension-induced CMD and to prevent the transition of cardiac hypertrophy to HF.

Regulatory role of TIGAR on endothelial metabolism and angiogenesis

Endothelial glycolytic metabolism plays an important role in the process of angiogenesis. TP53-induced glycolysis and apoptosis regulator (TIGAR) is a significant mediator of cellular energy homeostasis. However, the role of TIGAR in endothelial metabolism, angiogenesis, and coronary flow reserve (CFR) has not been studied. The present study investigated whether knockout (KO) of TIGAR improves endothelial glycolytic function and angiogenesis. In vitro, aortic endothelial cells (ECs) from TIGAR KO mice exhibited increased expression of 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase isoform-3 (PFKFB3) and increased glycolytic function. These were accompanied by increased mitochondrial basal/maximal respiration and ATP production. Furthermore, knockout of TIGAR in ECs enhanced endothelial proliferation, migration, and tube formation. Knockout of TIGAR also significantly increased aortic sprouting ex vivo. In vivo, knockout of TIGAR increased the expression of proangiogenic factor, angiopoietin-1 (Ang-1) in mouse hearts. Knockout of TIGAR also significantly increased coronary capillary density with enhanced CFR in these hearts. Furthermore, TIGAR KO mice subjected to pressure overload (PO), a common model to study angiogenesis and cardiac hypertrophy, exhibited elevated expression of Ang-1, VEGF, and PFKFB3 than that of the wild-type (WT) mice. WT mice subjected to PO exhibited a significant reduction of coronary capillary density and impaired CFR, but TIGAR KO mice did not. In addition, knockout of TIGAR blunted TAC-induced cardiac hypertrophy and dysfunction seen in the WT mice. In conclusion, knockout of TIGAR improves endothelial angiogenetic capabilities by enhancing the endothelial glycolytic function, mitochondrial respiration, and proangiogenic signaling, which leads to increased coronary capillary density and vascular function and protects against chronic stress.

Lipoxin A4 attenuates uric acid-activated, NADPH oxidase-dependent oxidative stress by interfering with translocation of p47phox in human umbilical vein endothelial cells

LipoxinA4 (LXA4) is a well-known key mediator of endogenous anti-inflammation and of the resolution of inflammation. Considerable oxidative stress occurs during inflammation due to the generation of reactive oxidative species (ROS). Moreover, high levels of uric acid (UA) contribute to endothelial cell dysfunction, which can promote disease-related morbidity, and NADPH oxidase-derived ROS are crucial regulatory factors in these responses. However, LXA4 also has the potential to reduce oxidative stress. The aim of the present study was to examine whether LXA4 could suppress UA-induced oxidative stress in human umbilical vein endothelial cells (HUVECs) and to investigate its mechanisms of action in vitro. HUVECs were incubated with or without LXA4, followed by the addition of UA. ROS levels were then measured using 2,7-dichlorodihydrofluorescein diacetate and lucigenin-enhanced chemiluminescence was used to evaluate NADPH oxidase activity. p47phox or p22phox small interfering (si)RNA were transfected into HUVECs and protein levels of p47phox were detected using western blot analysis. LXA4 significantly inhibited UA-induced generation of ROS to the same extent as the NADPH oxidase inhibitor, diphenyleneiodonium chloride. Notably, transfection of p47phox siRNA attenuated the generation of ROS and the activation of NADPH oxidase. Cells transfected with p22phox siRNA demonstrated a significant reduction in the expression of p47phox on the membrane. Further experiments demonstrated that LXA4 interfered with the transfer of p47phox from the cytoplasm to the cell membrane. These findings suggested that LXA4 inhibited the release of NADPH oxidase derived ROS in HUVECs stimulated by UA. A potential mechanism of action underlying this effect could be LXA4-mediated suppression of NADPH oxidase activity, leading to inhibition of p47phox translocation from the cytoplasm to the cell membrane.

Redox Regulation of the Microcirculation

The microcirculation maintains tissue homeostasis through local regulation of blood flow and oxygen delivery. Perturbations in microvascular function are characteristic of several diseases and may be early indicators of pathological changes in the cardiovascular system and in parenchymal tissue function. These changes are often mediated by various reactive oxygen species and linked to disruptions in pathways such as vasodilation or angiogenesis. This overview compiles recent advances relating to redox regulation of the microcirculation by adopting both cellular and functional perspectives. Findings from a variety of vascular beds and models are integrated to describe common effects of different reactive species on microvascular function. Gaps in understanding and areas for further research are outlined. © 2020 American Physiological Society. Compr Physiol 10:229-260, 2020.

Endothelial specific SIRT3 deletion impairs glycolysis and angiogenesis and causes diastolic dysfunction

Endothelial glycolysis plays a critical role in the regulation of angiogenesis. We investigated the role of Sirtuin 3 (SIRT3) on endothelial cell (EC) glycolytic metabolism, angiogenesis, and diastolic function. Our aim was to test the hypothesis that loss of SIRT3 in ECs impairs endothelial glycolytic metabolism and angiogenesis and contributes to myocardial capillary rarefaction and the development of diastolic dysfunction. Using SIRT3 deficient ECs, SIRT3 was found to regulate a metabolic switch between mitochondrial respiration and glycolysis. SIRT3 knockout (KO)-ECs exhibited higher mitochondrial respiration and reactive oxygen species (ROS) formation. SIRT3 knockout (KO)-ECs exhibited a reduction in the expression of glycolytic enzyme, PFKFB3, and a fall in glycolysis and angiogenesis. Blockade of PFKFB3 reduced glycolysis and downregulated expression of VEGF and Angiopoietin-1 (Ang-1) in ECs. Deletion of SIRT3 in ECs also impaired hypoxia-induced expression of HIF-2α, VEGF, and Ang-1, as well as reduced angiogenesis. In vivo, endothelial-specific SIRT3 KO (ECKO) mice exhibited a myocardial capillary rarefaction together with a reduced coronary flow reserve (CFR) and diastolic dysfunction. Histologic study further demonstrated that knockout of SIRT3 in ECs significantly increased perivascular fibrosis in the coronary artery. These results implicate a role of SIRT3 in modulating endothelial function and cardiac function. Ablation of SIRT3 leads to impairment of EC glycolytic metabolism and angiogenic signaling, which may contribute to coronary microvascular rarefaction and diastolic dysfunction in SIRT3 ECKO mice.

Redox modification of caveolar proteins in the cardiovascular system- role in cellular signalling and disease

Rapid and coordinated release of a variety of reactive oxygen species (ROS) such as superoxide (O₂^.-), hydrogen peroxide (H₂O₂) and peroxynitrite, in specific microdomains, play a crucial role in cell signalling in the cardiovascular system. These reactions are mediated by reversible and functional modifications of a wide variety of key proteins. Dysregulation of this oxidative signalling occurs in almost all forms of cardiovascular disease (CVD), including at the very early phases. Despite the heavily publicized failure of "antioxidants" to improve CVD progression, pharmacotherapies such as those targeting the renin-angiotensin system, or statins, exert at least part of their large clinical benefit via modulating cellular redox signalling. Over 250 proteins, including receptors, ion channels and pumps, and signalling proteins are found in the caveolae. An increasing proportion of these are being recognized as redox regulated-proteins, that reside in the immediate vicinity of the two major cellular sources of ROS, nicotinamide adenine dinucleotide phosphate oxidase (Nox) and uncoupled endothelial nitric oxide synthase (eNOS). This review focuses on what is known about redox signalling within the caveolae, as well as endogenous protective mechanisms utilized by the cell, and new approaches to targeting dysregulated redox signalling in the caveolae as a therapeutic strategy in CVD.

NADPH Oxidases, Angiogenesis, and Peripheral Artery Disease

Peripheral artery disease (PAD) is caused by narrowing of arteries in the limbs, normally occurring in the lower extremities, with severe cases resulting in amputation of the foot or leg. A potential approach for treatment is to stimulate the formation of new blood vessels to restore blood flow to limb tissues. This is a process called angiogenesis and involves the proliferation, migration, and differentiation of endothelial cells. Angiogenesis can be stimulated by reactive oxygen species (ROS), with NADPH oxidases (NOX) being a major source of ROS in endothelial cells. This review summarizes the recent evidence implicating NOX isoforms in their ability to regulate angiogenesis in vascular endothelial cells in vitro, and in PAD in vivo. Increasing our understanding of the involvement of the NOX isoforms in promoting therapeutic angiogenesis may lead to new treatment options to slow or reverse PAD.

4-isothiocyanate-2, 2, 6, 6-tetramethyl piperidinooxyl inhibits angiogenesis by suppressing VEGFR2 and Tie2 phosphorylation

Reactive oxygen species (ROS) are involved in the signaling pathway and are triggered by angiogenic factors, including vascular endothelial growth factor and angiopoietins. 4-isothiocyanate-2, 2, 6, 6-tetramethyl piperidinooxyl (4-ISO-Tempo) is one of the nitroxides that exhibits antioxidant activity. However, the anti-angiogenic effect of 4-ISO-Tempo remains unknown. The aim of this study was to investigate the effect of 4-ISO-Tempo on tumor proliferation and angiogenesis as well as its underlying mechanisms. Our results revealed that 4-ISO-Tempo significantly inhibited the viability of neoplastic and endothelial cells. Furthermore, the effective concentration of 4-ISO-Tempo on human microvascular endothelial cell 1 (HMEC-1) was lower than that on human lung adenocarcinoma A549 and human colon cancer SW620 cells. This suggested that endothelial cells were more sensitive to 4-ISO-Tempo than tumor cells. Furthermore, we demonstrated that 4-ISO-Tempo also suppressed secretion of matrix metalloproteinase (MMP)-2 and MMP-9, and migration and tube formation of HMEC-1 cells. The mechanism is attributed to the decreasing ROS generation and further phosphorylation of vascular endothelial growth factor receptor 2 and Tie2. Our findings suggest that 4-ISO-Tempo should be investigated for its usefulness in anti-angiogenesis therapies.

S6K2-mediated regulation of TRBP as a determinant of miRNA expression in human primary lymphatic endothelial cells

MicroRNAs (miRNAs) are short non-coding RNAs that silence mRNAs. They are generated following transcription and cleavage by the DROSHA/DGCR8 and DICER/TRBP/PACT complexes. Although it is known that components of the miRNA biogenesis machinery can be phosphorylated, it remains poorly understood how these events become engaged during physiological cellular activation. We demonstrate that S6 kinases can phosphorylate the extended C-terminal domain of TRBP and interact with TRBP in situ in primary cells. TRBP serines 283/286 are essential for S6K-mediated TRBP phosphorylation, optimal expression of TRBP, and the S6K-TRBP interaction in human primary cells. We demonstrate the functional relevance of this interaction in primary human dermal lymphatic endothelial cells (HDLECs). Angiopoietin-1 (ANG1) can augment miRNA biogenesis in HDLECs through enhancing TRBP phosphorylation and expression in an S6K2-dependent manner. We propose that the S6K2/TRBP node controls miRNA biogenesis in HDLECs and provides a molecular link between the mTOR pathway and the miRNA biogenesis machinery.

Oxidative Stress in Placenta: Health and Diseases

During pregnancy, development of the placenta is interrelated with the oxygen concentration. Embryo development takes place in a low oxygen environment until the beginning of the second trimester when large amounts of oxygen are conveyed to meet the growth requirements. High metabolism and oxidative stress are common in the placenta. Reactive oxidative species sometimes harm placental development, but they are also reported to regulate gene transcription and downstream activities such as trophoblast proliferation, invasion, and angiogenesis. Autophagy and apoptosis are two crucial, interconnected processes in the placenta that are often influenced by oxidative stress. The proper interactions between them play an important role in placental homeostasis. However, an imbalance between the protective and destructive mechanisms of autophagy and apoptosis seems to be linked with pregnancy-related disorders such as miscarriage, preeclampsia, and intrauterine growth restriction. Thus, potential therapies to hold oxidative stress in leash, promote placentation, and avoid unwanted apoptosis are discussed.

Behind the Link between Copper and Angiogenesis: Established Mechanisms and an Overview on the Role of Vascular Copper Transport Systems

Angiogenesis critically sustains the progression of both physiological and pathological processes. Copper behaves as an obligatory co-factor throughout the angiogenic signalling cascades, so much so that a deficiency causes neovascularization to abate. Moreover, the progress of several angiogenic pathologies (e.g. diabetes, cardiac hypertrophy and ischaemia) can be tracked by measuring serum copper levels, which are being increasingly investigated as a useful prognostic marker. Accordingly, the therapeutic modulation of body copper has been proven effective in rescuing the pathological angiogenic dysfunctions underlying several disease states. Vascular copper transport systems profoundly influence the activation and execution of angiogenesis, acting as multi-functional regulators of apparently discrete pro-angiogenic pathways. This review concerns the complex relationship among copper-dependent angiogenic factors, copper transporters and common pathological conditions, with an unusual accent on the multi-faceted involvement of the proteins handling vascular copper. Functions regulated by the major copper transport proteins (CTR1 importer, ATP7A efflux pump and metallo-chaperones) include the modulation of endothelial migration and vascular superoxide, known to activate angiogenesis within a narrow concentration range. The potential contribution of prion protein, a controversial regulator of copper homeostasis, is discussed, even though its angiogenic involvement seems to be mainly associated with the modulation of endothelial motility and permeability.

Relationship between expression of NADPH oxidase 2 and invasion and prognosis of human gastric cancer

AIM: To assess the expression and prognostic value of nicotinamide adenine dinucleotide phosphate oxidase 2 (NOX2) in gastric cancer, and its correlation with vascular endothelial growth factor (VEGF) and epidermal growth factor receptor (EGFR).

METHODS: Tumor and adjacent tissues were obtained from 123 patients who underwent radical surgery for gastric cancer at Renmin Hospital of Wuhan University from 2008-2009. The expression of NOX2, VEGF, EGFR and CD68 in tumor tissues was detected by immunohistochemistry. The expression of NOX2 in gastric cancer and adjacent tissues was detected by Western blot analysis. Spearman^’s correlation was performed to elucidate the relationship of NOX2 with VEGF and EGFR. The Kaplan-Meier method was used to calculate survival time, and the log-rank test was used to evaluate differences in survival. Cox‘s proportional hazards regression model was applied in a stepwise manner to analyze the independent prognostic factors.

RESULTS: NOX2 exhibited positive expression in 47.2% (58/123) of the gastric cancer tissues. Western blot analysis revealed that NOX2 was up-regulated in tumor tissues compared to the adjacent tissue [39.0% (48/123)]. Immunohistochemistry staining revealed that CD68, which is a specific marker of macrophages, and NOX expression presented a similar localization and staining intensity. The expression of NOX2 was positively correlated with that of VEGF and EGFR. Comparison of the 5-year survival rates of the NOX2 positive and NOX2 negative groups showed that the NOX2 positive group presented a poor prognosis.

CONCLUSION: NOX2 positively correlates with the levels of VEGF and EGFR. NOX2 may be used as a new biomarker and a potential therapeutic target for gastric cancer.

Understanding the biology of reactive oxygen species and their link to cancer: NADPH oxidases as novel pharmacological targets

Reactive oxygen species (ROS), the cellular products of myriad physiological processes, have long been understood to lead to cellular damage if produced in excess and to be a causative factor in cancer through the oxidation and nitration of various macromolecules. Reactive oxygen species influence various hallmarks of cancer, such as cellular proliferation and angiogenesis, through the promotion of cell signalling pathways intrinsic to these processes and can also regulate the function of key immune cells, such as macrophages and regulatory T cells, which promote angiogenesis in the tumour environment. Herein we emphasize the family of NADPH oxidase enzymes as the most likely source of ROS, which promote angiogenesis and tumourigenesis through signalling pathways within endothelial, immune and tumour cells. In this review we focus on the pharmacological inhibitors of NADPH oxidases and suggest that, compared with traditional anti-oxidants, they are likely to offer better alternatives for suppression of tumour angiogenesis. Despite the emerging enthusiasm towards the use of NADPH oxidase inhibitors for cancer therapy, this field is still in its infancy; in particular, there is a glaring lack of knowledge of the roles of NADPH oxidases in in vivo animal models and in human cancers. Certainly a clearer understanding of the relevant signalling pathways influenced by NADPH oxidases during angiogenesis in cancer is likely to yield novel therapeutic approaches.

Hypoxia-independent drivers of melanoma angiogenesis

Tumor angiogenesis is a process which is traditionally regarded as the tumor’s response to low nutrient supply occurring under hypoxic conditions. However, hypoxia is not a pre-requisite for angiogenesis. The fact that even single tumor cells or small tumor cell aggregates are capable of attracting blood vessels reveals the early metastatic capability of tumor cells. This review sheds light on the hypoxia-independent mechanisms of tumor angiogenesis in melanoma.

Lipopolysaccharide (LPS)-mediated angiopoietin-2-dependent autocrine angiogenesis is regulated by NADPH oxidase 2 (Nox2) in human pulmonary microvascular endothelial cells

Sepsis-mediated endothelial Angiopoeitin-2 (Ang2) signaling may contribute to microvascular remodeling in the developing lung. The mechanisms by which bacterial cell wall components such as LPS mediate Ang2 signaling in human pulmonary microvascular endothelial cells (HPMECs) remain understudied. In HPMEC, LPS-induced Ang2, Tie2, and VEGF-A protein expression was preceded by increased superoxide formation. NADPH oxidase 2 (Nox2) inhibition, but not Nox4 or Nox1 inhibition, attenuated LPS-induced superoxide formation and Ang2, Tie2, and VEGF-A expression. Nox2 silencing, but not Nox4 or Nox1 silencing, inhibited LPS-mediated inhibitor of κ-B kinase β (IKKβ) and p38 phosphorylation and nuclear translocation of NF-κB and AP-1. In HPMECs, LPS increased the number of angiogenic tube and network formations in Matrigel by >3-fold. Conditioned media from LPS-treated cells also induced angiogenic tube and network formation in the presence of Toll-like receptor 4 blockade but not in the presence of Ang2 and VEGF blockade. Nox2 inhibition or conditioned media from Nox2-silenced cells attenuated LPS-induced tube and network formation. Ang2 and VEGF-A treatment rescued angiogenesis in Nox2-silenced cells. We propose that Nox2 regulates LPS-mediated Ang2-dependent autocrine angiogenesis in HPMECs through the IKKβ/NF-κB and MAPK/AP-1 pathways.

Loss of Sirt3 limits bone marrow cell-mediated angiogenesis and cardiac repair in post-myocardial infarction

Sirtuin-3 (Sirt3) has a critical role in the regulation of human aging and reactive oxygen species (ROS) formation. A recent study has identified Sirt3 as an essential regulator of stem cell aging. This study investigated whether Sirt3 is necessary for bone marrow cell (BMC)-mediated cardiac repair in post-myocardial infarction (MI). In vitro, BMC-derived endothelial progenitor cells (EPCs) from wild type (WT) and Sirt3KO mice were cultured. EPC angiogenesis, ROS formation and apoptosis were assessed. In vivo, WT and Sirt3 KO mice were subjected to MI and BMCs from WT and Sirt3 KO mice were injected into ischemic area immediately. The expression of VEGF and VEGFR2 was reduced in Sirt3KO-EPCs. Angiogenic capacities and colony formation were significantly impaired in Sirt3KO-EPCs compared to WT-EPCs. Loss of Sirt3 further enhanced ROS formation and apoptosis in EPCs. Overexpression of Sirt3 or treatment with NADPH oxidase inhibitor apocynin (Apo, 200 and 400 microM) rescued these abnormalities. In post-MI mice, BMC treatment increased number of Sca1⁺/c-kit⁺ cells; enhanced VEGF expression and angiogenesis whereas Sirt3KO-BMC treatment had little effects. BMC treatment also attenuated NADPH oxidase subunits p47^phox and gp91^phox expression, and significantly reduced ROS formation, apoptosis, fibrosis and hypertrophy in post-MI mice. Sirt3KO-BMC treatment did not display these beneficial effects. In contrast, Sirt3KO mice treated with BMCs from WT mice attenuated myocardial apoptosis, fibrosis and improved cardiac function. Our data demonstrate that Sirt3 is essential for BMC therapy; and loss of Sirt3 limits BMC-mediated angiogenesis and cardiac repair in post-MI.

Panax notoginseng saponins inhibits atherosclerotic plaque angiogenesis by down-regulating vascular endothelial growth factor and nicotinamide adenine dinucleotide phosphate oxidase subunit 4 expression

OBJECTIVE

To investigate the mechanism of Panax notoginseng saponins (PNS), an effective component extracted from Panax notoginseng, on atherosclerotic plaque angiogenesis in atherosclerosis-prone apolipoprotein E-knockout (ApoE-KO) mice fed with high-fat, high-cholesterol diet.

METHODS

Twenty ApoE-KO mice were divided into two groups, the model group and the PNS group. Ten normal C57BL/6J mice were used as a control group. PNS (60 mg/kg) was orally administered daily for 12 weeks in the PNS group. The ratio of plaque area to vessel area was examined by histological staining. The tissue sample of aortic root was used to detect the CD34 and vascular endothelial growth factor (VEGF) expression areas by immunohistochemistry. The expression of VEGF and nicotinamide adenine dinucleotide phosphate oxidase subunit 4 (NOX4) were measured by reverse transcription polymerase chain reaction and Western blotting respectively.

RESULTS

After treatment with PNS, the plaque areas were decreased (P<0.05). CD34 expressing areas and VEGF expression areas in plaques were significantly decreased (P<0.05). Meanwhile, VEGF and NOX4 mRNA expression were decreased after treatment with PNS. VEGF and NOX4 protein expression were also decreased by about 72% and 63%, respectively (P<0.01).

CONCLUSION

PNS, which decreases VEGF and NOX4 expression, could alleviate plaque angiogenesis and attenuate atherosclerosis.

Apelin gene therapy increases myocardial vascular density and ameliorates diabetic cardiomyopathy via upregulation of sirtuin 3

Microvascular insufficiency contributes to cardiac hypertrophy and worsens heart dysfunction in diabetic cardiomyopathy. Our recent study shows that apelin may protect ischemic heart failure via upregulation of sirtuin 3 (Sirt3) and angiogenesis. This study investigated whether apelin promotes angiogenesis and ameliorates diabetic cardiomyopathy via activation of Sirt3. Wild-type (WT) and diabetic db/db mice were administrated with adenovirus-apelin to overexpressing apelin. In WT mice, overexpression of apelin increased Sirt3, VEGF/VEGFR2, and angiopoietin-1 (Ang-1)/Tie-2 expression in the heart. In vitro, treatment of endothelial cells (EC) with apelin increased VEGF and Ang-1 expression. In EC isolated from Sirt3KO mice, however, apelin treatment did not upregulate VEGF and Ang-1 expression. Moreover, apelin-induced angiogenesis was diminished in Sirt3KO mice. In db/db mice, the basal levels of apelin and Sirt3 expression were significantly reduced in the heart. This was accompanied by a significant reduction of capillary and arteriole densities in the heart. Overexpression of apelin increased Sirt3, VEGF/VEGFR2, and Ang-1/Tie-2 expression together with improved vascular density in db/db mice. Overexpression of apelin further improved cardiac function in db/db mice. Treatment with apelin significantly attenuated high glucose (HG)-induced reactive oxygen species (ROS) formation and EC apoptosis. The protection of apelin against HG-induced ROS formation and EC apoptosis was diminished in Sirt3KO-EC. We conclude that apelin gene therapy increases vascular density and alleviates diabetic cardiomyopathy by a mechanism involving activation of Sirt3 and upregulation of VEGF/VEGFR2 and Ang-1/Tie-2 expression.

Regulation of angiopoietin-1/Tie-2 receptor signaling in endothelial cells by dual-specificity phosphatases 1, 4, and 5

Background

Angiopoietin‐1 (Ang‐1) promotes survival and migration of endothelial cells, in part through the activation of mitogen‐activated protein kinase (MAPK) pathways downstream of Tie‐2 receptors. Dual‐specificity phosphatases (DUSPs) dephosphorylate phosphotyrosine and phosphoserine/phosphothreonine residues on target MAPKs. The mechanisms by which DUSPs modulate MAPK activation in Ang‐1/Tie‐2 receptor signaling are unknown in endothelial cells.

Methods and Results

Expression of various DUSPs in human umbilical vein endothelial cells exposed to Ang‐1 was measured. The functional roles of DUSPs in Ang‐1‐induced regulation of MAPK activation, endothelial cell survival, migration, differentiation, and permeability were measured using selective siRNA oligos. Ang‐1 differentially induces DUSP1, DUSP4, and DUSP5 in human umbilical vein endothelial cells through activation of the PI‐3 kinase, ERK1/2, p38, and SAPK/JNK pathways. Lack‐of‐function siRNA screening revealed that DUSP1 preferentially dephosphorylates p38 protein and is involved in Ang‐1‐induced cell migration and differentiation. DUSP4 preferentially dephosphorylates ERK1/2, p38, and SAPK/JNK proteins and, under conditions of serum deprivation, is involved in Ang‐1‐induced cell migration, several antiapoptotic effects, and differentiation. DUSP5 preferentially dephosphorylates ERK1/2 proteins and is involved in cell survival and inhibition of permeability.

Conclusions

DUSP1, DUSP4, and DUSP5 differentially modulate MAPK signaling pathways downstream of Tie‐2 receptors, thus highlighting the importance of these phosphatases to Ang‐1‐induced angiogenesis.

Oxidative stress in angiogenesis and vascular disease

Despite the damaging effect on tissues at a high concentration, it has been gradually established that oxidative stress plays a positive role during angiogenesis. In adults, physiological or pathological angiogenesis is initiated by tissue demands for oxygen and nutrients, resulting in a hypoxia/reoxygenation cycle, which, in turn promotes the formation of reactive oxygen species (ROS). The ROS can be generated either endogenously, through mitochondrial electron transport chain reactions and nicotinamide adenine dinucleotide phosphate oxidase, or exogenously, resulting from exposure to environmental agents, such as ultraviolet or ionizing radiation. In many conditions, ROS promotes angiogenesis, either directly or via the generation of active oxidation products, including peroxidized lipids. The latter lipid metabolites are generated in excess during atherosclerosis, thereby linking atherogenic processes and pathological angiogenesis. Although the main mechanism of oxidative stress-induced angiogenesis involves hypoxia-inducible factor/vascular endothelial growth factor (VEGF) signaling, recent studies have identified several pathways that are VEGF-independent. This review aims to provide a summary of the past and present views on the role of oxidative stress as a mediator and modulator of angiogenesis, and to highlight newly identified mechanisms.

Ethers and esters derived from apocynin avoid the interaction between p47phox and p22phox subunits of NADPH oxidase: evaluation in vitro and in silico

NOX (NADPH oxidase) plays an important role during several pathologies because it produces the superoxide anion (O₂^•−), which reacts with NO (nitric oxide), diminishing its vasodilator effect. Although different isoforms of NOX are expressed in ECs (endothelial cells) of blood vessels, the NOX2 isoform has been considered the principal therapeutic target for vascular diseases because it can be up-regulated by inhibiting the interaction between its p47phox (cytosolic protein) and p22phox (transmembrane protein) subunits. In this research, two ethers, 4-(4-acetyl-2-methoxy-phenoxy)-acetic acid (1) and 4-(4-acetyl-2-methoxy-phenoxy)-butyric acid (2) and two esters, pentanedioic acid mono-(4-acetyl-2-methoxy-phenyl) ester (3) and heptanedioic acid mono-(4-acetyl-2-methoxy-phenyl) ester (4), which are apocynin derivatives were designed, synthesized and evaluated as NOX inhibitors by quantifying O₂^•− production using EPR (electron paramagnetic resonance) measurements. In addition, the antioxidant activity of apocynin and its derivatives were determined. A docking study was used to identify the interactions between the NOX2′s p47phox subunit and apocynin or its derivatives. The results showed that all of the compounds exhibit inhibitory activity on NOX, being 4 the best derivative. However, neither apocynin nor its derivatives were free radical scavengers. On the other hand, the in silico studies demonstrated that the apocynin and its derivatives were recognized by the polybasic SH3A and SH3B domains, which are regions of p47phox that interact with p22phox. Therefore this experimental and theoretical study suggests that compound 4 could prevent the formation of the complex between p47phox and p22phox without needing to be activated by MPO (myeloperoxidase), this being an advantage over apocynin.

Monocyte chemotactic protein-induced protein (MCPIP) promotes inflammatory angiogenesis via sequential induction of oxidative stress, endoplasmic reticulum stress and autophagy

Major diseases such as cardiovascular diseases, rheumatoid arthritis, diabetes, obesity and tumor growth are known to involve inflammation. Inflammatory molecules such as MCP-1, TNF-α, IL-1β and IL-8 are known to promote angiogenesis. MCP-induced protein (MCPIP), originally discovered as a novel zinc finger protein induced by MCP-1, is also induced by other inflammatory agents. MCPIP was shown to mediate MCP-1-induced angiogenesis. Whether angiogenesis induced by other inflammatory agents is mediated via MCPIP is unknown and the molecular mechanisms involved in angiogenesis induced by MCPIP have not been elucidated. The aim of this study was to bridge this gap and delineate the sequential processes involved in angiogenesis mediated via MCPIP. siRNA knockdown of MCPIP was used to determine whether different inflammatory agents, MCP-1, TNF-α, IL-1β and IL-8, mediate angiogenesis via MCPIP in human umbilical vein endothelial cells (HUVECs). Chemical inhibitors and specific gene knockdown approach were used to inhibit each process postulated. Oxidative stress was inhibited by apocynin or cerium oxide nanoparticles or knockdown of NADPH oxidase subunit, phox47. Endoplasmic reticulum (ER) stress was blocked by tauroursodeoxycholate or knockdown of ER stress signaling protein IRE-1 and autophagy was inhibited by the use of 3'methyl adenine, or LY 294002 or by specific knockdown of beclin1. Matrigel assay was used as a tool to study angiogenic differentiation induced by inflammatory agents or MCPIP overexpression in HUVECs. Tube formation induced by inflammatory agents, TNF-α, IL-1β, IL-8 and MCP-1 was inhibited by knockdown of MCPIP. Forced MCPIP-expression induced oxidative stress, ER stress, autophagy and angiogenic differentiation in HUVECs. Inhibition of each step caused inhibition of each subsequent step postulated. The results reveal that angiogenesis induced by inflammatory agents is mediated via induction of MCPIP that causes oxidative and nitrosative stress resulting in ER stress leading to autophagy required for angiogenesis. The sequence of events suggested to be involved in inflammatory angiogenesis by MCPIP could serve as possible targets for therapeutic intervention of angiogenesis-related disorders.

Redox balance dynamically regulates vascular growth and remodeling

Vascular growth and remodeling responses entail several complex biochemical, molecular, and cellular responses centered primarily on endothelial cell activation and function. Recent studies reveal that changes in endothelial cell redox status critically influence numerous cellular events that are important for vascular growth under different conditions. It has been known for some time that oxidative stress actively participates in many aspects of angiogenesis and vascular remodeling. Initial studies in this field were largely exploratory with minimal insight into specific molecular mechanisms and how these responses could be regulated. However, it is now clear that intracellular redox mechanisms involving hypoxia, NADPH oxidases (NOX), xanthine oxidase (XO), nitric oxide and its synthases, and intracellular antioxidant defense pathways collectively orchestrate a redox balance system whereby reactive oxygen and nitrogen species integrate cues controlling vascular growth and remodeling. In this review, we discuss key redox regulation pathways that are centrally important for vascular growth in tissue health and disease. Important unresolved questions and issues are also addressed that requires future investigation.

Inhibition of protein tyrosine phosphatase improves angiogenesis via enhancing Ang-1/Tie-2 signaling in diabetes

Diabetes is associated with impairment of angiogenesis such as reduction of myocardial capillary formation. Our previous studies demonstrate that disruption of Angiopoietin-1 (Ang-1)/Tie-2 signaling pathway contributes to the diabetes-associated impairment of angiogenesis. Protein tyrosine phosphatase (PTP) has a critical role in the regulation of insulin signal by inhibition of tyrosine kinase phosphorylation. In present study, we examined the role of protein tyrosine phosphatase-1 (SHP-1) in diabetes-associated impairment of Ang-1/Tie-2 angiogenic signaling and angiogenesis. SHP-1 expression was significantly increased in diabetic db/db mouse hearts. Furthermore, SHP-1 bond to Tie-2 receptor and stimulation with Ang-1 led to SHP-1 dissociation from Tie-2 in mouse heart microvascular endothelial cell (MHMEC). Exposure of MHMEC to high glucose (HG, 30 mmol/L) increased SHP-1/Tie-2 association accompanied by a significant reduction of Tie-2 phosphorylation. Exposure of MHMEC to HG also blunted Ang-1-mediated SHP-1/Tie-2 dissociation. Knockdown of SHP-1 significantly attenuated HG-induced caspase-3 activation and apoptosis in MHMEC. Treatment with PTP inhibitors restored Ang-1-induced Akt/eNOS phosphorylation and angiogenesis. Our data implicate a critical role of SHP-1 in diabetes-associated vascular complications, and that upregulation of Ang-1/Tie-2 signaling by targeting SHP-1 should be considered as a new therapeutic strategy for the treatment of diabetes-associated impairment of angiogenesis.

20-HETE in neovascularization

Cytochrome P450 4A/F (CYP4A/F) converts arachidonic acid (AA) to 20-HETE by ω-hydroxylation. The contribution of 20-HETE to the regulation of myogenic response, blood pressure, and mitogenic actions has been well summarized. This review focuses on the emerging role of 20-HETE in physiological and pathological vascularization. 20-HETE has been shown to regulate vascular smooth muscle cells (VSMC) and endothelial cells (EC) by affecting their proliferation, migration, survival, and tube formation. Furthermore, the proliferation, migration, secretion of proangiogenic molecules (such as HIF-1α, VEGF, SDF-1α), and tube formation of endothelial progenitor cells (EPC) are stimulated by 20-HETE. These effects are mediated through c-Src- and EGFR-mediated downstream signaling pathways, including MAPK and PI3K/Akt pathways, eNOS uncoupling, and NOX/ROS system activation. Therefore, the CYP4A/F-20-HETE system may be a therapeutic target for the treatment of abnormal angiogenic diseases.

Overexpression of angiopoietin-2 impairs myocardial angiogenesis and exacerbates cardiac fibrosis in the diabetic db/db mouse model

The angiopoietins/Tie-2 system is essential for the maintenance of vascular integrity and angiogenesis. The functional role of angiopoietin-2 (Ang-2) in the regulation of angiogenesis is dependent on other growth factors such as VEGF and a given physiopathological conditions. This study investigates the potential role of Ang-2 in myocardial angiogenesis and fibrosis formation in the diabetic db/db mouse. Diabetic db/db mice received intramyocardial administration of either adenovirus Ang-2 (Ad-CMV-Ang-2) or Ad-β-gal. The levels of Tie-2, VEGF, caspase-3, Wnt7b, fibroblast-specific protein-1 (FSP-1), and adhesion molecules (ICAM-1 and VCAM-1) expression were measured. Apoptosis, capillary density, and cardiac fibrosis were also analyzed in the db/db mouse hearts. Overexpression of Ang-2 suppressed Tie-2 and VEGF expression in db/db mouse hearts together with significant upregulation of Wnt7b expression. Overexpression of Ang-2 also sensitizes ICAM-1 and VCAM-1 expression in db/db mouse hearts. Immunohistochemical analysis revealed that overexpression of Ang-2 resulted in a gradual apoptosis as well as interstitial fibrosis formation, these leading to a significant loss of capillary density. Data from these studies were confirmed in cultured mouse heart microvascular endothelial cells (MHMEC) exposed to excessive Ang-2. Exposure of MHMEC to Ang-2 resulted in increased caspase-3 activity and endothelial apoptosis. Knockdown of Ang-2 attenuated high glucose-induced endothelial cell apoptosis. Further, counterbalance of Ang-2 by overexpression of Ang-1 reversed loss of capillary density and fibrosis formation in db/db mouse hearts. Our data demonstrate that Ang-2 increases endothelial apoptosis, sensitizes myocardial microvascular inflammation, and promotes cardiac fibrosis and thus contributes to loss of capillary density in diabetic diseases.

Membrane depolarization is the trigger for PI3K/Akt activation and leads to the generation of ROS

Loss of fluid shear stress (ischemia) to the lung endothelium causes endothelial plasma membrane depolarization via ATP-sensitive K(+) (K(ATP)) channel closure, initiating a signaling cascade that leads to NADPH oxidase (NOX2) activation and ROS production. Since wortmannin treatment significantly reduces ROS production with ischemia, we investigated the role of phosphoinositide 3-kinase (PI3K) in shear-associated signaling. Pulmonary microvascular endothelial cells in perfused lungs subjected to abrupt stop of flow showed membrane depolarization and ROS generation. Stop of flow in flow-adapted mouse pulmonary microvascular endothelial cells in vitro resulted in the activation of PI3K and Akt as well as ROS generation. ROS generation in the lungs in situ was almost abolished by the PI3K inhibitor wortmannin and the PKC inhibitor H7. The combination of the two (wortmannin and H7) did not have a greater effect. Activation of NOX2 was greatly diminished by wortmannin, knockout of Akt1, or dominant negative PI3K, whereas membrane depolarization was unaffected. Ischemia-induced Akt activation (phosphorylation) was not observed with K(ATP) channel-null cells, which showed minimal changes in membrane potential with ischemia. Activation of Akt was similar to wild-type cells in NOX2-null cells, which do not generate ROS with ischemia. Cromakalim, a K(ATP) channel agonist, prevented both membrane depolarization and Akt phosphorylation with ischemia. Thus, Akt1 phosphorylation follows cell membrane depolarization and precedes the activation of NOX2. These results indicate that PI3K/Akt and PKC serve as mediators between endothelial cell membrane depolarization and NOX2 assembly.

Unforeseen decreases in dissolved oxygen levels affect tube formation kinetics in collagen gels

The availability of oxygen (O(2)) is a critical parameter affecting vascular tube formation. In this study, we hypothesize that dissolved oxygen (DO) levels in collagen gels change during the three-dimensional (3D) culture of human umbilical vein endothelial cells (HUVECs) in atmospheric conditions and that such changes affect the kinetics of tube formation through the production of reactive oxygen species (ROS). We demonstrate a decrease in O(2) tension during 3D cultures of HUVECs. Noninvasive measurements of DO levels during culture under atmospheric conditions revealed a profound decrease that reached as low as 2% O(2) at the end of 24 h. After media replacement, DO levels rose rapidly and equilibrated at ∼15% O(2), creating a reoxygenated environment. To accurately estimate DO gradients in 3D collagen gels, we developed a 3D mathematical model and determined the Michaelis-Menten parameters, V(max) and K(m), of HUVECs in collagen gels. We detected an increase in ROS levels throughout the culture period. Using diphenyliodonium to inhibit ROS production resulted in the complete inhibition of tube formation. Interference RNA studies further showed that hypoxia-inducible factors (HIFs)-1α and -2α are not involved in the formation of 3D tubes in collagen gels. We conclude that ROS affect the tubulogenesis process through HIFα-independent pathways, where the levels of ROS are influenced by the uncontrolled variations in DO levels. This study is the first demonstration of the critical and unexpected role of O(2) during 3D in vitro culture models of tubulogenesis in atmospheric conditions.

NADPH oxidase-mediated redox signaling: roles in cellular stress response, stress tolerance, and tissue repair

NADPH oxidase (Nox) has a dedicated function of generating reactive oxygen species (ROS). Accumulating evidence suggests that Nox has an important role in signal transduction in cellular stress responses. We have reviewed the current evidence showing that the Nox system can be activated by a collection of chemical, physical, and biological cellular stresses. In many circumstances, Nox activation fits to the cellular stress response paradigm, in that (1) the response can be initiated by various forms of cellular stresses; (2) Nox-derived ROS may activate mitogen-activated protein kinases (extracellular signal-regulated kinase, p38) and c-Jun NH(2)-terminal kinase, which are the core of the cell stress-response signaling network; and (3) Nox is involved in the development of stress cross-tolerance. Activation of the cell survival pathway by Nox may promote cell adaptation to stresses, whereas Nox may also convey signals toward apoptosis in irreversibly injured cells. At later stage after injury, Nox is involved in tissue repair by modulating cell proliferation, angiogenesis, and fibrosis. We suggest that Nox may have an integral role in cell stress responses and the subsequent tissue repair process. Understanding Nox-mediated redox signaling mechanisms may be of prominent significance at the crossroads of directing cellular responses to stress, aiming at either enhancing the stress resistance (in such situations as preventing ischemia-reperfusion injuries and accelerating wound healing) or sensitizing the stress-induced cytotoxicity for proliferative diseases such as cancer. Therefore, an optimal outcome of interventions on Nox will only be achieved when this is dealt with in a timely and disease-and stage-specific manner.

Receptor activation of NADPH oxidases

Reactive oxygen species (ROS) have been implicated in many intra- and intercellular processes. High levels of ROS are generated as part of the innate immunity in the respiratory burst of phagocytic cells. Low levels of ROS, however, are generated in a highly controlled manner by various cell types to act as second messengers in redox-sensitive pathways. A NADPH oxidase has been initially described as the respiratory burst enzyme in neutrophils. Stimulation of this complex enzyme system requires specific signaling cascades linking it to membrane-receptor activation. Subsequently, a family of NADPH oxidases has been identified in various nonphagocytic cells. They mainly differ in containing one out of seven homologous catalytic core proteins termed NOX1 to NOX5 and DUOX1 or 2. NADPH oxidase activity is controlled by regulatory subunits, including the NOX regulators p47phox and p67phox, their homologs NOXO1 and NOXA1, or the DUOX1 or 2 regulators DUOXA1 and 2. In addition, the GTPase Rac modulates activity of several of these enzymes. Recently, additional proteins have been identified that seem to have a regulatory function on NADPH oxidase activity under certain conditions. We will thus summarize molecular pathways linking activation of different membrane-bound receptors with increased ROS production of NADPH oxidases.

Identification of cardiovascular genes in omentum from morbidly obese patients with type 2 diabetes

BACKGROUND

The metabolic syndrome describes the association between obesity and co-morbidities including insulin resistance, hypertension, dyslipidemia, and cardiovascular (CV) disease. Adipokines produced from omentum contribute to the risk of CV disease and increase the inflammatory state. This study examines the gene expression differences in the omental tissue of morbidly obese diabetic and non-diabetic patients.

METHODS

Twenty morbidly obese patients undergoing bariatric surgery were included. Ten patients were diabetic and 10 were non-diabetic. Omental samples were collected intraoperatively and snap frozen. Total RNA was extracted using the Trizol reagent and purified with the RNeasy kit (Qiagen). Microarray experiments were performed using the Affymetrix Gene 1.0 ST array and data was analyzed with the Partek 6.3 program using an unpaired t-test (P<0.05). The gene expression profiles of the diabetic group were compared with the non-diabetic group. Using the Ingenuity program, the gene list generated from the microarray analysis was evaluated and real-time quantitative PCR (qPCR) was used to validate the array data.

RESULTS

Compared with the non-diabetic group, the diabetic obese patients showed 79 upregulated genes and 4 downregulated genes with >1.4-fold difference in expression. Ingenuity analysis showed numerous dysregulated genes associated with CV disease including leptin, Von Willebrand factor, P-selectin, angiopoietin-1 (ANGPT1), phospholipase A2 (group VII), and periostin osteoblast specific factor. Microarray results for the earlier mentioned genes were confirmed with qPCR. The results were analyzed with respect to the presence or absence of hyperlipidemia, hypertension, and coronary artery disease. In patients with hyperlipidemia, ANGPT1 and P-selectin were upregulated 1.9- and 2.9-fold, respectively.

CONCLUSIONS

This microarray analysis of omental tissue from morbidly obese diabetic patients documents a host of upregulated genes related to CV disease. This study provides further evidence that diabetic status predisposes obese patients to a higher risk of developing CV disease.

Cardiomyocyte PDGFR-beta signaling is an essential component of the mouse cardiac response to load-induced stress

PDGFR is an important target for novel anticancer therapeutics because it is overexpressed in a wide variety of malignancies. Recently, however, several anticancer drugs that inhibit PDGFR signaling have been associated with clinical heart failure. Understanding this effect of PDGFR inhibitors has been difficult because the role of PDGFR signaling in the heart remains largely unexplored. As described herein, we have found that PDGFR-beta expression and activation increase dramatically in the hearts of mice exposed to load-induced cardiac stress. In mice in which Pdgfrb was knocked out in the heart in development or in adulthood, exposure to load-induced stress resulted in cardiac dysfunction and heart failure. Mechanistically, we showed that cardiomyocyte PDGFR-beta signaling plays a vital role in stress-induced cardiac angiogenesis. Specifically, we demonstrated that cardiomyocyte PDGFR-beta was an essential upstream regulator of the stress-induced paracrine angiogenic capacity (the angiogenic potential) of cardiomyocytes. These results demonstrate that cardiomyocyte PDGFR-beta is a regulator of the compensatory cardiac response to pressure overload-induced stress. Furthermore, our findings may provide insights into the mechanism of cardiotoxicity due to anticancer PDGFR inhibitors.

Novel role of NADPH oxidase in angiogenesis and stem/progenitor cell function

Neovascularization is involved in normal development and wound repair as well as ischemic heart disease and peripheral artery disease. Both angiogenesis and vasculogenesis [de novo new vessel formation through mobilization of stem/progenitor cells from bone marrow (BM) and their homing to the ischemic sites] contribute to the formation of new blood vessels after tissue ischemia. Angiogenesis is dependent on cell proliferation, migration, and capillary tube formation in endothelial cells (ECs). Stem/progenitor cells have been used for cell-based therapy to promote revascularization after peripheral or myocardial ischemia. Excess amounts of reactive oxygen species (ROS) are involved in senescence and apoptosis of ECs and stem/progenitor cells, causing defective neovascularization. ROS at low levels function as signaling molecules to mediate cell proliferation, migration, differentiation, and gene expression. NADPH oxidase is one of the major sources of ROS in ECs and stem/progenitor cells, and is activated by various growth factors, cytokines, hypoxia, and ischemia. ROS derived from NADPH oxidase play an important role in redox signaling linked to angiogenesis ECs, as well as stem/progenitor cell mobilization, homing, and differentiation, thereby promoting neovascularization. Understanding these mechanisms may provide insight into NADPH oxidase and its mediators as potential therapeutic targets for ischemic heart and limb disease.

Redox-sensitive Akt and Src regulate coronary collateral growth in metabolic syndrome

We have recently shown that the inability of repetitive ischemia (RI) to activate p38 MAPK (p38) and Akt in metabolic syndrome [JCR:LA-cp (JCR)] rats was associated with impaired coronary collateral growth (CCG). Furthermore, Akt and p38 activation correlated with optimal O(2)(-). levels and were altered in JCR rats, and redox-sensitive p38 activation was required for CCG. Here, we determined whether the activation of Src, a possible upstream regulator, was altered in JCR rats and whether redox-dependent Src and Akt activation were required for CCG. CCG was assessed by myocardial blood flow (microspheres) and kinase activation was assessed by Western blot analysis in the normal zone and collateral-dependent zone (CZ). RI induced Src activation (approximately 3-fold) in healthy [Wistar-Kyoto (WKY)] animals but not in JCR animals. Akt inhibition decreased (approximately 50%), and Src inhibition blocked RI-induced CCG in WKY rats. Src inhibition decreased p38 and Akt activation. Myocardial oxidative stress (O(2)(-). and oxidized/reduced thiols) was measured quantitatively (X-band electron paramagnetic resonance). An antioxidant, apocynin, reduced RI-induced oxidative stress in JCR rats to levels induced by RI in WKY rats versus the reduction in WKY rats to very low levels. This resulted in a significant restoration of p38 (approximately 80%), Akt (approximately 65%), and Src (approximately 90%) activation in JCR rats but decreased the activation in WKY rats (p38: approximately 45%, Akt: approximately 65%, and Src: approximately 100%), correlating with reduced CZ flow in WKY rats (approximately 70%), but significantly restored CZ flow in JCR rats (approximately 75%). We conclude that 1) Akt and Src are required for CCG, 2) Src is a redox-sensitive upstream regulator of RI-induced p38 and Akt activation, and 3) optimal oxidative stress levels are required for RI-induced p38, Akt, and Src activation and CCG.

NADPH oxidase-dependent signaling in endothelial cells: role in physiology and pathophysiology

Reactive oxygen species (ROS) including superoxide (O(2)(.-)) and hydrogen peroxide (H(2)O(2)) are produced endogenously in response to cytokines, growth factors; G-protein coupled receptors, and shear stress in endothelial cells (ECs). ROS function as signaling molecules to mediate various biological responses such as gene expression, cell proliferation, migration, angiogenesis, apoptosis, and senescence in ECs. Signal transduction activated by ROS, "oxidant signaling," has received intense investigation. Excess amount of ROS contribute to various pathophysiologies, including endothelial dysfunction, atherosclerosis, hypertension, diabetes, and acute respiratory distress syndrome (ARDS). The major source of ROS in EC is a NADPH oxidase. The prototype phagaocytic NADPH oxidase is composed of membrane-bound gp91phox and p22hox, as well as cytosolic subunits such as p47(phox), p67(phox) and small GTPase Rac. In ECs, in addition to all the components of phagocytic NADPH oxidases, homologues of gp91(phox) (Nox2) including Nox1, Nox4, and Nox5 are expressed. The aim of this review is to provide an overview of the emerging area of ROS derived from NADPH oxidase and oxidant signaling in ECs linked to physiological and pathophysiological functions. Understanding these mechanisms may provide insight into the NADPH oxidase and oxidant signaling components as potential therapeutic targets.

NADPH oxidase isoform selective regulation of endothelial cell proliferation and survival

Proliferation and apoptosis of endothelial cells are crucial angiogenic processes that contribute to carcinogenesis and tumor progression. Emerging evidence implicates the regulation of proliferation and apoptosis by reactive oxygen species (ROS) such as superoxide and hydrogen peroxide (H(2)O(2)). In the present study, we investigated the roles of the ROS-generating Nox4- and Nox2-containing reduced nicotinamide adenine dinucleotide phosphate (NADPH) oxidases in proliferation of human endothelial cells by examining the impact of these enzyme systems on (1) specific proliferative and tumorigenic kinases, extracellular regulated kinase1/2 (ERK1/2) and Akt, (2) cytoskeletal organization, and (3) the mechanisms that influence cellular apoptosis. ROS production and the expression of NADPH oxidase subunit Nox4, but not Nox2, were markedly higher in proliferating than in quiescent endothelial cells. Addition of the H(2)O(2) scavenger catalase or downregulation of Nox4 protein with specific siRNA reduced ROS levels, cell proliferation, and ERK1/2 phosphorylation but had no effect on either cell morphology or caspase 3/7 activity. Although downregulation of Nox2 protein with siRNA also reduced ROS production and cell proliferation, it caused an increase in caspase 3/7 activity, reduced Akt phosphorylation, and caused cytoskeletal disorganization. Therefore, in endothelial cells, Nox4-derived H(2)O(2) activates ERK1/2 to promote proliferation, whereas Nox2-containing NADPH oxidase maintains the cytoskeleton and prevents apoptosis to support cell survival. Our study provides a new understanding of the molecular mechanisms that underpin endothelial cell survival and a rationale for the combined suppression of Nox4- and Nox2-containing NADPH oxidases for unwanted angiogenesis in cancer.

Oxidative-dependent integration of signal transduction with intercellular gap junctional communication in the control of gene expression

Research on oxidative stress focused primarily on determining how reactive oxygen species (ROS) damage cells by indiscriminate reactions with their macromolecular machinery, particularly lipids, proteins, and DNA. However, many chronic diseases are not always a consequence of tissue necrosis, DNA, or protein damage, but rather to altered gene expression. Gene expression is highly regulated by the coordination of cell signaling systems that maintain tissue homeostasis. Therefore, much research has shifted to the understanding of how ROS reversibly control gene expression through cell signaling mechanisms. However, most research has focused on redox regulation of signal transduction within a cell, but we introduce a more comprehensive-systems biology approach to understanding oxidative signaling that includes gap junctional intercellular communication, which plays a role in coordinating gene expression between cells of a tissue needed to maintain tissue homeostasis. We propose a hypothesis that gap junctions are critical in modulating the levels of second messengers, such as low molecular weight reactive oxygen, needed in the transduction of an external signal to the nucleus in the expression of genes. Thus, any comprehensive-systems biology approach to understanding oxidative signaling must also include gap junctions, in which aberrant gap junctions have been clearly implicated in many human diseases.

Tyrosine phosphatase beta regulates angiopoietin-Tie2 signaling in human endothelial cells

OBJECTIVES

The endothelial cell (EC)-selective receptor tyrosine kinase, Tie2, and its ligands angiopoietin Ang-1 and Ang-2, are essential for blood vessel maintenance and repair. Ang-1 is an agonist of Tie2 receptor activation, whereas Ang-2 is a context-dependent antagonist/agonist. Therefore, we investigated the role of the EC-selective phosphatase, human protein tyrosine phosphatase beta (HPTPbeta), in regulating Tie2 activity.

METHODS AND RESULTS

siRNA silencing of HPTPbeta enhanced Ang-1 and Ang-2-induced Tie2 phosphorylation at 10 min (2.5-fold, P < 0.001; and 1.8-fold, P < 0.05, respectively). The cell survival response to Ang-1, but not Ang-2, was enhanced by HPTPbeta silencing as measured by flow cytometry (0.85-fold to 0.66-fold, P < 0.05) and ELISA (0.88-fold to 0.53-fold, P < 0.01). Hypoxia, which upregulated HPTPbeta expression in endothelial cells, impaired Ang-1-induced Tie2 phosphorylation.

CONCLUSIONS

These results reveal a novel role for HPTPbeta in modulating Ang-1-Tie2 signaling and endothelial cell survival.

Critical role of the NADPH oxidase subunit p47phox on vascular TLR expression and neointimal lesion formation in high-fat diet-induced obesity

Reactive oxygen species (ROS) formation is associated with inflammation and vasculature dysfunction. We investigated the potential role of the NADPH oxidase on vascular Toll-like receptor (TLR) expression and carotid neointimal formation in high-fat (HF) diet-induced obesity (DIO) model. Using mice DIO and common carotid artery flow cessation-induced lesion formation models, we examined vascular TLR2 and TLR4 expression and neointimal formation in NADPH oxidase subunit p47(phox)-deficient (p47(phox-/-)) mice. Feeding C57BL/6J mice an HF diet for 22 weeks resulted in significant increases in p47(phox), TLR2 and TLR4 expression in vascular tissues compared with mice fed a low-fat (LF) diet. Minimal changes in TLR2 and TLR4 expression was detected in p47(phox-/-) DIO mice. Furthermore, flow cessation-induced angiogenic and inflammatory response and neointimal formation were significantly attenuated in p47(phox-/-) DIO mice compared with wild-type DIO mice. In addition, exposure of endothelial cells to leptin led to ROS formation; this was accompanied by upregulation of TLR2, TLR4 expression and its downstream signaling. Leptin also increased endothelial cell migration and proliferation. Pharmacological inhibition of NADPH oxidase or genetic deletion of p47(phox) significantly diminished these alterations. Obesity increases neointimal formation via a mechanism involving p47(phox)-TLRs signaling, suggesting that the NADPH oxidase may represent a potential novel therapeutic target for the treatment of obesity-associated vascular inflammation and dysfunction.