Glucocorticoid receptor sensitivity in early pregnancy in an African American cohort.

PROBLEM: Disruption in homeostatic feedback loops between inflammatory mediators and the hypothalamic-pituitary-adrenal (HPA) axis is a key mechanism linking chronic stress to inflammation and adverse health outcomes, including those occurring during pregnancy. In particular, alterations in glucocorticoid sensitivity may occur as a result of chronic stress, including that due to racial discrimination, and may be implicated in the persistent adverse maternal and infant health outcomes experienced by African Americans. While there are a few large-scale studies in human pregnancy that measure both cytokines and HPA axis hormones, to our knowledge, none directly measure glucocorticoid sensitivity at the cellular level, especially in an African American population. METHOD OF STUDY: We measured the full range of the dexamethasone (DEX) dose-response suppression of TNF-α in first-trimester blood samples from 408 African American women and estimated leukocyte cell type contribution to the production of TNF-α. RESULTS: The mean (SD) DEX level needed to inhibit TNF-α production by 50% (ie, DEX IC50 ) was 9.8 (5.8) nmol/L. Monocytes appeared to be the main driver of Uninhibited TNF-α production, but monocyte counts explained only 14% of the variation. Monocyte counts were only weakly correlated with the DEX IC50 (r = -.11, P < .05). Moreover, there was no statistically significant correlation between the DEX IC50 and circulating pro-inflammatory (CRP, IL-6, IFN-γ) or anti-inflammatory (IL-10) mediators (P > .05). CONCLUSION: These findings challenge some prior assumptions and position this comprehensive study of glucocorticoid sensitivity as an important anchor point in the growing recognition of interindividual variation in maternal HPA axis regulation and inflammatory responses.

SQSTM1/p62 and PPARGC1A/PGC-1alpha at the interface of autophagy and vascular senescence.

Defective macroautophagy/autophagy and mitochondrial dysfunction are known to stimulate senescence. The mitochondrial regulator PPARGC1A (peroxisome proliferator activated receptor gamma, coactivator 1 alpha) regulates mitochondrial biogenesis, reducing senescence of vascular smooth muscle cells (VSMCs); however, it is unknown whether autophagy mediates PPARGC1A-protective effects on senescence. Using ppargc1a-/- VSMCs, we identified the autophagy receptor SQSTM1/p62 (sequestosome 1) as a major regulator of autophagy and senescence of VSMCs. Abnormal autophagosomes were observed in VSMCs in aortas of ppargc1a-/- mice. ppargc1a-/- VSMCs in culture presented reductions in LC3-II levels; in autophagosome number; and in the expression of SQSTM1 (protein and mRNA), LAMP2 (lysosomal-associated membrane protein 2), CTSD (cathepsin D), and TFRC (transferrin receptor). Reduced SQSTM1 protein expression was also observed in aortas of ppargc1a-/- mice and was upregulated by PPARGC1A overexpression, suggesting that SQSTM1 is a direct target of PPARGC1A. Inhibition of autophagy by 3-MA (3 methyladenine), spautin-1 or Atg5 (autophagy related 5) siRNA stimulated senescence. Rapamycin rescued the effect of Atg5 siRNA in Ppargc1a+/+ , but not in ppargc1a-/- VSMCs, suggesting that other targets of MTOR (mechanistic target of rapamycin kinase), in addition to autophagy, also contribute to senescence. Sqstm1 siRNA increased senescence basally and in response to AGT II (angiotensin II) and zinc overload, two known inducers of senescence. Furthermore, Sqstm1 gene deficiency mimicked the phenotype of Ppargc1a depletion by presenting reduced autophagy and increased senescence in vitro and in vivo. Thus, PPARGC1A upregulates autophagy reducing senescence by a SQSTM1-dependent mechanism. We propose SQSTM1 as a novel target in therapeutic interventions reducing senescence. ABBREVIATIONS: 3-MA: 3 methyladenine; ACTA2/SM-actin: actin, alpha 2, smooth muscle, aorta; ACTB/ß-actin: actin beta; AGT II: angiotensin II; ATG5: autophagy related 5; BECN1: beclin 1; CAT: catalase; CDKN1A: cyclin-dependent kinase inhibitor 1A (P21); Chl: chloroquine; CTSD: cathepsin D; CYCS: cytochrome C, somatic; DHE: dihydroethidium; DPBS: Dulbecco's phosphate-buffered saline; EL: elastic lamina; EM: extracellular matrix; FDG: fluorescein-di-ß-D-galactopyranoside; GAPDH: glyceraldehyde-3-phosphate dehydrogenase; γH2AFX: phosphorylated H2A histone family, member X, H2DCFDA: 2',7'-dichlorodihydrofluorescein diacetate; LAMP2: lysosomal-associated membrane protein 2; MASMs: mouse vascular smooth muscle cells; MEF: mouse embryonic fibroblast; NBR1: NBR1, autophagy cargo receptor; NFKB/NF-κB: nuclear factor of kappa light polypeptide gene enhancer in B cells; MTOR: mechanistic target of rapamycin kinase; NFE2L2: nuclear factor, erythroid derived 2, like 2; NOX1: NADPH oxidase 1; OPTN: optineurin; PFA: paraformaldehyde; PFU: plaque-forming units; PPARGC1A/PGC-1α: peroxisome proliferator activated receptor, gamma, coactivator 1 alpha; Ptdln3K: phosphatidylinositol 3-kinase; RASMs: rat vascular smooth muscle cells; ROS: reactive oxygen species; SA-GLB1/ß-gal: senescence-associated galactosidase, beta 1; SASP: senescence-associated secretory phenotype; SIRT1: sirtuin 1; Spautin 1: specific and potent autophagy inhibitor 1; SQSTM1/p62: sequestosome 1; SOD: superoxide dismutase; TEM: transmission electron microscopy; TFEB: transcription factor EB; TFRC: transferrin receptor; TRP53/p53: transformation related protein 53; TUBG1: tubulin gamma 1; VSMCs: vascular smooth muscle cells; WT: wild type.

PGC-1α Modulates Telomere Function and DNA Damage in Protecting against Aging-Related Chronic Diseases.

Cellular senescence and organismal aging predispose age-related chronic diseases, such as neurodegenerative, metabolic, and cardiovascular disorders. These diseases emerge coincidently from elevated oxidative/electrophilic stress, inflammation, mitochondrial dysfunction, DNA damage, and telomere dysfunction and shortening. Mechanistic linkages are incompletely understood. Here, we show that ablation of peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α) accelerates vascular aging and atherosclerosis, coinciding with telomere dysfunction and shortening and DNA damage. PGC-1α deletion reduces expression and activity of telomerase reverse transcriptase (TERT) and increases p53 levels. Ectopic expression of PGC-1α coactivates TERT transcription and reverses telomere malfunction and DNA damage. Furthermore, alpha lipoic acid (ALA), a non-dispensable mitochondrial cofactor, upregulates PGC-1α-dependent TERT and the cytoprotective Nrf-2-mediated antioxidant/electrophile-responsive element (ARE/ERE) signaling cascades, and counteracts high-fat-diet-induced, age-dependent arteriopathy. These results illustrate the pivotal importance of PGC-1α in ameliorating senescence, aging, and associated chronic diseases, and may inform novel therapeutic approaches involving electrophilic specificity.

Metformin beyond diabetes: pleiotropic benefits of metformin in attenuation of atherosclerosis.

BACKGROUND: Clinical studies show that metformin attenuates all­cause mortality and myocardial infarction compared with other medications for type 2 diabetes, even at similar glycemic levels. However, there is paucity of data in the euglycemic state on the vasculoprotective effects of metformin. The objectives of this study are to evaluate the effects of metformin on ameliorating atherosclerosis. METHODS AND RESULTS: Using ApoE−/− C57BL/6J mice, we found that metformin attenuates atherosclerosis and vascular senescence in mice fed a high­fat diet and prevents the upregulation of angiotensin II type 1 receptor by a high­fat diet in the aortas of mice. Thus, considering the known deleterious effects of angiotensin II mediated by angiotensin II type 1 receptor, the vascular benefits of metformin may be mediated, at least in part, by angiotensin II type 1 receptor downregulation. Moreover, we found that metformin can cause weight loss without hypoglycemia. We also found that metformin increases the antioxidant superoxide dismutase­1. CONCLUSION: Pleiotropic effects of metformin ameliorate atherosclerosis and vascular senescence.

Peroxisome proliferator-activated receptor γ coactivator-1α is a central negative regulator of vascular senescence.

OBJECTIVE: Cellular senescence influences organismal aging and increases predisposition to age-related diseases, in particular cardiovascular disease, a leading cause of death and disability worldwide. Peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α) is a master regulator of mitochondrial biogenesis and function, oxidative stress, and insulin resistance. Senescence is associated with telomere and mitochondrial dysfunction and oxidative stress, implying a potential causal role of PGC-1α in senescence pathogenesis. APPROACH AND RESULTS: We generated a PGC-1α(+/-)/apolipoprotein E(-/-) mouse model and showed that PGC-1α deficiency promotes a vascular senescence phenotype that is associated with increased oxidative stress, mitochondrial abnormalities, and reduced telomerase activity. PGC-1α disruption results in reduced expression of the longevity-related deacetylase sirtuin 1 (SIRT1) and the antioxidant catalase, and increased expression of the senescence marker p53 in aortas. Further, angiotensin II, a major hormonal inducer of vascular senescence, induces prolonged lysine acetylation of PGC-1α and releases the PGC-1α-FoxO1 complex from the SIRT1 promoter, thus reducing SIRT1 expression. The phosphorylation-defective mutant PGC-1α S570A is not acetylated, is constitutively active for forkhead box O1-dependent SIRT1 transcription, and prevents angiotensin II-induced senescence. Acetylation of PGC-1α by angiotensin II interrupts the PGC-1α-forkhead box O1-SIRT1 feed-forward signaling circuit leading to SIRT1 and catalase downregulation and vascular senescence. CONCLUSIONS: PGC-1α is a primary negative regulator of vascular senescence. Moreover, the central role of posttranslational modification of PGC-1α in regulating angiotensin II-induced vascular senescence may inform development of novel therapeutic strategies for mitigating age-associated diseases, such as atherosclerosis.

Angiotensin II requires zinc and downregulation of the zinc transporters ZnT3 and ZnT10 to induce senescence of vascular smooth muscle cells.

Senescence, a hallmark of mammalian aging, is associated with the onset and progression of cardiovascular disease. Angiotensin II (Ang II) signaling and zinc homeostasis dysfunction are increased with age and are linked to cardiovascular disease, but the relationship among these processes has not been investigated. We used a model of cellular senescence induced by Ang II in vascular smooth muscle cells (VSMCs) to explore the role of zinc in vascular dysfunction. We found that Ang II-induced senescence is a zinc-dependent pathway mediated by the downregulation of the zinc transporters ZnT3 and ZnT10, which work to reduce cytosolic zinc. Zinc mimics Ang II by increasing reactive oxygen species (ROS), activating NADPH oxidase activity and Akt, and by downregulating ZnT3 and ZnT10 and inducing senescence. Zinc increases Ang II-induced senescence, while the zinc chelator TPEN, as well as overexpression of ZnT3 or ZnT10, decreases ROS and prevents senescence. Using HEK293 cells, we found that ZnT10 localizes in recycling endosomes and transports zinc into vesicles to prevent zinc toxicity. Zinc and ZnT3/ZnT10 downregulation induces senescence by decreasing the expression of catalase. Consistently, ZnT3 and ZnT10 downregulation by siRNA increases ROS while downregulation of catalase by siRNA induces senescence. Zinc, siZnT3 and siZnT10 downregulate catalase by a post-transcriptional mechanism mediated by decreased phosphorylation of ERK1/2. These data demonstrate that zinc homeostasis dysfunction by decreased expression of ZnT3 or ZnT10 promotes senescence and that Ang II-induced senescence is a zinc and ROS-dependent process. Our studies suggest that zinc might also affect other ROS-dependent processes induced by Ang II, such as hypertrophy and migration of smooth muscle cells.

FoxO1 mediates an autofeedback loop regulating SIRT1 expression.

Forkhead transcription factor FoxO1 and the NAD(+)-dependent histone deacetylase SIRT1 are evolutionarily conserved regulators of the development of aging, oxidative stress resistance, insulin resistance, and metabolism in species ranging from invertebrates to mammals. SIRT1 deacetylates FoxO1 and enables activation of FoxO1 transcription in multiple systems. The functional consequences of the interactions between FoxO1 and SIRT1 remain incompletely understood. Here, we demonstrate that the 1.5-kb rat sirt1 promoter region contains a cluster of five putative FoxO1 core binding repeat motifs (5×IRS-1) and a forkhead-like consensus binding site (FKHD-L). Luciferase promoter assays demonstrate that FoxO1 directly activates SIRT1 promoter activity and that both the IRS-1 and FKHD-L enable FoxO1-dependent SIRT1 transcription. Electrophoretic mobility shift and chromatin immunoprecipitation assays show that FoxO1 binds to the IRS-1 and FKHD-L sites of the SIRT1 promoter. Consistently, FoxO1 overexpression increases SIRT1 expression, and FoxO1 depletion by siRNA reduces SIRT1 expression at both the messenger RNA and protein levels in vascular smooth muscle cells and HEK293 cells. Thus, endogenous FoxO1 is a positive transcriptional regulator of SIRT1. Conversely, SIRT1 promotes FoxO1-driven SIRT1 autotranscription through interacting with and deacetylating FoxO1. Moreover, resveratrol, a plant polyphenol activator of SIRT1, increases FoxO1-dependent SIRT1 transcription activity and thus induces its expression. These findings suggest that positive feedback mechanisms regulate FoxO1-dependent SIRT1 transcription and indicate a previously unappreciated function for FoxO1. This signaling network may coordinate multiple pathways acting upon immune, inflammatory, regenerative, and metabolic processes.

Early endosomal antigen 1 (EEA1) is an obligate scaffold for angiotensin II-induced, PKC-alpha-dependent Akt activation in endosomes.

Akt/protein kinase B (PKB) activation/phosphorylation by angiotensin II (Ang II) is a critical signaling event in hypertrophy of vascular smooth muscle cells (VSMCs). Conventional wisdom asserts that Akt activation occurs mainly in plasma membrane domains. Recent evidence that Akt activation may take place within intracellular compartments challenges this dogma. The spatial identity and mechanistic features of these putative signaling domains have not been defined. Using cell fractionation and fluorescence methods, we demonstrate that the early endosomal antigen-1 (EEA1)-positive endosomes are a major site of Ang II-induced Akt activation. Akt moves to and is activated in EEA1 endosomes. The expression of EEA1 is required for phosphorylation of Akt at both Thr-308 and Ser-473 as well as for phosphorylation of its downstream targets mTOR and S6 kinase, but not for Erk1/2 activation. Both Akt and phosphorylated Akt (p-Akt) interact with EEA1. We also found that PKC-α is required for organizing Ang II-induced, EEA1-dependent Akt phosphorylation in VSMC early endosomes. EEA1 expression enables PKC-α phosphorylation, which in turn regulates Akt upstream signaling kinases, PDK1 and p38 MAPK. Our results indicate that PKC-α is a necessary regulator of EEA1-dependent Akt signaling in early endosomes. Finally, EEA1 down-regulation or expression of a dominant negative mutant of PKC-α blunts Ang II-induced leucine incorporation in VSMCs. Thus, EEA1 serves a novel function as an obligate scaffold for Ang II-induced Akt activation in early endosomes.

PGC-1 alpha serine 570 phosphorylation and GCN5-mediated acetylation by angiotensin II drive catalase down-regulation and vascular hypertrophy.

Angiotensin II (Ang II) is a pleuripotential hormone that is important in the pathophysiology of multiple conditions including aging, cardiovascular and renal diseases, and insulin resistance. Reactive oxygen species (ROS) are important mediators of Ang II-induced signaling generally and have a well defined role in vascular hypertrophy, which is inhibited by overexpression of catalase, inferring a specific role of H(2)O(2). The molecular mechanisms are understood incompletely. The transcriptional coactivator peroxisome proliferator-activated receptor gamma coactivator-1 alpha (PGC-1 alpha) is a key regulator of energy metabolism and ROS-scavenging enzymes including catalase. We show that Ang II stimulates Akt-dependent PGC-1 alpha serine 570 phosphorylation, which is required for the binding of the histone acetyltransferase GCN5 (general control nonderepressible 5) to PGC-1 alpha and for its lysine acetylation. These sequential post-translational modifications suppress PGC-1 alpha activity and prevent its binding to the catalase promoter through the forkhead box O1 transcription factor, thus decreasing catalase expression. We demonstrate that overexpression of the phosphorylation-defective mutant PGC-1 alpha (S570A) prevents Ang II-induced increases in H(2)O(2) levels and hypertrophy ([(3)H]leucine incorporation). Knockdown of PGC-1 alpha by small interfering RNA promotes basal and Ang II-stimulated ROS and hypertrophy, which is reversed by polyethylene glycol-conjugated catalase. Thus, endogenous PGC-1 alpha is a negative regulator of vascular hypertrophy by up-regulating catalase expression and thus reducing ROS levels. We provide novel mechanistic insights by which Ang II may mediate its ROS-dependent pathophysiologic effects on multiple cardiometabolic diseases.

Role of protein tyrosine phosphatase 1B in vascular endothelial growth factor signaling and cell-cell adhesions in endothelial cells.

Vascular endothelial growth factor (VEGF) binding induces phosphorylation of VEGF receptor (VEGFR)2 in tyrosine, which is followed by disruption of VE-cadherin-mediated cell-cell contacts of endothelial cells (ECs), thereby stimulating EC proliferation and migration to promote angiogenesis. Tyrosine phosphorylation events are controlled by the balance of activation of protein tyrosine kinases and protein tyrosine phosphatases (PTPs). Little is known about the role of endogenous PTPs in VEGF signaling in ECs. In this study, we found that PTP1B expression and activity are markedly increased in mice hindlimb ischemia model of angiogenesis. In ECs, overexpression of PTP1B, but not catalytically inactive mutant PTP1B-C/S, inhibits VEGF-induced phosphorylation of VEGFR2 and extracellular signal-regulated kinase 1/2, as well as EC proliferation, whereas knockdown of PTP1B by small interfering RNA enhances these responses, suggesting that PTP1B negatively regulates VEGFR2 signaling in ECs. VEGF-induced p38 mitogen-activated protein kinase phosphorylation and EC migration are not affected by PTP1B overexpression or knockdown. In vivo dephosphorylation and cotransfection assays reveal that PTP1B binds to VEGFR2 cytoplasmic domain in vivo and directly dephosphorylates activated VEGFR2 immunoprecipitates from human umbilical vein endothelial cells. Overexpression of PTP1B stabilizes VE-cadherin-mediated cell-cell adhesions by reducing VE-cadherin tyrosine phosphorylation, whereas PTP1B small interfering RNA causes opposite effects with increasing endothelial permeability, as measured by transendothelial electric resistance. In summary, PTP1B negatively regulates VEGFR2 receptor activation via binding to the VEGFR2, as well as stabilizes cell-cell adhesions through reducing tyrosine phosphorylation of VE-cadherin. Induction of PTP1B by hindlimb ischemia may represent an important counterregulatory mechanism that blunts overactivation of VEGFR2 during angiogenesis in vivo.

IQGAP1 mediates VE-cadherin-based cell-cell contacts and VEGF signaling at adherence junctions linked to angiogenesis.

OBJECTIVE: Vascular endothelial growth factor (VEGF) induces angiogenesis by stimulating reactive oxygen species (ROS) production primarily through the VEGF receptor-2 (VEGFR2). One of the initial responses in established vessels to stimulate angiogenesis is loss of vascular endothelial (VE)-cadherin-based cell-cell adhesions; however, little is known about the underlying mechanisms. IQGAP1 is a novel VEGFR2 binding protein, and it interacts directly with actin, cadherin, and beta-catenin, thereby regulating cell motility and morphogenesis. METHODS AND RESULTS: Confocal microscopy analysis shows that IQGAP1 colocalizes with VE-cadherin at cell-cell contacts in unstimulated human endothelial cells (ECs). VEGF stimulation reduces staining of IQGAP1 and VE-cadherin at the adherens junction without affecting interaction of these proteins. Knockdown of IQGAP1 using siRNA inhibits localization of VE-cadherin at cell-cell contacts, VEGF-stimulated recruitment of VEGFR2 to the VE-cadherin/beta-catenin complex, ROS-dependent tyrosine phosphorylation of VE-cadherin, which is required for loss of cell-cell contacts and capillary tube formation. IQGAP1 expression is increased in a mouse hindlimb ischemia model of angiogenesis. CONCLUSIONS: IQGAP1 is required for establishment of cell-cell contacts in quiescent ECs. To induce angiogenesis, it may function to link VEGFR2 to the VE-cadherin containing adherens junctions, thereby promoting VEGF-stimulated, ROS-dependent tyrosine phosphorylation of VE-cadherin and loss of cell-cell contacts.

IQGAP1 regulates reactive oxygen species-dependent endothelial cell migration through interacting with Nox2.

OBJECTIVE: Endothelial cell (EC) migration is a key event for repair process after vascular injury and angiogenesis. EC migration is regulated by reorganization of the actin cytoskeleton at the leading edge and localized production of reactive oxygen species (ROS) at the site of injury. However, underlying mechanisms are unclear. We reported that IQGAP1, an actin binding scaffold protein, mediates VEGF-induced activation of gp91phox (Nox2)-dependent NAD(P)H oxidase and EC migration. We thus hypothesized that Nox2 and IQGAP1 may play important roles in ROS-dependent EC migration in response to injury. METHODS AND RESULTS: Using a monolayer scratch assay with confluent ECs, we show that ROS production is increased at the margin of scratch area and Nox2 translocates to the leading edge, where it colocalizes and associates with both actin and IQGAP1 in migrating ECs. Knockdown of IQGAP1 using siRNA and inhibition of the actin cytoskeleton blocked scratch injury-induced H2O2 production, Nox2 translocation and its interaction with actin, and EC migration toward the injured site. CONCLUSIONS: These suggest that IQGAP1 may function to link Nox2 to actin at the leading edge, thereby facilitating ROS production at the site of injury, which may contribute to EC migration.

cAbl tyrosine kinase mediates reactive oxygen species- and caveolin-dependent AT1 receptor signaling in vascular smooth muscle: role in vascular hypertrophy.

Important output signals of the angiotensin subtype 1 receptor (AT1R) in vascular smooth muscle cells (VSMCs) are mediated by angiotensin II (Ang II)-stimulated transactivation of the epidermal growth factor receptor (EGF-R), which is critical for vascular hypertrophy. Ang II-induced EGF-R transactivation is mediated through cSrc, a proximal target of reactive oxygen species (ROS) derived from NAD(P)H oxidase (NOX) and is dependent on AT(1)R trafficking through caveolin1 (Cav1)-enriched lipid rafts. Underlying molecular mechanisms are incompletely understood. The nonreceptor tyrosine kinase, proto-oncogene cAbl is a substrate of Src and is a major mediator for ROS-dependent tyrosine phosphorylation of Cav1. We thus hypothesized that cAbl is important for ROS-, cSrc-, and Cav1-dependent growth-related AT1R signal transduction. Here we show that Ang II induces tyrosine phosphorylation of cAbl in rat VSMCs and mouse aorta, and that Ang II promotes association of cAbl with AT(1)R, both of which are Src-dependent. Pretreatment of rat VSMCs with the NOX inhibitor diphenylene iodonium or the antioxidants N-acetylcysteine or ebselen significantly inhibited Ang II-induced cAbl phosphorylation. Cell fractionation shows that both EGF-Rs and cAbl are found basally in Cav1-enriched membrane fractions. Knockdown of cAbl protein using small interference RNA inhibits Ang II-stimulated: (1) trafficking of AT1R into, and EGF-R out of, Cav1-enriched lipid rafts; (2) EGF-R transactivation; (3) appearance of the transactivated EGF-R and phospho-Cav1 at focal adhesions; and (4) vascular hypertrophy. These studies provide a novel role of cAbl in the spatial and temporal organization of growth-related AT1R signaling in VSMCs and suggest that cAbl may be generally important in signaling of G-protein coupled receptors.

Caveolin-1 is essential for activation of Rac1 and NAD(P)H oxidase after angiotensin II type 1 receptor stimulation in vascular smooth muscle cells: role in redox signaling and vascular hypertrophy.

OBJECTIVE: Angiotensin II (Ang II) is a potent mediator of vascular hypertrophy in vascular smooth muscle cells (VSMCs). These effects are mediated through the Ang II type 1 receptor (AT1R) and require its trafficking through caveolin-1 (Cav1)-enriched lipid rafts and reactive oxygen species (ROS) derived from Rac1-dependent NAD(P)H oxidase. The specific role(s) of Cav1 in AT1R signaling is incompletely understood. METHODS AND RESULTS: Knockdown of Cav1 protein by small interfering RNA (siRNA) inhibits Ang II-stimulated Rac1 activation and membrane translocation, H2O2 production, ROS-dependent epidermal growth factor receptor (EGF-R) transactivation, and subsequent phosphorylation of Akt without affecting ROS-independent extracellular signal-regulated kinase 1/2 phosphorylation. Ang II stimulates tyrosine phosphorylation of Sos-1, a Rac-guanine nucleotide exchange factor, which is inhibited by Cav1 siRNA, demonstrating involvement of Cav1 in Rac1 activation. Detergent-free fractionation showed that EGF-Rs are found basally in Cav1-enriched lipid raft membranes and associate with Cav1. Ang II stimulates AT1R movement into these microdomains contemporaneously with the egress of EGF-R. Both aspects of this bidirectional receptor trafficking are inhibited by Cav1 siRNA. Moreover, Cav1 siRNA inhibits Ang II-induced vascular hypertrophy. CONCLUSIONS: Cav1 plays an essential role in AT1R targeting into Cav1-enriched lipid rafts and Rac1 activation, which are required for proper organization of ROS-dependent Ang II signaling linked to VSMC hypertrophy.

Role of gp91phox (Nox2)-containing NAD(P)H oxidase in angiogenesis in response to hindlimb ischemia.

BACKGROUND: Neovascularization is potentially important for the treatment of ischemic heart and limb disease. We reported that reactive oxygen species (ROS) derived from gp91phox (Nox2)-containing NAD(P)H oxidase are involved in angiogenesis in mouse sponge models as well as in vascular endothelial growth factor (VEGF) signaling in cultured endothelial cells. The role of gp91phox-derived ROS in neovascularization in response to tissue ischemia is unknown, however. METHODS AND RESULTS: Here, we show that neovascularization in the ischemic hindlimb is significantly impaired in gp91phox-/- mice as compared with wild-type (WT) mice as evaluated by laser Doppler flow, capillary density, and microsphere measurements. In WT mice, inflammatory cell infiltration in the ischemic hindlimb was maximal at 3 days, whereas capillary formation was prominent at 7 days when inflammatory cells were no longer detectable. Increased O2*- production and gp91phox expression were present at both time points. The dihydroethidium staining of ischemic tissues indicates that O2*- is mainly produced from inflammatory cells at 3 days and from neovasculature at 7 days after operation. Relative to WT mice, ischemia-induced ROS production in gp91phox-/- mice at both 3 and 7 days was diminished, whereas VEGF expression was enhanced and the inflammatory response was unchanged. Infusion of the antioxidant ebselen into WT mice also significantly blocked the increase in blood flow recovery and capillary density after ischemia. CONCLUSIONS: gp91phox-derived ROS play an important role in mediating neovascularization in response to tissue ischemia. NAD(P)H oxidases and their products are potential therapeutic targets for regulating angiogenesis in vivo.

Novel role of ARF6 in vascular endothelial growth factor-induced signaling and angiogenesis.

Vascular endothelial growth factor (VEGF) stimulates endothelial cell (EC) migration and proliferation primarily through the VEGF receptor-2 (VEGFR2). We have shown that VEGF stimulates a Rac1-dependent NAD(P)H oxidase to produce reactive oxygen species (ROS) that are involved in VEGFR2 autophosphorylation and angiogenic-related responses in ECs. The small GTPase ARF6 is involved in membrane trafficking and cell motility; however, its roles in VEGF signaling and physiological responses in ECs are unknown. In this study, we show that overexpression of dominant-negative ARF6 [ARF6(T27N)] almost completely inhibits VEGF-induced Rac1 activation, ROS production, and VEGFR2 autophosphorylation in ECs. Fractionation of caveolae/lipid raft membranes demonstrates that ARF6, Rac1, and VEGFR2 are localized in caveolin-enriched fractions basally. VEGF stimulation results in the release of VEGFR2 from caveolae/lipid rafts and caveolin-1 without affecting localization of ARF6, Rac1, or caveolin-1 in these fractions. The egress of VEGFR2 from caveolae/lipid rafts is contemporaneous with the tyrosine phosphorylation of caveolin-1 (Tyr14) and VEGFR2 and with their association with each other. ARF6(T27N) significantly inhibits both VEGF-induced responses. Immunofluorescence studies show that activated VEGFR2 and phosphocaveolin colocalize at focal complexes/adhesions after VEGF stimulation. Both overexpression of ARF6(T27N) and mutant caveolin-1(Y14F), which cannot be phosphorylated, block VEGF-stimulated EC migration and proliferation. Moreover, ARF6 expression is markedly upregulated in association with an increase in capillary density in a mouse hindlimb ischemia model of angiogenesis. Thus, ARF6 is involved in the temporal-spatial organization of caveolae/lipid rafts- and ROS-dependent VEGF signaling in ECs as well as in angiogenesis in vivo.

IQGAP1, a novel vascular endothelial growth factor receptor binding protein, is involved in reactive oxygen species--dependent endothelial migration and proliferation.

Endothelial cell (EC) proliferation and migration are important for reendothelialization and angiogenesis. We have demonstrated that reactive oxygen species (ROS) derived from the small GTPase Rac1-dependent NAD(P)H oxidase are involved in vascular endothelial growth factor (VEGF)-mediated endothelial responses mainly through the VEGF type2 receptor (VEGFR2). Little is known about the underlying molecular mechanisms. IQGAP1 is a scaffolding protein that controls cellular motility and morphogenesis by interacting directly with cytoskeletal, cell adhesion, and small G proteins, including Rac1. In this study, we show that IQGAP1 is robustly expressed in ECs and binds to the VEGFR2. A pulldown assay using purified proteins demonstrates that IQGAP1 directly interacts with active VEGFR2. In cultured ECs, VEGF stimulation rapidly promotes recruitment of Rac1 to IQGAP1, which inducibly binds to VEGFR2 and which, in turn, is associated with tyrosine phosphorylation of IQGAP1. Endogenous IQGAP1 knockdown by siRNA shows that IQGAP1 is involved in VEGF-stimulated ROS production, Akt phosphorylation, endothelial migration, and proliferation. Wound assays reveal that IQGAP1 and phosphorylated VEGFR2 accumulate and colocalize at the leading edge in actively migrating ECs. Moreover, we found that IQGAP1 expression is dramatically increased in the VEGFR2-positive regenerating EC layer in balloon-injured rat carotid artery. These results suggest that IQGAP1 functions as a VEGFR2-associated scaffold protein to organize ROS-dependent VEGF signaling, thereby promoting EC migration and proliferation, which may contribute to repair and maintenance of the functional integrity of established blood vessels.