KIF13B regulates angiogenesis through Golgi to plasma membrane trafficking of VEGFR2

Although the trafficking of newly synthesized VEGFR2 to the plasma membrane is a key determinant of angiogenesis, the molecular mechanisms of Golgi to plasma membrane trafficking are unknown. Here, we have identified a key role of the kinesin family plus-end molecular motor KIF13B in delivering VEGFR2 cargo from the Golgi to the endothelial cell surface. KIF13B is shown to interact directly with VEGFR2 on microtubules. We also observed that overexpression of truncated versions of KIF13B containing the binding domains that interact with VEGFR2 inhibited VEGF-induced capillary tube formation. KIF13B depletion prevented VEGF-mediated endothelial migration, capillary tube formation and neo-vascularization in mice. Impairment in trafficking induced by knockdown of KIF13B shunted VEGFR2 towards the lysosomal degradation pathway. Thus, KIF13B is an essential molecular motor required for the trafficking of VEGFR2 from the Golgi, and its delivery to the endothelial cell surface mediates angiogenesis.

Combinatorial therapy with acetylation and methylation modifiers attenuates lung vascular hyperpermeability in endotoxemia-induced mouse inflammatory lung injury

Impairment of tissue fluid homeostasis and migration of inflammatory cells across the vascular endothelial barrier are crucial factors in the pathogenesis of acute lung injury (ALI). The goal for treatment of ALI is to target pathways that lead to profound dysregulation of the lung endothelial barrier. Although studies have shown that chemical epigenetic modifiers can limit lung inflammation in experimental ALI models, studies to date have not examined efficacy of a combination of DNA methyl transferase inhibitor 5-Aza 2-deoxycytidine and histone deacetylase inhibitor trichostatin A (herein referred to as Aza+TSA) after endotoxemia-induced mouse lung injury. We tested the hypothesis that treatment with Aza+TSA after lipopolysaccharide induction of ALI through epigenetic modification of lung endothelial cells prevents inflammatory lung injury. Combinatorial treatment with Aza+TSA mitigated the increased endothelial permeability response after lipopolysaccharide challenge. In addition, we observed reduced lung inflammation and lung injury. Aza+TSA also significantly reduced mortality in the ALI model. The protection was ascribed to inhibition of the eNOS-Cav1-MLC2 signaling pathway and enhanced acetylation of histone markers on the vascular endothelial-cadherin promoter. In summary, these data show for the first time the efficacy of combinatorial Aza+TSA therapy in preventing ALI in lipopolysaccharide-induced endotoxemia and raise the possibility of an essential role of DNA methyl transferase and histone deacetylase in the mechanism of ALI.

Cooperative signaling via transcription factors NF-κB and AP1/c-Fos mediates endothelial cell STIM1 expression and hyperpermeability in response to endotoxin

Stromal interacting molecule 1 (STIM1) regulates store-operated Ca(2+) entry (SOCE). Here we show that STIM1 expression in endothelial cells (ECs) is increased during sepsis and, therefore, contributes to hyperpermeability. LPS induced STIM1 mRNA and protein expression in human and mouse lung ECs. The induced STIM1 expression was associated with augmented SOCE as well as a permeability increase in both in vitro and in vivo models. Because activation of both the NF-κB and p38 MAPK signaling pathways downstream of TLR4 amplifies vascular inflammation, we studied the influence of these two pathways on LPS-induced STIM1 expression. Inhibition of either NF-κB or p38 MAPK activation by pharmacological agents prevented LPS-induced STIM1 expression. Silencing of the NF-κB proteins (p65/RelA or p50/NF-κB1) or the p38 MAPK isoform p38α prevented LPS-induced STIM1 expression and increased SOCE in ECs. In support of these findings, we found NF-κB and AP1 binding sites in the 5'-regulatory region of human and mouse STIM1 genes. Further, we demonstrated that LPS induced time-dependent binding of the transcription factors NF-κB (p65/RelA) and AP1 (c-Fos/c-Jun) to the STIM1 promoter. Interestingly, silencing of c-Fos, but not c-Jun, markedly reduced LPS-induced STIM1 expression in ECs. We also observed that silencing of p38α prevented c-Fos expression in response to LPS in ECs, suggesting that p38α signaling mediates the expression of c-Fos. These results support the proposal that cooperative signaling of both NF-κB and AP1 (via p38α) amplifies STIM1 expression in ECs and, thereby, contributes to the lung vascular hyperpermeability response during sepsis.

Differential role for p120-catenin in regulation of TLR4 signaling in macrophages

Activation of TLR signaling through recognition of pathogen-associated molecular patterns is essential for the innate immune response against bacterial and viral infections. We have shown that p120-catenin (p120) suppresses TLR4-mediated NF-кB signaling in LPS-challenged endothelial cells. In this article, we report that p120 differentially regulates LPS/TLR4 signaling in mouse bone marrow-derived macrophages. We observed that p120 inhibited MyD88-dependent NF-κB activation and release of TNF-α and IL-6, but enhanced TIR domain-containing adapter-inducing IFN-β-dependent IFN regulatory factor 3 activation and release of IFN-β upon LPS exposure. p120 silencing diminished LPS-induced TLR4 internalization, whereas genetic and pharmacological inhibition of RhoA GTPase rescued the decrease in endocytosis of TLR4 and TLR4-MyD88 signaling, and reversed the increase in TLR4-TIR domain-containing adapter-inducing IFN-β signaling induced by p120 depletion. Furthermore, we demonstrated that altered p120 expression in macrophages regulates the inflammatory phenotype of LPS-induced acute lung injury. These results indicate that p120 functions as a differential regulator of TLR4 signaling pathways by facilitating TLR4 endocytic trafficking in macrophages, and support a novel role for p120 in influencing the macrophages in the lung inflammatory response to endotoxin.

Regulating the regulator of ROS production

Balancing inflammatory reactive oxygen species (ROS) production is essential for safely eliminating pathogenic microbes. The newly described protein Negative Regulator of ROS (NRROS) dampens ROS production by restricting NOX2 availability, and thus "cools-off" inflammation.

Evidence of a common mechanism of disassembly of adherens junctions through Gα13 targeting of VE-cadherin

The heterotrimeric G protein Gα13 transduces signals from G protein-coupled receptors (GPCRs) to induce cell spreading, differentiation, migration, and cell polarity. Here, we describe a novel GPCR-independent function of Gα13 in regulating the stability of endothelial cell adherens junctions (AJs). We observed that the oxidant H2O2, which is released in response to multiple proinflammatory mediators, induced the interaction of Gα13 with VE-cadherin. Gα13 binding to VE-cadherin in turn induced Src activation and VE-cadherin phosphorylation at Tyr 658, the p120-catenin binding site thought to be responsible for VE-cadherin internalization. Inhibition of Gα13-VE-cadherin interaction using an interfering peptide derived from the Gα13 binding motif on VE-cadherin abrogated the disruption of AJs in response to inflammatory mediators. These studies identify a unique role of Gα13 binding to VE-cadherin in mediating VE-cadherin internalization and endothelial barrier disruption and inflammation.

Prevention of vascular inflammation by nanoparticle targeting of adherent neutrophils

Inflammatory diseases such as acute lung injury and ischaemic tissue injury are caused by the adhesion of a type of white blood cell--polymorphonuclear neutrophils--to the lining of the circulatory system or vascular endothelium and unchecked neutrophil transmigration. Nanoparticle-mediated targeting of activated neutrophils on vascular endothelial cells at the site of injury may be a useful means of directly inactivating neutrophil transmigration and hence mitigating vascular inflammation. Here, we report a method employing drug-loaded albumin nanoparticles, which efficiently deliver drugs into neutrophils adherent to the surface of the inflamed endothelium. Using intravital microscopy of tumour necrosis factor-α-challenged mouse cremaster post-capillary venules, we demonstrate that fluorescently tagged albumin nanoparticles are largely internalized by neutrophils adherent to the activated endothelium via cell surface Fcɣ receptors. Administration of albumin nanoparticles loaded with the spleen tyrosine kinase inhibitor, piceatannol, which blocks 'outside-in' β2 integrin signalling in leukocytes, detached the adherent neutrophils and elicited their release into the circulation. Thus, internalization of drug-loaded albumin nanoparticles into neutrophils inactivates the pro-inflammatory function of activated neutrophils, thereby offering a promising approach for treating inflammatory diseases resulting from inappropriate neutrophil sequestration and activation.

Reactive oxygen species in inflammation and tissue injury

Abstract Reactive oxygen species (ROS) are key signaling molecules that play an important role in the progression of inflammatory disorders. An enhanced ROS generation by polymorphonuclear neutrophils (PMNs) at the site of inflammation causes endothelial dysfunction and tissue injury. The vascular endothelium plays an important role in passage of macromolecules and inflammatory cells from the blood to tissue. Under the inflammatory conditions, oxidative stress produced by PMNs leads to the opening of inter-endothelial junctions and promotes the migration of inflammatory cells across the endothelial barrier. The migrated inflammatory cells not only help in the clearance of pathogens and foreign particles but also lead to tissue injury. The current review compiles the past and current research in the area of inflammation with particular emphasis on oxidative stress-mediated signaling mechanisms that are involved in inflammation and tissue injury.

Therapeutic administration of the chemokine CXCL1/KC abrogates autoimmune inflammatory heart disease

Myocarditis, often due to an aberrant immune response to infection, is a major cause of dilated cardiomyopathy. Microbial pattern recognition receptors, such as TLRs, orchestrate the cytokine and chemokine responses that augment or limit the severity of myocarditis. Using the mouse model of experimental autoimmune myocarditis (EAM), in which disease is induced by immunization with a heart-specific self peptide and the agonist to multiple TLRs, complete Freund's adjuvant, we found that increased serum concentrations of the chemokine CXCL1/KC correlated directly with decreased severity of myocarditis. To directly test whether CXCL1/KC caused the amelioration of myocarditis, we treated mice, after challenge with heart-specific self peptide, with exogenous recombinant CXCL1/KC. We found that the administration of recombinant mouse CXCL1/KC completely abrogated heart inflammatory infiltration and cardiomyocyte damage. Moreover, we show that TLR4 signaling is required to increase serum protein concentrations of CXCL1/KC in EAM, and we demonstrate that the administration of the TLR4 agonist LPS significantly decreased severity and prevalence of EAM and reduced the number of heart-specific self peptide reactive effector T cells. These findings reveal a novel function of CXCL1/KC in the context of organ-specific autoimmune disease that may prove useful for the treatment of inflammatory conditions that underlie human heart disease.

The transcription factor DREAM represses the deubiquitinase A20 and mediates inflammation

Here we show that the transcription-repressor DREAM binds to the A20 promoter to repress the expression of A20, the deubiquitinase suppressing inflammatory NF-κB signaling. DREAM-deficient (Dream^−/−) mice displayed persistent and unchecked A20 expression in response to endotoxin. DREAM functioned by transcriptionally repressing A20 through binding to downstream regulatory elements (DREs). In contrast, USF1 binding to the DRE-associated E-box domain activated A20 expression in response to inflammatory stimuli. These studies define the critical opposing functions of DREAM and USF1 in inhibiting and inducing A20 expression, respectively, and thereby the strength of NF-κB signaling. Targeting of DREAM to induce USF1-mediated A20 expression is therefore a potential anti-inflammatory strategy in diseases such as acute lung injury associated with unconstrained NF-κB activity.

Flk1+ and VE-cadherin+ endothelial cells derived from iPSCs recapitulates vascular development during differentiation and display similar angiogenic potential as ESC-derived cells

RATIONALE

Induced pluripotent stem (iPS) cells have emerged as a source of potentially unlimited supply of autologous endothelial cells (ECs) for vascularization. However, the regenerative function of these cells relative to adult ECs and ECs derived from embryonic stem (ES) cells is unknown. The objective was to define the differentiation characteristics and vascularization potential of Fetal liver kinase (Flk)1(+) and Vascular Endothelial (VE)-cadherin(+) ECs derived identically from mouse (m)ES and miPS cells.

METHODS AND RESULTS

Naive mES and miPS cells cultured in type IV collagen (IV Col) in defined media for 5 days induced the formation of adherent cell populations, which demonstrated similar expression of Flk1 and VE-cadherin and the emergence of EC progenies. FACS purification resulted in 100% Flk1(+) VE-cadherin(+) cells from both mES and miPS cells. Emergence of Flk1(+)VE-cadherin(+) cells entailed expression of the vascular developmental transcription factor Er71, which bound identically to Flk1, VE-cadherin, and CD31 promoters in both populations. Immunostaining with anti-VE-cadherin and anti-CD31 antibodies and microscopy demonstrated the endothelial nature of these cells. Each cell population (unlike mature ECs) organized into well-developed vascular structures in vitro and incorporated into CD31(+) neovessels in matrigel plugs implanted in nude mice in vivo.

CONCLUSION

Thus, iPS cell-derived Flk1(+)VE-cadherin(+) cells expressing the Er71 are as angiogenic as mES cell-derived cells and incorporate into CD31(+) neovessels. Their vessel forming capacity highlights the potential of autologous iPS cells-derived EC progeny for therapeutic angiogenesis.

Caveolin-1 Tyr14 phosphorylation induces interaction with TLR4 in endothelial cells and mediates MyD88-dependent signaling and sepsis-induced lung inflammation

Activation of TLR4 by the endotoxin LPS is a critical event in the pathogenesis of Gram-negative sepsis. Caveolin-1, the signaling protein associated with caveolae, is implicated in regulating the lung inflammatory response to LPS; however, the mechanism is not understood. In this study, we investigated the role of caveolin-1 in regulating TLR4 signaling in endothelial cells. We observed that LPS interaction with CD14 in endothelial cells induced Src-dependent caveolin-1 phosphorylation at Tyr(14). Using a TLR4-MD2-CD14-transfected HEK-293 cell line and caveolin-1-deficient (cav-1(-/-)) mouse lung microvascular endothelial cells, we demonstrated that caveolin-1 phosphorylation at Tyr(14) following LPS exposure induced caveolin-1 and TLR4 interaction and, thereby, TLR4 activation of MyD88, leading to NF-κB activation and generation of proinflammatory cytokines. Exogenous expression of phosphorylation-deficient Y14F caveolin-1 mutant in cav-1(-/-) mouse pulmonary vasculature rendered the mice resistant to LPS compared with reintroduction of wild-type caveolin-1. Thus, caveolin-1 Y14 phosphorylation was required for the interaction with TLR4 and activation of TLR4-MyD88 signaling and sepsis-induced lung inflammation. Inhibiting caveolin-1 Tyr(14) phosphorylation and resultant inactivation of TLR4 signaling in pulmonary vascular endothelial cells represent a novel strategy for preventing sepsis-induced lung inflammation and injury.

Cooperative interaction of trp melastatin channel transient receptor potential (TRPM2) with its splice variant TRPM2 short variant is essential for endothelial cell apoptosis

RATIONALE

Oxidants generated by activated endothelial cells are known to induce apoptosis, a pathogenic feature of vascular injury and inflammation from multiple pathogeneses. The melastatin-family transient receptor potential 2 (TRPM2) channel is an oxidant-sensitive Ca2+ permeable channel implicated in mediating apoptosis; however, the mechanisms of gating of the supranormal Ca2+ influx required for initiating of apoptosis are not understood.

OBJECTIVE

Here, we addressed the role of TRPM2 and its interaction with the short splice variant TRPM2 short variant (TRPM2-S) in mediating the Ca2+ entry burst required for induction of endothelial cell apoptosis.

METHODS AND RESULTS

We observed that TRPM2-S was basally associated with TRPM2 in the endothelial plasmalemma, and this interaction functioned to suppress TRPM2-dependent Ca2+ gating constitutively. Reactive oxygen species production in endothelial cells or directly applying reactive oxygen species induced protein kinase C-α activation and phosphorylation of TRPM2 at Ser 39. This in turn stimulated a large entry of Ca2+ and activated the apoptosis pathway. A similar TRPM2-dependent endothelial apoptosis mechanism was seen in intact vessels. The protein kinase C-α-activated phosphoswitch opened the TRPM2 channel to allow large Ca2+ influx by releasing TRPM2-S inhibition of TRPM2, which in turn activated caspase-3 and cleaved the caspase substrate poly(ADP-ribose) polymerase.

CONCLUSIONS

Here, we describe a fundamental mechanism by which activation of the trp superfamily TRPM2 channel induces apoptosis of endothelial cells. The signaling mechanism involves reactive oxygen species-induced protein kinase C-α activation resulting in phosphorylation of TRPM2-S that allows enhanced TRPM2-mediated gating of Ca2+ and activation of the apoptosis program. Strategies aimed at preventing the uncoupling of TRPM2-S from TRPM2 and subsequent Ca2+ gating during oxidative stress may mitigate endothelial apoptosis and its consequences in mediating vascular injury and inflammation.

Caveolin-1 Tyr14 phosphorylation induces interaction with TLR4 in endothelial cells and mediates MyD88-dependent signaling and sepsis-induced lung inflammation

Activation of TLR4 by the endotoxin LPS is a critical event in the pathogenesis of Gram-negative sepsis. Caveolin-1, the signaling protein associated with caveolae, is implicated in regulating the lung inflammatory response to LPS; however, the mechanism is not understood. In this study, we investigated the role of caveolin-1 in regulating TLR4 signaling in endothelial cells. We observed that LPS interaction with CD14 in endothelial cells induced Src-dependent caveolin-1 phosphorylation at Tyr(14). Using a TLR4-MD2-CD14-transfected HEK-293 cell line and caveolin-1-deficient (cav-1(-/-)) mouse lung microvascular endothelial cells, we demonstrated that caveolin-1 phosphorylation at Tyr(14) following LPS exposure induced caveolin-1 and TLR4 interaction and, thereby, TLR4 activation of MyD88, leading to NF-κB activation and generation of proinflammatory cytokines. Exogenous expression of phosphorylation-deficient Y14F caveolin-1 mutant in cav-1(-/-) mouse pulmonary vasculature rendered the mice resistant to LPS compared with reintroduction of wild-type caveolin-1. Thus, caveolin-1 Y14 phosphorylation was required for the interaction with TLR4 and activation of TLR4-MyD88 signaling and sepsis-induced lung inflammation. Inhibiting caveolin-1 Tyr(14) phosphorylation and resultant inactivation of TLR4 signaling in pulmonary vascular endothelial cells represent a novel strategy for preventing sepsis-induced lung inflammation and injury.

Cytoskeletal dynamics and lung fluid balance

This article examines the role of the endothelial cytoskeleton in the lung's ability to restrict fluid and protein to vascular space at normal vascular pressures and thereby to protect lung alveoli from lethal flooding. The barrier properties of microvascular endothelium are dependent on endothelial cell contact with other vessel-wall lining cells and with the underlying extracellular matrix (ECM). Focal adhesion complexes are essential for attachment of endothelium to ECM. In quiescent endothelial cells, the thick cortical actin rim helps determine cell shape and stabilize endothelial adherens junctions and focal adhesions through protein bridges to actin cytoskeleton. Permeability-increasing agonists signal activation of "small GTPases" of the Rho family to reorganize the actin cytoskeleton, leading to endothelial cell shape change, disassembly of cortical actin rim, and redistribution of actin into cytoplasmic stress fibers. In association with calcium- and Src-regulated myosin light chain kinase (MLCK), stress fibers become actinomyosin-mediated contractile units. Permeability-increasing agonists stimulate calcium entry and induce tyrosine phosphorylation of VE-cadherin (vascular endothelial cadherin) and β-catenins to weaken or pull apart endothelial adherens junctions. Some permeability agonists cause latent activation of the small GTPases, Cdc42 and Rac1, which facilitate endothelial barrier recovery and eliminate interendothelial gaps. Under the influence of Cdc42 and Rac1, filopodia and lamellipodia are generated by rearrangements of actin cytoskeleton. These motile evaginations extend endothelial cell borders across interendothelial gaps, and may initiate reannealing of endothelial junctions. Endogenous barrier protective substances, such as sphingosine-1-phosphate, play an important role in maintaining a restrictive endothelial barrier and counteracting the effects of permeability-increasing agonists.

Bioluminescent detection of peroxynitrite with a boronic acid-caged luciferin

Peroxynitrite, a highly reactive biological oxidant, is formed under pathophysiologic conditions from the diffusion-limited reaction of nitric oxide and superoxide radical anion. Peroxynitrite has been implicated as the mediator of nitric oxide toxicity in many diseases and as an important signaling disrupting molecule (L. Liaudet et al., Front. Biosci.14, 4809-4814, 2009) [1]. Biosensors effective at capturing peroxynitrite in a specific and fast enough manner for detection, along with readouts compatible with in vivo studies, are lacking. Here we report that the boronic acid-based bioluminescent system PCL-1 (peroxy-caged luciferin-1), previously reported as a chemoselective sensor for hydrogen peroxide (G.C. Van de Bittner et al., Proc. Natl. Acad. Sci. USA107, 21316-21321, 2010) [2], reacts with peroxynitrite stoichiometrically with a rate constant of 9.8±0.3×10(5)M(-1)s(-1) and a bioluminescence detection limit of 16nM, compared to values of 1.2±0.3M(-1)s(-1) and 231nM for hydrogen peroxide. Further, we demonstrate bioluminescent detection of peroxynitrite in the presence of physiological competitors: carbon dioxide, glutathione, albumin, and catalase. We also demonstrate the utility of this method to assess peroxynitrite formation in mammalian cells by measuring peroxynitrite generated under normal culture conditions after stimulation of macrophages with bacterial endotoxin lipopolysaccharide. Thus, the PCL-1 method for measuring peroxynitrite generation shows superior selectivity over other oxidants under in vivo conditions.

Transcriptional regulation of endothelial cell and vascular development

The establishment and maintenance of the vascular system is critical for embryonic development and postnatal life. Defects in endothelial cell development and vessel formation and function lead to embryonic lethality and are important in the pathogenesis of vascular diseases. Here, we review the underlying molecular mechanisms of endothelial cell differentiation, plasticity, and the development of the vasculature. This review focuses on the interplay among transcription factors and signaling molecules that specify the differentiation of vascular endothelial cells. We also discuss recent progress on reprogramming of somatic cells toward distinct endothelial cell lineages and its promise in regenerative vascular medicine.

Store-operated Ca2+ entry (SOCE) induced by protease-activated receptor-1 mediates STIM1 protein phosphorylation to inhibit SOCE in endothelial cells through AMP-activated protein kinase and p38β mitogen-activated protein kinase

The Ca(2+) sensor STIM1 is crucial for activation of store-operated Ca(2+) entry (SOCE) through transient receptor potential canonical and Orai channels. STIM1 phosphorylation serves as an "off switch" for SOCE. However, the signaling pathway for STIM1 phosphorylation is unknown. Here, we show that SOCE activates AMP-activated protein kinase (AMPK); its effector p38β mitogen-activated protein kinase (p38β MAPK) phosphorylates STIM1, thus inhibiting SOCE in human lung microvascular endothelial cells. Activation of AMPK using 5-aminoimidazole-4-carboxamide-1-β-d-ribofuranoside (AICAR) resulted in STIM1 phosphorylation on serine residues and prevented protease-activated receptor-1 (PAR-1)-induced Ca(2+) entry. Furthermore, AICAR pretreatment blocked PAR-1-induced increase in the permeability of mouse lung microvessels. Activation of SOCE with thrombin caused phosphorylation of isoform α1 but not α2 of the AMPK catalytic subunit. Moreover, knockdown of AMPKα1 augmented SOCE induced by thrombin. Interestingly, SB203580, a selective inhibitor of p38 MAPK, blocked STIM1 phosphorylation and led to sustained STIM1-puncta formation and Ca(2+) entry. Of the three p38 MAPK isoforms expressed in endothelial cells, p38β knockdown prevented PAR-1-mediated STIM1 phosphorylation and potentiated SOCE. In addition, inhibition of the SOCE downstream target CaM kinase kinase β (CaMKKβ) or knockdown of AMPKα1 suppressed PAR-1-mediated phosphorylation of p38β and hence STIM1. Thus, our findings demonstrate that SOCE activates CaMKKβ-AMPKα1-p38β MAPK signaling to phosphorylate STIM1, thereby suppressing endothelial SOCE and permeability responses.