Adhesion of Candida parapsilosis to Bovine Serum Albumin under Fluid Shear.

C. parapsilosis (Cp) is an emerging cause of bloodstream infections in certain populations. The Candida clade, including Cp, is increasingly developing resistance to the first and the second line of antifungals. Cp is frequently isolated from hands and skin surfaces, as well as the GI tract. Colonization by Candida predisposes individuals to invasive bloodstream infections. To successfully colonize or invade the host, yeast must be able to rapidly adhere to the body surfaces to prevent elimination by host defense mechanisms. Here we describe a method to measure adhesion of Cp to immobilized proteins under physiologic fluid shear, using an end-point adhesion assay in a commercially available multichannel microfluidic device. This method is optimized to improve reproducibility, minimize subjectivity, and allow for the fluorescent quantification of individual isolates. We also demonstrate that some clinical isolates of Cp show increased adhesion when grown in conditions mimicking a mammalian host, whereas a frequently used lab strain, CDC317, is non-adhesive under fluid shear.

The Center of Biomedical Research Excellence (COBRE) for Perinatal Biology - Accomplishments, Impact, and Long-term Results.

The COBRE for Perinatal Biology (CPB) was the third grant in Rhode Island to be funded by the COBRE mechanism. The CPB was based at Women & Infants Hospital, and housed in the Kilguss Research Institute, in the Jewelry District in Providence. The scientific focus of the CPB was on perinatal diseases such as preeclampsia and preterm birth, as well as more broadly on cardiopulmonary development and reproductive biology. Over the course of three phases and 17 years, the CPB funded 22 projects. CPB investigators, in turn, generated over $27.5 million in independent funding from federal and non-federal sources. Besides providing scientific and career mentorship to new investigators in Rhode Island, the CPB established a Research Core. The Kilguss Research Core remains active and flourishing and provides advanced imaging, molecular biology and flow cytometry abilities to researchers at Women & Infants as well as the greater Rhode Island scientific community.

Transcription Profiles Associated with Inducible Adhesion in Candida parapsilosis.

Candida parapsilosis has emerged as a frequent cause of invasive candidiasis with increasing evidence of unique biological features relative to C. albicans As it adapts to conditions within a mammalian host, rapid changes in gene expression are necessary to facilitate colonization and persistence in this environment. Adhesion of the organism to biological surfaces is a key first step in this process and is the focus of this study. Building on previous observations showing the importance of a member of the ALS gene family in C. parapsilosis adhesion, three clinical isolates were cultured under two conditions that mimic the mammalian host and promote adhesion, incubation at 37°C in tissue culture medium 199 or in human plasma. Transcriptional profiles using RNA-seq were obtained in these adhesion-inducing conditions and compared to profiles following growth in yeast media that suppress adhesion to identify gene expression profiles associated with adhesion. Overall gene expression profiles among the three strains were similar in both adhesion-inducing conditions and distinct from adhesion-suppressing conditions. Pairwise analysis among the three growth conditions identified 133 genes that were differentially expressed at a cutoff of ±4-fold, with the most upregulated genes significantly enriched in iron acquisition and transmembrane transport, while the most downregulated genes were enriched in oxidation-reduction processes. Gene family enrichment analysis identified gene families with diverse functions that may have an important role in this important step for colonization and disease.IMPORTANCE Invasive Candida infections are frequent complications of the immunocompromised and are associated with substantive morbidity and mortality. Although C. albicans is the best-studied species, emerging infections by non-albicans Candida species have led to increased efforts to understand aspects of their pathogenesis that are unique from C. albicansC. parapsilosis is a frequent cause of invasive infections, particularly among premature infants. Recent efforts have identified important virulence mechanisms that have features distinct from C. albicansC. parapsilosis can exist outside a host environment and therefore requires rapid modifications when it encounters a mammalian host to prevent its clearance. An important first step in the process is adhesion to host surfaces. This work takes a global, nonbiased approach to investigate broad changes in gene expression that accompany efficient adhesion. As such, biological pathways and individual protein targets are identified that may be amenable to manipulation to reduce colonization and disease from this organism.

Pathology of Neonatal Non- albicans Candidiasis: Autopsy Study and Literature Review.

INTRODUCTION/OBJECTIVES: Non- albicans Candida species such as Candida parapsilosis and Candida glabrata have emerged as prevalent pathogens in premature infants. The aim of this study was to systematically delineate the histopathologic findings in neonatal non- albicans candidiasis. METHODS: We performed a retrospective clinicopathologic analysis of extremely premature (23-28 weeks' gestation) infants diagnosed with invasive candidiasis. Archival autopsy tissues were subjected to periodic acid-Schiff, methenamine-silver and anti- Candida (immuno)histochemical stains, as well as dual anti- Candida and anti-cytokeratin or anti-CD31 immunofluorescence assays. In addition, we studied the prevalence of intestinal Candida colonization in a consecutive autopsy series of extremely premature infants. RESULTS: Based on positive postmortem blood and/or lung cultures, invasive candidiasis (3 non- albicans and 11 Candida albicans) was diagnosed in 14 of the 187 extremely premature infants examined between 1995 and 2017. In contrast to the well-known inflammatory and tissue-destructive phenotype of congenital C. albicans infection, invasive non- albicans candidiasis/candidemia caused by C. parapsilosis and C. glabrata was inconspicuous by routine hematoxylin-eosin-based histopathologic analysis despite a heavy fungal presence detected in intestines, lungs, and blood by targeted (immuno)histochemical assays. Intestinal colonization by Candida species was identified in 16 of the 26 (61%) extremely premature neonates who had lived for at least 1 week, as assessed by anti- Candida immunostaining. CONCLUSION: Invasive neonatal non- albicans candidiasis/candidemia appears to have no distinct histopathologic signature. Based on the notoriously low sensitivity of fungal blood cultures and the observed high frequency of Candida intestinal colonization (>50%), it is likely that non- albicans candidiasis/candidemia may be underdiagnosed in (deceased) preterm infants. Routine inclusion of targeted (immuno)histochemical fungal detection strategies in the perinatal autopsy may lead to deeper insight into the prevalence and clinical relevance of neonatal non- albicans candidiasis.

Role of the Inducible Adhesin CpAls7 in Binding of Candida parapsilosis to the Extracellular Matrix under Fluid Shear.

The yeast Candida parapsilosis is an increasingly common cause of systemic fungal infections among immunocompromised individuals, including premature infants. Adhesion to host surfaces is an important step in pathogenesis, but this process has not been extensively studied in this organism. A microfluidics assay was developed to test the ability of C. parapsilosis to adhere to immobilized host extracellular matrix proteins under physiological fluid shear conditions. Growth in mammalian tissue culture medium at 37°C for 3 to 6 h led to the induction of an adhesive phenotype at shear forces of 1 to 5 dynes/cm2 in some isolates of C. parapsilosis Glutamic acid, proline, and calcium appeared to be the minimally necessary requirements for increased adhesion in these assays. To determine whether genes homologous to the ALS gene family of C. albicans were important for the adhesive phenotype, the expression levels of 5 homologous C. parapsilosis genes were quantified by using quantitative PCR (qPCR) under conditions leading to increased adhesion. CPAR2_404800 (CpALS7) and CPAR2_404780 showed increased expression levels compared to those in control yeast. The extent of adhesion was variable among different isolates, and linear regression identified the expression of CpALS7 but not CPAR2_404780 as having a strong positive correlation with adhesion. A homozygous CpALS7 deletion strain was deficient in adhesion, whereas the expression of CpALS7 in Saccharomyces cerevisiae resulted in increased adhesion. Together, these data provide strong evidence that CpAls7 aids in the adherence of C. parapsilosis to the extracellular matrix under shear forces and support its previously reported role in virulence.

Protection of Candida parapsilosis from neutrophil killing through internalization by human endothelial cells.

Candida parapsilosis is a fungal pathogen that is associated with hematogenously disseminated disease in premature neonates, acutely ill or immunocompromised patients. In cell culture, C. parapsilosis cells are actively and avidly endocytosed by endothelial cells via actin polymerization mediated by N-WASP. Here we present evidence that C. parapsilosis that were internalized by endothelial cells remained alive, and avoided being acidified or otherwise damaged via the host cell. Internalized fungal cells reproduced intracellularly and eventually burst out of the host endothelial cell. When neutrophils were added to endothelium and C. parapsilosis, they patrolled the endothelial surface and efficiently killed most adherent fungal cells prior to endocytosis. But after endocytosis by endothelial cells, internalized fungal cells evaded neutrophil killing. Silencing endothelial N-WASP blocked endocytosis of C. parapsilosis and left fungal cells stranded on the cell surface, where they were susceptible to neutrophil killing. These observations suggest that for C. parapsilosis to escape from the bloodstream, fungi may adhere to and be internalized by endothelial cells before being confronted and phagocytosed by a patrolling leukocyte. Once internalized by endothelial cells, C. parapsilosis may safely replicate to cause further rounds of infection. Immunosurveillance of the intravascular lumen by leukocytes crawling on the endothelial surface and rapid killing of adherent yeast may play a major role in controlling C. parapsilosis dissemination and infected endothelial cells may be a significant reservoir for fungal persistence.

Mechanotransduction via TRPV4 regulates inflammation and differentiation in fetal mouse distal lung epithelial cells.

BACKGROUND: Mechanical ventilation plays a central role in the injury of premature lungs. However, the mechanisms by which mechanical signals trigger an inflammatory cascade to promote lung injury are not well-characterized. Transient receptor potential vanilloid 4 (TRPV4), a calcium-permeable mechanoreceptor channel has been shown to be a major determinant of ventilator-induced acute lung injury in adult models. However, the role of these channels as modulators of inflammation in immature lungs is unknown. In this study, we tested the hypothesis that TRPV4 channels are important mechanotransducers in fetal lung injury. METHODS: Expression of TRPV4 in the mouse fetal lung was investigated by immunohistochemistry, Western blot and qRT-PCR. Isolated fetal epithelial cells were exposed to mechanical stimulation using the Flexcell Strain Unit and inflammation and differentiation were analyzed by ELISA and SP-C mRNA, respectively. RESULTS: TRPV4 is developmentally regulated in the fetal mouse lung; it is expressed in the lung epithelium and increases with advanced gestation. In contrast, in isolated epithelial cells, TRPV4 expression is maximal at E17-E18 of gestation. Mechanical stretch increases TRPV4 in isolated fetal epithelial cells only during the canalicular stage of lung development. Using the TRPV4 agonist GSK1016790A, the antagonist HC-067047, and the cytokine IL-6 as a marker of inflammation, we observed that TRPV4 regulates release of IL-6 via p38 and ERK pathways. Interestingly, stretch-induced differentiation of fetal epithelial cells was also modulated by TRPV4. CONCLUSION: These studies demonstrate that TRPV4 may play an important role in the transduction of mechanical signals in the fetal lung epithelium by modulating not only inflammation but also the differentiation of fetal epithelial cells.

Human endothelial cells internalize Candida parapsilosis via N-WASP-mediated endocytosis.

Candida parapsilosis is a frequent cause of disseminated candidiasis and is associated with significant morbidity and mortality. Although important in pathogenesis, interactions of this organism with endothelial cells have received less attention than those of Candida albicans. Internalization of C. parapsilosis by monolayers of human endothelial cells was examined in an in vitro assay and compared to that of C. albicans. Both live and heat-killed yeast were efficiently internalized, with heat-killed yeast subsequently being detected in an acidic subcompartment. Internalization was marked by a process of engulfment by thin membrane extensions from the endothelium. Efficiency of internalization differed among different clinical isolates and species of yeast. Opsonization of C. parapsilosis by serum factors was not sufficient to cause endocytosis; instead, serum appeared to directly stimulate endothelial uptake. Colocalization of endothelial actin and N-WASP at sites of C. parapsilosis internalization was observed. A Förster-resonance energy transfer (FRET) probe for N-WASP activity showed active N-WASP at sites of internalization for both live and heat-killed C. parapsilosis and C. albicans. An actin nucleation inhibitor (cytochalasin D) and an N-WASP inhibitor (wiskostatin) both inhibited uptake of heat-killed C. parapsilosis, as did short interfering RNA-mediated ablation of N-WASP. Thus, endocytosis by endothelial cells may represent a means of traversal of the blood vessel wall by yeast during disseminated candidiasis, and N-WASP may play a key role in the process.

ß-Adrenergic receptor-PI3K signaling crosstalk in mouse heart: elucidation of immediate downstream signaling cascades.

Sustained ß-adrenergic receptors (ßAR) activation leads to cardiac hypertrophy and prevents left ventricular (LV) atrophy during LV unloading. The immediate signaling pathways downstream from ßAR stimulation, however, have not been well investigated. The current study was to examine the early cardiac signaling mechanism(s) following ßAR stimulation. In adult C57BL/6 mice, acute ßAR stimulation induced significant increases in PI3K activity and activation of Akt and ERK1/2 in the heart, but not in lungs or livers. In contrast, the same treatment did not elicit these changes in ß(1)/ß(2)AR double knockout mice. We further showed the specificity of ß(2)AR in this crosstalk as treatment with formoterol, a ß(2)AR-selective agonist, but not dobutamine, a predominantly ß(1)AR agonist, activated cardiac Akt and ERK1/2. Acute ßAR stimulation also significantly increased the phosphorylation of mTOR (the mammalian target of rapamycin), P70S6K, ribosomal protein S6, GSK-3α/ß (glycogen synthase kinase-3α/ß), and FOXO1/3a (the forkhead box family of transcription factors 1 and 3a). Moreover, acute ßAR stimulation time-dependently decreased the mRNA levels of the muscle-specific E3 ligases atrogin-1 and muscle ring finger protein-1 (MuRF1) in mouse heart. Our results indicate that acute ßAR stimulation in vivo affects multiple cardiac signaling cascades, including the PI3K signaling pathway, ERK1/2, atrogin-1 and MuRF1. These data 1) provide convincing evidence for the crosstalk between ßAR and PI3K signaling pathways; 2) confirm the ß(2)AR specificity in this crosstalk in vivo; and 3) identify novel signaling factors involved in cardiac hypertrophy and LV unloading. Understanding of the intricate interplay between ß(2)AR activation and these signaling cascades should provide critical clues to the pathogenesis of cardiac hypertrophy and enable identification of targets for early clinical interaction of cardiac lesions.

Relative actin nucleation promotion efficiency by WASP and WAVE proteins in endothelial cells.

The mammalian genome encodes multiple Wiskott-Aldrich syndrome protein (WASP)/WASP-family Verprolin homologous (WAVE) proteins. Members of this family interact with the actin related protein (Arp) 2/3 complex to promote growth of a branched actin network near the plasma membrane or the surface of moving cargos. Arp2/3 mediated branching can further lead to formation of comet tails (actin rockets). Despite their similar domain structure, different WASP/WAVE family members fulfill unique functions that depend on their subcellular location and activity levels. We measured the relative efficiency of actin nucleation promotion of full-length WASP/WAVE proteins in a cytoplasmic extract from primary human umbilical vein endothelial cells (HUVEC). In this assay WAVE2 and WAVE3 complexes showed higher nucleation efficiency than WAVE1 and N-WASP, indicating distinct cellular controls for different family members. Previously, WASP and N-WASP were the only members that were known to stimulate comet formation. We observed that in addition to N-WASP, WAVE3 also induced short actin tails, and the other WAVEs induced formation of asymmetric actin shells. Differences in shape and structure of actin-based growth may reflect varying ability of WASP/WAVE proteins to break symmetry of the actin shell, possibly by differential recruitment of actin bundling or severing (pruning or debranching) factors.

Evidence for participation of uterine natural killer cells in the mechanisms responsible for spontaneous preterm labor and delivery.

OBJECTIVE: The purpose of this study was to determine in a mouse model whether uterine natural killer (uNK) cell cytotoxic activation induces infection/inflammation-associated preterm labor and delivery. STUDY DESIGN: Wild type or interleukin (IL)-10(-/-) mice were injected intraperitoneally with lipopolysaccharide on gestational day 14. Mice were either killed for collection of uteroplacental tissue, spleen, and serum or allowed to deliver. Uteroplacental tissue was used for histology and characterization of uNK cells. RESULTS: Low-dose lipopolysaccharide treatment triggered preterm labor and delivery in IL-10(-/-), but not wild type mice, in a manner independent of progesterone levels. Preterm labor and delivery in IL-10(-/-) mice was associated with an increased number and placental infiltration of cytotoxic uNK cells and placental cell death. Depletion of NK cells or tumor necrosis factor (TNF)-alpha neutralization in these mice restored term delivery. Furthermore, TNF-alpha neutralization prevented uNK cell infiltration and placental cell apoptosis. CONCLUSION: The uNK cell-TNF-alpha-IL-10 axis plays an important role in the genesis of infection/inflammation-induced preterm labor/delivery.

Roles of RhoA and Rac1 on actin remodeling and cell alignment and differentiation in fetal type II epithelial cells exposed to cyclic mechanical stretch.

Mechanical forces are critical for normal fetal lung development. However, the signaling events that promote lung maturation are not fully understood. In this study, the authors analyzed the role of Rho family guanidine triphosphatases (GTPases) in isolated embryonic day 19 (E19) fetal type II epithelial cells exposed to 5% cyclic stretch. The results showed that mechanical strain stimulated RhoA within 5 minutes of initiation of force. Rac1 was also activated, but not Cdc42. After 6 hours of equibiaxial stretch, actin filaments were oriented parallel to the long axis of the cells. By 16 hours, actin fibers still maintained the same orientation, but their intensity decreased when compared to 6 hours. These findings temporally correlated with a decrease in RhoA stimulation. Using adenoviruses encoding dominant negative mutants of RhoA and Rac1, the authors observed that both GTPases are important for strain-induced stress fiber formation, cell alignment, and extracellular signal-regulated kinase (ERK) phosphorylation. However, whereas inhibition of Rho increased surfactant protein C (SP-C) mRNA expression (a marker of type II cell differentiation), suppression of Rac had no effects. These studies suggest that RhoA and Rac1 regulate actin remodeling and cell alignment in fetal type II cells exposed to mechanical stretch. RhoA is a negative regulator of stretch-induced type II cell maturation.

A novel indole ethyl isothiocyanate (7Me-IEITC) with anti-proliferative and pro-apoptotic effects on platinum-resistant human ovarian cancer cells.

OBJECTIVE: A novel indole ethyl isothiocyanate derivative (7Me-IEITC) was defined as a potent growth-suppressing agent to cell lines derived from ovarian cancers. Key mechanisms of the cellular response in vitro were studied and suggest a potential of 7Me-IEITC as a therapeutic drug. METHODS: The viability of ovarian cancer cell lines (SKOV-3, OVCAR-3) in comparison to pancreatic and prostate cancer cell lines, primary fibroblast and immortalized trophoblasts after treatment with 7Me-IEITC was analyzed. Morphological and apoptotic responses of SKOV-3 were studied by fluorescence microscopy (DAPI staining, TUNEL assay). SKOV-3 proliferation was estimated by a standardized BrdU incorporation assay. The phosphorylation of MAP-Kinases, pro-survival factors and the activation of caspases and PARP-1 were analyzed by western blotting. Changes of the mitochondrial transmembrane-potential and in cell-cycle progression were studied by FACS analysis. MAP-Kinase and caspase inhibitors were employed in cytotoxicity studies. RESULTS: 7Me-IEITC selectively reduced the viability of SKOV-3, OVCAR-3, BXPC-3 and PC-3 cells (IC(50) values < or = 5 microM), while the viability of fibroblasts or trophoblasts remained un-affected at concentrations below 20 microM. 7Me-IEITC treatment down-regulated pro-survival kinases and transcription factors (STAT-3, IKKalpha and NF-kappaB), caused rapid loss of the mitochondrial transmembrane-potential and inactivation of PARP-1 along with activation of caspases. The use of p38 MAP-Kinase-and caspase inhibitors suppressed the cytotoxicity of the drug. 7Me-IEITC acted as an anti-proliferative agent and arrested the cell-cycle progression of SKOV-3 in G2/M phase. CONCLUSION: 7Me-IEITC is a potent and growth-suppressing agent to cell lines derived from ovarian cancers by causing deactivation of survival signals, apoptosis, and cell-cycle arrest.

TRAIL is a novel antiviral protein against dengue virus.

Dengue fever is an important tropical illness for which there is currently no virus-specific treatment. To shed light on mechanisms involved in the cellular response to dengue virus (DV), we assessed gene expression changes, using Affymetrix GeneChips (HG-U133A), of infected primary human cells and identified changes common to all cells. The common response genes included a set of 23 genes significantly induced upon DV infection of human umbilical vein endothelial cells (HUVECs), dendritic cells (DCs), monocytes, and B cells (analysis of variance, P < 0.05). Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), one of the common response genes, was identified as a key link between type I and type II interferon response genes. We found that DV induces TRAIL expression in immune cells and HUVECs at the mRNA and protein levels. The induction of TRAIL expression by DV was found to be dependent on an intact type I interferon signaling pathway. A significant increase in DV RNA accumulation was observed in anti-TRAIL antibody-treated monocytes, B cells, and HUVECs, and, conversely, a decrease in DV RNA was seen in recombinant TRAIL-treated monocytes. Furthermore, recombinant TRAIL inhibited DV titers in DV-infected DCs by an apoptosis-independent mechanism. These data suggest that TRAIL plays an important role in the antiviral response to DV infection and is a candidate for antiviral interventions against DV.

Early response of endothelial cells to flow is mediated by VE-cadherin.

Endothelial cells are known to respond to flow onset by increasing actin turnover rate. Current models assume that an increase in the actin turnover rate should result in a rise in cell crawling speed. Here we report that confluent endothelial monolayer shows an unexpected behavior: cell crawling speed decreases by approximately 40% within the first 30 min of flow onset. A drop in crawling speed has not been observed in either subconfluent endothelial cells or in VE-cadherin-deficient cells. We found that flow onset caused an increase in the number of VE-cadherin-GFP molecules in the junctions and elicited changes in the cytoskeleton-associated fractions of alpha, beta -catenins and VE-cadherin. Flow application also increased the strength of interactions of endothelial cells with surfaces coated with recombinant VE-cadherin. These observations suggest that endothelial cell junctional proteins respond to flow transiently by increasing the strength of intercellular attachments early after flow onset and support the view on the active role of intercellular adhesions in mechanotransduction.

Endothelial cell cortactin coordinates intercellular adhesion molecule-1 clustering and actin cytoskeleton remodeling during polymorphonuclear leukocyte adhesion and transmigration.

Endothelial cell ICAM-1 interacts with leukocyte beta(2) integrins to mediate adhesion and transmit outside-in signals that facilitate leukocyte transmigration. ICAM-1 redistribution and clustering appear necessary for leukocyte transmigration, but the mechanisms controlling ICAM-1 redistribution and clustering have not been identified. We recently reported that Src kinase phosphorylation of endothelial cortactin regulates polymorphonuclear cell (PMN) transmigration. In this study, we tested the hypotheses that the Src family kinase-cortactin pathway mediates association of ICAM-1 with the actin cytoskeleton and that this association is required for ICAM-1 clustering and leukocyte transmigration. Cross-linking ICAM-1 induced cytoskeletal remodeling and a decrease in ICAM-1 lateral mobility, as assessed by fluorescence recovery after photobleaching. Cytoskeletal remodeling after ICAM-1 cross-linking was reduced by knockdown of cortactin by small interfering RNA, by expression of a cortactin mutant deficient in Src phosphorylation sites (cortactin3F), and by the Src kinase inhibitor PP2. Pretreatment of cytokine-activated human endothelial monolayers with cortactin small interfering RNA significantly decreased both actin and ICAM-1 clustering around adherent PMN and the formation of actin-ICAM-1 clusters required for PMN transmigration. Our data suggest a model in which tyrosine phosphorylation of cortactin dynamically links ICAM-1 to the actin cytoskeleton, enabling ICAM-1 to form clusters and facilitate leukocyte transmigration.

Discovering innate immunity genes using differential display: a story of RNA helicases.

In this review we discuss the current literature for RNA helicases in response to RNA virus infection. We show the use of Differential Display Reverse Transcription PCR methodology (DD) to analyze virus-host interactions and we present current findings in dengue virus-induced gene expression of RNA helicases.

Emerging topics in the regulation of leukocyte transendothelial migration.

This year marks the 50th Anniversary of the founding of the Microcirculatory Society. Since the formation of this society this field has witnessed tremendous progress in understanding the process of leukocyte recruitment during inflammation, injury, and immune reactions. This topic has been an important focus of many of the members of the Microcirculatory Society as well as our colleagues worldwide. The goal of this brief review is to bring attention to a few emerging topics in inflammation research. Here the focus is on one particular model of how one leukocyte type (PMN) can regulate the recruitment of a second different leukocyte type (T cell) and provide an outline of other aspects that bear on spatial and temporal behavior of specific leukocyte and endothelial cell adhesion molecules during leukocyte transmigration under dynamic shear flow in vitro.

Regulation of vascular endothelial barrier function by Epac, a cAMP-activated exchange factor for Rap GTPase.

Endothelial cell-cell junctional proteins and cortical actin are of central importance for regulating vascular permeability. Rap1, a member of the Ras family of GTPases, is enriched at endothelial cell-cell contacts and activated by cyclic AMP (cAMP) through a PKA-independent pathway. Activation of a cAMP-inducible guanine-exchange factor for Rap, Epac, results in markedly enhanced basal endothelial barrier function by increasing cortical actin and subsequent redistribution of adherens and tight junctional molecules to cell-cell contacts. Activation of Epac also counteracts thrombin-induced hyperpermeability through down-regulation of Rho GTPase activation, suggesting cross-talk between Rap and Rho GT-Pases. Thus, Epac/Rap activation represents a new pathway for regulating endothelial cell barrier function.

Coordinated redistribution of leukocyte LFA-1 and endothelial cell ICAM-1 accompany neutrophil transmigration.

The leukocyte integrin lymphocyte function-associated antigen 1 (LFA-1) and its endothelial ligand intercellular adhesion molecule (ICAM)-1 play an important role in transmigration as demonstrated by in vivo and in vitro models of inflammation. Despite the prominent role, little is known concerning the distribution and dynamic behavior of these adhesion molecules during leukocyte transmigration. Therefore, we examined the spatial and temporal distribution of LFA-1 on neutrophils actively transmigrating tumor necrosis factor-alpha-activated human umbilical vein endothelial monolayers under shear flow. Upon neutrophil arrest, LFA-1 was evenly distributed. However, once neutrophils initiated transmigration, LFA-1 rapidly redistributed to form a ringlike cluster at the neutrophil-endothelial junctional interface through which transmigration occurred. As transmigration was completed, LFA-1 redistributed to the neutrophil uropod. Endothelial ICAM-1 and JAM-A both colocalized with the ringlike LFA-1 cluster. Further analysis of PMA-stimulated neutrophils, which increase mobility of LFA-1, showed a rapid redistribution of LFA-1 and ICAM-1, but not endothelial JAM-A. Thus, endothelial JAM-A does not appear to contribute to adhesion or transmigration in this system. This is the first demonstration that neutrophil LFA-1 rapidly redistributes to form a ringlike structure that coclusters with endothelial ICAM-1 as the neutrophil transmigrates.