Sensitive and accurate quantification of human leukocyte migration using high-content Discovery-1 imaging system and ATPlite assay

Cell-based actin polymerization assay to analyze chemokine inhibitors

Chemokines play an important role in various diseases as signaling molecules for immune cells. Therefore, the inhibition of the chemokine-receptor interaction and the characterization of potential inhibitors are important steps in the development of new therapies. Here, we present a new cell-based assay for chemokine-receptor interaction, using chemokine-dependent actin polymerization as a readout. We used interleukin-8 (IL-8, CXCL8) as a model chemokine and measured the IL-8-dependent actin polymerization with Atto565-phalloidin by monitoring the fluorescence intensity in the cell layer after activation with IL-8. This assay needs no transfection, is easy to perform and requires only a few working steps. It can be used to confirm receptor activation and to characterize the effect of chemokine receptor antagonists. Experiments with the well-known CXCR1/2 inhibitor reparixin confirmed that the observed increase in fluorescence intensity is a result of chemokine receptor activation and can be inhibited in a dose-dependent manner. With optimized parameters, the difference between positive and negative control was highly significant and statistical Z´-factors of 0.4 were determined on average.

The functional and inflammatory response of brain endothelial cells to Toll-Like Receptor agonists

Toll-Like receptors (TLRs) represent an important early warning mechanism for the immune system to detect infection or tissue damage. The focus of this research was to determine the neuroinflammatory responses to commercial TLR ligands and their effects on brain endothelial barrier strength. Using biosensor technology we screened TLR ligands to all human TLRs and found that the brain endothelial hCMVECs cell line only responded to Poly(I:C) (TLR3-ligand), LPS (TLR4-ligand) and Imiquimod (TLR7 ligand). Both Poly(I:C) and LPS induced pronounced pro-inflammatory cytokine secretion as expected, whereas Imiquimod did not induce secretion of any pro-inflammatory cytokines. Using ECIS technology to measure endothelial barrier function, LPS and Poly(I:C) both acutely reduced barrier-strength, whereas Imiquimod caused immediate and sustained strengthening of the barrier. Further cytokine and ECIS studies showed that Imiquimod could abrogate some of the pro-inflammatory responses to Poly(I:C) and LPS. Most surprisingly, PCR revealed that the hCMVECs lacked TLR7 but expressed both TLR3 and TLR4 and did not respond to other structurally different TLR7 ligands. These data demonstrate that brain endothelial cells can be regulated by TLR 3 and TLR4 ligands in a pro-inflammatory manner and have receptors to Imiquimod, distinct to the classical TLR7, that function in an anti-inflammatory manner.

A Broad-Spectrum Chemokine-Binding Protein of Bovine Papular Stomatitis Virus Inhibits Neutrophil and Monocyte Infiltration in Inflammatory and Wound Models of Mouse Skin

Bovine papular stomatitis virus (BPSV) is a Parapoxvirus that induces acute pustular skin lesions in cattle and is transmissible to humans. Previous studies have shown that BPSV encodes a distinctive chemokine-binding protein (CBP). Chemokines are critically involved in the trafficking of immune cells to sites of inflammation and infected tissue, suggesting that the CBP plays a role in immune evasion by preventing immune cells reaching sites of infection. We hypothesised that the BPSV-CBP binds a wide range of inflammatory chemokines particularly those involved in BPSV skin infection, and inhibits the recruitment of immune cells from the blood into inflamed skin. Molecular analysis of the purified protein revealed that the BPSV-CBP is a homodimeric polypeptide with a MW of 82.4 kDa whilst a comprehensive screen of inflammatory chemokines by surface plasmon resonance showed high-affinity binding to a range of chemokines within the CXC, CC and XC subfamilies. Structural analysis of BPSV-CBP, based on the crystal structure of orf virus CBP, provided a probable explanation for these chemokine specificities at a molecular level. Functional analysis of the BPSV-CBP using transwell migration assays demonstrated that it potently inhibited chemotaxis of murine neutrophils and monocytes in response to CXCL1, CXCL2 as well as CCL2, CCL3 and CCL5 chemokines. In order to examine the effects of CBP in vivo, we used murine skin models to determine its impact on inflammatory cell recruitment such as that observed during BPSV infection. Intradermal injection of BPSV-CBP blocked the influx of neutrophils and monocytes in murine skin in which inflammation was induced with lipopolysaccharide. Furthermore, intradermal injection of BPSV-CBP into injured skin, which more closely mimics BPSV lesions, delayed the influx of neutrophils and reduced the recruitment of MHC-II+ immune cells to the wound bed. Our findings suggest that the CBP could be important in pathogenesis of BPSV infections.

SLIT2/ROBO2 signaling pathway inhibits nonmuscle myosin IIA activity and destabilizes kidney podocyte adhesion

The repulsive guidance cue SLIT2 and its receptor ROBO2 are required for kidney development and podocyte foot process structure, but the SLIT2/ROBO2 signaling mechanism regulating podocyte function is not known. Here we report that a potentially novel signaling pathway consisting of SLIT/ROBO Rho GTPase activating protein 1 (SRGAP1) and nonmuscle myosin IIA (NMIIA) regulates podocyte adhesion downstream of ROBO2. We found that the myosin II regulatory light chain (MRLC), a subunit of NMIIA, interacts directly with SRGAP1 and forms a complex with ROBO2/SRGAP1/NMIIA in the presence of SLIT2. Immunostaining demonstrated that SRGAP1 is a podocyte protein and is colocalized with ROBO2 on the basal surface of podocytes. In addition, SLIT2 stimulation inhibits NMIIA activity, decreases focal adhesion formation, and reduces podocyte attachment to collagen. In vivo studies further showed that podocyte-specific knockout of Robo2 protects mice from hypertension-induced podocyte detachment and albuminuria and also partially rescues the podocyte-loss phenotype in Myh9 knockout mice. Thus, we have identified SLIT2/ROBO2/SRGAP1/NMIIA as a potentially novel signaling pathway in kidney podocytes, which may play a role in regulating podocyte adhesion and attachment. Our findings also suggest that SLIT2/ROBO2 signaling might be a therapeutic target for kidney diseases associated with podocyte detachment and loss.

Plasmin and regulators of plasmin activity control the migratory capacity and adhesion of human T cells and dendritic cells by regulating cleavage of the chemokine CCL21

The homeostatic chemokine CCL21 has a pivotal role in lymphocyte homing and compartment localisation within the lymph node, and also affects adhesion between immune cells. The effects of CCL21 are modulated by its mode of presentation, with different cellular responses seen for surface-bound and soluble forms. Here we show that plasmin cleaves surface-bound CCL21 to release the C-terminal peptide responsible for CCL21 binding to glycosaminoglycans on the extracellular matrix and cell surfaces, thereby generating the soluble form. Loss of this anchoring peptide enabled the chemotactic activity of CCL21 and reduced cell tethering. Tissue plasminogen activator did not cleave CCL21 directly but enhanced CCL21 processing through generation of plasmin from plasminogen. The tissue plasminogen activator inhibitor neuroserpin prevented processing of CCL21 and blocked the effects of soluble CCL21 on cell migration. Similarly, the plasmin-specific inhibitor α2-antiplasmin inhibited CCL21-mediated migration of human T cells and dendritic cells and tethering of T cells to APCs. We conclude that the plasmin system proteins plasmin, tissue plasminogen activator and neuroserpin regulate CCL21 function in the immune system by controlling the balance of matrix- and cell-bound CCL21.

Application of xCELLigence RTCA Biosensor Technology for Revealing the Profile and Window of Drug Responsiveness in Real Time

The xCELLigence technology is a real-time cellular biosensor, which measures the net adhesion of cells to high-density gold electrode arrays printed on custom-designed E-plates. The strength of cellular adhesion is influenced by a myriad of factors that include cell type, cell viability, growth, migration, spreading and proliferation. We therefore hypothesised that xCELLigence biosensor technology would provide a valuable platform for the measurement of drug responses in a multitude of different experimental, clinical or pharmacological contexts. In this manuscript, we demonstrate how xCELLigence technology has been invaluable in the identification of (1) not only if cells respond to a particular drug, but (2) the window of drug responsiveness. The latter aspect is often left to educated guess work in classical end-point assays, whereas biosensor technology reveals the temporal profile of the response in real time, which enables both acute responses and longer term responses to be profiled within the same assay. In our experience, the xCELLigence biosensor technology is suitable for highly targeted drug assessment and also low to medium throughput drug screening, which produces high content temporal data in real time.

Exposure to inflammatory cytokines IL-1β and TNFα induces compromise and death of astrocytes; implications for chronic neuroinflammation

Background

Astrocytes have critical roles in the human CNS in health and disease. They provide trophic support to neurons and are innate-immune cells with keys roles during states-of-inflammation. In addition, they have integral functions associated with maintaining the integrity of the blood-brain barrier.

Methods

We have used cytometric bead arrays and xCELLigence technology to monitor the to monitor the inflammatory response profiles and astrocyte compromise in real-time under various inflammatory conditions. Responses were compared to a variety of inflammatory cytokines known to be released in the CNS during neuroinflammation. Astrocyte compromise measured by xCELLigence was confirmed using ATP measurements, cleaved caspase 3 expression, assessment of nuclear morphology and cell death.

Results

Inflammatory activation (IL-1β or TNFα) of astrocytes results in the transient production of key inflammatory mediators including IL-6, cell surface adhesion molecules, and various leukocyte chemoattractants. Following this phase, the NT2-astrocytes progressively become compromised, which is indicated by a loss of adhesion, appearance of apoptotic nuclei and reduction in ATP levels, followed by DEATH.

The earliest signs of astrocyte compromise were observed between 24-48h post cytokine treatment. However, significant cell loss was not observed until at least 72h, where there was also an increase in the expression of cleaved-caspase 3. By 96 hours approximately 50% of the astrocytes were dead, with many of the remaining showing signs of compromise too. Numerous other inflammatory factors were tested, however these effects were only observed with IL-1β or TNFα treatment.

Conclusions

Here we reveal direct sensitivity to mediators of the inflammatory milieu. We highlight the power of xCELLigence technology for revealing the early progressive compromise of the astrocytes, which occurs 24-48 hours prior to substantive cell loss. Death induced by IL-1β or TNFα is relevant clinically as these two cytokines are produced by various peripheral tissues and by resident brain cells.

Membrane configuration optimization for a murine in vitro blood-brain barrier model

A powerful experimental tool used to study the dynamic functions of the blood-brain barrier (BBB) is an in vitro cellular based system utilizing cell culture inserts in multi-well plates. Currently, usage of divergent model configurations without explanation of selected variable set points renders data comparisons difficult and limits widespread understanding. This work presents for the first time in literature a comprehensive screening study to optimize membrane configuration, with aims to unveil influential membrane effects on the ability of cerebral endothelial cells to form a tight monolayer. First, primary murine brain endothelial cells and astrocytes were co-cultured in contact and non-contact orientations on membranes of pore diameter sizes ranging from 0.4 μm to 8.0 μm, and the non-contact orientation and smallest pore diameter size were shown to support a significantly tighter monolayer formation. Then, membranes made from polyethylene terephthalate (PET) and polycarbonate (PC) purchased from three different commercial sources were compared, and PET membranes purchased from two manufacturers facilitated a significantly tighter monolayer formation. Models were characterized by transendothelial electrical resistance (TEER), sodium fluorescein permeability, and immunocytochemical labeling of tight junction proteins. Finally, a murine brain endothelial cell line, bEnd.3, was grown on the different membranes, and similar results were obtained with respect to optimal membrane configuration selection. The results and methodology presented here on high throughput 24-well plate inserts can be translated to other BBB systems to advance model understanding.