TrackSOM: Mapping immune response dynamics through clustering of time-course cytometry data.

Mapping the dynamics of immune cell populations over time or disease-course is key to understanding immunopathogenesis and devising putative interventions. We present TrackSOM, a novel method for delineating cellular populations and tracking their development over a time- or disease-course cytometry datasets. We demonstrate TrackSOM-enabled elucidation of the immune response to West Nile Virus infection in mice, uncovering heterogeneous subpopulations of immune cells and relating their functional evolution to disease severity. TrackSOM is easy to use, encompasses few parameters, is quick to execute, and enables an integrative and dynamic overview of the immune system kinetics that underlie disease progression and/or resolution.

Optimal Isolation Protocols for Examining and Interrogating Mononuclear Phagocytes From Human Intestinal Tissue.

The human intestine contains numerous mononuclear phagocytes (MNP), including subsets of conventional dendritic cells (cDC), macrophages (Mf) and monocytes, each playing their own unique role within the intestinal immune system and homeostasis. The ability to isolate and interrogate MNPs from fresh human tissue is crucial if we are to understand the role of these cells in homeostasis, disease settings and immunotherapies. However, liberating these cells from tissue is problematic as many of the key surface identification markers they express are susceptible to enzymatic cleavage and they are highly susceptible to cell death. In addition, the extraction process triggers immunological activation/maturation which alters their functional phenotype. Identifying the evolving, complex and highly heterogenous repertoire of MNPs by flow cytometry therefore requires careful selection of digestive enzyme blends that liberate viable cells and preserve recognition epitopes involving careful selection of antibody clones to enable analysis and sorting for functional assays. Here we describe a method for the anatomical separation of mucosa and submucosa as well as isolating lymphoid follicles from human jejunum, ileum and colon. We also describe in detail the optimised enzyme digestion methods needed to acquire functionally immature and biologically functional intestinal MNPs. A comprehensive list of screened antibody clones is also presented which allows for the development of high parameter flow cytometry panels to discriminate all currently identified human tissue MNP subsets including pDCs, cDC1, cDC2 (langerin+ and langerin-), newly described DC3, monocytes, Mf1, Mf2, Mf3 and Mf4. We also present a novel method to account for autofluorescent signal from tissue macrophages. Finally, we demonstrate that these methods can successfully be used to sort functional, immature intestinal DCs that can be used for functional assays such as cytokine production assays.

Visualizing murine breast and melanoma tumor microenvironment using intravital multiphoton microscopy.

Intravital multiphoton imaging of the tumor milieu allows for the dissection of intricate and dynamic biological processes in situ. Herein, we present a step-by-step protocol for setting up an experimental cancer imaging model that has been optimized for solid tumors such as breast cancer and melanoma implanted in the flanks of mice. This protocol can be utilized for dissecting tumor-immune cell dynamics in vivo or other tumor-specific biological questions. For complete details on the use of this protocol for intravital imaging of breast cancer, please refer to Tikoo et al. (2021a), and for intravital imaging of melanoma, please refer to Tikoo et al. (2021b).

Monocyte M1/M2 profile is altered in paediatric burn patients with hypertrophic scarring.

Hypertrophic scars (HTS) remain a common outcome of burn injury, particularly in children. They can arise from variations in the wound healing stages, such as an excessive inflammatory response or inefficient remodelling. Of the cells contributing to these healing stages, macrophages and fibrocytes are crucial. Specifically, the inflammatory phase is dominated by M1 macrophages, the proliferation/remodelling stages by M2 macrophages, and scar tissue contains numerous fibrocytes. As the progenitors to these cells, monocytes, can also exhibit M1- and M2-skewing, we proposed that their profile, or circulating fibrocyte counts, could be used to predict poor healing outcomes. To investigate this, we obtained blood samples from paediatric controls and burns patients, which were then divided into HTS and NoHTS groups upon scar assessment at 12 months. The samples were assessed by whole blood flow cytometry to quantify fibrocytes and monocyte subset proportions and to determine monocyte levels of M1 (CD86, CD120b, CD319) and M2 (CD93, CD163, CD200R) markers. Both burns groups had higher proportions of classical monocytes compared to controls, indicating increased cell turnover and/or entry of other subsets into the wound. In burns patients who took more than 21 days to heal, the HTS group had lower M2 (CD200R) expression with the ratio of M1/M2 (CD86/CD200R) being significantly higher. These results suggest an elevated early inflammatory monocyte response contributes to development of HTS. Correlations of marker expression with remaining healing time revealed a significant positive correlation with M1 (CD120b) and M1/M2 (CD120b/CD200R), suggesting a potential role for CD120b as an indicator of healing delay. Fibrocytes did not significantly differ between the groups. In conclusion, increased monocyte inflammation likely contributes to slower healing and development of scarring, but further studies are needed to determine the predictive power of monocyte inflammatory profile.

Core liver homeostatic co-expression networks are preserved but respond to perturbations in an organism- and disease-specific manner.

Findings about chronic complex diseases are difficult to extrapolate from animal models to humans. We reason that organs may have core network modules that are preserved between species and are predictably altered when homeostasis is disrupted. To test this idea, we perturbed hepatic homeostasis in mice by dietary challenge and compared the liver transcriptome with that in human fatty liver disease and liver cancer. Co-expression module preservation analysis pointed to alterations in immune responses and metabolism (core modules) in both human and mouse datasets. The extent of derailment in core modules was predictive of survival in the cancer genome atlas (TCGA) liver cancer dataset. We identified module eigengene quantitative trait loci (module-eQTL) for these predictive co-expression modules, targeting of which may resolve homeostatic perturbations and improve patient outcomes. The framework presented can be used to understand homeostasis at systems levels in pre-clinical models and in humans. A record of this paper's transparent peer review process is included in the supplemental information.

Plasmacytoid dendritic cells have divergent effects on HIV infection of initial target cells and induce a pro-retention phenotype.

Although HIV infection inhibits interferon responses in its target cells in vitro, interferon signatures can be detected in vivo soon after sexual transmission, mainly attributed to plasmacytoid dendritic cells (pDCs). In this study, we examined the physiological contributions of pDCs to early HIV acquisition using coculture models of pDCs with myeloid DCs, macrophages and the resting central, transitional and effector memory CD4 T cell subsets. pDCs impacted infection in a cell-specific manner. In myeloid cells, HIV infection was decreased via antiviral effects, cell maturation and downregulation of CCR5 expression. In contrast, in resting memory CD4 T cells, pDCs induced a subset-specific increase in intracellular HIV p24 protein expression without any activation or increase in CCR5 expression, as measured by flow cytometry. This increase was due to reactivation rather than enhanced viral spread, as blocking HIV entry via CCR5 did not alter the increased intracellular p24 expression. Furthermore, the load and proportion of cells expressing HIV DNA were restricted in the presence of pDCs while reverse transcriptase and p24 ELISA assays showed no increase in particle associated reverse transcriptase or extracellular p24 production. In addition, pDCs also markedly induced the expression of CD69 on infected CD4 T cells and other markers of CD4 T cell tissue retention. These phenotypic changes showed marked parallels with resident memory CD4 T cells isolated from anogenital tissue using enzymatic digestion. Production of IFNα by pDCs was the main driving factor for all these results. Thus, pDCs may reduce HIV spread during initial mucosal acquisition by inhibiting replication in myeloid cells while reactivating latent virus in resting memory CD4 T cells and retaining them for immune clearance.

Immunophenotyping of Peripheral Blood Mononuclear Cells in Septic Shock Patients With High-Dimensional Flow Cytometry Analysis Reveals Two Subgroups With Differential Responses to Immunostimulant Drugs.

Sepsis is associated with a dysregulated inflammatory response to infection. Despite the activation of inflammation, an immune suppression is often observed, predisposing patients to secondary infections. Therapies directed at restoration of immunity may be considered but should be guided by the immune status of the patients. In this paper, we described the use of a high-dimensional flow cytometry (HDCyto) panel to assess the immunophenotype of patients with sepsis. We then isolated peripheral blood mononuclear cells (PBMCs) from patients with septic shock and mimicked a secondary infection by stimulating PBMCs for 4 h in vitro with lipopolysaccharide (LPS) with or without prior exposure to either IFN-γ, or LAG-3Ig. We evaluated the response by means of flow cytometry and high-resolution clustering cum differential analysis and compared the results to PBMCs from healthy donors. We observed a heterogeneous immune response in septic patients and identified two major subgroups: one characterized by hypo-responsiveness (Hypo) and another one by hyper-responsiveness (Hyper). Hypo and Hyper groups showed significant differences in the production of cytokines/chemokine and surface human leukocyte antigen-DR (HLA-DR) expression in response to LPS stimulation, which were observed across all cell types. When pre-treated with either interferon gamma (IFN-γ) or lymphocyte-activation gene 3 (LAG)-3 recombinant fusion protein (LAG-3Ig) prior to LPS stimulation, cells from the Hypo group were shown to be more responsive to both immunostimulants than cells from the Hyper group. Our results demonstrate the importance of patient stratification based on their immune status prior to any immune therapies. Once sufficiently scaled, this approach may be useful for prescribing the right immune therapy for the right patient at the right time, the key to the success of any therapy.

Pharmacologic targeting of renal ischemia-reperfusion injury using a normothermic machine perfusion platform.

Normothermic machine perfusion (NMP) is an emerging modality for kidney preservation prior to transplantation. NMP may allow directed pharmacomodulation of renal ischemia-reperfusion injury (IRI) without the need for systemic donor/recipient therapies. Three proven anti-IRI agents not in widespread clinical use, CD47-blocking antibody (αCD47Ab), soluble complement receptor 1 (sCR1), and recombinant thrombomodulin (rTM), were compared in a murine model of kidney IRI. The most effective agent was then utilized in a custom NMP circuit for the treatment of isolated porcine kidneys, ascertaining the impact of the drug on perfusion and IRI-related parameters. αCD47Ab conferred the greatest protection against IRI in mice after 24 hours. αCD47Ab was therefore chosen as the candidate agent for addition to the NMP circuit. CD47 receptor binding was demonstrated by immunofluorescence. Renal perfusion/flow improved with CD47 blockade, with a corresponding reduction in oxidative stress and histologic damage compared to untreated NMP kidneys. Tubular and glomerular functional parameters were not significantly impacted by αCD47Ab treatment during NMP. In a murine renal IRI model, αCD47Ab was confirmed as a superior anti-IRI agent compared to therapies targeting other pathways. NMP enabled effective, direct delivery of this drug to porcine kidneys, although further efficacy needs to be proven in the transplantation setting.

Standardisation of flow cytometry for whole blood immunophenotyping of islet transplant and transplant clinical trial recipients.

Understanding the immunological phenotype of transplant recipients is important to improve outcomes and develop new therapies. Immunophenotyping of whole peripheral blood (WPB) by flow cytometry is a rapid method to obtain large amounts of data relating to the outcomes of different transplant treatments with limited patient impact. Healthy individuals and patients with type 1 diabetes (T1D) enrolled in islet transplantation were recruited and WPB was collected. 46 fluorochrome-conjugated mouse-anti-human antibodies were used (43 of 46 antibodies were titrated). BD cytometer setup and tracking beads were used to characterize and adjust for cytometer performance. Antibody cocktails were pre-mixed <60 minutes before staining. Multicolour panels were designed based on fluorochrome brightness, antigen density, co-expression, and fluorochrome spillover into non-primary detectors in each panel on a 5 laser flow cytometer. WPB sample staining used 50-300 µl WPB for each panel and was performed within 2 hours of blood sample collection. Samples were acquired on a BD-LSRFortessa. The operating procedures, including specimen collection, antibody cocktails, staining protocol, flow-cytometer setup and data analysis, were standardized. The staining index of 43 antibodies and the spillover spreading matrix for each panel was calculated. The final concentrations for the 46 antibodies used was determined for staining of WPB samples. Absolute cell-count and 7 leukocyte profiling panels consisting of subsets and/or status of granulocytes, monocytes, dendritic, B, NK, and T cells including regulatory T cells (Tregs) and NKT were designed and established on a 5 laser BD-LSR Fortessa. 13 T1D patients, including 4 islet transplant recipients and 8 healthy controls, were evaluated. The ability to reproducibly measure immune subsets and immune-profiles of islet transplant patients up to 18 months post transplantation has been established as a tool to measure immune cell reconstitution after transplantation.

Activated protein C targets immune cells and rheumatoid synovial fibroblasts to prevent inflammatory arthritis in mice.

OBJECTIVES: To investigate whether activated protein C (APC), a physiological anticoagulant can inhibit the inflammatory/invasive properties of immune cells and rheumatoid arthritis synovial fibroblasts (RASFs) in vitro and prevent inflammatory arthritis in murine antigen-induced arthritis (AIA) and CIA models. METHODS: RASFs isolated from synovial tissues of patients with RA, human peripheral blood mononuclear cells (PBMCs) and mouse thymus cells were treated with APC or TNF-α/IL-17 and the following assays were performed: RASF proliferation and invasion by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) and cell invasion assays, respectively; cytokines and signalling molecules using ELISA or western blot; Th1 and Th17 phenotypes in human PBMCs or mouse thymus cells by flow cytometry. The in vivo effect of APC was evaluated in AIA and CIA models. RESULTS: In vitro, APC inhibited IL-1ß, IL-17 and TNF-α production, IL-17-stimulated cell proliferation and invasion and p21 and nuclear factor κB activation in RASFs. In mouse thymus cells and human PBMCs, APC suppressed Th1 and Th17 phenotypes. In vivo, APC inhibited pannus formation, cartilage destruction and arthritis incidence/severity in both CIA and AIA models. In CIA, serum levels of IL-1ß, IL-6, IL-17, TNF-α and soluble endothelial protein C receptor were significantly reduced by APC treatment. Blocking endothelial protein C receptor, the specific receptor for APC, abolished the early or preventative effect of APC in AIA. CONCLUSION: APC prevents the onset and development of arthritis in CIA and AIA models via suppressing inflammation, Th1/Th17 phenotypes and RASF invasion, which is likely mediated via endothelial protein C receptor.

Isolation of Human Skin Epidermal Stem Cells Based on the Expression of Endothelial Protein C Receptor.

Skin epidermis is a continuous self-renewal tissue maintained by interfollicular epidermal stem cells (IESCs) that reside in the basal layer of epidermis. IESCs also contribute to the repair and regeneration of the epidermis during wound healing. The great plasticity and easy accessibility afforded by IESCs make them a promising source of stem cells for scientific research and clinical applications. Thus, simple methods to isolate and define pure and viable IESCs are a valuable resource. Here, we provide a method for isolating IESCs from human skin epidermis. This method relies exclusively on selecting cells with a higher expression of the endothelial protein C receptor, using fluorescence-activated cell sorting.

Novel Surrogate Markers of CNS Inflammation in CSF in the Diagnosis of Autoimmune Encephalitis.

Background: Autoimmune encephalitis (AE) is an important cause of refractory epilepsy, rapidly progressive cognitive decline, and unexplained movement disorders in adults. Whilst there is identification of an increasing number of associated autoantibodies, patients remain with a high clinical probability of autoimmune encephalitis but no associated characterized autoantibody. These patients represent a diagnostic and treatment dilemma. Objective: To evaluate routine and novel diagnostic tests of cerebrospinal fluid (CSF) in patients with a high probability of AE to attempt to identify better biomarkers of neuroinflammation. Methods: Over 18 months (2016-2018), adult patients with a high clinical probability of AE were recruited for a pilot cross-sectional explorative study. We also included viral polymerase-chain-reaction (PCR) positive CSF samples and CSF from neurology patients with "non-inflammatory" (NI) diagnoses for comparison. CSF was examined with standard investigations for encephalitis and novel markers (CSF light chains, and cytokines). Results and Conclusions: Thirty-two AE patients were recruited over 18 months. Twenty-one viral controls, 10 NI controls, and five other autoimmune neurological disease controls (AOND) were also included in the analysis. Our study found that conventional markers: presence of CSF monocytosis, oligoclonal bands, anti-neuronal immunofluorescence, and magnetic resonance imaging (MRI) changes could be suggestive of AE, but these investigations were neither sensitive nor specific. Promising novel makers of autoimmune encephalitis were the CSF cytokines IL-21 and IP10 which may provide better delineation between viral infections and autoimmune encephalitis than conventional markers, potentially leading to more immediate diagnosis and management of these patients.

Characterization of Human Monocyte Subsets by Whole Blood Flow Cytometry Analysis.

Monocytes are key contributors in various inflammatory disorders and alterations to these cells, including their subset proportions and functions, can have pathological significance. An ideal method for examining alterations to monocytes is whole blood flow cytometry as the minimal handling of samples by this method limits artifactual cell activation. However, many different approaches are taken to gate the monocyte subsets leading to inconsistent identification of the subsets between studies. Here we demonstrate a method using whole blood flow cytometry to identify and characterize human monocyte subsets (classical, intermediate, and non-classical). We outline how to prepare the blood samples for flow cytometry, gate the subsets (ensure contaminating cells have been removed), and determine monocyte subset expression of surface markers - in this example M1 and M2 markers. This protocol can be extended to other studies that require a standard gating method for assessing monocyte subset proportions and monocyte subset expression of other functional markers.

The Endothelial Protein C Receptor Is a Potential Stem Cell Marker for Epidermal Keratinocytes.

Endothelial protein C receptor (EPCR) is a specific receptor for anticoagulant protein C and expressed by human epidermis and cultured keratinocytes. Here we investigated whether: (a) the level of EPCR in keratinocytes is associated with their growth potential; and (b) EPCR is a potential marker for human epidermal stem cells. Human keratinocytes isolated from foreskins or adult skin tissues were transfected with EPCR siRNA or EPCR overexpressing plasmids. Cell proliferation, long term proliferation potential, colony forming efficiency (CFE), and in vitro epidermal regeneration ability of EPCRhigh and EPCRl °w cells were assessed. The expression and colocalization of EPCR with stem cell markers p63, integrin ß1, and activation of MAP kinases were detected by flow cytometry, immunofluorescence staining, or Western blot. Results showed that EPCR was highly expressed by the basal layer of skin epidermis. EPCRhigh cells were associated with the highest levels of p63 and integrin ß1. Most EPCRhigh cells were smaller in size, formed larger colonies and had a greater long term growth potential, CFE, holoclone formation, and in vitro epidermal regeneration ability when compared to EPCRl °w cells. Blocking EPCR resulted in keratinocyte apoptosis, particularly in nondifferentiated conditions. Cell proliferation and p63 expression were reduced by blocking EPCR and enhanced by overexpressing this receptor. These data indicate that EPCR can regulate p63, is associated with highly proliferative keratinocytes, and is a potential human epidermal stem cell marker. Stem Cells 2017;35:1786-1798.

A Sample-to-Sequence Protocol for Genus Targeted Transcriptomic Profiling: Application to Marine Synechococcus.

Recent studies using whole community metagenomic and metatranscriptomic approaches are revealing important new insights into the functional potential and activity of natural marine microbial communities. Here, we complement these approaches by describing a complete ocean sample-to-sequence protocol, specifically designed to target a single bacterial genus for purposes of both DNA and RNA profiling using fluorescence activated cell sorting (FACS). The importance of defining and understanding the effects of a sampling protocol are critical if we are to gain meaningful data from environmental surveys. Rigorous pipeline trials with a cultured isolate, Synechococcus sp. BL107 demonstrate that water filtration has a well-defined but limited impact on the transcriptomic profile of this organism, whilst sample storage and multiple rounds of cell sorting have almost no effect on the resulting RNA sequence profile. Attractively, the means to replicate the sampling strategy is within the budget and expertise of most researchers.

Activated protein C inhibits pancreatic islet inflammation, stimulates T regulatory cells, and prevents diabetes in non-obese diabetic (NOD) mice.

Activated protein C (aPC) is a natural anticoagulant with strong cyto-protective and anti-inflammatory properties. aPC inhibits pancreatic inflammation and preserves functional islets after intraportal transplantation in mice. Whether aPC prevents the onset or development of type 1 diabetes (T1D) is unknown. In this study, when human recombinant aPC was delivered intraperitoneally, twice weekly for 10 weeks (from week 6 to 15) to non-obese diabetic (NOD) mice, a model for T1D, the incidence of diabetes was reduced from 70% (saline control) to 7.6% by 26 weeks of age. Islets of aPC-treated mice exhibited markedly increased expression of insulin, aPC/protein C, endothelial protein C receptor, and matrix metalloproteinase (MMP)-2 when examined by immunostaining. The insulitis score in aPC-treated mice was 50% less than that in control mice. T regulatory cells (Tregs) in the spleen, pancreatic islets, and pancreatic lymph nodes were increased 37, 53, and 59%, respectively, in NOD mice following aPC treatment. These Tregs had potent suppressor function and, after adoptive transfer, delayed diabetes onset in NOD.severe combined immunodeficiency mice. The culture of NOD mouse spleen cells with aPC reduced the secretion of inflammatory cytokines interleukin (IL)-1ß and interferon-γ but increased IL-2 and transforming growth factor-ß1, two cytokines required for Treg differentiation. In summary, our results indicate that aPC prevents T1D in the NOD mouse. The aPC mechanism of action is complex, involving induction of Treg differentiation, inhibition of inflammation, and possibly direct cyto-protective effects on ß cells.

Protease-activated receptor 2, rather than protease-activated receptor 1, contributes to the aggressive properties of synovial fibroblasts in rheumatoid arthritis.

OBJECTIVE: To investigate whether protease-activated receptor 1 (PAR-1) and/or PAR-2 promotes the invasiveness/proliferation of synovial fibroblasts (SFs) and to determine the signaling mechanisms of these pathways. METHODS: SFs were isolated from the synovial tissue of patients with rheumatoid arthritis (RA), patients with osteoarthritis (OA), and PAR-1- or PAR-2-knockout (KO) mice. Expression of PAR-1 and PAR-2 was detected by immunofluorescence and Western blotting. The invasion and proliferation of SFs were measured by invasion assay and MTT assay, respectively. Matrix metalloproteinase 2 (MMP-2) and MMP-9 were detected by zymography, and cytokines were measured by enzyme-linked immunosorbent assay. RESULTS: PAR-1 and PAR-2 were colocalized with SFs in RA and OA synovium and, to a considerably lesser extent, in normal synovium. Inhibition of PAR-2 by small interfering RNA (siRNA) inhibited RASF invasion and proliferation, whereas blocking of PAR-1 by siRNA had the reverse effects. SFs from PAR-2-KO mice exhibited slower rates of proliferation and invasion. SFs from PAR-1-KO mice produced less MMP-2 and, in response to tumor necrosis factor α (TNFα) stimulation, had increased MMP-9 secretion when compared to SFs from wild-type and PAR-2-KO mice. Inhibition of PAR-1, but not PAR-2, stimulated the secretion of interleukin-17 (IL-17) and TNFα by RASFs. Furthermore, PAR-1 and PAR-2 had opposing effects on the activation of ERK, p38, and NF-κB. CONCLUSION: Activation of PAR-1 stimulates MMP-2 secretion, inhibits RASF growth and invasion, and decreases production of IL-17 and TNFα by RASFs, whereas activation of PAR-2 stimulates RASF growth and invasion and increases production of TNFα. Thus, although PAR-1 and PAR-2 are coexpressed by RASFs, PAR-2 alone appears to be responsible for the aggressive properties of RASFs and is likely to contribute to the pathologic progression of RA.

Protease activated receptor-2 mediates activated protein C-induced cutaneous wound healing via inhibition of p38.

Activated protein C (APC) is a natural anticoagulant that exerts anti-inflammatory and cytoprotective properties mediated through the protease activated receptor (PAR)-1. APC can also proteolytically cleave PAR-2, although subsequent function is unknown. On the basis of recent evidence that APC promotes wound healing, the aim of this study was to determine whether APC acts through PARs to heal murine excisional wounds or to regulate human cultured keratinocyte function and to determine the signaling mechanisms. Topical administration of APC accelerated wound healing in wild-type mice and, unexpectedly, in PAR-1 knockout mice. PAR-2 knockout mice healed significantly slower than wild-type mice, and healing was not altered by adding APC, indicating that APC acts through PAR-2 to heal wounds. In cultured human primary keratinocytes, APC enhanced PAR-2, stimulated proliferation, activated phosphatidylinositol 3-kinase/Src/Akt, and inhibited phosphorylated (P)-p38. Inhibiting PAR-1 or PAR-2, by small-interfering RNA or blocking antibody, reversed APC-induced keratinocyte proliferation and Akt activation. Blocking PAR-2, but not PAR-1, reversed the inhibition of P-p38 by APC. Furthermore, inhibition of P-p38 accelerated wound healing in wild-type mice. In summary, although APC acts through both PAR-1 and PAR-2 to activate Akt and to increase keratinocyte proliferation, APC-induced murine wound healing depends on PAR-2 activity and inhibition of P-p38.

Activated protein C enhances human keratinocyte barrier integrity via sequential activation of epidermal growth factor receptor and Tie2.

Keratinocytes play a critical role in maintaining epidermal barrier function. Activated protein C (APC), a natural anticoagulant with anti-inflammatory and endothelial barrier protective properties, significantly increased the barrier impedance of keratinocyte monolayers, measured by electric cell substrate impedance sensing and FITC-dextran flux. In response to APC, Tie2, a tyrosine kinase receptor, was rapidly activated within 30 min, and relocated to cell-cell contacts. APC also increased junction proteins zona occludens, claudin-1 and VE-cadherin. Inhibition of Tie2 by its peptide inhibitor or small interfering RNA abolished the barrier protective effect of APC. Interestingly, APC did not activate Tie2 through its major ligand, angiopoietin-1, but instead acted by binding to endothelial protein C receptor, cleaving protease-activated receptor-1 and transactivating EGF receptor. Furthermore, when activation of Akt, but not ERK, was inhibited, the barrier protective effect of APC on keratinocytes was abolished. Thus, APC activates Tie2, via a mechanism requiring, in sequential order, the receptors, endothelial protein C receptor, protease-activated receptor-1, and EGF receptor, which selectively enhances the PI3K/Akt signaling to enhance junctional complexes and reduce keratinocyte permeability.