Endothelial membrane reorganization during leukocyte extravasation

Magnesium lithospermate B enhances the potential of human-induced pluripotent stem cell-derived cardiomyocytes for myocardial repair

BACKGROUND

We previously reported that activation of the cell cycle in human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) enhances their remuscularization capacity after human cardiac muscle patch transplantation in infarcted mouse hearts. Herein, we sought to identify the effect of magnesium lithospermate B (MLB) on hiPSC-CMs during myocardial repair using a myocardial infarction (MI) mouse model.

METHODS

In C57BL/6 mice, MI was surgically induced by ligating the left anterior descending coronary artery. The mice were randomly divided into five groups ( n = 10 per group); a MI group (treated with phosphate-buffered saline only), a hiPSC-CMs group, a MLB group, a hiPSC-CMs + MLB group, and a Sham operation group. Cardiac function and MLB therapeutic efficacy were evaluated by echocardiography and histochemical staining 4 weeks after surgery. To identify the associated mechanism, nuclear factor (NF)-κB p65 and intercellular cell adhesion molecule-1 (ICAM1) signals, cell adhesion ability, generation of reactive oxygen species, and rates of apoptosis were detected in human umbilical vein endothelial cells (HUVECs) and hiPSC-CMs.

RESULTS

After 4 weeks of transplantation, the number of cells that engrafted in the hiPSC-CMs + MLB group was about five times higher than those in the hiPSC-CMs group. Additionally, MLB treatment significantly reduced tohoku hospital pediatrics-1 (THP-1) cell adhesion, ICAM1 expression, NF-κB nuclear translocation, reactive oxygen species production, NF-κB p65 phosphorylation, and cell apoptosis in HUVECs cultured under hypoxia. Similarly, treatment with MLB significantly inhibited the apoptosis of hiPSC-CMs via enhancing signal transducer and activator of transcription 3 (STAT3) phosphorylation and B-cell lymphoma-2 (BCL2) expression, promoting STAT3 nuclear translocation, and downregulating BCL2-Associated X, dual specificity phosphatase 2 (DUSP2), and cleaved-caspase-3 expression under hypoxia. Furthermore, MLB significantly suppressed the production of malondialdehyde and lactate dehydrogenase and the reduction in glutathione content induced by hypoxia in both HUVECs and hiPSC-CMs in vitro .

CONCLUSIONS

MLB significantly enhanced the potential of hiPSC-CMs in repairing injured myocardium by improving endothelial cell function via the NF-κB/ICAM1 pathway and inhibiting hiPSC-CMs apoptosis via the DUSP2/STAT3 pathway.

ICAM-1 nanoclusters regulate hepatic epithelial cell polarity by leukocyte adhesion-independent control of apical actomyosin

Epithelial intercellular adhesion molecule (ICAM)-1 is apically polarized, interacts with, and guides leukocytes across epithelial barriers. Polarized hepatic epithelia organize their apical membrane domain into bile canaliculi and ducts, which are not accessible to circulating immune cells but that nevertheless confine most of ICAM-1. Here, by analyzing ICAM-1_KO human hepatic cells, liver organoids from ICAM-1_KO mice and rescue-of-function experiments, we show that ICAM-1 regulates epithelial apicobasal polarity in a leukocyte adhesion-independent manner. ICAM-1 signals to an actomyosin network at the base of canalicular microvilli, thereby controlling the dynamics and size of bile canalicular-like structures. We identified the scaffolding protein EBP50/NHERF1/SLC9A3R1, which connects membrane proteins with the underlying actin cytoskeleton, in the proximity interactome of ICAM-1. EBP50 and ICAM-1 form nano-scale domains that overlap in microvilli, from which ICAM-1 regulates EBP50 nano-organization. Indeed, EBP50 expression is required for ICAM-1-mediated control of BC morphogenesis and actomyosin. Our findings indicate that ICAM-1 regulates the dynamics of epithelial apical membrane domains beyond its role as a heterotypic cell-cell adhesion molecule and reveal potential therapeutic strategies for preserving epithelial architecture during inflammatory stress.

Lung single-cell RNA profiling reveals response of pulmonary capillary to sepsis-induced acute lung injury

Background

Sepsis-induced acute lung injury (ALI) poses a significant threat to human health. Endothelial cells, especially pulmonary capillaries, are the primary barriers against sepsis in the lungs. Therefore, investigating endothelial cell function is essential to understand the pathophysiological processes of sepsis-induced ALI.

Methods

We downloaded single-cell RNA-seq expression data from GEO with accession number GSE207651. The mice underwent cecal ligation and puncture (CLP) surgery, and lung tissue samples were collected at 0, 24, and 48 h. The cells were annotated using the CellMarker database and FindAllMarkers functions. GO enrichment analyses were performed using the Metascape software. Gene set enrichment Analysis (GSEA) and variation Analysis (GSVA) were performed to identify differential signaling pathways. Differential expression genes were collected with the "FindMarkers" function. The R package AUCell was used to score individual cells for pathway activities. The Cellchat package was used to explore intracellular communication.

Results

Granulocytes increased significantly as the duration of endotoxemia increased. However, the number of T cells, NK cells, and B cells declined. Pulmonary capillary cells were grouped into three sub-clusters. Capillary-3 cells were enriched in the sham group, but declined sharply in the CLP.24 group. Capillary-1 cells peaked in the CLP.24 group, while Capillary-2 cells were enriched in the CLP.48 group. Furthermore, we found that Cd74+ Capillary-3 cells mainly participated in immune interactions. Plat+ Capillary-1 and Clec1a+ Capillary-2 are involved in various physiological processes. Regarding cell-cell interactions, Plat+ Capillary-1 plays the most critical role in granulocyte adherence to capillaries during ALI. Cd74+ Capillary cells expressing high levels of major histocompatibility complex (MHC) and mainly interacted with Cd8a+ T cells in the sham group.

Conclusion

Plat+ capillaries are involved in the innate immune response through their interaction with neutrophils via ICAM-1 adhesion during endotoxemia, while Cd74+ capillaries epxressed high level of MHC proteins play a role in adaptive immune response through their interaction with T cells. However, it remains unclear whether the function of Cd74+ capillaries leans towards immunity or tolerance, and further studies are needed to confirm this.

Connexin 43 Expression in Cutaneous Biopsies of Lupus Erythematosus

INTRODUCTION

Gap junctions are channels between adjacent cells formed by connexins (Cxs). Cxs also form hemichannels that connect the cell with its extracellular milieu. These channels allow the transport of ions, metabolites, and small molecules; therefore, Cxs, and more specifically, connexin (Cx) 43 has been demonstrated to be in control of several crucial events such as inflammation and cell death.

MATERIAL AND METHODS

We examined the immunostaining of Cx43 in the endothelia of the cutaneous blood vessels of biopsies from 28 patients with several variants of lupus erythematosus.

RESULTS

In 19 cases (67.86%), staining of more than half of the dermal vessels including both vessels of the papillary and of the reticular dermis was identified. Only in 4 cases (14.28%), less than 25% of the vessels in the biopsy showed expression of the marker.

CONCLUSIONS

Our results suggest a role of Cx43 in regulating the endothelial activity in lupus erythematosus, which also opens a door for targeted therapeutic options.

The Role of Heparin and Glycocalyx in Blood-Brain Barrier Dysfunction

The blood-brain barrier (BBB) functions as a dynamic boundary that protects the central nervous system from blood and plays an important role in maintaining the homeostasis of the brain. Dysfunction of the BBB is a pathophysiological characteristic of multiple neurologic diseases. Glycocalyx covers the luminal side of vascular endothelial cells(ECs). Damage of glycocalyx leads to disruption of the BBB, while inhibiting glycocalyx degradation maintains BBB integrity. Heparin has been recognized as an anticoagulant and it protects endothelial glycocalyx from destruction. In this review, we summarize the role of glycocalyx in BBB formation and the therapeutic potency of heparin to provide a theoretical basis for the treatment of neurological diseases related to BBB breakdown.

Plasmolipin regulates basolateral-to-apical transcytosis of ICAM-1 and leukocyte adhesion in polarized hepatic epithelial cells

Apical localization of Intercellular Adhesion Receptor (ICAM)-1 regulates the adhesion and guidance of leukocytes across polarized epithelial barriers. Here, we investigate the molecular mechanisms that determine ICAM-1 localization into apical membrane domains of polarized hepatic epithelial cells, and their effect on lymphocyte-hepatic epithelial cell interaction. We had previously shown that segregation of ICAM-1 into apical membrane domains, which form bile canaliculi and bile ducts in hepatic epithelial cells, requires basolateral-to-apical transcytosis. Searching for protein machinery potentially involved in ICAM-1 polarization we found that the SNARE-associated protein plasmolipin (PLLP) is expressed in the subapical compartment of hepatic epithelial cells in vitro and in vivo. BioID analysis of ICAM-1 revealed proximal interaction between this adhesion receptor and PLLP. ICAM-1 colocalized and interacted with PLLP during the transcytosis of the receptor. PLLP gene editing and silencing increased the basolateral localization and reduced the apical confinement of ICAM-1 without affecting apicobasal polarity of hepatic epithelial cells, indicating that ICAM-1 transcytosis is specifically impaired in the absence of PLLP. Importantly, PLLP depletion was sufficient to increase T-cell adhesion to hepatic epithelial cells. Such an increase depended on the epithelial cell polarity and ICAM-1 expression, showing that the epithelial transcytotic machinery regulates the adhesion of lymphocytes to polarized epithelial cells. Our findings strongly suggest that the polarized intracellular transport of adhesion receptors constitutes a new regulatory layer of the epithelial inflammatory response.

Cellular transformers for targeted therapy

Employing natural cells as drug carriers has been a hotspot in recent years, attributing to their biocompatibility and inherent dynamic properties. In the earlier stage, cells were mainly used as vehicles by virtue of their lipid-delimited compartmentalized structures and native membrane proteins. The scope emphasis was 'what cell displays' instead of 'how cell changes'. More recently, the dynamic behaviours, such as changes in surface protein patterns, morphologies, polarities and in-situ generation of therapeutics, of natural cells have drawn more attention for developing advanced drug delivery systems by fully taking advantage of these processes. In this review, we revolve around the dynamic cellular transformation behaviours which facilitate targeted therapy. Cellular deformation in geometry shape, spitting smaller vesicles, activation of antigen present cells, polarization between distinct phenotypes, local production of therapeutics, and hybridization with synthetic materials are involved. Other than focusing on the traditional delivery of concrete cargoes, more functional 'handles' that are derived from the cells themselves are introduced, such as information exchange, cellular communication and interactions between cell and extracellular environment.

Thousands of CpGs Show DNA Methylation Differences in ACPA-Positive Individuals

High levels of anti-citrullinated protein antibodies (ACPA) are often observed prior to a diagnosis of rheumatoid arthritis (RA). We undertook a replication study to confirm CpG sites showing evidence of differential methylation in subjects positive vs. negative for ACPA, in a new subset of 112 individuals sampled from the population cohort and biobank CARTaGENE in Quebec, Canada. Targeted custom capture bisulfite sequencing was conducted at approximately 5.3 million CpGs located in regulatory or hypomethylated regions from whole blood; library and protocol improvements had been instituted between the original and this replication study, enabling better coverage and additional identification of differentially methylated regions (DMRs). Using binomial regression models, we identified 19,472 ACPA-associated differentially methylated cytosines (DMCs), of which 430 overlapped with the 1909 DMCs reported by the original study; 814 DMRs of relevance were clustered by grouping adjacent DMCs into regions. Furthermore, we performed an additional integrative analysis by looking at the DMRs that overlap with RA related loci published in the GWAS Catalog, and protein-coding genes associated with these DMRs were enriched in the biological process of cell adhesion and involved in immune-related pathways.

Autophagy modulates endothelial junctions to restrain neutrophil diapedesis during inflammation

The migration of neutrophils from the blood circulation to sites of infection or injury is a key immune response and requires the breaching of endothelial cells (ECs) that line the inner aspect of blood vessels. Unregulated neutrophil transendothelial cell migration (TEM) is pathogenic, but the molecular basis of its physiological termination remains unknown. Here, we demonstrated that ECs of venules in inflamed tissues exhibited a robust autophagic response that was aligned temporally with the peak of neutrophil trafficking and was strictly localized to EC contacts. Genetic ablation of EC autophagy led to excessive neutrophil TEM and uncontrolled leukocyte migration in murine inflammatory models, while pharmacological induction of autophagy suppressed neutrophil infiltration into tissues. Mechanistically, autophagy regulated the remodeling of EC junctions and expression of key EC adhesion molecules, facilitating their intracellular trafficking and degradation. Collectively, we have identified autophagy as a modulator of EC leukocyte trafficking machinery aimed at terminating physiological inflammation.

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Inflamed venular ECs exhibit an autophagic response that localizes to EC contacts

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EC ATG5 deficiency promotes excessive and faster neutrophil TEM

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Ablation of EC autophagy increases cell surface expression of adhesion molecules

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Non-canonical autophagy operates in inflamed ECs and controls neutrophil migration

Distinct subsets of T cells and macrophages impact venous remodeling during arteriovenous fistula maturation

Patients with end-stage renal failure depend on hemodialysis indefinitely without renal transplantation, requiring a long-term patent vascular access. While the arteriovenous fistula (AVF) remains the preferred vascular access for hemodialysis because of its longer patency and fewer complications compared with other vascular accesses, the primary patency of AVF is only 50-60%, presenting a clinical need for improvement. AVF mature by developing a thickened vascular wall and increased diameter to adapt to arterial blood pressure and flow volume. Inflammation plays a critical role during vascular remodeling and fistula maturation; increased shear stress triggers infiltration of T-cells and macrophages that initiate inflammation, with involvement of several different subsets of T-cells and macrophages. We review the literature describing distinct roles of the various subsets of T-cells and macrophages during vascular remodeling. Immunosuppression with sirolimus or prednisolone reduces neointimal hyperplasia during AVF maturation, suggesting novel approaches to enhance vascular remodeling. However, M2 macrophages and CD4+ T-cells play essential roles during AVF maturation, suggesting that total immunosuppression may suppress adaptive vascular remodeling. Therefore it is likely that regulation of inflammation during fistula maturation will require a balanced approach to coordinate the various inflammatory cell subsets. Advances in immunosuppressive drug development and delivery systems may allow for more targeted regulation of inflammation to improve vascular remodeling and enhance AVF maturation.

How many cadherins do human endothelial cells express?

The vasculature is the paradigm of a compartment generated by parallel cellular barriers that aims to transport oxygen, nutrients and immune cells in complex organisms. Vascular barrier dysfunction leads to fatal acute and chronic inflammatory diseases. The endothelial barrier lines the inner side of vessels and is the main regulator of vascular permeability. Cadherins comprise a superfamily of 114 calcium-dependent adhesion proteins that contain conserved cadherin motifs and form cell-cell junctions in metazoans. In mature human endothelial cells, only VE (vascular endothelial)-cadherin and N (neural)-cadherin have been investigated in detail. Although both cadherins are essential for regulating endothelial permeability, no comprehensive expression studies to identify which other family members could play a relevant role in endothelial cells has so far been performed. Here, we have reviewed gene and protein expression databases to analyze cadherin expression in mature human endothelium and found that at least 24 cadherin superfamily members are significantly expressed. Based on data obtained from other cell types, organisms and experimental models, we discuss their potential functions, many of them unrelated to the formation of endothelial cell-cell junctions. The expression of this new set of endothelial cadherins highlights the important but still poorly defined roles of planar cell polarity, the Hippo pathway and mitochondria metabolism in human vascular homeostasis.

The Functional Implications of Endothelial Gap Junctions and Cellular Mechanics in Vascular Angiogenesis

Angiogenesis—the sprouting and growth of new blood vessels from the existing vasculature—is an important contributor to tumor development, since it facilitates the supply of oxygen and nutrients to cancer cells. Endothelial cells are critically affected during the angiogenic process as their proliferation, motility, and morphology are modulated by pro-angiogenic and environmental factors associated with tumor tissues and cancer cells. Recent in vivo and in vitro studies have revealed that the gap junctions of endothelial cells also participate in the promotion of angiogenesis. Pro-angiogenic factors modulate gap junction function and connexin expression in endothelial cells, whereas endothelial connexins are involved in angiogenic tube formation and in the cell migration of endothelial cells. Several mechanisms, including gap junction function-dependent or -independent pathways, have been proposed. In particular, connexins might have the potential to regulate cell mechanics such as cell morphology, cell migration, and cellular stiffness that are dynamically changed during the angiogenic processes. Here, we review the implication for endothelial gap junctions and cellular mechanics in vascular angiogenesis.

The Role of Gap Junction-Mediated Endothelial Cell-Cell Interaction in the Crosstalk between Inflammation and Blood Coagulation

Endothelial cells (ECs) play a pivotal role in the crosstalk between blood coagulation and inflammation. Endothelial cellular dysfunction underlies the development of vascular inflammatory diseases. Recent studies have revealed that aberrant gap junctions (GJs) and connexin (Cx) hemichannels participate in the progression of cardiovascular diseases such as cardiac infarction, hypertension and atherosclerosis. ECs can communicate with adjacent ECs, vascular smooth muscle cells, leukocytes and platelets via GJs and Cx channels. ECs dynamically regulate the expression of numerous Cxs, as well as GJ functionality, in the context of inflammation. Alterations to either result in various side effects across a wide range of vascular functions. Here, we review the roles of endothelial GJs and Cx channels in vascular inflammation, blood coagulation and leukocyte adhesion. In addition, we discuss the relevant molecular mechanisms that endothelial GJs and Cx channels regulate, both the endothelial functions and mechanical properties of ECs. A better understanding of these processes promises the possibility of pharmacological treatments for vascular pathogenesis.

How tetraspanins shape endothelial and leukocyte nano-architecture during inflammation

Tetraspanins are ubiquitous membrane proteins that induce local membrane curvature and hence co-ordinate cell-to-cell contacts. This review highlights their role in inflammation, which requires control of the nano-architecture of attachment sites between endothelial cells and leukocytes. The active role of endothelial cells in preparing for transmigration of leukocytes and determining the severity of an inflammation is often underscored. A clear hint to endothelial pre-activation is their ability to protrude clustered adhesion proteins upward prior to leukocyte contact. The elevation of molecular adhesive platforms toward the blood stream is crucially dependent on tetraspanins. In addition, leukocytes require tetraspanins for their activation. The example of the B-cell receptor is referenced in some detail here, since it provides deeper insights into the receptor-coreceptor interplay. To lift the role of tetraspanins from an abstract model of inflammation toward a player of clinical significance, two pathologies are analyzed for the known contributions of tetraspanins. The recent publication of the first crystal structure of a full-length tetraspanin revealed a cholesterol-binding site, which provides a strong link to the pathophysiological condition of atherosclerosis. Dysregulation of the inflammatory cascade in autoimmune diseases by endothelial cells is exemplified by the involvement of tetraspanins in multiple sclerosis.

Unfractionated heparin after TBI reduces in vivo cerebrovascular inflammation, brain edema and accelerates cognitive recovery

BACKGROUND

Severe traumatic brain injury (TBI) may increase the risk of venous thromboembolic complications; however, early prevention with heparinoids is often withheld for its anticoagulant effect. New evidence suggests low molecular weight heparin reduces cerebral edema and improves neurological recovery after stroke and TBI, through blunting of cerebral leukocyte (LEU) recruitment. It remains unknown if unfractionated heparin (UFH) similarly affects brain inflammation and neurological recovery post-TBI. We hypothesized that UFH after TBI reduces cerebral edema by reducing LEU-mediated inflammation and improves neurological recovery.

METHODS

CD1 male mice underwent either TBI by controlled cortical impact (CCI) or sham craniotomy. UFH (75 U/kg or 225 U/kg) or vehicle (VEH, 0.9% saline) was administered 2, 11, 20, 27, and 34 hours after TBI. At 48 hours, pial intravital microscopy through a craniotomy was used to visualize live brain LEUs interacting with endothelium and microvascular fluorescein isothiocyanate-albumin leakage. Neurologic function (Garcia Neurological Test, GNT) and body weight loss ratios were evaluated 24 and 48 hours after TBI. Cerebral and lung wet-to-dry ratios were evaluated post mortem. ANOVA with Bonferroni correction was used to determine significance (p < 0.05).

RESULTS

Compared to positive controls (CCI), both UFH doses reduced post-TBI in vivo LEU rolling on endothelium, concurrent cerebrovascular albumin leakage, and ipsilateral cerebral water content after TBI. Additionally, only low dose UFH (75 U/kg) improved GNT at both 24 and 48 hours after TBI. High dose UFH (225 U/kg) significantly increased body weight loss above sham at 48 hours. Differences in lung water content and blood pressure between groups were not significant.

CONCLUSIONS

UFH after TBI reduces LEU recruitment, microvascular permeability, and brain edema to injured brain. Lower UFH doses concurrently improve neurological recovery whereas higher UFH may worsen functional recovery. Further study is needed to determine if this is caused by increased bleeding from injured brain with higher UFH doses.

Porcine circovirus 2 (PCV2) increases the expression of endothelial adhesion/junction molecules

Porcine circovirus type 2 (PCV2) is the primary causative agent of porcine circovirus disease, a complex multisystem syndrome in domestic pigs. Despite the significant economic losses caused by porcine circovirus disease, the mechanisms of pathogenesis underlying the clinical findings remain largely unclear. As various reports have highlighted the potential key role of vascular lesions in the pathogenesis of porcine circovirus disease, the aim of this work was to investigate effects of PCV2 infection on vascular endothelial cells, focusing on cell viability and expression of adhesion/junction molecules. PCV2 infection reduced endothelial cell viability, while viral infection did not affected the viability of several other classical cell lines. Also, PCV2 infection in endothelial cells displayed a dual/biphasic effect: initially, infection increased ICAM-1 expression, which can favor leukocyte recruitment and emigration to tissues and possibly inducing characteristic porcine circovirus disease inflammatory lesions; then, secondarily, infection caused an increase in zonula occludens 1 tight junction protein (ZO-1) expression, which in turn can result in difficulties for cell traffic across the endothelium and a potential impairment the immune response in peripheral tissues. These virus-induced endothelial changes could directly impact the inflammatory process of porcine circovirus disease and associated vascular/immune system disturbances. Data suggest that, among the wide range of effects induced by PCV2 on the host, endothelial modulation can be a pivotal process which can help to explain PCV2 pathogenesis in some porcine circovirus disease presentations.

Endothelial Cell Junctional Adhesion Molecules: Role and Regulation of Expression in Inflammation

Endothelial cells line the lumen of all blood vessels and play a critical role in maintaining the barrier function of the vasculature. Sealing of the vessel wall between adjacent endothelial cells is facilitated by interactions involving junctionally expressed transmembrane proteins, including tight junctional molecules, such as members of the junctional adhesion molecule family, components of adherence junctions, such as VE-Cadherin, and other molecules, such as platelet endothelial cell adhesion molecule. Of importance, a growing body of evidence indicates that the expression of these molecules is regulated in a spatiotemporal manner during inflammation: responses that have significant implications for the barrier function of blood vessels against blood-borne macromolecules and transmigrating leukocytes. This review summarizes key aspects of our current understanding of the dynamics and mechanisms that regulate the expression of endothelial cells junctional molecules during inflammation and discusses the associated functional implications of such events in acute and chronic scenarios.

Does enoxaparin interfere with HMGB1 signaling after TBI? A potential mechanism for reduced cerebral edema and neurologic recovery

BACKGROUND

Enoxaparin (ENX) has been shown to reduce cerebral edema and improve neurologic recovery after traumatic brain injury (TBI), through blunting of cerebral leukocyte (LEU) recruitment. High mobility group box 1 (HMGB1) protein may induce inflammation through LEU activation. We hypothesized that ENX after TBI reduces LEU-mediated edema through blockade of HMGB1 signaling.

METHODS

Twenty-three CD1 mice underwent severe TBI by controlled cortical impact and were randomized to one of four groups receiving either monoclonal antibody against HMGB1 (MAb) or isotype (Iso) and either ENX (1 mg/kg) or normal saline (NS): NS + Iso (n = 5), NS + MAb (n = 6), ENX + Iso (n = 6), ENX + MAb (n = 6). ENX or NS was administered 2, 8, 14, 23 and 32 hours after TBI. MAb or Iso (25 μg) was administered 2 hours after TBI. At 48 hours, cerebral intravital microscopy served to visualize live LEU interacting with endothelium and microvascular fluorescein isothiocyanate-albumin leakage. The Neurological Severity Score (NSS) graded neurologic recovery; wet-to-dry ratios determined cerebral/lung edema. Analysis of variance with Bonferroni correction was used for statistical analyses.

RESULTS

ENX and MAb similarly reduced in vivo pial LEU rolling without demonstrating additive effect. In vivo albumin leakage was greatest in vehicle-treated animals but decreased by 25% with either MAb or ENX but by 50% when both were combined. Controlled cortical impact-induced cerebral wet-to-dry ratios were reduced by MAb or ENX without additive effect. Postinjury lung water was reduced by ENX but not by MAb. Neurologic recovery at 24 hours and 48 hours was similarly improved with ENX, MAb, or both treatments combined.

CONCLUSION

Mirroring ENX, HMGB1 signaling blockade reduces LEU recruitment, cerebrovascular permeability, and cerebral edema following TBI. ENX further reduced lung edema indicating a multifaceted effect beyond HMGB1 blockade. Further study is needed to determine how ENX may play a role in blunting HMGB1 signaling in brain injury patients.

BLT1 signalling protects the liver against acetaminophen hepatotoxicity by preventing excessive accumulation of hepatic neutrophils

Leukotriene B₄ (LTB₄) is a potent chemoattractant for neutrophils. Signalling of LTB₄ receptor type 1 (BLT₁) has pro-inflammatory functions through neutrophil recruitment. In this study, we investigated whether BLT₁ signalling plays a role in acetaminophen (APAP)-induced liver injury by affecting inflammatory responses including the accumulation of hepatic neutrophils. BLT₁-knockout (BLT₁^−/−) mice and their wild-type (WT) counterparts were subjected to a single APAP overdose (300 mg/kg), and various parameters compared within 24 h after treatment. Compared with WT mice, BLT₁^−/− mice exhibited exacerbation of APAP-induced liver injury as evidenced by enhancement of alanine aminotransferase level, necrotic area, hepatic neutrophil accumulation, and expression of cytokines and chemokines. WT mice co-treated with APAP and ONO-0457, a specific antagonist for BLT₁, displayed amplification of the injury, and similar results to those observed in BLT₁^−/− mice. Hepatic neutrophils in BLT₁^−/− mice during APAP hepatotoxicity showed increases in the production of reactive oxygen species and matrix metalloproteinase-9. Administration of isolated BLT₁-deficient neutrophils into WT mice aggravated the liver injury elicited by APAP. These results demonstrate that BLT₁ signalling dampens the progression of APAP hepatotoxicity through inhibiting an excessive accumulation of activated neutrophils. The development of a specific agonist for BLT₁ could be useful for the prevention of APAP hepatotoxicity.

Neuroinflammatory response to experimental stroke is inhibited by eriodictyol

BACKGROUND

Cerebral ischemia is a common disease and one of the most common causes of death and disability worldwide. The lack of glucose and oxygen in neuronal tissue leads to a series of inflammatory events, culminating in neuronal death. Eriodictyol is a flavonoid isolated from the Chinese herb Dracocephalum rupestre that has been proven to have anti-inflammatory properties.

HYPOTHESIS/PURPOSE

Thus, the present study was designed to explore whether eriodictyol has neuroprotective effects against the neuronal damage, motor and memory deficits induced by permanent middle cerebral artery occlusion (pMCAO) in mice.

STUDY DESIGN

Animals were orally treated with eriodictyol (1, 2 and 4mg/kg) or vehicle (saline) 30min before pMCAO, 2h after, and then once daily for the following five days.

METHODS

The parameters studied were neuronal viability, brain infarcted area; sensorimotor deficits; exploratory activity; working and aversive memory; myeloperoxidase (MPO) activity; TNFα, iNOS and GFAP immunoreactivity.

RESULTS

The treatment with eriodictyol prevented neuronal death, reduced infarct area and improved neurological and memory deficits induced by brain ischemia. The increase of MPO activity and TNF-α, iNOS and GFAP expression were also reduced by eriodictyol treatment.

CONCLUSION

These findings demonstrate that eriodictyol exhibit promising neuroprotection effects against the permanent focal ischemia cerebral injury in the mice experimental model and the underlying mechanisms might be mediated through inhibition of neuroinflammation.

Impact of HIV infection on the haemostatic response during sepsis and malaria

Patients positive for the human immunodeficiency virus (HIV) are more susceptible to sepsis and malaria, two conditions known to activate the coagulation system. As chronic HIV infection also influences haemostatic mechanisms, we determined the influence of HIV co-infection on coagulation, anticoagulation and the endothelium during sepsis or malaria. We performed a prospective observational study in 325 subjects with or without HIV infection (103 with sepsis, 127 with malaria and 95 asymptomatic controls) in an HIV endemic area in Central Africa. We measured plasma biomarkers indicative of activation of distinct haemostatic mechanisms. Sepsis and malaria had similar effects with elevated markers of coagulation, reduced anticoagulation markers and activation of endothelium. In particular, asymptomatic HIV infection reduced the plasma levels of the anticoagulant co-factor free protein S, and increased activation of the vascular endothelium, which were not normalized by combination antiretroviral therapy. HIV co-infection during sepsis and malaria caused more profound changes in free protein S and von Willebrand factor in sepsis and malaria, and ADAMTS13 in sepsis, while not influencing sepsis- or malaria-induced coagulation activation. These results show for the first time that HIV infection augments selective haemostatic changes during sepsis and malaria, which may contribute to the enhanced morbidity of these conditions in HIV patients.

Leukocytes Crossing the Endothelium: A Matter of Communication

Leukocytes cross the endothelial vessel wall in a process called transendothelial migration (TEM). The purpose of leukocyte TEM is to clear the causing agents of inflammation in underlying tissues, for example, bacteria and viruses. During TEM, endothelial cells initiate signals that attract and guide leukocytes to sites of tissue damage. Leukocytes react by attaching to these sites and signal their readiness to move back to endothelial cells. Endothelial cells in turn respond by facilitating the passage of leukocytes while retaining overall integrity. In this review, we present recent findings in the field and we have endeavored to synthesize a coherent picture of the intricate interplay between endothelial cells and leukocytes during TEM.

Nanoscale Imaging Reveals a Tetraspanin-CD9 Coordinated Elevation of Endothelial ICAM-1 Clusters

Endothelial barriers have a central role in inflammation as they allow or deny the passage of leukocytes from the vasculature into the tissue. To bind leukocytes, endothelial cells form adhesive clusters containing tetraspanins and ICAM-1, so-called endothelial adhesive platforms (EAPs). Upon leukocyte binding, EAPs evolve into docking structures that emanate from the endothelial surface while engulfing the leukocyte. Here, we show that TNF-α is sufficient to induce apical protrusions in the absence of leukocytes. Using advanced quantitation of atomic force microscopy (AFM) recordings, we found these structures to protrude by 160 ± 80 nm above endothelial surface level. Confocal immunofluorescence microscopy proved them positive for ICAM-1, JAM-A, tetraspanin CD9 and f-actin. Microvilli formation was inhibited in the absence of CD9. Our findings indicate that stimulation with TNF-α induces nanoscale changes in endothelial surface architecture and that—via a tetraspanin CD9 depending mechanism—the EAPs rise above the surface to facilitate leukocyte capture.

Na(+) /H(+) exchanger regulatory factor 1 knockout mice have an attenuated hepatic inflammatory response and are protected from cholestatic liver injury

The intercellular adhesion molecule 1 (ICAM-1) is induced in mouse liver after bile duct ligation (BDL) and plays a key role in neutrophil-mediated liver injury in BDL mice. ICAM-1 has been shown to interact with cytoskeletal ezrin-radixin-moesin (ERM) proteins that also interact with the PDZ protein, Na(+) /H(+) exchanger regulatory factor 1 (NHERF-1/EBP50). In NHERF-1(-/-) mice, ERM proteins are significantly reduced in brush-border membranes from kidney and small intestine. ERM knockdown reduces ICAM-1 expression in response to tumor necrosis factor alpha. Here we show that NHERF-1 assembles ERM proteins, ICAM-1 and F-actin into a macromolecule complex that is increased in mouse liver after BDL. Compared to wild-type (WT) mice, both sham-operated and BDL NHERF-1(-/-) mice have lower levels of activated ERM and ICAM-1 protein in the liver accompanied by significantly reduced hepatic neutrophil accumulation, serum alanine aminotransferase, and attenuated liver injury after BDL. However, total bile acid concentrations in serum and liver of sham and BDL NHERF-1(-/-) mice were not significantly different from WT controls, although hepatic tetrahydroxylated bile acids and Cyp3a11 messenger RNA levels were higher in NHERF-1(-/-) BDL mice.

CONCLUSION

NHERF-1 participates in the inflammatory response that is associated with BDL-induced liver injury. Deletion of NHERF-1 in mice leads to disruption of the formation of ICAM-1/ERM/NHERF-1 complex and reduction of hepatic ERM proteins and ICAM-1, molecules that are up-regulated and are essential for neutrophil-mediated liver injury in cholestasis. Further study of the role of NHERF-1 in the inflammatory response in cholestasis and other forms of liver injury should lead to discovery of new therapeutic targets in hepatic inflammatory diseases.

Endothelial actin-binding proteins and actin dynamics in leukocyte transendothelial migration

The endothelium is the first barrier that leukocytes have to overcome during recruitment to sites of inflamed tissues. The leukocyte extravasation cascade is a complex multistep process that requires the activation of various adhesion molecules and signaling pathways, as well as actin remodeling, in both leukocytes and endothelial cells. Endothelial adhesion molecules, such as E-selectin or ICAM-1, are connected to the actin cytoskeleton via actin-binding proteins (ABPs). Although the contribution of receptor-ligand interactions to leukocyte extravasation has been studied extensively, the contribution of endothelial ABPs to the regulation of leukocyte adhesion and transendothelial migration remains poorly understood. This review focuses on recently published evidence that endothelial ABPs, such as cortactin, myosin, or α-actinin, regulate leukocyte extravasation by controlling actin dynamics, biomechanical properties of endothelia, and signaling pathways, such as GTPase activation, during inflammation. Thus, ABPs may serve as targets for novel treatment strategies for disorders characterized by excessive leukocyte recruitment.

The saponin DT-13 attenuates tumor necrosis factor-α-induced vascular inflammation associated with Src/NF-кB/MAPK pathway modulation

This study aimed to explore the effect of DT-13 (25(R,S)-ruscogenin- 1-O- [β-d-glucopyranosyl- (1→2)][β-d-xylopyranosyl-(1→3)]-β -d- fucopyranoside) on tumor necrosis factor (TNF)-α-induced vascular inflammation and the potential molecular mechanisms. In vitro, DT-13 suppressed TNF-α-induced adhesion and migration of human umbilical vein endothelial cells (HUVECs) by inhibiting the expression of intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1). DT-13 markedly suppressed NF-кB p65 phosphorylation, and when NF-кB p65 was over-expressed, the inhibitory effect of DT-13 on adhesion molecular decreased. DT-13 also suppressed TNF-α induced luciferase activities of ICAM-1 and VCAM-1 promoter containing NF-κB binding sites. Furthermore, DT-13 markedly suppressed p38 phosphorylation and Src degradation induced by TNF-α, whereas had no significant effect on ERK and JNK activation. In vivo, DT-13 at 4 mg/kg prevented vascular inflammation and the expression of adhesion molecules induced by TNF-α in mice. These findings suggest that DT-13 abrogates vascular inflammation by down-regulating adhesion molecules associated with modulating the NF-кB, p38MAPK, Src signaling pathways, and NF-κB binding site is at least one of the targets of DT-13. This study provides novel information regarding the mechanism by which DT-13 exerts its effects on vascular inflammation, which is important for the onset and progression of various diseases.

MUC1-mediated motility in breast cancer: a review highlighting the role of the MUC1/ICAM-1/Src signaling triad

Breast cancer is the most common cancer in women with the leading cause of death being metastasis, the spread of cancer to distant organs. For those patients with high-risk estrogen receptor positive (ER+) breast cancer, an increased expression of the glycoprotein MUC1 is associated with resistance to anti-hormonal therapy, metastasis and death. Tumor cells may use MUC1 to metastasize by exploiting the vascular adhesion pathways used by leukocytes during the inflammatory response. MUC1 is a type 1 transmembrane protein whose cytoplasmic tail acts as a scaffold for several signaling pathways including the non-receptor kinase Src, a signaling molecule involved in cell differentiation, proliferation, adhesion and motility. This review will highlight our current knowledge of how MUC1/ICAM-1 binding can lead to the recruitment and activation of Src and propose a novel role for lipid raft microdomains in this promigratory signaling. Improved understanding of the mechanism of metastases and the underlying signaling cascade is a prerequisite to the discovery of therapeutic targets to prevent metastasis and death in ER+ breast cancer patients.

Cannabinoid receptor type-2 stimulation, blockade, and deletion alter the vascular inflammatory responses to traumatic brain injury

BACKGROUND

Immunomodulatory therapies have been identified as interventions for secondary injury after traumatic brain injury (TBI). The cannabinoid receptor type-2 (CB2R) is proposed to play an important, endogenous role in regulating inflammation. The effects of CB2R stimulation, blockade, and deletion on the neurovascular inflammatory responses to TBI were assessed.

METHODS

Wild-type C57BL/6 or CB2R knockout mice were randomly assigned to controlled cortical impact (CCI) injury or to craniotomy control groups. The effects of treatment with synthetic, selective CB2R agonists (0-1966 and JWH-133), a selective CB2R antagonist, or vehicle solution administered to CCI groups were assessed at 1-day after injury. Changes in TNF-α, intracellular adhesion molecule (ICAM-1), inducible nitric oxide synthase (iNOS), macrophage/microglial ionized calcium-binding adaptor molecule, and blood-brain-barrier (BBB) permeability were assessed using ELISA, quantitative RT-PCR, immunohistochemistry, and fluorometric analysis of sodium fluorescein uptake. CB2R knockouts and wild-type mice with CCI injury were treated with a CB2R agonist or vehicle treatment.

RESULTS

TNF-α mRNA increased at 6 hours and 1 to 3 days after CCI; a CB2R antagonist and genetic knockout of the CB2R exacerbated TNF-α mRNA expression. Treatment with a CB2R agonist attenuated TNF-α protein levels indicating post-transcriptional mechanisms. Intracellular adhesion molecule (ICAM-1) mRNA was increased at 6 hours, and at 1 to 2 days after CCI, reduced in mice treated with a CB2R agonist, and increased in CB2R knockout mice with CCI. Sodium fluorescein uptake was increased in CB2R knockouts after CCI, with and without a CB2R agonist. iNOS mRNA expression peaked early (6 hours) and remained increased from 1 to 3 days after injury. Treatment with a CB2R agonist attenuated increases in iNOS mRNA expression, while genetic deletion of the CB2R resulted in substantial increases in iNOS expression. Double label immunohistochemistry confirmed that iNOS was expressed by macrophage/microglia in the injured cortex.

CONCLUSION

Findings demonstrate that the endogenous cannabinoid system and CB2R play an important role in regulating inflammation and neurovascular responses in the traumatically injured brain. CB2R stimulation with two agonists (0-1966 and JWH-133) dampened post-traumatic inflammation, while blockade or deletion of the CB2R worsened inflammation. Findings support previous evidence that modulating the CB2R alters infiltrating macrophages and activated resident microglia. Further investigation into the role of the CB2R on specific immune cell populations in the injured brain is warranted.

Intranasal administration of human MSC for ischemic brain injury in the mouse: in vitro and in vivo neuroregenerative functions

Intranasal treatment with C57BL/6 MSCs reduces lesion volume and improves motor and cognitive behavior in the neonatal hypoxic-ischemic (HI) mouse model. In this study, we investigated the potential of human MSCs (hMSCs) to treat HI brain injury in the neonatal mouse. Assessing the regenerative capacity of hMSCs is crucial for translation of our knowledge to the clinic. We determined the neuroregenerative potential of hMSCs in vitro and in vivo by intranasal administration 10 d post-HI in neonatal mice. HI was induced in P9 mouse pups. 1×10⁶ or 2×10⁶ hMSCs were administered intranasally 10 d post-HI. Motor behavior and lesion volume were measured 28 d post-HI. The in vitro capacity of hMSCs to induce differentiation of mouse neural stem cell (mNSC) was determined using a transwell co-culture differentiation assay. To determine which chemotactic factors may play a role in mediating migration of MSCs to the lesion, we performed a PCR array on 84 chemotactic factors 10 days following sham-operation, and at 10 and 17 days post-HI. Our results show that 2×10⁶ hMSCs decrease lesion volume, improve motor behavior, and reduce scar formation and microglia activity. Moreover, we demonstrate that the differentiation assay reflects the neuroregenerative potential of hMSCs in vivo, as hMSCs induce mNSCs to differentiate into neurons in vitro. We also provide evidence that the chemotactic factor CXCL10 may play an important role in hMSC migration to the lesion site. This is suggested by our finding that CXCL10 is significantly upregulated at 10 days following HI, but not at 17 days after HI, a time when MSCs no longer reach the lesion when given intranasally. The results described in this work also tempt us to contemplate hMSCs not only as a potential treatment option for neonatal encephalopathy, but also for a plethora of degenerative and traumatic injuries of the nervous system.

Cancer cells remodel themselves and vasculature to overcome the endothelial barrier

Metastasis refers to the spread of cancer cells from a primary tumor to distant organs mostly via the bloodstream. During the metastatic process, cancer cells invade blood vessels to enter circulation, and later exit the vasculature at a distant site. Endothelial cells that line blood vessels normally serve as a barrier to the movement of cells into or out of the blood. It is thus critical to understand how metastatic cancer cells overcome the endothelial barrier. Epithelial cancer cells acquire increased motility and invasiveness through epithelial-to-mesenchymal transition (EMT), which enables them to move toward vasculature. Cancer cells also express a variety of adhesion molecules that allow them to attach to vascular endothelium. Finally, cancer cells secrete or induce growth factors and cytokines to actively prompt vascular hyperpermeability that compromises endothelial barrier function and facilitates transmigration of cancer cells through the vascular wall. Elucidation of the mechanisms underlying metastatic dissemination may help develop new anti-metastasis therapeutics.

Apicobasal polarity controls lymphocyte adhesion to hepatic epithelial cells

Loss of apicobasal polarity is a hallmark of epithelial pathologies. Leukocyte infiltration and crosstalk with dysfunctional epithelial barriers are crucial for the inflammatory response. Here, we show that apicobasal architecture regulates the adhesion between hepatic epithelial cells and lymphocytes. Polarized hepatocytes and epithelium from bile ducts segregate the intercellular adhesion molecule 1 (ICAM-1) adhesion receptor onto their apical, microvilli-rich membranes, which are less accessible by circulating immune cells. Upon cell depolarization, hepatic ICAM-1 becomes exposed and increases lymphocyte binding. Polarized hepatic cells prevent ICAM-1 exposure to lymphocytes by redirecting basolateral ICAM-1 to apical domains. Loss of ICAM-1 polarity occurs in human inflammatory liver diseases and can be induced by the inflammatory cytokine tumor necrosis factor alpha (TNF-α). We propose that adhesion receptor polarization is a parenchymal immune checkpoint that allows functional epithelium to hamper leukocyte binding. This contributes to the haptotactic guidance of leukocytes toward neighboring damaged or chronically inflamed epithelial cells that expose their adhesion machinery.

Invasive meningococcal disease: a disease of the endothelial cells

Neisseria meningitidis is an extracellular pathogen, which, once in the bloodstream, has the ability to form microcolonies on the apical surface of endothelia. Pathogen interaction with microvessels is mediated by bacterial type IV pili and two receptors on endothelial cells: CD147 and the β2-adrenoceptor. CD147 facilitates the adhesion of diplococci to the endothelium, whereas the β2-adrenoceptor facilitates cell signaling, and crossing of the blood-brain barrier. In this review, we discuss how meningococcal interaction with endothelial cells is responsible for the specific clinical features of invasive meningococcal infection such as meningitis, and a peripheral thrombotic/vascular leakage syndrome possibly leading to purpura fulminans.

TNF-induced endothelial barrier disruption: beyond actin and Rho

The decrease of endothelial barrier function is central to the long-term inflammatory response. A pathological alteration of the ability of endothelial cells to modulate the passage of cells and solutes across the vessel underlies the development of inflammatory diseases such as atherosclerosis and multiple sclerosis. The inflammatory cytokine tumour necrosis factor (TNF) mediates changes in the barrier properties of the endothelium. TNF activates different Rho GTPases, increases filamentous actin and remodels endothelial cell morphology. However, inhibition of actin-mediated remodelling is insufficient to prevent endothelial barrier disruption in response to TNF, suggesting that additional molecular mechanisms are involved. Here we discuss, first, the pivotal role of Rac-mediated generation of reactive oxygen species (ROS) to regulate the integrity of endothelial cell-cell junctions and, second, the ability of endothelial adhesion receptors such as ICAM-1, VCAM-1 and PECAM-1, involved in leukocyte transendothelial migration, to control endothelial permeability to small molecules, often through ROS generation. These adhesion receptors regulate endothelial barrier function in ways both dependent on and independent of their engagement by immune cells, and orchestrate the crosstalk between leukocyte transendothelial migration and endothelial permeability during inflammation.

VEGF-A isoforms differentially regulate ATF-2-dependent VCAM-1 gene expression and endothelial-leukocyte interactions

VEGF-A isoforms differentially stimulate endothelial VCAM-1 gene expression via an ERK1/2 protein kinase and ATF-2 transcription factor–dependent mechanism. Such signal transduction enables VEGF-A isoform–specific stimulation of leukocyte binding to endothelial cells, explaining how inflammation could be differentially regulated.

Vascular endothelial growth factor A (VEGF-A) regulates many aspects of vascular physiology. VEGF-A stimulates signal transduction pathways that modulate endothelial outputs such as cell migration, proliferation, tubulogenesis, and cell–cell interactions. Multiple VEGF-A isoforms exist, but the biological significance of this is unclear. Here we analyzed VEGF-A isoform–specific stimulation of VCAM-1 gene expression, which controls endothelial–leukocyte interactions, and show that this is dependent on both ERK1/2 and activating transcription factor-2 (ATF-2). VEGF-A isoforms showed differential ERK1/2 and p38 MAPK phosphorylation kinetics. A key feature of VEGF-A isoform–specific ERK1/2 activation and nuclear translocation was increased phosphorylation of ATF-2 on threonine residue 71 (T71). Using reverse genetics, we showed ATF-2 to be functionally required for VEGF-A–stimulated endothelial VCAM-1 gene expression. ATF-2 knockdown blocked VEGF-A–stimulated VCAM-1 expression and endothelial–leukocyte interactions. ATF-2 was also required for other endothelial cell outputs, such as cell migration and tubulogenesis. In contrast, VCAM-1 was essential only for promoting endothelial–leukocyte interactions. This work presents a new paradigm for understanding how soluble growth factor isoforms program complex cellular outputs and responses by modulating signal transduction pathways.

Knock down of caveolin-1 affects morphological and functional hallmarks of human endothelial cells

Caveolin-1 (CAV1) is the principal structural component of caveolae which functions as scaffolding protein for the integration of a variety of signaling pathways. In this study, we investigated the involvement of CAV1 in endothelial cell (EC) functions and show that siRNA-induced CAV1 silencing in the human EC line EA.hy926 induces distinctive morphological changes, such as a marked increase in cell size and formation of stress fibers. Design-based stereology was employed in this work to make unbiased quantification of morphometric properties such as volume, length, and surface of CAV1 silenced versus control cells. In addition, we showed that downregulation of CAV1 affects cell cycle progression at G1/S phase transition most likely by perturbation of AKT signaling. With the aim to assess the contribution of CAV1 to typical biological processes of EC, we report here that CAV1 targeting affects cell migration and matrix metalloproteinases (MMPs) activity, and reduces angiogenesis in response to VEGF, in vitro. Taken together our data suggest that the proper expression of CAV1 is important not only for maintaining the appropriate morphology and size of ECs but it might represent a prospective molecular target for studying key biological mechanisms such as senescence and tumorigenesis.

Host response to respiratory bacterial pathogens as identified by integrated analysis of human gene expression data

Respiratory bacterial pathogens are one of the leading causes of infectious death in the world and a major health concern complicated by the rise of multi-antibiotic resistant strains. Therapeutics that modulate host genes essential for pathogen infectivity could potentially avoid multi-drug resistance and provide a wider scope of treatment options. Here, we perform an integrative analysis of published human gene expression data generated under challenges from the gram-negative and Gram-positive bacteria pathogens, Pseudomonas aeruginosa and Streptococcus pneumoniae, respectively. We applied a previously described differential gene and pathway enrichment analysis pipeline to publicly available host mRNA GEO datasets resulting from exposure to bacterial infection. We found 72 canonical human pathways common between four GEO datasets, representing P. aeruginosa and S. pneumoniae. Although the majority of these pathways are known to be involved with immune response, we found several interesting new interactions such as the SUMO1 pathway that might have a role in bacterial infections. Furthermore, 36 host-bacterial pathways were also shared with our previous results for respiratory virus host gene expression. Based on our pathway analysis we propose several drug-repurposing opportunities supported by the literature.

MYADM controls endothelial barrier function through ERM-dependent regulation of ICAM-1 expression

The endothelium maintains a barrier between blood and tissue that becomes more permeable during inflammation. Membrane rafts are ordered assemblies of cholesterol, glycolipids, and proteins that modulate proinflammatory cell signaling and barrier function. In epithelial cells, the MAL family members MAL, MAL2, and myeloid-associated differentiation marker (MYADM) regulate the function and dynamics of ordered membrane domains. We analyzed the expression of these three proteins in human endothelial cells and found that only MYADM is expressed. MYADM was confined in ordered domains at the plasma membrane, where it partially colocalized with filamentous actin and cell-cell junctions. Small interfering RNA (siRNA)-mediated MYADM knockdown increased permeability, ICAM-1 expression, and leukocyte adhesion, all of which are features of an inflammatory response. Barrier function decrease in MYADM-silenced cells was dependent on ICAM-1 expression. Membrane domains and the underlying actin cytoskeleton can regulate each other and are connected by ezrin, radixin, and moesin (ERM) proteins. In endothelial cells, MYADM knockdown induced ERM activation. Triple-ERM knockdown partially inhibited ICAM-1 increase induced by MYADM siRNA. Importantly, ERM knockdown also reduced ICAM-1 expression in response to the proinflammatory cytokine tumor necrosis factor-α. MYADM therefore regulates the connection between the plasma membrane and the cortical cytoskeleton and so can control the endothelial inflammatory response.