CD43 polarization in unprimed T cells can be dissociated from raft coalescence by inhibition of HMG CoA reductase

Cholesterol metabolism and lipid droplet vacuoles; a potential target for the therapy of aggressive lymphoma

Cholesterol uptake via LDL receptor (LDLR) is increased in some malignant tumors, and incorporated LDL contribute to lipid droplet formation. Burkitt's lymphoma is known to have a large number of vacuoles in the cytoplasm, however, intracellular vacuoles are also seen in high-grade lymphomas such as adult T-cell leukemia/lymphoma, diffuse large B-cell lymphoma and primary central nervous system lymphoma. Recent studies have shown that esterified cholesterol is the main component of these vacuoles and the expression of cholesterol metabolism-related molecules such as LDLR, acetyl-CoA acetyltransferase 1 (ACAT1) which esterifies free cholesterol, and scavenger receptor class B type I (SR-BI) which effluxes free cholesterol, was significantly upregulated in lymphoma cells. Moreover, negative feedback of LDLR was not regulated even under cholesterol-rich conditions in lymphoma cells. We found that cytoplasmic free cholesterol was increased by ACAT and SR-BI inhibitors (CI-976 and BLT-1, respectively), and the accumulation of free cholesterol induced lymphoma cell apoptosis. In addition, overexpression of lipid droplet surface proteins has been correlated with poor prognosis in several malignant tumor such as ovarian cancer and clear cell renal cell carcinoma, and it is important to evaluate lipid droplet formation in malignant tumors including lymphomas.

Modular transcriptional repertoire and MicroRNA target analyses characterize genomic dysregulation in the thymus of Down syndrome infants

Trisomy 21-driven transcriptional alterations in human thymus were characterized through gene coexpression network (GCN) and miRNA-target analyses. We used whole thymic tissue--obtained at heart surgery from Down syndrome (DS) and karyotipically normal subjects (CT)--and a network-based approach for GCN analysis that allows the identification of modular transcriptional repertoires (communities) and the interactions between all the system's constituents through community detection. Changes in the degree of connections observed for hierarchically important hubs/genes in CT and DS networks corresponded to community changes. Distinct communities of highly interconnected genes were topologically identified in these networks. The role of miRNAs in modulating the expression of highly connected genes in CT and DS was revealed through miRNA-target analysis. Trisomy 21 gene dysregulation in thymus may be depicted as the breakdown and altered reorganization of transcriptional modules. Leading networks acting in normal or disease states were identified. CT networks would depict the "canonical" way of thymus functioning. Conversely, DS networks represent a "non-canonical" way, i.e., thymic tissue adaptation under trisomy 21 genomic dysregulation. This adaptation is probably driven by epigenetic mechanisms acting at chromatin level and through the miRNA control of transcriptional programs involving the networks' high-hierarchy genes.

Oversulfated chondroitin sulfate binds to chemokines and inhibits stromal cell-derived factor-1 mediated signaling in activated T cells

Oversulfated chondroitin sulfate (OSCS), a member of the glycosaminoglycan (GAG) family, was a contaminant in heparin that was linked to the 2008 heparin adverse events in the US. Because of its highly negative charge, OSCS can interact with many components of the contact and immune systems. We have previously demonstrated that OSCS inhibited the complement classical pathway by binding C1 inhibitor and potentiating its interaction with C1s. In the present study, by using surface plasmon resonance, we found OSCS interacts with T cell chemokines that can impact adaptive immunity. The binding of OSCS to stromal cell-derived factor-1 (SDF-1) chemokines, SDF-1α and SDF-1β, caused a significant change in the secondary structures of these chemokines as detected by far-ultraviolet circular dichroism spectra analysis. Functionally, OSCS binding profoundly inhibited SDF-1-induced calcium mobilization and T cell chemotaxis. Imaging flow cytometry revealed T cell morphological changes mediated by SDF-1α were completely blocked by OSCS. We conclude that the OSCS, a past contaminant in heparin, has broad interactions with the components of the human immune system beyond the contact and complement systems, and that may explain, in part, prior OSCS-related adverse events, while suggesting potentially useful therapeutic applications for related GAGs in the control of inflammation.

Analysis of detergent-free lipid rafts isolated from CD4+ T cell line: interaction with antigen presenting cells promotes coalescing of lipid rafts

Background

Lipid rafts present on the plasma membrane play an important role in spatiotemporal regulation of cell signaling. Physical and chemical characterization of lipid raft size and assessment of their composition before, and after cell stimulation will aid in developing a clear understanding of their regulatory role in cell signaling. We have used visual and biochemical methods and approaches for examining individual and lipid raft sub-populations isolated from a mouse CD4⁺ T cell line in the absence of detergents.

Results

Detergent-free rafts were analyzed before and after their interaction with antigen presenting cells. We provide evidence that the average diameter of lipid rafts isolated from un-stimulated T cells, in the absence of detergents, is less than 100 nm. Lipid rafts on CD4⁺ T cell membranes coalesce to form larger structures, after interacting with antigen presenting cells even in the absence of a foreign antigen.

Conclusions

Findings presented here indicate that lipid raft coalescence occurs during cellular interactions prior to sensing a foreign antigen.

Statins prevent tissue factor induction by protease-activated receptors 1 and 2 in human umbilical vein endothelial cells in vitro

BACKGROUND

Protease-activated receptors (PARs) are G-protein-coupled receptors that function in hemostasis and thrombosis, as well as in the inflammatory and proliferative responses triggered by tissue injury. We have previously shown that PAR1 or PAR2 occupancy by specific PAR-agonist peptides (PAR-APs) induces tissue factor (TF) expression in human umbilical vein endothelial cells (HUVECs), where TF regulation by PAR1 (but not by PAR2) requires intact endothelial caveolin-enriched membrane microdomains in which PAR1 and caveolin-1 associate.

OBJECTIVES

The aim of this study was to determine the effects of cholesterol-lowering agents (statins) and cholesterol-loading lipoprotein on PAR1-AP-mediated and PAR2-AP-mediated TF induction in HUVECs.

RESULTS

Statins completely prevented TF induction by PAR-APs in an isoprenoid-independent manner, induced the delocalization of PAR1 from caveolin-enriched membrane microdomains without affecting PAR1 mRNA, and decreased PAR2 mRNA and protein levels. Statins also prevented PAR-AP-mediated extracellular signal-related kinase 1/2 activation, which is crucial for TF induction. The redistribution of PAR1 is accompanied by the relocation of the membrane microdomain-associated G-protein α, caveolin-1, and Src, which we previously showed to play a key role in signal transduction and TF induction. Conversely, cholesterol loading potently amplified PAR1-AP-induced TF, probably as a result of the increased abundance of PAR1 and the Src and G-protein α signaling molecules in the caveolin-1-enriched fraction, without affecting PAR1 mRNA.

CONCLUSIONS

As PARs have important functions in hemostasis, cancer, thrombosis, and inflammatory processes, our findings that statins prevent TF induction by PAR-APs altering the membrane localization of PAR1 and the expression of PAR2 suggest that they may provide health benefits other than reducing atherosclerosis.

Flotillins are involved in the polarization of primitive and mature hematopoietic cells

Background

Migration of mature and immature leukocytes in response to chemokines is not only essential during inflammation and host defense, but also during development of the hematopoietic system. Many molecules implicated in migratory polarity show uniform cellular distribution under non-activated conditions, but acquire a polarized localization upon exposure to migratory cues.

Methodology/Principal Findings

Here, we present evidence that raft-associated endocytic proteins (flotillins) are pre-assembled in lymphoid, myeloid and primitive hematopoietic cells and accumulate in the uropod during migration. Furthermore, flotillins display a polarized distribution during immunological synapse formation. Employing the membrane lipid-order sensitive probe Laurdan, we show that flotillin accumulation in the immunological synapse is concomittant with membrane ordering in these regions.

Conclusions

Together with the observation that flotillin polarization does not occur in other polarized cell types such as polarized epithelial cells, our results suggest a specific role for flotillins in hematopoietic cell polarization. Based on our results, we propose that in hematopoietic cells, flotillins provide intrinsic cues that govern segregation of certain microdomain-associated molecules during immune cell polarization.

Influenza virus infection augments NK cell inhibition through reorganization of major histocompatibility complex class I proteins

The killing by natural killer (NK) cells is regulated by inhibitory, costimulatory, and activating receptors. The inhibitory receptors recognize mainly major histocompatibility complex (MHC) class I molecules, while the activating NK receptors recognize stress-induced ligands and viral products. Thus, changes in the expression of the various inhibitory and activating ligands will determine whether target cells will be killed or protected. Here, we demonstrate that after influenza virus infection the binding of the two NK inhibitory receptors, KIR2DL1 and the LIR1, to the infected cells is specifically increased. The increased binding occurs shortly after the influenza virus infection, prior to the increased recognition of the infected cells by the NK activating receptor, NKp46. We also elucidate the mechanism responsible for this effect and demonstrate that, after influenza virus infection, MHC class I proteins redistribute on the cell surface and accumulate in the lipid raft microdomains. Such redistribution allows better recognition by the NK inhibitory receptors and consequently increases resistance to NK cell attack. In contrast, T-cell activity was not influenced by the redistribution of MHC class I proteins. Thus, we present here a novel mechanism, developed by the influenza virus, of inhibition of NK cell cytotoxicity, through the reorganization of MHC class I proteins on the cell surface.

Down-regulation of autoreactive T-cells by HMG CoA reductase inhibitors

The inhibitors of HMG CoA reductase (statins) are widely used as cholesterol-lowering drugs with excellent safety records in hypercholesterolemic patients. Statins exert pleiotropic effects on a variety of cells, and they were recently described as a new class of immune modulators. Depending on their structure, dose, and route of administration, statins regulate the function of both the antigen-presenting cells and T-cells by HMG CoA reductase-dependent and independent mechanisms. Herein, we describe these mechanisms leading to prevention, amelioration, and reversal of autoimmune diseases. We also present data from our laboratories showing for the first time that in a double transgenic mouse model for autoimmune diabetes, atorvastatin (lipitor) prevented the onset of disease when administered in the neonatal period, and stabilized the glucose levels when administered in mice developing a mild form of diabetes.

Effects of methyl-β-cyclodextrin on T lymphocytes lipid rafts with aging

Aging is associated with a decline in immune functions. Among them, T-cell activation is altered at several points of the signaling cascade following TCR engagement. Recent findings suggest that lipid rafts act as a platform in the initiation of T-cell activation. We have previously demonstrated that cholesterol content in T-cells increased with aging, especially in lipid rafts. Cholesterol, which is a major component of lipid rafts, serves to stabilize their structure. We hypothesized that restoring T-cell cholesterol content and membrane fluidity would restore, at least in part, T-cell function via lipid rafts. We measured the lipid rafts coalescence, the p56(Lck) and linker of activated T-cell (LAT) signaling molecules recruitment and activation, the cholesterol content and fluidity in T-cell membrane after different methyl-beta-cyclodextrin (MBCD) treatments. Our results show that high concentration of MBCD (10 mM) completely disorganized the lipid rafts in T-cell membranes of young and elderly donors, however, T-cells from elderly donors were less sensitive than T-cells of young donors to low concentration of MBCD (0.5 mM). p56(Lck) and LAT recruitment and activation were affected in T-cells of both aged groups. MBCD treatment did not affect the cholesterol content and fluidity of T-cell membranes of young donors, while the cholesterol content was decreased and fluidity increased in lipid rafts of elderly donors. These results suggested that cholesterol extraction by MBCD increased the fluidity and disrupted lipid rafts organization. The increase in cholesterol content in lipid rafts with aging and its decrease by biochemical extraction were able to affect early signaling molecules activation. Restoring cholesterol content and fluidity may have beneficial effects, however, MBCD disorganized the membrane and this might not completely restore the T-cell activation via lipid rafts with aging. Altogether these results suggest that defects in cholesterol cellular homeostasis may be part of T-cell immunosenescence via lipid rafts dysfunction.

Simvastatin induces apoptosis of Epstein-Barr virus (EBV)-transformed lymphoblastoid cell lines and delays development of EBV lymphomas

Simvastatin and pravastatin are inhibitors of 3-hydroxy-3-methylglutaryl CoA reductase, and are used as antihypercholesterolemia drugs. Simvastatin, but not pravastatin, binds to the inserted domain of leukocyte function antigen (LFA)-1 and inhibits the function of LFA-1, including adhesion and costimulation of lymphocytes. Epstein-Barr virus (EBV)-transformed lymphoblastoid cell lines (LCLs) express high levels of LFA-1 on their surface and grow in tight clumps. Here we show that simvastatin (2 microM) inhibits clump formation and induces apoptosis of EBV-transformed LCLs. The apoptosis-inducing effect of simvastatin depends on binding to the inserted domain of LFA-1. Simvastatin, but not pravastatin, dissociates EBV latent membrane protein 1 from lipid rafts of LCLs, resulting in down-regulation of nuclear factor kappaB activity and induction of apoptosis. Analysis of multiple EBV-positive and -negative cell lines indicated that both LFA-1 and EBV latent membrane protein 1 expression were required for simvastatin's effects. Administration of simvastatin to severe combined immunodeficiency mice followed by inoculation with LCLs resulted in delayed development of EBV lymphomas and prolonged survival of animals. To our knowledge, this is the first report in which a drug that targets LFA-1 has been used to treat B cell lymphoma. These data suggest that simvastatin may have promise for treatment or prevention of EBV-associated lymphomas that occur in immunocompromised persons.

Gene Expression in Macrophage-Rich Inflammatory Cell Infiltrates in Human Atherosclerotic Lesions as Studied by Laser Microdissection and DNA Array

OBJECTIVE

Inflammatory cells play an important role in atherogenesis. However, more information is needed about their gene expression profiles in human lesions.

METHODS AND RESULTS

We used laser microdissection (LMD) to isolate macrophage-rich shoulder areas from human lesions. Gene expression profiles in isolated cells were analyzed by cDNA array and compared with expression patterns in normal intima and THP-1 macrophages. Upregulation of 72 genes was detected with LMD and included 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, interferon regulatory factor-5 (IRF-5), colony stimulating factor (CSF) receptors, CD11a/CD18 integrins, interleukin receptors, CD43, calmodulin, nitric oxide synthase (NOS), and extracellular superoxide dismutase (SOD). Several of these changes were also present in PMA-stimulated THP-1 macrophages in vitro. On the other hand, expression of several genes, such as VEGF, tissue factor pathway inhibitor 2, and apolipoproteins C-I and C-II, decreased.

CONCLUSIONS

Overexpression of HMG-CoA reductase in macrophage-rich lesion areas may explain some beneficial effects of statins, which can also modulate increased expression of CD11a/CD18 and CD43 found in microdissected cells. We also found increased expression of CSF receptors, IRF-5, and interleukin receptors, which could become useful therapeutic targets for the treatment of atherosclerotic diseases.

Inhibition of hydroxymethylglutaryl-coenzyme a reductase reduces Th1 development and promotes Th2 development

Several prospective clinical studies have indicated that hydroxymethylglutaryl-coenzyme A reductase inhibitors, statins, prevent cardiovascular events in part through their antiinflammatory properties. Because inflammation is positively and negatively regulated by T helper (Th) 1 cells and Th2 cells, respectively, we examined the effects of statins on the Th polarization in vitro and in vivo. Here we demonstrated that the statins tested, ie, cerivastatin, simvastatin, lovastatin, and atorvastatin, promoted Th2 polarization through both inhibition of Th1 development and augmentation of Th2 development of CD4+ T cells primed in vitro with anti-CD3 antibody and splenic antigen-presenting cells. Cerivastatin exerted most potent effect on modulation of Th1/Th2 development, and the effect was completely abrogated by an addition of mevalonate. Consistent with in vitro experiments, cerivastatin treatment decreased IFN-gamma production of lymph node cells from mice immunized with ovalbumin emulsified in complete Freund's adjuvant, indicating that Th1 development is also suppressed in an in vivo proinflammatory environment. In this murine model, cerivastatin significantly reduced mesangial matrix expansion of glomeruli in the kidney and attenuated proteinuria. The decrease of glomerular sclerosis by cerivastatin treatment was positively related to the suppression of interferon (IFN)-gamma-producing Th1 response in draining lymph node cells. Hence, these findings strongly suggest that statins' inhibition of 3-hydroxy-3-methylglutaryl-coenzyme A reductase regulates Th1/Th2 polarization in vivo and such a mechanism possibly plays a pathophysiological role in immune-related glomerular injury.

Engagement of CD43 enhances human immunodeficiency virus type 1 transcriptional activity and virus production that is induced upon TCR/CD3 stimulation

Human immunodeficiency virus type 1 (HIV-1) transcriptional activity is regulated by several cytokines and T cell activators. CD43 (sialophorin) is a sialoglycoprotein expressed on the surface of a wide variety of blood cells including T lymphocytes. Several studies have shown that CD43 ligation induces proliferation and activation of human T lymphocytes. We were thus interested in defining whether CD43-mediated signaling events can modulate the life cycle of HIV-1. We demonstrate here that CD43 cross-linking potentiates HIV-1 promoter-driven activity and virus production that is seen following the engagement of the T-cell receptor (TCR).CD3 complex. This effect is independent of the CD28 co-stimulatory molecule and is mediated by both NF-kappaB and NFAT transcription factors. A number of signal transducers known to be involved in the TCR/CD3-dependent signal transduction pathway, including p56(lck), p36(lat), and SLP-76, as well as capacitative entry of calcium, are crucial for the noticed CD43 co-stimulatory effect. Calcium mobilization studies indicate that a synergy is occurring between CD43- and TCR/CD3-mediated signaling events leading to an augmented calcium release. These data suggest that CD43 can be seen as a co-stimulatory cell surface constituent that can modulate HIV-1 expression in T lymphocytes.