T-lymphocyte signalling in systemic lupus erythematosus: a lipid raft perspective

Pre-organized landscape of T cell surface

T cell activation is initiated by the recognition of specific antigenic peptides and subsequently accomplished by complex signaling cascades. These aspects have been extensively studied for decades as pivotal factors in the establishment of adaptive immunity. However, how receptors or signaling molecules are organized in the resting state prior to encountering antigens has received less attention. Recent advancements in super-resolution microscopy techniques have revealed topographically controlled pre-formed organization of key molecules involved in antigen recognition and signal transduction on microvillar projections of T cells before activation and substantial effort has been dedicated to characterizing the topological structure of resting T cells over the past decade. This review will summarize our current understanding of how key surface receptors are pre-organized on the T-cell plasma membrane and discuss the potential role of these receptors, which are preassembled prior to ligand binding in the early activation events of T cells.

Attenuated Total Reflectance-Fourier Transform Infrared (ATR-FTIR) Spectroscopy Discriminates the Elderly with a Low and High Percentage of Pathogenic CD4+ T Cells

In the aging process, the presence of interleukin (IL)-17-producing CD4+CD28-NKG2D+T cells (called pathogenic CD4+ T cells) is strongly associated with inflammation and the development of various diseases. Thus, their presence needs to be monitored. The emergence of attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy empowered with machine learning is a breakthrough in the field of medical diagnostics. This study aimed to discriminate between the elderly with a low percentage (LP; ≤3%) and a high percentage (HP; ≥6%) of pathogenic CD4+CD28-NKG2D+IL17+ T cells by utilizing ATR-FTIR coupled with machine learning algorithms. ATR spectra of serum, exosome, and HDL from both groups were explored in this study. Only exosome spectra in the 1700–1500 cm⁻¹ region exhibited possible discrimination for the LP and HP groups based on principal component analysis (PCA). Furthermore, partial least square-discriminant analysis (PLS-DA) could differentiate both groups using the 1700–1500 cm⁻¹ region of exosome ATR spectra with 64% accuracy, 69% sensitivity, and 61% specificity. To obtain better classification performance, several spectral models were then established using advanced machine learning algorithms, including J48 decision tree, support vector machine (SVM), random forest (RF), and neural network (NN). Herein, NN was considered to be the best model with an accuracy of 100%, sensitivity of 100%, and specificity of 100% using serum spectra in the region of 1800–900 cm⁻¹. Exosome spectra in the 1700–1500 and combined 3000–2800 and 1800–900 cm⁻¹ regions using the NN algorithm gave the same accuracy performance of 95% with a variation in sensitivity and specificity. HDL spectra with the NN algorithm also showed excellent test performance in the 1800–900 cm⁻¹ region with 97% accuracy, 100% sensitivity, and 95% specificity. This study demonstrates that ATR-FTIR coupled with machine learning algorithms can be used to study immunosenescence. Furthermore, this approach can possibly be applied to monitor the presence of pathogenic CD4+ T cells in the elderly. Due to the limited number of samples used in this study, it is necessary to conduct a large-scale study to obtain more robust classification models and to assess the true clinical diagnostic performance.

The impact of sex on susceptibility to systemic lupus erythematosus and rheumatoid arthritis; a bioinformatics point of view

The unknown etiology of systemic autoimmune diseases, such as Systemic Lupus Erythematosus (SLE) and Rheumatoid Arthritis (RA), with a remarkable predominance of female, have prompted many researchers for unveiling the precise molecular mechanisms involved in this gender bias. In fact, depending on hormones and transcribed genes from sex chromosomes, at least, the initial mechanisms involved in pathogenesis might differ largely. With the aim of elucidating the above mechanisms, we have tried to specify the differentially expressed genes (DEGs) extracted from microarray libraries from both female and male SLE and RA patients. Subsequently, the androgen and estrogen receptor elements (ARE and ERE) among differentially expressed transcription factors (TFs) and the DEGs located on X or Y chromosomes have been determined. Moreover, the pathways regarding the common DEGs in both sexes are enriched. Our data revealed several ARE and ERE-containing genes (LCN2, LTF, RPL31, RPL9, RPS17, RPS24, RPS27L, S100A8, ABCA1, HIST1H2BD, ISG15, MAFB, GNLY, EVL, and HDC) to be associated with the related autoimmune disease and sex. Also, two DEGs (KDM5D and RPS4Y1) in SLE patients were determined to be on Y chromosome with one had been proved to be associated with autoantigens in SLE. Altogether, our data showed a number of plausible pathways in both autoimmune conditions together with the relevance of several sex-related genes in the mentioned diseases pathogenesis.

Expression of caveolin family proteins in serum of patients with systemic lupus erythematosus

OBJECTIVES

Caveolin family proteins, including caveolin-1 (Cav-1), caveolin-2 (Cav-2), and caveolin-3 (Cav-3), are identified as the principal protein components of caveolae in mammalian cells. Circulating form of caveolin family proteins can be used as a good potential biomarker for predicting disease.

METHODS

To investigate the clinical significance of the serological levels of caveolin family proteins in patients with systemic lupus erythematosus (SLE), we evaluated the soluble serum levels of caveolin family proteins in patients with SLE by enzyme-linked immunosorbent assay (ELISA) and assessed their associations with various known clinical variables.

RESULTS

The major findings of our study are as follows: Cav-2 was not detected in serum of SLE patients and normal controls (NCs). Serum Cav-1 and Cav-3 levels were higher in SLE patients compared with NCs. There were no significant correlations between serum Cav-1 and Cav-3 levels and SLE disease activity. Further analysis showed that serum Cav-3 may be more valuable as a marker than serum Cav-1 in SLE patients.

CONCLUSION

Serum levels of Cav-1 and Cav-3 might have a diagnostic role in patients with SLE. However, their predictive and prognostic value was not determined. Further studies are necessary to determine the potential clinical significance of these assays in SLE.

Lipid rafts in immune signalling: current progress and future perspective

Lipid rafts are dynamic assemblies of proteins and lipids that harbour many receptors and regulatory molecules and so act as a platform for signal transduction. They float freely within the liquid-disordered bilayer of cellular membranes and can cluster to form larger ordered domains. Alterations in lipid rafts are commonly found to be associated with the pathogenesis of several human diseases and recent reports have shown that the raft domains can also be perturbed by targeting raft proteins through microRNAs. Over the last few years, the importance of lipid rafts in modulating both innate and acquired immune responses has been elucidated. Various receptors present on immune cells like B cells, T cells, basophils and mast cells associate with lipid rafts on ligand binding and initiate signalling cascades leading to inflammation. Furthermore, disrupting lipid raft integrity alters lipopolysaccharide-induced cytokine secretion, IgE signalling, and B-cell and T-cell activation. The objective of this review is to summarize the recent progress in understanding the role of lipid rafts in the modulation of immune signalling and its related therapeutic potential for autoimmune diseases and inflammatory disorders.

Cardiovascular disease complications in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a highly variable autoimmune disease characterized by aberrant host-immune responses and chronic inflammation. Recently, a strong association between cardiovascular (CV) disease and SLE has emerged. Thus, low serum, high-density lipoprotein strongly correlated with elevated erythrocyte sedimentation rate, IL-6, TNF-alpha and the SLE disease activity index after adjusting for age, gender, race, BMI, insulin sensitivity and any concurrent drug use. In SLE, CV disease is characterized by increased VEGF, which may alter vascular hemostasis and promote neoangiogenesis. Increased low-density lipoprotein-cholesterol and proinflammatory high-density lipoprotein-cholesterol uptake by monocytes together with enhanced low-density lipoprotein-cholesterol oxidation results in the deposition of altered cholesterol forms into the vascular wall. This contributes to precocious and accelerated development of coronary artery plaques. Cholesterol-reducing drugs should be considered in the standard of care of SLE patients, especially in those with an unfavorable CV disease risk profile, which could reduce the probability of atherosclerosis progressing to CV disease or stroke in these patients.

Lupus and T cells

T-cell abnormalities and aberrant T helper cytokine profiles have been implicated in the loss of immune tolerance to nuclear and cytoplasmic antigens and linked to a variety of clinical manifestations in systemic lupus erythematosus (SLE). Here, we review the role of T cells in promoting and maintaining SLE in relation to their cellular and molecular abnormalities and provide an update on recent T cell-targeted therapeutic approaches for the restoration of T cell homeostasis in the disease.

Comparative effects of DHA and EPA on cell function

Fish oil supplementation has been reported to be generally beneficial in autoimmune, inflammatory and cardiovascular disorders. Most researchers have attributed these beneficial effects to the high content of omega-3 fatty acids in fish oil (FO). The effects of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are not differentiated in most studies. In fact, up to 1990, purified DHA was not available for human use and there was no study regarding its effects on human immune response. In this review, the differences in the effects of these two fatty acids on cell function are discussed. Studies have shown that EPA and DHA have also different effects on leukocyte functions such as phagocytosis, chemotactic response and cytokine production. DHA and EPA modulate differently expression of genes in lymphocytes. Activation of intracellular signaling pathways involved with lymphocyte proliferation is also differently affected by these two fatty acids. In relation to insulin producing cell line RINm5F, DHA and EPA are cytotoxic at different concentrations and the proteins involved with cell death are differently modulated by these two fatty acids. Substantial improvement in the therapeutic usage of omega-3 fatty acid-rich FO will be possible with the discovery of the different mechanisms of actions of DHA and EPA.

Lysosomal targeting and trafficking of acid sphingomyelinase to lipid raft platforms in coronary endothelial cells

OBJECTIVE

The purpose of this study was to determine whether lysosome trafficking and targeting of acid sphingomyelinase (ASMase) to this organelle contribute to the formation of lipid raft (LR) signaling platforms in the membrane of coronary arterial endothelial cells (CAECs).

METHODS AND RESULTS

By measurement of fluorescent resonance energy transfer (FRET), it was found that in FasL-stimulated CAECs, membrane lamp1 (a lysosome marker protein) or Fas and GM1 (a LR marker) were trafficking together. Cofocal colocalization assay showed that ceramide was enriched in these LR platforms. Further studies demonstrated that these ceramide molecules in LR platforms were colocalized with ASMase, a ceramide producing enzyme. Fluorescence imaging of living CAECs loaded with lysosomal specific dyes demonstrated that lysosomes fused with membrane on FasL stimulation. In the presence of lysosome function inhibitors, bafilomycin (Baf) or glycyl-L-phenylalanine-beta-naphthylamide (GPN), these FasL-induced changes were abolished. Moreover, this FasL-induced formation of LR platforms was also blocked in ECs transfected with siRNA of sortilin, an intracellular transporter for targeting of ASMase to lysosomes. Functionally, FasL-induced impairment of vasodilator response was reversed by lysosomal inhibitors or sortilin gene silencing.

CONCLUSIONS

Lysosomal trafficking and targeting of ASMase are importantly involved in LRs clustering in ECs membrane, leading to the formation of signaling platforms or signalosomes.

Altered T and B lymphocyte signaling pathways in lupus

Systemic lupus erythematosus (SLE) has long been recognized to be characterized by dysregulated signaling pathways in T and B lymphocytes, beginning with observations of cellular hyperactivity and hyperresponsiveness, and evolving to recent studies focused upon the genetic and molecular bases of such phenomena. This review focuses on recently elucidated signaling abnormalities currently thought to be intrinsic to T and/or B cells in human SLE.

Agrin signalling contributes to cell activation and is overexpressed in T lymphocytes from lupus patients

It is shown in this study that the heparan sulfate proteoglycan agrin is overexpressed in T cells isolated from patients with the autoimmune disease systemic lupus erythematosus (SLE). Freshly isolated CD4(+) and CD8(+) subpopulations both exhibited higher expression over healthy controls, which however, gradually declined when cells were cultured in vitro. Agrin expression was induced following in vitro activation of cells via their Ag receptor, or after treatment with IFN-alpha, a cytokine shown to be pathogenic in lupus. Furthermore, serum from SLE patients with active disease was able to induce agrin expression when added to T cells from healthy donors, an increase that was partially blocked by neutralizing anti-IFN-alpha Abs. Cross-linking agrin with mAbs resulted in rapid reorganization of the actin cytoskeleton, activation of the ERK MAPK cascade, and augmentation of anti-CD3-induced proliferation and IL-10 production, indicating that agrin is a functional receptor in T cells. These results demonstrate that agrin expression in human T cells is regulated by cell activation and IFN-alpha, and may have an important function during cell activation with potential implications for autoimmunity.

Critical role of lipid raft redox signaling platforms in endostatin-induced coronary endothelial dysfunction

OBJECTIVE

Endostatin (EST) was found to initiate a redox signaling cascade associated with activation of NADPH oxidase in endothelial cells (ECs). The present study tested whether EST stimulates clustering of ceramide-enriched lipid rafts (LRs), which assembles and activates NADPH oxidase to form redox signaling platforms.

METHODS AND RESULTS

Using confocal microscopy, we first demonstrated a colocalization of LR clusters with NADPH oxidase subunits, gp91(phox) and p47(phox) in the ECs membrane on EST stimulation. Immunoblot analysis of floated detergent-resistant membrane fractions found that in LR fractions NADPH oxidase subunits gp91(phox) and p47(phox) are enriched and that the activity of this enzyme increased dramatically, as measured by electron spin resonance (ESR) spectrometry. This EST-increased LR platform formation was shown to be attenuated by inhibition or RNA interference of acid sphingomyelinase (A-SMase). Functionally, EST pretreatment significantly impaired bradykinin or A23187-induced vasodilation in isolated small coronary arteries, which could be partially reversed by LR disruptors.

CONCLUSIONS

The early injury effect of EST on the vascular endothelium is associated with the formation of redox signaling platforms via lipid raft clustering.

Contribution of lysosomal vesicles to the formation of lipid raft redox signaling platforms in endothelial cells

We have demonstrated that the formation of lipid raft (LR)-redox signaling platforms membrane is associated with activation of acid sphingomyelinase (ASMase) in coronary arterial endothelial cells (CAECs). Given that the trafficking of lysosomal vesicles might play an essential role in ASMase activation, the present study tested whether lysosomal vesicles contribute to the formation of LR redox signaling platforms. By confocal microscopy, we found that Fas ligand (FasL) induced the formation of LR clusters in the plasma membrane of CAECs, accompanied by aggregation of NAD(P)H oxidase subunits, gp91phox and p47phox, and ROS production. When the cells were pretreated with two structurally different lysosomal vesicle function inhibitors, bafilomycin A1 (Baf) and glycyl-L-phenylalanine-beta-naphthylamide (GPN), the FasL-induced LRs clustering was substantially blocked, and corresponding ROS production significantly decreased. By confocal microscopic observations in living CAECs by using LysoTracker, a colocalization of LRs and lysosomal vesicles was found around the cell membrane, which was abolished by Baf or GPN. Functionally, FasL-induced inhibition of endothelium-dependent vasorelaxation was also reduced by both inhibitors of lysosome function. These results suggest that lysosomal vesicles importantly contribute to the formation of LR-redox signaling platforms and thereby participate in the oxidative injury of endothelial function during activation of death receptor-Fas in coronary arteries.

Altered dynamics of Kv1.3 channel compartmentalization in the immunological synapse in systemic lupus erythematosus

Aberrant T cell responses during T cell activation and immunological synapse (IS) formation have been described in systemic lupus erythematosus (SLE). Kv1.3 potassium channels are expressed in T cells where they compartmentalize at the IS and play a key role in T cell activation by modulating Ca(2+) influx. Although Kv1.3 channels have such an important role in T cell function, their potential involvement in the etiology and progression of SLE remains unknown. This study compares the K channel phenotype and the dynamics of Kv1.3 compartmentalization in the IS of normal and SLE human T cells. IS formation was induced by 1-30 min exposure to either anti-CD3/CD28 Ab-coated beads or EBV-infected B cells. We found that although the level of Kv1.3 channel expression and their activity in SLE T cells is similar to normal resting T cells, the kinetics of Kv1.3 compartmentalization in the IS are markedly different. In healthy resting T cells, Kv1.3 channels are progressively recruited and maintained in the IS for at least 30 min from synapse formation. In contrast, SLE, but not rheumatoid arthritis, T cells show faster kinetics with maximum Kv1.3 recruitment at 1 min and movement out of the IS by 15 min after activation. These kinetics resemble preactivated healthy T cells, but the K channel phenotype of SLE T cells is identical to resting T cells, where Kv1.3 constitutes the dominant K conductance. The defective temporal and spatial Kv1.3 distribution that we observed may contribute to the abnormal functions of SLE T cells.

Atorvastatin restores Lck expression and lipid raft-associated signaling in T cells from patients with systemic lupus erythematosus

Loss of tolerance to self-Ags in patients with systemic lupus erythematosus (SLE), a prototypic autoimmune disease, is associated with dysregulation of T cell signaling, including the depletion of total levels of lymphocyte-specific protein kinase (Lck) from sphingolipid-cholesterol-enriched membrane microdomains (lipid rafts). Inhibitors of 3-hyroxy-3-methylgluteryl CoA reductase (statins) can modify the composition of lipid rafts, resulting in alteration of T cell signaling. In this study, we show that atorvastatin targets the distribution of signaling molecules in T cells from SLE patients, by disrupting the colocalization of total Lck and CD45 within lipid rafts, leading to a reduction in the active form of Lck. Upon T cell activation using anti-CD3/anti-CD28 in vitro, the rapid recruitment of total Lck to the immunological synapse was inhibited by atorvastatin, whereas ERK phosphorylation, which is decreased in SLE T cells, was reconstituted. Furthermore, atorvastatin reduced the production of IL-10 and IL-6 by T cells, implicated in the pathogenesis of SLE. Thus, atorvastatin reversed many of the signaling defects characteristic of SLE T cells. These findings demonstrate the potential for atorvastatin to target lipid raft-associated signaling abnormalities in autoreactive T cells and provide a rationale for its use in therapy of autoimmune disease.

CD134 expression on CD4+ T cells is associated with nephritis and disease activity in patients with systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is characterized by a deviation of the immune system that involves T cell-dependent autoantibody production. The aim of this study was to investigate the role of co-stimulatory markers on T cells in this disease. Twenty-eight patients with SLE as defined by the American College of Rheumatology (ACR) criteria and 11 healthy controls were included into the study. Eleven patients had biopsy-proven lupus nephritis while 17 patients had no clinical evidence of lupus nephritis. Clinical disease activity was assessed according to the systemic lupus erythematosus disease index (SLEDAI). CD4+ T cell populations in the peripheral blood were analysed for the expression of co-stimulatory markers CD45RO, CD70, CD80, CD86, CD137, CD137L, CD134, CD152, CD154 and ICOS. SLE patients showed an increased frequency of peripheral CD4+ T cells expressing high levels of CD80, CD86 and CD134 compared to healthy controls (7.1 +/- 1.5% versus 1.7 +/- 0.9%; P < 0.005; 2.3 +/- 0.4% versus 1.0 +/- 0.2%; P = 0.008, 20.2 +/- 2.0% versus 10.6 +/- 1.9%; P < 0.005, respectively). Significantly higher levels of CD80 on CD4+ T cells were detected in SLE patients with lupus nephritis compared to patients without nephritis (11.9 +/- 3.3% versus 4.0 +/- 0.7%; P < 0.005). There was an increased presence of CD134+ CD4+ cells in SLE patients with lupus nephritis (27.5 +/- 4.0% versus 15.5 +/- 1.3%; P < 0.005). CD80 and CD134 expression was significantly correlated with SLEDAI (r = 0.42, P = 0.03; r = 0.56, P < 0.005). Co-stimulatory molecules on CD4+ T cells are associated with renal disease and disease activity in patients with systemic lupus erythematosus.

Lipid rafts in T cell receptor signalling

The molecular events and the protein components that are involved in signalling by the T cell receptor (TCR) for antigen have been extensively studied. Activation of signalling cascades following TCR stimulation depends on the phosphorylation of the receptor by the tyrosine kinase Lck, which localizes to the cytoplasmic face of the plasma membrane by virtue of its post-translational modification. However, the precise order of events during TCR phosphorylation at the plasma membrane, remains to be defined. A current theory that describes early signalling events incorporates the function of lipid rafts, microdomains at the plasma membrane with distinct lipid and protein composition. Lipid rafts have been implicated in diverse biological functions in mammalian cells. In T cells, molecules with a key role in TCR signalling, including Lck, localize to these domains. Importantly, mutant versions of these proteins which fail to localise to raft domains were unable to support signalling by the TCR. Biochemical studies using purified detergent-resistant membranes (DRM) and confocal microscopy have suggested that upon stimulation, the TCR and Lck-containing lipid rafts may come into proximity allowing phosphorylation of the receptor. Further, there are data suggesting that phosphorylation of the TCR could depend on a transient increase in Lck activity that takes place within lipid rafts to initiate signalling. Current results and a model of how lipid rafts may regulate TCR signalling are discussed.

The role of nitric oxide in abnormal T cell signal transduction in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a chronic autoimmune disease characterized by production of antinuclear autoantibodies and diverse array of clinical manifestations. T cells from patients with SLE have been shown to be activated in vivo and provide help to autoreactive B cells. Lupus T cells exhibit enhanced spontaneous and diminished activation-induced apoptosis and predisposition to necrosis. Persistent mitochondrial hyperpolarization and ATP depletion - associated with significantly increased mitochondrial mass - characterize T lymphocyte dysfunction in SLE. In addition to cell death abnormalities, mitochondrial dysfunction is associated with altered signal transduction through the T cell receptor and Ca2+ fluxing. Exposure of normal T cell to nitric oxide induces mitochondrial hyperpolarization and biogenesis and regenerates the Ca2+ signaling profile of lupus T cells. This article reviews a novel understanding of the role of nitric oxide in signal transduction and cell death abnormalities in SLE.

Regulation of T-cell receptor signalling by membrane microdomains

There is now considerable evidence suggesting that the plasma membrane of mammalian cells is compartmentalized by functional lipid raft microdomains. These structures are assemblies of specialized lipids and proteins and have been implicated in diverse biological functions. Analysis of their protein content using proteomics and other methods revealed enrichment of signalling proteins, suggesting a role for these domains in intracellular signalling. In T lymphocytes, structure/function experiments and complementary pharmacological studies have shown that raft microdomains control the localization and function of proteins which are components of signalling pathways regulated by the T-cell antigen receptor (TCR). Based on these studies, a model for TCR phosphorylation in lipid rafts is presented. However, despite substantial progress in the field, critical questions remain. For example, it is unclear if membrane rafts represent a homogeneous population and if their structure is modified upon TCR stimulation. In the future, proteomics and the parallel development of complementary analytical methods will undoubtedly contribute in further delineating the role of lipid rafts in signal transduction mechanisms.