Differential expression and molecular associations of Syk in systemic lupus erythematosus T cells

Cellular targeting in autoimmunity

Many biologic agents that were first approved for the treatment of malignancies are now being actively investigated and used in a variety of autoimmune diseases such as rheumatoid arthritis (RA), antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis, systemic lupus erythematosus (SLE), and Sjogren's syndrome. The relatively recent advance of selective immune targeting has significantly changed the management of autoimmune disorders and in part can be attributed to the progress made in understanding effector cell function and their signaling pathways. In this review, we will discuss the recent FDA-approved biologic therapies that directly target immune cells as well as the most promising investigational drugs affecting immune cell function and signaling for the treatment of autoimmune disease.

Targeting the SYK-BTK axis for the treatment of immunological and hematological disorders: recent progress and therapeutic perspectives

Spleen Tyrosine Kinase (SYK) and Bruton's Tyrosine Kinase (BTK) are non-receptor cytoplasmic tyrosine kinases that are primarily expressed in cells of hematopoietic lineage. Both are key mediators in coupling activated immunoreceptors to downstream signaling events that affect diverse biological functions, from cellular proliferation, differentiation and adhesion to innate and adaptive immune responses. As such, pharmacological inhibitors of SYK or BTK are being actively pursued as potential immunomodulatory agents for the treatment of autoimmune and inflammatory disorders. Deregulation of SYK or BTK activity has also been implicated in certain hematological malignancies. To date, from a clinical perspective, pharmacological inhibition of SYK activity has demonstrated encouraging efficacy in patients with rheumatoid arthritis (RA), while patients with relapsed or refractory chronic lymphocytic leukemia (CLL)/small lymphocytic lymphoma (SLL) have benefited from covalent inhibitors of BTK in early clinical studies. Here, we review and discuss recent insights into the emerging role of the SYK-BTK axis in innate immune cell function as well as in the maintenance of survival and homing signals for tumor cell progression. The current progress on the clinical development of SYK and BTK inhibitors is also highlighted.

Rational design of highly selective spleen tyrosine kinase inhibitors

A novel approach to design selective spleen tyrosine kinase (Syk) inhibitors is described. Inhibition of spleen tyrosine kinase has attracted much attention as a mechanism for the treatment of autoimmune diseases such as asthma, rheumatoid arthritis, and SLE. Fostamatinib, a Syk inhibitor that successfully completed phase II clinical trials, also exhibits some undesirable side effects. More selective Syk inhibitors could offer safer, alternative treatments. Through a systematic evaluation of the kinome, we identified Pro455 and Asn457 in the Syk ATP binding site as a rare combination among sequence aligned kinases and hypothesized that optimizing the interaction between them and a Syk inhibitor molecule would impart high selectivity for Syk over other kinases. We report the structure-guided identification of three series of selective spleen tyrosine kinase inhibitors that support our hypothesis and offer useful guidance to other researchers in the field.

Altered AKT1 and MAPK1 gene expression on peripheral blood mononuclear cells and correlation with T-helper-transcription factors in systemic lupus erythematosus patients

Kinases have been implicated in the immunopathological mechanisms of Systemic Lupus Erythematosus (SLE). v-akt murine-thymoma viral-oncogene-homolog 1 (AKT1) and mitogen-activated-protein-kinase 1 (MAPK1) gene expressions in peripheral mononuclear cells from thirteen SLE patients with inactive or mild disease were evaluated using quantitative real-time reverse-transcription polymerase-chain-reaction and analyzed whether there was any correlation with T-helper (Th) transcription factors (TF) gene expression, cytokines, and S100A8/S100A9-(Calprotectin). Age- and gender-matched thirteen healthy controls were examined. AKT1 and MAPK1 expressions were upregulated in SLE patients and correlated with Th17-(Retinoic acid-related orphan receptor (ROR)-C), T-regulatory-(Treg)-(Transforming Growth Factor Beta (TGFB)-2), and Th2-(interleukin (IL)-5)-related genes. MAPK1 expression correlated with Th1-(IL-12A, T-box TF-(T-bet)), Th2-(GATA binding protein-(GATA)-3), and IL-10 expressions. IL-10 expression was increased and correlated with plasma Tumor Necrosis Factor (TNF)-α and Th0-(IL-2), Th1-(IL-12A, T-bet), GATA3, Treg-(Forkhead/winged-helix transcription factor- (FOXP)-3), and IL-6 expressions. FOXP3 expression, FOXP3/RORC, and FOXP3/GATA3 expression ratios were increased. Plasma IL-1β, IL-12(p70), Interferon-(IFN)-γ, and IL-6 cytokines were augmented. Plasma IL-1β, IL-6, IL-2, IFN-γ, TNF-α, IL-10, and IL-13 correlated with C-reactive protein, respectively. Increased Calprotectin correlated with neutrophils. Conclusion, SLE patients presented a systemic immunoinflammatory activity, augmented AKT1 and MAPK1 expressions, proinflammatory cytokines, and Calprotectin, together with increased expression of Treg-related genes, suggesting a regulatory feedback opposing the inflammatory activity.

Altered BCR signalling quality predisposes to autoimmune disease and a pre-diabetic state

The spleen tyrosine kinase family members Syk and Zap-70 are pivotal signal transducers downstream of antigen receptors and exhibit overlapping expression patterns at early lymphocytic developmental stages. To assess their differential kinase fitness in vivo, we generated mice, which carry a Zap-70 cDNA knock-in controlled by intrinsic Syk promoter elements that disrupts wild-type Syk expression. Kinase replacement severely compromised Erk1/2-mediated survival and proper selection of developing B cells at central and peripheral checkpoints, demonstrating critical dependence on BCR signalling quality. Furthermore, ITAM- and hemITAM-mediated activation of platelets and neutrophils was completely blunted, while surprisingly FcγR-mediated phagocytosis in macrophages was retained. The alteration in BCR signalling quality resulted in preferential development and survival of marginal zone B cells and prominent autoreactivity, causing the generation of anti-insulin antibodies and age-related glomerulonephritis. Development of concomitant fasting glucose intolerance in knock-in mice highlights aberrant B cell selection as a potential risk factor for type 1 diabetes, and suggests altered BCR signalling as a mechanism to cause biased cellular and Ig repertoire selection, ultimately contributing to B cell-mediated autoimmune predisposition.

CREMα suppresses spleen tyrosine kinase expression in normal but not systemic lupus erythematosus T cells

OBJECTIVE

T cells from patients with systemic lupus erythematosus (SLE) display increased amounts of spleen tyrosine kinase (Syk), which is involved in the aberrant CD3/T cell receptor-mediated signaling process, and increased amounts of CREMα, which suppresses the production of interleukin-2. Syk expression can be suppressed by CREMα. This study was undertaken to investigate why CREMα fails to suppress Syk expression in SLE T cells.

METHODS

CREMα was overexpressed in healthy T cells by transfection with CREMα expression vector, and Syk expression and phosphorylation were measured. A newly identified cAMP response element (CRE) site on the SYK promoter was characterized by chromatin immunoprecipitation (ChIP) and electrophoretic mobility shift assay. The CREMα-mediated repression of Syk expression was further evaluated by analyzing SYK promoter activity. T cells from SLE patients and healthy individuals were subjected to ChIP to evaluate CREMα binding and histone H3 acetylation.

RESULTS

Increased CREMα levels suppressed Syk expression by direct binding to a CRE site of the SYK promoter in T cells from healthy individuals but failed to do so in T cells from SLE patients. The failure of CREMα to suppress Syk expression in SLE T cells was due to weaker binding to the CRE site of the SYK promoter compared to healthy T cells because the promoter site is hypoacetylated in SLE T cells and therefore of limited access to transcription factors.

CONCLUSION

Our findings indicate that epigenetic alteration of the SYK promoter in SLE T cells results in the inability of the transcriptional repressor CREMα to bind and suppress the expression of Syk, resulting in aberrant T cell signaling.

Molecular basis for T cell response induced by altered peptide ligand of type II collagen

Mounting evidence from animal models has demonstrated that alterations in peptide-MHC interactions with the T cell receptor (TCR) can lead to dramatically different T cell outcomes. We have developed an altered peptide ligand of type II collagen, referred to as A9, which differentially regulates TCR signaling in murine T cells leading to suppression of arthritis in the experimental model of collagen-induced arthritis. This study delineates the T cell signaling pathway used by T cells stimulated by the A9·I-A(q) complex. We have found that T cells activated by A9 bypass the requirement for Zap-70 and CD3-ζ and signal via FcRγ and Syk. Using collagen-specific T cell hybridomas engineered to overexpress either Syk, Zap-70, TCR-FcRγ, or CD3-ζ, we demonstrate that A9·I-A(q) preferentially activates FcRγ/Syk but not CD3-ζ/Zap-70. Moreover, a genetic absence of Syk or FcRγ significantly reduces the altered peptide ligand induction of the nuclear factor GATA3. By dissecting the molecular mechanism of A9-induced T cell signaling we have defined a new alternate pathway that is dependent upon FcRγ and Syk to secrete immunoregulatory cytokines. Given the interest in using Syk inhibitors to treat patients with rheumatoid arthritis, understanding this pathway may be critical for the proper application of this therapy.

Role of CREM in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a complex autoimmune disease. Immune complex, autoantibodies and autoreactive lymphocytes are involved in manifestations of SLE. Recently, investigations have indicated that expression of the transcription factor cAMP responsive element modulator (CREM) is abnormal in T cells and might play an important role in the pathogenesis of SLE. CREM has much influence on the promoters, such as IL-2, c-fos, TCR ζ, and SYK. Moreover, activity of CREM itself has been demonstrated, particularly with an auto-regulatory feedback mechanism. Therefore, we will discuss the association of CREM and SLE based on current knowledge to unravel the mechanism of CREM performance.

Immune complexes and late complement proteins trigger activation of Syk tyrosine kinase in human CD4(+) T cells

In systemic lupus erythematosus (SLE), the autoantibodies that form immune complexes (ICs) trigger activation of the complement system. This results in the formation of membrane attack complex (MAC) on cell membrane and the soluble terminal complement complex (TCC). Hyperactive T cell responses are hallmark of SLE pathogenesis. How complement activation influences the T cell responses in SLE is not fully understood. We observed that aggregated human γ-globulin (AHG) bound to a subset of CD4(+) T cells in peripheral blood mononuclear cells and this population increased in the SLE patients. Human naive CD4(+) T cells, when treated with purified ICs and TCC, triggered recruitment of the FcRγ chain with the membrane receptor and co-localized with phosphorylated Syk. These events were also associated with aggregation of membrane rafts. Thus, results presented suggest a role for ICs and complement in the activation of Syk in CD4(+) T cells. Thus, we propose that the shift in signalling from ζ-chain-ZAP70 to FcRγ chain-Syk observed in T cells of SLE patients is triggered by ICs and complement. These results demonstrate a link among ICs, complement activation and phosphorylation of Syk in CD4(+) T cells.

c-Jun and Ets2 proteins regulate expression of spleen tyrosine kinase in T cells

Effector T cells and T cells from patients with systemic lupus erythematosus (SLE) express increased levels of the spleen tyrosine kinase (Syk). Syk binds to the T cell receptor (TCR)-CD3 complex and transduces the TCR-mediated signal in the cell more efficiently than the canonical CD3ζ chain. The reasons for the increased expression of Syk are unclear. In the present study, we found that Syk is regulated by the transcription factor c-Jun in cooperation with Ets2. c-Jun and Ets2 bound to the SYK promoter in close proximity and increased the promoter activity in a specific manner. Disruption of c-Jun and Ets2 expression by siRNA resulted in decreased expression of Syk. Overexpression of c-Jun but not Ets2 resulted in increase in Syk protein. c-Jun and Ets2 co-immunoprecipitated and had an additive effect on Syk expression. c-Jun-driven SYK promoter activation showed a similar pattern in B cells; however, as expected, basal promoter activity was much higher in B cells as compared with T cells. Overexpression of c-Jun led to increase in intracytoplasmic calcium flux following TCR stimulation. Moreover, we found that SLE T cells had increased levels of c-Jun at baseline and phosphorylated c-Jun upon activation. Finally, disruption of c-Jun and Ets2 in SLE T cells resulted in a decrease in calcium flux upon TCR stimulation. In conclusion, c-Jun in cooperation with Ets2 increases the expression of Syk and contributes to Syk-mediated heightened calcium responses in SLE T cells.

Targeting lymphocyte signaling pathways as a therapeutic approach to systemic lupus erythematosus

PURPOSE OF REVIEW

Over the past year several key pathways in systemic lupus erythematosus (SLE) lymphocyte signaling have been identified. Pathways that can be exploited for therapy are discussed in this review.

RECENT FINDINGS

Inhibition of SLE T cell activation by blocking spleen tyrosine kinase (Syk) and SLE T cell migration by blocking CD44 or CXCR4 lead to amelioration of lupus in lupus-prone mice. Similar results can be achieved by boosting CD8+ Treg numbers. Small molecules that block the kinases CaMKIV (calcium and calmodulin dependent kinase IV) and Bruton Tyrosine kinase (Btk) and the phosphatase calcineurin were shown to be effective in treating murine lupus. Finally, gene methylation status determines the expression of several key genes in SLE and strategies to correct it have shown promising results in preclinical studies.

SUMMARY

Molecules that enhance T cell receptor (TCR) signaling or increase lymphocyte migration can be inhibited successfully with significant improvement of disease intensity in lupus-prone mice using small molecules. Manipulation of promoter methylation and histone acetylation represents a novel way to alter gene transcription in SLE.

T cells stimulated with an analog peptide of type II collagen require the Fc receptor γ-chain to secrete interleukin-4 and suppress autoimmune arthritis in mice

OBJECTIVE

To explore the characteristics of the T cell population that responds to an analog peptide (A9) of type II collagen and regulates autoimmunity, using the collagen-induced arthritis (CIA) model.

METHODS

Analog peptide A9 is a 26-amino acid peptide analogous to the sequence of a segment of type II collagen (CII245-270) but with substitutions at amino acid positions 260 (alanine for isoleucine), 261 (hydroxyproline for alanine), and 263 (asparagine for phenylalanine). We previously showed that A9 profoundly suppressed CIA and immune responses to type II collagen. In order to determine the mechanism of suppression, we used transgenic mice whose T cells express a type II collagen-specific receptor (T cell receptor) and performed passive cell transfer experiments.

RESULTS

The results demonstrated that suppression of CIA by A9 is dependent on T cells. Using multiparameter flow cytometry, we determined that the cells responsible for suppression were CD4+ and expressed high levels of Fcε receptor Iγ chain (FcRγ). To establish the significance of this finding, we obtained mice genetically deficient in FcRγ in order to perform passive transfer experiments. The resulting FcRγ-/- CD4+ T cells, when primed by culture with A9, could not transfer the suppression of arthritis or secrete cytokines in response to A9.

CONCLUSION

Taken together, the results of this study suggest that the suppression of arthritis and the Th2 cytokine profile elicited by A9 is dependent on the presence of FcRγ in T cells. These findings are novel and may have therapeutic potential for patients with autoimmune arthritis.

Novel treatments for systemic lupus erythematosus

There are many new therapeutic directions for the disease systemic lupus erythematosus (SLE). Despite this, the US Food and Drug Administration (FDA) has approved only one biological agent and it involves B cells, now thought to play a significant role in the pathogenesis of SLE. The name of the drug is belimumab, which is an agent that removes the B-cell cytokine called B lymphocyte stimulation factor (BLyS). Rituximab did not achieve its primary endpoints, even though the consensus is that it may be effective in some forms of SLE including renal disease. The anticytokine therapies against interleukin (IL)-6, IL-10, IL-17 and tumor necrosis factor (TNF) are effective in their own ways and phase II and III trials are in progress. Of particular interest to immunologists are the anti-interferon alpha and gamma drugs, which show promise in the animal models. Modulation of costimulatory molecules; specifically, the anti CD40, CTLA-***Ig and ICOS/B7RP blockade agents offer possibilities for the future using new pathways heretofore limited to rheumatoid arthritis. Finally, the use of tyrosine kinase inhibitors is another direction that has been successful in the inhibition of SLE in the murine model; early trials in human SLE have begun.

Calcium signaling in systemic lupus erythematosus T cells: a treatment target

OBJECTIVE

Systemic lupus erythematosus (SLE) T cells display a hyperactive calcineurin/NF-AT pathway. The aim of this study was to determine whether this pathway is responsible for the aberrant SLE T cell function and to test the effectiveness of the recently recognized calcineurin inhibitor dipyridamole in limiting SLE-related pathology.

METHODS

T cells and mononuclear cells were isolated from the peripheral blood of SLE patients and healthy individuals. Murine cells were isolated from the spleens and lymph nodes of lupus-prone MRL/lpr mice and control MRL/MpJ mice. Cells were treated in vitro with tacrolimus, dipyridamole, or control. MRL/lpr mice were injected intraperitoneally with 50 mg/kg of dipyridamole 3 times a week for 3 weeks.

RESULTS

MRL/lpr T cells, especially CD3+CD4-CD8- cells, displayed a robust calcium influx upon activation and increased levels of NF-ATc1. MRL/lpr T cells (both CD4+ and CD3+CD4-CD8- cells) provided help to B cells to produce immunoglobulin in a calcineurin-dependent manner. Dipyridamole treatment of SLE T cells significantly inhibited CD154 expression, interferon-γ, interleukin-17 (IL-17), and IL-6 production, and T cell-dependent B cell immunoglobulin secretion. Treatment of MRL/lpr mice with dipyridamole alleviated lupus nephritis and prevented the appearance of skin ulcers.

CONCLUSION

NF-AT activation is a key step in the activation of SLE T cells and the production of immunoglobulin. Dipyridamole inhibits SLE T cell function and improves pathologic changes of the disease in lupus-prone mice. We propose that dipyridamole can be used in treatment regimens for patients with SLE.

The oral spleen tyrosine kinase inhibitor fostamatinib attenuates inflammation and atherogenesis in low-density lipoprotein receptor-deficient mice

OBJECTIVE

Spleen tyrosine kinase (SYK) has come into focus as a potential therapeutic target in chronic inflammatory diseases, such as rheumatoid arthritis and asthma, as well as in B-cell lymphomas. SYK has also been involved in the signaling of immunoreceptors, cytokine receptors, and integrins. We therefore hypothesized that inhibition of SYK attenuates the inflammatory process underlying atherosclerosis and reduces plaque development.

METHODS AND RESULTS

Low-density lipoprotein receptor-deficient mice consuming a high-cholesterol diet supplemented with 2 doses of the orally available SYK inhibitor fostamatinib for 16 weeks showed a dose-dependent reduction in atherosclerotic lesion size by up to 59±6% compared with the respective controls. Lesions of fostamatinib-treated animals contained fewer macrophages but more smooth muscle cells and collagen-characteristics associated with more stable plaques in humans. Mechanistically, fostamatinib attenuated adhesion and migration of inflammatory cells and limited macrophage survival. Furthermore, fostamatinib normalized high-cholesterol diet -induced monocytosis and inflammatory gene expression.

CONCLUSIONS

We present the novel finding that the SYK inhibitor fostamatinib attenuates atherogenesis in mice. Our data identify SYK inhibition as a potentially fruitful antiinflammatory therapeutic strategy in atherosclerosis.

Abnormalities of T cell signaling in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is an autoimmune disease resulting from a loss of tolerance to multiple self antigens, and characterized by autoantibody production and inflammatory cell infiltration in target organs, such as the kidneys and brain. T cells are critical players in SLE pathophysiology as they regulate B cell responses and also infiltrate target tissues, leading to tissue damage. Abnormal signaling events link to defective gene transcription and altered cytokine production, contributing to the aberrant phenotype of T cells in SLE. Study of signaling and gene transcription abnormalities in SLE T cells has led to the identification of novel targets for therapy.

Fostamatinib Disodium

The non-receptor tyrosine kinase Syk has a diverse range of biological functions, including a critical role in the intracellular signalling cascade for the surface immunoglobulin receptor on B lymphocytes, and the Fc receptor expressed on numerous immune effector cells. It is therefore seen as a potential therapeutic target in a variety of conditions, including autoimmune, allergic and malignant diseases. Fostamatinib disodium is the orally bioavailable prodrug of R406, a relatively selective small molecule inhibitor of Syk, that has accordingly shown activity in numerous cell types in vitro, and efficacy in a remarkable range of animal models in vivo, including rodent models of asthma, inflammatory arthritis, lupus, glomerulonephritis, diabetes and lymphoma. Success in these models has translated to phase II clinical trials in autoimmune thrombocytopenia, lymphoma and, most notably, rheumatoid arthritis, in which larger phase III trials are currently in progress. Whilst the diverse biological functions of Syk, coupled to the potential off-target effects of this kinase inhibitor are a source of possible toxicity, the available data thus far augurs well for future clinical use of Fostamatinib in a wide range of human diseases.

A systemic lupus erythematosus gene expression array in disease diagnosis and classification: a preliminary report

Systemic lupus erythematosus (SLE) is a clinically heterogeneous disease diagnosed on the presence of a constellation of clinical and laboratory findings. At the pathogenetic level, multiple factors using diverse biochemical and molecular pathways have been recognized. Succinct recognition and classification of clinical disease subsets, as well as the availability of disease biomarkers, remains largely unsolved. Based on information produced by the present authors' and other laboratories, a lupus gene expression array consisting of 30 genes, previously claimed to contribute to aberrant function of T cells, was developed. An additional eight genes were included as controls. Peripheral blood was obtained from 10 patients (19 samples) with SLE and six patients with rheumatoid arthritis (RA) as well as 19 healthy controls. T cell mRNA was subjected to reverse transcription and PCR, and the gene expression levels were measured. Conventional statistical analysis was performed along with principal component analysis (PCA) to capture the contribution of all genes to disease diagnosis and clinical parameters. The lupus gene expression array faithfully informed on the expression levels of genes. The recorded changes in expression reflect those reported in the literature by using a relatively small (5 ml) amount of peripheral blood. PCA of gene expression levels placed SLE samples apart from normal and RA samples regardless of disease activity. Individual principal components tended to define specific disease manifestations such as arthritis and proteinuria. Thus, a lupus gene expression array based on genes previously claimed to contribute to immune pathogenesis of SLE may define the disease, and principal components of the expression of 30 genes may define patients with specific disease manifestations.

Gene network analysis of bone marrow mononuclear cells reveals activation of multiple kinase pathways in human systemic lupus erythematosus

Background

Gene profiling studies provide important information for key molecules relevant to a disease but are less informative of protein-protein interactions, post-translational modifications and regulation by targeted subcellular localization. Integration of genomic data and construction of functional gene networks may provide additional insights into complex diseases such as systemic lupus erythematosus (SLE).

Methodology/Principal Findings

We analyzed gene expression microarray data of bone marrow mononuclear cells (BMMCs) from 20 SLE patients (11 with active disease) and 10 controls. Gene networks were constructed using the bioinformatic tool Ingenuity Gene Network Analysis. In SLE patients, comparative analysis of BMMCs genes revealed a network with 19 central nodes as major gene regulators including ERK, JNK, and p38 MAP kinases, insulin, Ca²⁺ and STAT3. Comparison between active versus inactive SLE identified 30 central nodes associated with immune response, protein synthesis, and post-transcriptional modification. A high degree of identity between networks in active SLE and non-Hodgkin's lymphoma (NHL) patients was found, with overlapping central nodes including kinases (MAPK, ERK, JNK, PKC), transcription factors (NF-kappaB, STAT3), and insulin. In validation studies, western blot analysis in splenic B cells from 5-month-old NZB/NZW F1 lupus mice showed activation of STAT3, ITGB2, HSPB1, ERK, JNK, p38, and p32 kinases, and downregulation of FOXO3 and VDR compared to normal C57Bl/6 mice.

Conclusions/Significance

Gene network analysis of lupus BMMCs identified central gene regulators implicated in disease pathogenesis which could represent targets of novel therapies in human SLE. The high similarity between active SLE and NHL networks provides a molecular basis for the reported association of the former with lymphoid malignancies.

Spleen tyrosine kinase inhibition prevents tissue damage after ischemia-reperfusion

Reperfusion injury to tissue following an ischemic event occurs as a consequence of an acute inflammatory response that can cause significant morbidity and mortality. Components of both the innate (complement, immunoglobulin, monocytes, and neutrophils) and adaptive (B and T lymphocytes) immune systems have been demonstrated to mediate tissue injury. Spleen tyrosine kinase (Syk) is responsible for membrane-mediated signaling in various cell types including B lymphocytes, macrophages, and T cells. We investigated the ability of a small drug Syk inhibitor, R788, to protect mice against mesenteric ischemia-reperfusion (I/R)-induced local (intestine) and remote lung injury. Mice were fed with chow containing a Syk inhibitor for 6 days before the performance of intestinal I/R, which resulted in silencing of the expression of the active phosphorylated Syk. Syk inhibition significantly suppressed both local and remote lung injury. The beneficial effect was associated with reduced IgM and complement 3 deposition in the tissues and significant reduction of polymorphonuclear cell infiltration. Our data place Syk upstream of events leading to the binding of natural antibodies to the ischemia-conditioned tissues and urge the consideration of the use of Syk inhibitors in the prevention or improvement of tissue injury of organs exposed to ischemia or hypoperfusion.

Suppression of skin and kidney disease by inhibition of spleen tyrosine kinase in lupus-prone mice

OBJECTIVE

Spleen tyrosine kinase (Syk) is involved in membrane-mediated signaling in various cells, including immune cells. It is overexpressed in T cells from patients with systemic lupus erythematosus (SLE), and its inhibition has been shown to improve T cell function as well as to improve disease manifestations in (NZB x NZW)F(1) lupus-prone mice and in patients with rheumatoid arthritis. While clinical trials examining Syk inhibition in patients with SLE are being considered, the aim of our experiments was to determine whether the therapeutic effects of Syk inhibition extend to other strains of lupus-prone mice and whether they result in improvement in skin disease and modification of established disease.

METHODS

Female MRL/lpr or BAK/BAX mice were studied. Starting either at age 4 weeks (before disease) or at age 16 weeks (after established disease) and continuing for up to 16 weeks, mice were fed chow containing the Syk inhibitor R788 or control chow.

RESULTS

We found that inhibition of Syk in MRL/lpr and BAK/BAX mice prevented the development of skin disease and significantly reduced established skin disease. Similarly, Syk inhibition reduced the size of the spleen and lymph nodes, suppressed the development of renal disease, and suppressed established renal disease. Discontinuation of treatment resulted in extended suppression of skin disease for at least 8 weeks and suppression of renal disease for 4 weeks.

CONCLUSION

Syk inhibition suppresses the development of lupus skin and kidney disease in lupus-prone mice, suppresses established disease in lupus-prone mice, and may represent a valuable treatment for patients with SLE.

Central role of nitric oxide in the pathogenesis of rheumatoid arthritis and systemic lupus erythematosus

Nitric oxide (NO) has been shown to regulate T cell functions under physiological conditions, but overproduction of NO may contribute to T lymphocyte dysfunction. NO-dependent tissue injury has been implicated in a variety of rheumatic diseases, including systemic lupus erythematosus (SLE) and rheumatoid arthritis (RA). Several studies reported increased endogenous NO synthesis in both SLE and RA, and recent evidence suggests that NO contributes to T cell dysfunction in both autoimmune diseases. The depletion of intracellular glutathione may be a key factor predisposing patients with SLE to mitochondrial dysfunction, characterized by mitochondrial hyperpolarization, ATP depletion and predisposition to death by necrosis. Thus, changes in glutathione metabolism may influence the effect of increased NO production in the pathogenesis of autoimmunity.

Tyrosine kinases in inflammatory dermatologic disease

Tyrosine kinases (TKs) are enzymes that catalyze the phosphorylation of tyrosine residues on protein substrates. They are key components of signaling pathways that drive an array of cellular responses including proliferation, differentiation, migration, and survival. Specific TKs have recently been identified as critical to the pathogenesis of several autoimmune and inflammatory diseases. Small-molecule inhibitors of TKs are emerging as a novel class of therapy that may provide benefit in certain patient subsets. In this review, we highlight TK signaling implicated in inflammatory dermatologic diseases, evaluate strategies aimed at inhibiting these aberrant signaling pathways, and discuss prospects for future drug development.

T cells as therapeutic targets in SLE

T cells contribute to the initiation and perpetuation of autoimmunity in systemic lupus erythematosus (SLE), and seem to be directly involved in the development of related organ pathology. Defects associated with CD8(+) and T-regulatory (T(REG)) cell function manifest in parallel with the expanded CD3(+)CD4(-)CD8(-) T cell lineage. The cytokine expression pattern is uniquely characterized by decreased expression of interleukin (IL)-2 and increased production of IL-17 and related cytokines. Therapeutic approaches that limit the cognate interaction between T cells and B cells, prevent inappropriate tissue homing and restore T(REG) cell function and the normal cytokine milieu have been entertained. Biochemical characterization of SLE T cells has revealed distinct early and late signaling aberrations, and has enabled the identification of novel molecular targets that can be corrected with small molecules, and biomarkers that may foretell disease activity and predict organ damage.

Pathogenesis of human systemic lupus erythematosus: recent advances

Systemic lupus erythematosus (SLE) is an autoimmune disease with manifestations derived from the involvement of multiple organs including the kidneys, joints, nervous system and hematopoietic organs. Immune system aberrations, as well as heritable, hormonal and environmental factors interplay in the expression of organ damage. Recent contributions from different fields have developed our understanding of SLE and reshaped current pathogenic models. Here, we review recent findings that deal with (i) genes associated with disease expression; (ii) immune cell molecular abnormalities that lead to autoimmune pathology; (iii) the role of hormones and sex chromosomes in the development of disease; and (iv) environmental and epigenetic factors thought to contribute to the expression of SLE. Finally, we highlight molecular defects intimately associated with the disease process of SLE that might represent ideal therapeutic targets and disease biomarkers.

Systems biology of lupus: mapping the impact of genomic and environmental factors on gene expression signatures, cellular signaling, metabolic pathways, hormonal and cytokine imbalance, and selecting targets for treatment

Systemic lupus erythematosus (SLE) is characterized by the dysfunction of T cells, B cells, and dendritic cells, the release of pro-inflammatory nuclear materials from necrotic cells, and the formation of antinuclear antibodies (ANA) and immune complexes of ANA with DNA, RNA, and nuclear proteins. Activation of the mammalian target of rapamycin (mTOR) has recently emerged as a key factor in abnormal activation of T and B cells in SLE. In T cells, increased production of nitric oxide and mitochondrial hyperpolarization (MHP) were identified as metabolic checkpoints upstream of mTOR activation. mTOR controls the expression T-cell receptor-associated signaling proteins CD4 and CD3zeta through increased expression of the endosome recycling regulator Rab5 and HRES-1/Rab4 genes, enhances Ca2+ fluxing and skews the expression of tyrosine kinases both in T and B cells, and blocks the expression of Foxp3 and the generation of regulatory T cells. MHP, increased activity of mTOR, Rab GTPases, and Syk kinases, and enhanced Ca2+ flux have emerged as common T and B cell biomarkers and targets for treatment in SLE.

Fyn and CD70 expression in CD4+ T cells from patients with systemic lupus erythematosus

OBJECTIVE

CD4+ T cells from patients with systemic lupus erythematosus (SLE) display defective function that contributes to abnormal activation of B cells and autoantibody production.

METHODS

We compared the transcript and protein levels of Fyn and CD70 in CD4+ T cells from patients with SLE (n = 41) and healthy individuals (n = 34). The CD4+ T cells were isolated by positive biomagnetic separation technique. The quantitative analysis of messenger RNA was performed by reverse transcription and real-time quantitative PCR. The protein contents in the CD4+ T cells were determined by Western blotting analysis.

RESULTS

We observed significantly higher levels of Fyn (p = 0.03) and CD70 (p = 0.029) transcripts in SLE CD4+ T cells than in controls. There was a significant increase in CD70 protein levels (p < 0.0001), but not Fyn protein levels (p = 0.081) in CD4+ T cells from patients with SLE compared to healthy individuals. In the group with high disease activity [SLE Disease Activity Index (SLEDAI) >/= 9], we observed a significantly higher Fyn protein content than in controls (p = 0.030). There was no correlation between Fyn and CD70 protein levels in SLE CD4+ T cells and disease activity as expressed in the SLEDAI scale.

CONCLUSION

We confirmed previous observations of higher expression of CD70 in CD4+ T cells from patients with SLE. Our findings suggest that increased Fyn protein content in CD4+ T cells can be associated with high SLE disease activity.

Tyrosine phosphorylation of 3BP2 regulates B cell receptor-mediated activation of NFAT

Adaptor protein c-Abl SH3 domain-binding protein-2 (3BP2, also referred to SH3BP2) regulates immune receptor-mediated signal transduction. In this report we focused on the molecular mechanism of 3BP2 function in B cell receptor (BCR) signaling. Engagement of BCR induces tyrosine phosphorylation of 3BP2. Genetic analysis demonstrated that Syk is critical for BCR-mediated tyrosine phosphorylation of 3BP2. Mutational analysis of 3BP2 revealed that both Tyr(183) and Src homology 2 (SH2) domain are necessary for 3BP2-mediated BCR-induced activation of nuclear factor of activated T cells (NFAT). Point mutation of Tyr(183) or Arg(486) in the SH2 domain of 3BP2 diminished BCR-mediated tyrosine phosphorylation of 3BP2. Endogenous 3BP2 forms a complex with tyrosine-phosphorylated cellular signaling molecules. Peptide binding experiments demonstrated that only phosphorylated Tyr(183) in 3BP2 could form a complex with the SH2 domain(s) of phospholipase Cgamma2 and Vav1 from B cell lysates. These interactions were represented by using bacterial glutathione S-transferase-phospholipase Cgamma2 or -Vav1 SH2 domain. Furthermore, pulldown and Far Western experiments showed that the 3BP2-SH2 domain directly binds to B cell linker protein (BLNK) after BCR stimulation. These results demonstrated that 3BP2 induces the protein complex with cellular signaling molecules through phosphorylation of Tyr(183) and SH2 domain leading to the activation of NFAT in B cells.

T cell receptor signaling induced by an analog peptide of type II collagen requires activation of Syk

We have previously described an analog peptide of type II collagen (CII) that can suppress collagen-induced arthritis (CIA). This analog peptide represents CII(245-270), the immunodominant epitope of CII, but with substitutions at 260, 261, and 263 - CII(245-270) (A(260), B(261), and N(263)) (A9). To elucidate the mechanisms responsible for suppression, we used mice transgenic for a collagen-specific T cell receptor (TCR). When we found that APCs pulsed with A9 failed to induce T cell phosphorylation of TCR-zeta and ZAP-70, we explored alternative signaling pathways. We determined that A9 instead induced phosphorylation of spleen tyrosine kinase (Syk). The importance of Syk was confirmed by the use of chemical Syk inhibitors, which blocked both cytokine secretion and activation of GATA-3 mediated by peptide A9. In summary, T cells use an alternative pathway in response to A9 that involves Syk. This novel T cell pathway may represent an important means for altering T cell phenotypes.

T-cell and B-cell signaling biomarkers and treatment targets in lupus

PURPOSE OF REVIEW

Systemic lupus erythematosus is characterized by the production of antinuclear autoantibodies and dysfunction of T-cells, B-cells, and dendritic cells. Here, we review newly recognized genetic factors and mechanisms that underlie abnormal intracellular signal processing and intercellular communication within the immune system in systemic lupus erythematosus.

RECENT FINDINGS

Activation of the mammalian target of rapamycin plays a pivotal role in abnormal activation of T and B-cells in systemic lupus erythematosus. In T-cells, increased production of nitric oxide and mitochondrial hyperpolarization were identified as metabolic checkpoints upstream of mammalian target of rapamycin activation. Mammalian target of rapamycin controls the expression T-cell receptor-associated signaling proteins CD4 and CD3zeta through increased expression of the endosome recycling regulator HRES-1/Rab4 gene, mediates enhanced Ca2+ fluxing and skews the expression of tyrosine kinases both in T and B-cells, and blocks the expression of Foxp3 and the expansion of regulatory T-cells. Mitochondrial hyperpolarization and the resultant ATP depletion predispose T-cells to necrosis, thus promoting the dendritic cell activation, antinuclear autoantibody production, and inflammation.

SUMMARY

Mitochondrial hyperpolarization, increased activity of mammalian target of rapamycin and Syk kinases, enhanced receptor recycling and Ca2+ flux have emerged as common T and B-cell biomarkers and targets for treatment in systemic lupus erythematosus.

Systemic lupus erythematosus: new molecular targets

T cells from patients with systemic lupus erythematosus exhibit a notable array of defects that probably contribute to the origin and development of the disease. Such abnormalities include an abnormal response to stimulation, aberrant expression of molecules that play key roles in intracellular signalling pathways, altered transcription factor activation and binding, and skewed gene expression. The combination of these alterations leads the cell to the expression of a particular phenotype that intense research has gradually uncovered over the last years. The aim of this article is to review the findings that have allowed us to better understand the behaviour of the lupus T cell and highlight the molecules that represent potential therapeutic targets.