Katalin Kis-Toth

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.

The dysregulation of cytokine networks in systemic lupus erythematosus.

Systemic lupus erythematosus (SLE) is an autoimmune disease associated with chronic immune activation and tissue damage. Organ damage in SLE results from the deposition of immune complexes and the infiltration of activated T cells into susceptible organs. Cytokines are intimately involved in every step of the SLE pathogenesis. Defective immune regulation and uncontrolled lymphocyte activation, as well as increased antigen presenting cell maturation are all influenced by cytokines. Moreover, expansion of local immune responses as well as tissue infiltration by pathogenic cells is instigated by cytokines. In this review, we describe the main cytokine abnormalities reported in SLE and discuss the mechanisms that drive their aberrant production as well as the pathogenic pathways that their presence promotes.

Suppression of autoimmunity and organ pathology in lupus-prone mice upon inhibition of calcium/calmodulin-dependent protein kinase type IV.

OBJECTIVE Systemic lupus erythematosus (SLE) is a chronic inflammatory disease associated with aberrant immune cell function. Treatment involves the use of indiscriminate immunosuppression, which results in significant side effects. SLE T cells express high levels of calcium/calmodulin-dependent protein kinase type IV (CaMKIV), which translocates to the nucleus upon engagement of the T cell receptor-CD3 complex and accounts for abnormal T cell function. The purpose of this study was to determine whether inhibition of CaMKIV would improve disease pathology. METHODS We treated MRL/lpr mice with KN-93, a CaMKIV inhibitor, starting at week 8 or week 12 of age and continuing through week 16 and evaluated skin lesions, proteinuria, kidney histopathology, proinflammatory cytokine production, and costimulatory molecule expression. We also determined the effect of silencing of CAMK4 on interferon-γ (IFNγ) expression by human SLE T cells. RESULTS CaMKIV inhibition in MRL/lpr mice resulted in significant suppression of nephritis and skin disease, decreased expression of the costimulatory molecules CD86 and CD80 on B cells, and suppression of IFNγ and tumor necrosis factor α production. In human SLE T cells, silencing of CAMK4 resulted in suppression of IFNγ production. CONCLUSION We conclude that suppression of CaMKIV mitigates disease development in lupus-prone mice by suppressing cytokine production and costimulatory molecule expression. Specific silencing of CAMK4 in human T cells results in similar suppression of IFNγ production. Our data justify the development of small-molecule CaMKIV inhibitors for the treatment of patients with SLE.

Deletion of microRNA-155 reduces autoantibody responses and alleviates lupus-like disease in the Fas(lpr) mouse

Significance The host immune system provides diverse defense mechanisms to fight harmful bacteria and viruses. One of these mechanisms is the production of antibodies targeting infectious agents. However, the production of antibodies has to be tightly controlled. Insufficient control of the immune system may result in the development of autoimmune diseases, including lupus. Lupus is characterized by the production of antibodies attacking the kidneys, leading to life-threatening kidney failure if untreated. In this study, we show that microRNA-155, one member of a family of regulatory molecules, promotes the production of antibodies. By deleting microRNA-155, we can prevent the production of harmful antibodies and alleviate lupus-like disease in mice. Our results suggest the possibility of targeting microRNA-155 to treat autoimmune diseases. MicroRNA-155 (miR-155) regulates antibody responses and subsequent B-cell effector functions to exogenous antigens. However, the role of miR-155 in systemic autoimmunity is not known. Using the death receptor deficient (Faslpr) lupus-prone mouse, we show here that ablation of miR-155 reduced autoantibody responses accompanied by a decrease in serum IgG but not IgM anti-dsDNA antibodies and a reduction of kidney inflammation. MiR-155 deletion in Faslpr B cells restored the reduced SH2 domain-containing inositol 5′-phosphatase 1 to normal levels. In addition, coaggregation of the Fc γ receptor IIB with the B-cell receptor in miR-155−/−-Faslpr B cells resulted in decreased ERK activation, proliferation, and production of switched antibodies compared with miR-155 sufficient Faslpr B cells. Thus, by controlling the levels of SH2 domain-containing inositol 5′-phosphatase 1, miR-155 in part maintains an activation threshold that allows B cells to respond to antigens.

Cytokine-controlled RANKL and osteoprotegerin expression by human and mouse synovial fibroblasts: fibroblast-mediated pathologic bone resorption.

OBJECTIVE To determine whether proinflammatory cytokine treatment or the complete absence of select cytokines modulates the expression of RANKL and osteoprotegerin (OPG) in synovial fibroblasts. METHODS Fibroblasts were isolated from normal and rheumatoid human synovium and from normal or arthritic joints of wild-type and cytokine gene-deficient (interleukin-4-knockout [IL-4 (-/-)] and interferon-gamma-knockout [IFNgamma (-/-)]) mice. Fibroblasts were stimulated with proinflammatory cytokines (tumor necrosis factor alpha [TNFalpha], IL-1beta, and IL-17) or antiosteoclastogenic cytokines (IL-4 and IFNgamma), alone or in combination, and the expression of RANKL and OPG was measured. RESULTS Proinflammatory cytokine-stimulated fibroblasts from rheumatoid and arthritic mouse joints expressed higher levels of RANKL and OPG than those from normal joints. IL-4 suppressed RANKL expression and increased OPG expression, IFNgamma reduced the production of both RANKL and OPG, and IL-17 had only a modest effect on the expression of RANKL or OPG. Additive effects of combination treatment (TNFalpha/IL-17 or IL-1beta/IL-17) were observed only in the human system. Extensive destruction was observed in the arthritic joints of IL-4 (-/-) mice, with a corresponding upward shift of the RANKL:OPG ratios. However, an IL-17 deficiency did not attenuate arthritis or reduce bone resorption. CONCLUSION Proinflammatory cytokines induce the expression of RANKL and OPG in both human and murine synovial fibroblasts. The RANKL:OPG ratios are shifted in favor of bone protection by IL-4 treatment, and, to a lesser extent, by IFNgamma treatment. Unexpectedly, an IL-17 deficiency alone does not induce reduced inflammatory bone destruction. Our results suggest that synovial fibroblasts may significantly contribute to bone resorption through modulation of RANKL and OPG production in a cytokine-rich milieu of inflamed joints.

Cytosolic DNA-activated Human Dendritic Cells are Potent Activators of the Adaptive Immune Response

Recent studies in cell lines and genetically engineered mice have demonstrated that cytosolic dsDNA could activate dendritic cells (DCs) to become effector APCs. Recognition of DNA might be a major factor in antimicrobial immune responses against cytosolic pathogens and also in human autoimmune diseases such as systemic lupus erythematosus. However, the role of cytosolic dsDNA in human DC activation and its effects on effector T and B cells are still elusive. In this study, we demonstrate that intracellular dsDNA is a potent activator of human monocyte-derived DCs as well as primary DCs. Activation by dsDNA depends on NF-κB activation, partially on the adaptor molecule IFN-promoter stimulator-1 and the novel cytosolic dsDNA receptor IFI16, but not on the previously recognized dsDNA sentinels absent in melanoma 2, DNA-dependent activator of IFN regulatory factor 3, RNA polymerase III, or high-mobility group boxes. More importantly, we report for the first time, to our knowledge, that human dsDNA-activated DCs, rather than LPS- or inflammatory cytokine mixture-activated DCs, represent the most potent inducers of naive CD4+ T cells to promote Th1-type cytokine production and generate CD4+ and CD8+ cytotoxic T cells. dsDNA-DCs, but not LPS- or mixture-activated DCs, induce B cells to produce complement-fixing IgG1 and IgG3 Abs. We propose that cytosolic dsDNA represents a novel, more effective approach to generate DCs to enhance vaccine effectiveness in reprogramming the adaptive immune system to eradicate infectious agents, autoimmunity, allergy, and cancer.

cAMP-responsive element modulator α (CREMα) suppresses IL-17F protein expression in T lymphocytes from patients with systemic lupus erythematosus (SLE).

Background: CREMα is increased in SLE T cells, and although it suppresses IL-2, it enhances IL-17A production. Results: CREMα binds to the IL17F promoter and suppresses its expression in SLE T cells. Conclusion: CREMα disrupts the balance between IL-17A and IL-17F in SLE T cells in favor of IL-17A. Significance: Understanding the molecular basis of the aberrant cytokine network in SLE will help in devising approaches to correct it. The proinflammatory cytokines IL-17A and IL-17F are primarily produced by Th17 lymphocytes. Both are involved in host defense mechanisms against bacterial and fungal pathogens and contribute to the development of various autoimmune diseases. T lymphocytes from patients with systemic lupus erythematosus (SLE) display increased expression of transcription factor cAMP-responsive element modulator α (CREMα), which has been documented to account for aberrant T cell function and contributes to the pathogenesis of SLE. Here, we provide evidence that IL-17F expression is reduced in SLE T cells. We demonstrate that CREMα binds to a yet unidentified CRE site within the proximal promoter. This results in reduced IL-17F expression in SLE T lymphocytes and is independent of activating epigenetic patterns (increased histone H3 Lys-18 acetylation, reduced histone H3 Lys-27 trimethylation, and CpG-DNA demethylation). Forced CREMα expression in human T lymphocytes results in reduced IL-17F expression. Our findings demonstrate extended involvement of CREMα in cytokine dysregulation in SLE by contributing to a disrupted balance between IL-17A and IL-17F. An increased IL-17A/IL-17F ratio may aggravate the proinflammatory phenotype of SLE.

Voltage-Gated Sodium Channel Nav1.7 Maintains the Membrane Potential and Regulates the Activation and Chemokine-Induced Migration of a Monocyte-Derived Dendritic Cell Subset

Expression of CD1a protein defines a human dendritic cell (DC) subset with unique functional activities. We aimed to study the expression of the Nav1.7 sodium channel and the functional consequences of its activity in CD1a− and CD1a+ DC. Single-cell electrophysiology (patch-clamp) and quantitative PCR experiments performed on sorted CD1a− and CD1a+ immature DC (IDC) showed that the frequency of cells expressing Na+ current, current density, and the relative expression of the SCN9A gene encoding Nav1.7 were significantly higher in CD1a+ cells than in their CD1a− counterparts. The activity of Nav1.7 results in a depolarized resting membrane potential (−8.7 ± 1.5 mV) in CD1a+ IDC as compared with CD1a− cells lacking Nav1.7 (−47 ± 6.2 mV). Stimulation of DC by inflammatory signals or by increased intracellular Ca2+ levels resulted in reduced Nav1.7 expression. Silencing of the SCN9A gene shifted the membrane potential to a hyperpolarizing direction in CD1a+ IDC, resulting in decreased cell migration, whereas pharmacological inhibition of Nav1.7 by tetrodotoxin sensitized the cells for activation signals. Fine-tuning of IDC functions by a voltage-gated sodium channel emerges as a new regulatory mechanism modulating the migration and cytokine responses of these DC subsets.

Developmental Switch of the Expression of Ion Channels in Human Dendritic Cells

Modulation of the expression and activity of plasma membrane ion channels is one of the mechanisms by which immune cells can regulate their intracellular Ca2+ signaling pathways required for proliferation and/or differentiation. Voltage-gated K+ channels, inwardly rectifying K+ channels, and Ca2+-activated K+ channels have been described to play a major role in controlling the membrane potential in lymphocytes and professional APCs, such as monocytes, macrophages, and dendritic cells (DCs). Our study aimed at the characterization and identification of ion channels expressed in the course of human DC differentiation from monocytes. We report in this study for the first time that immature monocyte-derived DCs express voltage-gated Na+ channels in their plasma membrane. The analysis of the biophysical and pharmacological properties of the current and PCR-based cloning revealed the presence of Nav1.7 channels in immature DCs. Transition from the immature to a mature differentiation state, however, was accompanied by the down-regulation of Nav1.7 expression concomitant with the up-regulation of voltage-gated Kv1.3 K+ channel expression. The presence of Kv1.3 channels seems to be common for immune cells; hence, selective Kv1.3 blockers may emerge as candidates for inhibiting various functions of mature DCs that involve their migratory, cytokine-secreting, and T cell-activating potential.

Increased Expression of SLAM Receptors SLAMF3 and SLAMF6 in Systemic Lupus Erythematosus T Lymphocytes Promotes Th17 Differentiation

Altered T cell function in systemic lupus erythematosus (SLE) is determined by various molecular and cellular abnormalities, including increased IL-17 production. Recent evidence suggests a crucial role for signaling lymphocyte activation molecules (SLAMs) in the expression of autoimmunity. In this study, we demonstrate that SLAMF3 and SLAMF6 expression is increased on the surface of SLE T cells compared with normal cells. SLAM coengagement with CD3 under Th17 polarizing conditions results in increased IL-17 production. SLAMF3 and SLAMF6 T cell surface expression and IL-17 levels significantly correlate with disease activity in SLE patients. Both naive and memory CD4+ T cells produce more IL-17 in response to SLAM costimulation as compared with CD28 costimulation. In naive CD4+ cells, IL-17 production after CD28 costimulation peaks on day 3, whereas costimulation with anti-SLAMF3 and anti-SLAMF6 Abs results in a prolonged and yet increasing production during 6 d. Unlike costimulation with anti-CD28, SLAM costimulation requires the presence of the adaptor molecule SLAM-associated protein. Thus, engagement of SLAMF3 and SLAMF6 along with Ag-mediated CD3/TCR stimulation represents an important source of IL-17 production, and disruption of this interaction with decoy receptors or blocking Abs should mitigate disease expression in SLE and other autoimmune conditions.