Cytokines in the Immunopathogenesis of Lupus

Decreased T cell ERK pathway signaling may contribute to the development of lupus through effects on DNA methylation and gene expression

T cells from patients with active lupus have multiple biochemical abnormalities. One of these is DNA hypomethylation, which in model systems alters gene expression and induces lupus-like autoimmunity. Recent reports indicate that DNA methylation is regulated in part by the ERK pathway, and that ERK pathway signaling is diminished in lupus T cells. This suggests a model in which defective T cell ERK pathway signaling contributes to the development of autoimmunity by decreasing DNA methyltransferase expression, modifying DNA methylation patterns and altering gene expression. This mechanism could contribute to idiopathic and drug-induced lupus.

Mitochondrial dysfunction in T cells of patients with systemic lupus erythematosus

Activation, proliferation, or programmed cell death of T lymphocytes are dependent on controlled reactive oxygen intermediates (ROI) production and ATP synthesis in mitochondria. The mitochondrial transmembrane potential (Delta Psi(m)) also plays a decisive role in cell survival by controlling activity of redox-sensitive caspases. T lymphocytes of patients with systemic lupus erythematosus (SLE) exhibit mitochondrial hyperpolarization, increased ROI production, diminished intracellular glutathione levels, cytoplasmic alkalinization, and ATP depletion that mediate enhanced spontaneous and diminished activation-induced apoptosis and sensitize lupus T cells to necrosis. These redox and metabolic checkpoints represent novel targets for pharmacological intervention in SLE.

Possible mechanisms of gender bias in SLE: a new hypothesis involving a comparison of SLE with atopy

The prevalence of systemic lupus erythematosus (SLE) is far higher in females than in males, and numerous investigations of this gender bias have been performed from several perspectives. Sex hormones, particularly estrogens, may be significant in causing the gender discrepancy. This article discusses the possible importance of estrogens in regulating the expression of and responsivity to autoantigens in SLE and in atopic disorders, which are associated with hyperreactivity to exogenous antigens. Estrogens seem to play an important role in the overexpression of endogenous autoantigens, such as human endogenous retroviruses (HERV), and this may be related to the existence of a gender bias in the incidence of SLE but not atopy.

Persistent mitochondrial hyperpolarization, increased reactive oxygen intermediate production, and cytoplasmic alkalinization characterize altered IL-10 signaling in patients with systemic lupus erythematosus

Abnormal death signaling in lymphocytes of systemic lupus erythematosus (SLE) patients has been associated with elevation of the mitochondrial transmembrane potential (Delta psi(m)) and increased production of reactive oxygen intermediates (ROI). The resultant ATP depletion sensitizes T cells for necrosis that may significantly contribute to inflammation in patients with SLE. In the present study, the role of mitochondrial signal processing in T cell activation was investigated. CD3/CD28 costimulation of PBL elicited transient mitochondrial hyperpolarization and intracellular pH (pH(i)) elevation, followed by increased ROI production. Baseline Delta psi(m), ROI production, and pH(i) were elevated, while T cell activation-induced changes were blunted in 15 patients with SLE in comparison with 10 healthy donors and 10 rheumatoid arthritis patients. Similar to CD3/CD28 costimulation, treatment of control PBL with IL-3, IL-10, TGF-beta(1), and IFN-gamma led to transient Delta psi(m) elevation. IL-10 had diametrically opposing effects on mitochondrial signaling in lupus and control donors. Unlike healthy or rheumatoid arthritis PBL, cells of lupus patients were resistant to IL-10-induced mitochondrial hyperpolarization. By contrast, IL-10 enhanced ROI production and cell death in lupus PBL without affecting ROI levels and survival of control PBL. Ab-mediated IL-10 blockade or stimulation with antagonistic lymphokine IL-12 normalized baseline and CD3/CD28-induced changes in ROI production and pH(i) with no impact on Delta psi(m) of lupus PBL. The results suggest that mitochondrial hyperpolarization, increased ROI production, and cytoplasmic alkalinization play crucial roles in altered IL-10 responsiveness in SLE.

Deficient protein kinase a in systemic lupus erythematosus: a disorder of T lymphocyte signal transduction

Systemic lupus erythematosus (SLE) is an idiopathic autoimmune disease characterized by impaired T lymphocyte immune effector functions. We have identified a disorder of signal transduction in SLE T cells involving the cyclic AMP/protein kinase A (cAMP/PKA) pathway. Cyclic AMP-stimulated PKA-catalyzed protein phosphorylation is markedly diminished owing to profound deficiencies of both type I (PKA-I) and type II (PKA-II) isozyme activities. Deficient PKA-I isozyme is characterized by a significant reduction in the amount of type I regulatory beta subunit (RI beta) steady state mRNA by competitive polymerase chain reaction. This is associated with a 30% decrease in RI alpha protein and a 65% reduction in RI beta protein. Indeed, T cells from approximately 25% of SLE subjects have no detectable RI beta protein. Transient transfection of T cells not expressing RI beta protein with autologous SLE RI beta cDNA bypassed the block in translation, reconstituting PKA activity and augmenting IL-2 production. Of importance was the initial identification of novel RI alpha mRNA mutations characterized by heterogeneous transcript mutations, including deletions, transitions, and transversions. Most mutations are clustered adjacent to GAGAG motifs and CT repeats. By contrast, deficient PKA-II activity is the result of spontaneous dissociation of the cytosolic RII beta(2)C(2) holoenzyme, aberrant RII beta translocation to the nucleus from the cytosol, and retention of RII beta in the nucleus. In conclusion, distinct mechanisms account for deficient PKA-I and PKA-II isozyme activities in SLE T cells.

Autoreactive murine Th1 and Th2 cells kill syngeneic macrophages and induce autoantibodies

D10 cells, a cloned Th2 line, become autoreactive following treatment with DNA methylation inhibitors like 5-azacytidine (5-azaC), and induce anti-DNA antibodies if injected into unirradiated syngenic mice. The mechanism by which the autoreactive cells break tolerance is unknown. To further define effector functions required, we asked if 5-azaC-treated Th1 cells could also induce autoimmunity. AE7 cells, a cloned Th1 line, were treated with 5-azaC and shown to become autoreactive and induce anti-DNA antibodies in vivo. Comparison of effector mechanisms demonstrated that the two cell lines secreted a distinct repertoire of cytokines, and that only killing of syngeneic Mø was common to both AE7 and D10 cells. This suggests that Mø killing may be an early step in the induction of anti-DNA antibodies, providing antigenic nucleosomes and decreasing clearance of apoptotic material. Secretion of cytokines promoting B cell differentiation may play a role, but no one cytokine is required.

Mitochondrial hyperpolarization and ATP depletion in patients with systemic lupus erythematosus

OBJECTIVE

Peripheral blood lymphocytes (PBLs) from systemic lupus erythematosus (SLE) patients exhibit increased spontaneous and diminished activation-induced apoptosis. We tested the hypothesis that key biochemical checkpoints, the mitochondrial transmembrane potential (deltapsim) and production of reactive oxygen intermediates (ROIs), mediate the imbalance of apoptosis in SLE.

METHODS

We assessed the deltapsim with potentiometric dyes, measured ROI production with oxidation-sensitive fluorochromes, and monitored cell death by annexin V and propidium iodide staining of lymphocytes, using flow cytometry. Intracellular glutathione levels were measured by high-performance liquid chromatography, while ATP and ADP levels were assessed by the luciferin-luciferase assay.

RESULTS

Both deltapsim and ROI production were elevated in the 25 SLE patients compared with the 25 healthy subjects and the 10 rheumatoid arthritis patients. Intracellular glutathione contents were diminished, suggesting increased utilization of reducing equivalents in SLE. H2O2, a precursor of ROIs, increased deltapsim and caused apoptosis in normal PBLs. In contrast, H2O2-induced apoptosis and deltapsim elevation were diminished, particularly in T cells, and the rate of necrotic cell death was increased in patients with SLE. The intracellular ATP content and the ATP:ADP ratio were reduced and correlated with the deltapsim elevation in lupus. CD3:CD28 costimulation led to transient elevation of the deltapsim, followed by ATP depletion, and sensitization of normal PBLs to H2O2-induced necrosis. Depletion of ATP by oligomycin, an inhibitor of F0F1-ATPase, had similar effects.

CONCLUSION

T cell activation and apoptosis are mediated by deltapsim elevation and increased ROI production. Mitochondrial hyperpolarization and the resultant ATP depletion sensitize T cells for necrosis, which may significantly contribute to inflammation in patients with SLE.

Disassociation of sex hormone levels and cytokine production in SLE patients

This study examines whether changes in the cytokine milieu of patients with systemic lupus erythematosus (SLE) are associated with abnormal levels of sex hormone levels in serum. The concentration of 17beta-estradiol (E2), progesterone (Pg) and dehydroepiandrosterone-sulphate (DHEAS) was monitored in sera from 128 lupus patients and 96 controls, and correlated with the activity of their cytokine secreting cells. Results indicate that SLE patients have (i) significantly fewer cells secreting IFNgamma, (ii) increased serum E2 and Pg levels, and (iii) reduced serum DHEAS levels compared to normal controls. However, the observed abnormalities in the cytokine milieu of SLE patients did not correlate with abnormalities in serum sex hormone levels. Instead, the association between IFNgamma production and DHEAS levels evident in healthy controls is absent in SLE patients, suggesting that cells from lupus patients are defective in their ability to produce IFNgamma in response to physiologic stimuli. Similarly, the normal correlation between IL-4 production and E2 levels was lost in patients with severe disease. Thus, while it remains possible that increased E2 and reduced DHEAS levels in lupus patients may help induce cytokine abnormalities early in disease, the subsequent cytokine imbalance does not correlate with sex hormone levels.

Lessons from the NZM2410 model and related strains

SLE susceptibility requires the interplay of an unknown number of genes and equally unidentified triggering events. The past few years have seen significant advances in our understanding of SLE susceptibility through the genetic analysis of murine models. The NZM2410 strain, which is derived from the NZB/WF1 model has played a significant role in these advances. The main advantages presented by this strain over other models are the genetic homozygozity at all loci and an highly penetrant early onset lupus nephritis in both males and females, indicating that the strongest BWF1 susceptibility loci were retained in NZM2410. After identification of NZM2410 susceptibility loci via linkage analyses, congenic strains have been derived in order to convert a polygenic system into a series of monogenic traits. These congenic strains have been analyzed in an integrated process which has provided simultaneously 1) novel functional characterization of the Sle susceptibility loci, 2) high resolution genetic maps that will lead to the identification of the corresponding susceptibility genes by either candidate locus or positional cloning, and 3) insights into the mechanisms by which these loci interact to produce systemic autoimmunity with fatal end-organ damage.

Trichostatin A reverses skewed expression of CD154, interleukin-10, and interferon-gamma gene and protein expression in lupus T cells

In systemic lupus erythematosus (SLE), T helper cells exhibit increased and prolonged expression of cell-surface CD40 ligand (CD154), spontaneously overproduce interleukin-10 (IL-10), but underproduce interferon-gamma (IFN-gamma). We tested the hypothesis that the imbalance of these gene products reflects skewed expression of CD154, IL-10, and IFN-gamma genes. Here, we demonstrate that the histone deacetylase inhibitor, trichostatin A, significantly down-regulated CD154 and IL-10 and up-regulated IFN-gamma gene expression in SLE T cells. This reversal corrected the aberrant expression of these gene products, thereby enhancing IFN-gamma production and inhibiting IL-10 and CD154 expression. That trichostatin A can simultaneously reverse the skewed expression of multiple genes implicated in the immunopathogenesis of SLE suggests that this pharmacologic agent may be a candidate for the treatment of this autoimmune disease.

Lessons from animal models of vasculitis

Vasculitis can occur as a primary disease or as a secondary manifestation of either another illness or a type-III hypersensitivity response to a foreign antigen. Over the past four decades, a number of animal models of vasculitis have been described. These models have served as important tools for enhancing our understanding of the basic mechanisms underlying the pathogenesis of vasculitis. In addition, animal models have made possible the preclinical testing of new therapeutic agents. Animal models of vasculitis can be broadly classified into two types--those that are experimentally induced and those that occur spontaneously. Vasculitis can be experimentally induced in animals through the stimulation of a type-III hypersensitivity response to a variety of foreign antigens, by viral or bacterial infection of vascular cells and the immune response to that infection, or by the in-vivo administration of antineutrophil cytoplasmic antibodies, estrogen, or mercuric chloride (HgCl(2)). Systemic vasculitis spontaneously develops in several strains of mice and rats. This paper reviews the current state of knowledge of several animal models of vasculitis and the lessons that have been learned from them.