Kim Ohl

A functional heteromeric MIF receptor formed by CD74 and CXCR4.

MINT‐7234499: CXCR4 (uniprotkb:P61073) and CD74 (uniprotkb:P04233) colocalize (MI:0403) by fluorescence microscopy (MI:0416)

Inflammatory Cytokines in Systemic Lupus Erythematosus

Systemic lupus erythematosus (SLE) is an autoimmune disease of unknown origin affecting virtually all organ systems. Beyond genetic and environmental factors, cytokine imbalances contribute to immune dysfunction, trigger inflammation, and induce organ damage. The key cytokine that is involved in SLE pathogenesis is interferon alpha. Interferon secretion is induced by immune complexes and leads to upregulation of several inflammatory proteins, which account for the so-called IFN signature that can be found in the majority of SLE PBMCs. Additionally IL-6 and IFN-y as well as T-cell-derived cytokines like IL-17, IL-21, and IL-2 are dysregulated in SLE. The latter induce a T-cell phenotype that is characterized by enhanced B-cell help and enhanced secretion of proinflammatory cytokines but reduced induction of suppressive T cells and activation-induced cell death. This paper will focus on these cytokines and highlights pathophysiological approaches and therapeutic potential.

Regulatory T cells in systemic lupus erythematosus

Systemic lupus erythematosus (SLE), an autoimmune disease, develops when immunologic self‐tolerance fails. Treg cells are a subset of CD4+ T cells that maintain self‐tolerance by suppressing autoreactive lymphocytes. Defects in Treg cells are therefore considered to be an aspect of SLE pathogenesis. Nevertheless, reports on the numbers and function of Treg cells in SLE are contradictory and the definitive role of Treg cells in SLE remains unclear. In this review, we summarize findings from murine models and ex vivo experiments, which provide insights into the mechanisms that result in the breakdown of tolerance. We also include recent findings about Treg‐cell subsets and their markers in human SLE. The identification of unique markers to identify bona fide Treg cells, as well as therapies to reconstitute the balance between Treg cells and autoreactive T cells in SLE, are the future challenges for SLE research.

MIF promotes B cell chemotaxis through the receptors CXCR4 and CD74 and ZAP-70 signaling.

Macrophage migration inhibitory factor (MIF) is a proinflammatory cytokine with chemokine-like functions that plays a pivotal role in the pathogenesis of inflammatory diseases by promoting leukocyte recruitment. We showed that MIF promotes the atherogenic recruitment of monocytes and T cells through its receptors CXCR2 and CXCR4. Effects of MIF on B cell recruitment have not been addressed. In this study, we tested the involvement of MIF in B cell chemotaxis and studied the underlying mechanism. We show that MIF promotes primary murine B cell chemotaxis in a dose-dependent manner, comparable to the B cell chemokines CXCL13 and CXCL12. Splenic B cells express CXCR4 and the receptor CD74 but not CXCR2. Inhibition of CXCR4 or CD74 or a genetic deficiency of Cd74 in primary B cells fully abrogated MIF-mediated B cell migration, implying cooperative involvement of both receptors. MIF stimulation of B cells resulted in a rapid increase in intracellular Ca2+ mobilization and F-actin polymerization. Intriguingly, the tyrosine kinase ZAP-70 was activated upon MIF and CXCL12 treatment in a CXCR4- and CD74-dependent manner. Pharmacological inhibition of ZAP-70 resulted in abrogation of primary B cell migration. Functional involvement of ZAP-70 was confirmed by small interfering RNA–mediated knockdown in Ramos B cell migration. Finally, primary B cells from ZAP-70 gene–deficient mice exhibited ablated transmigration in response to MIF or CXCL12. We conclude that MIF promotes the migration of B cells through a ZAP-70–dependent pathway mediated by cooperative engagement of CXCR4 and CD74. The data also suggest that MIF may contribute to B cell recruitment in vivo (e.g., in B cell–related immune disorders).

Oxidative stress in multiple sclerosis: Central and peripheral mode of action

Accumulating evidence suggests that oxidative stress plays a major role in the pathogenesis of multiple sclerosis (MS). Reactive oxygen species (ROS), which if produced in excess lead to oxidative stress, have been implicated as mediators of demyelination and axonal damage in both MS and its animal models. One of the most studied cell populations in the context of ROS-mediated tissue damage in MS are macrophages and their CNS companion, microglia cells. However, and this aspect is less well appreciated, the extracellular and intracellular redox milieu is integral to many processes underlying T cell activation, proliferation and apoptosis. In this review article we discuss how oxidative stress affects central as well as peripheral aspects of MS and how manipulation of ROS pathways can potentially affect the course of the disease. It is our strong belief that the well-directed shaping of ROS pathways has the potential to ameliorate disease progression in MS.

cAMP-responsive Element Modulator α (CREMα) Contributes to Decreased Notch-1 Expression in T Cells from Patients with Active Systemic Lupus Erythematosus (SLE)

Background: T cells from SLE patients display multiple signaling aberrations, many of which are attributed to increased presence of transcription factor CREMα. Results: Notch-1 expression is significantly reduced in T cells from active SLE patients. Both epigenetic and transcriptional effects mediated through CREMα contribute to dysregulated Notch-1 expression in SLE T cells. Conclusion: Notch-1 levels inversely correlate with SLE disease activity. Significance: Boosting endogenous Notch-1 levels may redirect T cell function in SLE patients. Notch signaling constitutes an evolutionarily conserved pathway that transduces signals between neighboring cells and determines major decisions in cell proliferation, survival, and differentiation. Notch signaling has been shown to play a pivotal role during T cell lineage determination. T lymphocytes from patients with systemic lupus erythematosus (SLE) display a severely altered phenotype with several molecular and functional aberrations, including defective capacities to up-regulate Notch-1 receptor expression upon T cell receptor activation. Here, we demonstrate that basal Notch-1 expression is decreased in T cells from active SLE patients at the mRNA and protein levels in various T cell subpopulations. Notch-1 transcript numbers inversely correlate with disease activity in SLE patients. We provide evidence that both enhanced histone H3 methylation and CpG DNA methylation of the human Notch-1 promoter contribute to decreased Notch-1 expression in SLE T cells. Previous data from our group identified cAMP-responsive element modulator α (CREMα), which is up-regulated in SLE T cells, as a key regulator of epigenetic patterns and gene transcription, e.g. that of IL2 and IL17 genes. In this study, we observed increased CREMα binding to the Notch-1 promoter, which eventually resulted in significantly reduced Notch-1 promoter activity and gene transcription. Notably, decreased Notch-1 levels were associated with elevated IL-17A levels. Our data suggest a role for Notch-1 in SLE immunopathogenesis, and for the first time, we present molecular mechanisms that mediate dysregulated Notch-1 expression in SLE T cells.

Cyclic adenosine monophosphate–responsive element modulator alpha overexpression impairs function of hepatic myeloid‐derived suppressor cells and aggravates immune‐mediated hepatitis in mice

Molecular factors driving immune‐mediated inflammation in the liver are incompletely understood. The transcription factor, cyclic adenosine monophosphate‐responsive element modulator alpha (CREMα) can endorse differentiation of T lymphocytes toward T‐helper (Th)17 cells, thereby promoting autoimmunity in systemic lupus erythematosus or lung inflammation. To investigate the role of CREMα in liver disease, we subjected transgenic (Tg) mice overexpressing CREMα under control of the CD2 promoter (cremtg mice), which restrains expression mainly to lymphocytes (T, natural killer [NK], and NKT cells), to acute and chronic liver injury models. Already in steady state, Tg CREMα overexpression broadly reduced hepatic immune cell numbers by decreasing their viability, but did not affect immune cell migration or the fibrogenic response to chronic liver injury. Strikingly, cremtg mice developed more severe immune‐mediated hepatitis with a higher mortality rate, compared to wild‐type (wt) mice, upon concanavalin A (ConA) administration. Unlike in T cells from spleen, CREMα overexpression did not induce a predominant Th17 response in intrahepatic T cells, given that hepatic cremtg CD4+ T cells expressed less interleukin (IL)‐17 than wt T cells. Reconstitution of Rag1−/− mice with Crem−/− T cells did not ameliorate ConA hepatitis. Overexpression of CREMα did not influence NK and NKT‐cell effector functions either. Interestingly, a subset of monocytic myeloid‐derived suppressor cells (MDSCs) also expressed CD2 and CREMα. Cremtg MDSCs isolated from liver expressed reduced inducible nitric oxide synthase and arginase 1 and displayed a reduced T‐cell suppressive activity. The adoptive transfer of wt MDSCs was capable of reducing the fulminant immune‐mediated liver damage in cremtg mice to wt level. Conclusion: These results suggest compartmental differences of T cell activation pathways between liver and other organs in autoimmunity and define a functional role of CREMα in hepatic monocytic MDSCs for the pathogenesis of immune‐mediated liver disease. (Hepatology 2015;61:990–1002)

Neurodegeneration Triggers Peripheral Immune Cell Recruitment into the Forebrain

Brain-intrinsic degenerative cascades have been proposed to be an initial factor driving lesion formation in multiple sclerosis (MS). Here, we identify neurodegeneration as a potent trigger for peripheral immune cell recruitment into the mouse forebrain. Female C57BL/6 mice were fed cuprizone for 3 weeks, followed by a period of 2 weeks on normal chow to induce the formation of lesion foci in the forebrain. Subsequent immunization with myelin oligodendrocyte glycoprotein 35–55 peptide, which induces myelin autoreactive T cells in the periphery, resulted in massive immune cell recruitment into the affected forebrain. Additional adoptive transfer experiments together with flow cytometry analysis underline the importance of brain-derived signals for immune cell recruitment. This study clearly illustrates the significance of brain-intrinsic degenerative cascades for immune cell recruitment and MS lesion formation. Additional studies have to address the signaling cascades and mechanistic processes that form the top-down communication between the affected brain area, neurovascular unit, and peripheral immune cells. SIGNIFICANCE STATEMENT We identify neurodegeneration as a potent trigger for peripheral immune cell recruitment into the forebrain. Thus, immune cell recruitment might be a second step during the formation of new inflammatory lesions in multiple sclerosis. A better understanding of factors regulating neurodegeneration-induced immune cell recruitment will pave the way for the development of novel therapeutic treatment strategies.

Interleukin-2 treatment reverses effects of cAMP-responsive element modulator α-over-expressing T cells in autoimmune-prone mice.

Systemic autoimmune diseases, such as systemic lupus erythematosus (SLE), are often characterized by a failure of self‐tolerance and result in an uncontrolled activation of B cells and effector T cells. Interleukin (IL)‐2 critically maintains homeostasis of regulatory T cells (Treg) and effector T cells in the periphery. Previously, we identified the cAMP‐responsive element modulator α (CREMα) as a major factor responsible for decreased IL‐2 production in T cells from SLE patients. Additionally, using a transgenic mouse that specifically over‐expresses CREMα in T cells (CD2CREMαtg), we provided in‐vivo evidence that CREMα indeed suppresses IL‐2 production. To analyse the effects of CREMα in an autoimmune prone mouse model we introduced a Fas mutation in the CD2CREMαtg mice (FVB/Fas–/–CD2CREMαtg). Overexpression of CREMα strongly accelerated the lymphadenopathy and splenomegaly in the FVB/Fas–/– mice. This was accompanied by a massive expansion of double‐negative (DN) T cells, enhanced numbers of interferon (IFN)‐γ‐producing T cells and reduced percentages of Tregs. Treatment of FVB/Fas–/–CD2CREMαtg mice with IL‐2 restored the percentage of Tregs and reversed increased IFN‐γ production, but did not affect the number of DNTs. Our data indicate that CREMα contributes to the failure of tolerance in SLE by favouring effector T cells and decreasing regulatory T cells, partially mediated by repression of IL‐2 in vivo.

Overexpression of CREMα in T Cells Aggravates Lipopolysaccharide-Induced Acute Lung Injury

Transcription factor cAMP response element modulator (CREM)α contributes to various cellular and molecular abnormalities in T cells, including increased IL-17 and decreased IL-2 expression. For development of acute lung injury (ALI), the invasion and regulation of immune cells are highly important, but the role of T cells remains unclear. In this study, we show that CREMα is upregulated in LPS-induced ALI. During the early phase of ALI (day 1), T cell–specific CREMα overexpression enhances the numbers of T cells and expression of TNF-α in bronchoalveolar lavage fluid and deteriorates lung functions. On day 3 of ALI, CREMα transgenic mice present a stronger inflammatory response with higher levels of TNF-α, IL-6, and IL-17 correlating with increased numbers of T cells and neutrophils in bronchoalveolar lavage fluid, whereas expression of Foxp3 and IL-2 and numbers of regulatory T cells are decreased. These changes result in restricted lung function in CREMα transgenic mice. Finally, an adoptive transfer of CREM−/− CD4+ T cells, but not of wild-type T cells into RAG-1−/− mice results in ameliorated disease levels. Thus, levels of CREM in T cells determine the outcome of ALI, and CREMα transgenic animals represent a model in which proinflammatory T cells aggravate ALI in different phases of the disease. Given the fact that patients with autoimmune diseases like systemic lupus erythematosus show higher levels of CREMα and an increased susceptibility toward infectious complications, our finding is of potential clinical significance and may enable new therapeutic strategies.