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Objectives: The concept of trained innate immunity describes a long-term proinflammatory memory in innate immune cells. Trained innate immunity is regulated through reprogramming of cellular metabolic pathways including cholesterol and fatty acid synthesis. Here, we have analyzed the role of Liver X Receptor (LXR), a key regulator of cholesterol and fatty acid homeostasis, in trained innate immunity., Methods and Results: Human monocytes were isolated and incubated with different stimuli for 24 h, including LXR agonists, antagonists and Bacillus Calmette-Guerin (BCG) vaccine. After 5 days resting time, cells were restimulated with the TLR2-agonist Pam3cys. LXR activation did not only increase BCG trained immunity, but also induced a long-term inflammatory activation by itself. This inflammatory activation by LXR agonists was accompanied by characteristic features of trained innate immunity, such as activating histone marks on inflammatory gene promoters and metabolic reprogramming with increased lactate production and decreased oxygen consumption rate. Mechanistically, LXR priming increased cellular acetyl-CoA levels and was dependent on the activation of the mevalonate pathway and IL-1β signaling. In contrast to mevalonate pathway inhibition, blocking fatty acid synthesis further increased proinflammatory priming by LXR., Conclusion: We demonstrate that LXR activation induces a proinflammatory trained immunity phenotype in human monocytes through epigenetic and metabolic reprogramming. Our data reveal important novel aspects of LXR signaling in innate immunity., (Copyright © 2020 Sohrabi, Sonntag, Braun, Lagache, Liebmann, Klotz, Godfrey, Kahles, Waltenberger and Findeisen.)

In the last decade the role of environmental factors as modulators of disease activity and progression has received increasing attention. In contrast to classical environmental modulators such as exposure to sun-light or fine dust pollution, nutrition is an ideal tool for a personalized human intervention. Various studies demonstrate a key role of dietary factors in autoimmune diseases including Inflammatory Bowel Disease (IBD), rheumatoid arthritis or inflammatory central nervous system (CNS) diseases such as Multiple Sclerosis (MS). In this review we discuss the connection between diet and inflammatory processes via the gut-CNS-axis. This axis describes a bi-directional communication system and comprises neuronal signaling, neuroendocrine pathways and modulation of immune responses. Therefore, the gut-CNS-axis represents an emerging target to modify CNS inflammatory activity ultimately opening new avenues for complementary and adjunctive treatment of autoimmune diseases such as MS., Competing Interests: The authors declare no conflict of interest. Heinz Wiendl received compensation for serving on Scientific Advisory Boards/Steering Committees for Bayer Healthcare, Biogen Idec, Genzyme, Merck Serono, Novartis and Sanofi Aventis. He has received speaker honoraria and travel support from Bayer Vital GmbH, Bayer Schering AG, Biogen Idec, CSL Behring, Fresenius Medical Care, Genzyme, Glaxo Smith Kline, GW Pharmaceuticals, Lundbeck, Merck Serono, Omniamed, Novartis and Sanofi Aventis. He has received compensation as a consultant from Biogen Idec, Merck Serono, Novartis and Sanofi Aventis. Heinz Wiendl received research support from Bayer Vital, Biogen Idec, Genzyme Merck Serono, Novartis, Sanofi Aventis Germany, Sanofi US. Luisa Klotz received compensation for serving on Scientific Advisory Boards for Genzyme and Novartis. She received speaker honoraria and travel support from Novartis, Merck Serono and CSL Behring. She receives research support from Novartis and Biogen Idec. Detlef Schuppan received compensation for serving on Scientific Advisory Boards for Amarin, BMS, Boehringer-Ingelheim, Gilead, Nestle, Nimbus, Novartis, Roivant, Takeda and Zealand. He has received research support from Boehringer-Ingelheim.

Background and Purpose: Peripheral immune cell infiltration contributes to neural injury after ischemic stroke. However, in contrast to lymphocytes and neutrophils, the role of different monocyte/macrophage subsets remains to be clarified. Therefore, we evaluated the effects of selective and unselective monocyte/macrophage depletion and proinflammatory (M1-) and anti-inflammatory (M2-) macrophage transfer on the outcome after experimental cerebral ischemia., Methods: To assess short-term effects of monocytes/macrophages in acute ischemic stroke, mice underwent transient middle cerebral artery occlusion and received either clodronate liposomes for unselective macrophage depletion, MC-21-antibody for selective depletion of proinflammatory Ly-6C high monocytes, or proinflammatory (M1-) or anti-inflammatory (M2-) macrophage transfer. In addition, the impact of MC-21-antibody administration and M2-macrophage transfer on long-term neural recovery was investigated after photothrombotic stroke. Neurobehavioral tests were used to analyze functional outcomes, infarct volumes were determined, and immunohistochemical analyses were performed to characterize the postischemic inflammatory reaction., Results: Selective and unselective monocyte/macrophage depletion and M1- and M2-macrophage transfer did not influence tissue damage and neurobehavioral outcomes in the acute phase after middle cerebral artery occlusion. Beyond, selective depletion of Ly-6C high monocytes and M2-macrophage transfer did not have an impact on neural recovery after photothrombotic stroke., Conclusions: Targeting different monocyte/macrophage subsets has no impact on outcome after ischemic stroke in mice. Altogether, our study could not identify monocytes/macrophages as relevant therapeutic targets in acute ischemic stroke., (© 2017 American Heart Association, Inc.)

Background: Western lifestyle has been associated with an increase in relapsing–remitting multiple sclerosis (RRMS). In mice, dietary wheat amylase–trypsin inhibitors (ATIs) activate intestinal myeloid cells and augment T cell-mediated systemic inflammation. Objective: The aim of this study was to assess whether a wheat- and thus ATI-reduced diet might exert beneficial effects in RRMS patients with modest disease activity. Methods: In this 6-month, crossover, open-label, bicentric proof-of-concept trial, 16 RRMS patients with stable disease course were randomized to either 3 months of a standard wheat-containing diet with consecutive switch to a > 90% wheat-reduced diet, or vice versa. Results: The primary endpoint was negative, as the frequency of circulating pro-inflammatory T cells did not decrease during the ATI-reduced diet. We did, however, observe decreased frequencies of CD14+ CD16++ monocytes and a concomitant increase in CD14++ CD16− monocytes during the wheat-reduced diet interval. This was accompanied by an improvement in pain-related quality of life in health-related quality of life assessed (SF-36). Conclusion: Our results suggest that the wheat- and thus ATI-reduced diet was associated with changes in monocyte subsets and improved pain-related quality of life in RRMS patients. Thus, a wheat (ATI)-reduced diet might be a complementary approach accompanying immunotherapy for some patients. Registration: German Clinical Trial Register (No. DRKS00027967). [ABSTRACT FROM AUTHOR]

Despite the large number of immunomodulatory or immunosuppressive treatments available to treat relapsing–remitting multiple sclerosis (MS), treatment of the progressive phase of the disease has not yet been achieved. This lack of successful treatment approaches is caused by our poor understanding of the mechanisms driving disease progression. Emerging concepts suggest that a combination of persisting focal and diffuse inflammation within the CNS and a gradual failure of compensatory mechanisms, including remyelination, result in disease progression. Therefore, promotion of remyelination presents a promising intervention approach. However, despite our increasing knowledge regarding the cellular and molecular mechanisms regulating remyelination in animal models, therapeutic increases in remyelination remain an unmet need in MS, which suggests that mechanisms of remyelination and remyelination failure differ fundamentally between humans and demyelinating animal models. New and emerging technologies now allow us to investigate the cellular and molecular mechanisms underlying remyelination failure in human tissue samples in an unprecedented way. The aim of this Review is to summarize our current knowledge regarding mechanisms of remyelination and remyelination failure in MS and in animal models of the disease, identify open questions, challenge existing concepts, and discuss strategies to overcome the translational roadblock in the field of remyelination-promoting therapies. Here, the authors summarize current knowledge regarding mechanisms of remyelination and remyelination failure in multiple sclerosis and animal models of the disease and discuss strategies to overcome the translational roadblock in the field of remyelination-promoting therapies. Key points: Promotion of remyelination is an unmet therapeutic need in multiple sclerosis. Animal models only partially reflect the human pathology of multiple sclerosis. The relationship between inflammation and remyelination is still unsolved. New models are needed to more precisely mimic remyelination in multiple sclerosis. [ABSTRACT FROM AUTHOR]

Mechanisms keeping leukocytes distant of local inflammatory processes in a resting state despite systemic release of inflammatory triggers are a pivotal requirement for avoidance of overwhelming inflammation but are ill defined. Dimers of the alarmin S100A8/S100A9 activate Toll‐like receptor‐4 (TLR4) but extracellular calcium concentrations induce S100A8/S100A9‐tetramers preventing TLR4‐binding and limiting their inflammatory activity. So far, only antimicrobial functions of released S100A8/S100A9‐tetramers (calprotectin) are described. It is demonstrated that extracellular S100A8/S100A9 tetramers significantly dampen monocyte dynamics as adhesion, migration, and traction force generation in vitro and immigration of monocytes in a cutaneous granuloma model and inflammatory activity in a model of irritant contact dermatitis in vivo. Interestingly, these effects are not mediated by the well‐known binding of S100A8/S100A9‐dimers to TLR‐4 but specifically mediated by S100A8/S100A9‐tetramer interaction with CD69. Thus, the quaternary structure of these S100‐proteins determines distinct and even antagonistic effects mediated by different receptors. As S100A8/S100A9 are released primarily as dimers and subsequently associate to tetramers in the high extracellular calcium milieu, the same molecules promote inflammation locally (S100‐dimer/TLR4) but simultaneously protect the wider environment from overwhelming inflammation (S100‐tetramer/CD69). [ABSTRACT FROM AUTHOR]

T cells critically depend on reprogramming of metabolic signatures to meet the bioenergetic demands during activation and clonal expansion. Here we identify the transcription factor Nur77 as a cellintrinsic modulator of T cell activation. Nur77-deficient T cells are highly proliferative, and lack of Nur77 is associated with enhanced T cell activation and increased susceptibility for T cell-mediated inflammatory diseases, such as CNS autoimmunity, allergic contact dermatitis and collagen-induced arthritis. Importantly, Nur77 serves as key regulator of energy metabolism in T cells, restricting mitochondrial respiration and glycolysis and controlling switching between different energy pathways. Transcriptional network analysis revealed that Nur77 modulates the expression of metabolic genes, most likely in close interaction with other transcription factors, especially estrogen-related receptor α. In summary, we identify Nur77 as a transcriptional regulator of T cell metabolism, which elevates the threshold for T cell activation and confers protection in different T cell-mediated inflammatory diseases. [ABSTRACT FROM AUTHOR]

The nuclear receptor Liver X Receptor (LXR) is a ligand-activated transcription factor that has been implicated in control of chronic inflammation by downregulating pro-inflammatory T cell responses. An impaired function of regulatory T cells, a subset of CD4+ T cells with a crucial role in maintaining lymphocytes homeostasis and immune regulation, is frequently observed in chronic inflammatory diseases. We observed that pharmacological activation of LXR in T cells not only resulted in a thorough suppression of Th1 and Th17 polarization in vitro, but also significantly induced regulatory T cells (Treg) cell differentiation in a receptor-specific fashion. In line with this, systemic LXR activation by oral treatment of mice with the LXR agonist GW3965 induced gut-associated regulatory T cells in vivo. Importantly, such LXR-activated Tregs had a higher suppressive capacity in functional in vitro coculture assays with effector T cells. Our data thus point towards a dual role of LXR-mediated control of inflammation by suppression of pro-inflammatory T cells and reciprocal induction of regulatory T cells. [ABSTRACT FROM AUTHOR]

Abstract: An important step in the pathogenesis of multiple sclerosis is adhesion and transmigration of encephalitogenic T cells across brain endothelial cells (EC) which strongly relies on interaction with EC-expressed adhesion molecules. We provide molecular evidence that the transcription factor peroxisome proliferator-activated receptor gamma (PPARγ) is a negative regulator of brain EC inflammation. The PPARγ agonist pioglitazone reduces transendothelial migration of encephalitogenic T cells across TNFα-stimulated brain EC. This effect is clearly PPARγ mediated, as lentiviral PPARγ overexpression in brain EC results in selective abrogation of inflammation-induced ICAM-1 and VCAM-1 upregulation and subsequent adhesion and transmigration of T cells. We therefore propose that PPARγ in brain EC may be exploited to target detrimental EC-T cell interactions under inflammatory conditions. [Copyright &y& Elsevier]

Abstract Cerebral inflammatory events play an important part in the pathogenesis of Alzheimer's disease (AD). Agonists of the peroxisome proliferator-activated receptor gamma (PPARγ), a nuclear hormone receptor that mediates anti-inflammatory actions of non-steroidal anti-inflammatory drugs (NSAIDs) and thiazolidinediones, have been therefore proposed as a potential treatment of AD. Experimental evidence suggests that cortical noradrenaline (NA) depletion due to degeneration of the locus ceruleus (LC) – a pathological hallmark of AD – plays a permissive role in the development of inflammation in AD. To study a possible relationship between NA depletion and PPARγ-mediated suppression of inflammation we investigated the influence of NA on PPARγ expression in murine primary cortical astrocytes and neurons. Incubation of astrocytes and neurons with 100 µm NA resulted in an increase of PPARγ mRNA as well as PPARγ protein levels in both cell types. These effects were blocked by the β-adrenergic antagonist propranolol but not by the α-adrenergic antagonist phentolamine, suggesting that they might be mediated by β-adrenergic receptors. Our results indicate for the first time that PPARγ expression can be modulated by the cAMP signalling pathway, and suggest that the anti-inflammatory effects of NA on brain cells may be partly mediated by increasing PPARγ levels. Conversely, decreased NA due to LC cell death in AD may reduce endogenous PPARγ expression and therefore potentiate neuroinflammatory processes. [ABSTRACT FROM AUTHOR]

The nuclear receptor peroxisome proliferator-activated receptor gamma (PPARγ) regulates target gene expression upon ligand binding. Apart from its effects on metabolism, PPARγ activity can inhibit the production of pro-inflammatory cytokines by several immune cells, including dendritic cells and macrophages. In chronic inflammatory disease models, PPARγ activation delays the onset and ameliorates disease severity. Here, we investigated the effect of PPARγ activation by the agonist Pioglitazone on the function of hepatic immune cells and its effect in a murine model of immune-mediated hepatitis. Cytokine production by both liver sinusoidal endothelial cells (IL-6) and in T cells ex vivo (IFNγ) was decreased in cells from Pioglitazone-treated mice. However, PPARγ activation did not decrease pro-inflammatory tumor necrosis factor alpha TNFα production by Kupffer cells after Toll-like receptor (TLR) stimulation ex vivo. Most interestingly, although PPARγ activation was shown to ameliorate chronic inflammatory diseases, it did not improve hepatic injury in a model of immune-mediated hepatitis. In contrast, Pioglitazone-induced PPARγ activation exacerbated D-galactosamine (GalN)/lipopolysaccharide (LPS) hepatitis associated with an increased production of TNFα by Kupffer cells and increased sensitivity of hepatocytes towards TNFα after in vivo Pioglitazone administration. These results unravel liver-specific effects of Pioglitazone that fail to attenuate liver inflammation but rather exacerbate liver injury in an experimental hepatitis model. [ABSTRACT FROM AUTHOR]