EBI2 Expression and Function: Robust in Memory Lymphocytes and Increased by Natalizumab in Multiple Sclerosis

Inflammation switches the chemoattractant requirements for naive lymphocyte entry into lymph nodes

Sustained lymphocyte migration from blood into lymph nodes (LNs) is important for immune responses. The CC-chemokine receptor-7 (CCR7) ligand CCL21 is required for LN entry but is downregulated during inflammation, and it has been unclear how recruitment is maintained. Here, we show that the oxysterol biosynthetic enzyme cholesterol-25-hydroxylase (Ch25h) is upregulated in LN high endothelial venules during viral infection. Lymphocytes become dependent on oxysterols, generated through a transcellular endothelial-fibroblast metabolic pathway, and the receptor EBI2 for inflamed LN entry. Additionally, Langerhans cells are an oxysterol source. Ch25h is also expressed in inflamed peripheral endothelium, and EBI2 mediates B cell recruitment in a tumor model. Finally, we demonstrate that LN CCL19 is critical in lymphocyte recruitment during inflammation. Thus, our work explains how naive precursor trafficking is sustained in responding LNs, identifies a role for oxysterols in cell recruitment into inflamed tissues, and establishes a logic for the CCR7 two-ligand system.

Accelerated remyelination and immune modulation by the EBI2 agonist 7α,25-dihydroxycholesterol analogue in the cuprizone model

Research indicates a role for EBI2 receptor in remyelination, demonstrating that its deficiency or antagonism inhibits this process. However, activation of EBI2 with its endogenous ligand, oxysterol 7α,25-dihydroxycholesterol (7α,25OHC), does not enhance remyelination beyond the levels observed in spontaneously remyelinating tissue. We hypothesized that the short half-life of the natural ligand might explain this lack of beneficial effects and tested a synthetic analogue, CF3-7α,25OHC, in the cuprizone model. The data showed that extending the bioavailability of 7α,25OHC is sufficient to accelerate remyelination in vivo. Moreover, the analogue, in contrast to the endogenous ligand, upregulated brain expression of Ebi2 and the synthesis of 15 lipids in the mouse corpus callosum. Mechanistically, the increased concentration of oxysterol likely disrupted its gradient in demyelinated areas of the brain, leading to the dispersion of infiltrating EBI2-expressing immune cells rather than their accumulation in demyelinated regions. Remarkably, the analogue CF3-7α,25OHC markedly decreased the lymphocyte and monocyte counts mimicking the key mechanism of action of some of the most effective disease-modifying therapies for multiple sclerosis. Furthermore, the Cd4+ transcripts in the cerebellum and CD4+ cell number in the corpus callosum were reduced compared to vehicle-treated mice. These findings suggest a mechanism by which EBI2/7α,25OHC signalling modulates the immune response and accelerates remyelination in vivo.

Implication of Oxysterols and Phytosterols in Aging and Human Diseases

Cholesterol is easily oxidized and can be transformed into numerous oxidation products, among which oxysterols. Phytosterols are plant sterols related to cholesterol. Both oxysterols and phytosterols can have an impact on human health and diseases.Cholesterol is a member of the sterol family that plays essential roles in biological processes, including cell membrane stability and myelin formation. Cholesterol can be metabolized into several molecules including bile acids, hormones, and oxysterols. On the other hand, phytosterols are plant-derived compounds structurally related to cholesterol, which can also have an impact on human health. Here, we review the current knowledge about the role of oxysterols and phytosterols on human health and focus on the impact of their pathways on diseases of the central nervous system (CNS), autoimmune diseases, including inflammatory bowel diseases (IBD), vascular diseases, and cancer in both experimental models and human studies. We will first discuss the implications of oxysterols and then of phytosterols in different human diseases.

25-Hydroxycholesterol in health and diseases

Cholesterol is an essential structural component of all membranes of mammalian cells where it plays a fundamental role not only in cellular architecture, but also, for example, in signaling pathway transduction, endocytosis process, receptor functioning and recycling, or cytoskeleton remodeling. Consequently, intracellular cholesterol concentrations are tightly regulated by complex processes, including cholesterol synthesis, uptake from circulating lipoproteins, lipid transfer to these lipoproteins, esterification, and metabolization into oxysterols that are intermediates for bile acids. Oxysterols have been considered for long time as sterol waste products, but a large body of evidence has clearly demonstrated that they play key roles in central nervous system functioning, immune cell response, cell death, or migration and are involved in age-related diseases, cancers, autoimmunity, or neurological disorders. Among all the existing oxysterols, this review summarizes basic as well as recent knowledge on 25-hydroxycholesterol which is mainly produced during inflammatory or infectious situations and that in turn contributes to immune response, central nervous system disorders, atherosclerosis, macular degeneration, or cancer development. Effects of its metabolite 7α,25-dihydroxycholesterol are also presented and discussed.

Combined PD-L1/TGFβ blockade allows expansion and differentiation of stem cell-like CD8 T cells in immune excluded tumors

TGFβ signaling is associated with non-response to immune checkpoint blockade in patients with advanced cancers, particularly in the immune-excluded phenotype. While previous work demonstrates that converting tumors from excluded to inflamed phenotypes requires attenuation of PD-L1 and TGFβ signaling, the underlying cellular mechanisms remain unclear. Here, we show that TGFβ and PD-L1 restrain intratumoral stem cell-like CD8 T cell (TSCL) expansion and replacement of progenitor-exhausted and dysfunctional CD8 T cells with non-exhausted T effector cells in the EMT6 tumor model in female mice. Upon combined TGFβ/PD-L1 blockade IFNγhi CD8 T effector cells show enhanced motility and accumulate in the tumor. Ensuing IFNγ signaling transforms myeloid, stromal, and tumor niches to yield an immune-supportive ecosystem. Blocking IFNγ abolishes the anti-PD-L1/anti-TGFβ therapy efficacy. Our data suggest that TGFβ works with PD-L1 to prevent TSCL expansion and replacement of exhausted CD8 T cells, thereby maintaining the T cell compartment in a dysfunctional state.

Higher frequency of Human herpesvirus-6 (HHV-6) viral DNA simultaneously with low frequency of Epstein-Barr virus (EBV) viral DNA in a cohort of multiple sclerosis patients from Rio de Janeiro, Brazil

Multiple sclerosis (MS) is a chronic neuroinflammatory and neurodegenerative disease of the central nervous system (CNS). The etiology of MS is not well understood, but it's likely one of the genetic and environmental factors. Approximately 85% of patients have relapsing-remitting MS (RRMS), while 10-15% have primary progressive MS (PPMS). Epstein-Barr virus (EBV) and Human herpesvirus 6 (HHV-6), members of the human Herpesviridae family, are strong candidates for representing the macroenvironmental factors associated with MS) pathogenesis. Antigenic mimicry of EBV involving B-cells has been implicate in MS risk factors and concomitance of EBV and HHV-6 latent infection has been associated to inflammatory MS cascade. To verify the possible role of EBV and HHV-6 as triggering or aggravating factors in RRMS and PPMS, we compare their frequency in blood samples collected from 166 MS patients. The presence of herpes DNA was searched by real-time PCR (qPCR). The frequency of EBV and HHV-6 in MS patients were 1.8% (3/166) and 8.9% (14/166), respectively. Among the positive patients, 100% (3/3) EBV and 85.8% (12/14) HHV-6 are RRMS and 14.4% (2/14) HHV-6 are PPMS. Detection of EBV was 1.2% (2/166) and HHV-6 was 0.6% (1/166) in blood donors. About clinical phenotype of these patients, incomplete multifocal myelitis, and optic neuritis were the main CNS manifestations. These are the first data about concomitant infection of these viruses in MS patients from Brazil. Up to date, our findings confirm a higher prevalence in female with MS and a high frequency of EBV and HHV-6 in RRMS patients.

Skin γδ T cell inflammatory responses are hardwired in the thymus by oxysterol sensing via GPR183 and calibrated by dietary cholesterol

Dietary components and metabolites have a profound impact on immunity and inflammation. Here, we investigated how sensing of cholesterol metabolite oxysterols by γδ T cells impacts their tissue residency and function. We show that dermal IL-17-producing γδ T (Tγδ17) cells essential for skin-barrier homeostasis require oxysterols sensing through G protein receptor 183 (GPR183) for their development and inflammatory responses. Single-cell transcriptomics and murine reporter strains revealed that GPR183 on developing γδ thymocytes is needed for their maturation by sensing medullary thymic epithelial-cell-derived oxysterols. In the skin, basal keratinocytes expressing the oxysterol enzyme cholesterol 25-hydroxylase (CH25H) maintain dermal Tγδ17 cells. Diet-driven increases in oxysterols exacerbate Tγδ17-cell-mediated psoriatic inflammation, dependent on GPR183 on γδ T cells. Hence, cholesterol-derived oxysterols control spatially distinct but biologically linked processes of thymic education and peripheral function of dermal T cells, implicating diet as a focal parameter of dermal Tγδ17 cells.

Endothelial cell-derived oxysterol ablation attenuates experimental autoimmune encephalomyelitis

The vasculature is a key regulator of leukocyte trafficking into the central nervous system (CNS) during inflammatory diseases including multiple sclerosis (MS). However, the impact of endothelial-derived factors on CNS immune responses remains unknown. Bioactive lipids, in particular oxysterols downstream of Cholesterol-25-hydroxylase (Ch25h), promote neuroinflammation but their functions in the CNS are not well-understood. Using floxed-reporter Ch25h knock-in mice, we trace Ch25h expression to CNS endothelial cells (ECs) and myeloid cells and demonstrate that Ch25h ablation specifically from ECs attenuates experimental autoimmune encephalomyelitis (EAE). Mechanistically, inflamed Ch25h-deficient CNS ECs display altered lipid metabolism favoring polymorphonuclear myeloid-derived suppressor cell (PMN-MDSC) expansion, which suppresses encephalitogenic T lymphocyte proliferation. Additionally, endothelial Ch25h-deficiency combined with immature neutrophil mobilization into the blood circulation nearly completely protects mice from EAE. Our findings reveal a central role for CNS endothelial Ch25h in promoting neuroinflammation by inhibiting the expansion of immunosuppressive myeloid cell populations.

CD56bright CD16- natural killer cells as an important regulatory mechanism in chronic graft-versus-host disease

Chronic graft-versus-host disease (cGvHD) is a major cause of morbidity after hematopoietic stem cell transplantation (HSCT). In large patient populations, we have shown a CD56bright natural killer (NK) population to strongly associate with a lack of cGvHD and we hypothesize that these cells function to suppress cGvHD. We aimed to isolate and define the characteristics of regulatory NK (NKreg) cells associated with suppression of cGvHD. Immunophenotypic evaluation of a large pediatric population found the CD56bright NK population associated with a lack of cGvHD to be perforin-, Granzyme B-, and CD335+. Transcriptome analysis of a small patient cohort of CD56bright compared to CD56dim NK cells found the NKreg cells to also overexpress Granzyme K, IL-7R, GPR183, RANK, GM-CSFR, TCF7, and IL23A. Further analysis of this CD56bright NKreg population found a subpopulation that overexpressed IRF1, and TNF. We also found that viable NKreg cells may be isolated by sorting on CD56+ and CD16- NK cells, and this population can suppress allogeneic CD4+ T cells, but not Treg cells or CD8+ T cells through a non-cytolytic, cell-cell contact dependent mechanism. Suppression was not reliant upon the NKp44, NKp46, or GPR183 receptors. Additionally, NKreg cells do not kill leukemic cells. Moreover, this is the first paper to clearly establish that a CD56brightCD3-CD16-perforin- NKreg population associates with a lack of cGvHD and has several unique characteristics, including the suppression of helper T-cell function in vitro. With further investigation we may decipher the mechanism of NKreg suppression and operationalize expansion of NKreg cells associated with cGvHD suppression.

Comprehensive Investigations Relationship Between Viral Infections and Multiple Sclerosis Pathogenesis

Multiple sclerosis (MS) is a chronic autoimmune disease that affects the central nervous system (CNS). Compared to other types of self-limiting myelin disorders, MS compartmentalizes and maintains chronic inflammation in the CNS. Even though the exact cause of MS is unclear, it is assumed that genetic and environmental factors play an important role in susceptibility to this disease. The progression of MS is triggered by certain environmental factors, such as viral infections. The most important viruses that affect MS are Epstein-Barr virus (EBV), human herpes virus 6 (HHV-6), human endogenous retrovirus (HERV), cytomegalovirus (CMV), and varicella zoster virus (VZV). These viruses all have latent stages that allow them to escape immune detection and reactivate after exposure to various stimuli. Furthermore, their tropism for CNS and immune system cells explains their possible deleterious function in neuroinflammation. In this study, the effect of viral infections on MS disease focuses on the details of viruses that can change the risk of the disease. Paying attention to the most recent articles on the role of SARS-CoV-2 in MS disease, laboratory indicators show the interaction of the immune system with the virus. Also, strategies to prevent viruses that play a role in triggering MS are discussed, such as EBV, which is one of the most important.

Intestinal single-cell atlas reveals novel lymphocytes in pigs with similarities to human cells

Lymphocytes can heavily influence intestinal health, but resolving intestinal lymphocyte function is challenging as the intestine contains a vastly heterogeneous mixture of cells. Pigs are an advantageous biomedical model, but deeper understanding of intestinal lymphocytes is warranted to improve model utility. Twenty-six cell types were identified in the porcine ileum by single-cell RNA sequencing and further compared with cells in human and murine ileum. Though general consensus of cell subsets across species was revealed, some porcine-specific lymphocyte subsets were identified. Differential tissue dissection and in situ analyses conferred spatial context, revealing similar locations of lymphocyte subsets in Peyer's patches and epithelium in pig-to-human comparisons. Like humans, activated and effector lymphocytes were abundant in the ileum but not periphery of pigs, suggesting tissue-specific and/or activation-associated gene expression. Gene signatures for peripheral and ileal innate lymphoid cells newly discovered in pigs were defined and highlighted similarities to human innate lymphoid cells. Overall, we reveal novel lymphocyte subsets in pigs and highlight utility of pigs for intestinal research applications.

Dietary Cholesterol Metabolite Regulation of Tissue Immune Cell Development and Function

Obesity is considered the primary environmental factor associated with morbidity and severity of wide-ranging inflammatory disorders. The molecular mechanism linking high-fat or cholesterol diet to imbalances in immune responses, beyond the increased production of generic inflammatory factors, is just beginning to emerge. Diet cholesterol by-products are now known to regulate function and migration of diverse immune cell subsets in tissues. The hydroxylated metabolites of cholesterol oxysterols as central regulators of immune cell positioning in lymphoid and mucocutaneous tissues is the focus of this review. Dedicated immunocyte cell surface receptors sense spatially distributed oxysterol tissue depots to tune cell metabolism and function, to achieve the "right place at the right time" axiom of efficient tissue immunity.

Abnormal lower expression of GPR183 in peripheral blood T and B cell subsets of systemic lupus erythematosus patients

G protein-coupled receptor 183 (GPR183) has been indicated to mediate the migration and localisation of immune cells in T cell-dependent antibody responses. Systemic lupus erythematosus (SLE) is a canonical autoimmune disease involving B cell-mediated tolerance destruction and excessive pathogenic autoantibody production, in which multiple GPCRs play a role. To date, there has been no systematic study regarding the expression of GPR183 in lymphocyte subsets of SLE patients. In this research, firstly, we observed the expression trends of GRP183 in various T and B cell subsets in human tonsil tissues. These lymphocyte subsets include CD4⁺, CD8⁺, naïve T, effector T, Tfh, activated Tfh, Th1, Th2, Th17, Treg, CD19⁺CD27^-, CD19⁺CD27⁺, naïve B, germinal centre B, memory B, and plasma cells. Further, compared with healthy controls (HCs), GPR183 expression levels in above peripheral blood lymphocyte subsets of patients with SLE were reduced overall. The differential expression of GPR183 expression between inactive and active SLE patients indicates that GPR183 expression may be concerned with the disease activity of SLE. This was further confirmed through the strong negative correlation with SLEDAI score and positive correlation with serum complement protein C3, C4 and C1q levels. Further receiver operating characteristic (ROC) curve analysis revealed that GPR183 expression in circulating CD27^-IgD⁺ B cells may be beneficial in distinguishing between inactive and active SLE patients. In addition, type I interferon stimulation could down-regulate the expression of GPR183 in peripheral blood T and B cell subsets. Aberrant expression of GPR183 may provide some novel insights into disease activity prediction and underlying pathogenesis of SLE.

The CSF in neurosarcoidosis contains consistent clonal expansion of CD8 T cells, but not CD4 T cells

The tissue-specific drivers of neurosarcoidosis remain poorly defined. To identify cerebrospinal fluid (CSF) specific, antigen-driven T and B cell responses, we performed single-cell RNA sequencing of CSF and blood cells from neurosarcoid participants coupled to T and B cell receptor sequencing. In contrast to pulmonary sarcoidosis, which is driven by CD4 T cells, we found CD8 T cell clonal expansion enriched in the neurosarcoid CSF. These CSF-enriched CD8 T cells were composed of two subsets with differential expression of EBI2, CXCR3, and CXCR4. Lastly, our data suggest that IFNγ signaling may distinguish neurosarcoidosis from other neurological disorders.

Cholesterol metabolism: from lipidomics to immunology

Oxysterols, the oxidized forms of cholesterol or of its precursors, are formed in the first steps of cholesterol metabolism. Oxysterols have interested chemists, biologists, and physicians for many decades, but their exact biological relevance in vivo, other than as intermediates in bile acid biosynthesis, has long been debated. However, in the first quarter of this century, a role for side-chain oxysterols and their C-7 oxidized metabolites has been convincingly established in the immune system. 25-Hydroxycholesterol has been shown to be synthesized by macrophages in response to the activation of Toll-like receptors and to offer protection against microbial pathogens, whereas 7α,25-dihydroxycholesterol has been shown to act as a chemoattractant to lymphocytes expressing the G protein-coupled receptor Epstein-Barr virus-induced gene 2 and to be important in coordinating the action of B cells, T cells, and dendritic cells in secondary lymphoid tissue. There is a growing body of evidence that not only these two oxysterols but also many of their isomers are of importance to the proper function of the immune system. Here, we review recent findings related to the roles of oxysterols in immunology.

Immune microenvironment-related gene mapping predicts immunochemotherapy response and prognosis in diffuse large B-cell lymphoma

Diffuse large B-cell lymphoma (DLBCL) is the most common subtype of non-Hodgkin's lymphoma (NHL). The R-CHOP immunochemotherapy regimen is the first-line treatment option for DLBCL patients and has greatly improved the prognosis of DLBCL, making it a curable disease. However, drug resistance or relapse is the main challenge for current DLBCL treatment. Studies have shown that the tumor microenvironment plays an important role in the onset, development, and responsiveness to drugs in DLBCL. Here, we used the CIBERSORT algorithm to resolve the composition of the immune microenvironment of 471 DLBCL patients from the GEO database. We found that activated memory CD4+ T cells and γδ T cells were significantly associated with immunochemotherapy response. Weighted gene co-expression networks (WGCNA) were constructed using differentially expressed genes from immunochemotherapy responders and non-responders. The module most associated with these two types of T cells was defined as hub module. Enrichment analysis of the hub module showed that baseline immune status was significantly stronger in responders than in non-responders. A protein-protein interaction (PPI) network was constructed for hub module to identify hub genes. After survival analysis, five prognosis-related genes (CD3G, CD3D, GNB4, FCHO2, GPR183) were identified and all these genes were significantly negatively associated with PD1. Using our own patient cohort, we validated the efficacy of CD3G and CD3D in predicting immunochemotherapy response. Our study showed that CD3G, CD3D, GNB4, FCHO2, and GPR183 are involved in the regulation of the immune microenvironment of DLBCL. They can be used as biomarkers for predicting immunochemotherapy response and potential therapeutic targets in DLBCL.

Crosstalk of Microorganisms and Immune Responses in Autoimmune Neuroinflammation: A Focus on Regulatory T Cells

Regulatory T cells (Tregs) are the major determinant of peripheral immune tolerance. Many Treg subsets have been described, however thymus-derived and peripherally induced Tregs remain the most important subpopulations. In multiple sclerosis, a prototypical autoimmune disorder of the central nervous system, Treg dysfunction is a pathogenic hallmark. In contrast, induction of Treg proliferation and enhancement of their function are central immune evasion mechanisms of infectious pathogens. In accordance, Treg expansion is compartmentalized to tissues with high viral replication and prolonged in chronic infections. In friend retrovirus infection, Treg expansion is mainly based on excessive interleukin-2 production by infected effector T cells. Moreover, pathogens seem also to enhance Treg functions as shown in human immunodeficiency virus infection, where Tregs express higher levels of effector molecules such as cytotoxic T-lymphocyte-associated protein 4, CD39 and cAMP and show increased suppressive capacity. Thus, insights into the molecular mechanisms by which intracellular pathogens alter Treg functions might aid to find new therapeutic approaches to target central nervous system autoimmunity. In this review, we summarize the current knowledge of the role of pathogens for Treg function in the context of autoimmune neuroinflammation. We discuss the mechanistic implications for future therapies and provide an outlook for new research directions.

Multiple Targets for Oxysterols in Their Regulation of the Immune System

Oxysterols, or cholesterol oxidation products, are naturally occurring lipids which regulate the physiology of cells, including those of the immune system. In contrast to effects that are mediated through nuclear receptors or by epigenetic mechanism, which take tens of minutes to occur, changes in the activities of cell-surface receptors caused by oxysterols can be extremely rapid, often taking place within subsecond timescales. Such cell-surface receptor effects of oxysterols allow for the regulation of fast cellular processes, such as motility, secretion and endocytosis. These cellular processes play critical roles in both the innate and adaptive immune systems. This review will survey the two broad classes of cell-surface receptors for oxysterols (G-protein coupled receptors (GPCRs) and ion channels), the mechanisms by which cholesterol oxidation products act on them, and their presence and functions in the different cell types of the immune system. Overall, this review will highlight the potential of oxysterols, synthetic derivatives and their receptors for physiological and therapeutic modulation of the immune system.

EBI2 is expressed in glial cells in multiple sclerosis lesions, and its knock-out modulates remyelination in the cuprizone model

EBI2 receptor regulates the immune system, and in multiple, sclerosis is upregulated in the central nervous system infiltrating lymphocytes. In newborn EBI2-deficient mice, myelin development is delayed, and its persistent antagonism inhibits remyelination in chemically demyelinated organotypic cerebellar slices. We used the cuprizone model of multiple sclerosis to elucidate the role of central nervous system-expressed EBI2 in de- and remyelination. The wild-type and EBI2 knock-out mice were fed 0.2% cuprizone in chow for 5 weeks and allowed to recover on a normal diet for 2 weeks. The data showed less efficient recovery of myelin, attenuated oligodendrocyte loss, fewer astrocytes and increased total cholesterol levels in the EBI2 knock-out mice after recovery. Moreover, the wild-type mice upregulated EBI2 expression after recovery confirming the involvement of EBI2 signalling during recovery from demyelination in the cuprizone model. The pro-inflammatory cytokine levels were at comparable levels in the wild-type and EBI2 knock-out mice, with only minor differences in TNFα and IL1β levels either at peak or during recovery. The neuroinflammatory signalling molecules, Abl1 kinase and NFКB1 (p105/p50) subunit, were significantly downregulated in the EBI2 knock-out mice at peak of disease. Immunohistochemical investigations of EBI2 receptor distribution in the central nervous system (CNS) cells in multiple sclerosis (MS) brain revealed strong expression of EBI2 in astrocytes and microglia inside the plaques implicating glia-expressed EBI2 in multiple sclerosis pathophysiology. Taken together, these findings demonstrate the involvement of EBI2 signalling in the recovery from demyelination rather than in demyelination and as such warrant further research into the role of EBI2 in remyelination.

EBI2-expressing B cells in neuromyelitis optica spectrum disorder with AQP4-IgG: Association with acute attacks and serum cytokines

Epstein-Barr virus-induced G-protein coupled receptor 2 (EBI2) is important in regulating B cell activation. We investigated whether EBI2 expression on B cells is associated with acute attacks in neuromyelitis optica spectrum disorder with aquaporin-4 IgG (AQP4-IgG(+) NMOSD). Blood samples were collected from patients with AQP4-IgG(+) NMOSD, multiple sclerosis (MS), and patients without inflammatory demyelinating diseases (non-IDD controls). CD19+ B cells and CD4+ T cells were analyzed for surface expression of EBI2. Serum cytokine levels were also analyzed. The EBI2+CD19+ to EBI2-CD19+ cell ratio was significantly higher in patients with AQP4-IgG(+) NMOSD enrolled within 2 months of an attack than in those with non-IDDs (p = 0.007) and MS (p = 0.003). Patients with AQP4-IgG(+) NMOSD enrolled within 2 months of an attack had a higher EBI2+CD19+ cell frequency than patients with AQP4-IgG(+) NMOSD enrolled 2 months after a recent attack (p = 0.001). The EBI2+CD19+ cell frequency was positively correlated with interleukin (IL)-6 and IL-10. EBI2 expression on B cells could be associated with acute attacks of AQP4-IgG(+) NMOSD, possibly through IL-6- or IL-10-related pathways.

EBI2 Is Temporarily Upregulated in MO3.13 Oligodendrocytes during Maturation and Regulates Remyelination in the Organotypic Cerebellar Slice Model

The EBI2 receptor regulates the immune system and is expressed in various immune cells including B and T lymphocytes. It is also expressed in astrocytes in the central nervous system (CNS) where it regulates pro-inflammatory cytokine release, cell migration and protects from chemically induced demyelination. Its signaling and expression are implicated in various diseases including multiple sclerosis, where its expression is increased in infiltrating immune cells in the white matter lesions. Here, for the first time, the EBI2 protein in the CNS cells in the human brain was examined. The function of the receptor in MO3.13 oligodendrocytes, as well as its role in remyelination in organotypic cerebellar slices, were investigated. Human brain sections were co-stained for EBI2 receptor and various markers of CNS-specific cells and the human oligodendrocyte cell line MO3.13 was used to investigate changes in EBI2 expression and cellular migration. Organotypic cerebellar slices prepared from wild-type and cholesterol 25-hydroxylase knock-out mice were used to study remyelination following lysophosphatidylcholine (LPC)-induced demyelination. The data showed that EBI2 receptor is present in OPCs but not in myelinating oligodendrocytes in the human brain and that EBI2 expression is temporarily upregulated in maturing MO3.13 oligodendrocytes. Moreover, we show that migration of MO3.13 cells is directly regulated by EBI2 and that its signaling is necessary for remyelination in cerebellar slices post-LPC-induced demyelination. The work reported here provides new information on the expression and role of EBI2 in oligodendrocytes and myelination and provides new tools for modulation of oligodendrocyte biology and therapeutic approaches for demyelinating diseases.

The oxysterol receptor GPR183 in inflammatory bowel diseases

Immune cell trafficking is an important mechanism for the pathogenesis of inflammatory bowel disease (IBD). The oxysterol receptor GPR183 and its ligands, dihydroxylated oxysterols, can mediate positioning of immune cells including innate lymphoid cells. GPR183 has been mapped to an IBD risk locus, however another gene, Ubac2 is encoded on the reverse strand and associated with Behçet's disease, therefore the role of GPR183 as a genetic risk factor requires validation. GPR183 and production of its oxysterol ligands are up-regulated in human IBD and murine colitis. Gpr183 inactivation reduced severity of colitis in group 3 innate lymphoid cells-dependent colitis and in IL-10 colitis but not in dextran sodium sulphate colitis. Irrespectively, Gpr183 knockout strongly reduced accumulation of intestinal lymphoid tissue in health and all colitis models. In conclusion, genetic, translational and experimental studies implicate GPR183 in IBD pathogenesis and GPR183-dependent cell migration might be a therapeutic drug target for IBD. LINKED ARTICLES: This article is part of a themed issue on Oxysterols, Lifelong Health and Therapeutics. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v178.16/issuetoc.

Diverse Immunoregulatory Roles of Oxysterols-The Oxidized Cholesterol Metabolites

Intermediates of both cholesterol synthesis and cholesterol metabolism can have diverse roles in the control of cellular processes that go beyond the control of cholesterol homeostasis. For example, oxidized forms of cholesterol, called oxysterols have functions ranging from the control of gene expression, signal transduction and cell migration. This is of particular interest in the context of immunology and immunometabolism where we now know that metabolic processes are key towards shaping the nature of immune responses. Equally, aberrant metabolic processes including altered cholesterol homeostasis contribute to immune dysregulation and dysfunction in pathological situations. This review article brings together our current understanding of how oxysterols affect the control of immune responses in diverse immunological settings.

GPR183-Oxysterol Axis in Spinal Cord Contributes to Neuropathic Pain

Neuropathic pain is a debilitating public health concern for which novel non-narcotic therapeutic targets are desperately needed. Using unbiased transcriptomic screening of the dorsal horn spinal cord after nerve injury we have identified that Gpr183 (Epstein-Barr virus-induced gene 2) is upregulated after chronic constriction injury (CCI) in rats. GPR183 is a chemotactic receptor known for its role in the maturation of B cells, and the endogenous ligand is the oxysterol 7α,25-dihydroxycholesterol (7α,25-OHC). The role of GPR183 in the central nervous system is not well characterized, and its role in pain is unknown. The profile of commercially available probes for GPR183 limits their use as pharmacological tools to dissect the roles of this receptor in pathophysiological settings. Using in silico modeling, we have screened a library of 5 million compounds to identify several novel small-molecule antagonists of GPR183 with nanomolar potency. These compounds are able to antagonize 7α,25-OHC-induced calcium mobilization in vitro with IC₅₀ values below 50 nM. In vivo intrathecal injections of these antagonists during peak pain after CCI surgery reversed allodynia in male and female mice. Acute intrathecal injection of the GPR183 ligand 7α,25-OHC in naïve mice induced dose-dependent allodynia. Importantly, this effect was blocked using our novel GPR183 antagonists, suggesting spinal GPR183 activation as pronociceptive. These studies are the first to reveal a role for GPR183 in neuropathic pain and identify this receptor as a potential target for therapeutic intervention. SIGNIFICANCE STATEMENT: We have identified several novel GPR183 antagonists with nanomolar potency. Using these antagonists, we have demonstrated that GPR183 signaling in the spinal cord is pronociceptive. These studies are the first to reveal a role for GPR183 in neuropathic pain and identify it as a potential target for therapeutic intervention.

Neuro-oxysterols and neuro-sterols as ligands to nuclear receptors, GPCRs, ligand-gated ion channels and other protein receptors

The brain is the most cholesterol rich organ in the body containing about 25% of the body's free cholesterol. Cholesterol cannot pass the blood-brain barrier and be imported or exported; instead, it is synthesised in situ and metabolised to oxysterols, oxidised forms of cholesterol, which can pass the blood-brain barrier. 24S-Hydroxycholesterol is the dominant oxysterol in the brain after parturition, but during development, a myriad of other oxysterols are produced, which persist as minor oxysterols after birth. During both development and in later life, sterols and oxysterols interact with a variety of different receptors, including nuclear receptors, membrane bound GPCRs, the oxysterol/sterol sensing proteins INSIG and SCAP, and the ligand-gated ion channel NMDA receptors found in nerve cells. In this review, we summarise the different oxysterols and sterols found in the CNS whose biological activity is transmitted via these different classes of protein receptors. LINKED ARTICLES: This article is part of a themed issue on Oxysterols, Lifelong Health and Therapeutics. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v178.16/issuetoc.

Epstein-Barr Virus in Multiple Sclerosis: Theory and Emerging Immunotherapies

New treatments for multiple sclerosis (MS) focused on B cells have created an atmosphere of excitement in the MS community. B cells are now known to play a major role in disease, demonstrated by the highly impactful effect of a B cell-depleting antibody on controlling MS. The idea that a virus may play a role in the development of MS has a long history and is supported mostly by studies demonstrating a link between B cell-tropic Epstein–Barr virus (EBV) and disease onset. Efforts to develop antiviral strategies for treating MS are underway. Although gaps remain in our understanding of the etiology of MS, the role, if any, of viruses in propagating pathogenic immune responses deserves attention.

Oxysterols as lipid mediators: Their biosynthetic genes, enzymes and metabolites

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Pathways of oxysterol biosynthesis.

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Pathways of oxysterol metabolism.

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Oxysterols as bioactive molecules.

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Disorders of oxysterol metabolism.

There is growing evidence that oxysterols are more than simple metabolites in the pathway from cholesterol to bile acids. Recent data has shown oxysterols to be ligands to nuclear receptors and to G protein-coupled receptors, modulators of N-methyl-d-aspartate receptors and regulators of cholesterol biosynthesis. In this mini-review we will discuss the biosynthetic mechanisms for the formation of different oxysterols and the implication of disruption of these mechanisms in health and disease.

Oxysterols in Autoimmunity

Cholesterol is a member of the sterol family that plays essential roles in biological processes, including cell membrane stability and myelin formation. Cholesterol can be metabolized into several molecules including bile acids, hormones, and oxysterols. Studies from the last few decades have demonstrated that oxysterols are not only active metabolites but are further involved in the modulation of immune responses. Liver X Receptors (LXRs), nuclear receptors for oxysterols, are important for cholesterol homeostasis and regulation of inflammatory response but are still poorly characterized during autoimmune diseases. Here we review the current knowledge about the role of oxysterols during autoimmune conditions and focus on the implication of LXR-dependent and LXR-independent pathways. We further highlight the importance of these pathways in particular during central nervous system (CNS) autoimmunity and inflammatory bowel diseases (IBD) in both experimental models and human studies. Finally, we discuss our vision about future applications and research on oxysterols related to autoimmunity.

Elevated oxysterol levels in human and mouse livers reflect nonalcoholic steatohepatitis

Nonalcoholic steatohepatitis (NASH), a primary cause of liver disease, leads to complications such as fibrosis, cirrhosis, and carcinoma, but the pathophysiology of NASH is incompletely understood. Epstein-Barr virus-induced G protein-coupled receptor 2 (EBI2) and its oxysterol ligand 7α,25-dihydroxycholesterol (7α,25-diHC) are recently discovered immune regulators. Several lines of evidence suggest a role of oxysterols in NASH pathogenesis, but rigorous testing has not been performed. We measured oxysterol levels in the livers of NASH patients by LC-MS and tested the role of the EBI2-7α,25-diHC system in a murine feeding model of NASH. Free oxysterol profiling in livers from NASH patients revealed a pronounced increase in 24- and 7-hydroxylated oxysterols in NASH compared with controls. Levels of 24- and 7-hydroxylated oxysterols correlated with histological NASH activity. Histological analysis of murine liver samples demonstrated ballooning and liver inflammation. No significant genotype-related differences were observed in Ebi2^−/− mice and mice with defects in the 7α,25-diHC synthesizing enzymes CH25H and CYP7B1 compared with wild-type littermate controls, arguing against an essential role of these genes in NASH pathogenesis. Elevated 24- and 7-hydroxylated oxysterol levels were confirmed in murine NASH liver samples. Our results suggest increased bile acid synthesis in NASH samples, as judged by the enhanced level of 7α-hydroxycholest-4-en-3-one and impaired 24S-hydroxycholesterol metabolism as characteristic biochemical changes in livers affected by NASH.

The EBI2-oxysterol axis promotes the development of intestinal lymphoid structures and colitis

The gene encoding for Epstein-Barr virus-induced G-protein-coupled receptor 2 (EBI2) is a risk gene for inflammatory bowel disease (IBD). Together with its oxysterol ligand 7α,25-dihydroxycholesterol, EBI2 mediates migration and differentiation of immune cells. However, the role of EBI2 in the colonic immune system remains insufficiently studied. We found increased mRNA expression of EBI2 and oxysterol-synthesizing enzymes (CH25H, CYP7B1) in the inflamed colon of patients with ulcerative colitis and mice with acute or chronic dextran sulfate sodium (DSS) colitis. Accordingly, we detected elevated levels of 25-hydroxylated oxysterols, including 7α,25-dihydroxycholesterol in mice with acute colonic inflammation. Knockout of EBI2 or CH25H did not affect severity of DSS colitis; however, inflammation was decreased in male EBI2^-/- mice in the IL-10 colitis model. The colonic immune system comprises mucosal lymphoid structures, which accumulate upon chronic inflammation in IL-10-deficient mice and in chronic DSS colitis. However, EBI2^-/- mice formed significantly less colonic lymphoid structures at baseline and showed defects in inflammation-induced accumulation of lymphoid structures. In summary, we report induction of the EBI2-7α,25-dihydroxycholesterol axis in colitis and a role of EBI2 for the accumulation of lymphoid tissue during homeostasis and inflammation. These data implicate the EBI2-7α,25-dihydroxycholesterol axis in IBD pathogenesis.

EBI2 regulates pro-inflammatory signalling and cytokine release in astrocytes

The endogenous oxysterol 7α, 25-dihydroxycholesterol (7α25HC) ligand activates the G protein-coupled receptor EBI2 to regulate T cell-dependant antibody response and B cell migration. We have demonstrated that EBI2 is expressed in human and mouse astrocytes, that 7α25HC induces intracellular signalling and astrocyte migration, and that EBI2 plays a role in the crosstalk between astrocytes and macrophages. Recently, we demonstrate that EBI2 regulates myelin development and inhibits LPC-induced demyelination. Here, we show that 7α25HC inhibits LPS- and IL17/TNF-induced pro-inflammatory cytokine release in astrocytes. We observe the following: 1. Human astrocytes treated with IL17/TNF increases the nuclear translocation of NFκB, which is attenuated by pre-treatment with 7α25HC; 2. IL17/TNF increases cell impedance in human astrocytes, which is also attenuated by pre-treatment with 7α25HC; 3. The EBI2 antagonist NIBR189 inhibits these effects of 7α25HC, supporting the role of EBI2; 4. in vivo data corroborate these in vitro findings, showing that EBI2 knock-out (KO) animals display enhanced pro-inflammatory cytokine in response to LPS challenge, in the brain. These results demonstrate a role for oxysterol/EBI2 signalling in attenuating the response of astrocytes to pro-inflammatory signals as well as limiting the levels of pro-inflammatory cytokines in the brain.

EBI2 receptor regulates myelin development and inhibits LPC-induced demyelination

BACKGROUND

The G protein-coupled receptor EBI2 (Epstein-Barr virus-induced gene 2) is activated by 7α, 25-dihydroxycholesterol (7α25HC) and plays a role in T cell-dependant antibody response and B cell migration. Abnormal EBI2 signaling is implicated in a range of autoimmune disorders; however, its role in the CNS remains poorly understood.

METHODS

Here we characterize the role of EBI2 in myelination under normal and pathophysiological conditions using organotypic cerebellar slice cultures and EBI2 knock-out (KO) animals.

RESULTS

We find that MBP expression in brains taken from EBI2 KO mice is delayed compared to those taken from wild type (WT) mice. In agreement with these in vivo findings, we show that antagonism of EBI2 reduces MBP expression in vitro. Importantly, we demonstrate that EBI2 activation attenuates lysolecithin (LPC)-induced demyelination in mouse organotypic slice cultures. Moreover, EBI2 activation also inhibits LPC-mediated release of pro-inflammatory cytokines such as IL6 and IL1β in cerebellar slices.

CONCLUSIONS

These results, for the first time, display a role for EBI2 in myelin development and protection from demyelination under pathophysiological conditions and suggest that modulation of this receptor may be beneficial in neuroinflammatory and demyelinating disorders such as multiple sclerosis.

IL-27-Induced Type 1 Regulatory T-Cells Produce Oxysterols that Constrain IL-10 Production

The behaviors of lymphocytes, including CD4⁺ T helper cells, are controlled on many levels by internal metabolic properties. Lipid metabolites have recently been ascribed a novel function as immune response modulators and perturbation of steroids pathways modulates inflammation and potentially promotes a variety of diseases. However, the impact of lipid metabolism on autoimmune disease development and lymphocyte biology is still largely unraveled. In this line, oxysterols, oxidized forms of cholesterol, have pleiotropic roles on the immune response aside from their involvements in lipid metabolism. The oxysterols 25-hydroxycholesterol (25-OHC) and 7α,25-dihydroxycholesterol (7α,25-OHC) regulate antiviral immunity and immune cell chemotaxis. However, their physiological effects on adaptive immune response in particular on various subset CD4⁺ T lymphocytes are largely unknown. Here, we assessed oxysterol levels in subset of CD4⁺ T cells and demonstrated that 25-OHC and transcript levels of its synthesizing enzyme, cholesterol 25-hydroxylase, were specifically increased in IL-27-induced type 1 regulatory T (T_R1) cells. We further showed that 25-OHC acts as a negative regulator of T_R1 cells in particular of IL-10 secretion via liver X receptor signaling. Not only do these findings unravel molecular mechanisms accounting for IL-27 signaling but also they highlight oxysterols as pro-inflammatory mediators that dampens regulatory T cell responses and thus unleash a pro-inflammatory response.