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

Si-Ni-San alleviates intestinal and liver damage in ulcerative colitis mice by regulating cholesterol metabolism

ETHNOPHARMACOLOGICAL RELEVANCE

Si-Ni-San (SNS), a traditional Chinese medicinal formula derived from Treatise on Febrile Diseases, is considered effective in the treatment of inflammatory bowel diseases based upon thousands of years of clinical practice. However, the bioactive ingredients and underlying mechanisms are still unclear and need further investigation.

AIM OF THE STUDY

This study aimed to evaluate the effect, explore the bioactive ingredients and the underlying mechanisms of SNS in ameliorating ulcerative colitis (UC) and associated liver injury in dextran sodium sulphate (DSS)-induced mouse colitis models.

MATERIALS AND METHODS

The effect of SNS (1.5, 3, 6 g/kg) on 3% DSS-induced acute murine colitis was evaluated by disease activity index (DAI), colon length, inflammatory cytokines, hematoxylin-eosin (H&E) staining, tight junction proteins expression, ALT, AST, and oxidative stress indicators. HPLC-ESI-IT/TOF MS was used to analyze the chemical components of SNS and the main xenobiotics in the colon of UC mice after oral administration of SNS. Network pharmacological study was then conducted based on the main xenobiotics. Flow cytometry and immunohistochemistry techniques were used to demonstrate the inhibitory effect of SNS on Th17 cells differentiation and the amelioration of Th17/Treg cell imbalance. LC-MS/MS, Real-time quantitative polymerase chain reaction (RT-qPCR), and western blotting techniques were performed to investigate the oxysterol-Liver X receptor (LXRs) signaling activity in colon. Targeted bile acids metabolomics was conducted to reveal the change of the two major pathways of bile acid synthesis in the liver, and the expression of key metabolic enzymes of bile acids synthesis was characterized by RT-qPCR and western blotting techniques.

RESULTS

SNS (1.5, 3, 6 g/kg) decreased the DAI scores, protected intestinal mucosa barrier, suppressed the production of pro-inflammatory cytokines, improved hepatic and splenic enlargement and alleviated liver injury in a dose-dependent manner. A total of 22 components were identified in the colon of SNS (6 g/kg) treated colitis mice, and the top 10 components ranked by relative content were regarded as the potential effective chemical components of SNS, and used to conduct network pharmacology research. The efficacy of SNS was mediated by a reduction of Th17 cell differentiation, restoration of Th17/Treg cell homeostasis in the colon and spleen, and the experimental results were consistent with our hypothesis and the biological mechanism predicted by network pharmacology. Mechanistically, SNS regulated the concentration of 25-OHC and 27-OHC by up-regulated CH25H, CYP27A1 protein expression in colon, thus affected the expression and activity of LXR, ultimately impacted Th17 differentiation and Th17/Treg balance. It was also found that SNS repressed the increase of hepatic cholesterol and reversed the shift of BA synthesis to the acidic pathway in UC mice, which decreased the proportion of non-12-OH BAs in total bile acids (TBAs) and further ameliorated colitis and concomitant liver injury.

CONCLUSIONS

This study set the stage for considering SNS as a multi-organ benefited anti-colitis prescription based on the significant effect of ameliorating intestinal and liver damage, and revealed that derivatives of cholesterol, namely oxysterols and bile acids, were closely involved in the mechanism of SNS anti-colitis effect.

Bile acid metabolism modulates intestinal immunity involved in ulcerative colitis progression

The bile acids (BA) in the intestine promote inflammation by interacting with immune cells, playing a crucial role in the progression of UC, but the specific mechanism between the two remains elusive. This study aims to explore the relationship between BAMand UC inflammation and determine its potential mechanisms.Firstly, we employed a hybrid approach using Lasso regression and support vector machine (SVM) feature selection in bioinformatics to identify genes linked to UC and BAM. The relationship between these genes and immune infiltration was explored, along with their correlation with immune factors in the Tumor-Immune System Interaction Database (TISIDB) database. Gene Set Enrichment Analysis (GSEA) pathway enrichment analysis was then used to predict signaling pathways associated with key genes in UC. Single-cell data from the GSE13464 dataset was also analyzed. Finally, Five differentially expressed genes (DEGs) related to BAM (APOA1, AMACR, PEX19, CH25H, and AQP9) were significantly upregulated/downregulated in UC immune cells. The expression of important genes in UC tissue was confirmed in the experimental validation section and AQP9, which showed significant differential expression, was chosen for further validation. The results showed that the AQP9 gene may regulate the IFN - γ/JAK signaling axis, thereby promoting CD8+T cell activation. This research has greatly advanced our comprehension of the pathogenesis and underlying mechanism of BAM in immune cells linked to UC.

Exploring the Activation Mechanism of the GPR183 Receptor

The G protein-coupled receptors (GPCRs) play a pivotal role in numerous biological processes as crucial cell membrane receptors. However, the dynamic mechanisms underlying the activation of GPR183, a specific GPCR, remain largely elusive. To address this, we employed computational simulation techniques to elucidate the activation process and key events associated with GPR183, including conformational changes from inactive to active state, binding interactions with the Gi protein complex, and GDP release. Our findings demonstrate that the association between GPR183 and the Gi protein involves the formation of receptor-specific conformations, the gradual proximity of the Gi protein to the binding pocket, and fine adjustments of the protein conformation, ultimately leading to a stable GPR183-Gi complex characterized by a high energy barrier. The presence of Gi protein partially promotes GPR183 activation, which is consistent with the observation of GPCR constitutive activity test experiments, thus illustrating the reliability of our calculations. Moreover, our study suggests the existence of a stable partially activated state preceding complete activation, providing novel avenues for future investigations. In addition, the relevance of GPR183 for various diseases, such as colitis, the response of eosinophils to Mycobacterium tuberculosis infection, antiviral properties, and pulmonary inflammation, has been emphasized, underscoring its therapeutic potential. Consequently, understanding the activation process of GPR183 through molecular dynamic simulations offers valuable kinetic insights that can aid in the development of targeted therapies.

Discovery of a Highly Potent Oxysterol Receptor GPR183 Antagonist Bearing the Benzo[d]thiazole Structural Motif for the Treatment of Inflammatory Bowel Disease (IBD)

Accumulating evidence has demonstrated a critical pathological role of oxysterol receptor GPR183 in various inflammatory and autoimmune diseases, including inflammatory bowel disease (IBD). However, the currently reported GPR183 antagonists are very limited and not qualified for in vivo studies due to their inferior druglike properties. Herein, we conducted a structural elaboration focusing on improving its PK and safety profile based on a reference antagonist NIBR189. Of note, compound 33, bearing an aminobenzothiazole motif, exhibited reduced hERG inhibition, improved PK properties, and robust antagonistic activity (IC50 = 0.82 nM) with high selectivity against GPR183. Moreover, compound 33 displayed strong in vitro antimigration and anti-inflammatory activity in monocytes. Oral administration of compound 33 effectively improved the pathological symptoms of DSS-induced experimental colitis. All of these findings demonstrate that compound 33 is a novel and promising GPR183 antagonist suitable for further investigation to treat IBD.

Development of non-alcoholic steatohepatitis is associated with gut microbiota but not with oxysterol enzymes CH25H, EBI2, or CYP7B1 in mice

Liver steatosis is the most frequent liver disorder and its advanced stage, non-alcoholic steatohepatitis (NASH), will soon become the main reason for liver fibrosis and cirrhosis. The "multiple hits hypothesis" suggests that progression from simple steatosis to NASH is triggered by multiple factors including the gut microbiota composition. The Epstein Barr virus induced gene 2 (EBI2) is a receptor for the oxysterol 7a, 25-dihydroxycholesterol synthesized by the enzymes CH25H and CYP7B1. EBI2 and its ligand control activation of immune cells in secondary lymphoid organs and the gut. Here we show a concurrent study of the microbial dysregulation and perturbation of the EBI2 axis in a mice model of NASH.We used mice with wildtype, or littermates with CH25H-/-, EBI2-/-, or CYP7B1-/- genotypes fed with a high-fat diet (HFD) containing high amounts of fat, cholesterol, and fructose for 20 weeks to induce liver steatosis and NASH. Fecal and small intestinal microbiota samples were collected, and microbiota signatures were compared according to genotype and NASH disease state.We found pronounced differences in microbiota composition of mice with HFD developing NASH compared to mice did not developing NASH. In mice with NASH, we identified significantly increased 33 taxa mainly belonging to the Clostridiales order and/ or the family, and significantly decreased 17 taxa. Using an Elastic Net algorithm, we suggest a microbiota signature that predicts NASH in animals with a HFD from the microbiota composition with moderate accuracy (area under the receiver operator characteristics curve = 0.64). In contrast, no microbiota differences regarding the studied genotypes (wildtype vs knock-out CH25H-/-, EBI2-/-, or CYP7B1-/-) were observed.In conclusion, our data confirm previous studies identifying the intestinal microbiota composition as a relevant marker for NASH pathogenesis. Further, no link of the EBI2 - oxysterol axis to the intestinal microbiota was detectable in the current study.

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.

Discovery of a First-in-Class GPR183 Antagonist for the Potential Treatment of Rheumatoid Arthritis

GPR183 is required for humoral immune responses, and its polymorphisms have been associated with inflammatory autoimmune diseases. Despite increasing attention to GPR183 as a potential therapeutic target for autoimmune diseases, relatively few antagonists have been reported, and none of them have progressed to the clinical stage. In this study, we discovered a highly potent GPR183 antagonist, compound 32, with good aqueous solubility, excellent selectivity, and pharmacokinetic properties. Meanwhile, compound 32 showed exceptional efficacy for rheumatoid arthritis (RA) disease in a mouse collagen-induced arthritis (CIA) model, with an efficacious dose of 0.1 mg/kg. Functionally, compound 32 significantly reduced the swelling of paws and joints, the gene expression of proinflammatory cytokines, MCP-1, MMPs, and VEGF, inflammatory cell infiltration, cartilage damage, pannus formation, and bone erosion in the joints of CIA mice in a dose-dependent manner. Hence, these findings suggest compound 32 as a valuable molecule for further development.

Research progress on the mechanism of cholesterol-25-hydroxylase in intestinal immunity

Inflammatory bowel disease (IBD), a general term encompassing Crohn's disease (CD) and ulcerative colitis (UC), and other conditions, is a chronic and relapsing autoimmune disease that can occur in any part of the digestive tract. While the cause of IBD remains unclear, it is acknowledged that the disease has much to do with the dysregulation of intestinal immunity. In the intestinal immune regulatory system, Cholesterol-25-hydroxylase (CH25H) plays an important role in regulating the function of immune cells and lipid metabolism through catalyzing the oxidation of cholesterol into 25-hydroxycholesterol (25-HC). Specifically, CH25H focuses its mechanism of regulating the inflammatory response, signal transduction and cell migration on various types of immune cells by binding to relevant receptors, and the mechanism of regulating lipid metabolism and immune cell function via the transcription factor Sterol Regulator-Binding Protein. Based on this foundation, this article will review the function of CH25H in intestinal immunity, aiming to provide evidence for supporting the discovery of early diagnostic and treatment targets for IBD.

Emerging roles of host and microbial bioactive lipids in inflammatory bowel diseases

The intestinal tract harbors diverse microorganisms, host- and microbiota-derived metabolites, and potentially harmful dietary antigens. The epithelial barrier separates the mucosa, where diverse immune cells exist, from the lumen to avoid excessive immune reactions against microbes and dietary antigens. Inflammatory bowel disease (IBD), such as ulcerative colitis and Crohn's disease, is characterized by a chronic and relapsing disorder of the gastrointestinal tract. Although the precise etiology of IBD is still largely unknown, accumulating evidence suggests that IBD is multifactorial, involving host genetics and microbiota. Alterations in the metabolomic profiles and microbial community are features of IBD. Advances in mass spectrometry-based lipidomic technologies enable the identification of changes in the composition of intestinal lipid species in IBD. Because lipids have a wide range of functions, including signal transduction and cell membrane formation, the dysregulation of lipid metabolism drastically affects the physiology of the host and microorganisms. Therefore, a better understanding of the intimate interactions of intestinal lipids with host cells that are implicated in the pathogenesis of intestinal inflammation might aid in the identification of novel biomarkers and therapeutic targets for IBD. This review summarizes the current knowledge on the mechanisms by which host and microbial lipids control and maintain intestinal health and diseases.

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.

Metabolic dialogs between B cells and the tumor microenvironment: Implications for anticancer immunity

Immunometabolism, a branch of biology describing the link between immunity and metabolism, is an emerging topic in cancer immunology. It is currently well accepted that B cells and tertiary lymph structures formed by them are associated with favorable outcomes when patients undergo cancer immunotherapy. Understanding the determinants of B-cell fate and function in cancer patients is necessary for improving cancer immunotherapy. Accumulating evidence points to the tumor microenvironment being a critical metabolic hurdle to an efficient antitumor B-cell response. At the same time, several B-cell-derived metabolites have recently been reported to inhibit anticancer immunity. In this literature review, key B-cell immunometabolism studies and the metabolic life of B cells were summarized. Then, we discussed the intrinsic metabolic pathways of B cells themselves and how the tumor microenvironment and B cells in tumors metabolically influence each other. Finally, we pointed out key questions to provide some inspiration for further study of the role of B-cell immunometabolism in the antitumor immune response.

Macrophages in health and disease

The heterogeneity of tissue macrophages, in health and in disease, has become increasingly transparent over the last decade. But with the plethora of data comes a natural need for organization and the design of a conceptual framework for how we can better understand the origins and functions of different macrophages. We propose that the ontogeny of a macrophage-beyond its fundamental derivation as either embryonically or bone marrow-derived, but rather inclusive of the course of its differentiation, amidst steady-state cues, disease-associated signals, and time-constitutes a critical piece of information about its contribution to homeostasis or the progression of disease.

Impact of Epstein-Barr virus infection in patients with inflammatory bowel disease

A high prevalence of Epstein-Barr virus (EBV) infection in patients with inflammatory bowel disease (IBD) has been reported in many case reports and studies; thus, the association between EBV and IBD has gained increasing attention. Patients with IBD are at an increased risk of opportunistic EBV infection owing to the common use of immunomodulators. EBV infection in IBD patients can cause various complications, including superimposed viral colitis, which is associated with chronicity, exacerbation, and poor prognosis of refractory IBD, and can induce progression to lymphoproliferative disorders, such as EBV-positive mucocutaneous ulcer (EBVMCU), lymphomatoid granulomatosis (LYG), hemophagocytic lymphohistiocytosis (HLH) and diffuse large B-cell lymphoma (DLBCL). It has been suggested to screen for EBV before initiating immunosuppressive therapy and monitor the status of EBV infection in patients with IBD, especially those who are EBV-seronegative and have a risk of primary EBV infection. Clinicians should also be careful of misdiagnosing IBD and EBV-associated lymphoproliferative diseases due to similarities in both clinical symptoms and endoscopic manifestations. Withdrawal of immunosuppressants has been shown to be an effective strategy to achieve remission of disease at the time of EBV diagnosis, but antiviral therapy remains controversial. The present review aims to describe the characteristics of the complications caused by EBV infection and generalize the recent research progress on and challenges caused by EBV infection in IBD patients. The literature for writing this review was collected from 'PubMed' research engine. The keywords 'inflammatory bowel disease and Epstein-Barr virus' or 'ulcerative colitis and Epstein-Barr virus' or 'Crohn's disease and Epstein-Barr virus' were used to collect the literature and relevant papers were collected to help writing this review.

CD4+-mediated colitis in mice is independent of the GPR183 and GPR18 pathways

Colitis is characterized by an exacerbated intestinal immune response, but the genetic and other mechanisms regulating immune activation remain incompletely understood. In order to identify new pathways leading to colitis, we sought to identify genes with increased expression in the colons of patients that also are near loci identified by genome wide association studies (GWAS) associated with IBD risk. One such SNP, rs9557195 was of particular interest because it is within an intron of G-protein-coupled receptor (GPR) 183, known to be important for lymphocyte migration. Furthermore, this SNP is in close proximity to the gene encoding another G-protein coupled receptor, GPR18. Analyzing publicly available datasets, we found transcripts of GPR183 and GPR18 to be increased in colon biopsies from ulcerative colitis and Crohn's disease patients, and GPR183 was even more increased in patients resistant to TNF treatment. Expression of both genes also was increased in mouse models of colitis. Therefore, our aim was to understand if increased expression of these GPRs in the intestine is related to disease severity in colitis models. Here we investigated the role of these receptors in the T cell transfer model and the dextran sulfate sodium model. In the T cell transfer model, GPR183 expression on donor T cells, as well as on other cell types in the Rag-/- recipients, was not essential for severe colitis induction. Furthermore, deficiency in Rag-/- mice for the enzyme that synthesizes a cholesterol metabolite that is a major ligand for GPR183 also did not affect disease. Similarly, lack of GPR18 expression in T cells or other cell types did not affect colitis pathogenesis in the T cell transfer or in the dextran sulfate sodium model. Therefore, despite increased expression of transcripts for these genes in the intestine during inflammation in humans and mice, they are not required for disease severity in mouse models of colitis induced by chemical injury or T cell cytokines, perhaps due to redundancy in mechanisms important for homing and survival of lymphocytes to the inflamed intestine.

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.

Effects of Oxysterols on Immune Cells and Related Diseases

Oxysterols are the products of cholesterol oxidation. They have a wide range of effects on several cells, organs, and systems in the body. Oxysterols also have an influence on the physiology of the immune system, from immune cell maturation and migration to innate and humoral immune responses. In this regard, oxysterols have been involved in several diseases that have an immune component, from autoimmune and neurodegenerative diseases to inflammatory diseases, atherosclerosis, and cancer. Here, we review data on the participation of oxysterols, mainly 25-hydroxycholesterol and 7α,25-dihydroxycholesterol, in the immune system and related diseases. The effects of these oxysterols and main oxysterol receptors, LXR and EBI2, in cells of the immune system (B cells, T cells, macrophages, dendritic cells, oligodendrocytes, and astrocytes), and in immune-related diseases, such as neurodegenerative diseases, intestinal diseases, cancer, respiratory diseases, and atherosclerosis, are discussed.

Setd2 determines distinct properties of intestinal ILC3 subsets to regulate intestinal immunity

Subsets of group 3 innate lymphoid cells (ILC3s) are heterogeneous in development and function and play differential roles in intestinal immunity. Histone modifications are involved in the fate commitment of immune cells, including ILC3s. Here, we report that deletion of Setd2, histone H3K36 methyltransferase, in ILC3s results in increased generation of NKp46⁺ILC3s with enhanced cytotoxic signatures and tumor-suppressive capacity. Meanwhile, Rag1^-/-Rorc^CreSetd2^flox/flox mice have fewer CCR6⁺ILC3s and less defective solitary intestinal lymphoid tissue formation, accompanied by reduced granulocyte-macrophage colony-stimulating factor (GM-CSF) production by NKp46^-ILC3s and decreased CD11b⁺CD103⁺ dendritic cell accumulation. The deficiency of Setd2^-/-NKp46^-ILC3s may contribute to disturbed RORγt⁺Treg homeostasis and intestinal inflammation in Rag1^-/-Rorc^CreSetd2^flox/flox mice upon T cell reconstitution. Setd2 regulates genome accessibility imprinting gene mRNA expression, with a more profound effect on NKp46⁺ILC3s than NKp46^-ILC3s. Therefore, Setd2 determines distinct chromatin status and transcriptomic programs of ILC3 subsets to affect their function and intestinal immunity.

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.

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.

Cholesterol metabolism: a new molecular switch to control inflammation

The immune system protects the body against harm by inducing inflammation. During the immune response, cells of the immune system get activated, divided and differentiated in order to eliminate the danger signal. This process relies on the metabolic reprogramming of both catabolic and anabolic pathways not only to produce energy in the form of ATP but also to generate metabolites that exert key functions in controlling the response. Equally important to mounting an appropriate effector response is the process of immune resolution, as uncontrolled inflammation is implicated in the pathogenesis of many human diseases, including allergy, chronic inflammation and cancer. In this review, we aim to introduce the reader to the field of cholesterol immunometabolism and discuss how both metabolites arising from the pathway and cholesterol homeostasis are able to impact innate and adaptive immune cells, staging cholesterol homeostasis at the centre of an adequate immune response. We also review evidence that demonstrates the clear impact that cholesterol metabolism has in both the induction and the resolution of the inflammatory response. Finally, we propose that emerging data in this field not only increase our understanding of immunometabolism but also provide new tools for monitoring and intervening in human diseases, where controlling and/or modifying inflammation is desirable.

Gut-inhabiting Clostridia build human GPCR ligands by conjugating neurotransmitters with diet- and human-derived fatty acids

Human physiology is regulated by endogenous signalling compounds, including fatty acid amides (FAAs), chemical mimics of which are made by bacteria. The molecules produced by human-associated microbes are difficult to identify because they may only be made in a local niche or they require a substrate sourced from the host, diet or other microbes. We identified a set of uncharacterized gene clusters in metagenomics data from the human gut microbiome. These clusters were discovered to make FAAs by fusing exogenous fatty acids with amines. Using an in vitro assay, we tested their ability to incorporate 25 fatty acids and 53 amines known to be present in the human gut, from which the production of six FAAs was deduced (oleoyl dopamine, oleoyl tyramine, lauroyl tryptamine, oleoyl aminovaleric acid, α-linolenoyl phenylethylamine and caproyl tryptamine). These molecules were screened against panels of human G-protein-coupled receptors to deduce their putative human targets. Lauroyl tryptamine is found to be an antagonist to the immunomodulatory receptor EBI2 against its native oxysterol ligand (0.98 μM half-maximal inhibitory concentration), is produced in culture by Eubacterium rectale and is present in human faecal samples. FAAs produced by Clostridia may serve as a mechanism to modulate their host by mimicking human signalling molecules.

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.

Innate Lymphoid Cells and Adaptive Immune Cells Cross-Talk: A Secret Talk Revealed in Immune Homeostasis and Different Inflammatory Conditions

The inflammatory immune response has evolved to protect the host from different pathogens, allergens, and endogenous death or damage-associated molecular patterns. Both innate and adaptive immune components are crucial in inducing an inflammatory immune response depending on the stimulus type and its duration of exposure or the activation of the primary innate immune response. As the source of inflammation is removed, the aggravated immune response comes to its homeostatic level. However, the failure of the inflammatory immune response to subside to its normal level generates chronic inflammatory conditions, including autoimmune diseases and cancer. Innate lymphoid cells (ILCs) are newly discovered innate immune cells, which are present in abundance at mucosal surfaces, including lungs, gastrointestinal tract, and reproductive tract. Also, they are present in peripheral blood circulation, skin, and lymph nodes. They play a crucial role in generating the pro-inflammatory immune response during diverse conditions. On the other hand, adaptive immune cells, including different types of T and B cells are major players in the pathogenesis of autoimmune diseases (type 1 diabetes mellitus, rheumatoid arthritis, psoriasis, and systemic lupus erythematosus, etc.) and cancers. Thus the article is designed to discuss the immunological role of different ILCs and their interaction with adaptive immune cells in maintaining the immune homeostasis, and during inflammatory autoimmune diseases along with other inflammatory conditions (excluding pathogen-induced inflammation), including cancer, graft-versus-host diseases, and human pregnancy.

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.

Lipid Metabolism in Tumor-Associated B Cells

Breakthroughs have been made in the cancer immunotherapy field focusing on utilizing T cells' antitumor immunity, and the lipid metabolism of tumor-associated B cells is not well studied compared to T cells. Accumulating evidence suggested that B cells also play important roles in tumor biology and antitumor immunity, especially the germinal center B cells that present in the tumor-related tertiary lymphoid structures. Due to scarce studies on lipid metabolisms of tumor-associated B cells, this chapter mainly summarized findings on B cell lipid metabolism and discussed B cell development and major transcription factors, tumor-associated B cell populations and their potential functions in antitumor immunity, fatty acid oxidation in germinal center B cells, and tumor microenvironment factors that potentially affect B cell lipid metabolism, focusing on hypoxia and nutrients competition, as well as lipid metabolites that affect B cell function, including cholesterol, geranylgeranyl pyrophosphate, oxysterols, and short-chain fatty acids.

Bioactive lipids in inflammatory bowel diseases - From pathophysiological alterations to therapeutic opportunities

Inflammatory bowel diseases (IBDs), such as Crohn's disease and ulcerative colitis, are lifelong diseases that remain challenging to treat. IBDs are characterized by alterations in intestinal barrier function and dysregulation of the innate and adaptive immunity. An increasing number of lipids are found to be important regulators of inflammation and immunity as well as gut physiology. Therefore, the study of lipid mediators in IBDs is expected to improve our understanding of disease pathogenesis and lead to novel therapeutic opportunities. Here, through selected examples - such as fatty acids, specialized proresolving mediators, lysophospholipids, endocannabinoids, and oxysterols - we discuss how lipid signaling is involved in IBD physiopathology and how modulating lipid signaling pathways could affect IBDs.

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.

Cholesterol 25-hydroxylase protects against experimental colitis in mice by modulating epithelial gut barrier function

Cholesterol 25-hydroxylase (CH25H) encodes the enzyme that converts cholesterol to 25-hydroxycholesterol (25-HC). 25-HC has been demonstrated to be involved in the pathogenesis of inflammatory bowel disease. However, the role of CH25H in experimental colitis remains unknown. Dextran sulfate sodium (DSS)-induced colitis was monitored in wild type and Ch25h^−/− mice in 8-week-old male for 7 days by assessment of body weight, histology, inflammatory cellular infiltration, and colon length. The function of CH25H was investigated using loss-of-function and gain-of-function such as Ch25h-deficient mice, supplementation with exogenous 25-HC and treatment of 25-HC into Caco2 and HCT116 colonic epithelial cells. Ch25h^−/− mice with DSS-induced colitis exhibited aggravated injury, including higher clinical colitis scores, severe injury of the epithelial barrier, lower tight junction protein levels and higher levels of IL-6. Supplementation with exogenous 25-HC ameliorated disease symptoms and reduced the extent of damage in DSS-induced colitis, which was characterized by lower colon damage, higher tight junction protein expression, significantly decreased local and systemic production of pro-inflammatory cytokines IL-6. In Caco2 and HCT116 cells, 25-HC induced tight junction genes expression in colon cancer epithelial cells. These effects of CH25H were obtained by promoting ATF3 expression. Taken together, our findings reveal a protective role for 25-HC in DSS-induced colitis and the ability of CH25H to maintain epithelial gut barrier function through ATF3 expression. Supplementation with exogenous 25-HC ameliorates disease symptoms, which provides a new therapeutic strategy for ulcerative colitis.

Tissue-resident lymphocytes: weaponized sentinels at barrier surfaces

Tissue-resident immune cells stably localize in tissues largely independent of the circulatory system. While initial studies have focused on the recognition of CD8 ⁺ tissue-resident memory T (CD8 T _RM) cells, it is now clear that numerous cell types such as CD4 ⁺ T cells, gd T cells, innate lymphoid cells and mucosal-associated invariant T (MAIT) cells form stable populations in tissues. They are enriched at the barrier surfaces and within non-lymphoid compartments. They provide an extensive immune network capable of sensing local perturbations of the body’s homeostasis. This positioning enables immune cells to positively influence immune protection against infection and cancer but paradoxically also augment autoimmunity, allergy and chronic inflammatory diseases. Here, we highlight the recent studies across multiple lymphoid immune cell types that have emerged on this research topic and extend our understanding of this important cellular network. In addition, we highlight the areas that remain gaps in our knowledge of the regulation of these cells and how a deeper understanding may result in new ways to ‘target’ these cells to influence disease outcome and treatments.

Cholesterol 25-hydroxylase (CH25H) as a promoter of adipose tissue inflammation in obesity and diabetes

Objective

Expansion of visceral adipose tissue (VAT) and metabolic inflammation are consequences of obesity and associated with type 2 diabetes (T2DM). Metabolically activated adipose tissue macrophages (ATMs) undergo qualitative and quantitative changes that influence their inflammatory responses. How these cells contribute to insulin resistance (IR) in humans is not well understood. Cholesterol 25-Hydroxylase (CH25H) converts cholesterol into 25-Hydroxycholesterol (25-HC), an oxysterol that modulates immune responses. Using human and murine models, we investigated the role of CH25H in metabolic inflammation.

Methods

We performed transcriptomic (RNASeq) analysis on the human whole AT biopsies and sorted ATMs from obese non-diabetic (NDM) and obese diabetic (DM) subjects to inquire if CH25H was increased in DM. We challenged mice lacking Ch25h with a high-fat diet (HFD) to characterize their metabolic and immunologic profiling. Ch25h KO mice and human adipose tissue biopsies from NDM and DM subjects were analyzed. LC-MS was conducted to measure 25-HC level in AT. In vitro analysis permitted us to investigate the effect of 25-HC on cytokine expression.

Results

In our RNASeq analysis of human visceral and subcutaneous biopsies, gene pathways related to inflammation were increased in obese DM vs. non-DM subjects that included CH25H. CH25H was enriched in the stromal vascular fraction of human adipose tissue and highly expressed in CD206⁺ human ATMs by flow cytometry analysis. We measured the levels of the oxysterols, 25-HC and 7α25diHC, in human visceral adipose tissue samples and showed a correlation between BMI and 25-HC. Using mouse models of diet-induced obesity (DIO), we found that HFD-induced Ch25h expression in eWAT and increased levels of 25-HC in AT. On HFD, Ch25h KO mice became obese but exhibited reduced plasma insulin levels, improved insulin action, and decreased ectopic lipid deposit. Improved insulin sensitivity in Ch25h KO mice was due to attenuation of CD11c⁺ adipose tissue macrophage infiltration in eWAT. Finally, by testing AT explants, bone marrow-derived macrophages (BMDMs) and SVF cells from Ch25h deficient mice, we observed that 25-HC is required for the expression of pro-inflammatory genes. 25-HC was also able to induce inflammatory genes in preadipocytes.

Conclusions

Our data suggest a critical role for CH25H/25-HC in the progression of meta-inflammation and insulin resistance in obese humans and mouse models of obesity. In response to obesogenic stimuli, CH25H/25-HC could exert a pro-inflammatory role.

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CH25H upregulation in visceral adipose tissue is associated with diabetes in humans.

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ATMs are the primary site of CH25H expression in humans and mice.

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DIO in mice activates Ch25h expression and 25-HC production in visceral adipose tissue.

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Obese Ch25h KO mice have improved insulin sensitivity due to attenuated adipose tissue inflammation.

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In response to inflammatory stimuli, Ch25h/25-HC potentiates myeloid activation.

Infection of Epstein-Barr Virus is Associated with the Decrease of Helios+FoxP3+Regulatory T Cells in Active Ulcerative Colitis Patients

Background: Loss of immune homeostasis to enteric pathogens is considered to be involved in the pathogenesis of ulcerative colitis (UC), and regulatory T cells (Tregs) are key for this immune homeostasis. Helios exhibits an important effect on regulating the suppressive function of Tregs. Epstein-Barr virus (EBV) is more commonly detected in UC. However, whether there is an association between EBV infection and Helios⁺Tregs and its impact on disease activity of UC remain unclear. We aimed to explore the clinical significance of Helios⁺Tregs and their potential association with EBV infection in UC. Methods: Seventy-six UC patients and 38 controls were consecutively enrolled. Helios⁺FoxP3⁺Tregs were analyzed using flow cytometry and compared among groups. Eight active UC patients treated with 5-aminosalicylic acid were followed up. Correlation analyses were conducted between Helios⁺FoxP3⁺Tregs and disease activity indicators. In addition, EBV viral loads in the mucosal lesion were quantified in active UC by quantitative polymerase chain reaction and were comprehensively analyzed in subgroups of different disease severity, and their associations with Helios⁺FoxP3⁺Tregs were also analyzed. Results: Helios⁺FoxP3⁺Tregs were significantly decreased in active UC and were inversely correlated with serum C-reactive protein and Mayo score. Moreover, we observed the recovery of Helios⁺FoxP3⁺Tregs in followed-up active UC achieving remission after treatment. EBV loads were higher in active UC, and levels of Helios⁺FoxP3⁺Tregs in the EBV-positive subgroup were lower than the EBV-negative subgroup in moderate and severe active patients. Most importantly, we found that Helios⁺FoxP3⁺Tregs were significantly negatively correlated with EBV viral loads. Conclusion: Helios⁺FoxP3⁺Tregs are likely to play a pivotal role in disease activity of UC and may be influenced by EBV infection.

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.

Metabolic Control of Innate Lymphoid Cell Migration

Innate lymphoid cells (ILCs) are specialized immune cells that rapidly respond to environmental challenges, such as infection and tissue damage. ILCs play an important role in organ homeostasis, tissue repair, and host defense in the mucosal tissues intestine and lung. ILCs are sentinels of healthy tissue function, yet it is poorly understood how ILCs are recruited, strategically positioned, and maintained within tissues. Accordingly, ILC migration is an area that has recently come into focus and it is important to define the signals that control ILC migration to and within tissues. In this context, signals from the local tissue microenvironment are relevant. For example, ILCs in the intestine are exposed to an environment that is rich in dietary, microbial, and endogenous metabolites. It has been shown that the Vitamin A metabolite retinoic acid promotes ILC1 and ILC3 homing to the intestine. In addition, recent studies have discovered cholesterol metabolites (oxysterols) as a novel class of molecules that regulate ILC migration through the receptor GPR183. ILCs are considered to be largely tissue-resident cells, yet recent data indicate that ILCs actively migrate during inflammation. Furthermore, the discovery of circulating ILC precursors in humans and their presence within tissues has fueled the concept of local ILC-poiesis. However, it is unclear how circulating ILCs enter tissue during embryogenesis and inflammation and how they are directed to local tissue niches. In this review, I will discuss the metabolic signals that regulate ILC homing and their strategic positioning in healthy and inflamed tissues. It is becoming increasingly clear that ILC function is closely linked to their tissue localization. Therefore, understanding the tissue signals that control ILC migration could open new avenues for the treatment of chronic inflammatory diseases and cancer.

Identification of genetic markers associated with milk production traits in Chinese Holstein cattle based on post genome-wide association studies

With the rapid development of dairy industry, the breeding process of dairy cows has been accelerated. In previous genome-wide association studies (GWAS), a large number of genetic markers have been reported which may contribute to the selection of Holstein populations with superior milk-producing traits, but they remain to be further verified before practical application. In this study, 90 single nucleotide polymorphisms (SNPs) were selected, which were reported to be significantly associated with five milk production traits, including 305-day milk yield (305MY), 305-day milk fat percent (305FC), 305-day milk protein percent (305PC), 305-day milk fat yield (305FY) and 305-day milk protein yield (305PY). Effective 305-day data and fresh DNA samples were obtained from 295 healthy cows with gestational age of 1-4. Matrix-assisted laser desorption/ionization-time of flight (MALDI-TOF) was used to perform precise genotyping of these loci, followed by site association and haplotype analysis. Results showed that 36 out of 90 loci were supported to be used as genetic markers. In particular, several novel and effective haplotypes were also presented. Overall, our results verified tens of useful markers and provided a basis for further development of breeding strategies.

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.