Reduced Plasma Levels of 25-Hydroxycholesterol and Increased Cerebrospinal Fluid Levels of Bile Acid Precursors in Multiple Sclerosis Patients

Bile acid metabolism in multiple sclerosis is perturbed and associated with the risk of confirmed disability worsening

BACKGROUND

Bile acids (BAs) have emerged as important mediators in neuroinflammation and neurodegeneration, important features of multiple sclerosis (MS). This study aimed to examine serum BA levels in newly diagnosed people with MS (pwMS) and explore their association with disability worsening.

METHODS

The study included 907 pwMS and 907 matched controls from the Swedish population-based EIMS cohort, with clinical follow-up data from the Swedish MS Registry. Serum BA levels were analyzed using liquid chromatography-high-resolution mass spectrometry. Differential expression analysis was used to study differences in BAs between pwMS and controls. Cox proportional-hazard models were used to assess associations between BA concentrations and confirmed disability worsening (CDW) and the risk of reaching EDSS milestones 4.0 and 6.0.

RESULTS

PwMS had lower concentrations of the primary conjugated BA, glycochenodeoxycholic acid (GCDCA, log2 FC - 0.29, p = 0.009) compared to controls. In relapsing-remitting MS compared to controls, lower concentrations of primary conjugated BAs (log2 FC - 0.30, p = 8.40E - 5), secondary conjugated BAs (log2 FC - 0.18, p = 0.007), and total BAs (log2 FC - 0.22, p = 2.99E - 4) were found. Sex-specific differences were also found, with male pwMS showing more substantial BA alterations. Elevated total BA levels were associated with increased risk for CDW (HR 1.22, 95% CI 1.08-1.39), driven mainly by primary conjugated (HR 1.19, 95% CI 1.06-1.33) and secondary conjugated BAs (HR 1.21, 95% CI 1.08-1.39).

CONCLUSIONS

This study identified alterations in serum BA profiles in pwMS compared to controls, with strong associations between conjugated BAs and the risk of disability worsening. These findings underscore the potential role of BAs in MS pathogenesis and disability worsening, suggesting they may be promising targets for future therapeutic interventions. Further research is warranted to clarify the underlying mechanisms of these associations.

A panel of altered blood oxysterols in patients with mild cognitive impairment: A novel combined diagnostic marker

Perturbed cholesterol metabolism may play an important role in the development of dementia and its preclinical stage, mild cognitive impairment (MCI). Oxysterols, the metabolites generated during cholesterol oxidation, also appear to be risk factors for MCI. Therefore, we aimed to investigate if the metabolic profile of blood oxysterols could be used to characterize MCI risk. This cross-sectional study incorporated 501 participants-253 patients with MCI and 248 cognitively normal controls. Serum levels of 22 free oxysterols were measured, and a set of 27 oxysterol-related gene polymorphisms was genotyped. Five [27-hydroxycholesterol (27-OHC), 27-OHC periphery-derived metabolite 3β-hydroxy-5-cholestenoic acid (27-CA) and brain-derived metabolite 7α-hydroxy-3-oxo-4-cholestenoic acid (7-HOCA), 4β-hydroxycholesterol (4β-OHC); 4α-hydroxycholesterol (4α-OHC)] of the twenty-two oxysterols detected in serum significantly differed between the patients with MCI and controls, greatly distinguishing patients with MCI from control individuals (AUC=0.834, 95 % CI: 0.804-0.866). Association analyses demonstrated significant correlations between these candidate oxysterol biomarkers with younger age, higher blood lipids, worse cognitive performance, and higher monounsaturated fatty acid intake. This panel of serum free oxysterols as candidate serum oxysterol biomarkers for MCI highlighted the essential role of 27-OHC in the pathogenesis of early dementia prevention. (The study registered in the Chinese Clinical Trial Registry as ChiCTR-OOC-17011882).

Differential expression and modulation of EBI2 and 7α,25-OHC synthesizing (CH25H, CYP7B1) and degrading (HSD3B7) enzymes in mouse and human brain vascular cells

The endogenous ligand for the EBI2 receptor, oxysterol 7α,25OHC, crucial for immune responses, is finely regulated by CH25H, CYP7B1 and HSD3B7 enzymes. Lymphoid stromal cells and follicular dendritic cells within T cell follicles maintain a gradient of 7α,25OHC, with stromal cells increasing and dendritic cells decreasing its concentration. This gradient is pivotal for proper B cell positioning in lymphoid tissue. In the animal model of multiple sclerosis, the experimental autoimmune encephalomyelitis, the levels of 7α,25OHC rapidly increase in the central nervous system driving the migration of EBI2 expressing immune cells through the blood-brain barrier (BBB). To explore if blood vessel cells in the brain express these enzymes, we examined normal mouse brain microvessels and studied changes in their expression during inflammation. Ebi2 was abundantly expressed in endothelial cells, pericytes/smooth muscle cells, and astrocytic endfeet. Ch25h, Cyp7b1, and Hsd3b7 were variably detected in each cell type, suggesting their active involvement in oxysterol 7α,25OHC synthesis and gradient maintenance under normal conditions. Significant species-specific differences emerged in EBI2 and the enzyme levels between mouse and human BBB-forming cells. Under acute inflammatory conditions, Ebi2 and synthesizing enzyme modulation occurred in the brain, with the magnitude and direction of change based on the enzyme. Lastly, in an in vitro astrocyte migration model, CYP7B1 inhibitor clotrimazole, as well as EBI2 antagonist, NIBR189, inhibited lipopolysaccharide-induced cell migration indicating the involvement of EBI2 and its ligand in brain cell migration under inflammatory conditions.

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.

25-Hydroxycholesterol attenuates tumor necrosis factor alpha-induced blood-brain barrier breakdown in vitro

Intracellular cholesterol metabolism is regulated by the SREBP-2 and LXR signaling pathways. The effects of inflammation on these molecular mechanisms remain poorly studied, especially at the blood-brain barrier (BBB) level. Tumor necrosis factor α (TNFα) is a proinflammatory cytokine associated with BBB dysfunction. Therefore, the aim of our study was to investigate the effects of TNFα on BBB cholesterol metabolism, focusing on its underlying signaling pathways. Using a human in vitro BBB model composed of human brain-like endothelial cells (hBLECs) and brain pericytes (HBPs), we observed that TNFα increases BBB permeability by degrading the tight junction protein CLAUDIN-5 and activating stress signaling pathways in both cell types. TNFα also promotes cholesterol release and decreases cholesterol accumulation and APOE secretion. In hBLECs, the expression of SREBP-2 targets (LDLR and HMGCR) is increased, while ABCA1 expression is decreased. In HBPs, only LDLR and ABCA1 expression is increased. TNFα treatment also induces 25-hydroxycholesterol (25-HC) production, a cholesterol metabolite involved in the immune response and intracellular cholesterol metabolism. 25-HC pretreatment attenuates TNFα-induced BBB leakage and partially alleviates the effects of TNFα on ABCA1, LDLR, and HMGCR expression. Overall, our results suggest that TNFα favors cholesterol efflux via an LXR/ABCA1-independent mechanism at the BBB, while it activates the SREBP-2 pathway. Treatment with 25-HC partially reversed the effect of TNFα on the LXR/SREBP-2 pathways. Our study provides novel perspectives for better understanding cerebrovascular signaling events linked to BBB dysfunction and cholesterol metabolism in neuroinflammatory diseases.

Serum Low-Density Lipoprotein Cholesterol Levels are Associated with Relapse in Neuromyelitis Optica Spectrum Disorder

Background

The relationship between serum low-density lipoprotein cholesterol (LDL-C) and the risk of relapse in neuromyelitis optica spectrum disorder (NMOSD) remains uncertain. We aimed to examine the association between serum LDL-C level and relapse in NMOSD patients.

Methods

We conducted an analysis of the prospective observational NMOSD cohort study with consecutive 184 hospitalized NMOSD patients from department of neurology. Blood samples were collected to measure LDL-C level upon admission. Primary and relapse were evaluated during hospitalization. The relationship between serum LDL-C level and relapse were analyzed by linear curve fitting analyses. Crude and adjusted odds ratios (OR) of LDL-C for relapse with 95% confidence intervals were analyzed using multiple logistic regression models. ROC curve analysis was used to identify the target lipid-lowering value of LDL-C and the probability of relapse was evaluated by the Kaplan-Meier Plot.

Results

Over a mean disease course of 100±87 days, 59.24% (n=109) participants developed relapse with higher LDL-C than the primary group (n=75) (p<0.001). Adjusted smoothed plots suggested that there were linear relationships between serum LDL-C level and relapse (p< 0.001). The OR (95% CI) between serum LDL-C level and relapse were 2.67 (1.76-4.04, p<0.001), and 2.38 (1.48-3.83, p<0.001) respectively in NMOSD patients before and after adjusting for potential confounders. The target LDL-C lowering values were 2.795 mmol/L with potential benefits to prevent relapse in NMOSD.

Conclusion

In this sample of NMOSD patients, we found that the elevated serum LDL-C was independently and positively associated with the relapse, and serum LDL-C should be well-controlled to prevent the relapse of NMOSD.

Exploring the role of a novel postbiotic bile acid: Interplay with gut microbiota, modulation of the farnesoid X receptor, and prospects for clinical translation

The gut microbiota, mainly resides in the colon, possesses a remarkable ability to metabolize different substrates to create bioactive substances, including short-chain fatty acids, indole-3-propionic acid, and secondary bile acids. In the liver, bile acids are synthesized from cholesterol and then undergo modification by the gut microbiota. Beyond those reclaimed by the enterohepatic circulation, small percentage of bile acids escaped reabsorption, entering the systemic circulation to bind to several receptors, such as farnesoid X receptor (FXR), thereby exert their biological effects. Gut microbiota interplays with bile acids by affecting their synthesis and determining the production of secondary bile acids. Reciprocally, bile acids shape out the structure of gut microbiota. The interplay of bile acids and FXR is involved in the development of multisystemic conditions, encompassing metabolic diseases, hepatobiliary diseases, immune associated disorders. In the review, we aim to provide a thorough review of the intricate crosstalk between the gut microbiota and bile acids, the physiological roles of bile acids and FXR in mammals' health and disease, and the clinical translational considerations of gut microbiota-bile acids-FXR in the treatment of the diseases.

Serum lipids and cognitive outcomes in multiple sclerosis; a systematic review and meta-analysis

BACKGROUND

Cognitive impairment is highly prevalent in multiple sclerosis (MS) with poorly understood underlying mechanisms. Lipids are considered to be associated with MS progression through the inflammatory and oxidative stress pathways, brain atrophy, cellular signaling, and tissue physiology. In addition, serum lipids are proposed as a modifiable factor affecting the neuropsychiatric condition; therefore, this study aims to assess the association between serum lipid levels and cognitive outcomes in MS.

METHODS

This study was carried out following the PRISMA 2020 statement. A systematic search was conducted in PubMed, Scopus, Web of Science, and Embase in March 2023, and the Joanna Briggs Institute (JBI)'s critical appraisal tools were utilized for risk of bias (RoB) assessments in the included studies. The quantitative synthesis was performed with the comprehensive meta-analysis (CMA3) software.

RESULTS

Out of 508 screened records, 7 studies were eventually found to meet our inclusion criteria. In two studies, the course of MS in the sample of the study was only Relapsing-Remitting MS (RRMS), whereas the other five studies' sample was a combination of different phenotypes. Studies utilized different scales such as Minimal Assessment of Cognitive Function in MS (MACFIMS), Brief International Cognitive Assessment for MS (BICAMS), Montreal Cognitive Assessment (MoCA), Brief Repeatable Battery of Neuropsychological Tests (BRB-N) for cognitive evaluations. Dealing with possible confounders such as age, disease duration and level of disability was the most common possible source of bias in the included studies. One study revealed an inverse relationship between serum levels of apolipoproteins (including ApoA-I, ApoB, and ApoB/ApoA-I) and Symbol Digit Modalities Test (SDMT) scores. Also, a correlation between 24S-hydroxycholesterol (24OHC) serum concentrations and SDMT score was reported in one study. The association between serum total cholesterol (TC) and low-density lipoprotein cholesterol (LDL) and different aspects of cognitive function was reported in the studies; however, serum levels of high-density lipoprotein cholesterol (HDL) were not found to be associated. The quantitative synthesis revealed a significant correlation between TC and the MoCA scores (r =-0.238; 95 %CI: -0.366 to -0.100; p-value = 0.001); however, the correlation between TG levels and MoCA were not statistically significant (r:-0.070; 95 %CI: -0.209 to 0.072; p-value: 0.334). In addition, the mata-analyses were not associated with significant findings regarding the correlation between lipid profiles (including HDL, LDL, TG, and TC) and other cognitive assessment scales including SDMT, Brief Visuospatial Memory Test (BVMT), and California Verbal Learning Test (CVLT) (p-values>0.05).

DISCUSSION

Available evidence suggested a link between TC and LDL with cognitive outcomes of MS patients which was not evident in our quantitative synthesis. The limited number of studies, high RoB, different cognitive assessment scales and reporting methods, and the cross-sectional design of the included studies, were the main limitations that alleviate the clinical significance of the findings of this study and suggested further investigations on this topic.

FUNDING AND REGISTRATION

The research protocol was approved and supported by the Student Research Committee, Tabriz University of Medical Sciences (grant number: 71,909). This study is registered in the international prospective register of systematic reviews (PROSPERO ID: CRD42023441625).

Gut-Brain Interactions and Their Impact on Astrocytes in the Context of Multiple Sclerosis and Beyond

Multiple Sclerosis (MS) is a chronic autoimmune inflammatory disease of the central nervous system (CNS) that leads to physical and cognitive impairment in young adults. The increasing prevalence of MS underscores the critical need for innovative therapeutic approaches. Recent advances in neuroimmunology have highlighted the significant role of the gut microbiome in MS pathology, unveiling distinct alterations in patients' gut microbiota. Dysbiosis not only impacts gut-intrinsic processes but also influences the production of bacterial metabolites and hormones, which can regulate processes in remote tissues, such as the CNS. Central to this paradigm is the gut-brain axis, a bidirectional communication network linking the gastrointestinal tract to the brain and spinal cord. Via specific routes, bacterial metabolites and hormones can influence CNS-resident cells and processes both directly and indirectly. Exploiting this axis, novel therapeutic interventions, including pro- and prebiotic treatments, have emerged as promising avenues with the aim of mitigating the severity of MS. This review delves into the complex interplay between the gut microbiome and the brain in the context of MS, summarizing current knowledge on the key signals of cross-organ crosstalk, routes of communication, and potential therapeutic relevance of the gut microbiome. Moreover, this review places particular emphasis on elucidating the influence of these interactions on astrocyte functions within the CNS, offering insights into their role in MS pathophysiology and potential therapeutic interventions.

Mass Spectrometry Imaging of Cholesterol and Oxysterols

Mass spectrometry imaging (MSI) is a new technique in the toolbox of the analytical biochemist. It allows the generation of a compound-specific image from a tissue slice where a measure of compound abundance is given pixel by pixel, usually displayed on a color scale. As mass spectra are recorded at each pixel, the data can be interrogated to generate images of multiple different compounds all in the same experiment. Mass spectrometry (MS) requires the ionization of analytes, but cholesterol and other neutral sterols tend to be poorly ionized by the techniques employed in most MSI experiments, so despite their high abundance in mammalian tissues, cholesterol is poorly represented in the MSI literature. In this chapter, we discuss some of the MSI studies where cholesterol has been imaged and introduce newer methods for its analysis by MSI. Disturbed cholesterol metabolism is linked to many disorders, and the potential of MSI to study cholesterol, its precursors, and its metabolites in animal models and from human biopsies will be discussed.

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.

Filarial DAF-12 sense the host serum to resume iL3 development during infection

Nematode parasites enter their definitive host at the developmentally arrested infectious larval stage (iL3), and the ligand-dependent nuclear receptor DAF-12 contributes to trigger their development to adulthood. Here, we characterized DAF-12 from the filarial nematodes Brugia malayi and Dirofilaria immitis and compared them with DAF-12 from the non-filarial nematodes Haemonchus contortus and Caenorhabditis elegans. Interestingly, Dim and BmaDAF-12 exhibit high sequence identity and share a striking higher sensitivity than Hco and CelDAF-12 to the natural ligands Δ4- and Δ7-dafachronic acids (DA). Moreover, sera from different mammalian species activated specifically Dim and BmaDAF-12 while the hormone-depleted sera failed to activate the filarial DAF-12. Accordingly, hormone-depleted serum delayed the commencement of development of D. immitis iL3 in vitro. Consistent with these observations, we show that spiking mouse charcoal stripped-serum with Δ4-DA at the concentration measured in normal mouse serum restores its capacity to activate DimDAF-12. This indicates that DA present in mammalian serum participate in filarial DAF-12 activation. Finally, analysis of publicly available RNA sequencing data from B. malayi showed that, at the time of infection, putative gene homologs of the DA synthesis pathways are coincidently downregulated. Altogether, our data suggest that filarial DAF-12 have evolved to specifically sense and survive in a host environment, which provides favorable conditions to quickly resume larval development. This work sheds new light on the regulation of filarial nematodes development while entering their definitive mammalian host and may open the route to novel therapies to treat filarial infections.

Liver's influence on the brain through the action of bile acids

The liver partakes as a sensor and effector of peripheral metabolic changes and a regulator of systemic blood and nutrient circulation. As such, abnormalities arising from liver dysfunction can influence the brain in multiple ways, owing to direct and indirect bilateral communication between the liver and the brain. Interestingly, altered bile acid composition resulting from perturbed liver cholesterol metabolism influences systemic inflammatory responses, blood-brain barrier permeability, and neuron synaptic functions. Furthermore, bile acids produced by specific bacterial species may provide a causal link between dysregulated gut flora and neurodegenerative disease pathology through the gut-brain axis. This review will cover the role of bile acids-an often-overlooked category of active metabolites-in the development of neurological disorders associated with neurodegeneration. Further studies into bile acid signaling in the brain may provide insights into novel treatments against neurological disorders.

Bile Acids Induce Neurite Outgrowth in Nsc-34 Cells via TGR5 and a Distinct Transcriptional Profile

Increasing evidence supports a neuroprotective role for bile acids in major neurodegenerative disorders. We studied major human bile acids as signaling molecules for their two cellular receptors, farnesoid X receptor (FXR or NR1H4) and G protein-coupled bile acid receptor 1 (GPBAR1 or TGR5), as potential neurotrophic agents. Using quantitative image analysis, we found that 20 μM deoxycholic acid (DCA) could induce neurite outgrowth in NSC-34 cells that was comparable to the neurotrophic effects of the culture control 1 μM retinoic acid (RA), with lesser effects observed for chenodexoycholic acid (CDCA) at 20 μM, and similar though less robust neurite outgrowth in SH-SY5Y cells. Using chemical agonists and antagonists of FXR, LXR, and TGR5, we found that TGR5 agonism was comparable to DCA stimulation and stronger than RA, and that neither FXR nor liver X receptor (LXR) inhibition could block bile acid-induced neurite growth. RNA sequencing identified a core set of genes whose expression was regulated by DCA, CDCA, and RA. Our data suggest that bile acid signaling through TGR5 may be a targetable pathway to stimulate neurite outgrowth.

Vitamin D in Neurological Diseases

Vitamin D may have multiple effects on the nervous system and its deficiency can represent a possible risk factor for the development of many neurological diseases. Recent studies are also trying to clarify the different effects of vitamin D supplementation over the course of progressive neurological diseases. In this narrative review, we summarise vitamin D chemistry, metabolism, mechanisms of action, and the recommended daily intake. The role of vitamin D on gene transcription and the immune response is also reviewed. Finally, we discuss the scientific evidence that links low 25-hydroxyvitamin D concentrations to the onset and progression of severe neurological diseases, such as multiple sclerosis, Parkinson's disease, Alzheimer's disease, migraine, diabetic neuropathy and amyotrophic lateral sclerosis. Completed and ongoing clinical trials on vitamin D supplementation in neurological diseases are listed.

Bile acids and neurological disease

This review will focus on how bile acids are being used in clinical trials to treat neurological diseases due to their central involvement with the gut-liver-brain axis and their physiological and pathophysiological roles in both normal brain function and multiple neurological diseases. The synthesis of primary and secondary bile acids species and how the regulation of the bile acid pool may differ between the gut and brain is discussed. The expression of several bile acid receptors in brain and their currently known functions along with the tools available to manipulate them pharmacologically are examined, together with discussion of the interaction of bile acids with the gut microbiome and their lesser-known effects upon brain glucose and lipid metabolism. How dysregulation of the gut microbiome, aging and sex differences may lead to disruption of bile acid signalling and possible causal roles in a number of neurological disorders are also considered. Finally, we discuss how pharmacological treatments targeting bile acid receptors are currently being tested in an array of clinical trials for several different neurodegenerative diseases.

Expression and mechanisms of interferon-stimulated genes in viral infection of the central nervous system (CNS) and neurological diseases

Interferons (IFNs) bind to cell surface receptors and activate the expression of interferon-stimulated genes (ISGs) through intracellular signaling cascades. ISGs and their expression products have various biological functions, such as antiviral and immunomodulatory effects, and are essential effector molecules for IFN function. ISGs limit the invasion and replication of the virus in a cell-specific and region-specific manner in the central nervous system (CNS). In addition to participating in natural immunity against viral infections, studies have shown that ISGs are essential in the pathogenesis of CNS disorders such as neuroinflammation and neurodegenerative diseases. The aim of this review is to present a macroscopic overview of the characteristics of ISGs that restrict viral neural invasion and the expression of the ISGs underlying viral infection of CNS cells. Furthermore, we elucidate the characteristics of ISGs expression in neurological inflammation, neuropsychiatric disorders such as depression as well as neurodegenerative disorders, including Alzheimer's disease (AD), Parkinson's disease (PD), and amyotrophic lateral sclerosis (ALS). Finally, we summarize several ISGs (ISG15, IFIT2, IFITM3) that have been studied more in recent years for their antiviral infection in the CNS and their research progress in neurological diseases.

How Microbiota-Derived Metabolites Link the Gut to the Brain during Neuroinflammation

Microbiota-derived metabolites are important molecules connecting the gut to the brain. Over the last decade, several studies have highlighted the importance of gut-derived metabolites in the development of multiple sclerosis (MS). Indeed, microbiota-derived metabolites modulate the immune system and affect demyelination. Here, we discuss the current knowledge about microbiota-derived metabolites implications in MS and in different mouse models of neuroinflammation. We focus on the main families of microbial metabolites that play a role during neuroinflammation. A better understanding of the role of those metabolites may lead to new therapeutical avenues to treat neuroinflammatory diseases targeting the gut–brain axis.

Thinking outside the box: non-canonical targets in multiple sclerosis

Multiple sclerosis (MS) is an immune-mediated disease of the central nervous system that causes demyelination, axonal degeneration and astrogliosis, resulting in progressive neurological disability. Fuelled by an evolving understanding of MS immunopathogenesis, the range of available immunotherapies for clinical use has expanded over the past two decades. However, MS remains an incurable disease and even targeted immunotherapies often fail to control insidious disease progression, indicating the need for new and exceptional therapeutic options beyond the established immunological landscape. In this Review, we highlight such non-canonical targets in preclinical MS research with a focus on five highly promising areas: oligodendrocytes; the blood-brain barrier; metabolites and cellular metabolism; the coagulation system; and tolerance induction. Recent findings in these areas may guide the field towards novel targets for future therapeutic approaches in MS.

Selected plasma oxysterols as a potential multi-marker biosignature panel for Behçet's Disease

Clinical, genetic, and medical evidence has shown the inflammatory vasculitis aspect of Behçet's Disease (BD). Whereas oxysterols are vital factors in inflammation and oxidative stress, it is still unknown whether they are involved in the pathophysiology of BD. The current study aims to explore the profile of oxysterols in plasma of BD patients. Thirty patients diagnosed with BD and forty healthy controls matched for age and gender were included. Results showed that the cholestane-3β,5α,6β-triol, 27-hydroxycholesterol (27-OHC) and cholestanol levels were higher in BD than controls. In addition, plasma levels of 7-ketocholesterol (7-KC) and 25-hydroxycholesterol (25-OHC) were lower in BD patient. However, levels of 24S-hydroxycholesterol (24-OHC) did not significantly differ. For BD patients, the plasma 7-KC level was negatively correlated with the BD activity index (BDAI) while 27-OHC was positively correlated with high-sensitivity C-reactive protein (hs-CRP) in patients with active course of the disease. According to ROC analysis, a remarkable increase in the area under the curve (AUC) with a higher sensitivity (Se) and specificity (Sp) for 7-KC, 25-OHC and 27-OHC combined markers was observed. The present study indicated that the identification of the predictive value of these three-selected biomarkers related to oxidative stress and inflammation in patients should lead to a better identification of the etiological mechanism of BD.

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.

New Function of Cholesterol Oxidation Products Involved in Osteoporosis Pathogenesis

Osteoporosis (OP) is a systemic bone disease characterized by decreased bone strength, microarchitectural changes in bone tissues, and increased risk of fracture. Its occurrence is closely related to various factors such as aging, genetic factors, living habits, and nutritional deficiencies as well as the disturbance of bone homeostasis. The dysregulation of bone metabolism is regarded as one of the key influencing factors causing OP. Cholesterol oxidation products (COPs) are important compounds in the maintenance of bone metabolic homeostasis by participating in several important biological processes such as the differentiation of mesenchymal stem cells, bone formation in osteoblasts, and bone resorption in osteoclasts. The effects of specific COPs on mesenchymal stem cells are mainly manifested by promoting osteoblast genesis and inhibiting adipocyte genesis. This review aims to elucidate the biological roles of COPs in OP development, starting from the molecular mechanisms of OP, pointing out opportunities and challenges in current research, and providing new ideas and perspectives for further studies of OP pathogenesis.

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.

Site of Cholesterol Oxidation Impacts Its Localization and Domain Formation in the Neuronal Plasma Membrane

Cholesterol is integral to the structure of mammalian cell membranes. Oxidation of cholesterol alters how it behaves in the membrane and influences the membrane biophysical properties. Elevated levels of oxidized cholesterol are associated with neurodegenerative diseases such as Alzheimer's disease, Parkinson's disease, multiple sclerosis, and Huntington's disease. Previous work has investigated the impact of oxidized cholesterol in the context of simple model membrane systems. However, there is a growing body of literature that shows that complex membranes possessing physiological phospholipid distributions have different properties from those of binary or trinary model membranes. In the current work, the impact of oxidized cholesterol on the biophysical properties of a complex neuronal plasma membrane is investigated using coarse-grained Martini molecular dynamics simulations. Comparison of the native neuronal membrane to neuronal membranes containing 10% tail-oxidized or 10% head-oxidized cholesterol shows that the site of oxidization changes the behavior of the oxidized cholesterol in the membrane. Furthermore, species-specific domain formation is observed between each oxidized cholesterol and minor lipid classes. Although both tail-oxidized and head-oxidized cholesterols modulate the biophysical properties of the membrane, smaller changes are observed in the complex neuronal membrane than seen in the previous work on simple binary or trinary model membranes. This work highlights the presence of compensatory effects of lipid diversity in the complex neuronal membrane. Overall, this study improves our molecular-level understanding of the effects of oxidized cholesterol on the properties of neuronal tissue and emphasizes the importance of studying membranes with realistic lipid compositions.

The Cerebrospinal Fluid Profile of Cholesterol Metabolites in Parkinson's Disease and Their Association With Disease State and Clinical Features

Disordered cholesterol metabolism is linked to neurodegeneration. In this study we investigated the profile of cholesterol metabolites found in the cerebrospinal fluid (CSF) of Parkinson’s disease (PD) patients. When adjustments were made for confounding variables of age and sex, 7α,(25R)26-dihydroxycholesterol and a second oxysterol 7α,x,y-trihydroxycholest-4-en-3-one (7α,x,y-triHCO), whose exact structure is unknown, were found to be significantly elevated in PD CSF. The likely location of the additional hydroxy groups on the second oxysterol are on the sterol side-chain. We found that CSF 7α-hydroxycholesterol levels correlated positively with depression in PD patients, while two presumptively identified cholestenoic acids correlated negatively with depression.

Myeloid-Derived Suppressive Cells Deficient in Liver X Receptor α Protected From Autoimmune Hepatitis

Myeloid-derived suppressor cells (MDSCs) emerge as a promising candidate for the immunotherapy of autoimmune hepatitis (AIH). However, targets for modulating MDSC in AIH are still being searched. Liver X receptors (LXRs) are important nuclear receptors linking lipid metabolism and immune responses. Despite the extensive studies of LXR in myeloid compartment, its role in MDSCs is currently less understood. Herein, expression of LXRα was found to be upregulated in AIH patients and colocalized with hepatic MDSCs. In ConA-induced hepatitis, deletion of LXRα led to increased expansion of MDSCs in the liver and alleviated the hepatic injury. MDSCs in LXRα-/- mice exhibited enhanced proliferation and survival comparing with WT mice. T-cell proliferation assay and adoptive cell transfer experiment validated the potent immunoregulatory role of MDSCs in vitro and in vivo. Mechanistically, MDSCs from LXRα-/- mice possessed significantly lower expression of interferon regulatory factor 8 (IRF-8), a key negative regulator of MDSC differentiation. Transcriptional activation of IRF-8 by LXRα was further demonstrated.

Conclusion

We reported that abrogation of LXRα facilitated the expansion of MDSCs via downregulating IRF-8, and thereby ameliorated hepatic immune injury profoundly. Our work highlights the therapeutic potential of targeting LXRα in AIH.

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 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.

Deep mining of oxysterols and cholestenoic acids in human plasma and cerebrospinal fluid: Quantification using isotope dilution mass spectrometry

Both plasma and cerebrospinal fluid (CSF) are rich in cholesterol and its metabolites. Here we describe in detail a methodology for the identification and quantification of multiple sterols including oxysterols and sterol-acids found in these fluids. The method is translatable to any laboratory with access to liquid chromatography – tandem mass spectrometry. The method exploits isotope-dilution mass spectrometry for absolute quantification of target metabolites. The method is applicable for semi-quantification of other sterols for which isotope labelled surrogates are not available and approximate quantification of partially identified sterols. Values are reported for non-esterified sterols in the absence of saponification and total sterols following saponification. In this way absolute quantification data is reported for 17 sterols in the NIST SRM 1950 plasma along with semi-quantitative data for 8 additional sterols and approximate quantification for one further sterol. In a pooled (CSF) sample used for internal quality control, absolute quantification was performed on 10 sterols, semi-quantification on 9 sterols and approximate quantification on a further three partially identified sterols. The value of the method is illustrated by confirming the sterol phenotype of a patient suffering from ACOX2 deficiency, a rare disorder of bile acid biosynthesis, and in a plasma sample from a patient suffering from cerebrotendinous xanthomatosis, where cholesterol 27-hydroxylase is deficient.

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Absolute quantification of oxysterols and cholestenoic acids.

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Methodology applicable to plasma and cerebrospinal fluid.

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Data generated for non-esterified and total sterols.

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Diastereoisomers at C-24 and C-25 separated and quantified.

Standardizing and increasing the utility of lipidomics: a look to the next decade

Introduction: We present our views on the current application of mass spectrometry (MS) based lipidomics and how lipidomics can develop in the next decade to be most practical use to society. That is not to say that lipidomics has not already been of value. In-fact, in its earlier guise as metabolite profiling most of the pathways of steroid biosynthesis were uncovered and via focused lipidomics many inborn errors of metabolism are routinely clinically identified. However, can lipidomics be extended to improve biochemical understanding of, and to diagnose, the most prevalent diseases of the 21^st century? Areas covered: We will highlight the concept of 'level of identification' and the equally crucial topic of 'quantification'. Only by using a standardized language for these terms can lipidomics be translated to fields beyond academia. We will remind the lipid scientist of the value of chemical derivatization, a concept exploited since the dawn of lipid biochemistry. Expert opinion: Only by agreement of the concepts of identification and quantification and their incorporation in lipidomics reporting can lipidomics maximize its value.

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.

Is There a Role for Vitamin D in Amyotrophic Lateral Sclerosis? A Systematic Review and Meta-Analysis

Background: Amyotrophic lateral sclerosis (ALS) is a neurodegenerative condition characterized by the progressive loss of motor neurons. Patients usually die 3–5 years after diagnosis from respiratory failure. Several studies investigated the role of vitamin D as a biomarker or a therapeutic option for ALS patients. To clarify the scientific evidence, we performed a systematic review and different meta-analyses regarding the potential role of vitamin D in ALS.

Methods: We performed a systematic review of clinical trials, cohorts, and case–control studies retrieved from PubMed, EMBASE, and Cochrane databases reporting vitamin D levels as a putative biomarker for ALS diagnosis or prognosis or the effect of vitamin D supplementation in ALS patients. Whenever possible, data were pooled using a random-effects model, with an assessment of heterogeneity.

Results: Out of 2,996 articles retrieved, we finally included 13 research articles, 12 observational studies (50% prospective), and 1 clinical trial. We found that ALS patients had slightly lower levels of vitamin D than controls (mean difference −6 ng/ml, 95% CI [−10.8; −1.3]), but important confounding factors were not considered in the studies analyzed. We found no relationship between vitamin D levels and ALS functional rate score—revised (ALSFRS-R), with highly heterogeneous results. Discordant results were reported in three studies regarding survival. Finally, five studies reported the effects of vitamin D supplementation with discordant results. Two of them showed a small improvement, whereas two others showed a deleterious effect on ALSFRS-R. One very small clinical trial with important methodological limitations showed some improvement in ALSFRS-R with high doses of vitamin D compared with normal doses.

Conclusions: Our review did not find evidence to support the role of vitamin D on ALS diagnosis, prognosis, or treatment. Most studies had important limitations, mostly regarding the risk of bias for not considering confounding factors. Vitamin D supplementation should be offered to ALS patients to avoid other health issues related to vitamin D deficiency, but there is not enough evidence to support the use of vitamin D as a therapy for ALS.

Bile Acid Signaling in Neurodegenerative and Neurological Disorders

Bile acids are commonly known as digestive agents for lipids. The mechanisms of bile acids in the gastrointestinal track during normal physiological conditions as well as hepatic and cholestatic diseases have been well studied. Bile acids additionally serve as ligands for signaling molecules such as nuclear receptor Farnesoid X receptor and membrane-bound receptors, Takeda G-protein-coupled bile acid receptor and sphingosine-1-phosphate receptor 2. Recent studies have shown that bile acid signaling may also have a prevalent role in the central nervous system. Some bile acids, such as tauroursodeoxycholic acid and ursodeoxycholic acid, have shown neuroprotective potential in experimental animal models and clinical studies of many neurological conditions. Alterations in bile acid metabolism have been discovered as potential biomarkers for prognosis tools as well as the expression of various bile acid receptors in multiple neurological ailments. This review explores the findings of recent studies highlighting bile acid-mediated therapies and bile acid-mediated signaling and the roles they play in neurodegenerative and neurological diseases.

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.

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.

Regulation of Brain Cholesterol: What Role Do Liver X Receptors Play in Neurodegenerative Diseases?

Liver X Receptors (LXR) alpha and beta are two members of nuclear receptor superfamily documented as endogenous cholesterol sensors. Following conversion of cholesterol in oxysterol, both LXR isoforms detect intracellular concentrations and act as transcription factors to promote expression of target genes. Among their numerous physiological roles, they act as central cholesterol-lowering factors. In the central nervous system (CNS), cholesterol has been shown to be an essential determinant of brain function, particularly as a major constituent of myelin and membranes. In the brain, LXRs act as cholesterol central regulators, and, beyond this metabolic function, LXRs have additional roles such as providing neuroprotective effects and lowering neuroinflammation. In many neurodegenerative disorders, including amyotrophic lateral sclerosis (ALS), Alzheimer's disease (AD), and multiple sclerosis (MS), dysregulations of cholesterol and oxysterol have been reported. In this paper, we propose to focus on recent advances in the knowledge of the LXRs roles on brain cholesterol and oxysterol homeostasis, neuroinflammation, neuroprotection, and their putative involvement in neurodegenerative disorders. We will discuss their potential use as candidates for both molecular diagnosis and as promising pharmacological targets in the treatment of ALS, AD, or MS patients.

Oxysterol research: a brief review

In the present study, we discuss the recent developments in oxysterol research. Exciting results have been reported relating to the involvement of oxysterols in the fields of neurodegenerative disease, especially in Huntington's disease, Parkinson's disease and Alzheimer's disease; in signalling and development, in particular, in relation to Hedgehog signalling; and in cancer, with a special focus on (25R)26-hydroxycholesterol. Methods for the measurement of oxysterols, essential for understanding their mechanism of action in vivo, and valuable for diagnosing rare diseases of cholesterol biosynthesis and metabolism are briefly considered.

EBI2 - Sensor for dihydroxycholesterol gradients in neuroinflammation

Dihydroxycholesterols such as 7α,25-dihydroxysterols (7α,25-OHC) and 7α,27-OHC are generated from cholesterol by the enzymes CH25H, CYP7B1 and CYP27A1 in steady state but also in the context of inflammation. The G-protein coupled receptor (GPCR) Epstein-Barr virus-induced gene 2 (EBI2), also known as GPR183, senses these oxysterols and induces chemotactic migration of immune cells towards higher concentrations of these ligands. We recently showed that these ligands are upregulated in the CNS in experimental autoimmune encephalomyelitis (EAE), an animal model for multiple sclerosis and that EBI2 enhanced early infiltration of encephalitogenic T cells into the CNS. In this short-review we discuss the role of dihydroxysterol-sensing by immune cells in neuroinflammation.

Oxysterol levels and metabolism in the course of neuroinflammation: insights from in vitro and in vivo models

Background

Oxysterols are cholesterol derivatives that have been suggested to play a role in inflammatory diseases such as obesity, atherosclerosis, or neuroinflammatory diseases. However, the effect of neuroinflammation on oxysterol levels has only been partially studied so far.

Methods

We used an HPLC-MS method to quantify over ten oxysterols both in in vitro and in vivo models of neuroinflammation. In the same models, we used RT-qPCR to analyze the expression of the enzymes responsible for oxysterol metabolism. Using the BV2 microglial cell line, we explored the effect of lipopolysaccharide (LPS)-induced (M1-type) and IL-4-induced (M2-type) cell activation on oxysterol levels. We also used LPS-activated co-cultures of mouse primary microglia and astrocytes. In vivo, we induced a neuroinflammation by administering LPS to mice. Finally, we used a mouse model of multiple sclerosis, namely the experimental autoimmune encephalomyelitis (EAE) model, that is characterized by demyelination and neuroinflammation.

Results

In vitro, we found that LPS activation induces profound alterations in oxysterol levels. Interestingly, we could discriminate between control and LPS-activated cells based on the changes in oxysterol levels both in BV2 cells and in the primary co-culture of glial cells. In vivo, the changes in oxysterol levels were less marked than in vitro. However, we found in both models increased levels of the GPR183 agonist 7α,25-dihydroxycholesterol. Furthermore, we studied in vitro the effect of 14 oxysterols on the mRNA expression of inflammatory markers in LPS-activated co-culture of microglia and astrocytes. We found that several oxysterols decreased the LPS-induced expression of pro-inflammatory markers.

Conclusions

These data demonstrate that inflammation profoundly affects oxysterol levels and that oxysterols can modulate glial cell activation. This further supports the interest of a large screening of oxysterol levels when studying the interplay between neuroinflammation and bioactive lipids.

Electronic supplementary material

The online version of this article (10.1186/s12974-018-1114-8) contains supplementary material, which is available to authorized users.

An update on oxysterol biochemistry: New discoveries in lipidomics

Oxysterols are oxidised derivatives of cholesterol or its precursors post lanosterol. They are intermediates in the biosynthesis of bile acids, steroid hormones and 1,25-dihydroxyvitamin D_3. Although often considered as metabolic intermediates there is a growing body of evidence that many oxysterols are bioactive and their absence or excess may be part of the cause of a disease phenotype. Using global lipidomics approaches oxysterols are underrepresented encouraging the development of targeted approaches. In this article, we discuss recent discoveries important in oxysterol biochemistry and some of the targeted lipidomic approaches used to make these discoveries.

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Oxysterols can regulate both the innate and adaptive immune systems.

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Oxysterols can be tumour suppressors and on cometabolites.

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Oxysterols can inhibit or activate the Hh signalling pathway.

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.