Background
Microglia are resident innate immune cells of the CNS and contribute to CNS inflammation and repair through multiple functions including scavenging, phagocytosis, antigen presentation and production of reactive oxygen/nitrogen species, cytokines and neurotropic factors [
1]. Reactive microgliosis, or a state of persistent microglial activation, has been implicated in the pathogenesis of a number of neuroinflammatory and neurodegenerative diseases including multiple sclerosis, Parkinson disease and Alzheimer disease [
2]. The production of excess reactive oxygen and reactive nitrogen species by activated microglia is thought to contribute to neurodegeneration by way of oxidative stress [
3]. Inhibiting microglial activation or function has the potential to ameliorate neuroinflammatory and neurodegenerative disorders [
4,
5]. Defining the signals that control microglial activation, therefore, has important implications for modulating neuroinflammatory and neurodegenerative processes.
The liver X receptor (LXR) is an oxysterol-activated nuclear receptor [
6]. Together with retinoid X receptor (RXR), with which LXR forms an obligate heterodimer, LXR controls gene transcription by modulating the function of nuclear receptor corepressor (NCoR) and nuclear receptor coactivator (NCoA) complexes [
7]. LXR is known to control the expression of genes involved in reverse cholesterol transport such as
Abca1,
Abcg1,
Apoa1,
Apoe and
Cyp7a1 [
8,
9]. In cells of the myeloid lineage, LXR has also been shown to control inflammatory responses by transcriptional repression of a number of genes including
Nos2,
Cox2 and
Il6 [
10]. Thus, LXR is one among a number of biological signal pathways that link lipid metabolism and inflammation [
11]. Previous studies have shown that activation of LXR by oxysterols inhibits proinflammatory responses in cultures of microglia and astrocytes, suggesting that the LXR pathway might serve a compensatory antiinflammatory function in response to oxidative stress [
12,
13]. In addition, previous studies have shown that LXR agonists reduced the severity of experimental allergic encephalomyelitis (EAE), an animal model of neuroinflammation, during its induction phase by an immunomodulatory effect on T helper lymphocyte differentiation [
14,
15].
Several questions remain regarding the role of LXR in CNS inflammation. It is unknown whether or not endogenous activation of LXR in the CNS functions to modulate the course of CNS inflammation. A related question is whether or not targeting LXR confers protection in the setting of already established CNS inflammation, independent of its immunomodulatory effects on peripheral lymphocytes. We examined LXR function and the mechanism of transcriptional repression in cultured microglia as well as the effect of LXR activation during CNS inflammation.
Methods
Reagents
Culture media, fetal calf serum, all media supplements, buffered solutions, Griess reagent kit and RNAi Max were from Life Technologies (Carlsbad, CA). GW3965 and fluorobexarotene were from R & D Systems (Minneapolis, MN). LPS, trichostatin A, C646 and TMB peroxidase substrate were from Sigma-Aldrich (St. Louis, MO).
Primary murine microglial cultures
Timed-pregnant ICR mice were purchased form Harlan (Indianapolis, IN). Primary microglia-enriched cultures were prepared from whole brains of 1- to 2-day-old ICR pups using a previously described protocol [
16]. Briefly, following removal of meninges and blood vessels, brains were mechanically dissociated by trituration then seeded in 150-cm
3 flasks in supplemented DMEM/F12 media containing 10% fetal calf serum (4 to 5 brains per flask). Media were replaced at day 3 and 7 of culture. Microglia were shaken off at days 14 and 21 of culture and re-plated at 1 × 10
5 cells/well in DMEM containing 2% fetal calf serum. Cells were treated 24 h after re-plating.
Real-time reverse transcription-polymerase chain reaction (RT-PCR)
Real-time RT-PCR analyses of
Abca1,
Abcg1,
Apoa1,
Nos2,
Il1b,
Il6,
Lxra,
Lxrb and
Tnf were performed using commercially available primer and probes sets and Taqman RNA-to-C
T 1-Step Kit (Life Technologies, Carlsbad, CA) according to the manufacturer’s protocol. Total RNA was extracted using RNeasy Mini Kit (Qiagen, Valencia, CA) according to the manufacturer’s protocol. Relative quantitation of mRNA was performed using the comparative threshold (delta delta C
T) method [
17] using
Actb as endogenous control.
Cytokine ELISA
Interleukin-1β (IL-1β) and tumor necrosis factor (TNF) in conditioned media were measured using the antibodies and reference standards contained in R & D Systems DuoSet ELISA kits (R & D, Minneapolis, MN) according to the manufacturer’s protocol. Test samples and reference standards were incubated for 2 h in wells that had been coated overnight with 0.8 μg/ml goat anti-mouse TNF or 4.0 μg/ml rat anti-mouse IL-1β capture antibodies in phosphate-buffered saline (PBS) and blocked for 1 h with 300 μl of 1% w/v bovine serum albumin (BSA) in PBS. Captured cytokines were detected with biotinylated goat anti-mouse TNF or IL-1β detection antibodies, visualized by incubation for 30 min with streptavidin-HRP followed by timed incubation with TMB peroxidase substrate. The enzyme reactions were quenched by addition of 2 N H2SO4, and the absorbance of the resulting solutions was measured using a microplate spectrophotometer (BioTek, Winnoski, VT). The cytokine concentration in each test sample was calculated by the instrument software using the formula of the four-parameter best-fit curve to the standards.
Griess assay (nitrite production)
Fresh or frozen aliquots of conditioned media were analyzed for the presence of nitrite using the reagents provided in the Griess Reagent Kit according to the manufacturer’s protocol. The reaction was started by the addition of 20 μl of freshly prepared Greiss reagent to wells containing 200 μl of deionized water and 50 μl of sample media or standards (1–100 μM sodium nitrite prepared in naïve media). Following a 30-min incubation at room temperature in the dark, the absorbance at 548 nm was measured using a microplate spectrophotometer.
Immunoblotting
Nuclear extracts of BV2 cells were isolated using the NE-PER nuclear and cytoplasmic extraction reagent (Thermo Scientific, Rockford, IL) according to the manufacturer’s protocol. Protein concentration was measured using DC Protein Assay (Bio-Rad, Hercules, CA). Nuclear extracts were combined with a Laemmli sample buffer (Bio-Rad) separated on 10% Mini-PROTEAN TGX precast gels (Bio-Rad) at 200 V for 35 to 40 min, then transferred to a polyvinylidene difluoride membrane (Bio-Rad) at 30 V over 24 h at 4°C. Following transfer, the membrane was blocked with PBS/10% Tween-20/5% dry milk for 30 min, then incubated overnight with anti-p50 antibody (sc-1190, Santa Cruz Biotechnology, Dallas, TX) diluted 1:500 in PBS/10% Tween-20/5% dry milk at 4 C. After three washes in PBS/10% Tween-20, the membrane was incubated with donkey anti-goat IgG antibody conjugated to HRP (sc-2020, Santa Cruz Biotechnology) diluted 1:10,000 in PBS/10% Tween-20/5% dry milk for 45 min at room temperature. After 3 washes in PBS, the bands were visualized using SuperSignal West Femto Chemiluminescent Substrate (Thermo Scientific). Chemiluminescence was detected and saved as TIFF file images using a digital imaging system (VersaDoc MP 4000, Bio-Rad). For beta-actin immunoblot, membranes were stripped using Restore Western Blot Stripping Buffer (Thermo Scientific), then incubated in anti-beta actin antibody (clone AC-74, Sigma Aldrich) diluted 1:10,000 in PBS/10% Tween-20 for 3 h at room temperature, followed by washes and incubation in donkey anti-mouse IgG antibody conjugated to HRP (sc-2314, Santa Cruz Biotechnology) diluted 1:10,000 in PBS/10% Tween-20. Beta-actin bands were visualized using Immobilon Western Chemiluminescent HRP Substrate (EMD Millipore, Billerica, MA). Chemiluminescence images were analyzed on ImageJ to acquire relative density measurements. p50 band relative density measurements were normalized to corresponding beta-actin relative density measurements for each sample.
Chromatin immunoprecipitation (ChIP)
ChIP assays were performed using the Magna ChIP A/G kit (Millipore, Billerica, MA) according to the manufacturer’s protocol. BV2 cells were plated in 15-cm culture dishes overnight. Following treatment, cells were fixed in freshly prepared formaldehyde (1% final concentration) to cross-link protein and DNA. Cells were scraped and re-suspended in protease inhibitor cocktail containing buffer, lysed, then sheared by sonication. Genomic DNA fragments were typically less than 500 bases in size; 10-μl (2%) aliquots were set aside as input. Following overnight immunoprecipitation with anti-acetylated histone 4 antibody (Millipore, Billerica, MA) or anti-NF-kappaB1 p50 antibody (sc-1190, Santa Cruz Biotechnology, Dallas, TX), protein/DNA cross-linking was reversed and DNA purified prior to assay by PCR. Primers for PCR were designed using Primer3 software [
18] based on
Nos2 gene and 5′ flanking sequences obtained from UCSC Genome Bioinformatics [
19]. Primer sequences are listed in Table
1. PCR was performed using QuantiFast SYBR Green PCR Kit (Qiagen, Valencia, CA) on a real-time PCR instrument (Life Technologies, Carlsbad, CA). Percent input was calculated as the delta C
T between input DNA and ChIP DNA. Fold enrichment was calculated using the delta delta C
T method with normalization against either isotype IgG ChIP DNA or a negative locus primer set.
Table 1
PCR primer sequences
Nos2_ChIP | GGAGTGTCCATCATGAATGAG | CAACTCCCTGTAAAGTTGTGACC | −159 to −15 |
Nos2_ChIP2 | CCAGAACAAAATCCCTCAGC | CTCATGCAAGGCCATCTCTT | −355 to −198 |
Nos2_ChIP3 | AGCACAGCCCATCCACTATT | CGGAGCTCTCTGGCTTTCT | −551 to −359 |
Nos2_ChIP4 | AAAGGCTTATGCCACCACAC | TTTTCTCAGTGGCATTCTCTCTC | −748 to −572 |
Nos2_ChIP5 | AATTCCATGCCATGTGTGAA | TGATCCCTGAGTTTGGGCTA | −936 to −779 |
Nos2_ChIP6 | TTGAGGCCACACACTTTTTG | TGACAGTGTTAGGGGAAAAGG | −1124 to −959 |
Nos2_ChIP7 | TCACCACACCCAGCATTTTA | GGGAGATGGCTCAGTTGGTA | −1387 to −1188 |
Nos2_ChIP8 | GGGTGTTGCCTGGATAAAGA | GTTCCAGGCTGGTGAGAGAT | −1654 to −1472 |
Nos2_ChIP9 | AAGGGTTCCATTGTGACAAAC | CCCAATACTTGGGAAAGACG | −1855 to −1663 |
Nos2_ChIP10 | CAGCCAAGCACTCCAATGTA | TTACAGCTACGCCTGCAACA | −2002 to −1880 |
Nos2_ChIP11 | AAACTTCTCAGCCACCTTGG | TTCCCAAGCAGGAAGACACT | 30 to 189 |
Nos2_ChIP12 | AAACCAGGCTTTCCCTTCTC | TTGCAGAGAAGAAATCTGACCA | 198 to 336 |
Nos2 a | GCTTCACTCAGCACAGCCCATCCAC | GCTAAACCACATACCCTGGCTTGCAG | −560 to −308 |
Nos2 b | GCCAGCCTCCCTCCCTAGTGAGTCC | GACCCTGGCAGCAGCCATCAGGTAT | −299 to −34 |
Nos2 c | CCTGCTTGGGAAAGCCCAGAAAACC | TGGGGCAGAGGGCACATCTCATAAA | 178 to 462 |
TNF a | TCTAAATGGGACATCCATGGGGGAGA | TCCGTGAATTCCCAGGGCTGAGTTC | −673 to −424 |
TNF b | ACACCCTCCTGATTGGCCCCAGATT | CTTGCTGTCCTCGCTGAGGGAGCTT | −278 to 18 |
TNF c | CCCCTCCACACTCTCCTCCACCTTG | GGCAGAAGAGGCACTCCCCCAAAAG | 191 to 464 |
GAPDH | AGTGCCCACTCCCCTTCCCAGTTTC | GAGGCCCAGCTACTCGCGGCTTTA | −178 to 98 |
Rhodopsin | CAGCCTGAGGCCACCAGACTGACAT | CACAGCGCAACTCCAGGCACTGAC | −268 to −6 |
DNase accessibility assay
DNase accessibility was measured in primary microglia cells using the EpiQ Chromatin Analysis Kit (BioRad, Hercules, CA) according to the manufacturer’s protocol. Microglia were plated in 48-well culture plates at a density of 2 × 10
5 cells per well and incubated overnight prior to treatment. Following treatment, chromatin was digested
in situ by incubation at 37°C for 15 min with 100 μl of EpiQ chromatin buffer containing 2 μl DNase. Cells incubated with chromatin buffer without added DNase were used as the undigested control. Addition of Stop Buffer halted DNase activity and caused cells to detach during a 10-min incubation at 37°C. The resulting cell solutions were combined with Lysis Solution and 100% ethanol, mixing after each addition, and then transferred to the supplied mini columns for isolation of DNA. Following the application of alternating low and high stringency wash solutions, purified genomic DNA was eluted using DNA elution solution preheated to 70°C. Samples were analyzed by quantitative PCR using primers designed to amplify
Nos2 and
Tnf genes, promoters and flanking regions. Primers were designed using Primer3 software [
18] based on sequences obtained from UCSC Genome Bioinformatics [
19]. Primer sequences are listed in Table
1. Delta C
T was calculated as the difference in C
T between undigested and DNase digested samples. Low absolute value delta C
T corresponded to genomic DNA with high nucleosome occupancy (heterochromatin), and high absolute value delta C
T corresponded to genomic DNA with low nucleosome occupancy (euchromatin). The promoter region of the rhodopsin (
Rho) gene, which is not expressed in microglia, consistently showed no shift in C
T between the undigested and digested samples, indicating a heterochromatin structure. Conversely, the promoter region of
Gapdh, which is constitutively expressed, consistently showed a shift in C
T between the undigested and digested samples, indicating an euchromatin structure (data not shown).
Percent chromatin accessibility was calculated using the delta delta C
T method using
Rho gene promoter as the reference region: (1- (2^(delta C
T target gene - delta C
T
Rho))) × 100.
Transfection with small interfering RNA (siRNA)
Primary murine microglia were transfected with siRNA directed at HDAC3 or non-targeting siRNA (10 pmol/1 × 105 cells; Dharmacon) using RNAi Max according to the manufacturer’s protocol; 72 h following transfection, cells were treated, and RNA was obtained using the RNeasy Mini Kit (Qiagen). The efficiency of RNA knockdown was routinely 70–80% based on real-time RT-PCR.
EAE: induction and treatment
EAE was actively induced in 6 to 8-week-old (17 to 20 g) C57BL/6 mice purchased from Harlan (Indianapolis, IN) as previously described [
20]. Mice were administered subcutaneous injection of 300 μg myelin oligodendrocyte glycoprotein peptide (MOG
35–55) in complete Freund’s adjuvant, followed by intraperitoneal injection of 300 ng pertussis toxin. Pertussis toxin injection was repeated 48 h later. A control group of mice received complete Freund’s adjuvant and pertussis toxin without MOG
35–55. Groups of mice were administered daily intraperitoneal injections of either GW3965 or vehicle beginning day 8 post induction. GW3965 was dissolved in dimethyl sulfoxide (DMSO), mixed 1 to 1 with PBS, and 50 μl of this mixture containing 500 μg of GW3965 (or 25 to 30 mg/kg) was administered daily. Vehicle controls received 50 μl mixture of DMSO and PBS (1:1) administered daily. Mice were scored as follows: 0, no overt signs of disease; 1, limp tail or hind limb weakness but not both; 2, limp tail and hind limb weakness; 3, partial hind limb paralysis; 4, complete hind limb paralysis; 5, moribund state. Primary clinical outcome was the mean cumulative EAE score (sum of clinical scores from induction until the day of sacrifice for individual mice divided by the number of mice). Mice that did not get sick were excluded from analysis. Following euthanasia, animals underwent transcardiac perfusion with up to 50 ml of normal saline using a rate-controlled pump. Spines were dissected and cords were pushed out of the column using hydraulic pressure applied through a 19-gauge needle and syringe filled with PBS.
Fluorescence-assisted cell-sorting (FACS) analysis
Following euthanasia, the cervical and axillary lymph nodes and spleen were removed. Single cell suspensions were prepared by grinding the tissue over a 70-μm sterile cell strainer using the rubber end of a syringe plunger then washing with RPMI media. Cells were washed again and re-suspended in RPMI supplemented with L-glutamine, penicillin/streptomycin and 10% FCS. Cells were then plated in 24-well plates and stimulated with PMA/ionomycin/brefeldin A for 6 h as previously described [
21]. Cells were fixed with 4% paraformaldehyde, permeabilized with Perm/Wash Buffer (BD Biosciences, San Jose, CA), then incubated with anti-CD3-PE-Cy5 (clone 17A2), anti-CD4-FITC antibody (clone GK1.5), anti-interleukin-17A-PE antibody (clone TC11-18H10) and anti-interferon-γ-APC antibody (clone XMG1.2, BD Biosciences) for 30 min. FACS data were acquired on a FACSCalibur (BD Biosciences) and analyzed using FlowJo software (FLOWJO, Ashland, OR). FSC vs. SSC plots were used to gate on live cells. CD3 vs. CD4 plots were used to gate on CD3 + CD4+ cells. Interleukin-17 vs. interferon-γ plots were used to gate on interleukin-17 positive, interferon-γ positive and double-positive cells.
Statistical analysis
Mann–Whitney was used for two group comparisons. Kruskal-Wallis test with Dunn’s post-hoc analysis was used for multiple comparisons. Statistical analysis was performed using Prism software (GraphPad, La Jolla, CA).
Discussion
Persistent microglial activation has been implicated in the pathogenesis of a number of neuroinflammatory and neurodegenerative disorders [
2]. Reactive oxygen species, reactive nitrogen species and inflammatory cytokines have been identified as potentially deleterious products of chronic microglial activation in these disorders, leading to oxidative stress and mitochondrial dysfunction [
3]. Mechanisms that inhibit microglial activation, therefore, have the potential to modulate deleterious effects of microglial response in neuroinflammatory and neurodegenerative diseases.
In this report, we confirmed that the activation of the nuclear receptor LXR modifies microglial response to the inflammatory mediator LPS
in vitro. In particular, LXR activation inhibited microglial production of the reactive nitrogen species nitric oxide. We observed partial inhibition of IL-1β production. LXR-dependent inhibition of nitric oxide and IL-1β production corresponded to reductions in
Nos2 and
Il1b expressions. The effect of LXR activation on TNF production was less reliable. These results are in agreement with previous studies that identified
Nos2 and
Il1b, but not
Tnf, as LXR-repressed genes [
25]. The effect of LXR activation on microglial response to interferon-γ was less reliable. There was a trend to decreased nitric oxide production by microglia pretreated with LXR agonist that did not reach statistical significance in the setting of interferon-γ stimulation, possibly indicating a smaller magnitude of LXR-dependent inhibition. Stimulus-specific differences in LXR-dependent inhibition are likely to be important in neuroinflammatory diseases such as multiple sclerosis, where both Toll-like receptor and interferon-γ signaling have been reported [
26-
29].
LXR activation did not inhibit nuclear translocation of NF-kappaB1 p50, indicating that the mechanism of LXR-dependent repression of inflammatory genes does not involve limiting the amount of NF-kappaB transcription factor available for binding DNA in the nucleus. A previous study showed that ligand-dependent transcriptional repression by LXR involves post-translational modification by SUMOylation and subsequent stabilization of the LXR-NCoR complex on the promoters of target genes [
7]. Histone deacetylase (HDAC) and BRG1 are components of the NCoR complex, suggesting that the mechanism of LXR-dependent transcriptional repression involves epigenetic modification [
22,
30]. We detected peak of LPS-induced NF-kappaB1 p50 binding at −159 to −15 bases upstream of the
Nos2 transcription start site, which corresponds to the previously reported proximal enhancer cluster on the
Nos2 promoter [
31]. In addition, we detected histone 4 acetylation upstream of the
Nos2 gene in response to LPS stimulation of microglia, with the peak of histone 4 acetylation detected between −551 to −359 bases upstream of the
Nos2 transcriptional start site. Thus, the peaks of NF-kappaB1 p50 binding and histone 4 acetylation are within 2 to 3 nucleosome distances of each other upstream of the
Nos2 gene. Inhibition of histone acetyltransferase reduced NF-kappaB1 p50 binding on the
Nos2 promoter, suggesting that histone acetylation results in promoter configuration that permits p50 occupancy. Both histone 4 acetylation and p50 binding were partially inhibited by LXR activation, providing additional evidence for a mechanistic link between histone acetylation and NF-kappaB1 p50 binding on the
Nos2 promoter. The addition of HDAC inhibitor or HDAC3 siRNA partially reversed the LXR-dependent repression of nitric oxide production, indicating that LXR-dependent gene repression may be vulnerable to HDAC inhibitors. The interpretation of HDAC inhibitor/siRNA experiments are confounded by that fact that the addition of HDAC inhibitor alone or HDAC3 siRNA alone resulted in increased nitric oxide production or
Nos2 expression above baseline, indicating that HDAC activity exerts basal repression of
Nos2 transcription independent of LXR ligand. DNase accessibility assay indicated that unlike the
Tnf promoter region, which demonstrated constitutive nucleosome depletion, the
Nos2 promoter appears to be an activation-dependent, inducible nucleosome-depleted region in the microglia. In the resting state, the
Nos2 promoter region showed high nucleosome occupancy. Stimulation with LPS resulted in depletion of nucleosome on the
Nos2 promoter, indicating a shift to euchromatin. Addition of LXR agonist did not alter DNase accessibility at the
Nos2 promoter. Together, these data suggest that the mechanism of LXR-dependent
Nos2 repression involves histone deacetylation that likely alters the local transcription factor access to response elements without a change in the regional nucleosome occupancy.
A key question addressed by this study is whether or not LXR activation can regulate CNS inflammation. A related question is whether or not endogenous LXR activity is a physiologic regulator of CNS inflammation. A previous study reported that LXR knockout animals showed increased clinical disease severity during EAE that was explained by the loss of inhibitory influence on lymphocyte Th17 lineage differentiation [
14]. Thus, LXR appears to exert physiologic control over peripheral lymphocyte activation during the induction phase of EAE. In the CNS compartment, however, we found reduced expression of LXR and LXR-dependent genes, indicating that the endogenous LXR activity is, in fact, diminished in the context of CNS inflammation. The reduction in LXR and LXR-dependent genes in the CNS is consistent with previous reports of LXR expression in several other organs. In hepatocytes, renal cells and adipocytes, induction of acute phase response by LPS, TNF and/or IL-1β is associated with reduction in nuclear receptor levels including LXR [
32-
34]. Thus, inflammatory cytokine-induced suppression of LXR expression also appears to occur in the CNS.
The administration of LXR ligand, nevertheless, partially reversed the diminished LXR activity during EAE. LXR ligand administration increased the expression of LXR-dependent genes involved in reverse cholesterol transport including
Abca1 and
Abcg1 above those in vehicle treated animals, indicating upregulation of LXR activity in the CNS. The administration of LXR ligand had a less reliable effect with respect to repression of inflammatory genes. In particular, we did not see significant repression of
Nos2 expression in the spinal cord of EAE animals following LXR agonist administration. LXR agonist delayed the onset of clinical disease in EAE, but did not impact the severity of clinical disease at later time points, likely reflecting the failure of LXR activation to establish repression of CNS inflammatory genes in EAE. Several explanations are possible. We found a more reliable inhibitory effect of LXR on LPS-induced microglial activation compared to interferon-γ-induced microglial activation. Therefore, CNS inflammatory conditions such as EAE and MS where both Toll-like receptor and interferon-γ signaling are detected may be less responsive to inhibitory action of LXR [
26,
27]. Alternatively, the threshold for transcriptional activation and transcriptional repression by LXR may be different in the context of CNS inflammation. Whereas genes involved in reverse cholesterol transport are coordinately regulated by LXR transcriptional activation involving exchange of NCoR for NCoA, the antiinflammatory effects of LXR are under SUMOylation-dependent transcriptional repression [
35]. There is evidence that the activation and repression functions of LXR can be uncoupled [
36]. Although we found no change in the frequency of Th17 cells at day 14 post induction, it remains possible that the delay in onset of EAE clinical disease in LXR agonist treated animals might reflect an inhibitory effect of LXR activation on peripheral lymphocytes.
There are several limitations to the study. Analysis of gene expression was performed on spinal cord homogenates, representing multiple cell types. It is possible that analysis of isolated microglia/macrophage might have detected a statistically significant effect of LXR activation on inflammatory gene expression. However, LXR-dependent repression of inflammatory genes has been reported in multiple cell types including astrocytes [
37] and therefore would have been expected to have broader antiinflammatory effects. This study differs from previous studies testing the effect of LXR agonist in EAE with respect to either onset of drug administration or the specific drug administered. Two previous studies examined the effect of LXR agonist administered during the induction phase [
14,
38], whereas LXR agonist was administered during the effector phase in the current study. A previous study tested a different LXR agonist (T091317) during the effector phase of EAE [
38]. T0901317 has turned out to be a rather non-specific LXR agonist, with additional activity toward pregnane X receptor and farnesoid X receptor, not seen in GW3965 [
39,
40].
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Competing interest
The authors declare that they have no competing interests.
Authors’ contributions
JRSM carried out the acquisition and analysis of the data and helped draft the manuscript. HAO carried out the acquisition and analysis of the data and helped draft the manuscript. UO conceived and designed the study, interpreted the data and drafted the manuscript. All authors have read and approved the final manuscript.