Skip to main page content
Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
, 25 (13), 3774-3785.e4

LXR Suppresses Inflammatory Gene Expression and Neutrophil Migration Through cis-Repression and Cholesterol Efflux

Affiliations

LXR Suppresses Inflammatory Gene Expression and Neutrophil Migration Through cis-Repression and Cholesterol Efflux

David G Thomas et al. Cell Rep.

Abstract

The activation of liver X receptor (LXR) promotes cholesterol efflux and repression of inflammatory genes with anti-atherogenic consequences. The mechanisms underlying the repressive activity of LXR are controversial and have been attributed to cholesterol efflux or to transrepression of activator protein-1 (AP-1) activity. Here, we find that cholesterol efflux contributes to LXR repression, while the direct repressive functions of LXR also play a key role but are independent of AP-1. We use assay for transposase-accessible chromatin using sequencing (ATAC-seq) to show that LXR reduces chromatin accessibility in cis at inflammatory gene enhancers containing LXR binding sites. Targets of this repressive activity are associated with leukocyte adhesion and neutrophil migration, and LXR agonist treatment suppresses neutrophil recruitment in a mouse model of sterile peritonitis. These studies suggest a model of repression in which liganded LXR binds in cis to canonical nuclear receptor binding sites and represses pro-atherogenic leukocyte functions in tandem with the induction of LXR targets mediating cholesterol efflux.

Keywords: LXR; cholesterol; cholesterol efflux; cis-repression; liver X receptor; neutrophil migration; nuclear receptor; oxysterol; peritonitis; transrepression.

Conflict of interest statement

DECLARATION OF INTERESTS

The authors declare no competing interests.

Figures

Figure 1.
Figure 1.. Cholesterol Efflux Transporters Partly Mediate LXR Repression
(A) Abca1fl/flAbcg1fl/fl (floxed ctrl) or LysMCre Abca1fl/flAbcg1fl/fl (Mac-ABCDKO) BMDMs were treated for 3 hr with 500 nM T0 before stimulation with 10 ng/mL LPS for 2 hr. (B) Data in (A) plotted as percent repression normalized to the extent of LPS-inducible gene expression in each genotype. (C) Wild-type (WT) or Myd88–/– BMDMs were treated as in (A). (D) Lpcat3fl/fl (floxed ctrl) or LysMCre Lpcat3fl/fl (Mac-Lpcat3KO) BMDMs were treated as in (A). (E) BMDMs were transfected with siSCD2 SMARTpool siRNA or non-targeting siRNA (siCtrl) for 24 hr, rested for 24 hr, and then treated as in (A). (F) BMDM were treated with MAPK inhibitors (10 μM PD0325901 and 1 μM BIRB0796) and then treated as in (A). mRNA expression was evaluated by qPCR, and mean ± SEM is plotted. n = 4 biological replicates. Significance was determined by one-way ANOVA with Tukey’s post hoc test (A and C–F) or Student’s t test with Benjamini-Hochberg multiple testing correction (B). *p < 0.05, **p < 0.01, and ***p < 0.001 for T0 treatment versus control; #p < 0.05, ##p < 0.01, and ###p < 0.001 for alternative genotype; †p < 0.05, ††p < 0.01, and †††p < 0.001 for LPS versus vehicle (Veh). Data are representative of two independent experiments. See also Figure S1.
Figure 2.
Figure 2.. LXR Agonist Closes Chromatin at Inflammatory Gene Enhancers
WT BMDMs were treated for 3 hr with 500 nM T0 before stimulation with 10 ng/mL LPS for 2 hr and harvested for ATAC-seq. Accessible regions were determined from ATAC-seq data, and analysis was restricted to macrophage H3K4me2- or H3K27ac-marked enhancers defined by Oishi et al. (2017). (A and B) Representative genome browser track of chromatin accessibility signal around the T0-repressed gene Il1b (A) and the T0-induced gene Srebf1 (B) with vehicle or T0 treatment. Signal is plotted in units of reads per genomic content (RPGC). (C) PANTHER GO categories enriched in genes nearest to T0-closed enhancers (Bonferroni-adjusted p < 0.05). (D) HOMER de novo motifs enriched in T0-closed enhancers (p < 1 3 10–12; top 5 motifs displayed). FE, fold enrichment; LXRE, LXR response element; NR-half, nuclear receptor half-site. (E) PANTHER GO categories enriched in genes nearest to LPS-opened enhancers (Bonferroni-adjusted p < 0.05). (F) HOMER de novo motifs enriched in LPS-opened enhancers (p < 1 3 10–12; top 5 motifs displayed). n = 4 biological replicates. FE, fold enrichment. See also Figure S2 and Tables S1–S5.
Figure 3.
Figure 3.. LXR Binding by ChIP-Seq Localizes at T0-Closed Enhancers
The LXR ChIP-seq signal from Oishi et al. (2017) was plotted at enhancer sets derived from ATAC-seq of BMDMs treated for 3 hr with 500 nM T0 before stimulation with 10 ng/mL LPS for 2 hr. (A) Representative genome browser track of the LXR ChIP signal around the T0-repressed gene Il1b. The signal is plotted in units of reads per genomic content (RPGC). (B) Histogram of the LXR ChIP-seq signal centered on T0-closed enhancers. LXR-GW, chromatin from thioglycolate-elicited macrophages (TGEMs) treated with the LXR agonist GW3965 for 24 hr; LXR-KLA1h, chromatin from TGEMs stimulated with the TLR4 agonist KLA for 1 hr; LXR-notr, chromatin from resting TGEMs immunoprecipitated with anti-LXR antibody (notr, no treatment). (C) Heatmap of the LXR ChIP-seq signal as in (B) centered on T0-closed enhancers. n = 4 biological replicates (ATAC-seq) or 1 biological replicate (LXR ChIP-seq). See also Figure S3.
Figure 4.
Figure 4.. Chromatin Accessibility Changes with T0 Are Linked to Gene Expression Changes
Transcription start site (TSS) positions of differentially expressed genes in RNA-seq of BMDMs treated with T0 for 3 hr and 10 ng/mL LPS for 2 hr were compared to positions of enhancers opened or closed by T0 in ATAC-seq data collected from BMDMs in the same conditions. (A and B) Percentage of genes in T0-induced, T0-repressed, or random genes with an enhancer opened by T0 (A) or closed by T0 (B) in the control or LPS-stimulated condition within 100 kb of the TSS. (C and D) Distribution of distances from the TSS to the nearest enhancer for T0-induced, T0-repressed, or random genes to enhancers opened by T0 (C) or closed by T0 (D) in the control or LPS-stimulated condition. n = 4 biological replicates (ATAC-seq) or 3 biological replicates (RNA-seq). Significance was determined by Kruskal-Wallis nonparametric one-way ANOVA with Dunn post hoc test. *p < 0.05, **p < 0.01, ***p < 0.001; ns, not significant.
Figure 5.
Figure 5.. LXR Represses Neutrophil Migration Genes
WT BMDMs were treated for 3 hr with 500 nM T0 before stimulation with 10 ng/mL LPS for 2 hr and harvested for RNA-seq. (A) Heatmap of all induced or repressed genes at 5% FDR, colored by row-normalized Z score, with extent of induction by LPS indicated on right. (B) PANTHER GO categories enriched in T0-repressed genes (Bonferroni-adjusted p < 0.05). (C) PANTHER GO categories enriched in T0-induced genes (Bonferroni-adjusted p < 0.05). (D and E) Row-normalized Z score for T0-repressed genes in the GO category “Leukocyte cell-cell adhesion” (D) or “Granulocyte chemotaxis” (E). n = 3 biological replicates. See also Table S6.
Figure 6.
Figure 6.. LXR Activation Suppresses Neutrophil Migration In Vivo
Mice were treated with T0 or vehicle before induction of zymosan peritonitis. (A) Dosing schedule for treatments and harvest of peritoneal exudates. (B–D) Total peritoneal exudate cell (B), neutrophil (C), and macrophage (D) counts at 0, 12, or 24 hr after zymosan injection. Cell counts were determined by flow cytometry. (E) Peritoneal exudate cell mRNA expression at 4 hr after zymosan injection was measured by qPCR. (F) Peritoneal exudate leukocyte subsets were isolated using anti-Ly6G- or anti-F4/80-conjugated magnetic beads at 4 hr after zymosan injection and mRNA expression was measured by qPCR. Mean ± SEM is plotted; n = 4–5 biological replicates. Significance was determined by two-way ANOVA with Sidak’s post hoc test (B–D) or by Student’s t test with Benjamini-Hochberg multiple testing correction (E and F). *p < 0.05, **p < 0.01, and ***p < 0.001 for individual time point; †p < 0.05, ††p < 0.01, and †††p < 0.001 for treatment effect by 2-way ANOVA; #p < 0.05, ##p < 0.01, and ###p < 0.001 for leukocyte subset effect. Data are representative of two independent experiments. See also Figure S4.

Similar articles

See all similar articles

Cited by 6 PubMed Central articles

See all "Cited by" articles

References

    1. A-Gonzalez N, Bensinger SJ, Hong C, Beceiro S, Bradley MN, Zelcer N, Deniz J, Ramirez C, Díaz M, Gallardo G, et al. (2009). Apoptotic cells promote their own clearance and immune tolerance through activation of the nuclear receptor LXR. Immunity 31, 245–258. - PMC - PubMed
    1. Alberti S, Schuster G, Parini P, Feltkamp D, Diczfalusy U, Rudling M, Angelin B, Björkhem I, Pettersson S, and Gustafsson JA (2001). Hepatic cholesterol metabolism and resistance to dietary cholesterol in LXRbeta-deficient mice. J. Clin. Invest 107, 565–573. - PMC - PubMed
    1. Bannenberg GL, Chiang N, Ariel A, Arita M, Tjonahen E, Gotlinger KH, Hong S, and Serhan CN (2005). Molecular circuits of resolution: formation and actions of resolvins and protectins. J. Immunol 174, 4345–4355. - PubMed
    1. Bell O, Tiwari VK, Thomä NH, and Schübeler D (2011). Determinants and dynamics of genome accessibility. Nat. Rev. Genet 12, 554–564. - PubMed
    1. Bligh EG, and Dyer WJ (1959). A rapid method of total lipid extraction and purification. Can. J. Biochem. Physiol 37, 911–917. - PubMed

Publication types

Feedback