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Desmosterol suppresses inflammasome activation and protects against atherosclerosis II

ABSTRACT: Cholesterol biosynthetic intermediates such as lanosterol and desmosterol are emergent immune regulators of macrophages in response to inflammatory stimuli or lipid overloading, respectively. However, the participation of these sterols in regulating macrophage functions in the physiological context of atherosclerosis, an inflammatory disease driven by the accumulation of cholesterol-laden macrophages in the artery wall, has remained elusive. Here we report that desmosterol, the most abundant cholesterol biosynthetic intermediate in human coronary artery lesions, plays an essential role during atherogenesis, serving as a key molecule integrating cholesterol homeostasis and immune responses in macrophages. Depletion of desmosterol in myeloid cells by overexpression of 3β-hydroxysterol Δ24-reductase (DHCR24), the enzyme that catalyzes conversion of desmosterol to cholesterol, promotes the progression of atherosclerosis. Single cell transcriptomics in isolated CD45+CD11b+ cells from atherosclerotic plaques demonstrate that depletion of desmosterol increases interferon (IFN) responses and attenuates the expression of anti-inflammatory macrophage markers. Lipidomic and transcriptomic analysis of in vivo macrophage foam cells demonstrate that desmosterol is a major endogenous liver X receptor (LXR) ligand involved in LXR/RXR activation and thus, macrophage foam cell formation. Decreased desmosterol accumulation in mitochondria promotes macrophage mito-ROS production and NLRP3-dependent inflammasome activation. Deficiency of NLRP3 or ASC rescues the increased inflammasome activity and atherogenesis observed in desmosterol-depleted macrophages. Altogether, these findings underscore the critical function of desmosterol in the atherosclerotic plaque to dampen inflammation, by integrating with macrophage cholesterol metabolism and inflammatory activation, and protecting from disease progression.

ORGANISM(S): Mus musculus

PROVIDER: GSE175312 | GEO | 2021/12/01

REPOSITORIES: GEO

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Project description:Background: Cardiovascular diseases remain the leading cause of morbidity and mortality worldwide, most of which are caused by atherosclerosis. Discerning processes that participate in macrophage-to-foam cell formation are critical for understanding the basic mechanisms underlying atherosclerosis. To explore the molecular mechanisms of foam cell formation, the differentially expressed proteins were identified. Methods: In this paper, human monocytes, macrophage colony-stimulating factor induced macrophages, and oxidized low-density lipoprotein induced foam cells were cultured, and tandem mass tag (TMT) labeling combined with mass spectrometry (MS) were performed to find associations between foam cell transformation and proteome profiles. Results: Totally, 5146 quantifiable proteins were identified, among which 1515 and 182 differentially expressed proteins (DEPs) were found in macrophage/monocyte and foam cell/macrophage, respectively, using a cutoff of 1.5-fold change. Subcellular localization analysis revealed that downregulated DEPs of macrophages/monocytes were mostly located in the nucleus and upregulated DEPs of foam cells/macrophages mostly located in the plasma membrane and extracellular. Functional analysis of DEPs demonstrated that cholesterol metabolism related proteins were upregulated in foam cells, whereas the immune response-related proteins were downregulated in foam cells. The protein-interaction network showed that the DEPs with the highest interaction intensity between macrophages and foam cells were mainly concentrated in lysosomes and the endoplasmic reticulum. Conclusions: This study for the first time to perform quantitative proteomic investigation by TMT labeling and LC-MS/MS to identify differentially expressed proteins in human monocyte, macrophage, and foam cell. The results confirmed cholesterol metabolism was upregulated in foam cells, while immune response was suppressed, which suggested that foam cells were not the population that promote inflammation. In addition, KEGG enrichment analysis and protein-protein interaction indicated that the differentially expressed proteins locating in the endoplasmic reticulum and lysosomes may be key targets to regulate foam cell formation. These data provide a basis for identifying the potential proteins associated with the molecular mechanism involved in the transformation of macrophages to foam cells.

Project description:To investigate the relationship between hypercholesterolemia, foam cell formation and inflammation, we performed lipidomic and transcriptomic analyses of elicited peritoneal macrophages in wild type (WT) or LDL receptor knockout (LDLR KO) mice fed either a normal cholesterol, normal fat (NCNF) diet or a high cholesterol, high fat (HCHF) 'Western' style diet. The combination of the LDLR KO genotype and the HCHF diet results in the formation of macrophage foam cells in the elicited peritoneal macrophage population. Analysis of macrophages from the above four experimental groups revealed massive reprogramming of the lipidome in response to both diet and genotype. These studies confirmed and extended prior knowledge regarding the roles of SREBP and LXR signaling in cholesterol and fatty acid homeostasis. Unexpectedly, peritoneal macrophage foam cells exhibited a strongly 'deactivated' phenotype, with marked suppression of pro-inflammatory mediators that are normally characteristic of the inflammatory responses associated with atherosclerotic lesions. Many of these changes in gene expression and lipid metabolism appear to be related to the paradoxical accumulation of high levels of desmosterol, the last intermediate in the Bloch pathway of cholesterol biosynthesis. WT or LDLR KO mice were fed either a NCNF diet or a HCHF diet for twelve weeks to establish four experimental groups (WT-NCNF diet, WT-HCHF diet, KO-NCNF diet, and KO-HCHF diet). As expected, the combination of the HCHF diet and LDLR KO genotype resulted in a synergistic effect on serum lipid levels. Elicited peritoneal macrophages (92-96% F4/80-positive) were immediately prepared for analysis, thereby preserving in vivo gene expression and lipid profiles. Macrophages derived from LDLR KO mice fed the HCHF diet contained nearly four-fold more total cholesterol than cells from WT mice fed the same diet. Quantitative analysis of 245 lipid species revealed significant changes in nearly all major lipid classes. Using a two-way ANOVA model, we found that 176 (72%) of the lipids analyzed were significantly affected by the HCHF diet, 133 (54%) by the LDLR KO genotype, and 114 (46%) by interactions between the HCHF diet and LDLR KO genotype. Many of the observed interactions (60%) were synergistic.

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Desmosterol suppresses inflammasome activation and protects against atherosclerosis II

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