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HDL suppresses the type I interferon response

ABSTRACT: Background: High density lipoprotein (HDL) protects the artery wall by removing cholesterol from lipid-laden macrophages. However, recent evidence suggests that it might also inhibit atherogenesis by combating inflammation. Methods and Results: To identify potential anti-inflammatory mechanisms, we challenged macrophages with lipopolysaccharide (LPS), an inflammatory microbial ligand for Toll-like receptor 4 (TLR4). HDL inhibited the expression of 33% (301 of 911) of the genes normally induced by LPS, microarray analysis revealed. One of its major targets was the type I interferon response pathway, a family of potent viral immunoregulators controlled by TLR4 and the TRAM/TRIF signaling pathway. Unexpectedly, HDL’s ability to inhibit gene expression was independent of cellular cholesterol stores. Moreover, it was unaffected by downregulation of two ATP-binding cassette transporters, ABCA1 and ABCG1, that promote cholesterol efflux. To examine the pathway’s potential in vivo relevance, we used mice deficient in apolipoprotein (apo) A-I, HDL’s major protein. After infection with Salmonella (a Gram-negative bacterium that expresses LPS), apoA-I–deficient mice had 6-fold higher plasma levels of interferon-beta-a key regulator of the type I interferon response than did wild-type mice. Conclusions: HDL inhibits a subset of LPS-stimulated macrophage genes that regulate the type I interferon response, and its action is independent of sterol metabolism. These findings raise the possibility that regulation of macrophage genes by HDL might link innate immunity and cardioprotection.

ORGANISM(S): Mus musculus

PROVIDER: GSE19340 | GEO | 2010/10/01

SECONDARY ACCESSION(S): PRJNA121713

REPOSITORIES: GEO

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Project description:Despite considerable progress understanding genes that affect the HDL particle, its function, and cholesterol content, genes identified to date explain only a small percentage of the genetic variation. We used N-ethyl-N-nitrosourea mutagenesis in mice to discover novel genes that affect HDL cholesterol levels. Two mutant lines (Hlb218 and Hlb320) with low HDL cholesterol levels were established. Causal mutations in these lines were mapped using linkage analysis: For line Hlb218 within a 12 Mbp region on Chr 10; and for line Hlb320 within a 17 Mbp region on Chr 7. High-throughput sequencing of Hlb218 liver RNA identified a mutation in Pla2g12b. The transition of G to A leads to a cysteine to tyrosine change and most likely causes a loss of a disulfide bridge. Microarray analysis of Hlb320 liver RNA showed a 7-fold downregulation of Hpn; sequencing identified a mutation in the 3M-bM-^@M-2 splice site of exon 8. Northern blot confirmed lower mRNA expression level in Hlb320 and did not show a difference in splicing, suggesting that the mutation only affects the splicing rate. In addition to affecting HDL cholesterol, the mutated genes also lead to reduction in serum non-HDL cholesterol and triglyceride levels. Despite low HDL cholesterol levels, the mice from both mutant lines show similar atherosclerotic lesion sizes compared to control mice. These new mutant mouse models are valuable tools to further study the role of these genes, their affect on HDL cholesterol levels, and metabolism. Mutant mice were generated as part of The Jackson LaboratoryM-bM-^@M-^Ys Heart, Lung, Blood, and Sleep Disorder Mutagenesis Program by treating male C57BL/6J (B6) mice with N-ethyl-N-nitrosourea (ENU). Third generation (G3) mice were phenotyped to ensure capture of both dominant and recessive mutations. Two unique G3 animals with low HDL cholesterol levels were then used to establish new inbred lines (Hlb218 and Hlb320) by mating them with B6 mice and intercrossing the offspring with low HDL cholesterol for 7 generations. Livers from 3 Hlb218, 3 Hlb320 males, and 6 B6 male controls were obtained for gene expression analysis. The samples were randomized over Illumina Mouse-6 Expression 1.1 BeadChips .

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HDL suppresses the type I interferon response

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