Expression of gamma-IFN responsive genes in scavenger receptor over-expressing monocytes is associated with xanthomatosis

Gene expression profiling in elderly patients with familial hypercholesterolemia with and without coronary heart disease

BACKGROUND AND AIMS

Elderly familial hypercholesterolemia (FH) patients are at high risk of coronary heart disease (CHD) due to high cholesterol burden and late onset of effective cholesterol-lowering therapies. A subset of these individuals remains free from any CHD event, indicating the potential presence of protective factors. Identifying possible cardioprotective gene expression profiles could contribute to our understanding of CHD prevention and future preventive treatment. Therefore, this study aimed to investigate gene expression profiles in elderly event-free FH patients.

METHODS

Expression of 773 genes was analysed using the Nanostring Metabolic Pathways Panel, in peripheral blood mononuclear cells (PBMCs) from FH patients ≥65 years without CHD (FH event-free, n = 44) and with CHD (FH CHD, n = 39), and from healthy controls ≥70 years (n = 39).

RESULTS

None of the genes were differentially expressed between FH patients with and without CHD after adjusting for multiple testing. However, at nominal p < 0.05, we found 36 (5%) differentially expressed genes (DEGs) between the two FH groups, mainly related to lipid metabolism (e.g. higher expression of ABCA1 and ABCG1 in FH event-free) and immune responses (e.g. lower expression of STAT1 and STAT3 in FH event-free). When comparing FH patients to controls, the event-free group had fewer DEGs than the CHD group; 147 (19%) and 219 (28%) DEGs, respectively.

CONCLUSIONS

Elderly event-free FH patients displayed a different PBMC gene expression profile compared to FH patients with CHD. Differences in gene expression compared to healthy controls were more pronounced in the CHD group, indicating a less atherogenic gene expression profile in event-free individuals. Overall, identification of cardioprotective factors could lead to future therapeutic targets.

Class A scavenger receptors, macrophages, and atherosclerosis

The scope of this review is to discuss the new advances in our understanding of the role of scavenger receptor class A in the initiation and modulation of the atherosclerotic process. Through the approaches of gene manipulation in the mouse model, a substantial body of literature has accumulated that depicts scavenger receptor class A as a central player in atherogenesis. In studies of scavenger receptor class A overexpression in macrophages through bone marrow transplantation using transgenic donor material, recipient mice with hyperlipidemia caused either by apolipoprotein E or LDL receptor deficiency did not show convincing changes in the degree of atherosclerosis development compared with controls. Conversely, the deletion of the scavenger receptor class A gene in the mouse has shown, in a consistent and significant fashion, that this receptor serves a pro-atherogenic function under hyperlipidemic conditions, as both apolipoprotein E and LDL receptor-deficient mice had reduced atherosclerosis in the absence of scavenger receptor class A. In addition, we have recently shown that C57BL/6 mice are protected from diet-induced atherosclerosis when they lack scavenger receptor class A, and that the macrophage is the cell type responsible for the effect of scavenger receptor class A deficiency in reducing lesion formation in C57BL/6 and LDL receptor null mice. Together, these results demonstrate that macrophage scavenger receptor class A contributes significantly to atherosclerotic lesion formation, and suggest that the uptake of oxidized or modified lipoproteins by vessel wall macrophages is a central process in atherogenesis.

Identification of a γ-Interferon–Responsive Element in the Promoter of the Human Macrophage Scavenger Receptor A Gene

Abstract —In the present study, we demonstrate γ-interferon (γ-IFN)–inducible scavenger receptor A (SR-A) mRNA expression during the early stages of THP-1 and blood monocyte differentiation. Predominant induction of SR-A type II mRNA parallels the increased accumulation of cholesteryl esters under these conditions. A potential signal transducer and activator of transcription (STAT1) binding site (γ-interferon activation site) in the SR-A promoter demonstrates γ-IFN–inducible DNA binding activity and is most likely responsible for the γ-IFN–dependent expression of an SR-A promoter–luciferase fusion construct. In contrast, γ-IFN inhibits SR-A expression in mature macrophages as well as after prolonged γ-IFN incubation of THP-1 monocytes. Taken together, these results demonstrate opposite effects of γ-IFN on SR-A expression and activity during the early versus late stages of monocyte maturation. γ-IFN–induced STAT1 activation, leading to increased SR-A expression, could therefore play an important role in the initial steps of foam cell formation and xanthomatosis.

Interferon-gamma induces downregulation of Tangier disease gene (ATP-binding-cassette transporter 1) in macrophage-derived foam cells

Cholesterol efflux is a fundamental process that serves to mitigate cholesterol accumulation and macrophage foam cell formation. Recently, we reported that cholesterol efflux to high density lipoprotein subfraction 3 was reduced by interferon-gamma (IFN-gamma) and that this decrease was associated with an increase in acyl coenzyme A:cholesterol acyltransferase (ACAT) expression. In the present study, although treatment of murine peritoneal macrophages with IFN-gamma resulted in a 2-fold decrease in HDL-mediated cholesterol efflux, efflux to lipid-free apolipoprotein A-I was reduced >4-fold and approached basal levels. This decrease was associated with a 3- to 4-fold reduction in ATP-binding-cassette transporter 1 (ABC1) mRNA content, the gene responsible for the defect in Tangier disease. Consistent with the reduction in cholesterol and phospholipid efflux in Tangier fibroblasts, downregulation of ABC1 expression by IFN-gamma also resulted in reduced phosphatidylcholine and sphingomyelin efflux to apolipoprotein A-I. Whereas foam cells had a 3-fold increase in ABC1 mRNA, the decrease in ABC1 message levels by IFN-gamma was observed in foam cells and control macrophages. This effect of IFN-gamma was independent of general macrophage activation (inasmuch as similar changes were not detected with granulocyte-macrophage colony-stimulating factor) and was not observed with other ABC transporters (inasmuch as the expression of the transporter in antigen processing was upregulated 4-fold in these same cells). Therefore, by decreasing cholesterol efflux through pathways that include the upregulation of ACAT and the downregulation of ABC1, IFN-gamma can shift the equilibrium between macrophages and foam cells and thus impact the progression of an atherosclerotic lesion.