Monocytes of patients with familial hypercholesterolemia show alterations in cholesterol metabolism

Sandy Mosig,Siegfried Krause,Petra Büttner,Harald Funke,Regine Heller,Knut Rennert,Dieter Lütjohann,Muhidien Soufi

doi:10.1186/1755-8794-1-60

Abstract

BackgroundElevated plasma cholesterol promotes the formation of atherosclerotic lesions in which monocyte-derived lipid-laden macrophages are frequently found. To analyze, if circulating monocytes already show increased lipid content and differences in lipoprotein metabolism, we compared monocytes from patients with Familial Hypercholesterolemia (FH) with those from healthy individuals.MethodsCholesterol and oxidized cholesterol metabolite serum levels of FH and of healthy, gender/age matched control subjects were measured by combined gas chromatography – mass spectroscopy. Monocytes from patients with FH and from healthy subjects were isolated by antibody-assisted density centrifugation. Gene expression profiles of isolated monocytes were measured using Affymetrix HG-U 133 Plus 2.0 microarrays. We compared monocyte gene expression profiles from FH patients with healthy controls using a Welch T-test with correction for multiple testing (p < 0.05; Benjamini Hochberg correction, False Discovery Rate = 0.05). The differential expression of FH associated genes was validated at the mRNA level by qRT-PCR and/or at the protein level by Western Blot or flow cytometry. Functional validation of monocyte scavenger receptor activities were done by binding assays and dose/time dependent uptake analysis using native and oxidized LDL.ResultsUsing microarray analysis we found in FH patients a significant up-regulation of 1,617 genes and a down-regulation of 701 genes compared to monocytes from healthy individuals. These include genes of proteins that are involved in the uptake, biosynthesis, disposition, and cellular efflux of cholesterol. In addition, plasma from FH patients contains elevated amounts of sterols and oxysterols. An increased uptake of oxidized as well as of native LDL by FH monocytes combined with a down-regulation of NPC1 and ABCA1 explains the lipid accumulation observed in these cells.ConclusionOur data demonstrate that circulating FH monocytes show differences in cell physiology that may contribute to the early onset of atherosclerosis in this disease.

Highlights

Elevated plasma cholesterol promotes the formation of atherosclerotic lesions in which monocyte-derived lipid-laden macrophages are frequently found
Using microarray analysis we found in Familial Hypercholesterolemia (FH) patients a significant up-regulation of 1,617 genes and a down-regulation of 701 genes compared to monocytes from healthy individuals
An increased uptake of oxidized as well as of native LDL by FH monocytes combined with a down-regulation of NPC1 and ABCA1 explains the lipid accumulation observed in these cells

Summary

Introduction

Elevated plasma cholesterol promotes the formation of atherosclerotic lesions in which monocyte-derived lipid-laden macrophages are frequently found. Atherosclerosis is the primary cause of coronary heart disease (CHD) and stroke in Western societies [1]. It is characterized by the development of lipid-rich lesions in the arterial wall, in which foam cells, monocyte-derived lipidladen macrophages, are frequently found. An important regulator of cellular cholesterol content is the sterol regulatory element binding protein (SREBP) pathway, which controls, by transcriptional regulation, the uptake of cholesterol via LDL-receptor and several steps in the de novo synthesis of cholesterol. In healthy individuals cells ingest cholesterol by endocytosis of LDL bound to the LDL-receptor (LDLR). It is assumed that Npc has a pivotal role in cholesterol efflux as it aids in the cellular distribution of lysosomal cholesterol which enables Abca dependent efflux [3,4]

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