Atherosclerotic Lesions Of Human Aorta Research Articles

Immunohistochemical analysis of adiponectin in atherosclerotic lesions of human aorta.

BACKGROUNDMetabolic syndrome, a cluster of interrelated disorders including abdominal obesity, insulin resistance, dyslipidemia, and hypertension (HTN) plays an important role in development of atherosclerotic lesions in arterial wall. Dysregulation of adipose tissue hormones (adipokines) production is a possible link between abdominal obesity and other manifestations of metabolic syndrome. Adiponectin is a well-known adipokine which affects metabolism and inflammatory response. However, data on its role in atherogenesis are still controversial. The aim of this study is to investigate whether adiponectin is present in atherosclerotic lesions of human aorta.METHODSThirty-five autopsy segments from abdominal, thoracic aortas, and aortic arch of four men (mean age: 57 years) were fixed and stained for lipids [Oil Red O (ORO)], cells [hematoxylin-eosin (H&E)], and adiponectin [indirect immunoperoxidase assay (IPA) method]. Samples of both stable and unstable plaques were selected for analysis. Human adipose tissue, THP-1 monocytes/macrophages, and human endothelial hybrid cell line (EA.hy926) were chosen for detection of adiponectin messenger ribonucleic acid (mRNA) using reverse transcription polymerase chain reaction (RT-PCR).RESULTSAdiponectin accumulations were found inside endothelial cells covering both stable and unstable atherosclerotic plaques. Focal depositions of adiponectin were also found in fibrous caps of stable lesions and atheromatous core of both stable and unstable plaques and also in adventitia. RT-PCR revealed mRNA expression of adiponectin gene in adipose tissue, but not in mononuclears and endothelial cells.CONCLUSIONAdiponectin is present in aortic plaques of humans, but is not synthesized in endothelial cells and mononuclears, at least in culture conditions. Detection of adiponectin in atherosclerotic lesions can serve as indirect evidence of possible participation of this adipokine in atherogenesis.

Heteroplasmic Variants and Copy Number of Mitochondrial DNA in Different Types of Atherosclerotic Lesions of Human Aorta

Heteroplasmic Variants and Copy Number of Mitochondrial DNA in Different Types of Atherosclerotic Lesions of Human Aorta

Neopterin Counters Vascular Inflammation and Atherosclerosis.

BackgroundNeopterin, a metabolite of GTP, is produced by activated macrophages and is abundantly expressed within atherosclerotic lesions in human aorta and carotid and coronary arteries. We aimed to clarify the influence of neopterin on both vascular inflammation and atherosclerosis, as neither effect had been fully assessed.Methods and ResultsWe investigated neopterin expression in coronary artery lesions and plasma from patients with coronary artery disease. We assessed the atheroprotective effects of neopterin in vitro using human aortic endothelial cells, human monocyte‐derived macrophages, and human aortic smooth muscle cells. In vivo experiments included a study of aortic lesions in apolipoprotein E–deficient mice. Neopterin expression in coronary artery lesions and plasma was markedly increased in patients with versus without coronary artery disease. In human aortic endothelial cells, neopterin reduced proliferation and TNF‐α (tumor necrosis factor α)–induced upregulation of MCP‐1 (monocyte chemotactic protein 1), ICAM‐1 (intercellular adhesion molecule 1), and VCAM‐1 (vascular cell adhesion molecule 1). Neopterin attenuated TNF‐α–induced monocyte adhesion to human aortic endothelial cells and the inflammatory macrophage phenotype via NF‐κB (nuclear factor‐κB) downregulation. Neopterin suppressed oxidized low‐density lipoprotein–induced foam cell formation associated with CD36 downregulation and upregulation of ATP‐binding cassette transporters A1 and G1 in human monocyte‐derived macrophages. In human aortic smooth muscle cells, neopterin suppressed angiotensin II–induced migration and proliferation via c‐Src/Raf‐1/ERK1/2 downregulation without inducing apoptosis. Exogenous neopterin administration and endogenous neopterin attenuation with its neutralizing antibody for 4 weeks retarded and promoted, respectively, the development of aortic atherosclerotic lesions in apolipoprotein E–deficient mice.ConclusionsOur results indicate that neopterin prevents both vascular inflammation and atherosclerosis and may be induced to counteract the progression of atherosclerotic lesions. Consequently, neopterin could be of use as a novel therapeutic target for atherosclerotic cardiovascular diseases.

Role of long non-coding RNA-RNCR3 in atherosclerosis-related vascular dysfunction.

Atherosclerosis is one of the most common vascular disorders. Endothelial cell (EC) dysfunction and vascular smooth muscle cell (VSMC) proliferation contributes to the development of atherosclerosis. Long non-coding RNAs (lncRNAs) have been implicated in several biological processes and human diseases. Here we show that lncRNA-RNCR3 is expressed in ECs and VSMCs. RNCR3 expression is significantly upregulated in mouse and human aortic atherosclerotic lesions, and cultured ECs and VSMCs upon ox-LDL treatment in vitro. RNCR3 knockdown accelerates the development of atherosclerosis, aggravates hypercholesterolemia and inflammatory factor releases, and decreases EC and VSMC proliferation in vivo. RNCR3 knockdown also reduces the proliferation and migration, and accelerates apoptosis development of EC and VSMC in vitro. RNCR3 acts as a ceRNA, and forms a feedback loop with Kruppel-like factor 2 and miR-185-5p to regulate cell function. This study reveals that RNCR3 has an atheroprotective role in atherosclerosis, and its intervention is a promising strategy for treating atherosclerosis-related vascular dysfunction.

Variability of heteroplasmic mitochondrial DNA mutations in different types of atherosclerotic lesions in human aorta: NGS data

Variability of heteroplasmic mitochondrial DNA mutations in different types of atherosclerotic lesions in human aorta: NGS data

Involvement of TLR2 and TLR4, <i>Chlamydophila pneumoniae</i> and <i>Mycoplasma pneumoniae</i> in adventitial inflammation of aortic atherosclerotic aneurysm

Aortic atherosclerotic aneurysm (AAA) is associated with adventitial inflammation where infection is suggested to have a role. Co-infection with Chlamydophila pneumoniae (Cp) and Mycoplasma pneumoniae (Mp) was linked with coronary plaque rupture, in association with vessel dilatation and adventitial inflammation. Pathogens are recognized by Toll-like receptors (TLRs) development of the inflammatory process. Objective: Here, we studied whether co-infection by Cp and Mp was involved in the increased inflammation present in AAA and if it could be associated with deficient expression of TLRs. We compared human samples of AAA with non-dilated human aortic atherosclerotic lesions, regarding the amount of Cp and Mp antigens, and expression of TLR2 and TLR4. Methods: Two groups of aorta fragments were analyzed: G1 (n = 13) moderate atherosclerosis and G2 (n = 14) AAA samples, through immunohisto-chemistry and in situ hybridization methods. Results: Mp and Cp antigens in intima/medial layer were greater in G2 than G1, with no difference in adventitia. TLR2 and TLR4 were higher in G2 than G1 adventitia fat. There was a correlation between Mp versus TLR2 and of TLR4 in intima/medial layer and in adventitia of G1, but there was a lack of correlation in G2. In Cp adventitia, the correlation in G1 was high with TLR2 but not with TLR4, and in G2 the correlation was positive for both TLRs. Conclusion: This study favors the concept that symbiotic co-infection by Cp and Mp participates in the pathogenesis of AAA. It also emphasizes that adventitial fat is the initial site for colonization of these bacteria that probably reach the tissue through vasa vasorum. An exacerbated immune reaction is not efficient to control the infection that reaches and proliferates in high levels at the medial and intimal layer, contributing to the development of vessel dilatation.

Abstract 553: Expression of TNFalfa and CCL18 is Increased as a Result of Cholesterol Accumulation in Macrophages

Innate immunity plays important role in atherogenesis. Immune reaction in artery wall involves both pro-and anti-inflammatory cytokines. We investigated cytokines’ mRNA expression in uninvolved and atherosclerotic human aortic intima. TNF-α and CCL18 were localized in autopsy aortic samples using immunohistochemistry. Expression of cytokine mRNA was measured by PCR or qPCR in the same samples. Primary culture of blood-derived monocytes/macrophages from healthy donors was used to study TNF-α and CCL18 mRNA expression induced by IFN-gamma and IL-4, respectively. Intracellular lipid accumulation was induced by incubation of cultured cells with atherogenic modified LDL isolated from blood of patients with documented coronary atherosclerosis. Immunohistochemistry demonstrated that the number of cytokine-positive cells (both TNF-α and CCL18) were increased in atherosclerotic lesions as compared with unaffected aortic intima. Cytokines were associated with different cell types including macrophages and non-macrophage cells. Both TNF-α and CCL18 were manly occurred in macrophages. Rice of both cytokines’ mRNA expression measured by PCR was observed in atherosclerotic lesion. In lipid-rich atherosclerotic lesion cytokine expression was the most considerable. Correlation between lipid content in aortic intima and cytokine expression was found. To elucidate the mechanism of elevation of lipid-associated cytokine expression, cell culture study was performed. Cultured monocytes/macrophages were incubated with atherogenic modified LDL of atherosclerotic patients and non-atherogenic LDL from healthy donors. In contrast to non-atherogenic LDL patients’ LDL induced intracellular cholesterol accumulation and increased mRNA expression of both TNF-α and CCL18 in cell culture. Thus, i ntracellular lipid accumulation caused by atherogenic modified LDL from atherosclerotic patients induces overexpression of TNFa and CCL18. This finding can explain the elevation of TNF-α and CCL18 expression in lipid-rich atherosclerotic lesions of human aorta.

Changes of mitochondria in atherosclerosis: Possible determinant in the pathogenesis of the disease

Electron-microscopic analysis of atherosclerotic lesions demonstrated a high variability in the ultrastructural appearance of mitochondria in human aortic atherosclerotic lesions compared with the appearance of mitochondria in the normal parts of the aortic intima. This prompted us to suggest that the structural variations in the appearance of mitochondria might reflect the existence of somatic mutations in the human mitochondrial genome which could be a determinant of atherosclerosis. To test this hypothesis, we have compared the levels of heteroplasmy for several mitochondrial mutations previously proposed to be associated with different types of atherosclerotic lesions. The homogenates of unaffected aortic intimae and lipofibrous plaques of 12 male aortas were compared to reveal the average level of heteroplasmy for A1555G, C3256T, T3336T, G12315A, G14459A, and G15059A mutations of human mitochondrial genome. It has been shown at least four mutations of mitochondrial genome, namely, A1555G in MT-RNR1 gene, C3256T in MT-TL1 gene, G12315A in MT-TL2 gene, and G15059A in MT-CYB gene have significantly higher prevalence and mean value in lipofibrous plaques as compared to non-atherosclerotic intima, and therefore are associated with atherosclerosis. Somatic mutations in the human mitochondrial genome might play a role in the development of atherosclerosis. The mitochondrial mutations observed in our study should encourage further exploration of the concept that mitochondrial DNA heteroplasmy might be used as a biomarker of atherogenesis.

Expression of Retinoic Acid-inducible gene-I (RIG-I) in Macrophages: Possible Involvement of RIG-I in Atherosclerosis

Retinoic acid-inducible gene-I (RIG-I) is one of the genes induced by interferon (IFN)-gamma which plays an important role in atherosclerosis. The aim of this study is to examine if RIG-I is involved in atherosclerosis. The expression of RIG-I in atherosclerotic lesions in human aorta was examined by immunohistochemical analysis. The expression of RIG-I in THP-1 monocytic cell line or human monocyte-derived macrophages was studied by western blot and RT-PCR analyses. Intense immunoreactivity for RIG-I was detected in intimal macrophages in atherosclerotic lesions. IFN-gamma slightly enhanced the RIG-I expression in THP-1 cells. Treatment of the cells with phorbol 12-myristate 13-acetate, which induces the differentiation of the cells into macrophage-like cells, significantly enhanced the IFN-gamma -induced RIG-I expression. IFN-gamma also stimulated the expression of RIG-I in monocyte-derived macrophages. These results suggest that RIG-I may be involved in differentiation and activation of macrophages, playing a role in atherosclerosis.

Evaluation of Differences in Coronary Plaque Mechanical Behavior in Individuals With and Without Type 2 Diabetes Mellitus

Diabetes mellitus is a major risk factor for the development of atherosclerosis.1 Although there has been a significant amount of work examining histological factors which predispose to plaque rupture and subsequent acute coronary syndromes,2 less is known about the role of plaque and vessel biomechanical properties. We have previously shown using intravascular ultrasound (IVUS), that there is a significant change in coronary plaque area between systole and diastole, and this is a major determinant of coronary compliance.3 In the current study we used IVUS to assess coronary plaque characteristics in individuals with and without type 2 diabetes mellitus. All patients scheduled for percutaneous coronary intervention of lesions in the circumflex or left anterior descending (LAD) arteries were considered eligible for inclusion, other than those undergoing emergent revascularization for acute myocardial infarction. Diabetic patients were identified as those who had their diabetes diagnosed in adult life with biochemical confirmation including a fasting glucose >7.0 mmol/L. The study was approved by the Human Ethics Committee of the Alfred Hospital. Collection …

Physiological and pathological roles of a multi-ligand receptor CD36 in atherogenesis; insights from CD36-deficient patients

Oxidized low density lipoprotein (LDL) (Ox-LDL) plays an important role in the pathogenesis of atherosclerosis. Oxidized LDL is taken up by macrophages via scavenger receptors. CD36 is an 88 kDa glycoprotein expressed on platelets, monocyte-macrophages, microvascular endothelial cells, adipose tissue, skeletal muscles and heart. We found patients with CD36 deficiency and identified several mutations in the CD36 gene. We also reported that CD36-deficient macrophages showed a 50% reduction in the binding of Ox-LDL, suggesting that CD36 is one of the major receptors for Ox-LDL. CD36 was expressed on macrophages in the atherosclerotic lesions of human aorta and coronary arteries especially on foamed macrophages. The distribution of CD36 expression was slightly different from that of scavenger receptor class A types I and II. The expression of CD36 on macrophages was up-regulated by Ox-LDL and down-regulated by interferon gamma. Since CD36 is a transporter of long-chain fatty acids (LCFA), CD36-deficient patients showed a defect in the uptake of an LCFA analog, BMIPP, by the heart. Furthermore, the secretion of IL-1beta and TNF-alpha from monocyte-derived macrophages induced by Ox-LDL was markedly reduced and the activation of NF-kappaB was attenuated in CD36-deficient subjects compared with controls, suggesting that CD36-mediated signaling is also impaired in CD36 deficiency. To elucidate the roles of CD36 in vivo, we characterized the clinical profile of CD36-deficient patients. Most of them were accompanied by hyperlipidemia (mainly hypertriglyceridemia), increased remnant lipoproteins and mild elevation of fasting plasma glucose level and blood pressure. Glucose clamp technique revealed mean whole body glucose uptake was reduced in CD36-deficient patients, indicating the presence of insulin resistance. The frequency of CD36 deficiency was higher in patients with coronary heart disease (CHD) than in control subjects. Taken together, CD36 deficiency is accompanied by (1) hyperlipidemia and increased remnant lipoproteins, (2) impaired glucose metabolism based upon insulin resistance, and (3) mild hypertension, and comprises one of the genetic backgrounds of the metabolic syndrome, leading to the development of CHD.

Plaque Neovascularization Is Increased in Ruptured Atherosclerotic Lesions of Human Aorta: Implications for Plaque Vulnerability

Plaque Neovascularization Is Increased in Ruptured Atherosclerotic Lesions of Human Aorta: Implications for Plaque Vulnerability

Matrix metalloproteinase-12 gene expression in human vascular smooth muscle cells.

Matrix metalloproteinases (MMPs) play an important role in smooth muscle cell (SMC) migration and proliferation during vascular remodelling. To investigate the expression of MMP-12 by SMCs, we examined the protein secretion and mRNA expression of MMP-12 by cultured medial SMCs and intimal SMCs derived from human aortic atherosclerotic lesions. To further elucidate the molecular mechanism for MMP-12 expression in SMCs, we determined the sequence requirements for MMP-12 gene transcriptional activity. Cultured medial SMCs and intimal SMCs showed substantial MMP-12 expression at both the protein and mRNA levels. A series of 5'-deletion and site-directed mutants of the human MMP-12 promoter demonstrated that an AP-1 site spanning -81 to -75 bp was critical for the MMP-12 promoter activity in SMCs. An electrophoretic mobility shift assay confirmed the AP-1 binding activity in SMCs and showed that the protein bound to the AP-1 site consisted predominantly of c-Jun, JunD and Fra-1. Two structurally different inhibitors of phosphatidylinositol 3-kinase, wortmannin and LY294002, inhibited MMP-12 transcriptional activity and AP-1 binding. These results indicated the expression of MMP-12 in vascular SMCs and showed that the MMP-12 gene expression was dependent on the AP-1 binding activity. Phosphatidylinositol 3-kinase signalling may be involved in MMP-12 transcriptional activation through AP-1 binding activity.

Cytochrome b558-dependent NAD(P)H oxidase-phox units in smooth muscle and macrophages of atherosclerotic lesions.

Despite studies implicating superoxide anion-producing oxidases in atherosclerosis, their characteristics, expression, and regulation in cells of lesions are poorly understood. We examined the following: (1) whether cytochrome b558-dependent NAD(P)H oxidase-phox peptides are expressed by intimal smooth muscle cells (iSMCs) and macrophages of human aortic atherosclerotic lesions and their regulation and (2) whether cytochrome b558-dependent NAD(P)H oxidase represents a major NAD(P)H oxidase in iSMCs. Using a combination of immunochemical and reverse transcription-polymerase chain reaction procedures, we demonstrate that p22(phox) and gp91(phox) (cytochrome b558) expression in normal intima was restricted to a quarter of the iSMCs. In fatty streaks, a similar fraction of iSMCs expressed cytochrome b558, whereas macrophages also expressed low levels of p47(phox) and p67(phox). In fibrofatty lesions, the majority of iSMCs expressed the cytochrome b558 subunits; p67(phox) was also detected. Macrophages and macrophage-derived foam cells expressed the 4 phox subunits that constitute superoxide-producing cytochrome b558-dependent NAD(P)H oxidase. These were upregulated by transforming growth factor-beta1 and interferon-gamma. Aortic lesions also expressed Thox1 and Nox4, and although their expression also increases with lesion severity, their expression is less frequent than that of gp91(phox). In human aortic fibrofatty lesions, a cytochrome b558-dependent NAD(P)H oxidase appears to be a major iSMC and macrophage oxidase whose expression is upregulated by cytokines.

Cholesterol Sulfate

Cholesterol 3-sulfate is present on a variety of cells and in human LDL, and it has been found in atherosclerotic lesions of human aorta. Its precise biological role has not yet been described. In this study, we investigated the interaction of platelets with cholesterol sulfate. Platelets adhered in a concentration-dependent and saturable manner to cholesterol sulfate but did not adhere to cholesterol, cholesterol acetate, estrone sulfate, or dehydroepiandrosterone sulfate, suggesting that the specificity of this interaction is determined not only by the cholesterol moiety but also by the sulfate group. This adhesion did not increase after platelet activation, and it was not cation-dependent. Soluble cholesterol sulfate inhibited adhesion in a concentration-dependent manner. However, antibodies against glycoprotein Ib, glycoprotein IIb/IIIa, CD36, P-selectin, von Willebrand factor, or thrombospondin had no significant effect on platelet adhesion to cholesterol sulfate. Perfusion of whole blood in a parallel-plate flow chamber resulted in the rapid and progressive adhesion of platelets to cholesterol sulfate but not to cholesterol acetate or estrone sulfate. Cholesterol sulfate supports platelet adhesion and may be one of the factors determining the prothrombotic potential of atherosclerotic lesions.

Gp91(phox) and p22(phox) expression is highly upregulated in endothelium, smooth muscle cells and macrophages of lipid-rich human aortic atherosclerotic lesions

gp91(phox) and p22(phox) expression is highly upregulated in endothelium, smooth muscle cells and macrophages of lipid-rich human aortic atherosclerotic lesions

Coexpression of cyclooxygenase-2 and matrix metalloproteinases in human aortic atherosclerotic lesions.

Inflammation appears to have a major role in the development of atherosclerosis. Cyclooxygenase-2 (COX-2) is involved in the inflammatory response via the generation of prostanoids that, in turn, are involved in the production of matrix metalloproteinases (MMPs). This study aimed to investigate atherosclerosis in human aortas for in situ tissue distribution of COX-2, MMPs including MMP-9 and membrane type 1 MMP (MT1-MMP), and tissue inhibitor of metalloproteinase-2 (TIMP-2). Immunohistochemical studies were performed on atherosclerotic lesions of aortas from patients with aortic aneurysms (n = 4) and dissections (n = 3) by using antibodies to COX-2, MMP-9, MT1-MMP, and TIMP-2. Control tissues were obtained from traumatically dissected aortas (n = 2). All specimens from diseased aortas had atherosclerotic lesions ranging from fatty streak to atheromatous plaques. In control, there was no expression of COX-2, MMP-9, and MT1-MMP in all aortic layers. Immunoreactivity for COX-2 was predominantly noted in macrophages and smooth muscle cells (SMCs) of the intima including atherosclerotic plaque itself and the medial layer of the plaque base, as well as in SMCs and endothelial lining of the vasa vasorum in the adventitia. Immunoreactivity for MMP-9 and MT1-MMP was found in the same distribution as that of COX-2. Additionally, the expression of TIMP-2 increased in relation to MMP-9 expression. This study demonstrates that COX-2 is coexpressed with MMP-9 and MT1-MMP, not only by macrophages and SMCs in atherosclerotic lesions, but also in endothelial lining of the vasa vasorum of human aortas. Thus, vascular inflammatory reactions may influence extracellular matrix remodeling by coactivation of MMPs in the development of atherosclerosis and, in turn, the progression of disease.

Adrenomedullin in monocytes and macrophages: possible involvement of macrophage-derived adrenomedullin in atherogenesis

Macrophages secrete a variety of growth factors, cytokines and vasoactive peptides, which are related to the progression of atherosclerosis. Adrenomedullin (ADM) is a potent vasodilator peptide and inhibits proliferation and migration of vascular smooth muscle cells. In this study, we investigated the production and secretion of ADM by monocytes and macrophages by Northern blot analysis, RIA and immunocytochemistry. Northern blot analysis showed that ADM mRNA was expressed in human monocytes obtained from peripheral blood and monocyte-derived macrophages. The expression level of ADM mRNA in monocyte-derived macrophages was about five times higher than that in monocytes. Treatment with lipopolysaccharide (100 ng/ml) for 24 h increased ADM mRNA expression levels in both monocytes and monocyte-derived macrophages. The levels of immunoreactive ADM in the media of monocyte-derived macrophages were about three times higher than that of monocytes (0. 718+/-0.046 fmol/24 h/10(5) cells, n=8 compared with 0.259+/-0.018 fmol/24 h/10(5) cells, n=8; mean+/-S.E.M., P<0.01). The secretion was also increased by treatment with lipopolysaccharide. Immunocytochemistry showed positive ADM immunostaining in macrophages in atherosclerotic lesions of human aorta obtained at autopsy. ADM secreted from activated macrophages may play an inhibitory role in atherogenesis.

Adrenomedullin in monocytes and macrophages: possible involvement of macrophage-derived adrenomedullin in atherogenesis

Macrophages secrete a variety of growth factors, cytokines and vasoactive peptides, which are related to the progression of atherosclerosis. Adrenomedullin (ADM) is a potent vasodilator peptide and inhibits proliferation and migration of vascular smooth muscle cells. In this study, we investigated the production and secretion of ADM by monocytes and macrophages by Northern blot analysis, RIA and immunocytochemistry. Northern blot analysis showed that ADM mRNA was expressed in human monocytes obtained from peripheral blood and monocyte-derived macrophages. The expression level of ADM mRNA in monocyte-derived macrophages was about five times higher than that in monocytes. Treatment with lipopolysaccharide (100 ng/ml) for 24 h increased ADM mRNA expression levels in both monocytes and monocyte-derived macrophages. The levels of immunoreactive ADM in the media of monocyte-derived macrophages were about three times higher than that of monocytes (0. 718+/-0.046 fmol/24 h/10(5) cells, n=8 compared with 0.259+/-0.018 fmol/24 h/10(5) cells, n=8; mean+/-S.E.M., P<0.01). The secretion was also increased by treatment with lipopolysaccharide. Immunocytochemistry showed positive ADM immunostaining in macrophages in atherosclerotic lesions of human aorta obtained at autopsy. ADM secreted from activated macrophages may play an inhibitory role in atherogenesis.

Expression of human scavenger receptor class B type I in cultured human monocyte-derived macrophages and atherosclerotic lesions.

The scavenger receptor class B type I (SR-BI) and its human homologue CLA-1 (CD36 and LIMPII Analogous-1) have recently been identified to bind HDL and mediate the selective uptake of HDL lipids. Tissue distribution of both murine and human receptors is quite similar, in that they are expressed abundantly in liver and steroidogenic tissues. However, expression and function of the human SR-BI (hSR-BI), in the periphery of reverse cholesterol transport such as macrophages, are still unclear. In the present study, we have raised two different kinds of anti-hSR-BI polypeptide antibodies (Abs): one against the extracellular domain and the other against the intracellular domain. We have investigated the expression of hSR-BI mRNA and immunoreactive mass in freshly isolated cultured human monocyte-derived macrophages (hMphi) and in atherosclerotic lesions. Contrary to the earlier report, hSR-BI mRNA was expressed in cultured hMphi and markedly upregulated with differentiation, determined by Northern blot and reverse transcriptase-based polymerase chain reaction analyses. The mRNA expression pattern during differentiation of hMphi was very similar to those of SR class A and another member of SR class B, CD36. Protein expression was confirmed by Western blot analyses with the above Abs to show a major 83-kDa band. Modified lipoproteins such as oxidized LDL and acetylated LDL induced a 5-fold increase in mRNA and protein expression of hSR-BI. Confocal immunofluorescence microscopy demonstrated that hSR-BI immunoreactive mass was detectable as a heterogeneous, punctate staining pattern. Furthermore, immunohistochemical analysis showed that immunoreactive mass of hSR-BI was detected in foam cells in human aortic atherosclerotic lesions and that there was no significant difference of staining patterns between the two Abs. This study clearly demonstrates that hSR-BI is expressed in the lipid-laden macrophages in human atherosclerotic lesions, suggesting that it is very important to know its function and regulation in hMphi to understand the biological utility of this molecule.