Naomi Sakashita

Multifunctional roles of macrophages in the development and progression of atherosclerosis in humans and experimental animals

 In atherosclerosis, macrophages are important for intracellular lipid accumulation and foam cell formation. Monocytes respond to chemotactic factors, cytokines, and macrophage growth factors produced by vascular endothelial cells, smooth muscle cells, and infiltrated cells, by migrating from peripheral blood into the arterial intima and differentiating into macrophages in atherosclerotic lesions. Although various chemotactic factors are known to induce monocyte migration, monocyte chemoattractant protein-1 is the most important and powerful inducer of migration into atherosclerotic lesions. Macrophage colony-stimulating factor is crucial for monocyte/macrophage differentiation and proliferation, and for the survival of macrophages in these lesions. A minor population of macrophages can proliferate in the atherosclerotic lesions themselves, particularly in the early stage. The macrophages express a variety of receptors, particularly scavenger receptors, and take up modified lipoproteins, including oxidized low-density lipoprotein, β-very-low-density lipoprotein, and/or enzymatically degraded low-density lipoprotein. These cells accumulate cholesterol esters in the cytoplasm, which leads to foam cell formation in lesion development. Among various scavenger receptors, class A type I and type II macrophage scavenger receptors (MSR-A I,II) play the most important role in the uptake of oxidized low-density lipoprotein by macrophages. In addition, macrophages and macrophage-derived foam cells produce ceroid and advanced glycation end-products (AGEs) and accumulate these substances in their cytoplasm. Extracellularly generated AGEs are taken up by macrophages via receptors for AGEs, including MSR-AI,II. Most foam cells die in loco because of apoptosis, and some foam cells escape from the lesions into peripheral blood. Macrophages also play multifaceted roles in inducing plaque rupture, blood coagulation, and fibrinolysis via the production of various enzymes, activators, inhibitors, and bioactive mediators. During the development of atherosclerosis, macrophages interact with vascular endothelial cells, medial smooth muscle cells, and infiltrated inflammatory cells, particularly T cells and dendritic cells. This review, based on data accumulated in studies of atherosclerosis in humans and experimental animals, focuses on the multifunctional roles of macrophages in the pathogenesis and progression of atherosclerosis.

Expression of ACAT-1 Protein in Human Atherosclerotic Lesions and Cultured Human Monocytes-Macrophages

The acyl coenzyme A:cholesterol acyltransferase (ACAT) gene was first cloned in 1993 (Chang et al, J Biol Chem. 1993;268:20747-20755; designated ACAT-1). Using affinity-purified antibodies raised against the N-terminal portion of human ACAT-1 protein, we performed immunohistochemical localization studies and showed that the ACAT-1 protein was highly expressed in atherosclerotic lesions of the human aorta. We also performed cell-specific localization studies using double immunostaining and showed that ACAT-1 was predominantly expressed in macrophages but not in smooth muscle cells. We then used a cell culture system in vitro to monitor the ACAT-1 expression in differentiating monocytes-macrophages. The ACAT-1 protein content increased by up to 10-fold when monocytes spontaneously differentiated into macrophages. This increase occurred within the first 2 days of culturing the monocytes and reached a plateau level within 4 days of culturing, indicating that the increase in ACAT-1 protein content is an early event during the monocyte differentiation process. The ACAT-1 protein expressed in the differentiating monocytes-macrophages was shown to be active by enzyme assay in vitro. The high levels of ACAT-1 present in macrophages maintained in culture can explain the high ACAT-1 contents found in atherosclerotic lesions. Our results thus support the idea that ACAT-1 plays an important role in differentiating monocytes and in forming macrophage foam cells during the development of human atherosclerosis.

AM-3K, an Anti-macrophage Antibody, Recognizes CD163, a Molecule Associated with an Anti-inflammatory Macrophage Phenotype

CD163 is a member of the scavenger receptor cysteine-rich superfamily restricted to the monocyte/macrophage lineage and is thought to be a useful marker for anti-inflammatory or alternatively activated macrophages. In this study we used mass spectrometric analysis to determine that the antigen recognized by the antibody AM-3K, which we previously generated as a tissue macrophage-specific monoclonal antibody, was CD163. An anti-inflammatory subtype of macrophages stimulated by dexamethasone or interleukin-10 showed strong reactivity for AM-3K and increased expression of CD163 mRNA. Immunohistochemical staining of routinely processed pathological specimens revealed that AM-3K recognized a specialized subpopulation of macrophages. In granulomatous diseases such as tuberculosis, sarcoidosis, or foreign body reactions, tissue macrophages around granulomas, but not component cells of the granulomas such as epithelioid cells and multinucleated giant cells, showed positive staining for AM-3K. In atherosclerotic lesions, scattered macrophages in diffuse intimal lesions were strongly positive for AM-3K, whereas foamy macrophages in atheromatous plaques demonstrated only weak staining. We therefore suggest that, in routine pathological specimens, AM-3K is a useful marker for anti-inflammatory macrophages because these cells can be distinguished from inflammatory or classically activated macrophages. Because AM-3K cross-reacts with macrophage subpopulations in different animal species including rats, guinea pigs, rabbits, cats, dogs, goats, pigs, bovine species, horses, monkeys, and cetaceans, it will have wide application for detection of CD163 in various animals.

Differentiation of mouse and human embryonic stem cells into hepatic lineages

We recently reported a novel method to induce embryonic stem (ES) cells differentiate into an endodermal fate, especially pancreatic, using a supporting cell line. Here we describe the modified culture condition with the addition and withdrawal of secreted growth factors could induce ES cells to selectively differentiate into a hepatic fate efficiently. The signaling of BMP and FGF that have been implicated in hepatic differentiation during normal embryonic development are shown to play pivotal roles in generating hepatic cells from the definitive endoderm derived from ES cells. Moreover, the expression of AFP, Albumin or a biliary molecular marker appeared sequentially thus suggested the differentiation of ES cells recapitulated normal developmental processes of liver. The ES cell‐derived differentiated cells showed evidence of glycogen storage, secreted Albumin, exhibited drug metabolism activities and expressed a set of cytochrome or drug conjugate enzymes, drug transporters specifically expressed in mature hepatocytes. With the same procedure, human ES cells also gave rise to cells with mature hepatocytes’ characteristics. In conclusion, this novel procedure for hepatic differentiation will be useful for elucidation of molecular mechanisms of hepatic fate decision at gut regionalization, and could represent an attractive approach for a surrogate cell source for pharmaceutical studies such as toxicology.

Targeted Deletion of Class A Macrophage Scavenger Receptor Increases the Risk of Cardiac Rupture After Experimental Myocardial Infarction

Background— Class A macrophage scavenger receptor (SR-A) is a macrophage-restricted multifunctional molecule that optimizes the inflammatory response by modulation of the activity of inflammatory cytokines. This study was conducted with SR-A–deficient (SR-A−/−) mice to evaluate the relationship between SR-A and cardiac remodeling after myocardial infarction. Methods and Results— Experimental myocardial infarction (MI) was produced by ligation of the left coronary artery in SR-A−/− and wild-type (WT) male mice. The number of mice that died within 4 weeks after MI was significantly greater in SR-A−/− mice than in WT mice (P=0.03). Importantly, death caused by cardiac rupture within 1 week after MI was 31% (17 of 54 mice) in SR-A−/− mice and 12% (6 of 51 mice) in WT mice (P=0.01). In situ zymography demonstrated augmented gelatinolytic activity in the infarcted myocardium in SR-A−/− mice compared with WT mice. Real-time reverse transcription–polymerase chain reaction at day 3 after MI showed that the expression of matrix metalloproteinase-9 mRNA increased significantly in the infarcted myocardium in SR-A−/− mice compared with WT mice. Furthermore, SR-A−/− mice showed augmented expression of tumor necrosis factor-α and reduction of interleukin-10 in the infarcted myocardium at day 3 after MI. In vitro experiments also demonstrated increased tumor necrosis factor-α and decreased interleukin-10 expression in activated SR-A−/− macrophages. Conclusions— The present findings suggest that SR-A deficiency might cause impairment of infarct remodeling that results in cardiac rupture via insufficient production of interleukin-10 and enhanced expression of tumor necrosis factor-α and of matrix metalloproteinase-9. SR-A might contribute to the prevention of cardiac rupture after MI.

Expression of von Hippel–Lindau Protein in Normal and Pathological Human Tissues

To examine the localization of von Hippel–Lindau (VHL) protein in human tissues, we produced four novel monoclonal antibodies against human VHL protein. Western blot analysis revealed that two of these antibodies recognized the epitope in amino acid sequence 60–89 of the VHL protein and the others recognized sequences 54–60 and 189–213. In a wild-type VHL gene-transfected cell line, immunocytochemistry and immunoelectron microscopy demonstrated the intracytoplasmic localization of VHL protein, particularly in mitotic cells. In normal human tissues, VHL protein was detected immunohistochemically in epithelial cells covering the body surface and the alimentary, respiratory, and genitourinary tracts; in secretory epithelial cells of exocrine and endocrine organs; in parenchymal cells of visceral organs; in cardiomyocytes; in neurons in nervous tissue; in lymphocytes in lymphoid tissue; and in macrophages. In pathological specimens, VHL protein was expressed in VHL-related tumor, as well as in endothelial cells, fibroblasts, and pericytes, all of which are involved in active angiogenesis. These findings suggest that these monoclonal antibodies can be useful for various immunological assays and that the VHL protein plays fundamental roles in physiological and pathological situations, especially in neovascularization.

Induction of macrophage scavenger receptor MARCO in nonalcoholic steatohepatitis indicates possible involvement of endotoxin in its pathogenic process

Nonalcoholic steatohepatitis (NASH) is one of the life‐threatening hepatic diseases; however, its pathogenesis is still unknown. To evaluate the causative role of hyperlipidaemia and high‐fat diet, we compared C57BL/6 mice with inherited hyperlipidaemic model mice (LDLR–/–mice and ApoE–/– mice) fed a normal or a high‐fat diet. LDLR–/– and ApoE–/– mice fed the normal diet showed significantly higher serum cholesterol level than that of C57BL/6 mice fed the high‐fat diet. These mice, however, have shown neither significant elevation of serum alanine transaminase (ALT) level nor histopathologic features of steatohepatitis. High‐fat diet groups of all three strains showed histopathological characteristics of steatohepatitis with elevated serum ALT levels and high expression of macrophage scavenger receptor MARCO mRNA in the liver. Semiquantitative endotoxin analysis showed an elevated serum endotoxin level in the portal vein but not in the vena cava in ApoE–/– mice fed the high‐fat diet. These results indicate that long‐term feeding of a high‐fat diet induces NASH, whereas hyperlipidaemia alone is not enough to induce NASH. Liver‐restricted induction of MARCO in mice with high‐fat diet and portal endotoxaemia in ApoE–/– mice fed the high‐fat diet suggest the possible involvement of endotoxin in the pathogenesis of NASH.

Acyl-Coenzyme A:Cholesterol Acyltransferase 2 (ACAT2) Is Induced in Monocyte-Derived Macrophages: In Vivo and In Vitro Studies

To test the possibility that acyl-coenzyme A:cholesterol acyltransferase 2 (ACAT2) may be expressed in human macrophages under pathologic conditions, we employed specific anti-ACAT2 antibodies and found clear ACAT2 signals in lipid-laden as well as lipid-free macrophages under various disease conditions, including atherosclerosis. However, no ACAT2 signal was detectable in macrophages under normal physiologic conditions. Using cultured human macrophages derived from blood-borne monocytes, immunoblot and RT-PCR analyses demonstrated that immature macrophages expressed only ACAT1, but the fully differentiated macrophages expressed both ACAT1 and ACAT2. Furthermore, RT-PCR clearly revealed the presence of both ACAT1 and ACAT2 mRNAs in human atherosclerotic aorta. Double immunohistochemical staining indicated that in human atherosclerotic aorta, all macrophages expressed ACAT1, while approximately 70% to 80% of macrophages also expressed ACAT2. In congenital hyperlipidemic mice, immunohistochemistry and RT-PCR demonstrated that ACAT2 was also present in lipid-laden cells of the atheromatous plaques. Our results suggest that in atherosclerotic plaque, the ability of macrophage foam cell transformation may be augmented by the dual expressions of ACAT1 and ACAT2. Additional immunoblot and RT-PCR experiments showed that the ACAT2 signal was clearly detectable in thioglycollate-elicited exudate mouse macrophages but not in peritoneal resident macrophages. We conclude that under various pathologic conditions, fully differentiated macrophages express ACAT2 in addition to ACAT1.

Pulmonary tumor thrombotic microangiopathy resulting from metastatic signet ring cell carcinoma of the stomach.

Pulmonary tumor thrombotic microangiopathy is an unusual malignancy‐related respiratory complication characterized by multiple microthrombi and intimal myofibroblast proliferation. Its clinical manifestation is subacute respiratory failure with pulmonary hypertension. Herein is reported a case of pulmonary tumor thrombotic microangiopathy associated with gastric signet ring cell carcinoma. A 51‐year‐old woman with gastric cancer died of subacute respiratory failure. Autopsy showed gastric signet ring cell carcinoma with diffuse metastasis of pulmonary lymphatics and pleurae; every organ examined lacked a space‐occupying tumor mass. Histologically, proliferated intimal myofibroblasts obliterated most of the pulmonary vascular lumen, and a few stenosed vascular lumina contained cancer cells. In addition, pulmonary vasculature associated with intimal proliferation contained microthrombi. Most cancer cells in the stomach and pulmonary lymphatics were typical signet ring cells, whereas those in vascular lesions were cells of poorly differentiated adenocarcinoma without mucous production. Consistent with a previous report, the latter expressed vascular endothelial growth factor (VEGF) and tissue factor (TF). The proliferated intimal myofibroblasts also expressed type 2A serotonin receptor (5‐HT2A). These findings suggest that local expression of VEGF, TF, and 5‐HT2A may be linked to the pathogenesis of this unusual pulmonary complication.

c-Ret–mediated hearing loss in mice with Hirschsprung disease

A significantly increased risk for dominant sensorineural deafness in patients who have Hirschsprung disease (HSCR) caused by endothelin receptor type B and SOX10 has been reported. Despite the fact that c-RET is the most frequent causal gene of HSCR, it has not been determined whether impairments of c-Ret and c-RET cause congenital deafness in mice and humans. Here, we show that impaired phosphorylation of c-Ret at tyrosine 1062 causes HSCR-linked syndromic congenital deafness in c-Ret knockin (KI) mice. The deafness involves neurodegeneration of spiral ganglion neurons (SGNs) with not only impaired phosphorylation of Akt and NF-κB but decreased expression of calbindin D28k in inner ears. The congenital deafness involving neurodegeneration of SGNs in c-Ret KI mice was rescued by introducing constitutively activated RET. Taken together with our results for three patients with congenital deafness with c-RET–mediated severe HSCR, our results indicate that c-Ret and c-RET are a deafness-related molecule in mice and humans.