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Intercellular adhesion molecule-1 and CD36 synergize to mediate adherence of Plasmodium falciparum-infected erythrocytes to cultured human microvascular endothelial cells.

We have compared the adhesion of Plasmodium falciparum-infected erythrocytes to human dermal microvascular endothelial cells (HDMEC) and human umbilical vein endothelial cells (HUVEC) and have assessed the relative roles of the receptors CD36 and intercellular adhesion molecule-1 (ICAM-1). HUVEC (a cell line that expresses high levels of ICAM-1 but no CD36) mediate low levels of adhesion, whereas HDMEC (which constitutively express CD36) mediate high levels of adhesion even before ICAM-1 induction ICAM-1 expression leads to yet greater levels of adhesion, which are inhibited both by anti-ICAM-1 and CD36 mAbs, despite no increase in the expression of CD36. The results indicate the presence of a substantial population of infected cells that require the presence of both receptors to establish adhesion. Synergy between these receptors could be demonstrated using a number of parasite lines, but it could not be predicted from the binding of these same parasite lines to purified ICAM-1 and CD36. This phenomenon could not be reproduced using either purified receptors presented on plastic, or formalin-fixed HDMEC, suggesting that receptor mobility is important. This is the first study to demonstrate receptor synergy in malaria cytoadherence to human endothelial cells, a phenomenon necessary for parasite survival and associated with disease severity.

Animals↗

Increased CD36 protein as a response to defective insulin signaling in macrophages.

Accelerated atherosclerosis is a major cause of morbidity and death in insulin-resistant states such as obesity and the metabolic syndrome, but the underlying mechanisms are poorly understood. We show that macrophages from obese (ob/ob) mice have increased binding and uptake of oxidized LDL, in part due to a post-transcriptional increase in CD36 protein. Macrophages from ob/ob mice are also insulin resistant, as shown by reduced expression and signaling of insulin receptors. Three lines of evidence indicate that the increase in CD36 is caused by defective insulin signaling: (a) Treatment of wild-type macrophages with LY294002, an inhibitor of insulin signaling via PI3K, results in an increase in CD36; (b) insulin receptor knockout macrophages show a post-transcriptional increase in CD36 protein; and (c) administration of thiazolidinediones to intact ob/ob mice and ob/ob, LDL receptor-deficient mice results in a reversal of macrophage insulin receptor defects and decreases CD36 protein. The last finding contrasts with the increase in CD36 that results from treatment of macrophages with these drugs ex vivo. The results suggest that defective macrophage insulin signaling predisposes to foam cell formation and atherosclerosis in insulin-resistant states and that this is reversed in vivo by treatment with PPAR-gamma activators.

Animals↗

CD36 involvement in orosensory detection of dietary lipids, spontaneous fat preference, and digestive secretions.

Rats and mice exhibit a spontaneous attraction for lipids. Such a behavior raises the possibility that an orosensory system is responsible for the detection of dietary lipids. The fatty acid transporter CD36 appears to be a plausible candidate for this function since it has a high affinity for long-chain fatty acids (LCFAs) and is found in lingual papillae in the rat. To explore this hypothesis further, experiments were conducted in rats and in wild-type and CD36-null mice. In mice, RT-PCR experiments with primers specific for candidate lipid-binding proteins revealed that only CD36 expression was restricted to lingual papillae although absent from the palatal papillae. Immunostaining studies showed a distribution of CD36 along the apical side of circumvallate taste bud cells. CD36 gene inactivation fully abolished the preference for LCFA-enriched solutions and solid diet observed in wild-type mice. Furthermore, in rats and wild-type mice with an esophageal ligation, deposition of unsaturated LCFAs onto the tongue led to a rapid and sustained rise in flux and protein content of pancreatobiliary secretions. These findings demonstrate that CD36 is involved in oral LCFA detection and raise the possibility that an alteration in the lingual fat perception may be linked to feeding dysregulation.

Animals↗

Genetics of Cd36 and the clustering of multiple cardiovascular risk factors in spontaneous hypertension.

Disorders of carbohydrate and lipid metabolism have been reported to cluster in patients with essential hypertension and in spontaneously hypertensive rats (SHRs). A deletion in the Cd36 gene on chromosome 4 has recently been implicated in defective carbohydrate and lipid metabolism in isolated adipocytes from SHRs. However, the role of Cd36 and chromosome 4 in the control of blood pressure and systemic cardiovascular risk factors in SHRs is unknown. In the SHR. BN-Il6/Npy congenic strain, we have found that transfer of a segment of chromosome 4 (including Cd36) from the Brown Norway (BN) rat onto the SHR background induces reductions in blood pressure and ameliorates dietary-induced glucose intolerance, hyperinsulinemia, and hypertriglyceridemia. These results demonstrate that a single chromosome region can influence a broad spectrum of cardiovascular risk factors involved in the hypertension metabolic syndrome. However, analysis of Cd36 genotypes in the SHR and stroke-prone SHR strains indicates that the deletion variant of Cd36 was not critical to the initial selection for hypertension in the SHR model. Thus, the ability of chromosome 4 to influence multiple cardiovascular risk factors, including hypertension, may depend on linkage of Cd36 to other genes trapped within the differential segment of the SHR. BN-Il6/Npy strain.

Animals↗

Targeted disruption of the class B scavenger receptor CD36 protects against atherosclerotic lesion development in mice.

Macrophage scavenger receptors have been implicated as key players in the pathogenesis of atherosclerosis. To assess the role of the class B scavenger receptor CD36 in atherogenesis, we crossed a CD36-null strain with the atherogenic apo E-null strain and quantified lesion development. There was a 76.5% decrease in aortic tree lesion area (Western diet) and a 45% decrease in aortic sinus lesion area (normal chow) in the CD36-apo E double-null mice when compared with controls, despite alterations in lipoprotein profiles that often correlate with increased atherogenicity. Macrophages derived from CD36-apo E double-null mice bound and internalized more than 60% less copper-oxidized LDL and LDL modified by monocyte-generated reactive nitrogen species. A similar inhibition of in vitro lipid accumulation and foam cell formation after exposure to these ligands was seen. These results support a major role for CD36 in atherosclerotic lesion development in vivo and suggest that blockade of CD36 can be protective even in more extreme proatherogenic circumstances.

Animals↗

Glycolaldehyde-modified bovine serum albumin downregulates leptin expression in mouse adipocytes via a CD36-mediated pathway.

Previous observations by us have clarified that proteins modified by advanced glycation end products (AGEs) are recognized as effective ligands by CD36-overexpressed CHO cells and undergo receptor-mediated endocytosis. CD36, a member of the class B scavenger receptor family, also acts as a fatty acid transporter in adipocytes. Oxidized low-density lipoprotein (Ox-LDL), a ligand for CD36, is known to upregulate CD36 by activating peroxisome proliferator-activated receptor gamma (PPAR-gamma) in macrophages, whereas PPAR-gamma ligands such as troglitazone and 15-deoxy-delta12,14-prostaglandin J2 decrease leptin secretion from adipocytes. The purpose of this study was to examine effects of AGE ligands on leptin expression in adipocytes. Glycolaldehyde-modified bovine serum albumin (GA-BSA) decreased leptin expression at both the protein and mRNA levels in 3T3-L1 adipocytes and mouse epididymal adipocytes. The binding to and subsequent endocytic degradation of GA-BSA by 3T3-L1 adipocytes were effectively inhibited by a neutralizing anti-CD36 antibody. These results indicate that the ligand interaction of GA-BSA with CD36 leads to downregulation of leptin expression in 3T3-L1 adipocytes, suggesting that AGE-induced leptin downregulation is linked to reduction of the insulin sensitivity in metabolic syndrome.

3T3 Cells↗

Hypertrophic cardiomyopathy with type I CD36 deficiency.

CD36 is a multifunctional membrane-type receptor glycoprotein that reacts with oxidized low-density lipoprotein and long-chain fatty acid (LCFA). A patient presented with hereditary hypertrophic cardiomyopathy (HCM) and type I CD36 deficiency (neither platelets nor monocytes expressed CD36) but showed no myocardial LCFA accumulation. CD36 was expressed in the capillary endothelial cells of the cardiac muscle of a control subject, while the patient's myocardial capillary endothelial cells were completely CD36-negative. These results suggest that type I CD36 deficiency is closely related to hereditary HCM and lack of myocardial LCFA accumulation.

CD36 Antigens↗

Ex vivo and in vitro impairment of CD36 expression and tumor necrosis factor-alpha production in human monocytes in response to Plasmodium falciparum-parasitized erythrocytes.

Severe malaria is associated with the failure of host defenses to control parasite replication, with the excessive secretion of proinflammatory cytokines such as tumor necrosis factor-alpha (TNF-alpha), and with the sequestration of parasitized erythrocytes (PEs) in the microcirculation of vital organs. The scavenger receptor CD36, known as a major sequestration receptor, has also been identified as an important factor in mediating nonopsonic phagocytosis of PEs by monocytes and macrophages. The specific consequence of this phagocytosis is a decrease in parasite-induced TNF-alpha secretion. We evaluated the variations in CD36 level and in lipopolysaccharide (LPS)-induced TNF-alpha production in monocytes from Plasmodium falciparum-infected patients and in vitro in the presence of PEs. Both the monocytes from infected patients and from in vitro culture showed a decrease of CD36 expression and a reduced production of TNF-alpha induced by LPS. Using incubation assays with no contact between monocytes and PEs, or in the presence of a soluble supernatant obtained from the incubation of monocytes and PEs, this study shows that decreased CD36 expression was posttranscriptional and not directly related to PEs phagocytosis. In addition, these culture models suggest that the reduced capacity of TNF-alpha production occurred in 2 phases. The early phase (24 hr) appeared to be CD36 dependent and the second phase (48 hr) was due to a soluble factor produced by PEs. These observations suggest that the control of the TNF-alpha production in malaria by monocytes was not entirely dependent on the phagocytosis of PEs by CD36 and that soluble factors produced by PEs could play a role in this process.

Animals↗

Sulfated glycoconjugates enhance CD36-dependent adhesion of Plasmodium falciparum-infected erythrocytes to human microvascular endothelial cells.

A novel adhesive pathway that enhances the adhesion of Plasmodium falciparum-infected erythrocytes (IEs) to endothelial cells has been identified. The sulfated glycoconjugates heparin, fucoidan, dextran sulfate 5000, and dextran sulfate 500 000 caused a dramatic increase in adhesion of IEs to human dermal microvascular endothelial cells. The same sulfated glycoconjugates had little effect on IE adhesion to human umbilical vein endothelial cells, a CD36-negative cell line. The effect was abolished by a monoclonal antibody directed against CD36, suggesting that enhanced adhesion to endothelium is dependent on CD36. No effect was observed on adhesion to purified platelet CD36 cells immobilized on plastic. The same sulfated glycoconjugates enhanced adhesion of infected erythrocytes to COS cells transfected with CD36, and this was inhibited by the CD36 monoclonal antibody. These findings demonstrate a role for sulfated glycoconjugates in endothelial adherence that may be important in determining the location and magnitude of sequestration through endogenous carbohydrates. In addition, they highlight possible difficulties that may be encountered from the proposed use of sulfated glycoconjugates as antiadhesive agents in patients with severe malaria.

Animals↗

Phenotype-genotype correlation in CD36 deficiency types I and II.

CD36 deficiency was studied with attention to the phenotype-genotype relationship. The diagnosis of CD36 deficiency was made when CD36 was negative on platelets (type II) or on both platelets and monocytes (type I). Among 827 apparently healthy Japanese volunteers, the type I and II deficiencies were found in 8 (1.0%) and 48 (5.8%), respectively. The T for C substitution at nt478 for Pro90Ser and the insertion of A at nt 1159 constituted the major causes of type I and II deficiencies. The dinucleotide deletion at nt539 had a minor role. In two family studies, we found a previously unreported polymorphic site in the 5'-proximal flanking region and the 3'-untranslated region. Including these new polymorphisms, DNA sequence other than the three known mutations affecting CD36 expression was not observed in the CD36 gene, calling into question the previous hypothesis that a platelet-specific silent allele exists near or at the CD36 gene.

Alleles↗

Metabolic changes in human CD36 deficiency displayed by glucose loading.

Previous in vitro studies have shown that CD36 participates in cellular fatty acid (FA) uptake. In vivo evidence for a physiologic role of CD36 in this process is poor and mostly obtained in animals. To examine the metabolic role of human CD36, we performed a glucose loading test for normals (n = 16) and subjects with CD36 deficiency, both Type I (n = 5) and Type II (n = 16). After 30 min, FA levels had fallen by 60.1% in normals but by only 31.7% in Type II deficiency (P <0.01 vs. normals) and 16.5% in Type I deficiency which remained significantly higher than the other two groups out to 2 h. Further, changes in triglyceride and glucose metabolism were observed in the both types of CD36 deficiency. Impaired fast FA clearance by muscle and consequently increased hepatic FA uptake seem to underlie these changes. We conclude that human CD36 deficiency causes systemic metabolic changes.

Adult↗

Intestinal lipid absorption is not affected in CD36 deficient mice.

Increasing evidence has implicated the membrane protein CD36 (or fatty acid translocase, FAT) to be involved in high affinity fatty acid uptake. CD36 is expressed in tissues active in fatty acid metabolism, like adipose tissue and skeletal and cardiac muscle, but also in intestine. CD36 is localized in the intestine mainly in the jejunal villi, where it is confined to enterocyte apical membrane. The aim was to determine the role of CD36 in intestinal lipid absorption. Lipid absorption was determined by administering 3H-labeled triolein and 14C-labeled palmitic acid as an olive oil bolus by intragastric gavage and determine appearance of 3H and 14C label in plasma, after blocking lipolysis by i.v. injections of Triton WR 1339. Surprisingly, no differences in plasma appearance of 3H-label or 14C-label were observed in CD36(-/-) mice compared to wild type controls. These results suggest that CD36 does not play a role in intestinal lipid absorption after an acute lipid load.

Animals↗

Involvement of CD36 on erythrocytes as a rosetting receptor for Plasmodium falciparum-infected erythrocytes.

Plasmodium falciparum-infected erythrocytes (parasitized red blood cells [PRBCs]) can adhere to uninfected erythrocytes (RBCs) to form rosettes, and adhere to the endothelial cell (EC) surface antigen CD36. These adherence phenomena have previously been considered quite different. We show that anti-CD36 monoclonal antibodies (MoAbs) reverse rosetting of PRBCs from both a culture-adapted line (Malayan Camp [MC] strain) and a natural isolate, GAM425. Three MoAbs that block adherence of PRBCs to ECs or C32 melanoma cells also reversed rosetting by greater than 50% at levels of less than 1 microgram/mL (OKM5, OKM8, and 8A6). Two other MoAbs that react with purified CD36 (1D3 and 1B1), but do not react with the surface of C32 cells, failed to reverse rosetting. When rosettes were disrupted and the RBCs and PRBCs were pretreated separately with antibodies before mixing to allow rosette reformation, only pretreatment of RBCs had an effect. MoAb 8A6 pretreatment of RBCs blocked rosette reformation, while MoAb 1B1 pretreatment did not. Rosetting was also reversed by purified human platelet CD36. In conjunction with evidence that CD36 is expressed on normal human erythrocytes (van Schravendijk et al, Blood 80:2105, 1992), we conclude that this CD36 is able to act as a host receptor for rosetting in the MC strain and some natural isolates of P falciparum.

Animals↗

Ribozyme mediated down-regulation of thrombospondin receptor CD36 inhibits the growth of the human osteosarcoma cell line.

Thrombospondin-1 (TSP1) is known to possess tumor suppressor functions. In contradiction, TSP1 enhances the stromal vascularization and growth of certain cancers. A cell adhesion receptor, CD36, has been shown to interact with a ligand TSP1. We studied how CD36 affects the growth of the osteosarcoma cell line (HOS) expressing TSP1. We used the anti-CD36 ribozyme to specifically suppress CD36 gene expression in the HOS. The expression of the CD36 mRNA was significantly suppressed in the ribozyme-introduced cell line (HOS/Rz). The transformant HOS/Rz markedly decreased its growth. The growth of the osteosarcoma cell line HOS may be regulated by autocrine or paracrine loop TSP1 and CD36.

Antigens, CD↗

CD36: a multiligand molecule.

CD36 is a multiligand receptor associated with a broad array of physiological processes and involved in markedly diverse disorders, including atherosclerosis, insulin resistance and diabetes, dyslipidemia, tumor angiogenesis, and host defense against Plasmodium falciparum. CD36 deficiency has proved to be common, particularly in ethnic groups such as African Americans and Asians. CD36 is commonly expressed on blasts in acute monocytic leukemia, megakaryoblastic leukemia, and erythroleukemia. The role of CD36 in sickle cell crises and cerebral malaria is debatable. As a receptor for thrombospondin 1, CD36 plays a role in the regulation of angiogenesis, which may be a therapeutic strategy for controlling the dissemination of malignant neoplasms. The future challenge will be to further understand the mechanisms by which CD36 affects these diverse functions and to design therapeutic strategies that can alter the course of the diseases.

Antigens, CD↗

Keratinocyte and epidermal leukocyte expression of CD36 (OKM5) in benign and malignant skin diseases.

CD36 recognizes a 88 Kd glycoprotein, found on different cell populations involved in immunoregulation and are induced on keratinocytes by in vitro treatment with gamma-interferon. Therefore, we obtained skin biopsies from 48 patients with various dermatological diseases and from 5 healthy volunteers and stained these with monoclonal antibodies OKM5 (CD36), anti-HLA-DR and OKT6 (CD1a) using a three stage immunoperoxidase method. In normal skin, CD36 expression was not observed. In contrast, keratinocytes in diseased skin were CD36+. In most cases, the staining was restricted to the stratum granulosum and the stratum spinosum, but in psoriasis, squamous cell carcinoma and lymphomatoid papulosis, more extensive staining of keratinocytes was seen. In addition, CD36+ epidermal leukocytes were found in allergic patch-test infiltrates and in mycosis fungoides. The findings of CD36 expression by epidermal cells within a broad spectrum of dermatological diseases indicate a role for these cells in the regulation of immune reactions in the skin.

Antibodies, Monoclonal↗

Collagen induces normal signal transduction in platelets deficient in CD36 (platelet glycoprotein IV).

The receptor involved in platelet activation by collagen has not been identified. Platelet glycoprotein IV, now known as CD36, has been implicated in interaction with collagen and also been shown to be associated with intracellular tyrosine kinases. In order to investigate the possible role of collagen-mediated signal transduction via CD36, platelets were obtained from a donor that were deficient in CD36. The collagen-induced intracellular mobilization of Ca2+ in the CD36 deficient cells was of the same magnitude as that seen in platelets from normal donors. In addition, serotonin secretion did not appear to be impaired. Tyrosine phosphorylation was also comparable between the CD36-deficient and normal platelets. Thus, it is unlikely that CD36 plays a major role in collagen-dependent platelet signal transduction.

Antigens, CD↗

Expression cloning of SR-BI, a CD36-related class B scavenger receptor.

Scavenger receptors are integral membrane proteins that mediate the endocytosis of modified lipoproteins. The first of these to be purified and cloned were the type I and II macrophage scavenger receptors (SR-AI and SR-AII; class A scavenger receptors). Subsequently, the cell surface protein CD36 was shown to bind oxidized low density lipoprotein (oxidized LDL). From a Chinese hamster ovary (CHO) cell variant we have cloned by expression the cDNA for a new member of the CD36 family of membrane proteins, SR-BI, whose predicted protein sequence of 509 amino acids is approximately 30% identical to those of the four previously identified family members. Both SR-BI and CD36 displayed high affinity binding for acetylated LDL with an apparent dissociation constant on the order of approximately 5 micrograms of protein/ml. The ligand binding specificities of CD36 and SR-BI, determined by direct binding or competition assays, were similar, but not identical; both bind modified proteins (acetylated LDL, oxidized LDL, maleylated bovine serum albumin), but not the broad array of other polyanions (e.g. fucoidin, polyguanosinic acid, carrageenan) which are ligands of the class A receptors. Thus, SR-BI and CD36 define a second class of scavenger receptors, designated class B. Native LDL, which does not bind to either class A receptors or CD36, unexpectedly bound with high affinity to SR-BI. Northern blot analysis of murine tissues showed that SR-BI was most abundantly expressed in fat and was present at moderate levels in lung and liver. Furthermore, SR-BI mRNA expression was induced upon differentiation of 3T3-L1 cells into adipocytes. Thus, the tissue distribution of expression and ligand binding properties of SR-BI raise the possibility that this cell surface receptor may play an important role in lipid metabolism.

Amino Acid Sequence↗