CD36-null Mice Research Articles

CD36/Lyn kinase interactions within macrophages promotes pulmonary fibrosis in response to oxidized phospholipid

Recent data from human studies and animal models have established roles for type II alveolar epithelial cell (AEC2) injury/apoptosis and monocyte/macrophage accumulation and activation in progressive lung fibrosis. Although the link between these processes is not well defined, we have previously shown that CD36-mediated uptake of apoptotic AEC2s by lung macrophages is sufficient to drive fibrosis. Importantly, apoptotic AEC2s are rich in oxidized phospholipids (oxPL), and amongst its multiple functions, CD36 serves as a scavenger receptor for oxPL. Recent studies have established a role for oxPLs in alveolar scarring, and we hypothesized that uptake and accrual of oxPL by CD36 would cause a macrophage phenotypic change that promotes fibrosis. To test this hypothesis, we treated wild-type and CD36-null mice with the oxPL derivative oxidized phosphocholine (POVPC) and found that CD36-null mice were protected from oxPL-induced scarring. Compared to WT mice, fewer macrophages accumulated in the lungs of CD36-null animals, and the macrophages exhibited a decreased accumulation of intracellular oxidized lipid. Importantly, the attenuated accrual of oxPL in CD36-null macrophages was associated with diminished expression of the profibrotic mediator, TGFβ. Finally, the pathway linking oxPL uptake and TGFβ expression was found to require CD36-mediated activation of Lyn kinase. Together, these observations elucidate a causal pathway that connects AEC2 injury with lung macrophage activation via CD36-mediated uptake of oxPL and suggest several potential therapeutic targets.

Overexpression of CD36, Driven By STAT3, Mediates Free Fatty Acid Uptake in CLL Cells

Overexpression of CD36, Driven By STAT3, Mediates Free Fatty Acid Uptake in CLL Cells

Brain Perivascular Macrophages Initiate the Neurovascular Dysfunction of Alzheimer Aβ Peptides.

Increasing evidence indicates that alterations of the cerebral microcirculation may play a role in Alzheimer disease, the leading cause of late-life dementia. The amyloid-β peptide (Aβ), a key pathogenic factor in Alzheimer disease, induces profound alterations in neurovascular regulation through the innate immunity receptor CD36 (cluster of differentiation 36), which, in turn, activates a Nox2-containing NADPH oxidase, leading to cerebrovascular oxidative stress. Brain perivascular macrophages (PVM) located in the perivascular space, a major site of brain Aβ collection and clearance, are juxtaposed to the wall of intracerebral resistance vessels and are a powerful source of reactive oxygen species. We tested the hypothesis that PVM are the main source of reactive oxygen species responsible for the cerebrovascular actions of Aβ and that CD36 and Nox2 in PVM are the molecular substrates of the effect. Selective depletion of PVM using intracerebroventricular injection of clodronate abrogates the reactive oxygen species production and cerebrovascular dysfunction induced by Aβ applied directly to the cerebral cortex, administered intravascularly, or overproduced in the brain of transgenic mice expressing mutated forms of the amyloid precursor protein (Tg2576 mice). In addition, using bone marrow chimeras, we demonstrate that PVM are the cells expressing CD36 and Nox2 responsible for the dysfunction. Thus, deletion of CD36 or Nox2 from PVM abrogates the deleterious vascular effects of Aβ, whereas wild-type PVM reconstitute the vascular dysfunction in CD36-null mice. The data identify PVM as a previously unrecognized effector of the damaging neurovascular actions of Aβ and unveil a new mechanism by which brain-resident innate immune cells and their receptors may contribute to the pathobiology of Alzheimer disease.

Platelet CD36 Potentiates Thrombus Formation in Hyperlipidemic Conditions By Activating Redox Sensitive MAP Kinase ERK5

Atherosclerotic plaque instability is a pathological process that can lead to ischemic emergencies, such as myocardial infarction (MI) and stroke. Thrombosis in this context is promoted by circulating oxidized lipids present in LDL particles (oxLDL), which are generated during plaque formation. These particles are recognized by scavenger receptor CD36 present on platelets. CD36 binding to oxLDL lowers the threshold for platelet activation by recruitment and activation of Src kinases Fyn and Lyn, followed by signaling including generation of reactive oxygen species (ROS) through NADPH oxidase (Nox). Although these effectors are important for the prothrombotic properties of CD36, the downstream signaling that links CD36 to classic agonist-induced platelet activation pathways is incompletely defined. We hypothesize that platelet CD36 promotes thrombosis by generating specific ROS to modulate critical redox-sensitive signaling pathways in hyperlipidemia. Platelet MAP kinase ERK5 is a redox sensor that was shown to be required for optimal platelet activation in MI, a condition with greatly elevated ROS. We previously reported that oxLDL-CD36 signaling leads to the generation of the specific ROS superoxide radical anion (O2●-) and that O2●-/hydrogen peroxide (H2O2) are important mediators of platelet aggregation. Additionally, we reported that platelet ERK5 was activated by oxLDL in a CD36-dependent pathway requiring Src kinases, Nox and O2●-/H2O2 to promote platelet activation. We now report the function of platelet ERK5 in this context by performing an ex vivo microfluidic thrombosis assay in which mice whole blood is perfused over immobilized collagen. Platelet adhesion and accumulation were visualized in real time via mepacrine-tagged platelets. We found that stimulating whole blood from wild type C57Bl6 mice with oxLDL promoted platelet adhesion and accumulation by 12.9% compared to buffer stimulation (p=0.033). Whole blood from CD36 null mice showed indistinguishable platelet adhesion and accumulation when stimulated with oxLDL or buffer, suggesting CD36-dependency. We used the platelet ERK5 null mice, which was generated by crossing ERK5flox mice with PF4-cre+ mice (ERK5flox/PF4-cre+), and showed that platelet adhesion and accumulation by oxLDL was abrogated compared to control ERK5flox mice. Additionally, the in vivo relevance of platelet ERK5 activation by CD36 was determined by performing a novel collagen-mediated murine thrombosis assay. This assay is dependent on syngeneic transplantation of the epigastric artery into the carotid artery, where the collagen-rich outer adventitial layer is exposed to blood flow, thus generating a thrombus. Platelets and fibrin accumulation were visualized in real time by Rhodamine 6G and fluorophore-tagged anti-fibrin antibody, respectively. We transplanted bone marrows from donor ERK5flox mice or ERK5flox/PF4-cre+ mice into recipient atherogenic apoE null mice and generated hyperlipidemia by feeding the mice a high fat diet (HFD). ApoE null mice with ERK5flox bone marrows (apoE:ERK5floxBM) on HFD developed rapid platelet accumulation with subsequent thromboembolisms compared to apoE null mice with platelet ERK5-null bone marrows (apoE:ERK5flox/PF4-cre+BM) (p<0.01 at 10 min), demonstrating that this model is sensitive to detect a prothrombotic phenotype in diet-induced hyperlipidemia. Chow fed mice do not show potentiation of platelet accumulation in both apoE chimeras (p=0.56). Additionally, HFD-fed apoE:ERK5floxBM showed accelerated fibrin accumulation compared to apoE:ERK5flox/PF4-cre+BM, suggesting a role for CD36-ERK5 signaling in platelet procoagulant properties. Control diet-fed apoE null chimeras have indistinguishable fibrin accumulation kinetics. Subsequent studies to determine the mechanism for fibrin accumulation (via fluorophore-tagged Annexin V binding) showed that exposure of platelets to oxLDL induced dose-dependent phosphatidylserine (PS) exposure, a mechanism required for platelets to promote coagulation. Buffer or LDL controls had no effect. A CD36 blocking antibody, FA6, was able to abrogate oxLDL-mediated PS exposure compared to control antibody (p=0.041). These findings suggest that platelet CD36 potentiates thrombosis through a specific redox-regulated pathway requiring ERK5 and that ERK5 is a critical modulator of thrombosis in hyperlipidemic conditions. DisclosuresNo relevant conflicts of interest to declare.

Oxidized LDL-bound CD36 recruits an Na⁺/K⁺-ATPase-Lyn complex in macrophages that promotes atherosclerosis.

One characteristic of atherosclerosis is the accumulation of lipid-laden macrophage foam cells in the arterial wall. We have previously shown that the binding of oxidized low-density lipoprotein (oxLDL) to the scavenger receptor CD36 activates the kinase Lyn, initiating a cascade that inhibits macrophage migration and is necessary for foam cell generation. We identified the plasma membrane ion transporter Na(+)/K(+)-ATPase as a key component in the macrophage oxLDL-CD36 signaling axis. Using peritoneal macrophages isolated from Atp1a1 heterozygous or Cd36-null mice, we demonstrated that CD36 recruited an Na(+)/K(+)-ATPase-Lyn complex for Lyn activation in response to oxLDL. Macrophages deficient in the α1 Na(+)/K(+)-ATPase catalytic subunit did not respond to activation of CD36, showing attenuated oxLDL uptake and foam cell formation, and oxLDL failed to inhibit migration of these macrophages. Furthermore, Apoe-null mice, which are a model of atherosclerosis, were protected from diet-induced atherosclerosis by global deletion of a single allele encoding the α1 Na(+)/K(+)-ATPase subunit or reconstitution with macrophages that lacked an allele encoding the α1 Na(+)/K(+)-ATPase subunit. These findings identify Na(+)/K(+)-ATPase as a potential target for preventing or treating atherosclerosis.

Abstract 382: Oxidized LDL Signaling “Primes” GPVI-Mediated Platelet Activation in a CD36-Dependent Manner

CD36 acts as an important participant in the prothrombotic state associated with chronic inflammatory diseases such as atherosclerosis and diabetes by serving as a signaling relay point for danger-associated molecular patterns (DAMPs), including oxidized low-density lipoproteins (oxLDL) and advanced glycated proteins. Although CD36-mediated signaling pathways have been well characterized in macrophages, less is known about CD36-mediated signaling in platelets. Our group identified important roles for specific Src family kinases (SFK) Lyn and Fyn, and for the guanine nucleotide exchange factors Vav1 and Vav3. Since platelet activation by the collagen receptor GPVI also involves downstream activation of SFKs, we now hypothesize that oxLDL signaling via CD36 primes platelets for hyperactivity by activating components of the GPVI signaling pathway. To test this hypothesis, we treated fluorescently labeled murine platelets with either native LDL (nLDL) or oxLDL and exposed them to immobilized collagen under defined shear flow in a microfluidic flow chamber. A significant increase (~1.2 fold) in platelet accumulation was observed with oxLDL treatment. No increase in accumulation was observed in oxLDL-treated platelets from cd36 null mice, suggesting that this phenomenon was CD36-dependent. Furthermore, addition of tirofiban ablated the oxLDL-induced increase in platelet accumulation, suggesting that the increase was likely due to enhanced platelet-platelet contacts (i.e. enhanced platelet activation). This supports previous data from our laboratory showing that treatment of murine platelets with oxLDL alone resulted in activation of αIIbβ3 integrin. Additionally, oxLDL-treated platelets from vav1/vav3 double null mice phenocopied cd36 null platelets and displayed no increase in platelet accumulation compared to nLDL-treated platelets, strengthening the functional link between CD36 and GPVI signaling pathways. These data suggest a functional link between CD36 and GPVI signaling pathways in platelets, which may contribute to platelet hyperactivity in athero-inflammatory diseases.

Commentary on Fatty Acid Wars

Cluster of Differentiation 36 (CD36) is an integral membrane protein and a member of the class B scavenger receptor family that binds many ligands—oxidized low-density lipoprotein,1,2 native lipoproteins,3 and oxidized phospholipids.4 In addition, CD36 has been shown to enhance the uptake of long-chain fatty acids,5 and CD36 null mice show a defect in fatty acid uptake6 as well as intestinal processing of dietary fat.7,8 CD36 has been implicated in fatty acid transport in heart,9 skeletal muscle,9 adipocytes,10 human pancreatic β-cells,11 and fibroblasts12; muscle-specific CD36 overexpression enhances fatty acid oxidation in contracting muscle, reduces plasma triglycerides and fatty acids, while increasing plasma glucose and insulin,13 thereby producing a diabetic phenotype. Based on these findings, CD36 has been postulated to be a fatty acid transporter; yet, many questions remain about the function of this promiscuous lipoprotein receptor. At the molecular level, what is the activity of CD36, what are the consequences of that activity, and what are the attendant mechanisms? The existence of fatty acid translocators in cells has been somewhat controversial. Although there is a clear …

The thrombospondin-1 receptor CD36 is an important mediator of ovarian angiogenesis and folliculogenesis.

BackgroundOvarian angiogenesis is a complex process that is regulated by a balance between pro- and anti-angiogenic factors. Physiological processes within the ovary, such as folliculogenesis, ovulation, and luteal formation are dependent upon adequate vascularization and anything that disrupts normal angiogenic processes may result in ovarian dysfunction, and possibly infertility. The objective of this study was to evaluate the role of the thrombospondin-1 (TSP-1) receptor CD36 in mediating ovarian angiogenesis and regulating ovarian function.MethodsThe role of CD36 was evaluated in granulosa cells in vitro and ovarian morphology and protein expression were determined in wild type and CD36 null mice.ResultsIn vitro, CD36 inhibition increased granulosa cell proliferation and decreased apoptosis. Granulosa cells in which CD36 was knocked down also exhibited an increase in expression of survival and angiogenic proteins. Ovaries from CD36 null mice were hypervascularized, with increased expression of pro-angiogenic vascular endothelial growth factor (VEGF) and its receptor VEGFR-2. Ovaries from CD36 null mice contained an increase in the numbers of pre-ovulatory follicles and decreased numbers of corpora lutea. CD36 null mice also had fewer number of offspring compared to wild type controls.ConclusionsThe results from this study demonstrate that CD36 is integral to the regulation of ovarian angiogenesis by TSP-1 and the expression of these family members may be useful in the control of ovarian vascular disorders.

Krüppel-like factor 2 promotes liver steatosis through upregulation of CD36

The Krüppel-like factor (KLF) family of transcription factors regulates diverse biological processes that include proliferation, differentiation, apoptosis, development, and responses to external stress. In the present study, we aim to investigate the roles of KLF2 in hepatic steatosis. Our results showed that mRNA and protein levels of KLF2 were significantly elevated in livers from obese mice. Adenoviruses-mediated overexpression of KLF2 induced accumulation of triglycerides in C57BL/6 mice, whereas KLF2 silencing ameliorates hepatosteatosis in ob/ob mice. At the molecular level, our data established CD36 as a novel transcriptional target of KLF2. KLF2 upregulated CD36 expression through a consensus binding site on its proximal promoter region. Additionally, the steatotic effect of KLF2 was dramatically inhibited in CD36-null mice. Therefore, our study reveals a novel link between KLF2-induced hepatic triglyceride accumulation and the expression of CD36.

The involvement of CD36 in monocyte activation by antiphospholipid antibodies

CD36, known as a scavenger receptor, is a transmembrane glycoprotein expressed on monocytes, platelets and endothelial cells, recognizes multiple ligands, including phosphatidylserine, and regulates atherogenesis and thrombosis. The objective of this study is to investigate the possible involvement of CD36 in the pathophysiology of thrombosis in patients with antiphospholipid syndrome (APS). First, rs3765187, a missense mutation linked to CD36 deficiency, was investigated by TaqMan polymerase chain reaction (PCR) genotyping method in 819 Japanese, including 132 patients with APS, 265 with systemic lupus erythematosus (SLE) in the absence of APS, and 422 healthy subjects. Then, the involvement of CD36 in antiphospholipid antibody (aPL)-induced tissue factor (TF) expression was examined using CD36-null mice or anti-CD36. Purified IgG from patients with APS and a monoclonal phosphatidylserine-dependent antiprothrombin antibody were used in these experiments. TF expression was tested by real-time PCR and flow cytometry. Minor allele carrier of rs3765187 was less frequent in patients with APS (3.8% p=0.032), but not in patients with SLE in the absence of APS (7.9% p=0.32), compared with healthy subjects (10.2%). The aPL-induced TF expression was significantly suppressed on peritoneal macrophages from CD36-null mice compared to wild type and significantly inhibited by anti-CD36 on human monocytes. The gene mutation linked to CD36 deficiency was less frequent in patients with APS. The deficient or suppressed CD36 function significantly reduced aPL-induced TF expression in vitro. Taken together, in a susceptible background CD36 scavenger receptor function may be involved in the thrombotic pathophysiology in patients with APS.

High-capacity selective uptake of cholesteryl ester from native LDL during macrophage foam cell formation

Macrophage foam cells are a defining pathologic feature of atherosclerotic lesions. Recent studies have demonstrated that at high concentrations associated with hypercholesterolemia, native LDL induces macrophage lipid accumulation. LDL particles are taken up by macrophages as part of bulk fluid pinocytosis. However, the uptake and metabolism of cholesterol from native LDL during foam cell formation has not been clearly defined. Previous reports have suggested that selective cholesteryl ester (CE) uptake might contribute to cholesterol uptake from LDL independently of particle endocytosis. In this study we demonstrate that the majority of macrophage LDL-derived cholesterol is acquired by selective CE uptake in excess of LDL pinocytosis and degradation. Macrophage selective CE uptake does not saturate at high LDL concentrations and is not down-regulated during cholesterol accumulation. In contrast to CE uptake, macrophages exhibit little selective uptake of free cholesterol (FC) from LDL. Following selective uptake from LDL, CE is rapidly hydrolyzed by a novel chloroquine-sensitive pathway. FC released from LDL-derived CE hydrolysis is largely effluxed from cells but also is subject to ACAT-mediated reesterification. These results indicate that selective CE uptake plays a major role in macrophage metabolism of LDL.

CD36 mediates proximal tubular binding and uptake of albumin and is upregulated in proteinuric nephropathies

Dysregulation of renal tubular protein handling in proteinuria contributes to the development of chronic kidney disease. We investigated the role of CD36 as a novel candidate mediator of albumin binding and endocytosis in the kidney proximal tubule using both in vitro and in vivo approaches, and in nephrotic patient renal biopsy samples. In CD36-transfected opossum kidney proximal tubular cells, both binding and uptake of albumin were substantially enhanced. A specific CD36 inhibitor abrogated this effect, but receptor-associated protein, which blocks megalin-mediated endocytosis of albumin, did not. Mouse proximal tubular cells expressed CD36 and this was absent in CD36 null animals, whereas expression of megalin was equal in these animals. Compared with wild-type mice, CD36 null mice demonstrated a significantly increased urinary protein-to-creatinine ratio and albumin-to-creatinine ratio. Proximal tubular cells expressed increased CD36 when exposed to elevated albumin concentrations in culture medium. Expression of CD36 was studied in renal biopsy tissue obtained from adult patients with heavy proteinuria due to minimal change disease, membranous nephropathy, or focal segmental glomerulosclerosis. Proximal tubular CD36 expression was markedly increased in proteinuric individuals. We conclude that CD36 is a novel mediator influencing binding and uptake of albumin in the proximal tubule that is upregulated in proteinuric renal diseases. CD36 may represent a potential therapeutic target in proteinuric nephropathy.

Context Dependent Role of the CD36 - Thrombospondin - Histidine-Rich Glycoprotein Axis in Tumor Angiogenesis and Growth

The angiogenic switch is a promising therapeutic target in cancer. Work by our laboratory and others has described an important endogenous anti-angiogenic pathway mediated by interactions of CD36, a receptor on microvascular endothelial cells, with proteins containing thrombospondin (TSP) type I repeat domains (TSR). Recent studies revealed that circulating Histidine Rich Glycoprotein (HRG) inhibits the anti-angiogenic potential of the CD36-TSR pathway by functioning as a decoy receptor that binds and sequesters TSR proteins. As tumors of different origin display variable expression profiles of numerous targets, we hypothesized that the TSP-CD36-HRG axis regulates vascularization and growth in the tumor microenvironment in a context, or tumor type, dependent manner. Growth of Lewis Lung Carcinoma (LL2) and B16F1 Melanoma tumor cell implants in syngeneic wild type (WT), hrg, or cd36 null mice were used as a model to interrogate this signaling axis. LL2 tumor volumes were greater in cd36 null mice and smaller in hrg null mice compared to WT. Immunofluorescent staining showed increased vascularity in cd36 null vs. WT and WT vs. hrg null mice. No differences in tumor growth or vascularity were observed with B16F1 implants, consistent with lack of expression of TSP-1 in B16F1 cells. When TSR expression was induced in B16F1 cells by cDNA transfection, tumor growth and vascularity were similar to that seen with LL2 cells. These data show a role for CD36-mediated anti-angiogenic activity in the tumor microenvironment when TSR proteins are available and demonstrate that HRG modulates this activity. Further, they suggest a mechanism by which tumor microenvironments may regulate sensitivity to TSR containing proteins.

Advanced glycation end products induce a prothrombotic phenotype in mice via interaction with platelet CD36

AbstractDiabetes mellitus has been associated with platelet hyperreactivity, which plays a central role in the hyperglycemia-related prothrombotic phenotype. The mechanisms responsible for this phenomenon are not established. In the present study, we investigated the role of CD36, a class-B scavenger receptor, in this process. Using both in vitro and in vivo mouse models, we demonstrated direct and specific interactions of platelet CD36 with advanced glycation end products (AGEs) generated under hyperglycemic conditions. AGEs bound to platelet CD36 in a specific and dose-dependent manner, and binding was inhibited by the high-affinity CD36 ligand NO2LDL. Cd36-null platelets did not bind AGE. Using diet- and drug-induced mouse models of diabetes, we have shown that cd36-null mice had a delayed time to the formation of occlusive thrombi compared with wild-type (WT) in a FeCl3-induced carotid artery injury model. Cd36-null mice had a similar level of hyperglycemia and a similar level of plasma AGEs compared with WT mice under this condition, but WT mice had more AGEs incorporated into thrombi. Mechanistic studies revealed that CD36-dependent JNK2 activation is involved in this prothrombotic pathway. Therefore, the results of the present study couple vascular complications in diabetes mellitus with AGE-CD36–mediated platelet signaling and hyperreactivity.

Caffeine‐stimulated fatty acid oxidation is blunted in CD36 null mice

The increase in skeletal muscle fatty acid metabolism during exercise has been associated with the release of calcium. We examined whether this increase in fatty acid oxidation was attributable to a calcium-induced translocation of the fatty acid transporter CD36 to the sarcolemma, thereby providing an enhanced influx of fatty acids to increase their oxidation. Calcium release was triggered by caffeine (3 mm) to examine fatty acid oxidation in intact soleus muscles of WT and CD36-KO mice, while fatty acid transport and mitochondrial fatty acid oxidation were examined in giant vesicles and isolated mitochondria, respectively, from caffeine-perfused hindlimb muscles of WT and CD36-KO mice. Western blotting was used to examine calcium-induced signalling. In WT, caffeine stimulated muscle palmitate oxidation (+136%), but this was blunted in CD36-KO mice (-70%). Dantrolene inhibited (WT) or abolished (CD36-KO) caffeine-induced palmitate oxidation. In muscle, caffeine-stimulated palmitate oxidation was not attributable to altered mitochondrial palmitate oxidation. Instead, in WT, caffeine increased palmitate transport (+55%) and the translocation of fatty acid transporters CD36, FABPpm, FATP1 and FATP4 (26-70%) to the sarcolemma. In CD36-KO mice, caffeine-stimulated FABPpm, and FATP1 and 4 translocations were normal, but palmitate transport was blunted (-70%), comparable to the reductions in muscle palmitate oxidation. Caffeine did not alter the calcium-/calmodulin-dependent protein kinase II phosphorylation but did increase the phosphorylation of AMPK and acetyl-CoA carboxylase comparably in WT and CD36-KO. These studies indicate that sarcolemmal CD36-mediated fatty acid transport is a primary mediator of the calcium-induced increase in muscle fatty acid oxidation.

Link between intestinal CD36 ligand binding and satiety induced by a high protein diet in mice.

CD36 is a ubiquitous membrane glycoprotein that binds long-chain fatty acids. The presence of a functional CD36 is required for the induction of satiety by a lipid load and its role as a lipid receptor driving cellular signal has recently been demonstrated. Our project aimed to further explore the role of intestinal CD36 in the regulation of food intake. Duodenal infusions of vehicle or sulfo-N-succinimidyl-oleate (SSO) was performed prior to acute infusions of saline or Intralipid (IL) in mice. Infusion of minute quantities of IL induced a decrease in food intake (FI) compared to saline. Infusion of SSO had the same effect but no additive inhibitory effect was observed in presence of IL. No IL- or SSO-mediated satiety occurred in CD36-null mice. To determine whether the CD36-mediated hypophagic effect of lipids was maintained in animals fed a satietogen diet, mice were subjected to a High-Protein diet (HPD). Concomitantly with the satiety effect, a rise in intestinal CD36 gene expression was observed. No satiety effect occurred in CD36-null mice. HPD-fed WT mice showed a diminished FI compared to control mice, after saline duodenal infusion. But there was no further decrease after lipid infusion. The lipid-induced decrease in FI observed on control mice was accompanied by a rise in jejunal oleylethanolamide (OEA). Its level was higher in HPD-fed mice than in controls after saline infusion and was not changed by lipids. Overall, we demonstrate that lipid binding to intestinal CD36 is sufficient to produce a satiety effect. Moreover, it could participate in the satiety effect induced by HPD. Intestine can modulate FI by several mechanisms including an increase in OEA production and CD36 gene expression. Furthermore, intestine of mice adapted to HPD have a diminished capacity to modulate their food intake in response to dietary lipids.

Caffeine-stimulated fatty acid oxidation is blunted in CD36 null mice

Caffeine-stimulated fatty acid oxidation is blunted in CD36 null mice

CD9 Tetraspanin Interacts with CD36 on the Surface of Macrophages: A Possible Regulatory Influence on Uptake of Oxidized Low Density Lipoprotein

CD36 is a type 2 scavenger receptor with multiple functions. CD36 binding to oxidized LDL triggers signaling cascades that are required for macrophage foam cell formation, but the mechanisms by which CD36 signals remain incompletely understood. Mass spectrometry analysis of anti-CD36 immuno-precipitates from macrophages identified the tetraspanin CD9 as a CD36 interacting protein. Western blot showed that CD9 was precipitated from mouse macrophages by anti-CD36 monoclonal antibody and CD36 was likewise precipitated by anti-CD9, confirming the mass spectrometry results. Macrophages from cd36 null mice were used to demonstrate specificity. Membrane associations of the two proteins on intact cells was analyzed by confocal immunofluorescence microscopy and by a novel cross linking assay that detects proteins in close proximity (<40 nm). Functional significance was determined by assessing lipid accumulation, foam cell formation and JNK activation in wt, cd9 null and cd36 null macrophages exposed to oxLDL. OxLDL uptake, lipid accumulation, foam cell formation, and JNK phosphorylation were partially impaired in cd9 null macrophages. The present study demonstrates that CD9 associates with CD36 on the macrophage surface and may participate in macrophage signaling in response to oxidized LDL.

Activation of Vascular Cells by Microparticles and Other Danger Signals Via the CD36 Scavenger Receptor

Abstract SCI-12 Clinically significant thrombotic events are common complications of many systemic diseases associated with chronic inflammation, including atherosclerosis, diabetes mellitus, cancer, and chronic autoimmune rheumatologic disorders. Many of these potentially life-threatening thrombi occur in the arterial circulation and likely relate to inappropriate platelet activation and/or vessel wall injury. CD36 is a type B scavenger receptor expressed on platelets, monocytes, microvascular endothelial cells (MVEC), and vascular smooth muscle cells (VSMC) that recognizes and responds to endogenous and exogenous “danger signals” including advanced glycated proteins (AGE), microbial cell wall components, and oxidized phospholipids that are found on the surface of oxidized LDL (oxLDL) and cell-derived microparticles (MP). Mouse FeCl3 thrombosis model systems revealed that genetic deletion of cd36 rescued the prothrombotic phenotypes associated with hyperlipidemia, oxidant stress, or diabetes/hyperglycemia. Interestingly, compared to wild type mice, fewer MP were incorporated into thrombi formed in cd36 null mice after FeCl3-induced vascular injury. Cd36 deficiency also provides partial protection from atherosclerosis in experimental mouse models. On a cellular level, the prothrombotic, pro-atherogenic, and anti-angiogenic activities of CD36 relate to ligand-dependent alterations of platelet, macrophage, and vessel wall cellular functions. For example, CD36 binding to MP, AGE, or oxLDL “sensitizes” platelets to activation by low doses of agonists, such as ADP. In macrophages, CD36 interactions with oxLDL leads to lipid internalization, foam cell formation, and inhibition of migration. In the vessel wall CD36 promotes VSMC oxidant stress and MVEC apoptosis. Mechanistically, CD36 transmits intracellular signals in response to ligand engagement that involve recruitment of specific Src family kinases to its short cytoplasmic tail, with subsequent activation of specific MAP kinase pathways and Vav family guanine nucleotide exchange factors. These signaling pathways remain incompletely understood, but impact many important cellular processes, including cytoskeletal dynamics, cell polarity, transcription of antioxidant genes controlled by the transcription factor Nrf2, and activation of NADPH oxidases. Specific components of CD36 signaling pathways depend on the cellular context and in some cases involve engagement of co-receptors, including integrins, TLRs, and tetraspanins. Recent targeted genome-wide association studies suggest that cd36 polymorphisms associate with CD36 expression levels on platelets and monocytes as well as with risk of thrombotic, metabolic, and atherosclerotic disorders. Targeting CD36 may therefore provide novel approaches to many important human vascular diseases. Disclosures: No relevant conflicts of interest to declare.

Scavenger receptor CD36 is essential for the cerebrovascular oxidative stress and neurovascular dysfunction induced by amyloid-β

Increasing evidence indicates that cerebrovascular dysfunction plays a pathogenic role in Alzheimer's dementia (AD). Amyloid-β (Aβ), a peptide central to the pathogenesis of AD, has profound vascular effects mediated, for the most part, by reactive oxygen species produced by the enzyme NADPH oxidase. The mechanisms linking Aβ to NADPH oxidase-dependent vascular oxidative stress have not been identified, however. We report that the scavenger receptor CD36, a membrane glycoprotein that binds Aβ, is essential for the vascular oxidative stress and neurovascular dysfunction induced by Aβ1-40. Thus, topical application of Aβ1-40 onto the somatosensory cortex attenuates the increase in cerebral blood flow elicited by neural activity or by endothelium-dependent vasodilators in WT mice but not in CD36-null mice (CD36(0/0)). The cerebrovascular effects of infusion of Aβ1-40 into cerebral arteries are not observed in mice pretreated with CD36 blocking antibodies or in CD36(0/0) mice. Furthermore, CD36 deficiency prevents the neurovascular dysfunction observed in transgenic mice overexpressing the Swedish mutation of the amyloid precursor protein Tg2576 despite elevated levels of brain Aβ1-40. CD36 is also required for the vascular oxidative stress induced by exogenous Aβ1-40 or observed in Tg2576 mice. These observations establish CD36 as a key link between Aβ1-40 and the NADPH oxidase-dependent vascular oxidative stress underlying the neurovascular dysfunction and suggest that CD36 is a potential therapeutical target to counteract the cerebrovascular dysfunction associated with Aβ.