Oxidized alkyl phospholipids stimulate sodium transport in proximal tubules via a nongenomic PPARγ-dependent pathway.

Oxidized phospholipids have been shown to exhibit pleiotropic effects in numerous biological contexts. For example, 1-O-hexadecyl-2-azelaoyl-sn-glycero-3-phosphocholine (azPC), an oxidized phospholipid formed from alkyl phosphatidylcholines, is a peroxisome proliferator-activated receptor gamma (PPARγ) nuclear receptor agonist. Although it has been reported that PPARγ agonists including thiazolidinediones can induce plasma volume expansion by enhancing renal sodium and water retention, the role of azPC in renal transport functions is unknown. In the present study, we investigated the effect of azPC on renal proximal tubule (PT) transport using isolated PTs and kidney cortex tissues and also investigated the effect of azPC on renal sodium handling in vivo. We showed using a microperfusion technique that azPC rapidly stimulated Na+/HCO3- cotransporter 1 (NBCe1) and luminal Na+/H+ exchanger (NHE) activities in a dose-dependent manner at submicromolar concentrations in isolated PTs from rats and humans. The rapid effects (within a few minutes) suggest that azPC activates NBCe1 and NHE via nongenomic signaling. The stimulatory effects were completely blocked by specific PPARγ antagonist GW9662, ERK kinase inhibitor PD98059, and CD36 inhibitor sulfosuccinimidyl oleate. Treatment with an siRNA against PPAR gamma completely blocked the stimulation of both NBCe1 and NHE by azPC. Moreover, azPC induced ERK phosphorylation in rat and human kidney cortex tissues, which were completely suppressed by GW9662 and PD98059 treatments. These results suggest that azPC stimulates renal PT sodium-coupled bicarbonate transport via a CD36/PPARγ/mitogen-activated protein/ERK kinase/ERK pathway. We conclude that the stimulatory effects of azPC on PT transport may be partially involved in volume expansion.

Targeting metastasis-initiating cells through the fatty acid receptor CD36.

The fact that the identity of the cells that initiate metastasis in most human cancers is unknown hampers the development of antimetastatic therapies. Here we describe a subpopulation of CD44bright cells in human oral carcinomas that do not overexpress mesenchymal genes, are slow-cycling, express high levels of the fatty acid receptor CD36 and lipid metabolism genes, and are unique in their ability to initiate metastasis. Palmitic acid or a high-fat diet specifically boosts the metastatic potential of CD36+ metastasis-initiating cells in a CD36-dependent manner. The use of neutralizing antibodies to block CD36 causes almost complete inhibition of metastasis in immunodeficient or immunocompetent orthotopic mouse models of human oral cancer, with no side effects. Clinically, the presence of CD36+ metastasis-initiating cells correlates with a poor prognosis for numerous types of carcinomas, and inhibition of CD36 also impairs metastasis, at least in human melanoma- and breast cancer-derived tumours. Together, our results indicate that metastasis-initiating cells particularly rely on dietary lipids to promote metastasis.

CD36 regulates LPS-induced acute lung injury by promoting macrophages M1 polarization.

M1 polarization of macrophages works as a promoter in pathogenesis of acute lung injury / acute respiratory distress syndrome (ALI/ARDS) by the secretion of pro-inflammatory cytokines and recruiting other inflammatory cells. Lipopolysaccharide (LPS), a critical component of the wall of gram-negative bacteria, can induce M1 polarization and ALI. Recently, cluster of differentiation 36 (CD36) has been reported to be associated with inflammatory responses. However, it has not yet been clarified whether CD36 in macrophages is involved in LPS-induced ALI. Herein, we demonstrated that in macrophages, LPS-induced ALI was regulated by CD36. Loss of CD36 attenuated LPS-induced ALI by reducing M1 polarization. Mechanistically, CD36 promoted macrophage M1 polarization by regulating CD14 associated with TLR4 during LPS stimulation. The findings of this study, clarified the mechanism of LPS-induced ALI through CD36 in macrophages, which provides a potential target for the prevention and treatment of ALI.

Involvement of lysosomal integral membrane protein-2 in the activation of autophagy.

Lysosomal integral membrane protein-2 (LIMP-2) is a type III transmembrane protein that is highly glycosylated and mainly localized to the lysosomal membrane. The diverse functions of LIMP-2 are currently being uncovered; however, its participation in macroautophagy, usually described as autophagy, has not yet been well-investigated. To determine the possible involvement of LIMP-2 in autophagic activity, we examined the intracellular amount of microtubule-associated protein 1 light chain 3 (LC3)-II, which is well-correlated with autophagosome levels, in exogenous rat LIMP-2-expressing COS7 and HEK293 cells. Transient or stable expression of LIMP-2-myc significantly increased the levels of LC3-II. Conversely, knockdown of LIMP-2 decreased the LC3-II levels in NIH3T3 cells. Furthermore, approaches using lysosomal protease inhibitors and mCherry-GFP-LC3 fluorescence suggested that exogenous expression of LIMP-2 increased the biogenesis of autophagosomes rather than decreased the lysosomal turnover of LC3-II. Considering the results of the biochemical assay and the quantitative fluorescence assay together, it is suggested that LIMP-2 has a possible involvement in autophagic activity, especially autophagosome biogenesis.

Impact of CD36 on Chemoresistance in Pancreatic Ductal Adenocarcinoma.

BACKGROUND: CD36, a multi-ligand scavenger receptor, has been associated with several cancers. Many studies have revealed that CD36 contributed to cancer malignancy. This study aimed to reveal the function of CD36 expression in pancreatic ductal adenocarcinoma (PDAC). METHODS: CD36 expression was characterized using immunohistochemistry in 95 clinical specimens resected from patients with PDAC. We divided patients into two groups, with different CD36 expression levels, and analyzed and compared their prognoses. CD36 expression was also assessed in PDAC cell lines. Gemcitabine-resistant (GR) PDAC cell lines were transfected with small interfering RNA (siRNA) that specifically targeted CD36 to evaluate chemoresistance and apoptosis. RESULTS: In resected PDAC samples, CD36 expression was significantly correlated with microinvasion into the venous system (p = 0.0284). Patients with high CD36 expression had significantly lower overall survival (OS) and recurrence-free survival (RFS) rates than patients with low expression; thus, CD36 was an independent prognostic factor for OS and RFS. In subgroup analyses, CD36 was an independent risk factor for OS and RFS in 59 patients treated with gemcitabine adjuvant chemotherapy. CD36 expression was upregulated in PDAC-GR cell lines compared with the PDAC parent cell line. Transduction with siRNA downregulated CD36, which reduced PDAC cell resistance to gemcitabine and inhibited anti-apoptosis proteins. CONCLUSION: CD36 expression influenced gemcitabine resistance by regulating anti-apoptosis proteins. High CD36 expression was a significant, unfavorable prognostic factor in PDAC. Anti-CD36 treatment might serve as an optional treatment for lowering resistance to gemcitabine.

CD36 in Atherosclerosis: Pathophysiological Mechanisms and Therapeutic Implications.

PURPOSE OF REVIEW: Atherosclerosis is a chronic disease characterized by lipid retention and inflammation in the artery wall. The retention and oxidation of low-density lipoprotein (LDL) in sub-endothelial space play a critical role in atherosclerotic plaque formation and destabilization. Oxidized LDL (ox-LDL) and other modified LDL particles are avidly taken up by endothelial cells, smooth muscle cells, and macrophages mainly through several scavenger receptors, including CD36 which is a class B scavenger receptor and membrane glycoprotein. RECENT FINDINGS: Animal studies performed on CD36-deficient mice suggest that deficiency of CD36 prevents the development of atherosclerosis, though with some debate. CD36 serves as a signaling hub protein at the crossroad of inflammation, lipid metabolism, and fatty acid metabolism. In addition, the level of soluble CD36 (unattached to cells) in the circulating blood was elevated in patients with atherosclerosis and other metabolic disorders. We performed a state-of-the-art review on the structure, ligands, functions, and regulation of CD36 in the context of atherosclerosis by focusing on the pathological role of CD36 in the dysfunction of endothelial cells, smooth muscle cells, monocytes/macrophages, and platelets. Finally, we highlight therapeutic possibilities to target CD36 expression/activity in atherosclerosis.

Inhibition of the CD36 receptor reduces visceral fat accumulation and improves insulin resistance in obese mice carrying the BDNF-Val66Met variant.

Obesity-induced metabolic dysfunctions increase the risk for vascular diseases, including type II diabetes and stroke. Managing obesity is of interest to address the worldwide health problem; however, the role of genetic variability in human obesity development and specific targets for obesity-related metabolic disease have not been thoroughly studied. A SNP in the brain-derived neurotropic factor (BDNF) gene that results in the substitution of a valine with a methionine at codon 66 (Val66Met) occurs with a high frequency in humans. This study addressed the effect of genetic variability in developing obesity and the efficacy of the inhibition of cluster of differentiation 36 (CD36), a multifunctional receptor implicated in obesity and insulin resistance, in WT mice and mice with the BDNF Val66Met variant. CD36 inhibition by salvionolic acid B (SAB) in diet-induced obese WT mice reduced visceral fat accumulation and improved insulin resistance. The benefit of SAB was abrogated in CD36 knockout mice, showing the specificity of SAB. In addition, mice with the Val66Met variant in both alleles (BDNFM/M) fed a high-fat diet exhibited extreme obesity with increased CD36 gene and protein levels in macrophages. Chronic SAB treatment in BDNFM/M mice significantly decreased visceral fat accumulation and improved insulin resistance. Notably, the effect of SAB was greater in the extremely obese BDNFM/M mice compared with the WT mice. The study demonstrated a link between BDNF Val66Met and elevated CD36 expression and suggested that CD36 inhibition may be a potential strategy to improve metabolic dysfunctions and to normalize risk factors for vascular diseases in the obese population.

Protein Kinase Cθ Via Activating Transcription Factor 2-Mediated CD36 Expression and Foam Cell Formation of Ly6Chi Cells Contributes to Atherosclerosis.

BACKGROUND: Although the role of thrombin in atherothrombosis is well studied, its role in the pathogenesis of diet-induced atherosclerosis is not known. METHODS: Using a mouse model of diet-induced atherosclerosis and molecular biological approaches, here we have explored the role of thrombin and its G protein-coupled receptor signaling in diet-induced atherosclerosis. RESULTS: In exploring the role of G protein-coupled receptor signaling in atherogenesis, we found that thrombin triggers foam cell formation via inducing CD36 expression, and these events require Par1-mediated Gα12-Pyk2-Gab1-protein kinase C (PKC)θ-dependent ATF2 activation. Genetic deletion of PKCθ in apolipoprotein E (ApoE)-/- mice reduced Western diet-induced plaque formation. Furthermore, thrombin induced Pyk2, Gab1, PKCθ, and ATF2 phosphorylation, CD36 expression, and foam cell formation in peritoneal macrophages of ApoE-/- mice. In contrast, thrombin only stimulated Pyk2 and Gab1 but not ATF2 phosphorylation or its target gene CD36 expression in the peritoneal macrophages of ApoE-/-:PKCθ-/- mice, and it had no effect on foam cell formation. In addition, the aortic root cross-sections of Western diet-fed ApoE-/- mice showed increased Pyk2, Gab1, PKCθ, and ATF2 phosphorylation and CD36 expression as compared with ApoE-/-:PKCθ-/- mice. Furthermore, although the monocytes from peripheral blood and the aorta of Western diet-fed ApoE-/- mice were found to contain more of Ly6Chi cells than Ly6Clo cells, the monocytes from Western diet-fed ApoE-/-:PKCθ-/- mice were found to contain more Ly6Clo cells than Ly6Chi cells. It is interesting to note that the Ly6Chi cells showed higher CD36 expression with enhanced capacity to form foam cells as compared with Ly6Clo cells. CONCLUSIONS: These findings reveal for the first time that thrombin-mediated Par1-Gα12 signaling via targeting Pyk2-Gab1-PKCθ-ATF2-dependent CD36 expression might be playing a crucial role in diet-induced atherogenesis.

CD36 promotes the epithelial-mesenchymal transition and metastasis in cervical cancer by interacting with TGF-ß.

BACKGROUND: Accumulating evidence indicates that CD36 initiates metastasis and correlates with an unfavorable prognosis in cancers. However, there are few reports regarding the roles of CD36 in initiation and metastasis of cervical cancer. METHODS: Using immunohistochemistry, we analyzed 133 cervical cancer samples for CD36 protein expression levels, and then investigated the correlation between changes in its expression and clinicopathologic parameters. The effect of CD36 expression on the epithelial-mesenchymal transition (EMT) in cervical cancer cells was evaluated by Western immunoblotting analysis. In vitro invasion and in vivo metastasis assays were also used to evaluate the role of CD36 in cervical cancer metastasis. RESULTS: In the present study, we confirmed that CD36 was highly expressed in cervical cancer samples relative to normal cervical tissues. Moreover, overexpression of CD36 promoted invasiveness and metastasis of cervical cancer cells in vitro and in vivo, while CD36 knockdown suppressed proliferation, migration, and invasiveness. We demonstrated that TGF-ß treatment attenuated E-cadherin expression and enhanced the expression levels of CD36, vimentin, slug, snail, and twist in si-SiHa, si-HeLa, and C33a-CD36 cells, suggesting that TGF-ß synergized with CD36 on EMT via active CD36 expression. We also observed that the expression levels of TGF-ß in si-SiHa cells and si-HeLa cells were down-regulated, whereas the expression levels of TGF-ß were up-regulated in C33a-CD36 cells. These results imply that CD36 and TGF-ß interact with each other to promote the EMT in cervical cancer. CONCLUSIONS: Our findings suggest that CD36 is likely to be an effective target for guiding individualized clinical therapy of cervical cancer.

Palmitate aggravates proteinuria-induced cell death and inflammation via CD36-inflammasome axis in the proximal tubular cells of obese mice.

High levels of serum free fatty acids (FFAs) and proteinuria have been implicated in the pathogenesis of obesity-related nephropathy. CD36, a class B scavenger receptor, is highly expressed in the renal proximal tubules and mediates FFA uptake. It is not clear whether FFA- and proteinuria-mediated CD36 activation coordinates NLRP3 inflammasomes to induce renal tubular injury and inflammation. In this study, we investigated the roles of CD36 and NLRP3 inflammasomes in FFA-induced renal injury in high-fat diet (HFD)-induced obesity. HFD-fed C57BL/6 mice and palmitate-treated HK2 renal tubular cells were used as in vivo and in vitro models. Immunohistochemical staining showed that CD36, IL-1ß, and IL-18 levels increased progressively in the kidneys of HFD-fed mice. Sulfo- N-succinimidyl oleate (SSO), a CD36 inhibitor, attenuated the HFD-induced upregulation of NLRP3, IL-1ß, and IL-18 and suppressed the colocalization of NLRP3 and ASC in renal tubular cells. In vitro, SSO abolished the palmitate-induced activation of IL-1ß, IL-18, and caspase-1 in HK2 proximal tubular cells. Furthermore, treatment with SSO and the knockdown of caspase-1 expression by siRNA both inhibited palmitate-induced cell death and apoptosis in HK2 cells. Collectively, palmitate causes renal tubular inflammation, cell death, and apoptosis via the CD36/NLRP3/caspase-1 axis, which may explain, at least in part, the mechanism underlying FFA-related renal tubular injury. The blockade of CD36-induced cellular processes is therefore a promising strategy for treating obesity-related nephropathy.

CD36 Is a Marker of Human Adipocyte Progenitors with Pronounced Adipogenic and Triglyceride Accumulation Potential.

White adipose tissue (WAT) expands in part through adipogenesis, a process involving fat cell generation and fatty acid (FA) storage into triglycerides (TGs). Several findings suggest that inter-individual and regional variations in adipogenesis are linked to metabolic complications. We aimed to identify cellular markers that define human adipocyte progenitors (APs) with pronounced adipogenic/TG storage ability. Using an unbiased single cell screen of passaged human adipose-derived stromal cells (hADSCs), we identified cell clones with similar proliferation rates but discordant capabilities to undergo adipogenic differentiation. Transcriptomic analyses prior to induction of differentiation showed that adipogenic clones displayed a significantly higher expression of CD36, encoding the scavenger receptor CD36. CD36+ hADSCs, in comparison with CD36-cells, displayed almost complete adipogenic differentiation while CD36 RNAi attenuated lipid accumulation. Similar findings were observed in primary CD45-/CD34+/CD31-APs isolated from human WAT where the subpopulation of MSCA1+/CD36+ cells displayed a significantly higher differentiation degree/TG storage capacity than MSCA1+/CD36-cells. Functional analyses in vitro and ex vivo confirmed that CD36 conferred APs an increased capacity to take up FAs thereby facilitating terminal differentiation. Among primary APs from subcutaneous femoral, abdominal and visceral human WAT, the fraction of CD36+ cells was significantly higher in depots associated with higher adipogenesis and reduced metabolic risk (i.e., femoral WAT). We conclude that CD36 marks APs with pronounced adipogenic potential, most probably by facilitating lipid uptake. This may be of value in developing human adipocyte cell clones and possibly in linking regional variations in adipogenesis to metabolic phenotype. Stem Cells 2017;35:1799-1814.

Synthetic Amphipathic Helical Peptides Targeting CD36 Attenuate Lipopolysaccharide-Induced Inflammation and Acute Lung Injury.

Synthetic amphipathic helical peptides (SAHPs) designed as apolipoprotein A-I mimetics are known to bind to class B scavenger receptors (SR-Bs), SR-BI, SR-BII, and CD36, receptors that mediate lipid transport and facilitate pathogen recognition. In this study, we evaluated SAHPs, selected for targeting human CD36, by their ability to attenuate LPS-induced inflammation, endothelial barrier dysfunction, and acute lung injury (ALI). L37pA, which targets CD36 and SR-BI equally, inhibited LPS-induced IL-8 secretion and barrier dysfunction in cultured endothelial cells while reducing lung neutrophil infiltration by 40% in a mouse model of LPS-induced ALI. A panel of 20 SAHPs was tested in HEK293 cell lines stably transfected with various SR-Bs to identify SAHPs with preferential selectivity toward CD36. Among several SAHPs targeting both SR-BI/BII and CD36 receptors, ELK-B acted predominantly through CD36. Compared with L37pA, 5A, and ELK SAHPs, ELK-B was most effective in reducing the pulmonary barrier dysfunction, neutrophil migration into the lung, and lung inflammation induced by LPS. We conclude that SAHPs with relative selectivity toward CD36 are more potent at inhibiting acute pulmonary inflammation and dysfunction. These data indicate that therapeutic strategies using SAHPs targeting CD36, but not necessarily mimicking all apolipoprotein A-I functions, may be considered a possible new treatment approach for inflammation-induced ALI and pulmonary edema.

Long-chain fatty acid activates hepatocytes through CD36 mediated oxidative stress.

BACKGROUND: Accumulating evidence suggests that activated hepatocytes are involved in the deposition of the excess extracellular matrix during liver fibrosis via the epithelial to mesenchymal transition. Lipid accumulation in hepatocytes are implicated in the pathogenesis of chronic liver injury. CD36 is known to mediate long-chain fatty acid (LCFA) uptake and lipid metabolism. However, it is unclear whether LCFA directly promotes hepatocyte activation and the involved mechanisms have not been fully clarified. METHODS: Mice were fed with a high fat diet (HFD) and normal hepatocyte cells (Chang liver cells) were treated with palmitic acid (PA) in vivo and in vitro. Real-time polymerase chain reaction (RT-PCR) and western blotting were used to examine the gene and protein expression of molecules involved in hepatic fibrogenesis and hepatocyte activation. CD36 was knocked down by transfecting CD36 siRNA into hepatocyte cells. Hydrogen peroxide (H2O2) and reactive oxygen species (ROS) levels were detected using commercial kits. RESULTS: HFD induced a profibrogenic response and up-regulated CD36 expression in vivo. Analogously, PA increased lipid accumulation and induced human hepatocyte activation in vitro, which was also accompanied by increased CD36 expression. Interestingly, knockdown of CD36 resulted in a reduction of hepatocyte lipid deposition and decreased expression of Acta2 (34% decrease), Vimentin (29% decrease), Desmin (60% decrease), and TGF-ß signaling pathway related genes. In addition, HFD and PA increased the production of H2O2 in vivo (48% increase) and in vitro (385% increase), and the antioxidant, NAC, ameliorated PA-induced hepatocyte activation. Furthermore, silencing of CD36 in vitro markedly attenuated PA-induced oxidative stress (H2O2: 41% decrease; ROS: 39% decrease), and the anti-activation effects of CD36 knockdown could be abolished by pretreatment with H2O2. CONCLUSIONS: Our study demonstrated that LCFA facilitates hepatocyte activation by up-regulating oxidative stress through CD36, which could be an important mechanism in the development of hepatic fibrosis.

Tet38 Efflux Pump Affects Staphylococcus aureus Internalization by Epithelial Cells through Interaction with CD36 and Contributes to Bacterial Escape from Acidic and Nonacidic Phagolysosomes.

We previously reported that the Tet38 efflux pump is involved in internalization of Staphylococcus aureus by A549 lung epithelial cells. A lack of tet38 reduced bacterial uptake by A549 cells to 36% of that of the parental strain RN6390. Using invasion assays coupled with confocal microscopy imaging, we studied the host cell receptor(s) responsible for bacterial uptake via interaction with Tet38. We also assessed the ability of S. aureus to survive following alkalinization of the phagolysosomes by chloroquine. Antibody to the scavenger receptor CD36 reduced the internalization of S. aureus RN6390 by A549 cells, but the dependence on CD36 was reduced in QT7 tet38, suggesting that an interaction between Tet38 and CD36 contributed to S. aureus internalization. Following fusion of the S. aureus-associated endosomes with lysosomes, alkalinization of the acidic environment with chloroquine led to a rapid increase in the number of S. aureus RN6390 bacteria in the cytosol, followed by a decrease shortly thereafter. This effect of chloroquine was not seen in the absence of intact Tet38 in mutant QT7. These data taken together suggest that Tet38 plays a role both in bacterial internalization via interaction with CD36 and in bacterial escape from the phagolysosomes.

CD36 is upregulated in mice with periodontitis and metabolic syndrome and involved in macrophage gene upregulation by palmitate.

BACKGROUND: We reported that high-fat diet (HFD)-induced metabolic syndrome (MetS) exacerbates lipopolysaccharide (LPS)-stimulated periodontitis and palmitate, the major saturated fatty acid in the HFD, amplified LPS-stimulated gene expression in vitro. As CD36 is a major receptor for fatty acids, we investigated periodontal CD36 expression in mice with periodontitis and MetS, and the role of CD36 in inflammatory gene expression in macrophages stimulated by palmitate. METHODS: MetS and periodontitis were induced in mice by HFD and periodontal injection of LPS, respectively. The periodontal CD36 expression and its relationship with alveolar bone loss were studied using immunohistochemistry, real-time PCR, and correlation analysis. The role of CD36 in upregulation of inflammatory mediators by LPS and palmitate in macrophages was assessed using pharmacological inhibitor and small interfering RNA. RESULTS: Periodontal CD36 expression was higher in mice with both MetS and periodontitis than that in mice with periodontitis or MetS alone and was correlated with osteoclastogenesis and alveolar bone loss. In vitro studies showed that CD36 expression in macrophages was upregulated by LPS and palmitate, and targeting CD36 attenuated palmitate-enhanced gene expression. CONCLUSION: CD36 expression is upregulated in mice with periodontitis and MetS and involved in gene expression in macrophages stimulated by palmitate and LPS.

Antagonism of scavenger receptor CD36 by 5A peptide prevents chronic kidney disease progression in mice independent of blood pressure regulation.

Scavenger receptor CD36 participates in lipid metabolism and inflammatory pathways important for cardiovascular disease and chronic kidney disease (CKD). Few pharmacological agents are available to slow the progression of CKD. However, apolipoprotein A-I-mimetic peptide 5A antagonizes CD36 in vitro. To test the efficacy of 5A, and to test the role of CD36 during CKD, we compared wild-type to CD36 knockout mice and wild-type mice treated with 5A, in a progressive CKD model that resembles human disease. Knockout and 5A-treated wild-type mice were protected from CKD progression without changes in blood pressure and had reductions in cardiovascular risk surrogate markers that are associated with CKD. Treatment with 5A did not further protect CD36 knockout mice from CKD progression, implicating CD36 as its main site of action. In a separate model of kidney fibrosis, 5A-treated wild-type mice had less macrophage infiltration and interstitial fibrosis. Peptide 5A exerted anti-inflammatory effects in the kidney and decreased renal expression of inflammasome genes. Thus, CD36 is a new therapeutic target for CKD and its associated cardiovascular risk factors. Peptide 5A may be a promising new agent to slow CKD progression.

LDL acts as an opsonin enhancing the phagocytosis of group A Streptococcus by monocyte and whole human blood.

Low-density lipoprotein (LDL) binds to group A Streptococcus (GAS) through Sc11 protein, and scavenger receptor CD36 of monocyte mediates the endocytosis of native or modified LDL. Therefore, we hypothesized that LDL might be an opsonin enhancing the phagocytosis of LDL-bound GAS by monocyte. The results showed that LDL could significantly promote U937 cell to phagocytose M28 (ATCC BAA1064) and M41 (ATCC 12373, AM41)-type GAS, and the phagocytosis rates were significantly increased, compared with LDL-free group. LDL, however, did not enhance the phagocytosis of M41 (CMCC 32198, CM41) or M6 (ATCC BAA946)-type GAS since these two strains did not bind to LDL. CD36 was the major scavenger receptor mediating the uptake of LDL-bound GAS by monocyte U937 cells since anti-CD36 antibody abolished the phagocytosis of LDL-opsonized GAS but anti-CD4 antibody did not. Most of AM41-type GAS cells were killed in human blood, whereas only a few CM41-type cells were phagocytosed. Moreover, recombinant Scl1 (rScl1) derived from M41-type GAS could significantly decrease the opsonophagocytosis of AM41 but not CM41-type GAS because the rScl1 competitively blocked the binding of AM41-type GAS to LDL. Therefore, our findings suggest that LDL may be an opsonin to enhance CD36-dependent opsonic phagocytosis of GAS by monocyte.

Puerarin Suppresses Na+-K+-ATPase-Mediated Systemic Inflammation and CD36 Expression, and Alleviates Cardiac Lipotoxicity In Vitro and In Vivo.

Puerarin, a type of isoflavone, was shown to have multiple protective effects on myocardial injury. The objective of this study was to investigate the role of puerarin in the progression of lipotoxic cardiomyopathy. Primary cardiomyocytes were isolated from FATP1 transgenic (Tg) mice with lipotoxic cardiomyopathy, and various concentrations of puerarin were used to incubate with the cardiomyocytes. Our results showed low-dose puerarin (≤20 µM) treatment increased the cell viability and decreased the accumulation of free fatty acid (FFA). The data on enzyme-linked immunosorbent assay indicated that 15 µM puerarin treatment greatly increased Na-K-ATPase activity and decreased C-reactive protein secretion, thus suppressing the expression of CD36, a key contributor to the FFA accumulation. Additionally, low-dose puerarin (≤100 mg/kg body weight) administration improved Na-K-ATPase activity. Our data on serum analysis and histological detection in vivo indicated that systemic inflammation, CD36-induced lipid infiltration, and cardiomyocyte apoptosis were markedly alleviated in Tg mice injected with 90 mg/kg dose of puerarin. Finally, the uptake rates of H-palmitate and C-glucose were monitored on ex vivo working hearts that were obtained from wild-type (WT), Tg-control, and Tg-puerarin mice. Compared with WT hearts, Tg hearts displayed a significant decrease in Na/K-ATPase activity and glucose consumption rate and an increase in palmitate uptake rate and FFA accumulation. In Tg-puerarin hearts, Na/K-ATPase activity and glucose consumption rate were significantly rescued, and palmitate uptake and FFA accumulation were sharply suppressed. In conclusion, low-dose puerarin suppressed Na-K-ATPase-mediated CD36 expression and systemic inflammation and alleviated cardiac lipotoxicity in vitro and in vivo.

Simvastatin inhibited oxLDL-induced proatherogenic effects through calpain-1-PPARγ-CD36 pathway.

We previously reported that simvastatin, an inhibitor of HMG-CoA reductase, inhibits atherosclerosis in rats. The present study was designed to investigate the effect of simvastatin on mouse peritoneal macrophage foam cell formation, the early feature of atherosclerosis, and explore its mechanisms. The results showed that simvastatin decreased cholesterol content and DiI-oxLDL (1,1'-didodecyl 3,3,3',3'-indocarbocyanine perchlorate - oxidized low-density lipoprotein) uptake, reduced the levels of tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) in the medium, down-regulated the mRNA and protein expression of CD36 (a fatty acid receptor), and reduced the mRNA expressions of peroxisome proliferator-activated receptor gamma (PPARγ), TNF-α, and IL-6 in macrophages treated with oxLDL. However, PPARγ agonist troglitazone partly abolished the effects of simvastatin on foam cells. In addition, simvastatin reduced the protein expression of calpain-1, a Ca2+-sensitive cysteine protease, in oxLDL-treated macrophages. Furthermore, PD150606, a specific calpain inhibitor, reduced mRNA expressions of PPARγ and CD36 in macrophages treated with oxLDL. Combination of simvastatin and PD150606 had no further effect on mRNA expression of PPARγ and CD36 compared with either alone. However, over-expression of calpain-1 in macrophages partly reversed the simvastatin effects, including cell cholesterol content, mRNA expressions of PPARγ, and CD36. The results suggested that simvastatin inhibits foam cell formation of oxLDL-treated macrophages through a calpain-1-PPARγ-CD36 pathway.

A single aldehyde group can serve as a structural element for recognition by transmembrane protein CD36.

Transmembrane protein CD36 is considered to bind its distinct ligands such as long-chain fatty acids primarily by recognizing their terminal carboxyl moiety. In this study, we provide evidence that long-chain fatty aldehydes, such as oleic aldehyde, can be recognized by CD36. We suggest that a single aldehyde group may also serve as one of the structural elements recognizable by CD36.