Molecular basis of CD36 deficiency. Evidence that a 478C-->T substitution (proline90-->serine) in CD36 cDNA accounts for CD36 deficiency

Haplotypes analysis reveals the genetic basis of type I CD36 deficiency

CD36, also known as glycoprotein IV, is classified into two distinct subgroups based on the presence or absence of its expression on monocytes. The CD36 gene spans approximately 50,000 base pairs. Historically, research has focused on identifying CD36 mutations through Sanger sequencing and next-generation sequencing (NGS), with limited exploration of haplotypes. In this study, we collected blood samples from donors with type I and type II CD36 deficiencies as well as from healthy controls, and employed single-molecule long-read sequencing (also known as Third-Generation Sequencing) of genomic DNA to analyze the genetic basis of CD36. The study identified 180 genetic variants, 12 of which were found to alter the amino acid sequence. Notably, four of these mutations (c.220 C > T; c.329_330delAC; c.430-1 G > C; c.1006 + 2 T > G) are premature termination mutations that lead to protein truncation. Using Fisher's exact test, we statistically analyzed a specific haplotype, c.-132A > C and c.329_330delAC, along with their clinical phenotypes, revealing a strong association between these variants in the 5' block and type I CD36 deficiency. We analyzed the CD36 gene sequences in platelet donors and patients with PTR (platelet transfusion refractoriness) and FNAIT (fetal and neonatal alloimmune thrombocytopenia), conducting a detailed haplotype analysis associated with type I CD36 deficiency and FNAIT.

The polymorphism analysis for CD36 among platelet donors

CD36 may defect on platelets and/or monocytes in healthy individuals, which was defined as CD36 deficiency. However, we did not know the correlation between the molecular and protein levels completely. Here, we aim to determine the polymorphisms of the CD36 gene, RNA level, and CD36 on platelets and in plasma. The individuals were sequenced by Sanger sequencing. Bioinformational analysis was used by the HotMuSiC, CUPSAT, SAAFEC-SEQ, and FoldX. RNA analysis and CD36 protein detection were performed by qPCR, flow cytometry, and ELISA. In this study, we found c.1228_1239delATTGTGCCTATT (allele frequency = 0.0072) with the highest frequency among our cohort, and one mutation (c.1329_1354dupGATAGAAATGATCTTACTCAGTGTTG) was not present in the dbSNP database. 5 mutations located in the extracellular domain sequencing region with confirmation in deficient individuals, of which c.284T>C, c.512A>G, c.572C>T, and c.869T>C were found to have a deleterious impact on CD36 protein stability. Furthermore, the MFI of CD36 expression on platelets in the mutation-carry, deleterious-effect, and deficiency group was significantly lower than the no-mutation group (P < 0.0500). In addition, sCD36 levels in type II individuals were significantly lower compared with positive controls (P = 0.0060). Nevertheless, we found the presence of sCD36 in a type I individual. RNA analysis showed CD36 RNA levels in platelets of type II individuals were significantly lower than the positive individuals (P = 0.0065). However, no significant difference was observed in monocytes (P = 0.7500). We identified the most prevalent mutation (c.1228_1239delATTGTGCCTATT) among Kunming donors. Besides, our results suggested RNA level alterations could potentially underlie type II deficiency. Furthermore, sCD36 may hold promise for assessing immune reaction risk in CD36-deficient individuals, but more studies should be conducted to validate this hypothesis.

Frequency and molecular basis of CD36 deficiency among platelet donors in Kunming, China

CD36 is a multifunctional receptor expressed on the surface of many cell types. Among healthy individuals, CD36 may be absent on platelets and monocytes (type I deficiency) or platelets alone (type II deficiency). However, the exact molecular mechanisms underlying CD36 deficiency remain unclear. In this study, we aimed to identify individuals with CD36 deficiency and investigate the molecular basis underlying it. Blood samples were collected from platelet donors at Kunming Blood Center. Platelets and monocytes were isolated and CD36-expression levels were analyzed using flow cytometry. DNA from whole blood and mRNA isolated from monocytes and platelets of individuals with CD36 deficiency were analyzed using polymerase chain reaction (PCR) testing. The PCR products were cloned and sequenced. Among the 418 blood donors,7 (1.68%) were CD36 deficient: 1 (0.24%) with type I deficiency and 6(1.44%) with type II deficiency. Six heterozygous mutations occurred, including c.268C>T (in type I individuals), c.120 + 1 G>T, c.268C>T, c.329_330del/AC, c.1156 C>T, c.1163A>C, and c.1228_1239del/ATTGTGCCTATT (in type II individuals). Mutations were not detected in one type II individual . At the cDNA level, only mutant, but not wild-type, transcripts were detected in the platelets and monocytes of type I individual. In type II individuals, only mutant transcripts were found in platelets, whereas monocytes possessed wild-type and mutant transcripts. Interestingly, only alternative splicing transcripts were observed in the individual without mutation. We report the incidence rates of type I and II CD36 deficiencies among platelet donors in Kunming. Molecular genetic analyses of DNA and cDNA demonstrated that homozygous mutations on the cDNA level in platelets and monocytes or platelets alone identified type I and II deficiencies, respectively. Furthermore, alternatively spliced products also potentially contribute to the mechanism of CD36 deficiency.

Severe Platelet Transfusion Refractoriness in Association with Antibodies Against CD36

Platelet-transfusion refractoriness (PTR) is common in patients with hematological malignancies. The etiology of immune PTR is typically human leukocyte antigen (HLA) antibodies (Abs) from pregnancy or previous transfusion. Herein, we report PTR in the setting of induction chemotherapy for acute myelogenous leukemia (AML) from Abs against CD36/glycoprotein (GP)IV. A 66-year-old African American woman presented with anemia and thrombocytopenia. She was found to have transfusion-dependent AML, and a 7 + 3 regimen (7 days of standard-dose cytarabine and 3 days of an anthracycline antibiotic or an anthracenedione, most often daunorubicin) was initiated. The patient developed profound thrombocytopenia, with platelet nadir of 0 by day 13. The results of HLA antibody screening were negative. However, the results of a screening test for platelet-specific antibodies screen showed Abs against cluster of differentiation (CD)36. The platelets of the patient lacked expression of CD36, and DNA analysis showed mutations in the CD36 gene. HLA Ab-mediated PTR is common in patients with hematological malignancies. However, once HLA Abs are excluded, other less-frequent Abs should be considered, particularly in patient populations of Asian, African, or Middle Eastern descent.

Platelet CD36 deficiency is present in 2.6% of Arabian individuals and can cause NAIT and platelet refractoriness

BACKGROUND

CD36 isoantibodies are capable of inducing neonatal alloimmune thrombocytopenia (NAIT) and platelet refractoriness. As to now the CD36 type I deficiency has been reported in East Asian and African individuals. However, it is virtually unknown in Caucasians. The aim of this study was to display the prevalence of the CD36 deficiency within parts of the Arabian population in Germany. Secondly, we are presenting the case of a newborn suffering from NAIT which was induced by CD36 antibody.

METHODS

Platelet (p) CD36 was determined by flow cytometry on 1328 samples mainly from individuals of Arabian origin and a family with a neonate affected by NAIT. DNA sequencing was performed on all pCD36-negative samples.

RESULTS

Thirty-five (2.64%) of all donor samples were pCD36 negative, 19 (1.43%) had a weak expression. Including only individuals from the Arabian peninsula, frequencies were 3.39% and 1.75%, respectively. CD36 type I deficiency on both platelets and monocytes combined with a CD36 isoantibody were detected in the mother of the NAIT baby. The baby was successfully transfused with two HPA-unselected platelet concentrates. In case of need, two platelet units with a weak pCD36 expression were on hand. A total of 45 different CD36 mutations were detected within pCD36-negative individuals, some being homozygous, most of them only present on one allele.

CONCLUSION

The CD36-negative phenotype is present in a significant number of individuals of Arabian origin and enables CD36 isoimmunization in NAIT or refractoriness. Blood transfusion services should be aware of such cases.

New molecular basis associated with CD36-negative phenotype in the sub-Saharan African population

BACKGROUND

CD36 glycoprotein is expressed by various cell types, including platelets (PLTs), monocytes, and erythroid precursors, and is also the receptor for several ligands. However, absence of CD36 expression seems asymptomatic and is poorly described in Caucasians. In contrast, the frequency reaches 7% and 11% in African Caribbean and Asian persons, respectively. Lack of CD36 expression exposes to the risk of immunization in case of pregnancy or PLT transfusion. Two types of deficiency have been described: in Type I, PLTs and monocytes lack CD36 expression and the subjects are homozygous or compound heterozygous for CD36 mutations, whereas in Type II, only PLTs (Type IIa), and rarely also erythroid cells (Type IIb), are affected. Molecular events leading to Type II deficiency are poorly understood.

CASE REPORT

An African girl, diagnosed with homozygous sickle cell disease and regularly transfused, was assessed for PLT CD36 expression by immunofluorescence microscopy. The deficiency was then confirmed by monoclonal antibody immobilization of PLT antigen (MAIPA) assay, and the subtype was assessed by flow cytometry. The underlying molecular basis was characterized by DNA sequencing. Furthermore, we tested the serum for possible anti-CD36 immunization.

RESULTS AND CONCLUSION

Flow cytometric analysis on the patient's blood samples allowed the diagnosis of Type I CD36 deficiency. CD36 antibodies, probably due to her past history of red blood cell transfusions, were identified by MAIPA and by Luminex technology assay. Interestingly, we identified through sequencing a new molecular basis involved in CD36 deficiency: two adenines were replaced by one guanine in Exon 4 (c.367_368delAAinsG) leading to a stop codon at Position 76.

PSCAN: Spatial scan tests guided by protein structures improve complex disease gene discovery and signal variant detection

Germline disease-causing variants are generally more spatially clustered in protein 3-dimensional structures than benign variants. Motivated by this tendency, we develop a fast and powerful protein-structure-based scan (PSCAN) approach for evaluating gene-level associations with complex disease and detecting signal variants. We validate PSCAN's performance on synthetic data and two real data sets for lipid traits and Alzheimer's disease. Our results demonstrate that PSCAN performs competitively with existing gene-level tests while increasing power and identifying more specific signal variant sets. Furthermore, PSCAN enables generation of hypotheses about the molecular basis for the associations in the context of protein structures and functional domains.

Fatty acids - from energy substrates to key regulators of cell survival, proliferation and effector function

Recent advances in immunology and cancer research show that fatty acids, their metabolism and their sensing have a crucial role in the biology of many different cell types. Indeed, they are able to affect cellular behaviour with great implications for pathophysiology. Both the catabolic and anabolic pathways of fatty acids present us with a number of enzymes, receptors and agonists/antagonists that are potential therapeutic targets, some of which have already been successfully pursued. Fatty acids can affect the differentiation of immune cells, particularly T cells, as well as their activation and function, with important consequences for the balance between anti- and pro-inflammatory signals in immune diseases, such as rheumatoid arthritis, psoriasis, diabetes, obesity and cardiovascular conditions. In the context of cancer biology, fatty acids mainly provide substrates for energy production, which is of crucial importance to meet the energy demands of these highly proliferating cells. Fatty acids can also be involved in a broader transcriptional programme as they trigger signals necessary for tumorigenesis and can confer to cancer cells the ability to migrate and generate distant metastasis. For these reasons, the study of fatty acids represents a new research direction that can generate detailed insight and provide novel tools for the understanding of immune and cancer cell biology, and, more importantly, support the development of novel, efficient and fine-tuned clinical interventions. Here, we review the recent literature focusing on the involvement of fatty acids in the biology of immune cells, with emphasis on T cells, and cancer cells, from sensing and binding, to metabolism and downstream effects in cell signalling.

Functionalization of CD36 cardiovascular disease and expression associated variants by interdisciplinary high throughput analysis

CD36 is a platelet membrane glycoprotein whose engagement with oxidized low-density lipoprotein (oxLDL) results in platelet activation. The CD36 gene has been associated with platelet count, platelet volume, as well as lipid levels and CVD risk by genome-wide association studies. Platelet CD36 expression levels have been shown to be associated with both the platelet oxLDL response and an elevated risk of thrombo-embolism. Several genomic variants have been identified as associated with platelet CD36 levels, however none have been conclusively demonstrated to be causative. We screened 81 expression quantitative trait loci (eQTL) single nucleotide polymorphisms (SNPs) associated with platelet CD36 expression by a Massively Parallel Reporter Assay (MPRA) and analyzed the results with a novel Bayesian statistical method. Ten eQTLs located 13kb to 55kb upstream of the CD36 transcriptional start site of transcript ENST00000309881 and 49kb to 92kb upstream of transcript ENST00000447544, demonstrated significant transcription shifts between their minor and major allele in the MPRA assay. Of these, rs2366739 and rs1194196, separated by only 20bp, were confirmed by luciferase assay to alter transcriptional regulation. In addition, electromobility shift assays demonstrated differential DNA:protein complex formation between the two alleles of this locus. Furthermore, deletion of the genomic locus by CRISPR/Cas9 in K562 and Meg-01 cells results in upregulation of CD36 transcription. These data indicate that we have identified a variant that regulates expression of CD36, which in turn affects platelet function. To assess the clinical relevance of our findings we used the PhenoScanner tool, which aggregates large scale GWAS findings; the results reinforce the clinical relevance of our variants and the utility of the MPRA assay. The study demonstrates a generalizable paradigm for functional testing of genetic variants to inform mechanistic studies, support patient management and develop precision therapies.

Platelets are anucleate cells that are best known as regulators of vascular hemostasis and thrombosis but also play important roles in cancer, angiogenesis, and inflammation. CD36 is a platelet surface marker that can activate platelet in response to oxidized low density lipoprotein (oxLDL). CD36 has been associated with numerous cardiovascular traits in human including blood lipid levels, platelet count, and cardiovascular disease prevalence in human genetic studies. Human variability in platelet CD36 levels are associated with the platelet response to oxLDL. However, the genetic mechanisms responsible for the variability of CD36 levels are unknown. We examined 81 genetic variants associated with CD36 levels for functionality using a high-throughput assay. Of the ten variants that were identified in that assay, one doublet, rs2366739 and rs1194196, were confirmed using additional molecular and cellular assays. Deletion of the genomic region containing rs2366739 and rs1194196 resulted in overexpression of CD36 in a cell culture system. This finding indicates a control locus which can serve as a potential target in modulating CD36 expression and altering platelet function in cardiovascular disease.

Cluster of differentiation 36 gene polymorphism (rs1761667) is associated with dietary MUFA intake and hypertension in a Japanese population

Cluster of differentiation 36 (CD36) is a membrane receptor expressed on a wide variety of human cells. CD36 polymorphisms are reportedly associated with oral fat perception, dietary intake and metabolic disorders. The present study examined associations of two CD36 polymorphisms (rs1761667 and rs1527483) and dietary fat intake, and metabolic phenotypes in a Japanese population. This cross-sectional study was conducted based on clinical information collected from health check-ups in Japan (n 495). Dietary nutrient intake was estimated from a validated short FFQ and adjusted for total energy intake using the residual method. Mean blood pressure was calculated from systolic blood pressure (SBP) and diastolic blood pressure (DBP). Hypertension was defined as SBP ≥ 130 mmHg and/or DBP ≥ 85 mmHg, or use of antihypertensive drugs. Genotyping was performed using PCR with confronting two-pair primers method. Mean age was 63·4 (sd 9·9) years. Individuals with the AA genotype showed higher total fat and MUFA intake (standardised β = 0·110 and 0·087, P = 0·01 and 0·05, respectively) compared with the GG and GA genotypes. For metabolic phenotypes, the AA genotype of rs1761667 had a lower blood pressure compared with the GG genotype (standardised β = -0·123, P = 0·02). Our results suggested that the AA genotype of rs1761667 in the CD36 gene was associated with higher intake of total fat and MUFA and lower risk of hypertension in a Japanese population.

Treatment with medium chain fatty acids milk of CD36-deficient preschool children

OBJECTIVE

CD36 deficiency is characterized by limited cellular long chain fatty acid uptake in the skeletal and cardiac muscles and often causes energy crisis in these muscles. However, suitable treatment for CD36 deficiency remains to be established. The aim of this study was to evaluate the clinical and metabolic effects of medium chain triacylglycerols (MCTs) in two CD36-deficient preschool children who often developed fasting hypoglycemia and exercise-induced myalgia.

METHODS

Fasting blood glucose, total ketone bodies, and free fatty acids were examined and compared for usual supper diets and for diets with replacement of one component with 2 g/kg of 9% MCT-containing milk (MCT milk). Changes in serum creatine kinase and alanine aminotransferase levels, resulting from replacement of glucose water intake with 1 g/kg of MCT milk and determined by using bicycle pedaling tasks, were examined and compared. Hypoglycemic and/or myalgia episodes in daily life were also investigated.

RESULTS

Biochemically, participants' blood glucose and total ketone bodies levels after overnight fasting substantially increased after dietary suppers containing MCT milk. Increases in serum creatine kinase and alanine aminotransferase levels resulting from the bicycle pedaling task were suppressed by MCT milk. Hypoglycemia leading to unconsciousness and tachycardia before breakfast decreased after introduction of dietary suppers containing MCT milk. Occurrence of myalgia in the lower limbs also decreased after intakes of MCT milk before long and/or strenuous exercising.

CONCLUSION

Our results suggest that MCTs can prevent fasting hypoglycemia and exercise-induced myalgia in CD36-deficient young children.

Diverse CD36 expression among Japanese population: defective CD36 mutations cause platelet and monocyte CD36 reductions in not only deficient but also normal phenotype subjects

INTRODUCTION

CD36 is a multifunctional glycoprotein expressed on various human cells, including platelets and monocytes. Five CD36 gene mutations (C268T, 949insA, 329-339del, 1228-1239del and 629-631del/insAAAAC) are mainly responsible for CD36-deficient phenotypes in Japan. It has also been reported that platelet CD36 expression varies widely among normal phenotype individuals. Here, in order to obtain further insight into CD36 expression, we investigated the association between platelet and monocyte CD36 expression levels and defective mutations in the Japanese population.

MATERIALS AND METHODS

Blood samples were collected from 135 healthy Japanese volunteers. CD36 expression levels on platelets and monocytes were quantitatively analyzed by flow cytometry. Real-time PCR, PCR-RFLP and allele-specific PCR were performed to detect mutant genotypes.

RESULTS

In this population, we found 2 (1.5%) and 9 (6.7%) CD36-deficient subjects as type I and type II, respectively. Among normal phenotype subjects, CD36 expression levels ranged from 1,259 to 11,002 (4,487±2,017) molecules/platelet and from 211 to 5,150 (1,628±986) molecules/monocyte. Genotyping assay showed that heterozygotes with the defective mutations were present in normal (12.9%) and type II-deficient (66.7%) subjects, and that these heterozygous mutations led to decreases in CD36 surface expression on platelets and monocytes.

CONCLUSIONS

Heterozygous CD36 mutations, previously known to lead to deficiency in this molecule, are one of the factors responsible for the diversity of CD36 surface expression levels on platelets and monocytes in normal phenotype subjects.

CD36 binds oxidized low density lipoprotein (LDL) in a mechanism dependent upon fatty acid binding

The association of unesterified fatty acid (FA) with the scavenger receptor CD36 has been actively researched, with focuses on FA and oxidized low density lipoprotein (oxLDL) uptake. CD36 has been shown to bind FA, but this interaction has been poorly characterized to date. To gain new insights into the physiological relevance of binding of FA to CD36, we characterized FA binding to the ectodomain of CD36 by the biophysical method surface plasmon resonance. Five structurally distinct FAs (saturated, monounsaturated (cis and trans), polyunsaturated, and oxidized) were pulsed across surface plasmon resonance channels, generating association and dissociation binding curves. Except for the oxidized FA HODE, all FAs bound to CD36, with rapid association and dissociation kinetics similar to HSA. Next, to elucidate the role that each FA might play in CD36-mediated oxLDL uptake, we used a fluorescent oxLDL (Dii-oxLDL) live cell assay with confocal microscopy imaging. CD36-mediated uptake in serum-free medium was very low but greatly increased when serum was present. The addition of exogenous FA in serum-free medium increased oxLDL binding and uptake to levels found with serum and affected CD36 plasma membrane distribution. Binding/uptake of oxLDL was dependent upon the FA dose, except for docosahexaenoic acid, which exhibited binding to CD36 but did not activate the uptake of oxLDL. HODE also did not affect oxLDL uptake. High affinity FA binding to CD36 and the effects of each FA on oxLDL uptake have important implications for protein conformation, binding of other ligands, functional properties of CD36, and high plasma FA levels in obesity and type 2 diabetes.

Free fatty acid uptake in humans with CD36 deficiency

Animal models have demonstrated that CD36 facilitates cell membrane free fatty acid (FFA) transport, but its role in human metabolism is not well understood. We measured heart, liver, adipose (three depots), and muscle (truncal postural and thigh locomotive) FFA uptake using [(11)C]palmitate positron emission tomography (PET) scans in a family of five carrying the Pro90Ser CD36 mutation (2 homozygotes had no CD36) and matched control volunteers. PET scans were done under conditions of suppressed and slightly increased palmitate concentrations. During suppressed palmitate conditions, muscle and adipose palmitate uptake were markedly reduced in homozygotes but not heterozygotes for the Pro90Ser CD36 mutation, whereas when palmitate concentration was slightly increased, uptake in muscle and adipose did not differ between control subjects and homozygous family members. Hepatic FFA uptake was similar in all participants regardless of palmitate concentrations, whereas myocardial FFA uptake was diminished in the Pro90Ser homozygotes during both suppressed and increased palmitate conditions. We conclude that CD36 1) facilitates FFA transport into muscle and adipose tissue in humans when extracellular concentrations are reduced but not when they are modestly elevated, 2) is not rate limiting for hepatic FFA uptake, and 3) is needed for normal cardiac FFA uptake over a range of FFA concentrations from low to slightly elevated.

Incidence and molecular basis of CD36 deficiency in Shanghai population

BACKGROUND

CD36 is a multifunctional membrane receptor and is expressed in several cell lines. Individuals who lack platelet (PLT) CD36 are at risk for immunization against this antigen, leading to several clinical syndromes. This study aimed to investigate the frequency and molecular basis of CD36 deficiency in Shanghai.

STUDY DESIGN AND METHODS

Whole blood samples were collected from healthy blood donors, and the PLTs and monocytes were analyzed using flow cytometry to determine CD36 deficiency type. After genomic DNA was extracted, Exons 3 to 14 of CD36 gene including a part of relevant flanking introns were amplified. Direct nucleotide sequencing and sequence alignment were performed. The samples that showed mutations were confirmed by clonal sequencing.

RESULTS

Of the 1022 healthy blood donors analyzed, 22 individuals failed to express CD36 on PLTs; two of them expressed no CD36 on their monocytes either. These results demonstrated that the frequencies of Type I (lacking CD36 expression on PLTs and monocytes) and Type II (lacking CD36 expression on PLTs only) CD36 deficiency among the study population were 0.2 and 2.0%, respectively. Nucleotide sequencing analysis revealed nine different mutations including six mutations that were not yet reported. The most frequent mutations among the study population were 329-330delAC and 1228-1239delATTGTGCCTATT.

CONCLUSION

The study findings have confirmed the fact that the frequency of CD36 deficiency in the Chinese population is slightly lower than that in other Asian countries. The identification of several new mutation types indicated the polymorphism of CD36 gene in the Shanghai population.

Studies on CD36 deficiency in South China: Two cases demonstrating the clinical impact of anti-CD36 antibodies

CD36 (also known as GPIV) deficiency is known to be responsible for the production of anti-Nak(a) antibodies in different clinical settings such as fetal/neonatal alloimmune thrombocytopenia (FNAIT), platelet transfusion refractoriness (PTR) and post-transfusion purpura (PTP). However, no data regarding the relevance of CD36 immunisation is currently available for China. In this study, healthy blood donors were typed for CD36 deficiency using flow cytometry. Nucleotide sequencing was performed to identify the molecular basis underlying the CD36 deficiency. Anti-Nak(a) antibodies in CD36-deficient individuals were analysed by ELISA and flow cytometry. By analysis of 998 healthy blood donors, 18 individuals failed to express CD36 on their platelets. In 5/12 individuals no CD36 expression was detected both on platelets and monocytes. This result suggested that the frequencies of type I CD36 deficiency (platelets and monocytes) and type II CD36 deficiency (platelets only) are approximately 0.5 and 1.3%, respectively. Nucleotide sequencing analysis of type I CD36 deficient individuals revealed eight different mutations; four of them were not described so far. However, 1228-1239del ATTGTGCCTATT and 329-330delAC appear to be the most common mutations related to type I CD36 deficiency in South Chinese population. Further analysis showed that 1/5 type I CD36 deficient individuals developed anti-Nak(a) antibodies. In addition, anti-Nak(a) antibodies could be identified in two cases of thrombocytopenia associated with FNAIT and PTR. In conclusion, more than 0.5% of CD36 type I-deficient individuals are at risk to be immunised through blood transfusion or pregnancy in China. Testing of anti-Nak(a) antibodies should be considered in FNAIT and PTR suspected cases. A registry of CD36-deficient donors should be established to allow treatment of immune-mediated bleeding disorders caused by anti-Nak(a) antibodies.

Comparative Studies of Vertebrate Platelet Glycoprotein 4 (CD36)

Platelet glycoprotein 4 (CD36) (or fatty acyl translocase [FAT], or scavenger receptor class B, member 3 [SCARB3]) is an essential cell surface and skeletal muscle outer mitochondrial membrane glycoprotein involved in multiple functions in the body. CD36 serves as a ligand receptor of thrombospondin, long chain fatty acids, oxidized low density lipoproteins (LDLs) and malaria-infected erythrocytes. CD36 also influences various diseases, including angiogenesis, thrombosis, atherosclerosis, malaria, diabetes, steatosis, dementia and obesity. Genetic deficiency of this protein results in significant changes in fatty acid and oxidized lipid uptake. Comparative CD36 amino acid sequences and structures and CD36 gene locations were examined using data from several vertebrate genome projects. Vertebrate CD36 sequences shared 53-100% identity as compared with 29-32% sequence identities with other CD36-like superfamily members, SCARB1 and SCARB2. At least eight vertebrate CD36 N-glycosylation sites were conserved which are required for membrane integration. Sequence alignments, key amino acid residues and predicted secondary structures were also studied. Three CD36 domains were identified including cytoplasmic, transmembrane and exoplasmic sequences. Conserved sequences included N- and C-terminal transmembrane glycines; and exoplasmic cysteine disulphide residues; TSP-1 and PE binding sites, Thr92 and His242, respectively; 17 conserved proline and 14 glycine residues, which may participate in forming CD36 'short loops'; and basic amino acid residues, and may contribute to fatty acid and thrombospondin binding. Vertebrate CD36 genes usually contained 12 coding exons. The human CD36 gene contained transcription factor binding sites (including PPARG and PPARA) contributing to a high gene expression level (6.6 times average). Phylogenetic analyses examined the relationships and potential evolutionary origins of the vertebrate CD36 gene with vertebrate SCARB1 and SCARB2 genes. These suggested that CD36 originated in an ancestral genome and was subsequently duplicated to form three vertebrate CD36 gene family members, SCARB1, SCARB2 and CD36.

Preliminary studies on CD36 gene in type 2 diabetic patients from north India

BACKGROUND & OBJECTIVES

The greater tendency to diabetes in Indians may be due to genetic factors in addition to environment and diet. CD36, a class B scavenger cell surface receptor mediates internalization of oxidized low density lipoprotein (Ox-LDL) leading to the formation of macrophage foam cells. CD36 deficiency is related to phenotypic expression of the metabolic syndrome, frequently associated with atherosclerotic cardiovascular diseases resulting in raised levels of glucose thereby contributing to type 2 diabetes (T2DM). Therefore, the association of human CD36 gene mutation to T2DM needs investigation. We undertook this study to investigate CD36 gene status in north Indian subjects by screening for the deletion of exons 3, 4 and 5 and certain polymorphisms.

METHODS

Clinical characteristics were compared between 300 T2DM patients and 100 healthy controls. Deletion analysis was carried out for exons 3, 4 and 5 of CD36 gene in 300 T2DM patients using PCR and agarose gel electrophoresis. Genotype analysis for two polymorphisms 478C>T and delAC in exons 4 and 5 respectively was carried out using PCR-RFLP method.

RESULTS

Biochemical parameters such as fasting and post-prandial glucose levels, total cholesterol, LDL-cholesterol and blood pressure were slightly raised in the T2DM patients when compared with controls with lowered HDL-cholesterol. No exonic deletion was observed in the 300 patients and 100 controls screened. All individuals were found to be homozygous (CC and -/-) for the two polymorphisms studied.

INTERPRETATION & CONCLUSIONS

Although no exonic deletion was found in T2DM patients, our study suggests that all 15 exons need to be screened for mutations which lead to CD36 deficiency. Genotyping studies of the two SNPs in the CD36 gene confirmed the absence of exons 4 and 5 deletion. This is perhaps the first report from India suggesting that CD36 is one of the several important genes that need to be explored in relation to T2DM.

CD36 deficiency predisposing young children to fasting hypoglycemia

Fatty acid (FA) β-oxidation defects cause hypoglycemia. Our aim was to determine if CD36--a membrane transporter for long-chain FAs--deficiency predisposes children to hypoglycemia. After overnight fasting, we measured parameters for carbohydrate and FA metabolisms at 12-, 14-, and 16-hour fasting points in 51 preschool children with histories of episodic hypoglycemia and 49 age-matched healthy controls. Simultaneously, the expressions of CD36 on platelets and monocytes were examined to determine the phenotypes. Six of the 51 hypoglycemic children and none of the 49 control children were diagnosed as having type I CD36 deficiency. Four and 3 children were diagnosed as having type II CD36 deficiency, respectively. Hypoglycemia was often recurrent in the type I CD36 group. At any fasting point, the type I CD36 group showed significantly lower blood glucose and insulin concentrations than the other groups: glucose, P < .001 vs control group and P < .01 or P < .001 vs type II/wild-type CD36 hypoglycemic groups; insulin, P < .001 vs control group and P < .01 vs type II/wild-type CD36 hypoglycemic groups. Free FA concentration in the type I group was always 1.5- to 2.0-fold higher than that in the other groups, whereas the total ketone body concentration was consistently about two thirds of that in the other groups. Among the type II, wild-type, and control groups, there were no significant differences in the parameters except that the wild-type group showed significantly lower FFA concentration (P < .05). These results suggested that type I CD36 deficiency but not type II CD36 deficiency predisposes preschool children to hypoglycemia.

Plasmodium falciparum malaria and the immunogenetics of ABO, HLA, and CD36 (platelet glycoprotein IV)

Plasmodium falciparum malaria has long been a killer of the young, and has selected for polymorphisms affecting not only erythrocytes, but the immunogenetics of three histocompatibility systems: ABO, human leukocyte antigen (HLA), and CD36. The ABO system is important because the original allele, encoding glycosylation with the A sugar, acts as an adhesion ligand with infected red blood cells (iRBC), thereby promoting vasoocclusion. The prevalence of blood group O, which reduces this cytoadhesion, has increased in endemic areas. Other adaptations which could mitigate A-mediated rosetting include weaker A expression and increased soluble A secretion. The role of the HLA system in malaria has been harder to verify. Although HLA-B53 and DRB1*04 may be associated with clinical outcome, HLA studies are challenged by numerous comparisons in this most polymorphic of systems, and confounded by increasingly heterogeneous populations. Certain HLA markers may also reflect linkage artefact with other malaria-relevant polymorphisms. HLA may be less important because the parasite predominantly invades a compartment which does not express HLA. Adhesion of iRBCs is also mediated by CD36, expressed on platelets, monocytes, and microvascular endothelium. CD36 on monocytes is involved in clearing iRBC, while CD36 on platelets and the endothelium may play a role in tissue sequestration. The genetics of CD36 expression are complex, and recent research is fraught with inconsistent results. The solution may lie in examining genotype-phenotype correlations, zygosity effects on differential tissue expression, or other mechanisms altering CD36 tissue expression. Carefully designed prospective studies should bridge the gap between in-vitro observations and clinical outcomes.

Palmitoylation of CD36/FAT regulates the rate of its post-transcriptional processing in the endoplasmic reticulum

CD36/FAT is a transmembrane glycoprotein that functions in the cellular uptake of long-chain fatty acids and also as a scavenger receptor. As such it plays an important role in lipid homeostasis and, pathophysiologically, in the progression of type 2 diabetes and atherosclerosis. CD36 expression is tightly regulated at the levels of both transcription and translation. Here we show that its expression and location are also regulated post-translationally, by palmitoylation. Although palmitoylation of CD36 was not required for receptor maturation and cell surface expression, inhibition of palmitoylation either pharmacologically with cerulenin or by mutation of the relevant cysteines delayed processing at the ER and trafficking through the secretory pathway. The absence of palmitoylation also reduced the half life of the CD36 protein. Additionally, the CD36 palmitoylation mutant did not incorporate efficiently into lipid rafts, a site known to be required for its function of fatty acid uptake, and this reduced the efficiency of uptake of oxidized low density lipoprotein. These findings provide an added level of sophistication where translocation of CD36 to the plasma membrane may be physiologically regulated by palmitoylation.

Positive selection of a CD36 nonsense variant in sub-Saharan Africa, but no association with severe malaria phenotypes

The prevalence of CD36 deficiency in East Asian and African populations suggests that the causal variants are under selection by severe malaria. Previous analysis of data from the International HapMap Project indicated that a CD36 haplotype bearing a nonsense mutation (T1264G; rs3211938) had undergone recent positive selection in the Yoruba of Nigeria. To investigate the global distribution of this putative selection event, we genotyped T1264G in 3420 individuals from 66 populations. We confirmed the high frequency of 1264G in the Yoruba (26%). However, the 1264G allele is less common in other African populations and absent from all non-African populations without recent African admixture. Using long-range linkage disequilibrium, we studied two West African groups in depth. Evidence for recent positive selection at the locus was demonstrable in the Yoruba, although not in Gambians. We screened 70 variants from across CD36 for an association with severe malaria phenotypes, employing a case–control study of 1350 subjects and a family study of 1288 parent–offspring trios. No marker was significantly associated with severe malaria. We focused on T1264G, genotyping 10 922 samples from four African populations. The nonsense allele was not associated with severe malaria (pooled allelic odds ratio 1.0; 95% confidence interval 0.89–1.12; P = 0.98). These results suggest a range of possible explanations including the existence of alternative selection pressures on CD36, co-evolution between host and parasite or confounding caused by allelic heterogeneity of CD36 deficiency.

CD36 polymorphism and its relationship with body mass index and coronary artery disease in a Korean population

BACKGROUND

CD36 is a multifunctional membrane receptor and a cell-adhesion molecule that is expressed in platelets, monocytes/macrophages, microvascular endothelial cells, cardiac monocytes and adipocytes. In this study, we investigated whether genetic polymorphisms of the CD36 gene are associated with risk of coronary artery disease (CAD) in a Korean population.

METHODS

PCR and polyacrylamide gel electrophoresis or PCR-restriction fragment length polymorphism assays were performed to analyze the following CD36 gene polymorphisms: a (TG) repeat in intron 3 and the base substitution 478C>T (Pro90Ser). A total of 219 patients with significant CAD and 236 control subjects were examined with regard to their genotypes, lipid profiles and other risk factors for CAD.

RESULTS

The frequency of (TG) 11- or 12-repeat homozygotes was significantly higher in male CAD patients than in control men (28.4% vs. 15.7%, OR=2.13, p=0.018). Homozygosity for the (TG) 11- or 12-repeat allele was also significantly associated with a higher body mass index (BMI) compared to non-carriers in 134 control men after controlling for age, smoking and hypertension, and explains a 13% BMI variation observed in this study (p=0.015, analysis of covariance). For the 478C >T mutation, which has been reported to be associated with CD36 deficiency, there was no difference in the frequency of the 478T allele between CAD patients and control subjects. However, the 478T allele was found to be closely linked with a (TG) 11- or 12-repeat allele of intron 3 in the control subjects (chi2=18.88, p<0.001).

CONCLUSIONS

The (TG) repeat polymorphism in intron 3 of the CD36 gene is associated with a higher BMI and cardiovascular risk for men in a Korean population.

High tissue factor-expressing human monocytes carry low surface CD36: application to intersubject variability

BACKGROUND

The 'high and low responder' phenomenon describes an intersubject variability in mononuclear cell (MNC) prothrombotic reactivity to lipopolysaccharide (LPS) stimulation. Because alterations in surface CD36 expression in monocytes were associated with impaired monocyte function, we studied the relationship between the levels of surface CD36 presentation and the prothrombotic reactivity of monocytes from high-responder (HR) and low-responder (LR) individuals.

METHODS AND RESULTS

The relationship between levels of tissue factor (TF) expression and surface CD36 presentation in MNCs from HR individuals (n = 7) and LR individuals (n = 8) was investigated. Resting MNCs from HR individuals contained significantly more TF mRNA but levels of TF antigen and procoagulant activity similar to MNCs from LR individuals. Resting CD14+ MNCs from HR individuals expressed significantly lower surface CD36, as mean fluorescence intensities (MFIs) were 70.4 +/- 6.3 vs. 132.0 +/- 14.5 arbitrary units (AU) in HR and LR individuals, respectively. MFI from surface TF negatively correlated with surface CD36 in the population of resting (r = -0.598, P = 0.031) and LPS-stimulated (r = -0.672, P = 0.009) CD14+ cells. LPS-stimulated MNCs from HR individuals contained significantly more TF in a surface pool (2079 +/- 199 vs. 786 +/- 57 AU) along with higher TF procoagulant activity (57.3 +/- 15.2 vs. 21.1 +/- 4.5 mU 10(6) cells(-1)) as compared with LR individuals. CD14+ MNCs from HR individuals expressed less surface CD36 during a 2-h LPS challenge.

CONCLUSIONS

A novel phenotype of monocytes characterized by high TF and low CD36 presentation could be further developed for use as a marker for detection of HR individuals prone to developing prothrombotic conditions.

Molecular basis of human CD36 gene mutations

CD36 is a transmembrane glycoprotein of the class B scavenger receptor family. The CD36 gene is located on chromosome 7 q11.2 and is encoded by 15 exons. Defective CD36 is a likely candidate gene for impaired fatty acid metabolism, glucose intolerance, atherosclerosis, arterial hypertension, diabetes, cardiomyopathy, Alzheimer disease, and modification of the clinical course of malaria. Contradictory data concerning the effects of antiatherosclerotic drugs on CD36 expression indicate that further investigation of the role of CD36 in the development of atherosclerosis may be important for the prevention and treatment of this disease. This review summarizes current knowledge of CD36 gene structure, splicing, and mutations and the molecular, metabolic, and clinical consequences of these phenomena.

Molecular basis of human CD36 gene mutations

CD36 is a transmembrane glycoprotein of the class B scavenger receptor family. The CD36 gene is located on chromosome 7 q11.2 and is encoded by 15 exons. Defective CD36 is a likely candidate gene for impaired fatty acid metabolism, glucose intolerance, atherosclerosis, arterial hypertension, diabetes, cardiomyopathy, Alzheimer disease, and modification of the clinical course of malaria. Contradictory data concerning the effects of antiatherosclerotic drugs on CD36 expression indicate that further investigation of the role of CD36 in the development of atherosclerosis may be important for the prevention and treatment of this disease. This review summarizes current knowledge of CD36 gene structure, splicing, and mutations and the molecular, metabolic, and clinical consequences of these phenomena.

Genetic Analysis of Innate Immunity

The inflammatory response to microbes--and host perception of microbes in general--is largely initiated by a single class of receptors, named for their similarity to the prototypic Toll receptor of Drosophila. The mammalian Toll-like receptors (TLRs) are ultimately responsible for most phenomena associated with infection. This includes both "good" effects of infection (e.g., the induction of lasting specific immunity to an infectious agent) and "bad" effects of infection (systemic inflammation and shock). Although they are essential for host defense, no other endogenous proteins can match their lethal potential. The TLR complexes transduce the toxicity of lipopolysaccharide (LPS), cysteinyl lipopeptides, and many other molecules of microbial origin. The identification of the TLRs as the key conduit to host awareness of microbial infection was a victory for reductionism, proving that the complexity of infectious inflammation as a phenomenon belies the simplicity of its origins. It was achieved by a classical genetic approach, proceeding from phenotype to gene. Further analysis of the signaling pathways activated by the TLRs has depended on both classical and reverse genetic methods. Additional work will ultimately disclose the extent to which sterile inflammatory diseases are mediated by aberrations in these pathways.

Increased risk of colorectal cancer due to interactions between meat consumption and the CD36 gene A52C polymorphism among Japanese

A previous study showed expression of CD36, recently reported to play important roles in metabolism of oxidized low-density lipoprotein and long-chain fatty acids and to be positively correlated with colon cancer prognosis. To examine relationships between colorectal cancer and the CD36 gene A52C polymorphism according to meat consumption as a surrogate for saturated fatty acid intake, we conducted the present hospital-based, case-control study of 128 cases and 238 non-cancer controls. Consumption of meat and vegetables/fruit was divided into three (low, moderate, and high) and two (low and high) groups, respectively. Regarding the risk of colorectal cancer on cross-classifying subjects for the CD36 genotype and meat consumption, the odds ratio (OR) for the C/C genotype with moderate meat consumption relative to the A/A genotype with low meat consumption was 8.30 (95% confidence interval, CI=2.15-32.00). None of individuals with the C/C genotype was in the high meat consumption group. In the low vegetables/fruit consumption group, the OR for the C/C genotype relative to the A/A genotype was 3.03 (95% CI=1.12-7.90). Our findings suggest that interactions between moderate-high meat consumption and the CD36 gene A52C polymorphism may increase the risk of colorectal cancer.

Expression and subcellular localization of WAVE isoforms in the megakaryocyte/platelet lineage

WAVE isoforms, which consist of WAVE-1, WAVE-2 and WAVE-3, are members of the Wiskott-Aldrich syndrome protein (WASP) family. They are implicated in the regulation of actin-cytoskeletal reorganization downsteam of the small GTPase, Rac. Since platelet attachment to extracellular matrices leads to filopodial and lamellipodial extension, we examined the expression and subcellular localization of WAVEs in platelets. Employing primary megakaryocytic cells derived from cord blood as well as megakaryocytic cell lines, we also examined their expression during megakaryocytic differentiation. Immunoblotting and immunohistochemical analysis revealed that platelets expressed WAVE-1 and WAVE-2, whereas WAVE-3 expression was hardly to be detected. WAVE-1 expression was associated with megakaryocytic differentiation, whereas WAVE-2 and WAVE-3 expression was not changed by the differentiation. In adhered platelets both WAVE-1 and WAVE-2 were localized at the edge of the lamellipodia and at the tips of filopodia. In WASP-deficient platelets we found normal lamellipodial formation and localization of WAVE-1 and WAVE-2 at the edges of lamellipodia. Furthermore, we demonstrated that WAVE-1 and WAVE-2 moved from a detergent-soluble cytosolic fraction to insoluble cytoskeleton fraction after platelet aggregation. These results suggest that WAVE-1 and WAVE-2 regulate actin reorganization during platelet spreading and aggregate formation.

A naturally occurring Tyr143His alpha IIb mutation abolishes alpha IIb beta 3 function for soluble ligands but retains its ability for mediating cell adhesion and clot retraction: comparison with other mutations causing ligand-binding defects

The molecular basis for the interaction between a prototypic non-I-domain integrin, alpha(IIb)beta(3), and its ligands remains to be determined. In this study, we have characterized a novel missense mutation (Tyr143His) in alpha(IIb) associated with a variant of Glanzmann thrombasthenia. Osaka-12 platelets expressed a substantial amount of alpha(IIb)beta(3) (36%-41% of control) but failed to bind soluble ligands, including a high-affinity alpha(IIb)beta(3)-specific peptidomimetic antagonist. Sequence analysis revealed that Osaka-12 is a compound heterozygote for a single (521)T>C substitution leading to a Tyr143His substitution in alpha(IIb) and for the null expression of alpha(IIb) mRNA from the maternal allele. Given that Tyr143 is located in the W3 4-1 loop of the beta-propeller domain of alpha(IIb), we examined the effects of Tyr143His or Tyr143Ala substitution on the expression and function of alpha(IIb)beta(3) and compared them with KO (Arg-Thr insertion between 160 and 161 residues of alpha(IIb)) and with the Asp163Ala mutation located in the same loop by using 293 cells. Each of them abolished the binding function of alpha(IIb)beta(3) for soluble ligands without disturbing alpha(IIb)beta(3) expression. Because immobilized fibrinogen and fibrin are higher affinity/avidity ligands for alpha(IIb)beta(3), we performed cell adhesion and clot retraction assays. In sharp contrast to KO mutation and Asp163Ala alpha(IIb)beta(3), Tyr143His alpha(IIb)beta(3)-expressing cells still had some ability for cell adhesion and clot retraction. Thus, the functional defect induced by Tyr143His alpha(IIb) is likely caused by its allosteric effect rather than by a defect in the ligand-binding site itself. These detailed structure-function analyses provide better understanding of the ligand-binding sites in integrins.

Platelet receptors and their role in diseases

The absence or deficiency of specific platelet glycoprotein receptors has a well-defined role in causing several rare bleeding disorders such as Bernard-Soulier syndrome or Glanzmann's thrombasthenia. Several new rare disorders caused by defects in other receptors or their signalling pathways have recently been described. Platelet receptors are also often targets for antibodies in pathological conditions. The roles of platelet receptors or their polymorphism variants in diseases such as cardiovascular disorders have started to be intensively investigated over the last 5 years. Many of these findings still remain controversial. Recent evidence points to a fundamental role for platelets and their receptors in the origins of atherosclerosis. Studies on the role of platelet receptors in diseases such as asthma, diabetes and HIV are still at an early stage.

Fatty acid transport across membranes: relevance to nutrition and metabolic pathology

Long-chain fatty acids are an important constituent of the diet and they contribute to a multitude of cellular pathways and functions. Uptake of long-chain fatty acids across plasma membranes is the first step in fatty acid utilization, and recent evidence supports an important regulatory role for this process. Although uptake of fatty acids involves two components, passive diffusion through the lipid bilayer and protein-facilitated transfer, the latter component appears to play the major role in mediating uptake by key tissues. Identification of several proteins as fatty acid transporters, and emerging evidence from genetically altered animal models for some of these proteins, has contributed significant insight towards understanding the limiting role of transport in the regulation of fatty acid utilization. We are also beginning to better appreciate how disturbances in fatty acid utilization influence general metabolism and contribute to metabolic pathology.

CD36 genotype and long-chain fatty acid uptake in the heart

Homozygous or compound heterozygous mutation of the CD36 gene (CD36-/-) in humans results in severe defects of the uptake of long-chain fatty acids (LCFAs) in the heart. Because the effect of a single mutation of this gene (CD36+/-) on the LCFA uptake is not known, it was evaluated in 29 subjects with the CD36 wild-type gene (WT) (6 healthy subjects, 10 patients with heart disease), CD36+/- (4 healthy subjects, 5 patients) and CD36-/- (4 patients). The CD36 genotype was identified in the coding region of genomic DNA, and the expression of CD36 protein was examined by flow cytometry after staining with monoclonal anti-CD36 antibody. The LCFA uptake in the heart was assessed as the radioactivity accumulation ratio of heart to mediastinum after intravenous administration of iodine-123 15-(p-iodophenyl)-3-R, S-methylpentadecanoic acid (H/M ratio). The H/M ratios in WT, CD36+/- and CD36-/- were 2.28 +/- 0.10, 1.90 +/- 0.06 and 1.40 +/- 0.11, respectively (p < 0.0001, among groups). The H/M ratio between healthy subjects and patients with heart disease for WT and CD36+/- did not differ significantly (ie, those of WT and CD36+/- in healthy subjects and patients were 2.29 +/- 0.08 vs 2.27 +/- 0.12 and 1.90+/- 0.07 vs 1.89 +/- 0.05, respectively). Not only CD36-/- but also CD36+/- resulted in a significant reduction of the LCFA uptake in the heart independent of heart disease, suggesting genotype dependency and that CD36 might be a fundamental determinant of myocardial LCFA uptake.

Genomic heterogeneity of type II CD36 deficiency

BACKGROUND

CD36 deficiency has been classified in two types, i.e., type I and type II CD36 deficiency. Possible pathological involvement of CD36 deficiency has been suggested in humans, but is still confounding. Homozygous or compound heterozygous mutations (CD36(-/-)) were demonstrated in type I CD36 deficiency, while the genomic or molecular background of type II CD36 deficiency is still unclear, which may bring confounding interpretations of the cause-and-effect events in human CD36 deficiency. In this study, we analyzed the genotype and frequency of type II CD36 deficiency in Japanese populations, and its hereditary pattern in three families.

METHODS

Genotypes and protein expression levels of CD36 were examined in 238 Japanese subjects. Genotype was analyzed in the coding region of the CD36 gene. The expression level of CD36 protein was analyzed by flow cytometry after staining with monoclonal anti-CD36 antibody and assessed as mean fluorescence intensity (MFI).

RESULTS

Among 238 subjects, subjects for wild-type gene (WT), a single mutation (CD36(+/-)), and CD36(-/-) were 141, 44 and 53, respectively. Monocyte MFI (mean+/-SD) in subjects for WT, CD36(+/-), and CD36(-/-) were 35.7+/-8.5, 15.2+/-3.4, and 0.4+/-0.3, respectively (P<0.0001, between groups). Those of platelets in subjects for WT, CD36(+/-), and CD36(-/-) were 27.1+/-10.6, 11.5+/-6.3, and 0.5+/-0.3, respectively (P<0.0001, between groups). Subjects of both WT and CD36(+/-) were observed in type II CD36 deficiency. Monocyte and platelet MFI in family members of type II CD36 deficiency and 218 unrelated Japanese suggested that the expression level of CD36 protein in monocytes was directly dependent on genotypes. On the other hand, those in platelets were affected by additional heritable factor(s) in addition to the coding region genotype.

CONCLUSIONS

MFI in monocytes showed a strong gene-dosage-dependency. On the other hand, MFI in platelets was affected by heritable factor(s) in addition to the coding region genotype, which resulted in heterogeneity of type II CD36 deficiency.

Role of CD36 in membrane transport of long-chain fatty acids

CD36 is a multispecific membrane glycoprotein that has been postulated to have a variety of functions. Evidence generated in isolated cells and in mice and rat models of altered CD36 expression has indicated an important role for CD36 in membrane transport of long-chain fatty acids. The cumulative data indicate that CD36 facilitates a major fraction of fatty acid uptake by muscle and fat, and that CD36 deficiency is associated with a large (60-80%) defect in fatty acid uptake by those tissues. In humans, polymorphisms in the CD36 gene may underlie defective fatty acid metabolism and some forms of heart disease. Herein we review our current understanding of the transport function and regulation of CD36. The realization that the transport step rate limits cellular fatty acid utilization suggests that abnormalities in CD36 expression or function may impact on susceptibility to certain metabolic diseases such as obesity and insulin resistance.

Missense mutations in the beta(3) subunit have a different impact on the expression and function between alpha(IIb)beta(3) and alpha(v)beta(3)

Alpha(IIb)beta(3) and alpha(v)beta(3) belong to the beta(3) integrin subfamily. Although the beta(3) subunit is a key regulator for the biosynthesis of beta(3) integrins, it remains obscure whether missense mutations in beta(3) may induce the same defects in both alpha(IIb)beta(3) and alpha(v)beta(3). In this study, it is revealed that thrombasthenic platelets with a His280Pro mutation in beta(3), which is prevalent in Japanese patients with Glanzmann thrombasthenia, did contain significant amounts of alpha(v)beta(3) (about 50% of control) using sensitive enzyme-linked immunosorbent assay. Expression studies showed that the His280Probeta(3) mutation impaired alpha(IIb)beta(3) expression but not alpha(v)beta(3) expression in 293 cells. To extend these findings, the effects of several beta(3) missense mutations leading to an impaired alpha(IIb)beta(3) expression on alpha(v)beta(3) function as well as expression was examined: Leu117Trp, Ser162Leu, Arg216Gln, Cys374Tyr, and a newly created Arg216Gln/Leu292Ser mutation. Leu117Trp and Cys374Tyr beta(3) mutations did impair alpha(v)beta(3) expression, while Ser162Leu, Arg216Gln, and Arg216Gln/Leu292Ser mutations did not. With regard to ligand binding function, Ser162Leu mutation induced especially distinct effects between 2 beta(3) integrins: it markedly impaired ligand binding to alpha(IIb)beta(3) but not to alpha(v)beta(3) at all. These data clearly demonstrate that the biosynthesis and the ligand binding function of alpha(IIb)beta(3) and those of alpha(v)beta(3) are regulated in part by different mechanisms. Present data would be a clue to elucidate the regulatory mechanism of expression and function of beta(3) integrins.

Association of the Pro90Ser CD36 mutation with elevated free fatty acid concentrations but not with insulin resistance syndrome in Japanese

BACKGROUND

CD36 deficiency is reportedly an underlying factor about insulin resistance, defective fatty acid metabolism and hypertriglyceridemia in spontaneously hypertensive rat (SHR), and may be involved in the pathogenesis of insulin resistance and hyperlipidemia in humans.

METHODS

We examined 831 adults undergoing health screening. The majority (780) was Pro90 homozygous for the CD36 gene product, but 51 displayed a CD36 mutation (2 homozygous and 49 heterozygous for Ser90). This is the major mutation site involved in CD36 deficiency in Japanese.

RESULTS

Among parameters related to insulin resistance, there were no differences in body mass index (BMI), HDL cholesterol, total cholesterol, triglycerides, insulin and insulin resistance index (HOMA IR), or blood pressure between 91 normal subjects (45 male and 46 female) randomly selected from the 780 Pro90 homozygotes and the 51 (29 male and 22 females) CD36-deficient subjects (Ser90 homozygote and Pro90Ser heterozygote). Free fatty acid concentrations, however, were higher in Ser90 CD36 subjects than in Pro90 control subjects.

CONCLUSIONS

The CD36Pro90Ser mutation is not necessarily related to the insulin resistance syndrome, but is associated with high free fatty acid concentrations in Japanese.

Variability of the CD36 gene in West Africa

Studying 12 selected individuals from a malaria-endemic area in West Africa, 24 variants of the CD36 gene were found, 21 of them novel ones. These included three single-nucleotide substitutions causing non-conservative amino acid exchanges E123K, T174A, and I271T as well as a three base pair (bp) insertion resulting in the addition of an asparagine residue (N232-233ins). The E123K variant was located within the putative ligand-binding domain for oxidized low density lipoprotein, while the other substitutions resided outside any of the binding sites for reaction partners mapped on CD36 so far. Twelve single-nucleotide polymorphisms (SNPs) were identified in untranslated parts of the exons and in introns. Five additional SNPs were located in the promoter region whereby -144G-->T, -53G-->T, and -2A-->G alter putative binding sites for the transcription factors purine factor (PuF), phorbol ester-responsive element AP-2, and CCAAT/enhancer-binding protein. A G-->T exchange at position -50 appears to introduce a new recognition site for PuF. Calculations of nucleotide diversity revealed extraordinarily high numbers for all parts of the gene, which may, however, to some extent be due to the selection of individuals studied.

Erythroid involvement in CD36 deficiency

OBJECTIVE

The CD36 molecule is expressed in platelets, monocytes, erythroblasts, and other different tissues. The two types of platelet CD36 deficiency, types I and II, are associated with the absence and presence of CD36 on monocytes, respectively. To clarify the involvement of the erythroid lineage in CD36 deficiency, we investigated the phenotype and RNA expression of CD36.

MATERIALS AND METHODS

CD36 expression was examined in 296 patients with several cardiovascular diseases in our outpatient clinic. There were 12 patients with type I deficiency and 16 with type II CD36 deficiency. A bone marrow sample was examined in five type I and four type II patients. Expression of CD36 mRNA was examined in burst-forming unit-erythroid (BFU-E). The sequences of reverse transcriptase polymerase chain reaction (RT-PCR) products of the CD36 mRNA from monocytes were examined.

RESULTS

As expected, CD36 was deficient in erythroblasts from all five patients with type I deficiency. CD36 was present in erythroblasts from three of the four with type II deficiency, suggesting that their abnormality is restricted to platelets (type IIa). CD36 was unexpectedly absent from erythroblasts of a single type II patient (type IIb). CD36-specific mRNA was identified in BFU-E from each of two normals, six type I, and six type II patients, including type IIb. The sequences of RT-PCR products of the CD36 mRNA in a patient with type IIa and another with type IIb showed homozygous wild alleles.

CONCLUSION

The findings provide evidence for further heterogeneity among CD36-deficient individuals and the existence of a basic principle mechanism of type II, such as glycosylation abnormality.