Circulating sCD36 is associated with unhealthy fat distribution and elevated circulating triglycerides in morbidly obese individuals

CD36 regulates macrophage and endothelial cell activation and multinucleate giant cell formation in anti neutrophil cytoplasm antibody vasculitis

OBJECTIVE

To investigate CD36 in ANCA-associated vasculitis (AAV), a condition characterized by monocyte/macrophage activation and vascular damage.

METHODS

CD36 expression was assessed in AAV patients and healthy controls (HC). The impact of palmitic acid (PA) stimulation on multinucleate giant cell (MNGC) formation, macrophage, and endothelial cell activation, with or without CD36 knockdown, was examined.

RESULTS

CD36 was overexpressed on AAV patients' monocytes compared to HC, regardless of disease activity. AAV patients exhibited elevated soluble CD36 levels in serum and plasma and PR3-ANCA patients' monocytes demonstrated increased MNGC formation following PA stimulation compared to HC. PA stimulation of macrophages or endothelial cells resulted in heightened CD36 expression, cell activation, increased macrophage migration inhibitory factor (MIF) production, and c-Myc expression, with attenuation upon CD36 knockdown.

CONCLUSION

CD36 participates in macrophage and endothelial cell activation and MNGC formation, features of AAV pathogenesis. AAV treatment may involve targeting CD36 or MIF.

Soluble Receptors Affecting Stroke Outcomes: Potential Biomarkers and Therapeutic Tools

Soluble receptors are widely understood to be freestanding moieties formed via cleavage from their membrane-bound counterparts. They have unique structures, are found among various receptor families, and have intriguing mechanisms of generation and release. Soluble receptors’ ability to exhibit pleiotropic action by receptor modulation or by exhibiting a dual role in cytoprotection and neuroinflammation is concentration dependent and has continually mystified researchers. Here, we have compiled findings from preclinical and clinical studies to provide insights into the role of soluble/decoy receptors, focusing on the soluble cluster of differentiation 36, the soluble cluster of differentiation 163, and soluble lipoprotein-related protein 1 (sCD36, sCD163, and sLRP1, respectively) and the functions they could likely serve in the management of stroke, as they would notably regulate the bioavailability of the hemoglobin and heme after red blood cell lysis. The key roles that these soluble receptors play in inflammation, oxidative stress, and the related pharmacotherapeutic potential in improving stroke outcomes are described. The precise pleiotropic physiological functions of soluble receptors remain unclear, and further scientific investigation/validation is required to establish their respective role in diagnosis and therapy.

The Multifunctionality of CD36 in Diabetes Mellitus and Its Complications-Update in Pathogenesis, Treatment and Monitoring

CD36 is a multiligand receptor contributing to glucose and lipid metabolism, immune response, inflammation, thrombosis, and fibrosis. A wide range of tissue expression includes cells sensitive to metabolic abnormalities associated with metabolic syndrome and diabetes mellitus (DM), such as monocytes and macrophages, epithelial cells, adipocytes, hepatocytes, skeletal and cardiac myocytes, pancreatic β-cells, kidney glomeruli and tubules cells, pericytes and pigment epithelium cells of the retina, and Schwann cells. These features make CD36 an important component of the pathogenesis of DM and its complications, but also a promising target in the treatment of these disorders. The detrimental effects of CD36 signaling are mediated by the uptake of fatty acids and modified lipoproteins, deposition of lipids and their lipotoxicity, alterations in insulin response and the utilization of energy substrates, oxidative stress, inflammation, apoptosis, and fibrosis leading to the progressive, often irreversible organ dysfunction. This review summarizes the extensive knowledge of the contribution of CD36 to DM and its complications, including nephropathy, retinopathy, peripheral neuropathy, and cardiomyopathy.

Effect of Bariatric Surgery on Serum Inflammatory Factors of Obese Patients: a Systematic Review and Meta-Analysis

Obesity is one of the main causes of inflammation. Previous studies have reported inconclusive results regarding the effect of bariatric surgery on inflammatory markers. This systematic review and meta-analysis is aimed at describing the effect of bariatric surgery on C-reactive protein (CRP), interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α). PubMed/Medline and Scopus were systematically searched for all eligible studies from inception to June 2018. Results are expressed as weighted mean difference (MD) with 95% confidence intervals (CI) using a random effects model. Overall, 116 studies which evaluated serum CRP, IL-6, and TNF-α after bariatric surgery were included. Pooled effect size showed significant reduction in serum CRP (- 5.30 mg/l, 95% CI - 5.46, - 5.15, P < 0.001), IL-6 (- 0.58 pg/ml, 95% CI - 0.64, - 0.53, P < 0.001), and TNF-α (- 0.20 pg/ml, 95% CI - 0.39, - 0.02, P = 0.031) with significant heterogeneity across studies (> 95% for all factors). Bariatric surgery significantly lowered inflammatory factors; however, baseline BMI, follow-up duration and type of surgery could impact the extent of observed effects.

Contribution of rare coding mutations in CD36 to type 2 diabetes and cardio-metabolic complications

We sequenced coding regions of the cluster of differentiation 36 (CD36) gene in 184 French individuals of European ancestry presenting simultaneously with type 2 diabetes (T2D), arterial hypertension, dyslipidemia, and coronary heart disease. We identified rare missense mutations (p.Pro191Leu/rs143150225 and p.Ala252Val/rs147624636) in two heterozygous cases. The two CD36 mutation carriers had no family history of T2D and no clustering of cardio-metabolic complications. While the p.Pro191Leu mutation was found in 84 heterozygous carriers from five ethnic groups from the genome aggregation database (global frequency: 0.0297%, N = 141,321), only one European carrier of the p.Ala252Val mutation was identified (global frequency: 0.00040%, N = 125,523). The Pro191 and Ala252 amino acids were not conserved (74.8% and 68.9% across 131 animal species, respectively). In vitro experiments showed that the two CD36 mutant proteins are expressed and trafficked to the plasma membrane where they bind modified low-density-lipoprotein (LDL) cholesterol as normal. However, molecular modelling of the recent CD36 crystal structure showed that Pro191 was located at the exit/entrance gate of the lipid binding chamber and Ala252 was in line with the chamber. Overall, our data do not support a major contribution of CD36 rare coding mutations to T2D and its cardio-metabolic complications in the French population.

Plasma sCD36 as non-circadian marker of chronic circadian disturbance in shift workers

Shift work induces chronic circadian disturbance, which might result in increased health risks, including cardio-metabolic diseases. Previously, we identified sCD36 as a potential non-circadian biomarker of chronic circadian disturbance in mice. The aim of the current study (n = 232 individuals) was to identify whether sCD36 measured in plasma can be used as a non-circadian marker of chronic circadian disturbance in humans, which would allow its use to measure the effects of interventions and monitoring in large-scale studies. We compared levels of plasma sCD36 of day workers with recent (< 2 years) and experienced (> 5 years) night-shift workers within the Klokwerk study. We detected no differences in sCD36 levels between day workers and recent or experienced night-shift workers, measured during a day or afternoon shift. In addition, sCD36 levels measured directly after a night shift were not different from sCD36 levels measured during day or afternoon shifts, indicating no acute effect of night shifts on sCD36 levels in our study. In summary, our study does not show a relation between night-shift work experience (recent or long-term) and plasma levels of sCD36. Since we do not know if and for which time span night-shift work is associated with changes in sCD36 levels, and our study was relatively small and cross-sectional, further evidence for an association between chronic circadian disruption and this candidate biomarker sCD36 should be gathered from large cohort studies.

Associations of plasma CD36 and body fat distribution

CONTEXT

CD36 is a class B scavenger-receptor involved in the uptake of fatty acids in liver and adipose tissue. It is unknown whether plasma CD36 levels are related to liver fat content or adipose tissue in the general population.

METHODS

We measured plasma CD36 from 575 participants of the community-based PopGen-cohort who underwent magnetic resonance imaging (MRI) to quantify visceral (VAT) and subcutaneous (SAT) adipose tissue and liver signal intensity (LSI), a proxy for liver fat content. Non-alcoholic fatty liver disease (NAFLD) was defined as LSI ≥3.0 in the absence of high alcohol intake. The relations between plasma CD36 and body mass index (BMI), VAT, SAT, LSI, and NAFLD were evaluated using multivariable-adjusted linear and logistic regression analysis.

RESULTS

Plasma CD36 concentrations were correlated with BMI (r=0.11; P=0.01), SAT (r=0.16; P<0.001), and VAT (r=0.15, P<0.001), but not with LSI (P=0.44). In multivariable-adjusted regression models, mean BMI values rose across CD36-quartiles (Q1: 27.8 kg/m2; Q4: 28.9 kg/m2; P-trend=0.013). Similarly, VAT (Q1: 4.13 dm3; Q4: 4.71 dm3; P-trend<0.001) and SAT (Q1: 7.61 dm3; Q4: 8.74 dm3; P-trend<0.001) rose across CD36 quartiles. Plasma CD36 concentrations were unrelated to LSI (P-trend=0.36), and NAFLD (P-trend=0.64). Participants with NAFLD and elevated alanine aminotransferase (ALT), a marker for liver damage, had higher CD36 compared to NAFLD participants with normal ALT.

CONCLUSIONS

Higher plasma concentrations of CD36 were associated with greater general and abdominal adiposity, but not with liver fat content or NAFLD in this community-based sample. However, plasma CD36 may reflect more severe liver damage in NAFLD.

BLTR1 and CD36 Expressing Microvesicles in Atherosclerotic Patients and Healthy Individuals

Aims: Monocytes/macrophages play a crucial role in the development, progression, and complication of atherosclerosis. In particular, foam cell formation driven by CD36 mediated internalization of oxLDL leads to activation of monocytes and subsequent release of microvesicles (MVs) derived from monocytes (MMVs). Further, pro-inflammatory leukotriene B4 (LTB4) derived from arachidonic acid promotes atherosclerosis through the high-affinity receptor BLTR1. Thus, we aimed to investigate the correlation between different MMV phenotypes (CD14⁺ MVs) on the one hand, and arachidonic acid and eicosapentaenoic acid contents in different compartments including atherosclerotic plaques, plasma, and granulocytes on the other.

Methods and Results: Samples from patients with femoral atherosclerosis and healthy controls were analyzed on an Apogee A60 Micro-PLUS flow cytometer. Platelet-poor plasma was labeled with lactadherin-FITC, anti-CD14-APC, anti-CD36-PE, and anti-BLTR1-AF700. Eicosapentaenoic acid and arachidonic acid content in different compartments in patients were analyzed using gas chromatography. Compared to controls, patients had lower levels of BLTR1⁺ MVs (p = 0.007), CD14⁺BLTR1⁺ MVs (p = 0.007), and CD14⁺BLTR1⁺CD36⁺ MVs (p = 0.001). Further, in patients CD14⁺ MVs and CD14⁺CD36⁺ MVs correlated inversely with arachidonic acid in granulocytes (r = −0.302, p = 0.039 and r = −0.322, p = 0.028, respectively). Moreover, CD14⁺CD36⁺ MVs correlated inversely with arachidonic acid in plasma phospholipids in patients (r = −0.315, p = 0.029), and positively with triglyceride in both patients (r = 0.33, p = 0.019) and controls (r = 0.46, p = 0.022).

Conclusion: This is the first study of its kind and thus the results are explorative and only indicative. BLTR1⁺ MVs and CD14⁺CD36⁺ MVs has potential as markers of atherosclerosis pathophysiology, but this needs further investigation.

Bariatric surgery reduces CD36-bearing microvesicles of endothelial and monocyte origin

Background

Bariatric surgery is a widely adopted treatment for obesity and its secondary complications. In the past decade, microvesicles (MVs) and CD36 have increasingly been considered as possible biomarkers for obesity, the metabolic syndrome (MetSy), type 2 diabetes mellitus (T2DM). Thus, the purpose of this study was to investigate how weight loss resulting from bariatric surgery affects levels of specific MV phenotypes and their expression of CD36 scavenger receptor. Additionally, we hypothesised that subjects with MetSy had higher baseline concentrations of investigated MV phenotypes.

Methods

Twenty individuals undergoing Roux-en-Y gastric bypass surgery were evaluated before and 3 months after surgery. MVs were characterised by flow cytometry at both time points and defined as lactadherin-binding particles within a 100-1000 nm size gate. MVs of monocyte (CD14) and endothelial (CD62E) origin were defined by cell-specific markers, and their expression of CD36 was investigated.

Results

Following bariatric surgery, subjects incurred an average BMI reduction (delta) of − 8.4 ± 1.4 (p < 0.0001). Significant reductions were observed for the total MVs (− 66.55%, p = 0.0017) and MVs of monocyte (− 36.11%, p = 0.0056) and endothelial (− 40.10%, p = 0.0007) origins. Although the bulk of CD36-bearing MVs were unaltered, significant reductions were observed for CD36-bearing MVs of monocyte (− 60.04%, p = 0.0192) and endothelial (− 54.93%, p = 0.04) origin. No differences in levels of MVs were identified between subjects who presented with MetSy at baseline (n = 13) and those that did not (n = 7).

Conclusion

Bariatric surgery resulted in significantly altered levels of CD36-bearing MVs of monocyte and endothelial origin. This likely reflects improvements in ectopic fat distribution, plasma lipid profile, low-grade inflammation, and oxidative stress following weight loss. Conversely, however, the presence of MetSy at baseline had no impact on MV phenotypes.

Electronic supplementary material

The online version of this article (10.1186/s12986-018-0309-4) contains supplementary material, which is available to authorized users.

Lack of pronounced changes in the expression of fatty acid handling proteins in adipose tissue and plasma of morbidly obese humans

Background/Objectives

Fatty acid handling proteins are involved in the process of accumulation of lipids in different fat tissue depots. Thus, the aim of the study was to estimate the expression of both fatty acid transport and binding proteins in the subcutaneous (SAT) and visceral adipose tissue (VAT) of patients with morbid obesity without metabolic syndrome, as well as the plasma concentrations of these transporters.

Subjects/Methods

Protein (Western blotting) and mRNA (Real-time PCR) expression of selected fatty acid handling proteins was assessed in the visceral and subcutaneous adipose tissue of 30 patients with morbid obesity. The control group consisted of 10 lean age-matched patients. Plasma levels of fatty acid protein transporters were also evaluated using ELISA method. Moreover, total plasma fatty acid composition and concentration was determined by gas-liquid chromatography (GLC).

Results

Significant increase in fatty acid translocase (FAT/CD36) mRNA (P = 0.03) and plasmalemmal (P = 0.01) expression was observed in VAT of patients with morbid obesity vs. lean subjects together with elevation of lipoprotein lipase (LPL), as well as peroxisome proliferator-activated receptor γ (PPARγ) in both examined compartments of adipose tissue. Moreover, in obese subjects plasma concentration of RBP4 was markedly elevated (P = 0.04) and sCD36 level presented a tendency for an increase (P = 0.08) with concomitant lack of changes in FABP4 concentration (P > 0.05).

Conclusions

Fatty acid transport into adipocytes may be, at least in part, related to the increased expression of FAT/CD36 in the VAT of morbidly obese patients, which is accompanied by augmented expression of LPL, as well as PPARγ. Probably, alternations in plasma concentrations of RBP4 and sCD36 in obese patients are associated with “unhealthy” fat distribution.

Microvesicles Correlated with Components of Metabolic Syndrome in Men with Type 2 Diabetes Mellitus and Lowered Testosterone Levels But Were Unaltered by Testosterone Therapy

Aims. To investigate how circulating microvesicle phenotypes correlate with insulin sensitivity, body composition, plasma lipids, and hepatic fat accumulation. We hypothesized that changes elicited by testosterone replacement therapy are reflected in levels of microvesicles. Methods. Thirty-nine type 2 diabetic males with lowered testosterone levels were assigned to either testosterone replacement therapy or placebo and evaluated at baseline and after 24 weeks. Microvesicles were analysed by flow cytometry and defined as lactadherin-binding particles within the 0.1-1.0 μm gate. Microvesicles of platelet, monocyte, and endothelial cell origin were identified by cell-specific markers and their expression of CD36 was investigated. Results. Triglycerides correlated positively with all investigated microvesicle phenotypes in this study (p < 0.05), and indicators of hepatic fat accumulation, alanine aminotransferase, and gamma glutamyltransferase correlated with platelet and endothelial microvesicles and CD36-expressing microvesicles from platelets and monocytes (p < 0.05). BMI, waist circumference, and fat percentage correlated with CD36-expressing monocyte microvesicles (p < 0.05), while insulin sensitivity did not correlate with any microvesicle phenotypes. Microvesicle levels were unaffected by testosterone therapy. Conclusions. Metabolic syndrome components and hepatic fat accumulation correlated with microvesicle phenotypes, supporting the involvement of especially CD36 on monocytes in metabolic syndrome pathogenesis. Although testosterone therapy improved body composition measures, microvesicle phenotype levels were unaffected. This trial was registered at ClinicalTrials.gov (NCT01560546).

Low CD36 and LOX-1 Levels and CD36 Gene Subexpression Are Associated with Metabolic Dysregulation in Older Individuals with Abdominal Obesity

Background. Obesity study in the context of scavenger receptors has been linked to atherosclerosis. CD36 and LOX-1 are important, since they have been associated with atherogenic and metabolic disease but not fat redistribution. The aim of our study was to determinate the association between CD36 and LOX-1 in presence of age and abdominal obesity. Methods. This is a cross-sectional study that included 151 healthy individuals, clinically and anthropometrically classified into two groups by age (<30 and ≥30 years old) and abdominal obesity (according to World Health Organization guidelines). We excluded individuals with any chronic and metabolic illness, use of medication, or smoking. Fasting blood samples were taken to perform determination of CD36 mRNA expression by real-time PCR, lipid profile and metabolic and low grade inflammation markers by routine methods, and soluble scavenger receptors (CD36 and LOX-1) by ELISA. Results. Individuals ≥30 years old with abdominal obesity presented high atherogenic index, lower soluble scavenger receptor levels, and subexpression of CD36 mRNA (54% less). On the other hand, individuals <30 years old with abdominal adiposity presented higher levels in the same parameters, except LOX-1 soluble levels. Conclusion. In this study, individuals over 30 years of age presented low soluble scavenger receptors levels pattern and CD36 gene subexpression, which suggest the chronic metabolic dysregulation in abdominal obesity.

Reduced sCD36 following weight loss corresponds to improved insulin sensitivity, dyslipidemia and liver fat in obese children

BACKGROUND/OBJECTIVES

Childhood obesity is a major health problem with serious long-term metabolic consequences. CD36 is important for the development of obesity-related complications among adults. We aimed to investigate circulating sCD36 during weight loss in childhood obesity and its associations with insulin resistance, dyslipidemia, hepatic fat accumulation and low-grade inflammation.

SUBJECTS/METHODS

The impact of a 10-week weight loss camp for obese children (N=113) on plasma sCD36 and further after a 12-month follow-up (N=68) was investigated. Clinical and biochemical data were collected, and sCD36 was measured by an in-house assay. Liver fat was estimated by ultrasonography and insulin resistance by the homeostasis model assessment (HOMA-IR).

RESULTS

Along with marked weight loss, sCD36 was reduced by 21% (P=0.0013) following lifestyle intervention, and individual sCD36 reductions were significantly associated with the corresponding decreases in HOMA-IR, triglycerides and total cholesterol. The largest sCD36 decrease occurred among children who reduced HOMA-IR and liver fat. After 12 months of follow-up, sCD36 was increased (P=0.014) and the metabolic improvements were largely lost.

CONCLUSIONS

Weight-loss-induced sCD36 reduction, coincident with improved insulin resistance, circulating lipids and hepatic fat accumulation, proposes that sCD36 may be an early marker of long-term health risk associated with obesity-related complications.

Soluble cluster of differentiation 36 concentrations are not associated with cardiovascular risk factors in middle-aged subjects

Cluster of differentiation 36 (CD36) is involved in the development of atherosclerosis by enhancing macrophage endocytosis of oxidized low-density lipoproteins and foam cell formation. Soluble CD36 (sCD36) was found to be elevated in type 2 diabetic patients and possibly acted as a marker of insulin resistance and atherosclerosis. In young subjects, sCD36 was associated with cardiovascular risk factors including obesity and hypertriglyceridemia. The present study was conducted to further investigate the association between plasma sCD36 and cardiovascular risk factors among middle-aged patients with metabolic syndrome (MetS) and healthy controls. sCD36 concentrations were determined by enzyme-linked immunosorbent assays (ELISA) for 41 patients with MetS and 36 healthy controls. Data for other variables were obtained from patient medical records. sCD36 concentrations were relatively low compared to the majority of other studies and were not significantly different between the MetS group and controls (P=0.17). sCD36 was also not correlated with age, body mass index, glucose, lipid profile, serum electrolytes and blood counts. sCD36 was not significantly different between subjects with obesity, hyperglycemia, dyslipidemia, hypertension or cardiovascular disease, and those without these abnormalities (P>0.05). The inconsistency between results reported in the present study and other studies may be unique to the study population or be a result of the lack of a reliable standardized method for determining absolute sCD36 concentrations. However, further investigations are required to assess CD36 tissue expression in the study population and to assess the accuracy of various commercially available sCD36 ELISA kits. Thus, the availability of a standardized simple sCD36 ELISA that could be performed in any basic laboratory would be more favorable to the specialized flow cytometry methods that detect CD36+ microparticles if it was to be used as a biomarker.

Characterization of functional methylomes by next-generation capture sequencing identifies novel disease-associated variants

Most genome-wide methylation studies (EWAS) of multifactorial disease traits use targeted arrays or enrichment methodologies preferentially covering CpG-dense regions, to characterize sufficiently large samples. To overcome this limitation, we present here a new customizable, cost-effective approach, methylC-capture sequencing (MCC-Seq), for sequencing functional methylomes, while simultaneously providing genetic variation information. To illustrate MCC-Seq, we use whole-genome bisulfite sequencing on adipose tissue (AT) samples and public databases to design AT-specific panels. We establish its efficiency for high-density interrogation of methylome variability by systematic comparisons with other approaches and demonstrate its applicability by identifying novel methylation variation within enhancers strongly correlated to plasma triglyceride and HDL-cholesterol, including at CD36. Our more comprehensive AT panel assesses tissue methylation and genotypes in parallel at ∼4 and ∼3 M sites, respectively. Our study demonstrates that MCC-Seq provides comparable accuracy to alternative approaches but enables more efficient cataloguing of functional and disease-relevant epigenetic and genetic variants for large-scale EWAS.