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

Lack of change in serum sCD36 concentration in children with non-alcoholic fatty liver disease - A preliminary study

PURPOSE

Non-alcoholic fatty liver disease (NAFLD) is increasingly being recognized in the pediatric population, therefore, the search for non-invasive parameters to predict progression of NAFLD is of great interest. The aim of this study was to assess serum concentration of sCD36 in children with obesity and to determine its diagnostic value in pediatric NAFLD.

PATIENTS AND METHODS

The study group consisted of 50 children with obesity aged 8-17.5 years, admitted to our Department because of suspected liver pathology. Selected liver diseases were excluded in the examined group. Anthropometry, laboratory tests (including the concentration of sCD36) and liver ultrasound, were performed in all subjects.

RESULTS

NAFLD was confirmed in 16 out of 50 patients with obesity. There was significantly higher activity of ALT, AST, GGT, and increased waist-hip ratio WHR in individuals with NAFLD in comparison to non-hepatopathic children with obesity. We did not find a significant difference between sCD36 concentration in patients with obesity and NAFLD and non-hepathopathic patients with obesity. We also did not find a significant difference between sCD36 concentration in children with obesity in comparison to the control group and between mild (grade 1) vs. advanced (grade ≥2) steatosis. Correlation of sCD36 concentration with anthropometric, biochemical, and bioimpedance parameters in children with obesity was confirmed only with body fat percentage.

CONCLUSIONS

sCD36 is not a suitable parameter to differentiate children with NAFLD from non-hepatopathic children with obesity and controls without obesity. Further studies on a larger pediatric population are needed to confirm these findings.

MicroRNA-20a-5p Ameliorates Non-alcoholic Fatty Liver Disease via Inhibiting the Expression of CD36

Fatty acid translocase CD36 (CD36) plays an important role in the initiation and pathogenesis of chronic liver disease and non-alcoholic fatty liver disease (NAFLD). The purpose of this study is to investigate the regulation of microRNA-20a-5p (miR-20a-5p) on CD36 in the pathogenesis of NAFLD. Human plasma samples were obtained from NAFLD patients and healthy controls. Mice were fed with high-fat diet to induce an in vivo NAFLD model. Histology staining was performed to examine the morphology and lipid deposition of mouse liver tissue. Real-time PCR, dual-luciferase assay, and western blotting were employed to detect the relationship between miR-20a-5p and CD36. The expression level of miR-20a-5p was decreased in NAFLD patients, HFD mice, and free fatty acid (FFA)-treated HepG2 cells or primary mouse hepatocytes, accompanied by increased lipid production in hepatocytes. MiR-20a-5p suppressed the expression of CD36 to reduce lipid accumulation via binding to its 3'-untranslated region (UTR). However, under the condition of interference with CD36, further inhibition of miR-20a-5p would not cause lipid over-accumulation. In this study, we found that miR-20a-5p played a protective role in lipid metabolic disorders of NAFLD by targeting CD36, which indicated the prospect of miR-20a-5p as a biomarker and treatment target for NAFLD.

MicroRNA-20a-5p Ameliorates Non-alcoholic Fatty Liver Disease via Inhibiting the Expression of CD36

Fatty acid translocase CD36 (CD36) plays an important role in the initiation and pathogenesis of chronic liver disease and non-alcoholic fatty liver disease (NAFLD). The purpose of this study is to investigate the regulation of microRNA-20a-5p (miR-20a-5p) on CD36 in the pathogenesis of NAFLD. Human plasma samples were obtained from NAFLD patients and healthy controls. Mice were fed with high-fat diet to induce an in vivo NAFLD model. Histology staining was performed to examine the morphology and lipid deposition of mouse liver tissue. Real-time PCR, dual-luciferase assay, and western blotting were employed to detect the relationship between miR-20a-5p and CD36. The expression level of miR-20a-5p was decreased in NAFLD patients, HFD mice, and free fatty acid (FFA)-treated HepG2 cells or primary mouse hepatocytes, accompanied by increased lipid production in hepatocytes. MiR-20a-5p suppressed the expression of CD36 to reduce lipid accumulation via binding to its 3'-untranslated region (UTR). However, under the condition of interference with CD36, further inhibition of miR-20a-5p would not cause lipid over-accumulation. In this study, we found that miR-20a-5p played a protective role in lipid metabolic disorders of NAFLD by targeting CD36, which indicated the prospect of miR-20a-5p as a biomarker and treatment target for NAFLD.

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.

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.

CD36 plays a negative role in the regulation of lipophagy in hepatocytes through an AMPK-dependent pathway

Fatty acid translocase cluster of differentiation (CD36) is a multifunctional membrane protein that facilitates the uptake of long-chain fatty acids. Lipophagy is autophagic degradation of lipid droplets. Accumulating evidence suggests that CD36 is involved in the regulation of intracellular signal transduction that modulates fatty acid storage or usage. However, little is known about the relationship between CD36 and lipophagy. In this study, we found that increased CD36 expression was coupled with decreased autophagy in the livers of mice treated with a high-fat diet. Overexpressing CD36 in HepG2 and Huh7 cells inhibited autophagy, while knocking down CD36 expression induced autophagy due to the increased autophagosome formation in autophagic flux. Meanwhile, knockout of CD36 in mice increased autophagy, while the reconstruction of CD36 expression in CD36-knockout mice reduced autophagy. CD36 knockdown in HepG2 cells increased lipophagy and β-oxidation, which contributed to improving lipid accumulation. In addition, CD36 expression regulated autophagy through the AMPK pathway, with phosphorylation of ULK1/Beclin1 also involved in the process. These findings suggest that CD36 is a negative regulator of autophagy, and the induction of lipophagy by ameliorating CD36 expression can be a potential therapeutic strategy for the treatment of fatty liver diseases through attenuating lipid overaccumulation.

Developmental Exposure to 2,2',4,4'-Tetrabromodiphenyl Ether Induces Long-Lasting Changes in Liver Metabolism in Male Mice

Polybrominated diphenyl ethers (PBDEs) were used as flame-retardant additives in a wide range of polymers. The generations born when environmental concentrations of PBDEs reached their maximum account in the United States for one-fifth of the total population. We hypothesized that exposure to PBDEs during sensitive developmental windows might result in long-lasting changes in liver metabolism. The present study was based on experiments with CD-1 mice and human hepatocellular carcinoma cells (human hepatoma cell line, HepG2). Pregnant mice were exposed to 0.2 mg/kg 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) from gestation day 8 until postnatal day 21. The metabolic health-related outcomes were analyzed on postnatal day 21 and postnatal week 20 in male offspring. Several groups of metabolic genes, including ribosomal and mitochondrial genes, were significantly upregulated in the liver at both points. Genes regulated via mechanistic target of rapamycin (mTOR) pathway, the gatekeeper of metabolic homeostasis, were whether up- or downregulated at both measurement points. On postnatal day 21, but not week 20, both mTOR complexes in the liver were activated, as measured by phosphorylation of their targets. mTOR complexes were also activated by BDE-47 in HepG2 cells in vitro. The following changes were observed at week 20: a decreased number of polyploid hepatocytes, suppressed cytoplasmic S6K1, twofold greater blood insulin-like growth factor-1 and triglycerides, and 2.5-fold lower expression of fatty acid uptake membrane receptor CD36 in liver tissue. Thus, perinatal exposure to environmentally relevant doses of BDE-47 in laboratory mice results in long-lasting changes in liver physiology. Our evidence suggests involvement of the mTOR pathway in the observed metabolic programming of the liver.

Arterial Stiffness, Thickness and Association to Suitable Novel Markers of Risk at the Origin of Cardiovascular Disease in Obese Children

Atherosclerosis origins early in childhood. Aim of the study was to investigate vascular signature and phenotypes of cardiovascular disease in obese children and adolescents identifying novel potential circulating markers of risk. Cross-sectional study of intima-media-thickness (IMT), pulse wave velocity (PWV), augmentation index (AIX@75), circulating markers (E-selectin, soluble-intercellular-adhesion-molecule1_ICAM1, chemerin, fatty-acid-binding protein 4, sCD36, lipopolysaccharides_LPS, oxLDL, fetuin) in 123 obese (body mass index, BMI z-score >1.645 SD) children (N=55, age ≤10 years-old) and adolescents (N=68, age >10 years-old). Adolescents had significantly higher uric acid (p=0.002), non-HDL-cholesterol (p=0.02), fasting glucose (p=0.04), systolic blood pressure (p=0.005) and PWV (p=0.02) than children. Obese adolescent patients with metabolic syndrome (MetS) abnormalities had higher PWV (p<0.05) than peers without. No differences were observed in circulating biomarkers in relationship to age and MetS status. oxLDL, sCD36 and LPS were correlated to AIX@75 and/or IMT_M in children and adolescents (p ranging from <0.05 to <0.0001). Total cholesterol, non-HDL-cholesterol, TG/HDL ratio, oxLDL, sCD36, ICAM1, LPS were significantly different across AIX@75 tertiles (p between 0.03 and 0.001). Early phenotypes of cardiovascular alterations in young severely obese patients encompass increased IMT, stiffness of intermediate size and resistance vasculature. Novel biomarkers investigated in the present study were associated to estimates of stiffness and thickness not differently from traditional risk factor such as non-HDL-cholesterol and TG/HDL ratio.