Cellular fatty acid uptake: a pathway under construction

Dyslipidemia in Kidney Disorders: Perspectives on Mitochondria Homeostasis and Therapeutic Opportunities

To excrete body nitrogen waste and regulate electrolyte and fluid balance, the kidney has developed into an energy factory with only second to the heart in mitochondrial content in the body to meet the high-energy demand and regulate homeostasis. Energy supply from the renal mitochondria majorly depends on lipid metabolism, with programed enzyme systems in fatty acid β-oxidation and Krebs cycle. Renal mitochondria integrate several metabolic pathways, including AMPK/PGC-1α, PPARs, and CD36 signaling to maintain energy homeostasis for dynamic and static requirements. The pathobiology of several kidney disorders, including diabetic nephropathy, acute and chronic kidney injuries, has been primarily linked to impaired mitochondrial bioenergetics. Such homeostatic disruption in turn stimulates a pathological adaptation, with mitochondrial enzyme system reprograming possibly leading to dyslipidemia. However, this alteration, while rescuing oncotic pressure deficit secondary to albuminuria and dissipating edematous disorder, also imposes an ominous lipotoxic consequence. Reprograming of lipid metabolism in kidney injury is essential to preserve the integrity of kidney mitochondria, thereby preventing massive collateral damage including excessive autophagy and chronic inflammation. Here, we review dyslipidemia in kidney disorders and the most recent advances on targeting mitochondrial energy metabolism as a therapeutic strategy to restrict renal lipotoxicity, achieve salutary anti-edematous effects, and restore mitochondrial homeostasis.

Carbon source modify lipids composition of Rhodococcus opacus intended for infant formula

Human milk fat substitutes (HMFSs) are the structured lipids intended for infant formula. It provides energy and essential fatty acid for infant. HMFSs are mainly prepared by enzymatic method. In this study, we aim to explore the potential for producing HMFSs by fermentation using R. opacus. The results indicated that different compounds with chain length from 12 to 18, used as carbon source, could be incorporated into triacylglycerols directly. Polyunsaturated fatty acids in term of ARA, EPA, DHA could enter the kennedy pathway directly and involved in the biosynthesis of triacylglycerols. GC, UPLC-MS and ¹³C-NMR analysis demonstrated that typical structured lipids β-OPL (40.09%) was synthesized in R. opacus. Transcriptome analysis revealed that β-oxidation, fatty acid elongation and kennedy pathways existed in R. opacus. It was concluded that fatty acid supplied as carbon source could enter the kennedy pathways directly or via the de novo fatty acid biosynthesis pathway depending on the chain length, thus, affect the triacylglycerol species formed in the Rhodococcus opacus.

Low-arginine and low-protein diets induce hepatic lipid accumulation through different mechanisms in growing rats

Background

Dietary protein deficiency and amino acid imbalance cause hepatic fat accumulation. We previously demonstrated that only arginine deficiency or total amino acid deficiency in a diet caused significant hepatic triglyceride (TG) accumulation in young Wistar rats. In this study, we explored the mechanisms of fatty liver formation in these models.

Methods

We fed 6-week-old male Wistar rats a control diet (containing an amino acid mixture equivalent to 15% protein), a low-total-amino acid diet (equivalent to 5% protein; 5PAA), and a low-arginine diet (only the arginine content is as low as that of the 5PAA diet) for 2 weeks.

Results

Much greater hepatic TG accumulation was observed in the low-arginine group than in the low-total-amino acid group. The lipid consumption rate and fatty acid uptake in the liver did not significantly differ between the groups. In contrast, the low-total-amino acid diet potentiated insulin sensitivity and related signaling in the liver and enhanced de novo lipogenesis. The low-arginine diet also inhibited hepatic very-low-density lipoprotein secretion without affecting hepatic insulin signaling and lipogenesis.

Conclusions

Although the arginine content of the low-arginine diet was as low as that of the low-total-amino acid diet, the two diets caused fatty liver via completely different mechanisms. Enhanced lipogenesis was the primary cause of a low-protein diet-induced fatty liver, whereas lower very-low-density lipoprotein secretion caused low-arginine diet-induced fatty liver.

Cathepsin B deficiency ameliorates liver lipid deposition, inflammatory cell infiltration, and fibrosis after diet-induced nonalcoholic steatohepatitis

Nonalcoholic steatohepatitis (NASH) is a severe form of nonalcoholic fatty liver disease characterized by fat accumulation and inflammation in liver. Yet, the mechanistic insight and diagnostic and therapeutic options of NASH remain incompletely understood. This study tested the roles of cysteine protease cathepsin B (CatB) in mouse NASH development. Immunoblot revealed increased liver CatB expression in NASH mice. Fructose-palmitate-cholesterol diet increased body weight gain, liver to body weight ratio, blood fasting glucose, plasma total cholesterol and alanine transaminase levels, and liver triglyceride, but decreased plasma high-density lipoprotein in wild-type mice. All these changes were blunted in CatB-deficient (Ctsb^-/-) mice. In parallel to reduced expression of genes involved in liver lipid transport and lipogenesis, liver CD36, FABP4, and PPARγ protein levels were also significantly decreased in Ctsb^-/- mice, although CatB deficiency did not affect liver gluconeogenesis and fatty acid beta-oxidation-associated gene expression. Mechanistic studies showed that CatB deficiency decreased liver expression of adhesion molecules, inflammatory cytokine, and chemokine, along with reduced liver inflammatory cell infiltration. CatB deficiency also promoted M2 macrophage polarization and reduced liver TGF-β1 signaling and fibrosis. Together, CatB deficiency improves liver function in NASH mice by suppressing de novo lipogenesis and liver inflammation and fibrosis.

An Overview of Lipid Metabolism and Nonalcoholic Fatty Liver Disease

The occurrence of nonalcoholic fatty liver disease (NAFLD) is associated with major abnormalities of hepatic lipid metabolism. We propose that lipid abnormalities directly or indirectly contribute to NAFLD, especially fatty acid accumulation, arachidonic acid metabolic disturbance, and ceramide overload. The effects of lipid intake and accumulation on NAFLD and NAFLD treatment are explained with theoretical and experimental details. Overall, these findings provide further understanding of lipid metabolism in NAFLD and may lead to novel therapies.

Metabolic Escape Routes of Cancer Stem Cells and Therapeutic Opportunities

Although improvement in early diagnosis and treatment ameliorated life expectancy of cancer patients, metastatic disease still lacks effective therapeutic approaches. Resistance to anticancer therapies stems from the refractoriness of a subpopulation of cancer cells-termed cancer stem cells (CSCs)-which is endowed with tumor initiation and metastasis formation potential. CSCs are heterogeneous and diverge by phenotypic, functional and metabolic perspectives. Intrinsic as well as extrinsic stimuli dictated by the tumor microenvironment (TME)have critical roles in determining cell metabolic reprogramming from glycolytic toward an oxidative phenotype and vice versa, allowing cancer cells to thrive in adverse milieus. Crosstalk between cancer cells and the surrounding microenvironment occurs through the interchange of metabolites, miRNAs and exosomes that drive cancer cells metabolic adaptation. Herein, we identify the metabolic nodes of CSCs and discuss the latest advances in targeting metabolic demands of both CSCs and stromal cells with the scope of improving current therapies and preventing cancer progression.

Gender-specific associations of CD36 polymorphisms with the lipid profile and susceptibility to premature multi-vessel coronary artery heart disease in the Northern Han Chinese

BACKGROUND

The aim of the present study was to detect potential gender-specific associations between some common CD36 single nucleotide polymorphisms (SNPs) and the lipid profile, as well as the susceptibility to premature multi-vessel coronary artery heart disease (CHD) in the Han population of Northern China.

METHODS

A systematic three-step study process was employed to detect associations between CD36 gene variants and blood lipid profiles, as well as premature multi-vessel CHD in a gender-specific manner.

RESULTS

The current study documented the following novel findings: (I) the full population-based association study in 329 Northern Han Chinese showed that four common CD36 polymorphisms were significantly related to extreme lipid profiles, with statistically significant effects based on gender interactions (rs1049673: P = 0.001; rs7755: P = 0.008; rs3211956: P = 0.034; and rs3173798: P = 0.004); (ii) these statistically significant effects could be decomposed into statistically significant atherogenic effects in males, but non-significant non-atherogenic effects in females; (iii) the results of logistic regression analysis indicated that current smoking status, low density lipoprotein cholesterol (LDL-C) levels, and type-2 diabetes were independent risk factors for premature multi-vessel CHD phenotype (P < 0.0001).

CONCLUSIONS

Four common CD36 polymorphisms (rs1049673, rs7755, rs3211956, and rs3173798) were identified to be significantly associated with extreme lipid profiles and had statistically opposite gender-specific clinical lipid profile effects. Thus, the 3'-untranslated regions (3'-UTR) CD36 SNPs could be a novel target for metabolic abnormalities in males of the Han nationality from Northern China.

A translation repressor, 4E-BP1, regulates the triglyceride level in rat liver during protein deprivation

Protein deprivation has been shown to induce fatty liver in humans and animals, but the molecular mechanisms underlying such induction are largely unknown. Our previous studies have shown that a low-protein diet increases eukaryotic translation initiation factor 4E-binding protein 1 (4E-BP1) protein and triglyceride (TG) levels in rat liver. 4E-BP1 is known to repress translation by binding to eIF4E. There is also evidence indicating that 4E-BP1 regulates lipid metabolism. Here, we examined the role of 4E-BP1 on TG accumulation in the livers of rats under protein deprivation. The low-protein diet rapidly increased the hepatic 4E-BP1 mRNA level within 1 day, followed by the induction of hepatic TG accumulation. The knockdown of hepatic 4E-BP1 attenuated the TG accumulation in rat liver induced by the low-protein diet. 4E-BP1 knockdown also increased the protein level of carnitine palmitoyltransferase 1A (CPT1A), a regulator of fatty acid oxidation, in the liver of rats fed a low-protein diet. These results indicate that a low-protein diet increases the amount of 4E-BP1, leading to TG accumulation in rat liver. We thus conclude that 4E-BP1 plays an important role in inducing hepatic steatosis under protein deprivation.

Understanding the distinct subcellular trafficking of CD36 and GLUT4 during the development of myocardial insulin resistance

CD36 and GLUT4 are the main cardiac trans-sarcolemmal transporters for long-chain fatty acids and glucose, respectively. Together they secure the majority of cardiac energy demands. Moreover, these transporters each represent key governing kinetic steps in cardiac fatty acid and glucose fluxes, thereby offering major sites of regulation. The underlying mechanism of this regulation involves a perpetual vesicle-mediated trafficking (recycling) of both transporters between intracellular stores (endosomes) and the cell surface. In the healthy heart, CD36 and GLUT4 translocation to the cell surface is under short-term control of the same physiological stimuli, most notably increased contraction and insulin secretion. However, under chronic lipid overload, a condition that accompanies a Western lifestyle, CD36 and GLUT4 recycling are affected distinctly, with CD36 being expelled to the sarcolemma while GLUT4 is imprisoned within the endosomes. Moreover, the increased CD36 translocation towards the cell surface is a key early step, setting the heart on a route towards insulin resistance and subsequent contractile dysfunction. Therefore, the proteins making up the trafficking machinery of CD36 need to be identified with special focus to the differences with the protein composition of the GLUT4 trafficking machinery. These proteins that are uniquely dedicated to either CD36 or GLUT4 traffic may offer targets to rectify aberrant substrate uptake seen in the lipid-overloaded heart. Specifically, CD36-dedicated trafficking regulators should be inhibited, whereas such GLUT4-dedicated proteins would need to be activated. Recent advances in the identification of CD36-dedicated trafficking proteins have disclosed the involvement of vacuolar-type H⁺-ATPase and of specific vesicle-associated membrane proteins (VAMPs). In this review, we summarize these recent findings and sketch a roadmap of CD36 and GLUT4 trafficking compatible with experimental findings.

Mesencephalic astrocyte-derived neurotrophic factor ameliorates steatosis in HepG2 cells by regulating hepatic lipid metabolism

BACKGROUND

Nonalcoholic fatty liver disease (NAFLD) is a global metabolism-associated liver disease. Mesencephalic astrocyte-derived neurotrophic factor (MANF) is a newly discovered secreted protein that is involved in metabolic homeostasis. However, much remains to be discovered about its function in hepatic lipid metabolism; thus, we assessed whether MANF could regulate hepatic metabolism.

AIM

To establish in vivo and in vitro NAFLD models to explore the role of MANF in hepatic lipid metabolism.

METHODS

HepG2 cells treated with free fatty acids (FFAs) and ob/ob mice were used as NAFLD models. Liver tissues collected from wild type and ob/ob mice were used to detect MANF expression. Cells were treated with FFAs for different durations. Moreover, we used lentiviral constructs to establish overexpression and knockdown cell models in order to interfere with MANF expression levels and observe whether MANF influences hepatic steatosis. Western blot analysis and quantitative real-time PCR were used to detect protein and gene expression, and oil red O staining was used to visualize intracellular lipid droplets.

RESULTS

Hepatic MANF protein and mRNA expression in wild type mice were 10-fold and 2-fold higher, respectively, than those in ob/ob mice. The MANF protein was temporarily increased by 1.3-fold after stimulation with FFAs for 24 h and gradually decreased to 0.66-fold that of the control at the 72 h time point in HepG2 cells. MANF deficiency upregulated the expression of genes involved in fatty acid synthesis, cholesterol synthesis, and fatty acid uptake and aggravated HepG2 cell steatosis, while MANF overexpression inhibited fatty acid synthesis and uptake and cholesterol synthesis, and rescued HepG2 cells from FFAs-induced steatosis. Furthermore, a significant decrease in triglyceride levels was observed in the MANF overexpression group compared with the control group (0.4288 ± 0.0081 mmol/g vs 0.3746 ± 0.0121 mmol/g, P < 0.05) upon FFAs treatment. There was also a 17% decrease in intracellular total cholesterol levels between the MANF overexpression group and the control group (0.1301 ± 0.0059 mmol/g vs 0.1088 ± 0.0009 mmol/g, P < 0.05) upon FFAs treatment. Moreover, MANF suppressed lipid deposition in HepG2 cells.

CONCLUSION

Our findings indicate that MANF improves the phenotype of liver cell steatosis and may be a potential therapeutic target in hepatic steatosis processes.

Spatiotemporal dynamic monitoring of fatty acid-receptor interaction on single living cells by multiplexed Raman imaging

Numerous fatty acid receptors have proven to play critical roles in normal physiology. Interactions among these receptor types and their subsequent membrane trafficking has not been fully elucidated, due in part to the lack of efficient tools to track these cellular events. In this study, we fabricated the surface-enhanced Raman scattering (SERS)-based molecular sensors for detection of two putative fatty acid receptors, G protein-coupled receptor 120 (GPR120) and cluster of differentiation 36 (CD36), in a spatiotemporal manner in single cells. These SERS probes allowed multiplex detection of GPR120 and CD36, as well as a peak that represented the cell. This multiplexed sensing system enabled the real-time monitoring of fatty acid-induced receptor activation and dynamic distributions on the cell surface, as well as tracking of the receptors' internalization processes on the addition of fatty acid. Increased SERS signals were seen in engineered HEK293 cells with higher fatty acid concentrations, while decreased responses were found in cell line TBDc1, suggesting that the endocytic process requires innate cellular components. SERS mapping results confirm that GPR120 is the primary receptor and may work synergistically with CD36 in sensing polyunsaturated fatty acids and promoting Ca²⁺ mobilization, further activating the process of fatty acid uptake. The ability to detect receptors' locations and monitor fatty acid-induced receptor redistribution demonstrates the specificity and potential of our multiplexed SERS imaging platform in the study of fatty acid-receptor interactions and might provide functional information for better understanding their roles in fat intake and development of fat-induced obesity.

CD44 Loss Disrupts Lung Lipid Surfactant Homeostasis and Exacerbates Oxidized Lipid-Induced Lung Inflammation

Alveolar macrophages (AMs) are CD44 expressing cells that reside in the alveolar space where they maintain lung homeostasis by serving critical roles in immunosurveillance and lipid surfactant catabolism. AMs lacking CD44 are unable to bind the glycosaminoglycan, hyaluronan, which compromises their survival and leads to reduced numbers of AMs in the lung. Using RNA sequencing, lipidomics and multiparameter flow cytometry, we demonstrate that CD44^−/− mice have impaired AM lipid homeostasis and increased surfactant lipids in the lung. CD44^−/− AMs had increased expression of CD36, a lipid scavenger receptor, as well as increased intracellular lipid droplets, giving them a foamy appearance. RNA sequencing revealed the differential expression of genes associated with lipid efflux and metabolism in CD44^−/− AMs. Lipidomic analysis showed increased lipids in both the supernatant and cell pellet extracted from the bronchoalveolar lavage of CD44^−/− mice. Phosphatidylcholine species, cholesterol, oxidized phospholipids and levels of reactive oxygen species (ROS) were increased in CD44^−/− AMs. Oxidized phospholipids were more cytotoxic to CD44^−/− AMs and induced greater lung inflammation in CD44^−/− mice. Reconstitution of CD44^+/+ mice with CD44^−/− bone marrow as well as adoptive transfer of CD44^−/− AMs into CD44^+/+ mice showed that lipid accumulation in CD44^−/− AMs occurred irrespective of the lung environment, suggesting a cell intrinsic defect. Administration of colony stimulating factor 2 (CSF-2), a critical factor in AM development and maintenance, increased AM numbers in CD44^−/− mice and decreased phosphatidylcholine levels in the bronchoalveolar lavage, but was unable to decrease intracellular lipid accumulation in CD44^−/− AMs. Peroxisome proliferator-activated receptor gamma (PPARγ), downstream of CSF-2 signaling and a regulator of lipid metabolism, was reduced in the nucleus of CD44^−/− AMs, and PPARγ inhibition in normal AMs increased their lipid droplets. Thus, CD44 deficiency causes defects in AMs that lead to abnormal lipid accumulation and oxidation, which exacerbates oxidized lipid-induced lung inflammation. Collectively, these findings implicate CD44 as a regulator of lung homeostasis and inflammation.

Reprogramming of fatty acid metabolism in cancer

A common feature of cancer cells is their ability to rewire their metabolism to sustain the production of ATP and macromolecules needed for cell growth, division and survival. In particular, the importance of altered fatty acid metabolism in cancer has received renewed interest as, aside their principal role as structural components of the membrane matrix, they are important secondary messengers, and can also serve as fuel sources for energy production. In this review, we will examine the mechanisms through which cancer cells rewire their fatty acid metabolism with a focus on four main areas of research. (1) The role of de novo synthesis and exogenous uptake in the cellular pool of fatty acids. (2) The mechanisms through which molecular heterogeneity and oncogenic signal transduction pathways, such as PI3K-AKT-mTOR signalling, regulate fatty acid metabolism. (3) The role of fatty acids as essential mediators of cancer progression and metastasis, through remodelling of the tumour microenvironment. (4) Therapeutic strategies and considerations for successfully targeting fatty acid metabolism in cancer. Further research focusing on the complex interplay between oncogenic signalling and dysregulated fatty acid metabolism holds great promise to uncover novel metabolic vulnerabilities and improve the efficacy of targeted therapies.

Effects of Dietary Fatty Acids on Bovine Oocyte Competence and Granulosa Cells

Here we assessed the effects of dietary essential fatty acids on the developmental competence of oocytes in cows and on the functionality of follicular granulosa cells (GC). Lactating German Holstein cows were supplemented from week 9 ante partum (ap) until week 8 post-partum (pp) in four dietary groups designed as (i) control (CTRL: coconut oil), (ii) essential fatty acid (EFA: linseed and safflower oil), (iii) conjugated linoleic acid (CLA: Lutalin®), and (iv) EFA+CLA (mixture of linseed oil, safflower oil and Lutalin®). EFA, CLA or EFA+CLA supplementation did not improve in vitro embryo production. However, higher proportions of α-linolenic acid (ALA) and cis-9, trans-11 CLA were observed in the follicular fluid suggesting the exposure of GC to relatively high levels of ALA and cis-9, trans-11 CLA. Consequently, we tested different concentrations of ALA and cis-9, trans-11 CLA in a bovine GC culture model for their effects on steroid production, marker gene expression and viability. Both fatty acids upregulated CD36 and downregulated the expression of FOXL2, while ALA significantly increased SOX 9 transcript levels. Both ALA and cis-9, trans-11 CLA reduced the CCND2 expression and cis-9, trans-11 CLA induced apoptosis. ALA and cis-9, trans-11 CLA significantly down-regulated the expression of STAR, CYP19A1, FSHR, LHCGR and decreased the 17β-Estradiol (E2) and progesterone (P4) production. In conclusion, dietary lipids did not improve in vitro embryo production, while ALA and cis-9, trans-11 CLA affected the morphology and functionality of GC. This could suggestively lead to compromised follicle development and ovarian cyclicity in dairy cows.

Cd36 gene expression in adipose and hepatic tissue mediates the lipids accumulation in liver of obese rats with sucrose-induced hepatic steatosis

Obesity is considered a global epidemic and is mainly associated with the development of diabetes, cardiovascular diseases and Non-Alcoholic Fatty Liver (NAFLD). The pathogenesis between obesity and hepatic steatosis is partially known, but could involve differentiated or tissue-specific participation of the expression of Cd36 mRNA that codes for a receptor which is a transporter of free fatty acids (FFA) in different tissues, favoring the lipids storage. This relative expression was evaluated in adipose and liver tissue in rats with steatosis after consumption of sucrose for 30 and 40 weeks. Ten Wistar rats were divided into two experimental groups (St-30 and St-40), which received a standard diet plus 30 % sucrose in their water intake. These rats showed a significant increase in abdominal fat, serum biochemical determinations, HOMA-IR; as well as, changes in adipocytes size and mild portal hepatitis and grade 2 hepatic steatosis. The relative expression of Cd36 mRNA increased in liver tissue after 30 (4.5-fold) and 40 (8.5-fold) weeks of sucrose ingestión but no in adipose tissue; with respect to control group (P < 0.05). This expression was associated with a significant increase in the levles of sCD36 in serum, which is indicator of the presence of the FFA transporter in the hepatocyte membrane causing lipids accumulation. The above shows the link between the adipose and hepatic tissue for the accumulation of steatotic fat in the liver through time, mediated by the relative expression of cd36 mRNA that encodes for the FFA transporter.

Oral fatty acid taste sensitivity in healthy young individuals of both sexes is related to body mass index and soluble CD36 serum levels

Introduction

Introduction: CD36 is a membrane protein that functions as a lingual receptor for lipids. The soluble CD36 fraction (sCD36) may correlate oral fatty acid fat taste sensitivity to body mass index (BMI) and adiposity. Objectives: to determine if the oral fatty acid taste sensitivity in healthy young individuals of both sexes is related to serum sCD36 levels, adiposity and BMI. Methods: a cross-sectional study was conducted in 72 healthy young individuals (18-25 years). Serum sCD36 was quantified for all subjects. Oral fatty acid taste sensitivity was determined using an ascending series of the three-alternate forced choice methodology. Additionally, BMI was calculated using anthropometry, and adiposity was determined by bioelectric impedance analysis. Results: there was a positive correlation between BMI and the oral fatty acid taste sensitivity threshold (r = 0.277, p < 0.05) and a negative correlation between BMI and serum sCD36 levels (r = -0.035, p < 0.01). Adiposity negatively correlated with the sCD36 levels only in women (r = -0.359, p < 0.05). The threshold for oral sensitivity to fatty acids in overweight individuals was 1.0 (IQR 1.16) mM vs 0.2 (IQR 0.29) mM in healthy weight individuals (p < 0.05), while sCD36 levels were 26.1 pg/ml (IQR 32.9) and 77.97 pg/ml (IQR 560.66) in overweight and normal weight individuals, respectively (p < 0.05). Conclusions: BMI positively correlates with the oral sensitivity threshold of fatty acids and negatively correlates with serum sCD36 levels. The threshold of oral sensitivity to fatty acids was significantly higher in overweight subjects, while sCD36 levels were significantly higher in the group of normal weight individuals.

Osteoprotegerin Promotes Liver Steatosis by Targeting the ERK-PPAR-γ-CD36 Pathway

Previous cross-sectional studies have established that circulating osteoprotegerin (OPG) levels are associated with nonalcoholic fatty liver disease (NAFLD). However, the role of OPG in metabolic diseases, such as diabetes and NAFLD, is still unclear. In the current study, we demonstrated that hepatic OPG expression was downregulated in NAFLD individuals and in obese mice. OPG deficiency decreased lipid accumulation and expression of CD36 and peroxisome proliferator-activated receptor-γ (PPAR-γ) in the livers of OPG^-/- mice and cultured cells, respectively, whereas OPG overexpression elicited the opposite effects. The stimulatory role of OPG in lipid accumulation was blocked by CD36 inactivation in hepatocytes isolated from CD36^-/- mice. The overexpression of OPG led to a decrease in extracellular signal-regulated kinase (ERK) phosphorylation in the livers of OPG^-/- mice and in cultured cells, while OPG deficiency resulted in the opposite effect. The inhibition of PPAR-γ or the activation of ERK blocked the induction of CD36 expression by OPG in cultured cells. Mechanistically, OPG facilitated CD36 expression by acting on PPAR response element (PPRE) present on the CD36 promoter. Taken together, our study revealed that OPG signaling promotes liver steatosis through the ERK-PPAR-γ-CD36 pathway. The downregulation of OPG in NAFLD might be a compensatory response of the body to dampen excess hepatic fat accumulation in obesity.

A single-center investigational study of CD36 antigen deficiency and platelet alloantibody distribution in different populations in Northern China as well as platelet alloantibodies effect on pregnancy

BACKGROUND

Platelet antibodies can lead to clinical diseases such as platelet transfusion refractoriness (PTR), fetal/neonatal alloimmune thrombocytopenia (FNAIT), etc. This study is aimed at understanding CD36 expression, platelet alloantibody distribution in different populations in Northern China, and effects of platelet alloantibodies on pregnancy.

STUDY DESIGN AND METHODS

Whole blood samples of 612 subjects including hematological patients, pregnant women, and blood donors were collected at a single center, then CD36 expressions were determined, followed by platelet antibody screening and characterization of platelet antibody specificity. A retrospective analysis was performed in 1552 pregnant women admitted to Department of Obstetrics, in order to investigate FNAIT occurrence.

RESULTS

Rate of CD36 deficiency expression was 2.12% (13/612), all cases exhibited type II deficiency without type I deficiency being detected, and such rate is lower than that in Southern China (3.43%), Japanese (4.87%) and in the black people (4.18%), and higher than that in the White people (0.09%). Positive rates of platelet antibody screening in hematological patient group (6.86%, 14/204) and in pregnant women group (6.31%, 13/206) are higher than that in blood donor group (0.49%, 1/202), P < .01. Out of 1552 pregnant women, there were not children with FNAIT.

CONCLUSION

The frequency of CD36 deficiency in northern China was low, all of them were type II deficiency, and no CD36 antibody was detected. It is speculated that the risk of immune-related thrombocytopenia caused by CD36 deficiency in this population is very low. Platelet antibodies should be monitored early in patients with hematological and multiple miscarriages pregnant.

Cathelicidin-WA Facilitated Intestinal Fatty Acid Absorption Through Enhancing PPAR-γ Dependent Barrier Function

The molecular mechanisms underlying the cellular uptake of long-chain fatty acids and the regulation of this process have been debated in recent decades. Here, we established an intestinal barrier dysfunction model in mice and Caco2 cell line by Lipopolysaccharide (LPS), and evaluated the fatty acid uptake capacity of the intestine. We found that LPS stimulation restricted the absorption of long chain fatty acid (LCFA), while Cathelicidin-WA (CWA) pretreatment facilitated this physiological process. At the molecular level, our results demonstrated that the stimulatory effects of CWA on intestinal lipid absorption were dependent on cluster determinant 36 and fatty acid transport protein 4, but not fatty acid–binding protein. Further, an enhanced intestinal barrier was observed in vivo and in vitro when CWA alleviated the fatty acid absorption disorder induced by LPS stimulation. Mechanistically, peroxisome proliferator-activated receptor (PPAR-γ) signaling was considered as a key pathway for CWA to enhance LCFA absorption and barrier function. Treatment with a PPAR-γ inhibitor led to impaired intestinal barrier function and suppressed LCFA uptake. Moreover, once PPAR-γ signaling was blocked, CWA pretreatment could not maintain the stability of the intestinal epithelial cell barrier or LCFA uptake after LPS stimulation. Collectively, these findings suggested that PPAR-γ may serve as a target for specific therapies aimed at alleviating fatty acid uptake disorder, and CWA showed considerable potential as a new PPAR-γ agonist to strengthen intestinal barrier function against fatty acid malabsorption.

Increased uptake of oxLDL does not exert lipotoxic effects in insulin-secreting cells

Modified lipoproteins can negatively affect beta cell function and survival. However, the mechanisms behind interactions of modified lipoproteins with beta cells - and in particular, relationships to increased uptake - are only partly clarified. By over-expressing the scavenger receptor CD36 (Tet-on), we increased the uptake of fluorescent low-density modified lipoprotein (oxLDL) into insulin-secreting INS-1 cells. The magnitude of uptake followed the degree of CD36 over-expression. CD36 over-expression increased concomitant efflux of 3H-cholesterol in proportion to the cellular contents of 3H-cholesterol. Exposure to concentrations of oxLDL from 20 to 100 µg/mL dose-dependently increased toxicity (evaluated by MTT) as well as apoptosis. However, the increased uptake of oxLDL due to CD36 over-expression did not exert additive effects on oxLDL toxicity - neither on viability, nor on glucose-induced insulin release and cellular content. Reciprocally, blocking CD36 receptors by Sulfo-N-Succinimidyl Oleate decreased the uptake of oxLDL but did not diminish the toxicity. Pancreatic islets of CD36-/- mice displayed reduced uptake of 3H-cholesterol-labeled oxLDL vs wild type but similar toxicity to oxLDL. OxLDL was found to increase the expression of CD36 in islets and INS-1 cells. In summary, given the experimental conditions, our results indicate that (1) increased uptake of oxLDL is not responsible for toxicity of oxLDL, (2) increased efflux of the cholesterol moiety of oxLDL counterbalances, at least in part, increased uptake and (3) oxLDL participates in the regulation of CD36 in pancreatic islets and in INS-1 cells.

Adipocyte lipolysis affects Perilipin 5 and cristae organization at the cardiac lipid droplet-mitochondrial interface

This study investigated the effects of elevated fatty acid (FA) supply from adipose tissue on the ultrastructure of cardiac lipid droplets (LDs) and the expression and organization of LD scaffold proteins perilipin-2 (PLIN2) and perilipin-5 (PLIN5). Stimulation of adipocyte lipolysis by fasting (24 h) or β3-adrenergic receptor activation by CL316, 243 (CL) increased cardiac triacylglycerol (TAG) levels and LD size, whereas CL treatment also increased LD number. LDs were tightly associated with mitochondria, which was maintained during LD expansion. Electron tomography (ET) studies revealed continuity of LD and smooth endoplasmic reticulum (SER), suggesting interconnections among LDs. Under fed ad libitum conditions, the cristae of mitochondria that apposed LD were mostly organized perpendicularly to the tangent of the LD surface. Fasting significantly reduced, whereas CL treatment greatly increased, the perpendicular alignment of mitochondrial cristae. Fasting and CL treatment strongly upregulated PLIN5 protein and PLIN2 to a lesser extent. Immunofluorescence and immuno-electron microscopy demonstrated strong targeting of PLIN5 to the cardiac LD-mitochondrial interface, but not to the mitochondrial matrix. CL treatment augmented PLIN5 targeting to the LD-mitochondrial interface, whereas PLIN2 was not significantly affected. Together, our results support the concept that the interface between LD and cardiac mitochondria represents an organized and dynamic "metabolic synapse" that is highly responsive to FA trafficking.

Cypate and Cypate-Glucosamine as Near-Infrared Fluorescent Probes for In Vivo Tumor Imaging

Near-infrared (NIR) imaging is a promising technique for use as a noninvasive and sensitive diagnostic tool. Although the NIR fluorescently labeled glucose analog glucosamine (cypate-glucosamine) has applications in preclinical imaging, the transport pathways and fate of this probe in tissues remain unaddressed. Here, we have synthesized and characterized cypate and cypate-glucosamine conjugate (cy-2-glu), and investigated the probable transport pathways of these probes in vitro and in vivo. We compared uptake of the probes in the presence and absence of excess d-glucose, "saturated cypate" and palmitic acid in two normal-cancer cell line pairs: lung cancer (A549)-normal (MRC9) and prostate cancer (DU145)-normal (BPH). Breast cancer (MDA-MB-231) and liver cancer (HepG2) cell lines were also examined. Results support use of the glucose transport pathway by cy-2-glu and fatty acid transport pathway by cypate. Mass spectrometry data on the in vitro extracts revealed deamidation of cy-2-glu in prostate and liver cells, suggesting release of glucosamine. In vivo biodistribution studies in mice engrafted with breast tumors showed a distinct accumulation of cy-2-glu in liver and tumors, and to a lesser extent in kidneys and spleen. A negligible accumulation of cypate alone in tumors was observed. Analysis of urine extracts revealed renal excretion of the cy-2-glu probe in the form of free cypate, indicating deamidation of cy-2-glu in tissues. Thus, investigation of the metabolic pathways used by NIR probes such as cy-2-glu advances their use in the detection and monitoring of tumor progression in preclinical animal studies.

Metabolomics-based identification of metabolic alterations in PARK2

Objective

Parkin is the causative gene for autosomal recessive familial Parkinson's disease (PD), although it remains unclear how parkin dysfunction is involved with the general condition. Recently, serum and/or plasma metabolomics revealed alterations in metabolic pathways that might reflect pathomechanisms of idiopathic PD (iPD). Thus, we hypothesized that serum metabolomics of patients with homozygous or compound heterozygous parkin mutations (namely, PARK2) might reflect metabolic alterations due to parkin dysfunction.

Methods

We enrolled 15 PARK2 patients (52 ± 17.6 years) confirmed with homozygous (seven cases) and compound heterozygous (eight cases) parkin mutations, along with 19 healthy age‐matched controls (51 ± 11.5 years). We analyzed 830 metabolites from participants’ serum using well‐established metabolomics technologies, including ultra‐high performance liquid chromatography/tandem mass spectroscopy.

Results

Based on metabolic profiles, hierarchical matrix analysis can divide samples between control and PARK2 subjects. Profiles from PARK2 patients showed significantly higher levels of fatty acid (FA) metabolites and oxidized lipids, and significantly lower levels of antioxidant, caffeine, and benzoate‐related metabolites.

Interpretation

Metabolomics can identify specific metabolic alterations in PARK2 patients compared with controls. Alterations in FA metabolites suggest a relationship between parkin function and lipid metabolism. The elevation of oxidized lipids in combination with decreasing antioxidants may reflect general hyperoxidative stress. Decreasing benzoate‐related metabolites might be due to the alteration in gut microbiota. Consequently, caffeine and its metabolites may be decreased due to malabsorption. These findings are similar to metabolic alterations in iPD. Thus, serum/plasma metabolomics may reflect the association between parkin dysfunction and parkinsonism.

Administration of Fenofibrate Markedly Elevates Fabp3 in Rat Liver and Plasma and Confounds Its Use as a Preclinical Biomarker of Cardiac and Muscle Toxicity

Proteins involved in lipid homeostasis are often regulated through the nuclear peroxisome proliferator-activated receptors (PPAR). PPARα is the target for the fibrate-class of drugs. Fenofibrate has been approved for its lipid-lowering effects in patients with hypercholesterolemia and hypertriglyceridemia. We were interested in understanding the expression of the energy transporters in energy-utilizing tissues like liver, heart, muscle, and adipose tissues in rat with the hypothesis that the change in transporter expression would align with the known lipid-lowering effects of PPARα agonists like fenofibrate. We found that several fatty-acid transporter proteins had significantly altered levels following 8 days of fenofibrate dosing. The mRNA levels of the highly abundant Fatp2 and Fatp5 in rat liver increased approximately twofold and decreased fourfold, respectively. Several fatty-acid-binding proteins and acyl-CoA-binding proteins had a significant increase in mRNA abundance but not the major liver fatty-acid-binding protein, Fabp1. Of particular interest was the increased liver expression of Fabp3 also known as heart-fatty acid binding protein (H-FABP or FABP3). FABP3 has been proposed as a circulating clinical biomarker for cardiomyopathy and muscle toxicity, as well as a preclinical marker for PPARα-induced muscle toxicity. Here, we show that fenofibrate induces liver mRNA levels of Fabp3 ~5000-fold resulting in an approximately 50-fold increase in FABP3 protein levels in the whole liver. This increased liver expression complicates the interpretation and potential use of FABP3 as a specific biomarker for PPARα-induced muscle toxicities.

A role for scavenger receptor B1 as a captor of specific fatty acids in taste buds of circumvallate papillae

Class B scavenger receptor family members, scavenger receptor B1 (SR-B1) and cluster of differentiation 36 (CD36), are broadly expressed cell-surface proteins, both of which are believed to serve as multifaceted players in lipid and lipoprotein metabolism in mammals. Because of its presence in the apical part of taste receptor cells within circumvallate taste buds and its ability to recognise long-chain fatty acids, CD36 has been believed to participate in the sensing of the lipid species within the oral cavity. However, there have been no attempts to address whether SR-B1 has such a role to date. In this study, by reverse transcription- polymerase chain reaction analysis, we detected SR-B1 mRNA in a total RNA sample isolated from the circumvallate papillae of mouse tongue. Immunohistochemical analysis of tongue sections from the animals revealed the expression of SR-B1 protein in a population of taste bud cells of circumvallate papillae. In addition, the pattern of staining in the papillae for SR-B1 agreed closely with that for CD36 in double immunostaining analysis. We performed a cell-free in-vitro assay utilising a peptide mimic of SR-B1 and provided evidence that the receptor could recognise certain of the unsaturated long-chain fatty acids such as oleic acid. Our present findings suggest an additional role for SR-B1 as a captor of specific fatty acids in the oral cavity of mammals and contribute to expanding our knowledge of the physiological function of the receptor.

Abrogation of GH action in Kupffer cells results in increased hepatic CD36 expression and exaggerated nonalcoholic fatty liver disease

OBJECTIVE

To investigate the effects of GH signaling on Kupffer cells and the resulting changes in lipid homeostasis and their underlying mechanism(s) in the livers of diet-induced obese (DIO) mice.

DESIGN

Male macrophage specific-growth hormone receptor knockout mice (MacGHR KO) and their litter mate controls were fed a high fat diet containing 60% calories from fat for 26 weeks. Lipid content and lipid profiles in the liver and circulation were analyzed. Expression levels of CD36 in the liver were quantified by RT-PCR and Western Blot.

RESULTS

Increased hepatic lipid content and abundance of long-chain unsaturated fatty acids were observed in the liver of MacGHR KO mice. These findings were associated with increased steady state levels of CD36 mRNA and protein in MacGHR KO mice when compared with their litter mate controls.

CONCLUSION

GH action in Kupffer cells is required for maintaining hepatic lipid homeostasis, in part via regulation of hepatic CD36 expression.

Polymorphisms of peroxisome proliferator-activated receptor γ (PPARγ) and cluster of differentiation 36 (CD36) associated with valproate-induced obesity in epileptic patients

RATIONALE

Valproate (VPA) is a choice for the treatment of primary generalized epilepsies and partial epilepsies. Unfortunately, weight gain or obesity is one of the most frequent adverse effects of VPA treatment. Genetic factors were shown to be involved in the effect.

OBJECTIVE

The aim of this study was to investigate the association of selected single nucleotide polymorphisms (SNPs) of cluster of differentiation 36 (CD36) and peroxisome proliferator-activated receptor γ (PPARγ) with VPA-induced weight gain and obesity in epileptic patients.

METHODS

A total of 225 Chinese Han epilepsy patients receiving VPA treatment were recruited in the study. Height and weight for the calculation of body mass index (BMI) were measured at the initiation of VPA therapy and in the follow-up examination. A BMI of 25 kg/m² or higher was defined as obesity on the basis of the World Health Organization (WHO) criteria for Asian populations. Four SNPs in CD36 (rs1194197, rs7807607) and PPARγ (rs10865710, rs2920502) were genotyped using the Sequenom^® MassArray iPlex platform.

RESULTS

About 19.6% of epileptic patients receiving VPA therapy were found to become obese. After covariate analysis of age, gender, sex, height, initial BMI, and VPA dosage, the CD36 rs1194197 C allele and rs7807607 T allele (OR, 0.31; 95%CI, 0.13-0.72; P = 0.009 and OR, 0.38; 95%CI; 0.18-0.83; P = 0.02, respectively) were identified as protective factors for VPA-induced obesity. The PPARγ rs10865710 C allele carriers were found to be less likely to suffer from VPA-induced obesity compared with GG genotype carriers (OR, 0.04; 95%CI, 0.01-0.12; P < 0.001). After a Bonferroni correction for multiple comparisons, the genotypic associations of CD36 rs1194197 and PPARγ rs10865710 and the allelic association of CD36 rs7807607 with obesity remained statistically significant.

CONCLUSIONS

Our data first indicated that CD36 and PPARγ polymorphisms may be associated with VPA-induced obesity and weight gain, suggesting that CD36 and PPARγ may have potential value in predicting VPA-induced obesity in Chinese Han epileptic patients.

Association between plasma CD36 levels and incident risk of coronary heart disease among Danish men and women

BACKGROUND AND AIMS

CD36 is a cholesterol receptor involved in the uptake of oxidized low-density lipoprotein cholesterol and development of atherosclerotic plaques. Cross-sectional studies have shown correlations between plasma CD36 and atherosclerosis but no prospective study has examined the association yet. We prospectively examined the association between plasma CD36 levels and risk of incident coronary heart disease (CHD) in a Danish population.

METHODS

Plasma CD36 levels were measured in a case-cohort study nested within the Danish population-based cohort, the Diet, Cancer and Health Study. A total of 1963 incident CHD events occurred between baseline (1993-1997) and 2008, and a sub-cohort of 1759 participants were randomly selected as reference. Cox proportional hazard regression models were used to compute the hazard ratio (HR) and corresponding 95% confidence interval (CI).

RESULTS

After adjusting for CHD risk factors, including history of hypercholesterolemia and diabetes, elevated plasma CD36 levels were not associated with higher CHD risk in the total population, and the HR comparing the highest versus lowest tertile of CD36 levels was 1.02 (95% CI: 0.84-1.23). High CD36 levels were only found to be associated with risk of CHD in combination with prevalent diabetes (HR = 2.83, 95% CI: 1.08-7.45) vs. the joint reference group of lowest CD36 tertile and no diabetes.

CONCLUSIONS

Plasma CD36 levels were not predictive of CHD risk in the general population.

Association between insulin resistance and the development of cardiovascular disease

For many years, cardiovascular disease (CVD) has been the leading cause of death around the world. Often associated with CVD are comorbidities such as obesity, abnormal lipid profiles and insulin resistance. Insulin is a key hormone that functions as a regulator of cellular metabolism in many tissues in the human body. Insulin resistance is defined as a decrease in tissue response to insulin stimulation thus insulin resistance is characterized by defects in uptake and oxidation of glucose, a decrease in glycogen synthesis, and, to a lesser extent, the ability to suppress lipid oxidation. Literature widely suggests that free fatty acids are the predominant substrate used in the adult myocardium for ATP production, however, the cardiac metabolic network is highly flexible and can use other substrates, such as glucose, lactate or amino acids. During insulin resistance, several metabolic alterations induce the development of cardiovascular disease. For instance, insulin resistance can induce an imbalance in glucose metabolism that generates chronic hyperglycemia, which in turn triggers oxidative stress and causes an inflammatory response that leads to cell damage. Insulin resistance can also alter systemic lipid metabolism which then leads to the development of dyslipidemia and the well-known lipid triad: (1) high levels of plasma triglycerides, (2) low levels of high-density lipoprotein, and (3) the appearance of small dense low-density lipoproteins. This triad, along with endothelial dysfunction, which can also be induced by aberrant insulin signaling, contribute to atherosclerotic plaque formation. Regarding the systemic consequences associated with insulin resistance and the metabolic cardiac alterations, it can be concluded that insulin resistance in the myocardium generates damage by at least three different mechanisms: (1) signal transduction alteration, (2) impaired regulation of substrate metabolism, and (3) altered delivery of substrates to the myocardium. The aim of this review is to discuss the mechanisms associated with insulin resistance and the development of CVD. New therapies focused on decreasing insulin resistance may contribute to a decrease in both CVD and atherosclerotic plaque generation.

Utilization of adipocyte-derived lipids and enhanced intracellular trafficking of fatty acids contribute to breast cancer progression

BACKGROUND

To determine whether adipocyte-derived lipids could be transferred into breast cancer cells and investigate the underlying mechanisms of subsequent lipolysis and fatty acid trafficking in breast cancer cells.

METHODS

A Transwell co-culture system was used in which human breast cancer cells were cultured in the absence or presence of differentiated murine 3 T3-L1 adipocytes. Migration/invasion and proliferation abilities were compared between breast cancer cells that were cultivated alone and those co-cultivated with mature adipocytes. The ability of lipolysis in breast cancer cells were measured, as well as the expression of the rate-limiting lipase ATGL and fatty acid transporter FABP5. ATGL and FABP5 were then ablated to investigate their impact on the aggressiveness of breast cancer cells that were surrounded by adipocytes. Further, immunohistochemistry was performed to detect differential expression of ATGL and FABP5 in breast cancer tissue sections.

RESULTS

The migration and invasion abilities of cancer cells were significantly enhanced after co-culture with adipocytes, accompanied by elevated lipolysis and expression of ATGL and FABP5. Abrogation of ATGL and FABP5 sharply attenuated the malignancy of co-cultivated breast cancer cells. However, this phenomenon was not observed if a lipid emulsion was added to the culture medium to substitute for adipocytes. Furthermore, epithelial-mesenchymal transaction was induced in co-cultivated breast cancer cells. That may partially due to the stimulation of PPARβ/δ and MAPK, which was resulted from upregulation of FABP5. As evidenced by immunohistochemistry, ATGL and FABP5 also had higher expression levels at the invasive front of the breast tumor, in where the adipocytes abound, compared to the central area in tissue specimens.

CONCLUSIONS

Lipid originating from tumor-surrounding adipocytes could be transferred into breast cancer cells. Adipocyte-cancer cell crosstalk rather than lipids alone induced upregulation of lipases and fatty acid transport protein in cancer cells to utilize stored lipids for tumor progression. The increased expression of the key lipase ATGL and intracellular fatty acid trafficking protein FABP5 played crucial roles in this process via fueling or signaling.

PRDM16 Gene Polymorphism Is Associated with Obesity and Blood Lipids Profiles in Saudi Population

Aims: The PR domain containing 16 (PRDM16) gene and the Phosphodiesterase 4D (PDE4) gene are both an essential regulators in the thermogenesis process in the brown adipose tissues (BAT). The influence of polymorphisms in those genes on obesity and blood lipids profile is unknown particularly in the Saudi population, so the current study is aiming to explore that. Methods: A case control format was used that involved 89 obese individual and 84 non-obese (control). The PRDM16 (rs2651899) and PDE4D (rs295978) polymorphisms were genotyped using KASP™ (Competitive Allele-Specific PCR) method. Results: The distributions of the AA, GG, and AG genotypes of PRDM16 (rs2651899) polymorphism were 0.19, 0.26 and 0.54, respectively. While the distribution of the mutated allele A was 0.7 in the obese group comparing to 0.34 in the non-obese group. Participants with the mutated genotypes, AA and AG, of PRDM16 (rs2651899) polymorphism were significantly more likely to be obese as compared to participants with wild type genotype (OR = 21, 95% CI = 5.4190 to 84.4231, p value < 0.0001 and OR = 44.6, 95% CI = 11.5984 to 172.0157, p value < 0.0001, respectively). The wild type GG genotype of this polymorphism was associated with higher blood cholesterol, HDL and LDL but lower blood triglyceride compared with the mutated genotypes (p = 0.003, p = 0.008, p = 0.02 and p = 0.003, respectively). In contrast, PDE4D (rs295978) polymorphism was not associated with risk of obesity and had no effects on blood lipids profile. Conclusions: We found that the PRDM16 polymorphism (rs2651899) is a risk factor for obesity and influence blood lipids profiles significantly in Saudi population. While the PDE4D (rs295978) polymorphism didn’t show significant effect on risk of obesity or blood lipids profiles.

Effects of CD36 Genotype on Oral Perception of Oleic Acid Supplemented Safflower Oil Emulsions in Two Ethnic Groups: A Preliminary Study

Previous studies demonstrate humans can detect fatty acids via specialized sensors on the tongue, such as the CD36 receptor. Genetic variation at the common single nucleotide polymorphism rs1761667 of CD36 has been shown to differentially impact the perception of fatty acids, but comparative data among different ethnic groups are lacking. In a small cohort of Caucasian and East Asian young adults, we investigated if: (1) participants could detect oleic acid (C18:1) added to safflower oil emulsions at a constant ratio of 3% (w/v); (2) supplementation of oleic acid to safflower oil emulsions enhanced perception of fattiness and creaminess; and (3) variation at rs1761667 influenced oleic acid detection and fat taste perception. In a 3-alternate forced choice test, 62% of participants detected 2.9 ± 0.7 mM oleic acid (or 0.08% w/v) in a 2.8% safflower oil emulsion. Supplementation of oleic acid did not enhance fattiness and creaminess perception for the cohort as a whole, though East Asians carrying the GG genotype perceived more overall fattiness and creaminess than their AA genotype counterparts (P < 0.001). No differences were observed for the Caucasians. These preliminary findings indicate that free oleic acid can be detected in an oil-in-water emulsion at concentrations found in commercial oils, but it does not increase fattiness or creaminess perception. Additionally, variation at rs1761667 may have ethnic-specific effects on fat taste perception.

Intestinal CD36 and Other Key Proteins of Lipid Utilization: Role in Absorption and Gut Homeostasis

Several proteins have been implicated in fatty acid (FA) transport by enterocytes including the scavenger receptor CD36 (SR-B2), the scavenger receptor B1 (SR-B1) a member of the CD36 family and the FA transport protein 4 (FATP4). Here, we review the regulation of enterocyte FA uptake and its function in lipid absorption including prechylomicron formation, assembly and transport. Emphasis is given to CD36, which is abundantly expressed along the digestive tract of rodents and humans and has been the most studied. We also address the pleiotropic functions of CD36 that go beyond lipid absorption and metabolism to include recent evidence of its impact on intestinal homeostasis and barrier maintenance. Areas of progress involving contribution of membrane phospholipid remodeling and of cytosolic FA-binding proteins, FABP1 and FABP2 to fat absorption will be covered. © 2018 American Physiological Society. Compr Physiol 8:493-507, 2018.

Adipocyte-induced CD36 expression drives ovarian cancer progression and metastasis

Ovarian cancer (OvCa) is characterized by widespread and rapid metastasis in the peritoneal cavity. Visceral adipocytes promote this process by providing fatty acids (FAs) for tumour growth. However, the exact mechanism of FA transfer from adipocytes to cancer cells remains unknown. This study shows that OvCa cells co-cultured with primary human omental adipocytes express high levels of the FA receptor, CD36, in the plasma membrane, thereby facilitating exogenous FA uptake. Depriving OvCa cells of adipocyte-derived FAs using CD36 inhibitors and short hairpin RNA knockdown prevented development of the adipocyte-induced malignant phenotype. Specifically, inhibition of CD36 attenuated adipocyte-induced cholesterol and lipid droplet accumulation and reduced intracellular reactive oxygen species (ROS) content. Metabolic analysis suggested that CD36 plays an essential role in the bioenergetic adaptation of OvCa cells in the adipocyte-rich microenvironment and governs their metabolic plasticity. Furthermore, the absence of CD36 affected cellular processes that play a causal role in peritoneal dissemination, including adhesion, invasion, migration and anchorage independent growth. Intraperitoneal injection of CD36-deficient cells or treatment with an anti-CD36 monoclonal antibody reduced tumour burden in mouse xenografts. Moreover, a matched cohort of primary and metastatic human ovarian tumours showed upregulation of CD36 in the metastatic tissues, a finding confirmed in three public gene expression data sets. These results suggest that omental adipocytes reprogram tumour metabolism through the upregulation of CD36 in OvCa cells. Targeting the stromal-tumour metabolic interface via CD36 inhibition may prove to be an effective treatment strategy against OvCa metastasis.

Chinese olive extract ameliorates hepatic lipid accumulation in vitro and in vivo by regulating lipid metabolism

Chinese olive contains plenty of polyphenols, which possess a wide range of biological actions. In this study, we aimed to investigate the role of the ethyl acetate fraction of Chinese olive fruit extract (CO-EtOAc) in the modulation of lipid accumulation in vitro and in vivo. In cellular studies, CO-EtOAc attenuated oleic acid-induced lipid accumulation; we then elucidated the molecular mechanisms of CO-EtOAc in FL83B mouse hepatocytes. CO-EtOAc suppressed the mRNA levels of fatty acid transporter genes (CD36 and FABP) and lipogenesis genes (SREBP-1c, FAS, and ACC1), but upregulated genes that govern lipolysis (HSL) and lipid oxidation (PPARα, CPT-1, and ACOX). Moreover, CO-EtOAc increased the protein expression of phosphorylated AMPK, ACC1, CPT-1, and PPARα, but downregulated the expression of mature SREBP-1c and FAS. AMPK plays an essential role in CO-EtOAc-mediated amelioration of lipid accumulation. Furthermore, we confirmed that CO-EtOAc significantly inhibited body weight gain, epididymal adipose tissue weight, and hepatic lipid accumulation via regulation of the expression of fatty acid transporter, lipogenesis, and fatty acid oxidation genes and proteins in C57BL/6 mice fed a 60% high-fat diet. Therefore, Chinese olive fruits may have the potential to improve the metabolic abnormalities associated with fatty liver under high fat challenge.

Gastrointestinal factors regulating lipid droplet formation in the intestine

Cytoplasmic lipid droplets (CLD) are considered as neutral lipid reservoirs, which protect cells from lipotoxicity. It became clear that these fascinating dynamic organelles play a role not only in energy storage and metabolism, but also in cellular lipid and protein handling, inter-organelle communication, and signaling among diverse functions. Their dysregulation is associated with multiple disorders, including obesity, liver steatosis and cardiovascular diseases. The central aim of this review is to highlight the link between intra-enterocyte CLD dynamics and the formation of chylomicrons, the main intestinal dietary lipid vehicle, after overviewing the morphology, molecular composition, biogenesis and functions of CLD.

Drugs Involved in Dyslipidemia and Obesity Treatment: Focus on Adipose Tissue

Metabolic syndrome can be defined as a state of disturbed metabolic homeostasis characterized by visceral obesity, atherogenic dyslipidemia, arterial hypertension, and insulin resistance. The growing prevalence of metabolic syndrome will certainly contribute to the burden of cardiovascular disease. Obesity and dyslipidemia are main features of metabolic syndrome, and both can present with adipose tissue dysfunction, involved in the pathogenic mechanisms underlying this syndrome. We revised the effects, and underlying mechanisms, of the current approved drugs for dyslipidemia and obesity (fibrates, statins, niacin, resins, ezetimibe, and orlistat; sibutramine; and diethylpropion, phentermine/topiramate, bupropion and naltrexone, and liraglutide) on adipose tissue. Specifically, we explored how these drugs can modulate the complex pathways involved in metabolism, inflammation, atherogenesis, insulin sensitivity, and adipogenesis. The clinical outcomes of adipose tissue modulation by these drugs, as well as differences of major importance for clinical practice between drugs of the same class, were identified. Whether solutions to these issues will be found in further adjustments and combinations between drugs already in use or necessarily in new advances in pharmacology is not known. To better understand the effect of drugs used in dyslipidemia and obesity on adipose tissue not only is challenging for physicians but could also be the next step to tackle cardiovascular disease.

Molecular Regulation of Fatty Acid Oxidation in Skeletal Muscle during Aerobic Exercise

This review summarizes how fatty acid (FA) oxidation is regulated in skeletal muscle during exercise. From the available evidence it seems that acetyl-CoA availability in the mitochondrial matrix adjusts FA oxidation to exercise intensity and duration. This is executed at the step of mitochondrial fatty acyl import, as the extent of acetyl group sequestration by carnitine determines the availability of carnitine for the carnitine palmitoyltransferase 1 (CPT1) reaction. The rate of glycolysis seems therefore to be central to the amount of β-oxidation-derived acetyl-CoA that is oxidized in the tricarboxylic acid (TCA) cycle. FA oxidation during exercise is also determined by FA availability to mitochondria, dependent on trans-sarcolemmal FA uptake via cluster of differentiation 36/SR-B2 (CD36) and FAs mobilized from myocellular lipid droplets.

Fatty acid transport protein 1 enhances the macrophage inflammatory response by coupling with ceramide and c-Jun N-terminal kinase signaling

Macrophages are important cells that need to be controlled at the site of inflammation. Several factors are involved in chronic inflammation and its timely resolution. Free fatty acids drive the inflammatory response in macrophages and contribute to the vicious cycle of the inflammatory response. However, the identity of the uptake pathways of fatty acids is not fully clear in macrophages and how the inflammatory responses are regulated by the uptake of fatty acids remain poorly understood. We investigated the relationship between fatty acid transport protein (FATP) and the inflammatory response signaling pathway in macrophages as the first report. The FATP family has composed six isoforms, FATP1-6. We found that FATP1 is the most highly expressed isoform in macrophages. Forced expression of FATP1 enhanced production of inflammatory cytokines, such as TNFα and IL-6 concomitant with the increased uptake of fatty acids, increased level of ceramide, and increased phosphorylation of c-Jun N-terminal kinase (JNK). The enhancement by FATP1 was abolished by treatment with a JNK inhibitor, NF-κB inhibitor, or ceramide synthesis inhibitor. siRNA-mediated knockdown of FATP1 strongly inhibited the production of TNFα and IL-6. Similarly, an inhibitor of FATP1 inhibited the production of TNFα and IL-6. Finally, an inhibitor of FATP1 attenuated the production of inflammatory cytokines in bronchoalveolar lavage fluid in an LPS-induced acute lung injury in vivo mouse model. In summary, we propose that FATP1 is an important regulator of inflammatory response signaling in macrophages. Our findings suggest that ceramide-JNK signaling is important to terminate or sustain inflammation.

Ubiquitinated CD36 sustains insulin-stimulated Akt activation by stabilizing insulin receptor substrate 1 in myotubes

Both the magnitude and duration of insulin signaling are important in executing its cellular functions. Insulin-induced degradation of insulin receptor substrate 1 (IRS1) represents a key negative feedback loop that restricts insulin signaling. Moreover, high concentrations of fatty acids (FAs) and glucose involved in the etiology of obesity-associated insulin resistance also contribute to the regulation of IRS1 degradation. The scavenger receptor CD36 binds many lipid ligands, and its contribution to insulin resistance has been extensively studied, but the exact regulation of insulin sensitivity by CD36 is highly controversial. Herein, we found that CD36 knockdown in C2C12 myotubes accelerated insulin-stimulated Akt activation, but the activated signaling was sustained for a much shorter period of time as compared with WT cells, leading to exacerbated insulin-induced insulin resistance. This was likely due to enhanced insulin-induced IRS1 degradation after CD36 knockdown. Overexpression of WT CD36, but not a ubiquitination-defective CD36 mutant, delayed IRS1 degradation. We also found that CD36 functioned through ubiquitination-dependent binding to IRS1 and inhibiting its interaction with cullin 7, a key component of the multisubunit cullin-RING E3 ubiquitin ligase complex. Moreover, dissociation of the Src family kinase Fyn from CD36 by free FAs or Fyn knockdown/inhibition accelerated insulin-induced IRS1 degradation, likely due to disrupted IRS1 interaction with CD36 and thus enhanced binding to cullin 7. In summary, we identified a CD36-dependent FA-sensing pathway that plays an important role in negative feedback regulation of insulin activation and may open up strategies for preventing or managing type 2 diabetes mellitus.

Polymorphism rs1761667 in the CD36 Gene Is Associated to Changes in Fatty Acid Metabolism and Circulating Endocannabinoid Levels Distinctively in Normal Weight and Obese Subjects

The multifunctional CD36 scavenger receptor facilitates fatty acid (FA) uptake and oxidation and it has been involved in the pathophysiology related to dysfunctional FA metabolism. The common variant in the CD36 gene, rs1761667 (A/G), whose allele A is characterized by a reduced protein expression, has been associated with taste sensitivity to and preference for fat. We therefore aimed at evaluating whether the CD36 polymorphism may influence fatty acid metabolism and endocannabinoid biosynthesis in normal weight (NW) and obese (OB) subjects. Red blood cell (RBC) fatty acid composition, and plasma endocannabinoid levels were determined. In NW subjects with AA genotype was found a marked reduction of RBC saturated fatty acids and palmitic/linoleic ratio (PA/LA), considered as de novo lipogenesis (DNL) biomarkers. Remarkably, to the reduction of DNL biomarkers corresponded an increase of omega-6 index, an indirect marker of the impact on fatty acid metabolism of dietary omega-6 fatty acids, endocannabinoid levels and a higher waist/hip ratio. The presence of the G allele was instead associated with increased endocannabinoid plasma levels and a trend for increased waist/hip ratio in obese subjects, even though exhibited decreased BMI with respect to those with AA genotype. These data indicate that the CD36 polymorphism, rs1761667, leads to a distinct metabolic pattern in NW and in OB subjects. Therefore, their determination may be crucial in developing personalized therapeutic strategies for ameliorating dyslipidemia and other metabolic disorders.

Cell culture models of fatty acid overload: Problems and solutions

High plasma levels of fatty acids occur in a variety of metabolic diseases. Cellular effects of fatty acid overload resulting in negative cellular responses (lipotoxicity) are often studied in vitro, in an attempt to understand mechanisms involved in these diseases. Fatty acids are poorly soluble, and thus usually studied when complexed to albumins such as bovine serum albumin (BSA). The conjugation of fatty acids to albumin requires care pertaining to preparation of the solutions, effective free fatty acid concentrations, use of different fatty acid species, types of BSA, appropriate controls and ensuring cellular fatty acid uptake. This review discusses lipotoxicity models, the potential problems encountered when using these cellular models, as well as practical solutions for difficulties encountered.

Lipid oxidation products in the pathogenesis of non-alcoholic steatohepatitis

Non-alcoholic fatty liver disease (NAFLD) is the major public health challenge for hepatologists in the twenty-first century. NAFLD comprises a histological spectrum ranging from simple steatosis or fatty liver, to steatohepatitis, fibrosis, and cirrhosis. It can be categorized into two principal phenotypes: (1) non-alcoholic fatty liver (NAFL), and (2) non-alcoholic steatohepatitis (NASH). The mechanisms of NAFLD progression consist of lipid homeostasis alterations, redox unbalance, insulin resistance, and inflammation in the liver. Even though several studies show an association between the levels of lipid oxidation products and disease state, experimental evidence suggests that compounds such as reactive aldehydes and cholesterol oxidation products, in addition to representing hallmarks of hepatic oxidative damage, may behave as active players in liver dysfunction and the development of NAFLD. This review summarizes the processes that contribute to the metabolic alterations occurring in fatty liver that produce fatty acid and cholesterol oxidation products in NAFLD, with a focus on inflammation, the control of insulin signalling, and the transcription factors involved in lipid metabolism.

Rab8a Deficiency in Skeletal Muscle Causes Hyperlipidemia and Hepatosteatosis by Impairing Muscle Lipid Uptake and Storage

Skeletal muscle absorbs long-chain fatty acids (LCFAs) that are either oxidized in mitochondria or temporarily stored as triglycerides in lipid droplets (LDs). So far, it is still not fully understood how lipid uptake and storage are regulated in muscle and whether these are important for whole-body lipid homeostasis. Here we show that the small GTPase Rab8a regulates lipid uptake and storage in skeletal muscle. Muscle-specific Rab8a deletion caused hyperlipidemia and exacerbated hepatosteatosis induced by a high-fat diet. Mechanistically, Rab8a deficiency decreased LCFA entry into skeletal muscle and inhibited LD fusion in muscle cells. Consequently, blood lipid levels were elevated and stimulated hepatic mammalian target of rapamycin, which enhanced hepatosteatosis by upregulating hepatic lipogenesis and cholesterol biosynthesis. Our results demonstrate the significance of lipid uptake and storage in muscle in regulating whole-body lipid homeostasis, and they shed light on the roles of skeletal muscle in the pathogenesis of hyperlipidemia and hepatosteatosis.

A past and present overview of macrophage metabolism and functional outcomes

In 1986 and 1987, Philip Newsholme et al. reported macrophages utilize glutamine, as well as glucose, at high rates. These authors measured key enzyme activities and consumption and production levels of metabolites in incubated or cultured macrophages isolated from the mouse or rat intraperitoneal cavity. Metabolic pathways essential for macrophage function were then determined. Macrophages utilize glucose to generate (i) ATP in the pathways of glycolysis and mitochondrial oxidative phosphorylation, (ii) glycerol 3-phosphate for the synthesis of phospholipids and triacylglycerols, (iii) NADPH for the production of reactive oxygen species (ROS) and (iv) ribose for the synthesis of RNA and subsequently production and secretion of protein mediators (e.g. cytokines). Glutamine plays an essential role in macrophage metabolism and function, as it is required for energy production but also provides nitrogen for synthesis of purines, pyrimidines and thus RNA. Macrophages also utilize fatty acids for both energy production in the mitochondria and lipid synthesis essential to plasma membrane turnover and lipid meditator production. Recent studies utilizing metabolomic approaches, transcriptional and metabolite tracking technologies have detailed mitochondrial release of tricarboxylic acid (TCA) intermediates (e.g. citrate and succinate) to the cytosol, which then regulate pro-inflammatory responses. Macrophages can reprogramme their metabolism and function according to environmental conditions and stimuli in order to polarize phenotype so generating pro- or anti-inflammatory cells. Changes in macrophage metabolism result in modified function/phenotype and vice versa. The plasticity of macrophage metabolism allows the cell to quickly respond to changes in environmental conditions such as those induced by hormones and/or inflammation. A past and present overview of macrophage metabolism and impact of endocrine regulation and the relevance to human disease are described in this review.

Debris buster is a Drosophila scavenger receptor essential for airway physiology

Scavenger receptors class B (SR-B) are multifunctional transmembrane proteins, which in vertebrates participate in lipid transport, pathogen clearance, lysosomal delivery and intracellular sorting. Drosophila has 14 SR-B members whose functions are still largely unknown. Here, we reveal a novel role for the SR-B family member Debris buster (Dsb) in Drosophila airway physiology. Larvae lacking dsb show yeast avoidance behavior, hypoxia, and severe growth defects associated with impaired elongation and integrity along the airways. Furthermore, in dsb mutant embryos, the barrier function of the posterior spiracles, which are critical for gas exchange, is not properly established and liquid clearance is locally impaired at the spiracular lumen. We found that Dsb is specifically expressed in a group of distal epithelial cells of the posterior spiracle organ and not throughout the entire airways. Furthermore, tissue-specific knockdown and rescue experiments demonstrate that Dsb function in the airways is only required in the posterior spiracles. Dsb localizes in intracellular vesicles, and a subset of these associate with lysosomes. However, we found that depletion of proteins involved in vesicular transport to the apical membrane, but not in lysosomal function, causes dsb-like airway elongation defects. We propose a model in which Dsb sorts components of the apical extracellular matrix which are essential for airway physiology. Since SR-B LIMP2-deficient mice show reduced expression of several apical plasma membrane proteins, sorting of proteins to the apical membrane is likely an evolutionary conserved function of Dsb and LIMP2. Our data provide insights into a spatially confined function of the SR-B Dsb in intracellular trafficking critical for the physiology of the whole tubular airway network.

Aggressive Crosstalk Between Fatty Acids and Inflammation in Macrophages and Their Influence on Metabolic Homeostasis

From the immunological point of view, macrophages are required to maintain metabolic homeostasis. Recently, there has been an increased focus on the influence of macrophage phenotypes in adipose tissue on the maintenance of metabolic homeostasis in healthy conditions because dysregulated metabolic homeostasis causes metabolic syndrome. This review notes several types of inflammatory and anti-inflammatory mediators in metabolic homeostasis. M1 macrophage polarization mediates inflammation, whereas M2 macrophage polarization mediates anti-inflammation. Fatty acids and their related factors mediate both inflammatory and anti-inflammatory responses. Saturated fatty acids and polyunsaturated fatty acids mediate inflammation, whereas marine-derived n-3 fatty acids, such as eicosapentaenoic acid and docosahexaenoic acid, mediate anti-inflammation. In this review, we discuss the current understanding of the crosstalk between fatty acids and inflammation in macrophages and their influence on metabolic homeostasis.