Defective uptake and utilization of long chain fatty acids in muscle and adipose tissues of CD36 knockout mice

Adipocyte Phenotype Flexibility and Lipid Dysregulation

The prevalence of obesity and associated cardiometabolic diseases continues to rise, despite efforts to improve global health. The adipose tissue is now regarded as an endocrine organ since its multitude of secretions, lipids chief among them, regulate systemic functions. The loss of normal adipose tissue phenotypic flexibility, especially related to lipid homeostasis, appears to trigger cardiometabolic pathogenesis. The goal of this manuscript is to review lipid balance maintenance by the lean adipose tissue’s propensity for phenotype switching, obese adipose tissue’s narrower range of phenotype flexibility, and what initial factors account for the waning lipid regulatory capacity. Metabolic, hypoxic, and inflammatory factors contribute to the adipose tissue phenotype being made rigid. A better grasp of normal adipose tissue function provides the necessary context for recognizing the extent of obese adipose tissue dysfunction and gaining insight into how pathogenesis evolves.

Targeting the KCa3.1 channel suppresses diabetes-associated atherosclerosis via the STAT3/CD36 axis

BACKGROUND

In diet-induced arterial atherosclerosis, increased KCa3.1 channel was associated with atherosclerotic plaque progression and instability. Macrophages are involved in the formation of atherosclerotic plaques, and the release of inflammatory cytokines and oxygen free radicals promotes plaque progression. However, whether the macrophage KCa3.1 channel facilitates diabetes-accelerated atherosclerosis is still unclear. This study investigated atherosclerotic plaque in ApoE^-/- mice regulated by the KCa3.1 channel.

METHODS AND RESULTS

In vivo, blocking KCa3.1channel inhibit the development of the atherosclerotic lesion in diabetic ApoE^-/- mice fed with a high-fat diet. In vitro, upregulation of KCa3.1 channel level occurred in RAW264.7 cells treated with HG plus ox-LDL in a time-dependent manner. Blocking KCa3.1 significantly reduced the uptake of ox-LDL in mice peritoneal macrophages. Further studies indicated the KCa3.1 siRNA and TRAM-34 (KCa3.1 inhibitor) attenuated the scavenger receptor CD36 expression via inhibiting STAT3 phosphorylation.

CONCLUSION

Blockade of macrophage KCa3.1 channel inhibit cellular oxidized low-density lipoprotein accumulation and decrease proinflammation factors expression via STAT3/CD36 axis. This study provided a novel therapeutic target to reduce the risk of atherosclerosis development in diabetic patients.

Emerging Insights on the Diverse Roles of Proprotein Convertase Subtilisin/Kexin Type 9 (PCSK9) in Chronic Liver Diseases: Cholesterol Metabolism and Beyond

Chronic liver diseases are commonly associated with dysregulated cholesterol metabolism. Proprotein convertase subtilisin/kexin type 9 (PCSK9) is a serine protease of the proprotein convertase family that is mainly synthetized and secreted by the liver, and represents one of the key regulators of circulating low-density lipoprotein (LDL) cholesterol levels. Its ability to bind and induce LDL-receptor degradation, in particular in the liver, increases circulating LDL-cholesterol levels in the blood. Hence, inhibition of PCSK9 has become a very potent tool for the treatment of hypercholesterolemia. Besides PCSK9 limiting entry of LDL-derived cholesterol, affecting multiple cholesterol-related functions in cells, more recent studies have associated PCSK9 with various other cellular processes, including inflammation, fatty acid metabolism, cancerogenesis and visceral adiposity. It is increasingly becoming evident that additional roles for PCSK9 beyond cholesterol homeostasis are crucial for liver physiology in health and disease, often contributing to pathophysiology. This review will summarize studies analyzing circulating and hepatic PCSK9 levels in patients with chronic liver diseases. The factors affecting PCSK9 levels in the circulation and in hepatocytes, clinically relevant studies and the pathophysiological role of PCSK9 in chronic liver injury are discussed.

Lipid Transport in Brown Adipocyte Thermogenesis

Non-shivering thermogenesis is an energy demanding process that primarily occurs in brown and beige adipose tissue. Beyond regulating body temperature, these thermogenic adipocytes regulate systemic glucose and lipid homeostasis. Historically, research on thermogenic adipocytes has focused on glycolytic metabolism due to the discovery of active brown adipose tissue in adult humans through glucose uptake imaging. The importance of lipids in non-shivering thermogenesis has more recently been appreciated. Uptake of circulating lipids into thermogenic adipocytes is necessary for body temperature regulation and whole-body lipid homeostasis. A wide array of circulating lipids contribute to thermogenic potential including free fatty acids, triglycerides, and acylcarnitines. This review will summarize the mechanisms and regulation of lipid uptake into brown adipose tissue including protein-mediated uptake, lipoprotein lipase activity, endocytosis, vesicle packaging, and lipid chaperones. We will also address existing gaps in knowledge for cold induced lipid uptake into thermogenic adipose tissue.

Endothelial Cell CD36 Reduces Atherosclerosis and Controls Systemic Metabolism

High-fat Western diets contribute to tissue dysregulation of fatty acid and glucose intake, resulting in obesity and insulin resistance and their sequelae, including atherosclerosis. New therapies are desperately needed to interrupt this epidemic. The significant idea driving this research is that the understudied regulation of fatty acid entry into tissues at the endothelial cell (EC) interface can provide novel therapeutic targets that will greatly modify health outcomes and advance health-related knowledge. Dysfunctional endothelium, defined as activated, pro-inflammatory, and pro-thrombotic, is critical in atherosclerosis initiation, in modulating thrombotic events that could result in myocardial infarction and stroke, and is a hallmark of insulin resistance. Dyslipidemia from high-fat diets overwhelmingly contributes to the development of dysfunctional endothelium. CD36 acts as a receptor for pathological ligands generated by high-fat diets and in fatty acid uptake, and therefore, it may additionally contribute to EC dysfunction. We created EC CD36 knockout (CD36°) mice using cre-lox technology and a cre-promoter that does not eliminate CD36 in hematopoietic cells (Tie2e cre). These mice were studied on different diets, and crossed to the low density lipoprotein receptor (LDLR) knockout for atherosclerosis assessment. Our data show that EC CD36° and EC CD36°/LDLR° mice have metabolic changes suggestive of an uncompensated role for EC CD36 in fatty acid uptake. The mice lacking expression of EC CD36 had increased glucose clearance compared with controls when fed with multiple diets. EC CD36° male mice showed increased carbohydrate utilization and decreased energy expenditure by indirect calorimetry. Female EC CD36°/LDLR° mice have reduced atherosclerosis. Taken together, these data support a significant role for EC CD36 in systemic metabolism and reveal sex-specific impact on atherosclerosis and energy substrate use.

Fatty acid metabolism and acyl-CoA synthetases in the liver-gut axis

Fatty acids are energy substrates and cell components which participate in regulating signal transduction, transcription factor activity and secretion of bioactive lipid mediators. The acyl-CoA synthetases (ACSs) family containing 26 family members exhibits tissue-specific distribution, distinct fatty acid substrate preferences and diverse biological functions. Increasing evidence indicates that dysregulation of fatty acid metabolism in the liver-gut axis, designated as the bidirectional relationship between the gut, microbiome and liver, is closely associated with a range of human diseases including metabolic disorders, inflammatory disease and carcinoma in the gastrointestinal tract and liver. In this review, we depict the role of ACSs in fatty acid metabolism, possible molecular mechanisms through which they exert functions, and their involvement in hepatocellular and colorectal carcinoma, with particular attention paid to long-chain fatty acids and small-chain fatty acids. Additionally, the liver-gut communication and the liver and gut intersection with the microbiome as well as diseases related to microbiota imbalance in the liver-gut axis are addressed. Moreover, the development of potentially therapeutic small molecules, proteins and compounds targeting ACSs in cancer treatment is summarized.

Lipid-induced S-palmitoylation as a Vital Regulator of Cell Signaling and Disease Development

Lipid metabolites are emerging as pivotal regulators of protein function and cell signaling. The availability of intracellular fatty acid is tightly regulated by glycolipid metabolism and may affect human body through many biological mechanisms. Recent studies have demonstrated palmitate, either from exogenous fatty acid uptake or de novo fatty acid synthesis, may serve as the substrate for protein palmitoylation and regulate protein function via palmitoylation. Palmitoylation, the most-studied protein lipidation, encompasses the reversible covalent attachment of palmitate moieties to protein cysteine residues. It controls various cellular physiological processes and alters protein stability, conformation, localization, membrane association and interaction with other effectors. Dysregulation of palmitoylation has been implicated in a plethora of diseases, such as metabolic syndrome, cancers, neurological disorders and infections. Accordingly, it could be one of the molecular mechanisms underlying the impact of palmitate metabolite on cellular homeostasis and human diseases. Herein, we explore the relationship between lipid metabolites and the regulation of protein function through palmitoylation. We review the current progress made on the putative role of palmitate in altering the palmitoylation of key proteins and thus contributing to the pathogenesis of various diseases, among which we focus on metabolic disorders, cancers, inflammation and infections, neurodegenerative diseases. We also highlight the opportunities and new therapeutics to target palmitoylation in disease development.

Relationships Between Placental Lipid Activated/Transport-Related Factors and Macrosomia in Healthy Pregnancy

To assess associations between infants with macrosomia and placental expression levels of lipid activated/transport-related factors and umbilical cord blood lipid concentrations in healthy pregnancy. We conducted a case-control study of 38 macrosomic neonates (MS group) and 39 normal-birth-weight newborns (NC group) in a healthy pregnancy. Cord blood lipid levels were measured by automatic biochemical analyzer, mRNA and protein expression levels of placental lipid activated/transport-related factors were determined by real-time polymerase chain reaction and western blot, respectively. Compared with NC group, cord blood total cholesterol (TC), low-density lipoprotein cholesterol (LDLC), and non-esterified fatty acid (NEFA) concentrations were decreased in the MS group. The mRNA and protein expression levels of placental peroxisome proliferator-activated receptors (PPARα, PPARγ), plasma membrane fatty acid-binding protein (FABPpm), and fatty acid translocase (FAT/CD36) were significantly higher in the MS group than the NC group. And there was a weak positive correlation between the expression of PPARγ, FABP4, and FABP3 mRNA in the placenta and the HDLC (r_s = 0.439; P = 0.005), NEFA (r_s = 0.342; P = 0.041), and TG (r_s = 0.349; P = 0.034) levels in the cord blood in the MS group, respectively. After multivariate adjustment, the logistic regression analysis showed that high placental PPARα (adjusted odds ratio [AOR] = 3.022; 95% confidence interval [CI] 1.032-8.853) and FAT/CD36 (AOR=2.989; 95%CI 1.029-8.679) and low LDLC concentration in the cord blood (AOR=0.246; 95%CI 0.080-0.759) increased the risk of macrosomia. The increased PPARα and FAT/CD36 expression levels may influence the occurrence of fetal macrosomia through regulating placental lipid transport.

Multi‑faceted role of cancer‑associated adipocytes in the tumor microenvironment (Review)

Adipocytes are a type of stromal cell found in numerous different tissues that serve an active role in the tumor microenvironment. Cancer-associated adipocytes (CAAs) display a malignant phenotype and are found at the invasive tumor front, which mediates the crosstalk network between adipocytes (the precursor cells that will become cancer-associated adipocytes in the future) and cancer cells. The present review covers the mechanisms of adipocytes in the development of cancer, including metabolic reprogramming, chemotherapy resistance and adipokine regulation. Furthermore, the potential mechanisms involved in the adipocyte-cancer cell cycle in various types of cancer, including breast, ovarian, colon and rectal cancer, are discussed. Deciphering the complex network of CAA-cancer cell crosstalk will provide insights into tumor biology and optimize therapeutic strategies.

Role of CD36 in Palmitic Acid Lipotoxicity in Neuro-2a Neuroblastoma Cells

Elevated level of palmitic acid (PA), a long-chain saturated fatty acid (SFA), is lipotoxic to many different types of cells including Neuro-2a (N2a) neuroblastoma cells. CD36 is a multifunctional membrane glycoprotein that acts as a fatty acid translocase (FAT) facilitating the transport of long-chain free fatty acids (FFAs) into cells, serves a fatty acid (FA) sensing function in areas including taste buds and the proximal gut, and acts as a scavenger receptor that binds to many ligands, including FAs, collagen, oxidized low-density lipoproteins, and anionic phospholipids. However, the involvement of CD36 in FA uptake and PA lipotoxicity in N2a cells remains unclear. In this study, we examined FA uptake in BSA- and PA-treated N2a cells and investigated the involvement of CD36 in FA uptake and PA lipotoxicity in N2a cells. Our data showed that PA treatment promoted FA uptake in N2a cells, and that treatment with sulfo-N-succinimidyl oleate (SSO), a CD36 inhibitor, significantly decreased FA uptake in BSA- and PA-treated N2a cells, and ameliorated PA-induced decrease of cell viability, decrease of diploid cells, and increase of tetraploid cells. We also found that CD36 knockdown significantly decreased FA uptake in both BSA- and PA-treated cells as compared to their corresponding wild-type controls, and dramatically attenuated PA-induced cell cycle defects in N2a cells. Our data suggest that CD36 may play a critical role in FA uptake and PA lipotoxicity in N2a cells. CD36 may therefore represent a regulatory target against pathologies caused by excess FAs.

Investigating the association of CD36 gene polymorphisms (rs1761667 and rs1527483) with T2DM and dyslipidemia: Statistical analysis, machine learning based prediction, and meta-analysis

CD36 (cluster of differentiation 36) is a membrane protein involved in lipid metabolism and has been linked to pathological conditions associated with metabolic disorders, such as diabetes and dyslipidemia. A case-control study was conducted and included 177 patients with type-2 diabetes mellitus (T2DM) and 173 control subjects to study the involvement of CD36 gene rs1761667 (G>A) and rs1527483 (C>T) polymorphisms in the pathogenesis of T2DM and dyslipidemia among Jordanian population. Lipid profile, blood sugar, gender and age were measured and recorded. Also, genotyping analysis for both polymorphisms was performed. Following statistical analysis, 10 different neural networks and machine learning (ML) tools were used to predict subjects with diabetes or dyslipidemia. Towards further understanding of the role of CD36 protein and gene in T2DM and dyslipidemia, a protein-protein interaction network and meta-analysis were carried out. For both polymorphisms, the genotypic frequencies were not significantly different between the two groups (p > 0.05). On the other hand, some ML tools like multilayer perceptron gave high prediction accuracy (≥ 0.75) and Cohen's kappa (κ) (≥ 0.5). Interestingly, in K-star tool, the accuracy and Cohen's κ values were enhanced by including the genotyping results as inputs (0.73 and 0.46, respectively, compared to 0.67 and 0.34 without including them). This study confirmed, for the first time, that there is no association between CD36 polymorphisms and T2DM or dyslipidemia among Jordanian population. Prediction of T2DM and dyslipidemia, using these extensive ML tools and based on such input data, is a promising approach for developing diagnostic and prognostic prediction models for a wide spectrum of diseases, especially based on large medical databases.

The effect of homocysteine on the expression of CD36, PPARγ, and C/EBPα in adipose tissue of normal and obese mice

The purpose of this study was to investigate the effect of homocysteine (Hcy) on CD36, PPARγ, and C/EBPα gene and protein expression in adipose tissue obtained from normal and high-calorie diet obesity models. CD36, PPARγ, and C/EBPα gene expression and protein levels in adipose tissue specimens were determined using the RT-PCR and ELISA methods, respectively. Significantly increased CD36 gene expression was observed in adipose tissue from obese mice, while Hcy significantly reduced CD36 gene expression in adipose tissue from normal and obese mice. PPARγ and C/EBPα gene expression levels decreased significantly in all groups compared to the normal group. In addition, levels of both PPARγ and C/EBPα gene expression were lower with Hcy supplementation compared to their own controls. In conclusion, Hcy's reduction of CD36 gene expression in adipose tissue may be one probable factor in hyperhomocysteinemia representing an independent risk factor for cardiovascular diseases.

TNAP: A New Multitask Enzyme in Energy Metabolism

Tissue-nonspecific alkaline phosphatase (TNAP) is mainly known for its necessary role in skeletal and dental mineralization, which relies on the hydrolysis of the mineralization inhibitor inorganic pyrophosphate (PP_i). Mutations in the gene encoding TNAP leading to severe hypophosphatasia result in strongly reduced mineralization and perinatal death. Fortunately, the relatively recent development of a recombinant TNAP with a bone anchor has allowed to correct the bone defects and prolong the life of affected babies and children. Researches on TNAP must however not be slowed down, because accumulating evidence indicates that TNAP activation in individuals with metabolic syndrome (MetS) is associated with enhanced cardiovascular mortality, presumably in relation with cardiovascular calcification. On the other hand, TNAP appears to be necessary to prevent the development of steatohepatitis in mice, suggesting that TNAP plays protective roles. The aim of the present review is to highlight the known or suspected functions of TNAP in energy metabolism that may be associated with the development of MetS. The location of TNAP in liver and its function in bile excretion, lipopolysaccharide (LPS) detoxification and fatty acid transport will be presented. The expression and function of TNAP in adipocyte differentiation and thermogenesis will also be discussed. Given that TNAP is a tissue- and substrate-nonspecific phosphatase, we believe that it exerts several crucial pathophysiological functions that are just beginning to be discovered.

Modulation of endothelium function by fatty acids

The endothelium acts as the barrier that prevents circulating lipids such as lipoproteins and fatty acids into the arterial wall; it also regulates normal functioning in the circulatory system by balancing vasodilation and vasoconstriction, modulating the several responses and signals. Plasma lipids can interact with endothelium via different mechanisms and produce different phenotypes. Increased plasma-free fatty acids (FFAs) levels are associated with the pathogenesis of atherosclerosis and cardiovascular diseases (CVD). Because of the multi-dimensional roles of plasma FFAs in mediating endothelial dysfunction, increased FFA level is now considered an essential link in the onset of endothelial dysfunction in CVD. FFA-mediated endothelial dysfunction involves several mechanisms, including dysregulated production of nitric oxide and cytokines, metaflammation, oxidative stress, inflammation, activation of the renin-angiotensin system, and apoptosis. Therefore, modulation of FFA-mediated pathways involved in endothelial dysfunction may prevent the complications associated with CVD risk. This review presents details as to how endothelium is affected by FFAs involving several metabolic pathways.

Fatty acids and evolving roles of their proteins in neurological, cardiovascular disorders and cancers

The dysregulation of fat metabolism is involved in various disorders, including neurodegenerative, cardiovascular, and cancers. The uptake of long-chain fatty acids (LCFAs) with 14 or more carbons plays a pivotal role in cellular metabolic homeostasis. Therefore, the uptake and metabolism of LCFAs must constantly be in tune with the cellular, metabolic, and structural requirements of cells. Many metabolic diseases are thought to be driven by the abnormal flow of fatty acids either from the dietary origin and/or released from adipose stores. Cellular uptake and intracellular trafficking of fatty acids are facilitated ubiquitously with unique combinations of fatty acid transport proteins and cytoplasmic fatty acid-binding proteins in every tissue. Extensive data are emerging on the defective transporters and metabolism of LCFAs and their clinical implications. Uptake and metabolism of LCFAs are crucial for the brain's functional development and cardiovascular health and maintenance. In addition, data suggest fatty acid metabolic transporter can normalize activated inflammatory response by reprogramming lipid metabolism in cancers. Here we review the current understanding of how LCFAs and their proteins contribute to the pathophysiology of three crucial diseases and the mechanisms involved in the processes.

Uptake of oxidized lipids by the scavenger receptor CD36 promotes lipid peroxidation and dysfunction in CD8+ T cells in tumors

A common metabolic alteration in the tumor microenvironment (TME) is lipid accumulation, a feature associated with immune dysfunction. Here, we examined how CD8+ tumor infiltrating lymphocytes (TILs) respond to lipids within the TME. We found elevated concentrations of several classes of lipids in the TME and accumulation of these in CD8+ TILs. Lipid accumulation was associated with increased expression of CD36, a scavenger receptor for oxidized lipids, on CD8+ TILs, which also correlated with progressive T cell dysfunction. Cd36-/- T cells retained effector functions in the TME, as compared to WT counterparts. Mechanistically, CD36 promoted uptake of oxidized low-density lipoproteins (OxLDL) into T cells, and this induced lipid peroxidation and downstream activation of p38 kinase. Inhibition of p38 restored effector T cell functions in vitro, and resolution of lipid peroxidation by overexpression of glutathione peroxidase 4 restored functionalities in CD8+ TILs in vivo. Thus, an oxidized lipid-CD36 axis promotes intratumoral CD8+ T cell dysfunction and serves as a therapeutic avenue for immunotherapies.

ILC2s Improve Glucose Metabolism Through the Control of Saturated Fatty Acid Absorption Within Visceral Fat

Background and aims

Group 2 innate lymphoid cells (ILC2s) have been implicated in the regulation of metabolic homeostasis in mice.

Methods

In this study, the role of ILC2s in white adipose tissue (WAT) was investigated using ST2, an IL-33 receptor that is expressed on ILC2 knockout mice.

Results

The deficiency of ST2 decreased ILC2s in WAT, whereas ex-ILC2, which acquired group 1 innate lymphoid cell (ILC1)-like traits, was increased. This led to significant metabolic disorders such as visceral fat obesity, decreased browning in WAT, reduction of energy metabolism, and impaired glucose tolerance, compared to wild type (WT) mice. Those metabolic abnormalities of ST2-knockout (ST2KO) mice were not ameliorated by IL-33 administration, but impaired glucose tolerance and visceral fat obesity were significantly improved by transplantation of ILCs from the bone marrow of WT mice. The relative expression of Cd36 in WAT increased due to the deficiency of ST2, and the storage of saturated fatty acids in WAT of ST2KO mice was significantly higher than that of WT mice. Moreover, saturated fatty acids aggravated the chronic inflammation in adipocytes, promoted the differentiation of M1-like macrophages, and inhibited that of M2-like macrophages.

Conclusions

Our results indicated that ILC2 regulates diet-induced obesity and chronic inflammation through the regulation of saturated fatty acid absorption in visceral adipose tissue.

Lipolytic enzymes and free fatty acids at the endothelial interface

Lipids released from circulating lipoproteins by intravascular action of lipoprotein lipase (LpL) reach parenchymal cells in tissues with a non-fenestrated endothelium by transfer through or around endothelial cells. The actions of LpL are controlled at multiple sites, its synthesis and release by myocytes and adipocytes, its transit and association with the endothelial cell luminal surface, and finally its activation and inhibition by a number of proteins and by its product non-esterified fatty acids. Multiple pathways mediate endothelial transit of lipids into muscle and adipose tissues. These include movement of fatty acids via the endothelial cell fatty acid transporter CD36 and movement of whole or partially LpL-hydrolyzed lipoproteins via other apical endothelial cell receptors such as SR-B1and Alk1. Lipids also likely change the barrier function of the endothelium and operation of the paracellular pathway around endothelial cells. This review summarizes in vitro and in vivo support for the key role of endothelial cells in delivery of lipids and highlights incompletely understood processes that are the focus of active investigation.

Metabolic Complications in Cardiac Aging

Aging is a process that can be accompanied by molecular and cellular alterations that compromise cardiac function. Although other metabolic disorders with increased prevalence in aged populations, such as diabetes mellitus, dyslipidemia, and hypertension, are associated with cardiovascular complications; aging-related cardiomyopathy has some unique features. Healthy hearts oxidize fatty acids, glucose, lactate, ketone bodies, and amino acids for producing energy. Under physiological conditions, cardiac mitochondria use fatty acids and carbohydrate mainly to generate ATP, 70% of which is derived from fatty acid oxidation (FAO). However, relative contribution of nutrients in ATP synthesis is altered in the aging heart with glucose oxidation increasing at the expense of FAO. Cardiac aging is also associated with impairment of mitochondrial abundance and function, resulting in accumulation of reactive oxygen species (ROS) and activation of oxidant signaling that eventually leads to further mitochondrial damage and aggravation of cardiac function. This review summarizes the main components of pathophysiology of cardiac aging, which pertain to cardiac metabolism, mitochondrial function, and systemic metabolic changes that affect cardiac function.

Cell surface markers for immunophenotyping human pluripotent stem cell-derived cardiomyocytes

Human pluripotent stem cells (hPSC) self-renew and represent a potentially unlimited source for the production of cardiomyocytes (CMs) suitable for studies of human cardiac development, drug discovery, cardiotoxicity testing, and disease modelling and for cell-based therapies. However, most cardiac differentiation protocols yield mixed cultures of atrial-, ventricular-, and pacemaker-like cells at various stages of development, as well as non-CMs. The proportions and maturation states of these cell types result from disparities among differentiation protocols and time of cultivation, as well as hPSC reprogramming inconsistencies and genetic background variations. The reproducible use of hPSC-CMs for research and therapy is therefore limited by issues of cell population heterogeneity and functional states of maturation. A validated method that overcomes issues of cell heterogeneity is immunophenotyping coupled with live cell sorting, an approach that relies on accessible surface markers restricted to the desired cell type(s). Here we review current progress in unravelling heterogeneity in hPSC-cardiac cultures and in the identification of surface markers suitable for defining cardiac identity, subtype specificity, and maturation states.

Trans Fatty Acid Intake Induces Intestinal Inflammation and Impaired Glucose Tolerance

Background and Aims

Many nutritional and epidemiological studies have shown that high consumption of trans fatty acids can cause several adverse effects on human health, including cardiovascular disease, diabetes, and cancer. In the present study, we investigated the effect of trans fatty acids on innate immunity in the gut by observing mice fed with a diet high in trans fatty acids, which have been reported to cause dysbiosis.

Methods

We used C57BL6/J mice and fed them with normal diet (ND) or high-fat, high-sucrose diet (HFHSD) or high-trans fatty acid, high-sucrose diet (HTHSD) for 12 weeks. 16S rRNA gene sequencing was performed on the mice stool samples, in addition to flow cytometry, real-time PCR, and lipidomics analysis of the mice serum and liver samples. RAW264.7 cells were used for the in vitro studies.

Results

Mice fed with HTHSD displayed significantly higher blood glucose levels and advanced fatty liver and intestinal inflammation, as compared to mice fed with HFHSD. Furthermore, compared to mice fed with HFHSD, mice fed with HTHSD displayed a significant elevation in the expression of CD36 in the small intestine, along with a reduction in the expression of IL-22. Furthermore, there was a significant increase in the populations of ILC1s and T-bet-positive ILC3s in the lamina propria in mice fed with HTHSD. Finally, the relative abundance of the family Desulfovibrionaceae, which belongs to the phylum Proteobacteria, was significantly higher in mice fed with HFHSD or HTHSD, than in mice fed with ND; between the HFHSD and HTHSD groups, the abundance was slightly higher in the HTHSD group.

Conclusions

This study revealed that compared to saturated fatty acid intake, trans fatty acid intake significantly exacerbated metabolic diseases such as diabetes and fatty liver.

SGLT2 Inhibition Does Not Affect Myocardial Fatty Acid Oxidation or Uptake, but Reduces Myocardial Glucose Uptake and Blood Flow in Individuals With Type 2 Diabetes: A Randomized Double-Blind, Placebo-Controlled Crossover Trial

Sodium-glucose cotransporter 2 (SGLT2) inhibition reduces cardiovascular morbidity and mortality in individuals with type 2 diabetes. Beneficial effects have been attributed to increased ketogenesis, reduced cardiac fatty acid oxidation, and diminished cardiac oxygen consumption. We therefore studied whether SGLT2 inhibition altered cardiac oxidative substrate consumption, efficiency, and perfusion. Thirteen individuals with type 2 diabetes were studied after 4 weeks' treatment with empagliflozin and placebo in a randomized, double-blind, placebo-controlled crossover study. Myocardial palmitate and glucose uptake were measured with ¹¹C-palmitate and ¹⁸F-fluorodeoxyglucose positron emission tomography (PET)/computed tomography (CT). Oxygen consumption and myocardial external efficiency (MEE) were measured with ¹¹C-acetate PET/CT. Resting and adenosine stress myocardial blood flow (MBF) and myocardial flow reserve (MFR) were measured using ¹⁵O-H₂O PET/CT. Empagliflozin did not affect myocardial free fatty acids (FFAs) uptake but reduced myocardial glucose uptake by 57% (P < 0.001). Empagliflozin did not change myocardial oxygen consumption or MEE. Empagliflozin reduced resting MBF by 13% (P < 0.01), but did not significantly affect stress MBF or MFR. In conclusion, SGLT2 inhibition did not affect myocardial FFA uptake, but channeled myocardial substrate utilization from glucose toward other sources and reduced resting MBF. However, the observed metabolic and hemodynamic changes were modest and most likely contribute only partially to the cardioprotective effect of SGLT2 inhibition.

Lipoprotein receptor signalling in atherosclerosis

The founding member of the lipoprotein receptor family, low-density lipoprotein receptor (LDLR) plays a major role in the atherogenesis through the receptor-mediated endocytosis of LDL particles and regulation of cholesterol homeostasis. Since the discovery of the LDLR, many other structurally and functionally related receptors have been identified, which include low-density lipoprotein receptor-related protein (LRP)1, LRP5, LRP6, very low-density lipoprotein receptor, and apolipoprotein E receptor 2. The scavenger receptor family members, on the other hand, constitute a family of pattern recognition proteins that are structurally diverse and recognize a wide array of ligands, including oxidized LDL. Among these are cluster of differentiation 36, scavenger receptor class B type I and lectin-like oxidized low-density lipoprotein receptor-1. In addition to the initially assigned role as a mediator of the uptake of macromolecules into the cell, a large number of studies in cultured cells and in in vivo animal models have revealed that these lipoprotein receptors participate in signal transduction to modulate cellular functions. This review highlights the signalling pathways by which these receptors influence the process of atherosclerosis development, focusing on their roles in the vascular cells, such as macrophages, endothelial cells, smooth muscle cells, and platelets. Human genetics of the receptors is also discussed to further provide the relevance to cardiovascular disease risks in humans. Further knowledge of the vascular biology of the lipoprotein receptors and their ligands will potentially enhance our ability to harness the mechanism to develop novel prophylactic and therapeutic strategies against cardiovascular diseases.

Endothelial Cell Receptors in Tissue Lipid Uptake and Metabolism

Lipid uptake and metabolism are central to the function of organs such as heart, skeletal muscle, and adipose tissue. Although most heart energy derives from fatty acids (FAs), excess lipid accumulation can cause cardiomyopathy. Similarly, high delivery of cholesterol can initiate coronary artery atherosclerosis. Hearts and arteries-unlike liver and adrenals-have nonfenestrated capillaries and lipid accumulation in both health and disease requires lipid movement from the circulation across the endothelial barrier. This review summarizes recent in vitro and in vivo findings on the importance of endothelial cell receptors and uptake pathways in regulating FAs and cholesterol uptake in normal physiology and cardiovascular disease. We highlight clinical and experimental data on the roles of ECs in lipid supply to tissues, heart, and arterial wall in particular, and how this affects organ metabolism and function. Models of FA uptake into ECs suggest that receptor-mediated uptake predominates at low FA concentrations, such as during fasting, whereas FA uptake during lipolysis of chylomicrons may involve paracellular movement. Similarly, in the setting of an intact arterial endothelial layer, recent and historic data support a role for receptor-mediated processes in the movement of lipoproteins into the subarterial space. We conclude with thoughts on the need to better understand endothelial lipid transfer for fuller comprehension of the pathophysiology of hyperlipidemia, and lipotoxic diseases such as some forms of cardiomyopathy and atherosclerosis.

Celastrol inhibits intestinal lipid absorption by reprofiling the gut microbiota to attenuate high-fat diet-induced obesity

Celastrol, a compound extracted from traditional Chinese medicine, has been reported as a potent anti-obesity agent with controversial mechanisms. Here both C57BL/6J and leptin-deficient (ob/ob) mice fed a high-fat diet (HFD) displayed body weight loss after celastrol therapy, opposing the previous viewpoint that celastrol improves obesity by sensitizing leptin signaling. More importantly, celastrol downregulated lipid transporters in the intestine, increased lipid excretion in feces, and reduced body weight gain in HFD mice. Meanwhile, analysis of gut microbiota revealed that celastrol altered the gut microbiota composition in HFD-fed mice, and modulating gut microbiota by antibiotics or fecal microbiota transplantation blocked the celastrol effect on intestinal lipid transport and body weight gain, suggesting a critical role of the gut microbiota composition in mediating the anti-obesity role of celastrol under HFD. Together, the findings revealed that celastrol reduces intestinal lipid absorption to antagonize obesity by resetting the gut microbiota profile under HFD feeding.

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Celastrol reduced intestinal lipid transporters and lipids absorption

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Celastrol reset gut microbiota profile to modulate intestinal lipid transport

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Celastrol attenuated obesity in leptin-deficient (ob/ob) mice fed high fat diet

The effect of type 2 diabetes on CD36 expression and the uptake of oxLDL: Diabetes affects CD36 and oxLDL uptake

We investigated whether type 2 diabetes mellitus (T2DM), a risk factor of stroke, affects the level of scavenger receptor CD36 and the uptake of its ligand, oxidized LDL (oxLDL); and whether pioglitazone, a drug that enhances CD36, promotes oxLDL uptake. Compared to normoglycemic db/+ mice, adult db/db mice showed a pronounced reduction in surface CD36 expression on myeloid cells from the blood, brain, and bone marrow as detected by flow cytometry, which correlated with elevated plasma soluble-CD36 as determined by ELISA. Increased CD36 expression was found in brain macrophages and microglia of both genotypes 7 days after ischemic stroke. In juvenile db/db mice, prior to obesity and hyperglycemia, only a mild reduction of surface CD36 was found in blood neutrophils, while all other myeloid cells showed no difference relative to the db/+ strain. In vivo, oral pioglitazone treatment for four weeks increased CD36 levels on myeloid cells in db/db mice. In vitro, uptake of oxLDL by bone marrow derived macrophages (BMDMs) of db/db mice was reduced relative to db/+ mice in normal glucose medium. OxLDL uptake inversely correlated with glucose levels in the medium in db/+ BMDMs. Furthermore, pioglitazone restored oxLDL uptake by BMDMs from db/db mice cultured in high glucose. Our data suggest that T2DM is associated with reduced CD36 on adult myeloid cells, and pioglitazone enhances CD36 expression in db/db cells. T2DM or high glucose reduces oxLDL uptake while pioglitazone enhances oxLDL uptake. Our findings provide new insight into the mechanism by which pioglitazone may be beneficial in the treatment of insulin resistance.

White tea drink (Camellia sinensis) improves endurance and body weight maintenance of rats

Purpose

White tea is an unfermented tea made from young shoots of Camellia sinensis protected from sunlight to avoid polyphenol degradation. White tea contains a high level of polyphenolic compounds known as catechins. Several types of evidence have suggested that tea consumption has benefits in body weight and endurance maintenance. This study was designed to evaluate the effect of white tea on body weight and endurance of animal models.

Design/methodology/approach

This research was an intervention design using 20 Wistar white rats (Rattus Norvegicus) in body weight between 150 and 200 g. The rats were randomized into four groups, three groups receiving white tea drink (WTD) with different doses and the other group receiving plain water in equal volume as a control group for four weeks. The forced swim test (FST) was done to measure their struggling capacity, and digital bodyweight to measure the weight.

Findings

Intervention (WTD Groups and Control) caused weight gain among except G3 with the highest doses of white tea. The result showed that WTD intake in G3 had a significant difference (p < 0.05) on body weight gain compared to control. The authors found that WTD in a specific dose (G3: 0.22 mg) tends to maintain the body weight of animals (219.2 ± 41.96; 212.6 ± 46.90, respectively), while other doses caused weight gain. WTD also significantly increased the swimming and struggling capacity of rats that represented improvements the endurance along with the test. There was a statistically significant difference in endurance among all groups (p < 0.05).

Research limitations/implications

The results of this study can be followed as human intervention research as an input for nutritionists and sports scientists to explore the beneficial effect of white tea.

Practical implications

The results of this study can be followed as human intervention research as an input for nutritionists and sports scientists to explore the beneficial effect of white tea.

Originality/value

This study adds more evidence and information about the advantages of white tea as potential beverages in future healthy lifestyles.

The RabGAPs TBC1D1 and TBC1D4 Control Uptake of Long-Chain Fatty Acids Into Skeletal Muscle via Fatty Acid Transporter SLC27A4/FATP4

The two closely related RabGTPase-activating proteins (RabGAPs) TBC1D1 and TBC1D4 play a crucial role in the regulation of GLUT4 translocation in response to insulin and contraction in skeletal muscle. In mice, deficiency in one or both RabGAPs leads to reduced insulin- and contraction-stimulated glucose uptake and to elevated fatty acid (FA) uptake and oxidation in both glycolytic and oxidative muscle fibers without altering mitochondrial copy number and the abundance of proteins for oxidative phosphorylation. Here we present evidence for a novel mechanism of skeletal muscle lipid utilization involving the two RabGAPs and the FA transporter SLC27A4/FATP4. Both RabGAPs control the uptake of saturated and unsaturated long-chain FAs (LCFAs) into skeletal muscle and knockdown (Kd) of a subset of RabGAP substrates, Rab8, Rab10, or Rab14, decreased LCFA uptake into these cells. In skeletal muscle from Tbc1d1 and Tbc1d4 knockout animals, SLC27A4/FATP4 abundance was increased and depletion of SLC27A4/FATP4 but not FAT/CD36 completely abrogated the enhanced FA oxidation in RabGAP-deficient skeletal muscle and cultivated C2C12 myotubes. Collectively, our data demonstrate that RabGAP-mediated control of skeletal muscle lipid metabolism converges with glucose metabolism at the level of downstream RabGTPases and involves regulated transport of LCFAs via SLC27A4/FATP4.

Aging and Immunometabolic Adaptations to Thermogenesis

Brown and subcutaneous adipose tissues play a key role in non-shivering thermogenesis both in mice and human, and their activation by adrenergic stimuli promotes energy expenditure, reduces adiposity, and protects against age-related metabolic diseases such as type 2 diabetes (T2D). Low-grade inflammation and insulin resistance characterize T2D. Even though the decline of thermogenic adipose tissues is well-established during ageing, the mechanisms by which this event affects immune system and contributes to the development of T2D is still poorly defined. It is emerging that activation of thermogenic adipose tissues promotes type 2 immunity skewing, limiting type 1 inflammation. Of note, metabolic substrates sustaining type 1 inflammation (e.g. glucose and succinate) are also used by activated adipocytes to promote thermogenesis. Keeping in mind this aspect, a nutrient competition between adipocytes and adipose tissue immune cell infiltrates could be envisaged. Herein, we reviewed the metabolic rewiring of adipocytes during thermogenesis in order to give important insight into the anti-inflammatory role of thermogenic adipose tissues and delineate how their decline during ageing may favor the setting of low-grade inflammatory states that predispose to type 2 diabetes in elderly. A brief description about the contribution of adipokines secreted by thermogenic adipocytes in modulation of immune cell activation is also provided. Finally, we have outlined experimental flow chart procedures and provided technical advices to investigate the physiological processes leading to thermogenic adipose tissue impairment that are behind the immunometabolic decline during aging.

DPP-4 inhibitor induces FGF21 expression via sirtuin 1 signaling and improves myocardial energy metabolism

Dipeptidyl peptidase-4 (DPP-4) inhibitors are widely used incretin-based therapy for the treatment of type 2 diabetes. We investigated the cardioprotective effect of a DPP-4 inhibitor, vildagliptin (vilda), on myocardial metabolism and cardiac performance under pressure overload. Mice were treated with either vehicle or vilda, followed by transverse aortic constriction (TAC). After 3 weeks of TAC, cardiac hypertrophy and impairment of systolic function were attenuated in vilda-treated mice. Pressure-volume analysis showed that vilda treatment significantly improved left-ventricular contractile efficiency in TAC heart. Myocardial energy substrate analysis showed that vilda treatment significantly increased glucose uptake as well as fatty acid uptake. Fibroblast growth factor 21 (FGF21), a peptide involved in the regulation of energy metabolism, increased in TAC heart and was further increased by vilda treatment. FGF21 was strongly expressed in cardiac fibroblasts than in cardiomyocytes in mouse heart after TAC with vilda treatment. Vilda treatment markedly induced FGF21 expression in human cardiac fibroblasts through a sirtuin (Sirt) 1-mediated pathway, suggesting that fibroblast-mediated FGF21 expression may regulate energy metabolism and exert vilda-mediated beneficial effects in stressed heart. Vilda induced a metabolic regulator, FGF21 expression in cardiac fibroblasts via Sirt1, and increased contractile efficiency in murine pressure-overloaded heart.

Molecular mechanisms of right ventricular dysfunction in pulmonary arterial hypertension: focus on the coronary vasculature, sex hormones, and glucose/lipid metabolism

Pulmonary arterial hypertension (PAH) is a rare, life-threatening condition characterized by dysregulated metabolism, pulmonary vascular remodeling, and loss of pulmonary vascular cross-sectional area due to a variety of etiologies. Right ventricular (RV) dysfunction in PAH is a critical mediator of both long-term morbidity and mortality. While combinatory oral pharmacotherapy and/or intravenous prostacyclin aimed at decreasing pulmonary vascular resistance (PVR) have improved clinical outcomes, there are currently no treatments that directly address RV failure in PAH. This is, in part, due to the incomplete understanding of the pathogenesis of RV dysfunction in PAH. The purpose of this review is to discuss the current understanding of key molecular mechanisms that cause, contribute and/or sustain RV dysfunction, with a special focus on pathways that either have led to or have the potential to lead to clinical therapeutic intervention. Specifically, this review discusses the mechanisms by which vessel loss and dysfunctional angiogenesis, sex hormones, and metabolic derangements in PAH directly contribute to RV dysfunction. Finally, this review discusses limitations and future areas of investigation that may lead to novel understanding and therapeutic interventions for RV dysfunction in PAH.

CD36 facilitates fatty acid uptake by dynamic palmitoylation-regulated endocytosis

Fatty acids (FAs) are essential nutrients, but how they are transported into cells remains unclear. Here, we show that FAs trigger caveolae-dependent CD36 internalization, which in turn delivers FAs into adipocytes. During the process, binding of FAs to CD36 activates its downstream kinase LYN, which phosphorylates DHHC5, the palmitoyl acyltransferase of CD36, at Tyr91 and inactivates it. CD36 then gets depalmitoylated by APT1 and recruits another tyrosine kinase SYK to phosphorylate JNK and VAVs to initiate endocytic uptake of FAs. Blocking CD36 internalization by inhibiting APT1, LYN or SYK abolishes CD36-dependent FA uptake. Restricting CD36 at either palmitoylated or depalmitoylated state eliminates its FA uptake activity, indicating an essential role of dynamic palmitoylation of CD36. Furthermore, blocking endocytosis by targeting LYN or SYK inhibits CD36-dependent lipid droplet growth in adipocytes and high-fat-diet induced weight gain in mice. Our study has uncovered a dynamic palmitoylation-regulated endocytic pathway to take up FAs.

Diurnal Rhythmicity Programs of Microbiota and Transcriptional Oscillation of Circadian Regulator, NFIL3

Circadian rhythms are a very exquisite mechanism to influence on transcriptional levels and physiological activities of various molecules that affect cell metabolic pathways. Long-term alteration of circadian rhythms increases the risk of cardiovascular diseases, hypertension, hypertriglyceridemia, and metabolic syndrome. A drastic change in dietary patterns can affect synchronizing the circadian clock within the metabolic system. Therefore, the interaction between the host and the bacterial community colonizing the mammalian gastrointestinal tract has a great impact on the circadian clock in diurnal programs. Here, we propose that the microbiota regulates body composition through the transcriptional oscillation of circadian regulators. The transcriptional regulator, NFIL3 (also called E4BP4) is a good example. Compositional change of the commensal bacteria influences the rhythmic expression of NFIL3 in the epithelium, which subsequently controls obesity and insulin resistance. Therefore, control of circadian regulators would be a promising therapeutic target for metabolic diseases.

Lipid Players of Cellular Senescence

Lipids are emerging as key players of senescence. Here, we review the exciting new findings on the diverse roles of lipids in cellular senescence, most of which are enabled by the advancements in omics approaches. Senescence is a cellular process in which the cell undergoes growth arrest while retaining metabolic activity. At the organismal level, senescence contributes to organismal aging and has been linked to numerous diseases. Current research has documented that senescent cells exhibit global alterations in lipid composition, leading to extensive morphological changes through membrane remodeling. Moreover, senescent cells adopt a secretory phenotype, releasing various components to their environment that can affect the surrounding tissue and induce an inflammatory response. All of these changes are membrane and, thus, lipid related. Our work, and that of others, has revealed that fatty acids, sphingolipids, and glycerolipids are involved in the initiation and maintenance of senescence and its associated inflammatory components. These studies opened up an exciting frontier to investigate the deeper mechanistic understanding of the regulation and function of these lipids in senescence. In this review, we will provide a comprehensive snapshot of the current state of the field and share our enthusiasm for the prospect of potential lipid-related protein targets for small-molecule therapy in pathologies involving senescence and its related inflammatory phenotypes.

Effect of Astaxanthin on the Inhibition of Lipid Accumulation in 3T3-L1 Adipocytes via Modulation of Lipogenesis and Fatty Acid Transport Pathways

Obesity is defined as a condition of excessive fat tissue accumulation. It was the major factor most closely associated with lifestyle-related diseases. In the present study, we investigated the effect of astaxanthin on the inhibition of lipid accumulation in 3T3-L1 adipocytes. 3T3-L1 adipocytes were treated with 0–25 µg/mL of astaxanthin for 0–48 h. The result indicated that astaxanthin significantly decreased the oil Red O stained material (OROSM), intracellular triglyceride accumulation, and glycerol 3-phosphate dehydrogenase (GPDH) activity in 3T3-L1 adipocytes (p < 0.05). At the molecular level, astaxanthin significantly down-regulated the mRNA expression of peroxisome proliferator-activated receptor-γ (PPARγ) in 3T3-L1 adipocytes (p < 0.05). Moreover, target genes of PPARγ on the inhibition of lipogenesis, such as Acetyl-CoA carboxylase (ACC), fatty acid synthase (FAS), fatty acid binding protein (aP2), cluster of differentiation 36 (CD36), and lipoprotein lipase (LPL) in 3T3-L1 adipocytes were significantly down-regulated at a time-dependent manner (p < 0.05). These results suggested that astaxanthin efficiently suppressed lipid accumulation in 3T3-L1 adipocytes and its action is associated with the down-regulation of lipogenesis-related genes and the triglyceride accumulation in 3T3-L1 adipocytes. Therefore, astaxanthin can be developed as a potential nutraceutical ingredient for the prevention of obesity in a niche market.

CD36-mediated uptake of myelin debris by macrophages and microglia reduces neuroinflammation

Background

The presence of foamy macrophages and microglia containing intracellular myelin remnants is a pathological hallmark of neurodegenerative disorders such as multiple sclerosis (MS). Despite the importance of myelin internalization in affecting both central nervous system repair and neuroinflammation, the receptors involved in myelin clearance and their impact on the phagocyte phenotype and lesion progression remain to be clarified.

Methods

Flow cytometry, quantitative PCR, and immunohistochemistry were used to define the mRNA and protein abundance of CD36 in myelin-containing phagocytes. The impact of CD36 and nuclear factor erythroid 2–related factor 2 (NRF2) on the phagocytic and inflammatory features of macrophages and microglia was assessed using a pharmacological CD36 inhibitor (sulfo-N-succinimidyl oleate) and Nrf2^−/− bone marrow-derived macrophages. Finally, the experimental autoimmune encephalomyelitis (EAE) model was used to establish the impact of CD36 inhibition on neuroinflammation and myelin phagocytosis in vivo.

Results

Here, we show that the fatty acid translocase CD36 is required for the uptake of myelin debris by macrophages and microglia, and that myelin internalization increased CD36 expression through NRF2. Pharmacological inhibition of CD36 promoted the inflammatory properties of myelin-containing macrophages and microglia in vitro, which was paralleled by a reduced activity of the anti-inflammatory lipid-sensing liver X receptors and peroxisome proliferator-activated receptors. By using the EAE model, we provide evidence that CD36 is essential for myelin debris clearance in vivo. Importantly, CD36 inhibition markedly increased the neuroinflammatory burden and disease severity in the EAE model.

Conclusion

Altogether, we show for the first time that CD36 is crucial for clearing myelin debris and suppressing neuroinflammation in demyelinating disorders such as MS.

Triphenyl phosphate is a selective PPARγ modulator that does not induce brite adipogenesis in vitro and in vivo

Triphenyl phosphate (TPhP) is an environmental PPARγ ligand, and growing evidence suggests that it is a metabolic disruptor. We have shown previously that the structurally similar ligand, tributyltin, does not induce brite adipocyte gene expression. Here, using in vivo and in vitro models, we tested the hypothesis that TPhP is a selective PPARγ ligand, which fails to induce brite adipogenesis. C57BL/6 J male mice were fed either a low or very high-fat diet for 13 weeks. From weeks 7-13, mice were injected intraperitoneally, daily, with vehicle, rosiglitazone (Rosi), or TPhP (10 mg/kg). Compared to Rosi, TPhP did not induce expression of browning-related genes (e.g. Elovl3, Cidea, Acaa2, CoxIV) in mature adipocytes isolated from inguinal adipose. To determine if this resulted from an effect directly on the adipocytes, 3T3-L1 cells and primary human preadipocytes were differentiated into adipocytes in the presence of Rosi or TPhP. Rosi, but not TPhP, induced expression of brite adipocyte genes, mitochondrial biogenesis and cellular respiration. Further, Rosi and TPhP-induced distinct proteomes and phosphoproteomes; Rosi enriched more regulatory pathways related to fatty acid oxidation and mitochondrial proteins. We assessed the role of phosphorylation of PPARγ in these differences in 3T3-L1 cells. Only Rosi protected PPARγ from phosphorylation at Ser273. TPhP gained the ability to stimulate brite adipocyte gene expression in the presence of the CDK5 inhibitor and in 3T3-L1 cells expressing alanine at position 273. We conclude that TPhP is a selective PPARγ modulator that fails to protect PPARγ from phosphorylation at ser273.

Identification and characterization of adipose surface epitopes

Adipose tissue is a central regulator of metabolism and an important pharmacological target to treat the metabolic consequences of obesity, such as insulin resistance and dyslipidemia. Among the various cellular compartments, the adipocyte cell surface is especially appealing as a drug target as it contains various proteins that when activated or inhibited promote adipocyte health, change its endocrine function and eventually maintain or restore whole-body insulin sensitivity. In addition, cell surface proteins are readily accessible by various drug classes. However, targeting individual cell surface proteins in adipocytes has been difficult due to important functions of these proteins outside adipose tissue, raising various safety concerns. Thus, one of the biggest challenges is the lack of adipose selective surface proteins and/or targeting reagents. Here, we discuss several receptor families with an important function in adipogenesis and mature adipocytes to highlight the complexity at the cell surface and illustrate the problems with identifying adipose selective proteins. We then discuss that, while no unique adipocyte surface protein might exist, how splicing, posttranslational modifications as well as protein/protein interactions can create enormous diversity at the cell surface that vastly expands the space of potentially unique epitopes and how these selective epitopes can be identified and targeted.

Sex-specific Effects of α2δ-1 in the Ventromedial Hypothalamus of Female Mice Controlling Glucose and Lipid Balance

The thrombospondin receptor alpha2delta-1 (α2δ-1) plays essential roles promoting the activity of SF1 neurons in the ventromedial hypothalamus (VMH) and mediating glucose and lipid metabolism in male mice. Its role in the VMH of female mice remains to be defined, especially considering that this hypothalamic region is sexually dimorphic. We found that α2δ-1 depletion in SF1 neurons differentially affects glucose and lipid balance control and sympathetic tone in females compared to males. Mutant females show a modest increase in relative body weight gain when fed a high-fat diet (HFD) and normal energy expenditure, indicating that α2δ-1 is not a critical regulator of energy balance in females, similar to males. However, diminished α2δ-1 function in the VMH leads to enhanced glycemic control in females fed a chow diet, in contrast to the glucose intolerance reported previously in mutant males. Interestingly, the effects of α2δ-1 on glucose balance in females are influenced by diet. Accordingly, females but not males lacking α2δ-1 exhibit diminished glycemic control as well as susceptibility to hepatic steatosis when fed a HFD. Increased hepatic sympathetic tone and CD36 mRNA expression and reduced adiponectin levels underlie these diet-induced metabolic alterations in mutant females. The results indicate that α2δ-1 in VMH SF1 neurons critically regulates metabolic function through sexually dimorphic mechanisms. These findings are clinically relevant since metabolic alterations have been reported as a side effect in human patients prescribed gabapentinoid drugs, known to inhibit α2δ-1 function, for the treatment of seizure disorders, neuropathic pain, and anxiety disorders.

Changes in Myocardial Metabolism Preceding Sudden Cardiac Death

Heart disease is widely recognized as a major cause of death worldwide and is the leading cause of mortality in the United States. Centuries of research have focused on defining mechanistic alterations that drive cardiac pathogenesis, yet sudden cardiac death (SCD) remains a common unpredictable event that claims lives in every age group. The heart supplies blood to all tissues while maintaining a constant electrical and hormonal feedback communication with other parts of the body. As such, recent research has focused on understanding how myocardial electrical and structural properties are altered by cardiac metabolism and the various signaling pathways associated with it. The importance of cardiac metabolism in maintaining myocardial function, or lack thereof, is exemplified by shifts in cardiac substrate preference during normal development and various pathological conditions. For instance, a shift from fatty acid (FA) oxidation to oxygen-sparing glycolytic energy production has been reported in many types of cardiac pathologies. Compounded by an uncoupling of glycolysis and glucose oxidation this leads to accumulation of undesirable levels of intermediate metabolites. The resulting accumulation of intermediary metabolites impacts cardiac mitochondrial function and dysregulates metabolic pathways through several mechanisms, which will be reviewed here. Importantly, reversal of metabolic maladaptation has been shown to elicit positive therapeutic effects, limiting cardiac remodeling and at least partially restoring contractile efficiency. Therein, the underlying metabolic adaptations in an array of pathological conditions as well as recently discovered downstream effects of various substrate utilization provide guidance for future therapeutic targeting. Here, we will review recent data on alterations in substrate utilization in the healthy and diseased heart, metabolic pathways governing cardiac pathogenesis, mitochondrial function in the diseased myocardium, and potential metabolism-based therapeutic interventions in disease.

Nitro-oleic acid, a ligand of CD36, reduces cholesterol accumulation by modulating oxidized-LDL uptake and cholesterol efflux in RAW264.7 macrophages

Macrophages play a pivotal role in the early stages of atherosclerosis development; they excessively accumulate cholesterol in the cytosol in response to modified Low Density Lipoprotein (mLDL). The mLDL are incorporated through scavenger receptors. CD36 is a high-affinity cell surface scavenger receptor that facilitates the binding and uptake of long-chain fatty acids and mLDL into the cell. Numerous structurally diverse ligands can initiate signaling responses through CD36 to regulate cell metabolism, migration, and angiogenesis. Nitro-fatty acids are endogenous electrophilic lipid mediators that react with and modulate the function of multiple enzymes and transcriptional regulatory proteins. These actions induce the expression of several anti-inflammatory and cytoprotective genes and limit pathologic responses in experimental models of atherosclerosis, cardiac ischemia/reperfusion, and inflammatory diseases. Pharmacological and genetic approaches were used to explore the actions of nitro-oleic acid (NO₂-OA) on macrophage lipid metabolism. Pure synthetic NO₂-OA dose-dependently increased CD36 expression in RAW264.7 macrophages and this up-regulation was abrogated in BMDM from Nrf2-KO mice. Ligand binding analysis revealed that NO₂-OA specifically interacts with CD36, thus limiting the binding and uptake of mLDL. Docking analysis shows that NO₂-OA establishes a low binding energy interaction with the alpha helix containing Lys164 in CD36. NO₂-OA also restored autophagy flux in mLDL-loaded macrophages, thus reversing cholesterol deposition within the cell. In aggregate, these results indicate that NO₂-OA reduces cholesterol uptake by binding to CD36 and increases cholesterol efflux by restoring autophagy.

Intralipid Increases Nitric Oxide Release from Human Endothelial Cells During Oxidative Stress

BACKGROUND

Intralipid (ILP), a lipid emulsion, protects organs against ischemia/reperfusion (IR) injury. We hypothesized that ILP activates endothelial nitric oxide synthase (eNOS) and increases NO release from endothelial cells (ECs) through a fatty-acid translocase cluster of differentiation (CD36) mediated endocytotic mechanism, acting as a potentially protective paracrine signal during oxidative stress.

METHODS

Human umbilical-vein ECs were exposed to 1% ILP for 2 hours followed by oxidative stress with 0.2-mM hydrogen peroxide for 2 hours. Western blots were conducted with anti-CD36, dynamin-2, src-kinase-1, eNOS, and phospho-eNOS; equal protein loading was confirmed with β-actin. CD36 immunoprecipitation was probed for caveolin-1 to determine if CD36 and caveolin-1 were complexed on the cell membrane. NO was measured by fluorescence of ECs.

RESULTS

ILP caused a 227% increase in CD36 expression vs controls. Immunoprecipitation indicated a CD36/caveolin-1 complex on ECs' membrane with exposure to ILP. Dynamin-2 increased 52% and src-kinase-1 340% after ILP treatment vs control cells. eNOS phosphorylation was confirmed by a 63% increase in the phospho-eNOS/eNOS ratio in ILP-treated cells, and NO fluorescence increased 102%.

CONCLUSION

ILP enters ECs via endocytosis by a CD36/caveolin-1 cell membrane receptor complex, which in turn is pulled into the cell by dynamin-2 activity. Upregulation of src-kinase-1 and eNOS phosphorylation suggest downstream mediators. Subsequent NO release from ECs serve as a paracrine signal to neighboring cells for protection against IR injury. Student t-test was utilized for single comparisons and analysis of variance with Bonferroni-Dunn post hoc modification for multiple comparisons; P < .05 was considered statistically significant.

Slc43a3 is a regulator of free fatty acid flux

Adipocytes take up long chain FAs through diffusion and protein-mediated transport, whereas FA efflux is considered to occur by diffusion. To identify potential membrane proteins that are involved in regulating FA flux in adipocytes, the expression levels of 55 membrane transporters without known function were screened in subcutaneous adipose samples from obese patients before and after bariatric surgery using branched DNA methodology. Among the 33 solute carrier (SLC) transporter family members screened, the expression of 14 members showed significant changes before and after bariatric surgery. One of them, Slc43a3, increased about 2.5-fold after bariatric surgery. Further investigation demonstrated that Slc43a3 is highly expressed in murine adipose tissue and induced during adipocyte differentiation in primary preadipocytes and in OP9 cells. Knockdown of Slc43a3 with siRNA in differentiated OP9 adipocytes reduced both basal and forskolin-stimulated FA efflux, while also increasing FA uptake and lipid droplet accumulation. In contrast, overexpression of Slc43a3 decreased FA uptake in differentiated OP9 cells and resulted in decreased lipid droplet accumulation. Therefore, Slc43a3 seems to regulate FA flux in adipocytes, functioning as a positive regulator of FA efflux and as a negative regulator of FA uptake.

Requirement for the intestinal epithelial insulin-like growth factor-1 receptor in the intestinal responses to glucagon-like peptide-2 and dietary fat

The intestinal hormone, glucagon-like peptide-2 (GLP-2), enhances the enterocyte chylomicron production. However, GLP-2 is known to require the intestinal-epithelial insulin-like growth factor-1 receptor (IE-IGF-1R) for its other actions to increase intestinal growth and barrier function. The role of the IE-IGF-1R in enterocyte lipid handling was thus tested in the GLP-2 signaling pathway, as well as in response to a Western diet (WD). IE-IGF-1R knockout (KO) and control mice were treated for 11 days with h(GLY² )GLP-2 or fed a WD for 18 weeks followed by a duodenal fat tolerance test with C¹⁴ -labeled triolein. Human Caco-2BBE cells were treated with an IGF-1R antagonist or signaling inhibitors to determine triglyceride-associated protein expression. The IE-IGF-1R was required for GLP-2-induced increases in CD36 and FATP-4 in chow-fed mice, and for expression in vitro; FATP-4 also required PI3K/Akt. Although WD-fed IE-IGF-1R KO mice demonstrated normal CD36 expression, the protein was incorrectly localized 2h post-duodenal fat administration. IE-IGF-1R KO also prevented the WD-induced increase in MTP and decrease in APOC3, increased jejunal mucosal C¹⁴ -fat accumulation, and elevated plasma triglyceride and C¹⁴ -fat levels. Collectively, these studies elucidate new roles for the IE-IGF-1R in enterocyte lipid handling, under basal conditions and in response to GLP-2 and WD-feeding.

Metabolic Changes in Spontaneously Hypertensive Rat Hearts Precede Cardiac Dysfunction and Left Ventricular Hypertrophy

Background

Sustained pressure overload leads to changes in cardiac metabolism, function, and structure. Both time course and causal relationships between these changes are not fully understood. Therefore, we studied spontaneously hypertensive rats (SHR) during early hypertension development and compared them to control Wistar Kyoto rats.

Methods and Results

We serially evaluated myocardial glucose uptake rates (Ki) with dynamic 2‐[¹⁸F] fluoro‐2‐deoxy‐D‐glucose positron emission tomography, and ejection fraction and left ventricular mass to body weight ratios with cardiac magnetic resonance imaging in vivo, determined glucose uptake and oxidation rates in isolated perfused hearts, and analyzed metabolites, mammalian target of rapamycin activity and endoplasmic reticulum stress in dissected hearts. When compared with Wistar Kyoto rats, SHR demonstrated increased glucose uptake rates (Ki) in vivo, and reduced ejection fraction as early as 2 months of age when hypertension was established. Isolated perfused SHR hearts showed increased glucose uptake and oxidation rates starting at 1 month. Cardiac metabolite analysis at 2 months of age revealed elevated pyruvate, fatty acyl‐ and branched chain amino acid‐derived carnitines, oxidative stress, and inflammation. Mammalian target of rapamycin activity increased in SHR beginning at 2 months. Left ventricular mass to body weight ratios and endoplasmic reticulum stress were elevated in 5 month‐old SHR.

Conclusions

Thus, in a genetic hypertension model, chronic cardiac pressure overload promptly leads to increased myocardial glucose uptake and oxidation, and to metabolite abnormalities. These coincide with, or precede, cardiac dysfunction while left ventricular hypertrophy develops only later. Myocardial metabolic changes may thus serve as early diagnostic markers for hypertension‐induced left ventricular hypertrophy.

SSO and other putative inhibitors of FA transport across membranes by CD36 disrupt intracellular metabolism, but do not affect FA translocation

Membrane-bound proteins have been proposed to mediate the transport of long-chain FA (LCFA) transport through the plasma membrane (PM). These proposals are based largely on reports that PM transport of LCFAs can be blocked by a number of enzymes and purported inhibitors of LCFA transport. Here, using the ratiometric pH indicator (2',7'-bis-(2-carboxyethyl)-5-(and-6-)-carboxyfluorescein and acrylodated intestinal FA-binding protein-based dual fluorescence assays, we investigated the effects of nine inhibitors of the putative FA transporter protein CD36 on the binding and transmembrane movement of LCFAs. We particularly focused on sulfosuccinimidyl oleate (SSO), reported to be a competitive inhibitor of CD36-mediated LCFA transport. Using these assays in adipocytes and inhibitor-treated protein-free lipid vesicles, we demonstrate that rapid LCFA transport across model and biological membranes remains unchanged in the presence of these purported inhibitors. We have previously shown in live cells that CD36 does not accelerate the transport of unesterified LCFAs across the PM. Our present experiments indicated disruption of LCFA metabolism inside the cell within minutes upon treatment with many of the "inhibitors" previously assumed to inhibit LCFA transport across the PM. Furthermore, using confocal microscopy and a specific anti-SSO antibody, we found that numerous intracellular and PM-bound proteins are SSO-modified in addition to CD36. Our results support the hypothesis that LCFAs diffuse rapidly across biological membranes and do not require an active protein transporter for their transmembrane movement.

Loss of CD36 impairs hepatic insulin signaling by enhancing the interaction of PTP1B with IR

A contradictory role of CD36 in insulin resistance was found to be related to the nutrient state. Here, we examined that the physiological functions of CD36 in insulin signal transduction in mice fed a low-fat diet. CD36 deficiency led to hepatic insulin resistance and decreased insulin-stimulated tyrosine phosphorylation of insulin receptor β (IRβ) in mice fed a low-fat diet. The ability of insulin to bind with IR did not differ between WT and CD36-deficient hepatocytes. CD36 formed a complex with IRβ and dissociation of CD36/Fyn complex or inhibition of Fyn only partially reversed the effects of CD36 on hepatic insulin signaling. Furthermore, we found that CD36 deficiency led to abnormally increased hepatic protein-tyrosine phosphatase 1B (PTP1B) expression and enhanced PTP1B and IR interactions, which contributed to the decreased insulin signaling and disordered glucose metabolism. In addition, increased endoplasmic reticulum (ER) stress was found in the livers of the CD36-deficient mice, while inhibited ER stress normalized the PTP1B expression and restored insulin signaling in the CD36-deficient mice. Our findings suggest that the loss of CD36 impairs hepatic insulin signaling by enhancing the PTP1B/IR interaction that is induced by ER stress, indicating a possible critical step in the progression of hepatic insulin resistance.

A systematic review of the effects of oleoylethanolamide, a high-affinity endogenous ligand of PPAR-α, on the management and prevention of obesity

Along with an increase in overweight and obesity among all age groups, the development of efficacious and safe anti-obesity strategies for patients, as well as health systems, is critical. Oleoylethanolamide (OEA), a high-affinity endogenous ligand of nuclear receptor peroxisome proliferator-activated receptor alpha (PPAR-α), plays important physiological and metabolic actions. OEA is derived from oleic acid, a monounsaturated fatty acid, which has beneficial effects on body composition and regional fat distribution. The role of OEA in the modulation of food consumption and weight management makes it an attractive molecule requiring further exploration in obesogenic environments. This systematic review was conducted to assess the effects of OEA on the obesity management, with emphasizing on its physiological roles and possible mechanisms of action in energy homeostasis. We searched PubMed/Medline, Google Scholar, ScienceDirect, Scopus, ProQuest, and EMBASE up until September 2019. Out of 712 records screened, 30 articles met the study criteria. The evidence reviewed here indicates that OEA, an endocannabinoid-like compound, leads to satiation or meal termination through PPAR-α activation and fatty acid translocase (FAT)/CD36. Additionally, the lipid-amide OEA stimulates fatty acid uptake, lipolysis, and beta-oxidation, and also promotes food intake control. OEA also exerts satiety-inducing effects by activating the hedonic dopamine pathways and increasing homeostatic oxytocin and brain histamine. In conclusion, OEA may be a key component of the physiological system involved in the regulation of dietary fat consumption and energy homeostasis; therefore, it is suggested as a possible therapeutic agent for the management of obesity.

Lactobacillus plantarum LMT1-48 exerts anti-obesity effect in high-fat diet-induced obese mice by regulating expression of lipogenic genes

Obesity is a major health problem and is known to be closely associated with metabolic diseases. Abnormal hepatic accumulation of fat causes fatty liver or hepatic steatosis, and long-term consumption of a high-fat diet is known to be a key obesity-causing factor. Recent studies have demonstrated that probiotics such as Lactobacillus strains, exert an anti-obesity effect by regulating adipogenesis. However, it is still unknown how the consumption of probiotics can reduce abdominal fat volume by regulating the hepatic expression of lipogenic genes. Therefore, we evaluated the effect of long-term ingestion of L. plantarum LMT1-48 on the expression of lipogenic genes in high-fat diet (HFD)-fed mice. We observed that treatment of 3T3-L1 adipocytes with L. plantarum LMT1-48 extract inhibited their differentiation and lipid accumulation by downregulating lipogenic genes, namely, PPARγ, C/EBPα, FAS, and FABP4. Interestingly, administration of L. plantarum LMT1-48 reduced liver weight and liver triglycerides concurrently with the downregulation of the lipogenic genes PPARγ, HSL, SCD-1, and FAT/CD36 in the liver, resulting in the reduction of body weight and fat volume in HFD-fed obese mice. Notably, we also observed that the administration of at least 10⁶ CFU of L. plantarum LMT1-48 significantly lowered body weight and abdominal fat volume in modified diet-fed mouse models. Collectively, these data suggest that L. plantarum LMT1-48 is a potential healthy food for obese people.