Cellular fatty acid uptake is acutely regulated by membrane-associated fatty acid-binding proteins

Cellular long-chain fatty acid uptake is believed to occur largely by protein-mediated transmembrane transport of fatty acids, and also by passive diffusional uptake. It is postulated that the membrane proteins function in trapping of fatty acids from extracellular sources, whereafter their transmembrane translocation occurs by passive diffusion through the lipid bilayer. The key membrane-associated proteins involved are plasma membrane fatty acid-binding protein (FABP(pm)) and fatty acid translocase (FAT/CD36). Their plasma membrane contents are positively correlated with rates of fatty acid uptake. In studies with heart and skeletal muscle we observed that FAT/CD36 is regulated acutely, in that both contraction and insulin can translocate FAT/CD36 from an intracellular depot to the sarcolemma, thereby increasing the rate of fatty acid uptake. In addition, from studies with obese Zucker rats, an established rodent model of obesity and insulin resistance, evidence has been obtained that in heart, muscle and adipose tissue FAT/CD36 is permanently relocated from an intracellular pool to the plasma membrane, resulting in increased fatty acid uptake rates in this condition. These combined observations indicate that protein-mediated fatty acid uptake is a key step in cellular fatty acid utilization, and suggest that malfunctioning of the uptake process could be a critical factor in the pathogenesis of insulin resistance.     

Links between fatty acids and expression of UCP2 and UCP3 mRNAs

Physiological and pathological states that are associated with elevated plasma fatty acids (FAs) increase uncoupling protein 2 (UCP2) mRNA in white adipose tissue and UCP3 mRNA in skeletal muscle and heart. A direct effect of unsaturated fatty acids from all classes has been shown in various cultured cells. There is evidence that FAs could induce expression of UCPs by acting as ligands for peroxisome proliferator-activated receptors, influencing the function of sterol responsive element binding protein or activating 5'-AMP-activated protein kinase. Oleic acid has been shown to stimulate the activity of the promoter regions of UCP2 and UCP3 genes and the FA responsive regions are beginning to be characterised.     

Acoustic biomechanical relationships of human forced exhalation in bronchial obstruction

A statistically significant bidirectional influence of the incidence and degree of bronchial obstruction on the acoustic parameters of forced expiration and the spirometry/body plethysmography indicators of lung function has been revealed by means of nonparametric analysis of variance in a sample of 218 subjects. It has been shown that the acoustic band pass times and energies of forced expiratory tracheal noises coordinate with both tidal resistance and residual volume.     

Macrophage polarization state affects lipid composition and the channeling of exogenous fatty acids into endogenous lipid pools

Adipose-tissue-resident macrophages (ATMs) maintain metabolic homeostasis but also contribute to obesity-induced adipose tissue inflammation and metabolic dysfunction. Central to these contrasting effects of ATMs on metabolic homeostasis is the interaction of macrophages with fatty acids. Fatty acid levels are increased within adipose tissue in various pathological and physiological conditions, but appear to initiate inflammatory responses only upon interaction with particular macrophage subsets within obese adipose tissue. The molecular basis underlying these divergent outcomes is likely due to phenotypic differences between ATM subsets, although how macrophage polarization state influences the metabolism of exogenous fatty acids is relatively unknown. Herein, using stable isotope-labeled and nonlabeled fatty acids in combination with mass spectrometry lipidomics, we show marked differences in the utilization of exogenous fatty acids within inflammatory macrophages (M1 macrophages) and macrophages involved in tissue homeostasis (M2 macrophages). Specifically, the accumulation of exogenous fatty acids within triacylglycerols and cholesterol esters is significantly higher in M1 macrophages, while there is an increased enrichment of exogenous fatty acids within glycerophospholipids, ether lipids, and sphingolipids in M2 macrophages. Finally, we show that functionally distinct ATM populations in vivo have distinct lipid compositions. Collectively, this study identifies new aspects of the metabolic reprogramming that occur in distinct macrophage polarization states. The channeling of exogenous fatty acids into particular lipid synthetic pathways may contribute to the sensitivity/resistance of macrophage subsets to the inflammatory effects of increased environmental fatty acid levels.     

Current approaches to unravel the mystery of dilated cardiomyopathy,a common cause of hereditary heart failure

As is well known, adipose tissue is an important site for lipid metabolism and insulin-responsive glucose uptake. The recent discovery of the endocrine function of adipose tissue and the association of obesity with chronic low-grade inflammation in adipose tissue has reinforced the concept of the central role of adipose tissue in mediating obesity-linked insulin resistance and metabolic dysregulation. The study of adipose cells has provided new insights into the mechanism underlying insulin resistance as well as the therapeutic strategies for diabetes. Numerous efforts have been made in identifying key molecular regulators of insulin action and metabolism, including the utilization of advanced proteomics technology. Various proteomic approaches have been applied to identify the adipose secretome, protein-expression profiling and post-translational modifications in adipose cells in the pathological state. In this review, we summarize the recent advances in the proteomics of adipose tissue, and discuss the identified proteins that potentially play important roles in insulin resistance and diabetes.     

Lipophagy in nonliver tissues and some related diseases: Pathogenic and therapeutic implications

Lipid autophagy (lipophagy) is defined as a selective autophagy process in which some intracellular lipid droplets are selectively degraded by autophagic lysosomes pathway. The occurrence of lipophagy was first discovered in liver tissues. Additionally, abundant evidence indicated that the occurrence of hepatic lipophagy has been implicated in many liver diseases including fatty liver diseases, nonalcoholic fatty liver diseases, liver fibrosis, and liver cirrhosis. However, recent studies suggested that hepatic lipophagy occurs not only in liver tissue but also in other nonliver tissues and cells. Furthermore, the occurrence of lipophagy plays a crucial role in nonliver tissues and some related diseases. For instance, lipophagy relieves insulin resistance in adipose tissue from obesity patient with type 2 diabetes. Additionally, lipophagy has the ability to remit neurodegenerative diseases by reducing activity-dependent neurodegeneration in nervous tissue. Lipophagy decreases muscle lipid accumulation and accordingly improves lipid storage myopathy in muscle tissue. Moreover, lipophagy alleviates the malignancy and metastasis of cancer in clear renal cell carcinoma tissue. Lipophagy is also involved in other processes, such as spermatogenesis, osteoblastogenesis, and mucosal ulceration. In conclusion, targeting lipophagy may be a critical regulator and a new therapeutic strategy for nonliver tissues and some related diseases.     

The clinical biochemistry of obesity

Obesity is essentially an excessive accumulation of triacylglycerols in fatty tissue that is the net result of excessive energy intake compared to energy usage. Severe forms of the disease are most likely to have a predominantly genetic basis and this is probably polygenic. The 'thrifty gene' hypothesis also describes the disturbance that a modern environment, including higher energy intake and decreased physical activity, has on otherwise advantageous genetic variations. While the physical consequences of obesity, such as arthritis, are debilitating and costly, the metabolic consequences are the drivers behind the modern epidemics of insulin resistance, diabetes, fatty liver disease, coronary artery disease, hypertension and polycystic ovary syndrome. The pathophysiological mechanisms behind these diseases are probably a combination of the toxic metabolic effects of free fatty acids and adipokines - the numerous messengers that adipose tissue has been discovered to produce.     

The effect of PPARgamma ligands on the adipose tissue in insulin resistance

Insulin resistance is frequently accompanied by obesity and both obesity and type 2 diabetes are associated with a mild chronic inflammation. Elevated levels of various cytokines, such as TNF-alpha and IL-6, are typically found in the adipose tissue in these conditions. It has been suggested that many cytokines produced in the adipose tissue are derived from infiltrated inflammatory cells. However, the adipose tissue itself has proven to be an important endocrine organ, secreting several hormones and cytokines, usually referred to as adipokines. Peroxisome proliferator-activated receptor (PPAR)gamma is essential for adipocyte proliferation and differentiation. In recent years, PPARgamma and its ligands, the thiazolidinediones (TZD), have achieved great attention due to their insulin sensitizing and anti-inflammatory properties. Treatment with TZDs result in improved insulin signaling and adipocyte differentiation, increased adipose tissue influx of free fatty acids and inhibition of cytokine expression and action. As a result, PPARgamma plays a central role in maintaining a functional and differentiated adipose tissue.     

Quantification of the concentration and 13C tracer enrichment of long-chain fatty acyl-coenzyme A in muscle by liquid chromatography/mass spectrometry

Recent diabetes and obesity research has been focused on the role of intracellular lipids in insulin resistance. Fatty acyl-coenzyme A (CoA) esters play a central role in the trafficking of intracellular lipids, but there has not previously been a method with which to quantify their kinetics using tracer methodology. We have therefore developed a high-performance liquid chromatography (HPLC)-mass spectrometry method to simultaneously measure the (13)C stable isotopic enrichment of palmitoyl-acyl-CoA ester and the concentrations of five individual long-chain fatty acyl-CoA esters extracted from muscle tissue samples. The long-chain fatty acyl-CoA can be effectively extracted from frozen muscle tissue samples and baseline separated by a reverse-phase HPLC with the presence of a volatile reagent-triethylamine. Negative ion electrospray mass spectrometry with selected ion monitoring was used to analyze the fatty acyl-CoAs to achieve reliable quantification of their concentrations and (13)C isotopic enrichment. Applying this protocol to rabbit muscle samples demonstrates that it is a sensitive, accurate, and precise method for the quantification of long-chain fatty acyl-CoA concentrations and enrichment.     

Contribution of triglyceride-rich lipoproteins to plasma free fatty acids.

Free fatty acids are the major lipid fuel of the body. Dysregulation of adipose tissue lipolysis results in increased plasma free fatty acid concentrations, and via that mechanism contributes to insulin resistance in obesity and type 2 diabetes mellitus. Adipose tissue hormone sensitive lipase is thought to be responsible for the production of the majority of free fatty acids. However, a separate contribution comes from the action of endothelial lipases, especially lipoprotein lipase, on triglyceride-rich lipoproteins via a process known as spillover. The primary substrate for spillover appears to be chylomicrons derived from dietary fat. The spillover of fatty acids into the free fatty acid pool varies from one tissue to another. For example, spillover is low ( approximately 14%) in the forearm of healthy volunteers, suggesting that triglyceride fatty acid storage is relatively efficient in skeletal muscle. In contrast, spillover appears to be higher in adipose tissue and may also be higher in the splanchnic bed, based on preliminary data. If systemic spillover is increased in insulin resistant states such as diabetes, this could represent a mechanism contributing to the abnormal increases in plasma concentrations of free fatty acids in that condition.     

A new dynamometric technique to measure and locate endocranial structures. Preliminary report

An apparatus for measuring and recording the resistance to penetration of endocranial tissue has been planned and built. The probe carrier, driven by a constant-speed electric motor, is fitted onto a stereotactic head frame which is used to guide the tool to the intended target. The displacement and resistance encountered when the tool penetrates intracranial structures are measured and recorded on an x-y recorder. Preliminary tests performed on calf brain specimens have documented that the apparatus can measure the different consistencies of normal cerebral tissue and suggest a new technique for morphological investigations based on the mechanical consistency of normal and pathological organic tissue. Moreover, the hypothesis of a plastic deformation in cerebral tissue has been confirmed, in that the same apparatus permits one to measure the displacement of tissues caused by the advancement of the surgical tool.     

Modulation of immune and inflammatory responses by dietary lipids

PURPOSE OF REVIEW: There continues to be considerable interest in the modulating effect of dietary lipids on immune and inflammatory responses. Although controversy still exists in research in this area, new concepts and approaches have emerged providing useful suggestions. Analysis of the recent findings will help in understanding certain paradoxical findings as well as introducing new strategies to guide future studies. RECENT FINDINGS: The tissue polyunsaturated fatty acid composition was found to be correlated with changes in certain indices of immune function in individuals consuming habitual diets. It seems that individuals or animals with disordered immune systems are more reactive to polyunsaturated fatty acid supplementation, and genetic variation is also a determinant. N-3 polyunsaturated fatty acids were shown to reduce both resistance to bacterial infection and host survival. The studies on other non-classic fatty acids also demonstrated interesting findings. A proposed immuno-enhancing effect of conjugated linoleic acid has not been confirmed by studies and even an adverse effect has been implied. Trans fatty acids have been shown to increase the production of inflammatory cytokines, which may contribute to their pro-atherogenic property. SUMMARY: Current data suggest that the intake of polyunsaturated fatty acids, particularly n-3 polyunsaturated fatty acids, can modulate immune and inflammatory responses, although a discrepancy is still present. Some recent studies have provided useful information explaining possible underlying reasons. Factors such as genetic variation, health status, disease, immune response stage, stimulation type, and possibly age, all contribute to the responsiveness to polyunsaturated fatty acid supplementation in terms of immune function.     

The role of epicardial and perivascular adipose tissue in the pathophysiology of cardiovascular disease

Obesity, insulin resistance and the metabolic syndrome, are characterized by expansion and inflammation of adipose tissue, including the depots surrounding the heart and the blood vessels. Epicardial adipose tissue (EAT) is a visceral thoracic fat depot located along the large coronary arteries and on the surface of the ventricles and the apex of the heart, whereas perivascular adipose tissue (PVAT) surrounds the arteries. Both fat depots are not separated by a fascia from the underlying tissue. Therefore, factors secreted from epicardial and PVAT, like free fatty acids and adipokines, can directly affect the function of the heart and blood vessels. In this review, we describe the alterations found in EAT and PVAT in pathological states like obesity, type 2 diabetes, the metabolic syndrome and coronary artery disease. Furthermore, we discuss how changes in adipokine expression and secretion associated with these pathological states could contribute to the pathogenesis of cardiac contractile and vascular dysfunction.     

Thyroid activity in common frogs and the heat resistance of their bodies and muscle tissue

Thyroid activity of single individuals of the grass frog has been studied during winter hybernation (2-5 degrees) and heat acclimation (15 degrees) in relation to the heat resistance of the organism and muscle tissue at 2-5 degrees. A positive correlation has been observed between thyroid activity and the organismal heat resistance. At 15 degrees thyroid activity increases. It is the highest in females with a low initial heat resistance of the organism. It is assumed that changes in the heat resistance of the organism and muscle tissue are controlled by the thyroid gland. However, no correlation has been found between the initial (winter) level of the heat resistance of muscle tissue and the activity of thyroid.     

特异性microRNAs在心血管系统中的功能研究进展

MicroRNAs(miRNAs)是经核糖核酸酶(Dicer)加工后的一类非编码小RNA分子。在真核生物中,miRNA具有组织特异性和时序性,只在特定的组织和特定的发育阶段表达,在细胞生长和发育过程中起多种作用。miRNAs在心脏发育、形态生成、血管生成、心肌凋亡等多个生理病理过程中发挥重要作用。最近有大量研究发现某些特异性的miRNA对心血管的发育和心血管疾病有一定的影响。如miRNA-126调控血管生成;miRNA-143和miRNA-145决定血管平滑肌(VSMC)的分化和增殖;miRNA-208对心肌肥厚的调节;miRNA-1和miRNA-133影响心肌的发育、形态发生、心肌凋亡、心肌肥厚等。     

Monitoring cell adhesion by using thickness shear mode acoustic wave sensors

The thickness shear mode (TSM) acoustic wave sensor attached with living cells has been shown to be an effective functional biosensing device to monitor the process of cell adhesion to a surface in real time. In this study, a multilayer sensor model that includes a quartz substrate, a cell-substrate interfacial layer and a cell layer was constructed based on the state of cell adhesion to the substrate. The dynamic process of cell adhesions as a function of cell seeding densities was monitored using the acoustic wave sensor. The mechanisms that are responsible for the frequency and resistance change are discussed according to the predictions of the acoustic wave sensor model. In addition, knowing that the actin cytoskeleton is important for cell adhesion, we investigated the motional resistance change caused by the disruption of actin cytoskeleton induced by fungal toxin cytochalasin D in the human skin fibroblasts. The results indicate that resistance changes are related to the disruption of actin cytoskeleton and dosage-dependent.     

Perfused heart studies to investigate lipid metabolism

The isolated perfused heart preparation is an invaluable model for investigating metabolism in a variety of physiological and pathological states. It avoids confounding systemic factors (e.g. endocrine, metabolic and work load changes) and permits simultaneous measurement of mechanical function. The ability to measure arteriovenous concentration differences across the myocardium and the coronary flow rate, together with the use of radiolabelled substrates, permits assessment of substrate assimilation and disposition of most potential energetic substrates. In the case of lipids, metabolism of non-esterified fatty acids has been extensively investigated in the perfused rat heart, but fatty acids may also be derived from circulating triacylglycerols (TAG) in lipoproteins [chylomicrons, very-low-density-lipoprotein (VLDL)]. TAG requires initial hydrolysis by the endothelial enzyme lipoprotein lipase and hence an intact heart preparation is vital to maintain tissue structural integrity. Chylomicron-TAG utilization and fate (oxidation, tissue-lipid deposition) in isolated working hearts has been studied using chylomicrons obtained from thoracic-duct catheters. However, lack of availability of sufficient quantities of VLDL has hindered examination of their cardiac utilization; the recent development of a technique to produce large quantities of radio-labelled rat VLDL has facilitated these studies and established that VLDL-TAG is an important metabolic substrate for working heart. Results relating to myocardial utilization of VLDL-TAG under varying physiological (lactation) and pathological (endotoxinaemia) conditions will be presented. The putative role of VLDL as a regulator of cardiac lipid metabolism will also be discussed.     

Metabolic consequences of ENPP1 overexpression in adipose tissue

Ectonucleotide pyrophosphate phosphodiesterase (ENPP1) has been shown to negatively modulate insulin receptor and to induce cellular insulin resistance when overexpressed in various cell types. Systemic insulin resistance has also been observed when ENPP1 is overexpressed in multiple tissues of transgenic models and attributed largely to tissue insulin resistance induced in skeletal muscle and liver. Another key tissue in regulating glucose and lipid metabolism is adipose tissue (AT). Interestingly, obese patients with insulin resistance have been reported to have increased AT ENPP1 expression. However, the specific effects of ENPP1 in AT have not been studied. To better understand the specific role of AT ENPP1 on systemic metabolism, we have created a transgenic mouse model (C57/Bl6 background) with targeted overexpression of human ENPP1 in adipocytes, using aP2 promoter in the transgene construct (AdiposeENPP1-TG). Using either regular chow or pair-feeding protocol with 60% fat diet, we compared body fat content and distribution and insulin signaling in adipose, muscle, and liver tissues of AdiposeENPP1-TG and wild-type (WT) siblings. We also compared response to intraperitoneal glucose tolerance test (IPGTT) and insulin tolerance test (ITT). Our results show no changes in Adipose ENPP1-TG mice fed a regular chow diet. After high-fat diet with pair-feeding protocol, AdiposeENPP1-TG and WT mice had similar weights. However, AdiposeENPP1-TG mice developed fatty liver in association with changes in AT characterized by smaller adipocyte size and decreased phosphorylation of insulin receptor Tyr(1361) and Akt Ser(473). These changes in AT function and fat distribution were associated with systemic abnormalities of lipid and glucose metabolism, including increased plasma concentrations of fatty acid, triglyceride, plasma glucose, and insulin during IPGTT and decreased glucose suppression during ITT. Thus, our results show that, in the presence of a high-fat diet, ENPP1 overexpression in adipocytes induces fatty liver, hyperlipidemia, and dysglycemia, thus recapitulating key manifestations of the metabolic syndrome.     

Fatty acid transport proteins and insulin resistance

PURPOSE OF REVIEW: Disturbed fatty acid metabolism and homeostasis is associated with insulin resistance. The aim of this review, therefore, is to summarize recent developments relating to the relevance and importance of the fatty acid transport proteins (FATPs) in the aetiology of insulin resistance. In particular, the potential differences between the six members of the FATP family will be considered. RECENT FINDINGS: FATP1 knockout mice failed to develop insulin resistance associated with lipid infusion or a high-fat diet, as wild-type mice did. FATP1-mediated fatty acid uptake may cause intramuscular lipid accumulation leading to insulin resistance in muscle if the fatty acids are not oxidized. While mouse models demonstrated an absolute requirement for FATP4 for survival, they provided no direct evidence for a role of FATP4 in insulin resistance. However, expression of FATP4 in human adipose tissue was increased in obesity (independent of genetic factors). While other members of the FATP family have important roles in fatty acid metabolism, they have not been clearly linked to insulin resistance. FATP-mediated fatty acid uptake may be driven by intrinsic acyl-CoA synthase activity. SUMMARY: Any role in the development of insulin resistance is likely to be different for each member of the FATP family. So far, both FATP1 and FATP4 have been associated with parameters related to insulin resistance. Whether increased FATP-mediated fatty acid uptake is beneficial or detrimental may be dependent on the tissue in question and on the subsequent fate of the fatty acids. These issues remain to be resolved.