Showing papers on "Fatty acid-binding protein published in 1997"

Role of long-chain fatty acyl-CoA esters in the regulation of metabolism and in cell signalling.

Abstract: The intracellular concentration of free unbound acyl-CoA esters is tightly controlled by feedback inhibition of the acyl-CoA synthetase and is buffered by specific acyl-CoA binding proteins. Excessive increases in the concentration are expected to be prevented by conversion into acylcarnitines or by hydrolysis by acyl-CoA hydrolases. Under normal physiological conditions the free cytosolic concentration of acyl-CoA esters will be in the low nanomolar range, and it is unlikely to exceed 200 nM under the most extreme conditions. The fact that acetyl-CoA carboxylase is active during fatty acid synthesis (Ki for acyl-CoA is 5 nM) indicates strongly that the free cytosolic acyl-CoA concentration is below 5 nM under these conditions. Only a limited number of the reported experiments on the effects of acyl-CoA on cellular functions and enzymes have been carried out at low physiological concentrations in the presence of the appropriate acyl-CoA-buffering binding proteins. Re-evaluation of many of the reported effects is therefore urgently required. However, the observations that the ryanodine-senstitive Ca2+-release channel is regulated by long-chain acyl-CoA esters in the presence of a molar excess of acyl-CoA binding protein and that acetyl-CoA carboxylase, the AMP kinase kinase and the Escherichia coli transcription factor FadR are affected by low nanomolar concentrations of acyl-CoA indicate that long-chain acyl-CoA esters can act as regulatory molecules in vivo. This view is further supported by the observation that fatty acids do not repress expression of acetyl-CoA carboxylase or Delta9-desaturase in yeast deficient in acyl-CoA synthetase.

Intracellular lipid-binding proteins and their genes

Abstract: Intracellular lipid-binding proteins are a family of low-molecular-weight single-chain polypeptides that form 1:1 complexes with fatty acids, retinoids, or other hydrophobic ligands. These proteins are products of a large multigene family of unlinked loci distributed throughout the genome. Each lipid-binding protein exhibits a distinctive pattern of tissue distribution. Transcriptional control, regulated by a combination of peroxisome proliferator activated receptors and CCAAT/enhancer-binding proteins, allows for a variety of both cell and tissue-specific expression patterns. In some cells, fatty acids increase the expression of the lipid-binding protein genes. Fatty acids, or their metabolites, are activators of the peroxisome proliferator-activated receptor family of transcription factors. Therefore, as the concentration of lipid in the diet increases, the expression of lipid-binding proteins coordinately increases. As revealed by X-ray crystallography, the lipid-binding proteins fold into beta-barrels, forming a large internal water-filled cavity. Fatty acid ligands are bound within the cavity, occupying only about one-third of the accessible volume. The bound fatty acid is stabilized via a combination of enthalpic and entropic forces that govern ligand affinity and selectivity. Cytoplasmic lipid-binding proteins are the intracellular receptors for hydrophobic ligands, delivering them to the appropriate site for use as metabolic fuels and regulatory agents.

Isoforms of rat liver fatty acid binding protein differ in structure and affinity for fatty acids and fatty acyl CoAs.

Abstract: Although native rat liver fatty acid binding protein (L-FABP) is composed of isoforms differing in isoelectric point, their comparative structure and function are unknown. These properties of apo- ...

Role of membrane-associated and cytoplasmic fatty acid-binding proteins in cellular fatty acid metabolism.

Abstract: A number of membrane-associated and cytoplasmic fatty acid-binding proteins (FABPs) are now being implicated in the cellular uptake and intracellular transport of long-chain fatty acids (FA). These proteins each have the capacity of non-covalent binding of FA, are present in tissues actively involved in FA metabolism, and are upregulated in conditions of increased cellular FA metabolism. To date, five distinct membrane FABPs have been described, ranging in mass from 22 to 88 kDa and each showing a characteristic tissue distribution. Evidence for involvement in cellular fatty acid uptake has been provided for several of them, because it was recently found that isolated cell lines transfected with 88-kDa putative fatty acid translocase (FAT; homologous to CD36) or with 63-kDa fatty acid-transport protein show an increased rate of FA uptake. The (at least nine) FABPs of cytoplasmic origin belong to a family of small (14-15 kDa) lipid binding proteins, all having a similar tertiairy structure but differing in binding properties and in tissue occurrence. The biological functions of the various FABPs, possibly exerted in a concerted action among them, comprise solubilization and compartmentalization of FA, facilitation of the cellular uptake and intracellular trafficking of FA, and modulation of mitosis, cell growth, and cell differentiation. In addition, the FABPs have been suggested to participate in and/or modulate FA-mediated signal transduction pathways and FA regulation of gene expression, and to prevent local high FA concentrations thereby contributing to the protection of cells against the toxic effects of FA. In conclusion, long-chain fatty acids are subject to continuous interaction with multiple proteins, which interplay influences their cellular metabolism.

Fatty acid regulation of fatty acid-binding protein expression in the small intestine.

Abstract: The effects of dietary oil intake and fatty acid infusions on the expression of intestinal and liver fatty acid-binding proteins (I-FABP and L-FABP, respectively) were investigated in the small intestine of mice. A daily force-feeding for 7 days with 0.2 ml sunflower oil specifically increased L-FABP mRNA and protein levels in duodenum and proximal jejunum. This upregulation was mediated in time- and dose-dependent manners by a minute quantity of linoleic acid, the main fatty acid found in sunflower oil. The L-FABP induction was only found with long-chain fatty acids, with the nonmetabolizable, substituted fatty acid alpha-bromopalmitate being far more active. A hormonally mediated effect is unlikely because long-chain fatty acids induced L-FABP mRNA in the Caco-2 cell line cultured in serum-free medium. Therefore, long-chain fatty acids are strong inducers of L-FABP gene expression in the small intestine. In contrast to data found in the rat, I-FABP gene expression appears to be unaffected by a lipid-enriched diet in the mouse.

Fatty acid transporters in animal cells.

Abstract: The mechanism by which fatty acids transverse the plasma membrane has been a controversial subject. Kinetic studies of fatty acid uptake suggested the presence of a protein carrier system in certain cells which exhibit rapid fatty acid influx and/or efflux such as hepatocytes, adipocytes and jejunal mucosal cells. Five plasma membrane proteins have been identified and proposed as candidates for fatty acid transporters thus far. These includes: Plasma Membrane Fatty Acid Binding Protein (FABPpm), Fatty Acid Translocase (FAT), caveolin, a 56-kDa renal fatty acid binding protein and Fatty Acid Transport Protein (FATP). The first four proteins were identified by classical biochemical techniques while FATP, the one most recently reported, was identified by expression cloning strategies. Each of these proteins has distinct primary amino acid sequence and tissue-specific pattern of expression. It remains to be determined whether the proteins identified to date function as individual polypeptides or as a single component of a larger complex. This review summarizes recent advances concerning the structure, function and regulation of these putative fatty acid transporters.

Multiple biochemical effects in the pathogenesis of alcoholic fatty liver

Abstract: The pathogenesis of alcoholic fatty liver is unknown, but several causes have been proposed based on biochemical findings. These include the metabolism of alcohol leading to a shift in the cytosolic [NAD+]/ [NADH] ratio to reduction, which in turn causes a direct inhibition of beta-oxidation and enhanced triacylglycerol formation via the [glycerol-3-phosphate]/[dihydroxyacetone phosphate] ratio. There are also chronic effects of ethanol on hepatic enzyme activities. Thus, increased activity of phosphatidate phosphohydrolase, an increased amount of fatty acid binding protein, decreased secretion of very low-density lipoprotein and impairment of the respiratory chain as a result of decreased protein synthesis or decreased amounts of ubiquinone could all lead to fat accumulation and steatosis. The interplay of each of these with nutritional and genetic factors would then lead to the heterogeneity of the severity and characteristics of the steatosis observed in human alcoholics.

Transport and Utilization of Lipids in Insect Flight Muscles

Abstract: In migrating lepidopteran and orthopteran insects, lipid is the preferred fuel for sustained flight activity. Diacylglycerol is delivered by lipophorin to the flight muscle and hydrolyzed to free fatty acid and glycerol. After penetrating the plasma membrane by an unknown mechanism, fatty acids are bound by the intracellular fatty acid binding protein (FABP) and transported through the cytosol. After their conversion to acyl-CoA esters, the fatty acids enter the mitochondrial matrix via the carnitine shuttle for subsequent β-oxida- tion. This article reviews the current knowledge of lipid metabolism in insect flight muscle, with particular emphasis on the structure and function of FABP and its expression during locust development and flight. comp biochem physiol 117B;4:475-482, 1997. © 1997 Elsevier Science Inc. Insects that engage in migratory flight activity usually de- to their CoA-esters that enter the β-oxidation pathway. pend on lipids as an energy source for the flight muscle. This brief description highlights both the parallels and Lipid utilization during sustained flight has been extensively differences in lipid metabolizing pathways in insects and studied in lepidopteran and orthopteran species. The pro- vertebrates. Extended activity in vertebrate red muscle is cesses involved in lipid release from the fat body and their fueled by β-oxidation of fatty acid as well. In the circulatory transport through the aqueous hemolymph have been de- system, proteins are also responsible for the transport of the scribed in detail in the reviews by Goldsworthy et al., van hydrophobic lipids, either triacylglycerol or free fatty acid. der Horst and van Marrewijk and Chino elsewhere in this Triglycerides are complexed in a large lipoprotein (very- issue. Upon stimulation by adipokinetic hormone, diacyl- low-density lipoprotein, VLDL), whereas free fatty acids are glycerol (DAG) is released from fat body into the hemo- transported by serum albumin, an abundant blood protein lymph, where it associates with the core high-density that has several high affinity and many additional low affin- lipophorin (HDLp) particle and free apolipophorin III ity binding sites for fatty acids (28). Free fatty acid is the (apoLp-III) to form a DAG-enriched low-density lipopro- only lipid that can enter the muscle cell; most muscles tein molecule. Low-density lipophorin (LDLp) delivers therefore rely on albumin to deliver the needed fatty acid, DAG to the flight muscle. DAG is hydrolyzed outside of but heart muscle in particular can also obtain its fatty acid the muscle cell, giving rise to free fatty acid, glycerol, the from the VHDL particle. To release fatty acid from the pro- DAG-depleted HDLp particle and free apoLp-III. Except tein, triacylglycerol must be first hydrolyzed by the action for the fatty acid, all these components are hydrophilic and of a membrane-bound lipoprotein lipase (for a review, see remain initially in the hemolymph. Fatty acids, however, (35)). are imported directly into the muscle cell. Once inside, the The fate of fatty acids within the muscle cell is similar hydrophobic fatty acid molecules must move through the in both insects and vertebrates. One important difference, aqueous cytosol. They are activated by coenzyme A and however, is that the metabolic activity and hence the rate

Adipocyte Fatty Acid-Binding Protein: Interaction with Phospholipid Membranes and Thermal Stability Studied by FTIR Spectroscopy†

Abstract: Fatty acid-binding proteins (FABPs) found in many tissues constitute a family of low molecular weight proteins that are suggested to function as intracellular transporters of fatty acids. Studies of the transfer kinetics of fluorescent anthroyloxy-labeled long-chain fatty acids from FABP to model membranes led to the suggestion that the FABPs, typically considered to be cytosolic proteins, could nevertheless interact directly with membranes [Wootan, M. G., et al. (1993) Biochemistry 32, 8622-8627]. In the current study, the interaction of the adipocyte FABP (A-FABP) with vesicles of various phospholipids has been directly measured and confirmed with FTIR spectroscopy. The strength of this interaction was inferred from the lowering of the gel-liquid-crystal phase transition temperature as monitored from temperature-induced variations in the acyl chain CH2 stretching frequencies and from the intensities of the components of the CH2 wagging progressions. A-FABP interacts more strongly with anionic phospholipids (phosphatidylserine and cardiolipin) than with zwitterionic phosphatidylcholine. Unsaturation in the acyl chains leads to a greater reduction in Tm (stronger lipid-protein interaction). In contrast, neutralization of A-FABP surface charges by acetylation considerably weakens the interaction. Comparison of the shifts in lipid melting temperatures with those induced by other proteins suggests that A-FABP behaves like a typical peripheral membrane protein. The degree of membrane interaction correlates directly with the rate of fatty acid transfer, suggesting that contact between A-FABP and membranes is functionally related to its fatty acid transport properties. As expected, the protein exhibits a predominantly beta-sheet structure. It was found to aggregate with increasing temperature. With the exception of minor differences between the pure and lipid-associated A-FABP in the 1640-1660 cm-1 region, both the protein structure and thermal stability appeared essentially unchanged upon interaction with the lipid.

Heart-type fatty acid binding protein — involvement in growth inhibition and differentiation

Abstract: Fatty acid binding proteins (FABPs) comprise a well-established family of cytoplasmic hydrophobic ligand binding proteins and are thought to be involved in lipid metabolism by binding and intracellular transport of long-chain fatty acids. However, from other studies role for FABPs in cell signalling, growth inhibition and differentiation has also been implied. In particular, the heart-type (H-FABP) is abundantly expressed in differentiated mammary gland and its relationship with a very homologous (95%) mammary derived growth inhibitor (MDGI) was disputed. Here we give a survey on the experimental evidence for the existence of such protein with growth inhibitory function. After cloning of the bovine adipocyte-type (A-)FABP cDNA from mammary gland we conclude that the reported MDGI sequence actually represents a mixture of bovine H- and A-FABP and that the MDGI function is exerted by H-FABP. We also monitored the H-FABP level during differentiation of C2C12 muscle cells from myoblasts to multiply nucleated myotubes. H-FABP expression is clearly detected after that of the transcription factor myogenin which is upregulated immediately upon onset of differentiation and after that of the typical muscle enzyme creatine kinase. This argues against an active role of H-FABP in muscle development unlike the situation in the mammary gland.

Cytoplasmic codiffusion of fatty acids is not specific for fatty acid binding protein.

Abstract: The intracellular movement of fatty acids is thought to be facilitated through codiffusion with fatty acid binding protein (FABP). Previous work suggested that FABP decreases fatty acid binding to ...

Fatty acid transport and metabolism in the feto-placental unit and the role of fatty acid-binding proteins

Abstract: It is generally accepted that essential fatty acids (EFA) and their long-chain polyunsaturated fatty acid (LCPUFA) derivatives play a crucial role in fetal development and pregnancy outcome. Surprisingly, however, little is known about the transport and metabolism of EFA and LCPUFA in the feto-placental unit. The critical importance of maternal LCPUFA synthesis and the subsequent preferential transport of these by the placenta to the fetus is now well recognized, however underlying mechanisms of these processes are poorly understood. Increasing evidence suggests that the cytosolic and plasma membrane-associated fatty acid-binding proteins (FABP and FABPpm' respectively) are involved in cellular fatty acid uptake, transport, and metabolism in several tissues: however, no information is available for the placenta. These proteins may also function in the fine-tuning of cellular events by modulating the metabolism of LCPUFA implicated in the regulation of cell growth and differentiation. In this review recent developments in the understanding of the mechanisms of EFA/LCPUFA transport by the human placenta and the role of the fatty acid-binding proteins in the sequestration of maternal EFA/LCPUFA for fetal delivery are discussed.

Long-term effects of fatty acids on cell viability and gene expression of neonatal cardiac myocytes

Abstract: Fatty acids are the most important source of energy for the adult heart. However, cardiac substrate preference changes during development and alters in pathophysiological states. Fatty acids have also been shown to be involved in signal transduction pathways, thereby affecting gene expression in various cell systems. In the present paper the significance of changes in substrate preference and the potential role of fatty acids in signal transduction in the cardiomyocyte are briefly reviewed. Furthermore, the development of a cellular model system, useful in exploring the long-term effects of fatty acids on the normal and hypertrophic cardiomyocyte, is described. Some aspects of this model system are illustrated by showing the effects of different fatty acid species on cell viability and the effects of fatty acids on the expression of heart type fatty acid-binding protein (H-FABP), a 15 kDa protein thought to be involved in intracellular trafficking of fatty acids. To this end primary cultures of rat neonatal ventricular myocytes were kept in defined medium containing various (combinations of) substrates for up to 48 h. First, the effects of prolonged exposure to different fatty acid species, complexed to BSA, on cell viability were investigated. Exposure of the cells to saturated fatty acids (C16:0 or C18:0), but not mono-unsaturated (C16:1 or C18:1) fatty acids, resulted in cell death, as evidenced by the release of intracellular proteins like lactate dehydrogenase. The detrimental effects of saturated fatty acids were nullified by the co-addition of mono-unsaturated fatty acids. Accordingly, the combination of C16:0/C18:1 was used to examine the effects of fatty acids on the expression of H-FABP. Therefore, the cells were incubated with either (i) glucose only, (ii) fatty acids only, or (iii) glucose plus fatty acids. Incubation with fatty acids (with or without glucose) resulted in a nearly four-fold increase of the H-FABP mRNA level. Similarly, at the protein level the cellular H-FABP/LDH ratio increased almost two-fold. In hypertrophic cardiomyocytes (stimulated with the alpha1-adrenergic agonist phenylephrine) the stimulatory effect of fatty acids on H-FABP expression was mitigated. These findings strongly suggest that fatty acids are able to modulate gene expression in the context of the cardiac muscle cell.

Threonine allele in codon 54 of the fatty acid binding protein 2 gene does not modify the fatty acid composition of serum lipids in obese subjects.

Abstract: Intestinal fatty acid binding protein (I-FABP) participates in the metabolism of fatty acids in the intestinal enterocytes. Threonine encoding allele in codon 54 of the I-FABP gene has been suggested as regulating the absorption of long-chain fatty acids. We examined the fatty acid composition of serum lipid fractions and the concentration of serum free fatty acids after an overnight fast in obese subjects, aged 24-56 years, on their habitual diet. The body mass index of the subjects ranged from 29.7 to 43.3 kg m -2 . Six subjects were homozygous for the Thr-54 allele of the I-FABP gene, 37 subjects were heterozygous for the Thr-54/Ala-54 allele and 24 subjects were homozygous for the Ala-54 allele. We did not find any consistent differences in the proportions of long-chain fatty acids in serum triglycerides, cholesterol esters or phospholipids, but the concentration of serum free fatty acids tended to be higher in subjects who were homozygous for the Thr-54 allele (P = 0.13, for trend). In conclusion, our findings suggest that a polymorphism at codon 54 of the I-FABP2 gene does not substantially modify the fatty acid composition of serum lipids in obese Finns.

Modelling intracellular fatty acid transport: possible mechanistic role of cytoplasmic fatty acid-binding protein

Abstract: A computer model is presented in which the role of cytoplasmic fatty acid-binding protein (FABP) in the intracellular translocation of fatty acids (FA) from one membrane to an opposite membrane is studied. The model consists of a cubical space, in which FABP and FA are allowed to diffuse at random. The amount of FA released from the donor membrane and reaching an opposite acceptor membrane is calculated in a variety of conditions. The data provided by the various simulations suggest that FABP can play a significant role in intracellular FA transport only if FABP is able to take up FA directly from FA containing membranes and to directly deliver FA to an acceptor membrane, thus preventing the unfavourable thermodynamical situation in which FA must solubilize in an aqueous environment prior to binding to FABP.

Method of detection of cardiac ischemia using fatty acid binding protein

Abstract: A method of detecting cardiac ischemia by detecting elevated levels of serum free fatty acids in serum unbound to serum albumin (FFA u ) compared to an average FAA u level in individuals without cardiac ischemia, wherein the detection method uses a free fatty acid binding protein derivatized with a fluorescent moiety, is disclosed.