Direct Interaction between EgFABP1, a Fatty Acid Binding Protein from Echinococcus granulosus,and Phospholipid Membranes

Background

Growth and maintenance of hydatid cysts produced by Echinococcus granulosus have a high requirement for host lipids for biosynthetic processes, membrane building and possibly cellular and developmental signalling. This requires a high degree of lipid trafficking facilitated by lipid transporter proteins. Members of the fatty acid binding protein (FABP) family have been identified in Echinococcus granulosus, one of which, EgFABP1 is expressed at the tegumental level in the protoscoleces, but it has also been described in both hydatid cyst fluid and secretions of protoscoleces. In spite of a considerable amount of structural and biophysical information on the FABPs in general, their specific functions remain mysterious.

Methodology/Principal Findings

We have investigated the way in which EgFABP1 may interact with membranes using a variety of fluorescence-based techniques and artificial small unilamellar vesicles. We first found that bacterial recombinant EgFABP1 is loaded with fatty acids from the synthesising bacteria, and that fatty acid binding increases its resistance to proteinases, possibly due to subtle conformational changes induced on EgFABP1. By manipulating the composition of lipid vesicles and the ionic environment, we found that EgFABP1 interacts with membranes in a direct contact, collisional, manner to exchange ligand, involving both ionic and hydrophobic interactions. Moreover, we observed that the protein can compete with cytochrome c for association with the surface of small unilamellar vesicles (SUVs).

Conclusions/Significance

This work constitutes a first approach to the understanding of protein-membrane interactions of EgFABP1. The results suggest that this protein may be actively involved in the exchange and transport of fatty acids between different membranes and cellular compartments within the parasite.     

Interaction of Strychnine-Insensitive Glycine Binding with MK-801 Binding in Brain Synaptic Membranes

Strychnine-insensitive [3H]glycine binding was detected in brain synaptic membranes treated with Triton X-100 using a filtration assay method. The binding was a time-dependent, inversely temperature-dependent, and reversible process with a relatively high affinity for the neuroactive amino acid. Scatchard analysis revealed that Triton treatment doubled both the affinity and density of the binding sites, which consisted of a single component. The binding was not only displaced by structurally-related amino acid such as D-serine and D-alanine, but also inhibited by some peptides containing glycine, including glycine methylester and N-methylglycine. These ligands invariably potentiated the binding of [3H](+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]- cyclohepten-5,10-imine ([3H]MK-801), a noncompetitive antagonist for the N-methyl-D-aspartate-sensitive subclass of the central excitatory amino acid receptors, in a concentration-dependent manner. Among various endogenous tryptophan metabolites, kynurenic acid significantly inhibited the strychnine-insensitive [3H]glycine binding. The Triton treatment did not affect the pharmacological profile of [3H]MK-801 binding sites. These results suggest that brain synaptic membranes treated with Triton X-100 are useful in evaluating the strychnine-insensitive and kynurenate-sensitive binding sites of glycine, which are functionally linked to N-methyl-D-aspartate- sensitive receptor channels.     

脂肪细胞型脂肪酸结合蛋白的研究进展

脂肪细胞型脂肪酸结合蛋白（adipocyte fatty acid binding protein,AFABP/aP2）作为脂肪酸结合蛋白（FABPS）超家族成员之一,广泛存在于各种正常的组织细胞中,参与脂肪酸贮存,运输与降解等过程。近年来,对脂肪细胞型脂肪酸结合蛋白的研究已成为热点,本文就其主要特征及其与各类疾病的关系作一简要综述。     

肝型脂肪酸结合蛋白研究进展

肝型脂肪酸结合蛋白(liver-type fatty acid binding protein,L-FABP,FABPI)是脂肪酸结合蛋白家族的成员之一,主要在肝脏、小肠、肾脏及胰腺等组织细胞中有表达.研究发现,L-FABP与脂肪酸的摄取、转运、代谢调节有关.近年研究表明,肝型脂肪酸结合蛋白(L-FABP)与肿瘤、肾脏疾病、脂肪肝、肥胖、糖尿病等多种疾病的发生发展密切相关.本文就肝型脂肪酸结合蛋白的分子结构、功能以及与疾病的关系作一综述.     

脂肪细胞型脂肪酸结合蛋白的研究进展

脂肪细胞型脂肪酸结合蛋白(adipocyte fatty acid binding protein,AFABP/aP2)作为脂肪酸结合蛋白(FABPS)超家族成员之一,广泛存在于各种正常的组织细胞中,参与脂肪酸贮存,运输与降解等过程。近年来,对脂肪细胞型脂肪酸结合蛋白的研究已成为热点,本文就其主要特征及其与各类疾病的关系作一简要综述。     

Heart-Type Fatty Acid Binding Protein Is Associated with Proteinuria in Obesity

Rationale

Lipid metabolism contributes to the formation of obesity-related glomerulopathy (ORG). Heart-type fatty acid binding protein (H-FABP or FABP3) is involved in lipid metabolism and was predicted to relate to renal lesions in obesity.

Methods

A total of 28 patients with ORG were investigated, and renal tissue from 7 kidney donors served as controls. Db/db mice with albuminuria were treated with Simvastatin for 12 weeks.

Results

Immunohistochemistry demonstrated the H-FABP staining in glomerular and tubular areas of patients with ORG, and the percentage of H-FABP in the glomerular area was significantly higher than in controls (15.8±1.62 versus 4.51±0.56%, P<0.001). Moreover, H-FABP expression correlated with proteinuria, high-density lipoprotein (HDL) cholesterol, waist circumference and the homeostatic model assessment – insulin resistance (HOMA-IR) among patients with ORG. Enhanced expression of H-FABP was also detected in the db/db mice, and expression increased from 8 to 20 weeks of age and was weakly related to increased albuminuria (r = 0.433; P = 0.020). Furthermore, H-FABP was co-localized with synaptopodin and demonstrated a podocyte pattern distribution. After Simvastation treatment, the urine albumin levels decreased with lipid levels and H-FABP expression in the glomeruli. The expression of H-FABP was related to Simvastatin treatment, albuminuria and triglycerides, while it was only linked with triglycerides and albuminuria (r = 0.643, P = 0.036).

Conclusions

This study confirmed an association of H-FABP with the pathogenesis of clinical and experimental ORG, and suggests that such a process might be related to podocytes and lipid dysmetabolism.     

Free Radical Scavenging by Myocardial Fatty Acid Binding Protein

Recent investigations have indicated the presence of a fatty acid binding protein (FABP) in mammalian heart. This protein binds free fatty acids and their esters with high affinity, however, its physiological role remains unknown. Since FABP constitutes a significant amount of cystolic protein, it is likely that it would be a target for free radical attack. To test this hypothesis, FABP was examined for scavenging against free radicals such as the superoxide anion (O^?₂,). hydroxyl radical (OH') and hypochlorite radical (OCl') which may be present in an ischemic reperfused heart. Our results suggest that FABP scavenges O^?₂, OH' and OCl' as indicated by the FABP inhibition of O^?₂-dependent reduction of cytochrome c, OH'-dependent hydroxybenzoic acid formation and OCl'-mediated chemiluminescence response. FABP was found to be a more potent scavenger of these free radicals compared to bovine serum albumin. Furthermore, FABP was more effective in scavenging OH' than O^?₂, and inhibited OH' mediated lipid peroxidation process. These results indicate that FABP can scavenge free radicals which may be present in an ischemic/reperfused heart and, thus, may play a significant physiological role in the heart during ischemia and reperfusion.     

Model of β-Sheet of Muscle Fatty Acid Binding Protein of Locusta migratoria Displays Characteristic Topology

The β-sheet of muscle fatty acid binding protein of Locusta migratoria (Lm-FABP) was modeled by employing 2-D NMR data and the Rigid Body Assembly method. The model shows the β-sheet to comprise ten β-strands arranged anti-parallel to each other. There is a β-bulge between Ser 13 and Gln 14 which is a difference from the published structure of β-sheet of bovine heart Fatty Acid Binding Protein. Also, a hydrophobic patch consisting of Ile 45, Phe 51, Phe 64 and Phe 66 is present on the surface which is characteristic of most Fatty Acid Binding Proteins. A “gap” is present between βD and βE that provides evidence for the presence of a portal or opening between the polypeptide chains which allows ligand fatty acids to enter the protein cavity and bind to the protein.     

Interaction Between Metals and Chelating Agents Affects Glutamate Binding on Brain Synaptic Membranes

The present study investigates the possible effects of Hg²⁺, Pb²⁺, and Cd²⁺ on [³H]-glutamate binding. To better understand the role of the thiol-disulfide status on the toxicity of such metals toward glutamatergic neurotransmission, we used three thiol chelating agents, 2,3-dimercaptopropanol (BAL), 2,3-dimercaptopropane 1-sulfonate (DMPS), and meso-2,3-dimercaptosuccinic acid (DMSA). Dithiotreitol (DTT) was tested for its ability to prevent metals-induced inhibition on [³H]-glutamate binding. Hg²⁺, Pb²⁺, and Cd²⁺ showed a concentration-dependent inhibition on [³H]-glutamate binding, and mercury was the most effective inhibitor. BAL did not prevent [³H]-glutamate binding inhibition by Hg²⁺, Cd²⁺, and Pb²⁺. However, DMPS and DMSA prevented the inhibition caused by Cd²⁺ and Pb²⁺, but not by Hg²⁺. DTT did not prevent the inhibition on [³H]-glutamate binding caused by 10 M Hg²⁺. In contrast, it was able to partially prevent [³H]-glutamate binding inhibition caused by 40 M Pb²⁺ and Cd²⁺. These results demonstrated that the heavy metals present an inhibitory effect on [³H]-glutamate binding. In addition, BAL was less effective to protect [³H]-glutamate binding inhibition caused by these metals than other chelating agents studied.     

Circulating Adipocyte Fatty Acid Binding Protein (FABP4) Levels Are Associated with Irisin in the Middle-Aged General Chinese Population

Background

Adipocyte fatty acid binding protein (FABP4) has been recently characterized as an adipokine that is closely associated with obesity and metabolic syndrome. Irisin, a novel myokine, activates thermogenesis by increasing the transformation of white adipocytes to brown, and it has improved glucose homeostasis in animal models. In this study, we aimed to explore the relationship between serum FABP4 and irisin in middle-aged Chinese subjects.

Methods

A total of 111 normal residents (56 men and 55 women) of Fengxian District who were 40 to 60 years of age were recruited. Circulating FABP4 and irisin were determined by enzyme-linked immunosorbent assay. Anthropometric parameters, oral glucose tolerance test results, hemoglobin A1C (HbA1C), blood lipids, homeostasis model assessment of insulin resistance, homeostasis model assessment-β and body fat composition were also determined.

Results

All participants were categorized by FABP4 tertiles. There were significant differences in blood pressure, body fat percentage, 2-h plasma glucose, and skeletal muscle mass among the three groups (P<0.05). Furthermore, FABP4 levels in the women were significantly higher than in the men (P<0.05). However, there was no sexual dimorphism in serum irisin (P>0.05). To exclude the effect of sex difference, partial correlations analysis showed that FABP4 was positively correlated with diastolic blood pressure (P<0.05) and body fat percentage (P<0.05) negatively correlated with skeletal muscle mass (P<0.05) and irisin (P<0.05), while irisin was positively correlated with HbA1c (P<0.05) and negatively correlated with creatinine (P<0.05). Multivariate regression analysis demonstrated that serum FABP4 was independently associated with skeletal muscle mass (P<0.001), diastolic blood pressure (P<0.05) and irisin (P<0.05) after adjustment for age, body mass index, body fat percentage, total cholesterol and HbA1C.

Conclusions

Elevated FABP4 levels increase the risks of obesity-related metabolic disorders and hypertension. Serum irisin might exert antagonistic effects on FABP4 in the middle-aged Chinese population.     

Buffer Interference with Protein Dynamics: A Case Study on Human Liver Fatty Acid Binding Protein

Selection of suitable buffer types is often a crucial step for generating appropriate protein samples for NMR and x-ray crystallographic studies. Although the possible interaction between MES buffer (2-(N-morpholino)ethanesulfonic acid) and proteins has been discussed previously, the interaction is usually thought to have no significant effects on the structures of proteins. In this study, we demonstrate the direct, albeit weak, interaction between MES and human liver fatty acid binding protein (hLFABP). Rather than affecting the structure of hLFABP, we found that the dynamics of hLFABP, which were previously proposed to be relevant to its functions, were significantly affected by the binding of hLFABP with MES. Buffer interference with protein dynamics was also demonstrated with Bis-Tris buffer, which is quite different from MES and fatty acids in terms of their molecular structures and properties. This result, to our knowledge, is the first published report on buffer interference with protein dynamics on a microsecond to millisecond timescale and could represent a generic problem in the studies of functionally relevant protein dynamics. Although being a fortuity, our finding of buffer-induced changes in protein dynamics offers a clue to how hLFABP accommodates its ligands.     

Isolation and Characterization of Two Fatty Acid Binding Proteins from Mouse Brain

Abstract: Two fatty acid binding proteins (FABPs) were isolated from Swiss Webster mouse brains. Neither protein cross-reacted with antisera to recombinant liver L-FABP. One protein, designated brain H-FABP, migrated on tricine sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) as a single band at 14.5 kDa with pl 4.9. Brain H-FABP bound NBD-stearic acid and cis -parinaric acid with K _D values near 0.02 and 0.5 µ M , respectively. Brain H-FABP cross-reacted with affinity-purified antisera to recombinant heart H-FABP. The second protein, mouse brain B-FABP, migrated on tricine SDS-PAGE gels as a doublet at 16.0 and 15.5 kDa with pl values of 4.5 and 4.7, respectively. Brain B-FABP bound NBD-stearic acid and cis -parinaric acid with K _D values near 0.01 and 0.7 µ M , respectively. The brain B-FABP doublet was immunoreactive with affinity-purified antibodies against recombinant mouse brain B-FABP, but not with affinity-purified antibodies against heart H-FABP. [³H]Oleate competition binding indicated that the two brain FABPs had distinct ligand binding specificities. Both bound fatty acids, fatty acyl CoA, and lysophosphatidic acid. Although both preferentially bound unsaturated fatty acids, twofold differences in specific saturated fatty acid binding were observed. Brain B-FABP and brain H-FABP represented 0.1 and 0.01% of brain total cytosolic protein, respectively. In summary, mouse brain contains two native fatty acid binding proteins, brain H-FABP and brain B-FABP.     

猪L-FABP基因的克隆、表达特征及遗传多态性研究

FABPs属于脂结合蛋白超家族成员,是一类分子量较小而对脂肪酸有高亲和力的蛋白质,广泛存在于脊椎动物和非脊椎动物的细胞质中.FABPs担当细胞内脂肪酸的运输任务,它们与脂肪酸结合将其运输到脂肪酸氧化的位置、脂肪酸脂化成甘油三醋或磷脂的位置,或者进入细胞核内发挥其可能的调控功能.因此FABPs对脂类代谢具有重要的调控作用.本研究把L-FABP基因作为影响猪肌内脂肪含量的候选基因.为此,利用cDNA末端快速扩增(RACE)和PCR技术,克隆到猪肝脏型脂肪酸结合蛋白基因(L-FABP)的全长cDNA序列(GenBank登录号AY960623)和部分基因组序列(GenBank登录号DQ182323).猪L-FABP基因的cDNA序列全长518 bp,该序列包括起始密码子TGA和38 bp的5'末端非编码区(5'URT),终止密码子TAG和99 bp的3'末端非编码区(3'URT),在3'URT结构区域中包含polyA加尾信号序列AATAAA.猪L-FABP基因与其他FABPs基因一样,也由4个外显子(67 bp、173 bp、93 bp和51 bp)和3个内含子组成,内含子1和3的大小是1 679bp和565 bp,没有获得内含子2的序列,外显子和内含子剪接处符合GT/AG规律.应用Clustal W/X程序对猪L-FABP与其他物种的L-FABP进行多重序列比对,发现猪L-FABP与人、大鼠、鸡的L-FABP的相似性分别为89.8%、81.9%和72.4%.亲水性分析表明,猪L-FABP也是一个潜在的跨膜蛋白,在氨基酸残基57-65之间有一个明显的跨膜α螺旋.应用半定量RT-PCR分析发现,猪L-FABP在猪体组织中广泛存在,但在肝脏和小肠组织中表达量最为丰富.分析还发现,所克隆得到的编码区核苷酸序列与已知猪L-FABP基因的编码区核苷酸序列存在一定的变异,分别是外显子2中T→C(116位)、C→T(231位)、C→A(236位)和A→C(258位),演绎成氨基酸在Leu74Met存在差异.为进一步证实这些突变位点在猪群中真实存在,利用PCR-SSCP检测方法对4个猪种(藏猪、大河猪、雅南猪和约克夏)的157头个体的外显子2全序列进行SNP位点多态性片段的基因型分型,结果发现一个C→T的单核苷酸多态,等位基因频率在中国地方猪种(藏猪、大河猪、雅南猪)与国外约克夏猪种间存在极显著的差异(P＜0.01).连锁分析发现,基因型CC的肌内脂肪含量(4.86±0.22%)显著的高于基因型CT(4.16±0.23%)和TT(4.05±0.27%)的肌内脂肪含量(P＜0.05).因此,推测L-FABP基因可能是影响猪肌内脂肪含量的主效基因或与主效基因紧密连锁的标记基因,并且能够在分子标记辅助选择中用于对猪肌内脂肪含量的遗传改良.     

Molecular Dynamics Simulation of Ligand Dissociation from Liver Fatty Acid Binding Protein

The mechanisms of how ligands enter and leave the binding cavity of fatty acid binding proteins (FABPs) have been a puzzling question over decades. Liver fatty acid binding protein (LFABP) is a unique family member which accommodates two molecules of fatty acids in its cavity and exhibits the capability of interacting with a variety of ligands with different chemical structures and properties. Investigating the ligand dissociation processes of LFABP is thus a quite interesting topic, which however is rather difficult for both experimental approaches and ordinary simulation strategies. In the current study, random expulsion molecular dynamics simulation, which accelerates ligand motions for rapid dissociation, was used to explore the potential egress routes of ligands from LFABP. The results showed that the previously hypothesized “portal region” could be readily used for the dissociation of ligands at both the low affinity site and the high affinity site. Besides, one alternative portal was shown to be highly favorable for ligand egress from the high affinity site and be related to the unique structural feature of LFABP. This result lends strong support to the hypothesis from the previous NMR exchange studies, which in turn indicates an important role for this alternative portal. Another less favored potential portal located near the N-terminal end was also identified. Identification of the dissociation pathways will allow further mechanistic understanding of fatty acid uptake and release by computational and/or experimental techniques.     

Inhibition of Fatty Acid Binding Proteins Elevates Brain Anandamide Levels and Produces Analgesia

The endocannabinoid anandamide (AEA) is an antinociceptive lipid that is inactivated through cellular uptake and subsequent catabolism by fatty acid amide hydrolase (FAAH). Fatty acid binding proteins (FABPs) are intracellular carriers that deliver AEA and related N-acylethanolamines (NAEs) to FAAH for hydrolysis. The mammalian brain expresses three FABP subtypes: FABP3, FABP5, and FABP7. Recent work from our group has revealed that pharmacological inhibition of FABPs reduces inflammatory pain in mice. The goal of the current work was to explore the effects of FABP inhibition upon nociception in diverse models of pain. We developed inhibitors with differential affinities for FABPs to elucidate the subtype(s) that contributes to the antinociceptive effects of FABP inhibitors.Inhibition of FABPs reduced nociception associated with inflammatory, visceral, and neuropathic pain. The antinociceptive effects of FABP inhibitors mirrored their affinities for FABP5, while binding to FABP3 and FABP7 was not a predictor of in vivo efficacy. The antinociceptive effects of FABP inhibitors were mediated by cannabinoid receptor 1 (CB₁) and peroxisome proliferator-activated receptor alpha (PPARα) and FABP inhibition elevated brain levels of AEA, providing the first direct evidence that FABPs regulate brain endocannabinoid tone. These results highlight FABPs as novel targets for the development of analgesic and anti-inflammatory therapeutics.     

Fatty Acid Binding Protein 4 Deficiency Protects against Oxygen-Induced Retinopathy in Mice

Retinopathy of prematurity (ROP) is a leading cause of blindness in children worldwide due to increasing survival rates of premature infants. Initial suppression, followed by increased production of the retinal vascular endothelial growth factor-A (VEGF) expression are key events that trigger the pathological neovascularization in ROP. Fatty acid binding protein 4 (FABP4) is an intracellular lipid chaperone that is induced by VEGF in a subset of endothelial cells. FABP4 exhibits a pro-angiogenic function in cultured endothelial cells and in airway microvasculature, but whether it plays a role in modulation of retinal angiogenesis is not known. We hypothesized that FABP4 deficiency could ameliorate pathological retinal vascularization and investigated this hypothesis using a well-characterized mouse model of oxygen-induced retinopathy (OIR). We found that FABP4 was not expressed in retinal vessels, but was present in resident macrophages/microglial cells and endothelial cells of the hyaloid vasculature in the immature retina. While FABP4 expression was not required for normal development of retinal vessels, FABP4 expression was upregulated and localized to neovascular tufts in OIR. FABP4^−/− mice demonstrated a significant decrease in neovessel formation as well as a significant improvement in physiological revascularization of the avascular retinal tissues. These alterations in retinal vasculature were accompanied by reduced endothelial cell proliferation, but no effect on apoptosis or macrophage/microglia recruitment. FABP4^−/− OIR samples demonstrated decreased expression of genes involved in angiogenesis, such as Placental Growth Factor, and angiopoietin 2. Collectively, our findings suggest FABP4 as a potential target of pathologic retinal angiogenesis in proliferative retinopathies.     

Protein and Fatty Acid Composition of Mesosomal Vesicles and Plasma Membranes of Staphylococcus aureus

Unsheared lysates of Bacillus subtilis 168T(-) containing uniformly labeled deoxyribonucleic acid (DNA) were exposed to varying doses of gamma rays to introduce double-strand scissions in the chromosome. From an estimate of the number-average molecular weight and the amount of DNA bound to membrane after irradiation, about 70 to 90 regions of the bacterial chromosome were detected in membrane fractions. Since this number was independent of the molecular weight of the DNA (i.e., the extent of fragmentation of the chromosome), it is thought to represent an upper limit in the number of membrane-binding sites per chromosome.     

Fatty Acid Interaction with Mitochondrial Uncoupling Proteins

The phenomena of fatty acid interaction with mitochondrial integral membrane proteins, namelyuncoupling proteins (UCPs), are reviewed to emphasize the fatty acid cycling mechanism thathas been suggested to explain the UCP function. Fatty acid-induced uncoupling is suggestedto serve in bioenergetic systems, to set the optimum efficiency, and to tune the degree ofcoupling of oxidative phosphorylation. Fatty acid interaction with the classic uncouplingprotein (UCP1) from mitochondria of thermogenic brown adipose tissue (BAT) is well known.UCP1 is considered to mediate purine nucleotide-sensitive uniport of monovalent unipolaranions, including anionic fatty acids. The return of protonated fatty acid leads to H⁺ uniportand uncoupling. Experiments supporting this mechanism are also reviewed for plant uncouplingmitochondrial protein (PUMP) and ADP/ATP carrier. The fatty acid cycling mechanism ispredicted, as well for the recently discovered uncoupling proteins, UCP2 and UCP3.     

Expression of the Extracellular Fatty Acid Binding Protein (Ex-FABP) during Muscle Fiber Formationin Vivoandin Vitro

We report that Ex-FABP, an extracellular protein belonging to the lipocalin family and involved in the extracellular transport of long-chain fatty acids, is expressed in the forming myotubes bothin vivoandin vitro.The presence of the protein and of the mRNA was observed in newly formed myotubes at early stages of chick embryo development by immunohistochemistry and byin situhybridization. At later stages of development myofibers still expressed both the mRNA and the protein. Ex-FABP expression was observed also in the developing myocardium and the muscular layer of large blood vessels. In agreement with these findings, an initial expression of the mRNA and protein secretion by cultured chicken myoblasts were observed only after the onset of myoblast fusion. Double-immunofluorescence staining of these cultured cells revealed that multinucleate myotubes were stained by antibodies directed against both the Ex-FABP and the sarcomeric myosin, whereas immature myotubes and single myoblasts were not. When added to cultured myoblasts, antibodies against the Ex-FABP induced a strong enhancement of the production of the same protein. In all experiments some cell sufferance and a transient impairment of myotube formation were also observed. The finding that the continuous removal of the Ex-FABP from the culture medium of myoblasts, due to the formation of immune complexes, resulted in an overproduction of the protein suggests a feedback (autocrine) control during myotube differentiation and maturation. We propose that the requirement for increased transport and metabolism of free fatty acid released from the membrane phospholipids and storage lipids, mediated by Ex-FABP, may be essential during differentiation of multinucleated myotubes or that an increased local demand of fatty acids and metabolites may act as a local hormone in tissues differentiating and undergoing morphogenesis.