The mammalian fatty acid-binding protein multigene family: molecular and genetic insights into function

Localization of fatty acid binding protein of epidermal type common to dendritic cells and presumptive macrophages in Peyer's patches and epithelial M cells of mouse intestine

Fatty acid binding protein of epidermal type (E-FABP) was expressed/localized in most, if not all, populations of the dendritic cells in the subepithelial domes, follicles and interfollicular regions of Peyer's patches and presumptive macrophages in their germinal centers, and all M cells in the follicle-associated epithelium of mouse intestine. The immunoreactivity in both of the cell populations makes it easy to recognize the accumulation of DCs in the subepithelial domes in close proximity to the base of M cells, which is essential for luminal antigens to be transported to Peyer's patches. E-FABP may play some important roles in the mucosal immune reaction through Peyer's patches and associated structures.

Probing the fibrate binding specificity of rat liver fatty acid binding protein

Liver-fatty acid binding protein (L-FABP) is found in high levels in enterocytes and is involved in cytosolic solubilization of fatty acids. In addition, L-FABP has been shown to bind endogenous and exogenous lipophilic compounds, suggesting that it may also play a role in modulating their absorption and disposition within enterocytes. Previously, we have described binding of L-FABP to a range of drugs, including a series of fibrates. In the present study, we have generated structural models of L-FABP-fibrate complexes and undertaken thermodynamic analysis of the binding of fibrates containing either a carboxylic acid or ester functionality. Analysis of the current data reveals that both the location and the energetics of binding are different for fibrates that contain a carboxylate compared to those that do not. As such, the data presented in this study suggest potential mechanisms that underpin molecular recognition and dictate specificity in the interaction between fibrates and L-FABP.

Activation of AMP-activated protein kinase (AMPK) inhibits fatty acid synthesis in bovine mammary epithelial cells

Activation of AMP-activated protein kinase (AMPK), a heterotrimeric energy-sensing protein, decreases lipid synthesis in liver tissue of various species; however, little is known about the role of AMPK in the regulation of fatty acid synthesis in bovine mammary epithelial cells. Here we report the presence of AMPK mRNA in MAC-T bovine mammary epithelial cells and mammary gland. Treatment of MAC-T with an AMPK activator dramatically decreased de novo fatty acid synthesis by inactivating acetyl-CoA carboxylase-alpha. Activation of AMPK also modified the mRNA expression of several lipogenic genes including fatty acid synthase, glycerol-3-phosphate acyltransferase, and fatty acid binding protein-3. Additionally, decreases in energy availability or rises in intracellular Ca(2+) most likely activated AMPK in MAC-T. These data suggest the presence of LKB1 and Ca(2+)/calmodulin-dependent kinase kinase, two known AMPK kinases, in MAC-T. Identifying AMPK as a molecular target capable of modifying energy substrate utilization may result in the development of new technologies that increase milk production or modify milk composition during periods of increased energy demand.

Comparison of the folding mechanism of highly homologous proteins in the lipid-binding protein family

The folding mechanism of two closely related proteins in the intracellular lipid-binding protein family, human bile acid-binding protein (hBABP), and rat bile acid-binding protein (rBABP) were examined. These proteins are 77% identical (93% similar) in sequence. Both of these single domain proteins fit well to a two-state model for unfolding by fluorescence and circular dichroism at equilibrium. Three phases were observed during the unfolding of rBABP by fluorescence but only one phase was observed during the unfolding of hBABP, suggesting that at least two kinetic intermediates accumulate during the unfolding of rBABP that are not observed during the unfolding of hBABP. Fluorine NMR was used to examine the equilibrium unfolding behavior of the W49 side chain in 6-fluorotryptophan-labeled rBABP and hBABP. The structure of rBABP appears to be more dynamic than that of hBABP in the vicinity of W49 in the absence of denaturant, and urea has a greater effect on this dynamic behavior for rBABP than for hBABP. As such, the folding behavior of highly sequence related proteins in this family can be quite different. These differences imply that moderately sized proteins with high sequence and structural similarity can still populate quite different structures during folding.

ADRP/ADFP and Mal1 expression are increased in macrophages treated with TLR agonists

Activation of macrophages by TLR agonists enhances foam cell formation, but the underlying mechanisms are not understood. We examined the effects of TLR agonists on ADRP/ADFP, a protein associated with forming lipid droplets, and Mal1 a fatty acid-binding protein, in two mouse macrophage cell lines and human monocytes. Low doses of LPS, a TLR4 agonist increased both mRNA and protein levels of ADRP/ADFP and Mal1 in RAW 264.7 macrophages. Following pretreatment with Intralipid, fatty acids, or acetyl-LDL to increase triglyceride or cholesterol ester storage, LPS treatment still increased ADRP/ADFP and Mal1 mRNA levels. LPS also induced ADRP/ADFP and Mal1 in J774 macrophages and ADRP/ADFP in human monocytes. Zymosan, a fungal product that activates TLR2, poly-I:C, a viral mimetic that activates TLR3, and imiquimod, a TLR7 agonist, also increased ADRP/ADFP. Zymosan, but not poly-I:C or imiquimod, induced Mal1. In contrast, neither gene was induced by TNFalpha, IL-1beta, IL-6, or interferon-gamma. Thus TLR agonists induce ADRP/ADFP and Mal1, which likely contributes to macrophage triglyceride and cholesterol ester storage leading to foam cell formation.

Differential transcriptional modulation of duplicated fatty acid-binding protein genes by dietary fatty acids in zebrafish (Danio rerio): evidence for subfunctionalization or neofunctionalization of duplicated genes

Background

In the Duplication-Degeneration-Complementation (DDC) model, subfunctionalization and neofunctionalization have been proposed as important processes driving the retention of duplicated genes in the genome. These processes are thought to occur by gain or loss of regulatory elements in the promoters of duplicated genes. We tested the DDC model by determining the transcriptional induction of fatty acid-binding proteins (Fabps) genes by dietary fatty acids (FAs) in zebrafish. We chose zebrafish for this study for two reasons: extensive bioinformatics resources are available for zebrafish at zfin.org and zebrafish contains many duplicated genes owing to a whole genome duplication event that occurred early in the ray-finned fish lineage approximately 230-400 million years ago. Adult zebrafish were fed diets containing either fish oil (12% lipid, rich in highly unsaturated fatty acid), sunflower oil (12% lipid, rich in linoleic acid), linseed oil (12% lipid, rich in linolenic acid), or low fat (4% lipid, low fat diet) for 10 weeks. FA profiles and the steady-state levels of fabp mRNA and heterogeneous nuclear RNA in intestine, liver, muscle and brain of zebrafish were determined.

Result

FA profiles assayed by gas chromatography differed in the intestine, brain, muscle and liver depending on diet. The steady-state level of mRNA for three sets of duplicated genes, fabp1a/fabp1b.1/fabp1b.2, fabp7a/fabp7b, and fabp11a/fabp11b, was determined by reverse transcription, quantitative polymerase chain reaction (RT-qPCR). In brain, the steady-state level of fabp7b mRNAs was induced in fish fed the linoleic acid-rich diet; in intestine, the transcript level of fabp1b.1 and fabp7b were elevated in fish fed the linolenic acid-rich diet; in liver, the level of fabp7a mRNAs was elevated in fish fed the low fat diet; and in muscle, the level of fabp7a and fabp11a mRNAs were elevated in fish fed the linolenic acid-rich or the low fat diets. In all cases, induction of the steady-state level of fabp mRNAs by dietary FAs correlated with induced levels of hnRNA for a given fabp gene. As such, up-regulation of the steady-state level of fabp mRNAs by FAs occurred at the level of initiation of transcription. None of the sister duplicates of these fabp genes exhibited an increase in their steady-state transcript levels in a specific tissue following feeding zebrafish any of the four experimental diets.

Conclusion

Differential induction of only one of the sister pair of duplicated fabp genes by FAs provides evidence to support the DDC model for retention of duplicated genes in the zebrafish genome by either subfunctionalization or neofunctionalization.

Regulation of adipose tissue lipolysis revisited

Human obesity and its complications are an increasing burden in developed and underdeveloped countries. Adipose tissue mass and the mechanisms that control it are central to elucidating the aetiology of obesity and insulin resistance. Over the past 15 years tremendous progress has been made in several avenues relating to adipose tissue. Knowledge of the lipolytic machinery has grown with the identification of new lipases, cofactors and interactions between proteins and lipids that are central to the regulation of basal and stimulated lipolysis. The dated idea of an inert lipid droplet has been appropriately revamped to that of a dynamic and highly-structured organelle that in itself offers regulatory control over lipolysis. The present review provides an overview of the numerous partners and pathways involved in adipose tissue lipolysis and their interaction under various metabolic states. Integration of these findings into whole adipose tissue metabolism and its systemic effects is also presented in the context of inflammation and insulin resistance.

Fatty acid binding protein 4 is a target of VEGF and a regulator of cell proliferation in endothelial cells

Fatty acid binding protein 4 (FABP4) plays an important role in maintaining glucose and lipid homeostasis. FABP4 has been primarily regarded as an adipocyte- and macrophage-specific protein, but recent studies suggest that it may be more widely expressed. We found strong FABP4 expression in the endothelial cells (ECs) of capillaries and small veins in several mouse and human tissues, including the heart and kidney. FABP4 was also detected in the ECs of mature human placental vessels and infantile hemangiomas, the most common tumor of infancy and ECs. In most of these cases, FABP4 was detected in both the nucleus and cytoplasm. FABP4 mRNA and protein levels were significantly induced in cultured ECs by VEGF-A and bFGF treatment. The effect of VEGF-A on FABP4 expression was inhibited by chemical inhibition or short-hairpin (sh) RNA-mediated knockdown of VEGF-receptor-2 (R2), whereas the VEGFR1 agonists, placental growth factors 1 and 2, had no effect on FABP4 expression. Knockdown of FABP4 in ECs significantly reduced proliferation both under baseline conditions and in response to VEGF and bFGF. Thus, FABP4 emerged as a novel target of the VEGF/VEGFR2 pathway and a positive regulator of cell proliferation in ECs.

A novel polymorphism in the chicken adipocyte fatty acid-binding protein gene (FABP4) that alters ligand-binding and correlates with fatness

Similar to the mammalian FABP4 gene, the chicken (Gallus gallus) FABP4 gene consists of four exons separated by three introns and encodes a 132 amino acid protein termed the adipocyte fatty acid-binding protein (AFABP). In the current study, a novel G/A polymorphism in exon 3 of the chicken FABP4 gene was identified associated with different chicken breeds that leads to either Ser or Asn at amino acid 89 of the AFABP protein. The Baier chicken averages 0.89+/-0.12% abdominal fat and expresses the G allele (Ser 89 isoform) while the Broiler chicken typically has 3.74+/-0.23% abdominal fat and expresses the A allele (Asn 89 isoforms). cDNAs corresponding to the two AFABP isoforms were cloned and expressed in Escherichia coli as GST fusions, purified by using glutathione sepharose 4B chromatography and evaluated for lipid binding using the fluorescent surrogate ligand 1-anilinonaphthalene 8-sulphonic acid (1,8-ANS). The results showed that AFABP Ser89 exhibited a lower ligand-binding affinity with apparent dissociation constants (Kd) of 7.31+/-3.75 microM, while the AFABP Asn89 isoform bound 1,8-ANS with an apparent dissociation constant of 2.99+/-1.00 microM (P=0.02). These results suggest that the Ser89Asn polymorphism may influence chicken AFABP function and ultimately lipid deposition through changing the ligand-binding activity of AFABP.

Early left ventricular gene expression profile in response to increase in blood pressure

The heart adapts to increased pressure overload by hypertrophic growth of terminally differentiated cardiomyocytes. At the genetic level, the hypertrophic response is characterized by the reprogramming of gene expression, i.e. upregulation of immediate early genes, natriuretic peptide genes and genes encoding structural proteins. In the present study, we characterized the early changes in gene expression with cDNA expression arrays in response to increase in blood pressure produced by arginine8-vasopressin infusion (0.05 microg/kg/min, i.v.) for 30 min and 4 h in conscious normotensive rats. Expression profiling revealed differential expression of 14 genes in the left ventricle, and several novel factors of immediate early genetic response to pressure overload were identified, such as growth arrest and DNA damage inducible protein 45 (GADD45alpha), epidermal fatty acid-binding protein (E-FABP) and Bcl-X. Administration of angiotensin II (Ang II) for 6 h by osmotic minipumps also increased left ventricular GADD45alpha, E-FABP and Bcl-X gene expression. Furthermore, the induction of GADD45alpha and Bcl-X gene expression by Ang II was blocked by angiotensin II type 1 receptor antagonist losartan. In summary, our analysis provided new insights into the pathogenesis of pressure overload-induced hypertrophy by suggesting the existence of novel regulators of the immediate early gene expression program.

Regulation of Th17 differentiation by epidermal fatty acid-binding protein

Epidermal fatty acid-binding protein, E-FABP, a lipid chaperone, has been shown to regulate the inflammatory function of macrophages and dendritic cells. Herein, we demonstrate that T cell expression of E-FABP promotes Th17 differentiation, while counterregulating development of FoxP3(+) regulatory T cells (Tregs). In response to immunization with myelin oligodendrocyte glycoprotein peptide (MOG(35-55)), E-FABP-deficient mice generated reduced levels of Th17 cells and elevated levels of Tregs, as compared with wild-type mice. Likewise, naive CD4(+) T cells isolated from E-FABP-deficient mice showed reduced expression of IL-17 and enhanced expression of FoxP3, in vitro, when subjected to Th17 or Treg polarizing conditions, respectively. It has been demonstrated previously that IL-21, induced by IL-6, stimulates the expression of the nuclear receptors retinoic acid-related orphan receptor (ROR)gammat and RORalpha, which in turn induce expression of IL-17. We found that the impaired Th17 differentiation by E-FABP-deficient CD4(+) T cells was associated with lower levels of IL-21 expression in response to IL-6, as well as reduced expression of RORgammat and RORalpha. However, E-FABP-deficient CD4(+) T cells expressed significantly higher levels of the nuclear receptor peroxisome proliferator-activating receptor (PPAR)gamma than did wild-type CD4(+) T cells, and treatment with the PPARgamma antagonist GW9662 restored expression of IL-21, RORgammat, RORalpha, and IL-17 by E-FABP-deficient T cells to wild-type levels. The negative influence of E-FABP deficiency on IL-17 expression was attributed to PPARgamma-mediated suppression of IL-6-induced STAT3 activity. Thus, taken together, our data indicate that expression of E-FABP by CD4(+) T cells contributes to the control of IL-6 stimulation of the IL-21/ROR/IL-17 pathway and to the Th17/Treg counterbalance.

Thr54 allele of fatty-acid binding protein 2 gene is associated with obesity but not type 2 diabetes mellitus in a Caucasian population

AIM

The fatty acid-binding protein 2 (FABP2) A54T polymorphism has been associated with type 2 diabetes mellitus (T2DM) and obesity in many but not all studies. Our aim was to investigate possible associations of FABP2 A54T polymorphism with T2DM and/or obesity in a Greek Caucasian population.

METHODS

242 subjects with T2DM and 188 control subjects were genotyped for the FABP2 A54T polymorphism using PCR-RFLP method. Of the total subjects included in both groups, 172 were classified as obese (BMI >or= 30 kg/m(2)) and 258 were classified as nonobese (BMI <30 kg/m(2)).

RESULTS

In the whole population, 218 subjects (50.7%) were genotyped as AA, 175 subjects (40.7%) as AT, and 37 subjects (8.6%) as TT for the FABP2 A54T polymorphism. According to the dominant model, the frequency of AA genotype was significantly lower in obese than in nonobese subjects (43.0% vs 55.8%, p=0.009). No significant difference was observed in genotypes between diabetic and nondiabetic subjects. According to the additive model, the presence of TT genotype was significantly associated with obesity after adjusting for age, sex, and the presence of T2DM (OR 2.32, p=0.028).

CONCLUSION

FABP2 A54T polymorphism may help identify Caucasian subjects at risk for obesity.

Interaction of adipocyte fatty acid-binding protein (AFABP) and JAK2: AFABP/aP2 as a regulator of JAK2 signaling

Adipocyte fatty acid-binding protein (AFABP/aP2) facilitates the intracellular solubilization and trafficking of lipids within the aqueous environment of the cell. Studies in the AFABP/aP2 knock-out mouse suggest that the protein may have roles in cellular processes broader than lipid transport. We present herein the finding that AFABP/aP2 interacts with JAK2 in a fatty acid-dependent manner. This interaction was established using yeast two-hybrid analysis, co-immunoprecipitation from adipose tissue, and 3T3-L1 adipocytes as well as in 293 cells overexpressing JAK2 and AFABP/aP2. Mutational analysis of AFABP/aP2 (R126L/Y128F) revealed that fatty acid binding activity is necessary for the interaction and that Asp(18) of the helix-turn-helix motif forms a component of the interaction domain. Mutational analysis of JAK2 (Y1007F/Y1008F) revealed that AFABP/aP2 associates with the basal unphosphorylated form of the protein. Interleukin-6, but not interleukin-10, stimulated phosphorylation of STAT3, and induction of SOCS3 mRNA expression were potentiated in a time- and dose-dependent manner in macrophage cell lines derived from AFABP/aP2-EFABP/mal1 double knock-out mice relative to cells from wild type animals. These results suggest that ligand-bound AFABP/aP2 binds to and attenuates JAK2 signaling and establishes a new role for AFABP/aP2 as a fatty acid sensor affecting cellular metabolism via protein-protein interactions.

Gene expression profiles of rat olfactory bulb at developmental stage

Microarray analysis may be a useful tool to identify some candidate genes related to the development of olfactory bulbs. In the present study, gene expression profiles of olfactory bulbs from postnatal day 1 (P1) rats and postnatal day 35 (P35) rats were analyzed by oligonucleotide-microarray and expression levels of some selected genes were also confirmed by RT-PCR and in situ hybridization. 9146 genes were commonly identified in six microarray chips. Among these genes, 76 were up-regulated and 130 were down-regulated three-folds or more at P1 olfactory bulbs. Out of these 76 up-regulated genes, 24 genes were annotated based on the NCBI database of reference sequences and expression levels of these 24 genes were confirmed by RT-PCR. Among them, 2 interesting genes (neurogenic differentiation 1 and retinoid acid receptor alpha) were localized in the P1 olfactory bulb by the use of in situ hybridization technique. Our results may provide basic information to identify genes associated with functional growth of olfactory bulbs.

Serum adipocyte fatty acid-binding protein levels are associated with nonalcoholic fatty liver disease in type 2 diabetic patients

OBJECTIVE

Adipocyte fatty acid-binding protein (A-FABP) is a major cytoplasmic protein in adipocytes and macrophages and is closely associated with metabolic syndrome, type 2 diabetes, and atherosclerosis. Here, we investigated whether A-FABP was associated with nonalcoholic fatty liver disease (NAFLD) in type 2 diabetes.

RESEARCH DESIGN AND METHODS

We enrolled 181 type 2 diabetic patients. Clinical and biochemical metabolic parameters were measured. The severity of NAFLD was measured by ultrasound. A-FABP, adiponectin, and retinol-binding protein-4 (RBP-4) were determined by enzyme-linked immunosorbent assay.

RESULTS

A-FABP levels, defined as more than a moderate degree of fatty liver compared with men, those without metabolic syndrome, and those without NAFLD, were higher in women, patients with metabolic syndrome, and patients with overt NAFLD, respectively. Adiponectin was decreased according to the severity of NAFLD, but RBP-4 showed no difference. Age- and sex-adjusted A-FABP showed positive correlations with BMI, waist-to-hip ratio, waist circumference, triglycerides, gamma-glutamyltransferase, fasting insulin, homeostasis model assessment of insulin resistance (HOMA-IR), A1C, and C-reactive protein (CRP) but showed negative correlation with HDL cholesterol. The odds ratio (OR) for the risk of overt NAFLD with increasing levels of sex-specific A-FABP was significantly increased (OR 2.90 [95% CI 1.15-7.29] vs. 7.87 [3.20-19.38]). The OR in the highest tertile of A-FABP remained significant after adjustments for BMI, waist circumference, A1C, HDL cholesterol, triglycerides, HOMA-IR, CRP, and hepatic enzymes.

CONCLUSIONS

Our study demonstrates that serum A-FABP is significantly associated with NAFLD in type 2 diabetes, independent of BMI, waist circumference, HOMA-IR, A1C, triglycerides, HDL cholesterol, and CRP.

Cellular retinol-binding protein type III is a PPARgamma target gene and plays a role in lipid metabolism

Cellular retinol-binding protein (CRBP) type III (CRBP-III) belongs to the family of intracellular lipid-binding proteins, which includes the adipocyte-binding protein aP2. In the cytosol, CRBP-III binds retinol, the precursor of retinyl ester and the active metabolite retinoic acid. The goal of the present work is to understand the regulation of CRBP-III expression and its role in lipid metabolism. Using EMSAs, luciferase reporter assays, and chromatin immunoprecipitation assays, we found that CRBP-III is a direct target of peroxisome proliferator-activated receptor-gamma (PPARgamma). Moreover, CRBP-III expression was induced in adipose tissue of mice after treatment with the PPARgamma agonist rosiglitazone. To examine a potential role of CRBP-III in regulating lipid metabolism in vivo, CRBP-III-deficient (C-III-KO) mice were maintained on a high-fat diet (HFD). Hepatic steatosis was decreased in HFD-fed C-III-KO compared with HFD-fed wild-type mice. These differences were partly explained by decreased serum free fatty acid levels and decreased free fatty acid efflux from adipose tissue of C-III-KO mice. In addition, the lack of CRBP-III was associated with reduced food intake, increased respiratory energy ratio, and altered body composition, with decreased adiposity and increased lean body mass. Furthermore, expression of genes involved in mitochondrial fatty acid oxidation in brown adipose tissue was increased in C-III-KO mice, and C-III-KO mice were more cold tolerant than wild-type mice fed an HFD. In summary, we demonstrate that CRBP-III is a PPARgamma target gene and plays a role in lipid and whole body energy metabolism.

Changes induced by dietary energy intake and divergent selection for muscle fat content in rainbow trout (Oncorhynchus mykiss), assessed by transcriptome and proteome analysis of the liver

BACKGROUND

Growing interest is turned to fat storage levels and allocation within body compartments, due to their impact on human health and quality properties of farm animals. Energy intake and genetic background are major determinants of fattening in most animals, including humans. Previous studies have evidenced that fat deposition depends upon balance between various metabolic pathways. Using divergent selection, we obtained rainbow trout with differences in fat allocation between visceral adipose tissue and muscle, and no change in overall body fat content. Transcriptome and proteome analysis were applied to characterize the molecular changes occurring between these two lines when fed a low or a high energy diet. We focused on the liver, center of intermediary metabolism and the main site for lipogenesis in fish, as in humans and most avian species.

RESULTS

The proteome and transcriptome analyses provided concordant results. The main changes induced by the dietary treatment were observed in lipid metabolism. The level of transcripts and proteins involved in intracellular lipid transport, fatty acid biosynthesis and anti-oxidant metabolism were lower with the lipid rich diet. In addition, genes and proteins involved in amino-acid catabolism and proteolysis were also under expressed with this diet. The major changes related to the selection effect were observed in levels of transcripts and proteins involved in amino-acid catabolism and proteolysis that were higher in the fat muscle line than in the lean muscle line.

CONCLUSION

The present study led to the identification of novel genes and proteins that responded to long term feeding with a high energy/high fat diet. Although muscle was the direct target, the selection procedure applied significantly affected hepatic metabolism, particularly protein and amino acid derivative metabolism. Interestingly, the selection procedure and the dietary treatment used to increase muscle fat content exerted opposite effects on the expression of the liver genes and proteins, with little interaction between the two factors. Some of the molecules we identified could be used as markers to prevent excess muscle fat accumulation.

The X-ray structure of zebrafish (Danio rerio) ileal bile acid-binding protein reveals the presence of binding sites on the surface of the protein molecule

The ileal bile acid-binding proteins (I-BABPs), also called ileal lipid-binding proteins or gastrotropins, belong to the family of the fatty acid-binding proteins and play an important role in the solubilization and transport of bile acids in the enterocyte. This article describes the expression, purification, crystallization, and three-dimensional structure determination of zebrafish (Danio rerio) I-BABP both in its apo form and bound to cholic acid. This is the first X-ray structure of an I-BABP. The structure of the apoprotein was determined to a resolution of 1.6 A, and two different monoclinic crystal forms of the holoprotein were solved and refined to 2.2 A resolution. Three protein molecules are present in the asymmetric unit of one of the co-crystal forms and two in the other, and therefore, the results of this study refer to observations made on five different protein molecules in the crystalline state. In every case, two cholate ligands were found bound in approximately the same position in the internal cavity of the protein molecules, but an unexpected result is the presence of clear and unambiguous electron density for several cholate molecules bound on hydrophobic patches on the surface of all the five independent protein molecules examined. Isothermal titration calorimetry was used for the thermodynamic characterization of the binding mechanism and has yielded results that are consistent with the X-ray data. Ligand binding is described in detail, and the conformational changes undergone by the protein molecule in the apo-to-holo transition are examined by superposition of the apo- and holoprotein models. The structure of the holoprotein is also compared with that of the liver BABP from the same species and those of other I-BABPs determined by NMR.

The emerging functions and mechanisms of mammalian fatty acid-binding proteins

Fatty acid-binding proteins (FABPs) are abundant intracellular proteins that bind long-chain fatty acids with high affinity. Nine separate mammalian FABPs have been identified, and their tertiary structures are highly conserved. The FABPs have unique tissue-specific distributions that have long suggested functional differences among them. In the last decade, considerable progress has been made in understanding the specific functions of the FABPs and, in some cases, their mechanisms of action at the molecular level. The FABPs appear to be involved in the extranuclear compartments of the cell by trafficking their ligands within the cytosol via interactions with organelle membranes and specific proteins. Several members of the FABP family have been shown to function directly in the regulation of cognate nuclear transcription factor activity via ligand-dependent translocation to the nucleus. This review will focus on these emerging functions and mechanisms of the FABPs, highlighting the unique functional properties of each as well as the similarities among them.

Liver-type fatty acid-binding protein and lipid transport

Liver-type fatty acid-binding protein (L-FABP), a member of the genetically related cytosolic fatty acid binding protein (FABP) family, has both similar and different function and conformation compared with other family members. L-FABP, which is mainly found in liver and small intestine, participates in transporting fatty acids and combining a variety of hydrophobic group and is associated with many diseases. In recent years, the transfer mechanism of L-FABP was attracting great attention, and the research methods were developed from in vitro to in vivo, and from cell molecular level to gene ablation animals. Although a part of the mechanism has been revealed, the research should be continued to demonstrate it in deepth and resolve some new questions. This article aims to review the characteristics, conformation and in vivo study status of L-FABP.

Spatio-temporal distribution of fatty acid-binding protein 6 (fabp6) gene transcripts in the developing and adult zebrafish (Danio rerio)

We have determined the structure of the fatty acid-binding protein 6 (fabp6) gene and the tissue-specific distribution of its transcripts in embryos, larvae and adult zebrafish (Danio rerio). Like most members of the vertebrate FABP multigene family, the zebrafish fabp6 gene contains four exons separated by three introns. The coding region of the gene and expressed sequence tags code for a polypeptide of 131 amino acids (14 kDa, pI 6.59). The putative zebrafish Fabp6 protein shared greatest sequence identity with human FABP6 (55.3%) compared to other orthologous mammalian FABPs and paralogous zebrafish Fabps. Phylogenetic analysis showed that the zebrafish Fabp6 formed a distinct clade with the mammalian FABP6s. The zebrafish fabp6 gene was assigned to linkage group (chromosome) 21 by radiation hybrid mapping. Conserved gene synteny was evident between the zebrafish fabp6 gene on chromosome 21 and the FABP6/Fabp6 genes on human chromosome 5, rat chromosome 10 and mouse chromosome 11. Zebrafish fabp6 transcripts were first detected in the distal region of the intestine of embryos at 72 h postfertilization. This spatial distribution remained constant to 7-day-old larvae, the last stage assayed during larval development. In adult zebrafish, fabp6 transcripts were detected by RT-PCR in RNA extracted from liver, heart, intestine, ovary and kidney (most likely adrenal tissue), but not in RNA from skin, brain, gill, eye or muscle. In situ hybridization of a fabp6 riboprobe to adult zebrafish sections revealed intense hybridization signals in the adrenal homolog of the kidney and the distal region of the intestine, and to a lesser extent in ovary and liver, a transcript distribution that is similar, but not identical, to that seen for the mammalian FABP6/Fabp6 gene.

The evolutionary relationship between the duplicated copies of the zebrafish fabp11 gene and the tetrapod FABP4, FABP5, FABP8 and FABP9 genes

We describe the structure of a fatty acid-binding protein 11 (fabp11b) gene and its tissue-specific expression in zebrafish. The 3.4 kb zebrafish fabp11b is the paralog of the previously described zebrafish fabp11a, with a deduced amino acid sequence for Fabp11B exhibiting 65% identity with that of Fabp11A. Whole mount in situ hybridization of a riboprobe to embryos and larvae showed that zebrafish fabp11b transcripts were restricted solely to the retina and were first detected at 24 h postfertilization. In situ hybridization revealed fabp11b transcripts along the spinal cord in adult zebrafish. However, the highly sensitive RT-PCR assay detected fabp11b transcripts in the brain, heart, ovary and eye in adult tissues. By contrast, fabp11a transcripts had been previously detected in the liver, brain, heart, testis, muscle, ovary and skin of adult zebrafish. Using the LN54 radiation hybrid panel, we assigned zebrafish fabp11b to linkage group 16. Phylogenetic analysis and conserved gene synteny with tetrapod genes indicated that the emergence of two copies of fabp11 in the zebrafish genome may have resulted from a fish-specific whole genome duplication event. Furthermore, we propose that the FABP4-FABP5-FABP8-FABP9 (PERF15) gene cluster on a single chromosome in the tetrapod genome and the fabp11 genes in the zebrafish genome originated from a common ancestral gene, which, following their divergence, gave rise to the fabp11 genes of zebrafish, and the progenitor of the FABP4, FABP5, FABP8 and FABP9 genes in tetrapods after the separation of the fish and tetrapod lineages.

A protocol for the combined sub-fractionation and delipidation of lipid binding proteins using hydrophobic interaction chromatography

Cellular lipids frequently co-purify with lipid binding proteins isolated from tissue extracts or heterologous host systems and as such hinder in vitro ligand binding approaches for which the apo-protein is a prerequisite. Here we present a technique for the complete removal of unesterified fatty acids, phospholipids, steroids and other lipophilic ligands bound to soluble proteins, without protein denaturation. Peroxisome proliferator activated receptor gamma ligand binding domain and intracellular fatty acid binding proteins were expressed in an Escherichia coli host and completely delipidated by hydrophobic interaction chromatography using phenyl sepharose. The delipidation procedure operates at room temperature with complete removal of bound lipids in a single step, as ascertained by mass spectrometry analysis of organic solvent extracts from purified protein samples. The speed and capacity of this method makes it amenable to scale-up and high-throughput applications. The method can also easily be adapted for other lipid binding proteins that require delipidation under native conditions.

The interaction of liver fatty-acid-binding protein (FABP) with anionic phospholipid vesicles: is there extended phospholipid anchorage under these conditions?

Liver FABP (fatty-acid-binding protein) binds a variety of non-polar anionic ligands including fatty acids, fatty acyl CoAs, lysophospholipids and bile acids. Liver FABP is also able to bind to anionic phospholipid vesicles under conditions of low ionic strength, and membrane binding results in the release of bound ligand. However, the molecular interactions involved in binding to the phospholipid interface and the mechanism of ligand release are not known. Ligand release could be due to a significant conformational change in the protein at the interface or interaction of a phospholipid molecule with the ligand-binding cavity of the protein resulting in ligand displacement. Two portal mutant proteins of liver FABP, L28W and M74W, have now been used to investigate the binding of liver FABP to anionic phospholipid vesicles, monitoring changes in fluorescence and also fluorescence quenching in the presence of brominated lipids. There is a large increase in fluorescence intensity when the L28W mutant protein binds to vesicles prepared from DOPG (dioleoyl-sn-phosphatidylglycerol), but a large decrease in fluorescence intensity when the M74W mutant binds to these vesicles. The Br(4)-phospholipid prepared by bromination of DOPG dramatically quenches both L28W and M74W, consistent with the close proximity of a fatty acyl chain to the tryptophan residues. The binding of liver FABP to DOPG vesicles is accompanied by only a minimal change in the CD spectrum. Overall, the results are consistent with a molecule of anionic phospholipid interacting with the central cavity of the liver FABP, possibly involving the phospholipid molecule in an extended conformation.

Adipocyte/macrophage fatty acid binding proteins in metabolic syndrome

The link between inflammation and the development of insulin resistance, type 2 diabetes, and atherosclerosis has been uncovered in the past decade. Although the molecular mechanisms underlying the co-occurrence of these metabolic and inflammatory diseases are not fully understood, several molecular players, integrating stress and inflammatory responses with metabolic homeostasis, were discovered recently. One of these molecular integration sites is through the action of cytosolic lipid chaperones or fatty acid binding proteins (FABPs), which are common to adipocytes and macrophages. Furthermore, studies in a variety of genetic models demonstrated that the FABPs aP2 and mal1 are critical mediators of many components of metabolic syndrome in mice. These exciting findings raise the possibility that FABPs represent desirable therapeutic targets for metabolic syndrome. In this review, we describe the findings demonstrating FABP's role in metabolic and inflammatory diseases and highlight recent advances in understanding the mechanisms of FABP function at the cellular and molecular level.

Docosahexaenoic acid (DHA) and hepatic gene transcription

The type and quantity of dietary fat ingested contributes to the onset and progression of chronic diseases, like diabetes and atherosclerosis. The liver plays a central role in whole body lipid metabolism and responds rapidly to changes in dietary fat composition. Polyunsaturated fatty acids (PUFA) play a key role in membrane composition and function, metabolism and the control of gene expression. Certain PUFA, like the n-3 PUFA, enhance hepatic fatty acid oxidation and inhibit fatty acid synthesis and VLDL secretion, in part, by regulating gene expression. Our studies have established that key transcription factors, like PPARalpha, SREBP-1, ChREBP and MLX, are regulated by n-3 PUFA, which in turn control levels of proteins involved in lipid and carbohydrate metabolism. Of the n-3 PUFA, 22:6,n-3 has recently been established as a key controller of hepatic lipid synthesis. 22:6,n-3 controls the 26S proteasomal degradation of the nuclear form of SREBP-1. SREBP-1 is a major transcription factor that controls the expression of multiple genes involved fatty acid synthesis and desaturation. 22:6,n-3 suppresses nuclear SREBP-1, which in turn suppresses lipogenesis. This mechanism is achieved, in part, through control of the phosphorylation status of protein kinases. This review will examine both the general features of PUFA-regulated hepatic gene transcription and highlight the unique mechanisms by which 22:6,n-3 impacts gene expression. The outcome of this analysis will reveal that changes in hepatic 22:6,n-3 content has a major impact on hepatic lipid and carbohydrate metabolism. Moreover, the mechanisms involve 22:6,n-3 control of several well-known signaling pathways, such as Akt, Erk1/2, Gsk3beta and PKC (novel or atypical). 22:6,n-3 control of these same signaling pathways in non-hepatic tissues may help to explain the diverse actions of n-3 PUFA on such complex physiological processes as visual acuity and learning.

Adipocyte fatty acid-binding protein in obese children before and after weight loss

Adipocyte fatty acid-binding protein (A-FABP) has been reported to be increased in obese adults and to be related to metabolic syndrome. Because studies concerning A-FABP in weight loss are limited and studies in obese children are missing, we analyzed A-FABP in obese children before and after weight loss. Fasting serum A-FABP, leptin, insulin, glucose, triglycerides, low-and high-density lipoprotein cholesterol, high-sensitivity C-reactive protein, and tumor necrosis factor alpha concentrations as markers of the metabolic syndrome, and weight status (body mass index and percentage body fat based on skinfold measurements) were determined in 30 obese children (median age, 11.9 years) before and after participating in a 1-year obesity intervention. Furthermore, A-FABP levels were measured in 10 nonobese children of similar age, sex, and pubertal stage. Obese children had significantly (P < .001) higher A-FABP concentrations compared with nonobese children. In backward multivariate linear regression analysis, A-FABP correlated significantly (P < .05) with percentage body fat and leptin, but not with any of the markers of the metabolic syndrome. Changes of A-FABP concentrations correlated significantly with changes of percentage body fat (r = 0.53, P = .001) and leptin (r = 0.55, P < .001), but not with any changes of parameters of the metabolic syndrome. Substantial weight loss in 10 children led to a significant (P < .05) decrease in A-FABP levels in contrast to the 20 children without change of weight status. In cross-sectional as well as longitudinal analyses, A-FABP levels were related to weight status and leptin levels. Further longitudinal studies are necessary to study the relationship between A-FABP concentrations and parameters of the metabolic syndrome.

The fatty acid binding protein-4 (FABP4) is a strong biomarker of metabolic syndrome and lipodystrophy in HIV-infected patients

BACKGROUND

The incidence of metabolic abnormalities in HIV-infected patients is increasing. Fatty acid binding protein-4 (FABP4) is an emerging biomarker for metabolic-related disturbances. We aimed to study FABP4 as a marker of metabolic syndrome (MS) or lipodystrophy (LD) in HIV patients.

METHODS

FABP4 plasma concentrations were measured by enzyme-linked immunoassays in 183 HIV-infected patients, enrolled as part of a study aimed at identifying predictors of atherosclerosis. The presence of MS or LD was diagnosed according to standard clinical methods. Univariate and multivariate statistical analyses were performed.

RESULTS

FABP4 concentration was significantly higher in those patients with either MS or LD criteria than those without any metabolic disturbance. Similarly, FABP4 concentration significantly increased with an increasing of MS features and was strongly correlated with body-mass index, triglycerides, HDL-cholesterol concentrations, insulin and blood pressure. Patients in the highest quartile of FABP4 presented a six-fold increased odds ratio for MS and a three-fold increased odds for LD, adjusted by age, sex, body-mass index and the antiretroviral therapy.

CONCLUSIONS

FABP4 is a strong plasma marker of metabolic disturbances in HIV-infected patients, and therefore, could serve to guide therapeutic intervention in this group of patients.

Serum adipocyte fatty acid binding protein as a new biomarker predicting the development of type 2 diabetes: a 10-year prospective study in a Chinese cohort

OBJECTIVE

Adipocyte fatty acid-binding protein (A-FABP) is abundantly expressed in adipocytes and plays a role in glucose homeostasis in experimental animals. We have previously shown that circulating A-FABP levels are associated with the metabolic syndrome, which confers an increased risk of type 2 diabetes. Here we investigated whether serum A-FABP levels could predict the development of diabetes in a 10-year prospective study.

RESEARCH DESIGN AND METHODS

Baseline serum A-FABP levels were measured with an enzyme-linked immunosorbent assay in 544 nondiabetic subjects, recruited from the Hong Kong Cardiovascular Risk Factor Prevalence Study cohort, who were followed prospectively to assess the development of type 2 diabetes. The role of A-FABP in predicting the development of type 2 diabetes over 10 years was investigated using Cox regression analysis.

RESULTS

At baseline, serum sex-adjusted A-FABP levels were higher in subjects with impaired glucose tolerance (IGT) or impaired fasting glucose (IFG) (P < 0.00001 versus normal glucose tolerance) and correlated positively with adverse cardiometabolic risk factors. Over 10 years, 96 subjects had developed type 2 diabetes. High baseline A-FABP was predictive of type 2 diabetes, independent of obesity, insulin resistance, or glycemic indexes (relative risk [RR] 2.25 [95% CI 1.40-3.65]; P = 0.001; above versus below sex-specific median). High A-FABP levels remained an independent predictor of type 2 diabetes in the high-risk IGT/IFG subgroup (adjusted RR 1.87 [1.12-3.15]; P = 0.018).

CONCLUSIONS

Serum A-FABP was associated with glucose dysregulation and predicted the development of type 2 diabetes in a Chinese cohort.

Loss of intestinal fatty acid binding protein increases the susceptibility of male mice to high fat diet-induced fatty liver

Mice lacking I-FABP (encoded by the Fabp2 gene) exhibit a gender dimorphic response to a high fat/cholesterol diet challenge characterized by hepatomegaly in male I-FABP-deficient mice. In this study, we determined if this gender-specific modification of liver mass in mice lacking I-FABP is attributable to the high fat content of the diet alone and whether hepatic Fabp1 gene (encodes L-FABP) expression contributes to this difference. Wild-type and Fabp2-/- mice of both genders were fed a diet enriched with either polyunsaturated or saturated fatty acids (PUFA or SFA, respectively) in the absence of cholesterol. Male Fabp2-/- mice, but not female Fabp2-/- mice, exhibited increased liver mass and hepatic triacylglycerol (TG) deposition as compared to corresponding wild-type mice. In wild-type mice that were fed the standard chow diet, there was no difference in the concentration of hepatic L-FABP protein between males and females although the loss of I-FABP did cause a slight reduction of hepatic L-FABP abundance in both genders. The hepatic L-FABP mRNA abundance in both male and female wild-type and Fabp2-/- mice was higher in the PUFA-fed group than in the SFA-fed group, and was correlated with L-FABP protein abundance. No correlation between hepatic L-FABP protein abundance and hepatic TG concentration was found. The results obtained demonstrate that loss of I-FABP renders male mice sensitive to high fat diet-induced fatty liver, and this effect is independent of hepatic L-FABP.

Plasma adipocyte and epidermal fatty acid binding protein is reduced after weight loss in obesity

AIM

Plasma adipocyte fatty acid binding protein (A-FABP) and epidermal fatty acid binding protein (E-FABP) concentrations have been linked to obesity and the metabolic syndrome. In this study, we investigated whether plasma A-FABP and E-FABP concentrations are altered by weight loss in obese patients.

METHODS

In a prospective study, fasting plasma A-FABP and E-FABP concentrations were measured before and 6 months after gastric banding in 33 morbidly obese patients, with a body mass index (BMI) of 46 +/- 5 kg/m(2). Eleven healthy subjects with a BMI < 25 kg/m(2) served as controls.

RESULTS

A-FABP and E-FABP plasma concentrations were higher in obese subjects (36.7 +/- 6.7 and 3.7 +/- 0.7 ng/ml, respectively) than in controls (18.1 +/- 0.6 and 2.6 +/- 0.5, respectively, p < 0.01). Gastric banding reduced BMI to 40 +/- 5 kg/m(2), A-FABP to 32.6 +/- 5.4 ng/ml and E-FABP to 1.9 +/- 0.7 ng/ml (all p < 0.05) after 6 months. Insulin sensitivity as estimated by the Homeostasis Model Assessment insulin resistance index was unchanged. A-FABP concentrations were significantly associated with BMI before and 6 months after surgery (p < 0.05, r = 0.42 and r = 0.37 respectively).

CONCLUSIONS

Elevated plasma A-FABP and E-FABP concentrations in morbidly obese subjects are reduced after gastric banding-induced weight loss. This suggests that FABP may be associated with improvement of metabolic conditions over time.

High Transcript Level of Fatty Acid-Binding Protein 11 but Not of Very Low-Density Lipoprotein Receptor Is Correlated to Ovarian Follicle Atresia in a Teleost Fish (Solea senegalensis)1

Transcripts encoding a fatty acid-binding protein (FABP), Fabp11, and two isoforms of very low-density lipoprotein receptor (Vldlr; vitellogenin receptor) were characterized from the ovary of Senegalese sole (Solea senegalensis). Phylogenetic analyses of vertebrate FABPs demonstrated that Senegalese sole Fabp11, as zebrafish (Danio rerio) homologous sequences, is part of a newly defined teleost fish FABP subfamily that is a sister clade of tetrapod FABP4/FABP5/FABP8/FABP9. RT-PCR revealed high levels of vldlr transcript splicing variants in the ovaries and, to a lesser extent, in somatic tissues, whereas fabp11 was highly expressed in the ovaries, liver, and adipose tissue. In situ hybridization analysis showed vldlr and fabp11 mRNAs in previtellogenic oocytes, whereas no hybridization signals were detected in the larger vitellogenic oocytes. Transcript expression of fabp11 was strongly upregulated in somatic cells surrounding atretic follicles. Real-time quantitative RT-PCR demonstrated that ovarian transcript levels of vldlr and fabp11 had a significant positive correlation with the percentage of follicles in previtellogenesis and atresia, respectively. These results suggest that the expression level of vldlr transcripts may be used as a precocious functional marker to quantify the number of oocytes recruited for vitellogenesis and that fabp11 mRNA may be a very useful molecular marker for determining cellular events and environmental factors that regulate follicular atresia in fish.

Adipocyte- and heart-type fatty acid binding proteins are both expressed in subcutaneous and intramuscular porcine ( Sus scrofa ) adipocytes

Adipocyte- (A) and heart- (H) type fatty acid binding proteins (FABP) contribute to efficient fat storage and utilization, respectively. To understand regional-differences in lipid metabolism between tissues, A- and H-FABP transcript and protein levels were studied in adipocytes isolated from subcutaneous adipose tissue or skeletal muscle in growing pigs (Sus scrofa). Interestingly, H-FABP was expressed in adipocytes isolated from both sites. We also showed that A-FABP and H-FABP were expressed at a lower level in intramuscular adipocytes than in subcutaneous adipocytes. A discrepancy was observed between age-related changes in A-FABP content in isolated adipocytes and cell diameter or lipid content variations in tissues during growth.

Deficiency of fatty acid-binding proteins in mice confers protection from development of experimental autoimmune encephalomyelitis

Fatty acid-binding proteins (FABPs) act as intracellular receptors for a variety of hydrophobic compounds, enabling their diffusion within the cytoplasmic compartment. Recent studies have demonstrated the ability of FABPs to simultaneously regulate metabolic and inflammatory pathways. We investigated the role of adipocyte FABP and epithelial FABP in the development of experimental autoimmune encephalomyelitis to test the hypothesis that these FABPs impact adaptive immune responses and contribute to the pathogenesis of autoimmune disease. FABP-deficient mice exhibited a lower incidence of disease, reduced clinical symptoms of experimental autoimmune encephalomyelitis and dramatically lower levels of proinflammatory cytokine mRNA expression in CNS tissue as compared with wild-type mice. In vitro Ag recall responses of myelin oligodendrocyte glycoprotein 35-55-immunized FABP(-/-) mice showed reduced proliferation and impaired IFN-gamma production. Dendritic cells deficient for FABPs were found to be poor producers of proinflammatory cytokines and Ag presentation by FABP(-/-) dendritic cells did not promote proinflammatory T cell responses. This study reveals that metabolic-inflammatory pathway cross-regulation by FABPs contributes to adaptive immune responses and subsequent autoimmune inflammation.

A single amino acid mutation in zebrafish (Danio rerio) liver bile acid-binding protein can change the stoichiometry of ligand binding

In all of the liver bile acid-binding proteins (L-BABPs) studied so far, it has been found that the stoichiometry of binding is of two cholate molecules per internal binding site. In this paper, we describe the expression, purification, crystallization, and three-dimensional structure determination of zebrafish (Danio rerio) L-BABP to 1.5A resolution, which is currently the highest available for a protein of this family. Since we have found that in zebrafish, the stoichiometry of binding in the protein cavity is of only one cholate molecule per wild type L-BABP, we examined the role of two crucial amino acids present in the binding site. Using site-directed mutagenesis, we have prepared, crystallized, and determined the three-dimensional structure of co-crystals of two mutants. The mutant G55R has the same stoichiometry of binding as the wild type protein, whereas the C91T mutant changes the stoichiometry of binding from one to two ligand molecules in the cavity and therefore appears to be more similar to the other members of the L-BABP family. Based on the presence or absence of a single disulfide bridge, it can be postulated that fish should bind a single cholate molecule, whereas amphibians and higher vertebrates should bind two. Isothermal titration calorimetry has also revealed the presence in the wild type protein and the G55R mutant of an additional binding site, different from the first and probably located on the surface of the molecule.

FABPs as determinants of myocellular and hepatic fuel metabolism

In vitro experiments and expression patterns have long suggested important roles for the genetically related cytosolic fatty acid binding proteins (FABPs) in lipid metabolism. However, evidence for such roles in vivo has become available only recently from genetic manipulation of FABP expression in mice. Here, we summarize the fuel-metabolic phenotypes of mice lacking the genes encoding heart-type FABP (H-/- mice) or liver-type FABP (L-/- mice). Cytosolic extracts from H-/- heart and skeletal muscle and from L-/- liver showed massively reduced binding of long chain fatty acids (LCFA) and, in case of L-/- liver, also of LCFA-CoA. Uptake, oxidation, and esterification LCFA, when measured in vivo and/or ex vivo, were markedly reduced in H-/- heart and muscle and in L-/- liver. The reduced LCFA oxidation in H-/- heart and L-/- liver was not due to reduced activity of PPARa, a fatty acid-sensitive transcription factor that determines the lipid-oxidative capacity in these organs. In H-/- mice, mechanisms of compensation were partially studied and included a redistribution of muscle mitochondria as well as increases of cardiac and skeletal muscle glucose uptakes and of hepatic ketogenesis. In skeletal muscle, the altered glucose uptake included decreased basal but increased insulin-dependent components. Metabolic compensation was only partial, however, since the H-/- mice showed decreased exercise tolerance. In conclusion, the recent studies established H- and L-FABP as major determinants of regional LCFA utilization; therefore the H-/- and L-/- mice are attractive models for studying principles of fuel selection and metabolic homeostasis.

Genetic evidence of a functional monocyte dichotomy

Human peripheral blood monocytes are found as two distinct populations based upon differential expression of chemokine receptors, adhesion molecules, Fc receptors, and cytokines. cDNA microarray analysis now reveals additional differences between these subsets that suggest dramatically diverse functions. One monocyte subset (CD14++CD16-) appears to be closely paired with neutrophils, and may have as its primary function the removal and recycling of apoptotic neutrophils at sites of inflammation. The other monocyte subset (CD14+CD16+) expresses numerous genes encoding proteins with antimicrobial activity and thus may be more directly involved in peripheral host defense. The production of monocytes capable of efficiently removing dying neutrophils may be necessary to prevent host tissue damage and autoimmune response induction. Therefore, species like humans that produce relatively high levels of circulating neutrophils must also produce relatively high numbers of the recycling monocytes. Conversely, species such as mice and rats that maintain relatively lower levels of circulating neutrophils require fewer recycling monocytes.

Treatment of diabetes and atherosclerosis by inhibiting fatty-acid-binding protein aP2

Adipocyte fatty-acid-binding protein, aP2 (FABP4) is expressed in adipocytes and macrophages, and integrates inflammatory and metabolic responses. Studies in aP2-deficient mice have shown that this lipid chaperone has a significant role in several aspects of metabolic syndrome, including type 2 diabetes and atherosclerosis. Here we demonstrate that an orally active small-molecule inhibitor of aP2 is an effective therapeutic agent against severe atherosclerosis and type 2 diabetes in mouse models. In macrophage and adipocyte cell lines with or without aP2, we also show the target specificity of this chemical intervention and its mechanisms of action on metabolic and inflammatory pathways. Our findings demonstrate that targeting aP2 with small-molecule inhibitors is possible and can lead to a new class of powerful therapeutic agents to prevent and treat metabolic diseases such as type 2 diabetes and atherosclerosis.

Examination of the Role of Intestinal Fatty Acid-Binding Protein in Drug Absorption Using a Parallel Artificial Membrane Permeability Assay

Transcellular diffusion across the absorptive epithelial cells (enterocytes) of the small intestine is the main route of absorption for most orally administered drugs. The process by which lipophilic compounds transverse the aqueous environment of the cytoplasm, however, remains poorly defined. In the present study, we have identified a structurally diverse group of lipophilic drugs that display low micromolar binding affinities for a cytosolic lipid-binding protein - intestinal fatty acid-binding protein (I-FABP). Binding to I-FABP significantly enhanced the transport of lipophilic drug molecules across a model membrane, and the degree of transport enhancement was related to both drug lipophilicity and I-FABP binding affinity. These data suggest that intracellular lipid-binding proteins such as I-FABP may enhance the membrane transport of lipophilic xenobiotics and facilitate drug access to the enterocyte cytoplasm and cytoplasmic organelles.

[Correlation of FABP2-A54T polymorphism and the metabolic syndrome in Maros County of Romania]

OBJECTIVE

The FABP2 (intestinal fatty acid-binding protein) gene is expressed in the intestinal epithelial cells and codes for a protein involved in the fatty acid metabolism. We investigated the association of the A54T polymorphism of the FABP2 gene with the metabolic syndrome defined according to the diagnostic criteria recommended by the IDF in 2005, in our region (Marosvásárhely - Tg. Mures, Romania).

RESEARCH DESIGN AND METHODS

A case-control study was carried out on 144 metabolic syndrome patients and 73 healthy persons with similar age and lifestyle. Insulin resistance was measured by the HOMA and QUICKI indices, and gene polymorphism was analyzed with PCR followed by restriction enzyme digestion with Hha I.

RESULTS

The T54 allele was more frequent in the metabolic syndrome group than in controls (35.71% vs. 28.08%, p < 0.05). In the presence of the T54 allele we have noticed a slight but statistically significant risk, more marked in the case of TT homozygotes (TT vs. AT + AA: OR = 4.31, CI 95% 1.21-5.29, p = 0.015 and TT vs. AA: OR = 4.61, CI95%: 1.24-7.03, p = 0.0195). No significant differences of the followed metabolic parameters were observed between persons having different genotypes in the two study groups.

CONCLUSIONS

These results suggest that the FABP2 T54 allele may have a minor contribution to the metabolic syndrome in our region.

Regulation of dendritic cell function and T cell priming by the fatty acid-binding protein AP2

The fatty acid-binding protein (FABP) family consists of a number of conserved cytoplasmic proteins with roles in intracellular lipid transport, storage, and metabolism. Examination of a comprehensive leukocyte gene expression database revealed strong expression of the adipocyte FABP aP2 in human monocyte-derived dendritic cells (DCs). We isolated bone marrow-derived DC from aP2-deficient mice, and showed that expression of DC cytokines including IL-12 and TNF was significantly impaired in these cells. Degradation of IkappaBalpha was also impaired in aP2-deficient DCs, indicative of reduced signaling through the IkappaB kinase-NF-kappaB pathway. The cytokine defect was selective because there was no effect on Ag uptake or expression of MHC class II, CD40, CD80, or CD86. In an MLR, aP2-deficient DCs stimulated markedly lower T cell proliferation and cytokine production than did wild-type DCs. Moreover, aP2-deficient mice immunized with keyhole limpet hemocyanin/CFA showed reduced production of IFN-gamma by restimulated draining lymph node cells, suggesting a similar defect in DC function in vivo. Similarly, infection of aP2-deficient mice with the natural mouse pathogen ectromelia virus resulted in substantially lower production of IFN-gamma by CD8+ T cells. Thus, FABP aP2 plays an important role in DC function and T cell priming, and provides an additional link between metabolic processes and the regulation of immune responses.

Potent and selective biphenyl azole inhibitors of adipocyte fatty acid binding protein (aFABP)

Herein we report the first disclosure of biphenyl azoles that are nanomolar binders of adipocyte fatty acid binding protein (aFABP or aP2) with up to thousand-fold selectivity against muscle fatty acid binding protein and epidermal fatty acid binding protein. In addition a new radio-ligand to determine binding against the three fatty acid binding proteins was also synthesized.

S100A7 (Psoriasin)--mechanism of antibacterial action in wounds

S100A7, also called psoriasin, is a member of the S100 multigene family that is encoded in the epidermal differentiation complex on chromosome 1q21. S100A7 is highly expressed in epidermal hyperproliferative disease; however, its function is not well understood. These studies show high levels of monomer and covalently crosslinked high molecular weight S100A7 in human wound exudate and granulation tissue. Immunohistological studies suggest that this S100A7 is produced by keratinocytes surrounding the wound and is released into the wound exudate. S100A7 is also detected in keratinocyte-conditioned cell culture medium. Studies using recombinant S100A7 indicate that it adheres to and reduces E. coli survival. Mutation of the conserved carboxyl-terminal EF-hand calcium-binding motif or heat denaturation slightly reduces S100A7 antibacterial activity; however, the antibacterial activity is destroyed by protease treatment. Mutation of the zinc-binding motif, located at the C-terminus, reduces antibacterial activity; however, this reduction can be reversed by simultaneous removal of the amino terminus. This indicates the surprising finding that the central region of S100A7, including only amino acids 35-80, is sufficient for full antibacterial activity. These studies also indicate that reduced S100A7 association with bacteria is associated with reduced antibacterial activity.