Mechanisms of regulation of liver fatty acid-binding protein

A versatile delivery vehicle for cellular oxygen and fuels or metabolic sensor? A review and perspective on the functions of myoglobin

A canonical view of the primary physiological function of myoglobin (Mb) is that it is an oxygen (O2) storage protein supporting mitochondrial oxidative phosphorylation, especially as the tissue O2 partial pressure (Po2) drops and Mb off-loads O2. Besides O2 storage/transport, recent findings support functions for Mb in lipid trafficking and sequestration, interacting with cellular glycolytic metabolites such as lactate (LAC) and pyruvate (PYR), and "ectopic" expression in some types of cancer cells and in brown adipose tissue (BAT). Data from Mb knockout (Mb-/-) mice and biochemical models suggest additional metabolic roles for Mb, especially regulation of nitric oxide (NO) pools, modulation of BAT bioenergetics, thermogenesis, and lipid storage phenotypes. From these and other findings in the literature over many decades, Mb's function is not confined to delivering O2 in support of oxidative phosphorylation but may serve as an O2 sensor that modulates intracellular Po2- and NO-responsive molecular signaling pathways. This paradigm reflects a fundamental change in how oxidative metabolism and cell regulation are viewed in Mb-expressing cells such as skeletal muscle, heart, brown adipocytes, and select cancer cells. Here, we review historic and emerging views related to the physiological roles for Mb and present working models illustrating the possible importance of interactions between Mb, gases, and small-molecule metabolites in regulation of cell signaling and bioenergetics.

Tissue-specific transcriptional modulation of fatty acid-binding protein genes, fabp2, fabp3 and fabp6, by fatty acids and the peroxisome proliferator, clofibrate, in zebrafish (Danio rerio)

All fabp genes, except fabp2, fabp3 and fabp6, exist as duplicates in the zebrafish genome owing to a whole genome duplication event ~230-400 million years ago. Transcription of some duplicated fabp genes is modulated by fatty acids (FAs) and/or clofibrate, a peroxisome proliferator-activated receptor (PPAR) agonist. We had also shown previously that the steady-state level of acyl-CoA oxidase 1 (acox1) mRNA, a marker of PPARα activation, was elevated in liver, intestine, heart and muscle of fish fed clofibrate demonstrating that zebrafish, unlike some fishes, is responsive to this drug. acox1 transcripts were not induced in the brain of fish fed clofibrate, which suggests this drug may not cross the blood brain barrier. Here, we investigated the effect of dietary FAs and clofibrate on the transcription of single copy fabp genes, fabp2, fabp3 and fabp6, in five tissues of inbred zebrafish. The steady-state level of fabp2 transcripts increased in intestine, while fabp3 mRNA increased in liver of fish fed diets differing in FA content. In fish fed clofibrate, fabp3 mRNA in intestine, and fabp6 mRNA in intestine and heart, were elevated. Based on these findings, modulation of fabp2, fabp3 and fabp6 transcription by FAs and/or clofibrate in zebrafish implicates control of these genes by PPAR interaction with peroxisome proliferator response elements (PPRE) most likely in fabp promoters. Moreover, transcriptional induction of these fabp genes by dietary FAs and/or clofibrate is over-ridden by a tissue-specific mechanism(s), e.g., transcriptional activator or repressor proteins.

Molecular cloning and functional analysis of the fatty acid-binding protein (Sp-FABP) gene in the mud crab (Scylla paramamosain)

Intracellular fatty acid-binding proteins (FABPs) are multifunctional cytosolic lipid-binding proteins found in vertebrates and invertebrates. In this work, we used RACE to obtain a full-length cDNA of Sp-FABP from the mud crab Scylla paramamosain. The open reading frame of the full length cDNA (886 bp) encoded a 136 amino acid polypeptide that showed high homology with related genes from other species. Real-time quantitative PCR identified variable levels of Sp-FABP transcripts in epidermis, eyestalk, gill, heart, hemocytes, hepatopancreas, muscle, ovary, stomach and thoracic ganglia. In ovaries, Sp-FABP expression increased gradually from stage I to stage IV of development and decreased in stage V. Sp-FABP transcripts in the hepatopancreas and hemocytes were up-regulated after a bacterial challenge with Vibrio alginnolyficus. These results suggest that Sp-FABP may be involved in the growth, reproduction and immunity of the mud crab.

Tissue-specific differential induction of duplicated fatty acid-binding protein genes by the peroxisome proliferator, clofibrate, in zebrafish (Danio rerio)

Background

Force, Lynch and Conery proposed the duplication-degeneration-complementation (DDC) model in which partitioning of ancestral functions (subfunctionalization) and acquisition of novel functions (neofunctionalization) were the two primary mechanisms for the retention of duplicated genes. The DDC model was tested by analyzing the transcriptional induction of the duplicated fatty acid-binding protein (fabp) genes by clofibrate in zebrafish. Clofibrate is a specific ligand of the peroxisome proliferator-activated receptor (PPAR); it activates PPAR which then binds to a peroxisome proliferator response element (PPRE) to induce the transcriptional initiation of genes primarily involved in lipid homeostasis. Zebrafish was chosen as our model organism as it has many duplicated genes owing to a whole genome duplication (WGD) event that occurred ~230-400 million years ago in the teleost fish lineage. We assayed the steady-state levels of fabp mRNA and heterogeneous nuclear RNA (hnRNA) transcripts in liver, intestine, muscle, brain and heart for four sets of duplicated fabp genes, fabp1a/fabp1b.1/fabp1b.2, fabp7a/fabp7b, fabp10a/fabp10b and fabp11a/fabp11b in zebrafish fed different concentrations of clofibrate.

Result

Electron microscopy showed an increase in the number of peroxisomes and mitochondria in liver and heart, respectively, in zebrafish fed clofibrate. Clofibrate also increased the steady-state level of acox1 mRNA and hnRNA transcripts in different tissues, a gene with a functional PPRE. These results demonstrate that zebrafish is responsive to clofibrate, unlike some other fishes. The levels of fabp mRNA and hnRNA transcripts for the four sets of duplicated fabp genes was determined by reverse transcription, quantitative polymerase chain reaction (RT-qPCR). The level of hnRNA coded by a gene is an indirect estimate of the rate of transcriptional initiation of that gene. Clofibrate increased the steady-state level of fabp mRNAs and hnRNAs for both the duplicated copies of fabp1a/fabp1b.1, and fabp7a/fabp7b, but in different tissues. Clofibrate also increased the steady-state level of fabp10a and fabp11a mRNAs and hnRNAs in liver, but not for fabp10b and fabp11b.

Conclusion

Some duplicated fabp genes have, most likely, retained PPREs, but induction by clofibrate is over-ridden by an, as yet, unknown tissue-specific mechanism(s). Regardless of the tissue-specific mechanism(s), transcriptional control of duplicated zebrafish fabp genes by clofibrate has markedly diverged since the WGD event.

Fatty acid binding protein 10 in the orange-spotted grouper (Epinephelus coioides): characterization and regulation under pH and temperature stress

We have isolated and characterized a fatty acid binding protein from the liver of the orange-spotted grouper (Epinephelus coioides). Amino acid sequence similarity of the Ec-FABP (E. coioides-FABP) was highest to FABP10s isolated from the livers of catfish, chicken, salamander and iguana. The open-reading frame of the Ec-FABP codes for a protein of 14.0 kDa with a calculated isoelectric point of 8.5. We first expressed a FABP10 protein from orange-spotted grouper (E. coioides) in Pichia pastoris, and then characterized the antioxidative potential of our recombinant Ec-FABP by DCF fluorescence assay. RT-PCR assays showed that endogenous Ec-FABP mRNA is most strongly expressed in liver with the most abundance and intestine. Change in the groupers' blood cells respiratory burst activity was examined during and after exposure to the pH and temperature stress using flow cytometry. Further analysis of Ec-FABP gene expression in liver tissue by quantitative real-time PCR demonstrated that Ec-FABP transcript levels increased when the fish were exposed to both pH and temperature stress, but the time when its mRNA expression level peaked differed under these stresses. Western blot analyses confirmed that the Ec-FABP protein was strongly expressed in the liver after exposure to the pH and temperature stress. These results suggest that Ec-FABP expression is stimulated by pH and temperature stress and that it may play important roles in general adaptive and antioxidant responses.

Liver fatty acid-binding protein and obesity

While low levels of unesterified long chain fatty acids (LCFAs) are normal metabolic intermediates of dietary and endogenous fat, LCFAs are also potent regulators of key receptors/enzymes and at high levels become toxic detergents within the cell. Elevated levels of LCFAs are associated with diabetes, obesity and metabolic syndrome. Consequently, mammals evolved fatty acid-binding proteins (FABPs) that bind/sequester these potentially toxic free fatty acids in the cytosol and present them for rapid removal in oxidative (mitochondria, peroxisomes) or storage (endoplasmic reticulum, lipid droplets) organelles. Mammals have a large (15-member) family of FABPs with multiple members occurring within a single cell type. The first described FABP, liver-FABP (L-FABP or FABP1), is expressed in very high levels (2-5% of cytosolic protein) in liver as well as in intestine and kidney. Since L-FABP facilitates uptake and metabolism of LCFAs in vitro and in cultured cells, it was expected that abnormal function or loss of L-FABP would reduce hepatic LCFA uptake/oxidation and thereby increase LCFAs available for oxidation in muscle and/or storage in adipose. This prediction was confirmed in vitro with isolated liver slices and cultured primary hepatocytes from L-FABP gene-ablated mice. Despite unaltered food consumption when fed a control diet ad libitum, the L-FABP null mice exhibited age- and sex-dependent weight gain and increased fat tissue mass. The obese phenotype was exacerbated in L-FABP null mice pair fed a high-fat diet. Taken together with other findings, these data suggest that L-FABP could have an important role in preventing age- or diet-induced obesity.

Osthole improves alcohol-induced fatty liver in mice by reduction of hepatic oxidative stress

The aim of our study was to examine the therapeutic effect of osthole, an active constituent isolated from the fruit of Cnidium monnieri (L.) Cusson, on alcohol-induced fatty liver in mice and investigate its potential mechanisms of treatment. A mouse alcoholic fatty liver model was established by feeding 52% alcohol for 4 weeks. These experimental mice were then treated with osthole 10, 20 and 40 mg/kg for 6 weeks. The levels of serum total cholesterol (TC), triglyceride (TG), low density lipoprotein-cholesterol (LDL-C) and hepatic tissue contents of TC, TG and malondialdehyde (MDA) in osthole-treated groups were significantly decreased, while the level of superoxide dismutase (SOD) was significantly increased compared with the model group. Moreover, the cytochrome P450 (CYP) 2E1 and diacylglycerol acyltransferase (DGAT) mRNA expressions in mouse liver were significantly decreased, and the carnitine palmitoyltransferase (CPT) 1A mRNA expression was increased by osthole treatment. Importantly, the histological evaluation of liver demonstrated that osthole dramatically decreased lipid accumulation. It was concluded that osthole was effective in treating mouse alcoholic fatty liver, and its main mechanisms might be related to reduction of hepatic oxidative stress, including the inhibition of reactive oxygen species (ROS) production, enhancement of antioxidative enzyme activity, and reduction of lipid accumulation and peroxidation.

Molecular cloning and tissue expression of the fatty acid-binding protein (Es-FABP) gene in female Chinese mitten crab (Eriocheir sinensis)

Background

Fatty acid-binding proteins (FABPs), small cytosolic proteins that function in the uptake and utilization of fatty acids, have been extensively studied in higher vertebrates while invertebrates have received little attention despite similar nutritional requirements during periods of reproductive activity.

Results

Therefore, a cDNA encoding Eriocheir sinensis FABP (Es-FABP) was cloned based upon EST analysis of a hepatopancreas cDNA library. The full length cDNA was 750 bp and encoded a 131 aa polypeptide that was highly homologous to related genes reported in shrimp. The 9108 bp Es-FABP gene contained four exons that were interrupted by three introns, a genomic organization common among FABP multigene family members in vertebrates. Gene expression analysis, as determined by RT-PCR, revealed the presence of Es-FABP transcripts in hepatopancreas, hemocytes, ovary, gills, muscle, thoracic ganglia, heart, and intestine, but not stomach or eyestalk. Real-time quantitative RT-PCR analysis revealed that Es-FABP expression in ovary, hemocytes, and hepatopancreas was dependent on the status of ovarian development, with peak expression observed in January.

Conclusions

Evidence provided in the present report supports a role of Es-FABP in lipid transport during the period of rapid ovarian growth in E. sinensis, and indirectly confirms the participation of the hepatopancreas, ovary, and hemocytes in lipid nutrient absorption and utilization processes.

Osthol regulates hepatic PPAR alpha-mediated lipogenic gene expression in alcoholic fatty liver murine

Our previous studies found that osthol, an active constituent isolated from Cnidium monnieri (L.) Cusson (Apiaceae), could ameliorate the accumulation of lipids and decrease the lipid levels in serum and hepatic tissue in alcohol-induced fatty liver mice and rats. The objective of this study was to investigate its possible mechanism of the lipid-lowering effect. A mouse model with alcoholic fatty liver was induced by orally feeding 52% erguotou wine by gavage when they were simultaneously treated with osthol 10, 20, 40 mg/kg for 4 weeks. The BRL cells (rat hepatocyte line) were cultured and treated with osthol at 25, 50, 100, 200 microg/ml for 24h. The mRNA expressions of peroxisome proliferator-activated receptor (PPAR) alpha, diacylglycerol acyltransferase (DGAT), 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase and cholesterol 7 alpha-hydroxylase (CYP7A) in mouse hepatic tissue or cultured hepatocytes were determined by reverse transcription polymerase chain reaction (RT-PCR). After treatment with osthol, the PPAR alpha mRNA expression in mouse liver and cultured hepatocytes was increased in dose dependent manner, while its related target genes for mRNA expression, e.g., DGAT and HMG-CoA reductase, were decreased, the CYP7A was inversely increased. And osthol-regulated mRNA expressions of DGAT, HMG-CoA reductase and CYP7A in the cultured hepatocytes were abrogated after pretreatment with specific inhibitor of PPAR alpha, MK886. It was concluded that osthol might regulate the gene expressions of DGAT, HMG-CoA reductase and CYP7A via increasing the PPAR alpha mRNA expression.

PPAR signaling pathway and cancer-related proteins are involved in celiac disease-associated tissue damage

Celiac disease (CD) is an immune-mediated disorder triggered by the ingestion of wheat gliadin and related proteins in genetically predisposed individuals. To find a proteomic CD diagnostic signature and to gain a better understanding of pathogenetic mechanisms associated with CD, we analyzed the intestinal mucosa proteome alterations using two dimensional difference gel electrophoresis (2D-DIGE) coupled with matrix assisted laser desorption ionization time of flight mass spectrometry (MALDI-TOF ms) of CD patients with varying degrees of histological abnormalities defined by Marsh criteria and controls. Our results clearly evidenced the presence of two groups of patients: Group A, including controls and Marsh 0-I CD patients; and Group B, consisting of CD subjects with grade II-III Oberhuber-Marsh classification. Differentially expressed proteins were involved mainly in lipid, protein and sugar metabolism. Interestingly, in Group B, several downregulated proteins (FABP1, FABP2, APOC3, HMGCS2, ACADM and PEPCK) were implicated directly in the peroxisome proliferator-activated receptor (PPAR) signaling pathway. Moreover, Group B patients presented a deregulation of some proteins involved in apoptosis/survival pathways: phosphatidylethanolamine-binding protein 1 (PEBP1), Ras-related nuclear protein (Ran) and peroxiredoxin 4 (PRDX4). PEBP1 downregulation and RAN and PRDX4 upregulation were associated with more severe tissue damage. Likewise, IgMs were found strongly upregulated in Group B. In conclusion, our results indicate that a downregulation of proteins involved in PPAR signaling and the modulation of several cancer-related proteins are associated with the highest CD histological score according to Oberhuber-Marsh classification.

A role of liver fatty acid-binding protein in cisplatin-induced acute renal failure

Previous studies from our laboratory showed that increased fatty acid oxidation by the kidney is cytoprotective during cisplatin (CP)-mediated nephrotoxicity. In this study, we determined the effects of CP and fibrates on peroxisome proliferation and the expression of liver fatty acid-binding protein (L-FABP) in normal mice, and in mice transgenically overexpressing human L-FABP (h-L-FABP). Labeling of peroxisomes demonstrated reduced peroxisomal staining in the proximal tubule of CP-treated mice compared with control mice. There was increased peroxisomal labeling in the proximal tubules of both control and CP-treated mice when either was treated with fibrate; a known peroxisome proliferator-activated receptor-alpha ligand. L-FABP protein expression, not detected in control or CP-treated mice, was significantly increased in the proximal tubules of fibrate-treated mice of either group. In the transgenic mice, CP increased the shedding of h-L-FABP in the urine, which was decreased by fibrate as was the acute renal failure. A cytosolic pattern of h-L-FABP expression was found in the proximal tubules of untreated transgenic mice with a nuclear presence in CP-treated mice. Fibrate pretreatment restored the cytosolic expression pattern in CP-treated mice. Our study shows that fibrate may improve CP-induced acute renal failure due to both peroxisome proliferation and increased L-FABP in the cytosol of the proximal tubule.

Localization of a portion of the liver isoform of fatty-acid-binding protein (L-FABP) to peroxisomes

The liver isoform of fatty-acid-binding protein (L-FABP) facilitates the cellular uptake, transport and metabolism of fatty acids and is also involved in the regulation of gene expressions and cell differentiation. Consistent with these functions, L-FABP is predominantly present in the cytoplasm and to a lesser extent in the nucleus; however, a significant portion of this protein has also been detected in fractions containing different organelles. More recent observations, notably on L-FABP-deficient mice, indicated a possible direct involvement of L-FABP in the peroxisomal oxidation of long-chain fatty acids. In order to clarify the links between L-FABP and peroxisomal lipid metabolism, we reinvestigated the subcellular distribution of the protein. Analytical subcellular fractionation by a method preserving the intactness of isolated peroxisomes, two-dimensional gel electrophoresis of peroxisomal matrix proteins combined with MS analysis, and immunoelectron microscopy of liver sections demonstrate the presence of L-FABP in the matrix of peroxisomes as a soluble protein. Peroxisomal L-FABP was highly inducible by clofibrate. The induction of L-FABP was accompanied by a marked increase in the binding capacity of peroxisomal matrix proteins for oleic acid and cis-parinaric acid. The peroxisomal beta-oxidation of palmitoyl-CoA and acyl-CoA thioesterase activity were stimulated by L-FABP, indicating that the protein modulates the function of peroxisomal lipid-metabolizing enzymes. The possible role of intraperoxisomal L-FABP in lipid metabolism is discussed.

Expression of cFABP and PPAR in trophoblast cells: effect of PPAR ligands on linoleic acid uptake and differentiation

Throughout gestation, fetal growth depends, in part, on placental transfer of maternal essential fatty acid (EFA) and long-chain polyunsaturated fatty acid. All fatty acid (FA) can cross lipid bilayer by simple diffusion, such as those in the syncytiotrophoblasts, the multinucleated, terminally differentiated trophoblast cells. The trophoblasts differentiation process is accompanied by an increase of human chorionic gonadotropin (hCG) secretion and an inhibition of Human Achaete-Scute Homologue-2 expression (Hash-2). Furthermore, a number of FA-binding proteins (FABPs) have been identified in membrane and cytoplasm of mammalian cells, which are thought to facilitate the transfer of FA across membranes and their intracellular channeling. Thus, the aim of this study was to investigate the implication of cFABPs in linoleic acid (LA) uptake by human trophoblast cells according to differentiation. Moreover, since peroxisome proliferator-activated receptor (PPARs) regulate the expression of cFABP and play an important role in trophoblast cells differentiation, the effects of PPARs ligands are verified on cFABP expression and differentiation. Herein, we reported the increase of the expression of liver and heart FABP (L- and H-FABP) upon differentiation of trophoblast cells, an inhibition of PPAR alpha and beta, while PPAR gamma levels remains unchanged. The nonselective peroxisome-proliferating agents, bezafibrate and LA, impaired trophoblast differentiation, and reduced L- and H-FABP expression. Furthermore, cobalt, a chemical agent known to mimic hypoxia, inhibits trophoblast cells differentiation and diminishes H-, L-FABP and PPARs expression. Finally, both treatments show no influence on LA uptake by trophoblast cells. In conclusion, this study showed that there is no correlation between the expression of H- and L-FABP and LA uptake by trophoblast cells and that bezafibrate and LA greatly impaired trophoblast cells differentiation.

Alcoholic fatty liver: its pathogenesis and mechanism of progression to inflammation and fibrosis

Liver disease in the alcoholic is due not only to malnutrition but also to ethanol's hepatotoxicity linked to its metabolism by means of the alcohol dehydrogenase and cytochrome P450 2E1 (CYP2E1) pathways and the resulting production of toxic acetaldehyde. In addition, alcohol dehydrogenase-mediated ethanol metabolism generates the reduced form of nicotinamide adenine dinucleotide (NADH), which promotes steatosis by stimulating the synthesis of fatty acids and opposing their oxidation. Steatosis is also promoted by excess dietary lipids and can be attenuated by their replacement with medium-chain triglycerides. Through reduction of pyruvate, elevated NADH also increases lactate, which stimulates collagen synthesis in myofibroblasts. Furthermore, CYP2E1 activity is inducible by its substrates, not only ethanol but also fatty acids. Their excess and metabolism by means of this pathway generate release of free radicals, which cause oxidative stress, with peroxidation of lipids and membrane damage, including altered enzyme activities. Products of lipid peroxidation such as 4-hydroxynonenal stimulate collagen generation and fibrosis, which are further increased through diminished feedback inhibition of collagen synthesis because acetaldehyde forms adducts with the carboxyl-terminal propeptide of procollagen in hepatic stellate cells. Acetaldehyde is also toxic to the mitochondria, and it aggravates their oxidative stress by binding to reduced glutathione and promoting its leakage. Oxidative stress and associated cellular injury promote inflammation, which is aggravated by increased production of the proinflammatory cytokine tumor necrosis factor-alpha in the Kupffer cells. These are activated by induction of their CYP2E1 as well as by endotoxin. The endotoxin-stimulated tumor necrosis factor-alpha release is decreased by dilinoleoylphosphatidylcholine, the active phosphatidylcholine (PC) species of polyenylphosphatidylcholine (PPC). Moreover, defense mechanisms provided by peroxisome proliferator-activated receptor alpha and omega fatty acid oxidation are readily overwhelmed, particularly in female rats and also in women who have low hepatic induction of fatty acid-binding protein (L-FABPc). Accordingly, the intracellular concentration of free fatty acids may become high enough to injure membranes, thereby contributing to necrosis, inflammation, and progression to fibrosis and cirrhosis. Eventually, hepatic S-adenosylmethionine and PCs become depleted in the alcoholic, with impairment of their multiple cellular functions, which can be restored by PC replenishment. Thus, prevention and therapy opposing the development of steatosis and its progression to more severe injury can be achieved by a multifactorial approach: control of alcohol consumption, avoidance of obesity and of excess dietary long-chain fatty acids, or their replacement with medium-chain fatty acids, and replenishment of S-adenosylmethionine and PCs by using PPC. Progress in the understanding of the pathogenesis of alcoholic fatty liver and its progression to inflammation and fibrosis has resulted in prospects for their better prevention and treatment.

Alcoholic liver injury in the rat is associated with reduced expression of peroxisome proliferator-alpha (PPARalpha)-regulated genes and is ameliorated by PPARalpha activation

Alcoholic liver disease is associated with a state of hepatic fatty acid overload. We examined the effect of ethanol and different types of dietary fat on the expression of mRNA for liver fatty acid binding protein (L-FABP), peroxisome proliferator-activated receptor-alpha (PPARalpha), and peroxisomal fatty acyl CoA oxidase (FACO). Four groups of rats (n = 5) were fed intragastrically, a liquid diet with or without ethanol (10-16 g/kg/day) for 4 weeks. Pair-fed controls received isocaloric amounts of dextrose. The source of fat was either corn oil or fish oil. Ethanolfed rats developed fatty liver, necrosis, and inflammation; the changes were more severe in the fish oil-ethanol (FE) rats. PPARalpha mRNA levels were not different between groups, although there was a trend toward increased levels in ethanol-fed rats. We calculated L-FABP/PPARalpha and FACO/PPARalpha ratios as a measure of FACO and L-FABP up-regulation relative to PPARalpha expression. Both FACO/PPARalpha and L-FABP/PPARalpha ratios were significantly decreased in FE rats. However, only L-FABP/PPARalpha was decreased in corn oil plus ethanol rats. Also, the level of L-FABP/mRNA correlated inversely with the degree of fatty liver in ethanol-fed rats. Since expression of PPARalpha response genes was impaired in ethanol-fed rats, we determined whether activation of PPARalpha would normalize the PPARalpha response and prevent the pathological changes in ethanol-fed rats. Treatment with clofibrate, a PPARalpha-activating ligand, led to a marked decrease in fatty liver and complete abrogation of necroinflammatory changes in FE rats. Also, nuclear factor kappaB activation and up-regulation of tumor necrosis factor-alpha and cyclooxygenase-2 was also abolished in clofibrate-treated rats. We conclude that adaptive gene regulation of FACO and L-FABP by PPARalpha is impaired in ethanol-fed rats and that treatment with clofibrate, a PPARalpha ligand, prevents alcohol-induced pathological liver injury, possibly by reversing the above changes.

Liver fatty acid binding protein is required for high rates of hepatic fatty acid oxidation but not for the action of PPARalpha in fasting mice

Liver fatty acid binding protein (L-FABP) has been proposed to limit the availability of long-chain fatty acids (LCFA) for oxidation and for peroxisome proliferator-activated receptor alpha (PPAR-alpha), a fatty acid binding transcription factor that determines the capacity of hepatic fatty acid oxidation. Here, we used L-FABP null mice to test this hypothesis. Under fasting conditions, this mutation reduced beta-hydroxybutyrate (BHB) plasma levels as well as BHB release and palmitic acid oxidation by isolated hepatocytes. However, the capacity for ketogenesis was not reduced: BHB plasma levels were restored by octanoate injection; BHB production and palmitic acid oxidation were normal in liver homogenates; and hepatic expression of key PPAR-alpha target (MCAD, mitochondrial HMG CoA synthase, ACO, CYP4A3) and other (CPT1, LCAD) genes of mitochondrial and extramitochondrial LCFA oxidation and ketogenesis remained at wild-type levels. During standard diet, mitochondrial HMG CoA synthase mRNA was selectively reduced in L-FABP null liver. These results suggest that under fasting conditions, hepatic L-FABP contributes to hepatic LCFA oxidation and ketogenesis by a nontranscriptional mechanism, whereas L-FABP can activate ketogenic gene expression in fed mice. Thus, the mechanisms whereby L-FABP affects fatty acid oxidation may vary with physiological condition.

Expression of liver fatty acid binding protein alters growth and differentiation of embryonic stem cells

Although expression of liver fatty acid binding protein (L-FABP) modulates cell growth, it is not known if L-FABP also alters cell morphology and differentiation. Therefore, pluripotent embryonic stem cells were transfected with cDNA encoding L-FABP and a series of clones expressing increasing levels of L-FABP were isolated. Untransfected ES cells, as well as ES cells transfected only with empty vector, spontaneously differentiated from rounded adipocyte-like to fibroblast-like morphology, concomitant with marked reduction in expression of stage-specific embryonic antigen (SSEA-1). These changes in morphology and expression of SSEA-1 were greatest in ES cell clones expressing L-FABP above a threshold level. Immunofluorescence confocal microscopy revealed that L-FABP was primarily localized in a diffuse-cytosolic pattern along with a lesser degree of punctate L-FABP expression in the nucleus. Nuclear localization of L-FABP was preferentially increased in clones expressing higher levels of L-FABP. In summary, L-FABP expression altered ES cell morphology and expression of SSEA-1. Taken together with the fact that L-FABP was detected in the nucleus, these data suggested that L-FABP may play a more direct, heretofore unknown, role in regulating ES cell differentiation by acting in the nucleus as well as cytoplasm.

Adaptive increase in pyruvate dehydrogenase kinase 4 during starvation is mediated by peroxisome proliferator-activated receptor alpha

Pyruvate dehydrogenase kinase isoform 4 (PDK4) is upregulated by starvation in many tissues of the body during starvation. This causes inactivation of the pyruvate dehydrogenase complex which blocks pyruvate oxidation and conserves lactate and alanine for gluconeogenesis. Enhanced PDK4 expression may be caused by the increase in free fatty acids that occurs during starvation. Free fatty acids can activate peroxisome proliferator-activated receptor alpha (PPARalpha), and activation of PPARalpha can promote PDK4 expression. This model is supported by the findings reported here that WY-14,643, a synthetic PPARalpha activator, increases PDK4 expression in wild-type mice but not in PPARalpha-null mice. Starvation likewise increases the expression of PDK4 in tissues of wild-type mice but not in tissues of PPARalpha-null mice. These findings document the functional importance of PPARalpha for PDK4 expression during starvation and suggest an important role for elevated free fatty acids in the induction.

Fatty acids and hypolipidemic drugs regulate peroxisome proliferator-activated receptors alpha - and gamma-mediated gene expression via liver fatty acid binding protein: a signaling path to the nucleus

Peroxisome proliferator-activated receptor alpha (PPARalpha) is a key regulator of lipid homeostasis in hepatocytes and target for fatty acids and hypolipidemic drugs. How these signaling molecules reach the nuclear receptor is not known; however, similarities in ligand specificity suggest the liver fatty acid binding protein (L-FABP) as a possible candidate. In localization studies using laser-scanning microscopy, we show that L-FABP and PPARalpha colocalize in the nucleus of mouse primary hepatocytes. Furthermore, we demonstrate by pull-down assay and immunocoprecipitation that L-FABP interacts directly with PPARalpha. In a cell biological approach with the aid of a mammalian two-hybrid system, we provide evidence that L-FABP interacts with PPARalpha and PPARgamma but not with PPARbeta and retinoid X receptor-alpha by protein-protein contacts. In addition, we demonstrate that the observed interaction of both proteins is independent of ligand binding. Final and quantitative proof for L-FABP mediation was obtained in transactivation assays upon incubation of transiently and stably transfected HepG2 cells with saturated, monounsaturated, and polyunsaturated fatty acids as well as with hypolipidemic drugs. With all ligands applied, we observed strict correlation of PPARalpha and PPARgamma transactivation with intracellular concentrations of L-FABP. This correlation constitutes a nucleus-directed signaling by fatty acids and hypolipidemic drugs where L-FABP acts as a cytosolic gateway for these PPARalpha and PPARgamma agonists. Thus, L-FABP and the respective PPARs could serve as targets for nutrients and drugs to affect expression of PPAR-sensitive genes.

Evidence for peroxisome proliferator-activated receptor (PPAR)alpha-independent peroxisome proliferation: effects of PPARgamma/delta-specific agonists in PPARalpha-null mice

Peroxisome proliferators are a diverse group of compounds that cause hepatic hypertrophy and hyperplasia, increase peroxisome number, and on chronic high-dose administration, lead to rodent liver tumorigenesis. Various lines of evidence have led to the conclusion that these agents induce their pleiotropic effects exclusively via agonism of peroxisome proliferator-activated receptor (PPAR)alpha, a member of the steroid receptor superfamily involved in the regulation of fatty acid metabolism. Recently, agonists of two other members of this receptor family have been identified. PPARgamma is predominantly expressed in adipocytes where it mediates differentiation; PPARdelta is a widely expressed orphan receptor with yet unresolved physiologic functions. In the course of characterizing newer PPAR ligands, we noted that highly selective PPARgamma agonists or dual PPARgamma/PPARdelta agonists, lacking apparent murine PPARalpha agonist activity, cause peroxisome proliferation in CD-1 mice. We therefore made use of PPARalpha knockout mice to investigate whether these effects resulted from agonism of PPARalpha by these agents at very high dose levels or whether PPARgamma (or PPARdelta) agonism alone can result in peroxisome proliferation. We report here that several parameters linked to the hepatic peroxisome proliferation response in mice that were seen with these agents resulted from PPARalpha-independent effects.

The fatty acid transport function of fatty acid-binding proteins

The intracellular fatty acid-binding proteins (FABPs) comprise a family of 14-15 kDa proteins which bind long-chain fatty acids. A role for FABPs in fatty acid transport has been hypothesized for several decades, and the accumulated indirect and correlative evidence is largely supportive of this proposed function. In recent years, a number of experimental approaches which more directly examine the transport function of FABPs have been taken. These include molecular level in vitro modeling of fatty acid transfer mechanisms, whole cell studies of fatty acid uptake and intracellular transfer following genetic manipulation of FABP type and amount, and an examination of cells and tissues from animals engineered to lack expression of specific FABPs. Collectively, data from these studies have provided strong support for defining the FABPs as fatty acid transport proteins. Further studies are necessary to elucidate the fundamental mechanisms by which cellular fatty acid trafficking is modulated by the FABPs.

cDNA sequence and tissue-specific expression of a basic liver-type fatty acid binding protein in adult zebrafish (Danio rerio)

We have determined the nucleotide sequence for a cDNA clone derived from zebrafish (Danio rerio) that codes for a fatty acid binding protein (FABP). Amino acid sequence similarity of the zebrafish FABP was highest to FABPs isolated from the livers of catfish, chicken, salamander and iguana. The open-reading frame of the zebrafish FABP cDNA codes for a protein of 14.0 kDa with a calculated isoelectric point of 8.8. The zebrafish liver-type FABP (L-FABP) cDNA hybridized to single restriction fragments of total zebrafish genomic DNA digested with the restriction endonucleases HaeIII or EcoRI suggesting that a single copy of the L-FABP gene is present in the zebrafish genome. Northern blot analysis demonstrated that the zebrafish L-FABP cDNA hybridized to a transcript of 700 nucleotides in total zebrafish RNA. In situ hybridization and emulsion autoradiography revealed that the L-FABP was expressed exclusively in the liver of the adult zebrafish. Based on amino acid sequence similarity, the isoelectric point and its tissue-specific pattern of expression, we conclude that this zebrafish FABP belongs to the basic liver-type FABPs only found, thus far, in non-mammalian vertebrates.

Permeation of dicarboxylic acids with different terminal position of two carboxylic groups through planar bilayer lipid membranes

Electrically silent hydrogen ion fluxes across a planar bilayer lipid membrane (BLM) induced by an addition of dicarboxylic (DC) acids at one side of BLM are monitored by measuring pH changes in the unstirred layers near the BLM surface via recording protonophore-dependent potentials. Two groups of DC acids are studied: (1) 2-n-alkylmalonic acids with an alkyl chain of different length which carry both carboxylic groups at one terminus of the hydrocarbon chain (alpha,alpha-DC acids); and (2) dicarboxylic acids of different linear chain length having carboxylic groups at the opposite ends of the hydrocarbon chain (alpha,omega-DC acids). It is shown that the pH optimum of hydrogen ion fluxes for the DC acids is shifted considerably to acidic pH values compared to monocarboxylic acids and is located near pH 5. For both types of DC acids at pH&z. Lt;5, the total transport is limited by diffusion of the anionic forms of the acids across the unstirred layers, while at pH&z.Gt;5 the transport is limited by diffusion of the neutral form across the membrane. The fluxes of alpha,alpha-DC acids are similar to those of alpha,omega-DC acids provided that the acids have the similar number of carbon atoms, the fluxes grow with the increase in the chain length of the alkyl radical.

Peroxisome proliferator-activated receptor alpha mediates the adaptive response to fasting

Prolonged deprivation of food induces dramatic changes in mammalian metabolism, including the release of large amounts of fatty acids from the adipose tissue, followed by their oxidation in the liver. The nuclear receptor known as peroxisome proliferator-activated receptor alpha (PPARalpha) was found to play a role in regulating mitochondrial and peroxisomal fatty acid oxidation, suggesting that PPARalpha may be involved in the transcriptional response to fasting. To investigate this possibility, PPARalpha-null mice were subjected to a high fat diet or to fasting, and their responses were compared with those of wild-type mice. PPARalpha-null mice chronically fed a high fat diet showed a massive accumulation of lipid in their livers. A similar phenotype was noted in PPARalpha-null mice fasted for 24 hours, who also displayed severe hypoglycemia, hypoketonemia, hypothermia, and elevated plasma free fatty acid levels, indicating a dramatic inhibition of fatty acid uptake and oxidation. It is shown that to accommodate the increased requirement for hepatic fatty acid oxidation, PPARalpha mRNA is induced during fasting in wild-type mice. The data indicate that PPARalpha plays a pivotal role in the management of energy stores during fasting. By modulating gene expression, PPARalpha stimulates hepatic fatty acid oxidation to supply substrates that can be metabolized by other tissues.

Gender differences in medium-chain dicarboxylic aciduria in alcoholic men and women

PURPOSE

Women appear to be more vulnerable to developing alcoholic liver disease than men. In rats, we previously found that the response of certain pathways of fatty acid metabolism to alcohol feeding was less efficient in females than in males, resulting in striking accumulation of fatty acids in the liver of the female rats. We sought to determine whether similar differences occurred in humans.

PATIENTS AND METHODS

Urinary excretion of medium chain (C6-C10) dicarboxylic acids (final products of fatty acid omega-oxidation) was determined in 40 recently drinking alcoholic subjects (24 men and 16 women) and 21 nonalcoholic subjects (12 men and nine women). Sebacic (C10), suberic (C8), and adipic (C6) acids were measured in urine by gas chromatography/mass spectrometry, and their excretion was expressed per mg of creatinine.

RESULTS

In nonalcoholic subjects, there was no gender difference in dicarboxylic aciduria. By contrast, alcoholic men (but not alcoholic women) developed dicarboxylic hyperaciduria. Alcoholic men had a marked increase in adipic acid excretion and in the adipic/sebacic (C6/C10) ratio (an index of peroxisomal beta-oxidation), whereas the values in alcoholic women did not differ from those in nonalcoholic women.

CONCLUSIONS

The lack of response in alcoholic women could contribute to an aggravation of liver injury by promoting deleterious accumulation of fatty acids.

Alcohol and lipids

Alcoholic fatty liver and hyperlipemia result from the interaction of ethanol and its oxidation products with hepatic lipid metabolism. An early target of ethanol toxicity is mitochondrial fatty acid oxidation. Acetaldehyde and reactive oxygen species have been incriminated in the pathogenesis of the mitochondrial injury. Microsomal changes offset deleterious accumulation of fatty acids, leading to enhanced formation of triacylglycerols, which are partly secreted into the plasma and partly accumulate in the liver. However, this compensatory mechanism fades with progression of the liver injury, whereas the production of toxic metabolites increases, exacerbating the lesions and promoting fibrogenesis. The early presence of these changes confers to the fatty liver a worse prognosis than previously thought. Alcoholic hyperlipemia results primarily from increased hepatic secretion of very-low-density lipoprotein and secondarily from impairment in the removal of triacylglycerol-rich lipoproteins from the plasma. Hyperlipemia tends to disappear because of enhanced lipolytic activity and aggravation of the liver injury. With moderate alcohol consumption, the increase in high-density lipoprotein becomes the predominant feature. Its mechanism is multifactorial (increased hepatic secretion and increased extrahepatic formation as well as decreased removal) and explains part of the enhanced cholesterol transport from tissues to bile. These changes contribute to, but do not fully account for, the effects on atherosclerosis and/or coronary heart disease attributed to moderate drinking.

Hormonal regulation of liver fatty acid-binding protein in vivo and in vitro: effects of growth hormone and insulin

Liver fatty acid-binding protein (LFABP) is an abundant protein in hepatocytes that binds most of the long chain fatty acids present in the cytosol. It is suggested to be of importance for fatty acid uptake and utilization in the hepatocyte. In the present study, the effects of bovine GH (bGH) and other hormones on the expression of LFABP and its messenger RNA (mRNA) were studied in hypophysectomized rats and in vitro using primary cultures of rat hepatocytes. One injection of bGH increased LFABP mRNA levels about 5-fold after 6 h, but there was no effect of this treatment on LFABP levels. However, 7 days of bGH treatment increased both LFABP mRNA and LFABP protein levels 2- to 5-fold. Female rats had higher levels of LFABP than male rats. Hypophysectomy of female rats, but not that of male rats, decreased LFABP levels markedly. Treatment of hypophysectomized rats with bGH for 7 days as two daily injections or as a continuous infusion increased LFABP levels to a similar degree. This finding indicates that the sex difference in the expression of LFABP is not regulated by the sexually dimorphic secretory pattern of GH. Neither insulin nor insulin-like growth factor I treatment of hypophysectomized rats for 6-7 days had any effect on LFABP mRNA or LFABP levels. In vitro, bGH dose-dependently increased the expression of LFABP mRNA, but only in the presence of insulin. Insulin alone had a marked dose-dependent effect on LFABP mRNA levels and was of importance for maintaining the expression of LFABP mRNA during the culture. Incubation with bGH increased LFABP mRNA levels within 3 h. GH had no effect on LFABP mRNA levels in the presence of actinomycin D, indicating a transcriptional effect of GH. Incubation with glucagon in vitro decreased LFABP mRNA levels markedly, indicating that glucagon, in contrast to GH, has an effect opposite that of insulin on LFABP mRNA expression. It is concluded that GH is an important regulator of LFABP in vivo and in vitro. In contrast to the effect of GH on insulin-like growth factor I mRNA, the presence of insulin was a prerequisite for the effect of GH on LFABP mRNA expression in vitro. The results emphasize the role of GH in the regulation of hepatic fatty acid metabolism.

Intracellular lipid-binding proteins and their genes

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.

Effect of peroxisome proliferator nafenopin on the cytotoxicity of dihaloalkanes in isolated rat hepatocytes

Hepatocytes were isolated from nafenopin-treated animals (80 mg/kg body weight in 1.2 ml/kg body weight olive oil for 2 consecutive days) and exposed to various doses of 1,2 dichloroethane (DCE) (64-159 mumol) and 1,2-dibromoethane (DBE) (5.5-27.5 mumol) for up to 3 hr to assess the effect of nafenopin on the toxicity of dihaloalkanes. The activity of biotransformation enzymes involved in the activation and detoxication of these solvents was measured. Although cytochrome P450IIE1 activity was apparently unaltered, glutathione S-transferase activity was significantly reduced; the reduction was 20% for 1-chloro-2,4-dinitrobenzene as substrate but 40% and 80%, respectively for DBE and DCE. DBE was more than 10 times more cytotoxic to nafenopin-treated hepatocytes than DCE, and while very little change in DCE cytotoxicity was observed in hepatocytes isolated from nafenopin pretreated rats compared with control animals, DBE cytotoxicity was significantly potentiated in cells isolated from nafenopin-pretreated rats compared with cells from controls. It is believed that enhanced toxicity of DBE in isolated cells from nafenopin-treated rats is the result of modulation of dihaloalkane metabolism (glutathione conjugation).

Xenobiotic receptor knockout mice

Administration of certain foreign chemicals to animals elicits responses that are due to receptor-mediated activation of gene expression. Among the most well studied receptors are the Ah receptor (AHR) that binds 2,3,7,8-tetrachlorodibenzo-p-dioxin and related compounds and the peroxisome proliferator-activated receptors, PPARs, that mediate gene activation by the diverse group of peroxisome proliferators. These receptors may also have critical roles in development or physiological homeostasis in addition to their abilities to allow animals to interact with exogenous chemicals or xenobiotics. To explore the function of AHR and PPAR alpha and to determine whether they participate in the adverse effects of dioxins and peroxisome proliferators, gene knockout mice were developed.

Fatty acid activation of peroxisome proliferator-activated receptor (PPAR)

Peroxisome proliferators such as clofibric acid, nafenopin, and WY-14,643 have been shown to activate peroxisome proliferator-activated receptor (PPAR), a member of the steroid nuclear receptor superfamily. We have cloned the cDNA from rat that is homologous to that from mouse, which encodes a 97% similar protein. To search for physiologically occurring activators, we established a transcriptional transactivation assay by stably expressing in CHO cells a chimera of rat PPAR and the human glucocorticoid receptor that activates expression of the placental alkaline phosphatase reporter gene under the control of the mouse mammary tumor virus promoter. 150 microM concentrations of arachidonic or linoleic acid but not of dehydroepiandrosterone, cholesterol, or 25-hydroxy-cholesterol, activated the receptor chimera. In addition, saturated fatty acids induced the reporter gene. Shortening the chain length to n = 6 or introduction of an omega-terminal carboxylic group abolished the activation potential of the fatty acid. To test whether a common PPAR binding metabolite might be formed from free fatty acids we tested the effects of differentially beta-oxidizable fatty acids and inhibitors of fatty acid metabolism. The peroxisomal proliferation-inducing, non-beta-oxidizable, tetradecylthioacetic acid activated PPAR to the same extent as the strong peroxisomal proliferator WY-14,643, whereas the homologous beta-oxidizable tetradecylthiopropionic acid was only as potent as a non-substituted fatty acid. Cyclooxygenase inhibitors, radical scavengers or cytochrome P450 inhibitors did not affect activation of PPAR. In conclusion, beta-oxidation is apparently not required for the formation of the PPAR-activating molecule and this moiety might be a fatty acid, its ester with CoA, or a further derivative of the activated fatty acid prior to beta-oxidation of the acyl-CoA ester.

Fatty acids in cell signalling: modulation by lipid binding proteins

Long-chain fatty acids and several of their metabolites have now been shown to be involved as primary or secondary messengers in specific cell signalling pathways. In view of their extremely low aqueous solubility, the extracellular as well as intracellular transport of these compounds is assumed to be facilitated by specific lipid binding proteins, such as cytoplasmic fatty acid-binding protein (FABP). In this paper a survey is given on the biological significance and possible modulatory action of intracellular lipid binding proteins for fatty acid-mediated signal transduction pathways.

Modulation of mitogenesis by liver fatty acid binding protein

Liver fatty acid binding protein (L-FABP), a cytoplasmic 14 kDa protein previously termed Z protein, is conventionally considered to be an intracellular carrier of fatty acids in rat hepatocytes. The following evidence now indicates that L-FABP is also a specific mediator of mitogenesis of rat hepatocytes: a. the synergy between the action of L-FABP and unsaturated fatty acids, especially linoleic acid, in the promotion of cell proliferation; b. the specific requirement for L-FABP in induction of mitogenesis by two classes of nongenotoxic hepatocarcinogenic peroxisome proliferators (amphipathic carboxylates and tetrazole-substituted acetophenones); c. the direct correlation between the binding avidities of different prostaglandins for L-FABP and their relative growth inhibitory activities toward cultured rat hepatocytes; d. the temporal coincidences between the covalent binding to L-FABP by chemically reactive metabolites of the genotoxic carcinogens, 2-acetylaminofluorene and aminoazo dyes, and their growth inhibitions of hepatocytes during liver carcinogenesis in rats; e. and f. the marked elevations of L-FABP in rat liver during mitosis in normal and regenerating hepatocytes, and during the entire cell cycle in the hyperplastic and malignant hepatocytes that are produced by the genotoxic carcinogens, 2-acetylaminofluorene and aminoazo dyes. These actions of L-FABP are consistent with those of a protein involved in regulation of hepatocyte multiplication. Discovery that L-FABP, the target protein of the two types of genotoxic carcinogens, is required for the mitogenesis induced by two classes of nongenotoxic carcinogens points to a common process by which both groups of carcinogens promote hepatocyte multiplication. The implication is that during tumor promotion of liver carcinogenesis, these genotoxic and nongenotoxic carcinogens modify the normal process by which L-FABP, functioning as a specific receptor of unsaturated fatty acids or their metabolites, promotes the multiplication of hepatocytes.

The expression pattern of a novel gene encoding brain-fatty acid binding protein correlates with neuronal and glial cell development

Fatty acid binding proteins (FABPs) are a multigene family of small intracellular proteins that bind hydrophobic ligands. In this report we describe the cloning and expression pattern of a novel member of this gene family that is specifically expressed in the developing and adult nervous system and thus was designated brain (B)-FABP. B-FABP is closely related to heart (H)-FABP with 67% amino acid identity. B-FABP expression was first detected at mouse embryonic day 10 in neuroepithelial cells and its pattern correlates with early neuronal differentiation. Upon further development, B-FABP was confined to radial glial cells and immature astrocytes. B-FABP mRNA and protein were found in glial cells of the peripheral nervous system such as satellite cells of spinal and cranial ganglia and ensheathing cells of the olfactory nerve layer from as early as embryonic day 11 until adulthood. In the adult mouse brain, B-FABP was found in the glia limitans, in radial glial cells of the hippocampal dentate gyrus and Bergman glial cells. These findings suggest a function of B-FABP during neurogenesis or neuronal migration in the developing nervous system. The partially overlapping expression pattern with that of cellular retinoid binding proteins suggests that B-FABP is involved in the metabolism of a so far unknown hydrophobic ligand with potential morphogenic activity during CNS development.