L-FABP T94A is associated with fasting triglycerides and LDL-cholesterol in women

Polymorphism in genes encoding two fatty acid binding proteins increases risk of ischemic stroke in a Chinese Han population

Background: Dyslipidemia is an independent predictor of ischemic stroke (IS). Genetic variations in lipid-metabolism related genes may increase the risk of IS. Fatty acid-binding protein 1 (FABP1) and fatty acid-binding protein 2 (FABP2) are lipid chaperones responsible for lipid transport and metabolism. The present study aimed to determine the association between FABP1 or FABP2 and ischemic stroke.

Methods: A total of 251 participants were recruited composed of 138 patients with ischemic stroke and 113 healthy subjects. DNA was extracted from peripheral blood samples. The rs2241883 polymorphism in FABP1 and rs1799883 polymorphism in FABP2 were genotyped using polymerase chain reaction-restriction fragment length polymorphism. Generalized multifactor dimensionality reduction (GMDR) was used to find out the interaction combinations between two SNPs and environmental factors.

Results: The GA genotype of FABP2 rs1799883 increased susceptibility to ischemic stroke under overdominant inheritance model (p = 0.042). After adjusting for the risk factors of IS, it was associated with a significantly higher risk of IS in the codominant inheritance model (adjust OR = 3.431, 95%CI = 1.060–11.103, p = 0.04). The interactions of FABP1 rs2241883 and FABP2 rs1799883 were not associated with IS risk (p = 0.172). Moreover, interaction analysis of two genes (rs1799883 and rs2241883) and two environmental factors (smoking and alcohol consumption) was associated with an increased risk of IS (p = 0.011).

Conclusion: The GA genotype of FABP2 rs1799883, interactions between rs1799883, rs2241883 and smoking and alcohol consumption were associated with IS risk in Chinese Han populations.

Importance of fatty acid binding proteins in cellular function and organismal metabolism

Fatty acid binding proteins (Fabps) are small soluble proteins that are abundant in the cytosol. These proteins are known to bind a myriad of small hydrophobic molecules and have been postulated to serve a variety of roles, yet their precise functions have remained an enigma over half a century of study. Here, we consider recent findings, along with the cumulative findings contributed by many laboratories working on Fabps over the last half century, to synthesize a new outlook for what functions Fabps serve in cells and organisms. Collectively, the findings illustrate that Fabps function as versatile multi-purpose devices serving as sensors, conveyors and modulators to enable cells to detect and handle a specific class of metabolites, and to adjust their metabolic capacity and efficiency.

Association of macro-and micro-nutrients dietary intakes with rs2241883 genetic variants of FABP 1 gene in MASHAD study population

INTRODUCTION

There is a relationship between macro-nutrient-intakes and the genes implicated in lipid metabolism. In this study, we assessed the association between macro-and micro-nutrients dietary intakes with rs2241883 genetic variants of the FABP1 gene.

METHODS

For this cross-sectional study 2737 subjects (including 2203 subjects with dyslipidemia and 534 healthy volunteers) were enrolled as part of the Mashhad Stroke and Heart Atherosclerotic Disorder (MASHAD) study cohort. Dyslipidemia was defined based on the National Cholesterol Education Program Adult Treatment Panel III (NCEP ATP III). A NanoDrop®-1000 instrument was used to do the quantitation of DNA. The rs2241883 polymorphisms were genotyped using double ARMs PCR reactions. Genotyping reagents were obtained from Applied Biosystems. Dietary intake was evaluated using a food frequency questionnaire (FFQ) and validated by 2 consecutive 24-h food recalls.

RESULTS

The results showed no significant association between subjects with and without dyslipidemia (P > 0.05), except for the zinc to copper ratio, the value for which was higher in the subjects with dyslipidemia (4.78 (1.62)) when compared to subjects without dyslipidemia (4.68 (1.82)) (p = 0.05). Using different genetic models we found that zinc and copper were significantly different in the additive (p = 0.01) and dominant (p = 0.01) genetic models. Although, this association was no longer significant after adjusting for confounding factors.

CONCLUSIONS

There were no associations between macro-and micro-nutrient dietary intakes with rs2241883 genetic variants after adjusting for confounding factors in the MASHAD study population.

The association between a Fatty Acid Binding Protein 1 (FABP1) gene polymorphism and serum lipid abnormalities in the MASHAD cohort study

INTRODUCTION

Dyslipidemia is a known risk factor for cardiovascular disease and is partially determined by genetic variations in the genes involved in lipoprotein metabolism. Therefore, we aimed to assess the association between a polymorphism of the Fatty Acid Binding Protein1 (rs2241883) gene locus and dyslipidemia in an Iranian cohort.

MATERIALS AND METHODS

This is a case-control study 2737 individuals were recruited (2203 subjects with dyslipidemia and 534 controls). Dyslipidemia was defined as total cholesterol≥200 mg/dl, or TG≥150 mg/dl, or LDL-C≥130 mg/dl, or HDL-C<40 mg/dl in males and <50 mg/dl in females. Serum lipid profile was determined using a Alcyon Abbott biochemical auto analyzer, USA. Genotyping was made through double amplification refractory mutation system polymerase chain reaction (ARMs PCR).

RESULT

The frequency of TT, CT, CC genotypes of rs2241883 polymorphism of FABP1 gene were 65.5, 33.4, 5.1 in subjects with dyslipidemia and 56.9%, 40.4%, 2.6% in subjects without dyslipidemia, respectively. Using a dominant genetic model, subjects carrying C allele (CC&CT genotypes) had a 22% lower risk of dyslipidemia (OR: 0.78, CI 95%: 0.62-0.98 P, 0.03). Individuals with CT vs. TT genotypes had a significantly lower risk of a high serum TC and LDL level. Further analysis showed that there was a positive association between FABP1 genotype (CT) and isolated HTG as well as combined dyslipidemia. The change of a polar amino acid (threonine) in position T94A to a hydrophobic amino acid (alanine) can cause transformation protein.

CONCLUSIONS

A CC genotype of the rs2241883 polymorphism of the FABP1 gene appears to confer a higher risk of dyslipidemia in our representative cohort of Iranian individuals.

From Congenital Disorders of Fat Malabsorption to Understanding Intra-Enterocyte Mechanisms Behind Chylomicron Assembly and Secretion

During the last two decades, a large body of information on the events responsible for intestinal fat digestion and absorption has been accumulated. In particular, many groups have extensively focused on the absorptive phase in order to highlight the critical "players" and the main mechanisms orchestrating the assembly and secretion of chylomicrons (CM) as essential vehicles of alimentary lipids. The major aim of this article is to review understanding derived from basic science and clinical conditions associated with impaired packaging and export of CM. We have particularly insisted on inborn metabolic pathways in humans as well as on genetically modified animal models (recapitulating pathological features). The ultimate goal of this approach is that "experiments of nature" and in vivo model strategy collectively allow gaining novel mechanistic insight and filling the gap between the underlying genetic defect and the apparent clinical phenotype. Thus, uncovering the cause of disease contributes not only to understanding normal physiologic pathway, but also to capturing disorder onset, progression, treatment and prognosis.

Distinct Alteration of Gene Expression Programs in the Small Intestine of Male and Female Mice in Response to Ablation of Intestinal Fabp Genes

Fatty acid-binding proteins (Fabps) make up a family of widely distributed cytoplasmic lipid-binding proteins. The small intestine contains three predominant Fabp species, Fabp1, Fabp2, and Fabp6. Our previous studies showed that Fabp2 and Fabp6 gene-disrupted mice exhibited sexually dimorphic phenotypes. In this study, we carried out a systematic comparative analysis of the small intestinal transcriptomes of 10 week-old wild-type (WT) and Fabp gene-disrupted male and female mice. We found that the small intestinal transcriptome of male and female mice showed key differences in the gene expression profiles that affect major biological processes. The deletion of specific Fabp genes induced unique and sex-specific changes in the gene expression program, although some differentially expressed genes in certain genotypes were common to both sexes. Functional annotation and interaction network analyses revealed that the number and type of affected pathways, as well as the sets of interacting nodes in each of the Fabp genotypes, are partitioned by sex. To our knowledge, this is the first time that sex differences were identified and categorized at the transcriptome level in mice lacking different intestinal Fabps. The distinctive transcriptome profiles of WT male and female small intestine may predetermine the nature of transcriptional reprogramming that manifests as sexually dimorphic responses to the ablation of intestinal Fabp genes.

Liver fatty acid-binding protein might be a predictive marker of clinical response to systemic treatment in psoriasis

Fatty acid-binding proteins play an inconclusive role in lipid metabolism and cardiometabolic diseases (CMDs) which are closely related with psoriasis. Aim of the study was to investigate the diagnostic value of serum liver fatty acid-binding protein (FABP1) level and associations with disease severity, inflammation or metabolic parameters and influence of systemic treatment in psoriatic patients. The study included thirty-three patients with active plaque-type psoriasis and eleven healthy volunteers. Blood samples were obtained before and after 12 weeks of therapy with methotrexate and acitretin. Serum FABP1 concentrations were analyzed by the enzyme-linked immunosorbent assay. Statistical analysis was performed for correlation of FABP1 with anthropometric, metabolic or inflammatory indices and treatment used. Serum liver-type FABP levels were significantly increased in psoriatic patients compared to the controls (p < 0.001). No statistical correlations between FABP1 and PASI (p = 0.25) was noted, however patients with severe psoriasis had the highest level of FABP1. No significance with metabolic parameters was obtained, beside a positive significant relation with BMI after therapy (p = 0.03). Liver-type FABP significantly correlated with CRP (p = 0.01) and morphotic blood elements. Systemic treatment combined resulted in significant decrease of FABP1 (p = 0.04), regardless of the drug: p = 0.1 in acitretin group, p = 0.3 in methotrexate group. Liver-type FABP might be a novel marker of psoriasis and predictor of clinical response to systemic therapy. FABP1 could be involved in CMDs risk assessment and perhaps link psoriasis with hematological disorders.

Human Liver Fatty Acid Binding Protein-1 T94A Variant, Nonalcohol Fatty Liver Disease, and Hepatic Endocannabinoid System

Hepatic endocannabinoids (EC) and their major binding/"chaperone" protein (i.e., liver fatty acid binding protein-1 [FABP1]) are associated with development of nonalcoholic fatty liver (NAFLD) in animal models and humans. Since expression of the highly prevalent human FABP1 T94A variant induces serum lipid accumulation, it is important to determine its impact on hepatic lipid accumulation and the EC system. This issue was addressed in livers from human subjects expressing only wild-type (WT) FABP1 T94T (TT genotype) or T94A variant (TC or CC genotype). WT FABP1 males had lower total lipids (both neutral cholesteryl esters, triacylglycerols) and phospholipids than females. WT FABP1 males' lower lipids correlated with lower levels of the N-acylethanolamide DHEA and 2-monoacylglycerols (2-MAG) (2-OG, 2-PG). T94A expression in males increased the hepatic total lipids (triacylglycerol, cholesteryl ester), which is consistent with their higher level of CB1-potentiating 2-OG and lower antagonistic EPEA. In contrast, in females, T94A expression did not alter the total lipids, neutral lipids, or phospholipids, which is attributable to the higher cannabinoid receptor-1 (CB1) agonist arachidonoylethanolamide (AEA) and its CB1-potentiator OEA being largely offset by reduced potentiating 2-OG and increased antagonistic EPEA. Taken together, these findings indicate that T94A-induced alterations in the hepatic EC system contribute at least in part to the hepatic accumulation of lipids associated with NAFLD, especially in males.

Ablating both Fabp1 and Scp2/Scpx (TKO) induces hepatic phospholipid and cholesterol accumulation in high fat-fed mice

Although singly ablating Fabp1 or Scp2/Scpx genes may exacerbate the impact of high fat diet (HFD) on whole body phenotype and non-alcoholic fatty liver disease (NAFLD), concomitant upregulation of the non-ablated gene, preference for ad libitum fed HFD, and sex differences complicate interpretation. Therefore, these issues were addressed in male and female mice ablated in both genes (Fabp1/Scp2/Scpx null or TKO) and pair-fed HFD. Wild-type (WT) males gained more body weight as fat tissue mass (FTM) and exhibited higher hepatic lipid accumulation than WT females. The greater hepatic lipid accumulation in WT males was associated with higher hepatic expression of enzymes in glyceride synthesis, higher hepatic bile acids, and upregulation of transporters involved in hepatic reuptake of serum bile acids. While TKO had little effect on whole body phenotype and hepatic bile acid accumulation in either sex, TKO increased hepatic accumulation of lipids in both, specifically phospholipid and cholesteryl esters in males and females and free cholesterol in females. TKO-induced increases in glycerides were attributed not only to complete loss of FABP1, SCP2 and SCPx, but also in part to sex-dependent upregulation of hepatic lipogenic enzymes. These data with WT and TKO mice pair-fed HFD indicate that: i) Sex significantly impacted the ability of HFD to increase body weight, induce hepatic lipid accumulation and increase hepatic bile acids; and ii) TKO exacerbated the HFD ability to induce hepatic lipid accumulation, regardless of sex, but did not significantly alter whole body phenotype in either sex.

Association of IL-1β, IL-1Ra and FABP1 gene polymorphisms with the metabolic features of polycystic ovary syndrome

BACKGROUND

Polycystic ovary syndrome (PCOS), a highly prevalent endocrinopathy is currently being designated as chronic low grade inflammatory state. IL-1β, IL-1Ra and FABP1 are critical mediators of inflammatory processes and are speculated to play a role in the pathogenesis of PCOS. The aim of this study was to study the association of IL-β, IL-1Ra and FABP1 gene polymorphisms with PCOS and related metabolic features.

SUBJECTS

95 PCOS and 45 age matched healthy control subjects were enrolled in this study.

METHODS

Polymorphism in genes IL-1β, IL-1Ra and FABP1 was studied by PCR, PCR-RFLP and sequencing methods, respectively. Hormonal and lipid profiles were evaluated for all the subjects.

RESULTS

Hormonal and lipid profiles showed significant differences between PCOS and control subjects. Allele and genotype frequencies of IL-1β, IL-1Ra and FABP1 gene polymorphisms did not vary between the control and PCOS group. However, T allele of C[-511]T variant of IL-1β, allele II in intron 2 of IL-1Ra and A allele of A/G variant of FABP1 (rs2197076) showed significant association with many metabolic features associated with PCOS.

CONCLUSIONS

Polymorphism in genes encoding cytokines and proteins involved in lipid metabolism can provide insights into the genetics of the disease and may contribute to assess the associated risk of cardiovascular diseases (CVD), dyslipidemia and metabolic syndrome (MetS) associated with PCOS.

Impact of dietary phytol on lipid metabolism in SCP2/SCPX/L-FABP null mice

In vitro studies suggest that liver fatty acid binding protein (L-FABP) and sterol carrier protein-2/sterol carrier protein-x (SCP2/SCPx) gene products facilitate uptake and metabolism and detoxification of dietary-derived phytol in mammals. However, concomitant upregulation of L-FABP in SCP2/SCPx null mice complicates interpretation of their physiological phenotype. Therefore, the impact of ablating both the L-FABP gene and SCP2/SCPx gene (L-FABP/SCP2/SCPx null or TKO) was examined in phytol-fed female wild-type (WT) and TKO mice. TKO increased hepatic total lipid accumulation, primarily phospholipid, by mechanisms involving increased hepatic levels of proteins in the phospholipid synthetic pathway. Concomitantly, TKO reduced expression of proteins in targeting fatty acids towards the triacylglycerol synthetic pathway. Increased hepatic lipid accumulation was not associated with any concomitant upregulation of membrane fatty acid transport/translocase proteins involved in fatty acid uptake (FATP2, FATP4, FATP5 or GOT) or cytosolic proteins involved in fatty acid intracellular targeting (ACBP). In addition, TKO exacerbated dietary phytol-induced whole body weight loss, especially lean tissue mass. Since individually ablating SCPx or SCP2/SCPx elicited concomitant upregulation of L-FABP, these findings with TKO mice help to resolve the contributions of SCP2/SCPx gene ablation on dietary phytol-induced whole body and hepatic lipid phenotype independent of concomitant upregulation of L-FABP.

Female Mice are Resistant to Fabp1 Gene Ablation-Induced Alterations in Brain Endocannabinoid Levels

Although liver fatty acid binding protein (FABP1, L-FABP) is not detectable in the brain, Fabp1 gene ablation (LKO) markedly increases endocannabinoids (EC) in brains of male mice. Since the brain EC system of females differs significantly from that of males, it was important to determine if LKO differently impacted the brain EC system. LKO did not alter brain levels of arachidonic acid (ARA)-containing EC, i.e. arachidonoylethanolamide (AEA) and 2-arachidonoylglycerol (2-AG), but decreased non-ARA-containing N-acylethanolamides (OEA, PEA) and 2-oleoylglycerol (2-OG) that potentiate the actions of AEA and 2-AG. These changes in brain potentiating EC levels were not associated with: (1) a net decrease in levels of brain membrane proteins associated with fatty acid uptake and EC synthesis; (2) a net increase in brain protein levels of cytosolic EC chaperones and enzymes in EC degradation; or (3) increased brain protein levels of EC receptors (CB1, TRVP1). Instead, the reduced or opposite responsiveness of female brain EC levels to loss of FABP1 (LKO) correlated with intrinsically lower FABP1 level in livers of WT females than males. These data show that female mouse brain endocannabinoid levels were unchanged (AEA, 2-AG) or decreased (OEA, PEA, 2-OG) by complete loss of FABP1 (LKO).

Fatty Acid Binding Protein-1 (FABP1) and the Human FABP1 T94A Variant: Roles in the Endocannabinoid System and Dyslipidemias

The first discovered member of the mammalian FABP family, liver fatty acid binding protein (FABP1, L-FABP), occurs at high cytosolic concentration in liver, intestine, and in the case of humans also in kidney. While the rat FABP1 is well studied, the extent these findings translate to human FABP1 is not clear-especially in view of recent studies showing that endocannabinoids and cannabinoids represent novel rat FABP1 ligands and FABP1 gene ablation impacts the hepatic endocannabinoid system, known to be involved in non-alcoholic fatty liver (NAFLD) development. Although not detectable in brain, FABP1 ablation nevertheless also impacts brain endocannabinoids. Despite overall tertiary structure similarity, human FABP1 differs significantly from rat FABP1 in secondary structure, much larger ligand binding cavity, and affinities/specificities for some ligands. Moreover, while both mouse and human FABP1 mediate ligand induction of peroxisome proliferator activated receptor-α (PPARα), they differ markedly in pattern of genes induced. This is critically important because a highly prevalent human single nucleotide polymorphism (SNP) (26-38 % minor allele frequency and 8.3 ± 1.9 % homozygous) results in a FABP1 T94A substitution that further accentuates these species differences. The human FABP1 T94A variant is associated with altered body mass index (BMI), clinical dyslipidemias (elevated plasma triglycerides and LDL cholesterol), atherothrombotic cerebral infarction, and non-alcoholic fatty liver disease (NAFLD). Resolving human FABP1 and the T94A variant's impact on the endocannabinoid and cannabinoid system is an exciting challenge due to the importance of this system in hepatic lipid accumulation as well as behavior, pain, inflammation, and satiety.

Association of single-nucleotide polymorphisms rs2197076 and rs2241883 of FABP1 gene with polycystic ovary syndrome

PURPOSE

The objective of this study was to evaluate the association between single-nucleotide polymorphisms (SNPs) rs2197076 and rs2241883 in fatty acid-binding protein 1 (FABP1) gene and polycystic ovary syndrome (PCOS).

METHODS

The two alleles rs2197076 and rs2241883 in FABP1 gene in 221 PCOS women and 198 normal women were amplified and sequenced. Allele frequency comparison was performed between the PCOS and control groups, and genotype-phenotype correlation analysis was performed using dominant and recessive models to assess the association of FABP1 and the main features of PCOS.

RESULTS

Allele frequency analyses showed a strong association of SNPs rs2197076 and rs2241883 of FABP1 gene with PCOS (P < 0.001). The additive, dominant, and recessive genotype model analyses further supported this association even after adjusting for age and body mass index (BMI). The minor allele frequency (MAF) of rs2241883 in obese PCOS women was less than that in obese control women. Further genotype-phenotype correlation analysis showed that SNP rs2197076 had a stronger association with the main features of PCOS than SNP rs2241883.

CONCLUSION

In the association of SNPs in FABP1 gene with PCOS, rs2197076 was more closely associated with its main features than rs2241883 and seemed to play a more important role in the pathogenesis of PCOS.

Recent insights into the biological functions of liver fatty acid binding protein 1

Over four decades have passed since liver fatty acid binding protein (FABP)1 was first isolated. There are few protein families for which most of the complete tertiary structures, binding properties, and tissue occurrences are described in such detail and yet new functions are being uncovered for this protein. FABP1 is known to be critical for fatty acid uptake and intracellular transport and also has an important role in regulating lipid metabolism and cellular signaling pathways. FABP1 is an important endogenous cytoprotectant, minimizing hepatocyte oxidative damage and interfering with ischemia-reperfusion and other hepatic injuries. The protein may be targeted for metabolic activation through the cross-talk among many transcriptional factors and their activating ligands. Deficiency or malfunction of FABP1 has been reported in several diseases. FABP1 also influences cell proliferation during liver regeneration and may be considered as a prognostic factor for hepatic surgery. FABP1 binds and modulates the action of many molecules such as fatty acids, heme, and other metalloporphyrins. The ability to bind heme is another cytoprotective property and one that deserves closer investigation. The role of FABP1 in substrate availability and in protection from oxidative stress suggests that FABP1 plays a pivotal role during intracellular bacterial/viral infections by reducing inflammation and the adverse effects of starvation (energy deficiency).

Association of a Human FABP1 Gene Promoter Region Polymorphism with Altered Serum Triglyceride Levels

Liver fatty acid-binding protein (L-FABP), also known as fatty acid-binding protein 1 (FABP1), is a key regulator of hepatic lipid metabolism. Elevated FABP1 levels are associated with an increased risk of cardiovascular disease (CVD) and metabolic syndromes. In this study, we examine the association of FABP1 gene promoter variants with serum FABP1 and lipid levels in a Chinese population. Four promoter single-nucleotide polymorphisms (SNPs) of FABP1 gene were genotyped in a cross-sectional survey of healthy volunteers (n = 1,182) from Fuzhou city of China. Results showed that only the rs2919872 G>A variant was significantly associated with serum TG concentration(P = 0.032).Compared with the rs2919872 G allele, rs2919872 A allele contributed significantly to reduced serum TG concentration, and this allele dramatically decreased the FABP1 promoter activity(P < 0.05). The rs2919872 A allele carriers had considerably lower serum FABP1 levels than G allele carriers (P < 0.01). In the multivariable linear regression analysis, the rs2919872 A allele was negatively associated with serum FABP1 levels (β = —0.320, P = 0.003), while serum TG levels were positively associated with serum FABP1 levels (β = 0.487, P = 0.014). Our data suggest that compared with the rs2919872 G allele, the rs2919872 A allele reduces the transcriptional activity of FABP1 promoter, and thereby may link FABP1 gene variation to TG level in humans.

Loss of L-FABP, SCP-2/SCP-x, or both induces hepatic lipid accumulation in female mice

Although roles for both sterol carrier protein-2/sterol carrier protein-x (SCP-2/SCP-x) and liver fatty acid binding protein (L-FABP) have been proposed in hepatic lipid accumulation, individually ablating these genes has been complicated by concomitant alterations in the other gene product(s). For example, ablating SCP2/SCP-x induces upregulation of L-FABP in female mice. Therefore, the impact of ablating SCP-2/SCP-x (DKO) or L-FABP (LKO) individually or both together (TKO) was examined in female mice. Loss of SCP-2/SCP-x (DKO, TKO) more so than loss of L-FABP alone (LKO) increased hepatic total lipid and total cholesterol content, especially cholesteryl ester. Hepatic accumulation of nonesterified long chain fatty acids (LCFA) and phospholipids occurred only in DKO and TKO mice. Loss of SCP-2/SCP-x (DKO, TKO) increased serum total lipid primarily by increasing triglycerides. Altered hepatic level of proteins involved in cholesterol uptake, efflux, and/or secretion was observed, but did not compensate for the loss of L-FABP, SCP-2/SCP-x or both. However, synergistic responses were not seen with the combinatorial knock out animals-suggesting that inhibiting SCP-2/SCP-x is more correlative with hepatic dysfunction than L-FABP. The DKO- and TKO-induced hepatic accumulation of cholesterol and long chain fatty acids shared significant phenotypic similarities with non-alcoholic fatty liver disease (NAFLD).

Human FABP1 T94A variant enhances cholesterol uptake

Although expression of the human liver fatty acid binding protein (FABP1) T94A variant alters serum lipoprotein cholesterol levels in human subjects, nothing is known whereby the variant elicits these effects. This issue was addressed by in vitro cholesterol binding assays using purified recombinant wild-type (WT) FABP1 T94T and T94A variant proteins and in cultured primary human hepatocytes expressing the FABP1 T94T (genotyped as TT) or T94A (genotyped as CC) proteins. The human FABP1 T94A variant protein had 3-fold higher cholesterol-binding affinity than the WT FABP1 T94T as shown by NBD-cholesterol fluorescence binding assays and by cholesterol isothermal titration microcalorimetry (ITC) binding assays. CC variant hepatocytes also exhibited 30% higher total FABP1 protein. HDL- and LDL-mediated NBD-cholesterol uptake was faster in CC variant than TT WT human hepatocytes. VLDL-mediated uptake of NBD-cholesterol did not differ between CC and TT human hepatocytes. The increased HDL- and LDL-mediated NBD-cholesterol uptake was not associated with any significant change in mRNA levels of SCARB1, LDLR, CETP, and LCAT encoding the key proteins in lipoprotein cholesterol uptake. Thus, the increased HDL- and LDL-mediated NBD-cholesterol uptake by CC hepatocytes may be associated with higher affinity of T94A protein for cholesterol and/or increased total T94A protein level.

Association of L-FABP T94A and MTP I128T polymorphisms with hyperlipidemia in Chinese subjects

The purpose of this study was to evaluate the relation between the L-FABP T94A and MTP I128T polymorphisms and hyperlipidemia in Chinese subjects. We recruited 390 volunteers: 201 hyperlipidemic and 189 healthy volunteers. The L-FABP T94A and MTP I128T polymorphisms were genotyped using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). Anthropometry, lipid profile, and liver function of the subjects were determined. We observed that male carriers of the L-FABP A94 allele had significantly higher body weight (P = 0.012), higher body mass index (BMI) (P = 0.014), and higher plasma triacylglycerol levels (TAG) (P = 0.033) and lower ratios of high-density lipoprotein cholesterol (HDL-C) to total cholesterol (TC) (P = 0.008) than T94 homozygotes. The MTP T128 allele was associated with significantly lower serum TC (P < 0.001) and low-density lipoprotein cholesterol (LDL-C) (P < 0.001) levels in males. There was a direct correlation between the MTP T128 allele and a decreased risk of hyperlipidemia after adjusting for body mass index (OR = 0.327, 95 % CI: 0.178-0.600, P < 0.001). In conclusion, both the MTP I128T and the L-FABP T94A polymorphisms can affect serum lipid levels in the Chinese population. The MTP T128 allele offers protection against hyperlipidemia in the Chinese population.

Enterocyte fatty acid-binding proteins (FABPs): different functions of liver and intestinal FABPs in the intestine

Fatty acid-binding proteins (FABP) are highly abundant cytosolic proteins that are expressed in most mammalian tissues. In the intestinal enterocyte, both liver- (LFABP; FABP1) and intestinal FABPs (IFABP; FABP2) are expressed. These proteins display high-affinity binding for long-chain fatty acids (FA) and other hydrophobic ligands; thus, they are believed to be involved with uptake and trafficking of lipids in the intestine. In vitro studies have identified differences in ligand-binding stoichiometry and specificity, and in mechanisms of FA transfer to membranes, and it has been hypothesized that LFABP and IFABP have different functions in the enterocyte. Studies directly comparing LFABP- and IFABP-null mice have revealed markedly different phenotypes, indicating that these proteins indeed have different functions in intestinal lipid metabolism and whole body energy homeostasis. In this review, we discuss the evolving knowledge of the functions of LFABP and IFABP in the intestinal enterocyte.

Association analysis of FABP1 gene polymorphisms with aspirin-exacerbated respiratory disease in asthma

Previously, we used a proteomic approach to demonstrate that the protein level of fatty acid-binding protein 1 (FABP1) is increased in nasal polyps in patients with aspirin-exacerbated respiratory disease (AERD). To reveal the genetic effect of FABP1 variants, we evaluated the association of FABP1 polymorphisms with the risk of AERD in 207 asthmatics with AERD and 1019 aspirin-tolerant asthmatics (ATA). Seven polymorphisms of FABP1 were selected from the National Center for Biotechnology Information (build 36) using minor allele frequency and linkage disequilibrium criteria. The genotype and haplotype distributions were not significantly different between the AERD and ATA groups in all of the genetic models. The percent decline of forced expiratory volume in 1 second (FEV1) after the oral aspirin challenge (OAC) test did not differ according to single-nucleotide polymorphism (SNP) genotypes. In haplotype analysis, asthmatic patients who were BL2ht2 homozygotes showed a greater decline in FEV1 after the OAC test than subjects who possessed 1 or no copy of BL2ht2 (P = 0.035). However, these observations were not significant after correction for multiple comparisons (corrected P value = 1.00). Neither genotype nor haplotype was associated with the presence of nasal polyposis in the study subjects. Although we did not find a significant association between the FABP1 polymorphisms and AERD, our data suggest that the 7 SNPs are not associated with the increased expression of FABP1 in asthmatic patients with AERD. Further studies of epigenetic factors that may contribute to the increased expression of FABP1 in AERD should be performed.

Human FABP1 T94A variant impacts fatty acid metabolism and PPAR-α activation in cultured human female hepatocytes

Although human liver fatty acid-binding protein (FABP1) T94A variant has been associated with nonalcoholic fatty liver disease and reduced ability of fenofibrate to lower serum triglycerides (TG) to target levels, molecular events leading to this phenotype are poorly understood. Cultured primary hepatocytes from female human subjects expressing the FABP1 T94A variant exhibited increased neutral lipid (TG, cholesteryl ester) accumulation associated with (1) upregulation of total FABP1, a key protein stimulating mitochondrial glycerol-3-phosphate acyltransferase (GPAM), the rate-limiting enzyme in lipogenesis; (2) increased mRNA expression of key enzymes in lipogenesis (GPAM, LPIN2) in heterozygotes; (3) decreased mRNA expression of microsomal triglyceride transfer protein; (4) increased secretion of ApoB100 but not TG; (5) decreased long-chain fatty acid (LCFA) β-oxidation. TG accumulation was not due to any increase in LCFA uptake, de novo lipogenesis, or the alternate monoacylglycerol O-acyltransferase pathway in lipogenesis. Despite increased expression of total FABP1 mRNA and protein, fenofibrate-mediated FABP1 redistribution to nuclei and ligand-induced peroxisome proliferator-activated receptor (PPAR-α) transcription of LCFA β-oxidative enzymes (carnitine palmitoyltransferase 1A, carnitine palmitoyltransferase 2, and acyl-coenzyme A oxidase 1, palmitoyl) were attenuated in FABP1 T94A hepatocytes. Although the phenotype of FABP1 T94A variant human hepatocytes exhibits some similarities to that of FABP1-null or PPAR-α-null hepatocytes and mice, expression of FABP1 T94A variant did not abolish or reduce ligand binding. Thus the FABP1 T94A variant represents an altered/reduced function mutation resulting in TG accumulation.

Structural and functional interaction of fatty acids with human liver fatty acid-binding protein (L-FABP) T94A variant

The human liver fatty acid-binding protein (L-FABP) T94A variant, the most common in the FABP family, has been associated with elevated liver triglyceride levels. How this amino acid substitution elicits these effects is not known. This issue was addressed using human recombinant wild-type (WT) and T94A variant L-FABP proteins as well as cultured primary human hepatocytes expressing the respective proteins (genotyped as TT, TC and CC). The T94A substitution did not alter or only slightly altered L-FABP binding affinities for saturated, monounsaturated or polyunsaturated long chain fatty acids, nor did it change the affinity for intermediates of triglyceride synthesis. Nevertheless, the T94A substitution markedly altered the secondary structural response of L-FABP induced by binding long chain fatty acids or intermediates of triglyceride synthesis. Finally, the T94A substitution markedly decreased the levels of induction of peroxisome proliferator-activated receptor α-regulated proteins such as L-FABP, fatty acid transport protein 5 and peroxisome proliferator-activated receptor α itself meditated by the polyunsaturated fatty acids eicosapentaenoic acid and docosahexaenoic acid in cultured primary human hepatocytes. Thus, although the T94A substitution did not alter the affinity of human L-FABP for long chain fatty acids, it significantly altered human L-FABP structure and stability, as well as the conformational and functional response to these ligands.

Meeting the fetal requirement for polyunsaturated fatty acids in pregnancy

PURPOSE OF REVIEW

The aim of this review is to summarize recent evidence on the importance of individual long chain polyunsaturated fatty acid (LCPUFA) to the developing fetus and the maternal dietary requirement for these.

RECENT FINDINGS

Large-scale randomized controlled trials and innovative genetic and stable isotope studies are providing new insights in this field.

SUMMARY

Large randomized controlled trials of LCPUFA supplementation in pregnancy suggest that higher n-3 LCPUFA intake reduces the risk of preterm birth and increases the length of gestation, with secondary effects on birth weight. There is little evidence of an effect on postnatal visual function and cognition, but interpretation is complicated by maternal metabolic adaptations and adipose tissue status in the newborn. The links between polymorphisms in the FADS genes and tissue fatty acid composition suggest that LCPUFA synthesis influences overall availability. Stable isotope studies have also demonstrated the capacity for LCPUFA synthesis in pregnancy, the fact that n-6 synthesis is greater than n-3, metabolic channeling of individual fatty acids to different fates, and selective placental transfer. Studies linking FADS genotype to cognition imply that n-3 LCPUFA synthesis could have an effect on infant cognition, but more large-scale genetic studies are needed.

Variation in genes related to hepatic lipid metabolism and changes in waist circumference and body weight

We analysed single nucleotide polymorphisms (SNPs) tagging the genetic variability of six candidate genes (ATF6, FABP1, LPIN2, LPIN3, MLXIPL and MTTP) involved in the regulation of hepatic lipid metabolism, an important regulatory site of energy balance for associations with body mass index (BMI) and changes in weight and waist circumference. We also investigated effect modification by sex and dietary intake. Data of 6,287 individuals participating in the European prospective investigation into cancer and nutrition were included in the analyses. Data on weight and waist circumference were followed up for 6.9 ± 2.5 years. Association of 69 tagSNPs with baseline BMI and annual changes in weight as well as waist circumference were investigated using linear regression analysis. Interactions with sex, GI and intake of carbohydrates, fat as well as saturated, monounsaturated and polyunsaturated fatty acids were examined by including multiplicative SNP-covariate terms into the regression model. Neither baseline BMI nor annual weight or waist circumference changes were significantly associated with variation in the selected genes in the entire study population after correction for multiple testing. One SNP (rs1164) in LPIN2 appeared to be significantly interacting with sex (p = 0.0003) and was associated with greater annual weight gain in men (56.8 ± 23.7 g/year per allele, p = 0.02) than in women (-25.5 ± 19.8 g/year per allele, p = 0.2). With respect to gene-nutrient interaction, we could not detect any significant interactions when accounting for multiple testing. Therefore, out of our six candidate genes, LPIN2 may be considered as a candidate for further studies.

The human liver fatty acid binding protein T94A variant alters the structure, stability, and interaction with fibrates

Although the human liver fatty acid binding protein (L-FABP) T94A variant arises from the most commonly occurring single-nucleotide polymorphism in the entire FABP family, there is a complete lack of understanding regarding the role of this polymorphism in human disease. It has been hypothesized that the T94A substitution results in the complete loss of ligand binding ability and function analogous to that seen with L-FABP gene ablation. This possibility was addressed using the recombinant human wild-type (WT) T94T and T94A variant L-FABP and cultured primary human hepatocytes. Nonconservative replacement of the medium-sized, polar, uncharged T residue with a smaller, nonpolar, aliphatic A residue at position 94 of the human L-FABP significantly increased the L-FABP α-helical structure content at the expense of β-sheet content and concomitantly decreased the thermal stability. T94A did not alter the binding affinities for peroxisome proliferator-activated receptor α (PPARα) agonist ligands (phytanic acid, fenofibrate, and fenofibric acid). While T94A did not alter the impact of phytanic acid and only slightly altered that of fenofibrate on the human L-FABP secondary structure, the active metabolite fenofibric acid altered the T94A secondary structure much more than that of the WT T94T L-FABP. Finally, in cultured primary human hepatocytes, the T94A variant exhibited a significantly reduced extent of fibrate-mediated induction of PPARα-regulated proteins such as L-FABP, FATP5, and PPARα itself. Thus, while the T94A substitution did not alter the affinity of the human L-FABP for PPARα agonist ligands, it significantly altered the human L-FABP structure, stability, and conformational and functional response to fibrate.

Impact of L-FABP and glucose on polyunsaturated fatty acid induction of PPARα-regulated β-oxidative enzymes

Liver fatty acid binding protein (L-FABP) is the major soluble protein that binds very-long-chain n-3 polyunsaturated fatty acids (n-3 PUFAs) in hepatocytes. However, nothing is known about L-FABP's role in n-3 PUFA-mediated peroxisome proliferator activated receptor-α (PPARα) transcription of proteins involved in long-chain fatty acid (LCFA) β-oxidation. This issue was addressed in cultured primary hepatocytes from wild-type, L-FABP-null, and PPARα-null mice with these major findings: 1) PUFA-mediated increase in the expression of PPARα-regulated LCFA β-oxidative enzymes, LCFA/LCFA-CoA binding proteins (L-FABP, ACBP), and PPARα itself was L-FABP dependent; 2) PPARα transcription, robustly potentiated by high glucose but not maltose, a sugar not taken up, correlated with higher protein levels of these LCFA β-oxidative enzymes and with increased LCFA β-oxidation; and 3) high glucose altered the potency of n-3 relative to n-6 PUFA. This was not due to a direct effect of glucose on PPARα transcriptional activity nor indirectly through de novo fatty acid synthesis from glucose. Synergism was also not due to glucose impacting other signaling pathways, since it was observed only in hepatocytes expressing both L-FABP and PPARα. Ablation of L-FABP or PPARα as well as treatment with MK886 (PPARα inhibitor) abolished/reduced PUFA-mediated PPARα transcription of these genes, especially at high glucose. Finally, the PUFA-enhanced L-FABP distribution into nuclei with high glucose augmentation of the L-FABP/PPARα interaction reveals not only the importance of L-FABP for PUFA induction of PPARα target genes in fatty acid β-oxidation but also the significance of a high glucose enhancement effect in diabetes.

Influence of SNPs in nutrient-sensitive candidate genes and gene–diet interactions on blood lipids: the DiOGenes study

Blood lipid response to a given dietary intervention could be determined by the effect of diet, gene variants or gene–diet interactions. The objective of the present study was to investigate whether variants in presumed nutrient-sensitive genes involved in lipid metabolism modified lipid profile after weight loss and in response to a given diet, among overweight European adults participating in the Diet Obesity and Genes study. By multiple linear regressions, 240 SNPs in twenty-four candidate genes were investigated for SNP main and SNP–diet interaction effects on total cholesterol, LDL-cholesterol, HDL-cholesterol and TAG after an 8-week low-energy diet (only main effect), and a 6-monthad libitumweight maintenance diet, with different contents of dietary protein or glycaemic index. After adjusting for multiple testing, a SNP–dietary protein interaction effect on TAG was identified for lipin 1 (LPIN1) rs4315495, with a decrease in TAG of − 0·26 mmol/l per A-allele/protein unit (95 % CI − 0·38, − 0·14,P= 0·000043). In conclusion, we investigated SNP–diet interactions for blood lipid profiles for 240 SNPs in twenty-four candidate genes, selected for their involvement in lipid metabolism pathways, and identified one significant interaction betweenLPIN1rs4315495 and dietary protein for TAG concentration.

Serum liver fatty acid binding protein levels correlate positively with obesity and insulin resistance in Chinese young adults

Background

Liver fatty acid–binding protein (FABP1) plays an inconclusive role in adiposity. We investigated the association of serum FABP1 levels with obesity and insulin resistance in Chinese young people under 30 years old.

Methodology and Principal Findings

Cross-sectional analysis including 200 obese and 172 normal-weight subjects matched for age and sex, anthropometric measurements were performed and serum FABP1 and biochemical characteristics were measured. Insulin resistance was determined by homeostasis model assessment of insulin resistance (HOMA-IR) and by the insulin sensitivity index (S_i) derived from Bergman’s minimal model. FABP1 levels in obese subjects were significantly higher than those in normal-weight subjects (p<0.001) and the significance remained after adjustment for age, gender, alanine and aspartate aminotransferases (p<0.001). Serum FABP1 levels were significantly correlated with many metabolic-related parameters, with BMI and triglycerides as the independent determinants. FABP1 levels remained an independent risk factor of insulin resistance assessed by binary S_i (OR = 1.868 per SD unit, 95% CI [1.035–3.373], p = 0.038) after adjustment for age, sex, BMI, waist circumference, systolic blood pressure, serum triacylglycerol, total cholesterol, HDL- and LDL-cholesterol,. FABP1 levels were also elevated with an increasing number of components of the metabolic syndrome (p for trend <0.001). Multiple regression modeling for the MetS and its components demonstrated that hypertriglyceridemia and low HDL-cholesterol were significantly correlated to serum FABP1 levels.

Conclusions and Significance

Serum FABP1 correlates positively with obesity and insulin resistance in Chinese young adults. Our data supports the fact that FABP1 might be an important mediator participating in fatty acid metabolism and energy balance.

Loss of intracellular lipid binding proteins differentially impacts saturated fatty acid uptake and nuclear targeting in mouse hepatocytes

The liver expresses high levels of two proteins with high affinity for long-chain fatty acids (LCFAs): liver fatty acid binding protein (L-FABP) and sterol carrier protein-2 (SCP-2). Real-time confocal microscopy of cultured primary hepatocytes from gene-ablated (L-FABP, SCP-2/SCP-x, and L-FABP/SCP-2/SCP-x null) mice showed that the loss of L-FABP reduced cellular uptake of 12-N-methyl-(7-nitrobenz-2-oxa-1,3-diazo)-aminostearic acid (a fluorescent-saturated LCFA analog) by ∼50%. Importantly, nuclear targeting of the LCFA was enhanced when L-FABP was upregulated (SCP-2/SCP-x null) but was significantly reduced when L-FABP was ablated (L-FABP null), thus impacting LCFA nuclear targeting. These effects were not associated with a net decrease in expression of key membrane proteins involved in LCFA or glucose transport. Since hepatic LCFA uptake and metabolism are closely linked to glucose uptake, the effect of glucose on L-FABP-mediated LCFA uptake and nuclear targeting was examined. Increasing concentrations of glucose decreased cellular LCFA uptake and even more extensively decreased LCFA nuclear targeting. Loss of L-FABP exacerbated the decrease in LCFA nuclear targeting, while loss of SCP-2 reduced the glucose effect, resulting in enhanced LCFA nuclear targeting compared with control. Simply, ablation of L-FABP decreases LCFA uptake and even more extensively decreases its nuclear targeting.

Lactase persistence and lipid pathway selection in the Maasai

The Maasai are a pastoral people in Kenya and Tanzania, whose traditional diet of milk, blood and meat is rich in lactose, fat and cholesterol. In spite of this, they have low levels of blood cholesterol, and seldom suffer from gallstones or cardiac diseases. Field studies in the 1970s suggested that the Maasai have a genetic adaptation for cholesterol homeostasis. Analysis of HapMap 3 data using Fixation Index (Fst) and two metrics of haplotype diversity: the integrated Haplotype Score (iHS) and the Cross Population Extended Haplotype Homozygosity (XP-EHH), identified genomic regions and single nucleotide polymorphisms (SNPs) as strong candidates for recent selection for lactase persistence and cholesterol regulation in 143-156 founder individuals from the Maasai population in Kinyawa, Kenya (MKK). The non-synonmous SNP with the highest genome-wide Fst was the TC polymorphism at rs2241883 in Fatty Acid Binding Protein 1(FABP1), known to reduce low density lipoprotein and tri-glyceride levels in Europeans. The strongest signal identified by all three metrics was a 1.7 Mb region on Chr2q21. This region contains the genes LCT (Lactase) and MCM6 (Minichromosome Maintenance Complex Component) involved in lactase persistence, and the gene Rab3GAP1 (Rab3 GTPase-activating Protein Catalytic Subunit), which contains polymorphisms associated with total cholesterol levels in a genome-wide association study of >100,000 individuals of European ancestry. Sanger sequencing of DNA from six MKK samples showed that the GC-14010 polymorphism in the MCM6 gene, known to be associated with lactase persistence in Africans, is segregating in MKK at high frequency (∼58%). The Cytochrome P450 Family 3 Subfamily A (CYP3A) cluster of genes, involved in cholesterol metabolism, was identified by Fst and iHS as candidate loci under selection. Overall, our study identified several specific genomic regions under selection in the Maasai which contain polymorphisms in genes associated with lactase persistence and cholesterol regulation.

Intracellular cholesterol-binding proteins enhance HDL-mediated cholesterol uptake in cultured primary mouse hepatocytes

A major gap in our knowledge of rapid hepatic HDL cholesterol clearance is the role of key intracellular factors that influence this process. Although the reverse cholesterol transport pathway targets HDL to the liver for net elimination of free cholesterol from the body, molecular details governing cholesterol uptake into hepatocytes are not completely understood. Therefore, the effects of sterol carrier protein (SCP)-2 and liver fatty acid-binding protein (L-FABP), high-affinity cholesterol-binding proteins present in hepatocyte cytosol, on HDL-mediated free cholesterol uptake were examined using gene-targeted mouse models, cultured primary hepatocytes, and 22-[N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)-amino]-23,24-bisnor-5-cholen-3β-ol (NBD-cholesterol). While SCP-2 overexpression enhanced NBD-cholesterol uptake, counterintuitively, SCP-2/SCP-x gene ablation also 1) enhanced the rapid molecular phase of free sterol uptake detectable in <1 min and initial rate and maximal uptake of HDL free cholesterol and 2) differentially enhanced free cholesterol uptake mediated by the HDL3, rather than the HDL2, subfraction. The increased HDL free cholesterol uptake was not due to increased expression or distribution of the HDL receptor [scavenger receptor B1 (SRB1)], proteins regulating SRB1 [postsynaptic density protein (PSD-95)/Drosophila disk large tumor suppressor (dlg)/tight junction protein (ZO1) and 17-kDa membrane-associated protein], or other intracellular cholesterol trafficking proteins (steroidogenic acute response protein D, Niemann Pick C, and oxysterol-binding protein-related proteins). However, expression of L-FABP, the single most prevalent hepatic cytosolic protein that binds cholesterol, was upregulated twofold in SCP-2/SCP-x null hepatocytes. Double-immunogold electron microscopy detected L-FABP sufficiently close to SRB1 for direct interaction, similar to SCP-2. These data suggest a role for L-FABP in HDL cholesterol uptake, a finding confirmed with SCP-2/SCP-x/L-FABP null mice and hepatocytes. Taken together, these results suggest that L-FABP, particularly in the absence of SCP-2, plays a significant role in HDL-mediated cholesterol uptake in cultured primary hepatocytes.

Loss of liver FA binding protein significantly alters hepatocyte plasma membrane microdomains

Although lipid-rich microdomains of hepatocyte plasma membranes serve as the major scaffolding regions for cholesterol transport proteins important in cholesterol disposition, little is known regarding intracellular factors regulating cholesterol distribution therein. On the basis of its ability to bind cholesterol and alter hepatic cholesterol accumulation, the cytosolic liver type FA binding protein (L-FABP) was hypothesized to be a candidate protein regulating these microdomains. Compared with wild-type hepatocyte plasma membranes, L-FABP gene ablation significantly increased the proportion of cholesterol-rich microdomains. Lack of L-FABP selectively increased cholesterol, phospholipid (especially phosphatidylcholine), and branched-chain FA accumulation in the cholesterol-rich microdomains. These cholesterol-rich microdomains are important, owing to enrichment therein of significant amounts of key transport proteins involved in uptake of cholesterol [SR-B1, ABCA-1, P-glycoprotein (P-gp), sterol carrier binding protein (SCP-2)], FA transport protein (FATP), and glucose transporters 1 and 2 (GLUT1, GLUT2) insulin receptor. L-FABP gene ablation enhanced the concentration of SCP-2, SR-B1, FATP4, and GLUT1 in the cholesterol-poor microdomains, with functional implications in HDL-mediated uptake and efflux of cholesterol. Thus L-FABP gene ablation significantly impacted the proportion of cholesterol-rich versus -poor microdomains in the hepatocyte plasma membrane and altered the distribution of lipids and proteins involved in cholesterol uptake therein.

Human liver fatty acid binding protein (hFABP1) gene is regulated by liver-enriched transcription factors HNF3β and C/EBPα

The human liver fatty acid binding protein (hFABP1) participates in cellular long-chain fatty acid trafficking and regulation of lipid metabolism and changes in hFABP1 are associated with an increased risk for type 2 diabetes, cardiovascular disease (CVD), and metabolic syndromes. Gene regulation of hFABP1 is not fully understood. Therefore, in the present study, the full length hFABP1 promoter (nucleotides -2125 to +51) and a series of truncated promoter regions were cloned. A luciferase reporter assay revealed that nucleotides -255 to +50 in the promoter region contained full of maximum hFABP1 promoter activity compared with the full length promoter. Furthermore high activity was shown when the plasmid was transfected into liver-derived cells such as the human hepatoblastoma cell line HepG2 and the hepatoma cell line Huh7. TFSEARCH and TESS programs were used to predict potential transcription factor binding sites. Two putative binding sites for the liver-enriched transcription factors hepatocyte nuclear factor 3β (HNF3β) and CCAAT/enhancer binding protein α (C/EBPα) were identified in the -255 nt to -155 nt hFABP1 promoter region. Site-directed mutagenesis of these two sites reduced dramatically hFABP1 promoter activity. In addition, the electrophoretic mobility shift assay (EMSA) and chromatin immunoprecipitation assay (ChIP) revealed that these binding sites were recognized by HNF3β and C/EBPα respectively. Overexpression of HNF3β and C/EBPα enhanced the transcription of hFABP1 and consequently improved the protein level of hFABP1 in HepG2 cells, while knockdown of HNF3β and C/EBPα showed the inverse effects. Taken together, the hFABP1 gene is highly transcribed in liver-derived cells, and regulated predominantly by liver-enriched transcription factors HNF3β and C/EBPα.

The human fatty acid-binding protein family: evolutionary divergences and functions

Fatty acid-binding proteins (FABPs) are members of the intracellular lipid-binding protein (iLBP) family and are involved in reversibly binding intracellular hydrophobic ligands and trafficking them throughout cellular compartments, including the peroxisomes, mitochondria, endoplasmic reticulum and nucleus. FABPs are small, structurally conserved cytosolic proteins consisting of a water-filled, interior-binding pocket surrounded by ten anti-parallel beta sheets, forming a beta barrel. At the superior surface, two alpha-helices cap the pocket and are thought to regulate binding. FABPs have broad specificity, including the ability to bind long-chain (C16-C20) fatty acids, eicosanoids, bile salts and peroxisome proliferators. FABPs demonstrate strong evolutionary conservation and are present in a spectrum of species including Drosophila melanogaster, Caenorhabditis elegans, mouse and human. The human genome consists of nine putatively functional protein-coding FABP genes. The most recently identified family member, FABP12, has been less studied.

Polymorphisms in fatty acid binding protein 5 show association with type 2 diabetes

Genes for the fatty acid binding proteins (FABP) family encode small 14-15 kDa cytosolic proteins and can be regulated during type 2 diabetes mellitus (T2DM) and obesity. This study compared association of single nucleotide polymorphisms (SNPs) in FABP1-5 with T2DM in different ethnic groups. Associations with T2DM of SNPs in these proteins were assessed in African American (AA), non-Hispanic White (NHW), and Hispanic American (HA) individuals. A total of 650 DNA samples were genotyped; control samples were obtained from Coriell's North American Human Variation Panel Repository (NAHVP) of apparently healthy individuals and T2DM cases were taken from the American Diabetes Association GENNID Study. The rs454550 SNP of FABP5 showed a significant association with T2DM in NHW (OR: 9.03, 95% CI: 1.13-71.73, p=0.014). Our analysis also identified a new FABP5 SNP (nSNP) that showed a significant association with T2DM in NHW (OR: 0.44, 95% CI: 0.19-0.99, p=0.045) and AA (OR: 0.17, 95% CI: 0.03-0.80, p=0.016). The Ala54Thr FABP2 polymorphism was significantly associated with T2DM in HA individuals only (OR: 1.85, 95% CI: 1.05-3.27, p=0.032). All other FABP SNPs did not show association with T2DM. These findings suggest a potential distinct role(s) of SNPs in FABP5 and FABP2 genes in T2DM in different populations.

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.

L-FABP T94A decreased fatty acid uptake and altered hepatic triglyceride and cholesterol accumulation in Chang liver cells stably transfected with L-FABP

Liver fatty acid-binding protein (L-FABP, FABP1) is a highly conserved key factor in lipid metabolism. This study was undertaken to verify whether the T94A mutation in the L-FABP gene affects fatty acid uptake and intracellular esterification into specific lipid pools. Candidate SNPs were recreated using site-directed mutagenesis and tested for physical function in stably transfected Chang liver cell lines. We found that the T94A mutant of L-FABP lowered FFA uptake but had no effect on FFA efflux. L-FABP T94A-expressing cells showed decreased triglyceride content and increased cholesterol accumulation compared to the wild-type control for cells incubated with an FFA mixture (oleate: palmitate, 2:1 ratio). In conclusion, our study provided additional indications of the functional relevance of the L-FABP T94A SNP in hepatic fatty acid and lipid metabolism in humans.

Univariate and bivariate linkage analysis identifies pleiotropic loci underlying lipid levels and type 2 diabetes risk

Dyslipidemia frequently co-occurs with type 2 diabetes (T2D) and with obesity. To investigate whether the co-occurrence is due to pleiotropic genes, we performed univariate linkage analysis of lipid levels and bivariate linkage analysis of pairs of lipid levels and of lipid levels paired with T2D, body mass index (BMI), and waist-hip ratio (WHR) in the African American subset of the Genetics of NIDDM (GENNID) sample. We obtained significant evidence for a pleiotropic low density lipoprotein cholesterol (LDL-C)-T2D locus on chromosome 1 at 16-19 megabases (MB) (bivariate lod = 4.41), as well as a non-pleiotropic triglyceride (TG) locus on chromosome 20 at 28-34 MB (univariate lod = 3.57). In addition, near-significant evidence supported TG-T2D loci on chromosome 2 at 81-101 MB (bivariate lod = 4.23) and 232-239 MB (bivariate lod = 4.27) and on chromosome 7 at 147-151 MB (univariate lod = 3.08 for TG with P = 0.041 supporting pleiotropy with T2D), as well as an LDL-C-BMI locus on chromosome 3 at 137-147 MB (bivariate lod score = 4.25). These findings provide evidence that at least some of the co-occurrence of dyslipidemia with T2D and obesity is due to common underlying genes.

Caveolin, sterol carrier protein-2, membrane cholesterol-rich microdomains and intracellular cholesterol trafficking

While the existence of membrane lateral microdomains has been known for over 30 years, interest in these structures accelerated in the past decade due to the discovery that cholesterol-rich microdomains serve important biological functions. It is increasingly appreciated that cholesterol-rich microdomains in the plasma membranes of eukaryotic cells represent an organizing nexus for multiple cellular proteins involved in transmembrane nutrient uptake (cholesterol, fatty acid, glucose, etc.), cell-signaling, immune recognition, pathogen entry, and many other roles. Despite these advances, however, relatively little is known regarding the organization of cholesterol itself in these plasma membrane microdomains. Although a variety of non-sterol markers indicate the presence of microdomains in the plasma membranes of living cells, none of these studies have demonstrated that cholesterol is enriched in these microdomains in living cells. Further, the role of cholesterol-rich membrane microdomains as targets for intracellular cholesterol trafficking proteins such as sterol carrier protein-2 (SCP-2) that facilitate cholesterol uptake and transcellular transport for targeting storage (cholesterol esters) or efflux is only beginning to be understood. Herein, we summarize the background as well as recent progress in this field that has advanced our understanding of these issues.

Hepatic phenotype of liver fatty acid binding protein gene-ablated mice

Although the function of liver fatty acid binding protein in hepatic fatty acid metabolism has been extensively studied, its potential role in hepatic cholesterol homeostasis is less clear. Although hepatic cholesterol accumulation was initially reported in L-FABP-null female mice, that study was performed with early N2 backcross generation mice. To resolve whether the hepatic cholesterol phenotype in these L-FABP(-/-) mice was attributable to genetic inhomogeneity, these L-FABP(-/-) mice were further backcrossed to C57Bl/6 mice up to the N10 (99.9% homogeneity) generation. Hepatic total cholesterol accumulation was observed in female, but not male, L-FABP(-/-) mice at all (N2, N4, N6, N10) backcross generations examined. The greater total cholesterol was due to increased hepatic levels of both unesterified (free) cholesterol and esterified cholesterol. Altered hepatic cholesterol accumulation correlated directly with L-FABP's ability to bind cholesterol with high affinity as shown by direct L-FABP binding of fluorescent cholesterol analogs (NBD-cholesterol, dansyl-cholesterol), a photoactivatable cholesterol analog [free cholesterol benzophenone (FCBP)], and free cholesterol (circular dichroism, isothermal titration microcalorimetry). One mole of fluorescent sterol was bound per mole of L-FABP. This was confirmed by photo-cross-linking studies with the photoactivatable cholesterol analog FCBP and by isothermal titration calorimetry with free cholesterol, which showed that L-FABP bound only one sterol molecule per L-FABP molecule. In contrast, the hepatic phenotype of male, but not female, L-FABP(-/-) mice was characterized by decreased hepatic triacylglycerol levels at all backcross generations examined. Taken together, these data support the hypothesis that L-FABP plays a role in physiological regulation of not only hepatic fatty acid metabolism, but also that of hepatic cholesterol.

L-FABP directly interacts with PPARalpha in cultured primary hepatocytes

Although studies with liver type fatty acid binding protein (L-FABP) gene ablated mice demonstrate a physiological role for L-FABP in hepatic fatty acid metabolism, little is known about the mechanisms whereby L-FABP elicits these effects. Studies indicate that L-FABP may function to shuttle lipids to the nucleus, thereby increasing the availability of ligands of nuclear receptors, such as peroxisome proliferator-activated receptor-alpha (PPARalpha). The data herein suggest that such mechanisms involve direct interaction of L-FABP with PPARalpha. L-FABP was shown to directly interact with PPARalpha in vitro through co-immunoprecipitation (co-IP) of pure proteins, altered circular dichroic (CD) spectra, and altered fluorescence spectra. In vitro fluorescence resonance energy transfer (FRET) between Cy3-labeled PPARalpha and Cy5-labeled L-FABP proteins showed that these proteins bound with high affinity (Kd approximately 156 nM) and in close proximity (intermolecular distance of 52A). This interaction was further substantiated by co-IP of both proteins from liver homogenates of wild-type mice. Moreover, double immunogold electron microscopy and FRET confocal microscopy of cultured primary hepatocytes showed that L-FABP was in close proximity to PPARalpha (intermolecular distance 40-49A) in vivo. Taken together, these studies were consistent with L-FABP regulating PPARalpha transcriptional activity in hepatocytes through direct interaction with PPARalpha. Our in vitro and imaging experiments demonstrate high affinity, structural molecular interaction of L-FABP with PPARalpha and suggest a functional role for L-FABP interaction with PPARalpha in long chain fatty acid (LCFA) metabolism.