Physiological properties and functions of intracellular fatty acid-binding proteins

Associations between Fatty Acid-Binding Protein 4⁻A Proinflammatory Adipokine and Insulin Resistance, Gestational and Type 2 Diabetes Mellitus

There is ample scientific evidence to suggest a link between the fatty acid-binding protein 4 (FABP4) and insulin resistance, gestational (GDM), and type 2 (T2DM) diabetes mellitus. This novel proinflammatory adipokine is engaged in the regulation of lipid metabolism at the cellular level. The molecule takes part in lipid oxidation, the regulation of transcription as well as the synthesis of membranes. An involvement of FABP4 in the pathogenesis of obesity and insulin resistance seems to be mediated via FABP4-dependent peroxisome proliferator-activated receptor γ (PPARγ) inhibition. A considerable number of studies have shown that plasma concentrations of FABP4 is increased in obesity and T2DM, and that circulating FABP4 levels are correlated with certain clinical parameters, such as body mass index, insulin resistance, and dyslipidemia. Since plasma-circulating FABP4 has the potential to modulate the function of several types of cells, it appears to be of extreme interest to try to develop potential therapeutic strategies targeting the pathogenesis of metabolic diseases in this respect. In this manuscript, representing a detailed review of the literature on FABP4 and the abovementioned metabolic disorders, various mechanisms of the interaction of FABP4 with insulin signaling pathways are thoroughly discussed. Clinical aspects of insulin resistance in diabetic patients, including women diagnosed with GDM, are analyzed as well.

Anti-obesity effect in high-fat-diet-induced obese C57BL/6 mice: Study of a novel extract from mulberry (Morus alba) leaves fermented with Cordyceps militaris

The therapeutic effects of mulberry (Morus alba) leaves on lipid metabolism, including lipogenesis, lipolysis and hyperlipidemia are widely known, although their fermented products are yet to be applied. To investigate the therapeutic effects of a novel extract of mulberry leaves fermented with Cordyceps militaris (EMfC) on lipid metabolism, the lipid profile of serum, lipid accumulation, lipolytic activity and lipogenesis regulation were measured in high fat diet (HFD)-induced obese C57BL/6 mice treated with EMfC for 12 weeks. Briefly, the concentrations of low-density lipoprotein, triglyceride, total cholesterol and glucose significantly decreased in the serum of the HFD+EMfC treated group when compared with the HFD+Vehicle treated group, while the levels of high-density lipoprotein increased in the HFD+EMfC group. The amount of abdominal fat and the size of adipocytes were significantly lower in the HFD+EMfC treated group when compared with the HFD+Vehicle treated group. The weight and number of lipid droplets of liver tissue exhibited a similar decrease. Furthermore, the mRNA levels of peroxisome proliferator-activated receptor-γ for adipogenesis as well as adipocyte protein 2 and Fas cell surface death receptor for lipogenesis reduced following EMfC treatment for 12 weeks. Phosphorylation of perilipin and hormone-sensitive lipase, and in the adipose triglyceride lipase expression showed a significant increase in the HFD+EMfC treated group. These results indicated that EMfC may prevent fat accumulation in the HFD-induced obese C57BL/6 mice through the inhibition of lipogenesis and by stimulating lipolysis. Thus, the results provide evidence for the potential use of EMfC as an anti-obesity complex in the treatment of obesity.

Role of FABP7 in tumor cell signaling

Lipids are major molecules for the function of organisms and are involved in the pathophysiology of various diseases. Fatty acids (FAs) signaling and their metabolism are some of the most important pathways in tumor development, as lipids serve as energetic sources during carcinogenesis. Fatty acid binding proteins (FABPs) facilitate FAs transport to different cell organelles, modulating their metabolism along with mediating other physiological activities. FABP7, brain-typed FABP, is thought to be an important molecule for cell proliferation in healthy as well as diseased organisms. Several studies on human tumors and tumor-derived cell lines put FABP7 in the center of tumorigenesis, and its high expression level has been reported to correlate with poor prognosis in different tumor types. Several types of FABP7-expressing tumors have shown an up-regulation of cell signaling activity, but molecular mechanisms of FABP7 involvement in tumorigenesis still remain elusive. In this review, we focus on the expression and function of FABP7 in different tumors, and possible mechanisms of FABP7 in tumor proliferation and migration.

Adipose tissue and body composition in women six years after gestational diabetes: factors associated with development of type 2 diabetes

Factors differentiating women at highest risk of progression to type 2 diabetes mellitus (T2DM) after gestational diabetes mellitus (GDM) are incompletely known. Our aim was to characterize adipose tissue and body composition in relation to glucose metabolism in women with a history of GDM and to identify factors associated with development of T2DM. We examined glucose tolerance (OGTT), insulin sensitivity (HOMA-IR), body composition (anthropometry, air displacement plethysmography), and blood chemistry in 39 women 6 years after GDM. An adipose tissue biopsy was obtained to assess the size, number, and lipolytic activity of adipocytes, and adipokine release and density of immune cells and blood vessels in adipose tissue. Normal glucose tolerance (NGT) was identified in 31 women and impaired glucose metabolism (IGM) in 8. Women with IGM had higher BMI/fat mass, and related expected adipose tissue features, than women with NGT. Ethnicity was similar in the groups, but numerically there was a higher proportion of European women in the NGT group and a higher proportion of non-European women in the IGM group. BMI was the best discriminator of NGT versus IGM (multivariable logistic regression: OR = 1.34, P < 0.01). Waist-to-height ratio and adipocyte volume were most strongly associated with HOMA-IR (multivariable linear regression: R² = 0.656, P < 0.001). After adjustment for BMI/ethnicity, women with IGM had increased serum adipocyte fatty acid-binding protein, weight gain after index pregnancy, and a lower proportion of fat-free mass. These factors, together with high BMI, abdominal fat distribution, and enlarged adipocytes, may increase the risk of progression to T2DM after GDM.

Anti-Obesity Activities of Chikusetsusaponin IVa and Dolichos lablab L. Seeds

Obesity, a condition where excess body fat accumulates to the extent, causes a negative effect on health. Previously, we reported the extract of Dolichos lablab L. (DLL-Ex) inhibited high-fat diet (HFD)-induced increases in body weight and body fat mass and ameliorated increases in body weight. In the present work, we studyed the molecular mechanism for the inhibitory effect of DLL-Ex or Chikusetsusaponin IVa (CS-IVa), as isolated from Dolichos lablab L. (DLL) seeds extract, on adipocyte differentiation. We evaluated the effect of DLL-Ex, an anti-obesity agent, and CS-IVa, an active component of DLL-Ex, on 3T3-L1 cell differentiation via Oil red O assay and Q-PCR, along with their effects on CCAAT element binding protein alpha (C/EBPα), peroxisome proliferator-activated receptor gamma (PPARγ), fatty acid synthase (FAS), and fatty acid-binding protein 4 (FABP4) mRNA transcriptions. FAS and FABP4 protein expression levels after exposure to CS-IVa were also tested. The results showed that DLL-Ex and CS-IVa have potent inhibitory activity on adipocyte differentiation. Therefore, DLL and CS-IVa may be developed as a functional food material to treat obesity.

Molecular Dynamics Exploration of Selectivity of Dual Inhibitors 5M7, 65X, and 65Z toward Fatty Acid Binding Proteins 4 and 5

Designing highly selective inhibitors of fatty acid binding proteins 4 and 5 (FABP4 and FABP5) is of importance for treatment of some diseases related with inflammation, metabolism, and tumor growth. In this study, molecular dynamics (MD) simulations combined with molecular mechanics generalized Born surface area (MM-GBSA) method were performed to probe binding selectivity of three inhibitors (5M7, 65X, and 65Z) to FABP4/FABP5 with K_i values of 0.022/0.50 μM, 0.011/0.086 μM, and 0.016/0.12 μM, respectively. The results not only suggest that all inhibitors associate more tightly with FABP4 than FABP5, but also prove that the main forces driving the selective bindings of inhibitors to FABP4 and FABP5 stem from the difference in the van der Waals interactions and polar interactions of inhibitors with two proteins. Meanwhile, a residue-based free energy decomposition method was applied to reveal molecular basis that inhibitors selectively interact with individual residues of two different proteins. The calculated results show that the binding difference of inhibitors to the residues (Phe16, Phe19), (Ala33, Gly36), (Phe57, Leu60), (Ala75, Ala78), (Arg126, Arg129), and (Tyr128, Tyr131) in (FABP4, FABP5) drive the selectivity of inhibitors toward FABP4 and FABP5. This study will provide great help for further design of effective drugs to protect against a series of metabolic diseases, arteriosclerosis, and inflammation.

Serum Adipocyte Fatty Acid-Binding Protein 4 Levels Are Independently Associated with Radioisotope Glomerular Filtration Rate in Type 2 Diabetic Patients with Early Diabetic Nephropathy

Serum fatty acid-binding protein 4 (FABP4) has been linked to renal dysfunction. This study evaluated the association between serum FABP4 and the radioisotope glomerular filtration rate (rGFR) in type 2 diabetic patients (T2DM) with early diabetic nephropathy. Twenty healthy controls and 172 patients with T2DM were enrolled. Serum FABP4 and renal impairment biomarkers including urinary albumin-to-creatinine ratio (UACR), serum retinal-binding protein 4 (RBP4), urinary cystatin C-to-creatinine ratio (CysC/Cr), and neutrophil gelatinase-associated lipocalin-to-creatinine ratio (NGAL/Cr) were measured. Diethylenetriaminepentaacetic acid (99mTc-DTPA) was used to test rGFR. Serum FABP4 levels were higher in T2DM patients compared with the controls. There was no significant correlation between serum FABP4 and UACR in patients with T2DM. Multivariate stepwise regression analysis showed that, in patients with T2DM, FABP4 was significantly associated with rGFR while CysC/Cr and RBP4 were significantly associated with UACR independently. But UACR had no independent association with rGFR. NGAL/Cr had no significant correlation with either rGFR or UACR. FABP4 might be an early biomarker for diabetic nephropathy if combined with UACR.

Serum concentrations of fatty acid-binding protein 4 in Chinese children with type 1 diabetes mellitus

OBJECTIVE

The aim of this study was to test the serum concentrations of fatty acid-binding protein 4(FABP4) in children with type 1 diabetes mellitus (T1DM) and to determine the relationship between patients with good and poor glycaemic control who were classified according to their glycated hemoglobin A1c (HbA1c) levels.

METHODS

Children with T1DM were selected consecutively from our department from May 2016 to May 2017. For comparison, the same non-diabetic, age, sex, BMI and pubertal stage-matched healthy children were selected consecutively among non-diabetic children. Serum levels of FABP4 were batch analyzed using a commercially available ELISA assay. Patients were categorized into two groups according to their glycaemic control (Poor glycaemic control is HbA1c>7.0% and good is ≤7.0%).

RESULTS

In this study, 118 children with T1DM and 118 control cases were included. The mean serum FABP4 concentrations were significantly (P<.001) higher in T1DM as compared to controls. There was a modest correlation between serum concentrations of FABP4 and duration of diabetes (r=0.484, P<.001). Fifty-two patients were defined as poor glycaemic control (HbA1c>7.0%). The mean serum FABP4 concentrations were significantly (P=.002) higher in the poor glycaemic control as compared to the good glycaemic control. After adjusting for all other predictors, FABP4 remained an independent poor glycaemic control indictor with an adjusted OR of 1.07 (95% CI, 1.01-1.13; P=.03).

CONCLUSIONS

The present results indicated that FABP4 concentrations were increased and independently associated with the poor glycaemic control in Chinese children with T1DM.

Association of genetic variants and expression levels of porcine FABP4 and FABP5 genes

The FABP4 and FABP5 genes, coding for fatty acid transport proteins, have long been studied as positional candidate genes for SSC4 QTL affecting fat deposition and composition traits in pigs. Polymorphisms in these genes, FABP4:g.2634_2635insC and FABP5:g.3000T>G, have previously been associated with fatness traits in an Iberian by Landrace cross (IBMAP). The aim of the present work was to evaluate the functional implication of these genetic variants. For this purpose, FABP4 and FABP5 mRNA expression levels in 114 BC1_LD animals (25% Iberian × 75% Landrace) were analyzed using real-time quantitative PCR in backfat and muscle. FABP4 gene expression in backfat, but not in muscle, was associated with FABP4:g.2634_2635insC. In contrast, FABP5:g.3000T>G was not associated with gene expression levels. An expression-based genome-wide association study highlighted the FABP4:g.2634_2635insC polymorphism as the polymorphism most associated with FABP4 gene expression in backfat. Furthermore, other genomic regions associated in trans with the mRNA expression of FABP4 in backfat and FABP5 in muscle were also identified. Finally, two putative transcription binding sites for PPARG and NR4A2 may be affected by the FABP4:g.2634_2635insC polymorphism, modifying FABP4 gene expression. Our results reinforce FABP4 as a candidate gene for fatness traits on SSC4.

Dopamine D2L receptor-interacting proteins regulate dopaminergic signaling

Dopamine receptor family proteins include seven transmembrane and trimeric GTP-binding protein-coupled receptors (GPCRs). Among them, the dopamine D2 receptor (D2R) is most extensively studied. All clinically used antipsychotic drugs serve as D2R antagonists in the mesolimbic dopamine system, and their ability to block D2R signaling is positively correlated with antipsychotic efficiency. Human genetic studies also show a significant association of DRD2 polymorphisms with disorders including schizophrenia and Parkinson's disease. D2R exists as two alternatively spliced isoforms, the long isoform (D2LR) and the short isoform (D2SR), which differ in a 29-amino acid (AA) insert in the third cytoplasmic loop. Importantly, previous reports demonstrate functional diversity between the two isoforms in humans. In this review, we focus on binding proteins that specifically interact with the D2LR 29AA insert. We discuss how D2R activities are mediated not only by heterotrimeric G proteins but by D2LR-interacting proteins, which in part regulate diverse D2R activities.

Fatty acid-binding protein 4 regulates fatty infiltration after rotator cuff tear by hypoxia-inducible factor 1 in mice

BACKGROUND

Fatty infiltration in skeletal muscle is directly linked to loss of muscle strength and is associated with various adverse physical outcomes such as muscle atrophy, inflammation, insulin resistance, mobility impairments, and even mortality in the elderly. Aging, mechanical unloading, muscle injury, and hormonal imbalance are main causes of muscle fat accumulation, and the fat cells are derived from muscle stem cells via adipogenic differentiation. However, the pathogenesis and molecular mechanisms of fatty infiltration in muscles are still not fully defined. Fatty acid-binding protein 4 (FABP4) is a carrier protein for fatty acids and is involved in fatty acid uptake, transport, and lipid metabolism. Rotator cuff tear (RCT) usually occurs in the elderly and is closely related with fatty infiltration in injured muscle. To investigate potential mechanisms for fatty infiltration other than adipogenic differentiation of muscle stem cells, we examined the role of FABP4 in muscle fatty infiltration in an RCT mouse model.

METHODS

In the RCT model, we evaluated the expression of FABP4 by qRT-PCR, western blotting, and immunohistochemical analyses. Histological changes such as inflammation and fat accumulation in the injured muscles were examined immunohistochemically. To evaluate whether hypoxia induces FABP4 expression, the levels of FABP4 mRNA and protein in C3H10T1/2 cells after hypoxia were examined. Using a transient transfection assay in 293T cells, we assessed the promoter activity of FABP4 by hypoxia-inducible factors (HIFs). Additionally, we evaluated the reduction in FABP4 expression and fat accumulation using specific inhibitors for HIF1 and FABP4, respectively.

RESULTS

FABP4 expression was significantly increased after RCT in mice, and its expression was localized in the intramuscular fatty region. Rotator cuff tear-induced FABP4 expression was up-regulated by hypoxia. HIF1α, which is activated by hypoxia, augmented the promoter activity of FABP4, together with HIF1β. Hypoxia-induced FABP4 expression was significantly decreased by HIF1 inhibitor treatment. Furthermore, in RCT model mice, fat accumulation was remarkably reduced by FABP4 inhibitor treatment.

CONCLUSIONS

This study shows that RCT induces FABP4 expression, leading to fat accumulation in injured muscle. FABP4 transcription is regulated by the direct binding of HIF1 to the FABP4 promoter in the hypoxic condition induced by RCT. Fat accumulation in injured muscle was reduced by the inhibition of FABP4. Ultimately, in the RCT model, we identified a novel mechanism for fatty infiltration by FABP4, which differs from adipogenic differentiation of muscle stem cells, and we found that fatty infiltration might be regulated by inhibition of HIF1 or FABP4.

Knockdown of lncRNA MIR31HG inhibits adipocyte differentiation of human adipose-derived stem cells via histone modification of FABP4

Adipogenesis plays an important role in the regulation of whole-body energy homeostasis and is inextricably related to obesity. Several studies have highlighted the relevance of microRNAs in adipocyte differentiation, but the contributions of long non-coding RNAs (lncRNAs) are still largely uncharacterized. Here, we determined that lncRNA MIR31HG is related to adipocyte lineage commitment. We demonstrated that knockdown of MIR31HG inhibited adipocyte differentiation, whereas overexpression of MIR31HG promoted adipogenesis in vitro and in vivo. Furthermore, inhibition of MIR31HG reduced the enrichment of active histone markers, histone H3 lysine 4 trimethylation (H3K4me3) and acetylation (AcH3), in the promoter of the adipogenic-related gene, fatty acid binding protein 4 (FABP4), leading to suppression of its expression and adipogenesis. These results provide new insights into the molecular mechanisms of MIR31HG in terms of adipogenesis and may have implications for obesity and associated disorders.

The long variant of human ileal bile acid-binding protein associated with colorectal cancer exhibits sub-cellular localization and lipid binding behaviour distinct from those of the common isoform

BACKGROUND

Ileal bile acid-binding protein, IBABP, participates in the intracellular trafficking of bile salts and influences their signaling activities. The recently discovered variant, IBABP-L, bearing an N-terminal 49-amino acid extension, was found to be associated with colorectal cancer and to protect cancer cells from the cytotoxic effects of deoxycholate. However, the precise function and the molecular properties of this variant are currently unknown.

METHODS

Bioinformatics tools and confocal microscopy were used to investigate the sub-cellular localization of IBABP-L; protein dynamics, ligand binding and interaction with membrane models were studied by 2D NMR and fluorescence spectroscopy.

RESULTS

Based on sub-cellular localization experiments we conclude that IBABP-L is targeted to the secretory pathway by a 24-residue signal peptide and, upon its cleavage, the mature protein is constitutively released into the extracellular space. Site-resolved NMR experiments indicated the distinct preference of primary and secondary bile salts to form either heterotypic or homotypic complexes with IBABP-L. The presence of the relatively dynamic N-terminal extension, originating only subtle conformational perturbations in the globular domain, was found to influence binding site occupation in IBABP-L as compared to IBABP. Even more pronounced differences were found in the tendency of the two variants to associate with phospholipid bilayers.

CONCLUSIONS

IBABP-L exhibits different sub-cellular localization, ligand-binding properties and membrane interaction propensity compared to the canonical short isoform.

GENERAL SIGNIFICANCE

Our results constitute an essential first step towards an understanding of the role of IBABP-L in bile salt trafficking and signaling under healthy and pathological conditions.

Molecular differences between human liver fatty acid binding protein and its T94A variant in their unbound and lipid-bound states

Liver fatty acid binding protein (L-FABP) is an abundant cytosolic protein playing a central role in intracellular lipid trafficking. The L-FABP T94A variant, originating from one of the most common polymorphisms in the FABP family, is associated with several lipid-related disorders. However, the molecular factors that determine the observed functional differences are currently unknown. In our work, we performed a high resolution comparative molecular analysis of L-FABP T94T and L-FABP T94A in their unbound states and in the presence of representative ligands of the fatty acid and bile acid classes. We collected residue-resolved NMR spectral fingerprints of the two variants, and compared secondary structures, backbone dynamics, side chain arrangements, binding site occupation, and intermolecular contacts. We found that threonine to alanine replacement did not result in strongly perturbed structural and dynamic features, although differences in oleic acid binding by the two variants were detected. Based on chemical shift perturbations at sites distant from position 94 and on differences in intermolecular contacts, we suggest that long-range communication networks in L-FABP propagate the effect of amino acid substitution at sites relevant for ligand binding or biomolecular recognition.

Role of the fatty acid-binding protein 4 in heart failure and cardiovascular disease

Obesity and ectopic fat accumulation in non-adipose tissues are major contributors to heart failure (HF) and cardiovascular disease (CVD). Adipocytes act as endocrine organs by releasing a large number of bioactive molecules into the bloodstream, which participate in a communication network between white adipose tissue and other organs, including the heart. Among these molecules, fatty acid-binding protein 4 (FABP4) has recently been shown to increase cardiometabolic risk. Both clinical and experimental evidence have identified FABP4 as a relevant player in atherosclerosis and coronary artery disease, and it has been directly related to cardiac alterations such as left ventricular hypertrophy (LVH) and both systolic and diastolic cardiac dysfunction. The available interventional studies preclude the establishment of a direct causal role of this molecule in CVD and HF and propose FABP4 as a biomarker rather than as an aetiological factor. However, several experimental reports have suggested that FABP4 may act as a direct contributor to cardiac metabolism and physiopathology, and the pharmacological targeting of FABP4 may restore some of the metabolic alterations that are conducive to CVD and HF. Here, we review the current knowledge regarding FABP4 in the context of HF and CVD as well as the molecular basis by which this protein participates in the regulation of cardiac function.

Ramelteon Improves Post-traumatic Stress Disorder-Like Behaviors Exhibited by Fatty Acid-Binding Protein 3 Null Mice

We previously reported that fatty acid-binding protein 3 (FABP3) knockout (Fabp3 ^-/-) mice exhibit abnormal dopamine-related behaviors such as enhanced dopamine D2 receptor antagonist-induced catalepsy behaviors. Here, we report that Fabp3 null mice exhibit cognitive deficits, hyperlocomotion and impaired fear extinction, and thus show post-traumatic stress disorder (PTSD)-like behaviors. Notably, chronic administration of ramelteon (1.0 mg/kg, p.o.), a melatonin receptor agonist, improved all PTSD-like behaviors tested in Fabp3 ^-/- mice. Relevant to mechanisms underlying impaired fear extinction, we observed significantly reduced levels of Ca²⁺/calmodulin-dependent protein kinase II (CaMKII) autophosphorylation without changes in ERK phosphorylation in the anterior cingulate cortex (ACC). Inversely, CaMKII autophosphorylation increased in the basolateral amygdala (BLA) but remained relatively unchanged in hippocampus of Fabp3 ^-/- mice. Likewise, the number of c-Fos-positive neurons in BLA significantly increased after exposure to contextual fear conditions but remained unchanged in the central nucleus of the amygdala (CeA). Importantly, chronic ramelteon administration (1.0 mg/kg, p.o.) restored abnormal c-Fos expression and CaMKII autophosphorylation in the ACC and BLA of Fabp3 ^-/- mice. Finally, the melatonin receptor antagonist luzindole (2.5 mg/kg, i.p.) blocked ramelteon-dependent improvements. Taken together, Fabp3 ^-/- mice show PTSD-like behaviors, and ramelteon is a likely attractive candidate for PTSD therapy.

Aggressive Crosstalk Between Fatty Acids and Inflammation in Macrophages and Their Influence on Metabolic Homeostasis

From the immunological point of view, macrophages are required to maintain metabolic homeostasis. Recently, there has been an increased focus on the influence of macrophage phenotypes in adipose tissue on the maintenance of metabolic homeostasis in healthy conditions because dysregulated metabolic homeostasis causes metabolic syndrome. This review notes several types of inflammatory and anti-inflammatory mediators in metabolic homeostasis. M1 macrophage polarization mediates inflammation, whereas M2 macrophage polarization mediates anti-inflammation. Fatty acids and their related factors mediate both inflammatory and anti-inflammatory responses. Saturated fatty acids and polyunsaturated fatty acids mediate inflammation, whereas marine-derived n-3 fatty acids, such as eicosapentaenoic acid and docosahexaenoic acid, mediate anti-inflammation. In this review, we discuss the current understanding of the crosstalk between fatty acids and inflammation in macrophages and their influence on metabolic homeostasis.

Fatty acid-binding protein 5 function in hepatocellular carcinoma through induction of epithelial-mesenchymal transition

Hepatocellular carcinoma (HCC) is a highly prevalent cancer with poor prognosis. The correlation between overexpression of fatty acid-binding protein 5 (FABP5) and malignant potential of tumor growth and metastasis in several cancers has been previously reported. However, the correlation between FABP5 expression and HCC malignant behavior remains unknown. We compared FABP5 expression and patient characteristics in paired HCC and adjacent noncancerous liver tissues from 243 patients who underwent surgical resection of primary HCC. Cell proliferation, invasion, and migration assays were performed in HCC cell lines overexpressing FABP5 or downregulated for FABP5. Tumor growths were monitored in xenograft model, and liver and lung metastasis models were established. In the 243 HCC patients, FABP5-positive staining (n = 139/243, 57.2%) was associated with poor prognosis and recurrence (P < 0.0001) and showed positive correlation with distant metastasis, tumor size and vascular invasion (P < 0.05). Cell proliferation, invasion, and migration in vitro were enhanced by upregulation of FABP5 and decreased by downregulation of FABP5 in HCC cell lines. Similar results in tumor formation and metastasis were obtained through in vivo analyses. PCR array results revealed upregulation of SNAI1 in FABP5-overexpressing HepG2 cells. Western blot analysis showed significantly increased expression of E-cadherin and ZO-1 and decreased SNAI1 expression and nuclear translocation of β-catenin by knockdown of FABP5. We revealed a significant role for FABP5 in HCC progression and metastasis through the induction of epithelial-to-mesenchymal transition. FABP5 may be a potential novel prognostic biomarker and new therapeutic target for HCC.

Serum adipocyte-fatty acid binding protein (FABP4) levels in women from Mexico exposed to polycyclic aromatic hydrocarbons (PAHs)

Recent studies indicate that exposure to polycyclic aromatic hydrocarbons (PAHs) is a very important risk factor for the development of cardiovascular diseases (CVDs). Correspondingly, adipocyte-fatty acid binding protein (FABP4, also known as aP2 and AFABP) has been proposed as a new, meaningful and useful biomarker to predict metabolic and cardiovascular diseases. Therefore, the aim of this study was to evaluate serum FABP4 levels in Mexican women exposed to PAHs. Urinary 1-hydroxypyrene ((1-OHP), exposure biomarker for PAHs) levels were quantified using a high-performance liquid chromatography (HPLC) technique, and serum FABP4 concentrations were analyzed using a commercially available ELISA kit. The mean urinary 1-OHP level found in women participating in this study was 1.30 ± 1.10 μmol/mol creatinine (2.45 ± 2.10 μg/g creatinine). Regarding serum FABP4 concentrations, the levels ranged from 3.80 to 62.5 ng/mL in the assessed population. Moreover, a significant association (p < 0.001) was found between urinary 1-OHP levels and serum FABP4 concentrations in women after adjusting for potential confounding variables. The presented data in this study can be considered only as a starting point for further studies. Then, in order to elucidate whether FABP4 represents a risk factor for CVD disease in humans exposed to air contaminants (such as PAHs), large epidemiological studies are necessary.

Macrophage Apoptosis and Efferocytosis in the Pathogenesis of Atherosclerosis

Macrophage apoptosis and the ability of macrophages to clean up dead cells, a process called efferocytosis, are crucial determinants of atherosclerosis lesion progression and plaque stability. Environmental stressors initiate endoplasmic reticulum (ER) stress and activate the unfolded protein response (UPR). Unresolved ER stress with activation of the UPR initiates apoptosis. Macrophages are resistant to apoptotic stimuli, because of activity of the PI3K/Akt pathway. Macrophages express 3 Akt isoforms, Akt1, Akt2 and Akt3, which are products of distinct but homologous genes. Akt displays isoform-specific effects on atherogenesis, which vary with different vascular cell types. Loss of macrophage Akt2 promotes the anti-inflammatory M2 phenotype and reduces atherosclerosis. However, Akt isoforms are redundant with regard to apoptosis. c-Jun NH₂-terminal kinase (JNK) is a pro-apoptotic effector of the UPR, and the JNK1 isoform opposes anti-apoptotic Akt signaling. Loss of JNK1 in hematopoietic cells protects macrophages from apoptosis and accelerates early atherosclerosis. IκB kinase α (IKKα, a member of the serine/threonine protein kinase family) plays an important role in mTORC2-mediated Akt signaling in macrophages, and IKKα deficiency reduces macrophage survival and suppresses early atherosclerosis. Efferocytosis involves the interaction of receptors, bridging molecules, and apoptotic cell ligands. Scavenger receptor class B type I is a critical mediator of macrophage efferocytosis via the Src/PI3K/Rac1 pathway in atherosclerosis. Agonists that resolve inflammation offer promising therapeutic potential to promote efferocytosis and prevent atherosclerotic clinical events. (Circ J 2016; 80: 2259-2268).

Clinical significance of elevated serum A-FABP and free fatty acid in neonates with hypoxic ischemic brain damage

The main function of adipocyte fatty acid-binding protein (A-FABP) is to regulate fatty acid metabolism as its molecular chaperone. The clinical significance of A-FABP in hypoxic-ischemic brain damage (HIBD) neonates is not yet clear. Free fatty acid (FFA) in cerebral cortex increases along with hypoxia ischemia degree. Thus, we aimed to investigate whether FFA can induce A-FABP expression and elevate the serum A-FABP level in HIBD neonates. In the present study, 42 HIBD neonates were selected including 11 cases as mild, 16 cases as moderate and 15 cases as severe. The serum was collected from peripheral vein at 72 h after the first visit (acute stage) and 7 days after birth (recovery stage), and the serum from 10 normal neonates was used as the control. The serum level of A-FABP and FFA in 42 neonates with acute phase and recovery phase HIBD were detected using ELISA and copper colorimetric method. The overall serum A-FABP content in HIBD neonates at the acute stage was significantly higher compared to the normal neonates (P<0.05). The serum A-FABP level in severe HIBD neonates was significantly higher than that in mild HIBD, moderate HIBD and normal neonates (P<0.05). The serum FFA level in HIBD neonates at the acute stage was 1,521.57±605.63 µmol/l, which was significantly higher than that in the normal neonates 838.24±294.22 µmol/l. The serum FFA levels in mild, moderate and severe HIBD neonates were significantly higher than those in the normal neonates. The overall A-FABP level in HIBD neonates at the recovery stage was significantly lower compared to the acute stage, which was significant in severe HIBD neonates. A-FABP levels in mild and moderate HIBD neonates at recovery stage were decreased compared with the acute stage, although there was no statistical difference. There was a positive correlation between serum A-FABP and FFA in HIBD neonates at acute stage (r=0.369, P<0.05). In conclusion, serum A-FABP and FFA levels were signifcantly increased in HIBD neonates at acute stage, and were positively correlated. The serum A-FABP level in HIBD neonates at recovery stage was significantly lower than that in the acute stage. The results suggested that serum A-FABP and FFA levels at acute stage can reflect the severity of HIBD. The detection of serum A-FABP and FFA can be applied as indicators for the early diagnosis of HIBD, but also provides a basis for the clinical evaluation of HIBD treatment.

A Photoisomerizing Rhodopsin Mimic Observed at Atomic Resolution

The members of the rhodopsin family of proteins are involved in many essential light-dependent processes in biology. Specific photoisomerization of the protein-bound retinylidene PSB at a specified wavelength range of light is at the heart of all of these systems. Nonetheless, it has been difficult to reproduce in an engineered system. We have developed rhodopsin mimics, using intracellular lipid binding protein family members as scaffolds, to study fundamental aspects of protein/chromophore interactions. Herein we describe a system that specifically isomerizes the retinylidene protonated Schiff base both thermally and photochemically. This isomerization has been characterized at atomic resolution by quantitatively interconverting the isomers in the crystal both thermally and photochemically. This event is accompanied by a large pKa change of the imine similar to the pKa changes observed in bacteriorhodopsin and visual opsins during isomerization.

Inflammatory profile in LRRK2-associated prodromal and clinical PD

Background

There is evidence for a relevant role of inflammation in the pathogenesis of Parkinson’s disease (PD). Mutations in the LRRK2 gene represent the most frequent genetic cause for autosomal dominant PD. LRRK2 is highly expressed in macrophages and microglia suggesting an involvement in inflammatory pathways. The objectives are to test (1) whether idiopathic PD and LRRK2-associated PD share common inflammatory pathways or present distinct profiles and (2) whether non-manifesting LRRK2 mutation carriers present with similar aspects of inflammatory profiles as seen in PD-affected patients.

Methods

We assessed serum profiles of 23 immune-associated markers and the brain-derived neurotrophic factor in 534 individuals from the MJFF LRRK2 consortium.

Results

A large proportion of inflammatory markers were gender-dependent. Both PD-affected cohorts showed increased levels of the pro-inflammatory marker fatty-acid-binding protein. Additionally, idiopathic PD but not LRRK2-associated PD patients showed increased levels of the pro-inflammatory marker interleukin-12-p40 as well as the anti-inflammatory species interleukin-10, brain-derived neurotrophic factor, and stem cell factor. Non-manifesting LRRK2 mutation carriers including those with prodromal characteristics of PD presented with control-like inflammatory profiles.

Conclusions

Concomitant inflammation seems to be associated with idiopathic and LRRK2-associated PD. Identifying PD patients in whom inflammatory processes play a major role in their pathophysiology might offer a new therapeutic window at least for a subgroup of patients. Since non-manifesting LRRK2 mutation carriers with symptoms of the prodromal phase of PD did not show inflammatory profiles, activation of the immune system seems not an early event in the disease cascade.

Electronic supplementary material

The online version of this article (doi:10.1186/s12974-016-0588-5) contains supplementary material, which is available to authorized users.

The two sides of a lipid-protein story

Protein-membrane interactions play essential roles in a variety of cell functions such as signaling, membrane trafficking, and transport. Membrane-recruited cytosolic proteins that interact transiently and interfacially with lipid bilayers perform several of those functions. Experimental techniques capable of probing changes on the structural dynamics of this weak association are surprisingly limited. Among such techniques, electron spin resonance (ESR) has the enormous advantage of providing valuable local information from both membrane and protein perspectives by using intrinsic paramagnetic probes in metalloproteins or by attaching nitroxide spin labels to proteins and lipids. In this review, we discuss the power of ESR to unravel relevant structural and functional details of lipid-peripheral membrane protein interactions with special emphasis on local changes of specific regions of the protein and/or the lipids. First, we show how ESR can be used to investigate the direct interaction between a protein and a particular lipid, illustrating the case of lipid binding into a hydrophobic pocket of chlorocatechol 1,2-dioxygenase, a non-heme iron enzyme responsible for catabolism of aromatic compounds that are industrially released in the environment. In the second case, we show the effects of GPI-anchored tissue-nonspecific alkaline phosphatase, a protein that plays a crucial role in skeletal mineralization, and on the ordering and dynamics of lipid acyl chains. Then, switching to the protein perspective, we analyze the interaction with model membranes of the brain fatty acid binding protein, the major actor in the reversible binding and transport of hydrophobic ligands such as long-chain, saturated, or unsaturated fatty acids. Finally, we conclude by discussing how both lipid and protein views can be associated to address a common question regarding the molecular mechanism by which dihydroorotate dehydrogenase, an essential enzyme for the de novo synthesis of pyrimidine nucleotides, and how it fishes out membrane-embedded quinones to perform its function.

High-resolution neutron and X-ray diffraction room-temperature studies of an H-FABP-oleic acid complex: study of the internal water cluster and ligand binding by a transferred multipolar electron-density distribution

Crystal diffraction data of heart fatty acid binding protein (H-FABP) in complex with oleic acid were measured at room temperature with high-resolution X-ray and neutron protein crystallography (0.98 and 1.90 Å resolution, respectively). These data provided very detailed information about the cluster of water molecules and the bound oleic acid in the H-FABP large internal cavity. The jointly refined X-ray/neutron structure of H-FABP was complemented by a transferred multipolar electron-density distribution using the parameters of the ELMAMII library. The resulting electron density allowed a precise determination of the electrostatic potential in the fatty acid (FA) binding pocket. Bader's quantum theory of atoms in molecules was then used to study interactions involving the internal water molecules, the FA and the protein. This approach showed H⋯H contacts of the FA with highly conserved hydrophobic residues known to play a role in the stabilization of long-chain FAs in the binding cavity. The determination of water hydrogen (deuterium) positions allowed the analysis of the orientation and electrostatic properties of the water molecules in the very ordered cluster. As a result, a significant alignment of the permanent dipoles of the water molecules with the protein electrostatic field was observed. This can be related to the dielectric properties of hydration layers around proteins, where the shielding of electrostatic interactions depends directly on the rotational degrees of freedom of the water molecules in the interface.

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).

Fatty Acid-Binding Protein 4 mediates apoptosis via endoplasmic reticulum stress in mesangial cells of diabetic nephropathy

Type 2 diabetes is characterized by hyperglycemia and deregulated lipid metabolism with increased plasma non-esterified fatty acids (NEFA). Apoptosis of glomerular cells is a hallmark in diabetic glomerulosclerosis. Fatty acid-binding protein 4 (FABP4), a carrier protein for fatty acids, has been linked to diabetes and diabetic nephropathy (DN). Here we aimed to investigate the link between FABP4 and apoptosis in diabetic glomerulosclerosis. We first evaluated the presence of FABP4 and ER stress markers as well as apoptosis-related proteins in renal biopsies of patients with DN. Then we used FABP4 inhibitor BMS309403 or siRNA to further investigate the role of FABP4 in ER stress and apoptosis induced by NEFA or high glucose in cultured human mesangial cells (HMCs). We found FABP4 was expressed mainly in glomerular mesangial cells of the human renal biopsies and the glomerular FABP4 was increased in renal biopsies of DN. The up-regulation of FABP4 was accompanied with increased glucose-regulated protein 78 (GRP78) and Caspase-12 as well as down-regulated B-cell CLL/lymphoma 2 (Bcl-2) in glomeruli. Along with the induction of FABP4 and apoptosis, GRP78 and its three sensors as well as C/EBP homologous protein (CHOP) and Caspase-12 were induced in HMCs treated with NEFA or high glucose and these responses were attenuated or even abrogated by treating with FABP4 inhibitor or FABP4 siRNA. Ultrastructure observation confirmed the lipotoxicity of oleic acid by showing the morphological damage in HMCs. Our data suggest that FABP4 in glomerular mesangial cells is up-regulated in DN and FABP4 mediates apoptosis via the ER stress in HMCs.

Subcutaneous Construction of Engineered Adipose Tissue with Fat Lobule-Like Structure Using Injectable Poly-Benzyl-L-Glutamate Microspheres Loaded with Adipose-Derived Stem Cells

Porous microcarriers were fabricated from synthesized poly(γ-benzyl-L-glutamate) (PBLG) polymer to engineer adipose tissue with lobule-like structure via the injectable approach. The adipogenic differentiation of human adipose-derived stem cells (hASCs) seeded on porous PBLG microcarriers was determined by adipogenic gene expression and glycerol-3-phosphate dehydrogenase enzyme activity. In vitro adipogenic cultivation was performed for 7 days, and induced hASC/PBLG complex (Adi-ASC/PBLG group) was subcutaneously injected into nude mice. Injections of PBLG microcarriers alone (PBLG group) and non-induced hASC/PBLG complex (ASC/PBLG group) served as controls. Newly formed tissues were harvested after 4 and 8 weeks. Generation of subcutaneous adipose tissue with typical lobule-like structure separated by fibrous septa was observed upon injection of adipogenic-induced hASC/microsphere complex. Adipogenesis significantly increased in the Adi-ASC/PBLG group compared with the control groups. The angiogenesis in the engineered adipose tissue was comparable to that in normal tissue as determined by capillary density and luminal diameter. Cell tracking assay demonstrated that labeled hASCs remained detectable in the neo-generated tissues 8 weeks post-injection using green fluorescence protein-labeled hASCs. These results indicate that adipose tissue with typical lobule-like structure could be engineered using injectable porous PBLG microspheres loaded with adipogenic-induced hASCs.

Autocrine secretion of 15d-PGJ2 mediates simvastatin-induced apoptotic burst in human metastatic melanoma cells

BACKGROUND AND PURPOSE

Despite new therapeutic approaches, metastatic melanomas still have a poor prognosis. Statins reduce low-density lipoprotein cholesterol and exert anti-inflammatory and anti-proliferative actions. We have recently shown that simvastatin triggers an apoptotic burst in human metastatic melanoma cells by the synthesis of an autocrine factor.

EXPERIMENTAL APPROACH

The current in vitro study was performed in human metastatic melanoma cell lines (A375, 518a2) and primary human melanocytes and melanoma cells. The secretome of simvastatin-stressed cells was analysed with two-dimensional difference gel electrophoresis and MS. The signalling pathways involved were analysed at the protein and mRNA level using pharmacological approaches and siRNA technology.

KEY RESULTS

Simvastatin was shown to activate a stress cascade, leading to the synthesis of 15-deoxy-12,14-PGJ2 (15d-PGJ2 ), in a p38- and COX-2-dependent manner. Significant concentrations of 15d-PGJ2 were reached in the medium of melanoma cells, which were sufficient to activate caspase 8 and the mitochondrial pathway of apoptosis. Inhibition of lipocalin-type PGD synthase, a key enzyme for 15d-PGJ2 synthesis, abolished the apoptotic effect of simvastatin. Moreover, 15d-PGJ2 was shown to bind to the fatty acid-binding protein 5 (FABP5), which was up-regulated and predominantly detected in the secretome of simvastatin-stressed cells. Knockdown of FABP5 abolished simvastatin-induced activation of PPAR-γ and amplified the apoptotic response.

CONCLUSIONS AND IMPLICATIONS

We characterized simvastatin-induced activation of the 15d-PGJ2 /FABP5 signalling cascades, which triggered an apoptotic burst in melanoma cells but did not affect primary human melanocytes. These data support the rationale for the pharmacological targeting of 15d-PGJ2 in metastatic melanoma.

The unique ligand binding features of subfamily-II iLBPs with respect to bile salts and related drugs

Intracellular lipid binding proteins (iLBPs) are a family of evolutionarily related small cytoplasmic proteins implicated in the transcellular transport of lipophilic ligands. Subfamily-II iLBPs include the liver fatty acid binding protein (L-FABP), and the ileal and the liver and ileal bile acid binding proteins (L-BABP and I-BABP). Atomic-level investigations during the past 15-20 years have delivered relevant information on bile acid binding by this protein group, revealing unique features including binding cooperativity, promiscuity, and site selectivity. Using NMR spectroscopy and other biophysical techniques, our laboratories have contributed to an understanding of the molecular determinants of some of these properties and their generality among proteins from different animal species. We focused especially on formation of heterotypic complexes, considering the mixed compositions of physiological bile acid pools. Experiments performed with synthetic bile acid derivatives showed that iLBPs could act as targets for cell-specific contrast agents and, more generally, as effective carriers of amphiphilic drugs. This review collects the major findings related to bile salt interactions with iLBPs aiming to provide keys for a deeper understanding of protein-mediated intracellular bile salt trafficking.

Pathways of polyunsaturated fatty acid utilization: implications for brain function in neuropsychiatric health and disease

Essential polyunsaturated fatty acids (PUFAs) have profound effects on brain development and function. Abnormalities of PUFA status have been implicated in neuropsychiatric diseases such as major depression, bipolar disorder, schizophrenia, Alzheimer's disease, and attention deficit hyperactivity disorder. Pathophysiologic mechanisms could involve not only suboptimal PUFA intake, but also metabolic and genetic abnormalities, defective hepatic metabolism, and problems with diffusion and transport. This article provides an overview of physiologic factors regulating PUFA utilization, highlighting their relevance to neuropsychiatric disease.

Fatty Acid-Binding Protein 4 (FABP4): Pathophysiological Insights and Potent Clinical Biomarker of Metabolic and Cardiovascular Diseases

Over the past decade, evidences of an integration of metabolic and inflammatory pathways, referred to as metaflammation in several aspects of metabolic syndrome, have been accumulating. Fatty acid-binding protein 4 (FABP4), also known as adipocyte FABP (A-FABP) or aP2, is mainly expressed in adipocytes and macrophages and plays an important role in the development of insulin resistance and atherosclerosis in relation to metaflammation. Despite lack of a typical secretory signal peptide, FABP4 has been shown to be released from adipocytes in a non-classical pathway associated with lipolysis, possibly acting as an adipokine. Elevation of circulating FABP4 levels is associated with obesity, insulin resistance, diabetes mellitus, hypertension, cardiac dysfunction, atherosclerosis, and cardiovascular events. Furthermore, ectopic expression and function of FABP4 in several types of cells and tissues have been recently demonstrated. Here, we discuss both the significant role of FABP4 in pathophysiological insights and its usefulness as a biomarker of metabolic and cardiovascular diseases.

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.

Uncoupling lipid metabolism from inflammation through fatty acid binding protein-dependent expression of UCP2

Chronic inflammation in obese adipose tissue is linked to endoplasmic reticulum (ER) stress and systemic insulin resistance. Targeted deletion of the murine fatty acid binding protein (FABP4/aP2) uncouples obesity from inflammation although the mechanism underlying this finding has remained enigmatic. Here, we show that inhibition or deletion of FABP4/aP2 in macrophages results in increased intracellular free fatty acids (FFAs) and elevated expression of uncoupling protein 2 (UCP2) without concomitant increases in UCP1 or UCP3. Silencing of UCP2 mRNA in FABP4/aP2-deficient macrophages negated the protective effect of FABP loss and increased ER stress in response to palmitate or lipopolysaccharide (LPS). Pharmacologic inhibition of FABP4/aP2 with the FABP inhibitor HTS01037 also upregulated UCP2 and reduced expression of BiP, CHOP, and XBP-1s. Expression of native FABP4/aP2 (but not the non-fatty acid binding mutant R126Q) into FABP4/aP2 null cells reduced UCP2 expression, suggesting that the FABP-FFA equilibrium controls UCP2 expression. FABP4/aP2-deficient macrophages are resistant to LPS-induced mitochondrial dysfunction and exhibit decreased mitochondrial protein carbonylation and UCP2-dependent reduction in intracellular reactive oxygen species. These data demonstrate that FABP4/aP2 directly regulates intracellular FFA levels and indirectly controls macrophage inflammation and ER stress by regulating the expression of UCP2.

Identification of KMU-3, a novel derivative of gallic acid, as an inhibitor of adipogenesis

Differentiation of preadipocyte, also called adipogenesis, leads to the phenotype of mature adipocyte. Excessive adipogenesis, however, is largely linked to the development of obesity. Herein we investigated a library of 53 novel chemicals, generated from a number of polyphenolic natural compounds, on adipogenesis. Strikingly, among the chemicals tested, KMU-3, a derivative of gallic acid, strongly suppressed lipid accumulation during the differentiation of 3T3-L1 preadipocytes into adipocytes. On mechanistic levels, KMU-3 inhibited expressions of CCAAT/enhancer-binding protein-α (C/EBP-α), peroxisome proliferator-activated receptor-γ (PPAR-γ), and fatty acid synthase (FAS) during adipocyte differentiation. Moreover, KMU-3 reduced expressions of adipokines, including retinol binding protein-4 (RBP-4), leptin, and regulated on activation, normal T cell expressed and secreted (RANTES) during adipocyte differentiation. Of further note, KMU-3 rapidly blocked the phosphorylation of signal transducer and activator of transcription-3 (STAT-3) during the early stage of adipogenesis. Importantly, pharmacological inhibition studies revealed that AG490, a JAK-2/STAT-3 inhibitor suppressed adipogenesis and STAT-3 phosphorylation, implying that early blockage of STAT-3 activity is crucial for the KMU-3-mediated anti-adipogenesis. These findings demonstrate firstly that KMU-3 inhibits adipogenesis by down-regulating STAT-3, PPAR-γ, C/EBP-α, and FAS. This work shows that KMU-3 is an inhibitor of adipogenesis and thus may have therapeutic potential against obesity.

Positive regulations of adipogenesis by Italian ryegrass [Lolium multiflorum] in 3T3-L1 cells

BACK GROUND

Intramuscular fat deposition in the meat animal is relatively new strategy for developing the meat quality. Fat deposition is largely depending on the adipocyte proliferation and differentiation. Therefore, we investigated the effect of chloroform extract of L. multiflorum [CELM] on cell proliferation, lipid accumulation and adipocyte differentiation in 3T3-L1 cells and body weight of mouse.

RESULTS

We identified 6,9-Octadecatrienoic acid, Hexadecanoic acid, 2-hydroxypropanoic acid, butane-2,3-diol and hexane-1,2,3,4,5,6-hexaol in CELM. L. multiflorum extract increased the cell viability, lipid accumulation, cell cycle progression and key transcriptional and secretory factors like PPRAγ2, C/CEBP-α, adiponectin, aP2, GLUT-4, FAS and SREBP-1 mRNA expression as compared with control cells. For in-vivo, mice administered with CELM significantly increased body weight throughout the experiment periods. Further, the identified fatty acids like 3, 6, 9-Octadecatrienoic acid and Hexadecanoic acid was docked with target protein [PPRAγ2] using HEX 6.12. The least binding energy considered as high affinity with target protein. The maximum affinity with the target protein was observed in the Hexadecanoic acid followed by 3, 6, 9-Octadecatrienoic acid. The binding efficacy of Hexadecanoic acid and 3, 6, 9-Octadecatrienoic acid to the active site of PPAR-γ2 may be enhanced the adipocyte differentiations.

CONCLUSION

These findings suggest that CELM stimulates adipogenesis via activating the PPARγ-mediated signaling pathway in adipocyte which could be useful for the development of meat quality in animals.

Expression of epidermal fatty acid binding protein (E-FABP) in septoclasts in the growth plate cartilage of mice

n-3 Polyunsaturated fatty acids play a role in regulating the growth of the long bones. Fatty acid-binding proteins (FABPs) bind and transport hydrophobic long-chain fatty acids intracellularly, and epidermal-type FABP (E-FABP) has an affinity for n-3 fatty acids. This study aimed to clarify the localization of E-FABP in the growth plate of the mouse tibia. At the chondro-osseous junction (COJ) of the growth plate, E-FABP-immunoreactivity was exclusively localized in mononuclear, spindle-shaped cells with several long processes. These E-FABP-immunoreactive cells were identified as being septoclasts, i.e., cells that resorb uncalcified transverse septa. The processes of these immunoreactive septoclasts terminated between the longitudinal and transverse septa. E-FABP-immunoreactivity was found in the entire cytoplasm and on the mitochondrial outer membrane. In ontogeny, immunoreactive septoclasts were observed immediately after emergence of the primary ossifying center and were distributed not only at the COJ but also in the metaphysis near the COJ. The number of septoclasts increased at the postnatal age of 1 week (P1w)-P2w, and thereafter gradually decreased; and the cells became concentrated at the COJ after P3w-P4w. The immunoreactivity for peroxisome proliferator-activated receptor (PPAR)β/δ was detected in these E-FABP-immunoreactive septoclasts. The present results suggest that fatty acids, preferably n-3 ones, are intracellularly transported by E-FABP to various targets, including mitochondria and nucleus, in which PPARβ/δ may play functional roles in the transcriptional regulation of genes involved in the endochondral ossification.

FABP3 protein promotes α-synuclein oligomerization associated with 1-methyl-1,2,3,6-tetrahydropiridine-induced neurotoxicity

α-Synuclein (αSyn) accumulation in dopaminergic (DA) neurons is partly regulated by long-chain polyunsaturated fatty acids. We found that fatty acid-binding protein 3 (FABP3, H-FABP), a factor critical for arachidonic acid (AA) transport and metabolism in brain, is highly expressed in DA neurons. Fabp3 knock-out (Fabp3(-/-)) mice were resistant to 1-methyl-1,2,3,6-tetrahydropiridine-induced DA neurodegeneration in the substantia nigra pars compacta and showed improved motor function. Interestingly, FABP3 interacted with αSyn in the substantia nigra pars compacta, and αSyn accumulation following 1-methyl-1,2,3,6-tetrahydropiridine treatment was attenuated in Fabp3(-/-) compared with wild-type mice. We confirmed that FABP3 overexpression aggravates AA-induced αSyn oligomerization and promotes cell death in PC12 cells, whereas overexpression of a mutant form of FABP3 lacking fatty-acid binding capacity did not. Taken together, αSyn oligomerization in DA neurons is likely aggravated by AA through FABP3 in Parkinson disease pathology.

Acyl-CoA metabolism and partitioning

Long-chain fatty acyl-coenzyme As (CoAs) are critical regulatory molecules and metabolic intermediates. The initial step in their synthesis is the activation of fatty acids by one of 13 long-chain acyl-CoA synthetase isoforms. These isoforms are regulated independently and have different tissue expression patterns and subcellular locations. Their acyl-CoA products regulate metabolic enzymes and signaling pathways, become oxidized to provide cellular energy, and are incorporated into acylated proteins and complex lipids such as triacylglycerol, phospholipids, and cholesterol esters. Their differing metabolic fates are determined by a network of proteins that channel the acyl-CoAs toward or away from specific metabolic pathways and serve as the basis for partitioning. This review evaluates the evidence for acyl-CoA partitioning by reviewing experimental data on proteins that are believed to contribute to acyl-CoA channeling, the metabolic consequences of loss of these proteins, and the potential role of maladaptive acyl-CoA partitioning in the pathogenesis of metabolic disease and carcinogenesis.

Association of serum adipocyte-specific Fatty Acid binding protein with Fatty liver index as a predictive indicator of nonalcoholic Fatty liver disease

BACKGROUND

Adipocyte-specific fatty acid-binding protein (A-FABP) is a cytoplasmic protein expressed in macrophages and adipocytes and it plays a role in insulin resistance and metabolic syndrome. Recently, the fatty liver index (FLI) was introduced as an indicator of nonalcoholic fatty liver disease (NAFLD). In this study, we aimed to investigate the relationship between baseline serum A-FABP levels and FLI after 4 years in apparently healthy subjects.

METHODS

A total of 238 subjects without a past history of alcoholism or hepatitis were recruited from a medical check-up program. The NAFLD state was evaluated 4 years later in the same subjects using FLI. Fatty liver disease was diagnosed as diffusely increased echogenicity of the hepatic parenchyma compared to the kidneys, vascular blurring, and deep-echo attenuation. NAFLD was defined as subjects with fatty liver and no history of alcohol consumption (>20 g/day).

RESULTS

Baseline serum A-FABP levels were significantly associated with FLI after adjustment for age and sex (P<0.001). The subjects with higher A-FABP levels had a higher mean FLI (P for trend=0.006). After adjusting for age and sex, serum A-FABP levels at baseline were shown to be significantly associated with FLI as a marker of development of NAFLD after 4 years (odds ratio, 2.68; 95% confidence interval, 1.24 to 5.80 for highest tertile vs. lowest tertile; P=0.012).

CONCLUSION

This study demonstrated that higher baseline serum A-FABP levels were associated with FLI as a predictive indicator of NAFLD after 4 years of follow-up in healthy Korean adults.

Metabolic syndrome and insulin resistance: underlying causes and modification by exercise training

Metabolic syndrome (MS) is a collection of cardiometabolic risk factors that includes obesity, insulin resistance, hypertension, and dyslipidemia. Although there has been significant debate regarding the criteria and concept of the syndrome, this clustering of risk factors is unequivocally linked to an increased risk of developing type 2 diabetes and cardiovascular disease. Regardless of the true definition, based on current population estimates, nearly 100 million have MS. It is often characterized by insulin resistance, which some have suggested is a major underpinning link between physical inactivity and MS. The purpose of this review is to: (i) provide an overview of the history, causes and clinical aspects of MS, (ii) review the molecular mechanisms of insulin action and the causes of insulin resistance, and (iii) discuss the epidemiological and intervention data on the effects of exercise on MS and insulin sensitivity.

Preparation and characterization of gelatin/hyaluronic acid cryogels for adipose tissue engineering: in vitro and in vivo studies

Macroporous elastic scaffolds containing gelatin (4% or 10%) and 0.25% hyaluronic acid (HA) were fabricated by cryogelation for application in adipose tissue engineering. These cryogels have interconnected pores (∼200 μm), high porosity (>90%) and a high degree of cross-linking (>99%). The higher gelatin concentration reduced the pore size, porosity and swelling ratio of the cryogel but improved its swelling kinetics. Compressive mechanical testing of cryogel samples demonstrated non-linear stress-strain behavior and hysteresis loops during loading-unloading cycles, but total recovery from large strains. The presence of more gelatin increased the elastic modulus, toughness and storage modulus and yielded a cryogel that was highly elastic, with a loss tangent equal to 0.03. Porcine adipose-derived stem cells (ADSCs) were seeded in the cryogel scaffolds to assess their proliferation and differentiation. In vitro studies demonstrated a good proliferation rate and the adipogenic differentiation of the ADSCs in the cryogel scaffolds, as shown by their morphological change from a fibroblast-like shape to a spherical shape, decreased actin cytoskeleton content, growth arrest, secretion of the adipogenesis marker protein leptin, Oil Red O staining for triglycerides and expression of early (LPL and PPARγ) and late (aP2 and leptin) adipogenic marker genes. In vivo studies of ADSCs/cryogel constructs implanted in nude mice and pigs demonstrated adipose tissue and new capillary formation, the expression of PPARγ, leptin and CD31 in immunostained explants, and the continued expression of adipocyte-specific genes. Both the in vitro and in vivo studies indicated that the gelatin/HA cryogel provided a structural and chemical environment that enabled cell attachment and proliferation and supported the biological functions and adipogenesis of the ADSCs.

Structure of the human-heart fatty-acid-binding protein 3 in complex with the fluorescent probe 1-anilinonaphthalene-8-sulphonic acid

Heart-type fatty-acid-binding protein (FABP3), which is a cytosolic protein abundantly found in cardiomyocytes, plays a role in trafficking fatty acids throughout cellular compartments by reversibly binding intracellular fatty acids with relatively high affinity. The fluorescent probe 1-anilinonaphthalene-8-sulfonate (ANS) is extensively utilized for examining the interaction of ligands with fatty-acid-binding proteins. The X-ray structure of FABP3 was determined in the presence of ANS and revealed the detailed ANS-binding mechanism. Furthermore, four water molecules were clearly identified in the binding cavity. Through these water molecules, the bound ANS molecule forms indirect hydrogen-bond interactions with FABP3. The adipocyte-type fatty-acid-binding protein (FABP4) exhibits 67% sequence identity with FABP3 and its crystal structure is almost the same as that of FABP3. However, FABP4 can bind with a higher affinity to ANS than FABP3. To understand the difference in their ligand specificities, a structural comparison was performed between FABP3-ANS and FABP4-ANS complexes. The result revealed that the orientation of ANS binding to FABP3 is completely opposite to that of ANS binding to FABP4, and the substitution of valine in FABP4 to leucine in FABP3 may result in greater steric hindrance between the side-chain of Leu115 and the aniline ring of ANS.

Neurophysiologic measures of auditory function in fish consumers: associations with long chain polyunsaturated fatty acids and methylmercury

BACKGROUND

Determining if associations exist between child neurodevelopment and environmental exposures, especially low level or background ones, is challenging and dependent upon being able to measure specific and sensitive endpoints. Psychometric or behavioral measures of CNS function have traditionally been used in such studies, but do have some limitations. Auditory neurophysiologic measures examine different nervous system structures and mechanisms, have fewer limitations, can more easily be quantified, and might be helpful additions to testing. To date, their use in human epidemiological studies has been limited. We reviewed the use of auditory brainstem responses (ABR) and otoacoustic emissions (OAE) in studies designed to determine the relationship of exposures to methyl mercury (MeHg) and nutrients from fish consumption with neurological development. We included studies of experimental animals and humans in an effort to better understand the possible benefits and risks of fish consumption.

OBJECTIVES

We reviewed the literature on the use of ABR and OAE to measure associations with environmental exposures that result from consuming a diet high in fish. We focused specifically on long chain polyunsaturated fatty acids (LCPUFA) and MeHg.

METHODS

We performed a comprehensive review of relevant studies using web-based search tools and appropriate search terms.

RESULTS

Gestational exposure to both LCPUFA and MeHg has been reported to influence the developing auditory system. In experimental studies supplemental LCPUFA is reported to prolong ABR latencies and human studies also suggest an association. Experimental studies of acute and gestational MeHg exposure are reported to prolong ABR latencies and impair hair cell function. In humans, MeHg exposure is reported to prolong ABR latencies, but the impact on hair cell function is unknown.

CONCLUSION

The auditory system can provide objective measures and may be useful in studying exposures to nutrients and toxicants and whether they are associated with children's neurodevelopment.

Serum adipocyte fatty acid-binding protein levels are independently associated with sarcopenic obesity

AIMS

Adipocyte fatty acid-binding protein (A-FABP) plays a key role in obesity-related insulin resistance and inflammation which may be involved in the pathogenesis of sarcopenic obesity (SO). This study examined the association of SO with serum A-FABP levels in Korean adults.

METHODS

Two hundred ninety eight adults aged 20-70 years were examined using dual X-ray absorptiometry and computed tomography and measuring serum A-FABP levels. Sarcopenia was defined as the appendicular skeletal muscle mass (ASM) divided by weight (%) of <1 SD below the mean values of young adults in both sexes. Obesity was defined as visceral fat area (VFA) ≥ 100 cm(2).

RESULTS

Serum A-FABP levels were higher in groups with SO compared to non-SO groups in both men and women. In the unadjusted model, serum A-FABP levels were positively associated with VFA and negatively associated with ASM/weight. Even after adjusting for possible confounding factors, ASM/weight was found to be independently and negatively associated with serum A-FABP levels. In addition, multiple logistic regression analysis showed that increased serum levels of A-FABP were independently associated with the presence of SO.

CONCLUSIONS

The present findings indicate that serum A-FABP levels may be valuable markers of the presence of SO.

Antiobesity effects of quercetin-rich onion peel extract on the differentiation of 3T3-L1 preadipocytes and the adipogenesis in high fat-fed rats

The aim of the present study was to examine the effect of quercetin-rich onion peel extract (OPE) on anti-differentiation in 3T3-L1 preadipocytes and the antiobesity in high-fat fed rats. We found that lipid accumulations and TG contents in 3T3-L1 cells were markedly suppressed by OPE. The mRNA levels of activating protein (AP2) were down-regulated and those of carnitine palmitoyl transferase-1 α (CPT-1α) and fatty acid binding protein 4 (FABP4) were up-regulated by 75 and 100 μg/ml OPE. Body weight, retroperitoneal and mesenteric fat weights of SD rats were significantly lower in the 8 week high fat (HF) diet+0.72% OPE group than in the HF group. Peroxisome proliferator-activated receptor (PPAR)γ mRNA levels were down-regulated in the epididymal fat of OPE than those of control and HF, and significant down-regulation of CCAAT/enhancer binding protein (C/EBP)α mRNA levels in OPE was also observed than the control. The mRNA levels of CPT-1α and uncoupling protein-1 (UCP-1) were up-regulated by the OPE, while those of fatty acid synthase (FAS) and acetyl-CoA carboxylase (ACC) were down-regulated in HF and OPE groups compared to control group. These results suggest that quercentin-enriched OPE may have antiobesity effects by suppressing preadipocyte differentiation and inhibiting adipogenesis.