FABP5 Deficiency Impairs Mitochondrial Function and Aggravates Pathological Cardiac Remodeling and Dysfunction.

Fatty acid-binding protein 5 (FABP5) is an important member of the FABP family and plays a vital role in the metabolism of fatty acids. However, few studies have examined the role of FABP5 in pathological cardiac remodeling and heart failure. The aim of this study was to explore the role of FABP5 in transverse aortic constriction (TAC)-induced pathological cardiac remodeling and dysfunction in mice. Quantitative RT-PCR (qRT-PCR) and western blotting (WB) analysis showed that the levels of FABP5 mRNA and protein, respectively, were upregulated in hearts of the TAC model. Ten weeks after TAC in FABP5 knockout and wild type control mice, echocardiography, histopathology, qRT-PCR, and WB demonstrated that FABP5 deficiency aggravated cardiac injury (both cardiac hypertrophy and fibrosis) and dysfunction. In addition, transmission electron microscopy, ATP detection, and WB revealed that TAC caused severe impairment to mitochondria in the hearts of FABP5-deficient mice compared with that in control mice. When FABP5 was downregulated by siRNA in primary mouse cardiac fibroblasts, FABP5 silencing increased oxidative stress, reduced mitochondrial respiration, and increased the expression of myofibroblast activation marker genes in response to treatment with transforming growth factor-ß. Our findings demonstrate that FABP5 deficiency aggravates cardiac pathological remodeling and dysfunction by damaging cardiac mitochondrial function.

Expression and enhancement of FABP4 in septoclasts of the growth plate in FABP5-deficient mouse tibiae.

In our previous study, fatty acid-binding protein 5 (FABP5) was expressed in septoclasts with long processes which are considered to resorb uncalcified matrix of the growth plate (GP) cartilage, and no apparent abnormalities were detected in the histo-architecture of the GP of FABP5-deficient (FABP5-/-) mice. Those finding lead us to hypothesize that another FABP can compensate the deletion of FABP5 in septoclasts of its gene-mutant mice. Based on the hypothesis, the present study examined the expression levels of several other FABPs in septoclasts and their morphology in FABP5-/- mouse tibiae. Processes of FABP5-/- septoclasts tend to be shorter than wild septoclasts. FABP4-positive septoclasts in FABP5-/- mice were more numerous than those cells in wild mice.Peroxisome proliferator-activated receptor (PPAR) γ was expressed in FABP4-positive septoclasts of FABP5-/- mice as well as mice administered with GW1929, a PPARγ agonist, suggesting that the occurrence of PPARγ induces an increase of FABP4-positive septoclasts. The present finding suggests that the functional exertion of FABP5 in septoclasts is supplemented by FABP4 in normal and FABP5-/- mice, and that the expression of FABP4 is up-regulated in accompany with PPARγ in FABP5-/- for maintenance of resorptive activity in the GP.

Malignant transformation of liver fatty acid binding protein-deficient hepatocellular adenomas: histopathologic spectrum of a rare phenomenon.

The molecular classification of hepatocellular adenomas highlights a distinctive genotype-phenotype correlation. Malignant transformation is an exceptionally rare complication of hepatocyte nuclear factor 1α (HNF1A)-inactivated hepatocellular adenomas. This subtype is characterized by loss of liver fatty acid binding protein immunoexpression. In this study, we characterized the histopathologic spectrum of 13 liver fatty acid binding protein-deficient hepatocellular adenoma cases showing malignant transformation from multiple centers. Clinicopathologic characteristics of these patients were evaluated. Stains for reticulin, liver fatty acid binding protein, beta-catenin and glutamine synthetase were applied to these lesions. Moreover, the findings were compared to patients with ß-catenin mutated hepatocellular adenoma. Liver fatty acid binding protein-deficient hepatocellular adenomas with borderline features/carcinoma were seen predominantly in females (77%) with an average age of 46 ± 18 years and multiple lesions (77%; five patients with adenomatosis). Meanwhile, ß-catenin mutated hepatocellular adenoma patients with malignant transformation were predominantly male (67%, p = 0.018) with single lesion (86%, p = 0.0009). The largest liver fatty acid binding protein-deficient hepatocellular adenoma nodule in each patient ranged from 4 to 15.5 cm. Loss of liver fatty acid binding protein by immunohistochemistry was noted in all adenoma and borderline/carcinoma components. Features of malignant transformation were pseudoglandular architecture (85%), cytologic atypia (85%), architectural atypia (100%) and lack of steatosis (100%). Other findings included myxoid change (39%), peliosis (46%) and sinusoidal dilatation (46%). Molecular studies confirmed somatic inactivation of HNF1A in 3 cases and absence of TERT promotor and exon 3 CTNNB1 mutations in five cases. To summarize, liver fatty acid binding protein-deficient hepatocellular adenoma with malignant transformation is most frequently seen in female patients with multiple lesions. Most of these lesions demonstrate pseudoglandular architecture, cytologic and architectural atypia, with lack of steatosis. The natural history of these lesions is relatively benign with the exception of disease recurrence in 1 patient.

Aneuploidy-inducing gene knockdowns overlap with cancer mutations and identify Orp3 as a B-cell lymphoma suppressor.

Aneuploidy can instigate tumorigenesis. However, mutations in genes that control chromosome segregation are rare in human tumors as these mutations reduce cell fitness. Screening experiments indicate that the knockdown of multiple classes of genes that are not directly involved in chromosome segregation can lead to aneuploidy induction. The possible contribution of these genes to cancer formation remains yet to be defined. Here we identified gene knockdowns that lead to an increase in aneuploidy in checkpoint-deficient human cancer cells. Computational analysis revealed that the identified genes overlap with recurrent mutations in human cancers. The knockdown of the three strongest selected candidate genes (ORP3, GJB3, and RXFP1) enhances the malignant transformation of human fibroblasts in culture. Furthermore, the knockout of Orp3 results in an aberrant expansion of lymphoid progenitor cells and a high penetrance formation of chromosomal instable, pauci-clonal B-cell lymphoma in aging mice. At pre-tumorous stages, lymphoid cells from the animals exhibit deregulated phospholipid metabolism and an aberrant induction of proliferation regulating pathways associating with increased aneuploidy in hematopoietic progenitor cells. Together, these results support the concept that aneuploidy-inducing gene deficiencies contribute to cellular transformation and carcinogenesis involving the deregulation of various molecular processes such as lipid metabolism, proliferation, and cell survival.

Hepatocyte and stellate cell deletion of liver fatty acid binding protein reveals distinct roles in fibrogenic injury.

Liver fatty acid binding protein (L-Fabp) modulates lipid trafficking in enterocytes, hepatocytes, and hepatic stellate cells (HSCs). We examined hepatocyte vs. HSC L-Fabp deletion in hepatic metabolic adaptation and fibrotic injury. Floxed L-Fabp mice were bred to different transgenic Cre mice or injected with adeno-associated virus type 8 (AAV8) Cre and fed diets to promote steatosis and fibrosis or were subjected to either bile duct ligation or CCl4 injury. Albumin-Cre-mediated L-Fabp deletion revealed recombination in hepatocytes and HSCs; these findings were confirmed with 2 other floxed alleles. Glial fibrillary acid protein-Cre and platelet-derived growth factor receptor ß-Cre-mediated L-Fabp deletion demonstrated recombination only in HSCs. Mice with albumin promoter-driven Cre recombinase (Alb-Cre)-mediated or AAV8-mediated L-Fabp deletion were protected against food withdrawal-induced steatosis. Mice with Alb-Cre-mediated L-Fabp deletion were protected against high saturated fat-induced steatosis and fibrosis, phenocopying germline L-Fabp-/- mice. Mice with HSC-specific L-Fabp deletion exhibited retinyl ester depletion yet demonstrated no alterations in fibrosis. On the other hand, fibrogenic resolution after CCl4 administration was impaired in mice with Alb-Cre-mediated L-Fabp deletion. These findings suggest cell type-specific roles for L-Fabp in mitigating hepatic steatosis and in modulating fibrogenic injury and reversal.-Newberry, E. P., Xie, Y., Lodeiro, C., Solis, R., Moritz, W., Kennedy, S., Barron, L., Onufer, E., Alpini, G., Zhou, T., Blaner, W. S., Chen, A., Davidson, N. O. Hepatocyte and stellate cell deletion of liver fatty acid binding protein reveal distinct roles in fibrogenic injury.

Glucose is preferentially utilized for biomass synthesis in pressure-overloaded hearts: evidence from fatty acid-binding protein-4 and -5 knockout mice.

Aims: The metabolism of the failing heart is characterized by an increase in glucose uptake with reduced fatty acid (FA) oxidation. We previously found that the genetic deletion of FA-binding protein-4 and -5 [double knockout (DKO)] induces an increased myocardial reliance on glucose with decreased FA uptake in mice. However, whether this fuel switch confers functional benefit during the hypertrophic response remains open to debate. To address this question, we investigated the contractile function and metabolic profile of DKO hearts subjected to pressure overload. Methods and results: Transverse aortic constriction (TAC) significantly reduced cardiac contraction in DKO mice (DKO-TAC), although an increase in cardiac mass and interstitial fibrosis was comparable with wild-type TAC (WT-TAC). DKO-TAC hearts exhibited enhanced glucose uptake by 8-fold compared with WT-TAC. Metabolic profiling and isotopomer analysis revealed that the pool size in the TCA cycle and the level of phosphocreatine were significantly reduced in DKO-TAC hearts, despite a marked increase in glycolytic flux. The ingestion of a diet enriched in medium-chain FAs restored cardiac contractile dysfunction in DKO-TAC hearts. The de novo synthesis of amino acids as well as FA from glycolytic flux was unlikely to be suppressed, despite a reduction in each precursor. The pentose phosphate pathway was also facilitated, which led to the increased production of a coenzyme for lipogenesis and a precursor for nucleotide synthesis. These findings suggest that reduced FA utilization is not sufficiently compensated by a robust increase in glucose uptake when the energy demand is elevated. Glucose utilization for sustained biomass synthesis further enhances diminishment of the pool size in the TCA cycle. Conclusions: Our data suggest that glucose is preferentially utilized for biomass synthesis rather than ATP production during pressure-overload-induced cardiac hypertrophy and that the efficient supplementation of energy substrates may restore cardiac dysfunction caused by energy insufficiency.

Fatty acid-binding proteins 5 and 7 gene deletion increases sucrose consumption and diminishes forced swim immobility time.

Inhibition and genetic deletion of fatty acid-binding proteins (FABPs) 5 and 7 have been shown to increase the levels of the endocannabinoid anandamide as well as the related N-acylethanolamine's palmitoylethanolamide and oleoylethanolamide. This study examined the role of these FABPs on forced-swim (FS) behavior and on sucrose consumption in two experiments: (experiment 1) using wild-type (WT) mice treated with the FABP inhibitor SBFI26 or vehicle and (experiment 2) using WT and FABP5/7 deficient mice. Results from experiment 1 showed that acute treatment with SBFI26 did not have any effect on sucrose intake or FS behavior in mice. In experiment 2, male and female FABP5/7 deficient mice showed significant increases in sucrose consumption (25 and 21%, respectively) compared with their WT counterparts. In addition, immobility time during the FS was decreased by 27% in both male and female FABP5/7 knockout mice compared with their WT counterparts. The fact that such differences were seen between the acute pharmacological approach and the genetic approach (gene deletion) of FABP needs to be further investigated. The function of FABPs and their specific effects on endocannabinoid anandamide, oleoylethanolamide, and palmitoylethanolamide may play an important role in the development of reward and mood behaviors and could provide opportunities for potential therapeutic targets.

Fatty acid binding protein deletion prevents stress-induced preference for cocaine and dampens stress-induced corticosterone levels.

Genetic and pharmacological manipulation of endocannabinoid (eCB) signaling has previously been shown to have an important role on the rewarding properties of drugs of abuse, including cocaine. Recently, fatty acid binding proteins (FABPs) have been proposed as intracellular transporters of the endocannabinoid anandamide (AEA) as well as other bioactive lipids to their catabolic enzyme, fatty acid amide hydrolase (FAAH). The role of these transporters in modulating the brains reward system has yet to be investigated. This study examined the effects of genetic deletion of FABP 5/7 on cocaine preference, as assessed by the Conditioned Place Preference (CPP) paradigm. Male and female wild type (WT) and FABP 5/7 KO mice showed similar acquisition of cocaine CPP, with no differences found in overall locomotor activity. In addition, while male and female WT mice showed stress-induced CPP for cocaine, male and female FABP 5/7 KO mice failed to show a stress-induced preference for the cocaine-paired chamber. Additionally, serum corticosterone levels were analyzed to explore any potential differences in stress response that may be responsible for the lack of stress-induced preference for cocaine. Serum samples were obtained in animals under basal conditions as well as following a 30-min tube restraint stress. Male and female FABP 5/7 KO mice showed reduced corticosterone levels under stress compared to their WT counterparts. The reduction in corticosterone response under stress may mediate that lack of a stress-induced preference for cocaine in the FABP 5/7 KO mice. Thus, the role of FABPs may play an important role in drug-seeking behavior under stressful conditions.

Perilipin 5 and liver fatty acid binding protein function to restore quiescence in mouse hepatic stellate cells.

Hepatic stellate cell (HSC) activation occurs along with decreased Perilipin5 (Plin5) and liver fatty acid-binding protein (L-Fabp) expression and coincident lipid droplet (LD) depletion. Conversely, the activated phenotype is reversible in WT HSCs upon forced expression of Plin5. Here, we asked if L-Fabp expression is required for Plin5-mediated rescue of the quiescent phenotype. Lentiviral Plin5 transduction of passaged L-Fabp-/- HSCs failed to reverse activation markers or restore lipogenic gene expression and LD formation. However, adenoviral L-Fabp infection of lentiviral Plin5 transduced L-Fabp-/- HSCs restored both the quiescent phenotype and LD formation, an effect also mediated by adenoviral intestine-Fabp or adipocyte-Fabp. Expression of exogenous Plin5 in activated WT HSCs induced a transcriptional program of lipogenic gene expression including endogenous L-Fabp, but none of the other FABPs. We further demonstrated that selective, small molecule inhibition of endogenous L-Fabp also eliminated the ability of exogenous Plin5 to rescue LD formation and reverse activation of WT HSCs. This functional coordination of L-Fabp with Plin5 was 5'-AMP-activated protein kinase (AMPK)-dependent and was eliminated by AMPK inhibition. Taken together, our results indicate that L-Fabp is required for Plin5 to activate a transcriptional program that restores LD formation and reverses HSC activation.

Ectopic Fatty Acid-Binding Protein 4 Expression in the Vascular Endothelium is Involved in Neointima Formation After Vascular Injury.

BACKGROUND: Fatty acid-binding protein 4 (FABP4) is expressed in adipocytes, macrophages, and endothelial cells of capillaries but not arteries. FABP4 is secreted from adipocytes in association with lipolysis, and an elevated circulating FABP4 level is associated with obesity, insulin resistance, and atherosclerosis. However, little is known about the link between FABP4 and endovascular injury. We investigated the involvement of ectopic FABP4 expression in endothelial cells in neointima hyperplasia after vascular injury. METHODS AND RESULTS: Femoral arteries of 8-week-old male mice were subjected to wire-induced vascular injury. After 4 weeks, immunofluorescence staining showed that FABP4 was ectopically expressed in endothelial cells of the hyperplastic neointima. Neointima formation determined by intima area and intima to media ratio was significantly decreased in FABP4-defficient mice compared with that in wild-type mice. Adenovirus-mediated overexpression of FABP4 in human coronary artery endothelial cells (HCAECs) in vitro increased inflammatory cytokines and decreased phosphorylation of nitric oxide synthase 3. Furthermore, FABP4 was secreted from HCAECs. Treatment of human coronary smooth muscle cells or HCAECs with the conditioned medium of Fabp4-overexpressed HCAECs or recombinant FABP4 significantly increased gene expression of inflammatory cytokines and proliferation- and adhesion-related molecules in cells, promoted cell proliferation and migration of human coronary smooth muscle cells, and decreased phosphorylation of nitric oxide synthase 3 in HCAECs, which were attenuated in the presence of an anti-FABP4 antibody. CONCLUSIONS: Ectopic expression and secretion of FABP4 in vascular endothelial cells contribute to neointima formation after vascular injury. Suppression of ectopic FABP4 in the vascular endothelium would be a novel strategy against post-angioplasty vascular restenosis.

Robust suppression of cardiac energy catabolism with marked accumulation of energy substrates during lipopolysaccharide-induced cardiac dysfunction in mice.

BACKGROUND: Myocardial contractile dysfunction in sepsis has been attributed mainly to increased inflammatory cytokines, insulin resistance, and impaired oxidative phosphorylation of fatty acids (FAs). However, precise molecular mechanisms underlying the cardiac dysfunction in sepsis remain to be determined. We previously reported major shift in myocardial energy substrates from FAs to glucose, and increased hepatic ketogenesis in mice lacking fatty acid-binding protein 4 (FABP4) and FABP5 (DKO). PURPOSE: We sought to determine whether a shift of energy substrates from FAs to glucose and increased availability of ketone bodies are beneficial or detrimental to cardiac function under the septic condition. METHODS: Lipopolysaccharide (LPS, 10mg/kg) was intraperitoneally injected into wild-type (WT) and DKO mice. Twelve hours after injection, cardiac function was assessed by echocardiography and serum and hearts were collected for further analyses. RESULTS: Cardiac contractile function was more deteriorated by LPS injection in DKO mice than WT mice despite comparable changes in pro-inflammatory cytokine production. LPS injection reduced myocardial uptake of FA tracer by 30% in both types of mice, while uptake of the glucose tracer did not significantly change in either group of mice in sepsis. Storage of glycogen and triacylglycerol in hearts was remarkably increased by LPS injection in both mice. Metabolome analysis revealed that LPS-induced suppression of pool size in the TCA cycle was more enhanced in DKO hearts. A tracing study with 13C6-glucose further revealed that LPS injection substantially reduced glucose-derived metabolites in the TCA cycle and related amino acids in DKO hearts. Consistent with these findings, glucose oxidation in vitro was similarly and markedly reduced in both mice. Serum concentration of ß-hydroxybutyrate and cardiac expression of genes associated with ketolysis were reduced in septic mice. CONCLUSIONS: Our study demonstrated that LPS-induced cardiac contractile dysfunction is associated with the robust suppression of catabolism of energy substrates including FAs, glucose and ketone bodies and accumulation of glycogen and triacylglycerol in the heart. Thus, a fuel shift from FAs to glucose and/or ketone bodies may be detrimental rather than protective under septic conditions.

Survival of tissue-resident memory T cells requires exogenous lipid uptake and metabolism.

Tissue-resident memory T (TRM) cells persist indefinitely in epithelial barrier tissues and protect the host against pathogens. However, the biological pathways that enable the long-term survival of TRM cells are obscure. Here we show that mouse CD8+ TRM cells generated by viral infection of the skin differentially express high levels of several molecules that mediate lipid uptake and intracellular transport, including fatty-acid-binding proteins 4 and 5 (FABP4 and FABP5). We further show that T-cell-specific deficiency of Fabp4 and Fabp5 (Fabp4/Fabp5) impairs exogenous free fatty acid (FFA) uptake by CD8+ TRM cells and greatly reduces their long-term survival in vivo, while having no effect on the survival of central memory T (TCM) cells in lymph nodes. In vitro, CD8+ TRM cells, but not CD8+ TCM cells, demonstrated increased mitochondrial oxidative metabolism in the presence of exogenous FFAs; this increase was not seen in Fabp4/Fabp5 double-knockout CD8+ TRM cells. The persistence of CD8+ TRM cells in the skin was strongly diminished by inhibition of mitochondrial FFA ß-oxidation in vivo. Moreover, skin CD8+ TRM cells that lacked Fabp4/Fabp5 were less effective at protecting mice from cutaneous viral infection, and lung Fabp4/Fabp5 double-knockout CD8+ TRM cells generated by skin vaccinia virus (VACV) infection were less effective at protecting mice from a lethal pulmonary challenge with VACV. Consistent with the mouse data, increased FABP4 and FABP5 expression and enhanced extracellular FFA uptake were also demonstrated in human CD8+ TRM cells in normal and psoriatic skin. These results suggest that FABP4 and FABP5 have a critical role in the maintenance, longevity and function of CD8+ TRM cells, and suggest that CD8+ TRM cells use exogenous FFAs and their oxidative metabolism to persist in tissue and to mediate protective immunity.

Loss of Fatty Acid Binding Protein 4/aP2 Reduces Macrophage Inflammation Through Activation of SIRT3.

Activation of proinflammatory macrophages plays an important role in the pathogenesis of insulin resistance, type 2 diabetes, and atherosclerosis. Previous work using high fat-fed mice has shown that ablation of the adipocyte fatty acid binding protein (FABP4/aP2) in macrophages leads to an antiinflammatory state both in situ and in vivo, and the mechanism is linked, in part, to increased intracellular monounsaturated fatty acids and the up-regulation of uncoupling protein 2. Here, we show that loss of FABP4/aP2 in macrophages additionally induces sirtuin 3 (SIRT3) expression and that monounsaturated fatty acids (C16:1, C18:1) lead to increased SIRT3 protein expression. Increased expression of SirT3 in FABP4/aP2 null macrophages occurs at the protein level with no change in SirT3 mRNA. When compared with controls, silencing of SIRT3 in Raw246.7 macrophages leads to increased expression of inflammatory cytokines, inducible nitric oxide synthase and cyclooxygenase 2. In contrast, loss of SIRT3 in FABP4/aP2-deficient macrophages attenuates the suppressed inflammatory signaling, reduced reactive oxygen species production, lipopolysaccharide-induced mitochondrial dysfunction, and increased fatty acid oxidation. These results suggest that the antiinflammatory phenotype of FABP4/aP2 null mice is mediated by increased intracellular monounsaturated fatty acids leading to the increased expression of both uncoupling protein 2 and SirT3.

Dual role of fatty acid-binding protein 5 on endothelial cell fate: a potential link between lipid metabolism and angiogenic responses.

Fatty acid-binding proteins (FABP) are small molecular mass intracellular lipid chaperones that are expressed in a tissue-specific manner with some overlaps. FABP4 and FABP5 share ~55 % amino acid sequence homology and demonstrate synergistic effects in regulation of metabolic and inflammatory responses in adipocytes and macrophages. Recent studies have shown that FABP4 and FABP5 are also co-expressed in a subset of endothelial cells (EC). FABP4, which has a primarily microvascular distribution, enhances angiogenic responses of ECs, including proliferation, migration, and survival. However, the vascular expression of FABP5 has not been well characterized, and the role of FABP5 in regulation of angiogenic responses in ECs has not been studied to date. Herein we report that while FABP4 and FABP5 are co-expressed in microvascular ECs in several tissues, FABP5 expression is also detected in ECs of larger blood vessels. In contrast to FABP4, EC-FABP5 levels are not induced by VEGF-A or bFGF. FABP5 deficiency leads to a profound impairment in EC proliferation and chemotactic migration. These effects are recapitulated in an ex vivo assay of angiogenesis, the aortic ring assay. Interestingly, in contrast to FABP4-deficient ECs, FABP5-deficient ECs are significantly more resistant to apoptotic cell death. The effect of FABP5 on EC proliferation and survival is mediated, only in part, by PPARδ-dependent pathways. Collectively, these findings demonstrate that EC-FABP5, similar to EC-FABP4, promotes angiogenic responses under certain conditions, but it can also exert opposing effects on EC survival as compared to EC-FABP4. Thus, the balance between FABP4 and FABP5 in ECs may be important in regulation of angiogenic versus quiescent phenotypes in blood vessels.

Fatty acid binding protein deletion suppresses inflammatory pain through endocannabinoid/N-acylethanolamine-dependent mechanisms.

BACKGROUND: Fatty acid binding proteins (FABPs) serve as intracellular carriers that deliver endocannabinoids and N-acylethanolamines to their catabolic enzymes. Inhibition of FABPs reduces endocannabinoid transport and catabolism in cells and FABP inhibitors produce antinociceptive and anti-inflammatory effects in mice. Potential analgesic effects in mice lacking FABPs, however, have not been tested. FINDINGS: Mice lacking FABP5 and FABP7, which exhibit highest affinities for endocannabinoids, possessed elevated levels of the endocannabinoid anandamide and the related N-acylethanolamines palmitoylethanolamide and oleoylethanolamide. There were no compensatory changes in the expression of other FABPs or in endocannabinoid-related proteins in the brains of FABP5/7 knockout mice. These mice exhibited reduced nociception in the carrageenan, formalin, and acetic acid tests of inflammatory and visceral pain. The antinociceptive effects in FABP5/7 knockout mice were reversed by pretreatment with cannabinoid receptor 1, peroxisome proliferator-activated receptor alpha, and transient receptor potential vanilloid 1 receptor antagonists in a modality specific manner. Lastly, the knockout mice did not possess motor impairments. CONCLUSIONS: This study demonstrates that mice lacking FABPs possess elevated levels of N-acylethanolamines, consistent with the idea that FABPs regulate the endocannabinoid and N-acylethanolamine tone in vivo. The antinociceptive effects observed in the knockout mice support a role for FABPs in regulating nociception and suggest that these proteins should serve as targets for the development of future analgesics.

Epidermal Fatty Acid binding protein promotes skin inflammation induced by high-fat diet.

Defining specific cellular and molecular mechanisms in most obesity-related diseases remains an important challenge. Here we report a serendipitous finding that consumption of a high-fat diet (HFD) greatly increased the occurrence of skin lesions in C57BL/6 mice. We demonstrated that HFD induced the accumulation of a specific type of CD11c(+) macrophages in skin preceding detectable lesions. These cells primed skin to induce IL-1ß and IL-18 signaling, which further promoted the cytokines IFN-γ- and IL-17-mediated skin inflammation. Mechanistically, epidermal fatty acid binding protein (E-FABP) was significantly upregulated in skin of obese mice, which coupled lipid droplet formation and NLRP3 inflammasome activation. Deficiency of E-FABP in obese mice decreased recruitment of CD11c(+) macrophages in skin tissues, reduced production of IL-1ß and IL-18, and consequently dampened activation of effector T cells. Furthermore, E-FABP-deficient mice are completely resistant to HFD-induced skin lesions. Collectively, E-FABP represents a molecular sensor triggering HFD-induced skin inflammation.

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.

Hepatic ATGL mediates PPAR-α signaling and fatty acid channeling through an L-FABP independent mechanism.

Adipose TG lipase (ATGL) catalyzes the rate-limiting step in TG hydrolysis in most tissues. We have shown that hepatic ATGL preferentially channels hydrolyzed FAs to ß-oxidation and induces PPAR-α signaling. Previous studies have suggested that liver FA binding protein (L-FABP) transports FAs from lipid droplets to the nucleus for ligand delivery and to the mitochondria for ß-oxidation. To determine if L-FABP is involved in ATGL-mediated FA channeling, we used adenovirus-mediated suppression or overexpression of hepatic ATGL in either WT or L-FABP KO mice. Hepatic ATGL knockdown increased liver weight and TG content of overnight fasted mice regardless of genotype. L-FABP deletion did not impair the effects of ATGL overexpression on the oxidation of hydrolyzed FAs in primary hepatocyte cultures or on serum ß-hydroxybutyrate concentrations in vivo. Moreover, L-FABP deletion did not influence the effects of ATGL knockdown or overexpression on PPAR-α target gene expression. Taken together, we conclude that L-FABP is not required to channel ATGL-hydrolyzed FAs to mitochondria for ß-oxidation or the nucleus for PPAR-α regulation.

Fatty acid binding protein 4 regulates VEGF-induced airway angiogenesis and inflammation in a transgenic mouse model: implications for asthma.

Neovascularization of the airways occurs in several inflammatory lung diseases, including asthma. Vascular endothelial growth factor (VEGF) plays an important role in vascular remodeling in the asthmatic airways. Fatty acid binding protein 4 (FABP4 or aP2) is an intracellular lipid chaperone that is induced by VEGF in endothelial cells. FABP4 exhibits a proangiogenic function in vitro, but whether it plays a role in modulation of angiogenesis in vivo is not known. We hypothesized that FABP4 promotes VEGF-induced airway angiogenesis and investigated this hypothesis with the use of a transgenic mouse model with inducible overexpression of VEGF165 under a CC10 promoter [VEGF-TG (transgenic) mice]. We found a significant increase in FABP4 mRNA levels and density of FABP4-expressing vascular endothelial cells in mouse airways with VEGF overexpression. FABP4(-/-) mouse airways showed a significant decrease in neovessel formation and endothelial cell proliferation in response to VEGF overexpression. These alterations in airway vasculature were accompanied by attenuated expression of proinflammatory mediators. Furthermore, VEGF-TG/FABP4(-/-) mice showed markedly decreased expression of endothelial nitric oxide synthase, a well-known mediator of VEGF-induced responses, compared with VEGF-TG mice. Finally, the density of FABP4-immunoreactive vessels in endobronchial biopsy specimens was significantly higher in patients with asthma than in control subjects. Taken together, these data unravel FABP4 as a potential target of pathologic airway remodeling in asthma.

Cigarette smoke decreases airway epithelial FABP5 expression and promotes Pseudomonas aeruginosa infection.

Cigarette smoking is the primary cause of Chronic Obstructive Pulmonary Disease (COPD), which is characterized by chronic inflammation of the airways and destruction of lung parenchyma. Repeated and sustained bacterial infections are clearly linked to disease pathogenesis (e.g., exacerbations) and a huge burden on health care costs. The airway epithelium constitutes the first line of host defense against infection and our previous study indicated that Fatty Acid Binding Protein 5 (FABP5) is down regulated in airway epithelial cells of smokers with COPD as compared to smokers without COPD. We hypothesized that cigarette smoke (CS) exposure down regulates FABP5, thus, contributing to a more sustained inflammation in response to bacterial infection. In this report, we show that FABP5 is increased following bacterial infection but decreased following CS exposure of primary normal human bronchial epithelial (NHBE) cells. The goal of this study was to address FABP5 function by knocking down or overexpressing FABP5 in primary NHBE cells exposed to CS. Our data indicate that FABP5 down regulation results in increased P. aeruginosa bacterial load and inflammatory cytokine levels (e.g., IL-8) and decreased expression of the anti-bacterial peptide, ß defensin-2. On the contrary, FABP5 overexpression exerts a protective function in airway epithelial cells against P. aeruginosa infection by limiting the production of IL-8 and increasing the expression of ß defensin-2. Our study indicates that FABP5 exerts immunomodulatory functions in the airway epithelium against CS exposure and subsequent bacterial infection through its modulation of the nuclear receptor peroxisome proliferator-activated receptor (PPAR)-γ activity. These findings support the development of FABP5/PPAR-γ-targeted therapeutic approach to prevent airway inflammation by restoring antimicrobial immunity during COPD exacerbations.