Fatty acid-binding protein 4 (FABP4) and FABP5 modulate cytokine production in the mouse thymic epithelial cells

Identification of Adipogenesis Subgroups and Immune Infiltration Characteristics in Diabetic Peripheral Neuropathy

Dysregulation of adipogenesis is related to diabetic peripheral neuropathy (DPN) pathogenesis, which may be mediated by immune infiltration. Nevertheless, the expression patterns of multiple adipogenesis-related genes and the differences of immune infiltration in different lipid metabolism levels remain unknown. GSE95849, a gene expression matrix containing DPN patients and healthy participants, was downloaded from Gene Expression Omnibus (GEO) database. Differentially expressed adipogenesis-related genes (DEARGs) were screened by overlapping the adipogenesis-related genes with differentially expressed genes (DEGs). DPN patients from GSE24290 and GSE148059 were divided into two adipogenesis subgroups according to the expression of DEARGs. The single-sample gene set enrichment analysis (ssGSEA) was used to estimate the abundance of the immune cells between two subgroups. The analysis of immune infiltration suggested that a variety of immune cells and immune processes were elevated in the high expression group of DEARGs. The differentially expressed genes of the two subgroups were mainly enriched in biological processes and signaling pathways related to lipid metabolism. PPARG, FABP4, LIPE, FASN, SCD, DGAT2, PNPLA2, ADIPOQ, LEP, and CEBPA were identified as the hub genes of the two subgroups, whose related transcription factors (TFs) and miRNAs were predicted. An immunohistochemical assay was used to verify the expression of hub genes in DPN nerve tissues. Our comprehensive analysis of adipogenesis subgroups in DPN illustrated that different expression patterns of DEARGs may lead to different immune and inflammatory states. The identification of DEARGs may help to further distinguish the different characteristics of DPN patients and lay the foundation for targeted treatment. Our findings may bring a novel perspective to the diagnosis and treatment of DPN patients.

Fatty acid-binding protein 4 in kidney diseases: From mechanisms to clinics

Considerable evidence indicated the relationship between fatty acid-binding protein 4 (FABP4) and kidney diseases. FABP4, a small molecular lipid chaperone, is identified to regulate fatty acid oxidation, inflammation, apoptosis, endoplasmic reticulum stress and macrophage-to-myofibroblast transition in kidney diseases. Many studies have shown that circulating FABP4 level is related to proteinuria, renal function decline, cardiovascular complications of end-stage renal disease and even the prognosis of kidney transplanted patients. Notably, pharmacological or genetic inhibition of FABP4 attenuated renal injury in the various experimental models of kidney diseases, making it promising to develop potential therapeutic strategies targeting FABP4 in kidney diseases. In this study, we updated and reviewed the mechanisms and clinical significance of FABP4 in kidney diseases.

Intracellular Lipid Accumulation Drives the Differentiation of Decidual Polymorphonuclear Myeloid-Derived Suppressor Cells via Arachidonic Acid Metabolism

Decidual polymorphonuclear myeloid-derived suppressor cells (PMN-MDSCs) are essential to immune tolerance during pregnancy. A reduction in the number of these cells is associated with unexplained recurrent pregnancy loss (URPL). In our previous study, we reported that PMN-MDSCs are a group of mature neutrophils that are activated by the decidua microenvironment. In the present study, we show that the decidua microenvironment induces substantial lipid accumulation in neutrophils during their differentiation to PMN-MDSCs. Lower levels of lipid accumulation are detected in PMN-MDSCs from URPL patients, and the amount of lipid in the PMN-MDSCs is positively correlated with the proportion of PMN-MDSCs. Next, we demonstrate that decidua-derived IL6 with the presence of arachidonic acid upregulates fatty acid-binding protein 5 (FABP5) via the phosphorylation of signal transducer and activator of transcription 3 (STAT3). Fy -60ABP5 then continuously stimulates intracellular lipid accumulation. Increased intracellular lipid accumulation mediates arachidonic acid metabolism, a pathway that is significantly activated by the induction of the decidua microenvironment, to stimulate the synthesis of prostaglandin E2 (PGE2) and finally induce the differentiation of PMN-MDSCs. To summarize, decidua-derived IL6 facilitates the differentiation of PMN-MDSCs from neutrophils via the pSTAT3/FABP5/PGE2 pathway. Defects in the process may result in impaired differentiation and dysfunction of PMN-MDSCs in URPL. These findings enhance our understanding of the physiological mechanisms of immune tolerance in pregnancy and provide therapeutic options for URPL.

The Biological Functions and Regulatory Mechanisms of Fatty Acid Binding Protein 5 in Various Diseases

In recent years, fatty acid binding protein 5 (FABP5), also known as fatty acid transporter, has been widely researched with the help of modern genetic technology. Emerging evidence suggests its critical role in regulating lipid transport, homeostasis, and metabolism. Its involvement in the pathogenesis of various diseases such as metabolic syndrome, skin diseases, cancer, and neurological diseases is the key to understanding the true nature of the protein. This makes FABP5 be a promising component for numerous clinical applications. This review has summarized the most recent advances in the research of FABP5 in modulating cellular processes, providing an in-depth analysis of the protein's biological properties, biological functions, and mechanisms involved in various diseases. In addition, we have discussed the possibility of using FABP5 as a new diagnostic biomarker and therapeutic target for human diseases, shedding light on challenges facing future research.

Effects of Fatty Acids on Proliferation of Cultured Wild-type and FABP5-KO Thymic Epithelial Cells

Lipids including fatty acids (FAs), which are water-insoluble molecules, are not only a cellular energy source but also signaling molecules that induce and modulate the expression of various cellular functions. Fatty acid-binding proteins (FABP) bind FAs in the cytoplasm, and are thought to determine the cellular localization of FAs. In a previous observation, FABP5 was expressed in thymic epithelial cells (TEC) in the thymus and was influenced by FAs. Fatty acids have mostly inhibitory effects on various cell types, including cancer cells, but their effects on TEC have not been well investigated. In this study, we investigated the effects of long-chain FAs (LCFAs) and the involvement of FABP5 in cell proliferation using a serum-free primary culture system. The results showed that saturated fatty acids did not affect proliferation, but n-3 long-chain polyunsaturated FA (LCPUFA) reduced, n-6 LCPUFA increased, and retinoic acid strongly reduced the percentage of proliferating wild-type TEC. The proliferation of FABP5-KO TEC was more significantly affected by LCPUFA, suggesting that FABP5 is an important modulator of FA-mediated TEC proliferation. These observations may provide a basis for exploring the properties of TEC.

Relations of heart-type and brain-type fatty acid-binding proteins with postoperative cognitive dysfunction in elderly patients undergoing spinal surgery

OBJECTIVE

The aim of this study is to analyze the relations of heart-type fatty acid-binding protein (H-FABP) and brain-type fatty acid-binding protein (B-FABP) with postoperative cognitive dysfunction (POCD) in elderly patients undergoing spinal surgery.

METHODS

One hundred and twenty-five patients who underwent spinal surgery were enrolled in this study. According to whether patients had POCD within 5 days after surgery, the participants were divided into POCD group and non-POCD group. Before surgery and 6 h after surgery, the serum H-FABP and B-FABP contents were detected.

RESULTS

There were 33 (26.4%) patients in POCD group, and 92 (73.60%) patients in non-POCD group. After surgery, the serum H-FABP and B-FABP contents in POCD group were significantly higher than those before surgery, respectively (p<0.05), and those in non-POCD group were significantly lower than those before surgery, respectively (p<0.05). After surgery, the serum H-FABP and B-FABP contents in POCD group were significantly higher than those in non-POCD group, respectively (p<0.05).

CONCLUSION

The serum H-FABP and B-FABP contents are positively related to the occurrence of POCD in elderly patients undergoing spinal surgery.

Changes in the host transcriptome and microbial metatranscriptome of the ileum of dairy calves subjected to artificial dosing of exogenous rumen contents

Development of a properly functioning gastrointestinal tract (GIT) at an early age is critical for the wellbeing and lifetime productivity of dairy cattle. The role of early microbial colonization on GIT development in neonatal cattle and the associated molecular changes remain largely unknown, particularly for the small intestine. In this study, we performed artificial dosing of exogenous rumen fluid during the early life of the calf, starting at birth through the weaning transition at 8 wk. Six calves were included in this study. At 8 wk of age, tissue from the ileum was collected and subjected to host transcriptome and microbial metatranscriptome analysis using RNA sequencing. A total of 333 genes showed significant differential expression (DE) (fold-change ≥2; adjusted P < 0.1, mean read-count ≥10) between the treated and control calves. Gene ontology analysis indicated that these DE genes are predominantly associated with processes related to the host immune response (P < 0.0001). Association analysis between the host gene expression and the microbial genus abundance identified 57 genes as having significant correlation with the ileum microbial genera (P < 0.0001). Of these, three genes showed significant association with six microbial genera: lysozyme 2 (LYZ2), fatty acid binding protein 5 (FABP5), and fucosyltransferase (FUT1). Specifically, the profound increase in expression of LYZ2 in treated calves suggests the initiation of antibacterial activity and innate response from the host. Despite the limitation of a relatively small sample size, this study sheds light on the potential impact of early introduction of microbes on the small intestine of calves.

Role of fatty acid binding proteins (FABPs) in cancer development and progression

Fatty acid binding proteins (FABPs) are small, water soluble proteins that bind long chain fatty acids and other biologically active ligands to facilitate intracellular localization. Twelve FABP family members have been identified to date, with 10 isoforms expressed in humans. Functionally, FABPs are important in fatty acid metabolism and transport, with distinct family members having the capacity to influence gene transcription. Expression of FABPs is usually cell/tissue specific to one predominant FABP family member. Dysregulation of FABP expression can occur through genetic mutation and/or environmental-lifestyle influences. In addition to intracellular function, exogenous, circulating FABP expression can occur and is associated with specific disease states such as insulin resistance. A role for FABPs is increasingly being reported in tumor biology with elevated exogenous FABP expression being associated with tumor progression and invasiveness. However, a less clear role has been appreciated for dysregulated FABP expression during cell transformation and early expansion.

GRAPHICAL MODELS FOR ZERO-INFLATED SINGLE CELL GENE EXPRESSION

Bulk gene expression experiments relied on aggregations of thousands of cells to measure the average expression in an organism. Advances in microfluidic and droplet sequencing now permit expression profiling in single cells. This study of cell-to-cell variation reveals that individual cells lack detectable expression of transcripts that appear abundant on a population level, giving rise to zero-inflated expression patterns. To infer gene co-regulatory networks from such data, we propose a multivariate Hurdle model. It is comprised of a mixture of singular Gaussian distributions. We employ neighborhood selection with the pseudo-likelihood and a group lasso penalty to select and fit undirected graphical models that capture conditional independences between genes. The proposed method is more sensitive than existing approaches in simulations, even under departures from our Hurdle model. The method is applied to data for T follicular helper cells, and a high-dimensional profile of mouse dendritic cells. It infers network structure not revealed by other methods; or in bulk data sets. An R implementation is available at https://github.com/amcdavid/HurdleNormal.

FABP7 Protects Astrocytes Against ROS Toxicity via Lipid Droplet Formation

Fatty acid-binding proteins (FABPs) bind and internalize long-chain fatty acids, controlling lipid dynamics. Recent studies have proposed the involvement of FABPs, particularly FABP7, in lipid droplet (LD) formation in glioma, but the physiological significance of LDs is poorly understood. In this study, we sought to examine the role of FABP7 in primary mouse astrocytes, focusing on its protective effect against reactive oxygen species (ROS) stress. In FABP7 knockout (KO) astrocytes, ROS induction significantly decreased LD accumulation, elevated ROS toxicity, and impaired thioredoxin (TRX) but not peroxiredoxin 1 (PRX1) signalling compared to ROS induction in wild-type astrocytes. Consequently, activation of apoptosis signalling molecules, including p38 mitogen-activated protein kinase (MAPK) and stress-activated protein kinase/c-Jun N-terminal kinase (SAPK/JNK), and increased expression of cleaved caspase 3 were observed in FABP7 KO astrocytes under ROS stress. N-acetyl L-cysteine (NAC) application successfully rescued the ROS toxicity in FABP7 KO astrocytes. Furthermore, FABP7 overexpression in U87 human glioma cell line revealed higher LD accumulation and higher antioxidant defence enzyme (TRX, TRX reductase 1 [TRXRD1]) expression than mock transfection and protected against apoptosis signalling (p38 MAPK, SAPK/JNK and cleaved caspase 3) activation. Taken together, these data suggest that FABP7 protects astrocytes from ROS toxicity through LD formation, providing new insights linking FABP7, lipid homeostasis, and neuropsychiatric/neurodegenerative disorders, including Alzheimer's disease and schizophrenia.

FABP4 inhibitors 3D-QSAR model and isosteric replacement of BMS309403 datasets

The data have been obtained from FABP4 inhibitor molecules previously published. The 120 compounds were used to build a 3D-QSAR model. The development of the QSAR model has been undertaken with the use of Forge software using the PM3 optimized structure and the experimental IC₅₀ of each compound. The QSAR model was also employed to predict the activity of 3000 new isosteric derivatives of BMS309403. The isosteric replacement was also validated by the synthesis and the biological screening of three new compounds reported in the related research article “3D-QSAR assisted identification of FABP4 inhibitors: An effective scaffold hopping analysis/QSAR evaluation” (Floresta et al., 2019).

Serological Epithelial Component Proteins Identify Intestinal Complications in Crohn's Disease

Crohn's Disease (CD) is a relapsing inflammation of the gastrointestinal tract that affects a young working age population and is increasing in developing countries. Half of all sufferers will experience stricturing or fistulizing intestinal complications that require extensive surgical interventions and neither genes nor clinical risk factors can predict this debilitating natural history. We applied discovery and verification phase studies as part of an NCI-FDA modeled biomarker pipeline to identify differences in the low-mass (<25kDa) blood-serum proteome between CD behavioral phenotypes. A significant enrichment of epithelial component proteins was identified in CD patients with intestinal complications using quantitative proteomic profiling with label-free Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS). DAVID 6.7 (NIH) was used for functional annotation analysis of detected proteins and immunoblotting and multiple reaction monitoring (MRM) to verify a priori findings in a secondary independent cohort of complicated CD (CCD), uncomplicated inflammatory CD (ICD), Th1/17 pathway inflammation controls (rheumatoid arthritis), inflammatory bowel disease controls (ulcerative colitis), and healthy controls. Seventy-six high-confidence serum proteins were modulated in CCD versus ICD by LC-MS/MS (p < 0.05, FDR q<0.01), annotating to pathways of epithelial barrier homeostasis (p < 0.01). In verification phase, a putative serology panel developed from discovery proteomics data consisting of desmoglein-1, desmoplakin, and fatty acid-binding protein 5 (FABP5) distinguished CCD from all other groups (p = 0.041) and discriminated complication in CD (70% sensitivity and 72.5% specificity at score ≥1.907, AUC = 0.777, p = 0.007). An MRM assay secondarily confirmed increased FABP5 levels in CCD (p < 0.001). In a longitudinal subanalysis-cohort, FABP5 levels were stable over a two-month period with no behavioral changes (p = 0.099). These studies along the biomarker development pipeline provide substantial proof-of-principle that a blood test can be developed specific to transmural intestinal injury. Data are available via the PRIDE proteomics data repository under identifier PXD001821 and PeptideAtlas with identifier PASS00661.

Successful reduction of inflammatory responses and arachidonic acid-cyclooxygenase 2 pathway in human pulmonary artery endothelial cells by silencing adipocyte fatty acid-binding protein

Background

Adipocyte fatty acid-binding protein, also known as aP2 or fatty acid-binding protein 4 (FABP4), plays an important role in inflammatory and metabolic responses in adipocytes and macrophages. Recent work has demonstrated that macrophage FABP4 integrates inflammatory and lipid metabolic responses, thereby contributing to the development of insulin resistance and atherosclerosis. However, it is not known whether FABP4 in human pulmonary artery endothelial cells(HPAECs) modulates inflammation.

Results

Here, we demonstrate that FABP4 and inflammatory cytokines are upregulated in lipopolysaccharide(LPS)-stimulated HPAECs. In addition, LPS increases the expression of molecules in the arachidonic acid(AA)–cyclooxygenase (COX) 2 signaling pathway in FABP4-expressing, but not FABP4-deficient, HPAECs.

Conclusions

Our findings demonstrate that silencing FABP4 could decrease inflammatory cytokines, which were reported to be expressed via the AA–COX2 pathway, in HPAECs. In addition, silencing FABP4 could inhibit the expression of molecules in the AA–COX2 pathways. So we speculate silencing FABP4 could decrease the inflammatory response in HPAECs, which involves in the AA–COX2 signaling pathway. Our study suggests that FABP4 could be a potential biomarker and intervention point for the inflammation-related disease in HPAECs such as pulmonary thromboembolism.

Fatty Acid Binding Protein 3 Is Involved in n-3 and n-6 PUFA transport in mouse trophoblasts

BACKGROUND

Low placental fatty acid (FA) transport during the embryonic period has been suggested to result in fetal developmental disorders and various adult metabolic diseases, but the molecular mechanism by which FAs are transported through the placental unit remains largely unknown.

OBJECTIVE

The aim of this study was to examine the distribution and functional relevance of FA binding protein (FABP), a cellular chaperone of FAs, in the mouse placenta.

METHODS

We clarified the localization of FABPs and sought to examine their function in placental FA transport through the phenotypic analysis of Fabp3-knockout mice.

RESULTS

Four FABPs (FABP3, FABP4, FABP5, and FABP7) were expressed with spatial heterogeneity in the placenta, and FABP3 was dominantly localized to the trophoblast cells. In placentas from the Fabp3-knockout mice (both sexes), the transport coefficients for linoleic acid (LA) were significantly reduced compared with those from wild-type mice by 25% and 44% at embryonic day (E) 15.5 and E18.5, respectively, whereas those for α-linolenic acid (ALA) were reduced by 19% and 17%, respectively. The accumulation of LA (18% and 27% at E15.5 and E18.5) and ALA (16% at E15.5) was also significantly less in the Fabp3-knockout fetuses than in wild-type fetuses. In contrast, transport and accumulation of palmitic acid (PA) were unaffected and glucose uptake significantly increased by 23% in the gene-ablated mice compared with wild-type mice at E18.5. Incorporation of LA (51% and 52% at 1 and 60 min, respectively) and ALA (23% at 60 min), but not PA, was significantly less in FABP3-knockdown BeWo cells than in controls, whereas glucose uptake was significantly upregulated by 51%, 50%, 31%, and 33% at 1, 20, 40, and 60 min, respectively.

CONCLUSIONS

Collectively FABP3 regulates n-3 (ω-3) and n-6 (ω-6) polyunsaturated FA transport in trophoblasts and plays a pivotal role in fetal development.

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.

Long chain fatty acids and gene expression in inflammation and immunity

PURPOSE OF REVIEW

The purpose of this review is to discuss recent studies reporting on the influence of fatty acids on gene expression in relation to inflammation and immune responses.

RECENT FINDINGS

Saturated fatty acids promote, whereas several n-3 fatty acids, in particular eicosapentaenoic and docosahexaenoic acids, some isomers of conjugated linoleic acid, and punicic acid suppress, expression of inflammatory genes. The most common targets of fatty acids are genes encoding cytokines, chemokines, cyclooxygenase, nitric oxide synthase, and matrix metalloproteinases. The anti-inflammatory actions of fatty acids often involve inhibition of activation of nuclear factor-κB and activation of peroxisome proliferator-activated receptors α and γ. Common upstream events include actions on Toll-like receptors and via G-protein coupled receptors. Fatty acids can influence expression of genes involved in immune and inflammatory cell development and differentiation. Recent studies using genome-wide analyses demonstrate that dietary fatty acids can alter expression of a large number (many hundreds) of genes in human peripheral blood mononuclear cells.

SUMMARY

A wide range of fatty acids alter expression of genes involved in development, differentiation, and function of cells involved in inflammation and immunity.