Integrated bioinformatics analysis and experimental validation reveal the relationship between ALOX5AP and the prognosis and immune microenvironment in glioma.

BACKGROUND: Treatment of gliomas, the most prevalent primary malignant neoplasm of the central nervous system, is challenging. Arachidonate 5-lipoxygenase activating protein (ALOX5AP) is crucial for converting arachidonic acid into leukotrienes and is associated with poor prognosis in multiple cancers. Nevertheless, its relationship with the prognosis and the immune microenvironment of gliomas remains incompletely understood. METHODS: The differential expression of ALOX5AP was evaluated based on public Databases. Kaplan-Meier, multivariate Cox proportional hazards regression analysis, time-dependent receiver operating characteristic, and nomogram were used to estimate the prognostic value of ALOX5AP. The relationship between ALOX5AP and immune infiltration was calculated using ESTIMATE and CIBERSORT algorithms. Relationships between ALOX5AP and human leukocyte antigen molecules, immune checkpoints, tumor mutation burden, TIDE score, and immunophenoscore were calculated to evaluate glioma immunotherapy response. Single gene GSEA and co-expression network-based GO and KEGG enrichment analysis were performed to explore the potential function of ALOX5AP. ALOX5AP expression was verified using multiplex immunofluorescence staining and its prognostic effects were confirmed using a glioma tissue microarray. RESULT: ALOX5AP was highly expressed in gliomas, and the expression level was related to World Health Organization (WHO) grade, age, sex, IDH mutation status, 1p19q co-deletion status, MGMTp methylation status, and poor prognosis. Single-cell RNA sequencing showed that ALOX5AP was expressed in macrophages, monocytes, and T cells but not in tumor cells. ALOX5AP expression positively correlated with M2 macrophage infiltration and poor immunotherapy response. Immunofluorescence staining demonstrated that ALOX5AP was upregulated in WHO higher-grade gliomas, localizing to M2 macrophages. Glioma tissue microarray confirmed the adverse effect of ALOX5AP in the prognosis of glioma. CONCLUSION: ALOX5AP is highly expressed in M2 macrophages and may act as a potential biomarker for predicting prognosis and immunotherapy response in patients with glioma.

Dysregulated Leukotriene Metabolism in Patients with COVID-19.

This study aimed to examine the leukotriene metabolism during COVID-19. In total, 180 participants were included in this study, of which 60 were healthy controls, 60 required intensive care units (ICU), and 60 did not require intensive care (non-ICU). The serum levels of 5-lipoxygenase (5-LO), 5-LO activating protein (ALOX5AP), and cysteinyl leukotriene (CYSLT) were measured, and the mRNA expression levels of 5-LO, ALOX5AP, and cysteinyl leukotriene receptor 1 (CYSLTR1) were investigated. Compared with the control group, both the non-ICU and ICU groups had lower levels of 5-LO and mRNA expression. ICU patients had lower levels of 5-LO and mRNA expression than non-ICU patients. CYSLTR1 mRNA expression was highest in the ICU group, followed by the non-ICU group, and healthy controls had the lowest mRNA expression levels. CYSLT levels were higher in the control group than in the non-ICU and ICU groups. CYSLTR1 expression was higher in patients than in controls; therefore, selective leukotriene receptor blockers can be used as treatment options. CYSLTR1 expression was higher in the ICU group than in the non-ICU group. Furthermore, CYSLTR1 mRNA expression may be a promising biomarker of COVID-19 severity.

ALOX5AP suppresses osteosarcoma progression via Wnt/ß-catenin/EMT pathway and associates with clinical prognosis and immune infiltration.

Osteosarcoma (OS) is one of the most common malignant neoplasms in children and adolescents. Immune infiltration into the microenvironment of the tumor has a positive correlation with overall survival in patients with OS. The purpose of this study was to search for potential diagnostic markers that are involved in immune cell infiltration for OS. Patients with OS who acquired metastases within 5 years (n = 34) were compared to patients who did not develop metastases within 5 years (n = 19). Differentially expressed genes (DEGs) were tested for in both patient groups. To discover possible biomarkers, the LASSO regression model and the SVM-RFE analysis were both carried out. With the assistance of CIBERSORT, the compositional patterns of the 22 different types of immune cell fraction in OS were estimated. In this research, a total of 33 DEGs were obtained: 33 genes were significantly downregulated. Moreover, we identified six critical genes, including ALOX5AP, HLA-DOA, HLA-DMA, HLA-DRB4, HCLS1 and LOC647450. ROC assays confirmed their diagnostic value with AUC > 0.7. In addition, we found that the six critical genes were associated with immune infiltration. Then, we confirmed the expression of ALOX5AP was distinctly decreased in OS specimens and cell lines. High expression of ALOX5AP predicted an advanced clinical stage and overall survival of OS patients. Functionally, we found that overexpression of ALOX5AP distinctly suppressed the proliferation, migration, invasion and EMT via modulating Wnt/ß-catenin signaling. Overall, we found that ALOX5AP overexpression inhibits OS development via regulation of Wnt/ß-catenin signaling pathways, suggesting ALOX5AP as a novel molecular biomarker for enhanced therapy of OS.

ALOX5AP is an Indicator for High CD8 Lymphocyte Infiltration and "Hot" Tumor Microenvironment in Osteosarcoma: A Bioinformatic Study.

Little progress has been made in the treatment and prognosis of osteosarcoma in the past 40 years. Tumor microenvironment (TME) plays a critical role in the progression of osteosarcoma. This study aims to determine immune-associated prognostic biomarkers for osteosarcoma patients. With the help of analytical tools including ESTIMATE, differential gene expression, LASSO, and univariate cox and multivariate cox regression analysis, osteosarcoma gene expression data from Gene Expression Omnibus (GEO) databases were investigated. Following the establishment of a prognostic risk score model, internal and external validations using the GEO and TARGET databases were carried out. A total of 44 and 55 samples respectively in the GSE21257 and the TARGET databases were included. Our analysis found 93 differentially expressed genes (DEGs) between the high and low-ImmuneScore groups. Through univariate cox and LASSO analysis, ALOX5AP was identified as an indicator of TME in osteosarcomas. ALOX5AP was then used to construct a prognostic risk model. Internal and external verification revealed that higher expression of ALOX5AP was correlated with lower risk. Through the CIBERSORT algorithm, the level of CD8 T cells was found to negatively correlate with the risk score. This study revealed that ALOX5AP is an indicator for predicting high CD8 lymphocyte infiltration and "hot" tumor microenvironment in osteosarcomas. Thus, ALOX5AP has the potential to act as a biomarker for effective immunotherapies in osteosarcoma patients.

Relationship between Arachidonate 5-Lipoxygenase-Activating Protein Gene and Peripheral Arterial Disease in Elderly Patients Undergoing General Surgery: A Retrospective Observational Study.

Patients with peripheral arterial disease (PAD) are at a higher risk of developing postoperative complications. Arachidonate 5-lipoxygenase-activating protein (ALOX5AP) plays an important role in atherosclerosis pathogenesis. In this study, the relationship between PAD and several single nucleotide polymorphisms (SNPs) of ALOX5AP (rs17216473, rs10507391, rs4769874, rs9551963, rs17222814, and rs7222842) was investigated in elderly patients undergoing general surgery. The medical records of 129 patients aged > 55 years who underwent elective general surgery between May 2018 and August 2019 were retrospectively reviewed. The A/A in rs17216473, A/A in rs10507391, G/G in rs4769874, and A/A in rs9551963 were calculated as 0 points and the rest as 1 point to define the genetic risk score. The prevalence of PAD tended to increase with higher genetic risk scores (patients had less ALOX5AP gene polymorphism of A/A in rs17216473, A/A in rs10507391, G/G in rs4769874, or A/A in rs9551963) (p = 0.005). Multivariate logistic regression analysis revealed that the genetic risk score (p = 0.009) and age (p = 0.007) were positively correlated with the prevalence of PAD. Genetic polymorphisms of ALOX5AP and age were associated with the prevalence of PAD in this study.

Identification of 2,4-Dinitro-Biphenyl-Based Compounds as MAPEG Inhibitors.

We identified 2,4-dinitro-biphenyl-based compounds as new inhibitors of leukotriene C4 synthase (LTC4 S) and 5-lipoxygenase-activating protein (FLAP), both members of the "Membrane Associated Proteins in Eicosanoid and Glutathione metabolism" (MAPEG) family involved in the biosynthesis of pro-inflammatory eicosanoids. By molecular docking we evaluated the putative binding against the targets of interest, and by applying cell-free and cell-based assays we assessed the inhibition of LTC4 S and FLAP by the small molecules at low micromolar concentrations. The present results integrate the previously observed inhibitory profile of the tested compounds against another MAPEG member, i. e., microsomal prostaglandin E2 synthase (mPGES)-1, suggesting that the 2,4-dinitro-biphenyl scaffold is a suitable molecular platform for a multitargeting approach to modulate pro-inflammatory mediators in inflammation and cancer treatment.

Microglia depletion diminishes key elements of the leukotriene pathway in the brain of Alzheimer's Disease mice.

Leukotrienes (LTs) contribute to the neuropathology of chronic neurodegenerative disorders including Alzheimer's Disease (AD), where they mediate neuroinflammation and neuronal cell-death. In consequence, blocking the action of Leukotrienes (LTs) ameliorates pathologies and improves cognitive function in animal models of neurodegeneration. Surprisingly, the source of Leukotrienes (LTs) in the brain is largely unknown. Here, we identified the Leukotriene (LT) synthesis rate-limiting enzyme 5-Lipoxygenase (5-Lox) primarily in neurons and to a lesser extent in a subpopulation of microglia in human Alzheimer´s Disease (AD) hippocampus brain sections and in brains of APP Swedish PS1 dE9 (APP-PS1) mice, a transgenic model for Alzheimer´s Disease (AD) pathology. The 5-Lipoxygenase (5-Lox) activating protein (FLAP), which anchors 5-Lipoxygenase (5-Lox) to the membrane and mediates the contact to the substrate arachidonic acid, was confined exclusively to microglia with the entire microglia population expressing 5-Lipoxygenase activating protein (FLAP). To define the contribution of microglia in the Leukotriene (LT) biosynthesis pathway, we ablated microglia using the colony stimulating factor 1 receptor (CSF1R) inhibitor PLX5622 in wildtype (WT) and APP-PS1 mice. Microglia ablation not only diminished the expression of FLAP and of the Leukotriene (LT) receptor Cysteinylleukotriene receptor 1 (CysLTR1), as expected based on their microglia cell type-specific expression, but also drastically reduced 5-Lipoxygenase (5-Lox) mRNA expression in the brain and its protein expression in neurons, in particular in wildtype (WT) mice. In conclusion i) microglia are key in Leukotriene (LT) biosynthesis, and ii) they regulate neuronal 5-Lipoxygenase (5-Lox) expression implying a yet unknown signaling mechanism between neurons and microglia.

The ALOXA5AP gene (rs38022789) is associated with diabetic nephropathy in Slovenian patients with type 2 diabetes mellitus.

BACKGROUND: Although the pathogenesis of diabetic nephropathy (DN) is multifactorial, and the precise mechanisms are unclear, there is a growing body of evidence suggesting that inflammatory processes and immune cells might be involved in the development and progression of DN. Leukotrienes (LTs) are a family of lipid mediators, which act as pro-inflammatory mediators. The study was designed to investigate the association between the polymorphism of the ALOX5 gene (rs12762303) and the ALOX5AP gene (rs3802278), and DN in patients with T2DM. METHODOLOGY: 651 subjects with diabetes mellitus type 2 (T2DM) were classified into two groups according to the presence of DN, and tested for ALOX5 and ALOX5AP gene polymorphisms using the KASPar genotyping chemistry with validated assay. Biochemical analyses were performed using standard biochemical methods. RESULTS: Logistic regression analysis demonstrated that the carriers of the CC genotype had a 3.14 higher risk for DN compared to TT genotype. Serum cystatin C was found to be statistically significantly higher in cases with DN in comparison with subjects without DN (p < 0.001). CONCLUSION: An association between the rs3803278 of the ALOX5AP gene and DN was found in Slovenian patients with T2DM. The rs3803278 CC allele appears to confer increased risk of DN possibly by increasing the production of LTs-potent drivers of inflammation.

[Relationship between Polymorphism in ALOX5, ALOX5AP and Susceptibility to Myeloid Leukemia].

OBJECTIVE: To investigate the correlation of single nucleotide polymorphisms (SNP) in arachidonate 5-lipoxygenase gene (ALOX5) rs2029253, rs2228064 and rs2228065 sites, 5-lipoxygenase activating protein gene (ALOX5AP) rs10507391, rs4769874 sites with the risk for genesis of adult myeloid leukemia. METHODS: By the approval from the hospital ethics committee and the informed consent of participants. 150 patients with myeloid leukemia (ML) as ML group and 134 healthy people as the control group were selected. The genomic DNA was extracted from the samples. Polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) combined with directly sequencing, PCR-amplified products were applied to test the polymorphism of 5 sites in ALOX5 and ALOX5AP gene. RESULTS: A allele frequencies of ALOX5 gene rs2029253 site in the ML group and the control group were 43.0% and 34.3%, respectively. And the G allele frequencies in the ML group and the control group were 57.0% and 65.7%, respectively. The genotype distributions of AA, AG and GG in ALOX5 gene rs2029253 site in the ML group were 32.2%, 21.5% and 46.3% respectively. That in the control group were 15.7%, 37.3% and 47.0% respectively. The genotype AA and A allele frequency of ALOX5 gene rs2029253 site were linked with the increased risk of myeloid leukemia (OR=2.26, 95% CI: 1.43-4.56, P＜0.05; OR=1.44, 95% CI: 1.02-2.03, P＜0.05). And the genotype AG and allele G reduced the susceptibility to myeloid leukemia (OR=0.46, 95% CI: 0.27-0.78, P＜0.01; OR=0.69, 95% CI: 0.50-0.98, P＜0.05), however, the polymorphisms of ALOX5 gene rs2228064 and rs2228065 site not correlated with the risk of myeloid leukemia (P＞0.05). The A allele frequency of ALOX5AP gene rs10507391 site in the ML group and the control group were 30.7% and 36.2% respectirely. The genotype distribution rates of AA, AT and TT in ALOX5AP gene rs10507391 site in the ML group was 1.3%, 58.7% and 40.0% respectively, that in the control group were 9.7%, 53.0% and 37.3% respectively. The genotype AA of ALOX5AP gene rs10507391 site correlated with the decreased risk of myeloid leukemia (OR=0.13, 95% CI: 0.03-0.57, P＜0.05), but the polymorphism of ALOX5AP gene rs4769874 site not correlated with the risk of myeloid leukemia (P＞0.05). CONCLUSION: The genotype AA, AG and allele A, G of ALOX5 rs2029253, as well as ALOX5AP rs10507391 may be correlate with the susceptibility to myeloid leukemia.

Key genes with prognostic values in suppression of osteosarcoma metastasis using comprehensive analysis.

BACKGROUND: Osteosarcoma is a primary malignant tumor originating from mesenchymal tissue, with a poor distant metastasis prognosis. The molecular mechanisms of osteosarcoma metastasis are extremely complicated. METHODS: A public data series (GSE21257) was used to identify differentially expressed genes (DEGs) in osteosarcoma patients that did, or did not, develop metastases. Functional enrichment analysis, a protein-protein interaction network, and survival analysis of DEGs were performed. DEGs with a prognostic value were considered as candidate genes and their functional predictions, different expression in normal and malignant tissues, and immune infiltration were analyzed. RESULTS: The DEGs were mainly enriched in the immune response. Three candidate genes (ALOX5AP, CD74, and FCGR2A) were found, all of which were expressed at higher levels in lungs and lymph nodes than in matched cancer tissues and were probably expressed in the microenvironment. CONCLUSIONS: Candidate genes can help us understand the molecular mechanisms underlying osteosarcoma metastasis and provide targets for future research.

Distribution pattern and molecular signature of cholinergic tuft cells in human gastro-intestinal and pancreatic-biliary tract.

Despite considerable recent insight into the molecular phenotypes and type 2 innate immune functions of tuft cells in rodents, there is sparse knowledge about the region-specific presence and molecular phenotypes of tuft cells in the human digestive tract. Here, we traced cholinergic tuft cells throughout the human alimentary tract with immunohistochemistry and deciphered their region-specific distribution and biomolecule coexistence patterns. While absent from the human stomach, cholinergic tuft cells localized to villi and crypts in the small and large intestines. In the biliary tract, they were present in the epithelium of extra-hepatic peribiliary glands, but not observed in the epithelia of the gall bladder and the common duct of the biliary tract. In the pancreas, solitary cholinergic tuft cells were frequently observed in the epithelia of small and medium-size intra- and inter-lobular ducts, while they were absent from acinar cells and from the main pancreatic duct. Double immunofluorescence revealed co-expression of choline acetyltransferase with structural (cytokeratin 18, villin, advillin) tuft cell markers and eicosanoid signaling (cyclooxygenase 1, hematopoietic prostaglandin D synthase, 5-lipoxygenase activating protein) biomolecules. Our results indicate that region-specific cholinergic signaling of tuft cells plays a role in mucosal immunity in health and disease, especially in infection and cancer.

Roles of cysteinyl leukotrienes and their receptors in immune cell-related functions.

The cysteinyl leukotrienes (cys-LTs), leukotriene C4, (LTC4), LTD4, and LTE4, are lipid mediators of inflammation. LTC4 is the only intracellularly synthesized cys-LT through the 5-lipoxygenase and LTC4 synthase pathway and after transport is metabolized to LTD4 and LTE4 by specific extracellular peptidases. Each cys-LT has a preferred functional receptor in vivo; LTD4 to the type 1 cys-LT receptor (CysLT1R), LTC4 to CysLT2R, and LTE4 to CysLT3R (OXGR1 or GPR99). Recent studies in mouse models revealed that there are multiple regulatory mechanisms for these receptor functions and each receptor plays a distinct role as observed in different mouse models of inflammation and immune responses. This review focuses on the integrated host responses to the cys-LT/CysLTR pathway composed of sequential ligands with preferred receptors as seen from mouse models. It also discusses potential therapeutic targets for LTC4 synthase, CysLT2R, and CysLT3R.

Integrative analysis identifies DNMTs against immune-infiltrating neutrophils and dendritic cells in colorectal cancer.

Molecular characterizations, including microsatellite instability (MSI) and the CpG island methylator phenotype (CIMP) showed strong associations in colorectal carcinoma (CRC) and provided a deeper understanding of the etiology of disease. However, the global relationship between epigenetic alternations and changes in mRNA expression in CRC remains largely undefined, especially regarding the roles of DNA methyltransferases (DNMTs). Here, we conducted a systematic network comparison to explore the global conservation between co-expressed and co-methylated modules. We successfully identified immune-related modules that were regulated by DNMTs and had strong associations with immune-infiltrating neutrophils and dendritic cells in CRC. Moreover, we found that genes in those modules were prognostic for CRC, with 97.1% (168/173) being significantly influenced by DNMTs. Thus, this study resolved an interaction between DNA methylation and mRNA expression through DNMTs. Additionally, we provided evidence that DNMTs control the global hypomethylation of oncogenes, including ALOX5AP and CSF3R that otherwise have high methylation in normal colons. Such genes were also more sensitive to DNMT changes, such as in CRC. Collectively, our analyzes provided a systems biology approach to investigate the association among different molecular phenotypes in diseases.

The organization of leukotriene biosynthesis on the nuclear envelope revealed by single molecule localization microscopy and computational analyses.

The initial steps in the synthesis of leukotrienes are the translocation of 5-lipoxygenase (5-LO) to the nuclear envelope and its subsequent association with its scaffold protein 5-lipoxygenase-activating protein (FLAP). A major gap in our understanding of this process is the knowledge of how the organization of 5-LO and FLAP on the nuclear envelope regulates leukotriene synthesis. We combined single molecule localization microscopy with Clus-DoC cluster analysis, and also a novel unbiased cluster analysis to analyze changes in the relationships between 5-LO and FLAP in response to activation of RBL-2H3 cells to generate leukotriene C4. We identified the time-dependent reorganization of both 5-LO and FLAP into higher-order assemblies or clusters in response to cell activation via the IgE receptor. Clus-DoC analysis identified a subset of these clusters with a high degree of interaction between 5-LO and FLAP that specifically correlates with the time course of LTC4 synthesis, strongly suggesting their role in the initiation of leukotriene biosynthesis.

Genetic variation in the leukotriene pathway is associated with myocardial infarction in the Chinese population.

BACKGROUND: Genetic variation in the genes ALOX5 (arachidonate 5-lipoxygenase), ALOX5AP (arachidonate 5-lipoxygenase-activating protein) and LTA4H (leukotriene A4 hydrolase) has previously been shown to contribute to the risk of MI (myocardial infarction) in Caucasian and African American populations. All genes encode proteins playing a role in the synthesis of the pro-inflammatory leukotriene B mediators, possibly providing a link between MI and inflammation. The aim of the present study was to investigate whether these associations could be confirmed in the study of China MI patients. The study included 401 Han Chinese MI patients and 409 controls. Six tag single nucleotide polymorphisms (SNPs)-ALOX5 rs12762303 and rs12264801, ALOX5AP rs10507391, LTA4H rs2072512, rs2540487 and rs2540477-were selected. SNP genotyping was performed by an improved multiplex ligation detection reaction assay. RESULTS: The rs2540487 genotype was associated with the risk of MI in overdominant model (P = 0.008). rs12762303 and rs10507391 SNPs were significantly associated with lipid levels in MI patients (P < 0.006-0.008). Several SNPs interacted with alcohol consumption, cigarette smoking, and hypertension to modify TC, TG, LDL-C and CRE levels, and the risk of MI (P < 0.0017 for all). No association between the SNPs of LT pathway and susceptibility to MI was found (P > 0.05 for all). CONCLUSIONS: Taken together, this study provides additional evidence that functional genetic variation of the LT pathway can mediate atherogenic processes and the risk of MI in Chinese.

Leukotriene biosynthetic enzymes as therapeutic targets.

Leukotrienes are powerful immune-regulating lipid mediators with established pathogenic roles in inflammatory allergic diseases of the respiratory tract - in particular, asthma and hay fever. More recent work indicates that these lipids also contribute to low-grade inflammation, a hallmark of cardiovascular, neurodegenerative, and metabolic diseases as well as cancer. Biosynthesis of leukotrienes involves oxidative metabolism of arachidonic acid and proceeds via a set of soluble and membrane enzymes that are primarily expressed by cells of myeloid origin. In activated immune cells, these enzymes assemble at the endoplasmic and perinuclear membrane, constituting a biosynthetic complex. This Review describes recent advances in our understanding of the components of the leukotriene-synthesizing enzyme machinery, emerging opportunities for pharmacological intervention, and the development of new medicines exploiting both antiinflammatory and pro-resolving mechanisms.

Cysteinyl-leukotriene pathway as a new therapeutic target for the treatment of atherosclerosis related to obstructive sleep apnea syndrome.

AIMS: Obstructive sleep apnea (OSA) characterized by nocturnal intermittent hypoxia (IH) is associated with atherosclerosis and cysteinyl-leukotrienes (CysLT) pathway activation. We aimed to identify the determinants of CysLT pathway activation and the role of CysLT in OSA-related atherosclerosis. METHODS AND RESULTS: Determinants of the urinary excretion of LTE4 (U-LTE4) including history of cardiovascular events, polysomnographic and biological parameters were studied in a cohort of 170 OSA patients and 29 controls, and in a subgroup of OSA patients free of cardiovascular event (n = 136). Mechanisms linking IH, the CysLT pathway and atherogenesis were investigated in Apolipoprotein E deficient (ApoE-/-) mice exposed to 8-week IH. In the whole cohort, U-LTE4 was independently influenced by age, minimal oxygen saturation, and a history of cardiovascular events, and correlated significantly with intima-media thickness. In the subgroup of OSA patients free of cardiovascular event, increased U-LTE4 was increased compared to controls and independently related to hypoxia severity and traditional risk factors aggregated in the 10-year cardiovascular risk score of European Society of Cardiology. In IH mice, atherosclerosis lesion size and mRNA levels of 5-lipoxygenase, 5-lipoxygenase activating protein (FLAP) and CysLT1 receptor were significantly increased. This transcriptional activation was associated with the binding of HIF-1 to the FLAP promoter and was strongly associated with atherosclerosis lesion size. CysLT1 receptor antagonism (montelukast) significantly reduced atherosclerosis progression in IH mice. CONCLUSIONS: IH-related CysLT pathway activation contributes to OSA-induced atherogenesis. In the era of personalized medicine, U-LTE4 may be a useful biomarker to identify OSA patients for whom CysLT1 blockade could represent a new therapeutic avenue for reducing cardiovascular risk.

Defining murine organogenesis at single-cell resolution reveals a role for the leukotriene pathway in regulating blood progenitor formation.

During gastrulation, cell types from all three germ layers are specified and the basic body plan is established 1 . However, molecular analysis of this key developmental stage has been hampered by limited cell numbers and a paucity of markers. Single-cell RNA sequencing circumvents these problems, but has so far been limited to specific organ systems 2 . Here, we report single-cell transcriptomic characterization of >20,000 cells immediately following gastrulation at E8.25 of mouse development. We identify 20 major cell types, which frequently contain substructure, including three distinct signatures in early foregut cells. Pseudo-space ordering of somitic progenitor cells identifies dynamic waves of transcription and candidate regulators, which are validated by molecular characterization of spatially resolved regions of the embryo. Within the endothelial population, cells that transition from haemogenic endothelial to erythro-myeloid progenitors specifically express Alox5 and its co-factor Alox5ap, which control leukotriene production. Functional assays using mouse embryonic stem cells demonstrate that leukotrienes promote haematopoietic progenitor cell generation. Thus, this comprehensive single-cell map can be exploited to reveal previously unrecognized pathways that contribute to tissue development.

Drug discovery approaches targeting 5-lipoxygenase-activating protein (FLAP) for inhibition of cellular leukotriene biosynthesis.

Leukotrienes are proinflammatory lipid mediators associated with diverse chronic inflammatory diseases such as asthma, COPD, IBD, arthritis, atherosclerosis, dermatitis and cancer. Cellular leukotrienes are produced from arachidonic acid via the 5-lipoxygenase pathway in which the 5-lipoxygenase activating protein, also named as FLAP, plays a critical role by operating as a regulatory protein for efficient transfer of arachidonic acid to 5-lipoxygenase. By blocking leukotriene production, FLAP inhibitors may behave as broad-spectrum leukotriene modulators, which might be of therapeutic use for chronic inflammatory diseases requiring anti-leukotriene therapy. The early development of FLAP inhibitors (i.e. MK-886, MK-591, BAY-X-1005) mostly concentrated on asthma cure, and resulted in promising readouts in preclinical and clinical studies with asthma patients. Following the recent elucidation of the 3D-structure of FLAP, development of new inhibitor chemotypes is highly accelerated, eventually leading to the evolution of many un-drug-like structures into more drug-like entities such as AZD6642 and BI665915 as development candidates. The most clinically advanced FLAP inhibitor to date is GSK2190918 (formerly AM803) that has successfully completed phase II clinical trials in asthmatics. Concluding, although there are no FLAP inhibitors reached to the drug approval phase yet, due to the rising number of indications for anti-LT therapy such as atherosclerosis, FLAP inhibitor development remains a significant research field. FLAP inhibitors reviewed herein are classified into four sub-classes as the first-generation FLAP inhibitors (indole and quinoline derivatives), the second-generation FLAP inhibitors (diaryl-alkanes and biaryl amino-heteroarenes), the benzimidazole-containing FLAP inhibitors and other FLAP inhibitors with polypharmacology for easiness of the reader. Hence, we meticulously summarize how FLAP inhibitors historically developed from scratch to their current advanced state, and leave the reader with a positive view that a FLAP inhibitor might soon reach to the need of patients who may require anti-LT therapy.

Pharmacological profile and efficiency in vivo of diflapolin, the first dual inhibitor of 5-lipoxygenase-activating protein and soluble epoxide hydrolase.

Arachidonic acid (AA) is metabolized to diverse bioactive lipid mediators. Whereas the 5-lipoxygenase-activating protein (FLAP) facilitates AA conversion by 5-lipoxygenase (5-LOX) to pro-inflammatory leukotrienes (LTs), the soluble epoxide hydrolase (sEH) degrades anti-inflammatory epoxyeicosatrienoic acids (EETs). Accordingly, dual FLAP/sEH inhibition might be advantageous drugs for intervention of inflammation. We present the in vivo pharmacological profile and efficiency of N-[4-(benzothiazol-2-ylmethoxy)-2-methylphenyl]-N'-(3,4-dichlorophenyl)urea (diflapolin) that dually targets FLAP and sEH. Diflapolin inhibited 5-LOX product formation in intact human monocytes and neutrophils with IC50 = 30 and 170 nM, respectively, and suppressed the activity of isolated sEH (IC50 = 20 nM). Characteristic for FLAP inhibitors, diflapolin (I) failed to inhibit isolated 5-LOX, (II) blocked 5-LOX product formation in HEK cells only when 5-LOX/FLAP was co-expressed, (III) lost potency in intact cells when exogenous AA was supplied, and (IV) prevented 5-LOX/FLAP complex assembly in leukocytes. Diflapolin showed target specificity, as other enzymes related to AA metabolism (i.e., COX1/2, 12/15-LOX, LTA4H, LTC4S, mPGES1, and cPLA2) were not inhibited. In the zymosan-induced mouse peritonitis model, diflapolin impaired vascular permeability, inhibited cysteinyl-LTs and LTB4 formation, and suppressed neutrophil infiltration. Diflapolin is a highly active dual FLAP/sEH inhibitor in vitro and in vivo with target specificity to treat inflammation-related diseases.