Seeing the future of bioactive lipid drug targets

Mast Cell–Tumor Interactions: Molecular Mechanisms of Recruitment, Intratumoral Communication and Potential Therapeutic Targets for Tumor Growth

Mast cells (MCs) are tissue-resident immune cells that are important players in diseases associated with chronic inflammation such as cancer. Since MCs can infiltrate solid tumors and promote or limit tumor growth, a possible polarization of MCs to pro-tumoral or anti-tumoral phenotypes has been proposed and remains as a challenging research field. Here, we review the recent evidence regarding the complex relationship between MCs and tumor cells. In particular, we consider: (1) the multifaceted role of MCs on tumor growth suggested by histological analysis of tumor biopsies and studies performed in MC-deficient animal models; (2) the signaling pathways triggered by tumor-derived chemotactic mediators and bioactive lipids that promote MC migration and modulate their function inside tumors; (3) the possible phenotypic changes on MCs triggered by prevalent conditions in the tumor microenvironment (TME) such as hypoxia; (4) the signaling pathways that specifically lead to the production of angiogenic factors, mainly VEGF; and (5) the possible role of MCs on tumor fibrosis and metastasis. Finally, we discuss the novel literature on the molecular mechanisms potentially related to phenotypic changes that MCs undergo into the TME and some therapeutic strategies targeting MC activation to limit tumor growth.

CrossTORC and WNTegration in Disease: Focus on Lymphangioleiomyomatosis

The mechanistic target of rapamycin (mTOR) and wingless-related integration site (Wnt) signal transduction networks are evolutionarily conserved mammalian growth and cellular development networks. Most cells express many of the proteins in both pathways, and this review will briefly describe only the key proteins and their intra- and extracellular crosstalk. These complex interactions will be discussed in relation to cancer development, drug resistance, and stem cell exhaustion. This review will also highlight the tumor-suppressive tuberous sclerosis complex (TSC) mutated, mTOR-hyperactive lung disease of women, lymphangioleiomyomatosis (LAM). We will summarize recent advances in the targeting of these pathways by monotherapy or combination therapy, as well as future potential treatments.

Bioactive lipids, inflammation and chronic diseases

Endogenous bioactive lipids are part of a complex network that modulates a plethora of cellular and molecular processes involved in health and disease, of which inflammation represents one of the most prominent examples. Inflammation serves as a well-conserved defence mechanism, triggered in the event of chemical, mechanical or microbial damage, that is meant to eradicate the source of damage and restore tissue function. However, excessive inflammatory signals, or impairment of pro-resolving/anti-inflammatory pathways leads to chronic inflammation, which is a hallmark of chronic pathologies. All main classes of endogenous bioactive lipids - namely eicosanoids, specialized pro-resolving lipid mediators, lysoglycerophopsholipids and endocannabinoids - have been consistently involved in the chronic inflammation that characterises pathologies such as cancer, diabetes, atherosclerosis, asthma, as well as autoimmune and neurodegenerative disorders and inflammatory bowel diseases. This review gathers the current knowledge concerning the involvement of endogenous bioactive lipids in the pathogenic processes of chronic inflammatory pathologies.

New Frontiers in Lipidomics Analyses using Structurally Selective Ion Mobility-Mass Spectrometry

The growth of lipidomics and the high isomeric complexity of the lipidome has revealed a need for analytical techniques capable of structurally characterizing lipids with a high degree of specificity. Lipids are morphologically diverse molecules that can exist as any one of a large number of isomeric species, and as such are often indistinguishable by mass spectrometry without a complementary separation method. Recent developments in the field of lipidomics aim to address these challenges by utilizing a combination of multiple analytical techniques which are selective to lipid primary structure. This review summarizes two emerging strategies for lipidomic analysis, namely, ion mobility-mass spectrometry and ion fragmentation via ozonolysis.

Atheroprotective Effects and Molecular Targets of Tanshinones Derived From Herbal Medicine Danshen

Medicinal plant-derived bioactive compounds modulate multiple therapeutic targets in cardiovascular diseases (CVDs), rendering herb-derived phytochemicals effective against one of the major CVDs-atherosclerosis. Danshen (Salvia milthiorriza Bunge) is a Chinese medicine that has been used in cardio- and cerebro-vascular therapeutic remedies in Asian countries for many years. Emerging evidence from cellular, animal, and clinical studies suggests that major lipophilic tanshinones from Danshen can treat atherosclerotic CVDs. In this review, we highlight recent advances in understanding the molecular mechanisms of tanshinones in treating atherosclerosis, ranging from endothelial dysfunction to chronic inflammation. We also overview new molecular targets of tanshinones, including endothelial nitric oxide synthase, AMP-activated protein kinase, ABC transporter A1, heme oxygenase 1, soluble epoxide hydrolase, 11β-hydroxysteroid dehydrogenase, estrogen receptor, and proprotein convertase subtilisin/kexin type 9. Thus, this review provides a new perspective for advancing our understanding of the "ancient" herb Danshen from "modern" biomedical perspectives, supporting the possibility of exploiting tanshinones and derivatives as effective therapeutics against atherosclerosis-related cardiovascular and metabolic diseases.

A Global Map of Lipid-Binding Proteins and Their Ligandability in Cells

Lipids play central roles in physiology and disease, where their structural, metabolic, and signaling functions often arise from interactions with proteins. Here, we describe a set of lipid-based chemical proteomic probes and their global interaction map in mammalian cells. These interactions involve hundreds of proteins from diverse functional classes and frequently occur at sites of drug action. We determine the target profiles for several drugs across the lipid-interaction proteome, revealing that its ligandable content extends far beyond traditionally defined categories of druggable proteins. In further support of this finding, we describe a selective ligand for the lipid-binding protein nucleobindin-1 (NUCB1) and show that this compound perturbs the hydrolytic and oxidative metabolism of endocannabinoids in cells. The described chemical proteomic platform thus provides an integrated path to both discover and pharmacologically characterize a wide range of proteins that participate in lipid pathways in cells.

Mechanosensitive PPAP2B Regulates Endothelial Responses to Atherorelevant Hemodynamic Forces

RATIONALE

PhosPhatidic Acid Phosphatase type 2B (PPAP2B), an integral membrane protein known as lipid phosphate phosphatase (LPP3) that inactivates lysophosphatidic acid, was implicated in coronary artery disease (CAD) by genome-wide association studies. However, it is unclear whether genome-wide association studies-identified coronary artery disease genes, including PPAP2B, participate in mechanotransduction mechanisms by which vascular endothelia respond to local atherorelevant hemodynamics that contribute to the regional nature of atherosclerosis.

OBJECTIVE

To establish the critical role of PPAP2B in endothelial responses to hemodynamics.

METHODS AND RESULTS

Reduced PPAP2B was detected in vivo in mouse and swine aortic arch (AA) endothelia exposed to chronic disturbed flow, and in mouse carotid artery endothelia subjected to surgically induced acute disturbed flow. In humans, PPAP2B was reduced in the downstream part of carotid plaques where low shear stress prevails. In culture, reduced PPAP2B was measured in human aortic endothelial cells under atherosusceptible waveform mimicking flow in human carotid sinus. Flow-sensitive microRNA-92a and transcription factor KLF2 were identified as upstream inhibitor and activator of endothelial PPAP2B, respectively. PPAP2B suppression abrogated atheroprotection of unidirectional flow; inhibition of lysophosphatidic acid receptor 1 restored the flow-dependent, anti-inflammatory phenotype in PPAP2B-deficient cells. PPAP2B inhibition resulted in myosin light-chain phosphorylation and intercellular gaps, which were abolished by lysophosphatidic acid receptor 1/2 inhibition. Expression quantitative trait locus mapping demonstrated PPAP2B coronary artery disease risk allele is not linked to PPAP2B expression in various human tissues but significantly associated with reduced PPAP2B in human aortic endothelial cells.

CONCLUSIONS

Atherorelevant flows dynamically modulate endothelial PPAP2B expression through miR-92a and KLF2. Mechanosensitive PPAP2B plays a critical role in promoting anti-inflammatory phenotype and maintaining vascular integrity of endothelial monolayer under atheroprotective flow.

A lipidomic screen of hyperglycemia-treated HRECs links 12/15-Lipoxygenase to microvascular dysfunction during diabetic retinopathy via NADPH oxidase

Retinal hyperpermeability and subsequent macular edema is a cardinal feature of early diabetic retinopathy (DR). Here, we investigated the role of bioactive lipid metabolites, in particular 12/15-lipoxygenase (LOX)-derived metabolites, in this process. LC/MS lipidomic screen of human retinal endothelial cells (HRECs) demonstrated that 15-HETE was the only significantly increased metabolite (2.4 ± 0.4-fold, P = 0.0004) by high glucose (30 mM) treatment. In the presence of arachidonic acid, additional eicosanoids generated by 12/15-LOX, including 12- and 11-HETEs, were significantly increased. Fluorescein angiography and retinal albumin leakage showed a significant decrease in retinal hyperpermeability in streptozotocin-induced diabetic mice lacking 12/15-LOX compared with diabetic WT mice. Our previous studies demonstrated the potential role of NADPH oxidase in mediating the permeability effect of 12- and 15-HETEs, therefore we tested the impact of intraocular injection of 12-HETE in mice lacking the catalytic subunit of NADPH oxidase (NOX2). The permeability effect of 12-HETE was significantly reduced in NOX2(-/-) mice compared with the WT mice. In vitro experiments also showed that 15-HETE induced HREC migration and tube formation in a NOX-dependent manner. Taken together our data suggest that 12/15-LOX is implicated in DR via a NOX-dependent mechanism.

Probing the Binding Site of Bile Acids in TGR5

TGR5 is a G-protein-coupled receptor (GPCR) mediating cellular responses to bile acids (BAs). Although some efforts have been devoted to generate homology models of TGR5 and draw structure-activity relationships of BAs, none of these studies has hitherto described how BAs bind to TGR5. Here, we present an integrated computational, chemical, and biological approach that has been instrumental to determine the binding mode of BAs to TGR5. As a result, key residues have been identified that are involved in mediating the binding of BAs to the receptor. Collectively, these results provide new hints to design potent and selective TGR5 agonists.