Leukotriene B4 promotes neovascularization and macrophage recruitment in murine wet-type AMD models

Targeting Ligand Independent Tropism of siRNA-LNP by Small Molecules for Directed Therapy of Liver or Myeloid Immune Cells

Hepatic clearance of lipid nanoparticles (LNP) with encapsulated nucleic acids restricts their therapeutic applicability. Therefore, tools for regulating hepatic clearance are of high interest for nucleic acid delivery. To this end, this work employs wild-type (WT) and low-density lipoprotein receptor (Ldlr)-/- mice pretreated with either a leukotriene B4 receptor inhibitor (BLT1i) or a high-density lipoprotein receptor inhibitor (HDLRi) prior to the injection of siRNA-LNP. This work is able to demonstrate significantly increased hepatic uptake of siRNA-LNP by the BLT1i in Ldlr-/- mice by in vivo imaging and discover an induction of specific uptake-related proteins. Irrespective of the inhibitors and Ldlr deficiency, the siRNA-LNP induced RNA-binding and transport-related proteins in liver, including haptoglobin (HP) that is also identified as most upregulated serum protein. This work observes a downregulation of proteins functioning in hepatic detoxification and of serum opsonins. Most strikingly, the HDLRi reduces hepatic uptake and increases siRNA accumulation in spleen and myeloid immune cells of blood and liver. RNA sequencing demonstrates leukocyte recruitment by the siRNA-LNP and the HDLRi through induction of chemokine ligands in liver tissue. The data provide insights into key mechanisms of siRNA-LNP biodistribution and indicate that the HDLRi has potential for extrahepatic and leukocyte targeting.

The Early Pathogenesis of Diabetic Retinopathy and Its Attenuation by Sodium-Glucose Transporter 2 Inhibitors

The early pathogenetic mechanism of diabetic retinopathy (DR) and its treatment remain unclear. Therefore, we used streptozotocin-induced diabetic mice to investigate the early pathogenic alterations in DR and the protective effect of sodium-glucose cotransporter 2 (SGLT2) inhibitors against these alterations. Retinal vascular leakage was assessed by dextran fluorescence angiography. Retinal thickness and vascular leakage were increased 2 and 4 weeks after onset of diabetes, respectively. Immunostaining showed that morphological change of microglia (amoeboid form) was observed at 2 weeks. Subsequently, increased angiopoietin-2 expression, simultaneous loss of pericytes and endothelial cells, decreased vessel density, retinal hypoxia, and increased vascular endothelial growth factor (VEGF)-A/VEGF receptor system occurred at 4 weeks. SGLT2 inhibitors (luseogliflozin and ipragliflozin) had a significant protective effect on retinal vascular leakage and retinal thickness at a low dose that did not show glucose-lowering effects. Furthermore, both inhibitors at this dose attenuated microglia morphological changes and these early pathogenic alterations in DR. In vitro study showed both inhibitors attenuated the lipopolysaccharide-induced activation of primary microglia, along with morphological changes toward an inactive form, suggesting the direct inhibitory effect of SGLT2 inhibitors on microglia. In summary, SGLT2 inhibitors may directly prevent early pathogenic mechanisms, thereby potentially playing a role in preventing DR.

ARTICLE HIGHLIGHTS

Role of macrophage in ocular neovascularization

Ocular neovascularization is the leading cause of blindness in clinical settings. Pathological angiogenesis of the eye can be divided into corneal neovascularization (CoNV), retinal neovascularization (RNV, including diabetic retinopathy and retinopathy of prematurity), and choroidal neovascularization (CNV) based on the anatomical location of abnormal neovascularization. Although anti-Vascular endothelial growth factor (VEGF) agents have wide-ranging clinical applications and are an effective treatment for neovascular eye disease, many deficiencies in this treatment strategy remain. Recently, emerging evidence has demonstrated that macrophages are vital during the process of physiological and pathological angiogenesis. Monocyte-macrophage lineage is diverse and plastic, they can shift between different activation modes and have different functions. Due to the obvious regulatory effect of macrophages on inflammation and angiogenesis, macrophages have been increasingly studied in the field of ophthalmology. Here, we detail how macrophage activated and the role of different subtypes of macrophages in the pathogenesis of ocular neovascularization. The complexity of macrophages has recently taken center stage owing to their subset diversity and tightly regulated molecular and metabolic phenotypes. In this review, we reveal the functional and phenotypic characterization of macrophage subsets associated with ocular neovascularization, more in-depth research is needed to explore the specific mechanisms by which macrophages regulate angiogenesis as well as macrophage polarization. Targeted regulation of macrophage differentiation based on their phenotype and function could be an effective approach to treat and manage ocular neovascularization in the future.

ERp29 Attenuates Nicotine-Induced Endoplasmic Reticulum Stress and Inhibits Choroidal Neovascularization

Nicotine-induced endoplasmic reticulum (ER) stress in retinal pigment epithelium (RPE) cells is thought to be one pathological mechanism underlying age-related macular degeneration (AMD). ERp29 attenuates tobacco extract-induced ER stress and mitigates tight junction damage in RPE cells. Herein, we aimed to further investigate the role of ERp29 in nicotine-induced ER stress and choroidal neovascularization (CNV). We found that the expression of ERp29 and GRP78 in ARPE-19 cells was increased in response to nicotine exposure. Overexpression of ERp29 decreased the levels of GRP78 and the C/EBP homologous protein (CHOP). Knockdown of ERp29 increased the levels of GRP78 and CHOP while reducing the viability of ARPE-19 cells under nicotine exposure conditions. In the ARPE-19 cell/macrophage coculture system, overexpression of ERp29 decreased the levels of M2 markers and increased the levels of M1 markers. The viability, migration and tube formation of human umbilical vein endothelial cells (HUVECs) were inhibited by conditioned medium from the ERp29-overexpressing group. Moreover, overexpression of ERp29 inhibits the activity and growth of CNV in mice exposed to nicotine in vivo. Taken together, our results revealed that ERp29 attenuated nicotine-induced ER stress, regulated macrophage polarization and inhibited CNV.

Macrophage/microglia polarization for the treatment of diabetic retinopathy

Macrophages/microglia are immune system defense and homeostatic cells that develop from bone marrow progenitor cells. According to the different phenotypes and immune responses of macrophages (Th1 and Th2), the two primary categories of polarized macrophages/microglia are those conventionally activated (M1) and alternatively activated (M2). Macrophage/microglial polarization is a key regulating factor in the development of inflammatory disorders, cancers, metabolic disturbances, and neural degeneration. Macrophage/microglial polarization is involved in inflammation, oxidative stress, pathological angiogenesis, and tissue healing processes in ocular diseases, particularly in diabetic retinopathy (DR). The functional phenotypes of macrophages/microglia affect disease progression and prognosis, and thus regulate the polarization or functional phenotype of microglia at different DR stages, which may offer new concepts for individualized therapy of DR. This review summarizes the involvement of macrophage/microglia polarization in physiological situations and in the pathological process of DR, and discusses the promising role of polarization in personalized treatment of DR.

The leukotriene B4 receptors BLT1 and BLT2 as potential therapeutic targets

Leukotriene B4 (LTB4 ) was recognized as an arachidonate-derived chemotactic factor for inflammatory cells and an important drug target even before the molecular identification of its receptors. We cloned the high- and low-affinity LTB4 receptors, BLT1 and BLT2, respectively, and examined their functions by generating and studying gene-targeted mice. BLT1 is involved in the pathogenesis of various inflammatory and immune diseases, including asthma, psoriasis, contact dermatitis, allergic conjunctivitis, age-related macular degeneration, and immune complex-mediated glomerulonephritis. Meanwhile, BLT2 is a high-affinity receptor for 12-hydroxyheptadecatrienoic acid, which is involved in the maintenance of dermal and intestinal barrier function, and the acceleration of skin and corneal wound healing. Thus, BLT1 antagonists and BLT2 agonists are promising candidates in the treatment of inflammatory diseases.

Damage-mediated macrophage polarization in sterile inflammation

Most of the leading causes of death, such as cardiovascular diseases, cancer, dementia, neurodegenerative diseases, and many more, are associated with sterile inflammation, either as a cause or a consequence of these conditions. The ability to control the progression of inflammation toward tissue resolution before it becomes chronic holds significant clinical potential. During sterile inflammation, the initiation of inflammation occurs through damage-associated molecular patterns (DAMPs) in the absence of pathogen-associated molecules. Macrophages, which are primarily localized in the tissue, play a pivotal role in sensing DAMPs. Furthermore, macrophages can also detect and respond to resolution-associated molecular patterns (RAMPs) and specific pro-resolving mediators (SPMs) during sterile inflammation. Macrophages, being highly adaptable cells, are particularly influenced by changes in the microenvironment. In response to the tissue environment, monocytes, pro-inflammatory macrophages, and pro-resolution macrophages can modulate their differentiation state. Ultimately, DAMP and RAMP-primed macrophages, depending on the predominant subpopulation, regulate the balance between inflammatory and resolving processes. While sterile injury and pathogen-induced reactions may have distinct effects on macrophages, most studies have focused on macrophage responses induced by pathogens. In this review, which emphasizes available human data, we illustrate how macrophages sense these mediators by examining the expression of receptors for DAMPs, RAMPs, and SPMs. We also delve into the signaling pathways induced by DAMPs, RAMPs, and SPMs, which primarily contribute to the regulation of macrophage differentiation from a pro-inflammatory to a pro-resolution phenotype. Understanding the regulatory mechanisms behind the transition between macrophage subtypes can offer insights into manipulating the transition from inflammation to resolution in sterile inflammatory diseases.

The leukotriene B4 /BLT1-dependent neutrophil accumulation exacerbates immune complex-mediated glomerulonephritis

Crescent formation is the most important pathological finding that defines the prognosis of nephritis. Although neutrophils are known to play an important role in the progression of crescentic glomerulonephritis, such as anti-neutrophil cytoplasmic antibody (ANCA)-associated glomerulonephritis, the key chemoattractant for neutrophils in ANCA-associated glomerulonephritis has not been identified. Here, we demonstrate that a lipid chemoattractant, leukotriene B₄ (LTB₄ ), and its receptor BLT1 are primarily involved in disease pathogenesis in a mouse model of immune complex-mediated crescentic glomerulonephritis. Circulating neutrophils accumulated into glomeruli within 1 h after disease onset, which was accompanied by LTB₄ accumulation in the kidney cortex, leading to kidney injury. LTB₄ was produced by cross-linking of Fc gamma receptors on neutrophils. Mice deficient in BLT1 or LTB₄ biosynthesis exhibited suppressed initial neutrophil infiltration and subsequent thrombotic glomerulonephritis and renal fibrosis. Depletion of neutrophils before, but not after, disease onset prevented proteinuria and kidney injury, indicating the essential role of neutrophils in the early phase of glomerulonephritis. Administration of a BLT1 antagonist before and after disease onset almost completely suppressed induction of glomerulonephritis. Finally, we found that the glomeruli from patients with ANCA-associated glomerulonephritis contained more BLT1-positive cells than glomeruli from patients with other etiologies. Taken together, the LTB₄ -BLT1 axis is the key driver of neutrophilic glomerular inflammation, and will be a novel therapeutic target for the crescentic glomerulonephritis.

Intestinal epithelial BLT1 promotes mucosal repair

Acute and chronic intestinal inflammation is associated with epithelial damage, resulting in mucosal wounds in the forms of erosions and ulcers in the intestinal tract. Intestinal epithelial cells (IECs) and immune cells in the wound milieu secrete cytokines and lipid mediators to influence repair. Leukotriene B4 (LTB4), a lipid chemokine, binds to its receptor BLT1 and promotes migration of immune cells to sites of active inflammation; however, a role for intestinal epithelial BLT1 during mucosal wound repair is not known. Here we report that BLT1 was expressed in IECs both in vitro and in vivo, where it functioned as a receptor not only for LTB4 but also for another ligand, resolvin E1. Intestinal epithelial BLT1 expression was increased when epithelial cells were exposed to an inflammatory microenvironment. Using human and murine primary colonic epithelial cells, we reveal that the LTB4/BLT1 pathway promoted epithelial migration and proliferation leading to accelerated epithelial wound repair. Furthermore, in vivo intestinal wound repair experiments in BLT1-deficient mice and bone marrow chimeras demonstrated an important contribution of epithelial BLT1 during colonic mucosal wound repair. Taken together, our findings show a potentially novel prorepair in IEC mechanism mediated by BLT1 signaling.

PGE2 promotes macrophage recruitment and neovascularization in murine wet-type AMD models

Age-related macular degeneration (AMD), a progressive chronic disease of the central retina, is a leading cause of blindness worldwide. Activated macrophages recruited to the injured eyes greatly contribute to the pathogenesis of choroidal neovascularization (CNV) in exudative AMD (wet AMD). This study describes the effects of cyclooxygenase-2 (COX2)/prostaglandin E₂ (PGE₂) signalling on the macrophage activation and CNV formation of wet AMD. In a mouse model of laser-induced wet AMD, the mice received an intravitreal injection of celecoxib (a selective COX2 inhibitor). Optical coherence tomography (OCT), fundus fluorescein angiography (FFA), choroidal histology of the CNV lesions, and biochemical markers were assessed. The level of PGE₂ expression was high in the laser-induced CNV lesions. Macrophage recruitment and CNV development were significantly less after celecoxib treatment. E-prostanoid1 receptor (EP₁R)/protein kinase C (PKC) signalling was involved in M2 macrophage activation and interleukin-10 (IL-10) production of bone marrow-derived macrophages (BMDMs) in vitro. In addition, IL-10 was found to induce the proliferation and migration of human choroidal microvascular endothelial cells (HCECs). Thus, the PGE₂/EP₁R signalling network serves as a potential therapeutic target for CNV of the wet-type AMD.

Identification of Potential Key Biomarkers and Immune Infiltration in Oral Lichen Planus

Background

Oral lichen planus (OLP) is a chronic autoimmune oral mucosal disease that seriously affects the life quality of the patients. But till now, the exact etiology and pathogenesis of OLP remain unclear. Our study is aimed at finding the key molecules and pathways involved in the pathogenesis mechanisms of OLP, providing more effective therapeutic strategies for OLP.

Methods

Data from GSE52130 were downloaded from GEO datasets for analysis. Then, we carried out enrichment analysis of the differentially expressed genes (DEGs) using Gene Ontology (GO) and KEGG pathway analyses. Next, the CIBERSORT algorithm was used to assess immune cell infiltration in OLP patients. Furthermore, we also constructed a protein-protein interaction network using STRING and Cytoscape and simultaneously sought potential transcription factors plug-in including MCODE CytoHubba and iRegulon. In addition, ROC analysis was employed to assess the diagnostic performance of these hub genes. Lastly, we identified 6 promising novel drugs to treat OLP through Connectivity Map.

Results

We illustrated that 255 DEGs were mainly enriched in the focal adhesion pathway and metabolism pathways. Besides, Cibersort analysis showed that M1 macrophages, T follicular helper cells, and T regulatory cells are more infiltrated in OLP samples. In addition, ROC analysis demonstrated that these hub genes owned higher diagnostic value in OLP, in which SPRR1B had the highest diagnostic value. And we also predicted that SOX7 was the most relevant transcription factor of those hub genes. Lastly, through the CMap database, we identified 6 small molecules as possible treatment drugs of OLP.

Conclusion

Our research identified that SPRR1B could be used as potential biomarkers for the early diagnosis of OLP. In addition, as a chronic autoimmune oral mucosal disease, OLP has different infiltration types of immune cells. Furthermore, 6 small molecules were proposed as promising novel treatment drugs for OLP patients. Therefore, our research may provide new impetus for the development of effective OLP biological treatment options.

LTB4 Promotes Acute Lung Injury via Upregulating the PLCε-1/TLR4/NF-κB Pathway in One-Lung Ventilation

Background

Mechanical ventilation (MV) can provoke acute lung injury (ALI) by increasing inflammation activation and disrupting the barrier in lung tissues even causing death. However, the inflammation-related molecules and pathways in MV-induced ALI remain largely unknown. Hence, the purposes of this study are to examine the role and mechanism of a novel inflammation-related molecule, leukotriene B4 (LTB4), in ALI.

Methods

The functions of LTB4 in one-lung ventilation (OLV) model were detected by the loss-of-function experiments. H&E staining was used to examine the pathologic changes of lung tissues. Functionally, PLCε-1 knockdown and Toll-like receptor 4 (TLR4)/NF-κB pathway inhibitor were used to detect the regulatory effects of LTB4 on the phospholipase Cε (PLCε-1)/TLR4/nuclear factor-kappa B (NF-κB) pathway. The levels of genes and proteins were determined by RT-qPCR and western blotting assay. The levels of inflammation cytokines and chemokines were measured by ELISA.

Results

Here, we found LTA4H, leukotriene B (4) receptor 1 (BLT1), LTB4, and PLCε-1 upregulated in OLV rats and associated with inflammatory activation and lung permeability changes of lung tissues. Inhibition of LTB4 alleviated the OLV-induced ALI by inhibiting inflammatory activation and lung permeability changes of lung tissues. For mechanism analyses, LTB4 promoted OLV-induced ALI by activating the PLCε-1/TLR4/NF-κB pathway.

Conclusion

LTB4 induced ALI in OLV rats by activating the PLCε-1/TLR4/NF-κB pathway. Our findings might supply a new potential therapeutic for OLV-induced ALI.

A target lipidomics approach to investigate the acute inflammatory irritation induced by indolealkylamines from Chansu water fraction in rats

Chansu has demonstrated adverse reactions in clinical settings, which is associated with its toxicity and limits its clinical applications. But there are methodological limitations for drug safety evaluation. In the current study, ultra-high performance liquid chromatography, lipidomic profiling, and molecular docking were used to systemically assess Chansu-induced acute inflammatory irritation and further identify the underlying drug targets. Compared with the EtOAc extract, Chansu water fraction containing indolealkylamines caused acute inflammatory irritation in rats, including acute pain (spontaneous raising foot reaction), and inflammation (paw edema). At the molecular level, lipids analysis revealed significantly higher levels of pro-inflammatory mediators of the COX and LOX pathways. However, anti-inflammatory mediators from the CYP 450, ALA, and DHA pathways markedly decreased after exposure to Chansu water fraction. Moreover, four indolealkylamines from Chansu showed a high theoretical affinity to a known irritation target, 5-HT_2AR. These results suggest that Chansu-induced inflammatory irritation is related to the distinct dysregulation of inflammatory lipids, and peripheral 5-HT_2AR is a potential target for irritation therapy. The strategy used in this study can be a crucial approach in the safety evaluation of natural medicinal substances.

Expression of leukotriene B4 receptor 1 defines functionally distinct DCs that control allergic skin inflammation

Leukotriene B4 (LTB4) receptor 1 (BLT1) is a chemotactic G protein-coupled receptor expressed by leukocytes, such as granulocytes, macrophages, and activated T cells. Although there is growing evidence that BLT1 plays crucial roles in immune responses, its role in dendritic cells remains largely unknown. Here, we identified novel DC subsets defined by the expression of BLT1, namely, BLT1hi and BLT1lo DCs. We also found that BLT1hi and BLT1lo DCs differentially migrated toward LTB4 and CCL21, a lymph node-homing chemoattractant, respectively. By generating LTB4-producing enzyme LTA4H knockout mice and CD11c promoter-driven Cre recombinase-expressing BLT1 conditional knockout (BLT1 cKO) mice, we showed that the migration of BLT1hi DCs exacerbated allergic contact dermatitis. Comprehensive transcriptome analysis revealed that BLT1hi DCs preferentially induced Th1 differentiation by upregulating IL-12p35 expression, whereas BLT1lo DCs accelerated T cell proliferation by producing IL-2. Collectively, the data reveal an unexpected role for BLT1 as a novel DC subset marker and provide novel insights into the role of the LTB4-BLT1 axis in the spatiotemporal regulation of distinct DC subsets.

Incomplete response to Anti-VEGF therapy in neovascular AMD: Exploring disease mechanisms and therapeutic opportunities

Intravitreal anti-vascular endothelial growth factor (VEGF) drugs have revolutionized the treatment of neovascular age-related macular degeneration (NVAMD). However, many patients suffer from incomplete response to anti-VEGF therapy (IRT), which is defined as (1) persistent (plasma) fluid exudation; (2) unresolved or new hemorrhage; (3) progressive lesion fibrosis; and/or (4) suboptimal vision recovery. The first three of these collectively comprise the problem of persistent disease activity (PDA) in spite of anti-VEGF therapy. Meanwhile, the problem of suboptimal vision recovery (SVR) is defined as a failure to achieve excellent functional visual acuity of 20/40 or better in spite of sufficient anti-VEGF treatment. Thus, incomplete response to anti-VEGF therapy, and specifically PDA and SVR, represent significant clinical unmet needs. In this review, we will explore PDA and SVR in NVAMD, characterizing the clinical manifestations and exploring the pathobiology of each. We will demonstrate that PDA occurs most frequently in NVAMD patients who develop high-flow CNV lesions with arteriolarization, in contrast to patients with capillary CNV who are highly responsive to anti-VEGF therapy. We will review investigations of experimental CNV and demonstrate that both types of CNV can be modeled in mice. We will present and consider a provocative hypothesis: formation of arteriolar CNV occurs via a distinct pathobiology, termed neovascular remodeling (NVR), wherein blood-derived macrophages infiltrate the incipient CNV lesion, recruit bone marrow-derived mesenchymal precursor cells (MPCs) from the circulation, and activate MPCs to become vascular smooth muscle cells (VSMCs) and myofibroblasts, driving the development of high-flow CNV with arteriolarization and perivascular fibrosis. In considering SVR, we will discuss the concept that limited or poor vision in spite of anti-VEGF may not be caused simply by photoreceptor degeneration but instead may be associated with photoreceptor synaptic dysfunction in the neurosensory retina overlying CNV, triggered by infiltrating blood-derived macrophages and mediated by Müller cell activation Finally, for each of PDA and SVR, we will discuss current approaches to disease management and treatment and consider novel avenues for potential future therapies.

Immune-Mediated Retinal Vasculitis in Posterior Uveitis and Experimental Models: The Leukotriene (LT)B4-VEGF Axis

Retinal vascular diseases have distinct, complex and multifactorial pathogeneses yet share several key pathophysiological aspects including inflammation, vascular permeability and neovascularisation. In non-infectious posterior uveitis (NIU), retinal vasculitis involves vessel leakage leading to retinal enlargement, exudation, and macular oedema. Neovascularisation is not a common feature in NIU, however, detection of the major angiogenic factor—vascular endothelial growth factor A (VEGF-A)—in intraocular fluids in animal models of uveitis may be an indication for a role for this cytokine in a highly inflammatory condition. Suppression of VEGF-A by directly targeting the leukotriene B4 (LTB4) receptor (BLT1) pathway indicates a connection between leukotrienes (LTs), which have prominent roles in initiating and propagating inflammatory responses, and VEGF-A in retinal inflammatory diseases. Further research is needed to understand how LTs interact with intraocular cytokines in retinal inflammatory diseases to guide the development of novel therapeutic approaches targeting both inflammatory mediator pathways.

Immunological Aspects of Age-Related Macular Degeneration

Increasing evidence over the past two decades points to a pivotal role for immune mechanisms in age-related macular degeneration (AMD) pathobiology. In this chapter, we will explore immunological aspects of AMD, with a specific focus on how immune mechanisms modulate clinical phenotypes of disease and severity and how components of the immune system may serve as triggers for disease progression in both dry and neovascular AMD. We will briefly review the biology of the immune system, defining the role of immune mechanisms in chronic degenerative disease and differentiating from immune responses to acute injury or infection. We will explore current understanding of the roles of innate immunity (especially macrophages), antigen-specific immunity (T cells, B cells, and autoimmunity), immune amplifications systems, especially complement activity and the NLRP3 inflammasome, in the pathogenesis of both dry and neovascular AMD, reviewing data from pathology, experimental animal models, and clinical studies of AMD patients. We will also assess how interactions between the immune system and infectious pathogens could potentially modulate AMD pathobiology via alterations in in immune effector mechanisms. We will conclude by reviewing the paradigm of "response to injury," which provides a means to integrate various immunologic mechanisms along with nonimmune mechanisms of tissue injury and repair as a model to understand the pathobiology of AMD.

Leukotriene B4 and Its Receptor in Experimental Autoimmune Uveitis and in Human Retinal Tissues: Clinical Severity and LTB4 Dependence of Retinal Th17 Cells

Nomacopan, a drug originally derived from tick saliva, has dual functions of sequestering leukotriene B₄ (LTB₄) and inhibiting complement component 5 (C5) activation. Nomacopan has been shown to provide therapeutic benefit in experimental autoimmune uveitis (EAU). Longer acting forms of nomacopan were more efficacious in mouse EAU models, and the long-acting variant that inhibited only LTB₄ was at least as effective as the long-acting variant that inhibited both C5 and LTB₄, preventing structural damage to the retina and a significantly reducing effector T helper 17 cells and inflammatory macrophages. Increased levels of LTB₄ and C5a (produced upon C5 activation) were detected during disease progression. Activated retinal lymphocytes were shown to express LTB₄ receptors (R) in vitro and in inflamed draining lymph nodes. Levels of LTB₄R-expressing active/inflammatory retinal macrophages were also increased. Within the draining lymph node CD4⁺ T-cell population, 30% expressed LTB₄R⁺ following activation in vitro, whereas retinal infiltrating cells expressed LTB₄R and C5aR. Validation of expression of those receptors in human uveitis and healthy tissues suggests that infiltrating cells could be targeted by inhibitors of the LTB₄-LTB4 receptor 1 (BLT1) pathway as a novel therapeutic approach. This study provides novel data on intraocular LTB₄ and C5a in EAU, their associated receptor expression by retinal infiltrating cells in mouse and human tissues, and in attenuating EAU via the dual inhibitor nomacopan.

Cysteinyl leukotriene receptor 1 modulates autophagic activity in retinal pigment epithelial cells

The retinal pigment epithelium (RPE), which is among the tissues in the body that are exposed to the highest levels of phagocytosis and oxidative stress, is dependent on autophagy function. Impaired autophagy and continuous cellular stress are associated with various disorders, such as dry age-related macular degeneration (AMD), a disease for which effective therapies are lacking. Cysteinyl leukotriene receptor (CysLTR) 1 is a potential modulator of autophagy; thus, the aim of this study was to investigate the role of CysLTR1 in autophagy regulation in the RPE cell line ARPE-19. The polarized ARPE-19 monolayer exhibited expression of CysLTR1, which was colocalized with β-tubulin III. In ARPE-19 cells, autophagic activity was rhythmically regulated and was increased upon CysLTR1 inhibition by Zafirlukast (ZK) treatment. H₂O₂ affected the proautophagic regulatory effect of ZK treatment depending on whether it was applied simultaneously with or prior to ZK treatment. Furthermore, mRNA levels of genes related to the leukotriene system, autophagy and the unfolded protein response were positively correlated. As CysLTR1 is involved in autophagy regulation under basal and oxidative stress conditions, a dysfunctional leukotriene system could negatively affect RPE functions. Therefore, CysLTR1 is a potential target for new treatment approaches for neurodegenerative disorders, such as AMD.

Protective Effects and Molecular Signaling of n-3 Fatty Acids on Oxidative Stress and Inflammation in Retinal Diseases

Oxidative stress and inflammation play crucial roles in the development and progression of retinal diseases. Retinal damage by various etiologies can result in retinopathy of prematurity (ROP), diabetic retinopathy (DR), and age-related macular degeneration (AMD). n-3 fatty acids are essential fatty acids and are necessary for homeostasis. They are important retinal membrane components and are involved in energy storage. n-3 fatty acids also have antioxidant and anti-inflammatory properties, and their suppressive effects against ROP, DR, and AMD have been previously evaluated. α-linolenic acid (ALA), eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), and their metabolites have been shown to alleviate retinal oxidative stress and inflammation involving various biological signaling pathways. In this review, we summarize the current understanding of the n-3 fatty acids effects on the mechanisms of these retinal diseases and how they exert their therapeutic effects, focusing on ALA, EPA, DHA, and their metabolites. This knowledge may provide new remedial strategies for n-3 fatty acids in the prevention and treatment of retinal diseases associated with oxidative stress and inflammation.

Betalain exerts a protective effect against glaucoma is majorly through the association of inflammatory cytokines

The present research aimed at evaluating the protective role of betalain on the in vitro glaucoma model using PC12 neuronal cells. The cultured neuronal cells in a customized pressurized chamber were analyzed for the onset of glutathione, myeloperoxidase (MPO), cathepsin, expression of inflammatory enzymes such as cyclooxygenase (COX-1), lipoxygenase (5- LOX), sPLA2 caveolin-1, glaucoma markers and other inflammatory cytokines in the presence and absence of betalain. The results have shown that a significant increase in the expression of oxidative stress with increased activity of cathepsin B and D. On the other hand, the activity of inflammatory enzymes such as COX-1, 5- LOX, sPLA2 were significantly increased in pressure exposed cells. In addition, glaucoma simulated cells demonstrated a significant increase in the VEGF, TGF-β, BDGF, and neuroserpin compared to control. Moreover, cells predisposed to hydrostatic pressure demonstrated an increase in (p < 0.01) inflammatory cytokines such as IL-6, CXCR4, IL-17, IL-1β, and TNF-α levels. However, cells pre-treated with betalain improved the glutathione levels with attenuated MPO activity. Simultaneously, the levels of inflammatory cytokines and other glaucoma marker genes found restored in drug pre-treated cells. Thus, the results of the present study demonstrate that the use of betalain on ocular cells can prevent the progression of the disease that can be a suggestive therapeutic for controlling glaucoma like conditions.

Leukotriene B4 receptors as therapeutic targets for ophthalmic diseases

Leukotriene B₄ (LTB₄) is an inflammatory lipid mediator produced from arachidonic acid by multiple reactions catalyzed by two enzymes 5-lipoxygenase (5-LOX) and LTA₄ hydrolase (LTA₄H). The two receptors for LTB₄ have been identified: a high-affinity receptor, BLT1, and a low-affinity receptor, BLT2. Our group identified 12(S)-hydroxy-5Z,8E,10E-heptadecatrienoic acid (12-HHT) as a high-affinity BLT2 ligand. Numerous studies have revealed critical roles for LTB₄ and its receptors in various systemic diseases. Recently, we also reported the roles of LTB₄, BLT1 and BLT2 in the murine ophthalmic disease models of mice including cornea wound, allergic conjunctivitis, and age-related macular degeneration. Moreover, other groups revealed the evidence of the ocular function of LTB₄. In the present review, we introduce the roles of LTB₄ and its receptors both in ophthalmic diseases and systemic inflammatory diseases. LTB₄ and its receptors are putative novel therapeutic targets for systemic and ophthalmic diseases.

Leukotriene B4 receptor 1 exacerbates inflammation following myocardial infarction

Leukotriene B₄ receptor 1 (BLT1), a high-affinity G-protein-coupled receptor for leukotriene B4 (LTB₄ ), is expressed on various inflammatory cells and plays critical roles in several inflammatory diseases. In myocardial infarction (MI), various inflammatory cells are known to be recruited to the infarcted area, but the function of BLT1 in MI is poorly understood. Here, we investigated the role of BLT1 in MI and the therapeutic effect of a BLT1 antagonist, ONO-4057, on MI. Mice with infarcted hearts showed increased BLT1 expression and LTB₄ levels. BLT1-knockout mice with infarcted hearts exhibited attenuated leukocyte infiltration, proinflammatory cytokine production, and cell death, which led to reduced mortality and improved cardiac function after MI. Bone-marrow transplantation studies showed that BLT1 expressed on bone marrow-derived cells was responsible for the exacerbation of inflammation in infarcted hearts. Furthermore, ONO-4057 administration attenuated the inflammatory responses in hearts surgically treated for MI, which resulted in reduced mortality and improved cardiac function after MI. Our study demonstrated that BLT1 contributes to excessive inflammation after MI and could represent a new therapeutic target for MI.

Promotion of Myofibroblast Differentiation and Tissue Fibrosis by the Leukotriene B4 -Leukotriene B4 Receptor Axis in Systemic Sclerosis

OBJECTIVE

To investigate the role of the inflammatory lipid mediator leukotriene B₄ (LTB₄ ) and its receptor, BLT1, in the development and progression of systemic sclerosis (SSc).

METHODS

Serum levels of LTB₄ were compared in 64 patients with SSc and 80 healthy controls. Skin and lung tissue sections from patients with SSc and healthy donors were immunostained for leukotriene A₄ hydrolase (LTA₄ H), the critical enzyme for LTB₄ synthesis, and BLT1, in combination with different cell markers. In mouse models of SSc using bleomycin or angiotensin II challenge or immunization with the DNA topoisomerase I, genetic or pharmacologic interruption of the LTB₄ -BLT1 axis in mice was carried out to assess its effects on systemic disease features and myofibroblast markers. Immunoblotting was performed to examine the signaling pathway in fibroblasts and endothelial cells following stimulation with LTB₄ or with serum from SSc patients.

RESULTS

Serum LTB₄ levels were 44.93% higher in patients with SSc than in matched healthy controls (mean ± SD 220.3 ± 74.75 pg/ml versus 152.0 ± 68.05 pg/ml; P < 0.0001), and this was associated with the patient subsets of SSc-associated interstitial lung disease and diffuse cutaneous SSc. Levels of LTA₄ H and BLT1 were increased in lesional areas of the skin and lungs of SSc patients, and both were abundant in myofibroblasts and endothelial cells. Interruption of the LTB₄ -BLT1 axis in mouse models of SSc significantly mitigated dermal and pulmonary fibrosis, with 54.00% and 52.65% fewer α-smooth muscle actin-positive myofibroblasts accumulating in the skin and lungs of mice, respectively, after bleomycin challenge. Immunoblotting of cultures with recombinant LTB₄ -stimulated fibroblasts and endothelial cells or with serum from SSc patients showed that fibroblast-myofibroblast and endothelial-mesenchymal transitions were promoted via BLT1, and that this was dependent on activation of the phosphatidylinositol 3-kinase (PI3K)/Akt/mechanistic target of rapamycin (mTOR) pathway but independent of the release of transforming growth factor β (TGFβ) by fibroblasts or endothelial cells.

CONCLUSION

The LTB₄ -BLT1 axis may contribute to fibrosis in SSc by directly promoting myofibroblast differentiation via the PI3K/Akt/mTOR pathway, and this appears to operate independently of autocrine secretion of TGFβ.

Innate immune response in retinal homeostasis and inflammatory disorders

Innate immune cells such as neutrophils, monocyte-macrophages and microglial cells are pivotal for the health and disease of the retina. For the maintenance of retinal homeostasis, these cells and immunosuppressive molecules in the eye actively regulate the induction and the expression of inflammation in order to prevent excessive activation and subsequent tissue damage. In the disease context, these regulatory mechanisms are modulated genetically and/or by environmental stimuli such as damage-associated molecular patterns (DAMPs), and a chronic innate immune response regulates or contributes to the formation of diverse retinal disorders such as uveitis, retinitis pigmentosa, retinal vascular diseases and retinal fibrosis. Here we summarize the recent knowledge regarding the innate immune response in both ocular immune regulation and inflammatory retinal diseases, and we describe the potential of the innate immune response as a biomarker and therapeutic target.

Datasets of microarray analysis to identify Gpr137b-dependent interleukin-4-responsive genes in the mouse macrophage cell line RAW264

Macrophages are classified mainly into two subtypes, M1 and M2, which exhibit distinct phenotypes, based on their microenvironment. We have recently demonstrated that Gpr137b is abundantly expressed in RAW264 macrophages, “Gpr137b is an orphan G-protein-coupled receptor associated with M2 macrophage polarization” (Islam et al., in press) [1]. Although recent studies have suggested that G-protein-coupled receptors (GPCRs) are associated with M1/M2 macrophage polarization (“G-protein-coupled bile acid receptor 1 (GPBAR1, TGR5) agonists reduce the production of proinflammatory cytokines and stabilize the alternative macrophage phenotype” (Hogenauer et al., 2014) [2], “Leukotriene B4 promotes neovascularization and macrophage recruitment in murine wet-type AMD models” (Sasaki et al., 2018) [3]), available information about GPCR-mediated macrophage polarization is still limited. This prompted us to generate Gpr137b-knockout (KO) RAW264 clones using the CRISPR/Cas9 genome editing system to elucidate the function of Gpr137b in interleukin (IL)-4-induced M2 macrophage polarization (Islam et al., in press) [1].

Here we present the datasets of a microarray analysis to identify Gpr137b-dependent IL-4-responsive genes in RAW264 cells. The raw microarray data are available in the Gene Expression Omnibus database (https://www.ncbi.nlm.nih.gov/geo/) under the accession number GSE117578, https://www.ncbi.nlm.nih.gov/geo/query/acc.cgi?acc=GSE117578.

The Role of Leukotrienes as Potential Therapeutic Targets in Allergic Disorders

Leukotrienes (LTs) are lipid mediators that play pivotal roles in acute and chronic inflammation and allergic diseases. They exert their biological effects by binding to specific G-protein-coupled receptors. Each LT receptor subtype exhibits unique functions and expression patterns. LTs play roles in various allergic diseases, including asthma (neutrophilic asthma and aspirin-sensitive asthma), allergic rhinitis, atopic dermatitis, allergic conjunctivitis, and anaphylaxis. This review summarizes the biology of LTs and their receptors, recent developments in the area of anti-LT strategies (in settings such as ongoing clinical studies), and prospects for future therapeutic applications.

Lipid Mediators, M2 Macrophages, and Pathological Neovascularization

Sasaki and colleagues [1] (JCI Insight 2018;3,e96902) identified the leukocyte inflammatory lipid mediator leukotriene B4 (LTB4)/LTB4 receptor 1 receptor-signaling axis in M2 macrophages as a causal pathway for the vascular endothelial growth factor-dependent pathological neovascularization in a mouse model that mimics wet age-related macular degeneration. This observation provides a novel mechanism by which an eicosanoid lipid mediator drives retinal vascular pathology and suggests a novel therapeutic target for proliferative retinal vascular diseases.