Scavenger receptor A (SR-A) is required for LPS-induced TLR4 mediated NF-κB activation in macrophages

Engineering injectable hyaluronic acid-based adhesive hydrogels with anchored PRP to pattern the micro-environment to accelerate diabetic wound healing

Diabetic wounds remain a global challenge due to disordered wound healing led by inflammation, infection, oxidative stress, and delayed proliferation. Therefore, an ideal wound dressing for diabetic wounds not only needs tissue adhesiveness, injectability, and self-healing properties but also needs a full regulation of the microenvironment. In this work, adhesive wound dressings (HA-DA/PRP) with injectability were fabricated by combining platelet rich plasma (PRP) and dopamine-modified-hyaluronic acid (HA-DA). The engineered wound dressings exhibited tissue adhesiveness, rapid self-healing, and shape adaptability, thereby enhancing stability and adaptability to irregular wounds. The in vitro experiments demonstrated that HA-DA/PRP adhesives significantly promoted fibroblast proliferation and migration, attributed to the loaded PRP. The adhesives showed antibacterial properties against both gram-positive and negative bacteria. Moreover, in vitro experiments confirmed that HA-DA/PRP adhesives effectively mitigated oxidative stress and inflammation. Finally, HA-DA/PRP accelerated the healing of diabetic wounds by inhibiting bacterial growth, promoting granulation tissue regeneration, accelerating neovascularization, facilitating collagen deposition, and modulating inflammation through inducing M1 to M2 polarization, in an in vivo model of infected diabetic wounds. Overall, HA-DA/PRP adhesives with the ability to comprehensively regulate the microenvironment in diabetic wounds may provide a novel approach to expedite the diabetic wounds healing in clinic.

Evolution of the Major Components of Innate Immunity in Animals

Innate immunity is present in all animals. In this review, we explore the main conserved mechanisms of recognition and innate immune responses among animals. In this sense, we discuss the receptors, critical for binding to pathogen-associated molecular patterns (PAMPs) or danger-associated molecular patterns (DAMPs); the downstream signaling proteins; and transcription factors that govern immune responses. We also highlight conserved inflammatory mediators that are induced after the recognition of DAMPs and PAMPs. At last, we discuss the mechanisms that are involved in the regulation and/or generation of reactive oxygen species (ROS), influencing immune responses, like heme-oxygenases (HOs).

Potential promising anticancer applications of β-glucans: a review

β-Glucans are valuable functional polysaccharides distributed in nature, especially in the cell walls of fungi, yeasts, bacteria, and cereals. The unique features of β-glucans, such as water solubility, viscosity, molecular weight, and so on, have rendered them to be broadly applied in various food systems as well as in medicine to improve human health. Moreover, inhibition of cancer development could be achieved by an increase in immune system activity via β-glucans. β-glucans, which are part of a class of naturally occurring substances known as biological response modifiers (BRMs), have also shown evidence of being anti-tumorogenic, anti-cytotoxic, and anti-mutagenic. These properties make them attractive candidates for use as pharmaceutical health promoters. Along these lines, they could activate particular proteins or receptors, like lactosylceramide (LacCer), Dickin-1, complement receptor 3 (CR3), scavenge receptors (SR), and the toll-like receptor (TLR). This would cause the release of cytokines, which would then activate other antitumor immune cells, like macrophages stimulating neutrophils and monocytes. These cells are biased toward pro-inflammatory cytokine synthesis and phagocytosis enhancing the elicited immunological responses. So, to consider the importance of β-glucans, the present review introduces the structure characteristics, biological activity, and antitumor functions of fungal β-glucans, as well as their application.

Exogenous heat shock proteins HSPA1A and HSPB1 regulate TNF-α, IL-1β and IL-10 secretion from monocytic cells

Endogenous molecules, such as heat shock proteins (HSP), can function as danger signals when released into the extracellular environment in response to cell stress, where they elicit an immune response such as cytokine secretion. There has also been some suggestion that contamination of exogenous HSPs with lipopolysaccharide (LPS) may be responsible for these effects. This study investigates the effects of exogenous HSPA1A and HSPB1 on the activation of immune cells and the resulting secretion of cytokines, which are involved in inflammatory responses. To address whether exogenous HSPs can directly activate cytokine secretion, naïve U937 cells, differentiated U937 cells and peripheral blood mononuclear cells (PBMCs) were treated with either exogenously applied HSPA1A or HSPB1 and then secreted IL-1β, TNF-α and IL-10 were measured by ELISA. Both HSPs were able to induce a dose-dependent increase in IL-10 secretion from naïve U937 cells and dose-dependent IL-1β, TNF-α and IL-10 secretion were also observed in differentiated U937 cells and PBMCs. We also observed that CD14 affects the secretion levels of IL-1β, TNF-α and IL-10 from cells in response to exogenous HSP treatment. In addition, HSPA1A and HSPB1 were shown to interact with CD14, CD36 and CD11b extracellular receptor proteins. Several approaches used in this study indicate that HSP-induced cytokine secretion is largely independent of any contaminating LPS in the samples.

Receptor basis of biological activity of polysaccharides

Polysaccharides, the most diverse forms of organic molecules in nature, exhibit a large number of different biological activities, such as immunomodulatory, radioprotective, antioxidant, regenerative, metabolic, signaling, antitumor, and anticoagulant. The reaction of cells to a polysaccharide is determined by its specific interaction with receptors present on the cell surface, the type of cells, and their condition. The effect of many polysaccharides depends non-linearly on their concentration. The same polysaccharide in different conditions can have very different effects on cells and organisms, up to the opposite; therefore, when conducting studies of the biological activity of polysaccharides, both for the purpose of developing new drugs or approaches to the treatment of patients, and in order to clarify the features of intracellular processes, information about already known research results is needed. There is a lot of scattered data on the biological activities of polysaccharides, but there are few reviews that would consider natural polysaccharides from various sources and possible molecular mechanisms of their action. The purpose of this review is to present the main results published at different times in order to facilitate the search for information necessary for conducting relevant studies.

Deficiency of SR-B1 reduced the tumor load of colitis-induced or APCmin /+ -induced colorectal cancer

BACKGROUND

Colorectal cancer (CRC) is one of the most common tumors in the world. Cholesterol plays an important role in the pathogenesis of tumors. One of the cholesterol transporters, scavenger receptor class B type 1 (SR-B1), a multi-ligand membrane receptor protein, is expressed in the intestines which also highly expressed in various tumors. But the potential mechanism of SR-B1 in CRC development has not been reported.

AIMS

This study aimed to clarify the importance of SR-B1 in the development and prognosis of CRC as much as possible to provide a possible strategy in CRC treatment.

MATERIALS & METHODS

In this study, we used SR-B1 gene knockdown mice to study the effect of SR-B1 on colitis-induced or APCmin/+ -induced CRC. The expression of related molecules were detected through the immunohistochemistry and hematoxylin-eosin staining, western blot analysis, and Flow cytometry. The gene expression and microbiota in microenvironment of CRC mice were analyzed through eukaryotic mRNA sequencing and 16S rRNA high-throughput sequencing.

RESULTS

The results showed that SR-B1 knockdown reduced the tumor load of colitis-induced or APCmin/+ -induced CRC. SR-B1 knockdown improved the immune microenvironment by affecting the level of tumor-associated macrophage (TAM), mononuclear myeloid-derived suppressor cells (M-MDSCs), granulocytic myeloid-derived suppressor cells (G-MDSCs), programmed cell death-ligand 1 (PD-L1), and human leukocyte antigen class I-B (HLA-B), and also reduced the level of low-density lipoprotein receptor (LDL-R), and increased the level of ATP binding cassette transporter A1 (ABCA1) to regulate the cholesterol metabolism, and regulated the expression of related genes and intestinal microbiota. SR-B1 knockdown can also trigger the anti-CRC effect of anti-PD 1 in colitis-induced CRC.

DISCUSSION

SR-B1 deficiency significantly improved the immunity in tumor microenvironment of colitis-induced or APCmin/+ -induced CRC. In addition, the microbiota changes caused by SR-B1 deficiency favor improving the immune response to chemotherapeutic drugs and anti-PD1 therapy. The mechanism of action of SR-B1 deficiency on the development of CRC still needs further in-depth research.

CONCLUSION

This study provides a new treatment strategy for treating CRC by affecting the expression of SR-B1 in intestine.

Recognition of Arboviruses by the Mosquito Immune System

Arthropod-borne viruses (arboviruses) pose a significant threat to both human and animal health worldwide. These viruses are transmitted through the bites of mosquitoes, ticks, sandflies, or biting midges to humans or animals. In humans, arbovirus infection often results in mild flu-like symptoms, but severe disease and death also occur. There are few vaccines available, so control efforts focus on the mosquito population and virus transmission control. One area of research that may enable the development of new strategies to control arbovirus transmission is the field of vector immunology. Arthropod vectors, such as mosquitoes, have coevolved with arboviruses, resulting in a balance of virus replication and vector immune responses. If this balance were disrupted, virus transmission would likely be reduced, either through reduced replication, or even through enhanced replication, resulting in mosquito mortality. The first step in mounting any immune response is to recognize the presence of an invading pathogen. Recent research advances have been made to tease apart the mechanisms of arbovirus detection by mosquitoes. Here, we summarize what is known about arbovirus recognition by the mosquito immune system, try to generate a comprehensive picture, and highlight where there are still gaps in our current understanding.

Potential therapeutic targets of macrophages in inhibiting immune damage and fibrotic processes in musculoskeletal diseases

Macrophages are a heterogeneous cell type with high plasticity, exhibiting unique activation characteristics that modulate the progression and resolution of diseases, serving as a key mediator in maintaining tissue homeostasis. Macrophages display a variety of activation states in response to stimuli in the local environment, with their subpopulations and biological functions being dependent on the local microenvironment. Resident tissue macrophages exhibit distinct transcriptional profiles and functions, all of which are essential for maintaining internal homeostasis. Dysfunctional macrophage subpopulations, or an imbalance in the M1/M2 subpopulation ratio, contribute to the pathogenesis of diseases. In skeletal muscle disorders, immune and inflammatory damage, as well as fibrosis induced by macrophages, are prominent pathological features. Therefore, targeting macrophages is of great significance for maintaining tissue homeostasis and treating skeletal muscle disorders. In this review, we discuss the receptor-ligand interactions regulating macrophages and identify potential targets for inhibiting collateral damage and fibrosis in skeletal muscle disorders. Furthermore, we explore strategies for modulating macrophages to maintain tissue homeostasis.

Scavenger receptor B1 facilitates the endocytosis of Escherichia coli via TLR4 signaling in mammary gland infection

SCARB1 belongs to class B of Scavenger receptors (SRs) that are known to be involved in binding and endocytosis of various pathogens. SRs have emerging role in regulating innate immunity and host-pathogen interactions by acting in co-ordination with Toll-like receptors.Query Little is known about the function of SCARB1 in milk-derived mammary epithelial cells (MECs). This study reports the role of SCARB1 in infection and its potential association in TLR4 signaling on bacterial challenge in Goat mammary epithelial cells (GMECs). The novelty in the establishment of MEC culture lies in the method that aims to enhance the viability of the cells with intact characteristics upto a higher passage number. We represent MEC culture to be used as a potential infection model for deeper understanding of animal physiology especially around the mammary gland. On E.coli challenge the expression of SCARB1 was significant in induced GMECs at 6 h. Endoribonuclease-esiRNA based silencing of SCARB1 affects the expression of TLR4 and its pathways i.e. MyD88 and TRIF pathways on infection. Knockdown also affected the endocytosis of E.coli in GMECs demonstrating that E.coli uses SCARB1 function to gain entry in cells. Furthermore, we predict 3 unique protein structures of uncharacterized SCARB1 (Capra hircus) protein. Overall, we highlight SCARB1 as a main participant in host defence and its function in antibacterial advances to check mammary gland infections. Video Abstract.

Implications of fractalkine on glial function, ablation and glial proteins/receptors/markers—understanding its therapeutic usefulness in neurological settings: a narrative review

Background

Fractalkine (CX3CL1) is a chemokine predominantly released by neurons. As a signaling molecule, CX3CL1 facilitates talk between neurons and glia. CX3CL1 is considered as a potential target which could alleviate neuroinflammation. However, certain controversial results and ambiguous role of CX3CL1 make it inexorable to decipher the overall effects of CX3CL1 on the physiopathology of glial cells.

Main body of the abstract

Implications of cross-talk between CX3CL1 and different glial proteins/receptors/markers will give a bird eye view of the therapeutic significance of CX3CL1. Keeping with the need, this review identifies the effects of CX3CL1 on glial physiopathology, glial ablation, and gives a wide coverage on the effects of CX3CL1 on certain glial proteins/receptors/markers.

Short conclusion

Pinpoint prediction of the therapeutic effect of CX3CL1 on neuroinflammation needs further research. This is owing to certain obscure roles and implications of CX3CL1 on different glial proteins/receptors/markers, which are crucial under neurological settings. Further challenges are imposed due to the dichotomous roles played by CX3CL1. The age-old chemokine shows many newer scopes of research in near future. Thus, overall assessment of the effect of CX3CL1 becomes crucial prior to its administration in neuroinflammation.

Role of macrophage scavenger receptor MSR1 in the progression of non-alcoholic steatohepatitis

Nonalcoholic steatohepatitis (NASH) is the progressive form of nonalcoholic fatty liver disease (NAFLD), and the dysregulation of lipid metabolism and oxidative stress are the typical features. Subsequent dyslipidemia and oxygen radical production may render the formation of modified lipids. Macrophage scavenger receptor 1 (MSR1) is responsible for the uptake of modified lipoprotein and is one of the key molecules in atherosclerosis. However, the unrestricted uptake of modified lipoproteins by MSR1 and the formation of cholesterol-rich foamy macrophages also can be observed in NASH patients and mouse models. In this review, we highlight the dysregulation of lipid metabolism and oxidative stress in NASH, the alteration of MSR1 expression in physiological and pathological conditions, the formation of modified lipoproteins, and the role of MSR1 on macrophage foaming and NASH development and progression.

Antibodies in action: the role of humoral immunity in the fight against atherosclerosis

The sequestering of oxidation-modified low-density lipoprotein by macrophages results in the accumulation of fatty deposits within the walls of arteries. Necrosis of these cells causes a release of intercellular epitopes and the activation of the adaptive immune system, which we predict leads to robust autoantibody production. T cells produce cytokines that act in the plaque environment and further stimulate B cell antibody production. B cells in atherosclerosis meanwhile have a mixed role based on subclass. The current model is that B-1 cells produce protective IgM antibodies in response to oxidation-specific epitopes that work to control plaque formation, while follicular B-2 cells produce class-switched antibodies (IgG, IgA, and IgE) which exacerbate the disease. Over the course of this review, we discuss further the validation of these protective antibodies while evaluating the current dogma regarding class-switched antibodies in atherosclerosis. There are several contradictory findings regarding the involvement of class-switched antibodies in the disease. We hypothesize that this is due to antigen-specificity, and not simply isotype, being important, and that a closer evaluation of these antibodies' targets should be conducted. We propose that specific antibodies may have therapeutical potential in preventing and controlling plaque development within a clinical setting.

The role of macrophage scavenger receptor 1 (MSR1) in inflammatory disorders and cancer

Macrophage scavenger receptor 1 (MSR1), also named CD204, holds key inflammatory roles in multiple pathophysiologic processes. Present primarily on the surface of various types of macrophage, this receptor variably affects processes such as atherosclerosis, innate and adaptive immunity, lung and liver disease, and more recently, cancer. As highlighted throughout this review, the role of MSR1 is often dichotomous, being either host protective or detrimental to the pathogenesis of disease. We will discuss the role of MSR1 in health and disease with a focus on the molecular mechanisms influencing MSR1 expression, how altered expression affects disease process and macrophage function, the limited cell signalling pathways discovered thus far, the emerging role of MSR1 in tumour associated macrophages as well as the therapeutic potential of targeting MSR1.

Distinct Uptake Routes Participate in Silver Nanoparticle Engulfment by Earthworm and Human Immune Cells

The consequences of engineered silver nanoparticle (AgNP) exposure and cellular interaction with the immune system are poorly understood. The immunocytes of the Eisenia andrei earthworm are frequently applied in ecotoxicological studies and possess functional similarity to vertebrate macrophages. Hence, we characterized and compared the endocytosis mechanisms for the uptake of 75 nm AgNPs by earthworm coelomocytes, human THP-1 monocytes, and differentiated THP-1 (macrophage-like) cells. Our results indicate that microtubule-dependent, scavenger-receptor, and PI3K signaling-mediated macropinocytosis are utilized during AgNP engulfment by human THP-1 and differentiated THP-1 cells. However, earthworm coelomocytes employ actin-dependent phagocytosis during AgNPs uptake. In both human and earthworm immunocytes, AgNPs were located in the cytoplasm, within the endo-/lysosomes. We detected that the internalization of AgNPs is TLR/MyD88-dependent, also involving the bactericidal/permeability-increasing protein (BPI) in the case of human immunocytes. The exposure led to decreased mitochondrial respiration in human immunocytes; however, in coelomocytes, it enhanced respiratory parameters. Our findings provide more data about NP trafficking as nano-carriers in the nanomedicine field, as well as contribute to an understanding of the ecotoxicological consequences of nanoparticle exposure.

Scavenger receptor A in immunity and autoimmune diseases: Compelling evidence for targeted therapy

INTRODUCTION

Scavenger receptor A (SR-A) is reported to be involved in innate and adaptive immunity and in recent years, the soluble form of SR-A has also been identified. Intriguingly, SR-A displays double-edged sword features in different diseases. Moreover, targeted therapy on SR-A, including genetic modulation, small molecule inhibitor, inhibitory peptides, fucoidan, and blocking antibodies, provides potential strategies for treatment. Currently, therapeutics targeting SR-A are in preclinical studies and clinical trials, revealing great perspectives in future immunotherapy.

AREAS COVERED

Through searching PubMed (January 1979-March 2022) and clinicaltrials.gov, we review most of the research and clinical trials involving SR-A. This review briefly summarizes recent study advances on SR-A, with particular concern on its role in immunity and autoimmune diseases.

EXPERT OPINION

Given the emerging evidence of SR-A in immunity, its targeted therapy has been studied in various diseases, especially autoimmune diseases. However, many challenges still remain to be overcome, such as the double-sworded effects and the specific isoform targeting. For further clinical success of SR-A targeted therapy, the crystal structure illustration and the dual function discrimination of SR-A should be further investigated. Nevertheless, although challenging, targeting SR-A would be a potential effective strategy in the treatment of autoimmune diseases and other immune-related diseases.

Expression of Macrophage Scavenger Receptor (MSR1) in Peripheral Blood Cells from Patients with Different Respiratory Diseases: Beyond Monocytes

Background: Macrophage scavenger receptor 1 (MSR1) has mostly been described in macrophages, but we previously found a significant gene expression increase in peripheral blood mononuclear cells (PBMCs) of asthmatic patients. Objective: To confirm those results and to define its cellular origin in PBMCs. Methods: Four groups of subjects were studied: healthy controls (C), nonallergic asthmatic (NA), allergic asthmatic (AA), and chronic obstructive pulmonary disease (COPD) patients. RNA was extracted from PBMCs. MSR1 gene expression was analyzed by RT-qPCR. The presence of MSR1 on the cellular surface of PBMC cellular subtypes was analyzed by confocal microscopy and flow cytometry. Results: MSR1 gene expression was significantly increased in the three clinical conditions compared to the healthy control group, with substantial variations according to disease type and severity. MSR1 expression on T cells (CD4⁺ and CD8⁺), B cells, and monocytes was confirmed by confocal microscopy and flow cytometry. In all clinical groups, the four immune cell subtypes studied expressed MSR1, with a greater expression on B lymphocytes and monocytes, exhibiting differences according to disease and severity. Conclusions: This is the first description of MSR1’s presence on lymphocytes’ surfaces and reinforces the potential role of MSR1 as a player in asthma and COPD.

Defining Endocytic Pathways of Fucoidan-Coated PIBCA Nanoparticles from the Design of their Surface Architecture

Purpose

This work investigated the endocytic pathways taken by poly(isobutylcyanoacrylate) (PIBCA) nanoparticles differing in their surface composition and architecture, assuming that this might determine their efficiency of intracellular drug delivery.

Methods

Nanoparticles (A0, A25, A100, R0, R25 ) were prepared by anionic or redox radical emulsion polymerization using mixtures of dextran and fucoidan (0, 25, 100 % in fucoidan). Cell uptake was evaluated by incubating J774A.1 macrophages with nanoparticles. Endocytic pathways were studied by incubating cells with endocytic pathway inhibitors (chlorpromazine, genistein, cytochalasin D, methyl-ß-cyclodextrin and nocodazole) and nanoparticle uptake was evaluated by flow cytometry and confocal microscopy.

Results

The fucoidan-coated PIBCA nanoparticles A₂₅ were internalized 3-fold more efficiently than R₂₅ due to the different architecture of the fucoidan chains presented on the surface. Different fucoidan density and architecture led to different internalization pathway preferred by the cells. Large A₁₀₀ nanoparticles with surface was covered with fucoidan chains in a loop and train configuration were internalized the most efficiently, 47-fold compared with A₀, and 3-fold compared with R₀ and R₂₅ through non-endocytic energy-independent pathways and reached the cell cytoplasm.

Conclusion

Internalization pathways of PIBCA nanoparticles by J774A.1 macrophages could be determined by nanoparticle fucoidan surface composition and architecture. In turn, this influenced the extent of internalization and localization of accumulated nanoparticles within cells. The results are of interest for rationalizing the design of nanoparticles for potential cytoplamic drug delivery by controlling the nature of the nanoparticle surface.

Graphical abstract

Supplementary Information

The online version contains supplementary material available at 10.1007/s11095-022-03202-4.

Scavenger Receptor A1 Signaling Pathways Affecting Macrophage Functions in Innate and Adaptive Immunity

First discovered on macrophages by Goldstein and Brown in 1979, Scavenger Receptors have since been shown to participate in a diverse number of cell functions; equally diverse are their structures and the ligands they bind. Macrophage activation is crucial in the outcome of an immune response. SR-A1 is highly abundant on macrophages and recognizes both host- and microorganism-derived molecules that impact processes that are initiated, perpetuated, or modified. This review summarizes the involvement of SR-A1 in both inflammatory and anti-inflammatory responses, the multiple-ligand internalization mechanisms and the diversity of signaling pathways that impact macrophage function and activation. Engagement of SR-A1 results in the stimulation of differential signaling pathways and patterns of cytokine expression, kinetics, magnitude of response and activation status. SR-A1 plays essential roles in phagocytosis and efferocytosis, interacting with other receptors and promoting tolerance in response to apoptotic cell uptake. In cell adhesion, tissue remodeling, and cell migration, SR-A1 signals through different pathways engaging different cytoplasmic motifs. We describe the role of SR-A1 during innate and adaptive immune responses, such as participation in macrophage polarization and interaction with other innate receptors, as well as in antigen uptake, processing, and presentation, regulating T and B cell activation. The dichotomous contribution of SR-A1 on macrophage functions is discussed. A better understanding of the role SR-A1 plays through molecular mechanisms and crosstalk with other receptors may provide insights into developing novel therapeutic strategies to modulate immune responses and immunopathologies.

Scavenger receptors in host defense: from functional aspects to mode of action

Scavenger receptors belong to a superfamily of proteins that are structurally heterogeneous and encompass the miscellaneous group of transmembrane proteins and soluble secretory extracellular domain. They are functionally diverse as they are involved in various disorders and biological pathways and their major function in innate immunity and homeostasis. Numerous scavenger receptors have been discovered so far and are apportioned in various classes (A-L). Scavenger receptors are documented as pattern recognition receptors and known to act in coordination with other co-receptors such as Toll-like receptors in generating the immune responses against a repertoire of ligands such as microbial pathogens, non-self, intracellular and modified self-molecules through various diverse mechanisms like adhesion, endocytosis and phagocytosis etc. Unlike, most of the scavenger receptors discussed below have both membrane and soluble forms that participate in scavenging; the role of a potential scavenging receptor Angiotensin-Converting Enzyme-2 has also been discussed whereby only its soluble form might participate in preventing the pathogen entry and replication, unlike its membrane-bound form. This review majorly gives an insight on the functional aspect of scavenger receptors in host defence and describes their mode of action extensively in various immune pathways involved with each receptor type. Video abstract.

Characterization and the potential immune role of class A scavenger receptor member 4 (SCARA4) in bacterial infection in turbot (Scophthalmus maximus L.)

The class A scavenger receptors play important roles in innate immunity and are distributed on plasma membrane of macrophages and other cell types. Notably, the class A scavenger receptor 4 (SCARA4) contains a typical C-type (calcium-dependent) lectin domain, which belongs to the collectin family of pattern recognition receptors and is involved in the immune response against infection. Here, one turbot SCARA4 gene was identified with a 2,292 bp open reading frame (ORF) encoding 763 amino acid residues. Multiple sequence analysis and phylogenetic analysis confirmed that SmSCARA4 gene was more close to that of P. olivaceus. Gene structure and syntenic analysis showed conserved exon/intron organization pattern and syntenic pattern across selected vertebrate species. Tissue distribution analysis showed SmSCARA4 was expressed in all the tested healthy tissues with the relative high expression levels in skin, gill and spleen. Following both E. tarda and V. anguillarum challenge in vivo, SmSCARA4 was significantly repressed in gill and intestine. Remarkably, SmSCARA4 showed the strongest binding ability to LPS and strongest upregulation in turbot head kidney macrophages in response to LPS. Knockdown and overexpression of SmSCARA4 revealed its interactions with the two pro-inflammatory cytokines, TNF-α and IL-1β. Finally, repression of SmSCARA4 via combined treatment of LPS and overexpression of SmSCARA4 construct in turbot head kidney macrophages further indicated an inhibitory role of SmSCARA4 in LPS-stimulated inflammation. Taken together, turbot SmSCARA4 plays an important role in turbot immunity, especially in the mucosa-related systems; SmSCARA4 possesses strong binding specificity to LPS, and exerts protective roles in response to LPS infection by reducing the release of pro-inflammatory cytokines. The mechanisms of inhibitory role of SmSCARA4 in LPS-elicited inflammation await further investigation.

A critical role for MSR1 in vesicular stomatitis virus infection of the central nervous system

Macrophage scavenger receptor 1 (MSR1) plays an important role in host defense to bacterial infections, M2 macrophage polarization, and lipid homeostasis. However, its physiological function in viral pathogenesis remains poorly defined. Herein, we report that MSR1 facilitates vesicular stomatitis virus (VSV) infection in the central nervous system. Msr1-deficient (Msr1^−/−) mice presented reduced morbidity, mortality, and viral loads in the spinal cord following lethal VSV infection, along with normal viremia and innate immune responses, compared to Msr1^+/− littermates and wild-type mice. Msr1 expression was most significantly upregulated in the spinal cord, the predominant target of VSV. Mechanistically, through its extracellular domains, MSR1 interacted with VSV surface glycoprotein and facilitated its cellular entry in a low-density lipoprotein receptor-dependent manner. In conclusion, our results demonstrate that MSR1 serves as a cofactor for VSV cellular entry and facilitates its infection preferentially in the spinal cord.

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MSR1 contributes to VSV pathogenesis in mice

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MSR1 is highly upregulated and facilitates VSV infection in the central nervous system

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MSR1 facilitates cellular entry of VSV in an LDLR family-dependent manner

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MSR1 interacts with VSV glycoprotein G via its extracellular domains

Epidermal SR-A Complexes Are Lipid Raft Based and Promote Nucleic Acid Nanoparticle Uptake

Scavenger receptors clear pathogens, transport lipid, and mediate polyanionic ligand uptake in macrophages, but their expression and role in the skin are poorly understood. Although the epidermal barrier typically excludes nucleic acid entry, topically applied, spherically arranged oligonucleotide nanoconjugates (spherical nucleic acids [SNAs]) penetrate mouse skin, three-dimensional (3D) skin equivalents, and human skin. We explored the mechanism of SNA uptake in normal human epidermal keratinocytes and 3D skin equivalents. Normal human epidermal keratinocytes and 3D raft treatment with SR-A inhibitors reduced SNA uptake by >80%. The human epidermis expresses SR-As SCARA3 and, to a lesser extent, MARCO. Simultaneous lentiviral knockdown of SCARA3 and MARCO reduced SNA uptake in normal human epidermal keratinocytes and 3D rafts after topical application, affirming a role for SR-As in SNA uptake and 3D raft penetration. Incubation of normal human epidermal keratinocytes at 4oC or with sodium azide prevented SNA uptake, suggesting active endocytosis. Endocytosis inhibitors, immunofluorescence, immunoprecipitation, and knockdown studies localized functional SR-As to FLOT-1-containing lipid rafts throughout the epidermis and CAV-1-containing rafts only in the upper epidermis. These studies suggest a central role for SR-A complexes in epidermal lipid rafts in mediating the uptake of nucleic acid‒laden nanoparticles.

High-Expressed Macrophage Scavenger Receptor 1 Predicts Severity Clinical Outcome in Transplant Patient in Idiopathic Pulmonary Fibrosis Disease

Background

Lung transplantation has been performed worldwide and admitted as an effective treatment for patients with various end-stage lung diseases. However, limit reliable clinical indicators exist to identify patients at high risk for allograft failure in lung transplant recipients. The recent advances in the knowledge of immunological aspects of the pulmonary diseases, for that innate macrophage activation, are induced by pathogen or pathogen-derived molecules and widely accepted as the critical evidence among the pathogenesis of lung inflammation and fibrosis. This study was aimed at evaluating the clinical significance of CD86- and macrophage scavenger receptor 1- (MSR1-) positive cells during the development of idiopathic pulmonary fibrosis (IPF) and pulmonary arterial hypertension (PAH), and their potential roles in the prediction of the outcomes after lung transplantation were examined.

Methods

Tissues from lung transplantation for 37 IPF and 15 PAH patients from the Department of Cardiothoracic Surgery in Wuxi People's Hospital from December 2015 to December 2016 were analyzed by immunohistochemistry (IHC) for detecting the expression and CD86 and MSR1 and correlated with clinical events after lung transplantation.

Results

IHC results showed that the expression of MSR1, IL-13, and arginase-1 (Arg1) but not CD86 in the lung section of IPF patients was dramatically enhanced when compared with that of PAH patients. The expression of MSR1, IL-13, and Arg1 but not CD86 in the lung from IPF patients with smoking was significantly increased when compared with that from nonsmoking subjects. In addition, the expression of MSR1-positive cells in IPF subjects with Klebsiella pneumoniae infection was dramatically enhanced than that in noninfection subjects. MSR1-positive macrophages were negatively associated with FEV1 and with FVC but not associated with TLC and with TL_CO. However, CD86-positive macrophages were not significantly associated with the above lung function-related factors. Furthermore, MSR1 had a higher area under the ROC curve (AUC) than CD86 for IPF diagnosis. Survival analysis indicated that high levels of MSR1-positive macrophages had a worse prognostic effect for IPF patients with lung transplantation.

Conclusion

Our study indicates the clinical significance of Klebsiella pneumoniae infection-related MSR1-positive cells in IPF progression, and it could be a prognostic marker in IPF after the lung transplant; development strategies to reduce the expression of MSR1-positive macrophages in IPF may be beneficial for the lung transplant.

Macrophage scavenger receptor 1 controls Chikungunya virus infection through autophagy in mice

Macrophage scavenger receptor 1 (MSR1) mediates the endocytosis of modified low-density lipoproteins and plays an important antiviral role. However, the molecular mechanism underlying MSR1 antiviral actions remains elusive. We report that MSR1 activates autophagy to restrict infection of Chikungunya virus (CHIKV), an arthritogenic alphavirus that causes acute and chronic crippling arthralgia. Msr1 expression was rapidly upregulated after CHIKV infection in mice. Msr1 knockout mice had elevated viral loads and increased susceptibility to CHIKV arthritis along with a normal type I IFN response. Induction of LC3 lipidation by CHIKV, a marker of autophagy, was reduced in Msr1^-/- cells. Mechanistically, MSR1 interacted with ATG12 through its cytoplasmic tail and this interaction was enhanced by CHIKV nsP1 protein. MSR1 repressed CHIKV replication through ATG5-ATG12-ATG16L1 and this was dependent on the FIP200-and-WIPI2-binding domain, but not the WD40 domain of ATG16L1. Our results elucidate an antiviral role for MSR1 involving the autophagic function of ATG5-ATG12-ATG16L1.

Molecular Targets and Related Biologic Activities of Fucoidan: A Review

Fucoidan-a marine natural active polysaccharide derived from brown algae with a variety of medicinal activities and low toxicity-has been used as clinical drug for renal diseases for nearly 20 years. The pharmacological mechanism of fucoidan has been well-investigated, based on target molecules and downstream signaling pathways. This review summarizes some important molecular targets of fucoidan and its related biologic activities, including scavenger receptor (SR), Toll-like receptors (TLRs), C-type lectin (CLEC) and some newly found target molecules, which may be beneficial for further understanding the pharmacological mechanism of fucoidan and discovering its new functions, as well as developing related clinical or adjuvant drugs and functional preparations.

Macrophage MSR1 promotes the formation of foamy macrophage and neuronal apoptosis after spinal cord injury

Background

A sustained inflammatory response following spinal cord injury (SCI) contributes to neuronal damage, inhibiting functional recovery. Macrophages, the major participants in the inflammatory response, transform into foamy macrophages after phagocytosing myelin debris, subsequently releasing inflammatory factors and amplifying the secondary injury. Here, we assessed the effect of macrophage scavenger receptor 1 (MSR1) in phagocytosis of myelin debris after SCI and explained its possible mechanism.

Methods

The SCI model was employed to determine the critical role of MSR1 in phagocytosis of myelin debris in vivo. The potential functions and mechanisms of MSR1 were explored using qPCR, western blotting, and immunofluorescence after treating macrophages and RAW264.7 with myelin debris in vitro.

Results

In this study, we found improved recovery from traumatic SCI in MSR1-knockout mice over that in MSR1 wild-type mice. Furthermore, MSR1 promoted the phagocytosis of myelin debris and the formation of foamy macrophage, leading to pro-inflammatory polarization in vitro and in vivo. Mechanistically, in the presence of myelin debris, MSR1-mediated NF-κB signaling pathway contributed to the release of inflammatory mediators and subsequently the apoptosis of neurons.

Conclusions

Our study elucidates a previously unrecognized role of MSR1 in the pathophysiology of SCI and suggests that its inhibition may be a new treatment strategy for this traumatic condition.

Formononetin attenuates atherosclerosis via regulating interaction between KLF4 and SRA in apoE-/- mice

Background and Purpose: Atherosclerosis is an underlying cause of coronary heart disease. Foam cell, a hallmark of atherosclerosis, is prominently derived from monocyte-differentiated macrophage, and vascular smooth muscle cells (VSMCs) through unlimitedly phagocytizing oxidized low-density lipoprotein (oxLDL). Therefore, the inhibition of monocyte adhesion to endothelium and uptake of oxLDL might be a breakthrough point for retarding atherosclerosis. Formononetin, an isoflavone extracted from Astragalus membranaceus, has exhibited multiple inhibitory effects on proatherogenic factors, such as obesity, dyslipidemia, and inflammation in different animal models. However, its effect on atherosclerosis remains unknown. In this study, we determined if formononetin can inhibit atherosclerosis and elucidated the underlying molecular mechanisms.

Methods: ApoE deficient mice were treated with formononetin contained in high-fat diet for 16 weeks. After treatment, mouse aorta, macrophage and serum samples were collected to determine lesions, immune cell profile, lipid profile and expression of related molecules. Concurrently, we investigated the effect of formononetin on monocyte adhesion, foam cell formation, endothelial activation, and macrophage polarization in vitro and in vivo.

Results: Formononetin reduced en face and aortic root sinus lesions size. Formononetin enhanced lesion stability by changing the composition of plaque. VSMC- and macrophage-derived foam cell formation and its accumulation in arterial wall were attenuated by formononetin, which might be attributed to decreased SRA expression and reduced monocyte adhesion. Formononetin inhibited atherogenic monocyte adhesion and inflammation. KLF4 negatively regulated the expression of SRA at transcriptional and translational level.

Conclusions: Our study demonstrate that formononetin can substantially attenuate the development of atherosclerosis via regulation of interplay between KLF4 and SRA, which suggests the formononetin might be a novel therapeutic approach for inhibition of atherosclerosis.

Association of Toll-like receptor 4 polymorphisms with the risk of coronary artery disease in the ethnic Zhuang population of the Guangxi Province of China

OBJECTIVES

Toll-like receptor 4 (TLR4) is known to be involved in the innate immunity and inflammatory responses that plays a crucial role in the pathogenesis of coronary artery disease (CAD). This study aimed to examine the potential relationship of TLR4 polymorphisms and serum TLR4 protein levels and the risk of CAD in the ethnic Zhuang population of China.

METHODS

1171 serum samples were collected from Zhuang patients, including 556 CAD cases (≥50% luminal stenosis of any coronary vessel) and 615 normal healthy controls (subjects with no luminal stenosis in coronary arteries). Detection of TLR4 polymorphisms was by single base extension polymerase chain reaction (Snapshot PCR) and DNA sequencing (rs11536879A/G and rs11536889G/C) gene sequence in all subjects. Serum TLR4 protein concentrations was measured by ELISA.

RESULTS

There are significant differences in the allele and genotype frequencies of TLR4 gene rs11536889 between Chinese Zhuang CAD patients and controls, especially in the males. Male carriers of rs11536879 andrs11536889 variant alleles show an increased risk of CAD compared to non-carriers. Serum TLR4 protein levels of CAD patients are higher than controls and the levels tended to increase with the number of coronary artery lesions. Serum TLR4 protein levels of CAD patients showed no correlation with rs11536879 and rs11536889 polymorphisms.

CONCLUSIONS

The rs11536879 and rs11536889 polymorphisms of TLR4 gene and serum TLR4 protein levels may contribute to the occurrence and development of CAD. However, the rs11536879 and rs11536889 polymorphisms have no significant effects on the expression of serum TLR4 protein in Zhuang patients with CAD.

Fucoidan from Undaria pinnatifida has anti-diabetic effects by stimulation of glucose uptake and reduction of basal lipolysis in 3T3-L1 adipocytes

Fucoidan, a sulfated polysaccharide derived from brown seaweeds, has been shown to reduce blood glucose levels and improve insulin sensitivity in mice. We investigated the effects of fucoidan on lipid accumulation, lipolysis, and glucose uptake in 3T3-L1 cells to test the hypothesis that fucoidan exerts an anti-diabetic function by acting directly on adipocytes. The 3T3-L1 cells were treated with 10, 50, 100, and 200 μg/mL of fucoidan from Undaria pinnatifida. Oil Red O staining and AdipoRed assay were used to determine lipid accumulation during adipocyte differentiation. Fucoidan was shown to reduce lipid accumulation and glycerol-3-phosphate dehydrogenase (GPDH) activity in a dose-dependent manner (P < .01). The expression of peroxisome proliferator-activated receptor γ (PPARγ), a major transcription factor associated with adipocyte differentiation, was also suppressed upon treatment with fucoidan. Treatment with fucoidan stimulated glucose uptake in normal adipocytes and restored insulin-stimulated glucose uptake in obesity-induced insulin resistant adipocytes, which were made by incubating hypertrophied 3T3-L1 cells with the conditioned media of RAW 264.7 macrophages (RAW-CM) (P < .01). In the presence of RAW-CM, fucoidan enhanced epinephrine-stimulated lipolysis but reduced basal lipolysis, as determined by non-esterified fatty acid into the culture medium (P < .001). These results suggest that fucoidan may have anti-diabetic effects by improving insulin-stimulated glucose uptake and inhibiting basal lipolysis in adipocytes without inducing adipogenesis.

Terminalia bellirica (Gaertn.) Roxb. Extract and Gallic Acid Attenuate LPS-Induced Inflammation and Oxidative Stress via MAPK/NF-κB and Akt/AMPK/Nrf2 Pathways

Excessive oxidative stress plays a critical role in the progression of various diseases. Recently, we showed that Terminalia bellirica (Gaertn.) Roxb. extract (TBE) inhibits inflammatory response and reactive oxygen species (ROS) production in THP-1 macrophages. However, molecular mechanisms underlying anti-inflammatory and antioxidant activities of TBE and its major polyphenolic compounds gallic acid (GA) and ellagic acid (EA) remain unclear. We found that TBE and GA attenuated LPS-induced inflammatory mediator expression, ROS production, and activation of mitogen-activated protein kinase (MAPK) and nuclear factor-kappa B (NF-κB) in RAW 264 macrophages. Furthermore, TBE and GA increased antioxidant enzyme expression along with upstream mediators nuclear factor erythroid-2-related factor 2 (Nrf2), Akt, and AMP-activated protein kinase (AMPK). Importantly, knockdown of Nrf2 by siRNA and specific inhibition of Akt and AMPK significantly reduced antioxidant enzyme expression induced by TBE and GA. Finally, in vivo effects on histopathology and gene expression were assessed in tissues collected after intraperitoneal injection of LPS with or without TBE treatment. TBE enhanced antioxidant enzyme expression and improved acute kidney injury in LPS-shock model mice. In conclusion, TBE and GA exert protective effects against inflammation and oxidative stress by suppressing MAPK/NF-κB pathway and by activating Akt/AMPK/Nrf2 pathway. These results suggest that TBE and GA might be effective for the treatment of inflammation-related diseases.

Overexpression of Toll-like Receptor 4-linked Mitogen-activated Protein Kinase Signaling Contributes to Internalization of Escherichia coli in Sheep

Escherichia coli is one of the most common causal pathogens of mastitis in milk-producing mammals. Toll-like receptor 4 (TLR4) is important for host recognition of this bacteria. Increased activation of TLR4 can markedly enhance the internalization of E. coli. In this study, the relationship between TLR4 and mitogen-activated protein kinase (MAPK) signaling pathways in mediating E. coli internalization was evaluated in sheep monocytes. Using a TLR4-overexpressing transgenic (Tg) sheep model, we explored the bacterial internalization mechanism in sheep. We found that monocytes of Tg sheep could phagocytize more bacteria and exhibited higher adhesive capacity. The specific inhibition of p38 MAPK or c-Jun N-terminal kinase (JNK) or extracellular signal-regulated kinases (ERKs) reduced TLR4-dependent internalization of bacteria into sheep monocytes. Furthermore, the inhibition of MAPK signaling down-regulated the adhesive capacity of monocytes and the expression of scavenger receptors and adhesion molecules. Taken together, the overexpression of TLR4 in transgenic sheep enhanced the internalization of E. coli via MAPK signaling.

Critical regulation of inflammation via class A scavenger receptor

Background

Inflammation is an important cause of COPD. Alveolar macrophages are the major innate immune cells that have an important role in COPD pathology. Class A scavenger receptor (SR-A) is a pattern recognition receptor expressed on macrophages. This study investigates the role of SR-A in COPD progression via regulation of inflammation.

Patients and methods

SR-A expression in COPD patients and control subjects (smokers and nonsmokers without COPD) was measured by immunohistochemistry, immunofluorescence, and real-time PCR. The cytokine levels in BAL were measured by enzyme-linked immunosorbent assay. To further prove our hypothesis, we treated RAW264.7 cells that overexpress SR-A with lipopolysaccharides, poly(I:C), cigarette smoke extract, and H1N1 influenza separated from patients for 24 h and examined the levels of inflammatory cytokines.

Results

In both groups, COPD and smokers without COPD, SR-A expression level was upregulated in alveolar macrophages. SR-A mRNA level was positively correlated with inflammatory cytokines and negatively correlated with FEV₁% predicted in COPD patients. In RAW-SR-A cells, level of inflammatory cytokines was significantly higher when compared with control ones.

Conclusion

SR-A could increase inflammation stimulated by cigarette smoke extracts, bacteria, and virus, leading to long-term inflammation in COPD, and thus might be used as a new therapeutic target for COPD treatment.

Effects of scavenger receptors-1 class A stimulation on macrophage morphology and highly modified advanced glycation end product-protein phagocytosis

Advanced glycation end-products (AGEs), which comprise non-enzymatically glycosylated proteins, lipids, and nucleic acid amino groups, play an important role in several diseases and aging processes including angiopathy, renal failure, diabetic complications, and neurodegenerative diseases. Among AGE-associated phenotypes, toxic AGEs, glyceraldehyde-derived AGE-2, and glycolaldehyde-derived AGE-3 are involved in the pathogenesis of diabetic complications. In addition, macrophages are reported to remove extracellular AGEs from tissues via scavenger receptors, leading to the progression of atherosclerosis. In the present study, we found that AGE-2 and AGE-3 enhanced their own endocytic uptake by RAW264.7 mouse macrophage-like cells in a concentration-dependent manner. Furthermore, we demonstrated, for the first time, the morphology of phagocytic macrophages and the endocytosis of AGE particles. The toxic AGEs induced the expression of a scavenger receptor, CD204/scavenger receptors-1 class A (SR-A). Notably, an antibody against CD204 significantly prevented toxic AGE uptake. Moreover, an SR-A antagonistic ligand, fucoidan, also attenuated the AGE-2- and AGE-3-evoked uptake in a concentration-dependent manner. These results indicated that SR-A stimulation, at least in part, plays a role in AGE uptake.

Activation of PPARγ suppresses proliferation and induces apoptosis of esophageal cancer cells by inhibiting TLR4-dependent MAPK pathway

Although substantial studies on peroxisome proliferator-activated receptor γ (PPARγ) have focused on the mechanisms by which PPARγ regulates glucose and lipid metabolism, recent reports have suggested that PPARγ shows tumorigenic or antitumorigenic effects. The roles and mechanisms of PPARγ activation in esophageal cancer remain unclarified. EC109 and TE10 esophageal cancer cells were treated with 0, 10, 20 and 40 mM of PPARγ agonist rosiglitazone (RGZ) for 24, 48, and 72 h, and the cell viability and apoptosis were detected using methyl thiazolyl tetrazolium (MTT) assay and Flow cytometric (FCM) analysis, respectively. Moreover, the effects of inhibition of PPARγ by antagonist or specific RNA interference on cell viability, apoptosis, the Toll-like receptor 4 (TLR4) and mitogen-activated protein kinase (MAPK) pathways were evaluated. Additionally, the effect of TLR4 signaling on the MAPK pathway, cell viability and apoptosis was assessed. The results showed that RGZ suppressed proliferation and induced apoptosis of esophageal cancer cells, which could be partly restored by inactivation of PPARγ. RGZ suppressed the MAPK and TLR4 pathways, and the inhibitory effect could be counteracted by PPARγ antagonist or specific RNA interference. We also suggested that MAPK activation was regulated by the TLR4 pathway and that blocking the TLR4 and MAPK pathways significantly suppressed proliferation and induced apoptosis of esophageal cancer cells. In conclusion, our data suggested that activation of PPARγ suppressed proliferation and induced apoptosis of esophageal cancer cells by inhibiting TLR4-dependent MAPK pathway.

Pycnogenol Reduces Toll-Like Receptor 4 Signaling Pathway-Mediated Atherosclerosis Formation in Apolipoprotein E-Deficient Mice

Pycnogenol (PYC) is an extract from French maritime pine bark. Its antioxidative and anti-inflammatory effects have been shown to be beneficial for atherosclerosis. Here, we tested whether PYC could suppress high cholesterol and fat diet (HCD)-induced atherosclerosis formation in apolipoprotein E (apoE)-deficient mice. In our study, PYC suppressed oxidized low-density lipoprotein (ox-LDL)-induced lipid accumulation in peritoneal macrophages. Apolipoprotein E-deficient mice were orally administered PYC or a control solvent for ten weeks, and these mice were fed a standard diet or high cholesterol and fat diet during the latter eight weeks. Pycnogenol markedly decreased the size of atherosclerotic lesions induced by high cholesterol and fat diet compared with the nontreated controls. In addition, TLR4 expression in aortic sinus was stimulated by high cholesterol and fat diet feeding and was significantly reduced by PYC. A mechanistic analysis indicated that lipopolysaccharide (LPS) significantly increased expression of fatty acid binding protein (aP2) and macrophage scavenger receptor class A (SR-A), which were blocked by a JNK inhibitor. Furthermore, PYC inhibited the lipopolysaccharide-induced upregulation of aP2 and scavenger receptor class A via the JNK pathway. In conclusion, PYC administration effectively attenuates atherosclerosis through the TLR4-JNK pathway. Our results suggest that PYC could be a potential prophylaxis or treatment for atherosclerosis in humans.

Scavenger Receptor CD36 Directs Nonclassical Monocyte Patrolling Along the Endothelium During Early Atherogenesis

OBJECTIVE

Nonclassical monocytes (NCM) function to maintain vascular homeostasis by crawling or patrolling along the vessel wall. This subset of monocytes responds to viruses, tumor cells, and other pathogens to aid in protection of the host. In this study, we wished to determine how early atherogenesis impacts NCM patrolling in the vasculature.

APPROACH AND RESULTS

To study the role of NCM in early atherogenesis, we quantified the patrolling behaviors of NCM in ApoE^-/- (apolipoprotein E) and C57BL/6J mice fed a Western diet. Using intravital imaging, we found that NCM from Western diet-fed mice display a 4-fold increase in patrolling activity within large peripheral blood vessels. Both human and mouse NCM preferentially engulfed OxLDL (oxidized low-density lipoprotein) in the vasculature, and we observed that OxLDL selectively induced NCM patrolling in vivo. Induction of patrolling during early atherogenesis required scavenger receptor CD36, as CD36^-/- mice revealed a significant reduction in patrolling activity along the femoral vasculature. Mechanistically, we found that CD36-regulated patrolling was mediated by a SFK (src family kinase) through DAP12 (DNAX activating protein of 12KDa) adaptor protein.

CONCLUSIONS

Our studies show a novel pathway for induction of NCM patrolling along the vascular wall during early atherogenesis. Mice fed a Western diet showed increased NCM patrolling activity with a concurrent increase in SFK phosphorylation. This patrolling activity was lost in the absence of either CD36 or DAP12. These data suggest that NCM function in an atheroprotective manner through sensing and responding to oxidized lipoprotein moieties via scavenger receptor engagement during early atherogenesis.

CHSE-214: A model for studying extracellular dsRNA sensing in vitro

Double-stranded RNA (dsRNA) is produced by almost all viruses during their replicative cycle and is a potent inducer of the innate antiviral immune response including inducing expression of type I interferons (IFNs) and interferon-stimulated genes (ISGs). During lytic virus infections intracellular dsRNA can escape into the extracellular space, where surface pattern recognition receptors, such as class A scavenger receptors (SR-As) facilitate its binding and entry into neighbouring cells. Studying extracellular dsRNA entry is difficult due to the ubiquitous expression profile and compensatory dsRNA binding characteristics of SR-As; a SR-A deficient cell line has yet to be identified. The present study suggests the Chinook salmon embryonic cell line, CHSE-214, as a model for studying extracellular dsRNA sensing in vitro. CHSE-214 is unable to bind and respond to extracellular dsRNA, can only respond to dsRNA when it is transfected into the cells, and is able to bind dsRNA when overexpressing human SR-AI. The applications for this model could include elucidating: dsRNA binding and entry mechanisms, including sequence and length effects, as well as SR-A and other putative surface dsRNA receptor ligand binding studies.

Role of scavenger receptors as damage-associated molecular pattern receptors in Toll-like receptor activation

Damage-associated molecular patterns (DAMPs) have been implicated in sterile inflammation in various tissue injuries. High-mobility group box 1 (HMGB1) is a representative DAMP, and has been shown to transmit signals through receptors for advanced glycation end products (RAGEs) and TLRs, including TLR2 and TLR4. HMGB1 does not, however, bind to TLRs with high affinity; therefore, the mechanism of HMGB1-mediated TLR activation remains unclear. In this study, we found that fluorescently labeled HMGB1 was efficiently internalized into macrophages through class A scavenger receptors. Although both M1- and M2-type macrophages internalized HMGB1, only M1-type macrophages secreted cytokines in response to HMGB1. The pan-class A scavenger receptor competitive inhibitor, maleylated bovine serum albumin (M-BSA), inhibited HMGB1 internalization and reduced cytokine production from macrophages in response to HMGB1 but not to LPS. The C-terminal acidic domain of HMGB1 is responsible for scavenger receptor-mediated internalization and cytokine production. HMGB1 and TLR4 co-localized in macrophages, and this interaction was disrupted by M-BSA, suggesting that class A scavenger receptors function as co-receptors of HMGB1 for TLR activation. M-BSA ameliorated LPS-induced sepsis and dextran sulfate sodium (DSS)-induced colitis models in which HMGB1 has been shown to play progressive roles. These data suggest that scavenger receptors function as co-receptors along with TLRs for HMGB1 in M1-type inflammatory macrophages.

Fucoidan induces Toll-like receptor 4-regulated reactive oxygen species and promotes endoplasmic reticulum stress-mediated apoptosis in lung cancer

Fucoidan, a sulfated polysaccharide extracted from brown algae, exhibits anti-cancer activity. However, the effects and mechanism of fucoidan-induced apoptosis via endoplasmic reticulum (ER) stress is unclear. In this study, we demonstrated that fucoidan prevents tumorigenesis and reduces tumor size in LLC1-xenograft male C57BL/6 mice. Fucoidan induces an ER stress response by activating the PERK-ATF4-CHOP pathway, resulting in apoptotic cell death in vitro and in vivo. Furthermore, ATF4 knockdown abolishes fucoidan-induced CHOP expression and rescues cell viability. Specifically, fucoidan increases intracellular reactive oxygen species (ROS), which increase ATF4 and CHOP in lung cancer cells. Using the ROS scavenger N-acetyl-l-cysteine (NAC), we found that ROS generation is involved in fucoidan-induced ER stress-mediated apoptosis. Moreover, via Toll-like receptor 4 (TLR4) knockdown, we demonstrated that fucoidan-induced ROS and CHOP expression were attenuated. Our study is the first to identify a novel mechanism for the antitumor activity of fucoidan. We showed that fucoidan inhibits tumor viability by activating the TLR4/ROS/ER stress axis and the downstream PERK-ATF4-CHOP pathway, leading to apoptosis and suppression of lung cancer cell progression. Together, these results indicate that fucoidan is a potential preventive and therapeutic agent for lung cancer that acts via activation of ROS-dependent ER stress pathways.

Exopolysaccharide from Bacillus subtilis Induces Anti-Inflammatory M2 Macrophages That Prevent T Cell-Mediated Disease

Commensal bacteria contribute to immune homeostasis in the gastrointestinal tract; however, the underlying mechanisms for this are not well understood. A single dose of exopolysaccharide (EPS) from the probiotic spore-forming bacterium Bacillus subtilis protects mice from acute colitis induced by the enteric pathogen Citrobacter rodentium Adoptive transfer of macrophage-rich peritoneal cells from EPS-treated mice confers protection from disease to recipient mice. In vivo, EPS induces development of anti-inflammatory M2 macrophages in a TLR4-dependent manner, and these cells inhibit T cell activation in vitro and in C. rodentium-infected mice. In vitro, M2 macrophages inhibit CD4⁺ and CD8⁺ T cells. The inhibition of CD4⁺ T cells is dependent on TGF-β, whereas inhibition of CD8⁺ T cells is dependent on TGF-β and PD-L1. We suggest that administration of B. subtilis EPS can be used to broadly inhibit T cell activation and, thus, control T cell-mediated immune responses in numerous inflammatory diseases.

An ethanol extract of Aster yomena (Kitam.) Honda inhibits lipopolysaccharide-induced inflammatory responses in murine RAW 264.7 macrophages

Aster yomena (Kitam.) Honda has been widely used as a traditional herbal medicine for centuries to treat cough, asthma, insect bites, etc. Recent reports indicate that A. yomena possesses a wide spectrum of pharmacological activities; however, few experiments have described its anti-inflammatory properties. The present study examined the anti-inflammatory effects of an ethanol extract of A. yomena leaves (EEAY) on lipopolysaccharide (LPS)-stimulated murine RAW 264.7 macrophages. Treatment with EEAY significantly reduced the secretion of pro-inflammatory molecules, such as nitric oxide and interleukin-1β, in LPS-stimulated RAW 264.7 cells, without incurring any significant cytotoxicity. These protective effects were accompanied by a marked reduction in the expression of regulatory genes at the transcription level. Treatment with EEAY also inhibited the DNA-binding activity of nuclear factor-κB (NF-κB) by suppression of nuclear translocation of NF-κB and by degradation of the inhibitor of NF-κB; these effects were associated with suppression of the phosphatidylinositol 3-kinase/Akt and mitogen-activated protein kinase signaling pathways. The EEAY treatment also potently suppressed LPS-induced toll like receptor (TLR) 4 expression and attenuated the binding of LPS to the macrophage cell surface. In addition, EEAY treatment markedly inhibited LPS-induced accumulation of intracellular reactive oxygen species in RAW 264.7 macrophages. Therefore, the inhibitory effects of EEAY on LPS-stimulated inflammatory responses in RAW 264.7 macrophages were apparently associated with suppression of the TLR-mediated NF-κB signaling pathway. More work is needed to fully understand the critical role and clinical usefulness of EEAY treatment, but the findings of the present study provide some insights into the potential of EEAY as a therapeutic agent for treatment of inflammatory disorders.

Impact of probable interaction of low temperature and ambient fine particulate matter on the function of rats alveolar macrophages

The present study aimed to explore the probable interaction of low temperature and ambient fine particulate matter (PM_2.5) on rat alveolar macrophages (AMs). AMs were separated from rat BALF and exposed to PM_2.5 (0, 25, 50, 100μg/ml) under different temperature (18, 24, 30, 37°C) for 8h. Results indicated that viability and phagocytosis function of AMs decreased with the decline of temperature and the rise of PM_2.5 dose, and the strongest toxicity was shown in the highest PM_2.5 (100μg/ml) exposure group at 18°C. Both PM_2.5 and lower temperature increased the releasing of tumor necrosis factor alpha (TNF-α), macrophage inflammatory protein 1α (MIP-1α) and interleukin-6 (IL-6), while significant interaction was only found in MIP-1α production. No obvious change was found in granulocyte-macrophage colony-stimulating factor (GM-CSF) detection. These results indicated that both the two factors are harmful to rat AMs and lower temperature could increase the toxicity of PM_2.5 on the AMs.

Insights into binding of S100 proteins to scavenger receptors: class B scavenger receptor CD36 binds S100A12 with high affinity

The EF-hand type calcium-binding protein S100A12 exerts numerous intra- and extracellular functions of (patho)physiological relevance. Therefore, receptors of S100A12 are of high interest for research and clinical applications. Beside the extensively studied receptor for advanced glycation endproducts (RAGE), G-protein coupled receptors and more recently, scavenger receptors are suggested to be putative S100A12 receptors. Own findings and further information from the literature predestined CD36, a class B scavenger receptor, as promising candidate. To substantiate or prove against this hypothesis, this study aimed at investigation of interaction of S100A12 and CD36 on molecular and cellular level by the use of surface plasmon resonance (SPR), radio- and fluorescence-tracer-based cell binding, and cell activation experiments. S100A12 revealed binding affinity to CD36 in the low nanomolar range, essentially, at the CD36 thrombospondin-1 binding site. Additionally, S100A12-mediated translocation of CD36 to the membrane and elevation of both CD36 and peroxisome proliferator-activated receptor γ (PPARγ) expression was observed, which suggest a potential regulatory function of S100A12–CD36 interaction.

Expression of scavenger receptor A in rat's liver tissue during acute obstructive cholangitis and its significance

Objective

Acute obstructive cholangitis (AOC) is a severe disease that leads to sepsis, shock and multiple organ dysfunction syndrome. Liver is the largest and the major organ for the defense mechanisms during the sepsis. Our aim was to investigate the expression of scavenger receptor A (SRA) in rat’s liver tissue during AOC and its relation with the inflammatory mediators and hepatic injury caused by endotoxins.

Methods

Ninety Wistar rats were randomly divided into three equal groups. In group one, the choledochus were ligagted and Escherichia coli O₁₁₁B4 injected into it to produce AOC model. Group two had choledochus ligated and group three had sham surgery. Six animals from each group were sacrificed at 0, 3, 6, 12 and 24 h for comparative analysis of endotoxins, tumor necrosis factor-alpha, interleukin-6 in plasma and expression of SRA protein and SRA mRNA in liver tissue. The P < 0.05 was considered significant. Ethical approval was obtained.

Results

The plasma endotoxins, tumor necrosis factor-alpha and interleukin-6 levels in AOC rats increased progressively with time. The SRA protein and SRA mRNA expression decreased with time. The differences among groups were significant (P < 0.01). Liver histopathology showed gradually aggravated hepatic injury with neutrophil infiltration, degeneration and necrosis of hepatocytes.

Conclusion

In AOC, the expression of SRA in liver gradually decreased with progressive increase in level of plasma endotoxins and hepatic injury suggesting its importance in the defense mechanism.

CD36 Differently Regulates Macrophage Responses to Smooth and Rough Lipopolysaccharide

Lipopolysaccharide (LPS) is the major pathogen-associated molecular pattern of Gram-negative bacterial infections, and includes smooth (S-LPS) and rough (R-LPS) chemotypes. Upon activation by LPS through CD14, TLR4/MD-2 heterodimers sequentially induce two waves of intracellular signaling for macrophage activation: the MyD88-dependent pathway from the plasma membrane and, following internalization, the TRIF-dependent pathway from endosomes. We sought to better define the role of scavenger receptors CD36 and CD204/SR-A as accessory LPS receptors that can contribute to pro-inflammatory and microbicidal activation of macrophages. We have found that CD36 differently regulates activation of mouse macrophages by S-LPS versus R-LPS. The ability of CD36 to substitute for CD14 in loading R-LPS, but not S-LPS onto TLR4/MD-2 allows CD14-independent macrophage responses to R-LPS. Conversely, S-LPS, but not R-LPS effectively stimulates CD14 binding to CD36, which favors S-LPS transfer from CD14 onto TLR4/MD-2 under conditions of low CD14 occupancy with S-LPS in serum-free medium. In contrast, in the presence of serum, CD36 reduces S-LPS binding to TLR4/MD-2 and the subsequent MyD88-dependent signaling, by mediating internalization of S-LPS/CD14 complexes. Additionally, CD36 positively regulates activation of TRIF-dependent signaling by both S-LPS and R-LPS, by promoting TLR4/MD-2 endocytosis. In contrast, we have found that SR-A does not function as a S-LPS receptor. Thus, by co-operating with CD14 in both R- and S-LPS loading onto TLR4/MD-2, CD36 can enhance the sensitivity of tissue-resident macrophages in detecting infections by Gram-negative bacteria. However, in later phases, following influx of serum to the infection site, the CD36-mediated negative regulation of MyD88-dependent branch of S-LPS-induced TLR4 signaling might constitute a mechanism to prevent an excessive inflammatory response, while preserving the adjuvant effect of S-LPS for adaptive immunity.

CD36 regulates lipopolysaccharide-induced signaling pathways and mediates the internalization of Escherichia coli in cooperation with TLR4 in goat mammary gland epithelial cells

The scavenger receptor CD36 is involved in pathogen recognition, phagocytosis, and pathogen-induced signaling. This study investigated the relationship between CD36 and TLR4 in modifying lipopolysaccharide (LPS)-induced signaling pathways and mediating Escherichia coli (E. coli) endocytosis in primary goat mammary epithelial cells (pGMECs). The manipulation of CD36 expression significantly influenced TLR4 and nuclear factor kappa B (NF-κB) mRNA expression in pGMECs stimulated with LPS for 12 h. NF-κB and activator protein-1 (AP-1) activity was regulated by the manipulation of CD36 expression in LPS-induced pGMECs. However, CD36-mediated AP-1 activation occurred primarily through c-Jun N-terminal kinase (c-JNK). Adaptor proteins and proinflammatory cytokines were also involved in these signaling pathways and acted by regulating CD36 expression in LPS-stimulated cells. Moreover, CD36 cooperated with TLR4 in TLR4-mediated phagocytosis following E. coli simulation, but this complex was not induced by LPS treatment. Our study is the first to illuminate CD36 as a scavenger receptor in ruminants. Additionally, this study indicates that CD36 plays a vital role in the LPS-induced activation of downstream signaling cascades and mediates E. coli phagocytosis via TLR4 in pGMECs, which offers a novel treatment strategy for mastitis.

The effect of local anesthetic on pro-inflammatory macrophage modulation by mesenchymal stromal cells

Administering local anesthetics (LAs) peri- and post-operatively aims to prevent or mitigate pain in surgical procedures and after tissue injury in cases of osteoarthritis (OA) and other degenerative diseases. Innovative tissue protective and reparative therapeutic interventions such as mesenchymal stromal cells (MSCs) are likely to be exposed to co-administered drugs such as LAs. Therefore, it is important to determine how this exposure affects the therapeutic functions of MSCs and other cells in their target microenvironment. In these studies, we measured the effect of LAs, lidocaine and bupivacaine, on macrophage viability and pro-inflammatory secretion. We also examined their effect on modulation of the macrophage pro-inflammatory phenotype in an in vitro co-culture system with MSCs, by quantifying macrophage tumor necrosis factor (TNF)-α secretion and MSC prostaglandin E2 (PGE2) production. Our studies indicate that both LAs directly attenuated macrophage TNF-α secretion, without significantly affecting viability, in a concentration- and potency-dependent manner. LA-mediated attenuation of macrophage TNF-α was sustained in co-culture with MSCs, but MSCs did not further enhance this anti-inflammatory effect. Concentration- and potency-dependent reductions in macrophage TNF-α were concurrent with decreased PGE2 levels in the co-cultures further indicating MSC-independent macrophage attenuation. MSC functional recovery from LA exposure was assessed by pre-treating MSCs with LAs prior to co-culture with macrophages. Both MSC attenuation of TNF-α and PGE2 secretion were impaired by pre-exposure to the more potent bupivacaine and high dose of lidocaine in a concentration-dependent manner. Therefore, LAs can affect anti-inflammatory function by both directly attenuating macrophage inflammation and MSC secretion and possibly by altering the local microenvironment which can secondarily reduce MSC function. Furthermore, the LA effect on MSC function may persist even after LA removal.