Class A scavenger receptor promotes cerebral ischemic injury by pivoting microglia/macrophage polarization

Class A1 scavenger receptor antibody improves murine colitis by influencing macrophage and gut microbiota

This study aimed to investigate whether class A1 scavenger receptor (SR-A1) regulated macrophage polarization and gut microbial alteration during intestinal inflammation of colitis. A murine colitis model was established by feeding with dextran sulfate sodium (DSS), and treatment groups were injected intravenously with SR-A1 antibody. Results showed a preventive effect on colitis symptoms and fewer inflammatory cell infiltrates in treatment groups. Down-regulation of inflammatory cytokines and up-regulation of anti-inflammatory cytokine related to macrophages were seen in murine PBMC and LPMC after injected with SR-A1 antibody. The percentage of M2 macrophages was also elevated in treatment groups. In addition, SR-A1 antibody treatment resulted in the decreased apoptosis and increased proliferation of colonic epithelial cells. Other findings indicated that SR-A1 antibody injection could mediate its anti-inflammatory effect via inhibiting TLR4-MyD88-NF-kB signaling pathway and alterating the gut microbiota composition. Our research identified SR-A1 as a potential therapeutic target in inflammatory bowel disease (IBD).

Neurological-related proteomic profiling in plasma of children with metabolic healthy and unhealthy overweight/obesity

OBJECTIVE

Children with overweight/obesity (OW/OB) exhibit poor cardiometabolic health, yet mechanisms influencing brain health remain unclear. We examined the differences in neurological-related circulating proteins in plasma among children with metabolically healthy obesity (MHO) and metabolically unhealthy obesity (MUO) and the association with metabolic syndrome markers.

METHODS

In this cross-sectional study, we included 84 Caucasian children (39% girls), aged 10.1 ± 1.1 years, from the ActiveBrains project (NCT02295072). A ninety-two-protein targeted approach using Olink's® technology was used.

RESULTS

We identified distinct concentrations of CD38, LAIR2, MANF and NRP2 proteins in MHO compared with MUO. Moreover, individual metabolic syndrome (MS) markers were linked to nine proteins (CD38, CPM, EDA2R, IL12, JAMB, KYNU, LAYN, MSR1 and SMOC2) in children with OW/OB. These proteins play crucial roles in diverse biological processes (e.g., angiogenesis, cholesterol transport, nicotinamide adenine dinucleotide (NAD+) catalysis and maintenance of blood-brain barrier) related to brain health.

CONCLUSION

Our proteomics study suggests that cardiometabolic health (represented by MHO/MUO or individual MS markers) is associated with the concentration in plasma of several proteins involved in brain health. Larger-scale studies are needed to contrast/confirm these findings, with CD38 standing out as a particularly noteworthy and robust discovery.

Hydrogen Sulfide and Liver Health: Insights into Liver Diseases

Significance: Hydrogen sulfide (H2S) is a recently recognized gasotransmitter involved in physiological and pathological conditions in mammals. It protects organs from oxidative stress, inflammation, hypertension, and cell death. With abundant expression of H2S-production enzymes, the liver is closely linked to H2S signaling. Recent Advances: Hepatic H2S comes from various sources, including gut microbiota, exogenous sulfur salts, and endogenous production. Recent studies highlight the importance of hepatic H2S in liver diseases such as nonalcoholic fatty liver disease (NAFLD), liver injury, and cancer, particularly at advanced stages. Endogenous H2S production deficiency is associated with severe liver disease, while exogenous H2S donors protect against liver dysfunction. Critical Issues: However, the roles of H2S in NAFLD, liver injury, and liver cancer are still debated, and its effects depend on donor type, dosage, treatment duration, and cell type, suggesting a multifaceted role. This review aimed to critically evaluate H2S production, metabolism, mode of action, and roles in liver function and disease. Future Direction: Understanding H2S's precise roles and mechanisms in liver health will advance potential therapeutic applications in preclinical and clinical research. Targeting H2S-producing enzymes and exogenous H2S sources, alone or in combination with other drugs, could be explored. Quantifying endogenous H2S levels may aid in diagnosing and managing liver diseases. Antioxid. Redox Signal. 40, 122-144.

Promoting AMPK/SR-A1-mediated clearance of HMGB1 attenuates chemotherapy-induced peripheral neuropathy

BACKGROUND

Chemotherapy-induced peripheral neuropathy (CIPN) is a serious side effect of chemotherapy with poorly understood mechanisms and few treatments. High-mobility group box 1 (HMGB1)-induced neuroinflammation is the main cause of CIPN. Here, we aimed to illustrate the role of the macrophage scavenger receptor A1 (SR-A1) in HMGB1 clearance and CIPN resolution.

METHODS

Oxaliplatin (L-OHP) was used to establish a CIPN model. Recombinant HMGB1 (rHMGB1) (his tag) was used to evaluate the phagocytosis of HMGB1 by macrophages.

RESULTS

In the clinic, HMGB1 expression and MMP-9 activity were increased in the plasma of patients with CIPN. Plasma HMGB1 expression was positively correlated with the cumulative dose of L-OHP and the visual analog scale. In vitro, engulfment and degradation of rHMGB1 increased and inflammatory factor expression decreased after AMP-activated protein kinase (AMPK) activation. Neutralizing antibodies, inhibitors, or knockout of SR-A1 abolished the effects of AMPK activation on rHMGB1 engulfment. In vivo, AMPK activation increased SR-A1 expression in the dorsal root ganglion, decreased plasma HMGB1 expression and MMP-9 activity, and attenuated CIPN, which was abolished by AMPK inhibition or SR-A1 knockout in the CIPN mice model.

CONCLUSION

Activation of the AMPK/SR-A1 axis alleviated CIPN by increasing macrophage-mediated HMGB1 engulfment and degradation. Therefore, promoting HMGB1 clearance may be a potential treatment strategy for CIPN. Video abstract.

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.

MSR1 characterized by chromatin accessibility mediates M2 macrophage polarization to promote gastric cancer progression

BACKGROUND

M2 macrophages play an important role in gastric cancer progression and metastasis, but the underlying tumor-promoting mechanisms are largely unknown.

METHODS

The TCIA database was used to identify the infiltration profile of macrophages. Integrated ATAC-seq, RNA-seq, and single-cell RNA sequencing (scRNA-seq) data from GC samples were used for the analysis. Using ATAC-seq profiles and RNA-seq datasets, combined with cox univariate survival analysis, we identified prognosis-related differentially expressed genes (DEGs) with chromatin accessibility, which were identified as hub genes. The CIBERSORTx algorithm was utilized to estimate the relative infiltration level of M2 macrophages, and Pearson correlation analysis was performed to investigate the relationship between hub genes and M2 macrophages. Multidimensional database validations were carried out to avoid biases. The expression level and function of hub genes in the clusters of macrophages were evaluated by using scRNA-seq data. The role of hub genes in the alternative activation of macrophages and gastric cancer malignant behaviors, as well as their potential regulatory mechanism in gastric cancer progression, were further explored.

RESULTS

17,334 genes were acquired with chromatin accessibility in promoter regions by ATAC-seq. 2,714 genes were identified with both chromatin accessibility and differential expression based on the gene expression profiles (RNA-seq). By performing Cox univariate survival analysis, 171 survival-related DEGs with chromatin accessibility were identified as hub genes. Through the CIBERSORTx algorithm and Pearson correlation analysis, the gene MSR1 most associated with M2 macrophages was screened out. According to the scRNA-seq analysis, MSR1 was highly expressed in the clusters of macrophages and may be involved in regulating M2 macrophage polarization. In vitro experiments confirmed that M2 macrophage polarization and its induced malignant behavior of gastric cancer cells were inhibited by knockdown of MSR1. Furthermore, MSR1 mediated M2 macrophage polarization by regulating arginine and proline metabolism, thereby activating the AMPK/mTOR pathway to promote gastric cancer progression.

CONCLUSION

We identified a gene-MSR1-characterized by chromatin accessibility, associated with poor prognosis in gastric cancer. This gene dictates the progression of gastric cancer by facilitating M2 macrophage polarization.

The Role of Hydrogen Sulfide Regulation of Autophagy in Liver Disorders

Autophagy is a complex process of degradation of senescent or dysfunctional organelles in cells. Dysfunctional autophagy is associated with many diseases such as cancers, immune dysfunction, and aging. Hydrogen sulfide (H₂S) is considered to be the third gas signal molecule after nitrous oxide and carbon monoxide. In recent years, H₂S has been found to have a variety of important biological functions, and plays an important role in a variety of physiological and pathological processes. In this review, we review the recent role and mechanism of H₂S in regulating autophagy in liver disorders, in order to provide a basis for further research in the future.

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.

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.

'A picture is worth a thousand words': The use of microscopy for imaging neuroinflammation

Since the first studies of the nervous system by the Nobel laureates Camillo Golgi and Santiago Ramon y Cajal using simple dyes and conventional light microscopes, microscopy has come a long way to the most recent techniques that make it possible to perform images in live cells and animals in health and disease. Many pathological conditions of the central nervous system have already been linked to inflammatory responses. In this scenario, several available markers and techniques can help imaging and unveil the neuroinflammatory process. Moreover, microscopy imaging techniques have become even more necessary to validate the large quantity of data generated in the era of 'omics'. This review aims to highlight how to assess neuroinflammation by using microscopy as a tool to provide specific details about the cell's architecture during neuroinflammatory conditions. First, we describe specific markers that have been used in light microscopy studies and that are widely applied to unravel and describe neuroinflammatory mechanisms in distinct conditions. Then, we discuss some important methodologies that facilitate the imaging of these markers, such as immunohistochemistry and immunofluorescence techniques. Emphasis will be given to studies using two-photon microscopy, an approach that revolutionized the real-time assessment of neuroinflammatory processes. Finally, some studies integrating omics with microscopy will be presented. The fusion of these techniques is developing, but the high amount of data generated from these applications will certainly improve comprehension of the molecular mechanisms involved in neuroinflammation.

Myocardin-Related Transcription Factor A Mediates LPS-Induced iNOS Transactivation

Macrophage-dependent inflammation plays a critical role in atherogenesis. Inducible nitric oxide synthase (iNOS) is one of key pro-inflammatory mediators produced in macrophages and its levels can be upregulated by lipopolysaccharide (LPS). The epigenetic mechanism whereby LPS induces iNOS transcription is incompletely understood. We show here myocardin-related transcription factor A (MRTF-A) potentiated iNOS promoter activity in macrophages. There was a decrease in LPS-induced iNOS expression in several cell models due to the lack of MRTF-A. LPS treatment promoted nuclear accumulation of MRTF-A and its interaction with NF-κB/p65 on the iNOS promoter. The absence of MRTF-A prevented the accumulation of active histone marks on the iNOS promoter in response to LPS treatment. Mechanistically, MRTF-A recruited ASH2, a key component of the mammalian histone H3K4 methyltransferase complex, to the iNOS promoter. Silencing of ASH2 attenuated iNOS expression following LPS treatment. Together, our data highlight a role for MRTF-A-dependent recruitment of H3K4 methyltransferase in iNOS induction and as such provide a novel target in the intervention of atherosclerosis.

Exogenous Hydrogen Sulfide Plays an Important Role Through Regulating Autophagy in Ischemia/Reperfusion Injury

Ischemia/reperfusion (I/R) injury is characterized by limiting blood supply to organs, then restoring blood flow and reoxygenation. It leads to many diseases, including acute kidney injury, myocardial infarction, circulatory arrest, ischemic stroke, trauma, and sickle cell disease. Autophagy is an important and conserved cellular pathway, in which cells transfer the cytoplasmic contents to lysosomes for degradation. It plays an important role in maintaining the balance of cell synthesis, decomposition and reuse, and participates in a variety of physiological and pathological processes. Hydrogen sulfide (H₂S), along with carbon monoxide (CO) and nitric oxide (NO), is an important gas signal molecule and regulates various physiological and pathological processes. In recent years, there are many studies on the improvement of I/R injury by H₂S through regulating autophagy, but the related mechanisms are not completely clear. Therefore, we summarize the related research in the above aspects to provide theoretical reference for future in-depth research.

Microglia-associated neuroinflammation is a potential therapeutic target for ischemic stroke

Microglia-associated neuroinflammation plays an important role in the pathophysiology of ischemic stroke. Microglial activation and polarization, and the inflammatory response mediated by these cells play important roles in the development, progression and outcome of brain injury after ischemic stroke. Currently, there is no effective strategy for treating ischemic stroke in clinical practice. Therefore, it is clinically important to study the role and regulation of microglia in stroke. In this review, we discuss the involvement of microglia in the neuroinflammatory process in ischemic stroke, with the aim of providing a better understanding of the relationship between ischemic stroke and microglia.

Aging-Related Phenotypic Conversion of Medullary Microglia Enhances Intraoral Incisional Pain Sensitivity

Activated microglia involved in the development of orofacial pain hypersensitivity have two major polarization states. The aim of this study was to assess the involvement of the aging-related phenotypic conversion of medullary microglia in the enhancement of intraoral pain sensitivity using senescence-accelerated mice (SAM)-prone/8 (SAMP8) and SAM-resistant/1 (SAMR1) mice. Mechanical head-withdrawal threshold (MHWT) was measured for 21 days post palatal mucosal incision. The number of CD11c-immunoreactive (IR) cells [affective microglia (M1)] and CD163-IR cells [protective microglia (M2)], and tumor-necrosis-factor-α (TNF-α)-IR M1 and interleukin (IL)-10-IR M2 were analyzed via immunohistochemistry on days 3 and 11 following incision. The decrease in MHWT observed following incision was enhanced in SAMP8 mice. M1 levels and the number of TNF-α-IR M1 were increased on day 3 in SAMP8 mice compared with those in SAMR1 mice. On day 11, M1 and M2 activation was observed in both groups, whereas IL-10-IR M2 levels were attenuated in SAMP8 mice, and the number of TNF-α-IR M1 cells increased, compared to those in SAMR1 mice. These results suggest that the mechanical allodynia observed following intraoral injury is potentiated and sustained in SAMP8 mice due to enhancement of TNF-α signaling, M1 activation, and an attenuation of M2 activation accompanying IL-10 release.

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.

Class A1 scavenger receptors mediated macrophages in impaired intestinal barrier of inflammatory bowel disease

Background

This study was to investigate the cytokines and phenotype of macrophages pre-treated with class A1 scavenger receptor (SR-A1) antibody in vitro and the influence on apoptotic pathway of colonic epithelial cells, and to explore the role of SR-A1 mediated macrophages in impaired intestinal barrier of inflammatory bowel diseases (IBDs).

Methods

Mouse macrophage RAW264.7 was pre-treated with SR-A1 antibody in the presence of lipopolysaccharide (LPS). Transwell system was employed for co-culture of RAW264.7 and Caco-2 in the presence of LPS and IFN-γ, with or without SR-A1 antibody pre-treatment. The percentage of F4/80⁺CD11c⁺ macrophages, apoptosis rate of Caco-2 cells, and expression of apoptosis and tight junction proteins in Caco-2 cells was determined.

Results

Pre-treatment with SR-A1 antibody up-regulated IL-10 expression in RAW264.7, whereas down-regulated the expression of TNF and iNOS. Immunofluorescence staining indicated the upregulation of NF-κB p-p56 after LPS stimulation was significantly inhibited in the presence of SR-A1 antibody. The increase in p-JNK expression was inhibited by SR-A1 antibody. Transwell assay showed the percentage of F4/80⁺CD11c⁺ macrophages and apoptotic Caco-2 cells increased after treatment with LPS and IFN-γ, which could be reversed in the presence of SR-A1 antibody. The induction of cleaved caspase-3 and claudin-1 in Caco-2 cells was also suppressed when SR-A1 antibody pre-treatment.

Conclusions

Pre-treatment with SR-A1 antibody can inhibit inflammatory response in LPS-induced macrophages in a NF-κB dependent manner. Pre-treatment with SR-A1 antibody also inhibits M1 phenotype expression of macrophages, and attenuates the pro-apoptotic effect on colonic epithelial cells and disruption of intestinal barrier integrity induced by macrophages.

Exogenous hydrogen sulfide protects fatty liver against ischemia-reperfusion injury by regulating endoplasmic reticulum stress-induced autophagy in macrophage through mediating the class A scavenger receptor pathway in rats

Fatty liver disease is a disease manifested with excessive alcohol intake and obese. Importantly, hydrogen sulfide (H₂ S) has been revealed to participate in the progression of fatty liver; however, the underlying mechanism has not been clearly elucidated yet. In this study, we aimed to investigate the effects of exogenous H₂ S on fatty liver ischemia-reperfusion injury (IRI) through mediating class A scavenger receptor (SRA) pathway in rats. By determining endoplasmic reticulum stress (ERS)-related factors, autophagy markers and apoptosis-related factors in liver tissue and liver function, levels of oxidative stress, inflammatory factors, and hepatocyte apoptosis, the effects of H₂ S on IRI-induced autophagy, oxidative stress, and inflammation were all examined in rat model of fatty liver IRI. Results from obtained data showed that H₂ S decreased the expression of SRA, Grp78, PERK, CHOP, and Caspase-3, and increased that of LC3-II/LC3-I, in addition to alleviating the pathological changes of liver and reducing the levels of ALT, AST, LDH TBARS, and MDA. Moreover, H₂ S decreased the levels of oxidative stress, the expression of pro-inflammatory factors including tumor necrosis factor α, interleukin 1, and interleukin 6, and the apoptosis of hepatocytes. Our findings suggested exogenous H₂ S could reduce ERS by mediating the SRA pathway and protect liver function by inducing autophagy, and protect against IRI by reducing oxidative stress and inflammation.

Microglial VPS35 deficiency regulates microglial polarization and decreases ischemic stroke-induced damage in the cortex

BACKGROUND

Vacuolar sorting protein 35 (VPS35), a critical component of retromer, is essential for selective endosome-to-Golgi retrieval of membrane proteins. It is highly expressed in microglial cells, in addition to neurons. We have previously demonstrated microglial VPS35's functions in preventing hippocampal, but not cortical, microglial activation, and in promoting adult hippocampal neurogenesis. However, microglial VPS35's role in the cortex in response to ischemic stroke remains largely unclear.

METHODS

We used mice with VPS35 cKO (conditional knockout) in microglial cells and examined and compared their responses to ischemic stroke with control mice. The brain damage, cell death, changes in glial cells and gene expression, and sensorimotor deficits were assessed by a combination of immunohistochemical and immunofluorescence staining, RT-PCR, Western blot, and neurological functional behavior tests.

RESULTS

We found that microglial VPS35 loss results in an increase of anti-inflammatory microglia in mouse cortex after ischemic stroke. The ischemic stroke-induced brain injury phenotypes, including brain damage, neuronal death, and sensorimotor deficits, were all attenuated by microglial VPS35-deficiency. Further analysis of protein expression changes revealed a reduction in CX3CR1 (CX3C chemokine receptor 1) in microglial VPS35-deficient cortex after ischemic stroke, implicating CX3CR1 as a potential cargo of VPS35 in this event.

CONCLUSION

Together, these results reveal an unrecognized function of microglial VPS35 in enhancing ischemic brain injury-induced inflammatory microglia, but suppressing the injury-induced anti-inflammatory microglia. Consequently, microglial VPS35 cKO mice exhibit attenuation of ischemic brain injury response.

Upregulation of IFN-β induced by Sema4D-dependent partial Erk1/2 inhibition promotes NO production in microglia

Interactions between Sema4D and its receptors, PlexinB1 and CD72, induce various functions, including axon guidance, angiogenesis, and immune activation. Our previous study revealed that Sema4D is involved in the upregulation of nitric oxide production in microglia after cerebral ischemia. In this study, we investigated the underlying mechanisms of the enhancement of microglial nitric oxide production by Sema4D. Primary microglia expressed PlexinB1 and CD72, and cortical microglia expressed CD72. Sema4D promoted nitric oxide production and slightly inhibited Erk1/2 phosphorylation in microglia. Partial Erk1/2 inhibition enhanced microglial nitric oxide production. Inhibition of Erk1/2 phosphorylation induced the expression of Ifn-β mRNA, and IFN-β promoted nitric oxide production in microglia. In the ischemic cortex, the expression of Ifn-β mRNA was downregulated by Sema4D deficiency. These findings indicated that the enhancement of nitric oxide production by Sema4D is involved in partial Erk1/2 inhibition and upregulation of IFN-β.

Kangfuxin Oral Liquid Attenuates Bleomycin-Induced Pulmonary Fibrosis via the TGF-β1/Smad Pathway

Idiopathic pulmonary fibrosis (IPF) is a fatal respiratory disease with a poor prognosis characterized by transforming growth factor (TGF)-β-induced proliferation, migration, and differentiation of fibroblasts, resulting in excessive extracellular matrix (ECM) deposition. Whether Kangfuxin oral liquid (KFXOL) has a protective function in pulmonary fibrosis is largely unknown. The goal of this study was to investigate the potential efficacy of KFXOL, as well as the underlying mechanism by which KFXOL regulates pulmonary fibrosis in vivo and in vitro. We found that KFXOL dramatically attenuated intratracheal bleomycin (BLM)-induced pulmonary fibrosis in terms of both severe alveolar architecture destruction and collagen deposition. KFXOL treatment significantly inhibited the proliferation, migration, and differentiation of pulmonary fibroblasts following activation using BLM/TGF-β1 and normalized the expression of ECM deposition-related proteins, including matrix metalloproteinase (MMP)-1, MMP-9, and tissue inhibitor of metalloproteinases 1. These effects were mediated via the inhibition of TGF-β1 and phosphorylated Smad2/3 activation in vivo. Taken together, our data suggest that KFXOL attenuates the development of pulmonary fibrosis via the TGF-β1/Smad signaling pathway and thus has potential utility in the treatment of pulmonary fibrosis.

Changes in L-arginine metabolism by Sema4D deficiency induce promotion of microglial proliferation in ischemic cortex

Cerebral ischemia induces neuroinflammation and microglial activation, in which activated microglia upregulate their proliferative activity and change their metabolic states. In activated microglia, l-arginine is metabolized competitively by inducible nitric oxide synthase (iNOS) and arginase (Arg), which then synthesize NO or polyamines, respectively. Our previous study demonstrated that Sema4D deficiency inhibits iNOS expression and promotes proliferation of ionized calcium-binding adaptor molecule 1 (Iba1)-positive (Iba1+) microglia in the ischemic cortex, although the underlying mechanisms were unclear. Using middle cerebral artery occlusion, we tested the hypothesis that Sema4D deficiency alters the balance of l-arginine metabolism between iNOS and Arg, leading to an increase in the production of polyamines, which are an essential factor for cell proliferation. In the peri-ischemic cortex, almost all iNOS+ and/or Arg1+ cells were Iba1+ microglia. In the peri-ischemic cortex of Sema4D-deficient (Sema4D^-/-) mice, the number of iNOS+ Arg1- Iba1+ microglia was smaller and that of iNOS- Arg1+ Iba1+ microglia was greater than those of wild-type (WT) mice. In addition, urea and polyamine levels in the ischemic cortex of Sema4D^-/- mice were higher than those of WT mice; furthermore, the presence of Sema4D inhibited polyamine production in primary microglia obtained from Sema4D^-/- mice. Finally, microglia cultured under polyamine putrescine-supplemented conditions demonstrated increased proliferation rates over non-supplemented controls. These findings indicate that Sema4D regulates microglial proliferation at least in part by regulating the competitive balance of l-arginine metabolism.

Early treatment with minocycline following stroke in rats improves functional recovery and differentially modifies responses of peri-infarct microglia and astrocytes

BACKGROUND

Altered neuronal connectivity in peri-infarct tissue is an important contributor to both the spontaneous recovery of neurological function that commonly develops after stroke and improvements in recovery that have been induced by experimental treatments in animal models. Microglia and astrocytes are primary determinants of the environment in peri-infarct tissue and hence strongly influence the potential for neuronal plasticity. However, the specific roles of these cells and the timing of critical changes in their function are not well understood. Minocycline can protect against ischemic damage and promote recovery. These effects are usually attributed, at least partially, to the ability of this drug to suppress microglial activation. This study tested the ability of minocycline treatment early after stroke to modify reactive responses in microglia and astrocytes and improve recovery.

METHODS

Stroke was induced by photothrombosis in the forelimb sensorimotor cortex of Sprague-Dawley rats. Minocycline was administered for 2 days after stroke induction and the effects on forelimb function assessed up to 28 days. The responses of peri-infarct Iba1-positive cells and astrocytes were evaluated using immunohistochemistry and Western blots.

RESULTS

Initial characterization showed that the numbers of Iba1-positive microglia and macrophages decreased in peri-infarct tissue at 24 h then increased markedly over the next few days. Morphological changes characteristic of activation were readily apparent by 3 h and increased by 24 h. Minocycline treatment improved the rate of recovery of motor function as measured by a forelimb placing test but did not alter infarct volume. At 3 days, there were only minor effects on core features of peri-infarct microglial reactivity including the morphological changes and increased density of Iba1-positive cells. The treatment caused a decrease of 57% in the small subpopulation of cells that expressed CD68, a marker of phagocytosis. At 7 days, the expression of glial fibrillary acidic protein and vimentin was markedly increased by minocycline treatment, indicating enhanced reactive astrogliosis.

CONCLUSIONS

Early post-stroke treatment with minocycline improved recovery but had little effect on key features of microglial activation. Both the decrease in CD68-positive cells and the increased activation of astrogliosis could influence neuronal plasticity and contribute to the improved recovery.

In Vivo MRI of Functionalized Iron Oxide Nanoparticles for Brain Inflammation

Microglia are intrinsic components of the brain immune system and are activated in many central nervous system disorders. The ability to noninvasively image these cells would provide valuable information for both research and clinical applications. Today, most imaging probes for activated microglia are mainly designed for positron emission tomography (PET) and target translocator proteins that also reside on other cerebral cells. The PET images obtained are not specific for microglia-driven inflammation. Here, we describe a potential PET/MRI multimodal imaging probe that selectively targets the scavenger receptor class A (SR-A) expressed on activated microglia. These sulfated dextran-coated iron oxide (SDIO) nanoparticles are avidly taken up by microglia and appear to be nontoxic when administered intravenously in a mouse model. Intravenous administration of this SDIO demonstrated visualization by T₂^∗-weighted MRI of microglia activated by intracerebral administration of tumor necrosis factor alpha (TNF-α). The contrast was significantly enhanced by SDIO, whereas there was little to no contrast change in animals treated with nontargeted nanoparticles or untreated controls. Thus, SR-A targeting represents a promising strategy to image activated microglia in the brain.

Effects of SC99 on cerebral ischemia-perfusion injury in rats: Selective modulation of microglia polarization to M2 phenotype via inhibiting JAK2-STAT3 pathway

Inhibition of Janus kinases 2-Signal transducers and activators of transcription3 (JAK2-STAT3) pathway has been shown to exert anti-inflammatory actions. SC99, a novel specific inhibitor targeting JAK2-STAT3 pathway, has been verified to negatively modulate platelet activation and aggregation in vitro. In current study, a middle cerebral artery occlusion and reperfusion (MCAO/R) model was established in Sprague Dawley rats and primary cultured microglia was exposed to oxygen and glucose deprivation (OGD/R) in vitro. Different dosages were employed to detect the effects of SC99 on cerebral ischemia-perfusion (I/R) injury and evaluate the underlying mechanisms. Our results showed that intracerebroventricular injection of SC99 (10 mmol/L, 15 μL) produced an effective inhibitory effect on the phosphorylation of JAK2 and STAT3. Correspondingly, SC99 ameliorated neuronal apoptosis and degeneration, neurobehavioral deficits, inflammatory response and brain edema. And SC99 promoted microglia polarization to an anti-inflammatory M2 phenotype. We concluded that SC99 could alleviate brain damage and play an anti-inflammatory action by promoting microglia polarization to an anti-inflammatory phenotype after I/R injury, which provides an emerging and promising alternative to protect the brain against MCAO/R injury in the future investigations.

Class A1 scavenger receptor modulates glioma progression by regulating M2-like tumor-associated macrophage polarization

Macrophages enhance glioma development and progression by shaping the tumor microenvironment. Class A1 scavenger receptor (SR-A1), a pattern recognition receptor primarily expressed in macrophages, is up-regulated in many human solid tumors. We found that SR-A1 expression in 136 human gliomas was positively correlated with tumor grade (P<0.01), but not prognosis or tumor recurrence. SR-A1-expressing macrophages originated primarily from circulating monocytes attracted to tumor tissue, and were almost twice as numerous as resident microglia in glioma tissues (P<0.001). The effects of SR-A1 on glioma proliferation and invasion were assessed in vivo using an SR-A1-deficient murine orthotopic glioma model. SR-A1 deletion promoted M2-like tumor-associated macrophage (TAM) polarization in mice by activating STAT3 and STAT6, which resulted in robust orthotopic glioma proliferation and angiogenesis. Finally, we found that HSP70 might be an endogenous ligand that activates SR-A1-dependent anti-tumorigenic pathways in gliomas, although its expression does not appear informative for diagnostic purposes. Our findings demonstrate a relationship between TAMs, SR-A1 expression and glioma growth and provide new insights into the pathogenic role of TAMs in glioma.

CD8 signaling in microglia/macrophage M1 polarization in a rat model of cerebral ischemia

Classical or M1 activity of microglia/macrophages has been described in several neurodegenerative and brain inflammatory conditions and has also been linked to expansion of ischemic injury in post-stroke brain. While different pathways of M1 polarization have been suggested to occur in the post-stroke brain, the precise underlying mechanisms remain undefined. Using a transient middle cerebral artery occlusion (MCAO) rat model, we showed a progressive M2 to M1 polarization in the perilesional brain region with M1 cells becoming one of the dominant subsets by day 4 post-stroke. Comparing key receptors involved in M1 polarization (CD8, IFNγR, Clec4, FcγR, TLR3 and TLR4) and their signal transducers (Syk, Stat1, Irf3, and Traf6) at the day 4 time point, we showed a strong upregulation of CD8 along with SYK transducer in dissected perilesional brain tissue. We further showed that CD8 expression in the post-stroke brain was associated with activated (CD68+) macrophages and that progressive accumulation of CD8+CD68+ cells in the post-stroke brain coincided with increased iNOS (M1 marker) and reduced Arg1 (M2 marker) expression on these cells. In vitro ligand-based stimulation of the CD8 receptor caused increased iNOS expression and an enhanced capacity to phagocytose E. coli particles; and interestingly, CD8 stimulation was also able to repolarize IL4-treated M2 cells to an M1 phenotype. Our data suggest that increased CD8 signaling in the post-stroke brain is primarily associated with microglia/macrophages and can independently drive M1 polarization, and that modulation of CD8 signaling could be a potential target to limit secondary post-stroke brain damage.

Yin-yang regulating effects of cancer-associated genes, proteins, and cells: An ancient Chinese concept in vogue in modern cancer research

Great achievements have been made in human cancer research, but most of this research is focused on conditions at the microscopic rather than the systemic level. Recent studies have increasingly cited the ancient Chinese theory of yin-yang in an effort to expand beyond the microscopic level. Various cancer-associated genes and proteins such as mitogen-activated protein kinase (MAPK), p38, p53, c-Myc, tumor necrosis factor (TNF)-α, NF-κB, Cyclin D1, and cyclin-dependent kinase (CDK) and cells such as T cells, B cells, macrophages, neutrophils, and fibroblasts have been reported to regulate various types of cancers in a yin-yang manner. These studies have brought the theory of yin-yang into vogue in cancer research worldwide.

Regulation of endothelial intracellular adenosine via adenosine kinase epigenetically modulates vascular inflammation

The molecular mechanisms underlying vascular inflammation and associated inflammatory vascular diseases are not well defined. Here we show that endothelial intracellular adenosine and its key regulator adenosine kinase (ADK) play important roles in vascular inflammation. Pro-inflammatory stimuli lead to endothelial inflammation by increasing endothelial ADK expression, reducing the level of intracellular adenosine in endothelial cells, and activating the transmethylation pathway through increasing the association of ADK with S-adenosylhomocysteine (SAH) hydrolase (SAHH). Increasing intracellular adenosine by genetic ADK knockdown or exogenous adenosine reduces activation of the transmethylation pathway and attenuates the endothelial inflammatory response. In addition, loss of endothelial ADK in mice leads to reduced atherosclerosis and affords protection against ischemia/reperfusion injury of the cerebral cortex. Taken together, these results demonstrate that intracellular adenosine, which is controlled by the key molecular regulator ADK, influences endothelial inflammation and vascular inflammatory diseases.

The molecular mechanisms underlying vascular inflammation are unclear. Here the authors show that pro-inflammatory stimuli lead to endothelial inflammation by increasing adenosine kinase expression, and that its knockdown in endothelial cells inhibits atherosclerosis and cerebral ischemic injury in mice.

MKL1 defines the H3K4Me3 landscape for NF-κB dependent inflammatory response

Macrophage-dependent inflammatory response is considered a pivotal biological process that contributes to a host of diseases when aberrantly activated. The underlying epigenetic mechanism is not completely understood. We report here that MKL1 was both sufficient and necessary for p65-dependent pro-inflammatory transcriptional program in immortalized macrophages, in primary human and mouse macrophages, and in an animal model of systemic inflammation (endotoxic shock). Extensive chromatin immunoprecipitation (ChIP) profiling and ChIP-seq analyses revealed that MKL1 deficiency erased key histone modifications synonymous with transactivation on p65 target promoters. Specifically, MKL1 defined histone H3K4 trimethylation landscape for NF-κB dependent transcription. MKL1 recruited an H3K4 trimethyltransferase SET1 to the promoter regions of p65 target genes. There, our work has identified a novel modifier of p65-dependent pro-inflammatory transcription, which may serve as potential therapeutic targets in treating inflammation related diseases.

Reactive astrogliosis in stroke: Contributions of astrocytes to recovery of neurological function

Alterations in neuronal connectivity, particularly in the "peri-infarct" tissue adjacent to the region of ischemic damage, are important contributors to the spontaneous recovery of function that commonly follows stroke. Peri-infarct astrocytes undergo reactive astrogliosis and play key roles in modulating the adaptive responses in neurons. This reactive astrogliosis shares many features with that induced by other forms of damage to the central nervous system but also differs in details that potentially influence neurological recovery. A subpopulation of astrocytes within a few hundred micrometers of the infarct proliferate and are centrally involved in the development of the glial scar that separates the damaged tissue in the infarct from surrounding normal brain. The intertwined processes of astrocytes adjacent to the infarct provide the core structural component of the mature scar. Interventions that cause early disruption of glial scar formation typically impede restoration of neurological function. Marked reactive astrogliosis also develops in cells more distant from the infarct but these cells largely remain in the spatial territories they occupied prior to stroke. These cells play important roles in controlling the extracellular environment and release proteins and other molecules that are able to promote neuronal plasticity and improve functional recovery. Treatments manipulating aspects of reactive astrogliosis can enhance neuronal plasticity following stroke. Optimising these treatments for use in human stroke would benefit from a more complete characterization of the specific responses of peri-infarct astrocytes to stroke as well as a better understanding of the influence of other factors including age, sex, comorbidities and reperfusion of the ischemic tissue.

Neuroprotective Properties of a Macrolide Antibiotic in a Mouse Model of Middle Cerebral Artery Occlusion: Characterization of the Immunomodulatory Effects and Validation of the Efficacy of Intravenous Administration

Repurposing the macrolide antibiotic azithromycin has recently been suggested as a promising neuroprotective strategy for the acute treatment of ischemic stroke. Here, we aim at further characterizing the immunomodulatory properties of intraperitoneal (i.p.) administration of this drug and, more importantly, at assessing whether neuroprotection can also be achieved by the more clinically relevant intravenous (i.v.) route of administration in a mouse model of focal cerebral ischemia induced by transient (30-min) middle cerebral artery occlusion (MCAo). A single i.p. injection of azithromycin (150 mg/kg) upon reperfusion prevented ischemia-induced spleen contraction and increased the number of MAC-1-immunopositive microglia/macrophages in the ischemic hemisphere 48 h after the insult. This was paralleled by an elevation of alternatively activated phenotypes (i.e., Ym1-immunopositive M2-polarized cells) and by a reduced expression of the pro-inflammatory marker myeloperoxidase. More importantly, i.v. administration of azithromycin upon reperfusion reduced MCAo-induced infarct volume and cerebral edema to an extent comparable to that obtained via the i.p. route. Although the i.p. route is often used for research purposes, it is impractical in the clinical setting; however, i.v. administration can easily be used in ischemic stroke patients who usually have i.v. access already established on hospital admission. The neuroprotective efficacy of the clinically relevant i.v. administration of azithromycin, together with its beneficial immunomodulatory properties reported in mice subjected to transient MCAo, suggests that this macrolide antibiotic can be effectively repurposed for the acute treatment of ischemic stroke. To this end, further work is needed to validate the efficacy of azithromycin in the clinical setting.

Ginkgolide B Protects Against Ischemic Stroke Via Modulating Microglia Polarization in Mice

AIM

Ginkgolide B (GB) has shown neuroprotective effect in treating ischemic stroke, related to its property of anti-inflammation. Nevertheless, it is unclear whether GB is able to modulate microglia/macrophage polarization, which has recently been proven to be vital in the pathology of ischemic stroke.

METHODS

We performed transient middle cerebral artery occlusion (tMCAO) on C57BL/6J male mice and induced cultured BV2 microglia and primary bone marrow-derived macrophages to be M1/2 phenotype by LPS+ interferon-γ and IL-4, respectively. Immunofluorescence and flow cytometry were used for detecting the specialized protein expression of M1/2, such as CD206 and CD16/32. qPCR was utilized to detect the signature gene change of M1/2.

RESULTS

GB significantly reduced cerebral ischemic damage and ameliorated the neurological deficits of mice after tMCAO. More importantly, our experiments proved that GB promoted microglia/macrophage transferring from inflammatory M1 phenotype to a protective, anti-inflammatory M2 phenotype in vivo or vitro. CV3988 and silencing the platelet activator factor (PAF) receptor by siRNA demonstrated that PAF receptor was involved in the modulation of microglia/macrophage polarization.

CONCLUSION

Our results reveal a novel pharmacological effect of GB in modulating microglia/macrophage polarization after tMCAO, thus deepening our understanding of neuroprotective mechanisms of GB in treatment of ischemic stroke. Furthermore, this new mechanism may allow GB to be used in many other microglia/macrophage polarization-related inflammatory diseases.

The biphasic function of microglia in ischemic stroke

Microglia are brain resident macrophages originated from primitive progenitor cells in the yolk sac. Microglia can be activated within hours and recruited to the lesion site. Traditionally, microglia activation is considered to play a deleterious role in ischemic stroke, as inhibition of microglia activation attenuates ischemia induced brain injury. However, increasing evidence show that microglia activation is critical for attenuating neuronal apoptosis, enhancing neurogenesis, and promoting functional recovery after cerebral ischemia. Differential polarization of microglia could likely explain the biphasic role of microglia in ischemia. We comprehensively reviewed the mechanisms involved in regulating microglia activation and polarization. The latest discoveries of microRNAs in modulating microglia function are discussed. In addition, the interaction between microglia and other cells including neurons, astrocytes, oligodendrocytes, and stem cells were also reviewed. Future therapies targeting microglia may not exclusively aim at suppressing microglia activation, but also at modulating microglia polarization at different stages of ischemic stroke. More work is needed to elucidate the cellular and molecular mechanisms of microglia polarization under ischemic environment. The roles of microRNAs and transplanted stem cells in mediating microglia activation and polarization during brain ischemia also need to be further studied.

Activation of RXR/PPARγ underlies neuroprotection by bexarotene in ischemic stroke

The identification of novel drug targets for the treatment of ischemic stroke is currently an urgent challenge. Recent experimental findings have highlighted the neuroprotective potential of immunomodulatory strategies, based on polarization of myeloid cells toward non-inflammatory, beneficial phenotypes. Given the role of retinoid X receptors (RXR) in myeloid cells differentiation and polarization, here we have explored the neuroprotective potential of the RXR agonist bexarotene in mice subjected to focal cerebral ischemia. Acute administration of bexarotene significantly reduced blood brain barrier leakage, brain infarct damage and neurological deficit produced by transient middle cerebral artery occlusion in mice, without affecting cerebral blood flow. The rexinoid exerted neuroprotection with a wide time-window, being effective when administered up to 4.5h after the insult. The amelioration of histological outcome, as well as the ability of bexarotene to revert middle cerebral artery occlusion (MCAo)-induced spleen atrophy, was antagonised by BR1211, a pan-RXR antagonist, or by the selective peroxisome proliferator-activated receptor (PPAR)γ antagonist bisphenol A diglycidyl ether (BADGE), highlighting the involvement of the RXR/PPARγ heterodimer in the beneficial effects exerted by the drug. Immunofluorescence analysis revealed that bexarotene elevates Ym1-immunopositive N2 neutrophils both in the ipsilateral hemisphere and in the spleen of mice subjected to transient middle cerebral artery occlusion, pointing to a major role for peripheral neutrophil polarization in neuroprotection. Thus, our findings suggest that the RXR agonist bexarotene exerts peripheral immunomodulatory effects under ischemic conditions to be effectively repurposed for the acute therapy of ischemic stroke.

Azithromycin protects mice against ischemic stroke injury by promoting macrophage transition towards M2 phenotype

To develop novel and effective treatments for ischemic stroke, we investigated the neuroprotective effects of the macrolide antibiotic azithromycin in a mouse model system of transient middle cerebral artery occlusion. Intraperitoneal administration of azithromycin significantly reduced blood-brain barrier damage and cerebral infiltration of myeloid cells, including neutrophils and inflammatory macrophages. These effects resulted in a dose-dependent reduction of cerebral ischemic damage, and in a remarkable amelioration of neurological deficits up to 7 days after the insult. Neuroprotection was associated with increased arginase activity in peritoneal exudate cells, which was followed by the detection of Ym1- and arginase I-immunopositive M2 macrophages in the ischemic area at 24-48 h of reperfusion. Pharmacological inhibition of peritoneal arginase activity counteracted azithromycin-induced neuroprotection, pointing to a major role for drug-induced polarization of migratory macrophages towards a protective, non-inflammatory M2 phenotype.

Rational modulation of the innate immune system for neuroprotection in ischemic stroke

The innate immune system plays a dualistic role in the evolution of ischemic brain damage and has also been implicated in ischemic tolerance produced by different conditioning stimuli. Early after ischemia, perivascular astrocytes release cytokines and activate metalloproteases (MMPs) that contribute to blood–brain barrier (BBB) disruption and vasogenic oedema; whereas at later stages, they provide extracellular glutamate uptake, BBB regeneration and neurotrophic factors release. Similarly, early activation of microglia contributes to ischemic brain injury via the production of inflammatory cytokines, including tumor necrosis factor (TNF) and interleukin (IL)-1, reactive oxygen and nitrogen species and proteases. Nevertheless, microglia also contributes to the resolution of inflammation, by releasing IL-10 and tumor growth factor (TGF)-β, and to the late reparative processes by phagocytic activity and growth factors production. Indeed, after ischemia, microglia/macrophages differentiate toward several phenotypes: the M1 pro-inflammatory phenotype is classically activated via toll-like receptors or interferon-γ, whereas M2 phenotypes are alternatively activated by regulatory mediators, such as ILs 4, 10, 13, or TGF-β. Thus, immune cells exert a dualistic role on the evolution of ischemic brain damage, since the classic phenotypes promote injury, whereas alternatively activated M2 macrophages or N2 neutrophils prompt tissue remodeling and repair. Moreover, a subdued activation of the immune system has been involved in ischemic tolerance, since different preconditioning stimuli act via modulation of inflammatory mediators, including toll-like receptors and cytokine signaling pathways. This further underscores that the immuno-modulatory approach for the treatment of ischemic stroke should be aimed at blocking the detrimental effects, while promoting the beneficial responses of the immune reaction.

Class A1 scavenger receptors in cardiovascular diseases

Class A1 scavenger receptors (SR-A1) are membrane glycoproteins that can form homotrimers. This receptor was originally defined by its ability to mediate the accumulation of lipids in macrophages. Subsequent studies reveal that SR-A1 plays critical roles in innate immunity, cell apoptosis and proliferation. This review highlights recent advances in understanding the structure, receptor pathway and regulation of SR-A1. Although its role in atherosclerosis is disputable, recent discoveries suggest that SR-A1 function in anti-inflammatory responses by promoting an M2 macrophage phenotype in cardiovascular diseases. Therefore, SR-A1 may be a potential target for therapeutic intervention of cardiovascular diseases.

Macrophage silica nanoparticle response is phenotypically dependent

Phagocytes are important players in host exposure to nanomaterials. Macrophages in particular are believed to be among the "first responders" and primary cell types that uptake and process nanoparticles, mediating host biological responses by subsequent interactions with inflammatory signaling pathways and immune cells. However, variations in local microenvironmental cues can significantly change the functional and phenotype of these cells, impacting nanoparticle uptake and overall physiological response. Herein we focus on describing the response of specific RAW 264.7 macrophage phenotypes (M1, INF-gamma/LPS induced and M2, IL-4 induced) to Stöber silica nanoparticle exposure in vitro and how this response might correlate with macrophage response to nanoparticles in vivo. It was observed that variations in macrophage phenotype produce significant differences in macrophage morphology, silica nanoparticle uptake and toxicity. High uptake was observed in M1, versus low uptake in M2 cells. M2 cells also displayed more susceptibility to concentration dependent proliferative effects, suggesting potential M1 involvement in in vivo uptake. Nanoparticles accumulated within liver and spleen tissues, with high association with macrophages within these tissues and an overall Th1 response in vivo. Both in vitro and in vivo studies are consistent in demonstrating that silica nanoparticles exhibit high macrophage sequestration, particularly those with Th1/M1 phenotype and in clearance organs. This sequestration and phenotypic response should be a primary consideration when designing new Stöber silica nanoparticle systems, as it might affect the overall efficacy.

Scavenger receptor-A (CD204): a two-edged sword in health and disease

Scavenger receptor A (SR-A), also known as the macrophage scavenger receptor and cluster of differentiation 204 (CD204), plays roles in lipid metabolism, atherogenesis, and a number of metabolic processes. However, recent evidence points to important roles for SR-A in inflammation, innate immunity, host defense, sepsis, and ischemic injury. Herein, we review the role of SR-A in inflammation, innate immunity, host defense, sepsis, cardiac and cerebral ischemic injury, Alzheimer's disease, virus recognition and uptake, bone metabolism, and pulmonary injury. Interestingly, SR-A is reported to be host protective in some disease states, but there is also compelling evidence that SR-A plays a role in the pathophysiology of other diseases. These observations of both harmful and beneficial effects of SR-A are discussed here in the framework of inflammation, innate immunity, and endoplasmic reticulum stress.

A cross talk between class A scavenger receptor and receptor for advanced glycation end-products contributes to diabetic retinopathy

In response to hyperglycemia in patients with diabetes, many signaling pathways contribute to the pathogenesis of diabetic complications, including diabetic retinopathy (DR). Excessive production of inflammatory mediators plays an important role in this process. Amadori-glycated albumin, one of the major forms of advanced glycated end-products, has been implicated in DR by inducing inflammatory responses in microglia/macrophages. Our goal was to delineate the potential cross talk between class A scavenger receptor (SR-A) and the receptor for advanced glycated end-product (RAGE) in the context of DR. We show here that SR-A ablation caused an exacerbated form of DR in streptozotocin-injected C57BL/6J mice as evidenced by fundus imaging and electroretinography. Immunohistochemical staining and RT-PCR assay indicated that there was augmented activation of proinflammatory macrophages with upregulated synthesis of proinflammatory mediators in the retina in Sr-a(-/-) mice. Overexpression of SR-A suppressed RAGE-induced mitogen-activated protein kinase (MAPK) signaling, whereas RAGE activation in macrophages favored a proinflammatory (M1) phenotype in the absence of SR-A. Mechanistic analysis on bone marrow-derived macrophages and HEK293 cell line revealed that SR-A interacted with and inhibited the phosphorylation of mitogen-activated protein kinase kinase 7, the major kinase in the RAGE-MAPK-NF-κB signaling, thereby leading to diminished secretion of proinflammatory cytokines. Our findings suggest that the antagonism between SR-A and RAGE contributes to the pathogenesis of DR by nurturing a disease-prone macrophage phenotype. Therefore, specific agonist that boosts SR-A signaling could potentially provide benefits in the prevention and/or intervention of DR.

Deletion of class A scavenger receptor deteriorates obesity-induced insulin resistance in adipose tissue

Chronic low-grade inflammation, particularly in the adipose tissue, orchestrates obesity-induced insulin resistance. In this process, polarized activation of macrophages plays a crucial role. However, how macrophages contribute to insulin resistance remains obscure. Class A scavenger receptor (SR-A) is a pattern recognition receptor primarily expressed in macrophages. Through a combination of in vivo and in vitro studies, we report here that deletion of SR-A resulted in reduced insulin sensitivity in obese mice. The anti-inflammatory virtue of SR-A was accomplished by favoring M2 macrophage polarization in adipose tissue. Moreover, we demonstrate that lysophosphatidylcholine (LPC) served as an obesity-related endogenous ligand for SR-A promoting M2 macrophage polarization by activation of signal transducer and activator of transcription 6 signaling. These data have unraveled a clear mechanistic link between insulin resistance and inflammation mediated by the LPC/SR-A pathway in macrophages.

MRTF-A mediates LPS-induced pro-inflammatory transcription by interacting with the COMPASS complex

Chronic inflammation underscores the pathogenesis of a range of human diseases. Lipopolysaccharide (LPS) elicits strong pro-inflammatory response in macrophages via the transcription factor NF-κB. The epigenetic mechanism underlying LPS-induced pro-inflammatory transcription is not completely appreciated. Herein we describe a role for myocardin related transcription factor A, or MRTF-A, in this process. MRTF-A over-expression potentiated while MRTF-A silencing dampened NF-κB dependent pro-inflammatory transcription. MRTF-A deficiency also alleviated the synthesis of pro-inflammatory mediators in a mouse model of colitis. LPS promoted the recruitment of MRTF-A to the promoters of pro-inflammatory genes in a NF-κB dependent manner. Reciprocally, MRTF-A influenced the nuclear enrichment and target binding of NF-κB. Mechanistically, MRTF-A was necessary for the accumulation of active histone modifications on NF-κB target promoters by communicating with the histone H3K4 methyltransferase complex (COMPASS). Silencing of individual members of COMPASS, including ASH2, WDR5, and SET1, down-regulated the production of pro-inflammatory mediators and impaired the NF-κB kinetics. In summary, our work has uncovered a previously unknown function for MRTF-A and provided insights into the rationalized development of anti-inflammatory therapeutic strategies.

Differential modulation of TREM2 protein during postnatal brain development in mice

During postnatal development, microglia, the resident innate immune cells of the central nervous system are constantly monitoring the brain parenchyma, cleaning the cell debris, the synaptic contacts overproduced and also maintaining the brain homeostasis. In this context, the postnatal microglia need some control over the innate immune response. One such molecule recently described to be involved in modulation of immune response is TREM2 (triggering receptor expressed on myeloid cells 2). Although some studies have observed TREM2 mRNA in postnatal brain, the regional pattern of the TREM2 protein has not been described. We therefore characterized the distribution of TREM2 protein in mice brain from Postnatal day (P) 1 to 14 by immunostaining. In our study, TREM2 protein was expressed only in microglia/macrophages and is developmentally downregulated in a region-dependent manner. Its expression persisted in white matter, mainly in caudal corpus callosum, and the neurogenic subventricular zone for a longer time than in grey matter. Additionally, the phenotypes of the TREM2+ microglia also differ; expressing CD16/32, MHCII and CD86 (antigen presentation markers) and CD68 (phagocytic marker) in different regions as well as with different intensity till P7. The mannose receptor (CD206) colocalized with TREM2 only at P1–P3 in the subventricular zone and cingulum, while others persisted at low intensities till P7. Furthermore, the spatiotemporal expression pattern and characterization of TREM2 indicate towards its other plausible roles in phagocytosis, progenitor’s fate determination or microglia phenotype modulation during postnatal development. Hence, the increase of TREM2 observed in pathologies may recapitulate their function during postnatal development, as a better understanding of this period may open new pathway for future therapies.

Innate immunity and neuroinflammation

Inflammation of central nervous system (CNS) is usually associated with trauma and infection. Neuroinflammation occurs in close relation to trauma, infection, and neurodegenerative diseases. Low-level neuroinflammation is considered to have beneficial effects whereas chronic neuroinflammation can be harmful. Innate immune system consisting of pattern-recognition receptors, macrophages, and complement system plays a key role in CNS homeostasis following injury and infection. Here, we discuss how innate immune components can also contribute to neuroinflammation and neurodegeneration.