Macrophage polarization: the link between inflammation and related diseases

Air particulate matter SRM 1648a primes macrophages to hyperinflammatory response after LPS stimulation

Objective

Exposure to air particulate matter (PM) is associated with chronic inflammatory and autoimmune diseases. Macrophages are responsible for the regulation of chronic inflammation. However, whether PM affects macrophage polarization remains unclear. The aim of this study was to evaluate whether nontoxic concentrations of urban PM are able to prime macrophages to altered inflammatory response upon LPS challenge.

Methods

We used two forms of the urban particulate matter SRM 1648a, intact PM and PM deprived of organic compounds (PM∆C). Peritoneal murine macrophages were exposed to different concentrations of PM for 24 h and then challenged with LPS. Production of inflammatory mediators by macrophages was measured to test immunostimulatory/priming capacity of PM.

Results

Particulate matter used at non-cytotoxic concentrations induced a dose-dependent production of proinflammatory cytokines (TNF-α, IL-6, IL-12p40). By contrast, PM∆C were not able to stimulate macrophages. However, macrophages primed with both forms of PM show proinflammatory response upon LPS challenge.

Conclusions

Our data indicate that exposure of macrophages to low concentrations of PM may prime the cells to hyperinflammatory response upon contact with LPS. Further studies are necessary to explain whether the exposure of patients suffering from chronic inflammatory diseases to particulate matter is responsible for the exacerbation of clinical symptoms during bacterial infections.

Macrophage Polarization in Chronic Inflammatory Diseases: Killers or Builders?

Macrophages are key cellular components of the innate immunity, acting as the main player in the first-line defence against the pathogens and modulating homeostatic and inflammatory responses. Plasticity is a major feature of macrophages resulting in extreme heterogeneity both in normal and in pathological conditions. Macrophages are not homogenous, and they are generally categorized into two broad but distinct subsets as either classically activated (M1) or alternatively activated (M2). However, macrophages represent a continuum of highly plastic effector cells, resembling a spectrum of diverse phenotype states. Induction of specific macrophage functions is closely related to the surrounding environment that acts as a relevant orchestrator of macrophage functions. This phenomenon, termed polarization, results from cell/cell, cell/molecule interaction, governing macrophage functionality within the hosting tissues. Here, we summarized relevant cellular and molecular mechanisms driving macrophage polarization in "distant" pathological conditions, such as cancer, type 2 diabetes, atherosclerosis, and periodontitis that share macrophage-driven inflammation as a key feature, playing their dual role as killers (M1-like) and/or builders (M2-like). We also dissect the physio/pathological consequences related to macrophage polarization within selected chronic inflammatory diseases, placing polarized macrophages as a relevant hallmark, putative biomarkers, and possible target for prevention/therapy.

Macrophage plasticity, polarization, and function in health and disease

Macrophages are heterogeneous and their phenotype and functions are regulated by the surrounding micro-environment. Macrophages commonly exist in two distinct subsets: 1) Classically activated or M1 macrophages, which are pro-inflammatory and polarized by lipopolysaccharide (LPS) either alone or in association with Th1 cytokines such as IFN-γ, GM-CSF, and produce pro-inflammatory cytokines such as interleukin-1β (IL-1β), IL-6, IL-12, IL-23, and TNF-α; and 2) Alternatively activated or M2 macrophages, which are anti-inflammatory and immunoregulatory and polarized by Th2 cytokines such as IL-4 and IL-13 and produce anti-inflammatory cytokines such as IL-10 and TGF-β. M1 and M2 macrophages have different functions and transcriptional profiles. They have unique abilities by destroying pathogens or repair the inflammation-associated injury. It is known that M1/M2 macrophage balance polarization governs the fate of an organ in inflammation or injury. When the infection or inflammation is severe enough to affect an organ, macrophages first exhibit the M1 phenotype to release TNF-α, IL-1β, IL-12, and IL-23 against the stimulus. But, if M1 phase continues, it can cause tissue damage. Therefore, M2 macrophages secrete high amounts of IL-10 and TGF-β to suppress the inflammation, contribute to tissue repair, remodeling, vasculogenesis, and retain homeostasis. In this review, we first discuss the basic biology of macrophages including origin, differentiation and activation, tissue distribution, plasticity and polarization, migration, antigen presentation capacity, cytokine and chemokine production, metabolism, and involvement of microRNAs in macrophage polarization and function. Secondly, we discuss the protective and pathogenic role of the macrophage subsets in normal and pathological pregnancy, anti-microbial defense, anti-tumor immunity, metabolic disease and obesity, asthma and allergy, atherosclerosis, fibrosis, wound healing, and autoimmunity.

Monocyte chemoattractant protein 1 and fractalkine play opposite roles in angiogenesis via recruitment of different macrophage subtypes

AIM

To explore the interaction between macrophages and chemokines [monocyte chemoattractant protein 1 (MCP-1/CCL2) and fractalkine/CX3CL1] and the effects of their interaction on neovascularization.

METHODS

Human peripheral blood mononuclear cells, donated by healthy volunteers, were separated and cultured in RPMI-1640 medium containing 10% fetal bovine serum, then induced into macrophages by stimulation with 30 µg/L granulocyte macrophage-colony stimulating factor (GM-CSF). The expression of CCR2 and/or CX3CR1 in the macrophages was examined using flow cytometry. Macrophages were then stimulated with recombinant human CCL2 (rh-CCL2) or recombinant human CX3CL1 (rh-CX3CL1). The expression of angiogenesis-related genes, including VEGF-A, THBS-1 and ADAMTS-1 were examined using real-time quantitative polymerase chain reaction (PCR). Supernatants from stimulated macrophages were used in an assay of human retinal endothelial cell (HREC) proliferation. Finally, stimulated macrophages were co-cultured with HREC in a migration assay.

RESULTS

The expression rate of CCR2 in macrophages stimulated by GM-CSF was 42%±1.9%. The expression rate of CX3CR1 was 71%±3.3%. Compared with vehicle-treated groups, gene expression of VEGF-A in the macrophages was greater in 150 mg/L CCL2-treated groups (P<0.05), while expression of THBS-1 and ADAMTS-1 was significantly lower (P<0.05). By contrast, compared with vehicle-treated groups, expression of VEGF-A in 150 mg/L CX3CL1-treated groups was significantly lower (P<0.05), while expression of THBS-1 and ADAMTS-1 was greater (P<0.05). Supernatants from CCL2 treated macrophages promoted proliferation of HREC (P<0.05), while supernatants from CX3CL1-treated macrophages inhibited the proliferation of HREC (P<0.05). HREC migration increased when co-cultured with CCL2-treated macrophages, but decreased with CX3CL1-treated macrophages (P<0.05).

CONCLUSION

CCL2 and CX3CL1 exert different effects in regulation of macrophage in expression of angiogenesis-related factors, including VEGF-A, THBS-1 and ADAMTS-1. Our findings suggest that CCL2 and CX3CL1 may be candidate proteins for further exploration of novel targets for treatment of ocular neovascularization.

MiRNA-Mediated Macrophage Polarization and its Potential Role in the Regulation of Inflammatory Response

Monocytes and macrophages are important components of the immune system, specialized in either removing pathogens as part of innate immunity or contributing to adaptive immunity through antigen presentation. Essential to such functions is classical activation (M1) and alternative activation (M2) of macrophages. M1 polarization of macrophages is characterized by production of pro-inflammatory cytokines, antimicrobial and tumoricidal activity, whereas M2 polarization of macrophages is linked to immunosuppression, tumorigenesis, wound repair, and elimination of parasites. MiRNAs are small non-coding RNAs with the ability to regulate gene expression and network of cellular processes. A number of studies have determined miRNA expression profiles in M1 and M2 polarized human and murine macrophages using microarray and RT-qPCR arrays techniques. More specifically, miR-9, miR-127, miR-155, and miR-125b have been shown to promote M1 polarization while miR-124, miR-223, miR-34a, let-7c, miR-132, miR-146a, and miR-125a-5p induce M2 polarization in macrophages by targeting various transcription factors and adaptor proteins. Further, M1 and M2 phenotypes play distinctive roles in cell growth and progression of inflammation-related diseases such as sepsis, obesity, cancer, and multiple sclerosis. Hence, miRNAs that modulate macrophage polarization may have therapeutic potential in the treatment of inflammation-related diseases. This review highlights recent findings in miRNA expression profiles in polarized macrophages from murine and human sources, and summarizes how these miRNAs regulate macrophage polarization. Last, therapeutic potential of miRNAs in inflammation-related diseases through modulation of macrophage polarization is also discussed.

Macrophage Polarization in Chronic Inflammatory Diseases: Killers or Builders?

Macrophages are key cellular components of the innate immunity, acting as the main player in the first-line defence against the pathogens and modulating homeostatic and inflammatory responses. Plasticity is a major feature of macrophages resulting in extreme heterogeneity both in normal and in pathological conditions. Macrophages are not homogenous, and they are generally categorized into two broad but distinct subsets as either classically activated (M1) or alternatively activated (M2). However, macrophages represent a continuum of highly plastic effector cells, resembling a spectrum of diverse phenotype states. Induction of specific macrophage functions is closely related to the surrounding environment that acts as a relevant orchestrator of macrophage functions. This phenomenon, termed polarization, results from cell/cell, cell/molecule interaction, governing macrophage functionality within the hosting tissues. Here, we summarized relevant cellular and molecular mechanisms driving macrophage polarization in “distant” pathological conditions, such as cancer, type 2 diabetes, atherosclerosis, and periodontitis that share macrophage-driven inflammation as a key feature, playing their dual role as killers (M1-like) and/or builders (M2-like). We also dissect the physio/pathological consequences related to macrophage polarization within selected chronic inflammatory diseases, placing polarized macrophages as a relevant hallmark, putative biomarkers, and possible target for prevention/therapy.

NLRC5 deficiency ameliorates diabetic nephropathy through alleviating inflammation

NOD-like receptor family caspase recruitment domain family domain containing 5 (NLRC5) has important roles in inflammation and innate immunity. NLRC5 was highly expressed in kidney from streptozotocin-induced diabetic mice, db/ db mice and patients with diabetes. Based on that evidence, the present study was designed to explore the roles of NLRC5 in the progression of diabetic nephropathy (DN). We examined kidney injury, including inflammation and fibrosis in Nlrc5 gene knockout ( Nlrc5^-/-) and wild-type (WT) diabetic mice. We found that Nlrc5^-/- mice developed less-severe diabetic kidney injury compared with WT mice, exhibiting lower albuminuria, less fibronectin and collagen IV expression, and reduced macrophage infiltration but greater levels of podocin and nephrin in the diabetic kidney. The underlying mechanisms were further investigated in vitro with peritoneal macrophages and mesangial cells treated with high glucose. Reduced proinflammatory effect was observed in peritoneal macrophages from Nlrc5^-/- mice, associated with NF-κB pathway suppression. Knocking down of NLRC5 in mesangial cells in high-glucose conditions was also associated with reduced NF-κB and TGF-β/Smad signaling. Taken together, NLRC5 promotes inflammation and fibrosis during DN progression partly through the effects on NF-κB and TGF-β/Smad pathways. NLRC5 may, therefore, be a promising therapeutic target for DN treatment.-Luan, P., Zhuang, J., Zou, J., Li, H., Shuai, P., Xu, X., Zhao, Y., Kou, W., Ji, S., Peng, A., Xu, Y., Su, Q., Jian, W., Peng, W. NLRC5 deficiency ameliorates diabetic nephropathy through alleviating inflammation.

Regulation of M1‑type and M2‑type macrophage polarization in RAW264.7 cells by Galectin‑9

Generally considered as a potent pro‑inflammatory signal, β‑galactosidelectin suppresses T cell receptor activation, can both promote and inhibit integrin‑mediated adhesion and is required in nuclear pre‑mRNA splicing. Galectin‑9 (Gal‑9), a member of β‑galactoside lectin, is involved many processes of T cell‑mediated diseases (such as autoimmune diseases and asthma) and immunomodulation of macrophages. Macrophages are involved in the occurrence of inflammation, development and digestion and other stages. At different stages of the inflammatory response, macrophages exhibit different phenotypes, but mainly two subtypes, classically (M1) or alternatively (M2) polarization. The purpose of this work is to investigate the effect of overexpression or knockdown of Gal‑9 on the macrophage polarization. Macrophage polarization was detected by flow cytometric profiling of secreted cytokines and specific surface markers expression, including nitric oxide synthase 2 (NOS2) and mannose receptor 1 (CD206). Protein and mRNA expression levels of TNF‑α, TGF‑β, IL‑6, IL‑10, NF‑κB, signal transducer and activator of transcription (Stat)1 and Stat3 were determined by ELISA, western blot analysis or qRT‑PCR. Our results implied that differentiation of the mouse macrophage line RAW264.7 into M1‑type and M2‑type macrophages is followed by marked variations of Gal‑9 expression. Furthermore, its overexpression and secretion are tightly associated with M2‑type macrophages, whereas its downregulation promotes macrophages to polarize into M1‑type macrophages, which confirmed by elevated CD206 and NOS2, respectively. In response to the changes of Gal‑9 expression, cytokines, transcription factors and regulators, including TNF‑α, IL‑6, NF‑κB, Stat1, TGF‑β, IL‑10, and Stat3, were tightly regulated and significantly associated with classically and alternatively activated macrophages. Consistent with characteristics of M1‑type macrophages, the transcriptional or translational expression levels or activity of TNF‑α, IL‑6, Stat1 and NF‑κB were markedly increased with knockdown of Gal‑9 in macrophages. By contrast, the expression levels or activity of TGF‑β, IL‑10 and Stat3 were clearly elevated in macrophages with Gal‑9 overexpression, which is closely related with M2‑type macrophages. Specific expression and secretion patterns of cytokines, transcription factors and regulators in M1‑type and M2‑type macrophages contribute to better understanding the role of Gal‑9 in regulation in macrophages. This study provides a new insight that Gal‑9 may be a new immunomodulatory target for macrophages.

SOCS molecules: the growing players in macrophage polarization and function

The concept of macrophage polarization is defined in terms of macrophage phenotypic heterogeneity and functional diversity. Cytokines signals are thought to be required for the polarization of macrophage populations toward different phenotypes at different stages in development, homeostasis and disease. The suppressors of cytokine signaling family of proteins contribute to the magnitude and duration of cytokines signaling, which ultimately control the subtle adjustment of the balance between divergent macrophage phenotypes. This review highlights the specific roles and mechanisms of various cytokines family and their negative regulators link to the macrophage polarization programs. Eventually, breakthrough in the identification of these molecules will provide the novel therapeutic approaches for a host of diseases by targeting macrophage phenotypic shift.

[Advances in macrophage function and its anti-inflammatory and proresolving activity and role in periodontitis development]

Macrophage plays an important role in human innate immune system. It has powerful functions, such as recognition, phagocytosis, and bacteria and foreign body removal. Periodontitis, which is a chronic infectious disease characterized by gum inflammation and bone loss, is a major cause of tooth loss in adults. Several studies demonstrated that periodontal tissue destruction is caused by the host immune response defending against infections. As an important part of host immune response, macrophage is also involved in periodontitis pathogenesis. Recently, anti-inflammatory and proresolving activities of macrophage was discovered. Thus, the complex function of macrophage in the occurrence, development, and resolution of inflammation and its potential role in periodontitis were reviewed.

Transcriptional control of microglia phenotypes in health and disease

Microglia are the main resident macrophage population of the CNS and perform numerous functions required for CNS development, homeostasis, immunity, and repair. Many lines of evidence also indicate that dysregulation of microglia contributes to the pathogenesis of neurodegenerative and behavioral diseases. These observations provide a compelling argument to more clearly define the mechanisms that control microglia identity and function in health and disease. In this Review, we present a conceptual framework for how different classes of transcription factors interact to select and activate regulatory elements that control microglia development and their responses to internal and external signals. We then describe functions of specific transcription factors in normal and pathological contexts and conclude with a consideration of open questions to be addressed in the future.

The inhibition of LPS-induced inflammation in RAW264.7 macrophages via the PI3K/Akt pathway by highly N-acetylated chitooligosaccharide

Chitooligosaccharide (COS) has been shown to regulate many biological functions, such as antimicrobial effect and antitumor activity. In the present study, highly N-acetylated chitooligosaccharide (NACOS) was prepared by N-acetylation of COS, and the anti-inflammatory activity of NACOS in macrophages were evaluated. The results indicated NACOS significantly suppressed the LPS-induced pro-inflammatory cytokines interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α) expression. Furthermore, the increased levels of reactive oxygen species (ROS) and nitric oxide (NO) were repressed by NACOS in a dose dependent manner. However, NACOS itself had no significant effect on the cell viability and cellular morphology. Signal transduction studies demonstrated that NACOS remarkably inhibited LPS-enhanced phosphorylation of phosphatidylinositol 3-kinase (PI3K) and Akt. These findings provide a possible molecular mechanism by which NACOS inhibit LPS-induced inflammatory response in macrophages, and a basis for utilizing NACOS in pharmaceutical therapy against inflammation.

Crotoxin stimulates an M1 activation profile in murine macrophages during Leishmania amazonensis infection

American tegumentary leishmaniasis is caused by different species of Leishmania. This protozoan employs several mechanisms to subvert the microbicidal activity of macrophages and, given the limited efficacy of current therapies, the development of alternative treatments is essential. Animal venoms are known to exhibit a variety of pharmacological activities, including antiparasitic effects. Crotoxin (CTX) is the main component of Crotalus durissus terrificus venom, and it has several biological effects. Nevertheless, there is no report of CTX activity during macrophage – Leishmania interactions. Thus, the main objective of this study was to evaluate whether CTX has a role in macrophage M1 polarization during Leishmania infection murine macrophages, Leishmania amazonensis promastigotes and L. amazonensis-infected macrophages were challenged with CTX. MTT [3-(4,5dimethylthiazol-2-yl)-2,5-diphenyl tetrasodium bromide] toxicity assays were performed on murine macrophages, and no damage was observed in these cells. Promastigotes, however, were affected by treatment with CTX (IC50 = 22·86 µg mL−1) as were intracellular amastigotes. Macrophages treated with CTX also demonstrated increased reactive oxygen species production. After they were infected with Leishmania, macrophages exhibited an increase in nitric oxide production that converged into an M1 activation profile, as suggested by their elevated production of the cytokines interleukin-6 and tumour necrosis factor-α and changes in their morphology. CTX was able to reverse the L. amazonensis-mediated inhibition of macrophage immune responses and is capable of polarizing macrophages to the M1 profile, which is associated with a better prognosis for cutaneous leishmaniasis treatment.

β-Patchoulene, isolated from patchouli oil, suppresses inflammatory mediators in LPS-stimulated RAW264.7 macrophages

β-Patchoulene (β-PAE) is a tricyclic sesquiterpene isolated from patchouli oil. According to our previous study, β-PAE has anti-inflammatory activity in vivo; however, its anti-inflammatory response still remains unconfirmed in vitro. Therefore, this study is committed to demonstrate the anti-inflammatory effect of β-PAE on lipopolysaccharide (LPS)-stimulated RAW264.7 macrophages. According to our results, pre-treatment with β-PAE significantly decreased the protein and messenger RNA (mRNA) levels of pro-inflammatory cytokines including tumor necrosis factor-α (TNF-α), interleukin (IL)-6, and IL-1β while increased the expressions of anti-inflammatory cytokines like IL-10 in a dose-dependent manner. In addition, real-time polymerase chain reaction (PCR) also revealed that β-PAE could interrupt the mRNA expressions of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) and thus decreased the levels of nitric oxide (NO) and prostaglandin E2 (PGE2) in LPS-stimulated RAW264.7 macrophages. In conclusion, these results indicated that β-PAE exerted potent anti-inflammatory activity by maintaining the balance between pro- and anti-inflammatory cytokines as well as suppressing iNOS and COX-2 signaling pathways.

Mangiferin antagonizes TNF-α-mediated inflammatory reaction and protects against dermatitis in a mice model

This study aimed to investigate whether mangiferin played a protective role in a well-established dermatitis mouse model and tumor necrosis factor alpha (TNF-α)-induced RAW264.7 macrophages. Contact dermatitis is an inflammatory skin disease in the clinic, while its underlying mechanism still remains to be elucidated. Mangiferin, 1,3,6,7-tetrahydroxyxanthone-C2-β-d-glucoside (C-glucosyl xanthone), a natural antioxidant that was reported to inhibit inflammatory reactions, has been recently proved to be a potential therapy for inflammation. As a result, the oxazolone-induced dermatitis mice models were established to explore whether mangiferin has an anti-inflammatory role in vivo. The phosphate-buffered saline treatment groups showed emblematic skin inflammation, whereas the administration of mangiferin obviously inhibited dermatitis in the mice models. Furthermore, exogenous mangiferin alleviated the inflammatory reaction in TNF-α-induced macrophages by suppressing the production of inflammation- and oxidative stress-associated molecules. Also, mangiferin treatment repressed the activation of nuclear factor-kappaB signaling pathway. To sum up, mangiferin could provide a new target for the therapy and prevention of skin inflammation.

Androgen Deprivation Accelerates the Prostatic Urethra Wound Healing After Thulium Laser Resection of the Prostate by Promoting Re-Epithelialization and Regulating the Macrophage Polarization

BACKGROUND

Complications after a thulium laser resection of the prostate (TmLRP) are related to re-epithelialization of the prostatic urethra. Since prostate growth and development are induced by androgen, the aim of this study was to determine the role and explore the mechanism of androgen in wound healing of the prostatic urethra.

METHODS

Beagles that received TmLRPs were randomly distributed into a castration group, a testosterone undecanoate (TU) group, and a control group. The prostate wound was assessed once a week using a cystoscope. Histological analysis was then carried out to study the re-epithelialization of the prostatic urethra in each group. The inflammatory response in the wound tissue and urine was also investigated.

RESULTS

The healing of the prostatic urethra after a TmLRP was more rapid in the castration group and slower in the TU group than that in the control group. Castration accelerated re-epithelialization by promoting basal cell proliferation in the wound surface and beneath the wound and by accelerating the differentiation of basal cells into urothelial cells. Castration reduced the duration of the inflammatory phase and induced the conversion of M1 macrophages to M2 macrophages, thus accelerating the maturation of the wound. By contrast, androgen supplementation enhanced the inflammatory response and prolonged the inflammatory phase. Moreover, the anti-inflammatory phase was delayed and weakened.

CONCLUSION

Androgen deprivation promotes re-epithelialization of the wound, regulates the inflammatory response, and accelerates wound healing of the prostatic urethra after a TmLRP. Prostate 77:708-717, 2017. © 2017 Wiley Periodicals, Inc.

Effect of iRoot SP and mineral trioxide aggregate (MTA) on the viability and polarization of macrophages

OBJECTIVE

This study was performed to investigate the effect of iRoot SP and mineral trioxide aggregate (MTA) on the viability and polarization of macrophages.

METHODS

The effect of iRoot SP and MTA on the viability of RAW 264.7 macrophages was tested using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay after 1 and 2days of culture. The gene expression levels of interleukin 1β (IL-1β), tumor necrosis factor α (TNF-α), interleukin 10 (IL-10), interleukin 12p40 (IL-12p40) were measured by quantitative real time polymerase chain reaction (qRT-PCR) after stimulation of the RAW 264.7 macrophages with iRoot SP and MTA. The expression levels of CD11c and CD206 in RAW 264.7 macrophages were examined by immunofluorescence and flow cytometry after stimulation with iRoot SP and MTA. The data were analyzed by one-way analysis of variance and the Tukey test.

RESULTS

Both iRoot SP and MTA were non-toxic to the RAW 264.7 macrophages. The use of iRoot SP and MTA increased the expression of IL-1β, TNF-α, IL-10, IL-12p40 on the first day of culture and could promote macrophage M1 and M2 polarization.

CONCLUSIONS

MTA and iRoot SP have good biocompatibility with macrophages, and they induced both M1 and M2 polarization of the RAW 264.7 macrophages.

Human macrophages chronically exposed to LPS can be reactivated by stimulation with MDP to acquire an antimicrobial phenotype

Macrophages are important in host defense and can differentiate into functionally distinct subsets named classically (M1) or alternatively (M2) activated. In several inflammatory disorders, macrophages become tolerized to prevent deleterious consequences. This tolerization reduces the ability of macrophages to respond to bacterial components (e.g., LPS) maintaining a low level of inflammation but compromising the ability of macrophages to mount an effective immune response during subsequent pathogen encounters. In this study, we aimed to reactivate human monocyte-derived macrophages chronically exposed to LPS by re-stimulation with muramyl dipeptide (MDP). We observed an undefined profile of cell surface marker expression during endotoxin tolerance and absence of TNFα production. Stimulating macrophages chronically exposed to LPS with LPS+MDP restored TNFα, production together with an increased production of IL1, IL6, IFNγ, IL4, IL5 and IL10. These results suggest that macrophages chronically exposed to LPS possess a mixed M1-M2 phenotype with sufficient antimicrobial and homeostatic potential.

Elimination of the unnecessary: Intra- and extracellular signaling by anionic phospholipids

High fidelity of biological systems is frequently achieved by duplication of the essential intracellular machineries or, removal of the entire cell, which becomes unnecessary or even harmful in altered physiological environments. Carefully controlled removal of these cells, without damaging normal cells, requires precise signaling, and is critical to maintaining homeostasis. This review describes how two anionic phospholipids - phosphatidylserine (PS) and cardiolipin (CL) - residing in distinct compartments of the cell, signal removal of "the unnecessary" using several uniform principles. One of these principles is realized by collapse of inherent transmembrane asymmetry and the externalization of the signal on the outer membrane surface - mitochondria for CL and the plasma membrane for PS - to trigger mitophagy and phagocytosis, respectively. Release from damaged cells of intracellular structures with externalized CL or externalized PS triggers their elimination by phagocytosis. Another of these principles is realized by oxidation of polyunsaturated species of CL and PS. Highly specific oxidation of CL by cytochrome c serves as a signal for mitochondria-dependent apoptosis, while oxidation of externalized PS improves its effectiveness to trigger phagocytosis of effete cells.

Characterization of adipose tissue macrophages and adipose-derived stem cells in critical wounds

Background

Subcutaneous adipose tissue is a rich source of adipose tissue macrophages and adipose-derived stem cells which both play a key role in wound repair. While macrophages can be divided into the classically-activated M1 and the alternatively-activated M2 phenotype, ASCs are characterized by the expression of specific stem cell markers.

Methods

In the present study, we have investigated the expression of common macrophage polarization and stem cell markers in acutely inflamed adipose tissue. Subcutaneous adipose tissue adjacent to acutely inflamed wounds of 20 patients and 20 healthy subjects were harvested and underwent qPCR and flow cytometry analysis.

Results

Expression levels of the M1-specific markers CD80, iNOS, and IL-1b were significantly elevated in inflammatory adipose tissue when compared to healthy adipose tissue, whereas the M2-specific markers CD163 and TGF-β were decreased. By flow cytometry, a significant shift of adipose tissue macrophage populations towards the M1 phenotype was confirmed. Furthermore, a decrease in the mesenchymal stem cell markers CD29, CD34, and CD105 was observed whereas CD73 and CD90 remained unchanged.

Discussion

This is the first report describing the predominance of M1 adipose tissue macrophages and the reduction of stem cell marker expression in acutely inflamed, non-healing wounds.

Bioglass promotes wound healing through modulating the paracrine effects between macrophages and repairing cells

Bioglass stimulates macrophages to switch to the M2 phenotype and modulates the paracrine effects between macrophages and repairing cells.

MiR-130b promotes obesity associated adipose tissue inflammation and insulin resistance in diabetes mice through alleviating M2 macrophage polarization via repression of PPAR-γ

Inflammatory pathways play an important role in impaired glucose metabolism and insulin production. Adipose tissue inflammation is characterized by infiltration and expansion of macrophages, leading to type 2 diabetes (T2D). Macrophage polarization contributes to various inflammatory responses and cytokine production profiles. MiR-130b is involved in regulating immune response and metabolism. However, the specific role in macrophage polarization and glucose metabolism of T2D has not been reported. In this study, C57BL/6 mice were fed a high-fat diet to induce T2D mice model. The peritoneal macrophages were isolated, miR-130b and M1/M2 polarization was analyzed. Glucose tolerance was also detected. In addition, the relationship between miR-130b and the target gene was identified. We showed that mice fed on high-fat diet demonstrated significantly higher body weight and impaired glucose tolerance. In addition, the miR-130b level was up-regulated in macrophage of high-fat diet mice, which regulated M1/M2 polarization, adipose tissue inflammation and glucose tolerance. Furthermore, we identified PPAR-γ as a miR-130b target gene and regulated macrophage polarization. In summary, our findings demonstrated that miR-130b was a novel regulator of macrophage polarization and contributed to adipose tissue inflammation and insulin tolerance via repression of PPAR-γ. Furthermore, miR-130b represented a promising target for T2D therapy in the clinic.

Modification of TAK1 by O-linked N-acetylglucosamine facilitates TAK1 activation and promotes M1 macrophage polarization

Macrophages play many different roles in tissue inflammation and immunity, and the plasticity of macrophage polarization is closely associated with acute inflammatory responses. O-GlcNAcylation is an important type of post-translational modification, which subtly modulates inflammation responses. Transforming growth factor (TGF)-β-activated kinase 1 (TAK1) is a key serine/threonine protein kinase that mediates signals transduced by pro-inflammatory cytokines such as TGF-β, tumor necrosis factor (TNF), and interleukin-1 (IL-1). It is here reported that TGFβ-activated kinase (TAK1) is modified with N-acetylglucosamine (O-GlcNAc) on S427. Both IL-1 and osmotic stress, which are known as the TAK1-signaling inducers, significantly trigger the O-GlcNAcylation of TAK1 in macrophages. By overexpressing wild-type (WT) or S427A TAK1 mutant into macrophages, it was determined that O-GlcNAcylation of TAK1 on S427 is required for T187/S192 phosphorylation and full activation of TAK1 upon stimulation with IL-1α and NaCl. Aborting O-GlcNAcylation of TAK1 on S427 was found to inhibit the downstream JNK and nuclear factor-κB activation and reduce the final amount of cytokines produced in activated macrophages to a great extent. Results also showed that overexpression of the O-GlcNAcylation-deficient mutant of TAK1 promotes LPS-mediated apoptosis in macrophages. Importantly, TAK1 O-GlcNAcylation was found to promote M1 macrophage polarization in activated macrophages. Taken together, these data demonstrate that O-GlcNAcylation of TAK1 on S427 critically regulates the pro-inflammatory activation and M1 polarization of macrophages via modulation of the TAK1/JNK/NF-κB signaling pathway.

The molecular mechanisms of action of PPAR-γ agonists in the treatment of corneal alkali burns (Review)

Corneal alkali burns (CAB) are characterized by injury-induced inflammation, fibrosis and neovascularization (NV), and may lead to blindness. This review evaluates the current knowledge of the molecular mechanisms responsible for CAB. The processes of cytokine production, chemotaxis, inflammatory responses, immune response, cell signal transduction, matrix metalloproteinase production and vascular factors in CAB are discussed. Previous evidence indicates that peroxisome proliferator-activated receptor γ (PPAR-γ) agonists suppress immune responses, inflammation, corneal fibrosis and NV. This review also discusses the role of PPAR-γ as an anti-inflammatory, anti-fibrotic and anti-angiogenic agent in the treatment of CAB, as well as the potential role of PPAR-γ in the pathological process of CAB. There have been numerous studies evaluating the clinical profiles of CAB, and the aim of this systematic review was to summarize the evidence regarding the treatment of CAB with PPAR-γ agonists.

Adipocyte-specific CD1d-deficiency mitigates diet-induced obesity and insulin resistance in mice

It has been shown that CD1d expression and glycolipid-reactive, CD1d-restricted NKT cells exacerbate the development of obesity and insulin resistance in mice. However, the relevant CD1d-expressing cells that influence the effects of NKT cells on the progression of obesity remain incompletely defined. In this study, we have demonstrated that 3T3-L1 adipocytes can present endogenous ligands to NKT cells, leading to IFN-γ production, which in turn, stimulated 3T3-L1 adipocytes to enhance expression of CD1d and CCL2, and decrease expression of adiponectin. Furthermore, adipocyte-specific CD1d deletion decreased the size of the visceral adipose tissue mass and enhanced insulin sensitivity in mice fed a high-fat diet (HFD). Accordingly, NKT cells were less activated, IFN-γ production was significantly reduced, and levels of adiponectin were increased in these animals as compared with control mice on HFD. Importantly, macrophage recruitment into the adipose tissue of adipocyte-specific CD1d-deficient mice was significantly blunted. These findings indicate that interactions between NKT cells and CD1d-expressing adipocytes producing endogenous NKT cell ligands play a critical role in the induction of inflammation and functional modulation of adipose tissue that leads to obesity.