Establishment of Green Fluorescent Protein and Firefly Luciferase Expressing Mouse Primary Macrophages for In Vivo Bioluminescence Imaging

Macrophages play a key role in tissue homeostasis as well as in a range of pathological conditions including atherosclerosis, cancer, and autoimmunity. Many aspects of their in vivo behavior are, however, poorly understood. Bioluminescence imaging (BLI) with green fluorescent protein (GFP) and firefly luciferase (FLUC) labelled autologous reporter macrophages could potentially offer a powerful tool to study macrophage biology, but this approach has been hindered by the relative difficulty of efficient gene transfer into primary macrophages. Here we describe a straightforward method for producing large numbers of GFP/FLUC expressing mouse primary macrophages utilizing lentivirus vector, cyclosporine, and a double infection strategy. Using this method we achieved up to 60% of macrophages to express GFP with correspondingly high FLUC signal. When injected into the circulation using a mouse model of local biomaterial induced inflammation and osteolysis, macrophages were initially detectable within the lungs, followed by systemic homing to the local area of chronic inflammation in the distal femur. In addition, transduced macrophages maintained their ability to assume M1 and M2 phenotypes although the GFP/FLUC expression was altered by the polarizing signals. These reporter macrophages could prove to be valuable tools to study the role of macrophages in health and disease.     

Selective suppression of M1 macrophages is involved in zinc inhibition of liver fibrosis in mice

Zinc deficiency is common in the liver of patients with chronic liver disease. Zinc supplementation suppresses the progression of liver fibrosis induced by bile duct ligation (BDL) in mice. The present study was undertaken to specifically investigate a possible mechanism by which zinc plays this role in the liver. Kunming mice were subjected to BDL for 4 weeks to induce liver fibrosis, and concomitantly treated with zinc sulfite or saline as control by gavage once a day. The results showed that zinc supplementation significantly suppressed liver fibrosis and inflammation along with inhibition of hepatic stellate cells activation induced by BDL. These inhibitory effects were accompanied by the reduction of collagen deposition and a significant reduction of macrophage infiltration affected livers. Importantly, zinc selectively inhibited M1 macrophage polarization and M1-related inflammatory cytokines. This inhibitory effect was further confirmed by the reduction of relevant biomarkers of M1 macrophages including inducible NO synthase (iNOS), monocyte chemotactic protein-1 (MCP-1/CCL2), and tumor necrosis factor-α in the zinc supplemented BDL livers. In addition, zinc inhibition of M1 macrophages was associated with a decrease of Notch1 expression. Taken together, these data indicated that zinc supplementation inhibited liver inflammation and fibrosis in BDL mice through selective suppression of M1 macrophages, which is associated with inhibition of Notch1 pathway in M1 macrophage polarization.     

Systemic and Cardiac Depletion of M2 Macrophage through CSF-1R Signaling Inhibition Alters Cardiac Function Post Myocardial Infarction

The heart hosts tissue resident macrophages which are capable of modulating cardiac inflammation and function by multiple mechanisms. At present, the consequences of phenotypic diversity in macrophages in the heart are incompletely understood. The contribution of cardiac M2-polarized macrophages to the resolution of inflammation and repair response following myocardial infarction remains to be fully defined. In this study, the role of M2 macrophages was investigated utilising a specific CSF-1 receptor signalling inhibition strategy to achieve their depletion. In mice, oral administration of GW2580, a CSF-1R kinase inhibitor, induced significant decreases in Gr1^lo and F4/80^hi monocyte populations in the circulation and the spleen. GW2580 administration also induced a significant depletion of M2 macrophages in the heart after 1 week treatment as well as a reduction of cardiac arginase1 and CD206 gene expression indicative of M2 macrophage activity. In a murine myocardial infarction model, reduced M2 macrophage content was associated with increased M1-related gene expression (IL-6 and IL-1β), and decreased M2-related gene expression (Arginase1 and CD206) in the heart of GW2580-treated animals versus vehicle-treated controls. M2 depletion was also associated with a loss in left ventricular contractile function, infarct enlargement, decreased collagen staining and increased inflammatory cell infiltration into the infarct zone, specifically neutrophils and M1 macrophages. Taken together, these data indicate that CSF-1R signalling is critical for maintaining cardiac tissue resident M2-polarized macrophage population, which is required for the resolution of inflammation post myocardial infarction and, in turn, for preservation of ventricular function.     

M2 macrophages induced by prostaglandin E2 and IL-6 from cervical carcinoma are switched to activated M1 macrophages by CD4+ Th1 cells

Monocytes attracted by tumor-induced chronic inflammation differentiate to APCs, the type of which depends on cues in the local tumor milieu. In this work, we studied the influence of human cervical cancer cells on monocyte differentiation and showed that the majority of cancer cells either hampered monocyte to dendritic cell differentiation or skewed their differentiation toward M2-like macrophages. Blocking studies revealed that M2 differentiation was caused by tumor-produced PGE(2) and IL-6. TGF-β, IL-10, VEGF, and macrophage colony-stimulating factor did not play a role. Notably, these CD14(+)CD163(+) M2 macrophages were also detected in situ. Activation of cancer cell-induced M2-like macrophages by several TLR-agonists revealed that compared with dendritic cells, these M2 macrophages displayed a tolerogenic phenotype reflected by a lower expression of costimulatory molecules, an altered balance in IL-12p70 and IL-10 production, and a poor capacity to stimulate T cell proliferation and IFN-γ production. Notably, upon cognate interaction with Th1 cells, these tumor-induced M2 macrophages could be switched to activated M1-like macrophages that expressed high levels of costimulatory molecules, produced high amounts of IL-12 and low amounts of IL-10, and acquired the lymphoid homing marker CCR7. The effects of the interaction between M2 macrophages and Th1 cells could partially be mimicked by activation of these APCs via CD40 in the presence of IFN-γ. Our data on the presence, induction, and plasticity of tumor-induced tolerogenic APCs in cervical cancer suggest that tumor-infiltrated Th1 cells can stimulate a tumor-rejecting environment by switching M2 macrophages to classical proinflammatory M1 macrophages.     

Moderate Increase of Indoxyl Sulfate Promotes Monocyte Transition into Profibrotic Macrophages

Objective

The uremic toxin Indoxyl-3-sulphate (IS), a ligand of Aryl hydrocarbon Receptor (AhR), raises in blood during early renal dysfunction as a consequence of tubular damage, which may be present even when eGFR is normal or only moderately reduced, and promotes cardiovascular damage and monocyte-macrophage activation. We previously found that patients with abdominal aortic aneurysms (AAAs) have higher CD14⁺CD16⁺ monocyte frequency and prevalence of moderate chronic kidney disease (CKD) than age-matched control subjects. Here we aimed to evaluate the IS levels in plasma from AAA patients and to investigate in vitro the effects of IS concentrations corresponding to mild-to-moderate CKD on monocyte polarization and macrophage differentiation.

Methods

Free IS plasma levels, monocyte subsets and laboratory parameters were evaluated on blood from AAA patients and eGFR-matched controls. THP-1 monocytes, treated with IS 1, 10, 20 μM were evaluated for CD163 expression, AhR signaling and then induced to differentiate into macrophages by PMA. Their phenotype was evaluated both at the stage of semi-differentiated and fully differentiated macrophages. AAA and control sera were similarly used to treat THP-1 monocytes and the resulting macrophage phenotype was analyzed.

Results

IS plasma concentration correlated positively with CD14⁺CD16⁺ monocytes and was increased in AAA patients. In THP-1 cells, IS promoted CD163 expression and transition to macrophages with hallmarks of classical (IL-6, CCL2, COX2) and alternative phenotype (IL-10, PPARγ, TGF-β, TIMP-1), via AhR/Nrf2 activation. Analogously, AAA sera induced differentiation of macrophages with enhanced IL-6, MCP1, TGF-β, PPARγ and TIMP-1 expression.

Conclusion

IS skews monocyte differentiation toward low-inflammatory, profibrotic macrophages and may contribute to sustain chronic inflammation and maladaptive vascular remodeling.     

The Role of M2 Macrophages in the Progression of Chronic Kidney Disease following Acute Kidney Injury

Introduction

Acute kidney injury (AKI) is a major risk factor in the development of chronic kidney disease (CKD). However, the mechanisms linking AKI to CKD remain unclear. We examined the alteration of macrophage phenotypes during an extended recovery period following ischemia/reperfusion injury (IRI) and determine their roles in the development of fibrosis.

Methods

The left renal pedicle of mice was clamped for 40 min. To deplete monocyte/macrophage, liposome clodronate was injected or CD11b-DTR and CD11c-DTR transgenic mice were used.

Results

Throughout the phase of IRI recovery, M2-phenotype macrophages made up the predominant macrophage subset. On day 28, renal fibrosis was clearly shown with increased type IV collagen and TGF-β. The depletion of macrophages induced by the liposome clodronate injection improved renal fibrosis with a reduction of kidney IL-6, type IV collagen, and TGF-β levels. Additionally, the adoptive transfer of the M2c macrophages partially reversed the beneficial effect of macrophage depletion, whereas the adoptive transfer of the M1 macrophages did not. M2 macrophages isolated from the kidneys during the recovery phase expressed 2.5 fold higher levels of TGF-β than the M1 macrophages. The injection of the diphtheria toxin into CD11b or CD11c-DTR transgenic mice resulted in lesser depletion or no change in M2 macrophages and had little impact on renal fibrosis.

Conclusion

Although M2 macrophages are known to be indispensible for short-term recovery, they are thought to be main culprit in the development of renal fibrosis following IRI.     

BMP-7 Treatment Increases M2 Macrophage Differentiation and Reduces Inflammation and Plaque Formation in Apo E-/- Mice

Inflammation plays a fundamental role in the inception and development of atherosclerosis (ATH). Mechanisms of inflammation include the infiltration of monocytes into the injured area and subsequent differentiation into either pro-inflammatory M1 macrophages or anti-inflammatory M2 macrophages. We have previously published data suggesting bone morphogenetic protein-7 (BMP-7) enhances M2 macrophage differentiation and anti-inflammatory cytokine secretion in vitro. In this regard, we hypothesized BMP-7 would inhibit plaque formation in an animal model of ATH through monocytic plasticity mediation. ATH was generated in male and female Apo E^-/- mice via partial left carotid artery (PLCA) ligation and mice were divided into 3 groups: Sham, PLCA, and PLCA+BMP-7 (200ug/kg; i.v.). Our data suggest that BMP-7 inhibits plaque formation and increases arterial systolic velocity. Furthermore, we report inhibition of monocyte infiltration and a decrease in associated pro-inflammatory cytokines (MCP-1, TNF-α, and IL-6) in the PLCA+BMP-7 mice. In contrast, our data suggest a significant (p<0.05) increase in M2 macrophage populations with consequential enhanced anti-inflammatory cytokine (IL-1RA, IL-10, and Arginase 1) expression following BMP-7 treatment. We have also observed that mechanisms promoting monocyte into M2 macrophage differentiation by BMP-7 involve the upregulation and activation of the BMP-7 receptor (BMP-7RII). In conclusion, we report that BMP-7 has the potential to mediate cellular plasticity and mitigate the inflammatory immune response, which results in decreased plaque formation and improved blood velocity.     

Control of macrophage lineage populations by CSF-1 receptor and GM-CSF in homeostasis and inflammation

There is recent interest in the role of monocyte/macrophage subpopulations in pathology. How the hemopoietic growth factors, macrophage-colony stimulating factor (M-CSF or CSF-1) and granulocyte macrophage (GM)-CSF, regulate their in vivo development and function is unclear. A comparison is made here on the effect of CSF-1 receptor (CSF-1R) and GM-CSF blockade/depletion on such subpopulations, both in the steady state and during inflammation. In the steady state, administration of neutralizing anti-CSF-1R monoclonal antibody (mAb) rapidly (within 3-4 days) lowered, specifically, the number of the more mature Ly6C(lo) peripheral blood murine monocyte population and resident peritoneal macrophages; it also reduced the accumulation of murine exudate (Ly6C(lo)) macrophages in two peritonitis models and alveolar macrophages in lung inflammation, consistent with a non-redundant role for CSF-1 (or interleukin-34) in certain inflammatory reactions. A neutralizing mAb to GM-CSF also reduced inflammatory macrophage numbers during antigen-induced peritonitis and lung inflammation. In GM-CSF gene-deficient mice, a detailed kinetic analysis of monocyte/macrophage and neutrophil dynamics in antigen-induced peritonitis suggested that GM-CSF was acting, in part, systemically to maintain the inflammatory reaction. A model is proposed in which CSF-1R signaling controls the development of the macrophage lineage at a relatively late stage under steady state conditions and during certain inflammatory reactions, whereas in inflammation, GM-CSF can be required to maintain the response by contributing to the prolonged extravasation of immature monocytes and neutrophils. A correlation has been observed between macrophage numbers and the severity of certain inflammatory conditions, and it could be that CSF-1 and GM-CSF contribute to the control of these numbers in the ways proposed.     

Vascular risk factors and renal failure

Patients with chronic kidney disease (CKD) have a substantially increased risk of cardiovascular disease (CVD) compared with the general population. The high prevalence of established traditional risk factors for atherosclerosis (diabetes, hypertension, dyslipidemia) in these patients undoubtedly contributes to the accelerated rate of vascular disease. In addition, several hypotheses have emerged to explain the high prevalence of CVD in patients with chronic renal failure. Growing evidence has been gathered over the last 15 years regarding the role of uremia-related risk factors such as inflammation and oxidant stress in the pathogenesis of atherosclerosis in subjects with renal failure. This paper will review current knowledge regarding the potential role of these non-traditional or uremia-related risk factors for atherosclerosis with special emphasis on prevalence, cardiac risk, and management in patients with CKD.     

Macrophages heterogeneity in atherosclerosis – implications for therapy

Atherosclerosis is a chronic inflammatory disease occurring within the artery wall and is an underlying cause of cardiovascular complications, including myocardial infarction, stroke and peripheral vascular disease. Its pathogenesis involves many immune cell types with a well accepted role for monocyte/macrophages. Cholesterol-loaded macrophages are a characteristic feature of plaques and are major players in all stages of plaque development. As well as modulating lipid metabolism, macrophages secrete inflammatory cytokines, chemokines and reactive oxygen and nitrogen species that drive pathogenesis. They also produce proteases and tissue factor that contribute to plaque rupture and thrombosis. Macrophages are however heterogeneous cells and when appropriately activated, they phagocytose cytotoxic lipoproteins, clear apoptotic bodies, secrete anti-inflammatory cytokines and synthesize matrix repair proteins that stabilize vulnerable plaques. Pharmacological modulation of macrophage activity therefore represents a potential therapeutic strategy for atherosclerosis. The aim of this review is to provide an overview of the current understanding of the different macrophage subsets and their monocyte precursors, and, the implications of these subsets for atherosclerosis. This will present a foundation for highlighting novel opportunities to exploit the heterogeneity of macrophages as important diagnostic and therapeutic targets for atherosclerosis and its associated diseases.     

Intravital lipid droplet labeling and imaging reveals the phenotypes and functions of individual macrophages in vivo

Macrophages play pivotal roles in the maintenance of tissue homeostasis. However, the reactivation of macrophages toward proinflammatory states correlates with a plethora of inflammatory diseases, including atherosclerosis, obesity, neurodegeneration, and bone marrow (BM) failure syndromes. The lack of methods to reveal macrophage phenotype and function in vivo impedes the translational research of these diseases. Here, we found that proinflammatory macrophages accumulate intracellular lipid droplets (LDs) relative to resting or noninflammatory macrophages both in vitro and in vivo, indicating that LD accumulation serves as a structural biomarker for macrophage phenotyping. To realize the staining and imaging of macrophage LDs in vivo, we developed a fluorescent fatty acid analog-loaded poly(lactic-co-glycolic acid) nanoparticle to label macrophages in mice with high efficiency and specificity. Using these novel nanoparticles, we achieved in situ functional identification of single macrophages in BM, liver, lung, and adipose tissues under conditions of acute or chronic inflammation. Moreover, with this intravital imaging platform, we further realized in vivo phenotyping of individual macrophages in the calvarial BM of mice under systemic inflammation. In conclusion, we established an efficient in vivo LD labeling and imaging system for single macrophage phenotyping, which will aid in the development of diagnostics and therapeutic monitoring. Moreover, this method also provides new avenues for the study of lipid trafficking and dynamics in vivo.     

Vitamin D Suppression of Endoplasmic Reticulum Stress Promotes an Antiatherogenic Monocyte/Macrophage Phenotype in Type 2 Diabetic Patients

Cardiovascular disease is the leading cause of morbidity/mortality in patients with type 2 diabetes mellitus (T2DM), but there is a lack of knowledge about the mechanism(s) of increased atherosclerosis in these patients. In patients with T2DM, the prevalence of 25-hydroxy vitamin D (25(OH)D) deficiency is almost twice that for nondiabetics and doubles the relative risk of developing cardiovascular disease compared with diabetic patients with normal 25(OH)D. We tested the hypothesis that monocytes from vitamin D-deficient subjects will have a proatherogenic phenotype compared with vitamin D-sufficient subjects in 43 patients with T2DM. Serum 25(OH)D level inversely correlated with monocyte adhesion to endothelial cells even after adjustment for demographic and comorbidity characteristics. Vitamin D-sufficient patients (≥30 ng/ml 25(OH)D) had lower monocyte endoplasmic reticulum (ER) stress, a predominance of M1 over M2 macrophage membrane receptors, and decreased mRNA expression of monocyte adhesion molecules PSGL-1, β₁-integrin, and β₂-integrin compared with patients with 25(OH)D levels of <30 ng/ml. In vitamin D-deficient macrophages, activation of ER stress increased adhesion and adhesion molecule expression and induced an M2-predominant phenotype. Moreover, adding 1,25(OH)₂D₃ to vitamin D-deficient macrophages shifted their phenotype toward an M1-predominant phenotype with suppressed adhesion. Conversely, deletion of the vitamin D receptor in macrophages from diabetic patients activated ER stress, accelerated adhesion, and increased adhesion molecule expression. The absence of ER stress protein CCAAT enhancer-binding protein homologous protein suppressed monocyte adhesion, adhesion molecule expression, and the M2-predominant phenotype induced by vitamin D deficiency. Thus, vitamin D is a natural ER stress reliever that induced an antiatherogenic monocyte/macrophage phenotype.     

TGF-beta driven lung fibrosis is macrophage dependent and blocked by Serum amyloid P

The pleiotropic growth factor TGFβ(1) promotes many of the pathogenic mechanisms observed in lung fibrosis and airway remodeling, such as aberrant extracellular matrix deposition due to both fibroblast activation and fibroblast to myofibroblast differentiation. Serum amyloid P (SAP), a member of the pentraxin family of proteins inhibits bleomycin-induced lung fibrosis through an inhibition of pulmonary fibrocyte and pro-fibrotic alternative (M2) macrophage accumulation. It is unknown if SAP has effects downstream of TGFβ(1), a major mediator of pulmonary fibrosis. Using the lung specific TGFβ(1) transgenic mouse model, we determined that SAP inhibits all of the pathologies driven by TGFβ(1) including apoptosis, airway inflammation, pulmonary fibrocyte accumulation and collagen deposition, without affecting levels of TGFβ(1). To explore the role of monocyte derived cells in this model we used liposomal clodronate to deplete pulmonary macrophages. This led to pronounced anti-fibrotic effects that were independent of fibrocyte accumulation. Administration of SAP mirrored these effects and reduced both pulmonary M2 macrophages and increased chemokine IP10/CXCL10 expression in a SMAD 3-independent manner. Interestingly, SAP concentrations were reduced in the circulation of IPF patients and correlated with disease severity. Last, SAP directly inhibited M2 macrophage differentiation of monocytes obtained from these patients. These data suggest that the beneficial anti-fibrotic effects of SAP in TGFβ(1)-induced lung disease are via modulating monocyte responses.     

Tumor associated macrophages and neutrophils in tumor progression

Tumor‐associated macrophages (TAMs) are a key component of the tumor microenvironment and orchestrate various aspects of cancer. Diversity and plasticity are hallmarks of cells of the monocyte–macrophage lineage. In response to distinct signals macrophages undergo M1 (classical) or M2 (alternative) activation, which represent extremes of a continuum in a spectrum of activation states. Metabolic adaptation is a key component of macrophage plasticity and polarization, instrumental to their function in homeostasis, immunity and inflammation. Generally, TAMs acquire an M2‐like phenotype that plays important roles in many aspects of tumor growth and progression. There is now evidence that also neutrophils can be driven towards distinct phenotypes in response to microenvironmental signals. The identification of mechanisms and molecules associated with macrophage and neutrophil plasticity and polarized activation provides a basis for new diagnostic and therapeutic strategies. J. Cell. Physiol. 228: 1404–1412, 2013. © 2012 Wiley Periodicals, Inc.     

Adiponectin Promotes Macrophage Polarization toward an Anti-inflammatory Phenotype

It is established that the adipocyte-derived cytokine adiponectin protects against cardiovascular and metabolic diseases, but the effect of this adipokine on macrophage polarization, an important mediator of disease progression, has never been assessed. We hypothesized that adiponectin modulates macrophage polarization from that resembling a classically activated M1 phenotype to that resembling alternatively-activated M2 cells. Peritoneal macrophages and the stromal vascular fraction (SVF) cells of adipose tissue isolated from adiponectin knock-out mice displayed increased M1 markers, including tumor necrosis factor-α, interleukin-6, and monocyte chemoattractant protein-1 and decreased M2 markers, including arginase-1, macrophage galactose N-acetyl-galactosamine specific lectin-1, and interleukin-10. The systemic delivery of adenovirus expressing adiponectin significantly augmented arginase-1 expression in peritoneal macrophages and SVF cells in both wild-type and adiponectin knock-out mice. In culture, the treatment of macrophages with recombinant adiponectin protein led to an increase in the levels of M2 markers and a reduction of reactive oxygen species and reactive oxygen species-related gene expression. Adiponectin also stimulated the expression of M2 markers and attenuated the expression of M1 markers in human monocyte-derived macrophages and SVF cells isolated from human adipose tissue. These data show that adiponectin functions as a regulator of macrophage polarization, and they indicate that conditions of high adiponectin expression may deter metabolic and cardiovascular disease progression by favoring an anti-inflammatory phenotype in macrophages.     

Naringenin suppresses macrophage infiltration into adipose tissue in an early phase of high-fat diet-induced obesity

Obese adipose tissue is characterized by increased macrophage infiltration, which results in chronic inflammation in adipose tissue and leads to obesity-related diseases such as type 2 diabetes mellitus and atherosclerosis. The regulation of macrophage infiltration into adipose tissue is an important strategy for preventing and treating obesity-related diseases. In this study, we report that naringenin, a citrus flavonoid, suppressed macrophage infiltration into adipose tissue induced by short-term (14 days) feeding of a high-fat diet in mice; although naringenin did not show any differences in high-fat diet-induced changes of serum biochemical parameters in this short administration period. Naringenin suppressed monocyte chemoattractant protein-1 (MCP-1) in adipose tissue, and this effect was mediated in part through inhibition of c-Jun NH₂-terminal kinase pathway. Naringenin also inhibited MCP-1 expression in adipocytes, macrophages, and a co-culture of adipocytes and macrophages. Our results suggest a mechanism by which daily consumption of naringenin may exhibit preventive effects on obesity-related diseases.     

Macrophages mediate lung inflammation in a mouse model of ischemic acute kidney injury

Serum IL-6 is increased in acute kidney injury (AKI) and inhibition of IL-6 reduces AKI-mediated lung inflammation. We hypothesized that circulating monocytes produce IL-6 and that alveolar macrophages mediate lung inflammation after AKI via chemokine (CXCL1) production. To investigate systemic and alveolar macrophages in lung injury after AKI, sham operation or 22 min of renal pedicle clamping (AKI) was performed in three experimental settings: 1) systemic macrophage depletion via diphtheria toxin (DT) injection to CD11b-DTR transgenic mice, 2) DT injection to wild-type mice, and 3) alveolar macrophage depletion via intratracheal (IT) liposome-encapsulated clodronate (LEC) administration to wild-type mice. In mice with AKI and systemic macrophage depletion (CD11b-DTR transgenic administered DT) vs. vehicle-treated AKI, blood monocytes and lung interstitial macrophages were reduced, renal function was similar, serum IL-6 was increased, lung inflammation was improved, lung CXCL1 was reduced, and lung capillary leak was increased. In wild-type mice with AKI administered DT vs. vehicle, serum IL-6 was increased. In mice with AKI and alveolar macrophage depletion (IT-LEC) vs. AKI with normal alveolar macrophage content, blood monocytes and lung interstitial macrophages were similar, alveolar macrophages were reduced, renal function was similar, lung inflammation was improved, lung CXCL1 was reduced, and lung capillary leak was increased. In conclusion, administration of DT in AKI is proinflammatory, limiting the use of the DTR-transgenic model to study systemic effects of AKI. Mice with AKI and either systemic mononuclear phagocyte depletion or alveolar macrophage depletion had reduced lung inflammation and lung CXCL1, but increased lung capillary leak; thus, mononuclear phagocytes mediate lung inflammation, but they protect against lung capillary leak after ischemic AKI. Since macrophage activation and chemokine production are key events in the development of acute lung injury (ALI), these data provide further evidence that AKI may cause ALI.     

Emerging role of targeting macrophages in rheumatoid arthritis: Focus on polarization,metabolism and apoptosis

Macrophages maintain a dynamic balance in physiology. Various known or unknown microenvironmental signals influence the polarization, activation and death of macrophages, which creates an imbalance that leads to disease. Rheumatoid arthritis (RA) is characterized by the massive infiltration of a variety of chronic inflammatory cells in synovia. Abundant activated macrophages found in RA synovia are an early hallmark of RA, and the number of these macrophages can be decreased after effective treatment. In RA, the proportion of M1 (pro‐inflammatory macrophages) is higher than that of M2 (anti‐inflammatory macrophages). The increased pro‐inflammatory ability of macrophages is related to their excessive activation and proliferation as well as an enhanced anti‐apoptosis ability. At present, there are no clinical therapies specific to macrophages in RA. Understanding the mechanisms and functional consequences of the heterogeneity of macrophages will aid in confirming their potential role in inflammation development. This review will outline RA‐related macrophage properties (focus on polarization, metabolism and apoptosis) as well as the origin of macrophages. The molecular mechanisms that drive macrophage properties also be elucidated to identify novel therapeutic targets for RA and other autoimmune disease.     

Tissue-type Plasminogen Activator (tPA) Promotes M1 Macrophage Survival through p90 Ribosomal S6 Kinase (RSK) and p38 Mitogen-activated Protein Kinase (MAPK) Pathway

Macrophage accumulation is one of the hallmarks of progressive kidney disease. Resting macrophages have a finite lifespan, but become resistant to apoptosis in response to pathogenic cues, whereas the underlying mechanism remains unknown. Tissue-type plasminogen activator (tPA), a protease up-regulated in the kidneys with chronic injury, has been shown to promote macrophage accumulation and renal inflammation. We hypothesized that tPA may be the endogenous factor that promotes macrophage survival and extends their lifespan that leads to their accumulation in the injured kidneys. We examined the role of tPA in macrophage survival, and found that tPA protected macrophages from both staurosporine and H₂O₂-induced apoptosis. tPA promoted the survival of both resting and lipopolysaccharide- or interferon-γ-induced M1 macrophages, but failed to do so in the interleukin 4 (IL4)-induced M2 macrophages. In the kidneys with unilateral ureteral obstruction, there were significantly more apoptotic M1 macrophages in tPA-deficient mice than their wild-type counterparts, and obstruction-induced M1 macrophages accumulation and M1 chemokine expression were markedly reduced in these knock-out mice. The cytoprotective effect of tPA required its receptor, LDL receptor-related protein-1 (LRP-1). tPA induced the phosphorylation of Erk1/2, p90 ribosomal S6 kinase (RSK), and p38 in a temporal order. The tPA-mediated macrophage survival was eliminated by PD98059, BI-D1870, or sc68376, the specific inhibitors for Erk1/2, p90RSK, or p38, respectively. Thus, it is clear that tPA promoted M1 macrophage survival through its receptor LRP-1-mediated novel signaling cascade involving Erk1/2, p90RSK, and p38, which leads to the accumulation of these cells in the injured kidneys.