Selective Depletion Of Macrophages Research Articles

Non-purulent myositis caused by direct invasion of skeletal muscle tissue by Leptospira in a hamster model.

Myalgia is a common symptom of Leptospira infection in humans. Autopsies have reported that muscle tissue shows degeneration and necrosis of the myofibers and infiltration of inflammatory cells composed mainly of macrophages and lymphocytes. It remains unclear whether Leptospira directly infects the muscle and how the infiltrating inflammatory cells are involved in muscle fiber destruction. This study evaluated the relationship between histopathological changes and leptospiral localization in the muscle tissue of a hamster model. The influence of macrophages in skeletal muscle injury was also investigated, using selective depletion of macrophages by administration of liposomal clodronate. Hamsters infected subcutaneously with Leptospira interrogans serovar Manilae strain UP-MMC-SM showed myositis of the thighs adjacent to the inoculated area beginning at 6 days post-infection. The myositis was non-purulent and showed sporadic degeneration and necrosis of muscle fibers. The degeneration of myofibers was accompanied by aggregations of macrophages. Immunofluorescence staining revealed leptospires surrounding the damaged muscle fibers. Subcutaneous injection of formalin-killed Leptospira or intraperitoneal injection of live Leptospira caused no myositis in hamster thighs. Liposomal clodronate treatment in infected hamsters reduced macrophage infiltration in muscle tissue without impacting bacterial clearance. Muscle necrosis was still observed in the infected hamsters treated with liposomal clodronate, and there was no significant change in serum creatine kinase levels compared to those in animals treated with liposomes alone. Our findings suggest that leptospiral invasion of muscle tissue from an inoculation site leads to the destruction of muscle fibers and causes non-purulent myositis, whereas the infiltrating macrophages contribute less to muscle destruction.

An immunometabolic patch facilitates mesenchymal stromal/stem cell therapy for myocardial infarction through a macrophage-dependent mechanism.

Mesenchymal stromal/stem cells (MSCs) have emerged as a promising approach against myocardial infarction. Due to hostile hyperinflammation, however, poor retention of transplanted cells seriously impedes their clinical applications. Proinflammatory M1 macrophages, which rely on glycolysis as their main energy source, aggravate hyperinflammatory response and cardiac injury in ischemic region. Here, we showed that the administration of an inhibitor of glycolysis, 2-deoxy-d-glucose (2-DG), blocked the hyperinflammatory response within the ischemic myocardium and subsequently extended effective retention of transplanted MSCs. Mechanistically, 2-DG blocked the proinflammatory polarization of macrophages and suppressed the production of inflammatory cytokines. Selective macrophage depletion abrogated this curative effect. Finally, to avoid potential organ toxicity caused by systemic inhibition of glycolysis, we developed a novel chitosan/gelatin-based 2-DG patch that directly adhered to the infarcted region and facilitated MSC-mediated cardiac healing with undetectable side effects. This study pioneered the application of an immunometabolic patch in MSC-based therapy and provided insights into the therapeutic mechanism and advantages of this innovative biomaterial.

Evaluation of Cisplatin-Induced Pathology in the Larval Zebrafish Lateral Line.

Cisplatin is an effective anticancer agent, but also causes permanent hearing loss by damaging hair cells-the sensory receptors essential for hearing. There is an urgent clinical need to protect cochlear hair cells in patients undergoing cisplatin chemotherapy. The zebrafish lateral line organ contains hair cells and has been frequently used in studies to screen for otoprotective compounds. However, these studies have employed a wide range of cisplatin dosages and exposure times. We therefore performed a comprehensive evaluation of cisplatin ototoxicity in the zebrafish lateral line with the goal of producing a standardized, clinically relevant protocol for future studies. To define the dose- and time-response patterns of cisplatin-induced hair-cell death, we treated 6-day-old larvae for 2 h in 50 µM-1 mM cisplatin and allowed them to recover. We observed delayed hair cell death, which peaked at 4-8 h post-exposure. Cisplatin also activated a robust inflammatory response, as determined by macrophage recruitment and phagocytosis of hair cells. However, selective depletion of macrophages did not affect hair cell loss. We also examined the effect of cisplatin treatment on fish behavior and found that cisplatin-induced lateral line injury measurably impaired rheotaxis. Finally, we examined the function of remaining hair cells that appeared resistant to cisplatin treatment. We observed significantly reduced uptake of the cationic dye FM1-43 in these cells relative to untreated controls, indicating that surviving hair cells may be functionally impaired. Cumulatively, these results indicate that relatively brief exposures to cisplatin can produce hair cell damage and delayed hair cell death. Our observations provide guidance on standardizing methods for the use of the zebrafish model in studies of cisplatin ototoxicity.

Conditional depletion of macrophages ameliorates cholestatic liver injury and fibrosis via lncRNA-H19

Although macrophages are recognized as important players in the pathogenesis of chronic liver diseases, their roles in cholestatic liver fibrosis remain incompletely understood. We previously reported that long noncoding RNA-H19 (lncRNA-H19) contributes to cholangiocyte proliferation and cholestatic liver fibrosis of biliary atresia (BA). We here show that monocyte/macrophage CD11B mRNA levels are increased significantly in livers of BA patients and positively correlated with the progression of liver inflammation and fibrosis. The macrophages increasingly infiltrate and accumulate in the fibrotic niche and peribiliary areas in livers of BA patients. Selective depletion of macrophages using the transgenic CD11b-diphtheria toxin receptor (CD11b-DTR) mice halts bile duct ligation (BDL)-induced progression of liver damage and fibrosis. Meanwhile, macrophage depletion significantly reduces the BDL-induced hepatic lncRNA-H19. Overexpression of H19 in livers using adeno-associated virus serotype 9 (AAV9) counteracts the effects of macrophage depletion on liver fibrosis and cholangiocyte proliferation. Additionally, both H19 knockout (H19−/−) and conditional deletion of H19 in macrophage (H19ΔCD11B) significantly depress the macrophage polarization and recruitment. lncRNA-H19 overexpressed in THP-1 macrophages enhance expression of Rho-GTPase CDC42 and RhoA. In conclusions, selectively depletion of macrophages suppresses cholestatic liver injuries and fibrosis via the lncRNA-H19 and represents a potential therapeutic strategy for rapid liver fibrosis in BA patients.

Role of macrophage-mediated Toll-like receptor 4\u2013interleukin-1R signaling in ectopic tongue pain associated with tooth pulp inflammation

BackgroundThe existence of referred pain and ectopic paresthesia caused by tooth pulp inflammation may make definitive diagnosis difficult and cause misdiagnosis or mistreatment; thus, elucidation of that molecular mechanism is urgent. In the present study, we investigated the mechanisms underlying ectopic pain, especially tongue hyperalgesia, after tooth pulp inflammation.MethodsA rat model with mandibular first molar tooth pulp exposure was employed. Tooth pulp exposure-induced heat and mechanical-evoked tongue hypersensitivity was measured, and immunohistochemical staining for Iba1, a marker of active macrophages, IL-1β, IL-1 type I receptor (IL-1RΙ), and toll-like receptor 4 in the trigeminal ganglion was performed. In addition, we investigated the effects of injections of liposomal clodronate Clophosome-A (LCCA), a selective macrophage depletion agent, lipopolysaccharide from Rhodobacter sphaeroides (LPS-RS, a toll-like receptor 4 antagonist), IL-1β, or heat shock protein 70 (Hsp70, a selective agonist of toll-like receptor 4), to examine changes in tongue hypersensitivity and in the regulation of IL-1RΙ, toll-like receptor 4, and transient receptor potential vanilloid 1 (TRPV1) biosynthesis.ResultsAt day 1 after tooth pulp exposure, obvious tooth pulp inflammation was observed. Tooth pulp exposure-induced heat and mechanical tongue hypersensitivity was observed from days 1 to 3 after tooth pulp exposure. The production of IL-1β in activated macrophages and toll-like receptor 4 and IL-1RΙ expression were significantly increased in trigeminal ganglion neurons innervating the tongue following tooth pulp exposure. Intra-trigeminal ganglion injection of LCCA significantly suppressed tongue hypersensitivity; however, toll-like receptor 4 and IL-1RΙ expression in trigeminal ganglion neurons innervating the tongue was not significantly altered. Intra-trigeminal ganglion injection of LPS-RS significantly suppressed tongue hypersensitivity and reduced IL-1RΙ expression in the trigeminal ganglion neurons innervating the tongue following tooth pulp exposure. Intra-trigeminal ganglion injection of recombinant Hsp70 significantly promoted tongue hypersensitivity and increased IL-1RI expression in trigeminal ganglion neurons innervating the tongue in naive rats. Furthermore, intra-trigeminal ganglion injection of recombinant IL-1β led to tongue hypersensitivity and enhanced TRPV1 expression in trigeminal ganglion neurons innervating the tongue in naive rats.ConclusionsThe present findings suggest that the neuron-macrophage interaction mediated by toll-like receptor 4 and IL-1RI activation in trigeminal ganglion neurons affects the pathogenesis of abnormal tongue pain following tooth pulp inflammation via IL-1RI and TRPV1 signaling in the trigeminal ganglion. Further research may contribute to the establishment of new therapeutic and diagnostic methods.

Wnt/\u03b2-catenin activation and macrophage induction during liver cancer development following steatosis

Obesity confers an independent risk for carcinogenesis. In the liver, steatosis often proceeds cancer formation; however, the mechanisms by which steatosis promotes carcinogenesis is unknown. We hypothesize that steatosis alters the microenvironment to promote proliferation of tumor initiating cells (TICs) and carcinogenesis. We used several liver cancer models to address the mechanisms underlying the role of obesity in cancer and verified these findings in patient populations. Using bioinformatics analysis and verified by biochemical assays, we identified that hepatosteatosis resulting from either Pten deletion or transgenic expression of HCV core/NS5A proteins, promotes the activation of Wnt/β-catenin. We verified that high fat diet lipid accumulation is also capable of inducing Wnt/β-catenin. Caloric restriction inhibits hepatosteatosis, reduces Wnt/β-catenin activation and blocks the expansion of TICs leading to complete inhibition of tumorigenesis without affecting the phosphatase and tensin homologue deleted on chromosome 10 (PTEN) loss regulated protein kinase B (AKT) activation. Pharmacological inhibition or loss of the Wnt/β-catenin signal represses TIC growth in vitro, and decreases the accumulation of TICs in vivo. In human liver cancers, ontology analysis of gene set enrichment analysis (GSEA)-defined Wnt signature genes indicates that Wnt signaling is significantly induced in tumor samples compared with healthy livers. Indeed, Wnt signature genes predict 90% of tumors in a cohort of 558 patient samples. Selective depletion of macrophages leads to reduction of Wnt and suppresses tumor development, suggesting infiltrating macrophages as a key source for steatosis-induced Wnt expression. These data established Wnt/β-catenin as a novel signal produced by infiltrating macrophages induced by steatosis that promotes growth of tumor progenitor cells, underlying the increased risk of liver tumor development in obese individuals.

Abstract IA21: Myeloid cells are required for PD-1/PD-L1 checkpoint activation and the establishment of an immune-suppressive environment in pancreatic cancer

Abstract Pancreatic cancer is characterized by the accumulation of a fibro-inflammatory stroma. Accumulation of the stroma is already evident surrounding Pancreatic Intraepithelial Neoplasias (PanINs), common precursor lesions to pancreatic cancer (Hezel et al., 2006). The stroma is abundantly infiltrated by immune cells, and myeloid cells are a predominant population (Clark et al., 2007). Different myeloid subsets have been correlated with tumor promotion and unmasking of anti-tumor immunity (Liou et al., 2015; Long et al., 2016; Mitchem et al., 2013; Stromnes et al., 2014). Both PanINs and pancreatic cancer and commonly associated with oncogenic mutations in the Kras gene (Biankin et al., 2012; Jones et al., 2010; Kanda et al., 2012). Expression of oncogenic Kras in the pancreas of genetically engineered mice recapitulates the PanIN to pancreatic cancer progression, including the accumulation of fibrotic stroma (Hingorani et al., 2003). We have described a mouse model that allows inducible and reversible expression of oncogenic Kras in the pancreas, the iKras* mouse. Inactivation of oncogenic Kras during the PanIN stage or in cancer leads to regression of the epithelial lesions as well as to remodeling of the stroma, indicating that the accumulation of the stroma is regulated by signals derived from oncogenic Kras-expressing epithelial cells (Collins et al., 2012a). In the current study, we have investigated the interaction between epithelial cells and myeloid cells that infiltrate the pancreas. For this purpose, we have used a combination of genetically engineered mice (iKras*p53* mice (Collins et al., 2012b)) and transplantation approaches into CD11b-DTR mice (Duffield et al., 2005), that allow depletion of myeloid cells upon administration of Diphtheria Toxin. Our results show that the infiltration and polarization of macrophages in the pancreas depends on signals derived from oncogenic Kras-expressing epithelial cells, either directly or through activation of a pro-inflammatory subset of stromal fibroblasts. Conversely, myeloid cells infiltration is required for the progression of PanINs and pancreatic cancer. Depletion of myeloid cells prevented KrasG12D driven pancreatic cancer initiation. In pre-established tumors, myeloid cell depletion resulted in arrest of growth or tumor regression. We observed that tumor progression was dependent on myeloid cell-mediated blockade of CD8+ T cell anti-tumor activity. Furthermore, myeloid cells regulate the expression of the Programmed death-ligand 1 (PD-L1) in tumor cells in an EGFR/MAPK dependent manner. Our results show that myeloid cells regulate a complex network of signals that ensure immune suppression within the pancreatic cancer microenvironment. Moreover, we show that depletion of the myeloid cell population restores anti-tumor immunity mediated by CD8+ T cells, a finding with implications for the design of immune therapies for pancreatic cancer.

Plaque-penetrating peptide inhibits development of hypoxic atherosclerotic plaque

Atherosclerosis treatments are generally aimed at altering systemic lipid metabolism such that atherogenesis, the formation of plaque, is curtailed. The plaques themselves offer some potential therapeutic targets. For example, selective depletion of macrophages, which play a key role in atherogenesis, inhibits plaque formation. However, it has not been possible to take advantage of these targets because the drugs that have been tested have not been sufficiently selective. We have developed a peptide, LyP-1, which specifically targets atherosclerotic plaques, penetrates into plaque interior, and accumulates in plaque macrophages. In tumors, LyP-1 can cause apoptosis in cells that take up the peptide. Here we show, using three different atherosclerosis models in ApoE null mice that prolonged systemic treatment with LyP-1 triggers apoptosis of plaque macrophages and reduces plaque in advanced hypoxic plaques, and that it does so without increasing necrotic core of plaques or causing detectable side effects. We also show that LyP-1 recognizes human plaque. These findings suggest that LyP-1 could serve as a lead compound for the development of a new class of anti-atherosclerosis drugs.

Inhibition of Ocular Neovascularization by Co-Inhibition of VEGF-A and PLGF

Background/Aims: Age-related macular degeneration (AMD) appears to be a disease with increasing incidence in Western countries and may develop into acquired blindness. Choroidal neovascularization (CNV) is the most frequent cause for AMD, and is commonly induced by regional inflammation. Past studies have highlighted vascular endothelial growth factor A (VEGF-A) as a major trigger for CNV. However, studies on the associated angiogenic factors other than VEGF-A are lacking. Methods: Here, we used a well-established laser burn (LB)-induced experimental CNV mouse model to study the molecular mechanisms underlying the development of CNV after ocular injury. We analyzed vessel density by lectin labeling. We isolated macrophages, endothelial cells and other cell types by flow cytometry, and analyzed levels of different angiogenic factors in these populations. We used antisera against VEGF-A (aVEGF) and/or antisera against placental growth factor (PLGF; aPLGF) to antagonize CNV. We used an antibody-driven toxin to selectively eliminate macrophages to evaluate the role of macrophages in CNV. We also examined expression of PLGF in macrophage subtypes. Results: The choroidal vessel density increased significantly 7 days after LB. LB increased significantly the levels of VEGF-A and PLGF in mouse eyes. Treatment with aVEGF significantly blunted increases in vessel density by LB. Treatment with aPLGF alone did not significantly reduce increases in vessel density. However, aPLGF significantly increased the inhibitory effects of aVEGF on vessel density increases. While VEGF-A was produced by endothelial cells, macrophages and other types at similar levels, PLGF seemed to be predominantly produced by macrophages. Selective macrophage depletion significantly reduced CNV. M2, but M1 macrophages produced high levels of PLGF. Conclusions: Together, our data suggest a previously unappreciated role of PLGF in coordination with VEGF-A to regulate CNV during ocular injury. Our study highlights macrophages and their production of PLGF as novel targets for CNV therapy.

The macrophage-derived proteins murine RELMα and human resistin regulate host immunity to helminth infection (MPF3P.801)

Abstract Th2 cells are essential for protective immunity to helminths but also contribute to chronic inflammation. Here we identify the REsistin-Like Molecules RELMα and Resistin as critical mediators of this balance between helminth Th2-mediated immunity and inflammation in both murine infection and human studies. Following infection with Nippostrongylus brasiliensis, we observed significant macrophage expression of RELMα in the lungs. When RELMα-/- mice were infected with N. brasiliensis, there were increased Th2-type responses, accelerated worm expulsion and exacerbated lung inflammation compared to wild-type mice, implicating a role for RELMα in dampening Th2 immune responses. Selective depletion of macrophages in RELMα-/- mice ameliorated N. brasiliensis-induced chronic lung inflammation, suggesting that RELMα modulates inflammation through effects on macrophages. In new translational studies, we investigated the function of human Resistin (hResistin) which shares sequence homology with RELMα. Employing transgenic mice that express hResistin, we observed increased macrophage expression of hResistin in N. brasiliensis-infected lungs. Moreover, hResistin inhibited Th2 immune responses and immunity to N. brasiliensis. Finally, we observed a strong correlation between parasite number and serum Resistin levels in a population of helminth-infected patients (n=46). Taken together, these studies identify a new RELM-mediated regulatory pathway in helminth immunity and inflammation.

Magnetic Resonance Imaging Investigation of Macrophages in Acute Cardiac Allograft Rejection After Heart Transplantation

Current immunosuppressive therapy after heart transplantation either generally suppresses the recipient's entire immune system or is mainly targeting T-lymphocytes. Monocytes/macrophages are recognized as a hallmark of acute allograft rejection, but the roles that they play are not well characterized in vivo, because the tools for accessing in situ macrophage infiltration are lacking. In this study, we used MRI to investigate the role of macrophages in acute heart allograft rejection by cellular and functional MRI with selectively depleted systemic macrophages without affecting other leukocyte population, as well as to explore the possibility that macrophages could be an alternative therapeutic target. A rodent heterotopic working heart-lung transplantation model was used for studying acute allograft rejection. Systemic macrophages were selectively depleted by treating recipient animals with clodronate-liposomes. Macrophage infiltration in the graft hearts was monitored by cellular MRI with in vivo ultrasmall superparamagnetic iron oxide particles labeling. Graft heart function was evaluated by tagging MRI followed by strain analysis. Clodronate-liposome treatment depletes circulating monocytes/macrophages in transplant recipients, and both cellular MRI and pathological examinations indicate a significant reduction in macrophage accumulation in the rejecting allograft hearts. In clodronate-liposome-treated group, allograft hearts exhibited preserved tissue integrity, partially reversed functional deterioration, and prolonged graft survival, compared with untreated controls. Cardiac cellular and functional MRI is a powerful tool to explore the roles of targeted immune cells in vivo. Our results indicate that macrophages are essential in acute cardiac allograft rejection, and selective depletion of macrophages with clodronate-liposomes protects hearts against allograft rejection, suggesting a potential therapeutic avenue. Our findings show that there is a finite risk of forming an intraventricular mass, presumably from the cellular debris or lipid material. Further optimization of the dosing protocol is necessary before clinical applications.

Investigating the role of macrophages in tumor formation using a MaFIA mouse model

Tumor-associated macrophages (TAMs) interact with tumors in their development, growth and metastatic activities. Using a transgenic mouse model that allows for the selective depletion of macrophages we were able to access the macrophage's potential to facilitate metastasis. In the MaFIA (Macrophage Fas-Induced Apoptosis) mouse, transgene-expressing cells of the myeloid lineage undergo death by apoptosis in the presence of the drug AP20187. Enhanced green fluorescent protein (EGFP) was fused to the suicide gene to allow identification of transgene-expressing cells. Tumor induction was accomplished by subdermal and intravenous injections of B16-F10 melanoma cells. Metastasis in mice with depleted macrophages was compared to metastasis in normal control mice. The lungs and kidneys were examined for metastatic cells. The macrophage-depleted groups showed significantly less metastasis (P>0.001) compared to the control groups. We theorize that macrophages may aid the metastatic process by fusing with melanoma cells. Using appropriate cell markers and fluorescence-activated cell sorting, we were able to detect a small population of double-positive cells. We confirmed cell fusion by microscopic analysis, visualizing the cell's morphology by both immunohistochemistry and immunofluorescence. The presence of double-positive cells suggests macrophage/cancer cell fusion could be a possible mechanism for metastasis.

Macrophage Colony-Stimulating Factor–Induced Macrophage Differentiation Promotes Regrowth in Atrophied Skeletal Muscles and C2C12 Myotubes

Skeletal muscle injury and regeneration are closely associated with an inflammatory reaction that is usually characterized by sequential recruitment of neutrophils and monocytes or macrophages. Selective macrophage depletion models have shown that macrophages are essential for complete regeneration of muscle fibers after freeze injuries, toxin injuries, ischemia-reperfusion, and hindlimb unloading and reloading. Although there is growing evidence that macrophages possess major myogenic capacities, it is not known whether the positive effects of macrophages can be optimized to stimulate muscle regrowth. We used invivo and invitro mouse models of atrophy to investigate the effects of stimulating macrophages with macrophage colony-stimulating factor (M-CSF) on muscle regrowth. When atrophied soleus muscles were injected intramuscularly with M-CSF, we observed a 1.6-fold increase in macrophage density and a faster recovery in muscle force (20%), combined with an increase in muscle fiber diameter (10%), after 7 days of reloading, compared with PBS-injected soleus muscles. Furthermore, coculture of atrophied myotubes with or without bone marrow-derived macrophages (BMDM) and/or M-CSF revealed that the combination of BMDMs and M-CSF was required to promote myotube growth (15%). More specifically, M-CSF promoted the anti-inflammatory macrophage phenotype, which in turn decreased protein degradation and MuRF-1 expression by 25% in growing myotubes. These results indicate that specific macrophage subsets can be stimulated to promote muscle cell regrowth after atrophy.

Inhibition of serine palmitoyltransferase delays the onset of radiation-induced pulmonary fibrosis through the negative regulation of sphingosine kinase-1 expression

The enforcement of sphingosine-1-phosphate (S1P) signaling network protects from radiation-induced pneumonitis. We now demonstrate that, in contrast to early postirradiation period, late postirradiation sphingosine kinase-1 (SphK1) and sphingoid base-1-phosphates are associated with radiation-induced pulmonary fibrosis (RIF). Using the mouse model, we demonstrate that RIF is characterized by a marked upregulation of S1P and dihydrosphingosine-1-phosphate (DHS1P) levels in the lung tissue and in circulation accompanied by increased lung SphK1 expression and activity. Inhibition of sphingolipid de novo biosynthesis by targeting serine palmitoyltransferase (SPT) with myriocin reduced radiation-induced pulmonary inflammation and delayed the onset of RIF as evidenced by increased animal lifespan and decreased expression of markers of fibrogenesis, such as collagen and α-smooth muscle actin (α-SMA), in the lung. Long-term inhibition of SPT also decreased radiation-induced SphK activity in the lung and the levels of S1P-DHS1P in the lung tissue and in circulation. In vitro, inhibition or silencing of serine palmitoyltransferase attenuated transforming growth factor-β1 (TGF-β)-induced upregulation of α-SMA through the negative regulation of SphK1 expression in normal human lung fibroblasts. These data demonstrate a novel role for SPT in regulating TGF-β signaling and fibrogenesis that is linked to the regulation of SphK1 expression and S1P-DHS1P formation.

Assaying macrophage activity in a murine model of inflammatory bowel disease using fluorine-19 MRI

Macrophages have an important role in the pathogenesis of most chronic inflammatory diseases. A means of non-invasively quantifying macrophage migration would contribute significantly towards our understanding of chronic inflammatory processes and aid the evaluation of novel therapeutic strategies. We describe the use of a perfluorocarbon tracer reagent and in vivo19F magnetic resonance imaging (MRI) to quantify macrophage burden longitudinally. We apply these methods to evaluate the severity and three-dimensional distribution of macrophages in a murine model of inflammatory bowel disease (IBD). MRI results were validated by histological analysis, immunofluorescence and quantitative real-time polymerase chain reaction. Selective depletion of macrophages in vivo was also performed, further validating that macrophage accumulation of perfluorocarbon tracers was the basis of 19F MRI signals observed in the bowel. We tested the effects of two common clinical drugs, dexamethasone and cyclosporine A, on IBD progression. Whereas cyclosporine A provided mild therapeutic effect, unexpectedly dexamethasone enhanced colon inflammation, especially in the descending colon. Overall, 19F MRI can be used to evaluate early-stage inflammation in IBD and is suitable for evaluating putative therapeutics. Due to its high macrophage specificity and quantitative ability, we envisage 19F MRI having an important role in evaluating a wide range of chronic inflammatory conditions mediated by macrophages.

Macrophages: Central regulators of hepatic fibrogenesis and fibrosis resolution

Hepatic fibrosis is the common end point to chronic injury of varied aetiology. There is now excellent evidence in both human studies and animal models that liver fibrosis is a bidirectional process with a significant reversible component. The hepatic stellate cell (HSC), following activation to a myofibroblast phenotype, is the principal cell producing extracellular matrix (ECM) during fibrogenesis and is the main source of TIMP-1, which inhibits the endogenous matrix-degrading activity of matrix metalloproteinases (MMPs), thus promoting scar deposition. Furthermore, apoptosis of activated HSCs is a critical feature of scar resolution. However, emerging evidence indicates that it is the hepatic macrophage that is the master regulator of this dynamic fibrogenesis–fibrosis resolution paradigm.

Plasminogen Receptor S100A10 Is Essential for the Migration of Tumor-Promoting Macrophages into Tumor Sites

Macrophages are critical drivers of tumor growth, invasion, and metastasis. Movement of macrophages into tumors requires the activity of cell surface proteases such as plasmin. In this study, we offer genetic evidence that plasminogen receptor S100A10 is essential for recruitment of macrophages to the tumor site. Growth of murine Lewis lung carcinomas or T241 fibrosarcomas was dramatically reduced in S100A10-deficient mice compared with wild-type mice. The tumor growth deficit corresponded with a decrease in macrophage density that could be rescued by intraperitoneal injection of wild-type but not S100A10-deficient macrophages. Notably, macrophages of either genotype could rescue tumor growth if they were injected into the tumor itself, establishing that S100A10 was required specifically for the migratory capability needed for tumor homing. Conversely, selective depletion of macrophages from wild-type mice phenocopied the tumor growth deficit seen in S100A10-deficient mice. Together, our findings show that S100A10 is essential and sufficient for macrophage migration to tumor sites, and they define a novel rate-limiting step in tumor progression.

Selective depletion of macrophages delays fracture healing

Selective depletion of macrophages delays fracture healing

Resident macrophages influence stem cell activity in the mammary gland

IntroductionMacrophages in the mammary gland are essential for morphogenesis of the ductal epithelial tree and have been implicated in promoting breast tumor metastasis. Although it is well established that macrophages influence normal mammopoiesis, the mammary cell types that these accessory cells influence have not been determined. Here we have explored a role for macrophages in regulating mammary stem cell (MaSC) activity, by assessing the ability of MaSCs to reconstitute a mammary gland in a macrophage-depleted fat pad.MethodsTwo different in vivo models were used to deplete macrophages from the mouse mammary fat pad, allowing us to examine the effect of macrophage deficiency on the mammary repopulating activity of MaSCs. Both the Csf1op/op mice and clodronate liposome-mediated ablation models entailed transplantation studies using the MaSC-enriched population.ResultsWe show that mammary repopulating ability is severely compromised when the wild-type MaSC-enriched subpopulation is transplanted into Csf1op/op fat pads. In reciprocal experiments, the MaSC-enriched subpopulation from Csf1op/op glands had reduced regenerative capacity in a wild-type environment. Utilizing an alternative strategy for selective depletion of macrophages from the mammary gland, we demonstrate that co-implantation of the MaSC-enriched subpopulation with clodronate-liposomes leads to a marked decrease in repopulating frequency and outgrowth potential.ConclusionsOur data reveal a key role for mammary gland macrophages in supporting stem/progenitor cell function and suggest that MaSCs require macrophage-derived factors to be fully functional. Macrophages may therefore constitute part of the mammary stem cell niche.

Opposite Roles of CCR2 and CX3CR1 Macrophages in Alkali-Induced Corneal Neovascularization

The purpose of this study was to investigate the role of infiltrating macrophages in the development of experimental corneal neovascularization. Corneal neovascularization was induced by alkali injury in mice deficient in a macrophage-tropic chemokine receptor, CCR2 or CX3CR1, or in mice treated with clodronate-liposomes (Cl2MDP-lip), which can selectively deplete monocytes/macrophages. Corneal neovascularization 2 weeks after alkali injury was assessed by immunostaining with anti-CD31 antibody. Intracorneal expression of proangiogenic and antiangiogenic factors was determined by reverse transcription-polymerase chain reaction. CCR2-deficient mice exhibited reduced alkali-induced corneal neovascularization with reduced macrophage infiltration, whereas CX3CR1-deficient mice developed a more severe form of alkali-induced corneal neovascularization with reduced macrophage infiltration. Selective macrophage depletion by Cl2MDP-lip treatment failed to affect alkali-induced corneal neovascularization as evidenced by immunohistochemical analysis using anti-CD31 antibody, whereas intracorneal macrophage infiltration was markedly reduced. Alkali injury enhanced the expression of proangiogenic molecules, including matrix metalloproteinase-2, matrix metalloproteinase-9, and tumor necrosis factor alpha, and antiangiogenic factors, including a disintegrin and metalloprotease with thrombospondin (ADAMTS)-1, thrombospondin-1, and thrombospondin-2. Cl2MDP-lip-treated mice exhibited a reduction in the messenger RNA expression of these molecules. Because CCR2- and CX3CR1-expressing macrophages exhibit opposite activities in angiogenesis, depletion of macrophages as a whole may not have apparent effects on alkali-induced corneal neovascularization.