IL4/PGE2 induction of an enlarged early endosomal compartment in mouse macrophages is Rab5-dependent

The endosomal compartment and the plasma membrane form a complex partnership that controls signal transduction and trafficking of different molecules. The specificity and functionality of the early endocytic pathway are regulated by a growing number of Rab GTPases, particularly Rab5. In this study, we demonstrate that IL4 (a Th-2 cytokine) and prostaglandin E2 (PGE2) synergistically induce Rab5 and several Rab effector proteins, including Rin1 and EEA1, and promote the formation of an enlarged early endocytic (EEE) compartment. Endosome enlargement is linked to a substantial induction of the mannose receptor (MR), a well-characterized macrophage endocytic receptor. Both MR levels and MR-mediated endocytosis are enhanced approximately 7-fold. Fluid-phase endocytosis is also elevated in treated cells. Light microscopy and fractionation studies reveal that MR colocalizes predominantly with Rab5a and partially with Rab11, an endosomal recycling pathway marker. Using retroviral expression of Rab5a:S34N, a dominant negative mutant, and siRNA Rab5a silencing, we demonstrate that Rab5a is essential for the large endosome phenotype and for localization of MR in these structures. We speculate that the EEE is maintained by activated Rab5, and that the EEE phenotype is part of some macrophage developmental program such as cell fusion, a characteristic of IL4-stimulated cells.     

Interleukin-1 Receptor-associated Kinase-4 (IRAK4) Promotes Inflammatory Osteolysis by Activating Osteoclasts and Inhibiting Formation of Foreign Body Giant Cells

Formation of foreign body giant cells (FBGCs) occurs following implantation of medical devices such as artificial joints and is implicated in implant failure associated with inflammation or microbial infection. Two major macrophage subpopulations, M1 and M2, play different roles in inflammation and wound healing, respectively. Therefore, M1/M2 polarization is crucial for the development of various inflammation-related diseases. Here, we show that FBGCs do not resorb bone but rather express M2 macrophage-like wound healing and inflammation-terminating molecules in vitro. We also found that FBGC formation was significantly inhibited by inflammatory cytokines or infection mimetics in vitro. Interleukin-1 receptor-associated kinase-4 (IRAK4) deficiency did not alter osteoclast formation in vitro, and IRAK4-deficient mice showed normal bone mineral density in vivo. However, IRAK4-deficient mice were protected from excessive osteoclastogenesis induced by IL-1β in vitro or by LPS, an infection mimetic of Gram-negative bacteria, in vivo. Furthermore, IRAK4 deficiency restored FBGC formation and expression of M2 macrophage markers inhibited by inflammatory cytokines in vitro or by LPS in vivo. Our results demonstrate that osteoclasts and FBGCs are reciprocally regulated and identify IRAK4 as a potential therapeutic target to inhibit stimulated osteoclastogenesis and rescue inhibited FBGC formation under inflammatory and infectious conditions without altering physiological bone resorption.     

Role of the mannose receptor in the immune response

The mannose receptor (MR) recognizes a range of carbohydrates present on the surface and cell walls of micro-organisms. The MR is primarily expressed on macrophages and dendritic cells and is involved in MR-mediated endocytosis and phagocytosis. In addition, the MR plays a key role in host defense and provides a link between innate and adaptive immunity. Herein, we will review the role of the MR in innate host defense as well as the recent evidence for its role in the adaptive response, for both humoral and cellular immune responses.     

Pulmonary surfactant protein A up-regulates activity of the mannose receptor,a pattern recognition receptor expressed on human macrophages

Inhaled particulates and microbes are continually cleared by a complex array of lung innate immune determinants, including alveolar macrophages (AMs). AMs are unique cells with an enhanced capacity for phagocytosis that is due, in part, to increased activity of the macrophage mannose receptor (MR), a pattern recognition receptor for various microorganisms. The local factors that "shape" AM function are not well understood. Surfactant protein A (SP-A), a major component of lung surfactant, participates in the innate immune response and can enhance phagocytosis. Here we show that SP-A selectively enhances MR expression on human monocyte-derived macrophages, a process involving both the attached sugars and collagen-like domain of SP-A. The newly expressed MR is functional. Monocyte-derived macrophages on an SP-A substrate demonstrated enhanced pinocytosis of mannose BSA and phagocytosis of Mycobacterium tuberculosis lipoarabinomannan-coated microspheres. The newly expressed MR likely came from intracellular pools because: 1) up-regulation of the MR by SP-A occurred by 1 h, 2) new protein synthesis was not necessary for MR up-regulation, and 3) pinocytosis of mannose BSA via MR recycling was increased. AMs from SP-A(-/-) mice have reduced MR expression relative to SP-A(+/+). SP-A up-regulation of MR activity provides a mechanism for enhanced phagocytosis of microbes by AMs, thereby enhancing lung host defense against extracellular pathogens or, paradoxically, enhancing the potential for intracellular pathogens to enter their intracellular niche. SP-A contributes to the alternative activation state of the AM in the lung.     

Macrophage lectins in host defence

Macrophage lectins contribute to host defence by a variety of mechanisms. The best characterised, mannose receptor (MR) and complement receptor three (CR3), are both able to mediate phagocytosis of pathogenic microbes and induce intracellular killing mechanisms. The regulation of the effector functions induced via MR is complex, and may involve both host and microbial factors. Therefore, MR is likely to play a dynamic role in the response to infection; it may act as a classical pattern recognition receptor in phagocytosis, whereas other poorly characterised factors may make a more decisive contribution to its function in physiologic settings. In contrast, the lectin site of CR3 appears to lack host-derived ligands and may be a true pattern recognition receptor. Further studies are required to evaluate the roles of other macrophage lectins in recognition of and responses to microbes.     

INHIBITION OF PHAGOCYTOSIS AND PLASMA MEMBRANE MOBILITY OF THE CULTIVATED MACROPHAGE BY CYTOCHALASIN B : Role of Subplasmalemmal Microfilaments

Functional and morphologic effects of cytochalasin B on the cultivated macrophage were examined to determine the basis for plasma membrane movements of the type required for endocytosis and/or spreading on a substratum. Inhibition of phagocytosis and changes in cell shape by cytochalasin B exhibited nearly identical dose-response curves requiring 2–5 x 10^-6 M and 1–2 x 10^-5 M cytochalasin B to inhibit these functions by 50% and 100%, respectively. In contrast, hexose transport was ten times more sensitive to the drug requiring 2–3 x 10^-7 M cytochalasin B to achieve 50% inhibition of 2-deoxyglucose uptake. Inhibition of phagocytosis and changes in cell shape could not be explained solely by drug effects on hexose transport. Analysis of serial thin sections showed that cytochalasin B doses inhibitory for hexose transport had no effect on distribution or organization of either of the two subplasmalemmal microfilament types. However, cytochalasin B concentrations (2.0 x 10^-5 M) that inhibited phagocytosis and altered cell shape disorganized and/or disrupted oriented bundles of 40–50-Å subplasmalemmal microfilaments, but had no effect on the microfilamentous network. Comparative dose-response studies showing positive correlations among cytochalasin B effects on phagocytosis, changes in cell shape, and alterations in oriented subplasmalemmal microfilament bundles provide additional support for the hypothesis that microfilamentous structures play a role in translocation of plasma membrane required for endocytosis and cell motility.     

SUBPLASMALEMMAL MICROFILAMENTS AND MICROTUBULES IN RESTING AND PHAGOCYTIZING CULTIVATED MACROPHAGES

The subplasmalemmal organization of the free and glass-attached surfaces of resting and phagocytizing cultivated macrophages were examined in an attempt to define specific membrane-associated structures related to phagocytosis. From analysis of serial thin sections of oriented cells it was found that the subplasmalemmal region of the attached cell surface has a complex microfilament and microtubule organization relative to the subplasmalemmal area of the free surface. A filamentous network composed of 40–50-Å microfilaments extended for a depth of 400–600 Å from the attached plasma membrane. Immediately subjacent to the filamentous network was a zone of oriented bundles of 40–50-Å microfilaments and a zone of microtubules. Additional microtubules were found to extend from the plasma membrane to the interior of the cell in close association with electron-dense, channellike structures. In contrast, the free aspect of the cultivated macrophage contained only the subplasmalemmal filamentous network. However, after a phagocytic pulse with polystyrene particles (14 µm diam) microtubules and oriented filaments similar to those found on the attached surface were observed surrounding the ingested particles. The observations reported in this paper provide support for the hypothesis that microfilaments and/or microtubules play a role in the translocation of plasma membrane required for the functionally similar processes of phagocytosis and cell attachment to glass.     

Role of caveolae in Leishmania chagasi phagocytosis and intracellular survival in macrophages

Caveolae are membrane microdomains enriched in cholesterol, ganglioside M1 (GM1) and caveolin-1. We explored whether caveolae facilitate the entry of Leishmania chagasi into murine macrophages. Transient depletion of macrophage membrane cholesterol by 1 h exposure to methyl-beta-cyclodextrin (MbetaCD) impaired the phagocytosis of non-opsonized and serum-opsonized virulent L. chagasi. In contrast, MbetaCD did not affect the phagocytosis of opsonized attenuated L. chagasi. As early as 5 min after phagocytosis, virulent L. chagasi colocalized with the caveolae markers GM1 and caveolin-1, and colocalization continued for over 48 h. We explored the kinetics of lysosome fusion. Whereas fluorescent-labelled dextran entered macrophage lysosomes by 30 min after addition, localization of L. chagasi in lysosomes was delayed for 24-48 h after phagocytosis. However, after transient depletion of cholesterol from macrophage membrane with MbetaCD, the proportion of L. chagasi-containing phagosomes that fused with lysosomes increased significantly. Furthermore, intracellular replication was impaired in parasites entering after transient cholesterol depletion, even though lipid microdomains were restored by 4 h after treatment. These observations suggest that virulent L. chagasi localize in caveolae during phagocytosis by host macrophages, and that cholesterol-containing macrophage membrane domains, such as caveolae, target parasites to a pathway that promotes delay of lysosome fusion and intracellular survival.     

秦皮素通过抑制EGFR及其下游AKT信号通路抑制MCF-7细胞增殖及迁移

表皮生长因子受体(EGFR)是细胞内多种信号调节通路的交汇点,其介导的信号通路与乳腺癌的发生、发展、转移和侵袭等密切相关,已成为乳腺癌治疗的新靶点之一。但目前关于秦皮素的抗乳腺癌作用与EGFR通路的关系,国内外尚未见相关报道。本研究结果表明,秦皮素能够通过抑制EGFR及其下游的AKT信号通路来发挥其抗乳腺癌作用。秦皮素在体外可促进T、B 淋巴细胞增殖及巨噬细胞吞噬能力,提示秦皮素可能促进小鼠免疫功能。Western印迹结果表明,秦皮素能显著抑制EGFR蛋白及其下游的AKT蛋白磷酸化水平。划痕实验结果表明,秦皮素能抑制MCF-7细胞的迁移。此外,秦皮素还能促进小鼠巨噬细胞的吞噬能力和代谢活力,促进T、B淋巴细胞的增殖,提高NK细胞的杀伤活力。本研究结果提示,秦皮素的抗乳腺癌作用是通过抑制EGFR信号通路,抑制MCF-7细胞迁移和促进小鼠的免疫功能等多种途径来实现的。     

Importance of complement 3 and mannose receptors in phagocytosis of Paracoccidioides brasiliensis conidia by Nramp1 congenic macrophages lines

Genetic factors influence susceptibility to Paracoccidioidomycosis, a Latin American endemic mycosis. The pattern of susceptibility of congenic mouse strains infected with Paracoccidioides brasiliensis resembles the pattern of the Nramp1 gene. Thus, congenic murine bone-marrow-derived macrophage lines B10R (Nramp1rGly169) and B10S (null Nramp1 protein expression, Nramp1sAsp169) were infected with P. brasiliensis conidia and compared, under opsonic and nonopsonic conditions. Opsonization increased the percentage of phagocytosis by both cell lines. B10R macrophages exhibited a higher percentage of cells with associated conidia and higher number of conidia per macrophage than B10S. Heat-inactivation and EDTA treatment of serum used for opsonization, and treatment of macrophages with anti-complement receptor 3 (CR3) decreased phagocytosis by both cell lines. alpha-methyl-d-mannoside reduced phagocytosis by B10R macrophages, suggesting that the mannose receptor participates in phagocytosis by these cells. The CR3 expression was similar on both cell lines and B10R expressed more mannose receptors, but neither cell line expressed CR1. IFNgamma decreased the conversion of conidia to the yeast form of P. brasiliensis in B10R, but not in B10S macrophages.     

Activation of JAK2/STAT1-alpha-dependent signaling events during Mycobacterium tuberculosis-induced macrophage apoptosis

Induction of apoptosis by Mycobacterium tuberculosis in murine macrophage involves TNF-alpha and nitric oxide (NO) production and caspase cascade activation; however, the intracellular signaling pathways implicated remain to be established. Our results indicate that infection of the B10R murine macrophage line with M. tuberculosis induces apoptosis independent of mycobacterial phagocytosis and that M. tuberculosis induces protein tyrosine kinase (PTK) activity, JAK2/STAT1-alpha phosphorylation, and STAT1-alpha nuclear translocation. Inhibitors of PTK (AG-126), or JAK2 (AG-490) inhibited TNF-alpha and NO production, caspase 1 activation and apoptosis, suggesting that M. tuberculosis-induction of these events depends on JAK2/STAT1-alpha activation. In addition, we have obtained evidence that ManLAM capacity to inhibit M. tuberculosis-induced apoptosis involves the activation of the PTP SHP-1. The finding that M. tuberculosis infection activate JAK2/STAT1-alpha pathway suggests that M. tuberculosis might mimic macrophage-activating stimuli.     

Soluble expression and characterization of a GFP-fused pea actin isoform（PEAc1）

A pea actin isoform PEAcl with green fluorescent protein (GFP) fusion to its C-terminus and His-tag to its Nterminus, was expressed in prokaryotic cells in soluble form, and highly purified with Ni-Chelating Sepharose^TM Fast Flow column. The purified fusion protein (PEAcl-GFP) efficiently inhibited DNase I activities before polymerization,and activated the myosin Mg-ATPase activities after polymerization. The PEAcl-GFP also polymerized into green fluorescent filamentous structures with a critical concentration of 0.75μM. These filamentous structures were labeled by TRITC-phalloidin, a specific agent for staining actin microfilaments, and identified as having 9 nm diameters by negative staining. These results indicated that PEAc 1 preserved the essential characteristics of actin even with His-tag and GFP fusion, suggesting a promising potential to use GFP fusion protein in obtainning soluble plant actin isoform to analyze its physical and biochemical properties in vitro. The PEAcl-GFP was also expressed in tobacco BY2 cells,which offers a new pathway for further studying its distribution and function in vivo.     

In vitro clustering and multiple fusion among macrophage endosomes

Early steps of receptor-mediated endocytosis appear to require the fusion of endosomes with each other. Recently, these fusion events have been reconstituted in vitro using vesicle preparations from J774 macrophages which have internalized ligands via the mannose receptor (Diaz, R., Mayorga, L., and Stahl, P. (1988) J. Biol. Chem. 263, 6093-6100). The present studies indicate that endosomes first form clusters when incubated under fusogenic conditions. Aggregation state was determined by electron microscopy using vesicles containing ligand-coated colloidal gold of different sizes previously internalized via the mannose receptor. Aggregation required cytosol and ATP. Afterwards, the limiting membranes of the vesicles composing these aggregates undergo multiple fusion and bring about the formation of large diameter vesicles that maintained the same density as endosomes when analyzed by Percoll gradient sedimentation. These large diameter vesicles were no longer fusogenic in the fusion assay. Multiple fusion was determined morphologically by the co-localization of three different size colloidal gold vesicles inside endocytic vesicles and biochemically by the fusion-dependent formation of triple immune complexes between three endocytic ligands internalized by receptor-mediated endocytosis: anti-dinitrophenol mouse IgG and dinitrophenol-derivatized beta-glucuronidase, ligands for the mannose receptor, and aggregated rabbit anti-mouse IgG, a ligand for the macrophage Fc receptor.     

Plasticity of Human THP–1 Cell Phagocytic Activity during Macrophagic Differentiation

Studies of the role of macrophages in phagocytosis are of great theoretical and practical importance for understanding how these cells are involved in the organism’s defense response and in the development of various pathologies. Here we investigated phagocytic plasticity of THP–1 (acute monocytic human leukemia) cells at different stages (days 1, 3, and 7) of phorbol ester (PMA)–induced macrophage differentiation. Analysis of cytokine profiles showed that PMA at a concentration of 100 nM induced development of the proinflammatory macrophage population. The functional activity of macrophages was assessed on days 3 and 7 of differentiation using unlabeled latex beads and latex beads conjugated with ligands (gelatin, mannan, and IgG Fc fragment) that bind to the corresponding specific receptors. The general phagocytic activity increased significantly (1.5–2.0–fold) in the course of differentiation; phagocytosis occurred mostly through the Fc receptors, as shown previously for M1 macrophages. On day 7, the levels of phagocytosis of gelatin-and Fc–covered beads were high; however, the intensity of ingestion of mannan–conjugated beads via mannose receptors increased 2.5–3.0–fold as well, which indicated formation of cells with an alternative phenotype similar to that of M2 macrophages. Thus, the type and the plasticity of phagocytic activity at certain stages of macrophage differentiation can be associated with the formation of functionally mature morphological phenotype. This allows macrophages to exhibit their phagocytic potential in response to specific ligands. These data are of fundamental importance and can be used to develop therapeutic methods for correcting the M1/M2 macrophage ratio in an organism.     

Lipopolysaccharide induces multinuclear cell from RAW264.7 line with increased phagocytosis activity

Lipopolysaccharide (LPS), an outer membrane component of Gram-negative bacteria, induces strong proinflammatory responses, including the release of cytokines and nitric oxide from macrophage. In this study, we found that a murine macrophage-derived line, RAW264.7, became multinuclear through cell-cell fusion after incubation with highly purified LPS or synthetic lipid A in the presence of Ca(2+). The same cell line is known to differentiate into multinuclear osteoclast, which expresses a specific proton pumping ATPase together with osteoclast markers on stimulation by the extracellular domain of receptor activator of nuclear factor κB ligand (Toyomura, T., Murata, Y., Yamamoto, A., Oka, T., Sun-Wada, G.-H., Wada, Y. and Futai, M., 2003). The LPS-induced multinuclear cells did not express osteoclast-specific enzymes including tartrate-resistant acid phosphatase and cathepsin K. During multinuclear cell formation, the cells internalized more and larger polystyrene beads (diameter 6-15μm) than mononuclear cells and osteoclasts. The internalized beads were located in lysosome-marker positive organelles, which were probably phagolysosomes. The LPS-induced multinuclear cell could be a good model system to study phagocytosis of large foreign bodies.     

Prostaglandin E specifically upregulates the expression of the mannose-receptor on mouse bone marrow-derived macrophages.

The macrophage mannose receptor (MMR) facilitates the binding and internalization of microorganisms and glycoproteins with terminal mannose residues. The receptor is progressively upregulated as bone marrow precursor cells mature into macrophages and thus may serve as a marker of differentiation. Prostaglandins of the E series (PGE) are known inhibitors of monocyte and macrophage precursor proliferation, an effect often associated with cellular maturation. MMR expression was therefore assessed after exposure of bone marrow macrophage precursor (BMMP) cells to these prostanoids. Receptor expression was determined by ligand binding and via immunoprecipitation of newly synthesized receptor molecules. PGE1 and PGE2 at 10(-9)-10(-6) M upregulated MMR surface expression and biosynthesis four- to sixfold in a dose-dependent manner. BMMPs responsive to prostaglandins were characterized by plastic adherence, F4/80 antigen expression, and nonspecific esterase activity. Prostaglandins accelerated the expression of the MMR in cells by 48-72h, with maximal levels of receptor expression being identical in control or treated cells. Thus, prostaglandins enhanced mannose receptor expression in adherent but not fully differentiated macrophage precursors. This effect is specific for PGE and is mimicked by dibutyrl cyclic AMP. These results indicate that prostaglandins accelerate MMR expression and hence the differentiation of macrophage precursor cells. Cells resident in the bone marrow secrete abundant prostaglandins, suggesting that a paracrine mechanism may exist to regulate MMR expression and function.     

Differences in human macrophage receptor usage, lysosomal fusion kinetics and survival between logarithmic and metacyclic Leishmania infantum chagasi promastigotes

The obligate intracellular protozoan, Leishmania infantum chagasi (Lic) undergoes receptor-mediated phagocytosis by macrophages followed by a transient delay in phagolysosome maturation. We found differences in the pathway through which virulent Lic metacyclic promastigotes or avirulent logarithmic promastigotes are phagocytosed by human monocyte-derived macrophages (MDMs). Both logarithmic and metacyclic promastigotes entered MDMs through a compartment lined by the third complement receptor (CR3). In contrast, many logarithmic promastigotes entered through vacuoles lined by mannose receptors (MR) whereas most metacyclic promastigotes did not ( P  < 0.005). CR3-positive vacuoles containing metacyclic promastigotes stained for caveolin-1 protein, suggesting CR3 localizes in caveolae during phagocytosis. Following entry, the kinetics of phagolysosomal maturation and intracellular survival also differed. Vacuoles containing metacyclic parasites did not accumulate lysosome-associated membrane protein-1 (LAMP-1) at early times after phagocytosis, whereas vacuoles with logarithmic promastigotes did. MDMs phagocytosed greater numbers of logarithmic than metacyclic promastigotes, yet metacyclics ultimately replicated intracellularly with greater efficiency. These data suggest that virulent metacyclic Leishmania promastigotes fail to ligate macrophage MR, and enter through a path that ultimately enhances intracellular survival. The relatively quiescent entry of virulent Leishmania spp. into macrophages may be accounted for by the ability of metacyclic promastigotes to selectively bypass deleterious entry pathways.     

Mannose receptor-mediated uptake of ricin toxin and ricin A chain by macrophages. Multiple intracellular pathways for a chain translocation

The role of the high mannose carbohydrate chains in the mechanism of action of ricin toxin was investigated. Ricin is taken up by two routes in macrophages, by binding to cell surface mannose receptors, or by binding of the ricin galactose receptor to cell surface glycoproteins. Removal of carbohydrate from ricin by periodate oxidation led to a large loss in toxicity via both routes of uptake by an effect on the B chain not due to a loss of galactose binding affinity. These data suggest that the carbohydrate chains of ricin B chain may be required for full toxicity. The pathway of uptake of ricin by the macrophage mannose receptor was found to differ in several respects from uptake via the galactose-specific pathway. Analysis of intoxication of macrophages by ricin in the presence of ammonium chloride suggested that mannose receptor bound ligand passes through acidic vesicles prior to translocation, unlike galactose bound ligand. Intoxication by ricin via galactose-specific uptake was potentiated by swainsonine but not by castanospermine, suggesting that ricin may be attacked by an endogenous mannosidase within the cell, and that ricin passes through either a lysosomal or a Golgi compartment prior to translocation.     

Macrophage Fusion Is Controlled by the Cytoplasmic Protein Tyrosine Phosphatase PTP-PEST/PTPN12

Macrophages can undergo cell-cell fusion, leading to the formation of multinucleated giant cells and osteoclasts. This process is believed to promote the proteolytic activity of macrophages toward pathogens, foreign bodies, and extracellular matrices. Here, we examined the role of PTP-PEST (PTPN12), a cytoplasmic protein tyrosine phosphatase, in macrophage fusion. Using a macrophage-targeted PTP-PEST-deficient mouse, we determined that PTP-PEST was not needed for macrophage differentiation or cytokine production. However, it was necessary for interleukin-4-induced macrophage fusion into multinucleated giant cells in vitro. It was also needed for macrophage fusion following implantation of a foreign body in vivo. Moreover, in the RAW264.7 macrophage cell line, PTP-PEST was required for receptor activator of nuclear factor kappa-B ligand (RANKL)-triggered macrophage fusion into osteoclasts. PTP-PEST had no impact on expression of fusion mediators such as β-integrins, E-cadherin, and CD47, which enable macrophages to become fusion competent. However, it was needed for polarization of macrophages, migration induced by the chemokine CC chemokine ligand 2 (CCL2), and integrin-induced spreading, three key events in the fusion process. PTP-PEST deficiency resulted in specific hyperphosphorylation of the protein tyrosine kinase Pyk2 and the adaptor paxillin. Moreover, a fusion defect was induced upon treatment of normal macrophages with a Pyk2 inhibitor. Together, these data argue that macrophage fusion is critically dependent on PTP-PEST. This function is seemingly due to the ability of PTP-PEST to control phosphorylation of Pyk2 and paxillin, thereby regulating cell polarization, migration, and spreading.