Factors regulating macrophage production and growth: identity of colony-stimulating factor and macrophage growth factor

Paracrine Ovarian Cancer Cell-Derived CSF1 Signaling Regulates Macrophage Migration Dynamics in a 3D Microfluidic Model that Recapitulates In Vivo Infiltration Patterns in Patient-Derived Xenografts

A high density of macrophages in the ovarian cancer microenvironment is associated with disease progression and poor outcomes. Understanding cancer-macrophage interaction mechanisms that establish this pro-tumorigenic microenvironment is critical for developing macrophage-targeted therapies. Here, 3D microfluidic assays and patient-derived xenografts are utilized to define the role of cancer-derived colony stimulating factor 1 (CSF1) on macrophage infiltration dynamics toward ovarian cancer cells. It is demonstrated that multiple ovarian cancer models promote the infiltration of macrophages into a 3D extracellular matrix in vitro in a cell density-dependent manner. Macrophages exhibit directional migration and increased migration speed under both direct interactions with cancer cells embedded within the matrix and paracrine crosstalk with cancer cells seeded in an independent microchannel. It is also found that platinum-based chemotherapy increases macrophage recruitment and the levels of cancer cell-derived CSF1. Targeting CSF1 signaling under baseline or chemotherapy-treatment conditions reduces the number of infiltrated macrophages. It is further shown that results obtained with the 3D microfluidic model reflect the recruitment profiles of macrophages in patient-derived xenografts in vivo. These findings highlight the role of CSF1 signaling in establishing macrophage-rich ovarian cancer microenvironments, as well as the utility of microfluidic models in recapitulating 3D tumor ecosystems and dissecting cancer-macrophage signaling.

The ubiquitin ligases Cbl and Cbl-b regulate macrophage growth by controlling CSF-1R import into macropinosomes

The ubiquitination of transmembrane receptors regulates endocytosis, intracellular traffic, and signal transduction. Bone marrow-derived macrophages from myeloid Cbl-/- and Cbl-b-/- double knockout (DKO) mice display sustained proliferation mirroring the myeloproliferative disease that these mice succumb to. Here, we found that the ubiquitin ligases Cbl and Cbl-b have overlapping functions for controlling the endocytosis and intracellular traffic of the CSF-1R. DKO macrophages displayed complete loss of ubiquitination of the CSF-1R whereas partial ubiquitination was observed for either single Cbl-/- or Cbl-b-/- macrophages. Unlike wild type, DKO macrophages were immortal and displayed slower CSF-1R internalization, elevated AKT signaling, and a failure to transport the CSF-1R into the lumen of nascent macropinosomes, leaving its cytoplasmic region available for signaling. CSF-1R degradation depended upon lysosomal vATPase activity in both WT and DKO macrophages, with this degradation confined to macropinosomes in WT but occurring in distributed/tubular lysosomes in DKO cells. RNA-sequencing comparison of Cbl-/-, Cbl-b-/- and DKO macrophages indicated that while the overall macrophage transcriptional program remained intact, DKO macrophages had alterations in gene expression associated with growth factor signaling, cell cycle, inflammation and senescence. Cbl-b-/- had minimal effect on the transcriptional program whereas Cbl-/- led to more alternations but only DKO macrophages demonstrated substantial changes in the transcriptome, suggesting overlapping but unique functions for the two Cbl-family members. Thus, Cbl/Cbl-b-mediated ubiquitination of CSF-1R regulates its endocytic fate, constrains inflammatory gene expression, and regulates signaling for macrophage proliferation.

Validation of CSF-1 receptor (CD115) staining for analysis of murine monocytes by flow cytometry

CD115, the receptor for colony stimulating factor 1, is essential for survival and differentiation of monocytes and macrophages and is therefore frequently used to define monocyte subsets and their progenitors in immunological assays. However, CD115 surface expression and detection by flow cytometry is greatly influenced by cell isolation and processing methods, organ source, and disease context. In a systematic analysis of murine monocytes, we define experimental conditions that preserve or limit CD115 surface expression and staining by flow cytometry. We also find that, independent of conditions, CD115 surface levels are consistently lower in Ly6Clo monocytes than in Ly6Chi monocytes, with the exception of Ly6Clo monocytes in the bone marrow. Furthermore, in contrast to IL-34, the presence of colony stimulating factor 1 impairs CD115 antibody staining in a dose-dependent manner, which, in a model of ischemic kidney injury with elevated levels of colony stimulating factor 1, influenced quantification of kidney monocytes. Thus, staining and experimental conditions affect quantitative and qualitative analysis of monocytes and may influence experimental conclusions.

Targeting CSF-1R represents an effective strategy in modulating inflammatory diseases

Colony-stimulating factor-1 receptor (CSF-1R), also known as FMS kinase, is a type I single transmembrane protein mainly expressed in myeloid cells, such as monocytes, macrophages, glial cells, and osteoclasts. The endogenous ligands, colony-stimulating factor-1 (CSF-1) and Interleukin-34 (IL-34), activate CSF-1R and downstream signaling pathways including PI3K-AKT, JAK-STATs, and MAPKs, and modulate the proliferation, differentiation, migration, and activation of target immune cells. Over the past decades, the promising therapeutic potential of CSF-1R signaling inhibition has been widely studied for decreasing immune suppression and escape in tumors, owing to depletion and reprogramming of tumor-associated macrophages. In addition, the excessive activation of CSF-1R in inflammatory diseases is consecutively uncovered in recent years, which may result in inflammation in bone, kidney, lung, liver and central nervous system. Agents against CSF-1R signaling have been increasingly investigated in preclinical or clinical studies for inflammatory diseases treatment. However, the pathological mechanism of CSF-1R in inflammation is indistinct and whether CSF-1R signaling can be identified as biomarkers remains controversial. With the background information aforementioned, this review focus on the dialectical roles of CSF-1R and its ligands in regulating innate immune cells and highlights various therapeutic implications of blocking CSF-1R signaling in inflammatory diseases.

Cancer co-opts differentiation of B-cell precursors into macrophage-like cells

We have recently reported that some cancers induce accumulation of bone marrow (BM) B-cell precursors in the spleen to convert them into metastasis-promoting, immunosuppressive B cells. Here, using various murine tumor models and samples from humans with breast and ovarian cancers, we provide evidence that cancers also co-opt differentiation of these B-cell precursors to generate macrophage-like cells (termed B-MF). We link the transdifferentiation to a small subset of CSF1R⁺ Pax5^Low cells within BM pre-B and immature B cells responding to cancer-secreted M-CSF with downregulation of the transcription factor Pax5 via CSF1R signaling. Although the primary source of tumor-associated macrophages is monocytes, B-MFs are phenotypically and functionally distinguishable. Compared to monocyte-derived macrophages, B-MFs more efficiently phagocytize apoptotic cells, suppress proliferation of T cells and induce FoxP3⁺ regulatory T cells. In mouse tumor models, B-MFs promote shrinkage of the tumor-infiltrating IFNγ⁺ CD4 T cell pool and increase cancer progression and metastasis, suggesting that this cancer-induced transdifferentiation pathway is functionally relevant and hence could serve as an immunotherapeutic target.

The tumour microenvironment has been shown to change the phenotypes and functionality of immune cells to enable tumour propagation. Here authors show that cancers can derail B cell development to give rise to macrophage-like cells, contributing to cancer progression and metastasis via disabling local T cell response.

Systematic assessment of salivary inflammatory markers and dental caries in children: an exploratory study

OBJECTIVE

To investigate associations between a wide panel of salivary inflammatory markers and the presence of dental caries among children.

MATERIAL AND METHODS

In this exploratory, cross-sectional study, 176 children, aged 7-9, underwent a dental examination. Information on the children's oral health habits and lifestyles was collected from their mothers. In addition, saliva samples were collected and analyzed using a multiplex immunoassay. Of 92 inflammatory markers measured, 56 were included in the statistical analyses. To identify potential inflammatory markers associated with caries, we applied low to advanced statistical analyses. First, we performed traditional logistic regression analysis followed by Bonferroni corrections. Thereafter, a more robust and less conservative statistical approach, i.e. Least Absolute Shrinkage and Selection Operator (LASSO), was applied. The models were adjusted for potential confounders.

RESULTS

Of the 176 children in the study, 22.2% were affected by caries. Among the 56 salivary inflammatory markers, only macrophage colony-stimulating factor 1 (CSF1) was selected by the LASSO and found to be positively associated with the presence of caries.

CONCLUSIONS

The observed association between CSF1 and the presence of caries may be of clinical value in caries risk management and early diagnosis. Larger studies are warranted to assess the replicability of our findings.

Onc201 reduces osteoclastogenesis and prevents ovariectomy-induced bone loss via inhibiting RANKL-induced NFATc1 activation and the integrin signaling pathway

Osteoporosis is an osteolytic disease with a disrupted balance between the resorption and formation of bone as well as bone microstructure degeneration, leading to bone loss and increased fracture risk, which greatly affects patients' quality of life. Currently, inhibition of osteoclast bone resorption remains the mainstream treatment for osteoporosis. Onc201, a new compound, induces the gene expression of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) and has an efficient anticancer effect in clinical trials. However, its effects on osteolytic disease and the mechanism of action are unclear. We examined the effect of Onc201 on nuclear factor κB ligand-receptor activator (RANKL)-induced osteoclasts via Cell Counting Kit-8, bone resorption assay, luciferase reporter assay, immunofluorescence staining, calcium ion intensity assay and employed an ovariectomy model to investigate the effect of Onc201 on osteoporosis in the mice. Results showed that Onc201 inhibited the function and formation of osteoclasts induced by RANKL in a manner that was dependent on time and concentration, and did not cause cytotoxicity. Mechanistically, Onc201 inhibited osteoclast-relevant genes and NFATc1 expression, the main transcriptional regulatory factor of the formation of osteoclasts induced by RANKL; meanwhile, downregulating the expressions of the osteoclast cytoskeleton key signal molecules integrin αvβ3, focal adhesion kinase (FAK), c-Src, and spleen-associated tyrosine kinase (SYK). In addition, Onc201 had a protective effect on the mouse model of bone loss caused by ovariectomy-induced estrogen deficiency, which is consistent with the in vitro results. Our findings suggest that the new small-molecular compound Onc201 has the potential to prevent osteoclast-related osteolytic diseases.

Transitional premonocytes emerge in the periphery for host defense against bacterial infections

Circulating Ly6C^hi monocytes often undergo cellular death upon exhaustion of their antibacterial effector functions, which limits their capacity for subsequent macrophage differentiation. This shrouds the understanding on how the host replaces the tissue-resident macrophage niche effectively during bacterial invasion to avert infection morbidity. Here, we show that proliferating transitional premonocytes (TpMos), an immediate precursor of mature Ly6C^hi monocytes (MatMos), were mobilized into the periphery in response to acute bacterial infection and sepsis. TpMos were less susceptible to apoptosis and served as the main source of macrophage replenishment when MatMos were vulnerable toward bacteria-induced cellular death. Furthermore, TpMo and its derived macrophages contributed to host defense by balancing the proinflammatory cytokine response of MatMos. Consequently, adoptive transfer of TpMos improved the survival outcome of lethal sepsis. Our findings hence highlight a protective role for TpMos during bacterial infections and their contribution toward monocyte-derived macrophage heterogeneity in distinct disease outcomes.

[Unintended Observations Leading to Macrophage Growth and Neutrophil Factor Research]

My research area in the pharmaceutical industry is innate immunity, especially in phagocytic cells. First, I studied the heat-stable growth factor of peripheral macrophages in tumorous ascitic fluid and found that lipoproteins are an influencing factor. Later, my colleagues and I found that lipid-containing substances, namely, oxidized low-density lipoprotein, dead neutrophils, or purified lipids that could be scavenged by macrophages, induce their growth. From the series of this study, I concluded that phagocytic substances induce macrophage growth by autocrine stimulation of granulocyte-macrophage colony-stimulating factor (GM-CSF). During the study, we found that neutrophils have growth-inhibitory effects against a variety of cells. Then, I elucidated that the primary factor is a zinc-binding protein, calprotectin, an abundant protein complex in the neutrophil cytosol. I found that calprotectin induces apoptosis in many cell types, including tumor cells and normal fibroblasts, and that the zinc-binding capacity is essential for its activity. Microscopic observations revealed that neutrophil extract contains factor-inducing three-dimensional cell aggregation of human mammary carcinoma, MCF-7. I elucidated that cathepsin G is responsible for this activity and that its effect is dependent on the activation of insulin-like growth factor-1. I believe that this modest, albeit novel, observation was crucial to my thirty-nine-year-long career researching phagocytic cells.

Functions of macrophage colony-stimulating factor (CSF1) in development, homeostasis, and tissue repair

Macrophage colony-stimulating factor (CSF1) is the primary growth factor required for the control of monocyte and macrophage differentiation, survival, proliferation and renewal. Although the cDNAs encoding multiple isoforms of human CSF1 were cloned in the 1980s, and recombinant proteins were available for testing in humans, CSF1 has not yet found substantial clinical application. Here we present an overview of CSF1 biology, including evolution, regulation and functions of cell surface and secreted isoforms. CSF1 is widely-expressed, primarily by cells of mesenchymal lineages, in all mouse tissues. Cell-specific deletion of a floxed Csf1 allele in mice indicates that local CSF1 production contributes to the maintenance of tissue-specific macrophage populations but is not saturating. CSF1 in the circulation is controlled primarily by receptor-mediated clearance by macrophages in liver and spleen. Administration of recombinant CSF1 to humans or animals leads to monocytosis and expansion of tissue macrophage populations and growth of the liver and spleen. In a wide variety of tissue injury models, CSF1 administration promotes monocyte infiltration, clearance of damaged cells and repair. We suggest that CSF1 has therapeutic potential in regenerative medicine.

The structural dynamics of macropinosome formation and PI3-kinase-mediated sealing revealed by lattice light sheet microscopy

Macropinosomes are formed by shaping actin-rich plasma membrane ruffles into large intracellular organelles in a phosphatidylinositol 3-kinase (PI3K)-coordinated manner. Here, we utilize lattice lightsheet microscopy and image visualization methods to map the three-dimensional structure and dynamics of macropinosome formation relative to PI3K activity. We show that multiple ruffling morphologies produce macropinosomes and that the majority form through collisions of adjacent PI3K-rich ruffles. By combining multiple volumetric representations of the plasma membrane structure and PI3K products, we show that PI3K activity begins early throughout the entire ruffle volume and continues to increase until peak activity concentrates at the base of the ruffle after the macropinosome closes. Additionally, areas of the plasma membrane rich in ruffling had increased PI3K activity and produced many macropinosomes of various sizes. Pharmacologic inhibition of PI3K activity had little effect on the rate and morphology of membrane ruffling, demonstrating that early production of 3'-phosphoinositides within ruffles plays a minor role in regulating their morphology. However, 3'-phosphoinositides are critical for the fusogenic activity that seals ruffles into macropinosomes. Taken together, these data indicate that local PI3K activity is amplified in ruffles and serves as a priming mechanism for closure and sealing of ruffles into macropinosomes.

The structural dynamics of macropinosome formation and PI3-kinase-mediated sealing revealed by lattice light sheet microscopy

Macropinosomes are formed by shaping actin-rich plasma membrane ruffles into large intracellular organelles in a phosphatidylinositol 3-kinase (PI3K)-coordinated manner. Here, we utilize lattice lightsheet microscopy and image visualization methods to map the three-dimensional structure and dynamics of macropinosome formation relative to PI3K activity. We show that multiple ruffling morphologies produce macropinosomes and that the majority form through collisions of adjacent PI3K-rich ruffles. By combining multiple volumetric representations of the plasma membrane structure and PI3K products, we show that PI3K activity begins early throughout the entire ruffle volume and continues to increase until peak activity concentrates at the base of the ruffle after the macropinosome closes. Additionally, areas of the plasma membrane rich in ruffling had increased PI3K activity and produced many macropinosomes of various sizes. Pharmacologic inhibition of PI3K activity had little effect on the rate and morphology of membrane ruffling, demonstrating that early production of 3'-phosphoinositides within ruffles plays a minor role in regulating their morphology. However, 3'-phosphoinositides are critical for the fusogenic activity that seals ruffles into macropinosomes. Taken together, these data indicate that local PI3K activity is amplified in ruffles and serves as a priming mechanism for closure and sealing of ruffles into macropinosomes.

Homeostatic functions of monocytes and interstitial lung macrophages are regulated via collagen domain-binding receptor LAIR1

Myeloid cells encounter stromal cells and their matrix determinants on a continual basis during their residence in any given organ. Here, we examined the impact of the collagen receptor LAIR1 on myeloid cell homeostasis and function. LAIR1 was highly expressed in the myeloid lineage and enriched in non-classical monocytes. Proteomic definition of the LAIR1 interactome identified stromal factor Colec12 as a high-affinity LAIR1 ligand. Proteomic profiling of LAIR1 signaling triggered by Collagen1 and Colec12 highlighted pathways associated with survival, proliferation, and differentiation. Lair1^-/- mice had reduced frequencies of Ly6C^- monocytes, which were associated with altered proliferation and apoptosis of non-classical monocytes from bone marrow and altered heterogeneity of interstitial macrophages in lung. Myeloid-specific LAIR1 deficiency promoted metastatic growth in a melanoma model and LAIR1 expression associated with improved clinical outcomes in human metastatic melanoma. Thus, monocytes and macrophages rely on LAIR1 sensing of stromal determinants for fitness and function, with relevance in homeostasis and disease.

Interleukin-20 Acts as a Promotor of Osteoclastogenesis and Orthodontic Tooth Movement

Objectives

Bones constitute organs that are engaged in constant self-remodelling. Osteoblast and osteoclast homeostasis during remodelling contribute to overall skeletal status. Orthodontics is a clinical discipline that involves the investigation and implementation of moving teeth through the bone. The application of mechanical force to the teeth causes an imbalance between osteogenesis and osteogenesis in alveolar bone, leading to tooth movement. Osteoimmunology comprises the crosstalk between the immune and skeletal systems that regulate osteoclast–osteoblast homeostasis. Interleukin- (IL-) 20, an IL-10 family member, is regarded as a proinflammatory factor for autoimmune diseases and has been implicated in bone loss disease. However, the mechanism by which IL-20 regulates osteoclast differentiation and osteoclastogenesis activation remains unclear. This study investigated the effects of IL-20 on osteoclast differentiation in a rat model; it explored the underlying molecular mechanism in vitro and the specific effects on orthodontic tooth movement in vivo.

Methods

For in vitro analyses, primary rat bone marrow-derived macrophages (BMMs) were prepared from Sprague–Dawley rats for osteoclast induction. After BMMs had been treated with combinations of recombinant IL-20 protein, siRNA, and plasmids, the expression levels of osteoclast-specific factors and signalling pathway proteins were detected through real-time polymerase chain reaction, western blotting, and immunofluorescence staining. For in vivo analyses, IL-20 was injected into the rat intraperitoneal cavity after the establishment of a rat orthodontic tooth movement (OTM) model. OTM distance was detected by Micro-CT and HE staining; the expression levels of protein were detected through immunofluorescence staining.

Results

In vitro analyses showed that a low concentration of IL-20 promoted preosteoclast proliferation and osteoclastogenesis. However, a high concentration of IL-20 inhibited BMM proliferation and osteoclastogenesis. IL-20 knockdown decreased the expression of osteoclast specific-markers, while IL-20 overexpression increased the expression of osteoclast specific-markers. Furthermore, IL-20 regulated osteoclast differentiation through the OPG/RANKL/RANK pathway. Overexpression of IL-20 could significantly upregulate RANKL-mediated osteoclast differentiation and osteoclast specific-marker expression; moreover, RANKL/NF-κB/NFATc1 acted as downstream signalling molecule for IL-20. In vivo analysis showed that OTM speed was significantly increased after intraperitoneal injection of IL-20; additionally, mechanical stress sensing proteins were markedly activated.

Conclusions

IL-20 augments osteoclastogenesis and osteoclast-mediated bone erosion through the RANKL/NF-κB/NFATc1 signalling pathway. IL-20 inhibition can effectively reduce osteoclast differentiation and diminish bone resorption. Furthermore, IL-20 can accelerate orthodontic tooth movement and activate mechanical stress sensing proteins.

Contribution of colony-stimulating factor 1 to neuropathic pain

Molecular and cellular interactions among spinal dorsal horn neurons and microglia, the resident macrophages of the central nervous system, contribute to the induction and maintenance of neuropathic pain after peripheral nerve injury. Emerging evidence also demonstrates that reciprocal interactions between macrophages and nociceptive sensory neurons in the dorsal root ganglion contribute to the initiation and persistence of nerve injury-induced mechanical hypersensitivity (allodynia). We previously reported that sensory neuron-derived colony-stimulating factor 1 (CSF1), by engaging the CSF1 receptor (CSF1R) that is expressed by both microglia and macrophages, triggers the nerve injury-induced expansion of both resident microglia in the spinal cord and macrophages in the dorsal root ganglion and induces their respective contributions to the neuropathic pain phenotype. Here, we review recent research and discuss unanswered questions regarding CSF1/CSF1R-mediated microglial and macrophage signaling in the generation of neuropathic pain.

IL-34 and CSF-1, deciphering similarities and differences at steady state and in diseases

Although IL-34 and CSF-1 share actions as key mediators of monocytes/macrophages survival and differentiation, they also display differences that should be identified to better define their respective roles in health and diseases. IL-34 displays low sequence homology with CSF-1 but has a similar general structure and they both bind to a common receptor CSF-1R, although binding and subsequent intracellular signaling shows differences. CSF-1R expression has been until now mainly described at a steady state in monocytes/macrophages and myeloid dendritic cells, as well as in some cancers. IL-34 has also 2 other receptors, protein-tyrosine phosphatase zeta (PTPζ) and CD138 (Syndecan-1), expressed in some epithelium, cells of the central nervous system (CNS), as well as in numerous cancers. While most, if not all, of CSF-1 actions are mediated through monocyte/macrophages, IL-34 has also other potential actions through PTPζ and CD138. Additionally, IL-34 and CSF-1 are produced by different cells in different tissues. This review describes and discusses similarities and differences between IL-34 and CSF-1 at steady state and in pathological situations and identifies possible ways to target IL-34, CSF-1, and its receptors.

Potential for Targeting Myeloid Cells in Controlling CNS Inflammation

Multiple Sclerosis (MS) is characterized by immune cell infiltration to the central nervous system (CNS) as well as loss of myelin. Characterization of the cells in lesions of MS patients revealed an important accumulation of myeloid cells such as macrophages and dendritic cells (DCs). Data from the experimental autoimmune encephalomyelitis (EAE) model of MS supports the importance of peripheral myeloid cells in the disease pathology. However, the majority of MS therapies focus on lymphocytes. As we will discuss in this review, multiple strategies are now in place to target myeloid cells in clinical trials. These strategies have emerged from data in both human and mouse studies. We discuss strategies targeting myeloid cell migration, growth factors and cytokines, biological functions (with a focus on miRNAs), and immunological activities (with a focus on nanoparticles).

Osteoblast-Osteoclast Communication and Bone Homeostasis

Bone remodeling is tightly regulated by a cross-talk between bone-forming osteoblasts and bone-resorbing osteoclasts. Osteoblasts and osteoclasts communicate with each other to regulate cellular behavior, survival and differentiation through direct cell-to-cell contact or through secretory proteins. A direct interaction between osteoblasts and osteoclasts allows bidirectional transduction of activation signals through EFNB2-EPHB4, FASL-FAS or SEMA3A-NRP1, regulating differentiation and survival of osteoblasts or osteoclasts. Alternatively, osteoblasts produce a range of different secretory molecules, including M-CSF, RANKL/OPG, WNT5A, and WNT16, that promote or suppress osteoclast differentiation and development. Osteoclasts also influence osteoblast formation and differentiation through secretion of soluble factors, including S1P, SEMA4D, CTHRC1 and C3. Here we review the current knowledge regarding membrane bound- and soluble factors governing cross-talk between osteoblasts and osteoclasts.

Macrophages and Cardiovascular Health

Research during the last decade has generated numerous insights on the presence, phenotype, and function of myeloid cells in cardiovascular organs. Newer tools with improved detection sensitivities revealed sizable populations of tissue-resident macrophages in all major healthy tissues. The heart and blood vessels contain robust numbers of these cells; for instance, 8% of noncardiomyocytes in the heart are macrophages. This number and the cell's phenotype change dramatically in disease conditions. While steady-state macrophages are mostly monocyte independent, macrophages residing in the inflamed vascular wall and the diseased heart derive from hematopoietic organs. In this review, we will highlight signals that regulate macrophage supply and function, imaging applications that can detect changes in cell numbers and phenotype, and opportunities to modulate cardiovascular inflammation by targeting macrophage biology. We strive to provide a systems-wide picture, i.e., to focus not only on cardiovascular organs but also on tissues involved in regulating cell supply and phenotype, as well as comorbidities that promote cardiovascular disease. We will summarize current developments at the intersection of immunology, detection technology, and cardiovascular health.

New Therapeutic Avenues of mCSF for Brain Diseases and Injuries

Macrophage colony-stimulating factor (mCSF) is a cytokine known to promote the recruitment of macrophages inducing the release of CCL2, a chemokine mobilizing monocytes to sites of inflammation. Additionally, it induces microglia/macrophage proliferation and the polarization of these cells towards a M2-like phenotype, impairing their ability to release pro-inflammatory factors and toxic mediators, while favoring the release of mediators promoting tissue repair. Another important player is the mCSF receptor CSFR1, which is highly expressed in monocytes, macrophages and microglia. Here, we discuss the new interesting therapeutic avenue of the mCSF/CSFR1 axis on brain diseases. More specifically, mCSF cascade might stimulate the survival/proliferation of oligodendrocytes, enhance the immune response as well as modulate the release of growth factors and the phagocytic activity of immune cells to remove myelin debris and toxic proteins from the brain.

Paracrine and endocrine actions of bone-the functions of secretory proteins from osteoblasts, osteocytes, and osteoclasts

The skeleton is a dynamic organ that is constantly remodeled. Proteins secreted from bone cells, namely osteoblasts, osteocytes, and osteoclasts exert regulation on osteoblastogenesis, osteclastogenesis, and angiogenesis in a paracrine manner. Osteoblasts secrete a range of different molecules including RANKL/OPG, M-CSF, SEMA3A, WNT5A, and WNT16 that regulate osteoclastogenesis. Osteoblasts also produce VEGFA that stimulates osteoblastogenesis and angiogenesis. Osteocytes produce sclerostin (SOST) that inhibits osteoblast differentiation and promotes osteoclast differentiation. Osteoclasts secrete factors including BMP6, CTHRC1, EFNB2, S1P, WNT10B, SEMA4D, and CT-1 that act on osteoblasts and osteocytes, and thereby influenceaA osteogenesis. Osteoclast precursors produce the angiogenic factor PDGF-BB to promote the formation of Type H vessels, which then stimulate osteoblastogenesis. Besides, the evidences over the past decades show that at least three hormones or "osteokines" from bone cells have endocrine functions. FGF23 is produced by osteoblasts and osteocytes and can regulate phosphate metabolism. Osteocalcin (OCN) secreted by osteoblasts regulates systemic glucose and energy metabolism, reproduction, and cognition. Lipocalin-2 (LCN2) is secreted by osteoblasts and can influence energy metabolism by suppressing appetite in the brain. We review the recent progresses in the paracrine and endocrine functions of the secretory proteins of osteoblasts, osteocytes, and osteoclasts, revealing connections of the skeleton with other tissues and providing added insights into the pathogenesis of degenerative diseases affecting multiple organs and the drug discovery process.

Inhibition of Local Macrophage Growth Ameliorates Focal Inflammation and Suppresses Atherosclerosis

OBJECTIVE

Macrophages play a central role in various stages of atherosclerotic plaque formation and progression. The local macrophages reportedly proliferate during atherosclerosis, but the pathophysiological significance of macrophage proliferation in this context remains unclear. Here, we investigated the involvement of local macrophage proliferation during atherosclerosis formation and progression using transgenic mice, in which macrophage proliferation was specifically suppressed.

APPROACH AND RESULTS

Inhibition of macrophage proliferation was achieved by inducing the expression of cyclin-dependent kinase inhibitor 1B, also known as p27^kip, under the regulation of a scavenger receptor promoter/enhancer. The macrophage-specific human p27^kip Tg mice were subsequently crossed with apolipoprotein E-deficient mice for the atherosclerotic plaque study. Results showed that a reduced number of local macrophages resulted in marked suppression of atherosclerotic plaque formation and inflammatory response in the plaque. Moreover, fewer local macrophages in macrophage-specific human p27^kip Tg mice helped stabilize the plaque, as evidenced by a reduced necrotic core area, increased collagenous extracellular matrix, and thickened fibrous cap.

CONCLUSIONS

These results provide direct evidence of the involvement of local macrophage proliferation in formation and progression of atherosclerotic plaques and plaque stability. Thus, control of macrophage proliferation might represent a therapeutic target for treating atherosclerotic diseases.

Biochemical and Clinical Impact of Organic Uremic Retention Solutes: A Comprehensive Update

In this narrative review, the biological/biochemical impact (toxicity) of a large array of known individual uremic retention solutes and groups of solutes is summarized. We classified these compounds along their physico-chemical characteristics as small water-soluble compounds or groups, protein bound compounds and middle molecules. All but one solute (glomerulopressin) affected at least one mechanism with the potential to contribute to the uremic syndrome. In general, several mechanisms were influenced for each individual solute or group of solutes, with some impacting up to 7 different biological systems of the 11 considered. The inflammatory, cardio-vascular and fibrogenic systems were those most frequently affected and they are one by one major actors in the high morbidity and mortality of CKD but also the mechanisms that have most frequently been studied. A scoring system was built with the intention to classify the reviewed compounds according to the experimental evidence of their toxicity (number of systems affected) and overall experimental and clinical evidence. Among the highest globally scoring solutes were 3 small water-soluble compounds [asymmetric dimethylarginine (ADMA); trimethylamine-N-oxide (TMAO); uric acid], 6 protein bound compounds or groups of protein bound compounds [advanced glycation end products (AGEs); p-cresyl sulfate; indoxyl sulfate; indole acetic acid; the kynurenines; phenyl acetic acid;] and 3 middle molecules [β₂-microglobulin; ghrelin; parathyroid hormone). In general, more experimental data were provided for the protein bound molecules but for almost half of them clinical evidence was missing in spite of robust experimental data. The picture emanating is one of a complex disorder, where multiple factors contribute to a multisystem complication profile, so that it seems of not much use to pursue a decrease of concentration of a single compound.

Macrophages orchestrate breast cancer early dissemination and metastasis

Cancer cell dissemination during very early stages of breast cancer proceeds through poorly understood mechanisms. Here we show, in a mouse model of HER2⁺ breast cancer, that a previously described sub-population of early-evolved cancer cells requires macrophages for early dissemination. Depletion of macrophages specifically during pre-malignant stages reduces early dissemination and also results in reduced metastatic burden at end stages of cancer progression. Mechanistically, we show that, in pre-malignant lesions, CCL2 produced by cancer cells and myeloid cells attracts CD206⁺/Tie2⁺ macrophages and induces Wnt-1 upregulation that in turn downregulates E-cadherin junctions in the HER2⁺ early cancer cells. We also observe macrophage-containing tumor microenvironments of metastasis structures in the pre-malignant lesions that can operate as portals for intravasation. These data support a causal role for macrophages in early dissemination that affects long-term metastasis development much later in cancer progression. A pilot analysis on human specimens revealed intra-epithelial macrophages and loss of E-cadherin junctions in ductal carcinoma in situ, supporting a potential clinical relevance.

CCR2-dependent monocyte-derived macrophages resolve inflammation and restore gut motility in postoperative ileus

OBJECTIVE

Postoperative ileus (POI) is assumed to result from myeloid cells infiltrating the intestinal muscularis externa (ME) in patients undergoing abdominal surgery. In the current study, we investigated the role of infiltrating monocytes in a murine model of intestinal manipulation (IM)-induced POI in order to clarify whether monocytes mediate tissue damage and intestinal dysfunction or they are rather involved in the recovery of gastrointestinal (GI) motility.

DESIGN

IM was performed in mice with defective monocyte migration to tissues (C-C motif chemokine receptor 2, Ccr2^{-/ -} mice) and wild-type (WT) mice to study the role of monocytes and monocyte-derived macrophages (MΦs) during onset and resolution of ME inflammation.

RESULTS

At early time points, IM-induced GI transit delay and inflammation were equal in WT and Ccr2 ^-/- mice. However, GI transit recovery after IM was significantly delayed in Ccr2 ^-/- mice compared with WT mice, associated with increased neutrophil-mediated immunopathology and persistent impaired neuromuscular function. During recovery, monocyte-derived MΦs acquire pro-resolving features that aided in the resolution of inflammation. In line, bone marrow reconstitution and treatment with MΦ colony-stimulating factor 1 enhanced monocyte recruitment and MΦ differentiation and ameliorated GI transit in Ccr2 ^-/- mice.

CONCLUSION

Our study reveals a critical role for monocyte-derived MΦs in restoring intestinal homeostasis after surgical trauma. From a therapeutic point of view, our data indicate that inappropriate targeting of monocytes may increase neutrophil-mediated immunopathology and prolong the clinical outcome of POI, while future therapies should be aimed at enhancing MΦ physiological repair functions.

Macrophages and skeletal health

Bone is in a constant state of remodeling, a process which was once attributed solely to osteoblasts and osteoclasts. Decades of research has identified many other populations of cells in the bone that participate and mediate skeletal homeostasis. Recently, osteal macrophages emerged as vital participants in skeletal remodeling and osseous repair. The exact mechanistic roles of these tissue-resident macrophages are currently under investigation. Macrophages are highly plastic in response to their micro-environment and are typically classified as being pro- or anti-inflammatory (pro-resolving) in nature. Given that inflammatory states result in decreased bone mass, proinflammatory macrophages may be negative regulators of bone turnover. Pro-resolving macrophages have been shown to release anabolic factors and may present a target for therapeutic intervention in inflammation-induced bone loss and fracture healing. The process of apoptotic cell clearance, termed efferocytosis, is mediated by pro-resolving macrophages and may contribute to steady-state bone turnover as well as fracture healing and anabolic effects of osteoporosis therapies. Parathyroid hormone is an anabolic agent in bone that is more effective in the presence of mature phagocytic macrophages, further supporting the hypothesis that efferocytic macrophages are positive contributors to bone turnover. Therapies which alter macrophage plasticity in tissues other than bone should be explored for their potential to treat bone loss either alone or in conjunction with current bone therapeutics. A better understanding of the exact mechanisms by which macrophages mediate bone homeostasis will lead to an expansion of pharmacologic targets for the treatment of osteoporosis and inflammation-induced bone loss.

CSF-1 receptor signalling is governed by pre-requisite EHD1 mediated receptor display on the macrophage cell surface

Colony stimulating factor-1 receptor (CSF-1R), a receptor tyrosine kinase (RTK), is the master regulator of macrophage biology. CSF-1 can bind CSF-1R resulting in receptor activation and signalling essential for macrophage functions such as proliferation, differentiation, survival, polarization, phagocytosis, cytokine secretion, and motility. CSF-1R activation can only occur after the receptor is presented on the macrophage cell surface. This process is reliant upon the underlying macrophage receptor trafficking machinery. However, the mechanistic details governing this process are incompletely understood. C-terminal Eps15 Homology Domain-containing (EHD) proteins have recently emerged as key regulators of receptor trafficking but have not yet been studied in the context of macrophage CSF-1R signalling. In this manuscript, we utilize primary bone-marrow derived macrophages (BMDMs) to reveal a novel function of EHD1 as a regulator of CSF-1R abundance on the cell surface. We report that EHD1-knockout (EHD1-KO) macrophages cell surface and total CSF-1R levels are significantly decreased. The decline in CSF-1R levels corresponds with reduced downstream macrophage functions such as cell proliferation, migration, and spreading. In EHD1-KO macrophages, transport of newly synthesized CSF-1R to the macrophage cell surface was reduced and was associated with the shunting of the receptor to the lysosome, which resulted in receptor degradation. These findings reveal a novel and functionally important role for EHD1 in governing CSF-1R signalling via regulation of anterograde transport of CSF-1R to the macrophage cell surface.

M-CSF Mediates Host Defense during Bacterial Pneumonia by Promoting the Survival of Lung and Liver Mononuclear Phagocytes

Gram-negative bacterial pneumonia is a common and dangerous infection with diminishing treatment options due to increasing antibiotic resistance among causal pathogens. The mononuclear phagocyte system is a heterogeneous group of leukocytes composed of tissue-resident macrophages, dendritic cells, and monocyte-derived cells that are critical in defense against pneumonia, but mechanisms that regulate their maintenance and function during infection are poorly defined. M-CSF has myriad effects on mononuclear phagocytes but its role in pneumonia is unknown. We therefore tested the hypothesis that M-CSF is required for mononuclear phagocyte-mediated host defenses during bacterial pneumonia in a murine model of infection. Genetic deletion or immunoneutralization of M-CSF resulted in reduced survival, increased bacterial burden, and greater lung injury. M-CSF was necessary for the expansion of lung mononuclear phagocytes during infection but did not affect the number of bone marrow or blood monocytes, proliferation of precursors, or recruitment of leukocytes to the lungs. In contrast, M-CSF was essential to survival and antimicrobial functions of both lung and liver mononuclear phagocytes during pneumonia, and its absence resulted in bacterial dissemination to the liver and hepatic necrosis. We conclude that M-CSF is critical to host defenses against bacterial pneumonia by mediating survival and antimicrobial functions of mononuclear phagocytes in the lungs and liver.

Transcriptome profiling of immune tissues reveals habitat-specific gene expression between lake and river sticklebacks

The observation of habitat-specific phenotypes suggests the action of natural selection. The three-spined stickleback (Gasterosteus aculeatus) has repeatedly colonized and adapted to diverse freshwater habitats across the northern hemisphere since the last glaciation, while giving rise to recurring phenotypes associated with specific habitats. Parapatric lake and river populations of sticklebacks harbour distinct parasite communities, a factor proposed to contribute to adaptive differentiation between these ecotypes. However, little is known about the transcriptional response to the distinct parasite pressure of those fish in a natural setting. Here, we sampled wild-caught sticklebacks across four geographical locations from lake and river habitats differing in their parasite load. We compared gene expression profiles between lake and river populations using 77 whole-transcriptome libraries from two immune-relevant tissues, the head kidney and the spleen. Differential expression analyses revealed 139 genes with habitat-specific expression patterns across the sampled population pairs. Among the 139 differentially expressed genes, eight are annotated with an immune function and 42 have been identified as differentially expressed in previous experimental studies in which fish have been immune challenged. Together, these findings reinforce the hypothesis that parasites contribute to adaptation of sticklebacks in lake and river habitats.

GM-CSF: An immune modulatory cytokine that can suppress autoimmunity

GM-CSF was originally identified as a colony stimulating factor (CSF) because of its ability to induce granulocyte and macrophage populations from precursor cells. Multiple studies have demonstrated that GM-CSF is also an immune-modulatory cytokine, capable of affecting not only the phenotype of myeloid lineage cells, but also T-cell activation through various myeloid intermediaries. This property has been implicated in the sustenance of several autoimmune diseases like arthritis and multiple sclerosis. In contrast, several studies using animal models have shown that GM-CSF is also capable of suppressing many autoimmune diseases such as Crohn's disease, Type-1 diabetes, Myasthenia gravis and experimental autoimmune thyroiditis. Knockout mouse studies have suggested that the role of GM-CSF in maintaining granulocyte and macrophage populations in the physiological steady state is largely redundant. Instead, its immune-modulatory role plays a significant role in the development or resolution of autoimmune diseases. This is mediated either through the differentiation of precursor cells into specialized non-steady state granulocytes, macrophages and dendritic cells, or through the modulation of the phenotype of mature myeloid cells. Thus, outside of myelopoiesis, GM-CSF has a profound role in regulating the immune response and maintaining immunological tolerance.

Regulation of miR-24, miR-30b, and miR-142-3p during macrophage and dendritic cell differentiation potentiates innate immunity

miRNAs are ubiquitous regulators of human biology. Parallel profiling of in vitro monocyte-to-Mφ and monocyte-to-DC differentiation revealed static, convergent, and divergent expression of miRNA. Bioinformatic and network analysis of differentially expressed miRNAs implicated miR-24, miR-30b, and miR-142-3p as negative regulators of intracellular signaling pathways, triggered not only by differentiation factors (M-CSF/GM-CSF/IL-4) but also from PRRs. Manipulation of miR-24, miR-30b, and miR-142-3p expression during the differentiation of mD-Mφ and mD-DC differentiation had minimal impact on the acquisition of phenotype but significantly abrogated the ability of these cells to mount inflammatory responses to pathogen-associated stimuli. Forced expression of these miRNAs, which are down-regulated during differentiation, inhibited release of inflammatory cytokines [TNF-α, IL-12(p40), IL-6] upon stimulation with LPS. Functional analysis revealed overlapping mechanisms of inhibition, including surface expression of TLR4/CD14/MD-1 and intracellular PKCα/NF-κB activation. Potential intermediary targets of the TLR4-NF-κB axis included members of the PI3K and MAPK families and PKC isoforms. These results demonstrate the requirement of miR-24, miR-30b, and miR-142-3p down-regulation for the generation of fully functional Mφs and DCs.

Tumor vessel up-regulation of INSR revealed by single-cell expression analysis of the tyrosine kinome and phosphatome in human cancers

The tyrosine kinome and phosphatome harbor oncogenes and tumor suppressor genes and important regulators of angiogenesis and tumor stroma formation. To provide a better understanding of their potential roles in cancer, we analyzed the expression of 85 tyrosine kinases and 42 tyrosine phosphatases by in situ hybridization 48 human normal and 24 tumor tissue specimens. Nine-tenths of the assessed transcripts had tumor cell expression concordant with expression array databases. Further, pan-cancer expression of AATK, PTPRK, and PTPRU and expression of PTPRS in a subset of tumors were observed. To demonstrate tumor subcompartment resolution, we validated the predicted tumor stroma-specific markers HTRA1, HTRA3, MXRA5, MXRA8, and SERPING1 in situ. In addition to known vascular and stromal markers such as PDGFRB, we observed stromal expression of PTK6 and TNS1 and vascular expression of INSR, PTPRF, PTPRG, PTPRU, and TNS1, of which INSR emerged as a tumor-specific vessel marker. This study demonstrates the feasibility of large-scale analyses to chart the transcriptome in situ in human cancers and their ability to identify novel cancer biomarkers.

IL-1β and TNFα promote monocyte viability through the induction of GM-CSF expression by rheumatoid arthritis synovial fibroblasts

BACKGROUND

Macrophages and synovial fibroblasts (SF) are two major cells implicated in the pathogenesis of rheumatoid arthritis (RA). SF could be a source of cytokines and growth factors driving macrophages survival and activation. Here, we studied the effect of SF on monocyte viability and phenotype.

METHODS

SF were isolated from synovial tissue of RA patients and CD14+ cells were isolated from peripheral blood of healthy donors. SF conditioned media were collected after 24 hours of culture with or without stimulation with TNFα or IL-1β. Macrophages polarisation was studied by flow cytometry.

RESULTS

Conditioned medium from SF significantly increased monocytes viability by 60% compared to CD14+ cells cultured in medium alone (P < 0.001). This effect was enhanced using conditioned media from IL-1β and TNFα stimulated SF. GM-CSF but not M-CSF nor IL34 blocking antibodies was able to significantly decrease monocyte viability by 30% when added to the conditioned media from IL-1β and TNFα stimulated SF (P < 0.001). Finally, monocyte cultured in presence of SF conditioned media did not exhibit a specific M1 or M2 phenotype.

CONCLUSION

Overall, rheumatoid arthritis synovial fibroblasts stimulated with proinflammatory cytokines (IL-1β and TNFα) promote monocyte viability via GM-CSF but do not induce a specific macrophage polarization.

TRPM7 regulates proliferation and polarisation of macrophages

Ion channels play pivotal roles in regulating important functions of macrophages, such as cytokine and chemokine production, migration, proliferation, phagocytosis and others. In this study, we have identified the transient receptor potential cation channel, subfamily M, member 7 (TRPM7) for the first time in macrophages. TRPM7 activity is differentially regulated in macrophages, i.e. current density in TRPM7 is significantly larger in anti-inflammatory M2-type macrophages than in untreated and in pro-inflammatory M1-type macrophages, whereas mRNA levels of TRPM7 remain unchanged upon cell polarisation. The specific TRPM7 inhibitors NS8593 and FTY720 abolish proliferation of macrophages induced by interleukin-4 (IL-4) and macrophage colony-stimulating factor (M-CSF), respectively, whereas proliferation arrest was not accompanied by induction of apoptosis or necrosis in macrophages. Furthermore, NS8593 and FTY720 prevented polarisation of macrophages towards the anti-inflammatory M2 phenotype. Inhibition of TRPM7 reduced IL-4-induced upregulation of arginase-1 (Arg1) mRNA levels and Arg1 activity, and abolished the inhibitory effects of IL-4 or M-CSF on LPS-induced TNF-α production by macrophages. In summary, our data suggest a main role of TRPM7 in the regulation of macrophage proliferation and polarisation.

Differential control of Mincle-dependent cord factor recognition and macrophage responses by the transcription factors C/EBPβ and HIF1α

Trehalose-6,6-dimycolate (TDM), the mycobacterial cord factor, and its synthetic analog Trehalose-6,6-dibehenate (TDB) bind to the C-type lectin receptors macrophage-inducible C-type lectin (Mincle) and Mcl to activate macrophages. Genetically, the transcriptional response to TDB/TDM has been defined to require FcRγ-Syk-Card9 signaling. However, TDB/TDM-triggered kinase activation has not been studied well, and it is largely unknown which transcriptional regulators bring about inflammatory gene expression. In this article, we report that TDB/TDM caused only weak Syk-phosphorylation in resting macrophages, consistent with low basal Mincle expression. However, LPS-priming caused MYD88-dependent upregulation of Mincle, resulting in enhanced TDB/TDM-induced kinase activation and more rapid inflammatory gene expression. TLR-induced Mincle expression partially circumvented the requirement for Mcl in the response to TDB/TDM. To dissect transcriptional responses to TDB/TDM, we mined microarray data and identified early growth response (Egr) family transcription factors as direct Mincle target genes, whereas upregulation of Cebpb and Hif1a required new protein synthesis. Macrophages and dendritic cells lacking C/EBPβ showed nearly complete abrogation of TDB/TDM responsiveness, but also failed to upregulate Mincle. Retroviral rescue of Mincle expression in Cebpb-deficient cells restored induction of Egr1, but not of G-CSF. This pattern of C/EBPβ dependence was also observed after stimulation with the Dectin-1 ligand Curdlan. Inducible expression of hypoxia-inducible factor 1α (HIF1α) also required C/EBPβ. In turn, HIF1α was not required for Mincle expression, kinase activation, and Egr1 or Csf3 expression, but critically contributed to NO production. Taken together, we identify C/EBPβ as central hub in Mincle expression and inflammatory gene induction, whereas HIF1α controls Nos2 expression. C/EBPβ also connects TLR signals to cord factor responsiveness through MYD88-dependent upregulation of Mincle.

Failed renoprotection by alternatively activated bone marrow macrophages is due to a proliferation-dependent phenotype switch in vivo

Alternatively activated macrophages (M2) regulate immune responses and ex vivo polarized splenic M2 are able to ameliorate renal injury including models of renal disease, such as adriamycin nephropathy. Whether M2 derived from other organs have similar protective efficacy is unknown. Here, we report adoptively transferred bone marrow M2 macrophages did not improve renal function or reduce renal injury in adriamycin nephropathy, whereas splenic M2 macrophages were protective. Bone marrow and splenic M2 macrophages showed similar regulatory phenotypes and suppressive functions in vitro. Within the inflamed kidney, suppressive phenotypes in bone marrow but not in splenic M2 macrophages, were dramatically reduced. Loss of the suppressive phenotype in bone marrow M2 was related to strong proliferation of bone marrow M2. Bone marrow M2 proliferation in vivo correlated with M-CSF expression by tubular cells in the inflamed kidney. Inhibition of M-CSF in vitro limited bone marrow M2 proliferation and prevented switch of phenotype. Proliferating cells derived from transfused bone marrow M2 were inflammatory rather than regulatory in their phenotype and function. Thus bone marrow in contrast to splenic M2 macrophages do not protect against renal structural and functional injury in murine adriamycin nephropathy. The failed renoprotection of bone marrow M2 is due to the switch of transfused M2 macrophages from a regulatory to an inflammatory phenotype.

Connexin43 is dispensable for phagocytosis

Macrophages that lack connexin43 (Cx43), a gap junction protein, have been reported to exhibit dramatic deficiencies in phagocytosis. In this study, we revisit these findings using well-characterized macrophage populations. Cx43 knockout (Cx43(-/-)) mice die soon after birth, making the harvest of macrophages from adult Cx43(-/-) mice problematic. To overcome this obstacle, we used several strategies: mice heterozygous for the deletion of Cx43 were crossed to produce Cx43(+/+) (wild type [WT]) and Cx43(-/-) fetuses. Cells isolated from 12- to 14-d fetal livers were used to reconstitute irradiated recipient animals. After reconstitution, thioglycollate-elicited macrophages were collected by peritoneal lavage and bone marrow was harvested. Bone marrow cells and, alternatively, fetal liver cells were cultured in media containing M-CSF for 7-10 d, resulting in populations of cells that were >95% macrophages based on flow cytometry. Phagocytic uptake was detected using flow cytometric and microscopic techniques. Quantification of phagocytic uptake of IgG-opsonized sheep erythrocytes, zymosan particles, and Listeria monocytogenes failed to show any significant difference between WT and Cx43(-/-) macrophages. Furthermore, the use of particles labeled with pH-sensitive dyes showed equivalent acidification of phagosomes in both WT and Cx43(-/-) macrophages. Our findings suggest that modulation of Cx43 levels in cultured macrophages does not have a significant impact on phagocytosis.

Design and pharmacology of a highly specific dual FMS and KIT kinase inhibitor

Inflammation and cancer, two therapeutic areas historically addressed by separate drug discovery efforts, are now coupled in treatment approaches by a growing understanding of the dynamic molecular dialogues between immune and cancer cells. Agents that target specific compartments of the immune system, therefore, not only bring new disease modifying modalities to inflammatory diseases, but also offer a new avenue to cancer therapy by disrupting immune components of the microenvironment that foster tumor growth, progression, immune evasion, and treatment resistance. McDonough feline sarcoma viral (v-fms) oncogene homolog (FMS) and v-kit Hardy-Zuckerman 4 feline sarcoma viral oncogene homolog (KIT) are two hematopoietic cell surface receptors that regulate the development and function of macrophages and mast cells, respectively. We disclose a highly specific dual FMS and KIT kinase inhibitor developed from a multifaceted chemical scaffold. As expected, this inhibitor blocks the activation of macrophages, osteoclasts, and mast cells controlled by these two receptors. More importantly, the dual FMS and KIT inhibition profile has translated into a combination of benefits in preclinical disease models of inflammation and cancer.

Therapeutic applications of macrophage colony-stimulating factor-1 (CSF-1) and antagonists of CSF-1 receptor (CSF-1R) signaling

Macrophage-colony stimulating factor (CSF-1) signaling through its receptor (CSF-1R) promotes the differentiation of myeloid progenitors into heterogeneous populations of monocytes, macrophages, dendritic cells, and bone-resorbing osteoclasts. In the periphery, CSF-1 regulates the migration, proliferation, function, and survival of macrophages, which function at multiple levels within the innate and adaptive immune systems. Macrophage populations elicited by CSF-1 are associated with, and exacerbate, a broad spectrum of pathologies, including cancer, inflammation, and bone disease. Conversely, macrophages can also contribute to immunosuppression, disease resolution, and tissue repair. Recombinant CSF-1, antibodies against the ligand and the receptor, and specific inhibitors of CSF-1R kinase activity have been each been tested in a range of animal models and in some cases, in patients. This review examines the potential clinical uses of modulators of the CSF-1/CSF-1R system. We conclude that CSF-1 promotes a resident-type macrophage phenotype. As a treatment, CSF-1 has therapeutic potential in tissue repair. Conversely, inhibition of CSF-1R is unlikely to be effective in inflammatory disease but may have utility in cancer.

Growth factor regulation of prostaglandin-endoperoxide synthase 2 (Ptgs2) expression in colonic mesenchymal stem cells

We previously found that a population of colonic stromal cells that constitutively express high levels of prostaglandin-endoperoxide synthase 2 (Ptgs2, also known as Cox-2) altered their location in the lamina propria in response to injury in a Myd88-dependent manner (Brown, S. L., Riehl, T. E., Walker, M. R., Geske, M. J., Doherty, J. M., Stenson, W. F., and Stappenbeck, T. S. (2007) J. Clin. Invest. 117, 258-269). At the time of this study, the identity of these cells and the mechanism by which they expressed high levels of Ptgs2 were unknown. Here we found that these colonic stromal cells were mesenchymal stem cells (MSCs). These colonic MSCs expressed high Ptgs2 levels not through interaction with bacterial products but instead as a consequence of mRNA stabilization downstream of Fgf9 (fibroblast growth factor 9), a growth factor that is constitutively expressed by the intestinal epithelium. This stabilization was mediated partially through a mechanism involving endogenous CUG-binding protein 2 (CUGbp2). These studies suggest that Fgf9 is an important factor in the regulation of Ptgs2 in colonic MSCs and may be a factor involved in its constitutive expression in vivo.

Macrophage colony stimulating factor: not just for macrophages anymore! A gateway into complex biologies

Macrophage colony stimulating factor (M-CSF, also called colony stimulating factor-1) has traditionally been viewed as a growth/differentiation factor for monocytes, macrophages, and some female-specific tumors. As a result of alternative mRNA splicing and post-translational processing, several forms of M-CSF protein are produced: a secreted glycoprotein, a longer secreted form containing proteoglycan, and a short membrane-bound isoform. These different forms of M-CSF all initiate cell signaling in cells bearing the M-CSF receptor, called c-fms. Here we review the biology of M-CSF, which has important roles in bone physiology, the intestinal tract, cancer metastases to the bone, macrophage-mediated tumor cell killing and tumor immunity. Although this review concentrates mostly on the membrane form of human M-CSF (mM-CSF), the biology of the soluble forms and the M-CSF receptor will also be discussed for comparative purposes. The mechanisms of the biological effects of the membrane-bound M-CSF reveal that this cytokine is unexpectedly involved in many complex molecular events. Recent experiments suggest that a tumor vaccine based on membrane-bound M-CSF-transduced tumor cells, combined with anti-angiogenic therapy, should be evaluated further for use in clinical trials.

Reactive nitrogen species contribute to innate host defense against Campylobacter jejuni

Campylobacter jejuni, a gram-negative, invasive organism, is a common cause of food-borne bacterial diarrheal disease. However, the relationship between C. jejuni and the innate immune system is not well described. To better characterize host defense against C. jejuni, we investigated the ability of nitric oxide/reactive nitrogen species to kill two strains of C. jejuni. C. jejuni viability was measured after exposure to reactive nitrogen species produced biochemically as acidified nitrite and by bone marrow-derived macrophages. We report that acidified nitrite caused a 3-log-increased kill of C. jejuni (P < 0.05) at doses that did not affect the viability of Salmonella enterica serovar Typhimurium. Expression of NOS2, the gene responsible for the production of inducible nitric oxide, was increased >100-fold in murine macrophages after incubation with C. jejuni (P < 0.001). These macrophages effected a 2-log-increased kill of C. jejuni over 24 h compared to that by NOS2-/- macrophages unable to produce nitric oxide (P < 0.05). These findings suggest that the mammalian host upregulates the production of nitric oxide in response to exposure to C. jejuni and that nitric oxide and reactive nitrogen species comprise part of the innate defense mechanisms that contribute to the resolution of C. jejuni infection.

HIV protease inhibitors activate the unfolded protein response in macrophages: implication for atherosclerosis and cardiovascular disease

Human immunodeficiency virus (HIV) protease inhibitors have been successfully used in highly active antiretroviral therapy for HIV-1 infection. Treatment of patients infected with HIV with HIV protease inhibitors is unfortunately associated with a number of clinically significant metabolic abnormalities and an increased risk of premature atherosclerosis and myocardial infarction. However, the cellular/molecular mechanisms of the HIV protease inhibitor-induced lipid dysregulation and atherosclerosis remain elusive. Macrophages are the most prominent cell type present in atherosclerotic lesions and play essential roles in both early lesion development and late lesion complications. In this study, we demonstrate that three different HIV protease inhibitors (ritonavir, indinavir, and atazanavir) induce endoplasmic reticulum stress and activate the unfolded protein response in mouse macrophages. Furthermore, at therapeutic concentrations (5-15 microM), these HIV protease inhibitors were found to increase the levels of transcriptionally active sterol regulatory element binding proteins, decrease endogenous cholesterol esterification, cause the accumulation of free cholesterol in intracellular membranes, deplete endoplasmic reticulum calcium stores, activate caspase-12, and increase apoptosis in macrophages. These findings provide possible cellular mechanisms by which HIV protease inhibitors promote atherosclerosis and cardiovascular disease in HIV-1 infected patients treated with HIV protease inhibitors.

Impaired toll-like receptor 9 expression in alveolar macrophages with no sensitivity to CpG DNA

Unmethylated CpG motifs in bacterial DNA or synthetic oligodeoxynucleotides (ODN) potently stimulate the innate immune system, and they are recognized by Toll-like receptor 9 (TLR9), which is expressed by monocytes/macrophages, dendritic cells, and B cells. However, it is unknown whether alveolar macrophages (AMs) express functional TLR9. To clarify this, we analyzed mRNA expressions of TLRs in murine AMs by real-time polymerase chain reaction, and compared with those in other tissue macrophages and lung antigen-presenting cells. In addition, we determined the sensitivity of these cell populations to CpG-ODN. Interestingly, TLR9 mRNA was almost absent in AMs, but highly expressed in bone marrow-derived macrophages and peritoneal macrophages, whereas TLR2 and TLR4 were present in all macrophage populations. Consistent with the receptor expression, AMs showed no sensitivity to CpG-ODN, whereas other macrophage populations secreted tumor necrosis factor alpha, interleukin 12 p40, and interleukin 6, and enhanced expression of CD40, CD80, and CD86, in response to CpG-ODN. Lung dendritic cells and B cells highly expressed TLR9 mRNA and responded to CpG-ODN. These results indicate selective loss of TLR9 expression in AMs with no sensitivity to CpG-ODN, suggesting that dendritic cells and B cells play a role in the immune response against bacterial DNA in the lung.

Regulation of cell survival during B lymphopoiesis in mouse bone marrow: enhanced pre-B-cell apoptosis in CSF-1-deficient op/op mutant mice

OBJECTIVE

Osteopetrotic (op/op) mice are deficient in macrophages and osteoclasts due to a CSF-1 gene mutation. The aim of this study was to evaluate the effect of these deficiencies and of CSF-1-dependent mechanisms on B lymphopoiesis in bone marrow, with special reference to the apoptotic activity of precursor B cells.

MATERIALS AND METHODS

B-cell development and apoptosis were examined in the bone marrow of op/op mice using immunofluorescence labeling and flow cytometry. Short-term cultures of bone marrow were used to evaluate the effect of recombinant CSF-1 on the rate of B-cell apoptosis.

RESULTS

Bone marrow cellularity was greatly reduced in op/op mice compared with normal littermates. However, precursor B cells were disproportionately decreased, most markedly at the pre-B-cell stage. Precursor B cells, particularly pre-B cells, displayed elevated apoptotic incidences both ex vivo and in short-term culture. Addition of recombinant CSF-1 reduced the incidence of apoptosis among precursor B cells in short-term cultures of whole bone marrow suspensions from normal mice but not in cultures of sorted B220+ B-lineage cells.

CONCLUSIONS

The finding of increased pre-B-cell apoptosis in op/op mice provides evidence that CSF-1-dependent mechanisms can strongly influence the survival of precursor B cells in mouse bone marrow, particularly at the pro-B/pre-B cell transition. It is proposed that the local or systemic levels of CSF-1 during ontogeny may thus play a role in regulating B-cell production within the bone marrow microenvironment.

Cis-acting DNA elements of mouse granulocyte/macrophage colony-stimulating factor gene responsive to oxidized low density lipoprotein

We previously demonstrated that the induction of granulocyte/macrophage colony-stimulating factor (GM-CSF) played an important role in oxidized low density lipoprotein (Ox-LDL)-induced macrophage growth as a growth priming factor. The present study was undertaken to elucidate the transcriptional regulation of the GM-CSF gene using Raw 264.7 cells, a mouse macrophage cell line. Transient transfection into Raw 264.7 cells of several 5'-flanking regions of GM-CSF gene-luciferase fusion plasmids revealed the presence of two positive regulatory sites in regions spanning from -97 to -59 and from -59 to -37 and one negative regulatory site from -120 to -97 in unstimulated cells. When cells were stimulated by Ox-LDL, there was one positive responsive site from -225 to -120 and one negative responsive site from -97 to -59, which contained the NF-kappaB binding site. Computer analysis revealed the presence of a putative AP-2 binding site from -169 to -160. Mutagenesis of a putative AP-2 binding site and tandem repeat of this site in plasmid resulted in a complete loss and increased responsiveness to Ox-LDL, respectively. Electrophoretic mobility shift assay showed that Ox-LDL increased the binding of certain nuclear protein(s) to a putative AP-2 binding site but decreased their binding to NF-kappaB binding site. Supershift assay showed that nuclear proteins bound to NF-kappaB binding site contained, at least, p50 and p65 but could not demonstrate nuclear protein(s) bound to a putative AP-2 binding site. Our results suggested that a putative AP-2 binding site from -169 to -160 was a positive responsive element to Ox-LDL and that the NF-kappaB binding site from -91 to -82 was a negative responsive element in Ox-LDL-induced GM-CSF transcription.

Induction of murine macrophage growth by oxidized low density lipoprotein is mediated by granulocyte macrophage colony-stimulating factor

We have examined whether certain secreted factor(s) is involved in oxidized low density lipoprotein (Ox-LDL)-induced murine macrophage growth. An antibody against granulocyte-macrophage colony-stimulating factor (GM-CSF) effectively inhibited Ox-LDL-induced macrophage growth by >80%. Ox-LDL as well as phospholipase A2-treated acetylated LDL enhanced mRNA levels and protein release of GM-CSF from macrophages, while neither acetylated LDL nor lysophosphatidylcholine (lyso-PC) showed such effects. The maximal induction of GM-CSF by Ox-LDL was noted at 4 h, followed by a time-dependent decrease to a basal level within 24 h. Ox-LDL-induced macrophage growth was inhibited by 75% by replacement of the culture medium at 24 h by a fresh medium containing the same concentration of Ox-LDL, when GM-CSF had already returned to the basal level. Thus, a cytokine(s) other than GM-CSF is also expected to participate in Ox-LDL-induced macrophage growth in a later phase. The Ox-LDL-induced GM-CSF release was inhibited by calphostin C, a protein kinase C inhibitor, and was significantly reduced in macrophages from the knockout mice lacking class A, type I and type II macrophage scavenger receptors (MSR-AI/AII). These results taken together indicate that effective endocytosis of lyso-PC of Ox-LDL by macrophages through MSR-AI/AII and subsequent protein kinase C activation have led to GM-CSF release into the medium which may play a priming role in conjunction with other cytokines in Ox-LDL-induced macrophage growth.