Macrophage-colony-stimulating factor (CSF-1) induces proliferation, chemotaxis, and reversible monocytic differentiation in myeloid progenitor cells transfected with the human c-fms/CSF-1 receptor cDNA

A specialized population of monocyte-derived tracheal macrophages promote airway epithelial regeneration through a CCR2-dependent mechanism

Macrophages are critical for maintenance and repair of mucosal tissues. While functionally distinct subtypes of macrophage are known to have important roles in injury response and repair in the lungs, little is known about macrophages in the proximal conducting airways. Single-cell RNA sequencing and flow cytometry demonstrated murine tracheal macrophages are largely monocyte-derived and are phenotypically distinct from lung macrophages at homeostasis. Following sterile airway injury, monocyte-derived macrophages are recruited to the trachea and activate a pro-regenerative phenotype associated with wound healing. Animals lacking the chemokine receptor CCR2 have reduced numbers of circulating monocytes and tracheal macrophages, deficient pro-regenerative macrophage activation and defective epithelial repair. Together, these studies indicate that recruitment and activation of monocyte-derived tracheal macrophages is CCR2-dependent and is required for normal airway epithelial regeneration.

Colony stimulating factor-1 receptor drives glomerular parietal epithelial cell activation in focal segmental glomerulosclerosis

Parietal epithelial cells (PECs) are kidney progenitor cells with similarities to a bone marrow stem cell niche. In focal segmental glomerulosclerosis (FSGS) PECs become activated and contribute to extracellular matrix deposition. Colony stimulating factor-1 (CSF-1), a hematopoietic growth factor, acts via its specific receptor, CSF-1R, and has been implicated in several glomerular diseases, although its role on PEC activation is unknown. Here, we found that CSF-1R was upregulated in PECs and podocytes in biopsies from patients with FSGS. Through in vitro studies, PECs were found to constitutively express CSF-1R. Incubation with CSF-1 induced CSF-1R upregulation and significant transcriptional regulation of genes involved in pathways associated with PEC activation. Specifically, CSF-1/CSF-1R activated the ERK1/2 signaling pathway and upregulated CD44 in PECs, while both ERK and CSF-1R inhibitors reduced CD44 expression. Functional studies showed that CSF-1 induced PEC proliferation and migration, while reducing the differentiation of PECs into podocytes. These results were validated in the Adriamycin-induced FSGS experimental mouse model. Importantly, treatment with either the CSF-1R-specific inhibitor GW2580 or Ki20227 provided a robust therapeutic effect. Thus, we provide evidence of the role of the CSF-1/CSF-1R pathway in PEC activation in FSGS, paving the way for future clinical studies investigating the therapeutic effect of CSF-1R inhibitors on patients with FSGS.

Neuroblastoma Interaction with the Tumour Microenvironment and Its Implications for Treatment and Disease Progression

Neuroblastoma, a paediatric malignancy of the peripheral nervous system, displays a wide range of clinical outcomes, including regression to fatality despite extensive treatment. Neuroblastoma tumours display a complex interplay with their surrounding environment, known as the tumour microenvironment, which may affect disease progression and patient prognosis. This study aimed to dissect the ways in which neuroblastoma biology, treatment, prognosis, progression, and relapse are linked with the extracellular matrix, the dichotomous identities of neuroblastoma, various regulatory proteins and RNA, and extracellular vesicles within the backdrop of the tumour microenvironment. In addition, other aspects, such as immune cell infiltration, therapeutic options including monoclonal antibodies and small molecule inhibitors; and the ways in which these may affect disease progression and immunosuppression within the context of the neuroblastoma tumour microenvironment, are addressed. Such studies may shed light on useful therapeutic targets within the tumour microenvironment that may benefit groups of NB patients. Ultimately, a detailed understanding of these aspects will enable the neuroblastoma scientific community to improve treatment options, patient outcomes, and quality of life.

Macrophage infiltration promotes regrowth in MYCN-amplified neuroblastoma after chemotherapy

Despite aggressive treatment, the 5-year event-free survival rate for children with high-risk neuroblastoma is <50%. While most high-risk neuroblastoma patients initially respond to treatment, often with complete clinical remission, many eventually relapse with therapy-resistant tumors. Novel therapeutic alternatives that prevent the recurrence of therapy-resistant tumors are urgently needed. To understand the adaptation of neuroblastoma under therapy, we analyzed the transcriptomic landscape in 46 clinical tumor samples collected before (PRE) or after (POST) treatment from 22 neuroblastoma patients. RNA sequencing revealed that many of the top-upregulated biological processes in POST MYCN amplified (MNA⁺) tumors compared to PRE MNA⁺ tumors were immune-related, and there was a significant increase in numerous genes associated with macrophages. The infiltration of macrophages was corroborated by immunohistochemistry and spatial digital protein profiling. Moreover, POST MNA⁺ tumor cells were more immunogenic compared to PRE MNA⁺ tumor cells. To find support for the macrophage-induced outgrowth of certain subpopulations of immunogenic tumor cells following treatment, we examined the genetic landscape in multiple clinical PRE and POST tumor samples from nine neuroblastoma patients revealing a significant correlation between an increased amount of copy number aberrations (CNA) and macrophage infiltration in POST MNA⁺ tumor samples. Using an in vivo neuroblastoma patient-derived xenograft (PDX) chemotherapy model, we further show that inhibition of macrophage recruitment with anti-CSF1R treatment prevents the regrowth of MNA⁺ tumors following chemotherapy. Taken together, our work supports a therapeutic strategy for fighting the relapse of MNA⁺ neuroblastoma by targeting the immune microenvironment.

Interactions in CSF1-Driven Tenosynovial Giant Cell Tumors

PURPOSE

A major component of cells in tenosynovial giant cell tumor (TGCT) consists of bystander macrophages responding to CSF1 that is overproduced by a small number of neoplastic cells with a chromosomal translocation involving the CSF1 gene. An autocrine loop was postulated where the neoplastic cells would be stimulated through CSF1R expressed on their surface. Here, we use single-cell RNA sequencing (scRNA-seq) to investigate cellular interactions in TGCT.

EXPERIMENTAL DESIGN

A total of 18,788 single cells from three TGCT and two giant cell tumor of bone (GCTB) samples underwent scRNA-seq. The three TGCTs were additionally analyzed using long-read RNA sequencing. Immunofluorescence and IHC for a range of markers were used to validate and extend the scRNA-seq findings.

RESULTS

Two recurrent neoplastic cell populations were identified in TGCT that are highly similar to nonneoplastic synoviocytes. We identified GFPT2 as a marker that highlights the neoplastic cells in TCGT. We show that the neoplastic cells themselves do not express CSF1R. We identified overlapping MAB features between the giant cells in TGCT and GCTB.

CONCLUSIONS

The neoplastic cells in TGCT are highly similar to nonneoplastic synoviocytes. The lack of CSF1R on the neoplastic cells indicates they may be unaffected by current therapies. High expression of GFPT2 in the neoplastic cells is associated with activation of the YAP1/TAZ pathway. In addition, we identified expression of the platelet-derived growth factor receptor in the neoplastic cells. These findings suggest two additional pathways to target in this tumor.

Colony stimulating factor-1 producing endothelial cells and mesenchymal stromal cells maintain monocytes within a perivascular bone marrow niche

Macrophage colony stimulating factor-1 (CSF-1) plays a critical role in maintaining myeloid lineage cells. However, congenital global deficiency of CSF-1 (Csf1^op/op) causes severe musculoskeletal defects that may indirectly affect hematopoiesis. Indeed, we show here that osteolineage-derived Csf1 prevented developmental abnormalities but had no effect on monopoiesis in adulthood. However, ubiquitous deletion of Csf1 conditionally in adulthood decreased monocyte survival, differentiation, and migration, independent of its effects on bone development. Bone histology revealed that monocytes reside near sinusoidal endothelial cells (ECs) and leptin receptor (Lepr)-expressing perivascular mesenchymal stromal cells (MSCs). Targeted deletion of Csf1 from sinusoidal ECs selectively reduced Ly6C^- monocytes, whereas combined depletion of Csf1 from ECs and MSCs further decreased Ly6C^hi cells. Moreover, EC-derived CSF-1 facilitated recovery of Ly6C^- monocytes and protected mice from weight loss following induction of polymicrobial sepsis. Thus, monocytes are supported by distinct cellular sources of CSF-1 within a perivascular BM niche.

PLX5622 Reduces Disease Severity in Lethal CNS Infection by Off-Target Inhibition of Peripheral Inflammatory Monocyte Production

PLX5622 is a CSF-1R inhibitor and microglia-depleting reagent, widely used to investigate the biology of this central nervous system (CNS)-resident myeloid population, but the indirect or off-target effects of this agent remain largely unexplored. In a murine model of severe neuroinflammation induced by West Nile virus encephalitis (WNE), we showed PLX5622 efficiently depleted both microglia and a sub-population of border-associated macrophages in the CNS. However, PLX5622 also significantly depleted mature Ly6C^hi monocytes in the bone marrow (BM), inhibiting their proliferation and lethal recruitment into the infected brain, reducing neuroinflammation and clinical disease scores. Notably, in addition, BM dendritic cell subsets, plasmacytoid DC and classical DC, were depleted differentially in infected and uninfected mice. Confirming its protective effect in WNE, cessation of PLX5622 treatment exacerbated disease scores and was associated with robust repopulation of microglia, rebound BM monopoiesis and markedly increased inflammatory monocyte infiltration into the CNS. Monoclonal anti-CSF-1R antibody blockade late in WNE also impeded BM monocyte proliferation and recruitment to the brain, suggesting that the protective effect of PLX5622 is via the inhibition of CSF-1R, rather than other kinase targets. Importantly, BrdU incorporation in PLX5622-treated mice, suggest remaining microglia proliferate independently of CSF-1 in WNE. Our study uncovers significantly broader effects of PLX5622 on the myeloid lineage beyond microglia depletion, advising caution in the interpretation of PLX5622 data as microglia-specific. However, this work also strikingly demonstrates the unexpected therapeutic potential of this molecule in CNS viral infection, as well as other monocyte-mediated diseases.

Hematopoietic Stem Cells: Nature and Niche Nurture

Like all cells, hematopoietic stem cells (HSCs) and their offspring, the hematopoietic progenitor cells (HPCs), are highly sociable. Their capacity to interact with bone marrow niche cells and respond to environmental cytokines orchestrates the generation of the different types of blood and immune cells. The starting point for engineering hematopoiesis ex vivo is the nature of HSCs, and a longstanding premise is that they are a homogeneous population of cells. However, recent findings have shown that adult bone marrow HSCs are really a mixture of cells, with many having lineage affiliations. A second key consideration is: Do HSCs "choose" a lineage in a random and cell-intrinsic manner, or are they instructed by cytokines? Since their discovery, the hematopoietic cytokines have been viewed as survival and proliferation factors for lineage committed HPCs. Some are now known to also instruct cell lineage choice. These fundamental changes to our understanding of hematopoiesis are important for placing niche support in the right context and for fabricating an ex vivo environment to support HSC development.

Targeting the CSF1/CSF1R Axis is a Potential Treatment Strategy for Malignant Meningiomas

BACKGROUND

Malignant meningiomas are fatal and lack effective therapy. As M2 macrophages are the most prevalent immune cell type in human meningiomas, we hypothesized that normalizing this immunosuppressive population would be an effective treatment strategy.

METHODS

We used CIBERSORTX to examine the proportions of 22 immune subsets in human meningiomas. We targeted the colony stimulating factor 1 (CSF1) or CSF1 receptor (CSF1R) axis, an important regulator of macrophage phenotype, using monoclonal antibodies (mAbs) in a novel immunocompetent murine model (MGS1) for malignant meningioma. RNA-seq was performed to identify changes in gene expression in the tumor microenvironment. Mass cytometry was used to delineate changes in immune subsets after treatment. We measured patients' plasma CSF1 levels using ELISA and CSF1R expression using multiplex quantitative immunofluorescence in a human meningioma tissue microarray.

RESULTS

Human meningiomas are heavily enriched for immunosuppressive myeloid cells. MGS1 recapitulates the tumor microenvironment of human meningiomas, including an abundance of myeloid cells, a paucity of infiltrating T cells, and low programmed-death ligand 1 (PD-L1) expression. Treatment of murine meningiomas with anti-CSF1/CSF1R, but not programmed cell death receptor 1 (PD-1), mAbs abrogate tumor growth. RNA-seq and mass cytometry analyses reveal a myeloid cell reprogramming with limited effect on T cells in the tumor microenvironment. CSF1 plasma levels are significantly elevated in human patients and CSF1R is highly expressed on CD163 + macrophages within the human tumor microenvironment.

CONCLUSION

Our findings suggests that anti-CSF1/CSF1R antibody treatment may be an effective normalization cancer immunotherapy for malignant meningiomas.

Muscularis macrophages establish cell-to-cell contacts with telocytes/PDGFRα-positive cells and smooth muscle cells in the human and mouse gastrointestinal tract

BACKGROUND AND AIM

Muscularis macrophages (MMs) not only mediate the innate immunity, but also functionally interact with cells important for gastrointestinal motility. The aim of this study was to determine the spatial relationship and types of contacts between the MMs and neighboring cells in the muscularis propria of human and mouse stomach, small intestine, and large intestine.

METHODS

The distribution and morphology of MMs and their contacts with other cells were investigated by immunohistochemistry and transmission electron microscopy.

KEY RESULTS

Immunohistochemistry showed variable shape and number of MMs according to their location in different portions of the muscle coat. By double labeling, a close association between MMs and neighboring cells, that is, neurons, smooth muscle cells, interstitial cells of Cajal (ICCs), telocytes (TCs)/PDGFRα-positive cells, was seen. Electron microscopy demonstrated that in the muscle layers of both animal species, MMs have similar ultrastructural features and have specialized cell-to-cell contacts with smooth muscle cells and TCs/PDGFRα-positive cells but not with ICCs and enteric neurons.

CONCLUSION & INFERENCES

This study describes varying patterns of distribution of MMs between different regions of the gut, and reports the presence of distinct and extended cell-to-cell contacts between MMs and smooth muscle cells and between MMs and TCs/PDGFRα-positive cells. In contrast, MMs, although close to ICCs and nerve elements, did not make contact with them. These findings indicate specialized and variable roles for MMs in the modulation of gastrointestinal motility whose significance should be more closely investigated in normal and pathological conditions.

The Telocytes: Ten Years after Their Introduction in the Scientific Literature. An Update on Their Morphology, Distribution, and Potential Roles in the Gut

Ten years ago, the term 'telocyte' was introduced in the scientific literature to describe a 'new' cell type described in the connective tissue of several organs by Popescu and Faussone-Pellegrini (2010). Since then, 368 papers containing the term 'telocyte' have been published, 261 of them in the last five years. These numbers underscore the growing interest in this cell type in the scientific community and the general acceptance of the name telocyte to indicate this interstitial cell. Most of these studies, while confirming the importance of transmission electron microscopy to identify the telocytes with certainty, highlight the variability of their immune phenotypes. This variability was interpreted as due to (i) the ability of the telocytes to adapt to the different sites in which they reside; (ii) the distinct functions they are likely to perform; and (iii) the existence of telocyte subtypes. In the present paper, an overview of the last 10 years of literature on telocytes located in the gut will be attempted, confining the revision to the morphological findings. A distinct chapter will be dedicated to the recently hypothesized role of the telocytes the intestinal mucosa. Through this review, it will be shown that telocytes, despite their variability, are a unique interstitial cell.

Towards a New Understanding of Decision-Making by Hematopoietic Stem Cells

Cells within the hematopoietic stem cell compartment selectively express receptors for cytokines that have a lineage(s) specific role; they include erythropoietin, macrophage colony-stimulating factor, granulocyte colony-stimulating factor, granulocyte/macrophage colony-stimulating factor and the ligand for the fms-like tyrosine kinase 3. These hematopoietic cytokines can instruct the lineage fate of hematopoietic stem and progenitor cells in addition to ensuring the survival and proliferation of cells that belong to a particular cell lineage(s). Expression of the receptors for macrophage colony-stimulating factor and granulocyte colony-stimulating factor is positively autoregulated and the presence of the cytokine is therefore likely to enforce a lineage bias within hematopoietic stem cells that express these receptors. In addition to the above roles, macrophage colony-stimulating factor and granulocyte/macrophage colony-stimulating factor are powerful chemoattractants. The multiple roles of some hematopoietic cytokines leads us towards modelling hematopoietic stem cell decision-making whereby these cells can 'choose' just one lineage fate and migrate to a niche that both reinforces the fate and guarantees the survival and expansion of cells as they develop.

ROLE OF OXYGEN CONCENTRATION IN THE OSTEOBLASTS BEHAVIOR: A FINITE ELEMENT MODEL

Oxygen concentration plays a key role in cell survival and viability. Besides, it has important effects on essential cellular biological processes such as cell migration, differentiation, proliferation and apoptosis. Therefore, the prediction of the cellular response to the alterations of the oxygen concentration can help significantly in the advances of cell culture research. Here, we present a 3D computational mechanotactic model to simulate all the previously mentioned cell processes under different oxygen concentrations. With this model, three cases have been studied. Starting with mesenchymal stem cells within an extracellular matrix with mechanical properties suitable for its differentiation into osteoblasts, and under different oxygen conditions to evaluate their behavior under normoxia, hypoxia and anoxia. The obtained results, which are consistent with the experimental observations, indicate that cells tend to migrate toward zones with higher oxygen concentration where they accelerate their differentiation and proliferation. This technique can be employed to control cell migration toward fracture zones to accelerate the healing process. Besides, as expected, to avoid cell apoptosis under conditions of anoxia and to avoid the inhibition of the differentiation and proliferation processes under conditions of hypoxia, the state of normoxia should be maintained throughout the entire cell-culture process.

Proliferation and Differentiation of Murine Myeloid Precursor 32D/G-CSF-R Cells

Understanding of the hematopoietic stem and progenitor cell biology has important implications for regenerative medicine and the treatment of hematological pathologies. Despite the most relevant data that can be acquired using in vivo models or primary cultures, the low abundance of hematopoietic stem and progenitor cells considerably restricts the pool of suitable techniques for their investigation. Therefore, the use of cell lines allows sufficient production of biological material for the performance of screenings or assays that require large cell numbers. Here we present a detailed description, readout, and interpretation of proliferation and differentiation assays which are used for the investigation of processes involved in myelopoiesis and neutrophilic differentiation. These experiments employ the 32D/G-CSF-R cytokine dependent murine myeloid cell line, which possesses the ability to proliferate in the presence of IL-3 and differentiate in G-CSF. We provide optimized protocols for handling 32D/G-CSF-R cells and discuss major pitfalls and drawbacks that might compromise the described assays and expected results. Additionally, this article contains protocols for lentiviral and retroviral production, titration, and transduction of 32D/G-CSF-R cells. We demonstrate that genetic manipulation of these cells can be employed to successfully perform functional and molecular studies, which can complement results obtained with primary hematopoietic stem and progenitor cells or in vivo models.

Numerical modeling of cell differentiation and proliferation in force-induced substrates via encapsulated magnetic nanoparticles

BACKGROUND AND OBJECTIVE

Cell migration, differentiation, proliferation and apoptosis are the main processes in tissue regeneration. Mesenchymal Stem Cells have the potential to differentiate into many cell phenotypes such as tissue- or organ-specific cells to perform special functions. Experimental observations illustrate that differentiation and proliferation of these cells can be regulated according to internal forces induced within their Extracellular Matrix. The process of how exactly they interpret and transduce these signals is not well understood.

METHODS

A previously developed three-dimensional (3D) computational model is here extended and employed to study how force-free substrates and force-induced substrate control cell differentiation and/or proliferation during the mechanosensing process. Consistent with experimental observations, it is assumed that cell internal deformation (a mechanical signal) in correlation with the cell maturation state directly triggers cell differentiation and/or proliferation. The Extracellular Matrix is modeled as Neo-Hookean hyperelastic material assuming that cells are cultured within 3D nonlinear hydrogels.

RESULTS

In agreement with well-known experimental observations, the findings here indicate that within neurogenic (0.1-1kPa), chondrogenic (20-25kPa) and osteogenic (30-45kPa) substrates, Mesenchymal Stem Cells differentiation and proliferation can be precipitated by inducing the substrate with an internal force. Therefore, cells require a longer time to grow and maturate within force-free substrates than within force-induced substrates. In the instance of Mesenchymal Stem Cells differentiation into a compatible phenotype, the magnitude of the net traction force increases within chondrogenic and osteogenic substrates while it reduces within neurogenic substrates. This is consistent with experimental studies and numerical works recently published by the same authors. However, in all cases the magnitude of the net traction force considerably increases at the instant of cell proliferation because of cell-cell interaction.

CONCLUSIONS

The present model provides new perspectives to delineate the role of force-induced substrates in remotely controlling the cell fate during cell-matrix interaction, which open the door for new tissue regeneration methodologies.

Role of Mechanical Cues in Cell Differentiation and Proliferation: A 3D Numerical Model

Cell differentiation, proliferation and migration are essential processes in tissue regeneration. Experimental evidence confirms that cell differentiation or proliferation can be regulated according to the extracellular matrix stiffness. For instance, mesenchymal stem cells (MSCs) can differentiate to neuroblast, chondrocyte or osteoblast within matrices mimicking the stiffness of their native substrate. However, the precise mechanisms by which the substrate stiffness governs cell differentiation or proliferation are not well known. Therefore, a mechano-sensing computational model is here developed to elucidate how substrate stiffness regulates cell differentiation and/or proliferation during cell migration. In agreement with experimental observations, it is assumed that internal deformation of the cell (a mechanical signal) together with the cell maturation state directly coordinates cell differentiation and/or proliferation. Our findings indicate that MSC differentiation to neurogenic, chondrogenic or osteogenic lineage specifications occurs within soft (0.1-1 kPa), intermediate (20-25 kPa) or hard (30-45 kPa) substrates, respectively. These results are consistent with well-known experimental observations. Remarkably, when a MSC differentiate to a compatible phenotype, the average net traction force depends on the substrate stiffness in such a way that it might increase in intermediate and hard substrates but it would reduce in a soft matrix. However, in all cases the average net traction force considerably increases at the instant of cell proliferation because of cell-cell interaction. Moreover cell differentiation and proliferation accelerate with increasing substrate stiffness due to the decrease in the cell maturation time. Thus, the model provides insights to explain the hypothesis that substrate stiffness plays a key role in regulating cell fate during mechanotaxis.

Macrophages in intestinal homeostasis and inflammation

The intestine contains the largest pool of macrophages in the body which are essential for maintaining mucosal homeostasis in the face of the microbiota and the constant need for epithelial renewal but are also important components of protective immunity and are involved in the pathology of inflammatory bowel disease (IBD). However, defining the biological roles of intestinal macrophages has been impeded by problems in defining the phenotype and origins of different populations of myeloid cells in the mucosa. Here, we discuss how multiple parameters can be used in combination to discriminate between functionally distinct myeloid cells and discuss the roles of macrophages during homeostasis and how these may change when inflammation ensues. We also discuss the evidence that intestinal macrophages do not fit the current paradigm that tissue-resident macrophages are derived from embryonic precursors that self-renew in situ, but require constant replenishment by blood monocytes. We describe our recent work demonstrating that classical monocytes constantly enter the intestinal mucosa and how the environment dictates their subsequent fate. We believe that understanding the factors that drive intestinal macrophage development in the steady state and how these may change in response to pathogens or inflammation could provide important insights into the treatment of IBD.

Macrophages in intestinal homeostasis and inflammation

The intestine contains the largest pool of macrophages in the body which are essential for maintaining mucosal homeostasis in the face of the microbiota and the constant need for epithelial renewal but are also important components of protective immunity and are involved in the pathology of inflammatory bowel disease (IBD). However, defining the biological roles of intestinal macrophages has been impeded by problems in defining the phenotype and origins of different populations of myeloid cells in the mucosa. Here, we discuss how multiple parameters can be used in combination to discriminate between functionally distinct myeloid cells and discuss the roles of macrophages during homeostasis and how these may change when inflammation ensues. We also discuss the evidence that intestinal macrophages do not fit the current paradigm that tissue-resident macrophages are derived from embryonic precursors that self-renew in situ, but require constant replenishment by blood monocytes. We describe our recent work demonstrating that classical monocytes constantly enter the intestinal mucosa and how the environment dictates their subsequent fate. We believe that understanding the factors that drive intestinal macrophage development in the steady state and how these may change in response to pathogens or inflammation could provide important insights into the treatment of IBD.

IκB kinase activity drives fetal lung macrophage maturation along a non-M1/M2 paradigm

In preterm infants, exposure to inflammation increases the risk of bronchopulmonary dysplasia, a chronic, developmental lung disease. Although macrophages are the key cells that initiate lung inflammation, less is known about lung macrophage phenotype and maturation. We hypothesized that fetal lung macrophages mature into distinct subpopulations during mouse development, and that activation could influence macrophage maturation. Expression of the fetal macrophage markers CD68, CD86, CD206, Ym1, fibrinogen-like protein 2, and indolamine-2, 3-dioxygenase was developmentally regulated, with each marker having different temporal patterns. Flow cytometry analysis showed macrophages within the fetal lung were less diverse than the distinctly separate subpopulations in newborn and adult lungs. Similar to adult alveolar macrophages, fetal lung macrophages responded to the TLR4 agonist LPS and the alternative activation cytokines IL-4 and IL-13. Using a macrophage-specific constitutively active IκB Kinase transgenic model (IKFM), we demonstrated that macrophage activation increased proinflammatory gene expression and reduced the response of fetal lung macrophages to IL-4 and IL-13. Activation also increased fetal lung macrophage proliferation. Fetal IKFM lungs contained increased percentages of more mature, CD11b(low)F4/80(high) cells that also expressed higher levels of the alternative activation markers CD204 and CD206. Development of fetal lung macrophages into mature alveolar macrophages may therefore include features of both proinflammatory and alternative activation paradigms.

IL-34 is overexpressed in the inflamed salivary glands of patients with Sjogren's syndrome and is associated with the local expansion of pro-inflammatory CD14(bright)CD16+ monocytes

OBJECTIVES

To investigate the expression of IL-34 in labial salivary glands (LSGs) of patients with primary SS (p-SS) and its role in inducing a pro-inflammatory monocyte phenotype.

METHODS

LSG biopsies were obtained from 20 patients with p-SS and 10 patients with non-Sjögren's sicca syndrome (n-SS). The expression of IL-34, IL-1β, TNF-α, IL-17 and IL-23 was assessed by real-time PCR. IL-34 expression was also investigated in LSGs by immunohistochemistry. The frequencies of subpopulations of CD14(+) monocytes were evaluated by flow cytometry among isolated mononuclear cells from peripheral blood and salivary glands from both patients and controls. The role of recombinant IL-34 on isolated peripheral blood mononuclear cells was also evaluated.

RESULTS

IL-34 m-RNA was overexpressed in the inflamed salivary glands of p-SS and associated with increased expression of TNF-α, IL-1β, IL-17 and IL-23p19. The increased expression of IL-34 was confirmed by immunohistochemistry in paraffin-embedded salivary glands from p-SS patients. IL-34 expression was accompanied by the expansion of pro-inflammatory CD14(bright)CD16(+) monocytes in the salivary glands. In vitro stimulation of peripheral blood mononuclear cells with IL-34 induced the expansion of both CD14(+)CD16(-) cells and CD14(bright)CD16(+) cells in p-SS and non-SS subjects.

CONCLUSION

IL-34 seems to be involved in the pathogenesis of salivary gland inflammation in p-SS.

Arterial colony stimulating factor-1 influences atherosclerotic lesions by regulating monocyte migration and apoptosis

Previous studies have shown that colony stimulating factor-1 (CSF-1) deficiency dramatically reduced atherogenesis in mice. In this report we investigate this mechanism and explore a therapeutic avenue based on inhibition of CSF-1 signaling. Lesions from macrophage colony stimulating factor-1 (Csf1)+/- mice showed increased numbers of apoptotic macrophages, decreased overall macrophage content, and inflammation. In vitro studies indicated that CSF-1 is chemotactic for monocytes. Bone marrow transplantation studies suggested that vascular cell-derived, rather than macrophage-derived, CSF-1 is responsible for the effect on atherosclerosis. Consistent with previous studies, CSF-1 affected lesion development in a dose-dependent manner, suggesting that pharmacological inhibition of CSF-1 might achieve similar results. Indeed, we observed that treatment of hyperlipidemic mice with a CSF-1 receptor kinase inhibitor inhibited plaque progression. This observation was accompanied by a reduction in the expression of adhesion factors (ICAM-1), macrophage markers (F4/80), inflammatory cytokines (Il-6, Il-1beta), and macrophage matrix degradation enzymes (MMP-9). We conclude that the M-CSF pathway contributes to monocyte recruitment and macrophage survival and that this pathway is a potential target for therapeutic intervention.

Antibody blockade of c-fms suppresses the progression of inflammation and injury in early diabetic nephropathy in obese db/db mice

AIMS/HYPOTHESIS

Macrophage-mediated renal injury plays an important role in the development of diabetic nephropathy. Colony-stimulating factor (CSF)-1 is a cytokine that is produced in diabetic kidneys and promotes macrophage accumulation, activation and survival. CSF-1 acts exclusively through the c-fms receptor, which is only expressed on cells of the monocyte-macrophage lineage. Therefore, we used c-fms blockade as a strategy to selectively target macrophage-mediated injury during the progression of diabetic nephropathy.

METHODS

Obese, type 2 diabetic db/db BL/KS mice with established albuminuria were treated with a neutralising anti-c-fms monoclonal antibody (AFS98) or isotype matched control IgG from 12 to 18 weeks of age and examined for renal injury.

RESULTS

Treatment with AFS98 did not affect obesity, hyperglycaemia, circulating monocyte levels or established albuminuria in db/db mice. However, AFS98 did prevent glomerular hyperfiltration and suppressed variables of inflammation in the diabetic kidney, including kidney macrophages (accumulation, activation and proliferation), chemokine CC motif ligand 2 levels (mRNA and urine protein), kidney activation of proinflammatory pathways (c-Jun amino-terminal kinase and activating transcription factor 2) and Tnf-alpha (also known as Tnf) mRNA levels. In addition, AFS98 decreased the tissue damage caused by macrophages including tubular injury (apoptosis and hypertrophy), interstitial damage (cell proliferation and myofibroblast accrual) and renal fibrosis (Tgf-beta1 [also known as Tgfb1] and Col4a1 mRNA).

CONCLUSIONS/INTERPRETATION

Blockade of c-fms can suppress the progression of established diabetic nephropathy in db/db mice by targeting macrophage-mediated injury.

Development of macrophages of cyprinid fish

The innate immune responses of early vertebrates, such as bony fishes, play a central role in host defence against infectious diseases and one of the most important effector cells of innate immunity are macrophages. In order for macrophages to be effective in host defence they must be present at all times in the tissues of their host and importantly, the host must be capable of rapidly increasing macrophage numbers during times of need. Hematopoiesis is a process of formation and development of mature blood cells, including macrophages. Hematopoiesis is controlled by soluble factors known as cytokines, that influence changes in transcription factors within the target cells, resulting in cell fate changes and the final development of specific effector cells. The processes involved in macrophage development have been largely derived from mammalian model organisms. However, recent advancements have been made in the understanding of macrophage development in bony fish, a group of organisms that rely heavily on their innate immune defences. Our understanding of the growth factors involved in teleost macrophage development, as well as the receptors and regulatory mechanisms in place to control them has increased substantially. Furthermore, model organisms such as the zebrafish have emerged as important instruments in furthering our understanding of the transcriptional control of cell development in fish as well as in mammals. This review highlights the recent advancements in our understanding of teleost macrophage development. We focused on the growth factors identified to be important in the regulation of macrophage development from a progenitor cell into a functional macrophage and discuss the important transcription factors that have been identified to function in teleost hematopoiesis. We also describe the findings of in vivo studies that have reinforced observations made in vitro and have greatly improved the relevance and importance of using teleost fish as model organisms for studying developmental processes.

Harnessing the tumour-derived cytokine, CSF-1, to co-stimulate T-cell growth and activation

Aberrant growth factor production is a prevalent mechanism in tumourigenesis. If T-cells responded positively to a cancer-derived cytokine, this might result in selective enhancement of function within the tumour microenvironment. Here, we have chosen colony-stimulating factor-1 (CSF-1) as a candidate to test this concept. CSF-1 is greatly overproduced in many cancers but has no direct effects upon T-lymphocytes, which do not express the c-fms-encoded CSF-1 receptor. To confer CSF-1-responsiveness, we have expressed the human c-fms gene in immortalized and primary T-cells. Addition of soluble CSF-1 resulted in synergistic enhancement of IL-2-driven T-cell proliferation. CSF-1 also co-stimulated the production of interferon (IFN)-gamma by activated T-cells. These effects required Y809 of the CSF-1R and activation of the Ras-MEK-MAP kinase cascade, but were independent of PI3K signalling. T-cells that express c-fms are also responsive to membrane-anchored CSF-1 (mCSF-1) which, unlike its soluble counterpart, could co-stimulate IL-2 production. CSF-1 promoted chemotaxis of c-fms-expressing primary human T-cells and greatly augmented proliferation mediated by a tumour-targeted chimeric antigen receptor, with preservation of tumour cytolytic activity. Taken together, these data establish that T-cells may be genetically modified to acquire responsiveness to CSF-1 and provide proof-of-principle for a novel strategy to enhance the effectiveness of adoptive T-cell immunotherapy.

Important roles for macrophage colony-stimulating factor, CC chemokine ligand 2, and mononuclear phagocytes in the pathogenesis of pulmonary fibrosis

RATIONALE

An increase in the number of mononuclear phagocytes in lung biopsies from patients with idiopathic pulmonary fibrosis (IPF) worsens prognosis. Chemokines that recruit mononuclear phagocytes, such as CC chemokine ligand 2 (CCL2), are elevated in bronchoalveolar lavage (BAL) fluid (BALF) from patients with IPF. However, little attention is given to the role of the mononuclear phagocyte survival and recruitment factor, macrophage colony-stimulating factor (M-CSF), in pulmonary fibrosis.

OBJECTIVES

To investigate the role of mononuclear phagocytes and M-CSF in pulmonary fibrosis.

METHODS

Wild-type, M-CSF-/-, or CCL2-/- mice received intraperitoneal bleomycin. Lung inflammation and fibrosis were measured by immunohistochemistry, ELISA, collagen assay, BAL differentials, real-time polymerase chain reaction, and Western blot analysis. Human and mouse macrophages were stimulated with M-CSF for CCL2 expression. BALF from patients with IPF was examined for M-CSF and CCL2.

MEASUREMENTS AND MAIN RESULTS

M-CSF-/- and CCL2-/- mice had less lung fibrosis, mononuclear phagocyte recruitment, collagen deposition, and connective tissue growth factor (CTGF) expression after bleomycin administration than wild-type littermates. Human and mouse macrophages stimulated with M-CSF had increased CCL2 production, and intratracheal administration of M-CSF in mice induced CCL2 production in BALF. Finally, BALF from patients with IPF contained significantly more M-CSF and CCL2 than BALF from normal volunteers. Elevated levels of M-CSF were associated with elevated CCL2 in BALF and the diagnosis of IPF.

CONCLUSIONS

These data suggest that M-CSF contributes to the pathogenesis of pulmonary fibrosis in mice and in patients with IPF through the involvement of mononuclear phagocytes and CCL2 production.

Vav activation and function as a rac guanine nucleotide exchange factor in macrophage colony-stimulating factor-induced macrophage chemotaxis

Signal transduction mediated by phosphatidylinositol 3-kinase (PI 3-kinase) is regulated by hydrolysis of its products, a function performed by the 145-kDa SH2 domain-containing inositol phosphatase (SHIP). Here, we show that bone marrow macrophages of SHIP(-/-) animals have elevated levels of phosphatidylinositol 3,4,5-trisphosphate [PI (3,4,5)P(3)] and displayed higher and more prolonged chemotactic responses to macrophage colony-stimulating factor (M-CSF) and elevated levels of F-actin relative to wild-type macrophages. We also found that the small GTPase Rac was constitutively active and its upstream activator Vav was constitutively phosphorylated in SHIP(-/-) macrophages. Furthermore, we show that Vav in wild-type macrophages is recruited to the membrane in a PI 3-kinase-dependent manner through the Vav pleckstrin homology domain upon M-CSF stimulation. Dominant inhibitory mutants of both Rac and Vav blocked chemotaxis. We conclude that Vav acts as a PI 3-kinase-dependent activator for Rac activation in macrophages stimulated with M-CSF and that SHIP regulates macrophage M-CSF-triggered chemotaxis by hydrolysis of PI (3,4,5)P(3).

Monocytes and macrophages form branched cell columns in matrigel: implications for a role in neovascularization

Linear arrays of cells, or cell columns, have been observed in the extracellular matrix prior to neovascularization, but their nature and significance remains elusive. Based on the emerging evidence implicating a role for monocytes and macrophages (MC/MPH) in vasculogenesis, we hypothesized that MC/MPH also can form linear or branched columns, facilitating the co-migration and the spatial arrangement of other cell types. To test this hypothesis, we studied the distribution of MC/MPH effected by chemotactic migration in novel in vitro and in vivo models of development. We induced transversal and lateral migration of THP-1 monocytoid cells in Matrigel in vitro. The effect of this process on co-localization of other micro-objects was assessed using erythrocytes and micron-sized plastic beads. In vivo, we analyzed MC/MPH infiltration in subcutaneously implanted Matrigel plugs containing angiogenic factors and across a microporous filter comprising the wall of a chamber filled with Matrigel, also placed subcutaneously in mice. In vitro, we found that migrating THP-1 cells induced the lasting degradation of Matrigel and produced cell columns, a process amplified by monocyte chemoattractant protein-1 (MCP-1). We also report the co-localization of erythrocytes with THP-1 cells in cell columns. Endothelium-free tunnels containing MC/MPH, neutrophils, or erythrocytes were also observed in the Matrigel-filled chambers. In free subcutaneous Matrigel plugs, we found MC/MPH-based columns harboring isolated Tie-2+ cells (a marker of endothelial progenitor phenotype), as well as fibroblasts, dendritic cells, and adypocytes. Many of these cell columns displayed conspicuous branching. Our data demonstrate formation of branched MC/MPH cell columns in vitro and in vivo, a previously unrecognized pattern of penetration of extracellular matrices by inflammatory cells. Thus, monocytes and macrophages influence the distribution of neovessels as well as their branching points. These cells are the "architects of development," assisting organogenesis, tumorigenesis, and wound healing by patterning the tissular space.

Fes tyrosine kinase promotes survival and terminal granulocyte differentiation of factor-dependent myeloid progenitors (32D) and activates lineage-specific transcription factors

The c-fps/fes proto-oncogene encodes a 92-kDa protein-tyrosine kinase that is involved in myeloid cell development and function. We have recently shown that expression of an activated allele of Fes (Fes(act)) in monocyte precursors resulted in their differentiation into functional macrophages through the activation of lineage-specific transcription factors. We now report that this kinase also plays a role in the survival and terminal differentiation of granulocyte progenitors. The expression of Fes(act) in factor-dependent 32D cells prevented their apoptotic death after interleukin-3 removal, but Fes(act)-expressing cells remained factor-dependent for proliferation. Removal of interleukin-3 from the Fes(act)-expressing cells was followed by granulocytic differentiation in the absence of granulocyte colony-stimulating factor within 4-8 days. The differentiated cells had distinctive granulocyte morphology and there was up-regulation of CD11b, Gr-1, and late differentiation markers such as lactoferrin, suggesting that this kinase induced terminal granulocytic differentiation. Concomitantly, Fes(act) down-regulated the macrophage marker F4/80, suggesting that the biological activity of Fes was coordinated in a lineage-specific manner. Further analysis showed that Fes(act) caused activation of CCAAT/enhancer-binding protein-alpha and STAT3, two transcription factors that are involved in granulocyte differentiation. Our results provide evidence that Fes may be a key component of the granulocyte differentiation machinery, and suggest a potential mechanism by which this kinase may regulate granulocyte-specific gene expression.

Reduced macrophage recruitment, proliferation, and activation in colony-stimulating factor-1-deficient mice results in decreased tubular apoptosis during renal inflammation

Kidney tubular epithelial cell (TEC) death may be dependent on the number and activation state of macrophages (M phi) during inflammation. Our prior studies indicate that activated M phi release soluble mediators that incite TEC death, and reducing intrarenal M phi during kidney disease diminishes TEC apoptosis. CSF-1 is required for M phi proliferation and survival. We hypothesized that in the absence of CSF-1, M phi-mediated TEC apoptosis would be prevented during renal inflammation. To test this hypothesis, we evaluated renal inflammation during unilateral ureter obstruction in CSF-1-deficient (Csf1(op)/Csf1(op)) mice. We detected fewer M phi and T cells and less apoptotic TEC in the obstructed kidneys of Csf1(op)/Csf1(op) mice compared with wild-type (WT) mice. The decrease in intrarenal M phi resulted from diminished recruitment and proliferation, not enhanced apoptosis. CSF-1 enhanced M phi activation. There were far fewer activated (CD69, CD23, Ia, surface expression) M phi in obstructed CSF-1-deficient compared with WT obstructed kidneys. Similarly, bone marrow M phi preincubated with anti-CSF-1 receptor Ab or anti-CSF-1 neutralizing Ab were resistant to LPS- and IFN-gamma-induced activation. We detected fewer apoptotic-inducing molecules (reactive oxygen species, TNF-alpha, inducible NO synthase) in 1) M phi propagated from obstructed Csf1(op)/Csf1(op) compared with WT kidneys, and 2) WT bone marrow M phi blocked with anti-CSF-1 receptor or anti-CSF-1 Ab compared with the isotype control. Furthermore, blocking CSF-1 or the CSF-1 receptor induced less TEC apoptosis than the isotype control. We suggest that during renal inflammation, CSF-1 mediates M phi recruitment, proliferation, activation, and, in turn, TEC apoptosis.

Expression of Mona (monocytic adapter) in myeloid progenitor cells results in increased and prolonged MAP kinase activation upon macrophage colony-stimulating factor stimulation

Mona is an SH3 and SH2 domain-containing adapter molecule that is induced during monocytic differentiation. Here we have first shown that M-CSFR is the major Mona partner in M-CSF signaling, the interaction being mediated through tyrosine 697 of the receptor. Next we asked whether Mona expression would alter the Ras/MAP kinase pathway since Mona is a likely competitor of Grb2 for binding to M-CSFR. We found that M-CSF induced late and massive phosphorylation of ERK molecules in Mona-expressing myeloid cells compared to non-expressing cells. These results suggest that Mona expression might modify M-CSF signaling during monocytic differentiation.

Both src-dependent and -independent mechanisms mediate phosphatidylinositol 3-kinase regulation of colony-stimulating factor 1-activated mitogen-activated protein kinases in myeloid progenitors

Colony-stimulating factor 1 (CSF-1) supports the proliferation, survival, and differentiation of bone marrow-derived cells of the monocytic lineage. In the myeloid progenitor 32D cell line expressing CSF-1 receptor (CSF-1R), CSF-1 activation of the extracellular signal-regulated kinase (ERK) pathway is both Ras and phosphatidylinositol 3-kinase (PI3-kinase) dependent. PI3-kinase inhibition did not influence events leading to Ras activation. Using the activity of the PI3-kinase effector, Akt, as readout, studies with dominant-negative and oncogenic Ras failed to place PI3-kinase downstream of Ras. Thus, PI3-kinase appears to act in parallel to Ras. PI3-kinase inhibitors enhanced CSF-1-stimulated A-Raf and c-Raf-1 activities, and dominant-negative A-Raf but not dominant-negative c-Raf-1 reduced CSF-1-provoked ERK activation, suggesting that A-Raf mediates a part of the stimulatory signal from Ras to MEK/ERK, acting in parallel to PI3-kinase. Unexpectedly, a CSF-1R lacking the PI3-kinase binding site (DeltaKI) remained capable of activating MEK/ERK in a PI3-kinase-dependent manner. To determine if Src family kinases (SFKs) are involved, we demonstrated that CSF-1 activated Fyn and Lyn in cells expressing wild-type (WT) or DeltaKI receptors. Moreover, CSF-1-induced Akt activity in cells expressing DeltaKI is SFK dependent since Akt activation was prevented by pharmacological or genetic inhibition of SFK activity. The docking protein Gab2 may link SFK to PI3-kinase. CSF-1 induced Gab2 tyrosyl phosphorylation and association with PI3-kinase in cells expressing WT or DeltaKI receptors. However, only in DeltaKI cells are these events prevented by PP1. Thus in myeloid progenitors, CSF-1 can activate the PI3-kinase/Akt pathway by at least two mechanisms, one involving direct receptor binding and one involving SFKs.

Priming effects of macrophage colony-stimulating factor on monocytic leukemia cells in combination with chemotherapy: induction of programmed cell death in vivo

Two elderly patients with chronic myelomonocytic leukemia were treated with cytosine arabinoside (Ara-C) and aclarubicin (ACR) under simultaneous administrations of macrophage colony-stimulating factor (M-CSF) (CAM), and both obtained good responses. Examination of apoptosis using flow cytometry revealed induction of apoptotic death of leukemia cells by CAM in Patient 2, while neither induction of apoptotic death of leukemia cells nor clinical response were seen with CAG (Ara-C, ACR, and granulocyte colony-stimulating factor) given prior to CAM in Patient 1. These findings suggested that chemotherapy combined with simultaneous administration of M-CSF could effectively reduce monocytic leukemia cells by inducing programmed cell death.

Estrogen and microglia: A regulatory system that affects the brain

Sex hormones are involved in the physiological regulation of several aspects of behavior and neuroendocrine events. It has been accepted that such effects are mediated directly by steroid actions on neurons; however, new studies have shown that the glial cells are also affected by gonadal steroids. The microglia are one specialized brain glial cell type, which is a target for estrogen actions. In fact, we believe that many of the immune and nonimmune regulatory functions of microglia in the brain are influenced directly by estrogen via expression and secretion of cytokines, and growth factors by the microglia. The present review details only a section of the known aspects of microglial function, focusing mainly on nonimmune regulatory actions in the brain and their functional relationship with sex hormones. Moreover, we present evidence for the presence of estrogen receptor-beta (ERbeta) in rat microglial cells.

Synergistic Activation of Mitogen-Activated Protein Kinase by Cyclic AMP and Myeloid Growth Factors Opposes Cyclic AMP’s Growth-Inhibitory Effects

Colony-stimulating factors (CSFs) promote the proliferation, differentiation, commitment, and survival of myeloid progenitors, whereas cyclic AMP (cAMP)-mediated signals frequently induce their growth arrest and apoptosis. The ERK/mitogen-activated protein kinase (MAPK) pathway is a target for both CSFs and cAMP. We investigated how costimulation by cAMP and colony-stimulating factor-1 (CSF-1) or interleukin-3 (IL-3) modulates MAPK in the myeloid progenitor cell line, 32D. cAMP dramatically increased ERK activity in the presence of CSF-1 or IL-3. IL-3 also synergized with cAMP to activate ERK in another myeloid cell line, FDC-P1. The increase in ERK activity was transmitted to a downstream target, p90rsk. cAMP treatment of 32D cells transfected with oncogenic Ras was found to recapitulate the superactivation of ERK seen with cAMP and CSF-1 or IL-3. ERK activation in the presence of cAMP did not appear to involve any of the Raf isoforms and was blocked by expression of dominant-negative MEK1 or treatment with a MEK inhibitor, PD98059. Although cAMP had an overall inhibitory effect on CSF-1–mediated proliferation and survival, the inhibition was markedly increased if ERK activation was blocked by PD98059. These findings suggest that upregulation of the ERK pathway is one mechanism induced by CSF-1 and IL-3 to protect myeloid progenitors from the growth-suppressive and apoptosis-inducing effects of cAMP elevations.

Synergistic Activation of Mitogen-Activated Protein Kinase by Cyclic AMP and Myeloid Growth Factors Opposes Cyclic AMP’s Growth-Inhibitory Effects

Colony-stimulating factors (CSFs) promote the proliferation, differentiation, commitment, and survival of myeloid progenitors, whereas cyclic AMP (cAMP)-mediated signals frequently induce their growth arrest and apoptosis. The ERK/mitogen-activated protein kinase (MAPK) pathway is a target for both CSFs and cAMP. We investigated how costimulation by cAMP and colony-stimulating factor-1 (CSF-1) or interleukin-3 (IL-3) modulates MAPK in the myeloid progenitor cell line, 32D. cAMP dramatically increased ERK activity in the presence of CSF-1 or IL-3. IL-3 also synergized with cAMP to activate ERK in another myeloid cell line, FDC-P1. The increase in ERK activity was transmitted to a downstream target, p90rsk. cAMP treatment of 32D cells transfected with oncogenic Ras was found to recapitulate the superactivation of ERK seen with cAMP and CSF-1 or IL-3. ERK activation in the presence of cAMP did not appear to involve any of the Raf isoforms and was blocked by expression of dominant-negative MEK1 or treatment with a MEK inhibitor, PD98059. Although cAMP had an overall inhibitory effect on CSF-1–mediated proliferation and survival, the inhibition was markedly increased if ERK activation was blocked by PD98059. These findings suggest that upregulation of the ERK pathway is one mechanism induced by CSF-1 and IL-3 to protect myeloid progenitors from the growth-suppressive and apoptosis-inducing effects of cAMP elevations.

ErbB2 expression increases the spectrum and potency of ligand-mediated signal transduction through ErbB4

Interleukin 3-dependent murine 32D cells do not detectably express members of the ErbB receptor family and do not proliferate in response to known ligands for these receptors. 32D transfectants were generated expressing human ErbB4 alone (32D.E4) or with ErbB2 (32D.E2/E4). Epidermal growth factor (EGF), neuregulin 1-beta (NRG1-beta), betacellulin (BTC), transforming growth factor-alpha (TGF-alpha), heparin binding-EGF (HB-EGF), and amphiregulin were analyzed for their ability to mediate mitogenesis in these transfectants. 32D.E4 responded mitogenically to NRG1-beta and BTC. Surprisingly, EGF also induced significant DNA synthesis and TGF-alpha was negligibly mitogenic on 32D.E4 cells, whereas HB-EGF and amphiregulin were inactive. Although coexpression of ErbB2 with ErbB4 in 32D.E2/E4 cells did not significantly alter DNA synthesis in response to NRG1-beta or BTC, it greatly enhanced mitogenesis elicited by EGF and TGF-alpha and unmasked the ability of HB-EGF to induce proliferation. EGF-related ligands that exhibited potent mitogenic activity on 32D.E2/E4 cells at low concentrations induced adherence, morphological alterations, and up-regulation of the Mac-1 integrin and FcgammaRII/III at higher concentrations. While 125I-EGF could be specifically crosslinked to both 32D.E4 and 32D.E2/E4 cells, its crosslinking capacity was greatly enhanced in the cotransfected cells. The ability of the various ligands to mediate proliferation and/or adhesion in the two transfectants correlated with their capacity to induce substrate tyrosine phosphorylation and to initiate and sustain activation of mitogen-activated protein kinase. We conclude that the ability of ErbB4 to mediate signal transduction through EGF-like ligands is broader than previously assumed and can be profoundly altered by the concomitant expression of ErbB2.

Features of Macrophage Differentiation Induced by p19INK4d, a Specific Inhibitor of Cyclin D–Dependent Kinases

The mitogen-dependent induction of cyclin D–dependent kinase activity is required for cells to enter the DNA synthetic (S) phase of their division cycle. Immature 32Dcl3 myeloid cells (32D) proliferating in the presence of interleukin-3 (IL-3) normally express cyclins D2 and D3, which assemble into binary holoenzyme complexes with their catalytic subunits, CDK4 and CDK6. When 32D cells are switched to medium containing granulocyte colony-stimulating factor (G-CSF ) instead of IL-3, D-type cyclins are degraded and, in the absence of their associated kinase activity, the cells arrest in the first gap phase (G1 ) of the cell cycle and differentiate to neutrophils. We derived 32D cells in which the expression of p19INK4d, a specific polypeptide inhibitor of CDK4 and CDK6, is regulated by the heavy metal-inducible sheep metallothionein promoter. Induction of p19INK4d in response to zinc prolonged cell survival in the absence of growth factor treatment. When maintained in medium containing both IL-3 and zinc, these cells lost cyclin D–dependent kinase activity, underwent G1 phase arrest, and acquired certain morphologic, antigenic, and functional properties of mononuclear phagocytes. Cells induced to express p19INK4d did not synthesize receptors for macrophage colony-stimulating factor (M-CSF/CSF-1) and reverted to an immature myeloid phenotype when shifted back into medium containing IL-3 alone. These cells exhibited accelerated differentiation to neutrophils in response to G-CSF but also gave rise to macrophage-like cells when maintained in medium containing both G-CSF and zinc. Therefore, the acquisition of macrophage properties in response to zinc treatment neither depended upon IL-3 nor upon G1 phase arrest per se and instead reflects some ability of p19INK4d, and presumably cyclin D–dependent kinases, to affect myeloid differentiation.

Features of Macrophage Differentiation Induced by p19INK4d, a Specific Inhibitor of Cyclin D–Dependent Kinases

The mitogen-dependent induction of cyclin D–dependent kinase activity is required for cells to enter the DNA synthetic (S) phase of their division cycle. Immature 32Dcl3 myeloid cells (32D) proliferating in the presence of interleukin-3 (IL-3) normally express cyclins D2 and D3, which assemble into binary holoenzyme complexes with their catalytic subunits, CDK4 and CDK6. When 32D cells are switched to medium containing granulocyte colony-stimulating factor (G-CSF ) instead of IL-3, D-type cyclins are degraded and, in the absence of their associated kinase activity, the cells arrest in the first gap phase (G1 ) of the cell cycle and differentiate to neutrophils. We derived 32D cells in which the expression of p19INK4d, a specific polypeptide inhibitor of CDK4 and CDK6, is regulated by the heavy metal-inducible sheep metallothionein promoter. Induction of p19INK4d in response to zinc prolonged cell survival in the absence of growth factor treatment. When maintained in medium containing both IL-3 and zinc, these cells lost cyclin D–dependent kinase activity, underwent G1 phase arrest, and acquired certain morphologic, antigenic, and functional properties of mononuclear phagocytes. Cells induced to express p19INK4d did not synthesize receptors for macrophage colony-stimulating factor (M-CSF/CSF-1) and reverted to an immature myeloid phenotype when shifted back into medium containing IL-3 alone. These cells exhibited accelerated differentiation to neutrophils in response to G-CSF but also gave rise to macrophage-like cells when maintained in medium containing both G-CSF and zinc. Therefore, the acquisition of macrophage properties in response to zinc treatment neither depended upon IL-3 nor upon G1 phase arrest per se and instead reflects some ability of p19INK4d, and presumably cyclin D–dependent kinases, to affect myeloid differentiation.

Aortic endothelial cells regulate proliferation of human monocytes in vitro via a mechanism synergistic with macrophage colony-stimulating factor. Convergence at the cyclin E/p27(Kip1) regulatory checkpoint

Monocyte-derived macrophages (Mphis) are pivotal participants in the pathogenesis of atherosclerosis. Evidence from both animal and human plaques indicates that local proliferation may contribute to accumulation of lesion Mphis, and the major Mphi growth factor, macrophage colony stimulating factor (MCSF), is present in atherosclerotic plaques. However, most in vitro studies have failed to demonstrate that human monocytes/Mphis possess significant proliferative capacity. We now report that, although human monocytes cultured in isolation showed only limited MCSF-induced proliferation, monocytes cocultured with aortic endothelial cells at identical MCSF concentrations underwent enhanced (up to 40-fold) and prolonged (21 d) proliferation. In contrast with monocytes in isolation, this was optimal at low seeding densities, required endothelial cell contact, and could not be reproduced by coculture with smooth muscle cells. Intimal Mphi isolated from human aortas likewise showed endothelial cell contact-dependent, MCSF-induced proliferation. Consistent with a two-signal mechanism governing Mphi proliferation, the cell cycle regulatory protein, cyclin E, was rapidly upregulated by endothelial cell contact in an MCSFindependent fashion, but MCSF was required for successful downregulation of the cell cycle inhibitory protein p27(Kip1) before cell cycling. Thus endothelial cells and MCSF differentially and synergistically regulate two Mphi genes critical for progression through the cell cycle.

Direct observation and quantification of macrophage chemoattraction to the growth factor CSF-1

The cloned mouse macrophage cell line, BAC1.25F, resembles primary macrophages in its dependence on colony stimulating factor-1 (CSF-1) for both viability and proliferation. Re-addition of CSF-1 to cytokine-deprived cells, which are rounded with diffusely organised F-actin, stimulates rapid cell spreading and cell polarisation. Using the Dunn chemotaxis chamber the movement of stimulated macrophages was monitored over a 2 hour period. Cells restimulated with 1.32 nM human recombinant CSF-1 migrated at a mean rate of 7.71 microns per hour, but showed no directional preferences. In a linear concentration gradient of CSF-1, cytokine-deprived cells were again stimulated to migrate and the mean rate of cell motility, at 6.88 microns per hour, was not significantly different from that measured in an isotropic environment of CSF-1. However, there was a strong preference for the cells to orientate so that their long axes aligned with the CSF-1 gradient and they migrated preferentially towards the source of CSF-1. Migrating cells contained abundant F-actin within the leading lamellae as judged by confocal imaging of fluorescent phalloidin, but the actin was not arranged into stress fibre-like structures. These data support the proposition that CSF-1 is both a chemokinetic and chemotactic agent for macrophages. Tumour necrosis factor (TNF-alpha) failed to stimulate cell migration and thus was neither chemokinetic nor a chemotactic agent. However, cells exposed to a dual concentration gradient of both TNF-alpha and CSF-1 did migrate successfully, although the chemotactic response to CSF-1 was abolished.

Wild-type p53 induces diverse effects in 32D cells expressing different oncogenes

Expression of exogenous wild-type (wt) p53 in different leukemia cell lines can induce growth arrest, apoptotic cell death, or cell differentiation. The hematopoietic cell lines that have been used so far to study wt p53 functions have in common the characteristic of not expressing endogenous p53. However, the mechanisms involved in the transformation of these cells are different, and the cells are at different stages of tumor progression. It can be postulated that each type of neoplastic cell offers a particular environment in which p53 might generate different effects. To test this hypothesis, we introduced individual oncogenes into untransformed, interleukin-3 (IL-3)-dependent myeloid precursor 32D cells to have a single transforming agent at a time. The effects induced by wt p53 overexpression were subsequently evaluated in each oncogene-expressing 32D derivative. We found that in not fully transformed, v-ras-expressing 32D cells, as already shown for the parental 32D cells, overexpression of the wt p53 gene caused no phenotypic changes and no reduction of the proliferative rate as long as the cells were maintained in their normal culture conditions (presence of IL-3 and serum). An accelerated rate of apoptosis was observed after IL-3 withdrawal. In contrast, in transformed, IL-3-independent 32D cells, wt p53 overexpression induced different effects. The v-abl-transformed cells manifested a reduction in growth rate, while the v-src-transformed cells underwent monocytic differentiation. These results show that the phenotype effects of wt p53 action(s) can vary as a function of the cellular environment.

Mutational analysis of the beta-type platelet-derived growth factor receptor defines the site of interaction with the bovine papillomavirus type 1 E5 transforming protein

The E5 polypeptide of bovine papillomavirus type 1 is a small membrane-bound protein which induces the transformation of immortalized fibroblasts, apparently via the formation of a ternary complex with the platelet-derived growth factor receptor (PDGFR) and the 16-kDa V-ATPase protein. This interaction seems to be mediated, at least in part, by their respective transmembrane domains. E5 also cooperates with transfected beta PDGFR to induce interleukin-3 (IL-3)-independent growth of a mouse myeloid precursor cell line (32D) which normally lacks expression of most known tyrosine kinase growth factor receptors. Cell proliferation induced by beta PDGFR and E5 is also highly specific, since the highly conserved alpha PDGFR and other related receptors did not physically or functionally interact with E5 in these cells. In the current study, analysis of chimeric alpha and beta PDGFRs confirmed that a short region encompassing the beta PDGFR transmembrane domain was sufficient for complex formation with E5, receptor autophosphorylation, and sustained proliferation of 32D cells in the absence of IL-3. Furthermore, a deletion mutant lacking the entire extracellular domain efficiently bound E5 and induced IL-3-independent growth. These data provide direct evidence that the interaction between E5 and the beta PDGFR involves amino acids 531 to 556 of the receptor transmembrane region and that this specific interaction is critical for activation of the PDGFR signaling complex.

Isolation of new oncogenic forms of the murine c-fms gene

The c-fms gene encodes the receptor for the macrophage colony-stimulating factor, which plays a key role in the proliferation and differentiation of cells of the myelomonocytic lineage. In order to study the effects of overexpression of the macrophage colony-stimulating factor receptor in hematopoietic cells, a Harvey sarcoma virus-derived retroviral vector containing the murine c-fms cDNA was pseudotyped with Friend murine leukemia virus and inoculated into newborn DBA/2 mice. This viral complex induced monoclonal or oligoclonal leukemias with a shorter latency than that for Friend murine leukemia virus alone. Unexpectedly, 60% of the integrated fms proviruses had deletions at the 5' end of the c-fms gene. Sequence analysis of seven mutant proviruses indicated that the deletions always included the c-fms ligand binding domain and either occurred within the c-fms sequences, leaving the fms open reading frame unchanged, or joined VL30 sequences located at the 5' end of the parental retroviral vector to internal c-fms sequences, resulting in truncated fms proteins devoid of the canonical signal peptide. In contrast to all tyrosine kinase receptors transduced in retroviruses, no helper gag- or env-derived sequences were fused to the rearranged fms sequences. Viral supernatants isolated from hematopoietic tumors with viruses with deletions were able to transform NIH 3T3 cells as efficiently as parental fms virus, indicating that deletions resulted in constitutive activation of the c-fms gene. These oncogenic variants differ from those transduced in the Suzan McDonough strain of feline sarcoma viruses (L. Donner, L. A. Fedele, C. F. Garon, S. J. Anderson, and C. J. Sherr, J. Virol. 41:489-500, 1982). The high rate of c-fms rearrangement and its relevance in the occurrence of hematopoietic tumors are discussed.

Raf-1 protein is required for growth factor-induced proliferation of hematopoietic cells

Raf-1 is a 74-kD serine/threonine kinase located in the cell cytoplasm that is activated by phosphorylation in cells stimulated with a variety of mitogens and growth factors, including hematopoietic growth factors. Using c-raf antisense oligonucleotides to block Raf-1 expression, we have established that Raf-1 is required for hematopoietic growth factor-induced proliferation of murine cell lines stimulated by growth factors whose receptors are members of several different structural classes: (a) the hematopoietin receptor family, including interleukin (IL)-2, IL-3, IL-4, granulocyte colony-stimulating factor, granulocyte/macrophage colony-stimulating factor (GM-CSF), and erythropoietin; (b) the tyrosine kinase receptor class, including Steel factor and CSF-1; and (c) IL-6, leukemia inhibitory factor, and oncostatin M, whose receptors include the gp130 receptor subunit. Although results of previous experiments had suggested that IL-4 does not phosphorylate or activate the Raf-1 kinase, c-raf antisense oligonucleotides inhibited IL-4-induced proliferation of both myeloid and T cell lines, and IL-4 activated Raf-1 kinase activity in an IL-4-dependent myeloid cell line. In colony assays, c-raf antisense oligonucleotides completely inhibited colony formation of unseparated normal murine bone marrow cells stimulated with either IL-3 or CSF-1 and partially inhibited cells stimulated with GM-CSF. In addition, c-raf antisense oligonucleotides completely inhibited both IL-3- and GM-CSF-induced colony formation of CD34+ purified human progenitors stimulated with these same growth factors. Thus, Raf-1 is required for growth factor-induced proliferation of leukemic murine progenitor cell lines and normal murine and human bone marrow-derived progenitor cells regardless of the growth factor used to stimulate cell growth.

Characterization of a protein kinase C-delta (PKC-delta) ATP binding mutant. An inactive enzyme that competitively inhibits wild type PKC-delta enzymatic activity

To investigate the function of protein kinase C (PKC)-delta, we mutated its ATP binding site by converting the invariant lysine in the catalytic domain (amino acid 376) to an arginine. Expression vectors containing wild type and mutant PKC-delta cDNAs were generated either with or without an influenza virus hemagglutinin epitope tag. After expression in 32D cells by transfection, the PKC-delta ATP binding mutant (PKC-delta K376R) was not able to phosphorylate itself or the PKC-delta pseudosubstrate region-derived substrate, indicating that PKC-delta K376R was an inactive enzyme. PKC activity was inhibited by 67% in 32D cells coexpressing both PKC-delta wild type (PKC-delta WT) and PKC-delta K376R when compared to 32D cells expressing only PKC-delta WT. Mixture of PKC-delta WT and PKC-delta K376R kinase sources in vitro also reduced the enzymatic activity of PKC-delta WT. These results suggest that PKC-delta K376R competes with PKC-delta WT and inhibits PKC-delta WT phosphorylation of its in vitro substrate. While PKC-delta WT overexpressed in 32D cells demonstrated 12-O-tetradecanoylphorbol-13-acetate (TPA)-dependent translocation from the cytosolic to the membrane fraction, PKC-delta K376R was exclusively localized in the membrane fraction even prior to TPA stimulation. Unlike PKC-delta WT which was phosphorylated on tyrosine residue(s) only after TPA treatment, PKC-delta K376R was constitutively phosphorylated on tyrosine residue(s). Although exposure of PKC-delta WT transfectants to TPA induced 32D monocytic differentiation, the 32D/PKC-delta K376R transfectants were resistant to TPA-induced differentiation. Thus, expression of active PKC-delta is required to mediate 32D monocytic differentiation in response to TPA stimulation.

Stimulation of the platelet-derived growth factor beta receptor signaling pathway activates protein kinase C-delta

The murine myeloid progenitor cell line 32D was recently shown to undergo monocytic differentiation when protein kinase C-delta (PKC-delta) was overexpressed and activated by 12-O-tetradecanoylphorbol-13-acetate (TPA) (H. Mischak, J.H. Pierce, J. Goodnight, M.G. Kazanietz, P.M. Blumberg, and J.F. Mushinski, J. Biol. Chem. 268:20110-20115, 1993). Tyrosine phosphorylation of PKC-delta occurred when PKC-delta-transfected 32D cells were stimulated by TPA (W. Li, H. Mischak, J.-C. Yu, L.-M. Wang, J.F. Mushinski, M.A. Heidaran, and J.H. Pierce, J. Biol. Chem. 269:2349-2352, 1994). In order to elucidate the role played by PKC-delta in response to activation of a receptor tyrosine kinase, we transfected platelet-derived growth factor beta receptor (PDGF-beta R) alone (32D/PDGF-beta R) or together with PKC-delta (32D/PDGF-beta R/PKC-delta) into 32D cells. NIH 3T3 cells which endogenously express both PDGF-alpha R and PDGF-beta R were also transfected with PKC-delta (NIH 3T3/PKC-delta). Like TPA treatment, PDGF-BB stimulation caused striking phosphorylation of PKC-delta in vivo and translocation of some PKC-delta from the cytosol fraction to the membrane fraction in both cell systems. Some of the phosphorylation induced by PDGF-BB treatment was found to be on a tyrosine residue(s). Tyrosine-phosphorylated PKC-delta was observed only for the membrane fraction after stimulation with PDGF-BB or TPA. The enzymatic activity of PKC-delta in the membrane fraction also increased after stimulation with TPA or PDGF, providing a positive correlation between PKC-delta tyrosine phosphorylation and its activation. Overnight treatment of 32D/PDGF-beta R/PKC-delta cells with PDGF-BB induced monocytic differentiation as judged by an increase in expression of cell surface macrophage differentiation markers. PDGF-BB had much weaker effects on 32D/PDGF-beta R cell differentiation, suggesting that increased PKC-delta expression enhanced monocytic differentiation. These results indicate that PKC-delta is a downstream molecule in the PDGFR signaling pathway and may play a pivotal role in PDGF-beta R-mediated cell differentiation.

Biological function of PDGF-induced PI-3 kinase activity: its role in alpha PDGF receptor-mediated mitogenic signaling

The tyrosine phosphorylation sites in the human alpha PDGF receptor (alpha PDGFR) required for association with PI-3 kinase have been identified as tyrosines 731 and 742. Mutation of either tyrosine substantially reduced PDGF-induced PI-3 kinase activity but did not impair the receptor-mediated mitogenic response. We sought to determine whether PDGF-induced PI-3 kinase activity could be further ablated so as to exclude a low threshold requirement for PDGFR signal transduction. Thus, we mutated both tyrosine 731 and 742 and expressed the double mutant (Y731F/Y742F) in 32D hematopoietic cells. In such transfectants, PDGF induced no detectable receptor-associated or anti-P-Tyr recoverable PI-3 kinase activity. Under the same conditions, neither mobility shift of raf-1 nor tyrosine phosphorylation of either PLC gamma or MAP kinase was impaired. 32D transfectants expressing the double mutant showed wild-type alpha PDGFR levels of mitogenic and chemotactic responses to PDGF. To examine the effect of the double mutation in cells that normally respond to PDGF, we generated chimeras in which the cytoplasmic domains of wild-type alpha PDGFR, Y731F, and Y731F/Y742F were linked to the extracellular domain of colony-stimulating factor-1 (CSF-1) receptor (fms). After introduction of the chimeric receptors into mouse NIH/3T3 fibroblasts, the ability of CSF-1 to stimulate growth of these transfectants was examined. Our data show that all these chimeric receptors exhibited similar abilities to mediate CSF-1-stimulated cell growth. These findings lead us to conclude that PDGF-induced PI-3 kinase activity is not required for PDGF-stimulated mitogenic pathway in both NIH/3T3 fibroblasts and 32D hematopoietic cells.