Rescue of the colony-stimulating factor 1 (CSF-1)-nullizygous mouse (Csf1(op)/Csf1(op)) phenotype with a CSF-1 transgene and identification of sites of local CSF-1 synthesis

CKIP-1 regulates macrophage proliferation by inhibiting TRAF6-mediated Akt activation

Macrophages play pivotal roles in development, homeostasis, tissue repair and immunity. Macrophage proliferation is promoted by macrophage colony-stimulating factor (M-CSF)-induced Akt signaling; yet, how this process is terminated remains unclear. Here, we identify casein kinase 2-interacting protein-1 (CKIP-1) as a novel inhibitor of macrophage proliferation. In resting macrophages, CKIP-1 was phosphorylated at Serine 342 by constitutively active GSK3β, the downstream target of Akt. This phosphorylation triggers the polyubiquitination and proteasomal degradation of CKIP-1. Upon M-CSF stimulation, Akt is activated by CSF-1R-PI3K and then inactivates GSK3β, leading to the stabilization of CKIP-1 and β-catenin proteins. β-catenin promotes the expression of proliferation genes including cyclin D and c-Myc. CKIP-1 interacts with TRAF6, a ubiquitin ligase required for K63-linked ubiquitination and plasma membrane recruitment of Akt, and terminates TRAF6-mediated Akt activation. By this means, CKIP-1 inhibits macrophage proliferation specifically at the late stage after M-CSF stimulation. Furthermore, CKIP-1 deficiency results in increased proliferation and decreased apoptosis of macrophages in vitro and CKIP-1(-/-) mice spontaneously develop a macrophage-dominated splenomegaly and myeloproliferation. Together, these data demonstrate that CKIP-1 plays a critical role in the regulation of macrophage homeostasis by inhibiting TRAF6-mediated Akt activation.

Colony-stimulating factor 1 potentiates lung cancer bone metastasis

Colony-stimulating factor 1 (CSF1) is essential for osteoclastogenesis that mediates osteolysis in metastatic tumors. Patients with lung cancer have increased CSF1 in serum and high levels are associated with poor survival. Adenocarcinomas metastasize rapidly and many patients suffer from bone metastasis. Lung cancer stem-like cells sustain tumor growth and potentiate metastasis. The purpose of this study was to determine the role of CSF1 in lung cancer bone metastasis and whether inhibition of CSF1 ameliorates the disease. Human lung adenocarcinoma A549 cells were examined in vitro for CSF1/CSF1R. A549-luc cells were injected intracardiac in NOD/SCID mice and metastasis was assessed. To determine the effect of CSF1 knockdown (KD) in A549 cells on bone metastasis, cells were stably transfected with a retroviral vector containing short-hairpin CSF1 (KD) or empty vector (CT). Results showed that A549 cells express CSF1/CSF1R; CSF1 increased their proliferation and invasion, whereas soluble CSF1R inhibited invasion. Mice injected with A549-luc cells showed osteolytic bone lesions 3.5 weeks after injection and lesions increased over 5 weeks. Tumors recapitulated adenocarcinoma morphology and showed osteoclasts along the tumor/bone interface, trabecular, and cortical bone loss. Analyses of KD cells showed decreased CSF1 protein levels, reduced colony formation in soft agar assay, and decreased fraction of stem-like cells. In CSF1KD mice, the incidence of tumor metastasis was similar to controls, although fewer CSF1KD mice had metastasis in both hind limbs. KD tumors showed reduced CSF1 expression, Ki-67+ cells, and osteoclasts. Importantly, there was a low incidence of large tumors >0.1 mm(2) in CSF1KD mice compared with control mice (10% vs 62.5%). This study established a lung osteolytic bone metastasis model that resembles human disease and suggests that CSF1 is a key determinant of cancer stem cell survival and tumor growth. Results may lead to novel strategies to inhibit CSF1 in lung cancer and improve management of bone metastasis.

Wild-type and IL10-null mice have differential colonic epithelial gene expression responses to dietary supplementation with synbiotic Bifidobacterium animalis subspecies lactis and inulin

Prebiotic plus probiotic (synbiotic) supplementations promote fermentation and have shown anti-inflammatory activity in colonic epithelium. However, in many instances, patients with inflammatory bowel disease (IBD) have demonstrated adverse effects after prebiotic supplementation at a dose well tolerated by normal individuals. To test the hypothesis that the host inflammation affects the colonic epithelial response to increased fermentation, the gene expression of colonic epithelium was analyzed. In a 1-way experimental design to test the effect of supplements in wild-type mice using the standard diet formulated by the American Institute of Nutrition (AIN-93G) as the control diet, fermentable fiber inulin (5%) in the absence or presence of the probiotic Bifidobacterium animalis subspecies lactis (Bb12) (10(8) CFU/kg diet) showed limited effects on gene expression as determined by whole-genome microarray. Bb12 supplementation alone was known not to increase fermentation and here instead significantly upregulated genes in nucleic acid metabolic processes. The effects of the synbiotic diet were then determined in mice exposed to LPS-induced inflammation in a 2-way experimental design testing the effect of diet and LPS. The microarray and quantitative reverse transcription-polymerase chain reaction analyses on the wild-type mice revealed that LPS-induced changes in the colonic epithelium were 4- to 10-fold less in the synbiotic diet group compared with the control diet group. Unlike the wild-type mice, anti-inflammatory cytokine interleukin 10 (IL10)-null mice (susceptible to IBD) given the synbiotic diet, compared with those given the control diet, had 3- to 40-fold increased expression of inflammation-related genes such as Cxcl1 (chemokine C-X-C motif ligand 1) and S100a9 (S100 calcium binding protein A9) in the absence and presence of LPS exposure. These contrasting intestinal epithelial responses to increased fermentation in wild-type and IL10-null mice are similar to the difference between healthy human individuals and those with IBD, suggesting that the host disease/genetic background should be considered before prebiotic/probiotic supplementation.

Elevated CSF1 serum concentration predicts poor overall survival in women with early breast cancer

Colony-stimulating factor 1 (CSF1) is a key regulator of mammary gland development, and a modulator of tissue macrophages. Expression of the CSF1 receptor gene C-FMS (CSF1R) is strongly associated with poor outcome in breast cancer and results in tumor cell invasiveness and pro-metastatic behavior in vitro. However, CSF1's role as a predictive factor in breast cancer remains unclear. We have prospectively measured circulating CSF1 using ELISA in 572 women with early breast cancer and in 688 women with benign breast lesions, and correlated these concentrations with overall survival (OS), nodal status, and other clinical and histological parameters. Serum CSF1 concentrations were significantly elevated in patients with early breast cancer when compared with those with benign tumors (P<0.0001). Within breast cancer patients, CSF1 was higher in women with axillary lymph nodes (P=0.03). Serum CSF1 correlated with tumor size (P=0.002), age (P<0.001), and Ki67 expression (P=0.006). Log CSF1 serum concentrations were predictive of poor survival in both univariate (hazard ratio (HR): 3.77, 95% CI: 1.65-8.65, P=0.002) and multivariate analyses (HR: 3.1, 95% CI: 1.03-9.33, P=0.04). Post- but not premenopausal women with CSF1 serum concentrations >873  pg/ml experienced a significantly poorer outcome (P=0.004 log-rank test). Serum CSF1 concentrations are elevated in women with malignant breast tumors. In early breast cancer, elevated serum CSF1 is associated with nodal involvement, and in postmenopausal women also with poor OS.

Tissue-resident macrophages

Tissue-resident macrophages are a heterogeneous population of immune cells that fulfill tissue-specific and niche-specific functions. These range from dedicated homeostatic functions, such as clearance of cellular debris and iron processing, to central roles in tissue immune surveillance, response to infection and the resolution of inflammation. Recent studies highlight marked heterogeneity in the origins of tissue macrophages that arise from hematopoietic versus self-renewing embryo-derived populations. We discuss the tissue niche-specific factors that dictate cell phenotype, the definition of which will allow new strategies to promote the restoration of tissue homeostasis. Understanding the mechanisms that dictate tissue macrophage heterogeneity should explain why simplified models of macrophage activation do not explain the extent of heterogeneity seen in vivo.

Induction of functional human macrophages from bone marrow promonocytes by M-CSF in humanized mice

Engraftment of human CD34⁺ hematopoietic stem/progenitor cells into immunodeficient mice leads to robust reconstitution of human T and B cells but not monocytes and macrophages. To identify the cause underlying the poor monocyte and macrophage reconstitution, we analyzed human myeloid cell development in humanized mice and found that it was blocked at the promonocyte stage in the bone marrow. Expression of human M-CSF or GM-CSF by hydrodynamic injection of cytokine-encoding plasmid completely abolished the accumulation of promonocytes in the bone marrow. M-CSF promoted the development of mature monocytes and tissue-resident macrophages whereas GM-CSF did not. Moreover, correlating with an increased human macrophages at the sites of infection, M-CSF-treated humanized mice exhibited an enhanced protection against influenza virus and Mycobacterium infection. Our study identifies the precise stage at which human monocyte/macrophage development is blocked in humanized mice and reveals overlapping and distinct functions of M-CSF and GM-CSF in human monocyte and macrophage development. The improved reconstitution and functionality of monocytes/macrophages in the humanized mice following M-CSF expression provide a superior in vivo system to investigate the role of macrophages in physiological and pathological processes.

A deficiency in CCR2+ monocytes: the hidden side of Alzheimer's disease

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by intracellular neurofibrillary tangle formation and extracellular amyloid-β (Aβ) deposition. To date, microglia seem to act as double-edged swords, being either beneficial (e.g. clearance of Aβ) or detrimental (e.g. secretion of neurotoxic factors) in AD. Following a rather intense debate on the question, a consensus has emerged that microglia can renew themselves via proliferation of already differentiated microglia as well as via the de novo recruitment of monocytes of mouse models of AD. However, recent advances suggest distinct function for resident and bone marrow-derived microglia (BMDM), and have emphasized the neuroprotective functions of BMDM. BMDM is the only subset of cells that restrict cerebral amyloidosis in the AD brain, which has been recently attributed to CCR2(+) monocytes. Moreover, an impaired recruitment of CCR2(+) monocytes has been reported in AD patients, as seen from the CCR2(+) monocytopenia found in the bloodstream and BM. The present review summarizes the current knowledge on the roles and dysfunctions of CCR2(+) monocytes in AD and their potential as key therapeutic targets.

Transcriptional profiling and pathway analysis of CSF-1 and IL-34 effects on human monocyte differentiation

CSF-1 is the well-known ligand for CSF-1R, which plays a vital role in monocyte-macrophage generation, survival, and function. IL-34 is a newly discovered cytokine that also signals through CSF-1R. Although there are limited data for downstream signaling and pathway activation for CSF-1, none are published, to date, for expression profiles of IL-34. The objective of this study was to characterize and compare the signaling pathways downstream of the CSF-1R receptor, based on these two ligands. This was accomplished through transcriptional profiling and pathway analysis of CD14(+) human monocytes differentiated with each ligand. Additionally, cells were treated with a CSF-1R inhibitor GW2580 to establish that observations associated with each ligand were CSF-1R mediated. Gene expression profiles were generated for each condition using Agilent 4x44K Whole Human Genome Microarrays. Overall profiles generated by each cytokine were similar (~75% of genes) with a dampened effect noted on some pathways (~25% of genes) with IL-34. One key difference observed, between the two cytokines was in the repression of CCR2 message. A similar divergence in protein level was established by FACS analysis. The differential effect on CCR2 expression has major implications for monocyte/macrophage biology including homeostasis and function. Further study of IL-34 effects on monocyte/macrophage biology will shed light on the specific role each ligand plays and the context in which these roles are important. To our knowledge, this study is the first to illustrate downstream transcriptional profiles and pathways of IL-34 in comparison with CSF-1 and identify notable differences in CCR2 expression.

The impact of the myeloid response to radiation therapy

Radiation therapy is showing potential as a partner for immunotherapies in preclinical cancer models and early clinical studies. As has been discussed elsewhere, radiation provides debulking, antigen and adjuvant release, and inflammatory targeting of effector cells to the treatment site, thereby assisting multiple critical checkpoints in antitumor adaptive immunity. Adaptive immunity is terminated by inflammatory resolution, an active process which ensures that inflammatory damage is repaired and tissue function is restored. We discuss how radiation therapy similarly triggers inflammation followed by repair, the consequences to adaptive immune responses in the treatment site, and how the myeloid response to radiation may impact immunotherapies designed to improve control of residual cancer cells.

Colony-stimulating factor 1 receptor (CSF1R) signaling in injured neurons facilitates protection and survival

Colony-stimulating factor 1 and IL-34 protect against and partially reverse neurodegeneration in mice in part via promoting CREB signaling.

Colony-stimulating factor 1 (CSF1) and interleukin-34 (IL-34) are functional ligands of the CSF1 receptor (CSF1R) and thus are key regulators of the monocyte/macrophage lineage. We discovered that systemic administration of human recombinant CSF1 ameliorates memory deficits in a transgenic mouse model of Alzheimer’s disease. CSF1 and IL-34 strongly reduced excitotoxin-induced neuronal cell loss and gliosis in wild-type mice when administered systemically before or up to 6 h after injury. These effects were accompanied by maintenance of cAMP responsive element–binding protein (CREB) signaling in neurons rather than in microglia. Using lineage-tracing experiments, we discovered that a small number of neurons in the hippocampus and cortex express CSF1R under physiological conditions and that kainic acid–induced excitotoxic injury results in a profound increase in neuronal receptor expression. Selective deletion of CSF1R in forebrain neurons in mice exacerbated excitotoxin-induced death and neurodegeneration. We conclude that CSF1 and IL-34 provide powerful neuroprotective and survival signals in brain injury and neurodegeneration involving CSF1R expression on neurons.

Donor and recipient cell surface colony stimulating factor-1 promote neointimal formation in transplant-associated arteriosclerosis

OBJECTIVE

Transplant-associated arteriosclerosis manifests as progressive vascular neointimal expansion throughout the arterial system of allografted solid organs, and eventually compromises graft perfusion and function. Allografts placed in colony stimulating factor (CSF)-1-deficient osteopetrotic (Csf1(op)/Csf1(op)) mice develop very little neointima, a finding attributed to impaired recipient macrophage function. We examined how CSF-1 affects neointima-derived vascular smooth muscle cells, tested the significance of CSF-1 expressed in donor tissue, and evaluated the contribution of secreted versus cell surface CSF-1 isoforms in transplant-associated arteriosclerosis.

METHODS AND RESULTS

CSF-1 activated specific signaling pathways to promote migration, survival, and proliferation of cultured vascular smooth muscle cells. Tumor necrosis factor-α addition increased CSF-1 and CSF-1 receptor expression, and tumor necrosis factor-α-driven proliferation was blocked by anti-CSF-1 antibody. In a mouse vascular allograft model, lack of recipient or donor CSF-1 impaired neointima formation; the latter suggests local CSF-1 function within the allograft. Moreover, reconstitution of donor or recipient cell surface CSF-1, without secreted CSF-1, restored neointimal formation.

CONCLUSIONS

Vascular smooth muscle cells activation, including that mediated by tumor necrosis factor-α, can be driven in an autocrine/juxtacrine manner by CSF-1. These studies provide evidence for local function of CSF-1 in neointimal expansion, and identify CSF-1 signaling in vascular smooth muscle cells, particularly cell surface CSF-1 signaling, as a target for therapeutic strategies in transplant-associated arteriosclerosis.

Cloning and expression of porcine Colony Stimulating Factor-1 (CSF-1) and Colony Stimulating Factor-1 Receptor (CSF-1R) and analysis of the species specificity of stimulation by CSF-1 and Interleukin 34

Macrophage Colony Stimulating Factor (CSF-1) controls the survival, differentiation and proliferation of cells of the mononuclear phagocyte system. A second ligand for the CSF-1R, Interleukin 34 (IL-34), has been described, but its physiological role is not yet known. The domestic pig provides an alternative to traditional rodent models for evaluating potential therapeutic applications of CSF-1R agonists and antagonists. To enable such studies, we cloned and expressed active pig CSF-1. To provide a bioassay, pig CSF-1R was expressed in the factor-dependent Ba/F3 cell line. On this transfected cell line, recombinant porcine CSF-1 and human CSF-1 had identical activity. Mouse CSF-1 does not interact with the human CSF-1 receptor but was active on pig. By contrast, porcine CSF-1 was active on mouse, human, cat and dog cells. IL-34 was previously shown to be species-specific, with mouse and human proteins demonstrating limited cross-species activity. The pig CSF-1R was equally responsive to both mouse and human IL-34. Based upon the published crystal structures of CSF-1/CSF-1R and IL34/CSF-1R complexes, we discuss the molecular basis for the species specificity.

Age-related changes in synaptic markers and monocyte subsets link the cognitive decline of APP(Swe)/PS1 mice

Alzheimer's disease (AD) is characterized by a progressive memory decline and numerous pathological abnormalities, including amyloid β (Aβ) accumulation in the brain and synaptic dysfunction. Here we wanted to study whether these brain changes were associated with alteration in the population of monocyte subsets since accumulating evidence supports the concept that the innate immune system plays a role in the etiology of this disease. We then determined the immune profile together with expression of genes encoding synaptic proteins and neurotrophins in APP_Swe/PS1 mice and their age-matched wild-type (WT) littermates. We found that the progressive cognitive decline and the dramatic decrease in the expression of numerous synaptic markers and neurotrophins correlated with a major defect in the subset of circulating inflammatory monocytes. Indeed the number of CX₃CR1^lowLy6-C^highCCR2⁺Gr1⁺ monocytes remained essentially similar between 5 weeks and 6 months of age in APP_Swe/PS1 mice, while these cells significantly increased in 6-month-old WT littermates. Of great interest is that the onset of cognitive decline was closely associated with the accumulation of soluble Aβ, disruption of synaptic activity, alteration in the BDNF system, and a defective production in the subset of CX₃CR1^lowLy6-C^highCCR2⁺Gr1⁺ monocytes. However, these memory impairments can be prevented or restored by boosting the monocytic production, using a short treatment of macrophage colony-stimulating factor (M-CSF). In conclusion, low CCR2⁺ monocyte production by the hematopoietic system may be a direct biomarker of the cognitive decline in a context of AD.

The CSF-1 receptor ligands IL-34 and CSF-1 exhibit distinct developmental brain expression patterns and regulate neural progenitor cell maintenance and maturation

The CSF-1 receptor (CSF-1R) regulates CNS microglial development. However, the localization and developmental roles of this receptor and its ligands, IL-34 and CSF-1, in the brain are poorly understood. Here we show that compared to wild type mice, CSF-1R-deficient (Csf1r-/-) mice have smaller brains of greater mass. They further exhibit an expansion of lateral ventricle size, an atrophy of the olfactory bulb and a failure of midline crossing of callosal axons. In brain, IL-34 exhibited a broader regional expression than CSF-1, mostly without overlap. Expression of IL-34, CSF-1 and the CSF-1R were maximal during early postnatal development. However, in contrast to the expression of its ligands, CSF-1R expression was very low in adult brain. Postnatal neocortical expression showed that CSF-1 was expressed in layer VI, whereas IL-34 was expressed in the meninges and layers II-V. The broader expression of IL-34 is consistent with its previously implicated role in microglial development. The differential expression of CSF-1R ligands, with respect to CSF-1R expression, could reflect their CSF-1R-independent signaling. Csf1r-/- mice displayed increased proliferation and apoptosis of neocortical progenitors and reduced differentiation of specific excitatory neuronal subtypes. Indeed, addition of CSF-1 or IL-34 to microglia-free, CSF-1R-expressing dorsal forebrain clonal cultures, suppressed progenitor self-renewal and enhanced neuronal differentiation. Consistent with a neural developmental role for the CSF-1R, ablation of the Csf1r gene in Nestin-positive neural progenitors led to a smaller brain size, an expanded neural progenitor pool and elevated cellular apoptosis in cortical forebrain. Thus our results also indicate novel roles for the CSF-1R in the regulation of corticogenesis.

Selective deletion of the membrane-bound colony stimulating factor 1 isoform leads to high bone mass but does not protect against estrogen-deficiency bone loss

To better define the biologic function of membrane-bound CSF1 (mCSF1) in vivo, we have generated mCSF1 knockout (k/o) mice. Spinal bone density (BMD) was 15.9% higher in k/o mice compared to wild-type (wt) controls (P < 0.01) and total BMD was increased by 6.8% (P < 0.05). A higher mean femur BMD was also observed but did not reach statistical significance (6.9% P = NS). The osteoclastogenic potential of bone marrow isolated from mCSF1 k/o mice was reduced compared to wt marrow. There were no defects in osteoblast number or function suggesting that the basis for the high bone mass phenotype was reduced resorption. In addition to a skeletal phenotype, k/o mice had significantly elevated serum triglyceride levels (123 ± 7 vs. 88 ± 3.2 mg/dl; k/o vs. wt, P < 0.001), while serum cholesterol levels were similar (122 ± 6 vs. 116 ± 6 mg/dl; k/o vs. wt, P = NS). One month after surgery, 5-month-old k/o and wt female mice experienced the same degree of bone loss following ovariectomy (OVX). OVX induced a significant fourfold increase in the expression of the soluble CSF1 isoform (sCSF1) in the bones of wt mice while expression of mCSF1 was unchanged. These findings indicate that mCSF1 is essential for normal bone remodeling since, in its absence, BMD is increased. Membrane-bound CSF1 does not appear to be required for estrogen-deficiency bone loss while in contrast; our data suggest that sCSF1 could play a key role in this pathologic process. The reasons why mCSF1 k/o mice have hypertriglyceridemia are currently under study.

CSF-1 receptor signalling from endosomes mediates the sustained activation of Erk1/2 and Akt in macrophages

Colony stimulating factor-1 (CSF-1) mediates its pleiotropic effects on macrophages through the CSF-1 receptor (CSF-1R), a receptor tyrosine kinase. Current models of CSF-1 signalling imply that the CSF-1R activates signalling pathways exclusively at the plasma membrane and the subsequent internalisation of the CSF-1R simply facilitates its lysosomal degradation in order to prevent on-going signalling. Here, we sought to establish if the CSF-1R may in fact continue to signal following its internalisation. Erk1/2, Akt and Stat3 activation were abrogated when the internalisation of the CSF-1R was impaired, with the effects on Stat3 distinct from those for Erk1/2 and Akt. Pharmacologic inhibition of the CSF-1R following its internalisation resulted in less sustained Erk1/2 and Akt activity, whereas Stat3 activity was unaffected. Significantly, the suppressive effects of the CSF-1R inhibitor on the up-regulation of gene expression by CSF-1 (e.g. cyclin D1 and Bcl-xL gene expression) were comparable irrespective of whether the inhibitor was added prior to CSF-1 stimulation or following the internalisation of the CSF-1R. Similarly, pharmacologic inhibition of Erk1/2 (or Akt) activity either prior to CSF-1 stimulation or subsequent to CSF-1R internalisation had comparable effects on the regulation of gene expression by CSF-1. Together, our data argue that key signalling responses to CSF-1 depend on the ability of the CSF-1R to signal from endosomes following its internalisation, thus adding an important spatiotemporal aspect to CSF-1R signalling.

HIV-1 proteins preferentially activate anti-inflammatory M2-type macrophages

HIV-1 proteins, including Tat, gp120, and Nef, activate macrophages (MΦ), which is consistent with the fact that HIV-1 infection is characterized by sustained immune activation. Meanwhile, MΦ are functionally classified into two types: proinflammatory M1-MΦ and anti-inflammatory M2-MΦ. We show that HIV-1 proteins, particularly Nef, preferentially activate M2-MΦ. Extracellular Tat, gp120, and Nef activated MAPK and NF-κB pathways in human peripheral blood monocyte-derived MΦ. However, the activation was marked in M-CSF-derived M2-MΦ but not GM-CSF-derived M1-MΦ. Nef was the most potent activator, and its signaling activation was comparable to that by TNF-α. Indeed, Nef was internalized more rapidly by M2-MΦ than by M1-MΦ. The myristoylation and proline-rich motif of Nef were responsible for the observed signaling activation. Consistent with the activation of MAPK/NF-κB pathways, Nef stimulated the production of a number of proinflammatory cytokines/chemokines by M2-MΦ. However, Nef reduced the expression of CD163 and phagocytosis, the characteristic markers of M2-MΦ, indicating that Nef drives an M2-like to M1-like phenotypic shift. Because the differentiation of most tissue MΦ depends on M-CSF and its receptor, which is the essential axis for the anti-inflammatory M2-MΦ phenotype, the current study reveals an efficient mechanism by which HIV-1 proteins, such as Nef, induce the proinflammatory MΦ.

Macrophage Migration and Its Regulation by CSF-1

Macrophages are terminally differentiated cells of the mononuclear phagocytic lineage and develop under the stimulus of their primary growth and differentiation factor, CSF-1. Although they differentiate into heterogeneous populations, depending upon their tissue of residence, motility is an important aspect of their function. To facilitate their migration through tissues, macrophages express a unique range of adhesion and cytoskeletal proteins. Notably, macrophages do not form large, stable adhesions or actin stress fibers but rely on small, short lived point contacts, focal complexes and podosomes for traction. Thus, macrophages are built to respond rapidly to migratory stimuli. As well as triggering growth and differentiation, CSF-1 is also a chemokine that regulates macrophage migration via activation the CSF-1 receptor tyrosine kinase. CSF-1R autophosphorylation of several intracellular tyrosine residues leads to association and activation of many downstream signaling molecules. However, phosphorylation of just one residue, Y721, mediates association of PI3K with the receptor to activate the major motility signaling pathways in macrophages. Dissection of these pathways will identify drug targets for the inhibition of diseases in which macrophages contribute to adverse outcomes.

Colony-stimulating factor-1 mediates macrophage-related neural damage in a model for Charcot-Marie-Tooth disease type 1X

Previous studies in our laboratory have shown that in models for three distinct forms of the inherited and incurable nerve disorder, Charcot-Marie-Tooth neuropathy, low-grade inflammation implicating phagocytosing macrophages mediates demyelination and perturbation of axons. In the present study, we focus on colony-stimulating factor-1, a cytokine implicated in macrophage differentiation, activation and proliferation and fostering neural damage in a model for Charcot-Marie-Tooth neuropathy 1B. By crossbreeding a model for the X-linked form of Charcot-Marie-Tooth neuropathy with osteopetrotic mice, a spontaneous null mutant for colony-stimulating factor-1, we demonstrate a robust and persistent amelioration of demyelination and axon perturbation. Furthermore, functionally important domains of the peripheral nervous system, such as juxtaparanodes and presynaptic terminals, were preserved in the absence of colony-stimulating factor-1-dependent macrophage activation. As opposed to other Schwann cell-derived cytokines, colony-stimulating factor-1 is expressed by endoneurial fibroblasts, as revealed by in situ hybridization, immunocytochemistry and detection of β-galactosidase expression driven by the colony-stimulating factor-1 promoter. By both light and electron microscopic studies, we detected extended cell-cell contacts between the colony-stimulating factor-1-expressing fibroblasts and endoneurial macrophages as a putative prerequisite for the effective and constant activation of macrophages by fibroblasts in the chronically diseased nerve. Interestingly, in human biopsies from patients with Charcot-Marie-Tooth type 1, we also found frequent cell-cell contacts between macrophages and endoneurial fibroblasts and identified the latter as main source for colony-stimulating factor-1. Therefore, our study provides strong evidence for a similarly pathogenic role of colony-stimulating factor-1 in genetically mediated demyelination in mice and Charcot-Marie-Tooth type 1 disease in humans. Thus, colony-stimulating factor-1 or its cognate receptor are promising target molecules for treating the detrimental, low-grade inflammation of several inherited neuropathies in humans.

Meox2Cre-mediated disruption of CSF-1 leads to osteopetrosis and osteocyte defects

CSF-1, a key regulator of mononuclear phagocyte production, is highly expressed in the skeleton by osteoblasts/osteocytes and in a number of nonskeletal tissues such as uterus, kidney and brain. The spontaneous mutant op/op mouse has been the conventional model of CSF-1 deficiency and exhibits a pleiotropic phenotype characterized by osteopetrosis, and defects in hematopoiesis, fertility and neural function. Studies to further delineate the biologic effect of CSF-1 within various tissues have been hampered by the lack of suitable models. To address this issue, we generated CSF-1 floxed/floxed mice and demonstrate that Cre-mediated recombination using Meox2Cre, a Cre line expressed in epiblast during early embryogenesis, results in mice with ubiquitous CSF-1 deficiency (CSF-1KO). Homozygous CSF-1KO mice lacked CSF-1 in all tissues and displayed, in part, a similar phenotype to op/op mice that included: failure of tooth eruption, osteopetrosis, reduced macrophage densities in reproductive and other organs and altered hematopoiesis with decreased marrow cellularity, circulating monocytes and B cell lymphopoiesis. In contrast to op/op mice, CSF-1KO mice showed elevated circulating and splenic T cells. A striking feature in CSF-1KO mice was defective osteocyte maturation, bone mineralization and osteocyte-lacunar system that was associated with reduced dentin matrix protein 1 (DMP1) expression in osteocytes. CSF-1KO mice also showed a dramatic reduction in osteomacs along the endosteal surface that may have contributed to the hematopoietic and cortical bone defects. Thus, our findings show that ubiquitous CSF-1 gene deletion using a Cre-based system recapitulates the expected osteopetrotic phenotype. Moreover, results point to a novel link between CSF-1 and osteocyte survival/function that is essential for maintaining bone mass and strength during skeletal development.

Colony-stimulating factor-1 promotes kidney growth and repair via alteration of macrophage responses

Colony-stimulating factor (CSF)-1 controls the survival, proliferation, and differentiation of macrophages, which are recognized as scavengers and agents of the innate and the acquired immune systems. Because of their plasticity, macrophages are endowed with many other essential roles during development and tissue homeostasis. We present evidence that CSF-1 plays an important trophic role in postnatal organ growth and kidney repair. Notably, the injection of CSF-1 postnatally enhanced kidney weight and volume and was associated with increased numbers of tissue macrophages. Moreover, CSF-1 promotes postnatal renal repair in mice after ischemia-reperfusion injury by recruiting and influencing macrophages toward a reparative state. CSF-1 treatment rapidly accelerated renal repair with tubular epithelial cell replacement, attenuation of interstitial fibrosis, and functional recovery. Analysis of macrophages from CSF-1-treated kidneys showed increased expression of insulin-like growth factor-1 and anti-inflammatory genes that are known CSF-1 targets. Taken together, these data suggest that CSF-1 is important in kidney growth and the promotion of endogenous repair and resolution of inflammatory injury.

Distinct roles of CSF-1 isoforms in lupus nephritis

Colony-stimulating factor-1 (CSF-1), the principal growth factor for macrophages, is increased in the kidney, serum, and urine of patients with lupus nephritis, and eliminating CSF-1 suppresses lupus in MRL-Fas(lpr) mice. CSF-1 has three biologically active isoforms: a membrane-spanning cell surface glycoprotein (csCSF-1), a secreted proteoglycan (spCSF-1), and a secreted glycoprotein (sgCSF-1); the role of each isoform in the circulation and kidney in autoimmune disease is not well understood. Here, we constructed mutant MRL-Fas(lpr) mice that only express csCSF-1 or precursors of the spCSF-1 and sgCSF-1 isoforms. Both csCSF-1 and spCSF-1 shifted monocytes toward proinflammatory, activated populations, enhancing their recruitment into the kidney during lupus nephritis. With advancing lupus nephritis, spCSF-1 was the predominant isoform responsible for increasing circulating CSF-1 and, along with the csCSF-1 isoform, for increasing intrarenal CSF-1. Thus, csCSF-1 appears to initiate and promote the local activation of macrophages within the kidney. Intrarenal expression of csCSF-1 and spCSF-1 increases with advancing nephritis, thereby promoting the intrarenal recruitment of monocytes and expansion of Ly6C(hi) macrophages, which induce apoptosis of the renal parenchyma. Taken together, these data suggest that the three CSF-1 isoforms have distinct biologic properties, suggesting that blocking both circulating and intrarenal CSF-1 may be necessary for therapeutic efficacy.

Coordinate regulation of tissue macrophage and dendritic cell population dynamics by CSF-1

CSF-1 drives the homeostatic expansion of macrophages within the growing myometrium of pregnant mice by stimulating in situ proliferation and inducing monocyte precursor recruitment from the blood.

Tissue macrophages (Mϕs) and dendritic cells (DCs) play essential roles in tissue homeostasis and immunity. How these cells are maintained at their characteristic densities in different tissues has remained unclear. Aided by a novel flow cytometric technique for assessing relative rates of blood-borne precursor recruitment, we examined Mϕ and DC population dynamics in the pregnant mouse uterus, where rapid tissue growth facilitated a dissection of underlying regulatory mechanisms. We demonstrate how Mϕ dynamics, and thus Mϕ tissue densities, are locally controlled by CSF-1, a pleiotropic growth factor whose in situ level of activity varied widely between uterine tissue layers. CSF-1 acted in part by inducing Mϕ proliferation and in part by stimulating the extravasation of Ly6C^hi monocytes (Mos) that served as Mϕ precursors. Mo recruitment was dependent on the production of CCR2 chemokine receptor ligands by uterine Mϕs in response to CSF-1. Unexpectedly, a parallel CSF-1–regulated, but CCR2-independent pathway influenced uterine DC tissue densities by controlling local pre-DC extravasation rates. Together, these data provide cellular and molecular insight into the regulation of Mϕ tissue densities under noninflammatory conditions and reveal a central role for CSF-1 in the coordination of Mϕ and DC homeostasis.

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

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

M-CSF potently augments RANKL-induced resorption activation in mature human osteoclasts

Macrophage-CSF (M-CSF) is critical for osteoclast (OC) differentiation and is reported to enhance mature OC survival and motility. However, its role in the regulation of bone resorption, the main function of OCs, has not been well characterised. To address this we analysed short-term cultures of fully differentiated OCs derived from human colony forming unit-granulocyte macrophages (CFU-GM). When cultured on dentine, OC survival was enhanced by M-CSF but more effectively by receptor activator of NFκB ligand (RANKL). Resorption was entirely dependent on the presence of RANKL. Co-treatment with M-CSF augmented RANKL-induced resorption in a concentration-dependent manner with a (200-300%) stimulation at 25 ng/mL, an effect observed within 4-6 h. M-CSF co-treatment also increased number of resorption pits and F-actin sealing zones, but not the number of OCs or pit size, indicating stimulation of the proportion of OCs activated. M-CSF facilitated RANKL-induced activation of c-fos and extracellular signal-regulated kinase (ERK) 1/2 phosphorylation, but not NFκB nor nuclear factor of activated T-cells, cytoplasmic-1 (NFATc1). The mitogen-activated protein kinase kinase (MEK) 1 inhibitor PD98059 partially blocked augmentation of resorption by M-CSF. Our results reveal a previously unidentified role of M-CSF as a potent stimulator of mature OC resorbing activity, possibly mediated via ERK upstream of c-fos.

Leukocytes in mammary development and cancer

Leukocytes, of both the innate and adaptive lineages, are normal cellular components of all tissues. These important cells not only are critical for regulating normal tissue homeostasis, but also are significant paracrine regulators of all physiologic and pathologic tissue repair processes. This article summarizes recent insights regarding the trophic roles of leukocytes at each stage of mammary gland development and during cancer development, with a focus on Murids and humans.

Pleiotropic role for monocyte C-fms protein in response to vascular injury: potential therapeutic target

OBJECTIVES

We examined the role of C-fms+ cells in response to vascular injury with a focus on the temporal and spatial platelet interactions, monocyte survival and proliferation within the evolving neointimal lesion and monocyte proliferation within the circulation and specified monocyte reservoir sites. Finally, we investigated the therapeutic effect of C-fms kinase inhibition (CFKI) on neointimal hyperplasia post vessel injury.

METHODS AND RESULTS

We utilized murine carotid-wire injury, a transgenic C-fms reporting mouse model, confocal microscopy, shear-flow studies, specific C-fms signalling inhibition to determine the activation, mobilization and recruitment of C-fms+ monocytes in the context of early and late vessel remodelling. C-fms+ cells were recruited as early as 4h and accumulated over time in the neointima following injury. Monocyte interaction with platelet thrombus under flow and in vivo, in addition to monocyte mobilisation into the circulation post-injury was impaired by CFKI administration. Sustained inhibition of C-fms over 1-2 weeks abrogated the neointimal response but preserved re-endothelialisation post-injury.

CONCLUSION

These data establish C-fms as a key regulator of the vascular response to injury and a potentially attractive therapeutic target in disease states where neointimal hyperplasia, monocyte activation and pathologic remodelling are prominent and endothelial homeostasis is desirable.

Dendritic cell-mediated in vivo bone resorption

Osteoclasts are resident cells of the bone that are primarily involved in the physiological and pathological remodeling of this tissue. Mature osteoclasts are multinucleated giant cells that are generated from the fusion of circulating precursors originating from the monocyte/macrophage lineage. During inflammatory bone conditions in vivo, de novo osteoclastogenesis is observed but it is currently unknown whether, besides increased osteoclast differentiation from undifferentiated precursors, other cell types can generate a multinucleated giant cell phenotype with bone resorbing activity. In this study, an animal model of calvaria-induced aseptic osteolysis was used to analyze possible bone resorption capabilities of dendritic cells (DCs). We determined by FACS analysis and confocal microscopy that injected GFP-labeled immature DCs were readily recruited to the site of osteolysis. Upon recruitment, the cathepsin K-positive DCs were observed in bone-resorbing pits. Additionally, chromosomal painting identified nuclei from female DCs, previously injected into a male recipient, among the nuclei of giant cells at sites of osteolysis. Finally, osteolysis was also observed upon recruitment of CD11c-GFP conventional DCs in Csf1r(-/-) mice, which exhibit a severe depletion of resident osteoclasts and tissue macrophages. Altogether, our analysis indicates that DCs may have an important role in bone resorption associated with various inflammatory diseases.

The contribution of dynamic stromal remodeling during mammary development to breast carcinogenesis

Breast cancer is a heterogeneous disease whose prognosis varies depending upon the developmental stage of the breast tissue at diagnosis. Notably, breast cancers associated with pregnancy exhibit increased rates of metastasis and poorer long-term survival compared to those diagnosed after menopause. However, postmenopausal breast cancers associated with obesity exhibit a more aggressive behavior and confer decreased overall patient survival compared to those diagnosed in non-obese individuals. Since the mammary gland is a dynamic tissue that undergoes significant changes throughout a woman's lifetime, especially during pregnancy and following menopause, we present evidence to support the notion that changes occurring throughout development within the mammary stromal compartment may account for some of the biological differences in breast cancer subtypes and behaviors.

Age affects gene expression in mouse spermatogonial stem/progenitor cells

Spermatogenesis in man starts with spermatogonial stem cells (SSCs), and leads to the production of sperm in approximately 64 days, common to old and young men. Sperm from elderly men are functional and able to fertilize eggs and produce offspring, even though daily sperm production is more than 50% lower and damage to sperm DNA is significantly higher in older men than in those who are younger. Our hypothesis is that the SSC/spermatogonial progenitors themselves age. To test this hypothesis, we studied the gene expression profile of mouse SSC/progenitor cells at several ages using microarrays. After sequential enzyme dispersion, we purified the SSC/progenitors with immunomagnetic cell sorting using an antibody to GFRA1, a known SSC/progenitor cell marker. RNA was isolated and used for the in vitro synthesis of amplified and labeled cRNAs that were hybridized to the Affymetrix mouse genome microarrays. The experiments were repeated twice with different cell preparations, and statistically significant results are presented. Quantitative RT-PCR analysis was used to confirm the microarray results. Comparison of four age groups (6 days, 21 days, 60 days, and 8 months old) showed a number of genes that were expressed specifically in the older mice. Two of them (i.e. Icam1 and Selp) have also been shown to mark aging hematopoietic stem cells. On the other hand, the expression levels of the genes encoding the SSC markers Gfra1 and Plzf did not seem to be significantly altered by age, indicating that age affects only certain SSC/progenitor properties.

Functional overlap but differential expression of CSF-1 and IL-34 in their CSF-1 receptor-mediated regulation of myeloid cells

CSF-1 is broadly expressed and regulates macrophage and osteoclast development. The action and expression of IL-34, a novel CSF-1R ligand, were investigated in the mouse. As expected, huIL-34 stimulated macrophage proliferation via the huCSF-1R, equivalently to huCSF-1, but was much less active at stimulating mouse macrophage proliferation than huCSF-1. Like muCSF-1, muIL-34 and a muIL-34 isoform lacking Q81 stimulated mouse macrophage proliferation, CSF-1R tyrosine phosphorylation, and signaling and synergized with other cytokines to generate macrophages and osteoclasts from cultured progenitors. However, they respectively possessed twofold and fivefold lower affinities for the CSF-1R and correspondingly, lower activities than muCSF-1. Furthermore, muIL-34, when transgenically expressed in a CSF-1-dependent manner in vivo, rescued the bone, osteoclast, tissue macrophage, and fertility defects of Csf1(op)/(op) mice, suggesting similar regulation of CSF-1R-expressing cells by IL-34 and CSF-1. Whole-mount IL34 in situ hybridization and CSF-1 reporter expression revealed that IL34 mRNA was strongly expressed in the embryonic brain at E11.5, prior to the expression of Csf1 mRNA. QRT-PCR revealed that compared with Csf1 mRNA, IL34 mRNA levels were lower in pregnant uterus and in cultured osteoblasts, higher in most regions of the brain and heart, and not compensatorily increased in Csf1(op/op) mouse tissues. Thus, the different spatiotemporal expression of IL-34 and CSF-1 allows for complementary activation of the CSF-1R in developing and adult tissues.

Role of CSF-1 in progression of epithelial ovarian cancer

Despite the dismal outcome seen in the majority of epithelial ovarian cancer patients, there is ongoing progress in understanding the disease at a molecular level. Elucidation of pathways underlying disease progression and metastasis of ovarian cancer is key to development of targeted therapeutics. It is only in this way that therapeutic potential can be translated to reality. Here, we describe the evidence to date for the role of CSF-1/c-fms signaling in ovarian cancer invasiveness and metastasis, including the recent understanding of how CSF-1/c-fms expression is regulated with identification of significant post-transcriptional regulators.

Pivotal Advance: Avian colony-stimulating factor 1 (CSF-1), interleukin-34 (IL-34), and CSF-1 receptor genes and gene products

Macrophages are involved in many aspects of development, host defense, pathology, and homeostasis. Their normal differentiation, proliferation, and survival are controlled by CSF-1 via the activation of the CSF1R. A recently discovered cytokine, IL-34, was shown to bind the same receptor in humans. Chicken is a widely used model organism in developmental biology, but the factors that control avian myelopoiesis have not been identified previously. The CSF-1, IL-34, and CSF1R genes in chicken and zebra finch were identified from respective genomic/cDNA sequence resources. Comparative analysis of the avian CSF1R loci revealed likely orthologs of mammalian macrophage-specific promoters and enhancers, and the CSF1R gene is expressed in the developing chick embryo in a pattern consistent with macrophage-specific expression. Chicken CSF-1 and IL-34 were expressed in HEK293 cells and shown to elicit macrophage growth from chicken BM cells in culture. Comparative sequence and co-evolution analysis across all vertebrates suggests that the two ligands interact with distinct regions of the CSF1R. These studies demonstrate that there are two separate ligands for a functional CSF1R across all vertebrates.

Circulating CSF-1 promotes monocyte and macrophage phenotypes that enhance lupus nephritis

Macrophages mediate kidney disease and are prominent in a mouse model (MRL-Fas(lpr)) of lupus nephritis. Colony stimulating factor-1 (CSF-1) is the primary growth factor for macrophages, and CSF-1 deficiency protects MRL-Fas(lpr) mice from kidney disease and systemic illness. Whether this renoprotection derives from a reduction of macrophages and whether systemic CSF-1, as opposed to intrarenal CSF-1, promotes macrophage-dependent lupus nephritis remain unclear. Here, we found that increasing systemic CSF-1 hastened the onset of lupus nephritis in MRL-Fas(lpr) mice. Using mutant MRL-Fas(lpr) strains that express high, moderate, or no systemic CSF-1, we detected a much higher tempo of kidney disease in mice with the highest level of CSF-1. Furthermore, we uncovered a multistep CSF-1-dependent systemic mechanism central to lupus nephritis. CSF-1 heightened monocyte proliferation in the bone marrow (SSC(low)CD11b(+)), and these monocytes subsequently seeded the circulation. Systemic CSF-1 skewed the frequency of monocytes toward "inflammatory" (SSC(low)CD11b(+)Ly6C(high)) and activated populations that homed to sites of inflammation, resulting in a more rapid accumulation of intrarenal macrophages (CD11b(+)CSF-1R(+) or CD68(+)) that induced apoptosis of tubular epithelial cells, damaging the kidney. In humans, we found increased levels of CSF-1 in the serum, urine, and kidneys of patients with lupus compared with healthy controls. Furthermore, serum and urine CSF-1 levels correlated with lupus activity, and intrarenal CSF-1 expression correlated with the histopathology activity index of lupus nephritis. Taken together, circulating CSF-1 is a potential therapeutic target for lupus nephritis.

The spermatogonial stem cell niche

Spermatogonial stem cells (SSCs; A(s) spermatogonia) and their direct descendants (A(pr) and A(al) spermatogonia) are preferentially located in those areas of the seminiferous tubules that border on the interstitial tissue. Fewer of these cells are present in tubule areas directly bordering on another tubule. Therefore, the SSC niche is related to the presence of interstitial tissue. The somatic cells within the seminiferous tubules, the Sertoli cells, are able to produce growth factors that stimulate self-renewal (GDNF, FGF2) and differentiation (activin A, BMP4, and SCF) of the SSCs. As Sertoli cells are everywhere on the basal membrane of the tubules, other factors coming from outside the tubules must determine, either directly or indirectly via Sertoli cells, whether in a particular area self-renewal of SSCs will be preferred or differentiation in the form of A(pr) formation. Self-renewal will be preferred in the stem cell niche and differentiation outside of the niche. Factors that could link the niche to the interstitial tissue are CSF1, produced by Leydig cells that stimulate stem cell proliferation and FSH, the concentration of which will be highest near blood vessels and that stimulates GDNF production by Sertoli cells.

MafB restricts M-CSF-dependent myeloid commitment divisions of hematopoietic stem cells

While hematopoietic stem cell (HSC) self-renewal is well studied, it remains unknown whether distinct control mechanisms enable HSC divisions that generate progeny cells with specific lineage bias. Here, we report that the monocytic transcription factor MafB specifically restricts the ability of M-CSF to instruct myeloid commitment divisions in HSCs. MafB deficiency specifically enhanced sensitivity to M-CSF and caused activation of the myeloid master-regulator PU.1 in HSCs in vivo. Single-cell analysis revealed that reduced MafB levels enabled M-CSF to instruct divisions producing asymmetric daughter pairs with one PU.1(+) cell. As a consequence, MafB(-/-) HSCs showed a PU.1 and M-CSF receptor-dependent competitive repopulation advantage specifically in the myelomonocytic, but not T lymphoid or erythroid, compartment. Lineage-biased repopulation advantage was progressive, maintained long term, and serially transplantable. Together, this indicates that an integrated transcription factor/cytokine circuit can control the rate of specific HSC commitment divisions without compromising other lineages or self-renewal.

Both cell-surface and secreted CSF-1 expressed by tumor cells metastatic to bone can contribute to osteoclast activation

Tumors metastatic to the bone produce factors that cause massive bone resorption mediated by osteoclasts in the bone microenvironment. Colony stimulating factor (CSF-1) is strictly required for the formation and survival of active osteoclasts, and is frequently produced by tumor cells. Here we hypothesize that the CSF-1 made by tumor cells contributes to bone destruction in osteolytic bone metastases. We show that high level CSF-1 protected osteoclasts from suppressive effects of transforming growth factor beta (TGF-beta). r3T cells, a mouse mammary tumor cell line that forms osteolytic bone metastases, express abundant CSF-1 in vitro as both a secreted and a membrane-spanning cell-surface glycoprotein, and we show that both the secreted and the cell-surface form of CSF-1 made by r3T cells can support osteoclast formation in co-culture experiments in the presence of RankL. Mice with r3T bone metastases have elevated levels of both circulating and bone-associated CSF-1, and the majority of CSF-1 found in bone metastases is associated with the tumor cells. These results support the idea that tumor-cell produced CSF-1 contributes to osteoclast development and survival in bone metastasis.

CSF-1 signals directly to renal tubular epithelial cells to mediate repair in mice

Tubular damage following ischemic renal injury is often reversible, and tubular epithelial cell (TEC) proliferation is a hallmark of tubular repair. Macrophages have been implicated in tissue repair, and CSF-1, the principal macrophage growth factor, is expressed by TECs. We therefore tested the hypothesis that CSF-1 is central to tubular repair using an acute renal injury and repair model, ischemia/reperfusion (I/R). Mice injected with CSF-1 following I/R exhibited hastened healing, as evidenced by decreased tubular pathology, reduced fibrosis, and improved renal function. Notably, CSF-1 treatment increased TEC proliferation and reduced TEC apoptosis. Moreover, administration of a CSF-1 receptor-specific (CSF-1R-specific) antibody after I/R increased tubular pathology and fibrosis, suppressed TEC proliferation, and heightened TEC apoptosis. To determine the contribution of macrophages to CSF-1-dependent renal repair, we assessed the effect of CSF-1 on I/R in mice in which CD11b+ cells were genetically ablated and determined that macrophages only partially accounted for CSF-1-dependent tubular repair. We found that TECs expressed the CSF-1R and that this receptor was upregulated and coexpressed with CSF-1 in TECs following renal injury in mice and humans. Furthermore, signaling via the CSF-1R stimulated proliferation and reduced apoptosis in human and mouse TECs. Taken together, these data suggest that CSF-1 mediates renal repair by both a macrophage-dependent mechanism and direct autocrine/paracrine action on TECs.

Colony stimulating factor-1 dependence of paneth cell development in the mouse small intestine

BACKGROUND & AIMS

Paneth cells (PCs) secrete defensins and antimicrobial enzymes that contribute to innate immunity against pathogen infections within the mucosa of the small intestine. We examined the role of colony stimulating factor-1 (CSF-1) in PC development.

METHODS

CSF-1-deficient and CSF-1 receptor (CSF-1R)-deficient mice and administration of neutralizing anti-CSF-1R antibody were used to study the requirement of CSF-1 for the development of epithelial cells of the small intestine. CSF-1 transgenic reporter mice and mice that express only the membrane-spanning, cell-surface CSF-1 isoform were used to investigate regulation by systemic versus local CSF-1.

RESULTS

Mice deficient in CSF-1 or CSF-1R had greatly reduced numbers of mature PCs. PCs express the CSF-1R, and administration of anti-CSF-1R antibody to neonatal mice significantly reduced the number of PCs. Analysis of transgenic CSF-1 reporter mice showed that CSF-1-expressing cells are in close proximity to PCs. CSF-1/CSF-1R-deficient mice also had reduced numbers of the proliferating epithelial cell progenitors and lamina propria macrophages. Expression of the membrane-spanning, cell-surface CSF-1 isoform in CSF-1-deficient mice completely rescued the deficiencies of PCs, proliferating progenitors, and lamina propria macrophages.

CONCLUSIONS

These results indicate local regulation by CSF-1 of PC development, either directly, in a juxtacrine/paracrine manner, or indirectly, by lamina propria macrophages. Therefore, CSF-1R hyperstimulation could be involved in hyperproliferative disorders of the small intestine, such as Crohn's disease and ulcerative colitis.

Increased connective tissue extracellular matrix in the op/op model of osteopetrosis

Mice that are homozygous for the recessive osteopetrosis spontaneous mutation (op/op) develop severe osteopetrosis due to a defect in the production of macrophage colony-stimulating factor (M-CSF) and a deficiency in monocyte-derived osteoclasts. Our study describes a novel soft tissue finding in an osteopetrosis (B6C3Fe a/a-Csf1(op)/J) mouse model. Tissues were obtained from B6C3Fe a/a-Csf1(op)/J mice and age-matched wild-type mice, processed for hematoxylin and eosin sections, and comprehensive light microscopic tissue evaluation was performed. Mutant mice had characteristic traits of op/op deficiency including missing incisors and domed skulls. Histologically, the bone marrow cavity was effaced by interweaving thick bony trabeculae consistent with osteopetrosis. An increase in a finely granular, basophilic interstitial extracellular matrix (ECM) was observed in the subcutaneous connective tissue of the op/op mice when compared with controls. Histochemically, the ECM was negative with periodic acid Schiff and stained dark blue with alcian blue at a pH of 2.5, indicating that it is composed primarily of nonsulfated glycosaminoglycans (GAGs). This work suggests an increased ECM that is composed mainly of GAGs located in the subcutaneous tissue in op/op mice. This increase in ECM may be related to altered matrix production or turnover because of changes in M-CSF production.

Colony stimulating factor 1 is an extrinsic stimulator of mouse spermatogonial stem cell self-renewal

Self-renewal and differentiation of spermatogonial stem cells (SSCs) provide the foundation for testis homeostasis, yet mechanisms that control their functions in mammals are poorly defined. We used microarray transcript profiling to identify specific genes whose expressions are augmented in the SSC-enriched Thy1(+) germ cell fraction of mouse pup testes. Comparisons of gene expression in the Thy1(+) germ cell fraction with the Thy1-depleted testis cell population identified 202 genes that are expressed 10-fold or higher in Thy1(+) cells. This database provided a mining tool to investigate specific characteristics of SSCs and identify novel mechanisms that potentially influence their functions. These analyses revealed that colony stimulating factor 1 receptor (Csf1r) gene expression is enriched in Thy1(+) germ cells. Addition of recombinant colony stimulating factor 1 (Csf1), the specific ligand for Csf1r, to culture media significantly enhanced the self-renewal of SSCs in heterogeneous Thy1(+) spermatogonial cultures over a 63-day period without affecting total germ cell expansion. In vivo, expression of Csf1 in both pre-pubertal and adult testes was localized to clusters of Leydig cells and select peritubular myoid cells. Collectively, these results identify Csf1 as an extrinsic stimulator of SSC self-renewal and implicate Leydig and myoid cells as contributors of the testicular stem cell niche in mammals.

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.

Targeted overexpression of the two colony-stimulating factor-1 isoforms in osteoblasts differentially affects bone loss in ovariectomized mice

Colony-stimulating factor-1 (CSF1) is one of two cytokines required for normal osteoclastogenesis. There are two major isoforms of CSF1, the cell-surface or membrane-bound isoform (mCSF1) and soluble CSF1 (sCSF1). Whether these isoforms serve nonredundant functions in bone is unclear. To explore this question, we generated transgenic mice expressing human sCSF1, human mCSF1, or both (s/mCSF1) in osteoblasts using the 2.3-kb rat alphaI-collagen promoter. Bone density determined by peripheral quantitative computed tomography was significantly reduced in mCSF1, sCSF1, and s/mCSF1 transgenic mice compared with wild-type animals. When analyzed by sex, sCSF1, and s/mCSF1, female animals but not mCSF1 female mice were found to have greater bone loss than their male littermates (-20 vs. -9.2%; P<0.05 for sCSF1 and -21.6 vs. -11.2% for s/mCSF1; P<0.01). By breeding CSF1 isoform-selective transgenic mice to an op/op background, mice were generated in which a single CSF1 isoform was the only source of the cytokine (sCSF1op/op and mCSF1op/op). Unlike osteoblast-targeted overexpression of mCSF1, selective transgenic expression of sCSF1 did not completely correct the op/op phenotype in 5-mo-old animals. Interestingly, compared with sham-ovariectomized mice of the same genotype, ovariectomy in sCSF1op/op mice led to a greater loss of spinal bone mineral density (22.1%) than was seen in either mCSF1op/op mice (12.9%) or in wild-type animals (10.9%). Our findings support the conclusion that sCSF1 and mCSF1 serve nonredundant functions in bone and that sCSF1 may play a role in mediating estrogen-deficiency bone loss.

Blood monocytes: development, heterogeneity, and relationship with dendritic cells

Monocytes are circulating blood leukocytes that play important roles in the inflammatory response, which is essential for the innate response to pathogens. But inflammation and monocytes are also involved in the pathogenesis of inflammatory diseases, including atherosclerosis. In adult mice, monocytes originate in the bone marrow in a Csf-1R (MCSF-R, CD115)-dependent manner from a hematopoietic precursor common for monocytes and several subsets of macrophages and dendritic cells (DCs). Monocyte heterogeneity has long been recognized, but in recent years investigators have identified three functional subsets of human monocytes and two subsets of mouse monocytes that exert specific roles in homeostasis and inflammation in vivo, reminiscent of those of the previously described classically and alternatively activated macrophages. Functional characterization of monocytes is in progress in humans and rodents and will provide a better understanding of the pathophysiology of inflammation.

Survival of monocytes and macrophages and their role in health and disease

Macrophages are versatile cells involved in health and disease. These cells act as scavengers to rid the body of apoptotic and senescent cells and debris through their phagocytic function. Although this is a primary function of these cells, macrophages play vital roles in inflammation and repair of damaged tissue. Macrophages secrete a large number of cytokines, chemokines and growth factors that recruit and activate a variety of cell types to inflamed tissue compartments. These cells are also critical in cell-mediated immunity and in the resolution of inflammation. Since macrophages, and their precursors, blood monocytes, are important in regulating and resolving inflammation, prolonged cellular survival in tissue compartments could be detrimental. Thus, factors that regulate the fate of monocyte and macrophage survival are important in cellular homeostasis. In this article, we will explore stimuli and the intracellular pathways important in regulating macrophage survival and implication in human disease.

Sunlight triggers cutaneous lupus through a CSF-1-dependent mechanism in MRL-Fas(lpr) mice

Sunlight (UVB) triggers cutaneous lupus erythematosus (CLE) and systemic lupus through an unknown mechanism. We tested the hypothesis that UVB triggers CLE through a CSF-1-dependent, macrophage (Mø)-mediated mechanism in MRL-Fas(lpr) mice. By constructing mutant MRL-Fas(lpr) strains expressing varying levels of CSF-1 (high, intermediate, none), and use of an ex vivo gene transfer to deliver CSF-1 intradermally, we determined that CSF-1 induces CLE in lupus-susceptible MRL-Fas(lpr) mice, but not in lupus-resistant BALB/c mice. UVB incites an increase in Møs, apoptosis in the skin, and CLE in MRL-Fas(lpr), but not in CSF-1-deficient MRL-Fas(lpr) mice. Furthermore, UVB did not induce CLE in BALB/c mice. Probing further, UVB stimulates CSF-1 expression by keratinocytes leading to recruitment and activation of Møs that, in turn, release mediators, which induce apoptosis in keratinocytes. Thus, sunlight triggers a CSF-1-dependent, Mø-mediated destructive inflammation in the skin leading to CLE in lupus-susceptible MRL-Fas(lpr) but not lupus-resistant BALB/c mice. Taken together, CSF-1 is envisioned as the match and lupus susceptibility as the tinder leading to CLE.

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.