Biology and action of colony--stimulating factor-1

Human monocytes differentiate into macrophages under the influence of human KPB-M15 conditioned medium

Culture medium conditioned by the L929 murine fibroblast cell line contains macrophage colony-stimulating factor (M-CSF), providing an alternative to recombinant M-CSF for in vitro generation of murine macrophages. No such alternative has been described for in vitro studies requiring human macrophages. We tested the differentiation of human blood monocytes into mature macrophages by culturing in media conditioned by the human KPB-M15 cell line, which produces M-CSF and interleukin 6 (IL-6). The phenotypes of macrophages cultured in KPB-M15 conditioned media and recombinant M-CSF were compared by examining viability, expression of cell surface markers, phagocytic/pinocytic activity, and cytokine/chemokine secretion in response to bacterial lipopolysaccharide (LPS). In conditioned medium, monocytes differentiated into a homogeneous population of large cells that exhibited higher expression of CD14 and the macrophage mannose receptor (CD206) than did M-CSF-cultured cells. Cells matured in KPB-M15 conditioned medium exhibited macrophage morphology, were phagocytic, and were activated in response to LPS. These data demonstrate that KPB-M15 conditioned medium can be used to differentiate human blood monocytes into macrophages in vitro.

SCL/Tal-1 is essential for hematopoietic commitment of the hemangioblast but not for its development

In this report, we have defined the stage at which Scl functions in the establishment of the hematopoietic system and provide evidence that its primary role is in the generation of the hematopoietic lineages from a progenitor called the blast colony-forming cell (BL-CFC), a cell considered to be the in vitro equivalent of the hemangioblast. Using an embryonic stem (ES) cell line in which lacZ cDNA has been targeted to the Scl locus, we show that most of the BL-CFCs are detected in the SCL/lacZ- population, indicating that this progenitor does not express Scl. In the blast colony assay, Scl-/- cells initiate colony growth but are unable to generate endothelial and hematopoietic progeny and thus form colonies consisting of vascular smooth muscle cells only. The capacity to give rise to blast colonies can be rescued by retroviral transduction of a wild-type Scl gene into Scl-/- FLK-1+ cells, suggesting that the BL-CFC is generated in this population. Finally, we show that Scl-/- endothelial cells display a growth deficiency in monolayer cultures that can be partially overcome by maintaining this population as 3-dimensional aggregates indicating that specific cellular interactions are required for maintenance of the Scl-/- endothelial lineage in vitro.

Molecular cloning and expression analysis of a macrophage-colony stimulating factor receptor-like gene from rainbow trout, Oncorhynchus mykiss

The M-CSF and its receptor (M-CSFR, CSF-1R or c-fms proto-oncogene) system were initially implicated as essential in mammals for normal monocyte development as well as for pregnancy. To allow a comparison with the M-CSF and M-CSFR system of an oviparous animal, we cloned a M-CSFR-like gene from rainbow trout (Oncorhynchus mykiss). The gene was cloned from a cDNA library of head kidney. It contained an open reading frame encoding 967 amino acids with a predicted size of 109 kDa. The putative amino acid sequence of rainbow trout M-CSFR showed 54% amino acid identity to fugu (Takifugu rubripes) M-CSFR, 52% to zebrafish (Danio rerio) M-CSFR and 40% to mouse (Mus musculus) and human (Homo sapiens) M-CSFR. The M-CSFR-like gene was constitutively expressed in head kidney, kidney, intestine, spleen and blood. The gene was detected especially in the ovary of immature female rainbow trout. These results suggest that a M-CSFR-like receptor may be involved in female reproductive tracts even in an oviparous animal like fish.

Diverse isoforms of colony-stimulating factor-1 have different effects on the development of stroma-dependent hematopoietic cells

Maintenance and differentiation of hematopoietic stem and progenitor cells are controlled by complex interactions with the stroma microenvironment. Stroma-cell interactions can be supported by locally expressed membrane-spanning cell-surface (cs) growth factors. CSF-1 is expressed by stroma as a soluble glycoprotein, as proteoglycan, or as a membrane-spanning cs glycoprotein. CSF-1 regulates the survival, proliferation, and differentiation of mononuclear phagocytes. Whereas the biological role of soluble CSF-1 is well characterized, the function of the membrane-spanning cell-surface CSF-1 (csCSF-1) remains unclear. To analyze the biological significance of csCSF-1 in vitro, we used an epithelial cell line to ectopically express the different CSF-1 isoforms. In co-cultures of CSF-1 transduced epithelial cells with primary, early hematopoietic progenitor cells we examined whether interaction between csCSF-1 and its receptor mediates cell proliferation, self-renewal, or differentiation. csCSF-1 induces long-lasting proliferation of stimulated cells and furthermore supports self-renewal. Ectopic secretion of soluble CSF-1 does not permit long-term growth of progenitor cells but induces differentiation of monocytes into macrophages. Previously, we showed that the soluble and cs isoforms of stroma-encoded SCF differently affect the development of hematopoietic cells. Cell-surface SCF (csSCF) promotes self-renewal of stimulated cells whereas soluble SCF causes clonal extinction. These results and those presented here for CSF-1 provide evidence for diverse functions of the isoforms of the ligands SCF and CSF-1 for two tyrosine kinase receptors of the subclass III both regulating hematopoiesis on stroma.

Evolutionary diversification of pigment pattern in Danio fishes: differential fms dependence and stripe loss in D. albolineatus

The developmental bases for species differences in adult phenotypes remain largely unknown. An emerging system for studying such variation is the adult pigment pattern expressed by Danio fishes. These patterns result from several classes of pigment cells including black melanophores and yellow xanthophores, which differentiate during metamorphosis from latent stem cells of presumptive neural crest origin. In the zebrafish D. rerio, alternating light and dark horizontal stripes develop, in part, owing to interactions between melanophores and cells of the xanthophore lineage that depend on the fms receptor tyrosine kinase; zebrafish fms mutants lack xanthophores and have disrupted melanophore stripes. By contrast, the closely related species D. albolineatus exhibits a uniform pattern of melanophores, and previous interspecific complementation tests identified fms as a potential contributor to this difference between species. Here, we survey additional species and demonstrate marked variation in the fms-dependence of hybrid pigment patterns, suggesting interspecific variation in the fms pathway or fms requirements during pigment pattern formation. We next examine the cellular bases for the evolutionary loss of stripes in D. albolineatus and test the simplest model to explain this transformation, a loss of fms activity in D. albolineatus relative to D. rerio. Within D. albolineatus, we demonstrate increased rates of melanophore death and decreased melanophore migration, different from wild-type D. rerio but similar to fms mutant D. rerio. Yet, we also find persistent fms expression in D. albolineatus and enhanced xanthophore development compared with wild-type D. rerio, and in stark contrast to fms mutant D. rerio. These findings exclude the simplest model in which stripe loss in D. albolineatus results from a loss of fms-dependent xanthophores and their interactions with melanophores. Rather, our results suggest an alternative model in which evolutionary changes in pigment cell interactions themselves have contributed to stripe loss, and we test this model by manipulating melanophore numbers in interspecific hybrids. Together, these data suggest evolutionary changes in the fms pathway or fms requirements, and identify changes in cellular interactions as a likely mechanism of evolutionary change in Danio pigment patterns.

Delayed graft function in kidney transplantation

Delayed graft function is a form of acute renal failure resulting in post-transplantation oliguria, increased allograft immunogenicity and risk of acute rejection episodes, and decreased long-term survival. Factors related to the donor and prerenal, renal, or postrenal transplant factors related to the recipient can contribute to this condition. From experimental studies, we have learnt that both ischaemia and reinstitution of blood flow in ischaemically damaged kidneys after hypothermic preservation activate a complex sequence of events that sustain renal injury and play a pivotal part in the development of delayed graft function. Elucidation of the pathophysiology of renal ischaemia and reperfusion injury has contributed to the development of strategies to decrease the rate of delayed graft function, focusing on donor management, organ procurement and preservation techniques, recipient fluid management, and pharmacological agents (vasodilators, antioxidants, anti-inflammatory agents). Several new drugs show promise in animal studies in preventing or ameliorating ischaemia-reperfusion injury and possibly delayed graft function, but definitive clinical trials are lacking. The goal of monotherapy for the prevention or treatment of is perhaps unattainable, and multidrug approaches or single drug targeting multiple signals will be the next step to reduce post-transplantation injury and delayed graft function.

Establishment and maintenance of human embryonic stem cell lines on human feeder cells derived from uterine endometrium under serum-free condition

Human embryonic stem (hES) cells are usually established and maintained on mouse embryonic fibroblast (MEFs) feeder layers. However, it is desirable to develop human feeder cells because animal feeder cells are associated with risks such as viral infection and/or pathogen transmission. In this study, we attempted to establish new hES cell lines using human uterine endometrial cells (hUECs) to prevent the risks associated with animal feeder cells and for their eventual application in cell-replacement therapy. Inner cell masses (ICMs) of cultured blastocysts were isolated by immunosurgery and then cultured on mitotically inactivated hUEC feeder layers. Cultured ICMs formed colonies by continuous proliferation and were allowed to proliferate continuously for 40, 50, and 55 passages. The established hES cell lines (Miz-hES-14, -15, and -9, respectively) exhibited typical hES cells characteristics, including continuous growth, expression of specific markers, normal karyotypes, and differentiation capacity. The hUEC feeders have the advantage that they can be used for many passages, whereas MEF feeder cells can only be used as feeder cells for a limited number of passages. The hUECs are available to establish and maintain hES cells, and the high expression of embryotrophic factors and extracellular matrices by hUECs may be important to the efficient growth of hES cells. Clinical applications require the establishment and expansion of hES cells under stable xeno-free culture systems.

A juxtamembrane tyrosine in the colony stimulating factor-1 receptor regulates ligand-induced Src association, receptor kinase function, and down-regulation

Recent literature implicates a regulatory function of the juxtamembrane domain (JMD) in receptor tyrosine kinases. Mutations in the JMD of c-Kit and Flt3 are associated with gastrointestinal stromal tumors and acute myeloid leukemias, respectively. Additionally, autophosphorylated Tyr559 in the JMD of the colony stimulating factor-1 (CSF-1) receptor (CSF-1R) binds to Src family kinases (SFKs). To investigate SFK function in CSF-1 signaling we established stable 32D myeloid cell lines expressing CSF-1Rs with mutated SFK binding sites (Tyr559-TFI). Whereas binding to I562S was not significantly perturbed, Y559F and Y559D exhibited markedly decreased CSF-1-dependent SFK association. All JMD mutants retained intrinsic kinase activity, but Y559F, and less so Y559D, showed dramatically reduced CSF-1-induced autophosphorylation. CSF-1-mediated wild-type (WT)-CSF-1R phosphorylation was not markedly affected by SFK inhibition, indicating that lack of SFK binding is not responsible for diminished Y559F phosphorylation. Unexpectedly, cells expressing Y559F were hyperproliferative in response to CSF-1. Hyperproliferation correlated with prolonged activation of Akt, ERK, and Stat5 in the Y559F mutant. Consistent with a defect in receptor negative regulation, c-Cbl tyrosine phosphorylation and CSF-1R/c-Cbl co-association were almost undetectable in the Y559F mutant. Furthermore, Y559F underwent reduced multiubiquitination and delayed receptor internalization and degradation. In conclusion, we propose that Tyr559 is a switch residue that functions in kinase regulation, signal transduction and, indirectly, receptor down-regulation. These findings may have implications for the oncogenic conversion of c-Kit and Flt3 with JMD mutations.

High dose M-CSF partially rescues the Dap12-/- osteoclast phenotype

Osteoclasts are macrophage derived cells and as such are subject to regulation by molecules impacting other members of the immune system. Dap12 is an adaptor protein expressed by NK cells and B and T lymphocytes. Dap12 also mediates maturation of myeloid cells and is expressed by osteoclasts which are dysfunctional in its absence. We find Dap12-/- osteoclast precursors fail to differentiate, in vitro, and the abnormality is partially rescued by high dose M-CSF. The relative paucity of osteoclast number, even in presence of high dose cytokine, is attended by dampened proliferation of precursor cells and their failure to normally migrate towards the osteoclast-recognized matrix protein, osteopontin. Furthermore, Dap12-/- osteoclasts generated in high dose M-CSF fail to normally organize their cytoskeleton. The incapacity of Dap12 null cells to undergo normal osteoclast differentiation is not due to blunted stimulation of major RANK ligand (RANKL) or M-CSF induced signaling pathways. On the other hand, when plated on osteopontin, Dap12-/- pre-osteoclasts do not activate the tyrosine kinase, Syk, which normally binds to the adaptor protein and transmits downstream signals. Attesting to the importance of the Dap12/Syk complex, Syk deficient macrophages do not undergo normal osteoclastogenesis. Furthermore, the same cells plated onto osteopontin, adhere poorly and fail to phosphorylate c-Src or Pyk2, two kinases central to organization of the osteoclast cytoskeleton.

The PDGF/VEGF Receptor Controls Blood Cell Survival in Drosophila

The Drosophila PDGF/VEGF receptor (PVR) has known functions in the guidance of cell migration. We now demonstrate that during embryonic hematopoiesis, PVR has a role in the control of antiapoptotic cell survival. In Pvr mutants, a large fraction of the embryonic hemocyte population undergoes apoptosis, and the remaining blood cells cannibalistically phagocytose their dying peers. Consequently, total hemocyte numbers drop dramatically during embryogenesis, and large aggregates of engorged macrophages carrying multiple apoptotic corpses form. Hemocyte-specific expression of the pan-caspase inhibitor p35 in Pvr mutants eliminates hemocyte aggregates and restores blood cell counts and morphology. Additional rescue experiments suggest involvement of the Ras pathway in PVR-mediated blood cell survival. In cell culture, we demonstrate that PVR directly controls survival of a hemocyte cell line. This function of PVR shows striking conservation with mammalian hematopoiesis and establishes Drosophila as a model to study hematopoietic cell survival in development and disease.

Development of a quantitative, high-throughput cell-based enzyme-linked immunosorbent assay for detection of colony-stimulating factor-1 receptor tyrosine kinase inhibitors

Inhibitors of receptor tyrosine kinases are implicated as therapeutic agents for the treatment of many human diseases including cancer, inflammation and diabetes. Cell-based assays to examine inhibition of receptor tyrosine kinase mediated intracellular signaling are often laborious and not amenable to high-throughput cell-based screening of compound libraries. Here we describe the development of a nonradioactive, sandwich enzyme-linked immunosorbent assay (ELISA) to quantify the activation and inhibition of ligand-induced phosphorylation of the colony-stimulating factor-1 receptor (CSF-1R) in 96-well microtiter plate format. The assay involves the capture of the Triton X-100 solubilized human CSF-1R, from HEK293E cells overexpressing histidine epitope-tagged CSF-1R (CSF-1R/HEK293E), with immobilized CSF-1R antibody and detection of phosphosphorylation of the activated receptor with a phosphotyrosine specific antibody. The assay exhibited a 5-fold increase in phosphorylated CSF-1R signal from CSF-1R/HEK293E cells treated with colony-stimulating factor (CSF-1) relative to treated vector control cells. Additionally, using a histidine epitope-specific capture antibody, this method can also be adapted to quantify the phosphorylation state of any recombinantly expressed, histidine-tagged receptor tyrosine kinase. This method is a substantial improvement in throughput and quantitation of CSF-1R phosphorylation over conventional immunoblotting techniques.

Overexpression of the Colony-Stimulating Factor (CSF-1) and/or Its Receptor c-fms in Mammary Glands of Transgenic Mice Results in Hyperplasia and Tumor Formation

A number of recent studies have suggested that the colony-stimulating factor (CSF-1) and its receptor c-fms may be involved in the development of mammary glands during lactation and breast cancer. To study the role of CSF-1 or its receptor in initiation of mammary tumorigenesis, we have generated two independent lines of transgenic mice that overexpress either CSF-1 or c-fms under the control of the mouse mammary tumor virus promoter. Mammary glands of the virgin CSF-1 transgenic mice show increased ductal branching, hyperplasia, dysplasia, and other preneoplastic changes, which are indicative of increased cellular proliferation. Similar changes were also evident in the mammary glands of the c-fms transgenic mice. These changes became more prominent with age and resulted in mammary tumor formation. Moreover, secondary events like dimethylbenz(a)anthracene treatment accelerated mammary tumor formation in these mice. Although the expression of estrogen receptor alpha was not significantly changed in either of the transgenic mouse strains, progesterone receptor levels was higher in both transgenic lines as compared with the nontransgenic littermates. Expression of G1 cyclins was prominently increased in the mammary glands of both the CSF-1 and c-fms transgenic lines, suggesting increased cell cycle progression in these strains. In addition, the proliferation marker proliferating cell nuclear antigen (PCNA) and the mitogen-responsive transcription factor c-jun were also increased as compared with the nontransgenic controls. These findings, along with the histological data, support the hypothesis that CSF-1 and its receptor are involved in the etiology of breast cancer.

Serum levels of macrophage-colony stimulating factor (M-CSF): a marker of kidney allograft rejection

BACKGROUND

Macrophage-colony stimulating factor (M-CSF) is the principal factor for survival of monocytes and macrophages that play an important role in allograft rejection. We studied M-CSF serum levels during successful renal transplantation and acute graft rejection.

METHODS

A total of 114 kidney allograft recipients were assessed for M-CSF levels by enzyme-linked immunosorbent assay (ELISA).

RESULTS

M-CSF serum levels were elevated in pre-transplant haemodialysis patients (611+/-355 IU/ml vs 168+/-61 in normal controls, P<0.01). Following successful renal transplantation, M-CSF decreased in the first month, stabilizing at 257+/-222 IU/ml (not significantly different from normal controls) in 52 post-transplant stable patients. There was no correlation between M-CSF level and creatinine clearance. M-CSF levels increased significantly (2-5 times) during biopsy-proven acute rejection episodes in 20 of 25 patients. All rejection episodes were successfully treated and serum M-CSF decreased rapidly to pre-rejection levels in 17/20 patients. In contrast, in five patients with cyclosporin toxicity and four patients with other causes of allograft dysfunction, M-CSF serum levels did not change.

CONCLUSIONS

M-CSF serum level might be a specific marker of acute rejection. The source of increased production during rejection warrants further investigation, with infiltrating T cells and resident kidney cells being likely candidates.

Imbalanced gp130-dependent signaling in macrophages alters macrophage colony-stimulating factor responsiveness via regulation of c-fms expression

The mechanisms by which interleukin-6 (IL-6) family cytokines, which utilize the common receptor signaling subunit gp130, influence monocyte/macrophage development remain unclear. Here we have utilized macrophages devoid of either gp130-dependent STAT1/3 (gp130(Delta STAT/Delta STAT)) or extracellular signal-regulated kinases 1 and 2 (ERK1/2) mitogen-activated protein (MAP) kinase (gp130(Y757F/Y757F)) activation to assess the individual contribution of each pathway to macrophage formation. While the inhibition by IL-6 of macrophage colony-stimulating factor (M-CSF)-induced colony formation observed in gp130(wt/wt) mice was abolished in gp130(Delta STAT/Delta STAT) mice, inhibition of macrophage colony formation was enhanced in gp130(Y757F/Y757F) mice. In gp130(Delta STAT/Delta STAT) bone marrow-derived macrophages (BMMs), both IL-6- and M-CSF-induced ERK1/2 tyrosine phosphorylation was enhanced. By contrast, tyrosine phosphorylation of ERK1/2 in response to M-CSF was reduced in gp130(Y757F/Y757F) BMMs, and the pattern of ERK1/2 activation in gp130 mutant BMMs correlated with their opposing responsiveness to M-CSF-induced proliferation. When compared to the level of expression in gp130(wt/wt) BMMs, c-fms expression was elevated in gp130(Delta STAT/Delta STAT) BMMs but reduced in gp130(Y757F/Y757F) BMMs. Finally, an ERK1/2 inhibitor suppressed M-CSF-induced BMM proliferation, and this result corresponded to a reduction in c-fms expression. Collectively, these results provide a functional and causal correlation between gp130-dependent ERK MAP kinase signaling and c-fms gene activation, a finding that provides a potential mechanism underlying the inhibition of M-CSF-dependent macrophage development by IL-6 family cytokines in mice.

PE-1/METS, an antiproliferative Ets repressor factor, is induced by CREB-1/CREM-1 during macrophage differentiation

The molecular mechanisms involved in regulating the balance between cellular proliferation and differentiation remain poorly understood. Members of the Ets-domain family of transcription factors are candidates for proteins that might differentially regulate cell cycle control and cell type-specific genes during the differentiation of myeloid progenitor cells. The Ets repressor PE-1/METS has been suggested to contribute to growth arrest during terminal macrophage differentiation by repressing Ets target genes involved in Ras-dependent proliferation. An important feature of this regulatory model is that PE-1/METS is itself induced by the program of macrophage differentiation elicited by M-CSF. Here, we present evidence that the PE-1/METS gene is a transcriptional target of the cyclic AMP response element-binding protein-1 (CREB-1). CREB-1 expression is dramatically up-regulated during macrophage differentiation and phosphorylation of CREB-1 and the related factor CREM-1 are stimulated by M-CSF in a SAPK2/p38-dependent manner. Chromatin immunoprecipitation experiments demonstrate that CREB-1/CREM-1 are recruited to the PE-1/METS promoter as well as to the promoters of other genes that are up-regulated during terminal macrophage differentiation. Overexpression of CREB-1 stimulates the activities of the PE-1/METS, and macrosialin promoters, while expression of a dominant negative form of CREB-1 during macrophage differentiation inhibits expression of the PE-1/METS and macrosialin genes. Inhibition of CREB function also results in reduced expression of CD54 and impaired cell adhesion. Taken together, these findings reveal new roles of CREB-1/CREM-1 as regulators of macrophage differentiation.

Obesity is associated with macrophage accumulation in adipose tissue

Obesity alters adipose tissue metabolic and endocrine function and leads to an increased release of fatty acids, hormones, and proinflammatory molecules that contribute to obesity associated complications. To further characterize the changes that occur in adipose tissue with increasing adiposity, we profiled transcript expression in perigonadal adipose tissue from groups of mice in which adiposity varied due to sex, diet, and the obesity-related mutations agouti (Ay) and obese (Lepob). We found that the expression of 1,304 transcripts correlated significantly with body mass. Of the 100 most significantly correlated genes, 30% encoded proteins that are characteristic of macrophages and are positively correlated with body mass. Immunohistochemical analysis of perigonadal, perirenal, mesenteric, and subcutaneous adipose tissue revealed that the percentage of cells expressing the macrophage marker F4/80 (F4/80+) was significantly and positively correlated with both adipocyte size and body mass. Similar relationships were found in human subcutaneous adipose tissue stained for the macrophage antigen CD68. Bone marrow transplant studies and quantitation of macrophage number in adipose tissue from macrophage-deficient (Csf1op/op) mice suggest that these F4/80+ cells are CSF-1 dependent, bone marrow-derived adipose tissue macrophages. Expression analysis of macrophage and nonmacrophage cell populations isolated from adipose tissue demonstrates that adipose tissue macrophages are responsible for almost all adipose tissue TNF-alpha expression and significant amounts of iNOS and IL-6 expression. Adipose tissue macrophage numbers increase in obesity and participate in inflammatory pathways that are activated in adipose tissues of obese individuals.

Differential voltage-dependent K+ channel responses during proliferation and activation in macrophages

Voltage-dependent K+ channels (VDPC) are expressed in most mammalian cells and involved in the proliferation and activation of lymphocytes. However, the role of VDPC in macrophage responses is not well established. This study was undertaken to characterize VDPC in macrophages and determine their physiological role during proliferation and activation. Macrophages proliferate until an endotoxic shock halts cell growth and they become activated. By inducing a schedule that is similar to the physiological pattern, we have identified the VDPC in non-transformed bone marrow-derived macrophages and studied their regulation. Patch clamp studies demonstrated that cells expressed outward delayed and inwardly rectifying K+ currents. Pharmacological data, mRNA, and protein analysis suggest that these currents were mainly mediated by Kv1.3 and Kir2.1 channels. Macrophage colony-stimulating factor-dependent proliferation induced both channels. Lipopolysaccharide (LPS)-induced activation differentially regulated VDPC expression. While Kv1.3 was further induced, Kir2.1 was down-regulated. TNF-alpha mimicked LPS effects, and studies with TNF-alpha receptor I/II double knockout mice demonstrated that LPS regulation mediates such expression by TNF-alpha-dependent and -independent mechanisms. This modulation was dependent on mRNA and protein synthesis. In addition, bone marrow-derived macrophages expressed Kv1.5 mRNA with no apparent regulation. VDPC activities seem to play a critical role during proliferation and activation because not only cell growth, but also inducible nitric-oxide synthase expression were inhibited by blocking their activities. Taken together, our results demonstrate that the differential regulation of VDPC is crucial in intracellular signals determining the specific macrophage response.

Proteomic approaches to the analysis of early events in colony-stimulating factor-1 signal transduction

The exposure of cells to growth factors leads to the rapid tyrosine phosphorylation of proteins that play critical roles in initiating cellular responses. These proteins are associated with other nontyrosine-phosphorylated proteins. Together, they represent less than 0.02% of the total cellular protein. To study their functions in growth factor signaling it is necessary to establish their identity, post-translational modifications, and interactions. We have focused on the characterization of this group of proteins during the early response of macrophages to the macrophage growth factor, colony-stimulating factor-1 (CSF-1). We review here the development of approaches to analysis of the rapid CSF-1-induced changes in the CSF-1 receptor tyrosine kinase and phosphotyrosyl signaling complexes. Recent advances in mass spectrometry technology are greatly facilitating the characterization of such complexes. These methods strongly support and enhance genetic approaches that are being used to analyze the function of individual signaling components and pathways.

Analysis of the mouse CSF-1 gene promoter in a transgenic mouse model

CSF-1 stimulates monocyte and osteoclast populations. However, the molecular mechanisms involved in regulating CSF-1 gene expression are unclear. To identify regulatory regions that control normal CSF-1 gene expression, a -774/+183-bp fragment of the murine CSF-1 promoter was analyzed in vitro and in vivo. Transcriptional activity was high in cultured osteoblasts that express CSF-1 mRNA compared to ARH-77 B cells that lack CSF-1 gene expression. Transient transfection of osteoblasts with promoter deletion constructs showed that the -774-bp fragment conferred the highest transcriptional activity and contained activator and repressor sequences. To assess the ability of the CSF-1 promoter to confer normal tissue expression of CSF-1, transgenic mice containing the -774/+183-bp region driving the E. coli beta-galactosidase (lacZ) reporter gene were generated. beta-Gal analysis of whole tissue extracts showed transgene expression in all tissues tested except liver and kidney. At the cellular level, the pattern of beta-gal expression in the spleen, thymus, bone, lung, and testes of adult transgenic mice mimicked normal endogenous CSF-1 mRNA expression in non-transgenic littermates detected by in situ hybridization. This region also directed appropriate transgene expression to sites in other tissues known to synthesize CSF-1, with the exception of the liver and kidney. These findings indicate that the -774-bp fragment contains cis-acting elements sufficient to direct CSF-1 gene expression in many tissues. CSF-1 promoter/lacZ mice may be useful for studying the transcriptional mechanisms involved in regulating CSF-1 gene expression in tissues throughout development.

Nondisposable materials, chronic inflammation, and adjuvant action

Why inflammatory responses become chronic and how adjuvants work remain unanswered. Macrophage-lineage cells are key components of chronic inflammatory reactions and in the actions of immunologic adjuvants. One explanation for the increased numbers of macrophages long term at sites of chronic inflammation could be enhanced cell survival or even local proliferation. The evidence supporting a unifying hypothesis for one way in which this macrophage survival and proliferation may be promoted is presented. Many materials, often particulate, of which macrophages have difficulty disposing, can promote monocyte/macrophage survival and even proliferation. Materials active in this regard and which can initiate chronic inflammatory reactions include oxidized low-density lipoprotein, inflammatory microcrystals (calcium phosphate, monosodium urate, talc, calcium pyrophosphate), amyloidogenic peptides (amyloid beta and prion protein), and joint implant biomaterials. Additional, similar materials, which have been shown to have adjuvant activity (alum, oil-in-water emulsions, heat-killed bacteria, CpG oligonucleotides, methylated bovine serum albumin, silica), induce similar responses. Cell proliferation can be striking, following uptake of some of the materials, when macrophage-colony stimulating factor is included at low concentrations, which normally promote mainly survival. It is proposed that if such responses were occurring in vivo, there would be a shift in the normal balance between cell survival and cell death, which maintains steady-state, macrophage-lineage numbers in tissues. Thus, there would be more cells in an inflammatory lesion or at a site of adjuvant action with the potential, following activation and/or differentiation, to perpetuate inflammatory or antigen-specific, immune responses, respectively.

Cyclin D1 governs adhesion and motility of macrophages

The cyclin D1 gene encodes the regulatory subunit of a holoenzyme that phosphorylates and inactivates the retinoblastoma protein, thereby promoting cell-cycle progression. Cyclin D1 is overexpressed in hematopoetic and epithelial malignancies correlating with poor prognosis and metastasis in several cancer types. Because tumor-associated macrophages have been shown to enhance malignant progression and metastasis, and cyclin D1-deficient mice are resistant to oncogene-induced malignancies, we investigated the function of cyclin D1-/- bone marrow-derived macrophages. Cyclin D1 deficiency increased focal complex formation at the site of substratum contact, and enhanced macrophage adhesion, yielding a flattened, circular morphology with reduced membrane ruffles. Migration in response to wounding, cytokine-mediated chemotaxis, and transendothelial cell migration of cyclin D1-/- bone marrow-derived macrophages were all substantially reduced. Thus, apart from proliferative and possible motility defects in the tumor cells themselves, the reduced motility and invasiveness of cyclin D1-/- tumor-associated macrophages may contribute to the tumor resistance of these mice.

A macrophage colony-stimulating factor receptor-green fluorescent protein transgene is expressed throughout the mononuclear phagocyte system of the mouse

The c-fms gene encodes the receptor for macrophage colony-stimulating factor (CSF-1). The gene is expressed selectively in the macrophage and trophoblast cell lineages. Previous studies have indicated that sequences in intron 2 control transcript elongation in tissue-specific and regulated expression of c-fms. In humans, an alternative promoter was implicated in expression of the gene in trophoblasts. We show that in mice, c-fms transcripts in trophoblasts initiate from multiple points within the 2-kilobase (kb) region flanking the first coding exon. A reporter gene construct containing 3.5 kb of 5' flanking sequence and the downstream intron 2 directed expression of enhanced green fluorescent protein (EGFP) to both trophoblasts and macrophages. EGFP was detected in trophoblasts from the earliest stage of implantation examined at embryonic day 7.5. During embryonic development, EGFP highlighted the large numbers of c-fms-positive macrophages, including those that originate from the yolk sac. In adult mice, EGFP location was consistent with known F4/80-positive macrophage populations, including Langerhans cells of the skin, and permitted convenient sorting of isolated tissue macrophages from disaggregated tissue. Expression of EGFP in transgenic mice was dependent on intron 2 as no lines with detectable EGFP expression were obtained where either all of intron 2 or a conserved enhancer element FIRE (the Fms intronic regulatory element) was removed. We have therefore defined the elements required to generate myeloid- and trophoblast-specific transgenes as well as a model system for the study of mononuclear phagocyte development and function.

Theiler's virus infection of primary cultures of bone marrow-derived monocytes/macrophages

Theiler's virus, a murine picornavirus, causes a persistent infection of macrophage/microglial cells in the central nervous systems of SJL/J mice. Viral replication is restricted in the majority of infected cells, whereas a minority of them contain large amounts of viral RNA and antigens. For the present work, we infected primary cultures of bone marrow monocytes/macrophages from SJL/J mice with Theiler's virus. During the first 10 h postinfection (p.i.), infected monocytes/macrophages were round and covered with filopodia and contained large amounts of viral antigens throughout their cytoplasm. Later on, they were large, flat, and devoid of filopodia and they contained only small amounts of viral antigens distributed in discrete inclusions. These two types of infected cells were very reminiscent of the two types of infected macrophages found in the spinal cords of SJL/J mice. At the peak of virus production, the viral yield per cell was approximately 200 times lower than that for BHK-21 cells. Cell death occurred in the culture during the first 24 h p.i. but not thereafter. No infected cells could be detected after 4 days p.i., and the infection never spread to 100% of the cells. This restriction was unchanged by treating the medium at pH 2 but was abolished by treating it with a neutralizing alpha/beta interferon antiserum, indicating a role for this cytokine in limiting virus expression in monocyte/macrophage cultures. The role of alpha/beta interferon was confirmed by the observation that monocytes/macrophages from IFNA/BR(-/-) mice were fully permissive.

Macrophage-colony-stimulating factor-induced activation of extracellular-regulated kinase involves phosphatidylinositol 3-kinase and reactive oxygen species in human monocytes

We previously reported that activation of the phosphatidylinositol (PI) 3-kinase pathway was important in M-CSF-induced monocyte survival. Because M-CSF also induces activation of the mitogen-activated protein (MAP) kinase extracellular-regulated kinase (Erk), we focused on dissecting the mechanism used by M-CSF to induce Erk activation in human monocytes. We found that, in addition to the MAP/Erk kinase inhibitor PD098059, the PI 3-kinase inhibitors LY294002 and wortmannin both suppressed Erk activation in M-CSF-treated monocytes, suggesting that 3-phosphorylated products of PI 3-kinase played a role in Erk activation. Investigating the biochemical pathways regulated by PI 3-kinase to activate Erk, we found that, in response to M-CSF, normal human monocytes induced reactive oxygen species (ROS), which were suppressed by the PI 3-kinase inhibitor wortmannin but not by the solvent control DMSO or the MAP/Erk kinase inhibitor PD098059. We next found that, in the absence of M-CSF, ROS could induce Erk activation in human monocytes. Exogenous H(2)O(2) induced Erk activation in human monocytes, which was suppressed by exogenous catalase. To determine whether ROS induced by M-CSF played a role in Erk activation, we found that N-acetylcysteine and diphenyleneiodonium both suppressed Erk activation in M-CSF-treated monocytes. Erk activation by M-CSF also seemed to play a role in cellular survival in monocytes. These data suggest that, in M-CSF-stimulated human monocytes, PI 3-kinase products and ROS production play a role in Erk activation and monocyte survival.

The osteopetrotic mutation toothless (tl) is a loss-of-function frameshift mutation in the rat Csf1 gene: Evidence of a crucial role for CSF-1 in osteoclastogenesis and endochondral ossification

The toothless (tl) mutation in the rat is a naturally occurring, autosomal recessive mutation resulting in a profound deficiency of bone-resorbing osteoclasts and peritoneal macrophages. The failure to resorb bone produces severe, unrelenting osteopetrosis, with a highly sclerotic skeleton, lack of marrow spaces, failure of tooth eruption, and other pathologies. Injections of CSF-1 improve some, but not all, of these. In this report we have used polymorphism mapping, sequencing, and expression studies to identify the genetic lesion in the tl rat. We found a 10-base insertion near the beginning of the open reading of the Csf1 gene that yields a truncated, nonfunctional protein and an early stop codon, thus rendering the tl rat CSF-1(null). All mutants were homozygous for the mutation and all carriers were heterozygous. No CSF-1 transcripts were identified in rat mRNA that would avoid the mutation via alternative splicing. The biology and actions of CSF-1 have been elucidated by many studies that use another naturally occurring mutation, the op mouse, in which a single base insertion also disrupts the reading frame. The op mouse has milder osteoclastopenia and osteopetrosis than the tl rat and recovers spontaneously over the first few months of life. Thus, the tl rat provides a second model in which the functions of CSF-1 can be studied. Understanding the similarities and differences in the phenotypes of these two models will be important to advancing our knowledge of the many actions of CSF-1.

Molecular and immunohistochemical characterization of the onset and resolution of human renal allograft ischemia-reperfusion injury

BACKGROUND Following allotransplantation, renal ischemia-reperfusion (I/R) injury initiates a series of events that provokes counter-adaptive immunity. Though T cells clearly mediate allospecific immunity, the manner in which reperfusion events augment their activation has not been established. In addition, comprehensive analysis of I/R injury in humans has been limited. METHODS To evaluate the earliest events occurring following allograft reperfusion and gain insight into those factors linking reperfusion to alloimmunity, we examined human renal allografts 30 to 60 minutes postreperfusion (n=10) and compared them with allografts with normal function that had resolved their I/R injury insult (>1 month posttransplant, n=6) and to normal kidneys (living donor kidneys before procurement, n=8). Biopsies were processed both for immunohistochemical analysis as well as for transcript analysis by real-time quantitative polymerase chain reaction (RT-PCR). RESULTS Reperfusion injury was characterized by increased levels of gene transcripts known to be involved in cellular adhesion, chemotaxis, apoptosis, and monocyte recruitment and activation. T-cell-associated transcripts were generally absent. However, recovered allografts exhibited increased levels of T-cell and costimulation-related gene transcripts despite normal allograft function. Consistent with these findings, the immediate postreperfusion state was characterized histologically by tubular injury and monocyte infiltration, while the stable posttransplant state was notable for T-cell infiltration. CONCLUSIONS These data suggest that monocytes and transcripts related to their recruitment dominate the immediate postreperfusion state. This gives way to a T-cell dominant milieu even in grafts selected for their stable function and absence of rejection. These data have implications for understanding the fundamental link between I/R injury and alloimmunity.

Hydrogen/deuterium exchange and mass spectrometric analysis of a protein containing multiple disulfide bonds: Solution structure of recombinant macrophage colony stimulating factor-beta (rhM-CSFbeta)

Studies with the homodimeric recombinant human macrophage colony-stimulating factor beta (rhM-CSFbeta), show for the first time that a large number (9) of disulfide linkages can be reduced after amide hydrogen/deuterium (H/D) exchange, and the protein digested and analyzed successfully for the isotopic composition by electrospray mass spectrometry. Analysis of amide H/D after exchange-in shows that in solution the conserved four-helix bundle of (rhM-CSFbeta) has fast and moderately fast exchangeable sections of amide hydrogens in the alphaA helix, and mostly slow exchanging sections of amide hydrogens in the alphaB, alphaC, and alphaD helices. Most of the amide hydrogens in the loop between the beta1 and beta4 sheets exhibited fast or moderately fast exchange, whereas in the amino acid 63-67 loop, located at the interface of the two subunits, the exchange was slow. Solvent accessibility as measured by H/D exchange showed a better correlation with the average depth of amide residues calculated from reported X-ray crystallographic data for rhM-CSFalpha than with the average B-factor. The rates of H/D exchange in rhM-CSFbeta appear to correlate well with the exposed surface calculated for each amino acid residue in the crystal structure except for the alphaD helix. Fast hydrogen isotope exchange throughout the segment amino acids 150-221 present in rhM-CSFbeta, but not rhM-CSFalpha, provides evidence that the carboxy-terminal region is unstructured. It is, therefore, proposed that the anomalous behavior of the alphaD helix is due to interaction of the carboxy-terminal tail with this helical segment.

M-CSF deficiency leads to reduced metallothioneins I and II expression and increased tissue damage in the brain stem after 6-aminonicotinamide treatment

6-Aminonicotinamide (6-AN) is a niacin antagonist, which leads to degeneration of gray-matter astrocytes followed by a vigorous inflammatory response. Macrophage colony stimulating factor (M-CSF) is important during inflammation, and in order to further clarify the roles for M-CSF in neurodegeneration and brain cell death, we have examined the effect of 6-AN on osteopetrotic mice with genetic M-CSF deficiency (op/op mice). The 6-AN-induced degeneration of gray-matter areas was comparable in control and op/op mice, but the numbers of reactive astrocytes, macrophages, and lymphocytes in the damaged areas were significantly decreased in op/op mice relative to controls. The levels of oxidative stress (as determined by using immunoreactivity for inducible nitric oxide synthase, nitrotyrosine, and malondialdehyde) and apoptotic cell death (as determined by using TUNEL and immunoreactivity for caspases and cytochrome c) were significantly increased in 6-AN-injected op/op mice relative to controls. From a number of antioxidant factors assayed, only metallothioneins I and II (MT-I+II) were decreased in op/op mice in comparison to controls. Thus, the present results indicate that M-CSF is an important growth factor for coping with 6-AN-induced central nervous system damage and suggest that MT-I+II are likely to have a significant role.

Increased expression of macrophage colony-stimulating factor after coronary artery balloon injury is inhibited by intracoronary brachytherapy

BACKGROUND

The mechanisms underlying the reduced neointimal proliferation (NP) by intracoronary brachytherapy (ICBT) are unknown. We hypothesized that ICBT inhibits NP by reducing expression of macrophage colony-stimulating factor (M-CSF).

METHODS AND RESULTS

Thirty coronary arteries from 10 pigs were divided into 3 groups of 10 each: control (C), balloon injury (BI), and BI followed by ICBT (16 Gy at 0.5-mm tissue depth with a (32)P balloon system). Pigs were killed at 24 hours (n=3) and at 7 (n=4) and 14 (n=3) days. Expression of M-CSF was assessed by Western blot, ELISA, and quantitative immunostaining. Persistently increased levels of M-CSF after BI (to 1.4+/-0.2 nmol/L [ELISA] and 29.4+/-4.9% of cross-sectional area stained [immunocytochemistry]; P< 0.001 versus control for both) were observed in the injured arteries. Treatment of BI arteries with ICBT reduced M-CSF expression compared with BI alone (to 0.7+/-0.1 nmol/L [ELISA] and 13.5+/-2.9% of cross-sectional area stained [immunocytochemistry]; P<0.001 versus BI and P=NS versus control for both) and remained similar to control M-CSF expression for the 14-day study period. Neointimal thickness increased after BI (to 4.8+/-2.9 mm(2); P<0.001 versus control), but this was reduced by ICBT (1.4+/-0.4 mm(2); P<0.001 versus BI).

CONCLUSIONS

In porcine coronary arteries, BI is associated with increased expression of M-CSF and NP, but neither occurs after ICBT. The beneficial effects of ICBT on NP involve inhibition of M-CSF expression.

Macrophage colony-stimulating factor expression and macrophage accumulation in renal allograft rejection

BACKGROUND

Studies of infiltrating cells from acutely rejecting renal allografts show that a high proportion of these cells are macrophages, and early macrophage infiltration is a poor prognostic sign for transplant survival. Macrophage colony-stimulating factor (M-CSF), produced by tubular and mesangial cells, has been associated with macrophage infiltration and proliferation in experimental and human kidney diseases. We investigated the expression of M-CSF in a model of acute rejection.

METHODS

Lewis rats underwent bilateral nephrectomies and received an orthotopic Dark Agouti allograft or Lewis isograft. Animals received cyclosporine (10 mg/kg/day) from day 0 to day 3 and were killed at days 4, 8, or 14 after transplantation. Macrophages (ED1+) and T cells (W3-13+) were identified by immunohistochemistry, and M-CSF expression was identified by Northern blotting and in situ hybridization.

RESULTS

Isografts had normal renal function without histological evidence of rejection. Allografts exhibited a moderate infiltrate at day 4 but progressed to severe rejection at day 14, with elevated serum creatinine level and severe tubulointerstitial damage. Macrophages and T cells were present in equal proportion in the infiltrate at day 4. At day 14, the number of macrophages increased fivefold (2580/mm2), although T cells were unchanged (380/mm2). Proliferating macrophages (ED1+, BrdU+) increased from day 4 (4%) to day 14 (10%). M-CSF mRNA expression was strongly up-regulated in allografts compared with isografts and normal rat. In situ hybridization demonstrated M-CSF expression by resident and infiltrating cells. Renal tubular expression was minimally increased at day 4 but strongly up-regulated at day 14 (more than 50% of tubules positive), particularly in areas of tubular damage. Tubular M-CSF expression colocalized with areas of intense macrophage infiltration and proliferation. Serial sections with double labeling demonstrated that T cells were the dominant source of M-CSF at day 4, yet later in the rejection (day 14) the predominant sites of production were both renal tubular cells and interstitial macrophages.

CONCLUSIONS

Renal production of M-CSF by graft-infiltrating (macrophages and T lymphocytes) and resident (tubular) cells was up-regulated during acute rejection. M-CSF promotes macrophage recruitment and proliferation and may thereby play a pathogenic role in acute rejection. The kinetics of M-CSF production during acute rejection suggest that local macrophage proliferation may be initiated by T cells and perpetuated by both renal tubular and autocrine release.

Regulation of colony stimulating factor-1 (CSF-1) in endometrial cells: glucocorticoids and oxidative stress regulate the expression of CSF-1 and its receptor c-fms in endometrial cells

OBJECTIVE

To evaluate the regulation and expression of CSF-1 and its receptor c-fms in endometrial cells.

DESIGN

In vitro study.

SETTING

Research and teaching institution.

PATIENT(S)

None.

INTERVENTION(S)

In vitro experimental study.

MAIN OUTCOME MEASURE(S)

The effect of glucocorticoid and oxidative stress on the expression of CSF-1 and c-fms in endometrial cells.

RESULT(S)

Cultured nonmalignant EM42 cells not only express CSF-1 and c-fms but are also capable of responding to exogenous CSF-1. We have also seen that glucocorticoids can regulate the expression of CSF-1/c-fms in endometrial cells. Furthermore, this study shows that oxidative stress plays a significant role in the induction of CSF-1 and its receptor c-fms.

CONCLUSION(S)

The results suggest that CSF-1 may promote the growth of nonmalignant endometrial cells in both an autocrine and paracrine manner and that endometrial cells under oxidative stress induce CSF-1 and c-fms.

Structural comparison of recombinant human macrophage colony stimulating factor beta and a partially reduced derivative using hydrogen deuterium exchange and electrospray ionization mass spectrometry

Hydrogen deuterium exchange, monitored by electrospray ionization mass spectrometry, has been employed to characterize structural features of a derivative of recombinant human macrophage colony stimulating factor beta (rhm-CSFbeta) in which two of the nine disulfide bridges (Cys157/Cys159-Cys'157/Cys'159) were selectively reduced and alkylated. Removal of these two disulfide bridges did not affect the biological activity of the protein. Similarities between CD and fluorescence spectra for rhm-CSFbeta and its derivative indicate that removing the disulfide bonds did not strongly alter the overall three-dimensional structure of rhm-CSFbeta. However, differences between deuterium exchange data of the intact proteins indicate that more NHs underwent fast deuterium exchange in the derivative than in rhm-CSFbeta. Regions located near the disulfide bond removal site were shown to exhibit faster deuterium exchange behavior in the derivative than in rhm-CSFbeta.

Alveolar macrophage deficiency in osteopetrotic mice deficient in macrophage colony-stimulating factor is spontaneously corrected with age and associated with matrix metalloproteinase expression and emphysema

Macrophage colony-stimulating factor (M-CSF) is one of several hematologic growth factors capable of regulating the survival, proliferation, and differentiation of macrophages, but its role in modulation of the accumulation and function of alveolar macrophages (AMs) in vivo is not well defined. Osteopetrotic (Op/Op) mice have no detectable M-CSF and show variable tissue-specific reductions in macrophage numbers. It was hypothesized that AMs would be decreased in number and have altered function in Op/Op mice because of the absence of M-CSF. Lung macrophages identified by Mac-3 staining in lung sections were decreased in number in 20-day-old Op/Op mice (P <.001) but not Op/Op mice older than 4 months (P =.68) compared with findings in age-matched littermate controls. The numbers of AMs recovered by bronchoalveolar lavage (BAL) were also reduced in young but not adult Op/Op mice compared with controls. Expression of interleukin-3 (IL-3) was increased in the lungs of Op/Op mice compared with controls as determined by quantification of IL-3 cytokine levels (P =.04), bioactivity (P =.02), and messenger RNA transcript levels. AMs of Op/Op mice spontaneously released higher levels of matrix metalloproteinases (MMPs) than AMs of controls as determined by immunohistochemical staining of AMs and zymographic assessment of BAL fluid and AM lysates. Consistent with an increased release of MMP, Op/Op mice had abnormal elastin deposition and spontaneously developed emphysema in the absence of molecular or cellular evidence of lung inflammation. These data show that the AM deficiency observed in young Op/Op mice is spontaneously corrected with age and is associated with increased lung levels of IL-3, spontaneous MMP expression by AMs, and destruction of lung tissue.

Cytokine upregulation in a murine model of familial amyotrophic lateral sclerosis

Although pronounced changes in astrocytes and microglia accompany the neuronal degeneration observed in a murine model of familial amyotrophic lateral sclerosis, the significance of non-neuronal cell contribution to the disease process remains unclear. Activated astrocytes and microglia are capable of secreting numerous cytokines, some of which may have potentially harmful effects on neuron survival. For this reason we wished to determine the expression pattern of various cytokines in the spinal cords of transgenic mice expressing a Cu-Zn superoxide dismutase mutation (Tgn G93A SOD1) by using semi-quantitative RT-PCR. Three different patterns of cytokine expression were observed in G93A SOD1 transgenic mice. For most cytokines, we were unable to detect mRNA expression in Tgn G93A SOD1 mouse spinal cords at any age, yet message was readily detected in spleen or activated splenocytes. A second pattern, typified by TNF-alpha, was characterized by mRNA expression prior to the onset of motor deficits and increasing until the terminal stages of the disease. For other cytokines, including TGF-beta1 and M-CSF, mRNA expression was detected in young presymptomatic Tgn G93A SOD1 mice (as well as wild-type and transgenic mice expressing wild-type SOD1 (Tgn SOD1)), with upregulation later occurring only in G93A SOD1 transgenic mice. These results indicate a temporal correlation between the expression of certain cytokines and the onset of motor dysfunction in Tgn G93A SOD1 mice and suggest a potential role for these molecules in the disease.

Tubules are the major site of M-CSF production in experimental kidney disease: correlation with local macrophage proliferation

BACKGROUND

Local proliferation of macrophages occurs within both the glomerulus and the interstitium in severe forms of human and experimental glomerulonephritis and plays an important role in amplifying renal injury. Macrophage colony-stimulating factor (M-CSF) is thought to be the growth factor driving this local macrophage proliferation. Previous studies have found that glomeruli are the predominant source of M-CSF production. However, this is difficult to reconcile with the prominent macrophage accumulation and proliferation seen in the interstitial compartment in glomerulonephritis. To address this issue, we localized M-CSF expression in rat models of glomerular versus tubulointerstitial injury and examined its relationship to local macrophage proliferation.

METHODS

M-CSF expression (Northern blotting, in situ hybridization, immunostaining, Western blotting) and local macrophage proliferation (double immunostaining) was examined in normal rat kidney on days 1 and 14 of rat anti-glomerular basement membrane (anti-GBM) glomerulonephritis and on day 5 following unilateral ureteric obstruction.

RESULTS

M-CSF mRNA and protein expression were identified in small numbers of glomerular podocytes, approximately 25% of cortical tubules, and most medullary tubules in normal rat kidney. Northern blotting showed a significant increase in whole kidney M-CSF mRNA in rat anti-GBM glomerulonephritis. Up-regulation of glomerular and, most prominently, tubular M-CSF production was confirmed by three independent methods: in situ hybridization, immunostaining, and Western blotting. The increase in M-CSF expression colocalized with local macrophage proliferation (ED1+PCNA+ cells) in both the glomerulus and tubulointerstitium. On day 5 after ureter ligation, there was a significant increase in tubular M-CSF mRNA and protein expression in the obstructed kidney, with no change in glomerular M-CSF. In parallel with M-CSF expression, macrophage accumulation and proliferation was prominent in the interstitium, but was absent from glomeruli.

CONCLUSIONS

The tubular epithelial cell is the major site of M-CSF production within the injured kidney. Indeed, substantial macrophage accumulation and local proliferation can occur in the tubulointerstitium in the absence of glomerular inflammation. These results suggest that M-CSF production within the kidney, particularly by tubular epithelial cells, plays an important role in regulating local macrophage proliferation in experimental kidney disease.

Local macrophage proliferation correlates with increased renal M-CSF expression in human glomerulonephritis

BACKGROUND

Macrophage accumulation is a prominent feature in many forms of glomerulonephritis. Local proliferation of macrophages within the kidney has been described in human and experimental glomerulonephritis and may have an important role in augmenting the inflammatory response. The current study examined the relationship between local macrophage proliferation and renal expression of macrophage colony-stimulating factor (M-CSF).

METHODS

A total of 118 renal biopsies of patients with a wide range of glomerulonephridities were examined for M-CSF protein and macrophage proliferation (KP1+PCNA+cells) by single and double immunohistochemistry staining, respectively.

RESULTS

Biopsies of thin membrane disease (TMD) with histologically normal kidney showed M-CSF protein expression by 33% of cortical tubules, while glomerular M-CSF expression was limited to resident macrophages and some podocytes. Glomerular M-CSF expression increased significantly in proliferative forms of glomerulonephritis, with M-CSF staining of infiltrating macrophages, podocytes and some mesangial cells. Segmental areas of strong M-CSF expression, particularly in crescents, co-localized with KP1+PCNA+ proliferating macrophages. There was also an increase in tubular M-CSF expression in most types of glomerulonephritis. Tubular M-CSF staining was strongest in areas of tubular damage and co-localized with KP1+ macrophages, including KP1+PCNA+ proliferating macrophages. Many interstitial macrophages and alpha-smooth muscle actin-positive myofibroblasts showed strong M-CSF staining. Statistical analysis showed a highly significant correlation between M-CSF expression and local macrophage proliferation in both the glomerulus and tubulointerstitium. Glomerular and tubular M-CSF expression gave a significant correlation with renal dysfunction.

CONCLUSIONS

Glomerular and tubulointerstitial M-CSF expression is up-regulated in human glomerulonephritis, being most prominent in proliferative forms of disease. This correlated with local macrophage proliferation, suggesting that increased renal M-CSF production plays an important role in regulating local macrophage proliferation in human glomerulonephritis.

Modulation of MHC class II transport and lysosome distribution by macrophage-colony stimulating factor in human dendritic cells derived from monocytes

The macrophage-colony stimulating factor (M-CSF) has been already shown to affect the function of dendritic cells (DC). Therefore, the differentiation of dendritic cells into macrophages (M(PHI)) might represent a pathway which could inhibit the immune response initiated by DC. Because Major Histocompatibility Complex class II molecules (MHC-II) are crucial for DC function, we asked whether M-CSF may influence the intracellular transport of MHC-II in monocyte derived DC. We found that, at early stages, M-CSF induced first a rapid redistribution of MHC-II from the MHC-II containing compartments (MIIC) to the plasma membrane and second an increase in MHC-II synthesis as observed with LPS or TNF-(alpha). These processes were associated with the sorting of MHC-II from lysosomal membranes which underwent a drastic structural reorganization. However, in contrast to tumor necrosis factor (TNF)-(alpha) or lipopolysaccharide (LPS), M-CSF neither potentiated the allostimulatory function of DC nor allowed the stabilization of MHC-II at the cell surface, but rather increased MHC-II turnover. We conclude that the rapid modulation of MHC-II transport and distribution may participate in the inhibitory effect of M-CSF on DC function and differentiation.

The role of macrophages in demyelinating peripheral nervous system of mice heterozygously deficient in p0

Mice heterozygously deficient in the p0 gene (P0(+/-)) are animal models for some forms of inherited neuropathies. They display a progressive demyelinating phenotype in motor nerves, accompanied by mild infiltration of lymphocytes and increase in macrophages. We have shown previously that the T lymphocytes are instrumental in the demyelination process. This study addresses the functional role of the macrophage in this monogenic myelin disorder. In motor nerves of P0(+/)- mice, the number of macrophages in demyelinated peripheral nerves was increased by a factor of five when compared with motor nerves of wild-type mice. Immunoelectron microscopy, using a specific marker for mouse macrophages, displayed macrophages not only in the endoneurium of the myelin mutants, but also within endoneurial tubes, suggesting an active role in demyelination. To elucidate the roles of the macrophages, we crossbred the myelin mutants with a spontaneous mouse mutant deficient in macrophage colony-stimulating factor (M-CSF), hence displaying impaired macrophage activation. In the P0-deficient double mutants also deficient in M-CSF, the numbers of macrophages were not elevated in the demyelinating motor nerves and demyelination was less severe. These findings demonstrate an active role of macrophages during pathogenesis of inherited demyelination with putative impact on future treatment strategies.

Resistance of bone marrow-derived macrophages to apoptosis is associated with the expression of X-linked inhibitor of apoptosis protein in primary cultures of bone marrow cells

In this study we investigated the underlying mechanisms that confer resistance on mature macrophages with the use of macrophage colony-stimulating factor (M-CSF)-induced bone marrow-derived macrophages (BMDM). In the presence of M-CSF, immature precursor cells were induced to undergo proliferation and differentiation into mature macrophages in vitro with cell morphology similar to that of tissue macrophages by day 7-10. Immunoblot analyses showed that bone marrow precursors express appreciable levels of caspase-3 and caspase-9 but no or very low levels of c-fms (M-CSF receptor) and the apoptosis regulators X-linked inhibitor of apoptosis protein (XIAP), c-IAP-1, Bcl-2 and Bax. The differentiation of BMDM is associated with a steady and gradual increase in the levels of c-fms, XIAP, c-IAP-1, Bcl-2 and Bax, reaching maximal levels by day 7. However, the levels of caspase-3 and caspase-9 stayed essentially unchanged even after prolonged incubation (more than 10 days) with M-CSF. Unlike bone marrow precursor cells, mature BMDM (day 7-10) were resistant to apoptosis induced by M-CSF depletion, which includes the activation of caspase-3 and caspase-9 and the degradation of XIAP, Bcl-2 and Bax proteins in the process. Treatment of day 7 BMDM with XIAP anti-sense oligonucleotides (oligos), but not sense oligos, partly abolished their resistance to apoptosis. By using a gel-shift assay and a specific nuclear factor kappaB (NF-kappaB) inhibitor, we demonstrated that NF-kappaB activity is responsible for the up-regulation of XIAP in M-CSF-treated macrophages. In addition, treatment of starved macrophages with M-CSF induced a rapid phosphorylation of Akt kinase before the activation of NF-kappaB. Our results showed that XIAP is one of the anti-apoptotic regulators that confer resistance on mature macrophages by M-CSF.

Inflammatory microcrystals induce murine macrophage survival and DNA synthesis

The interaction of particulates with resident macrophages is a consistent feature in certain forms of crystal-induced inflammation, for example, in synovial tissues, lung, and the peritoneum. The mitogenic activity of basic calcium phosphate (BCP) crystals and calcium pyrophosphate dihydrate (CPPD) crystals on synovial fibroblasts has been considered relevant to the synovial hyperplasia observed in crystal-induced arthritis. The aim of the study was to determine whether microcrystals such as these could enhance macrophage survival and induce DNA synthesis, thus indicating that they may contribute to the tissue hyperplasia. Murine bone-marrow-derived macrophages were treated in vitro with microcrystals, the cell numbers were monitored over time, and DNA synthesis was measured as the incorporation of [methyl-(3)H]thymidine (TdR). We report here that BCP, monosodium urate, talc, and, to a lesser extent, CPPD crystals promote macrophage survival and DNA synthesis; the latter response is particularly striking in the presence of low concentrations of macrophage-colony stimulating factor (M-CSF, CSF-1). Enhanced macrophage survival or proliferation may contribute to the synovial hyperplasia noted in crystal-associated arthropathies, as well as to talc-induced inflammation and granuloma formation. The crystals studied join the list of particulates having these effects on macrophages, indicating the generality of this type of response.

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.

Importance of membrane- or matrix-associated forms of M-CSF and RANKL/ODF in osteoclastogenesis supported by SaOS-4/3 cells expressing recombinant PTH/PTHrP receptors

SaOS-4/3, a subclone of the human osteosarcoma cell line SaOS-2, established by transfecting the human parathyroid hormone/parathyroid hormone-related protein (PTH/PTHrP) receptor complementary DNA (cDNA), supported osteoclast formation in response to PTH in coculture with mouse bone marrow cells. Osteoclast formation supported by SaOS-4/3 cells was completely inhibited by adding either osteoprotegerin (OPG) or antibodies against human macrophage colony-stimulating factor (M-CSF). Expression of messenger RNAs (mRNAs) for receptor activator of NF-kappaB ligand/osteoclast differentiation factor (RANKL/ODF) and both membrane-associated and secreted forms of M-CSF by SaOS-4/3 cells was up-regulated in response to PTH. SaOS-4/3 cells constitutively expressed OPG mRNA, expression of which was down-regulated by PTH. To elucidate the mechanism of PTH-induced osteoclastogenesis, SaOS-4/3 cells were spot-cultured for 2 h in the center of a culture well and then mouse bone marrow cells were uniformly plated over the well. When the spot coculture was treated for 6 days with both PTH and M-CSF, osteoclasts were induced exclusively inside the colony of SaOS-4/3 cells. Osteoclasts were formed both inside and outside the colony of SaOS-4/3 cells in coculture treated with a soluble form of RANKL/ODF (sRANKL/sODF) in the presence of M-CSF. When the spot coculture was treated with sRANKL/sODF, osteoclasts were formed only inside the colony of SaOS-4/3 cells. Adding M-CSF alone failed to support osteoclast formation in the spot coculture. PTH-induced osteoclast formation occurring inside the colony of SaOS-4/3 cells was not affected by the concentration of M-CSF in the culture medium. Mouse primary osteoblasts supported osteoclast formation in a similar fashion to SaOS-4/3 cells. These findings suggest that the up-regulation of RANKL/ODF expression is an essential step for PTH-induced osteoclastogenesis, and membrane- or matrix-associated forms of both M-CSF and RANKL/ ODF are essentially involved in osteoclast formation supported by osteoblasts/stromal cells.

Role of the membrane form of human colony-stimulating factor-1 (CSF-1) in proliferation of multipotent hematopoietic FDCP-mix cells expressing human CSF-1 receptor

Because IL-3-dependent multipotential FDCP-Mix cells expressing human colony-stimulating factor-1 (CSF-1) receptor did not proliferate in response to soluble CSF-1, we investigated whether their proliferation would be induced in co-culture with adherent cells expressing the membrane form of CSF-1 (MemCSF-1). FDCP-Mix cells with high CSF-1R expression (NAF21 cells) were placed on stromal MS-5 cells or STO fibroblasts expressing MemCSF-1 (2M-1 cells and STO-M2 cells, respectively), in absence of IL-3. NAF21 cells bound significantly to 2M-1 cells as compared to control FDCP-Mix cells. Adhesion of NAF21 cells was inhibited by anti-huCSF-1 antibodies, as well as anti-huCSF-1R antibodies. Interestingly, NAF21 cells proliferated on both 2M-1 and STO-M2 cells but with very different kinetics. Moreover, NAF21 cell proliferation was also supported by glutaraldehyde-fixed 2M-1 cells or highly concentrated MS-5 cell culture supernatant, but not by CSF-1 coated on culture dishes. These results strongly suggest that MemCSF-1/CSF-1R interaction mediates a specific adhesion of NAF21 cells to stromal cells and allows stimulation of hematopoietic cells by stromal cell-derived factors expressed in a membrane-bound form or concentrated within the extracellular matrix. Thus, cytokine receptors deficient in mitogenic signalling may nevertheless have a regulatory role in hematopoietic progenitor cell proliferation by acting as adhesion molecules.

Cellular cofactors potentiating induction of stress and cytotoxicity by amyloid beta-peptide

Insights into factors underlying causes of familial Alzheimer's disease (AD), such as mutant forms of beta-amyloid precursor protein and presenilins, and those conferring increased risk of sporadic AD, such as isoforms of apolipoprotein E and polymorphisms of alpha2-macroglobulin, have been rapidly emerging. However, mechanisms through which amyloid beta-peptide (Abeta), the fibrillogenic peptide most closely associated with neurotoxicity in AD, exerts its effects on cellular targets have only been more generally outlined. Late in the course of AD, when Abeta fibrils are abundant, non-specific interactions of amyloid with cellular elements are likely to induce broad cytotoxicity. However, early in AD, when concentrations of Abeta are much lower and extracellular deposits are infrequent, mechanisms underlying cellular dysfunction have not been clearly defined. The key issue in elucidating the means through which Abeta perturbs cellular properties early in AD is the possibility that protective therapy at such times may prevent cytotoxicity at a point when damage is still reversible. This brief review focusses on two cellular cofactors for Abeta-induced cellular perturbation: the cell surface immunoglobulin superfamily molecule RAGE (receptor for advanced glycation endproducts) and ABAD (Abeta binding alcohol dehydrogenase). Although final proof for the involvement of these cofactors in cellular dysfunction in AD must await the results of further in vivo experiments, their increased expression in AD brain, as well as other evidence described below, suggests the possibility of specific pathways for Abeta-induced cellular perturbation which could provide future therapeutic targets.

Macrophage colony-stimulating factor antagonists inhibit replication of HIV-1 in human macrophages

Macrophages infected with HIV-1 produce high levels of M-CSF and macrophage-inflammatory protein-1alpha (MIP-1alpha). M-CSF facilitates the growth and differentiation of macrophages, while the chemotactic properties of MIP-1alpha attract both T lymphocytes and macrophages to the site of HIV infection. Studies described in this work indicate M-CSF may function in an autocrine/paracrine manner to sustain HIV replication, and data suggest possible therapeutic strategies for decreasing viral load following HIV infection. We show that macrophage infection with measles virus or respiratory syncytial virus, in contrast to HIV-1, results in production of MIP-1alpha, but not M-CSF. Thus, M-CSF appears to be specifically produced upon infection of macrophages with HIV-1. Furthermore, addition of M-CSF antagonists to HIV-1-infected macrophages, including anti-M-CSF monoclonal or polyclonal Abs or soluble M-CSF receptors, dramatically inhibited HIV-1 replication and reduced production of MIP-1alpha. Our results suggest that biologic antagonists for M-CSF may represent novel strategies for inhibiting the spread of HIV-1 by 1) blocking virus replication in macrophages, 2) reducing recruitment of HIV-susceptible T cells and macrophages by MIP-1alpha, and 3) preventing the establishment and maintenance of infected macrophages as a reservoir for HIV.