The effects of interleukin 3 (IL-3) on cells responsive to macrophage colony-stimulating factor (CSF-1) in liquid murine bone marrow culture

Transcriptional mechanisms that control expression of the macrophage colony-stimulating factor receptor locus

The proliferation, differentiation, and survival of cells of the macrophage lineage depends upon signals from the macrophage colony-stimulating factor (CSF) receptor (CSF1R). CSF1R is expressed by embryonic macrophages and induced early in adult hematopoiesis, upon commitment of multipotent progenitors to the myeloid lineage. Transcriptional activation of CSF1R requires interaction between members of the E26 transformation-specific family of transcription factors (Ets) (notably PU.1), C/EBP, RUNX, AP-1/ATF, interferon regulatory factor (IRF), STAT, KLF, REL, FUS/TLS (fused in sarcoma/ranslocated in liposarcoma) families, and conserved regulatory elements within the mouse and human CSF1R locus. One element, the Fms-intronic regulatory element (FIRE), within intron 2, is conserved functionally across all the amniotes. Lineage commitment in multipotent progenitors also requires down-regulation of specific transcription factors such as MYB, FLI1, basic leucine zipper transcriptional factor ATF-like (BATF3), GATA-1, and PAX5 that contribute to differentiation of alternative lineages and repress CSF1R transcription. Many of these transcription factors regulate each other, interact at the protein level, and are themselves downstream targets of CSF1R signaling. Control of CSF1R transcription involves feed–forward and feedback signaling in which CSF1R is both a target and a participant; and dysregulation of CSF1R expression and/or function is associated with numerous pathological conditions. In this review, we describe the regulatory network behind CSF1R expression during differentiation and development of cells of the mononuclear phagocyte system.

IL-3 and CSF-1 interact to promote generation of CD11c+ IL-10-producing macrophages

Unraveling the mechanisms of hematopoiesis regulated by multiple cytokines remains a challenge in hematology. IL-3 is an allergic cytokine with the multilineage potential, while CSF-1 is produced in the steady state with restricted lineage coverage. Here, we uncovered an instructive role of CSF-1 in IL-3-mediated hematopoiesis. CSF-1 significantly promoted IL-3-driven CD11c⁺ cell expansion and dampened basophil and mast cell generation from C57BL/6 bone marrow. Further studies indicated that the CSF-1/CSF-1R axis contributed significantly to IL-3-induced CD11c⁺ cell generation through enhancing c-Fos-associated monopoiesis. CD11c⁺ cells induced by IL-3 or IL-3/CSF-1 were competent in cellular maturation and endocytosis. Both IL-3 and IL-3/CSF-1 cells lacked classical dendritic cell appearance and resembled macrophages in morphology. Both populations produced a high level of IL-10, in addition to IL-1, IL-6 and TNFα, in response to LPS, and were relatively poor T cell stimulators. Collectively, these findings reveal a role for CSF-1 in mediating the IL-3 hematopoietic pathway through monopoiesis, which regulates expansion of CD11c⁺ macrophages.

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

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

Macrophage activation and differentiation signals regulate schlafen-4 gene expression: evidence for Schlafen-4 as a modulator of myelopoiesis

BACKGROUND

The ten mouse and six human members of the Schlafen (Slfn) gene family all contain an AAA domain. Little is known of their function, but previous studies suggest roles in immune cell development. In this report, we assessed Slfn regulation and function in macrophages, which are key cellular regulators of innate immunity.

METHODOLOGY/PRINCIPAL FINDINGS

Multiple members of the Slfn family were up-regulated in mouse bone marrow-derived macrophages (BMM) by the Toll-like Receptor (TLR)4 agonist lipopolysaccharide (LPS), the TLR3 agonist Poly(I∶C), and in disease-affected joints in the collagen-induced model of rheumatoid arthritis. Of these, the most inducible was Slfn4. TLR agonists that signal exclusively through the MyD88 adaptor protein had more modest effects on Slfn4 mRNA levels, thus implicating MyD88-independent signalling and autocrine interferon (IFN)-β in inducible expression. This was supported by the substantial reduction in basal and LPS-induced Slfn4 mRNA expression in IFNAR-1⁻/⁻ BMM. LPS causes growth arrest in macrophages, and other Slfn family genes have been implicated in growth control. Slfn4 mRNA levels were repressed during macrophage colony-stimulating factor (CSF-1)-mediated differentiation of bone marrow progenitors into BMM. To determine the role of Slfn4 in vivo, we over-expressed the gene specifically in macrophages in mice using a csf1r promoter-driven binary expression system. Transgenic over-expression of Slfn4 in myeloid cells did not alter macrophage colony formation or proliferation in vitro. Monocyte numbers, as well as inflammatory macrophages recruited to the peritoneal cavity, were reduced in transgenic mice that specifically over-expressed Slfn4, while macrophage numbers and hematopoietic activity were increased in the livers and spleens.

CONCLUSIONS

Slfn4 mRNA levels were up-regulated during macrophage activation but down-regulated during differentiation. Constitutive Slfn4 expression in the myeloid lineage in vivo perturbs myelopoiesis. We hypothesise that the down-regulation of Slfn4 gene expression during macrophage differentiation is a necessary step in development of this lineage.

Differentiation and heterogeneity in the mononuclear phagocyte system

Cells of the mononuclear phagocyte system (MPS) are found in large numbers in every organ of the body, where they contribute to innate and acquired immunity and homeostasis. This review considers the locations of MPS cells, surface markers that distinguish subsets of monocytes and macrophages, the pathways of MPS differentiation, and the growth factors and transcription factors that guide them. Although the number of MPS sub-populations that can be defined is infinite, the features that unite the MPS remain compelling. Those features clearly include antigen-presenting dendritic cells within the MPS and argue against any basis for separating them from macrophages.

Transcription factor complex formation and chromatin fine structure alterations at the murine c-fms (CSF-1 receptor) locus during maturation of myeloid precursor cells

Expression of the gene for the macrophage colony stimulating factor receptor (CSF-1R), c-fms, has been viewed as a hallmark of the commitment of multipotent precursor cells to macrophages. Lineage-restricted expression of the gene is controlled by conserved elements in the proximal promoter and within the first intron. To investigate the developmental regulation of c-fms at the level of chromatin structure, we developed an in vitro system to examine the maturation of multipotent myeloid precursor cells into mature macrophages. The dynamics of chromatin fine structure alterations and transcription factor occupancy at the c-fms promoter and intronic enhancer was examined by in vivo DMS and UV-footprinting. We show that the c-fms gene is already transcribed at low levels in early myeloid precursors on which no CSF-1R surface expression can be detected. At this stage of myelopoiesis, the formation of transcription factor complexes on the promoter was complete. By contrast, occupancy of the enhancer was acutely regulated during macrophage differentiation. Our data show that cell-intrinsic differentiation decisions at the c-fms locus precede the appearance of c-fms on the cell surface. They also suggest that complex lineage-specific enhancers such as the c-fms intronic enhancer regulate local chromatin structure through the coordinated assembly and disassembly of distinct transcription factor complexes.

Recombinant Congenic Strains Derived from A/J and C57BL/6J: A Tool for Genetic Dissection of Complex Traits

Complex genetic traits can be dissected in mice, using well-defined sets of recombinant inbred strains, congenic strains, and recombinant congenic strains (RCS). We report the creation of a series of 37 independent RCS derived from the commonly used inbred strains of laboratory mouse A/J (A) and C57BL/6J (B6). These RCS were derived by systematic inbreeding of independent pairs of animals from a (F1 x A) x A and a (F1 x B) x B double backcross (N3), to create AcB and BcA strains, respectively. Fifteen AcB strains and 22 BcA strains at between 18 and 30 generations of inbreeding have been generated, are healthy, and show stable breeding performance. These strains have been genotyped for a total of 625 informative microsatellite DNA markers covering the entire genome, with an average spacing of 2.6 cM. Haplotype analyses indicate that on average, AcB and BcA strains contain 13.25% of the donor genome, a value close to the 12.5% expected from the breeding scheme used in their creation. In the AcB set, approximately 79% of the B6 genome has been transferred in independent strains, while in the BcA set approximately 84% of the A genome is represented on the B6 background. This represents an excellent coverage of congenic segments from both parental genomes in the two sets of strains, which can now be used to map simple and complex traits in a genome-wide fashion. As an example of the power of AcB/BcA strains as a mapping tool, the 37 strains were typed for susceptibility to infection with Legionella pneumophila, a monogenic trait controlled by the Lgn1 locus on Chromosome 13. Analysis of the strain distribution pattern of L. pneumophila susceptibility allowed direct mapping of Lgn1 to a 3-cM interval. The AcB/BcA set should prove a useful tool with which to investigate the complex genetic basis of known interstrain differences between A and B6 for many important diseases.

The magnitude of macrophage inflammatory response does not directly depend on ability of bone marrow cells to respond to interleukin-3 in mice of different strains

The multicolony stimulating factor Interleukin-3 (IL-3) has a role in regulating the proliferation, differentiation, and survival of myeloid stem cells and committed progenitor cells within each of the myeloid lineages. It has been referred to as an emergency factor appearing following triggering of an inflammatory response. The ability of bone marrow (BM) stem cells to respond to a stimulus such as IL-3 in vitro may reflect the in vivo capacity of BM stem cells to generate newly BM-derived macrophages being recruited to an inflammatory site. Both parameters, namely the BM cell response to in vitro IL-3 treatment and the magnitude of the macrophage inflammatory response vary among inbred mouse strains. Mice of the A/J strain are known to have weak macrophage inflammatory response to a phlogistic agent and their BM cells are hyporesponsive to IL-3 exposure. In contrast, mice of the C57BL/6 strain mount a high macrophage inflammatory reaction to a stimulus, and their BM cells strongly proliferate in response to the presence of IL-3. Thus, we examined whether or not the type of BM cell response to IL-3 (i.e., A/J- or C57BL/6-like) determines the magnitude of the macrophage inflammatory response using the A x B/B x A recombinant inbred (RI) mouse strain system. The two traits were found not to cosegregate, suggesting that they are not linked. The continuous strain distribution pattern of the magnitude of the macrophage inflammatory response obtained in mice of the A x B/B x A RI strains implies that this trait is under the control of several genes.

Induction of acute arthritis in mice by peptidoglycan derived from gram-positive bacteria and its possible role in cytokine production

The activities of a water-soluble peptidoglycan fragment derived from Staphylococcus epidermidis (SEPS) were examined as to their role in proliferation of spleen mononuclear cells (SMNC) from various strains of mice, the production of cytokines in vitro, and the induction of an inflammatory reaction in vivo. The proliferation of SMNC from C3H/HeN, C57BL/6, AKR, DBA/2, and ddY mice in reaction to SEPS in vitro showed a peak on day 3 and was greater than that of SMNC from BALB/c mice. The cells of SMNC from C3H/HeN mice responsive to SEPS were indicated to be mainly macrophages. A time kinetics experiment showed a coincidence in the proliferation of SMNC in reaction to SEPS and the detection of colony-stimulating factor (CSF) activity. Interleukin 2 (IL-2) activity was not detected during the incubation periods. When SEPS was administered to mice, much stronger mRNA transcripts of granulocyte-macrophage (GM)-CSF were detected in the lungs of C3H/HeN mice than in BALB/c mice. On the other hand, the amounts of IL-1 and PGE2 produced by SMNC of BALB/c mice stimulated by SEPS were greater than those produced in C3H/HeN mice. SEPS was confirmed to induce arthritis in BALB/c mice, but not in C3H/HeN mice. Our findings suggest that the production of GM-CSF is involved in the in vitro proliferation of SMNC in reaction to SEPS and that along with IL-1 and PGE2 production, contributes to the inflammation by SEPS in vivo.

Bone marrow cells from A/J mice do not proliferate in interleukin-3 but express normal numbers of interleukin-3 receptors

Haemopoietic cells from A/J mice do not form colonies (proliferate) in response to interleukin-3 (multi-CSF, IL-3). We have examined different populations of cells from A/J mice and shown that, despite their failure to proliferate in response to IL-3, cells from bone marrow, spleen and the peritoneum all bound 125I-labelled IL-3. A wide variety of cell types bound IL-3 as determined by autoradiography, including promyelocytes, myelocytes, metamyelocytes, polymorphs, promonocytes, monocytes, eosinophils and lymphocytes, but not nucleated erythroid cells, and the proportion of each cell type binding label was similar when cells from A/J mice were compared with those of C57B1/6 and Balb/c mice. Bone marrow cells from A/J mice internalized interleukin-3 with normal kinetics and mRNA extracted from these cells contains the same species of IL-3 receptor and IL-3 receptor-like mRNAs as are found in the other strains. Collectively the data suggest that the failure of haemopoietic cells from A/J mice to proliferate in response to IL-3 is related to a selective defect in signalling to proliferation specific genes. This defect is apparently not related to internalization or processing of the IL-3/IL-3-receptor complex, but may be due to failure to activate appropriate accessory molecules in the cell.

Interleukin 3 alone does not support the proliferation of bone marrow cells from A/J mice: a novel system for studying the synergistic activities of IL-3

The number of colonies produced by bone marrow cells in response to interleukin 3 (IL-3) in soft agar cultures varies according to the strain of the donor mice. A/J, AKR, A.TH and A.TL bone marrow cells are particularly hyporesponsive, producing only occasional colonies in the presence of IL-3. Bone marrow cells from all strains of mice, including A/J, produce distinctively large colonies in response to the combination of IL-3 and macrophage colony stimulating factor (M-CSF). In cultures of A/J bone marrow cells, the synergy between IL-3 and M-CSF is further reflected in an increase in both the number and the variety of colonies produced. The increase in colony numbers may be due to the priming of a population of A/J colony-forming-cells (CFCs) by IL-3, enabling them to respond to M-CSF. In support of this notion, IL-3 enhanced the level of c-fms (M-CSF receptor) messenger RNA in cultures of A/J bone marrow cells. It is also possible that a subpopulation of CFCs requires both IL-3 and M-CSF as co-mitogens. The A/J strain provides a novel system for studying the mechanisms involved in the interaction between IL-3 and M-CSF in haemopoiesis.