Cloning and expression of feline colony stimulating factor receptor (CSF-1R) and analysis of the species specificity of stimulation by colony stimulating factor-1 (CSF-1) and interleukin-34 (IL-34)

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

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

Transcriptomic Analysis of Rat Macrophages

The laboratory rat is widely used as a model for human diseases. Many of these diseases involve monocytes and tissue macrophages in different states of activation. Whilst methods for in vitro differentiation of mouse macrophages from embryonic stem cells (ESC) and bone marrow (BM) are well established, these are lacking for the rat. The gene expression profiles of rat macrophages have also not been characterised to the same extent as mouse. We have established the methodology for production of rat ESC-derived macrophages and compared their gene expression profiles to macrophages obtained from the lung and peritoneal cavity and those differentiated from BM and blood monocytes. We determined the gene signature of Kupffer cells in the liver using rats deficient in macrophage colony stimulating factor receptor (CSF1R). We also examined the response of BM-derived macrophages to lipopolysaccharide (LPS). The results indicate that many, but not all, tissue-specific adaptations observed in mice are conserved in the rat. Importantly, we show that unlike mice, rat macrophages express the CSF1R ligand, colony stimulating factor 1 (CSF1).

Biological functions and clinical implications of interleukin-34 in inflammatory diseases

Interleukin (IL)-34 is a recently discovered cytokine and ligand of the colony-stimulating factor (CSF)-1 receptor. Although CSF-1 and IL-34 share similar biological properties, their expression patterns and downstream signaling pathways are distinct. IL-34 can influence differentiation and has functions in multiple cell types (e.g., dendritic cells, monocytes, macrophages). In the pathological conditions, IL-34 is induced by pro-inflammatory stimuli (e.g., cytokines, pathogen-associated molecular patterns, and infection). Current evidence shows that IL-34 is a critical player in inflammatory response and is involved in the pathogenesis of inflammatory autoimmune dysfunction. Therefore, IL-34 may be a promising clinical biomarker and therapeutic target for treating inflammatory related disorders. In this article, we review the advances in biological functions of IL-34 and our understanding of its role in the development of inflammatory diseases as well as therapeutic applications.

Characterizing replication kinetics and plaque production of type I feline infectious peritonitis virus in three feline cell lines

Investigating type I feline coronaviruses (FCoVs) in tissue culture is critical for understanding the basic virology, pathogenesis, and virus-host interactome of these important veterinary pathogens. This has been a perennial challenge as type I FCoV strains do not easily adapt to cell culture. Here we characterize replication kinetics and plaque formation of a model type I strain FIPV Black in Fcwf-4 cells established at Cornell University (Fcwf-4 CU). We determined that maximum virus titers (>10⁷ pfu/mL) were recoverable from infected Fcwf-4 CU cell-free supernatant at 20 h post-infection. Type I FIPV Black and both biotypes of type II FCoV formed uniform and enumerable plaques on Fcwf-4 CU cells. Therefore, these cells were employable in a standardized plaque assay. Finally, we determined that the Fcwf-4 CU cells were morphologically distinct from feline bone marrow-derived macrophages and were less sensitive to exogenous type I interferon than were Fcwf-4 cells purchased from ATCC.

Interleukin-34, a comprehensive review

IL-34 is a novel cytokine that was identified in 2008 in a comprehensive proteomic analysis as a tissue-specific ligand of CSF-1 receptor (CSF-1R). IL-34 exists in all vertebrates including fish, amphibians, birds, and mammals, showing high conservation among species. Structurally, IL-34 belongs to the short-chain helical hematopoietic cytokine family but shows no apparent consensus structural domains, motifs, or sequence homology with other cytokines. IL-34 is synthesized as a secreted homodimeric glycoprotein that binds to the extracellular domains of CSF-1R and receptor-type protein-tyrosine phosphatase-zeta (PTP-ζ) in addition to the chondroitin sulfate chains of syndecan-1. These interactions result in activating several signaling pathways that regulate major cellular functions, including proliferation, differentiation, survival, metabolism, and cytokine/chemokine expression in addition to cellular adhesion and migration. In the steady state, IL-34 contributes to the development and maintenance of specific myeloid cell subsets in a tissue-specific manner: Langerhans cells in the skin and microglia in the brain. In pathological conditions, changes in IL-34 expression-increased or decreased-are involved in disease pathogenesis and correlate with progression, severity, and chronicity. One decade after its discovery, IL-34 has been introduced as a newcomer to the big family of interleukins with specific physiological functions, critical pathological roles, and promising clinical applications in disease diagnosis and treatment. In this review, we celebrate the 10th anniversary of IL-34 discovery, introducing its biological characteristics, and discussing the importance of IL-34 signaling network in health and disease.

Recent Advances of Colony-Stimulating Factor-1 Receptor (CSF-1R) Kinase and Its Inhibitors

Colony stimulation factor-1 receptor (CSF-1R), which is also known as FMS kinase, plays an important role in initiating inflammatory, cancer, and bone disorders when it is overstimulated by its ligand, CSF-1. Innate immunity, as well as macrophage differentiation and survival, are regulated by the stimulation of the CSF-1R. Another ligand, interlukin-34 (IL-34), was recently reported to activate the CSF-1R receptor in a different manner. The relationship between CSF-1R and microglia has been reviewed. Both CSF-1 antibodies and small molecule CSF-1R kinase inhibitors have now been tested in animal models and in humans. In this Perspective, we discuss the role of CSF-1 and IL-34 in producing cancer, bone disorders, and inflammation. We also review the newly discovered and improved small molecule kinase inhibitors and monoclonal antibodies that have shown potent activity toward CSF-1R, reported from 2012 until 2017.

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.

Expression profiling feline peripheral blood monocytes identifies a transcriptional signature associated with type two diabetes mellitus

Diabetes mellitus is a common disease of cats and is similar to type 2 diabetes (T2D) in humans, especially with respect to the role of obesity-induced insulin resistance, glucose toxicity, decreased number of pancreatic β-cells and pancreatic amyloid deposition. Cats have thus been proposed as a valuable translational model of T2D. In humans, inflammation associated with adipose tissue is believed to be central to T2D development, and peripheral blood monocytes (PBM) are important in the inflammatory cascade which leads to insulin resistance and β-cell failure. PBM may thus provide a useful window to study the pathogenesis of diabetes mellitus in cats, however feline monocytes are poorly characterised. In this study, we used the Affymetrix Feline 1.0ST array to profile peripheral blood monocytes from 3 domestic cats with T2D and 3 cats with normal glucose tolerance. Feline monocytes were enriched for genes expressed in human monocytes, and, despite heterogeneous gene expression, we identified a T2D-associated expression signature associated with cell cycle perturbations, DNA repair and the unfolded protein response, oxidative phosphorylation and inflammatory responses. Our data provide novel insights into the feline monocyte transcriptome, and support the hypothesis that inflammatory monocytes contribute to T2D pathogenesis in cats as well as in humans.

Amphibian macrophage development and antiviral defenses

Macrophage lineage cells represent the cornerstone of vertebrate physiology and immune defenses. In turn, comparative studies using non-mammalian animal models have revealed that evolutionarily distinct species have adopted diverse molecular and physiological strategies for controlling macrophage development and functions. Notably, amphibian species present a rich array of physiological and environmental adaptations, not to mention the peculiarity of metamorphosis from larval to adult stages of development, involving drastic transformation and differentiation of multiple new tissues. Thus it is not surprising that different amphibian species and their respective tadpole and adult stages have adopted unique hematopoietic strategies. Accordingly and in order to establish a more comprehensive view of these processes, here we review the hematopoietic and monopoietic strategies observed across amphibians, describe the present understanding of the molecular mechanisms driving amphibian, an in particular Xenopus laevis macrophage development and functional polarization, and discuss the roles of macrophage-lineage cells during ranavirus infections.

Grouper (Epinephelus coioides) IL-34/MCSF2 and MCSFR1/MCSFR2 were involved in mononuclear phagocytes activation against Cryptocaryon irritans infection

MCSF and its well-known receptor MCSFR had been well studied in humans, regulating the differentiation, proliferation, and survival of the mononuclear phagocyte system. IL-34, which is an alternative ligand of MCSF receptor, was recently identified as a novel cytokine and functionally overlaps with MCSF. However, the functional study of these receptors and their ligands in fish are largely unknown. In the present study, the cDNA of two potential grouper MCSFR ligands have been cloned, EcIL-34 (657 bp) and EcMCSF2 (804 bp), as well as an additional copy of grouper MCSFR, EcMCSFR2 (3141 bp). Sequence analysis showed that these three molecules had higher identities with other fish counterparts compared to mammals and their conserved structures and important functional residues were also analyzed. Tissue distribution analysis showed that EcIL-34 is dominant in brain, gill and spleen compared to EcMCSF2, which is dominant in head kidney, trunk kidney, skin, heart and muscle. EcMCSFR1 was dominant in the most tissues except head kidney and liver compared to EcMCSFR2. The different tissue distribution patterns of these two grouper MCSF receptors and their two ligands indicate the different mononuclear phagocyte differentiation and activation modes in different tissues. In Cryptocaryon irritans infected grouper, EcIL-34 and EcMCSFR2 were the most strongly up-regulated ligand and receptor in the infected sites, gill and skin. Their up-regulation confirmed the proliferation and activation of phagocytes in C. irritans infected sites, which would improve the antigen presentation and elicit the host local specific immune response. In C. irritans infected grouper head kidney, both ligands EcIL-34 and EcMCSF2 (especially EcMCSF2) were up-regulated, but both receptors EcMCSFR1 and EcMCSFR2 were down-regulated, which indicated that the phagocytes differentiation and proliferation may have occurred in this hemopoietic organ, and after that they migrated to the infected cites. The down-regulation of EcIL-34 and EcMCSF2 and no significant change of EcMCSFR1 and EcMCSFR2 in most time point of grouper spleen showed it was less involved in phagocytes response to C. irritans infection.

Divergent antiviral roles of amphibian (Xenopus laevis) macrophages elicited by colony-stimulating factor-1 and interleukin-34

Macrophages are integral to amphibian immunity against RVs, as well as to the infection strategies of these pathogens. Although CSF-1 was considered to be the principal mediator of macrophage development, the IL-34 cytokine, which shares no sequence identity with CSF-1, is now believed to contribute to vertebrate monopoiesis. However, the respective roles of CSF-1- and IL-34-derived macrophages are still poorly understood. To delineate the contribution of these macrophage populations to amphibian immunity against the RV FV3, we identified the Xenopus laevis IL-34 and transcriptionally and functionally compared this cytokine with the previously identified X. laevis CSF-1. The X. laevis CSF-1 and IL-34 displayed strikingly nonoverlapping developmental and tissue-specific gene-expression patterns. Furthermore, only CSF-1 but not IL-34 was up-regulated in the kidneys of FV3-challenged tadpoles. Intriguingly, recombinant forms of these cytokines (rXlCSF-1, rXlIL-34) elicited morphologically distinct tadpole macrophages, and whereas rXlCSF-1 pretreatment decreased the survival of FV3-infected tadpoles, rXlIL-34 administration significantly prolonged FV3-challenged animal survival. Compared with rXlIL-34-elicited macrophages, macrophages derived by rXlCSF-1 were more phagocytic but also significantly more susceptible to in vitro FV3 infections. By contrast, rXlIL-34-derived macrophages exhibited significantly greater in vitro antiranaviral activity and displayed substantially more robust gene expression of the NADPH oxidase components (p67(phox), gp91(phox)) and type I IFN. Moreover, FV3-challenged, rXlIL-34-derived macrophages exhibited several orders of magnitude greater up-regulation of the type I IFN gene expression. This marks the first report of the disparate roles of CSF-1 and IL-34 in vertebrate antiviral immunity.

Characterisation of a novel Fc conjugate of macrophage colony-stimulating factor

We have produced an Fc conjugate of colony-stimulating factor (CSF) 1 with an improved circulating half-life. CSF1-Fc retained its macrophage growth-promoting activity, and did not induce proinflammatory cytokines in vitro. Treatment with CSF1-Fc did not produce adverse effects in mice or pigs. The impact of CSF1-Fc was examined using the Csf1r-enhanced green fluorescent protein (EGFP) reporter gene in MacGreen mice. Administration of CSF1-Fc to mice drove extensive infiltration of all tissues by Csf1r-EGFP positive macrophages. The main consequence was hepatosplenomegaly, associated with proliferation of hepatocytes. Expression profiles of the liver indicated that infiltrating macrophages produced candidate mediators of hepatocyte proliferation including urokinase, tumor necrosis factor, and interleukin 6. CSF1-Fc also promoted osteoclastogenesis and produced pleiotropic effects on other organ systems, notably the testis, where CSF1-dependent macrophages have been implicated in homeostasis. However, it did not affect other putative CSF1 targets, notably intestine, where Paneth cell numbers and villus architecture were unchanged. CSF1 has therapeutic potential in regenerative medicine in multiple organs. We suggest that the CSF1-Fc conjugate retains this potential, and may permit daily delivery by injection rather than continuous infusion required for the core molecule.