Distinct In Vivo Roles of Colony-Stimulating Factor-1 Isoforms in Renal Inflammation

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

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

TMAO enhances TNF-α mediated fibrosis and release of inflammatory mediators from renal fibroblasts

Trimethylamine-N-oxide (TMAO) is a gut microbiota-derived metabolite and TNF-α is proinflammatory cytokine, both known to be associated with renal inflammation, fibrosis and chronic kidney disease. However, today there are no data showing the combined effect of TMAO and TNF-α on renal fibrosis-and inflammation. The aim of this study was to investigate whether TMAO can enhance the inflammatory and fibrotic effects of TNF-α on renal fibroblasts. We found that the combination of TNF-α and TMAO synergistically increased fibronectin release and total collagen production from renal fibroblasts. The combination of TMAO and TNF-α also promoted increased cell proliferation. Both renal proliferation and collagen production were mediated through Akt/mTOR/ERK signaling. We also found that TMAO enhanced TNF-α mediated renal inflammation by inducing the release of several cytokines (IL-6, LAP TGF-beta-1), chemokines (CXCL-6, MCP-3), inflammatory-and growth mediators (VEGFA, CD40, HGF) from renal fibroblasts. In conclusion, we showed that TMAO can enhance TNF-α mediated renal fibrosis and release of inflammatory mediators from renal fibroblasts in vitro. Our results can promote further research evaluating the combined effect of TMAO and inflammatory mediators on the development of kidney disease.

The role of inflammation in diabetic kidney disease

Diabetic kidney disease (DKD) has been the leading cause of chronic kidney disease for over 20 years. Yet, over these two decades, the clinical approach to this condition has not much improved beyond the administration of glucose-lowering agents, renin-angiotensin-aldosterone system blockers for blood pressure control, and lipid-lowering agents. The proportion of diabetic patients who develop DKD and progress to end-stage renal disease has remained nearly the same. This unmet need for DKD treatment is caused by the complex pathophysiology of DKD, and the difficulty of translating treatment from bench to bed, which further adds to the growing argument that DKD is not a homogeneous disease. To better capture the full spectrum of DKD in our design of treatment regimens, we need improved diagnostic tools that can better distinguish the subgroups within the condition. For instance, DKD is typically placed in the broad category of a non-inflammatory kidney disease. However, genome-wide transcriptome analysis studies consistently indicate the inflammatory signaling pathway activation in DKD. This review will utilize human data in discussing the potential for redefining the role of inflammation in DKD. We also comment on the therapeutic potential of targeted anti-inflammatory therapy for DKD.

IL-34 and CSF-1, deciphering similarities and differences at steady state and in diseases

Although IL-34 and CSF-1 share actions as key mediators of monocytes/macrophages survival and differentiation, they also display differences that should be identified to better define their respective roles in health and diseases. IL-34 displays low sequence homology with CSF-1 but has a similar general structure and they both bind to a common receptor CSF-1R, although binding and subsequent intracellular signaling shows differences. CSF-1R expression has been until now mainly described at a steady state in monocytes/macrophages and myeloid dendritic cells, as well as in some cancers. IL-34 has also 2 other receptors, protein-tyrosine phosphatase zeta (PTPζ) and CD138 (Syndecan-1), expressed in some epithelium, cells of the central nervous system (CNS), as well as in numerous cancers. While most, if not all, of CSF-1 actions are mediated through monocyte/macrophages, IL-34 has also other potential actions through PTPζ and CD138. Additionally, IL-34 and CSF-1 are produced by different cells in different tissues. This review describes and discusses similarities and differences between IL-34 and CSF-1 at steady state and in pathological situations and identifies possible ways to target IL-34, CSF-1, and its receptors.

Local M-CSF (Macrophage Colony-Stimulating Factor) Expression Regulates Macrophage Proliferation and Apoptosis in Atherosclerosis

OBJECTIVE

Previous studies have shown that deficiency of M-CSF (macrophage colony-stimulating factor; or CSF1 [colony stimulating factor 1]) dramatically reduces atherosclerosis in hyperlipidemic mice. We characterize the underlying mechanism and investigate the relevant sources of CSF1 in lesions. Approach and Results: We quantitatively assessed the effects of CSF1 deficiency on macrophage proliferation and apoptosis in atherosclerotic lesions. Staining of aortic lesions with markers of proliferation, Ki-67 and bromodeoxyuridine, revealed around 40% reduction in CSF1 heterozygous (Csf1+/-) as compared with WT (wild type; Csf1+/+) mice. Similarly, staining with a marker of apoptosis, activated caspase-3, revealed a 3-fold increase in apoptotic cells in Csf1+/- mice. Next, we determined the cellular sources of CSF1 contributing to lesion development. Cell-specific deletions of Csf1 in smooth muscle cells using SM22α-Cre (smooth muscle protein 22-alpha-Cre) reduced lesions by about 40%, and in endothelial cells, deletions with Cdh5-Cre (VE-cadherin-Cre) reduced lesions by about 30%. Macrophage-specific deletion with LysM-Cre (lysozyme M-Cre), on the other hand, did not significantly reduce lesions size. Transplantation of Csf1 null (Csf1-/-) mice bone marrow into Csf1+/+ mice reduced lesions by about 35%, suggesting that CSF1 from hematopoietic cells other than macrophages contributes to atherosclerosis. None of the cell-specific knockouts affected circulating CSF1 levels, and only the smooth muscle cell deletions had any effect on the percentage monocytes in the circulation. Also, Csf1+/- mice did not exhibit significant differences in Ly6Chigh/Ly6Clow monocytes as compared with Csf1+/+.

CONCLUSIONS

CSF1 contributes to both macrophage proliferation and survival in lesions. Local CSF1 production by smooth muscle cell and endothelial cell rather than circulating CSF1 is the primary driver of macrophage expansion in atherosclerosis.

The M-CSF receptor in osteoclasts and beyond

Colony-stimulating factor 1 receptor (CSF1R, also known as c-FMS) is a receptor tyrosine kinase. Macrophage colony-stimulating factor (M-CSF) and IL-34 are ligands of CSF1R. CSF1R-mediated signaling is crucial for the survival, function, proliferation, and differentiation of myeloid lineage cells, including osteoclasts, monocytes/macrophages, microglia, Langerhans cells in the skin, and Paneth cells in the intestine. CSF1R also plays an important role in oocytes and trophoblastic cells in the female reproductive tract and in the maintenance and maturation of neural progenitor cells. Given that CSF1R is expressed in a wide range of myeloid cells, altered CSF1R signaling is implicated in inflammatory, neoplastic, and neurodegenerative diseases. Inhibiting CSF1R signaling through an inhibitory anti-CSF1R antibody or small molecule inhibitors that target the kinase activity of CSF1R has thus been a promising therapeutic strategy for those diseases. In this review, we cover the recent progress in our understanding of the various roles of CSF1R in osteoclasts and other myeloid cells, highlighting the therapeutic applications of CSF1R inhibitors in disease conditions.

Drugs directed at a key signaling receptor involved in breaking down bone tissue could help treat diseases marked by pathological bone loss and destruction. In a review article, Kyung-Hyun Park-Min and colleagues from the Hospital for Special Surgery in New York, USA, discuss the essential roles played by the colony-stimulating factor 1 receptor (CSF1R) protein in the survival, function, proliferation and differentiation of myeloid lineage stem cells in the bone marrow, including bone-resorbing osteoclasts. They explore the links between the CSF1R-mediated signaling pathway and diseases such as cancer and neurodegeneration. The authors largely focus on bone conditions, highlighting mouse studies in which CSF1R-blocking drugs were shown to ameliorate bone loss and inflammatory symptoms in models of arthritis, osteoporosis and metastatic cancer. Clinical trials are ongoing to test therapeutic applications.

Dysferlinopathy Promotes an Intramuscle Expansion of Macrophages with a Cyto-Destructive Phenotype

Dysferlinopathies are a group of muscular dystrophies resulting from a genetic deficiency in Dysf. Macrophages, highly plastic cells that mediate tissue repair and destruction, are prominent within dystrophic skeletal muscles of dysferlinopathy patients. We hypothesized that Dysf-deficient muscle promotes recruitment, proliferation, and skewing of macrophages toward a cyto-destructive phenotype in dysferlinopathy. To track macrophage dynamics in dysferlinopathy, we adoptively transferred enhanced green fluorescent protein-labeled monocytes into Dysf-deficient BLA/J mice with age-related (2 to 10 months) muscle disease and Dysf-intact (C57BL/6 [B6]) mice. We detected an age- and disease-related increase in monocyte recruitment into Dysf-deficient muscles. Moreover, macrophages recruited into muscle proliferated locally and were skewed toward a cyto-destructive phenotype. By comparing Dysf-deficient and -intact monocytes, our data showed that Dysf in muscle, but not in macrophages, mediate intramuscle macrophage recruitment and proliferation. To further elucidate macrophage mechanisms related to dysferlinopathy, we investigated in vitro macrophage-myogenic cell interactions and found that Dysf-deficient muscle i) promotes macrophage proliferation, ii) skews macrophages toward a cyto-destructive phenotype, and iii) is more vulnerable to macrophage-mediated apoptosis. Taken together, our data suggest that the loss of Dysf expression in muscle, not macrophages, promotes the intramuscle expansion of cyto-destructive macrophages likely to contribute to dysferlinopathy. Identifying pathways within the Dysf-deficient muscle milieu that regulate cyto-destructive macrophages will potentially uncover therapeutic strategies for dysferlinopathies.

Immunity and inflammation in diabetic kidney disease: translating mechanisms to biomarkers and treatment targets

Increasing incidences of obesity and diabetes have made diabetic kidney disease (DKD) the leading cause of chronic kidney disease and end-stage renal disease worldwide. Despite current pharmacological treatments, including strategies for optimizing glycemic control and inhibitors of the renin-angiotensin system, DKD still makes up almost one-half of all cases of end-stage renal disease in the United States. Compelling and mounting evidence has clearly demonstrated that immunity and inflammation play a paramount role in the pathogenesis of DKD. This article reviews the involvement of the immune system in DKD and identifies important roles of key immune and inflammatory mediators. One of the most recently identified biomarkers is serum amyloid A, which appears to be relatively specific for DKD. Novel and evolving treatment approaches target protein kinases, transcription factors, chemokines, adhesion molecules, growth factors, advanced glycation end-products, and other inflammatory molecules. This is the beginning of a new era in the understanding and treatment of DKD, and we may have finally reached a tipping point in our fight against the growing burden of DKD.

Diverse in vivo effects of soluble and membrane-bound M-CSF on tumor-associated macrophages in lymphoma xenograft model

Macrophage colony-stimulating factor (M-CSF) is an important cytokine for monocyte/macrophage lineage. Secretory M-CSF (sM-CSF) and membrane-bound M-CSF (mM-CSF) are two major alternative splicing isoforms. The functional diversity of these isoforms in the activation of tumor-associated macrophages (TAMs), especially in lymphoma microenvironment, has not been documented. Here, we studied the effects of M-CSF isoforms on TAMs in xenograft mouse model. More infiltrating TAMs were detected in microenvironment with mM-CSF and sM-CSF. TAMs could be divided into three subpopulations based on their expression of CD206 and Ly6C. While sM-CSF had greater potential to recruit and induce differentiation of TAMs and TAM subpopulations, mM-CSF had greater potential to induce proliferation of TAMs and TAM subpopulations. Though both isoforms educated TAMs and TAM subpopulations to M2-like macrophages, mM-CSF and sM-CSF induced different spectrums of phenotype-associated genes in TAMs and TAM subpopulations. These results suggested the diverse effects of M-CSF isoforms on the activation of TAMs and TAM subpopulations in lymphoma microenvironments.

Regulation of Embryonic and Postnatal Development by the CSF-1 Receptor

Macrophages are found in all tissues and regulate tissue morphogenesis during development through trophic and scavenger functions. The colony stimulating factor-1 (CSF-1) receptor (CSF-1R) is the major regulator of tissue macrophage development and maintenance. In combination with receptor activator of nuclear factor κB (RANK), the CSF-1R also regulates the differentiation of the bone-resorbing osteoclast and controls bone remodeling during embryonic and early postnatal development. CSF-1R-regulated macrophages play trophic and remodeling roles in development. Outside the mononuclear phagocytic system, the CSF-1R directly regulates neuronal survival and differentiation, the development of intestinal Paneth cells and of preimplantation embryos, as well as trophoblast innate immune function. Consistent with the pleiotropic roles of the receptor during development, CSF-1R deficiency in most mouse strains causes embryonic or perinatal death and the surviving mice exhibit multiple developmental and functional deficits. The CSF-1R is activated by two dimeric glycoprotein ligands, CSF-1, and interleukin-34 (IL-34). Homozygous Csf1-null mutations phenocopy most of the deficits of Csf1r-null mice. In contrast, Il34-null mice have no gross phenotype, except for decreased numbers of Langerhans cells and microglia, indicating that CSF-1 plays the major developmental role. Homozygous inactivating mutations of the Csf1r or its ligands have not been reported in man. However, heterozygous inactivating mutations in the Csf1r lead to a dominantly inherited adult-onset progressive dementia, highlighting the importance of CSF-1R signaling in the brain.

IL-34 mediates acute kidney injury and worsens subsequent chronic kidney disease

Macrophages (Mø) are integral in ischemia/reperfusion injury-incited (I/R-incited) acute kidney injury (AKI) that leads to fibrosis and chronic kidney disease (CKD). IL-34 and CSF-1 share a receptor (c-FMS), and both cytokines mediate Mø survival and proliferation but also have distinct features. CSF-1 is central to kidney repair and destruction. We tested the hypothesis that IL-34-dependent, Mø-mediated mechanisms promote persistent ischemia-incited AKI that worsens subsequent CKD. In renal I/R, the time-related magnitude of Mø-mediated AKI and subsequent CKD were markedly reduced in IL-34-deficient mice compared with controls. IL-34, c-FMS, and a second IL-34 receptor, protein-tyrosine phosphatase ζ (PTP-ζ) were upregulated in the kidney after I/R. IL-34 was generated by tubular epithelial cells (TECs) and promoted Mø-mediated TEC destruction during AKI that worsened subsequent CKD via 2 distinct mechanisms: enhanced intrarenal Mø proliferation and elevated BM myeloid cell proliferation, which increases circulating monocytes that are drawn into the kidney by chemokines. CSF-1 expression in TECs did not compensate for IL-34 deficiency. In patients, kidney transplants subject to I/R expressed IL-34, c-FMS, and PTP-ζ in TECs during AKI that increased with advancing injury. Moreover, IL-34 expression increased, along with more enduring ischemia in donor kidneys. In conclusion, IL-34-dependent, Mø-mediated, CSF-1 nonredundant mechanisms promote persistent ischemia-incited AKI that worsens subsequent CKD.

Homeostasis in the mononuclear phagocyte system

The mononuclear phagocyte system (MPS) is a family of functionally related cells including bone marrow precursors, blood monocytes, and tissue macrophages. We review the evidence that macrophages and dendritic cells (DCs) are separate lineages and functional entities, and examine whether the traditional view that monocytes are the immediate precursors of tissue macrophages needs to be refined based upon evidence that macrophages can extensively self-renew and can be seeded from yolk sac/foetal liver progenitors with little input from monocytes thereafter. We review the role of the growth factor colony-stimulating factor (CSF)1, and present a model consistent with the concept of the MPS in which local proliferation and monocyte recruitment are connected to ensure macrophages occupy their well-defined niche in most tissues.

Failed renoprotection by alternatively activated bone marrow macrophages is due to a proliferation-dependent phenotype switch in vivo

Alternatively activated macrophages (M2) regulate immune responses and ex vivo polarized splenic M2 are able to ameliorate renal injury including models of renal disease, such as adriamycin nephropathy. Whether M2 derived from other organs have similar protective efficacy is unknown. Here, we report adoptively transferred bone marrow M2 macrophages did not improve renal function or reduce renal injury in adriamycin nephropathy, whereas splenic M2 macrophages were protective. Bone marrow and splenic M2 macrophages showed similar regulatory phenotypes and suppressive functions in vitro. Within the inflamed kidney, suppressive phenotypes in bone marrow but not in splenic M2 macrophages, were dramatically reduced. Loss of the suppressive phenotype in bone marrow M2 was related to strong proliferation of bone marrow M2. Bone marrow M2 proliferation in vivo correlated with M-CSF expression by tubular cells in the inflamed kidney. Inhibition of M-CSF in vitro limited bone marrow M2 proliferation and prevented switch of phenotype. Proliferating cells derived from transfused bone marrow M2 were inflammatory rather than regulatory in their phenotype and function. Thus bone marrow in contrast to splenic M2 macrophages do not protect against renal structural and functional injury in murine adriamycin nephropathy. The failed renoprotection of bone marrow M2 is due to the switch of transfused M2 macrophages from a regulatory to an inflammatory phenotype.

Mononuclear phagocyte system in kidney disease and repair

The mononuclear phagocyte system is comprised of circulating monocytes, tissue macrophages and dendritic cells (DCs) that play key roles in tissue homeostasis, immune surveillance, and immune and non-immune-mediated tissue injury and repair. This review summarizes the various subsets within this system that exhibit significant functional and phenotypic diversity that can adapt to their surrounding microenvironments during inflammation and in response to colony-stimulating factor (CSF)-1. The current understanding of the co-ordination of monocyte infiltration into the homeostatic and diseased kidney through adhesion molecules, chemokines and chemokine receptors, and cytokines are described. Furthermore, the significant confusion and controversy associated with monocyte differentiation into renal macrophages and DCs following infiltration into the kidney, the considerable functional and phenotypic overlap between both tissue populations and their respective roles in immune and non-immune-mediated renal is also discussed. Understanding the factors that control the activation and recruitment of cells from the mononuclear phagocyte system during renal injury may offer an avenue for the development of new cellular and growth factor-based therapies in combination with existing therapies as an alternative treatment option for patients with renal disease.

Aberrant macrophages mediate defective kidney repair that triggers nephritis in lupus-susceptible mice

CSF-1, required for macrophage (Mø) survival, proliferation, and activation, is upregulated in the tubular epithelial cells (TECs) during kidney inflammation. CSF-1 mediates Mø-dependent destruction in lupus-susceptible mice with nephritis and, paradoxically, Mø-dependent renal repair in lupus-resistant mice after transient ischemia/reperfusion injury (I/R). We now report that I/R leads to defective renal repair, nonresolving inflammation, and, in turn, early-onset lupus nephritis in preclinical MRL/MpJ-Faslpr/Fas(lpr) mice (MRL-Fas(lpr) mice). Moreover, defective renal repair is not unique to MRL-Fas(lpr) mice, as flawed healing is a feature of other lupus-susceptible mice (Sle 123) and MRL mice without the Fas(lpr) mutation. Increasing CSF-1 hastens renal healing after I/R in lupus-resistant mice but hinders healing, exacerbates nonresolving inflammation, and triggers more severe early-onset lupus nephritis in MRL-Fas(lpr) mice. Probing further, the time-related balance of M1 "destroyer" Mø shifts toward the M2 "healer" phenotype in lupus-resistant mice after I/R, but M1 Mø continue to dominate in MRL-Fas(lpr) mice. Moreover, hypoxic TECs release mediators, including CSF-1, that are responsible for stimulating the expansion of M1 Mø inherently poised to destroy the kidney in MRL-Fas(lpr) mice. In conclusion, I/R induces CSF-1 in injured TECs that expands aberrant Mø (M1 phenotype), mediating defective renal repair and nonresolving inflammation, and thereby hastens the onset of lupus nephritis.

The renal mononuclear phagocytic system

The renal mononuclear phagocytic system, conventionally composed of macrophages (Mø) and dendritic cells (DCs), plays a central role in health and disease of the kidney. Overlapping definitions of renal DCs and Mø, stemming from historically separate research tracks and the lack of experimental tools to specifically study the roles of these cells in vivo, have generated confusion and controversy, however, regarding their immunologic function in the kidney. This brief review provides an appraisal of the current state of knowledge of the renal mononuclear phagocytic system interpreted from the perspective of immunologic function. Physical characteristics, ontogeny, and known functions of the main subsets of renal mononuclear phagocytes as they relate to homeostasis, surveillance against injury and infection, and immune-mediated inflammatory injury and repair within the kidney are described. Gaps and inconsistencies in current knowledge are used to create a roadmap of key questions to be answered in future research.

Distinct roles of CSF-1 isoforms in lupus nephritis

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

Pro- and anti-inflammatory control of M-CSF-mediated macrophage differentiation

Macrophages play a key role in inflammation, tissue regeneration and tolerance. Their differentiation is regulated by tissue cells derived CSF-1 (M-CSF). The ability of macrophages to use autocrine M-CSF to control their differentiation and function remained controversial. In this study we investigated the regulation of M-CSF production by Th1 and Th2 cytokines (IFN-γ and IL-4) and tolerogenic stimuli - glucocorticoid dexamethasone in primary human monocyte derived macrophages. We show that IFN-γ and IL-4 efficiently induce production of M-CSF while glucocorticoid inhibited it in a dose dependent manner. Since glucocorticoid inhibits production of inflammatory cytokines we tested whether this effect is a result of inhibited M-CSF production. We showed that exogenous M-CSF rescues the ability of glucocorticoid-treated macrophages to produce TNF and IL-6 in response to LPS. These data indicate that glucocorticoid-treated macrophages retain the ability to respond to M-CSF. Analyzing the mechanism of this responsiveness, we showed that dexamethasone up-regulates surface expression of M-CSF receptor - CSF-1R. We conclude that the ability of macrophages to produce M-CSF secures macrophage differentiation under Th1 and Th2 conditions if tissue cells are unable to supply enough M-CSF. Increased surface expression of CSF-1R in tolerogenic conditions guarantees response to minute amounts of exogenous M-CSF.

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

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

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

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

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

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

Histone deacetylase modulates the proinflammatory and -fibrotic changes in tubulointerstitial injury

Histone deacetylase (HDAC) regulates gene expression by modifying chromatin structure. Although changes in the expression and activities of HDAC may affect the course of kidney disease, the role of HDAC in tubulointerstitial injury has not been explored. We therefore investigated the alterations in HDAC expression and determined the effects of HDAC inhibition on the tubulointerstitial injury induced by unilateral ureteral obstruction. The induction of HDAC1 and HDAC2, accompanied by a decrease in histone acetylation was observed in kidneys injured by ureteral obstruction. Immunohistochemical analysis revealed that HDAC1 and HDAC2 were induced in renal tubular cells. Treatment with an HDAC inhibitor, trichostatin A (TSA), attenuated macrophage infiltration and fibrotic changes in tubulointerstitial injury induced by ureteral obstruction. The induction of colony-stimulating factor-1 (CSF-1), a chemokine known to be involved in macrophage infiltration in tubulointerstitial injury, was reduced in injured kidneys from mice treated with TSA. TSA, valproate, and the knockdown of HDAC1 or HDAC2 significantly reduced CSF-1 induced by TNF-alpha in renal tubular cells. These results suggest that tubular HDAC1 and HDAC2, induced in response to injury, may contribute to the induction of CSF-1 and the initiation of macrophage infiltration and profibrotic responses. These findings suggest a potential of HDAC inhibition therapy aimed at reducing inflammation and fibrosis in tubulointerstitial injury.

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

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

Dendritic cells in the kidney

Dendritic cells (DC) in nonlymphoid organs function at the crossroads of innate and adaptive immunity, self-tolerance, and tissue homeostasis. This review provides an overview of the study of DC in the kidney, tracing its history leading to the current knowledge of the origins, migration, and function of renal DC. Together, these studies suggest that renal DC play a critical role in the health and disease of the kidney, opening the way to direct targeting of renal DC for therapeutic benefit.