IL-34-Dependent Intrarenal and Systemic Mechanisms Promote Lupus Nephritis in MRL-Faslpr Mice.

BACKGROUND: In people with SLE and in the MRL-Faslpr lupus mouse model, macrophages and autoantibodies are central to lupus nephritis. IL-34 mediates macrophage survival and proliferation, is expressed by tubular epithelial cells (TECs), and binds to the cFMS receptor on macrophages and to a newly identified second receptor, PTPRZ. METHODS: To investigate whether IL-34-dependent intrarenal and systemic mechanisms promote lupus nephritis, we compared lupus nephritis and systemic illness in MRL-Faslpr mice expressing IL-34 and IL-34 knockout (KO) MRL-Faslpr mice. We also assessed expression of IL-34 and the cFMS and PTPRZ receptors in patients with lupus nephritis. RESULTS: Intrarenal IL-34 and its two receptors increase during lupus nephritis in MRL-Faslpr mice. In knockout mice lacking IL-34, nephritis and systemic illness are suppressed. IL-34 fosters intrarenal macrophage accumulation via monocyte proliferation in bone marrow (which increases circulating monocytes that are recruited by chemokines into the kidney) and via intrarenal macrophage proliferation. This accumulation leads to macrophage-mediated TEC apoptosis. We also found suppression of circulating autoantibodies and glomerular antibody deposits in the knockout mice. This is consistent with fewer activated and proliferating intrarenal and splenic B cells in mice lacking IL-34, and with our novel discovery that PTPRZ is expressed by macrophages, B and T cells. These findings appear translatable to human patients with lupus nephritis, whose expression of IL-34, cFMS, and PTPRZ is similar to that seen in the MRL-Faslpr lupus mouse model. Moreover, expression of IL-34 in TECs correlates with disease activity. CONCLUSIONS: IL-34 is a promising novel therapeutic target for patients with lupus nephritis.

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.

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.

Colony-stimulating factor-1: a potential biomarker for lupus nephritis.

A noninvasive means to predict the onset and recurrence of lupus nephritis (LN) before overt renal injury is needed to optimize and individualize treatment. Colony-stimulating factor-1 (CSF-1) is expressed by kidney tubules at the onset of LN, increases with disease progression, and spills into the circulation in lupus-prone mice. We tested the hypothesis that amplified expression of CSF-1 detected in the serum or urine correlates with intrarenal CSF-1 expression and histopathology (increased macrophage accumulation, activity indices) and clinical kidney disease activity and predicts the onset and recurrence of nephritis in patients with systemic lupus erythematosus (SLE). We found increased serum or urine CSF-1 levels in patients with cutaneous, serositis, and musculoskeletal disease; however, the increase in CSF-1 levels was far greater in LN. Moreover, an elevation in serum or urine CSF-1 levels correlated with increasing intrarenal CSF-1 expression and histopathology. By longitudinally tracking patients, we found that elevated serum CSF-1 heralded the initial onset of disease, and a rise in serum or urine CSF-1 predicted recurrences of LN before clinical evidence of glomerular dysfunction and conventional serologic measures, even in patients with other manifestations of SLE. These findings indicate that serial monitoring for a rise in serum or urine CSF-1 levels in patients with SLE reflects kidney histopathology and may predict renal disease activity and the onset and recurrence of LN more accurately than conventional laboratory measures.

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.

Autocrine CSF-1 and CSF-1 receptor coexpression promotes renal cell carcinoma growth.

Renal cell carcinoma is increasing in incidence but the molecular mechanisms regulating its growth remain elusive. Coexpression of the monocytic growth factor colony-stimulating factor (CSF)-1 and its receptor CSF-1R on renal tubular epithelial cells (TEC) will promote proliferation and antiapoptosis during regeneration of renal tubules. Here, we show that a CSF-1-dependent autocrine pathway is also responsible for the growth of renal cell carcinoma (RCC). CSF-1 and CSF-1R were coexpressed in RCCs and TECs proximally adjacent to RCCs. CSF-1 engagement of CSF-1R promoted RCC survival and proliferation and reduced apoptosis, in support of the likelihood that CSF-1R effector signals mediate RCC growth. In vivo CSF-1R blockade using a CSF-1R tyrosine kinase inhibitor decreased RCC proliferation and macrophage infiltration in a manner associated with a dramatic reduction in tumor mass. Further mechanistic investigations linked CSF-1 and epidermal growth factor signaling in RCCs. Taken together, our results suggest that budding RCC stimulates the proximal adjacent microenvironment in the kidney to release mediators of CSF-1, CSF-1R, and epidermal growth factor expression in RCCs. Furthermore, our findings imply that targeting CSF-1/CSF-1R signaling may be therapeutically effective in RCCs.

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.

Targeting transcription factor Stat4 uncovers a role for interleukin-18 in the pathogenesis of severe lupus nephritis in mice.

Polymorphisms in the transcription factor Stat4 gene have been implicated as risk factors for systemic lupus erythematosus. Although some polymorphisms have a strong association with autoantibodies and nephritis, their impact on pathophysiology is still unknown. To explore this further we used signal transducers and activators of transcription 4 (Stat4) knockout MRL/MpJ-Fas(lpr)/Fas(lpr) (MRL-Fas(lpr)) mice and found that they did not differ in survival or renal function from Stat4-intact MRL-Fas(lpr) mice. Circulating interleukin (IL)-18 levels, however, were elevated in Stat4-deficient compared to Stat4-intact mice, suggesting that this interleukin might contribute to the progression of lupus nephritis independent of Stat4. In a second approach, Stat4 antisense or missense oligonucleotides or vehicle were given to MRL-Fas(lpr) mice with advanced nephritis. Each of these treatments temporarily ameliorated disease, although IL-18 was increased in each setting. Based on these findings, studies using gene transfer to overexpress IL-18 in MRL-Fas(lpr) and IL-12p40/IL-23 knockout MRL-Fas(lpr) mice reveal a critical role for IL-18 in mediating disease. Thus, the Stat4 and IL-12 (an activator of Stat4)-independent factor, IL-18, can drive autoimmune lupus nephritis in MRL-Fas(lpr) mice. Temporarily blocking Stat4 during advanced nephritis ameliorates disease, suggesting a time-dependent compensatory proinflammatory mechanism.

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.

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.

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

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

Programmed death ligand 1 regulates a critical checkpoint for autoimmune myocarditis and pneumonitis in MRL mice.

MRL/MpJ-Fas(lpr) (MRL-Fas(lpr)) mice develop a spontaneous T cell and macrophage-dependent autoimmune disease that shares features with human lupus. Interactions via the programmed death 1/programmed death ligand 1 (PD-1/PD-L1) pathway down-regulate immune responses and provide a negative regulatory checkpoint in mediating tolerance and autoimmune disease. Therefore, we tested the hypothesis that the PD-1/PD-L1 pathway suppresses lupus nephritis and the systemic illness in MRL-Fas(lpr) mice. For this purpose, we compared kidney and systemic illness (lymph nodes, spleen, skin, lung, glands) in PD-L1 null (-/-) and PD-L1 intact (wild type, WT) MRL-Fas(lpr) mice. Unexpectedly, PD-L1(-/-);MRL-Fas(lpr) mice died as a result of autoimmune myocarditis and pneumonitis before developing renal disease or the systemic illness. Dense infiltrates, consisting of macrophage and T cells (CD8(+) > CD4(+)), were prominent throughout the heart (atria and ventricles) and localized specifically around vessels in the lung. In addition, once disease was evident, we detected heart specific autoantibodies in PD-L1(-/-);MRL-Fas(lpr) mice. This unique phenotype is dependent on MRL-specific background genes as PD-L1(-/-);MRL(+/+) mice lacking the Fas(lpr) mutation developed autoimmune myocarditis and pneumonitis. Notably, the transfer of PD-L1(-/-);MRL(+/+) bone marrow cells induced myocarditis and pneumonitis in WT;MRL(+/+) mice, despite a dramatic up-regulation of PD-L1 expression on endothelial cells in the heart and lung of WT;MRL(+/+) mice. Taken together, we suggest that PD-L1 expression is central to autoimmune heart and lung disease in lupus-susceptible (MRL) mice.

CXCL9, but not CXCL10, promotes CXCR3-dependent immune-mediated kidney disease.

Chemokines are instrumental in macrophage- and T cell-dependent diseases. The chemokine CCL2 promotes kidney disease in two models of immune-mediated nephritis (MRL-Fas(lpr) mice and the nephrotoxic serum nephritis model), but evidence suggests that multiple chemokines are involved. For identification of additional therapeutic targets for immune-mediated nephritis, chemokine ligands and receptors in CCL2-/- and wild-type (WT) MRL-Fas(lpr) kidneys were profiled. The focus was on intrarenal chemokine ligand/receptor pairs that were highly upregulated downstream of CCL2; the chemokine CXCL10 and its cognate receptor, CXCR3, stood out as potential therapeutic targets. However, renal disease was not suppressed in CXCL10-/- MRL-Fas(lpr) mice, and CXCL10-/- C57BL/6 mice were not protected from nephrotoxic serum nephritis compared with WT mice. Because CXCR3 engages with the ligand CXCL9, CXCR3-/- , CXCL9-/- , and CXCL10-/- B6 mice were compared with WT mice with nephrotoxic serum nephritis. Kidney disease, measured by loss of renal function and histopathology, was suppressed in both CXCR3-/- and CXCL9-/- mice but not in CXCL10-/- mice. With nephrotoxic serum nephritis, CXCR3-/- and CXCL9-/- mice had fewer intrarenal activated T cells and activated macrophages. Both IgG glomerular deposits and antigen-specific IgG in serum were reduced in these mice, suggesting that although CXCR3 and CXCL9 initiate nephritis through cell-mediated events, renal inflammation may be sustained by their regulation of IgG. It is concluded that specific blockade of CXCL9

Programmed death 1 ligand (PD-L) 1 and PD-L2 limit autoimmune kidney disease: distinct roles.

The programmed death 1/programmed death 1 ligand (PD-L) pathway is instrumental in peripheral tolerance. Blocking this pathway exacerbates experimental autoimmune diseases, but its role in autoimmune kidney disease has not been explored. Therefore, we tested the hypothesis that the programmed death 1 ligands (PD-L1 and PD-L2), provide a protective barrier during T cell- and macrophage (Mphi)-dependent autoimmune kidney disease. For this purpose, we compared nephrotoxic serum nephritis (NSN) in mice lacking PD-L1 (PD-L1(-/-)), PD-L2 (PD-L2(-/-)), or both (PD-L1/L2(-/-)) to wild-type (WT) C57BL/6 mice. Kidney pathology, loss of renal function, and intrarenal leukocyte infiltrates were increased in each PD-L(-/-) strain as compared with WT mice. Although the magnitude of renal pathology was similar in PD-L1(-/-) and PD-L2(-/-) mice, our findings suggest that kidney disease in each strain is regulated by distinct mechanisms. Specifically, we detected increased CD68(+) cells along with elevated circulating IgG and IgG deposits in glomeruli in PD-L2(-/-) mice, but not PD-L1(-/-) mice. In contrast, we detected a rise in activated CD8(+) T cells in PD-L1(-/-) mice, but not PD-L2(-/-) mice. Furthermore, since PD-L1 is expressed by parenchymal and hemopoietic cells in WT kidneys, we explored the differential impact of PD-L1 expression on these cell types by inducing NSN in bone marrow chimeric mice. Our results indicate that PD-L1 expression on hemopoietic cells, and not parenchymal cells, is primarily responsible for limiting leukocyte infiltration during NSN. Taken together, our findings indicate that PD-L1 and PD-L2 provide distinct negative regulatory checkpoints poised to suppress autoimmune renal disease.

Distinct in vivo roles of colony-stimulating factor-1 isoforms in renal inflammation.

CSF-1, the major regulator of macrophage (Mphi) development, has three biologically active isoforms: a membrane-spanning, cell surface glycoprotein, a secreted glycoprotein, and a secreted proteoglycan. We hypothesized that there are shared and unique roles of individual CSF-1 isoforms during renal inflammation. To test this, we evaluated transgenic mice only expressing the cell surface or precursors of the secreted CSF-1 isoforms for Mphi accumulation, activation, and Mphi-mediated tubular epithelial cell (TEC) apoptosis during unilateral ureteral obstruction. The only difference between secreted proteoglycan and secreted glycoprotein CSF-1 isoforms is the presence (proteoglycan) or absence (glycoprotein) of an 18-kDa chondroitin sulfate glycosaminoglycan. We report that 1) cell surface CSF-1 isoform is sufficient to restore Mphi accumulation, activation, and TEC apoptosis to wild-type levels and is substantially more effective than the secreted CSF-1 isoforms; 2) the chondroitin sulfate glycosaminoglycan facilitates Mphi accumulation, activation, and TEC apoptosis; 3) increasing the level of secreted proteoglycan CSF-1 in serum amplifies renal inflammation; and 4) cell-cell contact is required for Mphi to up-regulate CSF-1-dependent expression of IFN-gamma. Taken together, we have identified central roles for the cell surface CSF-1 and the chondroitin sulfate chain on secreted proteoglycan CSF-1 during renal inflammation.

Inducible co-stimulator null MRL-Faslpr mice: uncoupling of autoantibodies and T cell responses in lupus.

MRL/MpJ-Tnfrsf6lpr (MRL-Faslpr) mice develop a spontaneous T cell-dependent autoimmune disease that shares features with human lupus, including fatal nephritis, systemic pathology, and autoantibodies (autoAb). The inducible co-stimulator (ICOS) is upregulated on activated T cells and modulates T cell-mediated responses. To investigate whether ICOS has an essential role in regulating autoimmune lupus nephritis and the systemic illness in MRL-Faslpr mice, ICOS null (-/-) MRL Faslpr and ICOS intact (+/+) MRL-Faslpr strains (wild-type [WT]) were generated and compared. It was determined that in ICOS-/- MRL-Faslpr as compared with the WT strain, (1) there is a significant reduction in circulating IgG and double-stranded DNA autoantibody isotype titers, and (2) there is an amplification of the frequency of intrarenal T cells generating IFN-gamma and TNF-alpha in ICOS-/- versus WT mice. Of note, eliminating ICOS in the MRL-Faslpr strain does not alter renal pathology or function. Despite the reduction in circulating IgG and autoantibody isotypes (G1, G2a, and G2b), the amount of these IgG isotypes depositing in kidneys is similar. Furthermore, the systemic illness (skin, salivary and lacrimal glands, lungs, lymphadenopathy, and splenomegaly) is equivalent in ICOS-/- MRL-Faslpr and WT mice. These findings highlight the danger of relying on individual parameters, such as quantitative serum Ig levels and T cell functions, as prognostic indicators of lupus.

Restoration of tubular epithelial cells during repair of the postischemic kidney occurs independently of bone marrow-derived stem cells.

Ischemia causes kidney tubular cell damage and abnormal renal function. The kidney is capable of morphological restoration of tubules and recovery of function. Recently, it has been suggested that cells repopulating the ischemically injured tubule derive from bone marrow stem cells. We studied kidney repair in chimeric mice expressing GFP or bacterial beta-gal or harboring the male Y chromosome exclusively in bone marrow-derived cells. In GFP chimeras, some interstitial cells but not tubular cells expressed GFP after ischemic injury. More than 99% of those GFP interstitial cells were leukocytes. In female mice with male bone marrow, occasional tubular cells (0.06%) appeared to be positive for the Y chromosome, but deconvolution microscopy revealed these to be artifactual. In beta-gal chimeras, some tubular cells also appeared to express beta-gal as assessed by X-gal staining, but following suppression of endogenous (mammalian) beta-gal, no tubular cells could be found that stained with X-gal after ischemic injury. Whereas there was an absence of bone marrow-derived tubular cells, many tubular cells expressed proliferating cell nuclear antigen, which is reflective of a high proliferative rate of endogenous surviving tubular cells. Upon i.v. injection of bone marrow mesenchymal stromal cells, postischemic functional renal impairment was reduced, but there was no evidence of differentiation of these cells into tubular cells of the kidney. Thus, our data indicate that bone marrow-derived cells do not make a significant contribution to the restoration of epithelial integrity after an ischemic insult. It is likely that intrinsic tubular cell proliferation accounts for functionally significant replenishment of the tubular epithelium after ischemia.

Negative role of colony-stimulating factor-1 in macrophage, T cell, and B cell mediated autoimmune disease in MRL-Fas(lpr) mice.

Inflammation in the kidney and other tissues (lung, and salivary and lacrimal glands) is characteristic of MRL-Fas(lpr) mice with features of lupus. Macrophages (Mphi) are prominent in these tissues. Given that 1) Mphi survival, recruitment, proliferation, and activation during inflammation is dependent on CSF-1, 2) Mphi mediate renal resident cell apoptosis, and 3) CSF-1 is up-regulated in MRL-Fas(lpr) mice before, and during nephritis, we hypothesized that CSF-1-deficient MRL-Fas(lpr) mice would be protected from Mphi-mediated nephritis, and the systemic illness. To test this hypothesis, we compared CSF-1-deficient MRL-Fas(lpr) with wild-type strains. Renal pathology is suppressed and function improved in CSF-1-deficient MRL-Fas(lpr) mice. There are far fewer intrarenal Mphi and T cells in CSF-1-deficient MRL-Fas(lpr) vs wild-type kidneys. This leukocytic reduction results from suppressed infiltration, and intrarenal proliferation, but not enhanced apoptosis. The CSF-1-deficient MRL-Fas(lpr) kidneys remain preserved as indicated by greatly reduced indices of injury (nephritogenic cytokines, tubular apoptosis, and proliferation). The renal protective mechanism in CSF-1-deficient mice is not limited to reduced intrarenal leukocytes; circulating Igs and autoantibodies, and renal Ig deposits are decreased. This may result from enhanced B cell apoptosis and fewer B cells in CSF-1-deficient MRL-Fas(lpr) mice. Furthermore, the systemic illness including, skin, lung, and lacrimal and salivary glands pathology, lymphadenopathy, and splenomegaly are dramatically suppressed in CSF-1-deficient MRL-Fas(lpr) as compared with wild-type mice. These results indicate that CSF-1 is an attractive therapeutic target to combat Mphi-, T cell-, and B cell-mediated autoimmune lupus.

IL-12 deficiency in MRL-Fas(lpr) mice delays nephritis and intrarenal IFN-gamma expression, and diminishes systemic pathology.

Autoimmune disease in MRL-Fas(lpr) mice is characterized by fatal nephritis, systemic pathology, and autoantibodies, mimicking human lupus. We previously reported that 1) intrarenal IL-12 elicits nephritis by fostering the accumulation of intrarenal IFN-gamma-secreting T cells, and 2) MRL-Fas(lpr) mice deficient in the IFN-gamma receptor were spared from nephritis. Therefore, we hypothesized that eliminating IL-12 in MRL-Fas(lpr) mice reduces IFN-gamma-secreting cells and thereby prevents systemic pathology. For this purpose, we constructed an IL-12p40-deficient MRL-Fas(lpr)(IL-12(-/-)) strain. We determined that glomerular and interstitial, but not perivascular, renal pathology were decreased in IL-12(-/-) mice vs the wild-type (WT) strain (5 mo of age). Similarly, systemic pathology (lung, lacrimal and salivary glands, skin, and lymphadenopathy) was diminished. The intrarenal accumulation of T cells (CD4(+), CD8(+), CD4(-)CD8(-)B220(+)) and macrophages was dramatically reduced in IL-12(-/-) MRL-Fas(lpr) kidneys. We determined that there were fewer IFN-gamma transcripts (>70%) in the IL-12(-/-) protected kidneys compared with the WT kidneys. Similarly, cells propagated from IL-12(-/-) MRL-Fas(lpr) kidneys generated substantially less IFN-gamma when stimulated with IL-12 and IL-18 compared with those from WT kidneys, and we detected fewer CD8 and B220 T cells producing IFN-gamma in these IL-12(-/-) MRL-Fas(lpr) kidneys. Of note, survival was modestly extended in the IL-12(-/-) MRL-Fas(lpr) mice. While lung and lacrimal and salivary gland pathology remained reduced in moribund IL-12(-/-) MRL-Fas(lpr) mice, renal pathology and IFN-gamma expression were equivalent to those in the WT strain. Thus, we suggest that IL-12 is a therapeutic target for multiple tissues in lupus; however blocking IL-12 alone is not sufficient to confer enduring protection from lupus nephritis.

Reduced macrophage recruitment, proliferation, and activation in colony-stimulating factor-1-deficient mice results in decreased tubular apoptosis during renal inflammation.

Kidney tubular epithelial cell (TEC) death may be dependent on the number and activation state of macrophages (M phi) during inflammation. Our prior studies indicate that activated M phi release soluble mediators that incite TEC death, and reducing intrarenal M phi during kidney disease diminishes TEC apoptosis. CSF-1 is required for M phi proliferation and survival. We hypothesized that in the absence of CSF-1, M phi-mediated TEC apoptosis would be prevented during renal inflammation. To test this hypothesis, we evaluated renal inflammation during unilateral ureter obstruction in CSF-1-deficient (Csf1(op)/Csf1(op)) mice. We detected fewer M phi and T cells and less apoptotic TEC in the obstructed kidneys of Csf1(op)/Csf1(op) mice compared with wild-type (WT) mice. The decrease in intrarenal M phi resulted from diminished recruitment and proliferation, not enhanced apoptosis. CSF-1 enhanced M phi activation. There were far fewer activated (CD69, CD23, Ia, surface expression) M phi in obstructed CSF-1-deficient compared with WT obstructed kidneys. Similarly, bone marrow M phi preincubated with anti-CSF-1 receptor Ab or anti-CSF-1 neutralizing Ab were resistant to LPS- and IFN-gamma-induced activation. We detected fewer apoptotic-inducing molecules (reactive oxygen species, TNF-alpha, inducible NO synthase) in 1) M phi propagated from obstructed Csf1(op)/Csf1(op) compared with WT kidneys, and 2) WT bone marrow M phi blocked with anti-CSF-1 receptor or anti-CSF-1 Ab compared with the isotype control. Furthermore, blocking CSF-1 or the CSF-1 receptor induced less TEC apoptosis than the isotype control. We suggest that during renal inflammation, CSF-1 mediates M phi recruitment, proliferation, activation, and, in turn, TEC apoptosis.