Cultured mesangial cells from autoimmune MRL-lpr mice have decreased secreted and surface M-CSF

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.

Nephritogenic cytokines and disease in MRL-Fas(lpr) kidneys are dependent on multiple T-cell subsets

BACKGROUND

Renal parenchymal cells produce cytokines, colony-stimulating factor-1 (CSF-1), granulocyte-macrophage colony-stimulating factor (GM-CSF), and tumor necrosis factor-alpha (TNF-alpha), which recruit autoreactive T cells and, in turn, elicit renal injury in MRL-Fas(lpr) mice.

METHODS

To determine whether select T-cell populations regulate intrarenal nephritogenic cytokines (CSF-1, GM-CSF, and TNF-alpha) and renal disease, we compared MRL-Fas(lpr) mice that are genetically deficient in T-cell receptor (TCR) alpha beta T cells, CD4 T cells, and major histocompatibility complex class I (MHC class I), lacking CD8 and double negative (DN) T cells, with wild-type mice. To identify the T cells instrumental in downstream (effector) events, we delivered CSF-1 or GM-CSF into the kidney via gene transfer in these select T-cell-deficient and wild-type strains.

RESULTS

Intrarenal CSF-1, GM-CSF, and TNF-alpha were absent or dramatically reduced in TCR alpha beta, CD4, and class I-deficient MRL-Fas(lpr) strains as compared with wild-type mice. In addition, the decrease in CSF-1, GM-CSF, and TNF-alpha was associated with a reduced kidney leukocytic infiltrates and spontaneous autoimmune nephritis. Intrarenal ex vivo retroviral gene transfer of CSF-1 and GM-CSF failed to elicit nephritis in these T-cell-deficient MRL strains (TCR alpha beta, CD4, CD8/DN) as compared with wild-type mice.

CONCLUSIONS

Multiple T-cell populations initiate renal disease by increasing intrarenal nephritogenic cytokines, CSF-1, GM-CSF, and TNF-alpha. CSF-1 and GM-CSF recruit additional CD4 and CD8 and DN T cells, which augment downstream events, resulting in progressive autoimmune renal disease. We suggest that MRL-Fas(lpr) kidney disease is driven by a T-cell amplification feedback loop dependent on multiple T-cell populations.

Gene transfer of RANTES elicits autoimmune renal injury in MRL-Fas(1pr) mice

We report that the beta-chemokine RANTES, a chemoattractant for macrophages and T cells, is up-regulated in the MRL-Fas(1pr) kidney prior to injury, but not normal kidneys (MRL-++, C3H-++) and increases with progressive injury. Furthermore, we establish an association between RANTES expression in the kidney and renal damage using a gene transfer approach. Tubular epithelial cells genetically modified to secrete RANTES infused under the renal capsule incites interstitial nephritis in MRL-Fas(1pr), but not MRL-++ or C3H-++ mice. RANTES recruits predominantly macrophages (M phi) and CD4+ and CD8+ T cells. In contrast, gene transfer of CSF-1, another molecule up-regulated simultaneously with RANTES in MRL-Fas(1pr) kidneys, promotes the influx of M phi, CD4+ T cells and the unique double-negative (DN) T cells (CD4-, CD8-), which are prominent in diseased MRL-Fas(1pr) kidneys. Thus, RANTES and CSF-1 recruit distinct T cell populations into the MRL-Fas(1pr) kidney. In addition, delivery of RANTES and CSF-1 into the kidney of MRL-Fas(1pr) mice causes an additive increase in pathology. We suggest that the complementary recruitment of T cell populations by RANTES (CD4, CD8) and CSF-1 (CD4, DN) promotes autoimmune nephritis in MRL-Fas(1pr) mice.

Systemic autoimmune nephritogenic components induce CSF-1 and TNF-alpha in MRL kidneys

MRL-Faslpr mice are an appealing strain to understand the importance of cytokines in the pathogenesis of autoimmune renal destruction, since injury is rapid and predictable. Colony stimulating factor 1 (CSF-1) and tumor necrosis factor alpha (TNF-alpha) are detected in the kidney and circulation prior to renal injury and continue to increase with progressive renal damage in MRL-Faslpr, Fas deficient mice, but not the congenic Fas intact MRL-(++) strain. Delivery of CSF-1, but not TNF-alpha, into the kidney via gene transfer incites local renal injury. By comparison, dual gene transfer of CSF-1 and TNF-alpha incites autoimmune renal injury that is far more severe than CSF-1 alone. The purpose of this study was to establish whether CSF-1 and TNF-alpha incites autoimmune renal injury that is far more severe than CSF-1 alone. The purpose of this study was to establish whether CSF-1 and TNF-alpha expression in the kidney of MRL-Faslpr mice induced by a circulating stimulant resulted from a primary defect in the kidney. Therefore, we transplanted (Tx) a MRL-(++) kidney without CSF-1, TNF-alpha and renal injury into an MRL-Faslpr recipient after removing nephritic kidney expressing CSF-1 and TNF-alpha. The Tx kidneys were examined after 2, 4, 5, 6, and 12 weeks. CSF-1 and TNF-alpha were rapidly induced in the MRL-(++) Tx kidney. CSF-1 and TNF-alpha were evident by two weeks and continually increased for 12 weeks post-transplantation. Within several weeks, the rapid expansion of M phi and T cells and induction of glomerulonephritis and interstitial nephritis in the MRL-(++) Tx kidney was similar to the age-matched native MRL-Faslpr kidney. In conclusion, we have constructed an experimental transplantation system that can explore whether cytokine expression in the kidney induced by a circulating stimulant is a result of a primary defect in the kidney. Using this approach, we established that the MRL-Faslpr kidney is not defective, but rather a circulating stimulant in the MRL-Faslpr mouse can induce CSF-1, TNF-alpha and renal injury in a normal MRL-(++) kidney. Thus, we exclude an intrinsic defect in the MRL-Faslpr kidney as the pathogenic mechanism responsible for tissue damage. We suggest purging the circulation of molecules that induce CSF-1 and TNF-alpha as a therapeutic strategy for autoimmune renal injury.

Transplant approach establishes that kidneys are responsible for serum CSF-1 but require a stimulus in MRL-lpr mice

Colony stimulating factor-1 (CSF-1) is a chemoattractant and growth factor for macrophages. In autoimmune MRL-lpr mice, CSF-1 is detected in the circulation and there is an increase in CSF-1 transcripts and macrophages in the kidney. The purpose of this study was to establish whether the MRL-lpr kidney is responsible for increasing serum CSF-1, and to determine if the expression of CSF-1 requires a circulating component in MRL-lpr mice. We transplanted a MRL-lpr kidney with nephritis [serum CSF-1 = 32.6 +/- 5.1 colony forming units (CFU)] into a bilaterally nephrectomized normal MRL-++ recipient. Circulating CSF-1 increased from 1.2 +/- CFU to 14.1 +/_ 5.6 CFU in recipients by one week. Continuous production of CSF-1 required a stimulating component since: (1) CSF-1 in the kidney and circulation disappeared several weeks after engraftment into MRL-++ mice and (2) isolated glomeruli from MRL-lpr required stimulation to express CSF-1. In the transplanted MRL-lpr kidney, hypercellularity in the glomerulus and interstitium (predominantly macrophages) returned to normal as rapidly as two weeks after engraftment into MRL-++. Thus, this study establishes that the kidney is responsible for circulating CSF-1 in MRL-lpr mice. Without the autoimmune environment CSF-1, macrophages, but not T cells, disappear and nephritis resolves.

Dysregulated cytokine expression in vivo in prediseased and diseased autoimmune-prone MRL mice

Macrophages (mø) from prediseased autoimmune-prone MRL/ + and MRL/lpr mice produce markedly decreased levels of IL-1 in vitro in response to LPS. In contrast, tissues from diseased MRL/lpr mice overexpress IL-1 in vivo. To determine whether IL-1 underproduction in the MRL strains is solely an in vitro phenomenon, we compared in vivo cytokine mRNA expression from prediseased age-matched MRL/ + and MRL/lpr mice to that from normal BALB/c and C3HeB/FeJ mice. Like mø in vitro, whole organ RNA from the spleen, liver, and kidney of MRL/ + and MRL/lpr mice showed down-regulation of IL-1 RNA following intraperitoneal injection of LPS. This abnormality in inducible IL-1 expression was present in all MRL mice, irrespective of disease stage or the presence of the lpr gene. On the other hand, only diseased MRL/lpr mice displayed elevated and constitutive expression of IL-1 in their livers and kidneys. We suggest that inducible expression is most indicative of the intrinsic, or genetic, capacity of cells to produce cytokine, whereas constitutive expression reflects extracellular disease-related inflammatory stimuli present only in the diseased MRL/lpr strains. By restricting our studies to prediseased MRL mice, we have tried to eliminate the effects of disease and to focus on the predisposing genetic background. The existence both in vitro and in vivo of a defect in inducible IL-1 expression by prediseased MRL mice suggests that the molecular abnormality underlying this defect may be a part of this predisposing background to autoimmunity.

Low-density lipoprotein stimulates the expression of macrophage colony-stimulating factor in glomerular mesangial cells

Disordered lipoprotein metabolism and the enhanced influx and accumulation of circulating mononuclear leukocytes into vascular tissue are common pathobiological phenomena associated with both atherosclerosis and glomerulosclerosis. Since atherogenic lipoproteins (such as low density lipoprotein, LDL) have been implicated in monocyte migration and proliferation into the glomerular mesangium, we examined the effect of LDL on mesangial cell expression of macrophage colony-stimulating factor (M-CSF), a cytoregulatory peptide associated with monocyte chemoattraction, differentiation and proliferation. Mesangial cell M-CSF gene expression, protein synthesis and secretion, and its biological activity to induce progenitor colony formation and monocyte proliferation were studied in murine mesangial cells. Incubation of either primary cultures or SV-40 transformed murine mesangial cells with LDL (0 to 200 micrograms/ml) induced M-CSF steady-state mRNA expression, in a dose-dependent manner (52 to 183% of control) when Northern blots were analyzed quantitatively by densitometric scanning. Similarly, Western blot analysis showed that LDL-activated SV-40 transformed mesangial cells increased M-CSF protein synthesis and secretion in a dose-dependent manner. The conditioned media obtained by incubating mesangial cells with LDL induced bone marrow progenitor colony formation that could be inhibited by specific neutralizing antibodies against murine M-CSF. Finally, the biological activity of M-CSF secreted by LDL-activated mesangial cells was further confirmed by its enhanced ability to induce monocyte proliferation. These data indicate that LDL, by activating mesangial cells to induce M-CSF and possibly other monocyte chemoattractants, may regulate the migration and proliferation of cells of mononuclear leukocytic origin into the mesangium supporting a pathobiological role for LDL in glomerular injury.

Is the osteopetrotic (op/op mutant) mouse completely deficient in expression of macrophage colony-stimulating factor?

The op/op mouse has a mutation in the macrophage colony-stimulating (CSF-1) gene. The phenotype of gross deficiency in the macrophage and osteoclast lineages corrects significantly with age, suggesting that other factors can substitute for CSF-1. This review examines the evidence that the op/op mouse is completely CSF-1 deficient and considers the possibility that alternative splicing within the CSF-1 gene might bypass the mutation, yielding an incompletely penetrant phenotype.

Abnormal splenic and thymic IL-4 and TNF-alpha expression in MRL-lpr/lpr mice

The MRL-lpr/lpr and MRL-(++) mice were studied for the expression of cytokines in the spleen, lymph node, thymus, kidney and brain through the reverse transcription-polymerase chain reaction (RT-PCR). The frequencies of IL-4 and TNF-alpha expression in the thymus and spleen were significantly higher in MRL-lpr/lpr mice than in MRL-(++) mice from the age of 17 to 32 weeks. More importantly, IL-4 transcript was demonstrated in the early rather than in the terminal stage of the lupus disease. At the 20th week, MRL-lpr/lpr mice with active disease exhibited higher concentrations of IL-1 alpha, IL-6 and TNF-alpha in serum than MRL-(++) mice. Interestingly, in MRL-lpr/lpr but not MRL-(++) mice, the IL-6 concentration in cultured supernatants of the thymic cells was significantly higher than that of the splenic or lymph node cells. On the other hand, IL-6 and IL-1 beta were expressed in the brain and kidney of MRL-lpr/lpr mice but not of MRL-(++) mice. Cultured MRL-lpr/lpr mesangial cells could also express IL-6 but to a lesser extent. These results suggest that the abnormal splenic and thymic IL-4 and TNF-alpha expression may predispose the development of autoimmune reactions. The expression of IL-1 beta and IL-6 in the brain and kidney may be implicated in the damage of these two organs in MRL-lpr/lpr mice.

Biosynthesis of colony-stimulating factor-1 (CSF-1) by mesangial cells of autoimmune mice

The amounts of colony-stimulating factor (CSF-1) produced by the mesangial cells of the kidney may be of pivotal importance in determining the outcome of nephritis, since CSF-1 activates macrophages, and macrophages have been shown to perform an important scavenger function in removing immune complexes which localize in the kidney. To test this hypothesis, the present study examined CSF-1 production by mesangial cells of the autoimmune MRL/MpJ-lpr-lpr strain of mice and also of their normal congenic MRL/MpJ-++ counterparts. It was found that mesangial cells of autoimmune mice produced diminished amounts of functional CSF-1 when measured by a bioassay, giving validation to the hypothesis proposed. Of interest, expression of CSF-1 mRNA was discordantly increased in mesangial cells of the MRL-lpr autoimmune mice. Based on current knowledge of the pathway for CSF-1 synthesis and secretion, it would appear that there may be a block in the post-transcriptional pathway for CSF-1 biosynthesis in autoimmune mesangial cells.