Macrophage Growth Factors Introduced into the Kidney Initiate Renal Injury

Improving Molecular Therapy in the Kidney

Mutations in approximately 80 genes have been implicated as the cause of various genetic kidney diseases. However, gene delivery to kidney cells from the blood is inefficient because of the natural filtering functions of the glomerulus, and research into and development of gene therapy directed toward kidney disease has lagged behind as compared with hepatic, neuromuscular, and ocular gene therapy. This lack of progress is in spite of numerous genetic mouse models of human disease available to the research community and many vectors in existence that can theoretically deliver genes to kidney cells with high efficiency. In the past decade, several groups have begun to develop novel injection techniques in mice, such as retrograde ureter, renal vein, and direct subcapsular injections to help resolve the issue of gene delivery to the kidney through the blood. In addition, the ability to retarget vectors specifically toward kidney cells has been underutilized but shows promise. This review discusses how recent advances in gene delivery to the kidney and the field of gene therapy can leverage the wealth of knowledge of kidney genetics to work toward developing gene therapy products for patients with kidney disease.

Unraveling the Role of Inflammation in the Pathogenesis of Diabetic Kidney Disease

Diabetic kidney disease (DKD) remains the leading cause of end-stage renal disease (ESRD) and is therefore a major burden on the healthcare system. Patients with DKD are highly susceptible to developing cardiovascular disease, which contributes to increased morbidity and mortality rates. While progress has been made to inhibit the acceleration of DKD, current standards of care reduce but do not eliminate the risk of DKD. There is growing appreciation for the role of inflammation in modulating the process of DKD. The focus of this review is on providing an overview of the current status of knowledge regarding the pathologic roles of inflammation in the development of DKD. Finally, we summarize recent therapeutic advances to prevent DKD, with a focus on the anti-inflammatory effects of newly developed agents.

Rho-kinase regulation of TNF-α-induced nuclear translocation of NF-κB RelA/p65 and M-CSF expression via p38 MAPK in mesangial cells

The small GTPase Rho and its downstream effector, Rho-associated coiled-coil containing protein kinase (Rho-kinase), regulate a number of cellular processes, including organization of the actin cytoskeleton, cell adhesion, and migration. While pharmacological inhibitors of Rho-kinase signaling are known to block renal inflammation, the molecular basis for this effect is unclear. Here, we provide evidence that proinflammatory TNF-α promotes mesangial expression of macrophage colony-stimulating factor (M-CSF), a key regulator for the growth and differentiation of mononuclear phagocytes, in a Rho-kinase-dependent manner. Consistent with this observation, TNF-α-mediated renal expression of M-CSF in insulin-resistant db/db mice was downregulated by Rho-kinase inhibition. Small interfering RNA-facilitated knockdown of Rho-kinase isoforms ROCK1 and ROCK2 indicated that both isoforms make comparable contributions to regulation of M-CSF expression in mesangial cells. From a mechanistic standpoint, Western blotting and EMSA showed that Rho-kinase and its downstream target p38 MAPK regulate nuclear translocation of NF-κB RelA/p65 and subsequent DNA binding activity, with no significant effects on IκBα degradation and RelA/p65 phosphorylation. Moreover, we showed that Rho-kinase-mediated cytoskeletal organization is required for the nuclear uptake of RelA/p65. Collectively, these findings identify Rho-kinase as a critical regulator of chemokine expression and macrophage proliferation.

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.

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.

Coordinate regulation of tissue macrophage and dendritic cell population dynamics by CSF-1

CSF-1 drives the homeostatic expansion of macrophages within the growing myometrium of pregnant mice by stimulating in situ proliferation and inducing monocyte precursor recruitment from the blood.

Tissue macrophages (Mϕs) and dendritic cells (DCs) play essential roles in tissue homeostasis and immunity. How these cells are maintained at their characteristic densities in different tissues has remained unclear. Aided by a novel flow cytometric technique for assessing relative rates of blood-borne precursor recruitment, we examined Mϕ and DC population dynamics in the pregnant mouse uterus, where rapid tissue growth facilitated a dissection of underlying regulatory mechanisms. We demonstrate how Mϕ dynamics, and thus Mϕ tissue densities, are locally controlled by CSF-1, a pleiotropic growth factor whose in situ level of activity varied widely between uterine tissue layers. CSF-1 acted in part by inducing Mϕ proliferation and in part by stimulating the extravasation of Ly6C^hi monocytes (Mos) that served as Mϕ precursors. Mo recruitment was dependent on the production of CCR2 chemokine receptor ligands by uterine Mϕs in response to CSF-1. Unexpectedly, a parallel CSF-1–regulated, but CCR2-independent pathway influenced uterine DC tissue densities by controlling local pre-DC extravasation rates. Together, these data provide cellular and molecular insight into the regulation of Mϕ tissue densities under noninflammatory conditions and reveal a central role for CSF-1 in the coordination of Mϕ and DC homeostasis.

Macrophages in renal development, injury, and repair

Macrophages have long been regarded as classic mediators of innate immunity because of their production of proinflammatory cytokines and their ability to induce apoptotic cell death. As a result of such activities and the detrimental long-term effect of kidney inflammation, macrophages principally have been regarded as mediators of glomerular damage, tubular cell death, and the downstream fibrotic events leading to chronic kidney disease. Although this has been the accepted consequence of macrophage infiltration in kidney disease, macrophages also play a critical role in normal organ development, cell turnover, and recovery from injury in many organs, including the kidney. There is also a growing awareness that there is considerable heterogeneity of phenotype and function within the macrophage population and that a greater understanding of these different states of activation may result in the development of therapies specifically designed to capitalize on this variation in phenotype and cellular responses. In this review, we discuss the current understanding of induction and consequences of classic versus alternative macrophage activation and highlight what additional therapeutic options this may provide for the management of both acute and chronic kidney disease as well as renal cancer.

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.

Pathogenic role of NF-kappaB activation in tubulointerstitial inflammatory lesions in human lupus nephritis

In vitro and in vivo experimental studies suggest that the transcription factor NF-kappaB plays a role in tubulointerstitial injury. We investigated possible cellular and molecular mechanisms involving NF-kappaB activation in the progression of tubulointerstitial lesions in human lupus nephritis (LN). Paraffin-embedded renal biopsies from 50 patients with LN and six control patients with minimal change disease (MCD) were examined by Southwestern histochemistry for in situ detection of active NF-kappaB and AP-1. Immunohistochemistry was performed to examine the expression of NF-kappaB, AP-1, and NF-kappaB regulatory proteins (IkappaB-alpha, p-IkappaB-alpha, and IKK-alpha proteins), as well as NF-kappaB and AP-1 downstream target proinflammatory molecules (ICAM-1, TNF-alpha, IL-1beta, IL-6, and GM-CSF) and NF-kappaB upstream signaling molecules (CD40 and CD40L). We observed extensive upregulation of activated NF-kappaB in renal tubular cells and interstitial cells, in parallel with overactivation of transcription factor AP-1 in LN, as compared with normal controls and MCD. Tubular expression of activated NF-kappaB correlated well with the degree of tubulointerstitial histopathological indices and/or renal function. Tubulointerstitial IKK-alpha expression was specifically upregulated in LN. IkappaB-alpha and p-IkappaB-alpha were detected only in interstitial cells in LN. Tubulointerstitial expression levels of NF-kappaB and AP-1 downstream inflammatory molecules and NF-kappaB upstream signaling molecules CD40 and CD40L were markedly enhanced in LN as compared with MCD or normal controls and were associated with tubulointerstitial histopathological indices and/or renal function. The results suggest that altered IKK-alpha expression and NF-kappaB activation along with AP-1 overexpression may play a pathogenic role in tubulointerstitial injury in human LN mediated through a network of downstream proinflammatory molecules.

Leukocyte-renal epithelial cell interactions regulate lupus nephritis

Renal disease is the major cause of morbidity in patients with lupus. MRL-Fas(lpr) mice share features with human lupus. The tempo, predictability, and homogeneous expression of disease in MRL-Fas(lpr) mice make them an excellent tool to probe the pathogenesis of lupus nephritis and to identify therapeutic targets. This article focuses on the concepts that renal parenchymal cells are active participants that regulate immune responses in the kidney, and that the interaction between parenchymal cells and leukocytes (macrophages, T cells) determine whether the kidney is protected or destroyed during lupus nephritis. In particular we review the role of macrophages, fueled by the principal macrophage developmental molecule, colony stimulating factor-1, in lupus nephritis, and we review T cells and costimulatory pathways and the interaction of these leukocytes with renal parenchymal cells that regulate lupus nephritis.

Circulating Immune Complexes (IC) and IC-Induced Levels of GM-CSF Are Increased in Sudanese Patients with Acute VisceralLeishmania donovaniInfection Undergoing Sodium Stibogluconate Treatment: Implications for Disease Pathogenesis

Infection with Leishmania donovani is associated with IL-10 as well as with GM-CSF. Immune complexes (IC) exert important functions by stimulation of monocytes/macrophage-mediated production of pro- and anti-inflammatory cytokines in rheumatic diseases. In this investigation, we have explored IC-induced cytokine production during Leishmania infection. Sera from 43 patients with visceral leishmaniasis (VL), 17 patients with post-kala-azar dermal leishmaniasis, and 20 healthy Sudanese controls were precipitated with polyethylene glycol (PEG). The PEG precipitates were added to serum-free PBMC for 20 h,whereupon supernatant levels of IL-1beta, IL-6, IL-10, IL-1 receptor antagonist protein, TNF-alpha, TNF receptor p75, and GM-CSF were investigated using ELISA. Circulating levels of C1q-binding IC were also measured in the serum samples. PEG precipitates from Leishmania-infected patients induced significantly higher levels of GM-CSF (p = 0.0037) and IL-10 (p < 0.0001), as well as of IL-6 (p < 0.0001) and IL-1 receptor antagonist (p = 0.0238) as compared with PEG precipitates from controls. Patients with acute VL as well as VL patients receiving sodium stibogluconate treatment displayed significantly increased levels of PEG precipitate-induced GM-CSF. The induction of GM-CSF by circulating IC was especially prominent in acute VL patients receiving sodium stibogluconate treatment; ANOVA revealed significant interaction between disease activity and treatment for PEG precipitate-induced levels of GM-CSF (disease activity, p = 0.0006; treatment, p = 0.0005; interaction, p = 0.0046). Parallel associations were determined for C1q-binding immune complexes, but not for any cytokine other than GM-CSF. The importance of IC-induced GM-CSF in leishmaniasis warrants further study.

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.

TGF-beta1 induces IL-8 and MCP-1 through a connective tissue growth factor-independent pathway

Transforming growth factor-beta(1) (TGF-beta(1)) functions as an important immunomodulatory cytokine in human kidney. Evidence suggests that connective tissue growth factor (CTGF) is an important downstream mediator of the profibrotic effects of TGF-beta(1). However, the role of CTGF in TGF-beta(1)-induced chemokine production remains unknown. This study was undertaken to determine whether CTGF is involved in mediating TGF-beta(1)-induced chemokine production in renal proximal tubular (HK-2) cells. Interleukin-8 (IL-8) and macrophage chemoattractant protein-1 (MCP-1) were measured. TGF-beta(1) induced an increase in IL-8 and MCP-1 (both P < 0.05) compared with control levels. CTGF was effectively silenced using small interference RNA (siRNA) in HK-2 cells. RT-PCR and real-time PCR confirmed a 94% reduction in CTGF mRNA. In the CTGF-silenced cells, TGF-beta(1)-stimulated IL-8 and MCP-1 secretion was not altered compared with control cells. Similarly, basal secretion of IL-8 and MCP-1 was not changed in CTGF-silenced cells. The direct effect of CTGF (20, 200, and 400 ng/ml) on IL-8 and MCP-1 was assessed at 24-, 48-, and 72-h time points and no stimulation was observed. Our studies further demonstrate that in the CTGF gene-silenced cells, CTGF partially mediates TGF-beta(1)-induced fibronectin and collagen IV secretion. These data suggest that TGF-beta(1) induced IL-8 and MCP-1 via CTGF-independent pathway. TGF-beta mediates both fibrosis and chemokine production in the proximal tubule of the kidney. However, CTGF plays a more specific role as a downstream mediator of TGF-beta(1)-induced fibrosis.

The renal papilla is a niche for adult kidney stem cells

Many adult organs contain stem cells, which are pluripotent and are involved in organ maintenance and repair after injury. In situ, these cells often have a low cycling rate and locate in specialized regions (niches). To detect such cells in the kidney, we administered a pulse of the nucleotide bromodeoxyuridine (BrdU) to rat and mouse pups and, after a long (more than 2-month) chase, examined whether the kidney contained a population of low-cycling cells. We found that in the adult kidney, BrdU-retaining cells were very sparse except in the renal papilla, where they were numerous. During the repair phase of transient renal ischemia, these cells entered the cell cycle and the BrdU signal quickly disappeared from the papilla, despite the absence of apoptosis in this part of the kidney. In vitro isolation of renal papillary cells showed them to have a plastic phenotype that could be modulated by oxygen tension and that when injected into the renal cortex, they incorporated into the renal parenchyma. In addition, like other stem cells, papillary cells spontaneously formed spheres. Single-cell clones of these cells coexpressed mesenchymal and epithelial proteins and gave rise to myofibroblasts, cells expressing neuronal markers, and cells of uncharacterized phenotype. These data indicate that the renal papilla is a niche for adult kidney stem cells.

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.

Approaches and methods in gene therapy for kidney disease

Renal gene therapy may offer new strategies to treat diseases of native and transplanted kidneys. Several experimental techniques have been developed and employed using nonviral, viral, and cellular vectors. The most efficient vector for in vivo transfection appears to be adenovirus. Glomeruli, blood vessels, interstitial cells, and pyelum can be transfected with high efficiency. In addition, electroporation and microbubbles with ultrasound, both being enhanced naked plasmid techniques, offer good opportunities. Trapping of mesangial cells into the glomeruli as well as natural targeting of monocytes or macrophages to inflamed kidneys are elegant methods for site-specific delivery of genes. For gene therapy in kidney transplantation, hemagglutinating virus of Japan liposomes are efficient vectors for tubular transfection, whereas enhanced naked plasmid techniques are suitable for glomerular transfection. However, adenovirus offers the best opportunities in a renal transplantation setup because varying parameters of graft perfusion allows targeting of different cell types. In renal grafts, lymphocytes can be used for selective targeting to sites of inflammation. In conclusion, for both in vivo and ex vivo renal transfection, enhanced naked plasmids and adenovirus offer the best perspectives for effective clinical application. Moreover, the development of safer, nonimmunogenic vectors and the large-scale production could make clinical renal gene therapy a realistic possibility for the near future.

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.

p38 Mitogen-activated protein kinase contributes to autoimmune renal injury in MRL-Fas lpr mice

The phosphorylation of p38 mitogen-activated protein kinase (MAPK) is responsible for the production and signal transduction of cytokines and chemokines. This study hypothesized that p38 MAPK activation is required for spontaneous autoimmune renal injury in MRL-Fas(lpr) mice, resembling human lupus erythematosus. FR167653, a specific inhibitor of p38 MAPK, is orally administrated from 3 or 4 mo of age in MRL-Fas(lpr) mice (at doses of 10 or 32mg/kg per day) until 6 mo of age. The phosphorylated p38 MAPK in kidneys of MRL-Fas(lpr) mice was evaluated. The number of phosphorylated p38 MAPK-positive cells was increased in diseased kidneys. The daily oral administration of FR167653 decreased p38 MAPK phosphorylation in kidneys, especially in a group of mice administered FR167653 (32 mg/kg per day) daily from 3 to 6 mo of age. FR167653 reduced the accumulation of macrophages and T cell and prevented kidney pathology, resulting in prolonged survival. In addition, FR167653 reduced expression of MCP-1 and TNF-alpha in the diseased kidneys and cultured tubular epithelial cells. Furthermore, FR167653 decreased IgG levels in the diseased kidneys and circulation. These results suggest that the phosphorylation of p38 MAPK is required for the pathogenesis of renal injury in MRL-Fas(lpr) mice followed by subsequent expression of renal cytokine/chemokine and IgG production. This study provides evidence that the regulation of p38 MAPK is a novel target for the therapy of renal injury in systemic lupus erythematosus.

Macrophage colony-stimulating factor expression and macrophage accumulation in renal allograft rejection

BACKGROUND

Studies of infiltrating cells from acutely rejecting renal allografts show that a high proportion of these cells are macrophages, and early macrophage infiltration is a poor prognostic sign for transplant survival. Macrophage colony-stimulating factor (M-CSF), produced by tubular and mesangial cells, has been associated with macrophage infiltration and proliferation in experimental and human kidney diseases. We investigated the expression of M-CSF in a model of acute rejection.

METHODS

Lewis rats underwent bilateral nephrectomies and received an orthotopic Dark Agouti allograft or Lewis isograft. Animals received cyclosporine (10 mg/kg/day) from day 0 to day 3 and were killed at days 4, 8, or 14 after transplantation. Macrophages (ED1+) and T cells (W3-13+) were identified by immunohistochemistry, and M-CSF expression was identified by Northern blotting and in situ hybridization.

RESULTS

Isografts had normal renal function without histological evidence of rejection. Allografts exhibited a moderate infiltrate at day 4 but progressed to severe rejection at day 14, with elevated serum creatinine level and severe tubulointerstitial damage. Macrophages and T cells were present in equal proportion in the infiltrate at day 4. At day 14, the number of macrophages increased fivefold (2580/mm2), although T cells were unchanged (380/mm2). Proliferating macrophages (ED1+, BrdU+) increased from day 4 (4%) to day 14 (10%). M-CSF mRNA expression was strongly up-regulated in allografts compared with isografts and normal rat. In situ hybridization demonstrated M-CSF expression by resident and infiltrating cells. Renal tubular expression was minimally increased at day 4 but strongly up-regulated at day 14 (more than 50% of tubules positive), particularly in areas of tubular damage. Tubular M-CSF expression colocalized with areas of intense macrophage infiltration and proliferation. Serial sections with double labeling demonstrated that T cells were the dominant source of M-CSF at day 4, yet later in the rejection (day 14) the predominant sites of production were both renal tubular cells and interstitial macrophages.

CONCLUSIONS

Renal production of M-CSF by graft-infiltrating (macrophages and T lymphocytes) and resident (tubular) cells was up-regulated during acute rejection. M-CSF promotes macrophage recruitment and proliferation and may thereby play a pathogenic role in acute rejection. The kinetics of M-CSF production during acute rejection suggest that local macrophage proliferation may be initiated by T cells and perpetuated by both renal tubular and autocrine release.

The requirement for granulocyte-macrophage colony-stimulating factor and granulocyte colony-stimulating factor in leukocyte-mediated immune glomerular injury

Proliferative glomerulonephritis in humans is characterized by the presence of leukocytes in glomeruli. Granulocyte-macrophage colony-stimulating factor (GM-CSF) and granulocyte colony-stimulating factor (G-CSF) can potentially stimulate or affect T cell, macrophage, and neutrophil function. To define the roles of GM-CSF and G-CSF in leukocyte-mediated glomerulonephritis, glomerular injury was studied in mice genetically deficient in either GM-CSF (GM-CSF -/- mice) or G-CSF (G-CSF -/- mice). Two models of glomerulonephritis were studied: neutrophil-mediated heterologous-phase anti-glomerular basement membrane (GBM) glomerulonephritis and T cell/macrophage-mediated crescentic autologous-phase anti-GBM glomerulonephritis. Both GM-CSF -/- and G-CSF -/- mice were protected from heterologous-phase anti-GBM glomerulonephritis compared with genetically normal (CSF WT) mice, with reduced proteinuria and glomerular neutrophil numbers. However, only GM-CSF -/- mice were protected from crescentic glomerular injury in the autologous phase, whereas G-CSF -/- mice were not protected and in fact had increased numbers of T cells in glomeruli. Humoral responses to the nephritogenic antigen were unaltered by deficiency of either GM-CSF or G-CSF, but glomerular T cell and macrophage numbers, as well as dermal delayed-type hypersensitivity to the nephritogenic antigen, were reduced in GM-CSF -/- mice. These studies demonstrate that endogenous GM-CSF plays a role in experimental glomerulonephritis in both the autologous and heterologous phases of injury.

Tubules are the major site of M-CSF production in experimental kidney disease: correlation with local macrophage proliferation

BACKGROUND

Local proliferation of macrophages occurs within both the glomerulus and the interstitium in severe forms of human and experimental glomerulonephritis and plays an important role in amplifying renal injury. Macrophage colony-stimulating factor (M-CSF) is thought to be the growth factor driving this local macrophage proliferation. Previous studies have found that glomeruli are the predominant source of M-CSF production. However, this is difficult to reconcile with the prominent macrophage accumulation and proliferation seen in the interstitial compartment in glomerulonephritis. To address this issue, we localized M-CSF expression in rat models of glomerular versus tubulointerstitial injury and examined its relationship to local macrophage proliferation.

METHODS

M-CSF expression (Northern blotting, in situ hybridization, immunostaining, Western blotting) and local macrophage proliferation (double immunostaining) was examined in normal rat kidney on days 1 and 14 of rat anti-glomerular basement membrane (anti-GBM) glomerulonephritis and on day 5 following unilateral ureteric obstruction.

RESULTS

M-CSF mRNA and protein expression were identified in small numbers of glomerular podocytes, approximately 25% of cortical tubules, and most medullary tubules in normal rat kidney. Northern blotting showed a significant increase in whole kidney M-CSF mRNA in rat anti-GBM glomerulonephritis. Up-regulation of glomerular and, most prominently, tubular M-CSF production was confirmed by three independent methods: in situ hybridization, immunostaining, and Western blotting. The increase in M-CSF expression colocalized with local macrophage proliferation (ED1+PCNA+ cells) in both the glomerulus and tubulointerstitium. On day 5 after ureter ligation, there was a significant increase in tubular M-CSF mRNA and protein expression in the obstructed kidney, with no change in glomerular M-CSF. In parallel with M-CSF expression, macrophage accumulation and proliferation was prominent in the interstitium, but was absent from glomeruli.

CONCLUSIONS

The tubular epithelial cell is the major site of M-CSF production within the injured kidney. Indeed, substantial macrophage accumulation and local proliferation can occur in the tubulointerstitium in the absence of glomerular inflammation. These results suggest that M-CSF production within the kidney, particularly by tubular epithelial cells, plays an important role in regulating local macrophage proliferation in experimental kidney disease.

Local macrophage proliferation correlates with increased renal M-CSF expression in human glomerulonephritis

BACKGROUND

Macrophage accumulation is a prominent feature in many forms of glomerulonephritis. Local proliferation of macrophages within the kidney has been described in human and experimental glomerulonephritis and may have an important role in augmenting the inflammatory response. The current study examined the relationship between local macrophage proliferation and renal expression of macrophage colony-stimulating factor (M-CSF).

METHODS

A total of 118 renal biopsies of patients with a wide range of glomerulonephridities were examined for M-CSF protein and macrophage proliferation (KP1+PCNA+cells) by single and double immunohistochemistry staining, respectively.

RESULTS

Biopsies of thin membrane disease (TMD) with histologically normal kidney showed M-CSF protein expression by 33% of cortical tubules, while glomerular M-CSF expression was limited to resident macrophages and some podocytes. Glomerular M-CSF expression increased significantly in proliferative forms of glomerulonephritis, with M-CSF staining of infiltrating macrophages, podocytes and some mesangial cells. Segmental areas of strong M-CSF expression, particularly in crescents, co-localized with KP1+PCNA+ proliferating macrophages. There was also an increase in tubular M-CSF expression in most types of glomerulonephritis. Tubular M-CSF staining was strongest in areas of tubular damage and co-localized with KP1+ macrophages, including KP1+PCNA+ proliferating macrophages. Many interstitial macrophages and alpha-smooth muscle actin-positive myofibroblasts showed strong M-CSF staining. Statistical analysis showed a highly significant correlation between M-CSF expression and local macrophage proliferation in both the glomerulus and tubulointerstitium. Glomerular and tubular M-CSF expression gave a significant correlation with renal dysfunction.

CONCLUSIONS

Glomerular and tubulointerstitial M-CSF expression is up-regulated in human glomerulonephritis, being most prominent in proliferative forms of disease. This correlated with local macrophage proliferation, suggesting that increased renal M-CSF production plays an important role in regulating local macrophage proliferation in human glomerulonephritis.

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.

Costimulation by B7-1 and B7-2 is required for autoimmune disease in MRL-Faslpr mice

Autoimmune lupus nephritis is dependent on infiltrating autoreactive leukocytes and Igs. B7 costimulatory molecules (B7-1 and B7-2) provide signals essential for T cell activation and Ig class switching. In MRL-Faslpr mice, a model of human lupus, although multiple tissues are targeted for autoimmune injury, nephritis is fatal. We identified intrarenal B7-1 and B7-2 expression, restricted to kidney-infiltrating leukocytes, before and increasing with progressive nephritis in MRL-Faslpr mice. Thus, we hypothesized that the B7 pathway is required for autoimmune disease in MRL-Faslpr mice. To investigate the role of B7 costimulatory molecules in this autoimmune disease, we generated a MRL-Faslpr strain deficient in B7-1 and B7-2. Strikingly, MRL-Faslpr mice lacking both B7 costimulators do not develop kidney (glomerular, tubular, interstitial, vascular) pathology, or proteinuria, and survive far longer. Intrarenal downstream effector transcripts (IFN-gamma, IL-12, monocyte chemoattractant protein-1, CSF-1) linked to nephritis remained at normal levels compared with wild-type mice. Skin lesions and lymphoid enlargement characteristic of MRL-Faslpr mice were diminished in B7-1/B7-2-deficient MRL-Faslpr mice. B7-1/B7-2-deficient MRL-Faslpr mice did not develop leukocytic infiltrates, elevated serum IgG and isotypes (G1,G2b,G3), autoantibodies, and intrarenal IgG deposits. Our findings demonstrate that B7-1 and B7-2 costimulatory pathways are critical to the pathogenesis of autoimmune lupus.

Gene therapy for kidney disease

Gene therapy has distinct potential to treat disease at the most fundamental level. However, the ability to pursue gene therapy for renal disease has been limited by the availability of an adequate system for gene delivery to the kidney and for regulation of transgene expression. Presently, there are several limitations to overcome before clinical use of viral vector systems for targeting kidney can be considered. Non-viral vectors such as haemagglutinating virus of Japan (HVJ)-liposome mediated gene transfer and cationic liposome are promising but need to be improved. Given that the systemic delivery of the functional protein can serve as therapy for the renal diseases, skeletal muscle targeting gene therapy might be an alternative strategy for the treatment of renal disease. Gene therapy to the transplant kidney may potentially improve the graft outcome by reducing acute and chronic rejection. We review emerging strategies of gene transfer with reference to the kidney and discuss the potential application of gene therapy to renal diseases.

Gene transfer targeting interstitial fibroblasts by the artificial viral envelope-type hemagglutinating virus of Japan liposome method

BACKGROUND

Tubulointerstitial inflammation and fibrosis are commonly associated with most human glomerular diseases. The degree of tubulointerstitial damage, rather than the glomerular injury, could correlate with the degree of renal functional impairment and accurately predict long-term prognosis. In an effort to understand the pathogenesis of the progressive interstitial fibrosis, we developed a new strategy of gene transfer to the interstitial fibroblasts.

METHODS

Either fluorescein isothiocyanate (FITC)-labeled oligodeoxynucleotides (ODNs) or pEBAct-NlacF expression vector was introduced into the kidney of normal rats retrogradely via ureter by using the artificial viral envelope (AVE)-type hemagglutinating virus of Japan (HVJ) liposome method.

RESULTS

FITC-labeled ODNs were accumulated diffusely in the nuclei of the interstitial cells in the transfected kidney 10 minutes after transfection, and the interstitial cells were identified as interstitial fibroblasts by immunostaining with ER-TR7. To examine the gene expression in the interstitium, pEBAct-NlacF gene-conjugated HVJ liposome was injected retrogradely through the ureter, and in consequence, nuclear beta-galactosidase activity was continuously observed in interstitial cells at least two weeks after transfection.

CONCLUSION

This new strategy of gene transfer to the interstitial fibroblasts is useful for the investigation of the pathophysiology of tubulointerstitial lesion, and furthermore, it may be a promising new therapeutic method for the progression of interstitial fibrosis.

Monocyte chemoattractant protein 1-dependent leukocytic infiltrates are responsible for autoimmune disease in MRL-Fas(lpr) mice

Infiltrating leukocytes may be responsible for autoimmune disease. We hypothesized that the chemokine monocyte chemoattractant protein (MCP)-1 recruits macrophages and T cells into tissues that, in turn, are required for autoimmune disease. Using the MRL-Fas(lpr) strain with spontaneous, fatal autoimmune disease, we constructed MCP-1-deficient MRL-Fas(lpr) mice. In MCP-1-intact MRL-Fas(lpr) mice, macrophages and T cells accumulate at sites (kidney tubules, glomeruli, pulmonary bronchioli, lymph nodes) in proportion to MCP-1 expression. Deleting MCP-1 dramatically reduces macrophage and T cell recruitment but not proliferation, protects from kidney, lung, skin, and lymph node pathology, reduces proteinuria, and prolongs survival. Notably, serum immunoglobulin (Ig) isotypes and kidney Ig/C3 deposits are not diminished in MCP-1-deficient MRL-Fas(lpr) mice, highlighting the requirement for MCP-1-dependent leukocyte recruitment to initiate autoimmune disease. However, MCP-1-deficient mice are not completely protected from leukocytic invasion. T cells surrounding vessels with meager MCP-1 expression remain. In addition, downstream effector cytokines/chemokines are decreased in MCP-1-deficient mice, perhaps reflecting a reduction of cytokine-expressing leukocytes. Thus, MCP-1 promotes MRL-Fas(lpr) autoimmune disease through macrophage and T cell recruitment, amplified by increasing local cytokines/chemokines. We suggest that MCP-1 is a principal therapeutic target with which to combat autoimmune diseases.

IL-12 Drives IFN-γ-Dependent Autoimmune Kidney Disease in MRL-Fas lpr Mice

IL-12 is secreted by kidney tubular epithelial cells in autoimmune MRL-Faslpr mice before renal injury and increases with advancing disease. Because IL-12 is a potent inducer of IFN-γ, the purpose of this study was to determine whether local provision of IL-12 elicits IFN-γ-secreting T cells within the kidney, which, in turn, incites injury in MRL-Faslpr mice. We used an ex vivo retroviral gene transfer strategy to construct IL-12-secreting MRL-Faslpr tubular epithelial cells (IL-12 “carrier cells”), which were implanted under the kidney capsule of MRL-Faslpr mice before renal disease for a sustained period (28 days). IL-12 “carrier cells” generated intrarenal and systemic IL-12. IL-12 fostered a marked, well-demarcated accumulation of CD4, CD8, and double negative (CD4−CD8− B220+) T cells adjacent to the implant site. We detected more IFN-γ-producing T cells (CD4 &gt; CD8 &gt; CD4−CD8− B220+) at 28 days (73 ± 14%) as compared with 7 days (20 ± 8%) after implanting the IL-12 “carrier cells;” the majority of these cells were proliferating (60–70%). By comparison, an increase in systemic IL-12 resulted in a diffuse acceleration of pathology in the contralateral (unimplanted) kidney. IFN-γ was required for IL-12-incited renal injury, because IL-12 “carrier cells” failed to elicit injury in MRL-Faslpr kidneys genetically deficient in IFN-γ receptors. Furthermore, IFN-γ “carrier cells” elicited kidney injury in wild-type MRL-Faslpr mice. Taken together, IL-12 elicits autoimmune injury by fostering the accumulation of IFN-γ-secreting CD4, CD8, and CD4−CD8− B220+ T cells within the kidney, which, in turn, promote a cascade of events culminating in autoimmune kidney disease in MRL-Faslpr mice.

Gene transfer in the kidney

Gene transfer approaches offer the promise of revolutionizing medicine. In this review, we focus on the current and future prospects of somatic gene transfer into the kidney. The advantages and disadvantages of current vector systems are described, and the ex vivo and in vitro approaches applicable to the kidney are reviewed. We discuss uses of gene transfer approaches to dissect the pathogenesis of kidney disease and the future directions and applications of gene transfer to combat kidney destruction.

MRL/lpr and MRL+/+ Macrophage DNA Synthesis in the Absence and the Presence of Colony-Stimulating Factor-1 and Granulocyte-Macrophage Colony-Stimulating Factor

Macrophage accumulation and proliferation as well as altered macrophage properties have been observed in autoimmune MRL mice. To determine whether there might be innate differences in the proliferative responses, we examined the DNA synthesis responses of peritoneal macrophages and macrophages derived in vitro from bone marrow precursors (bone marrow-derived macrophages (BMM)). Murine peritoneal exudate macrophages normally require the addition of macrophage CSF (CSF-1) to enter cell cycle in vitro. In contrast, we have found that many thioglycollate-induced adherent peritoneal macrophages, but not resident peritoneal macrophages, from both MRL/lpr and MRL+/+ mice atypically underwent DNA synthesis even in the absence of added CSF-1. They also responded very well to granulocyte-macrophage CSF. These findings may help to explain the appearance of increased macrophage numbers in MRL lesions. In contrast to a previous report, it was found that MRL/lpr and MRL+/+ BMM did not have an enhanced response to CSF-1 and that modulation of CSF-1 receptor expression was not more rapid in MRL BMM. We also found no evidence for abnormal CSF-1 internalization and degradation or for the lpr mutation to have any enhanced effect on BMM survival in the absence of CSF-1. TNF-α lowered the DNA synthesis response to CSF-1 of MRL/lpr BMM rather than enhanced it, as has been reported. Our data suggest that the enhanced accumulation of macrophages in the MRL/lpr kidney cannot be explained by a proposed model of enhanced responsiveness of MRL/lpr BMM to CSF-1, including a contribution by TNF-α.

IFN-γ Receptor Signaling Is Essential for the Initiation, Acceleration, and Destruction of Autoimmune Kidney Disease in MRL-Fas lpr Mice

CSF-1 and TNF-α in the kidney of MRL-Faslpr mice are proximal events that precede and promote autoimmune lupus nephritis, while apoptosis of renal parenchymal cells is a feature of advanced human lupus nephritis. In the MRL-Faslpr kidney, infiltrating T cells that secrete IFN-γ are a hallmark of disease. To examine the impact of IFN-γ on renal injury in MRL-Faslpr mice, we constructed a IFN-γR-deficient strain. In MRL-Faslpr mice lacking IFN-γR, circulating and intrarenal CSF-1 were absent, TNF-α was markedly reduced, survival was extended, lymphadenopathy and splenomegaly were prevented, and the kidneys remained protected from destruction. Mesangial cells (MC) that were signaled through the IFN-γR induced CSF-1 and TNF-α in MRL-Faslpr mice. We detected a large number of apoptotic renal parenchymal cells in advanced nephritis and determined that signaling via the IFN-γR induces apoptosis of tubular epithelial cells (TEC), but not MC. By comparison, TNF-α induces apoptosis in MC, but not TEC, of the MRL-Faslpr strain. Thus, IFN-γ is directly and indirectly responsible for apoptosis of TEC and MC in MRL-Faslpr mice, respectively. In conclusion, IFN-γR signaling is essential for the initiation (CSF-1), acceleration (CSF-1 and TNF-α), and apoptotic destruction of renal parenchymal cells in MRL-Faslpr autoimmune kidney disease.

Local macrophage proliferation in human glomerulonephritis

BACKGROUND

Local macrophage proliferation has been described in several animal models of glomerulonephritis (GN), but its significance in human disease is unknown.

METHODS

Double immunostaining for CD68 and the proliferating cell nuclear antigen (PCNA) was used to identify macrophage proliferation in 84 biopsies from a variety of glomerulonephridities.

RESULTS

A small resident population of glomerular and interstitial CD68+ macrophages was identified in normal human kidney, of which only 1 to 2% showed evidence of proliferation on the basis of PCNA expression. A mild macrophage infiltrate, with only occasional proliferating macrophages, was seen in the less aggressive forms of GN (minimal change disease, non-IgA mesangioproliferative GN and IgA nephropathy). This was in sharp contrast to the more aggressive forms of disease (lupus class IV, vasculitis-associated GN, crescentic GN and mesangiocapillary proliferative GN), in which the prominent macrophage infiltrates contained many proliferating macrophages, accounting for 28 to 47% of the total macrophage population. Macrophage proliferation was largely restricted to areas of severe tissue damage (glomerular segmental proliferative lesions, crescents and foci of tubulointerstitial damage), suggesting that local proliferation is a mechanism for amplifying macrophage-mediated injury. Glomerular and interstitial macrophage proliferation gave a significant correlation with loss of renal function (P < 0.0001) and histologic lesions (P < 0.0001), but not with proteinuria. Interstitial T-cell proliferation also gave a significant correlation with loss of renal function and histologic damage, even though proliferation within the T-cell population was much lower than in the macrophage population.

CONCLUSIONS

This study demonstrates that macrophage proliferation is a feature of the more aggressive forms of human GN. Local proliferation may be an important mechanism for amplifying macrophage-mediated renal injury. In addition, the degree of local macrophage proliferation may be a useful diagnostic and prognostic indicator for human GN.

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.

IFN-γ Limits Macrophage Expansion in MRL-Fas lpr Autoimmune Interstitial Nephritis: A Negative Regulatory Pathway

IFN-γ is capable of enhancing and limiting inflammation. Therefore, an increase in IFN-γ in autoimmune MRL-Faslpr mice could exacerbate or thwart renal injury. We have established a retroviral gene transfer approach to incite interstitial nephritis in MRL-Faslpr mice that is rapid, enduring, and circumscribed. Renal tubular epithelial cells (TEC) were genetically modified to secrete macrophage (Mφ) growth factors (CSF-1-TEC, GM-CSF-1-TEC) and infused under the renal capsule. To determine the impact of IFN-γ in Mφ growth factor-incited renal injury, we constructed a MRL-Faslpr IFN-γ-receptor (IFN-γR)-deficient strain. Gene transfer of CSF-1 or GM-CSF incited more severe interstitial nephritis in IFN-γR-deficient than in IFN-γR-intact MRL-Faslpr mice, consisting of an increase of Mφ. To determine the mechanism responsible for the increase in Mφ in IFN-γR-deficient MRL-Faslpr mice, we evaluated Mφ proliferation, apoptosis, and recruitment. Proliferation of bone marrow Mφ from IFN-γR-intact MRL-Faslpr costimulated with CSF-1 or GM-CSF and IFN-γ was reduced twofold, while the IFN-γR-deficient MRL-Faslpr bone marrow Mφ remained stable. Furthermore, we detected more proliferating and fewer apoptotic Mφ within the interstitium in IFN-γR-deficient MRL-Faslpr mice. Using unilateral ureteral ligation we established that IFN-γR signaling does not alter Mφ recruitment into the kidney. Thus, the increase in Mφ elicited by Mφ growth factors in IFN-γR-deficient MRL-Faslpr mice is a result of enhanced proliferation and decreased apoptosis, and is independent of recruitment. Taken together, we suggest that IFN-γ provides a negative regulatory pathway capable of limiting Mφ-mediated renal inflammation.

Strategies of gene transfer to the kidney

Kidney targeted gene transfer has been a realistic goal for many researchers since 1991, but unfortunately, to date there is no reliable gene transfer technique for gene therapy of renal diseases. However, at the experimental level, several in vivo gene transfer methods have attempted to target certain renal structures, for example, the HVJ-liposome method and renal perfusion of adenovirus for glomerular cells, intravenous injection of oligonucleotides (ODNs) for proximal tubule, intra-arterial injection of adenovirus followed by cold incubation with a vasodilator for interstitial vasculature of the outer medulla, and adenoviral injection into the renal pelvis for the inner medullary collecting duct. As an ex vivo gene transfer method targeting the glomerulus, the transfusion of genetically-modified mesangial cells has been attempted. Implantation of genetically-modified tubular epithelial cells into the subcapsular region has been employed for ex vivo transfection to the interstitium. Gene therapy has focused particularly on the transplanted kidney, where an exogenous gene can transferred in advance. In the future, an inducible system and individual cell targeting strategy should be developed. The improvement of gene transfer techniques, especially vectors for delivering genes, is crucial. The potential application of gene transfer technologies is enormous while the therapeutic approaches have just begun to be explored. Therapeutic interventions of the process of progression of glomerulonephritis in the rat have been directed towards inhibiting the actions of growth factors. Obviously, molecular biological intervention is coming of age and there is a tremendous excitement over its potential. We believe that gene transfer techniques will become common tools for the dissection of molecular aspects of diseases and possibly for gene therapy in the field of nephrology.

Local macrophage proliferation in the pathogenesis of glomerular crescent formation in rat anti-glomerular basement membrane (GBM) glomerulonephritis

Glomerular crescent formation is a feature of aggressive forms of glomerulonephritis. The conventional view of crescent formation within Bowman's space involves proliferation of parietal epithelial cells and the recruitment of blood monocytes. However, the potential role of local macrophage proliferation in this process has not been investigated. The current study examines macrophage proliferation within Bowman's space on the basis of expression of the proliferating cell nuclear antigen (PCNA) in a rat model of crescentic glomerulonephritis (accelerated anti-GBM disease). ED1+ macrophages accounted for 42% of cells within early cellular crescents, and 38% of these crescent macrophages were proliferating on the basis of PCNA expression. Macrophages became the dominant cell population in advanced cellular and fibrocellular crescents (64-71%), and there was a significant increase in the level of macrophage proliferation, with 62% and 67% of ED1+ macrophages expressing the PCNA, respectively. This high level of macrophage proliferation was confirmed by incorporation of bromodeoxyuridine and the presence of mitotic figures within crescents. Indeed, macrophages accounted for 73% of all proliferating cells within advanced and fibrocellular crescents. Macrophage proliferation within Bowman's space was a local event, as shown by a lack of proliferating monocytes in the circulation, the presence of mitotic figures within crescents and a reciprocal relationship between the numbers of ED1+ PCNA+ cells within Bowman's space compared with that in the capillary tuft during the progression from early to advanced and fibrocellular crescents. In conclusion, this study has changed the conventional view of the pathogenesis of crescent formation in glomerulonephritis with the demonstration of substantial local macrophage proliferation within Bowman's space. It is proposed that local proliferation is a major mechanism of macrophage accumulation within crescents and plays an important role in the progression of epithelial-dominated early cellular crescents to macrophage-dominated advanced and fibrocellular cellular crescents.