Distinct contribution of Fc receptors and angiotensin II-dependent pathways in anti-GBM glomerulonephritis

Unveiling the hidden role of the interaction between CD36 and FcγRIIb: implications for autoimmune disorders

BACKGROUND

The role of the scavenger receptor CD36 in cell metabolism and the immune response has been investigated mainly in macrophages, dendritic cells, and T cells. However, its involvement in B cells has not been comprehensively examined.

METHODS

To investigate the function of CD36 in B cells, we exposed Cd36fl/flMB1cre mice, which lack CD36 specifically in B cells, to apoptotic cells to trigger an autoimmune response. To validate the proteins that interact with CD36 in primary B cells, we conducted mass spectrometry analysis following anti-CD36 immunoprecipitation. Immunofluorescence and co-immunoprecipitation were used to confirm the protein interactions.

RESULTS

The data revealed that mice lacking CD36 in B cells exhibited a reduction in germinal center B cells and anti-DNA antibodies in vivo. Mass spectrometry analysis identified 30 potential candidates that potentially interact with CD36. Furthermore, the interaction between CD36 and the inhibitory Fc receptor FcγRIIb was first discovered by mass spectrometry and confirmed through immunofluorescence and co-immunoprecipitation techniques. Finally, deletion of FcγRIIb in mice led to decreased expression of CD36 in marginal zone B cells, germinal center B cells, and plasma cells.

CONCLUSIONS

Our data indicate that CD36 in B cells is a critical regulator of autoimmunity. The interaction of CD36-FcγRIIb has the potential to serve as a therapeutic target for the treatment of autoimmune disorders.

Role of angiotensin II in cellular entry and replication of dengue virus

Previous studies have demonstrated the relevance of several soluble molecules in the pathogenesis of dengue. In this regard, a possible role for angiotensin II (Ang II) in the pathophysiology of dengue has been suggested by the observation of a blockade of Ang II in patients with dengue, increased expression of molecules related to Ang II production in the plasma of dengue patients, increased expression of circulating cytokines and soluble molecules related to the action of Ang II, and an apparent relationship between DENV, Ang II effects, and miRNAs. In addition, in ex vivo experiments, the blockade of Ang II AT1 receptor and ACE-1 (angiotensin converting enzyme 1), both of which are involved in Ang II production and its function, inhibits infection of macrophages by DENV, suggesting a role of Ang II in viral entry or in intracellular viral replication of the virus. Here, we discuss the possible mechanisms of Ang II in the entry and replication of DENV. Ang II has the functions of increasing the expression of DENV entry receptors, creation of clathrin-coated vesicles, and increasing phagocytosis, all of which are involved in DENV entry. This hormone also modulates the expression of the Rab5 and Rab7 proteins, which are important in the endosomal processing of DENV during viral replication. This review summarizes the data related to the possible involvement of Ang II in the entry of DENV into cells and its replication.

Autoantibodies against laminin-521 are pathogenic in anti-glomerular basement membrane disease

Anti-glomerular basement membrane (anti-GBM) disease is an organ-specific autoimmune disorder characterized by autoantibodies against GBM components. Evidence from human inherited kidney diseases and animal models suggests that the α, β, and γ chains of laminin-521 are all essential for maintaining the glomerular filtration barrier. We previously demonstrated that laminin-521 is a novel autoantigen within the GBM and that autoantibodies to laminin-521 are present in about one-third of patients. In the present study, we investigated the pathogenicity of autoantibodies against laminin-521 with clinical and animal studies. Herein, a rare case of anti-GBM disease was reported with circulating autoantibodies binding to laminin-521 but not to the NC1 domains of α1-α5(IV) collagen. Immunoblot identified circulating IgG from this patient bound laminin α5 and γ1 chains. A decrease in antibody levels was associated with improved clinical presentation after plasmapheresis and immunosuppressive treatments. Furthermore, immunization with laminin-521 in female Wistar-Kyoto rats induced crescentic glomerulonephritis with linear IgG deposits along the GBM, complement activation along with infiltration of T cells and macrophages. Lung hemorrhage occurred in 75.0% of the rats and was identified by the presence of erythrocyte infiltrates and hemosiderin-laden macrophages in the lung tissue. Sera and kidney-eluted antibodies from rats immunized with laminin-521 demonstrated specific IgG binding to laminin-521 but not to human α3(IV)NC1, while the opposite was observed in human α3(IV)NC1-immunized rats. Thus, our patient data and animal studies imply a possible independent pathogenic role of autoantibodies against laminin-521 in the development of anti-GBM disease.

EGF-Receptor-Dependent TLR7 Signaling in Macrophages Promotes Glomerular Injury in Crescentic Glomerulonephritis

Glomerulonephritis (GN) is a group of inflammatory diseases and an important cause of morbidity and mortality worldwide. The initiation of the inflammatory process is quite different for each type of GN; however, each GN is characterized commonly and variably by acute inflammation with neutrophils and macrophages and crescent formation, leading to glomerular death. Toll-like receptor (TLR) 7 is a sensor for self-RNA and implicated in the pathogenesis of human and murine GN. Here, we show that TLR7 exacerbates glomerular injury in nephrotoxic serum nephritis (NTN), a murine model of severe crescentic GN. TLR7-/- mice were resistant to NTN, although TLR7-/- mice manifested comparable immune-complex deposition to wild-type mice without significant defects in humoral immunity, suggesting that endogenous TLR7 ligands accelerate glomerular injury. TLR7 was expressed exclusively in macrophages in glomeruli in GN but not in glomerular resident cells or neutrophils. Furthermore, we discovered that epidermal growth factor receptor (EGFR), a receptor-type tyrosine kinase, is essential for TLR7 signaling in macrophages. Mechanistically, EGFR physically interacted with TLR7 upon TLR7 stimulation, and EGFR inhibitor completely blocked the phosphorylation of TLR7 tyrosine residue(s). EGFR inhibitor attenuated glomerular damage in wild-type mice, and no additional glomerular protective effects by EGFR inhibitor were observed in TLR7-/- mice. Finally, mice lacking EGFR in macrophages were resistant to NTN. This study clearly demonstrated that EGFR-dependent TLR7 signaling in macrophages is essential for glomerular injury in crescentic GN.

The leukotriene B4 /BLT1-dependent neutrophil accumulation exacerbates immune complex-mediated glomerulonephritis

Crescent formation is the most important pathological finding that defines the prognosis of nephritis. Although neutrophils are known to play an important role in the progression of crescentic glomerulonephritis, such as anti-neutrophil cytoplasmic antibody (ANCA)-associated glomerulonephritis, the key chemoattractant for neutrophils in ANCA-associated glomerulonephritis has not been identified. Here, we demonstrate that a lipid chemoattractant, leukotriene B₄ (LTB₄ ), and its receptor BLT1 are primarily involved in disease pathogenesis in a mouse model of immune complex-mediated crescentic glomerulonephritis. Circulating neutrophils accumulated into glomeruli within 1 h after disease onset, which was accompanied by LTB₄ accumulation in the kidney cortex, leading to kidney injury. LTB₄ was produced by cross-linking of Fc gamma receptors on neutrophils. Mice deficient in BLT1 or LTB₄ biosynthesis exhibited suppressed initial neutrophil infiltration and subsequent thrombotic glomerulonephritis and renal fibrosis. Depletion of neutrophils before, but not after, disease onset prevented proteinuria and kidney injury, indicating the essential role of neutrophils in the early phase of glomerulonephritis. Administration of a BLT1 antagonist before and after disease onset almost completely suppressed induction of glomerulonephritis. Finally, we found that the glomeruli from patients with ANCA-associated glomerulonephritis contained more BLT1-positive cells than glomeruli from patients with other etiologies. Taken together, the LTB₄ -BLT1 axis is the key driver of neutrophilic glomerular inflammation, and will be a novel therapeutic target for the crescentic glomerulonephritis.

Overexpressed angiotensin-converting enzyme in neutrophils suppresses glomerular damage in crescentic glomerulonephritis

While angiotensin-converting enzyme (ACE) regulates blood pressure by producing angiotensin II as part of the renin-angiotensin system, we recently reported that elevated ACE in neutrophils promotes an effective immune response and increases resistance to infection. Here, we investigate if such neutrophils protect against renal injury in immune complex (IC)-mediated crescentic glomerulonephritis (GN) through complement. Nephrotoxic serum nephritis (NTN) was induced in wild-type and NeuACE mice that overexpress ACE in neutrophils. Glomerular injury of NTN in NeuACE mice was attenuated with much less proteinuria, milder histological injury, and reduced IC deposits, but presented with more glomerular neutrophils in the early stage of the disease. There were no significant defects in T and B cell functions in NeuACE mice. NeuACE neutrophils exhibited enhanced IC uptake with elevated surface expression of FcγRII/III and complement receptor CR1/2. IC uptake in neutrophils was enhanced by NeuACE serum containing elevated complement C3b. Given no significant complement activation by ACE, this suggests that neutrophil ACE indirectly preactivates C3 and that the C3b-CR1/2 axis and elevated FcγRII/III play a central role in IC elimination by neutrophils, resulting in reduced glomerular injury. The present study identified a novel renoprotective role of ACE in glomerulonephritis; elevated neutrophilic ACE promotes elimination of locally formed ICs in glomeruli via C3b-CR1/2 and FcγRII/III, ameliorating glomerular injury.NEW & NOTEWORTHY We studied immune complex (IC)-mediated crescentic glomerulonephritis in NeuACE mice that overexpress ACE only in neutrophils. Such mice show no significant defects in humoral immunity but strongly resist nephrotoxic serum nephritis (less proteinuria, milder histological damage, reduced IC deposits, and more glomerular neutrophils). NeuACE neutrophils enhanced IC uptake via increased surface expression of CR1/2 and FcgRII/III, as well as elevated serum complement C3b. These results suggest neutrophil ACE as a novel approach to reducing glomerulonephritis.

Cortical Bone Loss in a Spontaneous Murine Model of Systemic Lupus Erythematosus

Patients with systemic lupus erythematosus (SLE), a chronic inflammatory disease characterized by loss of T- and B-cell tolerance to autoantigens, are at increased risk for osteoporosis and fractures. Mice deficient in Fc gamma receptor IIb (FcγRIIB) exhibit spontaneous SLE and its restoration rescues the disease. To determine whether deleting FcγRIIB affects cortical bone mass and mechanical properties, we analyzed cortical bone phenotype of FcγRIIB knockouts at different ages. FACS analysis revealed that 6-month-old FcγRIIB^-/- mice had increased B220^lowCD138⁺ cells, markers of plasma cells, indicating active SLE disease. In contrast, 3-month-old FcγRIIB^-/- mice did not develop the active SLE disease. µCT analysis indicated that FcγRIIB deletion did not affect cortical bone in 3-month-old mutants. However, 6- and 10-month-old FcγRIIB^-/- males and females had osteopenic cortical bone and the severity of bone loss increased with disease duration. FcγRIIB deletion decreased cross-sectional area, cortical area, and marrow area in 6-month-old males. Cortical area and cortical thickness were decreased in 10-month-old FcγRIIB^-/- males. Lack of FcγRIIB decreased cortical thickness without affecting cortical area in females. However, deletion of a single FcγRIIB allele was insufficient to induce cortical bone loss. The bending strength was decreased in 6- and 10-month-old FcγRIIB-deficient males compared to WT controls. A microindentation analysis demonstrated significantly decreased hardness in both 10-month-old FcγRIIB^-/- males and females. Our data indicate that FcγRIIB contributes to the regulation of cortical bone homeostasis subsequent to SLE development and that deletion of FcγRIIB in mice leads to SLE-like disease associated with cortical bone loss and decreased bending strength and hardness.

(5R)-5-hydroxytriptolide ameliorates anti-glomerular basement membrane glomerulonephritis in NZW mice by regulating Fcγ receptor signaling

(5R)-5-hydroxytriptolide (LLDT-8) is a novel triptolide analog that has been identified as a promising candidate for treating autoimmune diseases and has been shown to be effective in treating murine collagen-induced arthritis and lupus nephritis. In the present study, we investigated the therapeutic effect and possible mechanism of action of LLDT-8 in a murine anti-glomerular basement membrane (GBM) glomerulonephritis model. NZW mice were injected with rabbit anti-GBM serum (500 μL, ip). The mice were orally treated with LLDT-8 (0.125 mg/kg, every other day) or a positive control prednisolone (2 mg/kg every day) for 14 d. Blood and urine samples as well as spleen and kidney tissues were collected for analyses. LLDT-8 treatment did not affect the generation of mouse anti-rabbit antibodies. LLDT-8 significantly reversed established proteinuria, improved renal histopathology and attenuated renal dysfunction in glomerulonephritis mice. Furthermore, LLDT-8 inhibited inflammation in the kidney evidenced by significantly decreasing C3 and IgG deposition, reducing the levels of the pathogenic cytokines TNF-α, IL-6, IL-17, and IFN-γ, and reducing related chemokine expression and leukocyte infiltration in kidneys. Moreover, LLDT-8 treatment significantly increased the expression of FcγRIIB in the kidney and spleen. In addition, the treatment restored the reduced expression of FcγRIIB on the surface of kidney effector cells, CD11b⁺ cells, and interfered with FcγR-dependent signaling, especially FcγRIIB-mediated downstream kinases, such as BTK. These results demonstrate that LLDT-8 ameliorates anti-GBM glomerulonephritis by regulating the Fcγ receptor signaling.

Lupus and proliferative nephritis are PAD4 independent in murine models

Though recent reports suggest that neutrophil extracellular traps (NETs) are a source of antigenic nucleic acids in systemic lupus erythematosus (SLE), we recently showed that inhibition of NETs by targeting the NADPH oxidase complex via cytochrome b-245, β polypeptide (cybb) deletion exacerbated disease in the MRL.Faslpr lupus mouse model. While these data challenge the paradigm that NETs promote lupus, it is conceivable that global regulatory properties of cybb and cybb-independent NETs confound these findings. Furthermore, recent reports indicate that inhibitors of peptidyl arginine deiminase, type IV (Padi4), a distal mediator of NET formation, improve lupus in murine models. Here, to clarify the contribution of NETs to SLE, we employed a genetic approach to delete Padi4 in the MRL.Faslpr model and used a pharmacological approach to inhibit PADs in both the anti-glomerular basement membrane model of proliferative nephritis and a human-serum-transfer model of SLE. In contrast to prior inhibitor studies, we found that deletion of Padi4 did not ameliorate any aspect of nephritis, loss of tolerance, or immune activation. Pharmacological inhibition of PAD activity had no effect on end-organ damage in inducible models of glomerulonephritis. These data provide a direct challenge to the concept that NETs promote autoimmunity and target organ injury in SLE.

FcγRIIB and autoimmunity

Autoimmune diseases are characterized by adaptive immune responses against self-antigens, including humoral responses resulting in the production of autoantibodies. Autoantibodies generate inflammation by activating complement and engaging Fcγ receptors (FcγRs). The inhibitory receptor FcγRIIB plays a central role in regulating the generation of autoantibodies and their effector functions, which include activation of innate immune cells and the cellular arm of the adaptive immune system, via effects on antigen presentation to CD4 T cells. Polymorphisms in FcγRIIB have been associated with susceptibility to autoimmunity but protection against infections in humans and mice. In the last few years, new mechanisms by which FcγRIIB controls the adaptive immune response have been described. Notably, FcγRIIB has been shown to regulate germinal center B cells and dendritic cell migration, with potential impact on the development of autoimmune diseases. Recent work has also highlighted the implication of FcγRIIB on the regulation of the innate immune system, via inhibition of Toll-like receptor- and complement receptor-mediated activation. This review will provide an update on the role of FcγRIIB in adaptive immune responses in autoimmunity, and then focus on their emerging function in innate immunity.

The many faces of Mac-1 in autoimmune disease

Mac-1 (CD11b/CD18) is a β2 integrin classically regarded as a pro-inflammatory molecule because of its ability to promote phagocyte cytotoxic functions and enhance the function of several effector molecules such as FcγR, uPAR, and CD14. Nevertheless, recent reports have revealed that Mac-1 also plays significant immunoregulatory roles, and genetic variants in ITGAM, the gene that encodes CD11b, confer risk for the autoimmune disease systemic lupus erythematosus (SLE). This has renewed interest in the physiological roles of this integrin and raised new questions on how its seemingly opposing biological functions may be regulated. Here, we provide an overview of the CD18 integrins and how their activation may be regulated as this may shed light on how the opposing roles of Mac-1 may be elicited. We then discuss studies that exemplify Mac-1's pro-inflammatory versus regulatory roles particularly in the context of IgG immune complex-mediated inflammation. This includes a detailed examination of molecular mechanisms that could explain the risk-conferring effect of rs1143679, a single nucleotide non-synonymous Mac-1 polymorphism associated with SLE.

Mouse and human FcR effector functions

Mouse and human FcRs have been a major focus of attention not only of the scientific community, through the cloning and characterization of novel receptors, and of the medical community, through the identification of polymorphisms and linkage to disease but also of the pharmaceutical community, through the identification of FcRs as targets for therapy or engineering of Fc domains for the generation of enhanced therapeutic antibodies. The availability of knockout mouse lines for every single mouse FcR, of multiple or cell-specific--'à la carte'--FcR knockouts and the increasing generation of hFcR transgenics enable powerful in vivo approaches for the study of mouse and human FcR biology. This review will present the landscape of the current FcR family, their effector functions and the in vivo models at hand to study them. These in vivo models were recently instrumental in re-defining the properties and effector functions of FcRs that had been overlooked or discarded from previous analyses. A particular focus will be made on the (mis)concepts on the role of high-affinity IgG receptors in vivo and on results from antibody engineering to enhance or abrogate antibody effector functions mediated by FcRs.

The function of mast cells in autoimmune glomerulonephritis

Immune-mediated glomerulonephritis is caused by deposition of immune complexes on the glomerular basement membrane or of autoantibodies directed against the glomerular basement membrane. Depositions lead to an inflammatory response that can ultimately destroy renal function and lead to chronic kidney disease. However, the pathological processes leading to the development of renal injury and disease progression remain poorly understood. To investigate the mechanisms of disease development in glomerulonephritis various animal models have been developed, which include as the most popular one the induction of glomerulonephritis by the injection of heterologous antibodies directed to the glomerular basement membrane. The role of mast cells and mast cell-derived mediators has been evaluated in these models. In this chapter we describe the methods that allow to set up and study the disease parameters of immune-mediated glomerulonephritis development.

The kinetics of glomerular deposition of nephritogenic IgA

Whether IgA nephropathy is attributable to mesangial IgA is unclear as there is no correlation between intensity of deposits and extent of glomerular injury and no clear mechanism explaining how these mesangial deposits induce hematuria and subsequent proteinuria. This hinders the development of a specific therapy. Thus, precise events during deposition still remain clinical challenge to clarify. Since no study assessed induction of IgA nephropathy by nephritogenic IgA, we analyzed sequential events involving nephritogenic IgA from IgA nephropathy-prone mice by real-time imaging systems. Immunofluorescence and electron microscopy showed that serum IgA from susceptible mice had strong affinity to mesangial, subepithelial, and subendothelial lesions, with effacement/actin aggregation in podocytes and arcade formation in endothelial cells. The deposits disappeared 24-h after single IgA injection. The data were supported by a fluorescence molecular tomography system and real-time and 3D in vivo imaging. In vivo imaging showed that IgA from the susceptible mice began depositing along the glomerular capillary from 1 min and accumulated until 2-h on the first stick in a focal and segmental manner. The findings indicate that glomerular IgA depositions in IgAN may be expressed under the balance between deposition and clearance. Since nephritogenic IgA showed mesangial as well as focal and segmental deposition along the capillary with acute cellular activation, all glomerular cellular elements are a plausible target for injury such as hematuria.

Dichotomy in FcγRIIB deficiency and autoimmune-prone SLAM haplotype clarifies the roles of the Fc receptor in development of autoantibodies and glomerulonephritis

Background

The significance of a unique inhibitory Fc receptor for IgG, FcγRIIB (RIIB), in the prevention of spontaneous production of autoantibodies remains controversial, due mainly to the fact that the RIIB locus is adjacent to the autoimmune-related SLAM locus harboring the genes coding for signaling lymphocyte activation molecules, making it difficult to isolate the effect of RIIB deletion from that of SLAM in gene-targeted mice. Our objective was to determine the influence of RIIB deletion on the spontaneous development of autoimmune diseases and to compare it with that of potentially pathogenic SLAM.

Results

We established two congenic C57BL/6 (B6) strains, one with the RIIB deletion and the other with SLAM, by backcrossing 129/SvJ-based RIIB-deficient mice into the B6 genetic background extensively. The RIIB deficiency indeed led to the production and/or accumulation of a small amount of anti-nuclear autoantibodies (ANAs) and to weak IgG immune-complex deposition in glomeruli without any obvious manifestation of lupus nephritis. In contrast, pathogenic SLAM in the B6 genetic background induced ANAs but no IgG immune-complex deposition in the kidneys. Naïve SLAM mice but not RIIB-deficient mice exhibited hyperplasia of splenic germinal centers.

Conclusion

The present results clarify the roles of RIIB in preventing production and/or accumulation of a small amount of ANAs, and development of glomerulonephritis. The combined effects of RIIB deletion and pathogenic SLAM can lead to severe lupus nephritis in the B6 genetic background.

Electronic supplementary material

The online version of this article (doi:10.1186/s12865-014-0047-y) contains supplementary material, which is available to authorized users.

Angiotensin II and canonical transient receptor potential-6 activation stimulate release of a signal transducer and activator of transcription 3-activating factor from mouse podocytes

Previous studies have shown that the transcription factor signal transducer and activator of transcription-3 (STAT3) in podocytes plays an important role in progression of HIV nephropathy and in collapsing forms of glomerulonephritis. Here, we have observed that application of 100 nM angiotensin II (Ang II) to cultured podocytes for 6-24 hours causes a marked increase in the phosphorylation of STAT3 on tyrosine Y705 but has no effect on phosphorylation at serine S727. By contrast, Ang II treatment of short periods (20-60 minutes) caused a small but consistent suppression of tyrosine phosphylation of STAT3. A similar biphasic effect was seen after treatment with the diacylglycerol analog 1-oleoyl-2-acetyl-sn-glycerol (OAG), an agent that causes activation of Ca(2+)-permeable canonical transient receptor potential-6 (TRPC6) channels in podocytes. The stimulatory effects of Ang II on STAT3 phosphorylation were abolished by small-interfering RNA knockdown of TRPC6 and also by inhibitors of the Ca(2+)-dependent downstream enzymes calcineurin and Ca(2+)-calmodulin-dependent protein kinase II. The stimulatory effects of Ang II appear to be mediated by secretion and accumulation of an unknown factor into the surrounding medium, as they are no longer detected when medium is replaced every 2 hours even if Ang II is continuously present. By contrast, the inhibitory effect of Ang II on STAT3 phosphorylation persists with frequent medium changes. Experiments with neutralizing and inhibitory antibodies suggest that the STAT3 stimulatory factor secreted from podocytes is not interleukin-6, but also suggest that this factor exerts its actions through a receptor system that requires glycoprotein 130.

Uncoupling of glomerular IgA deposition and disease progression in alymphoplasia mice with IgA nephropathy

Previous clinical and experimental studies have indicated that cells responsible for IgA nephropathy (IgAN), at least in part, are localized in bone marrow (BM). Indeed, we have demonstrated that murine IgAN can be experimentally reconstituted by bone marrow transplantation (BMT) from IgAN prone mice in not only normal mice, but also in alymphoplasia mice (aly/aly) independent of IgA⁺ cells homing to mucosa or secondary lymphoid tissues. The objective of the present study was to further assess whether secondary lymph nodes (LN) contribute to the progression of this disease. BM cells from the several lines of IgAN prone mice were transplanted into aly/aly and wild-type mice (B6). Although the transplanted aly/aly showed the same degree of mesangial IgA and IgG deposition and the same serum elevation levels of IgA and IgA-IgG immune-complexes (IC) as B6, even in extent, the progression of glomerular injury was observed only in B6. This uncoupling in aly/aly was associated with a lack of CD4⁺ T cells and macrophage infiltration, although phlogogenic capacity to nephritogenic IC of renal resident cells was identical between both recipients. It is suggested that secondary LN may be required for the full progression of IgAN after nephritogenic IgA and IgA/IgG IC deposition.

Glutathione S-transferase Mu 2-transduced mesenchymal stem cells ameliorated anti-glomerular basement membrane antibody-induced glomerulonephritis by inhibiting oxidation and inflammation

INTRODUCTION

Oxidative stress is implicated in tissue inflammation, and plays an important role in the pathogenesis of immune-mediated nephritis. Using the anti-glomerular basement membrane antibody-induced glomerulonephritis (anti-GBM-GN) mouse model, we found that increased expression of glutathione S-transferase Mu 2 (GSTM2) was related to reduced renal damage caused by anti-GBM antibodies. Furthermore, mesenchymal stem cell (MSC)-based therapy has shed light on the treatment of immune-mediated kidney diseases. The aim of this study was to investigate if MSCs could be utilized as vehicles to deliver the GSTM2 gene product into the kidney and to evaluate its potential therapeutic effect on anti-GBM-GN.

METHODS

The human GSTM2 gene (hGSTM2) was transduced into mouse bone marrow-derived MSCs via a lentivirus vector to create a stable cell line (hGSTM2-MSC). The cultured hGSTM2-MSCs were treated with 0.5 mM H2O2, and apoptotic cells were measured by terminal dUTP nick-end labeling (TUNEL) assay. The 129/svj mice, which were challenged with anti-GBM antibodies, were injected with 10⁶ hGSTM2-MSCs via the tail vein. Expression of hGSTM2 and inflammatory cytokines in the kidney was assayed by quantitative PCR and western blotting. Renal function of mice was evaluated by monitoring proteinuria and levels of blood urea nitrogen (BUN), and renal pathological changes were analyzed by histochemistry. Immunohistochemical analysis was performed to measure inflammatory cell infiltration and renal cell apoptosis.

RESULTS

MSCs transduced with hGSTM2 exhibited similar growth and differentiation properties to MSCs. hGSTM2-MSCs persistently expressed hGSTM2 and resisted H2O2-induced apoptosis. Upon injection into 129/svj mice, hGSTM2-MSCs migrated to the kidney and expressed hGSTM2. The anti-GBM-GN mice treated with hGSTM2-MSCs exhibited reduced proteinuria and BUN (58% and 59% reduction, respectively) and ameliorated renal pathological damage, compared with control mice. Mice injected with hGSTM2-MSCs showed alleviated renal inflammatory cell infiltration and reduced expression of chemokine (C-C motif) ligand 2 (CCL2), interleukin (IL)-1β and IL-6 (53%, 46% and 52% reduction, respectively), compared with controls. Moreover, hGSTM2-MSCs increased expression of renal superoxide dismutase and catalase, which may associate with detoxifying reactive oxygen species to prevent oxidative renal damage.

CONCLUSIONS

Our data suggest that the enhanced protective effect of GSTM2-transduced MSCs against anti-GBM-GN might be associated with inhibition of oxidative stress-induced renal cell apoptosis and inflammation, through over-expression of hGSTM2 in mouse kidneys.

Angiotensin II blockade and renal protection

Current national guidelines have recommended the use of renin-angiotensin system inhibitors, including angiotensin II type 1 receptor blockers (ARBs), in preference to other antihypertensive agents for treating hypertensive patients with chronic kidney disease. However, the mechanisms underlying the renoprotective effects of ARBs are multiple and complex. Blood pressure reduction by systemic vasodilation with an ARB contributes to its beneficial effects in treating kidney disease. Furthermore, ARB-induced renal vasodilation results in an increase in renal blood flow, leading to improvement of renal ischemia and hypoxia. ARBs are also effective in reducing urinary albumin excretion through a reduction in intraglomerular pressure and the protection of glomerular endothelium and/or podocyte injuries. In addition to blocking angiotensin II-induced renal cell and tissue injuries, ARBs can decrease intrarenal angiotensin II levels by reducing proximal tubular angiotensinogen and production of collecting duct renin, as well as angiotensin II accumulation in the kidney. In this review, we will briefly summarize our current understanding of the pharmacological effects of an ARB in the kidney. We will also discuss the possible mechanisms responsible for the renoprotective effects of ARBs on type 2 diabetic nephropathy.

Development of pyrrole-imidazole polyamide targeting fc receptor common gamma chain for the treatment of immune-complex related renal disease

Fcγ receptors I and III are thought to be involved in the development of lupus nephritis. Expression of Fc receptor common gamma chain (FcRγ) is necessary for the stable expression of Fcγ receptors I and III. The aim of this study was to develop a novel agent for the treatment of immune complex related renal disease using a gene regulator, pyrrole(Py)-imidazole(Im) (PI) polyamide, targeting the mouse FcRγ gene promoter. Two PI polyamides targeting FcRγ promoters were designed and synthesized. The effect of the PI polyamides on FcRγ mRNA expression was evaluated in J774.A cells by real-time polymerase chain reaction (PCR), and CD16/32 protein expression was determined by immunocytochemical analysis and flow cytometry. The effects of these polyamides on FcRγ gene expression and CD16/32 protein expression were evaluated in mouse peripheral blood mononuclear cells (PBMCs). One milligram per kilogram body weight of PI polyamide was injected via the tail vein every 2 d for 1 week and PBMCs were collected and analyzed. PI polyamide showed a specific binding to the target DNA in a gel mobility shift assay. Treatment of J774.A cells with 1.0 µM PI polyamide 1 significantly reduced FcRγ mRNA expression and CD16/32 surface protein expression in J774.A cells. Similarly, PI polyamide significantly decreased expression of FcRγ mRNA and CD16/32 in the PBMCs of C57B6 mice. PI polyamide designed to bind the FcRγ promoter decreased FcRγ gene and CD16/32 protein expression. PI polyamide targeting the FcRγ gene may be a novel gene regulator for the prevention of lupus nephritis or other immune complex-related disease.

Fcγ receptor deficiency attenuates diabetic nephropathy

Among patients with diabetes, increased production of immunoglobulins against proteins modified by diabetes is associated with proteinuria and cardiovascular risk, suggesting that immune mechanisms may contribute to the development of diabetes complications, such as nephropathy. We investigated the contribution of IgG Fcγ receptors to diabetic renal injury in hyperglycemic, hypercholesterolemic mice. We used streptozotocin to induce diabetes in apolipoprotein E-deficient mice and in mice deficient in both apolipoprotein E and γ-chain, the common subunit of activating Fcγ receptors. After 15 weeks, the mice lacking Fcγ receptors had significantly less albuminuria and renal hypertrophy, despite similar degrees of hyperglycemia and hypercholesterolemia, immunoglobulin production, and glomerular immune deposits. Moreover, diabetic Fcγ receptor-deficient mice had less mesangial matrix expansion, inflammatory cell infiltration, and collagen and α-smooth muscle actin content in their kidneys. Accordingly, expression of genes involved in leukocyte infiltration, fibrosis, and oxidative stress was significantly reduced in diabetic kidneys and in mesangial cells cultured from Fcγ receptor-deficient mice. In summary, preventing the activation of Fcγ receptors alleviates renal hypertrophy, inflammation, and fibrosis in hypercholesterolemic mice with diabetes, suggesting that modulating Fcγ receptor signaling may be renoprotective in diabetic nephropathy.

Neutrophil gelatinase-associated lipocalin is instrumental in the pathogenesis of antibody-mediated nephritis in mice

OBJECTIVE

The mechanism by which anti-DNA antibodies mediate lupus nephritis has yet to be conclusively determined. Previously, we found that treatment of mesangial cells with anti-DNA antibodies induced high expression of neutrophil gelatinase-associated lipocalin (NGAL), an iron-binding protein up-regulated in response to kidney injury. We undertook this study to determine whether NGAL is instrumental in the pathogenesis of nephritis, is induced as part of repair, or is irrelevant to damage/repair pathways.

METHODS

To investigate the role of NGAL in antibody-mediated nephritis, we induced nephrotoxic nephritis by passive antibody transfer to 129/SyJ and C57BL/6 mice. To determine if NGAL up-regulation is instrumental, we compared the severity of renal damage in NGAL wild-type mice and NGAL-knockout mice following induction of nephrotoxic nephritis.

RESULTS

We found that kidney NGAL expression, as well as urine NGAL levels, were significantly increased in mice with nephrotoxic nephritis as compared to control-injected mice. Tight correlations were observed between NGAL expression, renal histopathology, and urine NGAL excretion. NGAL-knockout mice had attenuated proteinuria and improved renal histopathology compared to wild-type mice. Similarly, following nephritis induction, NGAL injection significantly exacerbated nephritis and decreased survival. NGAL induced apoptosis via caspase 3 activation and up-regulated inflammatory gene expression in kidney cells in vitro and when injected in vivo.

CONCLUSION

We conclude that kidney binding of pathogenic antibodies stimulates local expression of NGAL, which plays a crucial role in the pathogenesis of nephritis via promotion of inflammation and apoptosis. NGAL blockade may be a novel therapeutic approach for the treatment of nephritis mediated by pathogenic antibodies, including anti-glomerular basement membrane disease and lupus nephritis.

Role of novel rat-specific Fc receptor in macrophage activation associated with crescentic glomerulonephritis

Crescentic glomerulonephritis (Crgn) is a complex disease where the initial insult is often the glomerular deposition of antibodies against intrinsic or deposited antigens in the glomerulus. The role of Fc receptors in the induction and progression of Crgn is increasingly recognized, and our previous studies have shown that copy number variation in Fcgr3 partially explains the genetic susceptibility of the Wistar-Kyoto (WKY) rat to nephrotoxic nephritis, a rat model of Crgn. The Fcgr3-related sequence (Fcgr3-rs) is a novel rat-specific Fc receptor with a cytoplasmic domain 6 amino acids longer than its paralogue, Fcgr3. The Fcgr3-rs gene is deleted from the WKY rat genome, and this deletion is associated with enhanced macrophage activity in this strain. Here, we investigated the mechanism by which the deletion of Fcgr3-rs in the WKY strain leads to increased macrophage activation. By lentivirus-mediated gene delivery, we generated stably transduced U937 cells expressing either Fcgr3-rs or Fcgr3. In these cells, which lack endogenous Fcgr3 receptors, we show that Fcgr3-rs interacts with the common Fc-γ chain but that Fc receptor-mediated phagocytosis and signaling are defective. Furthermore, in primary macrophages, expression of Fcgr3-rs inhibits Fc receptor-mediated functions, because WKY bone marrow-derived macrophages transduced with Fcgr3-rs had significantly reduced phagocytic activity. This inhibitory effect on phagocytosis was mediated by the novel cytoplasmic domain of Fcgr3-rs. These results suggest that Fcgr3-rs may act to inhibit Fcgr3-mediated signaling and phagocytosis and could be considered as a novel mechanism in the modulation of Fc receptor-mediated cell activation in autoimmune diseases.

Angiotensin II type I receptor blockade suppresses glomerular renin-angiotensin system activation, oxidative stress, and progressive glomerular injury in rat anti-glomerular basement membrane glomerulonephritis

Excessive renin-angiotensin system (RAS) activation within the kidney induces not only renal oxidative stress but also renal scarring and dysfunction. This study examined the effects of an angiotensin II (Ang II) type I receptor (AT1R) blocker (ARB) on the progression of renal injury in rat anti-glomerular basement membrane glomerulonephritis (GN), with a particular focus on the participation of glomerular RAS activation in glomerular structural alterations, inflammation, and oxidative stress. Nephritic rats were divided into 2 groups and treated with vehicle or ARB until day 28. Treatment with ARB improved proteinuria significantly in nephritic rats. Vehicle-treated nephritic rats developed crescentic GN accompanied by marked macrophage infiltration and the enhanced expression of glomerular α-smooth muscle actin (α-SMA), angiotensinogen (AGT), Ang II, AT1R, and NADPH oxidase (Nox2) on days 7 and 28 of GN. ARB improved pathologic alterations such as crescent formation and glomerulosclerosis, and it had a significant inhibitory effect on the levels of these parameters on day 28 of GN. Enhanced superoxide production in nephritic glomeruli was decreased also by ARB. Moreover, Ang II and transforming growth factor beta (TGF-β) in the supernatant of cultured glomeruli was increased significantly in vehicle-treated nephritic rats whereas ARB inhibited the production of these compounds significantly on day 28. These results indicate that increased glomerular RAS activity and the resulting Ang II play important roles in progressive glomerular injury-the induction of oxidative stress and TGF-β expression, and they suggest that AT1R blockade attenuates proteinuria and progressive glomerular remodeling via the suppression of glomerular RAS activation in GN.

Protective effects of L-type fatty acid-binding protein (L-FABP) in proximal tubular cells against glomerular injury in anti-GBM antibody-mediated glomerulonephritis

Background. In glomerulonephritis (GN), an overload of free fatty acids (FFA) bound to albumin in urinary protein may induce oxidative stress in the proximal tubules. Human liver-type fatty acid-binding protein (hL-FABP) expressed in human proximal tubules, but not rodents, participates in intracellular FFA metabolism and exerts anti-oxidative effects on the progression of tubulointerstitial damage. We examined whether tubular enhancement of this anti-oxidative action modulates the progression of glomerular damage in immune-mediated GN in hL-FABP chromosomal gene transgenic (Tg) mice.

Methods. Anti-glomerular basement membrane antibody-induced glomerulonephritis (anti-GBM GN) was induced in Tg and wild-type mice (WT). Proteinuria, histopathology, polymorphonuclear (PMN) influx, expression of tubulointerstitial markers for oxidative stress 4-hydroxy-2-Nonenal (HNE) and fibrosis (α-smooth muscle actin), proximal tubular damage (Kim-1), Peroxisome Proliferator-Activated Receptor γ (PPAR γ) and inflammatory cytokines [Monocyte Chemotactic Protein-1, tumor necrosis factor-alpha (TNF-α) and Transforming growth factor beta (TGF-β)] were analyzed. The mice were also treated with an angiotensin type II receptor blocker (ARB).

Results. The urinary protein level in Tg mice decreased significantly during the acute phase (∼Day 5). Tg mice survived for a significantly longer time than WT mice, with an attenuation of tubulointerstitial damage score and expression of each tubulointerstitial damage marker observed at Day 7. Expression of inflammatory cytokines on Day 7 was higher in WT mice than Tg mice and correlated strongly with PPARγ expression in WT mice, but not in Tg mice. Interestingly, Tg mice showed insufficient PMN influx at 3 and 6 h, with simultaneous elevation of urinary L-FABP and reduction in HNE expression. The two strains of mice showed different types of glomerular damage, with mild mesangial proliferation in Tg mice and severe endothelial swelling with vascular thrombosis in WT mice. The glomerular damage in Tg mice was improved by administration of an ARB.

Conclusions. The present experimental model suggests that tubular enhancement of L-FABP may protect mice with anti-GBM GN from progression of both tubulointerstitial and glomerular injury.

[Fcγ receptor and systemic autoimmune disease]

The systemic autoimmune disease such as systemic lupus erythematosus (SLE) is characterized by the deposition of immune complexes in multiple organs. Fcγ receptors (FcγR) recognize the Fc portion of IgG and are important in determining the response of leukocytes to deposited immune complexes. FcγR also provide positive and negative regulation of immune cell responses. The activatory FcγR including the FcR common γ chain take balance with Fcγ RIIB, the only inhibitory FcγR. Development of lupus-like autoimmune disease as well as monocytosis in BXSB mice is dependent on the activatory and inhibitory FcγR. In human SLE, dysregulated expression of FcγRIIB on memory B cells is reported and numbers of associations with genetic polymorphism are also reported. The cell-specific modulation of these activatory or inhibitory FcγRs are expected for the new therapeutic strategy in autoimmune diseases.

Addition of angiotensin II type 1 receptor blocker to CCR2 antagonist markedly attenuates crescentic glomerulonephritis

The monocyte chemoattractant protein-1 (MCP-1)/CC-chemokine receptor 2 (CCR2) pathway plays a critical role in the development of antiglomerular basement membrane (anti-GBM) nephritis. We recently showed angiotensin II (Ang II) infusion in rats activated MCP-1 and transforming growth factor-β1 (TGF-β1), which in turn induced macrophage infiltration of renal tissues. This study was performed to demonstrate that combination therapy with a CCR2 antagonist (CA) and an Ang II type 1 receptor blocker (ARB) ameliorated renal injury in the anti-GBM nephritis model. An anti-GBM nephritis rat model developed progressive proteinuria and glomerular crescent formation, accompanied by increased macrophage infiltration and glomerular expression of MCP-1, angiotensinogen, Ang II, and TGF-β1. Treatment with CA alone or ARB alone moderately ameliorated kidney injury; however, the combination treatment with CA and ARB dramatically prevented proteinuria and markedly reduced glomerular crescent formation. The combination treatment also suppressed the induction of macrophage infiltration, MCP-1, angiotensinogen, Ang II, and TGF-β1 and reversed the fibrotic change in the glomeruli. Next, primary cultured glomerular mesangial cells (MCs) stimulated by Ang II showed significant increases in MCP-1 and TGF-β1 expression. Furthermore, cocultured model consisting of MCs, parietal epithelial cells, and macrophages showed an increase in Ang II-induced cell proliferation and collagen secretion. ARB treatment attenuated these augmentations. These data suggest that Ang II enhances glomerular crescent formation of anti-GBM nephritis. Moreover, our results demonstrate that inhibition of the MCP-1/CCR2 pathway with a combination of ARB effectively reduces renal injury in anti-GBM nephritis.

Angiotensinogen Expression Is Enhanced in the Progression of Glomerular Disease

Intrarenal renin-angiotensin system (RAS) activation plays a critical role in the development and progression of renal injury. In the kidney, all of the RAS components are present and intrarenal angiotensin II (Ang II) is formed by multiple independent mechanisms. Angiotensinogen (AGT) is the only known substrate for renin that is a rate-limiting enzyme of the RAS. Recently, enhanced intrarenal AGT levels have been shown to reflect the intrarenal RAS status in hypertension, chronic glomerular disease and diabetic nephropathy. In this review, we focus on AGT expression of the diseased glomeruli in the progression of glomerular disease. An anti-glomerular basement membrane nephritis rat model developed progressive proteinuria and glomerular crescent formation, accompanied by increased macrophage infiltration and glomerular expression of AGT and Ang II. The addition of Ang II type 1 receptor blocker to CC-chemokine recaptor 2 antagonist markedly attenuated the induction of macrophage infiltration, AGT and Ang II, and reduced glomerular crescent formation. Next, the levels of glomerular AGT expression and marker of reactive oxygen species in Zucker diabetic fatty (ZDF) obese rats were higher than those in ZDF lean rats. Hydrogen peroxide (H(2)O(2)) induced an increase in the AGT expression in primary rat mesangial cells. Furthermore, the H(2)O(2)-induced upregulation of AGT was inhibited by a mitogen-activated protein kinase kinase and a c-Jun N-terminal kinase inhibitor. These data suggest the potential contribution of enhanced AGT expression in glomeruli to the intrarenal RAS activation for the development of glomerular disease.

Mouse mast cell protease-4 deteriorates renal function by contributing to inflammation and fibrosis in immune complex-mediated glomerulonephritis

Mast cells exert protective effects in experimental antiglomerular basement membrane-induced glomerulonephritis (GN), yet the responsible mediators have not been identified. In this study, we investigated the role of mouse mast cell protease (mMCP)-4, the functional homolog of human chymase, using mMCP-4-deficient mice. Compared with wild type animals, mMCP-4-deficient mice exhibited lower proteinuria, blood creatinine, and blood urea nitrogen levels, indicating an aggravating role of mMCP-4. Kidney histology confirmed less severe renal damage in mMCP-4-deficient mice with reduced deposits, glomerular and interstitial cellularity, and fibrosis scores. High amounts of mMCP-4 were detected in renal capsules, but not in the whole kidney, from wild type mice. Its expression in renal capsules was markedly decreased after GN induction, suggesting that locally released enzyme by degranulated mast cells could contribute to the functional and physiopathological hallmarks of GN. Supporting a proinflammatory role, glomerular and interstitial macrophage and T cell infiltration, levels of proinflammatory TNF and MCP-1 mRNA, and the expression of the profibrotic peptide angiotensin II together with type I collagen were markedly downregulated in kidneys of mMCP-4-deficient mice. We conclude that mMCP-4 chymase, contrary to the global anti-inflammatory action of mast cells, aggravates GN by promoting kidney inflammation. These results highlight the complexity of mast cell-mediated inflammatory actions and suggest that chymase inhibition may represent a novel therapeutic target in GN.

FcgammaRIIB in autoimmunity and infection: evolutionary and therapeutic implications

FcgammaRIIB is the only inhibitory Fc receptor. It controls many aspects of immune and inflammatory responses, and variation in the gene encoding this protein has long been associated with susceptibility to autoimmune disease, particularly systemic lupus erythematosus (SLE). FcgammaRIIB is also involved in the complex regulation of defence against infection. A loss-of-function polymorphism in FcgammaRIIB protects against severe malaria, the investigation of which is beginning to clarify the evolutionary pressures that drive ethnic variation in autoimmunity. Our increased understanding of the function of FcgammaRIIB also has potentially far-reaching therapeutic implications, being involved in the mechanism of action of intravenous immunoglobulin, controlling the efficacy of monoclonal antibody therapy and providing a direct therapeutic target.

FcgammaRIIb inhibits allergic lung inflammation in a murine model of allergic asthma

Allergic asthma is characterized by airway eosinophilia, increased mucin production and allergen-specific IgE. Fc gamma receptor IIb (FcγRIIb), an inhibitory IgG receptor, has recently emerged as a negative regulator of allergic diseases like anaphylaxis and allergic rhinitis. However, no studies to date have evaluated its role in allergic asthma. Our main objective was to study the role of FcγRIIb in allergic lung inflammation. We used a murine model of allergic airway inflammation. Inflammation was quantified by BAL inflammatory cells and airway mucin production. FcγRIIb expression was measured by qPCR and flow cytometry and the cytokines were quantified by ELISA. Compared to wild type animals, FcγRIIb deficient mice mount a vigorous allergic lung inflammation characterized by increased bronchoalveolar lavage fluid cellularity, eosinophilia and mucin content upon ragweed extract (RWE) challenge. RWE challenge in sensitized mice upregulated FcγRIIb in the lungs. Disruption of IFN-γ gene abrogated this upregulation. Treatment of naïve mice with the Th1-inducing agent CpG DNA increased FcγRIIb expression in the lungs. Furthermore, treatment of sensitized mice with CpG DNA prior to RWE challenge induced greater upregulation of FcγRIIb than RWE challenge alone. These observations indicated that RWE challenge upregulated FcγRIIb in the lungs by IFN-γ- and Th1-dependent mechanisms. RWE challenge upregulated FcγRIIb on pulmonary CD14+/MHC II+ mononuclear cells and CD11c+ cells. FcγRIIb deficient mice also exhibited an exaggerated RWE-specific IgE response upon sensitization when compared to wild type mice. We propose that FcγRIIb physiologically regulates allergic airway inflammation by two mechanisms: 1) allergen challenge mediates upregulation of FcγRIIb on pulmonary CD14+/MHC II+ mononuclear cells and CD11c+ cells by an IFN-γ dependent mechanism; and 2) by attenuating the allergen specific IgE response during sensitization. Thus, stimulating FcγRIIb may be a therapeutic strategy in allergic airway disorders.

Urine proteome analysis in murine nephrotoxic serum nephritis

BACKGROUND

Urine contains serum proteins filtered by the glomerulus or secreted by the renal tubules and proteins produced locally by the urinary tract. Proteomic analysis of urine holds the potential as a noninvasive means of studying or monitoring disease activity. In mice, large concentrations of albumin and lipocalins have complicated the ability to identify urinary biomarkers in disease models.

METHODS

Passive nephrotoxic serum nephritis was induced in mice. Urine proteins were identified and quantified by iTRAQ and MALDI-TOF mass spectrometry. Results were compared to Western blotting and multiplex immunoassays.

RESULTS

Large concentrations of major urinary proteins dominate the urine proteome of mice even in the context of acute nephritis. Increased proteinuria caused by nephrotoxic serum nephritis is transient and includes increased albumin excretion. There were no alterations in chemokine excretion. Altered hepcidin excretion was identified, most likely reflecting local production and renal retention.

CONCLUSION

Proteomic analysis of mouse urine remains challenging due to the abundance of a limited subset of proteins. iTRAQ analysis does not circumvent these challenges, but can provide information on post-translational processing of some proteins. Hepcidin is identified as a potential urinary marker of nephritis and its role in disease pathogenesis warrants further study.

Both complement and IgG fc receptors are required for development of attenuated antiglomerular basement membrane nephritis in mice

To elucidate the mechanisms of glomerulonephritis, including Goodpasture's syndrome, mouse models are used that use heterologous Abs against the glomerular basement membrane (GBM) with or without preimmunization with foreign IgG from the same species. These studies have revealed the requirement of either FcgammaR or complement, depending on the experimental model used. In this study, we provide evidence that both FcgammaR and complement are obligatory for a full-blown inflammation in a novel attenuated passive model of anti-GBM disease. We demonstrate that administration of subnephritogenic doses of rabbit anti-GBM Abs followed by a fixed dose of mouse mAbs to rabbit IgG, allowing timing and dosing for the induction of glomerulonephritis, resulted in reproducible complement activation via the classical pathway of complement and albuminuria in wild-type mice. Because albuminuria was absent in FcR-gamma-chain(-/-) mice and reduced in C3(-/-) mice, a role for both FcgammaR and complement is postulated. Because C1q(-/-) and C4(-/-) mice lacking a functional classical and lectin pathway did develop albuminuria, we suggest involvement of the alternative pathway of complement. Anti-GBM glomerulonephritis occurs acutely following the administration of mouse anti-rabbit IgG, and proceeds in a chronic fashion dependent on both FcgammaR and complement. This novel attenuated model allows elucidating the relative contribution of different mediator systems of the immune system to the development of renal injury, and also provides a platform for the assessment of different treatment protocols and evaluation of drugs that ultimately may be beneficial for the treatment of anti-GBM mediated glomerulonephritides.

Low-affinity Fcgamma receptors, autoimmunity and infection

Low-affinity Fcgamma receptors (FcgammaRs) mediate the effects of immunoglobulin G (IgG) antibodies on leukocytes, including recruitment to inflammatory lesions, phagocytosis, antibody-dependent cellular cytotoxicity, release of inflammatory mediators and regulation of B cell activation. These functions are an important part of the mammalian response to infection, but if deployed inappropriately can cause autoimmune disease. Although most FcgammaRs are activatory, there is also an inhibitory FcgammaR that, when bound to IgG immune complexes, is able to downregulate the effects of both the activatory FcgammaRs and the B cell receptor. This review discusses the role of the low-affinity FcgammaRs in a balanced immune response and how perturbations in FcgammaR function result in susceptibility to infection or autoimmunity.

Human neutrophil Fcgamma receptors initiate and play specialized nonredundant roles in antibody-mediated inflammatory diseases

Inflammation mediated by antibody-antigen complexes contributes to autoimmune diseases. Mice deficient in the common Fcgamma-chain are protected from IgG-mediated glomerulonephritis and the reverse passive Arthus (RPA) reaction and FcR-bearing macrophages, and mast cells have been assigned primary roles in these processes. Here we demonstrate that neutrophil-selective transgenic expression of the two uniquely human neutrophil Fc gamma receptors (FcgammaRs), FcgammaRIIA and FcgammaRIIIB, in Fcgamma-chain-deficient mice restored susceptibility to progressive glomerulonephritis and the cutaneous RPA reaction. FcgammaRIIIB and FcgammaRIIA mediated neutrophil accumulation, whereas FcgammaRIIA alone promoted organ injury. In a model of soluble immune complexes deposited within the vasculature, FcgammaRIIIB was responsible for neutrophil slow rolling and adhesion whereas in the cremaster RPA, induced by both vascular and tissue soluble immune complexes, FcgammaRIIA predominated. Thus, human FcgammaRs on neutrophils serve as molecular links between antibody and immunological disease, with FcgammaRIIA promoting tissue injury and FcgammaRIIIB and FcgammaRIIA displaying specialized context-dependent functions in neutrophil recruitment.

Critical but overlapping role of FcgammaRIII and FcgammaRIV in activation of murine neutrophils by immobilized immune complexes

Immune complex-induced activation of neutrophils through cell surface FcRs plays a central role in the pathogenesis of autoimmune inflammatory diseases. These diseases are often modeled using genetically modified mice. However, in contrast to the number of studies on human cells, the identity of FcRs involved in immune complex activation of murine neutrophils is at present unknown. Furthermore, little is known about the cellular functions mediated by the recently identified murine FcgammaRIV. In this study, we tested the identity of FcRs involved in the activation of neutrophils by plate-bound immune complexes, using various knockout mouse strains, function-blocking mAbs, or the combination of both approaches. Activation of murine neutrophils by immobilized IgG immune complexes was abrogated in FcR gamma-chain-deficient cells, but not by the single or combined deficiency of the gamma-chain-associated FcgammaRI and FcgammaRIII, or by blocking Abs against either FcgammaRIII or FcgammaRIV alone. However, treatment of FcgammaRIII-deficient neutrophils with FcgammaRIV-blocking Abs or simultaneous blocking of FcgammaRIII and FcgammaRIV in wild-type cells completely inhibited the immune complex-induced cellular responses. In parallel studies, activation of human neutrophils by immobilized immune complexes was abrogated by blocking Abs against either FcgammaRIIA or FcgammaRIIIB alone. Taken together, neutrophil activation by immobilized immune complexes requires the murine FcgammaRIII/FcgammaRIV or the human FcgammaRIIA/FcgammaRIIIB molecules. Although both of the two human receptors are required for this response, the two murine receptors play overlapping, redundant roles. These results promote our understanding of autoimmune diseases and identify an IgG-dependent cellular function of FcgammaRIV.

Amelioration of crescentic glomerulonephritis by RhoA kinase inhibitor, Fasudil, through podocyte protection and prevention of leukocyte migration

The small GTPase RhoA is activated by the angiotensin II (AngII) type 1 receptor (AT1R), which is part of the local renin-angiotensin system that is involved in podocyte injury preceding glomerular crescent formation. We demonstrated previously that inhibition of AT1R protects against crescentic glomerular injury in Fc receptor-deficient mice (gamma -/-) with anti-glomerular basement membrane antibody-induced glomerulonephritis (anti-GBM GN). Here, we hypothesized that the RhoA kinase inhibitor, fasudil, attenuates AT1R-dependent crescentic GN. We examined anti-GBM GN in gamma -/- mice with or without fasudil treatment, and further investigated the underlying mechanisms in cultured differentiated podocytes and leukocytes. Fasudil markedly attenuated crescentic GN with a significant decrease in proteinuria and hematuria, infiltration of T cells and monocytes/macrophages as well as their local proliferation, and preservation of podocyte-specific proteins, including WT-1 and nephrin, in glomeruli. In vitro studies showed that AngII induced the down-regulation of both nephrin and WT-1 expression in podocytes, which was reversed by fasudil in a dose-dependent manner. Additionally, fasudil blocked the AngII-induced migration of both macrophages and T cells. Furthermore, we also examined lipopolysaccharide-induced nephrotic syndrome in severe combined immunodeficiency disease mice and found that fasudil failed to block the development of proteinuria because of a B7-1-dependent podocyte injury. In conclusion, fasudil treatment prevents crescent formation and disease progression in anti-GBM GN by preventing AngII-induced podocyte injury and leukocyte migration.

Activating Fc gamma receptors participate in the development of autoimmune diabetes in NOD mice

Type 1 diabetes mellitus (T1D) in humans is an organ-specific autoimmune disease in which pancreatic islet beta cells are ruptured by autoreactive T cells. NOD mice, the most commonly used animal model of T1D, show early infiltration of leukocytes in the islets (insulitis), resulting in islet destruction and diabetes later. NOD mice produce various islet beta cell-specific autoantibodies, although it remains a subject of debate regarding whether these autoantibodies contribute to the development of T1D. Fc gammaRs are multipotent molecules that play important roles in Ab-mediated regulatory as well as effector functions in autoimmune diseases. To investigate the possible role of Fc gammaRs in NOD mice, we generated several Fc gammaR-less NOD lines, namely FcR common gamma-chain (Fc Rgamma)-deficient (NOD.gamma(-/-)), Fc gammaRIII-deficient (NOD.III(-/-)), Fc gammaRIIB-deficient (NOD.IIB(-/-)), and both Fc Rgamma and Fc gammaRIIB-deficient NOD (NOD.null) mice. In this study, we show significant protection from diabetes in NOD.gamma(-/-), NOD.III(-/-), and NOD.null, but not in NOD.IIB(-/-) mice even with grossly comparable production of autoantibodies among them. Insulitis in NOD.gamma(-/-) mice was also alleviated. Adoptive transfer of bone marrow-derived dendritic cells or NK cells from NOD mice rendered NOD.gamma(-/-) animals more susceptible to diabetes, suggesting a possible scenario in which activating Fc gammaRs on dendritic cells enhance autoantigen presentation leading to the activation of autoreactive T cells, and Fc gammaRIII on NK cells trigger Ab-dependent effector functions and inflammation. These findings highlight the critical roles of activating Fc gammaRs in the development of T1D, and indicate that Fc gammaRs are novel targets for therapies for T1D.

Experimental anti-GBM disease as a tool for studying spontaneous lupus nephritis

Lupus nephritis is an immune-mediated disease, where antibodies and T cells both play pathogenic roles. Since spontaneous lupus nephritis in mouse models takes 6-12 months to manifest, there is an urgent need for a mouse model that can be used to delineate the pathogenic processes that lead to immune nephritis, over a quicker time frame. We propose that the experimental anti-glomerular basement membrane (GBM) disease model might be a suitable tool for uncovering some of the molecular steps underlying lupus nephritis. This article reviews the current evidence that supports the use of the experimental anti-GBM nephritis model for studying spontaneous lupus nephritis. Importantly, out of about 25 different molecules that have been specifically examined in the experimental anti-GBM model and also spontaneous lupus nephritis, all influence both diseases concordantly, suggesting that the experimental model might be a useful tool for unraveling the molecular basis of spontaneous lupus nephritis. This has important clinical implications, both from the perspective of genetic susceptibility as well as clinical therapeutics.

Enhanced susceptibility to immune nephritis in DBA/1 mice is contingent upon IL-1 expression

The DBA/1 mouse strain is particularly sensitive to experimental immune-mediated nephritis. Previous studies have indicated that various chemokines/cytokines are elevated in strains of mice susceptible to immune-mediated glomerulonephritis. One of the many elevated cytokines is IL-1. This study was designed to determine if IL-1 is essential for the development of immune-mediated nephritis in the DBA/1 mouse strain that is particularly sensitive to this disease. Both male and female DBA/1 mice and DBA/1.IL-1R1(-/-) mice were challenged with anti-GBM sera. We then compared DBA/1 mice to DBA/1.IL-1R1(-/-) mice to determine the influence of IL-1 on immune-mediated nephritis. Compared to DBA/1 mice, DBA/1.IL-1R1(-/-) mice excreted significantly less protein post anti-GBM serum challenge. None of the DBA/1.IL-1R1(-/-) mice, male or female, had a BUN higher than 22 mg/dl post-challenge whereas wild-type DBA/1 mice had significantly elevated BUN. Wild-type DBA/1 mice exhibited pronounced glomerulonephritis, with crescent formation, as well as tubulo-interstitial disease compared to DBA/1.IL1R1(-/-) mice. These findings indicate that IL-1 is necessary for the development of nephritis in DBA/1 mice and suggest that the elevated IL-1 levels in these mice may be one reason why the DBA/1 strain is particularly sensitive to multiple end organ diseases.

Mast cells and inflammatory kidney disease

Inflammatory kidney disease involves a complex network of interactions between resident kidney and infiltrating hematopoietic cells. Mast cells (MCs) are constitutively found in kidneys in small numbers but increase considerably in various renal diseases. While this increase is usually interpreted as a sign of pathological involvement, recent data using MC-deficient animals show their ability to restore kidney homeostasis. In anti-glomerular basement membrane antibody-induced glomerulonephritis, MCs are protective by initiating repair and remodeling functions counteracting the devastating effects of glomerular injury. Protection may also include immunoregulatory capacities to limit autoreactive T-cell responses. MCs also control tubulointerstitial fibrosis by activating tissue remodeling and neutralizing fibrotic factors. Release of mediators by MCs during inflammation, however, could also promote unwanted responses that ultimately lead to destruction of kidney structure, as exemplified by data showing either protection or aggravation in related renal disease models. Similarly, while the action of proteases may initially be beneficial, the generation of fibrosis-promoting angiotensin II by chymase also shows the limits of adaptive responses to achieve homeostasis. Thus, it is likely the physiological context involving the interaction with other cells and inflammatory mediators that determines the final action of MCs in the development of kidney disease.

Fc alpha receptor I activation induces leukocyte recruitment and promotes aggravation of glomerulonephritis through the FcR gamma adaptor

Myeloid cells bear Fc receptors (FcR) that mediate inflammatory signaling through the ITAM-containing FcRgamma adaptor. They express FcRgamma-associated FcalphaRI, which modulate either activating or inhibitory signaling depending on the type of ligand interaction. The role of FcalphaRIgamma in disease progression remains unknown, notably in IgA nephropathy (IgAN), one of major causes of end-stage renal disease, in which large amounts of circulating IgA-immune complexes (IC) may mediate receptor activation. To analyze the involvement of FcalphaRI activation in glomerulonephritis (GN), we generated Tg mice expressing a mutated, signaling-incompetent, human FcalphaRI(R209L) that cannot associate with FcRgamma. Like FcalphaRI(wt)-Tg mice, they developed mesangial IgA deposits but not macrophage infiltration. FcalphaRI activation in FcalphaRI(wt), but not in FcalphaRI(R209L), Tg mice resulted in marked inflammation with severe proteinuria and leukocyte infiltration in spontaneous IgAN or anti-glomerular basement membrane Ab-induced GN models. Receptor triggering of syngenically transferred FcalphaRI(wt) Tg macrophages into non-Tg animals induced their recruitment into injured kidneys during GN development. FcalphaRI(wt) cross-linking on macrophages activated MAP kinases and production of TNF-alpha and MCP-1. Moreover, IgA-IC from IgAN patients activated FcalphaRI and induced TNF-alpha production. Thus, FcalphaRI activation mediates GN progression by initiating a cytokine/chemokine cascade that promotes leukocyte recruitment and kidney damage.

Genetic basis of murine lupus nephritis

Systemic lupus erythematosus is a generalized autoimmune disease affecting multiple end-organs including the kidneys. Glomerulonephritis is a leading cause of death in lupus, both in patients and murine models that develop disease spontaneously. Genetic mapping studies have uncovered several genetic intervals that confer susceptibility to nephritis both in human beings and in mice. This review surveys the genomic positions of these nephritis susceptibility loci in murine lupus. Currently we know very little about the molecular identities of the culprit genes within these mapped loci and whether these genetic elements contribute to nephritis directly in a renal-intrinsic fashion or indirectly by augmenting the formation of pathogenic autoantibodies. The next decade is likely to witness a significant broadening of our understanding of how different genes and molecules might facilitate end-organ damage in lupus.