Differential capacity of anti-RAP and anti-megalin antibodies to produce progressive passive Heymann nephritis — implications for the pathogenesis of idiopathic human membranous glomerulonephritis

Combination therapy with DHA and BMSCs suppressed podocyte injury and attenuated renal fibrosis by modulating the TGF-β1/Smad pathway in MN mice

Artemisinin has immunomodulatory, anti-inflammatory, and antifibrotic effects. Some studies have demonstrated that artemisinins have a protective effect on the kidney. DHA is a derivative of artemisinin and has effects similar to those of artemisinin. Human bone marrow-derived mesenchymal stem cells (BMSCs) accelerate renal repair following acute injury. In the study, we investigated the effects of combination therapy with DHA and BMSCs on membranous nephropathy (MN) mice. The 24-h urinary protein, serum total cholesterol (TC) and triglyceride (TG) levels, and renal histopathology, were measured to evaluate kidney damage. Anti-PLA2R, IgG, and complement 3 (C3) were detected by ELISA. The expression levels of the podocyte injury-related proteins were analyzed by immunohistochemistry. The protein expression levels of α-SMA, ED-1, TGF-β1, p-Smad2, and p-Smad3 were detected by western blot to analyze renal fibrosis and its regulatory mechanism. Results showed that combination therapy with DHA and BMSCs significantly ameliorated kidney damage in MN model mice by decreasing the levels of 24 h urinary protein, TC and TG. This combination therapy also improved renal histology and reduced the expression of IgG and C3 in the glomerulus. In addition, this combination therapy decreased the expression of podocin and nephrin and relieved renal fibrosis by downregulating α-SMA and ED-1. Furthermore, this combination therapy suppressed TGF-β1 expression and Smad2/3 phosphorylation. This result (i.e., this combination therapy inhibited the TGF-β1/Smad pathway) was also supported in vitro. Taken together, combination therapy with DHA and BMSCs ameliorated podocyte injury and renal fibrosis in MN mice by downregulating the TGFβ1/Smad pathway.

Crocin improves the renal autophagy in rat experimental membranous nephropathy via regulating the SIRT1/Nrf2/HO-1 signaling pathway

Membranous nephropathy (MN) is a glomerular disease. Crocin is isolated from saffron and gardenia. Its antioxidant, anti-inflammatory, anti-hyperlipidemic, anti-atherosclerotic, anti-tumor, free-radical scavenging and neuroprotective activities have been well established. We investigated the biological functions of crocin and its related mechanisms in MN. We established an experimental passive Heymann nephritis (PHN) rat model induced by anti-Fx1A antiserum. The rats were divided into sham, sham + crocin, PHN, PHN + crocin, and PHN + enalapril groups. Blood samples and kidneys of rats were collected for estimation of biochemical parameters in serum and oxidative stress indicators in kidney tissues. Histopathological changes of renal tissues were evaluated by hematoxylin and eosin, periodic acid-Schiff (PAS) and Masson staining. The podocyte number was estimated by immunohistochemistry staining of Wilms tumor type 1 (WT1). The deposition of rat anti-rabbit IgG antibodies, complement C3 and C5b-9 was detected by immunofluorescence staining. Western blotting was performed to measure the levels of Sirtuin 1 (Sirt1), nuclear factor erythroid 2-related factor 2 (Nrf2), heme oxygenase 1 (HO-1) and apoptosis-related proteins. The total cholesterol, triglycerides, creatinine, blood urea nitrogen, urine volume and urine albumin of PMN rats were significantly reduced by crocin. Additionally, crocin attenuated the renal histopathological changes. Moreover, the oxidative stress damage and podocyte loss and immune injury were relieved by crocin in PHN rats. Mechanistically, crocin administration activated the Sirt1/Nrf2/HO-1 pathways. The results provide a scientific basis that crocin could alleviate MN by inhibiting immune injury and podocyte damage through activating the Sirt1/Nrf2/HO-1 pathways.

Multi-antibody composition in lupus nephritis: isotype and antigen specificity make the difference

Research on autoimmune processes involved in glomerulonephritis has been for years based on experimental models. Recent progress in proteomics has radically modified perspectives: laser microdissection and proteomics were crucial for an in vivo analysis of autoantibodies eluted from human biopsies. Lupus nephritis has been the subject of recent independent researches. Main topics have been the definition of renal autoimmune components in human lupus biopsies; methods were laser capture of glomeruli and/or of single cells (CD38+ or Ki-67+) from tubulointerstitial areas as starting step followed by elution and characterization of renal antibodies by proteomics. The innovative approach highlighted different panels of autoantibodies deposited in glomeruli and in tubulo-interstitial areas that actually represented the unique autoimmune components in these patients. IgG2 was the major isotype; new podocyte proteins (αenolase, annexin AI) and already known implanted molecules (DNA, histone 3, C1q) were their target antigens in glomeruli. Vimentin was the antigen in tubulo-interstitial areas. Matching renal autoantibodies with serum allowed the definition of a typical autoantibody serum map that included the same anti-αenolase, anti-annexin AI, anti-DNA, and anti-histone 3 IgG2 already detected in renal tissue. Serum levels of specific autoantibodies were tenfold increased in patients with lupus nephritis allowing a clear differentiation from both rheumatoid arthritis and other glomerulonephritis. In all cases, targeted antigens were characterized as components of lupus NETosis. Matching renal/serum autoantibody composition in vivo furnishes new insights on human lupus nephritis and allows to refine composition of circulating antibodies in patients with lupus. A thoughtful passage from bench to bedside of new knowledge would expand our clinical and therapeutic opportunities.

Artemisinin analogue SM934 ameliorates the proteinuria and renal fibrosis in rat experimental membranous nephropathy

AIM

SM934 is a novel water-soluble artemisinin derivative with immunoregulatory activities that has been used to treat murine lupus nephritis. In the current study, we investigated the effects of SM934 on rat experimental membranous nephropathy.

METHODS

Passive Heymann nephritis (PHN) was induced in SD rats by intraperitoneal injection of anti-Fx1A serum. The rats were orally administered SM934 (12.5 and 25 mg·kg(-1)·d(-1)) or prednisolone (5 mg·kg(-1)·d(-1)) for 28 d. Blood and urine sample, and kidney tissue were collected for analyses. Human complement C3a-induced injury of HK-2 cells was used for in vitro experiments.

RESULTS

Treatment of PHN rats with SM934 or prednisolone attenuated the progression of glomerulonephritis and renal fibrosis, as evidenced by the reduced level of proteinuria and circulating antibodies, as well as by the reduced immune complex deposition, reversed podocyte injuries, and attenuated tubulointerstitial fibrosis in the kidneys. Furthermore, the two drugs suppressed TGF-β1 expression and Smad2/3 phosphorylation, and increased Smad7 expression in the kidneys. The two doses of SM934 produced almost identical therapeutic effects on PHN rats. Pretreatment with SM934 or a C3a receptor antagonist blocked the C3a-induced epithelial-mesenchymal transition in HK-2 cells in vitro.

CONCLUSION

SM934 ameliorates kidney injury and attenuates the tubulointerstitial fibrosis in PHN rats by down-regulation of the TGF-β1/Smad signaling pathway.

Idiopathic membranous nephropathy: an autoimmune disease

For more than 50 years researchers have debated the evidence for an autoimmune basis of human idiopathic membranous nephritis (MN). Work published in the past 2 years has substantially strengthened the belief that MN is indeed an autoimmune disease of the kidney. Autoantibodies of the IgG4 subclass to at least three podocyte membrane proteins including phospholipase A(2)-receptor, aldose reductase, and manganese superoxide dismutase have been detected by immunoblotting in sera as well as in acid eluates prepared from renal biopsy tissue of patients with this disease, using either whole tissue or microdissected glomeruli from frozen sections. In each case the podocyte antigen has been shown to co-localize with the subepithelial glomerular immune deposits in renal tissue of the same patients. It is not certain if any of these podocyte proteins is an inciting/primary autoantigen or whether they are secondary antigens recruited by intermolecular epitope-spreading, initiating from a yet-to-be-discovered autoantigen. Although it is clear that autoantibodies to podocyte membrane proteins are elicited in idiopathic MN and contribute to the formation of the subepithelial deposits, many questions remain concerning the triggers for their development and their contribution toward proteinuria and progression of the disease.

Experimental Models of Membranous Nephropathy

Membranous nephropathy (MN) is one of the commonest glomerular diseases, typically presenting in older males with nephrotic syndrome. The development and characterization of animal models of MN, in particular, the passive Heymann nephritis model (PHN), has greatly advanced our understanding of this disease. In this review we discuss the different animal models of human MN that are available, with an emphasis on the PHN model, including technical issues, the typical disease course and its application to human disease.

Inducible rodent models of acquired podocyte diseases

Glomerular diseases remain the leading cause of chronic and end-stage kidney disease. Significant advances in our understanding of human glomerular diseases have been enabled by the development and better characterization of animal models. Diseases of the glomerular epithelial cells (podocytes) account for the majority of proteinuric diseases. Rodents have been extensively used experimentally to better define mechanisms of disease induction and progression, as well as to identify potential targets and therapies. The development of podocyte-specific genetically modified mice has energized the research field to better understand which animal models are appropriate to study acquired podocyte diseases. In this review we discuss inducible experimental models of acquired nondiabetic podocyte diseases in rodents, namely, passive Heymann nephritis, puromycin aminonucleoside nephrosis, adriamycin nephrosis, liopolysaccharide, crescentic glomerulonephritis, and protein overload nephropathy models. Details are given on the model backgrounds, how to induce each model, the interpretations of the data, and the benefits and shortcomings of each. Genetic rodent models of podocyte injury are excluded.

Intramolecular epitope spreading in Heymann nephritis

Immunization with megalin induces active Heymann nephritis, which reproduces features of human idiopathic membranous glomerulonephritis. Megalin is a complex immunological target with four discrete ligand-binding domains (LBDs) that may contain epitopes to which pathogenic autoantibodies are directed. Recently, a 236-residue N-terminal fragment, termed "L6," that spans the first LBD was shown to induce autoantibodies and severe disease. We used this model to examine epitope-specific contributions to pathogenesis. Sera obtained from rats 4 weeks after immunization with L6 demonstrated reactivity only with the L6 fragment on Western blot, whereas sera obtained after 8 weeks demonstrated reactivity with all four recombinant fragments of interest (L6 and LBDs II, III, and IV). We demonstrated that the L6 immunogen does not contain the epitopes responsible for the reactivity to the LBD fragments. Therefore, the appearance of antibodies directed at LBD fragments several weeks after the primary immune response suggests intramolecular epitope spreading. In vivo, we observed a temporal association between increased proteinuria and the appearance of antibodies to LBD fragments. These data implicate B cell epitope spreading in antibody-mediated pathogenesis of active Heymann nephritis, a model that should prove valuable for further study of autoimmune dysregulation.

Target antigens and nephritogenic antibodies in membranous nephropathy: of rats and men

Membranous nephropathy, a disease characterized by an accumulation of immune deposits on the outer aspect of the glomerular basement membrane, is the most common cause of idiopathic nephrotic syndrome in white adults. In the rat model of Heymann nephritis, the target antigen of antibodies is megalin, a multiligand receptor expressed at the podocyte cell surface. This review summarizes key findings provided by this experimental model and by our discovery of neutral endopeptidase being the alloantigen involved in neonatal cases of membranous nephropathy. We discuss the role of alloimmunization as a new mechanism of renal disease and the approach that we use to identify new podocyte antigens. We also summarize current knowledge on the mechanism of proteinuria, with special emphasis on the role of complement. In conclusion, substantial progresses have been made in understanding molecular mechanisms of membranous nephropathy, which should lead to novel therapeutic approaches.

Podocyte antigens and glomerular disease

BACKGROUND

Membranous nephropathy (MN), a major cause of nephrotic syndrome in the adult, is an immune-mediated disease characterized by the accumulation of subepithelial immune deposits leading to complement activation and podocyte injury. However, the target antigens of circulating antibodies are unknown. Current treatments for patients with MN are entirely empirical, and concept-driven therapies are dramatically lacking.

METHODS

Specificity of circulating antibodies and composition of glomerular deposits were analyzed in Heymann nephritis (HN), a faithful rat model of MN, and in a subset of patients with antenatal MN.

RESULTS

20 years after the identification of megalin as the podocyte target antigen of nephritogenic antibodies in HN, we identified the human counterpart of megalin, the enzymatic podocyte antigen neutral endopeptidase (NEP). Antibodies to megalin or NEP induce formation of subepithelial immune deposits and of C5b-9, the membrane attack complex of complement.

CONCLUSION

It is likely that antigens involved in idiopathic MN are expressed at the podocyte membrane. Their identification together with that of immunodominant epitopes may lead to specific antigen/ epitope-based immunotherapy aimed at inducing specific tolerance.