Rapamycin attenuates PLA2R activation-mediated podocyte apoptosis via the PI3K/AKT/mTOR pathway.

Membranous nephropathy (MN) is the most common cause of nephrotic syndrome in adults without diabetes. Primary MN has been associated with circulating antibodies against native podocyte antigens, including phospholipase A2 receptor (PLA2R); however, precision therapy targeting the signaling cascade of PLA2R activation is lacking. Both PLA2R and the mammalian target of rapamycin (mTOR) exist in podocytes, but the interplay between these two proteins and their roles in MN warrants further exploration. This study aimed to investigate the crosstalk between PLA2R activation and mTOR signaling in a human podocyte cell line. We demonstrated that podocyte apoptosis was induced by Group IB secretory phospholipase A2 (sPLA2IB) in a concentration- and time-dependent manner via upregulation of phosphoinositide 3-kinase (PI3K), protein kinase B (AKT), and mTOR, and inhibited by rapamycin or LY294002. Furthermore, aberrant activation of the PI3K/AKT/mTOR pathway triggers both extrinsic (caspase-8 and caspase-3) and intrinsic (Bcl-2-associated X protein [BAX], B-cell lymphoma 2 [BCL-2], cytochrome c, caspase-9, and caspase-3) apoptotic cascades in podocytes. The therapeutic implications of our findings are that strategies to reduce PLA2R activation and PI3K/AKT/mTOR pathway inhibition in PLA2R-activated podocytes help protect podocytes from apoptosis. The therapeutic potential of rapamycin shown in this study provides cellular evidence supporting the repurposing of rapamycin for MN treatment.

Podocytic Infolding Glomerulopathy in a Patient with Phospholipase A2 Receptor-Positive Membranous Nephropathy and Review of the Literature.

Podocytic infolding glomerulopathy (PIG) is a rare diagnosis based on characteristic histopathologic findings on renal biopsy and was proposed as a new entity about a decade ago. It is a type of podocytic injury, characterized by invagination of the podocyte cell membrane (cytoplasmic projections from podocytes) into the glomerular basement membrane. The presence of microspheres and/or microtubules on electron microscopy is the characteristic finding. PIG is most often associated with autoimmune conditions like systemic lupus erythematosus. We report pathologic findings typical of PIG in a patient with phospholipase A2 receptor antibody-positive membranous nephropathy. She was treated with rituximab and responded well with decrease in proteinuria to the sub-nephrotic range.

Features of phospholipase A2 receptor and thrombospondin type-1 domain-containing 7A in malignancy-associated membranous nephropathy.

AIMS: Phospholipase A2 receptor (PLA2R) and thrombospondin type-1 domain-containing 7A (THSD7A) were identified as pathogenic antigens in patients with membranous nephropathy (MN). Notably, PLA2R is detected in few patients with malignancy-associated MN, and a high incidence of cancer is reported in patients with THSD7A-associated MN. Therefore, the roles of PLA2R and THSD7A in malignancy-associated MN must be clarified. METHODS: Serum anti-PLA2R antibodies and glomerular PLA2R staining were assessed in 36 patients with malignancy-associated MN, followed by examination of serum anti-THSD7A antibodies and glomerular THSD7A. THSD7A staining in cancer tissues was also assessed in 9 of the 36 patients. RESULTS: Twelve (33%) of 36 patients were positive for both glomerular PLA2R and serum anti-PLA2R antibodies, one of whom had enhanced glomerular THSD7A staining. Two patients were positive for either glomerular PLA2R or serum anti-PLA2R antibody. All these patients had IgG4-dominant deposits in glomeruli. Among the 22 (61%) patients who were double negative for glomerular PLA2R and serum anti-PLA2R antibodies, 17 of 20 (85%) had IgG1-dominant deposits in glomeruli, and 2 (9.1%) were positive for glomerular THSD7A staining. Serum anti-THSD7A antibody was not detected in any of the 36 patients. Among the nine patients with available cancer tissues, positive staining of THSD7A in the cancer tissues was observed in five (56%) patients, and one showed enhanced glomerular staining of THSD7A. CONCLUSIONS: Screening of glomerular PLA2R antigen and serum anti-PLA2R antibodies is necessary in patients with malignancy-associated MN, whereas the incidence of glomerular THSD7A antigen or circulating anti-THSD7A antibodies is uncommon.

Urine exosomal ceruloplasmin: a potential early biomarker of underlying kidney disease.

BACKGROUND: Previously we found that kidney tissue and urinary exosomes from patients of diabetic kidney disease showed high levels of ceruloplasmin (CP). Because CP is an acute-phase protein of kidney origin, it could be an early marker of many other kidney diseases. To investigate this hypothesis, we first measured urine exosomal and kidney expression of CP in non-diabetic chronic kidney disease (CKD) patients (membranous nephropathy, focal segmental glomerulosclerosis, lupus nephritis and IgA nephropathy) followed by a longitudinal study in rat passive Heymann nephritis (PHN), a model of human membranous nephropathy. METHODS: Urinary exosomes were isolated from urine of patients (and rats) by differential centrifugation. The exosomal extracts were used for measuring CP using ELISA. Kidney expression of CP was evaluated by immune-staining biopsy tissues. Similar techniques were applied in rat PHN model (produced by injection of anti-gp600 antiserum) to analyze urine exosomal and kidney CP. RESULTS: Urine exosomal CP levels were 10-20 times higher in CKD patients than in controls; consistent with this we found high immune-reactive CP localized in tubules and collecting ducts of biopsies of CKD patients. In the PHN model urinary exosomal CP level was significantly higher prior to the onset of proteinuria. Early rise of urine exosomal CP, which preceded proteinuria, correlated with high immunoreactive CP found in rat kidneys at this time. CONCLUSION: We propose that urine exosomal CP, observed to increase prior to proteinuria, makes it a potential urinary biomarker to diagnose early kidney disease.

Circulating antibodies to α-enolase and phospholipase A2 receptor and composition of glomerular deposits in Japanese patients with primary or secondary membranous nephropathy.

BACKGROUND: Phospholipase A2 receptor (PLA2R) is recognized as a target antigen in primary membranous nephropathy (MN); Anti-α-enolase antibody in primary and secondary MN has been proposed, however, little is known about the potential contribution of α-enolase to the pathogenesis of MN. METHODS: We evaluated circulating antibodies to α-enolase by a dot blotting system and PLA2R by indirect immunofluorescence, and glomerular deposition of these proteins in 25 patients with primary MN, 20 patients with secondary MN, 44 patients with collagen disease or severe infection, 60 patients with nephritis (each ten patients of IgA nephropathy, focal segmental gloemrulosclerosis, minimal change nephrotic syndrome, membranoproliferative glomeurlonephritis, diabetic glomerulosclerosis, and tubulointerstitial nephritis) as disease control, and 20 healthy subjects. RESULTS: In primary MN, 18 of 25 sera (72 %) showed anti-α-enolase antibody (IgG1 and IgG4, 11 pts; IgG4 alone, six pts; IgG1 alone, one pt). In secondary MN, 15 of 20 sera (75 %) contained anti-α-enolase antibody (IgG1 and IgG3, 13 pts; IgG3 alone, two pts). No circulating anti-α-enolase antibody was found in 44 collagen diseases or septic patients, 60 nephritis without MN, and 20 healthy subjects. Twelve of 25 sera (48 %) from patients with primary MN were positive for anti-PLA2R antibody, whereas all patients with secondary MN were negative. Eight of the 12 PLA2R-positive patients (67 %) with primary MN also had anti α-enolase antibody. Although PLA2R antigen was present in a subepithelial pattern in 10 of 19 (52 %) patients with primary MN, α-enolase was never detected in glomerular deposits in 19 and ten patients with primary and secondary MN, respectively. CONCLUSIONS: Circulating anti-α-enolase antibodies are highly present in both primary and secondary MN (about 70 %, respectively), while anti-PLA2R antibodies are specific for primary MN (48 %) with a prevalence apparently lower in the Japanese population than in Chinese and Caucasian populations. The absence of α-enolase from subepithelial immune deposits suggests that anti-α-enolase antibodies do not contribute directly to immune-deposit formation, although they may have other pathogenic effects.

Antibodies to m-type phospholipase A2 receptor in children with idiopathic membranous nephropathy.

Idiopathic membranous nephropathy (IMN), the commonest cause of adult nephrotic syndrome (NS), accounts for only a minority of paediatric NS. Antibodies to m-type phospholipase A2 receptor (PLA2R) are seen in two-thirds of adult IMN cases. PLA2R staining in glomerular deposits is observed in 74% and 45% of adult and paediatric IMN cases, respectively. However, there are no reports of anti-PLA2R in paediatric IMN. We evaluated anti-PLA2R levels and PLA2R in gloemrular deposits in paediatric IMN seen at our center. Five cases were enrolled, all the cases stained for PLA2R in glomeruli and three (60%) had antibodies to PLA2R antigen. There was a parellel reduction in proteinuria and anti-PLA2R titer. The present report suggests that PLA2R has a contributory role in the pathogenesis of paediatric IMN.

Anti-PLA2R-associated membranous nephropathy: a review with emphasis on diagnostic testing methods.

The majority of cases of primary membranous nephropathy (MN) are associated with auto-antibodies against the podocyte antigen M-type phospholipase A2 receptor (PLA2R). This particular subset of MN can be diagnosed by identifying anti-PLA2R within patient sera or by detecting PLA2R antigen within glomerular immune complexes in renal biopsy tissue. Since the discovery of anti-PLA2R in 2009, there has been an abundance of literature regarding PLA2R testing as a tool in the diagnosis and management of MN, and these tests are increasingly being implemented in clinical practice. However, questions still remain about a variety of issues such as PLA2R testing in the setting of presumably secondary MN and the significance of PLA2R negative primary MN. The goal of this review is to summarize the current PLA2R testing methods and highlight special features of anti- PLA2R-associated MN.

NF-κB upregulates ubiquitin C-terminal hydrolase 1 in diseased podocytes in glomerulonephritis.

Podocyte injury is a pivotal factor during the progression of glomerular diseases. It has been demonstrated that the expression of ubiquitin carboxy-terminal hydrolase L1 (UCH-L1) is increased in injured podocytes in a number of types of glomerulonephritis. However, its mechanism of regulation remains to be elucidated. A previous study by our group suggested that UCH-L1 is a downstream protein of nuclear factor (NF)-κB signaling. In the present study, the involvement of NF-κB in the regulation of the expression of UCH-L1 was investigated in diseased podocytes in vivo and in vitro. Increases in the expression of phosphorylated NF-κB at p65 and UCH-L1 were detected using immunohistochemical analysis of kidney biopsy tissues from 56 cases of nephritis, including immunoglobulin A nephropathy, membranous glomerulonephritis and lupus nephritis. The two indicators were also analyzed using western blot analysis in cultured murine podocytes stimulated by inflammatory factors. The results of the present study demonstrated that in human renal biopsies of several cases of immune complex-mediated glomerulonephritis, the increases of NF-κB and UCH-L1 were positively correlated with the number of diseased podocytes. By contrast, in non-immune complex-mediated glomerulonephritis, no clear activation of NF-κB and increase of UCH-L1 expression was observed. In vitro, immune stimulation also led to the upregulation of UCH-L1 through the NF-κB signaling pathway in mouse podocytes. In conclusion, the results of the present study suggested that the activation of NF-κB and upregulation of UCH-L1 in podocytes may be vital in podocyte injury associated with immune complex-mediated glomerulonephritis.

[Association of single nucleotide polymorphism in M-type phospholipase A2 receptor gene with membranous nephropathy].

OBJECTIVE: To assess the association between single nucleotide polymorphism in M-type phospholipase A2 receptor (PLA2R) gene and membranous nephropathy (MN) in a Chinese Han population. METHODS: A total of 430 non-related Chinese Hans were enrolled, which included 145 patients with idiopathic membranous nephropathy (IMN), 53 patients with secondary MN and 232 normal controls (NC). The polymorphism of rs35771982 in PLA2R gene was determined with polymerase chain reaction-restriction fragment length polymorphism assay. Serum anti-PLA2R antibodies were detected by Western blotting. RESULTS: The genotypic and allelic frequencies for rs35771982 was significantly different among the three groups (P=0.004; P<0.001). CC genotype and C allele were significantly more common in IMN group compared with NC group (P=0.002; P<0.001) or secondary MN group (P=0.011; P=0.001). In the IMN group, the CC genotype was correlated with serum albumin (Alb), 24-hour urine protein (24h UP) and positive rate of serum anti-PLA2R antibody (P<0.001, P<0.001, P=0.010), and was a risk factor for IMN (OR=8.927, 95%CI:2.107-37.821, P=0.003). CONCLUSION: The CC genotype and C allele at rs35771982 in PLA2R gene are associated with susceptibility to IMN in Chinese Hans. The associations between CC genotype and severity of IMN as well as serum anti-PLA2R antibody have indicated that production of anti-PLA2R autoantibody in IMN patients is associated with mutation at the rs35771982 locus of PLA2R gene.

Complement-mediated activation of calcium-independent phospholipase A2γ: role of protein kinases and phosphorylation.

In experimental membranous nephropathy, complement C5b-9-induces glomerular epithelial cell (GEC) injury and proteinuria. The effects of C5b-9 are mediated via signaling pathways, including calcium-independent phospholipase A(2)γ (iPLA(2)γ), and mitogen-activated protein kinases (MAPKs) such as extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK), and p38. The iPLA(2)γ pathway is cytoprotective. This study addresses the mechanisms of iPLA(2)γ activation. iPLA(2)γ activity was monitored by quantifying prostaglandin E(2) (PGE(2)) production. In GECs, iPLA(2)γ localized at the endoplasmic reticulum and mitochondria. Complement-mediated production of PGE(2) was amplified in GECs that overexpress iPLA(2)γ, compared with control cells, and was blocked by the iPLA(2)γ inhibitor bromoenol lactone in both iPLA(2)γ-overexpressing and control GECs. In GECs that overexpress iPLA(2)γ, complement-mediated PGE(2) production was reduced by inhibitors of MAP/ERK kinase 1 (MEK1) and p38 but not JNK. In COS-1 cells that overexpress iPLA(2)γ and cyclooxygenase-1, PGE(2) production was induced by co-expression of constitutively active MEK1 or MAPK-interacting kinase 1 (MNK1) as well as by stimulation with epidermal growth factor (EGF) + ionomycin. Complement- and EGF + ionomycin-stimulated iPLA(2)γ activity was attenuated by the S511A/S515A double mutation. Moreover, complement and EGF + ionomycin enhanced phosphorylation of Ser-511. Thus, complement-mediated activation of iPLA(2)γ is mediated via ERK and p38 pathways, and phosphorylation of Ser-511 and/or Ser-515 plays a key role in the catalytic activity and signaling of iPLA(2)γ. Defining the mechanisms by which complement activates iPLA(2)γ provides opportunities for development of novel therapeutic approaches to GEC injury and proteinuria.

Does treatment with corticosteroids and cyclosporine reduce transglutaminase type 2 expression in the renal tissue of patients with membranous nephropathy?

BACKGROUND/AIMS: Membranous nephropathy (MN) is the most common cause of nephrotic syndrome in adults. Transglutaminase type 2 (TG2) contributes to renal scarring through altering extracellular matrix homeostasis. In this study we hypothesized that immunosuppressive treatment would downregulate TG2 expression leading to reduced fibrosis, and subsequently TG2 would have value as a biomarker of progression of MN. METHODS: TG2 expression was studied by immunofluorescence in kidney biopsy sections from 32 patients with MN and was compared to control biopsies. All patients were subsequently treated by a combination of cyclosporine and prednisolone for at least 24 months with a repeat biopsy taken in 14 patients. RESULTS: Twenty-two out of 32 patients showed stable renal function, whereas 10 showed doubling of baseline serum creatinine and 5 of them reached end-stage renal disease during the 5-year follow-up. At the end of the follow-up, 22 out of 32 patients were in remission of nephrotic syndrome. TG2 immunostaining was increased in sections from patients with MN compared to healthy controls (p = 0.0002). TG2 at diagnosis was more intense in patients with severer interstitial fibrosis and advanced glomerular sclerosis. TG2 significantly increased in most patients in the repeat biopsies after treatment (p < 0.0001), whereas patients who showed a marked increase in interstitial fibrosis in the repeat biopsy had significantly more TG2 expression in the first biopsy (p = 0.02). CONCLUSION: TG2 expression is increased in MN patients and continues to increase despite immunosuppressive treatment. However, early detection of TG2 might be of value in MN since increased TG2 production seems to precede extensive interstitial fibrosis.

Coexistence of different circulating anti-podocyte antibodies in membranous nephropathy.

BACKGROUND AND OBJECTIVES: The discovery of different podocyte autoantibodies in membranous nephropathy (MN) raises questions about their pathogenetic and clinical meaning. This study sought to define antibody isotypes and correlations; to compare levels in MN, other glomerulonephritides, and controls; and to determine their association with clinical outcomes. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS: Serum IgG(1), IgG(3), and IgG(4) against aldose reductase (AR), SOD2, and α-enolase (αENO) were measured at diagnosis in 186 consecutive MN patients, in 96 proteinuric controls (36 with FSGS, and 60 with IgA nephropathy), and in 92 healthy people recruited in four Italian nephrology units. Anti-phospholipase A2 receptor (PLA2r) and anti-neutral endopeptidase (NEP) IgG(4) were titrated in the same specimens. Association with 1-year follow-up clinical parameters was studied in 120 patients. RESULTS: IgG(4) was the most common isotype for all antibodies; IgG(1) and IgG(3) were nearly negligible. IgG(4) levels were positive in a significant proportion of MN patients (AR, 34%; SOD2, 28%; αENO, 43%). Antibody titers were higher in MN than in healthy and pathologic controls (P<0.005). Anti-NEP IgG(4) did not differ from normal controls (P=0.12). Anti-PLA2r IgG(4) was detected in 60% of patients and correlated with anti-AR, anti-SOD2, and anti-αENO IgG(4) (P<0.001). In MN patients negative for the whole antibody panel (20%), 1-year proteinuria was lower compared with patients with at least one antibody positivity (P<0.05). CONCLUSIONS: Our data suggest that IgG(4) is the prevalent isotype for antibodies against cytoplasmic antigens of podocytes (AR, SOD2, αENO). Their levels were higher than in other proteinuric glomerulonephritides and in normal controls and were correlated with anti-PLA2r. Only baseline negativity for all known antibodies predicted lower 1-year proteinuria.

Computational prediction and experimental assessment of an HLA-A*0201-restricted cytotoxic T lymphocyte epitope from neutral endopeptidase.

Neutral endopeptidase (NEP) is the first target antigen identified on podocytes in human membranous nephropathy (MN). Cytotoxic T lymphocytes (CTLs) are considered essential for glomerular destruction in MN model. The aim of this study was to show that the CTL epitopes of NEP could be used to design more effective and better tolerated therapies. The CTL epitopes of NEP were screened using the long-distance prediction system SYFPEITHI and the Bioinformatics and Molecular Analysis Section of the MHC Peptide Binding Predictions program. Peptides were synthesized and immunoreactivity was assessed by peptide-MHC-binding affinity assay, cytotoxicity assay and HLA-A2.1/Kb transgenic mice immunization. Five candidates were identified according to the high scores generated by the computer predicting system. Peptide NEP(375-383) (FIMDLVSSL), which up-regulated HLA-A2.1 molecular expression, showed a high affinity to HLA-A2.1, whereas NEP(268-276), NEP(297--305) and NEP(492-500) (QLALEMNKV, MLLYNKMRL and KLNNEYLEL) showed a moderate affinity and NEP(559-567) (ILQPPFFSA) only had a low affinity. Cytotoxicity assay further showed that NEP(268-276) and NEP(375-383) could induce NEP-specific CTL responses in vitro. Unexpectedly, we found that a single CTL epitope, NEP(375-383), could induce proteinuria and glomerular injury in HLA-A2.1/K(b) transgenic mice in vivo. HLA-A*0201-restricted CTL epitope NEP(375-383) can serve as a potential candidate for designing MN vaccine.

Melatonin enhances endogenous heme oxygenase-1 and represses immune responses to ameliorate experimental murine membranous nephropathy.

Idiopathic membranous nephropathy (MN), an autoimmune-mediated glomerulonephritis, is one of the most common causes of nephrotic syndrome in adults. Therapeutic agents for MN remain ill defined. We assessed the efficacy of melatonin therapy for MN. Experimental murine MN was induced with cationic bovine serum albumin, and the mice were immediately administered 20 mg/kg melatonin or phosphate-buffered saline subcutaneously once a day. Disease severity was verified by examining serum and urine metabolic profiles and renal histopathology. The expression of cytokines and oxidative stress markers, cell apoptosis, and the associated mechanisms were also determined. Mice treated with melatonin displayed a significant reduction in proteinuria and a marked amelioration of glomerular lesions, with attenuated immunocomplex deposition. The subpopulations of T cells were not altered, but the CD19(+) B-cell subpopulation was significantly reduced in the MN mice treated with melatonin. The expression of cytokine mRNAs in splenocytes indicated that melatonin reduced the expression of proinflammatory cytokines and increased the expression of anti-inflammatory cytokines (interleukin 10). The production of reactive oxygen species and TUNEL-positive apoptotic cells in the kidney were also significantly reduced in the melatonin-treated MN mice. Melatonin also upregulated heme oxygenase 1 (HO1) and ameliorated MN. The blockade of HO1 expression with SnPP, a HO1 inhibitor, attenuated HO1 induction by melatonin and thus mitigated its renoprotective effects during MN. Our results suggest that melatonin treatment ameliorates experimental MN via multiple pathways, including by its antioxidative, antiapoptotic, and immunomodulatory effects. Melatonin should be considered a potential therapeutic intervention for MN in the future.

Effect of statin therapy on contrast-induced nephropathy after coronary angiography: a meta-analysis.

BACKGROUND: Although the pleiotropic effects of statins are postulated to be renoprotective, clinical studies have demonstrated conflicting results. We undertook a meta-analysis of published trials to evaluate the impact of statin therapy on the incidence of contrast-induced nephropathy (CIN) in patients undergoing coronary angiography. METHODS: We searched MEDLINE and EMBASE databases through December 2010 for articles evaluating the effect of statins on the incidence of CIN in patients undergoing coronary angiography. Odds ratios (OR) with 95% confidence intervals (CI) were calculated using random effects modeling. RESULTS: Three randomized controlled trials involving 770 patients (330 in the statin group and 340 in the control group) and 7 non-randomized studies involving 31,959 patients (11,936 statin-pretreated and 20,023 statin-naïve). The definition of CIN varied somewhat among the studies. Based on the pooled estimate across the 3 randomized controlled trials, statin therapy did not significantly reduce the incidence of CIN compared to control (OR=0.76, 95% CI: 0.41-1.41, p=0.39). No significant heterogeneity was found in the randomized studies (I(2)=0%, p=0.48). The pooled analysis of the non-randomized studies showed a marginally significant benefit associated with statin therapy (OR=0.60, 95% CI: 0.36-1.00, p=0.05). There was significant heterogeneity among the non-randomized studies (I(2)=88%, p<0.00001). CONCLUSIONS: Our meta-analysis suggests that statin therapy might be associated with a significant reduction in the incidence of CIN in patients undergoing coronary angiography. Further studies are warranted to clarify this issue.

Detection of myeloperoxidase in membranous nephropathy-like deposits in patients with anti-neutrophil cytoplasmic antibody-associated glomerulonephritis.

Anti-neutrophil cytoplasmic antibody-associated glomerulonephritis is usually classified as a pauci-immune type. However, it sometimes shows immune complex deposition of unknown origin. We examined the glomerular localization of myeloperoxidase by double immunofluorescence and immunoelectron microscopy in cases of anti-neutrophil cytoplasmic antibody-associated glomerulonephritis with membranous nephropathy-like immunoglobulin G deposition to investigate the immune complex antigens in these cases. Six (35%) of the biopsy samples from 17 cases with anti-neutrophil cytoplasmic antibody-associated glomerulonephritis showed granular deposition of immunoglobulin G along the glomerular capillary walls. Light microscopy revealed necrotizing crescentic glomerulonephritis with segmental thickening of the glomerular basement membrane. Electron microscopy showed electron-dense deposits in intramembranous and mesangial areas. However, the size and distribution of the deposits were irregular and segmental in the examined cases, unlike typical global and subepithelial lesions of membranous nephropathy. Double immunofluorescence using Alexa Fluor 594-labeled anti-myeloperoxidase antibody and fluorescein isothiocyanate-labeled anti-immunoglobulin G antibody, as well as immunoelectron microscopy using anti-myeloperoxidase antibody labeled with 25-nm gold particles revealed partial colocalization of myeloperoxidase and immunoglobulin G within the glomerular basement membrane and mesangium. In some cases of anti-neutrophil cytoplasmic antibody-associated glomerulonephritis, myeloperoxidase may form immune complexes and develop membranous nephropathy-like lesions.

Cytochrome P450 2B1 mediates complement-dependent sublytic injury in a model of membranous nephropathy.

Membranous nephropathy is a disease that affects the filtering units of the kidney, the glomeruli, and results in proteinuria accompanied by loss of kidney function. Passive Heymann nephritis is an experimental model that mimics membranous nephropathy in humans, wherein the glomerular epithelial cell (GEC) injury induced by complement C5b-9 leads to proteinuria. We examined the role of cytochrome P450 2B1 (CYP2B1) in this complement-mediated sublytic injury. Overexpression of CYP2B1 in GECs significantly increased the formation of reactive oxygen species, cytotoxicity, and collapse of the actin cytoskeleton following treatment with anti-tubular brush-border antiserum (anti-Fx1A). In contrast, silencing of CYP2B1 markedly attenuated anti-Fx1A-induced reactive oxygen species generation and cytotoxicity with preservation of the actin cytoskeleton. Gelsolin, which maintains an organized actin cytoskeleton, was significantly decreased by complement C5b-9-mediated injury but was preserved in CYP2B1-silenced cells. In rats injected with anti-Fx1A, the cytochrome P450 inhibitor cimetidine blocked an increase in catalytic iron and ROS generation, reduced the formation of malondialdehyde adducts, maintained a normal distribution of nephrin in the glomeruli, and provided significant protection at the onset of proteinuria. Thus, GEC CYP2B1 contributes to complement C5b-9-mediated injury and plays an important role in the pathogenesis of passive Heymann nephritis.

HO-1 induction ameliorates experimental murine membranous nephropathy: anti-oxidative, anti-apoptotic and immunomodulatory effects.

BACKGROUND: Therapeutic agents for membranous nephropathy (MN) remain ill-defined. Haeme oxygenase (HO)-1 is considered to play a protective role in various disorders. Here, we assessed the efficacy of HO-1 induction therapy for MN. METHODS: MN was induced in BALB/c mice with intravenous injections of cationic bovine serum albumin. Three groups of mice were administered 100 micromol/kg Cobalt protoporphyrin (CoPP, a potent HO-1 inducer), Tin protoporphyrin (SnPP, a potent HO-1 inhibitor) or phosphate-buffered saline via intra-peritoneal injections once a week starting from the induction of MN. Disease severity was verified by serum and urine metabolic profiles and by renal histopathology. Cytokine profiles, immunoglobulin production, the expression of oxidative stress markers (thiobarbituric acid reactive substances, TBARS) and apoptosis, as measured by TUNEL, were also determined. RESULTS: Mice treated with CoPP displayed a significant reduction in proteinuria and a marked amelioration of glomerular lesions, accompanied by attenuated immune-complex deposition. The production of immunoglobulins in MN mice treated with CoPP was significantly reduced compared with that of mice in the other two groups. TBARS in the serum and kidneys, as well as apoptosis, were also significantly reduced in CoPP-treated mice. Cytokine mRNA expression in the renal cortex indicated that CoPP not only decreased the expression of proinflammatory cytokines, but also increased the expression of anti-inflammatory cytokines (interleukin-10). CONCLUSIONS: HO-1 induction therapy may ameliorate experimental MN via multiple pathways, including anti-oxidative, anti-apoptotic and immunomodulatory effects. HO-1 inducing regimens should be considered as a potential therapeutic intervention in MN in the future.

Beta-2-microglobulin is superior to N-acetyl-beta-glucosaminidase in predicting prognosis in idiopathic membranous nephropathy.

BACKGROUND: An accurate prediction of prognosis in patients with idiopathic membranous nephropathy (iMN) would allow restriction of immunosuppressive treatment to patients who are at highest risk for end-stage renal disease (ESRD). Several markers of proximal tubular cell injury have been used as predictors of prognosis. In this study we compared the accuracy of urinary beta-2-microglobulin (U beta 2m) and N-acetyl-beta-glucosaminidase (U beta-NAG) in predicting renal insufficiency and remission rates. METHODS: Fifty-seven patients with iMN (38 M, 19 F; age 48 +/- 16 years), a nephrotic syndrome and a serum creatinine level <135 micromol/l were studied prospectively. At baseline, a standardised measurement was carried out to determine renal function and protein excretion. The end-point renal failure was defined as a serum creatinine exceeding 135 micromol/l or an increase in serum creatinine by >50%. Remission was defined as a proteinuria <2.0 g/day with stable renal function. RESULTS: The mean follow-up was 80 +/- 36 months. The mean serum creatinine concentration was 89 +/- 20 micromol/l, serum albumin 24 +/- 5.3 g/l and proteinuria 8.9 +/- 4.8 g/24 h. Thus far, 28 (49%) patients have reached the predefined end point of renal failure. Multivariate analysis identified U beta 2m as the strongest independent predictor for the development of renal insufficiency. Sensitivity and specificity were 81 and 90% respectively for U beta 2m (threshold value 54 microg/mmol cr), and 74 and 81% respectively for U beta-NAG (threshold value 2.64 U/mmol cr). The overall remission rate was 44%. A remission occurred in 78% of patients with low U beta 2m and in 14% of patients with high U beta 2m, and respectively in 71% of patients with low U beta-NAG and 21% of patients with high U beta-NAG. CONCLUSIONS: Although both U beta 2m and U beta-NAG predicted progression and remission in iMN, U beta 2m was more accurate. High specificity in predicting prognosis should be pursued to avoid unnecessary immunosuppressive therapy. We therefore conclude that U beta 2m is superior to U beta-NAG in predicting prognosis in patients with iMN.

Role of calcium-independent phospholipase A2 in complement-mediated glomerular epithelial cell injury.

In experimental membranous nephropathy, complement C5b-9-induced glomerular epithelial cell (GEC) injury leads to morphological changes in GEC and proteinuria, in association with phospholipase A(2) (PLA(2)) activation. The present study addresses the role of calcium-independent PLA(2) (iPLA(2)) in GEC injury. iPLA(2)beta short and iPLA(2)gamma were expressed in cultured rat GEC and normal rat glomeruli. To determine whether iPLA(2) is involved in complement-mediated arachidonic acid (AA) release, GEC were stably transfected with iPLA(2)gamma or iPLA(2)beta cDNAs (GEC-iPLA(2)gamma; GEC-iPLA(2)beta). Compared with control cells (GEC-Neo), GEC-iPLA(2)gamma and GEC-iPLA(2)beta demonstrated greater expression of iPLA(2) proteins and activities. Complement-mediated release of [(3)H]AA was augmented significantly in GEC-iPLA(2)gamma compared with GEC-Neo, and the augmented [(3)H]AA release was inhibited by the iPLA(2)-directed inhibitor bromoenol lactone (BEL). For comparison, overexpression of iPLA(2)gamma also amplified [(3)H]AA release after incubation of GEC with H(2)O(2), or chemical anoxia followed by reexposure to glucose (in vitro ischemia-reperfusion injury). In parallel with release of [(3)H]AA, complement-mediated production of prostaglandin E(2) was amplified in GEC-iPLA(2)gamma. Complement-mediated cytotoxicity was attenuated significantly in GEC-iPLA(2)gamma compared with GEC-Neo, and the cytoprotective effect of iPLA(2)gamma was reversed by BEL, and in part by indomethacin. Overexpression of iPLA(2)beta did not amplify complement-dependent [(3)H]AA release, but nonetheless attenuated complement-mediated cytotoxicity. Thus iPLA(2)gamma may be involved in complement-mediated release of AA. Expression of iPLA(2)gamma or iPLA(2)beta induces cytoprotection against complement-dependent GEC injury. Modulation of iPLA(2) activity may prove to be a novel approach to reducing GEC injury.