Cellular Response to Injury in Membranous Nephropathy

Serum anti-PLA2R antibody as a diagnostic biomarker of idiopathic membranous nephropathy: The optimal cut-off value for Chinese patients

BACKGROUND

The M-type phospholipase A2 receptor (PLA2R) is a specific target autoantigen identified in idiopathic membranous nephropathy (IMN). The autoantibody against PLA2R (anti-PLA2R) may be used to diagnose IMN. However, the appropriate diagnosis cut-off value for Chinese patients with IMN has not been established.

METHODS

In total, 119 patients who underwent renal biopsy (57 patients with IMN and 62 patients with non-IMN glomerulonephritis) and 22 healthy individuals were recruited for our observation study from Qianfoshan Hospital between September 2011 and March 2016. The serum concentration of anti-PLA2R was measured using a quantitative enzyme-linked immunosorbent assay (ELISA). The sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV) and receiver operating characteristic (ROC) curve of anti-PLA2R in diagnosing IMN were analysed based on the ELISA detection.

RESULTS

The sensitivity, specificity, PPV, and NPV of anti-PLA2R in the diagnosis of IMN in the Chinese patients were 82.5, 75, 69.1, and 86.3% for the 2RU/ml cut-off value; 78.9, 91.7, 86.5, and 86.5% for the 2.6RU/ml cut-off value; 59.6, 95.2, 89.5, and 77.7% for the 14RU/ml cut-off value; 50.9, 96.4, 90.6, and 74.3% for the 20RU/ml cut-off value; and 47.4, 97.6, 93.1, and 73.2% for the 40RU/ml cut-off value, respectively. The area under the ROC curve was 0.879.

CONCLUSIONS

The cut-off value of 2.6RU/ml is recommended for the use of anti-PLA2R for the diagnosis of IMN in Chinese patients based on the ELISA.

miR-217 Is a Useful Diagnostic Biomarker and Regulates Human Podocyte Cells Apoptosis via Targeting TNFSF11 in Membranous Nephropathy

Background

MicroRNAs have recently been verified as useful diagnostic biomarkers in various diseases. In this study, we investigated whether miR-217 is a useful diagnostic biomarker and the possible pathological mechanism of miR-217 in this disease.

Methods

Patients with focal segmental glomerulosclerosis (FSGS), membranous nephropathy (MN), and diabetic nephropathy (DN) and control patients were enrolled in this study. The miR-217 inhibitor and mimics were transfected into human podocyte cells to investigate the pathological mechanism of miR-217 in this disease. Relevant indicators were detected and tested.

Results

Compared with control patients, miR-217 was significantly downregulated and TNFSF11 was significantly upregulated in MN. Then, miR-217 had obvious separation between patients with MN and control patients, with an AUC of 0.941, a cutoff value of <750.0 copies/ul, and sensitivity and specificity of 88.9% and 75.9%. In addition, the TNFSF11 was confirmed to be the target gene of miR-217. Finally, in in vitro experiments, the upregulation of miR-217 could decrease the expression of TNFSF11 and not induce human podocyte cells apoptosis; however, the downregulation of miR-217 could bring about an opposite change.

Conclusions

miR-217 is a useful diagnostic biomarker and is involved in human podocyte cells apoptosis via targeting TNFSF11 in membranous nephropathy.

Complement C5-inhibiting therapy for the thrombotic microangiopathies: accumulating evidence, but not a panacea

Thrombotic microangiopathy (TMA), characterized by organ injury occurring consequent to severe endothelial damage, can manifest in a diverse range of diseases. In complement-mediated atypical haemolytic uraemic syndrome (aHUS) a primary defect in complement, such as a mutation or autoantibody leading to over activation of the alternative pathway, predisposes to the development of disease, usually following exposure to an environmental trigger. The elucidation of the pathogenesis of aHUS resulted in the successful introduction of the complement inhibitor eculizumab into clinical practice. In other TMAs, although complement activation may be seen, its role in the pathogenesis remains to be confirmed by an interventional trial. Although many case reports in TMAs other than complement-mediated aHUS hint at efficacy, publication bias, concurrent therapies and in some cases the self-limiting nature of disease make broader interpretation difficult. In this article, we will review the evidence for the role of complement inhibition in complement-mediated aHUS and other TMAs.

Blockage of the lysosome-dependent autophagic pathway contributes to complement membrane attack complex-induced podocyte injury in idiopathic membranous nephropathy

Dysregulation of autophagy-mediated podocyte homeostasis is proposed to play a role in idiopathic membranous nephropathy (IMN). In the present study, autophagic activity and lysosomal alterations were investigated in podocytes of IMN patients and in cultured podocytes exposed to sublytic terminal complement complex, C5b-9. C5b-9 upregulated the number of LC3 positive puncta and the expression of p62 in patient podocytes and in C5b-9 injuried podocyte model. The lysosomal turnover of LC3-II was not influenced, although the BECN1 expression level was upregulated after exposure of podocytes to C5b-9. C5b-9 also caused a significant increase in the number of autophagosomes but not autolysosomes, suggesting that C5b-9 impairs the lysosomal degration of autophagosomes. Moreover, C5b-9 exacerbated the apoptosis of podocytes, which could be mimicked by chloroquine treatment, indicating that C5b-9 triggered podocyte injury, at least partially through inhibiting autophagy. Subsequent studies revealed that C5b-9 triggered lysosomal membrane permeabilization, which likely caused the decrease in enzymatic activity, defective acidification of lysosomes, and suppression of DQ-ovalbumin degradation. Taken together, our results suggest that the lysosomal-dependent autophagic pathway is blocked by C5b-9, which may play a key role in podocyte injury during the development of IMN.

Betulinic acid, isolated from the leaves of Syzygium cumini (L.) Skeels, ameliorates the proteinuria in experimental membranous nephropathy through regulating Nrf2/NF-κB pathways

Membranous nephropathy (MN) is associated with increased oxidative stress and inflammatory markers in the kidney. Betulinic acid (BA) is a potent antioxidant and anti-inflammatory compound isolated from the leaves of Syzygium cumini (L.) Skeels. In the present study, we investigated the effects of BA on experimental MN in rats and explored the mechanisms by which it enhances antioxidant activities and resolves inflammatory condition in experimental MN. Passive Heymann nephritis (PHN) was induced in Sprague-Dawley rats by a single tail vein injection of anti- Fx1A antiserum. The rats were orally administered BA (25 and 50 mg kg ^-1 d ^-1) or dexamethasone (DEX; 0.07 mg kg-1, reference compound) for 4 weeks after the induction of PHN. Blood, urine, and kidney tissue were collected for analysis at the end of the study. Treatment of PHN rats with BA or DEX significantly attenuated renal dysfunction, histopathological alterations and reduced immune complex deposition in the kidneys. Furthermore, BA ameliorated mRNA and protein expression of NF-κB, iNOS, TNF-α, Nrf2, HO-1 and NQO1 in the kidney. BA also restored malondialdehyde level and antioxidant enzyme activities in the kidney. In a nutshell, the protective effect of BA can be explained by its anti-inflammatory and anti-oxidant activities, which in turn is due to downregulation of NF-κB pathway and activation of Nrf2. The results indicated that BA can effectively suppress experimental PHN in rats by regulating Nrf2/NF-κB pathways.

A podocyte view of membranous nephropathy: from Heymann nephritis to the childhood human disease

Membranous nephropathy (MN) is characterized by an accumulation of immune deposits on the subepithelial side of the glomerular basement membrane, which results in complement activation and proteinuria. Since 2002, several major antigens of the podocyte have been identified in human MN, the first one being neutral endopeptidase (NEP), the alloantigen involved in neonatal cases of MN that occur in newborns from NEP-deficient mothers. This discovery opened the field to the major advances that have occurred since then in the pathophysiology and treatment of MN. It is remarkable that experimental models such as Heymann nephritis and cationic bovine serum albumin-induced MN in the rabbit predicted the pathomechanisms of the human glomerulopathy. The podocyte is at the center of the pathogenesis of MN either by providing a source of endogenous antigens or by creating an environment favorable to deposition and accumulation of immune complexes containing exogenous (non-podocyte) antigens. The podocyte is also a victim of complement activation and antibody blocking activity against enzymes or receptors. A search for innovative drugs aimed at protecting this cell against complement activation and the effects of prolonged ER stress has become a priority.

Protein Array-Based Detection of Proteins in Kidney Tissues from Patients with Membranous Nephropathy

Membranous nephropathy (MN) is an autoimmune inflammatory disease in which proteins related with plenty of biological processes play an important role. However, the role of these proteins in the pathogenesis of MN is still unclear. This study aimed to screen differential proteins in kidney tissue samples from MN patients by using protein arrays and determine the pathways involved in the pathogenesis of MN. This study first tested a quantitative protein array (QAH-INF-3) and two semiquantitative protein arrays (L-493 and L-507) with normal renal tissue and identified L-493 as the most appropriate assay to compare protein levels between MN tissues and normal control tissues. The L-493 array identified 66 differentially expressed proteins (DEPs) that may be associated with MN. The gene oncology (GO) and protein-protein interaction (PPI) analyses revealed several processes potentially involved in MN, including extracellular matrix disassembly and organization, cell adhesion, cell-cell signaling, cellular protein metabolic process, and immune response (P < 0.05). We suggest that these different pathways work together via protein signaling and result in the pathogenesis and progression of MN.

NEPHROPATHIES IN THE EUROPEAN CAPTIVE CHEETAH (ACINONYX JUBATUS) POPULATION

According to previous studies in captive cheetah ( Acinonyx jubatus ) populations, one of the most threatening diseases besides amyloidosis, myelopathy, veno occlusive disease, and gastritis, is renal failure. Contrary to captive cheetahs in North America and South Africa, morphological data concerning renal lesions in the cheetah European Endangered Species Program (EEP) are lacking. This study details the histological characterization as well as immunohistochemical and morphometrical analysis of nephropathies in 35 captive cheetahs from the EEP, which were necropsied between 1985 and 2003. Examination of paraffin- and glycolmethacrylate-methylmethacrylate (GMA-MMA) embedded kidney samples by light microscopy revealed glomerulonephritis in 91%, with a high prevalence for glomerulosclerosis and glomerulonephritis with the histologic pattern of membranous glomerulonephritis (77%). Besides these predominating glomerulopathies, a wide range of other renal lesions, like acute tubular necrosis, interstitial nephritis, calcinosis, and amyloidosis, were present. Pathological expression of collagen type IV, complement C3, fibronectin, and IgG was demonstrated in the glomeruli of the cheetah kidneys with the use of the avidin-biotin complex method. Morphometrical analysis was performed on GMA-MMA embedded kidney samples to obtain glomerulosclerosis index and glomerulosclerosis incidence.

[Idiopathic membranous nephropathy: Evolution in understanding the problem]

The review highlights the evolution of ideas on the. mechanisms responsible for the 'development of membranous nephropathy(MN), glomerulopathy that is the most common cause of nephrotic syndrome in adults. Primary emphasis is placed on the primary form of MN. The important step to understanding the nature of this clinical and morphological form of glomerulonephritis is to create its animal model (Heymann nephritis), then to decipher the mechanisms of immune complex damage (complement activation,a role of cellular immunity), and to identify autoantigens responsible for the development of idiopathic MN in man (podocyteneutral endopeptidase, transmembrane M-type phospholipase A2 receptor, thrombospondin type-1 domain-containing 7A. The findings constituted the basis for developing current methods for the diagnosis and treatment of MN, including the pathogenetically sound inhibition of autoantibody production, as well as a molecular orientation effect on podocyte dysfunction.

Unraveling the immunopathogenesis of glomerular disease

Immune-mediated damage to glomerular structures is largely responsible for the pathology associated with the majority of glomerular diseases. Therefore, a detailed understanding of the basic immune mechanisms responsible for glomerular damage is needed to inform the design of novel intervention strategies. Glomerular injury of immune origin is complex and involves both inflammatory and non-inflammatory processes driven by elements of the innate and adaptive immune system. This review summarizes the basic immune mechanisms that cause glomerular injury leading to the nephritic and nephrotic syndromes. A major focus of the review is to highlight the mechanisms by which antibodies cause glomerular injury through their interactions with glomerular cells, complement proteins, phagocytes bearing complement and Fcγ receptors, and dendritic cells expressing the neonatal receptor for IgG, FcRn.

Patients With Combined Membranous Nephropathy and Focal Segmental Glomerulosclerosis Have Comparable Clinical and Autoantibody Profiles With Primary Membranous Nephropathy: A Retrospective Observational Study

Patients with combined membranous nephropathy (MN) and focal segmental glomerulosclerosis (FSGS) have been reported with different clinical significance. Investigations on the possible mechanisms of the combined glomerular lesions are necessary but scarce. Twenty patients with both MN and FSGS lesions were enrolled in the study. Sixty-five patients with primary MN and 56 patients with primary FSGS were used as disease controls. Clinical data on renal biopsy and during follow-up were collected. Circulating anti-phospholipase A2 receptor (PLA2R) antibody, glomerular PLA2R expression, IgG4 deposition, and soluble urokinase receptor (suPAR) levels were detected. We found that patients with combined lesions presented with older age, less proteinuria, higher albumin, and better renal function on biopsy. These were comparable to the patients with primary MN, but differed from the patients with primary FSGS. Patients with combined lesions showed higher stages of MN, no cellular variant on FSGS classification, and more common (100.0%) tubulointerstitial injury than both primary MN and primary FSGS patients. In the patients with combined lesions, 80.0% had circulating anti-PLA2R antibody and 68.4% had IgG4 predominant deposition in glomeruli, which were comparable to primary MN. The patients with combined lesions had significantly lower urinary suPAR concentrations, than the primary FSGS patients (315.6 ± 151.0 vs 752.1 ± 633.9 pg/μmol; P = 0.002), but similar to the primary MN patients (267.9 ± 147.5 pg/μmol). We conclude that patients with combined MN and FSGS may share the same underlying pathogenesis with primary MN. The FSGS lesion might be secondary to primary MN.

Advances in the evaluation of canine renal disease

Many recent advances in the evaluation of dogs with kidney disease have improved our diagnostic algorithms and have impacted our therapeutic strategies. Non-invasive techniques, such as urinary and serologic biomarker evaluation, can help a clinician diagnose and treat a patient that cannot undergo a renal biopsy for clinical or financial reasons. Some biomarkers might help localize the affected structure (glomerulus vs. tubule) and indicate the type or severity of injury present. Although more research is needed, studies indicate that some biomarkers (e.g. urine protein to creatinine ratio and urinary immunoglobulins) can be useful in predicting adverse outcomes. Importantly, the sensitivity and specificity of biomarkers for renal injury should be established and clinicians need to understand the limitations of these assays. If a renal biopsy is performed, then it should be evaluated by a specialty diagnostic service with expertise in nephropathology. A panel of special stains, immunofluorescence for the detection of immunoglobulins and complement factors, and transmission electron microscopy can be routinely employed in cases of glomerular disease. These advanced diagnostics can be used to detect immune deposits in order to definitively diagnose immune complex mediated glomerular disease. Integrating the results of biomarker assays and comprehensive renal biopsy evaluation, the clinician can make informed therapeutic decisions, such as whether or not to immunosuppress a patient.

Alternative Pathway Dysregulation and the Conundrum of Complement Activation by IgG4 Immune Complexes in Membranous Nephropathy

Membranous nephropathy (MN), a major cause of nephrotic syndrome, is a non-inflammatory immune kidney disease mediated by IgG antibodies that form glomerular subepithelial immune complexes. In primary MN, autoantibodies target proteins expressed on the podocyte surface, often phospholipase A2 receptor (PLA2R1). Pathology is driven by complement activation, leading to podocyte injury and proteinuria. This article overviews the mechanisms of complement activation and regulation in MN, addressing the paradox that anti-PLA2R1 and other antibodies causing primary MN are predominantly (but not exclusively) IgG4, an IgG subclass that does not fix complement. Besides immune complexes, alterations of the glomerular basement membrane (GBM) in MN may lead to impaired regulation of the alternative pathway (AP). The AP amplifies complement activation on surfaces insufficiently protected by complement regulatory proteins. Whereas podocytes are protected by cell-bound regulators, the GBM must recruit plasma factor H, which inhibits the AP on host surfaces carrying certain polyanions, such as heparan sulfate (HS) chains. Because HS chains present in the normal GBM are lost in MN, we posit that the local complement regulation by factor H may be impaired as a result. Thus, the loss of GBM HS in MN creates a micro-environment that promotes local amplification of complement activation, which in turn may be initiated via the classical or lectin pathways by subsets of IgG in immune complexes. A detailed understanding of the mechanisms of complement activation and dysregulation in MN is important for designing more effective therapies.

The Origin and Activities of IgA1-Containing Immune Complexes in IgA Nephropathy

IgA nephropathy (IgAN) is the most common primary glomerulonephritis, frequently leading to end-stage renal disease, as there is no disease-specific therapy. IgAN is diagnosed from pathological assessment of a renal biopsy specimen based on predominant or codominant IgA-containing immunodeposits, usually with complement C3 co-deposits and with variable presence of IgG and/or IgM. The IgA in these renal deposits is galactose-deficient IgA1, with less than a full complement of galactose residues on the O-glycans in the hinge region of the heavy chains. Research from the past decade led to the definition of IgAN as an autoimmune disease with a multi-hit pathogenetic process with contributing genetic and environmental components. In this process, circulating galactose-deficient IgA1 (autoantigen) is bound by antiglycan IgG or IgA (autoantibodies) to form immune complexes. Some of these circulating complexes deposit in glomeruli, and thereby activate mesangial cells and induce renal injury through cellular proliferation and overproduction of extracellular matrix components and cytokines/chemokines. Glycosylation pathways associated with production of the autoantigen and the unique characteristics of the corresponding autoantibodies in patients with IgAN have been uncovered. Complement likely plays a significant role in the formation and the nephritogenic activities of these complexes. Complement activation is mediated through the alternative and lectin pathways and probably occurs systemically on IgA1-containing circulating immune complexes as well as locally in glomeruli. Incidence of IgAN varies greatly by geographical location; the disease is rare in central Africa but accounts for up to 40% of native-kidney biopsies in eastern Asia. Some of this variation may be explained by genetically determined influences on the pathogenesis of the disease. Genome-wide association studies to date have identified several loci associated with IgAN. Some of these loci are associated with the increased prevalence of IgAN, whereas others, such as deletion of complement factor H-related genes 1 and 3, are protective against the disease. Understanding the molecular mechanisms and genetic and biochemical factors involved in formation and activities of pathogenic IgA1-containing immune complexes will enable the development of future disease-specific therapies as well as identification of non-invasive disease-specific biomarkers.

Podocyte injury and its consequences

Podocytes maintain the glomerular filtration barrier, and the stability of this barrier depends on their highly differentiated postmitotic phenotype, which also defines the particular vulnerability of the glomerulus. Recent podocyte biology and gene disruption studies in vivo indicate a causal relationship between abnormalities of single podocyte molecules and proteinuria and glomerulosclerosis. Podocytes live under various stresses and pathological stimuli. They adapt to maintain homeostasis, but excessive stress leads to maladaptation with complex biological changes including loss of integrity and dysregulation of cellular metabolism. Podocyte injury causes proteinuria and detachment from the glomerular basement membrane. In addition to "sick" podocytes and their detachment, our understanding of glomerular responses following podocyte loss needs to address the pathways from podocyte injury to sclerosis. Studies have found a variety of glomerular responses to podocyte dysfunction in vivo, such as disruption of podocyte-endothelial cross talk and activation of podocyte-parietal cell interactions, all of which help us to understand the complex scenario of podocyte injury and its consequences. This review focuses on the cellular aspects of podocyte dysfunction and the adaptive or maladaptive glomerular responses to podocyte injury that lead to its major consequence, glomerulosclerosis.

c-Abl contributes to glucose-promoted apoptosis via p53 signaling pathway in podocytes

AIM

To investigate the role of the non-receptor tyrosine kinase c-Abl in high glucose-induced podocyte injury and its possible signal transduction pathway.

METHODS

Sixteen C57BL/6 mice were randomly assigned to a group with diabetes and a normal control group. Subsequently, differentiated mouse podocytes were exposed to high-glucose conditions, and podocyte apoptosis was then assessed by flow cytometry and Hoechst 33258 staining. Western blot and immunofluorescence assay were used to measure c-Abl expression. Co-immunoprecipitation assay was used and c-Abl siRNA was applied to evaluate the interaction between c-Abl and p53.

RESULTS

High glucose promotes podocyte apoptosis. The c-Abl expression in podocytes was increased after exposure to high glucose, stimulating the p53 signaling pathway. Conversely, treatment with c-Abl siRNA restored high glucose-promoted podocyte apoptosis and resulted in the reduction of p53 expression.

CONCLUSION

c-Abl contributes to high glucose-induced podocyte apoptosis via p53 signaling pathway.

Anti-Phospholipase A2 Receptor Autoantibody: A New Biomarker for Primary Membranous Nephropathy

Primary membranous nephropathy (also known as idiopathic membranous nephropathy, IMN) is an organ specific autoimmune kidney disease characterized by the development of immune complex deposits in the sub-epithelial spaces, podocyte effacement and glomerular capillary wall thickening in the later stages. Clinical studies have demonstrated that over 70% of patients with IMN possess circulating autoimmune antibodies specifically targeting the phospholipase A₂ receptor (PLA₂R) on the surface of podocytes. The autoantibodies only bind to the extracellular portion of PLA₂R under the non-reducing condition, indicating that the epitope in PLA₂R is conformational requiring specific disulfide bonds to maintain its structure. We recently have successfully located the dominant epitope in PLA₂R to the extreme N-terminus of the receptor. This finding has opened a new direction for understanding the pathogenesis of anti-PLA₂R autoantibody induced IMN and offered a strong basis for developing sensitive clinical assays for IMN diagnosis and prognosis, and potentially, new therapeutic approaches for IMN treatment.

Immunology of membranous nephropathy: from animal models to humans

Membranous nephropathy (MN), the leading cause of nephrotic syndrome in adults, is characterized by the deposition of subepithelial immune deposits that consist mainly of immunoglobulin (Ig)G and complement. Most of the cases are primary or idiopathic (iMN), while only approximately 25% of the cases are secondary to some known disease such as systemic lupus erythematosus, hepatitis B, drugs and malignancies. Most of our knowledge on the pathogenesis of iMN has relied upon old experimental models (i.e. Heymann nephritis) that have shown that immune deposits are formed in situ by the reaction of autoantibodies against the respective podocyte antigen. Recent findings indicate that podocyte proteins also act as an autoantigen in human iMN. The M-type phospholipase A2 receptor (PLA2R) has been identified as the main target antigen, as it can be found in approximately 70% of iMN patients but only rarely in other glomerulonephritides. Podocytes damage in the experimental model of Heymann nephritis is complement-mediated. In humans, the presence of complement within the subepithelial deposits is well established, but IgG4, which does not activate complement by classical or alternative pathways, represents the predominant subclass of IgG anti-PLA2R. Some evidence suggests that IgG4 anti-PLA2R autoantibodies can bind mannan-binding lectin (MBL) and activate the lectin complement pathway. A genetic background for iMN has been demonstrated by genome-wide association studies that have shown highly significant associations of the PLA2R1 and the human leucocyte antigen (HLA)-DQA1 loci with iMN. In addition to their diagnostic value, anti-PLA2R antibodies may be useful to monitor disease activity and predict response to treatment.

Down-regulation of miR-186 contributes to podocytes apoptosis in membranous nephropathy

BACKGROUND AND AIM

Podocytes apoptosis is the key process in the development of membranous nephropathy and miR-186 is reported to be related with cell apoptosis. Here we investigated the expression of miR-186 in membranous nephropathy (MGN) patients and the mechanism underlying the podocytes apoptosis.

METHODS

Thirty patients with MGN and 30 healthy people were included in this study. The expression of miR-186 was detected in renal tissue and podocyte cells exposed to AngII by real-time PCR. Caspase-3 activity was used to evaluate podocytes apoptosis. TLR4 and P2×7 protein expression was quantified by western blotting. miR-186 inhibitor and miR-186 mimic were transfected into cells to investigate the mechanism underlying miR-186 in podocytes apoptosis.

RESULTS

In MGN patients, the level of miR-186 was significantly down-regulated as well as the protein expression of TLR4 and P2×7 was up-regulated in renal tissue. In vitro experiments, TLR4 siRNA increased the expression of miR-186 and miR-186 inhibitor elevated the mRNA and protein expression of P2×7 in podocytes exposed to AngII. In addition, the level of cleaved-caspase-3 was up-regulated by miR-186 inhibitor. The TUNEL-positive cells and caspase-3 activity of podocytes induced by AngII were down-regulated by miR-186 mimic.

CONCLUSIONS

We revealed that TLR4 is involved in the regulation of miR-186 expression, and the anti-apoptotic effect of miR-186 on podocytes is correlated with P2×7 regulation.

World Small Animal Veterinary Association Renal Pathology Initiative: Classification of Glomerular Diseases in Dogs

Evaluation of canine renal biopsy tissue has generally relied on light microscopic (LM) evaluation of hematoxylin and eosin-stained sections ranging in thickness from 3 to 5 µm. Advanced modalities, such as transmission electron microscopy (TEM) and immunofluorescence (IF), have been used sporadically or retrospectively. Diagnostic algorithms of glomerular diseases have been extrapolated from the World Health Organization classification scheme for human glomerular disease. With the recent establishment of 2 veterinary nephropathology services that evaluate 3-µm sections with a panel of histochemical stains and routinely perform TEM and IF, a standardized objective species-specific approach for the diagnosis of canine glomerular disease was needed. Eight veterinary pathologists evaluated 114 parameters (lesions) in renal biopsy specimens from 89 dogs. Hierarchical cluster analysis of the data revealed 2 large categories of glomerular disease based on the presence or absence of immune complex deposition: The immune complex-mediated glomerulonephritis (ICGN) category included cases with histologic lesions of membranoproliferative or membranous patterns. The second category included control dogs and dogs with non-ICGN (glomerular amyloidosis or focal segmental glomerulosclerosis). Cluster analysis performed on only the LM parameters led to misdiagnosis of 22 of the 89 cases-that is, ICGN cases moved to the non-ICGN branch of the dendrogram or vice versa, thereby emphasizing the importance of advanced diagnostic modalities in the evaluation of canine glomerular disease. Salient LM, TEM, and IF features for each pattern of disease were identified, and a preliminary investigation of related clinicopathologic data was performed.

Resveratrol ameliorates renal damage, increases expression of heme oxygenase-1, and has anti-complement, anti-oxidative, and anti-apoptotic effects in a murine model of membranous nephropathy

Background

Idiopathic membranous nephropathy (MN) is an autoimmune-mediated glomerulonephritis and a common cause of nephrotic syndrome in adults. There are limited available treatments for MN. We assessed the efficacy of resveratrol (RSV) therapy for treatment of MN in a murine model of this disease.

Methods

Murine MN was experimentally induced by daily subcutaneous administration of cationic bovine serum albumin, with phosphate-buffered saline used in control mice. MN mice were untreated or given RSV. Disease severity and pathogenesis was assessed by determination of metabolic and histopathology profiles, lymphocyte subsets, immunoglobulin production, oxidative stress, apoptosis, and production of heme oxygenase-1 (HO1).

Results

MN mice given RSV had significantly reduced proteinuria and a marked amelioration of glomerular lesions. RSV also significantly attenuated immunofluorescent staining of C3, although there were no changes of serum immunoglobulin levels or immunocomplex deposition in the kidneys. RSV treatment of MN mice also reduced the production of reactive oxygen species (ROS), reduced cell apoptosis, and upregulated heme oxygenase 1 (HO1). Inhibition of HO1 with tin protoporphyrin IX partially reversed the renoprotective effects of RSV. The HO1 induced by RSV maybe via Nrf2 signaling.

Conclusion

Our results show that RSV increased the expression of HO1 and ameliorated the effects of membranous nephropathy in a mouse model due to its anti-complement, anti-oxidative, and anti-apoptotic effects. RSV appears to have potential as a treatment for MN.

Current Understanding of the Role of Complement in IgA Nephropathy

Complement activation has a role in the pathogenesis of IgA nephropathy, an autoimmune disease mediated by pathogenic immune complexes consisting of galactose-deficient IgA1 bound by antiglycan antibodies. Of three complement-activation pathways, the alternative and lectin pathways are involved in IgA nephropathy. IgA1 can activate both pathways in vitro, and pathway components are present in the mesangial immunodeposits, including properdin and factor H in the alternative pathway and mannan-binding lectin, mannan-binding lectin-associated serine proteases 1 and 2, and C4d in the lectin pathway. Genome-wide association studies identified deletion of complement factor H-related genes 1 and 3 as protective against the disease. Because the corresponding gene products compete with factor H in the regulation of the alternative pathway, it has been hypothesized that the absence of these genes could lead to more potent inhibition of complement by factor H. Complement activation can take place directly on IgA1-containing immune complexes in circulation and/or after their deposition in the mesangium. Notably, complement factors and their fragments may serve as biomarkers of IgA nephropathy in serum, urine, or renal tissue. A better understanding of the role of complement in IgA nephropathy may provide potential targets and rationale for development of complement-targeting therapy of the disease.

IQGAP1 regulates actin cytoskeleton organization in podocytes through interaction with nephrin

Increasing data has shown that the cytoskeletal reorganization of podocytes is involved in the onset of proteinuria and the progression of glomerular disease. Nephrin behaves as a signal sensor of the slit diaphragm to transmit cytoskeletal signals to maintain the unique structure of podocytes. However, the nephrin signaling cascade deserves further study. IQGAP1 is a scaffolding protein with the ability to regulate cytoskeletal organization. It is hypothesized that IQGAP1 contributes to actin reorganization in podocytes through interaction with nephrin. IQGAP1 expression and IQGAP1-nephrin colocalization in glomeruli were progressively decreased and then gradually recovered in line with the development of foot process fusion and proteinuria in puromycin aminonucleoside-injected rats. In cultured human podocytes, puromycin aminonucleoside-induced disruption of F-actin and disorders of migration and spreading were aggravated by IQGAP1 siRNA, and these effects were partially restored by a wild-type IQGAP1 plasmid. Furthermore, the cytoskeletal disorganization stimulated by cytochalasin D in COS7 cells was recovered by cotransfection with wild-type IQGAP1 and nephrin plasmids but was not recovered either by single transfection of the wild-type IQGAP1 plasmid or by cotransfection of mutant IQGAP1 [△1443(S→A)] and wild-type nephrin plasmids. Co-immunoprecipitation analysis using lysates of COS7 cells overexpressing nephrin and each derivative-domain molecule of IQGAP1 demonstrated that the poly-proline binding domain and RasGAP domain in the carboxyl terminus of IQGAP1 are the target modules that interact with nephrin. Collectively, these findings showed that activated IQGAP1, as an intracellular partner of nephrin, is involved in actin cytoskeleton organization and functional regulation of podocytes.

Significance of urinary full-length megalin in patients with IgA nephropathy

Background and Objectives

Megalin is highly expressed at the apical membranes of proximal tubular epithelial cells. A urinary full-length megalin (C-megalin) assay is linked to the severity of diabetic nephropathy in type 2 diabetes. This study examined the relationship between levels of urinary C-megalin and histological findings in adult patients with IgA nephropathy (IgAN).

Design, Setting, Participants, & Measurements

Urine samples voided in the morning on the day of renal biopsy were obtained from 73 patients with IgAN (29 men and 44 women; mean age, 33 years) and 5 patients with membranous nephropathy (MN). Renal pathologic variables were analyzed using the Oxford classification of IgAN, the Shigematsu classification and the Clinical Guidelines of IgAN in Japan. The levels of urinary C-megalin were measured by sandwich ELISA.

Results

Histological analysis based on the Oxford classification revealed that the levels of urinary C-megalin were correlated with mesangial hypercellularity in IgAN patients (OR = 1.76, 95% CI: 1.04–3.27, P<0.05). There was a significant correlation between the levels of urinary C-megalin and the severity of chronic extracapillary abnormalities according to the Shigematsu classification in IgAN patients (β = 0.33, P = 0.008). The levels of urinary C-megalin were significantly higher in all risk levels of IgAN patients requiring dialysis using the Clinical Guidelines of IgAN in Japan than in the control group. The levels of urinary C-megalin were significantly higher in the high risk and very high risk grades than in the low risk grade (P<0.05). The levels of urinary C-megalin were significantly higher in MN patients compared to the control group.

Conclusions

The levels of urinary C-megalin are associated with histological abnormalities in adult IgAN patients. There is a possibility that urinary C-megalin is an independent predictor of disease progression of IgAN. In addition, our results suggest that urinary C-megalin is a marker of glomerular abnormalities in various glomerular diseases as well as IgAN.

sPLA2 IB induces human podocyte apoptosis via the M-type phospholipase A2 receptor

The M-type phospholipase A2 receptor (PLA2R) is expressed in podocytes in human glomeruli. Group IB secretory phospholipase A2 (sPLA2 IB), which is one of the ligands of the PLA2R, is more highly expressed in chronic renal failure patients than in controls. However, the roles of the PLA2R and sPLA2 IB in the pathogenesis of glomerular diseases are unknown. In the present study, we found that more podocyte apoptosis occurs in the kidneys of patients with higher PLA2R and serum sPLA2 IB levels. In vitro, we demonstrated that human podocyte cells expressed the PLA2R in the cell membrane. After binding with the PLA2R, sPLA2 IB induced podocyte apoptosis in a time- and concentration-dependent manner. sPLA2 IB-induced podocyte PLA2R upregulation was not only associated with increased ERK1/2 and cPLA2α phosphorylation but also displayed enhanced apoptosis. In contrast, PLA2R-silenced human podocytes displayed attenuated apoptosis. sPLA2 IB enhanced podocyte arachidonic acid (AA) content in a dose-dependent manner. These data indicate that sPLA2 IB has the potential to induce human podocyte apoptosis via binding to the PLA2R. The sPLA2 IB-PLA2R interaction stimulated podocyte apoptosis through activating ERK1/2 and cPLA2α and through increasing the podocyte AA content.

Idiopathic membranous nephropathy and IgG4: an interesting relationship

Idiopathic membranous nephropathy (iMN) is a single-organ autoimmune disease characterized by subepithelial deposition of immune complexes containing IgG4 resulting in proteinuria, nephrotic syndrome, and, in some, end-stage renal disease. The pathogenesis involves a chronic IgG4 response against specific podocyte antigens which have now been at least partially defined in the neonatal, early childhood, and adult varieties. More has recently been learned about the genetic predisposition as well. This review discusses the pathophysiology of iMN in light of these discoveries and what is known about the genesis and potential clinical ramifications of an antigen-specific IgG4 response.

Complement-mediated cellular injury

Complement activation and recruitment of inflammatory leukocytes is an important defense mechanism against bacterial infection. However, complement also can mediate cellular injury and contribute to the pathogenesis of various diseases. With the appreciation that the C5b-9 membrane attack complex can injure cells in the absence of leukocytes, a role for the terminal complement pathway in inducing cell injury and kidney disease was shown in several experimental models, including the rat passive Heymann nephritis model of human membranous nephropathy. In podocytes, sublytic C5b-9 activates a variety of downstream pathways including protein kinases, lipid metabolism, reactive oxygen species, growth factors/gene transcription, endoplasmic reticulum stress, and the ubiquitin-proteasome system, and it impacts the integrity of the cytoskeleton and slit diaphragm proteins. C5b-9 also injures other kidney cells, including mesangial, glomerular endothelial, and tubular epithelial cells, and it contributes to the pathogenesis of mesangial-proliferative glomerulonephritis, thrombotic microangiopathy, and acute kidney injury. Conversely, certain C5b-9 signals limit complement-induced injury, or promote recovery of cells. In addition to C5b-9, complement cleavage products, such as C5a and C1q, can injure kidney cells. Thus, the complement system contributes to various kidney pathologies by causing cellular damage in both an inflammation-dependent and inflammation-independent manner.

Immunopathogenesis of membranous nephropathy: an update

Membranous nephropathy (MN) is a non-inflammatory organ-specific autoimmune disease which affects the kidney glomerulus, resulting in the formation of immune deposits on the outer aspect of the glomerular basement membrane, complement-mediated proteinuria, and severe renal failure in 30% of patients. In the last 10 years, substantial advances have been made in the understanding of the molecular bases of MN, with the identification of several antigens and predisposing genes in children and adults. These ground-breaking findings already have a major impact on diagnosis and monitoring and to some extent on therapies. However, there is evidence that the disease is more complex and involves a variety of antigen-antibody systems and genes involved in immune response, progression, recovery, and protective mechanisms. We herein review these recent findings which open new perspectives of research. Understanding the complex pathogenesis of MN will offer many opportunities for future therapeutic interventions and will hopefully have a major impact on patient care. New insights into the molecular mechanisms of MN may also enlighten the pathogenesis of organ-specific autoimmune diseases.

Immunopathology of lupus nephritis

When patients with systemic lupus erythematosus (SLE) present with urinary abnormalities, a renal biopsy is usually needed to rule out or confirm lupus nephritis. Renal biopsy is also needed to define the type of renal manifestation as different entities are associated with different outcomes; hence, renal biopsy results shape lupus management. But why does lupus nephritis come in different shapes? Why do patients with SLE often show change over time in class of lupus nephritis or have mixed forms? How does autoimmunity in SLE evolve? Why does loss of tolerance against nuclear antigens preferentially affect the kidney? Why are immune complex deposits in different glomerular compartments associated with different outcomes? What determines crescent formation in lupus? In this review, we discuss these questions by linking the latest information on lupus pathogenesis into the context of the different classes of lupus nephritis. This should help the basic scientist, the pathologist, and the clinician to gain a more conceptual view on the immunopathology of lupus nephritis.

Actin-associated Proteins in the Pathogenesis of Podocyte Injury

Podocytes have a complex cellular architecture with interdigitating processes maintained by a precise organization of actin filaments. The actin-based foot processes of podocytes and the interposed slit diaphragm form the final barrier to proteinuria. The function of podocytes is largely based on the maintenance of the normal foot process structure with actin cytoskeleton. Cytoskeletal dynamics play important roles during normal podocyte development, in maintenance of the healthy glomerular filtration barrier, and in the pathogenesis of glomerular diseases. In this review, we focused on recent findings on the mechanisms of organization and reorganization of these actin-related molecules in the pathogenesis of podocyte injury and potential therapeutics targeting the regulation of actin cytoskeleton in podocytopathies.

The role of complement in membranous nephropathy

Membranous nephropathy (MN) describes a histopathologic pattern of injury marked by glomerular subepithelial immune deposits and collectively represents one of the most common causes of adult nephrotic syndrome. Studies in Heymann nephritis, an experimental model of MN, have established a paradigm in which these deposits locally activate complement to cause podocyte injury, culminating in cytoskeletal reorganization, loss of slit diaphragms, and proteinuria. There is much circumstantial evidence for a prominent role of complement in human MN because C3 and C5b-9 are found consistently within immune deposits. Secondary MN often shows the additional presence of C1q, implicating the classic pathway of complement activation. Primary MN, however, is IgG4-predominant and IgG4 is considered incapable of binding C1q and activating the complement pathway. Recent studies have identified the M-type phospholipase A2 receptor (PLA2R) as the major target antigen in primary MN. Early evidence hints that IgG4 anti-PLA2R autoantibodies can bind mannan-binding lectin and activate the lectin complement pathway. The identification of anti-PLA2R antibodies as likely participants in the pathogenesis of disease will allow focused investigation into the role of complement in MN. Definitive therapy for MN is immunosuppression, although future therapeutic agents that specifically target complement activation may represent an effective temporizing measure to forestall further glomerular injury.

Novel roles of complement in renal diseases and their therapeutic consequences

The complement system functions as a part of the innate immune system. Inappropriate activation of the complement pathways has a deleterious effect on kidneys. Recent advances in complement research have provided new insights into the pathogenesis of glomerular and tubulointerstitial injury associated with complement activation. A new disease entity termed 'C3 glomerulopathy' has recently been proposed and is characterized by isolated C3 deposition in glomeruli without positive staining for immunoglobulins. Genetic and functional studies have demonstrated that several different mutations and disease variants, as well as the generation of autoantibodies, are potentially associated with its pathogenesis. The data from comprehensive analyses suggest that complement dysregulation can also be associated with hemolytic uremic syndrome and more common glomerular diseases, such as IgA nephropathy and diabetic kidney disease. In addition, animal studies utilizing genetically modified mice have begun to elucidate the molecular pathomechanisms associated with the complement system. From a diagnostic point of view, a noninvasive, MRI-based method for detecting C3 has recently been developed to serve as a novel tool for diagnosing complement-mediated kidney diseases. While novel therapeutic tools related to complement regulation are emerging, studies evaluating the precise roles of the complement system in kidney diseases will still be useful for developing new therapeutic approaches.

The complement cascade in kidney disease: from sideline to center stage

Activation of the complement pathway is implicated in the pathogenesis of many kidney diseases. The pathologic and clinical features of these diseases are determined in part by the mechanism and location of complement activation within the kidney parenchyma. This review describes the physiology, action, and control of the complement cascade and explains the role of complement overactivation and dysregulation in kidney disease. There have been recent advances in the understanding of the effects of upregulation of the complement cascade after kidney transplantation. Complement plays an important role in initiating and propagating damage to transplanted kidneys in ischemia-reperfusion injury, antibody-mediated rejection, and cell-mediated rejection. Complement-targeting therapies presently are in development, and the first direct complement medication for kidney disease was licensed in 2011. The potential therapeutic targets for anticomplement drugs in kidney disease are described. Clinical and experimental studies are ongoing to identify further roles for complement-targeting therapy.

Proteinuria in membranous lupus nephritis: the pathology is in the podocyte

BACKGROUND

Patients with membranous lupus glomerulonephritis (MLN) can present with a broad range of urine protein excretion. The glomerular lesion underlying this functional abnormality has been presumed to be immune complexes which aggregate in the subepithelial area. However, the amount of proteinuria often fails to correlate with the quantity of immune deposits demonstrable on fluorescent and electron microscopy. The purpose of this study is to determine the correlation of alterations of the morphologic components of the glomerular capillary wall with the amount of proteinuria in MLN.

DESIGN

We conducted a retrospective clinicopathologic study of patients with lupus nephritis (n=236). In those with pure MLN and proteinuria (n=20), the degree of immune aggregates in the capillary walls and mesangium was detailed using fluorescent and electron microscopy. The degree of foot process effacement (FPE) was detailed using electron microscopy.

RESULT

Eleven patients had nephrotic range proteinuria (≥ 3 g proteinuria/g creatinine (g/g)) and nine demonstrated subnephrotic range proteinuria (<3 g/g) (nephrotic, 8.3 ± 5.1 g/g vs. subnephrotic, 1.63 ± 0.83 g/g, p=0.001). All patients demonstrated peripheral capillary wall granular deposits by immunofluorescence microscopy, and the degree of moderate (2+) to severe (3+) deposition was not different (nephrotic, 8/11, 73% vs. subnephrotic, 5/9, 55%, p=0.64). By electron microscopy, FPE (88.6 ± 11% vs. 48.3 ± 36.1%, p=0.002) and foot process width (1798 ± 736 nm vs. 1000 ± 333 nm, p=0.008) was greater in the nephrotic group compared with subnephrotic. There were no other histopathologic differences between the groups.

CONCLUSIONS

In patients with MLN, a distinguishing morphologic feature of those with nephrotic range proteinuria is diffuse visceral epithelial cell FPE. We conclude that nephrotic range proteinuria in patients with MLN may be a manifestation of concomitant glomerular visceral epithelial cell dysfunction.

IQGAP1 mediates angiotensin II-induced apoptosis of podocytes via the ERK1/2 MAPK signaling pathway

BACKGROUND/AIMS

The mechanism underlying angiotensin II (AngII)-promoted podocyte apoptosis has not been established. IQ domain GTPase-activating protein 1 (IQGAP1) is a scaffolding protein of the mitogen-activated protein kinases (MAPK) signaling pathway, and plays a significant role in apoptosis. The present study evaluates the role of IQGAP1 in AngII-induced podocyte apoptosis.

METHODS

We randomly assigned 36 male Wistar rats to a normal saline-infused group, an AngII-infused group, or a normal control group, and measured podocyte apoptosis by the terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling (TUNEL) assay and transmission electron microscopic analysis. In addition, we exposed differentiated mouse podocytes to AngII and then assessed apoptosis by flow cytometry and Hoechst-33258 staining. Expression of IQGAP1 was measured by Western blotting, real-time PCR and immunofluorescence assay in vivo and in vitro. IQGAP1 siRNA and MAPK pathway inhibitors were further introduced to investigate the role of IQGAP1 and MAPK signaling in the process. Coimmunoprecipitation was used to evaluate the interaction between ERK1/2 and IQGAP1.

RESULTS

AngII promoted podocyte apoptosis in vivo and in vitro. IQGAP1 had a linear distribution along the capillary loops of glomeruli in vivo, and was in the cellular membrane and cytoplasm of cultured podocytes. AngII stimulated IQGAP1 expression and increased phosphorylation of P38, JNK, and ERK1/2. Knockdown of IQGAP1 with siRNA prevented AngII-induced apoptosis of podocytes and reduced AngII-induced phosphorylation of ERK1/2, but not that of P38, JNK. This was accompanied by a reduced interaction between ERK1/2 and IQGAP1.

CONCLUSION

IQGAP1 contributes to AngII-induced apoptosis of podocytes by interacting with the ERK1/2 signaling protein.

Anti-neutral endopeptidase, natriuretic peptides disarrangement, and proteinuria onset in membranous nephropathy

Neutral endopeptidase (NEP) is the first podocytic antigen responsible for human membranous nephropathy (MN). Besides the prevailing pathogenetic mechanism of immune complex, NEP is also involved in the metabolism of natriuretic peptides (NP). The identification of anti-NEP antibodies in human MN suggests that the decreased circulating NEP may down-regulate the NP catabolism. In this context, we hypothesize that NP disarrangement secondary to anti-NEP antibodies may account, in part, for the onset of proteinuria in MN. Whereas the pathways for the onset of proteinuria caused by elevated NP level are still obscure. The data presented in this review focus on those which support this hypothesis with regards to evidence from the glomerular haemodynamic changes, endothelial permeability, glomerular basement membrane disruption, and podocyte detachment.

Systematic variations associated with renal disease uncovered by parallel metabolomics of urine and serum

Background

Membranous nephropathy is an important glomerular disease characterized by podocyte injury and proteinuria, but no metabolomics research was reported as yet. Here, we performed a parallel metabolomics study, based on human urine and serum, to comprehensively profile systematic metabolic variations, identify differential metabolites, and understand the pathogenic mechanism of membranous nephropathy.

Results

There were obvious metabolic distinctions between the membranous nephropathy patients with urine protein lower than 3.5 g/24 h (LUPM) and those higher than 3.5 g/24 h (HUPM) by Partial Least Squares Discriminant Analysis (PLS-DA) model analysis. In total, 26 urine metabolites and 9 serum metabolites were identified to account for such differences, and the majority of metabolites were significantly increased in HUPM patients for both urines and serums. Combining the results of urine with serum, all differential metabolites were classified to 5 classes. This classification helps globally probe the systematic metabolic alterations before and after blood flowing through kidney. Citric acid and 4 amino acids were markedly increased only in the serum samples of HUPM patients, implying more impaired filtration function of kidneys of HUPM patients than LUPM patients. The dicarboxylic acids, phenolic acids, and cholesterol were significantly elevated only in urines of HUPM patients, suggesting more severe oxidative attacks than LUPM patients.

Conclusions

Parallel metabolomics of urine and serum revealed the systematic metabolic variations associated with LUPM and HUPM patients, where HUPM patients suffered more severe injury of kidney function and oxidative stresses than LUPM patients. This research exhibited a promising application of parallel metabolomics in renal diseases.

An overview of molecular mechanism of nephrotic syndrome

Podocytopathies (minimal change disease (MCD) and focal segmental glomerulosclerosis (FSGS)) together with membranous nephropathy are the main causes of nephrotic syndrome. Some changes on the expression of nephrin, podocin, TGF-β, and slit diaphragm components as well as transcription factors and transmembrane proteins have been demonstrated in podocytopathies. Considering the pathogenesis of proteinuria, some elucidations have been directed towards the involvement of epithelial-mesenchymal transition. Moreover, the usefulness of some markers such as TGF-β1, nephrin, synaptopodin, dystroglycans, and malondialdehyde have been determined in the differentiation between MCD and FSGS. Experimental models and human samples indicated an essential role of autoantibodies in membranous glomerulonephritis, kidney damage, and proteinuria events. Megalin and phospholipase-A2-receptor have been described as antigens responsible for the formation of the subepithelial immune complexes and renal disease occurrence. In addition, the complement system seems to play a key role in basal membrane damage and in the development of proteinuria in membranous nephropathy. This paper focuses on the common molecular changes involved in the development of nephrotic proteinuria.

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.

Murine membranous nephropathy: immunization with α3(IV) collagen fragment induces subepithelial immune complexes and FcγR-independent nephrotic syndrome

Membranous nephropathy (MN) is a leading cause of nephrotic syndrome in adults and a significant cause of end-stage renal disease, yet current therapies are nonspecific, toxic, and often ineffective. The development of novel targeted therapies requires a detailed understanding of the pathogenic mechanisms, but progress is hampered by the lack of a robust mouse model of disease. We report that DBA/1 mice as well as congenic FcγRIII(-/-) and FcRγ(-/-) mice immunized with a fragment of α3(IV) collagen developed massive albuminuria and nephrotic syndrome, because of subepithelial deposits of mouse IgG and C3 with corresponding basement membrane reaction and podocyte foot process effacement. The clinical presentation and histopathologic findings were characteristic of MN. Although immunized mice produced genuine anti-α3NC1 autoantibodies that bound to kidney and lung basement membranes, neither crescentic glomerulonephritis nor alveolitis ensued, likely because of the predominance of mouse IgG1 over IgG2a and IgG2b autoantibodies. The ablation of activating IgG Fc receptors did not ameliorate injury, implicating subepithelial deposition of immune complexes and consequent complement activation as a major effector pathway. We have thus established an active model of murine MN. This model, leveraged by the availability of genetically engineered mice and mouse-specific reagents, will be instrumental in studying the pathogenesis of MN and evaluating the efficacy of novel experimental therapies.

Excretion of complement proteins and its activation marker C5b-9 in IgA nephropathy in relation to renal function

Background

Glomerular damage in IgA nephropathy (IgAN) is mediated by complement activation via the alternative and lectin pathways. Therefore, we focused on molecules stabilizing and regulating the alternative pathway C3 convertase in urine which might be associated with IgAN pathogenesis.

Methods

Membrane attack complex (MAC), properdin (P), factor H (fH) and Complement receptor type 1 (CR1) were quantified in urine samples from 71 patients with IgAN and 72 healthy controls. Glomerular deposition of C5, fH and P was assessed using an immunofluorescence technique and correlated with histological severity of IgAN and clinical parameters. Fibrotic changes and glomerular sclerosis were evaluated in renal biopsy specimens.

Results

Immunofluorescence studies revealed glomerular depositions of C5, fH and P in patients with IgAN. Urinary MAC, fH and P levels in IgAN patients were significantly higher than those in healthy controls (p < 0.001), but CR1 was significantly lower than that in healthy controls (p < 0.001). Urinary MAC and fH levels were positively correlated with serum creatinine (sCr), urinary N-acetyl-β-D-glucosaminidase (u-NAG), urinary β2 microglobulin (u-Bm), urinary protein (p < 0.001), interstitial fibrosis (MAC: p < 0.01, fH: p < 0.05) and the percentage of global glomerular sclerosis (p < 0.01). Urinary P was positively correlated with u-NAG, u-Bm, and urinary protein (p < 0.01).

Conclusions

Complement activation occurs in the urinary space in IgAN and the measurement of levels of MAC and fH in the urine could be a useful indicator of renal injury in patients with IgAN.