The Many Effects of Complement C3- and C5-Binding Proteins in Renal Injury

Identifying the hub genes for Duchenne muscular dystrophy and Becker muscular dystrophy by weighted correlation network analysis

Background

The goal of this study is to identify the hub genes for Duchenne muscular dystrophy (DMD) and Becker muscular dystrophy (BMD) via weighted correlation network analysis (WGCNA).

Methods

The gene expression profile of vastus lateralis biopsy samples obtained in 17 patients with DMD, 11 patients with BMD and 6 healthy individuals was downloaded from the Gene Expression Omnibus (GEO) database (GSE109178). After obtaining different expressed genes (DEGs) via GEO2R, WGCNA was conducted using R package, modules and genes that highly associated with DMD, BMD, and their age or pathology were screened. Gene Ontology (GO) and Kyoto Encyclopaedia of Genes and Genomes (KEGG) enrichment analysis and protein–protein interaction (PPI) network analysis were also conducted. Hub genes and highly correlated clustered genes were identified using Search Tool for the Retrieval of Interacting Genes (STRING) and Cystoscape software.

Results

One thousand four hundred seventy DEGs were identified between DMD and control, with 1281 upregulated and 189 downregulated DEGs. Four hundred and twenty DEGs were found between BMD and control, with 157 upregulated and 263 upregulated DEGs. Fourteen modules with different colors were identified for DMD vs control, and 7 modules with different colors were identified for BMD vs control. Ten hub genes were summarized for DMD and BMD respectively, 5 hub genes were summarized for BMD age, 5 and 3 highly correlated clustered genes were summarized for DMD age and BMD pathology, respectively. In addition, 20 GO enrichments were found to be involved in DMD, 3 GO enrichments were found to be involved in BMD, 3 GO enrichments were found to be involved in BMD age.

Conclusion

In DMD, several hub genes were identified: C3AR1, TLR7, IRF8, FYB and CD33(immune and inflammation associated genes), TYROBP, PLEK, AIF1(actin reorganization associated genes), LAPTM5 and NT5E(cell death and arterial calcification associated genes, respectively). In BMD, a number of hub genes were identified: LOX, ELN, PLEK, IKZF1, CTSK, THBS2, ADAMTS2, COL5A1(extracellular matrix associated genes), BCL2L1 and CDK2(cell cycle associated genes).

Complement-Related Proteins and Their Measurements: The Current Status of Clinical Investigation

Complement has been considered to be a factor that protects the host against invading microorganisms during infection. However, in recent years, complement-related protein deficiency has been found to be involved in the onset of various diseases, such as autoimmune and inflammatory diseases. In Japan, C3, C4, and CH50 tests were generally performed only when a complement system examination was necessary and there were not enough examinations for other complement factors. Since the complement system has a very complicated activation pathway, at present, it is not well known which molecule must be measured to understand the pathological condition or pathogenesis in complement-related diseases. Furthermore, since the frequency of complement factor gene alleles also differs depending on race, data from foreign countries cannot be directly applied to Japanese populations. Under these circumstances, the Japanese Association for Complement Research (JACR) has prepared approximately 20 items for complement-related examinations, including the 5 categories of functional analysis, complement factors, complement regulators, activation products, and autoantibodies.

Absence of complement factor H reduces physical performance in C57BL6 mice

Complement (C) system is a double edge sword acting as the first line of defense on the one hand and causing aggravation of disease on the other. C activation when unregulated affects different organs including muscle regeneration. However, the effect of factor H (FH), a critical regulator of the alternative C pathway in muscle remains to be studied. FH deficiency results in excessive C activation and generates proinflammatory fragments C5a and C3a as byproducts. C3a and C5a signal through their respective receptors, C5aR and C3aR. In this study, we investigated the role of FH and downstream C5a/C5aR signaling in muscle architecture and function. Using the FH knockout (fh-/-) and fh-/-/C5aR-/double knockout mice we explored the role of C, specifically the alternative C pathway in muscle dysfunction. Substantial C3 and C9 deposits occur along the walls of the fh-/- muscle fibers indicative of unrestricted C activation. Physical performance assessments of the fh-/- mice show reduced grip endurance (76 %), grip strength (14 %) and rotarod balance (36 %) compared to controls. Histological analysis revealed a shift in muscle fiber populations indicated by an increase in glycolytic MHC IIB fibers and reduction in oxidative MHC IIA fibers. Consistent with this finding, mitochondrial DNA (mtDNA) and citrate synthase (CS) expression were both reduced indicating possible reduction in mitochondrial biomass. In addition, our results showed a significant increase in TGFβ expression and altered TGFβ localization in this setting. The architecture of cytoskeletal proteins actin and vimentin in the fh-/- muscle was changed that could lead to contractile weakness and loss of skeletal muscle elasticity. The muscle pathology in fh-/- mice was reduced in fh-/-/C5aR-/- double knockout (DKO) mice, highlighting partial C5aR dependence. Our results for the first time demonstrate an important role of FH in physical performance and skeletal muscle health.

GSPE alleviates renal fibrosis by inhibiting the activation of C3/ HMGB1/ TGF-β1 pathway

Grape seed proanthocyanidin extract (GSPE) has been reported to exhibit a variety of protective effects, such as antioxidant, anti-atherosclerosis and other pharmacological effects. As a member of the complement system, complement component 3 (C3) deposition in the glomerulus is recognized as an important causative mediator of various kidney diseases. In this study, we aimed to identify the effect of GSPE on C3 in the chronic kidney fibrosis and evaluate the possible mechanism. We observed that administration of GSPE relieves inflammation and chronic renal fibrosis in mouse models of UUO. GSPE inhibited C3 secreted by macrophages to relieve renal interstitial inflammation. In vitro, we found that C3 stimulated HMGB1 translocation form nucleus to cytoplasm and promote the expression of pro-inflammatory cytokines including TGF-β1 in primary renal tubular epithelial cells (PTEC), which could be inhibited by GSPE. Meanwhile, GSPE could also decreased HMGB1-induced EMT of PTEC through suppresses the HMGB1/TLR4/p65/TGF-β1 pathway. In addition, the myofibroblast activation was inhibited by GSPE via TGF-β1/Smad2/3 signaling pathways in normal rat kidney fibroblast (NRK-49F) cells. Overall, these observations provide that GSPE alleviates renal fibrosis by inhibiting the C3/HMGB1/TGF-β1 pathway and could thus lead to find the potential therapy for the suppression of renal fibrosis.

Complement activation products in the circulation and urine of primary membranous nephropathy

Background

Complement activation plays a substantial role in the pathogenesis of primary membranous nephropathy (pMN). C5b-9, C3c, MBL, and factor B have been documented in the subepithelial immune deposits. However, the changing of complement activation products in circulation and urine is not clear.

Methods

We measured the circulating and urinary levels of C1q, MBL, C4d, Bb, properdin, C3a, C5a, and sC5b-9, in 134 patients with biopsy-proven pMN, by enzyme-linked immunosorbent assay. All the plasma values were corrected by eGFR and all the urinary values were corrected by urinary creatinine and urinary protein excretion. Anti-PLA2R antibodies were measured in all patients.

Results

The plasma complement activation products were elevated both in the patients with and without anti-PLA2R antibodies. C3a levels were remarkably increased in the circulation and urine, much higher than the elevated levels of C5a. C5b-9 was in normal range in plasma, but significantly higher in urine. The urinary C5a had a positive correlation with anti-PLA2R antibody levels and urinary protein. The plasma level of C4d was elevated, but C1q and MBL were comparable to healthy controls. Positive correlations were observed between plasma C4d/MBL and urinary protein, only in the patients with positive anti-PLA2R antibodies but not in those without. The plasma level of Bb was elevated and had positive correlation with urinary protein only in the patients without anti-PLA2R antibodies.

Conclusion

Complement activation products were remarkable increased in pMN and may serve as sensitive biomarkers of disease activity. The complement may be activated through lectin pathway with the existence of anti-PLA2R antibodies, while through alternative pathway in the absence of antibody.

ANCA associated vasculitis: The journey to complement-targeted therapies

ANCA associated vasculitis is a serious, very often recurrent disease that despite the current standard treatment with high-dose glucocorticoids and either cyclophosphamide or rituximab, patients have a nine-fold increased mortality risk in the first year compared with healthy controls, attributed to infections, vasculitis activity, and renal disease. During the last few years, novel findings have suggested that activation of the complement system, in particular the alternative complement system, has a significant role in ANCA associated vasculitis pathogenesis. Detection of several components of this system in the circulation and urine reflects disease activity, and thus may be useful for clinical prognosis and to set up personalised treatments. In fact, some components of the complement system, such as C5a, might be potential targets for therapy. In this Review an update on clinical evidence for the role of complement activation in AAV is provided and subsequently we discuss potential therapeutic strategies that target complement components and open the way for clinical use of this target therapy in the near future.

Nlrp3-inflammasome activation in non-myeloid-derived cells aggravates diabetic nephropathy

Diabetic nephropathy is a growing health concern with characteristic sterile inflammation. As the underlying mechanisms of this inflammation remain poorly defined, specific therapies targeting sterile inflammation in diabetic nephropathy are lacking. Intriguingly, an association of diabetic nephropathy with inflammasome activation has recently been shown, but the pathophysiological relevance of this finding remains unknown. Within glomeruli, inflammasome activation was detected in endothelial cells and podocytes in diabetic humans and mice and in glucose-stressed glomerular endothelial cells and podocytes in vitro. Abolishing Nlrp3 or caspase-1 expression in bone marrow-derived cells fails to protect mice against diabetic nephropathy. Conversely, Nlrp3-deficient mice are protected against diabetic nephropathy despite transplantation of wild-type bone marrow. Pharmacological IL-1R antagonism prevented or even reversed diabetic nephropathy in mice. Mitochondrial reactive oxygen species (ROS) activate the Nlrp3 inflammasome in glucose or advanced glycation end product stressed podocytes. Inhibition of mitochondrial ROS prevents glomerular inflammasome activation and nephropathy in diabetic mice. Thus, mitochondrial ROS and Nlrp3-inflammasome activation in non-myeloid-derived cells aggravate diabetic nephropathy. Targeting the inflammasome may be a potential therapeutic approach to diabetic nephropathy.

Comparative proteomic analysis of renal tissue in IgA nephropathy with iTRAQ quantitative proteomics

Immunoglobulin (Ig) A nephropathy (IgAN) is the most common form of glomerulonephritis. In clinical practice, it is difficult to monitor the repeating relapse in patients suffering from IgAN, which usually occurs within 10 years of end-stage renal disease. In order to identify and quantify the total protein content in the renal tissue of patients with IgAN, isobaric tags for relative and absolute quantification (iTRAQ) technology was performed. iTRAQ coupled with multiple chromatographic fractionation and tandem mass spectrometry was used to analyze the total protein of normal renal tissue in IgAN and healthy patients. The individual proteins were identified by the Mascot search engine and any that were differentially expressed were monitored. A total of 574 different proteins were identified, and 287 proteins were up- or downregulated by >1 fold alteration in levels. The results showed that iTRAQ-based quantitative proteomic technology for the identification and relative quantitation of the renal tissue proteome is efficiently applicable. The differential expression of the proteome profiles for IgAN patients was determined. Further studies using large cohorts of patient samples with long-term clinical follow-up data should be conducted to evaluate the usefulness of the pathogenesis and novel biomarker candidates of IgAN, which may develop a novel technique for the diagnosis of IgAN.

Tissue-specific deletion of Crry from mouse proximal tubular epithelial cells increases susceptibility to renal ischemia-reperfusion injury

The murine cell surface protein Crry (complement receptor 1-related protein/gene y) is a key complement regulator with similar activities to human membrane cofactor protein (MCP) and decay-accelerating factor. MCP has a critical role in preventing complement-mediated tissue injury and its mutation has been implicated in several human kidney diseases. The study of Crry in mice has relevance to understanding MCP activity in human diseases; however, such efforts have been hampered by the embryonic lethality phenotype of Crry gene knockout. Here we used a conditional gene-targeting approach and deleted Crry from the mouse proximal tubular epithelial cells where Crry is prominently expressed. Absence of Crry from proximal tubular epithelial cells resulted in spontaneous C3 deposition on the basolateral surface but no apparent renal disease in unchallenged mice. However, mice deficient in Crry on proximal tubular epithelial cells developed exacerbated renal injury when subjected to renal ischemia-reperfusion, showing increased blood urea nitrogen levels, higher tubular injury scores, more tubular epithelial cell apoptosis, and inflammatory infiltrates. Renal ischemia-reperfusion injury in the Crry conditional knockout mice was prevented by blocking C3 and C5 activation using an anti-properdin or anti-C5 monoclonal antibody (mAb), respectively. Thus, Crry has a critical role in protecting proximal tubular epithelial cells during ischemia-reperfusion challenge. Our results highlight the latent risk for inflammatory kidney injury associated with defects in membrane complement regulators.

A compendium of urinary biomarkers indicative of glomerular podocytopathy

It is well known that glomerular podocyte injury and loss are present in numerous nephropathies and that the pathophysiologic consecution of disease hinges upon the fate of the podocyte. While multiple factors play a hand in glomerulopathy progression, basic logic lends that if one monitors the podocyte's status, that may reflect the status of disease. Recent investigations have focused on what one can elucidate from the noninvasive collection of urine, and have proven that certain, specific biomarkers of podocytes can be readily identified via varying techniques. This paper has brought together all described urinary biomarkers of podocyte injury and is made to provide a concise summary of their utility and testing in laboratory and clinical theatres. While promising in the potential that they hold as tools for clinicians and investigators, the described biomarkers require further comprehensive vetting in the form of larger clinical trials and studies that would give their value true weight. These urinary biomarkers are put forth as novel indicators of glomerular disease presence, disease progression, and therapeutic efficacy that in some cases may be more advantageous than the established parameters/measures currently used in practice.

The C5a receptor has a key role in immune complex glomerulonephritis in complement factor H-deficient mice

Chronic serum sickness leads to the formation of glomerular immune complexes; however, C57BL/6 mice do not develop glomerulonephritis unless complement factor H (CFH) is absent from the plasma. Here we studied the role for C5a receptor (R) in this setting. The exaggerated humoral immune response in CFH^−/− mice was normalized in CFH^−/−C5aR^−/− double knockout mice, highlighting the C5aR dependence. The CFH knockout mice developed proliferative glomerulonephritis with endocapillary F4/80⁺ macrophage infiltration, a process reduced in the double knockout mice. There was no interstitial inflammation by histologic criteria or flow cytometry for F4/80⁺Ly6C^hiCCR2^hi inflammatory macrophages. There were, however, more interstitial CD3⁺CD4⁺ T lymphocytes in CFH knockout mice with chronic serum sickness, while double knockout mice had greater than 5-fold more Ly6C^loCCR2^lo anti-inflammatory macrophages compared to the CFH knockout mice. Mice lacking C5aR were significantly protected from functional renal disease as assessed by blood urea nitrogen levels. Thus, IgG- and iC3b-containing immune complexes are not inflammatory in C57BL/6 mice. Yet when these mice lack CFH, sufficient C3b persists in glomeruli to generate C5a and activate C5aR.

Basic and translational concepts of immune-mediated glomerular diseases

Genetically modified immune responses to infections and self-antigens initiate most forms of GN by generating pathogen- and danger-associated molecular patterns that stimulate Toll-like receptors and complement. These innate immune responses activate circulating monocytes and resident glomerular cells to release inflammatory mediators and initiate adaptive, antigen-specific immune responses that collectively damage glomerular structures. CD4 T cells are needed for B cell-driven antibody production that leads to immune complex formation in glomeruli, complement activation, and injury induced by both circulating inflammatory and resident glomerular effector cells. Th17 cells can also induce glomerular injury directly. In this review, information derived from studies in vitro, well characterized experimental models, and humans summarize and update likely pathogenic mechanisms involved in human diseases presenting as nephritis (postinfectious GN, IgA nephropathy, antiglomerular basement membrane and antineutrophil cytoplasmic antibody-mediated crescentic GN, lupus nephritis, type I membranoproliferative GN), and nephrotic syndrome (minimal change/FSGS, membranous nephropathy, and C3 glomerulopathies). Advances in understanding the immunopathogenesis of each of these entities offer many opportunities for future therapeutic interventions.

Review: Complement and its regulatory proteins in kidney diseases

Complement is a part of the body's innate immune system that helps defend the host from microbial infection. It is tightly controlled by a number of cell surface and fluid-phase proteins so that under normal circumstances injury to autologous tissues is avoided. In many pathological settings, such as when the complement regulatory mechanisms are dysfunctional or overwhelmed, complement attack of autologous tissues can occur with severe, sometimes life-threatening consequences. The kidney appears to be particularly vulnerable to complement-mediated inflammatory injury and many kidney pathologies have been linked to abnormal complement activation. Clinical and experimental studies have shown that complement attack can be a primary cause in rare, genetically predisposed kidney diseases or a significant contributor to kidney injury caused by other etiological factors. Here we provide a brief review of recent advances on the activation and regulation of the complement system in kidney disease, with a particular emphasis on the relevance of complement regulatory proteins.

Podocyte number predicts progression of proteinuria in IgA nephropathy

Podocyte injury is a feature of glomerulopathies associated with proteinuria, which in turn has been used as a clinical prognostic factor for glomerular diseases. The goal of this study is to investigate the relationship between podocyte injury found in biopsied renal tissue and change of proteinuria in IgA nephropathy (IgAN). In all, 35 patients with biopsy-proven IgAN and proteinuria (>1.0 g per 24 h) were enrolled in the IgAN group, while 8 patients with excision of renal harmatoma or carcinoma served as kidney controls (Control). Immunohistochemistry was applied to detect the expression of nestin, cell-cycle regulatory protein p27, as well as complement C5b-9 and complement receptor 1 (CR1). Podocyte foot process width (FPW) and podocyte population in renal biopsied samples were measured by morphometric analysis. On the basis of the podocyte density (Nv), the IgAN patients were divided into podocytopenic group (n=17, Nv<57.10 /microm(3) x 10(6)) and normopodocytic group (n=18, Nv> or =57.10 /microm(3) x 10(6)). Changes of proteinuria were followed for 18 months after biopsy. Compared with the Control, IgAN glomeruli had reduced podocyte expression of p27 and nestin along with decreased podocyte number. IgAN glomeruli also showed activation of C5b-9 in mesangial and subepithelial areas with decreased CR1 expression in podocytes. The C5b-9 positivity was inversely correlated with the number of WT-1-positive podocytes. Although the magnitude of proteinuria at biopsy correlated with podocyte FPW (P<0.05), the change in the amount of proteinuria expressed as proteinuria progression rate significantly correlated with the podocyte density. Thus, the normopodocytic group showed significantly lower proteinuria progression rate than the podocytopenic group regardless the comparable clinical features at biopsy and treatment regimen between the two groups. The results of this study indicate that, in IgAN, podocyte injury is involved in development of proteinuria and loss of podocytes predicts progression of the proteinuria. Complement activation may contribute to podocyte damage in IgAN.

Functional genomic analysis of peripheral blood during early acute renal allograft rejection

BACKGROUND

Acute graft rejection is an important clinical problem in renal transplantation and an adverse predictor for long-term graft survival. Peripheral blood biomarkers that provide evidence of early graft rejection may offer an important option for posttransplant monitoring, optimize the utility of graft biopsy, and permit timely and effective therapeutic intervention to minimize the graft damage.

METHODS

In this feasibility study (n=58), we have used gene expression profiling in a case-control design to compare whole blood samples between normal subjects (n=20) and patients with (n=11) or without (n=22) biopsy-confirmed acute rejection (BCAR) or borderline changes (n=5).

RESULTS

A total of 183 probe sets representing 160 genes were differentially expressed (false discovery rate [FDR] <0.01) between subjects with or without BCAR, from which linear discriminant analysis and cross-validation identified an initial gene signature of 24 probe sets, and a more refined set of 11 probe sets found to classify subject samples correctly. Cross-validation suggested an out-of-sample sensitivity of 73% and specificity of 91% for identification of samples with or without BCAR. An increase in classifier gene expression correlated closely with acute rejection during the first 3 months posttransplant. Biological evaluation indicated that the differentially expressed genes encompassed processes related to immune response, signal transduction, and cytoskeletal reorganization.

CONCLUSION

Preliminary evidence indicates that gene expression in the peripheral blood may yield a relevant measure for the occurrence of BCAR and offer a potential tool for immunologic monitoring. These results now require confirmation in a larger cohort.

NK cells induce apoptosis in tubular epithelial cells and contribute to renal ischemia-reperfusion injury

Renal ischemia-reperfusion injury (IRI) can result in acute renal failure with mortality rates of 50% in severe cases. NK cells are important participants in early-stage innate immune responses. However, their role in renal tubular epithelial cell (TEC) injury in IRI is currently unknown. Our data indicate that NK cells can kill syngeneic TEC in vitro. Apoptotic death of TEC in vitro is associated with TEC expression of the NK cell ligand Rae-1, as well as NKG2D on NK cells. In vivo following IRI, there was increased expression of Rae-1 on TEC. FACS analyses of kidney cell preparations indicated a quantitative increase in NKG2D-bearing NK cells within the kidney following IRI. NK cell depletion in wild-type C57BL/6 mice was protective, while adoptive transfer of NK cells worsened injury in NK, T, and B cell-null Rag2(-/-)gamma(c)(-/-) mice with IRI. NK cell-mediated kidney injury was perforin (PFN)-dependent as PFN(-/-) NK cells had minimal capacity to kill TEC in vitro compared with NK cells from wild-type, FasL-deficient (gld), or IFN-gamma(-/-) mice. Taken together, these results demonstrate for the first time that NK cells can directly kill TEC and that NK cells contribute substantially to kidney IRI. NK cell killing may represent an important underrecognized mechanism of kidney injury in diverse forms of inflammation, including transplantation.

Innate immunity as a driving force in renal disease

Mrug et al. propose that innate immunity is a hallmark of progressive polycystic kidney disease (PKD). We propose that innate immunity is a driving force in the progression of many renal diseases. Renal epithelial cells are capable of expressing a large variety of proinflammatory genes resulting in the production of cytokines, chemokines, cell-adhesion molecules, and complement components. We suggest that future therapeutic interventions should be directed toward control of innate immunity in renal disease.