New approaches to the treatment of dense deposit disease

Apolipoprotein E is enriched in dense deposits and is a marker for dense deposit disease in C3 glomerulopathy

C3 glomerulopathy (C3G) is a rare disease resulting from dysregulation of the alternative pathway of complement. C3G includes C3 glomerulonephritis (C3GN) and dense deposit disease (DDD), both of which are characterized by bright glomerular C3 staining on immunofluorescence studies. However, on electron microscopy (EM), DDD is characterized by dense osmiophilic mesangial and intramembranous deposits along the glomerular basement membranes (GBM), while the deposits of C3GN are not dense. Why the deposits appear dense in DDD and not in C3GN is not known. We performed laser microdissection (LCM) of glomeruli followed by mass spectrometry (MS) in 12 cases each of DDD, C3GN, and pretransplant kidney control biopsies. LCM/MS showed marked accumulation of complement proteins C3, C5, C6, C7, C8, C9 and complement regulating proteins CFHR5, CFHR1, and CFH in C3GN and DDD compared to controls. C3, CFH and CFHR proteins were comparable in C3GN and DDD. Yet, there were significant differences. First, there was a six-to-nine-fold increase of C5-9 in DDD compared to C3GN. Secondly, an unexpected finding was a nine-fold increase in apolipoprotein E (ApoE) in DDD compared to C3GN. Most importantly, immunohistochemical and confocal staining for ApoE mirrored the dense deposit staining in the GBM in DDD but not in C3GN or control cases. Validation studies using 31 C3G cases confirmed the diagnosis of C3GN and DDD in 80.6 % based on ApoE staining. Overall, there is a higher burden of terminal complement pathway proteins in DDD compared to C3GN. Thus, our study shows that dense deposits in DDD are enriched with ApoE compared to C3GN and control cases. Hence, ApoE staining may be used as an adjunct to EM for the diagnosis of DDD and might be valuable when EM is not available.

Recurrent C3 glomerulopathy after kidney transplantation

The complement system is part of innate immunity and is pivotal in protecting the body against pathogens and maintaining host homeostasis. Activation of the complement system is triggered through multiple pathways, including antibody deposition, a mannan-binding lectin, or activated complement deposition. C3 glomerulopathy (C3G) is a rare glomerular disease driven by complement dysregulation with high post-transplantation recurrence rates. Its treatment is mainly based on immunosuppressive therapies, specifically mycophenolate mofetil and glucocorticoids. Recent years have seen significant progress in understanding complement biology and its role in C3G pathophysiology. New complement-tergeting treatments have been developed and initial trials have shown promising results. However, challenges persist in C3G, with recurrent post-transplantation cases leading to suboptimal outcomes. This review discusses the pathophysiology and management of C3G, with a focus on its recurrence after kidney transplantation.

Clinical and pathological features of 52 patients with glomerulonephritis with dominant C3

OBJECTIVES

With the in-depth study of complement dysregulation, glomerulonephritis with dominant C3 has received increasing attention, with a variety of pathologic types and large differences in symptoms and prognosis between pathologic types. This study analyzes the clinical, pathological, and prognostic characteristics of different pathological types of glomerulonephritis with dominant C3, aiming to avoid misdiagnosis and missed diagnoses.

METHODS

The clinical, pathological, and follow-up data of 52 patients diagnosed as glomerulonephritis with dominant C3 by renal biopsy from June 2013 to October 2022 were retrospectively analyzed. According to the clinical feature and results of pathology, 15 patients with post-infectious glomerulonephritis (PIGN) and 37 patients with of non-infectious glomerulonephritis (N-PIGN) were classified. N-PIGN subgroup analysis was performed, and 16 patients were assigned into a C3-alone-deposition group and 21 in a C3-dominant-deposition group, or 27 in a C3 glomerulopathy (C3G) group and 10 in a non-C3 nephropathy (N-C3G) group.

RESULTS

The PIGN group had lower creatinine values (84.60 μmol/L vs179.62 μmol/L, P=0.001), lower complement C3 values (0.36 g/L vs0.74 g/L, P<0.001) at biopsy, and less severe pathological chronic lesions compared with the N-PIGN group. In the N-PIGN subgroup analysis, the C3-dominant-deposition group had higher creatinine values (235.30 μmol/L vs106.70 μmol/L, P=0.004) and higher 24-hour urine protein values (4 025.62 mg vs1 981.11 mg, P=0.037) than the C3-alone-deposition group. The prognosis of kidney in the PIGN group (P=0.049), the C3-alone-deposition group (P=0.017), and the C3G group (P=0.018) was better than that in the N-PIGN group, the C3-dominant-deposition group, and the N-C3G group, respectively.

CONCLUSIONS

Glomerulonephritis with dominant C3 covers a variety of pathological types, and PIGN needs to be excluded before diagnosing C3G because of considerable overlap with atypical PIGN and C3G; in addition, the deposition of C1q complement under fluorescence microscope may indicate poor renal prognosis, and relevant diagnosis, treatment, and follow-up should be strengthened.

Efficacy and Safety of Iptacopan in Patients With C3 Glomerulopathy

Introduction

Complement 3 glomerulopathy (C3G) is a rare inflammatory kidney disease mediated by dysregulation of the alternative complement pathway. No targeted therapy exists for this aggressive glomerulonephritis. Efficacy, safety, tolerability, pharmacokinetics (PK), and pharmacodynamics (PD) (measured by complement biomarkers) of iptacopan were assessed in patients with C3G.

Methods

In this phase 2, multicenter, open-label, single-arm, nonrandomized study, adults with biopsy-proven, native kidney C3G (native cohort) and kidney transplant recipients with C3G recurrence (recurrent kidney transplant [KT] cohort) received iptacopan twice daily (bid) for 84 days (days 1-21: 10-100 mg; days 22-84: 200 mg). The primary end point was the urine protein-to-creatinine ratio (UPCR; native cohort) and the change in the C3 deposit score of kidney biopsy (recurrent KT cohort). The complement pathway measures included Wieslab assay, soluble C5b9, and serum C3 levels.

Results

A total of 27 patients (16 native cohort and 11 recurrent KT cohort) were enrolled and all completed the study. In the native cohort, UPCR levels decreased by 45% from baseline to week 12 (P = 0.0003). In the recurrent KT cohort, the median C3 deposit score decreased by 2.50 (scale: 0-12) on day 84 versus baseline (P = 0.03). Serum C3 levels were normalized in most patients; complement hyperactivity observed pretreatment was reduced. Severe adverse events (AEs) included post-biopsy hematuria and hyperkalemia. No deaths occurred during the study.

Conclusion

Iptacopan resulted in statistically significant and clinically important reductions in UPCR and normalization of serum C3 levels in the native cohort and reduced C3 deposit scores in the recurrent KT cohort with favorable safety and tolerability. (ClinicalTrials.gov identifier: NCT03832114).

The role of complement in kidney disease

The complement cascade comprises soluble and cell surface proteins and is an important arm of the innate immune system. Once activated, the complement system rapidly generates large quantities of protein fragments that are potent mediators of inflammatory, vasoactive and metabolic responses. Although complement is crucial to host defence and homeostasis, its inappropriate or uncontrolled activation can also drive tissue injury. For example, the complement system has been known for more than 50 years to be activated by glomerular immune complexes and to contribute to autoimmune kidney disease. Notably, the latest research shows that complement is also activated in kidney diseases that are not traditionally thought of as immune-mediated, including haemolytic-uraemic syndrome, diabetic kidney disease and focal segmental glomerulosclerosis. Several complement-targeted drugs have been approved for the treatment of kidney disease, and additional anti-complement agents are being investigated in clinical trials. These drugs are categorically different from other immunosuppressive agents and target pathological processes that are not effectively inhibited by other classes of immunosuppressants. The development of these new drugs might therefore have considerable benefits in the treatment of kidney disease.

Complement: Functions, location and implications

The complement system, an arm of the innate immune system plays a critical role in both health and disease. The complement system is highly complex with dual possibilities, helping or hurting the host, depending on the location and local microenvironment. The traditionally known functions of complement include surveillance, pathogen recognition, immune complex trafficking, processing and pathogen elimination. The noncanonical functions of the complement system include their roles in development, differentiation, local homeostasis and other cellular functions. Complement proteins are present in both, the plasma and on the membranes. Complement activation occurs both extra- and intracellularly, which leads to considerable pleiotropy in their activity. In order to design more desirable and effective therapies, it is important to understand the different functions of complement, and its location-based and tissue-specific responses. This manuscript will provide a brief overview into the complex nature of the complement cascade, outlining some of their complement-independent functions, their effects at different locale, and their implication in disease settings.

[Diagnosis and treatment of glomerular diseases with a membranoproliferative glomerulonephritis (MPGN) pattern of injury]

Membranoproliferative glomerulonephritis (MPGN) represents a heterogeneous group of diseases. The common feature of a membranoproliferative lesion pattern in the kidney biopsy can either be idiopathic/primary or-much more frequently-have a secondary cause. The historical classification into MPGN types I to III has largely been abandoned and replaced in recent years by a pathogenesis-oriented classification. A MPGN with C1q, C3 and/or C4 deposits on light microscopy is referred to as immune complex GN (IC-GN), while a MPGN with dominant C3 deposits is referred to as C3 glomerulopathy (C3G). C3G is further divided into C3 glomerulonephritis (C3GN) and dense deposit disease (DDD). These diagnoses can only be made by a kidney biopsy. Possible causes of MPGN are chronic infections (especially hepatitis B and C, bacterial infections, infections with protozoa), autoimmune diseases (especially lupus, rheumatoid arthritis) or malignancies (especially hematological malignancies). Particularly in the case of C3G a comprehensive analysis of the complement system components is strongly recommended. Due to the low incidence and the heterogeneous clinical appearance of MPGN therapeutic decisions must be made individually; an optimal general therapy is unknown, except that supportive treatment as with other glomerular diseases should be optimized. In the case of a secondary MPGN it is generally recommended to treat the potential cause of the MPGN. If significant proteinuria persists and eGFR remains > 30 ml/min/1.73 m2, treatment with systemic steroids and mycophenolate mofetil is recommended. Other treatment options on an individual level after evaluation and discussion of the risk-benefit ratio with the patient are rituximab and eculizumab. Rapidly progressive MPGN should be treated like ANCA-associated vasculitis. The recurrence rates after kidney transplantation are very high and treatment is challenging.

Recurrent C3 Glomerulonephritis along with BK-Virus-Associated Nephropathy after Kidney Transplantation: A Case Report

C3 glomerulonephritis (C3GN) is a rare cause of end-stage kidney disease and frequently recurrent in allografts following kidney transplantation (KT). Herein, we describe the case of a kidney transplant recipient who developed recurrent C3GN along with BK-virus-associated nephropathy (BKVAN) following KT. A 33-year-old man diagnosed with membranoproliferative glomerulonephritis 17 years ago underwent preemptive KT with a donor kidney from his aunt. Proteinuria gradually increased after 3 months following KT, and graft biopsy was performed 30 months after KT. Histopathological examination revealed recurrent C3GN. The dosages of triple immunosuppressive maintenance therapy agents were increased. Subsequently, serum C3 levels recovered to normal levels. However, at 33 months following KT, the BK viral load increased and graft function gradually deteriorated; a second graft biopsy was performed at 46 months following KT, which revealed BKVAN and decreased C3GN activity. The dosages of immunosuppressive agents were decreased; subsequently, BKVAN improved and graft function was maintained with normal serum C3 levels at 49 months following KT. This case indicates that C3GN is highly prone to recurrence following KT and that immunosuppressive therapy for C3GN increases the risk of BKVAN.

Complement: The Road Less Traveled

The complement field has recently experienced a strong resurgence of interest because of the unexpected discovery of new complement functions extending complement's role beyond immunity and pathogen clearance, a growing list of diseases in which complement plays a role, and the proliferation of complement therapeutics. Importantly, although the majority of complement components in the circulation are generated by the liver and activated extracellularly, complement activation unexpectedly also occurs intracellularly across a broad range of cells. Such cell-autonomous complement activation can engage intracellular complement receptors, which then drive noncanonical cell-specific effector functions. Thus, much remains to be discovered about complement biology. In this brief review, we focus on novel noncanonical activities of complement in its "classic areas of operation" (kidney and brain biology, infection, and autoimmunity), with an outlook on the next generation of complement-targeted therapeutics.

Association of Histologic Parameters with Outcome in C3 Glomerulopathy and Idiopathic Immunoglobulin-Associated Membranoproliferative Glomerulonephritis

BACKGROUND AND OBJECTIVES

C3 glomerulopathy and idiopathic Ig-associated membranoproliferative GN are kidney diseases characterized by abnormal glomerular complement C3 deposition. These conditions are heterogeneous in outcome, but approximately 50% of patients develop kidney failure within 10 years.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

To improve identification of patients with poor prognosis, we performed a detailed analysis of percutaneous kidney biopsies in a large cohort of patients. Using a validated histologic scoring system, we analyzed 156 native diagnostic kidney biopsies from a retrospective cohort of 123 patients with C3 glomerulopathy and 33 patients with Ig-associated membranoproliferative GN. We used linear regression, survival analysis, and Cox proportional hazards models to assess the relationship between histologic and clinical parameters with outcome.

RESULTS

Frequent biopsy features were mesangial expansion and hypercellularity, glomerular basement membrane double contours, and endocapillary hypercellularity. Multivariable analysis showed negative associations between eGFR and crescents, interstitial inflammation, and interstitial fibrosis/tubular atrophy. Proteinuria positively associated with endocapillary hypercellularity and glomerular basement membrane double contours. Analysis of second native biopsies did not demonstrate associations between immunosuppression treatment and improvement in histology. Using a composite outcome, risk of progression to kidney failure associated with eGFR and proteinuria at the time of biopsy, cellular/fibrocellular crescents, segmental sclerosis, and interstitial fibrosis/tubular atrophy scores.

CONCLUSIONS

Our detailed assessment of kidney biopsy data indicated that cellular/fibrocellular crescents and interstitial fibrosis/tubular atrophy scores were significant determinants of deterioration in kidney function.

Characteristics and outcomes of glomerulonephritis with membranoproliferative pattern in children

BACKGROUND

Membranoproliferative glomerulonephritis (MPGN) is a rare histopathologic pattern of glomerular injury with limited studies in pediatric patients. Characteristics and outcomes of children with MPGN have also remained to be further explored.

METHODS

We retrospectively reviewed the clinicopathological features, genetic findings, treatments and outcomes in 17 pediatric patients pathologically diagnosed with MPGN from 2007 to 2020 in the Children's National Medical Center in China.

RESULTS

Median age at disease onset was 9.9 years (IQR, 5.6-11.9 years). Most of the patients (12/17) had nephrotic range of proteinuria, and nephritic-nephrotic syndrome was the most common clinical presentation (35.2%). Secondary causes were identified in eight patients including hepatitis B virus (HBV) infection (n=4), methylmalonic acidemia (MMA, n=2), rheumatoid arthritis (RA, n=1) and Aymé-Gripp Syndrome (n=1). The nine patients with primary MPGN were further identified as immune-complex mediated MPGN (n=8), and unclassifiable MPGN (U-MGPN, n=1). Genetic analyses identified pathogenic variants of MMACHC gene in two cases of MMA and established the diagnosis for Aymé-Gripp syndrome in one case with a de novo variant of MAF gene. Comparing study between the complete or partial remission group (n=8) and non-response group (n=9) showed a significant difference in the timing of renal biopsy (P<0.05). Normal renal function was preserved in ten patients at the last follow-up. Two patients developed into end-stage renal disease (ESRD).

CONCLUSIONS

Children with MPGN pattern present heterogenous clinical features. Genetic detection helps to explore underlying causes of MPGN. Early identification of the primary or secondary causes of MPGN in children is vital.

Complete Renal Recovery in Pediatric Patient with C3 Glomerulonephritis: A Case Report

C3 glomerulonephritis (C3GN) is a rare kidney disease resulting from dysregulation of the alternative complement cascade. Without treatment, approximately 70% of affected children and 30–50% of affected adults will develop worsening of proteinuria and progress to end-stage renal disease within 10 years of diagnosis. Here, we describe a 9-year-old Sudanese girl with no significant past medical history who presented to the Emergency Department with a 2-month history of fatigue, poor oral intake, and worsening facial and lower extremity edema, and subsequently found to have anemia, hypoalbuminemia, microscopic hematuria, and proteinuria. Additional laboratory testing revealed that the patient had low C3, high C3 nephritic factor (C3NeF), and high factor H. Renal function was normal. The diagnosis of C3GN was confirmed by renal biopsy. The patient was treated with ACE inhibitor, mycophenolate mofetil (600 mg per m² per dose, every 12 h), in combination with “pulse” methylprednisolone at 30 mg/kg/day IV bolus (maximum 1 g) for 3 consecutive days, followed by 2 months of daily oral prednisolone (2 mg/kg/day) and alternate-day prednisolone weaning from 1 mg/kg to 0.1 mg/kg for additional 12 months. Mycophenolate was continued throughout her treatment course and for maintenance therapy. In response to treatment, anemia, microscopic hematuria, hypoalbuminemia, and proteinuria resolved. Complete complement profile before and at 6 months therapy showed normalization of C3NeF, complement regulatory factor H and C3. This present case provides evidence of the full responsiveness of a rare form of complement dysregulation C3GN to a combination of mycophenolate and corticosteroids. The disease has NOT recurred in >2 years after initial presentation.

Recurrent glomerulonephritis after kidney transplantation: a practical approach

PURPOSE OF REVIEW

This review will provide a practical approach in the assessment of kidney failure patients with primary glomerulonephritides (GN) being considered for kidney transplantation, focusing on high-risk subtypes of immunoglobulin A nephropathy, focal segmental glomerulosclerosis, idiopathic membranous glomerulonephritis and membranoproliferative glomerulonephritis.

RECENT FINDINGS

Recurrent glomerulonephritis remains one of the most common causes of allograft loss in kidney transplant recipients. Although the epidemiology and clinical outcomes of glomerulonephritis recurrence occurring after kidney transplantation are relatively well-described, the natural course and optimal treatment strategies of recurrent disease in kidney allografts remain poorly defined. With a greater understanding of the pathophysiology and treatment responses of patients with glomerulonephritis affecting the native kidneys, these discoveries have laid the framework for the potential to improve the management of patients with high-risk glomerulonephritis subtypes being considered for kidney transplantation.

SUMMARY

Advances in the understanding of the underlying immunopathogenesis of primary GN has the potential to offer novel therapeutic options for kidney patients who develop recurrent disease after kidney transplantation. To test the efficacy of novel treatment options in adequately powered clinical trials requires a more detailed understanding of the clinical and histological characteristics of kidney transplant recipients with recurrent glomerulonephritis.

Local complement factor H protects kidney endothelial cell structure and function

Factor H (FH) is a critical regulator of the alternative complement pathway and its deficiency or mutation underlie kidney diseases such as dense deposit disease. Since vascular dysfunction is an important facet of kidney disease, maintaining optimal function of the lining endothelial cells is important for vascular health. To investigate the molecular mechanisms that are regulated by FH in endothelial cells, FH deficient and sufficient mouse kidney endothelial cell cultures were established. Endothelial FH deficiency resulted in cytoskeletal remodeling, increased angiogenic potential, loss of cellular layer integrity and increased cell proliferation. FH reconstitution prevented these FH-dependent proliferative changes. Respiratory flux analysis showed reduced basal mitochondrial respiration, ATP production and maximal respiratory capacity in FH deficient endothelial cells, while proton leak remained unaltered. Similar changes were observed in FH deficient human glomerular endothelial cells indicating the translational potential of these studies. Gene expression analysis revealed that the FH-dependent gene changes in mouse kidney endothelial cells include significant upregulation of genes involved in inflammation and the complement system. The transcription factor nuclear factor-kB, that regulates many biological processes, was translocated from the cytoplasm to the nucleus in the absence of FH. Thus, our studies show the functional relevance of intrinsic FH in kidney endothelial cells in man and mouse.

Amnion epithelial cells are an effective source of factor H and prevent kidney complement deposition in factor H-deficient mice

Complement factor H (FH) is the main plasma regulator of the alternative pathway of complement. Genetic and acquired abnormalities in FH cause uncontrolled complement activation amplifying, with the consequent accumulation of complement components on the renal glomeruli. This leads to conditions such as C3 glomerulopathy (C3G) and atypical hemolytic uremic syndrome (aHUS). There is no effective therapy for these diseases. Half of the patients progress to end-stage renal disease and the condition recurs frequently in transplanted kidneys. Combined liver/kidney transplantation is a valid option for these patients, but the risks of the procedure and donor organ shortages hamper its clinical application. Therefore, there is an urgent need for alternative strategies for providing a normal FH supply. Human amnion epithelial cells (hAEC) have stem cell characteristics, including the capability to differentiate into hepatocyte-like cells in vivo.Here, we administered hAEC into the livers of newborn Cfh^-/- mice, which spontaneously developed glomerular complement deposition and renal lesions resembling human C3G. hAEC engrafted at low levels in the livers of Cfh^-/- mice and produced sufficient human FH to prevent complement activation and glomerular C3 and C9 deposition. However, long-term engraftment was not achieved, and eventually hAEC elicited a humoral immune response in immunocompetent Cfh^-/- mice.hAEC cell therapy could be a valuable therapeutic option for patients undergoing kidney transplantation in whom post-transplant immunosuppression may protect allogeneic hAEC from rejection, while allogeneic cells provide normal FH to prevent disease recurrence.

A CHILD WITH DENSE DEPOSIT DISEASE AND DECREASED CLASSIC COMPLEMENT PATHWAY ACTIVITY

We report a rare case of nephritic syndrome underlying dense deposit disease (DDD) with alternative complement pathway dysfunction explained with both C3 nephritic factor (C3NeF) antibodies and DDD associated polymorphism of factor H. An 8-year-old boy presented with macroscopic hematuria, hypertension and periorbital edema followed by persistently low C3 during the 8-week follow-up. Positive C3 staining on immunofluorescence microscopy, supported by dense deposits within the glomerular basement membrane on electron microscopy, confirmed the diagnosis of DDD. Preliminary tests for complement activation showed decreased classic pathway and deficient alternative complement pathway, as well as slightly positive C3NeF, supporting the diagnosis of DDD. Genetic analysis revealed a polymorphism of the complement factor H gene with an increased risk of developing DDD. Supportive therapy led to satisfactory recovery of renal function and normalization of C3. Given the poor prognosis of the disease, proper approach to such specific glomerulopathy is important to avoid or at least slow down progression to end-stage renal disease.

Treatment of C3 Glomerulopathy in Adult Kidney Transplant Recipients: A Systematic Review

BACKGROUND

C3 glomerulopathy (C3G), a rare glomerular disease mediated by alternative complement pathway dysregulation, is associated with a high rate of recurrence and graft loss after kidney transplantation (KTx). We aimed to assess the efficacy of different treatments for C3G recurrence after KTx.

METHODS

Databases (MEDLINE, EMBASE, and Cochrane Database) were searched from inception through 3 May, 2019. Studies were included that reported outcomes of adult KTx recipients with C3G. Effect estimates from individual studies were combined using the random-effects, generic inverse variance method of DerSimonian and Laird., The protocol for this meta-analysis is registered with PROSPERO (no. CRD42019125718).

RESULTS

Twelve studies (7 cohort studies and 5 case series) consisting of 122 KTx patients with C3G (73 C3 glomerulonephritis (C3GN) and 49 dense deposit disease (DDD)) were included. The pooled estimated rates of allograft loss among KTx patients with C3G were 33% (95% CI: 12-57%) after eculizumab, 42% (95% CI: 2-89%) after therapeutic plasma exchange (TPE), and 81% (95% CI: 50-100%) after rituximab. Subgroup analysis based on type of C3G was performed. Pooled estimated rates of allograft loss in C3GN KTx patients were 22% (95% CI: 5-46%) after eculizumab, 56% (95% CI: 6-100%) after TPE, and 70% (95% CI: 24-100%) after rituximab. Pooled estimated rates of allograft loss in DDD KTx patients were 53% (95% CI: 0-100%) after eculizumab. Data on allograft loss in DDD after TPE (1 case series, 0/2 (0%) allograft loss at 6 months) and rituximab (1 cohort, 3/3 (100%) allograft loss) were limited. Among 66 patients (38 C3GN, 28 DDD) who received no treatment (due to stable allograft function at presentation and/or clinical judgment of physicians), pooled estimated rates of allograft loss were 32% (95% CI: 7-64%) and 53% (95% CI: 28-77%) for C3GN and DDD, respectively. Among treated C3G patients, data on soluble membrane attack complex of complement (sMAC) were limited to patients treated with eculizumab (N = 7). 80% of patients with elevated sMAC before eculizumab responded to treatment. In addition, all patients who responded to eculizumab had normal sMAC levels after post-eculizumab.

CONCLUSIONS

Our study suggests that the lowest incidence of allograft loss (33%) among KTX patients with C3G are those treated with eculizumab. Among those who received no treatment for C3G due to stable allograft function, there is a high incidence of allograft loss of 32% in C3GN and 53% in DDD. sMAC level may help to select good responders to eculizumab.

Dense deposit disease in an adolescent male mimicking acute post-streptococcal glomerulonephritis

BACKGROUND

Dense deposit disease (DDD), a subtype of complement factor 3 glomerulopathy (C3G), is a rare entity associated with dysregulation of the alternative complement pathway. It usually affects children, with a 50% likelihood of progression to end-stage renal disease within ten years of diagnosis. Description of the case: We report the case of an adolescent male with acute nephritic syndrome and nephrotic range proteinuria, initially diagnosed as acute post-streptococcal glomerulonephritis (APSGN). Despite his spontaneous improvement, renal biopsy, performed due to a persistently low C3 level for over 18 weeks, confirmed the diagnosis of DDD. Complement and genetic studies showed high levels of C3-nephritic factor and risk polymorphisms for developing the disease. He was treated with prednisolone and mycophenolate mofetil (MMF). At the last follow-up, 15 months from onset, the serum creatinine level and 24h-hour total protein excretion were normal.

CONCLUSION

C3G (including the DDD subtype) should be suspected in apparent APSGN with atypical clinical features at presentation/follow-up, even in the case of spontaneous improvement. Timely and accurate diagnosis, based on histopathological, complement, and genetic studies, is important to initiate the appropriate treatment aimed at preventing or slowing the disease progression. HIPPOKRATIA 2020, 24(4): 191-193.

C3-glomerulonephritis in New Zealand - a case series

Background

C3-glomerulonephritis can lead to progressive renal impairment from complement-mediated glomerular injury. Incidence and outcomes of C3-glomerulonephritis are not known in the New Zealand population.

Methods

We reviewed all cases of C3-glomerulonephritis from the past 10 years at a tertiary referral centre in New Zealand. Descriptive information on baseline characteristics and clinical outcomes was collected.

Results

Twenty-six patients were included (16 men; mean ± SD age 44 ± 25 years) with a median follow-up of 30 months. Disease incidence was 1.3 cases per million individuals, of which 42% were Pacific Islanders. Most patients presented with renal impairment, with a median (IQR) creatinine at diagnosis of 210 (146–300) μmol/L, and 11 (42%) patients presented with nephrotic syndrome. Seven (27%) patients progressed to end stage renal disease and 2 (8%) had died. End stage renal disease occurred in 20% of patients treated with immunosuppression and in 50% of those not treated. Complete remission was seen in 25% of patients treated with some form of immunosuppression and in 17% of those not treated.

Conclusions

Our results are consistent with previous descriptions of C3-glomerulonephritis. There was a suggestion of better clinical outcomes in patients treated with immunosuppression. There was a higher disease incidence in Pacific Islanders, which may indicate an underlying susceptibility to complement dysfunction in this population.

The impact of reclassification of C3 predominant glomerulopathies on diagnostic accuracy, outcome and prognosis in patients with C3 glomerulonephritis

Background

C3 glomerulonephritis is a recently described entity with heterogeneous histopathological features. This study was conducted to assess the effect of reclassification of C3 glomerulopathies on renal outcomes, mortality, and response to therapy.

Methods

We undertook a retrospective analysis of 857 renal biopsies collected at The Canberra Hospital. Samples with predominant C3 staining were reviewed by a renal histopathologist. Of 31 biopsies with predominant C3 staining, 10 fulfilled histological criteria for C3 glomerulonephritis, while the remaining 21 cases were used as C3 Controls.

Results

Aside from a higher incidence of C3 glomerulonephritis in Torres Strait islanders (40% vs 5% C3 Controls, p = 0.04), presentation demographics were similar between the two groups. Median creatinine at diagnosis was higher in patients with C3 glomerulonephritis (253 umol/L IQR 103–333 vs 127 umol/L C3 Controls, IQR 105–182, p = 0.01).

Prior to reclassification, a majority of C3 glomerulonephritis cases were diagnosed as membranoproliferative glomerulonephritis (60% vs 5% (C3 Controls) p < 0.01). Electron microscopy demonstrated all C3 glomerulonephritis patients had C3 deposition (100% vs 38% p = 0.02), these deposits were amorphous in nature (50% vs 5% respectively p = 0.007).

C3 glomerulonephritis patients had shorter median follow-up (405 days IQR 203–1197 vs 1822 days respectively, IQR 1243–3948, p = 0.02). Mortality was higher in C3 glomerulonephritis patients (30% vs 14% in C3 Controls (log rank p = 0.02)).

Conclusion

We have devised a diagnostic and treatment algorithm based on the results of literature review and our current study. Further prospective assessment is required to review diagnostic and treatment outcomes for this disease in Australian centres.

Diverse Clinical Presentations of C3 Dominant Glomerulonephritis

C3 dominant immunofluorescence staining is present in a subset of patients with idiopathic immune complex membranoproliferative glomerulonephritis (iMPGN). It is increasingly recognized that iMPGN may be complement driven, as are cases of "typical" C3 glomerulopathy (C3G). In both iMPGN and C3G, a frequent membranoproliferative pattern of glomerular injury may indicate common pathogenic mechanisms via complement activation and endothelial cell damage. Dysregulation of the alternative complement pathway and mutations in certain regulatory factors are highly implicated in C3 glomerulopathy (which encompasses C3 glomerulonephritis, dense deposit disease, and cases of C3 dominant MPGN). We report three cases that demonstrate that an initial biopsy diagnosis of iMPGN does not exclude complement alterations similar to the ones observed in patients with a diagnosis of C3G. The first patient is a 39-year-old woman with iMPGN and C3 dominant staining, with persistently low C3 levels throughout her course. The second case is a 22-year-old woman with elevated anti-factor H antibodies and C3 dominant iMPGN findings on biopsy. The third case is a 25-year-old woman with C3 dominant iMPGN, dense deposit disease, and a crescentic glomerulonephritis on biopsy. We present the varied phenotypic variations of C3 dominant MPGN and review clinical course, complement profiles, genetic testing, treatment course, and peri-transplantation plans. Testing for complement involvement in iMPGN is important given emerging treatment options and transplant planning.

A Narrative Review on C3 Glomerulopathy: A Rare Renal Disease

In April 2012, a group of nephrologists organized a consensus conference in Cambridge (UK) on type II membranoproliferative glomerulonephritis and decided to use a new terminology, "C3 glomerulopathy" (C3 GP). Further knowledge on the complement system and on kidney biopsy contributed toward distinguishing this disease into three subgroups: dense deposit disease (DDD), C3 glomerulonephritis (C3 GN), and the CFHR5 nephropathy. The persistent presence of microhematuria with or without light or heavy proteinuria after an infection episode suggests the potential onset of C3 GP. These nephritides are characterized by abnormal activation of the complement alternative pathway, abnormal deposition of C3 in the glomeruli, and progression of renal damage to end-stage kidney disease. The diagnosis is based on studying the complement system, relative genetics, and kidney biopsies. The treatment gap derives from the absence of a robust understanding of their natural outcome. Therefore, a specific treatment for the different types of C3 GP has not been established. Recommendations have been obtained from case series and observational studies because no randomized clinical trials have been conducted. Current treatment is based on corticosteroids and antiproliferative drugs (cyclophosphamide, mycophenolate mofetil), monoclonal antibodies (rituximab) or complement inhibitors (eculizumab). In some cases, it is suggested to include sessions of plasma exchange.

Outcome of C3 glomerulopathy patients: largest single-centre experience from South Asia

BACKGROUND

C3 glomerulopathy (C3G) is related to dysfunction of alternative complement pathway (ACP) because of its hyperactivation. Triggering factors and genetic profile are likely to be different in developing countries as compared to the Western world. Data regarding C3G from South Asian is scanty.

STUDY DESIGN

In the present study, 115 patients of C3G from 2012 to 2017 were analyzed. Clinical details were reviewed; serological levels of C3, C4, complement factor H or B and autoantibody testing was done by nephelometry/ELISA. Limited genetics workup for CFH and CFHR5 genes was done.

RESULTS

The prevalence of C3G was 1.52%. There was no difference in demographic and histopathologic profiles of C3G patients. Majority of patients had low functional assay and C3 levels. C3 nephritic factor was present in 47.5% of DDD and 38.6% of C3GN. Autoantibodies to CFH were present more often in the patients of C3GN (29.5%) than DDD (12.5%). Autoantibodies to CFB were equally common in both groups. Past history of infections was present in one-third patients and monoclonal paraproteins were present only in two patients. No pathogenic variants were noted in CFH/CFHR5 gene. On follow-up (3.2 + 1.6 years), complete and partial remission was achieved in one-fourth patients and 26% had resistance disease. About 40% progressed to ESRD and 18 underwent renal transplantation of which nine had a post-transplant recurrence.

CONCLUSIONS

Indian cohort had some differences in the immunological and genetic profile when compared to the Western literature; most significant was the absence of monoclonal immunoglobulins as a trigger for C3G.

Clinical course and outcome after kidney transplantation in patients with C3 glomerulonephritis due to CFHR5 nephropathy

BACKGROUND

Complement factor H-related protein 5 (CFHR5) nephropathy is an inherited renal disease characterized by microscopic and synpharyngitic macroscopic haematuria, C3 glomerulonephritis and renal failure. It is caused by an internal duplication of exons 2-3 within the CFHR5 gene resulting in dysregulation of the alternative complement pathway. The clinical characteristics and outcomes of transplanted patients with this rare familial nephropathy remain unknown.

METHODS

This is a retrospective case series study of 17 kidney transplant patients with the established founder mutation, followed-up over a span of 30 years.

RESULTS

The mean (±SD) age of patients at the time of the study and at transplantation was 58.6 ± 9.9 and 46.7 ± 8.8 years, respectively. The 10- and 15-year patient survival rates were 100 and 77.8%, respectively. Proteinuria was present in 33.3% and microscopic haematuria in 58.3% of patients with a functional graft. Serum complement levels were normal in all. 'Confirmed' and 'likely' recurrence of CFHR5 nephropathy were 16.6 and 52.9%, respectively; however, 76.5% of patients had a functional graft after a median of 120 months post-transplantation. Total recurrence was not associated with graft loss (P = 0.171), but was associated with the presence of microscopic haematuria (P = 0.001) and proteinuria (P = 0.018). Graft loss was associated with the presence of proteinuria (P = 0.025).

CONCLUSIONS

We describe for the first time the clinical characteristics and outcome of patients with CFHR5 nephropathy post-transplantation. Despite the recurrence of CFHR5 nephropathy, we provide evidence for a long-term favourable outcome and support the continued provision of kidney transplantation as a renal replacement option in patients with CFHR5 nephropathy.

Playing 'hide-and-seek' with factor H: game-theoretical analysis of a single nucleotide polymorphism

As a part of the complement system, factor H regulates phagocytosis and helps differentiate between a body's own and foreign cells. Owing to mimicry efforts, some pathogenic microorganisms such as Candida albicans are able to bind factor H on their cell surfaces and, thus, become similar to host cells. This implies that the decision between self and foreign is not clear-cut, which leads to a classification problem for the immune system. Here, two different alleles determining the binding affinity of factor H are relevant. Those alleles differ in the SNP Y402H; they are known to be associated with susceptibility to certain diseases. Interestingly, the fraction of both alleles differs in ethnic groups. The game-theoretical model proposed in this article explains the coexistence of both alleles by a battle of the sexes game and investigates the trade-off between pathogen detection and protection of host cells. Further, we discuss the ethnicity-dependent frequencies of the alleles. Moreover, the model elucidates the mimicry efforts by pathogenic microorganisms.

Mechanisms of haemolysis-induced kidney injury

Intravascular haemolysis is a fundamental feature of chronic hereditary and acquired haemolytic anaemias, including those associated with haemoglobinopathies, complement disorders and infectious diseases such as malaria. Destabilization of red blood cells (RBCs) within the vasculature results in systemic inflammation, vasomotor dysfunction, thrombophilia and proliferative vasculopathy. The haemoprotein scavengers haptoglobin and haemopexin act to limit circulating levels of free haemoglobin, haem and iron - potentially toxic species that are released from injured RBCs. However, these adaptive defence systems can fail owing to ongoing intravascular disintegration of RBCs. Induction of the haem-degrading enzyme haem oxygenase 1 (HO1) - and potentially HO2 - represents a response to, and endogenous defence against, large amounts of cellular haem; however, this system can also become saturated. A frequent adverse consequence of massive and/or chronic haemolysis is kidney injury, which contributes to the morbidity and mortality of chronic haemolytic diseases. Intravascular destruction of RBCs and the resulting accumulation of haemoproteins can induce kidney injury via a number of mechanisms, including oxidative stress and cytotoxicity pathways, through the formation of intratubular casts and through direct as well as indirect proinflammatory effects, the latter via the activation of neutrophils and monocytes. Understanding of the detailed pathophysiology of haemolysis-induced kidney injury offers opportunities for the design and implementation of new therapeutic strategies to counteract the unfavourable and potentially fatal effects of haemolysis on the kidney.

Recurrent and de novo Glomerulonephritis After Kidney Transplantation

The prevalence, pathogenesis, predictors, and natural course of patients with recurrent glomerulonephritis (GN) occurring after kidney transplantation remains incompletely understood, including whether there are differences in the outcomes and advances in the treatment options of specific GN subtypes, including those with de novo GN. Consequently, the treatment options and approaches to recurrent disease are largely extrapolated from the general population, with responses to these treatments in those with recurrent or de novo GN post-transplantation poorly described. Given a greater understanding of the pathogenesis of GN and the development of novel treatment options, it is conceivable that these advances will result in an improved structure in the future management of patients with recurrent or de novo GN. This review focuses on the incidence, genetics, characteristics, clinical course, and risk of allograft failure of patients with recurrent or de novo GN after kidney transplantation, ascertaining potential disparities between “high risk” disease subtypes of IgA nephropathy, idiopathic membranous glomerulonephritis, focal segmental glomerulosclerosis, and membranoproliferative glomerulonephritis. We will examine in detail the management of patients with high risk GN, including the pre-transplant assessment, post-transplant monitoring, and the available treatment options for disease recurrence. Given the relative paucity of data of patients with recurrent and de novo GN after kidney transplantation, a global effort in collecting comprehensive in-depth data of patients with recurrent and de novo GN as well as novel trial design to test the efficacy of specific treatment strategy in large scale multicenter randomized controlled trials are essential to address the knowledge deficiency in this disease.

Glomerular Complement Factor H-Related Protein 5 (FHR5) Is Highly Prevalent in C3 Glomerulopathy and Associated With Renal Impairment

Introduction

Therapeutic agents that target complement are increasingly available for glomerular diseases. However, the mechanisms linking glomerular complement deposition with inflammation and damage are incompletely understood. Complement factor H-related protein 5 (FHR5) interacts with complement C3 and is considered to promote activation. Circulating and glomerular FHR5 associates with IgA nephropathy and abnormal FHR5 associates with familial C3 glomerulopathy (C3G). We characterized glomerular FHR5 staining in C3G and assessed its relationships with histological features of glomerular injury and clinical outcome.

Methods

We developed FHR5 staining protocols for formalin-fixed paraffin-embedded (FFPE) renal tissue and applied them to surplus biopsy sections from a C3G cohort.

Results

Glomerular FHR5 was highly prevalent in native and transplant C3G and correlated with glomerular C3 and C5b-9 staining. Glomerular FHR5 staining correlated negatively with estimated glomerular filtration rate (eGFR) (P = 0.04, difference of medians 19.7 ml/min per 1.73 m²; 95% confidence interval [CI] 1.1-43.0) and positively with a membranoproliferative glomerulonephritis pattern at diagnostic biopsy (odds ratio 18; 95% CI 1.6-201; P = 0.049). Glomerular FHR5 staining intensity positively correlated with glomerular complement C3b/iC3b/C3c (Pearson's correlation coefficient [R] = 0.59; P = 0.0008), C3dg (R = 0.47; P = 0.02) and C5b9 (R = 0.44, P = 0.02).

Conclusions

Glomerular FHR5 is highly prevalent in C3G, interacts with glomerular C3, and is associated with markers of disease severity. Glomerular FHR5 likely exacerbates complement-mediated glomerular damage in C3G and its interaction with glomerular complement might be exploited to target complement therapeutic agents.

A novel mutation in complement 2 accompanied by susceptibility variants in C3 glomerulonephritis: A case study

BACKGROUND

C3 glomerulonephritis is a rare, chronic disease characterized by C3c-dominant staining on renal biopsy and is caused by inherited or acquired alternative complement pathway dysregulation.

CASE PRESENTATION

Here, we reported a 36-year-old man presenting with nephritic syndrome and normal renal function. Secondary causes were excluded by detailed clinical history and laboratory tests. His renal biopsy was consistent with C3 glomerulonephritis with a membranoproliferative glomerulonephritis pattern. To identify the etiology, we carried out genetic and autoantibody screening tests. The results showed he was negative for autoantibodies, while the next-generation sequencing revealed common variants of complement factor H (c.1204T>C; p.Tyr402His), (c.184G>A; p.Val62Ile) and thrombomodulin (c.1418C>T; p.Ala473Val), which have previously been reported to increase susceptibility to complement-mediated diseases. He also carried complement factor H (c.2808G>T; p.Glu936Asp) and mannose-binding lectin (c.161G>A; p.Gly54Asp), putting the patient at an increased risk of infections, which was an important trigger for C3 glomerulonephritis. A novel variant of complement 2 (c.53A>G; p.His18Arg) that might contribute to the occurrence of C3 glomerulonephritis when combined with these susceptibility variants was further identified. The patient was treated with ramipril and regular fresh frozen plasma infusion. He had a good response to treatment with well-controlled proteinuria, stable renal function and an increasing serum C3 level.

CONCLUSIONS

This case adds insight into the pathogenesis of C3 glomerulopathy by showing that a combination of susceptibility variants, genetic mutations and triggers might be responsible for the clinical and pathological phenotypes.

C3 glomerulopathy - understanding a rare complement-driven renal disease

The C3 glomerulopathies are a group of rare kidney diseases characterized by complement dysregulation occurring in the fluid phase and in the glomerular microenvironment, which results in prominent complement C3 deposition in kidney biopsy samples. The two major subgroups of C3 glomerulopathy - dense deposit disease (DDD) and C3 glomerulonephritis (C3GN) - have overlapping clinical and pathological features suggestive of a disease continuum. Dysregulation of the complement alternative pathway is fundamental to the manifestations of C3 glomerulopathy, although terminal pathway dysregulation is also common. Disease is driven by acquired factors in most patients - namely, autoantibodies that target the C3 or C5 convertases. These autoantibodies drive complement dysregulation by increasing the half-life of these vital but normally short-lived enzymes. Genetic variation in complement-related genes is a less frequent cause. No disease-specific treatments are available, although immunosuppressive agents and terminal complement pathway blockers are helpful in some patients. Unfortunately, no treatment is universally effective or curative. In aggregate, the limited data on renal transplantation point to a high risk of disease recurrence (both DDD and C3GN) in allograft recipients. Clinical trials are underway to test the efficacy of several first-generation drugs that target the alternative complement pathway.

Emerging immunotherapies for autoimmune kidney disease

Autoimmunity is a leading cause of chronic kidney disease and loss of native and transplanted kidneys. Conventional immunosuppressive therapies can be effective but are non-specific, noncurative, and risk serious side effects such as life-threatening infection and cancer. Novel therapies and targeted interventions are urgently needed. In this brief review we explore diverse strategies currently in development and under consideration to interrupt underlying disease mechanisms in immune-mediated renal injury. Because autoantibodies are prominent in diagnosis and pathogenesis in multiple human glomerulopathies, we highlight several promising therapies that interfere with functions of early mediators (IgG and complement) of the effector arm and with an epicenter (the germinal center) for induction of humoral immunity.

Novel Insights Into the Role of Glycans in the Pathophysiology of Glomerular Endotheliosis in Preeclampsia

The polysaccharide heparan sulfate is ubiquitously expressed as a proteoglycan in extracellular matrices and on cell surfaces. In the glomerular filtration barrier, the action of the heparan sulfate is directly related to the function of glomerular filtration, mostly attributed to the sulfated domains that occur along the polysaccharide chain, as evidenced by fact that release of fragments of heparan sulfate by heparanase significantly increases the permeability of albumin passage through the glomerular endothelium, event that originates proteinuria. This review aims to show the importance of the structural domains of heparan sulfate in the process of selective permeability and to demonstrate how these domains may be altered during the glomerular inflammation processes that occur in preeclampsia.

Prevention of Fatal C3 Glomerulopathy by Recombinant Complement Receptor of the Ig Superfamily

Background C3 glomerulopathy (C3G) is a life-threatening kidney disease caused by dysregulation of the alternative pathway of complement (AP) activation. No approved specific therapy is available for C3G, although an anti-C5 mAb has been used off-label in some patients with C3G, with mixed results. Thus, there is an unmet medical need to develop other inhibitors of complement for C3G.Methods We used a murine model of lethal C3G to test the potential efficacy of an Fc fusion protein of complement receptor of the Ig superfamily (CRIg-Fc) in the treatment of C3G. CRIg-Fc binds C3b and inhibits C3 and C5 convertases of the AP. Mice with mutations in the factor H and properdin genes (FH^m/mP^-/-) develop early-onset C3G, with AP consumption, high proteinuria, and lethal crescentic GN.Results Treatment of FH^m/mP^-/- mice with CRIg-Fc, but not a control IgG, inhibited AP activation and diminished the consumption of plasma C3, factor B, and C5. CRIg-Fc-treated FH^m/mP^-/- mice also had significantly improved survival and reduced proteinuria, hematuria, BUN, glomerular C3 fragment, C9 and fibrin deposition, and GN pathology scores.Conclusions Therapeutics developed on the basis of the mechanism of action of soluble CRIg may be effective for the treatment of C3G and should be explored clinically.

Membranoproliferative glomerulonephritis and C3 glomerulopathy in children: change in treatment modality? A report of a case series

Background

Membranoproliferative glomerulonephritis (MPGN) with immune complexes and C3 glomerulopathy (C3G) in children are rare and have a variable outcome, with some patients progressing to end-stage renal disease (ESRD). Mutations in genes encoding regulatory proteins of the alternative complement pathway and of complement C3 (C3) have been identified as concausative factors.

Methods

Three children with MPGN type I, four with C3G, i.e. three with C3 glomerulonephritis (C3GN) and one with dense deposit disease (DDD), were followed. Clinical, autoimmune data, histological characteristics, estimated glomerular filtration rate (eGFR), proteinuria, serum C3, genetic and biochemical analysis were assessed.

Results

The median age at onset was 7.3 years and the median eGFR was 72 mL/min/1.73 m². Six children had marked proteinuria. All were treated with renin-angiotensin-aldosterone system (RAAS) blockers. Three were given one or more immunosuppressive drugs and two eculizumab. At the last median follow-up of 9 years after diagnosis, three children had normal eGFR and no or mild proteinuria on RAAS blockers only. Among four patients without remission of proteinuria, genetic analysis revealed mutations in complement regulator proteins of the alternative pathway. None of the three patients with immunosuppressive treatment achieved partial or complete remission of proteinuria and two progressed to ESRD and renal transplantation. Two patients treated with eculizumab revealed relevant decreases in proteinuria.

Conclusions

In children with MPGN type I and C3G, the outcomes of renal function and response to treatment modality show great variability independent from histological diagnosis at disease onset. In case of severe clinical presentation at disease onset, early genetic and biochemical analysis of the alternative pathway dysregulation is recommended. Treatment with eculizumab appears to be an option to slow disease progression in single cases.

Gain of function mutant of complement factor B K323E mimics pathogenic C3NeF autoantibodies in convertase assays

Complement convertases are enzymatic complexes, which play a critical role in propagation and amplification of the complement cascade. Under physiological conditions, convertases decay shortly after being formed in either spontaneous or inhibitor-driven process. Prolongation of their half-life by C3NeF autoantibodies that prevent convertase dissociation results in pathogenic condition often manifested by renal diseases. However, the diagnosis of convertase abnormalities is difficult due to the labile nature of these enzymes and low credibility of existing methods. Only recently, two-step functional assays employing C5-depleted serum or C5 inhibitors were introduced. Their advantage is convertase formation in the physiological milieu of whole serum and the drawback is inter-assay variability due to variations in rabbit erythrocytes used for the haemolysis-based readout. Abovementioned problems demand the application of the internal standard in each experiment. Obtaining a defined preparation of autoantibodies is complicated due to ethical and practical considerations. We found that recombinant, his-tagged factor B (fB) variant K323E retains full hemolytic activity and possess the ability to form convertases with prolonged half-life either in fB-depleted serum or when mixed with normal human serum. Such dominant character of K323E mutation allows using recombinant protein as a reference in functional convertase assays, not limited to these using rabbit erythrocytes. Additionally, our results demonstrate that gain of function mutations in complement components mimic the phenotype of C3NeF. Hence, patients with such "genetic C3NeF" would not benefit from B-cell depletion (e.g. by rituximab) and therefore should be properly diagnosed in order to choose suitable therapeutic intervention.

Basement Membrane Defects in Genetic Kidney Diseases

The glomerular basement membrane (GBM) is a specialized structure with a significant role in maintaining the glomerular filtration barrier. This GBM is formed from the fusion of two basement membranes during development and its function in the filtration barrier is achieved by key extracellular matrix components including type IV collagen, laminins, nidogens, and heparan sulfate proteoglycans. The characteristics of specific matrix isoforms such as laminin-521 (α5β2γ1) and the α3α4α5 chain of type IV collagen are essential for the formation of a mature GBM and the restricted tissue distribution of these isoforms makes the GBM a unique structure. Detailed investigation of the GBM has been driven by the identification of inherited abnormalities in matrix proteins and the need to understand pathogenic mechanisms causing severe glomerular disease. A well-described hereditary GBM disease is Alport syndrome, associated with a progressive glomerular disease, hearing loss, and lens defects due to mutations in the genes COL4A3, COL4A4, or COL4A5. Other proteins associated with inherited diseases of the GBM include laminin β2 in Pierson syndrome and LMX1B in nail patella syndrome. The knowledge of these genetic mutations associated with GBM defects has enhanced our understanding of cell-matrix signaling pathways affected in glomerular disease. This review will address current knowledge of GBM-associated abnormalities and related signaling pathways, as well as discussing the advances toward disease-targeted therapies for patients with glomerular disease.

Characterization of C3 in C3 glomerulopathy

Background

C3 glomerulopathy (C3G) is caused by overactivity of the alternative pathway of complement that results in bright glomerular C3 staining with minimal or no deposition of immunoglobulins on immunofluorescence microscopy. Laser microdissection and mass spectrometry of the two subtypes, C3 glomerulonephritis (C3GN) and dense deposit disease (DDD), have identified C3 as the predominant glomerular complement protein, although lesser amounts of C9, C5, C6, C7 and C8 are detectable. C3 plays a central role in complement activity, with its proteolytic cleavage first generating C3a and C3b, followed by inactivation of C3b generating iC3b (which includes C3α and C3β), which undergoes further breakdown yielding C3c and terminal breakdown fragment C3dg. The composition of C3 breakdown products in C3G is not known.

Methods

In this study, we chose six cases each of C3GN and DDD to analyze the composition of C3 deposits. We analyzed the amino acid sequence of C3 spectra detected by mass spectrometry to determine the relative abundance of C3 fragments in C3G. Thus we were able to determine the amino acid sequences mapping to the various C3 activation products including C3dg, C3α (C3α1 and α2), and C3β that are part of C3b/iC3b/C3c.

Results

C3dg is the predominant cleavage product detected with the highest amino acid coverage. The remaining amino acids map to C3α (C3α1 and α2) and C3β. Amino acids mapping to C3a and C3f are absent. Taken together, the C3α and C3β amino acids represent iC3b prior to or after C3c cleavage of C3dg. The C3 spectra for both C3GN and DDD are surprisingly similar.

Conclusion

The finding of large amounts of C3dg suggests that C3b deposition in the glomerulus is an active process triggered by thioester binding of C3b to the glycocalyx overlying the glomerular endothelial cells and glomerular basement membrane. Regulatory protein-mediated inactivation of C3b results in the generation of iC3b. After additional cleavages, mostly C3dg remains.

Targeted Delivery of Neutralizing Anti-C5 Antibody to Renal Endothelium Prevents Complement-Dependent Tissue Damage

Complement activation is largely implicated in the pathogenesis of several clinical conditions and its therapeutic neutralization has proven effective in preventing tissue and organ damage. A problem that still needs to be solved in the therapeutic control of complement-mediated diseases is how to avoid side effects associated with chronic neutralization of the complement system, in particular, the increased risk of infections. We addressed this issue developing a strategy based on the preferential delivery of a C5 complement inhibitor to the organ involved in the pathologic process. To this end, we generated Ergidina, a neutralizing recombinant anti-C5 human antibody coupled with a cyclic-RGD peptide, with a distinctive homing property for ischemic endothelial cells and effective in controlling tissue damage in a rat model of renal ischemia/reperfusion injury (IRI). As a result of its preferential localization on renal endothelium, the molecule induced complete inhibition of complement activation at tissue level, and local protection from complement-mediated tissue damage without affecting circulating C5. The ex vivo binding of Ergidina to surgically removed kidney exposed to cold ischemia supports its therapeutic use to prevent posttransplant IRI leading to delay of graft function. Moreover, the finding that the ex vivo binding of Ergidina was not restricted to the kidney, but was also seen on ischemic heart, suggests that this RGD-targeted anti-C5 antibody may represent a useful tool to treat organs prior to transplantation. Based on this evidence, we propose preliminary data showing that Ergidina is a novel targeted drug to prevent complement activation on the endothelium of ischemic kidney.

Rituximab for Treatment of Membranoproliferative Glomerulonephritis and C3 Glomerulopathies

Membranoproliferative glomerulonephritis (MPGN) is a histological pattern of injury resulting from predominantly subendothelial and mesangial deposition of immunoglobulins or complement factors with subsequent inflammation and proliferation particularly of the glomerular basement membrane. Recent classification of MPGN is based on pathogenesis dividing MPGN into immunoglobulin-associated MPGN and complement-mediated C3 glomerulonephritis (C3GN) and dense deposit disease (DDD). Current guidelines suggest treatment with steroids, cytotoxic agents with or without plasmapheresis only for subjects with progressive disease, that is, nephrotic range proteinuria and decline of renal function. Rituximab, a chimeric B-cell depleting anti-CD20 antibody, has emerged in the last decade as a treatment option for patients with primary glomerular diseases such as minimal change disease, focal-segmental glomerulosclerosis, or idiopathic membranous nephropathy. However, data on the use of rituximab in MPGN, C3GN, and DDD are limited to case reports and retrospective case series. Patients with immunoglobulin-associated and idiopathic MPGN who were treated with rituximab showed partial and complete responses in the majorities of cases. However, rituximab was not effective in few cases of C3GN and DDD. Despite promising results in immunoglobulin-associated and idiopathic MPGN, current evidence on this treatment remains weak, and controlled and prospective data are urgently needed.

Complement C3-Targeted Therapy: Replacing Long-Held Assertions with Evidence-Based Discovery

Complement dysregulation underlies several inflammatory disorders, and terminal complement inhibition has thus far afforded significant clinical gains. Nonetheless, emerging pathologies, fueled by complement imbalance and therapy-skewing genetic variance, underscore the need for more comprehensive, disease-tailored interventions. Modulation at the level of C3, a multifaceted orchestrator of the complement cascade, opens up prospects for broader therapeutic efficacy by targeting multiple pathogenic pathways modulated by C3-triggered proinflammatory crosstalk. Notably, C3 intervention is emerging as a viable therapeutic strategy for renal disorders with predominantly complement-driven etiology, such as C3 glomerulopathy (C3G). Using C3G as a paradigm, we argue that concerns about the feasibility of long-term C3 intervention need to be placed into perspective and weighed against actual therapeutic outcomes in prospective clinical trials.

Heparanase: roles in cell survival, extracellular matrix remodelling and the development of kidney disease

Heparanase has regulatory roles in various processes, including cell communication, gene transcription and autophagy. In addition, it is the only known mammalian endoglycosidase that is capable of degrading heparan sulfate (HS). HS chains are important constituents and organizers of the extracellular matrix (ECM), and have a key role in maintaining the integrity and function of the glomerular filtration barrier. In addition, HS chains regulate the activity of numerous bioactive molecules, such as cytokines and growth factors, at the cell surface and in the ECM. Given the functional diversity of HS, its degradation by heparanase profoundly affects important pathophysiological processes, including tumour development, neovascularization and inflammation, as well as progression of kidney disease. Heparanase-mediated degradation and subsequent remodelling of HS in the ECM of the glomerulus is a key mechanism in the development of glomerular disease, as exemplified by the complete resistance of heparanase-deficient animals to diabetes and immune-mediated kidney disease. This Review summarizes the role of heparanase in the development of kidney disease, and its potential as a therapeutic target.

Heparanase-driven inflammation from the AGEs-stimulated macrophages changes the functions of glomerular endothelial cells

AIMS

Amounts of macrophages were infiltrated in glomeruli in diabetic nephropathy. Heparanase has been thought to be closely related to proteinuria. Our aims were to determine the effect of heparanase on the inflammation in AGEs-stimulated macrophages and its role on the functions of glomerular endothelial cells (GEnCs).

METHODS

The expression of inflammation cytokines in macrophages were assayed by q-RT PCR, western, and ELISA. Then western was used to measure the expression of RAGE and key proteins in NF-κB pathway in macrophages. The expression of the adherence molecules and tight junction proteins in GEnCs were assessed by western. The adherence of mononuclear cells to GEnCs were observed by HE staining and transendothelial FITC-BSA were tested for the permeability of GEnCs.

RESULTS

HPA siRNA and heparanase inhibitor sulodexide could attenuate the increasing inflammatory factors (TNF-α and IL-1β) in AGEs-stimulated macrophages. NF-κB inhibitor PDTC could also decrease the augmented inflammation cytokines through inhibiting the activation of the NF-κB pathway induced by AGEs. The phosphorylation of NF-κB signaling pathway could be also attenuated by HPA siRNA and sulodexide, the same to the receptor of AGEs RAGE. When the macrophage-conditioned culture medium were added to the glomerular endothelial cells, we found HPA siRNA and sulodexide groups could decrease the increasing adherence and permeability of GEnCs induced by AGEs.

CONCLUSIONS

Heparanase increases the inflammation in AGEs-stimulated macrophages through activating the RAGE-NF-κB pathway. Heparanase driven inflammation from AGEs-stimulated macrophages increases the adherence of GEnCs and augments the permeability of GEnCs.

C5 inhibition prevents renal failure in a mouse model of lethal C3 glomerulopathy

C3 glomerulopathy is a potentially life-threatening disease of the kidney caused by dysregulated alternative pathway complement activation. The specific complement mediator(s) responsible for kidney injury in C3 glomerulopathy are yet to be defined and no specific therapy is currently available. We previously developed a mouse model of lethal C3 glomerulopathy with factor H and properdin gene double mutations. Therefore, we used this model to examine the role of C5 and C5a receptor (C5aR) in the pathogenesis of the disease. Disease severity in these factor H/properdin double-mutant mice was found to be correlated with plasma C5 levels, and prophylactic anti-C5 mAb therapy was effective in preventing lethal C3 glomerulopathy. When given to these double-mutant mice that had already developed active disease with severe proteinuria, anti-C5 mAb treatment also prevented death in half of the mice. Deficiency of C5aR significantly reduced disease severity, suggesting that C5aR-mediated inflammation contributed to C3 glomerulopathy. Thus, C5 and C5aR have a critical role in C3 glomerulopathy. Hence, early intervention targeting these pathways may be an effective therapeutic strategy for patients with C3 glomerulopathy.

C3 Glomerulopathy

Recent advances in our understanding of the disease pathology of membranoproliferative glomerulonephritis has resulted in its re-classification as complement C3 glomerulopathy (C3G) and immune complex-mediated glomerulonephritis (IC-GN). The new consensus is based on its underlying pathomechanism, with a key pathogenetic role for the complement alternative pathway (AP), rather than on histomorphological characteristics. In C3G, loss of AP regulation leads to predominant glomerular C3 deposition, which distinguishes C3G from IC-GN with predominant immunoglobulin G staining. Electron microscopy further subdivides C3G into C3 glomerulonephritis and dense deposit disease depending on the presence and distribution pattern of electron-dense deposits within the glomerular filter. Mutations or autoantibodies affecting the function of AP activators or regulators, in particular the decay of the C3 convertase (C3 nephritic factor), have been detected in up to 80 % of C3G patients. The natural outcome of C3G is heterogeneous, but 50 % of patients progress slowly and reach end-stage renal disease within 10-15 years. The new classification not only marks significant advancement in the pathogenic understanding of this rare disease, but also opens doors towards more specific treatment with the potential for improved outcomes.

Complement related kidney diseases: Recurrence after transplantation

The recurrence of renal disease after renal transplantation is becoming one of the main causes of graft loss after kidney transplantation. This principally concerns some of the original diseases as the atypical hemolytic uremic syndrome (HUS), the membranoproliferative glomerulonephritis (MPGN), in particular the MPGN now called C3 glomerulopathy. Both this groups of renal diseases are characterized by congenital (genetic) or acquired (auto-antibodies) modifications of the alternative pathway of complement. These abnormalities often remain after transplantation because they are constitutional and poorly influenced by the immunosuppression. This fact justifies the high recurrence rate of these diseases. Early diagnosis of recurrence is essential for an optimal therapeutically approach, whenever possible. Patients affected by end stage renal disease due to C3 glomerulopathies or to atypical HUS, may be transplanted with extreme caution. Living donor donation from relatives is not recommended because members of the same family may be affected by the same gene mutation. Different therapeutically approaches have been attempted either for recurrence prevention and treatment. The most promising approach is represented by complement inhibitors. Eculizumab, a monoclonal antibody against C5 convertase is the most promising drug, even if to date is not known how long the therapy should be continued and which are the best dosing. These facts face the high costs of the treatment. Eculizumab resistant patients have been described. They could benefit by a C3 convertase inhibitor, but this class of drugs is by now the object of randomized controlled trials.

Complement factor H in host defense and immune evasion

Complement is the major humoral component of the innate immune system. It recognizes pathogen- and damage-associated molecular patterns, and initiates the immune response in coordination with innate and adaptive immunity. When activated, the complement system unleashes powerful cytotoxic and inflammatory mechanisms, and thus its tight control is crucial to prevent damage to host tissues and allow restoration of immune homeostasis. Factor H is the major soluble inhibitor of complement, where its binding to self markers (i.e., particular glycan structures) prevents complement activation and amplification on host surfaces. Not surprisingly, mutations and polymorphisms that affect recognition of self by factor H are associated with diseases of complement dysregulation, such as age-related macular degeneration and atypical haemolytic uremic syndrome. In addition, pathogens (i.e., non-self) and cancer cells (i.e., altered-self) can hijack factor H to evade the immune response. Here we review recent (and not so recent) literature on the structure and function of factor H, including the emerging roles of this protein in the pathophysiology of infectious diseases and cancer.