IgM contributes to glomerular injury in FSGS

Prognostic role of mesangial IgM deposition in IgA nephropathy: a long-term cohort study

BACKGROUND

The clinical significance of mesangial immunoglobulin (Ig) M deposition in IgA nephropathy (IgAN) has been less explored and remains a topic of debate. Therefore, our study aimed to investigate the prognostic value of mesangial IgM deposition in a long-term follow-up cohort of IgAN patients.

METHODS

A unicentric retrospective study was conducted on 93 consecutive IgAN patients (median age 41 years, 68% male, eGFR 48.7 mL/min, proteinuria 1.1 g/g) from 2010 to 2015. They were followed until end-stage kidney disease (ESKD), death, or until the end of the study in January 2021, with a median follow-up of 7 years. An independent pathologist evaluated the IgM immunofluorescence pattern, Oxford MEST-C score, and transmission electron microscopy (TEM) lesions following a comprehensive protocol.

RESULTS

In our cohort, 70% had mesangial IgM-positive deposits, while 30% were IgM-negative. Both groups were similar in age, sex, prevalence of arterial hypertension, Charlson comorbidity scores, kidney function (eGFR and proteinuria), pathology findings (Oxford MEST-C score, IgG and C3 immune deposition), and TEM analysis. Treatment with RASI and immunosuppression, and death rates were also comparable. However, 37% of IgM-positive patients progressed to ESKD, significantly higher than the 11% in the IgM-negative group. Univariate and multivariate Cox proportional hazards regression analyses identified lower eGFR, higher Oxford MEST-C score, and mesangial IgM deposits as independent factors associated with shorter kidney survival.

CONCLUSIONS

Our study highlights mesangial IgM deposition as a potential risk factor for ESKD in patients with advanced IgAN, laying a foundation for further research in this area.

Management of adult patients with podocytopathies: an update from the ERA Immunonephrology Working Group

The histopathological lesions, minimal change disease (MCD) and focal segmental glomerulosclerosis (FSGS) are entities without immune complex deposits which can cause podocyte injury, thus are frequently grouped under the umbrella of podocytopathies. Whether MCD and FSGS may represent a spectrum of the same disease remains a matter of conjecture. Both frequently require repeated high-dose glucocorticoid therapy with alternative immunosuppressive treatments reserved for relapsing or resistant cases and response rates are variable. There is an unmet need to identify patients who should receive immunosuppressive therapies as opposed to those who would benefit from supportive strategies. Therapeutic trials focusing on MCD are scarce, and the evidence used for the 2021 Kidney Disease: Improving Global Outcomes (KDIGO) guideline for the management of glomerular diseases largely stems from observational and pediatric trials. In FSGS, the differentiation between primary forms and those with underlying genetic variants or secondary forms further complicates trial design. This article provides a perspective of the Immunonephrology Working Group (IWG) of the European Renal Association (ERA) and discusses the KDIGO 2021 Clinical Practice Guideline for the Management of Glomerular Diseases focusing on the management of MCD and primary forms of FSGS in the context of recently published evidence, with a special emphasis on the role of rituximab, cyclophosphamide, supportive treatment options and ongoing clinical trials in the field.

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.

CR1 variants contribute to FSGS susceptibility across multiple populations

Focal segmental glomerulosclerosis (FSGS) is a common cause of nephrotic syndrome with an annual incidence in the United States in African-Americans compared to European-Americans of 24 cases and 5 cases per million, respectively. Among glomerular diseases in Europe and Latin-America, FSGS was the second most frequent diagnosis, and in Asia the fifth. We expand previous efforts in understanding genetics of FSGS by performing a case-control study involving ethnically-diverse groups FSGS cases (726) and a pool of controls (13,994), using panel sequencing of approximately 2,500 podocyte-expressed genes. Through rare variant association tests, we replicated known risk genes - KANK1, COL4A4, and APOL1. A novel significant association was observed for the gene encoding complement receptor 1 (CR1). High-risk rare variants in CR1 in the European-American cohort were commonly observed in Latin- and African-Americans. Therefore, a combined rare and common variant analysis was used to replicate the CR1 association in non-European populations. The CR1 risk variant, rs17047661, gives rise to the Sl1/Sl2 (R1601G) allele that was previously associated with protection against cerebral malaria. Pleiotropic effects of rs17047661 may explain the difference in allele frequencies across continental ancestries and suggest a possible role for genetically-driven alterations of adaptive immunity in the pathogenesis of FSGS.

Clinical significance of IgM and C3 deposition in children with primary immunoglobulin A nephropathy

BACKGROUND

Mesangial IgM and C3 deposition is commonly observed in patients with primary immunoglobulin A nephropathy (IgAN), but its characteristics and prognosis have rarely been reported. The aim of this study was to investigate the relationship between combined mesangial IgM and C3 deposition and disease progression in children with IgAN.

METHODS

One hundred sixteen children diagnosed with IgAN between 2016 and 2020 were selected. Renal biopsies were scored by Oxford classification including the presence of mesangial hypercellularity, endocapillary hypercellularity, segmental glomerulosclerosis, tubular atrophy/interstitial fibrosis and crescents. The primary renal outcome was an event of either ≥ 50% reduction of eGFR from the baseline value or the onset of end-stage renal disease within the follow-up period. Cox regression analysis was performed to examine the effect of the combined mesangial IgM and C3 deposition on renal outcomes.

RESULTS

Forty-seven (40.52%) patients presented combined mesangial IgM and C3 deposition. Compared with children without combined IgM and C3 deposition, children with combined IgM and C3 deposition presented higher mesangial hypercellularity, endocapillary hypercellularity and cresentic lesions in kidney biopsies, and higher prevalence of renal dysfunction (19.15% versus 2.90%; P = 0.007). Renal outcome was also significantly worse as revealed by Kaplan-Meier curves (P = 0.0034). Multivariable Cox analysis identified tubular atrophy/interstitial fibrosis lesions [hazard ratio (HR) 14.843, 95% CI, 3.497-62.997, P < 0.001] and intensity of IgM deposition (HR 2.838, 95% CI, 1.321-6.094, P = 0.007) as independent risk factors for poor renal function.

CONCLUSIONS

Combined mesangial IgM and C3 deposition was associated with unfavorable histopathological features. Mesangial IgM deposition was an independent risk factor for poor renal outcomes in children with primary IgAN.

Female but Not Male Mice Deficient in Soluble IgM Are Susceptible to Chemically Induced Glomerular Injury

B cell-targeted therapies are effective for treating multiple different kidney diseases in humans and also protect mice from Adriamycin nephropathy. Because glomerular IgM is frequently seen in both humans and mice with "nonimmune" forms of glomerular disease, we hypothesized that natural IgM binds to epitopes displayed in the injured glomerulus, exacerbating injury. To test this hypothesis, we induced Adriamycin nephropathy in BALB/C mice that cannot secrete soluble IgM (sIgM-/- mice) and compared them with BALB/C controls. Contrary to our prediction, we found that female sIgM-/- mice developed higher mortality and more severe kidney injury after injection of Adriamycin. The absence of soluble IgM did not reduce glomerular complement activation, and IgG was seen deposited within the injured glomeruli. Furthermore, we discovered that female sIgM-/- mice have higher levels of anti-cardiolipin IgG, and that IgG from these mice binds to epitopes in the injured kidney. These findings indicate that natural IgM may prevent generation of autoreactive IgG. Circulating levels of anti-cardiolipin IgG decreased after induction of kidney injury in female mice, consistent with deposition of the Abs in injured tissues. Better understanding of the mechanisms by which the immune system modulates and amplifies kidney injury may enable the development of targeted therapies to slow kidney disease progression.

Current understanding of the molecular mechanisms of circulating permeability factor in focal segmental glomerulosclerosis

The pathogenetic mechanisms underlying the onset and the post-transplant recurrence of primary focal segmental glomerulosclerosis (FSGS) are complex and remain yet to be fully elucidated. However, a growing body of evidence emphasizes the pivotal role of the immune system in both initiating and perpetuating the disease. Extensive investigations, encompassing both experimental models and patient studies, have implicated T cells, B cells, and complement as crucial actors in the pathogenesis of primary FSGS, with various molecules being proposed as potential "circulating factors" contributing to the disease and its recurrence post kidney-transplantation. In this review, we critically assessed the existing literature to identify essential pathways for a comprehensive characterization of the pathogenesis of FSGS. Recent discoveries have shed further light on the intricate interplay between these mechanisms. We present an overview of the current understanding of the engagement of distinct molecules and immune cells in FSGS pathogenesis while highlighting critical knowledge gaps that require attention. A thorough characterization of these intricate immune mechanisms holds the potential to identify noninvasive biomarkers that can accurately identify patients at high risk of post-transplant recurrence. Such knowledge can pave the way for the development of targeted and personalized therapeutic approaches in the management of FSGS.

A clinicopathological and prognostic study of 18 children with C1q nephropathy and focal segmental glomerulosclerosis: an 18-year experience from a single center

BACKGROUND

C1q nephropathy is a relatively rare glomerulonephritis characterized by dominant mesangial deposition of C1q. Even though C1q nephropathy has been described for more than three decades, the clinicopathological features and renal outcomes remain unclear. C1q nephropathy may present diverse morphological patterns, including focal segmental glomerulosclerosis and, the notion of C1q nephropathy as a separate disease entity is still debated. This study aimed to describe the clinical and prognostic relevance of C1q nephropathy in children with primary focal segmental glomerulosclerosis.

METHODS

Three hundred eighty-nine children were diagnosed with primary focal segmental glomerulosclerosis in Jinling Hospital from 2003 to 2020. Among them, 18 cases fulfilled the criteria for C1q nephropathy. We then selected as a control group 18 children with primary focal segmental glomerulosclerosis without C1q nephropathy matched to those with C1q nephropathy for age, sex, and period of renal biopsy. Clinical and prognostic parameters were compared in children with and without C1q nephropathy. Renal end-point was defined as a ≥ 40% reduction in estimated glomerular filtration rate or end-stage renal disease.

RESULTS

Four point sixty-three percent (18/389) of primary focal segmental glomerulosclerosis cases were diagnosed with C1q nephropathy. The male-to-female ratio of patients diagnosed with C1q nephropathy was 1:1. The median age at biopsy and age at onset was 15.63 (13.00-16.50) years and 14.50 (9.00-16.00) years, respectively. The prevalence of nephrotic syndrome, hematuria, and hypertension was 38.90% (7/18), 72.20% (13/18), and 33.30% (5/18), respectively. Four (22.2%) patients were steroid-dependent, 13 (72.2%) patients were steroid-resistant, and 1 (5.6%) patient developed secondary steroid-resistance. During a follow-up of 52.24 (25.00-72.47) months, 10 (55.6%) patients achieved remission, and 5 (27.8%) progressed to the end-point [including 2 (11.11%) patients who developed end-stage kidney disease]. There was no significant difference in the estimated end-stage renal disease-free survival rates, the estimated end-point-free survival rates, and the long-term remission rate between patients with and without C1q nephropathy (Kaplan-Meier, Log-rank, all P > 0.05).

CONCLUSIONS

C1q nephropathy was rare in pediatric patients with focal segmental glomerulosclerosis. These patients usually had poor response to steroids. The long-term renal outcomes and remission of children with primary focal segmental glomerulosclerosis with C1q nephropathy were comparable to those without C1q nephropathy.

Focal segmental glomerulosclerosis with a mutation in the mitochondrially encoded NADH dehydrogenase 5 gene: A case report

NADH dehydrogenase 5 (ND5) is one of 44 subunits composed of Complex I in mitochondrial respiratory chain. Therefore, a mitochondrially encoded ND5 (MT-ND5) gene mutation causes mitochondrial oxidative phosphorylation (OXPHOS) disorder, resulting in the development of mitochondrial diseases. Focal segmental glomerulosclerosis (FSGS) which had podocytes filled with abnormal mitochondria is induced by mitochondrial diseases. An MT-ND5 mutation also causes FSGS. We herein report a Japanese woman who was found to have proteinuria and renal dysfunction in an annual health check-up at 29 years old. Because her proteinuria and renal dysfunction were persistent, she had a kidney biopsy at 33 years of age. The renal histology showed FSGS with podocytes filled with abnormal mitochondria. The podocytes also had foot process effacement and cytoplasmic vacuolization. In addition, the renal pathological findings showed granular swollen epithelial cells (GSECs) in tubular cells, age-inappropriately disarranged and irregularly sized vascular smooth muscle cells (AiDIVs), and red-coloured podocytes (ReCPos) by acidic dye. A genetic analysis using peripheral mononuclear blood cells and urine sediment cells detected the m.13513 G > A variant in the MT-ND5 gene. Therefore, this patient was diagnosed with FSGS due to an MT-ND5 gene mutation. Although this is not the first case report to show that an MT-ND5 gene mutation causes FSGS, this is the first to demonstrate podocyte injuries accompanied with accumulation of abnormal mitochondria in the cytoplasm.

IgM and C3 Deposition in Primary Focal Segmental Glomerulosclerosis (FSGS): A Clinical and Histopathological Spectrum

Focal segmental glomerulosclerosis (FSGS) is a common renal disorder, characterized by progressive segmental sclerosis of renal glomeruli and clinical symptoms corresponding to proteinuria. Classically, it is not considered to be an antibody-mediated disease, however, IgM and C3 deposition may be seen in a subset of cases of FSGS. The impact of this immune deposition on histopathological features in renal core biopsies, on the urinary biochemical parameters, and the clinical outcomes, has not been previously investigated in our population. The aim of this study is to analyze the aforementioned parameters in patients with primary FSGS having antibody deposition as compared to those who do not have any antibody deposition. Some 155 patients diagnosed with FSGS were retrospectively enrolled in our study. The renal biopsies were reviewed for histopathological features and immunofluorescence (IF) findings of IgM and C3 glomerular deposition. These histological features were then compared with the biochemical parameters as well as the clinical outcomes of patients. The patients were assigned to Groups 1 and 2 based on the IF findings. The IgM and/or C3 glomerular deposition had a low incidence in patients with primary FSGS in our study (28.3%). Patients having IgM and C3 co-deposition had a significantly longer time duration since the onset of their clinical symptoms; active disease duration (42 months vs 22 months, p=0.049). The mean pre-treatment serum creatinine of patients with IgM and C3 co-deposition was 6.00 mg/dL as compared to 3.29 mg/dL in patients with no immune deposition (p=0.037). The immune deposition was associated with higher rates of segmental and global glomerulosclerosis, but this finding along with other evaluated histological parameters did not show statistical significance. The number of patients having IgM and/or C3 deposition and with active steroid use/renal dialysis was similar to patients having no IgM and/or C3 deposition. The IgM and/or C3 deposition in FSGS has a low incidence within and is not associated with any significant differences in histological parameters on renal core biopsies of patients from the Pakistani population. IgM and/or C3 deposition is also associated with a significantly longer duration of active disease and these patients may present with higher pre-treatment serum creatinine. Other biochemical parameters and clinical outcomes appear comparable between the groups based on the available clinical data.

IgM deposition is a risk factor for delayed remission and early relapse of the pediatric minimal change disease

BACKGROUND

Minimal change disease (MCD) is the most common pathological subtype of pediatric idiopathic nephrotic syndrome (INS). It has been suggested that IgM deposition might predict kidney function deterioration in the course of MCD. However, the specific role of IgM deposition in the prognosis of MCD is still controversial. This study aims to investigate the clinical significance of IgM deposition on delayed remission and early relapse in a pediatric population.

METHODS

This study enrolled 283 children diagnosed with MCD by renal biopsy in a single center from 2010 to 2022. These cases were divided into two groups according to the histopathological deposition of IgM. Patients' demographics, clinical parameters, and follow-up data were collected and analyzed. The primary and secondary outcomes were defined as the time to the first remission and the first relapse.

RESULTS

The IgM-positive group had a weaker response to steroids (steroid-sensitive: 23.5% vs. 40.8%; steroid-dependent: 74.0% vs. 51.0%; steroid-resistant: 18.4% vs. 8.2%, P = 0.001), and showed more recurrent cases (47.2% vs. 34.4%, P = 0.047) compared with the IgM-negative group. The Kaplan-Meier analysis showed that the IgM-positive group had a lower cumulative rate of the first remission (Log-rank, P < 0.001) and a higher rate of the first relapse (Log-rank, P = 0.034) than the IgM-negative group. Multivariate Cox analysis showed that IgM deposition was independently associated with the delayed first remission (hazard ratio [HR] = 0.604, 95% confidence interval [CI] = 0.465-0.785, P < 0.001) and the early first relapse (HR = 1.593, 95% CI = 1.033-2.456, P = 0.035).

CONCLUSION

IgM deposition was associated with a weaker steroid response. MCD children with IgM deposition were prone to delayed first remission and early first relapse.

Glomerular capillary C3 deposition as a risk factor for unfavorable renal outcome in pediatric primary focal segmental glomerular sclerosis

Introduction

Some patients with primary focal segmental sclerosis (FSGS) demonstrate complement 3 (C3) deposition in glomerular capillary loops (Cap-C3) and/or mesangial area (Mes-C3). The clinicopathological and prognostic significance of C3 deposition remains incompletely investigated, especially in the pediatric cohort.

Methods

We retrospectively analyzed 264 children of biopsy-proven primary FSGS between January 2003 and December 2020. The correlation between Cap-C3 and renal outcome was evaluated by the Kaplan-Meier method and Cox multivariate regression analysis. Renal end-point event was defined as the development of end-stage renal disease, death for renal disease, or an estimated glomerular filtration rate reduction by at least 50% from baseline.

Results

Among the 264 patients, 30 (11.4%) had Cap-C3. Kaplan-Meier analysis showed that patients with Cap-C3 had significantly lower renal survival rates than patients without Cap-C3 (60.17% vs. 84.71% at 5 years, 39.49% vs. 65.55% at 10 years, P < 0.01). Cox multivariate regression analysis showed that Cap-C3 was an independent risk factor for poor renal outcome (HR 3.53, 95% CI 1.22-10.19, P = 0.02).

Conclusion

Glomerular capillary C3 deposition was an independent risk factor for unfavorable renal outcome in children with primary FSGS.

The Immune System and Idiopathic Nephrotic Syndrome

Idiopathic nephrotic syndrome often responds to immunosuppressive treatment. Nevertheless, this syndrome-and the drugs used to treat it-remain important causes of patient morbidity. Idiopathic nephrotic syndrome is usually caused by minimal change disease or FSGS, diseases that primarily affect the podocytes. In spite of decades of research, the underlying causes of both diseases remain incompletely understood. There is, however, a large body of observational and experimental data linking the immune system with both minimal change disease and FSGS, including associations with systemic infections and hematologic malignancies. Perhaps most compellingly, many different immunomodulatory drugs are effective for treating idiopathic nephrotic syndrome, including biologic agents that have well-defined immune targets. In fact, the unexpected efficacy of targeted therapeutic agents has provided important new insights into the pathogenesis of these diseases. Given the large number of drugs that are available to deplete or block specific cells and molecules within the immune system, a better understanding of the immunologic causes of idiopathic nephrotic syndrome may lead to better diagnostic and therapeutic approaches.

B cell phenotype, activity, and function in idiopathic nephrotic syndrome

Idiopathic nephrotic syndrome (INS) is the most frequent glomerular disease in childhood. However, its underlying etiology mechanism lacks thorough understanding. Previous studies have described INS as a T cell functional disorder resulting in increased plasma lymphocyte-derived permeability factors. In children with frequent relapses of nephrotic syndrome, the mechanism underlying the therapeutic efficacy of CD20 monoclonal antibodies in depleting B cells may provide additional evidence in exploring the critical role of B lymphocytes in INS pathogenesis. Previous studies have proposed that RTX bound to CD20 through antibody-dependent and complement-dependent cytotoxicity and led to lytic clearance of B cells. Additionally, RTX exerted an effect by blocking the interaction between B and T cells or regulating homeostasis and functions of T cell subsets. Recent studies on the development, differentiation, and activation of B-lymphocytes in glomerular diseases have suggested that the B-lymphocytes participate in the INS pathogenesis through interaction with T cells, secretion of antibodies, or production of cytokines. In this study, we aimed to provide a detailed description of the current knowledge on the development, differentiation, activity, functions, and related regulating factors of B cells involved in INS. Thus, further understanding of the immunopathogenesis of INS may offer some opportunities in precisely targeting B cells during therapeutic interventions. IMPACT: The topic "B cells play a role in glomerular disease" is a novel point, which is not completely described previously. We described interactions between T and B cells and immunoglobulin, IgG, IgM, IgE, etc. as well in glomerular disease. The research of regulatory factors associated with B cell's function, like BAFF, is a hot topic in other diseases; however, it is rare in glomerular disease.

Retinal drusen in glomerulonephritis with or without immune deposits suggest systemic complement activation in disease pathogenesis

Retinal drusen are characteristic of macular degeneration and complement activation, but also occur in C3, lupus and IgA nephropathy. This cross-sectional observational study compared drusen counts in different forms of glomerulonephritis. Consecutive individuals with glomerulonephritis attending a general renal or transplant clinic underwent retinal imaging with a non-mydriatic camera. Drusen were counted in deidentified images by trained graders, compared with matched hospital patients, and correlated with clinical features. Eighty-four individuals with glomerulonephritis had a mean drusen count of 10 ± 27 compared with 3 ± 8 in hospital controls (p = 0.007). Fourteen individuals with glomerulonephritis (17%) and 4 hospital controls (4/49, 8%) had increased drusen counts (≥ 10) (p = 0.20). Increased drusen counts ≥ 10 were present in 13 (13/63, 21%)  of those with glomerulonephritis and immune deposits [membranous (n = 8), antiglomerular basement membrane nephritis (n = 6), FSGS (n = 49)], and one of the 21 (5%) with glomerulonephritis without immune deposits [ANCA-associated (n = 15), minimal change disease (n = 6)]. In antibody-mediated glomerulonephritis (n = 14), mean drusen counts were 2 ± 3 in individuals with normal kidney function, 16 ± 41 with impaired function and 5 ± 7 with kidney failure . Mean counts were 24 ± 56 in individuals with glomerular IgG deposits and 1 ± 1 in those without (p = 0.76), and 23 ± 60 with complement deposits and 4 ± 8 in those without. Drusen counts were also less in immunosuppressed individuals (p = 0.049). The demonstration of retinal drusen in some forms of glomerulonephritis is consistent with systemic complement activation, and suggests that treatment targeting the complement pathways is worthwhile.

Comparative analysis of hypertensive nephrosclerosis in animal models of hypertension and its relevance to human pathology. Glomerulopathy

Current research on hypertension utilizes more than fifty animal models that rely mainly on stable increases in systolic blood pressure. In experimental hypertension, grading or scoring of glomerulopathy in the majority of studies is based on a wide range of opinion-based histological changes that do not necessarily comply with lesional descriptors for glomerular injury that are well-established in clinical pathology. Here, we provide a critical appraisal of experimental hypertensive glomerulopathy with the same approach used to assess hypertensive glomerulopathy in humans. Four hypertensive models with varying pathogenesis were analyzed–chronic angiotensin II infused mice, mice expressing active human renin in the liver (TTRhRen), spontaneously hypertensive rats (SHR), and Goldblatt two-kidney one-clip rats (2K1C). Analysis of glomerulopathy utilized the same criteria applied in humans–hyalinosis, focal segmental glomerulosclerosis (FSGS), ischemic, hypertrophic and solidified glomeruli, or global glomerulosclerosis (GGS). Data from animal models were compared to human reference values. Kidneys in TTRhRen mice, SHR and the nonclipped kidneys in 2K1C rats had no sign of hyalinosis, FSGS or GGS. Glomerulopathy in these groups was limited to variations in mesangial and capillary compartment volumes, with mild increases in collagen deposition. Histopathology in angiotensin II infused mice corresponded to mesangioproliferative glomerulonephritis, but not hypertensive glomerulosclerosis. The number of nephrons was significantly reduced in TTRhRen mice and SHR, but did not correlate with severity of glomerulopathy. The most substantial human-like glomerulosclerotic lesions, including FSGS, ischemic obsolescent glomeruli and GGS, were found in the clipped kidneys of 2K1C rats. The comparison of affected kidneys to healthy control in animals produces lesion values that are numerically impressive but correspond to mild damage if compared to humans. Animal studies should be standardized by employing the criteria and classifications established in human pathology to make experimental and human data fully comparable for comprehensive analysis and model improvements.

B-Cell Dysregulation in Idiopathic Nephrotic Syndrome: What We Know and What We Need to Discover

The therapeutic efficacy of B-cell depletion by anti-CD20 treatment in pediatric and, more recently, in adult idiopathic nephrotic syndrome patients suggests a key role of B cells in the pathogenesis of the disease. However, their exact role is still unclear. B cells are able to secrete a large variety of antibodies that can protect against infections. However, B-cell dysregulation is well-established in a variety of autoimmune diseases. In parallel with their ability to produce antibodies, pathogenic B cells display altered effector functions by expressing activating surface molecules, which can strongly modify the immune homeostasis, or by producing specific cytokines, which can directly affect either podocyte structure and functions or modulate T-cell homeostasis. Herein, we report the most relevant clinical and experimental evidences of a pathogenic role of B cells in idiopathic nephrotic syndrome. We further highlight similarities and differences between children and adults affected by non-genetic forms of the disease and discuss what needs to be investigated in order to define the exact mechanisms underlying the pathogenic role of B cells and to identify more tailored therapeutic approaches.

Molecular Mapping of Urinary Complement Peptides in Kidney Diseases

Defective complement activation has been associated with various types of kidney disease. This led to the hypothesis that specific urine complement fragments may be associated with kidney disease etiologies, and disease progression may be reflected by changes in these complement fragments. We investigated the occurrence of complement fragments in urine, their association with kidney function and disease etiology in 16,027 subjects, using mass spectrometry based peptidomics data from the Human Urinary Proteome/Peptidome Database. Twenty-three different urinary peptides originating from complement proteins C3, C4 and factor B (CFB) could be identified. Most C3-derived peptides showed inverse association with estimated glomerular filtration rate (eGFR), while the majority of peptides derived from CFB demonstrated positive association with eGFR. Several peptides derived from the complement proteins C3, C4 and CFB were found significantly associated with specific kidney disease etiologies. These peptides may depict disease-specific complement activation and could serve as non-invasive biomarkers to support development of complement interventions through assessing complement activity for patients’ stratification and monitoring of drug impact. Further investigation of these complement peptides may provide additional insight into disease pathophysiology and could possibly guide therapeutic decisions, especially when targeting complement factors.

Clinical relevance of glomerular IgM deposition in patients with lupus nephritis

BACKGROUND

The aim of the study was to investigate the clinical relevance of IgM deposition in patients with lupus nephritis (LN) in a large cohort.

RESULTS

217 patients with renal biopsy-proven active LN were enrolled. The associations between glomerular IgM deposition and clinicopathological parameters were further analyzed. IgM deposition was positively correlated with glomerular C1q and C3 deposition moderately (r = 0.436, P < 0.001; r = 0.408, P < 0.001, respectively), and inversely correlated with plasma levels of C3 and CFH mildly (r =  - 0.138, P = 0.043; r =  - 0.147, P = 0.037, respectively). By multivariate analysis, we found that glomerular IgM deposition independently contributed to glomerular C3 deposition in patients with LN (OR = 2.002, 95% CI 1.295-3.094, P = 0.002). In addition, we also found that patients with IgM 0-2+ had similar plasma CFH levels, but in patients with IgM3+-4+, plasma CFH levels were significantly lower (300.4 ± 155.8 μg/mL vs. 429.9 ± 187.5 μg/mL, P < 0.001). Furthermore, patients with high density of glomerular IgM and low levels of CFH had heavier proteinuria, higher serum creatinine and lower plasma C3 levels (5.7 ± 3.1 g/d vs. 4.7 ± 3.5 g/d, P = 0.037; 150.1 ± 121.0 μmol/L vs. 105.6 ± 97.1 μmol/L, P = 0.005; 0.3 ± 0.2 μg/L vs. 0.4 ± 0.2 μg/L, P = 0.04, respectively), comparing with those with low density of glomerular IgM and low levels of CFH.

CONCLUSIONS

Our results suggested the involvement of glomerular deposited IgM in complement activation and renal injury in LN.

Clinical characteristics and outcomes of idiopathic membranous nephropathy with glomerular IgM deposits

Glomerular IgM deposition is commonly shown in idiopathic membranous nephropathy, but the clinicopathological features and outcomes of IMN with IgM deposition are unclear. This single-center prospective cohort study enrolled 210 patients with biopsy-proven IMN from January 2016 to December 2018. Clinicopathological features, treatment responses, and kidney outcomes were compared between patients with and without IgM deposition. In total, 76 (36.2%) patients show glomerular IgM deposition. Patients with IgM deposition were younger (45 ± 13.30 vs. 50.59 ± 13.65 years, P = 0.006), had a higher estimated glomerular filtration rate (eGFR) (100.03 [81.31-111.37] vs. 92.67 [74.71-106.63] mL/min/1.73 m², P = 0.041), and had a lower proportion of nephrotic syndrome (60.5% vs. 75.4%, P = 0.024) at the time of kidney biopsy. Patients with IgM deposition had a significantly higher proportion of focal segmental glomerular sclerosis (FSGS) lesions (27.6% vs. 13.4%, P = 0.011) and C1q deposition (72.4% vs. 57.5%, P = 0.032). Although the treatments and initial treatment responses were comparable, patients with glomerular IgM deposition had a significantly greater proportion of eGFR decline of ≥ 5 mL/min/1.73 m² per year (log-rank test, P < 0.001) and eGFR decrease of ≥ 10% from baseline (log-rank test, P = 0.003). Cox regression analysis showed that IgM deposition was an independent risk factor of eGFR decline of ≥ 5 mL/min/1.73 m² per year (HR, 2.442; 95% CI, 1.550-3.848, P < 0.001) and eGFR decline by ≥ 10% from baseline (HR, 2.629; 95% CI, 1.578-4.385, P < 0.001) during follow-up. IgM deposition in the glomeruli is an independent risk factor for decreased renal function in patients with IMN.

Long-Term Renal Survival in Antineutrophil Cytoplasmic Antibody-Associated Glomerulonephritis With Complement C3 Deposition

Introduction

Recent studies have revealed the pivotal role of complement activation in the pathogenesis of antineutrophil cytoplasmic antibody–associated glomerulonephritis (ANCA-GN). This study investigated the clinicopathologic and prognostic significance of glomerular C3 deposition in the renal histopathology of patients with ANCA-GN.

Methods

We retrospectively identified 142 patients with ANCA-GN from 6 hospitals in Japan (2004–2020). C3 deposition was defined as C3 staining ≥1+ on a scale of 0 to 2+ using direct immunofluorescence (IF). The primary composite end points included a 30% reduction in estimated glomerular filtration rate (eGFR), end-stage kidney disease (ESKD), and death. We compared clinicopathologic features and long-term outcomes between patients with and without C3 deposition.

Results

C3 deposition was observed in 56 of 142 kidney biopsy samples (39.4%). Patients with C3 deposition had a lower serum C3 level (P = 0.002). During a median follow-up of 2.9 (interquartile range: 0.2–5.7) years, 69 events occurred and the cumulative event-free survival rate at 5 years was significantly lower in the C3-positive group than in the C3-negative group (log-rank: P = 0.002). In multivariable analysis, C3 deposition was significantly associated with the composite end points after adjusting for age, sex, baseline eGFR, serum C3 level, treatment, and the percentage of normal glomerulus, cellular crescents, global sclerosis, and interstitial damage (adjusted hazard ratio [HR] = 2.02, 95% confidence interval: 1.20–3.40, P = 0.008).

Conclusion

This study revealed that ANCA-GN patients with glomerular C3 deposition on IF had worse renal and overall survival rates.

Renal Outcome of IgM Nephropathy: A Comparative Prospective Cohort Study

Immunoglobulin M nephropathy (IgMN) is an idiopathic glomerulonephritis characterized by diffuse deposits of IgM in the glomerular mesangium. However, its renal prognosis remains unknown. We compared renal outcomes of IgMN patients with those of patients with minimal change disease (MCD), focal segmental glomerulosclerosis (FSGS), or mesangial proliferative glomerulonephritis (MsPGN) from a prospective observational cohort, with 1791 patients undergoing native kidney biopsy in eight hospitals affiliated with The Catholic University of Korea between December 2014 and October 2020. IgMN had more mesangial proliferation and matrix expansion than MsPGN and more tubular atrophy and interstitial fibrosis than MCD. IgMN patients had decreased eGFR than MCD patients in the earlier follow-up. However, there was no significant difference in urine protein or eGFR among all patients at the last follow-up. When IgMN was divided into three subtypes, patients with FSGS-like IgMN tended to have lower eGFR than those with MCD-like or MsPGN-like IgMN but higher proteinuria than MsPGN-like IgMN without showing a significant difference. The presence of hypertension at the time of kidney biopsy predicted ≥20% decline of eGFR over two years in IgMN patients. Our data indicate that IgMN would have a clinical course and renal prognosis similar to MCD, FSGS, and MsPGN.

Complement 9 in amyloid deposits

Amyloidosis is a disease group caused by pathological aggregation and deposition of peptides in diverse tissue sites. Apart from the fibril protein, amyloid deposits frequently enclose non-fibrillar constituents. In routine diagnostics, we noticed the presence of complement 9 (C9) in amyloid. Based on this observation, we systematically explored the occurrence of C9 in amyloid. Apolipoprotein E (apoE), caspase 3 and complement 3 (C3) served as controls. From the Amyloid Registry Kiel, we retrieved 118 formalin-fixed and paraffin-embedded tissue samples, including eight different amyloid- and 18 different tissue types. The expression patterns were assessed immunohistochemically in relation to amyloid deposits. A literature search on proteomic data was performed. Amyloid deposits stained for C9 and apoE in 117 (99.2%) and 112 of 118 (94.9%) cases, respectively. A homogeneous immunostaining of the entire amyloid deposits was found in 75.4% (C9) and 61.9% (apoE) of the cases. Caspase 3 and C3 were present only in 22 (19.3%) of 114 and 20 (36%) of 55 assessable cases, respectively. Caspase 3 and C3 immunostaining rarely covered substantial areas of the amyloid deposits. The literature search on proteomic data confirmed the frequent detection of apoE and the occurrence of C9 and C3 in amyloid deposits. No data were found regarding caspase 3. Our findings demonstrate the ubiquitous, spatial and specific enrichment of C9 in amyloid deposits irrespective of amyloid-, organ- or tissue type. Our findings lend support to the hypothesis that amyloidosis might activate the complement cascade, which could lead to the formation of the membrane attack complex and cell death.

Gastric perforation caused by secondary systemic amyloidosis

Amyloid A amyloidosis secondary to chronic inflammation involves systemic organs and tissues, including the gastrointestinal tract. In the present case, massive amyloid deposit caused gastric perforation. IgM co-deposition in the glomeruli was another finding of note.

Immune-mediated entities of (primary) focal segmental glomerulosclerosis

Focal segmental glomerulosclerosis (FSGS) represents a glomerular scar formation downstream of various different mechanisms leading to podocytopathy and podocyte loss. Recently, significant advances were made in understanding genetic factors, podocyte intrinsic mechanisms, and adaptive mechanisms causing FSGS. However, while most cases of nephrotic FSGS are being treated with immunosuppressants, the underlying immune dysregulation, involved immune cells, and soluble factors are only incompletely understood. Thus, we here summarize the current knowledge of proposed immune effector cells, secreted soluble factors, and podocyte response in immune-mediated (primary) FSGS.

Mesangial IgM deposition predicts renal outcome in patients with IgA nephropathy: a multicenter, observational study

Mesangial IgM deposition is found in patients with immunoglobulin A nephropathy (IgAN). This study aims to investigate the relationships between mesangial IgM deposition and disease progression in IgAN patients. A total of 1239 patients with biopsy-proven primary IgAN were enrolled in this multicenter, observational study between January 2013 and August 2017. According to the degree of IgM deposition, 1239 patients were divided into three groups: Grade 0 (no or trace; n = 713, 57.55%), Grade 1 (mild; n = 414, 33.41%), Grades 2 + 3 (moderate and marked; n = 112, 9.04%). Using a 1:1 propensity score matching (PSM) method identifying age, gender and treatment modality to minimize confounding factors, 1042 matched patients (out of 1239) with different degrees of IgM deposition were enrolled to evaluate the severity of baseline clinicopathological features and renal outcome: Grade 0 (n = 521, 50.00%), Grade 1 (n = 409, 39.25%), Grades 2 + 3 (n = 112, 10.75%). Kaplan-Meier and Cox proportional hazards analyses were performed to determine whether different degrees of mesangial IgM deposition are associated with varying renal outcomes in IgAN. During a mean follow-up of 48.90 ± 23.86 and 49.01 ± 23.73 months, before and after adjusting for propensity scores, respectively, the rate of complete remission (CR) was progressively lower with increased IgM deposition in both unmatched (63.39%, 46.14%, 45.54%) and matched cohort (61.80%, 46.45%, 45.54%), whereas the proportion of patients progressing to end-stage renal disease (ESRD) showed reverse correlation (P < 0.001). Kaplan-Meier analysis indicated negative correlation between the intensity of mesangial IgM deposits and cumulative renal survival (all P < 0.05). Moreover, Cox regression analysis revealed that the degree of mesangial IgM deposition predicted renal outcome independent of MESTC score and clinical variables in the unmatched (Grade 1, HR, 1.59; 95% CI, 1.11-2.29; P = 0.01; Grades 2 + 3, HR, 1.69; 95% CI, 1.02-2.08; P = 0.04) and matched cohort (Grade 1, HR, 1.84; 95% CI, 1.19-2.85; P = 0.01; Grades 2 + 3, HR, 1.91; 95% CI, 1.01-3.24; P = 0.04). Mesangial IgM deposition is associated with histological activity, clinical severity and renal outcome and is an independent risk factor for poor renal prognosis in IgAN. TRIAL REGISTRATION: TCTR, TCTR20140515001. Registered May 15, 2014, http://www.clinicaltrials.in.th/index.php?tp=regtrials&menu=trialsearch&smenu=fulltext&task=search&task2=view1&id=1074 .

β2-Adrenergic receptor agonism as a therapeutic strategy for kidney disease

Approximately 14% of the general population suffer from chronic kidney disease that can lead to acute kidney injury (AKI), a condition with up to 50% mortality for which there is no effective treatment. Hypertension, diabetes, and cardiovascular disease are the main comorbidities, and more than 660,000 Americans have kidney failure. β₂-Adrenergic receptors (β₂ARs) have been extensively studied in association with lung and cardiovascular disease, but with limited scope in kidney and renal diseases. β₂ARs are expressed in multiple parts of the kidney including proximal and distal convoluted tubules, glomeruli, and podocytes. Classical and noncanonical β₂AR signaling pathways interface with other intracellular mechanisms in the kidney to regulate important cellular functions including renal blood flow, electrolyte balance and salt handling, and tubular function that in turn exert control over critical physiology and pathology such as blood pressure and inflammatory responses. Nephroprotection through activation of β₂ARs has surfaced as a promising field of investigation; however, there is limited data on the pharmacology and potential side effects of renal β₂AR modulation. Here, we provide updates on some of the major areas of preclinical kidney research involving β₂AR signaling that have advanced to describe molecular pathways and identify potential drug targets some of which are currently under clinical development for the treatment of kidney-related diseases.

Immunofluorescence deposits in the mesangial area and glomerular capillary loops did not affect the prognosis of immunoglobulin a nephropathy except C1q:a single-center retrospective study

Background

Immunoglobulin A nephropathy (IgAN) is identified as mesangial IgA deposition and is usually accompanied by other immunofluorescence deposits. The impact of immunofluorescent features in IgAN patients, however, remains unclear.

Methods

Baseline clinicopathologic parameters and renal outcomes of 337 patients diagnosed with IgAN between January 2009 and December 2015 were analyzed. We then categorized these patients into four groups: without immunofluorescence deposits, mesangial-only, mesangial and glomerular capillary loops (GCLs), and GCLs-only. The study endpoint was end-stage kidney disease (ESKD) or a ≥ 50% decline in the estimated glomerular filtration rate (eGFR). Kaplan–Meier and Cox regression analyses were performed to calculate renal survival.

Results

Of the 337 IgAN patients, women comprised 57.0%. Compared to patients with IgA deposition in the mesangial-only group, patients with IgA deposition in the mesangial +GCLs group were much heavier, and exhibited higher systolic blood pressure, lower serum IgG levels, and heavier proteinuria (all P < 0.05). Patients with IgG deposition in the mesangial +GCLs group presented with higher levels of cholesterol, heavier proteinuria than IgG deposition in the mesangial-only group (both P < 0.05). Compared with the mesangial-only group exhibiting C3 deposits, patients in the mesangial +GCLs group with C3 deposition had a higher systolic blood pressure (P = 0.028). A total of 38 patients (11.3%) continued to the study endpoint after a median follow-up time of 63.5 months (range,49.8–81.4). Kaplan–Meier analysis and Cox regression analysis showed that C1q deposition in the mesangial +GCLs group predicted a poor renal prognosis.

Conclusions

IgA and IgG deposits in the mesangial region and GCLs were associated with more unfavorable clinical and histopathologic findings in IgAN patients. C1q deposition in the mesangial region and GCLs predicted a poor renal prognosis. However, the impact of the pattern of immunofluorescence deposits on renal outcomes remains to be proven by further investigation.

Autoimmunity in Focal Segmental Glomerulosclerosis: A Long-Standing Yet Elusive Association

Focal segmental glomerulosclerosis (FSGS) is a histological term that describes a pathologic renal entity affecting both adults and children, with a wide array of possible underlying etiologies. Podocyte damage with scarring, the hallmark of this condition, leads to altered permeability of the glomerular barrier, which may result in massive proteinuria and relentless renal function deterioration. A definite cause of focal segmental glomerulosclerosis can be confirmed in a minority of cases, while most forms have been traditionally labeled as primary or idiopathic. Despite this definition, increasing evidence indicates that primary forms are a heterogenous group rather than a single disease entity: several circulating factors that may affect glomerular permeability have been proposed as potential culprits, and both humoral and cellular immunity have been implicated in the pathogenesis of the disease. Consistently, immunosuppressive drugs are considered as the cornerstone of treatment for primary focal segmental glomerulosclerosis, but response to these agents and long-term outcomes are highly variable. In this review we provide a summary of historical and recent advances on the pathogenesis of primary focal segmental glomerulosclerosis, focusing on implications for its differential diagnosis and treatment.

Focal Segmental Glomerulosclerosis, Risk Factors for End Stage Kidney Disease, and Response to Immunosuppression

Background

FSGS is a heterogeneic glomerular disease. Risk factors for kidney disease ESKD and the effect of immunosuppression treatment (IST) has varied in previously published cohorts. These cohorts were limited by relatively small case numbers, short follow-up, lack of racial/ethnic diversity, a mix of adult and pediatric patients, lack of renin-angiotensin-aldosterone system (RAAS) inhibition, or lack of subgroup analysis of IST.

Methods

We compared demographics, clinical characteristics, histopathology, and IST to long-term renal survival in a large, ethnically diverse, adult cohort of 338 patients with biopsy-proven FSGS with long-term follow-up in the era of RAAS inhibition using data from the US Department of Defense health care network.

Results

Multivariate analysis showed that nephrotic-range proteinuria (NRP), eGFR <60 ml/min per 1.73 m², hypoalbuminemia, interstitial fibrosis and tubular atrophy, and interstitial inflammation at diagnosis and the absence of remission were all associated with worse long-term renal survival. IgM, C3, and a combination of IgM/C3 immunofluorescence staining were not associated with reduced renal survival. IST was not associated with improved renal survival in the whole cohort, or in a subgroup with NRP. However, IST was associated with better renal survival in a subgroup of patients with FSGS with both NRP and hypoalbuminemia and hypoalbuminemia alone.

Conclusions

Our study suggests that IST should be reserved for patients with FSGS and nephrotic syndrome. It also introduces interstitial inflammation as a potential risk factor for ESKD and does not support the proposed pathogenicity of IgM and complement activation.

Association of Glomerular Complement C4c Deposition With the Progression of Diabetic Kidney Disease in Patients With Type 2 Diabetes

Objectives: As accumulating data supporting the potential role of the complement system in the pathogenesis of diabetic kidney disease (DKD), the present study aimed to explore the association of glomerular complement C4c deposition with the baseline clinicopathological characteristics and the prognosis of DKD in type 2 diabetes (T2DM) patients.

Methods: A total of 79 T2DM patients with biopsy-proven DKD were enrolled. Clinicopathological features and renal outcomes were compared between groups divided by the glomerular C4c deposition patterns and median values of serum C4. Renal outcomes were defined by doubling of serum creatinine level or progression to end-stage renal disease (ESRD). A Cox proportional hazards model was employed to identify the risk factors associated with renal events.

Results: Patients with glomerular C4c deposition had worse renal insufficiency than those without C4c deposits, along with higher 24-h urinary protein, triglyceride, but lower serum albumin and higher interstitial inflammation score. Besides, serum C4 levels positively correlated with urinary protein and serum C3 levels. During 21.85 ± 16.32 months of follow-up, Kaplan-Meier curve analysis showed significantly faster deterioration of renal function for patients with positive glomerular C4c deposition as well as higher levels of serum C4. More specifically, more than 50% of the patients with glomerular C4c had co-deposition of C3c or C1q, and patients with glomerular complement complex of C4c and one or two of C3/C1q deposition had more severe proteinuria and a higher rate of DKD progression than those with negative C4c deposits. The univariate Cox regression indicated that factors of combined serum and glomerular C4, urinary protein, serum creatinine, serum C3, combined glomerular C4c and IgM and interstitial inflammation were associated with an increased risk of DKD, but only glomerular C4c intensity (HR 1.584, 95% CI [1.001, 2.508], p = 0.0497), as well as baseline age and diabetic neuropathy, were independent risk factors for renal survival by the multivariate Cox analysis.

Conclusions: Glomerular C4c deposition was associated with deteriorated renal function and outcomes in patients with T2DKD. Glomerular C4c deposition was an independent risk factor for DKD progression.

Successful treatment of a rare variant of mesangioproliferative glomerulonephritis with IgM deposits with Cyclosporin A

We present a case with a rare variant of glomerulonephritis, IgM nephropathy, which occurs mainly with nephrotic syndrome. The clinical features of this variant of kidney damage are characterized; the pathogenetic and the transformation of this form of nephritis into focal segmental glomerulosclerosis are discussed. The development of severe nephrotic syndrome at the beginning of the disease, the formation of secondary steroid resistance have confirmed this hypothesis and have justified the treatment with cyclosporin A aimed at the recovery of the function of the podocyte with remission of nephritis.

Complement activation profile of patients with primary focal segmental glomerulosclerosis

Background

Studies on adriamycin mice model suggest complement system is activated and together with IgM contributes to the glomerular injury of primary focal segmental glomerulosclerosis (FSGS). We recently reported primary FSGS patients with IgM and C3 deposition showed unfavorable therapeutic responses and worse renal outcomes. Here we examined the plasma and urinary complement profile of patients with primary FSGS, aiming to investigate the complement participation in FSGS pathogenesis.

Methods

Seventy patients with biopsy-proven primary FSGS were enrolled. The plasma and urinary levels of C3a, C5a, soluble C5b-9, C4d, C1q, MBL, and Bb were determined by commercial ELISA kits.

Results

The levels of C3a, C5a and C5b-9 in plasma and urine of FSGS patients were significantly higher than those in normal controls. The plasma and urinary levels of C5b-9 were positively correlated with urinary protein, renal dysfunction and interstitial fibrosis. The plasma C5a levels were positively correlated with the proportion of segmental sclerotic glomeruli. The urinary levels of Bb were elevated, positively correlated with C3a and C5b-9 levels, renal dysfunction, and interstitial fibrosis. The plasma C1q level was significantly decreased, and negatively correlated with urinary protein excretion. Urinary Bb level was a risk factor for no remission (HR = 3.348, 95% CI 1.264–8.870, P = 0.015) and ESRD (HR = 2.323, 95% CI 1.222–4.418, P = 0.010).

Conclusion

In conclusion, our results identified the systemic activation of complement in human primary FSGS, possibly via the classical and alternative pathway. The activation of complement system was partly associated with the clinical manifestations, kidney pathological damage, and renal outcomes.

ECM Characterization Reveals a Massive Activation of Acute Phase Response during FSGS

The glomerular basement membrane (GBM) and extra-cellular matrix (ECM) are essential to maintain a functional interaction between the glomerular podocytes and the fenestrated endothelial cells in the formation of the slit diaphragm for the filtration of blood. Dysregulation of ECM homeostasis can cause Focal segmental glomerulosclerosis (FSGS). Despite this central role, alterations in ECM composition during FSGS have not been analyzed in detail yet. Here, we characterized the ECM proteome changes in miR-193a-overexpressing mice, which suffer from FSGS due to suppression of Wilms' tumor 1 (WT1). By mass spectrometry we identified a massive activation of the acute phase response, especially the complement and fibrinogen pathways. Several protease inhibitors (ITIH1, SERPINA1, SERPINA3) were also strongly increased. Complementary analysis of RNA expression data from both miR-193a mice and human FSGS patients identified additional candidate genes also mainly involved in the acute phase response. In total, we identified more than 60 dysregulated, ECM-associated genes with potential relevance for FSGS progression. Our comprehensive analysis of a murine FSGS model and translational comparison with human data offers novel targets for FSGS therapy.

Complement and Complement Targeting Therapies in Glomerular Diseases

The complement cascade is part of the innate immune system whose actions protect hosts from pathogens. Recent research shows complement involvement in a wide spectrum of renal disease pathogenesis including antibody-related glomerulopathies and non-antibody-mediated kidney diseases, such as C3 glomerular disease, atypical hemolytic uremic syndrome, and focal segmental glomerulosclerosis. A pivotal role in renal pathogenesis makes targeting complement activation an attractive therapeutic strategy. Over the last decade, a growing number of anti-complement agents have been developed; some are approved for clinical use and many others are in the pipeline. Herein, we review the pathways of complement activation and regulation, illustrate its role instigating or amplifying glomerular injury, and discuss the most promising novel complement-targeting therapies.

Mitochondrial biogenesis induced by the β2-adrenergic receptor agonist formoterol accelerates podocyte recovery from glomerular injury

Podocytes have limited ability to recover from injury. Here, we demonstrate that increased mitochondrial biogenesis, to meet the metabolic and energy demand of a cell, accelerates podocyte recovery from injury. Analysis of events induced during podocyte injury and recovery showed marked upregulation of peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α), a transcriptional co-activator of mitochondrial biogenesis, and key components of the mitochondrial electron transport chain. To evaluate our hypothesis that increasing mitochondrial biogenesis enhanced podocyte recovery from injury, we treated injured podocytes with formoterol, a potent, specific, and long-acting β2-adrenergic receptor agonist that induces mitochondrial biogenesis in vitro and in vivo. Formoterol increased mitochondrial biogenesis and restored mitochondrial morphology and the injury-induced changes to the organization of the actin cytoskeleton in podocytes. Importantly, β2-adrenergic receptors were found to be present on podocyte membranes. Their knockdown attenuated formoterol-induced mitochondrial biogenesis. To determine the potential clinical relevance of these findings, mouse models of acute nephrotoxic serum nephritis and chronic (Adriamycin [doxorubicin]) glomerulopathy were used. Mice were treated with formoterol post-injury when glomerular dysfunction was established. Strikingly, formoterol accelerated the recovery of glomerular function by reducing proteinuria and ameliorating kidney pathology. Furthermore, formoterol treatment reduced cellular apoptosis and increased the expression of the mitochondrial biogenesis marker PGC-1α and multiple electron transport chain proteins. Thus, our results support β2-adrenergic receptors as novel therapeutic targets and formoterol as a therapeutic compound for treating podocytopathies.

Co-Deposition of IgM and C3 May Indicate Unfavorable Renal Outcomes in Adult Patients with Primary Focal Segmental Glomerulosclerosis

BACKGROUND/AIMS

We aimed to investigate the effects of glomerular IgM and C3 deposition on outcomes of adult patients with primary focal segmental glomerulosclerosis (FSGS).

METHODS

In this retrospective analysis, 86 consecutive adult patients with biopsy-proven primary FSGS were stratified into 3 groups according to their histopathological features: IgM- C3-, IgM+ C3-, and IgM+ C3+. Primary outcome was defined as at least a 50% reduction in baseline estimated glomerular filtration rate (eGFR) or development of kidney failure, while complete or partial remission rates were secondary outcomes.

RESULTS

Glomerular IgM deposits were found in 44 (51.1%) patients, 22 (25.5%) of which presented with accompanying C3 deposition. Patients in IgM+ C3+ group had higher level of proteinuria (5.6 g/24 h [3.77-8.5], p = 0.073), higher percentage of segmental glomerulosclerosis (20% [12.3-27.2], p = 0.001), and lower levels of eGFR (69 ± 37.2 mL/min/1.73 m2, p = 0.029) and serum albumin (2.71 ± 0.85 g/dL, p = 0.045) at the time of diagnosis. Despite 86.3% of patients in IgM+ C3+ group (19/22) received immunosuppressive treatment, the primary outcome was more common in patients in the IgM+ C3+ group compared with patients in IgM+ C3- and IgM- C3- groups (11 [50%] vs. 2 [9%] and 11 [26.1%] respectively [p = 0.010]). Complete or partial remission rates were lower in patients in the IgM+ C3+ group (5/22, 22.7%), as well (p = 0.043). Multivariate Cox regression analysis revealed that IgM and C3 co-deposition was an independent risk factor associated with primary outcome (hazard ratio 3.355, 95% CI 1.349-8.344, p = 0.009).

CONCLUSIONS

Glomerular IgM and C3 co-deposition is a predictor of unfavorable renal outcomes in adult patients with primary FSGS.

Glomerular C4d deposition can precede the development of focal segmental glomerulosclerosis

Recent studies suggest that complement plays a role in the pathogenesis of focal segmental glomerulosclerosis (FSGS). Moreover, co-localization of IgM and C3 deposits with FSGS lesions has frequently been reported. Here, we investigated whether glomerular complement deposition precedes the development of FSGS and whether it represents local complement activation. Renal biopsies from 40 patients with primary FSGS, 84 patients with minimal change disease, and 10 healthy individuals were stained for C4d, C1q, and mannose-binding lectin. C4d deposits were also measured in renal allograft biopsies from 34 patients with native primary FSGS, 18 of whom subsequently developed recurrent FSGS. Lastly, we measured C4d deposits in the Munich Wistar Frömter rat model of FSGS. The prevalence of C4d-positive glomeruli was significantly higher among patients with FSGS (73%) compared to patients with minimal change disease (21%) and healthy individuals (10%). Moreover, segmental sclerosis was absent in 42% of C4d-positive glomeruli. Glomerular C1q was significantly more prevalent in FSGS compared to minimal change disease or healthy individuals, while mannose-binding lectin was infrequently observed. C4d deposition was significantly more prevalent in recurrent FSGS (72%) before the development of sclerotic lesions compared to control transplant samples (27%). Finally, at the onset of albuminuria but before the development of FSGS lesions, Munich Wistar Frömter rats had a significantly higher percentage of C4d-positive glomeruli (31%) compared to control rats (4%). Thus, glomerular C4d deposition can precede the development of FSGS, suggesting that complement activation may play a pathogenic role in the development of FSGS.

Glomerular C3 Deposition Is an Independent Risk Factor for Allograft Failure in Kidney Transplant Recipients With Transplant Glomerulopathy

Introduction

Transplant glomerulopathy (TG) becomes increasingly prevalent in kidney transplant recipients over time, and it is strongly associated with allograft failure. To date, our prognostic biomarkers and understanding of the processes of immunologic injury in TG are limited.

Methods

This is a retrospective cohort analysis of kidney transplant recipients with TG (double contours of the glomerular basement membrane as defined by the chronic glomerulopathy score). Glomerular deposition of the complement protein C3 was determined, and its association with allograft survival was analyzed by Cox regression analysis.

Results

Of the 111 patients with TG, 72 (65%) had allograft failure, with a median follow-up time of 3 years from biopsy diagnosis of TG. C3-positive compared to C3-negative patients did not differ with respect to cause of end-stage renal disease, induction or maintenance immunosuppression, or sensitization. A greater proportion of patients with glomerular C3 deposition developed allograft failure compared to those with no C3 deposition (78% vs. 55%, P = 0.01). C3 deposition was independently associated with allograft failure in multivariate analyses (adjusted hazard ratio [HR] = 1.38, 95% confidence interval [CI] = 1.13−1.69, P = 0.002). There was no association between C4d or C1q deposition and allograft failure. Chronicity score was also associated with allograft failure in multivariate analysis (adjusted HR 1.26, 95% CI 1.12-1.41, P = 0.0001).

Conclusion

In this cohort of patients with TG, glomerular C3 deposition was independently associated with a higher risk of allograft failure. These findings identify glomerular C3 as a novel prognostic indicator in patients with TG.

Mesangial C4d deposition is independently associated with poor renal survival in patients with primary focal segmental glomerulosclerosis

BACKGROUND

C4d deposition is defined as the footprint of immune injury and it is associated with unfavorable renal outcomes in patients with IgA nephropathy. We searched whether mesangial C4d deposition is associated with poor renal survival in patients with primary focal segmental glomerulosclerosis (FSGS).

METHODS

Biopsy specimens were stained with anti-C4d antibody. Patients were classified based on mesangial C4d deposition as C4d-negative and C4d-positive. Groups were compared according to baseline and follow-up clinical variables. Factors that predict renal progression and treatment failure were determined using Cox-regression and multivariate logistic regression models, respectively.

RESULTS

Forty-one FSGS patients were followed for a mean of 67.7 ± 40.8 months. C4d-positive group included 18 patients while remaining 23 patients were C4d-negative. Urinary protein excretion and serum creatinine levels at baseline were comparable between groups. Fifteen patients reached the composite primary endpoint which included serum creatinine increasing > 30% from the baseline and reaching > 1.5 mg/dl, and/or evolution to end-stage renal disease (36.6%). In multivariate regression analysis, baseline eGFR (OR 0.71, 95% CI 0.53-0.94; p = 0.016) and mesangial C4d deposition (OR 10.5, 95% CI 1.51-73.18; p = 0.018) were independently associated with treatment failure rates. Mesangial C4d deposition was independently associated with the progression to the primary endpoint (HR 6.54, 95% CI 1.49-28.7, p = 0.013).

CONCLUSION

We showed for the first time that mesangial C4d deposition is an independent predictor of disease progression and treatment failure in patients with primary FSGS.

Complete B Cell Deficiency Reduces Allograft Inflammation and Intragraft Macrophages in a Rat Kidney Transplant Model

BACKGROUND

Increasingly, it is being appreciated that B cells have broad roles beyond the humoral response and are able to contribute to and regulate inflammation. The specific role of B cells in the pathogenesis of early allograft inflammation remains unclear.

METHODS

To address this question, we generated B cell-deficient (B) Lewis rats via clustered regularly interspaced short palindromic repeats (CRISPR) technology. In a full mismatch transplant model, kidneys from Brown Norway donors were transplanted into B Lewis recipients or wild type Lewis recipients. T cell-mediated rejection was attenuated with cyclosporine.

RESULTS

Renal inflammation was reduced at 1 week after transplant (Banff scores for interstitial inflammation, microvascular inflammation, glomerulitis, and C4d) in allografts from B recipients. The reduction in interstitial inflammation was predominantly due to a decline in graft infiltrating macrophages. Intragraft T-cell numbers remained unchanged. In addition, B-cell deficiency was associated with increased T regulatory cells and reduced splenic T follicular helper cells at baseline; and significantly increased intragraft and splenic IL-10 mRNA levels after transplant. In vitro, B and wild type splenic T cells produced similar levels of IFN-γ in response to T cell-specific activation.

CONCLUSIONS

B-cell deficiency in this model produced an anti-inflammatory phenotype with a shift toward regulatory T-cell populations, production of anti-inflammatory cytokines (IL-10), and a reduction in allograft inflammation. These findings define a role for B cells to influence the cell populations and mediators involved in the pathogenesis of early allograft inflammation.

Clinical significance of mesangial IgM deposition in patients with IgA nephropathy

BACKGROUND

Glomerular immunoglobulin G deposition in patients with immunoglobulin A nephropathy (IgAN) has been shown to be associated with adverse renal outcomes. Clinical significance of mesangial immunoglobulin M (IgM) deposition in these patients remains to be proven.

METHODS

One hundred patients who had a diagnosis of IgAN between 2001 and 2017 were enrolled. Patients were divided into two groups based on mesangial IgM deposition status. Groups were compared for demographic, clinical, and pathologic variables at baseline and in follow-up. Cox regression analysis was performed to evaluate the effect of mesangial IgM positivity on renal survival.

RESULTS

IgM-positive group included 51% of participants. Baseline demographic and clinical parameters were not significantly different between groups. Mesangial IgM deposition was significantly associated with a higher segmental sclerosis score (p = 0.008). At last visit, median serum creatinine was higher (p = 0.021) and eGFR was lower (p = 0.006) in IgM-positive group. Nineteen (19%) of all patients reached the combined primary outcome which includes doubling in serum creatinine or evolution to ESRD. Cumulative renal survival was lower (p = 0.001) and resistant disease was more frequent in IgM-positive group (p = 0.026). Renal survival at 15 years was 94.2% and 59.7% in IgM-negative and IgM-positive groups, respectively (p = 0.006). Time-averaged proteinuria (HR 2.9; 95% CI 1.9-4.5; p < 0.001) and mesangial IgM deposition (HR, 13.2; 95% CI 1.9-93.1; p = 0.01) were found to be independent predictors of unfavorable renal outcomes.

CONCLUSIONS

In conclusion, we demonstrated that mesangial IgM deposition independently associated with worse renal outcomes in patients with IgA nephropathy.

The Clinical Impact of Glomerular Immunoglobulin M Deposition in Patients with Type 2 Diabetic Nephropathy

BACKGROUND

Glomerular immunoglobulin M (IgM) deposition is common in diabetic kidney disease. The clinical implication of IgM deposition in the renal tissues of type 2 diabetes mellitus patients with biopsy-proven diabetic nephropathy remains unclear.

MATERIALS AND METHODS

One hundred thirty-two patients with type 2 diabetes and biopsy-proven pure diabetic nephropathy were enrolled retrospectively. Clinicopathological features and renal outcomes were compared between patients with and without glomerular capillary IgM deposition. A Cox proportional hazards model was employed to identify the risk factors associated with renal survival.

RESULTS

Fifty-two patients had positive linear glomerular capillary IgM staining. Patients with glomerular capillary IgM deposition presented with heavier proteinuria, and lower serum albumin. During 35.5 (12, 107) months of follow-up, patients with glomerular tuft IgM deposition had shorter renal survival than those with negative IgM deposition (39 [23.74, 54.26] versus (vs.) 64 [45.82, 82.18] months, P = 0.01). Patients with glomerular complement 1q (C1q) deposition showed worse renal survival than those lacking glomerular C1q deposition (36 [23.82, 48.18] vs. 60 [50.27, 69.74] months, P = 0.001). Worse renal outcome was observed in patients with glomerular C3 deposition than in those without glomerular C3 deposition (37 [22.43, 51.56] vs. 63 [51.75, 74.25] months, P = 0.001). Multivariate Cox proportional analysis demonstrated that combined glomerular capillary IgM and C1q deposition was an independent predictor of end-stage renal disease (hazard ratio 3.75, 95% CI[ 1.68,8.35], P = 0.001).

CONCLUSIONS

Patients with diabetic nephropathy and combined glomerular capillary IgM and C1q deposition had unfavorable renal outcome, which indicates that IgM derived from B cells might be involved in diabetic kidney injury.

Complement factor H protects mice from ischemic acute kidney injury but is not critical for controlling complement activation by glomerular IgM

Natural IgM binds to glomerular epitopes in several progressive kidney diseases. Previous work has shown that IgM also binds within the glomerulus after ischemia/reperfusion (I/R) but does not fully activate the complement system. Factor H is a circulating complement regulatory protein, and congenital or acquired deficiency of factor H is a strong risk factor for several types of kidney disease. We hypothesized that factor H controls complement activation by IgM in the kidney after I/R, and that heterozygous factor H deficiency would permit IgM-mediated complement activation and injury at this location. We found that mice with targeted heterozygous deletion of the gene for factor H developed more severe kidney injury after I/R than wild-type controls, as expected, but that complement activation within the glomeruli remained well controlled. Furthermore, mice that are unable to generate soluble IgM were not protected from renal I/R, even in the setting of heterozygous factor H deficiency. These results demonstrate that factor H is important for limiting injury in the kidney after I/R, but it is not critical for controlling complement activation by immunoglobulin within the glomerulus in this setting. IgM binds to glomerular epitopes after I/R, but it is not a significant source of injury.

Differentiating Primary, Genetic, and Secondary FSGS in Adults: A Clinicopathologic Approach

FSGS describes a renal histologic lesion with diverse causes and pathogenicities that are linked by podocyte injury and depletion. Subclasses of FSGS include primary, genetic, and secondary forms, the latter comprising maladaptive, viral, and drug-induced FSGS. Despite sharing certain clinical and histologic features, these subclasses differ noticeably in management and prognosis. Without an accepted nongenetic biomarker that discriminates among these FSGS types, classification of patients is often challenging. This review summarizes the clinical and histologic features, including the onset and severity of proteinuria as well as the presence of nephrotic syndrome, that may aid in identifying the specific FSGS subtype. The FSGS lesion is characterized by segmental sclerosis and must be differentiated from nonspecific focal global glomerulosclerosis. No light microscopic features are pathognomonic for a particular FSGS subcategory. The characteristics of podocyte foot process effacement on electron microscopy, while helpful in discriminating between primary and maladaptive FSGS, may be of little utility in detecting genetic forms of FSGS. When FSGS cannot be classified by clinicopathologic assessment, genetic analysis should be offered. Next generation DNA sequencing enables cost-effective screening of multiple genes simultaneously, but determining the pathogenicity of a detected genetic variant may be challenging. A more systematic evaluation of patients, as suggested herein, will likely improve therapeutic outcomes and the design of future trials in FSGS.

Complement Activation in Patients With Diabetic Nephropathy

Introduction

Complement activation plays a role in various organs in patients with diabetes. However, in diabetic nephropathy (DN), the role of complement activation is poorly understood. We examined the prevalence and clinical significance of complement deposits in the renal tissue of cases with type 1 and type 2 diabetes with and without DN.

Methods

We measured the prevalence of glomerular C4d, C1q, mannose-binding lectin (MBL), and C5b-9 deposits in 101 autopsied diabetic cases with DN, 59 autopsied diabetic cases without DN, and 41 autopsied cases without diabetes or kidney disease. The presence of complement deposits was scored by researchers who were blinded with respect to the clinical and histological data.

Results

C4d deposits were more prevalent in cases with DN than in cases without DN in both the glomeruli (46% vs. 26%) and the arterioles (28% vs. 12%). C1q deposits were also increased in the glomerular hili (77% vs. 55%) and arterioles (33% vs.14%), and were correlated with DN (P < 0.01). MBL deposits were only rarely observed. C5b-9 deposits were more prevalent in the cases with diabetes mellitus (DM) than in the cases without DM (69% vs. 32%; P < 0.001). Finally, glomerular C4d and C5b-9 deposits were correlated with the severity of DN (ρ = 0.341 and 0.259, respectively; P < 0.001).

Conclusion

Complement activation is correlated with both the presence and severity of DN, suggesting that the complement system is involved in the development of renal pathology in patients with diabetes and is a promising target for inhibiting and/or preventing DN in these patients.

IgM as a novel predictor of disease progression in secondary focal segmental glomerulosclerosis

Aim

To determine the role of immunoglobulin M (IgM) deposits in clinical manifestations, disease outcome, and treatment response of idiopathic and secondary focal segmental glomerulosclerosis (FSGS).

Methods

Kidney biopsy specimens of 171 patients diagnosed with FSGS (primary and secondary) and 50 control patients were retrospectively included in the study. For each patient, clinical and outcome data were obtained and compared to morphological parameters, including immunofluorescence analysis of mesangial IgM and complement 3 (C3) deposits analyzed on kidney biopsy samples.

Results

There were significant positive correlations between IgM and C3 deposition in secondary FSGS (P < 0.001) and between IgM and mesangial deposits detected by electron microscopy in secondary FSGS (P = 0.015), which indicated that higher IgM deposition correlated with higher C3 deposition and mesangial deposits only in secondary FSGS. Patients with secondary FSGS and the deposition of IgM showed inferior renal outcomes at earlier time points in comparison with patients with negative IgM expression (P = 0.022).

Conclusions

We detected a positive correlation between IgM and C3 in secondary FSGS. The association between IgM deposition and worse renal outcome in secondary FSGS indicates that IgM may play a role in the progression of this disease.

The impact of IgM deposits on the outcome of Nephrotic syndrome in children

BACKGROUND

The significance of IgM deposits in glomerular mesangium has been controversial since they were first described due to the variations in the both the definitions used and described impact on clinical outcome. The aim of our study was to evaluate the significance of the IgM deposits in the glomerular mesangium for outcomes of nephrotic syndrome (NS) in children.

METHODS

Forty-five children with NS who underwent renal biopsy at tertiary pediatric hospital from January 1st, 2000 to December 31st, 2015 and the pathology diagnosis of minimal change disease, focal segmental glomerulosclerosis and mesangial hypercellularity (MH) were retrospectively analyzed. IgM positivity was defined as ≥1+ imunofluorescence with predominantly mesangial distribution. The patients were stratified into IgM-positive (n = 18) and IgM-negative (n = 27).

RESULTS

At the end of the median follow-up 4.5 years (range 0.17-13.14), the IgM-positive group was represented by 11 patients (61.1%) in remission, 3 patients (16.7%) with active disease and normal kidney function, 2 (11.1%) patients with active disease and impaired kidney function, 2 (11.1%) patients on renal replacement therapy. Accordingly, the IgM-negative group included 13 patients (48.1%) in remission, 12 (44.4%) with active disease and normal kidney function, 1 (3.7%) with active disease and impaired kidney function, 1 (3.7%) on renal replacement therapy, with no statistical significance between groups (p = 0.186).

CONCLUSIONS

This study did not reveal significant differences of the disease outcomes between IgM-positive and IgM-negative groups.

Investigational drugs in development for focal segmental glomerulosclerosis

INTRODUCTION

Focal segmental glomerulosclerosis is an important cause of end stage kidney disease and is a paradigm for the study of glomerular scarring. There are no FDA approved treatments for this condition. Current therapies, assessed based on reduction in proteinuria, are generally effective in a subset of patients which suggests that FSGS is a heterogeneous group of glomerular disorders or podocytopathies that converge on a common histopathological phenotype. Areas covered: We searched for investigational drugs agents that target different pathophysiological pathways using the key words 'FSGS' and 'podocyte' in American and European clinical trial registers (clinicaltrials.gov; clinicaltrialsregister.eu). Published articles were searched in PubMed, Medline, the Web of Science and the Cochrane Central Register of Controlled Trials Library. Expert opinion: Progress is being made in defining the mechanism of action of subtypes of FSGS. Current and investigational therapies for FSGS target these different pathways of injury. It is anticipated that advances in systems biology will further refine the classification of FSGS by subdividing the disease based on the primary mechanism of glomerular injury, identify biomarkers to discriminate between different subtypes, and enable appropriate selection of appropriate therapy for each individual in accordance with the goals of precision medicine.