Podocyte injury induced by mesangial-derived cytokines in IgA nephropathy

Evidence from the large VALIGA cohort validates the subclassification of focal segmental glomerulosclerosis in IgA nephropathy

Evidence from the Oxford IgA nephropathy (IgAN) cohort supports the clinical value of subclassifying focal segmental glomerulosclerosis lesions (S1). Using the larger Validation in IgA (VALIGA) study cohort, we investigated the association between podocytopathic changes and higher proteinuria, kidney outcome and response to immunosuppressive therapy. All biopsies were evaluated for glomeruli with segmental capillary occlusion by matrix ("not otherwise specified", NOS lesion), simple capsular adhesion without capillary occlusion (Adh), tip lesions, and podocyte hypertrophy (PH). S1 required a NOS lesion and/or Adh. A Chi-Squared Automatic Interaction Detection method was used to identify subgroups of FSGS lesions associated with distinctive proteinuria at biopsy. We assessed survival from a combined event (kidney failure or 50% decline in estimated glomerular filtration rate). Finally, we evaluated within each subgroup if immunosuppression was associated with a favorable outcome using propensity analysis. In 1147 patients, S1 was found in 70% of biopsies. Subclassification found NOS lesions in 44%, Adh in 59%, PH in 13%, and tip lesions in 3%, with much overlap. Four subgroups were identified with progressively higher proteinuria: from lowest, S1 without NOS, S1 with NOS but without Adh/PH, to highest, S1 with NOS and Adh but without PH, and S1 with NOS and PH. These four subgroups showed progressively worse kidney survival. Immunosuppression was associated with a better outcome only in the two highest proteinuria subgroups. Propensity analysis in these two groups, adjusted for clinical and pathological findings, found a significantly reduced time-dependent hazard of combined outcome with corticosteroids. Podocyte hypertrophy and glomeruli with simple adhesions appeared to reflect active lesions associated with a response to corticosteroids, while other S1 lesions defined chronicity. Thus, our findings support subclassifying S1 lesions in IgAN.

Primary IgA Nephropathy: New Insights and Emerging Therapies

Primary IgA nephropathy (IgAN) is a common glomerular disorder defined by predominant mesangial IgA deposition. Once thought to follow a progressive course in 10-20% of those diagnosed, emerging evidence now suggests most will progress to kidney failure over their lifetimes. Although the lack of safe and effective treatments to impede disease progression continues to present a challenge, the landscape of IgAN has dramatically evolved over the last 2 years. Driven by fundamental changes to accepted end points for IgAN clinical trials as well as fascinating new insights into the pathophysiology of IgAN, a swathe of novel and repurposed therapies are currently being evaluated. Already, two novel drugs, targeted-release formulation budesonide and sparsentan, have received conditional approvals for the treatment of IgAN, with sodium glucose co-transporter 2 inhibitors establishing themselves as further options. Soon to join this ensemble are likely to be treatments that modulate the complement system and B-cell activity; several are currently undergoing clinical trials in IgAN with promising interim results. In this review, we provide an overview of evolving epidemiological insights, disease mechanisms, emerging therapies, and contemporary challenges surrounding the management of IgAN.

The CXCR4-AT1 axis plays a vital role in glomerular injury via mediating the crosstalk between podocyte and mesangial cell

Glomeruli stand at the center of nephrons to accomplish filtration and albumin interception. Podocytes and mesangial cells are the major constituents in the glomeruli. However, their interdependency in glomerular injury has rarely been reported. Herein, we investigated the role of C-X-C chemokine receptor type 4 (CXCR4) in mediating the crosstalk between podocytes and mesangial cells. We found CXCR4 and angiotensin II (AngII) increased primarily in injured podocytes. However, type-1 receptor of angiotensin II (AT1) and stromal cell-derived factor 1α (SDF-1α), a ligand of CXCR4, were evidently upregulated in mesangial cells following the progression of podocyte injury. Ectopic expression of CXCR4 in 5/6 nephrectomy mice increased the decline of renal function and glomerular injury, accelerated podocyte injury and mesangial cell activation, and initiated CXCR4-AT1 axis signals. Additionally, treatment with losartan, an AT1 blocker, interrupted the cycle of podocyte injury and mesangial matrix deposition triggered by CXCR4. Podocyte-specific ablation of CXCR4 gene blocked podocyte injury and mesangial cell activation. In vitro, CXCR4 overexpression induced oxidative stress and renin angiotensin system (RAS) activation in podocytes, and triggered the communication between podocytes and mesangial cells. In cultured mesangial cells, AngII treatment induced the expression of SDF-1α, which was secreted into the supernatant to further promote oxidative stress and cell injury in podocytes. Collectively, these results demonstrate that the CXCR4-AT1 axis plays a vital role in glomerular injury via mediating pathologic crosstalk between podocytes and mesangial cells. Our findings uncover a novel pathogenic mechanism by which the CXCR4-AT1 axis promotes glomerular injury.

Effect of SGLT2 Inhibitor on Cardiomyopathy in a Rat Model of T2DM: Possible involvement of Cardiac Aquaporins

Diabetic cardiomyopathy (DCM) causes arrhythmia, heart failure, and sudden death. Empagliflozin, an SGLT-2 (Sodium glucose co-transporter) inhibitor, is an anti-diabetic medication that decreases blood glucose levels by stimulating urinary glucose excretion. Several aquaporins (AQPs) including AQP-1-3 and - 4 and their involvement in the pathogenesis in different cardiac diseases were detected. In the current study the effect of Empagliflozin on diabetic cardiomyopathy and the possible involvement of cardiac AQPs were investigated.

METHODS

56 adult male Sprague-Dawley rats were divided into 4 groups: Control, DCM: type 2 diabetic rats, low EMPA+DCM received empagliflozin (10 mg/kg/day) and high EMPA+DCM received empagliflozin (30 mg/kg/day) for 6 weeks.

RESULTS

Administration of both EMPA doses, especially in high dose group, led to significant improvement in ECG parameters. Also, a significant improvement in biochemical and cardiac oxidative stress markers (significant decrease in serum CK-MB, and malondialdehyde while increasing catalase) with decreased fibrosis and edema in histopathological examination and a significant attenuation in apoptosis (caspase-3) and edema (AQP-1& -4).

CONCLUSION

Both doses of Empagliflozin have a cardioprotective effect and reduced myocardial tissue edema with high dose having a greater effect. This might be due to attenuation of oxidative stress, fibrosis and edema mediated through AQP-1, - 3& - 4 expression.

IgA nephropathy

IgA nephropathy (IgAN), the most prevalent primary glomerulonephritis worldwide, carries a considerable lifetime risk of kidney failure. Clinical manifestations of IgAN vary from asymptomatic with microscopic or intermittent macroscopic haematuria and stable kidney function to rapidly progressive glomerulonephritis. IgAN has been proposed to develop through a 'four-hit' process, commencing with overproduction and increased systemic presence of poorly O-glycosylated galactose-deficient IgA1 (Gd-IgA1), followed by recognition of Gd-IgA1 by antiglycan autoantibodies, aggregation of Gd-IgA1 and formation of polymeric IgA1 immune complexes and, lastly, deposition of these immune complexes in the glomerular mesangium, leading to kidney inflammation and scarring. IgAN can only be diagnosed by kidney biopsy. Extensive, optimized supportive care is the mainstay of therapy for patients with IgAN. For those at high risk of disease progression, the 2021 KDIGO Clinical Practice Guideline suggests considering a 6-month course of systemic corticosteroid therapy; however, the efficacy of systemic steroid treatment is under debate and serious adverse effects are common. Advances in understanding the pathophysiology of IgAN have led to clinical trials of novel targeted therapies with acceptable safety profiles, including SGLT2 inhibitors, endothelin receptor blockers, targeted-release budesonide, B cell proliferation and differentiation inhibitors, as well as blockade of complement components.

Intestinal homeostasis in the gut-lung-kidney axis: a prospective therapeutic target in immune-related chronic kidney diseases

In recent years, the role of intestinal homeostasis in health has received increasing interest, significantly improving our understanding of the complex pathophysiological interactions of the gut with other organs. Microbiota dysbiosis, impaired intestinal barrier, and aberrant intestinal immunity appear to contribute to the pathogenesis of immune-related chronic kidney diseases (CKD). Meanwhile, the relationship between the pathological changes in the respiratory tract (e.g., infection, fibrosis, granuloma) and immune-related CKD cannot be ignored. The present review aimed to elucidate the new underlying mechanism of immune-related CKD. The lungs may affect kidney function through intestinal mediation. Communication is believed to exist between the gut and lung microbiota across long physiological distances. Following the inhalation of various pathogenic factors (e.g., particulate matter 2.5 mum or less in diameter, pathogen) in the air through the mouth and nose, considering the anatomical connection between the nasopharynx and lungs, gut microbiome regulates oxidative stress and inflammatory states in the lungs and kidneys. Meanwhile, the intestine participates in the differentiation of T cells and promotes the migration of various immune cells to specific organs. This better explain the occurrence and progression of CKD caused by upper respiratory tract precursor infection and suggests the relationship between the lungs and kidney complications in some autoimmune diseases (e.g., anti-neutrophil cytoplasm antibodies -associated vasculitis, systemic lupus erythematosus). CKD can also affect the progression of lung diseases (e.g., acute respiratory distress syndrome and chronic obstructive pulmonary disease). We conclude that damage to the gut barrier appears to contribute to the development of immune-related CKD through gut-lung-kidney interplay, leading us to establish the gut-lung-kidney axis hypothesis. Further, we discuss possible therapeutic interventions and targets. For example, using prebiotics, probiotics, and laxatives (e.g., Rhubarb officinale) to regulate the gut ecology to alleviate oxidative stress, as well as improve the local immune system of the intestine and immune communication with the lungs and kidneys.

The role of the mesangium in glomerular function

When discussing glomerular function, one cell type is often left out, the mesangial cell (MC), probably since it is not a part of the filtration barrier per se. The MCs are instead found between the glomerular capillaries, embedded in their mesangial matrix. They are in direct contact with the endothelial cells and in close contact with the podocytes and together they form the glomerulus. The MCs can produce and react to a multitude of growth factors, cytokines, and other signaling molecules and are in the perfect position to be a central hub for crosstalk communication between the cells in the glomerulus. In certain glomerular diseases, for example, in diabetic kidney disease or IgA nephropathy, the MCs become activated resulting in mesangial expansion. The expansion is normally due to matrix expansion in combination with either proliferation or hypertrophy. With time, this expansion can lead to fibrosis and decreased glomerular function. In addition, signs of complement activation are often seen in biopsies from patients with glomerular disease affecting the mesangium. This review aims to give a better understanding of the MCs in health and disease and their role in glomerular crosstalk and inflammation.

Metformin combined with rapamycin ameliorates podocyte injury in idiopathic membranous nephropathy through the AMPK/mTOR signaling pathway

Autophagy activation protects against podocyte injury in idiopathic membranous nephropathy (IMN). The AMPK/mTOR signaling pathway is a vital autophagy regulatory pathway. Metformin promotes autophagy, whereas rapamycin is an autophagy agonist. However, the therapeutic mechanisms of metformin and rapamycin in IMN remain unclear. Thus, we examined the mechanisms of action of metformin and rapamycin in IMN by regulating the AMPK/mTOR autophagy signaling pathway. Female Sprague-Dawley (SD) rats were treated with cationic bovine serum albumin (C-BSA) to establish an IMN model and were randomly divided into IMN model, metformin, rapamycin, and metformin + rapamycin groups. A control group was also established. Metformin and rapamycin were used as treatments. Renal histological changes, urinary protein excretion, the protein expression levels of key AMPK/mTOR signaling pathway proteins, renal tissue cell apoptosis, and autophagy-associated proteins (Beclin 1 and LC3) were examined. In addition, a C5b-9 sublysis model using the MPC-5 mouse podocyte cell line was established to verify the effect of metformin combined with rapamycin on podocytes. Metformin combined with rapamycin improved urinary protein excretion in IMN rats. Metformin combined with rapamycin attenuated the inflammatory response, renal fibrosis, and podocyte foot process fusion. In addition, it improved autophagy in podocytes as demonstrated by the enhanced expression of Beclin-1, p-AMPK/AMPK, LC3-II/I, and autophagosomes in podocytes and decreased p-mTOR/mTOR expression. In conclusion, metformin combined with rapamycin decreased proteinuria, improved renal fibrosis and podocyte autophagy via AMPK/mTOR pathway in IMN rats. The metformin and rapamycin decreased proteinuria and inproved renal fibrosis in IMN model rats.

Mitofusin2 expression is associated with podocyte injury in IgA nephropathy

BACKGROUND

Podocyte injury is associated with IgA nephropathy (IgAN) prognosis. Mitochondrial dysfunction is a major contributor to podocyte injury and death. Mitofusin2 (Mfn2) plays an important role in regulating the morphology and function of mitochondria. This study aimed to investigate the potential of Mfn2 as a biomarker to evaluate the degree of podocyte injury.

METHODS

This single-center, retrospective study enrolled 114 patients with biopsy-proven IgAN. Immunofluorescence and TUNEL staining were applied, and clinical and pathological features were compared between patients with different patterns of Mfn2 expression.

RESULTS

In IgAN, Mfn2 is mainly expressed in podocytes and significantly associated with nephrin, TUNEL, and Parkin staining. Among the 114 IgAN patients, 28 (24.56%) did not exhibit Mfn2 expression in podocytes. The patients in the Mfn2-negative group had lower serum albumin (34.43 ± 4.64 g/L vs. 36.48 ± 3 .52 g/L, P = 0.015) and estimated glomerular filtration rate (eGFR) (76.59 ± 35.38 mL/min vs. 92.13 ± 25.35 mL/min, P = 0.013), higher 24 h proteinuria (2.48 ± 2.72 g/d vs. 1.27 ± 1.31 g/d, P = 0.002), serum creatinine (Scr) (107.39 ± 57.97 μmol/L vs. 84.70 ± 34.95 μmol/L, P = 0.015), blood urea nitrogen (BUN) (7.36 ± 4.45 mmol/L vs. 5.68 ± 2.14 mmol/L, P = 0.008), and higher S/T scores (92.86% vs. 70.93% and 42.85% vs. 15.12%, respectively, P < 0.05). In the Mfn2-negative group, the mitochondria were punctate and round ridges disappeared, and a lower length-to-width ratio and much higher M/A ratio were observed. Correlation analysis showed that the intensity of Mfn2 was negatively correlated with Scr (r = - 0.232, P = 0.013), 24 h proteinuria (r = - 0.541, P = 0.001), and the degree of podocyte effacement (r = - 0.323, P = 0.001), and positively correlated with eGFR (r = 0.213, P = 0.025). Logistic regression analysis showed that the Mfn2-negative group had a higher risk of severe podocyte effacement (≥ 50%) (OR = 3.061, P = 0.019).

CONCLUSION

Mfn2 was negatively correlated with proteinuria and renal function. A lack of Mfn2 in podocytes indicates severe podocyte injury and a high degree of podocyte effacement.

Association between microscopic hematuria and albuminuria in patients with chronic kidney disease caused by diabetes and hypertension: the Fukuoka Kidney disease Registry Study

BACKGROUND

The association between microscopic hematuria (MH) and albuminuria in patients with chronic kidney disease (CKD) caused by diabetes and hypertension remains unclear.

METHODS

The Fukuoka Kidney disease Registry Study is a Japanese multicenter prospective cohort study of 4476 patients with non-dialysis-dependent CKD. In this cohort, we conducted a cross-sectional study in 994 patients with diabetic nephropathy and hypertensive nephrosclerosis. Patients were divided into three groups according to erythrocyte count in urine sediment [T1: < 5/high power field (HPF); T2: 5-9/HPF; T3: ≥ 10/HPF]. Macroalbuminuria was defined as urinary albumin-creatinine ratio > 300 mg/g. Associations between the degree of MH (T1-T3) and the prevalence of macroalbuminuria were analyzed using logistic regression.

RESULTS

The prevalence of macroalbuminuria was 50.8%, 50.4%, and 67.4% in T1 (n = 725), T2 (n = 226), and T3 (n = 43), respectively. The multivariable-adjusted odds ratios for the presence of macroalbuminuria were 0.95 [95% confidence interval (CI) 0.65-1.39; P = 0.86] and 2.50 (95% CI 1.15-5.47; P = 0.022) for patients in T2 and T3, respectively, compared with patients in T1.

CONCLUSIONS

MH with erythrocytes ≥ 10/HPF was significantly associated with increased prevalence of macroalbuminuria in patients with non-dialysis-dependent CKD caused by diabetes and hypertension.

Molecular profiling of urinary extracellular vesicles in chronic kidney disease and renal fibrosis

Chronic kidney disease (CKD) is a long-term kidney damage caused by gradual loss of essential kidney functions. A global health issue, CKD affects up to 16% of the population worldwide. Symptoms are often not apparent in the early stages, and if left untreated, CKD can progress to end-stage kidney disease (ESKD), also known as kidney failure, when the only possible treatments are dialysis and kidney transplantation. The end point of nearly all forms of CKD is kidney fibrosis, a process of unsuccessful wound-healing of kidney tissue. Detection of kidney fibrosis, therefore, often means detection of CKD. Renal biopsy remains the best test for renal scarring, despite being intrinsically limited by its invasiveness and sampling bias. Urine is a desirable source of fibrosis biomarkers as it can be easily obtained in a non-invasive way and in large volumes. Besides, urine contains biomolecules filtered through the glomeruli, mirroring the pathological state. There is, however, a problem of highly abundant urinary proteins that can mask rare disease biomarkers. Urinary extracellular vesicles (uEVs), which originate from renal cells and carry proteins, nucleic acids, and lipids, are an attractive source of potential rare CKD biomarkers. Their cargo consists of low-abundant proteins but highly concentrated in a nanosize-volume, as well as molecules too large to be filtered from plasma. Combining molecular profiling data (protein and miRNAs) of uEVs, isolated from patients affected by various forms of CKD, this review considers the possible diagnostic and prognostic value of uEVs biomarkers and their potential application in the translation of new experimental antifibrotic therapeutics.

Molecular insight in intrarenal inflammation affecting four main types of cells in nephrons in IgA nephropathy

Immunoglobulin A nephropathy (IgAN) is the most common primary glomerulonephritis and the leading cause of kidney failure in the world. The current widely accepted framework for its pathogenesis is the "multi-hit hypothesis." In this review, we mainly discussed the intrarenal inflammation in IgAN, which is initiated by immune complex deposition with complement molecule activation, by focusing on four main types of cells in nephrons including mesangial cells, endothelial cells, podocytes, and tubular epithelial cells (TECs). Galactose-deficient IgA1 (Gd-IgA1)-containing immune complexes deposit in the mesangium and activate complement molecules and mesangial cells. Activation of mesangial cells by Gd-IgA1 deposition with enhanced cellular proliferation, extracellular matrix (ECM) expansion, and inflammatory response plays a central role in the pathogenesis of IgAN. Regional immune complex deposition and mesangial-endothelial crosstalk result in hyperpermeability of endothelium with loss of endothelial cells and infiltration barrier proteins, and recruitment of inflammatory cells. Podocyte damage is mainly derived from mesangial-podocyte crosstalk, in which tumor necrosis factor-α (TNF-α), transforming growth factor-β (TGF-β), renin-angiotensin-aldosterone system (RAAS), and micro-RNAs are the major players in podocyte apoptosis and disorganization of slit diaphragm (SD) related to proteinuria in patients with IgAN. In addition to filtrated proteins into tubulointerstitium and mesangial-tubular crosstalk involved in the injury of TECs, retinoic acid has been discovered innovatively participating in TEC injury.

How to take advantage of easily available biomarkers in patients with IgA nephropathy: IgA and C3 in serum and kidney biopsies

IgA nephropathy (IgAN) is the most common glomerulonephritis worldwide. It is diagnosed based on clinical and histological features including predominant IgA deposits in kidney biopsy. The multi-hit theory, based on the production of GDIgA1 and anti-GDIgA1 antibodies, and complement activation via alternative and lectin pathways and also a genetic tendency are crucial in the pathogenesis of IgAN. The aim of the present review is to summarize the utility of routine diagnostic tests in IgA nephropathy, such as IgA and C3 in serum and kidney biopsy specimens, for predicting the disease progression. The paper also contains data on new markers used in the diagnosis and prognosis of IgA nephropathy.

The Glomerulus According to the Mesangium

The glomerulus is the functional unit for filtration of blood and formation of primary urine. This intricate structure is composed of the endothelium with its glycocalyx facing the blood, the glomerular basement membrane and the podocytes facing the urinary space of Bowman's capsule. The mesangial cells are the central hub connecting and supporting all these structures. The components as a unit ensure a high permselectivity hindering large plasma proteins from passing into the urine while readily filtering water and small solutes. There has been a long-standing interest and discussion regarding the functional contribution of the different cellular components but the mesangial cells have been somewhat overlooked in this context. The mesangium is situated in close proximity to all other cellular components of the glomerulus and should be considered important in pathophysiological events leading to glomerular disease. This review will highlight the role of the mesangium in both glomerular function and intra-glomerular crosstalk. It also aims to explain the role of the mesangium as a central component involved in disease onset and progression as well as signaling to maintain the functions of other glomerular cells to uphold permselectivity and glomerular health.

Immunological drivers of IgA nephropathy: Exploring the mucosa-kidney link

IgA nephropathy (IgAN) is the most common pattern of primary glomerular disease reported worldwide. Up to 40% of those with IgAN progress to end-stage kidney disease within 20 years of diagnosis, with no currently available disease-specific treatment. This is likely to change rapidly, with evolving insights into the mechanisms driving this disease. IgAN is an immune-complex-mediated disease, and its pathophysiology has been framed by the 'four-hit hypothesis', which necessitates four events to occur for clinically significant disease to develop. However, this hypothesis does not explain the wide variability observed in its presentation or clinical progression. Recently, there has been great interest in exploring the role of the mucosal immune system in IgAN, especially given the well-established link between mucosal infections and disease flares. Knowledge of antigen-mucosal interactions is now being successfully leveraged for therapeutic purposes; the gut-directed drug Nefecon (targeted release formulation-budesonide) is on track to become the first medication to be approved specifically for the treatment of IgAN. In this review, we examine established immunological paradigms in IgAN, explore how antigen-mucosal immune responses drive disease, and discuss how this knowledge is being used to develop new treatments.

Renal diseases and the role of complement: Linking complement to immune effector pathways and therapeutics

The complement system is an ancient and phylogenetically conserved key danger sensing system that is critical for host defense against pathogens. Activation of the complement system is a vital component of innate immunity required for the detection and removal of pathogens. It is also a central orchestrator of adaptive immune responses and a constituent of normal tissue homeostasis. Once complement activation occurs, this system deposits indiscriminately on any cell surface in the vicinity and has the potential to cause unwanted and excessive tissue injury. Deposition of complement components is recognized as a hallmark of a variety of kidney diseases, where it is indeed associated with damage to the self. The provenance and the pathophysiological role(s) played by complement in each kidney disease is not fully understood. However, in recent years there has been a renaissance in the study of complement, with greater appreciation of its intracellular roles as a cell-intrinsic system and its interplay with immune effector pathways. This has been paired with a profusion of novel therapeutic agents antagonizing complement components, including approved inhibitors against complement components (C)1, C3, C5 and C5aR1. A number of clinical trials have investigated the use of these more targeted approaches for the management of kidney diseases. In this review we present and summarize the evidence for the roles of complement in kidney diseases and discuss the available clinical evidence for complement inhibition.

Pathogenesis of IgA Nephropathy: Current Understanding and Implications for Development of Disease-Specific Treatment

IgA nephropathy, initially described in 1968 as a kidney disease with glomerular “intercapillary deposits of IgA-IgG”, has no disease-specific treatment and is a common cause of kidney failure. Clinical observations and laboratory analyses suggest that IgA nephropathy is an autoimmune disease wherein the kidneys are damaged as innocent bystanders due to deposition of IgA1-IgG immune complexes from the circulation. A multi-hit hypothesis for the pathogenesis of IgA nephropathy describes four sequential steps in disease development. Specifically, patients with IgA nephropathy have elevated circulating levels of IgA1 with some O-glycans deficient in galactose (galactose-deficient IgA1) and these IgA1 glycoforms are recognized as autoantigens by unique IgG autoantibodies, resulting in formation of circulating immune complexes, some of which deposit in glomeruli and activate mesangial cells to induce kidney injury. This proposed mechanism is supported by observations that (i) glomerular immunodeposits in patients with IgA nephropathy are enriched for galactose-deficient IgA1 glycoforms and the corresponding IgG autoantibodies; (ii) circulatory levels of galactose-deficient IgA1 and IgG autoantibodies predict disease progression; and (iii) pathogenic potential of galactose-deficient IgA1 and IgG autoantibodies was demonstrated in vivo. Thus, a better understanding of the structure–function of these immunoglobulins as autoantibodies and autoantigens will enable development of disease-specific treatments.

Podocyte-derived microparticles in IgA nephropathy

Microparticles are a general term for different types of cell plasma membrane-originated vesicles that are released into the extracellular environment. The paracrine action of these nano-sized vesicles is crucial for intercellular communications through the transfer of diverse lipids, cytosolic proteins, RNA as well as microRNAs. The progression of different diseases influences the composition, occurrence, and functions of these cell-derived particles. Podocyte injury has been shown to have an important role in the pathophysiology of many glomerular diseases including IgA nephropathy (IgAN). This review would focus on the possible potential of podocyte-derived microparticles detected in urine to be used as a diagnostic tool in IgAN.

Informatics Analysis of Health Indicators and Pathological Manifestations of Foot-Process in Patients with Primary IgA Nephropathy

Objective: This paper focuses on the foot-process in renal biopsies of patients with lgA, and examines their correlation with baseline clinical indicators and pathological manifestations in patients with lgA. Method: A retrospective data of patients who performed renal biopsy proven IgA nephropathy was selected. The patients who reached the agreed standard were grouped based on the degree of foot-process. There were three groups (ABC Groups) (Du, Y. and Huang, C, 2009. The value of proteinuria and foot process fusion in the onset of prognosis of acute kidney disease. Chinese Journal of Integrated Traditional and Western Medicine, 10(1), pp.44-45): group A for patients with no obvious foot-process lesion; group B for patients with segmental foot-process; group C for patients with massive foot-process. The three groups were reviewed in the aspects of baseline clinical indicators and Oxford classification, so as to discover foot-process’ effect on patients with IgA nephropathy. Results: A total of 129 patients with IgA nephropathy were included in the study. Concerning about the clinical baseline indicators related to the degree of foot-process, the 24-hour proteinuria level at admission was statistically significant and positively correlated (r = 0.324, P = 0.000). The comparison between groups showed there was statistically significant difference between group C and group A and group B (P = 0.001, P = 0.035). According to the Oxford Classification, only the differences of mesangial hypercellularity (M) and segmental sclerosis/adhesion (S) were statistically significant (r = 0.239, P = 0.006; r = 0.257, P = 0.003) and were positively correlated. In terms of mesangial hypercellularity (M), the differences between group A and B, group A and C were statistically significant (P = 0.01, P = 0.003). The comparison between group B and group C showed statistical difference (P = −0.031) in segmental sclerosis/adhesion (S). Among the 76 patients with S0 revealed by the Oxford classification, there were 55 patients of glomerulosclerosis, which was positively correlated with the degree of foot process (r = 0.211, P = 0.016). The comparison between group A and group C showed statistical difference (P = 0.014). Conclusion: The severity foot-process was positively correlated with the level of proteinuria. Foot-process is positively related with mesangial hypercellularity, segmental sclerosis and glomerulosclerosis. With more severe the foot-process, there will be more serious mesangial hypercellularity and irreversible glomerular injury. Foot-process is positively correlated with Lee’s Pathological Grading.

Chronic Inflammation in Chronic Kidney Disease Progression: Role of Nrf2

Despite recent advances in the management of chronic kidney disease (CKD), morbidity and mortality rates in these patients remain high. Although pressure-mediated injury is a well-recognized mechanism of disease progression in CKD, emerging data indicate that an intermediate phenotype involving chronic inflammation, oxidative stress, hypoxia, senescence, and mitochondrial dysfunction plays a key role in the etiology, progression, and pathophysiology of CKD. A variety of factors promote chronic inflammation in CKD, including oxidative stress and the adoption of a proinflammatory phenotype by resident kidney cells. Regulation of proinflammatory and anti-inflammatory factors through NF-κB- and nuclear factor, erythroid 2 like 2 (Nrf2)-mediated gene transcription, respectively, plays a critical role in the glomerular and tubular cell response to kidney injury. Chronic inflammation contributes to the decline in glomerular filtration rate (GFR) in CKD. Whereas the role of chronic inflammation in diabetic kidney disease (DKD) has been well-elucidated, there is now substantial evidence indicating unresolved inflammatory processes lead to fibrosis and eventual end-stage kidney disease (ESKD) in several other diseases, such as Alport syndrome, autosomal-dominant polycystic kidney disease (ADPKD), IgA nephropathy (IgAN), and focal segmental glomerulosclerosis (FSGS). In this review, we aim to clarify the mechanisms of chronic inflammation in the pathophysiology and disease progression across the spectrum of kidney diseases, with a focus on Nrf2.

Role of Human Mesangial-Tubular Crosstalk in Secretory IgA-Induced IgA Nephropathy

BACKGROUND

IgA nephropathy (IgAN) is characterized by the mesangial deposition of pathogenic IgA. We previously detected the deposition of pathogenic secretory IgA (SIgA) in the mesangium of about one-third of IgAN patients. Tubulointerstitial injury has an important role in the development of IgAN. However, the relationship between SIgA and tubulointerstitial damage is currently unclear. In this work, the role of the mesangial-tubular crosstalk was explored in the tubulointerstitial damage in SIgA-induced IgAN.

METHODS

SIgA deposition in renal tissues of IgAN patients was detected by immunofluorescence. Flow cytometry was used to assess the binding of SIgA to human renal mesangial cells (HRMC) and human proximal tubule epithelial (HK-2) cells. HK-2 was co-cultured with HRMC added with SIgA isolated from patients or normal volunteers. Protein synthesis and gene expressions of TNF-α, TGF-β1, and MCP-1 were determined by ELISA and PCR, respectively. The expressions of the above cytokines in renal tissues of patients and normal controls were detected by immunohistochemistry.

RESULTS

Twenty-nine of 96 patients had SIgA deposition in the mesangium, but SIgA was rarely detected in the tubulointerstitium. The binding rate of SIgA to HK-2 (2.79%) was significantly lower than that of HRMC (81.6%) (p < 0.001). The expressions of TNF-α, TGF-β1, and MCP-1 in HRMC were significantly higher than in SIgA-stimulated HK-2 (p < 0.05), and their expressions were significantly higher in the SIgA-stimulated co-culture group compared with SIgA-stimulated HRMC (p < 0.05). The expressions of the above cytokines were mainly detected in tubulointerstitium of IgAN patients with positive and negative SIgA deposition, without significant difference between the 2 groups, but to a significantly higher level than that in normal controls, and their expressions positively correlated with tubulointerstitial injury.

CONCLUSION

Inflammatory factors released from the mesangium after SIgA deposition might mediate tubulointerstitial damage via mesangial-tubular crosstalk in IgAN.

Experimental evidence of pathogenic role of IgG autoantibodies in IgA nephropathy

BACKGROUND

IgA nephropathy is thought to be an autoimmune disease wherein galactose-deficient IgA1 (Gd-IgA1) is recognized by IgG autoantibodies, resulting in formation and renal accumulation of nephritogenic immune complexes. Although this hypothesis is supported by recent findings that, in renal immunodeposits of IgA nephropathy patients, IgG is enriched for Gd-IgA1-specific autoantibodies, experimental proof is still lacking.

METHODS

IgG isolated from sera of IgA nephropathy patients or produced as a recombinant IgG (rIgG) was mixed with human Gd-IgA1 to form immune complexes. IgG from healthy individuals served as a control. Nude and SCID mice were injected with human IgG and Gd-IgA1, in immune complexes or individually, and their presence in kidneys was ascertained by immunofluorescence. Pathologic changes in the glomeruli were evaluated by quantitative morphometry and exploratory transcriptomic profiling was performed by RNA-Seq.

RESULTS

Immunodeficient mice injected with Gd-IgA1 mixed with IgG autoantibodies from patients with IgA nephropathy, but not Gd-IgA1 mixed with IgG from healthy individuals, displayed IgA, IgG, and mouse complement C3 glomerular deposits and mesangioproliferative glomerular injury with hematuria and proteinuria. Un-complexed Gd-IgA1 or IgG did not induce pathological changes. Moreover, Gd-IgA1-rIgG immune complexes injected into immunodeficient mice induced histopathological changes characteristic of human disease. Exploratory transcriptome profiling of mouse kidney tissues indicated that these immune complexes altered gene expression of multiple pathways, in concordance with the changes observed in kidney biopsies of patients with IgA nephropathy.

CONCLUSIONS

This study provides the first in vivo evidence for a pathogenic role of IgG autoantibodies specific for Gd-IgA1 in the pathogenesis of IgA nephropathy.

The implications of focal segmental glomerulosclerosis in children with IgA nephropathy

Focal segmental glomerular sclerotic lesions in IgA nephropathy (IgAN), considered for years a chronic histologic feature related to proteinuria in remnant nephrons without any active role in the pathogenesis and progression of glomerular damage of IgAN, have been recently reconsidered. The Oxford classification of IgAN reported it as the "S" score and found it to be an independent risk factor for progression of IgAN. Its prognostic value was confirmed also in children. The identification of some histologic subvariants of the S lesion has produced interesting insights into different pathogenetic mechanisms of glomerular damage in IgAN. Tip lesion and podocyte hypertrophy are considered secondary to active podocytopathy and are correlated with higher levels of proteinuria and a faster decline in glomerular filtration rate. Moreover, endocapillary and mesangial hypercellularity might contribute in children with IgAN to formation and progression of S lesions. Considering the pathophysiology of these processes, children with some S features may benefit not only from nephroprotective measures but also from immunosuppression.

Severity of foot process effacement is associated with proteinuria in patients with IgA nephropathy

Background

Proteinuria is a significant risk factor for progression of IgA nephropathy (IgAN) and has a positive correlation with severity of foot process effacement (FPE). We evaluated the relationship of FPE with proteinuria and histologic characteristics, including the Oxford classification.

Methods

Patients who underwent renal biopsy and were diagnosed with IgAN at a single center were retrospectively reviewed. Patients aged less than 18 years and those with the possibility of secondary causes were excluded from the study. Subsequently, we evaluated the association between degree of proteinuria, severity of FPE, and histologic characteristics, including the Oxford classification and other immunofluorescence stains.

Results

A total of 805 cases of renal biopsy was performed at our institution, and 327 patients were diagnosed with IgAN. Among them, 82 patients were excluded. Severity of FPE had an impact on the degree of proteinuria. Notably, the group with diffuse FPE had more than about 1.3 g/day of urine protein compared to those with rare FPE. Among the histologic characteristics, M1 score and immune deposition of IgG affected severity of FPE (hazard ratios [95% confidence interval], 1.90 [1.10 to 3.26], and 3.77 [1.66 to 8.54], respectively).

Conclusion

Severity of FPE had an impact on the degree of proteinuria and may be associated with the pathogenesis of IgAN.

A Personalized Update on IgA Nephropathy: A New Vision and New Future Challenges

IgA nephropathy (IgAN) is the most common primary glomerulonephritis in the world among patients undergoing renal biopsy. Approximately 30% of patients with IgAN develop end-stage kidney disease 20 years after renal biopsy. It is a glomerulopathy with a very broad clinical presentation, making it difficult to stratify and treat. IgAN is characterized by dysregulation of the immune system, which causes an abnormal synthesis of IgA1 that is deglycosylated causing its mesangial deposition. IgAN pathogenesis is incompletely understood; the current multi-hit hypothesis of IgAN pathogenesis does not explain the range of glomerular inflammation and renal injury associated with mesangial IgA deposition. Although associations between IgAN and glomerular and circulating markers of complement activation are established, the mechanism of complement activation and contribution to glomerular inflammation and injury are not defined. On the other hand, the renal-gut connection can also play an important role in the pathogenesis of IgAN with possible therapeutic implications. In order to standardize the histological findings, the Oxford Classification has allowed clarifying renal lesions that confer potential risk of progression. Currently, except for the blockade of the renin-angiotensin-aldosterone system, no other therapies are available in clinical setting for the treatment of IgAN, although the range of new drugs under investigation is extensive. The incorporation in the next trials of clinical parameters such as the amount of hematuria and histological lesions may allow more personalized therapeutic approaches. To summarize, in recent years, several important efforts have taken place in the understanding of IgAN, but still, further studies are warranted to elucidate the best therapeutic strategies according to the risk to improve the prognosis of this entity.

The Role of Immune Modulation in Pathogenesis of IgA Nephropathy

IgA nephropathy (IgAN) is the most prevalent primary glomerulonephritis worldwide, with diverse clinical manifestations characterized by recurrent gross hematuria or microscopic hematuria, and pathological changes featuring poorly O-galactosylated IgA1 deposition in the glomerular mesangium. Pathogenesis has always been the focus of IgAN studies. After 50 years of research, most scholars agree that IgAN is a group of clinicopathological syndromes with certain common immunopathological characteristics, and multiple mechanisms are involved in its pathogenesis, including immunology, genetics, and environmental or nutritional factors. However, the precise pathogenetic mechanisms have not been fully determined. One hypothesis about the pathogenesis of IgAN suggests that immunological factors are engaged in all aspects of IgAN development and play a critical role. A variety of immune cells (e.g., dendritic cells, NK cells, macrophages, T-lymphocyte subsets, and B-lymphocytes, etc.) and molecules (e.g., IgA receptors, Toll-like receptors, complements, etc.) in innate and adaptive immunity are involved in the pathogenesis of IgAN. Moreover, the abnormality of mucosal immune regulation is the core of IgAN immunopathogenesis. The roles of tonsil immunity or intestinal mucosal immunity, which have received more attention in recent years, are supported by mounting evidence. In this review, we will explore the latest research insights on the role of immune modulation in the pathogenesis of IgAN. With a better understanding of immunopathogenesis of IgAN, emerging therapies will soon become realized.

IgA nephropathy is associated with elevated urinary mitochondrial DNA copy numbers

Mitochondrial injury plays important roles in the pathogenesis of various kidney diseases. However, mitochondrial injury in IgA nephropathy (IgAN) remains largely unexplored. Here, we examined the associations among mitochondrial injury, IgAN, and treatment outcomes. We prospectively enrolled patients with IgAN and age-/sex-matched healthy volunteers (HVs) as controls (n = 31 each). Urinary copy numbers of the mitochondrial DNA (mtDNA) genes cytochrome-c oxidase-3 (COX3) and nicotinamide adenine dinucleotide dehydrogenase subunit-1 (ND1) were measured. Urinary mtDNA levels were elevated in the IgAN group compared with that in HVs (p < 0.001). Urinary ND1 levels were significantly higher in the low proteinuria group than in the high proteinuria group (p = 0.027). Changes in urinary levels of ND1 and COX3 were positively correlated with changes in proteinuria (p = 0.038 and 0.024, respectively) and inversely correlated with changes in the estimated glomerular filtration rate (p = 0.033 and 0.017, respectively) after medical treatment. Mitochondrial injury played important roles in IgAN pathogenesis and may be involved in early-stage glomerular inflammation, prior to pathological changes and increased proteinuria. The correlation between changes in urinary mtDNA and proteinuria suggest that these factors may be promising biomarkers for treatment outcomes in IgAN.

Mesangial C4d deposition at diagnosis in childhood immunoglobulin A nephropathy

BACKGROUND

Immunoglobulin A nephropathy (IgAN) is a major cause of end-stage renal disease. Complement activation via the lectin pathway influences outcomes in IgAN. We examined the association of glomerular C4d deposition with clinicopathological severity at diagnosis and the disappearance of proteinuria in Japanese pediatric IgAN patients.

METHODS

We retrospectively analyzed 25 children newly diagnosed with IgAN at Hokkaido University Hospital. We evaluated glomerular C4d immunofluorescent staining at diagnosis. We compared clinical findings, pathological findings (based on Oxford classification), and the disappearance of proteinuria within 24 months after renal biopsy between C4d-positive and C4d-negative patients.

RESULTS

Glomerular C4d staining was observed in 14 patients (56.0%). C4d-positive patients had significantly higher proteinuria at diagnosis than C4d-negative patients (2.03 g/gCr vs 0.78 g/gCr; P = 0.005). The number of glomeruli with segmental glomerulosclerosis or adhesion (8.0% vs 0.0%; P = 0.046) and the extent of tubular atrophy/interstitial fibrosis (9.46% vs 2.86%; P = 0.031) were significantly increased in C4d-positive patients compared with C4d-negative patients. Further, the proportion of patients with modified T1 (>10%) was significantly higher in the C4d-positive group than the C4d-negative group. There was no significant difference, however, in the disappearance rate of proteinuria at 24 months after renal biopsy between groups (64% vs 82%; P = 0.149).

CONCLUSIONS

Glomerular C4d deposition was associated with clinicopathological severity at diagnosis in Japanese pediatric patients with IgAN. Glomerular C4d deposition, however, was not a predictor of the disappearance of proteinuria within 24 months after diagnosis in Japanese pediatric patients with IgAN.

TGF-β1 inhibits the autophagy of podocytes by activating mTORC1 in IgA nephropathy

IgA nephropathy (IgAN) is a mesangial proliferative glomerulonephritis which often shows proteinuria, an indicator for podocyte damage. TGF-β1 has been known to contribute to podocyte injury by inducing apoptosis, cytoskeleton relocation or cytoskeleton loss. And Decorin, a small proteoglycan known to neutralize TGF-β1, was reported to induce autophagy in vascular endothelial cells. However, it remains unknown how TGF-β1 and Decorin can affect podocyte autophagy in mesangial proliferative glomerulonephritis. In this study, we used in vivo and in vitro models to find out the effect of TGF-β1 and Decorin on podocyte autophagy. P-rpS6 and p-ULK1 were detected by Western blot to show the activation of mTORC1 pathway following TGF-β1 treatment. Also, we collected serum from IgAN patients and anti-Thy1.1 nephritis, and quantified TGF-β1 and Decorin using ELISA. Together, we showed that TGF-β1 could activate mTORC1 and inhibit autophagy, while Decorin has precisely the opposite effect. As the mesangial cells (MCs) proliferate, TGF-β1 increases and Decorin decreases in the serum of IgAN and anti-Thy1.1 nephritis. This finding deepened our understanding regarding how MC proliferation could finally result in podocyte dysfunction.

Relationship between complement deposition and the Oxford classification score and their combined effects on renal outcome in immunoglobulin A nephropathy

Background

Complement activation has been highlighted in immunoglobulin (Ig) A nephropathy pathogenesis. However, whether the complement system can affect the downstream phenotype of IgA nephropathy remains unknown. Herein, we investigated the association of mesangial C3 deposition with the Oxford classification and their joint effects on worsening kidney function.

Methods

We investigated 453 patients with biopsy-proven IgA nephropathy. C3 deposition was defined as an immunofluorescence intensity of C3 ≥2+ within the mesangium. The subjects were classified according to the combination of C3 deposition and Oxford classification lesions. The primary endpoint was a composite of ≥30% decline in the estimated glomerular filtration rate or an increase in proteinuria ≥3.5 g/g during follow-up.

Results

Among the Oxford classification lesions, mesangial hypercellularity (M1), segmental glomerulosclerosis (S1) and tubulointerstitial fibrosis (T1–2) and crescentic lesion significantly correlated with C3 deposition. During a median follow-up of 33.0 months, the primary endpoint occurred more in patients with M1, S1, T1–2 and mesangial C3 deposition than in those without. In individual multivariable-adjusted Cox analyses, the presence of M1, S1, T1–2 and C3 deposition was significantly associated with higher risk of reaching primary endpoint. In the combined analyses of C3 deposition and the Oxford classification lesions, the hazard ratios for the composite outcome were significantly higher in the presence of C3/M1, C3/S1 and C3/crescent than in the presence of each lesion alone.

Conclusions

Complement deposition can strengthen the significance of the Oxford classification, and the presence of both components portends a poorer prognosis in IgA nephropathy.

The role of complement in IgA nephropathy

IgA nephropathy (IgAN) is common and often progresses to end stage renal disease. IgAN encompasses a wide range of histology and clinical features. IgAN pathogenesis is incompletely understood; the current multi-hit hypothesis of IgAN pathogenesis does not explain the range of glomerular inflammation and renal injury associated with mesangial IgA deposition. Although associations between IgAN and glomerular and circulating markers of complement activation are established, the mechanism of complement activation and contribution to glomerular inflammation and injury are not defined. Recent identification of specific complement pathways and proteins in severe IgAN cases had advanced our understanding of complement in IgAN pathogenesis. In particular, a growing body of evidence implicates the complement factor H related proteins 1 and 5 and lectin pathway as pathogenic in a subset of patients with severe disease. These data suggest complement deregulation and activity may be dominant drivers of renal injury in IgAN. Thereby, markers of complement activation may identify IgAN patients likely to progress to significant renal impairment and complement inhibition may emerge as an effective method of preventing and reducing glomerular injury in IgAN.

Role of Mesangial-Podocytic-Tubular Cross-Talk in IgA Nephropathy

IgA nephropathy (IgAN), a common primary glomerulonephritis worldwide, is associated with a substantial risk of progression to end-stage renal failure. The disease runs a highly variable clinical course with frequent involvement of tubulointerstitial damage. A subgroup of IgAN with proximal tubular epithelial cells (PTECs) and tubulointerstitial damage often is associated with rapid progression to end-stage renal failure. Human mesangial cell-derived mediators lead to podocyte and tubulointerstitial injury via mesangial-podocytic-tubular cross-talk. Although mesangial-podocytic communication plays a pathogenic role in podocytic injury, the implication of a podocyte-PTEC cross-talk pathway in the progression of tubulointerstitial injury in IgAN should not be underscored. We review the role of mesangial-podocytic-tubular cross-talk in the progression of IgAN. We discuss how podocytopathy in IgAN promotes subsequent PTEC dysfunction and whether tubulointerstitial injury affects the propagation of podocytic injury in IgAN. A thorough understanding of the cross-talk mechanisms among mesangial cells, podocytes, and PTECs may lead to better design of potential therapeutic options for IgAN.

Approach to the Child with Hematuria

The causes of macroscopic and microscopic hematuria overlap; both are often caused by urinary tract infections or urethral/bladder irritation. Coexistent hypertension and proteinuria should prompt investigation for glomerular disease. The most common glomerulonephritis in children is postinfectious glomerulonephritis. In most patients, and especially with isolated microscopic hematuria, the diagnostic workup reveals no clear underlying cause. In those cases whereby a diagnosis is made, the most common causes of persistent microscopic hematuria are thin basement membrane nephropathy, immunoglobulin A nephropathy, or idiopathic hypercalciuria. Treatment and long-term prognosis varies with the underlying disease.

Podocytopathy in the mesangial proliferative immunoglobulin A nephropathy: new insights into the mechanisms of damage and progression

Immunoglobulin A nephropathy (IgAN) was defined as a mesangiopathic disease, since the primary site of deposition of IgA immune material is the mesangium, and proliferation of mesangial cells and matrix excess deposition are the first histopathologic lesions. However, the relentless silent progression of IgAN is mostly due to the development of persistent proteinuria, and recent studies indicate that a major role is played by previous damage of function and anatomy of podocytes. In IgAN, the podocytopathic changes are the consequence of initial alterations in the mesangial area with accumulation of IgA containing immune material. Podocytes are therefore affected by interactions of messages originally driven from the mesangium. After continuous insult, podocytes detach from the glomerular basement membrane. This podocytopathy favours not only the development of glomerular focal and segmental sclerosis, but also the progressive renal function loss. It is still debated whether these lesions can be prevented or cured by corticosteroid/immunosuppressive treatment. We aimed to review recent data on the mechanisms implicated in the podocytopathy present in IgAN, showing new molecular risk factors for progression of this disease. Moreover, these observations may indicate that the target for new drugs is not only focused on decreasing the activity of mesangial cells and inflammatory reactions in IgAN, but also on improving podocyte function and survival.

Inflammatory Mediators and Renal Fibrosis

Renal inflammation is the initial, healthy response to renal injury. However, prolonged inflammation promotes the fibrosis process, which leads to chronic pathology and eventually end-stage kidney disease. There are two major sources of inflammatory cells: first, bone marrow-derived leukocytes that include neutrophils, macrophages, fibrocytes and mast cells, and second, locally activated kidney cells such as mesangial cells, podocytes, tubular epithelial cells, endothelial cells and fibroblasts. These activated cells produce many profibrotic cytokines and growth factors that cause accumulation and activation of myofibroblasts, and enhance the production of the extracellular matrix. In particular, activated macrophages are key mediators that drive acute inflammation into chronic kidney disease. They produce large amounts of profibrotic factors and modify the microenvironment via a paracrine effect, and they also transdifferentiate to myofibroblasts directly, although the origin of myofibroblasts in the fibrosing kidney remains controversial. Collectively, understanding inflammatory cell functions and mechanisms during renal fibrosis is paramount to improving diagnosis and treatment of chronic kidney disease.

The Xanthine Oxidase Inhibitor Febuxostat Suppresses the Progression of IgA Nephropathy, Possibly via Its Anti-Inflammatory and Anti-Fibrotic Effects in the gddY Mouse Model

Recent clinical studies have demonstrated the protective effect of xanthine oxidase (XO) inhibitors against chronic kidney diseases, although the underlying molecular mechanisms remain unclear. However, to date, neither clinical nor basic research has been carried out to elucidate the efficacy of XO inhibitor administration for IgA nephropathy. We thus investigated whether febuxostat, an XO inhibitor, exerts a protective effect against the development of IgA nephropathy, using gddY mice as an IgA nephropathy rodent model. Eight-week-old gddY mice were provided drinking water with (15 μg/mL) or without febuxostat for nine weeks and then subjected to experimentation. Elevated serum creatinine and degrees of glomerular sclerosis and fibrosis, judged by microscopic observations, were significantly milder in the febuxostat-treated than in the untreated gddY mice, while body weights and serum IgA concentrations did not differ between the two groups. In addition, elevated mRNA levels of inflammatory cytokines such as TNFα, MCP-1, IL-1β, and IL-6, collagen isoforms and chemokines in the gddY mouse kidneys were clearly normalized by the administration of febuxostat. These data suggest a protective effect of XO inhibitors against the development of IgA nephropathy, possibly via suppression of inflammation and its resultant fibrotic changes, without affecting the serum IgA concentration.

Characterization of a novel disease-associated mutation within NPHS1 and its effects on nephrin phosphorylation and signaling

Mutations in the transmembrane protein nephrin (encoded by NPHS1) underlie nearly half of all cases of congenital nephrotic syndrome (CNS), which is caused by aberrations in the blood filtering function of glomerular podocytes. Nephrin directly contributes to the structure of the filtration barrier, and it also serves as a signaling scaffold in podocytes, undergoing tyrosine phosphorylation on its cytoplasmic tail to recruit intracellular effector proteins. Nephrin phosphorylation is lost in several human and experimental models of glomerular disease, and genetic studies have confirmed its importance in maintenance of the filtration barrier. To date, however, the effect of CNS-associated NPHS1 variants on nephrin phosphorylation remains to be determined, which hampers genotype-phenotype correlations. Here, we have characterized a novel nephrin sequence variant, A419T, which is expressed along with C623F in a patient presenting with CNS. Nephrin localization is altered in kidney biopsies, and we further demonstrate reduced surface expression and ER retention of A419T and C623F in cultured cells. Moreover, we show that both mutations impair nephrin tyrosine phosphorylation, and they exert dominant negative effects on wildtype nephrin signaling. Our findings thus reveal that missense mutations in the nephrin extracellular region can impact nephrin signaling, and they uncover a potential pathomechanism to explain the spectrum of clinical severity seen with mild NPHS1 mutations.

Aberrant Glycosylation of the IgA1 Molecule in IgA Nephropathy

IgA nephropathy, the most common primary glomerulonephritis in the world and a frequent cause of end-stage renal disease, is characterized by typical mesangial deposits of IgA1, as described by Berger and Hinglaise in 1968. Since then, it has been discovered that aberrant IgA1 O-glycosylation is involved in disease pathogenesis. Progress in glycomic, genomic, clinical, analytical, and biochemical studies has shown autoimmune features of IgA nephropathy. The autoimmune character of the disease is explained by a multihit pathogenesis model, wherein overproduction of aberrantly glycosylated IgA1, galactose-deficient in some O-glycans, by IgA1-secreting cells leads to increased levels of circulatory galactose-deficient IgA1. These glycoforms induce production of autoantibodies that subsequently bind hinge-region of galactose-deficient IgA1 molecules, resulting in the formation of nephritogenic immune complexes. Some of these complexes deposit in the kidney, activate mesangial cells, and incite glomerular injury. Thus, galactose-deficient IgA1 is central to the disease process. In this article, we review studies concerning IgA1 O-glycosylation that have contributed to the current understanding of the role of IgA1 in the pathogenesis of IgA nephropathy.

The Emerging Role of Pathogenesis of IgA Nephropathy

IgA nephropathy is an autoimmune disease induced by fthe ormation of galactose-deficient IgA1 and anti-glycans autoantibody. A multi-hit hypothesis was promoted to explain full expression of IgA nephropathy. The deposition of immune complex resulted in activation of the complement, increasing oxidative stress, promoting inflammatory cascade, and inducing cell apoptosis via mesangio-podocytic-tubular crosstalk. The interlinked signaling pathways of immune-complex-mediated inflammation can offer a novel target for therapeutic approaches. Treatments of IgA nephropathy are also summarized in our review article. In this article, we provide an overview of the recent basic and clinical studies in cell molecular regulation of IgAN for further treatment interventions.

Higher serum galactose-deficient immunoglobulin A1 concentration is associated with stronger mesangial cellular inflammatory response and more severe histologic findings in immunoglobulin A nephropathy

Background

Galactose-deficient immunoglobulin A1 (Gd-IgA1) is known to play a key role in the pathogenesis of IgA nephropathy (IgAN). We aimed to evaluate whether serum Gd-IgA1 is associated with in vitro activation of mesangial cells in individual patients and how this affects the clinical and histologic parameters.

Methods

Serum samples and clinical and histologic data were collected in the University Hospital Basel and Hammersmith Hospital, London. Serum levels of IgA1 and Gd-IgA1 were measured by enzyme-linked immunosorbent assay (ELISA) and lectin-binding assay using lectin Helix aspersa (HA). Primary human mesangial cells were stimulated with IgA1 isolated from serum from individual patients and the concentrations of monocyte chemoattractant protein-1 and interleukin-6 were measured in cell culture supernatant by ELISA.

Results

Thirty-three patients were enrolled. A significant correlation was observed between serum Gd-IgA1 levels and the concentration of MCP-1 in the culture supernatant in individual patients (Spearman r = 0.5969, P = 0.0002). There was no significant correlation between serum Gd-IgA1 levels and proteinuria or estimated glomerular filtration rate at diagnosis. However, the serum Gd-IgA1 level was significantly higher in patients with segmental glomerulosclerosis (S0 versus S1, P = 0.0245) and tubular atrophy/interstitial fibrosis (T0 versus T1 and T2, P = 0.0336; T0 versus T2, P = 0.0225).

Conclusions

Higher serum Gd-IgA1 concentration is associated with stronger mesangial cell inflammatory response with production of a greater amount of MCP-1 in vitro. This in turn is associated with severe histologic changes. The disease progression with worse renal outcome in patients with higher serum Gd-IgA1 may be therefore mediated by more pronounced mesangial cell inflammatory response leading to more severe histologic changes.

Value of urinary levels of interleukin-6, epidermal growth factor, monocyte chemoattractant protein type1 and transforming growth factor β1 in predicting the extent of fibrosis lesions in kidney biopsies of patients with IgA nephropathy

OBJECTIVE

To analyse the associations between urinary levels of IL-6 EGF, MCP-1 and TGFβ1 and clinical, biochemical and histopathological characteristics in patients with primary IgA nephropathy and their ability to predict the extent of lesions of glomerular and/or interstitial sclerosis.

PATIENTS AND METHODS

A total of 58 patients with IgA nephropathy were studied. We determined the urine levels of IL-6, EGF, MCP-1, and TGFβ1 at the time of diagnosis. The extent of glomerular and interstitial fibrosis was analyzed by quantitative morphometry and kidney biopsies were classified according to the Oxford criteria. We analysed the ability of these molecules to predict the extent of glomerular and interstitial fibrosis lesions.

RESULTS

IL-6, TGFβ1 and MCP-1 were associated with focal glomerulosclerosis and interstitial fibrosis extension but not with the presence of mesangial, extracapillary or endocapillary proliferation. EGF showed a negative association with interstitial fibrosis. By categorising patients according to the Oxford classification, patients with T1 and T2 scores had significantly higher levels of IL-6, MCP-1, TGF-β1 and significantly lower levels of EGF than patients with T0 scores. By multiple regression and logistic regression analyses, the levels of MCP-1, IL-6 and EGF were independent predictors of the fibrosis surface, after adjusting for age and eGFR.

CONCLUSION

The urinary concentration of IL-6, EGF and MCP-1 provides additional information that significantly improves the estimation of the surface of interstitial fibrosis in patients with IgA nephropathy.

New insights into the pathogenesis of IgA nephropathy

IgA nephropathy is the most common form of glomerulonephritis in many parts of the world and remains an important cause of end-stage renal disease. Current evidence suggests that IgA nephropathy is not due to a single pathogenic insult, but rather the result of multiple sequential pathogenic "hits". An abnormally increased level of circulating poorly O-galactosylated IgA1 and the production of O-glycan-specific antibodies leads to the formation of IgA1-containing immune complexes, and their subsequent mesangial deposition results in inflammation and glomerular injury. While this general framework has formed the foundation of our current understanding of the pathogenesis of IgA nephropathy, much work is ongoing to try to precisely define the genetic, epigenetic, immunological, and molecular basis of IgA nephropathy. In particular, the precise origin of poorly O-galactosylated IgA1 and the inciting factors for the production of O-glycan-specific antibodies continue to be intensely evaluated. The mechanisms responsible for mesangial IgA1 deposition and subsequent renal injury also remain incompletely understood. In this review, we summarize the current understanding of the key steps involved in the pathogenesis of IgA nephropathy. It is hoped that further advances in our understanding of this common glomerulonephritis will lead to novel diagnostic and prognostic biomarkers, and targeted therapies to ameliorate disease progression.

Effects of Hydroxychloroquine on Proteinuria in Immunoglobulin A Nephropathy

BACKGROUND

Hydroxychloroquine (HCQ) is a well-known immunomodulator that is useful as in the treatment for lupus because of its inhibitory effect on toll-like receptors and cytokines, which are speculated to play a role in the pathogenesis of Immunoglobulin A (IgA) nephropathy (IgAN). However, there was only one study that investigated the effect of HCQ on proteinuria in patients with IgAN.

METHODS

Ninety patients with IgAN who received HCQ in addition to optimized dosage of renin-angiotensin-aldosterone system inhibitors (RAASi) were recruited for this study, and 90 matched historical controls who received RAASi alone were selected from our registry by the propensity score matching method. Their clinical data were compared at baseline and during follow-up till the termination of HCQ or addition of immunosuppressive agents.

RESULTS

The median baseline proteinuria level of the 90 patients who received HCQ was comparable with the RAASi-alone group (1.5 [1.2, 2.1] vs. 1.5 [1.2, 1.9] g/day, p = 0.74). At 6 months post-study initiation, the median proteinuria level in the HCQ group was lower than that in the RAASi-alone group (0.8 [0.7, 1.2] vs. 1.2 [0.8, 1.8] g/day, p = 0.02). The percentage by which proteinuria was reduced in the HCQ group was significantly higher than that in the RAASi-alone group (-43% [-57, -12] vs. -19% [-46, 17], p = 0.01). No serious adverse effects were documented during treatment with HCQ.

CONCLUSION

The addition of HCQ to RAASi resulted in a significant and safe reduction in proteinuria in patients with IgAN.

TREM-1 Contributes to Inflammation in IgA Nephropathy

Background

Circulating IgA1-containing immune complexes (cIgA1) were shown to play important roles in IgA nephropathy (IgAN). They could induce the release of multiple inflammatory factors, including MCP-1 and IL-6, and elevated urinary inflammatory factors were also reported in patients with IgAN, which suggested that inflammation is a major contributor to kidney injury in IgAN. After the previous identification of the upregulated release of soluble triggering receptor expressed on myeloid cells-1 (sTREM-1) by mesangial cells under cIgA1 challenge using cytokine array, in the present study, we further explored the role of TREM-1, an amplifier of inflammation, in cIgA1-induced kidney injury.

Methods

In total, 35 patients with IgAN and 17 healthy controls were enrolled. The cIgA1 was isolated from plasma and used to treat cultured mesangial cells. The mRNA expression of TREM-1 as well as levels of sTREM-1, MCP-1, and IL-6 in the mesangial cell supernatant and urine samples were detected.

Results

We found that cIgA1 from patients with IgAN could significantly upregulate the expression of TREM-1 in mesangial cells compared to healthy controls. The levels of ΔsTREM-1 were positively correlated with MCP-1 levels in the mesangial supernatant. Similarly, higher urinary levels of sTREM-1 were also observed in patients with IgAN compared to healthy controls. Moreover, IgAN patients with detectable urinary sTREM-1 presented with severe clinical and pathological manifestations, including higher IgA and lower eGFR levels, compared to patients whose urinary sTREM-1 levels were below the limit of quantification.

Conclusion

Our present study suggested that TREM-1 in cIgA1 induced inflammatory kidney injury in IgAN.

Inflammation in IgA nephropathy

Immunoglobulin A nephropathy (IgAN) is the most frequently occurring primary glomerulonephritis in Caucasian and Asian populations. Nonetheless, therapeutic recommendations are based on weak evidence, large controlled trials are scarce and, in particular, the additional value of immunosuppression beyond comprehensive supportive measures is not well-established. The use of immunosuppressants is supported by experimental insights into IgAN pathogenesis that suggest an autoimmune component in disease development. The so-called "multi-hit" theory comprises multiple steps, starting with defective glycosylation of IgA subclass IgA1 that results in overproduction of galactose-deficient IgA1 (Gd-IgA1), occurrence of anti-Gd-IgA1 autoantibodies, and mesangial deposition of nephritogenic immune complexes. This eventually results in an increased mesangial cell proliferation, inflammatory responses, and complement activation. Recent genome-wide association studies have identified several susceptibility genes, many of which support the "multi-hit" concept. In light of these discoveries, it is astonishing that the vast majority of adult IgAN patients obviously do not need and/or benefit from immunosuppressive therapies in the first place. In fact, a number of supportive measures are highly effective in reducing the risk for disease progression in many patients. These measures need to be optimized before immunosuppression should be considered at all. In this review we focus on the underlying pathogenetic cornerstones and the central question of whether systemic inflammation in adult IgAN patients should be treated. Treatment options in children with IgAN are also discussed.

Pathogenic role of glycan-specific IgG antibodies in IgA nephropathy

Background

Accumulating evidences proved the important roles of circulating IgA1-containing immune complexes (cIgA1) in IgA nephropathy (IgAN). Galactose-deficient IgA1 (Gd-IgA1) and glycan-specific IgG antibody have been identified as major components in cIgA1. Before, Gd-IgA1 was reported as a vital factor in IgAN, partly via of its pathogenic role to induce mesangial cells activation. However, we still lack direct evidences to clarify the biological effect of glycan-specific IgG antibody in IgAN.

Methods

In the present study, we enrolled 35 IgAN patients and 17 age- and sex-matched healthy controls. Using uniform aberrant glycosylated IgA1 molecules, and IgG from different individuals, we in vitro prepared IgG-ddIgA1 complexes, and compared the biological differences among these immune complexes regarding their proliferative and inflammatory effects on mesangial cells.

Results

IgG-ddIgA1 complexes from both patients with IgA nephropathy (IgAN-IgG-dd-IgA1) and healthy controls (HC-IgG-dd-IgA1) could induce the proliferation of mesangial cells and up-regulate expression of MCP-1, IL-6 and CXCL1. The levels of mesangial cells proliferation induced by IgAN-IgG-dd-IgA1 were significantly higher than those induced by HC-IgG-dd-IgA1 (1.10 ± 0.05 vs. 1.03 ± 0.03; p < 0.001). However, the levels of secreted MCP-1, IL-6 and CXCL1 from mesangial cells challenged by IgAN-IgG-dd-IgA1 and HC-IgG-dd-IgA1 were comparable.

Conclusions

We found that glycan-specific IgG antibodies derived from patients with IgAN had the biological effect to induce mesangial cells proliferation. Moreover, in the present study we also established a method for in vitro preparation of pathogenic IgG-ddIgA1 complexes, which could be applied in future studies exploring IgAN pathogenesis.

Identification of novel molecular signatures of IgA nephropathy through an integrative -omics analysis

IgA nephropathy (IgAN) is the most prevalent among primary glomerular diseases worldwide. Although our understanding of IgAN has advanced significantly, its underlying biology and potential drug targets are still unexplored. We investigated a combinatorial approach for the analysis of IgAN-relevant -omics data, aiming at identification of novel molecular signatures of the disease. Nine published urinary proteomics datasets were collected and the reported differentially expressed proteins in IgAN vs. healthy controls were integrated into known biological pathways. Proteins participating in these pathways were subjected to multi-step assessment, including investigation of IgAN transcriptomics datasets (Nephroseq database), their reported protein-protein interactions (STRING database), kidney tissue expression (Human Protein Atlas) and literature mining. Through this process, from an initial dataset of 232 proteins significantly associated with IgAN, 20 pathways were predicted, yielding 657 proteins for further analysis. Step-wise evaluation highlighted 20 proteins of possibly high relevance to IgAN and/or kidney disease. Experimental validation of 3 predicted relevant proteins, adenylyl cyclase-associated protein 1 (CAP1), SHC-transforming protein 1 (SHC1) and prolylcarboxypeptidase (PRCP) was performed by immunostaining of human kidney sections. Collectively, this study presents an integrative procedure for -omics data exploitation, giving rise to biologically relevant results.

Clinical usefulness of the Oxford classification in determining immunosuppressive treatment in IgA nephropathy

BACKGROUND

The Oxford classification has been widely used in IgA nephropathy. However, its clinical usefulness of determining immunosuppression is unknown.

AIM

Whether the Oxford classification could predict the development of proteinuria ≥1 g/g Cr and worsening kidney function, as well as the clinical efficacy of corticosteroid treatment according to each histologic variable of the Oxford-MEST.

METHODS

We included 377 patients with early-stage IgA nephropathy. The study endpoints were the development of a heavy proteinuria and a decline renal function.

RESULTS

The results showed that among the Oxford-MEST lesions, only M1 predicted the risk of the development of proteinuria ≥1.0 g/g Cr compared to other lesions in a time-varying Cox model adjusted for multiple confounding factors. In addition, the risk of reaching a 30% decline in eGFR was significantly higher in patients with M1 than in those with M0. Furthermore, patients with M1 had a greater decline of eGFR than patients with M0. However, steroid treatment in M1 lesion was not associated with improving clinical outcomes in the unmatched and propensity score matched cohort.

CONCLUSIONS

This finding may provide a rationale for using the Oxford classification as a guidance to initiate immunosuppression in the early stages of IgA nephropathy. KEY MESSAGES M1 has independently predictive role among the Oxford lesions in IgA nephropathy. Oxford classification should be defined during pathologic approach. Decision of starting immunosuppression according to the Oxford lesions.

Rapamycin Induces Autophagy and Reduces the Apoptosis of Podocytes Under a Stimulated Condition of Immunoglobulin A Nephropathy

Backgroud/Aims: The aim of this study was to investigate the potential renoprotective effect of rapamycin on the autophagy of podocytes treated with the supernatant of mesangial cells cultured with aggregated IgA1 (aIgA1) from immunoglobulin A nephropathy (IgAN) patients.

METHODS

Monomeric IgA1 (mIgA1) was isolated from the serum of IgAN patients or healthy volunteers, and then transformed to aIgA1 by heating. Subsequently, the aIgA1-mesangial cell supernatant was prepared by collecting the medium of mouse mesangial cells (MSC1097) cultured with aIgA1 (100 mg/L) from different IgAN patients or healthy volunteers for 48 h. Subsequently mouse podocytes (MPC5) were exposed to the supernatant of the aIgA1-mesangial cells for 24 h, using 100 mg/L aIgA1 from healthy volunteers as the control group or 100 mg/L aIgA1 from IgAN patients as the IgANs group, in RPMI 1640 medium. The MPC5 cells in the IgANs+Rap group were cultured with rapamycin (10 nmol/L) and the supernatant of MSC-1097 cells cultured with aIgA1 from IgAN patients in RPMI 1640 medium. Autophagy was assessed by western blot analysis (LC3, p62), electron microscopy, and immunofluorescence staining (LC3, p62, and CD63). The apoptosis of podocytes was evaluated by flow cytometry, and the expression of apoptosis-associated proteins cleaved-caspase-3 and caspase-3 were determined by western blot analysis.

RESULTS

Deficient autophagy, which was evident by decreased LC3-II and CD63 levels, caused accumulation of p62, and fewer autophagosomes were observed in the MPC5 cells cultured with the IgAN supernatant, along with stronger expression of cleaved caspase-3 and a higher apoptosis rate. Inhibition of autophagy was alleviated in the IgANs+Rap group. The LC3-II/LC3-I ratio increased by almost 30%, the accumulated p62 amount was reduced by 50%, and the number of autophagosomes per podocyte increased to about 7 times that of the IgAN groups. These results were confirmed by immunofluorescence staining. In addition, the apoptosis rate of MPC5 cells decreased from 19.88% in the IgAN group to 16.78% in the IgANs+Rap group, which was accompanied by a weaker expression level of cleaved caspase-3.

CONCLUSIONS

Rapamycin can reduce the apoptosis of podocytes by inducing autophagy in IgAN.

Proteomic approach for identification of IgA nephropathy-related biomarkers in urine

Proteinuria is often used as a surrogate marker in monitoring and predicting outcome in patients with chronic kidney diseases, but it is non-specific. IgAN belongs to the most common primary glomerulonephritis worldwide with serious prognosis. The main aim of this work was to assess differences in urine proteins in patients with IgA nephropathy and to identify abnormal proteins as potential biomarkers of IgA nephropathy or the renal disease. In our pilot project, we selected 20 patients and compared them with 20 healthy volunteers. Protein quantification was performed using iTRAQ (isobaric tag for relative and absolute quantitation) labeling method. The peptides were separated by the isoelectric focusing method (IEF) and nano-LC with C18 column and identified by mass spectrometry using MALDI-TOF/TOF MS. Proteins´ lists obtained from IEF-LC-MS-MS/MS analysis were combined and contained 201 proteins. It was found out that 113 proteins were common in both experiments. 30 urinary proteins were significantly up- or down-regulated in patients with IgA nephropathy. We characterized potential biomarkers such as alpha-1-antitrypsin, apolipoprotein A-I, CD44 antigen or kininogen. Potential biomarkers of IgAN should be validated in further studies.