The glomerular response to IgA deposition in IgA nephropathy

GALNT14 deficiency: connecting multiple links in the IgA nephropathy pathogenetic chain

IgA nephropathy (IgAN) is a highly prevalent type of primary glomerulonephritis. IgAN involves mesangial deposition of immune complexes leading to complement activation, inflammation, and glomerular injury. A key hit for pathogenesis involves aberrant O-glycosylation in the hinge region of IgA. Despite its prevalence, however, the mechanisms underlying IgAN remain incompletely understood. In this issue of the JCI, Prakash and colleagues used whole-exome sequencing of two IgAN probands to identify loss-of-function variants in GALNT14 leading to loss of the enzyme GalNAc-T14, which is involved in O-glycosylation. The authors then performed a classical bedside-to-bench investigation using a Galnt14-/- mouse model and connected loss of GalNAc-T14 to excess IgA production, impaired B lymphocyte homing, and defective intestinal mucus production. These findings build a more unified understanding of IgAN pathogenesis from defective O-glycosylation with loss-of-function variants in GALNT14.

The rodent models of arteriovenous fistula

Arteriovenous fistulas (AVFs) have long been used as dialysis access in patients with end-stage renal disease; however, their maturation and long-term patency still fall short of clinical needs. Rodent models are irreplaceable to facilitate the study of mechanisms and provide reliable insights into clinical problems. The ideal rodent AVF model recapitulates the major features and pathology of human disease as closely as possible, and pre-induction of the uremic milieu is an important addition to AVF failure studies. Herein, we review different surgical methods used so far to create AVF in rodents, including surgical suturing, needle puncture, and the cuff technique. We also summarize commonly used evaluations after AVF placement. The aim was to provide recent advances and ideas for better selection and induction of rodent AVF models. At the same time, further improvements in the models and a deeper understanding of AVF failure mechanisms are expected.

Immunoglobulin A vasculitis nephritis: Current understanding of pathogenesis and treatment

The clinical spectrum of immunoglobulin A vasculitis nephritis (IgAVN) ranges from the relatively common transitory microscopic hematuria and/or low-grade proteinuria to nephritic or nephrotic syndrome, rapidly progressive glomerulonephritis, or even renal failure. Clinical and experimental studies have shown a multifactor pathogenesis: Infection triggers, impaired glycosylation of IgA1, complement activation, Toll-like-receptor activation and B cell proliferation. This knowledge can identify IgAVN patients at a greater risk for adverse outcome and increase the evidence for treatment recommendations.

Gut-kidney axis in IgA nephropathy: Role on mesangial cell metabolism and inflammation

IgA Nephropathy (IgAN) is the commonest primary glomerular disease around the world and represents a significant cause of end-stage renal disease. IgAN is characterized by mesangial deposition of IgA-immune complexes and mesangial expansion. The pathophysiological process includes an abnormally glycosylated IgA1, which is an antigenic target. Autoantibodies specifically recognize galactose-deficient IgA1 forming immune complexes that are amplified in size by the soluble IgA Fc receptor CD89 leading to deposition in the mesangium through interaction with non-classical IgA receptors. The local production of cytokines promotes local inflammation and complement system activation, besides the stimulation of mesangial proliferation. The spectrum of clinical manifestations is quite variable from asymptomatic microscopic hematuria to rapidly progressive glomerulonephritis. Despite all the advances, the pathophysiology of the disease is still not fully elucidated. The mucosal immune system is quoted to be a factor in triggering IgAN and a "gut-kidney axis" is proposed in its development. Furthermore, many recent studies have demonstrated that food intake interferes directly with disease prognosis. In this review, we will discuss how mucosal immunity, microbiota, and nutritional status could be interfering directly with the activation of intrinsic pathways of the mesangial cells, directly resulting in changes in their function, inflammation and development of IgAN.

Studying Kidney Diseases Using Organoid Models

The prevalence of chronic kidney disease (CKD) is rapidly increasing over the last few decades, owing to the global increase in diabetes, and cardiovascular diseases. Dialysis greatly compromises the life quality of patients, while demand for transplantable kidney cannot be met, underscoring the need to develop novel therapeutic approaches to stop or reverse CKD progression. Our understanding of kidney disease is primarily derived from studies using animal models and cell culture. While cross-species differences made it challenging to fully translate findings from animal models into clinical practice, primary patient cells quickly lose the original phenotypes during in vitro culture. Over the last decade, remarkable achievements have been made for generating 3-dimensional (3D) miniature organs (organoids) by exposing stem cells to culture conditions that mimic the signaling cues required for the development of a particular organ or tissue. 3D kidney organoids have been successfully generated from different types of source cells, including human pluripotent stem cells (hPSCs), adult/fetal renal tissues, and kidney cancer biopsy. Alongside gene editing tools, hPSC-derived kidney organoids are being harnessed to model genetic kidney diseases. In comparison, adult kidney-derived tubuloids and kidney cancer-derived tumoroids are still in their infancy. Herein, we first summarize the currently available kidney organoid models. Next, we discuss recent advances in kidney disease modelling using organoid models. Finally, we consider the major challenges that have hindered the application of kidney organoids in disease modelling and drug evaluation and propose prospective solutions.

Aberrantly Glycosylated IgA1 in IgA Nephropathy: What We Know and What We Don't Know

IgA nephropathy (IgAN), the most common primary glomerular disease worldwide, is characterized by glomerular deposition of IgA1-containing immune complexes. The IgA1 hinge region (HR) has up to six clustered O-glycans consisting of Ser/Thr-linked N-acetylgalactosamine usually with β1,3-linked galactose and variable sialylation. Circulating levels of IgA1 with abnormally O-glycosylated HR, termed galactose-deficient IgA1 (Gd-IgA1), are increased in patients with IgAN. Current evidence suggests that IgAN is induced by multiple sequential pathogenic steps, and production of aberrantly glycosylated IgA1 is considered the initial step. Thus, the mechanisms of biosynthesis of aberrantly glycosylated IgA1 and the involvement of aberrant glycoforms of IgA1 in disease development have been studied. Furthermore, Gd-IgA1 represents an attractive biomarker for IgAN, and its clinical significance is still being evaluated. To elucidate the pathogenesis of IgAN, it is important to deconvolute the biosynthetic origins of Gd-IgA1 and characterize the pathogenic IgA1 HR O-glycoform(s), including the glycan structures and their sites of attachment. These efforts will likely lead to development of new biomarkers. Here, we review the IgA1 HR O-glycosylation in general and the role of aberrantly glycosylated IgA1 in the pathogenesis of IgAN in particular.

Mast Cell Chymase and Kidney Disease

A sizable part (~2%) of the human genome encodes for proteases. They are involved in many physiological processes, such as development, reproduction and inflammation, but also play a role in pathology. Mast cells (MC) contain a variety of MC specific proteases, the expression of which may differ between various MC subtypes. Amongst these proteases, chymase represents up to 25% of the total proteins in the MC and is released from cytoplasmic granules upon activation. Once secreted, it cleaves the targets in the local tissue environment, but may also act in lymph nodes infiltrated by MC, or systemically, when reaching the circulation during an inflammatory response. MC have been recognized as important components in the development of kidney disease. Based on this observation, MC chymase has gained interest following the discovery that it contributes to the angiotensin-converting enzyme's independent generation of angiotensin II, an important inflammatory mediator in the development of kidney disease. Hence, progress regarding its role has been made based on studies using inhibitors but also on mice deficient in MC protease 4 (mMCP-4), the functional murine counterpart of human chymase. In this review, we discuss the role and actions of chymase in kidney disease. While initially believed to contribute to pathogenesis, the accumulated data favor a more subtle view, indicating that chymase may also have beneficial actions.

MicroRNA-146a-deficient mice develop immune complex glomerulonephritis

MicroRNAs (miRNAs) play an important role in the kidneys under physiological and pathological conditions, but their role in immune glomerulonephritis is unclear. miR-146a has been identified as a key player in innate immunity and inflammatory responses, and in the kidney, this miRNA is involved in the response of injured tubular cells. We studied the renal and immune phenotypes of miR-146a^+/+ and miR-146a^−/− mice at 12 months of age, and the results showed that miR-146a^−/− mice developed autoimmunity during aging, as demonstrated by circulating antibodies targeting double-stranded DNA and an immune complex-mediated glomerulonephritis associated with a mild renal immune infiltrate. In addition, miR-146a^−/− mice showed reduced expression of the transmembrane protein Kim1/Tim1, a key regulator of regulatory B cell (Breg) homeostasis, in the kidney and the immune cells. The numbers of memory B cells and plasmablasts were increased in miR-146a^−/− mice compared with the numbers in wild-type mice, whereas Bregs were decreased in number and displayed an altered capacity to produce IL-10. Finally, we showed that miR-146a^−/− mice develop an autoimmune syndrome with increasing age, and this syndrome includes immune complex glomerulonephritis, which might be due to altered B cell responses associated with Kim1/Tim1 deficiency. This study unravels a link between miR-146a and Kim1 and identifies miR-146a as a significant player in immune-mediated glomerulonephritis pathogenesis.

A non-invasive diagnostic model of immunoglobulin A nephropathy and serological markers for evaluating disease severity

BACKGROUND

Immunoglobulin A nephropathy (IgAN) is the most common pathological type of glomerular disease. Kidney biopsy, the gold standard for IgAN diagnosis, has not been routinely applied in hospitals worldwide due to its invasion nature. Thus, we aim to establish a non-invasive diagnostic model and determine markers to evaluate disease severity by analyzing the serological parameters and pathological stages of patients with IgAN.

METHODS

A total of 272 biopsy-diagnosed IgAN inpatients and 518 non-IgA nephropathy inpatients from the Department of Nephrology of Chinese People's Liberation Army General Hospital were recruited for this study. Routine blood examination, blood coagulation testing, immunoglobulin-complement testing, and clinical biochemistry testing were conducted and pathological stages were analyzed according to Lee grading system. The serological parameters and pathological stages were analyzed. The receiver operating characteristic (ROC) analysis was performed to estimate the diagnostic value of the clinical factors. Logistic regression was used to establish the diagnostic model.

RESULTS

There were 15 significantly different serological parameters between the IgAN and non-IgAN groups (all P < 0.05). The ROC analysis was performed to measure the diagnostic value for IgAN of these parameters and the results showed that the area under the ROC curve (AUC) of total protein (TP), total cholesterol (TC), fibrinogen (FIB), D-dimer (D2), immunoglobulin A (IgA), and immunoglobulin G (IgG) were more than 0.70. The AUC of the "TC + FIB + D2 + IgA + age" combination was 0.86, with a sensitivity of 85.98% and a specificity of 73.85%. Pathological grades of I, II, III, IV, and V accounted for 2.21%, 17.65%, 62.50%, 11.76%, and 5.88%, respectively, with grade III being the most prevalent. The levels of urea nitrogen (UN) (13.57 ± 5.95 vs. 6.06 ± 3.63, 5.92 ± 2.97, 5.41 ± 1.73, and 8.41 ± 3.72 mmol/L, respectively) and creatinine (Cr) (292.19 ± 162.21 vs. 80.42 ± 24.75, 103.79 ± 72.72, 96.41 ± 33.79, and 163.04 ± 47.51 μmol/L, respectively) were significantly higher in grade V than in the other grades, and the levels of TP (64.45 ± 7.56, 67.16 ± 6.94, 63.22 ± 8.56, and 61.41 ± 10.86 vs. 37.47 ± 5.6 mg/d, respectively), direct bilirubin (DB) (2.34 ± 1.23, 2.58 ± 1.40, 1.91 ± 0.97, and 1.81 ± 1.44 vs. 0.74 ± 0.57 μmol/L, respectively), and IgA (310.35 ± 103.78, 318.48 ± 107.54, 292.58 ± 81.85, and 323.29 ± 181.67 vs. 227.17 ± 68.12 g/L, respectively) were significantly increased in grades II-V compared with grade I (all P < 0.05).

CONCLUSIONS

The established diagnostic model that combined multiple factors (TC, FIB, D2, IgA, and age) might be used for IgAN non-invasive diagnosis. TP, DB, IgA, Cr, and UN have the potential to be used to evaluate IgAN disease severity.

Recent advances in the physiopathology of IgA nephropathy

Immunoglobulin A nephropathy or Berger's disease is the most common type of primary glomerulonephritis, which is characterized by IgA1-containing immune-deposits in the glomerular mesangium. Microscopic haematuria and proteinuria are the most common presentations. Mesangial cell proliferation with IgA deposition is found on renal biopsy. Mechanims of the disease implicate at least four key molecules have been implicated in immune complex formation: galactose-deficient IgA1, autoantibodies anti-galactose-deficient-IgA1, soluble CD89 (Fc receptor for IgA) and the CD71 mesangial IgA receptor (transferrin receptor). These factors associated with environmental factors (antigens, food and microbiota) are correlated with disease progression and recurrence after transplantation. This review exploits recent data on the role of these molecular players of the disease, which may improve future therapeutic management of immunoglobulin A nephropathy.

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.

Kidney disease models: tools to identify mechanisms and potential therapeutic targets

Acute kidney injury (AKI) and chronic kidney disease (CKD) are worldwide public health problems affecting millions of people and have rapidly increased in prevalence in recent years. Due to the multiple causes of renal failure, many animal models have been developed to advance our understanding of human nephropathy. Among these experimental models, rodents have been extensively used to enable mechanistic understanding of kidney disease induction and progression, as well as to identify potential targets for therapy. In this review, we discuss AKI models induced by surgical operation and drugs or toxins, as well as a variety of CKD models (mainly genetically modified mouse models). Results from recent and ongoing clinical trials and conceptual advances derived from animal models are also explored.

The relationship between red cell distribution width and the risk of Henoch-Schönlein purpura nephritis

INTRODUCTION

Red blood cell distribution width (RDW) is elevated in various inflammatory diseases, but its clinical significance in Henoch-Schönlein purpura nephritis (HSPN) in unknown. The aim of this study was to determine the value of RDW as a risk factor or marker for HSPN in children.

METHODS

This was a case-control study of 105 Henoch-Schönlein purpura (HSP) patients, 120 HSPN patients and 192 healthy controls. The relationship between RDW-coefficient of variation (RDW-CV) and the clinical characteristics of HSPN patients was determined by a multiple logistic regression analysis (MVLRA). Receiver operating characteristic (ROC) curves were applied to compare the diagnostic potential of the RDW-CV, a panel of routine markers and combinations of these indices.

RESULTS

The RDW-CV values were significantly higher in the HSPN group than the HSP group and controls (P < 0.001). Significant correlations were found between RDW-CV and ESR (P = 0.001). A combination of RDW-CV and ESR in a ROC curve showed 80% sensitivity and 84.9% specificity in the HSP patients, and 85.8% sensitivity and 93.8% specificity in the HSPN patients. The MVLRA revealed that RDW-CV (OR 1.69, 95% CI 1.16-2.48, P = 0.007) was an independent predictor of HSPN.

CONCLUSIONS

The RDW levels were highest in the HPSN group, suggesting that RDW, especially the combination of RDW and ESR, may have value when assessing the risk of HSPN.

Effect of Immunosuppressive Drugs on the Changes of Serum Galactose-Deficient IgA1 in Patients with IgA Nephropathy

Galactose-deficient IgA1 (Gd-IgA1) and IgA-IgG complexes are known to play an important role in the pathogenesis of IgA nephropathy (IgAN). We aimed therefore to determine the impact of immunosuppression on the serum levels of Gd-IgA1, total IgA1 and IgA-IgG complexes in IgAN patients. In a retrospective study, serum samples from IgAN patients collected before transplantation (t0) and at 3- and 6-month posttransplant (t3 & t6) were used to measure the levels of Gd-IgA1, total IgA1 and IgA-IgG complexes. The area under the curves (AUC) of immunosuppressants was calculated by the plot of plasma trough level or dosage of each immunosuppressant versus time and was interpreted as the extent of drug exposure. Thirty-six out of 64 IgAN patients, who underwent kidney transplantation between 2005 and 2012, were enrolled. From t0 to t3, serum Gd-IgA1 and total IgA1 decreased significantly (24.7 AU (18.6-36.1) to 17.2 (13.1-29.5) (p<0.0001); 4.1 mg/ml (3.6-5.1) to 3.4 (3.0-4.1) (p = 0.0005)), whereas IgA-IgG complexes remained similar. From t3 to t6, Gd-IgA1 and IgA-IgG complexes significantly increased (17.2 AU (13.1-29.5) to 23.9 (16.8-32.0) (p = 0.0143); OD 0.16 (0.06-0.31) to 0.26 (0.14-0.35) (p = 0.0242)), while total IgA1 remained similar. According to median regression analysis, AUC of prednisone t0-6 was significantly associated with the decrease of Gd-IgA1 t0-6 (P = 0.01) and IgA1 t0-6 (p = 0.002), whereas AUC of tacrolimus t0-6 was associated with the decrease of IgA1 t0-6 (p = 0.02). AUC of prednisone t0-3 was associated with the decrease of IgA-IgG complexes t0-3 (p = 0.0036). The association of AUC prednisone t0-6 with Gd-IgA1 t0-6 remained highly significant after adjustment for other immunosuppressants (p = 0.0036). Serum levels of Gd-IgA1, total IgA1 and IgA-IgG in patients with IgAN vary according to the changing degrees of immunosuppression. The exposure to prednisone most clearly influenced the serum levels of Gd-IgA1.

Why, when and how should immunosuppressive therapy considered in patients with immunoglobulin A nephropathy?

IgA nephropathy (IgAN) is the most common primary glomerulonephritis worldwide. Lifelong mesangial deposition of IgA1 complexes subsist inflammation and nephron loss, but the complex pathogenesis in detail remains unclear. In regard to the heterogeneous course, classical immunosuppressive and specific therapeutic regimens adapted to the loss of renal function will here be discussed in addition to the essential common renal supportive therapy. Renal supportive therapy alleviates secondary, surrogate effects or sequelae on renal function and proteinuria of high intraglomerular pressure and subsequent nephrosclerosis by inhibition of the renin angiotensin system (RAASB). In patients with physiological (ΔGFR < 1·5 ml/min/year) or mild (ΔGFR 1·5-5 ml/min/year) decrease of renal function and proteinuric forms (> 1 g/day after RAASB), corticosteroids have shown a reduction of proteinuria and might protect further loss of renal function. In patients with progressive loss of renal function (ΔGFR > 3 ml/min within 3 months) or a rapidly progressive course with or without crescents in renal biopsy, cyclophosphamide with high-dose corticosteroids as induction therapy and azathioprine maintenance has proved effective in one randomized controlled study of a homogeneous cohort in loss of renal function (ΔGFR). Mycophenolic acid provided further maintenance in non-randomized trials. Differentiated, precise, larger, randomized, placebo-controlled studies focused on the loss of renal function in the heterogeneous forms of IgAN are still lacking. Prospectively, fewer toxic agents will be necessary in the treatment of IgAN.

Immunoglobulin A nephropathy: a pathophysiology view

BACKGROUND AND AIM

IgA nephropathy is one of the leading causes of primary glomerulonephritis worldwide and an important etiology of renal disease in young adults. IgA nephropathy is considered an immune complex-mediated disease.

METHODS

This review article summarizes recent evidence on the pathophysiology of IgA nephropathy.

RESULTS

Current studies indicate an ordered sequence of multi-hits as fundamental to disease occurrence. Altered glycan structures in the hinge region of the heavy chains of IgA1 molecules act as auto-antigens, potentially triggering the production of glycan-specific autoantibodies. Recognition of novel epitopes by IgA and IgG antibodies leads to the formation of immune complexes galactose deficient-IgA1/anti-glycan IgG or IgA. Immune complexes of IgA combined with FcαRI/CD89 have also been implicated in disease exacerbation. These nephritogenic immune complexes are formed in the circulation and deposited in renal mesangium. Deposited immune complexes ultimately induce glomerular injury, through the release of pro-inflammatory cytokines, secretion of chemokines and the resultant migration of macrophages into the kidney. The TfR1/CD71 receptor has a pivotal role in mesangial cells. New signaling intracellular mechanisms have also been described.

CONCLUSION

The knowledge of the whole pathophysiology of this disease could provide the rational bases for developing novel approaches for diagnosis, for monitoring disease activity, and for disease-specific treatment.

Urinary myeloid IgA Fc alpha receptor (CD89) and transglutaminase-2 as new biomarkers for active IgA nephropathy and henoch-Schönlein purpura nephritis

BACKGROUND

IgA nephropathy (IgAN) and Henoch-Schönlein purpura nephritis (HSPN) are glomerular diseases that share a common and central pathogenic mechanism. The formation of immune complexes containing IgA1, myeloid IgA Fc alpha receptor (FcαRI/CD89) and transglutaminase-2 (TG2) is observed in both conditions. Therefore, urinary CD89 and TG2 could be potential biomarkers to identify active IgAN/HSPN.

METHODS

In this multicenter study, 160 patients with IgAN or HSPN were enrolled. Urinary concentrations of CD89 and TG2, as well as some other biochemical parameters, were measured.

RESULTS

Urinary CD89 and TG2 were lower in patients with active IgAN/HSPN compared to IgAN/HSPN patients in complete remission (P < 0.001). The CD89xTG2 formula had a high ability to discriminate active from inactive IgAN/HSPN in both situations: CD89xTG2/proteinuria ratio (AUC: 0.84, P < 0.001, sensitivity: 76%, specificity: 74%) and CD89xTG2/urinary creatinine ratio (AUC: 0.82, P < 0.001, sensitivity: 75%, specificity: 74%). Significant correlations between urinary CD89 and TG2 (r = 0.711, P < 0.001), proteinuria and urinary CD89 (r = - 0.585, P < 0.001), and proteinuria and urinary TG2 (r = - 0.620, P < 0.001) were observed.

CONCLUSIONS

Determination of CD89 and TG2 in urine samples can be useful to identify patients with active IgAN/HSPN.

IgA nephropathy

Globally, IgA nephropathy (IgAN) is the most common primary glomerulonephritis that can progress to renal failure. The exact pathogenesis of IgAN is not well defined, but current biochemical and genetic data implicate overproduction of aberrantly glycosylated IgA1. These aberrant immunoglobulins are characterized by galactose deficiency of some hinge-region O-linked glycans. However, aberrant glycosylation alone is insufficient to induce renal injury: the participation of glycan-specific IgA and IgG autoantibodies that recognize the undergalactosylated IgA1 molecule is required. Glomerular deposits of immune complexes containing undergalactosylated IgA1 activate mesangial cells, leading to the local overproduction of cytokines, chemokines and complement. Emerging data indicate that mesangial-derived mediators that are released following mesangial deposition of IgA1 lead to podocyte and tubulointerstitial injury via humoral crosstalk. Patients can present with a range of signs and symptoms, from asymptomatic microscopic haematuria to macroscopic haematuria. The clinical progression varies, with 30-40% of patients reaching end-stage renal disease 20-30 years after the first clinical presentation. Currently, no IgAN-specific therapies are available and patients are managed with the aim of controlling blood pressure and maintaining renal function. However, new therapeutic approaches are being developed, building upon our ever-improving understanding of disease pathogenesis.

A computational model of flow and species transport in the mesangium

A variety of macromolecules accumulate in the glomerular mesangium in many different diseases, but the physics of the transport of these molecules within the mesangial matrix has not been extensively studied. We present a computational model of convection and diffusion within the porous mesangial matrix and apply this model to the specific instance of immunoglobulin A (IgA) transport in IgA nephropathy. We examine the influence of physiological factors including glomerular basement membrane (GBM) thickness and mesangial matrix density on the total accumulation of IgA. Our results suggest that IgA accumulation can be understood by relating convection and diffusion, thus demonstrating the importance of intrinsic glomerular factors.

Update on immunoglobulin A nephropathy, Part I: Pathophysiology

Immunoglobulin A (IgA) nephropathy is one of the most common glomerulonephritis and its frequency is probably underestimated because in most patients the disease has an indolent course and the kidney biopsy is essential for the diagnosis. In the last years its pathogenesis has been better identified even if still now several questions remain to be answered. The genetic wide association studies have allowed to identifying the relevance of genetics and several putative genes have been identified. The genetics has also allowed explaining why some ancestral groups are affected with higher frequency. To date is clear that IgA nephropathy is related to auto antibodies against immunoglobulin A1 (IgA1) with poor O-glycosylation. The role of mucosal infections is confirmed, but which are the pathogens involved and which is the role of Toll-like receptor polymorphism is less clear. Similarly to date whether the disease is due to the circulating immunocomplexes deposition on the mesangium or whether the antigen is already present on the mesangial cell as a "lanthanic" deposition remains to be clarified. Finally also the link between the mesangial and the podocyte injury and the tubulointerstitial scarring, as well as the mechanisms involved need to be better clarified.

miR-744 enhances type I interferon signaling pathway by targeting PTP1B in primary human renal mesangial cells

Renal mesangial cells (RMCs) constitute a population of cells in glomerular mesangium. Inflammatory cytokines produced by RMCs play a vital role in renal inflammation. miRNAs are key regulators of inflammatory cytokine expression. The abnormal expression of renal miRNAs and the consequent changes in inflammatory signal transduction are closely associated with renal inflammation. However, our knowledge of the functions of renal miRNAs is still limited. In this study, we investigated the role of miR-744 in type I interferon (IFN) signaling pathway in primary human RMCs. We show that overexpression of miR-744 enhances IFN-induced CCL2, CCL5, CXCL10, and IL6 expression specifically in RMCs. We found that the activation of TYK2, STAT1 and STAT3 was significantly enhanced by miR-744. miR-744 also enhanced the activation of non-classical signal components, such as ERK and p38. We then identified PTP1B, a ubiquitously expressed phosphatase, as the target of miR-744 that is responsible for enhancing type I IFN response. Finally, miR-744 expression was induced by type I IFN in RMCs. Collectively, our data indicate that by targeting PTP1B, miR-744 plays a feed-forward role in regulating type I IFN signaling pathway. These findings give us new insights into the functions of renal miRNAs in regulating important signaling pathways.

Diagnosis and monitoring of IgA nephropathy: the role of biomarkers as an alternative to renal biopsy

IgA nephropathy (IgAN) is the most prevalent form of chronic glomerulonephritis in the world. The underlying pathogenesis of this autoimmune disease comprises the formation of immune complexes, including glycan-specific IgA1 or IgG antibodies and an aberrant glycosylation of IgA1. Until now, anatomopathological analysis of renal biopsies is essential for the diagnosis of IgAN and different histological classification systems have been proposed, e.g. the Oxford classification. However, a percutaneous renal biopsy is frequently not performed for several reasons and the Oxford classification system has some limitations. Since the poor prognosis of IgAN patients is partly the result of a delayed diagnosis, there is an urgent need for reliable noninvasive biomarkers that might be applicable in routine clinical practice. This article reviews the advances on the understanding of the underlying pathophysiological mechanisms of IgAN and discusses in depth the recent development of new biomarkers, including the use of proteomics and microRNAs.

Henoch-Schönlein purpura nephritis in children: incidence, pathogenesis and management

BACKGROUND

Henoch-Schönlein purpura (HSP) is one of the most common vasculitides in children. It is manifested by skin purpura, arthritis, abdominal pain, renal involvement, etc. Typically, HSP is considered to be self-limiting, although renal involvement (HSP purpura nephritis, HSPN) is the principal cause of morbidity from this disease. For this reason, it is important to clarify the mechanism of onset and clinical manifestations of HSPN and to ascertain the most appropriate treatment for HSPN. In this article, we review the updated pathophysiology and treatment strategies for HSPN.

DATA SOURCES

We searched databases including PubMed, Elsevier and Wanfang for the following key words: Henoch-Schönlein purpura, nephritis, mechanism and treatment, and we selected those publications written in English that we judged to be relevant to the topic of this review.

RESULTS

Based on the data present in the literature, we reviewed the following topics: 1) the possible pathogenesis of HSPN: several studies suggest that immunoglobulin A immune complexes deposit in the mesangium and induce renal injury; 2) multiple-drug treatment for HSPN: although there have been few evidence-based treatment strategies for HSPN, several studies have suggested that immunosuppressive drugs and multiple drug combination therapy were effective in ameliorating proteinuria and histological severity.

CONCLUSIONS

HSPN is a severe disease of childhood. To better understand this disease, detailed investigations into the pathogenesis of HSPN and prospective randomized controlled treatment studies on children with severe HSPN are needed.

Henoch-Schönlein purpura nephritis in childhood: pathogenesis, prognostic factors and treatment

Henoch-Schönlein purpura (HSP) is a systemic disorder characterized by leukocytoclastic vasculitis involving the capillaries and the deposition of IgA immune complexes. Renal involvement is the principal cause of morbidity and mortality in children with HSP. Thus, it is important to clarify the onset mechanism as well as the prognostic factors of Henoch-Schönlein purpura nephritis (HSPN) and to identify the most appropriate treatment. We herein review the pathogenesis, the prognostic factors and treatment of HSPN. As to the pathogenesis, several studies suggest that galactose-deficient IgA1 (Gd-IgA1) is recognized by anti-glycan antibodies, leading to the formation of circulating immune complexes and their mesangial deposition, thereby inducing renal injury. With regard to the prognostic factors, a number of factors have been suggested including nephrotic syndrome, decreased factor XIII activity, hypertension, severe renal injury, high renal accumulation of activated macrophage, alpha-smooth muscle actin, and high serum myeloid-related protein levels. For the treatment of severe HSPN, aggressive therapies including multiple drug combination therapy and plasmapheresis have been shown to be effective in ameliorating proteinuria and histological severity. Nevertheless, detailed investigation into the pathogenesis of HSPN and double-blind randomized control studies on children with HSPN are still necessary.

New insights into the pathogenesis of IgA nephropathy

IgA nephropathy (IgAN) is the most common diagnosis amongst primary glomerular diseases in most countries where renal biopsies are regularly performed. Only a fraction of these patients is at high risk of losing glomerular filtration rate (GFR) in particular those with high grade proteinuria, uncontrolled hypertension or already impaired GFR at diagnosis, and those with renal scars in the renal biopsy. Genetic modifiers of IgAN onset and/or course are emerging. Spontaneous animal models of IgAN are problematic given considerable species differences between the rodent and human IgA system. However, new transgenic models help to better understand the pathogenesis. A key pathogenetic role appears to be played by underglycated IgA1 as well as autoantibodies to these IgA glycoforms and IgA receptors such as CD89 and transferrin receptor 1. Once IgA and/or IgA-containing immune complexes are deposited or formed in the mesangium, secondary effector mechanisms become important including complement activation, release of mesangial growth factors (in particular platelet-derived growth factor), and finally non-IgAN-specific events that culminate in glomerular and subsequently renal tubulointerstitial scaring. Here, we review these processes and describe potential novel therapeutic targets in IgAN.

Potential of immunoglobulin A to prevent allergic asthma

Allergic asthma is characterized by bronchial hyperresponsiveness, a defective barrier function, and eosinophilic lower airway inflammation in response to allergens. The inflammation is dominated by Th2 cells and IgE molecules and supplemented with Th17 cells in severe asthma. In contrast, in healthy individuals, allergen-specific IgA and IgG4 molecules are found but no IgE, and their T cells fail to proliferate in response to allergens, probably because of the development of regulatory processes that actively suppress responses to allergens. The presence of allergen-specific secretory IgA has drawn little attention so far, although a few epidemiological studies point at a reverse association between IgA levels and the incidence of allergic airway disease. This review highlights the latest literature on the role of mucosal IgA in protection against allergic airway disease, the mechanisms described to induce secretory IgA, and the role of (mucosal) dendritic cells in this process. Finally, we discuss how this information can be used to translate into the development of new therapies for allergic diseases based on, or supplemented with, IgA boosting strategies.

Association of noninvasively measured renal protein biomarkers with histologic features of lupus nephritis

OBJECTIVE

To investigate the relationship of urinary biomarkers and established measures of renal function to histologic findings in lupus nephritis (LN), and to test whether certain combinations of the above-mentioned laboratory measures are diagnostic for specific histologic features of LN.

METHODS

Urine samples from 76 patients were collected within 2 months of kidney biopsy and assayed for the urinary biomarkers lipocalin-like prostaglandin D synthase (L-PGDS), α(1) -acid glycoprotein (AAG), transferrin (TF), ceruloplasmin (CP), neutrophil gelatinase-associated lipocalin (NGAL), and monocyte chemotactic protein 1 (MCP-1). Using nonparametric analyses, levels of urinary biomarkers and established markers of renal function were compared with histologic features seen in LN, i.e., mesangial expansion, capillary proliferation, crescent formation, necrosis, wire loops, fibrosis, tubular atrophy, and epimembranous deposits. The area under the receiver operating characteristic curve (AUC) was calculated to predict LN activity, chronicity, or membranous LN.

RESULTS

There was a differential increase in levels of urinary biomarkers that formed a pattern reflective of specific histologic features seen in active LN. The combination of MCP-1, AAG, and CP levels plus protein:creatinine ratio was excellent in predicting LN activity (AUC 0.85). NGAL together with creatinine clearance plus MCP-1 was an excellent diagnostic test for LN chronicity (AUC 0.83), and the combination of MCP-1, AAG, TF, and creatinine clearance plus C4 was a good diagnostic test for membranous LN (AUC 0.75).

CONCLUSION

Specific urinary biomarkers are associated with specific tissue changes observed in conjunction with LN activity and chronicity. Especially in combination with select established markers of renal function, urinary biomarkers are well-suited for use in noninvasive measurement of LN activity, LN chronicity, and the presence of membranous LN.

IgA nephropathy: molecular mechanisms of the disease

Studies of molecular and cellular interactions involved in the pathogenesis of IgA nephropathy have revealed the autoimmune nature of this most common primary glomerulonephritis. In patients with this disease, altered glycan structures in the unique hinge region of the heavy chains of IgA1 molecules lead to the exposure of antigenic determinants, which are recognized by naturally occurring antiglycan antibodies of the IgG and/or IgA1 isotype. As a result, nephritogenic immune complexes form in the circulation and deposit in the glomerular mesangium. Deposited immune complexes induce proliferation of resident mesangial cells, increased production of extracellular matrix proteins and cytokines, and ultimately loss of glomerular function. Structural elucidation of the nature of these immune complexes and their biological activity should provide a rational basis for an effective, immunologically mediated inhibition of the formation of nephritogenic immune complexes that could be used as a disease-specific therapeutic approach.

Spleen tyrosine kinase is important in the production of proinflammatory cytokines and cell proliferation in human mesangial cells following stimulation with IgA1 isolated from IgA nephropathy patients

IgA immune complexes are capable of inducing human mesangial cell (HMC) activation, resulting in release of proinflammatory and profibrogenic mediators. The subsequent inflammation, cellular proliferation, and synthesis of extracellular matrix lead to the progression of IgA nephropathy (IgAN). Spleen tyrosine kinase (SYK) is an intracellular protein tyrosine kinase involved in cell signaling downstream of immunoreceptors. In this study, we determined whether SYK is involved in the downstream signaling of IgA1 stimulation in HMC, leading to production of proinflammatory cytokines/chemokines and cell proliferation. Incubation of HMC with IgA1 purified from IgAN patients significantly increased the synthesis of MCP-1 in a dose-dependent manner. There was also significantly increased production of IL-6, IL-8, IFN-γ-inducible protein-10, RANTES, and platelet-derived growth factor-BB. Stimulation of HMC with heat-aggregated IgA1 purified from IgAN patients induced significantly increased HMC proliferation. Both pharmacological inhibition of SYK and knockdown of SYK by small interfering RNA significantly reduced the synthesis of these mediators and inhibited HMC proliferation. Moreover, positive immunostaining for total and phospho-SYK in glomeruli of kidney biopsies from IgAN patients strongly suggests the involvement of SYK in the pathogenesis of IgAN. To our knowledge, we demonstrate, for the first time, the involvement of SYK in the downstream signaling of IgA1 stimulation in HMC and in the pathogenesis of IgAN. Hence, SYK represents a potential therapeutic target for IgAN.

Pathogenesis of IgA nephropathy

Since its first description in 1968, IgA nephropathy has remained the most common form of idiopathic glomerulonephritis leading to chronic kidney disease in developed countries. The exact pathogenesis of IgA nephropathy is still not well defined. Current data implicate an important genetic factor, especially in promoting the overproduction of an aberrant form of IgA1. The immunochemical aberrancy of IgA nephropathy is characterized by the undergalactosylation of O-glycans in the hinge region of IgA1. However, such aberrant glycosylation alone does not cause renal injury. The next stage of disease development requires the formation of glycan-specific IgG and IgA antibodies that recognize the undergalactosylated IgA1 molecule. These antibodies often have reactivity against antigens from extrinsic microorganisms and might arise from recurrent mucosal infection. B cells that respond to mucosal infections, particularly tonsillitis, might produce the nephritogenic IgA1 molecule. With increased immune-complex formation and decreased clearance owing to reduced uptake by the liver, IgA1 binds to the glomerular mesangium via an as yet unidentified receptor. Glomerular IgA1 deposits trigger the local production of cytokines and growth factors, leading to the activation of mesangial cells and the complement system. Emerging data suggest that mesangial-derived mediators following glomerular deposition of IgA1 lead to podocyte and tubulointerstitial injury via mesangio-podocytic-tubular crosstalk. This Review summarizes the latest findings in the pathogenesis of IgA nephropathy.

Basic and translational concepts of immune-mediated glomerular diseases

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

Mechanism of onset and exacerbation of chronic glomerulonephritis and its treatment

Immunoglobulin A nephropathy (IgAN) is one of the most common causes of chronic glomerulonephritis (CGN) in the world. The proliferative and crescentic forms of IgA are found in up to 30% of cases and are associated with nephritic-range proteinuria, accelerated hypertension, and accelerated decline toward end-stage renal disease. On the other hand, Henoch-Schönlein purpura (HSP) is a systemic disorder characterized by leukocytoclastic vasculitis involving the capillaries and the deposition of IgA immune complexes. Renal involvement is the principal cause of morbidity and mortality in children with HSP. Two entity diseases are important as renal diseases in childhood. We herein review the mechanism of the onset and exacerbation of IgAN and HSP nephritis (HSPN) and its treatment. As to the pathogenesis, we found that CB4 provoked exacerbation of renal pathologic findings in hyper IgA mice via endothelial injury, γ-interferon production, and dysfunction of the mesangial pathway and could possibly become one of the factors involved in the mechanism of the onset or evolution of human IgAN. As to the treatment of IgAN and HSPN, we evaluated the efficacy of multidrug combination therapy (prednisolone, warfarin, and dipyridamole, including mizoribine) for diffuse IgAN and the efficacy of methylprednisolone and urokinase pulse therapy plus immunosuppressive drugs for severe HSPN in children. These therapies were effective in ameliorating the proteinuria and histologic severity of patients with IgAN or HSPN. In future, detailed investigations into the pathogenesis of CGN and double-blind randomized control studies on children with IgAN or HSPN will be necessary.

Clinical and histopathological spectrum of IgA nephropathy in Kuwait

BACKGROUND

Little is known about the nature and the course of IgA nephropathy (IgAN) in Arab countries. The aim of this work was to study the spectrum of clinical presentation and histopathological findings at our institution.

DESIGN AND SETTING

Retrospective review, all renal biopsies at the Mubarak Al Kabeer Hospital between January 2000 and December 2004.

METHODS

Cases of IgA nephropathy were selected, and their medical records and biopsy findings were reviewed.

RESULTS

Eighty patients (9.2% of all native kidney biopsies) were diagnosed to have IgAN nephropathy. Sixty-nine biopsies were included in the study;11 were excluded. Forty-three (62.3%) patients were male and 26 (37.7) patients were female. Fifty (72.5%) patients were below the age of 40 years. Mean (SD) duration of follow-up was 3.6 (1.3) years. The first presentation included nephritic-range proteinuria (49.3%) and renal impairment (50.7%). During the follow-up period, 56 (81.2%) patients were stable or improved. Hass classification of biopsies showed 36.2% had class I, 27.5% had class II, 13.0% had class III, 5.8% had class IV, and 17.4% had class V IgAN. Females had milder forms of the disease than males. Macroscopic hematuria and renal impairment at presentation were seen more in patients with class IV and V IgAN. The presenting serum creatinine and uric acid values were higher in those with Hass classes III to V. Deterioration of renal function during the follow-up period was more significant in the presence of hypertension, renal impairment, or macroscopic hematuria at the time of biopsy .

CONCLUSION

The prevalence of IgAN in Kuwait is about 9.2%. Renal impairment or macroscopic hematuria at presentation was seen in patients with more aggressive renal lesions and contributed to poor outcome.

Macrophages and renal fibrosis

Renal fibrosis is a key determinant of the progression of renal disease irrespective of the original cause and thus can be regarded as a final common pathway that dictates eventual outcome. The development of renal fibrosis involves many cellular and molecular mediators including leukocytes, myofibroblasts, cytokines, and growth factors, as well as metalloproteinases and their endogenous inhibitors. Study of experimental and human renal disease has shown the involvement of macrophages in renal fibrosis resulting from diverse disease processes. Recent work exploring the nature of both circulating monocytes and tissue macrophages has highlighted their multifaceted phenotype and this impacts their role in renal fibrosis in vivo. In this review we outline the key players in the fibrotic response of the injured kidney and discuss the role of monocytes and macrophages in renal scarring.

Changes in glomerular mesangium in kidneys with congenital nephrotic syndrome of the Finnish type

Congenital nephrotic syndrome of the Finnish type (NPHS1, CNF) is an autosomal recessive disease caused by mutations in a major podocyte protein, nephrin. NPHS1 is associated with heavy proteinuria and the development of glomerular scarring. We studied the cellular and molecular changes affecting the glomerular mesangium in NPHS1 kidneys. Marked hyperplasia of mesangial cells (MC) was mainly responsible for the early mesangial expansion in NPHS1 glomeruli. The levels of the proliferation marker, mindbomb homolog 1 and the major MC mitogen, platelet-derived growth factor, and its receptors, however, were quite normal. Only a small number of cells were positive for CD68 (marker for phagocytic cells) and CD34 (marker for mesenchymal precursor cells) in the NPHS1 mesangium. MCs strongly expressed alpha-smooth muscle actin, indicating myofibloblast transformation. The expression levels of the profibrotic mediators osteopontin and transforming growth factor beta were up-regulated in NPHS1 glomeruli by 3.2 and 1.6-fold, respectively, compared to the controls. The synthesis by MCs of the typical fibroblast products collagen I, fibronectin, and tenascin, however, was low, and the extracellular matrix increase was caused by the accumulation of a normal MC product, collagen IV. The results indicate that severe glomerular sclerosis can develop without major qualitative cellular or molecular changes in the mesangium.