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.

O- and N-Glycosylation of Serum Immunoglobulin A is Associated with IgA Nephropathy and Glomerular Function

Background: Immunoglobulin A (IgA) nephropathy (IgAN) is the most common primary glomerular disease worldwide, and is a leading cause of renal failure. The disease mechanisms are not completely understood, but a higher abundance of galactose-deficient IgA is recognized to play a crucial role in IgAN pathogenesis. While both types of human IgA (IgA1 and IgA2) have several N-glycans as posttranslational modification, only IgA1 features extensive hinge-region O-glycosylation. IgA1 galactose-deficiency on the O-glycans is commonly detected by a lectin-based method. To date, limited detail is known about IgA O- and N-glycosylation in IgAN. Methods: To gain insights into the complex O- and N-glycosylation of serum IgA1 and IgA2 in IgAN, we employed liquid chromatography-mass spectrometry (LC-MS) for the analysis of tryptic glycopeptides of serum IgA from 83 IgAN patients and 244 age and sex-matched healthy controls. Results: Multiple structural features of N-glycosylation of IgA1 and IgA2 were associated with IgAN and glomerular function in our cross-sectional study. These features included differences in galactosylation, sialylation, bisection, fucosylation, and N-glycan complexity. Moreover, IgA1 O-glycan sialylation was associated with both disease risk and glomerular function. Finally, glycopeptides were a better predictor of IgAN and glomerular function than galactose-deficient IgA1 levels measured by lectin-based ELISA. Conclusions: Our high-resolution data suggest that IgA O- and N-glycopeptides are promising targets for future investigations on the pathophysiology of IgAN and as potential noninvasive biomarkers for disease prediction and deteriorating kidney function.

An Update on the Current State of Management and Clinical Trials for IgA Nephropathy

IgA nephropathy remains the most common primary glomerular disease worldwide. It affects children and adults of all ages, and is a leading cause of end-stage kidney disease, making it a considerable public health issue in many countries. Despite being initially described over 50 years ago, there are still no disease specific treatments, with current management for most patients being focused on lifestyle measures and renin-angiotensin-aldosterone system blockade. However, significant advances in the understanding of its pathogenesis have been made particularly over the past decade, leading to great interest in developing new therapeutic strategies, and a significant rise in the number of interventional clinical trials being performed. In this review, we will summarise the current state of management of IgAN, and then describe major areas of interest where new therapies are at their most advanced stages of development, that include the gut mucosal immune system, B cell signalling, the complement system and non-immune modulators. Finally, we describe clinical trials that are taking place in each area and explore future directions for translational research.

Fractalkine Deficiency Attenuates LPS-Induced Acute Kidney Injury and Podocytes Apoptosis by Targeting PI3K/Akt Signal Pathway

Podocytes injury is a major biomarker of primary glomerular disease that leads to massive proteinuria and kidney failure. The increased production of chemokine Fractalkine (FKN, CX3CL1) implicated as a hallmark in multiple inflammatory disease. However, the underlying mechanism of FKN on podocytes injury remains unknown. Here, we studied the effects of FKN in LPS-induced acute kidney injury (AKI) in wild type (WT) and FKN knockout (FKN-KO) mice. LPS stimulation resulted in kidney damage, increased expression of Bcl-2 family apoptosis protein while decreased the podocytes marker protein (nephrin and podocin) abundance compared with the control. LPS-induced FKN-KO mice exhibited reduced lethality and attenuated inflammatory cells infiltration, podocytes apoptosis and PI3K/Akt signal pathway inhibition compared with WT mice. Depletion of FKN served a protective effect in LPS-induced AKI by activating the PI3K/Akt signal pathway. In cultured podocytes, the interaction between FKN and PI3K/Akt signal pathway is well confirmed. FKN knockdown reduced podocytes apoptosis by regulating the Bcl-2 family, while this protective effect was reversed by co-administration of PI3K/Akt inhibitor (LY294002). These studies reveal a novel mechanistic property of FKN, PI3K/Akt signal and podocytes apoptosis.

Gene Expression as a Guide to the Development of Novel Therapies in Primary Glomerular Diseases

Despite improvements in understanding the pathogenic mechanisms of primary glomerular diseases, therapy still remains nonspecific. We sought to identify novel therapies targeting kidney-intrinsic injury of distinct primary glomerulonephritides through computational systems biology approaches. We defined the unique transcriptional landscape within kidneys from patients with focal segmental glomerulosclerosis (FSGS), minimal change disease (MCD), immunoglobulin A nephropathy (IgAN), membranous nephropathy (MN) and thin basement membrane nephropathy (TBMN). Differentially expressed genes were functionally annotated with enrichment analysis, and distinct biological processes and pathways implicated in each primary glomerular disease were uncovered. Finally, we identified novel drugs and small-molecule compounds that may reverse each glomerulonephritis phenotype, suggesting they should be further tested as precise therapy in primary glomerular diseases.

MO084THE INFLUENCE OF INTRAVENOUS CORTICOSTEROIDS ON PLASMA SIRTUIN-1 AND SCLEROSTIN LEVELS IN PATIENTS WITH PRIMARY GLOMERULAR DISEASE

Background and Aims SIRT-1 is member of seven protein family that are involved in the cellular response to inflammatory, metabolic, and oxidative stress. The sirtuin family is a group of class III histone deacetylases. The best known of the family is SIRT-1. It may induce organ protection through inactivation of apoptosis and anti-inflammatory action. Sclerostin is a glycoprotein produced by the osteocytes and an inhibitor of Wnt signaling. Increased activity of sclerostin increases the resorption of bone tissue and inhibits osteogenesis. It has been hypothesized that by deacetylating histones SIRT-1 could negatively regulate sclerostin gene. That mechanism requires a confirmation in clinical setting. This exploratory study was designed to assess the influence of high doses of intravenous methylprednisolone on plasma SIRT-1 and sclerostin levels in patients with primary glomerular disease. Method The study included 40 patients (25 M, 15 F; mean age 53.1±14 years, mean eGFR 58.9±31.3 ml/min) in different stages of chronic kidney disease. 20 patients had eGFR below the median value of 46 ml/min. The main inclusion criterion was the clinical and histopathological diagnosis of primary glomerular disease and urine protein excretion >2.0 g/24h. The main biopsy-proven diagnoses were IgA nephropathy (13 patients) and focal segmental glomerulonephritis (FSGS) (13 patients). The patients were hospitalized to receive scheduled intravenous pulses of methylprednisolone 20-30 mg/kg/day for three consecutive days followed by oral prednisone 0.8-1.0 mg/kg/day. The blood was taken before the administration of methylprednisolone to assess SIRT-1, sclerostin, calcium, phosphate and PTH and urine for was taken for the measurement of calcium, phosphate and albumin to creatinine ratio. The same laboratory tests were repeated after 4, 7 and 30 days of steroid therapy. Results Plasma SIRT-1 during increased significantly during steroid administration (Fig.1). Plasma sclerostin did not change significantly during the study however a statistically significant correlation between the changes of SIRT-1 levels and sclerostin was found. In a multiple regression model the changes of plasma sclerotin induced by steroid therapy explained the largest part of the variance of the respective changes of plasma SIRT-1. Conclusion Plasma SIRT-1 increases during high-dose corticosteroids therapy. The negative relation between the changes of plasma SIRT-1 and plasma sclerostin may suggest a protective role of SIRT-1 against the rapid bone loss induced by corticosteroids.

Urinary Extracellular Vesicle Protein Profiles Discriminate Different Clinical Subgroups of Children with Idiopathic Nephrotic Syndrome

Idiopathic nephrotic syndrome (INS) is the most frequent primary glomerular disease in children, displaying high grade proteinuria and oedema. The mainstay of therapy are steroids, and patients are usually classified according to the treatment response (sensitive vs. resistant). The mechanisms involved in INS pathogenesis and treatment responsiveness have not yet been identified. In this context, the analysis of urinary extracellular vesicles (UEv) is interesting, since they represent a molecular snapshot of the parental cells, offering a “fingerprint” for monitoring their status. Therefore, the aim of this study is to verify the feasibility of using UEv of INS patients as indicators of therapy response and its prediction. UEv were isolated from the urine of pediatric patients in remission after therapy; they showed characteristic electrophoresis profiles that matched specific patient subgroups. We then built a statistical model to interpret objectively each patient UEv protein profile: in particular, steroid-resistant patients cluster together with a very distinct pattern from other INS patients and controls. In conclusion, the evaluation of the UEv protein profile looks promising in the investigation of INS, showing a disease signature that might predict clinical evolution.

Inebriated liver causing mesangial turmoil

IgA nephropathy is the most common primary glomerular disease worldwide, diagnosed 10% of renal biopsies in the United States, up to 20% in Europe and approximately 40% in Asia, the latter being the leading cause of ESRD in Asia. Multiple studies have shown the relationship between cirrhosis and the development of glomerular lesions leading IgA deposition in the mesangium causing IgAN. Here we present an unusual case of a 64-year-old female presenting with IgA nephropathy induced by liver cirrhosis.