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BACKGROUND - We performed a discovery phase of urinary proteomic profile in children with idiopathic nephrotic syndrome and validated selected biomarkers.
METHODS - Urinary proteomic profile was performed using isobaric tags for relative and absolute quantitation labeling, coupled with liquid chromatography-matrix assisted laser desorption and ionization analysis. Validation of biomarkers apolipoprotein A1, alpha 2 macroglobulin, orosomucoid 2, retinol binding protein 4 and leucine-rich alpha 2-glycoprotein 1 was done by enzyme-linked immunosorbent assay.
RESULTS - Apolipoprotein A1 levels of <0.48 µg/mg of creatinine-differentiated steroid-resistant nephrotic syndrome (SRNS) from first episode nephrotic syndrome, area under curve (AUC) [0.99 (CI 0.9-1.0), 100 % sensitivity and 100 % specificity] and a value of <0.24 µg/mg of creatinine could differentiate SRNS from frequently relapsing nephrotic syndrome/steroid dependent nephrotic syndrome [AUC 0.99 (CI 0.9-1.0), 100 % sensitivity and 100 % specificity]. Alpha 2 macroglobulin could differentiate children with SRNS-focal segmental glomerulosclerosis (FSGS) from SRNS-minimal change disease (MCD) at values >3.3 µg/mg of creatinine [AUC 0.84 (CI 0.62-1.0), 90 % sensitivity and 85 % specificity]. Orosomucoid 2 >1.81 µg/mg of creatinine could distinguish SRNS-FSGS from SRNS-MCD [AUC 0.84 (CI 0.62-1.0), sensitivity 90 % and specificity 85.5 %]. RBP 4 value of >1.54 µg/mg of creatinine differentiated SRNS-FSGS from SRNS-MCD [AUC 0.87 (CI 0.68-1.0), sensitivity 90 % and specificity 85.7 %].
CONCLUSIONS - Lower level of apolipoprotein A1 in urine is suggestive of SRNS. Alpha 2 macroglobulin, retinol binding protein 4 and orosomucoid 2 are markers associated with FSGS, with alpha 2 macroglobulin being most predictive.
Type 2 diabetes mellitus is a leading health issue worldwide. Among cases of diabetes mellitus nephropathy (DN), the major complication of type 2 diabetes mellitus, the nephrotic phenotype is often intractable to clinical intervention and demonstrates the rapid decline of renal function to end-stage renal disease. We recently identified the gene for glypican-5 (GPC5), a cell-surface heparan sulfate proteoglycan, as conferring susceptibility for acquired nephrotic syndrome and additionally identified an association through a genome-wide association study between a variant in GPC5 and DN of type 2 diabetes mellitus. In vivo and in vitro data showed a progressive increase of GPC5 in type 2 DN along with severity; the excess was derived from glomerular mesangial cells. In this study, diabetic kidney showed that accumulation of fibroblast growth factor (Fgf)2 strikingly induced progressive proteinuria that was avoided in Gpc5 knockdown mice. The efficacy of Gpc5 inhibition was exerted through expression of the Fgf receptors 3 and 4 provoked in the diabetic kidney attributively. Extraglomerular Fgf2 was pathogenic in DN, and the deterrence of Gpc5 effectively inhibited the glomerular accumulation of Fgf2, the subsequent increase of mesangial extracellular matrix, and the podocytes' small GTPase activity. These findings elucidate the pivotal role of GPC5, identified as a susceptible gene in the genome-wide association study, in hyperglycemia-induced glomerulopathy.
Copyright © 2015 American Society for Investigative Pathology. Published by Elsevier Inc. All rights reserved.
Schimke Immunoosseous Dysplasia (SIOD) is a rare, autosomal recessive disorder of childhood characterized by spondyloepiphyseal dysplasia, focal segmental glomerulosclerosis and renal failure, T-cell immunodeficiency, and cancer in certain instances. Approximately half of patients with SIOD are reported to have biallelic mutations in SMARCAL1 (SWI/SNF-related matrix-associated actin-dependent regulator of chromatin, subfamily a-like 1), which encodes a DNA translocase that localizes to sites of DNA replication and repairs damaged replication forks. We present a novel mutation (NM_014140.3:c.2070+2insT) that results in defective SMARCAL1 mRNA splicing in a child with SIOD. This mutation, within the donor site of intron 12, results in the skipping of exon 12, which encodes part of a critical hinge region connecting the two lobes of the ATPase domain. This mutation was not recognized as deleterious by diagnostic SMARCAL1 sequencing, but discovered through next generation sequencing and found to result in absent SMARCAL1 expression in patient-derived lymphoblasts. The splicing defect caused by this mutation supports the concept of exon definition. Furthermore, it illustrates the need to broaden the search for SMARCAL1 mutations in patients with SIOD lacking coding sequence variants.
© 2015 Wiley Periodicals, Inc.
Proteinuria and hyperphosphatemia are cardiovascular risk factors independent of GFR. We hypothesized that proteinuria induces relative phosphate retention via increased proximal tubule phosphate reabsorption. To test the clinical relevance of this hypothesis, we studied phosphate handling in nephrotic children and patients with CKD. Plasma fibroblast growth factor 23 (FGF-23) concentration, plasma phosphate concentration, and tubular reabsorption of phosphate increased during the proteinuric phase compared with the remission phase in nephrotic children. Cross-sectional analysis of a cohort of 1738 patients with CKD showed that albuminuria≥300 mg/24 hours is predictive of higher phosphate levels, independent of GFR and other confounding factors. Albuminuric patients also displayed higher plasma FGF-23 and parathyroid hormone levels. To understand the molecular mechanisms underlying these observations, we induced glomerular proteinuria in two animal models. Rats with puromycin-aminonucleoside-induced nephrotic proteinuria displayed higher renal protein expression of the sodium-phosphate co-transporter NaPi-IIa, lower renal Klotho protein expression, and decreased phosphorylation of FGF receptor substrate 2α, a major FGF-23 receptor substrate. These findings were confirmed in transgenic mice that develop nephrotic-range proteinuria resulting from podocyte depletion. In vitro, albumin did not directly alter phosphate uptake in cultured proximal tubule OK cells. In conclusion, we show that proteinuria increases plasma phosphate concentration independent of GFR. This effect relies on increased proximal tubule NaPi-IIa expression secondary to decreased FGF-23 biologic activity. Proteinuria induces elevation of both plasma phosphate and FGF-23 concentrations, potentially contributing to cardiovascular disease.
Copyright © 2015 by the American Society of Nephrology.
Podocytes are specialized actin-rich epithelial cells that line the kidney glomerular filtration barrier. The interface between the podocyte and the glomerular basement membrane requires integrins, and defects in either α3 or β1 integrin, or the α3β1 ligand laminin result in nephrotic syndrome in murine models. The large cytoskeletal protein talin1 is not only pivotal for integrin activation, but also directly links integrins to the actin cytoskeleton. Here, we found that mice lacking talin1 specifically in podocytes display severe proteinuria, foot process effacement, and kidney failure. Loss of talin1 in podocytes caused only a modest reduction in β1 integrin activation, podocyte cell adhesion, and cell spreading; however, the actin cytoskeleton of podocytes was profoundly altered by the loss of talin1. Evaluation of murine models of glomerular injury and patients with nephrotic syndrome revealed that calpain-induced talin1 cleavage in podocytes might promote pathogenesis of nephrotic syndrome. Furthermore, pharmacologic inhibition of calpain activity following glomerular injury substantially reduced talin1 cleavage, albuminuria, and foot process effacement. Collectively, these findings indicate that podocyte talin1 is critical for maintaining the integrity of the glomerular filtration barrier and provide insight into the pathogenesis of nephrotic syndrome.
BACKGROUND - Homocysteine metabolism is altered in children with idiopathic nephrotic syndrome. Hyperhomocysteinemia is a risk factor of early atherosclerosis and glomerulosclerosis and may occur at time of first occurrence of idiopathic nephrotic syndrome.
METHODS - Thirty children with first episode of idiopathic nephrotic syndrome (FENS) aged 1-16 years along with 30 age- and sex-matched healthy controls were enrolled in this study. Homocysteine and cysteine were measured with HPLC; vitamin B12 and folic acid were measured with electro-chemilumiscence immunoassay. Primary outcome measure was plasma homocysteine level in children with FENS and in controls. Secondary outcome measures were (1) plasma and urine homocysteine and cysteine levels in children with FENS at 12 weeks and 1 year (remission) and (2) plasma and urine levels of vitamin B12 and folic acid in children with FENS, at 12 weeks and 1 year (remission).
RESULTS - Plasma homocysteine and cysteine levels were comparable to controls in children with FENS, at 12 weeks and 1-year remission. Plasma levels of vitamin B12 and folic acid were significantly decreased compared to controls in FENS due to increased urinary excretion, which normalize during remission at 12 weeks and 1 year. Urinary homocysteine and cysteine levels were significantly raised in FENS compared to controls and continued to be raised even at 12-week and 1-year remission.
CONCLUSION - Homocysteine metabolism is deranged in children with FENS. Renal effects of long-term raised urinary homocysteine levels need to be studied.
© 2014 Wiley Periodicals, Inc.
The National Kidney Foundation and the U.S. Food and Drug Administration (FDA) convened a symposium in September 2010, bringing together more than 70 experts, including representatives from the FDA, the National Institutes of Health, the Critical Path Institute, nephrologists, patients, and the pharmaceutical industry to discuss the feasibility and process of developing patient-reported outcome (PRO) measures to access how patients feel or function to be used in clinical trials for regulatory review of treatment benefit. Three disease areas were evaluated for development of end point models in which PRO measures may be useful: anemia secondary to chronic kidney disease, autosomal dominant polycystic kidney disease (ADPKD), and nephrotic syndrome. The participants thought it valuable to use observational data to generate hypotheses regarding patient baseline characteristics that are likely to predict clinically important changes in PROs in response to anemia treatment and to design adequately powered blinded randomized controlled trials of anemia treatment using PROs as primary rather than secondary end points. Validated PRO instruments that reflect the patient experience in ADPKD and nephrotic syndrome are essential to incorporate into clinical trials of new therapeutic interventions because glomerular filtration rate decline may occur late in the disease course, at which point therapeutic benefit is less likely. Conference attendees addressed how PRO measures could be used to evaluate, monitor, provide care, and facilitate the introduction of treatments for patients with these challenging conditions.
Copyright © 2013 National Kidney Foundation, Inc. Published by Elsevier Inc. All rights reserved.
Schimke Immunoosseous Dysplasia (SIOD) is a rare, autosomal recessive disorder of childhood with classical features of spondyloepiphyseal dysplasia, renal failure, and T cell immunodeficiency. SIOD has been associated with several malignancies, including non-Hodgkin lymphoma and osteosarcoma. About half of SIOD patients have biallelic mutations in SMARCAL1 (SWI/SNF-related matrix-associated actin-dependent regulator of chromatin, subfamily a-like 1). This gene encodes an annealing helicase and replication stress response protein that localizes to damage-stalled DNA replication forks. We report a child with SIOD and a novel S859P missense mutation in SMARCAL1 who developed undifferentiated carcinoma of the sinus.
Copyright © 2013 Wiley Periodicals, Inc.
Membranous nephropathy (MN) is a leading cause of nephrotic syndrome in adults and a significant cause of end-stage renal disease, yet current therapies are nonspecific, toxic, and often ineffective. The development of novel targeted therapies requires a detailed understanding of the pathogenic mechanisms, but progress is hampered by the lack of a robust mouse model of disease. We report that DBA/1 mice as well as congenic FcγRIII(-/-) and FcRγ(-/-) mice immunized with a fragment of α3(IV) collagen developed massive albuminuria and nephrotic syndrome, because of subepithelial deposits of mouse IgG and C3 with corresponding basement membrane reaction and podocyte foot process effacement. The clinical presentation and histopathologic findings were characteristic of MN. Although immunized mice produced genuine anti-α3NC1 autoantibodies that bound to kidney and lung basement membranes, neither crescentic glomerulonephritis nor alveolitis ensued, likely because of the predominance of mouse IgG1 over IgG2a and IgG2b autoantibodies. The ablation of activating IgG Fc receptors did not ameliorate injury, implicating subepithelial deposition of immune complexes and consequent complement activation as a major effector pathway. We have thus established an active model of murine MN. This model, leveraged by the availability of genetically engineered mice and mouse-specific reagents, will be instrumental in studying the pathogenesis of MN and evaluating the efficacy of novel experimental therapies.
BACKGROUND - Peroxisome proliferator-activated receptor gamma (PPARγ) agonists have beneficial effects on renal structure and function in models of diabetes and chronic kidney diseases. However, the increased incidence of weight gain and edema potentially limits their usefulness. We studied an acute minimal-change disease-like nephrotic syndrome model to assess effects of PPARγ agonist on acute podocyte injury and effects on fluid homeostasis.
METHODS - Acute podocyte injury and nephrotic syndrome were induced by puromycin aminonucleoside (PAN) injection in rats.
RESULTS - PPARγ agonist, given at the time or after, but not before PAN, reduced proteinuria, restored synaptopodin, decreased desmin and trended to improve foot process effacement. There was no significant difference in glomerular filtration, effective circulating volume, blood pressure or fractional sodium excretion. PAN-injured podocytes had decreased PPARγ, less nephrin and α-actinin-4, more apoptosis and reduced phosphorylated Akt. In PAN-injured cultured podocytes, PPARγ agonist also reversed abnormalities only when given simultaneously or after injury.
CONCLUSIONS - These results show that PPARγ agonist has protective effects on podocytes in acute nephrotic syndrome without deleterious effects on fluid homeostasis. PPARγ agonist-induced decrease in proteinuria in acute nephrotic syndrome is dependent at least partially on regulation of peroxisome proliferator-response element-sensitive gene expression such as α-actinin-4 and nephrin and the restoration of podocyte structure.