Nephrin redistribution on podocytes is a potential mechanism for proteinuria in patients with primary acquired nephrotic syndrome

Effect of proteinuria at relapse on shear wave velocity assessed using ultrasound elastography in children with idiopathic nephrotic syndrome

PURPOSE

Shear wave velocity (SWV) is an ultrasound elastography technique that provides much information for kidney disease assessment. However, the factors that alter SWV are not fully understood; it is unclear whether the variation in SWV seen in proteinuria associated with disease progression is due to tissue or proteinuria. This study investigated the effect of proteinuria on SWV.

METHODS

This prospective observational study compared SWV at remission with SWV at relapse in children treated for idiopathic nephrotic syndrome (INS) between April 2020 and December 2023. All relapses without oral steroids during the observation period were measured. SWV at remission was defined as the date closest to relapse during which repeated measurements were taken approximately every 3 months after steroid discontinuation.

RESULTS

Eight patients were treated for INS with a median observation period of 21.9 months (11.8-27.1). Of the 15 relapses, five that met the definition were considered for the study. The median interval between the measurement at relapse and remission was 40 days (11-55). SWV was significantly lower at relapse than remission (2.40 ± 0.20 m/s vs. 2.14 ± 0.15 m/s, P < 0.01).

CONCLUSIONS

SWV decreased in the presence of severe proteinuria at relapse compared to the remission measurements. Although more cases need to be studied, the decrease in SWV may reflect the mechanism by which protein leaks into the urine, not just a direct change caused by the presence of proteinuria.

Mechanisms of podocyte injury and implications for diabetic nephropathy

Albuminuria is the hallmark of both primary and secondary proteinuric glomerulopathies, including focal segmental glomerulosclerosis (FSGS), obesity-related nephropathy, and diabetic nephropathy (DN). Moreover, albuminuria is an important feature of all chronic kidney diseases (CKDs). Podocytes play a key role in maintaining the permselectivity of the glomerular filtration barrier (GFB) and injury of the podocyte, leading to foot process (FP) effacement and podocyte loss, the unifying underlying mechanism of proteinuric glomerulopathies. The metabolic insult of hyperglycemia is of paramount importance in the pathogenesis of DN, while insults leading to podocyte damage are poorly defined in other proteinuric glomerulopathies. However, shared mechanisms of podocyte damage have been identified. Herein, we will review the role of haemodynamic and oxidative stress, inflammation, lipotoxicity, endocannabinoid (EC) hypertone, and both mitochondrial and autophagic dysfunction in the pathogenesis of the podocyte damage, focussing particularly on their role in the pathogenesis of DN. Gaining a better insight into the mechanisms of podocyte injury may provide novel targets for treatment. Moreover, novel strategies for boosting podocyte repair may open the way to podocyte regenerative medicine.

Discovery of Autoantibodies Targeting Nephrin in Minimal Change Disease Supports a Novel Autoimmune Etiology

BACKGROUND

Failure of the glomerular filtration barrier, primarily by loss of slit diaphragm architecture, underlies nephrotic syndrome in minimal change disease. The etiology remains unknown. The efficacy of B cell-targeted therapies in some patients, together with the known proteinuric effect of anti-nephrin antibodies in rodent models, prompted us to hypothesize that nephrin autoantibodies may be present in patients with minimal change disease.

METHODS

We evaluated sera from patients with minimal change disease, enrolled in the Nephrotic Syndrome Study Network (NEPTUNE) cohort and from our own institutions, for circulating nephrin autoantibodies by indirect ELISA and by immunoprecipitation of full-length nephrin from human glomerular extract or a recombinant purified extracellular domain of human nephrin. We also evaluated renal biopsies from our institutions for podocyte-associated punctate IgG colocalizing with nephrin by immunofluorescence.

RESULTS

In two independent patient cohorts, we identified circulating nephrin autoantibodies during active disease that were significantly reduced or absent during treatment response in a subset of patients with minimal change disease. We correlated the presence of these autoantibodies with podocyte-associated punctate IgG in renal biopsies from our institutions. We also identified a patient with steroid-dependent childhood minimal change disease that progressed to end stage kidney disease; she developed a massive post-transplant recurrence of proteinuria that was associated with high pretransplant circulating nephrin autoantibodies.

CONCLUSIONS

Our discovery of nephrin autoantibodies in a subset of adults and children with minimal change disease aligns with published animal studies and provides further support for an autoimmune etiology. We propose a new molecular classification of nephrin autoantibody minimal change disease to serve as a framework for instigation of precision therapeutics for these patients.

Renal pathology in a mouse model of severe Spinal Muscular Atrophy is associated with downregulation of Glial Cell-Line Derived Neurotrophic Factor (GDNF)

Spinal muscular atrophy (SMA) occurs as a result of cell-ubiquitous depletion of the essential survival motor neuron (SMN) protein. Characteristic disease pathology is driven by a particular vulnerability of the ventral motor neurons of the spinal cord to decreased SMN. Perhaps not surprisingly, many other organ systems are also impacted by SMN depletion. The normal kidney expresses very high levels of SMN protein, equivalent to those found in the nervous system and liver, and levels are dramatically lowered by ~90-95% in mouse models of SMA. Taken together, these data suggest that renal pathology may be present in SMA. We have addressed this using an established mouse model of severe SMA. Nephron number, as assessed by gold standard stereological techniques, was significantly reduced. In addition, morphological assessment showed decreased renal vasculature, particularly of the glomerular capillary knot, dysregulation of nephrin and collagen IV, and ultrastructural changes in the trilaminar filtration layers of the nephron. To explore the molecular drivers underpinning this process, we correlated these findings with quantitative PCR measurements and protein analyses of glial cell-line-derived neurotrophic factor, a crucial factor in ureteric bud branching and subsequent nephron development. Glial cell-line-derived neurotrophic factor levels were significantly reduced at early stages of disease in SMA mice. Collectively, these findings reveal significant renal pathology in a mouse model of severe SMA, further reinforcing the need to develop and administer systemic therapies for this neuromuscular disease.

ADAM10-Mediated Ectodomain Shedding Is an Essential Driver of Podocyte Damage

BACKGROUND

Podocytes embrace the glomerular capillaries with foot processes, which are interconnected by a specialized adherens junction to ultimately form the filtration barrier. Altered adhesion and loss are common features of podocyte injury, which could be mediated by shedding of cell-adhesion molecules through the regulated activity of cell surface-expressed proteases. A Disintegrin and Metalloproteinase 10 (ADAM10) is such a protease known to mediate ectodomain shedding of adhesion molecules, among others. Here we evaluate the involvement of ADAM10 in the process of antibody-induced podocyte injury.

METHODS

Membrane proteomics, immunoblotting, high-resolution microscopy, and immunogold electron microscopy were used to analyze human and murine podocyte ADAM10 expression in health and kidney injury. The functionality of ADAM10 ectodomain shedding for podocyte development and injury was analyzed, in vitro and in vivo, in the anti-podocyte nephritis (APN) model in podocyte-specific, ADAM10-deficient mice.

RESULTS

ADAM10 is selectively localized at foot processes of murine podocytes and its expression is dispensable for podocyte development. Podocyte ADAM10 expression is induced in the setting of antibody-mediated injury in humans and mice. Podocyte ADAM10 deficiency attenuates the clinical course of APN and preserves the morphologic integrity of podocytes, despite subepithelial immune-deposit formation. Functionally, ADAM10-related ectodomain shedding results in cleavage of the cell-adhesion proteins N- and P-cadherin, thus decreasing their injury-related surface levels. This favors podocyte loss and the activation of downstream signaling events through the Wnt signaling pathway in an ADAM10-dependent manner.

CONCLUSIONS

ADAM10-mediated ectodomain shedding of injury-related cadherins drives podocyte injury.

Slit diaphragm maintenance requires dynamic clathrin-mediated endocytosis facilitated by AP-2, Lap, Aux and Hsc70-4 in nephrocytes

Background

The Slit diaphragm (SD) is the key filtration structure in human glomerular kidney that is affected in many types of renal diseases. SD proteins are known to undergo endocytosis and recycling to maintain the integrity of the filtration structure. However, the key components of this pathway remain unclear.

Methods

Using the Drosophila nephrocyte as a genetic screen platform, we screened most genes involved in endocytosis and cell trafficking, and identified the key components of the cell trafficking pathway required for SD protein endocytosis and recycling.

Results

We discovered that the SD protein endocytosis and recycling pathway contains clathrin, dynamin, AP-2 complex, like-AP180 (Lap), auxilin and Hsc70-4 (the endocytosis part) followed by Rab11 and the exocyst complex (the recycling part). Disrupting any component in this pathway led to disrupted SD on the cell surface and intracellular accumulation of mislocalized SD proteins. We also showed the first in vivo evidence of trapped SD proteins in clathrin-coated pits at the plasma membrane when this pathway is disrupted.

Conclusions

All genes in this SD protein endocytosis and recycling pathway, as well as SD proteins themselves, are highly conserved from flies to humans. Thus, our results suggest that the SD proteins in human kidney undergo the same endocytosis and recycling pathway to maintain the filtration structure, and mutations in any genes in this pathway could lead to abnormal SD and renal diseases.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13578-021-00595-4.

MicroRNAs in childhood nephrotic syndrome

The discovery of microRNAs (miRNAs) has opened up new avenues of research to understand the molecular basis of a number of diseases. Because of their conservative feature in evolution and important role in the physiological function, microRNAs could be treated as predictors for disease classification and clinical process based on the specific expression. The identification of novel miRNAs and their target genes can be considered as potential targets for novel drugs. Furthermore, currently, the circulatory and urinary exosomal miRNAs are gaining increasing attention as their expression profiles are often associated with specific diseases, and they exhibit great potential as noninvasive or minimally invasive biomarkers for the diagnosis of various diseases. The remarkable stability of these extracellular miRNAs circulating in the blood or excreted in the urine underscored their key importance as biomarkers of certain diseases. There is voluminous literature concerning the role of microRNAs in other diseases, such as cardiovascular diseases, diabetic nephropathy, and so forth. However, little is known about their diagnostic ability for the pediatric nephrotic syndrome (NS). The present review article highlights the recent advances in the role of miRNAs in the pathogenesis and molecular basis of NS with an aim to bring new insights into further research applications for the development of new therapeutic agents for NS.

Endoplasmic reticulum-associated degradation is required for nephrin maturation and kidney glomerular filtration function

Podocytes are key to the glomerular filtration barrier by forming a slit diaphragm between interdigitating foot processes; however, the molecular details and functional importance of protein folding and degradation in the ER remain unknown. Here, we show that the SEL1L-HRD1 protein complex of ER-associated degradation (ERAD) is required for slit diaphragm formation and glomerular filtration function. SEL1L-HRD1 ERAD is highly expressed in podocytes of both mouse and human kidneys. Mice with podocyte-specific Sel1L deficiency develop podocytopathy and severe congenital nephrotic syndrome with an impaired slit diaphragm shortly after weaning and die prematurely, with a median lifespan of approximately 3 months. We show mechanistically that nephrin, a type 1 membrane protein causally linked to congenital nephrotic syndrome, is an endogenous ERAD substrate. ERAD deficiency attenuated the maturation of nascent nephrin, leading to its retention in the ER. We also show that various autosomal-recessive nephrin disease mutants were highly unstable and broken down by SEL1L-HRD1 ERAD, which attenuated the pathogenicity of the mutants toward the WT allele. This study uncovers a critical role of SEL1L-HRD1 ERAD in glomerular filtration barrier function and provides insights into the pathogenesis associated with autosomal-recessive disease mutants.

Altered glycosylation of IgG4 promotes lectin complement pathway activation in anti-PLA2R1-associated membranous nephropathy

Primary membranous nephropathy (pMN) is a leading cause of nephrotic syndrome in adults. In most cases, this autoimmune kidney disease is associated with autoantibodies against the M-type phospholipase A2 receptor (PLA2R1) expressed on kidney podocytes, but the mechanisms leading to glomerular damage remain elusive. Here, we developed a cell culture model using human podocytes and found that anti-PLA2R1-positive pMN patient sera or isolated IgG4, but not IgG4-depleted sera, induced proteolysis of the 2 essential podocyte proteins synaptopodin and NEPH1 in the presence of complement, resulting in perturbations of the podocyte cytoskeleton. Specific blockade of the lectin pathway prevented degradation of synaptopodin and NEPH1. Anti-PLA2R1 IgG4 directly bound mannose-binding lectin in a glycosylation-dependent manner. In a cohort of pMN patients, we identified increased levels of galactose-deficient IgG4, which correlated with anti-PLA2R1 titers and podocyte damage induced by patient sera. Assembly of the terminal C5b-9 complement complex and activation of the complement receptors C3aR1 or C5aR1 were required to induce proteolysis of synaptopodin and NEPH1 by 2 distinct proteolytic pathways mediated by cysteine and aspartic proteinases, respectively. Together, these results demonstrated a mechanism by which aberrantly glycosylated IgG4 activated the lectin pathway and induced podocyte injury in primary membranous nephropathy.

Urinary Markers of Podocyte Dysfunction in Chronic Glomerulonephritis

Chronic glomerulonephritis (CGN) is a disease with a steady progressive course that involves the development of nephrosclerosis, which is especially evident in clinical courses with incidences of high proteinuria (PU). Currently, proteinuria is considered the main laboratory feature (sign) of CGN activity and progression because proteinuria is closely related to the process of tubulointerstitial fibrosis, which is correlated with the grade of renal insufficiency. The injury to podocytes, which are key components of the filtration barrier, plays a central role in proteinuria development. The detachment of podocytes from the glomerular basement membrane leading to podocytopenia is suggested to induce glomerulosclerosis and hyalinosis with obliteration of capillary loops and the progression of chronic kidney disease. Urinary markers of podocyte dysfunction could serve as useful tools while monitoring the activity and prognosis of CGN. In this chapter, the most important mechanisms of podocyte loss and urinary markers of this process are discussed.

Morphological analyses of nephrin expression in progressive glomerulonephropathy of common marmosets

In this study, we focused on nephrin, one of the key molecules within the slit diaphragm of podocytes, as although there have been reports on its expression in humans and rats, their presence in common marmosets has not been reported. We investigated nephrin expression and changes in glomeruli, depending on the development of spontaneous progressive glomerulonephropathy in common marmosets. Nineteen common marmosets at two to ten years of age were evaluated. The kidney was examined by microscopy with hematoxylin and eosin and immunohistochemical staining for nephrin. The lesions were classified into three grades according to a renal lesion grading system reported previously. The nephrin-positive area was measured by morphometric analysis, and the nephrin-positive ratio was calculated. Nephrin expression was observed along the glomerular capillary loop in a continuous linear pattern in renal lesion grades 0 to 2 and either discontinuous linear or coarse granular pattern in grade 3. Nephrin expression tended to decrease significantly depending on the grade of renal lesions. Alteration in nephrin expression has been suggested to play an important role in the progression of renal lesions.

Loss of slit protein nephrin is associated with reduced antioxidant superoxide dismutase expression in podocytes shed from women with preeclampsia

Recent findings of podocyte shedding/podocyturia highlight the central significance of podocyte injury in preeclampsia, a hypertensive disorder unique to human pregnancy. To test the hypothesis that oxidative stress contributes to kidney podocyte injury in preeclampsia, we specifically examined expression and distribution of antioxidant CuZn‐SOD with nephrin and podoplanin in shed podocytes from women with preeclampsia. Human podocyte AB 8/13 cells served as control. We found that CuZn‐SOD was localized at the front/outreach region of nephrin at the cell periphery (foot process areas) in control podocytes and expression of CuZn‐SOD, nephrin, and podoplanin were all dislocated or lost in shed podocytes from preeclamptic patients. We further tested oxidative stress‐induced nephrin shedding in podocytes, in which AB 8/13 podocytes were cultured under lowered oxygen condition (2%O₂) or treated with hypoxic mimicking agent cobalt chloride. Our results showed that reduced nephrin and podoplanin expression were associated with downregulation of CuZn‐SOD expression in podocytes when cells were cultured under lowered oxygen or hypoxic conditions. Nephrin shed in urinary specimen from preeclamptic women was also determined by immunoprecipitation/immunoblotting. The molecular sizes of nephrin that corresponded to that were lost when cells were cultured under hypoxic conditions. We concluded that increased oxidative stress plays a significant role in inducing podocyte protein shedding in preeclampsia.

Podocin and uPAR are good biomarkers in cases of Focal and segmental glomerulosclerosis in pediatric renal biopsies

There are controversies whether Minimal Change Disease (MCD) and Focal and Segmental Glomerulosclerosis (FSGS) are distinct glomerular lesions or different manifestations within the same spectrum of diseases. The uPAR (urokinase-type plasminogen activator receptor) and some slit diaphragm proteins may be altered in FSGS glomeruli and may function as biomarkers of the disease in renal biopsies. Thus, this study aims to evaluate the diagnostic potential of uPAR and glomerular proteins for differentiation between MCD and FSGS in renal pediatric biopsy. Renal biopsies from 50 children between 2 and 18 years old were selected, with diagnosis of MCD (n = 29) and FSGS (n = 21). Control group consisted of pediatric autopsies (n = 15) from patients younger than 18 years old, with no evidences of renal dysfunction. In situ expressions of WT1, nephrin, podocin and uPAR were evaluated by immunoperoxidase technique. Renal biopsy of patients with MCD and FSGS expressed fewer WT1 (p≤0.0001, F = 19.35) and nephrin (p<0.0001; H = 21.54) than patients in the control group. FSGS patients expressed fewer podocin than control (p<0.0359, H = 6.655). FSGS cases expressed more uPAR than each of control and MCD (p = 0.0019; H = 12.57) and there was a positive and significant correlation between nephrin and podocin (p = 0.0026, rS = 0.6502) in these cases. Podocin had sensitivity of 73.3% and specificity of 86.7% (p = 0.0068) and uPAR had sensitivity of 78.9% and specificity of 73.3% (p = 0.0040) for diagnosis of FSGS patients. The main limitation of the study is the limited number of cases due to the difficulty in performing biopsy in pediatric patients. Podocin and uPAR are good markers for FSGS and differentiate these cases from MCD, reinforcing the theory of distinct glomerular diseases. These findings suggest that podocin and uPAR can be used as biomarkers in the routine analysis of renal biopsies in cases of podocytopathies when the lesion (sclerosis) is not sampled.

The human nephrin Y1139RSL motif is essential for podocyte foot process organization and slit diaphragm formation during glomerular development

Nephrin is an immunoglobulin-type cell-adhesion molecule with a key role in the glomerular interpodocyte slit diaphragm. Mutations in the nephrin gene are associated with defects in the slit diaphragm, leading to early-onset nephrotic syndrome, typically resistant to treatment. Although the endocytic trafficking of nephrin is essential for the assembly of the slit diaphragm, nephrin's specific endocytic motifs remain unknown. To search for endocytic motifs, here we performed a multisequence alignment of nephrin and identified a canonical YXXØ-type motif, Y¹¹³⁹RSL, in the nephrin cytoplasmic tail, expressed only in primates. Using site-directed mutagenesis, various biochemical methods, single-plane illumination microscopy, a human podocyte line, and a human nephrin-expressing zebrafish model, we found that Y¹¹³⁹RSL is a novel endocytic motif and a structural element for clathrin-mediated nephrin endocytosis that functions as a phosphorylation-sensitive signal. We observed that Y¹¹³⁹RSL motif-mediated endocytosis helps to localize nephrin to specialized plasma membrane domains in podocytes and is essential for normal foot process organization into a functional slit diaphragm between neighboring foot processes in zebrafish. The importance of nephrin Y¹¹³⁹RSL for healthy podocyte development was supported by population-level analyses of genetic variations at this motif, revealing that such variations are very rare, suggesting that mutations in this motif have autosomal-recessive negative effects on kidney health. These findings expand our understanding of the mechanism underlying nephrin endocytosis and may lead to improved diagnostic tools or therapeutic strategies for managing early-onset, treatment-resistant nephrotic syndrome.

Podocyte-Specific Sialylation-Deficient Mice Serve as a Model for Human FSGS

BACKGROUND

The etiology of steroid-resistant nephrotic syndrome, which manifests as FSGS, is not completely understood. Aberrant glycosylation is an often underestimated factor for pathologic processes, and structural changes in the glomerular endothelial glycocalyx have been correlated with models of nephrotic syndrome. Glycans are frequently capped by sialic acid (Sia), and sialylation's crucial role for kidney function is well known. Human podocytes are highly sialylated; however, sialylation's role in podocyte homeostasis remains unclear.

METHODS

We generated a podocyte-specific sialylation-deficient mouse model (PCmas^-/- ) by targeting CMP-Sia synthetase, and used histologic and ultrastructural analysis to decipher the phenotype. We applied CRISPR/Cas9 technology to generate immortalized sialylation-deficient podocytes (asialo-podocytes) for functional studies.

RESULTS

Progressive loss of sialylation in PCmas^-/- mice resulted in onset of proteinuria around postnatal day 28, accompanied by foot process effacement and loss of slit diaphragms. Podocyte injury led to severe glomerular defects, including expanded capillary lumen, mesangial hypercellularity, synechiae formation, and podocyte loss. In vivo, loss of sialylation resulted in mislocalization of slit diaphragm components, whereas podocalyxin localization was preserved. In vitro, asialo-podocytes were viable, able to proliferate and differentiate, but showed impaired adhesion to collagen IV.

CONCLUSIONS

Loss of cell-surface sialylation in mice resulted in disturbance of podocyte homeostasis and FSGS development. Impaired podocyte adhesion to the glomerular basement membrane most likely contributed to disease development. Our data support the notion that loss of sialylation might be part of the complex process causing FSGS. Sialylation, such as through a Sia supplementation therapy, might provide a new therapeutic strategy to cure or delay FSGS and potentially other glomerulopathies.

Correlation between endocapillary proliferative and nephrotic-range proteinuria in children with Henoch-Schönlein purpura nephritis

BACKGROUND

The endocapillary proliferative (EP) lesion is not included in the International Study of Kidney Disease in Children (ISKDC) pathological classification of Henoch-Schönlein purpura nephritis (HSPN). The main objective of the study was to determine the pathological importance of EP in the development of proteinuria in children with Henoch-Schönlein purpura nephritis (HSPN).

METHODS

The pathological features of 148 HSPN children with nephrotic-range proteinuria were investigated retrospectively. Urinary IgG, transferrin, and albumin levels were measured by immunonephelometry. The correlations between EP lesion and 24-h proteinuria, urinary IgG, urinary transferrin, and urinary albumin were analyzed. Renal biopsy specimens were immunohistochemically stained for nephrin and podocalyxin.

RESULTS

Of the total 581 cases of children with HSPN who underwent renal biopsy, 148 cases (25.5%) presented with nephrotic-range proteinuria. The pathological types of HSPN with nephrotic-range proteinuria were categorized as IIb, IIIa, IIIb, IIIb with diffuse EP, IVb, pure focal EP type, and pure diffuse EP type. Among these types, pure diffuse EP type accounted for 7.4%. The levels of 24-h proteinuria and urinary albumin were the highest in pure diffuse EP type among all pathological types, and the percentage of EP correlated with 24-h proteinuria and urinary albumin levels. 24-h proteinuria was significantly higher in pure diffuse EP type relative to HSPN IIb type, and significantly higher in IIIb with EP, compared with HSPN IIIb. Nephrin, but not podocalyxin, was downregulated in EP segment.

CONCLUSIONS

EP is an independent pathogenic factor in HSPN with nephrotic-range proteinuria. Downregulation of nephrin in EP segment is a potential molecular mechanism of nephrotic-range proteinuria. Albumin is the major urinary protein component in HSPN with EP.

Analysis of the genomic architecture of a complex trait locus in hypertensive rat models links Tmem63c to kidney damage

Unraveling the genetic susceptibility of complex diseases such as chronic kidney disease remains challenging. Here, we used inbred rat models of kidney damage associated with elevated blood pressure for the comprehensive analysis of a major albuminuria susceptibility locus detected in these models. We characterized its genomic architecture by congenic substitution mapping, targeted next-generation sequencing, and compartment-specific RNA sequencing analysis in isolated glomeruli. This led to prioritization of transmembrane protein Tmem63c as a novel potential target. Tmem63c is differentially expressed in glomeruli of allele-specific rat models during onset of albuminuria. Patients with focal segmental glomerulosclerosis exhibited specific TMEM63C loss in podocytes. Functional analysis in zebrafish revealed a role for tmem63c in mediating the glomerular filtration barrier function. Our data demonstrate that integrative analysis of the genomic architecture of a complex trait locus is a powerful tool for identification of new targets such as Tmem63c for further translational investigation.

The human kidneys filter the entire volume of the blood about 300 times each day. This ability depends on specialized cells, known as podocytes, which wrap around some of the blood vessels in the kidney. These cells control which molecules leave the blood based on their size. Normally large molecules like proteins are blocked, while smaller molecules including waste products, toxins, excess water and salts pass through into the urine.

If this filtration system is damaged, by high blood pressure, for example, it can lead to chronic kidney disease. A hallmark of this disease, often called CKD for short, is high levels of the protein albumin in the urine. Previous studies involving rats with high blood pressure have found several regions of the genome that contribute to high levels of albumin in the urine, including one on chromosome 6. However, this region contains several genes and it was unclear which genes affected the condition.

Schulz et al. set out to narrow down the list and find specific genes that might contribute to elevated albumin in the urine of rats with high blood pressure. This search identified the gene for a protein called TMEM63c as a likely candidate. This protein spans the outer membrane of podocyte cells. Analysis of kidney biopsies showed that patients with chronic kidney disease also had low levels of this protein in their podocytes. Further experiments, this time in zebrafish, showed that reducing the activity of the gene for tmem63c led to damaged podocytes and a leakier filter in the kidneys.

The results suggest that this gene plays an important role in the integrity of the kidneys filtration barrier. It is possible that faulty versions of this gene are behind some cases of chronic kidney disease. If this proves to be the case, a better understanding of the role of this gene may lead to new treatments for the condition.

FAM40A alters the cytoskeleton of podocytes in familial focal and segmental glomerulosclerosis by regulating F-actin and nephrin

INTRODUCTION

Familial focal and segmental glomerulosclerosis (FFSGS) was found in a large cohort of patients in our previous study. Under the sponsorship of the National Natural Science Foundation of China, we conducted linkage analysis and full exon sequencing on the genomes of 54 patients diagnosed with FFSGS. The results revealed a FAM40A gene signature in those patients. To determine whether FAM40A was associated with podocyte lesions and whether changes in the podocyte cytoskeleton could affect podocyte function, mouse podocytes (MPs) were used in this study.

MATERIAL AND METHODS

FAM40A silencing, over-expression and mutant-type over-expression models of renal MPs were established, whereby roles of wild-type FAM40A and mutant FAM40A (c.1562T>C, p521M>T) in regulating the function of the MP cytoskeleton were explored by using cellular immunofluorescence, RT-qPCR and Western blot.

RESULTS

FAM40A was expressed and localized in MPs and significantly enriched in the nucleus and perinuclear zone. Changes of FAM40A expression altered the morphology of the MPs and their cytoskeletal organization, which was characterized by disordered distribution of F-actin, loss of the foot process architecture and the functional protein of the slit diaphragm nephrin (p < 0.05 or p < 0.01). FAM40A mutation (p521M>T) led to the formation of round and blunt morphology of the MPs and loss of the foot-process structure. In addition, expression of the cytoskeletal protein F-actin was increased and concentrated in FAM40A mutated cells, whereas the expression of nephrin decreased in those cells (p < 0.01).

CONCLUSIONS

FAM40A played an important role in maintaining the normal morphology and function of MPs by stabilizing the cytoskeleton of MPs. Moreover, mutant FAM40A (p521M>T) was able to alter the morphology and cytoskeleton of the MPs, and to decrease the expression of nephrin, which may be the main factor contributing to FSGS.

Glomeruli from patients with nephrin mutations show increased number of ciliated and poorly differentiated podocytes

BACKGROUND

Podocytes are postmitotic, highly specialized cells which maintain the glomerular filtration barrier (GFB). Their injury is characterized by foot processes effacement and change in protein expression leading to proteinuria and end-stage kidney disease.

METHODS

Our study focuses on the morphological and immunohistochemical changes of human podocytes during normal development and postnatal period, compared to congenital nephrotic syndrome of the Finnish type (CNF). Kidney tissues taken from 17 human conceptuses 8th-38th weeks old, two healthy and three CNF kidneys were embedded in paraffin for immunohistochemical or double immunofluorescence methods, or were embedded in resin for electron microscopy. Paraffin sections were stained with markers for proliferation (Ki-67), proteins nephrin and nestin, and alpha-tubulin. Quantification of positive cells were performed using Mann Whitney and Kruskal-Wallis test.

RESULTS

Tissue analysis showed that proliferation of podocytes gradually decreased during development and disappeared in postnatal period. Decrease in number of ciliated glomerular cells and visceral podocytes (from 47% to 3%), and parietal epithelial cells (from 32% to 7%) characterized normal development. Nestin and nephrin co-expressed in developing podocytes in different cellular compartments. During development, nephrin expression increased (from 17% to 75%) and postnatally changed its pattern, while nestin positive glomerular cells decreased from 98% to 40%. CNF glomeruli displayed increased number of immature ciliated podocytes (6%) and parietal epithelial cells (9%).

CONCLUSION

Changes in cytoplasmic alpha-tubulin expression and reduced nephrin expression (20%) indicating association of incomplete podocyte maturation with failure of GFB function and appearance of prenatal proteinuria in CNF patients.

Accelerated Glomerular Cell Senescence in Experimental Lupus Nephritis

BACKGROUND The aim of this study was to determine whether senescence in renal glomeruli is involved in lupus nephritis (LN); the expression of senescence-associated β-galactosidase (SA-β-Gal) and its association with glomerular lesions were investigated in a mouse model of LN. MATERIAL AND METHODS Eighteen MRL/lpr mice with severe proteinuria were randomly divided into 2 equal groups and intraperitoneally injected with dexamethasone (DEX) or saline; 4 age-matched mice with mild proteinuria served as controls. Serum creatinine and urinary protein levels were analyzed, and kidney histological changes were observed by periodic acid-Schiff and Sirius Red staining. SA-β-Gal was detected via histochemistry. Glomerular expression of collagen IV, α-SMA, and nephrin was analyzed by immunohistochemistry, and glomerular complement C3 deposition was tested by immunofluorescence. The relationships between SA-β-Gal expression and renal function or glomerular lesion markers were determined by Spearman's correlation analysis. RESULTS Mice with severe proteinuria exhibited glomerular segmental sclerosis and endothelial cell proliferation. DEX administration suppressed these lesions but had no significant effect on 24-hour urinary protein levels. The elevated glomerular expression of SA-β-Gal in proteinuric mice was attenuated by DEX treatment. In addition, DEX treatment markedly downregulated glomerular C3 deposition and collagen IV and α-SMA expression, while significantly increasing nephrin expression. Furthermore, SA-β-Gal expression was positively correlated with urinary protein levels and expression of α-SMA. CONCLUSIONS Accelerated senescence of glomerular cells may contribute to glomerular injury in LN.

The role of podocytes dysfunction in chronic glomerulonephritis progression

In the review, the mechanisms of podocytes damage underlying the development of proteinuria and progression of glomerulosclerosis in chronic glomerulonephritis are discussed in detail. The results of experimental and clinical studies are presented. Under the different immune and non-immune factors the podocytes form a stereotyped response to damage consisting in the reorganization of the actin cytoskeleton, foot process effacement, the detachment of podocytes from the glomerular basement membrane, and the appearance of specific podocyte proteins and whole cells (podocyturia) in the urine. Massive podocyturia in a limited proliferative capacity of podocytes leads to reduce their total count in the glomerulus (podocytopenia) and the development of glomerulosclerosis. The authors describe the line of markers of the podocyte injury and invasive and non-invasive methods of their assessment. In addition, the relationship of podocyturia level with proteinuria and renal dysfunction are discussed, the prospects of assessment the podocyte proteins in urine for assessing of glomerular damage severity and glomerulosclerosis risk are examined.

Nephrin is necessary for podocyte recovery following injury in an adult mature glomerulus

Nephrin (Nphs1) is an adhesion protein that is expressed at the podocyte intercellular junction in the glomerulus. Nphs1 mutations in humans or deletion in animal genetic models results in a developmental failure of foot process formation. A number of studies have shown decrease in expression of nephrin in various proteinuric kidney diseases as well as in animal models of glomerular disease. Decrease in nephrin expression has been suggested to precede podocyte loss and linked to the progression of kidney disease. Whether the decrease in expression of nephrin is related to loss of podocytes or lead to podocyte detachment is unclear. To answer this central question we generated an inducible model of nephrin deletion (Nphs1Tam-Cre) in order to lower nephrin expression in healthy adult mice. Following tamoxifen-induction there was a 75% decrease in nephrin expression by 14 days. The Nphs1Tam-Cre mice had normal foot process ultrastructure and intact filtration barriers up to 4-6 weeks post-induction. Despite the loss of nephrin expression, the podocyte number and density remained unchanged during the initial period. Unexpectedly, nephrin expression, albeit at low levels persisted at the slit diaphragm up to 16-20 weeks post-tamoxifen induction. The mice became progressively proteinuric with glomerular hypertrophy and scarring reminiscent of focal and segmental glomerulosclerosis at 20 weeks. Four week-old Nphs1 knockout mice subjected to protamine sulfate model of podocyte injury demonstrated failure to recover from foot process effacement following heparin sulfate. Similarly, Nphs1 knockout mice failed to recover following nephrotoxic serum (NTS) with persistence of proteinuria and foot process effacement. Our results suggest that as in development, nephrin is necessary for maintenance of a healthy glomerular filter. In contrast to the developmental phenotype, lowering nephrin expression in a mature glomerulus resulted in a slowly progressive disease that histologically resembles FSGS a disease linked closely with podocyte depletion. Podocytes with low levels of nephrin expression are both susceptible and unable to recover following perturbation. Our results suggest that decreased nephrin expression independent of podocyte loss occurring as an early event in proteinuric kidney diseases might play a role in disease progression.

Soluble CD40 ligand directly alters glomerular permeability and may act as a circulating permeability factor in FSGS

CD40/CD40 ligand (CD40L) dyad, a co-stimulatory bi-molecular complex involved in the adaptive immune response, has also potent pro-inflammatory actions in haematopoietic and non-haematopoietic cells. We describe here a novel role for soluble CD40L (sCD40L) as modifier of glomerular permselectivity directly acting on glomerular epithelial cells (GECs). We found that stimulation of CD40, constitutively expressed on GEC cell membrane, by the sCD40L rapidly induced redistribution and loss of nephrin in GECs, and increased albumin permeability in isolated rat glomeruli. Pre-treatment with inhibitors of CD40-CD40L interaction completely prevented these effects. Furthermore, in vivo injection of sCD40L induced a significant reduction of nephrin and podocin expression in mouse glomeruli, although no significant increase of urine protein/creatinine ratio was observed after in vivo injection. The same effects were induced by plasma factors partially purified from post-transplant plasma exchange eluates of patients with focal segmental glomerulosclerosis (FSGS), and were blocked by CD40-CD40L inhibitors. Moreover, 17 and 34 kDa sCD40L isoforms were detected in the same plasmapheresis eluates by Western blotting. Finally, the levels of sCD40Lwere significantly increased in serum of children both with steroid-sensitive and steroid-resistant nephrotic syndrome (NS), and in adult patients with biopsy-proven FSGS, compared to healthy subjects, but neither in children with congenital NS nor in patients with membranous nephropathy.

Our results demonstrate that sCD40L directly modifies nephrin and podocin distribution in GECs. Moreover, they suggest that sCD40L contained in plasmapheresis eluates from FSGS patients with post-transplant recurrence may contribute, presumably cooperating with other mediators, to FSGS pathogenesis by modulating glomerular permeability.

Interaction of CD80 with Neph1: a potential mechanism of podocyte injury

BACKGROUND

The induction of CD80 on podocytes has been shown in animal models of podocyte injury and in certain cases of nephrotic syndrome. In a lipopolysaccharide (LPS)-induced mouse model of albuminuria, we have recently shown a signalling axis of LPS-myeloid cell activation-TNFα production-podocyte CD80 induction-albuminuria. Therefore, in this report, we investigated the cellular and molecular consequences of TNFα addition and CD80 expression on cultured podocytes.

METHODS

A murine podocyte cell line was used for TNFα treatment and for over-expressing CD80. Expression and localization of various podocyte proteins was analysed by reverse transcriptase-polymerase chain reaction, western blotting and immunofluorescence. HEK293 cells were used to biochemically characterize interactions.

RESULTS

Podocytes treated with LPS in vitro did not cause CD80 upregulation but TNFα treatment was associated with an increase in CD80 levels, actin derangement and poor wound healing. Podocytes stably expressing CD80 showed actin derangement and co-localization with Neph1. CD80 and Neph1 interaction was confirmed by pull down assays of CD80 and Neph1 transfected in HEK293 cells.

CONCLUSION

Addition of TNFα to podocytes causes CD80 upregulation, actin reorganization and podocyte injury. Overexpressed CD80 and Neph1 interact via their extracellular domain. This interaction implies a mechanism of slit diaphragm disruption and possible use of small molecules that disrupt CD80-Neph1 interaction as a potential for treatment of nephrotic syndrome associated with CD80 upregulation.

Wolf-Hirschhorn syndrome candidate 1-like 1 epigenetically regulates nephrin gene expression

Altered expression of nephrin underlies the pathophysiology of proteinuria in both congenital and acquired nephrotic syndrome. However, the epigenetic mechanisms of nephrin gene regulation remain elusive. Here, we show that Wolf-Hirschhorn syndrome candidate 1-like 1 long form (WHSC1L1-L) is a novel epigenetic modifier of nephrin gene regulation. WHSC1L1-L was associated with histone H3K4 and H3K36 in human embryonic kidney cells. WHSC1L1-L gene was expressed in the podocytes, and functional protein product was detected in these cells. WHSC1L1-L was found to bind nephrin but not other podocyte-specific gene promoters, leading to its inhibition/suppression, abrogating the stimulatory effect of WT1 and NF-κB. Gene knockdown of WHSC1L1-L in primary cultured podocytes accelerated the transcription of nephrin but not CD2AP. An in vivo zebrafish study involving the injection of Whsc1l1 mRNA into embryos demonstrated an apparent reduction of nephrin mRNA but not podocin and CD2AP mRNA. Immunohistochemistry showed that both WHSC1L1-L and nephrin emerged at the S-shaped body stage in glomeruli. Immunofluorescence and confocal microscopy displayed WHSC1L1 to colocalize with trimethylated H3K4 in the glomerular podocytes. Chromatin immunoprecipitation assay revealed the reduction of the association of trimethylated H3K4 at the nephrin promoter regions. Finally, nephrin mRNA was upregulated in the glomerulus at the early proteinuric stage of mouse nephrosis, which was associated with the reduction of WHSC1L1. In conclusion, our results demonstrate that WHSC1L1-L acts as a histone methyltransferase in podocytes and regulates nephrin gene expression, which may in turn contribute to the integrity of the slit diaphragm of the glomerular filtration barrier.

Effects of linagliptin on human immortalized podocytes: a cellular system to study dipeptidyl-peptidase 4 inhibition

BACKGROUND AND PURPOSE

Dipeptidyl-peptidase 4 (DPP4) is expressed by resident renal cells, including glomerular cells. DPP4 inhibitors (gliptins) exert albuminuria lowering effects, but the role of renal DPP4 as a pharmacological target has not been elucidated. To better understand the actions of gliptins, the effects of linagliptin on the behaviour of immortalized human podocytes and mesangial cells were evaluated.

EXPERIMENTAL APPROACH

The expression of DPP4 was measured at both the mRNA and protein levels. The effects of linagliptin on DPP4 activity, cell growth and cell cycle progression were determined. The contribution of the stromal cell-derived factor-1- CXCR4/CXCR7 signalling pathways was evaluated by studying the effects of AMD3100 (a CXCR4 antagonist and CXCR7 agonist) alone and in combination with linagliptin. The contribution of ERK1/2 activation was analysed by studying the effects of the MAPK kinase 1/2 inhibitor AZD6244.

KEY RESULTS

DPP4 was highly expressed in podocytes. The activity of DPP4 and podocyte growth were reduced by linagliptin. The effects of sitagliptin on podocyte growth were similar to those of linagliptin, were associated with inhibition of cell proliferation and mimicked by AMD3100. Moreover, linagliptin and AMD3100 were found to have a synergistic interaction, whereas no interaction was seen between linagliptin and AZD6244.

CONCLUSIONS AND IMPLICATIONS

Our cultures of human glomerular cells represent a reliable system for investigating the actions of gliptins. Moreover, DPP4 contributes to the regulation of podocyte behaviour. Inhibition of DPP4 in podocytes could underlie the effects of linagliptin on glomerular cells.

Ameliorating Effect of Gemigliptin on Renal Injury in Murine Adriamycin-Induced Nephropathy

Background. Previous studies have shown the antiapoptotic and anti-inflammatory potential of DPP-IV inhibitor in experimental models of renal injury. We tested whether DPP-IV inhibitor (gemigliptin) ameliorates renal injury by suppressing apoptosis, inflammation, and oxidative stress in mice with adriamycin nephropathy. Methods. Mice were treated with normal saline (control), gemigliptin (GM), adriamycin (ADR), or adriamycin combined with gemigliptin (ADR+GM). Apoptosis, inflammation, and oxidative stress were analyzed via western blotting, real-time PCR, light microscopy, and immunofluorescence. Results. In the ADR+GM group, urine albumin creatinine ratio decreased significantly compared with that in the ADR group on day 15. Glomerulosclerosis index and tubulointerstitial injury index in mice with adriamycin-induced nephropathy decreased after gemigliptin treatment. ADR group showed higher levels of apoptosis, inflammation, and oxidative stress-related molecules compared with the control group. The upregulation of these molecules was significantly reduced by gemigliptin. In the ADR group, the staining intensities of WT-1 and nephrin reduced, but these changes were ameliorated in the ADR+GM group. Conclusion. We demonstrated that gemigliptin ameliorates nephropathy by suppressing apoptosis, inflammation, and oxidative stress in mice administered adriamycin. Our data demonstrate that gemigliptin has renoprotective effects on adriamycin-induced nephropathy.

Protective effects of astragaloside in rats with adriamycin nephropathy and underlying mechanism

The present study was designed to determine the mechanism underlying the treatment of nephrotic syndrome using astragaloside by observing the effects of astragaloside on the expression of nephrin and podocin proteins and genes in kidneys of rats with adriamycin nephropathy. The rats were injected with adriamycin and, after successful model establishment, randomly divided into a model group, a Methylprednisolone (MP) group, and an astragaloside group. The 24-h complete urine samples were collected. Biochemical indicators were monitored, and kidney tissues were collected for pathological analysis using light microscopy and electron microscopy. The mRNA expression of nephrin and podocin was measured in the kidney tissues using the real-time qPCR, and the protein expression levels of nephrin and podocin were detected using Western blot analysis. At the end of 12 weeks of drug intervention, the urinary protein level was lower in the MP and astragaloside groups than that in the model group (P = 0.008 and P = 0.01, respectively). Serum albumin was higher in the MP and astragaloside groups than in the model group (P < 0.001 and P = 0.012, respectively). Podocytes in the MP group were nearly normal, and fusion of podocytes in the astragaloside group was significantly less than that in the control group. The nephrin and podocin mRNA and protein expression levels in the intervention groups were higher (P < 0.05) than that in the model group. Due to the increased expression of podocyte-related nephrin and podocin proteins, astragaloside maintained slit diaphragm integrity and decreased the level of proteinuria in rats with adriamycin nephropathy.

A novel assay to assess the effect of pharmaceutical compounds on the differentiation of podocytes

BACKGROUND AND PURPOSE

Therapeutic options for treating glomerulopathies, the main cause of chronic kidney disease, are limited. Podocyte dedifferentiation is a major event in the pathogenesis of glomerulopathies. The goal of the present study was, therefore, to develop an assay to monitor podocyte differentiation suitable for compound screening.

EXPERIMENTAL APPROACH

We isolated and cultured glomeruli from transgenic mice, expressing cyan fluorescent protein (CFP) under the control of the promoter of nephrin, a marker of podocyte differentiation. Mean CFP fluorescence intensity per glomerulus (MFG) was determined by summation of all glomerular voxels from confocal z-stacks in the absence and presence of pharmaceutical compounds.

KEY RESULTS

In untreated cultured glomeruli, MFG remained fairly stable during the first 5 days, when foot processes were already effaced, and the level of many podocyte-specific proteins was only mildly affected, as revealed by proteomics. Between day 6 and 9, MFG decreased to almost zero. The decrease in MFG was paralleled by a decrease in CFP and nephrin expression, as determined by RT-PCR, western blots and proteomics. Puromycin aminonucleoside (PAN), which damages podocytes, concentration-dependently induced a complete loss of MFG. Dexamethasone (25 μM) and pioglitazone (10 μM) markedly attenuated the effect of 0.6 μg·mL^-1 PAN on MFG.

CONCLUSION AND IMPLICATIONS

In summary, we established a novel assay to assess the effect of pharmaceutical compounds on the differentiation of podocytes in situ. Our assay is suitable for compound screening to identify drugs for the treatment of glomerulopathies.

Pathogenesis of proteinuria in idiopathic minimal change disease: molecular mechanisms

Minimal change disease (MCD) is the most common type of nephrotic syndrome in children and adolescents. The pathogenesis of proteinuria in this condition is currently being reassessed. Following the Shalhoub hypothesis, most efforts have been placed on identifying the putative circulating factor, but recent advancement in podocyte biology has focused attention on the molecular changes at the glomerular capillary wall, which could explain the mechanism of proteinuria in MCD. This report critically reviews current knowledge on the different postulated mechanisms at the glomerular capillary wall level for increased permeability to plasma proteins in MCD. The report helps describe the rationale behind novel therapies and suggests future targeted therapies for MCD.

Structural Analysis of the Myo1c and Neph1 Complex Provides Insight into the Intracellular Movement of Neph1

The Myo1c motor functions as a cargo transporter supporting various cellular events, including vesicular trafficking, cell migration, and stereociliary movements of hair cells. Although its partial crystal structures were recently described, the structural details of its interaction with cargo proteins remain unknown. This study presents the first structural demonstration of a cargo protein, Neph1, attached to Myo1c, providing novel insights into the role of Myo1c in intracellular movements of this critical slit diaphragm protein. Using small angle X-ray scattering studies, models of predominant solution conformation of unliganded full-length Myo1c and Myo1c bound to Neph1 were constructed. The resulting structures show an extended S-shaped Myo1c with Neph1 attached to its C-terminal tail. Importantly, binding of Neph1 did not induce a significant shape change in Myo1c, indicating this as a spontaneous process or event. Analysis of interaction surfaces led to the identification of a critical residue in Neph1 involved in binding to Myo1c. Indeed, a point mutant from this site abolished interaction between Neph1 and Myo1c when tested in the in vitro and in live-cell binding assays. Live-cell imaging, including fluorescence recovery after photobleaching, provided further support for the role of Myo1c in intracellular vesicular movement of Neph1 and its turnover at the membrane.

DA-1229, a dipeptidyl peptidase IV inhibitor, protects against renal injury by preventing podocyte damage in an animal model of progressive renal injury

Although dipeptidyl peptidase IV (DPPIV) inhibitors are known to have renoprotective effects, the mechanism underlying these effects has remained elusive. Here we investigated the effects of DA-1229, a novel DPPIV inhibitor, in two animal models of renal injury including db/db mice and the adriamycin nephropathy rodent model of chronic renal disease characterized by podocyte injury. For both models, DA-1229 was administered at 300 mg/kg/day. DPPIV activity in the kidney was significantly higher in diabetic mice compared with their nondiabetic controls. Although DA-1229 did not affect glycemic control or insulin resistance, DA-1229 did improve lipid profiles, albuminuria and renal fibrosis. Moreover, DA-1229 treatment resulted in decreased urinary excretion of nephrin, decreased circulating and kidney DPPIV activity, and decreased macrophage infiltration in the kidney. In adriamycin-treated mice, DPPIV activity in the kidney and urinary nephrin loss were both increased, whereas glucagon-like peptide-1 concentrations were unchanged. Moreover, DA-1229 treatment significantly improved proteinuria, renal fibrosis and inflammation associated with decreased urinary nephrin loss, and kidney DPP4 activity. In cultured podocytes, DA-1229 restored the high glucose/angiotensin II-induced increase of DPPIV activity and preserved the nephrin levels in podocytes. These findings suggest that activation of DPPIV in the kidney has a role in the progression of renal disease, and that DA-1229 may exert its renoprotective effects by preventing podocyte injury.

Podocyte-specific NF-κB inhibition ameliorates proteinuria in adriamycin-induced nephropathy in mice

BACKGROUND

Podocytes play a central role in the formation of the glomerular filtration barrier in the kidney, and their dysfunction has been shown to result in proteinuria. In the present study, we sought to determine the cell-autonomous role of NF-κB, a proinflammatory signaling, within podocytes in proteinuric kidney disease.

METHODS

Podocyte-specific IκBΔN transgenic (Pod-IκBΔN) mice, in which NF-κB was inhibited specifically in podocytes, were generated by the Cre-loxP technology, and their phenotype was compared with control mice in adriamycin-induced nephropathy.

RESULTS

Pod-IκBΔN mice were phenotypically normal and did not exhibit proteinuria at the physiological condition. By the intravenous administration of adriamycin, overt proteinuria appeared in Pod-IκBΔN mice, as well as in control mice. However, of interest, the amount of proteinuria was significantly lower in adriamycin-injected Pod-IκBΔN mice (373 ± 122 mg albumin/g creatinine), compared with adriamycin-injected control mice (992 ± 395 mg albumin/g creatinine). Expression of podocyte-selective slit diaphragm-associated proteins, such as nephrin and synaptopodin, was markedly decreased by adriamycin injection in control mice, whereas the reduction was attenuated in Pod-IκBΔN mice. Adriamycin-induced reduction in synaptopodin expression was also seen in cultured podocytes derived from control mice, but not in those from Pod-IκBΔN mice.

CONCLUSIONS

Because nephrin and synaptopodin are essential for the maintenance of the slit diaphragm in podocytes, these results suggest that proteinuria in adriamycin-induced nephropathy is caused by the reduction in expression of these proteins. The results also suggest that the NF-κB signalling in podocytes cell-autonomously contributes to proteinuria through the regulation of these proteins.

Huaiqihuang Granules () reduce proteinuria by enhancing nephrin expression and regulating necrosis factor κB signaling pathway in adriamycin-induced nephropathy

OBJECTIVE

To investigate the effects of Huaiqihuang Granules (, HQH), a mixture of Chinese herbs including Trametes robiniophila Murr, Fructus Lycii and Polygonatum sibiricum, on adriamycininduced nephropathy (ADRN) in rats and its underlying mechanisms.

METHODS

Rats with ADRN were divided into four groups: the sham group, the model group (distilled water), the low-dose HQH-treated (2 g/kg) group, and the high-dose HQH-treated (4 g/kg) group. Body weight and 24-h urinary protein (Upro) were checked every week. After 5-week intervention, at the end of the study, the rats were sacrificed and blood samples were collected for examination of biochemical parameters, including glomerular morphological makers, podocyte shape, cellular apoptosis, expressions of nephrin, inflammatory and apoptosis markers.

RESULTS

HQH ameliorated the rat's general status, proteinuria, renal morphological appearance and glomerulosclerosis. The decreased expression of nephrin in ADRN rats was increased by HQH, as well as the impaired podocyte foot process fusion. Cytosolic levels of p65 and inhibitor of nuclear factor κBα (IκBα) were decreased in ADRN rats, and recovered by the treatment of HQH. Consistently, the induced expression of tumor necrosis factor α (TNF-α), phosphorylated nuclear factor κB p65 (p-NFκB p65) and IκBα in ADRN were markedly suppressed by HQH. In addition, induction of Bax, cleaved caspase-3 and cytochrome C in ADRN rats were suppressed by HQH, indicating the amelioration of apoptosis.

CONCLUSION

HQH could ameliorate renal impairments in ADRN rats by increasing nephrin expression, inhibiting NF-κB signaling pathway via the down-regulation of p-NF-κB p65 and p-IκBα, and suppression of glomerular and tubular apoptosis.

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.

Alteration in the podoplanin-ezrin-cytoskeleton linkage is an important initiation event of the podocyte injury in puromycin aminonucleoside nephropathy, a mimic of minimal change nephrotic syndrome

Podoplanin was identified as a protein associated with the transformation of arborized foot processes of glomerular epithelial cells (podocytes) to flat feet. However, the function of podoplanin in the podocyte is not yet fully clarified. In this study, we analyzed the molecular nature of podoplanin, and its expression in rat nephrotic models and patients with minimal change nephrotic syndrome (MCNS). We demonstrated here that podoplanin has two forms: one contains abundant sialic acid and the other a lesser amount of sialic acid. Podoplanin bound ezrin to interact with the cytoskeleton. The silencing of podoplanin in cultured podocytes caused a change in the cell shape and the distribution of ezrin and actin. The expression of podoplanin was clearly reduced before the onset of proteinuria in puromycin aminonucleoside (PAN) nephropathy, a mimic of MCNS, and the decrease in the expression of podoplanin became more evident at the proteinuric stage. Podoplanin was detected in normal urine samples, and the amount of urinary podoplanin markedly increased on day 1 of PAN nephropathy. Urinary ezrin was also detected. The amount of the phosphorylated ezrin was reduced, while the amount of the podoplanin-interacting ezrin increased. The podoplanin expression was reduced in a patient with active-phase MCNS. It is conceivable that the alteration of the podoplanin-ezrin-cytoskeleton linkage is an important event of the podocyte injury in MCNS.

Inflammation in diabetic nephropathy: moving toward clinical biomarkers and targets for treatment

Diabetic nephropathy (DN) is a leading cause of end stage renal failure and there is an urgent need to identify new clinical biomarkers and targets for treatment to effectively prevent and slow the progression of the complication. Many lines of evidence show that inflammation is a cardinal pathogenetic mechanism in DN. Studies in animal models of experimental diabetes have demonstrated that there is a low-grade inflammation in the diabetic kidney. Both pharmacological and genetic strategies targeting inflammatory molecules have been shown to be beneficial in experimental DN. In vitro studies have cast light on the cellular mechanisms whereby diabetes triggers inflammation and in turn inflammation magnifies the kidney injury. Translation of this basic science knowledge into potential practical clinical applications is matter of great interest for researchers today. This review focuses on key pro-inflammatory systems implicated in the development of DN: the tumor necrosis factor(TNF)-α/TNF-α receptor system, the monocyte chemoattractant protein-1/CC-chemokine receptor-2 system, and the Endocannabinoid system that have been selected as they appear particularly promising for future clinical applications.

Histamine receptor expression in human renal tubules: a comparative pharmacological evaluation

OBJECTIVE AND DESIGN

The aim of this study is to evaluate the expression of the histamine receptors, particularly focusing on the H4R in human renal tubules.

MATERIAL

The ex vivo evaluation was carried on specimens from human renal cortex. Primary and immortalized tubular epithelial cells (TECs) and the HK-2 cell line were used as in vitro models.

TREATMENT

Cells were pretreated for 10 min with chlorpheniramine maleate 10 μM (H1R antagonist), ranitidine 10 µM (H2R antagonist), GSK189254 1 µM (H3R antagonist) or JNJ7777120 10 µM (H4R antagonist), and then exposed to histamine (3 pM-10 nM) for 30 min.

METHODS

The ex vivo evaluation on specimens from human renal cortex was performed by immunohistochemistry. The expression of histamine receptors on primary and immortalized TECs and the HK-2 cell line was evaluated at both gene (RT-PCR) and protein (immunocytofluorescence) levels. The pharmacological analysis was performed by TR-FRET measurements of second messenger (IP3 and cAMP) production induced by histamine with or without the selective antagonists.

RESULTS

Our data revealed the presence of all histamine receptors in human tubules; however, only TECs expressed all the receptors. Indeed, histamine elicited a sigmoid dose-response curve for IP3 production, shifted to the right by chlorpheniramine maleate, and elicited a double bell-shaped curve for cAMP production, partially suppressed by the selective H2R, H3R and H4R antagonists when each added alone, and completely ablated when combined together.

CONCLUSIONS

Herein, we report the identification of all four histamine receptors in human renal tubules.

Enhanced Steroid Therapy in Adult Minimal Change Nephrotic Syndrome: A Systematic Review and Meta-analysis

The best regimen for adult minimal change nephrotic syndrome (MCNS) is still unknown. Due to an excessive number of adverse events caused by oral steroid monotherapy, enhanced steroid therapy (low dose of prednisolone with a short course of methylprednisolone or with another immunosuppressant) has been studied extensively for years. In this study, the PubMed, Embase, EBSCO and Cochrane Library databases were searched for clinical trials which compared enhanced steroid therapy with oral steroid monotherapy in adult MCNS and a meta-analysis was performed. Seven studies involving 357 patients were included. We found that patients treated with enhanced steroid therapy responded more quickly to complete remission (CR) [mean difference = -9.52, 95% confidence interval (CI): -12.66--6.39, p<0.00001] and showed fewer adverse events [risk radio (RR) = 0.72, 95% CI: 0.54-0.97, p=0.03] than patients receiving oral steroid monotherapy. The CR rate (RR= 0.96, 95% CI: 0.83-1.10, p=0.53) and relapse rate (RR=0.87, 95% CI: 0.57-1.34, p=0.53) were similar in both groups.

The PI3K/p-Akt signaling pathway participates in calcitriol ameliorating podocyte injury in DN rats

OBJECTIVES

The present study aimed to investigate the relationship between PI3K/p-Akt signaling pathway and podocyte impairment in DN rats as well as the protective effect of calcitriol.

METHODS

SD rats were randomly divided into four groups: normal control (NC), normal treated with calcitriol (NC+VD), diabetic nephropathy (DN) and DN treated with calcitriol (DN+VD); all VD rats were treated with 0.1 μg/kg/d calcitriol by gavage. DN model rats were established by intraperitoneal injections of streptozotocin (STZ). Rats were sacrificed after 18 weeks of treatments.

RESULTS

In the present study, increased albuminuria was observed as early as 3 weeks of diabetes and continued to increase more than six-fold throughout the length of the study (18 weeks). Expectedly, animals receiving the treatment with calcitriol was protected from this increase, lower about one third. Meanwhile, the expression of podocyte specific markers, including nephrin and podocin, together with PI3K/p-Akt was significantly decreased in DN rats, whereas calcitriol reversed these above changes accompanied by elevated the expression levels of VDR. Additionally, a positive correlation was observed between the expression levels of nephrin and VDR (r = 0.776, P < 0.05). Likewise, the expression of nephrin was positively correlated with both PI3K-p85 and p-Akt (r = 0.736, P < 0.05; r = 0.855, P < 0.05, respectively).

CONCLUSION

PI3K/p-Akt signaling pathway participates in calcitriol ameliorating podocyte injury in DN rats. The manipulation of calcitriol might act as a promising therapeutic intervention for diabetic nephropathy.

Detection of urinary podocytes and nephrin as markers for children with glomerular diseases

The purpose of this study was to detect the urinary podocytes and its related protein, nephrin, in the urine of the children with glomerular disease in order to analyze the relationship of the clinical testing with the significance of the glomerular disease. A total of 65 children with nephrotic syndrome were selected for this study. The podocytes and nephrin were detected in the urinary sediment by indirect immunofluorescence, enzyme-linked immunosorbent assay, and Western blotting. The urinary podocytes and nephrin positive rates were 53.8% and 50.8%, respectively, in the children with glomerular disease. The serum total protein and albumin decreased in the podocyte-positive children, while the urine total protein at 24 h, urinary albumin/creatinine ratio, blood urea nitrogen, and serum creatinine were significantly elevated as compared to those of the podocyte-negative patients. Furthermore, the results were the same in the patients with positive nephrin as compared to that of the patients with negative nephrin. The podocyte number and nephrin level were significantly higher in the lupus nephritis group as compared to those of the other groups. Likewise, the podocyte number and nephrin level dramatically increased in the focal segmental glomerulosclerosis group as compared to those of the mesangial proliferative glomerulonephritis and minimal change disease groups. In addition, the podocyte numbers and nephrin expression were significantly higher in severe proteinuria group as compared to those of the mild proteinuria group. The urinary nephrin expression was positively related to podocyte and urinary albumin/creatinine ratio. We concluded that the detection of the urinary podocytes and nephrin could be taken as markers for children with glomerular disease, reflecting the type of the disease. Therefore, this can be used as a noninvasive method to evaluate the severity of the kidney disease in children.

Therapeutic target for nephrotic syndrome: Identification of novel slit diaphragm associated molecules

The slit diaphragm bridging the neighboring foot processes functions as a final barrier of glomerular capillary wall for preventing the leak of plasma proteins into primary urine. It is now accepted that the dysfunction of the sit diaphragm contributes to the development of proteinuria in several glomerular diseases. Nephrin, a gene product of NPHS1, a gene for a congenital nephrotic syndrome of Finnish type, constitutes an extracellular domain of the slit diaphragm. Podocin was identified as a gene product of NPHS2, a gene for a familial steroid-resistant nephrotic syndrome of French. Podocin binds the cytoplasmic domain of nephrin. After then, CD2 associated protein, NEPH1 and transient receptor potential-6 were also found as crucial molecules of the slit diaphragm. In order to explore other novel molecules contributing to the development of proteinuria, we performed a subtraction hybridization assay with a normal rat glomerular RNA and a glomerular RNA of rats with a puromycin aminonucleoside nephropathy, a mimic of a human minimal change type nephrotic syndrome. Then we have found that synaptic vesicle protein 2B, ephrin-B1 and neurexin were already downregulated at the early stage of puromycin aminonucleoside nephropathy, and that these molecules were localized close to nephrin. It is conceivable that these molecules are the slit diaphragm associated molecules, which participate in the regulation of the barrier function. These molecules could be targets to establish a novel therapy for nephrotic syndrome.

Expression patterns of podocyte-associated mRNAs in patients with proliferative or non-proliferative glomerulopathies

AIM

It is not clear how the podocyte damage manifests in different glomerulopathies. This study evaluated the podocyte-associated mRNA profiles in renal tissue and urine of patients with proliferative (PGs) or non-proliferative (NPGs) glomerulopathies.

METHODS

Messenger RNA levels of nephrin, podocin, podocalyxin, synaptopodin, and alpha-actinin-4 were measured in the kidney tissue and urinary cells by real-time polymerase chain reaction. Podocyte-associated mRNAs were correlated with proteinuria and renal function, and the effect of immunosuppressive treatment of PGs and NPGs on urine mRNAs was assessed up to one year of follow up.

RESULTS

Podocyte-associated mRNAs were expressed consistently less in kidney tissue from patients with NPGs, and urinary podocyte mRNA levels were significantly higher in the PG group. After six months of immunosuppressive therapy, patients with PGs showed a significant reduction in the expression of podocin, podocalyxin, and alpha-actinin-4 compared with baseline (p<0.001). In the NPG group, alpha-actinin-4 levels decreased (p=0.008), and there was also a trend toward reduced podocalyxin mRNA (p=0.08). Urine podocyte-associated mRNAs correlated with the level of proteinuria at baseline and at six months, and there was a trend toward an inverse correlation between urinary mRNAs and kidney function at one year of follow up.

CONCLUSIONS

Podocyte-associated mRNAs were inhibited in kidney tissue concomitantly with their increase in urine in these patients with glomerulopathies. Different profiles of mRNA expression were seen, pointing to a higher degree of intra-renal podocytopenia in the NPGs and of podocyturia in the PGs. The immunosuppressive therapy effectively reduced the urinary levels of podocyte-associated mRNAs.

Comparison of methylprednisolone plus prednisolone with prednisolone alone as initial treatment in adult-onset minimal change disease: a retrospective cohort study

BACKGROUND AND OBJECTIVES

Previous studies suggested that intravenous methylprednisolone possibly accelerates remission of proteinuria in adult-onset minimal change disease; its impact on relapse of proteinuria is unknown.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

This multicenter retrospective cohort study included 125 adult-onset minimal change disease patients diagnosed by kidney biopsy between 2000 and 2009 and treated initially with corticosteroid in five nephrology centers in Japan participating in the Study of Outcomes and Practice Patterns of Minimal Change Disease. Times to first remission and first relapse of proteinuria after initiating the first immunosuppressive therapy were compared between 65 patients with initial use of intravenous methylprednisolone followed by prednisolone and 60 patients with initial use of prednisolone alone using multivariate Cox proportional hazards models. After calculating the probability of receiving methylprednisolone and prednisolone using a logistic regression model (propensity score), the results were ascertained using propensity score-matched and -stratified models.

RESULTS

During the median 3.6 years of observation (interquartile range=2.0-6.9), all 65 patients in the methylprednisolone and prednisolone group achieved remission within 11 (8-20) days of the corticosteroid initiation, whereas in the prednisolone group, 58 of 60 patients (96.7%) achieved remission within 19 (12-37) days (P<0.001). After achieving first remission, 32 (49.2%) patients in the methylprednisolone and prednisolone group and 43 (74.1%) patients in the prednisolone group developed at least one relapse. Multivariate Cox proportional hazards models revealed that methylprednisolone and prednisolone use was significantly associated with early remission (multivariate-adjusted hazard ratio, 1.56; 95% confidence interval, 1.06 to 2.30) and lower incidence of relapse (0.50; 95% confidence interval, 0.29 to 0.85) compared with prednisolone use alone. These results were ascertained in propensity score-based models. No significant difference was observed in incidence of adverse events, including infection, aseptic osteonecrosis, cataract, diabetes, and gastrointestinal bleeding.

CONCLUSIONS

Initial use of methylprednisolone was associated with earlier remission and lower incidence of relapse in adult-onset minimal change disease patients. Efficacy of methylprednisolone should be evaluated in randomized controlled trials.

Effect of Cordyceps sinensis and Tripterygium wilfordii polyglycosidium on podocytes in rats with diabetic nephropathy

The aim of the present study was to investigate the effects of Cordyceps sinensis (CS) and Tripterygium wilfordii polyglycosidium (TWP) on podocytes in rats with diabetic nephropathy (DN). DN rat models were established and divided randomly into normal control (group A), DN (group B), CS (group C), TWP (group D) and CS and TWP groups (group E). After 12 weeks, levels of 24-h urinary protein, blood urea nitrogen (BUN), serum creatinine (SCR), white blood cells, blood glucose (GLU), aspartate aminotransferase, alanine aminotransferase and kidney weight (KW)/body weight (BW) were determined. Renal pathological changes were evaluated using hematoxylin and eosin staining, whereas the structural changes in the podocytes were observed under a transmission electron microscope. The expression levels of nephrin and podocin were evaluated using immunofluorescence staining. Compared with group A, the SCR and BUN levels in group B were higher (P<0.05) and the GLU, KW/BW and the 24-h urine protein were markedly higher (P<0.01). Moreover, incidences of glomerular disorders, chronic tubulointerstitial damage and glomerular podocyte lesions in groups B, C, D and E were observed, compared with group A. The high cortical expression of nephrin and podocin protein decreased. Compared with group B, the KW/BW and 24-h urinary protein level in groups C, D and E were lower (P<0.01). The glomeruli, tubules and podocytes exhibited pathomorphological improvements and the nephrin and podocin protein expression levels were higher in the nephridial tissue. A decrease in KW/BW and the 24-h urinary protein level, as well as improvements in glomerular disorder, chronic tubulointerstitial damage and glomerular podocyte lesions, were observed in groups C, D and E. Therefore, the results demonstrated that CS and TWP exhibited a protective effect on the podocytes of rats with DN. Moreover, CS combined with TWP increased this protective effect.

aPKCλ maintains the integrity of the glomerular slit diaphragm through trafficking of nephrin to the cell surface

The slit diaphragm (SD), the specialized intercellular junction between renal glomerular epithelial cells (podocytes), provides a selective-filtration barrier in renal glomeruli. Dysfunction of the SD results in glomerular diseases that are characterized by disappearance of SD components, such as nephrin, from the cell surface. Although the importance of endocytosis and degradation of SD components for the maintenance of SD integrity has been suggested, the dynamic nature of the turnover of intact cell-surface SD components remained unclear. Using isolated rat glomeruli we show that the turnover rates of cell-surface SD components are relatively high; they almost completely disappear from the cell surface within minutes. The exocytosis, but not endocytosis, of heterologously expressed nephrin requires the kinase activity of the cell polarity regulator atypical protein kinase C (aPKC). Consistently, we demonstrate that podocyte-specific deletion of aPKCλ resulted in a decrease of cell-surface localization of SD components, causing massive proteinuria. In conclusion, the regulation of SD turnover by aPKC is crucial for the maintenance of SD integrity and defects in aPKC signalling can lead to proteinuria. These findings not only reveal the pivotal importance of the dynamic turnover of cell-surface SD components but also suggest a novel pathophysiological basis in glomerular disease.