Familial focal segmental glomerulosclerosis with Alport-like glomerular basement changes caused by paired box protein 2 gene variant

Paired box protein 2 (PAX2) gene variant causes renal coloboma syndrome (MIM#120330). Further, they are associated with focal segmental glomerulosclerosis and characterized by basement membrane changes similar to Alport syndrome.Herein, we report an 8-year-old boy who presented with proteinuria and decreased renal function. His paternal uncle has focal segmental glomerulosclerosis and renal failure, and his paternal grandmother has renal failure and is receiving peritoneal dialysis. Further, his father has stage 2 chronic kidney disease. At 3 years of age, his serum creatinine-estimated glomerular filtration rate was 40-50 mL/min/1.73 m2. At 8 years of age, his renal function further decreased and he had proteinuria (urinary protein/Cr 3.39 g/g Cr). Renal histopathology showed oligonephronia and focal segmental glomerulosclerosis. A partial basket-weave pattern, similar to Alport syndrome, was also observed on a transmission electron microscope, and low-vacuum scanning electron microscopy revealed coarse meshwork changes in the glomerular basement membrane. Genetic analysis revealed a PAX2 heterozygous variant (NM_003987.4:c.959C  >  G), a nonsense variant in which the serine at position 320 changes to a stop codon, in our patient and his father. PAX2 is a transcription factor that is important for the podocyte variant. However, podocytes with PAX2 gene variants may cause abnormal basement membrane production and repair, thereby resulting in Alport-like changes.

Radiation nephropathy: Mechanisms of injury and recovery in a murine model

BACKGROUND

Radiation nephropathy (RN) can be a severe late complication for patients treated with radiotherapy (RT) targeting abdominal and paraspinal tumors. Recent studies investigating the mechanisms of RT-mediated injury in the kidney have demonstrated that RT disrupts the cellular integrity of renal podocytes leading to cell death and loss of renal function.

AIM

To determine if RT-induced renal dysfunction is associated with alterations in podocyte and glomerular function, and whether RT-induced podocyte alterations were associated with changes in the glomerular basement membrane (GBM).

METHODS

C57BL/6 mice were treated with focal bilateral X-irradiation using a single dose (SD) of 4 Gy, 10 Gy, or 14 Gy or fractionated dosing (FD) of 5x6Gy or 24x2Gy. Then, 10-40 weeks after RT parameters of renal function were measured, along with glomerular filtration rate (GFR) and glomerular histology, as well as ultrastructural changes in GBM by transmission electron microscopy.

RESULTS

RT treatment resulted in persistent changes in renal function beginning at 10 weeks with little recovery up to 40 weeks post RT. Dose dependent changes were seen with increasing SD but no functional sparing was evident after FD. RT-induced loss of renal function was associated with expansion of the GBM and significant increases in foot process width, and associated with significant reduction in GFR, podocyte loss, and renal fibrosis.

CONCLUSION

For the first time, these data show that expansion of the GBM is one consequence of radiation injury, and disarrangement of the GBM might be associated with the death of podocytes. These data shed new light on the role podocyte injury and GBM in RT-induced renal dysfunction.

Spatial composition and turnover of the main molecules in the adult glomerular basement membrane

The glomerular basement membrane (GBM) is an important tissue structure in kidney function. It is the membrane through which filtrate and solutes must pass to reach the nephron tubules. This review focuses on the spatial location of the main extracellular matrix components of the GBM. It also attempts to explain this organization in terms of their synthesis, transport, and loss. The picture that emerges is that the collagen IV and laminin content of GBM are in a very slow dynamic disequilibrium, leading to GBM thickening with age, and in contrast, some heparan sulfate proteoglycans are in a dynamic equilibrium with a very rapid turnover (i.e. half-life measured in ~hours) and flow direction against the flow of filtrate. The highly rapid heparan sulfate turnover may serve several roles, including an unclogging mechanism for the GBM, compressive stiffness of the GBM fiber network, and/or enabling podocycte-endothelial crosstalk against the flow of filtrate.

[Electron microscopy in nephropathology]

Non-neoplastic kidney diseases represent a broad spectrum of diseases. Although their pathogenesis differs, the histological findings may be similar in terms of conventional morphology. A precise classification of these diseases is a prerequisite for correct therapy and prognostic assessment. In the diagnostic process, the magnification achieved by electron microscopy is essential and cannot be replaced by any other technique. The most frequent diagnostic questions addressed by ultrastructural studies represent (1) alterations of podocytes (e.g., minimal-change disease), (2) changes of the thickness and structure of the glomerular basement membrane (e.g., diabetic glomerulosclerosis or Alport disease), (3) the presence, characteristics and exact localisation of immune complexes (e.g., membranous glomerulonephritis or lupus nephritis), (4) alterations of endothelial cells and capillaries (e.g., thrombotic microangiopathy) and (5) diseases of the tubular cells (e.g., light-chain nephropathy or toxic effects). Therefore, ultrastructural investigations are-together with conventional microscopy and immunohistochemistry (or immunofluorescence)-an integral part of the so-called triple-diagnostics in routine nephropathology.

A high-impact FN1 variant correlates with fibronectin-mediated glomerulopathy via decreased binding to collagen type IV

The glomerular basement membrane (GBM) consists of laminins, collagen IV, nidogens, and fibronectin and is essential for filtration barrier integrity in the kidney. Critically, structural and functional abnormalities in the GBM are involved in chronic kidney disease (CKD) occurrence and development. Fibronectin is encoded by FN1 and is essential for podocyte-podocyte and podocyte-matrix interactions. However, disrupted or disordered fibronectin occurs in many kidney diseases. In this study, we identified a novel mutation (c.3415G>A) in FN1 that causes glomerular fibronectin-specific deposition in a gain-of-function manner, that may be associated with thin basement membrane nephropathy (TBMN) and expand the spectrum of phenotypes seen in glomerulopathy with fibronectin deposits (GFND). Our studies confirmed this variant increased fibronectin's ability to bind to integrin, thereby maintaining podocyte adhesion. Also, we hypothesised that TBMN arose as the fibronectin variant exhibited a decreased capacity to bind COL4A3/4. Our study is the first to identify and link this novel pathogenic mutation (c.3415G>A) in FN1 to GFND as well as TBMN, which may broaden the phenotype and mutation spectrums of the FN1 gene. We believe our data will positively impact genetic counselling and prenatal diagnostics for GFND with TBMN and other associated conditions that may be commonly benign conditions in humans, and may not require proteinuria-lowering treatments or renal biopsy.

In Vitro Models to Evaluate Molecular Permeability of the Kidney Filtration Barrier

The glomerular basement membrane (GBM) is an important component of the kidney filtration barrier. The ability to evaluate the molecular transport properties of the GBM and determining how changes in the structure, composition, and mechanical properties of the GBM regulate its size selective transport properties may provide additional insight into glomerular function. This chapter details a method for making in vitro models of the glomerular filtration barrier using animal-derived decellularized glomeruli. FITC-labelled Ficoll is used as a filtration probe to evaluate the molecular transport properties during passive diffusion and under applied pressure. These systems can serve as a platform to evaluate the molecular permeability of basement membrane systems using conditions that simulate normal or pathophysiological conditions.

IgG subclass deposition in diabetic nephropathy

Purpose

This study aimed to analyze the distribution of IgG subclass in diabetic nephropathy (DN) and its association with clinicopathological features.

Methods

This is a single-center retrospective study enrolling 108 patients with biopsy-proven DN. Immunofluorescence and immunohistochemistry staining were applied, and clinicopathological features and renal outcomes were compared between patients with different patterns or categories of IgG subclass deposition.

Results

Both IgG and its subclasses colocalized with collagen IV α5 on glomerular basement membrane (GBM) and some of tubular basement membrane (TBM). IgG1 and the Mixed type were two predominant types of deposition, no matter on GBM or TBM, and IgG1 showed a much higher deposition rate on GBM than that on TBM (P = 0.004). IgG subclass deposit on multi-location was more associated with a shorter duration of nephropathy and severer tubular interstitial injury (P < 0.05). The mixed type of IgG subclass deposit on GBM was merely associated with higher levels of proteinuria, whereas the deposition on TBM was more associated with higher levels of proteinuria, lower levels of albumin, more KIM-1 positive area, and thicker TBM (P < 0.05). Survival analysis revealed that none of the pattern or the category of IgG subclass deposit was a risk factor or a renal outcome indicator.

Conclusions

IgG subclass was selectively deposited along GBM and/or TBM in DN, and the mixed type of IgG subclass deposition on TBM had more clinical significance than the isotype and that on GBM. IgG subclass deposition is merely a manifestation or a consequence rather than a cause in DN.

Generation of a Glomerular Filtration Barrier on a Glomerulus-on-a-Chip Platform

Despite an enormous investment of clinical and financial resources, chronic kidney disease (CKD) remains a global health threat. The lack of reliable in vitro systems that can efficiently mimic the renal and glomerular environment has hampered our ability to successfully develop novel and more renal specific drugs. Even though some success in generating in vitro tubule analogues and kidney organoids has been described, a major challenge remains for the in vitro assembly of the filtration unit of the kidney, the glomerulus. We have recently developed a novel glomerulus-on-a-chip system that mimics the characteristic and functionality of the glomerular filtration barrier, including its response to injury. This system recapitulates the functions and structure of the in vivo glomerulus, including permselectivity; indeed, we have confirmed free diffusion of insulin as well as impermeability to physiological concentrations of albumin. Exposure to nephrotoxic agents like puromycin aminonucleoside leads to a significant increase in albumin leakage. When exposed to sera from patients with anti-podocyte autoantibodies, the chip shows albumin leakage to an extent proportional to in vivo clinical data, phenomenon not observed with sera from either healthy controls, confirming functional response to injury. We describe here the detailed procedure to obtain a glomerulus-on-a-chip system that replicates both phenotypically and functionally the in vivo glomerular microenvironment.

A Novel LMX1B Variant Identified in a Patient Presenting with Severe Renal Involvement and Thin Glomerular Basement Membrane

We report a case of nail-patella syndrome (NPS) with unusual thinning of the glomerular basement membrane (GBM) associated with a novel heterozygous variant in the LMX1B gene. A 43-year-old female patient with a previous diagnosis of NPS, referred to our hospital for persistent proteinuria, underwent a renal biopsy, which revealed minor glomerular abnormalities. She underwent a second renal biopsy at the age of 56 owing to the presence of persistent proteinuria and decline in serum albumin, meeting the diagnostic criteria for nephrotic syndrome. Light microscopy demonstrated glomerulosclerosis and cystic dilatation of the renal tubules. Notably, electron microscopy revealed unusual thinning of the GBM, which is quite different from typical biopsy findings observed in patients with NPS, characterized by thick GBM with fibrillary material and electron-lucent structures. Comprehensive genetic screening for 168 known genes responsible for inherited kidney diseases using a next-generation sequencing panel identified a novel heterozygous in-frame deletion-insertion (c.723_729delinsCAAC: p.[Ser242_Lys243delinsAsn]) in exon 4 of the LMX1B gene, which may account for the disrupted GBM structure. Further studies are warranted to elucidate the complex genotype-phenotype relationship between LMX1B and proper GBM morphogenesis.

Utility of glomerular Gd-IgA1 staining for indistinguishable cases of IgA nephropathy or Alport syndrome

BACKGROUND

Pathological findings in Alport syndrome frequently show mesangial proliferation and sometimes incidental IgA deposition, in addition to unique glomerular basement membrane (GBM) changes including thin basement membrane and/or lamellation. However, similar GBM abnormalities are also often observed in IgA nephropathy. Both diseases are also known to show hematuria, proteinuria, and sometimes macrohematuria when associated with viral infection. Therefore, it can be difficult to make a differential diagnosis, even based on clinical and pathological findings. Some recent articles demonstrated that galactose-deficient IgA1 (Gd-IgA1)-specific monoclonal antibody (KM55) could potentially enable incidental IgA deposition to be distinguished from IgA nephropathy.

METHODS

We performed comprehensive gene screening and glomerular Gd-IgA1 and type IV collagen α5 chain immunostaining for five cases with both IgA deposition and GBM changes to confirm that Gd-IgA1 can help to distinguish these two diseases.

RESULTS

Four of the cases were genetically diagnosed with Alport syndrome (Cases 1-4) and one was IgA nephropathy with massive GBM changes, which had a negative gene test result (Case 5). In Cases 1-4, glomerular Gd-IgA1 deposition was not detected, although there was positivity for IgA in the mesangial area. In Case 5, glomerular Gd-IgA1 deposition was observed.

CONCLUSION

Gd-IgA1 expression analysis could clearly differentiate these two disorders. This approach can be applied to identify these two diseases showing identical clinical and pathological findings.

NPHS2 gene polymorphism aggravates renal damage caused by focal segmental glomerulosclerosis with COL4A3 mutation

Focal segmental glomerulosclerosis (FSGS), a type of primary glomerular disease, is the leading cause of end-stage renal disease (ESRD). Several studies have revealed that certain single-gene mutations are involved in the pathogenesis of FSGS; however, the main cause of FSGS has not been fully elucidated. Homozygous mutations in the glomerular basement membrane gene can lead to early renal failure, while heterozygous carriers develop renal failure symptoms late. Here, molecular genetic analysis of clinical information collected from clinical reports and medical records was performed. Results revealed that nephrosis 2 (NPHS2) gene polymorphism aggravated renal damage in three FSGS families with heterozygous COL4A3 mutation, leading to early renal failure in index patients. Our findings suggest that COL4A3 and NPHS2 may have a synergistic effect on renal injury caused by FSGS. Further analysis of the glomerular filtration barrier could help assess the cause of kidney damage. Moreover, a detailed analysis of the glomerular basement membrane-related genes and podocyte structural proteins may help us better understand FSGS pathogenesis and provide insights into the prognosis and treatment of hereditary glomerulonephropathy.

Genetic background, recent advances in molecular biology, and development of novel therapy in Alport syndrome

Alport syndrome (AS) is a progressive inherited kidney disease characterized by hearing loss and ocular abnormalities. There are three forms of AS depending on inheritance mode: X-linked Alport syndrome (XLAS), autosomal recessive AS (ARAS), and autosomal dominant AS (ADAS). XLAS is caused by pathogenic variants in COL4A5, which encodes type IV collagen α5 chain, while ADAS and ARAS are caused by variants in COL4A3 or COL4A4, which encode type IV collagen α3 or α4 chain, respectively. In male XLAS or ARAS cases, end-stage kidney disease (ESKD) develops around a median age of 20 to 30 years old, while female XLAS or ADAS cases develop ESKD around a median age of 60 to 70 years old. The diagnosis of AS is dependent on either genetic or pathological findings. However, determining the pathogenicity of the variants detected by gene tests can be difficult. Recently, we applied the following molecular investigation tools to determine pathogenicity: 1) in silico and in vitro trimer formation assay of α345 chains to assess triple helix formation ability, 2) kidney organoids constructed from patients’ induced pluripotent stem cells to identify α5 chain expression on the glomerular basement membrane, and 3) in vitro splicing assay to detect aberrant splicing to determine the pathogenicity of variants. In this review article, we discuss the genetic background and novel assays for determining the pathogenicity of variants. We also discuss the current treatment approaches and introduce exon skipping therapy as one potential treatment option.

A glycine substitution in the collagenous domain of Col4a3 in mice recapitulates late onset Alport syndrome

Alport syndrome (AS) is a severe inherited glomerulopathy caused by mutations in the genes encoding the α-chains of type-IV collagen, the most abundant component of the extracellular glomerular basement membrane (GBM). Currently most AS mouse models are knockout models for one of the collagen-IV genes. In contrast, about half of AS patients have missense mutations, with single aminoacid substitutions of glycine being the most common. The only mouse model for AS with a homozygous knockin missense mutation, Col4a3-p.Gly1332Glu, was partly described before by our group. Here, a detailed in-depth description of the same mouse is presented, along with another compound heterozygous mouse that carries the glycine substitution in trans with a knockout allele. Both mice recapitulate essential features of AS, including shorten lifespan by 30–35%, increased proteinuria, increased serum urea and creatinine, pathognomonic alternate GBM thinning and thickening, and podocyte foot process effacement. Notably, glomeruli and tubuli respond differently to mutant collagen-IV protomers, with reduced expression in tubules but apparently normal in glomeruli. However, equally important is the fact that in the glomeruli the mutant α3-chain as well as the normal α4/α5 chains seem to undergo a cleavage at, or near the point of the mutation, possibly by the metalloproteinase MMP-9, producing a 35 kDa C-terminal fragment. These mouse models represent a good tool for better understanding the spectrum of molecular mechanisms governing collagen-IV nephropathies and could be used for pre-clinical studies aimed at better treatments for AS.

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Two mouse models were generated that recapitulate essential features of AS patients.

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Glomeruli and tubuli respond differently to mutant collagen IV protomers.

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The mutant colIV protomers in glomeruli probably undergo a cleavage process by MMP9.

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The two AS mouse models represent a good tool for studying collagen-IV nephropathies.

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These models could be used for pre-clinical studies aimed at better treatments.

Discoidin domain receptor 1 activation links extracellular matrix to podocyte lipotoxicity in Alport syndrome

Background

Discoidin domain receptor 1 (DDR1) is a receptor tyrosine kinase that is activated by collagens that is involved in the pathogenesis of fibrotic disorders. Interestingly, de novo production of the collagen type I (Col I) has been observed in Col4a3 knockout mice, a mouse model of Alport Syndrome (AS mice). Deletion of the DDR1 in AS mice was shown to improve survival and renal function. However, the mechanisms driving DDR1-dependent fibrosis remain largely unknown.

Methods

Podocyte pDDR1 levels, Collagen and cluster of differentiation 36 (CD36) expression was analyzed by Real-time PCR and Western blot. Lipid droplet accumulation and content was determined using Bodipy staining and enzymatic analysis. CD36 and DDR1 interaction was determined by co-immunoprecipitation. Creatinine, BUN, albuminuria, lipid content, and histological and morphological assessment of kidneys harvested from AS mice treated with Ezetimibe and/or Ramipril or vehicle was performed.

Findings

We demonstrate that Col I-mediated DDR1 activation induces CD36-mediated podocyte lipotoxic injury. We show that Ezetimibe interferes with the CD36/DDR1 interaction in vitro and prevents lipotoxicity in AS mice thus preserving renal function similarly to ramipril.

Interpretation

Our study suggests that Col I/DDR1-mediated lipotoxicity contributes to renal failure in AS and that targeting this pathway may represent a new therapeutic strategy for patients with AS and with chronic kidney diseases (CKD) associated with Col4 mutations.

Funding

This study is supported by the NIH grants R01DK117599, R01DK104753, R01CA227493, U54DK083912, UM1DK100846, U01DK116101, UL1TR000460 (Miami Clinical Translational Science Institute, National Center for Advancing Translational Sciences and the National Institute on Minority Health and Health Disparities), F32DK115109, Hoffmann-La Roche and Alport Syndrome Foundation.

Goodpasture syndrome and hemorrhage after renal biopsy: A case report

BACKGROUND

Goodpasture syndrome (GS) is a rare disease, the morbidity of which is estimated to be 0.5-0.8 per million per year. Hemorrhage is the most serious complication in renal biopsy. Despite the fact that both GS and hemorrhage after renal biopsy are rare, it has not been reported that they are likely to occur in the same patient.

CASE SUMMARY

A 30-year-old man with diffuse pulmonary hemorrhage and rapid progressive renal function caused by anti-glomerular basement membrane disease presented atypical symptoms without hemoptysis, accompanied by life-threatening hypoxemia. Plasmapheresis was performed, and glucocorticoids and cyclophosphamide were administered. The patient started to show signs of improvement. Percutaneous renal biopsy is an appropriate diagnostic measure that is commonly safe, but this patient experienced hemorrhage after operation, thus necessitating embolization of the renal artery to stop the bleeding. The patient’s condition was improved, and the serum anti-glomerular basement membrane antibody level was 106 AU/mL (normal range: < 24 AU/mL) and slowly decreased. His discharge medications were oral daily prednisone (30 mg) and continued maintenance hemodialysis.

CONCLUSION

GS is a rare organ-specific autoimmune disease that is invariably ubiquitous in the lung and kidney areas. Renal biopsy is the appropriate procedure for the treatment of GS disease, although it is an invasive measure.

Podocyte infolding glomerulopathy; report of the first case in Latin America and review of the literature

BACKGROUND

Podocyte infolding glomerulopathy (PIG) is a condition of uncertain origin, frequently associated with autoimmune diseases. Its specific treatment and clinical course are unknown. It is characterised by thickening of the capillary walls due to the presence of non-argyrophilic intramembranous bubbles similar to those found in membranous glomerulopathy, but without electron-dense deposits of immune complexes in the ultrastructure, where translucent microspheres generated by invagination of the podocyte cytoplasm into the basement membranes are observed.

OBJECTIVES

Generally reported in young females patients. To date, few cases in Asian patients have been reported. Our case is the first to be reported in a Latin American Caucasian patient.

METHODS

A 38-year-old woman with SLE. In 2014 she presented with nephrotic syndrome empirically treated with corticosteroids (CO) and intravenous cyclophosphamide with good response. She had a relapse in April 2015 with normal renal function and no extrarenal lupus activity, so she was referred to our hospital to be biopsied.

RESULTS

The biopsy reported focal segmental glomerular sclerosis without deposits of immune complexes in the immunofluorescence. However, methenamine silver staining revealed clear spaces in the capillary walls accompanied by marked podocyte alterations. On electron microscope study, numerous aggregates of microvesicular and cylindrical ultrastructures bound to the membranes were observed, without evidence of dense deposits, and diffuse effacement of pedicel foot processes, confirming the suspected diagnosis.

CONCLUSIONS

This is the first reported case of what can be considered a new pathological glomerular entity in a Latin American Caucasian patient, whose clinical course and therapy are still unknown.

Alport syndrome: deducing the mode of inheritance from the presence of haematuria in family members

The diagnosis of Alport syndrome is suspected when an individual has haematuria or renal failure, together with a hearing loss; haematuria or renal failure, and a family history of Alport syndrome; or a pathognomonic Alport feature, such as lenticonus, fleck retinopathy, a lamellated glomerular basement membrane (GBM), or a GBM that lacks the collagen IV α3α4α5 network. The diagnosis of Alport syndrome is optimally confirmed by the demonstration of a mutation in the COL4A5 gene or two mutations in trans in the COL4A3 or COL4A4 genes. In practice, genetic testing for Alport syndrome is not widely available, and even with testing, causative mutations are not demonstrated in 5% of cases. Often, haematuria is only known in some family members, and the other characteristic features are not present or have not been sought. Where Alport syndrome remains likely, it is important to distinguish between X-linked inheritance, which occurs in 85% of families, and autosomal recessive inheritance, in the remaining 15%. This distinction is important because different modes of inheritance mean that different family members are at risk of being affected. Clinicians generally rely on the presence of haematuria to identify affected individuals in families with suspected Alport syndrome and on the information from three-generational family trees to assess the likely mode of inheritance. While often helpful, this strategy can also be misleading. The major sources of error are families with few members or where few members are tested; families comprising mainly women, where the typical Alport features are absent; families where the father is not available for testing for haematuria; and families with a coincidental renal disease. These difficulties emphasise the helpfulness of genetic testing in distinguishing between X-linked and autosomal recessively inherited forms of Alport syndrome.

Age-related glomerular lesions with albuminuria in male cotton rats

The increased prevalence of aging-related chronic kidney disease (CKD) among humans is a problem worldwide. Aged cotton rats (Sigmodon hispidus) are considered novel model animals for studying CKD, especially as the females develop severe tubulointerstitial lesions with anemia. To investigate the renal pathologic features in aged male cotton rats and their characteristic glomerular injuries, the animals were divided into young, adult, old-aged, and advanced-aged groups (1-4, 5-8, 9-12, and 13-17 months, respectively) and pathologically analyzed. Anemia and renal dysfunction, as indicated by hematologic and serologic parameters, were significantly milder in the advanced-aged males than in the old-aged females. The males had increased urinary albumin-to-creatinine ratios from the old-age period, with the advanced-aged males having significantly higher levels than those in the old-aged females and young males. The old-aged females did not show clear glomerular injuries, whereas the advanced-aged males showed membranous lesions characterized by irregular and thickened glomerular basement membranes (GBMs). Characteristically, several large-sized projections from the GBM toward the podocytes were observed by microscopy, and podocytes covering these projections effaced their foot processes. The advanced-aged males showed aging-related IgG immune-complex depositions in the paramesangial regions and along the GBM. Furthermore, the positive reaction for podocin (a podocyte molecule) was granulated along the GBM. Thus, we clarified the albuminuria associated with altered glomerular structures in advanced-aged cotton rats, and that these phenotypes were closely associated with aging. These data help to clarify the aging-related pathogenesis of glomerular injury.

Podocyte penetration of the glomerular basement membrane to contact on the mesangial cell at the lesion of mesangial interposition in lupus nephritis: a three-dimensional analysis by serial block-face scanning electron microscopy

BACKGROUND

The interaction among the glomerular components plays an important role in the development of glomerular lesions; thus, investigation of the ultrastructural three-dimensional (3D) configuration of the human glomerular cells and extracellular matrix (ECM) is important for understanding the pathogenesis of glomerulosclerosis, especially glomerulonephritis.

METHODS

We applied a new technique of serial block-face scanning electron microscopy (SBF-SEM), which helps to acquire serial electron microscopic images to reconstruct a 3D ultrastructure, to a human kidney biopsy specimen obtained from a 25-year-old woman with lupus nephritis.

RESULTS

SBF-SEM demonstrated that the cytoplasmic processes of the podocyte penetrated into the lamina densa of the glomerular basement membrane, and was in direct contact with the cytoplasm of mesangial cells at the site of mesangial interposition.

CONCLUSION

Although this is a single-case observational study, SBF-SEM revealed a unique 3D configuration, suggesting a novel mechanism of direct intercellular cross-communication between podocytes and mesangial cells, aside from the presumed paracrine communication.

Pathologic glomerular characteristics and glomerular basement membrane alterations in biopsy-proven thin basement membrane nephropathy

BACKGROUND

Thin basement membrane nephropathy (TBMN) is diagnosed by diffuse thinning of the glomerular basement membrane (GBM) without any clinical and pathologic findings of Alport syndrome and the other renal diseases. TBMN is characterized clinically by benign familial hematuria but rarely develops into end-stage renal disease.

METHODS

In 27 cases of biopsy-proven TBMN, we evaluated the pathologic characteristics of TBMN, and examined the correlation between these pathologic characterizations and renal dysfunction.

RESULTS

All patients had hematuria, and 21 patients (77.8%) had proteinuria. In six patients (28.6%) who were more than 50 years of age, the estimated glomerular filtration rate (eGFR) decreased from G3a to G4 in the chronic kidney disease stage. Pathologically, an irregular decrease in intensity of type IV collagen α5(IV) chain was seen in GBM, and irregular thinning with diffuse rough etched images was observed on the GBM surface with several sizes of holes by low-vacuum scanning electron microscopy. The glomerular morphology of TBMN was characterized by an increased number of small glomerular capillaries with an increased extracellular matrix (ECM). These characteristic morphologic alterations were evident from a young age in patients with TBMN, but were not correlated directly with the decrease of eGFR, the degree of hematuria, and proteinuria. The decrease of eGFR in patients with TBMN who were more than 50 years of age might be primarily mediated by arteriolosclerosis-associated glomerulosclerosis and interstitial fibrosis.

CONCLUSION

Characteristic pathological glomerular findings and GBM alterations occurred from a young age but were not associated directly with renal impairment in biopsy-proven TBMN.

[Clinical and pathological features and mutational types of WT1 mutation-associated nephropathy]

Objective: To explore the clinical and pathological features and mutational types and their relations with WT1 mutation-associated nephropathy (WT1MAN). Methods: The clinical and pathological data and the results of WT1 mutation analysis of the cases from Nanfang Hospital of Southern Medical University, Sun Yat-sen Memorial Hospital and The First Affiliated Hospital of Sun Yat-sen University whom we recruited recently and reported during the last ten years were analyzed. Results: Totally, 20 cases (6 males and 14 females), included 5 newly diagnosed cases, were recruited. (1) Ten children were diagnosed with Denys-Drash syndrome (DDS): The median onset age of proteinuria was 1 year and 7 months. Diffuse mesangial sclerosis (DMS) were revealed in 3 cases, minimal lesions (MCD) in 4 cases, and focal segmental glomerulosclerosis (FSGS) in 1 case; renal pathology was not available in the other 2 cases. Glomerular basement membrane (GBM) thickening was observed in 2 cases. Calcineurin inhibitors (CNIs) were administered in 5 cases, complete remission of proteinuria was observed in 3 cases, partial remission in the other 2 cases. Genetic analysis revealed that six cases had WT1 missense mutation, 3 had nonsense mutation, and 1 had frameshift mutation. (2) Two cases were diagnosed with Frasier syndrome (FS): proteinuria was observed at 1 year and 1 month of age and 1 year and 9 months of age, respectively. FSGS with GBM layering were observed in both cases. They progressed to ESRD at 1 year and 6 months of age and 6 years and 6 months of age, respectively. CNI was tried in 1 case with partial proteinuria remission. Both patients were detected to have WT1 splice mutation. (3) Isolated nephropathy (IN) was observed in 8 cases: three had splice mutation, 5 had missense mutation. Of the 3 patients with splice mutation, one was found to have nephropathy and renal failure at the age of 5 months. The other two cases (1 was FSGS and another MCD), both had GBM layering. CNIs were tried on both of them, one got partial remission with normal renal function at the age of fourteen years, the other one had no response and entered ESRD at the age of 6 years and 9 months. Of the 5 cases with missense mutation, 3 had DMS, 2 of them entered ESRD within 6 months of age, another case had DMS entered ESRD at 9 years of age. One case with FSGS, was treated with CNIs and got complete remission. Conclusions: Slow progression (7/10) nephropathy was observed in DDS patients. Missense mutation (11/20) was the most common type of WT1 variants, followed by splice mutation (5/20) in this group of patients. Early onset nephropathy (4/5), rapid progression (4/5) and GBM layering (4/4) wereobserved in patients with splice mutation. CNI was effective in reducing or even eliminating proteinuria in WT1 MAN patients (8/9).

[The pathology of renal transplants]

In order to make an objective assessment of the histopathology of a renal biopsy during a kidney transplant, all the various elements involved in the process must be understood. It is important to know the characteristics of the donor organ, especially if the donor is older than 65. The histopathological features of the donor biopsy, especially its vascular status, are often related to an initial poor function of the transplanted kidney. The T lymphocyte inflammatory response is characteristic in acute cellular rejection; the degree of tubulitis, together with the amount of affected parenchyme, are important factors. The proportion of cellular sub-populations, such as plasma cells and macrophages, is also important, as they can be related to antibody-mediated humoral rejection. Immunofluorescent or immunohistochemical studies are necessary to rule out C4d deposits or immunogloblulins. The presence of abundant deposits of C4d in tubular basement membranes supports a diagnosis of humoral rejection, as does the presence of capillaritis, glomerulitis which, together with vasculitis, are typical diagnostic findings in C4d negative cases. Interstitial fibrosis, tubular atrophy and glomerular sclerosis, although non-specific, imply a chronic phase. Transplant glomerulopathy and multilamination in more than 6 layers of the tubular and glomerular basement membranes are quasi-specific characteristics of chronic humoral rejection. Electron microscopy is essential to identify of these pathologies as well as to demonstrate the presence of other glomerular renal diseases.

A unique evolution of the kidney phenotype in a patient with autosomal recessive Alport syndrome

Alport syndrome is due to mutations in one of the genes encoding (α3,4,5) type IV collagen resulting in defective type IV collagen, a key component of the glomerular basement membrane (GBM). The GBM is initially thin and, with ongoing remodeling, develops a thickened basket-woven appearance. We report a unique case of a 9-year-old boy who underwent biopsy for hematuria and proteinuria, diagnosed as IgA nephropathy, with normal GBM appearance and thickness. Because of a family history of hematuria and chronic kidney disease, he subsequently underwent genetic evaluation, and a mutation of α3 type IV collagen (COL4A3) was detected. Additional studies of the initial biopsy demonstrated abnormal type IV collagen immunostaining. A repeat biopsy 4 years later showed characteristic glomerular basement membrane morphology of Alport syndrome and scarring consistent with sequelae of IgA nephropathy. This is the first description of this unusual transition from an initial normal appearance of the glomerular basement membrane to the classic Alport phenotype.

Human podocytes responses to alternatively spliced Extra domain A Fibronectin in culture

The interactions of the extracellular matrix (ECM) proteins with cells strongly regulate cell behaviour. The glomerular basement membrane (GBM) is a dynamic structure made up of protein secreted by endothelial cells and podocyte. These proteins could regulate the behaviour of these cells in health and diseases. Extra Domain A + Fn (EDA+Fn) is an alternatively spliced form of Fibronectin (Fn) recently identified in GBM and a recognised marker of various pathologies. In this study for the first time, we have investigated the responses of human podocytes cultured on different composition of GBM proteins which are cellular Fn (EDA+), plasma Fn (EDA-) and collagen IV. Conditionally immortalised human podocyte were grown on the dishes coated with different matrices; collagen IV (Col IV), cellular fibronectin (CFn) containing the EDA Exon, plasma fibronectin (PFn), which lacks the EDA Exon (EDA-Fn). We have performed western blotting to characterise the expression of the different proteins, real time PCR and RT-PCR to look for gene expression and alternative splicing of EDA+Fn. We have used TGFβ1 as a stimulator. We have used HEK-Blue-hTLR4 cells to determine the biological activity of cellular Fn. Conditionally immortalised human podocyte show marked differences in their morphology grown on the dishes coated with different matrices; Col IV, CFn, and PFn. CFn was biologically active as it activated the TLR4 signalling in HEK-Blue-hTLR4 cells. Different matrices effects basal as well as TGFβ1 mediated alternative splicing of EDA+Fn. TGFβ1 was active on different matrices as it induced phosphorylation of pSmad3 however it did not affect phosphorylation of pAkt and p38. Interestingly, different cellular matrices affected basal phosphorylation of pAkt. CFn downregulated gene expression of synaptopodin and increased gene expression of collagen I and Fn. CFn increased cell death in detached human podocytes. Alteration of the constituents of the GBM is likely to significantly alter podocyte cellular responses to growth factors involved in podocytopathies, such as TGFβ.

New structural insights into podocyte biology

The last 5 years have witnessed tremendous advances in both light- and electron-microscopic techniques in the biomedical sciences. Application of these new cutting-edge methods to glomerular biology has advanced considerably and, in part, completed our endeavor to draw a detailed map of the glomerular tuft. The scope of this review is to illustrate these new insights within both the morphometry of podocyte cells and the architecture of the glomerular filtration barrier and to assess whether these findings have indeed had an impact on our biological understanding of glomerular function.

Macroscopic hematuria with normal renal biopsy-following the chain to the diagnosis: Answers

BACKGROUND

Alport syndrome (AS) is an inherited glomerular disease associated with hearing and eye defects; its morbidity is a public health issue in developed countries. AS results from mutations in COL4A3, COL4A4, or COL4A5 genes, respectively encoding the alpha-3, alpha-4, and alpha-5 chains of type IV collagen, a major component of the renal glomerular basement membrane (GBM). The diagnosis is usually confirmed by a renal biopsy showing a thinning/thickening of the GBM, with a longitudinal splitting of the lamina densa.

CASE DIAGNOSIS

We report the case of a 10-year-old patient who presented multiple episodes of macroscopic hematuria. On the renal biopsy, the electron microscopy analysis of the GBM was normal, as was the COL4A5 immunofluorescence assay. Genetic analyses showed a homozygous duplication of exons 44 to 47 of the COL4A3 gene, confirming the diagnosis of autosomal recessive AS.

CONCLUSIONS

Our report suggests that in patients with clinical evidence of AS, genetic testing should be performed whenever pathological analysis is not in favor of AS diagnosis. This will ensure that AS patients benefit from an early diagnosis, adequate treatment, and that end-stage renal disease (ESRD) onset is delayed.

Macroscopic hematuria with normal renal biopsy-following the chain to the diagnosis: Questions

BACKGROUND

Alport syndrome (AS) is an inherited glomerular disease associated with hearing and eye defects; its morbidity is a public health issue in developed countries. AS results from mutations in COL4A3, COL4A4, or COL4A5 genes, respectively encoding the alpha-3, alpha-4, and alpha-5 chains of type IV collagen, a major component of the renal glomerular basement membrane (GBM). The diagnosis is usually confirmed by a renal biopsy showing a thinning/thickening of the GBM, with a longitudinal splitting of the lamina densa.

CASE DIAGNOSIS

We report the case of a 10-year-old patient who presented multiple episodes of macroscopic hematuria. On renal biopsy, the electron microscopy analysis of the GBM was normal, as was the COL4A5 immunofluorescence assay. Genetic analyses showed a homozygous duplication of exons 44 to 47 of the COL4A3 gene, confirming the diagnosis of autosomal recessive AS.

CONCLUSIONS

Our report suggests that, in patients with clinical evidence of AS, genetic testing should be performed whenever pathological analysis is not in favor of AS diagnosis. This will ensure that AS patients benefit from an early diagnosis, adequate treatment, and that end-stage renal disease (ESRD) onset is delayed.

Neutrophil Protease Cleavage of Von Willebrand Factor in Glomeruli - An Anti-thrombotic Mechanism in the Kidney

Adequate cleavage of von Willebrand factor (VWF) prevents formation of thrombi. ADAMTS13 is the main VWF-cleaving protease and its deficiency results in development of thrombotic microangiopathy. Besides ADAMTS13 other proteases may also possess VWF-cleaving activity, but their physiological importance in preventing thrombus formation is unknown. This study investigated if, and which, proteases could cleave VWF in the glomerulus. The content of the glomerular basement membrane (GBM) was studied as a reflection of processes occurring in the subendothelial glomerular space. VWF was incubated with human GBMs and VWF cleavage was assessed by multimer structure analysis, immunoblotting and mass spectrometry. VWF was cleaved into the smallest multimers by the GBM, which contained ADAMTS13 as well as neutrophil proteases, elastase, proteinase 3 (PR3), cathepsin-G and matrix-metalloproteinase 9. The most potent components of the GBM capable of VWF cleavage were in the serine protease or metalloprotease category, but not ADAMTS13. Neutralization of neutrophil serine proteases inhibited GBM-mediated VWF-cleaving activity, demonstrating a marked contribution of elastase and/or PR3. VWF-platelet strings formed on the surface of primary glomerular endothelial cells, in a perfusion system, were cleaved by both elastase and the GBM, a process blocked by elastase inhibitor. Ultramorphological studies of the human kidney demonstrated neutrophils releasing elastase into the GBM. Neutrophil proteases may contribute to VWF cleavage within the subendothelium, adjacent to the GBM, and thus regulate thrombus size. This anti-thrombotic mechanism would protect the normal kidney during inflammation and could also explain why most patients with ADAMTS13 deficiency do not develop severe kidney failure.

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Neutrophil proteases in the glomerular basement membrane cleave VWF and may protect the kidney from microthrombi.

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VWF cleavage would be activated by neutrophil influx and compensate for the prothrombotic mechanisms during inflammation.

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This mechanism may compensate for lack of ADAMTS13 and explain why TTP patients seldom develop end-stage renal failure.

The study demonstrates a mechanism by which the kidney is protected from blood clotting during inflammation. In the inflammatory setting white blood cells infiltrate tissues. In this study we showed that enzymes released from white blood cells into the kidney decrease the size of blood clots. This is a general mechanism but could also explain why patients with thrombotic thrombocytopenic purpura, who develop widespread blood clots in many organs, do not usually develop severe kidney failure.

Glomerular basement membrane heparan sulfate in health and disease: A regulator of local complement activation

The glomerular basement membrane (GBM) is an essential component of the glomerular filtration barrier. Heparan sulfate proteoglycans such as agrin are major components of the GBM, along with α345(IV) collagen, laminin-521 and nidogen. A loss of GBM heparan sulfate chains is associated with proteinuria in several glomerular diseases and may contribute to the underlying pathology. As the major determinants of the anionic charge of the GBM, heparan sulfate chains have been thought to impart charge selectivity to the glomerular filtration, a view challenged by the negligible albuminuria in mice that lack heparan sulfate in the GBM. Recent studies provide increasing evidence that heparan sulfate chains modulate local complement activation by recruiting complement regulatory protein factor H, the major inhibitor of the alternative pathway in plasma. Factor H selectively inactivates C3b bound to surfaces bearing host-specific polyanions such as heparan sulfate, thus limiting complement activation on self surfaces such as the GBM, which are not protected by cell-bound complement regulators. We discuss mechanisms whereby the acquired loss of GBM heparan sulfate can impair the local regulation of the alternative pathway, exacerbating complement activation and glomerular injury in immune-mediated kidney diseases such as membranous nephropathy and lupus nephritis.

Goodpasture's syndrome with absence of circulating anti-glomerular basement membrane antibodies: a case report

Background

Goodpasture’s syndrome, a rare disease, is an organ-specific autoimmune disease mediated by anti-glomerular basement membrane antibodies. Its pathology is characterized by crescentic glomerulonephritis with linear immunofluorescent staining for immunoglobulin G on the glomerular basement membrane. Although rare, a few cases with absence of circulating anti-glomerular membrane antibodies have been described.

Case presentation

The objective of this clinical case report is to describe and discuss a case of a 27-year-old white man who was hospitalized with a 1-year history of weight loss and a 1-month history of hemoptysis, with aggravation  the day before, having developed dyspnea and cough in the previous 24 hours. An analytical study showed normocytic normochromic anemia with a hemoglobin level of 7.2 g/dL and leukocytosis with normal renal function and coagulation times. A blood transfusion was performed without complications. Chest computed tomography revealed a reticulonodular infiltrate of both lungs. Bronchoscopy showed no apparent lesions. Sputum cultures, rapid urine antigens for Legionella pneumophila and Streptococcus pneumoniae, studies for Influenza, virologic markers and serologic studies for autoimmunity were all negative. At the end of the tenth day his general state deteriorated with fatigue, hematuria, and in 3 days he developed aggravation of renal function with recurrent hemoptysis and anemia. Immunosuppression with daily prednisolone 1 g administered intravenously was initiated. An urgent bronchoscopy showed no lesions. A kidney biopsy showed fibrinoid necrosis and cellular crescents. Immunofluorescence revealed a linear immunoglobulin G deposition compatible with Goodpasture’s syndrome. Immunosuppressive therapy with daily cyclophosphamide 120 mg orally was added. Subsequently he was transferred to a referral center at which 21 sessions of plasmapheresis and four sessions of hemodialysis were performed with good response; he currently has no need of hemodialysis.

Conclusions

The absence of circulating anti-glomerular basement membrane antibodies in Goodpasture’s syndrome adds complexity to the diagnosis creating an unusual setting in a rare disease. In our case a kidney biopsy was essential for diagnosis and clinical approach. Studies have shown that early aggressive therapy leads to an improved prognosis. Physicians should consider tissue diagnoses such as bronchoscopy and kidney biopsy in pulmonary renal syndrome.

Glomerular basement membrane thickness among the Saudi population

The aim of this work was to determine the mean glomerular basement membrane (GBM) thickness in the Saudi population. We calculated the average GBM thickness in patients diagnosed with minimal change disease, and the ultrastructural analysis of at least three glomeruli was reviewed using a digital camera installed in an electron microscope. There were a total of 53 cases from 53 Saudi patients aged 2-70 years old. The mean GBM thickness for all cases was 323.6 ± 49.5 nm. There was no significant statistical difference in the mean GBM thickness between males and females. There were significant differences in the mean GBM thickness between all age groups, except for between the age groups 18-60 and >60 years old, where GBM thickness did not differ significantly. Age was significantly correlated with definite progression or diminution in the thickness of the GBM. The mean GBM thickness in our Saudi sample population was comparable to the very few reported measurements in the literature. There was no significant association between GBM thickness and gender; however, GBM thickness is directly proportional to age, up to 60 years old.

Podocyte-specific Nox4 deletion affords renoprotection in a mouse model of diabetic nephropathy

AIMS/HYPOTHESIS

Changes in podocyte morphology and function are associated with albuminuria and progression of diabetic nephropathy. NADPH oxidase 4 (NOX4) is the main source of reactive oxygen species (ROS) in the kidney and Nox4 is upregulated in podocytes in response to high glucose. We assessed the role of NOX4-derived ROS in podocytes in vivo in a model of diabetic nephropathy using a podocyte-specific NOX4-deficient mouse, with a major focus on the development of albuminuria and ultra-glomerular structural damage.

METHODS

Streptozotocin-induced diabetes-associated changes in renal structure and function were studied in male floxedNox4 and podocyte-specific, NOX4 knockout (podNox4KO) mice. We assessed albuminuria, glomerular extracellular matrix accumulation and glomerulosclerosis, and markers of ROS and inflammation, as well as glomerular basement membrane thickness, effacement of podocytes and expression of the podocyte-specific protein nephrin.

RESULTS

Podocyte-specific Nox4 deletion in streptozotocin-induced diabetic mice attenuated albuminuria in association with reduced vascular endothelial growth factor (VEGF) expression and prevention of the diabetes-induced reduction in nephrin expression. In addition, podocyte-specific Nox4 deletion reduced glomerular accumulation of collagen IV and fibronectin, glomerulosclerosis and mesangial expansion, as well as glomerular basement membrane thickness. Furthermore, diabetes-induced increases in renal ROS, glomerular monocyte chemoattractant protein-1 (MCP-1) and protein kinase C alpha (PKC-α) were attenuated in podocyte-specific NOX4-deficient mice.

CONCLUSIONS/INTERPRETATION

Collectively, this study shows the deleterious effect of Nox4 expression in podocytes by promoting podocytopathy in association with albuminuria and extracellular matrix accumulation in experimental diabetes, emphasising the role of NOX4 as a target for new renoprotective agents.

Podocyturia: What is in a name?

The podocyte is a highly differentiated cell located in the outer space of the glomerular basement membrane that deals with many different functions. This phylogenetically preserved cell that is responsible for the virtually absence of proteins in the urine lacks of the capacity to divide under normal conditions. When podocytes receive molecular insults, which normally occur during stress conditions as glomerulonephritis, hyperfiltration or metabolic disturbances, they adapt to the new situation by contracting their actin fibers. This adaptive behavior puts at risk the quality of the plasmatic filtration due to the denudation of the glomerular basement membrane, the potential mesangial inflammation and the appearance of proteinuria; podocytes run the risk of detachment from the basement membrane due to a decrease in the adherence to the surrounding matrix after contraction, a process called foot processes effacement. Podocytes change their shape and under constant mechanical stress they finally detach, rendering the glomerular basement membrane unprotected unless other contiguous podocytes are capable of covering the surface. However, these still anchored podocytes are generally also under the same stress situation and follow the same pathway. Podocyturia refers to the presence of these differentiated cells in the urinary sediment. Noteworthy, the podocytes that are encountered in the urine are viable despite the glomerular hostile environment and the urinary acidity. Podocyturia can precede proteinuria and can aggravate it. Therefore, in diseases that can threaten the glomerular normal environment, the presence and the quantification of urinary podocytes can be of remarkable relevance, as it can herald or accompany the appearance of proteinuria, and could offer another view to the interpretation and clinical approach and outcome of proteinuria. However, its identification needs a wide-spread training among biochemists and technicians, as well as commercially available kits.

Autoimmunity to the alpha 3 chain of type IV collagen in glomerulonephritis is triggered by 'autoantigen complementarity'

'Autoantigen complementarity' is a theory proposing that the initiator of an autoimmune response is not necessarily the autoantigen or its molecular mimic, but may instead be a peptide that is 'antisense/complementary' to the autoantigen. We investigated whether such complementary proteins play a role in the immunopathogenesis of autoimmune glomerulonephritis. Experimental autoimmune glomerulonephritis, a model of anti-glomerular basement membrane (GBM) disease, can be induced in Wistar Kyoto (WKY) rats by immunization with the α3 chain of type IV collagen. In this study, WKY rats were immunized with a complementary α3 peptide (c-α3-Gly) comprised of amino acids that 'complement' the well characterized epitope on α3(IV)NC1, pCol(24-38). Within 8 weeks post-immunization, these animals developed cresentic glomerulonephritis, similar to pCol(24-38)-immunized rats, while animals immunized with scrambled peptide were normal. Anti-idiotypic antibodies to epitopes from c-α3-Gly-immunized animals were shown to be specific for α3 protein, binding in a region containing sense pCol(24-38) sequence. Interestingly, anti-complementary α3 antibodies were identified in sera from patients with anti-GBM disease, suggesting a role for 'autoantigen complementarity' in immunopathogenesis of the human disease. This work supports the idea that autoimmune glomerulonephritis can be initiated through an immune response against a peptide that is anti-sense or complementary to the autoantigen. The implications of this discovery may be far reaching, and other autoimmune diseases could be due to responses to these once unsuspected 'complementary' antigens.

Cell-cell interactions driving kidney morphogenesis

The mammalian kidney forms via cell-cell interactions between an epithelial outgrowth of the nephric duct and the surrounding nephrogenic mesenchyme. Initial morphogenetic events include ureteric bud branching to form the collecting duct (CD) tree and mesenchymal-to-epithelial transitions to form the nephrons, requiring reciprocal induction between adjacent mesenchyme and epithelial cells. Within the tips of the branching ureteric epithelium, cells respond to mesenchyme-derived trophic factors by proliferation, migration, and mitosis-associated cell dispersal. Self-inhibition signals from one tip to another play a role in branch patterning. The position, survival, and fate of the nephrogenic mesenchyme are regulated by ECM and secreted signals from adjacent tip and stroma. Signals from the ureteric tip promote mesenchyme self-renewal and trigger nephron formation. Subsequent fusion to the CDs, nephron segmentation and maturation, and formation of a patent glomerular basement membrane also require specialized cell-cell interactions. Differential cadherin, laminin, nectin, and integrin expression, as well as intracellular kinesin and actin-mediated regulation of cell shape and adhesion, underlies these cell-cell interactions. Indeed, the capacity for the kidney to form via self-organization has now been established both via the recapitulation of expected morphogenetic interactions after complete dissociation and reassociation of cellular components during development as well as the in vitro formation of 3D kidney organoids from human pluripotent stem cells. As we understand more about how the many cell-cell interactions required for kidney formation operate, this enables the prospect of bioengineering replacement structures based on these self-organizing properties.

Glomerular basement membrane injuries in IgA nephropathy evaluated by double immunostaining for α5(IV) and α2(IV) chains of type IV collagen and low-vacuum scanning electron microscopy

BACKGROUND

The glomerulus contains well-developed capillaries, which are at risk of injury due to high hydrostatic pressure, hyperfiltration, hypertension and inflammation. However, the pathological alterations of the injured glomerular basement membrane (GBM), the main component of the glomerular filtration barrier, are still uncertain in cases of glomerulonephritis.

METHODS

We examined the alterations of the GBM in 50 renal biopsy cases with IgA nephropathy (31.8 ± 17.6 years old) using double immunostaining for the α2(IV) and α5(IV) chains of type IV collagen, and examining the ultrastructural alterations by transmission electron microscopy (TEM) and low-vacuum scanning electron microscopy (LV-SEM).

RESULTS

The GBM of IgA nephropathy cases showed various morphological and qualitative alterations. In the TEM findings, thinning, gaps, rupture, thickening with a lamellar and reticular structure and double contours were detected in the GBM. Double immunostaining for α5(IV) and α2(IV) showed thickening of the GBM with reduced α5(IV) and increased α2(IV), or mosaic images of α5(IV) and α2(IV), and holes, fractures, spiny projections and rupture of α5(IV) in the GBM. In addition, LV-SEM showed an etched image and multiple holes in a widening and wavy GBM. These findings might be associated with the development of a brittle GBM in IgA nephropathy.

CONCLUSION

Glomerular basement membrane alterations were frequently noted in IgA nephropathy, and were easily evaluated by double immunostaining for α2(IV) and α5(IV) of type IV collagen and LV-SEM. The application of these analyses to human renal biopsy specimens may enhance our understanding of the alterations of the GBM that occur in human glomerular diseases.

Glomerular Filtration Barrier Assembly: An insight

A glomerulus is the network of capillaries that resides in the Bowman's capsule that functions as a filtration unit of kidney. The glomerular function ensures that essential plasma proteins are retained in blood and the filtrate is passed on as urine. The glomerular filtration assembly is composed of three main cellular barriers that are critical for the ultrafiltration process, the fenestrated endothelium, glomerular basement membrane and highly specialized podocytes. The podocytes along with their specialized junctions "slit diaphragm" form the basic backbone of this filtration assembly. The presence of high amounts of protein in urine a condition commonly referred as proteinuria indicates a defective glomerular filtration barrier. Various glomerular disorders including Nephrotic syndrome are characterized by significant alteration in the structure of podocytes that is associated with prolonged increase in the glomerular permeability leading to heavy proteinuria. Recent identification of proteins that are specifically localized at the slit diaphragm whose mutations and knockouts are known to result in loss of renal function has significantly advanced our understanding of the molecular makeup of this filtration assembly. The present review is an effort to summarize the recent developments in this field and highlight our understanding of the glomerular filtration barrier assembly.

Association between urinary IgG and relative risk for factors affecting proteinuria in type 2 diabetic patients

Abnormal glomerular permeability is the primary step towards the glomerulosclerosis. The progression rate of glomerulosclerosis is proportionate to abundance and severity of lesions created at incipient stage, which is reflected as proteinuria even though eGFR remains in the normal range. Therefore, there is a current need to find out the association between relative risks for the factors leading to proteinuria. The relations could be more informative, if it is with respect to the macromolecules like "IgG" excretion in urine. Type 2 diabetic patients were selected for this study with eGFR > 75 ml/min/1.73 m(2) and grouped into four quartiles based on UIgGCR. The markers of key factors affecting progression of proteinuria were estimated through biochemical tests. The impact of these markers on proteinuria was accessed by applying multinomial logistic regression. The adjusted odds ratio for the UGAGCR was 1.186 (95 % CI: 1.061-1.327) P < 0.003 in highest quartiles of UIgGCR, followed by odds ratio for markers of collagen catabolism 1.051 (95 % CI: 1.025-1.079) P < 0.001, and USACR 1.044 (95 % CI: 1.013-1.077) P < 0.006 respectively. The marker of glycation, i.e., glycated hemoglobin showed the highest odds ratio 5.449 (95 % CI: 1.132-26.236) P < 0.035. In addition, odds for the systolic blood pressure was observed 1.387 (95 % CI: 1.124-1.712) P < 0.002. The higher odds inform and could help to discriminate the diabetic patients with fast progressive diabetic nephropathy. The study describes critical relationship between the urinary excretion of IgG and factors leading to proteinuria in type 2 diabetic patients.

Renoprotective action of a matrix metalloproteinase inhibitor in progressive mesangioproliferative nephritis

Background/Aim

Matrix metalloproteinases (MMPs) play pivotal roles in extracellular matrix turnover and are involved in chronic kidney disease. The renoprotective action of a synthetic MMP inhibitor, compound A, was investigated in chronic nephritis.

Methods

Nephritis was induced by a single injection of anti-Thy1.1 antibody to unilaterally nephrectomized rats. The effects of compound A on proteinuria, blood urea nitrogen, and matrix-related gene expressions were evaluated. Collagen accumulation, as assessed by periodic acid-Schiff staining and hydroxyproline content, was determined. The integrity of glomerular epithelial cells and glomerular basement membrane was evaluated with desmin immunohistochemistry and electron microscopic detection of anionic charge sites, respectively.

Results

Treatment with compound A notably attenuated proteinuria, ameliorated blood urea nitrogen, and prevented glomerulosclerosis. Gene upregulation of collagen and transforming growth factor β1 in the cortex was prevented in the treated animals. Glomerular epithelial cell injury was milder, and glomerular basement membrane anionic sites were protected with the treatment.

Conclusion

A novel MMP inhibitor, compound A, exerts protective effects in progressive glomerulonephritis. Compound A ameliorates various aspects of renal injuries and may have therapeutic potential toward kidney diseases.

Attenuation of Immune-Mediated Renal Injury by Telmisartan, an Angiotensin Receptor Blocker and a Selective PPAR-γ Activator

BACKGROUND/AIMS

Anti-glomerular basement membrane (GBM) nephritis is characterized by activation of the renin-angiotensin system. This study aimed to determine the question of whether a temporary angiotensin II blockade at the initial stage of anti-GBM nephritis is able to attenuate the disease as well as differences in renoprotection among angiotensin II receptor blockers (ARBs) with distinct peroxisome proliferator-activated receptor (PPAR)-γ-modulating activities.

METHODS

C57BL/6J mice were immunized with rabbit IgG, followed by intravenous injection of rabbit anti-mouse antibodies. Mice were then treated with telmisartan, losartan, and telmisartan + GW9662 (a PPAR-γ antagonist) for 5 days, or hydralazine for 9 days. On days 8 and 13, mice were sacrificed to obtain tissues for histological analysis.

RESULTS

The temporary administration of telmisartan significantly suppressed glomerular damage compared to hydralazine. Losartan showed a similar effect but was less effective. Co-administration of GW9662 attenuated the renoprotective effect of telmisartan, almost to levels observed with losartan. In particular, it limited the decreased infiltration of inflammatory cells and preservation of capillaries in the glomeruli induced by telmisartan.

CONCLUSION

Temporary angiotensin II blockade at the initial stage of anti-GBM disease dramatically inhibited its progression. In addition to a class effect of ARBs, telmisartan modified inflammation and endothelial damage in the kidney through its PPAR-γ-agonistic action.

Thickness of glomerular and tubular basement membranes in preclinical and clinical stages of diabetic nephropathy

AIMS

This study aimed to elucidate the early renal changes in diabetes mellitus (DM) with and without clinical symptoms related to renal damage.

METHODS

Renal biopsy was studied in 25 patients (14 with microalbuminuria and 11 with albuminuria) both by light and electron microscopies (LM and EM, respectively) for renal changes and morphometry was performed to study glomerular and tubular basement membranes (GBM and TBM, respectively) width using a Soft Imaging System GmBH (analysis 3).

RESULTS

A significant increase was noted in the mean GBM and TBM thickness in both the preclinical and clinical groups compared to the control group. The changes in the TBM were noted to be predominant in both preclinical and clinical patients.

CONCLUSIONS

This study indicates the importance of morphometric evaluation of the GBM and TBM width in the elucidation of early renal damage in diabetic nephropathy, especially in the absence of LM changes. The significance of identification of early renal changes using morphometric techniques for better management of these patients requires further studies.