Podocyte proteins in Galloway-Mowat syndrome

Galloway-Mowat syndrome is an autosomal recessive disorder characterized by early onset nephrotic syndrome and central nervous system anomalies. Mutations in podocyte proteins, such as nephrin, α-actinin 4, and podocin, are associated with proteinuria and nephrotic syndrome. The genetic defect in Galloway-Mowat syndrome is as yet unknown. We postulated that in Galloway-Mowat syndrome the mutation would be in a protein that is expressed both in podocytes and neurons, such as synaptopodin, GLEPP1, or nephrin. We therefore analyzed kidney tissue from normal children (n=3), children with congenital nephrotic syndrome of the Finnish type (CNF, n=3), minimal change disease (MCD, n=3), focal segmental glomerulosclerosis (FSGS, n=3), and Galloway-Mowat syndrome (n=4) by immunohistochemistry for expression of synaptopodin, GLEPP1, intracellular domain of nephrin (nephrin-I), and extracellular domain of nephrin (nephrin-E). Synaptopodin, GLEPP1, and nephrin were strongly expressed in normal kidney tissue. Nephrin was absent, and synaptopodin and GLEPP1 expression were decreased in CNF. The expression of all three proteins was reduced in MCD and FSGS; the decrease in expression being more marked in FSGS. Synaptopodin, GLEPP1, and nephrin expression was present, although reduced in Galloway-Mowat syndrome. We conclude that the reduced expression of synaptopodin, GLEPP1, and nephrin in Galloway- Mowat syndrome is a secondary phenomenon related to the proteinuria, and hence synaptopodin, GLEPP1, and nephrin are probably not the proteins mutated in Galloway-Mowat syndrome. Received: 27 April 2001 / Revised: 15 June 2001 / Accepted: 18 June 2001     

Cell-cycle regulatory proteins in podocyte cell in idiopathic nephrotic syndrome of childhood

BACKGROUND: The podocyte cell is believed to play an important role in idiopathic nephrotic syndrome (INS) of childhood. In adults with cellular and collapsing focal segmental glomerulosclerosis (FSGS), the expression of cell-cycle regulatory proteins such as p27, p57, and cyclin D is decreased and expression of cyclin A, Ki-67, and p21 is observed in podocyte cells suggestive of a dysregulated podocyte phenotype. We investigated for alterations in the expression of cyclin kinase inhibitors, p27, p57, p21, and cyclins D and A in the podocyte cell of children with INS. METHODS: Forty-two kidney biopsies were investigated; 14 with minimal-change disease (MCD), seven with diffuse mesangial hypercellularity (DMH), 12 with FSGS, four with Alport syndrome (AS), and five normal biopsies. The sections were examined by immunohistochemistry using dual staining method. Podocyte cells were first identified by Wilm's tumor-1 staining after which expressions of cell-cycle regulatory proteins were analyzed. A quantitative analysis was performed for the proportion of podocyte cells that expressed each cell cycle regulatory protein. RESULTS: On light microscopy, all podocyte cells expressed p27, while p57 and p21 expression was seen in a portion of podocyte cells in normal kidney biopsies. Cyclin D was expressed in a small percent of podocyte cells though the expression was more marked in mesangial and endothelial cells. Cyclin A expression was not seen in normal biopsies. The mean expression of p27 decreased significantly in order from normal (100%), MCD (45.9%), DMH (22.4%), and FSGS (16.7%), and the difference between MCD and FSGS was significant. p21 was significantly and equally reduced in MCD (2.3%), DMH (0%), and FSGS (0.7%) compared to normal (66.6%). There was no significant difference in expression of p57, cyclin D and cyclin A in the podocyte cells between normal and children with INS. Children with AS showed a significant decrease in p27 and p21 expression, while the expression of p57, cyclin D and cyclin A were unchanged from normal, thus demonstrating a pattern similar to INS. CONCLUSION: The podocyte cell in children with INS down-regulates expression of cyclin kinase inhibitors such as p21 and p27, but not p57, but does not up-regulate cyclin D and cyclin A that are needed to overcome the G1/S transition and move the cell forward in the cell cycle process. Thus, the podocyte cell remains trapped in the G1 arrest phase. In children with INS or AS, the dysregulated podocyte phenotype is different than the one described in adults with cellular or collapsing FSGS.     

Reduced podocin expression in minimal change disease and focal segmental glomerulosclerosis is related to the level of proteinuria

Background

Glomerular podocyte molecules are involved in the pathogenesis of congenital nephrotic syndrome. However, their role in primary nephrotic syndrome is not clear. This study investigated the expression of nephrin, podocin and synaptopodin in primary nephrotic syndrome.

Methods

Eighty-seven patients with primary nephrotic syndrome including minimal change disease (MCD), focal segmental glomerulosclerosis (FSGS), membranous nephropathy (MN) and membranoproliferative glomerulonephritis Type I (MPGN) were included in the study. Glomerular expression of nephrin, podocin and synaptopodin was studied in renal biopsies by immunofluorescence and immunohistochemistry. Correlation of expression with clinical and biochemical parameters was performed.

Results

The pattern of expression for all podocyte proteins in controls was uniform fine granular along the capillary walls towards the visceral epithelial cell aspect. Glomerular expression of nephrin was present in all renal biopsies and was similar to that in controls. Glomerular synaptopodin expression was seen in all MN and MPGN patients, while it was seen in 74 % (17/23) MCD and 93.5 % (29/31) FSGS. Reduced synaptopodin expression showed no correlation with clinical and biochemical factors. Podocin expression was present in 5/23 MCD (22 %), 3/31 FSGS (9.6 %), 13/17 MN (76.4 %) and 13/16 MPGN (81 %) patients. The reduced expression of podocin significantly correlated with the degree of proteinuria (p = 0.032). No correlation with age, gender and serum creatinine level was observed.

Conclusion

Reduction of glomerular podocin expression found in MCD and FSGS is related to the amount of proteinuria. Our findings suggest that alteration in podocyte phenotype may not be a primary event and may reflect the degree of podocyte injury in primary nephrotic syndrome.     

儿童原发性肾病综合征中血管生成素样蛋白3的表达

目的 研究血管生成素样蛋白3 (angiopoietin-like 3 protein，ANGPTL3)在儿童原发性肾病综合征(PNS)患者肾组织中表达分布及其参与蛋白尿发生的机制。方法 ANGPTL3分别与足细胞核标记抗原(WT1)、基底膜标记抗原类肝素硫酸蛋白多糖perlecan进行双标记法免疫荧光染色。应用免疫组化的方法检测ANGPTL3和perlecan在不同病理类型的69例PNS及血尿患儿，包括微小病变(MCD)31例、膜性肾病(MN)6例、局灶节段硬化性肾小球肾炎(FSGS)6例、IgA肾病16例、薄基底膜肾病(TBMN)10例以及2例正常对照肾组织中表达，并以IMS彩色图像分析系统量化为免疫组化指数。在MCD病例中将尿蛋白肌酐比值分别与肾组织中ANGPTL3和perlecan肾小球内染色强度及电镜下平均足突宽度(FWP)进行相关分析。对不同病理诊断时间(发病至肾穿刺)分组患儿肾小球ANGPTL3和perlecan的表达进行比较。结果 (1)ANGPTL3在正常肾组织呈现微弱的沉积，而在不同病理类型的肾病综合征患儿的肾组织的肾小球和肾小管存在不同程度的表达。肾小球内ANGPTL3表达量在MCD(7.49±1.96)、MN(6.27±0.98)中显著高于正常对照(0.02±0.001)、TBMN(0.02±0.001)及FSGS(3.14±0.49)(均P < 0.05)。在IgA肾病(系膜增生型)中，蛋白尿组肾小球中ANGPTL3表达量显著高于单纯血尿组(1.90±0.81比0.03±0.01， P < 0.05)。(2) 在MCD肾组织中，WT1及perlecan荧光双标记染色显示， ANGPTL3在足细胞胞浆及沿肾小球血管袢表达。(3) ANGPTL3在肾小球表达量分别与尿蛋白肌酐比值及电镜下平均足突宽度正相关(r为0.86、0.84，P均<0.05)，并与perlecan在肾小球内表达量负相关(r为-0.83，P < 0.05)。(4)不同发病年限的MCD患儿肾组织中肾小球ANGPTL3及perlecan的表达无显著性差异。结论 在不同程度的蛋白尿及不同足突融合程度的肾组织中存在ANGPTL3的表达差异。在MCD中，ANGPTL3主要在足细胞胞浆表达，肾小球中ANGPTL3的表达与蛋白尿程度及足细胞融合程度呈正相关。     

In situ evaluation of podocin in normal and glomerular diseases

BACKGROUND: Mutations of the NPHS2 gene are responsible for autosomal-recessive steroid-resistant nephrotic syndrome. Its product, podocin, faces the slit diaphragm area with its two ends in the cytoplasm of foot processes. METHODS: We generated rabbit polyclonal antibodies against conjugated peptides from human podocin N- and C-termini, and studied podocin and synaptopodin using kidney tissues of normal humans and those with glomerular diseases. RESULTS: Antipodocin antibodies detected the original 42 kD fragment and an extra smaller fragment by Western blot analysis using human isolated mature glomeruli. RNA analysis showed two bands, the original and the other of a decreased length. Immunohistochemically, podocin was detected in a linear pattern along the glomerular capillary loop. Antipodocin antibody (C-terminal) stained the smooth muscles of renal arterioles and aorta. Among 42 patients, podocin was normally expressed in glomeruli in purpura nephritis, IgA nephropathy (IgAN), and minimal-change disease (MCD), while it was either decreased or absent in most subjects with focal segmental glomerulosclerosis (FSGS). The expression of synaptopodin was similar to that of podocin, although some discrepancy existed. CONCLUSION: Although indirect, our data suggest the existence of a vascular isoform of podocin with a different molecular mass. We propose that examination of podocin expression may help differentiate MCD from FSGS.     

Is mesangial hypercellularity with glomerular immaturity a variant of glomerulosclerosis?

Our aim was to correlate an immunohistochemical pattern of selected podocyte cytoskeleton-associated proteins in children diagnosed with focal segmental glomerulosclerosis (FSGS) and diffuse mesangial proliferation accompanied by glomerular immaturity (Im-DMP) with the clinical courses of both diseases. The material included 33 renal biopsies obtained from children diagnosed with DMP with or without signs of glomerular immaturity (ten and 15 participants, respectively) or FSGS (eight patients). Ezrin, podocalyxin, synaptopodin and nephrin expression was evaluated by immunohistochemical assay. A positive reaction for ezrin, podocalyxin, synaptopodin and nephrin was observed in the most superficial, continuous 'layer' of podocytes in Im-DMP patients. This distribution closely mimicked the immunohistochemical pattern observed in FSGS. The severe initial course of Im-DMP was transient. Resistance to steroids (six children) and renal insufficiency (two patients) in these subjects subsided, whilst, in the FSGS patients, the resistance to steroids recognized in all the children and the renal insufficiency diagnosed in three of them were still present. Mimicry between the immunohistochemical pattern of glomerular immaturity in DMP and focal segmental glomerulosclerosis might explain the severe initial course of this nephrotic syndrome in children. The transient clinical character of the former may also indicate that it is not a variant of FSGS.     

APOL1 localization in normal kidney and nondiabetic kidney disease

In patients of African ancestry, genetic variants in APOL1, which encodes apolipoprotein L1, associate with the nondiabetic kidney diseases, focal segmental glomerulosclerosis (FSGS), HIV-associated nephropathy (HIVAN), and hypertensive nephropathy. Understanding the renal localization of APOL1 may provide clues that will ultimately help elucidate the mechanisms by which APOL1 variants promote nephropathy. Here, we used immunohistology to examine APOL1 localization in normal human kidney sections and in biopsies demonstrating either FSGS (n = 8) or HIVAN (n = 2). Within normal glomeruli, APOL1 only localized to podocytes. Compared with normal glomeruli, fewer cells stained for APOL1 in FSGS and HIVAN glomeruli, even when expression of the podocyte markers GLEPP1 and synaptopodin appeared normal. APOL1 localized to proximal tubular epithelia in normal kidneys, FSGS, and HIVAN. We detected APOL1 in the arteriolar endothelium of normal and diseased kidney sections. Unexpectedly, in both FSGS and HIVAN but not normal kidneys, the media of medium artery and arterioles contained a subset of α-smooth muscle actin-positive cells that stained for APOL1. Comparing the renal distribution of APOL1 in nondiabetic kidney disease to normal kidney suggests that a previously unrecognized arteriopathy may contribute to disease pathogenesis in patients of African ancestry.     

Histopathological spectrum of childhood nephrotic syndrome in Indian children

Nephrotic syndrome in children is a clinical manifestation of different histopathological subtypes. There is a paucity of recent large studies dealing with the histopathological spectrum from developing countries. A prospective study was performed from January 1990 to December 2000 at our center, involving 600 children (with age of onset up to 16 years) with idiopathic nephrotic syndrome (INS). The objectives were: (1) to study the histopathological distribution of different subtypes of INS and (2) to compare the clinical and biochemical parameters at the time of diagnosis of minimal change disease (MCD) with non-MCD subtypes. For the purpose of this study we analyzed only those children with INS who underwent biopsies. The study group included 290 children in which adequate biopsy reports were available. There were 213 males and 77 females. Mean age at onset of INS was 7.9+5.1 years. Facial edema was found in 286 (98.6%), microhematuria in 120 (41.3%), gross hematuria in 7 (2.5%), and hypertension in 77(26.8%) patients. All patients of the study group were seronegative for HBsAg and HIV. Focal and segmental glomerulosclerosis (FSGS) was the most common histopathological subtype, occurring in 110 of 290 children (38%). Other subtypes included MCD in 95 children (32%), membranoproliferative glomerulonephritis (MPGN) in 44 children (15%), mesangioproliferative glomerulonephritis in 33 children (11%), membranous glomerulonephritis in 5 children (2%), and diffuse mesangial sclerosis in 3 children (1%). In children under 8 years of age, MCD was the most common entity, whereas FSGS predominated in children with age at onset greater than 8 years. The age at onset of nephrotic syndrome was significantly higher in the non-MCD group than the MCD group. The incidence of hypertension, microhematuria, and gross hematuria was significantly lower in the MCD group. MCD remains the most common histopathological subtype in Indian children with INS and onset under 8 years of age. The incidence of MPGN continues to be high. MCD can be differentiated from non-MCD subtype by younger age at onset, absence of hypertension, and absence of microscopic hematuria.     

MicroRNA-206 and its down-regulation of Wilms’Tumor-1 dictate podocyte health in adriamycin-induced nephropathy

Background: Focal segmental glomerulosclerosis (FSGS) is a frequent and severe glomerular disease characterized by destabilization of podocyte foot processes. Emerging evidence suggests that microRNAs play crucial roles in podocyte homeostasis. The aim of the present study was to determine the role of miR-206 in podocyte injury and to elucidate the mechanisms responsible for the damage to podocyte. Methods: FSGS nephropathy model was induced by a single intravenous injection of Adriamycin (ADR) in BALB/c mice and the levels of proteinuria were measured on week of 1,3,5. The conditionally immortalized mouse podocyte cell line 5 was either transfected with microRNA mimics or negative control. Real-time PCR analysis was conducted to demonstrate the microRNA level in the glomeruli. Expression of Wilms’ tumor-1 (WT1) and synaptopodin were detected by immunofluorescence and western blotting. Results: The results revealed that miR-206 was up-regulated in ADR nephropathy mice, which led to severe podocyte injury and inhibited the expression of WT1 and synaptopodin. Using luciferase reporter assays, WT1 was identified as a target gene of miR-206. In vitro, over expression of miR-206 induced WT1 and synaptopodin degradation and actin rearrangement, initiating a catastrophic collapse of the entire podocyte-stabilizing system. Conclusions: Over expression of miR-206 promotes podocyte injury via downregulation of WT1, which provides a new pathogenic mechanism for FSGS and miR-206 may be a potential therapeutic target.     

High incidence of focal segmental glomerulosclerosis in nephrotic syndrome of childhood

In recent adult literature, there have been reports of an increasing incidence of focal segmental glomerulosclerosis (FSGS) among patients with nephrotic syndrome. To examine whether this observation is also relevant to the pediatric population we utilized our hospital computerized database to analyze the data on children with primary nephrotic syndrome seen first between the years 1984 and 1995. A questionnaire was also sent to all metropolitan Kansas City pediatricians to identify possible patients outside the database. The inclusion criteria were clinical nephrotic syndrome or proteinuria with a kidney biopsy. A total of 148 patients (group A) were identified; 86 of them from metropolitan Kansas City (group B). In group A the incidence of minimal change disease (MCD) and FSGS was 52.7% [95% confidence interval (CI) 44%-60%] and 23.0% (95% CI 16-29%), respectively and in group B 54.7% (95% CI 44%-65%) and 24.5% (95% CI 15%-33%), respectively. Those numbers were significantly different from the International Study of Kidney Disease in Children (IS-KDC) reported incidence of 76.4% for MCD and 6.9% for FSGS. Similar to the ISKDC, in our population children over 6 years had a higher incidence of FSGS than younger children (32.8% vs. 16.7%, P = 0.028). The annual incidence rate for nephrotic syndrome in group B was 2.2 cases/10(5) children per year, of which MCD comprised 1.22 cases/10(5) children per year and FSGS 0.5 cases/10(5) children per year. The annual incidence rates of both primary nephrotic syndrome (3.6) and FSGS (1.6) were significantly higher in African-Americans, than Caucasians (1.8 and 0.3 cases/10(5) children per year, respectively). Our study indicates nearly no change in the annual incidence of pediatric primary nephrotic syndrome, but a higher incidence of FSGS with reciprocal decline in the incidence of MCD. The possibility of primary nephrotic syndrome being caused by a non-MCD entity is further raised among African-American and in children over 6 years. We conclude that our perception of primary nephrotic syndrome of childhood as a benign condition has to be carefully reexamined and a more-guarded prognostic approach adopted in our geographic area.     

Urinary low-molecular-weight protein excretion in pediatric idiopathic nephrotic syndrome

Background

Minimal change disease (MCD) and focal segmental glomerulosclerosis (FSGS) are the most common causes of idiopathic nephrotic syndrome (INS). We have evaluated the reliability of urinary neutrophil-gelatinase-associated lipocalin (uNGAL), urinary alpha1-microglobulin (uα1M) and urinary N-acetyl-beta-D-glucosaminidase (uβNAG) as markers for differentiating MCD from FSGS. We have also evaluated whether these proteins are associated to INS relapses or to glomerular filtration rate (GFR).

Methods

The patient cohort comprised 35 children with MCD and nine with FSGS; 19 healthy age-matched children were included in the study as controls. Of the 35 patients, 28 were in remission (21 MCD, 7 FSGS) and 16 were in relapse (14 MCD, 2 FSGS). The prognostic accuracies of these proteins were assessed by receiver operating characteristic (ROC) curve analyses.

Results

The level of uNGAL, indexed or not to urinary creatinine (uCreat), was significantly different between children with INS and healthy children (p?=?0.02), between healthy children and those with FSGS (p?=?0.007) and between children with MCD and those with FSGS (p?=?0.01). It was not significantly correlated to proteinuria or GFR levels. The ROC curve analysis showed that a cut-off value of 17 ng/mg for the uNGAL/uCreat ratio could be used to distinguish MCD from FSGS with a sensitivity of 0.77 and specificity of 0.78. uβNAG was not significantly different in patients with MCD and those with FSGS (p?=?0.86). Only uα1M, indexed or not to uCreat, was significantly (p?<?0.001) higher for patients in relapse compared to those in remission.

Conclusions

Our results indicate that in our patient cohort uNGAL was a reliable biomarker for differentiating MCD from FSGS independently of proteinuria or GFR levels.     

Is rituximab effective in childhood nephrotic syndrome? Yes and no

The idiopathic nephrotic syndrome (i.e. MCNS and FSGS) in children has been regarded as a disorder of T-cell function. Recent studies, however, also describe abnormalities of B-cell function. This supports the use of B-cell modulating treatment for idiopathic nephrotic syndrome (INS), especially rituximab, which has been used in other glomerular disorders as well. Many studies indicate that rituximab is effective in steroid-sensitive and -dependent nephrotic syndrome, by either inducing long-term remission or reducing relapses. In most series, children with primary (and recurrent) focal segmental glomerulosclerosis (FSGS) do not respond as well. The exact mechanisms of action of rituximab (as well as those of the other treatment options) in INS are as yet unclear. In addition to hosting mechanisms a direct stabilizing effect on the podocyte may also be of relevance, especially in FSGS. Although results are encouraging especially in steroid-sensitive patients, further studies on the clinical use of rituximab and the short- and long-term immunological effects and side-effects are necessary.     

Glomerular tip lesion: a distinct entity within the minimal change disease/focal segmental glomerulosclerosis spectrum

BACKGROUND: The glomerular tip lesion (GTL) is a distinctive but controversial histopathologic lesion occurring in patients with idiopathic nephrotic syndrome. The relationship of GTL to minimal change disease (MCD) and idiopathic focal segmental glomerulosclerosis (FSGS) has been disputed. METHODS: In order to define the clinical features and natural history of GTL, we retrospectively reviewed the presenting clinical features, biopsy findings and outcome of 47 cases. Presenting clinical features of GTL were compared to those of controls with MCD (N= 61) or idiopathic FSGS (N= 50). RESULTS: The cohort of GTL consisted of 45 adults and two children (mean age 47.5 years; range 12 to 79 years), including 76.6% Caucasians and 53% males. At presentation, 93.6% of patients had edema, 89.1% had nephrotic syndrome (mean urine protein 8.31 g, mean serum albumin 2.27 g/dL, and mean cholesterol 340.6 mg/dL), and 34.8% had renal insufficiency. Mean time from onset of renal disease to biopsy was 2.4 months. At biopsy, glomerular segmental lesions included GTL alone in 26%, GTL and peripheral lesions in 6%, GTL and indeterminate lesions in 36%, and GTL with peripheral and indeterminate lesions in 32%. No initial biopsy contained perihilar sclerosis and most (81%) segmental lesions were cellular. Follow-up data were available in 29 patients, of whom 21 received steroids alone and eight received sequential therapy with steroids and a cytotoxic agent. At a mean follow-up of 21.5 months, 58.6% of patients achieved complete remission of nephrotic syndrome, 13.8% had partial remission, and 27.6% had persistent nephrotic proteinuria. Only one patient progressed to end-stage renal disease (ESRD). Predictors of nonremission included severity of proteinuria at presentation and % peripheral lesions. When compared to controls with MCD and idiopathic FSGS, GTL more closely resembled MCD with respect to high incidence of nephrotic syndrome (P < 0.001), severity of proteinuria (P < 0.05), short duration from onset to biopsy (P < 0.001), and absence of chronic tubulointerstitial disease (P < 0.0054). CONCLUSION: Within the MCD/FSGS spectrum, GTL is a distinctive and prognostically favorable clinical-pathologic entity whose presenting features and outcome more closely approximate those of MCD.     

Differential expression of cyclin-dependent kinase inhibitors in human glomerular disease: role in podocyte proliferation and maturation

BACKGROUND: Normal human podocytes are terminally differentiated and quiescent cells. It is not known why podocytes fail to proliferate in response to most forms of injury. Proliferation is regulated by cell cycle proteins and their inhibitors. The Cip/Kip family of cyclin-dependent kinase (CDK) inhibitors (p21, p27, p57) in general prevent proliferation by inhibiting cyclin-CDK complexes. In the current study, we determined the expression and possible role of specific CDK inhibitors in podocyte proliferation in human disease characterized by podocyte injury. METHODS: Immunostaining was performed for the CDK inhibitors p21, p27, and p57 and the proliferation marker Ki-67 on renal biopsies from patients with minimal change disease (MCD; N = 6), membranous glomerulopathy (MGN; N = 19), cellular variant of focal segmental glomerulosclerosis (FSGS; N = 12), collapsing glomerulopathy (CG; N = 9), and HIV-associated nephropathy (HIVAN; N = 16). Adult nephrectomy specimens without evidence of glomerular disease served as controls (N = 9). RESULTS: Normal quiescent podocytes express p27 and p57, but not p21. In diseases without podocyte proliferation (MCD, MGN), p21, p27, and p57 expression did not change. In contrast, there was a uniform decrease in p27 and p57 immunostaining in diseases with podocyte proliferation (cellular FSGS, CG, and HIVAN). This was accompanied by the de novo expression of p21 in podocytes. CONCLUSIONS: Our results show that podocyte quiescence may require the presence of the CDK inhibitors p27 and p57. In human glomerular diseases, a decrease in p27 and p57 may be permissive for the altered proliferative podocyte phenotype. p21 may have a multifactorial role in podocyte cell cycle regulation.     

Ultrastructural Features and Expression of Cytoskeleton Proteins of Podocyte from Patients with Minimal Change Disease and Focal Segmental Glomerulosclerosis

Focal segmental glomerulosclerosis (FSGS) and minimal change disease (MCD) have been suggested for the category of podocytopathies. An ultrastructural observation and immunogold labeling for cytoskeleton proteins of podocytes on 11 cases each of FSGS and MCD were performed. Compared to MCD, more severe ultrastructural alterations of podocyte were identified in FSGS, which were characterized by higher frequency of mat-like condensation of microfilaments in the foot process and the detachment of the foot process from glomerular basement membrane. The labeling of α-actinin of podocytes in FSGS was significantly higher than MCD, which suggested an abnormal expression of cytoskeleton protein of podocyte in FSGS. The present study demonstrated a much more severe podocyte injury at the ultrastructural level in FSGS than in MCD.     

Ultrastructural features and expression of cytoskeleton proteins of podocyte from patients with minimal change disease and focal segmental glomerulosclerosis

Focal segmental glomerulosclerosis (FSGS) and minimal change disease (MCD) have been suggested for the category of podocytopathies. An ultrastructural observation and immunogold labeling for cytoskeleton proteins of podocytes on 11 cases each of FSGS and MCD were performed. Compared to MCD, more severe ultrastructural alterations of podocyte were identified in FSGS, which were characterized by higher frequency of mat-like condensation of microfilaments in the foot process and the detachment of the foot process from glomerular basement membrane. The labeling of alpha-actinin of podocytes in FSGS was significantly higher than MCD, which suggested an abnormal expression of cytoskeleton protein of podocyte in FSGS. The present study demonstrated a much more severe podocyte injury at the ultrastructural level in FSGS than in MCD.     

Rituximab in idiopathic nephrotic syndrome: does it make sense?

Idiopathic nephrotic syndrome (INS) includes three different entities: minimal change disease (MCD), focal segmental glomerulosclerosis (FSGS), and mesangial proliferative glomerulonephritis. Historically, this condition has been attributed to a T-cell disorder resulting in the secretion of a circulating factor that increases glomerular permeability to plasma proteins. The therapeutic approach to control the proteinuria of INS remains the use of drugs that have been considered to suppress the production of the “circulating factor” secreted by T cells. Recently, rituximab (RTX), a chimeric monoclonal antibody directed against the CD20 cell surface receptor expressed on B cells, has emerged as potential therapeutic agent. The number of publications reporting clinical experience with RTX in the treatment of nephrotic syndrome has greatly increased in the last few years. However, there is currently no good evidence from clinical or experimental studies that support a role of RTX in the treatment of MCD and FSGS proteinuria. In summary, there is the need for a better understanding of the pathogenesis of the proteinuria in INS and the potential role of RTX in this condition.     

Cell-cycle regulatory proteins in the podocyte in collapsing glomerulopathy in children

Podocyte is a terminally committed cell in G1 arrest of cell cycle, and is unable to overcome G1/S transition phase in children with minimal change disease (MCD) and classic focal segmental glomerulosclerosis (FSGS), in contrast to dysregulated proliferative phenotype of idiopathic collapsing glomerulopathy (CGN) in adults. Forty-two kidney biopsies, MCD (14), FSGS (12), CGN (4), and normal (CON) (12), were evaluated by immunohistochemistry using dual staining for expression of p27, p21, and p57, and cyclins D and A, in podocytes of children with CGN. On light microscopy, all podocytes expressed p27, whereas p21 and p57 expression was seen in a portion of podocytes in normal kidney biopsies. Cyclin D was expressed in a small percentage of podocytes. Cyclin A expression was absent in normal biopsies. The staining for p27 decreased significantly, in order, from normal (100%) to MCD (45.8%) to CGN (24.2%) to FSGS (16.6%). p21 staining was significantly decreased from normal (69.8%) to CGN (15.5%) to MCD (2.2%) to FSGS (0.6%), and the difference between CGN and MCD and FSGS was also significant. There was no significant difference in staining of p57. Cyclin D staining was significantly increased in CGN (26.8%) compared to normal (7.2%), MCD (1.6%), and FSGS (0.0%), and the difference between CGN and MCD and FSGS was also significant. De novo cyclin A staining was only observed in children with CGN. Thus, p27 and p21 but not p57 was decreased in CGN, as in FSGS when compared to normal. Both cyclins D and A staining were increased in CGN. The staining pattern in CGN would suggest that podocyte is able to overcome G1/S transition phase, and has a proliferative phenotype. We propose, based on the significant contrast observed in podocytes injury response between CGN (proliferative) and classic FSGS (non-proliferative), that CGN not be considered as a morphological variant of FSGS.