Expression profile of nephrin, podocin, and CD2AP in Chinese children with MCNS and IgA nephropathy

Research Progress in Acute Hypertensive Renal Injury by "in Vivo Cryotechnique"

Arterial hypertension has a large prevalence in the general population and as a major hypertensive target organ, the involvement of kidney is usually hard to avoid and gradually develops into chronic kidney disease (CKD). Acute hypertension is defined as a blood pressure greater than 180/120, also known as hypertensive emergency (HE). In acute severe hypertension, the pathophysiology damage to the kidney tends to worsen on the basis of chronic damage, and accounts for more significant mortality. However, the mechanisms of renal injury induced by acute hypertension remain unclear. This review summarizes the clinical and histopathological features of hypertensive renal injury by using "in vivo cyrotechnique" and focusses on the interplay of distinct systemic signaling pathways, which drive glomerular podocyte injury. A thorough understanding of the cellular and molecular mechanisms of kidney damage and repair in hypertension will provide significant insight into the development of new research methods and therapeutic strategies for global CKD progression.

Human podocyte injury in the early course of hypertensive renal injury

BACKGROUND

Hypertension is prevalent in the general population and is regarded as the second leading cause of renal damage and dysfunction, outnumbered only by diabetes. However, the mechanisms remain unclear.

AIM

To investigate podocyte injury induced by hypertension in the early course without massive proteinuria or renal dysfunction.

METHODS

The hypertension group comprised 18 patients with hypertension accompanied by microalbuminuria, diagnosed with hypertensive renal injury according to biopsy results. For a comparison of pathological changes in renal tissue, control group 1 comprised 10 healthy volunteers, and control group 2 comprised 16 patients who underwent surgery for renal trauma.

RESULTS

The hypertension group had significantly higher blood pressure (P = 0.000) and microalbuminuria (P = 0.000) compared with control group 1. In the hypertension group, urinary podocytes were detected following positive staining of podocyte-specific nephrin and/or CD2-associated protein (CD2AP) in urine sediment. Podocyte foot process fusion and a significant decrease in nephrin and/or CD2AP expression in glomeruli were observed in the hypertension group compared with control group 2. This indicated that hypertension caused podocyte injury and detachment from the glomerular basement membrane, which was consistent with urinary detection of podocytes.

CONCLUSION

Our results suggest that podocyturia appears early in the course of hypertensive renal injury, and may be a sensitive marker for early prediction of hypertensive renal injury.

Chronic ethanol ingestion induces glomerular filtration barrier proteins genes expression alteration and increases matrix metalloproteinases activity in the kidney of rats

Background

Chronic alcohol ingestion-induced kidney structure and function alterations are very well known, but the precise underlying molecular mediators involved in ethanol-induced kidney abnormalities remain elusive. The aim of this study was to investigate the effect of chronic ethanol exposure on matrix metalloproteinase 2, 9 (MMP), glomerular filtration barrier proteins (nephrin and podocin), as well as vascular endothelial growth factor receptor 1, 2 (VEGFRs) isoforms gene expression in the kidney of rats.

Methods

Sixteen male Wistar rats with an initial body weight of 220 ± 10 g were divided into the following two groups: (1) control and (2) ethanol (4.5 g/kg BW).

Results

After 6 weeks of treatment, the results revealed a significant increase in isoforms VEGFR1 and VEGFR2 of VEGFR gene expression, significant increases of MMP2 and MMP9 activities, as well as significant decrease of nephrin and podocin gene expressions in the ethanol group, compared with that in the control group.

Conclusion

These findings indicate that ethanol-induced kidney abnormalities may be in part associated with alteration in expressions of VEGFRs, nephrin, and podocin and in increasing activities of MMP2 and MMP9 as key molecular mediators in the kidney function.

Triptolide Attenuates Podocyte Injury by Regulating Expression of miRNA-344b-3p and miRNA-30b-3p in Rats with Adriamycin-Induced Nephropathy

Objectives. We investigated the action of triptolide in rats with adriamycin-induced nephropathy and evaluated the possible mechanisms underlying its protective effect against podocyte injury. Methods. In total, 30 healthy male Sprague-Dawley rats were randomized into three groups (normal group, model group, and triptolide group). On days 7, 28, 42, and 56, 24 h urine samples were collected. All rats were sacrificed on day 56, and their blood and renal tissues were collected for determination of biochemical and molecular biological parameters. Expression of miRNAs in the renal cortex was analyzed by a biochip assay and RT-PCR was used to confirm observed differences in miRNA levels. Results. Triptolide decreased proteinuria, improved renal function without apparent adverse effects on the liver, and alleviated renal pathological lesions. Triptolide also elevated the nephrin protein level. Furthermore, levels of miR-344b-3p and miR-30b-3p were elevated in rats with adriamycin-induced nephropathy, while triptolide treatment reversed the increase in the expression of these two miRNAs. Conclusions. These results suggest that triptolide may attenuate podocyte injury in rats with adriamycin-induced nephropathy by regulating expression of miRNA-344b-3p and miRNA-30b-3p.

Diabetic conditions downregulate the expression of CD2AP in podocytes via PI3-K/Akt signalling

BACKGROUND

Proteinuria is typically accompanied by structural and compositional changes of the foot processes and of the slit diaphragms between podocytes. CD2-associated protein (CD2AP) in podocytes serves as an adaptor protein binding to nephrin and podocin, anchoring these slit diaphragm proteins to actin filaments of podocyte cytoskeleton and sending signals inward or outward.

METHODS

In the present study, we prepared streptozotocin-induced diabetic renal tissues and cultured podocytes in diabetic conditions to investigate podocyte phenotypical changes, including quantitative and distributional changes of CD2AP protein and search for the signalling mechanisms in diabetic conditions. We prepared cultured rat glomerular epithelial cells and mouse podocytes to study how high glucose and advanced glycosylation end products (AGE) induce phenotypical changes of cultured podocyte, under (1) normal glucose (5 mM, = control), (2) high glucose (30 mM), (3) AGE-added or (4) high glucose plus AGE-added conditions.

RESULTS

According to diabetic duration, density of CD2AP in renal tissue of experimental diabetic nephropathy became conglomerulated and diminished. In cultured podocytes, CD2AP co-localized with nephrin and zonula occludens-1 by confocal imaging. High glucose and high glucose plus AGE induced the relocalization and concentration of CD2AP at internal cytoplasmic and perinuclear areas of podocytes. High glucose plus AGE-added condition also decreased CD2AP protein amount and its mRNA expression compared with normal glucose or osmotic control conditions. In addition, LY294002, a phosphoinositide 3-kinase inhibitor, prevented the quantitative and distributional changes of CD2AP induced by high glucose and AGE.

CONCLUSIONS

These findings suggest that diabetic conditions induce the phenotypical changes of podocyte CD2AP possibly via phosphoinositide 3-kinase/Akt signalling.

Extracellular vesicles in the urine: markers and mediators of tissue damage and regeneration

As in several body fluids, urine is a rich reservoir of extracellular vesicles (EVs) directly originating from cells facing the urinary lumen, including differentiated tubular cells, progenitor cells and infiltrating inflammatory cells. Several markers of glomerular and tubular damage, such as WT-1, ATF3 and NGAL, as well as of renal regeneration, such as CD133, have been identified representing an incredible source of information for diagnostic purposes. In addition, urinary extracellular vesicles (uEVs) appear to be involved in the cell-to-cell communication along the nephron, although this aspect needs further elucidation. Finally, uEVs emerge as potential amplifying or limiting factors in renal damage. Vesicles from injured cells may favour fibrosis and disease progression whereas those from cells with regenerative potential appear to promote cell survival. Here, we will discuss the most recent findings of the literature, on the light of the role of EVs in diagnosis and therapy for damage and repair of the renal tissue.

Podocyte proteins in congenital and minimal change nephrotic syndrome

BACKGROUND

Podocyte foot process effacement is a uniform finding in kidneys with heavy proteinuria. Its molecular mechanisms, however, are unsolved. We analyzed the expression of podocyte proteins in two kidney disorders: Congenital nephrotic syndrome of the Finnish type (CNF) and minimal change nephrotic syndrome (MCNS).

METHODS

Immunoperoxidase and immunofluorescence stainings were used to semiquantitatively analyze the expression of 13 and 4 podocyte proteins from different cellular compartments in CNF and MCNS, respectively.

RESULTS

The expression of a major slit diaphragm (SD) protein, Neph 1, showed a 46-fold decrease (p < 0.0001) in CNF kidneys as compared to controls. The three cytosolic adaptor proteins, podocin, NCK1/2, CD2AP, connecting SD proteins to the actin cytoskeleton were slightly upregulated (1.1-fold, 1.4-fold, and 3.3-fold, respectively). Also, the staining of the two actin-regulator proteins, ACTN4 and INF2, was modestly increased (2.2-fold and 1.7-fold, respectively, p < 0.0001). Staining for α3-integrin showed 1.9-fold increase (p < 0.0001) indicating that the major podocyte anchoring complex, α3β1, was well preserved in CNF glomeruli. In contrast to CNF kidneys, Neph1 FAT1, ACTN4, and CD2AP were quite normally expressed in proteinuric and non-proteinuric MCNS kidneys.

CONCLUSION

CNF kidneys lacking nephrin show decreased expression of other SD proteins but not cytosolic podocyte proteins involved in the foot process architecture or function. In MCNS kidneys, these changes in expression were not observed.

Heterogeneous genetic alterations in sporadic nephrotic syndrome associate with resistance to immunosuppression

In children, sporadic nephrotic syndrome can be related to a genetic cause, but to what extent genetic alterations associate with resistance to immunosuppression is unknown. In this study, we designed a custom array for next-generation sequencing analysis of 19 target genes, reported as possible causes of nephrotic syndrome, in a cohort of 31 children affected by sporadic steroid-resistant nephrotic syndrome and 38 patients who exhibited a similar but steroid-sensitive clinical phenotype. Patients who exhibited extrarenal symptoms, had a familial history of the disease or consanguinity, or had a congenital onset were excluded. We identified a genetic cause in 32.3% of the children with steroid-resistant disease but zero of 38 children with steroid-sensitive disease. Genetic alterations also associated with lack of response to immunosuppressive agents in children with steroid-resistant disease (0% of patients with alterations versus 57.9% of patients without alterations responded to immunosuppressive agents), whereas clinical features, age at onset, and pathologic findings were similar in steroid-resistant patients with and without alterations. These results suggest that heterogeneous genetic alterations in children with sporadic forms of nephrotic syndrome associate with resistance to steroids as well as immunosuppressive treatments. In these patients, a comprehensive screening using such an array may, thus, be useful for genetic counseling and may help clinical decision making in a fast and cost-efficient manner.

Podocin and beta dystroglycan expression to study podocyte-podocyte and basement membrane matrix connections in adult protienuric states

BACKGROUND

Podocytes can be the primary site of injury or secondarily involved in various protienuric states. Cross talk between adjacent foot processes and with basement membrane is important for slit diaphragm function. Does expression of podocyte associated proteins in kidney biopsies alter with site/type of primary injury? Genetic mutations of podocin result in steroid resistant FSGS. Can protein expression of podocin predict resistant cases to initiate further genetic evaluation?

METHODS

Adult patients (n-88) with protienuria- minimal change disease(MCD)-22, focal segmental glomerulosclerosis(FSGS)-21,membranous glomerulonephritis(MGN)-25 and IgA nephropathy(IgAN)-20 were selected for immunohistochemistry with podocin and beta dystroglycan . Results were graded (0 - 3+scale )and compared with control biopsies and internal control. Treatment and follow up (6 months -2 ½ years) of FSGS and MCD cases were collected.

RESULTS

There was intense to moderate staining of the podocytes with podocin and β dystroglycan in the glomeruli in all cases (MCD, FSGS, IgAN and MGN) except for weak staining with β dystroglycan in 3 cases of MCD. There was loss of immunostains in areas of segmental/global sclerosis. There was no significant difference in the staining pattern between the groups. In primary podocytopathies, staining pattern did not differ between steroid resistant, sensitive or dependent cases.

CONCLUSIONS

Immunohistochemical expression of podocin and β dystroglycan does not differ in nephropathies which have different site of injury depending on absence (MCD and FSGS) or presence of immune deposits and their localization (MGN and IgAN). Podocin and β dystroglycan staining did not differentiate steroid sensitive and resistant cases, hence, does not give clue to initiate genetic studies. However, analysis of bigger cohort may be required.

SUMMARY

Podocin and β dystroglycan immunohistochemistry was done to analyze podocyte - podocyte and podocyte -basement membrane matrix connections in adult protienuric states. Primary podocytopathies i.e. MCD and FSGS and secondary podocytopathy due to immune complex deposition, i.e., MGN (subepithelial) and IgAN (mesangial) were analyzed. There was no difference in staining patterns between primary and secondary podocytopathies or between steroid sensitive, resistant and dependent cases of FSGS and MCD.

VIRTUAL SLIDES

The virtual slide(s) for this article can be found here: http://www.diagnosticpathology.diagnomx.eu/vs/2258608781052786.

Qi-Dan Fang ameliorates adriamycin-induced nephrotic syndrome rat model by enhancing renal function and inhibiting podocyte injury

ETHNOPHARMACOLOGICAL RELEVANCE

Nephrotic syndrome (NS) is a clinical syndrome with a variety of causes, mainly characterized by heavy proteinuria. Podocyte injury plays a key role in proteinuria, one of the principal means for the control of NS is to prevent podocyte injury. Qi-Dan Fang consists of two of the most extensively applied herbal remedies among Traditional Chinese Medicine (TCM) (Radix Astragali Mongolici and Radix Salviae Miltiorrhizae, with a weight ratio of 5:1) which are specifically used for the treatment of various kidney diseases. In previous studies, we found that Qi-Dan Fang provides improvement to patients with adriamycin-induced nephrotic syndrome by alleviating proteinuria and serum lipid. The aim of this study is to study the efficiency of Qi-Dan Fang on NS model rat with renal dysfunction and podocyte injury, something which has not been carried out yet.

MATERIALS AND METHODS

The rats were divided into Normal, Model, Jin Gui Shen Qi Pill (4.12 g/kg), Qi-Dan Fang (3.09, 6.17 and 12.34 g/kg/d) groups, they were each given a single tail intravenous injection of Adriamycin (6.0 mg/kg) except for the Normal group and were orally administered dosages of Qi-Dian Fang and Jin Gui Shen Qi pills once daily for 7 weeks. Following the treatment, the content of cystation C (CysC), blood urea nitrogen (BUN), serum creatinine (Scr) were measured with an autobiochemical analyser. The pathomorphological changes to the glomeruli, the mRNA expressions of nephrin, podocin, CD2AP genes and p53, bax, bcl-2 proteins expressions were also carried out to probe the effects of Qi-Dan Fang.

RESULTS

(1) Qi-Dan Fang treatment raised the level of CysC in blood serum while lowering the content of BUN and Scr in the adriamycin-induced nephrotic syndrome rat model; (2) Long-term administration of Qi-Dan Fang was able to ameliorate pathomorphological change of glomeruli and repair the organization structure of Glomerulus; (3) Qi-Dan Fang could increase the mRNA expression of nephrin, podocin and CD2AP genes, down-regulate the expression of p53, bax proteins, while increased bcl-2 protein to protect the podocyte and restore Glomerular selective filtration function.

CONCLUSIONS

Results of our present studies reveal that Qi-Dan Fang is able to enhance renal function, inhibit podocyte injury to provide improvements to the Adriamycin-induced nephrotic syndrome.

CD2AP mRNA in urinary exosome as biomarker of kidney disease

AIMS

Podocyte injury plays an important role in the pathogenesis of kidney disease. Urinary exosomes are microvesicles released by tubular epithelial cells and podocytes containing information of their originated cells. This study investigated for the first time whether podocyte related mRNA in urinary exosome could serve as novel biomarkers for kidney disease.

METHODS

Urine samples were collected from 32 patients of kidney disease who underwent kidney biopsy and 7 controls. CD2AP, NPHS2 and synaptopodin were detected by real-time RT-PCR on RNA isolated from urinary exosome.

RESULTS

The pellet microvesicles were positively stained with exosome and podocyte marker, AQP2, CD9 and nephrin. CD2AP mRNA was lower (p=0.008) in kidney disease patients compared with controls and decreased with the increasing severity of proteinuria (p=0.06). CD2AP correlated with serum creatinine (r=-0.373, p=0.035), BUN (r=-0.445, p=0.009) and eGFR (r=0.351, p=0.046). Neither NPHS2 nor synaptopodin correlated with parameters of renal function. CD2AP mRNA correlated negatively with 24 hour urine protein (r=-0.403, p=0.022), severity of tubulointerstitial fibrosis (r=-0.394, p=0.026) and glomerulosclerosis (r=-0.389, p=0.031) and could discriminate kidney disease from controls with AUC of 0.821 (p=0.008).

CONCLUSIONS

Urinary exosome mRNA of CD2AP might be a non-invasive tool for detecting both renal function and fibrosis of kidney disease.

Morphine induces albuminuria by compromising podocyte integrity

Morphine has been reported to accelerate the progression of chronic kidney disease. However, whether morphine affects slit diaphragm (SD), the major constituent of glomerular filtration barrier, is still unclear. In the present study, we examined the effect of morphine on glomerular filtration barrier in general and podocyte integrity in particular. Mice were administered either normal saline or morphine for 72 h, then urine samples were collected and kidneys were subsequently isolated for immunohistochemical studies and Western blot. For in vitro studies, human podocytes were treated with morphine and then probed for the molecular markers of slit diaphragm. Morphine-receiving mice displayed a significant increase in albuminuria and showed effacement of podocyte foot processes. In both in vivo and in vitro studies, the expression of synaptopodin, a molecular marker for podocyte integrity, and the slit diaphragm constituting molecules (SDCM), such as nephrin, podocin, and CD2-associated protein (CD2AP), were decreased in morphine-treated podocytes. In vitro studies indicated that morphine modulated podocyte expression of SDCM through opiate mu (MOR) and kappa (KOR) receptors. Since morphine also enhanced podocyte oxidative stress, the latter seems to contribute to decreased SDCM expression. In addition, AKT, p38, and JNK pathways were involved in morphine-induced down regulation of SDCM in human podocytes. These findings demonstrate that morphine has the potential to alter the glomerular filtration barrier by compromising the integrity of podocytes.

Temporal and spatial expression of podocyte-associated molecules are accompanied by proteinuria in IgA nephropathy rat model

We used a rat model to assess the role of nephrin, podocin, and desmin in the pathogenesis of IgA nephropathy (IgAN). A rat IgAN model was established by administration of BSA, CCl(4), and lipopolysaccharide (LPS) and compared with healthy control rats. Urinary protein, urine red blood cells, and biochemical parameters were measured for 12 weeks. Renal morphology and ultrastructure were examined by light and electron microscopy. Immunofluorescence was used to assess IgA deposition in the glomeruli and to measure expression of nephrin, podocin, and desmin. Real-time quantitative PCR was used to measure expression of nephrin, podocin, and desmin mRNAs. IgAN rats developed proteinuria at week-6 and this worsened over time. Pathological changes were evident under light microscopy at week-8 and under electron microscopy at week-4. Immunofluorescence analysis showed deposition of IgA in the kidneys of IgAN rats, but not control rats. IgAN rats had increased expression of glomerular podocin, nephrin, and desmin mRNAs and proteins at week-4. The expression of nephrin, podocin and desmin proteins and the expression of podocin and desmin mRNAs preceded the increase in urinary protein. Taken together, our study of a rat model of IgAN indicates that changes in the expression and distribution of nephrin, podocin, and desmin precede and may cause foot process fusion and proteinuria.

Treatment of tacrolimus or cyclosporine A in children with idiopathic nephrotic syndrome

BACKGROUND

Cyclosporine A (CsA) and tacrolimus (TAC) are often alternative treatment choices for patients with nephrotic syndrome.

METHODS

In this prospective study, the efficacy and safety of CsA and TAC in inducing and maintaining remission in 74 children with idiopathic nephrotic syndrome (INS) were evaluated.

RESULTS

In terms of short-term efficacy, TAC was more effective than CsA in children with steroid-resistant nephrotic syndrome (χ(2) = 13.75, P = 0.001), although no significant difference in number of episodes of relapse were found in patients with complete remission between the two treatment groups (first year: χ(2) = 0.261, P = 0.88; second year: χ(2) = 2.685, P = 0.26). In patients with frequently relapsing or steroid-dependent nephrotic syndrome, no significant difference in short-term remission (χ(2) = 1.908, P = 0.39) or in relapse frequency during follow-up (within first year: χ(2) = 1.046, P = 0.59; within second year: χ(2) = 0.587, P = 0.75) were found between the two groups. There was a difference in the rate of adverse effects between the two treatment groups [nephrotoxicity: 4/24 (CsA) vs .0/50 (TAC), P = 0.002; hirsutism: 8/24 (CsA) vs. 0/50 (TAC), P < 0.001].

CONCLUSIONS

In our pediatric patient cohort, the treatment of steroid-resistant nephrotic syndrome with tacrolimus was associated with higher efficacy and lower renal toxicity in comparison to CsA, although no favorable outcome in relapse rate during long-term follow-up was seen. On the other hand, tacrolimus was not always the better choice to replace CsA in the treatment of severe frequently relapsing or steroid-dependent nephrotic syndrome.

Relevance of VEGF and nephrin expression in glomerular diseases

The glomerular filtration barrier is affected in a large number of acquired and inherited diseases resulting in extensive leakage of plasma albumin and larger proteins, leading to nephrotic syndrome and end-stage renal disease. Unfortunately, the molecular mechanisms governing the development of the nephrotic syndrome remain poorly understood. Here, I give an overview of recent investigations that have focused on characterizing the interrelationships between the slit diaphragm components and podocytes-secreted VEGF, which have a significant role for maintaining the normal podocyte structure and the integrity of the filtering barrier.

Podocyte main slit diaphragm proteins, nephrin and podocin, are affected at early stages of lupus nephritis and correlate with disease histology

Renal podocytes and their slit diaphragms ensure the integrity of the renal basement membrane that forms the barrier to urinary protein loss. A putative disruption of the slit diaphragm and its main protein components, nephrin and podocin, may be implicated in the pathogenesis of lupus nephritis (LN). We studied the glomerular protein expression of nephrin and podocin in NZB/W LN mice by Western blot and immunofluorescence; mRNA levels were measured by real-time PCR. Human kidney biopsies of class II (n = 5), IV (n = 4), V (n = 7) LN were evaluated for nephrin expression by immunohistochemistry. Glomerular protein expression of nephrin and podocin were significantly reduced in NZB/W LN, starting from the earlier stages (mild mesangial LN) and becoming pronounced at advanced histological forms (focal and diffuse proliferative LN). Nephrin and podocin mRNA levels were substantially decreased in diffuse proliferative disease. Decreased expression of both proteins correlated with electron microscopy findings of distorted slit diaphragms. In patients with LN, nephrin was decreased particularly in diffuse proliferative LN. The main slit diaphragm proteins, nephrin and podocin, are affected from the earlier stages of LN and their expression correlates with disease histology. Our findings suggest a novel role of podocytes and their structures in immune-mediated nephritis.

Focal segmental glomerulosclerosis plays a major role in the progression of IgA nephropathy. II. Light microscopic and clinical studies

It is well known that lesions morphologically identical with focal segmental glomerulosclerosis (FSGS) may appear in IgA nephropathy (IgAN). Capsular adhesions without underlying abnormalities in the tuft, often the first sign of FSGS, are frequent in IgAN. In this retrospective study, a new cohort of 128 adult patients with IgAN was used to validate the new Oxford classification system of IgAN, and shown to have highly significant associations with clinical and outcome parameters. We then used these patients to determine the extent to which IgAN could be accounted for in terms of FSGS. Some form of lesion consistent with FSGS, notably hyalinosis and collapsing glomerulopathy, was found in 101 of these patients. No glomerular lesions were found in 16 patients, and 11 had mild lesions not definable as FSGS. Those with FSGS had significantly worse renal survival at 80 months than those without. Comparison of pure forms of FSGS (excluding collapsing glomerulopathy) with cases of FSGS having other glomerular lesions (mesangial hyperplasia, endocapillary hypercellularity, glomerular necroses, extracapillary proliferation) revealed that those with FSGS and other superimposed lesions did significantly worse than cases of pure FSGS at 80 months following diagnosis. Importantly, patients with pure FSGS had relatively poor survival even without other superimposed glomerular abnormalities. Thus, the majority of cases of IgAN can be interpreted as representing one or another variant of FSGS. Hence, interpreting IgAN in terms of FSGS emphasizes the role that podocyte lesions may play in the pathogenesis and progression of this disease.

Focal segmental glomerulosclerosis plays a major role in the progression of IgA nephropathy. I. Immunohistochemical studies

IgA nephropathy (IgAN) often shows lesions morphologically identical with those of focal segmental glomerulosclerosis (FSGS). In order to determine the possible role of FSGS in IgAN lesions, we measured glomerular capsular adhesions, often the first step toward FSGS, in biopsies from 127 patients with IgAN, 100 with lupus nephritis, and 26 with primary FSGS. Capsular adhesions with no lesions in the underlying tuft, consistent with podocyte abnormality or loss, were found regularly in FSGS and IgAN, but infrequently in lupus. Fifteen biopsies of patients with IgAN were studied immunohistochemically using markers for podocytes, Bowman's parietal epithelial cells, proliferating cells, and macrophages. Cytokeratins CK-8 and C2562 differentiated normal podocytes (negative) from parietal epithelial cells (variably positive). There was focal loss of the podocyte markers synaptopodin, glomerular epithelial protein 1 (GLEPP-1), nephrin, and vascular endothelial growth factor (VEGF), particularly at sites of capsular adhesions in otherwise histologically normal glomeruli. Cells displaying the parietal epithelial cell markers PAX2 (paired box gene 2) and the cytokeratins were also positive for the proliferating cell marker, proliferating cell nuclear antigen. These cells gathered at sites of adhesion, and in response to active lesions in the tuft, grew inward along the adhesion onto the tuft, forming a monolayer positive for parietal markers and the podocyte marker Wilms tumor protein-1 (WT-1). These cells deposited a layer of collagen over the sclerosing tuft. Thus, all biopsies of patients with IgAN had changes basically identical to those classically described in FSGS. Hence, our study strongly suggests that podocytopathy of a type similar to that in primary FSGS occurs frequently in IgAN.

Induction of mesenchymal/epithelial marker expression in human amniotic fluid stem cells

Although dialysis and transplantation are widely applied therapies for renal failure, drawbacks such as morbidity, shortage of compatible organs and high cost are limiting factors. Recently, interest has increased in the potential use of stem cells for the repair of kidney injury, which has been considered as an alternative therapeutic strategy. Due to their high proliferation rates, their pluripotent differentiation potential, the finding that they do not induce tumour formation and the fact that they do not raise the ethical concerns connected with human embryonic stem cells, human amniotic fluid stem cells are considered to be a very promising cell source. This study demonstrates that the expression of the mesenchymal markers CD29 and CD44, the epithelial markers CD51 and ZO-1 and the podocyte markers CD2AP and NPHS2 can be induced in these cells via incubation with epidermal growth factor/platelet-derived growth factor BB and fibroblast growth factor 4/hepatocyte growth factor, respectively. Since podocytes are visceral epithelial cells in the kidneys, which form the essential part of the glomerular filtration barrier, these findings warrant further investigation of the potential use of human amniotic fluid stem cells for cell-based kidney therapies.

Expression of Toll-like receptor 9 in renal podocytes in childhood-onset active and inactive lupus nephritis

BACKGROUND

Childhood-onset systemic lupus erythematosus (SLE) is frequently complicated with lupus nephritis (LN), which is characterized by the deposition of DNA-containing immune complex to the glomerulus. Toll-like receptor 9 (TLR9), capable of recognizing the microbially derived CpG oligonucleotide, plays a crucial role in the innate immunity. TLR9 is also assumed to be related to the aetiology of SLE in the recognition of anti-DNA antibody-containing immune complex, but this remains controversial. We conducted a study to elucidate the association between TLR9 and LN in childhood-onset SLE.

METHODS

We compared the expression and localization of TLR9 and the slit membrane-related protein in the biopsied kidney sample by immunostaining in four children with active or inactive LN. We also evaluated their laboratory findings, such as anti-DNA antibody, complement and proteinuria at biopsy, to assess the correlation to the findings of the immunostaining.

RESULTS

TLR9 is not expressed in a normal control kidney. However, TLR9 develops in podocytes only in active LN but disappears in remission. Meanwhile, the slit membrane-related proteins such as nephrin, podocin and synaptopodin in podocytes express clearly and uniformly in remission, but their expression is markedly diminished in active LN, which results in podocyte injury. When TLR9 is expressed in podocytes, all the patients simultaneously showed hypocomplementaemia, high titre of anti-double-stranded DNA (dsDNA) antibody and proteinuria.

CONCLUSION

Injured podocytes in active LN express TLR9. This expression could be associated with proteinuria and increased anti-dsDNA antibody. This is the first report indicating that TLR9 is involved in the aetiology of LN and that it may play some role in podocyte injury.

Advanced oxidation protein products decrease expression of nephrin and podocin in podocytes via ROS-dependent activation of p38 MAPK

Accumulation of plasma advanced oxidation protein products (AOPPs) promotes progression of proteinuria and glomerulosclerosis. To investigate the molecular basis of AOPPs-induced proteinuria, normal Sprague-Dawley rats were treated with AOPPs-modified rat serum albumin. The expression of glomerular podocyte slit diaphragm (PSD)-associated proteins, nephrin and podocin, was significantly decreased coincident with the onset of albuminuria in rats treated with AOPPs. Chronic inhibition of NADPH oxidase by apocynin prevented down-regulation of nephrin and podocin and decreased albuminuria in AOPPs-challenged rats. This suggested that accumulation of AOPPs promotes proteinuria, possibly via down-regulating the expression of PSD-associated proteins.

TbetaRI independently activates Smad- and CD2AP-dependent pathways in podocytes

TGF-beta regulates differentiation, growth, and apoptosis of podocytes and mediates podocyte depletion in glomerulosclerosis. TGF-beta promotes proapoptotic signaling mediated by Smad3 but also activates prosurvival pathways such as phosphoinositide-3 kinase (PI3K)/AKT; the latter requires the CD2-associated adaptor protein (CD2AP) in podocytes. Whether the opposing activities mediated by Smad proteins and CD2AP involve molecular cross-talk is unknown. Here, we report that CD2AP-dependent early activation of the antiapoptotic PI3K/AKT pathway does not require TGF-beta receptor-regulated Smad2 and Smad3. We found that the C-terminal region of CD2AP interacts directly with the cytoplasmic tail of the TGF-beta receptor type I (TbetaRI) in a kinase-dependent manner and that the interaction between the TbetaRI and the p85 subunit of PI3K requires CD2AP. Consistent with the proapoptotic function of Smad signaling, Smad2/3-deficient podocytes were hyperproliferative and resistant to TGF-beta-induced growth inhibition and apoptosis. In contrast, CD2AP-deficient cells were hypoproliferative and hypersensitive to TGF-beta-induced apoptosis. In vivo, to determine the effects of reduced Smad3 or CD2AP gene dosage on podocyte apoptosis and proteinuria characteristic of TGF-beta1 transgenic mice, we generated TGF-beta1 transgenic mice deficient for Smad3 or heterozygous for CD2AP. Smad3 deficiency ameliorated podocyte apoptosis, and CD2AP heterozygosity increased both podocyte apoptosis and proteinuria. These data define distinct canonical (Smad) and noncanonical (CD2AP/PI3K/AKT) pathways that arise from direct, independent interactions with the TbetaRI and that mediate opposing signals for podocyte death or survival.

Molecular pathology of nephrotic syndrome in childhood: a contemporary approach to diagnosis

Molecular and genetic studies in the last 2 decades have shed new light on the understanding of congenital and infantile nephrotic syndrome (NS). Glomerular pathology may appear as minimal change disease, focal segmental glomerulosclerosis, or diffuse mesangial sclerosis, glomerular diseases now recognized as podocyte injuries and in part caused by altered podocyte genes. Even though genetic mutations are not implicated in all infants with NS, the study of familial disease and congenital NS reveals that proteinuria is in many patients due to specific gene mutations. The most common mutations are in 4 genes, 3 of which are podocyte genes: NPHS1 (Finnish nephropathy), NPHS2 (podocin-induced focal segmental glomerulosclerosis), WT1 (diffuse mesangial sclerosis), and LAMB2 (Pierson syndrome). Furthermore, these studies have improved our understanding of steroid-resistant NS in older children, particularly girls, in whom proteinuria may be due to WT1 mutations. Availability of molecular genetic testing and antibodies to specific gene products are closing the gap between histopathology of pediatric glomerular disease and molecular genetic diagnosis. Recognition of NS variants, which may be reversible (eg, mitochondrial mutations, viral disease), is important. This review discusses the most common entities and the differential diagnosis of pediatric NS from the pathologist's point of view, with an emphasis on congenital (<3 months) and infantile (3 months to 1 year) NS in light of molecular and genetic studies.

Parietal epithelia cells in the urine as a marker of disease activity in glomerular diseases

BACKGROUND

The detection of viable podocytes in the urine of patients with proteinuric diseases has been described as a non-invasive method to monitor disease activity. Most of the published studies use podocalyxin (PDX) as a podocyte specific marker.

METHODS

We examined the excretion of viable PDX-positive cells in a random set of spot urine from patients with biopsy-proven focal segmental glomerulosclerosis (FSGS), membranous nephropathy (MGN) or membranoproliferative glomerulonephritis (MPGN) and characterized the excreted cells for podocyte and parietal epithelia markers as well as for proliferation activity.

RESULTS

We found that untreated patients with active disease excrete high numbers of PDX-positive cells in their urine. In contrast to that we were not able to detect significant amounts of PDX-positive cells in the urine of patients with active minimal change disease (MCD) and patients with FSGS or MGN in full remission. When we further characterized the cells we rarely detected expression of podocyte specific markers in the PDX-positive cells, but at least 50% of the PDX-positive cells were double positive for cytokeratin (CK8-18). Immunohistochemistry of the corresponding renal biopsies showed that 100% of podocytes and parietal cells stained positive for PDX. Semiquantitative analysis revealed that 45% of parietal cells were positive for CK8-18 and 100% of proximal tubular cells. No cells of the glomerular epithelial layer stained positive for CK8-18.

CONCLUSIONS

PDX-positive cells are lost in the urine in disease states that require podocyte regeneration and are a useful non-invasive marker for glomerular disease activity. These cells are possibly derived from the parietal epithelial layer.

Beneficial effects of the Rho kinase inhibitor Y27632 in murine puromycin aminonucleoside nephrosis

BACKGROUND AND AIMS

Rho kinase (ROCK) inhibition reduces systemic blood pressure (BP) and decreases renal damage in animal models of kidney disease. The aim of this study was to determine if ROCK inhibition might have beneficial effects in glomerular disease processes that are independent of systemic BP.

METHODS

We investigated the effects of the ROCK inhibitor Y27632 and hydralazine in murine puromycin aminonucleoside (PAN) nephrosis.

RESULTS

Treatment with either Y27632 or hydralazine similarly reduced systolic BP compared to vehicle-treated controls. Seven days after treatment with PAN, albuminuria, proteinuria and effacement of podocyte foot processes were significantly reduced in Y27632- and hydralazine-treated mice compared to vehicle-treated animals. Treatment with PAN significantly reduced expression of the podocyte proteins nephrin and Neph1, and the loss of glomerular nephrin was attenuated by treatment with Y27632 but not by treatment with hydralazine. In cultured podocytes, PAN potently activated both Rho and ROCK, and PAN-induced ROCK activation was prevented by Y27632.

CONCLUSIONS

The ROCK inhibitor Y27632 attenuated glomerular nephrin loss in murine PAN nephrosis independent of its effects on systemic BP.

Lack of association between NPHS2 gene polymorphisms and sporadic IgA nephropathy

AIM

IgA nephropathy (IgAN) is the most common primary form of glomerulonephritis worldwide. In the present study, the genetic structure of the NPHS2 gene was studied to verify if podocin plays a role in the pathogenesis of IgAN.

METHODS

Clinical characteristics and DNA samples were collected from 26 Chinese children with sporadic IgAN. A direct sequencing was performed after polymerase chain reaction amplification to all the eight exons of the NPHS2 gene.

RESULTS

Three synonymous variants as known polymorphisms (954T-->C homozygous, 1038A-->G heterozygous and homozygous) were found in 3, 4 and 1 patients, respectively. There was no significant difference in the genotypic and allelic frequencies of 954T > C and 1038A > G polymorphisms between the patients and normal controls.

CONCLUSION

No significant difference in the genotypic and allelic frequencies of the identified 954T > C and 1038A > G polymorphisms between the patients and normal controls was found.

Lack of association between NPHS2 gene polymorphisms and Henoch-Schönlein purpura nephritis

Henoch-Schönlein purpura (HSP) is one of the most common forms of small-vessel vasculitis in childhood, and renal involvement (HSP nephritis, HSPN) is the main determinant of morbidity after acute phase. Considering the racial diversity and clinical heterogeneity in the prevalence, genetic factors might play a role in pathogenesis of HSP and HSPN. Direct sequencing was performed after PCR amplification of all 8 exons of the NPHS2 gene in 20 Chinese children with HSPN and 30 controls in present study. The genetic analyses revealed 3 polymorphisms (954T > C heterozygous, 1038A > G heterozygous and homozygous, all in exon 8) in 7 out of 20 patients studied, but there was no significant difference in the genotypic and allelic frequencies of these polymorphisms between the patients and controls. The result did not support the possible role of the NPHS2 gene in susceptibility to HSPN in the population studied. Studies in a larger sample population with different genetic backgrounds will be necessary in the future.