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Glomerüldeki hasarlar glomerül kaybına ve devamında da börek fonksiyonlarının yitirilmesine sebep olabilmektedir. Son zamanlardaki çalışmalar JAK/STAT yolağının glomerüler hasarlarda rol aldığını ortaya koymuştur. STAT3'ün hem büyüme faktörleri gibi hücre dışı hem de oksidatif stres gibi hücre içi uyarımlardan etkileniyor oluşu STAT3'ü glomerül açısından önemli kılmıştır. Glomerüler hasar modellerinden birisi olan PAN'ın oksidatif strese dayalı olarak geliştiği düşünülmektedir. Bu çalışmada PAN modeli kullanılarak glomerül hasarında STAT3 proteinlerinin etkilenmesi incelenmiştir.Kontrol grubu ve 5 gün boyunca 1,5 mg/100 gr PA'nın i.p. olarak uygulanmasına takiben farklı günlerde sakrifiye edilen 5., 15. ve 25. Gün grupları oluşturuldu. Deney esnasında farklı günlerde toplanan 24 saatlik idrarlarla proteinüri takibi yapıldı ve deney bitiminde böbrek dokuları pSTAT ve tSTAT antikorlarıyla immünohistokimyasal, PAS-Hemaluan boyasıyla ışık mikroskobik ve elektron mikroskobisiyle ultrastrüktürel olarak incelendi.Kontrol ve 5. Gün grupları proteinüri göstermezken, 15. Gün grubunda proteinüri seviyesi en yüksek değerlere ulaştı ve 25. Gün grubunda azalarak Kontrol grubuna yakın değerlere yaklaştı. Ultrastrüktürel inceleme ve ölçümlerde 5. ve 15. Gün gruplarında SP sayısının azalması, GBM kalınlığının giderek artması, podositlerin hipertrofik hale gelmesi, PAG granüllerinin oluşması gibi glomerüler hasarlar tespit edildi. Yine 5. ve 15. Gün gruplarında belirgin bir biçimde giderek artan mezangial matriks ve pSTAT immünoreaktivitesi artışı tespit edildi. Bu değerler iyileşme gösteren 25. Gün grubunda azalarak Kontrol grubu değerlerine yakın seviyelere yaklaştı. tSTAT immünoreaktivitesi ise ilk artışını 15. Gün grubunda gösterdi ve daha sonra 25. Gün grubunda pSTAT'la birlikte hafif azalma sergiledi.Tüm gruplar birlikte değerlendirildiğinde pSTAT ve tSTAT artışlarının hipertrofik podositler, mezangial matriks artışı ve anjiyogenezle ilişkili olduğu düşünülmüştür. Glomerular damages may lead to glomerular losses which can result in end stage renal diseases. Recent studies showed that JAK/STAT pathway has some roles in glomerular damages. The fact that STAT3 could be activated both by extracellular (e.g. growth factors) and intracellular (e.g. oxidative stress) stimulants make STAT3 very important for the glomerulus. One of the animal models that represent glomerular damages is PAN model which is thought to be due to oxidative stress. In this study, glomerular STAT3 expression changes are aimed to be evaluated in PAN model.Along with a Control group, three PAN groups which were sacrificed on different days were formed by the i.p. injection of PA for 5 days. Throughout the experiment, 24-hour-urines were collected on specific days and level of urinary proteins was monitored. At the end of the experiments, tissue specimens were stained with pSTAT and tSTAT antibodies. Moreover they also examined ultrastructurally in electron-microscope and stained with PAS-Hemaluan for light-microscope.The proteinuria levels did not increase in Control and 5th Day groups but showed a dramatic increase in 15th Day group. In 25th Day group, urinary protein levels decreased and become close to Control group. Ultrastructural findings showed glomerular damages such as decrease in SP number, a gradual increase in GBM thickness, podocyte hypertrophy and formation of PAGs in 5th and 15th Day groups. Increase in mesangial matrix and pSTAT immunoreactivity was detected. These changes come close to Control group levels in 25th Day group which showed a recovery. On the other hand tSTAT immunoreactivity showed its first increase in 15th Day group.Regarding all the groups, it was thought that the increases in the pSTAT and tSTAT immunoreactivity levels are related to hypertrophy in podocytes, mesangial matrix expansion and angiogenesis. 89

Maintenance of the physiological morphologies of different types of cells and tissues is essential for the normal functioning of each system in the human body. Dynamic variations in cell and tissue morphologies depend on accurate adjustments of the cytoskeletal system. The cytoskeletal system in the glomerulus plays a key role in the normal process of kidney filtration. To enhance the understanding of the possible roles of the cytoskeleton in glomerular diseases, we constructed the Glomerular Cytoskeleton Network (GCNet), which shows the protein-protein interaction network in the glomerulus, and identified several possible key cytoskeletal components involved in glomerular diseases. In this study, genes/proteins annotated to the cytoskeleton were detected by Gene Ontology analysis, and glomerulus-enriched genes were selected from nine available glomerular expression datasets. Then, the GCNet was generated by combining these two sets of information. To predict the possible key cytoskeleton components in glomerular diseases, we then examined the common regulation of the genes in GCNet in the context of five glomerular diseases based on their transcriptomic data. As a result, twenty-one cytoskeleton components as potential candidate were highlighted for consistently down- or up-regulating in all five glomerular diseases. And then, these candidates were examined in relation to existing known glomerular diseases and genes to determine their possible functions and interactions. In addition, the mRNA levels of these candidates were also validated in a puromycin aminonucleoside(PAN) induced rat nephropathy model and were also matched with existing Diabetic Nephropathy (DN) transcriptomic data. As a result, there are 15 of 21 candidates in PAN induced nephropathy model were consistent with our predication and also 12 of 21 candidates were matched with differentially expressed genes in the DN transcriptomic data. By providing a novel interaction network and prediction, GCNet contributes to improving the understanding of normal glomerular function and will be useful for detecting target cytoskeleton molecules of interest that may be involved in glomerular diseases in future studies.

The calcineurin inhibitors cyclosporine A (CsA) and tacrolimus are widely used in the treatment of proteinuria diseases. As the direct target of these drugs, calcineurin has previously been demonstrated to play a role in proteinuria diseases. However, aside from its immune-related effects, the local status of calcineurin in renal inherent cells has not been fully explored in the settings of proteinuria disease and podocyte injury. In this study, calcineurin activity and protein expression in the well-known puromycin aminonucleoside (PAN)-induced podocyte injury model were examined. Interestingly, we found that calcineurin activity was abnormally increased in PAN-treated podocytes, whereas the expression of the full-length 60-kDa calcineurin protein was decreased. This result suggests that there may be another activated form of calcineurin that is independent of the full-length phosphatase. To investigate whether calpain is involved in regulating calcineurin, we exposed PAN-treated podocytes to both pharmacological inhibitors of calpain and specific siRNAs against calpain. Calpain blockade reduced the enhanced calcineurin activity and restored the down-regulated expression of 60-kDa calcineurin. In addition, purified calpain protein was incubated with podocyte extracts, and a 45-kDa fragment of calcineurin was identified; this finding was confirmed in PAN-induced podocyte injury and calpain inhibition experiments. We conclude that calcineurin activity is abnormally increased during PAN-induced podocyte injury, whereas the expression of the full-length 60-kDa calcineurin protein is down-regulated due to over-activated calpain that cleaves calcineurin to form a 45-kDa fragment.

In non-neuronal cells, glutamate is an extracellular signaling mediator. Since podocytes have glutamate-containing vesicles, we sought to determine glutamate receptor presence and action in glomerular cells. The metabotropic glutamate receptors (mGluR) 1, 5, 6, and 8 were found to be expressed in mouse brain and glomeruli; predominantly in podocytes. In two models of proteinuria (BalB/C mice with puromycin aminonucleoside- and doxorubicin-induced podocyte injury) we found that the selective mGluR1/5 agonist (S)-3,5-dihydroxyphenylglycine (DHPG) attenuated albuminuria and improved the expression of the podocyte marker WT-1. TUNEL staining showed that the number of podocytes undergoing apoptosis was inversely correlated with the number of WT-1–positive cells in glomeruli. When podocytes were treated with DHPG in vitro , they generated cyclic AMP and activated CREB (cyclic AMP response element binding protein). The selective mGluR1/5 antagonist ( RS )-1-aminoindan-1,5-dicarboxylic acid, the adenylate cyclase inhibitor SQ22536, and RNA interference knockdown of mGluR1 or mGluR5 all prevented DHPG-induced cAMP generation and CREB activation. DHPG inhibited apoptosis and the decrease of aminonucleoside-induced mitochondrial membrane potential in podocytes but had no effect in the presence of SQ22536 with knockdown mGluR1 or mGluR5. Thus, functional mGluR1 and mGluR5 are expressed in podocytes and their activation protects against albuminuria and podocyte apoptosis, processes that are, at least in part, dependent on cAMP.

Background/Aims: Recent studies have demonstrated that erythropoiesis-stimulating agents (ESAs) induce a tissue-protective effect in the kidney. In this study, we examined whether continuous erythropoietin receptor activator (CERA), a long-acting ESA, could prevent kidney injury, especially podocyte damage, in a rat model of nephrotic syndrome induced by puromycin aminonucleoside (PAN). Methods: Rats were injected with CERA (30 µg/kg) or vehicle 4 h before the injection of PAN (50 mg/kg). Renal function, kidney injury, and podocyte damage were assessed at 7 days. Results: The levels of proteinuria, BUN, and plasma creatinine significantly increased in rats with PAN-induced nephrosis. Treatment with CERA significantly prevented these deteriorations induced by PAN. Glomerular lesions, especially vacuolation of podocytes, and the increase of desmin expression in PAN-treated rats were significantly ameliorated by treatment with CERA. Treatment with CERA also significantly prevented the decrease in the protein productions of nephrin and podocin in the kidneys of PAN-treated rats. We found persistent activation of the Akt signaling pathway in the kidneys of CERA-treated rats. Conclusion: CERA could ameliorate renal dysfunction in PAN-induced nephrosis, which might be due to the amelioration of podocyte injury. CERA inhibited the depletion of nephrin and podocin, key components of the glomerular filtration barrier, and alleviated proteinuria. Activation of the Akt signaling pathway might be involved in the renoprotective effect of CERA

Podocyte injury is considered to play important roles in the pathogenesis of human glomerular disease. There is accumulating evidence suggesting that hepatocyte growth factor (HGF) elicits preventive activity for glomerular cells in animal models of chronic renal diseases. In this study, we demonstrated that delivery of a naked plasmid vector encoding the human HGF gene into mice by a hydrodynamic-based in vivo gene transfection approach markedly reduced proteinuria and attenuated podocyte injury in a mouse model induced by puromycin aminonucleoside (PAN) injection. Systemic administration by rapid injection via the tail vein of a naked plasmid containing HGF cDNA driven under a cytomegalovirus promoter (pCMV-HGF) produced a remarkable level of human HGF protein in the circulation. Tissue distribution studies suggested that the kidney expressed a high level of the HGF transgene. Meanwhile, compared with tubules and interstitium, a higher level of exogenous HGF protein was detected in the glomeruli. Administration of pCMV-HGF dramatically abated the urine albumin excretion and podocyte injury in PAN nephropathy in mice. Exogenous expression of HGF produced evidently beneficial effects, leading to restoration of Wilms' tumor-1 (WT1) and α-actinin-4 expression and attenuation of ultrastructural damage of the podocytes. In vitro, HGF not only restored WT1 and α-actinin-4 expression but also inhibited albumin leakage of podocytes incubated with PAN in a Transwell culture chamber. These results suggest that HGF might provide a novel strategy for amelioration of podocyte injury.

The state-of-the-art cultured podocyte is conditionally immortalized by expression of a temperature-sensitive mutant of the SV40 large-T antigen. These cultures proliferate at 33°C and differentiate at 37°C into arborized cells that more closely resemble in vivo podocytes. However, the degree of resemblance remains controversial. In this study, several parameters were measured in podocyte cell lines derived from mouse (JR, KE), human (MS), and rat (HK). In all lines, the quantities of NEPH1 and podocin proteins and NEPH1 and SYNPO mRNAs were comparable to glomeruli, while synaptopodin and nephrin proteins and NPHS1 and NPHS2 mRNAs were > KE, and of doxorubicin was JR ∼ KE > MS, while HK cells were almost unaffected. Process formation was largely a result of contractile action after formation of lamellipodia. These findings demonstrate dramatic differences in marker expression, response to toxins, and motility between lines of podocytes from different species and even between similarly-derived mouse lines.

Background. The slit diaphragm (SD) is a complex of podocyte-specific proteins and plays a significant role in glomerular filtration. To understand podocyte biology, it is important to determine the expression amount of the SD complex proteins. This study aimed to quantify the absolute amount of nephrin, which is believed to be a major component of SD, in podocytes and to apply that method to normal and puromycin aminonucleoside (PAN) nephrosis rats. Methods. The counting method for podocyte number in a glomerulus was developed by three-dimensional reconstruction imaging of Wilms tumor (WT-1) immunofluorescence on isolated glomeruli. Absolute amount of nephrin was quantified by mass spectrometry using the selected reaction monitoring (SRM) mode with a stable isotopelabeled peptide. Results. The number of podocytes per glomerulus was 95.5 6 17.6 in the control rats, 90.7 6 19.2 on Day 4 and 90.7 6 26.2 on Day 7 in PAN nephrosis rats. The amount of nephrin per glomerulus in control rats was 1.02 6 0.11 fmol and those in PAN nephrosis rats were reduced to 0.46 6 0.06 fmol and 0.35 6 0.04 fmol on Day 4 and Day 7. The nephrin amount per podocyte was significantly decreased association with the development of proteinuria in PAN nephrosis rats. Conclusions. This study established the absolute quantification of nephrin and determined the amount of nephrin in a podocyte of normal and PAN nephrosis rat kidneys. This highly sensitive and selective quantification method for protein is a useful tool for the analysis of SD protein in a podocyte.

Our previous studies using puromycin aminonucleoside (PAN) established that podocyte damage leads to glomerular growth arrest during development and glomerulosclerosis later in life. The present study examined the potential benefit of maintaining podocyte-derived vascular endothelial growth factor (VEGF) in podocyte defense and survival following PAN injury using conditional transgenic podocytes and mice, in which human VEGF-A (hVEGF) transgene expression is controlled by tetracycline responsive element (TRE) promoter and reverse tetracycline transactivator (rtTA) in podocytes. In vitro experiments used primary cultured podocytes harvested from mice carrying podocin-rtTA and TRE-hVEGF transgenes, in which hVEGF can be induced selectively. Induction of VEGF in PAN-exposed podocytes resulted in preservation of intrinsic VEGF, α-actinin-4 and synaptopodin, anti-apoptotic marker Bcl-xL/Bax, as well as attenuation in apoptotic marker cleaved/total caspase-3. In vivo, compared with genotype controls, PAN-sensitive neonatal mice with physiologically relevant levels of podocyte-derived VEGF showed significantly larger glomeruli. Further, PAN-induced up-regulation of desmin, down-regulation of synaptopodin and nephrin, and disruption of glomerular morphology was significantly attenuated in VEGF-induced transgenic mice. Our data indicate that podocyte-derived VEGF provides self-preservation functions, which can rescue the cell following injury and preempt subsequent deterioration of the glomerulus in developing mice.

Tight junctions are the main intercellular junctions of podocytes of the renal glomerulus under nephrotic conditions. Their requisite components, claudins, still remain to be identified. We have measured the mRNA levels of claudin subtypes by quantitative real-time PCR using isolated rat glomeruli. Claudin-5 was found to be expressed most abundantly in glomeruli. Mass spectrometric analysis of membrane preparation from isolated glomeruli also confirmed only claudin-5 expression without any detection of other claudin subtypes. In situ hybridization and immunolocalization studies revealed that claudin-5 was localized mainly in glomeruli where podocytes were the only cells expressing claudin-5. Claudin-5 protein was observed on the entire surface of podocytes including apical and basal domains of the plasma membrane in the normal condition and was inclined to be concentrated on tight junctions in puromycin aminonucleoside nephrosis. Total protein levels of claudin-5 in isolated glomeruli were not significantly upregulated in the nephrosis. These findings suggest that claudin-5 is a main claudin expressed in podocytes and that the formation of tight junctions in the nephrosis may be due to local recruitment of claudin-5 rather than due to total upregulation of the claudin protein levels.

Background/Aims: SM22α, transgelin, is abundantly expressed in smooth muscle tissues and our previous work demonstrated that it is a novel marker of injured glomerular epithelial cells in rat antiglomerular basement membrane nephritis. In this study, we investigated SM22α expression in models of glomerular and interstitial renal injury. Methods: The 5/6 nephrectomy (Nx) model, ischemia-reperfusion (I/R) model and puromycin aminonucleoside (PAN) nephrosis of rats were studied. Immunohistochemical analyses and immunoelectron microscopic studies of SM22α expression were performed. Results: In the 5/6 Nx model, SM22α was first expressed in peritubular interstitial cells and was also expressed in injured glomerular epithelial cells at 8 weeks. In the I/R model, SM22α expression was induced in peritubular interstitial cells as early as 12 h after I/R with expression sustained at 7 days. However, SM22α was not detected in any glomerular cells or tubular epithelial cells. In PAN nephrosis, SM22α was only expressed in glomerular epithelial cells after 1 week, but expression was transient. Conclusion: SM22α was expressed in glomerular epithelial cells and interstitial cells in renal injury. SM22α is differentially upregulated in various models of renal injury and merits further study.

≪背景≫種々の病態により生じる酸化ストレスにより腎糸球体は組織学的な障害を受ける．Free radical scavengerであるエダラボンによる腎障害への保護効果はいくつか報告されている．この保護作用の機序を解明するため，我々は慢性 puromycine aminonucleoside (PAN) nephrosisモデルを用いて脂質過酸化のマーカーおよび腎組織学的検討を行った．≪方法≫慢性PANモデルは，PANを腹腔内投与し作成した（第1病日に130 mg/kg，腹腔内投与，第14病日に 60 mg/kg, 腹腔内投与）．ポジティブコントロール群(慢性PAN）(n＝4)，エダラボン投与群（慢性PAN＋Eda：Eda 3.0 mg/kg/day）（n＝4）の2群にグループ分けした．また，生理食塩水を腹腔内投与したwistarラット5匹をネガティブコントロール群とした．血液・尿を毎週採取し，実験終了日に麻酔下にラットより腎組織を採取した．≪結果≫慢性PAN＋Eda群では慢性PAN群に比べ，尿中アルブミン量および8-isoprostane排泄量の有意な低下を認めた(p＜0.01)．TBARSは，2群間で有意な差を認めなかった．組織学的検討では，慢性PAN＋Eda群がC-PAN群に比べ，糸球体障害度，4-hydroxy-2-nonenal（ 4-HNE）陽性面積(p＜0.01)，ED-1陽性細胞浸潤(p＜0.05)，アポトーシス細胞数の有意な減少(p＜0.05)を認めた．≪結論≫エダラボンのC-PAN群に対する投与により，尿中アルブミンを減少させ糸球体障害を改善することができた．慢性PANラットにおいて酸化ストレスおよび脂質過酸化に関連するマーカーは治療により減少し，マクロファージ浸潤および糸球体でのアポトーシス細胞の減少に相関していた．これら結果より，抗過酸化治療はC-PANにおいて糸球体障害軽減作用を有する可能性が示唆された．, Excessive oxidants play roles in the pathogenesis of glomerular injury. Several studies have demonstrated protective effects of edaravone, a free radical scavenger, against renal injury. To clarify the protective effects of edaravone, we investigated changes in chemical markers of lipid peroxidation and renal histology in rats with chronic puromycin aminonucleoside (PAN) nephrosis (C-PAN). C-PAN was induced by intraperitoneal injections of PAN (130 mg/kg on day 1 and 60 mg/kg on day 14). Rats administered normal saline served as controls (n＝5). C-PAN rats were divided into two groups (each group: n＝4). In one group (C-PAN＋Eda), rats received 3.0 mg/kg/day of edaravone for five weeks. Blood and urinary samples were collected every week. Animals were sacrificed at the end of experiment for histological analysis. In C-PAN＋Eda rats, urinary excretion of albumin and 8-isoPGF2α were significantly decreased compared with that in C-PAN rats (p＜0.01), whereas levels of urinary thiobarbituric acid-reactive substances (TBARS) did not differ between the two groups. On histological examination, the scores for glomerular injury and area positive for 4-HNE were significantly lower in C-PAN＋Eda than in C-PAN rats (p＜0.05, p＜0.01, respectively). Infiltration of macrophages was also suppressed in C-PAN＋Eda rats. Edaravone treatment of C-PAN was able to decrease albuminuria and to ameliorate glomerular injury. Levels of several markers related to oxidative stress and lipid peroxidation were reduced after treatment, accompanied by reduction of macrophage infiltration and decrease in apoptotic cells in the glomeruli. These findings indicate that edaravone has protective effects against the glomerular injury observed in C-PAN nephrosis.

Utilizing cytochrome P450 inhibitors we have recently demonstrated that P450 2B1 can serve as a site for reactive oxygen species generation in puromycin aminonucleoside (PAN)-induced nephrotic syndrome, which mimics minimal change disease in humans. In the current study, overexpression of P450 2B1 in glomerular epithelial cells significantly increased PAN-induced reactive oxygen species generation, cytotoxicity, cell death and collapse of the actin cytoskeleton. Silencing of P450 2B1 markedly attenuated reactive oxygen species generation, cytotoxicity, cell death and preserved the actin cytoskeleton. P450 2B1 protein content was significantly decreased while its mRNA level was markedly increased in the PAN-treated glomerular epithelial cells, indicating that the P450 2B1 protein decrease resulted from protein degradation rather than transcriptional inhibition. The degradation of P450 2B1 was accompanied by induction of heme oxygenase-1, an important indicator of heme-induced oxidative stress. This induction was significantly decreased in the P450 2B1-silenced cells treated with PAN. Treatment of the P450 2B1-silenced cells with PAN prevented cleavage of the endoplasmic reticulum-specific procaspase 12 and significantly decreased caspase 3 activity. Our data strongly suggests a pivotal role of P450 2B1 as an important site for reactive oxygen species production in PAN-induced cytotoxicity through an endoplasmic reticulum mediated pathway.

Background/Aims: It is still unclear what happens in the glomerulus when proteinuria starts. Using puromycin aminonucleoside nephrosis (PAN) rats, we studied early ultrastructural and permeability changes in relation to the expression of the podocyte-associated molecules nephrin, α-actinin, dendrin, and plekhh2, the last two of which were only recently discovered in podocytes. Methods: Using immune stainings, semiquantitative measurement was performed under the electron microscope. Permeability was assessed using isolated kidney perfusion with tracers. Possible effects of ACE inhibition were tested. Results: By day 2, some patchy foot process effacement, but no proteinuria, appeared. The amount of nephrin was reduced in both diseased and normal areas. The other proteins showed few changes, which were limited to diseased areas. By day 4, foot process effacement was complete and proteinuria appeared in parallel with signs of size barrier damage. Nephrin decreased further, while dendrin and plekhh2 also decreased but α-actinin remained unchanged. ACE inhibition had no significant protective effect. Conclusions: PAN glomeruli already showed significant pathology by day 4, despite relatively mild proteinuria. This was preceded by altered nephrin expression, supporting its pivotal role in podocyte morphology. The novel proteins dendrin and plekhh2 were both reduced, suggesting roles in PAN, whereas α-actinin was unchanged.

Angiopoietin-like 3 (ANGPTL3) is a secreted protein of the angiopoietin family and is involved in angiogenesis and lipid metabolism regulation. However, there is little data regarding the role of ANGPTL3 in kidney injury. We recently reported the glomerular distribution of ANGPTL3 in Adriamycin nephropathy in rats. In the present paper, we report expression of ANGPTL3 by murine podocytes in vitro. Puromycin-induced injury of cultured podocytes showed a time-dependent upregulation of ANGPTL3 accompanied by a time-dependent downregulation of perlecan and agrin by Western blot and RT-PCR analysis. In addition, the increased expression of ANGPTL3 following gene transfection upregulated the expression of perlecan and agrin in podocytes. Double immunolabeling demonstrated colocalization of perlecan and ANGPTL3 on podocytes following pcDNA3.1-ANGPTL3 transfection. To explore how ANGPTL3 transfection modulates the effect of puromycin on podocytes, we compared cell adhesion in untreated podocytes and ANGPTL3-transfected podocytes. ANGPTL3 gene transfection significantly ameliorated puromycin-induced podocyte detachment. In conclusion, ANGPTL3 expression is upregulated in puromycin-induced podocyte damage and is associated with the reduction of perlecan and agrin expression.

The tyrosine phosphorylation of nephrin is reported to regulate podocyte morphology via the Nck adaptor proteins. The Pak family of kinases are regulators of the actin cytoskeleton and are recruited to the plasma membrane via Nck. Here, we investigated the role of Pak in podocyte morphology. Pak1/2 were expressed in cultured podocytes. In mouse podocytes, Pak2 was predominantly phosphorylated, concentrated at the tips of the cellular processes, and its expression and/or phosphorylation were further increased when differentiated. Overexpression of rat nephrin in podocytes increased Pak1/2 phosphorylation, which was abolished when the Nck binding sites were mutated. Furthermore, dominant-negative Nck constructs blocked the Pak1 phosphorylation induced by antibody-mediated cross linking of nephrin. Transient transfection of constitutively kinase-active Pak1 into differentiated mouse podocytes decreased stress fibers, increased cortical F-actin, and extended the cellular processes, whereas kinase-dead mutant, kinase inhibitory construct, and Pak2 knockdown by shRNA had the opposite effect. In a rat model of puromycin aminonucleoside nephrosis, Pak1/2 phosphorylation was decreased in glomeruli, concomitantly with a decrease of nephrin tyrosine phosphorylation. These results suggest that Pak contributes to remodeling of the actin cytoskeleton in podocytes. Disturbed nephrin-Nck-Pak interaction may contribute to abnormal morphology of podocytes and proteinuria.

Aims: Idiopathic nephrotic syndrome is known as a disease of the renal glomerular epithelial cells (podocytes). Recent advances in podocyte biology showed that podocytopathy is the culprit of nephrotic syndrome. To obtain comprehensive information about the response of podocytes to injury, we investigated the gene expression profile of podocytes in response to puromycin aminonucleoside (PAN)-induced injury. Methods: Differentiated mouse podocyte cell line (MPC5) cells were treated with 25 µg/ml PAN for 24, 48, or 72 h. Gene expression profiles of these cells were analyzed. Real time PCR analysis was used to confirm the findings of microarray. Results: Expression levels of 23 genes (differentially expressed genes, DEGs), including laminin α1 and MMP3, were significantly different between PAN-treated podocytes and untreated cells. Gene ontology of DEGs indicated that their functional categories were cell adhesion, extracellular matrix (ECM) formation, and ECM degradation. Real-time PCR and indirect immunohistochemistry of PAN-treated and untreated podocytes confirmed the differential expression of DEGs. Conclusion: Using unbiased global gene expression profiling, we found that podocytes respond to PAN-induced injury by down-regulating the expression of genes involved in cell adhesion and extracellular matrix.

Background/Aims: The function of glomerular podocytes is closely associated with the actin cytoskeleton. In this study, we studied the role of the small Rho-GTPase, Rac1, in actin organization in podocytes. Methods: Conditionally immortalized mouse podocytes (MP) stably expressing nephrin or control plasmid were used. Results: In MP, Rac1 activity increased significantly at 1 week of differentiation. MP stably expressing nephrin showed Rac1 activity significantly higher and more sustained than vector-expressing control cells. Antibody-mediated cross-linking of nephrin also activated Rac1. Differentiated MP showed more distinct lamellipodia/cellular processes, as compared with undifferentiated cells, which was further augmented by nephrin expression. Transient transfection of constitutively active Rac1 markedly increased the number of lamellipodia/cellular processes in undifferentiated MP, while the Rac1 inhibitor caused actin cytoskeleton derangement in differentiating MP. In the rat model of puromycin aminonucleoside nephrosis, RhoA activity was increased at Day 7 (at the peak of proteinuria), while Rac1 activity increased significantly only at Day 14, when the recovery process had started. Conclusion: Rac1 is activated in differentiating MP and nephrin potentiates Rac1 activation. Rac1 likely contributes to lamellipodia formation in differentiating MP and may contribute to process formation in podocytes recovering from injuries.

Proteinuria caused by glomerular disease is characterized by podocyte injury. Vasopressin V2 receptor antagonists are effective in reducing albuminuria, although their actions on glomerular podocytes have not been explored. The objective of this study was to evaluate the effects of tolvaptan, a selective oral V2 receptor antagonist, on podocytes in a puromycin aminonucleoside (PAN)-induced nephrosis rat model. Rats were allocated to a control, PAN nephrosis, or tolvaptan-treated PAN nephrosis group (n = 9 per group). Urinary protein excretion and serum levels of total protein, albumin, creatinine, and total cholesterol were measured on day 10. The influence of tolvaptan on podocytes was examined in renal tissues by immunofluorescence and electron microscopy. PAN induced massive proteinuria and serum creatinine elevation on day 10, both of which were significantly ameliorated by tolvaptan. Immunofluorescence studies of the podocyte-associated proteins nephrin and podocin revealed granular staining patterns in PAN nephrosis rats. In tolvaptan-treated rats, nephrin and podocin expressions retained their normal linear pattern. Electron microscopy showed foot process effacement was ameliorated in tolvaptan-treated rats. Tolvaptan is protective against podocyte damage and proteinuria in PAN nephrosis. This study indicates that tolvaptan exerts a renoprotective effect by affecting podocyte morphology and probably function in PAN nephrosis. Tolvaptan is a promising pharmacological tool in the treatment of renal edema.

Background/Aims: Morphological change of podocytes is closely correlated with the development of proteinuria. Podocalyxin is a major sialoglycoprotein of the podocytes and is thought to be involved in the maintenance of the foot processes structure. Our aim was to examine the mechanism by which podocalyxin contributes to the morphological change of podocytes. Methods: We searched protein(s) which coprecipitate with podocalyxin using rat glomerular lysate. Localization of podocalyxin and the coprecipitated protein, cortactin, was studied in a model of puromycin aminonucleoside (PAN) nephrosis by immunocytochemistry. Tyrosine phosphorylation of cortactin was examined. Association of the podocalyxin/cortactin complex with the actin cytoskeleton was evaluated by extraction with Triton-X and immunoblotting. Results: Cortactin was found to be co-immunoprecipitated with podocalyxin. Immunocytochemical analysis revealed that these 2 proteins colocalized in the apical side of podocytes. In PAN nephrosis, localization of cortactin was altered after the onset of proteinuria, with increased tyrosine phosphorylation. Simultaneously, the dissociation of the podocalyxin/cortactin complex from the actin cytoskeleton was induced. Conclusions: These results indicate that cortactin mediates interaction between podocalyxin and actin filaments in podocytes and that alteration of this interaction may play a role in the process of morphological change of podocytes.

Eukaryotic expression vectors carrying the small hairpin RNA (shRNA) for TRPC6 mRNA were constructed, and the effects of knocking-down TRPC6 on puromycin aminonucleoside (PAN)-induced apoptosis of mouse podocytes were observed. Two eukaryotic expression vectors containing small hairpin structure targeting TRPC6 named pGCsi-TRPC6A and pGCsi-TRPC6B were designed and synthesized. The plasmids were transfected into conditionally immortalized murine podocyte cell line by liposome. The changes in the TRPC6 mRNA and protein expression were observed by RT-PCR and Western blot after 48 h. Cultured podocytes were divided into four groups: control group, PAN treatment group, PAN treatment+shRNA transfection group, and PAN treatment+ negative control group. The expression of Bax and Bcl-2 mRNA and proteins was detected by RT-PCR and Western-blot respectively. The apoptotic rate of podocytes was measured by flow cytometry. The results showed that the expression of TRPC6 mRNA and protein was decreased in the podocytes when transfected with pGCsi-TRPC6A, and pGCsi-TRPC6B. The expression of Bax was increased, and that of Bcl-2 was decreased at protein and mRNA levels in the podocytes after treated with PAN for 48 h. These changes was attenuated by knocking-down TRPC6. Knocking-down TRPC6 could effectively decrease the PAN-induced apoptosis of podocytes. It was concluded that TRPC6 may play an important role in the PAN-induced apoptosis of podocytes. Knocking-down TRPC6 gene could effectively prevent the podocytes from apoptosis induced by PAN.

The selective cyclooxygenase-2 (COX-2) and 5-lipoxygenase (LOX) inhibitors might inhibit prostaglandin synthesis and reduce proteinuria. The present study was designed to investigate the anti-proteinuric effects of nordihydroguaiaretic acid (NDGA) as compared with celecoxib in puromycin aminonucleoside (PAN) nephrosis rats. Fifty five male Sprague-Dawley rats were divided into 4 groups; A, normal control; B, PAN group; C, PAN+COX-2 inhibitor (celecoxib) group; and D, PAN+5-LOX inhibitor (NDGA) group. After induction of PAN nephrosis through repeated injections of PAN (7.5 and 15 mg/100 g body weight), rats were treated with celecoxib, NDGA, or vehicle for 2 weeks. Twenty four hour urine protein excretions were significantly lower in PAN+celecoxib and PAN+NDGA groups than in PAN group. Serum creatinine (SCr) concentrations and 24 hr urine creatinine clearances (CCr) were not significantly different in the four groups. Electron microscopy showed that podocyte morphology was changed after the induction of PAN nephrosis and was recovered after celecoxib or NDGA administration. Celecoxib significantly recovered the expressions of nephrin, CD2AP, COX-2, and TGF-beta. NDGA also recovered TGF-beta expression, but did not alter the expressions of nephrin, CD2AP and COX-2. The present study suggested that celecoxib and NDGA might effectively reduce proteinuria in nephrotic syndrome without impairing renal function.

Recent studies have demonstrated upregulation of transient receptor potential cation channel 6 (TRPC6) contributes to podocyte injury in acquired forms of proteinuric kidney diseases, such as focal segmental glomerulosclerosis (FSGS). However, under these pathophysiological conditions, the mechanisms of regulation of TRPC6 expression and activity remain unknown. The present study tested the hypothesis that NADPH oxidase-mediated redox signaling importantly participates in the development of podocyte injury by regulation of TRPC6 expression and activity. Injection of puromycin aminonucleoside (PAN) to rats produced severe proteinuria and mimics the lesions of FSGS. Podocyte effacement, NADPH oxidase subunit NOX4 expression, enzyme activity and TRPC6 expression were significant increased in glomeruli from PAN nephrosis rats. Inhibition of NADPH oxidase activity by apocynin ameliorated proteinuria and podocyte effacement and reduced TRPC6 expression. In in vitro study, PAN significantly increased NOX4 and TRPC6 expression levels in cultured podocytes. This increased TRPC6 expression was attenuated by apocynin or siRNA-NOX4. Our results provide direct evidence for the first time that NADPH oxidase-derived reactive oxygen species (ROS) is one of critical components of a signal transduction pathway that links PAN nephrosis to TRPC6-mediated Ca(2+) signaling.

The effects of traditional Chinese medicine (Sairei-to) on monoclonal antibody (mAb) inducing proteinuria were examined. Four hundred, 200 and 100mglkg body weight (BW) of Sairei-to and phosphate-buffered saline (PBS) as a control were injected intraperitoneally into four groups of female Wistar rats every day from 5 days before intravenous injection of mAb to the end of the experimental period. The amount of urinary protein excretion was significantly suppressed in roughly a dose-dependent manner. For example, 116.6 ± 89.7mg/day of proteinuria was observed in control groups compared to 4.2 ± 15.2 mglday in the 400 mglkg BW of Sairei-to treated group 2 days after mAb injection (P < 0.01). Statistically significant (P

Extracts of Tripterygium wilfordii Hook F have been used to treat glomerulonephritis for more than 30 years in China with dramatic antiproteinuric effects. Triptolide, a diterpene triepoxide, is one of the major active components of these extracts. To clarify its antiproteinuric effects we induced podocyte injury by puromycin aminonucleoside. Triptolide effectively reduced the proteinuria induced by puromycin in nephrotic rats without reducing the glomerular filtration rate. The antiproteinuric effect was associated with improvement in the foot process effacement, a decrease in the podocyte injury marker desmin as well as the restoration of nephrin and podocin expression and distribution. In cultured mouse podocytes triptolide pretreatment prevented the puromycin-induced disruption of the actin cytoskeleton and microfilament-associated synaptopodin while protecting nephrin and podocin expression. Triptolide suppressed reactive oxygen species generation and p38 mitogen-activated protein kinase activation while restoring RhoA signaling activity. These results show that triptolide ameliorates puromycin aminonucleoside-mediated podocyte injury in vivo and in vitro.

It is an a priori concept that protein molecules including albumin are filtrated through the slit membrane between the foot processes of podocytes. However, foot processes are effaced and the number of slit membranes is reduced in nephrotic syndrome, suggesting another pathway of albumin filtration through the foot process cell body. Thus, we investigated the pathway of gold-and fluorescein isothiocyanate (FITC)-labeled albumin filtration in the puromycin aminonucleoside (PAN) model of nephrotic syndrome in the rat. PAN rats at day 7 with established nephrotic proteinuria were injected with 8-nm gold-labeled albumin and FITC-labeled albumin through the jugular vein followed by kidney fixation at 10 or 30 min. Goldlabeled albumin was accumulated in the paramesangial area and in the endosomes of glomerular endothelial cells of both control and PAN rats by electron microscopy. On the other hand, FITC-labeled albumin was detected between foot processes in the control but more in the podocyte cell body in the PAN rat. In conclusion, albumin will be filtrated through the decreased numbers of slit diaphragms; however, albumin can be also taken up in the podocyte, the mesangium, and the glomerular endothelium, suggesting that there might be other routes of glomerular albumin clearance in nephrotic syndrome.

Tight junctions rarely exist in podocytes of the normal renal glomerulus, whereas they are the main intercellular junctions of podocytes in nephrosis and in the early stage of development. Claudins have been identified as tight junction-specific integral membrane proteins. Those of podocytes, however, remain to be elucidated. In the present study, we investigated the expression and localization of claudin-6 in the rat kidney, especially in podocytes. Western blot analysis and RT-PCR revealed that the neonatal kidney expressed much higher levels of claudin-6 than the adult kidney. Immunofluorescence microscopy showed intense claudin-6 staining in most of the tubules and glomeruli in neonates. The staining in tubules declined distinctly in adults, whereas staining in glomeruli was well preserved during development. Claudin-6 in glomeruli was distributed along the glomerular capillary wall and colocalized with zonula occludens-1. The staining became conspicuous after kidney perfusion with protamine sulfate (PS) to increase tight junctions in podocytes. Immunoelectron microscopy showed that immunogold particles for claudin-6 were accumulated at close cell-cell contact sites of podocytes in PS-perfused kidneys, whereas a very limited number of immunogold particles were detected, mainly on the basal cell membrane and occasionally at the slit diaphragm and close cell-cell contact sites in normal control kidneys. In puromycin aminonucleoside nephrosis, immunogold particles were also found mainly at cell-contact sites of podocytes. These findings indicate that claudin-6 is a transmembrane protein of tight junctions in podocytes during development and under pathological conditions.

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.

Background. We previously reported that puromycin aminonucleoside (PAN) increased adrenomedullin (AM) secretion and AM mRNA expression in podocytes, through overproduction of oxidative stress. To clarify the cytoprotective role of AM as antioxidative and antiapoptotic substance in podocytes, we investigated the effect of exogenous AM and AM antagonist on PAN-induced apoptosis in conditionally immortalized murine podocytes. Methods. The expression of AM, RAMP 2 and RAMP 3 was investigated using real-time PCR, western blotting analysis and immunofluorescence microscopy. Reactive oxygen species (ROS) production was measured by CM-H2DCFDA fluorescence intensity method. The percentage of apoptotic cells was measured by Hoechst 33342 staining. Results. PAN (100mg/ml) significantly (P < 0.01) increased ROS production, associated with an increase in apoptosis; the percentage of apoptotic cells is 5.3% þ 0.05% (P < 0.01) with 36 h treatment of PAN compared to 0.24 þ 0.16% with no treatment. Several antioxidants could markedly reduce PAN-induced apoptosis in cultured podocytes, suggesting that PAN-induced apoptosis might be attributable to the overproduction of ROS. Accordingly, the administration of exogenous AM (10 � 6 M) could significantly reduce not only ROS production via a PKA-dependent pathway, but also the resultant apoptosis induced by PAN. AM antagonists, CGRP8-37, augmented PAN-induced apoptosis, associated with increased ROS production, 2.2- and 2.3-Fold, respectively. RAMP 2 and RAMP 3 could be detected in podocytes and glomeruli. Conclusions. This suggests that ROS-induced upregulation of AM with PAN could counteract ROS-induced apoptosis, by the suppression of ROS production. Therefore, AM might have the endogenous antioxidant potential to protect against ROSinduced podocyte injury.

Previous studies from our own group and others have demonstrated that cyclooxygenase-2 (COX-2) inhibitors could reduce proteinuria in some experimental models of progressive renal disease. To investigate a possible role of COX-2 in podocytes during the course of self-limited glomerular injury, we administered puromycin nucleoside (PAN) on day 1 (15 mg/100 g BW) and day 3 (30 mg/100 g BW) to wild-type and transgenic mice with podocyte-specific COX-2 expression driven by a nephrin promoter. An additional group received both PAN and the COX-2-specific inhibitor, SC58236 (6 mg/l in drinking water). There was no significant difference in the albumin (µg)/creatinine (mg) ratio between wild-type (26.3 ± 4.2, n = 8) and transgenic (28.9 ± 2.3, n = 8) mice under baseline conditions. PAN induced significant albuminuria only in the transgenic mice with a peak at day 3: 72.1 ± 8.9 µg/mg creatinine (n = 12, p < 0.05, compared with basal level), which remitted by day 10 (37.4 ± 4.4 µg/mg, n = 7, p < 0.05, compared with day 3). Electron microscopy demonstrated that PAN caused 56.7 ± 4.2% foot process effacement in transgenic mice compared with 38.8 ± 4.1% in wild type at day 3. PAN increased immunoreactive COX-2 in glomeruli from transgenic mice (day 3: 1.47 ± 0.08 fold; day 10: 1.25 ± 0.16 fold, n = 5–9, p < 0.05 compared with basal level), which was restricted to podocytes. Real time PCR indicated that endogenous COX-2 mRNA increased (2.6 ± 0.1 fold of wild-type control at day 3 and 2.2 ± 0.2 at day 10, n = 4, p < 0.05), while the nephrin-driven COX-2 mRNA was unchanged. Nephrin mRNA and protein expression were decreased by PAN in the transgenic mice. The COX-2-specific inhibitor, SC58236, reduced foot process effacement in transgenic mice administered PAN to 21.7 ± 5.2% and significantly reduced the albuminuria at day 3 (42.2 ± 3.8, n = 13, p < 0.05 compared with untreated) without significantly altering COX-2 expression. In summary, in transgenic mice with podocyte COX-2 overexpression, PAN increased albuminuria and induced foot process fusion. Thus, increased COX-2 expression increased podocyte susceptibility to further injury.

Background Puromycin aminonucleoside-induced nephrosis is characterized by increased renal excretion of plasma proteins. We employed this experimental model to study the urinary clearance of dextran sulfate. Methods The dextran sulfate eliminated by the urine was determined using a metachromatic assay. Polysaccharide fragments were analyzed by chromatographic and electrophoretic procedures. Disaccharide composition of the glomerular heparan sulfate was assessed using digestion with specific lyases. Results In normal rats dextran sulfate is partially degraded to lower molecular weight fragments and only then eliminated by the urine. Surprisingly, in puromycin aminonucleoside-induced glomerulosclerosis the molecular size of the fragments of dextran sulfate found in the urine is the same or even lower than in control animals in spite of the marked proteinuria. Furthermore, urinary excretion of dextran sulfate decreases in the experimentally induced nephrosis. This observation cannot be totally attributed to a reduced number of physiologically active nephrons since the glomerular filtration rate decreases ∼ 32% after puromycin aminonucleoside administration while the urinary excretion of 8 kDa-dextran sulfate decreases 3-fold. The glomerular heparan sulfate shows reduced sulfation when compared with normal animals. Possibly puromycin aminonucleoside decreases the activity of kidney endoglycosidases, which reduce the molecular size of the sulfated polysaccharide, leading to a decrease in its renal clearance. Reduced sulfation of the glomerular heparan sulfate in the puromycin aminonucleoside-induced nephrosis does not alter the size of the dextran sulfate eliminated by the kidney, as suggested for protein. Conclusions Each pathological process induces a particular modification in the kidney, which in turn can affect the renal selectivity to specific macromolecules in different ways.

Podocyte injury and loss contribute to progressive glomerulosclerosis. Peroxisome proliferator-activated receptor-gamma (PPAR-gamma) is a nuclear hormone receptor, which we have found to be increased in podocytes in a variety of kidney diseases. It is not known if PPAR-gamma contributes to renal injury or if it serves as a countermeasure to limit renal injury during disease progression. We tested these possibilities utilizing the puromycin aminonucleoside (PAN) model of renal injury in immortalized mouse podocytes. The cultured podocytes expressed PPAR-gamma mRNA at baseline but this was decreased by PAN. Pioglitazone, a pharmacologic agonist of PPAR-gamma, increased both PPAR-gamma mRNA and activity in injured podocytes, as assessed by a reporter plasmid assay. Further, pioglitazone significantly decreased PAN-induced podocyte apoptosis and necrosis while restoring podocyte differentiation. The PPAR-gamma agonist significantly restored expression of the cyclin-dependent kinase inhibitor p27 and the antiapoptotic molecule Bcl-xL while significantly decreasing proapoptotic caspase-3 activity. Pioglitazone tended to decrease PAN-induced transforming growth factor-beta (TGF-beta) mRNA expression. Our study shows that PPAR-gamma is normally expressed by podocytes and its activation is protective against PAN-induced apoptosis and necrosis. We postulate that this protective effect may be mediated in part by effects on p27 and TGF-beta expression.

MicroRNAs (miRNAs) are small, noncoding RNAs that regulate protein levels posttranscriptionally. miRNAs play important regulatory roles in many cellular processes and have been implicated in several diseases. Recent studies have reported significant levels of miRNAs in a variety of body fluids, raising the possibility that miRNAs could serve as useful biomarkers. Here, changes in miRNA expression patterns are described in 2 different rodent models of glomerular injury (acute puromycin aminonucleoside nephropathy and passive Heymann nephritis). By employing 2 different modes of glomerular insult, oxidative stress and immune-mediated toxicity, miRNA changes in both isolated glomeruli as well as urine specimens allow for identification of urinary miRNA biomarkers that are suggestive of drug-induced injury specifically to the glomerulus. Subsets of glomerular urinary miRNAs associated with these different modes of glomerular toxicity seem to be dependent on the mechanism of the induced injury, while 9 miRNAs that changed early in both glomerular and urine specimens were common to both studies. We further show that the miRNAs identified as mechanism-specific early glomerular injury biomarkers target key pathways and transcripts relevant to the type of insult, while the insult-independent changes might serve as ideal glomerular injury biomarkers.

Objective: This study investigated the protective effect of FK506 in podocytes and the correlation of TRPC6 with podocyte injury repair. Methods: MPC5 were cultured in vitro, parallel with the control group, an Ang II stimulation group, and an FK506 intervention group. The apoptosis rate with flow cytometry also detected TRPC6 mRNA and protein expression by RT-PCR and Western blot, and then observed the distribution of TRPC6 with indirect immunofluorescence labeling under confocal microscope. Results: The activities of podocytes significantly increased after FK506 intervention for 24 hours and 48 hours when compared with the Ang II stimulation group, and the apoptosis rate was markedly lower than that of the Ang II stimulation group, while in contrast to TRPC6 mRNA and protein expression. Conclusion: FK506 can directly act on the podocytes to inhibit Ang II-induced damage on podocyte structures and reduce the apoptosis rate of podocytes, which may be related to stabilizing TRPC6 expression and distribution in podocytes by FK506, thus maintaining the structure and function integrity of the slit diaphragm and playing a role in protecting podocytes and antiproteinuria.

Drugs containing adrenocorticotropic hormone have been used as therapy for patients with nephrotic syndrome. We have previously shown that adrenocorticotropic hormone and a selective agonist for the melanocortin 1 receptor (MC1R) exert beneficial actions in experimental membranous nephropathy with reduced proteinuria, reduced oxidative stress, and improved glomerular morphology and function. Our hypothesis is that MC1R activation in podocytes elicits beneficial effects by promoting stress fibers and maintaining podocyte viability. To test the hypothesis, we cultured podocytes and used highly specific agonists for MC1R. Podocytes were subjected to the nephrotic-inducing agent puromycin aminonucleoside, and downstream effects of MC1R activation on podocyte survival, antioxidant defense, and cytoskeleton dynamics were studied. To increase the response and enhance intracellular signals, podocytes were transduced to overexpress MC1R. We showed that puromycin promotes MC1R expression in podocytes and that activation of MC1R promotes an increase of catalase activity and reduces oxidative stress, which results in the dephosphorylation of p190RhoGAP and formation of stress fibers through RhoA. In addition, MC1R agonists protect against apoptosis. Together, these mechanisms protect the podocyte against puromycin. Our findings strongly support the hypothesis that selective MC1R-activating agonists protect podocytes and may therefore be useful to treat patients with nephrotic syndromes commonly considered as podocytopathies.

Inhibition of the degradation of filtered albumin has been proposed as a widespread, benign form of albuminuria. There have however been recent reports that radiolabeled albumin fragments in urine are not exclusively generated by the kidney and that in albuminuric states albumin fragment excretion is not inhibited. In order to resolve this controversy we have examined the fate of various radiolabeled low molecular weight protein degradation products (LMWDPs) introduced into the circulation in rats. The influence of puromycin aminonucleoside nephrosis on the processing and excretion of LMWDPs is also examined. The status and destinies of radiolabeled LMWDPs in the circulation are complex. A major finding is that LMWDPs are rapidly eliminated from the circulation (>97% in 2 h) but only small quantities (24 h) due to binding to high molecular weight components in the circulation. If LMWDPs of albumin seen in the urine are produced by extra renal degradation it would require the degradation to far exceed the known catabolic rate of albumin. Alternatively, if an estimate of the role of extra renal degradation is made from the limit of detection of LMWDPs in plasma, then extra renal degradation would only contribute

Summary The mechanism responsible for trafficking of monocyte-derived macrophages into kidney in the puromycin aminonucleoside model of nephrotic syndrome in rats (PAN-NS), and the significance of this infiltration, remain largely unknown. CXCL10, a chemokine secreted in many T helper type 1 (Th1) inflammatory diseases, exhibits important roles in trafficking of monocytes and activated T cells. We hypothesized that induction of circulating interferon (IFN)-γ and glomerular tumour necrosis factor (TNF)-α during PAN-NS would stimulate the release of CXCL10 by podocytes, leading to infiltration of activated immune cells and greater glomerular injury. We found that serum IFN-γ, glomerular Cxcl10 mRNA and intra- and peri-glomerular macrophage infiltration were induced strongly during the late acute phase of PAN-NS in Wistar rats, but not in nude (Foxn1rnu/rnu) rats lacking functional effector T lymphocytes. Wistar rats also developed significantly greater proteinuria than nude rats, which could be abolished by macrophage depletion. Stimulation of cultured podocytes with both IFN-γ and TNF-α markedly induced the expression of Cxcl10 mRNA and CXCL10 secretion. Together, these data support our hypothesis that increased circulating IFN-γ and glomerular TNF-α induce synergistically the production and secretion of CXCL10 by podocytes, attracting activated macrophages into kidney tissue. The study also suggests that IFN-γ, secreted from Th1 lymphocytes, may prime proinflammatory macrophages that consequently aggravate renal injury.

In nephrotic syndrome, aberrant glomerular filtration of plasminogen and conversion to active plasmin in preurine are thought to activate proteolytically epithelial sodium channel (ENaC) and contribute to sodium retention and edema. The ENaC blocker amiloride is an off-target inhibitor of urokinase-type plasminogen activator (uPA) in vitro. It was hypothesized that uPA is abnormally filtered to preurine and is inhibited in urine by amiloride in nephrotic syndrome. This was tested by determination of Na+balance, uPA protein and activity, and amiloride concentration in urine from rats with puromycin aminonucleoside (PAN)-induced nephrotic syndrome. Urine samples from 6 adult and 18 pediatric patients with nephrotic syndrome were analyzed for uPA activity and protein. PAN treatment induced significant proteinuria in rats which coincided with increased urine uPA protein and activity, increased urine protease activity, and total plasminogen/plasmin concentration and Na+retention. Amiloride (2 mg·kg−1·24 h−1) concentration in urine was in the range 10–20 μmol/l and reduced significantly urine uPA activity, plasminogen activation, protease activity, and sodium retention in PAN rats, while proteinuria was not altered. In paired urine samples, uPA protein was significantly elevated in urine from children with active nephrotic syndrome compared with remission phase. In six adult nephrotic patients, urine uPA protein and activity correlated positively with 24 h urine protein excretion. In conclusion, nephrotic syndrome is associated with aberrant filtration of uPA across the injured glomerular barrier. Amiloride inhibits urine uPA activity which attenuates plasminogen activation and urine protease activity in vivo. Urine uPA is a relevant target for amiloride in vivo.

Minimal change nephropathy (MCN) is the third most common cause of primary nephrotic syndrome in adults. Most patients with MCN respond to corticosteroid therapy, but relapse is common. In children, steroid-dependent patients are often given alternative agents to spare the use of steroids and to avoid the cumulative steroid toxicity. In this respect, levamisole has shown promise due to its ability to effectively maintain remission in children with steroid-sensitive or steroid-dependent nephrotic syndrome. Despite clinical effectiveness, there is a complete lack of molecular evidence to explain its mode of action and there are no published reports on the use of this compound in adult patients. We studied the effectiveness of levamisole in a small cohort of adult patients and also tested the hypothesis that levamisole's mode of action is attributable to its direct effects on podocytes. In the clinic, we demonstrate that in our adult patients, cohort levamisole is generally well tolerated and clinically useful. Using conditionally immortalized human podocytes, we show that levamisole is able to induce expression of glucocorticoid receptor (GR) and to activate GR signalling. Furthermore, levamisole is able to protect against podocyte injury in a puromycin aminonucleoside (PAN)-treated cell model. In this model the effects of levamisole are blocked by the GR antagonist mifepristone (RU486), suggesting that GR signalling is a critical target of levamisole's action. These results indicate that levamisole is effective in nephrotic syndrome in adults, as well as in children, and point to molecular mechanisms for this drug's actions in podocyte diseases.

Increasing data has shown that the cytoskeletal reorganization of podocytes is involved in the onset of proteinuria and the progression of glomerular disease. Nephrin behaves as a signal sensor of the slit diaphragm to transmit cytoskeletal signals to maintain the unique structure of podocytes. However, the nephrin signaling cascade deserves further study. IQGAP1 is a scaffolding protein with the ability to regulate cytoskeletal organization. It is hypothesized that IQGAP1 contributes to actin reorganization in podocytes through interaction with nephrin. IQGAP1 expression and IQGAP1-nephrin colocalization in glomeruli were progressively decreased and then gradually recovered in line with the development of foot process fusion and proteinuria in puromycin aminonucleoside-injected rats. In cultured human podocytes, puromycin aminonucleoside-induced disruption of F-actin and disorders of migration and spreading were aggravated by IQGAP1 siRNA, and these effects were partially restored by a wild-type IQGAP1 plasmid. Furthermore, the cytoskeletal disorganization stimulated by cytochalasin D in COS7 cells was recovered by cotransfection with wild-type IQGAP1 and nephrin plasmids but was not recovered either by single transfection of the wild-type IQGAP1 plasmid or by cotransfection of mutant IQGAP1 [Δ1443(S → A)] and wild-type nephrin plasmids. Co-immunoprecipitation analysis using lysates of COS7 cells overexpressing nephrin and each derivative-domain molecule of IQGAP1 demonstrated that the poly-proline binding domain and RasGAP domain in the carboxyl terminus of IQGAP1 are the target modules that interact with nephrin. Collectively, these findings showed that activated IQGAP1, as an intracellular partner of nephrin, is involved in actin cytoskeleton organization and functional regulation of podocytes.

Synaptic vesicle protein 2B (SV2B) was identified by the subtraction hybridization technique as a molecule of which mRNA expression was decreased in puromycin aminonucleoside (PAN) nephropathy by glomerular cDNA subtraction assay. The expression of SV2B was detected in glomerular lysate with Western blot analysis. Dual-labeling immunofluorescence studies with glomerular cell markers demonstrated that SV2B is expressed in glomerular visceral epithelial cells (podocytes). The expression of SV2B is detected also in cultured podocyte and in human kidney section as podocytic pattern. The decrease of SV2B mRNA was already detected before the onset of proteinuria in PAN nephropathy. The mRNA expression of SV2B clearly is altered not only in PAN nephropathy but also in another proteinuric state that is caused by an antibody against nephrin, a functional molecule of the slit diaphragm. The decreased intensity in SV2B staining was already detected before the peak of proteinuria in both models with immunofluorescence study. A reduced amount of SV2B was detected in both models also with Western blot analysis. CD2AP, another functional molecule of the slit diaphragm, was observed in cytoplasm, including the processes area of the cultured podocyte, and when the podocyte was treated with small interfering RNA for SV2B, CD2AP staining at the process area was not detected. These results suggest that SV2B is a functional molecule of podocyte, and SV2B may play a role in the expression and proper localization of CD2AP.

Proteoglycans (PGs) are important for the glomerular barrier, for cell signaling, and for the anchorage of cells to the glomerular basement membrane. They are, however, complex macromolecules, and their production has not yet been thoroughly investigated in podocytes. In the present study, we studied the biosynthesis of PGs by highly differentiated human podocytes and in rats. The cells were treated with puromycin aminonucleoside (PAN; a nephrosis-inducing agent), steroids (used as primary treatment for nephrotic syndrome), or both. Analysis was made by TaqMan real-time PCR, Western blotting, and by metabolic labeling with35S and3H. We found that podocytes produce versican, syndecan-1, decorin, and biglycan together with the previously known PG syndecan-4, glypican, and perlecan. PAN treatment downregulated the mRNA and the protein expression of both versican (by 24 ± 6%, P < 0.01, for mRNA and by 50% for protein) and perlecan (by 14 ± 5%, P < 0.05, for mRNA and by 50% for protein). The decreased expression was confirmed by studying the glomerular gene expression in rats treated with PAN during a time course study. In addition, puromycin decreased the expression of enzymes involved in the glycosaminoglycan biosynthesis. Steroid treatment decreased perlecan (by 24 ± 3%, P < 0.01) and syndecan-1 expression (by 30 ± 4%, P < 0.01) but increased the expression of decorin 2.5-fold. The observed alterations of PG synthesis induced by PAN may lead to decreased glomerular anionic charge and disturbed podocyte morphology, factors that are important for the development of a nephrotic syndrome.