Roles of adaptor proteins in podocyte biology

GDF-15 Suppresses Puromycin Aminonucleoside-Induced Podocyte Injury by Reducing Endoplasmic Reticulum Stress and Glomerular Inflammation

GDF15, also known as MIC1, is a member of the TGF-beta superfamily. Previous studies reported elevated serum levels of GDF15 in patients with kidney disorder, and its association with kidney disease progression, while other studies identified GDF15 to have protective effects. To investigate the potential protective role of GDF15 on podocytes, we first performed in vitro studies using a Gdf15-deficient podocyte cell line. The lack of GDF15 intensified puromycin aminonucleoside (PAN)-triggered endoplasmic reticulum stress and induced cell death in cultivated podocytes. This was evidenced by elevated expressions of Xbp1 and ER-associated chaperones, alongside AnnexinV/PI staining and LDH release. Additionally, we subjected mice to nephrotoxic PAN treatment. Our observations revealed a noteworthy increase in both GDF15 expression and secretion subsequent to PAN administration. Gdf15 knockout mice displayed a moderate loss of WT1+ cells (podocytes) in the glomeruli compared to wild-type controls. However, this finding could not be substantiated through digital evaluation. The parameters of kidney function, including serum BUN, creatinine, and albumin-creatinine ratio (ACR), were increased in Gdf15 knockout mice as compared to wild-type mice upon PAN treatment. This was associated with an increase in the number of glomerular macrophages, neutrophils, inflammatory cytokines, and chemokines in Gdf15-deficient mice. In summary, our findings unveil a novel renoprotective effect of GDF15 during kidney injury and inflammation by promoting podocyte survival and regulating endoplasmic reticulum stress in podocytes, and, subsequently, the infiltration of inflammatory cells via paracrine effects on surrounding glomerular cells.

Immune podocytes in the immune microenvironment of lupus nephritis (Review)

Systemic lupus erythematosus (SLE) is a systemic autoimmune disorder caused by the loss of tolerance to endogenous nuclear antigens such as double‑stranded DNA, leading to the proliferation of T cells and subsequent activation of B cells, which results in serious organ damage and life‑threatening complications such as lupus nephritis. Lupus nephritis (LN) develops as a frequent complication of SLE, accounting for >60% of SLE cases, and is characterized by proteinuria and heterogeneous histopathological findings. Glomerular injury serves a role in proteinuria as podocyte damage is the leading contributor. Numerous studies have reported that podocytes are involved in the immune response that promotes LN progression. In LN, immune complex deposition stimulates dendritic cells to secrete inflammatory cytokines that activate T cells and B cells. B cells secrete autoantibodies that attack and damage the renal podocytes, leading to renal podocyte injury. The injured podocytes trigger inflammatory cells through the expression of toll‑like receptors and trigger T cells through major histocompatibility complexes and CD86, thereby participating in the local immune response and the exacerbation of podocyte injury. Based on the existing literature, the present review summarizes the research progress of podocytes in LN under the local immune microenvironment of the kidney, explores the mechanism of podocyte injury under the immune microenvironment, and evaluates podocytes as a potential therapeutic target for LN.

Upregulation of NADH/NADPH oxidase 4 by angiotensin II induces podocyte apoptosis

Background: Angiotensin II induces glomerular and podocyte injury via systemic and local vasoconstrictive or non-hemodynamic effects including oxidative stress. The release of reactive oxygen species (ROS) from podocytes may participate in the development of glomerular injury and proteinuria. We studied the role of oxidative stress in angiotensin II-induced podocyte apoptosis.Methods: Mouse podocytes were incubated in media containing various concentrations of angiotensin II at different incubation times and were transfected with NADH/NADPH oxidase 4 (Nox4) or angiotensin II type 1 receptor for 24 hours. The changes in intracellular and mitochondrial ROS production and podocyte apoptosis were measured according to the presence of angiotensin II.Results: Angiotensin II increased the generation of mitochondrial superoxide anions and ROS levels but suppressed superoxide dismutase activity in a dose- and time-dependent manner that was reversed by probucol, an antioxidant. Angiotensin II increased Nox4 protein and expression by a transcriptional mechanism that was also reversed by probucol. In addition, the suppression of Nox4 by small interfering RNA (siRNA) reduced the oxidative stress induced by angiotensin II. Angiotensin II treatment also upregulated AT1R protein. Furthermore, angiotensin II promoted podocyte apoptosis, which was reduced significantly by probucol and Nox4 siRNA and also recovered by angiotensin II type 1 receptor siRNA.Conclusion: Our findings suggest that angiotensin II increases the generation of mitochondrial superoxide anions and ROS levels via the upregulation of Nox4 and angiotensin II type 1 receptor. This can be prevented by Nox4 inhibition and/or antagonizing angiotensin II type 1 receptor as well as use of antioxidants.

Histone modification in podocyte injury of diabetic nephropathy

Diabetic nephropathy (DN), an important complication of diabetic microvascular disease, is one of the leading causes of end-stage renal disease (ESRD), which brings heavy burdens to the whole society. Podocytes are terminally differentiated glomerular cells, which act as a pivotal component of glomerular filtration barrier. When podocytes are injured, glomerular filtration barrier is damaged, and proteinuria would occur. Dysfunction of podocytes contributes to DN. And degrees of podocyte injury influence prognosis of DN. Growing evidences have shown that epigenetics does a lot in the evolvement of podocyte injury. Epigenetics includes DNA methylation, histone modification, and non-coding RNA. Among them, histone modification plays an indelible role. Histone modification includes histone methylation, histone acetylation, and other modifications such as histone phosphorylation, histone ubiquitination, histone ADP-ribosylation, histone crotonylation, and histone β-hydroxybutyrylation. It can affect chromatin structure and regulate gene transcription to exert its function. This review is to summarize documents about pathogenesis of podocyte injury, most importantly, histone modification of podocyte injury in DN recently to provide new ideas for further molecular research, diagnosis, and treatment.

Decreased GM3 correlates with proteinuria in minimal change nephrotic syndrome and focal segmental glomerulosclerosis

BACKGROUND

Glycolipids on cell membrane rafts play various roles by interacting with glycoproteins. Recently, it was reported that the glycolipid GM3 is expressed in podocytes and may play a role in podocyte protection. In this report, we describe the correlation between changes in GM3 expression in glomeruli and proteinuria in minimal change nephrotic syndrome (MCNS) and focal segmental glomerulosclerosis (FSGS) patients.

METHODS

We performed a case-control study of the correlation between nephrin/GM3 expression levels and proteinuria in MCNS and FSGS patients who underwent renal biopsy at our institution between 2009 and 2014. Normal renal tissue sites were used from patients who had undergone nephrectomy at our institution and gave informed consent.

RESULTS

Both MCNS and FSGS had decreased GM3 and Nephrin expression compared with the normal (normal vs. MCNS, FSGS; all p < 0.01). Furthermore, in both MCNS and FSGS, GM3 expression was negatively correlated with proteinuria (MCNS: r = - 0.61, p < 0.01, FSGS: r = - 0.56, p < 0.05). However, nephrin expression had a trend to correlate with proteinuria in FSGS (MCNS: r = 0.19, p = 0.58, FSGS: r = - 0.48, p = 0.06). Furthermore, in a simple linear regression analysis, GM3 expression also correlated with proteinuric change after 12 months of treatment (MCNS: r = 0.40, p = 0.38, FSGS: r = 0. 68, p < 0.05).

CONCLUSION

We showed for the first time that decreased GM3 expression correlates with proteinuria in MCNS and FSGS patients. Further studies are needed on the podocyte-protective effects of GM3.

CXCL16/ERK1/2 pathway regulates human podocytes growth, migration, apoptosis and epithelial mesenchymal transition

Primary nephrotic syndrome (PNS) is the commonest glomerular disease affecting children. Previous studies have confirmed that CXC motif chemokine ligand 16 (CXCL16) is involved in the pathogenesis of PNS. However, the exact mechanisms underlying the pathogenesis of PNS remain to be elucidated. Thus, the present study aimed to elucidate the role of CXCL16 in PNS. It was found that the expression of CXCL16 and extracellular signal‑regulated kinases 1 and 2 (ERK1/2) were significantly increased in clinical PNS renal tissues using reverse transcription‑quantitative PCR, western blot analysis and immunohistochemistry. Lentivirus overexpression or short hairpin RNA vector was used to induce the overexpression or knockdown of CXCL16 in podocytes, respectively. Overexpression of CXCL16 in podocytes could decrease the cell proliferation and increase the migration and apoptosis, whereas CXCL16 knockdown increased cell proliferation and decreased cell migration and apoptosis. Results of the present study further demonstrated that ERK2 protein expression was regulated by CXCL16. The knockdown of ERK2 expression reversed the effects of CXCL16 on the proliferation, apoptosis, migration and epithelial mesenchymal transition (EMT) of podocytes. Collectively, the findings of the present study highlighted that the CXCL16/ERK1/2 pathway regulates the growth, migration, apoptosis and EMT of human podocytes.

Deciphering nutritional interventions for podocyte structure and function

Despite increasing awareness and therapeutic options chronic kidney disease (CKD) is still and important health problem and glomerular diseases constitute and important percentage of CKD. Proteinuria/albuminuria is not just a marker; but it also plays a direct pathogenic role in renal disease progression of CKD. Glomerular filtration barrier (GFB) which consists of fenestrated endothelial cells, fused basal membrane and interdigitating podocyte foot process and filtration slits between foot process is the major barrier for proteinuria/albuminuria. Many glomerular diseases are characterized by disruption of GFB podocytes, foot process and slit diaphragm. Many proteinuric diseases are non-specifically targeted by therapeutic agents such as steroids and calcineurin inhibitors with systemic side effects. Thus, there is unmet need for more efficient and less toxic therapeutic options to treat glomerular diseases. In recent years, modification of dietary intake, has been gained to treat pathologic processes introducing the concept of 'food as a medicine'. The effect of various nutritional products on podocyte function and structure is also trending, especially in recent years. In the current review, we summarized the effect of nutritional interventions on podocyte function and structure.

Roles of microRNAs in renal disorders related to primary podocyte dysfunction

Through the regulation of gene expression, microRNAs (miRNAs) are capable of modulating vital biological processes, such as proliferation, differentiation, and apoptosis. Several mechanisms control the function of miRNAs, including translational inhibition and targeted miRNA degradation. Through utilizing high-throughput screening methods, such as small RNA sequencing and microarray, alterations in miRNA expression of kidneys have recently been observed both in rodent models and humans throughout the development of chronic kidney disease (CKD) and acute kidney injury (AKI). The levels of miRNAs in urine supernatant, sediment, and exosomal fraction could predict novel biomarker candidates in different diseases of kidneys, including IgA nephropathy, lupus nephritis, and diabetic nephropathy. The therapeutic potential of administrating anti-miRNAs and miRNAs has also been reported recently. The present study is aimed at reviewing the state-of-the-art research with regards to miRNAs involved in renal disorders related to primary podocyte dysfunction by laying particular emphasis on Focal Segmental Glomerulosclerosis (FSGS), Minimal Change Disease (MCD) and Membranous Nephropathy (MN).

MicroRNAs in childhood nephrotic syndrome

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

Regulation of the Actin Cytoskeleton in Podocytes

Podocytes are an integral part of the glomerular filtration barrier, a structure that prevents filtration of large proteins and macromolecules into the urine. Podocyte function is dependent on actin cytoskeleton regulation within the foot processes, structures that link podocytes to the glomerular basement membrane. Actin cytoskeleton dynamics in podocyte foot processes are complex and regulated by multiple proteins and other factors. There are two key signal integration and structural hubs within foot processes that regulate the actin cytoskeleton: the slit diaphragm and focal adhesions. Both modulate actin filament extension as well as foot process mobility. No matter what the initial cause, the final common pathway of podocyte damage is dysregulation of the actin cytoskeleton leading to foot process retraction and proteinuria. Disruption of the actin cytoskeleton can be due to acquired causes or to genetic mutations in key actin regulatory and signaling proteins. Here, we describe the major structural and signaling components that regulate the actin cytoskeleton in podocytes as well as acquired and genetic causes of actin dysregulation.

Dopamine 1 receptor activation protects mouse diabetic podocytes injury via regulating the PKA/NOX-5/p38 MAPK axis

Diabetic nephropathy (DN) is a major microvascular complication of diabetes that can lead to end-stage renal disease. Podocytes constitute the last barrier of glomerular filtration, whose damage are the direct cause of proteinuria. Dopamine receptors are involved in the regulation of diabetes-induced glomerular hyperfiltration, and only dopamine 1 receptor (D1R) can be amplified in cultured mouse podocytes. However, the exact effect of D1R on diabetic podocytes remains unclear. This study aims to investigate the protective role of D1R activation on diabetic podocytes injury in vivo and vitro as well as its potential mechanism. We observed D1R protective effect respectively in streptozotocin (STZ)-induced type 1 diabetes (T1D) mice as well as mouse podocytes (MPC5) cultured in high glucose (HG, 40 mM) medium. It showed that D1R and podocyte-associated proteins (Podocin, CD2AP and Nephrin) expression were significantly decreased both in the T1D mice (fed for 8 and 12 weeks) and HG-cultured MPC5 cells, while the NOX-5 expression increased. In T1D mice, the levels of 24-h urine protein, serum creatinine and urinary 8-OHdG were increased in a time-dependent manner, at the same time, hematoxylin-eosin (HE) staining and electron microscope observed the kidney lesion and podocytes injury. In vitro, HG induced podocytes oxidative stress and apoptosis, which could be inhibited by SKF38393 (a D1R agonist) and N-acetyl-l-cysteine (NAC, a reactive oxygen species scavenger). Furthermore, there was a decreasing Podocin expression and a significant increasing NOX-5 expression in podocytes transfected with D1R-small interfering RNA (siRNA). More importantly, the expression of phospho-CREB (the PKA downstream transcription factor) was decreased and phospho-p38 MAPK was increased in HG-induced podocytes, which can respectively be activated or blocked by SKF38393, 8-Bromo-CAMP (a PKA activator), NAC, and SB20380 (a p38 MAPK inhibitor). In conclusion, D1R activation can protect diabetic podocytes from apoptosis and oxidative damage, in part through the PKA/NOX-5/p38 MAPK pathway.

miR-939-5p decreases the enrichment of RNA polymerase II in the promoter region of CD2AP involved in nephrotic syndrome

The expression changes of CD2-associated protein (CD2AP) can lead to kidney diseases with proteinuria, including nephrotic syndrome (NS). A recent study reported that miRNAs may be important transcriptional regulators. In this study, we found increased expression of miR-939-5p and decreased expression of CD2AP in the peripheral blood of patients with NS. However, miR-939-5p did not show a regulatory effect on the 3'-untranslated region of CD2AP. The expression levels of specific protein 1 and adenovirus E2 promoter-binding factor 1, important transcription regulators in the promoter region of CD2AP, were also not affected by microRNA (miR)-939-5p. We confirmed that miR-939-5p is in the nucleus by fluorescent in situ hybridization and cytoplasmic separation polymerase chain reaction. The promoter plasmid and miR-939-5p were cotransfected into HEK-293 cells, and the luciferase reporter gene assay was used to analyze the promoter activity. We found that miR-939-5p binds to a specific sequence in the CD2AP promoter. miR-939-5p was confirmed to reduce the recruitment of RNA polymerase II to the CD2AP promoter region by chromatin immunoprecipitation. These findings improve our understanding of the mechanism of miR-939-5p in NS and provide potential molecular therapeutic targets for NS.

Engineering renal epithelial cells: programming and directed differentiation towards glomerular podocyte's progenitor and mature podocyte

Current knowledge of normal developmental physiology and identification of specific cell types of the kidney at molecular levels enables us to generate various cells of the kidney. The generation of renal specialized cells in vitro with its correct molecular and functional implications is the urgent need for cellular therapy in chronic kidney diseases and for organ formation. Glomerular podocytes are one of the major renal cells lose its functionality to maintain glomerular blood filtration function. In vitro, many inductions or reprogramming methods have been established for podocytes development. In these methods transcription factors, small molecules, and growth factors play the major role to remodel stem cells into podocyte progenitors and towards mature podocytes. Micro ribonucleic acids (miRNAs) have been utilizing as another strategy to generate podocyte. In this review, current protocols for in vitro glomerular podocyte differentiation have summarized emphasizing programming methods, signaling modulation, and cytoskeletal changes. Novel ideas are also pointed out, which are required for efficient optimal glomerular podocyte generation and their functional characterization in vitro with nanoarchitecture impression of the glomerular basement membrane.

Ginseng Total Saponin Attenuates Podocyte Apoptosis Induced by Diabetic Conditions Through the Recovery of CD2-Associated Protein

CD2-associated protein (CD2AP), an adaptor protein, plays several important roles in podocyte function, linking slit diaphragms to actin-based cytoskeleton and sending survival signals. Here, we investigated whether ginseng total saponin (GTS) had a protective role in the changes of podocyte CD2AP protein and podocyte apoptosis under in vitro diabetic conditions. Conditionally immortalized mouse podocytes cultured with normal glucose (5 mM) or high glucose (30 mM) and with or without advanced glycosylation end products were treated with GTS. We found that CD2AP co-localized with the F-actin fibers in podocyte cytoplasm using confocal imaging; however, diabetic conditions caused the podocytes to diminish and conglomerate CD2AP stainings in the peripheral cytoplasm, which were recovered by GTS. Diabetic conditions also suppressed CD2AP protein levels at 6 and 24 h in western blotting. These phenotypical changes of CD2AP protein were mitigated by GTS. Diabetic conditions also induced podocyte apoptosis at 24 h, which were attenuated by GTS. These findings provide a novel mechanism that diabetic conditions induce quantitative and qualitative changes of podocyte CD2AP protein and apoptosis, which would be restored by GTS.

Puromycin aminonucleoside triggers apoptosis in podocytes by inducing endoplasmic reticulum stress

Background

Puromycin aminonucleoside (PAN) is a known podocytotoxin. PAN-induced nephrosis is a widely used animal model for studying human idiopathic nephrotic syndrome. Abnormal protein accumulation associated with podocyte-specific endoplasmic reticulum (ER) stress damages cells structurally and functionally, which in turn induces apoptosis and severe proteinuria. In the present study, we investigated the effect of PAN on ER stress and apoptosis in podocytes in vitro.

Methods

Mouse podocytes were cultured and treated with various concentrations of PAN. ER stress markers were then evaluated by western blotting, and apoptosis was evaluated by fluorescence-activated cell sorting (FACS) and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assays.

Results

PAN treatment increased ER stress markers such as activating transcription factor (ATF) 6α and caspase-12 in a dose-dependent manner at 12 and 24 hours, respectively. These markers were reduced by chemical chaperones, such as sodium 4-phenylbutyric acid and tauroursodeoxycholic acid. PAN treatment also increased 78 kD glucose-regulated protein (GRP78)/binding immunoglobulin protein (BiP) at the earlier stage of 12 hours. PAN significantly induced podocyte apoptosis in concentration- and time-dependent manners, as seen using FACS and TUNEL assays. This result was improved by Nox4 siRNA, ATF6 siRNA, and chemical chaperones. LY294002, a PI3-kinase inhibitor, significantly boosted ER stress and apoptosis. PAN-induced ER stress increased oxidative stress and subsequently induced apoptosis, and could be mitigated by inhibition of PI3-kinase signaling.

Conclusion

Our findings suggest that PAN induces ER stress in podocytes mainly through the GRP78/BiP, ATF6α, and caspase-12 pathways, which trigger apoptosis via induction of oxidative stress. This stress is mitigated by inhibiting PI3-kinase signaling.

The Role of Glucocorticoid Receptors in Podocytes and Nephrotic Syndrome

Glucocorticoid receptor (GC), a founding member of the nuclear hormone receptor superfamily, is a glucocorticoid-activated transcription factor that regulates gene expression and controls the development and homeostasis of human podocytes. Synthetic glucocorticoids are the standard treatment regimens for proteinuria (protein in the urine) and nephrotic syndrome (NS) caused by kidney diseases. These include minimal change disease (MCD), focal segmental glomerulosclerosis (FSGS), membranous nephropathy (MN) and immunoglobulin A nephropathy (IgAN) or subsequent complications due to diabetes mellitus or HIV infection. However, unwanted side effects and steroid-resistance remain major issues for their long-term use. Furthermore, the mechanism by which glucocorticoids elicit their renoprotective activity in podocyte and glomeruli is poorly understood. Podocytes are highly differentiated epithelial cells that contribute to the integrity of kidney glomerular filtration barrier. Injury or loss of podocytes leads to proteinuria and nephrotic syndrome. Recent studies in multiple experimental models have begun to explore the mechanism of GC action in podocytes. This review will discuss progress in our understanding of the role of glucocorticoid receptor and glucocorticoids in podocyte physiology and their renoprotective activity in nephrotic syndrome.

Molecular mechanisms involved in podocyte EMT and concomitant diabetic kidney diseases: an update

Epithelial–mesenchymal transition (EMT) is a tightly regulated process by which epithelial cells lose their hallmark epithelial characteristics and gain the features of mesenchymal cells. For podocytes, expression of nephrin, podocin, P-cadherin, and ZO-1 is downregulated, the slit diaphragm (SD) will be altered, and the actin cytoskeleton will be rearranged. Diabetes, especially hyperglycemia, has been demonstrated to incite podocyte EMT through several molecular mechanisms such as TGF-β/Smad classic pathway, Wnt/β-catenin signaling pathway, Integrins/integrin-linked kinase (ILK) signaling pathway, MAPKs signaling pathway, Jagged/Notch signaling pathway, and NF-κB signaling pathway. As one of the most fundamental prerequisites to develop ground-breaking therapeutic options to prevent the development and progression of diabetic kidney disease (DKD), a comprehensive understanding of the molecular mechanisms involved in the pathogenesis of podocyte EMT is compulsory. Therefore, the purpose of this paper is to update the research progress of these underlying signaling pathways and expound the podocyte EMT-related DKDs.

A unified pathogenesis for kidney diseases, including genetic diseases and cancers, by the protein-homeostasis-system hypothesis

Every cell of an organism is separated and protected by a cell membrane. It is proposed that harmony between intercellular communication and the health of an organism is controlled by a system, designated the protein-homeostasis-system (PHS). Kidneys consist of a variety of types of renal cells, each with its own characteristic cell-receptor interactions and producing characteristic proteins. A functional union of these renal cells can be determined by various renal function tests, and harmonious intercellular communication is essential for the healthy state of the host. Injury to a kind of renal cells can impair renal function and induce an imbalance in total body health. Every acute or chronic renal disease has unknown etiologic substances that are responsible for renal cell injury at the molecular level. The immune/repair system of the host should control the etiologic substances acting against renal cells; if this system fails, the disease progresses to end stage renal disease. Each renal disease has its characteristic pathologic lesions where immune cells and immune proteins, such as immunoglobulins and complements, are infiltrated. These immune cells and immune proteins may control the etiologic substances involved in renal pathologic lesions. Also, genetic renal diseases and cancers may originate from a protein deficiency or malfunctioning protein under the PHS. A unified pathogenesis for renal diseases, including acute glomerulonephritis, idiopathic nephrotic syndrome, immunoglobulin A nephropathy, genetic renal diseases such as Alport syndrome, and malignancies such as Wilms tumor and renal cell carcinoma, is proposed using the PHS hypothesis.

Montelukast improves the changes of cytoskeletal and adaptor proteins of human podocytes by interleukin-13

OBJECTIVE AND DESIGN

Interleukin-13 (IL-13) has recently been reported to be a potential cytokine in the pathogenesis of minimal-change nephrotic syndrome (MCNS). However, the mechanistic insights associated with podocyte dysfunction mediated by IL-13-induced changes in various slit diaphragm (SD) and cytoskeletal molecules have not yet been shown in cultured human podocytes in vitro.

MATERIALS

Human conditionally immortalized podocytes were used.

TREATMENT

Podocytes were incubated with various concentrations of IL-13 during the indicated time periods (6, 12, and 24 h) and montelukast was administered with the dose of 0.1 μg.

RESULTS

Treatment of IL-13 resulted in a progressive decrease in distinct processes or projections of the human podocytes and high dose of IL-13 increased podocyte permeability in vitro at 6 h. IL-13 had a substantial impact on the redistribution and rearrangement of zonula occludens (ZO)-1, synaptopodin, α-actinin, CD2-associated protein (CD2AP) in podocytes and disrupted the cytoskeletal connections in a concentration-dependent manner on confocal microscopy. IL-13 also down-modulated ZO-1, synaptopodin, α-actinin, CD2AP, and p130Cas at protein levels and upregulated β-catenin and B7-1 in podocytes. Furthermore, we demonstrated that down-modulated changes in various SD and cytoskeletal structures of human podocytes induced by IL-13 was significantly restored after treatment with montelukast with upregulation of B7-1.

CONCLUSION

Our results suggest that targeting IL-13 may be one of the important cytokines in the pathogenesis of MCNS and targeting IL-13 could be one of the potential therapeutic strategies in MCNS.

Genetics of hereditary nephrotic syndrome: a clinical review

Advances in podocytology and genetic techniques have expanded our understanding of the pathogenesis of hereditary steroid-resistant nephrotic syndrome (SRNS). In the past 20 years, over 45 genetic mutations have been identified in patients with hereditary SRNS. Genetic mutations on structural and functional molecules in podocytes can lead to serious injury in the podocytes themselves and in adjacent structures, causing sclerotic lesions such as focal segmental glomerulosclerosis or diffuse mesangial sclerosis. This paper provides an update on the current knowledge of podocyte genes involved in the development of hereditary nephrotic syndrome and, thereby, reviews genotype-phenotype correlations to propose an approach for appropriate mutational screening based on clinical aspects.

Podocyte and Parietal Epithelial Cell Interactions in Health and Disease

The glomerulus has 3 resident cells namely mesangial cells that produce the mesangial matrix, endothelial cells that line the glomerular capillaries, and podocytes that cover the outer surface of the glomerular basement membrane. Parietal epithelial cells (PrECs), which line the Bowman's capsule are not part of the glomerular tuft but may have an important role in the normal function of the glomerulus. A significant progress has been made in recent years regarding our understanding of the role and function of these cells in normal kidney and in kidneys with various types of glomerulopathy. In crescentic glomerulonephritis necrotizing injury of the glomerular tuft results in activation and leakage of fibrinogen which provides the trigger for excessive proliferation of PrECs giving rise to glomerular crescents. In cases of collapsing glomerulopathy, podocyte injury causes collapse of the glomerular capillaries and activation and proliferation of PrECs, which accumulate within the urinary space in the form of pseudocrescents. Many of the noninflammatory glomerular lesions such as focal segmental glomerulosclerosis and global glomerulosclerosis also result from podocyte injury which causes variable loss of podocytes. In these cases podocyte injury leads to activation of PrECs that extend on to the glomerular tuft where they cause segmental and/or global sclerosis by producing excess matrix, resulting in obliteration of the capillary lumina. In diabetic nephropathy, in addition to increased matrix production in the mesangium and glomerular basement membranes, increased loss of podocytes is an important determinant of long-term prognosis. Contrary to prior belief there is no convincing evidence for an active podocyte proliferation in any of the above mentioned glomerulopathies.

Angiotensin II Modulates p130Cas of Podocytes by the Suppression of AMP-Activated Protein Kinase

Angiotensin II (Ang II) induces the pathological process of vascular structures, including renal glomeruli by hemodynamic and nonhemodynamic direct effects. In kidneys, Ang II plays an important role in the development of proteinuria by the modification of podocyte molecules. We have previously found that Ang II suppressed podocyte AMP-activated protein kinase (AMPK) via Ang II type 1 receptor and MAPK signaling pathway. In the present study, we investigated the roles of AMPK on the changes of p130Cas of podocyte by Ang II. We cultured mouse podocytes and treated them with various concentrations of Ang II and AMPK-modulating agents and analyzed the changes of p130Cas by confocal imaging and western blotting. In immunofluorescence study, Ang II decreased the intensity of p130Cas and changed its localization from peripheral cytoplasm into peri-nuclear areas in a concentrated pattern in podocytes. Ang II also reduced the amount of p130Cas in time and dose-sensitive manners. AMPK activators, metformin and AICAR, restored the suppressed and mal-localized p130Cas significantly, whereas, compound C, an AMPK inhibitor, further aggravated the changes of p130Cas. Losartan, an Ang II type 1 receptor antagonist, recovered the abnormal changes of p130Cas suppressed by Ang II. These results suggest that Ang II induces the relocalization and suppression of podocyte p130Cas by the suppression of AMPK via Ang II type 1 receptor, which would contribute to Ang II-induced podocyte injury.

Protective effects of Danggui Buxue Tang on renal function, renal glomerular mesangium and heparanase expression in rats with streptozotocin-induced diabetes mellitus

Danggui Buxue Tang (DBT) is a simple combination of Radix Astragali and Radix Angelica sinensis (5:1), with a variety pharmacological activities. In the present study, a single intravenous injection of 30 mg/kg streptozotocin and subsequent six weeks of high glucose diet in Sprague Dawley rats were used to induce diabetic nephropathy. Rats with diabetes mellitus showed increased levels of fasting blood glucose (FBG), blood urea nitrogen (BUN), serum creatinine (Scr), serum and urine β2-microglobulins (β2-MG), and type IV collagen (all P<0.05). DBT treatment significantly decreased the levels of FBG, BUN, Scr, serum and urine β2-MG, and type IV collagen. Furthermore, DBT treatment significantly and dose-dependently restored the ultrastructural injury, and reduced the expression of heparanase, compared with the vehicle (P<0.05). Therefore, DBT may be a novel therapeutic approach for the prevention and treatment of diabetic nephrology.

Cobrotoxin from Naja naja atra Venom Ameliorates Adriamycin Nephropathy in Rats

Chronic kidney disease (CKD) becomes a global health problem with high morbidity and mortality. Adriamycin- (ADR-) induced rodent chronic nephropathy is a classic experimental model of human minimal lesion nephrotic syndrome. The present study investigated the effect of cobrotoxin (CTX) on ADR-induced nephropathy. Rats were given 6 mg/kg ADR once through the tail vein to replicate ADR nephropathy model. CTX was administered to rats daily by placing a fast dissolving CTX membrane strip under the tongue starting from 5 days prior to ADR administration until the end of experiment. The results showed that CTX ameliorated the symptoms of ADR nephropathy syndrome with reduced body weight loss, proteinuria, hypoalbuminemia, dyslipidemia, serum electrolyte imbalance, oxidative stress, renal function abnormities, and kidney pathological lesions. Anti-inflammatory cytokine IL-10 expression was elevated after CTX administration in ADR nephropathy model. CTX inhibited the phosphorylation of IκB-α and NF-κB p65 nuclear translocation. Meanwhile, CTX upregulated the protein level of podocyte-specific nephrin and downregulated the level of fibrosis-related TGF-β. These findings suggest that CTX may be a potential drug for chronic kidney diseases.

Angiotensin II induces endoplasmic reticulum stress in podocyte, which would be further augmented by PI3-kinase inhibition

INTRODUCTION

Angiotensin II (Ang II) contributes to the pathological process of vascular structures, including renal glomeruli by hemodynamic and nonhemodynamic direct effects. On renal effects, Ang II plays an important role in the development of proteinuria and glomerulosclerosis by the modification of podocyte molecules and cell survival. In the present study, we investigated the effect of Ang II on endoplasmic reticulum (ER) stress in podocytes.

METHODS

We cultured mouse podocytes with increasing doses of Ang II and evaluated ER stress markers by Western blotting.

RESULTS

Ang II increased Bip protein, an ER chaperone, in a dose-dependent manner at 24 h, which was ameliorated by losartan, an angiotensin II type 1 receptor antagonist. Ang II also increased ER stress markers, such as phospho-PERK, phospho-eIF2α, and ATF4 proteins of podocyte, significantly in a dose-dependent manner at 24 h. Increased phospho-PERK and ATF4 proteins were further augmented by phosphoinositide 3 (PI3)-kinase inhibitor, LY294002, which suggested that Ang II could induce podocyte ER stress of PERK-eIF2α-ATF4 axis via PI3-kinase pathway.

DISCUSSION

These studies suggest that Ang II could induce podocyte ER stress of PERK-eIF2α-ATF4 axis via PI3-kinase pathway, which would contribute to the development of podocyte injury induced by Ang II, and the augmentation of PI3-kinase would be a therapeutic target.

Cell-cell interactions driving kidney morphogenesis

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

Using zebrafish to study podocyte genesis during kidney development and regeneration

During development, vertebrates form a progression of up to three different kidneys that are comprised of functional units termed nephrons. Nephron composition is highly conserved across species, and an increasing appreciation of the similarities between zebrafish and mammalian nephron cell types has positioned the zebrafish as a relevant genetic system for nephrogenesis studies. A key component of the nephron blood filter is a specialized epithelial cell known as the podocyte. Podocyte research is of the utmost importance as a vast majority of renal diseases initiate with the dysfunction or loss of podocytes, resulting in a condition known as proteinuria that causes nephron degeneration and eventually leads to kidney failure. Understanding how podocytes develop during organogenesis may elucidate new ways to promote nephron health by stimulating podocyte replacement in kidney disease patients. In this review, we discuss how the zebrafish model can be used to study kidney development, and how zebrafish research has provided new insights into podocyte lineage specification and differentiation. Further, we discuss the recent discovery of podocyte regeneration in adult zebrafish, and explore how continued basic research using zebrafish can provide important knowledge about podocyte genesis in embryonic and adult environments. genesis 52:771-792, 2014. © 2014 Wiley Periodicals, Inc.

Ginseng total saponin modulates the changes of α-actinin-4 in podocytes induced by diabetic conditions

Background

The actin cytoskeleton in podocytes is essential for the maintenance of its normal structure and function. Its disruption is a feature of podocyte foot-process effacement and is associated with proteinuria. α-Actinin-4 in podocytes serves as a linker protein binding the actin filaments of the cytoskeleton.

Methods

To investigate the effect of ginseng total saponin (GTS) on the pathological changes of podocyte α-actinin-4 induced by diabetic conditions, we cultured mouse podocytes under normal glucose (5mM) or high glucose (HG, 30mM) conditions, with or without the addition of advanced glycosylation end products (AGE), and treated with GTS.

Results

In confocal imaging, α-actinin-4 colocalized with the ends of F-actin fibers in cytoplasm, but diabetic conditions disrupted F-actin fibers and concentrated α-actinin-4 molecules at the peripheral cytoplasm. GTS upregulated α-actinin protein in a time- and dose-dependent manner, and suppressed the receptor for AGE levels in western blotting. Diabetic conditions, including HG, AGE, and both together, decreased cellular α-actinin-4 protein levels at 24 h and 48 h. Such quantitative and qualitative changes of α-actinin-4 protein induced by diabetic conditions were mitigated by GTS.

Conclusion

These findings imply that both HG and AGE have an influence on the distribution and amount of α-actinin-4 in podocytes that can be recovered by GTS.