Nephrin Expression In Podocytes Research Articles

Dendrobium officinale polysaccharide decreases podocyte injury in diabetic nephropathy by regulating IRS-1/AKT signal and promoting mitophagy.

High glucose (HG) caused oxidative stress and mitochondrial dysfunction, resulting in insulin resistance in podocytes, a key mechanism of diabetic nephropathy. Dendrobium officinale polysaccharide (DOP) was able to improve insulin resistance and antioxidant capability. The purpose of this study is to explore the mechanism by which DOP decreases the podocyte injury induced by HG. MPC5 cells were treated with HG, DOP, and IRS-1/2 inhibitor NT157. Afterwards, glucose consumption, generations of ROS and MDA were measured using the detection kits. Mitophagy was monitored using both MtphagTracyker and LysoTracker. The mitochondrial membrane potential was evaluated by JC-1 staining. DOP was also used in a mouse model of diabetes, with the measurements of urine albumin, blood creatinine and blood urea nitrogen. Treatment with DOP suppressed the HG-induced reduction of glucose consumption, the phosphorylation of IRS-1 (phospho Y632), AKT (phospho Ser473 and Thr308) and Nephrin. In addition, HG-induced augment of ROS and MDA, formation of γ-H2A.X foci and translocation of AKT to nucleus were inhibited by DOP. DOP enhanced mitophagy, which was associated with decreased mitochondrial membrane potential and ROS production. DOP conferred protective effect on podocyte in the diabetic mouse by reducing the albumin/creatinine ratio and blood urea nitrogen, and restoring Nephrin expression in podocytes. DOP alleviates HG-induced podocyte injuryby regulating IRS-1/AKT signal and promoting mitophagy.

Loss of sphingosine kinase 2 enhances Wilm's tumor suppressor gene 1 and nephrin expression in podocytes and protects from streptozotocin-induced podocytopathy and albuminuria in mice

The sphingosine 1-phosphate (S1P) is a bioactive sphingolipid that is now appreciated as key regulatory factor for various cellular functions in the kidney, including matrix remodeling. It is generated by two sphingosine kinases (Sphk), Sphk1 and Sphk2, which are ubiquitously expressed, but have distinct enzymatic activities and subcellular localizations. In this study, we have investigated the role of Sphk2 in podocyte function and its contribution to diabetic nephropathy. We show that streptozotocin (STZ)-induced nephropathy and albuminuria in mice is prevented by genetic depletion of Sphk2. This protection correlated with an increased protein expression of the transcription factor Wilm's tumor suppressor gene 1 (WT1) and its target gene nephrin, and a reduced macrophage infiltration in immunohistochemical renal sections of STZ-treated Sphk2-/- mice compared to STZ-treated wildtype mice.To investigate changes on the cellular level, we used an immortalized human podocyte cell line and generated a stable knockdown of Sphk2 (Sphk2-kd) by a lentiviral transduction method. These Sphk2-kd cells accumulated sphingosine as a consequence of the knockdown, and showed enhanced nephrin and WT1 mRNA and protein expressions similar to the finding in Sphk2 knockout mice. Treatment of wildtype podocytes with the highly selective Sphk2 inhibitor SLM6031434 caused a similar upregulation of nephrin and WT1 expression. Furthermore, exposing cells to the profibrotic mediator transforming growth factor β (TGFβ) resulted on the one side in reduced nephrin and WT1 expression, but on the other side, in upregulation of various profibrotic marker proteins, including connective tissue growth factor (CTGF), fibronectin (FN) and plasminogen activator inhibitor (PAI) 1. All these effects were reverted by Sphk2-kd and SLM6031434. Mechanistically, the protection by Sphk2-kd may depend on accumulated sphingosine and inhibited PKC activity, since treatment of cells with exogenous sphingosine not only reduced the phosphorylation pattern of PKC substrates, but also increased WT1 protein expression. Moreover, the selective stable knockdown of PKCδ increased WT1 expression, suggesting the involvement of this PKC isoenzyme in WT1 regulation.The glucocorticoid dexamethasone, which is a treatment option in many glomerular diseases and is known to mediate a nephroprotection, not only downregulated Sphk2 and enhanced cellular sphingosine, but also enhanced WT1 and nephrin expressions, thus, suggesting that parts of the nephroprotective effect of dexamethasone is mediated by Sphk2 downregulation.Altogether, our data demonstrated that loss of Sphk2 is protective in diabetes-induced podocytopathy and can prevent proteinuria, which is a hallmark of many glomerular diseases. Thus, Sphk2 could serve as a new attractive pharmacological target to treat proteinuric kidney diseases.

GAS5 promotes podocyte injury in sepsis by inhibiting PTEN expression.

To investigate the potential role of long noncoding RNA (lncRNA) growth arrest specific transcript 5 (GAS5) in sepsis-induced podocyte injury and its underlying mechanism. The sepsis model was established by lipopolysaccharide (LPS) induction in podocytes. The expression levels of Nephrin and GAS5 were detected by quantitative Real-time polymerase chain reaction (qRT-PCR) after LPS induction in podocytes for 12 h, 24 h and 36 h, respectively. Western blot was used to detect the expression level of Nephrin in sepsis-induced podocytes. The mRNA expressions of GAS5 and Nephrin in podocytes were detected after transfection of GAS5 siRNA. Albumin influx in podocytes after GAS5 knockdown was detected by Transwell assay. Western blot was used to detect the protein expression of Snail in sepsis after GAS5 knockdown. The target gene of GAS5 was predicted by bioinformatics analysis. QRT-PCR and Western blot were used to detect the protein and mRNA levels of PTEN (phosphatase and tensin homolog deleted on chromosome ten). Nephrin expression and the albumin inflow after PTEN knockdown were then measured. The expression of PI3K/AKT/GSK3β was also detected after GAS5 was downregulated while PTEN was upregulated. LPS stimulation downregulated the mRNA expression of Nephrin in podocytes and achieved the lowest level at 24 h. The protein expression change of Nephrin was consistent with its mRNA expression. In the septic state, the albumin influx of podocytes remarkably increased, but the function of podocyte barrier was weakened. Besides, GAS5 expression decreased in a time-dependent manner in LPS-induced podocytes. After GAS5 knockdown by siRNA, Nephrin expression and the function of podocyte barrier were significantly reduced. Snail expression was also upregulated in septic state, and GAS5 knockdown increased the expressions of phosphorylated Snail and PI3K/AKT/GSK3β. After knockdown of GAS5, the mRNA and protein levels of PTEN significantly decreased, which was contract to the expression of Snail. However, overexpression of PTEN could reverse the promotive effect of GAS5 on PI3K/AKT activation. GAS5 expression decreased in sepsis-induced podocyte injury, and GAS5 was involved in regulating sepsis-induced podocyte injury by reducing PTEN expression.

Reversal of albuminuria by combined AM6545 and perindopril therapy in experimental diabetic nephropathy.

The endocannabinoid (EC) system has been implicated in the pathogenesis of diabetic nephropathy (DN). We investigated the effects of peripheral blockade of the cannabinoid CB1 receptor as an add-on treatment to ACE-inhibition in type 1 diabetic mice (DM) with established albuminuria. Renal functional parameters (albumin excretion rate, creatinine clearance), tubular injury, renal structure, both EC and CB receptor levels and markers of podocyte dysfunction, fibrosis and inflammation were studied in streptozotocin-induced DM treated for 14weeks with vehicle, the ACE-inhibitor perindopril (2mg·kg-1 ·day-1 ), peripherally-restricted CB1 receptor antagonist AM6545 (10mg·kg-1 ·day-1 ) or both. Treatments began at 8weeks after diabetes onset, when early DN is established. CB1 receptors were overexpressed in DM and neither perindopril nor AM6545 altered this effect, while both drugs abolished diabetes-induced overexpression of angiotensin AT1 receptors. Single treatment with either AM6545 or perindopril significantly reduced progression of albuminuria, down-regulation of nephrin and podocin, inflammation and expression of markers of fibrosis. However, reversal of albuminuria was only observed in mice administered both treatments. The ability of the combination therapy to completely abolish slit diaphragm protein loss, monocyte infiltration, overexpression of inflammatory markers and favour macrophage polarization towards an M2 phenotype may explain this greater efficacy. In vitro experiments confirmed that CB1 receptor activation directly inhibits retinoic acid-induced nephrin expression in podocytes and IL-4-induced M2 polarization in macrophages. Peripheral CB1 receptor blockade used as add-on treatment to ACE-inhibition reverses albuminuria, nephrin loss and inflammation in DM.

Association of microRNA-155, interleukin 17A, and proteinuria in preeclampsia.

Background:This study aimed to explore the correlation between microRNA-155 (miR-155), interleukin 17A (IL-17), and late preeclampsia (PE) using biochemical parameters in maternal serum and urine.Methods:Sixty patients with PE were recruited to this study and were divided into 3 groups according to levels of urinary protein: mild urinary protein group (group A); moderate urinary protein group (group B); and severe urinary protein group (group C). All subjects presented with late onset PE (≥32 weeks). In addition, 20 healthy pregnant women were recruited as a normal group (NP). Maternal serum and urine samples were obtained from all participants and assayed using immunofluorescence, transmission electron and immune electron microscopy, and western blot. Furthermore, placentas were also collected and miR-155 and IL-17 expression was measured using an enzyme-linked immunosorbent assay.Results:Levels of miR-155 and IL-17 expression were found to be increased in PE placentas and serum, compared to the normal group (P <.05). IL-17 levels and podocytes had a positive association in the serum of patients with PE. In addition, over-expression of miR-155 resulted in increased IL-17 production by CD4+ T cells in vitro, and nephrin expression was decreased in podocytes. Furthermore, IL-17 reduced nephrin expression in podocytes and podocyte apoptosis in a dose and time-dependent manner.Conclusion:The results of this study demonstrate a correlation between miR-155 and IL-17 in the formation of proteinuria during late onset PE.

Epigallocatechin‑3‑gallate protects from high glucose induced podocyte apoptosis via suppressing endoplasmic reticulum stress.

Podocytes serve a critical role in the development of many glomerular diseases, including diabetic nephropathy (DN). Epigallocatechin‑3‑gallate (EGCG), a predominant polyphenolic component of green tea, has indicated its therapeutic effects in diabetes. In the present study, mouse podocyte cells were cultured invitro, cell injury was induced by high glucose, and the protective effect of EGCG on cell proliferation and apoptosis and the underlying mechanisms were investigated. The results demonstrated that high glucose significantly inhibited cell proliferation after 48 and 72h compared with normal glucose and mannitol treatment. EGCG (20µmol/l) markedly promoted podocyte proliferation after 24, 48 and 72h incubation with high glucose. Furthermore, high glucose significantly reduced WT‑1 and nephrin expression in podocytes compared with the normal glucose and mannitol groups, while EGCG (20µmol/l) treatment largely restored their expression. High glucose also significantly increased the apoptotic cell population compared with normal glucose and mannitol groups. However, EGCG combined with high glucose greatly decreased the apoptotic cell number compared with high glucose treatment alone. Furthermore, high glucose treatment was demonstrated to significantly increase glucose‑regulated protein 78 (GRP78), phosphorylated‑ PKR‑like ER kinase (p‑PERK) and caspase‑12 protein expression levels, which is representative of endoplasmic reticulum (ER) stress, compared with the normal glucose and mannitol groups. However, EGCG treatment significantly attenuated GRP78, p‑PERK and caspase‑12 protein expression induced by high glucose. These findings suggested that EGCG serves a protective role in glucose‑induced podocyte apoptosis via suppressing ER stress, and may provide a novel therapeutic strategy to ameliorate the process of DN.

Nicotine Induces Podocyte Apoptosis through Increasing Oxidative Stress.

BackgroundCigarette smoking plays an important role in the progression of chronic kidney disease (CKD). Nicotine, one of the major components of cigarette smoking, has been demonstrated to increase proliferation of renal mesangial cells. In this study, we examined the effect of nicotine on podocyte injury.MethodsTo determine the expression of nicotinic acetylcholine receptors (nAChR subunits) in podocytes, cDNAs and cell lysate of cultured human podocytes were used for the expression of nAChR mRNAs and proteins, respectively; and mouse renal cortical sections were subjected to immunofluorescant staining. We also studied the effect of nicotine on podocyte nephrin expression, reactive oxygen species (ROS) generation (via DCFDA loading followed by fluorometric analysis), proliferation, and apoptosis (morphologic assays). We evaluated the effect of nicotine on podocyte downstream signaling including phosphorylation of ERK1/2, JNK, and p38 and established causal relationships by using respective inhibitors. We used nAChR antagonists to confirm the role of nicotine on podocyte injury.ResultsHuman podocytes displayed robust mRNA and protein expression of nAChR in vitro studies. In vivo studies, mice renal cortical sections revealed co-localization of nAChRs along with synaptopodin. In vitro studies, nephrin expression in podocyte was decreased by nicotine. Nicotine stimulated podocyte ROS generation; nonetheless, antioxidants such as N-acetyl cysteine (NAC) and TEMPOL (superoxide dismutase mimetic agent) inhibited this effect of nicotine. Nicotine did not modulate proliferation but promoted apoptosis in podocytes. Nicotine enhanced podocyte phosphorylation of ERK1/2, JNK, and p38, and their specific inhibitors attenuated nicotine-induced apoptosis. nAChR antagonists significantly suppressed the effects of nicotine on podocyte.ConclusionsNicotine induces podocyte apoptosis through ROS generation and associated downstream MAPKs signaling. The present study provides insight into molecular mechanisms involved in smoking associated progression of chronic kidney disease.

AI-24 Calcium/calmodulin kinase controls T and renal cell function

Background Molecular abnormalities in SLE T cells account for their aberrant function including cytokine production, cytotoxic responses and help to B cells. Materials and methods Use of biochemical, molecular biology and engineered mice; study of kidney tissues and isolated kidney cells. Results Calcium calmodulin kinase IV (CaMK4) is expressed at high levels in T cells from patients with SLE and accounts for the decreased production of IL-2 and the increased production of il-17. The mechanisms involved modification of transcription factors and epigenetic changes. CaMK4 drives proliferation of mesangial cells in lupus prone mice and the production of IL-6. In parallel CaMK4 suppresses the expression of nephrin in podocytes resulting in proteinuria and also advances the expression of CD86 enabling thus podocytes to provide costimulation to passer-by T cells. Targeted delivery of a CaMK4 inhibitor to CD4 T cells reverses autoimmunity in lupus-prone mice. Conclusions CaMK4 accounts for the abnormal production of cytokines by SLE T cells, the proliferation of mesangial cells and the poor function of podocytes. Targeting CaMK4 and targeted delivery of CaMK4 inhibitors to T cells has proven promising in preclinical studies.

Establishment of Nephrin Reporter Mice and Use for Chemical Screening.

Nephrin is a critical component of glomerular filtration barrier, which is important to maintain glomerular structure and avoid proteinuria. Downregulation of nephrin expression is commonly observed at early stage of glomerular disorders, suggesting that methods to increase nephrin expression in podocytes may have therapeutic utility. Here, we generated a knockin mouse line carrying single copy of 5.5 kb nephrin promoter controlling expression of enhanced green fluorescent protein (EGFP) at Rosa26 genomic locus (Nephrin-EGFP mouse). In these mice, EGFP was specifically expressed in podocytes. Next, we isolated and cultivated glomeruli from these mice, and developed a protocol to automatically quantitate EGFP expression in cultured glomeruli. EGFP signal was markedly reduced after 5 days of culture but reduction was inhibited by vitamin D treatment. We confirmed that vitamin D increased mRNA and protein expression of endogenous nephrin in cultivated glomeruli. Thus, we generated a mouse line converting nephrin promoter activity into fluorescence, which can be used to screen compounds having activity to enhance nephrin gene expression.

Therapy with a Selective Cannabinoid Receptor Type 2 Agonist Limits Albuminuria and Renal Injury in Mice with Type 2 Diabetic Nephropathy

Background/Aims: A critical involvement of the endocannabinoid/cannabinoid receptor system in diabetes and its complications has been recognized. Experimental evidence suggested that activation of the cannabinoid receptor type 2 (CB₂), which is expressed in the kidney by podocytes and inflammatory cells, had a protective role in early streptozotocin-induced type 1 diabetes in mice. No experimental evidence is so far available on the effects of CB₂ agonists in type 2 diabetes. In this study, we investigated the effects of a CB₂ agonist given at a phase of overt disease on renal functional and structural changes in BTBR ob/ob mice, a model of type 2 diabetic nephropathy. Methods: BTBR ob/ob mice received, from 10 to 21 weeks of age, vehicle, the selective CB₂ agonist HU910, or lisinopril used as standard therapy for comparison. BTBR wild-type mice served as controls. Results: Treatment with CB₂ agonist reduced progressive albuminuria of BTBR ob/ob mice to a similar extent as ACE inhibitor. The antiproteinuric effect of CB₂ agonist was associated with the amelioration of the defective nephrin expression in podocytes of diabetic mice. CB₂ agonist limited mesangial matrix expansion, fibronectin accumulation and sclerosis. Glomerular infiltration of Mac-2-positive monocytes/machrophages was attenuated by CB₂ agonist, at least in part due to the drug's ability to reduce MCP-1 chemotactic signals. Renoprotective effects of CB₂ were similar to those achieved by ACE inhibitor. Conclusion: These results suggest that CB₂ agonism is a potential option to be added to the available therapeutic armamentarium for type 2 diabetic nephropathy.

Full-length soluble urokinase plasminogen activator receptor down-modulates nephrin expression in podocytes

Increased plasma level of soluble urokinase-type plasminogen activator receptor (suPAR) was associated recently with focal segmental glomerulosclerosis (FSGS). In addition, different clinical studies observed increased concentration of suPAR in various glomerular diseases and in other human pathologies with nephrotic syndromes such as HIV and Hantavirus infection, diabetes and cardiovascular disorders. Here, we show that suPAR induces nephrin down-modulation in human podocytes. This phenomenon is mediated only by full-length suPAR, is time-and dose-dependent and is associated with the suppression of Wilms’ tumor 1 (WT-1) transcription factor expression. Moreover, an antagonist of αvβ3 integrin RGDfv blocked suPAR-induced suppression of nephrin. These in vitro data were confirmed in an in vivo uPAR knock out Plaur−/− mice model by demonstrating that the infusion of suPAR inhibits expression of nephrin and WT-1 in podocytes and induces proteinuria. This study unveiled that interaction of full-length suPAR with αvβ3 integrin expressed on podocytes results in down-modulation of nephrin that may affect kidney functionality in different human pathologies characterized by increased concentration of suPAR.

Effects of MCP-1 Inhibition by Bindarit Therapy in a Rat Model of Polycystic Kidney Disease

Background/Aims: Experimental and clinical evidence suggested that monocyte chemoattractant protein-1 (MCP-1/CCL2) has a role in the development of interstitial inflammation and renal failure in polycystic kidney disease (PKD). We investigated whether bindarit, an inhibitor of MCP-1/CCL2 synthesis, could influence the evolution of PKD in PCK rats. Methods: PCK rats were treated from 5 to 15 weeks of age with vehicle or bindarit. Sprague-Dawley rats served as control. For in vitro studies, murine podocytes were exposed to albumin with or without bindarit. Results: MCP-1 mRNA was upregulated in the kidney of PCK rats and reduced by bindarit. Treatment limited overexpression of MCP-1 protein by epithelial cells of dilated tubules and cysts, and interstitial inflammatory cells. Excessive renal accumulation of monocytes/macrophages was lowered by bindarit by 41%. Serum creatinine slightly increased in PCK rats on vehicle and was similar to controls after bindarit. Kidney and liver cysts were not affected by treatment. Bindarit significantly reduced progressive proteinuria of PCK rats. The antiproteinuric effect was associated with the restoration of the defective nephrin expression in podocytes of PCK rats. Bindarit limited podocyte foot process effacement and ameliorated slit diaphragm frequency. In cultured podocytes, bindarit reduced MCP-1 production in response to albumin and inhibited albumin-induced cytoskeletal remodeling and cell migration. Conclusion: This study showed that although bindarit did not prevent renal cyst growth, it limited interstitial inflammation and renal dysfunction and reduced proteinuria in PKD. Thus, bindarit could be considered a therapeutic intervention complementary to therapies specifically acting to block renal cyst growth.

The novel role of TRPC6 in vitamin D ameliorating podocyte injury in STZ-induced diabetic rats.

Podocyte injury plays a critical role in the development and progression of diabetic nephropathy (DN). Over expression of TRPC6 on the podocytes has been revealed to cause podocyte injury in non-diabetic states. Besides, the emerging evidence from clinic revealed that vitamin D could reduce albuminuria and improve renal function, which was associated with podocyte protection. Our study aimed to investigate whether calcitriol ameliorating podocyte impairment is associated with regulation of the expression of TRPC6 in STZ-induced rats. Sprague-Dawley rats were randomly divided into three groups: normal control, DN, and DN treated with calcitriol (DN+VD); VD rats were treated with 0.1μg/kg/d calcitriol by gavage. DN model rats were established by intraperitoneal injections of streptozocin. The rats were sacrificed after 18weeks treatment. DN rats exhibited increased proteinuria accompanied by elevated TRPC6 expression. Treatment with calcitriol not only reduced proteinuria, but also normalized TRPC6 expression. Meanwhile, in DN rats, the expression of podocyte specific markers including nephrin and podocin was significantly decreased, accompanied by increased desmin, a marker of podocyte injury. Treatment with calcitriol reversed above changes. In addition, vitamin D receptor (VDR) was significantly decreased, whereas this reduction was attenuated by the calcitriol treatment. Moreover, TRPC6 was positively correlated with both 24h urinary protein and desmin. In contrast, TRPC6 was negatively correlated with both VDR and nephrin expression in podocytes. Calcitriol can ameliorate podocyte injury, which is contributed by the inhibition of enhanced TRPC6 expression in the early stages of DN rats.

Influence of Bushenhuoxue on podocytes of focal segmental glomerulosclerosis mice

ObjectiveTo observe the effects and mechanisms of Bushenhuoxue on desmin and nephrin expression in mice podocytes, and to investigate its effects on wt1 expression in Wilms' tumor. MethodsAdriamycin (ADR) was used to induce focal segmental glomerulous sclerosis (FSGS) in mice. Bushenhuoxue was used to treat FSGS for 6 weeks. We measured body mass and right renal mass, and determined serum albumin (ALB) levels, protein content in urine, and urinary protein and albumin creatinine ratio (UACR). Changes in renal tissue morphology were evaluated by microscopy. wt1 and nephrin expression in podocytes were detected using immunofluorescence. Expression levels of desmin, wt1 and nephrin mRNAs in renal tissue were determined using reverse transcription polymerase chain reaction assays. ResultsProtein levels in urine and UACR were significantly increased in FSGS model mice compared with Bushenhuoxue-treated and control mice. Body mass and ALB levels were decreased in FSGS mice compared with control and Bushenhuoxue-treated mice. Expression of the wt1 protein was observed in control mice. Compared with controls, wt1 expression levels were reduced in Bushenhuoxue-treated mice, and to a greater extent in FSGS mice. Nephrin protein expression was widespread in FSGS mice, and significantly reduced in control and Bushenhuoxue mice. Expression levels of wt1 and nephrin mRNAs in FSGS mice were lower compared with those in control and Bushenhuoxue-treated mice. Desmin mRNA levels in FSGS mice were reduced compared with those in control and Bushenhuoxue-treated mice. ConclusionBushenhuoxue ameliorated albuminuria in FSGS mice; this was possibly related to the up-regulation of wt1 and nephrin, and down-regulation of desmin.

NOD2 promotes renal injury by exacerbating inflammation and podocyte insulin resistance in diabetic nephropathy

An increasing number of clinical and animal model studies indicate that activation of the innate immune system and inflammatory mechanisms are important in the pathogenesis of diabetic nephropathy. Nucleotide-binding oligomerization domain containing 2 (NOD2), a member of the NOD-like receptor family, plays an important role in innate immune response. Here we explore the contribution of NOD2 to the pathogenesis of diabetic nephropathy and found that it was upregulated in kidney biopsies from diabetic patients and high-fat diet/streptozotocin-induced diabetic mice. Further, NOD2 deficiency ameliorated renal injury in diabetic mice. In vitro, NOD2 induced proinflammatory response and impaired insulin signaling and insulin-induced glucose uptake in podocytes. Moreover, podocytes treated with high glucose, advanced glycation end-products, tumor necrosis factor-α, or transforming growth factor-β (common detrimental factors in diabetic nephropathy) significantly increased NOD2 expression. NOD2 knockout diabetic mice were protected from the hyperglycemia-induced reduction in nephrin expression. Further, knockdown of NOD2 expression attenuated high glucose-induced nephrin downregulation in vitro, supporting an essential role of NOD2 in mediating hyperglycemia-induced podocyte dysfunction. Thus, NOD2 is one of the critical components of a signal transduction pathway that links renal injury to inflammation and podocyte insulin resistance in diabetic nephropathy.

Angiotensin II Contributes to Diabetic Renal Dysfunction in Rodents and Humans via Notch1/Snail Pathway

In nondiabetic rat models of renal disease, angiotensin II (Ang II) perpetuates podocyte injury and promotes progression to end-stage kidney disease. Herein, we wanted to explore the role of Ang II in diabetic nephropathy by a translational approach spanning from in vitro to in vivo rat and human studies, and to dissect the intracellular pathways involved. In isolated perfused rat kidneys and in cultured human podocytes, Ang II down-regulated nephrin expression via Notch1 activation and nuclear translocation of Snail. Hairy enhancer of split-1 was a Notch1-downstream gene effector that activated Snail in cultured podocytes. In vitro changes of the Snail/nephrin axis were similar to those in renal biopsy specimens of Zucker diabetic fatty rats and patients with advanced diabetic nephropathy, and were normalized by pharmacological inhibition of the renin-angiotensin system. Collectively, the present studies provide evidence that Ang II plays a relevant role in perpetuating glomerular injury in experimental and human diabetic nephropathy via persistent activation of Notch1 and Snail signaling in podocytes, eventually resulting in down-regulation of nephrin expression, the integrity of which is crucial for the glomerular filtration barrier.

Molecular Mechanism Underlying 1,25-Dihydroxyvitamin D Regulation of Nephrin Gene Expression

Nephrin plays a key role in maintaining the structure of the slit diaphragm in the glomerular filtration barrier. Our previous studies have demonstrated potent renoprotective activity for 1,25-dihydroxyvitamin D (1,25(OH)(2)D(3)). Here we showed that in podocytes 1,25(OH)(2)D(3) markedly stimulated nephrin mRNA and protein expression. ChIP scan of the 6-kb 5' upstream region of the mouse nephrin gene identified several putative vitamin D response elements (VDREs), and EMSA confirmed that the VDRE at -312 (a DR4-type VDRE) could be bound by vitamin D receptor (VDR)/retinoid X receptor. Luciferase reporter assays of the proximal nephrin promoter fragment (-427 to +173) showed strong induction of luciferase activity upon 1,25(OH)(2)D(3) treatment, and the induction was abolished by mutations within -312VDRE. ChIP assays showed that, upon 1,25(OH)(2)D(3) activation, VDR bound to this VDRE leading to recruitment of DRIP205 and RNA polymerase II and histone 4 acetylation. Treatment of mice with a vitamin D analog induced nephrin mRNA and protein in the kidney, accompanied by increased VDR binding to the -312VDRE and histone 4 acetylation. 1,25(OH)(2)D(3) reversed high glucose-induced nephrin reduction in podocytes, and vitamin D analogs prevented nephrin decline in both type 1 and 2 diabetic mice. Together these data demonstrate that 1,25(OH)(2)D(3) stimulates nephrin expression in podocytes by acting on a VDRE in the proximal nephrin promoter. Nephrin up-regulation likely accounts for part of the renoprotective activity of vitamin D.

Suppression of nephrin expression by TNF-α via interfering with the cAMP-retinoic acid receptor pathway

Nephrin, a crucial component of the slit diaphragm, is downregulated in proteinuric glomerular diseases including glomerulonephritis. We previously reported that 1) expression of nephrin in cultured podocytes is reinforced by retinoic acid (RA) and 1,25-dihydroxyvitamin D(3), 2) these effects are mediated by retinoic acid receptor (RAR) and vitamin D receptor (VDR), and 3) basal and inducible expression of nephrin is downregulated by TNF-alpha. In the present investigation, we identified that TNF-alpha selectively represses activity of RAR but not VDR. To elucidate mechanisms underlying this observation, we tested involvement of downstream targets for TNF-alpha: nuclear factor-kappaB (NF-kappaB), mitogen-activated protein (MAP) kinases, phosphatidylinositol 3-kinase (PI3K)-Akt, and cAMP-protein kinase A (PKA). TNF-alpha caused activation of NF-kappaB, MAP kinases, and PI3K-Akt in podocytes, whereas blockade of these molecules did not affect inhibition of RAR by TNF-alpha. In contrast, TNF-alpha depressed activity of cAMP-PKA, and blockade of PKA inhibited basal and RA-induced activation of RAR. Furthermore, activity of RAR was significantly upregulated by cAMP, and the suppressive effect of TNF-alpha on RAR was reversed by cAMP-elevating agents. These results suggest that 1) expression of nephrin in podocytes is regulated by the cAMP-RAR pathway and 2) suppression of nephrin by TNF-alpha is caused, at least in part, through selective inhibition of this pathway.

Mesangial medium with IgA1 from IgA nephropathy inhibits nephrin expression in mouse podocytes

IgA nephropathy (IgAN) is characterized by mesangial deposition of polymeric IgA1, and podocyte injury plays an important role in glomerulosclerosis of the disease. Our previous study indicated that medium of mesangial cells co-incubated with aggregated IgA1 (aIgA1), isolated from IgAN patients, down-regulated nephrin expression. Yet the mechanism remains unclear. Podocytes were incubated with a medium of mesangial cells co-incubated with aIgA1, which was isolated from IgAN patients, and enalaprilat (10(-5) M), valsartan (10(-5) M) and anti-mouse tumour necrosis factor-alpha antibody (50 ng mL(-1)) separately. Nephrin expression in podocytes was measured by real-time polymerase chain reaction and Western blot analysis. The level of angiotensinogen and angiotensin-converting enzyme mRNAs in podocytes, as well as angiotensin, was also increased by a medium of mesangial cells co-incubated with aIgA1 from IgAN patients (P<0.05). Enalaprilat or valsartan partly improved nephrin expression when compared with that by podocytes exposed to the mesangial medium (P<0.05), while the nephrin expression of podocytes with enalaprilat or valsartan was lower than that of podocytes exposed to medium of mesangial cells stimulated by aIgA1 from healthy control (P<0.05). However, anti-mouse tumour necrosis factor-alpha antibody did not show any improvement in nephrin expression. Our findings implicate that local renin angiotensin system activation in podocytes is partly involved in down-regulation of nephrin by mesangial medium in IgA nephropathy.

Effect of aggregated immunoglobulin A1 from immunoglobulin A nephropathy patients on nephrin expression in podocytes

Abnormal immunoglobulin (Ig)A1 is considered to play a pivotal role in IgA nephropathy. We used mouse podocytes as the experimental model to investigate the effect of aggregated IgA1 (aIgA1) isolated from IgA nephropathy (IgAN) patients on nephrin expression in podocytes through direct and indirect pathways. Jacalin affinity chromatography and Sephacryl S-200 molecular sieve chromatography were used to isolate IgA1 from blood of IgAN patients which was therefore became aIgA1. Podocytes were incubated with aIgA1 or special mesangial medium. Nephrin expression in podocytes was measured by real-time polymerase chain reaction and western blot analysis. Aggregated IgA1 from IgAN patients and healthy controls reduced nephrin expression in podocytes at mRNA and protein levels when compared with podocytes incubated with control medium (RPMI-1640 with 0.5% foetal bovine serum) (P<0.05). While medium from mesangial cells incubated with aIgA1 from IgAN inhibited nephrin expression in podocytes at mRNA and protein levels when compared with podocytes incubated with medium from mesangial cells with aIgA1 from healthy controls (P<0.05). Our findings implicate that aIgA1 from IgAN patients could inhibit nephrin expression through direct and indirect pathways, although these mechanisms remain to be clarified.