Role of the podocyte in proteinuria

Mapping the transcriptional and epigenetic landscape of organotypic endothelial diversity in the developing and adult mouse

The vascular endothelium features unique molecular and functional properties across different vessel types, such as between arteries, veins and capillaries, as well as between different organs, such as the leaky sinusoidal endothelium of the liver versus the impermeable vessels of the brain. However, the transcriptional networks governing endothelial organ specialization remain unclear. Here we profile the accessible chromatin and transcriptional landscapes of the endothelium from the mouse liver, lung, heart, kidney, brain and retina, across developmental time, to identify potential transcriptional regulators of endothelial heterogeneity. We then determine which of these putative regulators are conserved in human brain endothelial cells, and using single-cell transcriptomic profiling, we define which regulatory networks are active during brain maturation. Finally, we show that the putative transcriptional regulators identified by these three approaches molecularly and functionally reprogram naive endothelial cells. Thus, this resource can be used to identify potential transcriptional regulators controlling the establishment and maintenance of organ-specific endothelial specialization.

Saracatinib, a Src kinase inhibitor, enhances the renoprotective effect of metformin and losartan in diabetic nephropathy

OBJECTIVE

This research assesses renoprotective effects of saracatinib (Src) in diabetic nephropathy (DN) and the potential underlying processes.

MATERIALS AND METHODS

Rats were divided into: control, DN, DN + Met + Los, DN + Met + Src, and DN + Met + Los + Src. Rats' ABP, urinary albumin, urinary nephrin, and creatinine clearance were assessed. Blood samples were collected for measuring glycaemic state parameters, renal functions, oxidative stress markers, inflammatory mediators, aldosterone, and lipid profile. Kidneys were extracted for KIM-1 and nephrin gene expression, H&E, Masson's trichrome staining, and immunohistochemical assessment.

RESULTS

Significant increases in ABP, urinary albumin and nephrin, glycaemic measurements, urea, creatinine, aldosterone, inflammatory cytokines, MDA, lipids, renal fibrosis, H scores of VEGF and TGF-β, and renal KIM-1 expression were related to DN. However, there was a significant decrease in creatinine clearance, GSH, and nephrin expression in DN group compared with control group.

DISCUSSION AND CONCLUSION

The combination of metformin (Met), losartan (Los), and Src repaired DN alterations. Adding Src to Met and Los is superior to using them alone.

Ginsenoside Rk1 exerts protective effects of LPS-induced podocyte apoptosis and inflammation by inactivating JAK2/STAT3 and NF-κB pathways

Podocyte injury is a major biomarker of primary glomerular disease that leads to massive proteinuria and kidney failure. Ginsenoside Rk1, a substance derived from ginseng, has several pharmacological activities, such as anti-apoptotic, anti-inflammatory, and antioxidant effects. In this study, our goal is to investigate the roles and mechanisms of ginsenoside Rk1 in podocyte injury and acute kidney injury (AKI). C57BL/6 mice were intraperitoneally injected with 10 mg/kg LPS to mimic AKI-like conditions in vivo. One hour after the LPS challenge, ginsenoside Rk1 (10 mg/kg or 20 mg/kg) or vehicle was orally administered into mice every 6 h until sacrifice at 24 h. Renal functions were assessed by measuring blood urea nitrogen and creatinine. Renal histological changes were examined by hematoxylin and eosin staining. The production of proinflammatory cytokines in kidney tissues was evaluated by RT-qPCR and western blotting. A conditionally immortalized mouse MPC-5 podocyte cell line was treated with LPS and ginsenoside Rk1. Viability and apoptosis of MPC-5 cells were estimated by CCK-8 and flow cytometry. Western blotting was also conducted to measure the protein levels of apoptosis-related and pathway-related genes. The results of abovementioned experiments revealed that Ginsenoside Rk1 ameliorated LPS-stimulated podocyte apoptosis in vitro and relieved renal dysfunctions and inflammatory response in LPS-induced AKI mice. Mechanistically, ginsenoside Rk1 inactivated the JAK2/STAT3 and NF-κB pathways in LPS-treated podocytes and mice. In conclusion, this study shows that Ginsenoside Rk1 attenuates LPS-induced renal dysfunctions and inflammatory response in mice and LPS-induced podocyte apoptosis in vitro through inactivating the NF-κB and JAK2/STAT3 pathways.

Urolithin A Ameliorates the TGF Beta-Dependent Impairment of Podocytes Exposed to High Glucose

Increased activity of transforming growth factor-beta (TGF-β) is a key factor mediating kidney impairment in diabetes. Glomerular podocytes, the crucial component of the renal filter, are a direct target of TGF-β action, resulting in irreversible cell loss and progression of chronic kidney disease (CKD). Urolithin A (UA) is a member of the family of polyphenol metabolites produced by gut microbiota from ellagitannins and ellagic acid-rich foods. The broad spectrum of biological activities of UA makes it a promising candidate for the treatment of podocyte disorders. In this in vitro study, we investigated whether UA influences the changes exerted in podocytes by TGF-β and high glucose. Following a 7-day incubation in normal (NG, 5.5 mM) or high (HG, 25 mM) glucose, the cells were treated with UA and/or TGF-β1 for 24 h. HG and TGF-β1, each independent and in concert reduced expression of nephrin, increased podocyte motility, and up-regulated expression of b3 integrin and fibronectin. These typical-for-epithelial-to-mesenchymal transition (EMT) effects were inhibited by UA in both HG and NG conditions. UA also reduced the typically elevated HG expression of TGF-β receptors and activation of the TGF-β signal transducer Smad2. Our results indicate that in podocytes cultured in conditions mimicking the diabetic milieu, UA inhibits and reverses changes underlying podocytopenia in diabetic kidneys. Hence, UA should be considered as a potential therapeutic agent in podocytopathies.

The effectiveness of antioxidant agents in delaying progression of diabetic nephropathy: A systematic review of randomized controlled trials

Introduction

Oxidative stress plays a central role in the pathophysiology of diabetes mellitus and its complications, including diabetic nephropathy. Excessive production of reactive oxygen species (ROS) alters renal metabolic pathways, leading to inflammation, endothelial dysfunction, and fibrosis, ultimately resulting in end-stage renal disease (ESRD). Studies have shown that exogenous antioxidants can improve the pathophysiological condition of patients with diabetic nephropathy. Objective: This systematic review aims to investigate the types of antioxidant agents that inhibit the development of diabetic nephropathy and the effectiveness of antioxidant agent interventions to repair kidney structure and function.

Methods

A systematic review of randomized controlled trials that examined the role of antioxidants in improving diabetic nephropathy was conducted. The literature search was performed on PubMed, ScienceDirect, and EBSCO. The inclusion criteria covered articles on the antioxidant activity of herbal extracts and compounds that inhibit the progression of diabetic nephropathy in humans. In addition, the articles were written in English and published between 2012 and 2022. The reporting of the systematic review followed the Preferred Reporting Elements for Systematic Review and Meta-Analysis (PRISMA) guideline. The full texts of all potentially relevant systematic reviews were assessed for quality using the Risk of Bias 2 (RoB 2) tool.

Results

A total of 2,367 articles were identified in the three databases, of which only 15 articles met the inclusion criteria. Antioxidant agents that inhibit diabetic nephropathy can be classified as single antioxidants (silymarin, baicalin, epigallocatechin gallate, vitamin E, selenium, curcumin, α-lipoic acid, and tocotrienol-rich vitamin E) and combined antioxidants (α-lipoic acid with vitamin B6, and resveratrol with losartan). Antioxidant agents have been shown to reduce oxidative stress and inflammation, but their role in the progression of fibrosis remains unclear. The oxidative stress marker MDA was significantly reduced by silymarin, curcumin, vitamin E, tocotrienol-rich vitamin E, selenium, ALA, vitamin B, resveratrol and losartan. Silymarin was found to be the most effective (-3.43 µmol/L; 6.02 to 0.83). Compared to silymarin and epigallocatechin gallate, vitamin E was more effective (at -35.4 ng/L; P < 0.001) in reducing inflammation by decreasing TNF-α levels. In addition, tocotrienol-rich vitamin E, silymarin, baicalin, and selenium showed a decrease TGF-β levels, but did not show statistically significant differences between the placebo and intervention groups.

Conclusion

Potential antioxidant agents, such as flavonoids, vitamins, fatty acids, and antioxidant minerals, were examined in this systematic review. These agents contribute to reducing markers of oxidative stress and hyperglycemia-induced inflammation. Although several antioxidants play a role in reducing fibrosis markers, the effect does not appear to be statistically significant.

Downregulating lncRNA MIAT attenuates apoptosis of podocytes exposed to high glucose

AIMS

Diabetic nephropathy (DN), a destructive complication of diabetes mellitus (DM), is one of the leading causes of end-stage renal disease (ESRD). This study aimed to investigate the role of long non-coding RNA (lncRNA) MIAT in high-glucose (HG)-induced podocyte injury associated with DN.

METHODS

Three human kidney podocyte (HKP) cultures were treated with HG to mimic DN. Expression of lncRNA MIAT, podocyte-specific and injury-related proteins, and apoptosis were assessed before and after MIAT knockdown using MIAT shRNAs.

RESULTS

MIAT expression was upregulated in HKPs in response to glucose stress. HG treatment resulted in a significant increase in the apoptotic rate, Bax level, and levels of injury-related proteins desmin, fibroblast-specific protein 1 (FSP-1), and smooth muscle α-actin (α-SMA), and a significant reduction in Bcl-2 levels and the levels of podocyte-specific proteins synaptopodin and podocin. Transfection of HKPs with shRNAs significantly reduced MIAT levels (p < 0.05) and attenuated apoptosis in HG-medium. Correspondingly, the levels of synaptopodin and podocin were upregulated, and desmin, FSP-1, and α-SMA were reduced (p < 0.05). Western blot analysis also showed that anti-apoptotic active caspase-3 and Bax and proapoptotic Bcl-2 were elevated and decreased, respectively, after MIAT knockdown, suggesting that apoptosis pathways are deactivated after MIAT downregulation.

CONCLUSIONS

High glucose upregulates MIAT level in HKPs and induces cellular injury. Knockdown of MIAT alleviates the injury likely via deactivating apoptosis pathways.

Glomerular-tubular crosstalk via cold shock Y-box binding protein-1 in the kidney

Glomerular-tubular crosstalk within the kidney has been proposed, but the paracrine signals enabling this remain largely unknown. The cold-shock protein Y-box binding protein 1 (YBX1) is known to regulate inflammation and kidney diseases but its role in podocytes remains undetermined. Therefore, we analyzed mice with podocyte specific Ybx1 deletion (Ybx1ΔPod). Albuminuria was increased in unchallenged Ybx1ΔPod mice, which surprisingly was associated with reduced glomerular, but enhanced tubular damage. Tubular toll-like receptor 4 (TLR4) expression, node-like receptor protein 3 (NLRP3) inflammasome activation and kidney inflammatory cell infiltrates were all increased in Ybx1ΔPod mice. In vitro, extracellular YBX1 inhibited NLRP3 inflammasome activation in tubular cells. Co-immunoprecipitation, immunohistochemical analyses, microscale cell-free thermophoresis assays, and blunting of the YBX1-mediated TLR4-inhibition by a unique YBX1-derived decapeptide suggests a direct interaction of YBX1 and TLR4. Since YBX1 can be secreted upon post-translational acetylation, we hypothesized that YBX1 secreted from podocytes can inhibit TLR4 signaling in tubular cells. Indeed, mice expressing a non-secreted YBX1 variant specifically in podocytes (Ybx1PodK2A mice) phenocopied Ybx1ΔPod mice, demonstrating a tubular-protective effect of YBX1 secreted from podocytes. Lipopolysaccharide-induced tubular injury was aggravated in Ybx1ΔPod and Ybx1PodK2A mice, indicating a pathophysiological relevance of this glomerular-tubular crosstalk. Thus, our data show that YBX1 is physiologically secreted from podocytes, thereby negatively modulating sterile inflammation in the tubular compartment, apparently by binding to and inhibiting tubular TLR4 signaling. Hence, we have uncovered an YBX1-dependent molecular mechanism of glomerular-tubular crosstalk.

Deciphering the pharmacological mechanisms of Rostellularia procumbens (L) Nees. Extract alleviates adriamycin-induced nephropathy in vivo and in vitro

BACKGROUND

Rostellularia procumbens (L) Nees. is an effective traditional Chinese herbal medicine for the treatment of patients with chronic glomerulonephritis (CGN) in the clinic. However, the underlying molecular mechanisms need further elucidation.

PURPOSE

This study aims to investigate the renoprotective mechanisms of n-butanol extract from Rostellularia procumbens (L) Nees. (J-NE) in vivo and in vitro.

METHODS

The components of J-NE were analyzed by UPLC-MS/MS. In vivo, the nephropathy model was induced in mice by tail vein injection with adriamycin (10 mg·kg^-1), and mice were treated with vehicle or J-NE or benazepril by daily gavage. In vitro, MPC5 cells exposed to adriamycin (0.3 μg/ml) were treated with J-NE. The effects of J-NE inhibit podocyte apoptosis and protect against adriamycin-induced nephropathy were determined by Network pharmacology, RNA-seq, qPCR, ELISA, immunoblotting, flow cytometry, and TUNEL assay, according to the experimental protocols.

RESULT

The results showed that treatment significantly improved ADR-induced renal pathological changes, and the therapeutic mechanism of J-NE was related to the inhibition of podocyte apoptosis. Further molecular mechanism studies found that J-NE inhibited inflammation, increase the proteins expression levels of Nephrin and Podocin, reduce TRPC6 and Desmin expression levels and calcium ion levels in podocytes, and decrease the proteins expression levels of PI3K, p-PI3K, Akt and p-Akt to attenuated apoptosis. Furthermore, 38 compounds of J-NE were identified.

CONCLUSION

J-NE exerted the renoprotective effects by inhibiting podocyte apoptosis, which provides effective evidence for the treatment of J-NE targeting renal injury in CGN.

Quantifying Podocyte Number in a Small Sample Size of Glomeruli with CUBIC to Evaluate Podocyte Depletion of db/db Mice

The loss of podocyte is crucial for diagnosis and prognosis of diabetic kidney disease, whereas commonly two-dimensional methods for quantifying podocyte number existed with issues of low fidelity and accuracy. In this study, clear, unobstructed brain imaging cocktails and computational analysis (CUBIC), one of three-dimensional optical clearing approaches, was used which combines tissue clearing, immunolabeling, and a light-sheet microscope to image and evaluate podocytes in C57BL/6 (C57) and db/db mice. We discovered that 77 podocytes per glomerulus were in C57 mice. On the subject of db/db mice, there were 74 podocytes by the age of 8 w, 72 podocytes by the age of 12 w, and 66 podocytes by the age of 16 w, compared with 76 podocytes in the control group, suggesting that there was a significant decrease in podocyte number in db/db mice with the age of 16 w, showing a trend which positively correlated to the deterioration of kidney function. Sample size estimation using the PASS software revealed that taking 5%, 7.5%, and 10% of the mean podocyte number per glomerulus as the statistical allowable error and 95% as total confidence interval, 33, 15, and 9 glomeruli were independently needed to be sampled in C57 mice to represent the overall glomeruli to calculate podocyte number. Furthermore, in the control group of db/db mice, 36, 18, and 11 glomeruli were needed, compared with 46, 24, and 14 glomeruli in db/db mice by the age of 8 w, 43, 21, and 12 glomeruli by the age of 12 w, and 52, 27, and 16 by the age of 16 w. These findings indicated that precise quantification of podocyte number could judge the progression of diabetic kidney disease. In addition, a small number of glomeruli could be actually representative of the whole sample size, which indicated apparent practicability of CUBIC for clinical use.

Role of ion channels in the mechanism of proteinuria (Review)

Proteinuria is a common clinical manifestation of kidney diseases, such as glomerulonephritis, nephrotic syndrome, immunoglobulin A nephropathy and diabetic nephropathy. Therefore, proteinuria is considered to be a risk factor for renal dysfunction. Furthermore, proteinuria is also significantly associated with the progression of kidney diseases and increased mortality. Its occurrence is closely associated with damage to the structure of the glomerular filtration membrane. An impaired glomerular filtration membrane can affect the selective filtration function of the kidneys; therefore, several macromolecular substances, such as proteins, may pass through the filtration membrane and promote the manifestation of proteinuria. It has been reported that ion channels play a significant role in the mechanisms underlying proteinuria. Ion channel mutations or other dysfunctions have been implicated in several diseases, therefore ion channels could be used as major therapeutic targets. The mechanisms underlying the action of ion channels and ion transporters in proteinuria have been overlooked in the literature, despite their importance in identifying novel targets for treating proteinuria and delaying the progression of kidney diseases. The current review article focused on the four key ion channel groups, namely Na⁺, Ca²⁺, Cl^- and K⁺ ion channels and the associated ion transporters.

Increased Heparanase Levels in Urine during Acute Puumala Orthohantavirus Infection Are Associated with Disease Severity

Old–world orthohantaviruses cause hemorrhagic fever with renal syndrome (HFRS), characterized by acute kidney injury (AKI) with transient proteinuria. It seems plausible that proteinuria during acute HFRS is mediated by the disruption of the glomerular filtration barrier (GFB) due to vascular leakage, a hallmark of orthohantavirus–caused diseases. However, direct infection of endothelial cells by orthohantaviruses does not result in increased endothelial permeability, and alternative explanations for vascular leakage and diminished GFB function are necessary. Vascular integrity is partly dependent on an intact endothelial glycocalyx, which is susceptible to cleavage by heparanase (HPSE). To understand the role of glycocalyx degradation in HFRS–associated proteinuria, we investigated the levels of HPSE in urine and plasma during acute, convalescent and recovery stages of HFRS caused by Puumala orthohantavirus. HPSE levels in urine during acute HFRS were significantly increased and strongly associated with the severity of AKI and other markers of disease severity. Furthermore, increased expression of HPSE was detected in vitro in orthohantavirus–infected podocytes, which line the outer surfaces of glomerular capillaries. Taken together, these findings suggest the local activation of HPSE in the kidneys of orthohantavirus–infected patients with the potential to disrupt the endothelial glycocalyx, leading to increased protein leakage through the GFB, resulting in high amounts of proteinuria.

Relationship Between Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) and the Etiology of Acute Kidney Injury (AKI)

Coronavirus disease 2019 (COVID-19) is caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Since it was first recognized in December 2019, it has resulted in the ongoing worldwide pandemic. Although acute hypoxic respiratory failure (AHRF) and acute respiratory distress syndrome (ARDS) are the main features of the disease, the involvement of other organs needs to be explored. There has been a growing concern regarding the association between acute kidney injury (AKI) and poor outcomes in SARS-CoV-2 patients. Based on current observational data, AKI is the 2nd most common cause of morbidity and mortality behind ARDS in SARS-CoV-2 patients. Angiotensin-converting enzyme 2 (ACE2) receptor has been shown to be the cornerstone of SARS-CoV-2 infection and possibly plays a significant role in the occurrence of renal injury. The pathogenesis of AKI is likely multifactorial that involves not only direct viral invasion but also dysregulated immune response in the form of cytokine storm, ischemia to kidneys, hypercoagulable state, and rhabdomyolysis, among others. We performed a literature search of the Pubmed and Google Scholar database from 1996 to 2020 using the following keywords: severe acute respiratory syndrome coronavirus 2, coronavirus disease 2019, angiotensin-converting enzyme 2 receptor, and acute kidney injury to find the most pertinent and highest-quality of evidence. Any cited references were reviewed to identify relevant literature. The purpose of this review is to discuss, explore, and summarize the relationship between AKI in SARS-CoV-2 patients, with a focus on its epidemiology, association with ACE2 receptors, and pathophysiology of AKI.

Utilizing methylglyoxal and D-lactate in urine to evaluate saikosaponin C treatment in mice with accelerated nephrotoxic serum nephritis

The relationship between methylglyoxal (MGO) and D-lactate during saikosaponin C (SSC) treatment of mice with accelerated nephrotoxic serum (NTS) nephritis was investigated. NTS nephritis was induced by administration of anti-basement membrane antibodies to C57BL/6 mice and three dosages of SSC were administered for 14 days. Proteinuria, blood urea nitrogen, serum creatinine, renal histology, urinary MGO and d-lactate changes were examined. Compared to the NTS control group, the middle dosage (10 mg/kg/day) of SSC significantly alleviated the development of nephritis based on urine protein measurements (34.40 ± 6.85 vs. 17.33 ± 4.79 mg/day, p<0.05). Pathological observation of the glomerular basement membrane (GBM) revealed monocyte infiltration, hypertrophy, and crescents were alleviated, and injury scoring also showed improved efficacy for the middle dose of SSC during nephritis (7.92 ± 1.37 vs. 3.50 ± 1.14, p<0.05). Moreover, the significant decreases in urinary levels of MGO (24.71 ± 3.46 vs. 16.72 ± 2.36 μg/mg, p<0.05) and D-lactate (0.31 ± 0.04 vs. 0.23 ± 0.02 μmol/mg, p<0.05) were consistent with the biochemical and pathological examinations. This study demonstrates that MGO and D-lactate may reflect the extent of damage and the efficacy of SSC in NTS nephritis; further studies are required to enable clinical application.

New insight into podocyte slit diaphragm, a therapeutic target of proteinuria

Dysfunction of slit diaphragm, a cell–cell junction of glomerular podocytes, is involved in the development of proteinuria in several glomerular diseases. Slit diaphragm should be a target of a novel therapy for proteinuria. Nephrin, NEPH1, P-cadherin, FAT, and ephrin-B1 were reported to be extracellular components forming a molecular sieve of the slit diaphragm. Several cytoplasmic proteins such as ZO-1, podocin, CD2AP, MAGI proteins and Par-complex molecules were identified as scaffold proteins linking the slit diaphragm to the cytoskeleton. In this article, new insights into these molecules and the pathogenic roles of the dysfunction of these molecules were introduced. The slit diaphragm functions not only as a barrier but also as a signaling platform transfer the signal to the inside of the cell. For maintaining the slit diaphragm function properly, the phosphorylation level of nephrin is strictly regulated. The recent studies on the signaling pathway from nephrin, NEPH1, and ephrin-B1 were reviewed. Although the mechanism regulating the function of the slit diaphragm had remained unclear, recent studies revealed TRPC6 and angiotensin II-regulating mechanisms play a critical role in regulating the barrier function of the slit diaphragm. In this review, recent investigations on the regulation of the slit diaphragm function were reviewed, and a strategy for the establishment of a novel therapy for proteinuria was proposed.

Effect of shenyan xiaobai granule on nephrin and podocin of adriamycin-induced renal injury: A randomised controlled trial

ETHNOPHARMACOLOGICAL RELEVANCE

ShenYanXiaoBai granules is a traditional Chinese herbal medicine, It is used widely for the treatment of proteinuria caused by various kidney diseases.

AIM OF THE STUDY

This study investigated the mechanism of Shenyan Xiaobai Granule in the treatment of nephritis proteinuria.

MATERIALS AND METHODS

100 male wistar rats were divided into a blank group (n = 20) and a nephropathy group (n = 80) using random number table after 1 week adaptive feeded. Rats were injected with adriamycin (6.5 mg/kg) via the tail vein to induce nephropathy except for blank group. Every rat's urine protein was checked with urine protein dipstick test after three days that showed all rats in nephropathy group were successful modelled. Nephropathy group was divided into model group, benazepril group, ShenYanXiaoBai low dose group, ShenYanXiaoBai high dose group equally. Blank and model group were given distilled water 2 ml as control, then benazepril group received benazepril 0.90 mg/kg, ShenYanXiaoBai low dose group received ShenYanXiaoBai granules 1.80 g/kg as high dose group was given 3.60 g/kg, gavage for 6 days a week last for seven weeks. Urinary albumin/urinary creatinine were measured in seventh day every week. Three rats were randomly selected from each group to be executed in 3th and 5th weekend to detect the mRNA and protein expression level in kidney. The rest rats were as well.

CONCLUSIONS

The therapeutic effect of ShenYanXiaoBai high dose group was better than the two other treated groups from the 5th week to the 7th week, the comparison had a significant difference. The therapeutic effect of benazepril group was better than the ShenYanXiaoBai low dose group in the 7 weeks and the comparison had a significant difference.

A glomerulus-on-a-chip to recapitulate the human glomerular filtration barrier

In this work we model the glomerular filtration barrier, the structure responsible for filtering the blood and preventing the loss of proteins, using human podocytes and glomerular endothelial cells seeded into microfluidic chips. In long-term cultures, cells maintain their morphology, form capillary-like structures and express slit diaphragm proteins. This system recapitulates functions and structure of the glomerulus, including permselectivity. When exposed to sera from patients with anti-podocyte autoantibodies, the chips show albuminuria proportional to patients' proteinuria, phenomenon not observed with sera from healthy controls or individuals with primary podocyte defects. We also show its applicability for renal disease modeling and drug testing. A total of 2000 independent chips were analyzed, supporting high reproducibility and validation of the system for high-throughput screening of therapeutic compounds. The study of the patho-physiology of the glomerulus and identification of therapeutic targets are also feasible using this chip.

Role of Mesangial-Podocytic-Tubular Cross-Talk in IgA Nephropathy

IgA nephropathy (IgAN), a common primary glomerulonephritis worldwide, is associated with a substantial risk of progression to end-stage renal failure. The disease runs a highly variable clinical course with frequent involvement of tubulointerstitial damage. A subgroup of IgAN with proximal tubular epithelial cells (PTECs) and tubulointerstitial damage often is associated with rapid progression to end-stage renal failure. Human mesangial cell-derived mediators lead to podocyte and tubulointerstitial injury via mesangial-podocytic-tubular cross-talk. Although mesangial-podocytic communication plays a pathogenic role in podocytic injury, the implication of a podocyte-PTEC cross-talk pathway in the progression of tubulointerstitial injury in IgAN should not be underscored. We review the role of mesangial-podocytic-tubular cross-talk in the progression of IgAN. We discuss how podocytopathy in IgAN promotes subsequent PTEC dysfunction and whether tubulointerstitial injury affects the propagation of podocytic injury in IgAN. A thorough understanding of the cross-talk mechanisms among mesangial cells, podocytes, and PTECs may lead to better design of potential therapeutic options for IgAN.

Aberrant activation of Notch-1 signaling inhibits podocyte restoration after islet transplantation in a rat model of diabetic nephropathy

Signaling abnormalities play important roles during podocyte injury and have been indicated as crucial events for triggering many glomerular diseases. There is emerging evidence demonstrating significant improvements in preventing renal injury and restoring podocytes after islet transplantation. However, whether signaling abnormalities affect the therapeutic efficacy of islet transplantation remain unclear. This study was established to investigate the impact of Notch-1 signaling activation on renal injury and podocyte restoration after islet transplantation. Experiments were performed in vivo and in vitro under conditions of diabetic nephropathy and high-glucose medium, respectively. Podocyte injury in vitro was induced by high-glucose concentration, and expression levels of genes associated with the Notch-1 pathway were also regulated by Jagged-1/FC and N-[N-(3,5-Difluorophenacetyl)-L-alanyl]- S-phenylglycine t-butyl ester (DAPT). Podocytes were co-cultured with islets to investigate the protective effect of islets in high-glucose conditions. Histopathological staining and transmission electron microscopy were performed to assess pathological changes in podocytes in glomeruli. The results from this study showed that Notch-1 signaling in podocytes was significantly decreased by functional islet cells in vivo and in vitro. Compared with the co-cultured group and transplanted group, highly activated Notch-1 signaling significantly moderated the effect of islets in affecting podocyte restoration and renal injury. Renal damage and podocyte injury were alleviated after DAPT treatment. Furthermore, the balance between apoptosis and autophagy was diverse under different treatments. All the data in this study showed that highly activated Notch-1 signaling could affect the therapeutic efficacy of islet transplantation on renal injury and podocyte restoration in high-glucose conditions. The balance between apoptosis and autophagy was also closely associated with the degree of podocyte restoration. This finding may suggest that the in vivo microenvironment plays a critical role in podocyte restoration after islet transplantation, which provides a promising and individual assessment and targeting treatment for different diabetic nephropathy patients after islet transplantation into the future.

Cannabinoid-1 receptor deletion in podocytes mitigates both glomerular and tubular dysfunction in a mouse model of diabetic nephropathy

AIMS

To determine the specific role of podocyte-expressed cannabinoid-1 receptor (CB1 R) in the development of diabetic nephropathy (DN), relative to CB1 R in other renal cell types.

MATERIAL AND METHODS

We developed a mouse model with a podocyte-specific deletion of CB1 R (pCB1Rko) and challenged this model with streptozotocin (STZ)-induced type-1 DN. We also assessed the podocyte response to high glucose in vitro and its effects on CB1 R activation.

RESULTS

High glucose exposure for 48 hours led to an increase in CB1 R gene expression (CNR1) and endocannabinoid production in cultured human podocytes. This was associated with podocyte injury, reflected by decreased podocin and nephrin expression. These changes could be prevented by Cnr1-silencing, thus identifying CB1R as a key player in podocyte injury. After 12 weeks of chronic hyperglycaemia, STZ-treated pCB1Rko mice showed elevated blood glucose similar to that of their wild-type littermates. However, they displayed less albuminuria and less podocyte loss than STZ-treated wild-type mice. Unexpectedly, pCB1Rko mice also have milder tubular dysfunction, fibrosis and reduction of cortical microcirculation compared to wild-type controls, which is mediated, in part, by podocyte-derived endocannabinoids acting via CB1 R on proximal tubular cells.

CONCLUSIONS

Activation of CB1 R in podocytes contributes to both glomerular and tubular dysfunction in type-1 DN, which highlights the therapeutic potential of peripheral CB1 R blockade.

Paeoniflorin ameliorates Adriamycin-induced nephrotic syndrome through the PPARγ/ANGPTL4 pathway in vivo and vitro

Paeoniflorin (PF), an effective composition that is extracted from Radix Paeoniae Alba, plays a role in protecting against various kidney diseases. However, the mechanism of PF on nephrotic syndrome (NS) remains unclear. The aim of this study was to investigate the protective role of PF on Adriamycin (ADR)-induced NS in vivo and vitro as well as its potential mechanism. In animal study, PF significantly decreased the levels of 24-h urine protein, blood urea nitrogen, serum creatinine, total cholesterol and triglycerides in NS rats, but increased the total protein and albumin levels. Hematoxylin-eosin (HE) staining revealed that the kidney lesion was resolved upon PF treatment. After treatment with PF, the morphology and number of podocytes in renal tissue were restored to normal. PF increased expression of synaptopodin and decreased expression of desmin, demonstrating a protective effect in podocyte injury. Further studies revealed that PF upregulated Peroxisome proliferator-activated receptor gamma (PPARγ) and restrained Angiopointin-like 4 (ANGPTL4) in kidney tissue. In vitro study, PF reduced Caspase3 and Bax and increased Bcl-2, indicating that the apoptosis rate of podocytes induced by ADR was reduced by PF. Furthermore, PF ameliorated podocyte injury by upregulating synaptopodin and reducing desmin. In accordance with animal study, PF downregulated ANGPTL4 by activating PPARγ. However, the therapeutic effects of PF were reversed by GW9662 (PPARγ inhibitor), likely by suppressing ANGPTL4 degradation. In general, these results demonstrate that PF has a good therapeutic effect on NS by activating PPARγ and subsequently inhibiting ANGPTL4.

Novel Actions of Growth Hormone in Podocytes: Implications for Diabetic Nephropathy

The kidney regulates water, electrolyte, and acid-base balance and thus maintains body homeostasis. The kidney's potential to ensure ultrafiltered and almost protein-free urine is compromised in various metabolic and hormonal disorders such as diabetes mellitus (DM). Diabetic nephropathy (DN) accounts for ~20-40% of mortality in DM. Proteinuria, a hallmark of renal glomerular diseases, indicates injury to the glomerular filtration barrier (GFB). The GFB is composed of glomerular endothelium, basement membrane, and podocytes. Podocytes are terminally differentiated epithelial cells with limited ability to replicate. Podocyte shape and number are both critical for the integrity and function of the GFB. Podocytes are vulnerable to various noxious stimuli prevalent in a diabetic milieu that could provoke podocytes to undergo changes to their unique architecture and function. Effacement of podocyte foot process is a typical morphological alteration associated with proteinuria. The dedifferentiation of podocytes from epithelial-to-mesenchymal phenotype and consequential loss results in proteinuria. Poorly controlled type 1 DM is associated with elevated levels of circulating growth hormone (GH), which is implicated in the pathophysiology of various diabetic complications including DN. Recent studies demonstrate that functional GH receptors are expressed in podocytes and that GH may exert detrimental effects on the podocyte. In this review, we summarize recent advances that shed light on actions of GH on the podocyte that could play a role in the pathogenesis of DN.

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.

Nicotine Induces Podocyte Apoptosis through Increasing Oxidative Stress

Background

Cigarette 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.

Methods

To 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.

Results

Human 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.

Conclusions

Nicotine 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.

Effects of stromal interaction molecule 1 or Orai1 overexpression on the associated proteins and permeability of podocytes

AIM

The present study was conducted to determine whether two important signalling molecules of store-operated channel (SOC), stromal interaction molecule 1 (STIM1) and Orai1, were involved in glomerular podocyte injury. We explored the effects of STIM1/Orai1 overexpression on podocyte associated proteins and cell permeability.

METHODS

The expression of STIM1 and Orai1 were examined in the renal cortex of adriamycin-induced nephropathy mice by real-time RT-PCR. The recombinant plasmid of STIM1/Orai1, identified by restriction enzyme digestion and PCR, was transfected into MPC5 cells via lipofectamine 2000. The transfecting efficiency was observed by a fluorescence microscope. RT-PCR and Western blotting were used to evaluate the expression levels of STIM1, Orai 1 and some podocyte-associated molecules in the transfected MPC5 cells. In addition, we examined the diffusion of FITC-dextran across the podocyte monolayer to investigate whether STIM1/Orai1 overexpression could affect cell permeability.

RESULTS

We found that the mRNA levels of STIM1 and Orai1 were increased in adriamycin-induced nephropathy mice. STIM1/Orai1 overexpression significantly decreased the expression of podocin and CD2-associated protein (CD2AP), whereas it increased the expression of α-actinin-4. The permeability was significantly increased in the STIM1/Orai1 overexpression group.

CONCLUSION

Our findings suggested that STIM1/Orai1 overexpression could affect the cell permeability and the expression of partial podocyte-associated proteins, which may ultimately result in podocyte injury.

Wnt/β-catenin signalling and podocyte dysfunction in proteinuric kidney disease

Podocytes are unique, highly specialized, terminally differentiated cells that are integral components of the kidney glomerular filtration barrier. Podocytes are vulnerable to a variety of injuries and in response they undergo a series of changes ranging from hypertrophy, autophagy, dedifferentiation, mesenchymal transition and detachment to apoptosis, depending on the nature and extent of the insult. Emerging evidence indicates that Wnt/β-catenin signalling has a central role in mediating podocyte dysfunction and proteinuria. Wnts are induced and β-catenin is activated in podocytes in various proteinuric kidney diseases. Genetic or pharmacologic activation of β-catenin is sufficient to impair podocyte integrity and causes proteinuria in healthy mice, whereas podocyte-specific ablation of β-catenin protects against proteinuria after kidney injury. Mechanistically, Wnt/β-catenin controls the expression of several key mediators implicated in podocytopathies, including Snail1, the renin-angiotensin system and matrix metalloproteinase 7. Wnt/β-catenin also negatively regulates Wilms tumour protein, a crucial transcription factor that safeguards podocyte integrity. Targeted inhibition of Wnt/β-catenin signalling preserves podocyte integrity and ameliorates proteinuria in animal models. This Review highlights advances in our understanding of the pathomechanisms of Wnt/β-catenin signalling in mediating podocyte injury, and describes the therapeutic potential of targeting this pathway for the treatment of proteinuric kidney disease.

Therapeutic target for nephrotic syndrome: Identification of novel slit diaphragm associated molecules

The slit diaphragm bridging the neighboring foot processes functions as a final barrier of glomerular capillary wall for preventing the leak of plasma proteins into primary urine. It is now accepted that the dysfunction of the sit diaphragm contributes to the development of proteinuria in several glomerular diseases. Nephrin, a gene product of NPHS1, a gene for a congenital nephrotic syndrome of Finnish type, constitutes an extracellular domain of the slit diaphragm. Podocin was identified as a gene product of NPHS2, a gene for a familial steroid-resistant nephrotic syndrome of French. Podocin binds the cytoplasmic domain of nephrin. After then, CD2 associated protein, NEPH1 and transient receptor potential-6 were also found as crucial molecules of the slit diaphragm. In order to explore other novel molecules contributing to the development of proteinuria, we performed a subtraction hybridization assay with a normal rat glomerular RNA and a glomerular RNA of rats with a puromycin aminonucleoside nephropathy, a mimic of a human minimal change type nephrotic syndrome. Then we have found that synaptic vesicle protein 2B, ephrin-B1 and neurexin were already downregulated at the early stage of puromycin aminonucleoside nephropathy, and that these molecules were localized close to nephrin. It is conceivable that these molecules are the slit diaphragm associated molecules, which participate in the regulation of the barrier function. These molecules could be targets to establish a novel therapy for nephrotic syndrome.

Antepartum or immediate postpartum renal biopsies in preeclampsia/eclampsia of pregnancy: new morphologic and clinical findings

BACKGROUND

Preeclampsia (PE) and eclampsia remain leading causes of maternal and fetal mortality worldwide. The kidney is considered the first and most severely affected organ in women with PE/eclampsia. In this study, we analyzed new morphologic features of kidney biopsies and clinical findings in patients with PE or eclampsia at our hospital.

METHODS

Eight patients with PE/eclampsia underwent renal biopsies during the antepartum (3/8) or postpartum (5/8) period. Maternal clinical findings, major serological indices, neonatal outcomes, and renal histopathologic and immunofluorescent characteristics were reviewed for each case.

RESULTS

Most patients had abnormal serum cholesterol (8/8), triglyceride (6/8), albumin (7/8), and uric acid (5/8). The ratio of blood urea nitrogen (BUN) to serum creatinine (SCr) was elevated in all patients. Five of eight newborns survived. Various degrees of morphologic change were present in the renal glomeruli, and were associated with proteinuria. All patients had deposition of complement factor 4 (C4) in the renal glomeruli and seven had deposition of immunoglobulin M (IgM).

CONCLUSION

Endotheliosis, vacuolation of podocytes, proliferation of mesangial cells, and protein casts in the tubule lumens were found in the kidneys of women with PE/eclampsia. Immune depositions of C4 and IgM are major contributors to renal lesions in preeclamptic patients, whose neonates can generally survive. Eclampsia can occur without increased blood pressure.

Urinary podocyte excretion and proteinuria in patients treated with antivascular endothelial growth factor therapy for solid tumor malignancies

BACKGROUND

Urinary podocyte excretion (podocyturia) may function as a more specific marker of ongoing glomerular damage. This study sought to analyze the relationship between proteinuria and podocyturia in cancer patients treated with antivascular endothelial growth factor (anti-VEGF) agents.

METHODS

Thirty-seven patients treated with anti-VEGF medications were analyzed in a single-institution, cross-sectional study. Podocyte cultures were performed on random urine collections (50-100 ml), and podocytes were identified by positive podocin staining. The corresponding urine samples were analyzed for protein and creatinine (Cr) measurements.

RESULTS

Proteinuria ≥0.5 g/g Cr was found in 30% of the patients (median, 0.12; interquartile range, 0.04-0.86), and 62% had podocyturia. There was a significant difference in the amount of podocyturia between patients with proteinuria ≥0.5 g/g Cr and those with a value <0.5 g/g Cr (median podocyturia, 1.08 cells/mg Cr, range, 0-14.55 vs. 0.03 cells/mg Cr, range, 0-1.64, respectively; p < 0.001). A statistically significant correlation was observed between the cumulative dose of bevacizumab and both proteinuria (r = 0.48, p = 0.004) and podocyturia (r = 0.34, p = 0.045) as well as between proteinuria and podocyturia (r = 0.63, p < 0.001), suggesting that these are mechanistically related.

DISCUSSION

Ongoing podocyte loss may be mechanistically related to the onset and severity of proteinuria in patients treated with anti-VEGF agents.

Albuminuria and sodiuria in IUGR children

OBJECTIVE

Intrauterine growth restriction (IUGR) is associated with hyperfiltration, glomerulosclerosis and albuminuria. Albuminuria may further lead to tubulointerstitial inflammation, fibrosis and tubular atrophy. The time at which this may occur is unknown. This study was designed to assess the relationship between glomerular and tubular damage in IUGR children.

METHODS

We enrolled 50 children, 25 IUGR, categorized by estimated fetal weight <10th percentile and umbilical artery pulsatility index >2 SD, and 25 appropriate for gestational age (AGA) controls at 18 months of age. We compared albuminuria among IUGR and AGA children, to assess the relationship between albuminuria and contemporary sodium and lysozyme excretion, as a measure of tubular damage.

RESULTS

The albumin-creatinine (mg/g) and sodium-creatinine (μM/L) ratios (3.12 and 441.3, versus 1.39 and 226.1 in AGA; p = 0.002 and p = 0.012, respectively) were significantly higher in the IUGR subjects compared with AGA children, and significantly correlated (rho = 0.593, p = 0.002). Conversely, urinary lysozyme was undetectable or in normal excretion range.

CONCLUSIONS

Our results show glomerulosclerosis and albuminuria in IUGR children aged 18 months. Elevated sodium excretion in the absence of abnormal lysozymuria may represent a epiphenomenon of glomerulosclerosis and of albuminuria.

ELISA analysis of urinary nephrin and podocalyxin standardized by aquaporin-2 in adult patients with nephrotic syndrome

OBJECTIVE

To investigate urinary nephrin and podocalyxin standardized by aquaporin (AQP)-2 using the enzyme-linked immunosorbent assay (ELISA) method in adult nephrotic syndrome (NS) patients.

METHODS

In 107 adult NS patients (27 proliferative nephritis, 77 non-proliferative, and 3 amyloidosis) undergoing renal biopsy, urinary nephrin, podocalyxin and AQP2 were measured by ELISA. Urinary nephrin and podocalyxin were standardized by AQP2 (neph/AQP and PCX/AQP) and values were compared with 11 healthy controls.

RESULTS

Urinary neph/AQP correlated positively to PCX/AQP (r = 0.51, p < 0.001). Urinary neph/AQP and PCX/AQP were lower in controls than NS patients. Both proliferative and non-proliferative NS patients excreted high urinary neph/AQP and PCX/AQP without a significant difference between them (p > 0.05). Patients with focal segmental glomerular sclerosis (FSGS) excreted higher urinary neph/AQP (p = 0.09) and PCX/AQP (p < 0.05) compared to the other patients. Urinary neph/AQP and PCX/AQP were increased in the immunoglobulin M nephropathy patients. Amyloidosis patients excreted lower neph/AQP and PCX/AQP. The sensitivity was 0.87 and specificity 0.37 when the neph/AQP borderline value of 0.16 was adopted [area under the curve (AUC) = 0.61]. The sensitivity was 0.74 and specificity 0.61 when the PCX/AQP borderline value was 3.06 (AUC = 0.69).

CONCLUSIONS

Urinary neph/AQP and PCX/AQP are increased in NS patients, with FSGS patients showing the highest levels. To distinguish FSGS from other NS forms, the measurement of urinary PCX/AQP may be a practical method, and superior to neph/AQP.

A compendium of urinary biomarkers indicative of glomerular podocytopathy

It is well known that glomerular podocyte injury and loss are present in numerous nephropathies and that the pathophysiologic consecution of disease hinges upon the fate of the podocyte. While multiple factors play a hand in glomerulopathy progression, basic logic lends that if one monitors the podocyte's status, that may reflect the status of disease. Recent investigations have focused on what one can elucidate from the noninvasive collection of urine, and have proven that certain, specific biomarkers of podocytes can be readily identified via varying techniques. This paper has brought together all described urinary biomarkers of podocyte injury and is made to provide a concise summary of their utility and testing in laboratory and clinical theatres. While promising in the potential that they hold as tools for clinicians and investigators, the described biomarkers require further comprehensive vetting in the form of larger clinical trials and studies that would give their value true weight. These urinary biomarkers are put forth as novel indicators of glomerular disease presence, disease progression, and therapeutic efficacy that in some cases may be more advantageous than the established parameters/measures currently used in practice.

Calcitriol, calcidiol, parathyroid hormone, and fibroblast growth factor-23 interactions in chronic kidney disease

Objective

To review the inter-relationships between calcium, phosphorus, parathyroid hormone (PTH), parent and activated vitamin D metabolites (vitamin D, 25(OH)-vitamin D, 1,25(OH)₂-vitamin D, 24,25(OH)₂-vitamin D), and fibroblast growth factor-23 (FGF-23) during chronic kidney disease (CKD) in dogs and cats.

Data Sources

Human and veterinary literature.

Human Data Synthesis

Beneficial effects of calcitriol treatment during CKD have traditionally been attributed to regulation of PTH but new perspectives emphasize direct renoprotective actions independent of PTH and calcium. It is now apparent that calcitriol exerts an important effect on renal tubular reclamation of filtered 25(OH)-vitamin D, which may be important in maintaining adequate circulating 25(OH)-vitamin D. This in turn may be vital for important pleiotropic actions in peripheral tissues through autocrine/paracrine mechanisms that impact the health of those local tissues.

Veterinary Data Synthesis

Limited information is available reporting the benefit of calcitriol treatment in dogs and cats with CKD.

Conclusions

A survival benefit has been shown for dogs with CKD treated with calcitriol compared to placebo. The concentrations of circulating 25(OH)-vitamin D have recently been shown to be low in people and dogs with CKD and are related to survival in people with CKD. Combination therapy for people with CKD using both parental and activated vitamin D compounds is common in human nephrology and there is a developing emphasis using combination treatment with activated vitamin D and renin-angiotensin-aldosterone-system (RAAS) inhibitors.

Renal albumin filtration: alternative models to the standard physical barriers

Human kidneys produce more than 4 million litres of virtually protein-free primary urine in a lifetime. In healthy individuals, the sieving process is accomplished by the glomerular filter without the smallest sign of clogging, even in old age. How nature accomplishes this extraordinary task is a mystery, but unravelling the functioning of the glomerular filter is important. The basic principles that govern glomerular filtration are probably also true for peripheral filtering by fenestrated capillaries. In addition, understanding the sieving process is a prerequisite to understanding the pathogenesis of proteinuria (that is, the leakage of plasma proteins into the urine). Proteinuria is the hallmark of glomerular disease and a major risk factor for systemic cardiovascular complications, a fact that emphasizes the relationship between the glomerular and peripheral filtering capillaries. In this Review, we briefly summarize the major models that have been proposed for the mechanisms of glomerular filtration and discuss their strengths and limitations. A special emphasis is placed on the 'electrokinetic model' that we have proposed, a model that could potentially resolve many of the seemingly strange characteristics of the glomerular filtration barrier.

The glomerular filtration barrier function: new concepts

PURPOSE OF REVIEW

Each day, the human kidneys filter about 140 l of primary urine from plasma. Although this ultrafiltrate is virtually free of plasma protein, the glomerular filter never clogs under physiological conditions. Upto today it is still not entirely resolved as to how the kidney accomplishes this extraordinary task. Most of the proposed models for glomerular filtration have not considered electrical effects.

RECENT FINDINGS

In micropuncture studies, we have directly measured an electrical field across the glomerular filtration barrier. This potential difference is most likely generated by forced passage of the ionic solution of the plasma across the charged glomerular filter ('electrokinetic potential'). As all plasma proteins are negatively charged, the electrical field across the glomerular filtration barrier is predicted to drive plasma proteins from the filter toward the capillary lumen by electrophoresis.

SUMMARY

In this review, we examine our novel model for glomerular filtration in more detail. We outline the physical mechanisms by which electrokinetic effects (streaming potentials) are generated. We investigate the potential impact of the electrical field on the passage of albumin across the glomerular filtration barrier. We review the mathematical heteroporous model including electrical effects and analyse a selection of experimental studies for indications that electrical effects influence glomerular permeability significantly.

A pilot trial assessing urinary gene expression profiling with an mRNA array for diabetic nephropathy

Background

The initiation and progression of diabetic nephropathy (DN) is complex. Quantification of mRNA expression in urinary sediment has emerged as a novel strategy for studying renal diseases. Considering the numerous molecules involved in DN development, a high-throughput platform with parallel detection of multiple mRNAs is needed. In this study, we constructed a self-assembling mRNA array to analyze urinary mRNAs in DN patients with aims to reveal its potential in searching novel biomarkers.

Methods

mRNA array containing 88 genes were fabricated and its performance was evaluated. A pilot study with 9 subjects including 6 DN patients and 3 normal controls were studied with the array. DN patients were assigned into two groups according to their estimate glomerular rate (eGFR): DNI group (eGFR>60 ml/min/1.73 m², n = 3) and DNII group (eGFR<60 ml/min/1.73 m², n = 3). Urinary cell pellet was collected from each study participant. Relative abundance of these target mRNAs from urinary pellet was quantified with the array.

Results

The array we fabricated displayed high sensitivity and specificity. Moreover, the Cts of Positive PCR Controls in our experiments were 24±0.5 which indicated high repeatability of the array. A total of 29 mRNAs were significantly increased in DN patients compared with controls (p<0.05). Among these genes, α-actinin4, CDH2, ACE, FAT1, synaptopodin, COL4α, twist, NOTCH3 mRNA expression were 15-fold higher than those in normal controls. In contrast, urinary TIMP-1 mRNA was significantly decreased in DN patients (p<0.05). It was shown that CTGF, MCP-1, PAI-1, ACE, CDH1, CDH2 mRNA varied significantly among the 3 study groups, and their mRNA levels increased with DN progression (p<0.05).

Conclusion

Our pilot study demonstrated that mRNA array might serve as a high-throughput and sensitive tool for detecting mRNA expression in urinary sediment. Thus, this primary study indicated that mRNA array probably could be a useful tool for searching new biomarkers for DN.