Podocyte-Parietal Epithelial Cell Interdependence in Glomerular Development and Disease

Podocytes and parietal epithelial cells (PECs) are among the few principal cell types within the kidney glomerulus, the former serving as a crucial constituent of the kidney filtration barrier and the latter representing a supporting epithelial layer that adorns the inner wall of Bowman's capsule. Podocytes and PECs share a circumscript developmental lineage that only begins to diverge during the S-shaped body stage of nephron formation-occurring immediately before the emergence of the fully mature nephron. These two cell types, therefore, share a highly conserved gene expression program, evidenced by recently discovered intermediate cell types occupying a distinct spatiotemporal gene expression zone between podocytes and PECs. In addition to their homeostatic functions, podocytes and PECs also have roles in kidney pathogenesis. Rapid podocyte loss in diseases, such as rapidly progressive GN and collapsing and cellular subtypes of FSGS, is closely allied with PEC proliferation and migration toward the capillary tuft, resulting in the formation of crescents and pseudocrescents. PECs are thought to contribute to disease progression and severity, and the interdependence between these two cell types during development and in various manifestations of kidney pathology is the primary focus of this review.

Novel therapeutic perspectives for crescentic glomerulonephritis through targeting parietal epithelial cell activation and proliferation

INTRODUCTION

Kidney injury is clinically classified as crescentic glomerulonephritis (CrGN) when ≥50% of the glomeruli in a biopsy sample contain crescentic lesions. However, current strategies, such as systemic immunosuppressive therapy and plasmapheresis for CrGN, are partially effective, and these drugs have considerable systemic side effects. Hence, targeted therapy to prevent glomerular crescent formation and expansion remains an unmet clinical need.

AREAS COVERED

Hyperproliferative parietal epithelial cells (PECs) are the main constituent cells of the glomerular crescent with cell-tracing evidence. Crescents obstruct the flow of primary urine, pressure the capillaries, and degenerate the affected nephrons. We reviewed the markers of PEC activation and proliferation, potential therapeutic effects of thrombin and thrombin receptor inhibitors, and how podocytes cross-talk with PECs. These experiments may help identify potential early specific targets for the prevention and treatment of glomerular crescentic injury.

EXPERT OPINION

Inhibiting PEC activation and proliferation in CrGN can alleviate glomerular crescent progression, which has been supported by preclinical studies with evidence of genetic deletion. Clarifying the outcome of PEC transformation to the podocyte phenotype and suppressing thrombin, thrombin receptors, and PEC hyperproliferation in early therapeutic strategies will be the research goals in the next ten years.

The Role of Parietal Epithelial Cells in the Pathogenesis of Podocytopathy

Podocytopathy is the most common feature of glomerular disorder characterized by podocyte injury- or dysfunction-induced excessive proteinuria, which ultimately develops into glomerulosclerosis and results in persistent loss of renal function. Due to the lack of self-renewal ability of podocytes, mild podocyte depletion triggers replacement and repair processes mostly driven by stem cells or resident parietal epithelial cells (PECs). In contrast, when podocyte recovery fails, activated PECs contribute to the establishment of glomerular lesions. Increasing evidence suggests that PECs, more than just bystanders, have a crucial role in various podocytopathies, including minimal change disease, focal segmental glomerulosclerosis, membranous nephropathy, diabetic nephropathy, IgA nephropathy, and lupus podocytopathy. In this review, we attempt to dissect the diverse role of PECs in the pathogenesis of podocytopathy based on currently available information.

CCN2 Binds to Tubular Epithelial Cells in the Kidney

Cellular communication network-2 (CCN2), also called connective tissue growth factor (CTGF), is considered a fibrotic biomarker and has been suggested as a potential therapeutic target for kidney pathologies. CCN2 is a matricellular protein with four distinct structural modules that can exert a dual function as a matricellular protein and as a growth factor. Previous experiments using surface plasmon resonance and cultured renal cells have demonstrated that the C-terminal module of CCN2 (CCN2(IV)) interacts with the epidermal growth factor receptor (EGFR). Moreover, CCN2(IV) activates proinflammatory and profibrotic responses in the mouse kidney. The aim of this paper was to locate the in vivo cellular CCN2/EGFR binding sites in the kidney. To this aim, the C-terminal module CCN2(IV) was labeled with a fluorophore (Cy5), and two different administration routes were employed. Both intraperitoneal and direct intra-renal injection of Cy5-CCN2(IV) in mice demonstrated that CCN2(IV) preferentially binds to the tubular epithelial cells, while no signal was detected in glomeruli. Moreover, co-localization of Cy5-CCN2(IV) binding and activated EGFR was found in tubules. In cultured tubular epithelial cells, live-cell confocal microscopy experiments showed that EGFR gene silencing blocked Cy5-CCN2(IV) binding to tubuloepithelial cells. These data clearly show the existence of CCN2/EGFR binding sites in the kidney, mainly in tubular epithelial cells. In conclusion, these studies show that circulating CCN2(IV) can directly bind and activate tubular cells, supporting the role of CCN2 as a growth factor involved in kidney damage progression.

DR1 activation promotes vascular smooth muscle cell apoptosis via up-regulation of CSE/H2 S pathway in diabetic mice

The important role of hydrogen sulfide (H₂ S) as a novel gasotransmitter in inhibiting proliferation and promoting apoptosis of vascular smooth muscle cells (VSMCs) has been widely recognized. The dopamine D1 receptor (DR1), a G protein coupled receptor, inhibits atherosclerosis by suppressing VSMC proliferation. However, whether DR1 contributes to VSMC apoptosis via the induction of endogenous H₂ S in diabetic mice is unclear. Here, we found that hyperglycemia decreased the expressions of DR1 and cystathionine-γ-lyase (CSE, a key enzyme for endogenous H₂ S production) and reduced endogenous H₂ S generation in mouse arteries and cultured VSMCs. DR1 agonist SKF38393 increased DR1 and CSE expressions and stimulated endogenous H₂ S generation. Sodium hydrosulfide (NaHS, a H₂ S donor) increased CSE expressions and H₂ S generation but had no effect on DR1 expression. In addition, high glucose (HG) increased VSMC apoptosis, up-regulated IGF-1-IGF-1R and HB-EGF-EGFR, and stimulated ERK1/2 and PI3K-Akt pathways. Overexpression of DR1, the addition of SKF38393 or supply of NaHS further promoted VSMC apoptosis and down-regulated the above pathways. Knock out of CSE or the addition of the CSE inhibitor poly propylene glycol diminished the effect of SKF38393. Moreover, calmodulin (CaM) interacted with CSE in VSMCs; HG increased intracellular Ca²⁺ concentration and induced CaM expression, further strengthened the interaction of CaM with CSE in VSMCs, which were further enhanced by SKF38393. CaM inhibitor W-7, inositol 1,4,5-trisphosphate (IP₃ ) inhibitor 2-APB, or ryanodine receptor inhibitor tetracaine abolished the stimulatory effect of SKF38393 on CaM expression and intracellular Ca²⁺ concentration. Taken together, these results suggest that DR1 up-regulates CSE/H₂ S signaling by inducing the Ca²⁺ -CaM pathway followed by down-regulations of IGF-1-IGF-1R and HB-EGF-EGFR and their downstream ERK1/2 and PI3K-Akt, finally promoting the apoptosis of VSMCs in diabetic mice.

Renal Safety Profile of EGFR Targeted Therapies: A Study from VigiBase® the WHO Global Database of Individual Case Safety Reports

Kidney EGFR expression together with reported cases of glomerular diseases in the context of anti-EGFR drug administration raise concerns about the renal safety profile of these drugs. This issue is addressed in a case/non-case study carried out on VigiBase®, the WHO global database of individual case safety reports (ICRS). Disproportionality analysis of renal adverse effects related to the selected anti-EGFR drugs, erlotinib, gefitinib, afatinib, osimertinib, cetuximab and panitumumab, was assessed using the reporting odds ratio (ROR). Nine hundred and eighty-nine ICRSs were included. A signal of disproportionate reporting (SDR) was found for afatinib (ROR = 2.70; 95% CI [2.22-3.29]) and erlotinib (ROR = 1.73; 95% CI [1.46-2.04]) with acute kidney injury, and for afatinib (ROR = 2.41; 95% CI [1.78-3.27]), cetuximab (ROR = 1.42; 95% CI [1.14-1.78]) and erlotinib (ROR = 2.23; 95% CI [1.80-2.77]) with renal failure. The preferred term "diarrhoea" was frequently reported in the included cases. An SDR was found for erlotinib with haemolytic and uremic syndrome (ROR = 4.01; 95% CI [1.80-8.94]) and thrombotic microangiopathy (ROR = 4.94; 95% CI [2.80-8.72]). No SDR was seen for glomerular or tubule-interstitial diseases. This study showed that the anti-EGFR drug renal toxicity is mainly related to renal failure in the context of digestive toxicity.

The recruitment mechanisms and potential therapeutic targets of podocytes from parietal epithelial cells

Podocytes are differentiated postmitotic cells which cannot be replaced after podocyte injury. The mechanism of podocyte repopulation after injury has aroused wide concern. Parietal epithelial cells (PECs) are heterogeneous and only a specific subpopulation of PECs has the capacity to replace podocytes. Major progress has been achieved in recent years regarding the role and function of a subset of PECs which could transdifferentiate toward podocytes. Additionally, several factors, such as Notch, Wnt/ß-catenin, Wilms’ tumor-1, miR-193a and growth arrest-specific protein 1, have been shown to be involved in these processes. Finally, PECs serve as a potential therapeutic target in the conditions of podocyte loss. In this review, we discuss the latest observations and concepts about the recruitment of podocytes from PECs in glomerular diseases as well as newly identified mechanisms and the most recent treatments for this process.

Interplay between extracellular matrix components and cellular and molecular mechanisms in kidney fibrosis

Chronic kidney disease (CKD) is characterized by pathological accumulation of extracellular matrix (ECM) proteins in renal structures. Tubulointerstitial fibrosis is observed in glomerular diseases as well as in the regeneration failure of acute kidney injury (AKI). Therefore, finding antifibrotic therapies comprises an intensive research field in Nephrology. Nowadays, ECM is not only considered as a cellular scaffold, but also exerts important cellular functions. In this review, we describe the cellular and molecular mechanisms involved in kidney fibrosis, paying particular attention to ECM components, profibrotic factors and cell-matrix interactions. In response to kidney damage, activation of glomerular and/or tubular cells may induce aberrant phenotypes characterized by overproduction of proinflammatory and profibrotic factors, and thus contribute to CKD progression. Among ECM components, matricellular proteins can regulate cell-ECM interactions, as well as cellular phenotype changes. Regarding kidney fibrosis, one of the most studied matricellular proteins is cellular communication network-2 (CCN2), also called connective tissue growth factor (CTGF), currently considered as a fibrotic marker and a potential therapeutic target. Integrins connect the ECM proteins to the actin cytoskeleton and several downstream signaling pathways that enable cells to respond to external stimuli in a coordinated manner and maintain optimal tissue stiffness. In kidney fibrosis, there is an increase in ECM deposition, lower ECM degradation and ECM proteins cross-linking, leading to an alteration in the tissue mechanical properties and their responses to injurious stimuli. A better understanding of these complex cellular and molecular events could help us to improve the antifibrotic therapies for CKD.

Prevalence of clinical, pathological and molecular features of glomerular basement membrane nephropathy caused by COL4A3 or COL4A4 mutations: a systematic review

BACKGROUND

Patients heterozygous for COL4A3 or COL4A4 mutations show a wide spectrum of disease, extending from familial isolated microscopic haematuria, as a result of thin basement membranes (TBMs), to autosomal dominant Alport syndrome (ADAS) and end-stage renal disease (ESRD). Many patients are mentioned in the literature under the descriptive diagnosis of TBM nephropathy (TBMN), in which case it actually describes a histological finding that represents the carriers of autosomal recessive Alport syndrome (ARAS), a severe glomerulopathy, as most patients reach ESRD at a mean age of 25 years.

METHODS

We performed a systematic literature review for patients with heterozygous COL4A3/A4 mutations with the aim of recording the spectrum and frequency of pathological features. We searched three databases (PubMed, Embase and Scopus) using the keywords 'Autosomal Dominant Alport Syndrome' OR 'Thin Basement Membrane Disease' OR 'Thin Basement Membrane Nephropathy'. We identified 48 publications reporting on 777 patients from 258 families.

RESULTS

In total, 29% of the patients developed chronic kidney disease (CKD) and 15.1% reached ESRD at a mean age of 52.8 years. Extrarenal features and typical Alport syndrome (AS) findings had a low prevalence in patients as follows: hearing loss, 16%; ocular lesions, 3%; basement membrane thickening, 18.4%; and podocyte foot process effacement, 6.9%. Data for 76 patients from 54 families emphasize extensive inter- and intrafamilial heterogeneity, with age at onset of ESRD ranging between 21 and 84 years (mean 52.8).

CONCLUSIONS

The analysis enabled a comparison of the clinical course of patients with typical ARAS or X-linked AS with those with heterozygous COL4A mutations diagnosed with TBMN or ADAS. Despite the consequence of a potential ascertainment bias, an important outcome is that TBM poses a global high risk of developing severe CKD, over a long follow-up, with a variable spectrum of other findings. The results are useful to practicing nephrologists for better evaluation of patients.

Association between epidermal growth factor (EGF) and EGF receptor gene polymorphisms and end-stage renal disease and acute renal allograft rejection in a Korean population

Purpose

Epidermal growth factor (EGF) has been found to be associated with the development and repair mechanisms of several renal diseases. In this study, we hypothesized that single nucleotide polymorphisms (SNPs) in EGF or its receptor genes might have an association with end-stage renal disease (ESRD) or acute renal allograft rejection (AR) in a Korean population.

Methods

Three-hundred and forty seven recipients of the first renal transplants for ESRD, including 63 AR patients along with 289 healthy adults were included in the study. Five EGF gene SNPs (rs11568835, rs11568943, rs2237051, rs11569017, and rs3756261) and four EGFR gene SNPs (rs1140475, rs2293347, rs1050171, and rs6965469) were analyzed. The genotypes of these SNPs were analyzed using the AxiomTM genome-wide human assay. Statistical analysis was performed using SNPStats and Haploview version 4.2 software. Multiple logistic regression models (codominant, dominant, recessive, and Log-additive) were used to estimate the odds ratio (OR), 95% confidence interval (CI), and P value.

Results

One SNP (rs11569017) in the EGF gene showed significant association with ESRD but not with AR. Another SNP (rs11568835) in the EGF gene showed significant association with susceptibility to AR but not with ESRD. One SNP (rs1050171) in the EGFR gene showed significant association with susceptibility to AR but not with ESRD.

Conclusion

Our findings suggest that SNPs in the EGF and EGFR gene may be associated with the risk of ESRD and AR development in the Korean population.

Local miscommunications between glomerular cells as potential therapeutic targets for crescentic glomerulonephritides

Necrotizing and crescentic rapidly progressive glomerulonephritis or crescentic glomerulonephritis is one of the severest forms of acquired glomerular diseases with significant mortality. Risk of end-stage renal failure at 5 years is near 30%, with a number of patients developing chronic kidney disease. Currently, autoimmune crescentic glomerulonephritides are treated with broad-spectrum immunosuppression inducing remission of the injury in the majority of patients. However, treatment is associated with significant side effects and by the time remission is achieved the majority of patients have developed renal tissue damage and significant impairment of their kidney function with a steep slope of deterioration within the first weeks following initiation of immunosuppression. It is therefore important to develop complementary strategies that would be immediately active on the common process of destructive epithelial processes. We have worked to identify the major cellular pathways contributing to glomerular destruction in this context by a systematic comparison of patient tissues and experimental models. Our studies demonstrate the pivotal role of local intra- and intercellular communications in orchestrating the global glomerular tolerance to a severe rapidly progressive glomerulonephritis model with excellent anatomoclinical correlative expressions in kidney biopsies of individuals diagnosed with crescentic glomerulonephritis, irrespectively of the causal immune disorder. We hope that such approaches deciphering mechanisms of cellular adaptation that underlie kidney damage control in response to vasculitides, integrating both stress and damage responses, will delineate novel complementary therapies.

Role of Epidermal Growth Factor Receptor (EGFR) and Its Ligands in Kidney Inflammation and Damage

Chronic kidney disease (CKD) is characterized by persistent inflammation and progressive fibrosis, ultimately leading to end-stage renal disease. Although many studies have investigated the factors involved in the progressive deterioration of renal function, current therapeutic strategies only delay disease progression, leaving an unmet need for effective therapeutic interventions that target the cause behind the inflammatory process and could slow down or reverse the development and progression of CKD. Epidermal growth factor receptor (EGFR) (ERBB1), a membrane tyrosine kinase receptor expressed in the kidney, is activated after renal damage, and preclinical studies have evidenced its potential as a therapeutic target in CKD therapy. To date, seven official EGFR ligands have been described, including epidermal growth factor (EGF) (canonical ligand), transforming growth factor-α, heparin-binding epidermal growth factor, amphiregulin, betacellulin, epiregulin, and epigen. Recently, the connective tissue growth factor (CTGF/CCN2) has been described as a novel EGFR ligand. The direct activation of EGFR by its ligands can exert different cellular responses, depending on the specific ligand, tissue, and pathological condition. Among all EGFR ligands, CTGF/CCN2 is of special relevance in CKD. This growth factor, by binding to EGFR and downstream signaling pathway activation, regulates renal inflammation, cell growth, and fibrosis. EGFR can also be “transactivated” by extracellular stimuli, including several key factors involved in renal disease, such as angiotensin II, transforming growth factor beta (TGFB), and other cytokines, including members of the tumor necrosis factor superfamily, showing another important mechanism involved in renal pathology. The aim of this review is to summarize the contribution of EGFR pathway activation in experimental kidney damage, with special attention to the regulation of the inflammatory response and the role of some EGFR ligands in this process. Better insights in EGFR signaling in renal disease could improve our current knowledge of renal pathology contributing to therapeutic strategies for CKD development and progression.

Connective tissue growth factor induces renal fibrosis via epidermal growth factor receptor activation

Connective tissue growth factor (CCN2/CTGF) is a matricellular protein that is overexpressed in progressive human renal diseases, mainly in fibrotic areas. In vitro studies have demonstrated that CCN2 regulates the production of extracellular matrix (ECM) proteins and epithelial-mesenchymal transition (EMT), and could therefore contribute to renal fibrosis. CCN2 blockade ameliorates experimental renal damage, including diminution of ECM accumulation. We have reported that CCN2 and its C-terminal degradation product CCN2(IV) bind to epidermal growth factor receptor (EGFR) to modulate renal inflammation. However, the receptor involved in CCN2 profibrotic actions has not been described so far. Using a murine model of systemic administration of CCN2(IV), we have unveiled a fibrotic response in the kidney that was diminished by EGFR blockade. Additionally, in conditional CCN2 knockout mice, renal fibrosis elicited by folic acid-induced renal damage was prevented, and this was linked to inhibition of EGFR pathway activation. Our in vitro studies demonstrated a direct effect of CCN2 via the EGFR pathway on ECM production by fibroblasts and the induction of EMT in tubular epithelial cells. Our studies clearly show that the EGFR regulates CCN2 fibrotic signalling in the kidney, and suggest that EGFR pathway blockade could be a potential therapeutic option to block CCN2-mediated profibrotic effects in renal diseases. Copyright © 2017 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Targeting the tyrosine kinase signalling pathways for treatment of immune-mediated glomerulonephritis: from bench to bedside and beyond

Glomerulonephritis (GN) affects patients of all ages and is an important cause of morbidity and mortality. Non-selective immunosuppressive drugs have been used in immune-mediated GN but often result in systemic side effects and occasionally fatal infective complications. There is increasing evidence from both preclinical and clinical studies that abnormal activation of receptor and non-receptor tyrosine kinase signalling pathways are implicated in the pathogenesis of immune-mediated GN. Activation of spleen tyrosine kinase (SYK), Bruton's tyrosine kinase (BTK), platelet-derived growth factor receptor (PDGFR), epidermal growth factor receptor (EGFR) and discoidin domain receptor 1 (DDR1) have been demonstrated in anti-GBM disease. SYK is implicated in the pathogenesis of ANCA-associated GN. SYK, BTK, PDGFR, EFGR, DDR1 and Janus kinase are implicated in the pathogenesis of lupus nephritis. A representative animal model of IgA nephropathy (IgAN) is lacking. Based on the results from in vitro and human renal biopsy study results, a phase II clinical trial is ongoing to evaluate the efficacy and safety of fostamatinib (an oral SYK inhibitor) in high-risk IgAN patient. Various tyrosine kinase inhibitors (TKIs) have been approved for cancer treatment. Clinical trials of TKIs in GN may be justified given their long-term safety data. In this review we will discuss the current unmet medical needs in GN treatment and research as well as the current stage of development of TKIs in GN treatment and propose an accelerated translational research approach to investigate whether selective inhibition of tyrosine kinase provides a safer and more efficacious option for GN treatment.

Cetuximab Prevents Methotrexate-Induced Cytotoxicity in Vitro through Epidermal Growth Factor Dependent Regulation of Renal Drug Transporters

The combination of methotrexate with epidermal growth factor receptor (EGFR) recombinant antibody, cetuximab, is currently being investigated in treatment of head and neck carcinoma. As methotrexate is cleared by renal excretion, we studied the effect of cetuximab on renal methotrexate handling. We used human conditionally immortalized proximal tubule epithelial cells overexpressing either organic anion transporter 1 or 3 (ciPTEC-OAT1/ciPTEC-OAT3) to examine OAT1 and OAT3, and the efflux pumps breast cancer resistance protein (BCRP), multidrug resistance protein 4 (MRP4), and P-glycoprotein (P-gp) in methotrexate handling upon EGF or cetuximab treatment. Protein kinase microarrays and knowledge-based pathway analysis were used to predict EGFR-mediated transporter regulation. Cytotoxic effects of methotrexate were evaluated using the dimethylthiazol bromide (MTT) viability assay. Methotrexate inhibited OAT-mediated fluorescein uptake and decreased efflux of Hoechst33342 and glutathione-methylfluorescein (GS-MF), which suggested involvement of OAT1/3, BCRP, and MRP4 in transepithelial transport, respectively. Cetuximab reversed the EGF-increased expression of OAT1 and BCRP as well as their membrane expressions and transport activities, while MRP4 and P-gp were increased. Pathway analysis predicted cetuximab-induced modulation of PKC and PI3K pathways downstream EGFR/ERBB2/PLCg. Pharmacological inhibition of ERK decreased expression of OAT1 and BCRP, while P-gp and MRP4 were increased. AKT inhibition reduced all transporters. Exposure to methotrexate for 24 h led to a decreased viability, an effect that was reversed by cetuximab. In conclusion, cetuximab downregulates OAT1 and BCRP while upregulating P-gp and MRP4 through an EGFR-mediated regulation of PI3K-AKT and MAPKK-ERK pathways. Consequently, cetuximab attenuates methotrexate-induced cytotoxicity, which opens possibilities for further research into nephroprotective comedication therapies.

Epidermal growth factor receptor signaling mediates aldosterone-induced profibrotic responses in kidney

Aldosterone has been recognized as a risk factor for the development of chronic kidney disease (CKD). Studies have indicated that enhanced activation of epidermal growth factor receptor (EGFR) is associated with the development and progression of renal fibrosis. But if EGFR is involved in aldosterone-induced renal fibrosis is less investigated. In the present study, we examined the effect of erlotinib, an inhibitor of EGFR tyrosine kinase activity, on the progression of aldosterone-induced renal profibrotic responses in a murine model underwent uninephrectomy. Erlotinib-treated rats exhibited relieved structural lesion comparing with rats treated with aldosterone alone, as characterized by glomerular hypertrophy, mesangial cell proliferation and expansion. Also, erlotinib inhibited the expression of TGF-β, α-SMA and mesangial matrix proteins such as collagen Ⅳ and fibronectin. In cultured mesangial cells, inhibition of EGFR also abrogated aldosterone-induced expression of extracellular matrix proteins, cell proliferation and migration. We also demonstrated that aldosterone induced the phosphorylation of EGFR through generation of ROS. And the activation of EGFR resulted in the phosphorylation of ERK1/2, leading to the activation of profibrotic pathways. Taken together, we concluded that aldosterone-mediated tissue fibrosis relies on ROS induced EGFR/ERK activation, highlighting EGFR as a potential therapeutic target for modulating renal fibrosis.

Differential urinary glycoproteome analysis of type 2 diabetic nephropathy using 2D-LC-MS/MS and iTRAQ quantification

Background

Diabetic nephropathy (DN) is the leading cause of chronic kidney failure and end-stage kidney disease. More accurate and non-invasive test for the diagnosis and monitoring the progression of DN is urgently needed for the better care of such patients.

Methods

In this study we utilized urinary glycoproteome to discover the differential proteins during the course of type 2 DN. The urinary glycoproteins from normal controls, normalbuminuira, microalbuminura, and macroalbuminuria patients were enriched by concanavalin A (ConA) and analyzed by 2DLC/MS/MS and isobaric tags for relative and absolute quantitation quantification.

Results

A total of 478 proteins were identified and 408 were annotated as N-linked glycoproteins. A total of 72, 107 and 123 differential proteins were identified in normalbuminuria, microalbuminuria and macroalbuminuria, respectively. By bioinformatics analysis, in normalbuminruia state, cell proliferation and cell movement were activated, which might reflect the compensatory phase during the disease development. In micro- and macro-albuminuria, cell death and apoptosis was activated, which might reflect the de-compensatory phase. Pathway analysis showed acute phase proteins, the member of high density lipoprotein and low density lipoprotein proteins were changed, indicating the role of the inflammatory response and lipid metabolism abnormality in the pathogenesis of DN. Six selected differential proteins were validated by Western Blot. Alpha-1-antitrypsin (SERPINA1) and Ceruloplasmin are the two markers with excellent area under curve values (0.929 and 1.000 respectively) to distinguish the microalbuminuria and normalbuminuria. For the first time, we found pro-epidermal growth factor and prolactin-inducible protein were decreased in macroalbuminuria stage, which might reflect the inhibition of cell viability and the activation of cell death in kidney.

Conclusions

Above data indicated that urinary glycoproteome could be useful to distinguish the differences in protein profiles in different stages in DN, which will help better individualized care of patients in DN.

Electronic supplementary material

The online version of this article (doi:10.1186/s12967-015-0712-9) contains supplementary material, which is available to authorized users.

Epidermal growth factor receptor inhibition with erlotinib ameliorates anti-Thy 1.1-induced experimental glomerulonephritis

BACKGROUND

Mesangial proliferative glomerulonephritis is a common glomerular disorder that may lead to end-stage renal disease. Epidermal growth factor (EGF) plays an important role in the regulation of cell growth, proliferation, and differentiation and in the pathology of various renal diseases. Erlotinib is a novel, oral, highly selective tyrosine kinase inhibitor of the EGF receptor. It is clinically used to treat non-small cell lung and pancreatic cancers. Here, we investigated the effect of erlotinib on the progression of mesangioproliferative glomerulonephritis in an experimental model.

METHODS

Mesangial glomerulonephritis was induced with anti-rat Thy-1.1 antibody in male Wistar rats weighing 150-160 g. Rats were treated with erlotinib (10 mg/kg/day p.o.) or vehicle only (polyethylene glycol). Native Wistar rat kidneys were used as histological controls. Serum creatinine levels were measured at day 7. Kidneys were harvested 7 days after antibody administration for histology.

RESULTS

Native controls showed no histological signs of glomerular pathology. In the vehicle group, intense glomerular inflammation developed after 7 days and prominent mesangial cell proliferation and glomerular matrix accumulation was seen. Erlotinib was well tolerated and there were no adverse effects during the follow-up period. Erlotinib significantly prevented progression of the glomerular inflammatory response and glomerular mesangial cell proliferation as well as matrix accumulation when compared with the vehicle group. Erlotinib also preserved renal function.

CONCLUSION

These results indicate that erlotinib prevents the early events of experimental mesangial proliferative glomerulonephritis. Therefore, inhibition of the EGF receptor with erlotinib could prevent the progression of glomerulonephritis also in clinical nephrology.

New insights into glomerular parietal epithelial cell activation and its signaling pathways in glomerular diseases

The glomerular parietal epithelial cells (PECs) have aroused an increasing attention recently. The proliferation of PECs is the main feature of crescentic glomerulonephritis; besides that, in the past decade, PEC activation has been identified in several types of noninflammatory glomerulonephropathies, such as focal segmental glomerulosclerosis, diabetic glomerulopathy, and membranous nephropathy. The pathogenesis of PEC activation is poorly understood; however, a few studies delicately elucidate the potential mechanisms and signaling pathways implicated in these processes. In this review we will focus on the latest observations and concepts about PEC activation in glomerular diseases and the newest identified signaling pathways in PEC activation.

What is new in the management of rapidly progressive glomerulonephritis?

Rapidly progressive glomerulonephritis (RPGN) results from severe crescentic damage to glomeruli and leads to irreversible kidney failure if not diagnosed and managed in a timely fashion. Traditional treatment has relied on glucocorticoids and cyclophosphamide, with additional plasmapheresis for certain conditions. Here we describe updates in the management of RPGN, according to the underlying renal pathology. However, there remains a paucity of trials that have enrolled patients with more advanced renal disease, dialysis dependence or with RPGN, and we are therefore still reliant on extrapolation of data from studies of patients with a less severe form of disease. In addition, reporting bias results in publication of cases or cohorts showing benefit for newer agents in advanced disease or RPGN, but it remains unclear how many unsuccessful outcomes in these circumstances take place. Since clinical trials specifically in RPGN are unlikely, use of biologic registries or combination of sufficient sized cohort series may provide indications of benefit outside of a clinical trial setting and should be encouraged, in order to provide some evidence for the efficacy of therapeutic regimens in RPGN and advanced renal disease.

Epidermal growth factor receptor inhibition with erlotinib partially prevents cisplatin-induced nephrotoxicity in rats

The effects of blocking the epidermal growth factor receptor (EGFR) in acute kidney injury (AKI) are controversial. Here we investigated the renoprotective effect of erlotinib, a selective tyrosine kinase inhibitor that can block EGFR activity, on cisplatin (CP)-induced AKI. Groups of animals were given either erlotinib or vehicle from one day before up to Day 3 following induction of CP-nephrotoxicity (CP-N). In addition, we analyzed the effects of erlotinib on signaling pathways involved in CP-N by using human renal proximal tubular cells (HK-2). Compared to controls, rats treated with erlotinib exhibited significant improvement of renal function and attenuation of tubulointerstitial injury, and reduced the number of apoptotic and proliferating cells. Erlotinib-treated rats had a significant reduction of renal cortical mRNA for profibrogenic genes. The Bax/Bcl-2 mRNA and protein ratios were significantly reduced by erlotinib treatment. In vitro, we observed that erlotinib significantly reduced the phosphorylation of MEK1 and Akt, processes that were induced by CP in HK-2. Taken together, these data indicate that erlotinib has renoprotective properties that are likely mediated through decreases in the apoptosis and proliferation of tubular cells, effects that reflect inhibition of downstream signaling pathways of EGFR. These results suggest that erlotinib may be useful for preventing AKI in patients receiving CP chemotherapy.

EGFR signaling in renal fibrosis

Signaling through the epidermal growth factor receptor (EGFR) is involved in regulation of multiple biological processes, including proliferation, metabolism, differentiation, and survival. Owing to its aberrant expression in a variety of malignant tumors, EGFR has been recognized as a target in anticancer therapy. Increasingly, evidence from animal studies indicates that EGFR signaling is also implicated in the development and progression of renal fibrosis. The therapeutic value of EGFR inhibition has not yet been evaluated in human kidney disease. In this article, we summarize recent research into the role of EGFR signaling in renal fibrogenesis, discuss the mechanism by which EGFR regulates this process, and consider the potential of EGFR as an antifibrotic target.

Glomerular parietal epithelial cells in kidney physiology, pathology, and repair

PURPOSE OF REVIEW

We have summarized recently published glomerular parietal epithelial cell (PEC) research, focusing on their roles in glomerular development and physiology, and in certain glomerular diseases. The rationale is that PECs have been largely ignored until the recent availability of cell lineage tracing studies, human and murine PEC culture systems, and potential therapeutic interventions of PECs.

RECENT FINDINGS

Several new paradigms involving PECs have emerged demonstrating their significant contribution to glomerular physiology and numerous glomerular diseases. A subset of PECs serving as podocyte progenitors have been identified in normal human glomeruli. They provide a source for podocytes in adolescent mice, and their numbers increase in states of podocyte depletion. PEC progenitor number is increased by retinoids and angiotensin-converting enzyme inhibition. However, dysregulated growth of PEC progenitors leads to pseudo-crescent and crescent formation. In focal segmental glomerulosclerosis, considered a podocyte disease, activated PECs increase extracellular matrix production, which leads to synechial attachment and, when they move to the glomerular tuft, to segmental glomerulosclerosis. Finally, PECs might be adversely affected in proteinuric states by undergoing apoptosis.

SUMMARY

PECs play a critical role in glomerular repair through their progenitor function, but under certain circumstances paradoxically contribute to deterioration by augmenting scarring and crescent formation.

Tumor necrosis factor-like weak inducer of apoptosis (TWEAK) and kidney disease

PURPOSE OF REVIEW

The tumor necrosis factor-like weak inducer of apoptosis (TWEAK) cytokine has been linked to kidney injury by functional studies in experimental animals, and has biomarker potential in kidney disease.

RECENT FINDINGS

TWEAK was known to promote tubular cell injury and kidney inflammation. Recent studies have expanded these observations, identifying additional targets of TWEAK relevant to kidney injury. Thus, TWEAK upregulates the chemokine and cholesterol scavenger receptor CXCL16 and downregulates the antiaging and antifibrotic molecule Klotho in tubular cells. Furthermore, fibrogenic TWEAK actions on renal fibroblasts were described. TWEAK or factor-inducible molecule 14 targeting decreased the kidney fibrosis resulting from immune and nonimmune kidney injury induced by transient tubular or glomerular insults or by persistent urinary tract obstruction. TWEAK might also contribute to the link between chronic kidney disease and kidney cancer, as suggested by its role in other genitourinary cancers. Progress has also been made in TWEAK targeting. A phase I clinical trial showed that TWEAK targeting is well tolerated in humans, and an ongoing trial is exploring efficacy in lupus nephritis. Nanomolecules and inhibitors of epidermal growth factor receptor pathway may also protect from the adverse effects of TWEAK in the kidney.

SUMMARY

These findings suggest that TWEAK targeting has clinical potential in kidney injury of immune and nonimmune origin.

Update on crescentic glomerulonephritis

The recent years have seen a number of major progresses in the field of extracapillary glomerulonephritis. This entity is the final damage caused by unrelated immunological disorders such as immune complexes glomerular deposits or microvascular injury caused by proinflammatory cytokines, neutrophil extracellular traps (NET), and cell adhesion molecules in the context of antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV). This review provides a summary of recent advances in the understanding of crescentic glomerulonephritis, focusing on interplays of local immune cells and on local mediators participating to crescent formation especially in anti-glomerular basement membrane (anti-GBM) antibody disease. The recent advances about AAV and lupus nephritis are covered by other chapters of this issue. Nevertheless, these considerations may apply to the general case of crescentic glomerulonephritis of all causes.

TWEAK transactivation of the epidermal growth factor receptor mediates renal inflammation

TWEAK, a member of the TNF superfamily, binds to the Fn14 receptor, eliciting biological responses. EGFR signalling is involved in experimental renal injury. Our aim was to investigate the relationship between TWEAK and EGFR in the kidney. Systemic TWEAK administration into C57BL/6 mice increased renal EGFR phosphorylation, mainly in tubular epithelial cells. In vitro, in these cells TWEAK phosphorylated EGFR via Fn14 binding, ADAM17 activation and subsequent release of the EGFR ligands HB-EGF and TGFα. In vivo the EGFR kinase inhibitor Erlotinib inhibited TWEAK-induced renal EGFR activation and downstream signalling, including ERK activation, up-regulation of proinflammatory factors and inflammatory cell infiltration. Moreover, the ADAM17 inhibitor WTACE-2 also prevented those TWEAK-induced renal effects. In vitro TWEAK induction of proinflammatory factors was prevented by EGFR, ERK or ADAM17 inhibition. In contrast, EGFR transactivation did not modify TWEAK-mediated NF-κB activation. Our data suggest that TWEAK transactivates EGFR in the kidney, leading to modulation of downstream effects, including ERK activation and inflammation, and suggest that inhibition of EGFR signalling could be a novel therapeutic tool for renal inflammation.

Molecular genetics of familial hematuric diseases

The familial hematuric diseases are a genetically heterogeneous group of monogenic conditions, caused by mutations in one of several genes. The major genes involved are the following: (i) the collagen IV genes COL4A3/A4/A5 that are expressed in the glomerular basement membranes (GBM) and are responsible for the most frequent forms of microscopic hematuria, namely Alport syndrome (X-linked or autosomal recessive) and thin basement membrane nephropathy (TBMN). (ii) The FN1 gene, expressed in the glomerulus and responsible for a rare form of glomerulopathy with fibronectin deposits (GFND). (iii) CFHR5 gene, a recently recognized regulator of the complement alternative pathway and mutated in a recently revisited form of inherited C3 glomerulonephritis (C3GN), characterized by isolated C3 deposits in the absence of immune complexes. A hallmark feature of all conditions is the age-dependent penetrance and a broad phenotypic heterogeneity in the sense that subsets of patients progress to added proteinuria or proteinuria and chronic renal failure that may or may not lead to end-stage kidney disease (ESKD) anywhere between the second and seventh decade of life. In addition to other excellent laboratory tools that assist the clinician in reaching the correct diagnosis, the molecular analysis emerges as the gold standard in establishing the diagnosis in many cases of doubt due to equivocal findings that complicate the differential diagnosis. Recent work led to the description of candidate genetic modifiers which confer a variable risk for progressing to chronic renal failure when co-inherited on the background of a primary glomerulopathy. Finally, more families are still waiting to be studied and more genes to be mapped and cloned that are responsible for other forms of heritable hematuric diseases. The study of such genes and their protein products will likely shed more light on the structure and function of the glomerular filtration barrier and other important glomerular components.

Connective tissue growth factor is a new ligand of epidermal growth factor receptor

Chronic kidney disease is reaching epidemic proportions worldwide and there is no effective treatment. Connective tissue growth factor (CCN2) has been suggested as a risk biomarker and a potential therapeutic target for renal diseases, but its specific receptor has not been identified. Epidermal growth factor receptor (EGFR) participates in kidney damage, but whether CCN2 activates the EGFR pathway is unknown. Here, we show that CCN2 is a novel EGFR ligand. CCN2 binding to EGFR extracellular domain was demonstrated by surface plasmon resonance. CCN2 contains four distinct structural modules. The carboxyl-terminal module (CCN2(IV)) showed a clear interaction with soluble EGFR, suggesting that EGFR-binding site is located in this module. Injection of CCN2(IV) in mice increased EGFR phosphorylation in the kidney, mainly in tubular epithelial cells. EGFR kinase inhibition decreased CCN2(IV)-induced renal changes (ERK activation and inflammation). Studies in cultured tubular epithelial cells showed that CCN2(IV) binds to EGFR leading to ERK activation and proinflammatory factors overexpression. CCN2 interacts with the neurotrophin receptor TrkA, and EGFR/TrkA receptor crosstalk was found in response to CCN2(IV) stimulation. Moreover, endogenous CCN2 blockade inhibited TGF-β-induced EGFR activation. These findings indicate that CCN2 is a novel EGFR ligand that contributes to renal damage through EGFR signalling.

Epidermal growth factors in the kidney and relationship to hypertension

Members of the epidermal growth factor (EGF)-family bind to ErbB (EGFR)-family receptors that play an important role in the regulation of various fundamental cell processes in many organs including the kidney. In this field, most of the research efforts are focused on the role of EGF-ErbB axis in cancer biology. However, many studies indicate that abnormal ErbB-mediated signaling pathways are critical in the development of renal and cardiovascular pathologies. The kidney is a major site of the EGF-family ligands synthesis, and it has been shown to express all four members of the ErbB receptor family. The study of kidney disease regulation by ErbB receptor ligands has expanded considerably in recent years. In vitro and in vivo studies have provided direct evidence of the role of ErbB signaling in the kidney. Recent advances in the understanding of how the proteins in the EGF-family regulate sodium transport and development of hypertension are specifically discussed here. Collectively, these results suggest that EGF-ErbB signaling pathways could be major determinants in the progress of renal lesions, including its effects on the regulation of sodium reabsorption in collecting ducts.

Combined Effects of PPAR γ Agonists and Epidermal Growth Factor Receptor Inhibitors in Human Proximal Tubule Cells

We aimed to determine whether epidermal growth factor receptor (EGFR) inhibition, in addition to a peroxisome proliferator-activated receptor gamma (PPARγ) agonist, prevents high-glucose-induced proximal tubular fibrosis, inflammation, and sodium and water retention in human proximal tubule cells exposed to normal glucose; high glucose; high glucose with the PPARγ agonist pioglitazone or with the P-EGFR inhibitor, gefitinib; or high glucose with both pioglitazone and gefitinib. We have shown that high glucose increases AP-1 and NFκB binding activity, downstream phosphorylation of EGFR and Erk1/2, and fibronectin and collagen IV expression. Pioglitazone reversed these effects but upregulated NHE3 and AQP1 expression. Gefitinib inhibited high glucose induced fibronectin and collagen IV, and EGFR and Erk1/2 phosphorylation and reversed pioglitazone-induced increases in NHE3 and AQP1 expression. Our data suggests that combination of an EGFR inhibitor and a PPARγ agonist mitigates high-glucose-induced fibrosis and inflammation and reverses the upregulation of transporters and channels involved in sodium and water retention in human proximal tubule cells. Hence EGFR blockade may hold promise, not only in limiting tubulointerstitial pathology in diabetic nephropathy, but also in limiting the sodium and water retention observed in patients with diabetes and exacerbated by PPARγ agonists.