Albumin induces CD44 expression in glomerular parietal epithelial cells by activating extracellular signal-regulated kinase 1/2 pathway

The incidence of lower extremity amputation and its associated risk factors in patients with diabetic foot ulcers: A meta-analysis

This study analysed the incidence of lower extremity amputation and its associated risk factors in patients with diabetic foot ulcers. This study systematically searched both Chinese and English databases, including CNKI, Wanfang, VIP, PubMed, EMBASE and Web of Science, to identify cohort studies related to lower extremity amputation and associated risk factors in patients with diabetic foot ulcers up to October 2023. The patients were stratified based on whether they underwent lower extremity amputation, and relevant data, including basic information, patient characteristics, complications, comorbidities and pertinent laboratory test data, were extracted from the included studies. The literature quality assessment in this study utilized the Newcastle-Ottawa Scale to screen for high-quality literature, resulting in the inclusion of 16 cohort studies, all of which were of at least moderate quality. Meta-analysis of outcome indicators was conducted using the Stata 14.0 software. The results indicate that the overall amputation rate of lower extremities in patients with diabetic foot ulcers is 31% (0.25, 0.38). Among the 16 variables evaluated, gender (male), smoking history, body mass index (BMI), hypertension, cardiovascular disease, kidney disease, white blood cell count, haemoglobin and albumin levels were found to be correlated with the occurrence of lower extremity amputation in patients with diabetic foot ulcers. However, no significant correlation was observed between age, diabetes type, duration of diabetes, stroke, glycosylated haemoglobin, creatinine and total cholesterol levels and lower extremity amputation in patients with diabetic foot ulcers. This meta-analysis indicates that the overall amputation rate in patients with diabetic foot ulcers is 31%. Factors such as gender (male), smoking history, high BMI, hypertension, cardiovascular disease, kidney disease, white blood cell count, haemoglobin and albumin levels are identified as significant risk factors for lower extremity amputation in diabetic foot ulcer patients. These findings suggest that attention should be focused on these risk factors in patients with diabetic foot ulcers to reduce the risk of lower extremity amputation. Therefore, preventive and intervention measures targeting these risk factors are of significant importance in clinical practice. (Systematic review registration: https://www.crd.york.ac.uk/PROSPERO/, identifier [CRD42024497538]).

Elevated RHAMM as a biomarker for predicting diabetic kidney disease in patients with type 2 diabetes

Background

Diabetic kidney disease (DKD) poses a significant challenge globally as a complication of diabetes. Hyaluronan (HA), a critical non-sulfated glycosaminoglycan in the extracellular matrix, plays a pivotal role in the progression of DKD. This study assesses the predictive significance of HA's corresponding receptor, RHAMM (receptor for HA-mediated motility), in DKD pathogenesis in type 2 diabetes (T2DM) patients.

Methods

Enzyme-linked immunosorbent assays were utilized to measure plasma and urine levels of HA, CD44 and RHAMM in 99 diabetic patients. Immunohistochemistry staining was employed to examine HA deposition, CD44 and RHAMM expressions from 18 biopsy-proven DKD patients. Spearman correlation analysis, linear regression and receiver operating characteristic (ROC) analysis were conducted to establish associations between plasma HA, CD44 and RHAMM levels, and clinical parameters in DKD patients with T2DM.

Results

Elevated plasma and urine HA, CD44 and RHAMM levels were notably observed in the severe renal dysfunction group. Plasma RHAMM exhibited positive correlations with HA (r = 0.616, P < .001) and CD44 (r = 0.220, P < .001), and a negative correlation with estimated glomerular filtration rate (eGFR) (r = -0.618, P < .001). After adjusting for other potential predictors, plasma RHAMM emerged as an independent predictor of declining eGFR (β = -0.160, P < .05). Increased HA, CD44 and RHAMM levels in kidney biopsies of DKD patients were closely associated with heightened kidney injury. The ROC curve analysis highlighted an area under the curve (AUC) of 0.876 for plasma RHAMM, indicating superior diagnostic efficacy compared to CD44 in predicting DKD pathogenesis. The combined AUC of 0.968 for plasma RHAMM, HA and CD44 also suggested even greater diagnostic potential for DKD pathogenesis.

Conclusion

These findings provide initial evidence that elevated RHAMM levels predict DKD pathogenesis in T2DM patients. The formation of a triple complex involving HA, CD44 and RHAMM on the cell surface shows promise as a targetable biomarker for early intervention to mitigate severe renal dysfunctions.

Human parietal epithelial cells (PECs) and proteinuria in lupus nephritis: a role for ClC-5, megalin, and cubilin?

BACKGROUND

Parietal epithelial cells are a heterogeneous population of cells located on Bowman's capsule. These cells are known to internalize albumin with a still undetermined mechanism, although albumin has been shown to induce phenotypic changes in parietal epithelial cells. Proximal tubular cells are the main actors in albumin handling via the macromolecular complex composed by ClC-5, megalin, and cubilin. This study investigated the role of ClC-5, megalin, and cubilin in the parietal epithelial cells of kidney biopsies from proteinuric lupus nephritis patients and control subjects and identified phenotypical changes occurring in the pathological milieu.

METHODS

Immunohistochemistry and immunofluorescence analyses for ClC-5, megalin, cubilin, ANXA3, podocalyxin, CD24, CD44, HSA, and LTA marker were performed on 23 kidney biopsies from patients with Lupus Nephritis and 9 control biopsies (obtained from nephrectomies for renal cancer).

RESULTS

Two sub-populations of hypertrophic parietal epithelial cells ANXA3+/Podocalyxin-/CD44-, both expressing ClC-5, megalin, and cubilin and located at the tubular pole, were identified and characterized: the first one, CD24+/HSA-/LTA- had characteristics of human adult parietal epithelial multipotent progenitors, the second one, CD24-/LTA+/HSA+ committed to become phenotypically proximal tubular cells. The number of glomeruli presenting hypertrophic parietal epithelial cells positive for ClC-5, megalin, and cubilin were significantly higher in lupus nephritis patients than in controls.

CONCLUSIONS

Our results may provide further insight into the role of hypertrophic parietal epithelial cells located at the tubular pole and their possible involvement in protein endocytosis in lupus nephritis patients. These data also suggest that the presence of hypertrophic parietal epithelial cells in Bowman's capsule represents a potential resource for responding to protein overload observed in other glomerulonephritis.

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.

Renal tubular gen e biomarkers identification based on immune infiltrates in focal segmental glomerulosclerosis

OBJECTIVE

The present study identified novel renal tubular biomarkers that may influence the diagnosis and treatment of focal segmental glomerulosclerosis (FSGS) based on immune infiltration.

METHODS

Three FSGS microarray datasets, GSE108112, GSE133288 and GSE121211, were downloaded from the Gene Expression Omnibus (GEO) database. The R statistical software limma package and the combat function of the sva package were applied for preprocessing and to remove the batch effects. Differentially expressed genes (DEGs) between 120 FSGS and 15 control samples were identified with the limma package. Disease Ontology (DO) pathway enrichment analysis was conducted with statistical R software to search for related diseases. Gene set enrichment analysis (GSEA) was used to interpret the gene expression data and it revealed many common biological pathways. A protein-protein interaction (PPI) network was built using the Search Tool for the Retrieval of Interacting Genes (STRING) database, and hub genes were identified by the Cytoscape (version 3.7.2) plug-in CytoHubba. The plug-in Molecular Complex Detection (MCODE) was used to screen hub modules of the PPI network in Cytoscape, while functional analysis of the hub genes and hub nodes involved in the submodule was performed by ClusterProfiler. The least absolute shrinkage and selection operator (LASSO) regression and support vector machine recursive feature elimination (SVM-RFE) analysis were used to screen characteristic genes and build a logistic regression model. Receiver operating characteristic (ROC) curve analyses were used to investigate the logistic regression model and it was then validated by an external dataset GSE125779, which contained 8 FSGS samples and 8 healthy subjects. Cell-type identification by estimating relative subsets of RNA transcripts (CIBERSORT) was used to calculate the immune infiltration of FSGS samples.

RESULTS

We acquired 179 DEGs, 79 genes with downregulated expression (44.1%) and 100 genes with upregulated expression (55.9%), in the FSGS samples. The DEGs were significantly associated with arteriosclerosis, kidney disease and arteriosclerotic cardiovascular disease. GSEA revealed that these gene sets were significantly enriched in allograft rejection signaling pathways and activation of immune response in biological processes. Fifteen genes were demonstrated to be hub genes by PPI, and three submodules were screened by MCODE linked with FSGS. Analysis by machine learning methodologies identified nuclear receptor subfamily 4 group A member 1 (NR4A1) and dual specificity phosphatase 1 (DUSP1) as sensitive tubular renal biomarkers in the diagnosis of FSGS, and they were selected as hub genes, as well as hub nodes which were enriched in the MAPK signaling pathway. Immune cell infiltration analysis revealed that the genetic biomarkers were both correlated with activated mast cells, which may amplify FSGS biological processes.

CONCLUSION

DUSP1 and NR4A1 were identified as sensitive potential biomarkers in the diagnosis of FSGS. Activated mast cells have a decisive effect on the occurrence and development of FSGS through tubular lesions and tubulointerstitial inflammation, and they are expected to become therapeutic targets in FSGS.

Extended longevity geometrically-inverted proximal tubule organoids

This study reports the cellular self-organization of primary human renal proximal tubule epithelial cells (RPTECs) around a minimal Matrigel scaffold to produce basal-in and apical-out proximal tubule organoids (tubuloids). These tubuloids are produced and maintained in hanging drop cultures for 90+ days, the longest such culture of any kind reported to date. The tubuloids upregulate maturity markers, such as aquaporin-1 (AQP1) and megalin (LRP2), and exhibit less mesenchymal and proliferation markers, such as vimentin and Ki67, compared to 2D cultures. They also experience changes over time as revealed by a comparison of gene expression patterns of cells in 2D culture and in day 31 and day 67 tubuloids. Gene expression analysis and immunohistochemistry reveal an increase in the expression of megalin, an endocytic receptor that can directly bind and uptake protein or potentially assist protein uptake. The tubuloids, including day 90 tubuloids, uptake fluorescent albumin and reveal punctate fluorescent patterns, suggesting functional endocytic uptake through these receptors. Furthermore, the tubuloids release kidney injury molecule-1 (KIM-1), a common biomarker for kidney injury, when exposed to albumin in both dose- and time-dependent manners. While this study focuses on potential applications for modeling proteinuric kidney disease, the tubuloids may have broad utility for studies where apical proximal tubule cell access is required.

Urinary Protein Profiling for Potential Biomarkers of Chronic Kidney Disease: A Pilot Study

Proteinuria is a risk factor for chronic kidney disease (CKD) progression and associated complications. However, there is insufficient information on individual protein components in urine and the severity of CKD. We aimed to investigate urinary proteomics and its association with proteinuria and kidney function in early-stage CKD and in healthy individuals. A 24 h urine sample of 42 individuals (21-CKD and 21-healthy individuals) was used for mass spectrometry-based proteomics analysis. An exponentially modified protein abundance index (emPAI) was calculated for each protein. Data were analyzed by Mascot software using the SwissProt database and bioinformatics tools. Overall, 298 unique proteins were identified in the cohort; of them, 250 proteins belong to the control group with median (IQR) emPAI 39.1 (19−53) and 142 proteins belong to the CKD group with median (IQR) emPAI 67.8 (49−117). The level of 24 h proteinuria positively correlated with emPAI (r = 0.390, p = 0.011). The emPAI of some urinary proteomics had close positive (ALBU, ZA2G, IGKC) and negative (OSTP, CD59, UROM, KNG1, RNAS1, CD44, AMBP) correlations (r < 0.419, p < 0.001) with 24 h proteinuria levels. Additionally, a few proteins (VTDB, AACT, A1AG2, VTNC, and CD44) significantly correlated with kidney function. In this proteomics study, several urinary proteins correlated with proteinuria and kidney function. Pathway analysis identified subpathways potentially related to early proteinuric CKD, allowing the design of prospective studies that explore their response to therapy and their relationship to long-term outcomes.

A Glimpse of Inflammation and Anti-Inflammation Therapy in Diabetic Kidney Disease

Diabetic kidney disease (DKD) is a common complication of diabetes mellitus and a major cause of end-stage kidney disease (ESKD). The pathogenesis of DKD is very complex and not completely understood. Recently, accumulated evidence from in vitro and in vivo studies has demonstrated that inflammation plays an important role in the pathogenesis and the development of DKD. It has been well known that a variety of pro-inflammatory cytokines and related signaling pathways are involved in the procession of DKD. Additionally, some anti-hyperglycemic agents and mineralocorticoid receptor antagonists (MRAs) that are effective in alleviating the progression of DKD have anti-inflammatory properties, which might have beneficial effects on delaying the progression of DKD. However, there is currently a lack of systematic overviews. In this review, we focus on the novel pro-inflammatory signaling pathways in the development of DKD, including the nuclear factor kappa B (NF-κB) signaling pathway, toll-like receptors (TLRs) and myeloid differentiation primary response 88 (TLRs/MyD88) signaling pathway, adenosine 5′-monophosphate-activated protein kinase (AMPK) signaling pathways, inflammasome activation, mitochondrial DNA (mtDNA) release as well as hypoxia-inducible factor-1(HIF-1) signaling pathway. We also discuss the related anti-inflammation mechanisms of metformin, finerenone, sodium-dependent glucose transporters 2 (SGLT2) inhibitors, Dipeptidyl peptidase-4 (DPP-4) inhibitors, Glucagon-like peptide-1 (GLP-1) receptor agonist and traditional Chinese medicines (TCM).

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.

TNF-α induces Claudin-1 expression in renal tubules in Alport mice

Claudin-1 (CL-1) is responsible for the paracellular barrier function of glomerular parietal epithelial cells (PEC) in kidneys, but the role of CL-1 in proximal tubules remains to be elucidated. In this study, to evaluate CL-1 as a potential therapeutic drug target for chronic kidney disease, we investigated change of CL-1 expression in the proximal tubules of diseased kidney and elucidated the factors that induced this change. We established Alport mice as a kidney disease model and investigated the expression of CL-1 in diseased kidney using quantitative PCR and immunohistochemistry (IHC). Compared to wild type mice, Alport mice showed significant increases in plasma creatinine, urea nitrogen and urinary albumin excretion. CL-1 mRNA was increased significantly in the kidney cortex and CL-1 was localized on the adjacent cell surfaces of PECs and proximal tubular epithelial cells. The infiltration of inflammatory cells around proximal tubules and a significant increase in TNF-α mRNA were observed in diseased kidneys. To reveal factors that induce CL-1, we analyzed the induction of CL-1 by albumin or tumor necrosis factor (TNF)-α in human proximal tubular cells (RPTEC/TERT1) using quantitative PCR and Western blotting. TNF-α increased CL-1 expression dose-dependently, though albumin did not affect CL-1 expression in RPTEC/TERT1. In addition, both CL-1 and TNF-α expression were significantly increased in UUO mice, which are commonly used as a model of tubulointerstitial inflammation without albuminuria. These results indicate that CL-1 expression is induced by inflammation, not by albuminuria in diseased proximal tubules. Moreover, we examined the localization of CL-1 in the kidney of IgA nephropathy patients by IHC and found CL-1 expression was also elevated in the proximal tubular cells. Taken together, CL-1 expression is increased in the proximal tubular epithelial cells of diseased kidney. Inflammatory cells around the tubular epithelium may produce TNF-α which in turn induces CL-1 expression.

Bioinformatics Analysis Reveals Crosstalk Among Platelets, Immune Cells, and the Glomerulus That May Play an Important Role in the Development of Diabetic Nephropathy

Diabetic nephropathy (DN) is the main cause of end stage renal disease (ESRD). Glomerulus damage is one of the primary pathological changes in DN. To reveal the gene expression alteration in the glomerulus involved in DN development, we screened the Gene Expression Omnibus (GEO) database up to December 2020. Eleven gene expression datasets about gene expression of the human DN glomerulus and its control were downloaded for further bioinformatics analysis. By using R language, all expression data were extracted and were further cross-platform normalized by Shambhala. Differentially expressed genes (DEGs) were identified by Student's t-test coupled with false discovery rate (FDR) (P < 0.05) and fold change (FC) ≥1.5. DEGs were further analyzed by the Database for Annotation, Visualization, and Integrated Discovery (DAVID) to enrich the Gene Ontology (GO) terms and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway. We further constructed a protein-protein interaction (PPI) network of DEGs to identify the core genes. We used digital cytometry software CIBERSORTx to analyze the infiltration of immune cells in DN. A total of 578 genes were identified as DEGs in this study. Thirteen were identified as core genes, in which LYZ, LUM, and THBS2 were seldom linked with DN. Based on the result of GO, KEGG enrichment, and CIBERSORTx immune cells infiltration analysis, we hypothesize that positive feedback may form among the glomerulus, platelets, and immune cells. This vicious cycle may damage the glomerulus persistently even after the initial high glucose damage was removed. Studying the genes and pathway reported in this study may shed light on new knowledge of DN pathogenesis.

Castrated autoimmune glomerulonephritis mouse model shows attenuated glomerular sclerosis with altered parietal epithelial cell phenotype

Sex hormones help in maintaining proper immunity as well as renal homeostasis in mammals, and these multi-functional properties characterize the onset of sex-dependent diseases. To clarify the contribution of sex hormones to autoimmune disease-related renal pathogenesis, BXSB/MpJ-Yaa was investigated as a murine autoimmune glomerulonephritis model. BXSB/MpJ-Yaa and its wild-type, BXSB/MpJ-Yaa+ were castrated or sham-operated at three weeks and examined until six months of age. Both castrated strains showed significantly lower serum testosterone levels and body weights than sham-operated mice. Castration did not change the disease phenotypes in BXSB/MpJ-Yaa+. At three months, both sham-operated and castrated BXSB/MpJ-Yaa manifested splenomegaly, autoantibody production, and glomerulonephritis, and castrated BXSB/MpJ-Yaa tended to show heavier spleen weights than the sham-operated group. At six months, both the treated BXSB/MpJ-Yaa showed equivalent autoimmune disease conditions; however, castrated mice clearly showed milder glomerular sclerotic lesions than the sham-operated groups. Urinary albumin excretion in castrated BXSB/MpJ-Yaa was significantly milder than in sham-operated mice at four months, but those of both the treated BXSB/MpJ-Yaa were comparable at six months. The examined renal histopathological indices in parietal epithelial cells were remarkably altered by castration. Briefly, castration decreased the height of parietal epithelial cells and total parietal epithelial cell number in BXSB/MpJ-Yaa at six months. For immunostaining, parietal epithelial cells facing the injured glomeruli of BXSB/MpJ-Yaa expressed CD44, an activated parietal epithelial cell marker, and CD44-positive parietal epithelial cells showed nuclear localization of the androgen receptor and proliferation marker Ki67. CD44- or Ki67-positive parietal epithelial cells were significantly fewer in castrated group than in sham-operated BXSB/MpJ-Yaa at six months. Further, quantitative indices for CD44-positive parietal epithelial cell number and frequency in renal corpuscles positively correlated with glomerular sclerotic severity in BXSB/MpJ-Yaa. In conclusion, androgen seemed to have an effect on both systemic immunity and renal morpho-function; however, the effect on the latter could be more clearly observed in BXSB/MpJ-Yaa, as parietal epithelial cell activation resulted in glomerular sclerosis.

Albumin Reduces Oxidative Stress and Neuronal Apoptosis via the ERK/Nrf2/HO-1 Pathway after Intracerebral Hemorrhage in Rats

BACKGROUND

Albumin has been regarded as a potent antioxidant with free radical scavenging activities. Oxidative stress and neuronal apoptosis are responsible for its highly damaging effects on brain injury after intracerebral hemorrhage (ICH). Here, the present study investigated the neuroprotective effect of albumin against early brain injury after ICH and the potential underlying mechanisms.

METHODS

Adult male Sprague-Dawley rats were subjected to intrastriatal injection of autologous blood to induce ICH. Human serum albumin was given by intravenous injection 1 h after ICH. U0126, an inhibitor of extracellular signal-regulated kinase (ERK1/2), and ML385, an inhibitor of nuclear factor-E2-related factor 2 (Nrf2), were intraperitoneally administered 1 h before ICH induction. Short- and long-term neurobehavioral tests, western blotting, immunofluorescence staining, oxidative stress evaluations, and apoptosis measurements were performed.

RESULTS

Endogenous expression of albumin (peaked at 5 days) and heme oxygenase 1 (HO-1, peaked at 24 h) was increased after ICH compared with the sham group. Albumin and HO-1 were colocalized with neurons. Compared with vehicle, albumin treatment significantly improved short- and long-term neurobehavioral deficits and reduced oxidative stress and neuronal death at 72 h after ICH. Moreover, albumin treatment significantly promoted the phosphorylation of ERK1/2; increased the expression of Nrf2, HO-1, and Bcl-2; and downregulated the expression of Romo1 and Bax. U0126 and ML385 abolished the treatment effects of albumin on behavior and protein levels after ICH.

CONCLUSIONS

Albumin attenuated oxidative stress-related neuronal death may in part via the ERK/Nrf2/HO-1 signaling pathway after ICH in rats. Our study suggests that albumin may be a novel therapeutic method to ameliorate brain injury after ICH.

Parietal epithelial cells role in repair versus scarring after glomerular injury

PURPOSE OF REVIEW

The recent years have been marked by the publication of several articles highlighting the pathophysiological role of glomerular parietal epithelial cells (PEC) and refining their phenotypic heterogeneity.

RECENT FINDINGS

The present review synthetizes recent findings on (i) the potential regenerative role of PEC in glomerular diseases, and (ii) the mechanisms and signaling of leading to PEC pathogenic involvement in crescentic glomerulonephritis (CGN) and focal segmental glomerulosclerosis (FSGS).

SUMMARY

The debate is still open regarding the podocyte regenerative properties of PEC in glomerular disease, whereas the pathogenic involvement of PEC activation in glomerular disease is increasingly admitted. Recent highlights on the podocyte regenerative role of PEC, on one hand, and on their pathological function, on the other hand, for sure will feed the debate in the kidney community for the next years. Nevertheless, from a therapeutic perspective, the two options, boosting cellular regeneration and blocking PECs pathogenicity, should not be seen as antagonistic but, rather, complementary.

Diabetic condition induces hypertrophy and vacuolization in glomerular parietal epithelial cells

Diabetic nephropathy (DN) is accompanied by characteristic changes in the glomerulus, but little is known about the effect of diabetes on parietal epithelial cells (PECs). In this study, a descriptive analysis of PECs was undertaken in diabetic db/db mice and in diabetic patients. PEC hypertrophy was significantly more prominent in diabetic mice than in nondiabetic mice, and this was evident even at the early stage. Additionally, the number of vacuoles in PECs was markedly increased in diabetic mice, suggesting the presence of cellular injury in PECs in DN. Although rare, binuclear cells were observed in mice with early diabetes. In cultured PECs, a high glucose condition, compared with normal glucose condition, induced cellular hypertrophy and apoptosis. Flow cytometry showed that some PECs in the G0 phase reentered the cell cycle but got arrested in the S phase. Finally, in human diabetic subjects, hypertrophy and vacuolization were observed in the PECs. Our data showed that PECs undergo substantial changes in DN and may participate in rearrangement for differentiation into podocytes.

Genetics and phenotypic heterogeneity of Dent disease: the dark side of the moon

Dent disease is a rare genetic proximal tubulopathy which is under-recognized. Its phenotypic heterogeneity has led to several different classifications of the same disorder, but it is now widely accepted that the triad of symptoms low-molecular-weight proteinuria, hypercalciuria and nephrocalcinosis/nephrolithiasis are pathognomonic of Dent disease. Although mutations on the CLCN5 and OCRL genes are known to cause Dent disease, no such mutations are found in about 25–35% of cases, making diagnosis more challenging. This review outlines current knowledge regarding Dent disease from another perspective. Starting from the history of Dent disease, and reviewing the clinical details of patients with and without a genetic characterization, we discuss the phenotypic and genetic heterogeneity that typifies this disease. We focus particularly on all those confounding clinical signs and symptoms that can lead to a misdiagnosis. We also try to shed light on a concealed aspect of Dent disease. Although it is a proximal tubulopathy, its misdiagnosis may lead to patients undergoing kidney biopsy. In fact, some individuals with Dent disease have high-grade proteinuria, with or without hematuria, as in the clinical setting of glomerulopathy, or chronic kidney disease of uncertain origin. Although glomerular damage is frequently documented in Dent disease patients’ biopsies, there is currently no reliable evidence of renal biopsy being of either diagnostic or prognostic value. We review published histopathology reports of tubular and glomerular damage in these patients, and discuss current knowledge regarding the role of CLCN5 and OCRL genes in glomerular function.

From protein uptake to Dent disease: An overview of the CLCN5 gene

Proteinuria is a well-known risk factor, not only for renal disorders, but also for several other problems such as cardiovascular diseases and overall mortality. In the kidney, the chloride channel Cl^-/H⁺ exchanger ClC-5 encoded by the CLCN5 gene is actively involved in preventing protein loss. This action becomes evident in patients suffering from the rare proximal tubulopathy Dent disease because they carry a defective ClC-5 due to CLCN5 mutations. In fact, proteinuria is the distinctive clinical sign of Dent disease, and mainly involves the loss of low-molecular-weight proteins. The identification of CLCN5 disease-causing mutations has greatly improved our understanding of ClC-5 function and of the ClC-5-related physiological processes in the kidney. This review outlines current knowledge regarding the CLCN5 gene and its protein product, providing an update on ClC-5 function in tubular and glomerular cells, and focusing on its relationship with proteinuria and Dent disease.

Kidney Injury Molecule-1 Is Upregulated in Renal Lipotoxicity and Mediates Palmitate-Induced Tubular Cell Injury and Inflammatory Response

Diabetic nephropathy is increasingly recognized as a major contributor to kidney failure in patients with obesity and type 2 diabetes. This study was designed to identify the molecular mediators of kidney injury associated with metabolic syndrome with or without hyperglycemia. We compared renal gene expression profiles in Zucker lean (ZL), Zucker obese (ZO), and Zucker diabetic (ZD) rats using cDNA microarray with quantitative verification of selected transcripts by real-time PCR. Compared to the 20-week-old ZL control (glucose: 110 ± 8 mg/dL), both prediabetic ZO (glucose: 157 ± 11 mg/dL) and diabetic ZD (glucose: 481 ± 37 mg/dL) rats displayed hyperlipidemia and kidney injury with a high degree of proteinuria. cDNA microarray identified 25 inflammation and injury-related transcriptomes whose expression levels were similarly increased in ZO and ZD kidneys. Among them, kidney injury molecule-1 (KIM-1) was found to be the most highly upregulated in both ZO and ZD kidneys. Immunofluorescence staining of kidney sections revealed a strong correlation between lipid overload and KIM-1 upregulation in proximal tubules of ZO and ZD rats. In cultured primary renal tubular epithelial cells (TECs), administration of saturated fatty acid palmitate resulted in an upregulation of KIM-1, osteopontin, and CD44, which was greatly attenuated by U0126, an inhibitor of extracellular signal-regulated kinase (ERK)1/2. Moreover, knockdown of KIM-1 by siRNA interference inhibited palmitate-induced cleaved caspase-3, osteopontin, and CD44 proteins in primary TECs. Our results indicate that KIM-1 expression is upregulated in renal lipotoxicity and may play an important role in fatty acid-induced inflammation and tubular cell damage in obesity and diabetic kidney disease.