Upregulation of podocyte-secreted angiopoietin-like-4 in diabetic nephropathy

Identifying key genes for diabetic kidney disease by bioinformatics analysis

BACKGROUND

There are no reliable molecular targets for early diagnosis and effective treatment in the clinical management of diabetic kidney disease (DKD). To identify novel gene factors underlying the progression of DKD.

METHODS

The public transcriptomic datasets of the alloxan-induced DKD model and the streptozotocin-induced DKD model were retrieved to perform an integrative bioinformatic analysis of differentially expressed genes (DEGs) shared by two experimental animal models. The dominant biological processes and pathways associated with DEGs were identified through enrichment analysis. The expression changes of the key DEGs were validated in the classic db/db DKD mouse model.

RESULTS

The downregulated and upregulated genes in DKD models were uncovered from GSE139317 and GSE131221 microarray datasets. Enrichment analysis revealed that metabolic process, extracellular exosomes, and hydrolase activity are shared biological processes and molecular activity is altered in the DEGs. Importantly, Hmgcs2, angptl4, and Slco1a1 displayed a consistent expression pattern across the two DKD models. In the classic db/db DKD mice, Hmgcs2 and angptl4 were also found to be upregulated while Slco1a1 was downregulated in comparison to the control animals.

CONCLUSIONS

In summary, we identified the common biological processes and molecular activity being altered in two DKD experimental models, as well as the novel gene factors (Hmgcs2, Angptl4, and Slco1a1) which may be implicated in DKD. Future works are warranted to decipher the biological role of these genes in the pathogenesis of DKD.

Expression of Angiopoetin-Like Protein-4 and Kidney Injury Molecule-1 as Preliminary Diagnostic Markers for Diabetes-Related Kidney Disease: A Single Center-Based Cross-Sectional Study

The purpose of the study was to examine the urinary levels of kidney injury molecule-1 (KIM-1) and angiopoietin-like protein-4 (ANGPTL-4) in individuals with diabetic kidney disease (DKD) and their association with established DKD diagnostic markers such as albuminuria and estimated glomerular filtration rate (eGFR). Levels of ANGPTL-4 and KIM-1 were estimated in urine samples. A total of 135 participants were recruited into three groups: 45 diabetes type 2 patients in the control group and 90 DKD patients in two disease groups. Concentrations of ANGPTL-4 and KIM-1 were conclusively related to the urinary albumin-creatinine ratio (UACR). Also, the levels of both ANGPTL-4 and KIM-1 were negatively associated with the eGFR. Multivariable Poisson regression analysis showed that urinary ANGPTL-4 (PR: 3.40; 95% CI: 2.32 to 4.98; p < 0.001) and KIM-1 (PR: 1.25; 95% CI: 1.14 to 1.38; p < 0.001) were prevalent in DKD patients. Receiver operating characteristic (ROC) analysis of urinary ANGPTL-4 and KIM-1 in the combined form resulted in an area under curve (AUC) of 0.967 (95%CI: 0.932-1.000; p < 0.0001) in the microalbuminuria group and 1 (95%CI: 1.000-1.000; p < 0.0001) in the macroalbuminuria group. The association of urinary levels of ANGPTL-4 and KIM-1 with UACR and eGFR and significant prevalence in the diabetic kidney disease population illustrates the diagnostic potential of these biomarkers.

Crosstalk between the liver and kidney in diabetic nephropathy

Diabetic nephropathy (DN) is a serious complication of diabetes, and its pathogenesis has not been fully elucidated. Recently, communication between organs has gradually become a new focus in the study of diseases pathogenesis, and abnormal interorgan communication has been proven to be involved in the occurrence and progression of many diseases. As an important metabolic organ in the human body, the liver plays an important role in maintaining homeostasis in humans. The liver secretes a series of proteins called hepatokines that affect adjacent and distal organs through paracrine or endocrine signaling pathways. In this review, we summarize some of the hepatokines identified to date and describe their roles in DN to discuss the possibility that the liver-renal axis is potentially useful as a therapeutic target for DN. We summarize the important hepatokines identified thus far and discuss their relationship with DN. We propose for the first time that the "liver-renal axis" is a potential therapeutic target in individuals with DN.

ManNAc protects against podocyte pyroptosis via inhibiting mitochondrial damage and ROS/NLRP3 signaling pathway in diabetic kidney injury model

Podocyte pyroptosis is an inflammatory form of cell death associated with Diabetic nephropathy (DN). It is reported that hyposialylated Angiopoietin-like-4 (Angptl4) secreted by glomerular podocytes plays an important role in the formation of proteinuria. Previous study indicated that supplementation of sialic acid precursor N-acetylmannosamine (ManNAc) could inhibit podocyte apoptosis and actin cytoskeleton rearrangement. Nevertheless, whether ManNAc could improve diabetic kidney damage by inhibiting podocyte pyroptosis remains unclear. This study aimed to explore the effect of ManNAc therapy on alleviating diabetic renal injury and podocyte pyroptosis, and its possible mechanism was also figured out. The male 8-week-old C57BL/6 mice were divided into three groups: control group, Streptozocin (STZ)-induced DN group, and ManNAc treated diabetic group. Then, the changes in renal function, renal histopathology, podocyte pyroptosis, reactive oxygen species (ROS), and mitochondrial dysfunction were measured. Herein, we observed that the upregulated expression of Angptl4 was involved in podocyte injury. ManNAc treatment ameliorated podocyte ultrastructure, renal function, and renal histopathology in STZ-induced DN mice. In addition, ManNAc administration attenuated podocyte cell death and suppressed the activation of Nucleotide leukin-rich polypeptide 3 (NLRP3), caspase-1, and interleukin-1β (IL-1β), and the cleavage of gasdermin-D (GSDMD). Moreover, ManNAc inhibited ROS production and restored mitochondrial morphology in vivo and vitro. Further, ManNAc administration significantly alleviated podocyte pyroptosis through inhibiting ROS/NLRP3 signaling pathway. Therefore, these results elucidated that the upregulated expression of Angptl4 was involved in podocyte injury and ManNAc treatment protected against podocyte pyroptosis via inhibiting mitochondrial injury and ROS/NLRP3 signaling pathway in DN mice.

Urinary podocyte markers in kidney diseases

Podocytes play an important role in the maintenance of kidney function, and they are the primary focus of many kidney diseases. Podocyte injury results in the shedding of podocyte-derived cellular fragments and podocyte-specific molecular targets into the urine, which may serve as biomarkers of kidney diseases. Intact podocytes, either viable or dead, and podocyte-derived microvesicles could be quantified in the urine by various centrifugation, visualization and culture methods. Podocyte-specific protein targets from the nucleus, cytoplasm, slit-diaphragm, glomerular capillary basement membrane, and cytoskeleton, as well as their corresponding messenger RNA (mRNA), in the urine could be quantified by western blotting, ELISA, or quantitative polymerase chain reaction. Although some of these techniques may be expensive or labor-intensive at present, they may become widely available in the future because of the improvement in technology and automation. The application of urinary podocyte markers for the diagnosis and monitoring of various kidney diseases have been explored but the published data in this area are not sufficiently systematic and lack external validation. Further research should focus on standardizing, comparing, and automizing laboratory methods, as well as defining their added value to the routine clinical tests.

The Study of Angptl4-Modulated Podocyte Injury in IgA Nephropathy

Background

Increasing evidence shows that Angptl4 affects proteinuria in podocytes injured kidney disease, however, whether there is a relationship between Angptl4 and IgA nephropathy (IgAN) has not been studied yet.

Methods

Plasma and urine samples were obtained from 71 patients with IgAN and 61 healthy controls. Glomeruli from six renal biopsy specimens (three IgAN patients and three healthy controls) were separated by RNA-Seq. Differentially expressed genes (DEGs) related to podocytes and Angptl4 between IgAN patients and healthy controls were performed using the Limma package. Gene set enrichment analysis was used to determine whether there was a statistically significant difference between the two groups. STRING was used to create a protein-protein interaction network of DEGs. Association analysis between Angptl4 levels and clinical features of IgAN was performed.

Results

Thirty-three podocyte-related and twenty-three Angpt4-related DEGs were found between IgAN patients and healthy controls. By overlapping the genes, FOS and G6PC were found to be upregulated in IgAN patients, while MMP9 was downregulated in IgAN patients. Plasma and urine Angptl4 levels were closely related to the degree of podocyte injury and urine protein, but not to the protein-creatine ratio.

Conclusion

Our findings show that Angptl4 levels in plasma and urine are related to podocyte damage and, therefore, may be a promising tool for assessing the severity of IgAN patients to identify and reverse the progression to ESRD.

Weighted Gene Co-Expression Network Analysis Identifies ANGPTL4 as a Key Regulator in Diabetic Cardiomyopathy via FAK/SIRT3/ROS Pathway in Cardiomyocyte

BACKGROUND

Diabetic cardiomyopathy (DbCM) is characterized by initial impairment of left ventricular relaxation followed by contractile dysfunction. Despite intensive research, the exact mechanism remains so far unsolved.

METHODS

We constructed weighted gene co-expression network analysis (WGCNA) to screen gene modules that were closely related with DbCM based on the GSE5606 dataset, which contained expression data of the cardiac left ventricle in a rodent model of streptozotocin (STZ)-induced DbCM. Then, the most related hub gene, angiopoietin-like 4 (ANGPTL4), was selected for functional ex vivo and in vitro assays. In our experiments, STZ-induced diabetic mice (C57BL/6J) and human cardiomyocytes (AC16) were used to study the functional roles and potential mechanisms of ANGPTL4 in DbCM.

RESULTS

WGCNA analysis revealed the yellow and green modules were most correlated with DbCM, and identified ANGPTL4 as one of the most significantly upregulated hub genes (ANGPTL4, ACOT1, DECR1, HMGCS2, and PDK4). Consistent with the bioinformatic analysis, the amount of ANGPTL4 was significantly upregulated in diabetic mouse heart. DbCM group, compared with the control group, had increased phosphorylation of focal adhesion kinase (FAK), reduced SIRT3 expression, increased SOD2 acetylation, upregulated NADPH oxidase activation, elevated reactive oxygen species (ROS) produciton, and enhanced apoptosis in the diabetic mouse heart. Moreover, ANGPTL4 induced apoptosis via FAK/SIRT3/ROS pathway in human cardiomyocytes (AC16) under high glucose condition in vitro.These effects were abrogated by treatment of two independent siRNA for ANGPTL4, whereas exogenous recombinant ANGPLT4 protein treatment exacerbated those effects in AC16.

CONCLUSION

We found ANGPTL4, ACOT1, DECR1, HMGCS2, and PDK4 were significantly increased in diabetic heart. ANGPTL4 could promote cardiac apoptosis via a FAK/SIRT3/ROS dependent signaling pathway in DbCM.

Calcineurin inhibitors ameliorate PAN-induced podocyte injury through the NFAT-Angptl4 pathway

Podocyte injury plays a vital role in proteinuria and nephrotic syndrome. Calcineurin (CaN) inhibitors are effective in reducing proteinuria. However, their molecular mechanism is still not fully understood. Angiopoietin-like-4 (ANGPTL4) is a secreted protein that mediates proteinuria in podocyte-related nephropathy. In this study, we established a puromycin aminonucleoside (PAN)-induced minimal-change disease (MCD) rat model and a cultured podocyte injury model. We found that CaN inhibitors protected against PAN-induced podocyte injury, accompanied by an inhibition of Nfatc1 and Angptl4 both in vivo and in vitro. Nfatc1 overexpression and knockdown experiments indicated that Angptl4 was regulated by Nfatc1 in podocytes. ChIP assays further demonstrated that Nfatc1 increased Angptl4 expression by binding to the Angptl4 promoter. In addition, overexpression and knockdown of Angptl4 revealed that Angptl4 directly induced rearrangement of the cytoskeleton of podocytes, reduced the expression of synaptopodin, and enhanced PAN-induced podocyte apoptosis. Furthermore, in a cohort of 83 MCD and 94 membranous nephropathy (MN) patients, we found increased expression of serum ANGPTL4 compared to 120 healthy controls, and there were close correlations between serum ANGPTL4 and Alb, urinary protein, urinary Alb, eGFR, Scr, and BUN in MCD patients. No obvious correlation was found in MN patients. Immunofluorescence studies indicated that increased ANGPTL4 in MCD and MN patients was located mostly in podocytes. In conclusion, our results demonstrate that CaN inhibitors ameliorate PAN-induced podocyte injury by targeting Angptl4 through the NFAT pathway, and Angptl4 plays a vital role in podocyte injury and is involved in human podocyte-related nephropathy. © 2020 The Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Lipopolysaccharide-induced podocyte injury is regulated by calcineurin/NFAT and TLR4/MyD88/NF-κB signaling pathways through angiopoietin-like protein 4

Podocyte injury is an important cause of proteinuria. Angiopoietin-like protein 4 (Angptl4) is a secreted glycoprotein and has a role in proteinuria. However, the exact role of Angptl4 in podocyte injury and its upstream regulators has not been clarified. In this study, we used lipopolysaccharide (LPS)-induced mice and cultured podocytes as podocyte injury models. Our results indicated that LPS increased the expression of podocyte Angptl4 in vivo and in vitro. Furthermore, we showed that Angptl4 overexpression deteriorated LPS-induced podocyte injury by inducing podocyte cytoskeleton rearrangement, reducing the expression of synaptopodin while Angptl4 knockdown alleviated LPS-induced podocyte injury. In addition, we found that inhibitors and siRNA targeting TLR4/MyD88/NF-κB signaling inhibited the upregulation of Angptl4 in LPS-induced podocytes. Moreover, inhibitors and siRNA targeting calcineurin/NFAT signaling also relieved LPS-induced Angptl4 expression and podocyte injury in vivo and in vitro. Taken together, our study has elucidated that both of the TLR4/MyD88/NF-κB and calcineurin/NFAT signaling mediate the upregulation of Angptl4 in LPS-induced podocytes, which has important implications for further understanding the molecular mechanism of LPS-induced podocyte injury.

Hyposialylated angiopoietin-like-4 induces apoptosis of podocytes via β1 Integrin/FAK signaling in diabetic nephropathy

Angiopoietin-like-4 (ANGPTL4) is reported to mediate proteinuria in some types of glomerulonephropathy. However, the mechanism underlying the effect on podocytes of ANGPTL4 under pathologic conditions in diabetic nephropathy (DN) is unclear. We investigated the role of ANGPTL4 in the pathogenesis of DN. In DN rats, elevated ANGPTL4 expression was associated with increased proteinuria, glomerular hypertrophy, and ultrastructural changes in podocytes. In vitro, hyperglycemia induced the upregulation of ANGPTL4, which led to activation of integrin-β1/FAK signaling with increased apoptosis of podocytes and actin cytoskeleton derangement. These pathological changes were reversed by transfection with a lentivirus expressing short hairpin RNA against integrin-β1 or an ANGPTL4-neutralizing antibody in vitro. Furthermore, supplementation with the sialic acid precursor ManNAc reversed these pathological changes and conferred renoprotection in a mouse model of DN. Our findings suggest that ANGPTL4 mediates high glucose-induced loss of podocytes by modulating their detachment and apoptosis in vivo and in vitro. This study deepens our understanding of the mechanisms of podocyte loss in DN and shows targeting ANGPTL4-related signaling has therapeutic potential for DN.

Alteration of Angiopoietin-Like Protein 4 Levels in Serum or Urine Correlate with Different Biochemical Markers in Hyperlipidemia-Related Proteinuria

Angiopoietin-like protein 4 (ANGPTL4) is widely known as a key regulator of lipid metabolism. We investigated the relationship between ANGPTL4 expression in serum or urine and blood lipid or urine protein levels of patients with hyperlipidemia- (HL-) related proteinuria. Sixty-eight patients with HL-related proteinuria (HL-Pro group), 68 patients with HL without proteinuria (HL-NPro group), 46 patients with non-HL-related proteinuria (NHL-Pro group), and 50 healthy control (Con) subjects were selected. There were no significant differences in serum ANGPTL4 levels between the Con group (36.82 ± 17.03 ng/ml) and the HL-Pro group (27.94 (18.90, 53.72) ng/ml). Additionally, the serum ANGPTL4 levels in the HL-Pro group were significantly lower than those in the HL-NPro group (53.32 ± 24.01 ng/ml) (P < 0.001). The urine ANGPTL4/Cr levels in the HL-Pro group (52.01 (45.25, 79.79) μg/g) were significantly higher than those in the HL-NPro group (9.96 (8.35, 12.43) ng/ml) (P < 0.05). A significant alteration in urine ANGPTL4/Cr levels was observed in the NHL-Pro group (69.41 ± 55.36 μg/g) and the Con group (10.08 ± 2.38 μg/g) as well. There was no correlation between serum and urine ANGPTL4 levels of the four groups (P > 0.05). Serum ANGPTL4 levels (HL-Pro/HL-NPro group) were positively correlated with total cholesterol (TC) and triglyceride (TG) levels in hyperlipidemia patients. However, there was no correlation between urinary ANGPTL4 levels and TC or TG (P > 0.05). Urine ANGPTL4 levels were positively correlated with 24hUPro in patients with renal impairment (HL-Pro/NHL-Pro group). To summarize, ANGPTL4 may be considered an accurate predictor of proteinuria with HL. Notably, serum or urine ANGPTL4 levels indicated the degree of proteinuria or hyperlipidemia, respectively, in HL patients.

Knockdown of ANGPTL-4 inhibits inflammatory response and extracellular matrix accumulation in glomerular mesangial cells cultured under high glucose condition

Diabetic nephropathy (DN) is one of the major diabetic complications that lead to end-stage renal failure. Angiopoietin-like protein-4 (ANGPTL-4) has been reported to be dysregulated in diabetes mellitus and diabetic complications. However, the role of ANGPTL-4 in glomerular mesangial cells (MCs) during DN remains unclear. In the present study, we evaluated the role of ANGPTL-4 in MCs in response to high glucose (HG) condition and the potential mechanism. The results proved that ANGPTL-4 expression is significantly increased in HG-stimulated MCs. Knockdown of ANGPTL-4 suppressed HG-induced cell proliferation of MCs. The production of pro-inflammatory cytokines including TNF-α, IL-1β, IL-6 were decreased in ANGPTL-4 knocked down MCs. Inhibition of ANGPTL-4 markedly suppressed the expressions of extracellular matrix (ECM) proteins, collagen IV (Col IV) and fibronectin (FN), in HG-stimulated MCs. Furthermore, ANGPTL-4 knockdown inhibited the HG-induced activation of NF-κB signaling pathway in MCs. Collectively, knockdown of ANGPTL-4 suppressed HG-induced cell proliferation, inflammatory response, and ECM accumulation inhibiting NF-κB signaling pathway in MCs. These findings suggested that ANGPTL-4 might be a therapeutic target for the prevention and treatment of DN.

Nephroprotective effect of losartan in IgA model rat

Objective

This study was performed to investigate the possible nephroprotective effects of losartan in a rat model of experimental IgA nephropathy (IgAN).

Methods

Thirty male Sprague–Dawley rats were randomly divided into three groups. The rats in the model group were treated with bovine serum albumin (oral gavage), lipopolysaccharide (tail vein injection), and carbon tetrachloride (subcutaneous injection); rats in the losartan group received treatments similar to those of the model group, and were orally gavaged with losartan; and rats in the control group received phosphate-buffered saline alone (both orally and intravenously).

Results

Losartan treatment lowered the 24-hour urinary protein, serum blood urea nitrogen, and serum creatinine levels. Proliferating mesangial cells with a variable increase in the mesangial matrix were detected in the model group, whereas injury in the losartan group was significantly attenuated. Immunohistochemistry revealed that the expression levels of transforming growth factor (TGF)-β1 and α-smooth muscle actin were significantly elevated in the model group but reduced in the losartan group. The expression levels of TGF-β1 and monocyte chemoattractant protein-1 were minimal in the control group, significantly increased in the model group, and reduced in the losartan group.

Conclusion

Losartan has a protective effect against tubulointerstitial injury in IgAN.

Long-term expression of glomerular genes in diabetic nephropathy

Background

Although diabetic nephropathy (DN) is the most common cause for end-stage renal disease in western societies, its pathogenesis still remains largely unclear. A different gene pattern of diabetic and healthy kidney cells is one of the probable explanations. Numerous signalling pathways have emerged as important pathophysiological mechanisms for diabetes-induced renal injury.

Methods

Glomerular cells, as podocytes or mesangial cells, are predominantly involved in the development of diabetic renal lesions. While many gene assays concerning DN are performed with whole kidney or renal cortex tissue, we isolated glomeruli from black and tan, brachyuric (BTBR) obese/obese (ob/ob) and wildtype mice at four different timepoints (4, 8, 16 and 24 weeks) and performed an mRNA microarray to identify differentially expressed genes (DEGs). In contrast to many other diabetic mouse models, these homozygous ob/ob leptin-deficient mice develop not only a severe type 2 diabetes, but also diabetic kidney injury with all the clinical and especially histologic features defining human DN. By functional enrichment analysis we were able to investigate biological processes and pathways enriched by the DEGs at different disease stages. Altered expression of nine randomly selected genes was confirmed by quantitative polymerase chain reaction from glomerular RNA.

Results

Ob/ob type 2 diabetic mice showed up- and downregulation of genes primarily involved in metabolic processes and pathways, including glucose, lipid, fatty acid, retinol and amino acid metabolism. Members of the CYP4A and ApoB family were found among the top abundant genes. But more interestingly, altered gene loci showed enrichment for processes and pathways linked to angioneogenesis, complement cascades, semaphorin pathways, oxidation and reduction processes and renin secretion.

Conclusion

The gene profile of BTBR ob/ob type 2 diabetic mice we conducted in this study can help to identify new key players in molecular pathogenesis of diabetic kidney injury.

Do ANGPTL-4 and galectin-3 reflect the severity of coronary artery disease?

BACKGROUND

Coronary artery disease (CAD) is one of the leading causes of mortality and morbidity worldwide. We thereby sought to investigate whether the biomarkers, angiopoietin-like 4 (ANGPTL-4) and galectin-3, reflect the severity of CAD.

METHODS

Patients were screened based on inclusion/exclusion criteria and written informed consent was obtained from the patients. Serum ANGPTL-4 and galectin-3 was quantified using enzyme-linked immunosorbent assay (ELISA) and correlated with the Global Registry of Acute Coronary Events (GRACE) and GENSINI score using Spearman's rank correlation coefficient and multivariate analysis.

RESULTS

A total of 226 patients consisting of ST-segment elevation myocardial infarction (STEMI), non-STEMI/unstable angina (USA), chronic stable angina (CSA) and normal controls (NCs) participated in the study. ANGPTL-4 and galectin-3 were significantly higher in CAD than the NC group. ANGPTL-4 showed significant negative correlation with GRACE score in acute coronary syndrome (ACS) ( r = -0.211, p = 0.03) patients. ANGPTL-4 showed significant positive correlation with serum creatinine ( r = 0.304, p = 0.056) and body mass index (BMI) ( r = 0.424, p = 0.009) in CSA patients. A modest positive correlation was observed between the serum galectin-3 levels and GRACE score ( r = 0.187, p = 0.055) in ACS patients. However, on multivariate analysis the positive correlation relationship between ANGPTL-4 and galectin-3 with the severity of CAD was not sustained.

CONCLUSION

In conclusion, ANGPTL-4 and galectin-3 do not appear to have a promising role for assessing the severity of CAD. Nevertheless these biomarkers do warrant further exploration in improving the management of CAD.

Angiopoietin-like-4 and minimal change disease

Background

Minimal Change Disease (MCD) is the most common type of nephrotic syndrome in children. Angiopoietin-like-4 (Angplt4) has been proposed as mediator of proteinuria in MCD. The aim of this study was to evaluate the role of Angptl4 as a biomarker in MCD.

Methods

Patients with biopsy-proven primary MCD, focal segmental glomerulosclerosis, membranous nephropathy (60, 52 and 52 respectively) and 18 control subjects had urinary and serum Angptl4 measured by Elisa. Frozen kidney tissue sections were stained for Angptl4.

Results

Angptl4 was not identified in glomeruli of MCD patients in relapse. Urinary Angptl4 levels were elevated in MCD in relapse as well as in patients with massive proteinuria due to other glomerular diseases.

Conclusion

Neither serum nor urine Angptl4 appear to be good biomarkers in MCD. Elevated urinary Angptl4 n glomerular disease appears to reflect the degree of proteinuria rather than any specific disease.

Human Urine Proteomics: Analytical Techniques and Clinical Applications in Renal Diseases

Urine has been in the center of attention among scientists of clinical proteomics in the past decade, because it is valuable source of proteins and peptides with a relative stable composition and easy to collect in large and repeated quantities with a noninvasive procedure. In this review, we discuss technical aspects of urinary proteomics in detail, including sample preparation, proteomic technologies, and their advantage and disadvantages. Several recent experiments are presented which applied urinary proteome for biomarker discovery in renal diseases including diabetic nephropathy, immunoglobulin A (IgA) nephropathy, focal segmental glomerulosclerosis, lupus nephritis, membranous nephropathy, and acute kidney injury. In addition, several available databases in urinary proteomics are also briefly introduced.

Angiopoietin-Like-4, a Potential Target of Tacrolimus, Predicts Earlier Podocyte Injury in Minimal Change Disease

Podocyte injury plays central roles in proteinuria and kidney dysfunction, therefore, identifying specific biomarker to evaluate earlier podocyte injury is highly desirable. Podocyte-secreted angiopoietin-like-4 (Angptl4) mediates proteinuria in different types of podocytopathy. In the present study, we established an experimental minimal change disease (MCD) rat model, induced by adriamycin (ADR) and resulted in definite podocyte injury, to identify the dynamic changes in Angptl4 expression. We also investigated the direct effects of tacrolimus on Angptl4 and podocyte repair. We determined that the glomerular Angptl4 expression was rapidly upregulated and reached a peak earlier than desmin, an injured podocyte marker, in the ADR rats. Furthermore, this upregulation occurred prior to heavy proteinuria and was accompanied by increased urinary Angptl4. We observed that the Angptl4 upregulation occurred only when podocyte was mainly damaged since we didn’t observe little Angptl4 upregulation in MsPGN patients. In addition, we observed the glomerular Angptl4 mainly located in injured podocytes rather than normal podocytes. Moreover, we found that tacrolimus treatment significantly promoted podocyte repair and reduced glomerular and urinary Angptl4 expression at an earlier stage with a significant serum Angptl4 upregulation. And similar results were confirmed in MCD patients. In conclusion, this study represents the first investigation to demonstrate that Angptl4 can predict podocyte injury at earlier stages in MCD and the identification of earlier podocyte injury biomarkers could facilitate the prompt diagnosis and treatment of patients with podocytopathy, as well as determination of the prognosis and treatment efficacy in these diseases.