Inhibition of RAC attenuates Adriamycin-induced podocyte injury

Minimal Change Disease (MCD), which is associated with podocyte injury, is the leading cause of nephrotic syndrome in children. A considerable number of patients experience relapses and require prolonged use of prednisone and immunosuppressants. Multi-drug resistance and frequent relapses can lead to disease progression to focal and segmental glomerulosclerosis (FSGS). To identify potential targets for therapy of podocyte injury, we examined microarray data of mRNAs in glomerular samples from both MCD patients and healthy donors, obtained from the GEO database. Differentially expressed genes (DEGs) were used to construct the protein-protein interactions (PPI) network through the application of the search tool for the retrieval of interacting genes (STRING) tool. The most connected genes in the network were ranked using cytoHubba. 16 hub genes were selected and validated by qRT-PCR. RAC2 was identified as a potential therapeutic target for further investigation. By downregulating RAC2, Adriamycin (ADR)-induced human podocytes (HPCs) injury was attenuated. EHT-1864, a small molecule inhibitor that targets the RAC (RAC1, RAC2, RAC3) family, proved to be more effective than RAC2 silencing in reducing HPCs injury. In conclusion, our research suggests that EHT-1864 may be a promising new molecular drug candidate for patients with MCD and FSGS.

Manganese induces podocyte injury through regulating MTDH/ALKBH5/NLRP10 axis: Combined analysis at epidemiology and molecular biology levels

Manganese (Mn) is an essential micronutrient required for various biological processes but excess exposure to Mn can cause neurotoxicity. However, there are few reports regarding the toxicity effect of Mn on the kidney as well as the underlying molecule mechanism. Herein, in vivo experiments were adopted to assess the toxicity effects associated with Mn, and found that chronic Mn treatment induced the injury of glomerular podocytes but not renal tubule in rats. Genome-wide CRISPR/Cas9 knockout screen was then employed to explore the biotargets of the toxic effect of Mn on podocytes. Through functional analyses of the enriched candidate genes, NLRP10 was found to be significantly up-regulated and mediated Mn-induced podocyte apoptosis. Further mechanism investigation revealed that NLRP10 expression was regulated by demethylase AlkB homolog 5 (ALKBH5) in an m6A-dependent fashion upon Mn treatment. Moreover, Mn could directly bind to Metadherin (MTDH) and promoted its combination with ALKBH5 to promote NLRP10 expression and cell apoptosis. Finally, logistic regressions, restricted cubic spline regressions and uniform cubic B-spline were used to investigate the association between Mn exposure and the risk of chronic kidney disease (CKD). A U-shaped nonlinear relationship between CKD risk and plasma Mn level, and a positive linear relationship between CKD risk and urinary Mn levels was found in our case-control study. To sum up, our findings illustrated that m6A-dependent NLRP10 regulation is indispensable for podocyte apoptosis and nephrotoxicity induced by Mn, providing fresh insight into understanding the health risk of Mn and a novel target for preventing renal injury in Mn-intoxicated patients.

Scutellarin ameliorates diabetic nephropathy via TGF-β1 signaling pathway

Breviscapine, a natural flavonoid mixture derived from the traditional Chinese herb Erigeron breviscapus (Vant.) Hand-Mazz, has demonstrated a promising potential in improving diabetic nephropathy (DN). However, the specific active constituent(s) responsible for its therapeutic effects and the underlying pharmacological mechanisms remain unclear. In this study, we aimed to investigate the impact of scutellarin, a constituent of breviscapine, on streptozotocin-induced diabetic nephropathy and elucidate its pharmacological mechanism(s). Our findings demonstrate that scutellarin effectively ameliorates various features of DN in vivo, including proteinuria, glomerular expansion, mesangial matrix accumulation, renal fibrosis, and podocyte injury. Mechanistically, scutellarin appears to exert its beneficial effects through modulation of the transforming growth factor-β1 (TGF-β1) signaling pathway, as well as its interaction with the extracellular signal-regulated kinase (Erk) and Wnt/β-catenin pathways.

Metadherin orchestrates PKA and PKM2 to activate β-catenin signaling in podocytes during proteinuric chronic kidney disease

Podocyte damage is the major cause of glomerular injury and proteinuria in multiple chronic kidney diseases. Metadherin (MTDH) is involved in podocyte apoptosis and promotes renal tubular injury in mouse models of diabetic nephropathy and renal fibrosis; however, its role in podocyte injury and proteinuria needs further exploration. Here, we show that MTDH was induced in the glomerular podocytes of patients with proteinuric chronic kidney disease and correlated with proteinuria. Podocyte-specific knockout of MTDH in mice reversed proteinuria, attenuated podocyte injury, and prevented glomerulosclerosis after advanced oxidation protein products challenge or adriamycin injury. Furthermore, specific knockout of MTDH in podocytes repressed β-catenin phosphorylation at the Ser675 site and inhibited its downstream target gene transcription. Mechanistically, on the one hand, MTDH increased cAMP and then activated protein kinase A (PKA) to induce β-catenin phosphorylation at the Ser675 site, facilitating the nuclear translocation of MTDH and β-catenin; on the other hand, MTDH induced the deaggregation of pyruvate kinase M2 (PKM2) tetramers and promoted PKM2 monomers to enter the nucleus. This cascade of events leads to the formation of the MTDH/PKM2/β-catenin/CBP/TCF4 transcription complex, thus triggering TCF4-dependent gene transcription. Inhibition of PKA activity by H-89 or blockade of PKM2 deaggregation by TEPP-46 abolished this cascade of events and disrupted transcription complex formation. These results suggest that MTDH induces podocyte injury and proteinuria by assembling the β-catenin-mediated transcription complex by regulating PKA and PKM2 function.

CircGAB1 Facilitates Podocyte Injury Through Sponging miR-346 and Activating MAPK6 in Diabetic Nephropathy

BACKGROUND

Podocyte injury is very important process in diabetic nephropathy (DN) progression. Circular RNA (circRNA) takes part in regulating the advancement of DN. Herein, we explored the role and mechanism of circGAB1 in DN progression.

METHODS

The abundances of circGAB1, microRNA-346 (miR-346) and mitogen-activated protein kinase 6 (MAPK6) were detected by qRT-PCR in DN serum samples and podocyte HGPC. Moreover, cell viability and apoptosis were determined using CCK8 assay and flow cytometry. Also, the protein levels of MAPK6, proliferation-related markers and apoptosis-related markers were analyzed by western blot. ELISA assay was used to measure the levels of inflammatory factors, and corresponding kits were used to detect the levels of oxidative stress-related markers. The relationship between miR-346 and circGAB1 or MAPK6 was distinguished by dual-luciferase reporter assay.

RESULTS

CircGAB1 expression was increased in DN serum samples and HG-treated HGPC cells. CircGAB1 knockdown inhibited HG-induced apoptosis, inflammatory response and oxidative stress in HGPC cells. In terms of mechanism, circGAB1 sponged miR-346, and miR-346 targeted MAPK6. The inhibition effect of circGAB1 knockdown on HG-induced podocyte injury could be reversed by miR-346 inhibitor. Moreover, miR-346 overexpression repressed HG-induced podocyte injury by targeting MAPK6. CircGAB1 served as miR-346 sponge to positively regulate MAPK6.

CONCLUSION

CircGAB1 contributed to podocyte injury through mediating miR-346/MAPK6 axis, suggesting that circGAB1 might promote DN progression.

Amelioration of diabetic nephropathy in mice by a single intravenous injection of human mesenchymal stromal cells at early and later disease stages is associated with restoration of autophagy

BACKGROUND AND AIMS

Mesenchymal stromal cells (MSCs) a potentially effective disease-modulating therapy for diabetic nephropathy (DN) but their clinical translation has been hampered by incomplete understanding of the optimal timing of administration and in vivo mechanisms of action. This study aimed to elucidate the reno-protective potency and associated mechanisms of single intravenous injections of human umbilical cord-derived MSCs (hUC-MSCs) following shorter and longer durations of diabetes.

METHODS

A streptozotocin (STZ)-induced model of diabetes and DN was established in C57BL/6 mice. In groups of diabetic animals, human (h)UC-MSCs or vehicle were injected intravenously at 8 or 16 weeks after STZ along with vehicle-injected non-diabetic animals. Diabetes-related kidney abnormalities was analyzed 2 weeks later by urine and serum biochemical assays, histology, transmission electron microscopy and immunohistochemistry. Serum concentrations of pro-inflammatory and pro-fibrotic cytokines were quantified by ELISA. The expression of autophagy-related proteins within the renal cortices was investigated by immunoblotting. Bio-distribution of hUC-MSCs in kidney and other organs was evaluated in diabetic mice by injection of fluorescent-labelled cells.

RESULTS

Compared to non-diabetic controls, diabetic mice had increases in urine albumin creatinine ratio (uACR), mesangial matrix deposition, podocyte foot process effacement, glomerular basement membrane thickening and interstitial fibrosis as well as reduced podocyte numbers at both 10 and 18 weeks after STZ. Early (8 weeks) hUC-MSC injection was associated with reduced uACR and improvements in multiple glomerular and renal interstitial abnormalities as well as reduced serum IL-6, TNF-α, and TGF-β1 compared to vehicle-injected animals. Later (16 weeks) hUC-MSC injection also resulted in reduction of diabetes-associated renal abnormalities and serum TGF-β1 but not of serum IL-6 and TNF-α. At both time-points, the kidneys of vehicle-injected diabetic mice had higher ratio of p-mTOR to mTOR, increased abundance of p62, lower abundance of ULK1 and Atg12, and reduced ratio of LC3B to LC3A compared to non-diabetic animals, consistent with diabetes-associated suppression of autophagy. These changes were largely reversed in the kidneys of hUC-MSC-injected mice. In contrast, neither early nor later hUC-MSC injection had effects on blood glucose and body weight of diabetic animals. Small numbers of CM-Dil-labeled hUC-MSCs remained detectable in kidneys, lungs and liver of diabetic mice at 14 days after intravenous injection.

CONCLUSIONS

Single intravenous injections of hUC-MSCs ameliorated glomerular abnormalities and interstitial fibrosis in a mouse model of STZ-induced diabetes without affecting hyperglycemia, whether administered at relatively short or longer duration of diabetes. At both time-points, the reno-protective effects of hUC-MSCs were associated with reduced circulating TGF-β1 and restoration of intra-renal autophagy.

Roles of the mechanosensitive ion channel Piezo1 in the renal podocyte injury of experimental hypertensive nephropathy

Glomerular podocyte injury plays an essential role in proteinuria pathogenesis, a hallmark of chronic kidney disease, including hypertensive nephropathy. Although podocytes are susceptible to mechanical stimuli, their mechanotransduction pathways remain elusive. Piezo proteins, including Piezo1 and 2, are mechanosensing ion channels that mediate various biological phenomena. Although renal Piezo2 expression and its alteration in rodent dehydration and hypertension models have been reported, the role of Piezo1 in hypertensive nephropathy and podocyte injury is unclear. In this study, we examined Piezo1 expression and localization in the kidneys of control mice and in those of mice with hypertensive nephrosclerosis. Uninephrectomized, aldosterone-infused, salt-loaded mice developed hypertension, albuminuria, podocyte injury, and glomerulosclerosis. RNAscope in situ hybridization revealed that Piezo1 expression was enhanced in the podocytes, mesangial cells, and distal tubular cells of these mice compared to those of the uninephrectomized, vehicle-infused control group. Piezo1 upregulation in the glomeruli was accompanied by the induction of podocyte injury-related markers, plasminogen activator inhibitor-1 and serum/glucocorticoid regulated kinase 1. These changes were reversed by antihypertensive drug. Exposure of Piezo1-expressing cultured podocytes to mechanical stretch activated Rac1 and upregulated the above-mentioned markers, which was antagonized by the Piezo1 blocker grammostola mechanotoxin #4 (GsMTx4). Administration of Piezo1-specific agonist Yoda1 mimicked the effects of mechanical stretch, which was minimized by the Yoda1-specific inhibitor Dooku1 and Rac inhibitor. Rac1 was also activated in the above-mentioned hypertensive mice, and Rac inhibitor downregulated gene expression of podocyte injury-related markers in vivo. Our results suggest that Piezo1 plays a role in mechanical stress-induced podocyte injury.

Urinary podocyte markers of disease activity, therapeutic efficacy, and long-term outcomes in acute and chronic kidney diseases

A critical degree of podocyte depletion causes glomerulosclerosis, and persistent podocyte loss in glomerular diseases drives the progression to end-stage kidney disease. The extent of podocyte injury at a point in time can be histologically assessed by measuring podocyte number, size, and density ("Biopsy podometrics"). However, repeated invasive renal biopsies are associated with increased risk and cost. A noninvasive method for assessing podocyte injury and depletion is required. Albuminuria and proteinuria do not always correlate with disease activity. Podocytes are located on the urinary space side of the glomerular basement membrane, and as they undergo stress or detach, their products can be identified in urine. This raises the possibility that urinary podocyte products can serve as clinically useful markers for monitoring glomerular disease activity and progression ("Urinary podometrics"). We previously reported that urinary sediment podocyte mRNA reflects disease activity in both animal models and human glomerular diseases. This includes diabetes and hypertension which together account for 60% of new-onset dialysis induction patients. Improving approaches to preventing progression is an urgent priority for the renal community. Sufficient evidence now exists to indicate that monitoring urinary podocyte markers could serve as a useful adjunctive strategy for determining the level of current disease activity and response to therapy in progressive glomerular diseases.

QiDiTangShen granules alleviates diabetic nephropathy podocyte injury: A network pharmacology study and experimental validation in vivo and vitro

Background

QiDiTangShen granules (QDTS), a traditional Chinese medicine (TCM) compound prescription, have remarkable efficacy in diabetic nephropathy (DN) patients, and their pharmacological mechanism needs further exploration.

Methods

According to the active ingredients and targets of the QDTS in the TCMSP database, the network pharmacology of QDTS was investigated. The potential active ingredients were chosen based on the oral bioavailability and the drug similarity index. At the same time, targets for DN-related disease were obtained from GeneCards, OMIM, PharmGKB, TTD, and DrugBank. The TCM-component-target network and the protein-protein interaction (PPI) network were constructed with the Cytoscape and STRING platforms, respectively, and then the core targets of DN were selected with CytoNCA. GO and KEGG enrichment analysis using R software. Molecular docking to identify the core targets of QDTS for DN. In vivo, db/db mice were treated as DN models, and the urine microalbuminuria, the pathological changes in the kidney and the protein expression levels of p-PI3K, p-Akt, JUN, nephrin and synaptopodin were detected by immunohistochemistry, immunofluorescence method and Western blotting. After QDTS was used in vitro, the protein expression of mouse podocyte clone-5 (MPC5) cells was detected by immunohistochemistry, immunofluorescence and Western blot.

Results

Through network pharmacology analysis, 153 potential targets for DN in QDTS were identified, 19 of which were significant. The KEGG enrichment analysis indicated that QDTS might have therapeutic effects on IL-17, TNF, AGE-RAGE, PI3K-Akt, HIF-1, and EGFR through interfering with Akt1 and JUN. The main active ingredients in QDTS are quercetin, β-sitosterol, stigmasterol and kaempferol. Both in vivo and in vitro studies showed that QDTS could decrease the urine microalbuminuria and renal pathology of db/db mice, and alleviate podocyte injuries through the PI3K/Akt signaling pathway.

Conclusion

Through network pharmacology, in vivo and in vitro experiments, QDTS has been shown to improve the urine microalbuminuria and renal pathology in DN, and to reduce podocyte damage via the PI3K/Akt pathway.

ALCAT1-mediated abnormal cardiolipin remodelling promotes mitochondrial injury in podocytes in diabetic kidney disease

BACKGROUND

Cardiolipin (CL) plays a critical role in maintaining mitochondrial membrane integrity and overall mitochondrial homeostasis. Recent studies have suggested that mitochondrial damage resulting from abnormal cardiolipin remodelling is associated with the pathogenesis of diabetic kidney disease (DKD). Acyl-coenzyme A:lyso-cardiolipin acyltransferase-1 (ALCAT1) was confirmed to be involved in the progression of Parkinson's disease, diet-induced obesity and other ageing-related diseases by regulating pathological cardiolipin remodelling. Thus, the purpose of this investigation was to determine the role of ALCAT1-mediated CL remodelling in DKD and to explore the potential underlying mechanism.

METHODS

In vivo study, the mitochondrial structure was examined by transmission electron microscopy (TEM). The colocalization of ALCAT1 and synaptopodin was evaluated by double immunolabelling. Western blotting (WB) was performed to assess ALCAT1 expression in glomeruli. Lipidomics analysis was conducted to evaluate the composition of reconstructed cardiolipins. In vitro study, the lipidomics, TEM and WB analyses were similar to those in vivo. Mitochondrial function was evaluated by measuring the mitochondrial membrane potential (MMP) and the production of ATP and ROS.

RESULTS

Here, we showed that increased oxidized cardiolipin (ox-CL) and significant mitochondrial damage were accompanied by increased ALCAT1 expression in the glomeruli of patients with DKD. Similar results were found in db/db mouse kidneys and in cultured podocytes stimulated with high glucose (HG). ALCAT1 deficiency effectively prevented HG-induced ox-CL production and mitochondrial damage in podocytes. In contrast, ALCAT1 upregulation enhanced ox-CL levels and podocyte mitochondrial dysfunction. Moreover, treatment with the cardiolipin antioxidant SS-31 markedly inhibited mitochondrial dysfunction and cell injury, and SS-31 treatment partly reversed the damage mediated by ALCAT1 overexpression. We further found that ALCAT1 could mediate the key regulators of mitochondrial dynamics and mitophagy through the AMPK pathway.

CONCLUSIONS

Collectively, our studies demonstrated that ALCAT1-mediated cardiolipin remodelling played a crucial role in DKD, which might provide new insights for DKD treatment. Video Abstract.

Podocyte injury of diabetic nephropathy: Novel mechanism discovery and therapeutic prospects

Diabetic nephropathy (DN) is a severe complication of diabetes mellitus, posing significant challenges in terms of early prevention, clinical diagnosis, and treatment. Consequently, it has emerged as a major contributor to end-stage renal disease. The glomerular filtration barrier, composed of podocytes, endothelial cells, and the glomerular basement membrane, plays a vital role in maintaining renal function. Disruptions in podocyte function, including hypertrophy, shedding, reduced density, and apoptosis, can impair the integrity of the glomerular filtration barrier, resulting in elevated proteinuria, abnormal glomerular filtration rate, and increased creatinine levels. Hence, recent research has increasingly focused on the role of podocyte injury in DN, with a growing emphasis on exploring therapeutic interventions targeting podocyte injury. Studies have revealed that factors such as lipotoxicity, hemodynamic abnormalities, oxidative stress, mitochondrial dysfunction, and impaired autophagy can contribute to podocyte injury. This review aims to summarize the underlying mechanisms of podocyte injury in DN and provide an overview of the current research status regarding experimental drugs targeting podocyte injury in DN. The findings presented herein may offer potential therapeutic targets and strategies for the management of DN associated with podocyte injury.

The E3 ligase Trim63 promotes podocyte injury and proteinuria by targeting PPARα to inhibit fatty acid oxidation

Podocyte injury is a hallmark of glomerular disease and one of the leading causes of chronic kidney disease (CKD). Peroxisome proliferator-activated receptor α (PPARα) plays a key role in podocyte fatty acid oxidation (FAO). However, the underlying regulatory mechanisms remain unresolved. Trim63 is an E3 ubiquitin ligase that has been shown to inhibit PPARα activity; however, its role in fatty acid metabolism in the kidney has not been elucidated to date. In this study, we investigated the effects of overexpression and knockdown of Trim63 in Adriamycin (ADR)-induced nephropathy and diabetic nephropathy models and a podocyte cell line. In both rodents and human patients with proteinuric CKD, Trim63 was upregulated, particularly in the podocytes of injured glomeruli. In the ADR-induced nephropathy model, ectopic Trim63 application aggravated FAO deficiency and mitochondrial dysfunction and triggered intense lipid deposition, podocyte injury, and proteinuria. Notably, Trim63 inhibition alleviated FAO deficiency and mitochondrial dysfunction, and markedly restored podocyte injury and renal fibrosis in ADR-induced and diabetic nephropathy (DN) models. Additionally, Trim63 was observed to mediate PPARα ubiquitination and degradation, leading to podocyte injury. We demonstrate the pathological role of Trim63, which was previously unrecognized in kidney tissue, in FAO deficiency and podocyte injury. Targeting Trim63 may represent a viable therapeutic strategy for podocyte injury and proteinuria.

CDDO-Me ameliorates podocyte injury through anti-oxidative stress and regulation of actin cytoskeleton in adriamycin nephropathy

Podocyte injury is the common initiating event in focal segmental glomerulosclerosis (FSGS). Oxidative stress and inflammation mediate podocyte injury in FSGS. NRF2 pathway regulates the constitutive and inducible transcription of various genes that encode antioxidant proteins and anti-inflammatory proteins and have pivotal roles in the defense against cellular oxidative stress. In this study, we used adriamycin-induced nephropathy (ADR) in mice as a model of FSGS to confirm that CDDO-Me treatment ameliorated adriamycin-induced kidney damage by improving renal function and kidney histology. CDDO-Me inhibited the level of oxidative stress, inflammation, and apoptosis in adriamycin-induced podocyte injury by activating NRF2 pathway in vivo and in vitro. Furthermore, CDDO-Me stabled the cytoskeleton by regulating NRF2/srGAP2a pathway. Together, these findings show that by activating NRF2 pathway, CDDO-Me could be a therapeutic strategy to prevent the adverse effects of adriamycin-induced podocyte injury.

Klotho inhibits renal ox-LDL deposition via IGF-1R/RAC1/OLR1 signaling to ameliorate podocyte injury in diabetic kidney disease

OBJECTIVE

Diabetic kidney disease (DKD) is characterized by the abnormal deposition of oxidized low-density lipoprotein (ox-LDL), which contributes to podocyte damage. Klotho, an aging suppressor that plays a critical role in protecting podocytes in DKD, is mainly expressed in kidney tubular epithelium and secreted in the blood. However, it has not been established whether Klotho can alleviate podocyte injury by inhibiting renal ox-LDL deposition, and the potential molecular mechanisms require further investigation.

METHODS

We conducted a comprehensive analysis of serum and kidney biopsy samples obtained from patients diagnosed with DKD. Additionally, to explore the underlying mechanism of Klotho in the deposition of ox-LDL in the kidneys, we employed a mouse model of DKD with the Klotho genotype induced by streptozotocin (STZ). Furthermore, we conducted meticulous in vitro experiments on podocytes to gain further insights into the specific role of Klotho in the deposition of ox-LDL within the kidney.

RESULTS

Our groundbreaking study unveiled the remarkable ability of the soluble form of Klotho to effectively inhibit high glucose-induced ox-LDL deposition in podocytes affected by DKD. Subsequent investigations elucidated that Klotho achieved this inhibition by reducing the expression of the insulin/insulin-like growth factor 1 receptor (IGF-1R), consequently leading to a decrease in the expression of Ras-related C3 botulinum toxin substrate 1 (RAC1) and an enhancement of mitochondrial function. Ultimately, this series of events culminated in a significant reduction in the expression of the oxidized low-density lipoprotein receptor (OLR1), thereby resulting in a notable decrease in renal ox-LDL deposition in DKD.

CONCLUSION

Our findings suggested that Klotho had the potential to mitigate podocyte injury and reduced high glucose-induced ox-LDL deposition in glomerulus by modulating the IGF-1R/RAC1/OLR1 signaling. These results provided valuable insights that could inform the development of novel strategies for diagnosing and treating DKD.

Targeting ferroptosis attenuates podocytes injury and delays tubulointerstitial fibrosis in focal segmental glomerulosclerosis

Ferroptosis is a non-apoptotic form of cell death, involved in chronic kidney diseases (CKD) and acute kidney injury (AKI), so far, the role of ferroptosis in focal segmental glomerulosclerosis (FSGS) remains largely unknown. We aimed to investigate the role of ferroptosis in FSGS, in this study, we found the reduced expression of GPX4 in podocytes, as well as tubular epithelial cells (TECs), from patients with FSGS. Treatment with ferrostatin-1 (Fer-1), a potent and selective ferroptosis inhibitor, significantly reduced proteinuria, prevented glomerulosclerosis, attenuated podocyte injury in ADR-induced FSGS murine model. As expected, ADR treatment caused downregulation of GPX4 in human podocytes, treatment with Fer-1 greatly blocked the downregulation of GPX4, restored the GSH level and attenuated cell death. Furthermore, Fer-1 treatment greatly delayed the development of tubulointerstitial fibrosis in ADR-induced FSGS murine model. Taken together, ferroptosis is involved in the pathogenesis of FSGS, targeting ferroptosis is a promising therapeutic option for patients with FSGS.

Integrated single-cell RNA-seq analysis revealed podocyte injury through activation of the BMP7/AMPK/mTOR mediated autophagy pathway

BACKGROUND

Nephrotic syndrome (NS) is a chronic kidney disease mainly caused by impaired podocytes, ultimately resulting in massive proteinuria or even end-stage renal disease (ESRD).

METHODS

The objective of this study was to explore the potential pathogenesis of NS caused by podocyte injury, and further explore the underlying mechanism through data mining, bioinformatics analysis, and experimental verification. The integrated analyses including Seurat, CellChat, gene ontology (GO), and molecular docking were performed based on the single-cell RNA-seq data (scRNA-seq). The adriamycin (ADR)-induced podocyte injury model in vitro was established to conduct the experimental verification for bioinformatics analysis results through western blot and real-time quantitative PCR (RT-qPCR).

RESULTS

The results of bioinformatics analysis revealed that the bone morphogenetic protein (BMP) signaling pathway was involved in the podocyte-to-podocyte communication, which plays a crucial role in podocyte injury. The expression of BMP7 was significantly increased in ADR-induced podocytes through activating the Adenosine-monophosphate activated-protein kinase/Mammalian target of rapamycin (AMPK/mTOR) mediated autophagy pathway, and these findings were confirmed by in vitro experiments.

CONCLUSION

This study first demonstrated that BMP7 participated in ADR-induced podocyte injury. The BMP7/AMPK/mTOR mediated autophagy pathway may play a crucial role in podocyte injury, which may be the potential therapeutic target for NS patients.

Knockdown of USF2 inhibits pyroptosis of podocytes and attenuates kidney injury in lupus nephritis

As an essential factor in the prognosis of Systemic lupus erythematosus (SLE), lupus nephritis (LN) can accelerate the rate at which patients with SLE can transition to chronic kidney disease or even end-stage renal disease (ESRD). Proteinuria due to decreased glomerular filtration rate following podocyte injury is LN's most common clinical manifestation. Podocyte pyroptosis and related inflammatory factors in its process can promote lupus to involve kidney cells and worsen the occurrence and progression of LN, but its regulatory mechanism remains unknown. Accumulating evidence has shown that upstream stimulatory factor 2 (USF2) plays a vital role in the pathophysiology of kidney diseases. In this research, multiple experiments were performed to investigate the role of USF2 in the process of LN. USF2 was abnormally highly expressed in MRL/lpr mice kidney tissues. Renal function impairment and USF2 mRNA levels were positively correlated. Silencing of USF2 in MRL/lpr serum-stimulated cells significantly reduced serum-induced podocyte pyroptosis. USF2 enhanced NLRP3 expression at the transcriptional level. Silencing of USF2 in vivo attenuated kidney injury in MRL/lpr mice, which suggests that USF2 is important for LN development and occurrence.

Danggui Shaoyaosan attenuates doxorubicin induced Nephrotic Syndrome through regulating on PI3K/Akt Pathway

The study aimed to explore the role and the underlying mechanism of Danggui Shaoyaosan (DSS) in nephrotic syndrome (NS). NS rat model was induced by doxorubicin injection twice. After DSS treatment, inflammation and oxidative stress index were detected via ELISA. Western blot was used for the protein detection. Go and KEGG analysis was applied to evaluate target gene and signaling of DSS. MCP-5 cell was applied for the cell rescue experiments and mechanism exploration. The 24 h urine protein levels of NS rats increased significantly, which was reduced by DSS treatment in a concentration-dependent manner. After DSS treatment, levels of BUN, SCr, TG and TC were also decreased, and serum ALB and TP levels were increased in rats. GO and KEGG pathway enrichment identified PI3K-Akt to be the candidate signaling of DSS in the treatment of NS, which was activated in NS rats. The recuse experiments in MCP-5 demonstrated that IGF-1, the agonist of PI3K/AKT, abolished the beneficial role of DSS in podocyte cell viability, apoptosis, inflammation and oxidative stress. In conclusion, DSS exerts a protective role against the development of NS. The mechanism is related to the improvement of podocyte injury and the inhibition of PI3K/Akt pathway-related proteins.

BaoShenTongLuo formula protects against podocyte injury by regulating AMPK-mediated mitochondrial biogenesis in diabetic kidney disease

BACKGROUND

Mitochondrial dysfunction is considered to be an important contributor in podocyte injury under diabetic conditions. The BaoShenTongLuo (BSTL) formula has been shown to reduce podocyte damage and postpone the progression of diabetic kidney disease (DKD). The potential mechanisms underlying the effects of BSTL, however, have yet to be elucidated. In this study, we aimed to investigate whether the effects of BSTL are related to the regulation of mitochondrial biogenesis via the adenosine monophosphate-activated protein kinase (AMPK) pathway.

METHODS

High-Performance Liquid Chromatography Electrospray Ionization Mass Spectrometer (HPLC-ESI-MS) analysis was performed to investigate the characteristics of pure compounds in BSTL. db/db mice and mouse podocyte clone-5 (MPC5) cells were exposed to high glucose (HG) to induce DKD and podocyte damage. Body weight, random blood glucose, urinary albumin/creatinine ratio (UACR), indicators of renal function and renal histological lesions were measured. Markers of podocyte injury, mitochondrial morphology, mitochondrial deoxyribonucleic acid (mtDNA) content, mitochondrial respiratory chain complexes activities, reactive oxygen species (ROS) production, and mitochondrial membrane potential (MMP) levels were assessed. Protein expressions of AMPK, peroxisome proliferator-activated receptor gamma coactivator 1 alpha (PGC-1α), transcription factor A (TFAM), mitochondrial fusion protein 2 (MFN2) and dynamin-related protein 1 (DRP1) were also detected. MPC5 cells were transfected with AMPKα small interfering RNA (AMPKα siRNA) to determine the underlying mechanisms of BSTL improvement of mitochondrial function under diabetic conditions.

RESULTS

In vivo, treatment with BSTL reduced the UACR levels, reversed the histopathological changes in renal tissues, and alleviated the podocyte injury observed in db/db mice. After BSTL treatment, the decreased mtDNA content and mitochondrial respiratory chain complex I, III, and IV activities were significantly improved, and these effects were accompanied by maintenance of the protein expression of p-AMPKαT172, PGC-1α, TFAM and MFN2. The in vitro experiments also showed that BSTL reduced podocyte apoptosis, suppressed excessive cellular ROS production, and reversed the decreased in MMP that were observed under HG conditions. More importantly, the effects of BSTL in enhancing mitochondrial biogenesis and reducing podocyte apoptosis were inhibited in AMPKα siRNA-treated podocytes.

CONCLUSION

BSTL plays a crucial role in protecting against podocyte injury by regulating the AMPK-mediated mitochondrial biogenesis in DKD.

Deposition of platelet-derived microparticles in podocytes contributes to diabetic nephropathy

BACKGROUND

Diabetic nephropathy (DN) is the leading cause of end-stage renal disease in the developed world. Podocyte injury is a critical cellular event involved in the progression of DN. Our previous studies demonstrated that platelet-derived microparticles (PMPs) mediated endothelial injury in diabetic rats. This study aimed to investigate whether PMPs are deposited in podocytes and to assess their potential effects on podocyte injury in DN.

METHODS

The deposition of PMPs in podocytes was assessed by immunofluorescent staining and electron microscopy. The changes in renal pathology and ultra-microstructure were assessed by periodic acid-Schiff staining and electron microscopy, respectively. The expression of inflammatory cytokines and extracellular matrix proteins was measured by immuno-histochemical staining and western blot.

RESULTS

PMPs were widely deposited in podocytes of glomeruli in diabetic patients and animal models and closely associated with DN progression. Interestingly, aspirin treatment significantly inhibited the accumulation of PMPs in the glomeruli of diabetic rats, alleviated mesangial matrix expansion and fusion of foot processes, and decreased the protein expression of inflammatory cytokines and extracellular matrix secretion. An in vitro study further confirmed the deposition of PMPs in podocytes. Moreover, PMP stimulation induced the phenotypic transition of podocytes through decreased podocin protein expression and increased protein expression of α-SMA and fibronectin, which was correlated with increased production of inflammatory cytokines.

CONCLUSION

Our findings demonstrated for the first time that the deposition of PMPs in podocytes contributed to the development of DN.

Icariin synergizes therapeutic effect of dexamethasone on adriamycin-induced nephrotic syndrome

BACKGROUND

Glomerular damage is a common clinical indicator of nephrotic syndrome. High-dose hormone treatment often leads to hormone resistance in patients. How to avoid resistance and improve the efficiency of hormone therapy draws much attention to clinicians.

METHODS

Adriamycin (ADR) was used to induce nephropathy model in SD rats. The rats were treated with dexamethasone (DEX), icariin (ICA), and DEX + ICA combination therapy. The changes in urinary protein (UP), urea nitrogen (BUN), and serum creatinine (SCR) contents in rats were detected by enzyme-linked immunosorbent assay (ELISA), and the degree of pathological injury and the expression level of podocin were detected by HE staining and immunohistochemistry, to test the success of the model and the therapeutic effects of three different ways. The effect of treatments on podocytes autophagy was evaluated via transfection of mRFP-GFP-LC3 tandem adenovirus in vitro.

RESULTS

The contents of UP, SCR, and BUN were significantly increased, the glomerulus was seriously damaged, and the expression of Nephrosis2 (NPHS2) was significantly decreased in the ADR-induced nephrotic syndrome rat model compared to that of the control group. DEX, ICA, and the DEX + ICA combined treatment significantly alleviated these above changes induced by ADR. The combined treatment of DEX + ICA exhibited better outcome than single treatment. The combined treatment also restored the podocyte autophagy, increased the expression of microtubule-associated protein light-chain 3II (LC3II), and reduced the expression of p62 in vitro. The combined treatment protects podocytes by mediating the PI3K/AKT/mTOR (rapamycin complex) signaling pathway.

CONCLUSION

ICA enhances the therapeutic effect of DEX on the nephrotic syndrome.

ANGPTL4 promotes nephrotic syndrome by downregulating podocyte expression of ACTN4 and podocin

BACKGROUND

lipopolysaccharide (LPS) can induce nephrotic syndrome-like features such as massive proteinuria, hyperlipidemia, and fusion of glomerular podocytes with foot processes (FPs) in mice. Angiopoietin-like protein 4 (ANGPTL4) neutralized the negative charge of glomerular basement membrane charge and aggravated renal injury. The mechanism of ANGPTL4 aggravating podocyte injury has not been well clarified. In this study, we aimed to investigate the potential role of ANGPTL4 on podocyte FPs fusion and podocyte signal molecules.

METHODS

We built angptl4 gene knocked out in C57BL6 mice using CRISPR/Cas9 technique. Nephrotic model was built by LPS in wild type and angptl4-/- mice. Expression of ACTN4, podocin and TRPC6 in the glomerulus were determined by immunohistochemistry.

RESULTS

In physical condition, the wild type and angptl4-/- mice showed no significant differences in biochemical indicators and kidney pathology. But in nephrotic condition, compared with wild type mice hyperlipidemia and proteinuria with the angptl4-/- mice was significantly relieved. Moreover, the degree of FPs fusion was notably improved in the nephrotic mice knocked out angptl4 gene. Expression of ACTN4 and podocin decreased drastically in the glomerulus of wild-type nephrotic mice. Different from wild-type, the ACTN4 and podocin expression showed slight weakening in angptl4-/- nephrotic mice. As transient receptor potential cation channel subfamily member, TRPC6 expression had no visible change in glomerulus of each group.

CONCLUSIONS

ANGPTL4 induces hyperlipidemia and podocyte injury in nephrotic mice, thereby promoting the formation of proteinuria. Its molecular mechanism may be related to ANGPTL4 down-regulating actin cytoskeletal regulatory signals ACTN4 and podocin.

The serine protease plasmin plays detrimental roles in epithelial sodium channel activation and podocyte injury in Dahl salt-sensitive rats

Salt-sensitive hypertension is associated with poor clinical outcomes. The epithelial sodium channel (ENaC) in the kidney plays pivotal roles in sodium reabsorption and blood pressure regulation, in which its γ subunit is activated by extracellular serine proteases. In proteinuric nephropathies, plasmin filtered through injured glomeruli reportedly activates γENaC in the distal nephron and causes podocyte injury. We previously reported that Dahl salt-sensitive (DS) rats fed a high-salt (HS) diet developed hypertension and proteinuria along with γENaC activation and that a synthetic serine protease inhibitor, camostat mesilate, mitigated these changes. However, the role of plasmin in DS rats remained unclear. In this study, we evaluated the relationship between plasmin and hypertension as well as podocyte injury and the effects of plasmin inhibitors in DS rats. Five-week-old DS rats were divided into normal-salt diet, HS diet, and HS+plasmin inhibitor (either tranexamic acid [TA] or synthetic plasmin inhibitor YO-2) groups. After blood pressure measurement and 24 h urine collection over 5 weeks, rats were sacrificed for biochemical analyses. The HS group displayed severe hypertension and proteinuria together with activation of plasmin in urine and γENaC in the kidney, which was significantly attenuated by YO-2 but not TA. YO-2 inhibited the attachment of plasmin(ogen) to podocytes and alleviated podocyte injury by inhibiting apoptosis and inflammatory/profibrotic cytokines. YO-2 also suppressed upregulation of protease-activated receptor-1 and phosphorylated ERK1/2. These results indicate an important role of plasmin in the development of salt-sensitive hypertension and related podocyte injury, suggesting plasmin inhibition as a potential therapeutic strategy.

LncRNA TCF7 contributes to high glucose-induced damage in human podocytes by up-regulating SEMA3A via sponging miR-16-5p

AIMS/INTRODUCTION

Long non-coding RNAs (lncRNAs) exert essential functions in the pathogenesis of diabetic nephropathy (DN). LncRNA T-cell factor 7 (TCF7) and semaphorin-3A (SEMA3A) have been found to be involved in the progression of diabetic nephropathy. However, whether the effect of TCF7 on the pathogenesis of diabetic nephropathy is mediated by SEMA3A remains unclear.

MATERIALS AND METHODS

TCF7, miR-16-5p, and SEMA3A were quantified by a qRT-PCR or immunoblotting method. A CCK-8 assay gauged the cell viability. Measurement of cell apoptosis was done using flow cytometry. RNA immunoprecipitation (RIP), dual-luciferase reporter, and RNA pull-down assays were utilized to assay the targeted interactions among the variables.

RESULTS

The TCF7 and SEMA3A levels were elevated in serum from patients with diabetic nephropathy. TCF7 silencing or SEMA3A depletion ameliorated high glucose (HG)-induced podocyte injury. Moreover, TCF7 silencing protected against HG-induced podocyte injury by down-regulating SEMA3A. TCF7 targeted miR-16-5p, and miR-16-5p targeted SEMA3A. Furthermore, TCF7 affected the expression of SEMA3A by competing specifically for shared miR-16-5p.

CONCLUSIONS

These findings suggested that TCF7 silencing attenuated high glucose-induced podocyte damage partially through the miR-16-5p/SEMA3A regulation cascade.

The PDE5 inhibitor, vardenafil, ameliorates progressive pathological changes in a focal segmental glomerulosclerosis mouse model

AIMS

Phosphodiesterase 5 inhibitors (PDE5is) inhibit the hydrolysis of cyclic guanosine 5'-monophosphate in smooth muscle cells and are a widely known treatment for erectile dysfunction. Accumulating evidence also suggests that PDE5is exhibit potential benefits in cardiovascular and chronic kidney diseases. In this study, we examined the therapeutic effects of a PDE5i, vardenafil (VAR), in a focal segmental glomerulosclerosis (FSGS) mouse model.

MATERIALS AND METHODS

FSGS was induced in BALB/c mice by the intravenous administration of Adriamycin (AD, 11 mg/kg of body weight). After 24 h, VAR (at 12.5 μg/ml) was given in drinking water ad libitum until the animals were sacrificed. At the end of the experiment, plasma and kidney samples were harvested to evaluate clinical parameters, histopathological changes, and alterations in transcriptome and protein expressions.

KEY FINDINGS

In this study, VAR treatment attenuated the deterioration of proteinuria, renal dysfunction, and hypercholesterolemia in AD-induced FSGS. Treatment with VAR exhibited reductions in the severity of both glomerulosclerosis and tubulointerstitial injury in the histological analysis. In addition to relieving AD-induced podocyte loss, VAR also preserved endothelial cells in glomerular capillaries and ameliorated the accumulation of collagen fibers in the mesangial area and Bowman's capsule basement membrane. In addition, VAR showed an ability to suppress transforming growth factor-β-induced fibroblast-to-myofibroblast transdifferentiation.

SIGNIFICANCE

Our data suggest that VAR exhibited reno-therapeutic effects via attenuating podocyte loss, preserving the integrity of the glomerular vasculature, and ameliorating fibrotic changes. These findings suggest that PDE5is might be a promising treatment modality for nephrotic syndrome.

ANGPTL3 is involved in kidney injury in high-fat diet-fed mice by suppressing ACTN4 expression

Objective

We wanted to explore how angiopoietin-like 3 (ANGPTL3) impact hyperlipidemia-induced renal injury.

Methods

ANGPTL3 knockout mice and wild-type C57 mice were set up in four groups (N = 5) depending on a normal or 60% high-fat diet: wild-type with normal diet (WT), angptl3-/- with normal diet (KO), wild-type + high-fat diet (WT + HF) and angptl3-/- + high-fat diet (KO + HF). The detection time points were the 9th, 13th, 17th and 21st weeks after modeling. Serum lipid and urinary protein levels of mice in each group were detected, and pathological changes in the kidney were analyzed. Moreover, the expression of ANGPTL3, α-actinin-4 (ACTN4), CD2-associated protein (CD2AP) and podocin was tested in the glomerulus by immunohistochemistry (IHC).

Results

In the WT + HF group, hyperlipidemia and proteinuria could be observed at the 9th week and were gradually aggravated with time. Compared with WT + HF mice, the levels of serum lipids and proteinuria in KO + HF mice were significantly reduced, and the width of podocyte foot processes (FPs) fusion was also markedly improved. The IHC results suggested that in WT + HF mice, the expression of ANGPTL3 was significantly enhanced. After modeling, ACTN4 expression was markedly weakened in the glomeruli of WT + HF mice. Different to WT mice, ACTN4 expression was not observed obviously change in KO + HF mice. Compared with the normal diet group, the expression of podocin showed a decline in WT mice treated with high-fat diet and showed a significant difference from the 17th week. In addition, podocin expression in KO + HF glomeruli was also found to be weak but not significantly different from that in WT + HF glomeruli at the four time points. The expression of CD2AP showed similar results among the four groups.

Conclusion

ANGPTL3 could play a role in the mechanism of hyperlipidemia-associated podocyte injury via ACTN4.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12944-022-01700-3.

Sirtuins as novel pharmacological targets in podocyte injury and related glomerular diseases

Podocyte injury is a major cause of proteinuria in kidney diseases, and persistent loss of podocytes leads to rapid irreversible progression of kidney disease. Sirtuins, a class of nicotinamide adenine dinucleotide-dependent deacetylases, can promote DNA repair, modify transcription factors, and regulate the cell cycle. Additionally, sirtuins play a critical role in renoprotection, particularly against podocyte injury. They also have pleiotropic protective effects on podocyte injury-related glomerular diseases, such as improving the immune inflammatory status and oxidative stress levels, maintaining mitochondrial homeostasis, enhancing autophagy, and regulating lipid metabolism. Sirtuins deficiency causes podocyte injury in different glomerular diseases. Studies using podocyte sirtuin-specific knockout and transgenic models corroborate this conclusion. Of note, sirtuin activators have protective effects in different podocyte injury-related glomerular diseases, including diabetic kidney disease, focal segmental glomerulosclerosis, membranous nephropathy, IgA nephropathy, and lupus nephritis. These findings suggest that sirtuins are promising therapeutic targets for preventing podocyte injury. This review provides an overview of recent advances in the role of sirtuins in kidney diseases, especially their role in podocyte injury, and summarizes the possible rationale for sirtuins as targets for pharmacological intervention in podocyte injury-related glomerular diseases.

Potential therapeutic effects of natural compounds targeting autophagy to alleviate podocyte injury in glomerular diseases

Podocyte injury is a common cause of proteinuric kidney diseases. Uncontrollable progressive podocyte loss accelerates glomerulosclerosis and increases the risk of end-stage renal disease. To date, owing to the complex pathological mechanism, effective therapies for podocyte injury have been limited. Accumulating evidence supports the indispensable role of autophagy in the maintenance of podocyte homeostasis. A variety of natural compounds and their derivatives have been found to regulate autophagy through multiple targets, including promotes nuclear transfer of transcription factor EB and lysosomal repair. Here, we reviewed the recent studies on the use of natural compounds and their derivatives as autophagy regulators and discussed their potential applications in ameliorating podocyte injury. Several known natural compounds with autophagy-regulatory properties, such as quercetin, silibinin, kaempferol, and artemisinin, and their medical uses were also discussed. This review will help in improving the understanding of the podocyte protective mechanism of natural compounds and promote their development for clinical use.

Emerging role of tumor suppressor p53 in acute and chronic kidney diseases

p53 is a major regulator of cell cycle arrest, apoptosis, and senescence. While involvement of p53 in tumorigenesis is well established, recent studies implicate p53 in the initiation and progression of several renal diseases, which is the focus of this review. Ischemic-, aristolochic acid (AA) -, diabetic-, HIV-associated-, obstructive- and podocyte-induced nephropathies are accompanied by activation and/or elevated expression of p53. Studies utilizing chemical or renal-specific inhibition of p53 in mice confirm the pathogenic role of this transcription factor in acute kidney injury and chronic kidney disease. TGF-β1, NOX, ATM/ATR kinases, Cyclin G, HIPK, MDM2 and certain micro-RNAs are important determinants of renal p53 function in response to trauma. AA, cisplatin or TGF-β1-mediated ROS generation via NOXs promotes p53 phosphorylation and subsequent tubular dysfunction. p53-SMAD3 transcriptional cooperation downstream of TGF-β1 orchestrates induction of fibrotic factors, extracellular matrix accumulation and pathogenic renal cell communication. TGF-β1-induced micro-RNAs (such as mir-192) could facilitate p53 activation, leading to renal hypertrophy and matrix expansion in response to diabetic insults while AA-mediated mir-192 induction regulates p53 dependent epithelial G2/M arrest. The widespread involvement of p53 in tubular maladaptive repair, interstitial fibrosis, and podocyte injury indicate that p53 clinical targeting may hold promise as a novel therapeutic strategy for halting progression of certain acute and chronic renal diseases, which affect hundreds of million people worldwide.

GABA alleviates high glucose-induced podocyte injury through dynamically altering the expression of macrophage M1/M2-derived exosomal miR-21a-5p/miR-25-3p

Podocyte injury is the main clinical pathological feature of diabetic kidney disease (DKD). The studies showed that DKD is associated with the polarization of macrophages to different types (M1 or M2) and the inflammatory processes which they mediate. It is a hot research topic in the treatment of DKD that find and intervene genes which related to M1/M2 phenotype. The potential anti-inflammatory effects on γ-aminobutyric acid (GABA) have been shown to be related to the regulation of the polarization direction of macrophages. However, it remains unknown that whether GABA can alleviate DKD. The purpose of current study was to explore the role of GABA involved in high glucose (HG)-induced podocyte injury by regulating the M1/M2 phenotype. In the beginning, our results revealed that exogenous GABA treatment altered the direction of HG-induced macrophage polarization and suppressed the inflammatory response. Subsequently, macrophage-derived exosomes under HG treatment were found to be involved in aggravating HG-induced podocyte injury (decreased the proliferation capacity and increased apoptosis rate of cells). Furthermore, GABA treatment blocked the promotion of macrophage-mediated exosomes on podocyte injury under HG. Then, we found that GABA alleviated the promoting effect of macrophages on podocyte injury by regulating the expression of exosomal miR-21a-5p/miR-25-3p which mediated by macrophages. Finally, it was elucidated that Tnpo1/ATXN3 were the targets of miR-21a-5p/miR-25-3p, respectively, and mediated the promotion of podocyte injury by macrophage-derived exosomes under HG. This research suggested that GABA alleviated podocyte injury by reversing the M1/M2 polarization direction of macrophages under HG and regulating the miR-21a-5p-Tnpo1/miR-25-3p-ATXN3 signal axis of macrophage-derived exosomes.

PTEN-induced kinase 1 deficiency alters albumin permeability and insulin signaling in podocytes

Alterations of insulin signaling in diabetes are associated with podocyte injury, proteinuria, and renal failure. Insulin stimulates glucose transport to cells and regulates other intracellular processes that are linked to cellular bioenergetics, such as autophagy, gluconeogenesis, fatty acid metabolism, and mitochondrial homeostasis. The dysfunction of mitochondrial dynamics, including mitochondrial fusion, fission, and mitophagy, has been observed in high glucose-treated podocytes and renal cells from patients with diabetes. Previous studies showed that prolonged hyperglycemia is associated with the development of insulin resistance in podocytes, and high glucose-treated podocytes exhibit an increase in mitochondrial fission and decrease in markers of mitophagy. In the present study, we found that deficiency of the main mitophagy protein PTEN-induced kinase 1 (PINK1) significantly increased albumin permeability and hampered glucose uptake to podocytes. We suggest that PINK1 inhibition impairs the insulin signaling pathway, in which lower levels of phosphorylated Akt and membrane fractions of the insulin receptor and glucose transporter-4 were observed. Moreover, PINK1-depleted podocytes exhibited lower podocin and nephrin expression, thus identifying a potential mechanism whereby albumin leakage increases under hyperglycemic conditions when mitophagy is inhibited. In conclusion, we found that PINK1 plays an essential role in insulin signaling and the maintenance of proper permeability in podocytes. Therefore, PINK1 may be a potential therapeutic target for the treatment or prevention of diabetic nephropathy.

Targeting tissue-resident memory CD8+ T cells in the kidney is a potential therapeutic strategy to ameliorate podocyte injury and glomerulosclerosis

Although tissue-resident memory T (T_RM) cells, a recently identified non-circulating memory T cell population, play a crucial role in mediating local immune responses and protect against pathogens upon local reinfection, the composition, effector function, and specificity of T_RM cells in the kidney and their relevance for chronic kidney disease remain unknown. In this study, we found that renal tissue displayed high abundance of tissue-resident lymphocytes and the proportion of CD8⁺ T_RM cells was significantly increased in the kidney from patients and mice with focal segmental glomerulosclerosis (FSGS), diabetic kidney disease (DKD) and lupus nephritis (LN). Mechanistically, IL-15 significantly promoted CD8⁺ T_RM cell formation and activation, thereby promoting podocyte injury and glomerulosclerosis. Interestingly, Sparsentan, the dual angiotensin II (Ang II) receptor and endothelin Type A receptor antagonist, can also reduce T_RM cell responses by intervening IL-15 signaling, exploring its new pharmacological functions. Mechanistically, Sparsentan inhibited Ang II or endothelin-1 (ET-1)-mediated IL-15 signaling, thereby further regulating renal CD8⁺ T_RM cell fates. Collectively, our studies provide direct evidence for the pivotal role of renal CD8⁺ T_RM cells in podocyte injury, and further strengthen that targeting T_RM cells represents a novel therapeutic strategy for patients with glomerular diseases.

cAMP-response element binding protein mediates podocyte injury in diabetic nephropathy by targeting lncRNA DLX6-AS1

BACKGROUND

Progressive proteinuria is one of the earliest clinical features of diabetic nephropathy (DN). In our previous study, lncRNA DLX6-AS1 (DLX6-AS1, Dlx6os1 in the mouse) was found to be associated with the extent of albuminuria in DN patients. Furthermore, the lack of Dlx6os1 was pivotal in switching off the inflammatory response in db/db mouse model. However, the regulatory factors responsible for elevated DLX6-AS1 in DN remains unknown.

METHODS

To identify potential regulatory factors for DLX6-AS1, JASPAR database and DNA pull down combined subsequent liquid chromatography-tandem mass spectrometry were used. Dual-luciferase reporter assay and chromatin immunoprecipitation were then performed to confirm binding sites. We also investigated the effects of the regulatory factors on DN progression in db/db mouse model and cultured human podocytes.

RESULTS

Our analyses demonstrated that cAMP-response element binding protein (CREB) was highly expressed and closely associated with DLX6-AS1 in DN. In db/db mouse and in cultured podocytes, CREB silencing significantly reduced the level of DLX6-AS1 or Dlx6os1 and attenuated renal damage. Mechanistically, CREB overexpression aggravated renal inflammation and destroyed the structure of podocytes by targeting DLX6-AS1. The damaging role of CREB in podocyte injury was also inhibited by 666-15, a selective inhibitor, in a dose-dependent manner. In vivo, the inhibition of CREB by 666-15 significantly attenuated albuminuria and ameliorated inflammatory infiltration in podocytes.

CONCLUSIONS

Our findings indicated that CREB is a key mediator of podocyte injury and acts by regulating DLX6-AS1. Thus, CREB may be an effective and potential therapeutic target for the treatment of DN.

Penehyclidine hydrochloride suppresses inflammation response and reduces podocyte injury in diabetic nephropathy by targeting fibrinogen-like protein 2

BACKGROUND

Diabetic nephropathy (DN) is one of the main complications of diabetes. Penehyclidine hydrochloride (PHC) has anti-inflammatory, anti-apoptotic and anti-oxidative stress effects. Nevertheless, whether PHC can be used to prevent podocyte injury has not been reported.

OBJECTIVES

This present study aimed to identify the functional role of PHC in DN as well as its underlying mechanism.

METHODS

The high-glucose (HG)-induced podocyte damage in vitro model was established. The proliferation, apoptotic rate, inflammatory factors, and gene/protein expressions of HG-induced MPC5 cells were determined using CCK-8 assay, flow cytometry, ELISA, real-time PCR, and Western blot upon PHC treatment. Co-immunoprecipitation experiments and pull-down assay were performed to verify the interactions between fibrinogen-like protein 2 (Fgl2) and toll-like receptor 4 (TLR4) as well as TLR4 and NLRP3. A rat in vivo model was used to confirm the effect of PHC treatment.

RESULTS

PHC treatment reduced Fgl2 expression and inhibited HG-induced podocyte injury and DN-induced kidney damage. Flg2 was associated with TLR4 and NLRP3. It was further proved that PHC treatment suppressed the TLR4-NF-кB and NLRP3-Caspase-1 pathways through Fgl2, which eventually inhibited inflammatory cytokines and prevented HG-induced podocyte injury both in vitro and in vivo.

CONCLUSION

PHC treatment possibly ameliorates DN by preventing podocyte injury via inactivating the TLR4-NF-кB and NLRP3-Caspase-1 signaling pathways by Flg2.

Angiopoietin-like protein 4 promotes hyperlipidemia-induced renal injury by down-regulating the expression of ACTN4

OBJECTIVE

The molecular mechanism of in hyperlipidemia-induced renal injury has not been elucidated. Angiogenin-like protein 4 (ANGPTL4) is a key regulator of lipid metabolism. The role of ANGPTL4 hyperlipidemia-induced renal injury has not been reported.

METHODS

Wild type C57 mice and gene angptl4 knockout mice were fed with 60% high fat diet or normal diet respectively. The serum lipid, urinary albumin and renal pathology were tested at the 9th, 13th, 17th and 21st week with high fat diet.

RESULTS

Elevated blood lipids in the wild-type mice with high-fat diet were found at 9th week. At the 17th week, the level of urinary albumin in high-fat fed wild type mice were significantly higher than which with normal diet, correspondingly, segmental fusion of podocyte foot process in kidney could be observed in these hyperlipidemia mice. IHC showed that the expression of ANGPTL4 in glomeruli of high-fat fed wild type mice began significant elevated since the 9th week. When given high fat diet, compared to the wild type, the gene angptl4 knockout mice showed significantly alleviated the levels of hyperlipidemia, proteinuria and effacement of podocyte foot process. Finally, the expression of ACTN4 showed remarkably lower in glomeruli podocyte of wild type mice fed high fat diet than that of wild type mice with normal diet at each time-point (P < 0.01). Differently, the expression of ACTN4 in gene angptl4 knockout mice did not happen significantly weaken when given the same dose of high fat diet.

CONCLUSION

ANGPTL4 could play a role in hyperlipidemic-induced renal injury via down-regulating the expression of ACTN4 in kidney podocyte.

Spop ameliorates diabetic nephropathy through restraining NLRP3 inflammasome

Diabetic nephropathy (DN) is one of the most common causes for end-stage renal disease without effective therapies available. NLR family, pyrin domain-containing 3 (NLRP3) inflammasome possesses a fundamental effect to facilitate the pathogenesis of DN. Unfortunately, how NLRP3 inflammasome is mediated still remains largely unclear. In the present study, an E3 ubiquitin ligase Speckle-type BTB-POZ protein (Spop) was identified as a suppressor of NLRP3 inflammasome. We first showed that Spop expression was extensively down-regulated in kidney of DN patients, which was confirmed in kidney of streptozotocin (STZ)-challenged mice and in high glucose (HG)-stimulated podocytes. Intriguingly, we showed that conditional knockout (cKO) of Spop in podocytes considerably accelerated renal dysfunction and pathological changes in the glomerulus of STZ-induced mice with DN, along with severe podocyte injury. Furthermore, Spop specific ablation in podocytes dramatically facilitated inflammatory response in glomeruli of DN mice via enhancing NLRP3 inflammasome and nuclear factor κB (NF-κB) signaling pathways, which were confirmed in HG-cultured podocytes. Notably, our findings indicated that Spop directly interacted with NLRP3. More importantly, Spop promoted NLRP3 degradation via elevating K48-linked polyubiquitination of NLRP3. Collectively, our findings disclosed a mechanisms through which Spop limited NLRP3 inflammasome under HG condition, and illustrated that Spop may be a novel therapeutic target to suppress NLRP3 inflammasome, contributing to the DN management.

Rapamycin attenuated podocyte apoptosis via upregulation of nestin in Ang II-induced podocyte injury

Background

Angiotensin II (Ang II) contributes to the progression of glomerulosclerosis, mainly by inducing podocyte injury. Convincing evidence indicates that the mTOR inhibitor rapamycin could play a fundamental role in protection against podocyte injury. Nestin, a major cytoskeletal protein, is stably expressed in podocytes and correlates with podocyte damage. The purpose of this study was to investigate the effect of rapamycin on podocyte injury induced by Ang II and to clarify the role and mechanism of nestin in the protective effect of rapamycin of podocyte injury.

Methods and results

We established an Ang II perfusion animal model, and the effects of rapamycin treatment on podocytes were investigated in vivo. In vitro, podocytes were stimulated with Ang II and rapamycin to observe podocyte injury, and nestin-siRNA was transfected to investigate the underlying mechanisms. We observed that Ang II induced podocyte injury both in vivo and in vitro, whereas rapamycin treatment relieved Ang II-induced podocyte injury. We further found that nestin co-localized with p-mTOR in glomeruli, and the protective effect of rapamycin was reduced by nestin-siRNA in podocytes. Moreover, co-IP indicated the interaction between nestin and p-mTOR, and nestin could affect podocyte injury via the mTOR/P70S6K signaling pathway.

Conclusion

We demonstrated that rapamycin attenuated podocyte apoptosis via upregulation of nestin expression through the mTOR/P70S6K signaling pathway in an Ang II-induced podocyte injury.

A comprehensive insight into autophagy and its potential signaling pathways as a therapeutic target in podocyte injury

As part of the glomerular filtration membrane, podocyte is terminally differentiated, structurally unique, and highly specialized in maintaining kidney function. Proteinuria caused by podocyte injury (foot process effacement) is the clinical symptom of various kidney diseases (CKD), including nephrotic syndrome. Podocyte autophagy has become a powerful therapeutic strategy target in ameliorating podocyte injury. Autophagy is known to be associated significantly with sirtuin-1, proteinuria, and podocyte injury. Various key findings in podocyte autophagy were reported in the past ten years, such as the role of endoplasmic reticulum (ER) stress in podocyte autophagy impairment, podocyte autophagy-related gene, essential roles of the signaling pathways: Mammalian Target of Rapamycin (mTOR)/ Phosphoinositide 3-kinase (PI3k)/ serine/threonine kinase 1 (Akt) in podocyte autophagy. These significant factors caused podocyte injury associated with autophagy impairment. Sirtuin-1 was reported to have a vital key role in mTOR signaling, 5'AMP-activated protein kinase (AMPK) regulation, autophagy activation, and various critical pathways associated with podocyte's function and health; it has potential value to podocyte injury pathogenesis investigation. From these findings, podocyte autophagy has become an attractive therapeutic strategy to ameliorate podocyte injury, and this review will provide an in-depth review on therapeutic targets he podocyte autophagy.

Tetrandrine alleviates podocyte injury via calcium-dependent calpain-1 signaling blockade

BACKGROUND

Podocytes have become a crucial target for interventions in proteinuric kidney diseases. Many studies have reported that overexpression of transient receptor potential cation channel protein 6 (TRPC6) in podocyte injury upregulates intracellular Ca2+ influx and stimulates Ca2+-dependent protease calpain-1 signaling. The traditional Chinese drug, tetrandrine, a nonselective Ca2+ channel blocker, has long been used to treat chronic kidney disease. This research aimed to explore the possible mechanisms underlying the anti-proteinuric properties of tetrandrine.

METHODS

We investigated the involvement of tetrandrine in Ca2+ dependent calpain-1 signaling in mouse podocytes and adriamycin-induced nephropathy rats. Cyclosporine A (CsA) and U73122 were used as positive controls. Cell viability, cytotoxicity, Ca2+ concentration, calpain activity, and mRNA and protein expression levels of calpain-1 signaling pathways were examined. The clinical and pathological changes were measured.

RESULTS

Tetrandrine decreased intracellular Ca2+ influx in cultured TRPC6-overexpressing podocytes. In both in vitro and in vivo studies, the administration of tetrandrine downregulated calpain activity and the expression of calpain-1 and restored the expression of downstream Talin-1 and nephrin. Compared to CsA, tetrandrine treatment exhibited superior inhibitory effects on calpain activity and calpain-1 expression.

CONCLUSIONS

Tetrandrine has therapeutic potential in podocyte damage by blocking Ca2+-dependent activation of the calpain-1 signaling pathway. Tetrandrine reduced proteinuria, improved renal function, and alleviate renal pathological damage.

Sulfuretted hydrogen ameliorates high dose glucose-induced podocyte apoptosis via orchestrating AMPK/mTOR cascade-mediated anti-apoptotic effects

Background

Podocytes play a pivotal role in the glomerular filtration barrier and contribute to proteinuria and glomerulosclerosis through abnormal apoptosis. Longitudinal studies have indicated the protective properties of hydrogen sulfide (H₂S) against neuronal cell apoptosis, whereas the biological function and the underlying molecular mechanism on glucose-induced podocyte apoptosis are largely unknown.

Methods

Herein, we conducted multifaceted biological analyses to verify the potential function of H₂S in glucose-induced podocyte apoptosis by examining apoptotic proteins and markers (e.g., caspase 3, Hoechst) and antioxidative effects [e.g., reactive oxygen species (ROS), lipid peroxidation, superoxide dismutase (SOD), catalase (CAT)]. Then, we took advantage of transcriptome sequencing and biological analyses to further determine the potential influence of H₂S as well as the accompanying molecular mechanism.

Results

In this study, we found that glucose-induced podocyte apoptosis could be largely rescued by H₂S via antioxidative responses, which was further confirmed by transcriptome sequencing and bioinformatics analyses. According to apoptotic signaling analysis, the over-activated AMPK/mTOR signaling cascade in glucose-treated podocytes was effectively restrained.

Conclusions

For the first time, we indicated the protective effect and mechanism of H₂S in podocytes by restricting glucose-induced apoptosis and suppressing the abnormally activated AMPK/mTOR signaling cascade. Our findings provide new references for podocyte apoptosis-associated diseases and also indicate the potential of H₂S administration in clinical trials.

PPBP as a marker of diabetic nephropathy podocyte injury via Bioinformatics Analysis

Diabetic nephropathy (DN) is a type of kidney injuries associated with diabetes mellitus and the prevalence of DN has increased dramatically. However, DN still pose problems in therapy, and prognosis. Identifying new DN biomarkers would be helpful in reducing morbidity and mortality from DN and developing novel preventive approaches. In the study, from GSE36336 dataset with DN glomeruli samples, we screened for 238 differentially expressed genes. Enrichment analysis were performed to find out biological function and diseases of DEGs. Next, depended on protein-protein interaction network, We identified top 10 hub genes (Serpine1, Cxcl10, Cfd, Ppbp, Retn, Socs2, Ccr5, Mmp8, Pf4, Cxcl9) may played potential roles in DN. Meanwhile, transcriptome sequencing on podocyte were performed to reconfirm the reliability of Ppbp. To verify the efficiency of the selected genes as biomarkers, several experiments like qRT-PCR, renal histologic analysis and immunofluorescence were conducted to validate. Our results showed that PPBP have the potential to become a novel biomarker for DN podocyte injury.

Course monitoring of membranous nephropathy: Both autoantibodies and podocytes require multidimensional attention

A variety of podocyte antigens have been identified in human membranous nephropathy (MN), which is divided into various antigen-dominated subtypes, confirming the concept that MN is the common pattern of glomerular injury in multiple autoimmune responses. The detection of autoantibodies has been widely used, which promoted the clinical practice of MN toward personalized precision medicine. However, given the potential risks of immunosuppressive therapy, more autoantibodies and biomarkers need to be identified to predict the prognosis and therapeutic response of MN more accurately. In this review, we attempted to summarize the autoantigens/autoantibodies and autoimmune mechanisms that can predict disease states based on the current understanding of MN pathogenesis, especially the podocyte injury manifestations. In conclusion, both the autoimmune response and podocyte injury require multidimensional attention in the disease course of MN.

The RNA binding protein hnRNPK protects against adriamycin-induced podocyte injury

Background

Podocytes maintain the integrity of the glomerular filtration barrier and serve as the final barrier to protein loss. Podocyte injury may induce severe apoptosis, which can result in serious kidney damage and disease. Therefore, it is necessary to explore how podocyte injury can be prevented and to thereby discover a feasible therapy for kidney disease. However, the mechanism of podocyte injury is still unclear.

Methods

The mRNA and protein expression levels of synaptopodin and nephrin in MPC5 podocytes with adriamycin (ADR)-induced injury were detected by quantitative real-time PCR and western blot. The expression levels of heterogeneous nucleotide protein K (hnRNPK), caspase-3, Bax, and Bcl-2 protein in cells and tissues were measured using western blot. Proliferation were measured in treated MPC5 podocytes by Cell Counting Kit-8 (CCK-8) assay, EdU assay, and apoptosis was measured by Hoechst 32258 staining. Mitochondrial membrane potential disruption, lactate dehydrogenase (LDH) leakage, and reactive oxygen species (ROS) generation were measured using JC-1 staining, an LDH reagent kit, and a ROS detection kit. Hematoxylin and eosin (HE) staining was used to observe histological changes in mouse tissues.

Results

Synaptopodin and nephrin were downregulated in ADR-treated podocytes. Overexpression of hnRNPK ameliorated the inhibitive effect of ADR treatment on podocyte proliferation and reduced its promotion of podocyte apoptosis. LDH leakage and ROS generation were increased in ADR-treated podocytes, but were reduced by hnRNPK treatment.

Conclusions

ADR-induced podocyte injury is ameliorated by hnRNPK both in vivo and in vitro. This observation provides a basis for a feasible therapy to prevent podocyte injury and subsequent kidney disease.

A serine protease inhibitor camostat mesilate prevents podocyte apoptosis and attenuates podocyte injury in metabolic syndrome model rats

Metabolic syndrome (MetS) is associated with chronic kidney disease and proteinuria. Previously, we reported that a synthetic serine protease inhibitor, camostat mesilate (CM), mitigated hypertension and proteinuria in rodent disease models. The present study evaluated the anti-hypertensive and anti-proteinuric effects of CM in MetS model rats (SHR/ND mcr-cp). Rats were divided into normal salt-fed (NS), high salt-fed (HS), HS and CM-treated (CM), and HS and hydralazine-treated (Hyd) groups. Rats were sacrificed after four weeks of treatment. Severe hypertension and proteinuria were observed in the HS group. Although CM and Hyd equally alleviated hypertension, CM suppressed proteinuria and glomerular sclerosis more efficiently than Hyd. The HS group revealed a decrease in podocyte number and podocyte-specific molecules, together with an increase in glomerular apoptotic cells and apoptosis-related proteins in the kidney. These changes were significantly attenuated by CM, but not by Hyd. Furthermore, CM ameliorated the apoptotic signals in murine cultured podocytes stimulated with the high glucose and aldosterone medium. In conclusion, CM could exert renoprotective effects in MetS model rats, together with the inhibition of podocyte apoptosis. Our study suggests that serine protease inhibition may become a new therapeutic strategy against MetS-related hypertension and renal injuries.

Sarsasapogenin restores podocyte autophagy in diabetic nephropathy by targeting GSK3β signaling pathway

Podocyte injury following abnormal podocyte autophagy plays an indispensable role in diabetic nephropathy (DN), therefore, restoration of podocyte autophagy is considered as a feasible strategy for the treatment of DN. Here, we investigated the preventive effects of sarsasapogenin (Sar), the main active ingredient in Anemarrhena asphodeloides Bunge, on the podocyte injury in diabetic rats, and tried to illustrate the mechanisms underlying the effects in high glucose (HG, 40 mM)-treated podocytes (MPs). Diabetes model was established in rats with single streptozocin (60 mg· kg^-1) intraperitoneal administration. The rats were then treated with Sar (20, 60 mg· kg^-1· d^-1, i.g.) or a positive control drug insulin (INS) (40 U· kg^-1· d^-1, i.h.) for 10 weeks. Our results showed that both Sar and insulin precluded the decreases of autophagy-related proteins (ATG5, Beclin1 and LC3B) and podocyte marker proteins (podocin, nephrin and synaptopodin) in the diabetic kidney. Furthermore, network pharmacology was utilized to assess GSK3β as the potential target involved in the action of Sar on DN and were substantiated by significant changes of GSK3β signaling in the diabetic kidney. The underlying protection mechanisms of Sar were explored in HG-treated MPs. Sar (20, 40 μM) or insulin (50 mU/L) significantly increased the expression of autophagy- related proteins and podocyte marker proteins in HG-treated MPs. Furthermore, Sar or insulin treatment efficiently regulatedphosphorylation at activation and inhibition sites of GSK3β. To sum up, this study certifies that Sar meliorates experimental DN through targeting GSK3β signaling pathway and restoring podocyte autophagy.

SIRT1 Alleviates Aldosterone-Induced Podocyte Injury by Suppressing Mitochondrial Dysfunction and NLRP3 Inflammasome Activation

BACKGROUND

Podocyte injury contributes to progressive glomerulosclerosis. Previously, we demonstrated the important role of the NLR family pyrin domain containing 3 (NLRP3) inflammasome in mediating the podocyte injury induced by aldosterone. Silent mating type information regulation 2 homolog 1 (SIRT1) is an NAD+-dependent deacetylase that is associated with the regulation of cellular inflammation. However, whether the activation of the NLRP3 inflammasome in podocytes is regulated by SIRT1, and the mechanism involved, remains unknown.

METHODS

In this study, we detected SIRT1 expression in patients with podocyte disease and performed an aldosterone infusion model in podocyte-specific Sirt1 knockout mice. In cultured podocytes, we used plasmids to overexpress SIRT1 and treated the podocyte with aldosterone.

RESULTS

SIRT1 was significantly decreased in the glomeruli of patients with podocyte disease. Sirt1-deficient mice showed significant urinary albumin excretion after aldosterone infusion, and the severity of the glomerular injury was significantly greater in podocyte-specific Sirt1 knockout mice than in the wild-type mice. Moreover, podocyte conditional Sirt1 knockout aggravated NLRP3 inflammasome activation and mitochondrial dysfunction (MtD). In vitro, overexpression of SIRT1 inhibited NLRP3 activation, protected against MtD and podocyte injury.

CONCLUSION

Taken together, these findings revealed a novel regulatory mechanism of the NLRP3 inflammasome by SIRT1 by promoting mitochondrial function, which provides some potential targets for the treatment of glomerular diseases.

Monoterpene indole alkaloids from the roots of Bousigonia mekongensis and their anti-diabetic nephropathy activity

Four new monoterpene indole alkaloids (1-4) together with six known alkaloids (5-10) were isolated from the roots of Bousigonia mekongensis. Compounds 3 and 4 were the first examples of condylocarpan-adenine type alkaloids obtained from natural plant resource. Their structures were elucidated on the basis of spectroscopic data. All compounds were evaluated for their inhibiting glucose-induced mesanginal cell proliferation and protecting high glucose-evoked podocyte injury activities. (-)-demethoxycarbonyldihydrogambirtannine (5) can significantly antagonize glucose-induced podocyte injury with EC₅₀ value of 6.5 ± 1.2 μM.

Inhibition of NLRP3 inflammasome ameliorates podocyte damage by suppressing lipid accumulation in diabetic nephropathy

BACKGROUND

Nucleotide leukin-rich polypeptide 3 (NLRP3) inflammasome is documented as a potent target for treating metabolic diseases and inflammatory disorders. Our recent work demonstrated that inhibition of NLRP3 inflammasome activation inhibits renal inflammation and fibrosis in diabetic nephropathy. This study was to investigate the effect of NLRP3 inflammasome on podocyte injury and the underlying mechanism in diabetic nephropathy.

METHODS

In vivo, db/db mice were treated with MCC950, a NLRP3 inflammasome specific inhibitor. NLRP3 knockout (NKO) mice were induced to diabetes by intraperitoneal injections of streptozotocin (STZ). We assessed renal function, albuminuria, podocyte injury and glomerular lipid accumulation in diabetic mice. In vitro, apoptosis, cytoskeleton change, lipid accumulation, NF-κB p65 activation and reactive oxygen species (ROS) generation were evaluated in podocytes interfered with NLRP3 siRNA or MCC950 under high glucose (HG) conditions. In addition, the effect and mechanism of IL-1β on lipid accumulation was explored in podocytes exposed to normal glucose (NG) or HG.

RESULTS

MCC950 treatment improved renal function, attenuated albuminuria, mesangial expansion, podocyte loss, as well as glomerular lipid accumulation in db/db mice. The diabetes-induced podocyte loss and glomerular lipid accumulation were reversed in NLRP3 knockout mice. The increased expression of sterol regulatory element-binding protein1 (SREBP1) and SREBP2, and decreased expression of ATP-binding cassette A1 (ABCA1) in podocytes were reversed by MCC950 treatment or NLRP3 knockout in diabetic mice. In vitro, NLRP3 siRNA or MCC950 treatment markedly inhibited HG-induced apoptosis, cytoskeleton change, lipid accumulation, NF-κB p65 activation, and mitochondrial ROS production in cultured podocytes. In addition, BAY11-7082 or tempol treatment inhibited HG-induced lipid accumulation in podocytes. Moreover, exposure of IL-1β to podocytes induced lipid accumulation, NF-κB p65 activation and mitochondrial ROS generation.

CONCLUSION

Inhibition of NLRP3 inflammasome protects against podocyte damage through suppression of lipid accumulation in diabetic nephropathy. IL-1β/ROS/NF-κB p65 mediates diabetes-associated lipid accumulation in podocytes. The suppression of NLRP3 inflammasome activation may be an effective therapeutic approach to diabetic nephropathy.

LncRNA MALAT1/microRNA let-7f/KLF5 axis regulates podocyte injury in diabetic nephropathy

OBJECTIVE

The abnormal expression of microRNAs (miRNAs) and long non-coding RNAs (lncRNAs) has been demonstrated to exert pivotal effects in human diseases. We focused on the functions of metastasis associated lung adenocarcinoma transcript 1 (MALAT1) and microRNA let-7f on diabetic nephropathy (DN).

METHODS

The diabetes (db/db) mice were treated with silenced MALAT1, then the baseline indicators, pathology changes, marker proteins of podocyte injury (nephrin, podocin, desmin and Cleaved caspase-3), oxidative stress indicators and inflammatory factors in renal tissues were determined. Murine podocyte MPC5 cells were stimulated by high glucose (HG) and transfected with sh-MALAT1 or let-7f mimic, then the cell migration, adhesion ability and apoptosis were evaluated. Moreover, the binding relationship between MALAT1 and let-7f, and the targeting relationship between let-7f and krüppel-like factor 5 (KLF5) were confirmed.

RESULTS

Silenced MALAT1 could improve baseline indicators of DN mice, and also improved pathology, increased nephrin and podocin expression, decreased desmin and Cleaved caspase-3 expression, and restrained oxidative stress and inflammatory reaction in their renal tissues. Additionally, elevated let-7f and reduced MALAT1 could restrict migration and apoptosis of HG-induced MPC5 cells, and promoted the cell adhesion ability.

CONCLUSION

Results in our research indicated that the reduced MALAT1 could relieve the podocyte injury in DN by upregulating let-7f and inhibiting KLF5, which may be helpful for DN therapy.

Polydatin enhances glomerular podocyte autophagy homeostasis by improving Nrf2-dependent antioxidant capacity in fructose-fed rats

High fructose is considered a causative factor for oxidative stress and autophagy imbalance that cause kidney pathogenesis. Antioxidant polydatin isolated from Polygonum cuspidatum has been reported to protect against kidney injury. In this study, polydatin was found to ameliorate fructose-induced podocyte injury. It activated mammalian target of rapamycin complex 1 (mTORC1) and suppressed autophagy in glomeruli of fructose-fed rats and in fructose-exposed conditionally immortalized human podocytes (HPCs). Polydatin also enhanced nuclear factor-E2-related factor 2 (Nrf2)-dependent antioxidant capacity to suppress fructose-induced autophagy activation in vivo and in vitro, with the attenuation of fructose-induced up-regulation of cellular light chain 3 (LC3) II/I protein levels. This effect was abolished by Raptor siRNA in fructose-exposed HPCs. These results demonstrated that polydatin ameliorated fructose-induced autophagy imbalance in an mTORC1-dependent manner via improving Nrf2-dependent antioxidant capacity during podocyte injury. In conclusion, polydatin with anti-oxidation activity suppressed autophagy to protect against fructose-induced podocyte injury.