Mechanisms of podocyte injury in genetic kidney disease

Glomerular diseases are a leading cause of chronic kidney disease worldwide. Both acquired and hereditary glomerulopathies frequently share a common final disease mechanism: disruption of the glomerular filtration barrier, podocyte injury, and ultimately podocyte death and detachment. Over 70 monogenic causes of proteinuric kidney disease have been identified, and most of these genes are highly expressed in podocytes, regulating key processes such as maintenance of the slit diaphragm, regulation of actin cytoskeleton remodeling, and modulation of downstream transcriptional pathways. Collectively, these are increasingly being referred to as hereditary "podocytopathies," in which podocyte injury is the central feature driving proteinuria and kidney dysfunction. In this review, we provide an overview of the monogenic podocytopathies and discuss the molecular mechanisms by which single-gene defects lead to podocyte injury and ultimately glomerulosclerosis. We review how advances in genomic technology and a better understanding of the cell biological basis of disease have led to the development of more targeted and personalized therapeutic strategies, including an overview of small molecule and gene therapy approaches.

DOT1L protects against podocyte injury in diabetic kidney disease through phospholipase C-like 1

BACKGROUND

Podocyte injury causes proteinuria and accelerates glomerular sclerosis during diabetic kidney disease (DKD). Disruptor of telomeric silencing 1-like (DOT1L), an evolutionarily conserved histone methyltransferase, has been reported in preventing kidney fibrosis in chronic kidney disease models. However, whether DOT1L exerts beneficial effects in diabetes induced podocyte injury and the underlying molecular mechanisms need further exploration.

METHODS

The expression of DOT1L was confirmed by Western blotting in MPC-5 cells and cortex of kidney from db/db mice, as well as immunofluorescence staining in human renal biopsy samples. The effect of DOT1L on podocyte injury was obtained using MPC-5 cells and db/db mice. The potential target genes regulated by DOT1L was measured by RNA-sequencing. Then, a series of molecular biological experiments was performed to investigate the regulation of PLCL1 by DOT1L in MCP-5 cells and db/db mice. Lipid accumulation was assessed by UPLC-MS/MS analysis and Oil Red O staining.

RESULTS

DOT1L expression was significantly declined in high glucose (HG)-treated MPC-5 cells, podocyte regions of kidney tissues from db/db mice and human renal biopsy samples. Subsequent investigations revealed that upregulation of DOT1L ameliorated HG-induced cell apoptosis in MPC-5 cells as well as primary podocytes. Furthermore, podocyte-specific DOT1L overexpression inhibited diabetic podocyte injury in db/db mice. Mechanistically, we revealed that DOT1L upregulated phospholipase C-like 1 (PLCL1) expression by mediating H3K79me2 at its promoter and PLCL1 silencing suppressed the protective role of DOT1L on podocyte injury. Moreover, DOT1L improved diabetes induced abnormal fatty acid metabolism in podocytes and PLCL1 knockdown reversed its protective effects.

CONCLUSIONS

Taken together, our results indicate that DOT1L protects podocyte injury via PLCL1-mediated fatty acid metabolism and provides new insights into the therapeutic target of DKD.

Corilagin alleviates podocyte injury in diabetic nephropathy by regulating autophagy via the SIRT1-AMPK pathway

BACKGROUND

Diabetic nephropathy (DN) is the most frequent chronic microvascular consequence of diabetes, and podocyte injury and malfunction are closely related to the development of DN. Studies have shown that corilagin (Cor) has hepatoprotective, anti-inflammatory, antibacterial, antioxidant, anti-hypertensive, anti-diabetic, and anti-tumor activities.

AIM

To explore the protective effect of Cor against podocyte injury in DN mice and the underlying mechanisms.

METHODS

Streptozotocin and a high-fat diet were combined to generate DN mice models, which were then divided into either a Cor group or a DN group (n = 8 in each group). Mice in the Cor group were intraperitoneally injected with Cor (30 mg/kg/d) for 12 wk, and mice in the DN group were treated with saline. Biochemical analysis was used to measure the blood lipid profiles. Hematoxylin and eosin staining was used to detect pathological changes in kidney tissue. Immunohistochemistry and Western blotting were used to assess the protein expression of nephrin and podocin. Mouse podocyte cells (MPC5) were cultured and treated with glucose (5 mmol/L), Cor (50 μM), high glucose (HG) (30 mmol/L), and HG (30 mmol/L) plus Cor (50 μM). Real-time quantitative PCR and Western blotting were performed to examine the effects of Cor on podocyte autophagy.

RESULTS

Compared with the control group, the DN mice models had increased fasting blood glucose, glycosylated hemoglobin, triglycerides, and total cholesterol, decreased nephrin and podocin expression, increased apoptosis rate, elevated inflammatory cytokines, and enhanced oxidative stress. All of the conditions mentioned above were alleviated after intervention with Cor. In addition, Cor therapy improved SIRT1 and AMPK expression (P < 0.001), inhibited reactive oxygen species and oxidative stress, and elevated autophagy in HG-induced podocytes (P < 0.01).

CONCLUSION

Cor alleviates podocyte injury by regulating autophagy via the SIRT1-AMPK pathway, thereby exerting its protective impact on renal function in DN mice.

Rhodojaponin VI ameliorates podocyte injury related with MDM2/Notch1 pathway in rat experimental membranous nephropathy

AIM

Rhodojaponin VI (R-VI) is the key compound of Rhododendron molle G. Don (Ericaceae) (RM) with effective clinical application in rheumatoid arthritis and chronic glomerulonephritis. In our study, we tried to explore the effect of R-VI on the rat model of membranous nephropathy.

METHODS

The rat model of passive heymann nephritis (PHN) was established by injecting sheep anti-rat Fx1A serum at a single dose through the tail. The rats were orally administered R-VI (0.02 mg/kg) or FK506 (1 mg/kg) 1 day before PHN induction, which was kept for 4 weeks. Urine and blood samples as well as kidney tissue were collected for analysis. C5b-9-induced human podocyte cell (HPC) was employed for experiments in vitro.

RESULTS

R-VI could alleviate glomerulonephritis progression and podocyte injury in PHN rats, as indicated by the decreased proteinuria and the elevated level of albumin, accompanied with reduced immune deposits, reversed podocyte injury in the kidneys. Furthermore, R-VI suppressed murine double minute 2 (MDM2) expression without the alteration in the protein level of p53 and decreased Notch1 expression independent of Numb regulation. Pre-treatment with R-VI in C5b-9-induced HPC blocked MDM2/Notch1 signalling pathway.

CONCLUSION

Thus, R-VI ameliorates podocyte injury in rats with PHN, which was probably related with MDM2/Notch1 signalling pathway.

Activation of TAS2R4 signaling attenuates podocyte injury induced by high glucose

Bitter taste receptors (TAS2Rs) Tas2r108 gene possesses a high abundance in mouse kidney; however, the biological functions of Tas2r108 encoded receptor TAS2Rs member 4 (TAS2R4) are still unknown. In the present study, we found that mouse TAS2R4 (mTAS2R4) signaling was inactivated in chronic high glucose-stimulated mouse podocyte cell line MPC, evidenced by the decreased protein expressions of mTAS2R4 and phospholipase C β2 (PLCβ2), a key downstream molecule of mTAS2R4 signaling. Nonetheless, agonism of mTAS2R4 by quinine recovered mTAS2R4 and PLCβ2 levels, and increased podocyte cell viability as well as protein expressions of ZO-1 and nephrin, biomarkers of podocyte slit diaphragm, in high glucose-cultured MPC cells. However, blockage of mTAS2R4 signaling with mTAS2R4 blockers γ-aminobutyric acid and abscisic acid, a Gβγ inhibitor Gallein, or a PLCβ2 inhibitor U73122 all abolished the effects of quinine on NLRP3 inflammasome and p-NF-κB p65 as well as the functional podocyte proteins in MPC cells in a high glucose condition. Furthermore, knockdown of mTAS2R4 with lentivirus-carrying Tas2r108 shRNA also ablated the effect of quinine on the key molecules of the above inflammatory signalings and podocyte functions in high glucose-cultured MPC cells. In summary, we demonstrated that activation of TAS2R4 signaling alleviated the podocyte injury caused by chronic high glucose, and inhibition of NF-κB p65 and NLRP3 inflammasome mediated the protective effects of TAS2R4 activation on podocytes. Moreover, activation of TAS2R4 signaling could be an important strategy for prevention and treatment of diabetic kidney disease.

Zinc Deficiency Causes Glomerulosclerosis and Renal Interstitial Fibrosis Through Oxidative Stress and Increased Lactate Metabolism in Rats

Chronic kidney disease (CKD) is a highly prevalent condition characterized by renal fibrosis as its ultimate manifestation. Zinc deficiency is closely associated with CKD, evidenced by its link to renal fibrosis. Recently, local lactic acidosis has been demonstrated to promote renal fibrosis. Under zinc-deficient conditions, mitochondrial function is compromised and abnormal lactate metabolism might be induced potentially. However, it remains unclear whether zinc deficiency leads to renal fibrosis through local lactic acidosis. Zinc deficiency rat models were successfully established by feeding zinc-deficient diet. Western blot, qPCR, IHC, and other experiments were employed to investigate the key markers and molecular mechanisms of glomerulosclerosis and renal interstitial fibrosis. Our results indicate that zinc deficiency reduces specific markers of podocytes (podocalyxin, WT1, and nephrin) and activates the Wnt3a/β-catenin pathway, a key pathway in podocyte injury. Concurrently, glomerulosclerosis is indicated by increased urinary microalbumin and serum creatinine levels along with histological alteration observed through PAS and Masson staining in zinc-deficient rats. Furthermore, various degrees of upregulation for several markers of interstitial fibrosis including α-SMA, FN1 and collagen III are also revealed. These findings were further confirmed by Masson staining and IHC. Additionally, alterations in four markers in the EMT process, N-cadherin, E-cadherin, Vimentin, and snail, were consistent with expectations. We then confirmed the activation of the non-canonical TGF-β1 pathway known as the PI3K/AKT/mTOR pathway. An elevation in renal ROS levels accompanied by increased mitochondrial marker cytochrome C expression as well as an elevated NADH/NAD + ratio is also observed within the kidneys. Furthermore, the activity of both MMP/TIMP system and fibrinolytic system was abnormally enhanced under zinc deficiency conditions. Finally, we find zinc supplementation could significantly ameliorate relevant pathological alterations induced by zinc deficiency. These results collectively point that zinc deficiency causes podocyte damage ultimately resulting in glomerulosclerosis via accumulation of ROS and induces interstitial fibrosis via lactic acidosis.

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.

A simple protocol to establish a conditionally immortalized mouse podocyte cell line

Podocytes are specialized terminally differentiated cells in the glomerulus that are the primary target cells in many glomerular diseases. However, the current podocyte cell lines suffer from prolonged in vitro differentiation and limited survival time, which impede research progress. Therefore, it is necessary to establish a cell line that exhibits superior performance and characteristics. We propose a simple protocol to obtain an immortalized mouse podocyte cell (MPC) line from suckling mouse kidneys. Primary podocytes were cultured in vitro and infected with the SV40 tsA58 gene to obtain immortalized MPCs. The podocytes were characterized using Western blotting and quantitative real-time PCR. Podocyte injury was examined using the Cell Counting Kit-8 assay and flow cytometry. First, we successfully isolated an MPC line and identified 39 °C as the optimal differentiation temperature. Compared to undifferentiated MPCs, the expression of WT1 and synaptopodin was upregulated in differentiated MPCs. Second, the MPCs ceased proliferating at a nonpermissive temperature after day 4, and podocyte-specific proteins were expressed normally after at least 15 passages. Finally, podocyte injury models were induced to simulate podocyte injury in vitro. In summary, we provide a simple and popularized protocol to establish a conditionally immortalized MPC, which is a powerful tool for the study of podocytes.

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.

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.

Developmental Causes of Focal Segmental Glomerulosclerosis

Background

Focal segmental glomerulosclerosis (FSGS) is a histological pattern of glomerular damage that includes idiopathic conditions as well as genetic and non-genetic forms. Among these various etiologies, different phenotypes within the spectrum of congenital anomalies of the kidney and urinary tract (CAKUT) have been associated with FSGS.

Summary

Until recently, the main pathomechanism of how congenital kidney and urinary tract defects lead to FSGS was attributed to a reduced number of nephrons, resulting in biomechanical stress on the remaining glomeruli, detachment of podocytes, and subsequent inability to maintain normal glomerular architecture. The discovery of deleterious single-nucleotide variants in PAX2, a transcription factor crucial in normal kidney development and a known cause of papillorenal syndrome, in individuals with adult-onset FSGS without congenital kidney defects has shed new light on developmental defects that become evident during podocyte injury.

Key Message

In this mini-review, we challenge the assumption that FSGS in CAKUT is caused by glomerular hyperfiltration alone and hypothesize a multifactorial pathogenesis that includes overlapping cellular mechanisms that are activated in both damaged podocytes as well as nephron progenitor cells.

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.