Mouse Podocytes Research Articles

Integration of metabolomics and transcriptomics reveals the mechanism of TMEM30A downregulation induced FSGS podocyte injury.

Podocyte injury plays a critical role in the pathogenesis and progression of focal and segmental glomerulosclerosis (FSGS). Transmembrane protein 30A (TMEM30A) downregulation participates in podocyte injury. This study aimed to identify the critical pathways and molecules associated with the downregulation of TMEM30A in the context of FSGS podocyte injury. In our study, we found TMEM30A and podocyte marker Synaptopodin were significantly downregulated in kidney tissues from patients with FSGS compared to those in normal controls. Using transcriptomic and metabolomic analyses, we characterized Tmem30a knockdown (KD) and normal mouse podocytes to identify differentially expressed genes and metabolites. Then, Gene Ontology, Kyoto Encyclopedia of Genes and Genomes (KEGG), Gene Set Enrichment Analysis (GSEA), and Protein-Protein Interaction (PPI) network were constructed, and the differentially expressed genes and metabolites were enriched into glycolytic pathway. Furthermore, we found the key glycolytic enzymes were downregulated in patients with FSGS, podocyte-specific Tmem30aLoxP/LoxP; NPHS2-Cre mice, and Tmem30a KD mouse podocytes. For rescue experiments, shTmem30a-resistant cDNA (resTmem30a) was created to intervene Tmem30a KD mouse podocytes. And we observed that podocyte-related molecules were downregulated in the Tmem30a KD group, along with glycolysis-related molecules, but the resTmem30a partially reversed this trend. Our findings clarified TMEM30A downregulation initiates podocyte injury by reducing glycolysis-related molecules (ALDOA, HK2, LDHA, and GAPDH) in FSGS and have implications for early diagnosis, prevention, and treatment.

CircMRP4 orchestrates podocytes injury via the miR-499-5p/RRAGB/mTORC1 axis in diabetic kidney disease.

Diabetic kidney disease2 (DKD) is a chronic complication of diabetes characterized by kidney damage due to persistent hyperglycemia. A growing number of evidence indicated that circular RNAs3 (circRNAs) play a crucial role in diabetes and associated complications. However, the function and mechanism of circRNAs in DKD remain unclear. Herein, we investigated the expression profiles of circRNAs in DKD mice compared to non-diabetic mice using RNA-seq analysis. A novel circRNA, circMRP4, derived from the circularization of Multidrug resistance-associated protein 44 (MRP4) was identified. The expression of circMRP4 was significantly increased in both kidney tissues of DKD and mouse podocytes exposed to high glucose5 (HG). In addition, knockdown of circMRP4 alleviated podocytes apoptosis and inflammation induced by HG, while circMRP4 overexpression resulted in the opposite impact. Dual-luciferase reporter, RNA immunoprecipitation and RNA pull-down assay demonstrated that circMRP4 could directly target miR-499-5p which was closely associated with podocytes apoptosis and inflammation. Furthermore, circMRP4 was found to act as a sponge for miR-499-5p, leading to the upregulation of its target RRAGB, thereby activating the mTORC1/P70S6K signaling. In summary, our findings suggested that circMRP4 mediated podocytes apoptosis and inflammation in DKD by modulating the miR-499-5p/RRAGB/mTORC1/P70S6K axis, highlighting circMRP4 as a potential therapeutic target for DKD.

Fbxo11 maintains mitochondrial function and prevents podocyte injury in adriamycin-induced nephropathy by mediating the ubiquitin degradation of Fosl2

Mitochondrial dysfunction is a pivotal factor in the onset of podocyte damage, which is a central component in the pathogenesis of nephrotic syndrome (NS). However, the precise mechanisms underlying the changes in podocyte mitochondria remain elusive. Our study aims to clarify the potential mechanisms involved in the role of F-box protein 11 (Fbxo11) in NS, specifically concentrating on its impact on mitochondrial function. A mouse model was established by tail vein injection of adriamycin (ADR, 10 mg/kg) and was infected with lentivirus overexpressing Fbxo11. Mouse podocytes (MPC-5) were infected with lenti-Fbxo11-OE, followed by treatment with 0.4 μg/mL of ADR. We identified the decreased expression of Fbxo11 in mouse kidney tissues and MPC-5 cells induced by ADR. Lenti-Fbxo11-OE intervention relieved ADR-induced glomerular lesion, podocyte injury, and mitochondrial dysfunction. In vitro, overexpression of Fbxo11 in mouse podocytes improved mitochondrial function and reduced podocyte damage, thereby inhibiting podocyte apoptosis. Mechanistically, Fbxo11 decreased the protein expression of Fosl2 through ubiquitin-dependent proteasomal degradation. Rescue experiments revealed that overexpression of Fosl2 abolished the protective effects of Fbxo11 overexpression on mitochondrial damage and podocyte injury. Importantly, the regulatory effects of the Fbxo11/Fosl2 axis were reversed when treated with the mitochondrial fission inhibitor mdivi-1. Taken together, our results demonstrated that Fbxo11-mediated ubiquitin degradation of Fosl2 is critical for maintaining mitochondrial function and preventing podocyte injury during NS.

GLP-1/GIP dual agonist tirzepatide normalizes diabetic nephropathy via PI3K/AKT mediated suppression of oxidative stress.

Effective therapeutic approaches for the treatment of diabetic nephropathy (DN) with irreversible deterioration of renal function are currently lacking. In this study, we aimed to investigate the ability of the glucagon-likepeptide-1 (GLP-1)/ gastric inhibitory polypeptide (GIP) dual agonist, tirzepatide to alleviate DN in mice and its underlying mechanisms. We investigated the reno-protective effect of semaglutide and tirzepatide in a mouse model of DN, an insulin-treated positive control group was also included. Indicators of diabetic kidney injury and oxidative stress biomarkers were also assessed. RNA-seq analysis of renal tissue was conducted to explore the potential mechanism of action of tirzepatide and in vitro cell experiments were performed to validate its pathway. In DN mice, one-third the dose of tirzepatide was consistent with that of semaglutide in lowering glucose, body weight, and urine albumin-to-creatine ratio (UACR) and in improving antioxidative stress activities, while insulin treatment could not effectively restore the UACR. RNA-seq analysis revealed that the PI3K-AKT signaling pathway was significantly enriched after tirzepatide treatment compared with that in the DN model. Confirmatory experiments demonstrated that tirzepatide regulated oxidative stress and the PI3K-AKT pathway in mouse podocyte cell-5 cells exposed to high glucose. Further mechanistic validation suggested that the antioxidative activity of tirzepatide was reversed by PI3K inhibitor. These findings expand the potential effects and mechanics of tirzepatide in the treatment of DN, which may provide a novel therapeutic approach and therapeutic target for DN treatment.

Hyperactivation of p53 contributes to mitotic catastrophe in podocytes through regulation of the Wee1/CDK1/cyclin B1 axis

Podocyte loss in glomeruli is a fundamental event in the pathogenesis of chronic kidney diseases. Currently, mitotic catastrophe (MC) has emerged as the main cause of podocyte loss. However, the regulation of MC in podocytes has yet to be elucidated. The current work aimed to study the role and mechanism of p53 in regulating the MC of podocytes using adriamycin (ADR)-induced nephropathy. In vitro podocyte stimulation with ADR triggered the occurrence of MC, which was accompanied by hyperactivation of p53 and cyclin-dependent kinase (CDK1)/cyclin B1. The inhibition of p53 reversed ADR-evoked MC in podocytes and protected against podocyte injury and loss. Further investigation showed that p53 mediated the activation of CDK1/cyclin B1 by regulating the expression of Wee1. Restraining Wee1 abolished the regulatory effect of p53 inhibition on CDK1/cyclin B1 and rebooted MC in ADR-stimulated podocytes via p53 inhibition. In a mouse model of ADR nephropathy, the inhibition of p53 ameliorated proteinuria and podocyte injury. Moreover, the inhibition of p53 blocked the progression of MC in podocytes in ADR nephropathy mice through the regulation of the Wee1/CDK1/cyclin B1 axis. Our findings confirm that p53 contributes to MC in podocytes through regulation of the Wee1/CDK1/Cyclin B1 axis, which may represent a novel mechanism underlying podocyte injury and loss during the progression of chronic kidney disorder.

HBx promotes glomerular podocyte-induced immune cell responses

Background Podocytes, as intrinsic renal cells, can also express MHC-II and costimulatory molecules under inflammatory conditions, suggesting that they may act as antigen-presenting cells (APCs) to activate immune cell responses and then lead to immune-mediated renal injury. They are already recognized as main targets in the pathogenic mechanism of hepatitis B virus (HBV)-associated glomerulonephritis (HBV-GN). Previous studies also have indicated that inflammatory cells infiltration and immune-mediated tissue injury are evident in the kidney samples of patients with HBV-GN. However, the role of podocytes immune disorder in the pathogenic mechanism of HBV-GN remains unclear. Methods Renal function and inflammatory cells infiltration were measured in HBV transgenic (HBV-Tg) mice. In vitro, podocytes/CD4+ T cells or macrophages co-culture system was established. Then, the expression of HBx, CD4, and CD68 was determined by immunohistochemistry, while the expression of MHC-II, CD40, and CD40L was determined by immunofluorescence. Co-stimulatory molecules expression was examined by flow cytometry. The levels of inflammatory factors were detected by ELISA. Results In vivo, renal function was obviously impaired in HBV-Tg mice. HBx was significantly upregulated and immune cells infiltrated in the glomerulus of HBV-Tg mice. Expression of MHC-II and costimulatory molecule CD40 increased in the podocytes of HBV-Tg mice; CD4+ T cells exhibited increased CD40L expression in glomerulus. In vitro, CD40 expression was markedly elevated in HBx-podocytes. In co-culture systems, HBx-podocytes stimulated CD4+ T cells activation and caused the imbalance between IFN-γ and IL-4. HBx-podocytes also enhanced the adhesion ability of macrophages and induced the release of proinflammatory mediators. Conclusion Taken together, these podocyte-related immune disorder may be involved in the pathogenic mechanism of HBV-GN.

Dysregulation of Podocyte BK Channels and Nephrosis: Effects of Circulating Factors and Auxiliary β4 Subunits.

Podocytes express large-conductance Ca2+-activated K+ channels (BK channels) and at least two different pore-forming KCa1.1 subunit C-terminal splice variants, known as VEDEC and EMVYR, along with auxiliary β and γ subunits. Podocyte KCa1.1 subunits interact directly with TRPC6 channels and BK channels become active in response to Ca2+ influx through TRPC6. Here, we confirmed that Ca2+ influx through TRPC channels is reduced following the blockade of BK channels by paxilline. The overall abundance of KCa1.1 subunits, as well as that of β4 and γ3 subunits, were increased in glomeruli isolated from Sprague Dawley rats during chronic puromycin aminonucleoside (PAN) nephrosis. Exposing cultured mouse podocytes for 24 h to recombinant TNFα, a circulating factor implicated in pediatric nephrotic syndromes, did not affect the total abundance of KCa1.1, but did evoke significant increases in both β4 and γ3. However, TNFα evoked a marked increase in the surface abundance of KCa1.1 subunits, similar to that of its previously reported effects on TRPC6 channels. The effect of TNFα on the surface expression of KCa1.1 was eliminated following siRNA knockdown of the β4 subunits, suggesting a role for this subunit in KCa1.1 trafficking to the cell surface. By contrast, treating podocytes with suPAR did not affect the total or surface expression of KCa1.1. The coordinated activation of KCa1.1 channels may promote Ca2+ influx through TRPC channels during normal and abnormal podocyte function by maintaining a membrane potential that allows for the efficient permeation of divalent cations through TRPC pores.

PTHrP Promotes RBP4 Expression Under the Control of PPARγ in the Kidney.

Parathyroid hormone-related protein (PTHrP) and retinol-binding protein 4 (RBP4) have been associated with a worse prognosis of kidney disease. Recently, the direct interconnection between PTHrP and the peroxisome proliferator-activated receptor gamma (PPARγ), a nuclear receptor whose activation is nephroprotective, has been discovered. The aim of this study was to analyze the relationship between PTHrP, PPARγ, and RBP4. For this purpose, we analyzed the levels of these proteins, which were studied in the kidneys of five experimental groups of mice at 6 weeks of age: controls, diabetics, insulin-treated diabetics, transgenic mice overexpressing PTHrP at the renal level, and the latter mice that were also induced with diabetes. In addition, we also analyzed the expression levels of these molecules in two mouse podocyte cell lines, controls and PPARγKO, subjected to a lipotoxic insult by palmitic acid. We found that RBP4 and PTHrP are increased in the kidney in pathological conditions and that insulin and PPARγ act regulating PTHrP and RBP4 expression, suggesting that the regulation of this system is critical for the maintenance of renal homeostasis and how it becomes imbalanced in different pathophysiological conditions.

Astragaloside IV attenuates podocyte apoptosis via regulating TXNIP/NLRP3/GSDMD signaling pathway in diabetic nephropathy

ObjectivesAmong all the diabetes complications brought on by persistent inflammation is diabetic kidney disease (DKD). One essential method of the inflammatory response's programmed cell death is anthrax. One of the main causes of diabetic renal disease progression in a high-glycemic environment is the lysis of renal resident cells.MethodThis investigation sought to determine whether Astragaloside IV (AS-IV)'s anti-pyroptosis action provides a protective function for the kidneys. For 12 weeks, db/db mice received 40 mg/kg of AS-IV by transgastric gavage. To validate the possible in vitro mechanism, mouse podocytes were cultivated for additional experiments.ResultsIn vitro, AS-IV led to a significant reduction in blood urea nitrogen (BUN), urine albumen-to-creatinine ratio (UACR), serum creatinine (CREA), and hyperglycemia in db/db mice and lessen the pathological alterations in the kidney. Moreover, pyrin structural domain of the NLR family pyrin domain containing 3 (NLRP3), cleaved-caspase-1, gasdermin D (GSDMD), IL-18, and IL-1β were down-expressed and podocyte markers podocin and nphs1 were up-regulated following AS-IV intervention. By silencing GSDMD, we demonstrated in vitro that HG-stimulated podocytes undergo pyroptosis. We also discovered that AS-IV can mitigate this pyroptosis. To confirm that AS-IV prevented the NLRP3 inflammasome from activating, the NLRP3 inhibitor CY-09 was employed. It was also discovered that AS-IV prevents the expression of TXNIP and NLRP3 as well as their interaction. GSDMD expression was significantly downregulated following TXNIP-siRNA treatment, whereas GSDMD expression was upregulated in TXNIP overexpression cells; this upregulation could be undone with AS-IV.ConclusionsThe anti-pyroptosis effect of AS-IV via the TXNIP-NLRP3-GSDMD axis improves the renal function and podocyte damage of db/db mice and delays the onset of DKD, according to in vivo and in vitro experimental data.

Dynll1-PI31 Interaction Enhances Proteolysis via the Proteasome, Representing a Novel Therapeutic Target for INF2-Related FSGS.

The p.Arg218Gln (R218Q) mutation in the inverted formin 2 (INF2) gene causes podocytopathy prone to focal segmental glomerulosclerosis (FSGS). This mutation disrupts the ability of INF2 to sequester DYNLL1, thus promoting dynein-mediated mistrafficking of the slit diaphragm protein, nephrin, to proteolytic pathways. Bortezomib, a proteasome inhibitor (PI), stabilizes nephrin in R218Q knockin (KI) podocytes, suggesting a role for the ubiquitin proteasome system (UPS) in dynein-driven pathogenesis. However, the link between dynein and the UPS is unknown. This study tested the hypothesis that INF2 R218Q promotes proteasome-mediated degradation of nephrin via an increased interaction between Dynll1 and Proteasomal Inhibitor of 31kD (PI31), a Dynll1 adaptor that potentially couples the UPS with dynein cargoes. The essential role of PI31 in UPS-mediated degradation of nephrin, a known dynein cargo, was studied in cultured R218Q KI mouse podocytes by applying genetic or chemical interventions to inhibit the activity of PI31 or of the proteasome. The protective effect of bortezomib in dynein-driven podocytopathy and FSGS was tested in R218Q KI mice challenged with puromycin aminonucleoside (PA), a murine model of FSGS. The R218Q mutation in Inf2 disrupted sequestration of Dynll1 by Inf2, allowing Dynll1 to be captured by PI31 and promoting dynein-mediated transport of nephrin to the proteasome. Each of the following manipulations was sufficient to restore nephrin proteostasis in R218Q KI podocytes: knocking down Dynll1 or PI31, inactivating dynein, or inhibiting the activity of the proteasome. In R218Q KI mice challenged with PA, dynein-mediated mistrafficking and depletion of nephrin were correlated with increased Dynll1-PI31 interaction; the resulting podocytopathy and FSGS were ameliorated by bortezomib. The Dynll1-PI31 interaction facilitates dynein-driven trafficking of nephrin to the proteasome and proteasome-mediated degradation of nephrin in INF2-R218Q-mediated podocytopathy. This mechanism offers new therapeutic strategies for INF2-related FSGS by using pharmacologically available proteasome inhibitors.

Qufeng Tongluo Decoction May Alleviate Podocyte Injury Induced by High Glucose and Hydrogen Peroxide by Regulating Autophagy

Background: Diabetic kidney disease is a significant complication of diabetes. Previous studies have confirmed that Qufeng Tongluo (QFTL) decoction can alleviate podocyte injury in a diabetic rat model, but its mechanism remains unclear. The present in vitro study investigated QFTL’s mechanism in protecting podocytes. Methods: The mouse podocyte clone 5 (MPC-5) cell line stimulated by high glucose and hydrogen peroxide was used as a model for podocyte injury. The cells were treated with QFTL, QFTL + SC79 (activator of the phosphatidylinositol 3-kinase/protein kinase B (PI3K/Akt), and C2 ceramide (inhibitor of the PI3K/Akt). Immunofluorescence, western blot and polymerase chain reaction (PCR) were employed to detect the expression of microtubule-associated protein 1 light chain 3 (LC3), sequestosome 1 (SQSTM1/p62), PI3K, Akt, and phosphatase and tensin homolog (PTEN) proteins and their messenger RNA (mRNA) levels. Results: High glucose and hydrogen peroxide stimulation may disrupt podocytes’ cytoskeletal structure, while QFTL may mitigate these structural changes. After the SC79 intervention, QFTL’s alleviation of the cytoskeletal structure damage disappeared. High glucose and hydrogen peroxide stimulation decreased the expression of LC3 in MPC-5 cells, whereas QFTL upregulated its expression, but this effect was reversed by the SC79 intervention. Interestingly, P62 decreased after high glucose + hydrogen peroxide stimulation, and QFTL failed to upregulate P62. The expression levels of PI3K, Akt, and PTEN in the model group decreased, which were improved by QFTL. Conclusion: These results suggest that QFTL can maintain the stability of autophagic flux in injured podocytes, which may be related to its ability to improve P62 expression but not to regulating the PI3K/Akt signaling pathway.

Butyrate attenuates high-fat diet-induced glomerulopathy through GPR43-Sirt3 pathway.

The incidence of obesity-related glomerulopathy (ORG) is rising worldwide with very limited treatment methods. Paralleled with the gut–kidney axis theory, the beneficial effects of butyrate, one of the short-chain fatty acids (SCFA)produced by gut microbiota, on metabolism and certain kidney diseases have gained growing attention. However, the effects of butyrate on ORG and its underlying mechanism are largely unexplored. In this study, a mice model of ORG was established with a high-fat diet feeding for 16 weeks, and sodium butyrate treatment was initiated at the 8th week. Podocyte injury, oxidative stress and mitochondria function were evaluated in mice kidney and validated in vitro in palmitic acid-treated-mouse podocyte cell lines. Further, the molecular mechanisms of butyrate on podocytes were explored. Compared with controls, sodium butyrate treatment alleviated kidney injuries and renal oxidative stress in high-fat diet-fed mice. In mouse podocyte cell lines, butyrate ameliorated palmitic acid-induced podocyte damage and helped maintain the structure and function of the mitochondria. Moreover, the effects of butyrate on podocytes were mediated via the GPR43-Sirt3 signal pathway, as evidenced by the diminished effects of butyrate with the intervention of GPR43 or Sirt3 inhibitors. In summary, we conclude that butyrate has therapeutic potential for the treatment of ORG. It attenuates high-fat diet-induced ORG and podocyte injuries through the activation of the GPR43-Sirt3 signalling pathway.

Autoantibodies Targeting Proteasome Subunit Alpha Type 1 in Autoimmune Podocytopathies.

The antibody against proteasome subunit alpha type 1 (PSMA1) is a podocyte autoantibody in idiopathic nephrotic syndrome (INS) children identified in our previous study. The aim of this study was to explore the characteristics of INS in children and the mechanism underlying its involvement in the development of INS. The levels of serum anti-PSMA1 autoantibodies in children were detected via protein microarray and compared among different disease groups. The recombinant PSMA1 protein was injected subcutaneously and intraperitoneally into mice to observe glomerular morphology and function. The PSMA1-knockdown and PSMA1-overexpressing cell lines were constructed from mouse podocytes, and their cytoskeleton and function were analyzed. Homozygous zebrafish with psma1 knockout were observed. The levels of serum anti-PSMA1 autoantibodies were higher in INS children and varied with urinary protein. In mice immunized with PSMA1, the presence of serum anti-PSMA1 autoantibody caused albuminuria and damage to the glomerular filtration membrane. Deficiency of PSMA1 impaired the podocyte cytoskeleton and physiological function. Complete deletion of psma1 caused edema, abnormal glomerular morphology and effacement of foot processes in zebrafish. PSMA1 played an important role in the maintenance of podocyte morphology and function.

Obtusifolin inhibits podocyte apoptosis by inactivating NF-κB signaling in acute kidney injury.

Acute kidney injury (AKI) is a common clinical condition and is associated with unacceptable morbidity and mortality. Obtusifolin is an anthraquinone extracted from the seeds of Cassia obtusifolia with anti-inflammatory properties. This study focused on the role and mechanism of obtusifolin in AKI. The mouse podocyte cell line MPC5 was exposed to lipopolysaccharide (LPS) to establish a cell model of AKI. The viability of MPC5 cells treated with obtusifolin and/or LPS was detected by 3-(4, 5-Dimethylthiazol-2-yl)-2,5diphenyltetrazolium bromide assay. Cell apoptosis was analyzed by flow cytometry. The levels of podocyte injury- and apoptosis-related proteins as well as the nuclear factor-kappaB (NF-κB) signaling pathway was examined using western blotting analysis. The renal protective effects of obtusifolin were determined using an LPS-induced mouse model of AKI. Serum creatinine and blood urea nitrogen levels were measured. Hematoxylin-eosin staining of kidney sections was performed to evaluate renal histology. We found that MPC5 cells treated with LPS showed suppressed cell viability (p < 0.01) and increased cell apoptosis (p < 0.001). LPS reduced the protein expression of Bcl-2, nephrin, and synaptopodin as well as increased the protein levels of Bax and Cleaved Caspase-3 in podocytes in a concentration-dependent manner (p < 0.01). In addition, 10μg/ml LPS-repressed cell viability was rescued by obtusifolin in a concentration-dependent manner (p < 0.01). Moreover, LPS-induced increase in MPC5 cell apoptosis was reversed by obtusifolin treatment (p < 0.01). Obtusifolin administration ameliorated LPS-induced kidney injury and reduced blood urea nitrogen and serum creatinine levels in mice (p < 0.001). Additionally, obtusifolin inhibited LPS-induced activation of NF-κB signaling in vitro and in vivo (p < 0.01). Overall, obtusifolin was effective in protecting renal function against LPS-induced AKI via inactivation of NF-κB signaling, which suggested that obtusifolin may act as a valuable agent for AKI therapy.

Sex-specific molecular signature of mouse podocytes in homeostasis and in response to pharmacological challenge with rapamycin

BackgroundSex differences exist in the prevalence and progression of major glomerular diseases. Podocytes are the essential cell-type in the kidney which maintain the physiological blood-urine barrier, and pathological changes in podocyte homeostasis are critical accelerators of impairment of kidney function. However, sex-specific molecular signatures of podocytes under physiological and stress conditions remain unknown. This work aimed at identifying sexual dimorphic molecular signatures of podocytes under physiological condition and pharmacologically challenged homeostasis with mechanistic target of rapamycin (mTOR) inhibition. mTOR is a crucial regulator involved in a variety of physiological and pathological stress responses in the kidney and inhibition of this pathway may therefore serve as a general stress challenger to get fundamental insights into sex differences in podocytes.MethodsThe genomic ROSAmT/mG-NPHS2 Cre mouse model was used which allows obtaining highly pure podocyte fractions for cell-specific molecular analyses, and vehicle or pharmacologic treatment with the mTOR inhibitor rapamycin was performed for 3 weeks. Subsequently, deep RNA sequencing and proteomics were performed of the isolated podocytes to identify intrinsic sex differences. Studies were supplemented with metabolomics from kidney cortex tissues.ResultsAlthough kidney function and morphology remained normal in all experimental groups, RNA sequencing, proteomics and metabolomics revealed strong intrinsic sex differences in the expression levels of mitochondrial, translation and structural transcripts, protein abundances and regulation of metabolic pathways. Interestingly, rapamycin abolished prominent sex-specific clustering of podocyte gene expression and induced major changes only in male transcriptome. Several sex-biased transcription factors could be identified as possible upstream regulators of these sexually dimorphic responses. Concordant to transcriptomics, metabolomic changes were more prominent in males. Remarkably, high number of previously reported kidney disease genes showed intrinsic sexual dimorphism and/or different response patterns towards mTOR inhibition.ConclusionsOur results highlight remarkable intrinsic sex-differences and sex-specific response patterns towards pharmacological challenged podocyte homeostasis which might fundamentally contribute to sex differences in kidney disease susceptibilities and progression. This work provides rationale and an in-depth database for novel targets to be tested in specific kidney disease models to advance with sex-specific treatment strategies.

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

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. To explore the protective effect of Cor against podocyte injury in DN mice and the underlying mechanisms. 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. 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). Cor alleviates podocyte injury by regulating autophagy via the SIRT1-AMPK pathway, thereby exerting its protective impact on renal function in DN mice.

Exosomes secreted by podocytes regulate the differentiation of Th17/Treg cells in idiopathic nephrotic syndrome

BackgroundPrevious studies have demonstrated that immune cells release exosomes, which act as antigen-presenting vesicles to activate T cells. In our previous study, we discovered that podocytes, a type of kidney cell, can also exhibit antigen-presenting functions to naïve CD4+ T cells in idiopathic nephrotic syndrome (INS). Building upon these findings, the objective of this study was to investigate whether podocytes can regulate the balance between Th17 and Treg cells through the release of exosomes. MethodsWe co-cultured naïve CD4+ T cells with LPS-treated bone marrow dendritic cells (LPS-BMDC), LPS-treated mouse podocyte clone 5 (LPS-MPC-5), and exosomes derived from LPS-MPC-5 (LPS-EXO). As a control group, naïve CD4+ T cells were cultured with exosomes from untreated MPC-5 (EXO). After 48 h, we analyzed the percentages of Th17 and Treg cells using flow cytometry, measured the concentrations of IL-17A, IL-10, and IL-4 were using ELISA, and examined the expressions of IL-17a, IL-10, RORC, and FOXP3 using RT-qPCR. ResultsWe confirmed the presence of exosomes derived from podocytes based on their morphology, size distribution, concentrations, and the levels of exosomes-specific markers. The percentage of Th17 and Treg cells in the LPS-EXO group was significantly higher than that in the control groups, but lower than in the LPS-MPC-5 group. Furthermore, the ratio of Th17/Treg was relatively higher in the LPS-EXO group compared to the LPS-MPC-5 group. ConclusionThis study indicated further insights into the role of exosomes released from LPS-treated podocytes in regulating the balance between Th17 and Treg cells in INS.

Neuregulin 4 Attenuates Podocyte Injury and Proteinuria in Part by Activating AMPK/mTOR-Mediated Autophagy in Mice.

In this study, we investigate the effect of neuregulin 4 (NRG4) on podocyte damage in a mouse model of diabetic nephropathy (DN) and we elucidate the underlying molecular mechanisms. In vivo experiments were conducted using a C57BL/6 mouse model of DN to determine the effect of NRG4 on proteinuria and podocyte injury, and in vitro experiments were performed with conditionally immortalized mouse podocytes treated with high glucose and NRG4 to assess the protective effects of NRG4 on podocyte injury. Autophagy-related protein levels and related signaling pathways were evaluated both in vivo and in vitro. The involvement of the adenosine monophosphate-activated protein kinase (AMPK)/mammalian target of rapamycin (mTOR) pathway was detected using chloroquine or AMPK inhibitors. The results showed that the AMPK/mTOR pathway was involved in the protective roles of NRG4 against high glucose-mediated podocyte injury. Also, NRG4 significantly decreased albuminuria in DN mice. PAS staining indicated that NRG4 mitigated glomerular volume and mesangium expansion in DN mice. Consistently, western blot and RT-PCR analyses confirmed that NRG4 decreased the expression of pro-fibrotic molecules in the glomeruli of DN mice. The immunofluorescence results showed that NRG4 retained expression of podocin and nephrin, whereas transmission electron microscopy revealed that NRG4 alleviated podocyte injury. In DN mice, NRG4 decreased podocyte apoptosis and increased expression of nephrin and podocin, while decreasing the expression of desmin and HIF1α. Overall, NRG4 improved albuminuria, glomerulosclerosis, glomerulomegaly, and hypoxia in DN mice. The in vitro experiments showed that NRG4 inhibited HG-induced podocyte injury and apoptosis. Furthermore, autophagy of the glomeruli decreased in DN mice, but reactivated following NRG4 intervention. NRG4 intervention was found to partially activate autophagy via the AMPK/mTOR signaling pathway. Consequently, when the AMPK/mTOR pathway was suppressed or autophagy was inhibited, the beneficial effects of NRG4 intervention on podocyte injury were diminished. These results indicate that NRG4 intervention attenuates podocyte injury and apoptosis by promoting autophagy in the kidneys of DN mice, in part, by activating the AMPK/mTOR signaling pathway.

RIPK3 causes mitochondrial dysfunction and albuminuria in diabetic podocytopathy through PGAM5-Drp1 signaling

BackgroundReceptor-interacting protein kinase (RIPK)3 is an essential molecule for necroptosis and its role in kidney fibrosis has been investigated using various kidney injury models. However, the relevance and the underlying mechanisms of RIPK3 to podocyte injury in albuminuric diabetic kidney disease (DKD) remain unclear. Here, we investigated the role of RIPK3 in glomerular injury of DKD. MethodsWe analyzed RIPK3 expression levels in the kidneys of patients with biopsy-proven DKD and animal models of DKD. Additionally, to confirm the clinical significance of circulating RIPK3, RIPK3 was measured by ELISA in plasma obtained from a prospective observational cohort of patients with type 2 diabetes, and estimated glomerular filtration rate (eGFR) and urine albumin-to-creatinine ratio (UACR), which are indicators of renal function, were followed up during the observation period. To investigate the role of RIPK3 in glomerular damage in DKD, we induced a DKD model using a high-fat diet in Ripk3 knockout and wild-type mice. To assess whether mitochondrial dysfunction and albuminuria in DKD take a Ripk3-dependent pathway, we used single-cell RNA sequencing of kidney cortex and immortalized podocytes treated with high glucose or overexpressing RIPK3. ResultsRIPK3 expression was increased in podocytes of diabetic glomeruli with increased albuminuria and decreased podocyte numbers. Plasma RIPK3 levels were significantly elevated in albuminuric diabetic patients than in non-diabetic controls (p = 0.002) and non-albuminuric diabetic patients (p = 0.046). The participants in the highest tertile of plasma RIPK3 had a higher incidence of renal progression (hazard ratio [HR] 2.29 [1.05–4.98]) and incident chronic kidney disease (HR 4.08 [1.10–15.13]). Ripk3 knockout improved albuminuria, podocyte loss, and renal ultrastructure in DKD mice. Increased mitochondrial fragmentation, upregulated mitochondrial fission-related proteins such as phosphoglycerate mutase family member 5 (PGAM5) and dynamin-related protein 1 (Drp1), and mitochondrial ROS were decreased in podocytes of Ripk3 knockout DKD mice. In cultured podocytes, RIPK3 inhibition attenuated mitochondrial fission and mitochondrial dysfunction by decreasing p-mixed lineage kinase domain-like protein (MLKL), PGAM5, and p-Drp1 S616 and mitochondrial translocation of Drp1. ConclusionsThe study demonstrates that RIPK3 reflects deterioration of renal function of DKD. In addition, RIPK3 induces diabetic podocytopathy by regulating mitochondrial fission via PGAM5-Drp1 signaling through MLKL. Inhibition of RIPK3 might be a promising therapeutic option for treating DKD.

Foodborne toxin aflatoxin B1 induced glomerular podocyte inflammation through proteolysis of RelA, downregulation of miR-9 and CXCR4/TXNIP/NLRP3 pathway

Aflatoxin B1 (AFB1) is a naturally-occurring mycotoxin and recognized as the most toxic foodborne toxin, particularly causing damages to kidney. Glomerular podocytes are terminally differentiated epithelial cells. AFB1 induces podocyte inflammation, proteinuria and renal dysfunction. Studying the mechanism of AFB1-induced podocyte inflammation and murine kidney dysfunction, we detected that AFB1 increased ubiquitin-dependent degradation of the transcription factor RelA through enhanced interaction of RelA with E3 ubiquitin ligase tripartite motif containing 7 (TRIM7) in mouse podocyte clone-5 (MPC-5) and mouse glomeruli. Reduction of RelA resulted in decreasing microRNA-9 (miR-9) and activating the chemokine receptor 4 (CXCR4), thioredoxin interacting protein (TXNIP), and NOD-like receptor pyrin domain-containing 3 (NLRP3) signaling axis (CXCR4/TXNIP/NLRP3 pathway), leading to podocyte inflammation. We also determined that downregulation of miR-9 led to CXCR4 expression and the downstream TXNIP/NLRP3 pathway activation. Overexpression of miR-9 or deletion of CXCR4 suppressed AFB1-induced CXCR4/TXNIP/NLRP3 pathway, resulting in alleviating podocyte inflammation and kidney dysfunction. Our findings indicated that ubiquitin-dependent proteolysis of RelA, downregulation of miR-9, and activation of CXCR4/TXNIP/NLRP3 pathway played an essential role in AFB1-induced glomerular podocyte inflammation. Our study revealed a novel mechanism, via RelA, for the control of AFB1’s nephrotoxicity, leading to an effective protection of food safety and public health.