From podocyte biology to novel cures for glomerular disease

CD73 alleviates podocytes injury in adriamycin-induced nephrotic syndrome

Podocyte injury is considered one of the main causes of kidney diseases occurrence and development. We have demonstrated that Ecto-5'-Nucleotidase (CD73) upregulated during podocyte injury, yet its function in podocyte is still unclear. Mouse podocytes cell line (MPC5) were exposed to the adriamycin (ADR, 0.25 μg/ml) to establish the model of podocytes injury, as well as low expression CD73 with lentivirus transfected shRNA. CD73 expression was verified by western blot and immunofluorescence assay. Cytokines (IL-1β, IL-18), apoptosis and apoposis-related protein (Bax, Caspase-3, Desmin) levels were measured using ELISA assay, Flow cytometry and Western blot, respectively. CD73, the cytokines of IL-1β and IL-18, apoptosis rate and the expression of Bax, Caspase-3 and Desmin were significantly increased in ADR group compared with the control group. Moreover, we also successfully constructed a CD73 down-expressed podocytes cell line. However, in comparsion with the ADR group, the cytokines of IL-1β and IL-18, apoptosis rate and the expression of Bax, Caspase-3 and Desmin protein were remarkably lowered in the ADR+CD73 shRNA group. These findings demonstrate that CD73 alleviates podocyte damage by reducing the inflammation and increasing apoptosis.

Uncovering the mechanism of Huangkui capsule in the treatment of diabetic kidney disease based on network pharmacology and experimental validation

Diabetic kidney disease (DKD) is a main complication of diabetes mellitus. experimental in vitro validation and Network pharmacology were used in this study to explore the potential mechanism of Huangkui capsules (HKC) in treating DKD. First, we used CCK8 to analyze the optimal drug concentration of HKC. Next, we used flow cytometry, ELISA, Scratch test, and immunofluorescence to examine the apoptosis, oxidative stress, inflammatory factors, and fibrotic factors (FN and α-SMA) expression in HK-2 cells. Thereafter, in order to determine the potential molecular mechanisms underlying the therapeutic effect of HKC in DKD. Compounds contained in HKC were explored by UPLC-Q-TOF-MS/MS. SwissTargetPrediction was utilized for predicting potential gene targets of these compounds. OMIM, DisGeNet and GeneCards databases were employed to identify DKD-related genes. Meanwhile, the association of compounds with DKD genes was examined by protein-protein interaction, GO and KEGG analysis. Finally, molecular docking and molecular dynamics simulation were adopted for further validation. The results showed that HKC had 40 active ingredients, 1051 possible gene targets, and 133 DKD-HKC intersection genes. IL6, TNF, GAPDH, AKT1, PPARG, and TP53 were candidate hub genes by which HKC exerted its anti-DKD function based on molecular docking, molecular dynamics simulation and experimental results. To conclude, this study sheds more lights on the possible pharmacological activities of HKC in DKD and a foundation for further clinical application.

Rheb1 deficiency elicits mitochondrial dysfunction and accelerates podocyte senescence through promoting Atp5f1c acetylation

Podocyte senescence can cause persistent podocyte injury and albuminuria in diabetic kidney disease (DKD), but the mechanism remains obscure. In this study, podocyte senescence was confirmed by immunohistochemical staining in podocytes from patients and mice with DKD. Rheb1 knockout in podocytes aggravated podocyte senescence and injury in diabetic mice, but mitigated podocyte injury in mice with podocyte-specific mTORC1 activation induced by Tsc1 deletion. In cultured podocytes, Rheb1 knockdown remarkably accelerated podocyte senescence, independent of mTORC1. Mechanistically, PDH phosphorylation in podocyte was correlated with podocyte senescence in DKD patients. Rheb1 deficiency decreased ATP, mitochondrial membrane potential and partial components of respiratory chain complex, and enhanced ROS production and PDH phosphorylation, which indicates mitochondrial dysfunction, both in vitro and in vivo. Furthermore, Rheb1 interacted with Atp5f1c, and regulated its acetylation under a high-glucose condition. Together, Rheb1 deficiency elicits mitochondrial dysfunction and accelerates podocyte senescence through promoting Atp5f1c acetylation, in an mTORC1-independent manner, which provides experimental basis for the treatment of DKD.

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.

LncRNA evf-2 Exacerbates Podocyte Injury in Diabetic Nephropathy by Inducing Cell Cycle Re-entry and Inflammation Through Distinct Mechanisms Triggered by hnRNPU

Albuminuria is a hallmark of diabetic nephropathy (DN). Podocyte injury significantly contributes to proteinuria in DN. Our study found that lncRNA EVF-2 is upregulated in podocytes of DN patients, correlating with cell cycle re-entry and inflammation. Specific knockout or knockdown of lncRNA evf-2 in diabetic mice or cultured podocytes alleviated podocyte injury associated with these processes. RNA sequencing of evf-2-overexpressing podocytes unveiled a predominant enrichment of upregulated mRNAs in cell cycle and inflammation pathways, with alternative splicing in cell cycle-related mRNAs Ccnb1 and Tacc3. Chromatin isolation by RNA purification-mass spectrometry (ChIRP-MS) analysis highlighted the involvement of ribonucleoprotein complex and mRNA processing-related proteins, with hnRNPU as the main binding partner of evf-2 in spliceosomes. Knockdown of hnRNPU partially restored the upregulation of mRNAs induced by evf-2 overexpression, altering splice variants of Ccnb1 and Tacc3. This study is the first to reveal the splice variants of cell cycle-related genes in DN and elucidate the interaction between lncRNA evf-2 and hnRNPU. This interaction culminates in the upregulation of cell cycle-related genes and inflammatory factors through diverse pathways, potentially involving transcriptional activation, RNA stability modulation, alternative splicing or translational regulation. This highlights potential novel pathways for DN treatment.

Podocyte-targeted therapies - progress and future directions

Podocytes are the key target cells for injury across the spectrum of primary and secondary proteinuric kidney disorders, which account for up to 90% of cases of kidney failure worldwide. Seminal experimental and clinical studies have established a causative link between podocyte depletion and the magnitude of proteinuria in progressive glomerular disease. However, no substantial advances have been made in glomerular disease therapies, and the standard of care for podocytopathies relies on repurposed immunosuppressive drugs. The past two decades have seen a remarkable expansion in understanding of the mechanistic basis of podocyte injury, with prospects increasing for precision-based treatment approaches. Dozens of disease-causing genes with roles in the pathogenesis of clinical podocytopathies have been identified, as well as a number of putative glomerular permeability factors. These achievements, together with the identification of novel targets of podocyte injury, the development of potential approaches to harness the endogenous podocyte regenerative potential of progenitor cell populations, ongoing clinical trials of podocyte-specific pharmacological agents and the development of podocyte-directed drug delivery systems, contribute to an optimistic outlook for the future of glomerular disease therapy.

Ramulus Mori (Sangzhi) Alkaloids Alleviate Diabetic Nephropathy through Improving Gut Microbiota Disorder

Diabetic nephropathy (DN), one of the leading causes of end-stage kidney failure worldwide, is closely associated with high mortality in diabetic patients. However, therapeutic drugs for DN are still lacking. Ramulus Mori alkaloids (SZ-A), an effective component of alkaloids extracted from Ramulus Mori, have been found to improve glucose and lipid metabolism to mitigate diabetes and obesity; however, few studies have focused on their effects on DN progression. Thus, we investigated the protective role of SZ-A on DN through 16S rRNA sequencing, non-targeted metabolomics, and fecal microbiota transplantation (FMT) experiments. To address our hypothesis, we established the DN mouse model by combining a high-fat diet (HFD) with streptozotocin (STZ) injection. Herein, we demonstrated that SZ-A supplementation was recalcitrant to renal injury in DN mice, improving glomerular morphology, reversing the blood biochemistry parameters, and ameliorating podocyte injury. Importantly, the composition of the gut microbiota altered after SZ-A treatment, especially with the elevated abundance of Dubosiella and the increased level of serum pentadecanoic acid. FMT experiments further revealed that the gut microbiota exerted critical effects in mediating the beneficial roles of SZ-A. In vitro experiments proved that pentadecanoic acid administration improved podocyte apoptosis induced by AGEs. Taken together, SZ-A play a renoprotective role, possibly through regulating the gut microbiota and promoting pentadecanoic acid production. Our current study lends support to more extensive clinical applications of SZ-A.

Myeloid-derived growth factor in diseases: structure, function and mechanisms

Myeloid-derived growth factor (MYDGF) is a novel secreted protein with potent antiapoptotic and tissue-repairing properties that is present in nearly 140 human tissues and cell lines, with the highest abundance in the oral epithelium and skin. Initially, MYDGF was found in bone marrow-derived monocytes and macrophages for cardioprotection and repair after myocardial infarction. Subsequent studies have shown that MYDGF plays an important role in other cardiovascular diseases (e.g., atherosclerosis and heart failure), metabolic disorders, renal disease, autoimmune/inflammatory disorders, and cancers. Although the underlying mechanisms have not been fully explored, the role of MYDGF in health and disease may involve cell apoptosis and proliferation, tissue repair and regeneration, anti-inflammation, and glycolipid metabolism regulation. In this review, we summarize the current progress in understanding the role of MYDGF in health and disease, focusing on its structure, function and mechanisms. The graphical abstract shows the current role of MYDGF in different organs and diseases (Fig. 1).

Role of the β2-adrenergic receptor in podocyte injury and recovery

BACKGROUND

Podocytes have a remarkable ability to recover from injury; however, little is known about the recovery mechanisms involved in this process. We recently showed that formoterol, a long-acting β2-adrenergic receptor (β2-AR) agonist, induced mitochondrial biogenesis (MB) in podocytes and led to renoprotection in mice. However, it is not clear whether this effect was mediated by formoterol acting through the β2-AR or if it occurred through "off-target" effects.

METHODS

We genetically deleted the β2-AR specifically in murine podocytes and used these mice to determine whether formoterol acting through the podocyte β2-AR alone is sufficient for recovery of renal filtration function following injury. The podocyte-specific β2-AR knockout mice (β2-ARfl/fl/PodCre) were generated by crossing β2-AR floxed mice with podocin Cre (B6.Cg-Tg(NPHS2-cre)295Lbh/J) mice. These mice were then subjected to both acute and chronic glomerular injury using nephrotoxic serum (NTS) and adriamycin (ADR), respectively. The extent of injury was evaluated by measuring albuminuria and histological and immunostaining analysis of the murine kidney sections.

RESULTS

A similar level of injury was observed in β2-AR knockout and control mice; however, the β2-ARfl/fl/PodCre mice failed to recover in response to formoterol. Functional evaluation of the β2-ARfl/fl/PodCre mice following injury plus formoterol showed similar albuminuria and glomerular injury to control mice that were not treated with formoterol.

CONCLUSIONS

These results indicate that the podocyte β2-AR is a critical component of the recovery mechanism and may serve as a novel therapeutic target for treating podocytopathies.

The role of long non-coding RNAs in the development of diabetic kidney disease and the involved clinical application

Diabetic kidney disease (DKD), one of the common microvascular complications of diabetes, is increasing in prevalence worldwide and can lead to End-stage renal disease. However, there are still gaps in our understanding of the pathophysiology of DKD, and both current clinical diagnostic methods and treatment strategies have drawbacks. According to recent research, long non-coding RNAs (lncRNAs) are intimately linked to the developmental process of DKD and could be viable targets for clinical diagnostic decisions and therapeutic interventions. Here, we review recent insights gained into lncRNAs in pathological changes of DKD such as mesangial expansion, podocyte injury, renal tubular injury, and interstitial fibrosis. We also discuss the clinical applications of DKD-associated lncRNAs as diagnostic biomarkers and therapeutic targets, as well as their limitations and challenges, to provide new methods for the prevention, diagnosis, and treatment of DKD.

Angiotensin II and post-streptococcal glomerulonephritis

BACKGROUND

Post-streptococcal glomerulonephritis (PSGN) is a consequence of the infection by group A beta-hemolytic streptococcus. During this infection, various immunological processes generated by streptococcal antigens are triggered, such as the induction of antibodies and immune complexes. This activation of the immune system involves both innate and acquired immunity. The immunological events that occur at the renal level lead to kidney damage with chronic renal failure as well as resolution of the pathological process (in most cases). Angiotensin II (Ang II) is a molecule with vasopressor and pro-inflammatory capacities, being an important factor in various inflammatory processes. During PSGN some events are defined that make Ang II conceivable as a molecule involved in the inflammatory processes during the disease.

CONCLUSION

This review is focused on defining which reported events would be related to the presence of this hormone in PSGN.

Urinary podocyte markers in diabetic kidney disease

Podocytes are involved in maintaining kidney function and are a major focus of research on diabetic kidney disease (DKD). Urinary biomarkers derived from podocyte fragments and molecules have been proposed for the diagnosis and monitoring of DKD. Various methods have been used to detect intact podocytes and podocyte-derived microvesicles in urine, including centrifugation, visualization, and molecular quantification. Quantification of podocyte-specific protein targets and messenger RNA levels can be performed by Western blotting or enzyme-linked immunosorbent assay and quantitative polymerase chain reaction, respectively. At present, many of these techniques are expensive and labor-intensive, all limiting their widespread use in routine clinical tests. While the potential of urinary podocyte markers for monitoring and risk stratification of DKD has been explored, systematic studies and external validation are lacking in the current literature. Standardization and automation of laboratory methods should be a priority for future research, and the added value of these methods to routine clinical tests should be defined.

Myeloid-derived growth factor and its effects on cardiovascular and metabolic diseases

Myeloid-derived growth factor (MYDGF) is a paracrine protein produced by bone marrow-derived monocytes and macrophages. Current research shows that it has protective effects on the cardiovascular system, such as repairing heart tissue after myocardial infarction, enhancing cardiomyocyte proliferation, improving cardiac regeneration after myocardial injury, regulating proliferation and survival of endothelial cells, reducing endothelial cell damage, resisting pressure overload-induced heart failure, as well as protecting against atherosclerosis. Furthermore, regarding the metabolic diseases, MYDGF has effects of improving type 2 diabetes mellitus, relieving non-alcoholic fatty liver disease, alleviating glomerular diseases, and resisting osteoporosis. Herein, we will discuss the biology of MYDGF and its effects on cardiovascular and metabolic diseases.

Genetic imputation of kidney transcriptome, proteome and multi-omics illuminates new blood pressure and hypertension targets

Genetic mechanisms of blood pressure (BP) regulation remain poorly defined. Using kidney-specific epigenomic annotations and 3D genome information we generated and validated gene expression prediction models for the purpose of transcriptome-wide association studies in 700 human kidneys. We identified 889 kidney genes associated with BP of which 399 were prioritised as contributors to BP regulation. Imputation of kidney proteome and microRNAome uncovered 97 renal proteins and 11 miRNAs associated with BP. Integration with plasma proteomics and metabolomics illuminated circulating levels of myo-inositol, 4-guanidinobutanoate and angiotensinogen as downstream effectors of several kidney BP genes (SLC5A11, AGMAT, AGT, respectively). We showed that genetically determined reduction in renal expression may mimic the effects of rare loss-of-function variants on kidney mRNA/protein and lead to an increase in BP (e.g., ENPEP). We demonstrated a strong correlation (r = 0.81) in expression of protein-coding genes between cells harvested from urine and the kidney highlighting a diagnostic potential of urinary cell transcriptomics. We uncovered adenylyl cyclase activators as a repurposing opportunity for hypertension and illustrated examples of BP-elevating effects of anticancer drugs (e.g. tubulin polymerisation inhibitors). Collectively, our studies provide new biological insights into genetic regulation of BP with potential to drive clinical translation in hypertension.

MicroRNA-630 alleviates inflammatory reactions in rats with diabetic kidney disease by targeting toll-like receptor 4

BACKGROUND

Diabetic kidney disease (DKD) is a major complication of diabetes mellitus. Renal tubular epithelial cell (TEC) damage, which is strongly associated with the inflammatory response and mesenchymal trans-differentiation, plays a significant role in DKD; However, the precise molecular mechanism is unknown. The recently identified microRNA-630 (miR-630) has been hypothesized to be closely associated with cell migration, apoptosis, and autophagy. However, the association between miR-630 and DKD and the underlying mechanism remain unknown.

AIM

To investigate how miR-630 affects TEC injury and the inflammatory response in DKD rats.

METHODS

Streptozotocin was administered to six-week-old male rats to create a hyperglycemic diabetic model. In the second week of modeling, the rats were divided into control, DKD, negative control of lentivirus, and miR-630 overexpression groups. After 8 wk, urine and blood samples were collected for the kidney injury assays, and renal tissues were removed for further molecular assays. The target gene for miR-630 was predicted using bioinformatics, and the association between miR-630 and toll-like receptor 4 (TLR4) was confirmed using in vitro investigations and double luciferase reporter gene assays. Overexpression of miR-630 in DKD rats led to changes in body weight, renal weight index, basic blood parameters and histopathological changes.

RESULTS

The expression level of miR-630 was reduced in the kidney tissue of rats with DKD (P < 0.05). The miR-630 and TLR4 expressions in rat renal TECs (NRK-52E) were measured using quantitative reverse transcription polymerase chain reaction. The mRNA expression level of miR-630 was significantly lower in the high-glucose (HG) and HG + mimic negative control (NC) groups than in the normal glucose (NG) group (P < 0.05). In contrast, the mRNA expression level of TLR4 was significantly higher in these groups (P < 0.05). However, miR-630 mRNA expression increased and TLR4 mRNA expression significantly decreased in the HG + miR-630 mimic group than in the HG + mimic NC group (P < 0.05). Furthermore, the levels of tumor necrosis factor-alpha (TNF-α), interleukin-1β (IL-1β), and IL-6 were significantly higher in the HG and HG + mimic NC groups than in NG group (P < 0.05). However, the levels of these cytokines were significantly lower in the HG + miR-630 mimic group than in the HG + mimic NC group (P < 0.05). Notably, changes in protein expression were observed. The HG and HG + mimic NC groups showed a significant decrease in E-cadherin protein expression, whereas TLR4, α-smooth muscle actin (SMA), and collagen IV protein expression increased (P < 0.05). Conversely, the HG + miR-630 mimic group exhibited a significant increase in E-cadherin protein expression and a notable decrease in TLR4, α-SMA, and collagen IV protein expression than in the HG + mimic NC group (P < 0.05). The miR-630 targets TLR4 gene expression. In vivo experiments demonstrated that DKD rats treated with miR-630 agomir exhibited significantly higher miR-630 mRNA expression than DKD rats injected with agomir NC. Additionally, rats treated with miR-630 agomir showed significant reductions in urinary albumin, blood glucose, TLR4, and proinflammatory markers (TNF-α, IL-1β, and IL-6) expression levels (P < 0.05). Moreover, these rats exhibited fewer kidney lesions and reduced infiltration of inflammatory cells.

CONCLUSION

MiR-630 may inhibit the inflammatory reaction of DKD by targeting TLR4, and has a protective effect on DKD.

CCDC92 deficiency ameliorates podocyte lipotoxicity in diabetic kidney disease

BACKGROUND AND AIMS

Podocyte injury is considered as the most important early event contributing to diabetic kidney disease (DKD). Recent findings provide new insights into the roles of lipids and lipid-modulating proteins as key determinants of podocyte function in health and kidney disease. CCDC92, a novel member of coiled-coil domain-containing protein family, was indicated relevant to lipid metabolism, coronary heart disease and type 2 diabetes. However, the expression pattern and role of CCDC92 in the kidney is not clear. This study was designed to elucidate the contribution of CCDC92 in the pathogenesis of DKD.

METHODS

Sections with a pathological diagnosis of different classes of DKD, including subjects with mild DKD (class II, n = 6), subjects with moderate DKD (class III, n = 6) or subjects with severe DKD (class IV, n = 6), and control samples (n = 12) were detected for the expression level of CCDC92 and lipid accumulation. Two types of diabetic mice model (db/db and HFD/STZ) in podocyte-specific Ccdc92 knockout background were generated to clarify the role of CCDC92 in podocyte lipotoxicity.

RESULTS

The level of CCDC92 was increased in renal biopsies sections from patients with DKD, which was correlated with eGFR and lipid accumulation in glomeruli. In animal studies, CCDC92 were also induced in the kidney from two independent diabetic models, especially in podocytes. Podocyte-specific deletion of Ccdc92 ameliorated podocyte injury and ectopic lipid deposition under diabetic condition. Mechanically, CCDC92 promoted podocyte lipotoxicity, at least in part through ABCA1 signaling-mediated lipid homeostasis.

CONCLUSION

Our studies demonstrates that CCDC92 acts as a novel regulator of lipid homeostasis to promote podocyte injury in DKD, suggesting that CCDC92 might be a potential biomarker of podocyte injury in DKD, and targeting CCDC92 may be an effective innovative therapeutic strategy for patients with DKD.

Laminaria japonica polysaccharide attenuates podocyte epithelial-mesenchymal transformation via TGF-β1-mediated Smad3 and p38MAPK pathways

In the present work, we explored the interventional effect and potential mechanism of a purified Laminaria japonica polysaccharide (LJP61A) on podocyte epithelial-mesenchymal transition (EMT) in TGF-β1-induced podocytes and adriamycin-treated mice. Results showed that compared to the model groups, LJP61A significantly up-regulated the levels of epithelial markers (Nephrin, WT-1, podocin) and down-regulated the levels of mesenchymal markers (α-SMA, FN1) in vitro and in vivo, thus preventing EMT-like morphological changes of podocytes, proteinuria and kidney injury. Smad3 and p38MAPK are two central pathways mediating podocyte EMT activated by TGF-β1. We found that LJP61A suppressed TGF-β1-induced activation of Smad3, Smad4 and p38MAPK in vitro and in vivo. Moreover, the inhibitory actions of LJP61A on podocyte EMT were synergistically strengthened by Smad3 inhibitor SIS3 and p38MAPK inhibitor SB203580. Taken together, these findings revealed that LJP61A could prevent podocyte EMT, which might be related to the inhibition of TGF-β1-mediated Smad3 and p38MAPK pathways.

Intravenous injection of human umbilical cord-derived mesenchymal stem cells ameliorates not only blood glucose but also nephrotic complication of diabetic rats through autophagy-mediated anti-senescent mechanism

BACKGROUND

Diabetic nephropathy (DN) is one of the most severe complications of diabetes mellitus, which is characterized by early occurrence of albuminuria and end-stage glomerulosclerosis. Senescence and autophagy of podocytes play an important role in DN development. Human umbilical cord-derived mesenchymal stem cells (hucMSCs) have potential in the treatment of diabetes and its complications. However, the role of hucMSCs in the treatment of DN and the underlying mechanism remain unclear.

METHODS

In vivo, a streptozotocin-induced diabetic male Sprague Dawley rat model was established to determine the renoprotective effect of hucMSCs on DN by biochemical analysis, histopathology, and immunohistochemical staining of renal tissues. And the distribution of hucMSCs in various organs in rats within 168 h was analyzed. In vitro, CCK8 assay, wound healing assay, and β-galactosidase staining were conducted to detect the beneficial effects of hucMSCs on high glucose-induced rat podocytes. Real-time PCR and western blot assays were applied to explore the mechanism of action of hucMSCs.

RESULTS

The in vivo data revealed that hucMSCs were distributed into kidneys and significantly protected kidneys from diabetic damage. The in vitro data indicated that hucMSCs improved cell viability, wound healing, senescence of the high glucose-damaged rat podocytes through a paracrine action mode. Besides, the altered expressions of senescence-associated genes (p16, p53, and p21) and autophagy-associated genes (Beclin-1, p62, and LC3) were improved by hucMSCs. Mechanistically, hucMSCs protected high glucose-induced injury in rat podocytes by activating autophagy and attenuating senescence through the AMPK/mTOR pathway.

CONCLUSIONS

In conclusion, hucMSCs might be a promising therapeutic strategy for the clinical treatment of DN-induced renal damages.

Loss of Sirt1 promotes exosome secretion from podocytes by inhibiting lysosomal acidification in diabetic nephropathy

Podocyte injury is a characteristic feature of diabetic nephropathy (DN). The secretion of exosomes in podocytes increases significantly in DN; however, the precise mechanisms remain poorly understood. Here, we demonstrated that Sirtuin1 (Sirt1) was significantly downregulated in podocytes in DN, which correlated negatively with increased exosome secretion. Similar results were observed in vitro. We found that lysosomal acidification in podocytes following high glucose administration was markedly inhibited, resulting in the decreased lysosomal degradation of multivesicular bodies. Mechanistically, we indicated that loss of Sirt1 contributed to the inhibited lysosomal acidification by decreasing the expression of the A subunit of the lysosomal vacuolar-type H⁺ ATPase proton pump (ATP6V1A) in podocytes. Overexpression of Sirt1 significantly improved lysosomal acidification with increased expression of ATP6V1A and inhibited exosome secretion. These findings suggest that dysfunctional Sirt1-mediated lysosomal acidification is the exact mechanism of increased secretion of exosomes in podocytes in DN, providing insights into potential therapeutic strategies for preventing DN progression.

Intrarenal and Urinary Glycogen Synthase Kinase-3 Beta Levels in Diabetic and Nondiabetic Chronic Kidney Disease

BACKGROUND

Renal glycogen synthase kinase-3 beta (GSK3β) overactivity has been associated with a diverse range of kidney diseases. GSK3β activity in urinary exfoliated cells was reported to predict the progression of diabetic kidney disease (DKD). We compared the prognostic value of urinary and intrarenal GSK3β levels in DKD and nondiabetic chronic kidney disease (CKD).

METHODS

We recruited 118 consecutive biopsy-proved DKD patients and 115 nondiabetic CKD patients. Their urinary and intrarenal GSK3β levels were measured. They were then followed for dialysis-free survival and rate of renal function decline.

RESULTS

DKD group had higher intrarenal and urinary GSK3β levels than nondiabetic CKD (p < 0.0001 for both), but their urinary GSK3β mRNA levels were similar. Urinary p-GSK3β level is statistically significantly correlated with the baseline estimated glomerular filtration rate (eGFR), but urinary GSK3β level by ELISA, its mRNA level, the p-GSK3β level, or the p-GSK3β/GSK3β ratio had no association with dialysis-free survival or the slope of eGFR decline. In contrast, the intrarenal pY216-GSK3β/total GSK3β ratio significantly correlated with the slope of eGFR decline (r = -0.335, p = 0.006) and remained an independent predictor after adjusting for other clinical factors.

CONCLUSION

Intrarenal and urinary GSK3β levels were increased in DKD. The intrarenal pY216-GSK3β/total GSK3β ratio was associated with the rate of progression of DKD. The pathophysiological roles of GSK3β in kidney diseases deserve further studies.

Discovery of Fibrinogen γ-chain as a potential urinary biomarker for renal interstitial fibrosis in IgA nephropathy

BACKGROUND

IgA nephropathy (IgAN) is a major cause of chronic kidney disease (CKD). Renal interstitial fibrosis is a hallmark of CKD progression. Non-invasive biomarkers are needed to dynamically evaluate renal fibrosis. Data independent acquisition (DIA)-based liquid chromatography-mass spectrometry (DIA-MS) was used to identify candidate urinary biomarkers in IgAN patients with different renal interstitial fibrosis degrees.

METHODS

Eighteen biopsy-proven IgAN patients and six healthy controls were recruited in a discovery cohort. Interstitial fibrosis changes were evaluated according to Oxford MEST-C scores. Urinary samples were analyzed with DIA-MS to identify hub proteins. Hub proteins were then confirmed by enzyme-linked immunosorbent assay (ELISA) in a validation cohort and the associated gene mRNA expression was analyzed using public gene expression omnibus (GEO) datasets.

RESULTS

Complement and coagulation cascades pathway was the main KEGG pathway related to the over-expressed proteins. Fibrinogen γ-Chain (FGG) was selected as the potential urinary marker for further validation. Urinary FGG to creatinine ratio (uFGG/Cr) levels were higher in both disease controls and IgAN group than in healthy controls, but were not significantly different between IgAN and disease groups. uFGG/Cr was confirmed to be increased with the extent of renal fibrosis and presented moderate correlations with T score (r = 0.614, p < 0.01) and eGFR (r = -0.682, p < 0.01), and a mild correlation with UTP (r = 0.497, p < 0.01) in IgAN group. In disease control group, uFGG/Cr was higher in patients with T1 + 2 compared to those with T0. uFGG/Cr had a good discriminatory power to distinguish different fibrosis stages in IgAN: interstitial fibrosis ≤ 5% (minimal fibrosis) vs. interstitial fibrosis (mild fibrosis) > 5%, AUC 0.743; T0 vs. T1 + 2, AUC 0.839; T0 + 1 vs. T2, AUC 0.854. In disease control group, uFGG/Cr showed better performance of AUC than UTP between minimal and mild fibrosis (p = 0.038 for Delong's test). Moreover, GSE104954 dataset showed that FGG mRNA expression was up-regulated (fold change 1.20, p = 0.009) in tubulointerstitium of IgAN patients when compared to healthy living kidney donors.

CONCLUSION

Urinary FGG is associated with renal interstitial fibrosis and could be used as a noninvasive biomarker for renal fibrosis in IgAN.

Integrating network pharmacology approach and experimental validation to reveal the alleviation of Shenkangning capsule on chronic nephritis

ETHNOPHARMACOLOGICAL RELEVANCE

Shenkangning (SKN), a Chinese patent medicine composed by eight Chinese medicinal herbs, is commonly applied to treat chronic glomerulonephritis (CGN) in clinic. However, its mechanism is still not clear now.

AIM OF THE STUDY

This study is designed to evaluate the SKN-provided alleviation on adriamycin (ADR)-induced nephropathy, to reveal its mechanism by integrating network pharmacology analysis and experimental evidences, and to further find the main drug that makes a major contribution to its efficacy.

MATERIALS AND METHODS

ADR was intravenously injected to mice to induce focal segmental glomerulosclerosis (FSGS). Renal histological evaluation was conducted. The level of urinary protein, and serum amounts of creatinine, urea nitrogen (BUN) and albumin were detected. The potential mechanisms were predicted by network pharmacology analysis and further validated by Real-time polymerase chain reaction (RT-PCR), Western-blot and enzyme-linked immunosorbent assay (ELISA).

RESULTS

SKN (1, 10 g/kg) improved ADR-induced nephropathy in mice. Network pharmacology results predicted that inflammation and oxidative stress were crucially involved in the SKN-provided amelioration on nephropathy. SKN reduced the activation of nuclear factor-κB (NF-κB) and the expression of some pro-inflammatory cytokines, and increased the activation of nuclear factor erythroid 2-related factor 2 (Nrf2) and the expression of its downstream genes in ADR-induced nephropathy in mice. Furthermore, SKN also restored the reduced expression of both podocin and synaptopodin, which are podocyte-associated proteins. Further results showed that the toxic drug Danfupian (DFP) had no contribution to the SKN-provided alleviation on ADR-induced nephropathy in mice. After integrating the results from evaluating anti-inflammation, anti-oxidant and anti-injury of podocytes in vitro and from comparing the activity of the whole SKN and SKN without Astragali Radix (Huangqi, HQ) in vivo, we found that HQ played a crucial contribution to the SKN-provided amelioration on ADR-induced nephropathy in mice.

CONCLUSION

SKN improved ADR-induced nephropathy through suppressing renal inflammation and oxidative stress injury via abrogating NF-κB activation and activating Nrf2 signaling pathway. HQ played a main contribution to the SKN-provided amelioration on ADR-induced nephropathy.

B7-1 mediates podocyte injury and glomerulosclerosis through communication with Hsp90ab1-LRP5-β-catenin pathway

Podocyte injury is a hallmark of glomerular diseases; however, the underlying mechanisms remain unclear. B7-1 is increased in injured podocytes, but its intrinsic role is controversial. The clinical data here revealed the intimate correlation of urinary B7-1 with severity of glomerular injury. Through transcriptomic and biological assays in B7-1 transgenic and adriamycin nephropathy models, we identified B7-1 is a key mediator in podocyte injury and glomerulosclerosis through a series of signal transmission to β-catenin. Using LC-MS/MS, Hsp90ab1, a conserved molecular chaperone, was distinguished to be an anchor for transmitting signals from B7-1 to β-catenin. Molecular docking and subsequent mutant analysis further identified the residue K69 in the N terminal domain of Hsp90ab1 was the key binding site for B7-1 to activate LRP5/β-catenin pathway. The interaction and biological functions of B7-1-Hsp90ab1-LRP5 complex were further demonstrated in vitro and in vivo. We also found B7-1 is a novel downstream target of β-catenin. Our results indicate an intercrossed network of B7-1, which collectively induces podocyte injury and glomerulosclerosis. Our study provides an important clue to improve the therapeutic strategies to target B7-1.

Long noncoding RNA SNHG5 promotes podocyte injury via the microRNA-26a-5p/TRPC6 pathway in diabetic nephropathy

Podocyte injury is a characteristic pathological hallmark of diabetic nephropathy (DN). However, the exact mechanism of podocyte injury in DN is incompletely understood. This study was conducted using db/db mice and immortalized mouse podocytes. High-throughput sequencing was used to identify the differentially expressed long noncoding RNAs in kidney of db/db mice. The lentiviral shRNA directed against long noncoding RNA small nucleolar RNA host gene 5 (SNHG5) or microRNA-26a-5p (miR-26a-5p) agomir was used to treat db/db mice to regulate the SNHG5/miR-26a-5p pathway. Here, we found that the expression of transient receptor potential canonical type 6 (TRPC6) was significantly increased in injured podocytes under the condition of DN, which was associated with markedly decreased miR-26a-5p. We determined that miR-26a-5p overexpression ameliorated podocyte injury in DN via binding to 3'-UTR of Trpc6, as evidenced by the markedly reduced activity of luciferase reporters by miR-26a-5p mimic. Then, the upregulated SNHG5 in podocytes and kidney in DN was identified, and it was proved to sponge to miR-26a-5p directly using luciferase activity, RNA immunoprecipitation, and RNA pull-down assay. Knockdown of SNHG5 attenuated podocyte injury in vitro, accompanied by an increased expression of miR-26a-5p and decreased expression of TRPC6, demonstrating that SNHG5 promoted podocyte injury by controlling the miR-26a-5p/TRPC6 pathway. Moreover, knockdown of SNHG5 protects against podocyte injury and progression of DN in vivo. In conclusion, SNHG5 promotes podocyte injury via the miR-26a-5p/TRPC6 pathway in DN. Our findings provide novel insights into the pathophysiology of podocyte injury and a potential new therapeutic strategy for DN.

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.

Traditional Chinese Medicine in Treating Primary Podocytosis: From Fundamental Science to Clinical Research

Podocytes form a key component of the glomerular filtration barrier. Damage to podocytes is referred to as “podocyte disease.” There are many causes of podocyte injury, including primary injury, secondary injury, and gene mutations. Primary podocytosis mostly manifests as nephrotic syndrome. At present, first-line treatment is based on glucocorticoid administration combined with immunosuppressive therapy, but some patients still progress to end-stage renal disease. In Asia, especially in China, traditional Chinese medicine (TCM) still plays an important role in the treatment of kidney diseases. This study summarizes the potential mechanism of TCM and its active components in protecting podocytes, such as repairing podocyte injury, inhibiting podocyte proliferation, reducing podocyte apoptosis and excretion, maintaining podocyte skeleton structure, and upregulating podocyte-related protein expression. At the same time, the clinical efficacy of TCM in the treatment of primary podocytosis (including idiopathic membranous nephropathy, minimal change disease, and focal segmental glomerulosclerosis) is summarized to support the development of new treatment strategies for primary podocytosis.

Non-canonical Wnt/calcium signaling is protective against podocyte injury and glomerulosclerosis

Activation of canonical Wnt signaling has been implicated in podocyte injury and proteinuria. As Wnts are secreted proteins, whether Wnts derived from podocytes are obligatory for promoting proteinuria remains unknown. To address this, we generated conditional knockout mice where Wntless, a cargo receptor protein required for Wnt secretion, was specifically deleted in glomerular podocytes. Mice with podocyte-specific ablation of Wntless (Podo-Wntless-/-) were phenotypically normal. However, after inducing kidney damage with Adriamycin for six days, Podo-Wntless-/- mice developed more severe podocyte injury and albuminuria than their control littermates. Surprisingly, ablation of Wntless resulted in upregulation of β-catenin, accompanied by reduction of nephrin, podocin, podocalyxin, and Wilms tumor 1 proteins. In chronic injury induced by Adriamycin, increased albuminuria, aggravated podocyte lesions and extracellular matrix deposition were evident in Podo-Wntlessl-/- mice, compared to wild type mice. Mechanistically, specific ablation of Wntless in podocytes caused down-regulation of the nuclear factor of activated T cell 1 (NFAT1) and Nemo-like kinase (NLK), key downstream mediators of non-canonical Wnt/calcium signaling. In vitro, knockdown of either NFAT1 or NLK induced β-catenin activation while overexpression of NLK significantly repressed β-catenin induction and largely preserved nephrin in glomerular podocytes. Thus, our results indicate that podocyte-derived Wnts play an important role in protecting podocytes from injury by repressing β-catenin via activating non-canonical Wnt/calcium signaling.

Pathogenic Role of MicroRNA Dysregulation in Podocytopathies

MicroRNAs (miRNAs) participate in the regulation of various important biological processes by regulating the expression of various genes at the post-transcriptional level. Podocytopathies are a series of renal diseases in which direct or indirect damage of podocytes results in proteinuria or nephrotic syndrome. Despite decades of research, the exact pathogenesis of podocytopathies remains incompletely understood and effective therapies are still lacking. An increasing body of evidence has revealed a critical role of miRNAs dysregulation in the onset and progression of podocytopathies. Moreover, several lines of research aimed at improving common podocytopathies diagnostic tools and avoiding invasive kidney biopsies have also identified circulating and urine miRNAs as possible diagnostic and prognostic biomarkers for podocytopathies. The present review mainly aims to provide an updated overview of the recent achievements in research on the potential applicability of miRNAs involved in renal disorders related to podocyte dysfunction by laying particular emphasis on focal segmental glomerulosclerosis (FSGS), minimal change disease (MCD), membranous nephropathy (MN), diabetic kidney disease (DKD) and IgA nephropathy (IgAN). Further investigation into these dysregulated miRNAs will not only generate novel insights into the mechanisms of podocytopathies, but also might yield novel strategies for the diagnosis and therapy of this disease.

Alteration in DNA-binding affinity of Wilms tumor 1 protein due to WT1 genetic variants associated with steroid - resistant nephrotic syndrome in children

Approximately one third of children with steroid-resistant nephrotic syndrome (SRNS) carry pathogenic variants in one of the many associated genes. The WT1 gene coding for the WT1 transcription factor is among the most frequently affected genes. Cases from the Czech national SRNS database were sequenced for exons 8 and 9 of the WT1 gene. Eight distinct exonic WT1 variants in nine children were found. Three children presented with isolated SRNS, while the other six manifested with additional features. To analyze the impact of WT1 genetic variants, wild type and mutant WT1 proteins were prepared and the DNA-binding affinity of these proteins to the target EGR1 sequence was measured by microscale thermophoresis. Three WT1 mutants showed significantly decreased DNA-binding affinity (p.Arg439Pro, p.His450Arg and p.Arg463Ter), another three mutants showed significantly increased binding affinity (p.Gln447Pro, p.Asp469Asn and p.His474Arg), and the two remaining mutants (p.Cys433Tyr and p.Arg467Trp) showed no change of DNA-binding affinity. The protein products of WT1 pathogenic variants had variable DNA-binding affinity, and no clear correlation with the clinical symptoms of the patients. Further research is needed to clarify the mechanisms of action of the distinct WT1 mutants; this could potentially lead to individualized treatment of a so far unfavourable disease.

Myeloid-derived Growth Factor Deficiency Exacerbates Mitotic Catastrophe of Podocytes in Glomerular Disease

Podocytes are unique, highly specialized, terminally differentiated cells, which are restricted in a post-mitotic state with limited ability to repair or regenerate. Re-entering mitotic phase causes podocyte mitotic catastrophe, thereby leading to podocyte death and glomerular injury. Myeloid-derived growth factor (MYDGF) is a novel secreted protein and plays an important role on the regulation of cardiovascular function. However, whether MYDGF is expressed in kidney parenchymal cells and whether it has biological functions in the kidney remain unknown. Here, we found that MYDGF was expressed in kidney parenchymal cells and was significantly reduced in podocytes from mice with models of focal segmental glomerulosclerosis and diabetic kidney disease. Podocyte-specific deletion of MYDGF in mice exacerbated podocyte injury and proteinuria in both disease models. Functionally, MYDGF protected podocytes against mitotic catastrophe by reducing accumulation of podocytes in S phase, a portion of the cell cycle in which DNA is replicated. Mechanistically, MYDGF regulates the expression of the transcription factor RUNX2 which mediates part of MYDGF effects. Importantly, a significant reduction of MYDGF was found in glomeruli from patients with glomerular disease due to focal segmental glomerulosclerosis and diabetic kidney disease and the level of MYDGF was correlated with glomerular filtration rate, serum creatinine and podocyte loss. Thus, our studies indicate that MYDGF may be an attractive therapeutic target for glomerular disease.

Src Activation Aggravates Podocyte Injury in Diabetic Nephropathy via Suppression of FUNDC1-Mediated Mitophagy

Background and purpose: Mitophagy plays a significant role in the progression of diabetic nephropathy (DN), although the regulatory mechanisms remain unclear. Recently, accumulating evidence demonstrated that impaired mitochondrial function and mitophagy are involved in DN. Here, we are aimed to explore the role of c-Src (Src) and FUNDC1-related mitophagy in the development of DN.

Methods: The db/db mice were used to establish a DN mice model. The mice accepted PP2 (Src inhibitor) treatment to study the role of Src in DN. Kidney function was measured via biochemical testing. Renal histopathology and morphometric analysis were conducted via hematoxylin-eosin (HE), periodic acid-Schiff (PAS), Masson’s staining, and transmission electron microscopy (TEM). We measured degree of apoptosis in kidney by TUNEL assay. Indices of mitophagy (LC3 and p62) were evaluated by Western blotting and immunofluorescence. Complementary in vitro assays were conducted using human podocytes subjected to high glucose in combination with PP2 treatment or FUNDC1 small interfering RNAs (siRNAs). Flow cytometry was used to detect the apoptotic cells. Mitochondrial function was evaluated by JC-1 staining. Double immunofluorescence labeling of LC3 and TOMM20 used to assess the degree of mitophagy.

Results: Increased Src activation was detected in the kidneys of db/db mice, and its expression was positively correlated with mitochondrial damage, podocyte apoptosis, and renal dysfunction. Inhibition of Src activation with PP2 protected against mitochondrial damage and podocyte apoptosis. In vitro experiments in podocytes established that high glucose increased Src activation, promoting FUNDC1 phosphorylation and inhibiting mitophagy. Consistent with the mouse model, inhibiting Src activity protected podocytes against mitochondrial damage. FUNDC1 silencing negated the actions of PP2, indicating that FUNDC1-mediated mitophagy is downstream pathway of Src.

Conclusion: In summary, our data indicated that Src is a culprit factor in diabetic renal damage via suppression of FUNDC1-mediated mitophagy, promoting the development of DN.

Mutation of Beclin1 acetylation site at K414 alleviates high glucose-induced podocyte impairment in the early stage of diabetic nephropathy by inhibiting hyperactivated autophagy

BACKGROUND

Our group recently reported that a mutation of the novel Beclin1 K414R acetylation site impacts the stability of Beclin1 protein, which decreases autophagy in adipocytes and further impedes adipocyte differentiation and lipolysis. This study was to explore whether Beclin1 acetylation plays a role in the early renal injury induced by high glucose and to further investigate the K414R mutation site in podocytes.

METHODS

Male Sprague-Dawley rats were randomized to con (control) and diabetic nephropathy (DN) groups. The DN group was induced by a single 55 mg/kg intraperitoneal injection of streptozotocin and fed a high-fat and high-sugar diet (the con group received an equal volume of the vehicle and fed a plain diet), after 3 days of induction, blood glucose levels were measured to confirm the onset of diabetes. Then, at weeks 0 and 4, the biochemical index was assayed and renal cortex tissues were harvested. MPC5 podocytes were cultured in vitro. Beclin1 (K414R)-pLVX-ZsGreen1-N1(wild-type or mutant) lentiviral plasmids were transfected into podocytes. Western blot or immunoprecipitation was used to test proteins or the acetylation levels respectively, and immunohistochemistry was used to analyze morphological changes of podocytes. Immunofluorescence was used to detect the aggregation of LC3 puncta.

RESULTS

The acetylation level of Beclin1 was upregulated with podocyte injury exacerbated in high glucose at 24 h and that a mutation at K414R could inhibit hyperactivated autophagy, which ameliorated podocyte impairment.

CONCLUSION

These findings suggest that the acetylation site at K414 is a critical molecule and drug target and that further research into this area is warranted.

SSBP1 drives high fructose-induced glomerular podocyte ferroptosis via activating DNA-PK/p53 pathway

High fructose consumption is a significant risking factor for glomerular podocyte injury. However, the causes of high fructose-induced glomerular podocyte injury are still unclear. In this study, we reported a novel mechanism by which high fructose induced ferroptosis, a newly form of programmed cell death, in glomerular podocyte injury. We performed quantitative proteomic analysis in glomeruli of high fructose-fed rats to identify key regulating proteins involved in glomerular injury, and found that mitochondrial single-strand DNA-binding protein 1 (SSBP1) was markedly upregulated. Depletion of SSBP1 could alleviate high fructose-induced ferroptotic cell death in podocytes. Subsequently, we found that SSBP1 positively regulated a transcription factor p53 by interacting with DNA-dependent protein kinase (DNA-PK) and p53 to drive ferroptosis in high fructose-induced podocyte injury. Mechanically, SSBP1 activated DNA-PK to induce p53 phosphorylation at serine 15 (S15) to promote the nuclear accumulation of p53, and thereby inhibited expression of ferroptosis regulator solute carrier family 7 member 11 (SLC7A11) in high fructose-exposed podocytes. Natural antioxidant pterostilebene was showed to downregulate SSBP1 and then inhibit DNA-PK/p53 pathway in its alleviation of high fructose-induced glomerular podocyte ferroptosis and injury. This study identified SSBP1 as a novel intervention target against high fructose-induced podocyte ferroptosis and suggested that the suppression of SSBP1 by pterostilbene may be a potential therapy for the treatment of podocyte ferroptosis in glomerular injury.

miRNA-93-5p in exosomes derived from M2 macrophages improves lipopolysaccharide-induced podocyte apoptosis by targeting Toll-like receptor 4

Diabetic nephropathy (DN) is a common complication of diabetes mellitus which can result in renal failure and severely affect public health. Several studies have revealed the important role of podocyte injury in DN progression. Although, the involvement of exosomes derived from M2 macrophages has been reported in podocyte injury, the underlying molecular mechanism of M2 macrophage-secreted exosomes has not been fully elucidated. Our study suggests that M2 macrophages mitigate lipopolysaccharide (LPS)-induced injury of podocytes via exosomes. Moreover, we observed that miR-93-5p expression was markedly upregulated in exosomes from M2 macrophages. Inhibition of miR-93-5p derived from M2 macrophage exosomes resulted in apoptosis of LPS-treated podocytes. Additionally, TLR4 showed the potential to bind to miR-93-5p. Subsequently, we validated that TLR4 is a downstream target of miR-93-5p. Further findings indicated that silencing of TLR4 reversed the renoprotective effects of miR-93-5p-containing M2 macrophage exosomes on LPS-induced podocyte injury. In summary, our study demonstrated that M2 macrophage-secreted exosomes attenuated LPS-induced podocyte apoptosis by regulating the miR-93-5p/TLR4 axis, which provides a new perspective for the treatment of patients with DN.

IL-1 receptor signaling in podocytes limits susceptibility to glomerular damage

Interleukin (IL)-1 receptor type 1 (IL-1R1) activation triggers a proinflammatory signaling cascade that can exacerbate kidney injury. However, the functions of podocyte IL-1R1 in glomerular disease remain unclear. To study the role of IL-1R1 signaling in podocytes, we selectively ablated podocyte IL-1R1 in mice (PKO mice). We then subjected PKO mice and wild-type controls to two glomerular injury models: nephrotoxic serum (NTS)- and adriamycin-induced nephropathy. Surprisingly, we found that IL-1R1 activation in podocytes limited albuminuria and podocyte injury during NTS- and adriamycin-induced nephropathy. Moreover, deletion of IL-1R1 in podocytes drove podocyte apoptosis and glomerular injury through diminishing Akt activation. Activation of Akt signaling abrogated the differences in albuminuria and podocyte injury between wild-type and PKO mice during NTS. Thus, IL-1R1 signaling in podocytes limits susceptibility to glomerular injury via an Akt-dependent signaling pathway. These data identify an unexpected protective role for IL-1R1 signaling in podocytes in the pathogenesis of glomerular disease.NEW & NOTEWORTHY The present study establishes that activation of the receptor for interleukin-1 limits susceptibility to damage to the kidney glomerulus in preclinical mouse models by stimulating Akt signaling cascades inside the podocyte.

Ginsenoside Rb1 alleviates diabetic kidney podocyte injury by inhibiting aldose reductase activity

Panax notoginseng, a traditional Chinese medicine, exerts beneficial effect on diabetic kidney disease (DKD), but its mechanism is not well clarified. In this study we investigated the effects of ginsenoside Rb1 (Rb1), the main active ingredients of Panax notoginseng, in alleviating podocyte injury in diabetic nephropathy and the underlying mechanisms. In cultured mouse podocyte cells, Rb1 (10 μM) significantly inhibited high glucose-induced cell apoptosis and mitochondrial injury. Furthermore, Rb1 treatment reversed high glucose-induced increases in Cyto c, Caspase 9 and mitochondrial regulatory protein NOX4, but did not affect the upregulated expression of aldose reductase (AR). Molecular docking analysis revealed that Rb1 could combine with AR and inhibited its activity. We compared the effects of Rb1 with eparestat, a known aldose reductase inhibitor, in high glucose-treated podocytes, and found that both alleviated high glucose-induced cell apoptosis and mitochondrial damage, and Rb1 was more effective in inhibiting apoptosis. In AR-overexpressing podocytes, Rb1 (10 μM) inhibited AR-mediated ROS overproduction and protected against high glucose-induced mitochondrial injury. In streptozotocin-induced DKD mice, administration of Rb1 (40 mg·kg^-1·d^-1, ig, for 7 weeks) significantly mitigated diabetic-induced glomerular injuries, such as glomerular hypertrophy and mesangial matrix expansion, and reduced the expression of apoptotic proteins. Collectively, Rb1 combines with AR to alleviate high glucose-induced podocyte apoptosis and mitochondrial damage, and effectively mitigates the progression of diabetic kidney disease.

Cellular crosstalk of glomerular endothelial cells and podocytes in diabetic kidney disease

Diabetic kidney disease (DKD) is a serious microvascular complication of diabetes and is the leading cause of end-stage renal disease (ESRD). Persistent proteinuria is an important feature of DKD, which is caused by the destruction of the glomerular filtration barrier (GFB). Glomerular endothelial cells (GECs) and podocytes are important components of the GFB, and their damage can be observed in the early stages of DKD. Recently, studies have found that crosstalk between cells directly affects DKD progression, which has prospective research significance. However, the pathways involved are complex and largely unexplored. Here, we review the literature on cellular crosstalk of GECs and podocytes in the context of DKD, and highlight specific gaps in the field to propose future research directions. Elucidating the intricates of such complex processes will help to further understand the pathogenesis of DKD and develop better prevention and treatment options.

Mfn2 Regulates High Glucose-Induced MAMs Dysfunction and Apoptosis in Podocytes via PERK Pathway

The endoplasmic reticulum (ER) stress and mitochondrial dysfunction in high glucose (HG)-induced podocyte injury have been demonstrated to the progression of diabetic kidney disease (DKD). However, the pathological mechanisms remain equivocal. Mitofusin2 (Mfn2) was initially identified as a dynamin-like protein involved in fusing the outer mitochondrial membrane (OMM). More recently, Mfn2 has been reported to be located at the ER membranes that contact OMM. Mitochondria-associated ER membranes (MAMs) is the intercellular membrane subdomain, which connects the mitochondria and ER through a proteinaceous tether. Here, we observed the suppression of Mfn2 expression in the glomeruli and glomerular podocytes of patients with DKD. Streptozotocin (STZ)-induced diabetic rats exhibited abnormal mitochondrial morphology and MAMs reduction in podocytes, accompanied by decreased expression of Mfn2 and activation of all three unfolded protein response (UPR) pathways (IRE1, ATF6, and PERK). The HG-induced mitochondrial dysfunction, MAMs reduction, and increased apoptosis in vitro were accompanied by the downregulation of Mfn2 and activation of the PERK pathway. Mfn2 physically interacts with PERK, and HG promotes a decrease in Mfn2-PERK interaction. In addition, Mfn2-silenced podocytes showed mitochondrial dysfunction, MAMs reduction, activation of PERK pathway, and increased apoptosis. Conversely, all these effects of HG stimulation were alleviated significantly by Mfn2 overexpression. Furthermore, the inhibition of PERK phosphorylation protected mitochondrial functions but did not affect the expression of Mfn2 in HG-treated podocytes. Therefore, this study confirmed that Mfn2 regulates the morphology and functions of MAMs and mitochondria, and exerts anti-apoptotic effects on podocytes by inhibiting the PERK pathway. Hence, the Mfn2-PERK signaling pathway may be a new therapeutic target for preventing podocyte injury in DKD.

Repurposing Riociguat to Target a Novel Paracrine Nitric Oxide-TRPC6 Pathway to Prevent Podocyte Injury

Increased expression and activity of the Ca²⁺ channel transient receptor potential channel 6 (TRPC6) is associated with focal segmental glomerulosclerosis, but therapeutic strategies to target TRPC6 are currently lacking. Nitric oxide (NO) is crucial for normal glomerular function and plays a protective role in preventing glomerular diseases. We investigated if NO prevents podocyte injury by inhibiting injurious TRPC6-mediated signaling in a soluble guanylate cyclase (sGC)-dependent manner and studied the therapeutic potential of the sGC stimulator Riociguat. Experiments were performed using human glomerular endothelial cells and podocytes. Podocyte injury was induced by Adriamycin incubation for 24 h, with or without the NO-donor S-Nitroso-N-acetyl-DL-penicillamine (SNAP), the sGC stimulator Riociguat or the TRPC6 inhibitor Larixyl Acetate (LA). NO and Riociguat stimulated cGMP synthesis in podocytes, decreased Adriamycin-induced TRPC6 expression, inhibited the Adriamycin-induced TRPC6-mediated Ca²⁺ influx and reduced podocyte injury. The protective effects of Riociguat and NO were blocked when sGC activity was inhibited with 1H-[1,2,4]Oxadiazolo[4,3-a]quinoxalin-1-one (ODQ) or when TRPC6 activity was inhibited by LA. Our data demonstrate a glomerular (e)NOS-NO-sGC-cGMP-TRPC6 pathway that prevents podocyte injury, which can be translated to future clinical use by, e.g., repurposing the market-approved drug Riociguat.

Urinary podocyte markers in kidney diseases

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

Cholesterol-induced toxicity: An integrated view of the role of cholesterol in multiple diseases

High levels of cholesterol are generally considered to be associated with atherosclerosis. In the past two decades, however, a number of studies have shown that excess cholesterol accumulation in various tissues and organs plays a critical role in the pathogenesis of multiple diseases. Here, we summarize the effects of excess cholesterol on disease pathogenesis, including liver diseases, diabetes, chronic kidney disease, Alzheimer's disease, osteoporosis, osteoarthritis, pituitary-thyroid axis dysfunction, immune disorders, and COVID-19, while proposing that excess cholesterol-induced toxicity is ubiquitous. We believe this concept will help broaden the appreciation of the toxic effect of excess cholesterol, and thus potentially expand the therapeutic use of cholesterol-lowering medications.

Exercise training ameliorates early diabetic kidney injury by regulating the H2 S/SIRT1/p53 pathway

Exercise training exerts protective effects against diabetic nephropathy. This study aimed to investigate whether exercise training could attenuate diabetic renal injury via regulating endogenous hydrogen sulfide (H₂ S) production. First, C57BL/6 mice were allocated into the control, diabetes, exercise, and diabetes + exercise groups. Diabetes was induced by intraperitoneal injection of streptozotocin (STZ). Treadmill exercise continued for four weeks. Second, mice was allocated into the control, diabetes, H₂ S and diabetes + H₂ S groups. H₂ S donor sodium hydrosulfide (NaHS) was intraperitoneally injected once daily for four weeks. STZ-induced diabetic mice exhibited glomerular hypertrophy, tissue fibrosis and increased urine albumin levels, urine protein- and albumin-to-creatinine ratios, which were relieved by exercise training. Diabetic renal injury was associated with apoptotic cell death, as evidenced by the enhanced caspase-3 activity, the increased TdT-mediated dUTP nick-end labeling -positive cells and the reduced expression of anti-apoptotic proteins, all of which were attenuated by exercise training. Exercise training enhanced renal sirtuin 1 (SIRT1) expression in diabetic mice, accompanied by an inhibition of the p53-#ediated pro-apoptotic pathway. Furthermore, exercise training restored the STZ-mediated downregulation of cystathionine-β-synthase (CBS) and cystathionine-γ-lyase (CSE) and the reduced renal H₂ S production. NaHS treatment restored SIRT1 expression, inhibited the p53-mediated pro-apoptotic pathway and attenuated diabetes-associated apoptosis and renal injury. In high glucose-treated MPC5 podocytes, NaHS treatment inhibited the p53-mediated pro-apoptotic pathway and podocyte apoptosis in a SIRT1-dependent manner. Collectively, exercise training upregulated CBS/CSE expression and enhanced the endogenous H₂ S production in renal tissues, thereby contributing to the modulation of the SIRT1/p53 apoptosis pathway and improvement of diabetic nephropathy.

Twist1 in podocytes ameliorates podocyte injury and proteinuria by limiting CCL2-dependent macrophage infiltration

The transcription factor Twist1 regulates several processes that could impact kidney disease progression, including epithelial cell differentiation and inflammatory cytokine induction. Podocytes are specialized epithelia that exhibit features of immune cells and could therefore mediate unique effects of Twist1 on glomerular disease. To study Twist1 functions in podocytes during proteinuric kidney disease, we employed a conditional mutant mouse in which Twist1 was selectively ablated in podocytes (Twist1-PKO). Deletion of Twist1 in podocytes augmented proteinuria, podocyte injury, and foot process effacement in glomerular injury models. Twist1 in podocytes constrained renal accumulation of monocytes/macrophages and glomerular expression of CCL2 and the macrophage cytokine TNF-α after injury. Deletion of TNF-α selectively from podocytes had no impact on the progression of proteinuric nephropathy. By contrast, the inhibition of CCL2 abrogated the exaggeration in proteinuria and podocyte injury accruing from podocyte Twist1 deletion. Collectively, Twist1 in podocytes mitigated urine albumin excretion and podocyte injury in proteinuric kidney diseases by limiting CCL2 induction that drove monocyte/macrophage infiltration into injured glomeruli. Myeloid cells, rather than podocytes, further promoted podocyte injury and glomerular disease by secreting TNF-α. These data highlight the capacity of Twist1 in the podocyte to mitigate glomerular injury by curtailing the local myeloid immune response.

Preparation of single-cell suspensions of mouse glomeruli for high-throughput analysis

The kidney glomerulus is essential for proper kidney function. Until recently, technical challenges associated with glomerular isolation and subsequent dissolution into single cells have limited the detailed characterization of cells in the glomerulus. Previous techniques of kidney dissociation result in low glomerular cell yield, which limits high-throughput analysis. The ability to efficiently purify glomeruli and digest the tissue into single cells is especially important for single-cell characterization methods. Here, we present a detailed and comprehensive technique for the extraction and preparation of mouse glomerular cells, with high yield and viability. The method includes direct renal perfusion of Dynabeads via the renal artery followed by kidney dissociation and isolation of glomeruli by magnet; these steps provide a high number and purity of isolated glomeruli, which are further dissociated into single cells. The balanced representation of podocytes, mesangial and endothelial cells in single-cell suspensions of mouse glomeruli, and the high cell viability observed, confirm the efficiency of our method. With some practice, the procedure can be done in <3 h (excluding equipment setup and data analysis). This protocol provides a valuable technique for advancing future single-cell-based studies of the glomerulus in health, injury and disease.

Glomerular Damage in Trichloroethylene-Sensitized Mice: Targeting Cathepsin L-Induced Hyperactive mTOR Signaling

Trichloroethylene (TCE) is a serious health hazard for workers with daily exposure, causing occupational medicamentosa-like dermatitis due to TCE (OMDT) and glomerular damage. Recent studies suggest that mTORC1 signaling is activated in various glomerular disorders; however, the role of mTORC1 signaling in TCE-induced glomerular damage remains to be explored. In the present study, 6 OMDT patients were enrolled and a TCE-sensitized mouse model was established to investigate molecular mechanisms underlying the glomerular damage associated with OMDT. Glomerular damage was assessed by levels of urine nephrin, H&E staining, and renal function test. Ultrastructural change of podocyte was investigated by transmission electron microscopy. The podocyte-related molecules including nephrin, α-actinin-4, and integrin β1 were visualized by immunofluorescence. The activation of mTORC1 signaling was confirmed by Western blot. Glomerular apoptosis was examined by the TUNEL test and Western blotting. Expression and location of cathepsin L (CTSL) were assessed by RT-PCR and immunofluorescence. Our results showed that TCE sensitization caused damage to glomerular structural integrity and also increased the activation of mTORC1 signaling, which was accompanied by podocyte loss, hypertrophy, and glomerular apoptosis. Importantly, we also found that over-expressed CTSL was mainly located in podocyte and CTSL inhibition could partially block the activation of mTORC1 signaling. Thus, our findings suggested a novel mechanism whereby hyperactive mTOR signaling contributes to TCE sensitization–induced and immune-mediated glomerular damage via CTSL activation.

Mineralcorticoid receptor blockers in chronic kidney disease

There are many experimental data supporting the involvement of aldosterone and mineralcorticoid receptor (MR) activation in the genesis and progression of chronic kidney disease (CKD) and cardiovascular damage. Many studies have shown that in diabetic and non-diabetic CKD, blocking the renin-angiotensin-aldosterone (RAAS) system with conversion enzyme inhibitors (ACEi) or angiotensin II receptor blockers (ARBs) decreases proteinuria, progression of CKD and mortality, but there is still a significant residual risk of developing these events. In subjects treated with ACEi or ARBs there may be an aldosterone breakthrough whose prevalence in subjects with CKD can reach 50%. Several studies have shown that in CKD, the aldosterone antagonists (spironolactone, eplerenone) added to ACEi or ARBs, reduce proteinuria, but increase the risk of hyperkalemia. Other studies in subjects treated with dialysis suggest a possible beneficial effect of antialdosteronic drugs on CV events and mortality. Newer potassium binders drugs can prevent/decrease hyperkalemia induced by RAAS blockade, and may reduce the high discontinuation rates or dose reduction of RAAS-blockers. The nonsteroidal MR blockers, with more potency and selectivity than the classic ones, reduce proteinuria and have a lower risk of hyperkalemia. Several clinical trials, currently underway, will determine the effect of classic MR blockers on CV events and mortality in subjects with stage 3b CKD and in dialysis patients, and whether in patients with type 2 diabetes mellitus and CKD, optimally treated and with high risk of CV and kidney events, the addition of finerenone to their treatment produces cardiorenal benefits. Large randomized trials have shown that sodium glucose type 2 cotransporter inhibitors (SGLT2i) reduce mortality and the development and progression of diabetic and nondiabetic CKD. There are pathophysiological arguments, which raise the possibility that the triple combination ACEi or ARBs, SGLT2i and aldosterone antagonist provide additional renal and cardiovascular protection.

Potential role of extracellular vesicles in the pathophysiology of glomerular diseases

Extracellular vesicles (EVs) are membrane-bound vesicles released by most cells and are found in diverse biological fluids. The release of EVs provides a new mechanism for intercellular communication, allowing cells to transfer their functional cargoes to target cells. Glomerular diseases account for a large proportion of end-stage renal disease (ESRD) worldwide. In recent years, an increasing number of research groups have focused their effort on identifying the functional role of EVs in renal diseases. However, the involvement of EVs in the pathophysiology of glomerular diseases has not been comprehensively described and discussed. In this review, we first briefly introduce the characteristics of EVs. Then, we describe the involvement of EVs in the mechanisms underlying glomerular diseases, including immunological and fibrotic processes. We also discuss what functions EVs derived from different kidney cells have in glomerular diseases and how EVs exert their effects through different signaling pathways. Furthermore, we summarize recent advances in the knowledge of EV involvement in the pathogenesis of various glomerular diseases. Finally, we propose future research directions for identifying better management strategies for glomerular diseases.