Autophagy is activated to protect against podocyte injury in adriamycin-induced nephropathy

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.

Placenta-derived mesenchymal stem cells protect against diabetic kidney disease by upregulating autophagy-mediated SIRT1/FOXO1 pathway

Diabetic kidney disease (DKD) is a common chronic microvascular complication of diabetes mellitus. Although studies have indicated the therapeutic potential of mesenchymal stem cells (MSCs) for DKD, the underlying molecular mechanisms remain unclear. Herein, we explored the renoprotective effect of placenta-derived MSCs (P-MSCs) and the potential mechanism of SIRT1/FOXO1 pathway-mediated autophagy in DKD. The urine microalbumin/creatinine ratio was determined using ELISA, and renal pathological changes were detected by special staining techniques. Immunofluorescence was used for detecting the renal tissue expression of podocin and nephrin; immunohistochemistry for the renal expression of autophagy-related proteins (LC3, Beclin-1, SIRT1, and FOXO1); and western blotting and PCR for the expression of podocyte autophagy- and pathway-related indicators. We found that P-MSCs ameliorated renal tubular injury and glomerular mesangial matrix deposition and alleviated podocyte damage in DKD rats. PMSCs enhanced autophagy levels and increased SIRT1 and FOXO1 expression in DKD rat renal tissue, whereas the autophagy inhibitor 3-methyladenine significantly attenuated the renoprotective effect of P-MSCs. P-MSCs improved HG-induced Mouse podocyte clone5(MPC5)injury, increased podocyte autophagy, and upregulated SIRT1 and FOXO1 expression. Moreover, downregulation of SIRT1 expression blocked the P-MSC-mediated enhancement of podocyte autophagy and improvement of podocyte injury. Thus, P-MSCs can significantly improve renal damage and reduce podocyte injury in DKD rats by modulating the SIRT1/FOXO1 pathway and enhancing podocyte autophagy.

Inhibition of STIM1 alleviates high glucose-induced proliferation and fibrosis by inducing autophagy in mesangial cells

Diabetic nephropathy (DN) is a renal microvascular complication caused by diabetes mellitus. One of the most typical characteristics of DN is glomerular mesangial cells (GMCs) proliferation. Stromal interaction molecule 1 (STIM1), a Ca2+ channel, is involved in many diseases. In this study, we investigated the role of STIM1 in the proliferation and fibrosis in high glucose (HG)-induced HBZY-1 cells. We found that the expression of STIM1 was increased in renal tissues of diabetic rat and HBZY-1 cells stimulated by HG. Downregulation of STIM1-mediated SOCE suppressed hyperglycemic cell proliferation and fibrosis by activating autophagy. In addition, the inhibitory effect of downregulating STIM1 on cells was blocked by autophagy inhibitor Bafilomycin A1 (BafA1). Moreover, this experiment also showed that STIM1 regulated autophagy, cell proliferation and fibrosis via PI3K/AKT/mTOR signal pathway. These results clarify the role of STIM1 in HBZY-1 cells and its mechanism, and provide a new target for the treatment of DN.

PPAR-α Insufficiency Enhances Doxorubicin-Induced Nephropathy in PPAR-α Knockout Mice and a Murine Podocyte Cell Line

Peroxisome proliferator-activated receptor-alpha (PPAR-α) and its exogenous activators (fibrates) promote autophagy. However, whether the deleterious effects of PPAR-α deficiency on doxorubicin (DOX)-induced podocytopathy are associated with reduced autophagy remains to be clarified. We investigated the mechanisms of PPAR-α in DOX-induced podocytopathy and tubular injury in PPAR-α knockout (PAKO) mice and in a murine podocyte cell line. DOX-treated PAKO mice showed higher serum levels of triglycerides and non-esterified fatty acids and more severe podocytopathy than DOX-treated wild-type mice, as evidenced by higher urinary levels of proteins and podocalyxin at 3 days to 2 weeks and higher blood urea nitrogen and serum creatinine levels at 4 weeks. Additionally, there was an increased accumulation of p62, a negative autophagy marker, in the glomerular and tubular regions in DOX-treated PAKO mice at Day 9. Moreover, DOX-treated PAKO mice showed more severe glomerulosclerosis and tubular damage and lower podocalyxin expression in the kidneys than DOX-treated control mice at 4 weeks. Furthermore, DOX treatment increased p-p53, an apoptosis marker, and cleaved the caspase-3 levels and induced apoptosis, which was ameliorated by fenofibrate, a PPAR-α activator. Fenofibrate further enhanced AMPK activation and autophagy under fed and fasting conditions. Conclusively, PPAR-α deficiency enhances DOX-induced podocytopathy, glomerulosclerosis, and tubular injury, possibly by reducing autophagic activity in mouse kidneys.

Mechanisms and implications of podocyte autophagy in chronic kidney disease

Autophagy is a protective mechanism through which cells degrade and recycle proteins and organelles to maintain cellular homeostasis and integrity. An accumulating body of evidence underscores the significant impact of dysregulated autophagy on podocyte injury in chronic kidney disease (CKD). In this review, we provide a comprehensive overview of the diverse types of autophagy and their regulation in cellular homeostasis, with a specific emphasis on podocytes. Furthermore, we discuss recent findings that focus on the functional role of different types of autophagy during podocyte injury in chronic kidney disease. The intricate interplay between different types of autophagy and podocyte health requires further research, which is critical for understanding the pathogenesis of CKD and developing targeted therapeutic interventions.

Qufeng tongluo decoction decreased proteinuria in diabetic mice by protecting podocytes via promoting autophagy

Background

Diabetic kidney disease (DKD) is one of diabetic complications, which has become the leading cause of end-stage kidney disease. In addition to angiotensin-converting enzyme inhibitor/angiotensin II receptor blocker(ACEI/ARB) and sodium-glucose cotransporter-2 inhibitor (SGLT2i), traditional Chinese medicine (TCM) is an effective alternative treatment for DKD. In this study, the effect of Qufeng Tongluo (QFTL) decoction in decreasing proteinuria has been observed and its mechanism has been explored based on autophagy regulation in podocyte.

Methods

In vivo study, db/db mice were used as diabetes model and db/m mice as blank control. Db/db mice were treated with QFTL decoction, rapamycin, QFTL + 3-Methyladenine (3-MA), trehalose, chloroquine (CQ) and QFTL + CQ. Mice urinary albumin/creatinine (UACR), nephrin and autophagy related proteins (LC3 and p62) in kidney tissue were detected after intervention of 9 weeks. Transcriptomics was operated with the kidney tissue from model group and QFTL group. In vitro study, mouse podocyte clone-5 (MPC-5) cells were stimulated with hyperglycemic media (30 mmol/L glucose) or cultured with normal media. High-glucose-stimulated MPC-5 cells were treated with QFTL freeze-drying powder, rapamycin, CQ, trehalose, QFTL+3-MA and QFTL + CQ. Cytoskeletal actin, nephrin, ATG-5, ATG-7, Beclin-1, cathepsin L and cathepsin B were assessed. mRFP-GFP-LC3 was established by stubRFP-sensGFP-LC3 lentivirus transfection.

Results

QFTL decoction decreased the UACR and increased the nephrin level in kidney tissue and high-glucose-stimulated podocytes. Autophagy inhibitors, including 3-MA and chloroquine blocked the effects of QFTL decoction. Further study showed that QFTL decoction increased the LC3 expression and relieved p62 accumulation in podocytes of db/db mice. In high-glucose-stimulated MPC-5 cells, QFTL decoction rescued the inhibited LC3 and promoted the expression of ATG-5, ATG-7, and Beclin-1, while had no effect on the activity of cathepsin L and cathepsin B. Results of transcriptomics also showed that 51 autophagy related genes were regulated by QFTL decoction, including the genes of ATG10, SCOC, ATG4C, AMPK catalytic subunit, PI3K catalytic subunit, ATG3 and DRAM2.

Conclusion

QFTL decoction decreased proteinuria and protected podocytes in db/db mice by regulating autophagy.

A novel therapeutic target for kidney diseases: Lessons learned from starvation response

The prevalence of chronic kidney disease (CKD) is increasing worldwide, making the disease an urgent clinical challenge. Caloric restriction has various anti-aging and organ-protective effects, and unraveling its molecular mechanisms may provide insight into the pathophysiology of CKD. In response to changes in nutritional status, intracellular nutrient signaling pathways show adaptive changes. When nutrients are abundant, signals such as mechanistic target of rapamycin complex 1 (mTORC1) are activated, driving cell proliferation and other processes. Conversely, others, such as sirtuins and AMP-activated protein kinase, are activated during energy scarcity, in an attempt to compensate. Autophagy, a cellular self-maintenance mechanism that is regulated by such signals, has also been reported to contribute to the progression of various kidney diseases. Furthermore, in recent years, ketone bodies, which have long been considered to be detrimental, have been reported to play a role as starvation signals, and thereby to have renoprotective effects, via the inhibition of mTORC1. Therefore, in this review, we discuss the role of mTORC1, which is one of the most extensively studied nutrient-related signals associated with kidney diseases, autophagy, and ketone body metabolism; and kidney energy metabolism as a novel therapeutic target for CKD.

Evaluation of glomerular sirtuin-1 and claudin-1 in the pathophysiology of nondiabetic focal segmental glomerulosclerosis

Focal segmental glomerulosclerosis (FSGS) is the leading cause of nephrotic syndrome, which is characterized by podocyte injury. Given that the pathophysiology of nondiabetic glomerulosclerosis is poorly understood and targeted therapies to prevent glomerular disease are lacking, we decided to investigate the tight junction protein claudin-1 and the histone deacetylase sirtuin-1 (SIRT1), which are known to be involved in podocyte injury. For this purpose, we first examined SIRT1, claudin-1 and podocin expression in kidney biopsies from patients diagnosed with nondiabetic FSGS and found that upregulation of glomerular claudin-1 accompanies a significant reduction in glomerular SIRT1 and podocin levels. From this, we investigated whether a small molecule activator of SIRT1, SRT1720, could delay the onset of FSGS in an animal model of adriamycin (ADR)-induced nephropathy; 14 days of treatment with SRT1720 attenuated glomerulosclerosis progression and albuminuria, prevented transcription factor Wilms tumor 1 (WT1) downregulation and increased glomerular claudin-1 in the ADR + SRT1720 group. Thus, we evaluated the effect of ADR and/or SRT1720 in cultured mouse podocytes. The results showed that ADR [1 µM] triggered an increase in claudin-1 expression after 30 min, and this effect was attenuated by pretreatment of podocytes with SRT1720 [5 µM]. ADR [1 µM] also led to changes in the localization of SIRT1 and claudin-1 in these cells, which could be associated with podocyte injury. Although the use of specific agonists such as SRT1720 presents some benefits in glomerular function, their underlying mechanisms still need to be further explored for therapeutic use. Taken together, our data indicate that SIRT1 and claudin-1 are relevant for the pathophysiology of nondiabetic FSGS.

Minnelide combined with anti-ANGPTL3-FLD monoclonal antibody completely protects mice with adriamycin nephropathy by promoting autophagy and inhibiting apoptosis

Minimal change disease (MCD) is the common type of nephrotic syndrome (NS) in children. Currently, there is an urgent need to explore new treatments because of the significant side effects of long-term use of glucocorticoids and immunosuppressive drugs and the failure to reduce proteinuria in some patients. Angiopoietin-like protein 3 (Angptl3) is an essential target of NS, and anti-ANGPTL3-FLD monoclonal antibody (mAb) significantly reduces proteinuria in mice with adriamycin nephropathy (AN). However, some proteinuria is persistent. Minnelide, a water-soluble prodrug of triptolide, has been used for the treatment of glomerular disease. Therefore, the present study aimed to investigate whether minnelide combined with mAb could further protect mice with AN and the underlying mechanisms. 8-week-old C57BL/6 female mice were injected with 25 mg/kg of Adriamycin (ADR) by tail vein to establish the AN model. A dose of 200 μg/kg of minnelide or 20 mg/kg of mAb was administered intraperitoneally for the treatment. In vitro, the podocytes were treated with 0.4 μg/mL of ADR for 24 h to induce podocyte injury, and pretreatment with 10 ng/mL of triptolide for 30 min or 100 ng/mL of mAb for 1 h before ADR exposure was used to treat. The results showed that minnelide combined with mAb almost completely ameliorates proteinuria and restores the ultrastructure of the podocytes in mice with AN. In addition, minnelide combined with mAb restores the distribution of Nephrin, Podocin, and CD2AP and reduces the level of inflammatory factors in mice with AN. Mechanistically, minnelide combined with mAb could further alleviate apoptosis and promote autophagy in mice with AN by inhibiting the mTOR signaling pathway. In vitro, triptolide combined with mAb increases the expression of Nephrin, Podocin, and CD2AP, alleviates apoptosis, and promotes autophagy. Overall, minnelide combined with mAb completely protects the mice with AN by promoting autophagy and inhibiting apoptosis.

Autophagy Activation in Peripheral Blood Mononuclear Cells of Peritoneal Dialysis Patients

Introduction

The complete systemic deregulated biological network in patients on peritoneal dialysis (PD) is still only partially defined. High-throughput/omics techniques may offer the possibility to analyze the main biological fingerprints associated with this clinical condition.

Methods

We applied an innovative bioinformatic analysis of gene expression microarray data (mainly based on support vector machine (SVM) learning) to compare the transcriptomic profile of peripheral blood mononuclear cells (PBMCs) of healthy subjects (HS), chronic kidney disease (CKD) patients, and patients on PD divided into a microarray group (5 HS, 9 CKD, and 10 PD) and a validation group (10 HS, 15 CKD, and 15 PD). Classical well-standardized biomolecular approaches (western blotting and flow cytometry) were used to validate the transcriptomic results.

Results

Bioinformatics revealed a distinctive PBMC transcriptomic profiling for PD versus CKD and HS (n = 419 genes). Transcripts encoding for key elements of the autophagic pathway were significantly upregulated in PD, and the autophagy related 5 (ATG5) reached the top level of discrimination [-Log10 P-value = 11.3, variable importance in projection (VIP) score = 4.8, SVM rank:1]. Protein levels of ATG5 and microtubule associated protein 1 light chain 3 beta (LC3B), an important constituent of the autophagosome, validated microarray results. In addition, the incubation of PBMCs of HS with serum of patients on PD upregulated both proteins. Autophagy in PBMCs from patients on PD was attenuated by N-acetyl-cysteine or Resatorvid treatment.

Conclusions

Our data demonstrated, for the first time, that the autophagy pathway is activated in immune-cells of patients on PD, and this may represent a novel therapeutic target.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSION

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

Autophagy and podocytopathy

Autophagy is a complex process of lysosomal-dependent degradation of unwanted cellular material. In response to endogenous or exogenous stimuli, autophagy is induced and regulated by two kinases: the AMP activated kinase and the mammalian target of rapamycin (mTOR). Cells activated by Unc-51-like kinase 1 form a double membrane complex that sequesters the cargo (phagophore) and elongates producing spherical vesicles (autophagosomes). These reach and fuse with lysosomes, which degrade the cargo (autolysosomes). The resulting macromolecules are released back and recycled in the cytosol for reuse. In the podocyte, autophagy is a homeostatic mechanism that contributes to the formation and preservation of the morphological and functional integrity of actin cytoskeleton. Podocytes, fenestrated endothelial cells and glomerular basement membrane compose the glomerular filtration barrier. Podocyte damage may cause dysfunction of the glomerular barrier, proteinuria and glomerulosclerosis in different glomerular diseases and particularly in so-called podocytopathies, namely minimal change disease and focal segmental glomerulosclerosis. Several drugs and molecules may activate autophagic function in murine models. Among them, aldosterone inhibitors, mineralocorticoid inhibitors and vitamin D3 were proven to protect podocyte from injury and reduce proteinuria in clinical studies. However, no clinical trial with autophagy regulators in podocytopathies has been conducted. Caution is needed with other autophagy activators, such as mTOR inhibitors and metformin, because of potential adverse events.

The Interplay of Autophagy and Oxidative Stress in the Kidney: What Do We Know?

BACKGROUND

Autophagy, as an indispensable metabolism, plays pivotal roles in maintaining intracellular homeostasis. Nutritional stress, amino acid deficiency, oxidative stress, and hypoxia can trigger its initiation. Oxidative stress in the kidney activates essential signal molecules, like mammalian target of rapamycin (mTOR), adenosine monophosphate-activated protein kinase (AMPK), and silent mating-type information regulation 2 homolog-1 (SIRT1), to stimulate autophagy, ultimately leading to degradation of intracellular oxidative substances and damaged organelles. Growing evidence suggests that autophagy protects the kidney from oxidative stress during acute ischemic kidney injury, chronic kidney disease, and even aging.

SUMMARY

This review emphasizes the cross talk between reactive oxygen species (ROS) signaling pathways and autophagy during renal homeostasis and chronic kidney disease according to the current latest research and provides therapeutic targets during kidney disorders by adjusting autophagy and suppressing oxidative stress.

KEY MESSAGES

ROS arise through an imbalance of oxidation and antioxidant defense mechanisms, leading to impaired cellular and organ function. Targeting the overproduction of ROS and reactive nitrogen species, reducing the antioxidant enzyme activity and the recovery of the prooxidative-antioxidative balance provide novel therapeutic regimens to contribute to recovery in acute and chronic renal failure. Although, in recent years, great progress has been made in understanding the molecular mechanisms of oxidative stress and autophagy in acute and chronic renal failure, the focus on clinical therapies is still in its infancy. The growing number of studies on the interactive mechanisms of oxidative stress-mediated autophagy will be of great importance for the future treatment and prevention of kidney diseases.

Pharmacological investigation of indole alkaloids from Alstonia scholaris against chronic glomerulonephritis

BACKGROUND

As one of the most commonly used folk medicines in "Dai" ethno-medicine system, Alstonia scholaris (l.) R. Br. has also been used for treat "water related diseases", such as chronic kidney disease. However, few study was reported for it on the intervention of chronic glomerulonephritis (CGN).

PURPOSE

To investigate the effect and potential mechanism of indole alkaloids from A. scholaris leaves in ICR mice with adriamycin nephropathy, as well as providing experimental evidence for the further application.

METHODS

ICR Mice were selected for injections of adriamycin (ADR) to induce the CGN model and administered total alkaloids (TA) and four main alkaloids continuously for 42 and 28 days, respectively. The pharmacological effects were indicated by serum, urine, and renal pathological observations. The targets and pathways of indole alkaloids on CGN intervention were predicted using the network pharmacology approach, and the immortalized mice glomerular podocyte (MPC5) cells model stimulated by ADR was subsequently selected to further verify this by western blotting and RT-qPCR methods.

RESULTS

TA and four major compounds dramatically reduced the levels of urinary protein, serum urea nitrogen (BUN), and creatinine (CRE) in ADR - induced CGN mice, while increasing serum albumin (ALB) and total protein (TP) levels as well as ameliorating kidney damage. Moreover, four alkaloids effected on 33 major target proteins and 153 pathways in the CGN, among which, PI3K-Akt as the main pathway, an important pathway for kidney protection by network pharmacology prediction, and then the four target proteins - HRAS, CDK2, HSP90AA1, and KDR were screened. As a result, Val-and Epi can exert a protective effect on ADR-stimulated MPC5 cells injury at a concentration of 50 μM. Furthermore, the proteins and RNA expression of HRAS, HSP90AA1, and KDR were down-regulated, and CDK2 was up-regulated after the intervention of Val-and Epi, which were supported by Western blotting and RT-qPCR. Additionally, Val-and Epi inhibited ROS production in the MPC5 cells model.

CONCLUSION

This study is the first to confirm the potential therapeutic effect of alkaloids from A. scholaris on CGN. TA with major bioactive components (vallesamine and 19‑epi-scholaricine) could exert protective effects against the ADR-induced CGN by regulating four key proteins: HRAS, CDK2, HSP90AA1, and KDR of the PI3K-Akt pathway.

Autophagy and mitophagy: physiological implications in kidney inflammation and diseases

Autophagy is a ubiquitous intracellular cytoprotective quality control program that maintains cellular homeostasis by recycling superfluous cytoplasmic components (lipid droplets, protein, or glycogen aggregates) and invading pathogens. Mitophagy is a selective form of autophagy that by recycling damaged mitochondrial material, which can extracellularly act as damage-associated molecular patterns, prevents their release. Autophagy and mitophagy are indispensable for the maintenance of kidney homeostasis and exert crucial functions during both physiological and disease conditions. Impaired autophagy and mitophagy can negatively impact the pathophysiological state and promote its progression. Autophagy helps in maintaining structural integrity of the kidney. Mitophagy-mediated mitochondrial quality control is explicitly critical for regulating cellular homeostasis in the kidney. Both autophagy and mitophagy attenuate inflammatory responses in the kidney. An accumulating body of evidence highlights that persistent kidney injury-induced oxidative stress can contribute to dysregulated autophagic and mitophagic responses and cell death. Autophagy and mitophagy also communicate with programmed cell death pathways (apoptosis and necroptosis) and play important roles in cell survival by preventing nutrient deprivation and regulating oxidative stress. Autophagy and mitophagy are activated in the kidney after acute injury. However, their aberrant hyperactivation can be deleterious and cause tissue damage. The findings on the functions of autophagy and mitophagy in various models of chronic kidney disease are heterogeneous and cell type- and context-specific dependent. In this review, we discuss the roles of autophagy and mitophagy in the kidney in regulating inflammatory responses and during various pathological manifestations.

Autophagy gene Atg7 regulates the development of radiation-induced skin injury and fibrosis of skin

BACKGROUND

Radiation-induced skin injury, which may progress to fibrosis, is a severe side effect of radiotherapy in patients with cancer. However, currently, there is a lack of preventive or curative treatments for this injury. Meanwhile, the mechanisms underlying this injury remain poorly understood. Here, we elucidated whether autophagy is essential for the development of radiation-induced skin injury and the potential molecular pathways and mechanisms involved.

METHODS AND RESULTS

We used the myofibroblast-specific Atg7 knockout (namely, conditional Atg7 knockout) mice irradiated with a single electron beam irradiation dose of 30 Gy. Vaseline-based 0.2% rapamycin ointment was topically applied once daily from the day of irradiation for 30 days. On day 30 post irradiation, skin tissues were harvested for further analysis. In vitro, human foreskin fibroblast cells were treated with rapamycin (100 nM) for 24 h and pretreated with 3-MA (5 mM) for 12 h. Macroscopic skin manifestations, histological changes, and fibrosis markers at the mRNA and protein expression levels were measured. Post irradiation, the myofibroblast-specific autophagy-deficient (Atg7Flox/Flox Cre+ ) mice had increased fibrosis marker (COL1A1, CTGF, TGF-β1, and α-SMA) levels in the irradiated area and had more severe macroscopic skin manifestations than the control group (Atg7Flox/Flox Cre- ) mice. Treatment with an autophagy agonist rapamycin attenuated macroscopic skin injury scores and skin fibrosis marker levels with decreased epidermal thickness and dermal collagen deposition in Atg7Flox/Flox Cre+ mice compared with the vehicle control. Moreover, in vitro experiment results were consistent with the in vivo results. Together with studies at the molecular level, we found that these changes involved the Akt/mTOR pathway. In addition, this phenomenon might also relate to Nrf2-autophagy signaling pathway under oxidative stress conditions.

CONCLUSION

In conclusion, Atg7 and autophagy-related mechanisms confer radioprotection, and reactivation of the autophagy process can be a novel therapeutic strategy to reduce and prevent the occurrence of radiodermatitis, particularly skin fibrosis, in patients with cancer.

Epimedium sagittatum Maxim ameliorates adriamycin-induced nephropathy by restraining inflammation and apoptosis via the PI3K/AKT signaling pathway

BACKGROUND

Modern pharmacological studies show that Epimedium sagittatum Maxim (EPI) has antioxidant, antiapoptotic, anti-inflammatory effects. However, the effects of EPI on adriamycin-induced nephropathy are unclear.

AIM

The main purpose of this study is to investigate the effects of EPI on adriamycin-induced nephropathy in rats.

METHODS

The chemical composition of EPI was detected by high performance liquid chromatography. Network pharmacology was used to collect the effects of EPI on adriamycin nephropathy; renal histological changes, podocyte injury, inflammatory factors, oxidative stress levels, apoptosis levels, and the PI3K/AKT signaling pathway were examined. Moreover, analyze the effects of icariin (the representative component of EPI) on adriamycin-induced apoptosis and PI3K/AKT signaling pathway of NRK-52e cells.

RESULTS

Network pharmacological results suggested that EPI may ameliorate adriamycin-induced nephropathy by inhibiting inflammatory response and regulating the PI3K/AKT signaling pathway. The experimental results showed that EPI could improve pathological injury, renal function, podocyte injury, and inhibit inflammation, oxidative stress, apoptosis in adriamycin-induced nephropathy rats through the PI3K/AKT signaling pathway. Furthermore, icariin inhibited adriamycin-induced mitochondrial apoptosis in NRK-52e cells.

CONCLUSION

This study suggested that EPI ameliorates adriamycin-induced nephropathy by reducing inflammation and apoptosis through the PI3K/AKT signaling pathway, icariin may be the pharmacodynamic substance basis for this effect.

Stem cell-derived exosomal MicroRNAs: Potential therapies in diabetic kidney disease

The diabetic kidney disease (DKD) is chronic kidney disease caused by diabetes and one of the most common comorbidities. It is often more difficult to treat end-stage renal disease once it develops because of its complex metabolic disorders, so early prevention and treatment are important. However, currently available DKD therapies are not ideal, and novel therapeutic strategies are urgently needed. The potential of stem cell therapies partly depends on their ability to secrete exosomes. More and more studies have shown that stem cell-derived exosomes take part in the DKD pathophysiological process, which may offer an effective therapy for DKD treatment. Herein, we mainly review potential therapies of stem cell-derived exosomes mainly stem cell-derived exosomal microRNAs in DKD, including their protective effects on mesangial cells, podocytes and renal tubular epithelial cells. Using this secretome as possible therapeutic drugs without potential carcinogenicity should be the focus of further research.

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.

UCP2 deficiency impairs podocyte autophagy in diabetic nephropathy

OBJECTIVE

Podocytes have been indicated to be a critical factor for the development of diabetic kidney disease. Podocyte loss leads to irreversible glomerular injury and proteinuria in animal models. As terminal differentiated cells, autophagy is crucial for maintaining podocyte homeostasis. Previous studies have shown that Uncoupling proteins 2 (UCP2) regulate fatty acid metabolism, mitochondrial calcium uptake and reactive oxygen species (ROS) production. This study aimed to investigate whether UCP2 promote autophagy in podocyte and further explore the regulation mechanism of UCP2.

METHODS

For podocyte-specific UCP2-KO mice, we cross bred UCP2f^l/fl mouse strain with the podocin-Cre mice. Diabetic mice were obtained by daily intraperitoneally injections of 40 mg/kg streptozotocin for 3 days. After 6 weeks, mice were scarified, and kidney tissues were analyzed by histological stain, Western blot, Immunofluorescence, and immunohistochemistry. Also, urine samples were collected for protein quantification. For in vitro study, podocytes were primary cultured from UCP2f^l/fl mouse or transfected with adeno-associated virus (AAV)-UCP2.

RESULTS

Diabetic kidney showed elevated expression of UCP2 and specific ablation of UCP2 in podocyte aggravates diabetes-induced albuminuria and glomerulopathy. UCP2 protects hyperglycemia-induced podocyte injury by promoting autophagy in vivo and in vitro. Rapamycin treatment significantly ameliorates streptozotocin (STZ)-induced podocyte injury in UCP2^-/- mice.

CONCLUSION

UCP2 expression in podocyte increased under diabetic condition and appeared to be an initial compensatory response. UCP2 deficiency in podocyte impaired autophagy and exacerbates podocyte injury and proteinuria in diabetic nephropathy.

Beclin-1 dependent autophagy improves renal outcomes following Unilateral Ureteral Obstruction (UUO) injury

Background

Interstitial Fibrosis and Tubular Atrophy (IFTA) is the most common cause of long-term graft failure following renal transplant. One of the hallmarks of IFTA is the development of interstitial fibrosis and loss of normal renal architecture. In this study, we evaluated the role of autophagy initiation factor Beclin-1 in protecting against post-renal injury fibrosis.

Methods

Adult male wild type (WT) C57BL/6 mice were subjected to Unilateral Ureteral Obstruction (UUO), and kidney tissue samples were harvested at 72-hour, 1- and 3-week post-injury. The UUO-injured and uninjured kidney samples were examined histologically for fibrosis, autophagy flux, inflammation as well activation of the Integrated Stress Response (ISR). We compared WT mice with mice carrying a forced expression of constitutively active mutant form of Beclin-1, Becn1F121A/F121A .

Results

In all experiments, UUO injury induces a progressive development of fibrosis and inflammation. These pathological signs were diminished in Becn1F121A/F121A mice. In WT animals, UUO caused a strong blockage of autophagy flux, indicated by continuously increases in LC3II accompanied by an over 3-fold accumulation of p62 1-week post injury. However, increases in LC3II and unaffected p62 level by UUO were observed in Becn1F121A/F121A mice, suggesting an alleviation of disrupted autophagy. Beclin-1 F121A mutation causes a significant decrease in phosphorylation of inflammatory STING signal and limited production of IL6 and IFNγ, but had little effect on TNF-α, in response to UUO. Furthermore, activation of ISR signal cascade was detected in UUO-injured in kidneys, namely the phosphorylation signals of elF2S1 and PERK in addition to the stimulated expression of ISR effector ATF4. However, Becn1F121A/F121A mice did not reveal signs of elF2S1 and PERK activation under the same condition and had a dramatically reduced ATF level at 3-week post injury.

Conclusions

The results suggest that UUO causes a insufficient, maladaptive renal autophagy, which triggered downstream activation of inflammatory STING pathway, production of cytokines, and pathological activation of ISR, eventually leading to the development of fibrosis. Enhancing autophagy via Beclin-1 improved renal outcomes with diminished fibrosis, via underlying mechanisms of differential regulation of inflammatory mediators and control of maladaptive ISR.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSION

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

Autophagy as a Therapeutic Target for Chronic Kidney Disease and the Roles of TGF-β1 in Autophagy and Kidney Fibrosis

Autophagy is a lysosomal protein degradation system that eliminates cytoplasmic components such as protein aggregates, damaged organelles, and even invading pathogens. Autophagy is an evolutionarily conserved homoeostatic strategy for cell survival in stressful conditions and has been linked to a variety of biological processes and disorders. It is vital for the homeostasis and survival of renal cells such as podocytes and tubular epithelial cells, as well as immune cells in the healthy kidney. Autophagy activation protects renal cells under stressed conditions, whereas autophagy deficiency increases the vulnerability of the kidney to injury, resulting in several aberrant processes that ultimately lead to renal failure. Renal fibrosis is a condition that, if chronic, will progress to end-stage kidney disease, which at this point is incurable. Chronic Kidney Disease (CKD) is linked to significant alterations in cell signaling such as the activation of the pleiotropic cytokine transforming growth factor-β1 (TGF-β1). While the expression of TGF-β1 can promote fibrogenesis, it can also activate autophagy, which suppresses renal tubulointerstitial fibrosis. Autophagy has a complex variety of impacts depending on the context, cell types, and pathological circumstances, and can be profibrotic or antifibrotic. Induction of autophagy in tubular cells, particularly in the proximal tubular epithelial cells (PTECs) protects cells against stresses such as proteinuria-induced apoptosis and ischemia-induced acute kidney injury (AKI), whereas the loss of autophagy in renal cells scores a significant increase in sensitivity to several renal diseases. In this review, we discuss new findings that emphasize the various functions of TGF-β1 in producing not just renal fibrosis but also the beneficial TGF-β1 signaling mechanisms in autophagy.

Heparanase Increases Podocyte Survival and Autophagic Flux after Adriamycin-Induced Injury

The kidney glomerular filtration barrier (GFB) is enriched with heparan sulfate (HS) proteoglycans, which contribute to its permselectivity. The endoglycosidase heparanase cleaves HS and hence appears to be involved in the pathogenesis of kidney injury and glomerulonephritis. We have recently reported, nonetheless, that heparanase overexpression preserved glomerular structure and kidney function in an experimental model of Adriamycin-induced nephropathy. To elucidate mechanisms underlying heparanase function in podocytes-key GFB cells, we utilized a human podocyte cell line and transgenic mice overexpressing heparanase. Notably, podocytes overexpressing heparanase (H) demonstrated significantly higher survival rates and viability after exposure to Adriamycin or hydrogen peroxide, compared with mock-infected (V) podocytes. Immunofluorescence staining of kidney cryo-sections and cultured H and V podocytes as well as immunoblotting of proteins extracted from cultured cells, revealed that exposure to toxic injury resulted in a significant increase in autophagic flux in H podocytes, which was reversed by the heparanase inhibitor, Roneparstat (SST0001). Heparanase overexpression was also associated with substantial transcriptional upregulation of autophagy genes BCN1, ATG5, and ATG12, following Adriamycin treatment. Moreover, cleaved caspase-3 was attenuated in H podocytes exposed to Adriamycin, indicating lower apoptotic cell death in H vs. V podocytes. Collectively, these findings suggest that in podocytes, elevated levels of heparanase promote cytoprotection.

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.

Autophagy in lupus nephritis: A delicate balance between regulation and disease

Autophagy is a highly regulated process wherein an unwanted cargo of damaged and dysfunctional cytoplasmic components is removed, delivered to lysosomes for degradation, and released back into the cytoplasm. Accumulating evidence suggests an important role of autophagy in the pathophysiology of systemic lupus erythematosus, with profound effects on both innate and adaptive immunity. Autophagy downregulation results in the inhibition of antigen presenting cells, reduced release of neutrophil extracellular traps and decreased activation of effector T and B cells, leading to reduced autoantibody production and attenuated type 1 interferon signaling. However, defective autophagy may accelerate the production of other inflammatory cytokines and reduce the clearance of apoptotic cells, promoting lupus development. In addition, autophagy dysfunction can concur to the pathogenesis of kidney injury in lupus nephritis. Autophagy is a pivotal mechanism to maintain podocyte integrity and endothelial cell survival. Several animal models have demonstrated that defective autophagy leads to podocyte injury and can promote an endothelial pro-inflammatory and atherogenic phenotype. Moreover, autophagy is a key homeostatic regulator of renal tubular cells, and recent evidence has pointed out that chronic autophagy deficiency may accelerate kidney fibrosis. Targeting autophagy may theoretically improve lupus nephritis outcomes, but novel, non-invasive methods to measure and monitor autophagic activity are urgently needed. In addition, the extent and timing of autophagy inhibition still require additional studies before clinical translation may be attempted. In this review, we will also discuss the effect of several clinically available drugs that can regulate the autophagic flux and their effect in lupus nephritis patients.

Nano-Resveratrol: A Promising Candidate for the Treatment of Renal Toxicity Induced by Doxorubicin in Rats Through Modulation of Beclin-1 and mTOR

Background: Although doxorubicin (DXR) is one of the most used anticancer drugs, it can cause life-threatening renal damage. There has been no effective treatment for DXR-induced renal damage until now.

Aim: This work aims at examining the potential impact of nano-resveratrol (N-Resv), native resveratrol (Resv), and their combination with carvedilol (Card) against DXR-induced renal toxicity in rats and to investigate the mechanisms through which these antioxidants act to ameliorate DXR nephrotoxicity. Method: DXR was administered to rats (2 mg/kg, i.p.) twice weekly over 5 weeks. The antioxidants in question were taken 1 week before the DXR dose for 6 weeks.

Results: DXR exhibited an elevation in serum urea, creatinine, renal lipid peroxide levels, endoglin expression, kidney injury molecule-1 (KIM-1), and beclin-1. On the other hand, renal podocin and mTOR expression and GSH levels were declined. In addition, DNA fragmentation was markedly increased in the DXR-administered group. Treatment with either Resv or N-Resv alone or in combination with Card ameliorated the previously measured parameters.

Conclusion: N-Resv showed superior effectiveness relative to Resv in most of the measured parameters. Histopathological examination revealed amelioration of renal structural and cellular changes after DXR by Card and N-Resv, thus validating the previous biochemical and molecular results.

Stem cell-derived and circulating exosomal microRNAs as new potential tools for diabetic nephropathy management

BACKGROUND

Despite major advances in the treatment of diabetic nephropathy (DN) in recent years, it remains the most common cause of end-stage renal disease. An early diagnosis and therapy may slow down the DN progression. Numerous potential biomarkers are currently being researched. Circulating levels of the kidney-released exosomes and biological molecules, which reflect the DN pathology including glomerular and tubular dysfunction as well as mesangial expansion and fibrosis, have shown the potential for predicting the occurrence and progression of DN. Moreover, many experimental therapies are currently being investigated, including stem cell therapy and medications targeting inflammatory, oxidant, or pro-fibrotic pathways activated during the DN progression. The therapeutic potential of stem cells is partly depending on their secretory capacity, particularly exosomal microRNAs (Exo-miRs). In recent years, a growing line of research has shown the participation of Exo-miRs in the pathophysiological processes of DN, which may provide effective therapeutic and biomarker tools for DN treatment.

METHODS

A systematic literature search was performed in MEDLINE, Scopus, and Google Scholar to collect published findings regarding therapeutic stem cell-derived Exo-miRs for DN treatment as well as circulating Exo-miRs as potential DN-associated biomarkers.

FINDINGS

Glomerular mesangial cells and podocytes are the most important culprits in the pathogenesis of DN and, thus, can be considered valuable therapeutic targets. Preclinical investigations have shown that stem cell-derived exosomes can exert beneficial effects in DN by transferring renoprotective miRs to the injured mesangial cells and podocytes. Of note, renoprotective Exo-miR-125a secreted by adipose-derived mesenchymal stem cells can improve the injured mesangial cells, while renoprotective Exo-miRs secreted by adipose-derived stem cells (Exo-miR-486 and Exo-miR-215-5p), human urine-derived stem cells (Exo-miR-16-5p), and bone marrow-derived mesenchymal stem cells (Exo-miR-let-7a) can improve the injured podocytes. On the other hand, clinical investigations have indicated that circulating Exo-miRs isolated from urine or serum hold great potential as promising biomarkers in DN.

Controversies in Podocyte Loss: Death or Detachment?

Glomerular podocytes are characterized by terminally differentiated epithelial cells with limited proliferating ability; thus, podocyte loss could not be fully compensated by podocyte regeneration. A large body of clinical studies collectively demonstrated that podocyte loss correlated with glomerular diseases progression. Both podocyte death and podocyte detachment lead to podocyte loss; however, which one is the main cause remains controversial. Up to date, multiple mechanisms are involved in podocyte death, including programmed apoptotic cell death (apoptosis and anoikis), programmed nonapoptotic cell death (autophagy, entosis, and podoptosis), immune-related cell death (pyroptosis), and other types of cell death (necroptosis and mitotic catastrophe-related cell death). Apoptosis is considered a common mechanism of podocyte loss; however, most of the data were generated in vitro and the evidence of in vivo podocyte apoptosis is limited. The isolation of podocytes in the urine and subsequent culture of urinary podocytes in vitro suggest that detachment of viable podocytes could be another important mechanism for podocyte loss. In this review, we summarize recent advances that address this controversial topic on the specific circumstances of podocyte loss.

PP2A protects podocytes against Adriamycin-induced injury and epithelial-to-mesenchymal transition via suppressing JIP4/p38-MAPK pathway

Protein phosphatase 2A (PP2A) is one of the major protein serine/threonine phosphatases (PPPs) with regulatory effects on several cellular processes, but its role and function in Adriamycin (ADR)-treated podocytes injury needs to be further explored. Mice podocytes were treated with ADR and PP2A inhibitor (okadaic acid, OA). After transfection, cell apoptosis was detected by flow cytometry. Expressions of podocytes injury-, apoptosis- and epithelial-to-mesenchymal transition (EMT)- and JNK-interacting protein 4/p38-Mitogen-Activated Protein Kinase (JIP4/p38-MAPK) pathway-related factors were measured using quantitative real-time polymerase chain reaction (qRT-PCR) and Western blot as needed. Interaction between PP2A and JIP4/MAPK pathway was confirmed using co-immunoprecipitation (Co-Ip) assay. In podocytes, ADR inhibited PP2A, Nephrin and Wilms' tumor (WT) 1 expressions yet upregulated apoptosis and Desmin expression, and suppressing PP2A expressionenhanced the effects. PP2A overexpression reversed the effects of ADR on PP2A and podocyte injury-related factors expressions and apoptosis of podocytes. JIP4 was the candidate gene interacting with both PP2A and p38-MAPK pathway, and PP2A overexpression alleviated the effects of ADR on p38-MAPK pathway-related factors expressions. Additionally, in ADR-treated podocytes, PP2A suppression enhanced the effects of ADR, yet silencing of JIP4 reversed the effects of PP2A suppression on regulating p38-MAPK pathway-, apoptosis- and EMT-related factors expressions and apoptosis, with upregulations of B-cell lymphoma-2 (Bcl-2) and E-cadherin and down-regulations of Bcl-2 associated protein X (Bax), cleaved (C)-casapse-3, N-cadherin, Vimentin and Snail. PP2A protects ADR-treated podocytes against injury and EMT by suppressing JIP4/p38-MAPK pathway, showing their interaction in podocytes.

AMPK mediates regulation of glomerular volume and podocyte survival

Herein, we report that Shroom3 knockdown, via Fyn inhibition, induced albuminuria with foot process effacement (FPE) without focal segmental glomerulosclerosis (FSGS) or podocytopenia. Interestingly, knockdown mice had reduced podocyte volumes. Human minimal change disease (MCD), where podocyte Fyn inactivation was reported, also showed lower glomerular volumes than FSGS. We hypothesized that lower glomerular volume prevented the progression to podocytopenia. To test this hypothesis, we utilized unilateral and 5/6th nephrectomy models in Shroom3-KD mice. Knockdown mice exhibited less glomerular and podocyte hypertrophy after nephrectomy. FYN-knockdown podocytes had similar reductions in podocyte volume, implying that Fyn was downstream of Shroom3. Using SHROOM3 or FYN knockdown, we confirmed reduced podocyte protein content, along with significantly increased phosphorylated AMPK, a negative regulator of anabolism. AMPK activation resulted from increased cytoplasmic redistribution of LKB1 in podocytes. Inhibition of AMPK abolished the reduction in glomerular volume and induced podocytopenia in mice with FPE, suggesting a protective role for AMPK activation. In agreement with this, treatment of glomerular injury models with AMPK activators restricted glomerular volume, podocytopenia, and progression to FSGS. Glomerular transcriptomes from MCD biopsies also showed significant enrichment of Fyn inactivation and Ampk activation versus FSGS glomeruli. In summary, we demonstrated the important role of AMPK in glomerular volume regulation and podocyte survival. Our data suggest that AMPK activation adaptively regulates glomerular volume to prevent podocytopenia in the context of podocyte injury.

METTL14 aggravates podocyte injury and glomerulopathy progression through N6-methyladenosine-dependent downregulating of Sirt1

Podocytes are known to play a determining role in the progression of proteinuric kidney disease. N6-methyladenosine (m6A), as the most abundant chemical modification in eukaryotic mRNA, has been reported to participate in various pathological processes. However, its role in podocyte injury remains unclear. In this study, we observed the elevated m6A RNA levels and the most upregulated METTL14 expression in kidneys of mice with adriamycin (ADR) and diabetic nephropathy. METTL14 was also evidently increased in renal biopsy samples from patients with focal segmental glomerulosclerosis (FSGS) and diabetic nephropathy and in cultured human podocytes with ADR or advanced glycation end product (AGE) treatment in vitro. Functionally, we generated mice with podocyte-specific METTL14 deletion, and identified METTL14 knockout in podocytes improved glomerular function and alleviated podocyte injury, characterized by activation of autophagy and inhibition of apoptosis and inflammation, in mice with ADR nephropathy. Similar to the results in vivo, knockdown of METTL14 facilitated autophagy and alleviated apoptosis and inflammation in podocytes under ADR or AGE condition in vitro. Mechanically, we identified METTL14 knockdown upregulated the level of Sirt1, a well-known protective deacetylase in proteinuric kidney diseases, in podocytes with ADR or AGE treatment. The results of MeRIP-qPCR and dual-luciferase reporter assay indicated METTL14 promoted Sirt1 mRNA m6A modification and degradation in injured podocytes. Our findings suggest METTL14-dependent RNA m6A modification contributes to podocyte injury through posttranscriptional regulation of Sirt1 mRNA, which provide a potential approach for the diagnosis and treatment of podocytopathies.

The Role of Autophagy in Anti-Cancer and Health Promoting Effects of Cordycepin

Cordycepin is an adenosine derivative isolated from Cordyceps sinensis, which has been used as an herbal complementary and alternative medicine with various biological activities. The general anti-cancer mechanisms of cordycepin are regulated by the adenosine A3 receptor, epidermal growth factor receptor (EGFR), mitogen-activated protein kinases (MAPKs), and glycogen synthase kinase (GSK)-3β, leading to cell cycle arrest or apoptosis. Notably, cordycepin also induces autophagy to trigger cell death, inhibits tumor metastasis, and modulates the immune system. Since the dysregulation of autophagy is associated with cancers and neuron, immune, and kidney diseases, cordycepin is considered an alternative treatment because of the involvement of cordycepin in autophagic signaling. However, the profound mechanism of autophagy induction by cordycepin has never been reviewed in detail. Therefore, in this article, we reviewed the anti-cancer and health-promoting effects of cordycepin in the neurons, kidneys, and the immune system through diverse mechanisms, including autophagy induction. We also suggest that formulation changes for cordycepin could enhance its bioactivity and bioavailability and lower its toxicity for future applications. A comprehensive understanding of the autophagy mechanism would provide novel mechanistic insight into the anti-cancer and health-promoting effects of cordycepin.

A Personalized Glomerulus Chip Engineered from Stem Cell-Derived Epithelium and Vascular Endothelium

Progress in understanding kidney disease mechanisms and the development of targeted therapeutics have been limited by the lack of functional in vitro models that can closely recapitulate human physiological responses. Organ Chip (or organ-on-a-chip) microfluidic devices provide unique opportunities to overcome some of these challenges given their ability to model the structure and function of tissues and organs in vitro. Previously established organ chip models typically consist of heterogenous cell populations sourced from multiple donors, limiting their applications in patient-specific disease modeling and personalized medicine. In this study, we engineered a personalized glomerulus chip system reconstituted from human induced pluripotent stem (iPS) cell-derived vascular endothelial cells (ECs) and podocytes from a single patient. Our stem cell-derived kidney glomerulus chip successfully mimics the structure and some essential functions of the glomerular filtration barrier. We further modeled glomerular injury in our tissue chips by administering a clinically relevant dose of the chemotherapy drug Adriamycin. The drug disrupts the structural integrity of the endothelium and the podocyte tissue layers, leading to significant albuminuria as observed in patients with glomerulopathies. We anticipate that the personalized glomerulus chip model established in this report could help advance future studies of kidney disease mechanisms and the discovery of personalized therapies. Given the remarkable ability of human iPS cells to differentiate into almost any cell type, this work also provides a blueprint for the establishment of more personalized organ chip and 'body-on-a-chip' models in the future.

Mesenchymal stem cell-derived exosomes: a promising vector in treatment for diabetes and its microvascular complications

Mesenchymal stem cell-derived exosomes (MSC-exos) are phospholipid bimolecular vesicles containing various materials, and they mediate crosstalk among cells. MSC-exos can maintain glucose homeostasis and delay the progression of diabetes and its microvascular complications through multiple mechanisms, such as by improving β-cell viability and insulin resistance as well as through multiple signal transduction pathways. However, related knowledge has not yet been systematically summarized. Therefore, we reviewed the applications and relevant mechanisms of MSC-exos in treatments for diabetes and its microvascular complications, particularly treatments for improving islet β-cells viability, insulin resistance, diabetic nephropathy, and retinopathy.

A Homozygous Dab1-/- Is a Potential Novel Cause of Autosomal Recessive Congenital Anomalies of the Mice Kidney and Urinary Tract

This study aimed to explore morphology changes in the kidneys of Dab1^−/− (yotari) mice, as well as expression patterns of reelin, NOTCH2, LC3B, and cleaved caspase3 (CASP3) proteins, as potential determinants of normal kidney formation and function. We assumed that Dab1 functional inactivation may cause disorder in a wide spectrum of congenital anomalies of the kidney and urinary tract (CAKUT). Animals were sacrificed at postnatal days P4, P11, and P14. Paraffin-embedded kidney tissues were sectioned and analyzed by immunohistochemistry using specific antibodies. Kidney specimens were examined by bright-field, fluorescence, and electron microscopy. Data were analyzed by two-way ANOVA and t-tests. We noticed that yotari kidneys were smaller in size with a reduced diameter of nephron segments and thinner cortex. TEM microphotographs revealed foot process effacement in the glomeruli (G) of yotari mice, whereas aberrations in the structure of proximal convoluted tubules (PCT) and distal convoluted tubules (DCT) were not observed. A significant increase in reelin expression, NOTCH2, LC3B and cleaved CASP3 proteins was observed in the glomeruli of yotari mice. Renal hypoplasia in conjunction with foot process effacement and elevation in the expression of examined proteins in the glomeruli revealed CAKUT phenotype and loss of functional kidney tissue of yotari.

Podocyte Autophagy in Homeostasis and Disease

Autophagy is a protective mechanism that removes dysfunctional components and provides nutrition for cells. Podocytes are terminally differentiated specialized epithelial cells that wrap around the capillaries of the glomerular filtration barrier and show high autophagy level at the baseline. Here, we provide an overview of cellular autophagy and its regulation in homeostasis with specific reference to podocytes. We discuss recent data that have focused on the functional role and regulation of autophagy during podocyte injury in experimental and clinical glomerular diseases. A thorough understanding of podocyte autophagy could shed novel insights into podocyte survival mechanisms with injury and offer potential targets for novel therapeutics for glomerular disease.

Podocyte EGFR Inhibits Autophagy Through Upregulation of Rubicon in Type 2 Diabetic Nephropathy

Renal epidermal growth factor receptor (EGFR) signaling is activated in models of diabetic nephropathy (DN), and inhibition of the EGFR signaling pathway protects against the development of DN. We have now determined that in cultured podocytes, high glucose led to increases in activation of EGFR signaling but decreases in autophagy activity as indicated by decreased beclin-1 and inhibition of LC3B autophagosome formation as well as increased rubicon (an autophagy inhibitor) and SQSTM1 (autophagy substrate). Either genetic (small interfering [si]EGFR) or pharmacologic (AG1478) inhibition of EGFR signaling attenuated the decreased autophagy activity. In addition, rubicon siRNA knockdown prevented high glucose-induced inhibition of autophagy in podocytes. We further examined whether selective EGFR deletion in podocytes affected the progression of DN in type 2 diabetes. Selective podocyte EGFR deletion had no effect on body weight or fasting blood sugars in either db/db mice or nos3 ^-/-; db/db mice, a model of accelerated type 2 DN. However selective podocyte EGFR deletion led to relative podocyte preservation and marked reduction in albuminuria and glomerulosclerosis, renal proinflammatory cytokine/chemokine expression, and decreased profibrotic and fibrotic components in nos3 ^-/-; db/db mice. Podocyte EGFR deletion led to decreased podocyte expression of rubicon, in association with increased podocyte autophagy activity. Therefore, activation of EGFR signaling in podocytes contributes to progression of DN at least in part by increasing rubicon expression, leading to subsequent autophagy inhibition and podocyte injury.

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

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

Alleviation of the doxorubicin-induced nephrotoxicity by fasudil in vivo and in vitro

OBJECTIVE

Treatment with the chemotherapeutic agent, doxorubicin (DOX), is limited by side effects. We have previously demonstrated that fasudil, a Rho/ROCK inhibitor, has antioxidant, anti-inflammatory and anti-apoptotic effects in contrast-induced acute kidney injury model. The present study to investigated the possible protective effect of fasudil, on DOX-induced nephrotoxicity.

MATERIALS AND METHOD

In vivo: Forty male C57BL/6 male mice were randomly divided into 4 groups: Control group, DOX treatment group (DOX group), DOX + low dose fasudil (DOX + L group), DOX + high dose fasudil (DOX + H group). Mice in 2-4 groups received DOX (2.5 mg/kg, i.p.) once a week for 8 weeks. The 3 and 4 group were given 2 mg/kg/d or 10 mg/kg/d fasudil before DOX injection. respectively. Meanwhile, the control group received saline. At the end of week eight, blood samples were collected for biochemical testing. The kidneys were removed for histological, immunohistochemical, Western blot, quantitative real-time PCR (qRT-PCR), and molecular detection. In vitro: NRK-52E cells were treated with 40 uM fasudil for 12 h, then incubated with 1 uM DOX for 24 h. Cells then collected for qRT-PCR and Western blot.

RESULTS

In vivo, fasudil treatment ameliorated DOX-induced immunofluorescence reaction of DNA damage-related factors (8-OHdG), decreased the expression of Bax, Caspase-3, p16, p21 and p53, and increased the expression of protein of Bcl-2, Bmi-1 and Sirt-1. In the mouse model, administration of fasudil significantly ameliorated DOX-induced kidney damage, suppressed cell apoptosis and senescence, ameliorated redox imbalance and DNA damage. At the same time, DOX produced obvious kidney damage revealed by kidney functions changes: increased serum creatinine (SCr) and blood urea nitrogen (BUN) concentrations. In addition, kidney tissue staining in the DOX group showed abnormal structure and fibroproliferative disorders. And DOX could promote the oxidation and senescence of kidney cells, leading to increased expression of 8-OHdG and senescence and apoptosis-related factors. On the contrary, fasudil treatment can effectively inhibit redox imbalance and DNA damage caused by DOX, and inhibit cell senescence and apoptosis. Fasudil can inhibit excessive activation of Rho/ROCK signaling pathway, thereby improving kidney tissue fibrosis and recovery kidney function.

CONCLUSION

Fasudil has a protective effect on DOX-induced nephrotoxicity in mice and NRK-52E cells, which can inhibit oxidative stress and DNA damage, inhibit apoptosis, and delays cell senescence by inhibiting RhoA/Rho kinase (ROCK) signaling pathway.

mTOR Signaling in Kidney Diseases

The mammalian target of rapamycin (mTOR), a serine/threonine protein kinase, is crucial in regulating cell growth, metabolism, proliferation, and survival. Under physiologic conditions, mTOR signaling maintains podocyte and tubular cell homeostasis. In AKI, activation of mTOR signaling in tubular cells and interstitial fibroblasts promotes renal regeneration and repair. However, constitutive activation of mTOR signaling in kidneys results in the initiation and progression of glomerular hypertrophy, interstitial fibrosis, polycystic kidney disease, and renal cell carcinoma. Here, we summarize the recent studies about mTOR signaling in renal physiology and injury, and discuss the possibility of its use as a therapeutic target for kidney diseases.

Role of IRE1α in podocyte proteostasis and mitochondrial health

Glomerular epithelial cell (GEC)/podocyte proteostasis is dysregulated in glomerular diseases. The unfolded protein response (UPR) is an adaptive pathway in the endoplasmic reticulum (ER) that upregulates proteostasis resources. This study characterizes mechanisms by which inositol requiring enzyme-1α (IRE1α), a UPR transducer, regulates proteostasis in GECs. Mice with podocyte-specific deletion of IRE1α (IRE1α KO) were produced and nephrosis was induced with adriamycin. Compared with control, IRE1α KO mice had greater albuminuria. Adriamycin increased glomerular ER chaperones in control mice, but this upregulation was impaired in IRE1α KO mice. Likewise, autophagy was blunted in adriamycin-treated IRE1α KO animals, evidenced by reduced LC3-II and increased p62. Mitochondrial ultrastructure was markedly disrupted in podocytes of adriamycin-treated IRE1α KO mice. To pursue mechanistic studies, GECs were cultured from glomeruli of IRE1α flox/flox mice and IRE1α was deleted by Cre-lox recombination. In GECs incubated with tunicamycin, deletion of IRE1α attenuated upregulation of ER chaperones, LC3 lipidation, and LC3 transcription, compared with control GECs. Deletion of IRE1α decreased maximal and ATP-linked oxygen consumption, as well as mitochondrial membrane potential. In summary, stress-induced chaperone production, autophagy, and mitochondrial health are compromised by deletion of IRE1α. The IRE1α pathway is cytoprotective in glomerular disease associated with podocyte injury and ER stress.

Autophagy in kidney homeostasis and disease

Autophagy is a conserved lysosomal pathway for the degradation of cytoplasmic components. Basal autophagy in kidney cells is essential for the maintenance of kidney homeostasis, structure and function. Under stress conditions, autophagy is altered as part of the adaptive response of kidney cells, in a process that is tightly regulated by signalling pathways that can modulate the cellular autophagic flux - mammalian target of rapamycin, AMP-activated protein kinase and sirtuins are key regulators of autophagy. Dysregulated autophagy contributes to the pathogenesis of acute kidney injury, to incomplete kidney repair after acute kidney injury and to chronic kidney disease of varied aetiologies, including diabetic kidney disease, focal segmental glomerulosclerosis and polycystic kidney disease. Autophagy also has a role in kidney ageing. However, questions remain about whether autophagy has a protective or a pathological role in kidney fibrosis, and about the precise mechanisms and signalling pathways underlying the autophagy response in different types of kidney cells and across the spectrum of kidney diseases. Further research is needed to gain insights into the regulation of autophagy in the kidneys and to enable the discovery of pathway-specific and kidney-selective therapies for kidney diseases and anti-ageing strategies.

Protective role of Astragaloside IV in chronic glomerulonephritis by activating autophagy through PI3K/AKT/AS160 pathway

Astragaloside IV(AS-IV), a saponin purified from Astragalus membranaceus (Fisch.) Bge.var.mongholicus (Bge.) Hsiao, has been widely used in traditional Chinese medicine. However, the underlying mechanisms in treating chronic glomerular nephritis (CGN) have not been fully understood. The aim of the present study was to evaluate the potential mechanism of AS-IV on CGN. CGN rats were administrated with AS-IV at 10 mg·kg^-1 ·d^-1 (ASL) and 20 mg·kg^-1 ·d^-1 (ASH). Twenty four hour proteinuria, blood urea nitrogen (BUN), and serum creatinine (SCr) were detected. Hematoxylin-eosin (HE) and periodic acid-Schiff (PAS) staining were performed to evaluate the kidney lesion. Transmission electron microscope and GFP-RFP-LC3 transfection assay were used to monitor the effect of AS-IV on autophagy. IL-6 and IL-1β were detected. The expression of CyclinD1, PI3K/AKT/AS160 pathway and autophagy related proteins were detected by Western Blot. The results demonstrated that AS-IV improved kidney function, ameliorated kidney lesion, and diminished inflammatory in CGN rats. Further, both in vivo and vitro study demonstrated that AS-IV inhibited the proliferation of mesangial cells. AS-IV further displayed a remarkable effect on inhibiting the activation of PI3K/AKT/AS160 pathway and improved the activation of autophagy in vivo and vitro. These results suggested that AS-IV is a potential therapeutic agent for CGN and merits further investigation.

Role of autophagy in Puromycin Aminonucleoside-induced podocyte apoptosis

Objective: The aim of our study is to investigate the relationship between podocyte autophagy and apoptosis induced by Puromycin Aminonucleoside (PAN) and to clarify its mechanism.Methods: Podocytes were cultured in vitro. The apoptosis rates of each group were detected using flow cytometry. The expression of LC3-II protein and changes in distribution were detected through laser scanning confocal microscope, and the western blot protocol was employed for detection of protein expression of LC3-II. The autophagosomes were detected by transmission electron microscopy.Results: In this study, We found that autophagosome increased followed by apoptosis after podocyte injury. Furthermore, we conformed that the activation of autophagy could inhibit the apoptosis to alleviate the injury of podocyte at an early stage.Conclusions: Autophagy occurred earlier before apoptosis and autophagy mediated podocyte apoptosis induced by PAN. These findings indicate that autophagy may become a novel therapeutic target for the treatment of podocyte injury and proteinuria in the future.

Podocyte Lysosome Dysfunction in Chronic Glomerular Diseases

Podocytes are visceral epithelial cells covering the outer surface of glomerular capillaries in the kidney. Blood is filtered through the slit diaphragm of podocytes to form urine. The functional and structural integrity of podocytes is essential for the normal function of the kidney. As a membrane-bound organelle, lysosomes are responsible for the degradation of molecules via hydrolytic enzymes. In addition to its degradative properties, recent studies have revealed that lysosomes may serve as a platform mediating cellular signaling in different types of cells. In the last decade, increasing evidence has revealed that the normal function of the lysosome is important for the maintenance of podocyte homeostasis. Podocytes have no ability to proliferate under most pathological conditions; therefore, lysosome-dependent autophagic flux is critical for podocyte survival. In addition, new insights into the pathogenic role of lysosome and associated signaling in podocyte injury and chronic kidney disease have recently emerged. Targeting lysosomal functions or signaling pathways are considered potential therapeutic strategies for some chronic glomerular diseases. This review briefly summarizes current evidence demonstrating the regulation of lysosomal function and signaling mechanisms as well as the canonical and noncanonical roles of podocyte lysosome dysfunction in the development of chronic glomerular diseases and associated therapeutic strategies.

Nitrative Stress-Related Autophagic Insufficiency Participates in Hyperhomocysteinemia-Induced Renal Aging

The kidneys are important organs that are susceptible to aging. Hyperhomocysteinemia (HHcy) is a risk factor for nephropathy and is associated with chronic nephritis, purpuric nephritis, and nephrotic syndrome. Numerous studies have shown that elevated serum homocysteine levels can damage the kidneys; however, the underlying mechanism of HHcy on kidney damage remains unclear. In this study, we make use of a diet-induced HHcy rat model and in vitro cell culture to explore the role of autophagy in HHcy-induced renal aging and further explored the underlying mechanism. We demonstrated that HHcy led to the development of renal aging. Promoted kidney aging and autophagic insufficiency were involved in HHcy-induced renal aging. HHcy decreased the expression of transcription factor EB (TFEB), the key transcription factor of autophagy-related genes in renal tissue. Further experiments showed that nitrative stress levels were increased in the kidney of HHcy rats. Interestingly, pretreatment with the peroxynitrite (ONOO⁻) scavenger FeTMPyP not only reduced the Hcy-induced nitrative stress in vitro but also partially attenuated the decrease in TFEB in both protein and mRNA levels. Moreover, our results indicated that HHcy reduced TFEB expression and inhibited TFEB-mediated autophagy activation by elevating nitrative stress. In conclusion, this study showed an important role of autophagic insufficiency in HHcy-induced renal aging, in which downregulation of TFEB plays a major role. Furthermore, downexpression of TFEB was associated with increased nitrative stress in HHcy. This study provides a novel insight into the mechanism and therapeutic strategy for renal aging.

Autophagy Function and Regulation in Kidney Disease

Autophagy is a dynamic process by which intracellular damaged macromolecules and organelles are degraded and recycled for the synthesis of new cellular components. Basal autophagy in the kidney acts as a quality control system and is vital for cellular metabolic and organelle homeostasis. Under pathological conditions, autophagy facilitates cellular adaptation; however, activation of autophagy in response to renal injury may be insufficient to provide protection, especially under dysregulated conditions. Kidney-specific deletion of Atg genes in mice has consistently demonstrated worsened acute kidney injury (AKI) outcomes supporting the notion of a pro-survival role of autophagy. Recent studies have also begun to unfold the role of autophagy in progressive renal disease and subsequent fibrosis. Autophagy also influences tubular cell death in renal injury. In this review, we reported the current understanding of autophagy regulation and its role in the pathogenesis of renal injury. In particular, the classic mammalian target of rapamycin (mTOR)-dependent signaling pathway and other mTOR-independent alternative signaling pathways of autophagy regulation were described. Finally, we summarized the impact of autophagy activation on different forms of cell death, including apoptosis and regulated necrosis, associated with the pathophysiology of renal injury. Understanding the regulatory mechanisms of autophagy would identify important targets for therapeutic approaches.