Podocyte Injury in Diabetic Kidney Disease in Mouse Models Involves TRPC6-mediated Calpain Activation Impairing Autophagy

Inhibition of Drp1-mediated mitochondrial fission by P110 ameliorates renal injury in diabetic nephropathy

Diabetic nephropathy (DN) is a leading cause of end-stage renal disease, characterized by progressive renal injury driven by mitochondrial dysfunction and metabolic reprogramming. Excessive mitochondrial fission, mediated by dynamin-related protein 1 (Drp1), contributes to mitochondrial fragmentation and cellular injury in the diabetic kidney. Here, we investigate the therapeutic potential of P110, a selective inhibitor of Drp1-mediated mitochondrial fission, in experimental models of DN. We demonstrate that P110 effectively reduces mitochondrial fragmentation and restores metabolic balance in renal tubular cells from DN patients. In streptozotocin (STZ)-induced diabetic mice and db/db mice, P110 treatment significantly mitigates renal injury, as evidenced by decreased fibrosis, inflammation, and podocyte injury, despite having no impact on hyperglycemia or body weight loss. Mechanistically, P110 disrupts the interaction between Drp1 and Fis1, thereby inhibiting mitochondrial fission, and activates the AMPK/PGC-1α/TFAM pathway, promoting mitochondrial biogenesis and function. Our findings suggest that targeting mitochondrial fission with P110 offers a novel therapeutic strategy for preventing and treating DN, potentially addressing a critical gap in current diabetic nephropathy management.

Trim33 inhibited the growth and relieved the fibrosis of mesangial cells through inducing the ubiquitination degradation of Smad2

BACKGROUND

Diabetic nephropathy (DN) poses a significant global health burden due to its progressive nature leading to end-stage renal disease and increased mortality rates. Here, we explored the effects of Tripartite Motif Containing 33 (Trim33) on cell viability and fibrosis of mesangial cells (MCs).

METHODS

MCs were treated with 30 mM D-glucose (HG) and mice were injected with 50 mg/kg STZ to establish the DN model. Cell growth were detected by CCK-8 and EdU staining. The protein levels of fibronectin (FN), Collagen IV (Col-IV), α-SMA, Smad2, Smad3 and Smad4 were tested by western blot. Furthermore, the interaction between Trim33 and Smad2 were tested by Immunoprecipitation. Wild-type and mutation type of ubiquitin was used to analyze the ubiquitination levels of Smad2. Finally, the injury of kidneys in DN mice were observed by HE staining.

RESULTS

Trim33 was down regulated in HG treated MCs and DN mice. Trim33 verexpression decreased the cell viability and proliferation of MCs. Besides, the protein levels of FN, Col-IV, α-SMA, Smad2, Smad3 and Smad4 were decreased after Trim33 overexpression in vivo and in vitro. Furthermore, CO-IP assay confirmed that Trim33 interacted with Smad2. Trim33 regulated the Smad2 ubiquitination through the K48 site of Ub. Trim33 overexpression induced the protein degradation of Smad2. Additionally, Smad2 overexpression reversed the effects of Trim33 on the growth and fibrosis of HG treated MCs.

CONCLUSION

This study demonstrated that Trim33 overexpression inhibited the growth and fibrosis progression in HG treated MCs through inducing the ubiquitination degradation of Smad2 protein.

Upregulation of Piezo2 and increased extracellular matrix protein in diabetic kidney disease mice

Mechanical forces such as glomerular hyperfiltration are crucial in the pathogenesis and progression of diabetic kidney disease. Piezo2 is a mechanosensitive cation channel and plays a major role in various biological and pathophysiological phenomena. We previously reported Piezo2 expression in mouse and rat kidneys and its alteration by dehydration and hypertension. To elucidate the alteration of Piezo2 expression and its consequences in a mouse model of diabetic kidney disease, we used high salt-fed male KK-Ay mice, an accelerated genetic model of diabetic kidney disease. KK-Ay mice exhibited marked obesity, hyperglycemia, elevated blood pressure, higher creatinine clearance, and overt albuminuria. Histopathological analysis revealed glomerular hypertrophy, mesangial expansion, macrophage infiltration, tubular vacuolization, and interstitial fibrosis. The mRNA and protein expression analyses revealed (1) increased fibronectin protein expression in the glomerular areas, (2) upregulated Piezo2 expression in the glomerular mesangial cells and interstitial region, (3) increased Piezo2 and the fibronectin-coding gene Fn1 mRNA, and (4) a strong correlation of Piezo2 expression with that of Fn1 in the kidneys of diabetic kidney disease mice. Piezo2 upregulation and fibronectin accumulation were alleviated by an angiotensin II receptor blocker. In accordance with these in vivo results, in vitro study demonstrated that Piezo2 overexpression increased fibronectin production in HEK293T cells. In conclusion, we demonstrated that Piezo2 expression was upregulated in glomerular mesangial cells in a mouse model of diabetic kidney disease. Our results suggest that Piezo2 contributes to the progression of diabetic kidney disease by mediating glomerular fibronectin production, leading to glomerulosclerosis. Hyperfiltration is crucial in the pathogenesis of diabetic kidney disease. We showed that Piezo2 expression is upregulated in mesangial cells of diabetic kidney disease mice with glomerular fibronectin accumulation. Piezo2 overexpression increased fibronectin production in HEK293T cells. Piezo2 may contribute to diabetic kidney disease progression by mediating glomerular fibronectin production.

Extracellular vesicles derived from mesenchymal stem cells alleviate renal fibrosis via the miR-99b-5p/mTOR/autophagy axis in diabetic kidney disease

BACKGROUND

Diabetic kidney disease (DKD) is the leading cause of end-stage renal disease (ESRD) globally, presenting a significant therapeutic challenge. Extracellular vesicles (EVs) from mesenchymal stem cells (MSCs) have emerged as promising therapeutic agents. This study explored the therapeutic effects and mechanisms of EVs derived from human placental mesenchymal stem cells (hP-MSCs) on DKD.

METHODS

EVs were isolated from cultured hP-MSCs and administered to streptozotocin (STZ)-induced diabetic mice and high glucose-treated glomerular mesangial cells. The therapeutic impact of EVs was assessed through histological analysis and biochemical assays. miR-99b-5p expression in EVs and its role in modulating the mechanistic target of rapamycin (mTOR)/autophagy pathway were examined via western blotting and RT‒qPCR.

RESULTS

Treatment with hP-MSC-derived EVs significantly alleviated renal fibrosis and improved renal function in DKD models. These EVs were enriched with miR-99b-5p, which targeted and inhibited mTOR signaling, thereby increasing autophagic activity and reducing cellular proliferation and extracellular matrix accumulation in renal tissues.

CONCLUSIONS

hP-MSC-derived EVs can mitigate renal injury in DKD by modulating the miR-99b-5p/mTOR/autophagy pathway. These findings suggest a potential cell-free therapeutic strategy for managing DKD.

Exploring the subtle and novel renal pathological changes in diabetic nephropathy using clustering analysis with deep learning

To decrease the number of chronic kidney disease (CKD), early diagnosis of diabetic kidney disease is required. We performed invariant information clustering (IIC)-based clustering on glomerular images obtained from nephrectomized kidneys of patients with and without diabetes. We also used visualizing techniques (gradient-weighted class activation mapping (Grad-CAM) and generative adversarial networks (GAN)) to identify the novel and early pathological changes on light microscopy in diabetic nephropathy. Overall, 13,251 glomerular images (7,799 images from diabetes cases and 5,542 images from non-diabetes cases) obtained from 45 patients in Kanazawa Medical University were clustered into 10 clusters by IIC. Diabetic clusters that mainly contained glomerular images from diabetes cases (Clusters 0, 1, and 2) and non-diabetic clusters that mainly contained glomerular images from non-diabetes cases (Clusters 8 and 9) were distinguished in the t-distributed stochastic neighbor embedding (t-SNE) analysis. Grad-CAM demonstrated that the outer portions of glomerular capillaries in diabetic clusters had characteristic lesions. Cycle-GAN showed that compared to Bowman's space, smaller glomerular tufts was a characteristic lesion of diabetic clusters. These findings might be the subtle and novel pathological changes on light microscopy in diabetic nephropathy.

LncRNA HOXB3OS improves high glucose-mediated podocyte damage and progression of diabetic kidney disease through enhancing SIRT1 mRNA stability

High glucose (HG)-mediated podocyte damage can be ameliorated by lncRNA HOXB3OS, and exosomes derived from adipose-derived mesenchymal stem cells (ADSCs-Exo) can ameliorate the progression of diabetic kidney disease (DKD) dependening on RNA. To investigate the mechanism by which HOXB3OS improves podocyte injury and the effects of engineered ADSCs-Exo with a high abundance of HOXB3OS on DKD progression, MPC5 cells stimulated with HG and db/db mice were used to develop a podocyte injury model and type II DKD mouse model, respectively. HOXB3OS expression and mRNA level of SIRT1 were detected by qRT-PCR. The protein content of SIRT1 and Ythdc2 was measured through WB, IHC, and IF assays. CCK-8 assay and flow cytometry assay were used to detect cell viability and apoptosis rate of MPC5 cells. RIP assay was used to investigate the binding capacity of Ythdc2 to HOXB3OS or SIRT1 mRNA. Albuminuria, renal function and glomerular structure were observed by kits and PAS, respectively. Consequently, we found that HOXB3OS combined with Ythdc2 and inhibited the binding of Ythdc2 to SIRT1 mRNA, hence inhibiting SIRT1 mRNA degradation. SIRT1 siRNA inhibited the effect of Ythdc2 siRNA on HOXB3OS knock-down or HG-induced podocyte injury. ADSCs-Exo with a high content of HOXB3OS ameliorated HG-mediated podocyte damage and DKD progression. This suggests that engineered ADSCs-Exo with HOXB3OS can suppress Ythdc2-mediated SIRT1 mRNA degradation by disturbing the binding of Ythdc2 to SIRT1 mRNA as well as reverse SIRT1 down-regulation induced by HG, thereby ameliorating podocyte injury and DKD progression.

TRPC6-Calpain-1 Axis Promotes Tubulointerstitial Inflammation by Inhibiting Mitophagy in Diabetic Kidney Disease

Introduction

Renal tubulointerstitial inflammation represents an effective indicator for predicting the progression of diabetic kidney disease (DKD). Mitophagy abnormality is 1 of the most important factors involved in tubule injury. However, the exact molecular mechanism underlying mitophagy abnormality-mediated tubulointerstitial inflammation in DKD remains poorly understood.

Methods

In this study, a streptozotocin-induced DKD mouse model was established and HK-2 cells treated with high glucose (HG) served as an in vitro model. Tubular mitophagy was regulated through pharmacological urolithin A (UA) administration. The functional effect of the transient receptor potential cation channel, subfamily C, member 6 (TRPC6) was explored using genetic interventions in vivo and in vitro.

Results

We found that renal tubulointerstitial inflammation in DKD was closely associated with mitophagy inhibition, which was mediated by disturbance of PINK1/Parkin pathway. Mitophagy activation significantly attenuated tubular injury and tubulointerstitial inflammation. Further, it was found that TRPC6 was markedly increased in DKD and played an essential role in mitophagy inhibition by activating calpain-1. Knockdown of Trpc6 partially reversed mitophagy abnormality and consequently attenuated tubular injury and tubulointerstitial inflammation in vivo and in vitro. Finally, we found that tubular TRPC6-mediated mitophagy inhibition was blocked with BAPTA (a specific Ca2+ chelator) or calpeptin (a specific calpain-1 inhibitor).

Conclusion

Our study reveals that TRPC6-calpain-1 axis promotes tubulointerstitial inflammation in DKD by inhibiting mitophagy.

Magnolol Inhibits High Fructose-Induced Podocyte Inflammation via Downregulation of TKFC/Sp1/HDAC4/Notch1 Activation

BACKGROUND/OBJECTIVES

High fructose has been implicated as an important trigger of kidney inflammation in patients and experimental models. Magnolol, isolated from Magnolia officinalis, has an anti-inflammatory effect, but its protective role in podocytes remains underexplored. This study explored the protective effects and underlying mechanism of magnolol against high fructose-induced podocyte inflammation.

METHODS

The effects of magnolol on high fructose-induced podocyte inflammation were assessed in male Sprague Dawley rats administered 10% (w/v) fructose water for 12 weeks and heat-sensitive human podocyte cell lines (HPCs) exposed to 5 mM fructose. Podocyte foot processes were examined using transmission electron microscopy. The expression levels of nephrin, podocin, tumor necrosis factor-α (TNF-α), Notch1 intracellular domain (NICD1), triokinase/FMN cyclase (TKFC), specificity protein 1 (Sp1) and histone deacetylase 4 (HDAC4) were determined by Western blot, immunofluorescence and real-time quantitative polymerase chain reaction (qRT-PCR). The chromatin immunoprecipitation (ChIP) assay was performed to evaluate the interaction between Sp1 and the promoter region of HDAC4.

RESULTS

Magnolol mitigated the impairment of glomerular filtration function in high fructose-fed rats. Besides, it significantly alleviated the inflammatory responses in glomeruli and HPCs, evidenced by decreased protein levels of TNF-α and NICD1. Increased protein levels of TKFC, Sp1 and HDAC4 were observed in high fructose-stimulated HPCs and rat glomeruli. TMP195, an HDAC4 inhibitor, reduced TNF-α and NICD1 protein levels in high fructose-exposed HPCs. The increased Sp1 was shown to associate with the promoter region of HDAC4, promoting HDAC4 protein expression in high fructose-exposed HPCs. The knockdown of TKFC in HPCs by TKFC siRNA decreased Sp1, HDAC4 and NICD1 protein levels, alleviating podocyte inflammatory response. Furthermore, magnolol inhibited TKFC/Sp1/HDAC4/Notch1 activation in vivo and in vitro.

CONCLUSIONS

Magnolol attenuated high fructose-induced podocyte inflammation possibly through the suppression of TKFC/Sp1/HDAC4/Notch1 activation, providing new evidence for its potential role in podocyte protection.

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

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

Mesenchymal Stem Cell Therapy: Therapeutic Opportunities and Challenges for Diabetic Kidney Disease

Diabetic kidney disease (DKD) is the leading cause of end-stage renal disease (ESRD), which severely affects the quality of patients' lives. However, the current therapeutic approaches can only postpone its progression to ESRD. It is therefore imperative to develop a novel therapeutic strategy for renal injury in DKD, with the objective of restoring renal function and reversing the process of ESRD. In recent years, the potential of mesenchymal stem cell (MSC) therapy for DKD has garnered increasing attention within the scientific community. Preclinical research on MSC therapy has yielded promising results, and the safety of MSC treatment in vivo has been substantiated in clinical studies. An increasing body of evidence suggests that MSC therapy has significant potential for the treatment of DKD. This article reviews the existing research on MSCs and their derived exosomes in treating DKD and analyzes the underlying mechanism of MSC-based therapy for DKD. Additionally, we discuss the potential of combining MSC therapy with conventional pharmacological treatments, along with the constraints and prospects of MSC therapy for DKD. We hope this review can provide a precise and comprehensive understanding of MSCs for the treatment of DKD.

Podocyte Death in Diabetic Kidney Disease: Potential Molecular Mechanisms and Therapeutic Targets

Cell deaths maintain the normal function of tissues and organs. In pathological conditions, the abnormal activation or disruption of cell death often leads to pathophysiological effects. Diabetic kidney disease (DKD), a significant microvascular complication of diabetes, is linked to high mortality and morbidity rates, imposing a substantial burden on global healthcare systems and economies. Loss and detachment of podocytes are key pathological changes in the progression of DKD. This review explores the potential mechanisms of apoptosis, necrosis, autophagy, pyroptosis, ferroptosis, cuproptosis, and podoptosis in podocytes, focusing on how different cell death modes contribute to the progression of DKD. It recognizes the limitations of current research and presents the latest basic and clinical research studies targeting podocyte death pathways in DKD. Lastly, it focuses on the future of targeting podocyte cell death to treat DKD, with the intention of inspiring further research and the development of therapeutic strategies.

Targeting TRPs in autophagy regulation and human diseases

Transient receptor potential channels (TRPs) are widely recognized as a group of ion channels involved in various sensory perceptions, such as temperature, taste, pressure, and vision. While macroautophagy (hereafter referred to as autophagy) is primarily regulated by core machinery, the ion exchange mediated by TRPs between intracellular and extracellular compartments, as well as within organelles and the cytoplasm, plays a crucial role in autophagy regulation as an important signaling transduction mechanism. Moreover, certain TRPs can directly interact with autophagy regulatory proteins to participate in autophagy regulation. In this article, we provide an in-depth review of the current understanding of the regulatory mechanisms of autophagy, with a specific focus on TRPs. Furthermore, we highlight the potential prospects for drug development targeting TRPs in autophagy for the treatment of human diseases.

Non-voltage-gated Ca2+ channel signaling in glomerular cells in kidney health and disease

Positioned at the head of the nephron, the renal corpuscle generates a plasma ultrafiltrate to initiate urine formation. Three major cell types within the renal corpuscle, the glomerular mesangial cells, podocytes, and glomerular capillary endothelial cells, communicate via endocrine- and paracrine-signaling mechanisms to maintain the structure and function of the glomerular capillary network and filtration barrier. Ca2+ signaling mediated by several distinct plasma membrane Ca2+ channels impacts the functions of all three cell types. The past two decades have witnessed pivotal advances in understanding of non-voltage-gated Ca2+ channel function and regulation in the renal corpuscle in health and renal disease. This review summarizes the current knowledge of the physiological and pathological impact of non-voltage-gated Ca2+ channel signaling in mesangial cells, podocytes and glomerular capillary endothelium. The main focus is on transient receptor potential and store-operated Ca2+ channels, but ionotropic N-methyl-d-aspartate receptors and purinergic receptors also are discussed. This update of Ca2+ channel functions and their cellular signaling cascades in the renal corpuscle is intended to inform the development of therapeutic strategies targeting these channels to treat kidney diseases, particularly diabetic nephropathy.

Calcium signalling and transport in the kidney

The kidney plays a pivotal role in regulating calcium levels within the body. Approximately 98% of the filtered calcium is reabsorbed in the nephron, and this process is tightly controlled to maintain calcium homeostasis, which is required to facilitate optimal bone mineralization, preserve serum calcium levels within a narrow range, and support intracellular signalling mechanisms. The maintenance of these functions is attributed to a delicate balance achieved by various calcium channels, transporters, and calcium-binding proteins in renal cells. Perturbation of this balance due to deficiency or dysfunction of calcium channels and calcium-binding proteins can lead to severe complications. For example, polycystic kidney disease is linked to aberrant calcium transport and signalling. Furthermore, dysregulation of calcium levels can promote the formation of kidney stones. This Review provides an updated description of the key aspects of calcium handling in the kidney, focusing on the function of various calcium channels and the physiological stimuli that control these channels or are communicated through them. A discussion of the role of calcium as an intracellular second messenger and the pathophysiology of renal calcium dysregulation, as well as a summary of gaps in knowledge and future prospects, are also included.

Roles of Mitochondrial Dysfunction in Diabetic Kidney Disease: New Perspectives from Mechanism to Therapy

Diabetic kidney disease (DKD) is a common microvascular complication of diabetes and the main cause of end-stage renal disease around the world. Mitochondria are the main organelles responsible for producing energy in cells and are closely involved in maintaining normal organ function. Studies have found that a high-sugar environment can damage glomeruli and tubules and trigger mitochondrial dysfunction. Meanwhile, animal experiments have shown that DKD symptoms are alleviated when mitochondrial damage is targeted, suggesting that mitochondrial dysfunction is inextricably linked to the development of DKD. This article describes the mechanisms of mitochondrial dysfunction and the progression and onset of DKD. The relationship between DKD and mitochondrial dysfunction is discussed. At the same time, the progress of DKD treatment targeting mitochondrial dysfunction is summarized. We hope to provide new insights into the progress and treatment of DKD.

The regulatory role of miRNA and lncRNA on autophagy in diabetic nephropathy

Diabetic nephropathy (DN) is a serious complication of diabetes that causes glomerular sclerosis and end-stage renal disease, leading to ascending morbidity and mortality in diabetic patients. Excessive accumulation of aberrantly modified proteins or damaged organelles, such as advanced glycation end-products, dysfunctional mitochondria, and inflammasomes is associated with the pathogenesis of DN. As one of the main degradation pathways, autophagy recycles toxic substances to maintain cellular homeostasis and autophagy dysregulation plays a crucial role in DN progression. MicroRNA (miRNA) and long non-coding RNA (lncRNA) are non-coding RNA (ncRNA) molecules that regulate gene expression and have been implicated in both physiological and pathological conditions. Recent studies have revealed that autophagy-regulating miRNA and lncRNA have been involved in pathological processes of DN, including renal cell injury, mitochondrial dysfunction, inflammation, and renal fibrosis. This review summarizes the role of autophagy in DN and emphasizes the modulation of miRNA and lncRNA on autophagy during disease progression, for the development of promising interventions by targeting these ncRNAs in this disease.

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.

Deletion of IRE1α in podocytes exacerbates diabetic nephropathy in mice

Protein misfolding in the endoplasmic reticulum (ER) of podocytes contributes to the pathogenesis of glomerular diseases. Protein misfolding activates the unfolded protein response (UPR), a compensatory signaling network. We address the role of the UPR and the UPR transducer, inositol-requiring enzyme 1α (IRE1α), in streptozotocin-induced diabetic nephropathy in mice. Diabetes caused progressive albuminuria in control mice that was exacerbated in podocyte-specific IRE1α knockout (KO) mice. Compared to diabetic controls, diabetic IRE1α KO mice showed reductions in podocyte number and synaptopodin. Glomerular ultrastructure was altered only in diabetic IRE1α KO mice; the major changes included widening of podocyte foot processes and glomerular basement membrane. Activation of the UPR and autophagy was evident in diabetic control, but not diabetic IRE1α KO mice. Analysis of human glomerular gene expression in the JuCKD-Glom database demonstrated induction of genes associated with the ER, UPR and autophagy in diabetic nephropathy. Thus, mice with podocyte-specific deletion of IRE1α demonstrate more severe diabetic nephropathy and attenuation of the glomerular UPR and autophagy, implying a protective effect of IRE1α. These results are consistent with data in human diabetic nephropathy and highlight the potential for therapeutically targeting these pathways.

Disrupting circadian control of autophagy induces podocyte injury and proteinuria

The circadian clock influences a wide range of biological process and controls numerous aspects of physiology to adapt to the daily environmental changes caused by Earth's rotation. The kidney clock plays an important role in maintaining tubular function, but its effect on podocytes remains unclear. Here, we found that podocytes expressed CLOCK proteins, and that 2666 glomerular gene transcripts (13.4%), including autophagy related genes, had 24-hour circadian rhythms. Deletion of Clock in podocytes resulted in 1666 gene transcripts with the loss of circadian rhythm including autophagy genes. Podocyte-specific Clock knockout mice at age three and eight months showed deficient autophagy, loss of podocytes and increased albuminuria. Chromatin immunoprecipitation (ChIP) sequence analysis indicated autophagy related genes were targets of CLOCK in podocytes. ChIP-PCR further confirmed Clock binding to the promoter regions of Becn1 and Atg12, two autophagy related genes. Furthermore, the association of CLOCK regulated autophagy with chronic sleep fragmentation and diabetic kidney disease was analyzed. Chronic sleep fragmentation resulted in the loss of glomerular Clock rhythm, inhibition of podocyte autophagy, and proteinuria. Rhythmic oscillations of Clock also disappeared in high glucose treated podocytes and in glomeruli from diabetic mice. Finally, circadian differences in podocyte autophagy were also abolished in diabetic mice. Deletion Clock in podocytes aggravated podocyte injury and proteinuria in diabetic mice. Thus, our findings demonstrate that clock-dependent regulation of autophagy may be essential for podocyte survival. Hence. loss of circadian controlled autophagy may play an important role in podocyte injury and proteinuria.

Tangshen formula protects against podocyte apoptosis via enhancing the TFEB-mediated autophagy-lysosome pathway in diabetic nephropathy

ETHNOPHARMACOLOGICAL RELEVANCE

Diabetic nephropathy (DN) is the leading cause of end-stage kidney disease and currently there are no specific and effective drugs for its treatment. Podocyte injury is a detrimental feature and the major cause of albuminuria in DN. We previously reported Tangshen Formula (TSF), a Chinese herbal medicine, has shown therapeutic effects on DN. However, the underlying mechanisms remain obscure.

AIM OF THE STUDY

This study aimed to explore the protective effect of TSF on podocyte apoptosis in DN and elucidate the potential mechanism.

MATERIALS AND METHODS

The effects of TSF were assessed in a murine model using male KKAy diabetic mice, as well as in advanced glycation end products-stimulated primary mice podocytes. Transcription factor EB (TFEB) knockdown primary podocytes were employed for mechanistic studies. In vivo and in vitro studies were performed and results assessed using transmission electron microscopy, immunofluorescence staining, and western blotting.

RESULTS

TSF treatment alleviated podocyte apoptosis and structural impairment, decreased albuminuria, and mitigated renal dysfunction in KKAy mice. Notably, TSF extracted twice showed a more significant reduction in proteinuria than TSF extracted three times. Accumulation of autophagic biomarkers p62 and LC3, and aberrant autophagic flux in podocytes of DN mice were significantly altered by TSF therapy. Consistent with the in vivo results, TSF prevented the apoptosis of primary podocytes exposed to AGEs and activated autophagy. However, the anti-apoptosis capacity of TSF was countered by the autophagy-lysosome inhibitor chloroquine. We found that TSF increased the nuclear translocation of TFEB in diabetic podocytes, and thus upregulated transcription of its several autophagic target genes. Pharmacological activation of TFEB by TSF accelerated the conversion of autophagosome to autolysosome and lysosomal biogenesis, further augmented autophagic flux. Conversely, TFEB knockdown negated the favorable effects of TSF on autophagy in AGEs-stimulated primary podocytes.

CONCLUSIONS

These findings indicate TSF appears to attenuate podocyte apoptosis and promote autophagy in DN via the TFEB-mediated autophagy-lysosome system. Thus, TSF may be a therapeutic candidate for DN.

Network pharmacology combined with Mendelian randomization analysis to identify the key targets of renin-angiotensin-aldosterone system inhibitors in the treatment of diabetic nephropathy

Background

Diabetic Nephropathy (DN) is one of the microvascular complications of diabetes. The potential targets of renin-angiotensin-aldosterone system (RAAS) inhibitors for the treatment of DN need to be explored.

Methods

The GSE96804 and GSE1009 datasets, 729 RAAS inhibitors-related targets and 6,039 DN-related genes were derived from the public database and overlapped with the differentially expressed genes (DN vs. normal) in GSE96804 to obtain the candidate targets. Next, key targets were screened via the Mendelian randomization analysis and expression analysis. The diagnostic nomogram was constructed and assessed in GSE96804. Additionally, enrichment analysis was conducted and a 'core active ingredient-key target-disease pathway' network was established. Finally, molecular docking was performed.

Results

In total, 60 candidate targets were derived, in which CTSC and PDE5A were screened as the key targets and had a causal association with DN as the protective factors (P < 0.05, OR < 1). Further, a nomogram exhibited pretty prediction efficiency. It is indicated that Benadryl hydrochloride might play a role in the DN by affecting the pathways of 'cytokine cytokine receptor interaction', etc. targeting the CTSC. Moreover, PDE5A might be involved in 'ECM receptor interaction', etc. for the effect of NSAID, captopril, chlordiazepoxide on DN. Molecular docking analysis showed a good binding ability of benadryl hydrochloride and CTSC, NSAID and PDE5A. PTGS2, ITGA4, and ANPEP are causally associated with acute kidney injury.

Conclusion

CTSC and PDE5A were identified as key targets for RAAS inhibitors in the treatment of DN, which might provide some clinical significance in helping to diagnose and treat DN. Among the targets of RAAS inhibitors, PTGS2, ITGA4 and ANPEP have a causal relationship with acute kidney injury, which is worthy of further clinical research.

A Putative Role for TRPC6 in Immune-Mediated Kidney Injury

Excessive activation of the immune system is the cause of a wide variety of renal diseases. However, the pathogenic mechanisms underlying the aberrant activation of the immune system in the kidneys often remain unknown. TRPC6, a member of the Ca2+-permeant family of TRPC channels, is important in glomerular epithelial cells or podocytes for the process of glomerular filtration. In addition, TRPC6 plays a crucial role in the development of kidney injuries by inducing podocyte injury. However, an increasing number of studies suggest that TRPC6 is also responsible for tightly regulating the immune cell functions. It remains elusive whether the role of TRPC6 in the immune system and the pathogenesis of renal inflammation are intertwined. In this review, we present an overview of the current knowledge of how TRPC6 coordinates the immune cell functions and propose the hypothesis that TRPC6 might play a pivotal role in the development of kidney injury via its role in the immune system.