Drug Targets for Oxidative Podocyte Injury in Diabetic Nephropathy

miR-188-3p abolishes germacrone-mediated podocyte protection in a mouse model of diabetic nephropathy in type I diabetes through triggering mitochondrial injury

Mitochondrial injury-triggered podocyte apoptosis is a major risk factor for diabetic nephropathy (DN). However, the detailed relationship between mitochondrial homeostasis and podocyte apoptosis remains unclear. The present study aimed to explore the role and functional mechanism of germacrone in DN in type I diabetes (type I DN). A mouse model of type I DN was established by injecting streptozocin, and a podocyte injury model was constructed using high glucose (HG) induction. Histopathology was detected by hematoxylin and eosin and periodic acid-Schiff staining. Transmission electron microscopy and flow cytometry were used to evaluate the mitochondrial function. Germacrone simultaneously reduced blood glucose, 24 h proteinuria, and other nephrotic symptoms in a type 1 DN mouse model. Moreover, germacrone protected against mitochondrial damage, limited reactive oxygen species (ROS) accumulation, and restored glutathione peroxidase (GPX) activity and GPX4 protein expression, subsequently preventing podocyte apoptosis. Mechanistically, the increased miR-188-3p expression in type I DN mice was reversed in germacrone-challenged DN mice. HG induced miR-188-3p expression and the miR-188-3p antagonist abolished the HG-mediated increase in ROS. Notably, miR-188-3p was found to have a therapeutic effect against DN by aggravating mitochondrial damage and podocyte apoptosis. Germacrone alleviates DN progression in type I diabetes by limiting podocyte apoptosis, which was partly counteracted by miR-188-3p upregulation. The combination of germacrone and miR-188-3p antagonists is expected to be an effective therapeutic strategy for DN.Abbreviations DN: diabetic nephropathy; Type I DN: DN in Type I diabetes; STZ: streptozocin; ROS: reactive oxygen species; NcRNAs: non-coding RNAs; UTR: untranslated regions; NC: negative control; BUN: blood urea nitrogen; BUA: blood uric acid; Ucr: urine creatinine; Scr: serum creatinine; PAS: Periodic Acid-Schiff; IF: Immunofluorescence; FISH: Fluorescence in situ hybridization; TUG1: taurine upregulated gene 1; GPX: Glutathione Peroxidase; GPX4: glutathione peroxidase 4; EMT: epithelial-mesenchymal transition.

Interplay between extracellular matrix components and cellular and molecular mechanisms in kidney fibrosis

Chronic kidney disease (CKD) is characterized by pathological accumulation of extracellular matrix (ECM) proteins in renal structures. Tubulointerstitial fibrosis is observed in glomerular diseases as well as in the regeneration failure of acute kidney injury (AKI). Therefore, finding antifibrotic therapies comprises an intensive research field in Nephrology. Nowadays, ECM is not only considered as a cellular scaffold, but also exerts important cellular functions. In this review, we describe the cellular and molecular mechanisms involved in kidney fibrosis, paying particular attention to ECM components, profibrotic factors and cell-matrix interactions. In response to kidney damage, activation of glomerular and/or tubular cells may induce aberrant phenotypes characterized by overproduction of proinflammatory and profibrotic factors, and thus contribute to CKD progression. Among ECM components, matricellular proteins can regulate cell-ECM interactions, as well as cellular phenotype changes. Regarding kidney fibrosis, one of the most studied matricellular proteins is cellular communication network-2 (CCN2), also called connective tissue growth factor (CTGF), currently considered as a fibrotic marker and a potential therapeutic target. Integrins connect the ECM proteins to the actin cytoskeleton and several downstream signaling pathways that enable cells to respond to external stimuli in a coordinated manner and maintain optimal tissue stiffness. In kidney fibrosis, there is an increase in ECM deposition, lower ECM degradation and ECM proteins cross-linking, leading to an alteration in the tissue mechanical properties and their responses to injurious stimuli. A better understanding of these complex cellular and molecular events could help us to improve the antifibrotic therapies for CKD.

miR-30a-5p targets Becn1 to ameliorate high-glucose-induced glomerular podocyte injury in immortalized rat podocyte cell line

OBJECTIVE

Diabetic nephropathy (DN) is a serious kidney-based complication of diabetes, wherein podocyte injury is deemed crucial in the development of early stage. Various miRNAs, as report goes, is involved in the pathogenesis of varieties of kidney diseases including DN. In this study, we found a target relationship between miR-30a-5p and Becn1, of which there are few studies about the role in podocyte injury. We therefore used immortalized rat podocyte cell line to explore the role and molecular mechanism of miR-30a-5p targeting Becn1 gene in high-glucose-induced glomerular podocyte injury.

METHODS

The mRNA and protein expressions of miR-30a-5p and Becn1 were detected respectively by quantitative reverse transcriptase PCR and western blotting. The proliferation, apoptosis, and the levels of interleukin (IL)-6 and tumor necrosis factor (TNF)-α were detected by MTT assay, flow cytometry, and enzyme-linked immuno sorbent assay, respectively. Intracellular reactive oxygen species (ROS), superoxide dismutase (SOD) and malondialdehyde (MDA) levels were also determined.

RESULTS

Compared with normal group, miR-30a-5p in model groups were down-regulated, while Becn1 expression was significantly up-regulated, with slower proliferation, higher apoptosis rate, lower SOD level, and significantly higher ROS, MDA, IL-6, and TNF-α levels (all P<0.05). Overexpression of miR-30a-5p or Becn1 knock-out could lower Becn1 expression, apoptosis rate, promote proliferation, with relatively higher SOD level and lower ROS, MDA, Il-6, and TNF-α levels of model cells (all P<0.05).

CONCLUSION

Up-regulation of miR-30a-5p can suppress the expression of Becn1 to increase the growth and inhibit the apoptosis of immortalized rat podocyte cell line, therefore ameliorating podocyte injury induced by high glucose in vitro.

Protective effects of luteolin on nephrotoxicity induced by long-term hyperglycaemia in rats

Objective

This study aimed to investigate whether luteolin delays the progress of diabetic nephropathy (DN) induced by streptozotocin.

Methods

Fifty-three healthy, 8-week-old, male Sprague–Dawley rats were randomly divided into the control (n = 6), model (n = 23), and experimental groups (n = 24). The rat model of diabetic nephropathy was established by intraperitoneal injection of streptozotocin. Rats in the experimental group were administered luteolin suspension of 80 mg/kg daily for 8 weeks. Blood glucose levels and body weight were recorded until the fourth week. After intragastric administration, blood flow and the protective effect of luteolin on diabetic nephropathy were evaluated.

Results

The degree of renal apoptosis and fibrosis in the experimental group was milder, and glomerular structure was more complete compared with the model group. Nphs2 staining suggested that luteolin delayed apoptosis and deletion and fusion of podocytes under high glucose levels, and protected the filtration function of the basement membrane by upregulating Nphs2 protein expression. Time intensity curve results suggested that luteolin delayed deterioration of renal haemodynamics under hyperglycaemia.

Conclusions

This study shows that luteolin delays progression of diabetic nephropathy. This drug has potential wide applicability in future clinical application.

Ligustilide alleviates podocyte injury via suppressing the SIRT1/NF-κB signaling pathways in rats with diabetic nephropathy

Background

Diabetic nephropathy (DN) is one of the common chronic microvascular complications of diabetes, and podocyte injury and dysfunction are strictly related to the pathogenesis of DN. Studies have shown that ligustilide (LIG) has anti-inflammatory, antioxidant, and anti-apoptotic activities. This study was designed to investigate the therapeutic effect of LIG in DN rats and their mechanisms.

Methods

DN rat models (n=10) were induced by streptozotocin (STZ) combined with a high-fat diet. Rats in the LIG group were intragastrically administered with LIG daily for eight weeks, and animals in the positive control group were treated with Losartan potassium. The body weight and blood glucose were checked weekly during the treatment. The pathological changes of kidney tissue were observed with hematoxylin and eosin (HE) staining. Blood lipid profiles and renal function-related markers, including total cholesterol (TC), triglyceride (TG), low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), blood urea nitrogen (BUN), and serum creatinine (Scr) were monitored using a biochemical analyzer. The protein expression of nephrin was determined by immunohistochemistry and Western blotting. Finally, Western blot was used to determine the protein expression of Sirtuin 1 (SIRT1) and nuclear factor-kappa B (NF-κB).

Results

Compared with the healthy control group, rats in the DN group have slower weight gain, increased blood sugar level, renal lesions, and impaired renal function, along with decreased nephrin expression, abnormally activated NF-κB, and inhibited SIRT1 protein expression. All the above conditions were improved after intervention with either losartan potassium or LIG.

Conclusions

LIG attenuates podocyte injury by regulating the SIRT1/NF-κB signaling pathway and thereby exerts its protective effect on renal function in DN rats.

Inhibition of Ceramide Accumulation in Podocytes by Myriocin Prevents Diabetic Nephropathy

BACKGROUND

Ceramides are associated with metabolic complications including diabetic nephropathy in patients with diabetes. Recent studies have reported that podocytes play a pivotal role in the progression of diabetic nephropathy. Also, mitochondrial dysfunction is known to be an early event in podocyte injury. Thus, we tested the hypothesis that ceramide accumulation in podocytes induces mitochondrial damage through reactive oxygen species (ROS) production in patients with diabetic nephropathy.

METHODS

We used Otsuka Long Evans Tokushima Fatty (OLETF) rats and high-fat diet (HFD)-fed mice. We fed the animals either a control- or a myriocin-containing diet to evaluate the effects of the ceramide. Also, we assessed the effects of ceramide on intracellular ROS generation and on podocyte autophagy in cultured podocytes.

RESULTS

OLETF rats and HFD-fed mice showed albuminuria, histologic features of diabetic nephropathy, and podocyte injury, whereas myriocin treatment effectively treated these abnormalities. Cultured podocytes exposed to agents predicted to be risk factors (high glucose, high free fatty acid, and angiotensin II in combination [GFA]) showed an increase in ceramide accumulation and ROS generation in podocyte mitochondria. Pretreatment with myriocin reversed GFA-induced mitochondrial ROS generation and prevented cell death. Myriocin-pretreated cells were protected from GFA-induced disruption of mitochondrial integrity.

CONCLUSION

We showed that mitochondrial ceramide accumulation may result in podocyte damage through ROS production. Therefore, this signaling pathway could become a pharmacological target to abate the development of diabetic kidney disease.

Rosmarinic acid monotherapy is better than the combination of rosmarinic acid and telmisartan in preventing podocyte detachment and inhibiting the progression of diabetic nephropathy in rats

BACKGROUND

Podocyte injury and its subsequent detachment play a critical role in the development and progression of diabetic nephropathy (DN). The objective of this study was to investigate the effect of rosmarinic acid (RA) in preventing podocyte detachment and inhibiting the progression of DN in streptozotocin (STZ)-induced diabetic in rats.

METHODS

We used 20 adult male Wistar rats as experimental animals, which were randomly divided into 5 groups (n=4 per group): nondiabetic rat group (negative control) and 4 groups of STZ-induced diabetic rats, namely, 1 group untreated diabetic rats (positive control) and 3 groups treated diabetic rats with RA 75 mg/kg, telmisartan (TMS) 1 mg/kg and combination of RA 75 mg/kg with TMS 1 mg/kg), respectively. After 8 weeks of therapy, urinary levels of podocin, nephrin and albumin and also serum cystatin C levels were examined by ELISA. The expression of p65 nuclear factor-kB by immunohistochemistry whereas expression of podocin and nephrin glomerulus were examined by immunofluorescence.

RESULTS

In the treated diabetic groups, we found that urinary level of podocin and nephrin, albumin urine excretion and serum cystatin C levels were significantly lower than the positive control group. Compared to negative controls, the group of treated diabetic rats did not differ significantly in preventing increased excretion of urinary nephrin and podocin. Meanwhile, treatment with RA monotherapy was significantly better than TMS or a combination of RA with TMS in reducing albumin excretion and preventing decreased kidney function.

CONCLUSION

In STZ-induced diabetic rats, RA can prevent podocyte detachment. Treatment with RA and TMS either monotherapy or in combination can inhibit the development and progression of DN. However, the combination of both did not show a synergistic effect, even have higher urinary albumin excretion and worse kidney function compared to the RA monotherapy.

Anaerobic Glycolysis Maintains the Glomerular Filtration Barrier Independent of Mitochondrial Metabolism and Dynamics

The cellular responses induced by mitochondrial dysfunction remain elusive. Intrigued by the lack of almost any glomerular phenotype in patients with profound renal ischemia, we comprehensively investigated the primary sources of energy of glomerular podocytes. Combining functional measurements of oxygen consumption rates, glomerular metabolite analysis, and determination of mitochondrial density of podocytes in vivo, we demonstrate that anaerobic glycolysis and fermentation of glucose to lactate represent the key energy source of podocytes. Under physiological conditions, we could detect neither a developmental nor late-onset pathological phenotype in podocytes with impaired mitochondrial biogenesis machinery, defective mitochondrial fusion-fission apparatus, or reduced mtDNA stability and transcription caused by podocyte-specific deletion of Pgc-1α, Drp1, or Tfam, respectively. Anaerobic glycolysis represents the predominant metabolic pathway of podocytes. These findings offer a strategy to therapeutically interfere with the enhanced podocyte metabolism in various progressive kidney diseases, such as diabetic nephropathy or focal segmental glomerulosclerosis (FSGS).

Serotonin and Its Receptor as a New Antioxidant Therapeutic Target for Diabetic Kidney Disease

Diabetic kidney disease (DKD) is a widespread chronic microvascular complication of diabetes mellitus (DM), affects almost 30-50% of patients, and represents a leading cause of death of DM. Serotonin or 5-hydroxytryptamine (5-HT) is a multifunctional bioamine that has crucial roles in many physiological pathways. Recently, emerging evidence from experimental and clinical studies has demonstrated that 5-HT is involved in the pathogenesis of diabetic vascular complications. The 5-HT receptor (5-HTR) antagonists exert renoprotective effects by suppressing oxidative stress, suggesting that 5-HTR can be used as a potential target for treating DKD. In this review, therefore, we summarize the published information available for the involvement of 5-HT and 5-HTR antagonists in the pathogenesis of various diabetic complications with a particular focus of DKD. We conclude that 5-HTR is a potential therapeutic target for treating DKD, as it has been successfully applied in animal models and has currently being investigated in randomized and controlled clinical trials.

Chrysin ameliorates podocyte injury and slit diaphragm protein loss via inhibition of the PERK-eIF2α-ATF-CHOP pathway in diabetic mice

Glomerular epithelial podocytes are highly specialized cells that play a crucial role in maintaining normal function of the glomerular filtration barrier via their foot processes. Chrysin (5,7-dihydroxyflavone) is a natural flavonoid found in propolis and mushrooms that has anti-inflammatory, antioxidant and anticancer properties. This study aimed to evaluate the renoprotective effects of chrysin on podocyte apoptotic loss and slit diaphragm protein deficiency in high glucose-exposed podocytes and in db/db mouse kidneys. Exposure to high glucose (33 mmol/L) caused glomerular podocyte apoptosis in vitro, which was dose-dependently attenuated by nontoxic chrysin (1-20 μmol/L) through reduction of DNA fragmentation. Chrysin treatment dose-dependently restored the increased Bax/Bcl-2 ratio, and suppressed Apaf-1 induction and the elevated cytochrome c release in high glucose-exposed renal podocytes. In diabetic db/db mice, oral administration of chrysin (10 mg·kg^-1·d^-1, for 10 weeks) significantly attenuated proteinuria, and alleviated the abnormal alterations in glomerular ultrastructure, characterized by apoptotic podocytes and foot process effacement. In addition, this compound improved the induction of slit diaphragm proteins podocin/nephrin in the diabetic glomeruli. Exposure to high glucose elevated the unfolded protein response (UPR) to ER stress in renal podocytes, evidenced by up-regulation of PERK-eIF2α-ATF4-CHOP. Chrysin treatment blocked such ER stress responses pertinent to podocyte apoptosis and reduced synthesis of slit diaphragm proteins in vitro and in vivo. These observations demonstrate that targeting ER stress is an underlying mechanism of chrysin-mediated amelioration of diabetes-associated podocyte injury and dysfunction.

Apigenin ameliorates streptozotocin-induced diabetic nephropathy in rats via MAPK-NF-κB-TNF-α and TGF-β1-MAPK-fibronectin pathways

Diabetic nephropathy (DN), a microvascular complication of diabetes, has emerged as an important health problem worldwide. There is strong evidence to suggest that oxidative stress, inflammation, and fibrosis play a pivotal role in the progression of DN. Apigenin has been shown to possess antioxidant, anti-inflammatory, antiapoptotic, antifibrotic, as well as antidiabetic properties. Hence, we evaluated whether apigenin halts the development and progression of DN in streptozotocin (STZ)-induced diabetic rats. Male albino Wistar rats were divided into control, diabetic control, and apigenin treatment groups (5-20 mg/kg po, respectively), apigenin per se (20 mg/kg po), and ramipril treatment group (2 mg/kg po). A single injection of STZ (55 mg/kg ip) was administered to all of the groups except control and per se groups to induce type 1 diabetes mellitus. Rats with fasting blood glucose >250 mg/dl were included in the study and randomized to different groups. Thereafter, the protocol was continued for 8 mo in all of the groups. Apigenin (20 mg/kg) treatment attenuated renal dysfunction, oxidative stress, and fibrosis (decreased transforming growth factor-β1, fibronectin, and type IV collagen) in the diabetic rats. It also significantly prevented MAPK activation, which inhibited inflammation (reduced TNF-α, IL-6, and NF-κB expression) and apoptosis (increased expression of Bcl-2 and decreased Bax and caspase-3). Furthermore, histopathological examination demonstrated reduced inflammation, collagen deposition, and glomerulosclerosis in the renal tissue. In addition, all of these changes were comparable with those produced by ramipril. Hence, apigenin ameliorated renal damage due to DN by suppressing oxidative stress and fibrosis and by inhibiting MAPK pathway.

MiRNA-29c regulates the expression of inflammatory cytokines in diabetic nephropathy by targeting tristetraprolin

Diabetic nephropathy is one of the most prevalent chronic complications of Diabetes mellitus, but its pathogenesis remains elusive. This study was designed to determine the role of tristetraprolin (TTP), inflammatory cytokines and microRNAs (miRNAs) in DN. The blood and urine samples were obtained from 32 patients with DN, 33 patients with type 2 DM, and 35 normal healthy subjects as controls. Renal tissue samples were also obtained from 10 DN patients and 10 normal controls. The miRNA microarray analyses were performed in pooled plasma and urine sediment samples of eight DN patients and eight age- and sex-matched health control subjects and three paired renal tissues from patients with DN and normal controls. Conditionally immortalized mouse podocytes (MPC5) were used a cell model. The expressions of TTP and cytokines in patient samples and cultured cells were determined by qRT-PCR and Western blotting or ELISA. Our results indicated that miRNA-29c directly targeted TTP and promoted inflammatory response under hyperglycemic conditions. Overexpression of miRNA-29c in podocytes resulted in an increase in inflammatory cytokines and inhibition of miRNA-29c by using its inhibitor reduced the inflammatory cytokines in podocytes. Finally, miRNA-29c promoted the progression of DN by targeting TTP, providing a target for a therapeutic intervention of DN.

The Green Tea Polyphenol(-)-epigallocatechin-3-gallate and its beneficial roles in chronic kidney disease

Chronic kidney disease (CKD), a condition that affects around 10% of the population, has become a significant public health concern. Current therapeutic strategies to slow down the progression of CKD remain limited. Thus, it is urgent to develop new strategies to manage the patients with CKD. Work within the past decade has improved our understanding of the mechanisms contributing to CKD. In particular, oxidative stress as well as inflammation appears to play a pivotal role in CKD progression. ()-Epigallocatechin-3-gallate (EGCG), the major catechin of green tea extract, is known as a powerful antioxidant and reactive oxygen species scavenger. Various studies have shown EGCG has a potential role in chronic kidney disease models. It is suggested that EGCG modulates cellular and molecular mechanisms via inflammation-related NF-кB and Nrf2 signaling pathway, as well as apoptosis-related ER stress pathway and mitochondrial pathway. Therefore, based on these studies, this review attempts to present a recent state of our knowledge and understanding of mechanisms of its role on the process of CKD, with the aim of providing some clues for the future optimization of EGCG in renal diseases.