Autophagy in Chronic Kidney Diseases

Inhibiting PKCβ2 protects HK-2 cells against meglumine diatrizoate and AGEs-induced apoptosis and autophagy

Background

Contrast induced diabetic nephropathy (CIN) is an important cause of hospital-acquired acute renal failure. Our aim was to observe the effect of protein kinase C β2 (PKCβ2) knockdown on human proximal tubular epithelial cells (HK-2 cells) against meglumine diatrizoate and advanced glycation end products (AGEs)-induced apoptosis and autophagy.

Methods

Cell viability was detected using cell counting kit-8 (CCK-8) assay in HK-2 cells after disposal with meglumine diatrizoate and AGEs with or without PKCβ2 siRNA/inhibitor LY333531. Flow cytometry and western blot were used to test cell apoptosis and the related protein levels in meglumine diatrizoate and AGEs co-treated HK-2 cells with or without PKCβ2 siRNA/inhibitor LY333531. Autophagy related proteins were detected using western blot. Immunofluorescence staining was used to examine the autophagy-specific protein light chain 3 (LC3), and autophagosome and autolysosome formation was observed under a transmission electron microscopy.

Results

CCK-8 assay results showed that meglumine diatrizoate inhibited AGEs-induced HK-2 cell viability. Furthermore, meglumine diatrizoate promoted cell apoptosis and the expression level of caspase3 in AGEs-induced HK-2. Western blot results showed that meglumine diatrizoate elevated the expression levels of PKCβ2 and p-PKCβ2 in AGEs-induced HK-2 cells, and up-regulated the expression level of Beclin-1 and the ratio of LC3 II/LC3 I, and down-regulated the expression level of p62 in AGEs-induced HK-2 cells. We found that PKCβ2 knockdown alleviated meglumine diatrizoate and AGEs-induced HK-2 cell apoptosis and autophagy. Intriguingly, PKCβ2 inhibitor LY333531 reversed 3-methyladenine (3-MA)-induced autophagy inhibition in meglumine diatrizoate and AGEs-induced HK-2 cells.

Conclusions

Our findings reveal that inhibiting PKCβ2 protects HK-2 cells against meglumine diatrizoate and AGEs-induced apoptosis and autophagy, which provide a novel therapeutic insight for CIN in diabetic patients.

Targeting the progression of chronic kidney disease

Chronic kidney disease (CKD) is a devastating condition that is reaching epidemic levels owing to the increasing prevalence of diabetes mellitus, hypertension and obesity, as well as ageing of the population. Regardless of the underlying aetiology, CKD is slowly progressive and leads to irreversible nephron loss, end-stage renal disease and/or premature death. Factors that contribute to CKD progression include parenchymal cell loss, chronic inflammation, fibrosis and reduced regenerative capacity of the kidney. Current therapies have limited effectiveness and only delay disease progression, underscoring the need to develop novel therapeutic approaches to either stop or reverse progression. Preclinical studies have identified several approaches that reduce fibrosis in experimental models, including targeting cytokines, transcription factors, developmental and signalling pathways and epigenetic modulators, particularly microRNAs. Some of these nephroprotective strategies are now being tested in clinical trials. Lessons learned from the failure of clinical studies of transforming growth factor β1 (TGFβ1) blockade underscore the need for alternative approaches to CKD therapy, as strategies that target a single pathogenic process may result in unexpected negative effects on simultaneously occurring processes. Additional promising avenues include preventing tubular cell injury and anti-fibrotic therapies that target activated myofibroblasts, the main collagen-producing cells.

Metformin alleviates renal injury in diabetic rats by inducing Sirt1/FoxO1 autophagic signal axis

Diabetic nephropathy (DN) is the major microvascular complication of diabetes mellitus and the most important cause of end-stage renal disease worldwide. Metformin is the preferred oral hypoglycaemic drug for type 2 diabetes mellitus (T2DM). Recent studies have shown that besides lowering blood glucose, metformin also has protective effects on renal function, but its mechanism is not clear. In this study, we established a diabetic rat model by high-fat feeding combined with intraperitoneal injection of streptozotocin. Their changes of renal function, oxidative stress, histopathology and structure, and autophagy were observed after 8 weeks of metformin treatment at different dose. Sirt1 inhibitor EX527 and metformin were used to observe whether the protective effect of metformin on DN kidney was achieved through the Sirt1/FoxO1 autophagic signalling pathway. The results showed that metformin could protect renal function by up-regulating autophagy level, alleviating oxidative stress level of renal tissue and pathological and structural changes of glomeruli, and inhibiting the expression of extracellular matrix. Sirt1 inhibitor could block the protective effect of metformin on kidney of diabetic rats, suggesting that metformin could alleviate kidney injury in diabetic rats by inducing Sirt1/FoxO1 autophagy signal axis. So metformin could alleviate renal injury in diabetic rats, which may be achieved by regulating Sirt1/FoxO1 autophagic signalling pathway and inducing renal autophagy.

Berberine for prevention of dementia associated with diabetes and its comorbidities: A systematic review

BACKGROUND

A growing number of epidemiological studies indicate that metabolic syndrome (MetS) and its associated features play a key role in the development of certain degenerative brain disorders, including Alzheimer's disease and vascular dementia. Produced by several different medicinal plants, berberine is a bioactive alkaloid with a wide range of pharmacological effects, including antidiabetic effects. However, it is not clear whether berberine could prevent the development of dementia in association with diabetes.

OBJECTIVE

To give an overview of the therapeutic potential of berberine as a treatment for dementia associated with diabetes.

SEARCH STRATEGY

Database searches A and B were conducted using PubMed and ScienceDirect. In search A, studies on berberine's antidementia activities were identified using "berberine" and "dementia" as search terms. In search B, recent studies on berberine's effects on diabetes were surveyed using "berberine" and "diabetes" as search terms.

INCLUSION CRITERIA

Clinical and preclinical studies that investigated berberine's effects associated with MetS and cognitive dysfunction were included.

DATA EXTRACTION AND ANALYSIS

Data from studies were extracted by one author, and checked by a second; quality assessments were performed independently by two authors.

RESULTS

In search A, 61 articles were identified, and 22 original research articles were selected. In search B, 458 articles were identified, of which 101 were deemed relevant and selected. Three duplicates were removed, and a total of 120 articles were reviewed for this study. The results demonstrate that berberine exerts beneficial effects directly in the brain: enhancing cholinergic neurotransmission, improving cerebral blood flow, protecting neurons from inflammation, limiting hyperphosphorylation of tau and facilitating β-amyloid peptide clearance. In addition, evidence is growing that berberine is effective against diabetes and associated disorders, such as atherosclerosis, cardiomyopathy, hypertension, hepatic steatosis, diabetic nephropathy, gut dysbiosis, retinopathy and neuropathy, suggesting indirect benefits for the prevention of dementia.

CONCLUSION

Berberine could impede the development of dementia via multiple mechanisms: preventing brain damages and enhancing cognition directly in the brain, and indirectly through alleviating risk factors such as metabolic dysfunction, and cardiovascular, kidney and liver diseases. This study provided evidence to support the value of berberine in the prevention of dementia associated with MetS.

Catalpol Ameliorates Podocyte Injury by Stabilizing Cytoskeleton and Enhancing Autophagy in Diabetic Nephropathy

Catalpol, an iridoid glycoside extracted from Rehmannia glutinosa, has been found to ameliorate diabetic nephropathy (DN), but the mechanism has not been clarified. Podocyte injury play a key role in the pathogenesis of DN. This study mainly investigated the protective effect and potential mechanism of catalpol on podocyte injury of DN in vivo and in vitro. The results indicated that the pathological features of DN in mice were markedly ameliorated after treatment with catalpol. Moreover, podocyte foot process effacement, and down-regulation of nephrin and synaptopodin expression in DN mice were also significantly improved after treatment with catalpol. In vitro, catalpol rescued disrupted cytoskeleton and increased migration ratio in podocytes induced by high glucose, the effect might be attributable to the inhibition of RhoA and Cdc42 activities but not Rac1. Furthermore, the impaired podocyte autophagy in DN mice was significantly enhanced after catalpol treatment. And catalpol also enhanced autophagy and lysosome biogenesis in cultured podocytes under high glucose condition. In addition, we found that catalpol could inhibit mTOR activity and promote TFEB nuclear translocation in vivo and in vitro experiments. Our study demonstrated that catalpol could ameliorate podocyte injury in DN, and the protective effect of catalpol might be attributed to the stabilization of podocyte cytoskeleton and the improvement of impaired podocyte autophagy.

Recent Insights into the Mitochondrial Role in Autophagy and Its Regulation by Oxidative Stress

Autophagy is a self-digestive process that degrades intracellular components, including damaged organelles, to maintain energy homeostasis and to cope with cellular stress. Autophagy plays a key role during development and adult tissue homeostasis, and growing evidence indicates that this catalytic process also has a direct role in modulating aging. Although autophagy is essentially protective, depending on the cellular context and stimuli, autophagy outcome can lead to either abnormal cell growth or cell death. The autophagic process requires a tight regulation, with cellular events following distinct stages and governed by a wide molecular machinery. Reactive oxygen species (ROS) have been involved in autophagy regulation through multiple signaling pathways, and mitochondria, the main source of endogenous ROS, have emerged as essential signal transducers that mediate autophagy. In the present review, we aim to summarize the regulatory function of mitochondria in the autophagic process, particularly regarding the mitochondrial role as the coordination node in the autophagy signaling pathway, involving mitochondrial oxidative stress, and their participation as membrane donors in the initial steps of autophagosome assembly.

Autophagy in Kidney Disease

Autophagy is a cellular homeostatic program for the turnover of cellular organelles and proteins, in which double-membraned vesicles (autophagosomes) sequester cytoplasmic cargos, which are subsequently delivered to the lysosome for degradation. Emerging evidence implicates autophagy as an important modulator of human disease. Macroautophagy and selective autophagy (e.g., mitophagy, aggrephagy) can influence cellular processes, including cell death, inflammation, and immune responses, and thereby exert both adaptive and maladaptive roles in disease pathogenesis. Autophagy has been implicated in acute kidney injury, which can arise in response to nephrotoxins, sepsis, and ischemia/reperfusion, and in chronic kidney diseases. The latter includes comorbidities of diabetes and recent evidence for chronic obstructive pulmonary disease-associated kidney injury. Roles of autophagy in polycystic kidney disease and kidney cancer have also been described. Targeting the autophagy pathway may have therapeutic benefit in the treatment of kidney disorders.

Lysophosphatidic Acid Signaling in Diabetic Nephropathy

Lysophosphatidic acid (LPA) is a bioactive phospholipid present in most tissues and body fluids. LPA acts through specific LPA receptors (LPAR1 to LPAR6) coupled with G protein. LPA binds to receptors and activates multiple cellular signaling pathways, subsequently exerting various biological functions, such as cell proliferation, migration, and apoptosis. LPA also induces cell damage through complex overlapping pathways, including the generation of reactive oxygen species, inflammatory cytokines, and fibrosis. Several reports indicate that the LPA–LPAR axis plays an important role in various diseases, including kidney disease, lung fibrosis, and cancer. Diabetic nephropathy (DN) is one of the most common diabetic complications and the main risk factor for chronic kidney diseases, which mostly progress to end-stage renal disease. There is also growing evidence indicating that the LPA–LPAR axis also plays an important role in inducing pathological alterations of cell structure and function in the kidneys. In this review, we will discuss key mediators or signaling pathways activated by LPA and summarize recent research findings associated with DN.