The combination of sirolimus and rosiglitazone produces a renoprotective effect on diabetic kidney disease in rats

Hypoxia-induced long non-coding RNA plasmacytoma variant translocation 1 upregulation aggravates pulmonary arterial smooth muscle cell proliferation by regulating autophagy via miR-186/Srf/Ctgf and miR-26b/Ctgf signaling pathways

BACKGROUND

The lncRNA PVT1 reportedly functions as a competing endogenous RNA (ceRNA) of miR-186 and miR-26b in different tissue types. In this study, we investigated the possible involvement of the miR-186/Srf/Ctgf and miR-26b/Ctgf signaling pathways in the pathogenesis of hypoxia-induced PAH.

METHODS

Expression of PVT1, miR-186, miR-26b, and Srf and Ctgf mRNAs were evaluated by real-time polymerase chain reaction. Protein expression of SRF, CTGF, LC3B-I, LC3B-II, and Beclin-I was evaluated using western blotting. The regulatory relationship between the lncRNA, miRNAs, and target mRNAs was explored using luciferase assays. Immunohistochemistry was used to evaluate the expression of SRF and CTGF in situ. MTT assay was performed to assess the proliferation of PASMCs.

RESULTS

Exposure to hypoxia markedly altered the expression of PVT1, Srf, Ctgf, miR-186, and miR-26b in a rat model. MiR-186 binding sites in the sequences of Srf mRNA and PVT1 were confirmed by luciferase assays, indicating that miR-186 may interact with both PVT1 and Srf mRNA. Additionally, miR-26b binding sites were identified in the sequences of Ctgf mRNA and PVT1, suggesting that miR-26b may interact with both PVT1 and Ctgf mRNA. In line with this, we found that overexpression of PVT1 reduced expression of miR-26b and miR-186 but activated expression of Srf, Ctgf, LC3B-II, and Beclin-I.

CONCLUSIONS

Upregulation of PVT1 by exposure to hypoxia promoted the expression of CTGF, leading to deregulation of autophagy and abnormal proliferation of PASMCs. Dysregulation of the miR-186/Srf/Ctgf and miR-26b/Ctgf signaling pathways may be involved in the pathogenesis of hypoxia-induced PASMCs.

Aqueous Extract and Polysaccharide of Aconiti Lateralis Radix Induce Apoptosis and G0/G1 Phase Cell Cycle Arrest by PI3K/AKT/mTOR Signaling Pathway in Mesangial Cells

Mesangial proliferative glomerulonephritis (MesPGN) is a common renal disease that lacks effective drug intervention. Aconiti Lateralis Radix (Fuzi), a natural Chinese medical herb, is found with significant therapeutic effects on various diseases in the clinic. However, its effects on MesPGN have not been reported. This study is aimed to discuss the therapeutic effects of the aqueous extract of Aconiti Lateralis Radix (ALR) and the polysaccharides of Aconiti Lateralis Radix (PALR) on MesPGN as well as the underlying mechanism. In this study, we, firstly, studied the anti-MesPGN mechanism of ALR and PALR. ALR and PALR inhibit the proliferation of the mesangial cells through the PI3K/AKT/mTOR pathway, induce the G0/G1 phase of block and apoptosis, inhibit the activity of Cyclin E and CDK2, increase the expression of Bax, cleaved caspase-8/caspase-8, and cleaved caspase-3/caspase-3 proteins, and effectively inhibit the growth of the mesangial cells. Overall, our data suggest that ALR and PALR may be potential candidates for MesPGN and that PALR is more effective than ALR.

The Kidney-Related Effects of Polystyrene Microplastics on Human Kidney Proximal Tubular Epithelial Cells HK-2 and Male C57BL/6 Mice

BACKGROUND

Understanding the epidemic of chronic kidney disease of uncertain etiology may be critical for health policies and public health responses. Recent studies have shown that microplastics (MPs) contaminate our food chain and accumulate in the gut, liver, kidney, muscle, and so on. Humans manufacture many plastics-related products. Previous studies have indicated that particles of these products have several effects on the gut and liver. Polystyrene (PS)-MPs (PS-MPs) induce several responses, such as oxidative stress, and affect living organisms.

OBJECTIVES

The aim of this study was to investigate the effects of PS-MPs in kidney cells in vitro and in vivo.

METHODS

PS-MPs were evaluated in human kidney proximal tubular epithelial cells (HK-2 cells) and male C57BL/6 mice. Mitochondrial reactive oxygen species (ROS), endoplasmic reticulum (ER) stress, inflammation, and autophagy were analyzed in kidney cells. In vivo, we evaluated biomarkers of kidney function, kidney ultrastructure, muscle mass, and grip strength, and urine protein levels, as well as the accumulation of PS-MPs in the kidney tissue.

RESULTS

Uptake of PS-MPs at different concentrations by HK-2 cells resulted in higher levels of mitochondrial ROS and the mitochondrial protein Bad. Cells exposed to PS-MPs had higher ER stress and markers of inflammation. MitoTEMPO, which is a mitochondrial ROS antioxidant, mitigated the higher levels of mitochondrial ROS, Bad, ER stress, and specific autophagy-related proteins seen with PS-MP exposure. Furthermore, cells exposed to PS-MPs had higher protein levels of LC3 and Beclin 1. PS-MPs also had changes in phosphorylation of mitogen-activated protein kinase (MAPK) and protein kinase B (AKT)/mitogen-activated protein kinase (mTOR) signaling pathways. In an in vivo study, PS-MPs accumulated and the treated mice had more histopathological lesions in the kidneys and higher levels of ER stress, inflammatory markers, and autophagy-related proteins in the kidneys after PS-MPs treatment by oral gavage.

CONCLUSIONS

The results suggest that PS-MPs caused mitochondrial dysfunction, ER stress, inflammation, and autophagy in kidney cells and accumulated in HK-2 cells and in the kidneys of mice. These results suggest that long-term PS-MPs exposure may be a risk factor for kidney health. https://doi.org/10.1289/EHP7612.

ICAT acts as a Coactivator in Regulating PPARγ Transcriptional Activity in Mesangial Cells

AIMS

Our study aims to explore the role of β-catenin interaction protein-1(ICAT) in regulating peroxisome proliferator-activated receptor γ (PPARγ) transcriptional activity in mesangial cells. The abnormal ICAT expression in mesangial cells under high glucose(HG) contributes to the development of diabetes and its complications such as diabetic nephropathy (DN).

METHODS

Human mesangial cells (HMCs) were cultured in either 5.5 (normal control) or 30 (high glucose) mmol/L glucose medium. Overexpression and knock-down of ICAT or β-catenin were carried out by transient transfection. PPARγ transcriptional activity was evaluated by luciferase assay. Protein-protein interactions were tested by Coimmunoprecipitation and GST-pull down assay. Cell phenotype transition of HMCs was detected by the expression level of α-SMA and fibronectin, as well as MTT assay.

RESULTS

High β-catenin protein expression but low ICAT was accompanied by low PPARγ transcriptional activity in HMCs cultured in HG. By using bioinformatics prediction, protein-protein and protein-DNA interaction experimental methods, ICAT and β-catenin were confirmed to act as coactivators in regulating PPARγ transcriptional activity. Overexpression of ICAT could mitigate the decrease of PPARγ transcriptional activity and partly relieve cell phenotype transition in HMCs.

CONCLUSIONS

β-catenin and ICAT interact as coactivator to modulate PPARγ transcriptional activation. In HMCs cultured in HG, the low expression of ICAT leads to low PPARγ transcriptional activation.

Rapamycin for longevity: opinion article

From the dawn of civilization, humanity has dreamed of immortality. So why didn't the discovery of the anti-aging properties of mTOR inhibitors change the world forever? I will discuss several reasons, including fear of the actual and fictional side effects of rapamycin, everolimus and other clinically-approved drugs, arguing that no real side effects preclude their use as anti-aging drugs today. Furthermore, the alternative to the reversible (and avoidable) side effects of rapamycin/everolimus are the irreversible (and inevitable) effects of aging: cancer, stroke, infarction, blindness and premature death. I will also discuss why it is more dangerous not to use anti-aging drugs than to use them and how rapamycin-based drug combinations have already been implemented for potential life extension in humans. If you read this article from the very beginning to its end, you may realize that the time is now.

Fasting and rapamycin: diabetes versus benevolent glucose intolerance

Rapamycin (Sirolimus) slows aging, extends life span, and prevents age-related diseases, including diabetic complications such as retinopathy. Puzzlingly, rapamycin can induce insulin sensitivity, but may also induce insulin resistance or glucose intolerance without insulin resistance. This mirrors the effect of fasting and very low calorie diets, which improve insulin sensitivity and reverse type 2 diabetes, but also can cause a form of glucose intolerance known as benevolent pseudo-diabetes. There is no indication that starvation (benevolent) pseudo-diabetes is detrimental. By contrast, it is associated with better health and life extension. In transplant patients, a weak association between rapamycin/everolimus use and hyperglycemia is mostly due to a drug interaction with calcineurin inhibitors. When it occurs in cancer patients, the hyperglycemia is mild and reversible. No hyperglycemic effects of rapamycin/everolimus have been detected in healthy people. For antiaging purposes, rapamycin/everolimus can be administrated intermittently (e.g., once a week) in combination with intermittent carbohydrate restriction, physical exercise, and metformin.

The mystery of the ketogenic diet: benevolent pseudo-diabetes

Designed a century ago to treat epilepsy, the ketogenic diet (KD) is also effective against obesity and diabetes. Paradoxically, some studies in rodents have found that the KD seemingly causes diabetes, contradicting solid clinical data in humans. This paradox can be resolved by applying the concept of starvation pseudo-diabetes, which was discovered in starved animals almost two centuries ago, and has also been observed in some rapamycin-treated rodents. Intriguingly, use of the KD and rapamycin is indicated for a similar spectrum of diseases, including Alzheimer's disease and cancer. Even more intriguingly, benevolent (starvation) pseudo-diabetes may counteract type 2 diabetes or its complications.

Deregulated MTOR (mechanistic target of rapamycin kinase) is responsible for autophagy defects exacerbating kidney stone development

Kidney stone disease is a lifestyle-related disease prevalent in developed countries; however, effective medical treatment for the disease is not yet well established. As cellular damage in renal tubular cells (RTCs) is responsible for the disease, here, we focused on the role of macroautophagy/autophagy in RTCs. We found that autophagic activity was significantly decreased in mouse RTCs exposed to calcium oxalate (CaOx) monohydrate crystals and in the kidneys of GFP-conjugated MAP1LC3B (microtubule- associated protein 1 light chain 3 beta) transgenic mice with CaOx nephrocalcinosis induced by glyoxylate. This caused accumulation of damaged intracellular organelles, such as mitochondria and lysosomes, the normal functioning of which is mediated by functional autophagy. An impairment of autophagy was also observed in the mucosa with plaques of CaOx kidney stone formers. We determined that the decrease in autophagy was caused by an upregulation of MTOR (mechanistic target of rapamycin kinase), which consequently resulted in the suppression of the upstream autophagy regulator TFEB (transcription factor EB). Furthermore, we showed that an MTOR inhibitor could recover a decrease in autophagy and alleviate crystal-cell interactions and the formation of crystals associated with increased inflammatory responses. Taken together, we conclude that autophagy compromised by MTOR deregulation is a fundamental feature in the pathology of kidney stone formation, and propose that chemical inhibition of MTOR could be a prospective strategy for disease suppression.Abbreviations: ACTB: actin, beta; CaOx: calcium oxalate; CKD: chronic kidney disease; COM: calcium oxalate monohydrate; LGALS3/galectin-3: lectin, galactose binding, soluble 3; GFP: green fluorescent protein; GOX: glyoxylate; HE: hematoxylin and eosin; MAPLC3B: microtubule- associated protein 1 light chain 3 beta; MTOR: mechanistic target of rapamycin kinase; NAC: N-acetyl-L-cysteine; ROS: reactive oxygen species; RTC: renal tubular cell; SQSTM1/p62: sequestosome 1; TFEB: transcription factor EB; TEM: transmission electron microscopy; tfLC3: tandem fluorescent-tagged LC3; 3-MA: 3-methyladenine.

Induction of Fibrosis and Autophagy in Kidney Cells by Vinyl Chloride

Vinyl chloride (VC) is a noninfective occupational risk factor. It is found in industrial chemicals, volatile organic compounds, cigarette smoke ingredients, etc. It is a kind of toxic gas that causes many diseases. VC exposure causes an increased risk of liver fibrosis and can result in angiosarcoma of the liver. Previous studies have shown that high-doses of VC exposure in mice resulted in acute death with marked tubular necrosis of the renal cortex. In this study, we assessed the nephrotoxicity of VC in vitro and in vivo. As a result, we demonstrated that VC induced fibrosis-associated protein expression, such as connective tissue growth factor (CTGF), plasminogen activator inhibitor-1 (PAI-1) and collagen 1, and autophagy-associated protein expression, such as Beclin 1 and LC3-II, in kidney cells. The beclin1 siRNA experiments found that autophagy inhibited VC-induced fibrosis. Blood urea nitrogen (BUN) and creatinine levels were increased after VC treatment. Furthermore, VC caused glomerulosclerosis and tubular injury in mouse kidney tissues. Kidney tissue sections showed that VC induced fibrosis and autophagy in mouse kidney tissues. In summary, the results of VC-induced fibrosis suggest that autophagy plays an important role in kidney damage. VC may cause nephrotoxicity, and the results illustrate the importance of considering the toxicological hazards of VC in kidney cells.

Roles of Identified Long Noncoding RNA in Diabetic Nephropathy

Diabetes mellitus is the leading chronic disease in the world, and diabetic nephropathy (DN) as one of its complications could increase the mortality. The development of DN is associated to abnormal hemodynamic factors like cytokine networks and the intervention of metabolic risk factors like blood pressure, blood glucose, and blood lipid. However, the pathogenesis of DN is still poorly understood. Although glucose-lowering drugs and insulins have significant effects on blood glucose, the fluctuation of blood glucose or other risk factors could continuously damage the kidney. Recent studies reported that the progression of DN is closely related to the expression of long noncoding RNA (lncRNA), which is important for the early diagnosis and targeted intervention of DN. In this review, we briefly summarize the published studies on the functions and potential mechanism of reported lncRNA in the regulation of DN.

The Role of MicroRNAs in the Pathogenesis of Diabetic Nephropathy

Diabetic nephropathy (DN) is one of the most common microvascular complications in diabetic patients; it is also an important cause of renal dysfunction, renal fibrosis, and end-stage renal disease. Unfortunately, the pathogenesis of DN is complex and has not yet been fully elucidated; hence, the pathogenesis of DN to determine effective treatments of crucial importance is deeply explored. Early DN research focuses on hemodynamic changes and metabolic disorders, and recent studies have shown the regulatory role of microRNAs (miRNAs) in genes, which may be a new diagnostic marker and therapeutic target for diabetic nephropathy. In this review, we summarize the recent advances in the clinical value and molecular mechanisms of miRNAs in DN, providing new ideas for the diagnosis and treatment of DN.

Long noncoding RNA TUG1 alleviates extracellular matrix accumulation via mediating microRNA-377 targeting of PPARγ in diabetic nephropathy

Long noncoding RNA taurine-upregulated gene 1 (lncRNA TUG1) has been reported to play a key role in the progression of diabetic nephropathy (DN). However, the role of lncRNA TUG1 in the regulation of diabetic nephropathy remains largely unknown. The aim of the present study is to identify the regulation of lncRNA TUG1 on extracellular matrix accumulation via mediating microRNA-377 targeting of PPARγ, and investigate the underlying mechanisms in progression of DN. Microarray was performed to screen differentially expressed miRNAs in db/db DN mice. Afterwards, computational prediction programs (TargetScan, miRanda, PicTar and miRGen) was applied to predict the target gene of miRNAs. The complementary binding of miRNA and lncRNA was assessed by luciferase assays. Protein and mRNA expression were detected by western blot and real time quantitate PCR. MiRNA-377 was screened by miRNA microarray and differentially up-regulated in db/db DN mice. PPARγ was predicted to be the target of miR-377 and the prediction was verified by luciferase assays. Expression of miR-377 was up-regulated in mesangial cell treated with high glucose (25 mM), and overexpression of miR-377 inhibited PPARγ expression and promoted PAI-1 and TGF-β1 expression. The expression of TUG1 antagonized the effect of miR-377 on the downregulation of its target PPARγ and inhibited extracellular matrix accumulation, including PAI-1, TGF-β1, fibronectin (FN) and collagen IV (Col IV), induced by high glucose. LncRNA TUG1 acts as an endogenous sponge of miR-377 and downregulates miR-377 expression levels, and thereby relieving the inhibition of its target gene PPARγ and alleviates extracellular matrix accumulation of mesangial cells, which provides a novel insight of diabetic nephropathy pathogenesis.

Insights into the Mechanisms Involved in the Expression and Regulation of Extracellular Matrix Proteins in Diabetic Nephropathy

Diabetic Nephropathy (DN) is believed to be a major microvascular complication of diabetes. The hallmark of DN includes deposition of Extracellular Matrix (ECM) proteins, such as, collagen, laminin and fibronectin in the mesangium and renal tubulo-interstitium of the glomerulus and basement membranes. Such an increased expression of ECM leads to glomerular and tubular basement membranes thickening and increase of mesangial matrix, ultimately resulting in glomerulosclerosis and tubulointerstitial fibrosis. The characteristic morphologic glomerular mesangial lesion has been described as Kimmelstiel-Wilson nodule, and the process at times is referred to as diabetic nodular glomerulosclerosis. Thus, the accumulation of ECM proteins plays a critical role in the development of DN. The relevant mechanism(s) involved in the increased ECM expression and their regulation in the kidney in diabetic state has been extensively investigated and documented in the literature. Nevertheless, there are certain other mechanisms that may yet be conclusively defined. Recent studies demonstrated that some of the new signaling pathways or molecules including, Notch, Wnt, mTOR, TLRs and small GTPase may play a pivotal role in the modulation of ECM regulation and expression in DN. Such modulation could be operational for instance Notch through Notch1/Jagged1 signaling, Wnt by Wnt/β- catenin pathway and mTOR via PI3-K/Akt/mTOR signaling pathways. All these pathways may be critical in the modulation of ECM expression and tubulo-interstitial fibrosis. In addition, TLRs, mainly the TLR2 and TLR4, by TLR2- dependent and TGF-β-dependent conduits, may modulate ECM expression and generate a fibrogenic response. Small GTPase like Rho, Ras and Rab family by targeting relevant genes may also influence the accumulation of ECM proteins and renal fibrosis in hyperglycemic states. This review summarizes the recent information about the role and mechanisms by which these molecules and signaling pathways regulate ECM synthesis and its expression in high glucose ambience in vitro and in vivo states. The understanding of such signaling pathways and the molecules that influence expression, secretion and amassing of ECM may aid in developing strategies for the amelioration of diabetic nephropathy.

Autophagy in kidney health and disease

SIGNIFICANCE

Autophagy is emerging as an important pathway in many biological processes and diseases. This review summarizes the current progress on the role of autophagy in renal physiology and pathology.

RECENT ADVANCES

Studies from renal cells in culture, human kidney tissues, and experimental animal models implicate that autophagy regulates many critical aspects of normal and disease conditions in the kidney, such as diabetic nephropathy and other glomerular diseases, tubular injuries, kidney development and aging, cancer, and genetic diseases associated with the kidney.

CRITICAL ISSUES

The importance of autophagy in the kidney has just started to be elucidated. How the process of autophagy is altered in the pathogenesis of kidney diseases and how this alteration is beneficial or detrimental to kidney functions still need to be fully understood.

FUTURE DIRECTIONS

Investigations that uncover the precise mechanism and regulation of autophagy in various kidney diseases may lead to new strategies for therapeutic modulation.

20-HETE and EETs in diabetic nephropathy: a novel mechanistic pathway

Diabetic nephropathy (DN), a major complication of diabetes, is characterized by hypertrophy, extracellular matrix accumulation, fibrosis and proteinuria leading to loss of renal function. Hypertrophy is a major factor inducing proximal tubular epithelial cells injury. However, the mechanisms leading to tubular injury is not well defined. In our study, we show that exposure of rats proximal tubular epithelial cells to high glucose (HG) resulted in increased extracellular matrix accumulation and hypertrophy. HG treatment increased ROS production and was associated with alteration in CYPs 4A and 2C11 expression concomitant with alteration in 20-HETE and EETs formation. HG-induced tubular injury were blocked by HET0016, an inhibitor of CYPs 4A. In contrast, inhibition of EETs promoted the effects of HG on cultured proximal tubular cells. Our results also show that alteration in CYPs 4A and 2C expression and 20HETE and EETs formation regulates the activation of the mTOR/p70S6Kinase pathway, known to play a major role in the development of DN. In conclusion, we show that hyperglycemia in diabetes has a significant effect on the expression of Arachidonic Acid (AA)-metabolizing CYPs, manifested by increased AA metabolism, and might thus alter kidney function through alteration of type and amount of AA metabolites.

Mammalian target of rapamycin regulates Nox4-mediated podocyte depletion in diabetic renal injury

Podocyte apoptosis is a critical mechanism for excessive loss of urinary albumin that eventuates in kidney fibrosis. Pharmacological doses of the mammalian target of rapamycin (mTOR) inhibitor rapamycin reduce albuminuria in diabetes. We explored the hypothesis that mTOR mediates podocyte injury in diabetes. High glucose (HG) induces apoptosis of podocytes, inhibits AMP-activated protein kinase (AMPK) activation, inactivates tuberin, and activates mTOR. HG also increases the levels of Nox4 and Nox1 and NADPH oxidase activity. Inhibition of mTOR by low-dose rapamycin decreases HG-induced Nox4 and Nox1, NADPH oxidase activity, and podocyte apoptosis. Inhibition of mTOR had no effect on AMPK or tuberin phosphorylation, indicating that mTOR is downstream of these signaling molecules. In isolated glomeruli of OVE26 mice, there is a similar decrease in the activation of AMPK and tuberin and activation of mTOR with increase in Nox4 and NADPH oxidase activity. Inhibition of mTOR by a small dose of rapamycin reduces podocyte apoptosis and attenuates glomerular injury and albuminuria. Our data provide evidence for a novel function of mTOR in Nox4-derived reactive oxygen species generation and podocyte apoptosis that contributes to urinary albumin excretion in type 1 diabetes. Thus, mTOR and/or NADPH oxidase inhibition may represent a therapeutic modality of diabetic kidney disease.

Molecular mechanisms in the pathogenesis of diabetic nephropathy: an update

Diabetes mellitus is known to trigger retinopathy, neuropathy and nephropathy. Diabetic nephropathy, a long-term major microvascular complication of uncontrolled hyperglycemia, affects a large population worldwide. Recent findings suggest that numerous pathways are activated during the course of diabetes mellitus and that these pathways individually or collectively play a role in the induction and progression of diabetic nephropathy. However, clinical strategies targeting these pathways to manage diabetic nephropathy remain unsatisfactory, as the number of diabetic patients with nephropathy is increasing yearly. To develop ground-breaking therapeutic options to prevent the development and progression of diabetic nephropathy, a comprehensive understanding of the molecular mechanisms involved in the pathogenesis of the disease is mandatory. Therefore, the purpose of this paper is to discuss the underlying mechanisms and downstream pathways involved in the pathogenesis of diabetic nephropathy.

PPARγ as a therapeutic target in diabetic nephropathy and other renal diseases

PURPOSE OF REVIEW

Peroxisome proliferator-activated receptor gamma (PPARγ) is a ligand-activated nuclear transcription factor that regulates many important physiological processes including glucose and lipid metabolism, energy homeostasis, cell proliferation, inflammation, immunity and reproduction. The current review aims to summarize and discuss recent findings evaluating the protective effects of PPARγ against kidney diseases with a focus on diabetic nephropathy. We will also delineate the potential underlying mechanisms.

RECENT FINDINGS

PPARγ plays important roles in renal physiology and pathophysiology. Agonists of PPARγ exert protective effects against various kidney diseases including diabetic nephropathy, ischemic renal injury, IgA nephropathy, chemotherapy-associated kidney damage, polycystic kidney diseases and age-related kidney diseases via both systemic and renal actions.

SUMMARY

PPARγ agonists are effective in delaying and even preventing the progression of many renal diseases, especially diabetic nephropathy. PPARγ may represent a promising target for the treatment of renal diseases.