Sphingosine kinase 1 mediates AGEs-induced fibronectin upregulation in diabetic nephropathy

The contribution of the sphingosine 1-phosphate signaling pathway to chronic kidney diseases: recent findings and new perspectives

Chronic kidney disease (CKD) is a multifactorial condition with diverse etiologies, such as diabetes mellitus, hypertension, and genetic disorders, often culminating in end-stage renal disease (ESRD). A hallmark of CKD progression is kidney fibrosis, characterized by the excessive accumulation of extracellular matrix components, for which there is currently no effective anti-fibrotic therapy. Recent literature highlights the critical role of sphingosine 1-phosphate (S1P) signaling in CKD pathogenesis and renal fibrosis. This review provides an in-depth analysis of the latest findings on S1P metabolism and signaling in renal fibrosis and in specific CKDs, including diabetic nephropathy (DN), lupus nephritis (LN), focal segmental glomerulosclerosis (FSGS), Fabry disease (FD), and IgA nephropathy (IgAN). Emerging studies underscore the therapeutic potential of modulating S1P signaling with receptor modulators and inhibitors, such as fingolimod (FTY720) and more selective agents like ozanimod and cenerimod. Additionally, the current knowledge about the effects of established kidney protective therapies such as glucocorticoids and SGLT2 and ACE inhibitors on S1P signaling will be summarized. Furthermore, the review highlights the potential role of S1P as a biomarker for disease progression in CKD models, particularly in Fabry disease and diabetic nephropathy. Advanced technologies, including spatial transcriptomics, are further refining our understanding of S1P's role within specific kidney compartments. Collectively, these insights emphasize the need for continued research into S1P signaling pathways as promising targets for CKD treatment strategies.

Dihydromyricetin ameliorates diabetic renal fibrosis via regulating SphK1 to suppress the activation of NF-κB pathway

Dihydromyricetin (DHM) is a flavonoid from vine tea with broad pharmacological benefits, which improve inflammation by blocking the NF-κB pathway. A growing body of research indicates that chronic kidney inflammation is vital to the pathogenesis of diabetic renal fibrosis. Sphingosine kinase-1 (SphK1) is a key regulator of diabetic renal inflammation, which triggers the NF-κB pathway. Hence, we evaluated whether DHM regulates diabetic renal inflammatory fibrosis by acting on SphK1. Here, we demonstrated that DHM effectively suppressed the synthesis of fibrotic and inflammatory adhesion factors like ICAM-1, and VCAM-1 in streptozotocin-treated high-fat diet-induced diabetic mice and HG-induced glomerular mesangial cells (GMCs). Moreover, DHM significantly suppressed NF-κB pathway activation and reduced SphK1 activity and protein expression under diabetic conditions. Mechanistically, the results of molecular docking, molecular dynamics simulation, and cellular thermal shift assay revealed that DHM stably bound to the binding pocket of SphK1, thereby reducing sphingosine-1-phosphate content and SphK1 enzymatic activity, which ultimately inhibited NF-κB DNA binding, transcriptional activity, and nuclear translocation. In conclusion, our data suggested that DHM inhibited SphK1 phosphorylation to prevent NF-κB activation thus ameliorating diabetic renal fibrosis. This supported the clinical use and further drug development of DHM as a potential candidate for treating diabetic renal fibrosis.

Decoding the role of aldosterone in glycation-induced diabetic complications

Diabetes-mediated development of micro and macro-vascular complications is a global concern. One of the factors is hyperglycemia induced the non-enzymatic formation of advanced glycation end products (AGEs). Accumulated AGEs bind with receptor of AGEs (RAGE) causing inflammation, oxidative stress and extracellular matrix proteins (ECM) modifications responsible for fibrosis, cell damage and tissue remodeling. Moreover, during hyperglycemia, aldosterone (Aldo) secretion increases, and its interaction with mineralocorticoid receptor (MR) through genomic and non-genomic pathways leads to inflammation and fibrosis. Extensive research on individual involvement of AGEs-RAGE and Aldo-MR pathways in the development of diabetic nephropathy (DN), cardiovascular diseases (CVDs), and impaired immune system has led to the discovery of therapeutic drugs. Despite mutual repercussions, the cross-talk between AGEs-RAGE and Aldo-MR pathways remains unresolved. Hence, this review focuses on the possible interaction of Aldo and glycation in DN and CVDs, considering the clinical significance of mutual molecular targets.

Farnesoid X receptor prevents neutrophil extracellular traps via reduced sphingosine-1-phosphate in chronic kidney disease

Farnesoid X receptor (FXR) activation reduces renal inflammation, but the underlying mechanisms remain elusive. Neutrophil extracellular traps (NETs) are webs of DNA formed when neutrophils undergo specialized programmed cell death (NETosis). The signaling lipid sphingosine-1-phosphate (S1P) stimulates NETosis via its receptor on neutrophils. Here, we identify FXR as a negative regulator of NETosis via repressing S1P signaling. We determined the effects of the FXR agonist obeticholic acid (OCA) in mouse models of adenosine phosphoribosyltransferase (APRT) deficiency and Alport syndrome, both genetic disorders that cause chronic kidney disease. Renal FXR activity is greatly reduced in both models, and FXR agonism reduces disease severity. Renal NETosis and sphingosine kinase 1 (Sphk1) expression are increased in diseased mice, and they are reduced by OCA in both models. Genetic deletion of FXR increases Sphk1 expression, and Sphk1 expression correlates with NETosis. Importantly, kidney S1P levels in Alport mice are two-fold higher than controls, and FXR agonism restores them back to baseline. Short-term inhibition of sphingosine synthesis in Alport mice with severe kidney disease reverses NETosis, establishing a causal relationship between S1P signaling and renal NETosis. Finally, extensive NETosis is present in human Alport kidney biopsies (six male, nine female), and NETosis severity correlates with clinical markers of kidney disease. This suggests the potential clinical relevance of the newly identified FXR-S1P-NETosis pathway. In summary, FXR agonism represses kidney Sphk1 expression. This inhibits renal S1P signaling, thereby reducing neutrophilic inflammation and NETosis.NEW & NOTEWORTHY Many preclinical studies have shown that the farnesoid X receptor (FXR) reduces renal inflammation, but the mechanism is poorly understood. This report identifies FXR as a novel regulator of neutrophilic inflammation and NETosis via the inhibition of sphingosine-1-phosphate signaling. Additionally, NETosis severity in human Alport kidney biopsies correlates with clinical markers of kidney disease. A better understanding of this signaling axis may lead to novel treatments that prevent renal inflammation and chronic kidney disease.

A Novel Circ_Arf3/miR-452-5p/Mbnl1 Axis Regulates Proliferation and Expression of Fibrosis-Related Proteins of Mouse Mesangial Cells Under High Glucose

Background

Diabetic nephropathy (DN) is a serious microvascular complication of diabetes that may lead to chronic renal failure and end-stage renal disease. Circular RNAs (circRNAs) play important roles in DN progression. However, the action of circRNA ADP ribosylation factor 3 (circ_Arf3) in high glucose (HG)-induced change is still unclear.

Methods

Mouse mesangial cells (MCs) were treated with 30 mM HG as a DN cell model in vitro. Quantitative real-time polymerase chain reaction (qRT-PCR) was employed to examine the expression levels of circ_Arf3, microRNA (miR)-452-5p and muscleblind like splicing regulator 1 (Mbnl1). The proliferation of HG-treated MCs was assessed using 5 Ethynyl 2' deoxyuridine (EdU) and cell counting kit-8 (CCK-8) assays, and the levels of proliferation and fibrosis-related proteins and Mbnl1 were detected by Western blot. Dual-luciferase reporter and RNA pull-down assays were utilized to determine the relationship between miR-452-5p and circ_Arf3 or Mbnl1.

Results

Our results discovered that circ_Arf3 and Mbnl1 were lowly expressed in HG-treated MCs, while miR-452-5p expression was up-regulated. Moreover, circ_Arf3 was mainly located in the cytoplasm and had a ring-like stable structure. Functional assays demonstrated that overexpression of circ_Arf3 prevented cell proliferation and fibrous formation in HG-treated MCs. Circ_Arf3 could sponge miR-452-5p, and the effect of circ_Arf3 overexpression was reversed by enhanced expression of miR-452-5p. Mbnl1 was a direct target of miR-452-5p. Knockdown of Mbnl1 abolished the suppressive effects of miR-452-5p inhibitor on proliferation and fibrosis-related protein expression in HG-treated MCs. Moreover, circ_Arf3 regulated Mbnl1 through miR-452-5p.

Conclusion

Overexpression of circ_Arf3 prevents cell proliferation and fibrous formation in HG-treated MCs by regulating the expression of Mbnl1 via miR-452-5p.

Identifying the mechanisms and molecular targets of Hongjingtian injection on treatment of TGFβ1-induced HK-2 cells: coupling network pharmacology with experimental verification

Background

The study was designed to investigate the mechanism of Hongjingtian injection (HJT) in treating tubulointerstitial fibrosis (TIF) in chronic kidney diseases (CKD) based on network pharmacology and experimental verification.

Methods

First, active ingredients of HJT obtained from literature were screened using the Traditional Chinese Medicine Systems Pharmacology (TCMSP) database and putative targets of active ingredients were predicted using the Chemmapper, SEA and Swiss Target Prediction database. Subsequently, the "compound-target" network for HJT was established. In addition, TIF disease targets were obtained from the GEO gene chips (accession number GSE20247). The intersecting targets of HJT and TIF obtained through Venny 2.1.0. The key targets and signaling pathways were determined by protein-protein interaction (PPI) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis. Finally, quantitative polymerase chain reaction (qPCR) and Western blot (WB) were used to validate the predicted five key genes targets (GAD1, SPHK1, P4HA2, AKR1B1, PTGES). And immunofluorescence, wound healing assay and transwell assay were used to verify the anti-fibrosis effect of HJT on TGFβ1-induced HK-2 cells.

Results

The network pharmacology analysis results showed that there are 36 active compounds and 1,044 putative target genes in HJT. HJT may exert its inhibitory effects against TIF by acting on 79 key targets. Besides, KEGG analysis indicated that the anti-TIF effect of HJT was mediated by multiple pathways, such as the metabolic pathway, pathways in cancer and gap junction. Among them, GAD1, SPHK1, P4HA2, AKR1B1 and PTGES are enriched in the metabolic pathway. In vitro induced cell model experiments, the immunofluorescence experience showed that HJT could restore EMT of HK-2 cells. In addition, the qPCR and WB results showed that HJT significantly restored the expression of the SPHK1 in HK-2 cells induced by TGF-β1.

Conclusions

This study comprehensively illuminated the active compounds, potential targets, and molecular mechanism of HJT against TIF. HJT treatment of TIF may reverse EMT caused by TGF-β1 by targeting SPHK1.

Circular ribonucleic acid nucleoporin 98 knockdown alleviates high glucose-induced proliferation, fibrosis, inflammation and oxidative stress in human glomerular mesangial cells by regulating the microribonucleic acid-151-3p-high mobility group AT-hook 2 axis

AIMS/INTRODUCTION

This study aimed to investigate the role and mechanism of circular ribonucleic acid nucleoporin 98 (circNUP98) in diabetic nephropathy (DN).

MATERIALS AND METHODS

Human glomerular mesangial cells (HMCs) were stimulated with high glucose (HG) to imitate the growth environment of cells under the DN condition. Levels of genes and proteins were tested by quantitative reverse transcription polymerase chain reaction and western blot. Cell proliferation, apoptosis and inflammatory response were analyzed by using cell counting kit-8, flow cytometry and enzyme-linked immunosorbent assay analysis, respectively. Oxidative stress and fibrosis were evaluated by detecting the activity of reactive oxygen species, malondialdehyde, superoxide dismutase, fibronectin and collagen IV. The binding interaction between microribonucleic acid (miR)-151-3p and high mobility group AT-hook 2 (HMGA2) or circNUP98 was confirmed using dual-luciferase reporter, pull-down and ribonucleic acid immunoprecipitation assays. Exosomes were isolated by ultracentrifugation, and qualified by transmission electron microscopy, nanoparticle tracking analysis and western blot.

RESULTS

CircNUP98 expression was higher in the serum of DN patients and HG-stimulated HMCs. Functionally, circNUP98 knockdown alleviated HG-induced proliferation, fibrosis, inflammatory response and oxidative stress in HMCs. Mechanistically, circNUP98 directly sponged miR-151-3p, which targeted HMGA2. Rescue experiments showed that miR-151-3p reversed the inhibitory effects of circNUP98 knockdown on HG-induced HMC dysfunction. Furthermore, miR-151-3p re-expression also led to an inhibition of the aforementioned biological behaviors, which was attenuated by HMGA2 upregulation. Besides that, CircNUP98 was found to be packaged into exosomes of DN, and exosomal circNUP98 possessed diagnostic value for DN patients.

CONCLUSION

CircNUP98 knockdown alleviates HG-induced proliferation, fibrosis inflammation and oxidative stress in HMCs by regulating the miR-151-3p-HMGA2 axis, which might provide a potential approach for DN therapeutics.

Advanced Glycation End Product Blocker Drugs Have a Great Potential to Prevent Diabetic Cardiomyopathy in an Animal Model of Diabetes Mellitus Type-2

Introduction

Sphingosine 1 phosphate (S1P) is a product of the sphingosine kinase 1 (SphK1) enzyme. Increased S1P can lead to tissue fibrosis that is also one of the pathways for developing diabetic cardiomyopathy. Advanced glycation end products (AGEs) increase S1P in cells. The study is aimed at using aminoguanidine (AG) as an AGEs blocker drug to prevent diabetic cardiomyopathy. Materials and methods. 210 rats were enrolled in the study. Diabetes mellitus type-2 was induced, and rats were divided into AG treated diabetic and nondiabetic groups. The heart histology was assessed with Masson's trichrome and hematoxylin-eosin staining. Cardiac function was measured with transthoracic echocardiography. S1P level and SphK1 gene expression were measured by western-blot and RT-qPCR, respectively.

Results

Results showed that S1P level increases in diabetes, and its augmentation in cardiac tissue with K6PC-5 leads to cardiac fibrosis. 50 and 200 mg/kg of AG prevented cardiac fibrosis, but 100 mg/kg had no significant preventive effect. AG suppressed the SphK1 gene expression and reduced the fibrotic effect of S1P. AG preserved cardiac function by keeping ejection fraction and fractional shortening within the normal range in diabetic rats.

Conclusion

AG has a suppressor effect on SphK1 gene expression besides its AGEs blocker role. AG is a potential drug to use in diabetic patients for preventing the development of diabetic cardiomyopathy. Other drugs that have AGEs or S1P blocker effects are a good choice for diabetic cardiomyopathy prevention.

Mechanistic insights into the role of serum-glucocorticoid kinase 1 in diabetic nephropathy: A systematic review

Aberrant expression of serum-glucocorticoid kinase 1 (SGK1) contributes to the pathogenesis of multiple disorders, including diabetes, hypertension, obesity, fibrosis, and metabolic syndrome. SGK1 variant is expressed in the presence of insulin and several growth factors, eventually modulating various ion channels, carrier proteins, and transcription factors. SGK1 also regulates the enzymatic activity of Na⁺ K⁺ ATPase, glycogen synthase kinase-3, ubiquitin ligase Nedd4-2, and phosphomannose mutase impacting cell cycle regulation, neuroexcitation, and apoptosis. Ample evidence supports the crucial role of aberrant SGK1 expression in hyperglycemia-mediated secondary organ damage. Diabetic nephropathy (DN), a dreadful microvascular complication of diabetes, is the leading cause of end-stage renal failures with high morbidity and mortality rate. The complex pathogenesis of DN encompasses several influencing factors, including transcriptional factors, inflammatory markers, cytokines, epigenetic modulators, and abnormal enzymatic activities. SGK1 plays a pivotal role by controlling various physiological functions associated with the occurrence and progression of DN; therefore, targeting SGK1 may favorably influence the clinical outcome in patients with DN. This review aimed to provide mechanistic insights into SGK1 regulated DN pathogenesis and summarize the evidence supporting the therapeutic potential of SGK1 inhibition and its consequences on human health.

Role of circRNA-miRNA-mRNA interaction network in diabetes and its associated complications

The majority of the non-protein-coding RNAs are being identified with diversified functions that participate in cellular homeostasis. The circular RNAs (circRNAs) are emerging as noncoding transcripts with a key role in the initiation and development of many physiological and pathological conditions. The advancements in high-throughput RNA sequencing and bioinformatics tools help us to identify several circRNA regulatory pathways, one of which is microRNA (miRNA)-mediated regulation. Besides the direct influence over mRNA transcription, the circRNA can also control the target's expression via sponging miRNAs or the RNA-binding proteins. Studies have demonstrated the dysregulation of the circRNA-miRNA-mRNA interaction network in the pathogenesis of many diseases, including diabetes. This intricate mechanism is associated with the pathogenesis of diabetes and its complications. This review will focus on the circRNA-miRNA-mRNA interaction network that influences the gene expression in the progression of diabetes and its associated complications.

Evaluation of sphingolipid metabolism on diabetic retinopathy

Purpose:

To evaluate the aqueous and serum levels of sphingolipid metabolism mediators such as sphingosine 1 phosphate (S1P), sphingosine kinase 1 (SK1), sphingosine kinase 2 (SK2), ceramide kinase (CK), and acid sphingomyelinase (ASM) which are thought to take part in diabetic retinopathy (DR) pathogenesis, and development and severity of diabetic retinopathy (DR) in patients with type 2 diabetes.

Methods:

A prospective cross-sectional study was conducted on type 2 diabetic and control patients who underwent cataract surgery. Three different subgroups, namely, non-diabetic retinopathy (NDR), non-proliferative diabetic retinopathy (NPDR), and proliferative diabetic retinopathy (PDR), were allocated and the S1P, SK1, SK2, CK, and ASM levels in the serum and aqueous humor samples of diabetic and control patients were evaluated. Kolmogorov-Smirnov test, Student's t-test, and Mann-Whitney U test were used for the statistical analysis of the study.

Results:

Among a total of 45 patients, including diabetic and control patients, the mean aqueous levels of SK1 (P < 0.001), SK2 (P = 0.012), ASM (P = 0.006), and CK (P = 0.002) were higher in all diabetic patients. The mean aqueous level of S1P was significantly higher in the PDR group than in other groups (P = 0.003). The mean aqueous levels of SK2 and ASM also increased in the NDR, NPDR, and PDR subgroups, respectively (P < 0.001). In addition, the mean serum levels of S1P, SK1, and ASM were higher in the diabetic patients (P = 0.015, P = 0.034, and P = 0.006, respectively).

Conclusion:

According to our findings, both aqueous and serum levels of S1P, SK1, and ASM and only the aqueous levels of SK2 and CK were higher in diabetic patients. This study suggested that sphingolipid metabolism may play an important role in DR pathogenesis.

Circular RNA circ_0000712 regulates high glucose-induced apoptosis, inflammation, oxidative stress, and fibrosis in (DN) by targeting the miR-879-5p/SOX6 axis

Diabetic nephropathy (DN), a frequent diabetes complication, has complex pathogenesis. Circular RNAs (circRNAs) circ_0000712 has been reported to be upregulated in kidney tissues and high glucose (HG)-inducted Mesangial cells (MCs). This study is designed to explore the role and mechanism of circ_0000712 in the HG-inducted MCs injury in DN. Circ_0000712, microRNA-879-5p (miR-879-5p), and SRY-Box Transcription Factor 6 (SOX6) levels were detected by real-time quantitative polymerase chain reaction (RT-qPCR). Cell apoptosis was examined by flow cytometry assay. Protein levels of B-cell lymphoma-2 (Bcl-2), Bcl-2 related X protein (Bax), fibronectin (FN), collagen type I (Col. I), collagen type IV (Col. IV), and SOX6 were assessed by western blot assay. Levels of interleukin-1β (IL-1β), interleukin-6 (IL-6), and tumor necrosis factor α (TNF-α) were measured by enzyme-linked immunosorbent assay (ELISA). Reactive oxygen species (ROS) generation, Lactate Dehydrogenase (LDH) activity, and Superoxide Dismutase (SOD) activity were detected by the corresponding kits. The binding relationship between miR-879-5p and circ_0000712 or SOX6 was predicted by starBase and Targetscan, and then verified by a dual-luciferase reporter and RNA Immunoprecipitation (RIP) assays. Circ_0000712 and SOX6 were highly expressed, and miR-879-5p was decreased in db/db DN mice and HG-inducted SV40-MES13 cells. Furthermore, circ_0000712 deficiency repressed HG-caused apoptosis, inflammation, oxidative stress, and fibrosis in SV40-MES13 cells. Mechanically, circ_0000712 could regulate SOX6 expression by sponging miR-879-5p. Circ_0000712 knockdown could hinder HG-inducted SV40-MES13 cell injury through targeting the miR-879-5p/SOX6 axis, implying a possible circRNA-targeted therapy for DN.

Potential new therapeutic target for Alzheimer's disease: Glucagon-like peptide-1

Increasing evidence shows a close relationship between Alzheimer's disease (AD) and type 2 diabetes mellitus (T2DM). Recently, glucagon-like peptide-1 (GLP-1), a gut incretin hormone, has become a well-established treatment for T2DM and is likely to be involved in treating cognitive impairment. In this mini review, the similarities between AD and T2DM are summarised with the main focus on GLP-1-based therapeutics in AD.

MUC1 Promotes Mesangial Cell Proliferation and Kidney Fibrosis in Diabetic Nephropathy Through Activating STAT and β-Catenin Signal Pathway

Diabetic nephropathy (DN) is a complication of diabetes, which leads to most end-stage kidney diseases and threatens health of patients. Mucin 1 (MUC1) is a heterodimeric oncoprotein, which is abnormally expressed in tumors and hematologic diseases. The aim of this study is to clarify the mechanism and role of MUC1 in DN. The mesangial cells (MCs) suffered from high glucose (HG) treatment to mimic DN in vitro. The cell proliferation was detected by Cell Counting Kit-8 assay and 5-ethynyl-2-deoxyuridine (EdU) staining assay. The expression of MUC1 and fibrosis markers: fibronectin, collagen I, and collagen IV were assessed by western blot. In this study, we demonstrated that HG treatment induced MUC1 expression in MCs. With knockdown of MUC1 or overexpressed MUC1 in MCs, the results indicated that knockdown of MUC1 inhibited MCs proliferation and reduced kidney fibrosis markers expression, including fibronectin, collagen I, and collagen IV, whereas overexpression of MUC1 led to opposite results. Mechanically, MUC1 activated signal transducers and activators of transcription (STAT) and β-catenin signal pathway. After added AG490 (STAT inhibitor) or FH535 (β-catenin inhibitor), blocking STAT3 and β-catenin signal pathway attenuated MUC1-induced cell proliferation and fibronectin production in MCs. Finally, knockdown of MUC1 attenuated DN-induced kidney fibrosis in db/db mice. Therapeutic target for DN. In conclusion, MUC1 promotes MCs proliferation and kidney fibrosis in DN through activating STAT and β-catenin signal pathway, which can help to provide a novel therapeutic target for DN.

Altered hepatic sphingolipid metabolism in insulin resistant mice: Role of advanced glycation endproducts

High plasma levels of the sphingolipid intermediates ceramide (Cer) and sphingosine-1-phosphate (S1P) are suggested to be involved in the development of insulin resistance (IR). Recent evidence indicates that advanced glycation endproducts (AGEs) can alter the sphingolipids metabolism equilibrium. Since enzymes responsible for sphingolipid rheostat maintenance are highly expressed in liver, we thus investigated whether AGEs accumulation can affect hepatic sphingolipids metabolism in insulin resistant mice. Two different models of IR were examined: genetically diabetic LeptrDb-/- (DbDb) and diet-induced insulin resistant C57Bl/6J mice fed a 60% trans-fat diet (HFD). In addition, a group of HFD mice was supplemented with the anti-AGEs compound pyridoxamine. AGEs were evaluated in the liver by western blotting. Cer and S1P were measured by UHPLC-MS/MS. The expression of RAGE and of enzymes involved in sphingolipid metabolism were assessed by RT-PCR and western blotting. HepG2 cells were used to study the effect of the major AGE Nε-(carboxymethyl)lysine (CML)-albumin on sphingolipid metabolism and the role of the receptor of AGEs (RAGE). High levels of AGEs and RAGE were detected in the liver of both DbDb and HFD mice in comparison to controls. The expression of enzymes of sphingolipid metabolism was altered in both models, accompanied by increased levels of Cer and S1P. Specifically, ceramide synthase 5 and sphingosine kinase 1 were increased, while neutral ceramidase was reduced. Pyridoxamine supplementation to HFD mice diminished hepatic AGEs and prevented alterations of sphingolipid metabolism and the development of IR. CML administration to HepG2 cells evoked alterations similar to those observed in vivo, that were in part mediated by the binding to RAGE. The present study shows a direct involvement of AGEs in alterations of sphingolipid metabolism associated to the development of IR. The modulation of sphingolipids metabolism through the prevention of AGEs accumulation by pyridoxamine may reduce the development of IR.

Alleviative effects of 20(R)-Rg3 on HFD/STZ-induced diabetic nephropathy via MAPK/NF-κB signaling pathways in C57BL/6 mice

ETHNOPHARMACOLOGICAL RELEVANCE

Diabetic nephropathy (DN) is a major complication of diabetes. The kidney disease develops in nearly 20%-40% of type 2 diabetes (T2D) patients. Ginseng is the root of Panax ginseng C. A. Meyer and has been used in prevention and treatment of diseases for more than 2000 years as a traditional oriental medicine. The 20(R)-ginsenoside Rg3, an active saponin isolated from ginseng, can prevent and treat many diseases. The object of this research was to explore the alleviative effects of 20(R)-Rg3 on DN in mice.

MATERIALS AND METHODS

The T2D animal model was induced by continuous access to a high fat diet (HFD) combined with a single injection of 100 mg/kg streptozotocin (STZ) in C57BL/6 mice. The mice were treated by oral gavage of the 20(R)-Rg3 (10, 20 mg/kg) for 8 weeks. Functional and histopathological analyses of the kidneys were then performed. Protein expression levels of MAPKs and NF-κB signal pathways in the kidney were evaluated by western blotting. The expressions of HO-1 and NF-κB in the kidney were measured by fluorescent labeling staining. Other assessments including fasting blood glucose (FBG) levels, blood lipids, oxidative indicators, and inflammatory factors were all performed.

RESULTS

Abnormally elevated FBG levels were observed in HFD/STZ mice, contributing significantly to the occurrence of DN. Simultaneously, HFD/STZ mice showed the rise of serum total cholesterol (TC), triglyceride (TG), and low-density lipoprotein cholesterol (LDL-C) levels, and the decrease in high density lipoprotein cholesterol (HDL-C). DN was evidenced by the overproduction of malondialdehyde (MDA), decreased levels of superoxide dismutase (SOD) and catalase (CAT) enzymatic activities, high levels of serum blood urea nitrogen (BUN) and creatinine (Cr). Simultaneously, the results of the immunofluorescence assay showed an increased expression level in NF-κB p65 while a decrease in antioxidant enzyme HO-1 was observed. Herein, 20(R)-Rg3 treatment for 8 weeks not only attenuated FBG levels and advanced glycation end products (AGEs) levels but also improved insulin (INS) level, blood lipids, oxidative stress, and renal function by regulating MAPKs and NF-κB signal pathways in DN mice.

CONCLUSION

Taken together, the findings from the present study explicitly confirmed that 20(R)-Rg3 exerted ameliorative effects on DN mice via improving anti-oxidative activity and reducing renal inflammation.

Circular RNA Circ_0000064 promotes the proliferation and fibrosis of mesangial cells via miR-143 in diabetic nephropathy

Diabetic nephropathy (DN) as one of the most frequent microvascular complications of diabetic patients causes chronic renal failure and end-stage renal disease. Noncoding RNAs including circular RNAs (circRNAs) and micro RNAs (miRNAs) were widely reported to play a critical role in numerous human diseases including DN. This research was designed to investigate the role of circ_0000064 in diabetic nephropathy progression. The results showed that circ_0000064 significantly promoted mesangial cells proliferation and aggravated fibrosis in DN. In the subsequent mechanism investigation, we found that circ_0000064 was involved in this process by targeting micro RNA miR-143. The inhibition of miR-143 significantly reverses the effect of circ_0000064 silencing on DN. In conclusion, we demonstrated the regulatory role of circ_0000064 in DN and clarified that circ_0000064 play a role in DN via targeting miR-143. Circ_0000064 and miR-143 also showed the potential as a biomarker for DN.

A novel identified circular RNA, circ_0000491, aggravates the extracellular matrix of diabetic nephropathy glomerular mesangial cells through suppressing miR‑101b by targeting TGFβRI

Circular RNAs (circRNAs) have crucial roles in various diseases; however, the mechanisms of action underlying circRNAs in the occurrence and development of diabetic nephropathy (DN) remains largely unknown. The present study investigated the differentially expressed circRNAs in the DN mice kidney cortex using circRNA sequencing and elucidated the role of circRNAs in mesangial cells. It was revealed that 40 circRNAs were unconventionally expressed, including 18 upregulated circRNAs and 22 downregulated circRNAs. Furthermore, circ_0000491 levels were significantly augmented in both DN mice and high glucose (HG, 30 mM)-induced mouse mesangial cells (MES13 cells). Knockdown of circ_0000491 significantly suppressed the increase of vimentin, fibronectin and α-smooth muscle actin, as well as collagen type I, III and IV, whilst reversing the decrease of E-cadherin in HG-induced MES13 cells. It was further revealed that circRNA_0000491 sponged miR-101b and that miR-101b directly targets TGFβRI. In addition, the expression levels of miR-101b were negatively associated with the transcriptional level of circRNA_0000491 and miR-101b inhibitors reversed the suppression of extracellular matrix (ECM)-associated protein synthesis mediated by knocking-down circRNA_0000491. In conclusion, the present study investigated the circRNA_0000491/miR-101b/TGFβRI axis in ECM accumulation and fibrosis-associated protein expression levels of mesangial cells, which suggested that circRNA_0000491 may be beneficial for the development of an effective therapeutic target for DN.

Circular RNA HIPK3 exacerbates diabetic nephropathy and promotes proliferation by sponging miR-185

PURPOSE

The aim of the present study was to investigate expression levels of circular RNA HIPK3 (circHIPK3) in mice with diabetic nephropathy (DN) and the role of circHIPK3 in rat mesangial cells (MCs).

METHODS

Quantitative real-time polymerase chain reaction was performed to detect expression levels of circHIPK3, miR-185, cyclin D1, proliferating cell nuclear antigen (PCNA), transforming growth factor-β1 (TGF-β1), collagen Ⅰ (Col. Ⅰ), and fibronectin (FN) in mice with DN and rat mesangial cells. Luciferase assay was performed to investigate the binding sites of circHIPK3 and miR-185. Silencing cells of circHIPK3 and miR-185 were constructed using cell transfection assay.

RESULTS

Our results revealed that the levels of 24-hour urinary albumin and urinary 8-hydroxy-2'-deoxyguanosine (8-OH-dG) from diabetic mice increased considerably. Up-regulation of circHIPK3 was observed in the renal tissues of mice with DN. Similarly, circHIPK3 expression in rat mesangial cells increased significantly in a microenvironment of high glucose. A loss-of-function experiment indicated that down-regulation of circHIPK3 inhibited cell proliferation and significantly decreased mRNA abundance of cyclin D1, PCNA, TGF-β1, Col. I, and FN in MCs. Luciferase assay demonstrated that circHIPK3 can specifically sponge miR-185, and silencing of miR-185 can reverse the effects of knocking down circHIPK3 on cell proliferation and mRNA abundance of cyclin D1, PCNA, TGF-β1, Col. I, and FN in MCs.

CONCLUSION

Overall, circHIPK3 exhibits a promotive function in DN by sponging miR-185 and this evidence suggests that circHIPK3 might be a biomarker or therapeutic target for DN.

Circ-AKT3 inhibits the accumulation of extracellular matrix of mesangial cells in diabetic nephropathy via modulating miR-296-3p/E-cadherin signals

Diabetic nephropathy is a leading cause of end-stage renal disease globally. The vital role of circular RNAs (circRNAs) has been reported in diabetic nephropathy progression, but the molecular mechanism linking diabetic nephropathy to circRNAs remains elusive. In this study, we investigated the significant function of circ-AKT3/miR-296-3p/E-cadherin regulatory network on the extracellular matrix accumulation in mesangial cells in diabetic nephropathy. The expression of circ-AKT3 and fibrosis-associated proteins, including fibronectin, collagen type I and collagen type IV, was assessed via RT-PCR and Western blot analysis in diabetic nephropathy animal model and mouse mesangial SV40-MES13 cells. Luciferase reporter assays were used to investigate interactions among E-cadherin, circ-AKT3 and miR-296-3p in mouse mesangial SV40-MES13 cells. Cell apoptosis was evaluated via flow cytometry. The level of circ-AKT3 was significantly lower in diabetic nephropathy mice model group and mouse mesangial SV40-MES13 cells treated with high-concentration (25 mmol/L) glucose. In addition, circ-AKT3 overexpression inhibited the level of fibrosis-associated protein, such as fibronectin, collagen type I and collagen type IV. Circ-AKT3 overexpression also inhibited the apoptosis of mouse mesangial SV40-MES13 cells treated with high glucose. Luciferase reporter assay and bioinformatics tools identified that circ-AKT3 could act as a sponge of miR-296-3p and E-cadherin was the miR-296-3p direct target. Moreover, circ-AKT3/miR-296-3p/E-cadherin modulated the extracellular matrix of mouse mesangial cells in high-concentration (25 mmol/L) glucose, inhibiting the synthesis of related extracellular matrix protein. In conclusion, circ-AKT3 inhibited the extracellular matrix accumulation in diabetic nephropathy mesangial cells through modulating miR-296-3p/E-cadherin signals, which might offer novel potential opportunities for clinical diagnosis targets and therapeutic biomarkers for diabetic nephropathy.

Effects of Propolis Extract and Propolis-Derived Compounds on Obesity and Diabetes: Knowledge from Cellular and Animal Models

Propolis is a natural product resulting from the mixing of bee secretions with botanical exudates. Since propolis is rich in flavonoids and cinnamic acid derivatives, the application of propolis extracts has been tried in therapies against cancer, inflammation, and metabolic diseases. As metabolic diseases develop relatively slowly in patients, the therapeutic effects of propolis in humans should be evaluated over long periods of time. Moreover, several factors such as medical history, genetic inheritance, and living environment should be taken into consideration in human studies. Animal models, especially mice and rats, have some advantages, as genetic and microbiological variables can be controlled. On the other hand, cellular models allow the investigation of detailed molecular events evoked by propolis and derivative compounds. Taking advantage of animal and cellular models, accumulating evidence suggests that propolis extracts have therapeutic effects on obesity by controlling adipogenesis, adipokine secretion, food intake, and energy expenditure. Studies in animal and cellular models have also indicated that propolis modulates oxidative stress, the accumulation of advanced glycation end products (AGEs), and adipose tissue inflammation, all of which contribute to insulin resistance or defects in insulin secretion. Consequently, propolis treatment may mitigate diabetic complications such as nephropathy, retinopathy, foot ulcers, and non-alcoholic fatty liver disease. This review describes the beneficial effects of propolis on metabolic disorders.

PC-1 NF suppresses high glucose-stimulated inflammation and extracellular matrix accumulation in glomerular mesangial cells via the Wnt/β-catenin signaling

Diabetic nephropathy (DN) is the leading cause of end-stage renal disease worldwide with high morbidity and mortality. Glomerular mesangial cell (MC) proliferation, inflammatory cell infiltration and extracellular matrix (ECM) accumulation are the main pathological characteristics of DN. A previous study revealed that polycystin-1 N-terminal fragment (PC-1 NF) fusion protein could inhibit ECM accumulation in a mesangial proliferative glomerulonephritis model. However, the role of PC-1 NF fusion protein in DN remains unknown. The results of the present study indicated that PC-1 NF fusion protein significantly abolished high glucose (HG)-induced glomerular MC viability over three time points measured (24, 48 and 72 h). In addition, PC-1 NF suppressed the levels of monocyte chemotactic peptide-1 and tumor necrosis factor α, as well as the expression of fibronectin and collagen IV, in HG-stimulated MCs. Furthermore, PC-1 NF fusion protein efficiently inhibited the activation of Wnt/β-catenin signaling pathway in HG-stimulated MCs. Taken together, these data indicated that PC-1 NF fusion protein inhibited HG-induced MC proliferation, inflammation, and ECM expression via the modulation of the Wnt signaling pathway. The present study indicated that PC-1 NF fusion protein may be a potential agent in treating DN.

Advanced glycation end products and adipocytokines and oxidative stress in placental tissues of pregnant women with gestational diabetes mellitus

Correlation between expression levels of advanced glycation end products (AGEs) and adipocytokines and oxidative stress index malondialdehyde (MDA) in placental tissues of pregnant women with gestational diabetes mellitus (GDM) was investigated. Seventy-two cases of GDM pregnant women who received routine prenatal examination and gave birth in the Department of Obstetrics, Binzhou City Center Hospital from March 2016 to May 2017 were collected as the observation group. Another 80 cases of normal pregnant women who gave birth at the same time were selected as the control group. Enzyme linked immunosorbent assay (ELISA) was used to detect the expression levels of AGEs, visfatin, APN and IL-6 in the lysate of placental tissues. MDA levels were measured by thiobarbituric acid method. Correlation of expression levels of AGEs, visfatin, APN, IL-6 and MDA were analyzed. The expression level of MDA in placental tissues of the observation group was significantly higher than that of the control group (t=16.44, P<0.001). The correlation of expression levels between AGEs, adipocytokines and MDA in placental tissues of the two groups was analyzed, and it was found that the expression levels of AGEs, visfatin and IL-6 in the two groups were positively correlated with MDA. There was a significantly negative correlation between APN and MDA in the two groups. The incidence of cesarean section, neonatal hypoglycemia, fetal distress and macrosomia in the observation group was significantly higher than that in the control group (P<0.05). There was no significant difference in the incidence of membrane rupture and premature birth between the two groups (P>0.05). In conclusion, the expression levels of AGEs, visfatin and IL-6 in placental tissues of GDM pregnant women are positively correlated with MDA. There is a significant negative correlation between APN and MDA, and they play an important role in the pathogenesis of GDM.

Circular RNA circRNA_15698 aggravates the extracellular matrix of diabetic nephropathy mesangial cells via miR-185/TGF-β1

Circular RNAs (circRNAs) are a novel type of noncoding RNAs that modulate the pathogenesis of multiple diseases. Nevertheless, the role of circRNAs in diabetic nephropathy (DN) pathogenesis is still ambiguous. In the current study, our team aims to investigate the expression profiles of circRNAs in DN and identify the function of circRNA on mesangial cells. CircRNAs microarray analysis revealed dysregulated circRNA in db/db DN mice, and circRNA_15698 was validated to be upregulated in both db/db mice and mouse mesangial cells (SV40-MES13) that were exposed to high glucose (25 mM) using real-time polymerase chain reaction. Loss-of-functional experiments showed that circRNA_15698 knockdown significantly inhibited the expression levels of collagen type I (Col. I), collagen type IV (Col. IV), and fibronectin. Moreover, the cellular localization of circRNA_15698 was mainly in the cytoplasm. Bioinformatics tools and luciferase reporter assay confirmed that circRNA_15698 acted as a 'sponge' of miR-185, and then positively regulated the transforming growth factor-β1 (TGF-β1) protein expression, suggesting a circRNA_15698/miR-185/TGF-β1 pathway. Further validation experiments validated that circRNA_15698/miR-185/TGF-β1 promoted extracellular matrix (ECM)-related protein synthesis. In summary, our study preliminarily investigates the role of circRNAs in mesangial cells and ECM accumulation, providing a novel insight for DN pathogenesis.

Phagocytosis of Advanced Glycation End Products (AGEs) in Macrophages Induces Cell Apoptosis

Advanced glycation end products (AGEs) are the products of a series of nonenzymatic modifications of proteins by reducing sugars. AGEs play a pivotal role in development of diabetic complications and atherosclerosis. Accumulation of AGEs in a vessel wall may contribute to the development of vascular lesions. Although AGEs have a diverse range of bioactivities, the clearance process of AGEs from the extracellular space, including the incorporation of AGEs into specific cells, subcellular localization, and the fate of AGEs, remains unclear. In the present study, we examined the kinetics of the uptake of AGEs by mouse macrophage J774.1 cells in vitro and characterized the process. We demonstrated that AGEs bound to the surface of the cells and were also incorporated into the cytoplasm. The temperature- and time-dependent uptake of AGEs was saturable with AGE concentration and was inhibited by cytochalasin D but not chlorpromazine. We also observed the granule-like appearance of AGE immunoreactivity in subcellular localizations in macrophages. Higher concentrations of AGEs induced intracellular ROS and 4-HNE, which were associated with activation of the NF-κB pathway and caspase-3. These results suggest that incorporation of AGEs occurred actively by endocytosis in macrophages, leading to apoptosis of these cells through NF-κB activation.