High Glucose Impairs Insulin Signaling in the Glomerulus: An In Vitro and Ex Vivo Approach

Sirt6 ameliorates high glucose-induced podocyte cytoskeleton remodeling via the PI3K/AKT signaling pathway

BACKGROUND

Podocyte injury plays an important role in the occurrence and progression of diabetic kidney disease (DKD), which leads to albuminuria. Cytoskeletal remodeling is an early manifestation of podocyte injury in DKD. However, the underlying mechanism of cytoskeletal remodeling has not been clarified. Histone deacetylase sirtuin6 (Sirt6) has been found to play a key role in DKD progression, and the phosphatidylinositol 3-kinase (PI3K)/protein kinase B (PKB/AKT) pathway directly regulates the cytoskeletal structure of podocytes. Whereas, the relationship between Sirt6, the PI3K/AKT pathway and DKD progression remains unclear.

METHODS

Renal injury of db/db mice was observed by PAS staining and transmission electron microscope. Expression of Sirt6 in the glomeruli of db/db mice was detected by immunofluorescence. UBCS039, a Sirt6 activator, was used to explore the renal effects of Sirt6 activation on diabetic mouse kidneys. We also downregulating Sirt6 expression in podocytes using the Sirt6 inhibitor, OSS_128167, and induced upregulation of Sirt6 using a recombinant plasmid, after which the effects of Sirt6 on high glucose (HG)-induced podocyte damage were assessed in vitro. Podocyte cytoskeletal structures were observed by phalloidin staining. The podocyte apoptotic rate was assessed by flow cytometry, and PI3K/AKT signaling activation was measured by Western blotting.

RESULTS

Db/db mice exhibited renal damage including elevated urine albumin-to-creatinine ratio (ACR), increased mesangial matrix, fused podocyte foot processes, and thickened glomerular basement membrane. The expression of Sirt6 and PI3K/AKT pathway components was decreased in db/db mice. UBCS039 increased the expressions of Sirt6 and PI3K/AKT pathway components and ameliorated renal damage in db/db mice. We also observed consistent Sirt6 expression was in HG-induced podocytes in vitro. Activation of the PI3K/AKT pathway via a Sirt6 recombinant plasmid ameliorated podocyte cytoskeletal remodeling and apoptosis in HG-treated immortalized human podocytes in vitro, whereas Sirt6 inhibition by OSS_128167 accelerated HG-induced podocyte damage in vitro.

CONCLUSIONS

Sirt6 protects podocytes against HG-induced cytoskeletal remodeling and apoptosis through activation of the PI3K/AKT signaling pathway. These findings provide evidence supporting the potential efficacy of Sirt6 activation as a promising therapeutic strategy for addressing podocyte injury in DKD.

Validation of a physiological type 2 diabetes model in human periodontal ligament stem cells

OBJECTIVES

Type 2 diabetes (T2DM), a recognized risk factor for periodontitis, is characterized by insulin resistance. However, the molecular mechanisms concerning the role of insulin resistance in linking T2DM and periodontitis remain poorly elucidated due to the absence of an appropriate T2DM cell model. We aimed to explore an appropriate model of T2DM in human periodontal ligament stem cells (hPDLSCs) and uncover the involved mechanisms.

MATERIALS AND METHODS

hPDLSCs were incubated with common reagents for recapitulating insulin resistance state including high glucose (HG) (15, 25, 35, 45 mM), glucosamine (0.8, 8, 18, 28, 38 mM), or palmitic acid (PA; 100, 200, 400, 800 μM), combined with LPS for 48 h. The insulin signaling pathway, inflammation, and pyroptosis were detected by western blots and quantitative real-time polymerase chain reaction (RT-qPCR). The effects on osteogenesis were evaluated by alkaline phosphatase staining, alizarin red S staining, RT-qPCR, and western blots.

RESULTS

HG failed to recapitulate insulin resistance. Glucosamine was sufficient to induce insulin resistance but failed to trigger inflammation. In total, 100 and 200 μM PA exhibited the most proinflammatory, insulin resistance, and pyroptosis induced role, and inhibited the osteogenic differentiation of hPDLSCs.

CONCLUSION

Palmitic acid is a promising candidate for developing T2DM model in hPDLSCs.

Glucosamine substituted sulfonylureas: IRS-PI3K-PKC-AKT-GLUT4 insulin signalling pathway intriguing agent

Normally, skeletal muscle accounts for 70-80% of insulin-stimulated glucose uptake in the postprandial hyperglycemia state. Consequently, abnormalities in glucose uptake by skeletal muscle or insulin resistance (IR) are deemed as initial metabolic defects in the pathogenesis of type 2 diabetes mellitus (T2DM). Globally, T2DM is growing in exponential proportion. The majority of T2DM patients are treated with sulfonylureas in combination with other drugs to improve insulin sensitivity. Glycosylated sulfonylureas (sulfonylurea-glucosamine analogues) are modified analogues of sulfonylurea that have been previously reported to possess antidiabetic activity. The aim of this study was to evaluate the impact of glycosylated sulfonylureas on the insulin signalling pathway at the molecular level using L6 skeletal muscle cell (in vitro) and extracted soleus muscle (ex vivo) models. To create an in vitro model, insulin resistance was established utilizing a high insulin-glucose approach in differentiated L6 muscle cells from Rattus norvegicus. Additionally, for the ex vivo model, extracted soleus muscles, adult Sprague-Dawley rats were subjected to a solution containing 25 mmol L-1 glucose and 100 mmol L-1 insulin for 24 hours to induce insulin resistance. After insulin resistance, compounds under investigation and standard medicines (metformin and glimepiride) were tested. The differential expression of PI3K, IRS-1, PKC, AKT2, and GLUT4 genes involved in the insulin signaling pathway was evaluated using qPCR. The evaluated glycosylated sulfonylurea analogues exhibited a significant increase in the gene expression of insulin-dependent pathways both in vitro and ex vivo, confirming the rejuvenation of the impaired insulin signaling pathway genes. Altogether, glycosylated sulfonylurea analogues described in this study represent potential therapeutic anti-diabetic drugs.

Effects of Mulberry Leaf Fu Tea on the Intestines and Intestinal Flora of Goto-Kakizaki Type 2 Diabetic Rats

Type 2 diabetes mellitus is a disease caused by hyperglycemia, an imbalance in the intestinal flora and disruption of the endocrine system. At present, it is primarily controlled through drug treatment and an improved diet. Mulberry leaf and fu brick tea were considered to have excellent hypoglycemic effects. This study used mulberry leaves and fu brick tea as raw materials to develop a dietary regulator that can assist in the prevention and alleviation of diabetes. The experiment used the Goto-Kakizaki (GK) rat model to investigate the hypoglycemic effect of mulberry leaf fu tea (MFT) and its influence on the intestinal flora of diabetic rats through methods including ELISA, tissue section observation and 16S RNA microbial sequencing. The results showed that, compared with the GK group, the intervention of mulberry leaf fu tea significantly reduced the activities of α-glucosidase (p < 0.05) and α-amylase (p < 0.05) in the duodenum of GK diabetic rats. The height of the duodenal villi was significantly reduced (p < 0.001), leading to decreased intestinal sugar absorption. At the same time, MFT alleviates the imbalance of intestinal flora caused by high blood sugar, promotes the growth of beneficial bacteria (Lactobacillus, Bifidobacterium, etc.), and inhibits the reproduction of harmful bacteria (Blautia, Klebsiella, Helicobacter, Alistipes, etc.). MFT helps reduce the secretion of toxic substances (lipopolysaccharide, p < 0.001), decreases oxidative stress and inflammation, mitigates organ damage, and improves symptoms of diabetes. Finally, the random blood glucose value of GK rats dropped from 22.79 mmol/L to 14.06 mmol/L. In summary, mulberry leaf fu tea can lower sugar absorption in diabetic rats, reduce the body's oxidative stress and inflammatory response, regulate intestinal flora, and reduce blood sugar levels in GK rats. It is hinted that mulberry leaf fu tea could be used as a functional drink to help prevent the occurrence of diabetes.

Sweroside attenuates podocyte injury and proteinuria in part by activating Akt/BAD signaling in mice

In this study, we investigated the effects of sweroside on podocyte injury in diabetic nephropathy (DN) mice and elucidated its molecular mechanisms. We conducted in vivo experiments using a C57BL/6 mice model of DN to explore the effects of sweroside on proteinuria and podocyte injury in DN mice. In in vitro experiments, conditionally immortalized mouse podocytes were treated with high glucose and sweroside, and the protective effects of sweroside on podocyte injury were analyzed. In vitro, Akt/BAD pathways were detected using gene siRNA silencing assays and found to be involved in the protective roles of sweroside in high glucose-mediated podocyte injury. In vivo, sweroside significantly decreased albuminuria in DN mice (p < 0.01). periodic acid-Schiff staining showed that sweroside alleviated the glomerular volume and mesangium expansion in DN mice. Consistently, western blot and reverse transcription-polymerase chain reaction analyses showed that the profibrotic molecule expression in the glomeruli declined in sweroside-treated DN mice. Immunofluorescent results showed that sweroside preserved nephrin and podocin expression, and transmission electron microscopy showed that sweroside attenuated podocyte injury. In DN mice, sweroside decreased podocyte apoptosis, and increased nephrin, podocin expression and decreased desmin and HIF1α expression. These results confirmed that sweroside ameliorated albuminuria, glomerulomegaly, and glomerulosclerosis in these mice. Experiments in vitro revealed that sweroside improved HG-induced podocyte injury and apoptosis. Sweroside stimulated activation of the Akt/BAD pathway and upregulated Bcl-2-associated death promoter (BAD) and p-Akt. Overall, sweroside protected podocytes from injury and prevented the progression of DN, providing a novel strategy for the treatment of DN.

Excess glucose or fat differentially affects metabolism and appetite-related gene expression during zebrafish embryogenesis

Zebrafish embryos use their yolk sac reserve as the sole nutrient source during embryogenesis. The two main forms of energy fuel can be found in the form of glucose or fat. Zebrafish embryos were exposed to glucose or injected with free fatty acid/Triacylglycerol (FFA/TAG) into the yolk sac at 24 hpf. At 72 hpf, glucose exposed or FFA/TAG injected had differential effects on gene expression in embryos, with fat activating lipolysis and β-oxidation and glucose activating the insulin pathway. Bulk RNA-seq revealed that more gene expression was affected by glucose exposure compared to FFA/TAGs injection. Appetite-controlling genes were also differently affected by glucose exposure or FFA/TAG injections. Because the embryo did not yet feed itself at the time of our analysis, gene expression changes occurred in absence of actual hunger and revealed how the embryo manages its nutrient intake before active feeding.

Comparative Studies of Palmatine with Metformin and Glimepiride on the Modulation of Insulin Dependent Signaling Pathway In Vitro, In Vivo & Ex Vivo

(1) Insulin resistance, a symptom of type 2 diabetes mellitus (T2DM), is caused by the inactivation of the insulin signaling pathway, which includes IRS-PI3K-IRS-1-PKC-AKT2 and GLUT4. Metformin (biguanide) and glimepiride (sulfonylurea) are both drugs that are derivatives of urea, and they are widely used as first-line drugs for the treatment of type 2 diabetes mellitus. Palmatine has been previously reported to possess antidiabetic and antioxidant properties. (2) The current study compared palmatine to metformin and glimepiride in a type 2 diabetes model for ADME and insulin resistance via the PI3K/Akt/GLUT4 signaling pathway: in vitro, in vivo, ex vivo, and in silico molecular docking. (3) Methods: Differentiated L6 skeletal muscle cells and soleus muscle tissue were incubated in standard tissue culture media supplemented with high insulin and high glucose as a cellular model of insulin resistance, whilst streptozotocin (STZ)-induced Sprague Dawley rats were used as the diabetic model. The cells/tissue/animals were treated with palmatine, while glimepiride and metformin were used as standard drugs. The differential gene expression of PI3K, IRS-1, PKC-α, AKT2, and GLUT4 was evaluated using qPCR. (4) Results: The results revealed that the genes IRS-PI3K-IRS-1-PKC-AKT2 were significantly down-regulated, whilst PKC-α was upregulated significantly in both insulin-resistant cells and tissue animals. Interestingly, palmatine-treated cells/tissue/animals were able to reverse these effects. (5) Conclusions: Palmatine appears to have rejuvenated the impaired insulin signaling pathway through upregulation of the gene expression of IRS-1, PI3K, AKT2, and GLUT4 and downregulation of PKC-expression, according to in vitro, in vivo, and ex vivo studies.

The role of oxidative stress markers in Indonesian chronic kidney disease patients: a cross sectional study

Background: Several aspects of chronic kidney disease (CKD) such as the incidence rate and mortality rate are concerning. Oxidative stress contributes to progression and mortality in patients with CKD; however, a specific correlation between several markers of oxidative stress and the estimated glomerular filtration rate (eGFR) and albumin-creatinine ratio (ACR) in the Indonesian population has not been sufficiently described yet. Methods: This study was an analytic observational study with a sample of 56 patients with CKD in Universitas Airlangga Hospital, Surabaya, Indonesia, from December 2019 – March 2020. The markers for oxidative stress investigated were urinary 8-hydroxy-2 deoxyguanosine (8-OHdG), serum symmetric dimethylarginine (SDMA) and asymmetric dimethylarginine (ADMA). The correlations between each variable of oxidative stress and CKD were analyzed using Pearson analysis. Results: There was a positive correlation between 8-OHdG and eGFR (p=0.00, r=0.51); however, there was a negative correlation between 8-OHdG and ACR (p=0.025, r=-0.30). SDMA and eGFR showed a negative correlation (p=0.00, r=-0.648), while SDMA and ACR showed a positive correlation (p=0.03, r=0.349). ADMA showed a negative correlation with eGFR (p=0.00, r=-0.476). There were significantly decreased 8-OHdG but increased ADMA and SDMA as the CKD stage progressed (p=0.001, p=0.00, and p = 0.00, respectively). Higher urine 8-OHdG was detected in patients without history of hemodialysis, whereas ADMA and SDMA showed higher value in patients with hemodialysis (p=0.00, p=0.00, and p=0.004, respectively), patients with history of diabetes mellitus (DM) had higher mean 8-OHdG (p 0.000) yet lower serum ADMA and SDMA (p=0.004 and p=0.003, respectively). Conclusions: In patients with CKD in Indonesia, the markers for oxidative stress 8-OHdG, SDMA, and ADMA are correlated with eGFR and ACR levels. There were also significant difference in 8-OHdG, SDMA, and ADMA levels among CKD stages, between dialysis vs non dialysis, and DM vs non DM patients.

Organ-differential Roles of Akt/FoxOs Axis as a Key Metabolic Modulator during Aging

FoxOs and their post-translational modification by phosphorylation, acetylation, and methylation can affect epigenetic modifications and promote the expression of downstream target genes. Therefore, they ultimately affect cellular and biological functions during aging or occurrence of age-related diseases including cancer, diabetes, and kidney diseases. As known for its key role in aging, FoxOs play various biological roles in the aging process by regulating reactive oxygen species, lipid accumulation, and inflammation. FoxOs regulated by PI3K/Akt pathway modulate the expression of various target genes encoding MnSOD, catalases, PPARγ, and IL-1β during aging, which are associated with age-related diseases. This review highlights the age-dependent differential regulatory mechanism of Akt/FoxOs axis in metabolic and non-metabolic organs. We demonstrated that age-dependent suppression of Akt increases the activity of FoxOs (Akt/FoxOs axis upregulation) in metabolic organs such as liver and muscle. This Akt/FoxOs axis could be modulated and reversed by antiaging paradigm calorie restriction (CR). In contrast, hyperinsulinemia-mediated PI3K/Akt activation inhibited FoxOs activity (Akt/FoxOs axis downregulation) leading to decrease of antioxidant genes expression in non-metabolic organs such as kidneys and lungs during aging. These phenomena are reversed by CR. The results of studies on the process of aging and CR indicate that the Akt/FoxOs axis plays a critical role in regulating metabolic homeostasis, redox stress, and inflammation in various organs during aging process. The benefical actions of CR on the Akt/FoxOs axis in metabolic and non-metabolic organs provide further insights into the molecular mechanisms of organ-differential roles of Akt/FoxOs axis during aging.

NAD+ Homeostasis in Diabetic Kidney Disease

The redox reaction and energy metabolism status in mitochondria is involved in the pathogenesis of metabolic related disorder in kidney including diabetic kidney disease (DKD). Nicotinamide adenine dinucleotide (NAD+) is a cofactor for redox reactions and energy metabolism in mitochondria. NAD+ can be synthesized from four precursors through three pathways. The accumulation of NAD+ may ameliorate oxidative stress, inflammation and improve mitochondrial biosynthesis via supplementation of precursors and intermediates of NAD+ and activation of sirtuins activity. Conversely, the depletion of NAD+ via NAD+ consuming enzymes including Poly (ADP-ribose) polymerases (PARPs), cADPR synthases may contribute to oxidative stress, inflammation, impaired mitochondrial biosynthesis, which leads to the pathogenesis of DKD. Therefore, homeostasis of NAD+ may be a potential target for the prevention and treatment of kidney diseases including DKD. In this review, we focus on the regulation of the metabolic balance of NAD+ on the pathogenesis of kidney diseases, especially DKD, highlight benefits of the potential interventions targeting NAD+-boosting in the treatment of these diseases.

Zinc Supplementation and Strength Exercise in Rats with Type 2 Diabetes: Akt and PTP1B Phosphorylation in Nonalcoholic Fatty Liver

Type 2 diabetes mellitus (T2D) is a metabolic disorder caused by chronic hyperglycemia due to a deficiency in the secretion and/or action of insulin. Zinc (Zn) supplementation and strength exercise increases insulin signaling. We evaluate the effect of Zn supplementation and strength exercise on insulin resistance in the liver of rats with diet-induced T2D through the study of phosphorylation of Akt and protein tyrosine phosphatase 1B (PTP1B). Rats were fed with a high-fat diet (HFD) for 18 weeks to induce T2D and then assigned in four experimental groups: HFD, HFD-Zn (Zn), HFD-strength exercise (Ex), and HFD-Zn/strength exercise (ZnEx) and treated during 12 weeks. Serum Zn, lipid profile, transaminases, glucose, and insulin were measured. In the liver with/without insulin stimuli, total and phosphorylated Akt (pAkt^Ser473) and PTP1B (pPTP1B^Ser50) were determined by western blot. Hepatic steatosis was evaluated by histological staining with red oil and intrahepatic triglyceride (IHTG) content. There were no differences in biochemical and body-related variables. The ZnEx group showed a higher level of pAkt, both with/without insulin. The ZnEx group also showed higher levels of pPTP1B with respect to HFD and Zn groups. The ZnEx group had higher levels of pPTP1B than groups treated with insulin. Liver histology showed a better integrity and less IHTG in Ex and ZnEx with respect to the HFD group. The Ex and ZnEx groups had lower IHTG with respect to the HFD group. Our results showed that Zn supplementation and strength exercise together improved insulin signaling and attenuated nonalcoholic liver disease in a T2D rat model.

Improving the Dysregulation of FoxO1 Activity Is a Potential Therapy for Alleviating Diabetic Kidney Disease

A substantial proportion of patients with diabetes will develop kidney disease. Diabetic kidney disease (DKD) is one of the most serious complications in diabetic patients and the leading cause of end-stage kidney disease worldwide. Although some mechanisms have been revealed to contribute to the understanding of the pathogenesis of DKD and some drugs currently in use have been shown to be beneficial, prevention and management of DKD remain tricky and challenging. FoxO1 transcriptional factor is a crucial regulator of cellular homeostasis and posttranslational modification is a major mechanism to alter FoxO1 activity. There is increasing evidence that FoxO1 is involved in the regulation of various cellular processes such as stress resistance, autophagy, cell cycle arrest, and apoptosis, thereby playing an important role in the pathogenesis of DKD. Improving the dysregulation of FoxO1 activity by natural compounds, synthetic drugs, or manipulation of gene expression may attenuate renal cell injury and kidney lesion in the cells cultured under a high-glucose environment and in diabetic animal models. The available data imply that FoxO1 may be a potential clinical target for the prevention and treatment of DKD.

MiR-3138 deteriorates the insulin resistance of HUVECs via KSR2/AMPK/GLUT4 signaling pathway

Insulin resistance (IR) is a complex pathological condition resulting from the dysregulation of cellular response to insulin hormone in insulin-dependent cells and is recognized as a pathogenic hallmark and strong risk factor for metabolic syndrome. The present study aims to elucidate the molecular mechanism of the pathogenesis of IR. Here, we used human umbilical vein endothelial cells (HUVECs) to establish the IR cell model induced by 1 × 10^-6 mmol/L insulin. After 48 h, reactive oxygen species (ROS) and glucose consumption were measured by DCFH-DA and GOD-POD methods, respectively. The results of Microarray analysis demonstrated that there were 10 differentially expressed miRNAs (DEMs) selected based on Fold change (FC) and P value in the IR cell model compared with HUVECs. The enriched gene ontology (GO) terms analysis showed that the target genes of these 10 DEMs were significantly enriched in biological process, cellular component and molecular function, and the significantly enriched Kyoto Encyclopedia of Genes or Genomes (KEGG) pathways mainly include AMPK signaling pathway and PI3K signaling pathway. Amongst all, the expression level of miR-3138 was highest in the IR cell model evaluated by qRT-PCR. Through Targetscan, KSR2 mRNA was predicted as a target of miR-3138. And mRNA and protein expression levels of miR-3138, KSR2, GLUT4, AMPK, PI3K, Akt were examined using qRT-PCR and Western blotting, respectively. The interaction between miR-3138 and KSR2 was evaluated by dual-luciferase reporter assay. Our results showed that miR-3138 significantly deteriorated the IR of HUVECs via KSR2/AMPK/GLUT4 signaling pathway.

Identification of biomarkers and pathways in hypertensive nephropathy based on the ceRNA regulatory network

BACKGROUND

Hypertensive nephropathy (HTN) is a kind of renal injury caused by chronic hypertension, which seriously affect people's life. The purpose of this study was to identify the potential biomarkers of HTN and understand its possible mechanisms.

METHODS

The dataset numbered GSE28260 related to hypertensive and normotensive was downloaded from NCBI Gene Expression Omnibus. Then, the differentially expressed RNAs (DERs) were screened using R limma package, and functional analyses of DE-mRNA were performed by DAVID. Afterwards, a ceRNA network was established and KEGG pathway was analyzed based on the Gene Set Enrichment Analysis (GSEA) database. Finally, a ceRNA regulatory network directly associated with HTN was proposed.

RESULTS

A total of 947 DERs were identified, including 900 DE-mRNAs, 20 DE-lncRNAs and 27 DE-miRNAs. Based on these DE-mRNAs, they were involved in biological processes such as fatty acid beta-oxidation, IRE1-mediated unfolded protein response, and transmembrane transport, and many KEGG pathways like glycine, serine and threonine metabolism, carbon metabolism. Subsequently, lncRNAs KCTD21-AS1, LINC00470 and SNHG14 were found to be hub nodes in the ceRNA regulatory network. KEGG analysis showed that insulin signaling pathway, glycine, serine and threonine metabolism, pathways in cancer, lysosome, and apoptosis was associated with hypertensive. Finally, insulin signaling pathway was screened to directly associate with HTN and was regulated by mRNAs PPP1R3C, PPKAR2B and AKT3, miRNA has-miR-107, and lncRNAs SNHG14, TUG1, ZNF252P-AS1 and MIR503HG.

CONCLUSIONS

Insulin signaling pathway was directly associated with HTN, and miRNA has-miR-107 and lncRNAs SNHG14, TUG1, ZNF252P-AS1 and MIR503HG were the biomarkers of HTN. These results would improve our understanding of the occurrence and development of HTN.

MYDGF attenuates podocyte injury and proteinuria by activating Akt/BAD signal pathway in mice with diabetic kidney disease

AIMS/HYPOTHESIS

Myeloid-derived growth factor (MYDGF), mainly secreted by bone marrow-derived cells, has been known to promote glucagon-like peptide-1 production and improve glucose/lipid metabolism in mouse models of diabetes, but little is known about the functions of MYDGF in diabetic kidney disease (DKD). Here, we investigated whether MYDGF can prevent the progression of DKD.

METHODS

In vivo experiments, both loss- and gain-of-function strategies were used to evaluate the effect of MYDGF on albuminuria and pathological glomerular lesions. We used streptozotocin-treated Mydgf knockout and wild-type mice on high fat diets to induce a model of DKD. Then, albuminuria, glomerular lesions and podocyte injury were evaluated in Mydgf knockout and wild-type DKD mice treated with adeno-associated virus-mediated Mydgf gene transfer. In vitro and ex vivo experiments, the expression of slit diaphragm protein nephrin and podocyte apoptosis were evaluated in conditionally immortalised mouse podocytes and isolated glomeruli from non-diabetic wild-type mice treated with recombinant MYDGF.

RESULTS

MYDGF deficiency caused more severe podocyte injury in DKD mice, including the disruption of slit diaphragm proteins (nephrin and podocin) and an increase in desmin expression and podocyte apoptosis, and subsequently caused more severe glomerular injury and increased albuminuria by 39.6% compared with those of wild-type DKD mice (p < 0.01). Inversely, MYDGF replenishment attenuated podocyte and glomerular injury in both wild-type and Mydgf knockout DKD mice and then decreased albuminuria by 36.7% in wild-type DKD mice (p < 0.01) and 34.9% in Mydgf knockout DKD mice (p < 0.01). Moreover, recombinant MYDGF preserved nephrin expression and inhibited podocyte apoptosis in vitro and ex vivo. Mechanistically, the renoprotection of MYDGF was attributed to the activation of the Akt/Bcl-2-associated death promoter (BAD) pathway.

CONCLUSIONS/INTERPRETATION

The study demonstrates that MYDGF protects podocytes from injury and prevents the progression of DKD, providing a novel strategy for the treatment of DKD. Graphical abstract.

FOXO3a accumulation and activation accelerate oxidative stress-induced podocyte injury

Podocyte injury is the primary cause of glomerular injury in diabetic nephropathy (DN). Advanced oxidation protein products (AOPPs), the triggers and markers of oxidative stress in DN, have been linked to podocyte damage. However, the underlying mechanism is not yet clear. Here, we investigated the potential role of FOXO3a, a key transcription factor in the response to stress, in mediating AOPPs-induced podocyte injury. We found that FOXO3a expression was increased in the glomeruli of kidney biopsies from patients with DN and it was positively correlated with proteinuria. The serum from patients with DN significantly increased FOXO3a and its downstream genes FasL and Bim, thereby inducing the high level of cleaved caspase3 and the loss of nephrin and podocin expressions in podocytes. Blockade of AOPPs signaling by a neutralizing antibody against the receptor of advanced glycation end products (αRAGE) abolished the effect of DN serum on podocytes, confirming the pathogenic role of AOPPs in DN serum. Downregulation of FOXO3a decreased AOPPs-induced podocyte apoptosis and restored the levels of podocyte markers nephrin and podocin, and upregulation of FOXO3a exacerbated these changes in podocytes after AOPPs treatment. Furthermore, FOXO3a specifically activated proapoptotic genes in podocytes only in the presence of AOPPs. Mechanistically, AOPPs increased the FOXO3a protein levels by inhibiting their autophagic degradation in a ROS/mTOR-dependent manner. Moreover AOPPs activated the accumulated FOXO3a by maintaining FOXO3a in the nucleus, and this process was dependent on ROS-mediated AKT signaling deactivation. These studies suggest that FOXO3a plays a critical role in mediating AOPPs-induced podocyte injury and reveal a new mechanistic linkage of oxidative stress, FOXO3a activation and podocyte injury in DN.

Mesenchymal Stem Cells Attenuate Diabetic Lung Fibrosis via Adjusting Sirt3-Mediated Stress Responses in Rats

Diabetes affects a variety of organs such as the kidneys, eyes, and liver, and there is increasing evidence that the lung is also one of the target organs of diabetes and imbalance of Sirt3-mediated stress responses such as inflammation, oxidative stress, apoptosis, autophagy, and ER stress may contribute to diabetic lung fibrosis. Although previous studies have reported that mesenchymal stem cells (MSCs) have beneficial effects on various diabetic complications, the effect and mechanisms of MSCs on diabetes-induced lung injury are not clear. In this study, the STZ-induced diabetes model was constructed in rats, and the effect and potential mechanisms of bone marrow MSCs on diabetic lung fibrosis were investigated. The results revealed that fibrotic changes in the lung were successfully induced in the diabetic rats, while MSCs significantly inhibited or even reversed the changes. Specifically, MSCs upregulated the expression levels of Sirt3 and SOD2 and then activated the Nrf2/ARE signaling pathway, thereby controlling MDA, GSH content, and iNOS and NADPH oxidase subunit p22phox expression levels in the lung tissue. Meanwhile, high levels of Sirt3 and SOD2 induced by MSCs reduced the expression levels of IL-1β, TNF-α, ICAM-1, and MMP9 by suppressing the NF-κB/HMGB1/NLRP3/caspase-1 signaling pathway, as well as regulating the expression levels of cleaved caspasese-3, Bax, and Bcl2 by upregulating the expression level of P-Akt, thereby inhibiting the apoptosis of the lung tissue. In addition, MSCs also regulated the expression levels of LC3, P62, BiP, Chop, and PERK, thereby enhancing autophagy and attenuating endoplasmic reticulum stress. Taken together, our results suggest that MSCs effectively attenuate diabetic lung fibrosis via adjusting Sirt3-mediated responses, including inflammation, oxidative stress, apoptosis, autophagy, and endoplasmic reticulum stress, providing a theoretical foundation for further exploration of MSC-based diabetic therapeutics.

Transcriptomic characterization of culture-associated changes in murine and human precision-cut tissue slices

Our knowledge of complex pathological mechanisms underlying organ fibrosis is predominantly derived from animal studies. However, relevance of animal models for human disease is limited; therefore, an ex vivo model of human precision-cut tissue slices (PCTS) might become an indispensable tool in fibrosis research and drug development by bridging the animal-human translational gap. This study, presented as two parts, provides comprehensive characterization of the dynamic transcriptional changes in PCTS during culture by RNA sequencing. Part I investigates the differences in culture-induced responses in murine and human PCTS derived from healthy liver, kidney and gut. Part II delineates the molecular processes in cultured human PCTS generated from diseased liver, kidney and ileum. We demonstrated that culture was associated with extensive transcriptional changes and impacted PCTS in a universal way across the organs and two species by triggering an inflammatory response and fibrosis-related extracellular matrix (ECM) remodelling. All PCTS shared mRNA upregulation of IL-11 and ECM-degrading enzymes MMP3 and MMP10. Slice preparation and culturing activated numerous pathways across all PCTS, especially those involved in inflammation (IL-6, IL-8 and HMGB1 signalling) and tissue remodelling (osteoarthritis pathway and integrin signalling). Despite the converging effects of culture, PCTS display species-, organ- and pathology-specific differences in the regulation of genes and canonical pathways. The underlying pathology in human diseased PCTS endures and influences biological processes like cytokine release. Our study reinforces the use of PCTS as an ex vivo fibrosis model and supports future studies towards its validation as a preclinical tool for drug development.

Glucose Transporters in Diabetic Kidney Disease-Friends or Foes?

Diabetic kidney disease (DKD) is a major microvascular complication of diabetes and a common cause of end-stage renal disease worldwide. DKD manifests as an increased urinary protein excretion (albuminuria). Multiple studies have shown that insulin resistance correlates with the development of albuminuria in non-diabetic and diabetic patients. There is also accumulating evidence that glomerular epithelial cells or podocytes are insulin sensitive and that insulin signaling in podocytes is essential for maintaining normal kidney function. At the cellular level, the mechanisms leading to the development of insulin resistance include mutations in the insulin receptor gene, impairments in the phosphoinositide 3-kinase (PI3K)/AKT signaling pathway, or perturbations in the trafficking of glucose transporters (GLUTs), which mediate the uptake of glucose into cells. Podocytes express several GLUTs, including GLUT1, GLUT2, GLUT3, GLUT4, and GLUT8. Of these, the most studied ones are GLUT1 and GLUT4, both shown to be insulin responsive in podocytes. In the basal state, GLUT4 is preferentially located in perinuclear and cytosolic vesicular structures and to a lesser extent at the plasma membrane. After insulin stimulation, GLUT4 is sorted into GLUT4-containing vesicles (GCVs) that translocate to the plasma membrane. GCV trafficking consists of several steps, including approaching of the GCVs to the plasma membrane, tethering, and docking, after which the lipid bilayers of the GCVs and the plasma membrane fuse, delivering GLUT4 to the cell surface for glucose uptake into the cell. Studies have revealed novel molecular regulators of the GLUT trafficking in podocytes and unraveled unexpected roles for GLUT1 and GLUT4 in the development of DKD, summarized in this review. These findings pave the way for better understanding of the mechanistic pathways associated with the development and progression of DKD and aid in the development of new treatments for this devastating disease.

Vitamin D3 ameliorates podocyte injury through the nephrin signalling pathway

Renal podocytes form the main filtration barrier possessing unique phenotype maintained by proteins including podocalyxin and nephrin, which are modulated in pathological conditions. In diabetic nephropathy (DN), podocytes become structurally and functionally compromised. Nephrin, a structural backbone protein of the slit diaphragm, acts as regulator of podocyte intracellular signalling with renoprotective role. Vitamin D₃ through its receptor, VDR, provides renal protection in DN but limited data exist about its effect on podocytes. In this study, we used isolated rat glomeruli to assess podocalyxin and nephrin expression after treatment with the 1,25‐dihydroxyvitamin D₃ analogue paricalcitol in the presence of normal and diabetic glucose levels. The role of 1,25‐dihydroxyvitamin D₃ (calcitriol) and its analogue, paricalcitol, on podocyte morphology and survival was also investigated in the streptozotocin (STZ)‐diabetic animal model. In our ex vivo model, glomeruli exhibited high glucose‐mediated down‐regulation of podocalyxin, and nephrin, while paricalcitol reversed the high glucose‐induced decrease of nephrin and podocalyxin expression. Paricalcitol treatment enhanced VDR expression and promoted VDR and RXR co‐localization in the nucleus. Our data also indicated that hyperglycaemia impaired survival of cultured glomeruli and suggested that the implemented nephrin down‐regulation was reversed by paricalcitol treatment, initiating Akt signal transduction which may be involved in glomerular survival. Our findings were further verified in vivo, as in the STZ‐diabetic animal model, calcitriol and paricalcitol treatment resulted in significant amelioration of hyperglycaemia and restoration of nephrin signalling, suggesting that calcitriol and paricalcitol may provide molecular bases for protection against loss of the permselective renal barrier in DN.

Role of Sirtuin3 in high glucose-induced apoptosis in renal tubular epithelial cells

The apoptosis of renal tubular epithelial cells contributes to the pathogenesis of diabetic nephropathy. High glucose-induced mitochondrial oxidative stress is considered to be an important mediator for renal tubular cell apoptosis. Sirtuin3(Sirt3), a kind of mitochondria-localized nicotinamide adenine dinucleotide(NAD⁺)-dependent protein deacetylase, has been reported to regulate the generation of ROS in mitochondria through regulating acetylation level and activity of several key mitochondrial enzymes. In this study, we investigated the role of Sirt3 on high glucose-induced apoptosis in HK-2 cells. High glucose decreased the protein and mRNA expression of Sirt3 in a time-dependent manner, along with increased cell apoptosis in HK-2 cells. Furthermore, high glucose-induced oxidative stress and apoptosis were reversed by Sirt3 overexpression or antioxidant treatment. Meanwhile, we also found that overexpression of Sirt3 or antioxidant could regulate the activity of Akt/FoxO signaling pathway associated with cell apoptosis in diabetic nephropathy. In conclusion, our data suggest that Sirt3 overexpression antagonize high glucose-induced apoptosis by controlling ROS accumulation and ROS-sensitive Akt/FoxO signaling pathway in HK-2 cells.