Glucose-induced Insulin Resistance Research Articles

Interaction between the Neuroprotective and Hyperglycemia Mitigation Effects of Walnut-Derived Peptide LVRL via the Wnt3a/β-Catenin/GSK-3β Pathway in a Type 2 Diabetes Mellitus Model.

The term type 3 diabetes mellitus (T3DM) has been considered for Alzheimer's disease (AD) due to the common molecular and cellular characteristics found between type 2 diabetes mellitus (T2DM) and cognitive deficits. However, the specific mechanism of T3DM remains elusive, especially the neuroprotective effects of dietary components in hyperglycemic individuals. In this study, a peptide, Leu-Val-Arg-Leu (LVRL), found in walnuts significantly improved memory decline in streptozotocin (STZ)- and high-fat-diet (HFD)-stimulated T2DM mouse models (p < 0.05). The LVRL peptide also mitigated hyperglycemia, enhanced synaptic plasticity, and ameliorated mitochondrial dysfunction, as demonstrated by Morris water maze tests, immunoblotting, immunofluorescence, immunohistochemistry, transmission electron microscopy, and cellular staining. A Wnt3a inhibitor, DKK1, was subsequently used to verify the possible role of the Wnt3a/β-Catenin/GSK-3β pathway in glucose-induced insulin resistance in PC12 cells. In vitro LVRL treatment dramatically modulated the protein expression of p-Tau (Ser404), Synapsin-1, and PSD95, elevated the insulin level, increased glucose consumption, and relieved the mitochondrial membrane potential, and MitoSOX (p < 0.05). These data suggested that peptides like LVRL could modulate the relationship between brain insulin and altered cognition status via the Wnt3a/β-Catenin/GSK-3β pathway.

Interaction between the Neuroprotective and Hyperglycemia Mitigation Effects of Walnut-Derived Peptide LVRL via the Wnt3a/β-Catenin/GSK-3β Pathway in a Type 2 Diabetes Mellitus Model.

The term type 3 diabetes mellitus (T3DM) has been considered for Alzheimer's disease (AD) due to the common molecular and cellular characteristics found between type 2 diabetes mellitus (T2DM) and cognitive deficits. However, the specific mechanism of T3DM remains elusive, especially the neuroprotective effects of dietary components in hyperglycemic individuals. In this study, a peptide, Leu-Val-Arg-Leu (LVRL), found in walnuts significantly improved memory decline in streptozotocin (STZ)- and high-fat-diet (HFD)-stimulated T2DM mouse models (p < 0.05). The LVRL peptide also mitigated hyperglycemia, enhanced synaptic plasticity, and ameliorated mitochondrial dysfunction, as demonstrated by Morris water maze tests, immunoblotting, immunofluorescence, immunohistochemistry, transmission electron microscopy, and cellular staining. A Wnt3a inhibitor, DKK1, was subsequently used to verify the possible role of the Wnt3a/β-Catenin/GSK-3β pathway in glucose-induced insulin resistance in PC12 cells. In vitro LVRL treatment dramatically modulated the protein expression of p-Tau (Ser404), Synapsin-1, and PSD95, elevated the insulin level, increased glucose consumption, and relieved the mitochondrial membrane potential, and MitoSOX (p < 0.05). These data suggested that peptides like LVRL could modulate the relationship between brain insulin and altered cognition status via the Wnt3a/β-Catenin/GSK-3β pathway.

Therapeutic effects of a walnut-derived peptide on NLRP3 inflammasome activation, synaptic plasticity, and cognitive dysfunction in T2DM mice.

NLRP3 inflammasome activation plays a key role in the development of diabetes-induced cognitive impairment. However, strategies to inhibit NLRP3 inflammasome activation remain elusive. Herein, we evaluated the impact of a walnut-derived peptide, TWLPLPR (TW-7), on cognitive impairment in high-fat diet/streptozotocin-induced type 2 diabetes mellitus (T2DM) mice and explored its underlying mechanisms in high glucose-induced HT-22 cells. In the Morris water maze test, TW-7 alleviated cognitive deficits in mice; this was confirmed at the level of synaptic structure and dendritic spine density in the mouse hippocampus using transmission electron microscopy and Golgi staining. TW-7 increased the expression of synaptic plasticity-related proteins and suppressed the NEK7/NLRP3 inflammatory pathway, as determined by western blotting and immunofluorescence analysis. The mechanism of action of TW-7 was verified in an HT-22 cell model of high glucose-induced insulin resistance. Collectively, TW-7 could regulate T2DM neuroinflammation and synaptic function-induced cognitive impairment by inhibiting NLRP3 inflammasome activation and improving synaptic plasticity.

High glucose promotes the progression of colorectal cancer by activating the BMP4 signaling and inhibited by glucagon-like peptide-1 receptor agonist

BackgroundThe detailed molecular mechanism between type 2 diabetes mellitus (T2DM) and colorectal cancer (CRC) is still uncertain. Bone morphogenetic protein 4 (BMP4) dysregulation is implicated in T2DM and CRC, respectively. This study aims to investigate whether BMP4 can mediate the interaction of CRC with T2DM.MethodsWe firstly explored the expression of BMP4 in The Cancer Genome Altas (TCGA) databases and CRC patients with or without DM from the Shanghai Tenth People’s Hospital. The diabetic model of CRC cell lines in vitro and the mice model in vivo were developed to explore the BMP4 expression during CRC with or without diabetes. Further inhibition of BMP4 to observe its effects on CRC. Also, glucagon-like peptide-1 receptor agonist (GLP-1RA) was used to verify the underlying mechanism of hypoglycemic drugs on CRC via BMP4.ResultsBMP4 expression was upregulated in CRC patients, and significantly higher in CRC patients with diabetes (P < 0.05). High glucose-induced insulin resistance (IR)-CRC cells and diabetic mice with metastasis model of CRC had increased BMP4 expression, activated BMP4-Smad1/5/8 pathway, and improved proliferative and metastatic ability mediated by epithelial-mesenchymal transition (EMT). And, treated CRC cells with exogenously BMP inhibitor-Noggin or transfected with lentivirus (sh-BMP4) could block the upregulated metastatic ability of CRC cells induced by IR. Meanwhile, GLP-1R was downregulated by high glucose-induced IR while unregulated by BMP4 inhibitor noggin, and treated GLP-1RA could suppress the proliferation of CRC cells induced by IR through downregulated BMP4.ConclusionsBMP4 increased by high glucose promoted the EMT of CRC. The mechanism of the BMP4/Smad pathway was related to the susceptible metastasis of high glucose-induced IR-CRC. The commonly used hypoglycemic drug, GLP-1RA, inhibited the growth and promoted the apoptosis of CRC through the downregulation of BMP4. The result of our study suggested that BMP4 might serve as a therapeutic target in CRC patients with diabetes.

Inhibition of phosphodiesterase 5A by tadalafil improves SIRT1 expression and activity in insulin-resistant podocytes

A decrease in intracellular levels of 3′,5′-cyclic guanosine monophosphate (cGMP) has been implicated in the progression of diabetic nephropathy. Hyperglycemia significantly inhibits cGMP-dependent pathway activity in the kidney, leading to glomerular damage and proteinuria. The enhancement of activity of this pathway that is associated with an elevation of cGMP levels may be achieved by inhibition of the cGMP specific phosphodiesterase 5A (PDE5A) using selective inhibitors, such as tadalafil. Hyperglycemia decreased the insulin responsiveness of podocytes and impaired podocyte function. These effects were associated with lower protein amounts and activity of the protein deacetylase sirtuin 1 (SIRT1) and a decrease in the phosphorylation of adenosine monophosphate-dependent protein kinase (AMPK). We found that PDE5A protein levels increased in hyperglycemia, and PDE5A downregulation improved the insulin responsiveness of podocytes with reestablished SIRT1 expression and activity. PDE5A inhibitors potentiate nitric oxide (NO)/cGMP signaling, and NO modulates the activity and expression of SIRT1. Therefore, we investigated the effects of tadalafil on SIRT1 and AMPK in the context of improving the insulin sensitivity in podocytes and podocyte function in hyperglycemia. Our study revealed that tadalafil restored SIRT1 expression and activity and activated AMPK by increasing its phosphorylation. Tadalafil also restored stimulating effect of insulin on glucose transport in podocytes with high glucose-induced insulin resistance. Additionally, tadalafil improved the function of podocytes that were exposed to high glucose concentrations. Our results display novel mechanisms involved in the pathogenesis of glomerulopathies in diabetes, which may contribute to the development of more effective treatment strategies for diabetic nephropathy.

A diarylheptanoid compound from Alpinia officinarum Hance ameliorates high glucose-induced insulin resistance by regulating PI3K/AKT-Nrf2-GSK3β signaling pathways in HepG2 cells

Ethnopharmacological relevanceAlpinia officinarum Hance, a perennial natural medicine-food herb, has been traditionally used to treat colds, stomachache, and diabetes for thousands of years. 1,7-Diphenyl-4E-en-3-heptanone (DPH5), a diarylheptanoid isolated from the rhizome of A. officinarum has been reported to be safe and to have antioxidant and hypoglycemic effects, suggesting its potential in the treatment of insulin resistance (IR).Aim of the study: Aim of to investigate the protective effect of DPH5 on IR and elucidate its underlying mechanism of action. Materials and methodsHepG2 cells were used as the research objects. Glucose uptake and reactive oxygen species (ROS) levels in high glucose–induced insulin-resistant HepG2 cells were assessed using flow cytometry. Glucose consumption and the levels of malondialdehyde (MDA) and superoxide dismutase (SOD) were analyzed using the corresponding assay kits. The expression of mRNA and proteins related to insulin signaling, glucose metabolism, and antioxidant factor, including insulin receptor substrate-1 (IRS1), phosphatidylinositol 3-kinase (PI3K), protein kinase B (AKT), translocation of glucose transporter-4, glycogen synthase kinase-3β (GSK3β), glucokinase (GCK), pyruvate kinase (PK), phosphoenolpyruvate carboxykinase (PEPCK), glucose-6-phosphatase (G6Pase), nuclear factor-erythroid 2 related factor 2 (Nrf2), heme oxygenase-1 (HO-1), NADPH quinoneoxidoreductase (NQO1), and glutathione peroxidase (GSH-Px) was determined using real-time quantitative polymerase chain reaction and western blotting. Furthermore, molecular docking was performed to determine the spatial mechanism of DPH5 on the key targets PI3K, AKT, Nrf2, and GSK3β. ResultsDPH5 could improve IR that manifested as increased glucose uptake and glucose consumption in insulin-resistant HepG2 cells. Moreover, DPH5 could enhance antioxidant capacity by activating Nrf2/HO-1 elements, including increasing Nrf2, HO-1, SOD, NQO1, and GSH-Px expression and reducing MDA, ROS, and JNK levels, thereby improving oxidative stress and ultimately alleviating IR. Additionally, DPH5 could promote the expression of IRS1, PI3K, AKT, GSK3β, GCK, and PK, and downregulate the expression of PEPCK and G6pase, thereby accelerating glucose utilization and enhancing insulin sensitivity. The mechanism underlying the effect of DPH5 in alleviating IR was related to the PI3K/AKT- and Nrf2/HO-1-mediated regulation of the GSK3β signaling pathway, and the results were further confirmed using the specific inhibitors LY294002 and ML385. Results from molecular docking indicated that there were different regulatory sites and interacting forces between DPH5 and PI3K, AKT, Nrf2, and GSK3β; however, the binding force was relatively strong. ConclusionsDPH5 improved oxidative stress and glucose metabolism via modulating the PI3K/AKT-Nrf2-GSK3β pathway, thereby ameliorating IR. Overall, our findings suggest the potential of DPH5 as a natural medicine to treat type-2 diabetes mellitus.

Mechanisms by which smoothelin-like protein 1 reverses insulin resistance in myotubules and mice

Insulin resistance (InR) is manifested in skeletal muscle by decreased insulin-stimulated glucose uptake due to impaired insulin signaling and multiple post-receptor intracellular defects. Chronic glucose-induced insulin resistance leads to the activation of Ser/Thr kinases and elevated phosphorylation of insulin receptor substrate 1 (IRS1) on Ser residues. Phosphorylation of IRS1 triggers the dissociation of IRS1 and its downstream effector, phosphatidylinositol 3-kinase. In the present study, we provide evidence for the insulin-sensitizing role of smoothelin-like protein 1 (SMTNL1) that is a ligand-dependent co-regulator of steroid receptors, predominantly the progesterone receptor. SMTNL1 was transiently overexpressed in insulin-resistant C2C12 myotubes. A proteome profiler array revealed that mTOR and Ser/Thr kinases were SMTNL1-dependent signaling pathways. In the presence of progesterone, overexpression was coupled to decreased Ser phosphorylation of IRS1 at Ser307, Ser318, and Ser612 residues. SMTNL1 also induced the expression and activity of the p85 subunit of PI3K. SMTNL1 regulated the expression of PKCε, which phosphorylates IRS1 at Ser318 residue. SMTNL1 also regulated ERK1/2 and JNK, which phosphorylate IRS1 at Ser612 and Ser307, respectively. Real-time metabolic measurements of oxygen consumption rate and extracellular acidification rate revealed that SMTNL1 improved glycolysis and promoted the utilization of alternative carbon fuels. SMTNL1 also rescued the mitochondrial respiration defect induced by chronic insulin exposure. Collectively, SMTNL1 plays a crucial role in maintaining the physiological ratio of Tyr/Ser IRS1 phosphorylation and attenuates the insulin-signaling cascade that contributes to impaired glucose disposal, which makes it a potential therapeutic target for improving InR.

Plumbagin attenuates high glucose-induced trophoblast cell apoptosis and insulin resistance via activating AKT/mTOR pathway

Plumbagin, a bioactive phytoconstituent, is isolated from the root of Plumbago zeylanica L. Plumbagin possesses antidiabetic effect to mediate glucose homeostasis, wound healing and diabetic nephropathy. However, the involvement of plumbagin in gestational diabetes mellitus (GDM) has not been reported yet. Trophoblast cell line (HTR8/SVneo) was incubated with high glucose to establish cell model of GDM. Cell viability and proliferation were detected by MTT and EdU staining. Flow cytometry was used to investigate cell apoptosis. Cell viability of HTR8/SVneo was reduced by high glucose or incubation of plumbagin. Plumbagin restored reduced cell viability and proliferation of HTR8/SVneo induced by high glucose. Plumbagin attenuated high glucose-induced cell apoptosis in HTR8/SVneo cells through upregulation of Bcl-2 and down-regulation of Bax, cleaved caspase-3 and cleaved caspase-9. Protein expression of glucose transporter type 4 (GLUT-4), insulin receptor (INSR)-B and INSR substrate (IRS1) was decreased in high glucose-induced HTR8/SVneo but increased by plumbagin. The suppressive effects of high glucose on phosphorylation of AKT and mTOR in HTR8/SVneo were reversed by plumbagin. Plumbagin improved high glucose-induced cell apoptosis and insulin resistance of HTR8/SVneo through activation of AKT/mTOR pathway, suggesting that plumbagin might be used as a potential strategy for the prevention of GDM.

Nicorandil attenuates high glucose-induced insulin resistance by suppressing oxidative stress-mediated ER stress PERK signaling pathway

IntroductionGlucose-induced insulin resistance is a typical character of diabetes. Nicorandil is now widely used in ischemic heart disease. Nicorandil shows protective effects against oxidative and endoplasmic reticulum (ER) stress, which...

Nicorandil Attenuates High Glucose-Induced Insulin Resistance by Suppressing Oxidative Stress-Mediated Endoplasmic Reticulum Stress Protein Kinase RNA-Like Endoplasmic Reticulum Kinase Singling Pathway

Background: Glucose- induced insulin resistance (IR) is a typical character of diabetes. Nicorandil is widely used in ischemic heart disease. Nicorandil shows protective effects against oxidative and endoplasmic reticulum (ER) stress which are involved in insulin resistance. Here we investigated mechanisms of nicorandil’s novel pharmacological activity on IR in diabetes. Methods: Nicorandil was administrated to diabetic animals and high-glucose exposed skeletal muscle cells. IR and glucose tolerance were evaluated. Molecular mechanisms concerning oxidative stress, ER stress and glucose uptake were assessed. Findings: Nicorandil attenuated high- glucose induced IR without affecting fasting blood glucose and glucose tolerance in whole body and skeletal muscle in diabetic rats. Nicorandil treatment suppressed protein kinase C(PKC)/ nicotinamide adenine dinucleotide phosphate (NADPH) oxidases (NOX) system activities by reducing cytoplasmic free calcium level in skeletal muscle cells exposed to high glucose. As a result, the oxidative stress- mediated ER stress protein kinase RNA- like endoplasmic reticulum kinase (PERK)/ eukaryotic initiation factor (EIF) 2α/ activating transcription factor (ATF)4/CEBP homologous protein (CHOP)/tribbles homolog (TRB)3 signaling pathway activation was inhibited. Nicorandil down-regulated expression of TRB3 and thus facilitated Akt phosphorylation in response to insulin stimulation, leading to glucose transporter (GLUT)4 plasma membrane translocation which promoted glucose uptake capability of skeletal muscle cells. Interpretation: By reducing cytoplasmic calcium, nicorandil alleviated high-glucose induced IR by inhibiting oxidative stress- mediated ER stress PERK pathway. This study indicated nicorandil as a promising agent in treatment of patients with ischemic heart disease complicated with diabetes. Funding Statement: This study was supported by Innovative Talents Promotion Project of Shaanxi Province (2019KJXX-019); Fundamental Scientific Research Foundation of Xi’an Jiaotong University (xzy012019131); Health Scientific Foundation of Shaanxi Province (2018E11); Natural Science Basic Research Foundation of Shaanxi Province (2020JQ-941). Declaration of Interests: The authors declare no conflicts of interest. Ethics Approval Statement: The experimental protocols were reviewed and approved by Institutional Animal Care and Use Committee of Medical Research Institute of Northwestern Polytechnical University.

Polyphenol-rich extract of Zhenjiang aromatic vinegar ameliorates high glucose-induced insulin resistance by regulating JNK-IRS-1 and PI3K/Akt signaling pathways

Zhenjiang aromatic vinegar is a famous traditional fermented cooking ingredient in China, with multiple nutritional and medicinal applications. Zhenjiang aromatic vinegar extract (100–400 μg/mL) is rich in polyphenols increased the glucose uptake and glucose consumption in high glucose-induced insulin resistant HepG2 (IR-HepG2) cells. Zhenjiang aromatic vinegar extract enhanced glycogen synthesis and attenuated gluconeogenesis by regulating key enzymes in IR-HepG2 cells. In addition, Zhenjiang aromatic vinegar extract ameliorated high glucose-induced IR by inhibiting phosphorylated insulin receptor substrate-1 (IRS-1) expression and activating phosphatidylinositol 3-kinase (PI3K)/protein kinase B (Akt) pathway in IR-HepG2 cells. Moreover, Zhenjiang aromatic vinegar extract reduced reactive oxygen species generation and phosphorylated c-Jun NH2 terminal kinase (JNK) expression in IR-HepG2 cells. The attenuation of the high glucose is owned to the PI3K/Akt pathway activation, glycogen synthesis induction and gluconeogenesis suppression in IR-HepG2 cells.

Peptides from walnut (Juglans mandshurica Maxim.) protect hepatic HepG2 cells from high glucose-induced insulin resistance and oxidative stress

Oxidative stress is an important factor in the pathogenesis of insulin resistance (IR) in type 2 diabetes mellitus (T2DM). Bioactive peptides from nuts have been shown to alleviate oxidative stress and IR. However, the specific mechanisms underlying their activity remain unclear. This study investigated the protective effects of three novel peptides derived from Juglans mandshurica Maxim., LVRL, LRYL, and VLLALVLLR, against high glucose-induced IR and oxidative stress in HepG2 cells. The possible mechanisms underlying these effects were also elucidated. The walnut-derived peptides improved glucose consumption, glucose uptake, and glucose transporter type 4 (GLUT4) translocation, and elevated the phosphorylation of insulin receptor substrate 1 (IRS-1), phosphatidylinositol 3-kinase (PI3K), and protein kinase B (Akt). They also increased the activities of glutathione peroxidase (GSH-Px), catalase (CAT), and superoxide dismutase (SOD), the nuclear transport of nuclear factor E2-related factor 2 (Nrf2), and the protein expression of heme oxygenase-1 (HO-1). Furthermore, the walnut-derived peptides reduced high glucose-induced ROS overproduction and the phosphorylation of extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK), and p38. These results suggested that walnut-derived peptides protect HepG2 cells from high glucose-induced IR and oxidative stress by activating IRS-1/PI3 K/Akt and Nrf2/HO-1 signaling pathways.

The protective effect of silk fibroin on high glucose induced insulin resistance in HepG2 cells

The therapeutic use of silk-derived materials such as fibroin in biomedicine is well-established in Southeast Asian countries. Studies indicated that silk fibroin (SF) peptide enhances insulin sensitivity and glucose metabolism phenomena associated with type 2 diabetes mellitus (T2DM) suggesting this peptide may be beneficial to treat this disease. However, the mechanisms underlying protective effect of SF in insulin-mediated hepatic metabolic dysfunction remains unclear. The aim of this study was to investigate the influence of SF on insulin resistant HepG2 cells which were used a model of T2DM. Treatment of cells with 30 mmol/L of glucose and 10−6 mol/L insulin for 48 h significantly reduced glucose consumptions and intracellular glycogen levels but increased triglyceride (TG) levels. SF or metformin alone elevated glucose consumptions and glycogen accumulation accompanied by lower TG content. Greater effects in these metabolic parameters were found when SF and metformin were combined. Treatment of insulin resistant cells with SF or metformin alone decreased levels of reactive oxygen species (ROS), malondialdehyde (MDA), tumor necrosis factor (TNF-α) and interleukin-6 (IL-6); whereas antioxidant enzymes superoxide dismutase (SOD) and catalase (CAT) activity, as well as total antioxidant capacity (T-AOC) ability increased. The combination of SF and metformin produced greater changes in these parameters compared to metformin alone. Data indicated that the protective effect of SF or metformin in insulin resistant HepG2 cells involves inhibition of oxidant processes and that the combination of agents may prove more effective therapeutically.

Abstract 2524: A new mTOR-independent effect of rapamycin: Transcriptional regulation of TRIB3

Abstract Background: Mechanistic Target of Rapamycin (mTOR), a key component of the PI3K/Akt signaling pathway, coordinates various cellular processes such as metabolism, growth, cell proliferation and cell cycle progression. Dysregulations affecting mTOR frequently occur in cancer, and mTOR inhibitors/rapalogs are used as monotherapy or a part of combination therapy in breast or kidney metastatic cancer. Despite this, response rate is modest. Several mechanisms of resistance have been reported, but do not fully characterize insensitive tumor cells. Purpose: This study investigated new target genes of rapamycin/rapalogs. Methods: Expression levels of target genes were evaluated in a panel of cancer cell lines by transcriptomic analyses, real-time qPCR and western blot. Transcriptional regulation was investigated by in silico analyses of the promoter region, gene reporter assays using site-directed mutagenesis, and ChIP. Stably silenced cell lines were established by lentiviral transduction of shRNA sequences. Results: We identified one gene: TRIB3 (Tribbles Pseudokinase 3), whose expression is downregulated in the presence of rapamycin in a panel of cancer cell lines and in PBMCs isolated from cancer patients. This gene encodes for a pseudokinase involved in a glucose-induced insulin resistance in Type 2 Diabetes by inhibiting the activation of Akt1/2. We observed that silencing mTOR did not mimic rapamycin downregulation of TRIB3, suggesting an mTOR-independent effect of rapamycin. We identified a binding site for the transcriptional repressor GCF2/LRRFIP1 in the promoter region of TRIB3, and confirmed that the presence and the binding of GCF2 to TRIB3 promoter are required for TRIB3 downregulation by rapamycin. Finally, we identified FKBP3 (FK506-Binding Protein 3), a protein that can bind rapamycin with high affinity, as a GCF2 partner, confirming the direct effect of rapamycin on TRIB3 promoter. Conclusions: Taken together, our investigations identified a novel transcriptional target gene of rapamycin: TRIB3. We also characterized the molecular mechanism of regulation by rapamycin through a FKBP3/GCF2-dependent repression of TRIB3 promoter activity, and independently of mTOR signaling. Such variations in TRIB3 expression level in cancer cells could be linked to rapamycin sensitivity, and may represent a valuable therapeutic target. Citation Format: Bojana Stefanovska, Cécile Vicier, Véronique Scott, Guillaume Meurice, Fabrice André, Olivia Fromigué. A new mTOR-independent effect of rapamycin: Transcriptional regulation of TRIB3 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2524.

The Induction of TRIB3 Causing Glucose Toxicity in Muscle Requires the O-GlcNAcylation of SP1

Background: Glucose-induced insulin resistance is mediated by induction of the pseudokinase TRIB3, which requires glucose metabolism via the hexosamine biosynthetic pathway (HBP). We have also shown that the SP1 binding site in the TRIB3 promoter region is essential for glucose’s ability to induce TRIB3 in skeletal muscle. However, the mechanism by which glucose regulates TRIB3 gene expression remains unknown. Hypothesis: Since the HBP provides the substrate for O-GlcNAcylation, we hypothesize that glucose results in O-GlcNAcylation of SP1 and this modulates induction of TRIB3 causing insulin resistance. Results: When treated with 5mM or 25mM glucose, the induction of TRIB3 gene expression (P&amp;lt;0.01) in L6 myotubes is accompanied by upregulation of SP1 expression (P&amp;lt;0.01). When fully differentiated L6 myotubes are transiently transfected with SP1 siRNA, knockdown of SP1 produced a corresponding suppression of TRIB3 both in the high and low glucose (P&amp;lt;0.05). To identify whether O-GlcNAcylation is involved, we cultured L6 myotubes in either 5mM or 25mM glucose medium with or without OSMI-1, an inhibitor of rate-limiting O-GlcNAc transferase (OGT). OSMI-1 did not affect glucose’s ability to augment SP1 2-fold (p&amp;lt;0.01), but effectively blocked induction of TRIB3. At the same time, OSMI-1 downregulated O-GlcNAcylation of SP1 and other O-GlcNAc modified proteins. Conclusion: (1) Increased TRIB3 mRNA expression parallels with upregulated SP1 expression; (2) Glucose induction of TRIB3 mRNA and protein is eliminated when HBP flux and O-GlcNAcylation is disrupted by the inhibition of OGT; (3) SP1 sites are critical in the regulatory action of glucose on the TRIB3 promoter and can be modulated by SP1 O-GlcNAcylation. While further studies are underway, these data provide new insights regarding mechanisms causing glucose-induced insulin resistance, and TRIB3 and TRIB3 promoter regulation are attractive targets for prevention of glucose toxicity in diabetes. Disclosure X. Liu: None. M. Kang: None. W. Garvey: Advisory Panel; Self; Novo Nordisk Inc., Merck &amp; Co., Inc.. Research Support; Self; Sanofi, Pfizer Inc., Novo Nordisk Inc., AstraZeneca, Merck &amp; Co., Inc., Elcelyx Therapeutics, Inc., Lexicon Pharmaceuticals, Inc., Eisai Inc..

Combination Treatment of Deep Sea Water and Fucoidan Attenuates High Glucose-Induced Insulin-Resistance in HepG2 Hepatocytes.

Insulin resistance (IR) plays a central role in the development of several metabolic diseases, which leads to increased morbidity and mortality rates, in addition to soaring health-care costs. Deep sea water (DSW) and fucoidans (FPS) have drawn much attention in recent years because of their potential medical and pharmaceutical applications. This study investigated the effects and mechanisms of combination treatment of DSW and FPS in improving IR in HepG2 hepatocytes induced by a high glucose concentration. The results elucidated that co-treatment with DSW and FPS could synergistically repress hepatic glucose production and increase the glycogen level in IR-HepG2 cells. In addition, they stimulated the phosphorylation levels of the components of the insulin signaling pathway, including tyrosine phosphorylation of IRS-1, and serine phosphorylation of Akt and GSK-3β. Furthermore, they increased the phosphorylation of AMPK and ACC, which in turn decreased the intracellular triglyceride level. Taken together, these results suggested that co-treatment with DSW and FPS had a greater improving effect than DSW or FPS alone on IR. They might attenuate IR by targeting Akt/GSK-3β and AMPK pathways. These results may have some implications in the treatment of metabolic diseases.

Impact of diabetes on gingival wound healing via oxidative stress.

The aim of this study is to investigate the mechanisms linking high glucose to gingival wound healing. Bilateral wounds were created in the palatal gingiva adjacent to maxillary molars of control rats and rats with streptozotocin-induced diabetes. After evaluating postsurgical wound closure by digital imaging, the maxillae including wounds were resected for histological examinations. mRNA expressions of angiogenesis, inflammation, and oxidative stress markers in the surgical sites were quantified by real-time polymerase chain reaction. Primary fibroblast culture from the gingiva of both rats was performed in high glucose and normal medium. In vitro wound healing and cell proliferation assays were performed. Oxidative stress marker mRNA expressions and reactive oxygen species production were measured. Insulin resistance was evaluated via PI3K/Akt and MAPK/Erk signaling following insulin stimulation using Western blotting. To clarify oxidative stress involvement in high glucose culture and cells of diabetic rats, cells underwent N-acetyl-L-cysteine treatment; subsequent Akt activity was measured. Wound healing in diabetic rats was significantly delayed compared with that in control rats. Nox1, Nox2, Nox4, p-47, and tumor necrosis factor-α mRNA levels were significantly higher at baseline in diabetic rats than in control rats. In vitro study showed that cell proliferation and migration significantly decreased in diabetic and high glucose culture groups compared with control groups. Nox1, Nox2, Nox4, and p47 expressions and reactive oxygen species production were significantly higher in diabetic and high glucose culture groups than in control groups. Akt phosphorylation decreased in the high glucose groups compared with the control groups. Erk1/2 phosphorylation increased in the high glucose groups, with or without insulin treatment, compared with the control groups. Impaired Akt phosphorylation partially normalized after antioxidant N-acetyl-L-cysteine treatment. Thus, delayed gingival wound healing in diabetic rats occurred because of impaired fibroblast proliferation and migration. Fibroblast dysfunction may occur owing to high glucose-induced insulin resistance via oxidative stress.

Metformin overcomes high glucose-induced insulin resistance of podocytes by pleiotropic effects on SIRT1 and AMPK

Podocyte insulin sensitivity is critical for glomerular function, and the loss of appropriate insulin signaling leads to alterations and disorders featuring diabetic nephropathy. Energy-sensing pathways, such as AMP-dependent protein kinase (AMPK) and protein deacetylase SIRT1, have been shown to play an important role in insulin resistance. The absence of a stimulating effect of insulin on glucose uptake into podocytes after exposure to hyperglycemic conditions has been demonstrated to be related to a decreased level and activity of SIRT1 protein, leading to reduced AMPK phosphorylation.The present work was undertaken to investigate metformin's ability to restore the insulin responsiveness of podocytes by regulating SIRT1 and AMPK activities.Primary rat podocytes cultured with standard or high glucose concentrations for 5days were transfected with siRNAs targeting SIRT1, AMPKα1, or AMPKα2. SIRT1 activity was measured by a fluorometric method. Insulin-stimulated changes in glucose uptake were used to detect insulin resistance. Podocyte permeability was measured by a transmembrane albumin flux assay to examine podocytes functioning.Our results demonstrated that metformin activated SIRT1 and AMPK, prevented hyperglycemia-induced reduction of SIRT1 protein levels, ameliorated glucose uptake into podocytes, and decreased glomerular filtration barrier permeability. Furthermore, metformin activated AMPK in a SIRT1-independent manner, as the increase in AMPK phosphorylation after metformin treatment was not affected by SIRT1 downregulation. Therefore, the potentiating effect of metformin on insulin-resistant podocytes seemed to be dependent on AMPK, as well as SIRT1 activity, establishing multilateral effects of metformin action.

Repression of miR-217 protects against high glucose-induced podocyte injury and insulin resistance by restoring PTEN-mediated autophagy pathway

Podocyte damage is the initial hallmark of diabetic nephropathy (DN), leading to the increasing morbidity and mortality in diabetic patients. Recent researches have corroborated the critical roles of miRNAs in the pathological progression of DN. Here, elevation of miR-217 was verified in high glucose (HG)-stimulated podocytes. Moreover, blocking miR-217 expression antagonized HG-induced cell injury by attenuating the adverse role of HG on cell viability and inhibiting ROS levels and cell apoptosis. Simultaneously, miR-217 repression restored HG-disrupted insulin resistance by elevating glucose uptake and nephrin expression, an essential component for insulin-induced glucose uptake. Mechanism assay substantiated the defective autophagy in HG-treated podocytes, which was resumed by miR-217 cessation. Importantly, suppressing autophagy pathway with 3-MA alleviated the protective roles of miR-217 down-regulation in podocyte injury and insulin resistance. Luciferase reporter analysis confirmed that PTEN was a target of miR-217 in podocytes. Additionally, blocking PTEN expression restrained autophagy restoration in miR-217-decreased cells. Furthermore, PTEN down-regulation attenuated the beneficial role of miR-217 suppression in HG-induced injury and insulin resistance. Together, this study manifests that miR-217inhibition can protectively antagonize HG-induced podocyte damage and insulin resistance by restoring the defective autophagy pathway via targeting PTEN, representing a novel and promising therapeutic target against diabetic nephropathy.

Casein glycomacropeptide-derived peptide IPPKKNQDKTE ameliorates high glucose-induced insulin resistance in HepG2 cells via activation of AMPK signaling.

Recently, casein glycomacropeptide (GMP)-derived peptide was found to possess potent antioxidant and anti-inflammatory activities. In this study, the improvement effects and underlying molecular mechanisms of GMP-derived peptide on hepatic insulin resistance were investigated. The peptide IPPKKNQDKTE was identified from GMP papain hydrolysates by LC-ESI-MS/MS. Effects of IPPKKNQDKTE on glucose metabolism and expression levels of the hepatic insulin signaling proteins in high glucose-induced insulin-resistant HepG2 cells were evaluated. Results showed that IPPKKNQDKTE dose-dependently increased glucose uptake and intracellular glycogen in insulin-resistant HepG2 cells without affecting cell viability. IPPKKNQDKTE increased the phosphorylation of Akt and GSK3β and decreased the expression levels of p-GS, G6Pase and PEPCK. These IPPKKNQDKTE-mediated protection effects were reversed by PI3K/Akt inhibitor LY294002, showing the mediatory role of PI3K/Akt. Moreover, treatment with IPPKKNQDKTE reduced IRS-1 Ser307 phosphorylation and increased phosphorylation of AMPK. Knockdown AMPK using siRNA in HepG2 cells increased Ser307 phosphorylation of IRS-1 and reduced Akt phosphorylation in IPPKKNQDKTE-treated insulin-resistant cells. IPPKKNQDKTE prevents high glucose-induced insulin resistance in HepG2 cells by modulating the IRS-1/PI3K/Akt signaling pathway through AMPK activation, indicating that IPPKKNQDKTE plays a potential role in the prevention and treatment of hepatic insulin resistance and type 2 diabetes.