Phosphorylation Of IRS-1 Research Articles

Avenanthramides Ameliorate Insulin Resistance by Modulating Gluconeogenesis and Glycogen Synthesis in HepG2 Cells.

Diabetes mellitus (DM) is a multifaceted metabolic condition, mainly defined by elevated blood glucose levels. A feature of type 2 DM includes insulin resistance (IR), which involves impairments within the insulin signaling pathways. Avenanthramides (AVNs) are phenolic alkaloids found in Avena sativa L. The major AVNs are AVN A, AVN B, and AVN C. They have been reported to offer benefits in preventing inflammation, cancer, and cardiovascular diseases. However, the effects of AVNs on the liver glucose metabolism pathways remain unknown. This study examined the effects and underlying mechanisms through which AVNs alleviate IR induced by free fatty acid (FFA) in HepG2 cells. The results indicated that FFA treatment significantly decreased glucose consumption by 34.54% compared to the control. However, treatments with AVN A, B, and C at 100 μM increased glucose uptake by 57.93%, 58.28%, and 53.10%, respectively, compared to FFA treatment alone. This effect occurs through the increased expression of glucose transporter 4. Furthermore, AVNs significantly enhanced the glycogen content. AVNs induced increased phosphorylation of insulin receptor substrate-1 (IRS-1), phosphatidylinositol-3-kinase (PI3K), and protein kinase B (Akt). AVNs treatment decreased the levels of phosphoenolpyruvate carboxykinase and glucose-6-phosphatase in HepG2 cells. This effect was attributed to AMP-activated protein kinase activation and inhibition of forkhead box protein O1. Collectively, these results suggest that AVNs regulate glucose metabolism by activating the IRS-1/PI3K/Akt pathway, which is related to glycogen synthesis, and by inhibiting key molecules that promote gluconeogenesis.

Omentin increases glucose uptake, but not insulin sensitivity in human myotubes dependent on extracellular lactotransferrin.

Omentin (intelectin-1) is an adipokine produced by the stromal vascular fraction of visceral adipose tissue and has been positively associated with insulin sensitivity. The underlying mechanism of action, however, is largely unknown. It has been described that omentin may increase insulin sensitivity and glucose uptake of adipocytes, but effects on other insulin-sensitive tissues such as skeletal muscle are unexplored. We therefore investigated effects of omentin on insulin sensitivity and metabolism of primary human myotubes. Primary human myotubes were treated with 0.5 or 2 µg/mL omentin and subsequently protein detection, glucose uptake assay, lactate assay and lipidomics analysis were performed. Omentin did not affect skeletal muscle insulin signaling, as assessed by basal and insulin-stimulated phosphorylation of IRS1 and AKT. Omentin increased basal, but not insulin-stimulated glucose uptake. While increased glycolytic activity was confirmed by elevated lactate release after omentin treatment, effects on cellular lipid composition were limited to an increase in total triacylglycerol concentration. Increased glucose uptake by omentin was counteracted by addition of extracellular lactotransferrin, which can bind to omentin. Overall, increased basal glucose uptake in skeletal muscle cells suggests differential effects of omentin on insulin-sensitive tissues. Moreover, an involvement of lactotransferrin in omentin's mechanism of action may partially explain contradictory results of epidemiological studies on the role of omentin in different diseases.

Circulating extracellular vesicle-carried PTP1B and PP2A phosphatases as regulators of insulin resistance.

Metabolic disorders associated with abdominal obesity, dyslipidaemia, arterial hypertension and hyperglycaemia are risk factors for the development of insulin resistance. Extracellular vesicles (EVs) may play an important role in the regulation of metabolic signalling pathways in insulin resistance and associated complications. Circulating large EVs (lEVs) and small EVs (sEVs) from individuals with (IR group) and without insulin resistance (n-IR group) were isolated and characterised. lEVs and sEVs were administered by i.v. injection to mice and systemic, adipose tissue and liver insulin signalling were analysed. The role of phosphatases was analysed in target tissues and cells. Injection of lEVs and sEVs from IR participants impaired systemic, adipose tissue and liver insulin signalling in mice, while EVs from n-IR participants had no effect. Moreover, lEVs and sEVs from IR participants brought about a twofold increase in adipocyte size and adipogenic gene expression. EVs from IR participants expressed two types of phosphatases, phosphotyrosine 1 phosphatase (PTP1B) and protein phosphatase 2 (PP2A), IR lEVs being enriched with the active form of PTP1B while IR sEVs mainly carried active PP2A. Blockade of PTP1B activity in IR lEVs fully restored IRS1 and Akt phosphorylation in adipocytes and blunted insulin-induced Akt phosphorylation by inhibition of the macrophage secretome in hepatocytes. Conversely, blockade of PP2A activity in IR sEVs completely prevented insulin resistance in adipocytes and hepatocytes. These data demonstrate that inhibition of phosphatases carried by EVs from IR participants rescues insulin signalling in adipocytes and hepatocytes and point towards PTP1B and PP2A carried by IR EVs as being novel potential therapeutic targets against insulin resistance in adipose tissue and liver and the development of obesity.

Targeting insulin resistance: myricetin and isorhamnetin from Hardwickia binata, and luteolin from Hedysarum alpinum enhance glucose uptake and AMPK signaling in HepG2 cells

This study examined five plants (Xylopia aethiopica, Agave sisalana, Hardwickia binata, Hedysarum alpinum, and Toxicodendron vernicifluum) for their potential to address insulin resistance in type 2 diabetes. In-vitro assays showed that H. binata leaves and H. alpinum flowers inhibited α-glucosidase and α-amylase while enhancing glucose uptake in normal and insulin-resistant HepG2 cells. Phytochemical screening and SPE purification identified the key constituents responsible for the effects. The chromatographic and spectral analysis confirmed flavonoids in H. binata (myricetin, isorhamnetin, quercetin, kaempferol, and catechin) and H. alpinum (luteolin, quercetin, kaempferol, and apigenin). Myricetin, isorhamnetin, and luteolin significantly increased glucose uptake, enhanced hexokinase and pyruvate kinase activities, and promoted IRec and IRS-1 phosphorylation, modulating insulin signalling. They activated AMPK and Akt, with molecular docking confirming strong AMPK binding. These findings suggest that H. binata, H. alpinum, and their flavonoids are promising candidates for managing insulin resistance and type 2 diabetes, warranting further research.

Insulin receptor substrate 1 is a novel member of EGFR signaling in pancreatic cells

Pancreatic ductal adenocarcinoma is an extremely incurable cancer type characterized by cells with highly proliferative capacity and resistance against the current therapeutic options. Our study reveals that IRS1 acts as a bridging molecule between EGFR and IGFR/InsR signalization providing a potential mechanism for the interplay between signaling pathways and bypassing EGFR-targeted or IGFR/InsR-targeted therapies. The analysis of IRS1 phosphorylation status in four pancreatic cell lines identified the impact of EGFR signaling on IRS1 activation in comparison with InsR/IGFR signaling. Significantly reduced viability was observed in IRS1-silenced cells even upon EGF stimulation showing the critical role of IRS1 in the EGFR signaling network in both malignant and normal pancreatic cells. This study also demonstrated that EGFR binds directly to IRS1 and at least on two tyrosine sites, Y612 and Y896, IRS1 becomes phosphorylated in response to EGF stimulation. Mechanistically, the EGFR-mediated phosphorylation of IRS1 can further activate the MAPK signaling pathway with the recruitment of GRB2 protein. Collectively, in this study, IRS1 was identified as a crucial regulator in the EGFR signaling suggesting IRS1 as a potential target for more durable responses to targeted PDAC therapy.

The improvement of modified Si-Miao granule on hepatic insulin resistance and glycogen synthesis in type 2 diabetes mellitus involves the inhibition of TNF-α/JNK1/IRS-2 pathway: network pharmacology, molecular docking, and experimental validation

BackgroundModified Si-Miao granule (mSMG), a traditional Chinese medicine, is beneficial for T2DM and insulin resistance (IR), but the underlying mechanism remains unknown.MethodsUsing network pharmacology, we screened the compounds of mSMG and identified its targets and pathway on hepatic IR in T2DM. Using molecular docking, we identified the affinity between the compounds and hub target TNF-α. Then these were verified in KK-Ay mice and HepG2 cells.Results50 compounds and 170 targets of mSMG against IR in T2DM were screened, and 9 hub targets such as TNF and MAPK8 were identified. 170 targets were mainly enriched in insulin resistance and TNF pathway, so we speculated that mSMG might act on TNF-α, JNK1 and then regulate insulin signaling to mitigate IR. Experimental validation proved that mSMG ameliorated hyperglycemia, IR, and TNF-α, enhanced glucose consumption and glycogen synthesis, relieved the phosphorylation of JNK1 and IRS-2 (Ser388), and elevated the phosphorylation of Akt (Ser473) and GSK-3β (Ser9) and GLUT2 expression in KK-Ay mice. Molecular docking further showed berberine from mSMG had excellent binding capacity with TNF-α. Then, in vitro validation experiments, we found that 20% mSMG-MS or 50 μM berberine had little effect in IR-HepG2 cell viability, but significantly increased glucose consumption and glycogen synthesis and regulated TNF-α/JNK1/IRS-2 pathway.ConclusionNetwork pharmacology and molecular docking help us predict potential mechanism of mSMG and further guide experimental validation. mSMG and its representative compound berberine improve hepatic IR and glycogen synthesis, and its mechanism may be related to the inhibition of TNF-α/JNK1/IRS-2 pathway.

Cadmium exposure induces skeletal muscle insulin resistance through the reactive oxygen species-mediated PINK1/Parkin pathway

Epidemiological studies have suggested a positive association between environmental cadmium (Cd) exposure and type 2 diabetes mellitus (T2DM). Skeletal muscle insulin resistance (IR) plays a critical role in the pathogenesis of T2DM. This study aimed to investigate the effects of chronic low-level Cd exposure on skeletal muscle IR and its potential mechanism. Rats were exposed to drinking water containing 2 or 10 mg/L Cd for 24 weeks. Differentiated L6 myotubes were treated with Cd for 72 h. Immunofluorescence, flow cytometry assay, RNA-sequencing, and Seahorse analysis were conducted to determine the effects of Cd and its underlying mechanism on relevant parameters, including insulin sensitivity, glucose uptake, oxidative stress, mitophagy, and mitochondrial function in skeletal muscle and L6 myotubes. N-acetyl-cysteine (NAC), a scavenger of reactive oxygen species (ROS), and mitophagy inhibitor Cyclosporin A (CsA) were used to confirm the role of oxidative stress in mitophagy and mitochondrial dysfunction caused by Cd. We found that rats exposed to 10 mg/L Cd exhibited hyperglycemia and skeletal muscle IR. Cd markedly increased IRS-1 phosphorylation at Ser612, while decreased levels of phosphorylated PI3K, Akt, AS160, inhibited GLUT4 translocation and glucose uptake. Mechanistically, Cd increased the intracellular ROS, hydrogen peroxide, and malondialdehyde levels and decreased antioxidase activity in L6 myotubes. Furthermore, Cd upregulated the mRNA and protein levels of LC3II/I, PINK1, and Parkin. In addition, Cd induced the formation of mitophagosomes, reduced the mitochondrial membrane potential, decreased the adenosine triphosphate content, and impaired the mitochondrial respiratory capacity. Strikingly, NAC ameliorated oxidative stress, excessive mitophagy, and the associated reduction in myotube insulin sensitivity, while inhibition of mitophagy by CsA alleviated skeletal muscle IR. In conclusion, this study reveals a previously unrecognized mechanism that chronic low-level Cd exposure may induce mitophagy by activating the PINK1/Parkin signal pathway by increasing ROS, thus causing skeletal muscle IR and elevated blood glucose.

KIC (ketoisocaproic acid) and leucine have divergent effects on tissue insulin signaling but not on whole-body insulin sensitivity in rats.

Plasma levels of branched-chain amino acids and their metabolites, the branched-chain ketoacids are increased in insulin resistance. Our previous studies showed that leucine and its metabolite KIC suppress insulin-stimulated glucose uptake in L6 myotubes along with the activation of the S6K1-IRS-1 pathway. Because other tissue and fiber types can be differentially regulated by KIC, we analyzed the effect of KIC gavage on whole-body insulin sensitivity and insulin signaling in vivo. We hypothesized that KIC gavage would reduce whole-body insulin sensitivity and increase S6K1-IRS-1 phosphorylation in various tissues and muscle fibers. Five-week-old male Sprague-Dawley rats were starved for 24 hours and then gavaged with 0.75ml/100g of water, leucine (22.3g/L) or KIC (30g/L) twice, ten minutes apart. They were then euthanized at different time points post-gavage (0.5-3h), and muscle, liver, and heart tissues were dissected. Other sets of gavaged animals underwent an insulin tolerance test. Phosphorylation (ph) of S6K1 (Thr389), S6 (Ser235/6) and IRS-1 (Ser612) was increased at 30 minutes post leucine gavage in skeletal muscles irrespective of fiber type. Ph-S6 (Ser235/6) was also increased in liver and heart 30 minutes after leucine gavage. KIC gavage increased ph-S6 (Ser235/6) in the liver. Neither Leucine nor KIC influenced whole-body insulin tolerance, nor ph-Akt (Ser473) in skeletal muscle and heart. BCKD-E1 α abundance was highest in the heart and liver, while ph-BCKD-E1 α (Ser293) was higher in the gastrocnemius and EDL compared to the soleus. Our data suggests that only leucine activates the S6K1-IRS-1 signaling axis in skeletal muscle, liver and heart, while KIC only does so in the liver. The effect of leucine and KIC on the S6K1-IRS-1 signaling pathway is uncoupled from whole-body insulin sensitivity. These results suggest that KIC and leucine may not induce insulin resistance, and the contributions of other tissues may regulate whole-body insulin sensitivity in response to leucine/KIC gavage.

Rutin alleviates advanced glycosylation end products-induced insulin resistance by inhibiting SOCS3/IRS1 and activating PI3K/AKT signaling pathways in HepG2 cells

The accumulation of advanced glycosylation end products (AGEs) from food in the body disrupts normal physiological insulin activity and causes insulin resistance. This study compared the effects of ten types of polyphenols on AGEs production in both chemical and food models. It also investigated the impact of polyphenols on AGEs-induced insulin resistance in HepG2 cell models. Results showed that luteolin had the strongest inhibitory effect on fluorescent AGEs in the three chemical models. Rutin exhibited the most potent capacity to inhibit AGEs in biscuit models. Moreover, rutin alleviated the glucose metabolism disorders induced by representative AGEs (methylglyoxal-modified bovine serum albumin, MGO-BSA) in HepG2 cells. Mechanistic studies revealed that rutin could inhibit the phosphorylation of insulin receptor substrate 1 (IRS1) and the activity of suppressor of cytokine signaling 3 (SOCS3), while activating the phosphorylation of phosphoinositide 3-kinase (PI3K)/protein kinase B (AKT) to alleviate the MGO-BSA-induced insulin resistance in HepG2 cells.

New Glycotoxin Inhibitor from Sesuvium sesuvioides Mitigates Symptoms of Insulin Resistance and Diabetes by Suppressing AGE-RAGE Axis in Skeletal Muscle.

The current study intended to investigate the role of new natural compounds derived from the Sesuvium sesuvioides plant in mitigating symptoms of diabetes and insulin resistance in the diabetic mice model. Anti-advanced glycation activity, insulin, and adiponectin were quantified by enzyme-linked immunosorbent assay (ELISA). Glucose uptake was performed using enzymatic fluorescence assay, and glycogen synthesis was measured using PAS staining. Gene and protein expression was assessed using real time PCR (RT-PCR), and immunoblotting and fluorescent microscopy, respectively. The new flavonoid glycoside eupalitin 3-O-α-L-rhamnopyranosyl-(1→2)-β-D-glucopyranoside 1 isolated from S. sesuvioides exhibited anti-AGE activity by reducing human glycated albumin in liver cells. In a diabetic mouse model treated with compound 1, we observed improved glucose tolerance, increased adiponectin levels, and decreased insulin resistance. We also observed alleviated AGEs induced reduction in glucose uptake and restored glycogen synthesis in the compound 1-treated diabetic mice muscles. Exploring the molecular mechanism of action in skeletal muscle tissue of diabetic mice, we found that 1 reduced AGE-induced reactive oxygen species and the inflammatory gene in the muscle of diabetic mice. Additionally, 1 exhibited these effects by reducing the gene and protein expression of receptor for advanced glycation end products (RAGE) and inhibiting protein kinase C (PKC) delta activation. This further led us to demonstrate that compound 1 reduced serine phosphorylation of IRS-1, thereby restoring insulin sensitivity. We conclude that a new flavonoid glycoside from S. sesuvioides could be a therapeutic target for the treatment of symptoms of insulin resistance and diabetes.

Postprandial fatty acid-binding protein4 is associated with muscle insulin resistance.

Fatty acid-binding protein4 (FABP4) has been reported to act as a hepatic insulin resistance factor. We previously reported that fasting FABP4 was correlated with insulin resistance measurements derived from the glucose clamp, and another study reported that postprandial FABP4 levels were decreased in healthy volunteers but were not reported (or known) in participants with type 2 diabetes. We have limited knowledge about the direct effect of FABP4 on muscle cells. We investigated the postprandial FABP4 levels in participants with type 2 diabetes, and the basic mechanism of muscle insulin resistance and FABP4. We performed a meal tolerance test and hyperinsulinaemic-euglycaemic clamp in 22 participants with type 2 diabetes and 26 participants without diabetes. We measured fasting and postprandial serum FABP4. We cultured mouse C2C12 muscle cells, and investigated the effect of FABP4 on glucose uptake. We analysed insulin signalling by western blot and insulin binding assay. The postprandial FABP4 level in participants with type 2 diabetes was higher than that in participants without diabetes. Participants without diabetes had lower postprandial FABP4 than fasting except for one participant, whereas one-third of participants with type 2 diabetes had higher postprandial FABP4 than fasting. Postprandial FABP4 was correlated with the muscle insulin resistance M/I value from a glucose clamp in participants without diabetes (r=-0.42, p<0.05). The increase in FABP4 after a meal correlated with the muscle insulin resistance M/I value (r=-0.44, p<0.05) and the difference between fasting and postprandial glucagon in participants with type 2 diabetes (r=0.36, p<0.05). FABP4 alone appears to increase glucose uptake, and the combination of FABP4 and insulin decreases glucose uptake when compared with insulin alone. FABP4 inhibits insulin signalling of muscle cells through decreases in phosphorylation of insulin receptor substrate1 and Akt. The physiological concentration of FABP4 did not inhibit insulin binding to muscle cells. These results suggested that the postprandial FABP4 level is associated with insulin resistance, and FABP4 may suppress insulin signals.

NT157 as an Anticancer Drug Candidate That Targets Kinase- and Phosphatase-Mediated Signaling

Cancer, characterized by uncontrolled cell growth and metastasis, represents a significant challenge to public health. The IGF1/IGF1R axis plays a pivotal role in tumor proliferation and survival, presenting an attractive target for intervention. NT157, a small molecule tyrphostin, has emerged as a promising inhibitor of this axis, displaying potent antineoplastic effects across various cancer types. This review synthesizes the literature on NT157’s mechanism of action and its impact on cellular processes in experimental cancer models. Initially identified for inducing the serine phosphorylation of IRS1 and IRS2, leading to their degradation and inhibiting the IGF1R signaling cascade, subsequent studies revealed additional targets of NT157, including STAT3, STAT5, and AXL, suggesting a multifaceted mechanism. Experimental evidence demonstrates that NT157 effectively suppresses tumor growth, metastasis, and angiogenesis in diverse cancer models. Additionally, NT157 enhances chemotherapy efficacy in combination therapy. Moreover, NT157 impacts not only tumor cells but also the tumor microenvironment, modulating inflammation and immune responses by targeting cancer-associated fibroblasts, myeloid cells, and immune cells, creating a suppressive milieu hindering tumor progression and metastasis. In conclusion, NT157 exhibits remarkable versatility in targeting multiple oncogenic pathways and hallmarks of cancer, underscoring its potential as a promising therapeutic agent.

Hepatic WDR23 proteostasis mediates insulin homeostasis by regulating insulin-degrading enzyme capacity

Maintaining insulin homeostasis is critical for cellular and organismal metabolism. In the liver, insulin is degraded by the activity of the insulin-degrading enzyme (IDE). Here, we establish a hepatic regulatory axis for IDE through WDR23-proteostasis. Wdr23KO mice have increased IDE expression, reduced circulating insulin, and defective insulin responses. Genetically engineered human cell models lacking WDR23 also increase IDE expression and display dysregulated phosphorylation of insulin signaling cascade proteins, IRS-1, AKT2, MAPK, FoxO, and mTOR, similar to cells treated with insulin, which can be mitigated by chemical inhibition of IDE. Mechanistically, the cytoprotective transcription factor NRF2, a direct target of WDR23-Cul4 proteostasis, mediates the enhanced transcriptional expression of IDE when WDR23 is ablated. Moreover, an analysis of human genetic variation in WDR23 across a large naturally aging human cohort in the US Health and Retirement Study reveals a significant association of WDR23 with altered hemoglobin A1C (HbA1c) levels in older adults, supporting the use of WDR23 as a new molecular determinant of metabolic health in humans.

Identification of 1,3,4-Thiadiazolyl-Containing Thiazolidine-2,4-dione Derivatives as Novel PTP1B Inhibitors with Antidiabetic Activity.

Forty-one 1,3,4-thiadiazolyl-containing thiazolidine-2,4-dione derivatives (MY1-41) were designed and synthesized as protein tyrosine phosphatase 1B (PTP1B) inhibitors with activity against diabetes mellitus (DM). All synthesized compounds (MY1-41) presented potential PTP1B inhibitory activities, with half-maximal inhibitory concentration (IC50) values ranging from 0.41 ± 0.05 to 4.68 ± 0.61 μM, compared with that of the positive control lithocholic acid (IC50 = 9.62 ± 0.14 μM). The most potent compound, MY17 (IC50 = 0.41 ± 0.05 μM), was a reversible, noncompetitive inhibitor of PTP1B. Circular dichroism spectroscopy and molecular docking were employed to analyze the binding interaction between MY17 and PTP1B. In HepG2 cells, MY17 treatment could alleviate palmitic acid (PA)-induced insulin resistance by upregulating the expression of phosphorylated insulin receptor substrate and protein kinase B. In vivo, oral administration of MY17 could reduce the fasting blood glucose level and improve glucose tolerance and dyslipidemia in mice suffering from DM.

Thapsigargin and Tunicamycin Block SARS-CoV-2 Entry into Host Cells via Differential Modulation of Unfolded Protein Response (UPR), AKT Signaling, and Apoptosis.

SARS-Co-V2 infection can induce ER stress-associated activation of unfolded protein response (UPR) in host cells, which may contribute to the pathogenesis of COVID-19. To understand the complex interplay between SARS-Co-V2 infection and UPR signaling, we examined the effects of acute pre-existing ER stress on SARS-Co-V2 infectivity. Huh-7 cells were treated with Tunicamycin (TUN) and Thapsigargin (THA) prior to SARS-CoV-2pp transduction (48 h p.i.) to induce ER stress. Pseudo-typed particles (SARS-CoV-2pp) entry into host cells was measured by Bright GloTM luciferase assay. Cell viability was assessed by cell titer Glo® luminescent assay. The mRNA and protein expression was evaluated by RT-qPCR and Western Blot. TUN (5 µg/mL) and THA (1 µM) efficiently inhibited the entry of SARS-CoV-2pp into host cells without any cytotoxic effect. TUN and THA's attenuation of virus entry was associated with differential modulation of ACE2 expression. Both TUN and THA significantly reduced the expression of stress-inducible ER chaperone GRP78/BiP in transduced cells. In contrast, the IRE1-XBP1s and PERK-eIF2α-ATF4-CHOP signaling pathways were downregulated with THA treatment, but not TUN in transduced cells. Insulin-mediated glucose uptake and phosphorylation of Ser307 IRS-1 and downstream p-AKT were enhanced with THA in transduced cells. Furthermore, TUN and THA differentially affected lipid metabolism and apoptotic signaling pathways. These findings suggest that short-term pre-existing ER stress prior to virus infection induces a specific UPR response in host cells capable of counteracting stress-inducible elements signaling, thereby depriving SARS-Co-V2 of essential components for entry and replication. Pharmacological manipulation of ER stress in host cells might provide new therapeutic strategies to alleviate SARS-CoV-2 infection.

SWATH-MS reveals that bisphenol A and its analogs regulate pathways leading to disruption in insulin signaling and fatty acid metabolism

Bisphenol A (BPA) is an endocrine-disrupting chemical (EDC), associated with obesity and insulin resistance. The FDA prohibited the use of BPA-based polycarbonate resins in infant formula packaging; thus, its analogs, viz. Bisphenol S (BPS) and Bisphenol F (BPF) were considered alternatives in epoxy resins, plastics, and food cans. As these analogs might evoke a similar response, we investigated the role of Bisphenols (BPA, BPF, and BPS), on insulin signaling in CHO-HIRc-myc-GLUT4eGFP cells at environmentally relevant concentrations of 2 nM and 200 nM. Insulin signaling demonstrated that Bisphenols reduced phosphorylation of IR and AKT2, GLUT4 translocation, and glucose uptake. This was accompanied by increased oxidative stress. Furthermore, SWATH-MS-based proteomics of 3T3-L1 cells demonstrated that Bisphenol-treated cells regulate proteins in insulin resistance, adipogenesis, and fatty acid metabolism pathways differently. All three Bisphenols induced differentially expressed proteins enriched similar pathways, although their abundance differed for each Bisphenol. This might be due to their varying toxicity level, structural differences, and estrogen-mimetic activity. This study has important implications in addressing health concerns related to EDCs. Given that the analogs of BPA are considered alternatives to BPA, the findings of this study suggest they are equally potent in altering fatty acid metabolism and inducing insulin resistance.

The involvement of Akt, mTOR, and S6K in the in vivo effect of IGF-1 on the regulation of rat cardiac Na+/K+-ATPase.

We previously demonstrated that insulin-like growth factor-1 (IGF-1) regulates sodium/potassium adenosine triphosphatase (Na+/K+-ATPase) in vascular smooth muscle cells (VSMC) via phosphatidylinositol-3 kinase (PI3K). Taking into account that others' work show that IGF-1 activates the PI3K/protein kinase B (Akt) signaling pathway in many different cells, we here further questioned if the Akt/mammalian target of rapamycin (mTOR)/ribosomal protein p70 S6 kinase (S6K) pathway stimulates Na+/K+-ATPase, an essential protein for maintaining normal heart function. There were 14 adult male Wistar rats, half of whom received bolus injections of IGF-1 (50μg/kg) for 24h. We evaluated cardiac Na+/K+-ATPase expression, activity, and serum IGF-1 levels. Additionally, we examined the phosphorylated forms of the following proteins: insulin receptor substrate (IRS), phosphoinositide-dependent kinase-1 (PDK-1), Akt, mTOR, S6K, and α subunit of Na+/K+-ATPase. Additionally, the mRNA expression of the Na+/K+-ATPase α1 subunit was evaluated. Treatment with IGF-1 increases levels of serum IGF-1 and stimulates Na+/K+-ATPase activity, phosphorylation of α subunit of Na+/K+-ATPase on Ser23, and protein expression of α2 subunit. Furthermore, IGF-1 treatment increased phosphorylation of IRS-1 on Tyr1222, Akt on Ser473, PDK-1 on Ser241, mTOR on Ser2481 and Ser2448, and S6K on Thr421/Ser424. The concentration of IGF-1 in serum positively correlates with Na+/K+-ATPase activity and the phosphorylated form of mTOR (Ser2448), while Na+/K+-ATPase activity positively correlates with the phosphorylated form of IRS-1 (Tyr1222) and mTOR (Ser2448). These results indicate that the Akt/mTOR/S6K signalling pathway may be involved in the IGF-1 regulating cardiac Na+/K+-ATPase expression and activity.

The redox-sensitive GSK3β is a key regulator of glomerular podocyte injury in type 2 diabetic kidney disease

Emerging evidence suggests that GSK3β, a redox-sensitive transducer downstream of insulin signaling, acts as a convergent point for myriad pathways implicated in kidney injury, repair, and regeneration. However, its role in diabetic kidney disease remains controversial. In cultured glomerular podocytes, exposure to a milieu of type 2 diabetes elicited prominent signs of podocyte injury and degeneration, marked by loss of homeostatic marker proteins like synaptopodin, actin cytoskeleton disruption, oxidative stress, apoptosis, and stress-induced premature senescence, as shown by increased staining for senescence-associated β-galactosidase activity, amplified formation of γH2AX foci, and elevated expression of mediators of senescence signaling, like p21 and p16INK4A. These degenerative changes coincided with GSK3β hyperactivity, as evidenced by GSK3β overexpression and reduced inhibitory phosphorylation of GSK3β, and were averted by tideglusib, a highly-selective small molecule inhibitor of GSK3β. In agreement, post-hoc analysis of a publicly-available glomerular transcriptomics dataset from patients with type 2 diabetic nephropathy revealed that the curated diabetic nephropathy-related gene set was enriched in high GSK3β expression group. Mechanistically, GSK3β-modulated nuclear factor Nrf2 signaling is involved in diabetic podocytopathy, because GSK3β knockdown reinforced Nrf2 antioxidant response and suppressed oxidative stress, resulting in an improvement in podocyte injury and senescence. Conversely, ectopic expression of the constitutively active mutant of GSK3β impaired Nrf2 antioxidant response and augmented oxidative stress, culminating in an exacerbated diabetic podocyte injury and senescence. Moreover, IRS-1 was found to be a cognate substrate of GSK3β for phosphorylation at IRS-1S332, which negatively regulates IRS-1 activity. GSK3β hyperactivity promoted IRS-1 phosphorylation, denoting a desensitized insulin signaling. Consistently, in vivo in db/db mice with diabetic nephropathy, GSK3β was hyperactive in glomerular podocytes, associated with IRS-1 hyperphosphorylation, impaired Nrf2 response and premature senescence. Our finding suggests that GSK3β is likely a novel therapeutic target for treating type 2 diabetic glomerular injury.

Sterol Regulatory Element Binding Protein 1: A Mediator for High-Fat Diet–Induced Hepatic Gluconeogenesis and Glucose Intolerance in Fish

BackgroundSterol regulatory element binding protein (SREBP) 1 is considered to be a crucial regulator for lipid synthesis in vertebrates. However, whether SREBP1 could regulate hepatic gluconeogenesis under high-fat diet (HFD) condition is still unknown, and the underlying mechanism is also unclear. ObjectivesThis study aimed to determine gluconeogenesis-related gene and protein expressions in response to HFD in large yellow croaker and explore the role and mechanism of SREBP1 in regulating the related transcription and signaling. MethodsCroakers (mean weight, 15.61 ± 0.10 g) were fed with diets containing 12% crude lipid [control diet (ND)] or 18% crude lipid (HFD) for 10 weeks. The glucose tolerance, insulin tolerance, hepatic gluconeogenesis–related genes, and proteins expressions were determined. To explore the role of SREBP1 in HFD-induced gluconeogenesis, SREBP1 was inhibited by pharmacologic inhibitor (fatostatin) or genetic knockdown in croaker hepatocytes under palmitic acid (PA) condition. To explore the underlying mechanism, luciferase reporter and chromatin immunoprecipitation assays were conducted in HEK293T cells. Data were analyzed using analysis of variance or Student t test. ResultsCompared with ND, HFD increased the mRNA expressions of gluconeogenesis genes (2.40-fold to 2.60-fold) (P < 0.05) and reduced protein kinase B (AKT) phosphorylation levels (0.28-fold to 0.34-fold) (P < 0.05) in croakers. However, inhibition of SREBP1 by fatostatin addition or SREBP1 knockdown reduced the mRNA expressions of gluconeogenesis genes (P < 0.05) and increased AKT phosphorylation levels (P < 0.05) in hepatocytes, compared with that by PA treatment. Moreover, fatostatin addition or SREBP1 knockdown also increased the mRNA expressions of irs1 (P < 0.05) and reduced serine phosphorylation of IRS1 (P < 0.05). Furthermore, SREBP1 inhibited IRS1 transcriptions by binding to its promoter and induced IRS1 serine phosphorylation by activating diacylglycerol–protein kinase Cε signaling. ConclusionsThis study reveals the role of SREBP1 in hepatic gluconeogenesis under HFD condition in croakers, which may provide a potential strategy for improving HFD-induced glucose intolerance.

Anti-diabetic effect of anthocyanin cyanidin-3-O-glucoside: data from insulin resistant hepatocyte and diabetic mouse

BackgroundAnthocyanins are a group of natural products widely found in plants. They have been found to alleviate the disorders of glucose metabolism in type 2 diabetes mellitus (T2DM), while the underlying mechanisms remain unclear.MethodsHepG2 and L02 cells were incubated with 0.2 mM PA and 30 mM glucose for 24 h to induce IR, and cells treated with 5 mM glucose were used as the control. C57BL/6 J male mice and db/db male mice were fed with a chow diet and gavaged with pure water or cyanidin-3-O-glucoside (C3G) solution (150 mg/kg/day) for 6 weeks.ResultsIn this study, the anthocyanin C3G, extracted from red bayberry, was found to alleviate disorders of glucose metabolism, which resulted in increased insulin sensitivity in hepatocytes, and achieved by enhancing the glucose consumption as well as glycogen synthesis in insulin resistance (IR) hepatpcytes. Subsequently, the expression of key proteins involved in IR was detected by western blotting analysis. Protein tyrosine phosphatase-1B (PTP1B), a negative regulator of insulin signaling, could reduce cellular sensitivity to insulin by inhibiting the phosphorylation of insulin receptor substrate-2 (IRS-2). Results of this study showed that C3G inhibited the increase in PTP1B after high glucose and palmitic acid treatment. And this inhibition was accompanied by increased phosphorylation of IRS proteins. Furthermore, the effect of C3G on improving IR in vivo was validated by using a diabetic db/db mouse model.ConclusionThese findings demonstrated that C3G could alleviate IR in vitro and in vivo to increase insulin sensitivity, which may offer a new insight for regulating glucose metabolism during T2DM by using the natural dietary bioactive components.C3G promotes the phosphorylation of IRS-2 proteins by suppressing the expression of PTP1B, and then enhances the sensitivity of hepatocyte to insulin.