Insulin Resistance In Hepatocytes Research Articles

The effect of gelatinized brown rice extract on type 2 diabetes mellitus via inhibition of insulin resistance mediators in HepG2 cells

The purpose of this study evaluated effects of gelatinized brown rice extract (GBE) on type 2 diabetes mellitus by analyzing antioxidant activity, polysaccharide-degrading enzymes activity, and regulation of insulin secretion and glucose transport-related factors in human liver cells (HepG2). Quantified polyphenols and flavonoids in extract showed 6.7 mg gallic acid equivalent/g dry matter (DM) and 5.3 mg quercetin equivalent/g DM, respectively, with DPPH and ABTS radical scavenging activities confirmed to 67.1 ~ 77.7%. Additionally, extract inhibited alpha-glucosidase activity by 81.9%, thereby demonstrating potential for improving blood glucose regulation. To demonstrate alleviation of type 2 diabetes through mitigation of insulin resistance and promotion of glucose transport, expression of genes related to insulin receptor genes (Insulin Receptor Substrate-1, Protein Kinase B) increased by 18.5 ~ 28.3%, while expression of counterregulatory hormone genes (Insulin-like Growth Factor-1) decreased by 33.3%. Additionally, expression of glucose transporter proteins (Glucose Transporter Type-4, 2) increased by 30.9 ~ 42.0%, and expression of proteins that reduce insulin sensitivity (Insulin Receptor Substrate-2) decreased by 34.6%. These results indicated that insulin resistance in hepatocytes alleviated, and glucose transport promoted, leading to decreased blood glucose levels.

AuCePt porous hollow cascade nanozymes targeted delivery of disulfiram for alleviating hepatic insulin resistance

As the pathophysiological basis of type 2 diabetes mellitus (T2DM), insulin resistance (IR) is closely related to oxidative stress (OS) and inflammation, while nanozymes have a good therapeutic effect on inflammation and OS by scavenging reactive oxygen species (ROS). Hence, AuCePt porous hollow cascade nanozymes (AuCePt PHNs) are designed by integrating the dominant enzymatic activities of three metallic materials, which exhibit superior superoxide dismutase/catalase-like activities, and high drug loading capacity. In vitro experiments proved that AuCePt PHNs can ultra-efficiently scavenge endogenous and exogenous ROS. Moreover, AuCePt PHNs modified with lactobionic acid (LA) and loaded with disulfiram (DSF), named as AuCePt PHNs-LA@DSF, can significantly improve glucose uptake and glycogen synthesis in IR hepatocytes by regulating the insulin signaling pathways (IRS-1/AKT) and gluconeogenesis signaling pathways (FOXO-1/PEPCK). Intravenous administration of AuCePt PHNs-LA@DSF not only showed high liver targeting efficiency, but also reduced body weight and blood glucose and improved IR and lipid accumulation in high-fat diet-induced obese mice and diabetic ob/ob mice. This research elucidates the intrinsic activity of AuCePt PHNs for cascade scavenging of ROS, and reveals the potential effect of AuCePt PHNs-LA@DSF in T2DM treatment.Graphical abstract

Licochalcone D from Glycyrrhiza uralensis Improves High-Glucose-Induced Insulin Resistance in Hepatocytes.

This study investigated the therapeutic potential of licochalcone D (LicoD), which is derived from Glycyrrhiza uralensis, for improving glucose metabolism in AML12 hepatocytes with high-glucose-induced insulin resistance (IR). Ultra-high-performance liquid chromatography-mass spectrometry revealed that the LicoD content of G. uralensis was 8.61 µg/100 mg in the ethanol extract (GUE) and 0.85 µg/100 mg in the hot water extract. GUE and LicoD enhanced glucose consumption and uptake, as well as Glut2 mRNA expression, in high-glucose-induced IR AML12 cells. These effects were associated with the activation of the insulin receptor substrate/phosphatidylinositol-3 kinase signaling pathway, increased protein kinase B α phosphorylation, and suppression of gluconeogenesis-related genes, such as Pepck and G6pase. Furthermore, GUE and LicoD promoted glycogen synthesis by downregulating glycogen phosphorylase. Furthermore, LicoD and GUE mitigated the downregulated expression of mitochondrial oxidative phosphorylation proteins in IR hepatocytes by activating the PPARα/PGC1α pathway and increasing the mitochondrial DNA content. These findings demonstrate the potential of LicoD and GUE as therapeutic options for alleviating IR-induced metabolic disorders by improving glucose metabolism and mitochondrial function.

Vanadium Complexes with Thioanilide Derivatives of Amino Acids: Inhibition of Human Phosphatases and Specificity in Various Cell Models of Metabolic Disturbances.

In the text, the synthesis and characteristics of the novel ONS-type vanadium (V) complexes with thioanilide derivatives of amino acids are described. They showed the inhibition of human protein tyrosine phosphatases (PTP1B, LAR, SHP1, and SHP2) in the submicromolar range, as well as the inhibition of non-tyrosine phosphatases (CDC25A and PPA2) similar to bis(maltolato)oxidovanadium(IV) (BMOV). The ONS complexes increased [14C]-deoxy-D-glucose transport into C2C12 myocytes, and one of them, VC070, also enhanced this transport in 3T3-L1 adipocytes. These complexes inhibited gluconeogenesis in hepatocytes HepG2, but none of them decreased lipid accumulation in the non-alcoholic fatty liver disease model using the same cells. Compared to the tested ONO-type vanadium complexes with 5-bromosalicylaldehyde and substituted benzhydrazides as Schiff base ligand components, the ONS complexes revealed stronger inhibition of protein tyrosine phosphatases, but the ONO complexes showed greater activity in the cell models in general. Moreover, the majority of the active complexes from both groups showed better effects than VOSO4 and BMOV. Complexes from both groups activated AKT and ERK signaling pathways in hepatocytes to a comparable extent. One of the ONO complexes, VC068, showed activity in all of the above models, including also glucose utilizatiand ONO Complexes are Inhibitors ofon in the myocytes and glucose transport in insulin-resistant hepatocytes. The discussion section explicates the results within the wider scope of the knowledge about vanadium complexes.

Inositol-requiring enzyme 1α and c-Jun N-terminal kinase axis activation contributes to intracellular lipid accumulation in calf hepatocytes

During the perinatal period, dairy cows undergo negative energy balance, resulting in elevated circulating levels of nonesterified fatty acids (NEFA). Although increased blood NEFA concentrations are a physiological adaptation of early lactation, excessive NEFA in dairy cows is a major cause of fatty liver. Aberrant lipid metabolism leads to hepatic lipid accumulation and subsequently the development of fatty liver. Both inositol-requiring enzyme 1α (IRE1α) and c-Jun N-terminal kinase (JNK) have been validated for their association with hepatic lipid accumulation, including their regulatory functions in calf hepatocyte insulin resistance, oxidative stress, and apoptosis. Meanwhile, both IRE1α and JNK are involved in lipid metabolism in nonruminants. Therefore, the aim of this study was to investigate how IRE1α and JNK regulate lipid metabolism in bovine hepatocytes. An experiment was conducted on randomly selected 10 healthy cows (hepatic triglyceride [TG] content <1%) and 10 cows with fatty liver (hepatic TG content >5%). Liver tissue and blood samples were collected from experimental cows. Serum concentrations of NEFA and β-hydroxybutyrate (BHB) were greater, whereas serum concentrations of glucose and milk production were lower in cows with fatty liver. The western blot results revealed that dairy cows with fatty liver had higher phosphorylation levels of JNK, c-Jun, and IRE1α in the liver tissue. Three in vitro experiments were conducted using primary calf hepatocytes isolated from 5 healthy calves (body weight: 30-40 kg; 1 d old). First, hepatocytes were treated with NEFA (1.2 mM) for 0.5, 1, 2, 3, 5, 7, 9, or 12 h, which showed that the phosphorylated levels of JNK, c-Jun, and IRE1α increased in both linear and quadratic effects. In the second experiment, hepatocytes were treated with high concentrations of NEFA (1.2 mM) for 12 h with or without SP600125, a canonical inhibitor of JNK. Western blot results showed that SP600125 treatment could decrease the expression of lipogenesis-associated proteins (PPARγ and SREBP-1c) and increase the expression of fatty acid oxidation (FAO)-associated proteins (CPT1A and PPARα) in NEFA-treated hepatocytes. The perturbed expression of lipogenesis-associated genes (FASN, ACACA, and CD36) and FAO-associated gene ACOX1 were also recovered by JNK inhibition, indicating that JNK reduced excessive NEFA-induced lipogenesis and FAO dysregulation in calf hepatocytes. Third, short hairpin RNA targeting IRE1α (sh-IRE1α) was transfected into calf hepatocytes to silence IRE1α, and KIRA6 was used to inhibit the kinase activity of IRE1α. The blockage of IRE1α could at least partially suppressed NEFA-induced JNK activation. Moreover, the blockage of IRE1α downregulated the expression of lipogenesis genes and upregulated the expression of FAO genes in NEFA-treated hepatocytes. In conclusion, these findings indicate that targeting the IRE1α-JNK axis can reduce NEFA-induced lipid accumulation in bovine hepatocytes by modulating lipogenesis and FAO. This may offer a prospective therapeutic target for fatty liver in dairy cows.

4EBP2-regulated protein translation has a critical role in high-fat diet–induced insulin resistance in hepatocytes

A high-fat diet (HFD) plays a critical role in hepatocyte insulin resistance. Numerous models and factors have been proposed to elucidate the mechanism of palmitic acid (PA)-induced insulin resistance. However, proteomic studies of insulin resistance by HFD stimulation are usually performed under insulin conditions, leading to an unclear understanding of how a HFD alone affects hepatocytes. Here, we mapped the phosphorylation rewiring events in PA-stimulated HepG2 cells and found PA decreased the phosphorylation level of the eukaryotic translation initiation factor 4E-binding protein 2 (4EBP2) at S65/T70. Further experiments identified 4EBP2 as a key node of insulin resistance in either HFD mice or PA-treated cells. Reduced 4EBP2 levels increased glucose uptake and insulin sensitivity, whereas the 4EBP2_S65A/T70A mutation exacerbated PA-induced insulin resistance. Additionally, the nascent proteome revealed many glycolysis-related proteins translationally regulated by 4EBP2 such as hexokinase-2, pyruvate kinase PKM, TBC1 domain family member 4, and glucose-6-phosphate 1-dehydrogenase. In summary, we report the critical role of 4EBP2 in regulating HFD-stimulated insulin resistance in hepatocytes.

Natural exosomes-like nanoparticles in mung bean sprouts possesses anti-diabetic effects via activation of PI3K/Akt/GLUT4/GSK-3β signaling pathway

BackgroundType 2 diabetes mellitus (T2DM) is a chronic metabolic disease characterized by hyperglycemia and insulin resistance. Mung bean sprouts are traditionally considered a “folk” hypoglycemic food and their pharmacological effects and underlying mechanisms warrant further investigation.PurposeThis study aimed to investigate the anti-diabetic effects of the exosomes-like nanoparticles in mung bean sprouts (MELNs) and explore the related molecular mechanisms.ResultsMELNs were isolated using a differential centrifugation-polyethylene glycol (PEG) method, and the identification of MELNs were confirmed by PAGE gel electrophoresis, agarose gel electrophoresis, thin-layer chromatography (TLC), and transmission electron microscopy (TEM). In the high-fat diet/streptozotocin (HFD/STZ) mouse model, MELNs ameliorated the progression of T2DM by increasing oral glucose tolerance test (OGTT) and insulin tolerance test (ITT) results, decreasing the fasting blood glucose level, and reducing the serum triglycerides (TG) and total cholesterol (TC). Histopathological examinations indicated MELNs diminished inflammatory infiltration of hepatocytes and amplified the area of islet B cells. In addition, MELNs decreased the oxidative stress levels in liver tissue and had good biocompatibility. In vitro experiments verified that MELNs improved the viability of glucosamine (GlcN) induced insulin-resistant hepatocytes. Furthermore, this study also revealed that MELNs upregulated GLUT4 & Nrf2 and down-regulated GSK-3β via activating the PI3K/Akt signaling pathway, promoting the production of antioxidant enzymes, such as HO-1 and SOD, to reduce oxidative stress.ConclusionMELNs mitigated the progression of type 2 diabetes in HFD/STZ mouse model. The underlying molecular mechanism is related to PI3K/Akt/GLUT4/GSK-3β signaling pathway.

F6P/G6P-mediated ChREBP activation promotes the insulin resistance-driven hepatic lipid deposition in zebrafish

Insulin-sensitive lipogenesis dominates the body lipid deposition; however, nonalcoholic fatty liver disease (NAFLD) develops in the insulin-resistant state. The regulation mechanism of insulin resistance-driven NAFLD remains elusive. Using zebrafish model of insulin resistance (ZIR, insrb−/−) and mouse hepatocytes (NCTC 1469), we explored the regulation mechanism of insulin resistance-driven hepatic lipid deposition under the stimulation of carbohydrate diet (CHD). In ZIR model, insulin resistance induced hyperlipidemia and elevated hepatic lipid deposition via elevating the gene/protein expressions of lipogenic enzymes, that was activated by carbohydrate response element binding protein (ChREBP), rather than sterol regulatory element binding proteins 1c (SREBP-1c). The metabolomic analysis in zebrafish and silencing of chrebp in mouse hepatocytes revealed that the increased hepatic frucotose-6-phosphate (F6P) and glucose-6-phosphate (G6P) promoted the ChREBP-mediated lipid deposition. We further identified that F6P alone was sufficient to activate ChREBP-mediated lipid deposition by a SREBP-1c-independent manner. Moreover, we clarified the suppressed hepatic phosphofructokinase/glucose-6-phosphatase functions and the normal glucokinase function preserved by glucose transporter 2 (GLUT2) manipulated the increased F6P/G6P content in ZIR. In conclusion, the present study revealed that insulin resistance promoted hepatic lipid deposition via the F6P/G6P-mediated ChREBP activation. Our findings deciphered the main regulation pathway for the liver lipid deposition in the insulin-resistant state and identified F6P as a new potential regulator for ChREBP.

METTL3 exacerbates insulin resistance in hepatocytes by regulating m6A modification of cytochrome P450 2B6

BackgroundInsulin resistance (IR) in hepatocytes endangers human health, and frequently results in the development of non-alcoholic fatty liver disease (NAFLD). Research on m6A methylation of RNA molecules has gained popularity in recent years; however, the molecular mechanisms regulating the processes of m6A modification and IR are not known. The cytochrome P450 (CYP450) enzyme system, which is mainly found in the liver, is associated with the pathogenesis of NAFLD. However, few studies have been conducted on CYP450 related m6A methylation. Here, we investigated the role of the methyltransferase METTL3 in exacerbating IR in hepatocytes, mainly focusing on the regulation of m6A modifications in CYP2B6.Methods and resultsAnalysis using dot blot and epitranscriptomic chips revealed that the m6A modification pattern of the transcriptome in high-fat diet (HFD)-induced fatty liver and free fatty acid (FFA)-induced fatty hepatocytes showed significant changes. CYP450 family members, especially Cyp2b10, whose homolog in humans is CYP2B6, led to a noticeable increase in m6A levels in HFD-induced mice livers. Application of the METTL3 methyltransferase inhibitor, STM2457, increased the level of insulin sensitivity in hepatocytes. We then analyzed the role of METTL3 in regulating m6A modification of CYP2B6 in hepatocytes. METTL3 regulated the m6A modification of CYP2B6, and a positive correlation was found between the levels of CYP2B6 translation and m6A modifications. Furthermore, interference with METTL3 expression and exposure to STM2457 inhibited METTL3 activity, which in turn interfered with the phosphorylated insulin receptor substrate (pIRS)-glucose transporter 2 (GLUT2) insulin signaling pathway; overexpression of CYP2B6 hindered IRS phosphorylation and translocation of GLUT2 to membranes, which ultimately exacerbated IR.ConclusionThese findings offer unique insights into the role that METTL3-mediated m6A modifications of CYP2B6 play in regulating insulin sensitivity in hepatocytes and provide key information for the development of strategies to induce m6A modifications for the clinical treatment of NAFLD.

Links between oral microbiome and insulin resistance: Involvement of MAP kinase signaling pathway

Oral dysbiosis contributes to periodontitis and has implications for systemic diseases. Diabetes mellitus is a common metabolic disorder characterized by impaired glucose regulation. AMP-activated protein kinase (AMPK) plays a vital role in regulating glucose uptake and glycogenesis in the liver. This study aimed to investigate the association between periodontal bacteria and diabetes mellitus. A clinical trial was conducted to explore the association between oral bacteria and hyperglycemia. Additionally, we elucidated the molecular mechanisms by which periodontal bacteria cause insulin resistance. In the clinical trial, we discovered significant alterations in the expression levels of Fusobacterium nucleatum (Fn) and Tannerella forsythia (Tf) in patients with diabetes compared with healthy controls. Furthermore, Fn and Tf levels positively correlated with fasting blood glucose and glycated hemoglobin (HbA1C) levels. Moreover, we explored and elucidated the molecular mechanism by which Fusobacterium nucleatum culture filtrate (FNCF) induces cytokine release via the Toll-like receptor 2 (TLR2) signaling pathway in human gingival epithelial Smulow–Glickman (S–G) cells. This study investigated the effects of cytokines on insulin resistance pathways in liver cells. The use of an extracellular signal-regulated kinase (ERK) inhibitor (U0126) demonstrated that FNCF regulates the insulin receptor substrate 1 and protein kinase B (IRS1/AKT) signaling pathway, which affects key proteins involved in hepatic glycogen synthesis, including glycogen synthase kinase-3 beta (GSK3β) and glycogen synthase (GS), ultimately leading to insulin resistance. These findings suggest that ERK plays a crucial role in hepatocyte insulin resistance.

Saturated fatty acid-enriched small extracellular vesicles mediate a crosstalk inducing liver inflammation and hepatocyte insulin resistance

Background & AimsLipotoxicity triggers non-alcoholic fatty liver disease (NAFLD) progression owing to the accumulation of toxic lipids in hepatocytes including saturated fatty acids (SFAs), which activate pro-inflammatory pathways. We investigated the impact of hepatocyte- or circulating-derived small extracellular vesicles (sEV) secreted under NAFLD conditions on liver inflammation and hepatocyte insulin signalling. MethodssEV released by primary mouse hepatocytes, characterised and analysed by lipidomics, were added to mouse macrophages/Kupffer cells (KC) to monitor internalisation and inflammatory responses. Insulin signalling was analysed in hepatocytes exposed to conditioned media from sEV-loaded macrophages/KC. Mice were i.v. injected sEV to study liver inflammation and insulin signalling. Circulating sEV from mice and humans with NAFLD were used to evaluate macrophage–hepatocyte crosstalk. ResultsNumbers of sEV released by hepatocytes increased under NAFLD conditions. Lipotoxic sEV were internalised by macrophages through the endosomal pathway and induced pro-inflammatory responses that were ameliorated by pharmacological inhibition or deletion of Toll-like receptor-4 (TLR4). Hepatocyte insulin signalling was impaired upon treatment with conditioned media from macrophages/KC loaded with lipotoxic sEV. Both hepatocyte-released lipotoxic sEV and the recipient macrophages/KC were enriched in palmitic (C16:0) and stearic (C18:0) SFAs, well-known TLR4 activators. Upon injection, lipotoxic sEV rapidly reached KC, triggering a pro-inflammatory response in the liver monitored by Jun N-terminal kinase (JNK) phosphorylation, NF-κB nuclear translocation, pro-inflammatory cytokine expression, and infiltration of immune cells into the liver parenchyma. sEV-mediated liver inflammation was attenuated by pharmacological inhibition or deletion of TLR4 in myeloid cells. Macrophage inflammation and subsequent hepatocyte insulin resistance were also induced by circulating sEV from mice and humans with NAFLD. ConclusionsWe identified hepatocyte-derived sEV as SFA transporters targeting macrophages/KC and activating a TLR4-mediated pro-inflammatory response enough to induce hepatocyte insulin resistance. Impact and ImplicationsSmall extracellular vesicles (sEV) released by the hepatocytes under non-alcoholic fatty liver disease (NAFLD) conditions cause liver inflammation and insulin resistance in hepatocytes via paracrine hepatocyte–macrophage–hepatocyte crosstalk. We identified sEV as transporters of saturated fatty acids (SFAs) and potent lipotoxic inducers of liver inflammation. TLR4 deficiency or its pharmacological inhibition ameliorated liver inflammation induced by hepatocyte-derived lipotoxic sEV. Evidence of this macrophage–hepatocyte interactome was also found in patients with NAFLD, pointing to the relevance of sEV in SFA-mediated lipotoxicity in NAFLD.

ETNPPL impairs autophagy through regulation of the ARG2-ROS signaling axis, contributing to palmitic acid-induced hepatic insulin resistance.

Excessive free fatty acids (FFAs) accumulation is a leading risk factor for the pathogenesis of insulin resistance (IR) in metabolic tissues, including the liver. Ethanolamine-phosphate phospho-lyase (ETNPPL), a newly identified metabolic enzyme, catalyzes phosphoethanolamine (PEA) to ammonia, inorganic phosphate, and acetaldehyde and is highly expressed in hepatic tissue. Whether it plays a role in regulating FFA-induced IR in hepatocytes has yet to be understood. In this study, we established an in vitro palmitic acid (PA)-induced IR model in human HepG2 cells and mouse AML12cells with chronic treatment of PA. Next, we overexpressed ETNPPL by using lentivirus-mediated ectopic to investigate the effects of ETNPPL per se on IR without PA stimulation. We show that ETNPPL expression is significantly elevated in PA-induced IR and that silencing ETNPPL ameliorates this IR in hepatocytes. Inversely, overexpressing ETNPPL under normal conditions without PA promotes IR, reactive oxygen species generation, and ARG2 activation in both HepG2 and AML12cells. Moreover, ETNPPL depletion markedly down-regulates ARG2 expression in hepatocytes. Besides, silencing ARG2 prevents ETNPPL-induced ROS accumulation and inhibition of autophagic flux and IR in hepatocytes. Finally, we found that phytopharmaceutical disruption of ETNPPL by quercetin ameliorates PA-induced IR in hepatocytes. Our study discloses that ETNPPL inhibiting autophagic flux mediates insulin resistance triggered by PA in hepatocytes via ARG2/ROS signaling cascade. Our findings provide novel insights into elucidating the pathogenesis of obesity-associated hepatic IR, suggesting that targeting ETNPPL might represent a potential approach for T2DM therapy.

ETNPPL modulates hyperinsulinemia-induced insulin resistance through the SIK1/ROS-mediated inactivation of the PI3K/AKT signaling pathway in hepatocytes.

Hyperinsulinemia is a critical risk factor for the pathogenesis of insulin resistance (IR) in metabolic tissues, including the liver. Ethanolamine phosphate phospholyase (ETNPPL), a newly discovered metabolic enzyme that converts phosphoethanolamine (PEA) to ammonia, inorganic phosphate, and acetaldehyde, is abundantly expressed in liver tissue. Whether it plays a role in the regulation of hyperinsulinemia-induced IR in hepatocytes remains elusive. Here, we established an in vitro hyperinsulinemia-induced IR model in the HepG2 human liver cancer cell line and primary mouse hepatocyte via a high dose of insulin treatment. Next, we overexpressed ETNPPL by using lentivirus-mediated ectopic to investigate the effects of ETNPPL per se on IR without insulin stimulation. To explore the underlying mechanism of ETNPPL mediating hyperinsulinemia-induced IR in HepG2, we performed genome-wide transcriptional analysis using RNA sequencing (RNA-seq) to identify the downstream target gene of ETNPPL. The results showed that ETNPPL expression levels in both mRNA and protein were significantly upregulated in hyperinsulinemia-induced IR in HepG2 and primary mouse hepatocytes. Upon silencing ETNPPL, hyperinsulinemia-induced IR was ameliorated. Under normal conditions without IR in hepatocytes, overexpressing ETNPPL promotes IR, reactive oxygen species (ROS) generation, and AKT inactivation. Transcriptome analysis revealed that salt-inducible kinase 1 (SIK1) is markedly downregulated in the ETNPPL knockdown HepG2 cells. Moreover, disrupting SIK1 prevents ETNPPL-induced ROS accumulation, damage to the PI3K/AKT pathway and IR. Our study reveals that ETNPPL mediates hyperinsulinemia-induced IR through the SIK1/ROS-mediated inactivation of the PI3K/AKT signaling pathway in hepatocyte cells. Targeting ETNPPL may present a potential strategy for hyperinsulinemia-associated metabolic disorders such as type 2 diabetes.

Vanillic acid mitigates hyperinsulinemia induced ER stress mediated altered calcium homeostasis, MAMs distortion and surplus lipogenesis in HepG2 cells

Hyperinsulinemia (HI) induced insulin resistance (IR) and associated pathologies are the burning and unsolvable issues in diabetes treatment. The cellular, molecular and biochemical events associated with HI are not yet elucidated. Similarly, no focused research on designing therapeutic strategies with natural products for attenuation of HI are seen in literature. Keeping this in mind we planned the present study to evaluate the alterations occurring at ER/Ca2+ homeostasis/mitochondria associated endoplasmic reticulum membranes (MAMs) in HepG2 cells during HI and to evaluate the possible beneficial effect of vanillic acid (VA) to mitigate the complications. An in vitro model of HI was established by treating HepG2 cells with human insulin (1 μM) for 24 h. Then, ER stress, Ca2+ homeostasis, MAMs, IR and hepatic lipogenesis were studied at protein level. Various proteins critical to ER, Ca2+ homeostasis and MAMs such as p-IRE-1α, ATF6, p-PERK, p-eIF2α, CHOP, XBP1, p-CAMKII, InsP3R, SERCA, JNK, GRP78, VDAC, Cyp D, GRP75, MFN2, PTEN and mTORC were studied and found altered significantly causing ER stress, defect in Ca2+ movements and distortion of MAMs. The decreased expression of IRS2 and an unaltered expression of IRS1 confirmed the development of selective insulin resistance in hepatocytes during HI and this was the crucial factor for the progression of the hepatic lipid accumulation. We found simultaneous treatment of VA is beneficial up to a certain extent to protect HepG2 cells from the adverse effect of HI via its antioxidant, antilipogenic, mitochondrial and ER protection properties.

Protective effect of manganese treatment on insulin resistance in HepG2 hepatocytes.

manganese (Mn) is closely related to type 2 diabetes mellitus and insulin resistance (IR), but the exact mechanism is unclear. This study aimed to explore the regulatory effects and mechanism of Mn on IR using hepatocyte IR model induced by high palmitate (PA), high glucose (HG) or insulin. HepG2 cells were exposed to PA (200 μM), HG (25 mM) or insulin (100 nM) respectively, alone or with 5 μM Mn for 24 hours. The expression of key proteins in insulin signaling pathway, intracellular glycogen content and glucose accumulation, reactive oxygen species (ROS) level and Mn superoxide dismutase (MnSOD) activity were detected. compared with control group, the expression of phosphorylated protein kinase B (Akt), glycogen synthase kinase-3β (GSK-3β) and forkhead box O1 (FOXO1) in the three IR groups was declined, and this decrease was reversed by Mn. The reduction of intracellular glycogen content and increase in glucose accumulation in IR groups were also inhibited by Mn. Additionally, the production of ROS was increased in IR models, compared with normal control group, while Mn reduced the excessive production of ROS induced by PA, HG or insulin. However, Mn did not alter the activity of MnSOD in the three IR models. this study demonstrated that Mn treatment can improve IR in hepatocytes. The mechanism is probably by reducing the level of intracellular oxidative stress, enhancing the activity of Akt/GSK-3β/FOXO1 signal pathway, promoting glycogen synthesis, and inhibiting gluconeogenesis.

Secreted MUP1 that reduced under ER stress attenuates ER stress induced insulin resistance through suppressing protein synthesis in hepatocytes

Disturbed endoplasmic reticulum (ER) stress response driven by the excessive lipid accumulation in the liver is a characteristic feature in the pathogenesis of non-alcoholic fatty liver disease (NAFLD). Restoring metabolic homeostasis by targeting ER stress is a potentially therapeutic strategy for NAFLD. Here we aim to identify novel proteins or pathways involved in regulating ER stress response and therapeutic targets for alleviating NAFLD. Proteomic and transcriptomic analysis demonstrated that major urinary proteins (MUPs) were significantly reduced in the livers from NAFLD mouse models. Then we confirmed that MUP1, the major secreted form of MUPs, was reduced at mRNA and protein expression levels in hepatocytes both in vivo and in vitro under ER stress. We further illustrated that MUP1 protein levels in the urine were reduced in mice with NAFLD, which was reversed by GLP-1 receptor agonist treatment. To study the relationship between ER stress and MUP1 biology, our analysis demonstrated that MUP1 was misfolded and trapped in the ER under ER stress in vivo. Interestingly, we discovered that recombinant MUP1 treatment in hepatocytes increased calcium efflux from the ER, which resulted in transient ER stress response, including reduced protein synthesis. These responses facilitated the alleviation of chemical induced ER stress in hepatocytes, which was suggested as “pre-adaptive ER stress”. Besides, recombinant MUP1 pretreatment also improved ER stress-induced insulin resistance in hepatocytes. Our findings revealed a novel and critical role of MUP1, and recombinant MUP1 or its potential derivates may serve as a promising therapeutic target for alleviating NAFLD.

Novel active compounds and the anti-diabetic mechanism of mulberry leaves.

Mulberry (Morus alba L.) leaves have long been considered beneficial in traditional Chinese medicine to treat infectious and internal diseases. Recently studies have discovered that the mulberry leaf’s total flavonoids (MLF) display excellent hypoglycemia properties. However, the active ingredients and their molecular mechanisms are still uncharacterized. In this study, we explored the hypoglycemic effects of MLF and mulberry leaf polysaccharides (MLP) on ob/ob mice, an animal model of type 2 diabetes mellitus (T2DM), compared with Ramulus Mori (Sangzhi) alkaloid (RMA). Network pharmacology was employed to identify the potential available targets and active compounds of MLF and RMA against hyperglycemia. Molecular docking, an insulin-resistant cell model and qPCR were employed to verify the antidiabetic activity of the critical compounds and the gene expression profiles of the top molecular targets. Here, the results showed that MLF and MLP improved glucose uptake in insulin-resistant hepatocytes. MLF, MLP and RMA alleviated insulin resistance and glucose intolerance in ob/ob mice. Unlike MLF and MLP, RMA administration did not influence the accumulation of intrahepatic lipids. Network pharmacology analysis revealed that morusin, kuwanon C and morusyunnansin L are the main active compounds of MLF and that they amend insulin resistance and glycemia via the PI3K- Akt signaling pathway, lipid and atherosclerosis pathways, and the AGE-RAGE signaling pathway. Moreover, 1-deoxynojirimycin (DNJ), fagomine (FA), and N-methyl-1-deoxynojirimycin are the primary active ingredients of RMA and target carbohydrate metabolism and regulate alpha-glucosidase activity to produce a potent anti-diabetic effect. The molecular docking results indicated that morusin, kuwanon C and morusyunnansin L are the critical bioactive compounds of MLF. They had high affinities with the key targets adenosine A1 receptor (ADORA1), AKT serine/threonine kinase 1 (AKT1), peroxisome proliferator-activated receptor gamma (PPARγ), and glycogen synthase kinase 3 beta (GSK3β), which play crucial roles in the MLF-mediated glucose-lowering effect. Additionally, morusin plays a role in amending insulin resistance of hepatocytes by repressing the expression of the ADORA1 and PPARG genes. Our results shed light on the mechanism behind the glucose-lowering effects of MLF, suggesting that morusin, kuwanon C, and morusyunnansin L might be promising drug leads for the management of T2DM.

Exenatide improves hepatocyte insulin resistance induced by different regional adipose tissue.

Obesity is resulted from energy surplus and is characterized by abnormal adipose tissue accumulation and/or distribution. Adipokines secreted by different regional adipose tissue can induce changes in key proteins of the insulin signaling pathway in hepatocytes and result in impaired hepatic glucose metabolism. This study aimed to investigate whether exenatide affects key proteins of IRS2/PI3K/Akt2 signaling pathway in hepatocytes altered by the different regional fat depots. Six non-obese patients without endocrine diseases were selected as the research subjects. Their subcutaneous adipose tissue (SAT) and visceral adipose tissue (VAT)were co-cultured with HepG2 cells in the transwell chamber. In the presence or absence of exenatide, adipokines content in the supernatant of each experimental group was detected by ELISA. In addition, HepG2 cells in each co-culture group with and without insulin were collected, and the expression of key proteins IRS2, p-IRS2(S731), PI3K-p85, Akt2, and p-Akt2(S473) was detected by western blotting (WB). The results showed that the adipokines IL-8, MCP-1, VEGF, and sTNFR2 in the supernatant of HepG2 cells induced by different regional adipose tissue were significantly higher than those in the HepG2 group, and VAT released more adipokines than SAT. Furthermore, these adipokines were significantly inhibited by exenatide. Importantly, the different regional fat depot affects the IRS2/PI3K/Akt2 insulin signaling pathway of hepatocytes. Exenatide can up-regulate the expression of hepatocyte proteins IRS2, PI3K-p85, p-Akt2(S731) inhibited by adipose tissue, and down-regulate the expression of hepatocyte proteins p-IRS2(S731) promoted by adipose tissue. The effect of VAT on the expression of these key proteins in hepatocytes is more significant than that of SAT. But there was no statistical difference in the expression of Akt2 protein among each experimental group, suggesting that exenatide has no influence on the expression of Akt2 protein in hepatocytes. In conclusion, exenatide may improve hepatic insulin resistance (IR) by inhibiting adipokines and regulating the expression of key proteins in the IRS2/PI3K/Akt2 pathway.

Obesity induced Ext1 reduction mediates the occurrence of NAFLD

Non-alcoholic fatty liver disease (NAFLD) is the most common liver disorder with intricate etiology. It is closely associated with metabolic syndrome, insulin resistance and endoplasmic reticulum (ER) stress. Exostosin1 (Ext1) is an ER-resident transmembrane glycosyltransferase, which plays an important role in ER homeostasis. Loss-of-function mutations in Ext1 link to hereditary multiple exostosis (HME). The present research was undertaken to identify the effect of Ext1 in the progress of NAFLD. High-fat-diet induced mice obesity, hepatic steatosis and decreased hepatic Ext1 expression. In consistent with evaluation of NAFLD mice possessing down-regulated Ext1 expression, free fatty acid (FFA) treatment blunted Ext1 expression in hepatocytes. In human subjects, HME patients presented elevated fasting blood glucose—one of the criteria that define insulin resistance. In vitro experiments, Ext1 deficiency promoted FFA-induced insulin resistance in hepatocytes by analysis of glycogen storage and hallmarks of gluconeogenesis, ascertaining its association with insulin resistance. Mechanically, Ext1 silencing exacerbated ER stress triggered by FFA, which severely disrupted autophagy in hepatocytes, and thereby accelerated the progression of NAFLD. In conclusion, our study demonstrates a beneficial role for Ext1 during the development of NAFLD, which establishes a novel correlation between Ext1 and ER stress-induced perturbations of autophagy during NAFLD progression.

Bone marrow macrophage-derived exosomal miR-143-5p contributes to insulin resistance in hepatocytes by repressing MKP5.

ObjectiveIn this study, we aim to explore the role of bone marrow macrophage‐derived exosomes in hepatic insulin resistance, investigate the substance in exosomes that regulates hepatic insulin signalling pathways, reveal the specific molecular mechanisms involved in hepatic insulin resistance and further explore the role of exosomes in type 2 diabetes.Materials and methodsHigh‐fat diet (HFD)‐fed mice were used as obesity‐induced hepatic insulin resistance model, exosomes were isolated from BMMs which were extracted from HFD‐fed mice by ultracentrifugation. Exosomes were analysed the spectral changes of microRNA expression using a microRNA array. The activation of the insulin signalling pathway and the level of glycogenesis were examined in hepatocytes after transfected with miR‐143‐5p mimics. Luciferase assay and western blot were used to assess the target of miR‐143‐5p.ResultsBMMs from HFD‐fed mice were polarized towards M1, and miR‐143‐5p was significantly upregulated in exosomes of BMMs from HFD‐fed mice. Overexpression of miR‐143‐5p in Hep1‐6 cells led to decreased phosphorylation of AKT and GSK and glycogen synthesis. Dual‐luciferase reporter assay and western blot demonstrated that mitogen‐activated protein kinase phosphatase‐5 (Mkp5, also known as Dusp10) was the target gene of miR‐143‐5p. Moreover, the overexpression of MKP5 could rescue the insulin resistance induced by transfection miR‐143‐5p mimics in Hep1‐6.ConclusionBone marrow macrophage‐derived exosomal miR‐143‐5p induces insulin resistance in hepatocytes through repressing MKP5.