Irs1 serine 307 promotes insulin sensitivity in mice

Effects of acupuncture on the insulin signaling pathway and mitochondrial AMPK pathway in an animal model of type 2 diabetes mellitus: systematic evaluation and meta-analysis

BACKGROUND

Previous studies of acupuncture for type 2 diabetes mellitus (T2DM) have focused on lowering blood glucose and improving symptoms; however, the mechanisms underlying these effects have not been systematically reviewed. Acupuncture can improve impaired glucose-lipid metabolism and correct insulin resistance (IR) by modulating relevant pathway cytokines, which are both key process in T2DM pathogenesis.

OBJECTIVES

The aim of this study was to quantitatively assess the efficacy of acupuncture in an animal model of T2DM.

METHODS

Three researchers identified animal studies of acupuncture intervention in T2DM by searching nine databases, including PubMed, Scopus, Embase, the Cochrane Library, Web of Science, Ovide Medline, BIOSIS Previews , Wan Fang, CNKI, and VIP. Literature that met the inclusion criteria was screened, required data were extracted, and meta-analysis was performed using RevMan 5.4 and Stata 17.0.

RESULTS

A total of 31 studies with 619 animals were included-309 in the acupuncture group and 310 in the model group-all of which were male rodents. The mean quality score of the studies was 3.7, which indicated low quality. Meta-analysis showed that first acupuncture led to a significant reduction in body weight gain and hematological factors, and reduced food intake and water intake in T2DM animals. Second acupuncture significantly reduced blood glucose and serum insulin, increased insulin sensitivity, and decreased IR index in T2DM animals. Finally acupuncture had the following beneficial effects on the insulin signaling pathway and mitochondrial AMPK pathway: (1) insulin signaling pathway: Acupuncture can balance the phosphorylation levels of IRS-1 tyrosine 895 and IRS-1 serine/threonine 307 and promote the expression of all factors of the insulin signaling pathway, namely, IRS-1 mRNA, p-IRS-1, PI3K p85, PI3K mRNA, AKT, p-AKT, GLUT 4, and GLUT 4 mRNA-promoting glucose uptake, alleviating IR, and ameliorating impaired glucose metabolism. (2) Mitochondrial AMPK pathway: acupuncture significantly promoted AMPK, AMPK mRNA, p-AMPK, SIRT1, SIRT1 mRNA, PGC-1α, PGC-1α mRNA and NRF1, improved mitochondrial dysfunction, enhanced glucose metabolism, and alleviated T2DM symptoms.

CONCLUSION

Acupuncture can improve glucose-lipid metabolism, enhance insulin sensitivity, and correct IR, likely by promoting the expression of signaling factors in the insulin and mitochondrial AMPK pathways. These findings offer potential explanations for the mechanism of action and clinical effects of acupuncture in the treatment of T2DM.

Insulin resistance in type 2 diabetes mellitus

Insulin resistance is an integral pathophysiological feature of type 2 diabetes mellitus. Here, we review established and emerging cellular mechanisms of insulin resistance, their complex integrative features and their relevance to disease progression. While recognizing the heterogeneity of the elusive fundamental disruptions that cause insulin resistance, we endorse the view that effector mechanisms impinge on insulin receptor signalling and its relationship with plasma levels of insulin. We focus on hyperinsulinaemia and its consequences: acutely impaired but persistent insulin action, with reduced ability to lower glucose levels but preserved lipid synthesis and lipoprotein secretion. We emphasize the role of insulin sensitization as a therapeutic goal in type 2 diabetes mellitus.

Unraveling the Mystery of Insulin Resistance: From Principle Mechanistic Insights and Consequences to Therapeutic Interventions

Insulin resistance (IR) is a significant factor in the development and progression of metabolic-related diseases like dyslipidemia, T2DM, hypertension, nonalcoholic fatty liver disease, cardiovascular and cerebrovascular disorders, and cancer. The pathogenesis of IR depends on multiple factors, including age, genetic predisposition, obesity, oxidative stress, among others. Abnormalities in the insulin-signaling cascade lead to IR in the host, including insulin receptor abnormalities, internal environment disturbances, and metabolic alterations in the muscle, liver, and cellular organelles. The complex and multifaceted characteristics of insulin signaling and insulin resistance envisage their thorough and comprehensive understanding at the cellular and molecular level. Therapeutic strategies for IR include exercise, dietary interventions, and pharmacotherapy. However, there are still gaps to be addressed, and more precise biomarkers for associated chronic diseases and lifestyle interventions are needed. Understanding these pathways is essential for developing effective treatments for IR, reducing healthcare costs, and improving quality of patient life.

Mixtures of polystyrene micro and nanoplastics affects fat and glucose metabolism in 3T3-L1 adipocytes and zebrafish larvae

Microplastics (MPs) and nanoplastics (NPs) are pervasive pollutants that pose a hazard to human health. Although most previous studies have investigated the effects of MPs and NPs on digestion, oxidative stress, and inflammation in diverse models, the combined effect of plastic mixtures (PM) containing MPs and NPs on obesity and type 2 diabetes mellitus (T2DM) remains unknown. The hypothesis of our study is to verify the association between PM exposure and clinical features of metabolic diseases such as lipogenesis and insulin resistance. Therefore, we investigated the effects of PM on fat and glucose metabolism in 3T3-L1 cells and high-fat diet (HFD)-induced zebrafish larvae. PM exposure increased cell viability, differentiation, adipogenesis (PPARγ and C/EBPα), and lipogenesis (FAS and SREBP-1c), while it decreased glucose uptake and inhibited insulin signal (IRS1, PI3K, AKT, and GLUT4) expression 3T3-L1 cells. In zebrafish larvae, PM mainly bioaccumulated in the intestine and pancreatic tissue, reducing glucose uptake and increasing body weight and blood glucose compared to controls. Moreover, PM significantly increased adipogenic differentiation (PPARγ) and synthesis (FASN and FABP), proinflammatory cytokines (TNF-α and IL-6), and gluconeogenesis (PCK1 and G6Pase). Conversely, energy and fat metabolism (AMPKα and adiponectin), insulin production (INSα), signaling pathway (IRS1, AKT, and GLUT2), and anti-inflammatory cytokines (IL-10 and IL-4) were suppressed. Overall, this study sheds light on the mechanisms responsible for the detrimental effects of PM exposure on fat and glucose metabolism, providing insights into metabolic disorders, like type 2 diabetes, in both in vitro and in vivo models.

Self-assembly of the insulin-responsive vesicles creates a signaling platform for the insulin action on glucose uptake

In fat and skeletal muscle cells, insulin causes plasma membrane translocation of specialized insulin-responsive vesicles, or IRVs. These vesicles consist of multiple copies of Glut4, sortilin, IRAP, and LRP1 as well as several auxiliary components. Major IRV proteins have relatively long half-life inside the cell and survive multiple rounds of translocation to and from the cell surface. Here, we summarize evidence showing how the IRVs are self-assembled from pre-synthesized Glut4, sortilin, IRAP, and LRP1 after each translocation event. Furthermore, the cytoplasmic tail of sortilin binds Akt while cytoplasmic tails of IRAP and LRP1 interact with the Akt target, TBC1D4. Recruitment of signaling proteins to the IRVs may render insulin responsiveness to this compartment and thus distinguish it from other intracellular membrane vesicles.

The Interplay of Dietary Fibers and Intestinal Microbiota Affects Type 2 Diabetes by Generating Short-Chain Fatty Acids

Foods contain dietary fibers which can be classified into soluble and insoluble forms. The nutritional composition of fast foods is considered unhealthy because it negatively affects the production of short-chain fatty acids (SCFAs). Dietary fiber is resistant to digestive enzymes in the gut, which modulates the anaerobic intestinal microbiota (AIM) and fabricates SCFAs. Acetate, butyrate, and propionate are dominant in the gut and are generated via Wood-Ljungdahl and acrylate pathways. In pancreatic dysfunction, the release of insulin/glucagon is impaired, leading to hyperglycemia. SCFAs enhance insulin sensitivity or secretion, beta-cell function, leptin release, mitochondrial function, and intestinal gluconeogenesis in human organs, which positively affects type 2 diabetes (T2D). Research models have shown that SCFAs either enhance the release of peptide YY (PYY) and glucagon-like peptide-1 (GLP-1) from L-cells (entero-endocrine), or promotes the release of leptin hormone in adipose tissues through G-protein receptors GPR-41 and GPR-43. Dietary fiber is a component that influences the production of SCFAs by AIM, which may have beneficial effects on T2D. This review focuses on the effectiveness of dietary fiber in producing SCFAs in the colon by the AIM as well as the health-promoting effects on T2D.

Altered glucose metabolism in Alzheimer's disease: Role of mitochondrial dysfunction and oxidative stress

Increasing evidence suggests that abnormal cerebral glucose metabolism is largely present in Alzheimer's disease (AD). The brain utilizes glucose as its main energy source and a decline in its metabolism directly reflects on brain function. Weighing on recent evidence, here we systematically assessed the aberrant glucose metabolism associated with amyloid beta and phosphorylated tau accumulation in AD brain. Interlink between insulin signaling and AD highlighted the involvement of the IRS/PI3K/Akt/AMPK signaling, and GLUTs in the disease progression. While shedding light on the mitochondrial dysfunction in the defective glucose metabolism, we further assessed functional consequences of AGEs (advanced glycation end products) accumulation, polyol activation, and other contributing factors including terminal respiration, ROS (reactive oxygen species), mitochondrial permeability, PINK1/parkin defects, lysosome-mitochondrial crosstalk, and autophagy/mitophagy. Combined with the classic plaque and tangle pathologies, glucose hypometabolism with acquired insulin resistance and mitochondrial dysfunction potentiate these factors to exacerbate AD pathology. To this end, we further reviewed AD and DM (diabetes mellitus) crosstalk in disease progression. Taken together, the present work discusses the emerging role of altered glucose metabolism, contributing impact of insulin signaling, and mitochondrial dysfunction in the defective cerebral glucose utilization in AD.

Inhibitors of RNA and protein synthesis cause Glut4 translocation and increase glucose uptake in adipocytes

Insulin stimulates glucose uptake in adipocytes by triggering translocation of glucose transporter 4-containg vesicles to the plasma membrane. Under basal conditions, these vesicles (IRVs for insulin-responsive vesicles) are retained inside the cell via a “static” or “dynamic” mechanism. We have found that inhibitors of RNA and protein synthesis, actinomycin D and emetine, stimulate Glut4 translocation and glucose uptake in adipocytes without engaging conventional signaling proteins, such as Akt, TBC1D4, or TUG. Actinomycin D does not significantly affect endocytosis of Glut4 or recycling of transferrin, suggesting that it specifically increases exocytosis of the IRVs. Thus, the intracellular retention of the IRVs in adipocytes requires continuous RNA and protein biosynthesis de novo. These results point out to the existence of a short-lived inhibitor of IRV translocation thus supporting the “static” model.

Analysis of Insulin Resistance in Nonalcoholic Steatohepatitis

Insulin resistance is a major phenotype observed in nonalcoholic steatohepatitis (NASH), the advanced stage of nonalcoholic fatty liver disease (NAFLD). Insulin resistance in NASH is characterized by reductions in whole body, hepatic, and adipose tissue insulin sensitivity. The mechanisms underlying hepatic insulin resistance is primarily associated with hepatic glucose production (HGP) rate. Hepatic insulin resistance can also be a consequence or a driving factor of hepatic lipid accumulation by increasing free fatty acid synthesis, delivery, and catabolism. The common method to assess hepatic insulin resistance is to measure hepatic glucose production (HGP) using isotope tracer distribution technique. However, non-radioactive approaches have been developed to assess hepatic insulin resistance in the context of NASH. In this chapter, we describe the methods to evaluate hepatic insulin resistance in animal models of NASH by examining insulin sensitivity and glucose tolerance as well as the key molecules in hepatic insulin signaling pathways.

The aetiology and molecular landscape of insulin resistance

Insulin resistance, defined as a defect in insulin-mediated control of glucose metabolism in tissues - prominently in muscle, fat and liver - is one of the earliest manifestations of a constellation of human diseases that includes type 2 diabetes and cardiovascular disease. These diseases are typically associated with intertwined metabolic abnormalities, including obesity, hyperinsulinaemia, hyperglycaemia and hyperlipidaemia. Insulin resistance is caused by a combination of genetic and environmental factors. Recent genetic and biochemical studies suggest a key role for adipose tissue in the development of insulin resistance, potentially by releasing lipids and other circulating factors that promote insulin resistance in other organs. These extracellular factors perturb the intracellular concentration of a range of intermediates, including ceramide and other lipids, leading to defects in responsiveness of cells to insulin. Such intermediates may cause insulin resistance by inhibiting one or more of the proximal components in the signalling cascade downstream of insulin (insulin receptor, insulin receptor substrate (IRS) proteins or AKT). However, there is now evidence to support the view that insulin resistance is a heterogeneous disorder that may variably arise in a range of metabolic tissues and that the mechanism for this effect likely involves a unified insulin resistance pathway that affects a distal step in the insulin action pathway that is more closely linked to the terminal biological response. Identifying these targets is of major importance, as it will reveal potential new targets for treatments of diseases associated with insulin resistance.

A tale of two proteins: PACT and PKR and their roles in inflammation

Inflammation is a pathological hallmark associated with bacterial and viral infections, autoimmune diseases, genetic disorders, obesity and diabetes, as well as environmental stresses including physical and chemical trauma. Among numerous proteins regulating proinflammatory signaling, very few such as Protein kinase R (PKR), have been shown to play an all-pervading role in inflammation induced by varied stimuli. PKR was initially characterized as an interferon-inducible gene activated by viral double-stranded RNA with a role in protein translation inhibition. However, it has become increasingly clear that PKR is involved in multiple pathways that promote inflammation in response to stress activation, both dependent on and independent of its cellular protein activator of PKR (PACT). In this review, we discuss the signaling pathways that contribute to the initiation of inflammation, including Toll-like receptor, interferon, and RIG-I-like receptor signaling, as well as inflammasome activation. We go on to discuss the specific roles that PKR and PACT play in such proinflammatory signaling, as well as in metabolic syndrome- and environmental stress-induced inflammation.

Insulin signaling in health and disease

The molecular mechanisms of cellular insulin action have been the focus of much investigation since the discovery of the hormone 100 years ago. Insulin action is impaired in metabolic syndrome, a condition known as insulin resistance. The actions of the hormone are initiated by binding to its receptor on the surface of target cells. The receptor is an α2β2 heterodimer that binds to insulin with high affinity, resulting in the activation of its tyrosine kinase activity. Once activated, the receptor can phosphorylate a number of intracellular substrates that initiate discrete signaling pathways. The tyrosine phosphorylation of some substrates activates phosphatidylinositol-3-kinase (PI3K), which produces polyphosphoinositides that interact with protein kinases, leading to activation of the kinase Akt. Phosphorylation of Shc leads to activation of the Ras/MAP kinase pathway. Phosphorylation of SH2B2 and of Cbl initiates activation of G proteins such as TC10. Activation of Akt and other protein kinases produces phosphorylation of a variety of substrates, including transcription factors, GTPase-activating proteins, and other kinases that control key metabolic events. Among the cellular processes controlled by insulin are vesicle trafficking, activities of metabolic enzymes, transcriptional factors, and degradation of insulin itself. Together these complex processes are coordinated to ensure glucose homeostasis.

JNK downregulation improves olanzapine-induced insulin resistance by suppressing IRS1Ser307 phosphorylation and reducing inflammation

AIMS

c-jun N-terminal kinase (JNK) plays pivotal roles in many physiological processes, including inflammation and glucose metabolism. However, the effects of JNK on olanzapine-induced insulin resistance and the underlying mechanisms have not been fully elucidated. The aim of our study was to explore the role of JNK in olanzapine-induced insulin resistance and the underlying mechanisms.

METHODS

We studied glucose metabolism in olanzapine-treated female C57B/J mice and mice with adeno-associated virus (AAV)-mediated downregulation of JNK1 in epididymal white adipose tissue (eWAT). 3T3-L1 adipocytes were used to investigate the mechanism of JNK1 regulating insulin signaling after olanzapine treatment.

RESULTS

JNK was activated in eWAT after olanzapine treatment. JNK1 downregulation in eWAT ameliorated the insulin resistance and adipose tissue inflammation in olanzapine-treated mice. Furthermore, overexpression of JNK1 in adipocytes exacerbated the glucose disorder while JNK1 knockdown alleviated the impaired insulin signaling on olanzapine challenge, which was likely mediated by the reduced inflammation and insulin receptor substrate 1 (IRS1) phosphorylation. Moreover, the effect of JNK1 was attenuated by downregulation of IRS1 in adipocytes. Finally, the JNK1-IRS1 interaction and IRS1^S307 phosphorylation were required for JNK1-regulated olanzapine-induced insulin resistance in adipocytes.

CONCLUSIONS

Our results demonstrated that JNK1 activation by olanzapine induced insulin resistance by promoting IRS1^Ser307 phosphorylation and inflammation in eWAT. These results highlighted the importance of JNK1 in eWAT as a promising drug target for olanzapine-induced insulin resistance.

Blood glucose regulation in context of infection

The immune and endocrine systems collectively control homeostasis in the body. The endocrine system ensures that values of essential factors and nutrients such as glucose, electrolytes and vitamins are maintained within threshold values. The immune system resolves local disruptions in tissue homeostasis, caused by pathogens or malfunctioning cells. The immediate goals of these two systems do not always align. The immune system benefits from optimal access to nutrients for itself and restriction of nutrient availability to all other organs to limit pathogen replication. The endocrine system aims to ensure optimal nutrient access for all organs, limited only by the nutrients stores that the body has available. The actual state of homeostatic parameters such as blood glucose levels represents a careful balance based on regulatory signals from the immune and endocrine systems. This state is not static but continuously adjusted in response to changes in the current metabolic needs of the body, the amount of resources it has available and the level of threats it encounters. This balance is maintained by the ability of the immune and endocrine systems to interact and co-regulate systemic metabolism. In context of metabolic disease, this system is disrupted, which impairs functionality of both systems. The failure of the endocrine system to retain levels of nutrients such as glucose within threshold values impairs functionality of the immune system. In addition, metabolic stress of organs in context of obesity is perceived by the immune system as a disruption in local homeostasis, which it tries to resolve by the excretion of factors which further disrupt normal metabolic control. In this chapter, we will discuss how the immune and endocrine systems interact under homeostatic conditions and during infection with a focus on blood glucose regulation. In addition, we will discuss how this system fails in the context of metabolic disease.

Insulin action at a molecular level - 100 years of progress

The discovery of insulin 100 years ago and its application to the treatment of human disease in the years since have marked a major turning point in the history of medicine. The availability of purified insulin allowed for the establishment of its physiological role in the regulation of blood glucose and ketones, the determination of its amino acid sequence, and the solving of its structure. Over the last 50 years, the function of insulin has been applied into the discovery of the insulin receptor and its signaling cascade to reveal the role of impaired insulin signaling-or resistance-in the progression of type 2 diabetes. It has also become clear that insulin signaling can impact not only classical insulin-sensitive tissues, but all tissues of the body, and that in many of these tissues the insulin signaling cascade regulates unexpected physiological functions. Despite these remarkable advances, much remains to be learned about both insulin signaling and how to use this molecular knowledge to advance the treatment of type 2 diabetes and other insulin-resistant states.

Low-Dose Acrolein, an Endogenous and Exogenous Toxic Molecule, Inhibits Glucose Transport via an Inhibition of Akt-Regulated GLUT4 Signaling in Skeletal Muscle Cells

Urinary acrolein adduct levels have been reported to be increased in both habitual smokers and type-2 diabetic patients. The impairment of glucose transport in skeletal muscles is a major factor responsible for glucose uptake reduction in type-2 diabetic patients. The effect of acrolein on glucose metabolism in skeletal muscle remains unclear. Here, we investigated whether acrolein affects muscular glucose metabolism in vitro and glucose tolerance in vivo. Exposure of mice to acrolein (2.5 and 5 mg/kg/day) for 4 weeks substantially increased fasting blood glucose and impaired glucose tolerance. The glucose transporter-4 (GLUT4) protein expression was significantly decreased in soleus muscles of acrolein-treated mice. The glucose uptake was significantly decreased in differentiated C2C12 myotubes treated with a non-cytotoxic dose of acrolein (1 μM) for 24 and 72 h. Acrolein (0.5–2 μM) also significantly decreased the GLUT4 expression in myotubes. Acrolein suppressed the phosphorylation of glucose metabolic signals IRS1, Akt, mTOR, p70S6K, and GSK3α/β. Over-expression of constitutive activation of Akt reversed the inhibitory effects of acrolein on GLUT4 protein expression and glucose uptake in myotubes. These results suggest that acrolein at doses relevant to human exposure dysregulates glucose metabolism in skeletal muscle cells and impairs glucose tolerance in mice.

Insulin Resistance and Diabetes Mellitus in Alzheimer's Disease

Type 2 diabetes mellitus is a progressive disease that is characterized by the appearance of insulin resistance. The term insulin resistance is very wide and could affect different proteins involved in insulin signaling, as well as other mechanisms. In this review, we have analyzed the main molecular mechanisms that could be involved in the connection between type 2 diabetes and neurodegeneration, in general, and more specifically with the appearance of Alzheimer's disease. We have studied, in more detail, the different processes involved, such as inflammation, endoplasmic reticulum stress, autophagy, and mitochondrial dysfunction.

Potential Roles of Endoplasmic Reticulum Stress and Cellular Proteins Implicated in Diabesity

The role of the endoplasmic reticulum (ER) has evolved from protein synthesis, processing, and other secretory pathways to forming a foundation for lipid biosynthesis and other metabolic functions. Maintaining ER homeostasis is essential for normal cellular function and survival. An imbalance in the ER implied stressful conditions such as metabolic distress, which activates a protective process called unfolded protein response (UPR). This response is activated through some canonical branches of ER stress, i.e., the protein kinase RNA-like endoplasmic reticulum kinase (PERK), inositol-requiring enzyme 1α (IRE1α), and activating transcription factor 6 (ATF6). Therefore, chronic hyperglycemia, hyperinsulinemia, increased proinflammatory cytokines, and free fatty acids (FFAs) found in diabesity (a pathophysiological link between obesity and diabetes) could lead to ER stress. However, limited data exist regarding ER stress and its association with diabesity, particularly the implicated proteins and molecular mechanisms. Thus, this review highlights the role of ER stress in relation to some proteins involved in diabesity pathogenesis and provides insight into possible pathways that could serve as novel targets for therapeutic intervention.

Adenosine monophosphate activated protein kinase (AMPK) is essential for the memory improving effect of adiponectin

Adiponectin (APN) plays a major role in the regulation of insulin sensitivity and glucose homeostasis. Insulin and APN have a positive effect on memory. In this study, we examined whether the inhibition of AMPK could block the memory improving effect of APN or affect the IRS1 expression. Animal model of AD was developed by intracerebroventricular (icv) injection of 3 mg/kg streptozotocin (STZ), in 12 weeks old Wistar rats, on days 1 and 3 after cannulation. Dorsomorphin (DM) and APN (600 nM) were injected 30 and 20 min before the acquisition phase, respectively. DM was applied in 3 different doses (0.2, 2 and 20 μM). All behavioral tests were performed on days 15 and 16; the Preference Index (PI) was calculated for novel object recognition (NOR) test, while the step through latency (STL) and total time in dark compartment (TDC) were recorded and analyzed for the passive avoidance task. Relative expression of insulin receptor substrate-1 (IRS-1) protein in the hippocampus was measured by western blotting. In early retrieval test, STZ + APN treatment increased STL (P < 0.0001) and decreased TDC (P < 0.05) in comparison to STZ group, while STZ + APN + DM (2μM) caused a decrease in STL (P < 0.05) and increase in TDC (0.2μM and 2μM DM; P < 0.05). Icv injection of DM (0.2μM and 2μM) before APN decreased the PI significantly (P < 0.05) in comparison to STZ + APN group. APN treatment raised the IRS-1 expression and DM reversed this increment, significantly (P < 0.0001). It is concluded that the memory improving effect of APN is mediated, at least in part, by the AMPK pathway. APN is also able to boost insulin signaling by overexpression of IRS-1 in the hippocampus.

Mechanism of Electroacupuncture Regulating IRS-1 Phosphorylation in Skeletal Muscle to Improve Insulin Sensitivity

OBJECTIVE

To explore the possible mechanism of electroacupuncture to improve insulin sensitivity in type 2 diabetes rats.

METHODS

Fourteen Zucker Diabetic Fatty (ZDF) rats were randomly divided into two groups: a model group and an electroacupuncture group, with 7 rats in each group. Seven Zucker Lean (ZL) rats served as a control group. All rats were fed with Purina #5008 for 4 weeks, and the electroacupuncture group received 4-week electroacupuncture intervention, while the control group and model group received no intervention. We measured fasting blood glucose (FBG) on the fourth weekend. After 4 weeks of intervention, the expression levels of insulin receptor substrate-1 (IRS-1) tyrosine phosphorylation, IRS-1 serine/threonine phosphorylation, and GLUT4 in quadriceps femoris muscles were detected by western Blot.

RESULTS

Compared with the model group, the electroacupuncture group had a lower level of fasting blood glucose, serum insulin level, and insulin resistance index (P < 0.05). The electroacupuncture group had lower IRS-1 serine/threonine phosphorylation than the model group, with the difference showing statistical significance (P < 0.05). Furthermore, the mean score (MS) of the control group showed the lowest phosphorylation expression, followed by the electroacupuncture group, while the model group had the highest level of phosphorylated protein expression. The level of IRS-1 tyrosine phosphorylation at Tyr895 sites was compared, and the result showed that there was no significant difference between the electroacupuncture group and the control group (P > 0.05), and the electroacupuncture group had higher phosphorylation expression than the model group (P < 0.05). Compared with the control group and the model group, the expression level of GLUT4 protein in the electroacupuncture group was significantly increased (P < 0.05).

CONCLUSION

Electroacupuncture has the effect to improve the insulin sensitivity of type 2 diabetic ZDF rats by reducing fasting blood glucose, insulin level, and insulin resistance index, effectively up regulating the expression of GLUT4 protein in quadriceps femoris muscle. The mechanism is related to the regulation of skeletal muscle IRS-1 serine/threonine and tyrosine phosphorylation levels.

Stress kinases in the development of liver steatosis and hepatocellular carcinoma

Non-alcoholic fatty liver disease (NAFLD) is an important component of metabolic syndrome and one of the most prevalent liver diseases worldwide. This disorder is closely linked to hepatic insulin resistance, lipotoxicity, and inflammation. Although the mechanisms that cause steatosis and chronic liver injury in NAFLD remain unclear, a key component of this process is the activation of stress-activated kinases (SAPKs), including p38 and JNK in the liver and immune system. This review summarizes findings which indicate that the dysregulation of stress kinases plays a fundamental role in the development of steatosis and are important players in inducing liver fibrosis. To avoid the development of steatohepatitis and liver cancer, SAPK activity must be tightly regulated not only in the hepatocytes but also in other tissues, including cells of the immune system. Possible cellular mechanisms of SAPK actions are discussed.

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Hepatic JNK triggers steatosis and insulin resistance, decreasing lipid oxidation and ketogenesis in HFD-fed mice.

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Decreased liver expression of p38α/β in HFD increases lipogenesis.

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Hepatic p38γ/δ drive insulin resistance and inhibit autophagy, which may lead to steatosis.

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Macrophage p38α/β promote cytokine production and M1 polarization, leading to lipid accumulation in hepatocytes.

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Myeloid p38γ/δ contribute to cytokine production and neutrophil migration, protecting against steatosis, diabetes and NAFLD.

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JNK1 and p38γ induce HCC while p38α blocks it. However, deletion of hepatic JNK1/2 induces cholangiocarcinoma.

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SAPK are potential therapeutic target for metabolic disorders, steatohepatitis and liver cancer.

Endothelial TFEB (Transcription Factor EB) Improves Glucose Tolerance via Upregulation of IRS (Insulin Receptor Substrate) 1 and IRS2

OBJECTIVE

Vascular endothelial cells (ECs) play a critical role in maintaining vascular homeostasis. Aberrant EC metabolism leads to vascular dysfunction and metabolic diseases. TFEB (transcription factor EB), a master regulator of lysosome biogenesis and autophagy, has protective effects on vascular inflammation and atherosclerosis. However, the role of endothelial TFEB in metabolism remains to be explored. In this study, we sought to investigate the role of endothelial TFEB in glucose metabolism and underlying molecular mechanisms. Approach and Results: To determine whether endothelial TFEB is critical for glucose metabolism in vivo, we utilized EC-selective TFEB knockout and EC-selective TFEB transgenic mice fed a high-fat diet. EC-selective TFEB knockout mice exhibited significantly impaired glucose tolerance compared with control mice. Consistently, EC-selective TFEB transgenic mice showed improved glucose tolerance. In primary human ECs, small interfering RNA-mediated TFEB knockdown blunts Akt (AKT serine/threonine kinase) signaling. Adenovirus-mediated overexpression of TFEB consistently activates Akt and significantly increases glucose uptake in ECs. Mechanistically, TFEB upregulates IRS1 and IRS2 (insulin receptor substrate 1 and 2). TFEB increases IRS2 transcription measured by reporter gene and chromatin immunoprecipitation assays. Furthermore, we found that TFEB increases IRS1 protein via downregulation of microRNAs (miR-335, miR-495, and miR-548o). In vivo, Akt signaling in the skeletal muscle and adipose tissue was significantly impaired in EC-selective TFEB knockout mice and consistently improved in EC-selective TFEB transgenic mice on high-fat diet.

CONCLUSIONS

Our data revealed a critical role of TFEB in endothelial metabolism and suggest that TFEB constitutes a potential molecular target for the treatment of vascular and metabolic diseases.

Ugonin J improves metabolic disorder and ameliorates nonalcoholic fatty liver disease by regulating the AMPK/AKT signaling pathway

Closely associated with visceral obesity, hepatic steatosis resulting from non-alcoholic fatty liver disease (NAFLD) exacerbates insulin resistance. Developing effective drugs to treat NAFLD is imperative. Here, we investigated the pharmacological mechanism of ugonin J (UJ) in controlling metabolic disorder and ameliorating NAFLD pathophysiology in diet-induced obese mice. The effects of UJ were assessed in 5-week-old C57BL/6 J mice fed a high-fat diet (HFD) for 12 weeks. UJ treatment averted HFD-induced body weight gain by reducing fat deposition in adipose tissues and reduced HFD-induced hyperlipidemia and hepatic inflammation. UJ also improved HFD-induced glucose tolerance and insulin resistance. Moreover, the mode of action of UJ was analyzed in palmitate (PA)-induced steatotic human HuS-E/2 hepatocytes and in hyperglycemia-simulating rat BRIN-BD11 pancreatic β cells. In PA-induced steatotic human hepatocytes, UJ treatment promoted lipid clearance via pAMPK, pACC and CPT-1 upregulation and SREBP-1c downregulation. Interestingly, UJ upregulated Akt activity in hepatocytes and increased insulin secretion from β cells in acute insulin secretion tests. Taken together, UJ improved adipocyte hypertrophy, hyperinsulinemia, hyperglycemia, hyperlipidemia and fat deposition in livers. UJ also reduced fatty acid accumulation by modulating key metabolic regulators. Our findings demonstrated the therapeutic potential of UJ for the treatment of NAFLD and diet-induced metabolic disorders.

Altered Insulin Receptor Substrate 1 Phosphorylation in Blood Neuron-Derived Extracellular Vesicles From Patients With Parkinson's Disease

INTRODUCTION

Diabetes increases the risk of Parkinson's disease (PD). The phosphorylation of type 1 insulin receptor substrate (IRS-1) determines the function of insulin signaling pathway. Extracellular vesicles (EVs) are emerging as biomarkers of human diseases. The present study investigated whether PD patients exert altered phosphorylation IRS-1 (p-IRS-1) inside the blood neuron-derived extracellular vesicles (NDEVs).

RESEARCH DESIGN AND METHODS

In total, there were 94 patients with PD and 63 healthy controls recruited and their clinical manifestations were evaluated. Blood NDEVs were isolated using the immunoprecipitation method, and Western blot analysis was conducted to assess total IRS-1, p-IRS-1, and downstream substrates level in blood NDEVs. Statistical analysis was performed using SPSS 19.0, and p < 0.05 was considered significant.

RESULTS

The isolated blood EVs were validated according to the presence of CD63 and HSP70, nanoparticle tracking analysis and transmission electron microscopy. NDEVs were positive with neuronal markers. PD patients exerted significantly higher level of p-IRS-1S312 in blood NDEVs than controls. In addition, the p-IRS-1S312 levels in blood NDEVs was positively associated with the severity of tremor in PD patients after adjusting of age, sex, hemoglobin A1c, and body mass index (BMI).

CONCLUSION

PD patients exerted altered p-IRS-1S312 in the blood NDEVs, and also correlated with the severity of tremor. These findings suggested the association between dysfunctional insulin signaling pathway with PD. The role of altered p-IRS-1S312 in blood NDEVs as a segregating biomarker of PD required further cohort study to assess the association with the progression of PD.

The role of stress kinases in metabolic disease

Obesity is a health condition that has reached pandemic levels and is implicated in the development and progression of type 2 diabetes mellitus, cancer and heart failure. A key characteristic of obesity is the activation of stress-activated protein kinases (SAPKs), such as the p38 and JNK stress kinases, in several organs, including adipose tissue, liver, skeletal muscle, immune organs and the central nervous system. The correct timing, intensity and duration of SAPK activation contributes to cellular metabolic adaptation. By contrast, uncontrolled SAPK activation has been proposed to contribute to the complications of obesity. The stress kinase signalling pathways have therefore been identified as potential targets for the development of novel therapeutic approaches for metabolic syndrome. The past few decades have seen intense research efforts to determine how these kinases are regulated in a cell-specific manner and to define their contribution to the development of obesity and insulin resistance. Several studies have uncovered new and unexpected functions of the non-classical members of both pathways. Here, we provide an overview of the role of SAPKs in metabolic control and highlight important discoveries in the field.

Impact of Conventional and Atypical MAPKs on the Development of Metabolic Diseases

The family of mitogen-activated protein kinases (MAPKs) consists of fourteen members and has been implicated in regulation of virtually all cellular processes. MAPKs are divided into two groups, conventional and atypical MAPKs. Conventional MAPKs are further classified into four sub-families: extracellular signal-regulated kinases 1/2 (ERK1/2), c-Jun N-terminal kinase (JNK1, 2 and 3), p38 (α, β, γ, δ), and extracellular signal-regulated kinase 5 (ERK5). Four kinases, extracellular signal-regulated kinase 3, 4, and 7 (ERK3, 4 and 7) as well as Nemo-like kinase (NLK) build a group of atypical MAPKs, which are activated by different upstream mechanisms than conventional MAPKs. Early studies identified JNK1/2 and ERK1/2 as well as p38α as a central mediators of inflammation-evoked insulin resistance. These kinases have been also implicated in the development of obesity and diabetes. Recently, other members of conventional MAPKs emerged as important mediators of liver, skeletal muscle, adipose tissue, and pancreatic β-cell metabolism. Moreover, latest studies indicate that atypical members of MAPK family play a central role in the regulation of adipose tissue function. In this review, we summarize early studies on conventional MAPKs as well as recent findings implicating previously ignored members of the MAPK family. Finally, we discuss the therapeutic potential of drugs targeting specific members of the MAPK family.

Inhibition of Bruton's TK regulates macrophage NF-κB and NLRP3 inflammasome activation in metabolic inflammation

BACKGROUND AND PURPOSE

There are no medications currently available to treat metabolic inflammation. Bruton's tyrosine kinase (BTK) is highly expressed in monocytes and macrophages and regulates NF-κB and NLRP3 inflammasome activity; both propagate metabolic inflammation in diet-induced obesity.

EXPERIMENTAL APPROACH

Using an in vivo model of chronic inflammation, high-fat diet (HFD) feeding, in male C57BL/6J mice and in vitro assays in primary murine and human macrophages, we investigated if ibrutinib, an FDA approved BTK inhibitor, may represent a novel anti-inflammatory medication to treat metabolic inflammation.

KEY RESULTS

HFD-feeding was associated with increased BTK expression and activation, which was significantly correlated with monocyte/macrophage accumulation in the liver, adipose tissue, and kidney. Ibrutinib treatment to HFD-fed mice inhibited the activation of BTK and reduced monocyte/macrophage recruitment to the liver, adipose tissue, and kidney. Ibrutinib treatment to HFD-fed mice decreased the activation of NF-κB and the NLRP3 inflammasome. As a result, ibrutinib treated mice fed HFD had improved glycaemic control through restored signalling by the IRS-1/Akt/GSK-3β pathway, protecting mice against the development of hepatosteatosis and proteinuria. We show that BTK regulates NF-κB and the NLRP3 inflammasome specifically in primary murine and human macrophages, the in vivo cellular target of ibrutinib.

CONCLUSION AND IMPLICATIONS

We provide "proof of concept" evidence that BTK is a novel therapeutic target for the treatment of diet-induced metabolic inflammation and ibrutinib may be a candidate for drug repurposing as an anti-inflammatory agent for the treatment of metabolic inflammation in T2D and microvascular disease.

Interplay of Dietary Fatty Acids and Cholesterol Impacts Brain Mitochondria and Insulin Action

Overconsumption of high-fat and cholesterol-containing diets is detrimental for metabolism and mitochondrial function, causes inflammatory responses and impairs insulin action in peripheral tissues. Dietary fatty acids can enter the brain to mediate the nutritional status, but also to influence neuronal homeostasis. Yet, it is unclear whether cholesterol-containing high-fat diets (HFDs) with different combinations of fatty acids exert metabolic stress and impact mitochondrial function in the brain. To investigate whether cholesterol in combination with different fatty acids impacts neuronal metabolism and mitochondrial function, C57BL/6J mice received different cholesterol-containing diets with either high concentrations of long-chain saturated fatty acids or soybean oil-derived poly-unsaturated fatty acids. In addition, CLU183 neurons were stimulated with combinations of palmitate, linoleic acid and cholesterol to assess their effects on metabolic stress, mitochondrial function and insulin action. The dietary interventions resulted in a molecular signature of metabolic stress in the hypothalamus with decreased expression of occludin and subunits of mitochondrial electron chain complexes, elevated protein carbonylation, as well as c-Jun N-terminal kinase (JNK) activation. Palmitate caused mitochondrial dysfunction, oxidative stress, insulin and insulin-like growth factor-1 (IGF-1) resistance, while cholesterol and linoleic acid did not cause functional alterations. Finally, we defined insulin receptor as a novel negative regulator of metabolically stress-induced JNK activation.

Role of c-Jun N-terminal Kinase (JNK) in Obesity and Type 2 Diabetes

Obesity has been described as a global epidemic and is a low-grade chronic inflammatory disease that arises as a consequence of energy imbalance. Obesity increases the risk of type 2 diabetes (T2D), by mechanisms that are not entirely clarified. Elevated circulating pro-inflammatory cytokines and free fatty acids (FFA) during obesity cause insulin resistance and ß-cell dysfunction, the two main features of T2D, which are both aggravated with the progressive development of hyperglycemia. The inflammatory kinase c-jun N-terminal kinase (JNK) responds to various cellular stress signals activated by cytokines, free fatty acids and hyperglycemia, and is a key mediator in the transition between obesity and T2D. Specifically, JNK mediates both insulin resistance and ß-cell dysfunction, and is therefore a potential target for T2D therapy.

Utility of Neuronal-Derived Exosomes to Examine Molecular Mechanisms That Affect Motor Function in Patients With Parkinson Disease: A Secondary Analysis of the Exenatide-PD Trial

Importance

Exenatide, a glucagon-like peptide 1 agonist used in type 2 diabetes, was recently found to have beneficial effects on motor function in a randomized, placebo-controlled trial in Parkinson disease (PD). Accumulating evidence suggests that impaired brain insulin and protein kinase B (Akt) signaling play a role in PD pathogenesis; however, exploring the extent to which drugs engage with putative mechnisms in vivo remains a challenge.

Objective

To assess whether participants in the Exenatide-PD trial have augmented activity in brain insulin and Akt signaling pathways.

Design, Setting, and Participants

Serum samples were collected from 60 participants in the single-center Exenatide-PD trial (June 18, 2014, to June 16, 2016), which compared patients with moderate PD randomized to 2 mg of exenatide once weekly or placebo for 48 weeks followed by a 12-week washout period. Serum extracellular vesicles, including exosomes, were extracted, precipitated, and enriched for neuronal source by anti-L1 cell adhesion molecule antibody absorption, and proteins of interest were evaluated using electrochemiluminescence assays. Statistical analysis was performed from May 1, 2017, to August 31, 2017.

Main Outcomes and Measures

The main outcome was augmented brain insulin signaling that manifested as a change in tyrosine phosphorylated insulin receptor substrate 1 within neuronal extracellular vesicles at the end of 48 weeks of exenatide treatment. Additional outcome measures were changes in other insulin receptor substrate proteins and effects on protein expression in the Akt and mitogen-activated protein kinase pathways.

Results

Sixty patients (mean [SD] age, 59.9 [8.4] years; 43 [72%] male) participated in the study: 31 in the exenatide group and 29 in the placebo group (data from 1 patient in the exenatide group were excluded). Patients treated with exenatide had augmented tyrosine phosphorylation of insulin receptor substrate 1 at 48 weeks (0.27 absorbance units [AU]; 95% CI, 0.09-0.44 AU; P = .003) and 60 weeks (0.23 AU; 95% CI, 0.05-0.41 AU; P = .01) compared with patients receiving placebo. Exenatide-treated patients had elevated expression of downstream substrates, including total Akt (0.35 U/mL; 95% CI, 0.16-0.53 U/mL; P < .001) and phosphorylated mechanistic target of rapamycin (mTOR) (0.22 AU; 95% CI, 0.04-0.40 AU; P = .02). Improvements in Movement Disorders Society Unified Parkinson's Disease Rating Scale part 3 off-medication scores were associated with levels of total mTOR (F4,50 = 5.343, P = .001) and phosphorylated mTOR (F4,50 = 4.384, P = .04).

Conclusions and Relevance

The results of this study are consistent with target engagement of brain insulin, Akt, and mTOR signaling pathways by exenatide and provide a mechanistic context for the clinical findings of the Exenatide-PD trial. This study suggests the potential of using exosome-based biomarkers as objective measures of target engagement in clinical trials using drugs that target neuronal pathways.

Chronic aerobic exercise improves insulin sensitivity and modulates Nrf2 and NF‑κB/IκBα pathways in the skeletal muscle of rats fed with a high fat diet

The present study aimed to investigate the molecular mechanisms of the ameliorative effects of chronic aerobic exercise on non-alcoholic steatohepatitis (NASH) in rat skeletal muscle. Female Sprague-Dawley rats (n=6–9 per group) were divided into four groups: i) Rats fed with normal chow; ii) exercise rats fed with normal chow + exercise (run on a rotarod for 30 min per day from 9–12 weeks); iii) rats fed with a high-fat diet (HFD); iv) rats fed with an HFD + exercise. All HFD rats were fed with an HFD consisting of 30% fat from fish oil throughout the study for 12 weeks. Exercise decreased the levels of hepatic lipogenic markers carbohydrate-responsive element-binding protein, fat-specific protein 27 and liver X receptor and improved systemic glucose and insulin intolerance in the NASH animal model. The beneficial effects may have been mediated partly via the tripartite motif-containing family protein 72 (TRIM72)/PI3K/Akt/mTOR pathway, accompanied with an upregulation of glucose transporter 4 in the skeletal muscle. The exercise regimen activated the master regulator of antioxidant enzymes, nuclear factor erythroid 2-related factor 2, with upregulation of superoxide dismutase [Cu-Zn] expression and a corresponding decrease in kelch-like ECH-associated protein 1 expression, but failed to decrease the levels of the oxidative marker malondialdehyde in the HFD rat skeletal muscle. Chronic exercise decreased the expression of the inflammation marker NF-κB, followed by a decrease in interleukin-6 and tumor necrosis factor-α levels, as verified by a corresponding increase in the level of NF-κB inhibitor α expression. Exercise may exert its beneficial effects by improving muscle insulin sensitivity via the TRIM72/PI3K/Akt/mTOR pathway, contributing to the improvement of systemic insulin intolerance, and finally leading to decreased hepatic lipogenesis during NASH. The attenuation of insulin resistance by exercise may be partly achieved through a decrease in the level of inflammation and an increased antioxidant response.

Chronic Light Cycle Disruption Alters Central Insulin and Leptin Signaling as well as Metabolic Markers in Male Mice

Recent evidence suggests that the circadian timing system plays a role in energy and glucose homeostasis, and disruptions to this system are a risk factor for the development of metabolic disorders. We exposed animals to a constantly shifting lighting environment comprised of a 6-hour advance, occurring every 6 days, to chronically disrupt their circadian timing system. This treatment caused a gradual increase in body weight of 12 ± 2% after 12 phase shifts, compared with a 6 ± 1% increase in mice under control lighting conditions. Additionally, after the fifth phase shift, light cycle-disrupted (CD) animals showed a reversal in their diurnal pattern of energy homeostasis and locomotor activity, followed by a subsequent loss of this rhythm. To investigate potential molecular mechanisms mediating these metabolic alterations, we assessed central leptin and insulin sensitivity. We discovered that CD mice had a decrease in central leptin signaling, as indicated by a reduction in the number of phosphorylated signal transducer and activator of transcription 3 immunoreactive cells in the arcuate nucleus of the hypothalamus. Furthermore, CD animals exhibited a marked increase in fasting blood glucose (269.4 ± 21.1 mg/dL) compared with controls (108.8 ± 21.3 mg/dL). This dramatic increase in fasting glucose levels was not associated with an increase in insulin levels, suggesting impairments in pancreatic insulin release. Peripheral hyperglycemia was accompanied by central alterations in insulin signaling at the level of phospho Akt and insulin receptor substrate 1, suggesting that light cycle disruption alters central insulin signaling. These results provide mechanistic insights into the association between light cycle disruption and metabolic disease.

Deficiency of the autophagy gene ATG16L1 induces insulin resistance through KLHL9/KLHL13/CUL3-mediated IRS1 degradation

Connections between deficient autophagy and insulin resistance have emerged, however, the mechanism through which reduced autophagy impairs insulin-signaling remains unknown. We examined mouse embryonic fibroblasts lacking Atg16l1 (ATG16L1 KO mouse embryonic fibroblasts (MEFs)), an essential autophagy gene, and observed deficient insulin and insulin-like growth factor-1 signaling. ATG16L1 KO MEFs displayed reduced protein content of insulin receptor substrate-1 (IRS1), pivotal to insulin signaling, whereas IRS1myc overexpression recovered downstream insulin signaling. Endogenous IRS1 protein content and insulin signaling were restored in ATG16L1 KO mouse embryonic fibroblasts (MEF) upon proteasome inhibition. Through proximity-dependent biotin identification (BioID) and co-immunoprecipitation, we found that Kelch-like proteins KLHL9 and KLHL13, which together form an E3 ubiquitin (Ub) ligase complex with cullin 3 (CUL3), are novel IRS1 interactors. Expression of Klhl9 and Klhl13 was elevated in ATG16L1 KO MEFs and siRNA-mediated knockdown of Klhl9, Klhl13, or Cul3 recovered IRS1 expression. Moreover, Klhl13 and Cul3 knockdown increased insulin signaling. Notably, adipose tissue of high-fat fed mice displayed lower Atg16l1 mRNA expression and IRS1 protein content, and adipose tissue KLHL13 and CUL3 expression positively correlated to body mass index in humans. We propose that ATG16L1 deficiency evokes insulin resistance through induction of Klhl9 and Klhl13, which, in complex with Cul3, promote proteasomal IRS1 degradation.

Metabolites as regulators of insulin sensitivity and metabolism

The cause of insulin resistance in obesity and type 2 diabetes mellitus (T2DM) is not limited to impaired insulin signalling but also involves the complex interplay of multiple metabolic pathways. The analysis of large data sets generated by metabolomics and lipidomics has shed new light on the roles of metabolites such as lipids, amino acids and bile acids in modulating insulin sensitivity. Metabolites can regulate insulin sensitivity directly by modulating components of the insulin signalling pathway, such as insulin receptor substrates (IRSs) and AKT, and indirectly by altering the flux of substrates through multiple metabolic pathways, including lipogenesis, lipid oxidation, protein synthesis and degradation and hepatic gluconeogenesis. Moreover, the post-translational modification of proteins by metabolites and lipids, including acetylation and palmitoylation, can alter protein function. Furthermore, the role of the microbiota in regulating substrate metabolism and insulin sensitivity is unfolding. In this Review, we discuss the emerging roles of metabolites in the pathogenesis of insulin resistance and T2DM. A comprehensive understanding of the metabolic adaptations involved in insulin resistance may enable the identification of novel targets for improving insulin sensitivity and preventing, and treating, T2DM.

Serine Phosphorylation of IRS1 Correlates with Aβ-Unrelated Memory Deficits and Elevation in Aβ Level Prior to the Onset of Memory Decline in AD

The biological effects of insulin signaling are regulated by the phosphorylation of insulin receptor substrate 1 (IRS1) at serine (Ser) residues. In the brain, phosphorylation of IRS1 at specific Ser sites increases in patients with Alzheimer’s disease (AD) and its animal models. However, whether the activation of Ser sites on neural IRS1 is related to any type of memory decline remains unclear. Here, we show the modifications of IRS1 through its phosphorylation at etiology-specific Ser sites in various animal models of memory decline, such as diabetic, aged, and amyloid precursor protein (APP) knock-in ^NL-G-F (APPKI^NL-G-F) mice. Substantial phosphorylation of IRS1 at specific Ser sites occurs in type 2 diabetes- or age-related memory deficits independently of amyloid-β (Aβ). Furthermore, we present the first evidence that, in APPKI^NL-G-F mice showing Aβ42 elevation, the increased phosphorylation of IRS1 at multiple Ser sites occurs without memory impairment. Our findings suggest that the phosphorylation of IRS1 at specific Ser sites is a potential marker of Aβ-unrelated memory deficits caused by type 2 diabetes and aging; however, in Aβ-related memory decline, the modifications of IRS1 may be a marker of early detection of Aβ42 elevation prior to the onset of memory decline in AD.

Linoleic acid in diets of mice increases total endocannabinoid levels in bowel and liver: modification by dietary glucose

AIM

Linoleic acid (LA) is an essential fatty acid involved in the biosynthesis of arachidonic acid and prostaglandins. LA is known to induce obesity and insulin resistance. In this study, two concentrations of LA with or without added glucose (G) were fed to mice to investigate their effects on endocannabinoid (EC) biology.

MATERIALS AND METHODS

Four groups of C57BL/6 mice were provided with diets containing 1% or 8% LA with or without added G (LAG) for 8 weeks. Body weights, food intake, circulating glucose and insulin levels were measured throughout the study. Following euthanasia, plasma, bowel and hepatic ECs, monoacylglycerol lipase and fatty acid amide hydroxylase protein levels (enzymes responsible for EC degradation) and transcriptional activity of PPARα in liver were quantified. Liver was probed for evidence of insulin receptor activity perturbation.

RESULTS

Increasing dietary LA from 1% to 8% significantly increased circulating, small bowel and hepatic ECs. 1%LAG fed mice had lowest feed efficiency, and only liver levels of both ECs were reduced by addition of G. Addition of G to 1% LA diets resulted in elevated monoacylglycerol lipase and fatty acid amide hydroxylase protein levels (p < 0.001 and p < 0.001, respectively) in liver due to increased transcriptional activity of PPARα (p < 0.05). The reduced EC levels with addition of G also correlated with a measure of enhanced insulin action.

CONCLUSION

In conclusion, body weight of mice is influenced by the source of calorie intake. Furthermore, tissue EC/g are dependent on tissue-specific synthesis and degradation that are modulated by dietary LA and G which also influence food efficiency, and down-stream insulin signalling pathways. The findings could potentially be useful information for weight management efforts in humans.

High Fat Diet Triggers a Reduction in Body Fat Mass in Female Mice Deficient for Utx demethylase

Obesity increases the risk of metabolic disorders like diabetes mellitus and dyslipidemia. However, how metabolic status is sensed and regulates cellular behavior is unclear. Utx is an H3K27 demethylase that influences adipocyte function in vitro. To examine its role in vivo, we generated mice lacking Utx in adipocytes (UtxAKO). Although all UtxAKO mice grew normally on a normal chow diet (NCD), female UtxAKO mice on a high fat diet (HFD) showed striking reductions in body fat compared to control mice (Ctrl). Gene expression profiling of adipose tissues of HFD-fed UtxAKO female mice revealed decreased expression of rate-limiting enzymes of triacylglycerol synthesis but increased expression of those of cholesterol/steroid hormone synthesis. Moreover, these animals resisted adiposity induced by ovariectomy and exhibited increased estrogen in visceral adipose tissues. Thus, upon HFD feeding, Utx regulates lipid metabolism in adipose tissues by influencing the local hormonal microenvironment. Conversely, Utx deficiency skews lipid catabolism to enhance cholesterol/steroid hormone production and repress obesity.

Innate Immune Signaling in Drosophila Blocks Insulin Signaling by Uncoupling PI(3,4,5)P3 Production and Akt Activation

In obese adipose tissue, Toll-like receptor signaling in macrophages leads to insulin resistance in adipocytes. Similarly, Toll signaling in the Drosophila larval fat body blocks insulin-dependent growth and nutrient storage. We find that Toll acts cell autonomously to block growth but not PI(3,4,5)P₃ production in fat body cells expressing constitutively active PI3K. Fat body Toll signaling blocks whole-animal growth in rictor mutants lacking TORC2 activity, but not in larvae lacking Pdk1. Phosphorylation of Akt on the Pdk1 site, Thr342, is significantly reduced by Toll signaling, and expression of mutant Akt^T342D rescues cell and animal growth, nutrient storage, and viability in animals with active Toll signaling. Altogether, these data show that innate immune signaling blocks insulin signaling at a more distal level than previously appreciated, and they suggest that manipulations affecting the Pdk1 arm of the pathway may have profound effects on insulin sensitivity in inflamed tissues.

Estrogen and voluntary exercise attenuate cardiometabolic syndrome and hepatic steatosis in ovariectomized rats fed a high-fat high-fructose diet

The prevalence of cardiometabolic syndrome (CMS) is increased in women after menopause. While hormone replacement therapy has been prescribed to relieve several components of CMS in postmenopausal women, some aspects of cardiometabolic dysfunction cannot be completely restored. The present study examined the effectiveness of estrogen replacement alone and in combination with exercise by voluntary wheel running (VWR) for alleviating the risks of CMS, insulin-mediated skeletal muscle glucose transport, and hepatic fat accumulation in ovariectomized Sprague-Dawley rats fed a high-fat high-fructose diet (OHFFD). We compared a sham-operated group with OHFFD rats that were subdivided into a sedentary, estradiol replacement (E₂), and E₂ plus VWR for 12 wk. E₂ prevented the development of insulin resistance in skeletal muscle glucose transport and decreased hepatic fat accumulation in OHFFD rats. Furthermore, E₂ treatment decreased visceral fat mass and low-density lipoprotein (LDL)-cholesterol in OHFFD rats, while VWR further decreased LDL-cholesterol and increased the ratio of high-density lipoprotein-cholesterol to total cholesterol to a greater extent. Although E₂ treatment alone did not reduce serum triglyceride levels in OHFFD rats, the combined intervention of E₂ and VWR lowered serum triglycerides in E₂-treated OHFFD rats. The addition of VWR to E₂-treated OHFFD rats led to AMPK activation and upregulation of peroxisome proliferator-activated receptor-γ (PPARγ) coactivator-1α and PPARδ in skeletal muscle along with increased fatty acid oxidation and suppressed fatty acid synthesis in the liver. Collectively, our findings indicate that, to achieve greater health benefits, physical exercise is required for E₂-treated individuals under ovarian hormone deprivation with high-energy consumption.

Targeting RalGAPα1 in skeletal muscle to simultaneously improve postprandial glucose and lipid control

How insulin stimulates postprandial uptake of glucose and long-chain fatty acids (LCFAs) into skeletal muscle and the mechanisms by which these events are dampened in diet-induced obesity are incompletely understood. Here, we show that RalGAPα1 is a critical regulator of muscle insulin action and governs both glucose and lipid homeostasis. A high-fat diet increased RalGAPα1 protein but decreased its insulin-responsive Thr⁷³⁵-phosphorylation in skeletal muscle. A RalGAPα1^Thr735Ala mutation impaired insulin-stimulated muscle assimilation of glucose and LCFAs and caused metabolic syndrome in mice. In contrast, skeletal muscle-specific deletion of RalGAPα1 improved postprandial glucose and lipid control. Mechanistically, these mutations of RalGAPα1 affected translocation of insulin-responsive glucose transporter GLUT4 and fatty acid translocase CD36 via RalA to affect glucose and lipid homeostasis. These data indicated RalGAPα1 as a dual-purpose target, for which we developed a peptide-blockade for improving muscle insulin sensitivity. Our findings have implications for drug discovery to combat metabolic disorders.

IL1R1 is required for celastrol's leptin-sensitization and antiobesity effects

Celastrol, a pentacyclic triterpene is the most potent anti-obesity agent that has been reported to date¹. The mechanism of celastrol’s leptin sensitizing and anti-obesity effects has not yet been elucidated. In this study, we identified interleukin 1 receptor 1 (IL1R1) as a mediator of celastrol action by using temporally-resolved analysis of the hypothalamic transcriptome in celastrol-treated DIO, lean and db/db mice. We demonstrate that IL1R1-deficient mice are completely resistant to celastrol’s leptin sensitization, anti-obesity, anti-diabetic and anti-NASH effects. Thus, we conclude that IL1R1 is a gate-keeper for celastrol’s metabolic actions.

Sex Differences in Inflammatory Responses to Adipose Tissue Lipolysis in Diet-Induced Obesity

Males are known to have profound adipose tissue macrophage (ATM) accumulation in gonadal white adipose tissue (GWAT) during obesity, whereas females are protected from such an inflammatory response even with increased adiposity. The inflammatory tone in males is linked to insulin resistance and might be the underlying cause for sex differences in metabolic disease. Factors regulating the meta-inflammatory response remain unclear but enhanced lipid storage in females may explain the reduced inflammatory response to high-fat diets. In this study, we evaluated lean and obese females with stimulated lipolysis to understand whether a stress release of free fatty acids (FFAs) could induce female ATMs. We demonstrate that in both lean and obese females, GWAT CD11c- resident ATMs accumulate with β-3 adrenergic receptor-stimulated lipolysis. Lipolysis elevated serum FFA, triglyceride, and IL-6 levels in females that corresponded to significant phosphorylated hormone-sensitive lipase and adipose triglyceride lipase protein expression in obese female GWAT compared with males. Increased lipolytic response in obese females was associated with crown-like structures and induced Il6, Mcp1, Arg1, and Mgl1 expression in obese female GWAT, suggesting an environment of lipid clearance and adipose remodeling. With this finding we next investigated whether lipid storage and lipolytic mediators differed by sex. Diacylglycerol, ceramides, phospholipids, and certain fatty acid species associated with inflammation were elevated in male GWAT compared with obese female GWAT. Overall, our data demonstrate a role for GWAT lipid storage and lipolytic metabolites to induce inflammation in males and induce remodeling in females that might explain sex differences in overall metabolic health.

Excessive treadmill training enhances the insulin signaling pathway and glycogen deposition in mice hearts

Exhaustive and chronic physical exercise leads to peripheral inflammation, which is one of the molecular mechanisms responsible for the impairment of the insulin signaling pathway in the heart. Recently, 3 different running overtraining models performed downhill (OTR/down), uphill (OTR/up), and without inclination (OTR) increased the serum levels of proinflammatory cytokines. This proinflammatory status induced insulin signaling impairment in the skeletal muscle; however, the response of this signaling pathway in the cardiac muscle of overtrained mice was still unknown. Thus, we investigated the effects of OTR/down, OTR/up, and OTR protocols on the protein levels of phosphorylation of insulin receptor β (pIRβ) (Tyr), phosphorylation of protein kinase B (pAkt) (Ser473), plasma membrane glucose transporter-1 (GLUT1) and GLUT4, phosphorylation of insulin receptor substrate-1 (pIRS-1) (Ser307), phosphorylation of IκB kinase α/β) (pIKKα/β (Ser180/181), phosphorylation of p38 mitogen-activated protein kinase (p-p38MAPK) (Thr180/Tyr182), phosphorylation of stress-activated protein kinases-Jun amino-terminal kinases (pSAPK-JNK) (Thr183/Tyr185), and glycogen content in mice hearts. The rodents were divided into naïve (N, sedentary mice), control (CT, sedentary mice submitted to performance evaluations), trained (TR, performed the training protocol), OTR/down, OTR/up, and OTR groups. After the grip force test, the cardiac muscles (ie, left ventricle) were removed and used for immunoblotting and histology. Although the OTR/up and OTR groups exhibited higher cardiac levels of pIRβ (Tyr), only the OTR group exhibited higher cardiac levels of pAkt (Ser473) and plasma membrane GLUT4. On the contrary, the OTR/down group exhibited higher cardiac levels of pIRS-1 (Ser307). The OTR model enhanced the cardiac insulin signaling pathway. All overtraining models increased the left ventricle glycogen content, with this probably acting as a compensatory organ in response to skeletal muscle insulin signaling impairment.

Ablation of amyloid precursor protein increases insulin-degrading enzyme levels and activity in brain and peripheral tissues

The amyloid precursor protein (APP) is a type I transmembrane glycoprotein widely studied for its role as the source of β-amyloid peptide, accumulation of which is causal in at least some cases of Alzheimer's disease (AD). APP is expressed ubiquitously and is involved in diverse biological processes. Growing bodies of evidence indicate connections between AD and somatic metabolic disorders related to type 2 diabetes, and App^-/- mice show alterations in glycemic regulation. We find that App^-/- mice have higher levels of insulin-degrading enzyme (IDE) mRNA, protein, and activity compared with wild-type controls. This regulation of IDE by APP was widespread across numerous tissues, including liver, skeletal muscle, and brain as well as cell types within neural tissue, including neurons, astrocytes, and microglia. RNA interference-mediated knockdown of APP in the SIM-A9 microglia cell line elevated IDE levels. Fasting levels of blood insulin were lower in App^-/- than App^+/+ mice, but the former showed a larger increase in response to glucose. These low basal levels may enhance peripheral insulin sensitivity, as App^-/- mice failed to develop impairment of glucose tolerance on a high-fat, high-sucrose ("Western") diet. Insulin levels and insulin signaling were also lower in the App^-/- brain; synaptosomes prepared from App^-/- hippocampus showed diminished insulin receptor phosphorylation compared with App^+/+ mice when stimulated ex vivo. These findings represent a new molecular link connecting APP to metabolic homeostasis and demonstrate a novel role for APP as an upstream regulator of IDE in vivo.

Involvement of insulin receptor substrates in cognitive impairment and Alzheimer's disease

Type 2 diabetes—associated with impaired insulin/insulin-like growth factor-1 (IGF1) signaling (IIS)—is a risk factor for cognitive impairment and dementia including Alzheimer’s disease (AD). The insulin receptor substrate (IRS) proteins are major components of IIS, which transmit upstream signals via the insulin receptor and/or IGF1 receptor to multiple intracellular signaling pathways, including AKT/protein kinase B and extracellular-signal-regulated kinase cascades. Of the four IRS proteins in mammals, IRS1 and IRS2 play key roles in regulating growth and survival, metabolism, and aging. Meanwhile, the roles of IRS1 and IRS2 in the central nervous system with respect to cognitive abilities remain to be clarified. In contrast to IRS2 in peripheral tissues, inactivation of neural IRS2 exerts beneficial effects, resulting in the reduction of amyloid β accumulation and premature mortality in AD mouse models. On the other hand, the increased phosphorylation of IRS1 at several serine sites is observed in the brains from patients with AD and animal models of AD or cognitive impairment induced by type 2 diabetes. However, these serine sites are also activated in a mouse model of type 2 diabetes, in which the diabetes drug metformin improves memory impairment. Because IRS1 and IRS2 signaling pathways are regulated through complex mechanisms including positive and negative feedback loops, whether the elevated phosphorylation of IRS1 at specific serine sites found in AD brains is a primary response to cognitive dysfunction remains unknown. Here, we examine the associations between IRS1/IRS2-mediated signaling in the central nervous system and cognitive decline.

Obesity-Induced TNFα and IL-6 Signaling: The Missing Link between Obesity and Inflammation-Driven Liver and Colorectal Cancers

Obesity promotes the development of numerous cancers, such as liver and colorectal cancers, which is at least partly due to obesity-induced, chronic, low-grade inflammation. In particular, the recruitment and activation of immune cell subsets in the white adipose tissue systemically increase proinflammatory cytokines, such as tumor necrosis factor α (TNFα) and interleukin-6 (IL-6). These proinflammatory cytokines not only impair insulin action in metabolic tissues, but also favor cancer development. Here, we review the current state of knowledge on how obesity affects inflammatory TNFα and IL-6 signaling in hepatocellular carcinoma and colorectal cancers.