From mice to men: insights into the insulin resistance syndromes

Modulation of glycolipid metabolism in T2DM rats by Rubus irritans Focke extract: Insights from metabolic profiling and ERK/IRS-1 signaling pathway

ETHNOPHARMACOLOGICAL RELEVANCE

The extracellular regulated protein kinase (ERK) plays a crucial role in the mitogen-activated protein kinase (MAPK) family, influencing apoptosis, proliferation, and differentiation. It connection to the insulin (INS) signaling cascade and the development of type 2 diabetes mellitus (T2DM) has been established. Rubus irritans Focke, an indispensable herb in Chinese Tibetan medicine for diabetes mellitus treatment, lacks a comprehensive understanding of its effects and pharmacological mechanisms in T2DM.

AIM OF THE STUDY

This study aimed to elucidate the effects of Rubus irritans Focke extract (Rife) on a T2DM rat model, exploring its impact on glycemic and lipid metabolism, histopathological changes, and its potential targeting of the extracellular regulated protein kinase/insulin receptor substrate-1 (ERK/IRS-1) signaling pathway.

MATERIALS AND METHODS

A T2DM rat model was induced by streptozotocin (STZ) injection (40 mg/kg) in high-fat diet-fed (HFD) male Wistar rats. Rife and metformin (Met) were administered for 4 weeks, and glycemic, lipid metabolism indices, and histopathological changes were assessed. Protein expression of ERK, IRS-1 in rat liver tissues was examined to evaluate the impact on the ERK/IRS-1 pathway.

RESULTS

Rife reducing hepatic ERK and IRS-1 protein expression in T2DM rats. Untargeted metabolomics identified 13 potential biomarkers and 4 differential metabolic pathways related to glycolipid metabolism disorders.

CONCLUSIONS

Rife demonstrated improved glycolipid metabolism in T2DM rats by inhibiting the ERK/IRS-1 related signaling pathway and influencing multiple metabolic pathways. This study provides valuable insights into the potential therapeutic mechanisms of Rife in the context of T2DM.

B-Glycine as a marker for β cell imaging and β cell mass evaluation

PURPOSE

β cell mass (BCM) and function are essential to the diagnosis and therapy of diabetes. Diabetic patients serve β cell loss is, and damage of β cells leads to severe insulin deficiency. Our understanding of the role of BCM in diabetes progression is extremely limited by lacking efficient methods to evaluate BCM in vivo. In vitro methods of labeling islets, including loading of contrast reagent or integration of exogenous biomarker, require artificial manipulation on islets, of which the clinical application is limited. Imaging methods targeting endogenous biomarkers may solve the above problems. However, traditional reagents targeting GLP-1R and VAMT2 result in a high background of adjacent tissues, complicating the identification of pancreatic signals. Here, we report a non-invasive and quantitative imaging technique by using radiolabeled glycine mimics ([18F]FBG, a boron-trifluoride derivative of glycine) to assay islet function and monitor BCM changes in living animals.

METHODS

Glycine derivatives, FBG, FBSa, 2Me-FBG, 3Me-FBG, were successfully synthesized and labeled with 18F. Specificity of glycine derivatives were characterized by in vitro experiment. PET imaging and biodistribution studies were performed in animal models carring GLYT over-expressed cells. In vivo evaluation of BCM with [18F]FBG were performed in STZ (streptozocin) induced T1D (type 1 diabetes) models.

RESULTS

GLYT responds to excess blood glycine levels and transports glycine into islet cells to maintain the activity of the glycine receptor (GLYR). Best PET imaging condition was 80 min after given a total of 240 ~ 250 nmol imaging reagent (a mixture of [18F]FBG and natural glycine) intravenously. [18F]FBG can detect both endogenous and exogenous islets clearly in vivo. When applied to STZ induced T1D mouse models, total uptake of [18F]FBG in the pancreas exhibited a linear correlation with survival BCM.

CONCLUSION

[18F]FBG targeting the endogenous glycine transporter (GLYT), which is highly expressed on islet cells, avoiding extra modification on islet cells. Meanwhile the highly restricted expression pattern of GLYT excluded the background in adjacent tissues. This [18F]FBG-based imaging technique provides a non-invasive method to quantify BCM in vivo, implying a new evaluation index for diabetic assessment.

Deficiency of ASGR1 Alleviates Diet-Induced Systemic Insulin Resistance via Improved Hepatic Insulin Sensitivity

BACKGRUOUND

Insulin resistance (IR) is the key pathological basis of many metabolic disorders. Lack of asialoglycoprotein receptor 1 (ASGR1) decreased the serum lipid levels and reduced the risk of coronary artery disease. However, whether ASGR1 also participates in the regulatory network of insulin sensitivity and glucose metabolism remains unknown.

METHODS

The constructed ASGR1 knockout mice and ASGR1-/- HepG2 cell lines were used to establish the animal model of metabolic syndrome and the IR cell model by high-fat diet (HFD) or drug induction, respectively. Then we evaluated the glucose metabolism and insulin signaling in vivo and in vitro.

RESULTS

ASGR1 deficiency ameliorated systemic IR in mice fed with HFD, evidenced by improved insulin intolerance, serum insulin, and homeostasis model assessment of IR index, mainly contributed from increased insulin signaling in the liver, but not in muscle or adipose tissues. Meanwhile, the insulin signal transduction was significantly enhanced in ASGR1-/- HepG2 cells. By transcriptome analyses and comparison, those differentially expressed genes between ASGR1 null and wild type were enriched in the insulin signal pathway, particularly in phosphoinositide 3-kinase-AKT signaling. Notably, ASGR1 deficiency significantly reduced hepatic gluconeogenesis and glycogenolysis.

CONCLUSION

The ASGR1 deficiency was consequentially linked with improved hepatic insulin sensitivity under metabolic stress, hepatic IR was the core factor of systemic IR, and overcoming hepatic IR significantly relieved the systemic IR. It suggests that ASGR1 is a potential intervention target for improving systemic IR in metabolic disorders.

Emerging therapies: Potential roles of SGLT2 inhibitors in the management of pulmonary hypertension

Pulmonary hypertension (PH) is a pathophysiological disorder that may involve multiple clinical conditions and may be associated with a variety of cardiovascular and respiratory diseases. Pulmonary hypertension due to left heart disease (PH-LHD) currently lacks targeted therapies, while Pulmonary arterial hypertension (PAH), despite approved treatments, carries considerable residual risk. Metabolic dysfunction has been linked to the pathogenesis and prognosis of PH through various studies, with emerging metabolic agents offering a potential avenue for improving patient outcomes. Sodium-glucose cotransporter 2 inhibitor (SGLT-2i), a novel hypoglycemic agent, could ameliorate metabolic dysfunction and exert cardioprotective effects. Recent small-scale studies suggest SGLT-2i treatment may improve pulmonary artery pressure in patients with PH-LHD, and the PAH animal model shows that SGLT-2i can reduce pulmonary vascular remodeling and prevent progression in PAH, suggesting potential benefits for patients with PH-LHD and perhaps PAH. This review aims to succinctly review PH's pathophysiology, and the connection between metabolic dysfunction and PH, and investigate the prospective mechanisms of action of SGLT-2i in PH-LHD and PAH management.

The Supplementation of Berberine in High-Carbohydrate Diets Improves Glucose Metabolism of Tilapia (Oreochromis niloticus) via Transcriptome, Bile Acid Synthesis Gene Expression and Intestinal Flora

Berberine is an alkaloid used to treat diabetes. This experiment aimed to investigate the effects of berberine supplementation in high-carbohydrate diets on the growth performance, glucose metabolism, bile acid synthesis, liver transcriptome, and intestinal flora of Nile tilapia. The six dietary groups were the C group with 29% carbohydrate, the H group with 44% carbohydrate, and the HB1-HB4 groups supplemented with 25, 50, 75, and 100 mg/kg of berberine in group H. The results of the 8-week trial showed that compared to group C, the abundance of Bacteroidetes was increased in group HB2 (p < 0.05). The cholesterol-7α-hydroxylase (CYP7A1) and sterol-27-hydroxylase (CYP27A1) activities were decreased and the expression of FXR was increased in group HB4 (p < 0.05). The pyruvate carboxylase (PC) and phosphoenolpyruvate carboxykinase (PEPCK) activities was decreased in group HB4 (p < 0.05). The liver transcriptome suggests that berberine affects carbohydrate metabolic pathways and primary bile acid synthesis pathways. In summary, berberine affects the glucose metabolism in tilapia by altering the intestinal flora structure, enriching differentially expressed genes (DEGs) in the bile acid pathway to stimulate bile acid production so that it promotes glycolysis and inhibits gluconeogenesis. Therefore, 100 mg/kg of berberine supplementation in high-carbohydrate diets is beneficial to tilapia.

Interesterified palm oil promotes insulin resistance and altered insulin secretion and signaling in Swiss mice

Interesterified fats have been used to replace trans-fat in ultra-processed foods. However, their metabolic effects are not completely understood. Hence, this study aimed to investigate the effects related to glucose homeostasis in response to interesterified palm oil or refined palm oil intake. Four-week-old male Swiss mice were randomly divided into four experimental groups and fed the following diets for 8 weeks: a normocaloric and normolipidic diet containing refined palm oil (PO group) or interesterified palm oil (IPO group); a hypercaloric and high-fat diet containing refined PO (POHF group) or interesterified PO (IPOHF group). Metabolic parameters related to body mass, adiposity and food consumption showed no significant differences. As for glucose homeostasis parameters, interesterified palm oil diets (IPO and IPOHF) resulted in higher glucose intolerance than unmodified palm oil diets (PO and POHF). Euglycemic-hyperinsulinemic clamp assessment showed a higher endogenous glucose production in the IPO group compared with the PO group. Moreover, the IPO group showed significantly lower p-AKT protein content (in the muscle and liver tissues) when compared with the PO group. Analysis of glucose-stimulated static insulin secretion (11.1 mmol/L glucose) in isolated pancreatic islets showed a higher insulin secretion in animals fed interesterified fat diets (IPO and IPOHF) than in those fed with palm oil (PO and POHF). Interesterified palm oil, including in normolipidic diets, can impair insulin signaling in peripheral tissues and increase insulin secretion by β-cells, characterizing insulin resistance in mice.

Metabolic hormones are integral regulators of female reproductive health and function

The female reproductive system is strongly influenced by nutrition and energy balance. It is well known that food restriction or energy depletion can induce suppression of reproductive processes, while overnutrition is associated with reproductive dysfunction. However, the intricate mechanisms through which nutritional inputs and metabolic health are integrated into the coordination of reproduction are still being defined. In this review, we describe evidence for essential contributions by hormones that are responsive to food intake or fuel stores. Key metabolic hormones-including insulin, the incretins (glucose-dependent insulinotropic polypeptide and glucagon-like peptide-1), growth hormone, ghrelin, leptin, and adiponectin-signal throughout the hypothalamic-pituitary-gonadal axis to support or suppress reproduction. We synthesize current knowledge on how these multifaceted hormones interact with the brain, pituitary, and ovaries to regulate functioning of the female reproductive system, incorporating in vitro and in vivo data from animal models and humans. Metabolic hormones are involved in orchestrating reproductive processes in healthy states, but some also play a significant role in the pathophysiology or treatment strategies of female reproductive disorders. Further understanding of the complex interrelationships between metabolic health and female reproductive function has important implications for improving women's health overall.

Past and present of beta arrestins: A new perspective on insulin secretion and effect

BACKGROUND

Beta arrestins had been known as intracellular adaptors that uncouple and inactivate the G protein-coupled receptors that they interact with. Their roles as signal initiators for some receptors have recently been recognized.

SCOPE OF REVIEW

In this review, we focused on their role in mediating metabolic modulation primarily in relation to insulin signaling. Commenced by the upstream receptor, they seem to act like intracellular hubs that divert the metabolic profile of the cell. The amount of metabolic substrates in circulation and their usage/deposition by tissues are controlled by the contribution of all systems in the organism. This control is enabled by the release of hormones such as insulin, glucagon and glucagon-like peptide-1. Intriguingly, some ligands -either agonists or antagonists-of different classes of receptors have preferential properties mediated by β arrestins. This is not surprizing considering that substrate supply and usage should parallel physiological function such as hormone release or muscle contraction.

MAJOR CONCLUSIONS

Available data indicate that β arrestins conduct the regulatory role in insulin secretion and action. They may be good candidates to target when the upstream signal demands the function that may compromise the cell. An example is carvedilol that is protective by preventing the stimulatory effects of excessive catecholamines, stimulates mitochondrial function and has preferential clinical outcomes in metabolic disorders.

Rottlerin suppresses lipid accumulation by inhibiting de novo lipogenesis and adipogenesis via LRP6/mTOR/SREBP1C in 3T3-L1 adipocytes

Rottlerin is isolated from Mallotus japonicus, a plant rich in polyphenols. Rottlerin is a selective PKCδ-inhibitor and is also known as an uncoupler of oxidative phosphorylation and anti-neoplastic agent. However, its anti-obesity effect is yet to be established. Therefore, this study tested whether rottlerin inhibits adipogenesis and de novo lipogenesis via the LRP6/mTOR/SREBP1C pathway in 3T3-L1 adipocytes. Rottlerin dramatically decreased lipid accumulation assessed by Oil Red O as evidence to support the cellular phenotype (p < 0.001). Pivotal messenger RNA and protein expressions associated with de novo lipogenesis (SREBP1C, ACC1, FAS, and SCD1) and adipogenesis (PPARγ and C/EBPα) were subsequentially verified by rottlerin in a dose-dependent manner (p < 0.05). Further investigation revealed that rottlerin reduced the AKT/mTOR pathway via diminished total protein of LRP6 (p < 0.05). Collectively, these findings establish a causal link between rottlerin, LRP6, and the altered nutrient-sensing mTOR pathway, in which rottlerin regulates de novo lipogenesis and adipogenesis in white adipocytes.

CLK2 in GABAergic neurons is critical in regulating energy balance and anxiety-like behavior in a gender-specific fashion

Introduction

Cdc2-like kinase (CLK2) is a member of CLK kinases expressed in hypothalamic neurons and is activated in response to refeeding, leptin, or insulin. Diet-induced obesity and leptin receptor-deficient db/db mice lack CLK2 signal in the hypothalamic neurons. The neurotransmiter gamma-aminobutyric acid (GABA) is among the most prevalent in the central nervous system (CNS), particularly in the hypothalamus. Given the abundance of GABA-expressing neurons and their potential influence on regulating energy and behavioral homeostasis, we aimed to explore whether the deletion of CLK2 in GABAergic neurons alters energy homeostasis and behavioral and cognitive functions in both genders of mice lacking CLK2 in Vgat-expressing neurons (Vgat-Cre; Clk2loxP/loxP) on chow diet.

Methods

We generated mice lacking Clk2 in Vgat-expressing neurons (Vgat-Cre; Clk2loxP/loxP) by mating Clk2loxP/loxP mice with Vgat-IRES-Cre transgenic mice and employed behavior, and physiological tests, and molecular approaches to investigate energy metabolism and behavior phenotype of both genders.

Results and discussion

We showed that deletion of CLK2 in GABAergic neurons increased adiposity and food intake in females. The mechanisms behind these effects were likely due, at least in part, to hypothalamic insulin resistance and upregulation of hypothalamic Npy and Agrp expression. Besides normal insulin and pyruvate sensitivity, Vgat-Cre; Clk2loxP/loxP females were glucose intolerant. Male Vgat-Cre; Clk2loxP/loxP mice showed an increased energy expenditure (EE). Risen EE may account for avoiding weight and fat mass gain in male Vgat-Cre; Clk2loxP/loxP mice. Vgat-Cre; Clk2loxP/loxP mice had no alteration in cognition or memory functions in both genders. Interestingly, deleting CLK2 in GABAergic neurons changed anxiety-like behavior only in females, not males. These findings suggest that CLK2 in GABAergic neurons is critical in regulating energy balance and anxiety-like behavior in a gender-specific fashion and could be a molecular therapeutic target for combating obesity associated with psychological disorders in females.

Hepatocyte NLRP3 interacts with PKCε to drive hepatic insulin resistance and steatosis

Hepatic insulin resistance (IR), as a downstream sequela of nonalcoholic fatty liver disease (NAFLD), is strongly associated with liver steatosis. Despite numerous mechanism advancements, the molecular underpinnings and pathogenesis of hepatic IR, especially regarding the pattern recognition receptors in hepatocytes, remain elusive. Here, we identified hepatocyte NLRP3 as a direct and previously-unresolved driver of hepatic IR to promote steatosis response. Under the model of NAFLD, we identified hepatocyte NLRP3 as a crucial inducer of hepatic IR by undertaking multilayer transcriptomic searches and further confirmed that its expression was increased in the liver tissues from NAFLD patients and mouse models (high-fat diet (HFD), leptin-receptor-deficient (db/db) mice), and in palmitic acid (PA)-induced hepatocytes. Loss- or gain-of-function of hepatocyte-specific NLRP3 in HFD-induced mice ameliorated or exacerbated hepatic IR and steatosis, respectively. Mechanistically, NLRP3 directly bound to and promoted protein kinase C epsilon (PKCε) activation to impair insulin signaling and increase liver steatosis, while inhibition of PKCε activation dampened the beneficial effects seen in HFD-induced NLRP3-deficient mice. Moreover, we performed screening and discovered that the transcription factor Yin Yang 1 (YY1) positively controlled NLRP3 expression. In translational potential, adeno-associated virus serotype 8 (AAV8)-mediated NLRP3 knockdown in the liver alleviated hepatic IR and steatosis in db/db mice, and pharmacological inhibition of NLRP3 markedly alleviated diet-induced metabolic disorders. This finding reveals a previously-unexpected regulatory axis from YY1 to PKCε via NLRP3 induction for metabolic diseases and establishes the YY1-NLRP3-PKCε axis as a potential therapeutic target for NAFLD.

Individual and mixtures of polychlorinated biphenyls and organochlorine pesticides exposure in relation to metabolic syndrome among Chinese adults

Polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCPs) are commonly detected in humans due to their persistence and bioaccumulation, and are suspected risk factors for metabolic syndrome (MetS). However, most studies have focused on individual rather than combined exposure. We explored the associations between individual and combined PCBs/OCPs exposure and MetS to better assess the health effects of PCBs and OCPs. This cross-sectional study included 1996 adults from Wuhan, China. A total of 338 participants fulfilled criteria for MetS. Eight PCBs and OCPs were detected in >50 % of the samples. Most of the hexachlorocyclohexanes (HCHs) in the serum were derived from the recent environmental input of lindane, while the high levels of dichlorodiphenyltrichloroethane (DDTs) were mainly due to historical use. Multivariate linear regression analyses revealed that β-HCH, p,p'-dichlorodiphenyldichloroethylene (p,p'-DDE), PCB-52, PCB-153, and PCB-180 were positively correlated with increased odds of MetS. The profiles of the PCBs and OCPs associated with the different components of MetS were distinct. Furthermore, quantile-based g computation (qgcomp) analyses showed that PCB and OCP mixtures were positively associated with the risk of MetS, and p,p'-DDE was the largest contributor to our model. These findings suggest that PCB and OCP concentrations, both individually and as mixtures, are associated with MetS risk. Prospective studies are needed to confirm these results.

Cdc2-like kinases: structure, biological function, and therapeutic targets for diseases

The CLKs (Cdc2-like kinases) belong to the dual-specificity protein kinase family and play crucial roles in regulating transcript splicing via the phosphorylation of SR proteins (SRSF1-12), catalyzing spliceosome molecular machinery, and modulating the activities or expression of non-splicing proteins. The dysregulation of these processes is linked with various diseases, including neurodegenerative diseases, Duchenne muscular dystrophy, inflammatory diseases, viral replication, and cancer. Thus, CLKs have been considered as potential therapeutic targets, and significant efforts have been exerted to discover potent CLKs inhibitors. In particular, clinical trials aiming to assess the activities of the small molecules Lorecivivint on knee Osteoarthritis patients, and Cirtuvivint and Silmitasertib in different advanced tumors have been investigated for therapeutic usage. In this review, we comprehensively documented the structure and biological functions of CLKs in various human diseases and summarized the significance of related inhibitors in therapeutics. Our discussion highlights the most recent CLKs research, paving the way for the clinical treatment of various human diseases.

Taraxasterol Inhibits Hepatic Gluconeogenesis and Increases Glycogen Synthesis via the PI3K/Akt Signaling Pathway

Objective: Taraxasterol (TS) is the main active compound of Taraxacum, which plays a significant role in the treatment of diabetes in many classic prescriptions. However, the mechanisms of TS in the treatment of diabetes remain unclear. This study aimed to investigate the underlying mechanism of TS in hepatic gluconeogenesis and glycogen synthesis in HepG2 cells with insulin resistance (IR). Methods: Molecular docking was conducted by using Discovery Studio (DS) to predict the target of TS in the treatment of diabetes. Then we treated HepG2 cells with glucosamine for 18 h. After the cells were treated with TS, the glucose consumption was examined. Oil red O staining was used to detect the lipid accumulation of HepG2 cells, and cellular glucose uptake levels were assessed using fluorescent 2-(N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl) amino)-2-deoxy-D-glucose. The expression of the related proteins of the PI3K/Akt signaling pathway in the HepG2 cells was evaluated by western blot assay. Results: The molecular docking analysis revealed a good binding pose between the insulin receptor and TS. Furthermore, TS administration significantly enhanced glucose uptake and consumption, and reduced lipid accumulation in HepG2 cells with IR. The results of pharmacological mechanism study showed that TS up-regulated glycogenesis by PI3K/Akt/GSK3-motivated GS activation, and down-regulated gluconeogenesis by PI3K/Akt/FoxO1 expression of PEPCK and G6Pase in HepG2 cells with IR. Conclusions: Molecular docking and in vitro experimental results indicate that TS suppresses hepatic gluconeogenesis and augments glycogen synthesis by the PI3K/Akt signaling pathway, and it may have similar effects as insulin in regulating blood glucose.

Type 2 Diabetes and Alzheimer's Disease: The Emerging Role of Cellular Lipotoxicity

Type 2 diabetes (T2D) and Alzheimer's diseases (AD) represent major health issues that have reached alarming levels in the last decades. Although growing evidence demonstrates that AD is a significant comorbidity of T2D, and there is a ~1.4-2-fold increase in the risk of developing AD among T2D patients, the involvement of possible common triggers in the pathogenesis of these two diseases remains largely unknown. Of note, recent mechanistic insights suggest that lipotoxicity could represent the missing ring in the pathogenetic mechanisms linking T2D to AD. Indeed, obesity, which represents the main cause of lipotoxicity, has been recognized as a major risk factor for both pathological conditions. Lipotoxicity can lead to inflammation, insulin resistance, oxidative stress, ceramide and amyloid accumulation, endoplasmic reticulum stress, ferroptosis, and autophagy, which are shared biological events in the pathogenesis of T2D and AD. In the current review, we try to provide a critical and comprehensive view of the common molecular pathways activated by lipotoxicity in T2D and AD, attempting to summarize how these mechanisms can drive future research and open the way to new therapeutic perspectives.

Exploring the signal-dependent transcriptional regulation involved in the liver pathology of type 2 diabetes

Excess glucagon activity in diabetes increases hepatic glucose production via gluconeogenic gene induction, thus exacerbating hyperglycemia. Glucagon receptor-activated cAMP-dependent protein kinase A (PKA) induces proliferator-activated receptor gamma coactivator 1 alpha (PGC-1α) expression via the cAMP response element-binding protein (CREB)-regulated transcription coactivator 2 (CRTC2) pathway. Transcriptional coactivator PGC-1α subsequently coactivates transcription factors, such as forkhead box O1 (FoxO1) and hepatocyte nuclear factor 4 alpha (HNF4α), to induce gluconeogenic genes. The current review first summarizes the mechanism by which transcriptional cofactor CBP and p300-activated transactivator with glutamic acid and aspartic acid-rich COOH-terminal domain 2 (CITED2) activates gluconeogenesis via the regulation of PGC-1α and general control of amino acid synthesis protein 5-like 2 (GCN5). Type 2 diabetes is closely linked with non-alcoholic fatty liver disease (NAFLD). Between 10 and 20% of NAFLD progresses to non-alcoholic steatohepatitis (NASH), which can cause liver cirrhosis and can also lead to hepatocellular carcinoma. Liver macrophages are considered to be related to inflammation and fibrosis observed in NASH. This review outlines liver-derived signals underlying the differentiation of liver macrophages and the mechanism of myeloid cell diversification in NASH.

The Effect of Healthy Lifestyle Strategies on the Management of Insulin Resistance in Children and Adolescents with Obesity: A Narrative Review

Childhood obesity is characterized by an increased risk of several metabolic derangements including insulin resistance (IR). The strongest recommendations to prevent obesity and related complications are a balanced and adequate diet and practicing physical activity from early childhood. In this review, we propose to present the effects of healthy lifestyle strategies, including physical exercise and dietary approaches, on the management of IR and related metabolic derangements. All types of exercise (aerobic, resistance and combined training) effectively reduce IR in pediatric patients with obesity; it seems that aerobic and combined training stimulate greater improvements in IR compared to resistance training. Balanced normocaloric or hypocaloric dietary approaches are also valid strategies to address IR; it is not possible to assess the long-term impact of varying macronutrients on cardiometabolic risk. The glycemic index/load evaluation is a useful dietary approach to glucose metabolism control. Similarly, they should adopt the principle of the Mediterranean diet. Randomized studies with longer monitoring are needed to define the benefits of nutritional supplementation on IR. Considering that healthy style acquisition could track to later ages, programs of healthy lifestyle starting with children offer a better preventive strategy to preserve metabolic control and children's health.

Insulin Resistance and High Blood Pressure: Mechanistic Insight on the Role of the Kidney

The metabolic effects of insulin predominate in skeletal muscle, fat, and liver where the hormone binds to its receptor, thereby priming a series of cell-specific and biochemically diverse intracellular mechanisms. In the presence of a good secretory reserve in the pancreatic islets, a decrease in insulin sensitivity in the metabolic target tissues leads to compensatory hyperinsulinemia. A large body of evidence obtained in clinical and experimental studies indicates that insulin resistance and the related hyperinsulinemia are causally involved in some forms of arterial hypertension. Much of this involvement can be ascribed to the impact of insulin on renal sodium transport, although additional mechanisms might be involved. Solid evidence indicates that insulin causes sodium and water retention, and both endogenous and exogenous hyperinsulinemia have been correlated to increased blood pressure. Although important information was gathered on the cellular mechanisms that are triggered by insulin in metabolic tissues and on their abnormalities, knowledge of the insulin-related mechanisms possibly involved in blood pressure regulation is limited. In this review, we summarize the current understanding of the cellular mechanisms that are involved in the pro-hypertensive actions of insulin, focusing on the contribution of insulin to the renal regulation of sodium balance and body fluids.

Genetic association-based functional analysis detects HOGA1 as a potential gene involved in fat accumulation

Although there are a number of discoveries from genome-wide association studies (GWAS) for obesity, it has not been successful in linking GWAS results to biology. We sought to discover causal genes for obesity by conducting functional studies on genes detected from genetic association analysis. Gene-based association analysis of 917 individual exome sequences showed that HOGA1 attains exome-wide significance (p-value &lt; 2.7 × 10–6) for body mass index (BMI). The mRNA expression of HOGA1 is significantly increased in human adipose tissues from obese individuals in the Genotype-Tissue Expression (GTEx) dataset, which supports the genetic association of HOGA1 with BMI. Functional analyses employing cell- and animal model-based approaches were performed to gain insights into the functional relevance of Hoga1 in obesity. Adipogenesis was retarded when Hoga1 was knocked down by siRNA treatment in a mouse 3T3-L1 cell line and a similar inhibitory effect was confirmed in mice with down-regulated Hoga1. Hoga1 antisense oligonucleotide (ASO) treatment reduced body weight, blood lipid level, blood glucose, and adipocyte size in high-fat diet-induced mice. In addition, several lipogenic genes including Srebf1, Scd1, Lp1, and Acaca were down-regulated, while lipolytic genes Cpt1l, Ppara, and Ucp1 were up-regulated. Taken together, HOGA1 is a potential causal gene for obesity as it plays a role in excess body fat development.

Characterisation of an Atrx Conditional Knockout Mouse Model: Atrx Loss Causes Endocrine Dysfunction Rather Than Pancreatic Neuroendocrine Tumour

Simple Summary

ATRX and DAXX mutations occur in 30–40% of pancreatic neuroendocrine tumours (PanNETs), and there are no reports in the literature of any genetically engineered mouse model (GEMM) evaluating the effect of Atrx disruption as a putative driver event on PanNET initiation. We created a novel GEMM with Atrx conditional disruption in β cells. We observed that this genetic alteration, per se, was not tumourigenic, but we reported novel roles of Atrx on endocrine function, which resulted in dysglycaemia and the exacerbation of inflammageing (increased pancreatic inflammation and hepatic steatosis).

Abstract

ATRX is a chromatin remodeller that maintains telomere homeostasis. Loss of ATRX is described in approximately 10% of pancreatic neuroendocrine tumours (PanNETs) and associated with poorer prognostic features. Here, we present a genetically engineered mouse model (GEMM) addressing the role of Atrx loss (Atrx^KO) in pancreatic β cells, evaluating a large cohort of ageing mice (for up to 24 months (mo.)). Atrx loss did not cause PanNET formation but rather resulted in worsening of ageing-related pancreatic inflammation and endocrine dysfunction in the first year of life. Histopathological evaluation highlighted an exacerbated prevalence and intensity of pancreatic inflammation, ageing features, and hepatic steatosis in Atrx^KO mice. Homozygous floxed mice presented hyperglycaemia, increased weights, and glucose intolerance after 6 months, but alterations in insulinaemia were not detected. Floxed individuals presented an improper growth of their pancreatic endocrine fraction that may explain such an endocrine imbalance. A pilot study of BRACO-19 administration to Atrx^KO mice resulted in telomere instability, reinforcing the involvement of Atrx in the maintenance of β cell telomere homeostasis. Thereby, a non-obese dysglycaemic GEMM of disrupted Atrx is here presented as potentially useful for metabolic studies and putative candidate for inserting additional tumourigenic genetic events.

Sulforaphane alleviates high fat diet-induced insulin resistance via AMPK/Nrf2/GPx4 axis

Insulin resistance is a characteristic feature of type 2 diabetes. Sulforaphane (SFN) is a natural antioxidant extracted from the cruciferous vegetables. Recent study reported that SFN exhibits excellent anti-diabetic effects, however, the underlying mechanism is still unclear. This study aimed to investigate the therapeutic effects of SFN on a high-fat diet (HFD)-induced insulin resistance and potential mechanism. SFN was found to effectively reduce body weight, fasting blood glucose and hyperlipidemia, and improve liver function in HFD-fed mice. Furthermore, SFN effectively increased glucose uptake and improved insulin signaling in palmitic acid (PA)-induced HepG2 cells. SFN also led to increased expression of antioxidant genes downstream of Nrf2 and decreased accumulation of lipid peroxides MDA and 4-HNE, both in vivo and in vitro. Further studies revealed that SFN significantly reduced glutathione peroxidase 4 (GPx4) inactivation-mediated oxidative stress by activating the AMPK and Nrf2 signaling pathways. In PA-induced HepG2 cells and flies, the alleviation of insulin resistance by SFN was diminished by GPx4 inhibitor. Taken together, SFN ameliorated HFD-induced insulin resistance by activating the AMPK-Nrf2-GPx4 pathway, providing new insights into SFN as a therapeutic compound for the alleviation of insulin resistance.

[The insulin receptor discovery is 50 years old - A review of achieved progress]

The isolation of insulin from the pancreas and its purification to a degree permitting its safe administration to type 1 diabetic patients were accomplished 100 years ago at the University of Toronto by Banting, Best, Collip and McLeod and constitute undeniably one of the major medical therapeutic revolutions, recognized by the attribution of the 1923 Nobel Prize in Physiology or Medicine to Banting and McLeod. The clinical spin off was immediate as well as the internationalization of insulin's commercial production. The outcomes regarding basic research were much slower, in particular regarding the molecular mechanisms of insulin action on its target cells. It took almost a half-century before the determination of the tri-dimensional structure of insulin in 1969 and the characterization of its cell receptor in 1970-1971. The demonstration that the insulin receptor is in fact an enzyme named tyrosine kinase came in the years 1982-1985, and the crystal structure of the intracellular kinase domain 10 years later. The crystal structure of the first intracellular kinase substrate (IRS-1) in 1991 paved the way for the elucidation of the intracellular signalling pathways but it took 15 more years to obtain the complete crystal structure of the extracellular receptor domain (without insulin) in 2006. Since then, the determination of the structure of the whole insulin-receptor complex in both the inactive and activated states has made considerable progress, not least due to recent improvement in the resolution power of cryo-electron microscopy. I will here review the steps in the development of the concept of hormone receptor, and of our knowledge of the structure and molecular mechanism of activation of the insulin receptor.

ATP Secretion and Metabolism in Regulating Pancreatic Beta Cell Functions and Hepatic Glycolipid Metabolism

Diabetes (DM), especially type 2 diabetes (T2DM) has become one of the major diseases severely threatening public health worldwide. Islet beta cell dysfunctions and peripheral insulin resistance including liver and muscle metabolic disorder play decisive roles in the pathogenesis of T2DM. Particularly, increased hepatic gluconeogenesis due to insulin deficiency or resistance is the central event in the development of fasting hyperglycemia. To maintain or restore the functions of islet beta cells and suppress hepatic gluconeogenesis is crucial for delaying or even stopping the progression of T2DM and diabetic complications. As the key energy outcome of mitochondrial oxidative phosphorylation, adenosine triphosphate (ATP) plays vital roles in the process of almost all the biological activities including metabolic regulation. Cellular adenosine triphosphate participates intracellular energy transfer in all forms of life. Recently, it had also been revealed that ATP can be released by islet beta cells and hepatocytes, and the released ATP and its degraded products including ADP, AMP and adenosine act as important signaling molecules to regulate islet beta cell functions and hepatic glycolipid metabolism via the activation of P2 receptors (ATP receptors). In this review, the latest findings regarding the roles and mechanisms of intracellular and extracellular ATP in regulating islet functions and hepatic glycolipid metabolism would be briefly summarized and discussed.

Insulin and Its Key Role for Mitochondrial Function/Dysfunction and Quality Control: A Shared Link between Dysmetabolism and Neurodegeneration

Insulin was discovered and isolated from the beta cells of pancreatic islets of dogs and is associated with the regulation of peripheral glucose homeostasis. Insulin produced in the brain is related to synaptic plasticity and memory. Defective insulin signaling plays a role in brain dysfunction, such as neurodegenerative disease. Growing evidence suggests a link between metabolic disorders, such as diabetes and obesity, and neurodegenerative diseases, especially Alzheimer's disease (AD). This association is due to a common state of insulin resistance (IR) and mitochondrial dysfunction. This review takes a journey into the past to summarize what was known about the physiological and pathological role of insulin in peripheral tissues and the brain. Then, it will land in the present to analyze the insulin role on mitochondrial health and the effects on insulin resistance and neurodegenerative diseases that are IR-dependent. Specifically, we will focus our attention on the quality control of mitochondria (MQC), such as mitochondrial dynamics, mitochondrial biogenesis, and selective autophagy (mitophagy), in healthy and altered cases. Finally, this review will be projected toward the future by examining the most promising treatments that target the mitochondria to cure neurodegenerative diseases associated with metabolic disorders.

Preclinical and clinical evaluation of a new method to assess cardiac insulin resistance using nuclear imaging

BACKGROUND

Myocardial insulin resistance (IR) could be a predictive factor of cardiovascular events. This study aimed to introduce a new method using 123I-6-deoxy-6-iodo-D-glucose (6DIG), a pure tracer of glucose transport, for the assessment of IR using cardiac dynamic nuclear imaging.

METHODS

The protocol evaluated first in rat-models consisted in two 6DIG injections and one of insulin associated with planar imaging and blood sampling. Compartmental modeling was used to analyze 6DIG kinetics in basal and insulin conditions and to obtain an index of IR. As a part of a translational approach, a clinical study was then performed in 5 healthy and 6 diabetic volunteers.

RESULTS

In rodent models, the method revealed reproducible when performed twice at 7 days apart in the same animal. Rosiglitazone, an insulin-sensitizing drug, induced a significant increase of myocardial IR index in obese Zucker rats from 0.96 ± 0.18 to 2.26 ± 0.44 (P<.05) after 7 days of an oral treatment, and 6DIG IR indexes correlated with the gold standard IR index obtained through the hyperinsulinemic-euglycemic clamp (r=.68, P<.02). In human, a factorial analysis was applied on images to obtain vascular and myocardial kinetics before compartmental modeling. 1.5-fold to 2.2-fold decreases in mean cardiac IR indexes from healthy to diabetic volunteers were observed without reaching statistical significance.

CONCLUSIONS

These preclinical results demonstrate the reproducibility and sensibility of this novel imaging methodology. Although this first in-human study showed that this new method could be rapidly performed, larger studies need to be planned in order to confirm its performance.

Walnut Meal Extracts Rich In Polyphenols Mitigate Insulin Resistance and Modulate Gut Microbiota in High Fat Diet-Fed Rats

Walnut kernel is a traditional Chinese herb recorded in the Chinese Pharmacopoeia with the efficacies of invigorating kidney, tonifying lung, and relaxing bowel. However, the potential mechanisms were unclear. This article aims to uncover the interdict mechanisms of walnut meal extracts (WMP) on high-fat diet (HFD) induced metabolic disorders in rats and reveal how the WMP benefits are associated with changes in the intestinal flora. Sprague-Dawley (SD) rats were fed a standard chow diet or an HFD for 18 weeks. After 6 weeks, the HFD rats were supplemented with 750 mg WMP/kg body weight or the vehicle for 12 weeks. The structure of gut microbiota was assessed by analyzing 16S rDNA sequences. WMP suppressed the weight gain and visceral obesity. WMP treatment also improved lipid profiles and increased antioxidative activities. WMP fully reversed hepatic steatosis with the upregulation of adipocytokines involved in lipid catabolism (e.g., adiponectin, PPAR-γ, visfatin, CEBPα) and the increased activities of lipoprotein lipase and hormone-sensitive lipase, which were associated with glucose tolerance improvement and insulin resistance (IR) mitigation. As revealed by 16S rDNA sequencing, WMP restored the diversity of intestinal flora reduced by HFD. WMP dramatically reduced the abundance of Gram-negative bacteria, especially Fusobacterium varium and Bacteroides vulgatus, and sharply increased the abundance of Lactobacillus animalis decreased by HFD. Our findings demonstrated that WMP suppressed the weight gain and adiposity in HFD-fed rats and fully reversed HFD induced IR and hepatic steatosis while dramatically reducing the abundance of Fusobacteriaceae and Enterobacteriaceae, underscoring the gut-liver axis as a primary target of walnut polyphenols.

A Cardiac Amino-Terminal GRK2 Peptide Inhibits Maladaptive Adipocyte Hypertrophy and Insulin Resistance During Diet-Induced Obesity

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Heart disease remains the leading cause of death, in part due to increasing diabetes and obesity, though the exact mechanisms linking these disorders are not fully understood.

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In a diet-induced obesity model, we found that cardiac expression of an amino-terminal peptide of GRK2, βARKnt, preserves systemic glucose tolerance and insulin sensitivity despite normal weight gain.

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βARKnt enhanced metabolic flexibility, increased energy expenditure, protected against maladaptive visceral adipocyte hypertrophy, and induced visceral fat browning.

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βARKnt further elicited cardioprotection and increased insulin-mediated AS160 signaling during metabolic stress.

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These data point to a noncanonical cardiac regulation of systemic metabolic homeostasis that may lead to new treatment modalities for metabolic syndrome.

Heart disease remains the leading cause of death, and mortality rates positively correlate with the presence of obesity and diabetes. Despite the correlation between cardiac and metabolic dysregulation, the mechanistic pathway(s) of interorgan crosstalk still remain undefined. This study reveals that cardiac-restricted expression of an amino-terminal peptide of GRK2 (βARKnt) preserves systemic and cardiac insulin responsiveness, and protects against adipocyte maladaptive hypertrophy in a diet-induced obesity model. These data suggest a cardiac-driven mechanism to ameliorate maladaptive cardiac remodeling and improve systemic metabolic homeostasis that may lead to new treatment modalities for cardioprotection in obesity and obesity-related metabolic syndromes.

Thyroid-Stimulating Hormone Inhibits Insulin Receptor Substrate-1 Expression and Tyrosyl Phosphorylation in 3T3-L1 Adipocytes by Increasing NF-κB DNA-Binding Activity

Background. Abundant evidence indicates that thyroid-stimulating hormone (TSH) levels are associated with insulin resistance in adipocytes. However, the potential mechanism of the association remains uncertain. The objective of this study was to determine the potential role of TSH in the suppression of insulin receptor substrate-1 (IRS-1) expression and IRS-1 tyrosyl phosphorylation, which might contribute to insulin resistance. Methods. Mouse 3T3-L1 preadipocytes were differentiated into adipocytes. After treatment with 0.01, 0.1, and 1.0 mIU/ml bovine TSH, the TNF-α concentration in the medium was determined by enzyme-linked immunosorbent assay (ELISA). Nuclear factor-kappa B (NF-κB) DNA-binding activity was quantified by electrophoretic mobility shift assay (EMSA). IRS-1 levels in adipocytes were quantified by Western blotting, and tyrosine phosphorylation was measured by immunoprecipitation. Results. TSH induced TNF-α secretion in a dose-dependent manner. There was a significant positive correlation between NF-κB DNA-binding activity and TNF-α secretion. This effect and correlation were weakened by BAY 11-7082 (a nuclear NF-κB inhibitor) and H89 (an inhibitor of cyclic adenosine monophosphate- (cAMP-) dependent protein kinase A (PKA)). Treatment of cultured adipocytes with TSH inhibited insulin-stimulated IRS-1 tyrosyl phosphorylation but promoted TSH-dependent secretion of TNF-α and activation of NF-κB DNA-binding activity. The effects of TSH were significantly inhibited by BAY 11-7082 and H89 and were completely blocked by the TNF-α antagonist WP9QY. Conclusion. TSH inhibited IRS-1 protein expression and tyrosyl phosphorylation in 3T3-L1 adipocytes by stimulating TNF-α production via promotion of NF-κB DNA-binding activity. TSH might play a pivotal role in the development of insulin resistance.

DMRT2 Interacts With FXR and Improves Insulin Resistance in Adipocytes and a Mouse Model

Insulin resistance (IR) plays a critical role in cardiovascular diseases and metabolic diseases. In this study, we identified the downregulation of DMRT2 in adipose tissues from insulin-resistant subjects through bioinformatics analysis and in an insulin-resistant mouse model through experimental analysis. DMRT2 overexpression significantly attenuated HDF-induced insulin resistance and inflammation in mice. Moreover, in control and insulin-resistant differentiated mouse 3T3-L1 adipocytes, DMRT2 overexpression attenuated but DMRT2 knockdown enhanced the insulin resistance of 3T3-L1 adipocytes. DMRT2 interacted with FXR and positively regulated FXR level and transcription activity. In both control and insulin-resistant differentiated mouse 3T3-L1 adipocytes, FXR knockdown enhanced the insulin resistance and attenuated the effects of DMRT2 overexpression upon 3T3-L1 adipocyte insulin resistance. In conclusion, we identify the downregulation of DMRT2 in the insulin-resistant mouse model and cell model. DMRT2 interacts with FXR and improves insulin resistance in adipocytes.

Impact of moderate dietary protein restriction on glucose homeostasis in a model of oestrogen deficiency

The need to consume adequate dietary protein to preserve physical function during ageing is well recognized. However, the effect of protein intakes on glucose metabolism is still intensively debated. During age-related oestrogen withdrawal at the time of the menopause, it is known that glucose homeostasis may be impaired but the influence of dietary protein levels in this context is unknown. The aim of the present study is to elucidate the individual and interactive effects of oestrogen deficiency and suboptimal protein intake on glucose homeostasis in a preclinical model involving ovariectomy (OVX) and a 13-week period of a moderately reduced protein intake in 7-month-old ageing rats. To investigate mechanisms of action acting via the pancreas-liver-muscle axis, fasting circulating levels of insulin, glucagon, IGF-1, FGF21 and glycemia were measured. The hepatic lipid infiltration and the protein expression of GLUT4 in the gastrocnemius were analyzed. The gene expression of some hepatokines, myokines and lipid storage/oxidation related transcription factors were quantified in the liver and the gastrocnemius. We show that, regardless of the oestrogen status, moderate dietary protein restriction increases fasting glycaemia without modifying insulinemia, body weight gain and composition. This fasting hyperglycaemia is associated with oestrogen status-specific metabolic alterations in the muscle and liver. In oestrogen-replete (SHAM) rats, GLUT4 was down-regulated in skeletal muscle while in oestrogen-deficient (OVX) rats, hepatic stress-associated hyperglucagonaemia and high serum FGF21 were observed. These findings highlight the importance of meeting dietary protein needs to avoid disturbances in glucose homeostasis in ageing female rats with or without oestrogen withdrawal.

Epigenetics: key to improve delayed wound healing in type 2 diabetes

Diabetes-related delayed wound healing is a multifactorial, nuanced, and intertwined complication that causes substantial clinical morbidity. The etiology of diabetes and its related microvascular complications is affected by genes, diet, and lifestyle factors. Epigenetic modifications such as DNA methylation, histone modifications, and post-transcriptional RNA regulation (microRNAs) are subsequently recognized as key facilitators of the complicated interaction between genes and the environment. Current research suggests that diabetes-persuaded dysfunction of epigenetic pathways, which results in changed expression of genes in target cells and cause diabetes-related complications including cardiomyopathy, nephropathy, retinopathy, delayed wound healing, etc., which are foremost drivers to diabetes-related adverse outcomes. In this paper, we discuss the role of epigenetic mechanisms in controlling tissue repair, angiogenesis, and expression of growth factors, as well as recent findings that show the alteration of epigenetic events during diabetic wound healing.

Effects of bisphenol A on pancreas and thyroid gland of young and adult female Sprague Dawlеy rats

Bisphenol A (BPA), a chemical involved in formation of plastic vessels, is one of the most widespread endocrine disrupting chemicals. The study was designed to investigate the effect of BPA on pancreas and thyroid gland of young and adult female Sprague Dawley rats. The rats were exposed to 330 mg/kg BPA orally every other day for 12 weeks; control rats were exposed orally to ethyl alcohol and corn oil. Samples were collected at 4, 8 and 12 weeks for hormonal, biochemical assays and histopathological examination. The insulin hormone in exposed young rats was decreased, but its level in adult ones was increased; the biochemical assay for blood sugar level showed a significant increase in young rats and decrease in adult ones. T3 hormone was increased in treated young and adult rats; T4 hormone was increased in treated adults, while calcium level was decreased in treated adult rats. The histopathological findings of pancreas revealed vacuolation in its endocrine parts in young rats, while in adult ones there was intralobular fatty infiltration - a typical picture of diabetes. The thyroid gland in treated young female rats showed increased cellularity of parafollicular cells; moreover there was parafollicular haemorrhage, and in adult ones - desquamation in lining epithelium of follicular cells. In conclusion, exposure of young and adult female rats to BPA resulted in changes in the pancreatic and thyroid gland cells manifested by morphological, hormonal and biochemical parameters.

Empagliflozin Inhibits Hepatic Gluconeogenesis and Increases Glycogen Synthesis by AMPK/CREB/GSK3β Signalling Pathway

Increases in glucose production and decreases in hepatic glycogen storage induce glucose metabolic abnormalities in type 2 diabetes (T2DM). Empagliflozin, a sodium-dependent glucose transporter 2 (SGLT2) inhibitor, is an effective hypoglycemic drug; however, the effects of empagliflozin on hepatic gluconeogenesis and glycogenesis are still unclear. In this study, we investigated the effects and mechanisms of empagliflozin on hepatic gluconeogenesis and glycogenesis in vivo and in vitro. Empagliflozin was administered via gavage to db/db mice for 8 weeks, and human hepatocyte HL7702 cells were treated with empagliflozin after palmitic acid (PA) stimulation. Compared with the control db/db mice, empagliflozin-treated mice showed a significant reduction in urine glucose levels, blood glucose levels, body weight and intraperitoneal glucose tolerance test (IPGTT) blood glucose levels. Moreover, the expression levels and activities of key gluconeogenesis enzymes PEPCK and G6Pase were dramatically reduced in the empagliflozin-treated mice, and the protein expression levels of AMPK/CREB/GSK3β signalling pathway-related molecules were significantly changed. In HL7702 cells, empagliflozin ameliorated glucose production and PEPCK and G6Pase expression and activity. Empagliflozin could also prevent the decreases in glycogen content and regulate the protein expression levels of AMPK/CREB/GSK3β signalling pathway-related molecules. Then, we selected the AMPK agonist AICAR and inhibitor compound C to further verify the effects of the AMPK signalling pathway on hepatic gluconeogenesis and glycogen synthesis. The results of the 5-Aminoimidazole-4-carboxamide1-β-D-ribofuranoside (AIACR) intervention in HL7702 cells were consistent with those of empagliflozin treatment, and the effects of empagliflozin were abolished by compound C. In summary, empagliflozin could maintain glucose homoeostasis by reducing gluconeogenesis and increasing glycogenesis through the AMPK/CREB/GSK3β signalling pathway.

Possible Benefits of Faecalibacterium prausnitzii for Obesity-Associated Gut Disorders

Metabolic disorders are an increasing concern in the industrialized world. Current research has shown a direct link between the composition of the gut microbiota and the pathogenesis of obesity and diabetes. In only a few weeks, an obesity-inducing diet can lead to increased gut permeability and microbial dysbiosis, which contributes to chronic inflammation in the gut and adipose tissues, and to the development of insulin resistance. In this review, we examine the interplay between gut inflammation, insulin resistance, and the gut microbiota, and discuss how some probiotic species can be used to modulate gut homeostasis. We focus primarily on Faecalibacterium prausnitzii, a highly abundant butyrate-producing bacterium that has been proposed both as a biomarker for the development of different gut pathologies and as a potential treatment due to its production of anti-inflammatory metabolites.

Effects of Different Intensity Exercise on Glucose Metabolism and Hepatic IRS/PI3K/AKT Pathway in SD Rats Exposed with TCDD

The objective of the study was to investigate the effects of different intensity exercise and 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) exposure on glucose metabolism in Sprague Dawley (SD) rats, as well as the action of insulin receptor substrate (IRS)/phosphatidylinositol-3-kinases (PI3K)/protein kinase (AKT) signaling pathway in it. Besides that, we explored whether exercise can alleviate the toxicity induced by TCDD. Sixty male SD rats (8 weeks old) were randomly divided into non-exercise group, none-exercise toxic group, moderate-intensity exercise group, moderate-intensity exercise toxic group, high-intensity exercise group, high-intensity exercise toxic group. The toxic groups were intraperitoneally injected with TCDD, which the dose was 6.4 µg/kg· BW for the first week, then 21% of the above week dose for continuous 8 weeks. The 8-week treadmill running of moderate intensity (15 m/min, 60 min/day) and high intensity (26 m/min, 35 min/day) were implemented separately in exercise groups five times a week. After detecting the concentration of fasting serum glucose, insulin and C-peptide, the index of the homeostasis model assessment of insulin resistance (HOMA-IR) and islet β-cell secretion (HOMA-β) were calculated. We measured the hepatic mRNA expression levels of IRS2, phosphatidylinositol-3-kinases catalytic subunit alpha (PIK3CA), AKT by real-time PCR. The protein expression of total IRS2 (tIRS2), phosphorylated IRS2 at Ser731 (pSer731), total PIK3CA (tPIK3CA), total Akt (tAkt), phosphorylated Akt at Thr308 (pThr308) in liver were analyzed by western blot. We observed that compared to the non-exercise group, insulin and HOMA-IR index were significantly higher in the none-exercise toxic group (p < 0.05), while glucose, insulin, C-peptide and HOMA-IR index were significantly lower in the moderate-intensity exercise group (p < 0.05). In the high-intensity exercise group, the HOMA-IR index was significantly lower and the gene expression of IRS2 was significantly higher than in the non-exercise group (p < 0.05). Besides that, the HOMA-β index in the moderate-intensity exercise toxic group was significantly higher compared to the none-exercise toxic group and moderate-intensity exercise group (p < 0.05). The level of IRS2mRNA was significantly lower in the high-intensity exercise toxic group than in the high-intensity exercise group (p < 0.05). Our results demonstrated that 8-week TCDD exposure could induce insulin resistance in rats, while exercise could improve insulin sensitivity in which moderate intensity was more obvious than high intensity exercise. Meanwhile, both intensity exercise could not effectively alleviate the insulin resistance induced by TCDD, but high intensity exercise could promote compensatory insulin secretion to maintain glucose homeostasis. Although the gene expression of IRS2 was changed in high-intensity exercise groups, the mediation role of the hepatic IRS2/PI3K/AKT pathway in the effects of exercise and TCDD exposure on glucose metabolism remains very limited.

Feeding frequency affects glucose and lipid metabolism through SIRT1/AMPK pathway in growing pigs with the same amount of daily feed

Eating patterns are associated with obesity and metabolic health. However, the regulating mechanism of different eating patterns on body metabolism are not fully cleare. In this study, a pig model was used to evaluate the effects of feeding frequency on glucose and lipid metabolism and reveal its regulating mechanism. Twenty-four growing barrows were randomly allocated to 1-meal (M1), 3-meal (M3), or 5-meal (M5) per day groups with the same amount of daily feed. GSEA was conducted on the liver to investigate the pathways of different feeding frequencies on the metabolism. The serum glucose, NEFA, VLDL-C levels were higher for M1 group than for M3 and M5 groups, however, the hepatic TRIG level was lower. Liver transcriptome showed that glycolysis/gluconeogenesis and fatty acid metabolism pathways were suppressed with the increase of feeding frequency. The increase of gluconeogenic substrates (glycerol and lactate) and enzymes (PEPCK1 and G6Pase) in liver indicated that hepatic gluconeogenesis was enhanced in the M1 group. AMPK/PPARα signaling associated genes were positively correlated with NEFA and β-HB levels in M1 group, which promoted fatty acid oxidation and ketogenesis in liver. Moreover, compared with M3 and M5 groups, the higher NAD⁺/NADH ratio in the liver of M1 group activated SIRT1, which stimulated the AMPK signaling associated pathways by up-regulating the LKB1 gene. These findings provide evidence for the regulating roles of feeding frequency on glucose and lipid metabolism through SIRT1/AMPK pathway, which greatly contributes to the regulation of energy metabolism through daily eating patterns in animals.

The interplay among oxidative stress, brain insulin resistance and AMPK dysfunction contribute to neurodegeneration in type 2 diabetes and Alzheimer disease

Alzheimer's disease (AD) is the most common form of dementia in the elderly followed by vascular dementia. In addition to clinically diagnosed dementia, cognitive dysfunction has been reported in diabetic patients. Recent studies are now beginning to recognize type 2 diabetes mellitus (T2DM), characterized by chronic hyperglycemia and insulin resistance, as a risk factor for AD and other cognitive disorders. While studies on insulin action have remained traditionally in the domain of peripheral tissues, the detrimental effects of insulin resistance in the central nervous system on cognitive dysfunction are increasingly being reported in recent clinical and preclinical studies. Brain functions require continuous supply of glucose and oxygen and a tight regulation of metabolic processes. Loss of this metabolic regulation has been proposed to be a contributor to memory dysfunction associated with neurodegeneration. Within the above scenario, this review will focus on the interplay among oxidative stress (OS), insulin resistance and AMPK dysfunctions in the brain by highlighting how these neurotoxic events contribute to neurodegeneration. We provide an overview on the detrimental effects of OS on proteins regulating insulin signaling and how these alterations impact cell metabolic dysfunctions through AMPK dysregulation. Such processes, we assert, are critically involved in the molecular pathways that underlie AD.

Hypoglycemic Effect of Electroacupuncture at ST25 Through Neural Regulation of the Pancreatic Intrinsic Nervous System

Electroacupuncture (EA) is considered to have potential antidiabetic effects; however, the role of the pancreatic intrinsic nervous system (PINS) in EA-induced amelioration of type 2 diabetes (T2DM) remains unclear. Therefore, we investigated whether EA at ST25 exerts any beneficial effects on insulin resistance (IR), inflammation severity, and pancreatic β cell function via the PINS in a rat model of a high-fat diet-streptozotocin (HFD/STZ)-induced diabetes. To this end, Sprague Dawley rats were fed with HFD to induce IR, followed by STZ (35 mg/kg, i.p.) injection to establish the T2DM model. After hyperglycemia was confirmed as fasting glucose level > 16.7 mmol/L, the rats were treated with EA (2 mA, 2/15 Hz) for the next 28 days. Model rats showed increased serum glucose, insulin, IR, and TNF-α levels with a concomitant decrease in β cell function. Microscopy examination of the pancreas revealed pathological changes in islets, which reverted to near-normal levels after EA at ST25. EA improved islet cell morphology by increasing islet area and reducing vacuolation. EA at ST25 decreased transient receptor potential vanilloid 1 (TRPV1) and increased substance P (SP) and calcitonin gene-related peptide (CGRP) expression. Subsequently, insulin secretion decreased and impaired pancreatic endocrine function was restored through the TRPV1 channel (SP/CGRP)-insulin circuit. EA increased choline acetyltransferase and neuropeptide Y expression and controlled inflammation. It also enhanced the cocaine and amphetamine-regulated transcript prepropeptide expression and promoted glucagon-like peptide-1 secretion. Additionally, the electrophysiological activity of PINS during acupuncture (2.71 ± 1.72 Hz) was significantly increased compared to the pre-acupuncture frequency (0.32 ± 0.37 Hz, P < 0.05). Thus, our study demonstrated the beneficial effect of EA on β cell dysfunction via the PINS in rat models of HFD-STZ-induced T2DM.

Insulin at 100 years - is rebalancing its action key to fighting obesity-related disease?

One hundred years ago, insulin was purified and administered to people with diabetes to lower blood glucose, suppress ketogenesis and save lives. A century later, insulin resistance (IR) lies at the heart of the obesity-related disease pandemic. Multiple observations attest that IR syndrome is an amalgamation of gain and loss of insulin action, suggesting that IR is a misnomer. This misapprehension is reinforced by shortcomings in common model systems and is particularly pronounced for the tissue growth disorders associated with IR. It is necessary to move away from conceptualisation of IR as a pure state of impaired insulin action and to appreciate that, in the long term, insulin can harm as well as cure. The mixed state of gain and loss of insulin action, and its relationship to perturbed insulin-like growth factor (IGF) action, should be interrogated more fully in models recapitulating human disease. Only then may the potential of rebalancing insulin action, rather than simply increasing global insulin signalling, finally be appreciated.

GPR21 Inhibition Increases Glucose-Uptake in HepG2 Cells

GPR21 is a constitutively active, orphan, G-protein-coupled receptor, with in vivo studies suggesting its involvement in the modulation of insulin sensitivity. However, its precise contribution is not fully understood. As the liver is both a major target of insulin signalling and critically involved in glucose metabolism, the aim of this study was to examine the role of GPR21 in the regulation of glucose uptake and production in human hepatocytes. In particular, HepG2 cells, which express GPR21, were adopted as cellular models. Compared with untreated cells, a significant increase in glucose uptake was measured in cells treated with siRNA to downregulate GPR21 expression or with the GPR21-inverse agonist, GRA2. Consistently, a significantly higher membrane translocation of GLUT-2 was measured under these conditions. These effects were accompanied by an increased ratio of phAKT^(Ser473)/tot-AKT and phGSK-3β^(Ser9)/tot-GSK-3β, thus indicating a marked activation of the insulin signalling pathway. Moreover, a significant reduction in ERK activation was observed with GPR21 inhibition. Collectively, these results indicate that GPR21 mediates the negative effects on glucose uptake by the liver cells. In addition, they suggest that the pharmacological inhibition of GPR21 could be a novel strategy to improve glucose homeostasis and counteract hepatic insulin resistance.

Sargassum fusiforme fucoidan alleviates diet-induced insulin resistance by inhibiting colon-derived ceramide biosynthesis

Sargassum fusiforme fucoidan (SFF) is a highly sulfated heteropolysaccharide with various biological activities. As one of the causative factors of type 2 diabetes mellitus (T2DM), insulin resistance has become a global health issue. In this study, we investigated the potential pharmacological mechanisms by which SFF ameliorates insulin resistance in high-fat diet (HFD)-fed mice. SFF significantly enhanced tauroursodeoxycholic acid (TUDCA, a conjugated bile acid) levels and inhibited the farnesoid X receptor (FXR) signaling in the colon. SFF administration reduced ceramide levels in both serum and colonic tissue of HFD-fed mice, as well as reduced expression of SPT and CerS genes, which encode enzymes crucial to the biosynthesis of ceramides regulated by FXR signaling. Pearson's analysis showed that the TUDCA level was positively correlated with the gut bacteria Clostridium, and this was further validated in pseudo-germfree mice. Taken together, the results suggested that SFF increased TUDCA levels by remodeling gut microbiota, and TUDCA, a natural FXR antagonist, inhibited the FXR/SHP signaling pathway to reduce colon-derived biosynthesis of ceramide, thereby improving insulin resistance in the diet-induced obese (DIO) mice. This study has provided new insights into the therapeutic potential of S. fusiforme fucoidan in metabolic diseases.

Severe Hepatic Insulin Resistance Induces Vascular Dysfunction: Improvement by Liver-Specific Insulin Receptor Isoform A Gene Therapy in a Murine Diabetic Model

BACKGROUND

Cardiovascular dysfunction is linked to insulin-resistant states. In this paper, we analyzed whether the severe hepatic insulin resistance of an inducible liver-specific insulin receptor knockout (iLIRKO) might generate vascular insulin resistance and dysfunction, and whether insulin receptor (IR) isoforms gene therapy might revert it.

METHODS

We studied in vivo insulin signaling in aorta artery and heart from iLIRKO. Vascular reactivity and the mRNA levels of genes involved in vascular dysfunction were analyzed in thoracic aorta rings by qRT-PCR. Finally, iLIRKO mice were treated with hepatic-specific gene therapy to analyze vascular dysfunction improvement.

RESULTS

Our results suggest that severe hepatic insulin resistance was expanded to cardiovascular tissues. This vascular insulin resistance observed in aorta artery from iLIRKO mice correlated with a reduction in both PI3K/AKT/eNOS and p42/44 MAPK pathways, and it might be implicated in their vascular alterations characterized by endothelial dysfunction, hypercontractility and eNOS/iNOS levels' imbalance. Finally, regarding long-term hepatic expression of IR isoforms, IRA was more efficient than IRB in the improvement of vascular dysfunction observed in iLIRKO mice.

CONCLUSION

Severe hepatic insulin resistance is sufficient to produce cardiovascular insulin resistance and dysfunction. Long-term hepatic expression of IRA restored the vascular damage observed in iLIRKO mice.

Melatonin regulates maternal pancreatic remodeling and B-cell function during pregnancy and lactation

The endocrine pancreas of pregnant rats shows evident plasticity, which allows the morphological structures to return to the nonpregnant state right after delivery. Furthermore, it is well-known the role of melatonin in the maintenance of the endocrine pancreas and its tropism. Studies indicate increasing nocturnal serum concentrations of maternal melatonin during pregnancy in both humans and rodents. The present study investigated the role of melatonin on energy metabolism and in pancreatic function and remodeling during pregnancy and early lactation in rats. The results confirm that the absence of melatonin during pregnancy impairs glucose metabolism. In addition, there is a dysregulation in insulin secretion at various stages of the development of pregnancy and an apparent failure in the glucose-stimulated insulin secretion during the lactation period, evidencing the role of melatonin on the regulation of insulin secretion. This mechanism seems not to be dependent on the antioxidant effect of melatonin and probably dependent on MT2 receptors. We also observed changes in the mechanisms of death and cell proliferation at the end of pregnancy and beginning of lactation, crucial periods for pancreatic remodeling. The present observations strongly suggest that both functionality and remodeling of the endocrine pancreas are impaired in the absence of melatonin and its adequate replacement, mimicking the physiological increase seen during pregnancy, is able to reverse some of the damage observed. Thus, we conclude that pineal melatonin is important to metabolic adaptation to pregnancy and both the functionality of the beta cells and the remodeling of the pancreas during pregnancy and early lactation, ensuring the return to nonpregnancy conditions.

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.

Sex, Cells, and Asthma

There are marked sex differences in asthma prevalence and severity. Sex hormones play a central role in these sex biases and directly interact with multiple key cells involved in the pathogenesis of asthma. Here we review the known effects of estrogen, progesterone, and testosterone on airway epithelial cells, airway smooth muscle cells, the mononuclear phagocyte system, innate lymphoid cells, eosinophils, mast cells, T cells, and B cells, all in the context of asthma. Furthermore, we explore unresolved clinical questions, such as the role of sex hormones in the link between asthma and obesity.

The Key Role of Akt Protein Kinase in Metabolic-Inflammatory Pathways Cross-Talk: TNF-α Down-Regulation and Improving of Insulin Resistance in HepG2 Cell Line

BACKGROUND

Elevation of plasma free fatty acids as a principal aspect of type 2 diabetes maintains etiologically insulin insensitivity in target cells. TNF-α inhibitory effects on key insulin signaling pathway elements remain to be verified in insulinresistant hepatic cells. Thus, TNF-α knockdown effects on the key elements of insulin signaling were investigated in the palmitate-induced insulin-resistant hepatocytes. The Akt serine kinase, a key protein of the insulin signaling pathway, phosphorylation was monitored to understand the TNF-α effect on probable enhancing of insulin resistance.

METHODS

Insulin-resistant HepG2 cells were produced using 0.5 mM palmitate treatment and shRNA-mediated TNF-α gene knockdown and its down-regulation confirmed using ELISA technique. Western blotting analysis was used to assess the Akt protein phosphorylation status.

RESULTS

Palmitate-induced insulin resistance caused TNF-α protein overexpression 1.2-, 2.78, and 2.25- fold as compared to the control cells at post-treatment times of 8 h, 16 h, and 24 h, respectively. In the presence of palmitate, TNF-α expression showed around 30% reduction in TNF-α knockdown cells as compared to normal cells. In the TNF-α down-regulated cell, Akt phosphorylation was approximately 62% more than control cells after treatment with 100 nM insulin in conjugation with 0.5 mM palmitate.

CONCLUSIONS

The obtained data demonstrated that TNF-α protein expression reduction improved insulin-stimulated Akt phosphorylation in the HepG2 cells and decreased lipidinduced insulin resistance of the diabetic hepatocytes.

FGF21 is required for the metabolic benefits of IKKε/TBK1 inhibition

The protein kinases IKKε and TBK1 are activated in liver and fat in mouse models of obesity. We have previously demonstrated that treatment with the IKKε/TBK1 inhibitor amlexanox produces weight loss and relieves insulin resistance in obese animals and patients. While amlexanox treatment caused a transient reduction in food intake, long-term weight loss was attributable to increased energy expenditure via FGF21-dependent beiging of white adipose tissue (WAT). Amlexanox increased FGF21 synthesis and secretion in several tissues. Interestingly, although hepatic secretion determined circulating levels, it was dispensable for regulating energy expenditure. In contrast, adipocyte-secreted FGF21 may have acted as an autocrine factor that led to adipose tissue browning and weight loss in obese mice. Moreover, increased energy expenditure was an important determinant of improved insulin sensitivity by amlexanox. Conversely, the immediate reductions in fasting blood glucose observed with acute amlexanox treatment were mediated by the suppression of hepatic glucose production via activation of STAT3 by adipocyte-secreted IL-6. These findings demonstrate that amlexanox improved metabolic health via FGF21 action in adipocytes to increase energy expenditure via WAT beiging and that adipocyte-derived IL-6 has an endocrine role in decreasing gluconeogenesis via hepatic STAT3 activation, thereby producing a coordinated improvement in metabolic parameters.

Brain insulin, insulin-like growth factor 1 and glucagon-like peptide 1 signalling in Alzheimer's disease

Although the brain was once considered an insulin-independent organ, insulin signalling is now recognised as being central to neuronal health and to the function of synapses and brain circuits. Defective brain insulin signalling, as well as related signalling by insulin-like growth factor 1 (IGF-1), is associated with neurological disorders, including Alzheimer's disease, suggesting that cognitive impairment could be related to a state of brain insulin resistance. Here, I briefly review key epidemiological/clinical evidence of the association between diabetes, cognitive decline and AD, as well as findings of reduced components of insulin signalling in AD brains, which led to the initial suggestion that AD could be a type of brain diabetes. Particular attention is given to recent studies illuminating mechanisms leading to neuronal insulin resistance as a key driver of cognitive impairment in AD. Evidence of impaired IGF-1 signalling in AD is also examined. Finally, we discuss potentials and possible limitations of recent and on-going therapeutic approaches based on our increased understanding of the roles of brain signalling by insulin, IGF-1 and glucagon-like peptide 1 in AD.

FAM3C: an emerging biomarker and potential therapeutic target for cancer

FAM3C is a member of the FAM3 family. Recently, overexpression of FAM3C has been reported in numerous types of cancer, including breast and colon cancer. Increasing evidence suggests that elevated FAM3C and its altered subcellular localization are closely associated with tumor formation, invasion, metastasis and poor survival. Moreover, FAM3C has been found to be the regulator of various proteins that associate with cancer, including Ras, STAT3, TGF-β and LIFR. This review summarizes the current knowledge regarding FAM3C, including its structure, expression patterns, regulation, physiological roles and regulatory functions in various malignancies. These findings highlight the importance of FAM3C in cancer development and provide evidence that FAM3C is a novel biomarker and potential therapeutic target for various cancers.