Effect of acute physiological hyperinsulinemia on gene expression in human skeletal muscle in vivo

Unexplained Residual Risk In Type 2 Diabetes: How Big Is The Problem?

PURPOSE OF REVIEW

What is new? Cardiovascular disease (CVD) is the leading cause of mortality in type 2 diabetes (T2D) individuals. Of the major risk factors for CVD, less than 10% of T2D people meet the American Diabetes Association/American Heart Association recommended goals of therapy. The present review examines how much of the absolute cardiovascular (CV) risk in type 2 diabetes patients can be explained by major CV intervention trials.

RECENT FINDINGS

Multiple long-term cardiovascular (CV) intervention trials have examined the effect of specific target-directed therapies on the MACE endpoint. Only one prospective study, STENO-2, has employed a multifactorial intervention comparing intensified versus conventional treatment of modifiable risk factors in T2D patients, and demonstrated a 20% absolute CV risk reduction. If the absolute CV risk reduction in these trials is added to that in the only prospective multifactorial intervention trial (STENO-2), the unexplained CV risk is 44.1%. What are the clinical implications? Potential explanations for the unaccounted-for reduction in absolute CV risk in type 2 diabetes (T2D) patients are discussed.

HYPOTHESIS

failure to take into account synergistic interactions between major cardiovascular risk factors is responsible for the unexplained CV risk in T2D patients. Simultaneous treatment of all major CV risk factors to recommended AHA/ADA guideline goals is required to achieve the maximum reduction in CV risk.

Prolonged hyperinsulinemia increases the production of inflammatory cytokines in equine digital lamellae but not in striated muscle

Hyperinsulinemia is the key feature of equine metabolic syndrome (EMS) which leads to debilitating sequelae. Hyperinsulinemia-associated laminitis (HAL) is one of the major sequelae of EMS, although the pathophysiological mechanisms are not well elucidated. Using an equine model, we hypothesized that expression of inflammatory markers would be increased in digital lamellae and striated muscle following prolonged hyperinsulinemia. Healthy Standardbred horses (5.4 ± 1.9 years) were alternately assigned to a prolonged euglycemic-hyperinsulinemic clamp (pEHC) or control group (n = 4 per group). Following a 48 h pEHC or a 48 h infusion of a balanced electrolyte solution (controls), biopsies were collected from digital lamellar tissue, skeletal muscle and cardiac muscle were obtained. All hyperinsulinemic horses developed laminitis regardless of previous health status at enrollment. Protein expression was quantified via Western blotting. A significant (P < 0.05) upregulation of the protein expression of heat shock protein 90 (HSP90), alpha 2 macroglobulin (A2M) and fibrinogen (α, β isoforms), as well as inflammatory cytokines including interleukin-1β were detected in digital lamellae following prolonged hyperinsulinemia. In contrast, protein expression of cytokines and acute phase proteins in heart and skeletal muscle was unchanged following hyperinsulinemia. Upregulation of inflammatory cytokines and acute phase proteins in digital lamellae during prolonged hyperinsulinemia may reveal potential biomarkers and novel therapeutic targets for equine endocrinopathic laminitis. Further, the lack of increase of inflammatory proteins and acute phase proteins in striated muscle following prolonged hyperinsulinemia may highlight potential anti-inflammatory and cardioprotective mechanisms in these insulin-sensitive tissues.

In silico identification and functional prediction of differentially expressed genes in South Asian populations associated with type 2 diabetes

Type 2 diabetes (T2D) is one of the major metabolic disorders in humans caused by hyperglycemia and insulin resistance syndrome. Although significant genetic effects on T2D pathogenesis are experimentally proved, the molecular mechanism of T2D in South Asian Populations (SAPs) is still limited. Hence, the current research analyzed two Gene Expression Omnibus (GEO) and 17 Genome-Wide Association Studies (GWAS) datasets associated with T2D in SAP to identify DEGs (differentially expressed genes). The identified DEGs were further analyzed to explore the molecular mechanism of T2D pathogenesis following a series of bioinformatics approaches. Following PPI (Protein-Protein Interaction), 867 potential DEGs and nine hub genes were identified that might play significant roles in T2D pathogenesis. Interestingly, CTNNB1 and RUNX2 hub genes were found to be unique for T2D pathogenesis in SAPs. Then, the GO (Gene Ontology) showed the potential biological, molecular, and cellular functions of the DEGs. The target genes also interacted with different pathways of T2D pathogenesis. In fact, 118 genes (including HNF1A and TCF7L2 hub genes) were directly associated with T2D pathogenesis. Indeed, eight key miRNAs among 2582 significantly interacted with the target genes. Even 64 genes were downregulated by 367 FDA-approved drugs. Interestingly, 11 genes showed a wide range (9-43) of drug specificity. Hence, the identified DEGs may guide to elucidate the molecular mechanism of T2D pathogenesis in SAPs. Therefore, integrating the research findings of the potential roles of DEGs and candidate drug-mediated downregulation of marker genes, future drugs or treatments could be developed to treat T2D in SAPs.

Molecular Linkage between Immune System Disorders and Atherosclerosis

A strong relationship exists between immune dysfunction and cardiovascular disease. Immune dysregulation can promote the development of cardiovascular diseases as well as exacerbate their course. The disorders may occur due to the presence of primary immune defects (currently known as inborn errors of immunity) and the more common secondary immune deficiencies. Secondary immune deficiencies can be caused by certain chronic conditions (such as diabetes, chronic kidney disease, obesity, autoimmune diseases, or cancer), nutritional deficiencies (including both lack of nutrients and bioactive non-nutrient compounds), and medical treatments and addictive substances. This article unravels the molecular linkage between the aforementioned immune system disorders and atherosclerosis.

Dysregulation of early gene response to a mixed meal in skeletal muscle in obesity and type 2 diabetes

Obesity- and type 2 diabetes mellitus-induced changes in the expression of protein-coding genes in human skeletal muscle were extensively examined at baseline (after an overnight fast). We aimed to compare the early transcriptomic response to a typical single meal in skeletal muscle of metabolically healthy subjects and obese individuals without and with type 2 diabetes. Transcriptomic response (RNA-seq) to a mixed meal (nutritional drink, ∼25 kJ/kg of body mass) was examined in the vastus lateralis muscle (1 h after a meal) in 7 healthy subjects and 14 obese individuals without or with type 2 diabetes. In all obese individuals, the transcriptome response to a meal was dysregulated (suppressed and altered) and associated with different biological processes compared with healthy control. To search for potential transcription factors regulating transcriptomic response to a meal, the enrichment of transcription factor-binding sites in individual promoters of the human skeletal muscle was examined. In obese individuals, the transcriptomic response is associated with a different set of transcription factors than that in healthy subjects. In conclusion, metabolic disorders are associated with a defect in the regulation of mixed meal/insulin-mediated gene expression-insulin resistance in terms of gene expression. Importantly, this dysregulation occurs in obese individuals without type 2 diabetes, i.e., at the first stage of the development of metabolic disorders.NEW & NOTEWORTHY In skeletal muscle of metabolically healthy subjects, a typical single meal normalized to body mass induces activation of various transcription factors, expression of numerous receptor tyrosine kinases associated with the insulin signaling cascade, and transcription regulators. In skeletal muscle of obese individuals without and with type 2 diabetes, this signaling network is poorly regulated at the transcriptional level, indicating dysregulation of the early gene response to a mixed meal.

A stepwise activation model for the insulin receptor

The binding of insulin to the insulin receptor (IR) triggers a cascade of receptor conformational changes and autophosphorylation, leading to the activation of metabolic and mitogenic pathways. Recent advances in the structural and functional analyses of IR have revealed the conformations of the extracellular domains of the IR in inactive and fully activated states. However, the early activation mechanisms of this receptor remain poorly understood. The structures of partially activated IR in complex with aptamers provide clues for understanding the initial activation mechanism. In this review, we discuss the structural and functional features of IR complexed with various ligands and propose a model to explain the sequential activation mechanism. Moreover, we discuss the structures of IR complexed with biased agonists that selectively activate metabolic pathways and provide insights into the design of selective agonists and their clinical implications.

Obstructive sleep apnea-increased DEC1 regulates systemic inflammation and oxidative stress that promotes development of pulmonary arterial hypertension

Obstructive sleep apnea (OSA), characterized by chronic intermittent hypoxia (CIH), is a common risk factor for pulmonary arterial hypertension (PAH). As a hypoxia-induced transcription factor, differentially expressed in chondrocytes (DEC1) negatively regulates the transcription of peroxisome proliferative activated receptor-γ (PPARγ), a recognized protective factor of PAH. However, whether and how DEC1 is associated with PAH pathogenesis remains unclear. In the present study, we found that DEC1 was increased in lungs and pulmonary arterial smooth muscle cells (PASMCs) of rat models of OSA-associated PAH. Oxidative indicators and inflammatory cytokines were also elevated in the blood of the rats. Similarly, hypoxia-treated PASMCs displayed enhanced DEC1 expression and reduced PPARγ expression in vitro. Functionally, DEC1 overexpression exacerbated reactive oxygen species (ROS) production and the expression of pro-inflammatory cytokines (such as TNFα, IL-1β, IL-6, and MCP-1) in PASMCs. Conversely, shRNA knockdown of Dec1 increased PPARγ expression but attenuated hypoxia-induced oxidative stress and inflammatory responses in PASMCs. Additionally, DEC1 overexpression promoted PASMC proliferation, which was drastically attenuated by a PPARγ agonist rosiglitazone. Collectively, these results suggest that hypoxia-induced DEC1 inhibits PPARγ, and that this is a predominant mechanism underpinning oxidative stress and inflammatory responses in PASMCs during PAH. DEC1 could be used as a potential target to treat PAH.

Signaling and Gene Expression in Skeletal Muscles in Type 2 Diabetes: Current Results and OMICS Perspectives

Skeletal muscles mainly contribute to the emergence of insulin resistance, impaired glucose tolerance and the development of type 2 diabetes. Molecular mechanisms that regulate glucose uptake are diverse, including the insulin-dependent as most important, and others as also significant. They involve a wide range of proteins that control intracellular traffic and exposure of glucose transporters on the cell surface to create an extensive regulatory network. Here, we highlight advantages of the omics approaches to explore the insulin-regulated proteins and genes in human skeletal muscle with varying degrees of metabolic disorders. We discuss methodological aspects of the assessment of metabolic dysregulation and molecular responses of human skeletal muscle to insulin. The known molecular mechanisms of glucose uptake regulation and the first results of phosphoproteomic and transcriptomic studies are reviewed, which unveiled a large-scale array of insulin targets in muscle cells. They demonstrate that a clear depiction of changes that occur during metabolic dysfunction requires systemic and combined analysis at different levels of regulation, including signaling pathways, transcription factors, and gene expression. Such analysis seems promising to explore yet undescribed regulatory mechanisms of glucose uptake by skeletal muscle and identify the key regulators as potential therapeutic targets.

The effect of insulin and kruppel like factor 10 on osteoblasts in the dental implant osseointegration in diabetes mellitus patients

Diabetes mellitus, metabolic disease, is characterized by chronic hyperglycemia. Patients with diabetes mellitus are susceptible to infection and therefore have a higher prevalence and progression rate of periodontal disease. We aimed to study the effect of insulin and kruppel like factor 10 (KLF10) on osteoblasts proliferation and differentiation, and expression of bone metabolism-related molecules and related signaling pathway molecules of AKT serine/threonine kinase 1 (AKT) and nuclear factor kappa B subunit 1 (NF-κB) through in vitro experiments, which can provide theoretical basis for the dental implant osseointegration in diabetic patients. The osteoblasts (hFOB 1.19 cells) were subdivided into KLF10 gene over expression group, KLF10 gene knockdown group, and KLF10 gene knockdown + insulin treatment group. CCK-8 and ELISA were, respectively, used for analysis of cell proliferation and differentiation. In vitro experiments were applied to detect the mRNA and protein expression of bone metabolism-related molecules, respectively. GSE178351 dataset and GSE156993 dataset were utilized to explore the expression of KLF10 in periodontitis. In osteoblasts, insulin treatment increased the expression of KLF10. Insulin and KLF10 could reduce the proliferation and differentiation of osteoblasts. Knockdown of KLF10 could increase the expression of bone metabolism-related molecules and activate AKT and NF-κB pathways, whereas insulin reversed this effect. KLF10 was up-regulated in both patients with periodontitis and type 2 diabetes mellitus with periodontitis. It is assumed that knockdown of KLF10 in insulin resistance may promote osteoblasts differentiation and dental implant osseointegration in diabetic patients.

Insulin resistance in ischemic stroke: Mechanisms and therapeutic approaches

The pathological condition of insulin resistance prevents the neuroprotective effects of insulin. Numerous studies have demonstrated that insulin resistance, as an independent risk factor for ischemic stroke, accelerates the formation of thrombosis and promotes the development of atherosclerosis, both of which are major mechanisms of ischemic stroke. Additionally, insulin resistance negatively affects the prognosis of patients with ischemic stroke regardless of whether the patient has diabetes, but the mechanisms are not well studied. We explored the association between insulin resistance and the primary mechanisms of brain injury in ischemic stroke (inflammation, oxidative stress, and neuronal damage), looking for potential causes of poor prognosis in patients with ischemic stroke due to insulin resistance. Furthermore, we summarize insulin resistance therapeutic approaches to propose new therapeutic directions for clinically improving prognosis in patients with ischemic stroke.

Targeting Small GTPases and Their Prenylation in Diabetes Mellitus

A fundamental role of pancreatic β-cells to maintain proper blood glucose level is controlled by the Ras superfamily of small GTPases that undergo post-translational modifications, including prenylation. This covalent attachment with either a farnesyl or a geranylgeranyl group controls their localization, activity, and protein–protein interactions. Small GTPases are critical in maintaining glucose homeostasis acting in the pancreas and metabolically active tissues such as skeletal muscles, liver, or adipocytes. Hyperglycemia-induced upregulation of small GTPases suggests that inhibition of these pathways deserves to be considered as a potential therapeutic approach in treating T2D. This Perspective presents how inhibition of various points in the mevalonate pathway might affect protein prenylation and functioning of diabetes-affected tissues and contribute to chronic inflammation involved in diabetes mellitus (T2D) development. We also demonstrate the currently available molecular tools to decipher the mechanisms linking the mevalonate pathway’s enzymes and GTPases with diabetes.

Genetic background and diet affect brown adipose gene coexpression networks associated with metabolic phenotypes

Adipose is a dynamic endocrine organ that is critical for regulating metabolism and is highly responsive to nutritional environment. Brown adipose tissue is an exciting potential therapeutic target; however, there are no systematic studies of gene-by-environment interactions affecting function of this organ. We leveraged a weighted gene coexpression network analysis to identify transcriptional networks in brown adipose tissue from LG/J and SM/J inbred mice fed high- or low-fat diets and correlate these networks with metabolic phenotypes. We identified eight primary gene network modules associated with variation in obesity and diabetes-related traits. Four modules were enriched for metabolically relevant processes such as immune and cytokine response, cell division, peroxisome functions, and organic molecule metabolic processes. The relative expression of genes in these modules is highly dependent on both genetic background and dietary environment. Genes in the immune/cytokine response and cell division modules are particularly highly expressed in high fat-fed SM/J mice, which show unique brown adipose-dependent remission of diabetes. The interconnectivity of genes in these modules is also heavily dependent on diet and strain, with most genes showing both higher expression and coexpression under the same context. We highlight several genes of interest, Col28a1, Cyp26b1, Bmp8b, and Ngef, that have distinct expression patterns among strain-by-diet contexts and fall under metabolic quantitative trait loci previously mapped in an F16 generation of an advanced intercross between LG/J and SM/J. Each of these genes have some connection to obesity and diabetes-related traits, but have not been studied in brown adipose tissue. Our results provide important insights into the relationship between brown adipose and systemic metabolism by being the first gene-by-environment study of brown adipose transcriptional networks.

Multi-dimensional Transcriptional Remodeling by Physiological Insulin In Vivo

Regulation of gene expression is an important aspect of insulin action but in vivo is intertwined with changing levels of glucose and counter-regulatory hormones. Here we demonstrate that under euglycemic clamp conditions, physiological levels of insulin regulate interrelated networks of more than 1,000 transcripts in muscle and liver. These include expected pathways related to glucose and lipid utilization, mitochondrial function, and autophagy, as well as unexpected pathways, such as chromatin remodeling, mRNA splicing, and Notch signaling. These acutely regulated pathways extend beyond those dysregulated in mice with chronic insulin deficiency or insulin resistance and involve a broad network of transcription factors. More than 150 non-coding RNAs were regulated by insulin, many of which also responded to fasting and refeeding. Pathway analysis and RNAi knockdown revealed a role for lncRNA Gm15441 in regulating fatty acid oxidation in hepatocytes. Altogether, these changes in coding and non-coding RNAs provide an integrated transcriptional network underlying the complexity of insulin action.

Insulin Resistance and Atherosclerosis: Implications for Insulin-Sensitizing Agents

Patients with type 2 diabetes mellitus (T2DM) are at high risk for macrovascular complications, which represent the major cause of mortality. Despite effective treatment of established cardiovascular (CV) risk factors (dyslipidemia, hypertension, procoagulant state), there remains a significant amount of unexplained CV risk. Insulin resistance is associated with a cluster of cardiometabolic risk factors known collectively as the insulin resistance (metabolic) syndrome (IRS). Considerable evidence, reviewed herein, suggests that insulin resistance and the IRS contribute to this unexplained CV risk in patients with T2DM. Accordingly, CV outcome trials with pioglitazone have demonstrated that this insulin-sensitizing thiazolidinedione reduces CV events in high-risk patients with T2DM. In this review the roles of insulin resistance and the IRS in the development of atherosclerotic CV disease and the impact of the insulin-sensitizing agents and of other antihyperglycemic medications on CV outcomes are discussed.

Effects of long-term feeding of rapeseed meal on skeletal muscle transcriptome, production efficiency and meat quality traits in Norwegian Landrace growing-finishing pigs

This study was performed to investigate the effects of dietary inclusion of 20% rapeseed meal (RSM) as an alternative to soybean meal (SBM) in a three-month feeding experiment with growing finishing pigs. Dietary alteration affected growth performance, several carcass traits and transcriptional responses in the skeletal muscle, but did not affect measured meat quality traits. In general, pigs fed the RSM test diet exhibited reduced growth performance compared to pigs on SBM control diet. Significant transcriptional changes in the skeletal muscle of growing pigs fed RSM diet were likely the consequence of an increased amount of fiber and higher polyunsaturated fatty acids, and presence of bioactive phytochemicals, such as glucosinolates. RNAseq pipeline using Tophat2-Cuffdiff identified 57 upregulated and 63 downregulated genes in RSM compared to SBM pigs. Significantly enriched among downregulated pathways was p53-mediated signalling involved in cellular proliferation, while activation of negative growth regulators (IER5, KLF10, BTG2, KLF11, RETREG1, PRUNE2) in RSM fed pigs provided further evidence for reduced proliferation and increased cellular death, in accordance with the observed reduction in performance traits. Upregulation of well-known metabolic controllers (PDK4, UCP3, ESRRG and ESRRB), involved in energy homeostasis (glucose and lipid metabolism, and mitochondrial function), suggested less available energy and nutrients in RSM pigs. Furthermore, several genes supported more pronounced proteolysis (ABTB1, OTUD1, PADI2, SPP1) and reduced protein synthesis (THBS1, HSF4, AP1S2) in RSM muscle tissue. In parallel, higher levels of NR4A3, PDK4 and FGF21, and a drop in adropin, ELOVL6 and CIDEC/FSP27 indicated increased lipolysis and fatty acid oxidation, reflective of lower dressing percentage. Finally, pigs exposed to RSM showed greater expression level of genes responsive to oxidative stress, indicated by upregulation of GPX1, GPX2, and TXNIP.

Heterogeneous Nuclear Ribonucleoprotein F Mediates Insulin Inhibition of Bcl2-Modifying Factor Expression and Tubulopathy in Diabetic Kidney

We investigated the molecular mechanism(s) by which insulin prevents Bcl2-modifying factor (Bmf)-induced renal proximal tubular cell (RPTC) apoptosis and loss in diabetic mice. Transgenic mice (Tg) mice specifically overexpressing human BMF in RPTCs and non-Tg littermates were studied at 10 to 20 weeks of age. Non-diabetic littermates, diabetic Akita mice +/− insulin implant, Akita Tg mice specifically overexpressing heterogeneous nuclear ribonucleoprotein F (hnRNP F) in their RPTCs and immortalized rat renal proximal tubular cells (IRPTCs) were also studied. BMF-Tg mice exhibited higher systolic blood pressure, urinary albumin/creatinine ratio, RPTC apoptosis and urinary RPTCs than non-Tg mice. Insulin treatment in Akita mice and Akita mice overexpressing hnRNP F suppressed Bmf expression and RPTC apoptosis. In hyperinsulinemic-euglycemic wild type mice, renal Bmf expression was down-regulated with up-regulation of hnRNP F. In vitro, insulin inhibited high glucose-stimulation of Bmf expression, predominantly via p44/42 mitogen-activated protein kinase (MAPK) signaling. Transfection of p44/42 MAPK or hnRNP F small interfering RNA (siRNA) prevented insulin inhibition of Bmf expression. HnRNP F inhibited Bmf transcription via hnRNP F-responsive element in the Bmf promoter. Our results demonstrate that hnRNP F suppression of Bmf transcription is an important mechanism by which insulin protects RPTCs from apoptosis in diabetes.

Skeletal muscle Nur77 and NOR1 insulin responsiveness is blunted in obesity and type 2 diabetes but improved after exercise training

Obesity and type 2 diabetes (T2DM) are characterized by a blunted metabolic response to insulin, and strongly manifests in skeletal muscle insulin resistance. The orphan nuclear receptors, Nur77 and NOR1, regulate insulin-stimulated nutrient metabolism where Nur77 and NOR1 gene expression is increased with acute aerobic exercise and acute insulin stimulation. Whether Nur77 or NOR1 are associated with the insulin-sensitizing effects of chronic aerobic exercise training has yet to be elucidated. Fourteen lean healthy controls (LHC), 12 obese (OB), and 10 T2DM individuals (T2DM) underwent hyperinsulinemic-euglycemic clamps with skeletal muscle biopsies. Muscle was analyzed for Nur77 and NOR1 gene and protein expression at basal and insulin-stimulated conditions. Furthermore, a subcohort of 18 participants (OB, n = 12; T2DM, n = 6) underwent a 12-week aerobic exercise intervention (85% HRmax , 60 min/day, 5 days/week). In response to insulin infusion, LHC increased protein expression of Nur77 (8.7 ± 3.2-fold) and NOR1 (3.6 ± 1.1-fold), whereas OB and T2DM remained unaffected. Clamp-derived glucose disposal rates correlated with Nur77 (r2  = 0.14) and NOR1 (r2  = 0.12) protein expression responses to insulin, whereas age (Nur77: r2  = 0.22; NOR1: r2  = 0.25) and BMI (Nur77: r2  = 0.22; NOR1: r2  = 0.42) showed inverse correlations, corroborating preclinical data. In the intervention cohort, exercise improved Nur77 protein expression in response to insulin (PRE: -1.2 ± 0.3%, POST: 6.2 ± 1.5%). Also, insulin treatment of primary human skeletal muscle cells increased Nur77 and NOR1 protein. These findings highlight the multifactorial nature of insulin resistance in human obesity and T2DM. Understanding the regulation of Nur77 and NOR1 in skeletal muscle and other insulin-sensitive tissues will create opportunities to advance therapies for T2DM.

Identification and characterization of differentially expressed genes in Type 2 Diabetes using in silico approach

Diabetes mellitus is clinically characterized by hyperglycemia. Though many studies have been done to understand the mechanism of Type 2 Diabetes (T2D), however, the complete network of diabetes and its associated disorders through polygenic involvement is still under debate. The present study designed to re-analyze publicly available T2D related microarray raw datasets present in GEO database and T2D genes information present in GWAS catalog for screening out differentially expressed genes (DEGs) and identify key hub genes associated with T2D. T2D related microarray data downloaded from Gene Expression Omnibus (GEO) database and re-analysis performed with in house R packages scripts for background correction, normalization and identification of DEGs in T2D. Also retrieved T2D related DEGs information from GWAS catalog. Both DEGs lists were grouped after removal of overlapping genes. These screened DEGs were utilized further for identification and characterization of key hub genes in T2D and its associated diseases using STRING, WebGestalt and Panther databases. Computational analysis reveal that out of 99 identified key hub gene candidates from 348 DEGs, only four genes (CCL2, ELMO1, VEGFA and TCF7L2) along with FOS playing key role in causing T2D and its associated disorders, like nephropathy, neuropathy, rheumatoid arthritis and cancer via p53 or Wnt signaling pathways. MIR-29, and MAZ_Q6 are identified potential target microRNA and TF along with probable drugs alprostadil, collagenase and dinoprostone for the key hub gene candidates. The results suggest that identified key DEGs may play promising roles in prevention of diabetes.

Anabolic and Pro-metabolic Functions of CREB-CRTC in Skeletal Muscle: Advantages and Obstacles for Type 2 Diabetes and Cancer Cachexia

cAMP is one of the earliest described mediators of hormone action in response to physiologic stress that allows acute stress responses and adaptation in every tissue. The classic role of cAMP signaling in metabolic tissues is to regulate nutrient partitioning. In response to acute stress, such as epinephrine released during strenuous exercise or fasting, intramuscular cAMP liberates glucose from glycogen and fatty acids from triglycerides. In the long-term, activation of Gs-coupled GPCRs stimulates muscle growth (hypertrophy) and metabolic adaptation through multiple pathways that culminate in a net increase of protein synthesis, mitochondrial biogenesis, and improved metabolic efficiency. This review focuses on regulation, function, and transcriptional targets of CREB (cAMP response element binding protein) and CRTCs (CREB regulated transcriptional coactivators) in skeletal muscle and the potential for targeting this pathway to sustain muscle mass and metabolic function in type 2 diabetes and cancer. Although the muscle-autonomous roles of these proteins might render them excellent targets for both conditions, pharmacologic targeting must be approached with caution. Gain of CREB-CRTC function is associated with excess liver glucose output in type 2 diabetes, and growing evidence implicates CREB-CRTC activation in proliferation and invasion of different types of cancer cells. We conclude that deeper investigation to identify skeletal muscle specific regulatory mechanisms that govern CREB-CRTC transcriptional activity is needed to safely take advantage of their potent effects to invigorate skeletal muscle to potentially improve health in people with type 2 diabetes and cancer.

New insights into oxidative stress and inflammation during diabetes mellitus-accelerated atherosclerosis

Oxidative stress and inflammation interact in the development of diabetic atherosclerosis. Intracellular hyperglycemia promotes production of mitochondrial reactive oxygen species (ROS), increased formation of intracellular advanced glycation end-products, activation of protein kinase C, and increased polyol pathway flux. ROS directly increase the expression of inflammatory and adhesion factors, formation of oxidized-low density lipoprotein, and insulin resistance. They activate the ubiquitin pathway, inhibit the activation of AMP-protein kinase and adiponectin, decrease endothelial nitric oxide synthase activity, all of which accelerate atherosclerosis. Changes in the composition of the gut microbiota and changes in microRNA expression that influence the regulation of target genes that occur in diabetes interact with increased ROS and inflammation to promote atherosclerosis. This review highlights the consequences of the sustained increase of ROS production and inflammation that influence the acceleration of atherosclerosis by diabetes. The potential contributions of changes in the gut microbiota and microRNA expression are discussed.

Transcriptional and Epigenetic Changes Influencing Skeletal Muscle Metabolism in Women With Polycystic Ovary Syndrome

CONTEXT

Insulin resistance in skeletal muscle is a major risk factor for the development of type 2 diabetes in women with polycystic ovary syndrome (PCOS). Despite this, the mechanisms underlying insulin resistance in PCOS are largely unknown.

OBJECTIVE

To investigate the genome-wide DNA methylation and gene expression patterns in skeletal muscle from women with PCOS and controls and relate them to phenotypic variations.

DESIGN/PARTICIPANTS

In a case-control study, skeletal muscle biopsies from women with PCOS (n = 17) and age-, weight-, and body mass index‒matched controls (n = 14) were analyzed by array-based DNA methylation and mRNA expression profiling.

RESULTS

Eighty-five unique transcripts were differentially expressed in muscle from women with PCOS vs controls, including DYRK1A, SYNPO2, SCP2, and NAMPT. Furthermore, women with PCOS had reduced expression of genes involved in immune system pathways. Two CpG sites showed differential DNA methylation after correction for multiple testing. However, an mRNA expression of ∼30% of the differentially expressed genes correlated with DNA methylation levels of CpG sites in or near the gene. Functional follow-up studies demonstrated that KLF10 is under transcriptional control of insulin, where insulin promotes glycogen accumulation in myotubes of human muscle cells. Testosterone downregulates the expression levels of COL1A1 and MAP2K6.

CONCLUSION

PCOS is associated with aberrant skeletal muscle gene expression with dysregulated pathways. Furthermore, we identified specific changes in muscle DNA methylation that may affect gene expression. This study showed that women with PCOS have epigenetic and transcriptional changes in skeletal muscle that, in part, can explain the metabolic abnormalities seen in these women.

Feature selection with the R package MXM

Feature (or variable) selection is the process of identifying the minimal set of features with the highest predictive performance on the target variable of interest. Numerous feature selection algorithms have been developed over the years, but only few have been implemented in R as a package. The R package MXM is such an example, which not only offers a variety of feature selection algorithms, but has unique features that make it advantageous over its competitors: a) it contains feature selection algorithms that can treat numerous types of target variables, including continuous, percentages, time to event (survival), binary, nominal, ordinal, clustered, counts, left censored, etc; b) it contains a variety of regression models to plug into the feature selection algorithms; c) it includes an algorithm for detecting multiple solutions (many sets of equivalent features); and d) it includes memory efficient algorithms for high volume data, data that cannot be loaded into R. In this paper we qualitatively compare MXM with other relevant packages and discuss its advantages and disadvantages. We also provide a demonstration of its algorithms using real high-dimensional data from various applications.

Feature selection with the R package MXM

Feature (or variable) selection is the process of identifying the minimal set of features with the highest predictive performance on the target variable of interest. Numerous feature selection algorithms have been developed over the years, but only few have been implemented in R and made publicly available R as packages while offering few options. The R package MXM offers a variety of feature selection algorithms, and has unique features that make it advantageous over its competitors: a) it contains feature selection algorithms that can treat numerous types of target variables, including continuous, percentages, time to event (survival), binary, nominal, ordinal, clustered, counts, left censored, etc; b) it contains a variety of regression models that can be plugged into the feature selection algorithms (for example with time to event data the user can choose among Cox, Weibull, log logistic or exponential regression); c) it includes an algorithm for detecting multiple solutions (many sets of statistically equivalent features, plain speaking, two features can carry statistically equivalent information when substituting one with the other does not effect the inference or the conclusions); and d) it includes memory efficient algorithms for high volume data, data that cannot be loaded into R (In a 16GB RAM terminal for example, R cannot directly load data of 16GB size. By utilizing the proper package, we load the data and then perform feature selection.). In this paper, we qualitatively compare MXM with other relevant feature selection packages and discuss its advantages and disadvantages. Further, we provide a demonstration of MXM's algorithms using real high-dimensional data from various applications.

Mitochondrial inefficiency in infants born to overweight African-American mothers

Background

Currently 20–35% of pregnant women are obese, posing a major health risk for mother and fetus. It is postulated that an abnormal maternal-fetal nutritional environment leads to adverse metabolic programming, resulting in altered substrate metabolism in the offspring and predisposing to risks of obesity and diabetes later in life. Data indicate that oocytes from overweight animals have abnormal mitochondria. We hypothesized that maternal obesity is associated with altered mitochondrial function in healthy neonatal offspring.

Methods

Overweight and obese (Body mass index, (BMI) ≥ 25 kg/m², n=14) and lean (BMI < 25 kg/m², n=8), African American pregnant women carrying male fetuses were recruited from the Barnes Jewish Hospital obstetric clinic. Maternal and infant data were extracted from medical records. Infants underwent body composition testing in the first days of life. Circumcision skin was collected for isolation of fibroblasts. Fibroblast cells were evaluated for mitochondrial function, metabolic gene expression, nutrient uptake and oxidative stress.

Results

Skin fibroblasts of infants born to overweight mothers had significantly higher mitochondrial respiration without a concurrent increase in ATP production, indicating mitochondrial inefficiency. These fibroblasts had higher levels of reactive oxygen species and evidence of oxidative stress. Evaluation of gene expression in offspring fibroblasts revealed altered expression of multiple genes involved in fatty acid and glucose metabolism and mitochondrial respiration in infants of overweight mothers.

Conclusion

This study demonstrates altered mitochondrial function and oxidative stress in skin fibroblasts of infants born to overweight mothers. Future studies are needed to determine the long-term impact of this finding on the metabolic health of these children.

KLF10 transcription factor regulates hepatic glucose metabolism in mice

AIM/HYPOTHESIS

Abnormal activation of hepatic gluconeogenesis leads to hyperglycaemia. However, the molecular mechanisms underlying dysregulated hepatic gluconeogenesis remain to be fully defined. Here, we explored the physiological role of Krüppel-like factor 10 (KLF10) in regulating hepatic glucose metabolism in mice.

METHODS

Hepatic KLF10 expression in wild-type C57BL/6J mice, the db/db mouse model of diabetes, the ob/ob mouse model of obesity and high-fat-diet-induced obese (DIO) mice was measured. Adenoviruses expressing Klf10 or Klf10-specific short-hairpin RNA were injected into wild-type C57BL/6J mice, db/db or DIO mice. Expression of gluconeogenic genes in the liver and blood glucose levels were measured. GTTs and pyruvate tolerance tests were performed. The molecular mechanism by which KLF10 regulates hepatic glucose metabolism was explored.

RESULTS

Hepatic KLF10 expression was regulated by nutritional status in wild-type mice and upregulated in diabetic, obese and DIO mice. Overexpression of KLF10 in primary hepatocytes increased the expression of gluconeogenic genes and cellular glucose output. C57BL/6J mice with KLF10 overexpression in the liver displayed increased blood glucose levels and impaired glucose tolerance. Conversely, hepatic KLF10 knockdown in db/db and DIO mice decreased blood glucose levels and improved glucose tolerance. Furthermore, luciferase reporter gene assay and chromatin immunoprecipitation analysis indicated that KLF10 activates Pgc-1α (also known as Ppargc1a) gene transcription via directly binding to its promoter region.

CONCLUSIONS/INTERPRETATION

KLF10 is an important regulator of hepatic glucose metabolism and modulation of KLF10 expression in the liver may be an attractive approach for the treatment of type 2 diabetes.

Insulin Inhibits Nrf2 Gene Expression via Heterogeneous Nuclear Ribonucleoprotein F/K in Diabetic Mice

Oxidative stress induces endogenous antioxidants via nuclear factor erythroid 2-related factor 2 (Nrf2), potentially preventing tissue injury. We investigated whether insulin affects renal Nrf2 expression in type 1 diabetes (T1D) and studied its underlying mechanism. Insulin normalized hyperglycemia, hypertension, oxidative stress, and renal injury; inhibited renal Nrf2 and angiotensinogen (Agt) gene expression; and upregulated heterogeneous nuclear ribonucleoprotein F and K (hnRNP F and hnRNP K) expression in Akita mice with T1D. In immortalized rat renal proximal tubular cells, insulin suppressed Nrf2 and Agt but stimulated hnRNP F and hnRNP K gene transcription in high glucose via p44/42 mitogen-activated protein kinase signaling. Transfection with small interfering RNAs of p44/42 MAPK, hnRNP F, or hnRNP K blocked insulin inhibition of Nrf2 gene transcription. Insulin curbed Nrf2 promoter activity via a specific DNA-responsive element that binds hnRNP F/K, and hnRNP F/K overexpression curtailed Nrf2 promoter activity. In hyperinsulinemic-euglycemic mice, renal Nrf2 and Agt expression was downregulated, whereas hnRNP F/K expression was upregulated. Thus, the beneficial actions of insulin in diabetic nephropathy appear to be mediated, in part, by suppressing renal Nrf2 and Agt gene transcription and preventing Nrf2 stimulation of Agt expression via hnRNP F/K. These findings identify hnRNP F/K and Nrf2 as potential therapeutic targets in diabetes.

Tissue Non-Specific Genes and Pathways Associated with Diabetes: An Expression Meta-Analysis

We performed expression studies to identify tissue non-specific genes and pathways of diabetes by meta-analysis. We searched curated datasets of the Gene Expression Omnibus (GEO) database and identified 13 and five expression studies of diabetes and insulin responses at various tissues, respectively. We tested differential gene expression by empirical Bayes-based linear method and investigated gene set expression association by knowledge-based enrichment analysis. Meta-analysis by different methods was applied to identify tissue non-specific genes and gene sets. We also proposed pathway mapping analysis to infer functions of the identified gene sets, and correlation and independent analysis to evaluate expression association profile of genes and gene sets between studies and tissues. Our analysis showed that PGRMC1 and HADH genes were significant over diabetes studies, while IRS1 and MPST genes were significant over insulin response studies, and joint analysis showed that HADH and MPST genes were significant over all combined data sets. The pathway analysis identified six significant gene sets over all studies. The KEGG pathway mapping indicated that the significant gene sets are related to diabetes pathogenesis. The results also presented that 12.8% and 59.0% pairwise studies had significantly correlated expression association for genes and gene sets, respectively; moreover, 12.8% pairwise studies had independent expression association for genes, but no studies were observed significantly different for expression association of gene sets. Our analysis indicated that there are both tissue specific and non-specific genes and pathways associated with diabetes pathogenesis. Compared to the gene expression, pathway association tends to be tissue non-specific, and a common pathway influencing diabetes development is activated through different genes at different tissues.

Insulin Downregulates the Transcriptional Coregulator CITED2, an Inhibitor of Proangiogenic Function in Endothelial Cells

In patients with atherosclerotic complications of diabetes, impaired neovascularization of ischemic tissue in the myocardium and lower limb limits the ability of these tissues to compensate for poor perfusion. We identified 10 novel insulin-regulated genes, among them Adm, Cited2, and Ctgf, which were downregulated in endothelial cells by insulin through FoxO1. CBP/p300-interacting transactivator with ED-rich tail 2 (CITED2), which was downregulated by insulin by up to 54%, is an important negative regulator of hypoxia-inducible factor (HIF) and impaired HIF signaling is a key mechanism underlying the impairment of angiogenesis in diabetes. Consistent with impairment of vascular insulin action, CITED2 was increased in cardiac endothelial cells from mice with diet-induced obesity and from db/db mice and was 3.8-fold higher in arterial tissue from patients with type 2 diabetes than control subjects without diabetes. CITED2 knockdown promoted endothelial tube formation and endothelial cell proliferation, whereas CITED2 overexpression impaired HIF activity in vitro. After femoral artery ligation, induction of an endothelial-specific HIF target gene in hind limb muscle was markedly upregulated in mice with endothelial cell deletion of CITED2, suggesting that CITED2 can limit HIF activity in vivo. We conclude that vascular insulin resistance in type 2 diabetes contributes to the upregulation of CITED2, which impairs HIF signaling and endothelial proangiogenic function.

Peripheral Blood Transcriptomic Signatures of Fasting Glucose and Insulin Concentrations

Genome-wide association studies (GWAS) have successfully identified genetic loci associated with glycemic traits. However, characterizing the functional significance of these loci has proven challenging. We sought to gain insights into the regulation of fasting insulin and fasting glucose through the use of gene expression microarray data from peripheral blood samples of participants without diabetes in the Framingham Heart Study (FHS) (n = 5,056), the Rotterdam Study (RS) (n = 723), and the InCHIANTI Study (Invecchiare in Chianti) (n = 595). Using a false discovery rate q <0.05, we identified three transcripts associated with fasting glucose and 433 transcripts associated with fasting insulin levels after adjusting for age, sex, technical covariates, and complete blood cell counts. Among the findings, circulating IGF2BP2 transcript levels were positively associated with fasting insulin in both the FHS and RS. Using 1000 Genomes-imputed genotype data, we identified 47,587 cis-expression quantitative trait loci (eQTL) and 6,695 trans-eQTL associated with the 433 significant insulin-associated transcripts. Of note, we identified a trans-eQTL (rs592423), where the A allele was associated with higher IGF2BP2 levels and with fasting insulin in an independent genetic meta-analysis comprised of 50,823 individuals. We conclude that integration of genomic and transcriptomic data implicate circulating IGF2BP2 mRNA levels associated with glucose and insulin homeostasis.

Transcriptome Analysis and Postprandial Expression of Amino Acid Transporter Genes in the Fast Muscles and Gut of Chinese Perch (Siniperca chuatsi)

The characterization of the expression and regulation of growth-related genes in the muscles of Chinese perch is of great interest to aquaculturists because of the commercial value of the species. The transcriptome annotation of the skeletal muscles is a crucial step in muscle growth-related gene analysis. In this study, we generated 52 504 230 reads of mRNA sequence data from the fast muscles of the Chinese perch by using Solexa/Illumina RNA-seq. Twenty-one amino acid transporter genes were annotated by searching protein and gene ontology databases, and postprandial changes in their transcript abundance were assayed after administering a single satiating meal to Chinese perch juveniles (body mass, approximately 100 g), following fasting for 1 week. The gut content of the Chinese perch increased significantly after 1 h and remained high for 6 h following the meal and emptied within 48-96 h. Expression of eight amino acid transporter genes was assayed in the fast muscles through quantitative real-time polymerase chain reaction at 0, 1, 3, 6, 12, 24, 48, and 96 h. Among the genes, five transporter transcripts were markedly up-regulated within 1 h of refeeding, indicating that they may be potential candidate genes involved in the rapid-response signaling system regulating fish myotomal muscle growth. These genes display coordinated regulation favoring the resumption of myogenesis responding to feeding.

Impact of glucose-lowering drugs on cardiovascular disease in type 2 diabetes

Type 2 diabetes mellitus (T2DM) is characterized by multiple pathophysiologic abnormalities. With time, multiple glucose-lowering medications are commonly required to reduce and maintain plasma glucose concentrations within the normal range. Type 2 diabetes mellitus individuals also are at a very high risk for microvascular complications and the incidence of heart attack and stroke is increased two- to three-fold compared with non-diabetic individuals. Therefore, when selecting medications to normalize glucose levels in T2DM patients, it is important that the agent not aggravate, and ideally even improve, cardiovascular risk factors (CVRFs) and reduce cardiovascular morbidity and mortality. In this review, we examine the effect of oral (metformin, sulfonylureas, meglitinides, thiazolidinediones, DPP4 inhibitors, SGLT2 inhibitors, and α-glucosidase inhibitors) and injectable (glucagon-like peptide-1 receptor agonists and insulin) glucose-lowering drugs on established CVRFs and long-term studies of cardiovascular outcomes. Firm evidence that in T2DM cardiovascular disease can be reversed or prevented by improving glycaemic control is still incomplete and must await large, long-term clinical trials in patients at low risk using modern treatment strategies, i.e., drug combinations designed to maximize HbA1c reduction while minimizing hypoglycaemia and excessive weight gain.

Transcriptomic identification of ADH1B as a novel candidate gene for obesity and insulin resistance in human adipose tissue in Mexican Americans from the Veterans Administration Genetic Epidemiology Study (VAGES)

Type 2 diabetes (T2D) is a complex metabolic disease that is more prevalent in ethnic groups such as Mexican Americans, and is strongly associated with the risk factors obesity and insulin resistance. The goal of this study was to perform whole genome gene expression profiling in adipose tissue to detect common patterns of gene regulation associated with obesity and insulin resistance. We used phenotypic and genotypic data from 308 Mexican American participants from the Veterans Administration Genetic Epidemiology Study (VAGES). Basal fasting RNA was extracted from adipose tissue biopsies from a subset of 75 unrelated individuals, and gene expression data generated on the Illumina BeadArray platform. The number of gene probes with significant expression above baseline was approximately 31,000. We performed multiple regression analysis of all probes with 15 metabolic traits. Adipose tissue had 3,012 genes significantly associated with the traits of interest (false discovery rate, FDR ≤ 0.05). The significance of gene expression changes was used to select 52 genes with significant (FDR ≤ 10(-4)) gene expression changes across multiple traits. Gene sets/Pathways analysis identified one gene, alcohol dehydrogenase 1B (ADH1B) that was significantly enriched (P < 10(-60)) as a prime candidate for involvement in multiple relevant metabolic pathways. Illumina BeadChip derived ADH1B expression data was consistent with quantitative real time PCR data. We observed significant inverse correlations with waist circumference (2.8 x 10(-9)), BMI (5.4 x 10(-6)), and fasting plasma insulin (P < 0.001). These findings are consistent with a central role for ADH1B in obesity and insulin resistance and provide evidence for a novel genetic regulatory mechanism for human metabolic diseases related to these traits.

Dicholine succinate, the neuronal insulin sensitizer, normalizes behavior, REM sleep, hippocampal pGSK3 beta and mRNAs of NMDA receptor subunits in mouse models of depression

Central insulin receptor-mediated signaling is attracting the growing attention of researchers because of rapidly accumulating evidence implicating it in the mechanisms of plasticity, stress response, and neuropsychiatric disorders including depression. Dicholine succinate (DS), a mitochondrial complex II substrate, was shown to enhance insulin-receptor mediated signaling in neurons and is regarded as a sensitizer of the neuronal insulin receptor. Compounds enhancing neuronal insulin receptor-mediated transmission exert an antidepressant-like effect in several pre-clinical paradigms of depression; similarly, such properties for DS were found with a stress-induced anhedonia model. Here, we additionally studied the effects of DS on several variables which were ameliorated by other insulin receptor sensitizers in mice. Pre-treatment with DS of chronically stressed C57BL6 mice rescued normal contextual fear conditioning, hippocampal gene expression of NMDA receptor subunit NR2A, the NR2A/NR2B ratio and increased REM sleep rebound after acute predation. In 18-month-old C57BL6 mice, a model of elderly depression, DS restored normal sucrose preference and activated the expression of neural plasticity factors in the hippocampus as shown by Illumina microarray. Finally, young naïve DS-treated C57BL6 mice had reduced depressive- and anxiety-like behaviors and, similarly to imipramine-treated mice, preserved hippocampal levels of the phosphorylated (inactive) form of GSK3 beta that was lowered by forced swimming in pharmacologically naïve animals. Thus, DS can ameliorate behavioral and molecular outcomes under a variety of stress- and depression-related conditions. This further highlights neuronal insulin signaling as a new factor of pathogenesis and a potential pharmacotherapy of affective pathologies.

Whole blood gene expression profiles in insulin resistant Latinos with the metabolic syndrome

Although insulin resistance in skeletal muscle is well-characterized, the role of circulating whole blood in the metabolic syndrome phenotype is not well understood. We set out to test the hypothesis that genes involved in inflammation, insulin signaling and mitochondrial function would be altered in expression in the whole blood of individuals with metabolic syndrome. We further wanted to examine whether similar relationships that we have found previously in skeletal muscle exist in peripheral whole blood cells. All subjects (n=184) were Latino descent from the Arizona Insulin Resistance registry. Subjects were classified based on the metabolic syndrome phenotype according to the National Cholesterol Education Program’s Adult Treatment Panel III. Of the 184 Latino subjects in the study, 74 were classified with the metabolic syndrome and 110 were without. Whole blood gene expression profiling was performed using the Agilent 4x44K Whole Human Genome Microarray. Whole blood microarray analysis identified 1,432 probes that were altered in expression ≥1.2 fold and P<0.05 after Benjamini-Hochberg in the metabolic syndrome subjects. KEGG pathway analysis revealed significant enrichment for pathways including ribosome, oxidative phosphorylation and MAPK signaling (all Benjamini-Hochberg P<0.05). Whole blood mRNA expression changes observed in the microarray data were confirmed by quantitative RT-PCR. Transcription factor binding motif enrichment analysis revealed E2F1, ELK1, NF-kappaB, STAT1 and STAT3 significantly enriched after Bonferroni correction (all P<0.05). The results of the present study demonstrate that whole blood is a useful tissue for studying the metabolic syndrome and its underlying insulin resistance although the relationship between blood and skeletal muscle differs.

An acetylation rheostat for the control of muscle energy homeostasis

In recent years, the role of acetylation has gained ground as an essential modulator of intermediary metabolism in skeletal muscle. Imbalance in energy homeostasis or chronic cellular stress, due to diet, aging, or disease, translate into alterations in the acetylation levels of key proteins which govern bioenergetics, cellular substrate use, and/or changes in mitochondrial content and function. For example, cellular stress induced by exercise or caloric restriction can alter the coordinated activity of acetyltransferases and deacetylases to increase mitochondrial biogenesis and function in order to adapt to low energetic levels. The natural duality of these enzymes, as metabolic sensors and effector proteins, has helped biologists to understand how the body can integrate seemingly distinct signaling pathways to control mitochondrial biogenesis, insulin sensitivity, glucose transport, reactive oxygen species handling, angiogenesis, and muscle satellite cell proliferation/differentiation. Our review will summarize the recent developments related to acetylation-dependent responses following metabolic stress in skeletal muscle.

Cited2, a transcriptional modulator protein, regulates metabolism in murine embryonic stem cells

CREB-binding protein (CBP)/p300 interacting transactivator with glutamic acid (Glu) and aspartic acid (Asp)-tail 2 (Cited2) was recently shown to be essential for gluconeogenesis in the adult mouse. The metabolic function of Cited2 in mouse embryonic stem cells (mESCs) remains elusive. In the current study, the metabolism of glucose was investigated in mESCs, which contained a deletion in the gene for Cited2 (Cited2(Δ/-)). Compared with its parental wild type counterpart, Cited2(Δ/-) ESCs have enhanced glycolysis, alternations in mitochondria morphology, reduced glucose oxidation, and decreased ATP content. Cited2 is recruited to the hexokinase 1 (HK1) gene promoter to regulate transcription of HK1, which coordinates glucose metabolism in wild type ESCs. Reduced glucose oxidation and enhanced glycolytic activity in Cited2(Δ/-) ESCs correlates with defective differentiation during hypoxia, which is reflected in an increased expression of pluripotency marker (Oct4) and epiblast marker (Fgf5) and decreased expression of lineage specification markers (T, Gata-6, and Cdx2). Knockdown of hypoxia inducible factor-1α in Cited2(Δ/-) ESCs re-initiates the expression of differentiation markers T and Gata-6. Taken together, a deletion of Cited2 in mESCs results in abnormal mitochondrial morphology and impaired glucose metabolism, which correlates with a defective cell fate decision.

Inflammatory cytokines and the risk of cardiovascular complications in type 2 diabetes

This study evaluates peripheral blood T lymphocyte expression of inflammatory and proinflammatory cytokines as well as T regulatory (Treg) (FOXP3+CD25+CD4+) cells in type 2 diabetes (T2DM). Participants included 40 T2DM and 30 healthy control subjects. Twenty-four patients had no complications while 16 were afflicted with coronary heart disease (CHD). Relative to healthy subjects, all T2DM patients showed a significant increase in expression of CD4+IFN-ϒ+, CD4+TNF-α+, and CD4+IL-8+ T cells (P < 0.001) as well as CD4+IL-6+, CD4+IL-1β+, and IL-17+ T cells (P < 0.05) while the ratios of Treg/Th1(CD4+IFN-ϒ+) and Treg/Th-17(CD4+IL-17+) cells were significantly decreased (P < 0.05 and P < 0.01). T2DM patients with CHD showed a significant increase in CD4+IFN-ϒ+, CD4+TNF-α+, and CD4+IL-17+ T cells and a significant decrease in Treg/Th1 and Treg/IL-17 cells compared to T2DM patients without CHD (P < 0.05). In CHD-afflicted T2DM, HbA1c correlated positively with CD4+IFN-ϒ+ T cells (P < 0.01), HDL correlated negatively with each of CD4+IL-8+ T cells and CD4+IL-17+ T cells (P < 0.05), and LDL correlated positively with CD4+IL-1β+ T cells (P < 0.05). Conclusion. This study shows that hyperglycemia and dyslipidemia correlate with increased inflammatory cytokine expression and suggests the involvement of T cells in the development of diabetes and its complications.

Genome-wide association of single-nucleotide polymorphisms with weight loss outcomes after Roux-en-Y gastric bypass surgery

CONTEXT

Roux-en-Y gastric bypass (RYGB) is among the most effective treatments for extreme obesity and obesity-related complications. However, despite its potential efficacy, many patients do not achieve and/or maintain sufficient weight loss.

OBJECTIVE

Our objective was to identify genetic factors underlying the variability in weight loss outcomes after RYGB surgery.

DESIGN

We conducted a genome-wide association study using a 2-stage phenotypic extreme study design.

SETTING

Patients were recruited from a comprehensive weight loss program at an integrated health system.

PATIENTS

Eighty-six obese (body mass index >35 kg/m(2)) patients who had the least percent excess body weight loss (%EBWL) and 89 patients who had the most %EBWL at 2 years after surgery were genotyped using Affymetrix version 6.0 single-nucleotide polymorphism (SNP) arrays. A second group from the same cohort consisting of 164 patients in the lower quartile of %EBWL and 169 from the upper quartile were selected for evaluation of candidate regions using custom SNP arrays.

INTERVENTION

We performed RYGB surgery.

MAIN OUTCOME MEASURES

We assessed %EBWL at 2 years after RYGB and SNPs.

RESULTS

We identified 111 SNPs in the first-stage analysis whose frequencies were significantly different between 2 phenotypic extremes of weight loss (allelic χ(2) test P < .0001). Linear regression of %EBWL at 2 years after surgery revealed 17 SNPs that approach P < .05 in the validation stage and cluster in or near several genes with potential biological relevance including PKHD1, HTR1A, NMBR, and IGF1R.

CONCLUSIONS

This is the first genome-wide association study of weight loss response to RYGB. Variation in weight loss outcomes after RYGB may be influenced by several common genetic variants.

Independent and combined effects of acute physiological hyperglycaemia and hyperinsulinaemia on metabolic gene expression in human skeletal muscle

Physiological hyperglycaemia and hyperinsulinaemia are strong modulators of gene expression, which underpins some of their well-known effects on insulin action and energy metabolism. The aim of the present study was to examine whether acute in vivo exposure of healthy humans to hyperinsulinaemia and hyperglycaemia have independent or additive effects on expression of key metabolic genes in skeletal muscle. On three randomized occasions, seven young subjects underwent a 4 h (i) hyperinsulinaemic (50 m-units·m−2·min−1) hyperglycaemic (10 mmol/l) clamp (HIHG), (ii) hyperglycaemic (10 mmol/l) euinsulinaemic (5 m-units·m−2·min−1) clamp (LIHG) and (iii) hyperinsulinaemic (50 m-units·m−2·min−1) euglycaemic (4.5 mmol/l) clamp (HING). Muscle biopsies were obtained before and after each clamp for the determination of expression of genes involved in energy metabolism, and phosphorylation of key insulin signalling proteins. Hyperinsulinaemia and hyperglycaemia exerted independent effects with similar direction of modulation on PI3KR1 (phosphatidylinositol 3-kinase, regulatory 1), LXRα (liver X receptor α), PDK4 (pyruvate dehydrogenase kinase 4) and FOXO1 (forkhead box O1A) and produced an additive effect on PI3KR1, the gene that encodes the p85α subunit of PI3K in human skeletal muscle. Acute hyperglycaemia itself altered the expression of genes involved in fatty acid transport and oxidation [fatty acid transporter (CD36), LCAD (long-chain acyl-CoA dehydrogenase) and FOXO1], and lipogenesis [LXRα, ChREBP (carbohydrate-responseelement-binding protein), ABCA1 (ATP-binding cassette transporter A1) and G6PD (glucose-6-phosphate dehydrogenase). Surperimposing hyperinsulinaemia on hyperglycaemia modulated a number of genes involved in insulin signalling, glucose metabolism and intracellular lipid accumulation and exerted an additive effect on PI3KR1. These may be early molecular events that precede the development of glucolipotoxicity and insulin resistance normally associated with more prolonged periods of hyperglycaemia and hyperinsulinaemia.

Recent progress on the role of ChREBP in glucose and lipid metabolism

Carbohydrate response element binding protein (ChREBP) is a transcription factor activated by glucose that is highly expressed in liver, pancreatic β-cells, brown and white adipose tissues, and muscle. We reported that hepatic suppression of the Chrebp gene improves hepatic steatosis, glucose intolerance, and obesity in genetically obese mice. Moreover, we have studied the role of ChREBP with special reference to feedforward and feedback looping in liver and pancreatic β-cells. Recently, several groups reported that (1) glucose activates ChREBP-α transactivity and in turn ChREBP-α induces ChREBP-β on both transcriptional and translational levels in adipose tissues, and (2) ChREBP regulates glucose transporter type 4 mRNA levels, which may affect glucose uptake in adipose tissues. Moreover, in adipose tissues of obese patients, Chrebpb mRNA levels were much lower than those in lean subjects, while the levels were much higher in liver of obese patients than those in lean subjects. These findings suggest that Chrebpb mRNA levels are different in various tissues and probably in the stages of diabetes mellitus. Herein, we review recent progress in the study of ChREBP with special references to (1) the mechanisms regulating ChREBP transactivity (posttranslational modifications, intramolecular glucose sensing module, feedforward mechanism, and the feedback loop between ChREBP and its target genes), and (2) the role of ChREBP in liver, pancreatic islets and adipose tissues. Understanding the role of ChREBP in each tissue will provide important insight into the pathogenesis of metabolic syndrome.

The Ups and Downs of Insulin Resistance and Type 2 Diabetes: Lessons from Genomic Analyses in Humans

We are in the midst of a worldwide epidemic of type 2 diabetes (T2D) and obesity. Understanding the mechanisms underlying these diseases is critical if we are to halt their progression and ultimately prevent their development. The advent and widespread implementation of microarray technology has allowed analysis of small samples of human skeletal muscle, adipose, liver, pancreas and blood. While patterns differ in each tissue, several dominant themes have emerged from these studies, including altered expression of genes indicating increased inflammation and altered lipid and mitochondrial oxidative metabolism and insulin signaling in patients with T2D, and in some cases, in those at risk for disease. Unraveling which changes in gene expression are primary, and which are secondary to an insulin resistant or diabetes metabolic milieu remains a scientific challenge but we are one step closer.

Multifaceted role of insulin-like growth factors and mammalian target of rapamycin in skeletal muscle

This review describes the current literature on the interaction between insulin-like growth factors, endocrine hormones, and branched-chain amino acids on muscle physiology in healthy young individuals and during select pathologic conditions. Emphasis is placed on the mechanism by which physical and hormonal signals are transduced at the cellular level to either grow or atrophy skeletal muscle. The key role of the mammalian target of rapamycin and its ability to respond to hypertrophic and atrophic signals informs our understanding how a combination of physical, nutritional, and pharmacologic therapies may be used in tandem to prevent or ameliorate reductions in muscle mass.

Transcriptomic profiles of skeletal muscle tissue following an euglycemic-hyperinsulinemic clamp in insulin-resistant obese subjects

Insulin resistance in skeletal muscle is an early phenomenon in the pathogenesis of type 2 diabetes. Muscle is mainly responsible for insulin-stimulated glucose clearance from the bloodstream. Thus, regulation of gene expression in muscle tissue may be involved in the pathogenesis of insulin resistance. The objective was to investigate gene expression and metabolic pathways alterations in skeletal muscle tissue following an euglycemic-hyperinsulinemic clamp in obese insulin-resistant subjects. We carried out a transcriptome comparison of skeletal muscle tissue before and after a 3-h euglycemic-hyperinsulinemic clamp following 8-week supplementation with n-3 polyunsaturated fatty acid (PUFA) (1.8 g/day) with or without a supplement of fish gelatin (FG) (25 % of daily protein intake) in 16 obese insulin-resistant subjects. Results indicate that approximately 5 % (1932) of expressed transcripts were significantly changed after the clamp in both n-3 PUFA and n-3 PUFA + FG supplementation periods. Of these differentially expressed transcripts, 1394 genes associated with enzymes, transcription and translation regulators, transporters, G protein-coupled receptors, cytokines, and ligand-dependent nuclear receptors were modified. Metabolic pathways that were significantly modified included liver X receptor/retinoid X receptors (RXR) activation, vitamin D receptor/RXR activation, interleukin (IL)-8, acute phase response, IL10, triggering receptor expressed on myeloid cells 1, peroxisome proliferator-activated receptor, G-beta/gamma and hepatocyte growth factor and IL6 signaling. Taken together, results suggest that mainly inflammatory and transcription factors are modified following clamp in obese insulin-resistant subjects. Overall, understanding the changes in metabolic pathways due to insulin may be a potential target for the management of insulin resistance.

A Potential Role for Pro-Inflammatory Cytokines in the Development of Insulin Resistance in Horses

Insulin resistance is a metabolic condition involving reduced sensitivity of insulin-sensitive tissues to insulin-induced glucose disposal, including adipose tissue, skeletal muscle, and liver. Insulin resistance occurs in overweight and obese horses, and may increase risk for the development of laminitis. The development of insulin resistance is thought to occur in response to increased production of pro-inflammatory cytokines by adipose tissue in obesity, that then have an inhibitory effect on insulin signaling pathways in multiple tissues. This article reviews current knowledge of the involvement of pro-inflammatory cytokines in the development of insulin resistance in horses and uses data from other species to provide context.

Understanding the mechanisms involved in the development of insulin resistance in horses should enable development of effective treatment and prevention strategies. Current knowledge of these mechanisms is based upon research in obese humans and rodents, in which there is evidence that the increased production of pro-inflammatory cytokines by adipose tissue negatively influences insulin signaling in insulin-responsive tissues. In horses, plasma concentrations of the cytokine, tumor necrosis factor-α, have been positively correlated with body fatness and insulin resistance, leading to the hypothesis that inflammation may reduce insulin sensitivity in horses. However, little evidence has documented a tissue site of production and a direct link between inflammation and induction of insulin resistance has not been established. Several mechanisms are reviewed in this article, including the potential for macrophage infiltration, hyperinsulinemia, hypoxia, and lipopolysaccharide to increase pro-inflammatory cytokine production by adipose tissue of obese horses. Clearly defining the role of cytokines in reduced insulin sensitivity of horses will be a very important step in determining how obesity and insulin resistance are related.

Function-based discovery of significant transcriptional temporal patterns in insulin stimulated muscle cells

Background

Insulin action on protein synthesis (translation of transcripts) and post-translational modifications, especially of those involving the reversible modifications such as phosphorylation of various signaling proteins, are extensively studied but insulin effect on transcription of genes, especially of transcriptional temporal patterns remains to be fully defined.

Methodology/Principal Findings

To identify significant transcriptional temporal patterns we utilized primary differentiated rat skeletal muscle myotubes which were treated with insulin and samples were collected every 20 min for 8 hours. Pooled samples at every hour were analyzed by gene array approach to measure transcript levels. The patterns of transcript levels were analyzed based on a novel method that integrates selection, clustering, and functional annotation to find the main temporal patterns associated to functional groups of differentially expressed genes. 326 genes were found to be differentially expressed in response to in vitro insulin administration in skeletal muscle myotubes. Approximately 20% of the genes that were differentially expressed were identified as belonging to the insulin signaling pathway. Characteristic transcriptional temporal patterns include: (a) a slow and gradual decrease in gene expression, (b) a gradual increase in gene expression reaching a peak at about 5 hours and then reaching a plateau or an initial decrease and other different variable pattern of increase in gene expression over time.

Conclusion/Significance

The new method allows identifying characteristic dynamic responses to insulin stimulus, common to a number of genes and associated to the same functional group. The results demonstrate that insulin treatment elicited different clusters of gene transcript profile supporting a temporal regulation of gene expression by insulin in skeletal muscle cells.