Fat and physical inactivity are the most evident factors in the pathogenesis of obesity, and fat quality seems to play a crucial role for measures of glucose homeostasis. However, the impact of dietary fat quality on brain function, behavior, and sleep is basically unknown. In this study, mice were fed a diet supplemented with either monounsaturated fatty acids (MUFAs) or saturated fatty acids (SFAs) and their impact on glucose homeostasis, locomotion, brain activity, and sleep behavior was evaluated. MUFAs and SFAs led to a significant increase in fat mass but only feeding of SFAs was accompanied by glucose intolerance in mice. Radiotelemetry revealed a significant decrease in cortical activity in SFA-mice whereas MUFAs even improved activity. SFAs decreased wakefulness and increased non-rapid eye movement sleep. An intracerebroventricular application of insulin promoted locomotor activity in MUFA-fed mice, whereas SFA-mice were resistant. In humans, SFA-enriched diet led to a decrease in hippocampal and cortical activity determined by functional magnetic resonance imaging techniques. Together, dietary intake of MUFAs promoted insulin action in the brain with its beneficial effects for cortical activity, locomotion, and sleep, whereas a comparable intake of SFAs acted as a negative modulator of brain activity in mice and humans.

During energy stress, AMP-activated protein kinase (AMPK) promotes glucose transport and glycolysis for ATP production, while it is thought to inhibit anabolic glycogen synthesis by suppressing the activity of glycogen synthase (GS) to maintain the energy balance in muscle. Paradoxically, chronic activation of AMPK causes an increase in glycogen accumulation in skeletal and cardiac muscles, which in some cases is associated with cardiac dysfunction. The aim of this study was to elucidate the molecular mechanism by which AMPK activation promotes muscle glycogen accumulation.

Long-chain fatty acids (LCFAs) contribute to metabolic homeostasis in part via gene regulation. This study's objective was to identify novel LCFA target genes in human skeletal muscle cells (myotubes).

KCNQ1 gene polymorphisms are associated with type 2 diabetes. This linkage appears to be mediated by altered beta-cell function. In an attempt to study underlying mechanisms, we examined the effect of four KCNQ1 single nucleotide polymorphisms (SNPs) on insulin secretion upon different stimuli.

The role of free fatty acid receptor 1 (FFAR1/GPR40) in glucose homeostasis is still incompletely understood. Small receptor agonists stimulating insulin secretion are undergoing investigation for the treatment of type 2 diabetes. Surprisingly, genome-wide association studies did not discover diabetes risk variants in FFAR1. We reevaluated the role of FFAR1 in insulin secretion using a specific agonist, FFAR1-knockout mice and human islets. Nondiabetic individuals were metabolically phenotyped and genotyped. In vitro experiments indicated that palmitate and a specific FFAR1 agonist, TUG-469, stimulate glucose-induced insulin secretion through FFAR1. The proapoptotic effect of chronic exposure of β-cells to palmitate was independent of FFAR1. TUG-469 was protective, whereas inhibition of FFAR1 promoted apoptosis. In accordance with the proapoptotic effect of palmitate, in vivo cross-sectional observations demonstrated a negative association between fasting free fatty acids (NEFAs) and insulin secretion. Because NEFAs stimulate secretion through FFAR1, we examined the interaction of genetic variation in FFAR1 with NEFA and insulin secretion. The inverse association of NEFA and secretion was modulated by rs1573611 and became steeper for carriers of the minor allele. In conclusion, FFAR1 agonists support β-cell function, but variation in FFAR1 influences NEFA effects on insulin secretion and therefore could affect therapeutic efficacy of FFAR1 agonists.

To elucidate the molecular mechanisms behind physical inactivity-induced insulin resistance in skeletal muscle, 12 young, healthy male subjects completed 7 days of bed rest with vastus lateralis muscle biopsies obtained before and after. In six of the subjects, muscle biopsies were taken from both legs before and after a 3-h hyperinsulinemic euglycemic clamp performed 3 h after a 45-min, one-legged exercise. Blood samples were obtained from one femoral artery and both femoral veins before and during the clamp. Glucose infusion rate and leg glucose extraction during the clamp were lower after than before bed rest. This bed rest-induced insulin resistance occurred together with reduced muscle GLUT4, hexokinase II, protein kinase B/Akt1, and Akt2 protein level, and a tendency for reduced 3-hydroxyacyl-CoA dehydrogenase activity. The ability of insulin to phosphorylate Akt and activate glycogen synthase (GS) was reduced with normal GS site 3 but abnormal GS site 2+2a phosphorylation after bed rest. Exercise enhanced insulin-stimulated leg glucose extraction both before and after bed rest, which was accompanied by higher GS activity in the prior-exercised leg than the rested leg. The present findings demonstrate that physical inactivity-induced insulin resistance in muscle is associated with lower content/activity of key proteins in glucose transport/phosphorylation and storage.

The incretin hormone glucagon-like peptide 1 (GLP-1) promotes glucose homeostasis and enhances β-cell function. GLP-1 receptor agonists (GLP-1 RAs) and dipeptidyl peptidase-4 (DPP-4) inhibitors, which inhibit the physiological inactivation of endogenous GLP-1, are used for the treatment of type 2 diabetes. Using the Metabochip, we identified three novel genetic loci with large effects (30-40%) on GLP-1-stimulated insulin secretion during hyperglycemic clamps in nondiabetic Caucasian individuals (TMEM114; CHST3 and CTRB1/2; n = 232; all P ≤ 8.8 × 10(-7)). rs7202877 near CTRB1/2, a known diabetes risk locus, also associated with an absolute 0.51 ± 0.16% (5.6 ± 1.7 mmol/mol) lower A1C response to DPP-4 inhibitor treatment in G-allele carriers, but there was no effect on GLP-1 RA treatment in type 2 diabetic patients (n = 527). Furthermore, in pancreatic tissue, we show that rs7202877 acts as expression quantitative trait locus for CTRB1 and CTRB2, encoding chymotrypsinogen, and increases fecal chymotrypsin activity in healthy carriers. Chymotrypsin is one of the most abundant digestive enzymes in the gut where it cleaves food proteins into smaller peptide fragments. Our data identify chymotrypsin in the regulation of the incretin pathway, development of diabetes, and response to DPP-4 inhibitor treatment.

The ADAMTS9 rs4607103 C allele is one of the few gene variants proposed to increase the risk of type 2 diabetes through an impairment of insulin sensitivity. We show that the variant is associated with increased expression of the secreted ADAMTS9 and decreased insulin sensitivity and signaling in human skeletal muscle. In line with this, mice lacking Adamts9 selectively in skeletal muscle have improved insulin sensitivity. The molecular link between ADAMTS9 and insulin signaling was characterized further in a model where ADAMTS9 was overexpressed in skeletal muscle. This selective overexpression resulted in decreased insulin signaling presumably mediated through alterations of the integrin β1 signaling pathway and disruption of the intracellular cytoskeletal organization. Furthermore, this led to impaired mitochondrial function in mouse muscle-an observation found to be of translational character because humans carrying the ADAMTS9 risk allele have decreased expression of mitochondrial markers. Finally, we found that the link between ADAMTS9 overexpression and impaired insulin signaling could be due to accumulation of harmful lipid intermediates. Our findings contribute to the understanding of the molecular mechanisms underlying insulin resistance and type 2 diabetes and point to inhibition of ADAMTS9 as a potential novel mode of treating insulin resistance.

Recent studies suggest that interleukin 6 (IL-6) is released from contracting skeletal muscles; however, the cellular origin, secretion kinetics, and signaling mechanisms regulating IL-6 secretion are unknown. To address these questions, we developed imaging methodology to study IL-6 in fixed mouse muscle fibers and in live animals in vivo. Using confocal imaging to visualize endogenous IL-6 protein in fixed muscle fibers, we found IL-6 in small vesicle structures distributed throughout the fibers under basal (resting) conditions. To determine the kinetics of IL-6 secretion, intact quadriceps muscles were transfected with enhanced green fluorescent protein (EGFP)-tagged IL-6 (IL-6-EGFP), and 5 days later anesthetized mice were imaged before and after muscle contractions in situ. Contractions decreased IL-6-EGFP-containing vesicles and protein by 62% (P < 0.05), occurring rapidly and progressively over 25 min of contraction. However, contraction-mediated IL-6-EGFP reduction was normal in muscle-specific AMP-activated protein kinase (AMPK) α2-inactive transgenic mice. In contrast, the AMPK activator AICAR decreased IL-6-EGFP vesicles, an effect that was inhibited in the transgenic mice. In conclusion, resting skeletal muscles contain IL-6-positive vesicles that are expressed throughout myofibers. Contractions stimulate the rapid reduction of IL-6 in myofibers, occurring through an AMPKα2-independent mechanism. This novel imaging methodology clearly establishes IL-6 as a contraction-stimulated myokine and can be used to characterize the secretion kinetics of other putative myokines.

The liver-secreted protein fetuin-A induces insulin resistance in animals, and circulating fetuin-A is elevated in insulin resistance and fatty liver in humans. We investigated whether plasma fetuin-A levels predict the incidence of type 2 diabetes in a large prospective, population-based study.

The objective of this work was to investigate whether impaired insulin secretion can be restored by lifestyle intervention in specific subphenotypes of prediabetes. We assigned 1,045 participants from the Prediabetes Lifestyle Intervention Study (PLIS) to six recently established prediabetes clusters. Insulin secretion was assessed by a C-peptide-based index derived from oral glucose tolerance tests and modeled from three time points during a 1-year intervention. We also analyzed the change of glycemia, insulin sensitivity, and liver fat. All prediabetes high-risk clusters (cluster 3, 5, and 6) had improved glycemic traits during the lifestyle intervention, whereas insulin secretion only increased in clusters 3 and 5 (P < 0.001); however, high liver fat in cluster 5 was associated with a failure to improve insulin secretion (Pinteraction < 0.001). Thus, interventions to reduce liver fat have the potential to improve insulin secretion in a defined subgroup of prediabetes.

Genome-wide association studies (GWAS) have found few common variants that influence fasting measures of insulin sensitivity. We hypothesized that a GWAS of an integrated assessment of fasting and dynamic measures of insulin sensitivity would detect novel common variants. We performed a GWAS of the modified Stumvoll Insulin Sensitivity Index (ISI) within the Meta-Analyses of Glucose and Insulin-Related Traits Consortium. Discovery for genetic association was performed in 16,753 individuals, and replication was attempted for the 23 most significant novel loci in 13,354 independent individuals. Association with ISI was tested in models adjusted for age, sex, and BMI and in a model analyzing the combined influence of the genotype effect adjusted for BMI and the interaction effect between the genotype and BMI on ISI (model 3). In model 3, three variants reached genome-wide significance: rs13422522 (NYAP2; P = 8.87 × 10(-11)), rs12454712 (BCL2; P = 2.7 × 10(-8)), and rs10506418 (FAM19A2; P = 1.9 × 10(-8)). The association at NYAP2 was eliminated by conditioning on the known IRS1 insulin sensitivity locus; the BCL2 and FAM19A2 associations were independent of known cardiometabolic loci. In conclusion, we identified two novel loci and replicated known variants associated with insulin sensitivity. Further studies are needed to clarify the causal variant and function at the BCL2 and FAM19A2 loci.

Understanding the physiological mechanisms by which common variants predispose to type 2 diabetes requires large studies with detailed measures of insulin secretion and sensitivity. Here we performed the largest genome-wide association study of first-phase insulin secretion, as measured by intravenous glucose tolerance tests, using up to 5,567 individuals without diabetes from 10 studies. We aimed to refine the mechanisms of 178 known associations between common variants and glycemic traits and identify new loci. Thirty type 2 diabetes or fasting glucose-raising alleles were associated with a measure of first-phase insulin secretion at P < 0.05 and provided new evidence, or the strongest evidence yet, that insulin secretion, intrinsic to the islet cells, is a key mechanism underlying the associations at the HNF1A, IGF2BP2, KCNQ1, HNF1B, VPS13C/C2CD4A, FAF1, PTPRD, AP3S2, KCNK16, MAEA, LPP, WFS1, and TMPRSS6 loci. The fasting glucose-raising allele near PDX1, a known key insulin transcription factor, was strongly associated with lower first-phase insulin secretion but has no evidence for an effect on type 2 diabetes risk. The diabetes risk allele at TCF7L2 was associated with a stronger effect on peak insulin response than on C-peptide-based insulin secretion rate, suggesting a possible additional role in hepatic insulin clearance or insulin processing. In summary, our study provides further insight into the mechanisms by which common genetic variation influences type 2 diabetes risk and glycemic traits.

Metabolomic discovery of biomarkers of type 2 diabetes (T2D) risk may reveal etiological pathways and help to identify individuals at risk for disease. We prospectively investigated the association between serum metabolites measured by targeted metabolomics and risk of T2D in the European Prospective Investigation into Cancer and Nutrition (EPIC)-Potsdam (27,548 adults) among all incident cases of T2D (n = 800, mean follow-up 7 years) and a randomly drawn subcohort (n = 2,282). Flow injection analysis tandem mass spectrometry was used to quantify 163 metabolites, including acylcarnitines, amino acids, hexose, and phospholipids, in baseline serum samples. Serum hexose; phenylalanine; and diacyl-phosphatidylcholines C32:1, C36:1, C38:3, and C40:5 were independently associated with increased risk of T2D and serum glycine; sphingomyelin C16:1; acyl-alkyl-phosphatidylcholines C34:3, C40:6, C42:5, C44:4, and C44:5; and lysophosphatidylcholine C18:2 with decreased risk. Variance of the metabolites was largely explained by two metabolite factors with opposing risk associations (factor 1 relative risk in extreme quintiles 0.31 [95% CI 0.21-0.44], factor 2 3.82 [2.64-5.52]). The metabolites significantly improved T2D prediction compared with established risk factors. They were further linked to insulin sensitivity and secretion in the Tübingen Family study and were partly replicated in the independent KORA (Cooperative Health Research in the Region of Augsburg) cohort. The data indicate that metabolic alterations, including sugar metabolites, amino acids, and choline-containing phospholipids, are associated early on with a higher risk of T2D.

Recent data suggested that sex hormone-binding globulin (SHBG) levels decrease when fat accumulates in the liver and that circulating SHBG may be causally involved in the pathogenesis of type 2 diabetes in humans. In the present study, we investigated mechanisms by which high SHBG may prevent development to diabetes.

Dysregulation of skeletal muscle metabolism influences whole-body insulin sensitivity and glucose homeostasis. We hypothesized that type 2 diabetes-associated alterations in the plasma metabolome directly contribute to skeletal muscle immunometabolism and the subsequent development of insulin resistance. To this end, we analyzed the plasma and skeletal muscle metabolite profile and identified glutamine as a key amino acid that correlates inversely with BMI and insulin resistance index (HOMA-IR) in men with normal glucose tolerance or type 2 diabetes. Using an in vitro model of human myotubes and an in vivo model of diet-induced obesity and insulin resistance in male mice, we provide evidence that glutamine levels directly influence the inflammatory response of skeletal muscle and regulate the expression of the adaptor protein GRB10, an inhibitor of insulin signaling. Moreover, we demonstrate that a systemic increase in glutamine levels in a mouse model of obesity improves insulin sensitivity and restores glucose homeostasis. We conclude that glutamine supplementation may represent a potential therapeutic strategy to prevent or delay the onset of insulin resistance in obesity by reducing inflammatory markers and promoting skeletal muscle insulin sensitivity.