Context Use of continuous glucose monitoring (CGM) is increasing for insulin-requiring patients with diabetes. Although data on glycemic profiles of healthy, nondiabetic individuals exist for older sensors, assessment of glycemic metrics with new-generation CGM devices is lacking. Objective To establish reference sensor glucose ranges in healthy, nondiabetic individuals across different age groups using a current generation CGM sensor. Design Multicenter, prospective study. Setting Twelve centers within the T1D Exchange Clinic Network. Patients or Participants Nonpregnant, healthy, nondiabetic children and adults (age ≥6 years) with nonobese body mass index. Intervention Each participant wore a blinded Dexcom G6 CGM, with once-daily calibration, for up to 10 days. Main Outcome Measures CGM metrics of mean glucose, hyperglycemia, hypoglycemia, and glycemic variability. Results A total of 153 participants (age 7 to 80 years) were included in the analyses. Mean average glucose was 98 to 99 mg/dL (5.4 to 5.5 mmol/L) for all age groups except those over 60 years, in whom mean average glucose was 104 mg/dL (5.8 mmol/L). The median time between 70 to 140 mg/dL (3.9 to 7.8 mmol/L) was 96% (interquartile range, 93 to 98). Mean within-individual coefficient of variation was 17 ± 3%. Median time spent with glucose levels >140 mg/dL was 2.1% (30 min/d), and median time spent with glucose levels <70 mg/dL (3.9 mmol/L) was 1.1% (15 min/d). Conclusion By assessing across age groups in a healthy, nondiabetic population, normative sensor glucose data have been derived and will be useful as a benchmark for future research studies.

. Regulation of muscle GLUT4 enhancer factor and myocyte enhancer factor 2 by AMP-activated protein kinase.

Two-component regulatory systems that utilize a multistep phosphorelay mechanism often involve a histidine-containing phosphotransfer (HPt) domain. These HPt domains serve an essential role as histidinephosphorylated protein intermediates during phosphoryl transfer from one response regulator domain to another. In Saccharomyces cerevisiae, the YPD1 protein facilitates phosphoryl transfer from a hybrid sensor kinase, SLN1, to two distinct response regulator proteins, SSK1 and SKN7. Because the phosphorylation state largely determines the functional state of response regulator proteins, we have carried out a comparative study of the phosphorylated lifetimes of the three response regulator domains associated with SLN1, SSK1, and SKN7 (R1, R2, and R3, respectively). The isolated regulatory domains exhibited phosphorylated lifetimes within the range previously observed for other response regulator domains (i.e., several minutes to several hours). However, in the presence of YPD1, we found that the half-life of phosphorylated SSK1-R2 was dramatically extended (almost 200-fold longer than in the absence of YPD1). This stabilization effect was specific for SSK1-R2 and was not observed for SLN1-R1 or SKN7-R3. Our findings suggest a mechanism by which SSK1 is maintained in its phosphorylated state under normal physiological conditions and demonstrate an unprecedented regulatory role for an HPt domain in a phosphorelay signaling system. Two-component signal transduction systems in prokaryotic and eukaryotic organisms regulate cellular responses to environmental changes (6, 11). In their simplest form, these regulatory pathways involve an autophosphorylating transmembrane histidine kinase and a cytoplasmic response regulator that is phosphorylated on an aspartic acid residue. Modified and expanded versions of two-component regulatory pathways requiring multiple phosphoryl transfer reactions between several phosphodonor and phosphoreceiver domains have also been identified (1,6,25,27). Some of the more complex phosphorelay systems that have been described thus far include a hybrid sensor kinase (that also contains a phosphoaspartate receiver domain), a histidine-containing phosphotransfer (HPt) protein, and one or more response regulator proteins (4,5,7,8,14,29,34). HPt domains serve a dual purpose as a phosphoreceiver and phosphodonor in order to shuttle phosphoryl groups between two or more response regulator domains. It has also been suggested that the presence of HPt domains and use of multistep phosphorelay systems provide for additional points of regulation of signaling pathways (1, 11).In most cases, response regulator proteins are activated upon phosphorylation. Hence, the intrinsic lifetime of the phosphorylated state of a response regulator is an important factor in determining the duration of the cellular response. Phosphorylated half-lives ranging from seconds for CheY and CheB (10, 37) to several hours for OmpR and Spo0F (13, 40) have been observed. In addition to the intrinsic phosphatase activity of the respon...

Overexpression of GLUT4 exclusively in skeletal muscle enhances insulin action and improves glucose homeostasis. Transgenic studies have discovered two regions on the GLUT4 promoter conserved across several species that are required for normal GLUT4 expression in skeletal muscle. These regions contain binding motifs for the myocyte enhancer factor 2 (MEF2) family and GLUT4 enhancer factor (GEF). A single bout of exercise increases both GLUT4 transcription and mRNA abundance; however, the molecular mechanisms mediating this response remain largely unexplored. Thus, the aim of this study was to determine whether a single, acute bout of exercise increased the DNA-binding activities of MEF2 and GEF in human skeletal muscle. Seven subjects performed 60 min of cycling at approximately 70% of VO2peak. After exercise, the DNA-binding activities of both the MEF2A/D heterodimer and GEF were increased (P<0.05). There was no change in nuclear MEF2D or GEF abundance after exercise, but nuclear MEF2A abundance was increased (P<0.05). These data demonstrate that exercise increases MEF2 and GEF DNA binding and imply that these transcription factors could be potential targets for modulating GLUT4 expression in human skeletal muscle.

Mechanistic target of rapamycin complex 1 (mTORC1), defined by the presence of Raptor, is an evolutionarily conserved and nutrient-sensitive regulator of cellular growth and other metabolic processes. To date, all known functions of Raptor involve its scaffolding mTOR kinase with substrate. Here we report that mTORC1-independent (‘free') Raptor negatively regulates hepatic Akt activity and lipogenesis. Free Raptor levels in liver decline with age and in obesity; restoration of free Raptor levels reduces liver triglyceride content, through reduced β-TrCP-mediated degradation of the Akt phosphatase, PHLPP2. Commensurately, forced PHLPP2 expression ameliorates hepatic steatosis in diet-induced obese mice. These data suggest that the balance of free and mTORC1-associated Raptor governs hepatic lipid accumulation, and uncover the potentially therapeutic role of PHLPP2 activators in non-alcoholic fatty liver disease.