Impaired activation of AMP-Kinase and fatty acid oxidation by globular adiponectin in cultured human skeletal muscle of obese type 2 diabetics

Adiponectin is an adipocyte-derived hormone associated with antidiabetic actions. In rodent skeletal muscle, globular adiponectin (gAD) activates AMP-kinase (AMPK) and stimulates fatty acid oxidation effects mediated through the adiponectin receptors, AdipoR1 and AdipoR2. In the present study, we examined the mRNA expression of adiponectin receptors and the effects of gAD on AMPK activity and fatty acid oxidation in skeletal muscle myotubes from lean, obese, and obese type 2 diabetic subjects. Myotubes from all groups expressed approximately 4.5-fold more AdipoR1 mRNA than AdipoR2, and obese subjects tended to have higher AdipoR1 expression (P = 0.052). In lean myotubes, gAD activates AMPK[alpha]1 and -[alpha]2 by increasing Thr172 phosphorylation, an effect associated with increased acetyl-coenzyme A carboxylase (ACC[beta]) Ser221 phosphorylation and enhanced rates of fatty acid oxidation, effects similar to those observed after pharmacological AMPK activation by 5-aminoimidazole-4-carboxamide riboside. In obese myotubes, the activation of AMPK signaling by gAD at low concentrations (0.1 [mu]g/ml) was blunted, but higher concentrations (0.5 [mu]g/ml) stimulated AMPK[alpha]1 and -[alpha]2 activities, AMPK and ACC[beta] phosphorylation, and fatty acid oxidation. In obese type 2 diabetic myotubes, high concentrations of gAD stimulated AMPK[alpha]1 activity and AMPK phosphorylation; however, ACC[beta] phosphorylation and fatty acid oxidation were unaffected. Reduced activation of AMPK signaling and fatty acid oxidation in obese and obese diabetic myotubes was not associated with reduced protein expression of AMPK[alpha] and ACC[beta] or the expression and activity of the upstream AMPK kinase, LKB1. These data suggest that reduced activation of AMPK by gAD in obese and obese type 2 diabetic subjects is not caused by reduced adiponectin receptor expression but that aspects downstream of the receptor may inhibit AMPK signaling.

Chemerin is a novel adipokine associated with obesity and metabolic syndrome

Soluble protein hormones are key regulators of a number of metabolic processes, including food intake and insulin sensitivity. We have used a signal sequence trap to identify genes that encode secreted or membrane-bound proteins in Psammomys obesus, an animal model of obesity and type 2 diabetes (T2D). Using this signal sequence trap, we identified the chemokine chemerin as being a novel adipokine. Gene expression of chemerin and its receptor, chemokine-like receptor 1 (CMKLR1), was significantly higher in adipose tissue of obese and type 2 diabetic P. obesus compared with lean, normoglycemic P. obesus. Fractionation of P. obesus adipose tissue confirmed that chemerin was predominantly expressed in adipocytes, whereas CMKLR1 was expressed in both adipocytes and stromal-vascular cells of adipose tissue. In 3T3-L1 adipocytes, chemerin was markedly induced during differentiation, whereas CMKLR1 was down-regulated during differentiation. Serum chemerin levels were measured by ELISA in human plasma samples from 114 subjects with T2D and 142 normal glucose tolerant controls. Plasma chemerin levels were not significantly different between subjects with T2D and normal controls. However, in normal glucose tolerant subjects, plasma chemerin levels were significantly associated with body mass index, circulating triglycerides, and blood pressure. Here we report, for the first time, that chemerin is an adipokine, and circulating levels of chemerin are associated with several key aspects of metabolic syndrome.

The effect of calcium supplementation on bone density in premenarcheal females: a co-twin approach

The age and developmental stage at which calcium supplementation produces the greatest bone effects remain controversial. We tested the hypothesis that calcium supplementation may improve bone accrual in premenarcheal females. Fifty-one pairs of premenarcheal female twins (27 monozygotic and 24 dizygotic; mean ± SD age, 10.3 ± 1.5 yr) participated in a randomized, single-blind, placebo-controlled trial with one twin of each pair receiving a 1200-mg calcium carbonate (Caltrate) supplement. Areal bone mineral density (aBMD) was measured at baseline and 6, 12, 18 and 24 months. There were no within-pair differences in height, weight, or calcium intake at baseline. Calcium supplementation was associated (P < 0.05) with increased aBMD compared with placebo, adjusted for age, height, and weight at the following time points from baseline: total hip, 6 months (1.9%), 12 months (1.6%), and 18 months (2.4%); lumbar spine, 12 months (1.0%); femoral neck, 6 months (1.9%). Adjusted total body bone mineral content was higher in the calcium group at 6 months (2.0%), 12 months (2.5%), 18 months (4.6%), and 24 months (3.7%), respectively (all P < 0.001). Calcium supplementation was effective in increasing aBMD at regional sites over the first 12–18 months, but these gains were not maintained to 24 months.

The suppressor of cytokine signaling 3 inhibits leptin activation of AMP-Kinase in cultured skeletal muscle of obese humans

Context: Leptin is thought to regulate whole-body adiposity and insulin sensitivity, at least in part, by stimulating fatty acid metabolism via activation of AMP-kinase (AMPK) in skeletal muscle. Human obesity is associated with leptin resistance, and recent studies have demonstrated that hypothalamic expression of the suppressors of cytokine signaling 3 (SOCS3) regulates leptin sensitivity in rodents.

Objective: The objective of the study was to investigate the effects of leptin on fatty acid oxidation and AMPK signaling in primary myotubes derived from lean and obese skeletal muscle and evaluate the contribution of SOCS3 to leptin resistance and AMPK signaling in obese humans.

Results: We demonstrate that leptin stimulates AMPK activity and increases AMPK Thr172 and acetyl-CoA carboxylase-ß Ser222 phosphorylation and fatty acid oxidation in lean myotubes but that in obese subjects leptin-dependent AMPK signaling and fatty acid oxidation are suppressed. Reduced activation of AMPK was associated with elevated expression of IL-6 (~3.5-fold) and SOCS3 mRNA (~2.5-fold) in myotubes of obese subjects. Overexpression of SOCS3 via adenovirus-mediated infection in lean myotubes to a similar degree as observed in obese myotubes prevented leptin but not AICAR (5-amino-imidazole-4-carboxamide-1-ß-D-ribofuranoside) activation of AMPK signaling.

Conclusions: These data demonstrate that SOCS3 inhibits leptin activation of AMPK. These data suggest that this impairment of leptin signaling in skeletal muscle may contribute to the aberrant regulation of fatty acid metabolism observed in obesity and that pharmacological activation of AMPK may be an effective therapy to bypass SOCS3-mediated skeletal muscle leptin resistance for the treatment of obesity-related disorders.

Src homology 3-domain growth factor receptor-bound 2-like (endophilin) interacting protein 1, a novel neuronal protein that regulates energy balance

To identify genes involved in the central regulation of energy balance, we compared hypothalamic mRNA from lean and obese Psammomys obesus, a polygenic model of obesity, using differential display PCR. One mRNA transcript was observed to be elevated in obese, and obese diabetic, P. obesus compared with lean animals and was subsequently found to be increased 4-fold in the hypothalamus of lethal yellow agouti (Ay/a) mice, a murine model of obesity and diabetes. Intracerebroventricular infusion of antisense oligonucleotide targeted to this transcript selectively suppressed its hypothalamic mRNA levels and resulted in loss of body weight in both P. obesus and Sprague Dawley rats. Reductions in body weight were mediated by profoundly reduced food intake without a concomitant reduction in metabolic rate. Yeast two-hybrid screening, and confirmation in mammalian cells by bioluminescence resonance energy transfer analysis, demonstrated that the protein it encodes interacts with endophilins, mediators of synaptic vesicle recycling and receptor endocytosis in the brain. We therefore named this transcript Src homology 3-domain growth factor receptor-bound 2-like (endophilin) interacting protein 1 (SGIP1). SGIP1 encodes a large proline-rich protein that is expressed predominantly in the brain and is highly conserved between species. Together these data suggest that SGIP1 is an important and novel member of the group of neuronal molecules required for the regulation of energy homeostasis.

Adiponectin in umbillcal cord blood is inversely related to low-density lipoprotein cholesteril but not ethnicity

Context: Adiponectin is a recognized protective risk marker for cardiovascular disease in adults and is associated with an optimal lipid profile. The role of adiponectin at birth is not well understood, and its relationship with the neonatal lipid profile is unknown. Because ethnic disparities in cardiovascular risk have been attributed to low adiponectin and its associated low high-density lipoprotein cholesterol (HDL-C), investigation at birth may help determine the etiology of these risk patterns.

Objective: Our objective was to investigate the relationship between neonatal adiponectin and lipid profile at birth in two ethnic groups in cord blood.

Design, Setting, and Participants: Seventy-four healthy mothers and their newborns of South Asian and White European origin were studied in this cross-sectional study at St. Mary’s Hospital, Manchester, United Kingdom.

Main Outcome Measures: Serum adiponectin, total cholesterol, HDL-C, low-density lipoprotein cholesterol (LDL-C), and triglyceride levels were measured in umbilical venous blood at birth and in maternal blood collected at 28 wk gestation.

Results: Cord adiponectin was significantly inversely associated with cord LDL-C (r = –0.32; P = 0.005) but not HDL-C. In a multiple regression analysis, cord LDL-C remained the most significant association of cord adiponectin (ß = –0.13; P < 0.001). We did not find any significant ethnic differences in cord adiponectin or lipids with the exception of triglycerides, which were significantly lower in South Asian newborns (P < 0.05).

Conclusion: This is the first report of an inverse relationship between cord adiponectin and LDL-C at birth. In contrast to adult studies, we found no significant association between adiponectin and HDL-C in cord blood. Our results and the strong independent association between adiponectin and HDL-C observed in adult studies suggest a role for adiponectin in lipid metabolism. Ethnic differences in adiponectin may arise after birth.

Reduced Skeletal Muscle Uncoupling Protein-3 Content in Prediabetic Subjects and Type 2 Diabetic Patients: Restoration by Rosiglitazone Treatment

Context: The mitochondrial uncoupling protein-3 (UCP3) has been implicated in the protection of the mitochondrial matrix against lipid-induced mitochondrial damage. Recent evidence points toward mitochondrial aberrations as a major contributor to the development of insulin resistance and diabetes, and UCP3 is reduced in diabetes.
Objective: We compared skeletal muscle UCP3 protein levels in prediabetic subjects [i.e. impaired glucose tolerance (IGT)], diabetic patients, and healthy controls and examined whether rosiglitazone treatment was able to restore UCP3.
Patients, Design, Intervention: Ten middle-aged obese men with type 2 diabetes mellitus [age, 61.4 ± 3.1 yr; body mass index (BMI), 29.8 ± 2.9 kg/m2], nine IGT subjects (age, 59.0 ± 6.6 yr; BMI, 29.7 ± 3.0 kg/m2), and 10 age- and BMI-matched healthy controls (age, 57.3 ± 7.4 yr; BMI, 30.1 ± 3.9 kg/m2) participated in this study. After baseline comparisons, diabetic patients received rosiglitazone (2 x 4 mg/d) for 8 wk.
Main Outcome Measures: Muscle biopsies were sampled to determine UCP3 and mitochondrial protein (complex I–V) content.
Results: UCP3 protein content was significantly lower in prediabetic IGT subjects and in diabetic patients compared with healthy controls (39.0 ± 28.5, 47.2 ± 24.7, and 72.0 ± 23.7 arbitrary units, respectively; P < 0.05), whereas the levels of the mitochondrial protein complex I–V were similar between groups. Rosiglitazone treatment for 8 wk significantly increased insulin sensitivity and muscle UCP3 content (from 53.2 ± 29.9 to 66.3 ± 30.9 arbitrary units; P < 0.05).
Conclusion: We show that UCP3 protein content is reduced in prediabetic subjects and type 2 diabetic patients. Eight weeks of rosiglitazone treatment restores skeletal muscle UCP3 protein in diabetic patients.

Non-Schmid behaviour during secondary twinning in a polycrystalline magnesium alloy

The present work combines electron backscattering diffraction and Schmid analysis to investigate secondary twinning in the magnesium alloy Mg–3Al–1Zn. Inspection of the misorientations between the parent and ^{{1011} - {1012}} doubly twinned volumes reveals that there are four possible variants. One of these variants (the one that forms a misorientation with the matrix characterized by 38°^⟨1210⟩ ) is favoured much more than the others. This variant involves the activation of secondary twinning systems quite inconsistent with Schmid-type behaviour. For the secondary twin to grow significantly it must take on a shape enforced by the primary twin. This is non-optimal for strain compatibility. It is argued that the 38°^⟨1210⟩ variant occurs most because it provides the closest match between the primary and secondary twinning planes, thus minimizing the compatibility strain.

Characteristics of the contraction twins formed close to the fracture surface in Mg-3A1-1Zn alloy deformed in tension

Characteristics of the “contraction” twins, formed close to the fracture surface in Mg–3Al–1Zn alloy deformed in tension approximately perpendicular to the grain c-axes, are investigated using transmission electron microscopy. The grain c-axis contractions were largely accommodated by {1011}-{1012} source double-twins in a variant characterized by 38° ⟨1210⟩ source twin/matrix misorientation in conjunction with dislocation slip. A possible interpretation of the observed preference for this variant formation is given and some crystal plasticity modelling is performed to elucidate the matter.

Identification and rationalization of secondary twin variants in a magnesium alloy

The present work combines electron backscatter diffraction, transmission electron microscopy and Schmid analysis to investigate secondary twinning in the magnesium alloy Mg-3AI-1Zn. Inspection of the misorientations between the parent matrix and {1011} - {1012} doubly twinned volumes reveals that there are four possible variants. One of these variants characterized by 38°< 1210 > misorientation with the matrix is favoured much more than the others. This variant involves activation of the secondary twinning systems that are quite inconsistent with the Schmid-type behaviour. For the secondary twin to grow significantly it must take on a shape enforced by the primary twin, however, this is not optimal for strain compatibility. It is argued that the 38° < 1210 > variant occurs most frequently because it provides the closest match between the primary and secondaty twinning planes, thus minimizing the compatibility strain. This conjecture is confirmed by the simulations of twin activity m ellipsoidal grains performed using the visco-plastic self-consistent crystal plasticity model.

Sex difference in the suppressive effect of cortisol on pulsatile secretion of luteinizing hormone in sheep

We tested the hypothesis that there are sex differences in the inhibitory effect of cortisol on pulsatile LH secretion and pituitary responsiveness to GnRH in gonadectomized sheep. In experiment 1, pulsatile LH secretion was examined in gonadectomized ewes and rams infused with either saline, a low (250 µg/kg·h) or a high (500 µg/kg·h) dose of cortisol for 30 h. In experiment 2, direct pituitary actions of cortisol were assessed by monitoring LH pulse amplitude in response to exogenous GnRH in hypothalamo-pituitary disconnected ewes and rams infused with the low dose of cortisol. In experiment 1, the mean (±SEM) plasma LH concentration was (P < 0.05) reduced significantly during cortisol infusion in both sexes, but the effect was greater in rams. In ewes, LH pulse amplitude and frequency were reduced (P < 0.05) at the high, but not the low, cortisol dose, whereas total LH output (LH pulse amplitude multiplied by frequency) was reduced (P < 0.05) at both doses. In rams, LH pulse frequency and amplitude and total LH output were (P < 0.05) reduced significantly at both cortisol doses. In experiment 2, plasma LH concentration and pulse amplitude in response to exogenous GnRH were not affected by infusion of cortisol in either sex. We conclude that gonadectomized rams are more sensitive than gonadectomized ewes to the effects of cortisol to inhibit LH secretion and that sex differences exist in the specific actions of cortisol on LH pulses. The results of experiment 2 suggest that intact hypothalamic input to the pituitary is necessary for cortisol to inhibit pituitary responsiveness to GnRH.

Activation of the hypothalamo-pituitary-adrenal axis by isolation and restraint stress during lactation in ewes : effect of the presence of the lamb and suckling

We investigated the effect of the presence and absence of lambs and suckling by lambs to attenuate activation of the hypothalamo-pituitary-adrenal (HPA) axis to isolation and restraint stress in lactating sheep. In experiment 1, blood samples were collected every 10 min from nonlactating (n = 5) and lactating (n = 5) ewes for 4 h before and during stress. In experiment 2, ewes (n = 6) were allocated to 1) nonlactating, 2) lactating with lambs absent, 3) lactating with lambs present but unable to suckle, and 4) lactating with lambs present and able to suckle. Blood samples were collected over 8 h with no stress (control day) and for 4 h before and 4 h during stress (stress day). In experiment 1, the mean (±SEM) cortisol concentrations increased significantly (P < 0.05) in nonlactating ewes during stress but did not change in lactating ewes. In experiment 2, cortisol did not vary on the control day or pretreatment of the stress day but increased (P < 0.05) during stress in all groups except lactating ewes with lambs present and able to suckle. The greatest cortisol response occurred in nonlactating ewes followed by lactating ewes with lambs absent and lactating ewes with lambs present but unable to suckle. During stress, the ACTH concentrations increased (P < 0.05) in nonlactating ewes and lactating ewes with lambs absent but not in lactating ewes with lambs present. We conclude that the activity of the HPA axis during isolation and restraint is reduced in lactating ewes and that the presence of lambs increases this level of attenuation.

Chemerin is associated with metabolic syndrome phenotypes in a Mexican-American population

Context: Chemerin is a novel adipokine previously associated with metabolic syndrome phenotypes in a small sample of subjects from Mauritius. Objective: The aim of the study was to determine whether plasma chemerin levels were associated with metabolic syndrome phenotypes in a larger sample from a second, unrelated human population. Design, Setting, Patients, and Intervention: Plasma samples were obtained from the San Antonio Family Heart Study (SAFHS), a large family-based genetic epidemiological study including 1431 Mexican-American individuals. Individuals were randomly sampled without regard to phenotype or disease status. This sample is well-characterized for a variety of phenotypes related to the metabolic syndrome. Main Outcomes: Plasma chemerin levels were measured by sandwich ELISA. Linear regression and correlation analyses were used to determine associations between plasma chemerin levels and metabolic syndrome phenotypes. Results: Circulating chemerin levels were significantly higher in nondiabetic subjects with body mass index (BMI) greater than 30 kg/m2 compared with those with a BMI below 25 kg/m2 (P < 0.0001). Plasma chemerin levels were significantly associated with metabolic syndrome-related parameters, including BMI (P < 0.0001), fasting serum insulin (P < 0.0001), triglycerides (P < 0.0001), and high-density lipoprotein cholesterol (P = 0.00014), independent of age and sex in nondiabetic subjects. Conclusion: Circulating chemerin levels were associated with metabolic syndrome phenotypes in a second, unrelated human population. This replicated result using a large human sample suggests that chemerin may be involved in the development of the metabolic syndrome.