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Key Points: In lean individuals, 6 weeks of extended morning fasting increases the expression of genes involved in lipid turnover (ACADM) and insulin signalling (IRS2) in subcutaneous abdominal adipose tissue. In obese individuals, 6 weeks of extended morning fasting increases IRS2 expression in subcutaneous abdominal adipose tissue. The content and activation status of key proteins involved in insulin signalling and glucose transport (GLUT4, Akt1 and Akt2) were unaffected by extended morning fasting. Therefore, any observations of altered adipose tissue insulin sensitivity with extended morning fasting do not necessarily require changes in insulin signalling proximal to Akt. Insulin-stimulated adipose tissue glucose uptake rates are lower in obese versus lean individuals, but this difference is abolished when values are normalised to whole-body fat mass. This suggests a novel hypothesis which proposes that the reduced adipose glucose uptake in obesity is a physiological down-regulation to prevent excessive de novo lipogenesis., Abstract: This study assessed molecular responses of human subcutaneous abdominal adipose tissue (SCAT) to 6 weeks of morning fasting. Forty-nine healthy lean (n = 29) and obese (n = 20) adults provided SCAT biopsies before and after 6 weeks of morning fasting (FAST; 0 kcal until 12.00 h) or daily breakfast consumption (BFAST; ≥700 kcal before 11.00 h). Biopsies were analysed for mRNA levels of selected genes, and GLUT4 and Akt protein content. Basal and insulin-stimulated Akt activation and tissue glucose uptake rates were also determined. In lean individuals, lipid turnover and insulin signalling genes (ACADM and IRS2) were up-regulated with FAST versus BFAST (ACADM: 1.14 (95% CI: 0.97-1.30) versus 0.80 (95% CI: 0.64-0.96), P = 0.007; IRS2: 1.75 (95% CI: 1.33-2.16) versus 1.09 (95% CI: 0.67-1.51), P = 0.03, respectively). In obese individuals, no differential (FAST versus BFAST) expression was observed in genes involved in lipid turnover (all P > 0.1). GLUT4, Akt protein content and insulin-stimulated Akt phosphorylation were unaffected by FAST versus BFAST in both lean and obese cohorts (all P > 0.1). Lower insulin-stimulated glucose uptake rates in obese versus lean individuals were eradicated when normalised to whole-body fat mass (P = 0.416). We conclude that morning fasting up-regulates lipid turnover genes in SCAT of lean individuals. Secondly, altered SCAT insulin sensitivity with morning fasting is unlikely to be explained by signalling proximal to Akt. Finally, lower insulin-stimulated SCAT glucose uptake rates in obese individuals are proportional to whole-body fat mass, suggesting a compensatory down-regulation, presumably to prevent excessive de novo lipogenesis in adipose tissue. This trial was registered as ISRCTN31521726., (© 2017 The Authors. The Journal of Physiology published by John Wiley & Sons Ltd on behalf of The Physiological Society.)

Feeding profoundly affects metabolic responses to exercise in various tissues, but the effect of feeding status on human adipose tissue responses to exercise has never been studied. Ten healthy overweight men aged 26 ± 5 yr (mean ± SD) with a waist circumference of 105 ± 10 cm walked at 60% of maximum oxygen uptake under either fasted or fed conditions in a randomized, counterbalanced design. Feeding comprised 648 ± 115 kcal 2 h before exercise. Blood samples were collected at regular intervals to examine changes in metabolic parameters and adipokine concentrations. Adipose tissue samples were obtained at baseline and 1 h after exercise to examine changes in adipose tissue mRNA expression and secretion of selected adipokines ex vivo. Adipose tissue mRNA expression of pyruvate dehydrogenase kinase isozyme 4 ( PDK4 ), adipose triglyceride lipase, hormone-sensitive lipase ( HSL ), fatty acid translocase/CD36, glucose transporter type 4 ( GLUT4 ), and insulin receptor substrate 2 ( IRS2 ) in response to exercise were lower in fed compared with fasted conditions (all P ≤ 0.05). Postexercise adipose IRS2 protein was affected by feeding ( P ≤ 0.05), but Akt2, AMPK, IRS1, GLUT4, PDK4, and HSL protein levels were not different. Feeding status did not impact serum and ex vivo adipose secretion of IL-6, leptin, or adiponectin in response to exercise. This is the first study to show that feeding before acute exercise affects postexercise adipose tissue gene expression, and we propose that feeding is likely to blunt long-term adipose tissue adaptation to regular exercise., (Copyright © 2017 the American Physiological Society.)

We describe here the cloning, expression and characterisation of centaurin-alpha2 from a rat adipocyte cDNA library. The centaurin-alpha2 cDNA contains an open reading frame, which codes for a protein of 376 amino acids with predicted mass of 43.5 kDa. Centaurin-alpha2 shares 51-59% identity with centaurin-alpha1 proteins and has the same domain organisation, consisting of a predicted N-terminal ArfGAP domain followed by two successive pleckstrin homology domains. Despite the sequence similarity, there are a number of notable differences between the previously characterised centaurin-alpha1 proteins and the newly described centaurin-alpha2: (i) in vitro lipid binding experiments with centaurin-alpha2 do not reveal the same selectivity for phosphatidylinositol 3,4,5-trisphosphate over phosphatidylinositol 4,5-bisphosphate that has been shown for centaurin-alpha; (ii) unlike centaurin-alpha1 which is expressed mainly in the brain, centaurin-alpha2 has a broad tissue distribution, being particularly abundant in fat, heart and skeletal muscle; (iii) in contrast to centaurin-alpha1 which is found in both membrane and cytosolic fractions, endogenous centaurin-alpha2 is exclusively present in the dense membrane fractions of cell extracts, suggesting a constitutive membrane association. Insulin stimulation, which stimulates phosphatidylinositol 3,4,5-trisphosphate production, does not alter the subcellular distribution of centaurin-alpha2 between adipocyte membrane fractions. This observation is consistent with the lack of specificity of centaurin-alpha2 for phosphatidylinositol 3,4,5-trisphosphate over phosphatidylinositol 4,5-bisphosphate.