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Eight weeks of overfeeding alters substrate partitioning without affecting metabolic flexibility in men.

ABSTRACT: Impairments in metabolic flexibility (MF) and substrate handling are associated with metabolic syndrome. However, it is unknown whether metabolic inflexibility causes insulin resistance. We therefore measured MF and substrate handling before and after 8 weeks of overfeeding in initially healthy adults as a model of the early stages of insulin resistance.Twenty-nine healthy men (27±5 years old; body mass index 25.5±2.3?kg?m-2) were overfed by 40% above baseline energy requirements for 8 weeks and gained 7.6±2.1?kg of weight. Before and after overfeeding, energy expenditure, substrate oxidation and MF were measured in two ways: (a) during 1 day of eucaloric feeding in a whole-room indirect calorimeter and (b) during a two-step hyperinsulinemic-euglycemic clamp.Eight weeks of overfeeding decreased insulin sensitivity at low and high doses of insulin (P=0.001 and P=0.06, respectively). This was accompanied by decreases in the respiratory quotient (RQ) while sleeping (from 0.877±0.020 to 0.864±0.026; P=0.05) and at low insulin levels during the clamp (from 0.927±0.047 to 0.907±0.032; P=0.01). Overfeeding did not affect MF as measured during a clamp (P?0.17), but it tended to increase 24-h MF (awake RQ-sleep RQ) as measured by chamber by 0.010±0.028 (P=0.08). In terms of substrate oxidation, overfeeding increased protein oxidation by 13±23?g?day-1 (P=0.003) and tended to increase fat oxidation by 6±16?g?day-1 (P=0.07) but did not affect carbohydrate oxidation (P=0.64). Individuals with greater metabolic adaptation to overfeeding had higher carbohydrate oxidation rates (r=0.66, P=8 × 10-5) but not fat oxidation rates (P=0.09).The early stages of insulin resistance are accompanied by modest declines in the RQs during sleep and during a clamp, with no changes in fasting RQ or signs of metabolic inflexibility. Our data therefore suggest that metabolic inflexibility does not cause insulin resistance.

SUBMITTER: Peterson CM

PROVIDER: S-EPMC5461218 | biostudies-literature | 2017 Jun

REPOSITORIES: biostudies-literature

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Eight weeks of overfeeding alters substrate partitioning without affecting metabolic flexibility in men.

Peterson C M CM Zhang B B Johannsen D L DL Ravussin E E

International journal of obesity (2005) 20170306 6

<h4>Background/objective</h4>Impairments in metabolic flexibility (MF) and substrate handling are associated with metabolic syndrome. However, it is unknown whether metabolic inflexibility causes insulin resistance. We therefore measured MF and substrate handling before and after 8 weeks of overfeeding in initially healthy adults as a model of the early stages of insulin resistance.<h4>Subjects/methods</h4>Twenty-nine healthy men (27±5 years old; body mass index 25.5±2.3 kg m<sup>-2</sup>) were ...[more]

PMID: 28262678

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Project description:Cellular interactions between thymocytes and thymic stromal cells are critical for normal T cell development. Thymic epithelial cells (TECs) are important stromal niche cells that provide essential growth factors, cytokines, and present self-antigens to developing thymocytes. The identification of genes that mediate cellular crosstalk in the thymus is ongoing. One candidate gene, Adam17, encodes a metalloprotease that functions by cleaving the ectodomain of several transmembrane proteins and regulates various developmental processes. In conventional Adam17 knockout mice, a non-cell autonomous role for ADAM17 in adult T cell development was reported, which strongly suggested that expression of ADAM17 in TECs was required for normal T cell development. However, knockdown of Adam17 results in multisystem developmental defects and perinatal lethality, which has made study of the role of Adam17 in specific cell types difficult. Here, we examined T cell and thymic epithelial cell development using a conditional knockout approach.We generated an Adam17 conditional knockout mouse in which floxed Adam17 is deleted specifically in TECs by Cre recombinase under the control of the Foxn1 promoter. Normal T cell lineage choice and development through the canonical ?? T cell stages was observed. Interestingly, Adam17 deficiency in TECs resulted in reduced expression of the transcription factor Aire. However, no alterations in the patterns of TEC phenotypic marker expression and thymus morphology were noted.In contrast to expectation, our data clearly shows that absence of Adam17 in TECs is dispensable for normal T cell development. Differentiation of TECs is also unaffected by loss of Adam17 based on phenotypic markers. Surprisingly, we have uncovered a novel genetic link between Adam17and Aire expression in vivo. The cell type in which ADAM17 mediates its non-cell autonomous impact and the mechanisms by which it regulates intrathymic T cell development remain to be identified.

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Eight weeks of overfeeding alters substrate partitioning without affecting metabolic flexibility in men.

Publications

Eight weeks of overfeeding alters substrate partitioning without affecting metabolic flexibility in men.

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