Development of insulin-responsive glucose uptake and GLUT4 expression in differentiating human adipocyte precursor cells

Abstract

OBJECTIVE: In differentiating human preadipocytes glucose uptake in the presence of insulin is a prerequisite for lipid accumulation. The aim of this study was to characterize the insulin-regulated glucose transport system during and after differentiation. DESIGN AND METHODS: Human adipocyte precursor cells kept in primary culture were allowed to differentiate into fat cells under serum-free hormone-supplemented conditions. 2-Deoxy-glucose uptake was measured as a functional parameter of the glucose transport system, the amount of GLUT1 and GLUT4 protein was determined by Western blotting. RESULTS: In the undifferentiated state, cells did not increase 2-deoxy-glucose uptake in response to insulin. On day 16, when cells have acquired the adipocyte phenotype, there was a 3±4-fold stimulation of glucose transport by insulin compared to basal rates, whereas basal glucose uptake was dramatically diminished. Measurement of GLUT4 protein in cell extracts, showed a marked increase in the amount of this insulin-regulated transporter isoform during the differentiation period. On average, the amount of GLUT4 was 16.7-fold greater after than before differentiation. In contrast, the amount of GLUT1 protein decreased during differentiation to almost undetectable levels on day 16. When newly developed adipocytes were maintained in culture for another 14 d, the stimulation of glucose uptake and the amount of GLUT4 remained stable. CONCLUSION: Differentiating human fat cells in primary culture develops an insulin-responsive glucose transport system which exhibits a high stability, thereby providing a valuable model for long-term studies of glucose transport and GLUT4 expression in human adipocytes.

Apelin stimulates glucose uptake but not lipolysis in human adipose tissue ex vivo

“…C ATTANÉ and others 25 apelin had a modest effect on glucose uptake in human AT explants and isolated adipocytes. Insulin, at physiological concentrations, stimulated glucose transport in human AT explants twofold above basal, which is in agreement with previous studies performed on human isolated adipocytes (Iglesias-Osma et al 2005, Wanecq et al 2009) or differentiated cultured adipocytes (Hauner et al 1998). It should be noticed that conversion of glucose into fatty acids (de novo lipogenesis) especially in AT is much lower in humans compared to rodents (Zelewski & Swierczyń ski 1990).…”

Mature Adipocytes Inhibit In Vitro Differentiation of Human Preadipocytes via Angiotensin Type 1 Receptors

“…A possible clinical implication of our findings could well be that blockade of the RAS may increase the number of small, newly differentiated adipocytes, which are known to be more insulin-sensitive than older, larger adipocytes (43,44). This idea may indeed provide a novel explanation for the unexpected recent demonstration that RAS blockade may lower the risk for the development of type 2 diabetes (22,23).…”

Differential effects of IGF-I, IGF-II and insulin in human preadipocytes and adipocytes – Role of insulin and IGF-I receptors

“…Glucose uptake in preadipocytes tended to increase at 10 -9 M insulin and was significantly stimulated at 10 -8 -10 -7 M with an EC 50 value of 0.9x10 -9 M. As preadipocytes mainly express glucose transporter-1 (GLUT1) and not the insulin-regulated GLUT4 (Hauner et al, 1998;Bäck,Arnqvist, 2009), these effects of insulin in the preadipocytes could be due to relocation of GLUT1 in combination with enhanced metabolism of glucose. IGF-I or IGF-II stimulated glucose uptake with similar EC 50 values as insulin, 0.7x10 -9 M and 1.3x10 -9 M, respectively.…”