DEVELOPMENT OF INSULIN-RESPONSIVE GLUCOSE-UPTAKE AND GLUT4 EXPRESSIONIN DIFFERENTIATING HUMAN ADIPOCYTE PRECURSOR CELLS

OBJECTIVE: in differentiating human preadipocytes glucose uptake in th e presence of insulin is a prerequisite for lipid accumulation. The ai m of this study was to characterize the insulin-regulated glucose tran sport system during and after differentiation. DESIGN AND METHODS: Hum an adipocyte precursor cells kept in primary culture were allowed to d ifferentiate into fat cells under serum-free hormone-supplemented cond itions. 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 in sulin. On day 16, when cells have acquired the adipocyte phenotype, th ere was a 3-4-fold stimulation of glucose transport by insulin compare d to basal rates, whereas basal glucose uptake was dramatically dimini shed. Measurement of GLUT4 protein in cell extracts, showed a marked i ncrease in the amount of this insulin-regulated transporter isoform du ring the differentiation period. On average, the amount of GLUT4 was 1 6.7-fold greater after than before differentiation. In contrast, the a mount of GLUT1 protein decreased during differentiation to almost unde tectable levels on day 16. When newly developed adipocytes were mainta ined in culture for another 14 d, the stimulation of glucose uptake an d the amount of GLUT4 remained stable. CONCLUSION: Differentiating hum an 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 e xpression in human adipocytes.