INSULIN AND GLUCOSE MODULATE GLUCOSE-TRANSPORTER MESSENGER-RIBONUCLEIC-ACID EXPRESSION AND GLUCOSE-UPTAKE IN TROPHOBLASTS ISOLATED FROM FIRST-TRIMESTER CHORIONIC VILLI

OBJECTIVE: Our purpose was to determine the effects of insulin and glu cose on glucose transport and expression of GLUT1 glucose transporter messenger ribonucleic acid in first-trimester human trophoblast-like c ells. STUDY DESIGN: First-trimester human trophoblast-like cells were maintained as a continuous cell line. For 2[H-3]deoxy-D-glucose uptake and messenger ribonucleic acid studies the cells were incubated in th e presence or absence of insulin (10(-7) to 10(-11) mol/L) or D-glucos e (0 to 50 mmol/L) for 0 to 24 hours. Glucose transport was measured b y incubating cells with 0.1 mmol/L 2[H-3]deoxy-D-glucose for 5 minutes . Specific uptake was determined by incubating companion cultures with 10 mu mol/L cytochalasin B. The cells were then solubilized with sodi um hydroxide and the radioactivity counted. Data were expressed as nan omoles of 2[H-3]deoxy-D-glucose transported per milligram of protein p er 5 minutes and analyzed by one-way analysis of variance with post ho c testing by the method of Tukey. GLUT1 messenger ribonucleic acid was measured by Northern blotting of total ribonucleic acid samples hybri dized to a phosphorus 32-labeled complementary deoxyribonucleic encodi ng the rat GLUT1 glucose transporter. As a control for loading efficie ncy, blots were stripped and rehybridized to a 40-mer phosphorus 32-la beled beta-actin oligonucleotide probe. RESULTS: Insulin treatment res ulted in a dose-dependent increase in the transport of 2[H-3]deoxy-D-g lucose at 24 hours (p < 0.O01 at 10(-7) mol/L). This change was first detected at 12 hours of incubation. These data closely paralleled the insulin-induced increase in GLUT1 messenger ribonucleic acid seen in N orthern blots. In contrast to insulin, increasing concentrations of D- glucose did not change the transport of 2[H-3]deoxy-D-glucose However, when cells were incubated in low concentrations of D-glucose (0 or 1 mmol/L), an enhancement in the uptake of 2[H-3]deoxy-D-glucose (p < 0. 001) was observed. Kinetic studies indicated that D-glucose augmentati on of 2[H-3]deoxy-D-glucose uptake was significant at 9 hours (p < 0.0 5). The effects of D-glucose on GLUT1 messenger ribonucleic acid expre ssion paralleled the uptake of 2[H-3]deoxy-D-glucose, although the mod ulation of GLUT1 messenger ribonucleic acid levels by glucose was much less pronounced than in insulin-treated cells. CONCLUSION: Although i t has been assumed that the placenta has a limited role in influencing glucose transport to the fetus, our in vitro data demonstrate that bo th insulin and glucose can modulate glucose transport at the cellular level of the placental trophoblast. Thus maternal insulin and glycemic status may influence the expression of GLUT1, the major trophoblast g lucose transporter protein, therefore directly affecting first-trimest er placental glucose transport. These in vitro data may help explain t he association between maternal glucose abnormalities and impaired fet al development during the first trimester when placental GLUT1 messeng er ribonucleic acid expression is at its peak.