Effect of Maternal Diabetes on the Expression of Genes Regulating Fetal Brain Glucose Uptake

Diabetes alters adult brain glucose uptake and glucose transporter 1 gene expression. To investigate the effect of diabetes on genes regulating fetal brain glucose uptake, we examined the effect of moderate (blood glucose 10–16.7 mM, normoinsulinemia) and severe (blood glucose >16.8 mM, hypoinsulinemia) maternal diabetes on the expression of genes regulating fetal brain glucose uptake in the genetically nonobese diabetic mouse. In the moderately diabetic state, a 50% decline in fetal brain GLUT1 mRNA levels was associated with a 20% increase in the corresponding GLUT1 protein levels. Simultaneously, although fetal brain GLUT3 mRNA and protein levels were barely detectable, no change in hexokinase I enzyme mRNA, protein (115,000 and 100,000 M_r) or activity, was noted. In the severe form of maternal diabetes GLUT1 protein was unchanged, GLUT3 protein levels remained low, and a 2- to 3-fold increase in the lower molecular form of the hexokinase I protein (100,000 M_r) and enzyme activity occurred. These observations suggest that moderate and severe forms of maternal diabetes do not affect the fetal brain glucose transporter levels to a physiologically significant extent. The severe form of maternal diabetes, however, enhances 1.5- to 3-fold the expression and activity of hexokinase I. This enzyme mediates the rate-limiting step in brain glucose metabolism, namely the intracellular conversion of glucose to glucose–6-phosphate.