Effects of gestational hypoxia on mRNA levels of Glut3 and Glut4 transporters, hypoxia inducible factor-1 and thyroid hormone receptors in developing rat brain.

Alterations of brain development result from noxious intrauterine signals, as oxygen deprivation, which decrease glucose energetic yield. To verify the hypothesis that a defect of brain energetic adaptation is responsible for these alterations, we have studied the effects of gestational hypoxia (10% oxygen during the last 2 weeks of fetal life) on cerebral ontogenesis of glucose transporters which control the limiting step of glucose utilization by neurons. This study is realised in rats by quantification of whole brain Glut3 and Glut4 mRNA in 14- and 19-day-old embryos (E14, E19), newborn (P0) and 7 postnatal-day-old rats (P7) by using reverse transcription-polymerase chain reaction (RT-PCR) method. We have associated our study with the analysis of a transcriptional factor, the hypoxia inducible factor-1alpha (HIF-1alpha), known to control the expression of glucose transporter, and with a family of transcriptional factors, the thyroid hormone receptors (TR), regulating specific genes involved in brain development. The data show (1) for the first time the Glut4 and HIF-1alpha gene expression in fetal rat brain which are detected as soon as E14, (2) that gestational hypoxia induces an increase of mRNA transcript levels of Glut3, Glut4, TRalpha2, TRbeta1 and HIF-1alpha genes mainly or exclusively at E14, and (3) that the absence of response of Glut3 and HIF-1alpha at E19 in hypoxic vs. normoxic group could indicate an insufficient energetic adaptation at this period of development which could lead to the neural alterations observed postnatally.