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DEVELOPMENTAL PHYSIOLOGY AND PREGNANCY

Placental HIFs as markers of cerebral hypoxic distress in fetal mice

¹Department of Pediatrics, University of Erlangen, Erlangen, Germany; and ²Institute of Veterinary Physiology, and Zurich Center for Integrative Human Physiology, University of Zurich, Zurich, Switzerland

Submitted 25 January 2008 ; accepted in final form 29 September 2008

Reduced oxygen supply during the pre- and perinatal period often leads to acquired neonatal brain damage. So far, there are no reliable markers available to assess the hypoxic cerebral damage and the resulting prognosis during the immediate postnatal period. Thus we aimed to determine whether the hypoxia-inducible transcription factors (HIF-1 and HIF-2) and/or their target genes in the placenta represent reliable indicators of hypoxic distress of the developing brain during systemic hypoxia at the end of gestation. To this end, pregnant mice were exposed to systemic hypoxia (inspired O₂ fraction: 6%, 6 h) at gestational day 20. This hypoxic exposure significantly increased HIF-1 and HIF-2 protein levels in brain and placental tissue. Compared with normoxic controls, an increase of HIF-1-immunoreactive neurons and HIF-2-positive glial cells and vascular endothelial cells was observed in hypoxic cerebral cortex and hippocampus. In placenta, HIF-1 and HIF-2 were expressed in labyrinthine layer with increased staining intensity during hypoxia compared with normoxia. Significant upregulation of VEGF mRNA and protein in brain and placenta, as well as erythropoietin protein in placenta, indicated activity of the HIF system upon fetal hypoxia. Notably, hypoxia did not affect expression of the HIF target genes inducible nitric oxide synthase and GLUT-1. Taken together, at gestational day 20, systemic hypoxia led to upregulation of HIF- in mouse brain that was temporally paralleled in placenta, implying that -subunits of both HIF-1 and HIF-2 are indeed early markers of hypoxic distress in vivo. If our data reflect the situation in humans, analysis of the placenta will allow early identification of the hypoxic brain distress occurring near birth.

developing brain; mouse placenta; vascular endothelial growth factor; erythropoietin; inducible nitric oxide synthase