Abstract
Episodes of hypoxia and hypoxia/reoxygenation during foetal development have been associated with increased risk of neurodevelopmental conditions presenting in later life.The mechanism for this is not understood; however, several authors have suggested that the placenta plays an important role. Previously we found both placentas from a maternal hypoxia model and pre-eclamptic placentas from patients release factors lead to a loss of dendrite complexity in rodent neurons. Here to further explore the nature and origin of these secretions we exposed a simple in vitro model of the placental barrier, consisting of a barrier of human cytotrophoblasts, to hypoxia or hypoxia/reoxygenation. We then exposed cortical cultures from embryonic rat brains to the conditioned media (CM) from below these exposed barriers and examined changes in cell morphology, number, and receptor presentation.The barriers released factors that reduced dendrite and astrocyte process lengths, decreased GABAB1 staining, and increased astrocyte number. The changes in astrocytes required the presence of neurons and were prevented by inhibition of the SMAD pathway and by neutralising Bone Morphogenetic Proteins (BMPs) 2/4. Barriers exposed to hypoxia/reoxygenation also released factors that reduced dendrite lengths but increased GABAB1 staining. Both oxygen changes caused barriers to release factors that decreased GluN1, GABAAα1 staining and increased GluN3a staining. We find that hypoxia in particular will elicit the release of factors that increase astrocyte number and decrease process length as well as causing changes in the intensity of glutamate and GABA receptor staining. There is some evidence that BMPs are released and contribute to these changes.
Highlights
Abnormal blood flow in the placenta leading to acute hypoxia reperfusion has been linked to foetal brain damage [1]
We find that hypoxia in particular will elicit the release of factors that increase astrocyte number and decrease process length as well as causing changes in the intensity of glutamate and GABA receptor staining
In cultures that were exposed to hypoxic conditioned media (CM) there was a reduction in process length of both glial fibrillary acidic protein (GFAP)+ cells and neurons compared with control media below barriers at 21% oxygen (Figure 1)
Summary
Abnormal blood flow in the placenta leading to acute hypoxia reperfusion has been linked to foetal brain damage [1]. This acute reperfusion can occur in a variety of conditions including miscarriage, pre-eclampsia, and intrauterine growth restriction [2]. One important clinical example is early onset pre-eclampsia where there is deficient conversion of the spiral arteries and damage to the myometrial segments, leading to an intermittent perfusion of the placenta and a low-grade ischaemia–reperfusion injury. Pre-eclampsia with an onset before 37 weeks is a significant risk factor for cerebral palsy. A ‘direct’ effect of pre-eclampsia on foetal brain development seems likely [3].
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