Introduction: How does maternal diet influence cell composition and growth in the placenta? This study explores normal cellular development in the mouse placenta and how this can change in the face of maternal protein restriction. We hypothesize that many of the changes are adaptive, sustaining fetal growth and maintaining maternal health.
Methods: Stereology, immunohistochemistry, and cell cycle analysis were used to look at normal placental development between embryonic day (E) 8.5 and 18.5. Ki67 and PHH3 immunohistochemistry were used to look at the timing of trophoblast cell populations undergoing endoreduplication. C57bl/6 mice were fed a 6% protein diet for two weeks prior to mating, continuing throughout gestation. Placentas between E13.5 and 18.5 were assessed using stereology, in-situ hybridization, and qPCR. ANCOVA and regression analysis was used to explain the effect of diet, maternal weight and placental changes on fetal growth trajectories.
Results: We found that normal placental growth occurs not just by hyperplasia, but also through extensive polyploidy and cell hypertrophy, unique to each trophoblast subtype. In response to feeding a low protein diet, this normal program was altered, and influenced by the sex of the conceptus. Male fetuses showed intrauterine growth restriction (IUGR) at E18.5, just before term, whereas female fetuses showed IUGR at E16.5. This difference was correlated with the size of the labyrinth layer of the placenta. Functional changes were implied based on up-regulation of nutrient transporter genes. The junctional zone was also affected, with a reduction in both glycogen trophoblast and spongiotrophoblast cells, and increased expression of Phlda2 and reduced expression of Egfr. Polyploidy, which results from endoreduplication, is a normal feature of trophoblast giant cells (TGC) but also spongiotrophoblast cells. Ploidy was increased in sinusoidal-TGCs and spongiotrophoblast cells, but not parietal-TGCs, in low protein placentas.
Conclusion: This work sheds light on the incredible adaptive power of the placenta.
Jay Devine– PhD Student, University of Calgary
Elizabeth Bering– MSc Student, Alberta Children's Hospital Research Institute, University of Calgary
Matthew Workentine– Biostatistician, University of Calgary Veterinary Medicine
Benedikt Hallgrimsson– Department Head, Cell Biology & Anatomy, University of Calgary
James Cross– Professor, Alberta Children's Hospital Research Institute