Granulocyte-macrophage colony-stimulating factor (GM-CSF) regulates junctional zone trophoblast lineage commitment and thereby placental morphogenesis and function

Abstract

Objectives: Multiple trophoblast lineages differentiate during gestation and perform specialised roles which are essential for optimal placental function and fetal growth. GMCSF is expressed by the placenta and decidua and may modulate trophoblast differentiation. GM-CSF ablation results in placental dysmorphogenesis, characterised by an expanded junctional zone and a concomitant reduction in the labyrinth, associated with impaired fetal and postnatal growth and survival in mice (Biol Reprod 1999 60:251- 261). We aimed to determine the effect of GM-CSF deficiency on placental gene expression, trophoblast differentiation and fetal growth. Methods: GM-CSF null mutant (GM-/-) or WT mice were mated with males of the same genotype and killed on embryonic day (E) 13, 15 or 18. E13 placentae were subjected to microarray analyses (4 Affymetrix chips / genotype), while fetal and placental weights and placental structure were measured on E15 and E18. Transcription of genes selected as markers of trophoblast phenotypes or differentiation pathways in whole placenta or in the labyrinth (LZ) and junctional zones (JZ) of hemi-dissected E15 placenta was quantified by real-time RT-PCR. Results: Microarray analyses revealed differential expression of several genes in GM-/- whole placenta on E13. Of particular interest were those implicated in JZ development, including Ascl2 and Cdkn1c (P57Kip2), as well as members of the granzyme family, which have previously been localised to glycogen cells. Expression of the ligand specific a-subunit of the GM-CSF receptor (Csf2ra) was 6.5-fold greater in the JZ compared to the LZ and was further increased in the GM-/- JZ. Consistent with this, key inducers of differentiation of the ectoplacental cone pathway, Ascl2, P185, Rap250 and Hand1 were increased in the GM-/- JZ. GM-/- increased the abundance, proportion and size of connexin-31-positive glycogen cells. There was a trend to increased giant cell numbers and an increase in the ratio of P57Kip2 positive glycogen cells to P57Kip2 positive giant cells in the JZ. These changes were associated with an expanded JZ and a reduction in the area of the LZ on E15. Expression of several granzymes, which may be involved in glycogen cell invasion, were reduced in the GM-/- JZ, while expression of giant cell genes Pl1 and Plf were increased. Fetal weight was reduced in GM-/- litters on E15 but by E18 was comparable to wildtype. GM-/- reduced the fetal weight to placental weight ratio on E15 and E18. Conclusions: Our data suggest that GM-CSF is a pivotal regulator of placental functional maturation, particularly differentiation of glycogen cells and giant cells within the JZ. Aberrant gene expression in GM-/- mice may contribute to perturbed trophoblast differentiation and placental function and explain altered fetal and postnatal growth trajectory in these mice.