Human placental multipotentmesenchymal stromal cells modulate trophoblast migration via Rap1 activation

Introduction: Little is known about the interaction between human placental multipotent mesenchymal stromal cell (hPMSC) and trophoblast. We hypothesize that hPMSCs produce hepatocyte growth factor (HGF) which may interact with trophoblasts and regulate their migration during placentation.

Methods: hPMSCs were isolated from term placentas and conditioned medium was collected after 2 days of culture in hypoxic (<1% O2) or control (20% O2) conditions. Selective agonist and inhibitor or siRNA for protein kinase A (PKA) or Rap1 were combined with Rap1-GTP pull down assays, flow cytometry, integrin β1 activation assays and adhesion and migration studies to investigate HGF signaling effects in trophoblasts. The hPMSC abundance and HGF level in preeclamptic placentas were compared with gestational age-matched controls.

Results: HGF was expressed by hPMSCs and was decreased in hypoxia. HGF induced cAMP production and Rap1 activation in trophoblasts, which in turn activated integrin β1. The HGF and PKA activator 6-Bnz-cAMP induced Rap1 activation with increased trophoblast adhesion and migration. The alterations were inhibited by PKA inhibitor H89 or Rap1 siRNA. HGF and cAMP expression were reduced in preeclamptic placentas. hPMSC number was decreased in preeclamptic placenta compared to controls (0.68 ± 0.1% vs. 1.32 ± 0.5%; P = 0.026). hPMSC conditioned medium enhanced trophoblast migration which was inhibited by c-Met blocking antibody, but migration was reduced by conditioned medium from hPMSC cultured in hypoxia.

Conclusions: hPMSCs secrete HGF and increase trophoblast cAMP production. The cAMP effector PKA modulates adhesion and migration of trophoblast via signaling to Rap1 and integrin β1.