What are the paracrine contributions of MSCs to placental vascularisation?

Abstract

Introduction: In order to ensure successful fetal growth, the placenta is dependent on the processes of vasculogenesis and angiogenesis to meet the nutrient and oxygen demands of the growing fetus. Disturbances in these processes can lead to the development of aberrant vasculature, which has been implicated in pregnancies complicated by intrauterine growth restriction (IUGR). Mesenchymal stem cells (MSCs) are present in the placenta throughout pregnancy and found in a perivascular niche, suggesting their possible roles in facilitating placental vascularisation. Indeed, MSCs from other tissues have been shown to have pro-angiogenic properties through paracrine mechanisms. However, there has been no previous work looking at the differences in the paracrine secretions of pMSCs throughout gestation and the role of pMSCs in normal and pathological placental angiogenesis. Aims: To determine how placental MSCs may influence placental angiogenesis by paracrine mechanisms and determine whether these mechanisms are aberrant in IUGR placentae. Methods: MSCs were isolated from first trimester, term or IUGR placentae and phenotyped by multi-colour flow cytometry. Serum-free media conditioned by first trimester, term or IUGR pMSCs was used in conjunction with endothelial cell tube formation assays to determine how paracrine factors released from these cells may affect angiogenesis. Media conditioned by first trimester (n=5) or term (n=5) pMSCs was also subjected to cytokine array analysis. The addition of angiogenin or decorin to tube formation assays was used to determine whether individual cytokines identified to be of interest may affect placental angiogenesis. Results: Media conditioned by term pMSCs did not significantly affect mean tube length in comparison to control media (p= 0.61, n=5). However, media conditioned by first trimester pMSCs (n=5) or IUGR pMSCs (n=4) showed significant inhibition of mean tube length relative to media conditioned by term pMSCs (p=<0.001). First trimester and term pMSCs had different cytokine secretomes and these cytokines were involved in different pathways. The addition of 2-8ng/mL angiogenin (n=3) or 5-20ng/mL decorin (n=2) to angiogenesis tube formation assays did not significantly alter mean tube length. Discussion: The significant effect of media conditioned by first trimester, term or IUGR pMSCs on tube formation could arise as a result of differences in MSC cytokine secretomes. Dysregulation in the secretion of paracrine factors by IUGR pMSCs may contribute to the inadequate vascular development observed in these placentae.