Mesenchymal stem cells in human placental chorionic villi reside in a vascular Niche

Abstract

he chorionic villi of human term placentae are a rich source of mesenchymal stem cells (PMSCs). The stem cell ‘‘niche’’ within the chorionic villi regulates how PMSCs participate in placental tissue gener-ation, maintenance and repair, but the anatomic location of the niche has not been defined. A number ofcell surface markers for phenotypic characterisation of mesenchymal stem cells (MSCs) were employedto identify the stem cell niche within the chorionic villi of first trimester and term human placenta. This included antibodies to pericyte cell surface markers STRO-1 and 3G5, which have been used to identify mesenchymal stem cells in other tissues, but have not been studied in placental tissues. PMSCs were isolated from term human placentae and shown to have stem cell properties by their ability to grow onuntreated plastic culture ware, capacity for forming clones (i.e. clonogenicity) and their capability to differentiate into adipocytes, chondrocytes and osteocytes. Western analysis confirmed that STRO-1 and3G5 are present in placental protein extracts and in PMSCs. Immunocy to chemistry revealed PMSCs were positive for MSC cell surface markers (STRO-1, 3G5, CD105, CD106, CD146, CD49a,a-SMA) and negativefor haematopoietic stem cell markers (CD117, CD34) and endothelial markers (CD34, vWF). Immuno-histochemistry with antibodies to MSC cell surface markers on first trimester and term tissues revealeda vascular niche for PMSCs. Dual-label immunofluorescence analysis was used to compare STRO-1antibody staining with that of endothelial cell marker vWF and found no significant overlap in staining.This indicated that some PMSCs have a pericyte-like phenotype. We propose that the vascular nicheharbours a pool of PMSCs that can give rise to committed progenitors for tissue maintenance and repair,and that PMSCs contribute to vessel maturation and stabilization