The placenta is of interest to stem cell biologists since it is rich in mesenchymal stromal cells (MSC) and consists of both fetal (amnion and chorionic membranes) and maternal (decidua) tissues. This is true of all mammalian species including the mouse and human.
Fetal derived MSC may have different biological properties from maternal MSC, given their different origin and anatomical location and such differences may have implications in the potential use of MSC as therapeutic agents. Since the placenta contains both fetal (extra-embryonic mesoderm-derived from the blastocyst) and maternal components, it was therefore hypothesized, that both fetal and maternal mesenchymal stromal cells can be isolated from the placenta depending on the anatomical location sourced. In addition, it was proposed that fetal and maternal MSC have different genetic characteristics and different functional capabilities.
Wild type C57BL/6 female mice and C57BL/6 male mice expressing GFP ubiquitously under control of the ubiquitin promoter (GFP+/+ UBI) were bred to produce GFP+/- offspring. Placentas were dissected at E15-E18 and flow sorted according to GFP+/CD45-/Sca1+ (fetal, MSC-like cells) or GFP-/CD45-/Sca1+ (maternal, MSC-like cells) expression. However, very few fetal and maternal cells could be sorted and expanded in culture. Thus, studies with mice proved difficult because of an inability to isolate sufficient viable fetal and maternal cells from these murine tissues for experimental purposes. Hence, the remainder of this project focused on MSC from human term gestational products.
A robust method was successfully established for isolating human fetal and maternal derived MSC. Genotyping and fluorescent in situ hybridisation (FISH) analyses confirmed the amnion and chorion as fetal derived sources. In culture; however, the chorionic population of fetal derived MSC was overgrown by maternal cells. This was not seen with the amnion MSC population and therefore the amnion was subsequently used as the primary fetal MSC source and decidua as the primary maternal MSC source.
The clonal ability, cell proliferative capacity, cell surface phenotype, mesodermal differentiation potential and immune suppressive capacity of human term amnion, chorion and decidua MSC populations were analysed. All three populations showed similar cell morphology, a cell surface phenotype characteristic of MSC and osteogenic and chondrogenic differentiation potential typical of MSC. However, amnion and chorion MSC showed less adipogenic differentiation capability than decidua MSC, indicating a difference in their functional mesodermal multipotency ability. Additionally, amnion and chorion MSC displayed a higher clonal capacity than decidua MSC, yet displayed a lower cell proliferation rate than decidua MSC. All three MSC populations could significantly suppress T cell alloproliferation in a mixed leucocyte reaction, with amnion and chorion MSC displaying higher immune suppressive capability than decidua MSC. Together, these findings provided evidence that the three MSC populations were not identical. Therefore, gene expression profiling studies were undertaken to explore differences between the amnion (fetal) and decidua (maternal) populations at the molecular level and with regard to functional pathways.
Amnion MSC were primarily involved in cell death and hematological system development and function pathways, and may be involved in the neonatal innate immune system. Decidua MSC were primarily involved in cell development, growth and proliferation, reflecting their tissue of origin. CD46, a complement regulatory protein and NIPA-like domain containing 3 (NIPAL3) were enriched in the amnion MSC population. The progesterone receptor and CD97 were enriched in the decidua MSC population, along with two novel zinc finger proteins, zinc finger MIZ-type containing 1 (ZIMZI) and zinc finger protein 318 (ZNF318) with no known function. Thus, these molecules may discriminate between fetal and maternal populations. Future studies are required to confirm these findings at the protein level.
It was also found that amnion MSC failed to proliferate as efficiently as their maternal counterpart. Therefore, maternal (decidua) MSC are currently the preferred MSC for large scale production for clinical applications. These findings provide further evidence that human term placenta contains both fetal and maternal MSC populations. The amnion MSC population is fetal in origin and is preferred to chorion as a source for isolating such cells. Decidua MSC are maternal in origin and therefore the decidua is the preferred source for isolating a population of maternal MSC. Both fetal and maternal MSC populations exhibited unique functional characteristics that are reflective of their tissue source.