CHARACTERISATION OF HUMAN FETAL CELL POPULATIONS AND THEIR IMPLICATIONS FOR SKELETAL REGENERATION

Abstract

Tissue loss, as a result of injury or disease, provides reduced quality of life for many and with an increasingly ageing population there is a greater requirement for skeletal repair strategies. An emerging attractive approach, tissue engineering, is based on the use of an appropriate source of progenitor cells, a scaffold conducive to cell attachment and maintenance of cell function and the delivery of appropriate growth factors. As a cell source, mesenchymal stem cells (MSCs) or marrow stromal cells derived from adult human tissues offer tremendous potential for tissue regeneration. However, to date, the plasticity, multipotentiality and characteristics of potential stem cells from fetal skeletal tissue remain poorly defined. We have examined, in preliminary studies, the multipotentiality and phenotypic properties of cell populations derived from human fetal femurs collected at 8–12 weeks post-conception in comparison to adult-derived mesenchymal stem cell populations including those isolated using STRO-1 immunoselection. Fetal cells were culture expanded from explants in basal media then maintained for periods of up to 28 days in monolayer cultures in adipogenic and osteogenic conditions. Cells were also maintained in chondrogenic conditions via the pellet culture method, maintained in established media conditions including TGF-â3, with cultures taken to 7, 14, 21 and 28 days. Adipocyte formation was confirmed by morphology: large amounts of lipid accumulation were observed by Oil Red O staining and aP2 (FABP-3) immunocytochemistry. Osteogenic differentiation was also confirmed by Type I Collagen immunocytochemistry. The growth of fetal cells on biomimetic scaffolds and their osteogenic activity was confirmed by confocal microscopy and Alkaline Phosphatase staining respectively. In chondrogenic conditions, chondrocytes were embedded within lacunae and extensive matrix deposition was observed using Alcian blue/Sirius red staining. The chondrogenic phenotype was confirmed by positive staining via SOX9 immunocytochemistry. Differentiation and proliferation were accelerated in fetal populations compared to adult-derived immunoselected MSCs. Plasticity of fetal cells has been demonstrated by the formation of large numbers of adipocytes within osteogenic populations. In summary we demonstrate the proliferative and multi-potential properties of fetal-derived chondrocytic cells in direct comparison to adult-derived MSCs including STRO-1 immunoselected populations. Given the demographic challenges and ethical issues surrounding current embryonic cell research, fetal cell populations may also provide a unique half-way model to address stem cell differentiation in comparison to adult cells. Elucidation of immunogenecity and selective differentiation will confirm the potential of these fetal cells as a unique alternate cell source for therapeutic approaches in the restoration of damaged or diseased tissue.