Mesenchymal stem cells (MSCs) have been isolated from different tissues/organs, but it is not clear whether they possess distinct biological properties. We have previously characterized MSCs from the adult human synovial membrane (SM), which can differentiate at the single cell level to cartilage, bone, adipocytes, and skeletal muscle [1-3]. We have also reported that cells isolated from the adult human periosteum (P) are chondrogenic in vitro . In the present work, we show that expanded periosteal cells are multipotential. We then compare the chondrogenic and osteogenic potentials of P-MSCs with those of SM-MSCs.
MSC populations were enzymatically released from the SM and periosteum of four adult human donors. To test multipotency, P-MSCs were subjected to in vitro differentiation assays or injected into regenerating tibialis anterior muscles of nude mice. In vitro chondrogenesis was tested in micromass culture in the presence of transforming growth factor beta in a chemically defined medium and assessed by histochemistry for cartilage proteoglycans and by quantitative RT-PCR for chondrocyte markers. To investigate bone formation in vivo, MSCs were seeded into Collagraft scaffolds and implanted under the skin of nude mice. Bone formation was assessed by histology and the human origin investigated by in situ hybridization for human ALU genomic repeats and by RT-PCR for bone markers using primers specific for human cDNA.
P-MSCs underwent chondrogenesis, osteogenesis, and adipogenesis in vitro as well as myogenesis in vivo. Multipotency was inherent at the single cell level. P-MSCs were compared with SM-MSCs from the same donors in the capacity to form cartilage in vitro and bone in vivo. Under our experimental conditions, SM-MSCs displayed greater chondrogenic potential than P-MSCs with higher contents of cartilage-specific proteoglycans and higher expression levels of mature chondrocyte markers. For bone formation, engraftment of P-MSCs and SM-MSCs into Collagraft was comparable and either MSC population survived long term in vivo (20 weeks). Histologically, no bone was evident at 4 weeks. At later time points (8–20 weeks), abundant bone formation was detected consistently in all periosteal samples. In contrast, bone was rarely observed, and in small amounts, in the synovial samples, with most human cells contributing to a fibrous-like tissue. In all cases, bone was mostly of human origin. As evaluated by quantitative RT-PCR, the expression levels of human OC, normalized for human beta-actin, were significantly higher in the periosteal samples than in the synovial ones. Bone was neither retrieved in empty Collagraft scaffolds nor in Collagraft scaffolds seeded with human dermal fibroblasts used for a cell negative control.
Expanded P-MSCs can differentiate to cartilage, bone, adipocytes, and skeletal muscle. Importantly, SM-MSCs displayed a greater chondrogenic potential in vitro than P-MSCs. By contrast, P-MSCs formed bone in vivo consistently and reproducibly as opposed to SM-MSCs. Our results suggest that MSCs derived from different tissue have distinct biological properties, thereby pointing to a need for development of quality controls for MSC preparations in clinical settings.