Multiple surface markers have been utilized for the enrichment of bone marrow mesenchymal stromal cells (MSCs) and to define primitive stem cells. We classified human bone marrow-derived MSC populations according to tissue nonspecific alkaline phosphatase (TNAP) activity. TNAP expression varied among unexpanded primary MSCs, and its level was not related to colony-forming activity or putative surface markers, such as CD105 and CD29, donor age, or gender. TNAP levels were increased in larger cells, and a colony-forming unit-fibroblast assay revealed that the colony size was decreased during in vitro expansion. TNAP-positive (TNAP+) MSCs showed limited multipotential capacity, whereas TNAP-negative (TNAP-) MSCs retained the differentiation potential into 3 lineages (osteogenic-, adipogenic-, and chondrogenic differentiation). High degree of calcium mineralization and high level of osteogenic-related gene expression (osteopontin, dlx5, and cbfa1) were found in TNAP+cells. In contrast, during chondrogenic differentiation, type II collagen was successfully induced in TNAP- cells, but not in TNAP+cells. TNAP+cells showed high levels of the hypertrophic markers, type X collagen and cbfa1. Mesenchymal stem cell antigen-1 (MSCA-1) is identical to TNAP. Therefore, TNAP+cells were sorted by using antibody targeting MSCA-1. MSCA-1-positive cells sorted for TNAP+cells exhibited low proliferation rates. Expression of cell cycle-related genes (cyclin A2, CDK2, and CDK4) and pluripotency marker genes (rex1 and nanog) were higher in TNAP- MSC than in TNAP+ MSC. Therefore, TNAP- cells can be described as more primitive bone marrow-derived cells and TNAP levels in MSCs can be used to predict chondrocyte hypertrophy or osteogenic capacity.
All Science Journal Classification (ASJC) codes
- Developmental Biology
- Cell Biology