Identification and isolation of committed osteogenic progenitors from a heterogeneous population of mesenchymal stem cells using a Runx2 reporter adenovirus

BACKGROUND: Mesenchymal stem cells (MSC) are a heterogeneous population of adult stem cells characterized by their self-renewal capability and their multidifferentiation potential into several cell types of the mesenchymal lineage. Current isolation methods of MSCs are still rudimentary due to the lack of unique markers that characterize this stem cell population. Given the heterogeneity of MSCs, inconsistent results are obvious, which in turn slows down the progress in stem cell biology and related applied disciplines such as tissue engineering. This circumstance suggests investigating novel or improved approaches for the isolation of more homogeneous subpopulations of MSCs. In this study, a novel method for the identification and isolation of a committed osteogenic subpopulation of MSCs was developed. This was approached by functionally identifying and selecting a subpopulation of MSCs due to the expression of Runx2, the key transcription factor in osteogenesis [1]. The expression of the key transcription factor is coupled to expression of green fluorescent protein (GFP), and on the basis of that, these fluorescing cell can be selected by means of fluorescent activated cell sorting (FACS). The resulting cell populations, namely Runx2 GFP, Runx2 GFP, and the original unsorted cells, were subjected to comparative in vitro investigation for their ability to differentiate into the osteogenic lineage. To substantiate the characterization of the cell populations, proliferative capacity of the cell populations was assessed because it has been proposed that MSC differentiation is accompanied by decreased proliferation [2]. We expect our results will lead to an improved and more reproducible method to isolate committed osteogenic MSC subpopulation(s).