Periosteal tissue is a valuable source of multipotent stem cells for bone tissue engineering. To characterize these cells in detail, we generated an immortalized human cranial periosteal cell line and observed an increased MSCA-1 and CD146 expression, as well as an earlier and stronger mineralization compared to the parental cells. Further, we detected a higher osteogenic potential of MSCA-1high compared to MSCA-1low cranial periosteal cell (CPC) fractions. In the present study, a possible synergism of MSCA-1 and CD146 for periosteal cell mineralization was investigated.
MSCA-1/CD146 positive and negative CPCs were magnetically isolated (MACS) or sorted by flow cytometry (FACS) and subjected to osteogenic differentiation. The expression of osteogenic marker genes in the four subpopulations was analyzed by quantitative real-time PCR. Furthermore, the co-expression of osteogenic markers/antigens was analyzed by multispectral imaging flow cytometry (ImageStream, AMNIS). The mineralization potential was assessed by the quantification of alizarin stainings.
While the total cell yield after separation was higher using MACS compared to the FACS approach, the isolation of MSCA-1+/- and CD146+/- subpopulations was more efficient with the FACS separation. The accuracy of the FACS separation of the four distinguished cell subpopulations was confirmed by multispectral imaging flow cytometry. Further, we detected increasing levels of MSCA-1 and CD146 during in vitro differentiation in all subpopulations. However, MSCA-1 expression was significantly higher in the MSCA-1+/CD146+ and MSCA-1+/ CD146- subpopulations, while CD146 expression remained clearly lower in these fractions. Significantly higher gene expression levels of osteogenic markers, ALP and RUNX2, were detected in MSCA-1+ compared to MSCA-1- CPCs at different time points during in vitro differentiation. Staining and quantification of calcium phosphate precipitates revealed a significantly higher mineralization potential of MACS separated MSCA-1+ and CD146- CPCs, compared to their respective counterparts. FACS sorted CPCs displayed earlier mineralization in both MSCA-1+ fractions (d13), while later (d28) only the CD146+/MSCA-1- fraction had a significantly lower calcium phosphate concentration compared to all other fractions.
Our results demonstrate, that MSCA-1+ cells isolated from CPCs represent a subpopulation with a higher osteogenic potential. In contrast, we found a lower osteogenic potential in CD146+ CPCs. In conclusion, only MSCA-1, but not CD146, is a suitable marker for the isolation of osteoprogenitors from CPCs.