Resumen de The histopathology of a human mesenchymal stem cell experimental tumor model: support for an hMSC origin for Ewing¿s sarcoma?
Jorge S. Burns, Basem M. Abdallah, Henrik Daa Schrøder, Moustapha Kassem
Sarcomas display varied degrees of karyotypic abnormality, vascularity and mesenchymal differentiation. We have reported that a strain of telomerized adult human bone marrow mesenchymal stem cells (hMSC-TERT20) spontaneously evolved a tumorigenic phenotype after long-term continuous culture. We asked to what extent our hMSC-TERT20 derived tumors reflected events found in human sarcomas using routine histopathological procedures. Early versus late passage hMSC-TERT20 cultures persistently expressed mesenchymal lineage proteins e.g. CD105, CD44, CD99 and vimentin. However, late passage cultures, showed increased immuno-histochemical staining for CyclinD1 and p21WAF1/Cip1, whereas p27Kip1 staining was reduced. Notably, spectral karyotyping showed that tumorigenic hMSC-TERT20 cells retained a normal diploid karyotype, with no detectable chromosome abnormalities. Consistent with the bone-forming potential of early passage hMSC-TERT20 cells, tumors derived from late passage cells expressed early biomarkers of osteogenesis. However, hMSC-TERT20 cells were heterogeneous for alpha smooth muscle actin (ASMA) expression and one out of six hMSC-TERT20 derived single cell clones was strongly ASMA positive. Tumors from this ASMA+ clone had distinctive vascular qualities with hot spots of high CD34+ murine endothelial cell density, together with CD34- regions with a branching periodic acid Schiff reaction pattern. Such clone-specific differences in host vascular response provide novel models to explore interactions between mesenchymal stem and endothelial cells. Despite the lack of a characteristic chromosomal translocation, the histomorphology, biomarkers and oncogenic changes were similar to those prevalent for Ewing�s sarcomas. The phenotype and ontogenesis of hMSC-TERT20 tumors was consistent with the hypothesis that sarcomas may arise from hMSC, providing a unique diploid model for exploring human sarcoma biology.
