Endocrine Abstracts

Osteoblasts and adipocytes are derived from the same stem cell in adult marrow and plasticity exists between the two lineages. In Osteoporosis there are reduced osteoblast numbers and increased adipocyte numbers suggesting a disturbance in the normal balance of the cells' differentiation pathways, leading to defective osteoblastogenesis and favouring adipogenesis. The stage of adipocytic differentiation at which plasticity is lost and commitment is established is not known. We have previously shown that, by changing the environment primary in vitro cultures of adult human bone marrow adipocytic precursors and mature adipocytes can convert to osteoblasts. This study aims to extend these findings by genotypically typing clonal populations of STRO-1 positive stromal cells during in vitro adipocytic differentiation.
Local Ethical Committee approval was obtained. Stromal cells were isolated from a bone marrow sample by density gradient centrifugation. STRO-1 positive clones were produced by magnetic activated cell sorting and limiting dilution and stimulated down the adipocytic lineage. Histochemical staining for oil red O was noted at regular intervals. Cells were removed at regular intervals and subjected to poly A PCR. Specific RT PCR was then used to assess the level of expression of known markers of osteoblast and adipocyte differentiation in these poly A PCR products. Beta actin was used as a housekeeping gene. After 7 days in adipogenic medium all cells stained positive for oil red O and started expressing mRNA for leptin confirming adipocytic differentiation. mRNA for markers of osteoblast differentiation (core binding factor a 1, alkaline phosphatase, osteopontin and collagen type I) was expressed in cells of the adipocytic lineage at all time points. In conclusion, even at a late stage of differentiation cells of the adipocytic lineage retain their osteogenic potential. We propose that, if the factors responsible for the switch between adipocytes and osteoblasts were identified, they could be used for the development of novel therapeutic intervention in Osteoporosis.