DEMINERALIZED BONE-MATRIX MEDIATES DIFFERENTIATION OF BONE-MARROW STROMAL CELLS IN-VITRO - EFFECT OF AGE OF CELL DONOR

Bone maintenance requires a continuous source of osteoblasts throughou t life, Its remodeling and regeneration during fracture repair is ensu red by osteoprogenitor stem cells which are part of the stroma of the bone marrow (BM). Many investigators have reported that in cultured BM stromal cells there is a cell population that will differentiate alon g an osteogenic lineage if stimulated by the addition of osteogenic in ducers, such as dexamethasone (dex), beta-glycerophosphate (P-GP), tra nsforming growth factor beta-1 (TGF-beta 1) and bone morphogenetic pro tein-2 (BMP-2). Here we report the effects of demineralized bone matri x (DBM) on the osteogenic differentiation of BM stromal cells in vitro , using morphological criteria, alkaline phosphatase (AP) activity, an d calcium accumluation. DBM and DBM-conditioned medium (DBMcm) enhance d bone formation in the presence of dex and beta-GP, whereas DBM parti cles caused changes in the cell phenotype, Temporal expression of tota l and skeletal AP by BM stromal cells from 4-week-old rats showed a bi phasic pattern enhanced by DBM and suggesting the presence of two cell populations, In one population, AP synthesis reaches a maximum during the first week in culture, following,which cells either die or loose their ability to synthesize AP, A second, less abundant population beg ins to proliferate and synthesize AP during the second and third weeks . The synthesis of AP, which often decreases by the third week, can be maintained at high levels only if DBM is added to the cultures, BM st romal cells isolated from 24- and 48- week-old rats showed a decrease or loss of this biphasic AP expression pattern compared with cells iso lated from 4-week-old rats, The addition of DBM to cultures derived fr om 24- and 48-week-old rats stimulated mostly the second cell populati on to synthesize AP, suggesting that DBR;I contains a factor(s) that a cts on a specific bone marrow cell population by increasing the prolif eration of active cells or inducing the differentiation of dormant cel ls.