Estrogen regulation of growth and alkaline phosphatase expression by cultured human bone marrow stromal cells

Estrogen has been reported to regulate the growth and differentiation of cultured murine osteoprogenitor cells in bone marrow stroma. This study tested the ability of 17beta-estradiol (E2) to regulate growth and expression of alkaline phosphatase (ALP), an osteoblastic differentiation marker, in strains of normal human bone marrow stromal cells derived from different donors. In eight strains examined, E2 at 1 and 10 nM produced at most modest effectxs on growth and ALP activity. Growth inhibition, seen in 4 of the 8 strains, was more common than stimulation (2 of the 8 strains); the greatest observed E2 effect was an inhibition of ca. 50%. E2 altered ALP activity less dramatically than cell growth. Differences from control in total ALP per culture were seen in only two strains: one was a reduction, one an increase. Colony forming assays were used to determine if E2 changed the proportion of ALP-expressing cells in marrow stromal cell cultures. In contrast to growth experiments, ALP expression under colony forming conditions (200 cells per 35 mm-diameter well) was dependent on the type of serum supplementation used. Under permissive conditions using medium supplemented with 10% charcoal-treated fetal bovine serum, 10 nM E2 increased the number of ALP-positive colonies (cfu-ap) but not the total number of colonies formed (cfu-f). When cells cultured in the presence or absence of 10 nM E2 were replated at colony forming densities, significantly higher proportions of cfu-ap were found in 2 of 6 strains examined, while pretreatment with E2 affected the number of cfu-f in only 1 of the 6 strains. Similar results were obtained when colony formation was carried out in the presence of dexamethasone and ascorbate, although these agents themselves increased the formation of both cfu-f and cfu-ap. These results show that the direct effects of E2 on human marrow stromal cells are small and vary depending on the cell strain and on the experimental conditions; however, the E2 actions observed in this study were consistent with reports that E2 exerts direct actions on osteoblasts and osteoblast progenitor cells that favor rather than suppress their phenotypic expression.