Abnormal marrow fibroblasts in aplastic anemia.

Human bone marrow fibroblasts (BMF) were grown in vitro from normal (N) subjects and patients with aplastic anemia (AA). Growth studies in vitro revealed that both the N-BMF and AA-BMF had a logarithmic growth phase of eight days. Population doubling time for six of the 12 N-BMF and seven of the 12 AA-BMF was greater than 50 h. Five of the 12 AA-BMF studied in contrast to only two of the 12 N-BMF had a population doubling time of less than 50 h. The remaining four N-BMF had a population doubling time of greater than 100 h. During a similar duration in the logarithmic phase of growth, the AA-BMF underwent an average of 2.499 population doublings in comparison to 1.586 doublings by N-BMF (P = less than 0.01). The AA-BMF grew in multiple layers compared with the N-BMF, which usually grew as a monolayer. At the end of the logarithmic phase of growth, the AA-BMF also had a significantly higher number of cells per dish than the N-BMF (P = 0.02 on analysis of variance and covariance). These data suggest that a subgroup of AA-BMF grows faster than N-BMF and that the AA-BMF lack cell-to-cell inhibition. Testosterone, 3 alpha-etiocholanolone, and dexamethasone at 1 X 10(-8)M concentration, a physiological concentration, stimulated the growth of N-BMF as evidenced by increase in cell numbers and radioactive thymidine (3H-TdR) uptake. While dexamethasone had a stimulating effect on growth of N-BMF, it suppressed the growth of AA-BMF. Specific binding of radioactive dexamethasone (3H-dexa) was determined both for the N-BMF and AA-BMF. Specific binding sites for dexamethasone (Bmax) present on the N-BMF ranged from 460 to 770 fmol/mg protein). Bmax for AA-BMF was low (27-215 fmol/mg protein). In addition, the dissociation constant (Kd) was ten times lower for AA-BMF (1.0 X 10(-7) M) than for N-BMF (1.1 X 10(-8) M). The observations on the growth studies, the paradoxical response to dexamethasone, and the difference in the number of binding sites for dexamethasone indicate that the marrow fibroblasts from patients with aplastic anemia are abnormal.