Response of normal and osteoporotic human bone cells to mechanical stress in vitro.

Bone adapts to mechanical stress, and bone cell cultures from animal origin have been shown to be highly sensitive to mechanical stress in vitro. In this study, we tested whether bone cell cultures from human bone biopsies respond to stress in a similar manner as animal bone cells and whether bone cells from osteoporotic patients respond similarly to nonosteoporotic donors. Bone cell cultures were obtained as outgrowth from collagenase-stripped trabecular bone fragments from 17 nonosteoporotic donors between 7 and 77 yr of age and from 6 osteoporotic donors between 42 and 72 yr of age. After passage, the cells were mechanically stressed by treatment with pulsating fluid flow (PFF; 0.7 +/- 0.03 Pa at 5 Hz for 1 h) to mimic the stress-driven flow of interstitial fluid through the bone canaliculi, which is likely the stimulus for mechanosensation in bone in vivo. Similar to earlier studies in rodent and chicken bone cells, the bone cells from nonosteoporotic donors responded to PFF with enhanced release of prostaglandin E2 (PGE2) and nitric oxide as well as a reduced release of transforming growth factor-beta (TGF-beta). The upregulation of PGE2 but not the other responses continued for 24 h after 1 h of PFF treatment. The bone cells from osteoporotic donors responded in a similar manner as the nonosteoporotic donors except for the long-term PGE2 release. The PFF-mediated upregulation of PGE2 release during 24 h of postincubation after 1 h of PFF was significantly reduced in osteoporotic patients compared with six age-matched controls as well as with the whole nonosteoporotic group. These results indicate that enhanced release of PGE2 and nitric oxide, as well as reduced release of TGF-beta, is a characteristic response of human bone cells to fluid shear stress, similar to animal bone cells. The results also suggest that bone cells from osteoporotic patients may be impaired in their long-term response to mechanical stress.