Mechanical regulation of bone homeostasis: effects of cyclic pressure on bone cell function in vitro

The present in vitro study exposed rat osteoblasts and osteoclast-precursors in bone marrow cell populations to controlled regimes of cyclic pressure and examined various cell functions that are pertinent to bone homeostasis. The results provided evidence that osteoblasts are sensitive to the frequency of the applied cyclic pressure stimulus. Specifically, compared to controls (static conditions) and cells exposed to cyclic pressure at 0.25 Hz frequency, osteoblast proliferation was significantly (p < 0.05) lower, but alkaline phosphatase mRNA expression and enzyme activity were enhanced, only when these cells were exposed to cyclic pressure at 1.0 Hz frequency for 1 hour daily for 5 consecutive days. Furthermore, the results of the present study demonstrated that the timing of application of the cyclic pressure was critical for osteoclastic cell formation from precursors in bone marrow. Exposure of bone marrow cells to cyclic pressure immediately upon harvesting led to decreased formation of osteoclastic cells from their precursors; in contrast, the number of osteoclastic cells was not affected when the cyclic pressure was applied after 7 days of culture under static conditions.