In vitro effects of dynamic strain on the proliferative and metabolic activity of human osteoblasts

It has been well shown by human and animal studies that mechanical load is an important regulator of skeletal mass and architecture. However, cellular reactions which adapt bone tissue to the mechanical environment are not definitively determined. For this purpose we studied the cell activity of human bone derived cell cultures after mechanical stimulation by cyclic, uniaxial strain at a magnitude occurring in normal loaded bone tissue.

Human osteoblasts were isolated from cancellous bone biopsies of 5 different donors. Cell seeding was made in DMEM in a density of 10.000 cells/cm(2) on deformable culture dishes for three days prior to initiating cell stretching at 1000 microstrain, 1Hz for 1800 cycles for two subsequent days with an especially developed cell stretching device. 48h after the second stimulation cells were harvested and cell number was determined with a Coulter Counter. Cell bound alkaline phosphatase activity was analyzed in cell lysates by a colorimetric assay, osteocalcin and CICP (procollagen I propeptide) production were analyzed in cell supernatants with ELISAs. Three parallel cultures were tested.

Wilcoxon.

In all experiments mechanical stimulation resulted in a significant increase in cell number (10-48%) and CICP release (7-49%). Simultaneously a significant decrease in alkaline phosphatase activity (9-25%) and osteocalcin release (5-32%) could be observed.

The results demonstrate that cyclic strain at physiologic magnitude leads to an increase of early osteoblast activities related to matrix production while those activities which are characteristic for the differentiated osteoblast and relevant for matrix mineralization are decreased. These new findings confirm in vivo observations about the importance of dynamic strain for bone formation during fracture healing and bone remodeling and could contribute to the optimization of fracture healing.