[Human osteoblasts response to different magnitudes of mechanical stimulation in vitro]

To investigate the effect of different magnitudes of tensile strain on human osteoblasts differentiation.

According to the strain amplification mechanism at cellular level and a data calculated by finite element analysis, the cellular level strain of 0.8%, 1.6%, 2.4% and 3.2% was respectively applied to human osteoblasts for 48 h at a frequency of 1 Hz. Alkaline phosphatase activity and the expression of osteoblast-related genes were detected by Semi-Quantitative RT-PCR and densitometric analysis.

Alkaline phosphatase activity significantly increased at 0.8% and 1.6%. The level of osteocalcin mRNA increased at 2.4% and 3.2%. Cbfa1/Runx2 gene expression only increased at 3.2%. Comparing to static control, mRNA level of type I collagen increased at every magnitude. The mRNA level decreased at 0.8% and increased at 3.2% when compared to the group with 1.6% elongation.

Higher magnitudes of strain enhance expression of osteocalcin, type I collagen gene and Cbfa1/Runx2 in human osteoblasts, but lost the ability to increase ALP activity which is remained by lower magnitudes of strain. Type I collagen gene expression increases in a strain magnitude dependent manner.