Walking-Induced Bone Strain Stimulates Cultured Osteoblasts Accompanied by the Low-Magnitude, High Frequency Components

Abstract

The purpose of this study is to test a hypothesis that involvement of the low-magnitude, high frequency strain components in the walking-induced bone strain is essential to elicit the osteogenic response of osteoblasts to the bone strain. To this end, a strain waveform recorded in vivo on a radius of a walking dog (original strain) was used to stimulate osteoblasts cultured in a porous, hydroxyapatite-deposited collagen matrix. The cells were loaded under three different strain waveforms: the original strain with 0 - 50 Hz components, and low-pass filtered strains limited to either 0-5 Hz components or 0-2 Hz components. We found that the original strain and the 0-5 Hz strain elevated significantly mRNA levels of stress-sensitive or bone-formation related genes such as c-fos, cyclooxygenase 2, egr1 and osteocalcin. There was no significant difference between these two strains in the mRNA levels. The 0-2 Hz strain increased significantly only osteocalcin mRNA level, but the level was about 30% of those in the original and the 0-5 Hz strains. It was concluded that involvement of strains from 2 to 5 Hz is essential, but high-magnitude, lower frequency strains from 0 to 2 Hz and low-magnitude, higher frequency strains from 5 to 50 Hz are not, to elicit the osteoblastic response to the walking-induced bone strain.

Keywords

• osteoblasts
• mechanical loading
• 3d culture
• in vivo bone strain
• high frequency strain
• fluid flow