Evaluating the target cells of low-magnitude high-frequency vibration

Introduction:

Low-magnitude high-frequency vibration (LMHFV) is a potential non-invasive treatment for osteoporosis patients to enhance bone formation in the intact skeleton and during fracture healing. In a previous study, we found that osteoblasts are crucially involved in mechanotransduction of vibration therapy in vitro while requiring estrogen receptor α (ERα). Since chondrocytes are able to transdifferentiate into osteoblasts, it is tempting to speculate that chondrocytes might also be target cells of LMHFV during fracture healing. Additionally, both chondrocytes and osteoblasts in the fracture callus express ERα during the intermediate stage of fracture healing.

Material and methods:

Cultures of the chondrogenic ATDC5 cell line were subjected to vertical vibrations at 45 Hz and 0.3 g peak-to-peak acceleration on a custom-made vibration platform for 20 min/day for max. 5 days a week. Sham-vibrated cultures were placed on the same platform without turning on the vibration generator. The effects of LMHFV were assessed on cell proliferation by BrdU assay and on chondrogenic differentiation (qPCR).

Results:

After LMHFV treatment, cell proliferation under estrogen-deficient conditions was increased as determined by BrdU assay. On gene expression levels, chondrocyte differentiation marker expression was not significantly altered. This finding could be also confirmed when using other culturing settings such as pellet culture. Furthermore it could be demonstrated, that LMHFV treatment does not accelerate osteogenic transdifferentiation.

Discussion:

Our results indicate that chondrocytes might only be target cells of LMHFV in vitro in terms of proliferation. However, this has to be further determined by in vivo studies.

Key words:

Vibration, Mechanostimulation, Chondrocytes, Fracture healing