Cellular phenotyping of the mouse skeleton using synchrotron based nano-computed tomography

Abstract

Whole body vibration (WBV) is a promising tool for counteracting bone loss. Most WBV studies on animals have been performed at acceleration <1g and frequency between 30 and 90 Hz. Such WBV conditions trigger bone growth in osteopenia models, but not in healthy animals. In order to test the ability of WBV to promote osteogenesis in young animals, we exposed seven-week-old male mice to vibration at 90 Hz and 2g peak acceleration for 15 min/day, 5 days/week. We examined the effects on skeletal tissues with micro-computed tomography and histology. We also quantified bone vascularization and mechanosensitive osteocyte proteins, sclerostin and DMP1. Three weeks of WBV resulted in an increase of femur cortical thickness (+5%) and area (+6%), associated with a 25% decrease of sclerostin expression, and 35% increase of DMP1 expression in cortical osteocytes. Mass-structural parameters of trabecular bone were unaltered in femur or vertebra, while osteoclastic parameters and bone formation rate were increased at both sites. Three weeks of WBV resulted in higher blood vessel numbers (+23%) in the distal femoral metaphysis.After 9-week WBV, we have not observed the difference in structural cortical or trabecular parameters. However, the tissue mineral density of cortical bone was increased by 2.5%.Three or nine weeks of 2g/90 Hz WBV treatment did not affect longitudinal growth rate or body weight increase under our experimental conditions, indicating that these are safe to use.These results validate a potential of 2g/90 Hz WBV to stimulate trabecular bone cellular activity, accelerate cortical bone growth, and increase bone mineral density.