Disuse-related decline in trabecular bone structure

Sedentary life style may degrade bone mass and microstructure resulting in osteoporosis. We characterized trabecular bone structural properties to determine if the LRP5 G171V mutation will protect against disuse-related bone loss. Forty-eight adult male mice representing three genotypes (WT = wild type, KO = LRP5-knockout +/-, HBM = High bone with the LRP5 G171V mutation) were each randomly divided between control and disuse (4 week hindlimb suspension) groups. Trabecular bone volume fraction (BV/TV) declined in all the three genotypes. Trabecular thickness was lower in the HBM and LRP5 (+/-) KO disuse groups when compared to their respective controls. While the remaining measures of bone structure (Trabecular number, connectivity density, apparent and tissue density) were lower, the trabecular separation increased in the LRP5 (+/-) with disuse. Although the absolute loss in BV/TV was similar, the relative loss due to disuse was far greater in the LRP5 (+/-) mice (67%) than in the HBM mice (14%). The disuse caused 20% decrease in trabecular number and thickness for LRP5 (+/-), while the decline was between 6 and 11% for the HBM and WT mice.