Aging diminishes lamellar and woven bone formation induced by tibial compression in adult C57BL/6

Aging purportedly diminishes the ability of the skeleton to respond to mechanical loading, but recent data show that old age did not impair loading-induced accrual of bone in BALB/c mice. Here, we hypothesized that aging limits the response of the tibia to axial compression over a range of adult ages in the commonly used C57BL/6. We subjected the right tibia of old (22month), middle-aged (12month) and young-adult (5month) female C57BL/6 mice to peak periosteal strains (measured near the mid-diaphysis) of -2200με and -3000με (n=12-15/age/strain) via axial tibial compression (4Hz, 1200cycles/day, 5days/week, 2weeks). The left tibia served as a non-loaded, contralateral control. In mice of every age, tibial compression that engendered a peak strain of -2200με did not alter cortical bone volume but loading to a peak strain of -3000με increased cortical bone volume due in part to woven bone formation. Both loading magnitudes increased total volume, medullary volume and periosteal bone formation parameters (MS/BS, BFR/BS) near the cortical midshaft. Compared to the increase in total volume and bone formation parameters of 5-month mice, increases were less in 12- and 22-month mice by 45-63%. Moreover, woven bone incidence was greatest in 5-month mice. Similarly, tibial loading at -3000με increased trabecular BV/TV of 5-month mice by 18% (from 0.085mm³/mm³), but trabecular BV/TV did not change in 12- or 22-month mice, perhaps due to low initial BV/TV (0.032 and 0.038mm³/mm³, respectively). In conclusion, these data show that while young-adult C57BL/6 mice had greater periosteal bone formation following loading than middle-aged or old mice, aging did not eliminate the ability of the tibia to accrue cortical bone.