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

Abstract

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 (22 month), middle-aged (12 month) and young-adult (5 month) female C57BL/6 mice to peak periosteal strains (measured near the mid-diaphysis) of -2200 με and -3000 με (n=12-15/age/strain) via axial tibial compression (4 Hz, 1200 cycles/day, 5 days/week, 2 weeks). The left tibia served as a non-loaded, contralateral control. In mice of every age, tibial compression that engendered a peak strain of -2200 με did not alter cortical bone volume but loading to a peak strain of -3000 με 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 -3000 με increased trabecular BV/TV of 5-month mice by 18% (from 0.085 mm3/mm3), but trabecular BV/TV did not change in 12- or 22-month mice, perhaps due to low initial BV/TV (0.032 and 0.038 mm3/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.

Keywords: Aging; Bone formation; MicroCT; Mouse; Tibial compression.

Figure 1

(A) Contour plots of axial strain engendered by tibial compression (adapted from Patel et al., 2014, with permission). Shown is a 5-month sample at a force of 10 N. The peak tibial strain magnitude is compressive and occurs at the postero-lateral apex of the cross-section (arrow). The force magnitudes required to generate peak strains of –2200 and –3000 microstrain (με) in female C57Bl/6 mice were determined from strain gauge measurements [28] and are shown in the (B) table. L: Lateral, A: Anterior, M: Medial, P: Posterior.

Figure 2

Dynamic histomorphometry images of tibiae (right) from a range of adult mice subjected to tibial compression at –2200 με and –3000 με peak periosteal strain. Lamellar double-labeling was evident in all ages and both loading magnitudes, but loading at –3000 µε also induced woven bone formation.

Figure 3

a) MS/BS⁺, (b) MAR⁺, (c) BFR/BS⁺ and (d) incidence of woven bone (number of mice per group showing load-induced woven bone) of the periosteal and endocortical envelopes from a range of adult tibiae (only right tibiae) subjected to compression at –2200 με and –3000 με. Aging reduced the periosteal bone formation by tibial compression at –2200 με with minimal differences in bone formation outcomes between middle-aged and old tibiae and no endocortical changes between ages. Loading at –3000 με induced similar changes but enhanced periosteal bone formation of 5-month tibiae by inducing woven bone. Data are represented as mean±SD. Black bracket: significant difference between ages; “a”: significant difference between loading magnitudes of respective age. ⁺: Represents the combination of woven and lamellar values; p<0.05.

Figure 4

Relative change in (a) cortical bone volume, (b) total volume and (c) medullary volume over 2 weeks of tibial compression at –2200 με and –3000 με. Tibial compression at –2200 με increased total volume in an age-dependent manner but also increased medullary volume, resulting in no net change in cortical bone. By contrast, tibial compression at –3000 με increased total volume and cortical bone volume in an age-dependent manner, despite increased medullary volume. All control tibiae lost cortical bone volume. Data are represented as mean±SD. *: significant difference between final and initial value; Black bracket: significant difference between ages; “a”: significant difference between loading magnitudes of respective age; p<0.05.

Figure 5

Periosteal bone formation rates for tibiae loaded at a peak periosteal strain of –2200 με from our previous study in BALB/c mice [17] and current results in C57Bl/6. Data are represented as mean±SD.