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Exercise does not enhance aged bone's impaired response to artificial loading in C57Bl/6 mice.

ABSTRACT: Bones adapt their structure to their loading environment and so ensure that they become, and are maintained, sufficiently strong to withstand the loads to which they are habituated. The effectiveness of this process declines with age and bones become fragile fracturing with less force. This effect in humans also occurs in mice which experience age-related bone loss and reduced adaptation to loading. Exercise engenders many systemic and local muscular physiological responses as well as engendering local bone strain. To investigate whether these physiological responses influence bones' adaptive responses to mechanical strain we examined whether a period of treadmill exercise influenced the adaptive response to an associated period of artificial loading in young adult (17-week) and old (19-month) mice. After treadmill acclimatization, mice were exercised for 30 min three times per week for two weeks. Three hours after each exercise period, right tibiae were subjected to 40 cycles of non-invasive axial loading engendering peak strain of 2250 ??. In both young and aged mice exercise increased cross-sectional muscle area and serum sclerostin concentration. In young mice it also increased serum IGF1. Exercise did not affect bone's adaptation to loading in any measured parameter in young or aged bone. These data demonstrate that a level of exercise sufficient to cause systemic changes in serum, and adaptive changes in local musculature, has no effect on bone's response to loading 3h later. This study provides no support for the beneficial effects of exercise on bone in the elderly being mediated by systemic or local muscle-derived effects rather than local adaptation to altered mechanical strain.

SUBMITTER: Meakin LB

PROVIDER: S-EPMC4652609 | biostudies-literature | 2015 Dec

REPOSITORIES: biostudies-literature

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Exercise does not enhance aged bone's impaired response to artificial loading in C57Bl/6 mice.

Meakin Lee B LB Udeh Chinedu C Galea Gabriel L GL Lanyon Lance E LE Price Joanna S JS

Bone 20150702

Bones adapt their structure to their loading environment and so ensure that they become, and are maintained, sufficiently strong to withstand the loads to which they are habituated. The effectiveness of this process declines with age and bones become fragile fracturing with less force. This effect in humans also occurs in mice which experience age-related bone loss and reduced adaptation to loading. Exercise engenders many systemic and local muscular physiological responses as well as engenderin ...[more]

PMID: 26142929

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Project description:UnlabelledWe aimed to determine whether aged bone's diminished response to mechanical loading could be rescued by modulating habitual activity. By reducing background loading, aged bone's response to loading increased to a level no different to young mice. This suggests, given the right stimulus, that ageing bone can respond to mechanical loading.IntroductionAge-related decline in bone mass has been suggested to represent an impaired ability of bone to adapt to its mechanical environment. In young mice, the tibia's response to external mechanical loading has been shown to increase when habitual activity is reduced by sciatic neurectomy. Here we investigate if neurectomy can rescue bone's response to loading in old mice.MethodsThe effect of tibial disuse, induced by unilateral sciatic neurectomy (SN), on the adaptive response to a single peak magnitude of dynamic load-engendered mechanical strain was assessed in 19-month-old (aged) mice. In a second experiment, a range of peak loads was used to assess the load magnitude-related effects of loading on a background of disuse in young adult and aged mice. Bone architecture was analysed using micro-computed tomography (μCT) and dynamic histomorphometry.ResultsIn the first experiment, SN in aged mice was associated with a significant periosteal osteogenic response to loading not observed in sham-operated mice (7.98 ± 1.7 vs 1.02 ± 2.2 % increase in periosteally enclosed area, p < 0.05). In the second experiment, SN abrogated the expected age-related difference in the bones' osteogenic response to peak strain magnitude (p > 0.05).ConclusionsThese data suggest that bones' age-related decline in osteogenic responsiveness to loading does not originate in bone cells to either assess, or appropriately respond to strain, but rather is likely to be due to inhibitory "averaging" effects derived from the habitual strains to which the bone is already adapted. If such "strain averaging" is applicable to humans, it suggests that gentle exercise may degrade the beneficially osteogenic effects of short periods of more vigorous activity.

Dataset Information

Exercise does not enhance aged bone's impaired response to artificial loading in C57Bl/6 mice.

Publications

Exercise does not enhance aged bone's impaired response to artificial loading in C57Bl/6 mice.

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