Title: Differential bone adaptation to mechanical unloading and reloading in young, old, and osteocyte deficient mice

Abstract

Mechanical unloading causes rapid loss of bone structure and strength, which gradually recovers after resuming normal loading. However, it is not well established how this adaptation to unloading and reloading changes with age. Clinically, elderly patients are more prone to musculoskeletal injury and longer periods of bedrest, therefore it is important to understand how periods of disuse will affect overall skeletal health of aged subjects. Bone also undergoes an age-related decrease in osteocyte density, which may impair mechanoresponsiveness. In this study, we examined bone adaptation during unloading and subsequent reloading in mice. Specifically, we examined the differences in bone adaptation between young mice (3-month-old), old mice (18-month-old), and transgenic mice that exhibit diminished osteocyte density at a young age (3-month-old BCL-2 transgenic mice). Mice underwent 14 days of hindlimb unloading followed by up to 14 days of reloading. We analyzed trabecular and cortical bone structure in the femur, mechanical properties of the femoral cortical diaphysis, osteocyte density and cell death in cortical bone, and serum levels of inflammatory cytokines. We found that young mice lost ~10% cortical bone volume and 27–42% trabecular bone volume during unloading and early reloading, with modest recovery of metaphyseal trabecular bone and near total recoverymore » of epiphyseal trabecular bone, but no recovery of cortical bone after 14 days of reloading. Old mice lost 12–14% cortical bone volume and 35–50% trabecular bone volume during unloading and early reloading but had diminished recovery of trabecular bone during reloading and no recovery of cortical bone. In BCL-2 transgenic mice, no cortical bone loss was observed during unloading or reloading, but 28–31% trabecular bone loss occurred during unloading and early reloading, with little to no recovery during reloading. No significant differences in circulating inflammatory cytokine levels were observed due to unloading and reloading in any of the experimental groups. These results illustrate important differences in bone adaptation in older and osteocyte deficient mice, suggesting a possible period of vulnerability in skeletal health in older subjects during and following a period of disuse that may affect skeletal health in elderly patients.« less

Authors:

Cunningham, Hailey C.; Orr, Sophie; Murugesh, Deepa K.; Hsia, Allison W.; Osipov, Benjamin; Go, Lauren; Wu, Po Hung; Wong, Alice; Loots, Gabriela G.; Kazakia, Galateia J.; Christiansen, Blaine A.

Publication Date:

Wed Feb 01 00:00:00 EST 2023

Research Org.:

Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)

Sponsoring Org.:

USDOE National Nuclear Security Administration (NNSA); USDOD

OSTI Identifier:

1906738

Alternate Identifier(s):

OSTI ID: 2005066

Report Number(s):

LLNL-JRNL-841210
Journal ID: ISSN 8756-3282; S8756328222003234; 116646; PII: S8756328222003234

Grant/Contract Number:  

AC52-07NA27344

Resource Type:

Published Article

Journal Name:

Bone

Additional Journal Information:

Journal Name: Bone Journal Volume: 167 Journal Issue: C; Journal ID: ISSN 8756-3282

Publisher:

Elsevier

Country of Publication:

United States

Language:

English

Subject:

59 BASIC BIOLOGICAL SCIENCES; Hindlimb unloading; Osteocytes; Aging; Bone adaptation; Cortical porosity