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Old Mice Have Less Transcriptional Activation But Similar Periosteal Cell Proliferation Compared to Young-Adult Mice in Response to in vivo Mechanical Loading

Authors
  • Chermside-Scabbo, Christopher J1, 2
  • Harris, Taylor L1, 3
  • Brodt, Michael D1
  • Braenne, Ingrid4
  • Zhang, Bo5
  • Farber, Charles R4, 6, 7
  • Silva, Matthew J1, 3
  • 1 Musculoskeletal Research Center Department of Orthopaedic Surgery, Washington University, St. Louis, MO, USA
  • 2 Medical Scientist Training Program, Washington University School of Medicine, Washington University, St. Louis, MO, USA
  • 3 Department of Biomedical Engineering, Washington University, St. Louis, MO, USA
  • 4 Center for Public Health Genomics, University of Virginia, Charlottesville, VA, USA
  • 5 Center of Regenerative Medicine, Department of Developmental Biology, Washington University, St. Louis, MO, USA
  • 6 Department of Biochemistry and Molecular Genetics, University of Virginia, Charlottesville, VA, USA
  • 7 Department of Public Health Sciences, University of Virginia, Charlottesville, VA, USA
Type
Published Article
Journal
Journal of Bone and Mineral Research
Publisher
Wiley (John Wiley & Sons)
Publication Date
Jun 01, 2020
Volume
35
Issue
9
Pages
1751–1764
Identifiers
DOI: 10.1002/jbmr.4031
PMID: 32311160
PMCID: PMC7486279
Source
PubMed Central
Keywords
License
Unknown

Abstract

Mechanical loading is a potent strategy to induce bone formation, but with aging, the bone formation response to the same mechanical stimulus diminishes. Our main objectives were to (i) discover the potential transcriptional differences and (ii) compare the periosteal cell proliferation between tibias of young-adult and old mice in response to strain-matched mechanical loading. First, to discover potential age-related transcriptional differences, we performed RNA sequencing (RNA-seq) to compare the loading responses between tibias of young-adult (5-month) and old (22-month) C57BL/6N female mice following 1, 3, or 5 days of axial loading (loaded versus non-loaded). Compared to young-adult mice, old mice had less transcriptional activation following loading at each time point, as measured by the number of differentially expressed genes (DEGs) and the fold-changes of the DEGs. Old mice engaged fewer pathways and gene ontology (GO) processes, showing less activation of processes related to proliferation and differentiation. In tibias of young-adult mice, we observed prominent Wnt signaling, extracellular matrix (ECM), and neuronal responses, which were diminished with aging. Additionally, we identified several targets that may be effective in restoring the mechanoresponsiveness of aged bone, including nerve growth factor (NGF), Notum, prostaglandin signaling, Nell-1, and the AP-1 family. Second, to directly test the extent to which periosteal cell proliferation was diminished in old mice, we used bromodeoxyuridine (BrdU) in a separate cohort of mice to label cells that divided during the 5-day loading interval. Young-adult and old mice had an average of 15.5 and 16.7 BrdU+ surface cells/mm, respectively, suggesting that impaired proliferation in the first 5 days of loading does not explain the diminished bone formation response with aging. We conclude that old mice have diminished transcriptional activation following mechanical loading, but periosteal proliferation in the first 5 days of loading does not differ between tibias of young-adult and old mice.

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