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      Mechanisms of osteocyte stimulation in osteoporosis.

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          Abstract

          Experimental studies have shown that primary osteoporosis caused by oestrogen-deficiency results in localised alterations in bone tissue properties and mineral composition. Additionally, changes to the lacunar-canalicular architecture surrounding the mechanosensitive osteocyte have been observed in animal models of the disease. Recently, it has also been demonstrated that the mechanical stimulation sensed by osteocytes changes significantly during osteoporosis. Specifically, it was shown that osteoporotic bone cells experience higher maximum strains than healthy bone cells after short durations of oestrogen deficiency. However, in long-term oestrogen deficiency there was no significant difference between bone cells in healthy and normal bone. The mechanisms by which these changes arise are unknown. In this study, we test the hypothesis that complex changes in tissue composition and lacunar-canalicular architecture during osteoporosis alter the mechanical stimulation of the osteocyte. The objective of this research is to employ computational methods to investigate the relationship between changes in bone tissue composition and microstructure and the mechanical stimulation of osteocytes during osteoporosis. By simulating physiological loading, it was observed that an initial decrease in tissue stiffness (of 0.425GPa) and mineral content (of 0.66wt% Ca) relative to controls could explain the mechanical stimulation observed at the early stages of oestrogen deficiency (5 weeks post-OVX) during in situ bone cell loading in an oestrogen-deficient rat model of post-menopausal osteoporosis (Verbruggen et al., 2015). Moreover, it was found that a later increase in stiffness (of 1.175GPa) and mineral content (of 1.64wt% Ca) during long-term osteoporosis (34 weeks post-OVX), could explain the mechanical stimuli previously observed at a later time point due to the progression of osteoporosis. Furthermore, changes in canalicular tortuosity arising during osteoporosis were shown to result in increased osteogenic strain stimulation, though to a lesser extent than has been observed experimentally. The findings of this study indicate that changes in the extracellular environment during osteoporosis, arising from altered mineralisation and lacunar-canalicular architecture, lead to altered mechanical stimulation of osteocytes, and provide an enhanced understanding of changes in bone mechanobiology during osteoporosis.

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          Author and article information

          Journal
          J Mech Behav Biomed Mater
          Journal of the mechanical behavior of biomedical materials
          Elsevier BV
          1878-0180
          1878-0180
          Sep 2016
          : 62
          Affiliations
          [1 ] Biomechanics Research Centre (BMEC), Biomedical Engineering, College of Engineering and Informatics, National University of Ireland, Galway, Ireland.
          [2 ] Biomechanics Research Centre (BMEC), Biomedical Engineering, College of Engineering and Informatics, National University of Ireland, Galway, Ireland. Electronic address: Laoise.McNamara@nuigalway.ie.
          Article
          S1751-6161(16)30122-9
          10.1016/j.jmbbm.2016.05.004
          27203269
          b84b58b7-2d09-4598-979f-92b44af39c6b
          History

          Lacuna,Mechanobiology,Of the paper: Bone,Osteocyte,Osteoporosis

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