Microcracks and Osteoclast Resorption Activity In Vitro |
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Authors: | Monika Rumpler Tanja Würger Paul Roschger Elisabeth Zwettler Herwig Peterlik Peter Fratzl Klaus Klaushofer |
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Institution: | (1) Ludwig Boltzmann Institute of Osteology at the Hanusch Hospital of WGKK and AUVA Trauma Center Meidling, 1st Medical Department, Hanusch Hospital, Vienna, Austria;(2) Faculty of Physics, University of Vienna, Vienna, Austria;(3) Department of Biomaterials, Max Planck Institute of Colloids and Interfaces, Potsdam, Germany; |
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Abstract: | During bone remodeling osteoclasts resorb bone, thus removing material, e.g., damaged by microcracks, which arises as a result
of physiological loading and could reduce bone strength. Such a process needs targeted bone resorption exactly at damaged
sites. Osteocytic signaling plays a key role in this process, but it is not excluded that osteoclasts per se may possess toposensitivity
to recognize and resorb damaged bone since it has been shown that resorption spaces are associated with microcracks. To address
this question, we used an in vitro setup of a pure osteoclast culture and mineralized substrates with artificially introduced
microcracks and microscratches. Histomorphometric analyses and statistical evaluation clearly showed that these defects had
no effect on osteoclast resorption behavior. Osteoclasts did not resorb along microcracks, even when resorption started right
beside these damages. Furthermore, quantification of resorption on three different mineralized substrates, cortical bone,
bleached bone (bone after partial removal of the organic matrix), and dentin, revealed lowest resorption on bone, significantly
higher resorption on bleached bone, and highest resorption on dentin. The difference between native and bleached bone may
be interpreted as an inhibitory impact of the organic matrix. However, the collagen-based matrix could not be the responsible
part as resorption was highest on dentin, which contains collagen. It seems that osteocytic proteins, stored in bone but not
present in dentin, affect osteoclastic action. This demonstrates that osteoclasts per se do not possess a toposensitivity
to remove microcracks but may be influenced by components of the organic bone matrix. |
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