Sensitivity of notochordal disc cells to mechanical loading: an experimental animal study |
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Authors: | Thorsten Guehring Andreas Nerlich Markus Kroeber Wiltrud Richter Georg W Omlor |
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Institution: | (1) Department of Trauma and Orthopaedic Surgery, BG Trauma Center Ludwigshafen, University of Heidelberg, Ludwig Guttmann Str 13, 67071 Ludwigshafen, Germany;(2) Department of Pathology, Academic Hospital Munich-Bogenhausen, Munich, Germany;(3) Department of Orthopaedic Surgery, Kantonsspital St. Gallen, St. Gallen, Switzerland;(4) Division of Experimental Orthopaedics, Orthopaedic University Clinic Heidelberg, Heidelberg, Germany |
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Abstract: | The immature disc nucleus pulposus (NP) consists of notochordal cells (NCs). With maturation NCs disappear in humans, to be
replaced by chondrocyte-like mature NP cells (MNPCs); this change in cell phenotype coincidences with early signs of disc
degeneration. The reasons for NC disappearance are important to understand disc degeneration, but remain unknown, yet. This
study investigated, whether loading induced a change from a notochordal nucleus phenotype to a chondrocyte-like one. An in
vivo disc compression model with fixateur externe was used in 36 mature rabbits. Discs were compressed for different time
periods (1, 28, 56 days), and compared with uncompressed control discs (56 days without treatment), and discs with sham compression
(28 days). Nucleus cell phenotype was determined by histology and immunohistochemistry. NCs, but not MNPCs highly expressed
bone-morphogenetic-protein 2 and cytokeratin 8, thus NC and MNPC numbers could be determined. A histologic score was used
to detect structural endplate changes after compression (28 days). Control and sham compressed discs contained around 70%
NCs and 30% MNPCs, to be decreased to <10% NCs after 28–56 days of loading. NC density fell sharply by >50% after 28–56 days
of compression (P < 0.05 vs. controls). Signs of decreased endplate cellularity and increased endplate sclerosis and fibrosis were found after
loading. These experiments show that NCs were less resistant to mechanical stress than MNPCs suggesting that increased intradiscal
pressures after loading, and limited nutrition through structurally altered endplates could instigate the disappearance of
NCs. |
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Keywords: | Notochordal disc cells Mechanical stress Disc compression Animal model |
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