Abstract
ABSTRACTTenocytes express primary cilia, which elongate when tendon is maintained in the absence of biomechanical load. Previous work indicates differences in the morphology and metabolism of the tenocytes in the tendon fascicular matrix (FM) and the inter‐fascicular matrix (IFM). This study tests the hypothesis that primary cilia in these two regions respond differently to stress deprivation and that this is associated with differences in the biomechanical degradation of the extracellular matrix. Rat tail tendon fascicles were examined over a 7‐day period of either stress deprivation or static load. Seven days of stress deprivation induced cilia elongation in both regions. However, elongation was greater in the IFM compared to the FM. Stress deprivation also induced a loss of biomechanical integrity, primarily in the IFM. Static loading reduced both the biomechanical degradation and cilia elongation. The different responses to stress deprivation in the two tendon regions are likely to be important for the aetiology of tendinopathy. Furthermore, these data suggest that primary cilia elongate in response to biomechanical degradation rather than simply the removal of load. This response to degradation is likely to have important consequences for cilia signalling in tendon and as well as in other connective tissues. © 2016 The Authors. Journal of Orthopaedic Research Published by Wiley Periodicals, Inc. on behalf of Orthopaedic Research Society. J Orthop Res 34:2146–2153, 2016.
Highlights
Tenocytes express primary cilia, which elongate when tendon is maintained in the absence of biomechanical load
Fascicles were obtained by removing the skin of the proximal end of the tail, after which the tendon was cut at each end and the fascicles pulled out taking care to ensure that the inter-fascicular matrix (IFM) surrounding each fascicle was maintained
Considering regional differences in cilia length, there was no significant difference in cilia length between IFM and fascicular matrix (FM) cells in fresh samples
Summary
Tenocytes express primary cilia, which elongate when tendon is maintained in the absence of biomechanical load. Stress deprivation induced a loss of biomechanical integrity, primarily in the IFM Static loading reduced both the biomechanical degradation and cilia elongation. The different responses to stress deprivation in the two tendon regions are likely to be important for the aetiology of tendinopathy These data suggest that primary cilia elongate in response to biomechanical degradation rather than the removal of load. Tendons are hierarchical structures, composed at the macroscale of collagen rich fascicles, bound together by a softer highly hydrated matrix called the endotenon or inter-fascicular matrix (IFM) Both the collagen rich fascicular matrix and the IFM contain tenocytes which synthesize and maintain the extracellular matrix. Over the last 20–30 years a growing interest in their behavior has led to the discovery of their role in autosomal dominant polycystic kidney disease (ADPKD) and an increasing range of so called ciliopathies.[13]
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