Birch Helen L, Worboys Sarah, Eissa Sabry, Jackson Brendan, Strassburg Sandra, Clegg Peter D
Institute of Orthopaedics and Musculoskeletal Science, University College London, Stanmore Campus, Royal National Orthopaedic Hospital, Brockley Hill, Stanmore, HA7 4LP, UK.
Matrix Biol. 2008 Apr;27(3):182-9. doi: 10.1016/j.matbio.2007.10.004. Epub 2007 Oct 26.
Tendon matrix integrity is vital to ensure adequate mechanical properties for efficient function. Although historically tendon was considered to be relatively inert, recent studies have shown that tendon matrix turnover is active. During normal physiological activities some tendons are subjected to stress and strains much closer to their failure properties than others. Tendons with low safety margins are those which function as energy stores such as the equine superficial digital flexor tendon (SDFT) and human Achilles tendon (AT). We postulate therefore that energy storing tendons suffer a higher degree of micro-damage and thus have a higher rate of matrix turnover than positional tendons. The hypothesis was tested using tissue from the equine SDFT and common digital extensor tendon (CDET). Matrix turnover was assessed indirectly by a combination of measurements for matrix age, markers of degradation, potential for degradation and protein expression. Results show that despite higher cellularity, the SDFT has lower relative levels of mRNA for collagen types I and III. Non-collagenous proteins, although expressed at different levels per cell, do not appear to differ between tendon types. Relative levels of mRNA for MMP1, MMP13 and both pro-MMP3 and MMP13 protein activity were significantly higher in the CDET. Correspondingly levels of cross-linked carboxyterminal telopeptide of type I collagen (ICTP) were higher in the CDET and tissue fluorescence lower suggesting more rapid turnover of the collagenous component. Reduced or inhibited collagen turnover in the SDFT may account for the high level of degeneration and subsequent injury compared to the CDET.
肌腱基质的完整性对于确保有效的功能所需的足够力学性能至关重要。尽管从历史上看，肌腱被认为相对惰性，但最近的研究表明，肌腱基质周转是活跃的。在正常生理活动期间，一些肌腱承受的应力和应变比其他肌腱更接近其破坏特性。安全裕度低的肌腱是那些作为能量储存的肌腱，如马的浅指屈肌腱（SDFT）和人的跟腱（AT）。因此，我们推测能量储存肌腱比位置性肌腱遭受更高程度的微损伤，因此具有更高的基质周转率。使用来自马的SDFT和指总伸肌腱（CDET）的组织对该假设进行了测试。通过对基质年龄、降解标志物、降解潜力和蛋白质表达的测量组合间接评估基质周转。结果表明，尽管SDFT细胞密度较高，但其I型和III型胶原蛋白的mRNA相对水平较低。非胶原蛋白虽然每个细胞表达水平不同，但在不同类型的肌腱之间似乎没有差异。CDET中MMP1、MMP13以及前MMP3和MMP13蛋白活性的mRNA相对水平显著更高。相应地，I型胶原蛋白交联羧基末端肽（ICTP）的水平在CDET中更高，组织荧光更低，表明胶原成分的周转更快。与CDET相比，SDFT中胶原蛋白周转的减少或抑制可能是其高度退变和随后损伤的原因。
