Division of Surgery and Interventional Science, University College London, Institute of Orthopaedics and Musculoskeletal Science, Royal National Orthopaedic Hospital, London, UK.
J Biol Chem. 2010 May 21;285(21):15674-81. doi: 10.1074/jbc.M109.077503. Epub 2010 Mar 22.
Little is known about the rate at which protein turnover occurs in living tendon and whether the rate differs between tendons with different physiological roles. In this study, we have quantified the racemization of aspartic acid to calculate the age of the collagenous and non-collagenous components of the high strain injury-prone superficial digital flexor tendon (SDFT) and low strain rarely injured common digital extensor tendon (CDET) in a group of horses with a wide age range. In addition, the turnover of collagen was assessed indirectly by measuring the levels of collagen degradation markers (collagenase-generated neoepitope and cross-linked telopeptide of type I collagen). The fractional increase in D-Asp was similar (p = 0.7) in the SDFT (5.87 x 10(-4)/year) and CDET (5.82 x 10(-4)/year) tissue, and D/L-Asp ratios showed a good correlation with pentosidine levels. We calculated a mean (+/-S.E.) collagen half-life of 197.53 (+/-18.23) years for the SDFT, which increased significantly with horse age (p = 0.03) and was significantly (p < 0.001) higher than that for the CDET (34.03 (+/-3.39) years). Using similar calculations, the half-life of non-collagenous protein was 2.18 (+/-0.41) years in the SDFT and was significantly (p = 0.04) lower than the value of 3.51 (+/-0.51) years for the CDET. Collagen degradation markers were higher in the CDET and suggested an accumulation of partially degraded collagen within the matrix with aging in the SDFT. We propose that increased susceptibility to injury in older individuals results from an inability to remove partially degraded collagen from the matrix leading to reduced mechanical competence.
关于活体肌腱中蛋白质周转率的速率以及具有不同生理作用的肌腱之间的速率是否存在差异,目前知之甚少。在这项研究中,我们通过测定天冬氨酸的外消旋化来计算高应变易损伤的浅表背侧屈肌腱(SDFT)和低应变很少受伤的普通指总伸肌腱(CDET)的胶原和非胶原成分的年龄。此外,通过测量胶原降解标志物(胶原酶生成的新表位和 I 型胶原交联端肽)的水平,间接评估胶原的周转率。SDFT(5.87 x 10(-4)/year)和 CDET(5.82 x 10(-4)/year)组织中 D-Asp 的分数增加相似(p = 0.7),并且 D/L-Asp 比值与戊糖素水平呈良好相关性。我们计算出 SDFT 的平均(+/-S.E.)胶原半衰期为 197.53(+/-18.23)年,该半衰期随马龄显著增加(p = 0.03),明显高于 CDET(34.03(+/-3.39)年)。使用类似的计算方法,SDFT 中非胶原蛋白的半衰期为 2.18(+/-0.41)年,明显低于 CDET 的半衰期 3.51(+/-0.51)年(p = 0.04)。CDET 中的胶原降解标志物较高,表明随着 SDFT 年龄的增长,基质中部分降解的胶原积累。我们提出,老年人更容易受伤的原因是无法从基质中清除部分降解的胶原,导致机械能力降低。