Tendon glycosaminoglycan proteoglycan sidechains promote collagen fibril sliding-AFM observations at the nanoscale
Tendon glycosaminoglycan proteoglycan sidechains promote collagen fibril sliding-AFM observations at the nanoscale
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DOI：
10.1016/j.jbiomech.2012.11.017
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发表时间：
2013-02-22
影响因子：
2.4
通讯作者：
Snedeker, J. G.
中科院分区：
文献类型：
--
作者：
Rigozzi, S.;Mueller, R.;Snedeker, J. G.
肌腱的细胞外基质主要由不连续的I型胶原纤维和富含亮氨酸的小蛋白聚糖（PG）组成。宏观肌腱行为（如刚度和强度）由这些组件的超微结构排列决定。当肌腱承受负荷时，胶原原纤维相对于邻近的原纤维伸长和滑动。 PG 糖胺聚糖 (GAG) 侧链在介导原纤维间负荷分配中的作用仍然存在争议，竞争的结构功能理论表明 PG 可能以机械方式耦合相邻的胶原原纤维（交联它们以促进原纤维拉伸）或隔离它们（促进原纤维滑动）。在这项研究中，我们试图通过直接研究天然肌腱和 GAG 耗尽肌腱中胶原蛋白网络内单个胶原原纤维的机械响应来阐明 GAG 在拉伸肌腱力学中的功能作用。将成年小鼠的跟腱对照组与使用软骨素酶 ABC 酶促消耗 GAG 的肌腱进行比较。将肌腱加载到特定的目标应变上，在恒定负载下进行化学固定，然后用原子力显微镜（AFM）进行切片以进行形态分析。胶原原纤维周期性带状的增加（D-周期）或原纤维直径的减少被认为是胶原原纤维伸长的代表，并且在此基础上量化了超尺度 GAG 的机械贡献。在施加高水平的肌腱应变（10%）时，GAG 耗尽的肌腱表现出胶原拉伸增加（原纤维滑动减少）。我们得出的结论是，亲水性 GAG 似乎不会起到机械交联的作用，而是会促进胶原纤维在张力下滑动。 (C) 2012 Elsevier Ltd. 保留所有权利。
The extracellular matrix of tendon is mainly composed of discontinuous Type-I collagen fibrils and small leucine rich proteoglycans (PG). Macroscopic tendon behaviors like stiffness and strength are determined by the ultrastructural arrangement of these components. When a tendon is submitted to load, the collagen fibrils both elongate and slide relative to their neighboring fibrils. The role of PG glycosaminoglycan (GAG) sidechains in mediating inter-fibril load sharing remains controversial, with competing structure-function theories suggesting that PGs may mechanically couple neighboring collagen fibrils (cross-linking them to facilitate fibril stretch) or alternatively isolating them (promoting fibril gliding). In this study, we sought to clarify the functional role of GAGs in tensile tendon mechanics by directly investigating the mechanical response of individual collagen fibrils within their collagen network in both native and GAG depleted tendons. A control group of Achilles tendons from adult mice was compared with tendons in which GAGs were enzymatically depleted using chondroitinase ABC. Tendons were loaded to specific target strains, chemically fixed under constant load, and later sectioned for morphological analysis by an atomic force microscope (AFM). Increases in periodic banding of the collagen fibrils (D-period) or decreases in fibril diameter was considered to be representative of collagen fibril elongation and the mechanical contribution of GAGs at the ultrascale was quantified on this basis. At high levels of applied tendon strain (10%), GAG depleted tendons showed increased collagen stretch (less fibril sliding). We conclude that the hydrophilic GAGs seem thus not to act as mechanical crosslinks but rather act to promote collagen fibril sliding under tension. (C) 2012 Elsevier Ltd. All rights reserved.