标题： 肌腱内胶原纤维半径的均匀空间分布意味着在单个纤维上局部激活了pC-胶原蛋白 显示英文标题

标题： Uniform spatial distribution of collagen fibril radii within tendon implies local activation of pC-collagen at individual fibrils

摘要： 胶原纤维横截面半径在纤维束的内部和外围之间没有系统性变化，表明胶原蛋白整合到纤维中的有效速率在整个束中保持恒定。 这种空间均匀的整合限制了胶原蛋白前体从束边界来源到生长纤维汇的细胞外扩散。 通过一个粗粒度扩散方程，我们使用从发表的肌腱发育实验测量中提取的参数确定了严格的界限。 从出生后缺乏新纤维形成来看，我们进一步要求扩散前体的浓度保持在纤维成核临界浓度以下。 我们发现，扩散界限（需要较高浓度以确保均匀的纤维半径）和缺乏成核（需要较低浓度）的组合仅与使用保守界限的完全加工胶原蛋白略有一致。 更现实的界限可能不留有任何一致的浓度。 因此，我们提出未加工的pC-胶原蛋白从束外围扩散，随后局部C-蛋白酶活性以及随后在每个纤维中的胶原蛋白整合。 我们建议C-蛋白酶在径向纤维生长期间位于束内，在纤维表面。 与完全加工的胶原蛋白相比，pC-胶原蛋白的临界浓度要高得多，这则在均匀的纤维半径和纤维生长过程中缺乏纤维成核之间提供了广泛的协调。 显示英文摘要

摘要： Collagen fibril cross-sectional radii show no systematic variation between the interior and the periphery of fibril bundles, indicating an effectively constant rate of collagen incorporation into fibrils throughout the bundle. Such spatially homogeneous incorporation constrains the extracellular diffusion of collagen precursors from sources at the bundle boundary to sinks at the growing fibrils. With a coarse-grained diffusion equation we determine stringent bounds, using parameters extracted from published experimental measurements of tendon development. From the lack of new fibril formation after birth, we further require that the concentration of diffusing precursors stays below the critical concentration for fibril nucleation. We find that the combination of the diffusive bound, which requires larger concentrations to ensure homogeneous fibril radii, and lack of nucleation, which requires lower concentrations, is only marginally consistent with fully-processed collagen using conservative bounds. More realistic bounds may leave no consistent concentrations. Therefore, we propose that unprocessed pC-collagen diffuses from the bundle periphery followed by local C-proteinase activity and subsequent collagen incorporation at each fibril. We suggest that C-proteinase is localized within bundles, at fibril surfaces, during radial fibrillar growth. The much greater critical concentration of pC-collagen, as compared to fully-processed collagen, then provides broad consistency between homogeneous fibril radii and the lack of fibril nucleation during fibril growth.