Watanabe Takafumi, Kametani Kiyokazu, Koyama Yoh-Ichi, Suzuki Daisuke, Imamura Yasutada, Takehana Kazushige, Hiramatsu Kohzy
From the Faculty of Agriculture, Shinshu University, Minami-minowa, Kami-ina, Nagano 399-4598, Japan,
Department of Instrumental Analysis, Research Center for Human and Environmental Science, Shinshu University, Asahi, Matsumoto, Nagano 390-8621, Japan.
J Biol Chem. 2016 Nov 4;291(45):23704-23708. doi: 10.1074/jbc.M116.733857. Epub 2016 Sep 13.
Tendons are composed of collagen fibrils and proteoglycan predominantly consisting of decorin. Decorin is located on the d-band of collagen fibrils, and its glycosaminoglycan (GAG) chains have been observed between collagen fibrils with transmission electron microscopy. GAG chains have been proposed to interact with each other or with collagen fibrils, but its three-dimensional organization remains unclear. In this report, we used focused ion beam scanning electron microscopy to examine the three-dimensional organization of the GAG chain in the Achilles tendon of mature rats embedded in epoxy resin after staining with Cupromeronic blue, which specifically stains GAG chains. We used 250 serial back-scattered electron images of longitudinal sections with a 10-nm interval for reconstruction. Three-dimensional images revealed that GAG chains form a ring mesh-like structure with each ring surrounding a collagen fibril at the d-band and fusing with adjacent rings to form the planar network. This ring mesh model of GAG chains suggests that more than two GAG chains may interact with each other around collagen fibrils, which could provide new insights into the roles of GAG chains.
肌腱由胶原纤维和主要由核心蛋白聚糖组成的蛋白聚糖构成。核心蛋白聚糖位于胶原纤维的d带，通过透射电子显微镜观察到其糖胺聚糖（GAG）链存在于胶原纤维之间。有人提出GAG链彼此之间或与胶原纤维相互作用，但其三维结构仍不清楚。在本报告中，我们使用聚焦离子束扫描电子显微镜，在用专门染色GAG链的铜铬蓝染色后，检查包埋在环氧树脂中的成熟大鼠跟腱中GAG链的三维结构。我们使用间隔为10纳米的250张纵向切片的连续背散射电子图像进行重建。三维图像显示，GAG链形成环形网状结构，每个环在d带围绕一条胶原纤维，并与相邻的环融合形成平面网络。这种GAG链的环形网状模型表明，两条以上的GAG链可能在胶原纤维周围相互作用，这可能为深入了解GAG链的作用提供新的思路。
