Department of Molecular Biology, Princeton University, Princeton, NJ 08544.
Mol Biol Cell. 2021 Apr 15;32(8):739-752. doi: 10.1091/mbc.E20-08-0533. Epub 2021 Feb 24.
The physical structure of the extracellular matrix (ECM) is tissue-specific and fundamental to normal tissue function. Proper alignment of ECM fibers is essential for the functioning of a variety of tissues. While matrix assembly in general has been intensively investigated, little is known about the mechanisms required for formation of aligned ECM fibrils. We investigated the initiation of fibronectin (FN) matrix assembly using fibroblasts that assemble parallel ECM fibrils and found that matrix assembly sites, where FN fibrillogenesis is initiated, were oriented in parallel at the cell poles. We show that these polarized matrix assembly sites progress into fibrillar adhesions and ultimately into aligned FN fibrils. Cells that assemble an unaligned meshwork matrix form matrix assembly sites around the cell periphery, but the distribution of matrix assembly sites in these cells could be modulated through micropatterning or mechanical stretch. While an elongated cell shape corresponds with a polarized matrix assembly site distribution, these two features are not absolutely linked, since we discovered that transforming growth factor beta (TGF-β1) enhances matrix assembly site polarity and assembly of aligned fibrils independent of cell elongation. We conclude that the ultimate orientation of FN fibrils is determined by the alignment and distribution of matrix assembly sites that form during the initial stages of cell-FN interactions.
细胞外基质（ECM）的物理结构具有组织特异性，是正常组织功能的基础。ECM 纤维的正确排列对于各种组织的功能至关重要。尽管已经深入研究了基质的组装，但对于形成定向 ECM 原纤维所需的机制知之甚少。我们研究了使用组装平行 ECM 原纤维的成纤维细胞启动纤连蛋白（FN）基质组装的过程，发现 FN 原纤维发生起始的基质组装位点在细胞两极呈平行排列。我们表明，这些极化的基质组装位点进展为原纤维黏附物，并最终形成定向排列的 FN 原纤维。组装不成形网状基质的细胞在细胞周围形成基质组装位点，但通过微图案化或机械拉伸可以调节这些细胞中基质组装位点的分布。虽然拉长的细胞形状对应于极化的基质组装位点分布，但这两个特征并非绝对相关，因为我们发现转化生长因子β（TGF-β1）增强了基质组装位点极性以及定向排列的原纤维的组装，而不依赖于细胞伸长。我们得出结论，FN 原纤维的最终取向取决于在细胞-FN 相互作用的初始阶段形成的基质组装位点的定向和分布。
