The oxidation of tyrosine residues to generate o,o′-dityrosine cross-links in extracellular proteins is necessary for the proper function of the extracellular matrix (ECM) in various contexts in invertebrates. Tyrosine oxidation is also required for the biosynthesis of thyroid hormone in vertebrates, and there is evidence for oxidative cross-linking reactions occurring in extracellular proteins secreted by myofibroblasts. The ECM protein fibronectin circulates in the blood as a globular protein that dimerizes through disulfide bridges generated by cysteine oxidation. We found that cellular (fibrillar) fibronectin on the surface of transforming growth factor–β1 (TGF-β1)–activated human myofibroblasts underwent multimerization by o,o′-dityrosine cross-linking under reducing conditions that disrupt disulfide bridges, but soluble fibronectin did not. This reaction on tyrosine residues required both the TGF-β1–dependent production of hydrogen peroxide and the presence of myeloperoxidase (MPO) derived from inflammatory cells, which are active participants in wound healing and fibrogenic processes. Oxidative cross-linking of matrix fibronectin attenuated both epithelial and fibroblast migration and conferred resistance to proteolysis by multiple proteases. The abundance of circulating o,o′-dityrosine–modified fibronectin was increased in a murine model of lung fibrosis and in human subjects with interstitial lung disease compared to that in control healthy subjects. These studies indicate that tyrosine can undergo stable, covalent linkages in fibrillar fibronectin under inflammatory conditions and that this modification affects the migratory behavior of cells on such modified matrices, suggesting that this modification may play a role in both physiologic and pathophysiologic tissue repair.

酪氨酸残基的氧化在细胞外蛋白中产生o,o'-二酪氨酸交联对于无脊椎动物中细胞外基质 (ECM) 在各种情况下的正常功能是必要的。脊椎动物甲状腺激素的生物合成也需要酪氨酸氧化，并且有证据表明肌成纤维细胞分泌的细胞外蛋白质中发生氧化交联反应。ECM 蛋白纤连蛋白作为球状蛋白在血液中循环，通过半胱氨酸氧化产生的二硫桥二聚化。我们发现，转化生长因子β1（TGF-β1）激活的人肌成纤维细胞表面的细胞（纤维状）纤连蛋白在破坏二硫键的还原条件下通过o,o'-二酪氨酸交联发生多聚化，但可溶性纤连蛋白却发生了多聚化。不是。这种对酪氨酸残基的反应需要 TGF-β1 依赖性的过氧化氢产生和源自炎症细胞的髓过氧化物酶 (MPO) 的存在，炎症细胞是伤口愈合和纤维形成过程的积极参与者。基质纤连蛋白的氧化交联减弱了上皮细胞和成纤维细胞的迁移，并赋予对多种蛋白酶的蛋白水解的抗性。与对照健康受试者相比，在小鼠肺纤维化模型和患有间质性肺疾病的人类受试者中，循环中o,o'-二酪氨酸修饰的纤连蛋白的丰度有所增加。这些研究表明，在炎症条件下，酪氨酸可以在纤维状纤连蛋白中进行稳定的共价连接，并且这种修饰影响细胞在此类修饰基质上的迁移行为，表明这种修饰可能在生理和病理生理组织修复中发挥作用。