Institute of Chemical Engineering, Biotechnology and Environmental Technology, Faculty of Engineering, University of Southern Denmark, Niels Bohrs Allé 1, DK-5230 Odense M, Denmark.
Exp Eye Res. 2010 Jan;90(1):57-62. doi: 10.1016/j.exer.2009.09.011. Epub 2009 Sep 26.
Transforming growth factor beta induced protein (TGFBIp, also named keratoepithelin) is an extracellular matrix protein abundant in the cornea. The purpose of this study was to determine the expression and processing of TGFBIp in the normal human cornea during postnatal development and aging. TGFBIp in corneas from individuals ranging from six months to 86 years of age was detected and quantified by immunoblotting. The level of TGFBIp in the cornea increases about 30% between 6 and 14 years of age, and adult corneas contain 0.7-0.8 microg TGFBIp per mg wet tissue. Two-dimensional (2-D) immunoblots of the corneal extracts showed a characteristic "zig-zag" pattern formed by different lower-molecular mass TGFBIp isoforms (30-60 kDa). However, the relative abundance of the different isoforms was different between infant corneas (<1 year) and the child/adult corneas (>6 years). Matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry (MALDI-TOF MS) data of TGFBIp isoforms separated on large 2-D gels show that TGFBIp is proteolytically processed from the N-terminus. This observation was supported by in silico 2-D gel electrophoresis showing that sequential proteolytical trimming events from the N-terminus of mature TGFBIp generate TGFBIp isoforms which form a similar "zig-zag" pattern when separated by 2-D polyacrylamide gel electrophoresis (PAGE). This study shows that in humans TGFBIp is more abundant in mature corneas than in the developing cornea and that the processing of TGFBIp changes during postnatal development of the cornea. In addition, TGFBIp appears to be degraded in a highly orchestrated manner in the normal human cornea with the resulting C-terminal fragments being retained in the cornea. The age-related changes in the expression and processing of corneal TGFBIp suggests that TGFBIp may play a role in the postnatal development and maturation of the cornea. Furthermore, these observations may be relevant to the age at which mutant TGFBIp deposits in the cornea in those dystrophies caused by mutations in the transforming growth factor beta induced gene (TGFBI) as well as the mechanisms of corneal protein deposition.
转化生长因子β诱导蛋白（TGFBIp，也称为角蛋白上皮蛋白）是一种丰富存在于角膜中的细胞外基质蛋白。本研究旨在确定 TGFBIp 在正常人类角膜中的表达和加工在出生后发育和衰老过程中的作用。通过免疫印迹检测和定量分析了来自年龄在 6 个月至 86 岁之间的个体的角膜中的 TGFBIp。结果表明，角膜中 TGFBIp 的水平在 6 至 14 岁之间增加约 30%，而成人角膜中每毫克湿组织含有 0.7-0.8 微克 TGFBIp。角膜提取物的二维（2-D）免疫印迹显示，不同低分子量 TGFBIp 同工型（30-60 kDa）形成特征性的“之”字形图案。然而，婴儿角膜（<1 岁）和儿童/成人角膜（>6 岁）之间不同同工型的相对丰度不同。基质辅助激光解吸/电离-飞行时间质谱（MALDI-TOF MS）数据显示，TGFBIp 同工型在大型 2-D 凝胶上分离，表明 TGFBIp 是从 N 端进行蛋白水解加工的。这一观察结果得到了计算机模拟的 2-D 凝胶电泳的支持，表明成熟 TGFBIp 的 N 端的连续蛋白水解切割事件产生了 TGFBIp 同工型，当通过 2-D 聚丙烯酰胺凝胶电泳（PAGE）分离时，这些同工型形成类似的“之”字形图案。本研究表明，在人类中，TGFBIp 在成熟角膜中的丰度高于发育中的角膜，并且 TGFBIp 的加工在角膜的出生后发育过程中发生变化。此外，TGFBIp 在正常人类角膜中以高度协调的方式降解，其结果是 C 端片段保留在角膜中。角膜 TGFBIp 的表达和加工的年龄相关性变化表明，TGFBIp 可能在角膜的出生后发育和成熟中发挥作用。此外，这些观察结果可能与 TGFBI 基因突变引起的那些营养不良中突变 TGFBIp 在角膜中的沉积年龄以及角膜蛋白沉积的机制有关。
