Inoue Tadashi, Ohbayashi Tetsuya, Fujikawa Yusuke, Yoshida Hideyuki, Akama Tomoya O, Noda Kazuo, Horiguchi Masahito, Kameyama Katsuro, Hata Yoshio, Takahashi Kanji, Kusumoto Kenji, Nakamura Tomoyuki
Department of Pharmacology, Department of Plastic and Reconstructive Surgery.
Division of Laboratory Animal Science, Research Center for Bioscience and Technology and.
Hum Mol Genet. 2014 Nov 1;23(21):5672-82. doi: 10.1093/hmg/ddu283. Epub 2014 Jun 6.
Latent TGF-β-binding protein-2 (LTBP-2) is an extracellular matrix protein associated with microfibrils. Homozygous mutations in LTBP2 have been found in humans with genetic eye diseases such as congenital glaucoma and microspherophakia, indicating a critical role of the protein in eye development, although the function of LTBP-2 in vivo has not been well understood. In this study, we explore the in vivo function of LTBP-2 by generating Ltbp2(-/-) mice. Ltbp2(-/-) mice survived to adulthood but developed lens luxation caused by compromised ciliary zonule formation without a typical phenotype related to glaucoma, suggesting that LTBP-2 deficiency primarily causes lens dislocation but not glaucoma. The suppression of LTBP2 expression in cultured human ciliary epithelial cells by siRNA disrupted the formation of the microfibril meshwork by the cells. Supplementation of recombinant LTBP-2 in culture medium not only rescued the microfibril meshwork formation in LTBP2-suppressed ciliary epithelial cells but also restored unfragmented and bundled ciliary zonules in Ltbp2(-/-) mouse eyes under organ culture. Although several reported human mutant LTBP-2 proteins retain normal domain structure and keep the fibrillin-1-binding site intact, none of these mutant proteins were secreted from their producing cells, suggesting secretion arrest occurred to the LTBP-2 mutants owing to conformational alteration. The findings of this study suggest that LTBP-2 is an essential component for the formation of microfibril bundles in ciliary zonules.
潜伏性转化生长因子-β结合蛋白2（LTBP-2）是一种与微原纤维相关的细胞外基质蛋白。在患有先天性青光眼和小晶状体等遗传性眼病的人类中发现了LTBP2的纯合突变，这表明该蛋白在眼睛发育中起关键作用，尽管LTBP-2在体内的功能尚未得到很好的理解。在本研究中，我们通过生成Ltbp2(-/-)小鼠来探索LTBP-2的体内功能。Ltbp2(-/-)小鼠存活至成年，但由于睫状小带形成受损而出现晶状体脱位，且没有与青光眼相关的典型表型，这表明LTBP-2缺乏主要导致晶状体脱位而非青光眼。通过小干扰RNA抑制培养的人睫状上皮细胞中LTBP2的表达会破坏细胞微原纤维网络的形成。在培养基中补充重组LTBP-2不仅挽救了LTBP2抑制的睫状上皮细胞中的微原纤维网络形成，还在器官培养条件下恢复了Ltbp2(-/-)小鼠眼中完整且成束的睫状小带。尽管有报道称几种人类突变型LTBP-2蛋白保留了正常的结构域结构并保持原纤维蛋白-1结合位点完整，但这些突变蛋白均未从其产生细胞中分泌出来，这表明LTBP-2突变体由于构象改变而发生了分泌阻滞。本研究结果表明，LTBP-2是睫状小带中微原纤维束形成的必需成分。
