Lens Basement Membrane in SPARC-Null Cataractogenesis

说明(申请人提供)：SPARC(酸性和富含半胱氨酸的分泌蛋白)，又称骨连素和BM-40，是一种基质细胞糖蛋白，已被证明调节细胞周期、细胞形状改变、迁移、黏附、基因表达和细胞外基质产生等功能。SPARC缺失的小鼠是存活的，但表现出100%外显的白内障。晶状体囊膜是一种高度发达的晶状体基底膜，是一种特殊的细胞外基质结构，其功能是调节晶状体上皮细胞的行为和分化。SPARC作为一种主要的细胞-基质调节因子，定位于晶状体囊膜和晶状体上皮细胞，可能在晶状体BM结构、基质组织及其与细胞内通路的连接以及晶状体细胞-ECM的相互作用中发挥关键作用，这些缺陷可能会导致严重的病理后果，如白内障的形成。我们将验证这一假设，即SPARC的缺失导致晶状体BM结构和功能完整性的丧失，并导致晶状体细胞-ECM相互作用的改变，从而导致白内障的发生。 基于对SPARC结构和功能的理解，我们提出了三个目标来验证我们的假设：1)SPARC在晶状体BM的结构稳定性和组织中起着关键作用。缺乏SPARC的小鼠将出现晶状体BM成分的改变和晶状体囊膜结构的受损；2)SPARC通过调节粘连蛋白1和纤维连接蛋白的产生以及与它们的相互作用来调节晶状体上皮细胞的黏附；3)在SPARC缺失的晶状体中，晶状体囊膜的通透性受到损害，这在一定程度上导致了该模型中白内障的形成。 本申请中提出的实验将提供对SPARC在细胞外基质成分的组织、晶状体发育过程中细胞-ECM相互作用以及在SPARC基因缺失小鼠的白内障发生中的作用的了解。

DESCRIPTION (provided by applicant): SPARC (secreted protein acidic and rich in cysteine), also termed osteonectin and BM-40, is a matricellular glycoprotein which has been shown to regulate cell functions such as cell cycle, cell shape change, migration, adhesion, gene expression and ECM production. SPARC-null mice are viable but exhibit cataract with 100% penetrance. Lens capsule, a highly-developed lens basement membrane (BM), is a specialized ECM structure which functions to regulate cell behavior and differentiation of the lens epithelial cells. SPARC, as a major cell-matrix regulator that is localized in the lens capsule and lens epithelium, may play a pivotal role in the lens BM structure, matrix organization and its connections to intracellular pathways, and lens cell-ECM interactions, defects in which can have significant pathological consequences, such as cataract formation. We will test the hypothesis that the absence of SPARC contributes to a loss of the structural and functional integrity of the lens BM, and leads to alteration of lens cell-ECM interactions, that contribute to the generation of cataracts. Based on our understanding of SPARC structure and function, we propose three aims to test our hypotheses: 1) SPARC plays a pivotal role in structural stability and organization of the lens BM. Mice lacking SPARC will exhibit alterations of lens BM components and compromised lens capsule structure; 2) SPARC modulates lens epithelial cell adhesion through its regulation of the production of the adhesive proteins laminin 1 and fibronectin, and by its interaction with them; 3) Lens capsule permeability is compromised in SPARC-null lens, which contributes, in part, to the cataract formation in this model. The experiments proposed in this application will provide an understanding of the role of SPARC in the organization of ECM components, in cell-ECM interactions during lens development, and in the generation of cataracts in SPARC-null mice.