Collagens XII and XIV (FACITs) in capsular opacification and in cultured lens epithelial cells

Tenascins and osteopontin in biological response in cornea

The structural composition, integrity and regular curvature of the cornea contribute to the maintenance of its transparency and vision. Disruption of its integrity caused by injury results in scarring, inflammation and neovascularization followed by losses in transparency. These sight compromising effects is caused by dysfunctional corneal resident cell responses induced by the wound healing process. Upregulation of growth factors/cytokines and neuropeptides affect development of aberrant behavior. These factors trigger keratocytes to first transform into activated fibroblasts and then to myofibroblasts. Myofibroblasts express extracellular matrix components for tissue repair and contract the tissue to facilitate wound closure. Proper remodeling following primary repair is critical for restoration of transparency and visual function. Extracellular matrix components contributing to the healing process are divided into two groups; a group of classical tissue structural components and matrix macromolecules that modulate cell behaviors/activities besides being integrated into the matrix structure. The latter components are designated as matricellular proteins. Their functionality is elicited through mechanisms which modulate the scaffold integrity, cell behaviors, activation/inactivation of either growth factors or cytoplasmic signaling regulation. We discuss here the functional roles of matricellular proteins in mediating injury-induced corneal tissue repair. The roles are described of major matricellular proteins, which include tenascin C, tenascin X and osteopontin. Focus is directed towards dealing with their roles in modulating individual activities of wound healing-related growth factors, e. g., transforming growth factor β (TGF β). Modulation of matricellular protein functions could encompass a potential novel strategy to improve the outcome of injury-induced corneal wound healing.

Accumulation of thrombospondin-1 in post-operative capsular fibrosis and its down-regulation in lens cells during lens fiber formation

Thrombospondin-1 (TSP-1) is a glycoprotein involved in activation of latent transforming growth factor beta (TGFbeta) expression. We examined changes in its expression pattern during human capsular opacification (PCO) and anterior subcapsular cataractogenesis (ASC), as well as in a healing injured mouse lens. Its expression pattern was also compared in a mouse embryonic lens with that in an adult lens. Based on immunohistochemistry under light microscopy, TSP-1 expression and other matrix components were evident in the anterior epithelium of an uninjured human lens, whereas fiber-differentiating cells in the equator of human lens lack TSP-1 immunoreactivity. In contrast, in post-operative human lens epithelial or fibroblastic cells, there was TSP-1 immunoreactivity, whereas it decreased in fiber-differentiating cells in PCO. Matrix components accumulated on the healing capsule also labeled with anti-TSP-1 antibody like antibodies against collagen I, IV, V and laminin. In uninjured, injured mouse lens epithelial cells and its matrix, there was TSP-1 expression. Embryonic lens cells in the posterior pole, undergoing differentiation to fiber cells, began to express TSP-1 protein at embryonic day (E) 11.5 whereas anterior epithelial cells started to express it at E13.5 in association with marked expression in central fiber cells. At E16.5, TSP-1 was detected in fibers just beneath the anterior epithelium, but the fiber mass showed minimal expression. At E18.5 and post-natally day 1, lens fiber TSP-1 expression was no longer seen. On the other hand, it was evident in both intact human anterior epithelial and dispersed mouse cells. The results indicate that there is TSP-1 expression in uninjured human and mouse lens epithelial cells and their fibrous tissue. In contrast, in post-operative lens cells differentiating to fiber cells, its expression levels decline. Further study is needed to clarify the roles of TSP-1 in modulating lens cell phenotype expression.

Relationship between posterior capsule opacification and intraocular lens biocompatibility

The type of healing process that occurs in response to cataract surgery and intraocular lens (IOL) implantation is dependent on a complex set of variables. Their interactions determine whether or not optical clarity is restored as a result of this procedure. In this process, wound healing entails cells undergoing either epithelial-mesenchymal transition, resulting in the generation of fibroblastic cells and accumulation of extracellular matrix, or lenticular structure formation. Such desperate cellular behaviors are regulated by the localized release of different cytokines, including transforming growth factor beta and fibroblast growth factors, which can result in post-operative capsular opacification. Other factors affecting the biological and mechanical outcome of IOL implantation are its composition, surface properties and shape.