Secreted Protein Acidic and Rich in Cysteine in Ocular Tissue.

Secreted protein acidic and rich in cysteine (SPARC), also known as osteonectin or BM-40, is the prototypical matricellular protein. Matricellular proteins are nonstructural secreted proteins that provide an integration between cells and their surrounding extracellular matrix (ECM). Regulation of the ECM is important in maintaining the physiologic function of tissues. Elevated levels of SPARC have been identified in a variety of diseases involving pathologic tissue remodeling, such as hepatic fibrosis, systemic sclerosis, and certain carcinomas. Within the eye, SPARC has been identified in the trabecular meshwork, lens, and retina. Studies have begun to show the role of SPARC in these tissues and its possible role, specifically in primary open-angle glaucoma, cataracts, and proliferative vitreoretinopathy. SPARC may, therefore, be a therapeutic target in the treatment of certain ocular diseases. Further investigation into the mechanism of action of SPARC will be necessary in the development of SPARC-targeted therapy.