Primary open angle glaucoma (POAG) is one of the four major causes of blindness and visual disability. Two million people in the United States have glaucoma; 100,000 of them are blind. A key question in POAG is to identify cell factors that would adversely affect 1) normal aqueous humor outflow, 2) optic nerve function, and 3) glaucoma surgery. The extracellular matrix plays a vital role to all three. The matrix contains a variety of proteins organized in a hydrated gel composed of a network of glycosaminoglycan chains. Our biochemical studies and image analysis indicate that POAG is associated with a marked decrease in one glycosaminoglycan, hyaluronic acid, in the trabecular meshwork. It is recognized that hyaluronic acid, even at low concentrations, has important regulatory functions in cellular differentiation. The cell mechanism causing the hyaluronic acid decrease in aging or the further loss in POAG is unknown. One well characterized receptor for hyaluronic acid is CD44. CD44 is a transmembrane protein homologous to cartilage link protein and is known to have diverse functional properties. The ectodomain of CD44 is released from cells as soluble CD44. CD44 has multiple pro-inflammatory functions and may act as a trigger molecule involved in a cytolytic mechanism of cell death and apoptosis - all of which influence trabecular cell and retinal ganglion cell population as well as the surgical outcomes of glaucoma filtration surgery. We have identified a Triton X-100 soluble form of the CD44 that appears to biochemically and to immunocytochemically characterize POAG in the iris and ciliary body. The aqueous humor of POAG patients also has an increased concentration of soluble CD44 (P<0.00003) in comparison with the aqueous humor of age-matched normal patients. Our recent data support the concept that the CD44 receptor in POAG eyes is released as an activated soluble form as a result of upregulated expression. We plan to analyze normal and POAG hyaluronic acid and its receptor, CD44, in surgical samples of aqueous humor and in post-mortem donor eyes by 1) characterizing the amount and isoforms of CD44; 2) examining functional studies on the binding of CD44 to hyaluronic acid, and 3) determining a partial amino acid sequence of CD44 to determine whether there are cellular and molecular changes in CD44 in POAG. These studies will give insight into the cellular and molecular basis of the pathophysiology of the extracellular matrix in the trabecular meshwork, the optic nerve, and the surgical intervention in the POAG disease process.
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