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Abstract #6318 Published in IGR 3-2
Effects of mechanical stretching on trabecular matrix metalloproteinases
Bradley JMB; Kelley MJ; Zhu XH; Anderssohn AM; Alexander JP; Acott TSInvestigative Ophthalmology and Visual Science 2001; 42: 1505-1513
PURPOSE: The homeostatic mechanisms responsible for intraocular pressure (IOP) regulation are not understood. Studies were conducted to evaluate the hypothesis that trabecular meshwork (TM) cells sense increases in IOP as stretching or distortion of their extracellular matrix (ECM), and respond by increasing ECM turnover enzymes. METHODS: Flow rates were increased in perfused human anterior segment organ cultures and the matrix metalloproteinase (MMP) levels and IOP were evaluated. Human TMs in stationary anterior segment organ culture were mechanically stretched, and MMP levels were analyzed. TM cells were grown on membranes, which were then stretched, and MMP levels evaluated. Western immunoblots, zymography, and confocal immunohistochemistry were used to evaluate changes in MMPs and their tissue inhibitors, the TIMPs. RESULTS: Doubling the flow rate in perfused human organ cultures increased gelatinase A levels or stromelysin levels. Immediately after doubling the flow rate, the measured IOP doubled. However, over the next few days, the IOP gradually returned to the initial level, although the flow rate was maintained at double the initial value. Stretching stationary organ cultures or stretching TM cells grown on membranes resulted in similar increases in gelatinase A without changes in gelatinase B or stromelysin levels. The gelatinase A increases occurred between 24 and 72 hours and were approximately proportional to the degree of stretching. Although coating the membranes with different ECM molecule affected the gelatinase A response, the optimum response occurred when the cells had been grown for long enough to produce their own ECM. By Western immunoblot and confocal immunohistochemistry, the stretch-induced increases in gelatinase A were accompanied by strong decreased in TIMP-2 levels and moderate increases in one membrane type MMP, MTI-MMP. After mechanical stretching of the membrane, gelatinase A, MTI-MMP and TIMP-2 all exhibited a similar punctate immunostaining pattern over the TM cell surface. CONCLUSIONS: These results are compatible with the hypothesis that evaluations in IOP are sensed by TM cells as ECM stretch/distortion. TM cells response by increasing gelatinase A and MTI-MMP, while decreasing TIMP-2 levels. This will increase ECM turnover rates, reduce the trabecular resistance to aqueous humor outflow, and restore normal IOP levels. This hypothesis provides a regulatory feedback mechanism for IOP homeostasis.
Dr T.S. Acott, Casey Eye Institute (CERES), Oregon Health Sciences University, 3375 SW Terwilliger, Portland, OR 97201, USA. acott@ohsu.edu
Classification:
2.3 Sclera (Part of: 2 Anatomical structures in glaucoma)
2.5 Meshwork (Part of: 2 Anatomical structures in glaucoma)
3.3 Immunohistochemistry (Part of: 3 Laboratory methods)
