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W. Lo, C. Zhou, J.R. Reddan; Caveolae in the Lens . Invest. Ophthalmol. Vis. Sci. 2003;44(13):1234.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Caveolae are unique lipid membrane microdomains observed in many cell types. They are believed to play crucial roles in signal transduction. In this study we determined the existence and distribution of caveolae and caveolin-1, a major caveolar integral protein, in intact lenses of several species. We also examined the response of caveolae to methyl-beta-cyclodextrin (MBCD), a specific cholesterol depleting drug, in cultured rabbit lens epithelial cells. Methods: Electron microscopy, cytochemistry, immunofluorescence and immunoblotting were used for structural and protein detection. Cultured rabbit lens epithelial cells (line N/N1003A) were used for examining the effect of cholesterol depletion with MBCD. The lens epithelial cells were incubated in freshly prepared MEM medium plus 8% rabbit serum containing 10mM MBCD for 0 (control), 15, 30 or 60 minutes. Additional controls were cultured in MEM plus 8% rabbit serum for 60 minutes. The medium was removed and the cells were fixed at the times indicated and processed for TEM. Results: Among several species studied, lens epithelia of rabbit and guinea pig exhibited a large number of caveolae. These caveolae were pear shape, approximately 70 nm in diameter, and were found frequently along the lateral membranes of epithelial cells in the intact lens. In cultured lens epithelial cells, however, caveolae were observed along all membrane surfaces, but were more abundant at the apical membrane of the cells. In the intact cortical fibers, only a small number of caveolae were seen in the superficial cells. Immunofluorescence and immunoblot analyses confirmed the presence of caveolin-1 in the lens epithelium. HRP tracer study demonstrated that caveolae could undergo endocytosis, suggesting their involvement in molecular transport. The drug treatment study revealed that depletion of cholesterol abolished a majority of caveolae in cultured lens epithelial cells after 30-min incubation in 10mM MBCD medium. Conclusions: Caveolae and caveolin-1 are present in lens epithelia of rabbit and guinea pig under normal condition. The MBCD treatment confirms that caveolae are cholesterol-rich lipid raft domains which are likely to play important roles such as signal transduction in the lens.
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