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Joseh J. Smith, Weilue He, Cameron Atkinson, Jackie Pribyl, Beth Elledge, Srinivas Sripathi, Elizabeth Hager, Michael K. Gibson, Wan Jin Jahng; Cholesterol Modulation Changes Membrane Composition and Prohibitin Localization in RPE and Retina. Invest. Ophthalmol. Vis. Sci. 2011;52(14):884.
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Cholesterol is the primary sterol that maintains membrane integrity in the retinal pigment epithelium (RPE). We hypothesize that alteration of cholesterol or cholesterol precursors with β-cyclodextrin (βCD) will alter the expression of membrane proteins such as prohibitin (PHB) and subsequent alterations of the RPE. To evaluate the role of cholesterol in PHB translocalization, we employed both βCD-treated cells and mice with targeted deletion of the cholesterol enzyme mevalonate kinase (Mvk) to characterize the effects of reduced cholesterol on PHB localization in RPE.
ARPE-19 cells were cultured with cholesterol concentrations of 50, 100, 150, and 200 µM for 16 hours. ARPE-19 cells were also cultured with βCD for one hour to deplete cholesterol followed by one hour treatments with cholesterol/βCD complexes to replenish cholesterol. Eyes from Mvk and wild type mice were isolated and dissected for retina and RPE. Cytosolic, nuclear, and mitochondrial fractions were separated by SDS-PAGE and visualized by Western blot using PHB1 or PHB2 antibodies.
Supplementation with cholesterol revealed a corresponding increase in PHB expression. Treatment with βCD resulted in increased PHB expression for cholesterol- depleted cells. Conversely, βCD coupled with higher cholesterol concentrations resulted in down-regulation of PHB levels. Mvk mice demonstrated increased PHB in the nuclear fraction and altered PHB complexes in mitochondrial and cytosolic fractions.
Our results suggest that PHB expression and trafficking is dependent upon cholesterol concentrations. We speculate that alterations in the cellular capacity to phosphorylate mevalonate (in Mvk-deficient mice) may alter translocalization and trafficking of PHB. Overall, our preliminary studies suggest that cholesterol depletion is compensated in the RPE via altered expression and localization of PHB, in order to maintain membrane fluidity and mitochondrial function.
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