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Jaya Pranava Gnana Prakasam, Rajalakshmi Veeranan-Karmegam, Veena Coothankandaswamy, Sushma K. Reddy, Pamela M. Martin, Muthusamy Thangaraju, Sylvia B. Smith, Vadivel Ganapathy; Loss of Hfe Leads to Progression of Tumor Phenotype in Primary Retinal Pigment Epithelial Cells. Invest. Ophthalmol. Vis. Sci. 2012;53(14):6548.
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Hemochromatosis is a genetic disorder of iron overload resulting in oxidative stress. Mutations in HFE, which result in excessive iron accumulation in tissues, are found in ~ 85% of hemochromatosis patients. HFE is also expressed in retina, specifically in RPE, and plays an obligatory role in maintenance of retinal iron homeostasis. Hfe-/- mice accumulate excessive iron in retina and exhibit several features found in age-related macular degeneration, including hyperproliferation of retinal pigment epithelium (RPE). Here the mechanism underlying this particular phenotype in RPE was investigated.
The following biochemical characteristics were compared between primary cultures of mouse RPE prepared from wild type mice and Hfe-/- mice. Cellular senescence was monitored by senescence-specific β-galactosidase activity. Expression and location of survivin were determined by RT-PCR, Western blot, and immunofluorescence. Migration and invasion were monitored using appropriate kits. Expression and function of glucose transporters were determined by RT-PCR and uptake of 3-O-methyl-D-glucose. Expression and function of histone deacetylases (HDACs) were monitored by RT-PCR, catalytic activity, and acetylation status of histones H3 and H4. Expression of DNA methyltransferases (DNMTs) was studied by RT-PCR.
Compared to wild type RPE cells, Hfe-/- RPE cells exhibited slower senescence rate, accompanied with increased expression of the anti-apoptotic protein survivin. Hfe-/- cells migrated faster than wild type cells; however, the invasion rate was comparable. Hfe-/- cells possessed greater glucose uptake activity, accompanied with increased expression of glucose transporters SGLT1, GLUT1, GLUT3, and GLUT4. Levels of HDAC1 and HDAC3 were higher in Hfe-/- cells, demonstrable both at mRNA level and activity level. Similarly, expression of DNMT1 and DNMT3a was higher in Hfe-/- cells.
Hfe-/- RPE cells exhibit several features of tumor cells: decreased senescence, enhanced migration, increased glucose uptake, and elevated levels of epigenetic enzymes HDACs and DNMTs. These biochemical parameters underlie the hyperproliferative phenotype of Hfe-/- RPE cells.
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