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S. Mukherjee, J.L. King, C. Guidry; Retinal Pigment Epithelial Cell Expression of Insulin–Like Growth Factor Binding Proteins (IGFBPs) Changes With Phenotype . Invest. Ophthalmol. Vis. Sci. 2005;46(13):5355.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: In light of the probable involvement of RPE and the insulin–like growth factor system in the pathogenesis of proliferative retinal diseases, it is important to consider the functional consequences of changes in local IGFBP expression as a contributing mechanism. Although recent studies report IGFBP expression in human RPE, no information is available about the potential changes that occur in concert with RPE phenotype. Methods: RPE phenotype was characterized at varying times in culture by Western blots of detergent–extracted proteins and indirect immunofluorescence localization of cytoskeletal proteins. IGFBP expression was evaluated by RT–PCR of total RNA preparations at the same time points. Results: RPE in situ were immunoreactive for cytokeratin 18, vinculin, and paxillin, and expressed RT–PCR – detectable message for IGFBP–2, –3, –4, –5, and –6, but not IGFBP–1. RPE cells at 7 days in culture were polygonal and pigmented, continued to express cytokeratin 18, vinculin, and paxillin, and acquired expression of vimentin. At this stage, IGFBP expression included loss of IGFBP–2 and –4 without any changes in IGFBP–1, –3, –5 and –6. After 35 days in continuously proliferating culture, myofibroblastic RPE cells lost cytokeratin 18 expression, qualitatively increased expression of paxillin, vinculin and vimentin, and acquired expression of α–smooth muscle actin. IGFBP expression in these cells was unchanged from the 7 day cultures. Conclusions: RPE phenotype changes in culture can be defined by differential expression of cytoskeletal proteins and phenotype change has functional consequences on IGFBP expression. Normal RPE in situ express 5 of the 6 high–affinity IGFBPs (IGFBPs –2 through –6) but not IGFBP–1. RPE of the ‘early reactive’ (7d) and ‘myofibroblastic’ (35d) phenotypes lose expression of IGFBP–2 and –4. While the actions of specific IGFBPs on RPE biology are currently unknown, the established growth factor–modulating effects of these proteins in other experimental systems indicate that the observed changes in IGFBP expression should have functional consequences.
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