Phenotype-Associated Changes in Retinal Pigment Epithelial Cell Expression of Insulin-Like Growth Factor Binding Proteins
Sudipto Mukherjee 1,
Jeffery L King 2,
and
Clyde Guidry 3*
1 Visual Science, University of Alabama at Birmingham, Birmingham, Alabama, United States
2 Ophthalmology, University of Alabama School of Medicine, Birmingham, Alabama, United States
3 Department of Ophthalmology, University of Alabama School of Medicine, EFH DB106, Birmingham, Alabama, 35294, United States
* To whom correspondence should be addressed. E-mail: cguidry{at}uab.edu.
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Abstract |
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Purpose. The objectives of this study were to evaluate retinal pigment epithelial (RPE) cells as a source of insulin-like growth factor binding proteins (IGFBPs) and to characterize biosynthetic changes associated with the cell phenotype and vitreous growth factor stimuli known to be present in fibrocontractive diseases.
Methods. Early culture-associated changes in RPE phenotype were characterized by indirect immunofluorescence localization and Western blots of cell lysates. IGFBP expression was evaluated by RT-PCR and Northern blots of total RNA preparations.
Results. Normal unperturbed RPE are immunoreactive for cytokeratin 18 and negative for cytokeratin 19, vimentin and 
smooth muscle actin (SMA). Early reactive RPE (7 days in culture) express cytokeratins 18, 19 and vimentin. Myofibroblastic RPE (35 days in culture) express cytokeratin 19, vimentin and SMA. RT-PCR studies revealed that normal RPE can produce IGFBP-2, -3, -4, -5 and -6, but not IGFBP-1. Early reactive and myofibroblastic RPE possess detectable levels of message for IGFBP-3, -5 and -6. However, Northern blots suggest that IGFBP-5 is the predominant binding protein produced. Finally, stimulation with biologically relevant quantities of IGF-I and IGF-II had no detectable effects on IGFBP expression.
Conclusions. Changes in RPE phenotype are accompanied by dramatic changes in IGFBP expression profile with IGFBP-5 being the predominant binding protein produced by myofibroblastic RPE cells.
Key Words:
retinal pigment epithelium, growth factors, cell culture
