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Protein synthesis and secretion by cultured retinal pigment epithelia
A Jaworowski1, Z Fang, T F Khong
1Russell Grimwade School of Biochemistry, University of Melbourne, Parkville, Australia.
Insights
Retinal pigment epithelial (RPE) cells secrete key proteins like retinol binding protein (RBP) and transthyretin (TTR) involved in vitamin A transport. These proteins are secreted primarily towards the retina, establishing a valuable in vitro model for blood-retinal barrier research.
Area of Science:
- Ophthalmology
- Cell Biology
- Biochemistry
Background:
- The retinal pigment epithelium (RPE) plays a crucial role in maintaining ocular health and visual function.
- Understanding protein synthesis and secretion by RPE cells is vital for elucidating mechanisms of nutrient transport across the blood-retinal barrier.
- Retinol transport proteins, such as RBP and TTR, are essential for delivering vitamin A to the retina.
Purpose of the Study:
- To investigate protein synthesis and secretion by post-natal sheep and calf RPE cells.
- To identify specific proteins secreted by RPE cells and their transport directionality.
- To establish an in vitro cell culture model for studying transport across the blood-retinal barrier.
Main Methods:
- Primary RPE cells from post-natal sheep and calves were cultured.
- Cells, choroidal pieces, and cultured RPE cells were labeled with L-[U-14C] leucine to track protein synthesis.
- A two-chambered culture system was employed to assess the directionality of protein secretion.
Main Results:
- Post-natal RPE cells synthesize and secrete a specific set of proteins.
- Secreted proteins include retinol binding protein (RBP) and transthyretin (TTR), crucial for retinol transport.
- Protein secretion predominantly occurs across the apical pole of RPE cells, facing the retina.
- RBP and TTR secretion is predominantly apical, consistent with in vivo function.
Conclusions:
- Post-natal RPE cells secrete essential retinol transport proteins apically.
- The developed RPE cell culture system serves as a valuable in vitro model for studying the blood-retinal barrier.
- This model can facilitate research into transport mechanisms and potential therapeutic interventions for retinal diseases.
Abstract:
Protein synthesis and secretion by post-natal sheep and calf retinal pigment epithelial (RPE) cells was investigated following labelling of choroidal pieces, isolated RPE cells and RPE cells in tissue culture with L-[U-14C] leucine. We show that RPE cells secrete a specific set of proteins that includes retinol binding protein (RBP) and transthyretin (TTR), which are both involved in retinol transport in blood. Using a two-chambered culture system we show that protein secretion by the post-natal RPE cells occurs predominantly across the apical pole of the cells, i.e., across the surface of the cells which, in vivo, faces the retina. In agreement with results of others using foetal RPE cells (Ong, D.E., Davis, J.T., O'Day, W.T. and Bok, D. (1994) Biochemistry 33, 1835-1842) we show that RBP and, to a lesser extent, TTR are also secreted predominantly across the apical pole of the cell. We have developed a cell culture model for the RPE that may be used as an in vitro model for studying transport across the blood-retinal barrier.