Abstract | PURPOSE:
Osteonectin/SPARC is a secreted protein that has been implicated in ocular disease. Deletion of osteonectin/SPARC causes age-onset cataract in mice and the cataractous human lens has increased expression of osteonectin/SPARC. In this study, the expression and localization of osteonectin/SPARC in the monkey retina were determined as was secretion by cultured human retinal pigment epithelial (RPE) cells. METHODS: Adult Rhesus monkey eyes (Macaca mulatta) were dissected, and 5-mm macula and peripheral retina punches were obtained. Supernatants were collected from cultured human RPE cells. Subcellular fractionation of whole monkey retina was also performed. Osteonectin/SPARC expression and/or secretion was monitored by Northern and Western blot analyses, and localization was determined by immunocytochemistry. RESULTS: Outside of the retina osteonectin/SPARC mRNA is broadly expressed in many human tissues. Northern blot analysis shows that in the retina osteonectin/SPARC is expressed almost exclusively by the macular RPE/choroid. Western blot analysis revealed osteonectin/SPARC in both the macula and the peripheral neural retina but only in trace amounts in the RPE/choroid. In subcellular fractions of the whole retina, osteonectin/SPARC was detected, mainly in the soluble fraction but also in the membrane and nuclear fractions. Immunohistochemical analysis localized osteonectin/SPARC specifically to the outer plexiform layer. Western blot analysis of conditioned medium from human RPE cells cultured on porous substrates indicated that osteonectin/SPARC is secreted in large amounts from both the apical and basal sides of the RPE. CONCLUSIONS: Collectively these data provide evidence that osteonectin/SPARC is synthesized in the macular RPE, secreted, and subsequently transported to the outer plexiform layer. The expression pattern of osteonectin/SPARC in the subcellular retinal fractions is consistent with a soluble protein that is transported and internalized.
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Authors | I R Rodríguez, E F Moreira, D Bok, M Kantorow |
Journal | Investigative ophthalmology & visual science
(Invest Ophthalmol Vis Sci)
Vol. 41
Issue 9
Pg. 2438-44
(Aug 2000)
ISSN: 0146-0404 [Print] United States |
PMID | 10937551
(Publication Type: Journal Article, Research Support, Non-U.S. Gov't, Research Support, U.S. Gov't, P.H.S.)
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Chemical References |
- DNA Primers
- Eye Proteins
- Osteonectin
- RNA, Messenger
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Topics |
- Animals
- Biological Transport
(physiology)
- Blotting, Northern
- Blotting, Western
- Cells, Cultured
- DNA Primers
(chemistry)
- Electrophoresis, Polyacrylamide Gel
- Eye Proteins
(genetics, metabolism)
- Immunoenzyme Techniques
- Macaca mulatta
- Osteonectin
(genetics, metabolism)
- Pigment Epithelium of Eye
(cytology, metabolism)
- RNA, Messenger
(metabolism)
- Retina
(metabolism)
- Subcellular Fractions
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