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Ignacio R. Rodríguez, Ernesto F. Moreira, Dean Bok, Marc Kantorow; Osteonectin/SPARC Secreted by RPE and Localized to the Outer Plexiform Layer of the Monkey Retina. Invest. Ophthalmol. Vis. Sci. 2000;41(9):2438-2444.
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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
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
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