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S.C. Finnemann, Y.A. Kim, E.F. Nandrot; Effects of ß5 Knockout on Mouse RPE Function in vivo and in vitro Reveal an Important Role of vß5 Integrin Receptors in Phagocytosis by the Retinal Pigment Epithelium . Invest. Ophthalmol. Vis. Sci. 2003;44(13):368.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To characterize how constitutive loss of the RPE surface receptor αvß5 integrin affects neural retina and RPE function. Methods: ß5 integrin knockout mice that lack αvß5 receptors and wild-type mice of the same genetic background were bred to generate age-matched groups. Electroretinogram (ERG) recordings were used to assess retinal function. Eye cryosections were labeled with retinal markers or with toluidine blue and observed by fluorescence or light microscopy, respectively, to evaluate retinal morphology. OS phagosomes were counted in transmission electron micrographs. Phagocytosis of isolated outer segment fragments (OS) by unpassaged primary RPE cultures prepared from 12 to 16 day old wild-type and ß5 null mice was quantified in the presence and absence of integrin peptide inhibitors. Results: αvß5 integrin localized to the apical, phagocytic surface of RPE in the mouse eye, like in the rat and human eye. In 3 week old mice, ß5 null RPE in situ carried fewer phagocytosed OS 3 hours after light onset compared to wild-type RPE. In 14 month old mice, scotopic ERGs of ß5 null mice had significantly lower a- and b-wave amplitudes than those of wild-type mice. This indicated that ß5 knockout impaired the function of retinal neurons including photoreceptor rods. In young mice, ß5 null and wild-type retinas appeared similar. However, in mice of age, loss of ß5 specifically altered overall retinal morphology to varying degrees ranging from outer segment shortening to photoreceptor cell loss. After 1 hour of OS phagocytic challenge, total OS uptake by ß5 null RPE in primary culture was reduced by 75% as compared to wild-type control RPE suggesting a primary effect of ß5 knockout on OS recognition/binding. Integrin ligand mimetic peptides inhibited OS binding by mouse RPE in primary culture but did not affect uptake by ß5 null RPE. Thus, residual OS uptake in the absence of αvß5 did not utilize integrin receptors other than αvß5, which are present in ß5 null RPE. Importantly, loss of ß5 abrogated OS signaling to focal adhesion kinase and Rac1, which is essential for OS engulfment. Conclusions: Our results demonstrate that lack of αvß5 receptors (1) delays daily OS clearance by RPE in vivo, (2) severely impairs OS recognition/binding by RPE in vitro, and (3) abolishes OS signaling. Retinal dysfunction we observed in ß5 null mice of age may thus be a consequence of long-term reduced or arrhythmic OS clearance. These data illustrate the important contribution of αvß5 integrin receptors to the phagocytic activity of RPE.
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