αvβ5 Integrin Receptors at the Apical Surface of the RPE: One Receptor, Two Functions (original) (raw)
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Loss of Synchronized Retinal Phagocytosis and Age-related Blindness in Mice Lacking v 5 Integrin
Journal of Experimental Medicine, 2004
Daily phagocytosis by the retinal pigment epithelium (RPE) of spent photoreceptor outer segment fragments is critical for vision. In the retina, early morning circadian photoreceptor rod shedding precedes synchronized uptake of shed photoreceptor particles by RPE cells. In vitro, RPE cells use the integrin receptor ␣ v  5 for particle binding. Here, we tested RPE phagocytosis and retinal function in  5 integrin-deficient mice, which specifically lack ␣ v  5 receptors. Retinal photoresponses severely declined with age in  5 Ϫ / Ϫ mice, whose RPE accumulated autofluorescent storage bodies that are hallmarks of human retinal aging and disease.  5 Ϫ / Ϫ RPE in culture failed to take up isolated photoreceptor particles.  5 Ϫ / Ϫ RPE in vivo retained basal uptake levels but lacked the burst of phagocytic activity that followed circadian photoreceptor shedding in wild-type RPE. Rhythmic activation of focal adhesion and Mer tyrosine kinases that mediate wild-type retinal phagocytosis was also completely absent in  5 Ϫ / Ϫ retina. These results demonstrate an essential role for ␣ v  5 integrin receptors and their downstream signaling pathways in synchronizing retinal phagocytosis. Furthermore, they identify the  5 Ϫ / Ϫ integrin mouse strain as a new animal model of age-related retinal dysfunction.
Scientific Reports
retinal neurons and the RPE, but no glial cells, were labeled with FG-filled vesicles. The tracer reached the RPE 15 minutes after FG administration, and this labeling remained up to 30 days. Tracing for 15 minutes or 24 hours did not cause oxidative stress. Intraretinal tracing delineated the pathological retinal remodelling occurring in the dystrophic strains. The RPE of the P23H-1 strain was highly altered in aged animals, while the Rpe of the RcS strain, which is unable to phagocytose, did not accumulate the tracer even at young ages when the retinal neural circuit is still preserved. in both dystrophic strains, the Rpe cells were pleomorphic and polymegathic.
Photoreceptor Cell Biology and Inherited Retinal Degenerations, 2004
Advances in genomics and molecular biology have led, over the last decade, to the identification of numerous molecules that form the phagocytic machinery of the retinal pigment epithelium (RPE). This research has also shown that the RPE phagocytic mechanism belongs to a group of related clearance mechanisms that share common phagocytic receptors. However, the precise roles of any of these receptors in the daily phagocytic burst characteristic of the RPE remain to be explored. Here, we focus on contributions of the integrin receptor αvβ5 to outer segment phagocytosis by RPE cells. In vitro functional assays and developmental expression studies indicate an important function for αvβ5 receptors in phagocytosis by human, rat, and mouse RPE. We discuss recent evidence that signaling pathways via αvβ5 integrin in both directions across the RPE plasma membrane may promote synchronized, timely, and repeated phagocytosis unique to RPE. αvβ5 integrin engagement initiates a downstream signaling response that may serve to coordinate the activity of multiple components of the RPE phagocytic machinery. Furthermore, regulation of activities of αvβ5 integrin receptors themselves by RPE signaling mechanisms may prevent phagocytosis by RPE cells upon completion of their daily clearance of shed photoreceptor outer segment fragments.
PurposeTo examine the contribution of PEDF-R to the phagocytosis process. Previously, we identified PEDF-R, the protein encoded by thePNPLA2gene, as a phospholipase A2 in the retinal pigment epithelium (RPE). During phagocytosis, RPE cells ingest abundant phospholipids and protein in the form of photoreceptor outer segment (POS) tips, which are then hydrolyzed. The role of PEDF-R in RPE phagocytosis is not known.MethodsMice in whichPNPLA2was conditionally knocked out in the RPE were generated (cKO). Mouse RPE/choroid explants were cultured. Human ARPE-19 cells were transfected with siPNPLA2silencing duplexes. POS were isolated from bovine retinas. The phospholipase A2 inhibitor bromoenol lactone was used. Transmission electron microscopy, immunofluorescence, lipid labeling, pulse-chase experiments, western blots, and free fatty acid and β-hydroxybutyrate assays were performed.ResultsThe RPE of the cKO mice accumulated lipids as well as more abundant and larger rhodopsin particles co...
Proceedings of the National Academy of Sciences, 1997
Phagocytosis of shed photoreceptor rod outer segments (ROS) by the retinal pigment epithelium (RPE) is essential for retinal function. Here, we demonstrate that this process requires ␣v5 integrin, rather than ␣v3 integrin utilized by systemic macrophages. Although adult rat RPE expressed both ␣v3 and ␣v5 integrins, only ␣v3 was expressed at birth, when the retina is immature and phagocytosis is absent. Expression of ␣v5 was first detected in RPE at PN7 and reached adult levels at PN11, just before onset of phagocytic activity. Interestingly, ␣v5 localized in vivo to the apical plasma membrane, facing the photoreceptors, and to intracellular vesicles, whereas ␣v3 was expressed basolaterally. Using quantitative f luorimaging to assess in vitro uptake of f luorescent particles by human (ARPE-19) and rat (RPE-J) cell lines, ␣v5 function-blocking antibodies were shown to reduce phagocytosis by drastically decreasing (85%) binding of ROS but not of latex beads. In agreement with a role for ␣v5 in phagocytosis, immunof luorescence experiments demonstrated codistribution of ␣v5 integrin with internalized ROS. Control experiments showed that blocking ␣v3 function with antibodies did not inhibit ROS phagocytosis and that ␣v3 did not colocalize with phagocytosed ROS. Taken together, our results indicate that the RPE requires the integrin receptor ␣v5 specifically for the binding of ROS and that phagocytosis involves internalization of a ROS-␣v5 complex. ␣v5 integrin does not participate in phagocytosis by other phagocytic cells and is the first of the RPE receptors involved in ROS phagocytosis that may be specific for this process.
Proceedings of the National Academy of Sciences, 2014
Accumulation of lipofuscin bisretinoids (LBs) in the retinal pigment epithelium (RPE) is the alleged cause of retinal degeneration in genetic blinding diseases (e.g., Stargardt) and a possible etiological agent for age-related macular degeneration. Currently, there are no approved treatments for these diseases; hence, agents that efficiently remove LBs from RPE would be valuable therapeutic candidates. Here, we show that beta cyclodextrins (β-CDs) bind LBs and protect them against oxidation. Computer modeling and biochemical data are consistent with the encapsulation of the retinoid arms of LBs within the hydrophobic cavity of β-CD. Importantly, β-CD treatment reduced by 73% and 48% the LB content of RPE cell cultures and of eyecups obtained from Abca4-Rdh8 double knock-out (DKO) mice, respectively. Furthermore, intravitreal administration of β-CDs reduced significantly the content of bisretinoids in the RPE of DKO animals. Thus, our results demonstrate the effectiveness of β-CDs to complex and remove LB deposits from RPE cells and provide crucial data to develop novel prophylactic approaches for retinal disorders elicited by LBs.
Morphogenesis of the Retinal Pigment Epithelium: Toward Understanding Retinal Degenerative Diseasesa
Annals of the New York Academy of Sciences, 1998
The phenotype of an epithelial cell is defined by a unique combination of morphology, gene and protein expression, and protein localization. Results indicate that the terminal differentiation of the RPE cell can be described in part by changes in the polarity of its surface proteins αvβ5 integrin, Na,K-ATPase, N-CAM, and EMMPRIN. Changes in protein/gene expression and protein localization in late stages of RPE development indentify αvβ5 integrin as a key player in RPE phagocytosis, and N-CAM and EMMPRIN as potentially important molecules in other RPE functions necessary for photoreceptor survival. By studying the trafficking of the later two proteins it is shown that entry into an apical or basolateral pathway in RPE cells cannot be predicted by the distribution of a given protein in other epithelial cells, and that this distribution may change through the course of RPE development. The mechanisms used by RPE and other epithelia to establish and maintain their specific polarity properties are fundamental to the formation and maintenance of their specific epithelial phenotype. The ability to therapeutically direct molecules incorporated into RPE by gene therapy into apical or basal surfaces requires an understanding of protein localization and expression. Furthermore, evidence is provided that assays capitalizing on changes in gene/protein expression and protein localization during the late stages of RPE development can prove a productive way of identifying proteins used by RPE for photoreceptor support. This approach can continue to be exploited to identify other proteins essential for the mission of the RPE cell, that may thus be likely candidates for participation in retinal degenerative disease. a Supported by grants from the NIH (R01-EY08538) and Research to Prevent Blindness to E. R.B., and fellowships from NIH-F32-EY06669 to A.D.M., the Deutsche Forschungsgemeinschaft to S.C.F., and the Brazilian Research Council (CNPq) and the Macular Degeneration