Roles of αvβ5, FAK and MerTK in oxidative stress inhibition of RPE cell phagocytosis

Efficient phagocytosis of photoreceptor outer segments (POS) by retinal pigment epithelial cells (RPE) plays a key role in biological renewal of these highly peroxidizable structures and in maintenance of retina health. Here, we used an in vitro RPE cell phagocytosis assay to investigate how sub-lethal oxidative stress modifies the key components of the cell phagocytic machinery leading to severe impairment of phagocytosis. Sub-lethal oxidative treatment, induced by hydrogen peroxide (H2O2), significantly inhibited binding and uptake of POS by RPE cells. However, sub-lethal oxidative stress did not affect cell surface expression of αvβ5 or RPE cell adhesion to αvβ5. Similarly, the enzymatic activity of mature cathepsin D was not altered upon challenge by oxidative stress. In contrast, studies of signaling molecules in the RPE cell phagocytic machinery revealed that sub-lethal oxidative stress inhibits POS-induced activation of FAK and MerTK. Our data demonstrate that sub-lethal oxidative treatment with H2O2 inhibits phagocytic activity of ARPE-19 cells, in part by inhibiting FAK and MerTK.

► Oxidative stress inhibits RPE cell phagocytosis of photoreceptor outer segments (POS).
► Oxidative stress does not affect surface expression and binding activity of αvβ5.
► Oxidative stress inhibits POS-induced activation of tyrosine kinases FAK and MerTK.
► Oxidative stress reduces protein amount of pro-CatD without effect on CatD activity.
► Oxidative stress inhibits RPE cell phagocytosis, potentially by abrogating activation of FAK and MerTK.