Abstract
Purpose :
In the retinal pigment epithelium (RPE), efficient endolysosome function is crucial for clearing phagocytosed photoreceptor outer segments (POS) and disposing cellular debris by autophagy, which supports RPE and photoreceptor health. We recently discovered that the cytoskeleton-associated protein Ezrin can regulate this cellular process through mTORC1 modulation. However, how Ezrin modulates the endolysosomal degradation of OS is largely unknown.
Methods :
We utilized RPE from mice, medaka fish and human cell lines to evaluate the role of Ezrin on endolysosomal pathway. We carried out both transcriptomic and proteomic analyses, western blot, immunofluorescence, immunoelectron microscopy, TIRF microscopy, in vitro and in vivo to fully characterize the role of Ezrin and its protein interactors in this cellular process.
Results :
We identified EGFR as a main Ezrin's binding protein. Both genetic and pharmacological depletion of Ezrin disrupted EGFR internalization on endosome and its signaling. We found that Ezrin/EGFR molecular network controls translocation of TSC complex on the lysosome via AKT pathway. The Ezrin-mediated inhibition of TSC induces mTORC1 activity and represses autophagy in the dark phase. On the other hand, light-mediated inhibition of Ezrin activates endolysosomal function in diurnal phase. The physiological alternation of the activation and deactivation of autophagy during the light and dark phases ensure the correct degradation of POS and correct vision.
Disruption of Ezrin/EGFR/TSC molecular network in the RPE alters POS degradation and normal vision. Ezrin-/- medaka model exhibited a significant degeneration of rods and cones photoreceptors cells, accompanied from an incorrect autophagy pathway and POS degradation in the RPE cells.
Conclusions :
Ezrin plays a key role in the pathophysiology of RPE. Our results suggest that EZRIN/EGFR/TSC molecular network controls mTORC1 on lysosomes in the RPE. Depletion of Ezrin alters endosomal EGFR signaling thereby triggering defects in autophagy pathway and leading to retinal degeneration.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.