Abstract
The retinal pigment epithelium (RPE) is a unique epithelium, with major roles which are essential in the visual cycle and homeostasis of the outer retina. The RPE is a monolayer of polygonal and pigmented cells strategically placed between the neuroretina and Bruch membrane, adjacent to the fenestrated capillaries of the choriocapillaris. It shows strong apical (towards photoreceptors) to basal/basolateral (towards Bruch membrane) polarization. Multiple functions are bound to a complex structure of highly organized and polarized intracellular components: the cytoskeleton. A strong connection between the intracellular cytoskeleton and extracellular matrix is indispensable to maintaining the function of the RPE and thus, the photoreceptors. Impairments of these intracellular structures and the regular architecture they maintain often result in a disrupted cytoskeleton, which can be found in many retinal diseases, including age-related macular degeneration (AMD). This review article will give an overview of current knowledge on the molecules and proteins involved in cytoskeleton formation in cells, including RPE and how the cytoskeleton is affected under stress conditions—especially in AMD.
Highlights
The retinal pigment epithelium (RPE) is a cellular monolayer located between the photoreceptor outer segments and the choroidal vasculature
The purpose of this review is to summarize the composition, cellular localization, and function of RPE cytoskeletal constituents, with a special focus on changes in normal aging and in age-related macular degeneration (AMD)
Destabilization and fragmentation of the F-actin cytoskeleton is an observable finding in AMD-affected RPE cells
Summary
The retinal pigment epithelium (RPE) is a cellular monolayer located between the photoreceptor outer segments (apical) and the choroidal vasculature (basal). The RPE has several functions including the transportation of ions, water and metabolic products from the subretinal space to the blood vessels of the choriocapillaris [2]; on the other hand, it takes up nutritional and metabolic essentials such as fatty acids, retinol and glucose from choriocapillaris and delivers these products to the photoreceptors [3] It plays a central role in the visual cycle, i.e., re-isomerization from all-trans-retinal to 11-cis-retinal [4]. A hallmark of this monolayer is a strong apical to basal polarization, which enables the controlled trafficking of proteins and molecules, nutrients, oxygen, and waste products from and into RPE cells [7,8] This has been shown to be important for the RPE cellular metabolism, as well as maintaining outer retina health. The purpose of this review is to summarize the composition, cellular localization, and function of RPE cytoskeletal constituents, with a special focus on changes in normal aging and in age-related macular degeneration (AMD)
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