Current Understanding on the Role of Retinal Pigment Epithelium and its Pigmentation

Abstract

Retinal pigment epithelium (RPE) is a monolayer of cuboidal cells that is strategically placed between the rod and cone photoreceptors and the vascular bed of the choriocapillaris. It has many important functions, such as phagocytic uptake and breakdown of the shedded photoreceptor membranes, uptake, processing, transport and release of vitamin A (retinol), setting up the ion gradients within the interphotoreceptor matrix, building up the blood-retina barrier, and providing all transport from blood to the retina and back. This short review focuses on the role of the pigment granules in RPE. Although the biology of the pigment granules has been neglected in the past, they do seem to be involved in many important functions, such as protection from oxidative stress, detoxification of peroxides, and binding of zinc and drugs, and, therefore, serve as a versatile partner of the RPE cell. Melanin plays a role in the development of the fovea and routing of optic nerves. New findings show that the melanin granules are connected to the lysosomal degradation pathway. Most of these functions are not yet understood. Deficit of melanin pigment is associated with age-related macula degeneration, the leading cause of blindness.

Lentiviral gene replacement therapy of retinas in a mouse model for Usher syndrome type 1B

“…21 The role of melanosomes in the RPE is not well defined, however, their functions include light absorption, possibly a contribution to the digestion of phagosomes, and protection against lipid peroxidation and the formation of toxic oxiranes from ingested photoreceptor outer segment phospholipids. 22 An additional cellular defect in the retina has been observed in the photoreceptor cells of shaker1 mice. Their photoreceptor connecting cilia contain an excess of opsin, indicating an additional role for MYO7A in the renewal of the photoreceptor disk membranes.…”

Photoprotection of human retinal pigment epithelium cells against blue light-induced apoptosis by melanin free radicals from Sepia officinalis

“…Although lipofuscin involvement in blue light-induced RPE loss could be important in aged RPE (11)(12)(13), fetal RPE are also susceptible to blue light-induced apoptosis (BLIA) (14). Metabolically, RPE cells are highly active and contain large numbers of mitochondria (1). Blue light induces the production of reactive oxygen species (ROS) in the mitochondria of RPE cells (15) and has been shown to lead to cell apoptosis (14), potentially triggered by ROS damage to mtDNA (16).…”

“…RPE cells are nonregenerative and must last a lifetime to maintain sight (1,(3)(4)(5)(6)(7)(8). An accumulation of light-induced damage within RPE cells is believed to participate in RPE loss in the retina (3)(4)(5)(6)(7)(8).…”

“…T he retinal pigment epithelium (RPE) is a monolayer of cuboidal cells between the photoreceptors and choriocapillaris and is specialized to phagocytize and recycle the outer segment of photoreceptors and retinaldehyde, the chromophore of rhodopsin (1,2). RPE cells are nonregenerative and must last a lifetime to maintain sight (1,(3)(4)(5)(6)(7)(8).…”

Melanin photoprotection in the human retinal pigment epithelium and its correlation with light-induced cell apoptosis

“…continuous wave EPR ͉ electron spin polarization ͉ time-resolved EPR I n the eye, retinal pigment epithelium (RPE) is a monolayer of cuboidal cells between the photoreceptors and choriocapillaris of the eye and is specialized to uptake, phagocytize, and recycle the outer segment of photoreceptors and retinaldehyde, the chromophore of rhodopsin (1). RPE cell death plays a major role in the pathogenesis of age-related macular degeneration, the leading cause of blindness in the population Ͼ60 years of age in the developed world (2).…”