title: Origins and consequences of hyperosmolar stress in retinal pigmented epithelial cells.
abstract: The retinal pigmented epithelium (RPE) is composed of retinal pigmented epithelial cells joined by tight junctions and represents the outer blood-retinal barrier (BRB). The inner BRB is made of endothelial cells joined by tight junctions and glial extensions surrounding all the retinal blood vessels. One of the functions of the RPE is to maintain an osmotic transepithelial gradient created by ionic pumps and channels, avoiding paracellular flux. Under such physiological conditions, transcellular water movement follows the osmotic gradient and flows normally from the retina to the choroid through the RPE. Several diseases, such as diabetic retinopathy, are characterized by the BRB breakdown leading to leakage of solutes, proteins, and fluid from the retina and the choroid. The prevailing hypothesis explaining macular edema formation during diabetic retinopathy incriminates the inner BRB breakdown resulting in increased osmotic pressure leading in turn to massive water accumulation that can affect vision. Under these conditions, it has been hypothesized that RPE is likely to be exposed to hyperosmolar stress at its apical side. This review summarizes the origins and consequences of osmotic stress in the RPE. Ongoing and further research advances will clarify the mechanisms, at the molecular level, involved in the response of the RPE to osmotic stress and delineate potential novel therapeutic targets and tools.
authors.affiliation: Department of Ophthalmology, CHU Saint-Pierre and Brugmann Brussels, Belgium ; I.R.I.B.H.M, Université Libre de Bruxelles Brussels, Belgium.
authors.forename: François
authors.initials: F
authors.lastname: Willermain
authors.affiliation: Department of Ophthalmology, CHU Saint-Pierre and Brugmann Brussels, Belgium ; Laboratory of Pathophysiological and Nutritional Biochemistry, Department of Biochemistry, Université Libre de Bruxelles Brussels, Belgium.
authors.forename: Sarah
authors.initials: S
authors.lastname: Libert
authors.affiliation: Department of Ophthalmology, CHU Saint-Pierre and Brugmann Brussels, Belgium ; Laboratory of Pathophysiological and Nutritional Biochemistry, Department of Biochemistry, Université Libre de Bruxelles Brussels, Belgium.
authors.forename: Elie
authors.initials: E
authors.lastname: Motulsky
authors.affiliation: Department of Ophthalmology, CHU Saint-Pierre and Brugmann Brussels, Belgium ; Laboratory of Pathophysiological and Nutritional Biochemistry, Department of Biochemistry, Université Libre de Bruxelles Brussels, Belgium.
authors.forename: Dany
authors.initials: D
authors.lastname: Salik
authors.affiliation: Department of Ophthalmology, CHU Saint-Pierre and Brugmann Brussels, Belgium.
authors.forename: Laure
authors.initials: L
authors.lastname: Caspers
authors.affiliation: Laboratory of Pathophysiological and Nutritional Biochemistry, Department of Biochemistry, Université Libre de Bruxelles Brussels, Belgium.
authors.forename: Jason
authors.initials: J
authors.lastname: Perret
authors.affiliation: Laboratory of Pathophysiological and Nutritional Biochemistry, Department of Biochemistry, Université Libre de Bruxelles Brussels, Belgium.
authors.forename: Christine
authors.initials: C
authors.lastname: Delporte
keywords: age-related macular degeneration; blood-retinal barrier; diabetes; edema; hyperosmolar stress; retinal pigmented epithelium; uveitis