title: Osmotic stress decreases aquaporin-4 expression in the human retinal pigment epithelial cell line, ARPE-19.
abstract: The regulation of water movement is of utmost importance for normal retinal function. Under physiological conditions, water is transported, dependent on the osmotic gradient, through the retinal pigment epithelial cell layer from the subretinal space to the choroid. The osmotic gradient has been found to be modified in eye diseases, thus leading to water accumulation in the subretinal space and the sensory retina, and subsequently contributing to the formation of macular oedema. Understanding the regulation of aquaporin expression is therefore crucial. In this study, we investigated the effects of hyperosmolarity on aquaporin-4 (AQP4) protein expression in the human retinal pigment epithelial cell line, ARPE‑19. AQP4 expression was examined by PCR, western blot analysis and immunofluorescence. Ubiquitinylation was examined by immunoprecipitation. The results revealed that hyperosmotic stress rapidly decreased AQP4 expression in the ARPE-19 cells. The effect remained unmodified by lysosomal or mitogen-activated protein kinase inhibitors, but was reversed by proteasome inhibitors. However, no ubiquitinylation of AQP4 was detected. Our results suggest that hyperosmotic stress markedly reduces AQP4 expression possibly through a proteasome ubiquitinylation-independent pathway. This may represent an adaptation to hyperosmotic stress. The results presented in this study contribute to our understanding of the formation of macular oedema.
authors.affiliation: Department of Ophthalmology, CHU Saint-Pierre and Brugmann, Brussels, Belgium.
authors.forename: François
authors.initials: F
authors.lastname: Willermain
authors.affiliation: Department of Ophthalmology, CHU Saint-Pierre and Brugmann, Brussels, Belgium.
authors.forename: Sarah
authors.initials: S
authors.lastname: Janssens
authors.affiliation: Laboratory of Pathophysiological and Nutritional Biochemistry, Université Libre de Bruxelles, Brussels, Belgium.
authors.forename: Tatjana
authors.initials: T
authors.lastname: Arsenijevic
authors.affiliation: Laboratory of Pathophysiological and Nutritional Biochemistry, Université Libre de Bruxelles, Brussels, Belgium.
authors.forename: Isabelle
authors.initials: I
authors.lastname: Piens
authors.affiliation: Laboratory of Pathophysiological and Nutritional Biochemistry, Université Libre de Bruxelles, Brussels, Belgium.
authors.forename: Nargis
authors.initials: N
authors.lastname: Bolaky
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, Université Libre de Bruxelles, Brussels, Belgium.
authors.forename: Jason
authors.initials: J
authors.lastname: Perret
authors.affiliation: Laboratory of Pathophysiological and Nutritional Biochemistry, Université Libre de Bruxelles, Brussels, Belgium.
authors.forename: Christine
authors.initials: C
authors.lastname: Delporte
mesh_terms: D051401:Aquaporin 4 / Q000096:biosynthesis* / Q000378:metabolism; D002460:Cell Line; D005786:Gene Expression Regulation; D006801:Humans; D008269:Macular Edema / Q000235:genetics* / Q000473:pathology; D009997:Osmotic Pressure; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D012160:Retina / Q000378:metabolism / Q000473:pathology; D055213:Retinal Pigment Epithelium / Q000378:metabolism* / Q000473:pathology; D054875:Ubiquitination / Q000235:genetics
chemical_list: D051401:Aquaporin 4; D046988:Proteasome Endopeptidase Complex