Hypertonicity‐induced decrease in aquaporin‐4 expression in retinal pigmented epithelial cells

Abstract

Abstract Purpose Osmotic gradients regulate subretinal water content and might be acutely changed during macular oedema. Moreover, since RPE cells express tight junctions, water molecules must use specific channels to cross their hydrophobic membrane. Aquaporins (AQP) are good candidates to assume this function. In this work, we investigated the effects of osmotic stress on the expression of AQP in RPE cells. Methods ARPE‐19 cells were grown in different hypertonic conditions. AQP1 and AQP4 expressions were assessed by Western blot and RT‐PCR. Chemical inhibitors were used to specifically block lysosomes and proteasome function. Cell proliferation was investigated by BRDU incorporation, and cell viability by flow cytometry. Cell cycle was studied by Western blot and flow cytometry. Results Hypertonic stress rapidly decreased AQP4 expression on ARPE cells. The effect was reversed by proteasome inhibition, but was likely ubiquitinylation‐independent. At 24h post‐hypertonic stress, cell viability was not affected but cell proliferation was decreased. Cell cycle was also modified as the percentage of cells in G0/G1 phase decreased and the percentage of cells in S and G2/M phase increased. Conclusion Hypertonic stress strongly reduced AQP4 expression and RPE cell proliferation. Those results might contribute to our understanding of macular oedema formation.