Aquaporin 11, a regulator of water efflux at retinal Müller glial cell surface decreases concomitant with immune-mediated gliosis.
BACKGROUND
Müller glial cells are important regulators of physiological function of retina. In a model disease of retinal inflammation and spontaneous recurrent uveitis in horses (ERU), we could show that retinal Müller glial cells significantly change potassium and water channel protein expression during autoimmune pathogenesis. The most significantly changed channel protein in neuroinflammatory ERU was aquaporin 11 (AQP11). Aquaporins (AQP, 13 members) are important regulators of water and small solute transport through membranes. AQP11 is an unorthodox member of this family and was assigned to a third group of AQPs because of its difference in amino acid sequence (conserved sequence is only 11 %) and especially its largely unknown function.


METHODS
In order to gain insight into the distribution, localization, and function of AQP11 in the retina, we first developed a novel monoclonal antibody for AQP11 enabling quantification, localization, and functional studies.


RESULTS
In the horse retina, AQP11 was exclusively expressed at Müller glial cell membranes. In uveitic condition, AQP11 disappeared from gliotic Müller cells concomitant with glutamine synthase. Since function of AQP11 is still under debate, we assessed the impact of AQP11 channel on cell volume regulation of primary Müller glial cells under different osmotic conditions. We conclude a concomitant role for AQP11 with AQP4 in water efflux from these glial cells, which is disturbed in ERU. This could probably contribute to swelling and subsequent severe complication of retinal edema through impaired intracellular fluid regulation.


CONCLUSIONS
Therefore, AQP11 is important for physiological Müller glia function and the expression pattern and function of this water channel seems to have distinct functions in central nervous system. The significant reduction in neuroinflammation points to a crucial role in pathogenesis of autoimmune uveitis.
Experimental Ophthalmology, Philipps University of Marburg, Baldingerstrasse, 35033, Marburg, Germany. Cornelia.Deeg@uni-marburg.de.|Department of Veterinary Sciences, Institute of Animal Physiology, Ludwig-Maximilians University, Veterinärstr. 13, 80539, München, Germany. Cornelia.Deeg@uni-marburg.de.
Cornelia A
CA
Deeg
Department of Veterinary Sciences, Institute of Animal Physiology, Ludwig-Maximilians University, Veterinärstr. 13, 80539, München, Germany.
Barbara
B
Amann
Department of Veterinary Sciences, Institute of Animal Physiology, Ludwig-Maximilians University, Veterinärstr. 13, 80539, München, Germany.
Konstantin
K
Lutz
Department of Veterinary Sciences, Institute of Animal Physiology, Ludwig-Maximilians University, Veterinärstr. 13, 80539, München, Germany.
Sieglinde
S
Hirmer
Department of Veterinary Sciences, Institute of Animal Physiology, Ludwig-Maximilians University, Veterinärstr. 13, 80539, München, Germany.
Karina
K
Lutterberg
Helmholtz Zentrum München-German Research Center for Environmental Health (GmbH), Institute for Molecular Immunology, Marchioninistraße 25, 81377, München, Germany.
Elisabeth
E
Kremmer
Department of Protein Science, Helmholtz Zentrum München-German Research Center for Environmental Health (GmbH), Ingolstädter Landstr. 1, 85764, Neuherberg, Germany.
Stefanie M
SM
Hauck
D000818:Animals; D020346:Aquaporins / Q000276:immunology / Q000378:metabolism*; D001327:Autoimmune Diseases / Q000378:metabolism / Q000473:pathology / Q000662:veterinary*; D015153:Blotting, Western; D063928:Ependymoglial Cells / Q000378:metabolism*; D005911:Gliosis / Q000276:immunology / Q000378:metabolism / Q000662:veterinary*; D006734:Horse Diseases; D006736:Horses; D007150:Immunohistochemistry; D009997:Osmotic Pressure; D014605:Uveitis / Q000378:metabolism / Q000473:pathology / Q000662:veterinary*
D020346:Aquaporins
AQP11; AQP4; AQP5; Autoimmune uveitis; Cell volume regulation; Retinal inflammation; Superaquaporin; Water channel; Water efflux