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A role for aquaporin-4 during induction of form deprivation myopia in chick.

Goodyear MJ, Junghans BM, Giummarra L, Murphy MJ, Crewther DP, Crewther SG - Mol. Vis. (2008)

Bottom Line: Aquaporins (AQP) form a family of specialized water channels known to transport water across cell membranes and reduce osmotic gradients.The control eyes showed relatively constant levels of AQP4 expression until day 5 after which the level appeared to decrease.By comparison, positive AQP4 immunoreactivity in the nerve fiber layer increased significantly over the first 48 h in form-deprived eyes and in fellow eyes and then decreased over the next 48 h but not to the level of expression in the normal untreated eyes.

View Article: PubMed Central - PubMed

Affiliation: School of Psychological Science, La Trobe University, Melbourne, Australia.

ABSTRACT

Purpose: Aquaporins (AQP) form a family of specialized water channels known to transport water across cell membranes and reduce osmotic gradients. The isoform AQP4 is highly expressed in the astroglia of the brain and Müller cells in the retina. In the brain, AQP4 play a role in the control of cerebral edema by shunting excess fluid into blood vessels and by upregulating during conditions of hyperosmolarity. Thus, on the basis of the hyperosmolarity seen across the retina and choroid of hatchling chickens made myopic by form deprivation (FD), we predicted an upregulation of retinal AQP4 expression during induction of myopia.

Methods: Two-day-old hatchling chicks were monocularly form-deprived for 48, 72, or 96 h, and then after biometric assessment, the eyes of these animals and the normal controls of the same age were enucleated. Retinal tissue was prepared either for western blot analysis to show the presence of the AQP4 protein in the chick retina or for immunolocalization using polyclonal AQP4 antibodies to determine regional distribution and intensity of labeling during the induction of form deprivation myopia (FDM).

Results: As expected, ultrasonography demonstrated that all post hatchling eyes showed rapid elongation with occluded eyes elongating faster than fellow eyes or normal controls and becoming progressively more myopic with the duration of visual deprivation. Western blot analyses revealed an approximately 30 kDa band immunoreactive for AQP4 protein and confirmed the presence of AQP4 in chicks. Immunohistochemical staining showed the greatest positive immunoreactivity for antibodies to AQP4 in the inner retina along the vitreoretinal interface, nerve fiber layer, ganglion cell layer, and inner plexiform layer in all animals. The control eyes showed relatively constant levels of AQP4 expression until day 5 after which the level appeared to decrease. By comparison, positive AQP4 immunoreactivity in the nerve fiber layer increased significantly over the first 48 h in form-deprived eyes and in fellow eyes and then decreased over the next 48 h but not to the level of expression in the normal untreated eyes.

Conclusions: This is the first study to demonstrate the presence of AQP4 protein in the chick retina and to associate AQP4 expression in the inner retina with the initiation of form deprivation and the period of fastest axial elongation. This increased expression of AQP4 channels near the vitread border during the time of rapid growth suggests a role for AQP4 as a conduit for movement of retinal fluid into the vitreous in form-deprived chicks.

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Intensity of AQP4 antibody labeling in the nerve fiber layer of chick. The mean relative fluorescence (on an arbitrary scale of 0 to 255) of AQP4/Alexa 596 conjugated antibodies expressed in the nerve fiber layer of the retinae of age-matched normal control eyes (triangles) and both non-deprived eyes (squares) and fellow eyes that experienced form deprivation (diamonds) is plotted against time from initiation of occlusion of the experimental eye. Note that initially intensity of AQP4 labeling is slightly raised in normal eyes and falls with time and increase in eye size. In contrast, occlusion initially causes significant elevation of labeling intensity particularly in the form-deprived eye, but also in the non-occluded fellow eye, which falls with duration of form-deprivation to almost reach control levels after 4 days. Error bars are 1 standard error.
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f4: Intensity of AQP4 antibody labeling in the nerve fiber layer of chick. The mean relative fluorescence (on an arbitrary scale of 0 to 255) of AQP4/Alexa 596 conjugated antibodies expressed in the nerve fiber layer of the retinae of age-matched normal control eyes (triangles) and both non-deprived eyes (squares) and fellow eyes that experienced form deprivation (diamonds) is plotted against time from initiation of occlusion of the experimental eye. Note that initially intensity of AQP4 labeling is slightly raised in normal eyes and falls with time and increase in eye size. In contrast, occlusion initially causes significant elevation of labeling intensity particularly in the form-deprived eye, but also in the non-occluded fellow eye, which falls with duration of form-deprivation to almost reach control levels after 4 days. Error bars are 1 standard error.

Mentions: In the normal non-treated controls, the intensity of labeling in the NFL of the normal eyes remained steady until day 5 after which labeling decreased (Figure 4). The pattern and level of expression in the IPL in the control eyes was similar to that seen in the NFL over this period.


A role for aquaporin-4 during induction of form deprivation myopia in chick.

Goodyear MJ, Junghans BM, Giummarra L, Murphy MJ, Crewther DP, Crewther SG - Mol. Vis. (2008)

Intensity of AQP4 antibody labeling in the nerve fiber layer of chick. The mean relative fluorescence (on an arbitrary scale of 0 to 255) of AQP4/Alexa 596 conjugated antibodies expressed in the nerve fiber layer of the retinae of age-matched normal control eyes (triangles) and both non-deprived eyes (squares) and fellow eyes that experienced form deprivation (diamonds) is plotted against time from initiation of occlusion of the experimental eye. Note that initially intensity of AQP4 labeling is slightly raised in normal eyes and falls with time and increase in eye size. In contrast, occlusion initially causes significant elevation of labeling intensity particularly in the form-deprived eye, but also in the non-occluded fellow eye, which falls with duration of form-deprivation to almost reach control levels after 4 days. Error bars are 1 standard error.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2254964&req=5

f4: Intensity of AQP4 antibody labeling in the nerve fiber layer of chick. The mean relative fluorescence (on an arbitrary scale of 0 to 255) of AQP4/Alexa 596 conjugated antibodies expressed in the nerve fiber layer of the retinae of age-matched normal control eyes (triangles) and both non-deprived eyes (squares) and fellow eyes that experienced form deprivation (diamonds) is plotted against time from initiation of occlusion of the experimental eye. Note that initially intensity of AQP4 labeling is slightly raised in normal eyes and falls with time and increase in eye size. In contrast, occlusion initially causes significant elevation of labeling intensity particularly in the form-deprived eye, but also in the non-occluded fellow eye, which falls with duration of form-deprivation to almost reach control levels after 4 days. Error bars are 1 standard error.
Mentions: In the normal non-treated controls, the intensity of labeling in the NFL of the normal eyes remained steady until day 5 after which labeling decreased (Figure 4). The pattern and level of expression in the IPL in the control eyes was similar to that seen in the NFL over this period.

Bottom Line: Aquaporins (AQP) form a family of specialized water channels known to transport water across cell membranes and reduce osmotic gradients.The control eyes showed relatively constant levels of AQP4 expression until day 5 after which the level appeared to decrease.By comparison, positive AQP4 immunoreactivity in the nerve fiber layer increased significantly over the first 48 h in form-deprived eyes and in fellow eyes and then decreased over the next 48 h but not to the level of expression in the normal untreated eyes.

View Article: PubMed Central - PubMed

Affiliation: School of Psychological Science, La Trobe University, Melbourne, Australia.

ABSTRACT

Purpose: Aquaporins (AQP) form a family of specialized water channels known to transport water across cell membranes and reduce osmotic gradients. The isoform AQP4 is highly expressed in the astroglia of the brain and Müller cells in the retina. In the brain, AQP4 play a role in the control of cerebral edema by shunting excess fluid into blood vessels and by upregulating during conditions of hyperosmolarity. Thus, on the basis of the hyperosmolarity seen across the retina and choroid of hatchling chickens made myopic by form deprivation (FD), we predicted an upregulation of retinal AQP4 expression during induction of myopia.

Methods: Two-day-old hatchling chicks were monocularly form-deprived for 48, 72, or 96 h, and then after biometric assessment, the eyes of these animals and the normal controls of the same age were enucleated. Retinal tissue was prepared either for western blot analysis to show the presence of the AQP4 protein in the chick retina or for immunolocalization using polyclonal AQP4 antibodies to determine regional distribution and intensity of labeling during the induction of form deprivation myopia (FDM).

Results: As expected, ultrasonography demonstrated that all post hatchling eyes showed rapid elongation with occluded eyes elongating faster than fellow eyes or normal controls and becoming progressively more myopic with the duration of visual deprivation. Western blot analyses revealed an approximately 30 kDa band immunoreactive for AQP4 protein and confirmed the presence of AQP4 in chicks. Immunohistochemical staining showed the greatest positive immunoreactivity for antibodies to AQP4 in the inner retina along the vitreoretinal interface, nerve fiber layer, ganglion cell layer, and inner plexiform layer in all animals. The control eyes showed relatively constant levels of AQP4 expression until day 5 after which the level appeared to decrease. By comparison, positive AQP4 immunoreactivity in the nerve fiber layer increased significantly over the first 48 h in form-deprived eyes and in fellow eyes and then decreased over the next 48 h but not to the level of expression in the normal untreated eyes.

Conclusions: This is the first study to demonstrate the presence of AQP4 protein in the chick retina and to associate AQP4 expression in the inner retina with the initiation of form deprivation and the period of fastest axial elongation. This increased expression of AQP4 channels near the vitread border during the time of rapid growth suggests a role for AQP4 as a conduit for movement of retinal fluid into the vitreous in form-deprived chicks.

Show MeSH
Related in: MedlinePlus