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M Livia Bajenaru, Andrea Rachelle C Santos, Kevin K Park, Sander R Dubovy, Antonio Bermudez; Role of Focal Adhesion Kinase (FAK) in RGC in Glaucoma. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):2445.
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© ARVO (1962-2015); The Authors (2016-present)
Extensive remodeling of extracellular matrix (ECM) and changes in the expression of integrins are typical to glaucoma and associated with RGC death and degeneration. We recently showed that laminin-integrin-FAK-Akt pathway is disrupted in retinal ischemia. The purpose of this study is to investigate the role of FAK in RGC in glaucoma.
Experimental glaucoma was induced in the left eye of 30 Sprague Dawley rats by blocking the ocular outflow and producing increased intraocular pressure (IOP) using a diode laser. IOP was measured periodically in both eyes after laser photocoagulation (LP). A group of rats (n=8) was euthanized 9 weeks post LP. Their optic nerves and retinas were removed and processed for histology. Semi-automated counting of the axons was performed in optic nerve cross sections stained with toluidine blue. Corresponding flat mounted retinas were processed for immunofluorescence with a TUJ1 (βIII tubulin) antibody, and TUJ1 labeled RGC were counted with an inverted fluorescence microscope. Another group of rats (n=8) was euthanized 4 weeks post-LP and fluorogold (FG) labeled RGC were counted in flat mounted retinas. Retinal flat-mounts (n=4) from control and experimental glaucoma eyes 2 weeks post-LP, and human normal (n=2) and glaucomatous (n=4) retinas and optic nerves were processed for immunohistochemsitry with β1-integrin, FAK, phospho-FAK antibodies
Mean IOP was increased in the treated eye from 8.66±1.03 to 18.34±5.86 to a peak value of 25.73± 9.73 at 1 day, 16.44 ± 6.98 at 1, and 20.75 ± 7.27 mm Hg at 2 weeks post LP (*p<0.05). Axonal loss at 9 weeks post-LP, was 64.89% ± 11.05 (*p<0.05), in good correlation with RGC survival, 52.39% ± 4.74 (*p<0.01),Loss of FG labeled RGCs was aparent at 2 weeks, with significantly reduced FG+ RGCs in the glaucomatous eye at 4 weeks post LP (12.66% ± 9.21; *p<0.05), suggesting that many surviving RGCs are dysfunctional and have impaired retrograde active transport. Toluidine blue staining in optic nerve cross-sections showed swollen axons, collapsed myelin sheets, and axon bundles disarray 9 weeks post-LP in treated eyes. Immunohistochemistry showed decreased expression of β1-integrin and significantly reduced phospho/activated FAK in both human and experimental glaucoma.
Our results suggest that β1 integrin signaling is disrupted with significantly reduced FAK activation in RGC in glaucoma.
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