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Fabian Anders, Julia Teister, Franz H Grus, Norbert Pfeiffer, Sebastian Funke, Natarajan Perumal, Solon Thanos, Verena Prokosch; Alterations of crystallins in experimental model of glaucoma and their neuroprotective properties. Invest. Ophthalmol. Vis. Sci. 2016;57(12):2566. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Glaucoma is characterized by progressive irreversible loss of retinal ganglion cells (RGC). Increased intraocular pressure (IOP) is considered the main risk factor, but still molecular changes are not fully understood. Aim of this study was to explore the retinal protein expression pattern by MS/MS proteomics in an in vivo glaucoma model to better understand the pathophysiology of the disease and find new neuroprotective approaches.
IOP was increased in the left eye of Sprague Dawley rats (250g, f) by cauterization of three episcleral veins. Animals were sacrificed at 2 different timepoints after 3 (n=8) and 7 (n=7) weeks of IOP elevation. RGC count was conducted by immunohistological staining against BRN3A in retinal flatmounts and decrease of the retinal nerve fiber layer with optical coherence tomography (OCT). Proteomic changes within the retina were analyzed via in-gel digestion, followed by MS/MS. Neuroprotective properties of certain proteins were tested after intravitreal application of crystallins in vivo.
IOP increased in animals after cauterization significantly to 18.35±3.37 mmHg compared to 11.29±1.81 mmHg in contralateral controls (p<0.001). OCT showed a decrease in the retinal nerve fiber layer of about 7% (3 weeks elevated IOP) and 20% (7 weeks elevated IOP, p<0.001). The number of RGC exposed to elevated IOP was reduced about 12% (1309 RGC/mm2) after 3 weeks and 32% (1000 RGC/mm2) after 7 weeks in the respective group compared to controls (p<0.001). A total number of more than 1500 proteins could be quantified, including more than 100 significantly altered expression-patterns. Especially the protein family of α- and β-crystallins showed a partly significant (p<0.05) distinct down-regulation at the 3 weeks’ time point, followed by an up-regulation after 7 weeks of IOP enhancement with fold-changes of 2. Intravitreal injections of β-b2 crystallins enhanced RGC survival after optic nerve crush in vivo significantly (p<0.001).
Crystallins showed a specific downregulation early in the disease state and an upregulation after 7 weeks. Those long-considered lens specific proteins seem to have a significant impact in molecular changes in glaucoma. We suspect a correlation between crystalline decrease (and time-delayed up-regulation) and apoptotic effects in the RGC layer. Crystallin addition after optic nerve crush increased survival of RGCs significantly.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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