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Verena Prokosch, Kathrin Brockhaus, Fabian Anders, Melissa Meyer zu Horste, Norbert Pfeiffer, Solon Thanos; Elevated IOP primarily induces responses in the vascular cells in animal models of glaucoma in vivo and in vitro. Invest. Ophthalmol. Vis. Sci. 2016;57(12):3008.
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© ARVO (1962-2015); The Authors (2016-present)
Elevated intraocular pressure (IOP) is the major risk factor for glaucoma and lowering of IOP the mainstay of treatment. However, the pathophysiology is poorly understood. It remains a matter of debate whether elevated IOP harms the neurons directly or indirectly through alterations in the retinal vascularization. To address this question, we analyzed morphological and molecular changes within the retinal vasculature exposed to elevated IOP in vivo and in vitro to identify specific targets for adjunctive neuroprotective treatments.
Elevation of IOP in vivo was induced by cauterization of episcleral veins in rats and maintained elevated for 8 weeks. In vitro, primary dissociated brain endothelial cells and pericytes and retinal explants were exposed to controlled elevated pressure (atmospheric, 30 and 60 mmHg) within a high pressure incubation chamber. MS/MS was performed to analyse proteomic changes. Immunohistochemical staining, Western blotting and qT-PCR was done to analyze several molecular markers including beta-III Tubulin, VEGF, Endothelin-1, GFAP, GAP-43, Iba-1, Vimentin, alpha-SMA, PDGFR-beta2, Desmin and von Willebrand factor VIII.
IOP increased significantly (p<0.001) and RGC loss was significant both in vivo and in vitro to imitate glaucoma (p<0.001). Surprisingly using MS/MS we found a significant 1.3 fold upregulation of the RGC specific beta III tubulin despite significant RGC loss in glaucoma animals. For the first time, we found that beta-III-tubulin, a marker specifically expressed in neurons under normal conditions, was strongly upregulated in desmin-, PDGFR-β-, and α-SMA positive pericytes and endothelin-1 positive endothelial cells both in vivo and in vitro under elevated pressure. Beta-III-tubulin driven signaling pathways (ERK ½, pERK ½, cdc42/Rac) were also regulated. The unprecentended regulation of neuron-specific β-III-tubulin in pericytes and endothelial cells is likely associated with a role of the retinal vasculature in the IOP-induced development and manifestation of glaucomatous degenerative optic nerve response.
Retinal pericytes and endothelial cells respond sensitively to abnormal IOP-elevation by early expression of beta-III- tubulin-signaling preceding neuronal responses. The capillary responses may influence secondary neuronal responses which culminate in death of ganglion cells.
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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