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J. Lin, T. Nagasaki, V. Mahajan, C.K. Yamashita, S.H. Ngan, D.B. Farber, C.S. Lin, S.H. Tsang; Live Autofluorescence Imaging in a New Mouse Model for Age–Related Macular Degeneration (AMD) . Invest. Ophthalmol. Vis. Sci. 2006;47(13):4149.
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We hypothesize that thickening of Bruch’s membrane initiates RPE hypoxia leading to expression of hypoxia inducible–factors HIF–1α and –2 α. These are heterodimerized with constitutively expressed HIF–1ß and activate the hypoxia response element of erythropoietin and vascular endothelial growth factor (VEGF) in age related macular degeneration (AMD). HIF–1 α is quickly degraded in the presence of normoxia. Overexpression of HIF–1α has been shown to be more effective in promoting hypervascularization than VEGF164. Thus, we generated transgenic mice expressing a constitutively active mutant HIF–1 α to test if hypoxia contributes to manifestations of AMD.
The Rpe65 promoter was used to overexpress the HIF–1α transgene in RPE. Constructs containing a non–degradable form of HIF–1α were injected into B6CBAF2 oocytes. Transgenic animals and age–matched litter mate controls were examined for the presence of fundus autofluorescence non–invasively with a stereo fluorescence microscope that was adapted for fundus imaging, using a filter cube for green fluorescence protein. Fundus angiography was performed after intraperitoneal injection of sulforhodamine 101.
Fourteen founders were obtained. Fundus examination showed a punctuate pattern of small autofluorescence structures throughout the fundus at the level of the retinal pigment epithelium (RPE) in two lines. At nine weeks of age, one line developed subretinal deposits with indistinct borders as seen in patients with "soft drusen." Another line featured highly refractile subretinal deposits that mimicked "hard–drusen." In vivo time–lapse imaging of fundus fluorescence suggested that drusen–like materials may have been formed by accumulation of fluorescent materials at or near the RPE in both lines. Fundus angiography revealed somewhat irregular, localized choroidal hyperfluorescence, indicative of vascular leakage, but no obvious neovascularization was found in any of the fourteen lines at eight weeks.
Non–invasive fluorescence imaging can be used to monitor pathological conditions of the fundus in mice. HIF–transgenic mice develop abnormal fundus autofluorescence, and thus they are a valuable model for studying generation and proliferation of fluorescent structures in the retina, further allowing examination of a possible link between hypoxia and long–term retinal lesions such as seen in AMD. HIF pathway components may serve as future drug targets for AMD.
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