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L. R. Blakeley, N. P. Boyer, C. Chen, R. K. Crouch, Y. Koutalos; Formation of Lipofuscin Precursors in the Outer Segments of Single Mouse Rod Photoreceptors. Invest. Ophthalmol. Vis. Sci. 2010;51(13):1110.
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© ARVO (1962-2015); The Authors (2016-present)
To examine the formation of lipofuscin precursors from unreduced all-trans retinal in the outer segments of rod photoreceptor cells. All-trans retinal is formed from the photoisomerization of the 11-cis retinal chromophore of rhodopsin. Upon its release from photoactivated rhodopsin, all-trans retinal is reduced to all-trans retinol, which is then transported out of the outer segment.
Experiments were carried out with living isolated rod photoreceptors from wild type and Rpe65-/- mice. Animals were 2-3 months old. The reduction of all-trans retinal was measured from the fluorescence of the produced all-trans retinol (Ex: 360 nm; Em: >420 nm). Formation of lipofuscin precursors was measured from their characteristic orange fluorescence (Ex: 490 nm; Em: >515 nm).
In wild type photoreceptors, the reduction of endogenously generated all-trans retinal to retinol is suppressed in the absence of glucose, as well as in broken off rod outer segments separated from the rest of the cell. Rod photoreceptors from Rpe65-/- mice lack endogenous 11-cis retinal. In their case, intact rod cells reduce exogenously supplied all-trans retinal, but broken off rod outer segments cannot. For both the wild type and Rpe65-/- rod photoreceptors, suppression of the reduction of all-trans retinal resulted in the formation of lipofuscin-like fluorophores.
Failure to reduce the all-trans retinal generated from the photoisomerization of the chromophore of rhodopsin results in the formation of lipofuscin-like fluorophores in the rod outer segment. These fluorophores are a potential source of the lipofuscin that accumulates with age in the retinal pigment epithelium.Support: NIH/NEI grant EY014850 (YK), EY004939 (RKC), and an unrestricted grant to MUSC Storm Eye Institute from Research to Prevent Blindness, Inc., New York, NY.
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