Reduction of All-trans-retinal in Vertebrate Rod Photoreceptors Requires the Combined Action of RDH8 and RDH12

Chen, Chunhe; Thompson, Debra A.; Koutalos, Yiannis

doi:10.1074/jbc.m112.354514

Cited by 69 publications

(84 citation statements)

References 43 publications

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“…visual cycle. Small amounts of all-trans-retinal and 11-cis-retinal which diffuse from outer segments can be detoxified to retinol by RDH12 or other RDH isoforms localized in the inner segments and other cellular compartments (24). Although this study focuses on the role of ABCA4 in the transport of N-11-cis-retinylidene-PE, ABCA4 can also transport the all-trans isomer of N-retinylidene- Fig.…”

Section: Discussionmentioning

confidence: 98%

ATP-binding cassette transporter ABCA4 and chemical isomerization protect photoreceptor cells from the toxic accumulation of excess 11- cis -retinal

Quazi

Molday

2014

Proc. Natl. Acad. Sci. U.S.A.

113

101

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The visual cycle is a series of enzyme-catalyzed reactions which converts all-trans-retinal to 11-cis-retinal for the regeneration of visual pigments in rod and cone photoreceptor cells. Although essential for vision, 11-cis-retinal like all-trans-retinal is highly toxic due to its highly reactive aldehyde group and has to be detoxified by either reduction to retinol or sequestration within retinal-binding proteins. Previous studies have focused on the role of the ATP-binding cassette transporter ABCA4 associated with Stargardt macular degeneration and retinol dehydrogenases (RDH) in the clearance of all-trans-retinal from photoreceptors following photoexcitation. How rod and cone cells prevent the accumulation of 11-cis-retinal in photoreceptor disk membranes in excess of what is required for visual pigment regeneration is not known. Here we show that ABCA4 can transport N-11-cis-retinylidene-phosphatidylethanolamine (PE), the Schiff-base conjugate of 11-cis-retinal and PE, from the lumen to the cytoplasmic leaflet of disk membranes. This transport function together with chemical isomerization to its all-trans isomer and reduction to all-trans-retinol by RDH can prevent the accumulation of excess 11-cis-retinal and its Schiff-base conjugate and the formation of toxic bisretinoid compounds as found in ABCA4-deficient mice and individuals with Stargardt macular degeneration. This segment of the visual cycle in which excess 11-cis-retinal is converted to all-transretinol provides a rationale for the unusually high content of PE and its long-chain unsaturated docosahexaenoyl group in photoreceptor membranes and adds insight into the molecular mechanisms responsible for Stargardt macular degeneration.T he visual cycle plays a crucial role in the removal of all-transretinal from photoreceptor cells following photoexcitation and its conversion to 11-cis-retinal for the regeneration of visual pigments in rod and cone photoreceptor cells (1). Deficient clearance of all-trans-retinal and its Schiff-base conjugate N-retinylidenephosphatidylethanolamine (PE) from rod and cone photoreceptor outer segments results in condensation reactions which produce a mixture of bisretinoid products including the pyridinium bisretinoid compound A2PE and its hydrolytic product A2E (2, 3). These bisretinoid compounds accumulate as lipofuscin deposits in retinal pigment epithelial (RPE) cells upon phagocytosis of outer segments and have been implicated in the pathology of a number of retinal degenerative diseases. This is particularly evident in autosomal recessive Stargardt macular degeneration in which mutations in the ATP-binding cassette (ABC) transporter ABCA4 which impair the N-retinylidene-PE transport activity of ABCA4 cause a buildup of lipofuscin, atrophy of the central retina, and severe progressive loss in vision (4-8).In initial studies, Abca4 knockout mice were reported to show a light-dependent accumulation of all-trans-retinal, PE, and N-retinylidene-PE in photoreceptors and lipofuscin and A2E in RPE (9). This led to a model...

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Section: Discussionmentioning

confidence: 98%

ATP-binding cassette transporter ABCA4 and chemical isomerization protect photoreceptor cells from the toxic accumulation of excess 11- cis -retinal

Quazi

Molday

2014

Proc. Natl. Acad. Sci. U.S.A.

113

101

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“…Fluorescence Imaging-Fluorescence measurements were carried out as described previously (11,12), on the stage of an inverted Zeiss Axiovert 100 microscope with a 40ϫ oil immersion objective lens (N.A. ϭ 1.3).…”

Section: Animals-wild Type (129/sv) and Rpe65mentioning

confidence: 99%

“…To measure the Fex-340/Fex-380 fluorescence ratios for alltrans-retinol and all-trans-retinal, broken off rod outer segments (rod outer segments separated from the rest of the cell) were loaded with 50 M of either retinoid for 5 min, using 1% BSA as lipophilic carrier (10,11). To determine the intracellular pH of rod outer segments, BCECF, a ratiometric pH-sensitive dye was used, following published procedures used with isolated salamander rod photoreceptors (13).…”

Section: Animals-wild Type (129/sv) and Rpe65mentioning

confidence: 99%

“…As retinal and retinol fluoresce with excitation maxima at different wavelengths, this conversion can be monitored from the relative intensities of the rod outer segment fluorescence excited by 340 and 380 nm. The ratio Fex-340/Fex-380 of the intensities of the fluorescence excited by 340-and 380-nm light is a measure of the fraction of the released all-trans-retinal converted to all-trans-retinol (10,11). The conversion depends on the availability of NADPH.…”

Section: Measurement Of Nadph From Fluorescencementioning

confidence: 99%

“…All-trans-retinal and retinol both fluoresce and have a large difference in excitation maxima (9), which allows for the differentiation of their fluorescence signals (10,11). A ratio of the fluorescence excited by two appropriately chosen wavelengths (340 and 380 nm) reflects the all-trans-retinol to retinal ratio, which is a measure of the conversion of all-trans-retinal to retinol, and thereby of NADPH availability as well.…”

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confidence: 99%

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Mitochondria Contribute to NADPH Generation in Mouse Rod Photoreceptors

Adler

Chen

Koutalos

2014

Journal of Biological Chemistry

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Background:The major source of NADPH is considered to be the pentose phosphate pathway. Results: In isolated mouse rod photoreceptors, blocking metabolite entry into mitochondria substantially reduces NADPH generation. Mitochondrial metabolic substrates support NADPH generation. Conclusion: Mitochondria-linked pathways contribute substantially to NADPH generation in mouse rod photoreceptors. Significance: A wide range of photoreceptor cell functions depend on adequate NADPH supply.

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Kinetics of Rhodopsin’s Chromophore Monitored in a Single Photoreceptor

Adler

Boyer

Chen

et al. 2015

Methods in Molecular Biology

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Absorption of light isomerizes the retinyl chromophore of the photoreceptor pigment rhodopsin from 11-cis to all-trans, generating the photoactivated rhodopsin form. The photoisomerization of the chromophore however destroys rhodopsin, and its regeneration requires the removal of the all-trans and the supply of fresh 11-cis chromophore. The all-trans chromophore is removed through a series of steps beginning with its release from photoactivated rhodopsin in the form of all-trans-retinal, leaving behind the apoprotein opsin. All-trans-retinal is then reduced to all-trans-retinol, which is transported out of the photoreceptor. Rhodopsin is regenerated from opsin and fresh 11-cis-retinal arriving to the photoreceptor from the retinal pigment epithelium. Both all-trans and 11-cis-retinal can form precursors of lipofuscin, a pigment that accumulates with age in the lysosomal compartment of the retinal pigment epithelium. All-trans-retinal, all-trans-retinol, and lipofuscin precursors all emit significant and distinct fluorescence signals, allowing their monitoring in single photoreceptor cells with fluorescence imaging. Here we describe the procedures for measuring these fluorophores in single mouse rod photoreceptors.

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Reduction of All-trans-retinal in Vertebrate Rod Photoreceptors Requires the Combined Action of RDH8 and RDH12

Cited by 69 publications

References 43 publications

ATP-binding cassette transporter ABCA4 and chemical isomerization protect photoreceptor cells from the toxic accumulation of excess 11- cis -retinal

ATP-binding cassette transporter ABCA4 and chemical isomerization protect photoreceptor cells from the toxic accumulation of excess 11- cis -retinal

Mitochondria Contribute to NADPH Generation in Mouse Rod Photoreceptors

Kinetics of Rhodopsin’s Chromophore Monitored in a Single Photoreceptor

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