Positively charged retinoids are potent and selective inhibitors of the trans-cis isomerization in the retinoid (visual) cycle

Golczak, Marcin; Kuksa, Vladimir; Maeda, Tadao; Moise, Alexander R.; Palczewski, Krzysztof

doi:10.1073/pnas.0503318102

Cited by 114 publications

(171 citation statements)

References 29 publications

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“…Ret-NH 2 was synthesized as described (41). Mice were fed 1 mg of Ret-NH 2 suspended in vegetable oil via oral gavage.…”

Section: Methodsmentioning

confidence: 99%

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Inner retinal photoreception independent of the visual retinoid cycle

Tu¹,

Owens²,

Anderson³

et al. 2006

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

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Mice lacking the visual cycle enzymes RPE65 or lecithin-retinol acyl transferase (Lrat) have pupillary light responses (PLR) that are less sensitive than those of mice with outer retinal degeneration (rd͞rd or rdta). Inner retinal photoresponses are mediated by melanopsinexpressing, intrinsically photosensitive retinal ganglion cells (ipRGCs), suggesting that the melanopsin-dependent photocycle utilizes RPE65 and Lrat. To test this hypothesis, we generated rpe65 ؊/؊ ; rdta and lrat ؊/؊ ; rd͞rd mutant mice. Unexpectedly, both rpe65 ؊/؊ ; rdta and lrat ؊/؊ ; rd͞rd mice demonstrate paradoxically increased PLR photosensitivity compared with mice mutant in visual cycle enzymes alone. Acute pharmacologic inhibition of the visual cycle of melanopsin-deficient mice with all-trans-retinylamine results in a near-total loss of PLR sensitivity, whereas treatment of rd͞rd mice has no effect, demonstrating that the inner retina does not require the visual cycle. Treatment of rpe65 ؊/؊ ; rdta with 9-cis-retinal partially restores PLR sensitivity. Photic sensitivity in P8 rpe65 ؊/؊ and lrat ؊/؊ ipRGCs is intact as measured by ex vivo multielectrode array recording. These results demonstrate that the melanopsin-dependent ipRGC photocycle is independent of the visual retinoid cycle.melanopsin ͉ pupillary light response ͉ retinal degeneration ͉ retinal ganglion cell ͉ visual photocycle M ice blind from outer retinal degeneration retain the ability to entrain their circadian rhythms to external light-dark cycles, have active pupillary light responses (PLRs), and exhibit photically induced melatonin suppression (1-4). These responses depend on the opsin family member melanopsin (5), which is expressed exclusively in a subset of intrinsically photosensitive retinal ganglion cells (ipRGCs) (6-8). Mice with nonfunctional or degenerated rods and cones that also lack melanopsin show no photically influenced behavior or physiology (9, 10), and intrinsic photosensitivity of retinal ganglion cells is lost in the absence of melanopsin (9,11,12). Melanopsin forms a functional photopigment when heterologously expressed in COS cells (13), Xenopus oocytes (14), Neuro-2A cells (15), or HEK-293 cells (16). Melanopsin is thus necessary for ipRGC photoreception, and is sufficient to confer photosensitivity on intrinsically insensitive cell types. Taken together, these results strongly suggest that melanopsin is the photopigment of inner retinal photoreception.All opsin photopigments use a retinoid chromophore that undergoes isomerization upon absorption of an appropriate wavelength photon. In rod photoreceptors, 11-cis-retinal chromophore is photoisomerized to all-trans-retinal which dissociates from the opsin protein (17). This all-trans-retinal photoproduct is recycled to the active (11-cis) form by enzymatic conversion in the adjacent retinal pigment epithelium (RPE) (18). The chromophore used by melanopsin in situ is not presently known. ipRGCs are physically distant from the enzymatic chromophore regeneration machinery of the RPE. It is present...

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“…Ret-NH 2 was synthesized as described (41). Mice were fed 1 mg of Ret-NH 2 suspended in vegetable oil via oral gavage.…”

Section: Methodsmentioning

confidence: 99%

“…Mice gavaged with 1 mg of Ret-NH 2 show substantial loss of electroretinogram within one day (41). Wildtype mice treated with Ret-NH 2 by gastric gavage showed a Ϸ100-fold decrement in pupillary light responsiveness 24 h after gavage (Fig.…”

Section: Pharmacologic Inhibition Of Visual Retinoid Cycle Causes Losmentioning

confidence: 99%

Inner retinal photoreception independent of the visual retinoid cycle

Tu¹,

Owens²,

Anderson³

et al. 2006

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

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“…Thus, 13-cis-retinyl esters are formed independently of light. Second, when Rdh5−/−Rdh11−/−mice were gavaged with a potent inhibitor of 11-cisretinal production, all-trans-Ret-NH 2 (38), and then exposed 24 h later to intense light for 3 min at 500 cd·m −2 , only a modest increase in 13-cis-retinyl ester production was observed, whereas untreated control mice showed a severalfold increase in 13-cis-retinyl esters. No formation of these cis esters was observed in wild-type treated or untreated mice ( Figure 8A).…”

Section: -Cis-retinol Is Formed Through An Enzymatic Isomerization mentioning

confidence: 99%

“…Alternatively, not light, but thermal isomerization of retinoids could be the responsible factor. To test this possibility, we employed a very potent inhibitor of isomerization, Ret-NH 2 , which does not bind to most of the RPE65 pool present in the RPE (38,41). This inhibitor prevents the isomerization of all-trans-to both the 11-cis-and the 13-cis-retinol configuration, providing evidence that this reaction is enzymatic.…”

mentioning

confidence: 99%

Aberrant Metabolites in Mouse Models of Congenital Blinding Diseases: Formation and Storage of Retinyl Esters

Maeda

Imanishi

et al. 2006

Biochemistry

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Regeneration of the visual chromophore, 11-cis-retinal, is a critical step in restoring photoreceptors to their dark-adapted conditions. This regeneration process, called the retinoid cycle, takes place in the photoreceptor outer segments and the retinal pigment epithelium (RPE). Disabling mutations in nearly all of the retinoid cycle genes are linked to human conditions that cause congenital or progressive defects in vision. Several mouse models with disrupted genes related to this cycle contain abnormal fatty acid retinyl ester levels in the RPE. To investigate the mechanisms of retinyl ester accumulation, we generated single or double knockout mice lacking retinoid cycle genes. Alltrans-retinyl esters accumulated in mice lacking RPE65, but they are reduced in double knockout mice also lacking opsin, suggesting a connection between visual pigment regeneration and the retinoid cycle. Only Rdh5-deficient mice accumulate cis-retinyl esters, regardless of the simultaneous disruption of RPE65, opsin, and prRDH. 13-cis-Retinoids are produced at higher levels when the flow of retinoid through the cycle was increased, and these esters are stored in specific structures called retinosomes. Most importantly, retinylamine, a specific and effective inhibitor of the 11-cisretinol formation, also inhibits the production of 13-cis-retinyl esters. The data presented here support the idea that 13-cis-retinyl esters are formed through an aberrant enzymatic isomerization process.Vitamin A transformations in the eye are essential for vision. Absorption of light by the vitamin A-derived chromophore of visual pigments, 11-cis-retinal, leads to its photoisomerization to all-trans-retinal and the initiation of the signal transduction cascade (1-4). Through a chain of reactions, all-trans-retinal is recycled enzymatically back to 11-cis-retinal (5-8). These retinoid cycle reactions (Figure 1) take place in the outer segments of photoreceptor cells and in the adjacent retinal pigment epithelium (RPE). 1 Characterization of the knockout mice lacking genes involved in the retinoid cycle provides important insight into the flow of retinoids in the eye.11-cis-Retinol dehydrogenase (RDH), also known as RDH5, catalyzes the final oxidation reaction of 11-cis-retinol in the RPE (9, 10). Although RDH5 is responsible for the majority of 11-cis-RDH activity, RDH11 and other RDHs also have a measurable role in regenerating the visual pigment by complementing RDH5 in RPE cells (11). Disruption of the gene encoding RDH5 causes fundus albipunctatus in humans (12,13). Fundus albipunctatus is an autosomal recessive form of congenital stationary night blindness characterized by the appearance of numerous small white dots located in the RPE, a delayed course of dark adaptation, and † This research was supported by NIH Grant EY09339. Lipid droplet-like organelles known as retinosomes were characterized as specific sites of alltrans-retinyl ester accumulation in the RPE (19,20). All-trans-retinyl esters accumulate in the RPE of wild-type mice as the...

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“…tually a concerted ester cleavage/double-bond isomerization reaction in which an atypical ester hydrolysis results in the formation of a carbocation intermediate that allows the isomerization step to occur (13,16,17,(37)(38)(39)(40)(41) (reviewed in ref. 42).…”

Section: Proposed Role For the Iron Cofactor In Rpe65-catalyzed Retinoidmentioning

confidence: 99%

Structure of RPE65 isomerase in a lipidic matrix reveals roles for phospholipids and iron in catalysis

Kiser

Farquhar

Shi

et al. 2012

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

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RPE65 is a key metalloenzyme responsible for maintaining visual function in vertebrates. Despite extensive research on this membrane-bound retinoid isomerase, fundamental questions regarding its enzymology remain unanswered. Here, we report the crystal structure of RPE65 in a membrane-like environment. These crystals, obtained from enzymatically active, nondelipidated protein, displayed an unusual packing arrangement wherein RPE65 is embedded in a lipid-detergent sheet. Structural differences between delipidated and nondelipidated RPE65 uncovered key residues involved in substrate uptake and processing. Complementary iron K-edge Xray absorption spectroscopy data established that RPE65 as isolated contained a divalent iron center and demonstrated the presence of a tightly bound ligand consistent with a coordinated carboxylate group. These results support the hypothesis that the Lewis acidity of iron could be used to promote ester dissociation and generation of a carbocation intermediate required for retinoid isomerization.metalloprotein | monotopic membrane protein | extended X-ray absorption fine structure | isomerohydrolase V ision is a complex, multistep process whereby environmental information contained in light rays is converted to chemical and electrical signals in the retina that are relayed to the brain for interpretation. The initial step in this process is mediated by light receptors called rod and cone opsins and their associated G proteins in photoreceptor cells (1). These receptors contain a vitamin A-derived chromophore called 11-cis-retinal that undergoes cis to trans isomerization upon absorption of a photon. Isomerization of the chromophore converts the receptor to a state in which it can activate downstream signaling molecules that alter the electrochemical state of the photoreceptor cell (2, 3). Following photoisomerization, the Schiff base-linked chromophore is hydrolyzed and dissociates from the receptor. Continuous regeneration of 11-cis-retinal, required for maintenance of visual function, is critically dependent on a metabolic pathway known as the visual cycle (4, 5). At the heart of this cycle is the enzymatic conversion of all-transretinyl esters to 11-cis-retinol by the retinoid isomerase, RPE65, mutations of which cause the severe childhood blinding disease Leber congenital amaurosis (6, 7).RPE65 is an iron-dependent, membrane-bound enzyme expressed nearly exclusively in the retinal pigment epithelium (RPE) (8, 9). The iron dependence of RPE65 was anticipated on the basis of its evolutionarily relationship to carotenoid cleavage oxygenases (CCOs). However, CCO activity has not been demonstrated for RPE65, and it is likely that iron serves a different, albeit poorly understood, function in this enzyme. It is now appreciated that phospholipids constitute a second critical factor necessary for RPE65 activity. Purified RPE65 exhibited retinoid isomerase activity only when bound to all-trans-retinyl ester-incorporated membrane vesicles (10). Moreover, destruction of intact microsomal phosp...

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Positively charged retinoids are potent and selective inhibitors of the trans-cis isomerization in the retinoid (visual) cycle

Cited by 114 publications

References 29 publications

Inner retinal photoreception independent of the visual retinoid cycle

Inner retinal photoreception independent of the visual retinoid cycle

Aberrant Metabolites in Mouse Models of Congenital Blinding Diseases: Formation and Storage of Retinyl Esters

Structure of RPE65 isomerase in a lipidic matrix reveals roles for phospholipids and iron in catalysis

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