Abstract
The visual system produces visual chromophore, 11-cis-retinal from dietary vitamin A, all-trans-retinol making this vitamin essential for retinal health and function. These metabolic events are mediated by a sequential biochemical process called the visual cycle. Retinol dehydrogenases (RDHs) are responsible for two reactions in the visual cycle performed in retinal pigmented epithelial (RPE) cells, photoreceptor cells and Müller cells in the retina. RDHs in the RPE function as 11-cis-RDHs, which oxidize 11-cis-retinol to 11-cis-retinal in vivo. RDHs in rod photoreceptor cells in the retina work as all-trans-RDHs, which reduce all-trans-retinal to all-trans-retinol. Dysfunction of RDHs can cause inherited retinal diseases in humans. To facilitate further understanding of human diseases, mouse models of RDHs-related diseases have been carefully examined and have revealed the physiological contribution of specific RDHs to visual cycle function and overall retinal health. Herein we describe the function of RDHs in the RPE and the retina, particularly in rod photoreceptor cells, their regulatory properties for retinoid homeostasis and future therapeutic strategy for treatment of retinal diseases.
Highlights
Vitamin A and its derivatives play important roles in development of the eye and in day-to-day visual function
The eight amino acids at C-terminal tail of RDH5 is proposed to be crucial for activity and mutations within or close to this tail identified in patients with Fundus albipunctatus (FA) [23,24,25]
Immunohistochemistry assay revealed a signal of RDH11 expression in the retinal pigmented epithelial (RPE) in monkey and bovine eyes, whereas a faint signal was found in the rod photoreceptor inner segment and Müller cells [43]
Summary
Vitamin A and its derivatives play important roles in development of the eye and in day-to-day visual function. Continuous vision depends on recycling of the photoproduct all-trans-retinal back to visual chromophore 11-cis-retinal This process is enabled by the visual (retinoid) cycle, a series of biochemical reactions in photoreceptor, adjacent RPE and Müller cells. After exposed to light, all-trans-retinal was dissociated from discovered 11‐cis‐retinal which is bound to opsin by Schiff base formation to produce light sensitive rhodopsin These important discoveries brought him the Nobel Prize in 1967 in Physiology and rhodopsin [4,5,6]. The visual cycle is a series of biochemical reactions to regenerate and photo signals are converted to electrical signals which are transduced to the visual cortex of photoisomerized the brain. The visual cycle is a all-trans-retinal series of biochemical reactions to regenerate is.
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