Vitamin A Transporters in Visual Function: A Mini Review on Membrane Receptors for Dietary Vitamin A Uptake, Storage, and Transport to the Eye

Vitamins are essential compounds obtained through diet that are necessary for normal development and function in an organism. One of the most important vitamins for human physiology is vitamin A, a group of retinoid compounds and carotenoids, which generally function as a mediator for cell growth, d...

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Autores principales:	Nicasio Martin Ask, Matthias Leung, Rakesh Radhakrishnan, Glenn P. Lobo
Formato:	article
Lenguaje:	EN
Publicado:	MDPI AG 2021
Materias:	vitamin A transporters all-<i>trans</i> retinol retinyl esters LRAT STRA6 RBPR2 Nutrition. Foods and food supply TX341-641
Acceso en línea:	https://doaj.org/article/70e4b4595b73401e83225c6bcdfe8f69
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spelling	oai:doaj.org-article:70e4b4595b73401e83225c6bcdfe8f692021-11-25T18:35:51ZVitamin A Transporters in Visual Function: A Mini Review on Membrane Receptors for Dietary Vitamin A Uptake, Storage, and Transport to the Eye10.3390/nu131139872072-6643https://doaj.org/article/70e4b4595b73401e83225c6bcdfe8f692021-11-01T00:00:00Zhttps://www.mdpi.com/2072-6643/13/11/3987https://doaj.org/toc/2072-6643Vitamins are essential compounds obtained through diet that are necessary for normal development and function in an organism. One of the most important vitamins for human physiology is vitamin A, a group of retinoid compounds and carotenoids, which generally function as a mediator for cell growth, differentiation, immunity, and embryonic development, as well as serving as a key component in the phototransduction cycle in the vertebrate retina. For humans, vitamin A is obtained through the diet, where provitamin A carotenoids such as β-carotene from plants or preformed vitamin A such as retinyl esters from animal sources are absorbed into the body via the small intestine and converted into all-<i>trans</i> retinol within the intestinal enterocytes. Specifically, once absorbed, carotenoids are cleaved by carotenoid cleavage oxygenases (CCOs), such as Beta-carotene 15,15’-monooxygenase (BCO1), to produce all-<i>trans</i> retinal that subsequently gets converted into all-<i>trans</i> retinol. CRBP2 bound retinol is then converted into retinyl esters (REs) by the enzyme lecithin retinol acyltransferase (LRAT) in the endoplasmic reticulum, which is then packaged into chylomicrons and sent into the bloodstream for storage in hepatic stellate cells in the liver or for functional use in peripheral tissues such as the retina. All-trans retinol also travels through the bloodstream bound to retinol binding protein 4 (RBP4), where it enters cells with the assistance of the transmembrane transporters, stimulated by retinoic acid 6 (STRA6) in peripheral tissues or retinol binding protein 4 receptor 2 (RBPR2) in systemic tissues (e.g., in the retina and the liver, respectively). Much is known about the intake, metabolism, storage, and function of vitamin A compounds, especially with regard to its impact on eye development and visual function in the retinoid cycle. However, there is much to learn about the role of vitamin A as a transcription factor in development and cell growth, as well as how peripheral cells signal hepatocytes to secrete all-<i>trans</i> retinol into the blood for peripheral cell use. This article aims to review literature regarding the major known pathways of vitamin A intake from dietary sources into hepatocytes, vitamin A excretion by hepatocytes, as well as vitamin A usage within the retinoid cycle in the RPE and retina to provide insight on future directions of novel membrane transporters for vitamin A in retinal cell physiology and visual function.Nicasio Martin AskMatthias LeungRakesh RadhakrishnanGlenn P. LoboMDPI AGarticlevitamin A transportersall-<i>trans</i> retinolretinyl estersLRATSTRA6RBPR2Nutrition. Foods and food supplyTX341-641ENNutrients, Vol 13, Iss 3987, p 3987 (2021)
institution	DOAJ
collection	DOAJ
language	EN
topic	vitamin A transporters all-<i>trans</i> retinol retinyl esters LRAT STRA6 RBPR2 Nutrition. Foods and food supply TX341-641
spellingShingle	vitamin A transporters all-<i>trans</i> retinol retinyl esters LRAT STRA6 RBPR2 Nutrition. Foods and food supply TX341-641 Nicasio Martin Ask Matthias Leung Rakesh Radhakrishnan Glenn P. Lobo Vitamin A Transporters in Visual Function: A Mini Review on Membrane Receptors for Dietary Vitamin A Uptake, Storage, and Transport to the Eye
description	Vitamins are essential compounds obtained through diet that are necessary for normal development and function in an organism. One of the most important vitamins for human physiology is vitamin A, a group of retinoid compounds and carotenoids, which generally function as a mediator for cell growth, differentiation, immunity, and embryonic development, as well as serving as a key component in the phototransduction cycle in the vertebrate retina. For humans, vitamin A is obtained through the diet, where provitamin A carotenoids such as β-carotene from plants or preformed vitamin A such as retinyl esters from animal sources are absorbed into the body via the small intestine and converted into all-<i>trans</i> retinol within the intestinal enterocytes. Specifically, once absorbed, carotenoids are cleaved by carotenoid cleavage oxygenases (CCOs), such as Beta-carotene 15,15’-monooxygenase (BCO1), to produce all-<i>trans</i> retinal that subsequently gets converted into all-<i>trans</i> retinol. CRBP2 bound retinol is then converted into retinyl esters (REs) by the enzyme lecithin retinol acyltransferase (LRAT) in the endoplasmic reticulum, which is then packaged into chylomicrons and sent into the bloodstream for storage in hepatic stellate cells in the liver or for functional use in peripheral tissues such as the retina. All-trans retinol also travels through the bloodstream bound to retinol binding protein 4 (RBP4), where it enters cells with the assistance of the transmembrane transporters, stimulated by retinoic acid 6 (STRA6) in peripheral tissues or retinol binding protein 4 receptor 2 (RBPR2) in systemic tissues (e.g., in the retina and the liver, respectively). Much is known about the intake, metabolism, storage, and function of vitamin A compounds, especially with regard to its impact on eye development and visual function in the retinoid cycle. However, there is much to learn about the role of vitamin A as a transcription factor in development and cell growth, as well as how peripheral cells signal hepatocytes to secrete all-<i>trans</i> retinol into the blood for peripheral cell use. This article aims to review literature regarding the major known pathways of vitamin A intake from dietary sources into hepatocytes, vitamin A excretion by hepatocytes, as well as vitamin A usage within the retinoid cycle in the RPE and retina to provide insight on future directions of novel membrane transporters for vitamin A in retinal cell physiology and visual function.
format	article
author	Nicasio Martin Ask Matthias Leung Rakesh Radhakrishnan Glenn P. Lobo
author_facet	Nicasio Martin Ask Matthias Leung Rakesh Radhakrishnan Glenn P. Lobo
author_sort	Nicasio Martin Ask
title	Vitamin A Transporters in Visual Function: A Mini Review on Membrane Receptors for Dietary Vitamin A Uptake, Storage, and Transport to the Eye
title_short	Vitamin A Transporters in Visual Function: A Mini Review on Membrane Receptors for Dietary Vitamin A Uptake, Storage, and Transport to the Eye
title_full	Vitamin A Transporters in Visual Function: A Mini Review on Membrane Receptors for Dietary Vitamin A Uptake, Storage, and Transport to the Eye
title_fullStr	Vitamin A Transporters in Visual Function: A Mini Review on Membrane Receptors for Dietary Vitamin A Uptake, Storage, and Transport to the Eye
title_full_unstemmed	Vitamin A Transporters in Visual Function: A Mini Review on Membrane Receptors for Dietary Vitamin A Uptake, Storage, and Transport to the Eye
title_sort	vitamin a transporters in visual function: a mini review on membrane receptors for dietary vitamin a uptake, storage, and transport to the eye
publisher	MDPI AG
publishDate	2021
url	https://doaj.org/article/70e4b4595b73401e83225c6bcdfe8f69
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Vitamin A Transporters in Visual Function: A Mini Review on Membrane Receptors for Dietary Vitamin A Uptake, Storage, and Transport to the Eye

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