Abstract
The retinoids are a family of compounds that in nature are derived from vitamin A or pro-vitamin A carotenoids. An essential part of the diet for mammals, vitamin A has long been known to be essential for many organ systems in the adult. More recently, however, they have been shown to be necessary for function of the brain and new discoveries point to a central role in processes ranging from neuroplasticity to neurogenesis. Acting in several regions of the central nervous system including the eye, hippocampus and hypothalamus, one common factor in its action is control of biological rhythms. This review summarizes the role of vitamin A in the brain; its action through the metabolite retinoic acid via specific nuclear receptors, and the regulation of its concentration through controlled synthesis and catabolism. The action of retinoic acid to regulate several rhythms in the brain and body, from circadian to seasonal, is then discussed to finish with the importance of retinoic acid in the regular pattern of sleep.We review the role of vitamin A and retinoic acid (RA) as mediators of rhythm in the brain. In the suprachiasmatic nucleus and hippocampus they control expression of circadian clock genes while in the cortex retinoic acid is required for delta oscillations of sleep. Retinoic acid is also central to a second rhythm that keeps pace with the seasons, regulating function in the hypothalamus and pineal gland.
Highlights
This review summarizes the role of vitamin A in the brain; its action through the metabolite retinoic acid via specific nuclear receptors, and the regulation of its concentration through controlled synthesis and catabolism
Results point to an important role for retinoic acid (RA) in the adult central nervous system (CNS) and evidence suggests that RA mediates neuronal plasticity (McCaffery et al 2006; Chen et al 2012) as well as neurogenesis in both the hippocampus (Goodman et al 2012) and hypothalamus (Shearer et al 2012b)
extracellular signal-regulated kinase 1/2 (ERK1/2) mitogen-activated protein kinase (MAPK) pathways are activated in neuronal cells and embryonic stem cells by RA (Bost et al 2002; Masia et al 2007), while in other cells types p38MAPK is activated by RA (Alsayed et al 2001; Piskunov and Rochette-Egly 2012)
Summary
Vitamin A and related retinoid compounds (Fig. 1) have a similar chemical structure containing a 6 carbon b-ionone ring and an isoprenoid chain termed a retinyl group. ERK1/2 MAPK pathways are activated in neuronal cells and embryonic stem cells by RA (Bost et al 2002; Masia et al 2007), while in other cells types p38MAPK is activated by RA (Alsayed et al 2001; Piskunov and Rochette-Egly 2012) This latter pathway can be upstream of activation of MSK1 (Bruck et al 2009) and provides one mechanism by which a rapid action by RA to promote protein phosphorylation feeds back to RARs more traditional role of control of transcription. Retinoic acid catabolism The concentration of RA available to activate the RAR/RXR complex and to contribute to retinoid signalling within tissues is determined by the relative expression of both the synthetic and degradative enzymes. This is a key regulatory mechanism necessary to achieve appropriate vitamin A homeostasis
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
