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Developmental Dynamics : An Official... Aug 2021Retinol binding protein 1 (Rbp1) acts as an intracellular regulator of vitamin A metabolism and retinoid transport. In mice, Rbp1 deficiency decreases the capacity of...
BACKGROUND
Retinol binding protein 1 (Rbp1) acts as an intracellular regulator of vitamin A metabolism and retinoid transport. In mice, Rbp1 deficiency decreases the capacity of hepatic stellate cells to take up all-trans retinol and sustain retinyl ester stores. Furthermore, Rbp1 is crucial for visual capacity. Although the function of Rbp1 has been studied in the mature eye, its role during early anterior neural development has not yet been investigated in detail.
RESULTS
We showed that rbp1 is expressed in the eye, anterior neural crest cells (NCCs) and prosencephalon of the South African clawed frog Xenopus laevis. Rbp1 knockdown led to defects in eye formation, including microphthalmia and disorganized retinal lamination, and to disturbed induction and differentiation of the eye field, as shown by decreased rax and pax6 expression. Furthermore, it resulted in reduced rax expression in the prosencephalon and affected cranial cartilage. Rbp1 inhibition also interfered with neural crest induction and migration, as shown by twist and slug. Moreover, it led to a significant reduction of the all-trans retinoic acid target gene pitx2 in NCC-derived periocular mesenchyme. The Rbp1 knockdown phenotypes were rescued by pitx2 RNA co-injection.
CONCLUSION
Rbp1 is crucial for the development of the anterior neural tissue.
Topics: Animals; Embryonic Development; Eye Proteins; Gene Expression Regulation, Developmental; Gene Knockdown Techniques; Neural Crest; PAX6 Transcription Factor; Prosencephalon; Retinol-Binding Proteins, Cellular; Signal Transduction; Tretinoin; Xenopus Proteins; Xenopus laevis
PubMed: 33570783
DOI: 10.1002/dvdy.313 -
The Journal of Investigative Dermatology Jan 1996The potential for all-trans-retinoic acid to regulate the metabolism of 3H-retinol and 3H-3,4-didehydroretinol was examined in cultured human epidermal keratinocytes....
The potential for all-trans-retinoic acid to regulate the metabolism of 3H-retinol and 3H-3,4-didehydroretinol was examined in cultured human epidermal keratinocytes. Confluent cultures were treated daily with medium containing 5% fetal bovine serum or the same medium supplemented with nanomolar concentrations of all-trans-retinoic acid for up to 3 d. During the last 24 of treatment, cells were incubated with 3H-retinol or 3H-3,4-didehydroretinol for 24 h (isotopic steady state) to label the endogenous retinoids. After the labeling period, one group of cells was harvested and another group was allowed to incubate for an additional 24 h in the absence of medium retinol for the determination of endogenous 3H-retinoid utilization. The 3H-retinoids present in cells were extracted and quantitated by reverse-phased high-pressure liquid chromatography. Keratinocytes treated with retinoic acid and labeled with 3H-retinol exhibited time- and concentration-dependent (i) increases in retinyl ester mass, (ii) increases in the rate of retinyl ester synthesis, (iii) decreases in retinyl ester utilization, and (iv) decreases in the cellular concentrations of retinoic and 3,4-didehydroretinoic acids. There was no effect of exogenous retinoic acid on its own metabolism. Cells labeled with 3H-3,4-didehydroretinol exhibited exclusive labeling of vitamin A2-related retinoids suggesting that the A1 to A2 conversion is not reversible. Treatment of cells with low nanomolar concentrations of retinoic acid decreased the utilization of 3,4-didehydroretinyl esters, decreased the production of 3,4-didehydroretinoic acid but had no effect on the synthesis of 3,4-didehydroretinol or its esters. The results demonstrate that keratinocytes respond to extracellular retinoic acid by decreasing endogenous production of active retinoids, sequestering extracellular substrate retinol as retinyl ester, and decreasing ester utilization.
Topics: Adult; Cells, Cultured; Epidermal Cells; Epidermis; Humans; Keratinocytes; Male; Retinoids; Tretinoin; Vitamin A
PubMed: 8592069
DOI: 10.1111/1523-1747.ep12329900 -
Translational Psychiatry Feb 2023The small, hormone-like molecule retinoic acid (RA) is a vital regulator in several neurobiological processes that are affected in depression. Next to its involvement in...
The small, hormone-like molecule retinoic acid (RA) is a vital regulator in several neurobiological processes that are affected in depression. Next to its involvement in dopaminergic signal transduction, neuroinflammation, and neuroendocrine regulation, recent studies highlight the role of RA in homeostatic synaptic plasticity and its link to neuropsychiatric disorders. Furthermore, experimental studies and epidemiological evidence point to the dysregulation of retinoid homeostasis in depression. Based on this evidence, the present study investigated the putative link between retinoid homeostasis and depression in a cohort of 109 patients with major depressive disorder (MDD) and healthy controls. Retinoid homeostasis was defined by several parameters. Serum concentrations of the biologically most active Vitamin A metabolite, all-trans RA (at-RA), and its precursor retinol (ROL) were quantified and the individual in vitro at-RA synthesis and degradation activity was assessed in microsomes of peripheral blood-derived mononuclear cells (PBMC). Additionally, the mRNA expression of enzymes relevant to retinoid signaling, transport, and metabolism were assessed. Patients with MDD had significantly higher ROL serum levels and greater at-RA synthesis activity than healthy controls providing evidence of altered retinoid homeostasis in MDD. Furthermore, MDD-associated alterations in retinoid homeostasis differed between men and women. This study is the first to investigate peripheral retinoid homeostasis in a well-matched cohort of MDD patients and healthy controls, complementing a wealth of preclinical and epidemiological findings that point to a central role of the retinoid system in depression.
Topics: Male; Humans; Female; Retinoids; Depressive Disorder, Major; Leukocytes, Mononuclear; Tretinoin; Vitamin A; Homeostasis
PubMed: 36813763
DOI: 10.1038/s41398-023-02362-0 -
Photochemical & Photobiological... Oct 2020Retinal, the vitamin A aldehyde, is a potent photosensitizer that plays a major role in light-induced damage to vertebrate photoreceptors. 11-Cis retinal is the...
Retinal, the vitamin A aldehyde, is a potent photosensitizer that plays a major role in light-induced damage to vertebrate photoreceptors. 11-Cis retinal is the light-sensitive chromophore of rhodopsin, the photopigment of vertebrate rod photoreceptors. It is isomerized by light to all-trans, activating rhodopsin and beginning the process of light detection. All-trans retinal is released by activated rhodopsin, allowing its regeneration by fresh 11-cis retinal continually supplied to photoreceptors. The released all-trans retinal is reduced to all-trans retinol in a reaction using NADPH. We have examined the photooxidation mediated by 11-cis and all-trans retinal in single living rod photoreceptors isolated from mouse retinas. Photooxidation was measured with fluorescence imaging from the oxidation of internalized BODIPY C11, a fluorescent dye whose fluorescence changes upon oxidation. We found that photooxidation increased with the concentration of exogenously added 11-cis or all-trans retinal to metabolically compromised rod outer segments that lacked NADPH supply. In dark-adapted metabolically intact rod outer segments with access to NADPH, there was no significant increase in photooxidation following exposure of the cell to light, but there was significant increase following addition of exogenous 11-cis retinal. The results indicate that both 11-cis and all-trans retinal can mediate light-induced damage in rod photoreceptors. In metabolically intact cells, the removal of the all-trans retinal generated by light through its reduction to retinol minimizes all-trans retinal-mediated photooxidation. However, because the enzymatic machinery of the rod outer segment cannot remove 11-cis retinal, 11-cis-retinal-mediated photooxidation may play a significant role in light-induced damage to photoreceptor cells.
Topics: Animals; Mice; Mice, Knockout; Molecular Structure; Optical Imaging; Oxidation-Reduction; Photochemical Processes; Photoreceptor Cells; Retinaldehyde; Rod Cell Outer Segment; Vitamin A
PubMed: 32812970
DOI: 10.1039/d0pp00060d -
Nutrients Mar 2022Vitamin A is vital to maternal-fetal health and pregnancy outcomes. However, little is known about pregnancy associated changes in maternal vitamin A homeostasis and...
Vitamin A is vital to maternal-fetal health and pregnancy outcomes. However, little is known about pregnancy associated changes in maternal vitamin A homeostasis and concentrations of circulating retinol metabolites. The goal of this study was to characterize retinoid concentrations in healthy women ( = 23) during two stages of pregnancy (25-28 weeks gestation and 28-32 weeks gestation) as compared to ≥3 months postpartum. It was hypothesized that plasma retinol, retinol binding protein 4 (RBP4), transthyretin and albumin concentrations would decline during pregnancy and return to baseline by 3 months postpartum. At 25-28 weeks gestation, plasma retinol (-27%), 4-oxo-13--retinoic acid (-34%), and albumin (-22%) concentrations were significantly lower, and -retinoic acid (+48%) concentrations were significantly higher compared to ≥3 months postpartum in healthy women. In addition, at 28-32 weeks gestation, plasma retinol (-41%), retinol binding protein 4 (RBP4; -17%), transthyretin (TTR; -21%), albumin (-26%), 13--retinoic acid (-23%) and 4-oxo-13--retinoic acid (-48%) concentrations were significantly lower, whereas plasma -retinoic acid concentrations (+30%) were significantly higher than ≥3 months postpartum. Collectively, the data demonstrates that in healthy pregnancies, retinol plasma concentrations are lower, but -retinoic acid concentrations are higher than postpartum.
Topics: Female; Humans; Prealbumin; Pregnancy; Pregnant Women; Retinoids; Retinol-Binding Proteins, Plasma; Tretinoin; Vitamin A
PubMed: 35405978
DOI: 10.3390/nu14071365 -
Nutrients Jul 2013The visual cycle is a sequential enzymatic reaction for vitamin A, all-trans-retinol, occurring in the outer layer of the human retina and is essential for the... (Review)
Review
The visual cycle is a sequential enzymatic reaction for vitamin A, all-trans-retinol, occurring in the outer layer of the human retina and is essential for the maintenance of vision. The central source of retinol is derived from dietary intake of both retinol and pro-vitamin A carotenoids. A series of enzymatic reactions, located in both the photoreceptor outer segment and the retinal pigment epithelium, transform retinol into the visual chromophore 11-cis-retinal, regenerating visual pigments. Retina specific proteins carry out the majority of the visual cycle, and any significant interruption in this sequence of reactions is capable of causing varying degrees of blindness. Among these important proteins are Lecithin:retinol acyltransferase (LRAT) and retinal pigment epithelium-specific 65-kDa protein (RPE65) known to be responsible for esterification of retinol to all-trans-retinyl esters and isomerization of these esters to 11-cis-retinal, respectively. Deleterious mutations in these genes are identified in human retinal diseases that cause blindness, such as Leber congenital amaurosis (LCA) and retinitis pigmentosa (RP). Herein, we discuss the pathology of 11-cis-retinal deficiency caused by these mutations in both animal disease models and human patients. We also review novel therapeutic strategies employing artificial visual chromophore 9-cis-retinoids which have been employed in clinical trials involving LCA patients.
Topics: Acyltransferases; Animals; Clinical Trials as Topic; Disease Models, Animal; Humans; Retina; Retinal Diseases; Retinal Pigments; Retinaldehyde; Vision, Ocular; Vitamin A; cis-trans-Isomerases
PubMed: 23857173
DOI: 10.3390/nu5072646 -
Journal of Lipid Research Jul 2013By definition, a vitamin is a substance that must be obtained regularly from the diet. Vitamin A must be acquired from the diet, but unlike most vitamins, it can also be... (Review)
Review
By definition, a vitamin is a substance that must be obtained regularly from the diet. Vitamin A must be acquired from the diet, but unlike most vitamins, it can also be stored within the body in relatively high levels. For humans living in developed nations or animals living in present-day vivariums, stored vitamin A concentrations can become relatively high, reaching levels that can protect against the adverse effects of insufficient vitamin A dietary intake for six months, or even much longer. The ability to accumulate vitamin A stores lessens the need for routinely consuming vitamin A in the diet, and this provides a selective advantage to the organism. The molecular processes that underlie this selective advantage include efficient mechanisms to acquire vitamin A from the diet, efficient and overlapping mechanisms for the transport of vitamin A in the circulation, a specific mechanism allowing for vitamin A storage, and a mechanism for mobilizing vitamin A from these stores in response to tissue needs. These processes are considered in this review.
Topics: Animals; Esters; Humans; Vitamin A
PubMed: 23625372
DOI: 10.1194/jlr.R037648 -
Nutrients Apr 2022Cellular retinoic acid binding proteins (CRABP1 and CRABP2) bind -retinoic acid (RA), the active metabolite of vitamin A, with high affinity. CRABP1 and CRABP2 have been...
Cellular retinoic acid binding proteins (CRABP1 and CRABP2) bind -retinoic acid (RA), the active metabolite of vitamin A, with high affinity. CRABP1 and CRABP2 have been shown to interact with the RA-clearing cytochrome P450 enzymes CYP26B1 and CYP26C1 and with nuclear retinoic acid receptors (RARs). We hypothesized that CRABP1 and CRABP2 also alter RA metabolism and clearance by CYP26A1, the third key RA-metabolizing enzyme in the CYP26 family. Based on stopped-flow experiments, RA bound CRABP1 and CRABP2 with K values of 4.7 nM and 7.6 nM, respectively. The unbound RA K values for 4-OH-RA formation by CYP26A1 were 4.7 ± 0.8 nM with RA, 6.8 ± 1.7 nM with holo-CRABP1 and 6.1 ± 2.7 nM with holo-CRABP2 as a substrate. In comparison, the apparent k value was about 30% lower (0.71 ± 0.07 min for holo-CRABP1 and 0.75 ± 0.09 min for holo-CRABP2) in the presence of CRABPs than with free RA (1.07 ± 0.08 min). In addition, increasing concentrations in apo-CRABPs decreased the 4-OH-RA formation rates by CYP26A1. Kinetic analyses suggest that apo-CRABP1 and apo-CRABP2 inhibit CYP26A1 (K = 0.39 nM and 0.53 nM, respectively) and holo-CRABPs channel RA for metabolism by CYP26A1. These data suggest that CRABPs play a critical role in modulating RA metabolism and cellular RA concentrations.
Topics: Cytochrome P-450 Enzyme System; Retinoic Acid 4-Hydroxylase; Retinol-Binding Proteins; Tretinoin; Vitamin A
PubMed: 35565751
DOI: 10.3390/nu14091784 -
Biochemistry Feb 2007Metabolism of vitamin A, all-trans-retinol, leads to the formation of 11-cis-retinaldehyde, the visual chromophore, and all-trans-retinoic acid, which is involved in the...
Metabolism of vitamin A, all-trans-retinol, leads to the formation of 11-cis-retinaldehyde, the visual chromophore, and all-trans-retinoic acid, which is involved in the regulation of gene expression through the retinoic acid receptor. Enzymes and binding proteins involved in retinoid metabolism are highly conserved across species. We previously described a novel mammalian enzyme that saturates the 13-14 double bond of all-trans-retinol to produce all-trans-13,14-dihydroretinol, which then follows the same metabolic fate as that of all-trans-retinol. Specifically, all-trans-13,14-dihydroretinol is transiently oxidized to all-trans-13,14-dihydroretinoic acid before being oxidized further by Cyp26 enzymes. Here, we report the identification of two putative RetSat homologues in zebrafish, one of which, zebrafish RetSat A (zRetSat A), also had retinol saturase activity, whereas zebrafish RetSat B (zRetSat B) was inactive under similar conditions. Unlike mouse RetSat (mRetSat), zRetSat A had an altered bond specificity saturating either the 13-14 or 7-8 double bonds of all-trans-retinol to produce either all-trans-13,14-dihydroretinol or all-trans-7,8-dihydroretinol, respectively. zRetSat A also saturated the 13-14 or 7-8 double bonds of all-trans-3,4-didehydroretinol (vitamin A2), a second endogenous form of vitamin A in zebrafish. The dual enzymatic activity of zRetSat A displays a newly acquired specificity for the 13-14 double bond retained in higher vertebrates and also the evolutionarily preserved activity of bacterial phytoene desaturases and plant carotenoid isomerases. Expression of zRetSat A was restricted to the liver and intestine of hatchlings and adult zebrafish, whereas zRetSat B was expressed in the same tissues but at earlier developmental stages. Exogenous all-trans-retinol, all-trans-13,14-dihydroretinol, or all-trans-7,8-dihydroretinol led to the strong induction of the expression of the retinoic acid-metabolizing enzyme, Cyp26A1, arguing for an active signaling function of dihydroretinoid metabolites in zebrafish. These findings point to a conserved function but altered specificity of RetSat in vertebrates, leading to the generation of various dihydroretinoid compounds, some of which could have signaling functions.
Topics: Amino Acid Sequence; Animals; Catalysis; Molecular Sequence Data; Organ Specificity; Oxidoreductases Acting on CH-CH Group Donors; Stereoisomerism; Substrate Specificity; Vitamin A; Zebrafish; Zebrafish Proteins
PubMed: 17253779
DOI: 10.1021/bi062147u -
Proceedings of the National Academy of... Nov 2022For sustained vision, photoactivated rhodopsin (Rho*) must undergo hydrolysis and release of all--retinal, producing substrate for the visual cycle and apo-opsin...
For sustained vision, photoactivated rhodopsin (Rho*) must undergo hydrolysis and release of all--retinal, producing substrate for the visual cycle and apo-opsin available for regeneration with 11--retinal. The kinetics of this hydrolysis has yet to be described for rhodopsin in its native membrane environment. We developed a method consisting of simultaneous denaturation and chromophore trapping by isopropanol/borohydride, followed by exhaustive protein digestion, complete extraction, and liquid chromatography-mass spectrometry. Using our method, we tracked Rho* hydrolysis, the subsequent formation of -retinylidene-phosphatidylethanolamine (-ret-PE) adducts with the released all--retinal, and the reduction of all--retinal to all--retinol. We found that hydrolysis occurred faster in native membranes than in detergent micelles typically used to study membrane proteins. The activation energy of the hydrolysis in native membranes was determined to be 17.7 ± 2.4 kcal/mol. Our data support the interpretation that metarhodopsin II, the signaling state of rhodopsin, is the primary species undergoing hydrolysis and release of its all--retinal. In the absence of NADPH, free all--retinal reacts with phosphatidylethanolamine (PE), forming a substantial amount of -ret-PE (∼40% of total all--retinal at physiological pH), at a rate that is an order of magnitude faster than Rho* hydrolysis. However, -ret-PE formation was highly attenuated by NADPH-dependent reduction of all--retinal to all--retinol. Neither -ret-PE formation nor all--retinal reduction affected the rate of hydrolysis of Rho*. Our study provides a comprehensive picture of the hydrolysis of Rho* and the release of all--retinal and its reentry into the visual cycle, a process in which alteration can lead to severe retinopathies.
Topics: Rhodopsin; Retinaldehyde; Vitamin A; Hydrolysis; NADP
PubMed: 36322748
DOI: 10.1073/pnas.2213911119