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Mechanism of Action of Vitamin A
Published in Ayse Serap Karadag, Berna Aksoy, Lawrence Charles Parish, Retinoids in Dermatology, 2019
In the cell, it binds to the cellular retinol-binding protein (CRBPI, CRBPII, and CRBPIII) and is modified to produce retinaldehyde by alcohol dehydrogenases (ALDH), such as retinol dehydrogenase (7,8). Retinaldehyde dehydrogenase catalyzes the conversion of retinaldehyde to different forms of RA: all-trans-RA (ATRA), 9-cis RA, 11-cis RA, 13-cis RA, and 9,13-di-cis RA (Figure 2.2). These compounds are further metabolized to 4-OH-RA, 4-oxo-RA, 18-OH-RA, 16-OH-RA, and 18-OH-RA by CYP26A1 and CYP26B1 (cytochrome P450 enzymes) to be subsequently excreted (Figure 2.2). The oxidation of ATRA produces 4-OH-RA and is possibly the most important route of elimination of ATRA. Other relevant enzymes include retinyl ester hydrolase (REH) that is related to the hydrolysis and release of the stored retinol and lecithin retinol acyltransferase (LRAT) and diacylglycerol O-acyltransferase (DGAT1) that are associated with its esterification (2,9,10).
Comparative transcriptome analysis reveals the effects of different feeding times on the hepatopancreas of Chinese mitten crabs
Published in Chronobiology International, 2023
Yingkai Xu, Baoli Zhang, Changyue Yu, Ziwei Hung, Nan Hu, Yuqiao Cai, Yingdong Li
Between the 12:00 and 24:00 h groups, 80 DEGs were identified, most of which 54 were upregulated. According to KEGG pathway analysis, upregulated genes were mostly enriched in metabolic processes (Figure 4), while the most significantly enriched pathway was retinol metabolism (Table S6). Upregulated genes between the 12:00 and 18:00 h groups were also significantly enriched in this pathway. Similarly, we mapped the retinol metabolic pathway (Figure 3b) and found that beta,beta-carotene 15,15 genes were also enriched in this pathway and their expression levels were significantly downregulated. We identified retinol dehydrogenase 14 among the pathway-enriched upregulated genes, which plays a driving role in the regulation of the visual cycle and retinoic acid production (Table 3)
Vitamin A deficiency indicating as low expression of LRAT may be a novel biomarker of primary hypertension
Published in Clinical and Experimental Hypertension, 2021
Xiaohua Liang, Min Chen, Dong Wang, Jin Wen, Jie Chen
As expected, VA levels in the serum and liver were decreased in the VAD groups compared with the VAN groups. Retinol bound to retinol-binding protein 4 in plasma (RBP4), and retinol dehydrogenase 10 metabolizes retinol to retinaldehyde (Ral), which is then metabolized to RA by retinaldehyde dehydrogenases (RALDHs) (30). RA can be released from the cytoplasm and is taken up by the receiving cell or via autocrine signaling. Cellular retinoic-acid-binding protein 2 assists RA entry into the nucleus and binds to RA receptors (RARs) and retinoid X receptors (RXRs), which themselves heterodimerize and bind to a sequence of DNA known as the retinoic acid-response element (RARE), which will activate or repress the transcription of target genes (31,32). LRAT is the primary enzyme that catalyses vitamin A (all-trans-retinol) esterification (33,34). Hence, a lack of LRAT activity will cause lower retention of all-trans-retinol in peripheral tissues, which leads to vitamin A deficiency in vivo (35). Cristiana et al (36). found that the concentration of atRA in the heart was associated with the supplemented dose of atRA. In our study, the VA levels in the serum and liver, RARα mRNA and protein expression levels in the heart, and LRAT expression in the liver were markedly downregulated after 20 weeks of VAD intervention, which illustrated that dietary vitamin A deficiency will lead to a reduction of RA storage in vivo and affect the regulation of RA on target organs.
Quasidominance in autosomal recessive RDH12-Leber congenital amaurosis
Published in Ophthalmic Genetics, 2020
Ruben Jauregui, Ahra Cho, Christine L. Xu, Akemi J. Tanaka, Janet R. Sparrow, Stephen H. Tsang
The gene retinol dehydrogenase 12 (RDH12) encodes for a protein that is a member of the family of retinol dehydrogenases that localize to the inner segments of the rod and cone photoreceptors (5). Proposed roles for the protein RDH12 include the conversion of all-trans retinal (vitamin A) to all-trans retinol during the regeneration of photopigment and protection of the retina from excessive all-trans retinal accumulation (5,6). A study in 2004 described RDH12 as encoding a non-redundant retinal dehydrogenase, whose loss of function leads to childhood-onset severe retinal dystrophy; this contrasts to the mild visual impairment that patients with pathogenic variants in RDH5 present with, causing the disease fundus albipunctatus (7). Pathogenic variants in RDH12 are estimated to cause 2.7–10% of LCA/EOSRD cases (1,8).