Project description:Vitamin A (retinol) is an essential precursor for the production of retinoic acid (RA), which in turn is a major regulator of gene expression, affecting cell differentiation throughout the body. Understanding how vitamin A nutritional status, as well as therapeutic retinoid treatment, regulates the expression of retinoid homeostatic genes is important for improving dietary recommendations and therapeutic strategies using retinoids. This study investigated genes central to processes of retinoid uptake and storage, release to plasma, and oxidation in the liver of rats under steady-state conditions after different exposures to dietary vitamin A (deficient, marginal, adequate and supplemented), and acutely after administration of a therapeutic dose of all-trans-RA. Over a very wide range of dietary vitamin A, lecithin:retinol acyltransferase (LRAT) as well as multiple cytochrome P450s (CYP26A1, CYP26B1, and CYP2C22) differed by diet and were highly correlated with one another and with vitamin A status assessed by liver retinol concentration (all correlations, P<0.05). After acute treatment with RA, the same genes were rapidly and concomitantly induced, preceding RARß, a classical direct target of RA. CYP26A1 mRNA exhibited the greatest dynamic range (change of log26 in 3 h). Moreover, CYP26A1 increased more rapidly in the liver of RA-primed rats than naïve rats. By in situ hybridization, CYP26A1 mRNA was strongly regulated within hepatocytes, closely resembling RBP4 in location. Overall, whether RA is produced endogenously from retinol or administered exogenously, changes in retinoid homeostatic gene expression simultaneously favor both retinol esterification and RA oxidation, with CYP26A1 exhibiting the greatest dynamic change. All rats were housed in a room maintained at 22°C with a 12-h dark:light cycle, and food and water were freely available. For the Steady-State Vitamin A Study (experiment 1) and the Retinoic Acid 16-hour Kinetic Study (experiment 2), lactating female Sprague-Dawley rats with 12 female pups (purchased from Charles River Laboratories, Willmington, MA) were fed a vitamin A-deficient purified diet [AIN-93G diet, prepared by Research Diets, New Brunswick, NJ] to reduce the transfer of vitamin A in milk from mother to pups prior to the start of the study. For experiment 1, from weaning, the offspring were fed the same diet modified to contain vitamin A at one of four levels: 0 (vitamin A deficient), 0.4 mg retinol/kg diet (vitamin A marginal), 4 mg retinol/kg diet (vitamin A adequate control), or 100 mg retinol/kg diet (vitamin A supplemented). All rats were studied at 8 weeks of age. Rats were euthanized by carbon dioxide asphyxiation and blood and liver were collected rapidly and frozen in liquid nitrogen for storage at -80°C before analysis. In experiment 2, at 8 weeks of age female vitamin A-deficient rats were treated with ~100 ug of All-trans-Retinoic acid (at-RA) for 0 (vehicle only), 3, 6, 10 or 16 h (n=3-4/group). Tissues were collected and RNA was prepared in the same manner as in experiment 1. In the 90-minute "first pass" kinetic study (experiment 3), female rats were purchased at 6 weeks of age and fed a stock rodent diet. When the rats were 8 weeks old they were assigned to a control (naïve) group. Rats in the naive group received an equal amount of vehicle only (vegetable oil/5% ethanol). Food was removed immediately. Sixteen hours after priming, each rat was lightly anesthetized by isoflurane-oxygen inhalation and treated with ~25 ug all-trans-RA bound to albumin [10 ug RA per 100 g bo dy weight], injected into the exposed left common iliac vein. The incision was closed with a surgical staple. The rats were allowed to recover from the anesthesia. Rats were killed at 0 minute (vehicle injection), and 30, 60, and 90 min (n = 3/group) after injection of the RA test dose. Rats were euthanized by carbon dioxide asphyxiation and blood and liver were collected rapidly and frozen in liquid nitrogen for storage at -80°C before analysis. For experiment 1, five biological repeats were Vitamin A deficient, seven biological repeats were Vitamin A marginal, six biological repeats were Vitamin A adequate, and two biological repeats were Vitamin A supplemented. In experiment 2, three biological repeats were performed for each of the following treatments: untreated, at-RA for 3 hours, at-RA for 6 hours and at-RA for 16 hours. Four biological repeats were treated with at-RA for 10 hours. For experiment 3, two biological repeats were untreated and three biological repeats were performed for each of the following at-RA treatment times: 30, 60 and 90 minutes. A total of 47 samples were analyzed.

Project description:Retinoic acid (RA), an active derivative of the liposoluble vitamin A (retinol), acts as an important signaling molecule during embryonic development, regulating phenomenons as diverse as anterior-posterior axial patterning, forebrain and optic vesicle development, specification of hindbrain rhombomeres, pharyngeal arches and second heart field, somitogenesis, and differentiation of spinal cord neurons. This small molecule directly triggers gene activation by binding to nuclear receptors (RARs), switching them from potential repressors to transcriptional activators. The repertoire of RA-regulated genes in embryonic tissues is poorly characterized. We performed a comparative analysis of the transcriptomes of murine wild-type and Retinaldehyde Dehydrogenase 2 null-mutant (Raldh2-/-) embryos - unable to synthesize RA from maternally-derived retinol - using Affymetrix DNA microarrays. Transcriptomic changes were analyzed in two embryonic regions: anterior tissues including forebrain and optic vesicle, and posterior (trunk) tissues, at early stages preceding the appearance of overt phenotypic abnormalities. Several genes expected to be downregulated under RA deficiency appeared in the transcriptome data (e.g. Emx2, Foxg1 anteriorly, Cdx1, Hoxa1, Rarb posteriorly), whereas reverse-transcriptase-PCR and in situ hybridization performed for additional selected genes validated the changes identified through microarray analysis. Altogether, the affected genes belonged to numerous molecular pathways and cellular/organismal functions, demonstrating the pleiotropic nature of RA-dependent events. In both tissue samples, genes upregulated were more numerous than those downregulated, probably due to feedback regulatory loops. Bioinformatic clustering analysis allowed us to extract groups of genes displaying similar behaviors in mutant tissue samples. These data give an overview of the gene expression changes occurring under a state of embryonic RA deficiency, and provide new candidate genes and pathways for a better understanding of retinoid-dependent molecular events.

Project description:Retinoic acid (RA), an active derivative of the liposoluble vitamin A (retinol), acts as an important signaling molecule during embryonic development, regulating phenomenons as diverse as anterior-posterior axial patterning, forebrain and optic vesicle development, specification of hindbrain rhombomeres, pharyngeal arches and second heart field, somitogenesis, and differentiation of spinal cord neurons. This small molecule directly triggers gene activation by binding to nuclear receptors (RARs), switching them from potential repressors to transcriptional activators. The repertoire of RA-regulated genes in embryonic tissues is poorly characterized. We performed a comparative analysis of the transcriptomes of murine wild-type and Retinaldehyde Dehydrogenase 2 null-mutant (Raldh2-/-) embryos - unable to synthesize RA from maternally-derived retinol - using Affymetrix DNA microarrays. Transcriptomic changes were analyzed in two embryonic regions: anterior tissues including forebrain and optic vesicle, and posterior (trunk) tissues, at early stages preceding the appearance of overt phenotypic abnormalities. Several genes expected to be downregulated under RA deficiency appeared in the transcriptome data (e.g. Emx2, Foxg1 anteriorly, Cdx1, Hoxa1, Rarb posteriorly), whereas reverse-transcriptase-PCR and in situ hybridization performed for additional selected genes validated the changes identified through microarray analysis. Altogether, the affected genes belonged to numerous molecular pathways and cellular/organismal functions, demonstrating the pleiotropic nature of RA-dependent events. In both tissue samples, genes upregulated were more numerous than those downregulated, probably due to feedback regulatory loops. Bioinformatic clustering analysis allowed us to extract groups of genes displaying similar behaviors in mutant tissue samples. These data give an overview of the gene expression changes occurring under a state of embryonic RA deficiency, and provide new candidate genes and pathways for a better understanding of retinoid-dependent molecular events. Two sets of samples were used for analyzing transcriptome changes in Raldh2-/- embryos. The rostral part of the head (including the anterior forebrain, optic vesicles, and overlying tissues), was collected from wild-type and mutant embryos at the 14 somite stage.The posterior tissues were analyzed at the 4 somite stage, and samples were collected from a transverse section plane excluding all tissues from the level of the first branchial arch.

Dataset Information

Vitamin A nutritional status and retinoic acid as regulators of gene expression in rat liver

Similar Datasets

OmicsDI is part of the ELIXIR infrastructure