text: Regulation of retinal dehydrogenases and retinoic acid synthesis by cholesterol metabolites.
  Retinoic acid (RA) constitutes the major active ingredient of vitamin A and is required for various biological processes. The tissue RA level is maintained through a cascade of metabolic reactions where retinal dehydrogenases (RALDHs) catalyze the terminal reaction of RA biosynthesis from retinal, a rate-limiting step. We showed that dietary supplement of cholesterol enhanced the expression of RALDH1 and 2 genes and the cellular RA content in vital organs such as brain, kidney, liver and heart. Consistently, the cholesterol-lowering agent (pravastatin sodium) downregulated the expression of RALDH1 and 2 genes in several organs especially the liver and in cultured liver cells. Further, cholesterol metabolites, predominantly the oxysterols, the natural ligands for liver X receptor (LXR), induced these genes via upregulation of sterol regulatory element binding protein-1c (SREBP-1c) that bound to the regulatory regions of these genes. Knockdown of LXRalpha/beta or SREBP-1c downregulated the expression of RALDH genes, which could be rescued by re-expressing SREBP-1c, suggesting SREBP-1c as a direct positive regulator for these genes. This study uncovered a novel crosstalk between cholesterol and RA biosynthesis.
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entities.type: CHEMICAL CHEMICAL CHEMICAL CHEMICAL CHEMICAL CHEMICAL CHEMICAL CHEMICAL CHEMICAL GENE-N CHEMICAL GENE-Y GENE-Y GENE-N GENE-N GENE-N GENE-N GENE-N GENE-N GENE-Y GENE-Y CHEMICAL GENE-N GENE-Y CHEMICAL CHEMICAL CHEMICAL CHEMICAL CHEMICAL CHEMICAL CHEMICAL
entities.text: RA cholesterol pravastatin sodium vitamin A cholesterol oxysterols sterol retinoic acid cholesterol RALDH Retinoic acid SREBP-1c SREBP-1c retinal dehydrogenases RALDHs RALDH1 and 2 RALDH1 and 2 liver X receptor LXR sterol regulatory element binding protein-1c SREBP-1c cholesterol LXRalpha/beta SREBP-1c RA RA RA retinal RA retinal cholesterol