Given an abstract from a research paper, your task is to identify and label relationships between chemical compounds and genes mentioned in the abstract.

The relationship type must be one of ['DOWNREGULATOR', 'SUBSTRATE', 'INDIRECT-REGULATOR', 'PART-OF', 'MODULATOR-ACTIVATOR', 'REGULATOR', 'INHIBITOR', 'COFACTOR', 'UPREGULATOR', 'ACTIVATOR', 'ANTAGONIST', 'NOT', 'INDIRECT-DOWNREGULATOR', 'SUBSTRATE_PRODUCT-OF', 'INDIRECT-UPREGULATOR', 'AGONIST', 'PRODUCT-OF', 'MODULATOR', 'DIRECT-REGULATOR', 'UNDEFINED', 'AGONIST-INHIBITOR', 'AGONIST-ACTIVATOR', 'MODULATOR-INHIBITOR'].

Please format your output as a JSON array. Each entry in the array should express a single relation, formatted as ["<Entity_A>", "<RELATION_A_B>", "<Entity_B>"]. If no relations can be found, please output an empty JSON array [].

Abstract:

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.
[["retinal", "SUBSTRATE", "RALDHs"], ["cholesterol", "INDIRECT-UPREGULATOR", "sterol regulatory element binding protein-1c"], ["cholesterol", "INDIRECT-UPREGULATOR", "SREBP-1c"], ["oxysterols", "DIRECT-REGULATOR", "liver X receptor"], ["oxysterols", "INDIRECT-UPREGULATOR", "sterol regulatory element binding protein-1c"], ["retinal", "SUBSTRATE", "retinal dehydrogenases"], ["RA", "PRODUCT-OF", "retinal dehydrogenases"], ["oxysterols", "INDIRECT-UPREGULATOR", "SREBP-1c"], ["oxysterols", "DIRECT-REGULATOR", "LXR"], ["RA", "PRODUCT-OF", "RALDHs"], ["cholesterol", "DIRECT-REGULATOR", "LXR"], ["cholesterol", "DIRECT-REGULATOR", "liver X receptor"]]