Abstract
Hepatic stellate cells (HSCs) store a large amount of vitamin A within their cytoplasm as lipid droplets. HSCs store vitamin A as a form of retinylester through an enzymatic activity of lecithin:retinol acyltransferase (LRAT). Vitamin A and their active metabolites (retinoids) exert most of their physiological activities by transcription factors, retinoic acid receotors (RARα, β and γ) and retinoid X receptors (RXRα, β and γ). Cellular retinol-binding protein I (CRBP I) is one of the well characterized RAR target genes containing retinoic acid-responsive element (RARE). The mRNA levels of RARα, β and γ were decreased during rat HSC activation in vitro. Protein levels of RARα and β were increased during HSC activation. An RARE-containing luciferase assay indicated that HSCs became responsive to retinoids only after activation in vitro. CRBP I gene expression was up-regulated during HSC activation. CRBP I-bound retinol could be a good substrate of LRAT than retinol alone. Therefore, upregulation of RARα gene expression at the post-transcriptional level and subsequent upregulation of CRBP I gene expression at the transcriptional level make a feedback loop toward the recovery of vitamin A-containing lipid droplets within the activated hepatic stellate cells.