Retinoids stimulate apoA-I synthesis by induction of gene transcription in primary hepatocyte cultures from cynomolgus monkey (Macaca fascicularis)

Abstract

The influence of different retinoids on apolipoprotein A-I (apoA-I) synthesis and secretion was investigated in primary monolayer cultures of hepatocytes from cynomolgus monkeys. Addition of retinol (vitamin A) and retinoic acid to the culture medium resulted in a time- and dose-dependent increase in the secretion of apoA-I. No effect was observed during the first 24-hour incubation period; however, apoA-I secretion was enhanced 1.5-fold in the following 24-hour period in the presence of 10 μmol/L retinoic acid. Maximal stimulation (2.7-fold) was obtained at 10 μmol/L retinoic acid during a third 24-hour incubation. In these experiments apoB-100 secretion was unaffected. When [35S]methionine incorporation studies were performed de novo synthesis of apoA-I was increased, whereas total protein synthesis remained constant. These observations indicated that the induction of apoA-I synthesis is not part of a general effect of retinoic acid on hepatic protein synthesis. Among different natural and synthetic retinoids, retinoic acid and its 9-cis and 13-cis isomers were equally active and were the most potent inducers of apoA-I synthesis, whereas the maximal stimulation induced by retinol was lower (1.6-fold). ApoA-I mRNA abundance was increased threefold in hepatocytes exposed for 72 hours to 10 μmol/L retinoic acid, which was associated with a twofold increase in the transcriptional rate of the apoA-I gene. In contrast, no changes were found in the apoB-100 mRNA level and transcriptional activity of the apoB-100 gene. We conclude that retinoids enhance apoA-I synthesis in simian hepatocytes by transcrip-tional regulation.