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(Arteriosclerosis, Thrombosis, and Vascular Biology. 1996;16:889-897.)
© 1996 American Heart Association, Inc.

Articles

Selective Recruitment of ApoB-48 for the Assembly of VLDL in Rat Triacylglycerol-Enriched Hepatocytes

Peter J. Coussons; Catherine S. Bourgeois; David Wiggins; Geoffrey F. Gibbons

the Oxford Lipid Metabolism Group, Metabolic Research Laboratory, Nuffield Department of Clinical Medicine, University of Oxford, Radcliffe Infirmary, Oxford, UK.

Correspondence to Dr G.F. Gibbons, Metabolic Research Laboratory, Radcliffe Infirmary, Woodstock Road, Oxford OX2 6HE, UK.

Primary rat hepatocyte cultures were enriched in cellular triacylglycerol (TAG) by exposure to extracellular oleate for 3 days. Control cells were cultured for the same time without oleate. The large increase in TAG secretion into the medium of TAG-enriched cells during the final 24 hours (225±30 versus 40±10 µg/mg cell protein [control cells], P<.01) was not accompanied by a similar change in apolipoprotein B (apoB) secretion (4.22±0.94 versus 3.72±0.75 µg/mg per 24 hours, respectively). Instead, TAG-enriched cells recruited a larger proportion of apoB for the synthesis of very low density lipoprotein (VLDL), the secretion of which was substantially higher under these circumstances (1.46±0.39 versus 0.34±0.06 µg apoB per milligram cell protein per 24 hours, P<.05). The increase in VLDL assembly was accompanied by a selective 2.5-fold increase (P<.05) in the specific recruitment of apoB-48. There was no significant increase in the amount of apoB-100, which appeared in the VLDL fraction when cells were enriched with TAG. Under these circumstances there was an increase in net cellular synthesis of apoB-48 (5524±667 versus 2505±598 disintegrations per minute per milligram protein per hour, P<.05). The net cellular synthesis of apoB-100 was unchanged compared with that observed in control cell cultures (1548±237 versus 2000±897 dpm/mg per hour, respectively). A large proportion of the total secreted apoB was associated with small particles of density higher than VLDL, even when VLDL output was maximally stimulated, suggesting that apoB was oversecreted and in excess of the cells' requirement to transport TAG.

Key Words: apolipoprotein B • VLDL • triacylglycerol • hepatocyte culture • regulation

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