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Journal of Lipid Research, Vol 37, 493-507, Copyright © 1996 by Lipid Research, Inc.

ARTICLES

Synthesis and secretion of B-100 and A-I apolipoproteins in response to the changes of intracellular cholesteryl ester content in chick liver

P Tarugi, S Nicolini, G Ballarini, L Marchi, C Duvigneau, P Tartoni and S Calandra
Dipartimento di Scienze Biomediche, Universita di Modena, Italy.

We investigated in the chick whether the diet-induced changes of the hepatic content of cholesteryl esters (CE) influence the synthesis and the secretion of apoB- and apoA-I-containing lipoproteins. Control chicks received a low cholesterol diet for 2 (SD-1), 4 (SD-2), or 7 (SD- 3) weeks; the chicks in the experimental groups received a cholesterol- rich diet for 2 weeks and were killed at the end of the cholesterol feeding (CH-F), and after 2 (CH-D) or 5 (CH-DD) weeks of a low cholesterol diet. Hepatic CE content in CH-F chicks was 30-fold that observed in controls, but returned to the control level after 5 weeks of cholesterol depletion (CH-DD). The incorporation of 35S-labeled amino acids into cell and medium apoB and apoA-I was measured in liver slices. Intracellular 35S-labeled apoB was similar in all groups whereas medium 35S-labeled apoB was 2-fold higher in CH-F than in controls (SD-1). Pulse-chase experiments showed that radioactive apoB secreted by CH-F chicks at 120 min of chase was 2 times that of SD-1 chicks. This increased secretion of apoB was not found in CH-D chicks. In CH-F chicks, the intracellular and medium 35S-labeled apoA-I were 2- fold the values found in controls (SD-1); apoA-I production returned to the control level only after 5 weeks of cholesterol depletion (CH-DD). The increased secretion of apoB and apoA-I in CH-F chicks was associated with an increased secretion of very low, intermediate, and low density lipoproteins containing newly synthesized apoB and apoA-I and of high density lipoproteins containing predominantly apoA-I. Thus, in response to hepatic CE accumulation induced by cholesterol feeding, a larger proportion of newly synthesized apoB is driven to the secretory pathway and more apoA-I is synthesized. This promotes an increased secretion of plasma lipoproteins that contribute to the removal of CE from the liver.
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This article has been cited by other articles:

				P. Tarugi, G. Ballarini, B. Pinotti, A. Franchini, E. Ottaviani, and S. Calandra Secretion of apoB- and apoA-I-containing lipoproteins by chick kidney J. Lipid Res., April 1, 1998; 39(4): 731 - 743. [Abstract] [Full Text]