title: Apolipoprotein B-100 production and cholesteryl ester content in the liver of developing chick.
abstract: In the chick, the large cholesteryl ester (CE) store present in the liver during the last period of embryonic life increases at hatching and is rapidly depleted after 2-7 days of postnatal life. In this study we asked whether these changes were associated with variations in the hepatic production of apoB-containing lipoproteins. Liver slices taken from chicks at -3, 0 (hatching), 2, 4, 7, and 10 days of development were incubated with [35S]methionine in steady state incubations. ApoB production (cell + medium radioactivity) decreased from day -3 to day 0 (40%), increased at day 4 (54%), and decreased afterwards (45%). At day 4 the amount of 35S-labeled apoB-containing lipoproteins (VLDL-LDL) secreted into the medium was 1.7- and 1.5-times that found at days 0 and 7, respectively; the radioactivity incorporated into medium HDL (containing predominantly apoA-I) was 1.7-times that found at days 0 and 7. The incubation of liver slices with [3H]oleate showed that CE production at days 4 and 7 was 58% and 33%, respectively, of that found at day 0. The percentage of newly synthesized hepatic CE secreted into medium lipoproteins was 2.4%, 3.1%, and 2.2% at days 0, 4, and 7, respectively. The percentage of lipoprotein CE present in VLDL-LDL ranged from 38% at day 0 to 21% at day 7, and that present in HDL ranged from 62% at day 0 to 79% at day 7. To define whether the changes in the production of apoA-I- and apoB-containing lipoproteins were due to variations in apoB and apoA-I synthesis, the initial synthetic rate (pulse-labeling) and the mRNA content of these apolipoproteins were investigated. The initial apoB synthetic rate decreased 1.5-fold from day -3 to day 0, remained stable up to day 7, and decreased at day 10. Hepatic apoB mRNA followed a similar trend. The synthesis of apoA-I increased 2-fold from days -3/2 up to day 4 and did not change afterwards. In conclusion the increased hepatic CE content at hatching reflects a decreased production of apoB, while the depletion of CE observed from day 2 to day 7 is associated with an increased production of both apoB- and apoA-I-containing lipoproteins. The decreased apoB production at hatching is due to a decreased apoB synthesis whereas the increased apoB production at day 4 appears to be related to a post-translational event.
authors.affiliation: Dipartimento di Scienze Biomediche, Università di Modena, Italy.
authors.forename: P
authors.initials: P
authors.lastname: Tarugi
authors.forename: S
authors.initials: S
authors.lastname: Nicolini
authors.forename: L
authors.initials: L
authors.lastname: Marchi
authors.forename: G
authors.initials: G
authors.lastname: Ballarini
authors.forename: S
authors.initials: S
authors.lastname: Calandra
mesh_terms: D000818:Animals; D053299:Apolipoprotein B-100; D001055:Apolipoproteins B / Q000096:biosynthesis*; D015152:Blotting, Northern; D002642:Chick Embryo; D002645:Chickens / Q000254:growth & development* / Q000378:metabolism; D002788:Cholesterol Esters / Q000378:metabolism*; D004958:Estradiol / Q000097:blood; D007163:Immunosorbent Techniques; D008055:Lipids / Q000097:blood; D008075:Lipoproteins, HDL / Q000378:metabolism; D008077:Lipoproteins, LDL / Q000378:metabolism; D008079:Lipoproteins, VLDL / Q000378:metabolism; D008099:Liver / Q000196:embryology / Q000254:growth & development* / Q000378:metabolism; D008297:Male; D008715:Methionine / Q000378:metabolism; D019301:Oleic Acid; D009829:Oleic Acids / Q000378:metabolism; D013462:Sulfur Radioisotopes; D014316:Tritium
chemical_list: D053299:Apolipoprotein B-100; D001055:Apolipoproteins B; D002788:Cholesterol Esters; D008055:Lipids; D008075:Lipoproteins, HDL; D008077:Lipoproteins, LDL; D008079:Lipoproteins, VLDL; D009829:Oleic Acids; D013462:Sulfur Radioisotopes; D014316:Tritium; D019301:Oleic Acid; D004958:Estradiol; D008715:Methionine