Dietary and hypothyroid hypercholesterolemia induces hepatic apolipoprotein E expression in the rat: direct role of cholesterol.
Apolipoprotein E (apo E) exerts a protective effect against atherosclerosis, related to its role in intracellular cholesterol removal and remnants clearance. In this study we investigated the effect of dietary and hypothyroid hypercholesterolemia, induced respectively by a high cholesterol diet and by propylthiouracil, on hepatic apo E expression in Wistar male rats. The Northern and Western blot analysis of hepatic mRNA and protein levels showed a 2-3-fold increase of apo E in hypercholesterolemic rats compared to controls. The incubation of FAO rat hepatoma cells with 25-OH cholesterol and mevalonate led to a three-fold increase of apo E mRNA, demonstrating a direct role of cholesterol on apo E expression. This effect was completely abolished by elevating intracellular cAMP levels with forskolin. Immunoblot and immunofluorescence analysis revealed that 25-OH cholesterol/mevalonate strongly increased also apo E protein synthesis and secretion in FAO cells. Our data demonstrate that hypercholesterolemia, apart of the cause (diet or hypothyroidism) induces liver apo E expression in the rat and that this effect can be directly related, via cAMP, to cholesterol.
Santillo
M
M
Dipartimento di Neuroscienze e della Comunicazione Interumana-Sezione di Fisiologia, Università di Napoli 'Federico II', Napoli, Italy.
Migliaro
A
A
Mondola
P
P
Laezza
C
C
Damiano
S
S
Stingo
S
S
Fiorentino
L
L
Andreozzi
A
A
Vitale
M
M
Bifulco
M
M
D000818:Animals; D001057:Apolipoproteins E / Q000096:biosynthesis*; D015152:Blotting, Northern; D015153:Blotting, Western; D002462:Cell Membrane / Q000378:metabolism; D002791:Cholesterol, Dietary / Q000378:metabolism*; D003720:Densitometry; D006937:Hypercholesterolemia / Q000139:chemically induced / Q000378:metabolism*; D008099:Liver / Q000378:metabolism*; D008297:Male; D008856:Microscopy, Fluorescence; D011441:Propylthiouracil; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D014407:Tumor Cells, Cultured
D001057:Apolipoproteins E; D002791:Cholesterol, Dietary; D012333:RNA, Messenger; D011441:Propylthiouracil