TY - JOUR
T1 - Apolipoprotein E competitively inhibits receptor-dependent low density lipoprotein uptake by the liver but has no effect on cholesterol absorption or synthesis in the mouse
AU - Woollett, Laura A.
AU - Osono, Yasunori
AU - Herz, Joachim
AU - Dietschy, John M.
PY - 1995/12/19
Y1 - 1995/12/19
N2 - This study examines the question of whether apolipoprotein E (apoE) alters steady-state concentrations of plasma cholesterol carried in low density lipoproteins (LDL-C) by acting as a competitive inhibitor of hepatic LDL uptake or by altering the rate of net cholesterol delivery from the intestinal lumen to the liver. To differentiate between these two possibilities, rates of cholesterol absorption and synthesis and the kinetics of hepatic LDL-C transport were measured in vivo in mice with either normal (apoE(+/+)) or zero (apoE(-/-)) levels of circulating apoE. Rates of cholesterol absorption were essentially identical in both genotypes and equaled ≃44% of the daily dietary load of cholesterol. This finding was consistent with the further observation that the rates of cholesterol synthesis in the liver (≃2000 nmol/h) and extrahepatic tissues (≃3000 nmol/h) were also essentially identical in the two groups of mice. However, the apparent Michaelis constant for receptor-dependent hepatic LDL-C uptake was markedly lower in the apoE(-/-) mice (44 ± 4 mg/dl) than in the apoE(+/+) animals (329 ± 77 mg/dl) even though the maximal transport velocity for this uptake process was essentially the same (≃400 μg/h per g) in the two groups of mice. These studies, therefore, demonstrate that apoE- containing lipoproteins can act as potent competitive inhibitors of hepatic LDL-C transport and so can significantly increase steady-state plasma LDL-C levels. This apolipoprotein plays no role, however, in the regulation of cholesterol absorption, sterol biosynthesis, or hepatic LDL receptor number, at least in the mouse.
AB - This study examines the question of whether apolipoprotein E (apoE) alters steady-state concentrations of plasma cholesterol carried in low density lipoproteins (LDL-C) by acting as a competitive inhibitor of hepatic LDL uptake or by altering the rate of net cholesterol delivery from the intestinal lumen to the liver. To differentiate between these two possibilities, rates of cholesterol absorption and synthesis and the kinetics of hepatic LDL-C transport were measured in vivo in mice with either normal (apoE(+/+)) or zero (apoE(-/-)) levels of circulating apoE. Rates of cholesterol absorption were essentially identical in both genotypes and equaled ≃44% of the daily dietary load of cholesterol. This finding was consistent with the further observation that the rates of cholesterol synthesis in the liver (≃2000 nmol/h) and extrahepatic tissues (≃3000 nmol/h) were also essentially identical in the two groups of mice. However, the apparent Michaelis constant for receptor-dependent hepatic LDL-C uptake was markedly lower in the apoE(-/-) mice (44 ± 4 mg/dl) than in the apoE(+/+) animals (329 ± 77 mg/dl) even though the maximal transport velocity for this uptake process was essentially the same (≃400 μg/h per g) in the two groups of mice. These studies, therefore, demonstrate that apoE- containing lipoproteins can act as potent competitive inhibitors of hepatic LDL-C transport and so can significantly increase steady-state plasma LDL-C levels. This apolipoprotein plays no role, however, in the regulation of cholesterol absorption, sterol biosynthesis, or hepatic LDL receptor number, at least in the mouse.
KW - low density lipoprotein transport
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U2 - 10.1073/pnas.92.26.12500
DO - 10.1073/pnas.92.26.12500
M3 - Article
C2 - 8618929
AN - SCOPUS:0029585129
SN - 0027-8424
VL - 92
SP - 12500
EP - 12504
JO - Proceedings of the National Academy of Sciences of the United States of America
JF - Proceedings of the National Academy of Sciences of the United States of America
IS - 26
ER -