The very low- and intermediate-density lipoprotein fraction isolated from apolipoprotein E-knockout mice transforms macrophages to foam cells through an apolipoprotein E-independent pathway.
Apolipoprotein E (apoE)-knockout mice develop severe atherosclerosis associated with high levels of very low-density lipoprotein (VLDL) and intermediate-density lipoprotein (IDL) in plasma. To investigate the atherogenic role of VLDL and IDL, the lipoprotein fraction containing both VLDL and IDL (apoEko-VLDL/IDL) was isolated from plasma of apoE-knockout mice by ultracentrifugation, and its interaction with macrophages was studied. When peritoneal macrophages obtained from apoE-knockout mice were incubated with apoEko-VLDL/IDL, the level of cellular cholesteryl esters (CE) increased with the concentration of apoEko-VLDL/IDL. The level of cellular cholesteryl [3H]oleate formed reached 15.1 nmol/mg of cell protein upon incubation with 50 microg/mL apoEko-VLDL/IDL for 18 h, which was an 8.4-fold increase over the corresponding level induced by low-density lipoprotein (LDL). The cellular CE mass was also significantly increased by apoEko-VLDL/IDL. Morphologically, after exposure to apoEko-VLDL/IDL, macrophages became strongly stained with Sudan black B. The total binding of [125I]apoEko-VLDL/IDL to macrophages was effectively replaced by more than 80% by an excess of the unlabeled ligand. Specific binding, calculated by subtracting the nonspecific binding from the total binding, exhibited a saturation pattern. Similar results were obtained with cell association and degradation experiments. In addition, the endocytic degradation of [125I]apoEko-VLDL/IDL was partially inhibited by LDL, whereas acetyl-LDL did not show any effect. These results indicated that apoEko-VLDL/IDL in its unmodified form produced significant CE accumulation in macrophages through a specific and apoE-independent pathway. This pathway may explain, in part, the mechanisms of foam cell formation in arterial walls and the subsequent development of atherosclerosis in apoE-knockout mice.
Hakamata
H
H
Department of Biochemistry, Kumamoto University School of Medicine, Japan.
Sakaguchi
H
H
Zhang
C
C
Sakashita
N
N
Suzuki
H
H
Miyazaki
A
A
Takeya
M
M
Takahashi
K
K
Kitamura
N
N
Horiuchi
S
S
D000818:Animals; D001057:Apolipoproteins E / Q000235:genetics* / Q000378:metabolism / Q000502:physiology*; D002454:Cell Differentiation / Q000235:genetics; D002478:Cells, Cultured; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D002788:Cholesterol Esters / Q000378:metabolism; D005487:Foam Cells / Q000166:cytology / Q000378:metabolism*; D008074:Lipoproteins / Q000737:chemistry / Q000378:metabolism; D053419:Lipoproteins, IDL; D008077:Lipoproteins, LDL / Q000494:pharmacology; D008079:Lipoproteins, VLDL / Q000302:isolation & purification / Q000378:metabolism / Q000502:physiology*; D017737:Macrophages, Peritoneal / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D051379:Mice; D018345:Mice, Knockout
D001057:Apolipoproteins E; D002788:Cholesterol Esters; D008074:Lipoproteins; D053419:Lipoproteins, IDL; D008077:Lipoproteins, LDL; D008079:Lipoproteins, VLDL; C032629:acetyl-LDL