TY - JOUR
T1 - Disruption of LDL receptor gene in transgenic SREBP-1a mice unmasks hyperlipidemia resulting from production of lipid-rich VLDL
AU - Horton, Jay D.
AU - Shimano, Hitoshi
AU - Hamilton, Robert L.
AU - Brown, Michael S.
AU - Goldstein, Joseph L.
PY - 1999/4
Y1 - 1999/4
N2 - Transgenic mice that overexpress the nuclear form of sterol regulatory element binding protein-1a (SREBP-1a) in liver (TgBP-1a mice) were shown previously to overproduce cholesterol and fatty acids and to accumulate massive amounts of cholesterol and triglycerides in hepatocytes. Despite the hepatic overproduction of lipids, the plasma levels of cholesterol (~45 mg/dl) and triglycerides (~55 mg/dl) were not elevated, perhaps owing to degradation of lipid-enriched particles by low-density lipoprotein (LDL) receptors. To test this hypothesis, in the current studies we bred TgBP-1a mice with LDL receptor knockout mice. As reported previously, LDLR(-/-) mice manifested a moderate elevation in plasma cholesterol (~-215 mg/dl) and triglycerides (~155 mg/dl). In contrast, the doubly mutant TgBP1a;LDLR(-/-) mice exhibited marked increases in plasma cholesterol (~1,050 mg/dl) and triglycerides (~900 mg/dl). These lipids were contained predominantly within large very-low-density lipoprotein (VLDL) particles that were relatively enriched in cholesterol and apolipoprotein E. Freshly isolated hepatocytes from TgBP-1a and TgBP-1a;LDLR(-/-) mice overproduced cholesterol and fatty acids and secreted increased amounts of these lipids into the medium. Electron micrographs of livers from TgBP1a mice showed large amounts of enlarged lipoproteins within the secretory pathway. We conclude that the TgBP-1a mice produce large lipid-rich lipoproteins, but these particles do not accumulate in plasma because they are degraded through the action of LDL receptors.
AB - Transgenic mice that overexpress the nuclear form of sterol regulatory element binding protein-1a (SREBP-1a) in liver (TgBP-1a mice) were shown previously to overproduce cholesterol and fatty acids and to accumulate massive amounts of cholesterol and triglycerides in hepatocytes. Despite the hepatic overproduction of lipids, the plasma levels of cholesterol (~45 mg/dl) and triglycerides (~55 mg/dl) were not elevated, perhaps owing to degradation of lipid-enriched particles by low-density lipoprotein (LDL) receptors. To test this hypothesis, in the current studies we bred TgBP-1a mice with LDL receptor knockout mice. As reported previously, LDLR(-/-) mice manifested a moderate elevation in plasma cholesterol (~-215 mg/dl) and triglycerides (~155 mg/dl). In contrast, the doubly mutant TgBP1a;LDLR(-/-) mice exhibited marked increases in plasma cholesterol (~1,050 mg/dl) and triglycerides (~900 mg/dl). These lipids were contained predominantly within large very-low-density lipoprotein (VLDL) particles that were relatively enriched in cholesterol and apolipoprotein E. Freshly isolated hepatocytes from TgBP-1a and TgBP-1a;LDLR(-/-) mice overproduced cholesterol and fatty acids and secreted increased amounts of these lipids into the medium. Electron micrographs of livers from TgBP1a mice showed large amounts of enlarged lipoproteins within the secretory pathway. We conclude that the TgBP-1a mice produce large lipid-rich lipoproteins, but these particles do not accumulate in plasma because they are degraded through the action of LDL receptors.
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U2 - 10.1172/JCI6246
DO - 10.1172/JCI6246
M3 - Article
C2 - 10194480
AN - SCOPUS:0032900336
SN - 0021-9738
VL - 103
SP - 1067
EP - 1076
JO - Journal of Clinical Investigation
JF - Journal of Clinical Investigation
IS - 7
ER -