Disruption of LDL receptor gene in transgenic SREBP-1a mice unmasks hyperlipidemia resulting from production of lipid-rich VLDL
Jay D. Horton, … , Michael S. Brown, Joseph L. Goldstein
Jay D. Horton, … , Michael S. Brown, Joseph L. Goldstein
Published April 1, 1999
Citation Information: J Clin Invest. 1999;103(7):1067-1076. https://doi.org/10.1172/JCI6246.
View: Text | PDF
Article

Disruption of LDL receptor gene in transgenic SREBP-1a mice unmasks hyperlipidemia resulting from production of lipid-rich VLDL

Abstract

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 TgBP-1a;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 TgBP-1a 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.

Authors

Jay D. Horton, Hitoshi Shimano, Robert L. Hamilton, Michael S. Brown, Joseph L. Goldstein

×

Figure 6

Options: View larger image (or click on image) Download as PowerPoint
Plasma clearance of 125I-labeled VLDL in wild-type (WT), TgBP-1a, LDLR–/...
Plasma clearance of 125I-labeled VLDL in wild-type (WT), TgBP-1a, LDLR–/–, and TgBP- 1a;LDLR–/– mice. VLDL was isolated from four fasted male TgBP-1a;LDLR–/– mice and labeled with 125I as described in Methods. 125I-labeled VLDL (15 μg protein, 860 cpm/ng apo B protein) was injected intravenously into each of five 12-week-old male mice with the indicated genotype. Blood was drawn at the indicated times to quantify the content of 125I-labeled apo B in plasma. (a and b) Plasma content of 125I-labeled total apo B was measured by isopropanol precipitation followed by scintillation counting (as described in Methods). (c and d) Plasma samples were subjected to SDS-PAGE, and the signal generated by apo B-48 was quantified using a Fuji PhosphorImager as described in Methods. The data are plotted as the percent of the zero time value. *P < 0.05 (Student’s t test) compared with wild-type values. Each value represents the mean ± SEM of data from five mice.