Apolipoprotein E4 Exaggerates Diabetic Dyslipidemia and Atherosclerosis in Mice Lacking the LDL Receptor

Abstract

OBJECTIVE We investigated the differential roles of apolipoprotein E (apoE) isoforms in modulating diabetic dyslipidemia—a potential cause of the increased cardiovascular disease risk of patients with diabetes. RESEARCH DESIGN AND METHODS Diabetes was induced using streptozotocin (STZ) in human apoE3 (E3) or human apoE4 (E4) mice deficient in the LDL receptor (LDLR−/−). RESULTS Diabetic E3LDLR−/− and E4LDLR−/− mice have indistinguishable levels of plasma glucose and insulin. Despite this, diabetes increased VLDL triglycerides and LDL cholesterol in E4LDLR−/− mice twice as much as in E3LDLR−/− mice. Diabetic E4LDLR−/− mice had similar lipoprotein fractional catabolic rates compared with diabetic E3LDLR−/− mice but had larger hepatic fat stores and increased VLDL secretion. Diabetic E4LDLR−/− mice demonstrated a decreased reliance on lipid as an energy source based on indirect calorimetry. Lower phosphorylated acetyl-CoA carboxylase content and higher gene expression of fatty acid synthase in the liver indicated reduced fatty acid oxidation and increased fatty acid synthesis. E4LDLR−/− primary hepatocytes cultured in high glucose accumulated more intracellular lipid than E3LDLR−/− hepatocytes concomitant with a 60% reduction in fatty acid oxidation. Finally, the exaggerated dyslipidemia in diabetic E4LDLR−/− mice was accompanied by a dramatic increase in atherosclerosis. CONCLUSIONS ApoE4 causes severe dyslipidemia and atherosclerosis independent of its interaction with LDLR in a model of STZ-induced diabetes. ApoE4-expressing livers have reduced fatty acid oxidation, which contributes to the accumulation of tissue and plasma lipids.