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Department of Molecular Physiology and Biophysics, Vanderbilt University Medical Center, Nashville, Tennessee
Submitted 14 September 2007 ; accepted in final form 20 November 2007
Previous studies have demonstrated that macrophage-derived apolipoprotein E (apoE) reduces atherosclerotic lesion formation in lean apoE-deficient (–/–) mice. apoE has also been demonstrated to play a role in adipocyte differentiation and lipid accumulation. Because the prevalence of obesity has grown to epidemic proportions, we sought to determine whether macrophage-derived apoE could impact atherosclerotic lesion formation or adipose tissue expansion and inflammation in obese apoE–/– mice. To this end, we transplanted obese leptin-deficient (ob/ob) apoE–/– mice with bone marrow from either ob/ob;apoE–/– or ob/ob;apoE+/+ donors. There were no differences in body weight, total body adipose tissue, or visceral fat pad mass between recipient groups. The presence of macrophage-apoE had no impact on adipose tissue macrophage content or inflammatory cytokine expression. Recipients of apoE+/+ marrow demonstrated 3.7-fold lower plasma cholesterol (P < 0.001) and 1.7-fold lower plasma triglyceride levels (P < 0.01) by 12 wk after transplantation even though apoE was present in plasma at concentrations <10% of wild-type levels. The reduced plasma lipids reflected a dramatic decrease in very low density lipoprotein and a mild increase in high-density lipoprotein levels. Atherosclerotic lesion area was >10-fold lower in recipients of ob/ob;apoE+/+ marrow (P < 0.005). Similar results were seen in leptin receptor-deficient (db/db) apoE–/– mice. Finally, when bone marrow transplantation was performed in 4-mo-old ob/ob;apoE–/– and db/db;apoE–/– mice with preexisting lesions, recipients of apoE+/+ marrow had a 2.8-fold lower lesion area than controls (P = 0.0002). These results demonstrate that macrophage-derived apoE does not impact adipose tissue expansion or inflammatory status; however, even very low levels of macrophage-derived apoE are capable of reducing plasma lipids and atherosclerotic lesion area in obese mice.
obesity; very low-density lipoproteins; hyperlipidemia; atherosclerotic lesions
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