VLDL induces adipocyte differentiation in ApoE-dependent manner

Objective - To clarify the role of very low density lipoprotein ( VLDL) and apolipoprotein E ( apoE) in adipogenesis, we studied newly developed hyperlipidemic obese (ob/ob; apoE (-/-)) mice. Because hydrolysis of VLDL is believed to be the major source of adipogenic free fatty acids, a higher plasma level of VLDL in these mice should exaggerate obesity. Methods and Results - When fed a high-fat, high-cholesterol diet, ob/ob; apoE (-/-) mice did not show increased body weight or an increased amount of adipose tissue in spite of increased plasma VLDL levels, whereas ob/ob mice showed an increased body weight and amount of adipose tissue, suggesting that there is a novel apoE-dependent pathway for adipogenesis. In vitro experiments using bone marrow stromal cells and 3T3-L1 cells confirmed this notion. ApoE-deficient VLDL did not induce adipogenesis, whereas normal VLDL induced adipogenesis in these cells. The incubation of apoE-deficient VLDL with recombinant human apoE restored its adipogenic activity. Tetrahydrolipstatin, a lipoprotein lipase inhibitor, did not affect the adipogenic activity of VLDL, suggesting that hydrolysis of VLDL did not play a major role in its effects. In fact, lipid components of VLDL or free fatty acids induced only partial adipogenesis. Conclusions - Our findings indicate that VLDL induces adipogenesis in an apoE-dependent manner both in vitro and in vivo.