Metabolism of apolipoprotein E-containing human plasma lipoproteins by rat and human cells in culture.

Cultured preadipocytes from rat epididymal fat pads were able to bind, internalize, and degrade human plasma very-low-density lipoproteins (VLDL) more efficiently than low-density lipoproteins (LDL). VLDL, but not LDL, activated acyl-CoA: cholesterol acyltransferase (ACAT) and increased cholesterol accumulation in these cells. However, trypsin-treated VLDL (T-VLDL) lost the capacity to bind, activate ACAT, and increase cholesterol accumulation. After the treatment of VLDL with trypsin, SDS/polyacrylamide-gel electrophoresis and immunoblotting showed that apolipoprotein E (apo E) was completely degraded, whereas apolipoprotein CII (apo C-II) was preserved. ApoE complexed with dimyristoyl phosphatidylcholine (DMPC) was able to complete with VLDL for binding to the cells. Although T-VLDL did not bind to the preadipocytes, these cells accumulate triacylglycerols from T-VLDL, presumably after lipolysis, as efficiently as from native VLDL. Rat smooth muscle cells and skin fibroblasts also bind and metabolize human VLDL better than LDL. However, human skin fibroblasts and omental preadipocytes metabolized LDL better than VLDL. These studies indicate that rat tissues can recognize and metabolize apoE-containing human plasma VLDL although they cannot recognize human LDL.