Expression of heterologous human apolipoprotein E by J774 macrophages enhances cholesterol efflux to HDL3.

Expression of apolipoprotein (apo) E by macrophages is tightly regulated by cellular cholesterol content. We have investigated a potential modulating role for apoE on macrophage cholesterol homeostasis by stably transfecting the J774 macrophage, which does not express its endogenous apoE gene, with a human apoE cDNA expression vector and comparing cholesterol homeostasis in this cell line with that of a control line transfected with the neomycin resistance construct only. Incubation in serum-free medium after cholesterol loading produced no difference in cellular cholesterol content between apoE secreting and non-secreting J774 cells. Similarly, in serum-free medium there was no difference in the amount of radiolabeled cholesterol effluxed. Addition of cAMP or S58035 to cholesterol-loaded J774 cells did enhance efflux of radiolabeled cholesterol from apoE secreting compared to non-secreting macrophages but did not detectably alter cellular free cholesterol or cholesteryl ester mass. Incubation with HDL3 alone, however, significantly decreased macrophage cholesteryl ester mass compared to a 24-h incubation in serum-free medium from 10.5 +/- 3.9 to 3.2 +/- 2.0 (P < 0.01) in apoE-secreting J774 cells. During a 24-h incubation in HDL3, cholesteryl ester fell from 6.4 +/- 2.4 to 0.8 +/- 0.7 (delta = 5.6 micrograms/mg) in apoE-secreting cells and from 9.3 +/- 2.2 to 7.7 +/- micrograms/mg (delta = 1.6 micrograms/mg) in non-secreting cells (P < 0.005 apoE-secreting vs. non-secreting cells).(ABSTRACT TRUNCATED AT 250 WORDS)