Modulation of lipoprotein lipase activity in mouse peritoneal macrophages by recombinant human tumor necrosis factor

Thioglycollate-elicited mouse peritoneal macrophages spontaneously secrete lipoprotein lipase during culture. Exposure of the cultures to 50 ng/ml of recombinant human tumor necrosis factor (rTNF) for 48 h resulted in a 69% reduction in lipoprotein lipase activity in the culture medium with a concomitant decrease in cellular enzyme activity. The decrease in enzyme activity was not the result of rTNF-dependent reduction in the total protein synthesis, since the presence of rTNF did not affect [3H]leucine incorporation into cellular proteins. The effect of rTNF on lipoprotein lipase was reversible; upon TNF withdrawal, enzyme activity returned to basal levels after 60 h. The reduction of lipoprotein lipase in rTNF-treated cultures could be completely prevented by preincubation with a specific antiserum against recombinant human TNF. The late onset of decrease of lipoprotein lipase (LPL) activity suggests that rTNF might induce a mediator, which in turn suppresses LPL production. While rTNF was very effective in reducing lipoprotein lipase activity in mouse peritoneal macrophages, it did not affect lipoprotein lipase activity when added to the murine J774 cell line and to CT2 macrophage-like cells, a variant of the J774 cell line.