Characterization of differentiation factor/leukaemia inhibitory factor effect of lipoprotein lipase activity and mRNA in 3T3-L1 adipocytes

Abstract

Alterations in lipid metabolism characterized in major part by a decrease in lipoprotein lipase (LPL) activity in adispose tissue are a central feature of cachexia from chronic infection or malignancy. These metabolic derangements may be mediated in large part through endogenous host proteins produced in response to various pathological stimuli. Differentiation factor/leukaemia inhibitory factor (D-factor) is a cytokine whose functions overlap those of tumour necrosis factor-α (TNF), IL-6 and IL-1. Recombinant murine D-factor produced a dose- and time-dependent inhibition of heparin-releasable LPL activity in differentiated 3T3-L1 adipocytes. Although 2–10 fold less potent than recombinant murine TNF, D-factor inhibited LPL activity at concentrations of 1–10 ng/ml. When added together, D-factor and TNF produced a synergistic inhibition of LPL activity. Interleukin 6 (IL-6) was 100-fold less potent than D-factor; 0.1 ng/ml of D-factor or 10 ng/ml of IL-6 caused a 50% inhibition of LPL activity. D-factor and TNF increased IL-6 production in 3T3-L1 cells. Ten ng/ml of D-factor or 1.0 ng/ml of TNF stimulated the release of <1 ng/ml of IL-6 and inhibited LPL activity to 11 ± 3% and 3 ± 2% of control, respectively, whereas 50 ng/ml of recombinant IL-6 was required to decrease LPL activity to 24 ± 19% of control. TNF produced a marked decrease in LPL mRNA, whereas D-factor had minimal or no effect at doses which inhibited LPL activity almost completely. Western blot analysis of cell extracts showed that TNF caused a greater decrease in LPL protein production than D-factor. These results provide in vitro evidence that physiologically attainable concentrations of D-factor can produce catabolic alterations in fatty acid metabolism and suggest that D-factor inhibits LPL activity primarily through effects on post-transcriptional processing. D-factor, alone and in combination with TNF, may contribute to the manifestations of cachexia.