Nitric oxide mediates down regulation of lipoprotein lipase activity induced by tumor necrosis factor- α in brown adipocytes

Abstract

We previously reported that tumor necrosis factor- α (TNF- α)/cachectin suppresses lipoprotein lipase activity and its gene expression in brown adipocytes differentiated in culture. Recent evidence suggests that the effect of TNF- α over various cells is related to the enhanced production of nitric oxide (NO). The present study examined whether the suppressive effect of TNF- α on lipoprotein lipase activity is mediated by production of NO in the brown adipocytes. A reverse transcription-polymerase chain reaction (RT-PCR) assay revealed that TNF- α caused a concentration- and time-dependent expression of inducible NO synthase in brown adipocytes. Increasing concentrations of TNF- α (0.5–50 ng/ml) for 24 h resulted in a concentration-dependent decrease in lipoprotein lipase activity with reciprocal increase in nitrite production in the medium. The suppressive effect of TNF- α on lipoprotein lipase activity was significantly prevented by NO synthase inhibitors, N G-nitro- l-arginine methyl ester ( l-NAME) and aminoguanidine, but not by d-NAME, an inactive isomer. Furthermore, 8-bromoguanosine 3′,5′-cyclic monophosphate, cell permeant cGMP, suppressed lipoprotein lipase activity and 1 H-[1,2,4] oxadiazolo[4,3- a]quinoxalin-1-one, a selective inhibitor for soluble guanylate cyclase, restored the TNF- α-suppressed lipoprotein lipase activity. These results suggest that TNF- α stimulates brown adipocytes to express inducible NO synthase, followed by production of NO, which in turn mediates the suppressive effect of TNF- α on lipoprotein lipase activity. The effect of NO is mediated, at least partly, through production of cGMP.