Tumor Necrosis Factor- Suppresses Adipocyte-Specific Genes and Activates Expression of Preadipocyte Genes in 3T3-L1 Adipocytes Nuclear Factor- B Activation by TNF- Is Obligatory

Tumor necrosis factor(TNF) is a contributing cause of the insulin resistance seen in obesity and obesity-linked type 2 diabetes, but the mechanism(s) by which TNFinduces insulin resistance is not understood. By using 3T3-L1 adipocytes and oligonucleotide microarrays, we identified 142 known genes reproducibly upregulated by at least threefold after 4 h and/or 24 h of TNFtreatment, and 78 known genes downregulated by at least twofold after 24 h of TNFincubation. TNFinduced genes include transcription factors implicated in preadipocyte gene expression or NFB activation, cytokines and cytokine-induced proteins, growth factors, enzymes, and signaling molecules. Importantly, a number of adipocyte-abundant genes, including GLUT4, hormone sensitive lipase, long-chain fatty acyl-CoA synthase, adipocyte complement-related protein of 30 kDa, and transcription factors CCAAT/ enhancer binding protein, receptor retinoid X receptor, and peroxisome profilerator activated receptor were significantly downregulated by TNFtreatment. Correspondingly, 24-h exposure of 3T3-L1 adipocytes to TNFresulted in reduced protein levels of GLUT4 and several insulin signaling proteins, including the insulin receptor, insulin receptor substrate 1 (IRS-1), and protein kinase B (AKT). Nuclear factorB (NFB) was activated within 15 min of TNFaddition. 3T3-L1 adipocytes expressing I B -DN, a nondegradable NFB inhibitor, exhibited normal morphology, global gene expression, and insulin responses. However, absence of NFB activation abolished suppression of >98% of the genes normally suppressed by TNFand induction of 60–70% of the genes normally induced by TNF. Moreover, extensive cell death occurred in I B -DN expressing adipocytes after 2 h of TNFtreatment. Thus the changes in adipocyte gene expression induced by TNFcould lead to insulin resistance. Further, NFB is an obligatory mediator of most of these TNFresponses. Diabetes 51:1319–1336, 2002