Medina E A, Stanhope K L, Mizuno T M, Mobbs C V, Gregoire F, Hubbard N E, Erickson K L, Havel P J
Department of Cell Biology and Human Anatomy, School of Medicine, University of California, Davis 95616, USA.
Int J Obes Relat Metab Disord. 1999 Aug;23(8):896-903. doi: 10.1038/sj.ijo.0800970.
Our objective was to determine the effects of prolonged exposure to tumor necrosis factor-alpha (TNF-alpha) on leptin secretion from and leptin (OB) gene expression in isolated adipocytes. Because glucose uptake and the metabolism of glucose beyond lactate are important determinants of leptin production in adipocytes, we examined the effects of TNF-alpha on glucose uptake and lactate production and their relationship to leptin secretion.
Isolated rat adipocytes were anchored in a defined matrix of basement membrane components and cultured with media containing 5 mM glucose, 0.16 nM insulin and several concentrations of TNF-alpha. Leptin secretion, steady-state levels of leptin mRNA levels, glucose uptake, and lactate production were assessed over 96 h.
TNF-alpha at concentrations of 0.024, 0.24, 2.4 and 24 ng/ml did not affect leptin secretion over 24 h. TNF-alpha at concentrations of 0.24 to 24 ng/ml significantly inhibited leptin secretion over 96 h by 19-60%. TNF-alpha at concentrations of 0.024 to 24 ng/ml significantly decreased steady-state levels of leptin mRNA after 96 h by 32-95%. In addition, TNF-alpha at concentrations of 2.4 and 24 ng/ml significantly increased glucose uptake and lactate production over 96 h by 30-57%. TNF-alpha at a concentration of 0.024 ng/ml did not affect leptin secretion, glucose uptake or lactate production. Overall, for the TNF-alpha concentrations tested, leptin secretion was inversely related to the percent of glucose carbon released as lactate; however, TNF-alpha did not induce a proportional increase of lactate production from glucose.
Short-term (24 h) exposure of isolated adipocytes to TNF-alpha does not affect leptin secretion. Prolonged exposure to TNF-alpha produces a concentration-dependent inhibition of leptin secretion and gene expression. This suggests that the acute effect of TNF-alpha to increase circulating leptin levels in vivo may be indirect. TNF-alpha at higher concentrations increases glucose uptake, but does not increase the conversion of glucose to lactate. Therefore, TNF-alpha appears to induce a dissociation between adipocyte glucose metabolism and leptin production.
我们的目的是确定长时间暴露于肿瘤坏死因子-α（TNF-α）对分离的脂肪细胞中瘦素分泌及瘦素（OB）基因表达的影响。由于葡萄糖摄取以及葡萄糖在生成乳酸后的代谢是脂肪细胞中瘦素产生的重要决定因素，我们研究了TNF-α对葡萄糖摄取、乳酸生成及其与瘦素分泌关系的影响。
将分离的大鼠脂肪细胞固定在特定的基底膜成分基质中，并用含有5 mM葡萄糖、0.16 nM胰岛素和几种浓度TNF-α的培养基进行培养。在96小时内评估瘦素分泌、瘦素mRNA水平的稳态水平、葡萄糖摄取和乳酸生成。
浓度为0.024、0.24、2.4和24 ng/ml的TNF-α在24小时内不影响瘦素分泌。浓度为0.24至24 ng/ml的TNF-α在96小时内显著抑制瘦素分泌，抑制率为19%至60%。浓度为0.024至24 ng/ml的TNF-α在96小时后显著降低瘦素mRNA的稳态水平，降低率为32%至95%。此外，浓度为2.4和24 ng/ml的TNF-α在96小时内显著增加葡萄糖摄取和乳酸生成，增加率为30%至57%。浓度为0.024 ng/ml的TNF-α不影响瘦素分泌、葡萄糖摄取或乳酸生成。总体而言，对于所测试的TNF-α浓度，瘦素分泌与作为乳酸释放的葡萄糖碳百分比呈负相关；然而，TNF-α并未诱导葡萄糖生成乳酸的比例增加。
分离的脂肪细胞短期（24小时）暴露于TNF-α不影响瘦素分泌。长时间暴露于TNF-α会产生浓度依赖性的瘦素分泌和基因表达抑制。这表明TNF-α在体内增加循环瘦素水平的急性作用可能是间接的。较高浓度的TNF-α会增加葡萄糖摄取，但不会增加葡萄糖向乳酸的转化。因此，TNF-α似乎会诱导脂肪细胞葡萄糖代谢与瘦素产生之间的解离。
