Ajuwon Kolapo M, Jacobi Sheila K, Kuske Joanne L, Spurlock Michael E
Department of Animal Sciences, Comparative Medicine Program, Purdue University, West Lafayette, Indiana 47907-2054, USA.
Am J Physiol Regul Integr Comp Physiol. 2004 Mar;286(3):R547-53. doi: 10.1152/ajpregu.00585.2003. Epub 2003 Dec 4.
3T3-L1 adipocytes express the lipopolysaccharide (LPS) receptor and respond to direct stimulation with the antigen by increasing the expression of inflammatory mediators. Activation of this receptor by its ligand in the macrophage causes the activation and translocation of nuclear factor-kappaB (NF-kappaB) to the nucleus where it regulates the expression of proinflammatory cytokines and other target genes. We investigated whether LPS could stimulate NF-kappaB translocation in primary pig adipocytes and regulate the expression and secretion of TNF-alpha and IL-6. LPS clearly induced the nuclear translocation of NF-kappaB and also upregulated (P < 0.05) the mRNA expression and secretion of IL-6 into the culture medium. An induction of TNF-alpha expression by LPS was not detected, but with extended incubation (8 h), there was a modest increase (P < 0.09) in the media concentration of this cytokine. Inhibition of either ERK1/2, PKC, or the inhibitory G protein (Gi) with U-0126, bisindolylmaleimide HCl, and pertussis toxin, respectively, blocked (P < 0.05) the increase in IL-6 expression caused by LPS. Because LPS administration in vivo increases circulating concentrations of IFN-gamma, and because this cytokine also regulates multiple immune modulators in the adipocyte, we also determined whether IFN-gamma regulates cytokine expression in primary adipocytes. Although the expression of IL-6 and TNF-alpha was unresponsive to IFN-gamma, the expression of IL-15 was markedly upregulated (P < 0.01). Furthermore, the induction of IL-15 expression by IFN-gamma was blocked by inhibition of PKC. These data indicate that NF-kappaB is responsive to LPS in the adipocyte and also identify key mediators of LPS-induced IL-6 expression. In addition, we provide novel evidence that IFN-gamma targets the adipocyte to induce IL-15 expression, thus indicating a possible role for the adipocyte in the regulation of T-cell function and muscle metabolism during the innate immune response.
3T3-L1脂肪细胞表达脂多糖（LPS）受体，并通过增加炎症介质的表达来响应抗原的直接刺激。巨噬细胞中该受体被其配体激活会导致核因子-κB（NF-κB）激活并转移至细胞核，在细胞核中它调节促炎细胞因子和其他靶基因的表达。我们研究了LPS是否能刺激原代猪脂肪细胞中的NF-κB转移，并调节肿瘤坏死因子-α（TNF-α）和白细胞介素-6（IL-6）的表达与分泌。LPS明显诱导了NF-κB的核转移，并且还上调了（P < 0.05）IL-6的mRNA表达以及其向培养基中的分泌。未检测到LPS对TNF-α表达的诱导作用，但延长孵育时间（8小时）后，该细胞因子的培养基浓度有适度增加（P < 0.09）。分别用U-0126、双吲哚马来酰亚胺盐酸盐和百日咳毒素抑制细胞外信号调节激酶1/2（ERK1/2）、蛋白激酶C（PKC）或抑制性G蛋白（Gi），均能阻断（P < 0.05）LPS引起的IL-6表达增加。由于体内给予LPS会增加循环中γ干扰素（IFN-γ）的浓度，并且因为这种细胞因子也调节脂肪细胞中的多种免疫调节因子，我们还确定了IFN-γ是否调节原代脂肪细胞中的细胞因子表达。尽管IL-6和TNF-α的表达对IFN-γ无反应，但IL-15的表达明显上调（P < 0.01）。此外，IFN-γ对IL-15表达的诱导作用可被PKC抑制所阻断。这些数据表明NF-κB在脂肪细胞中对LPS有反应，并且还确定了LPS诱导IL-6表达的关键介质。此外，我们提供了新的证据表明IFN-γ作用于脂肪细胞以诱导IL-15表达，从而表明脂肪细胞在先天免疫反应期间调节T细胞功能和肌肉代谢中可能发挥作用。
