Division of Endocrinology, Diabetes, and Medical Genetics, Department of Medicine, Medical University of South Carolina, Charleston, South Carolina 29425.
Division of Endocrinology, Diabetes, and Medical Genetics, Department of Medicine, Medical University of South Carolina, Charleston, South Carolina 29425; From the Ralph H. Johnson Veterans Affairs Medical Center, Medical University of South Carolina, Charleston, South Carolina 29425.
J Biol Chem. 2010 Feb 5;285(6):3916-3927. doi: 10.1074/jbc.M109.033951. Epub 2009 Dec 10.
Although it has been reported that osteopontin, a matrix glycoprotein and proinflammatory cytokine, mediates obesity-induced adipose tissue macrophage infiltration and insulin resistance, it remains unclear how osteopontin is up-regulated in adipose tissue in obese humans and animals. In this study, we incubated U937 mononuclear cells with adipocytes in a transwell system and studied how cell interaction regulated osteopontin expression. Results showed that coculture of U937 cells with adipocytes led to a marked increase in osteopontin production when compared with that released by independent cultures of U937 cells. Moreover, lipopolysaccharide or palmitic acid-induced TLR4 activation and high glucose further augmented the coculture-stimulated osteopontin secretion. Similar observations were made in the coculture of human primary monocytes and adipocytes. Real time PCR studies showed that coculture of U937 cells and adipocytes increased osteopontin mRNA in U937 cells, but not adipocytes, suggesting that adipocyte-derived soluble factor may stimulate osteopontin expression by U937 cells. In our studies to explore the underlying mechanism, we found that the neutralizing antibodies against interleukin (IL)-6 or IL-6 small interfering RNA transfection in adipocytes effectively inhibited coculture-stimulated osteopontin expression, suggesting that IL-6 released by adipocytes plays an essential role in the coculture-stimulated osteopontin expression by U937 cells. In conclusion, this study has demonstrated that cell interaction, TLR4 activation, and high glucose up-regulate osteopontin expression, and adipocyte-derived IL-6 played a major role in the up-regulation.
虽然有研究报道，基质糖蛋白和前炎症细胞因子骨桥蛋白（osteopontin）介导肥胖诱导的脂肪组织巨噬细胞浸润和胰岛素抵抗，但骨桥蛋白在肥胖人群和动物脂肪组织中如何上调仍不清楚。在这项研究中，我们在 Transwell 系统中培养单核细胞 U937 与脂肪细胞共培养，并研究细胞间相互作用如何调节骨桥蛋白的表达。结果表明，与 U937 细胞独立培养释放的骨桥蛋白相比，U937 细胞与脂肪细胞共培养可显著增加骨桥蛋白的产生。此外，脂多糖或棕榈酸诱导的 TLR4 激活和高葡萄糖进一步增强了共培养刺激的骨桥蛋白分泌。在人原代单核细胞和脂肪细胞的共培养中也观察到了类似的现象。实时 PCR 研究表明，U937 细胞与脂肪细胞共培养可增加 U937 细胞中的骨桥蛋白 mRNA，但不增加脂肪细胞中的骨桥蛋白 mRNA，这表明脂肪细胞衍生的可溶性因子可能刺激 U937 细胞的骨桥蛋白表达。在我们探索潜在机制的研究中，我们发现脂肪细胞中中和抗体或 IL-6 小干扰 RNA 转染可有效抑制共培养刺激的骨桥蛋白表达，表明脂肪细胞释放的 IL-6 在共培养刺激 U937 细胞的骨桥蛋白表达中起关键作用。总之，本研究表明细胞间相互作用、TLR4 激活和高葡萄糖可上调骨桥蛋白的表达，而脂肪细胞衍生的 IL-6 在其中起主要作用。
