GLUCOSE SIGNALING AND REGULATION OF GENE EXPRESSION IN 3T3-L1 ADIPOCYTES

工作总结：转录因子 C/EBPalpha是几种转录的正调控因子， 脂肪细胞特异性基因在能量代谢中发挥作用。 这些包括胰岛素响应性葡萄糖转运蛋白GLUT 4， 脂质合成酶和瘦素，一种激素， 通过控制食欲中枢调节体重 和能量消耗。到目前为止， 关于C/EBPalpha表达的调节， 代谢信号在这项研究中，我们研究了葡萄糖的作用， 葡糖胺，己糖胺途径的产物，和木糖醇， 戊糖磷酸途径的激活剂，在C/EBPalpha基因上 表情添加葡萄糖导致剂量依赖性 抑制C/EBPalpha mRNA和蛋白水平 胰岛素处理的3 T3-L1脂肪细胞，而没有显著影响 C/EB β mRNA水平。增加了通过 己糖胺途径，通过葡糖胺或木糖醇，模拟 高血糖？降低C/EBPalpha mRNA表达的能力。 已知己糖胺途径的激活会增加 蛋白质糖基化底物的细胞内水平。我们发现 C/EBPalpha mRNA表达的调控是独立的， 蛋白质的糖基化。使用稳定转染了 C/EBPalpha启动子融合到报告基因，我们证明了 在该启动子内存在调节元件， 受代谢信号的影响。有趣的是，大鼠的治疗 与葡萄糖或葡萄糖胺一起导致C/EBPalpha减少 附睾脂肪中mRNA水平，但网膜脂肪组织中没有。 综上所述，这些结果表明，代谢信号 调节C/EBPalpha mRNA水平部分是通过影响 C/EBPalpha启动子。我们计划确定这种影响， C/EBPalpha基因的库特异性调控将对 控制局部肥胖和脂肪分布， 能量平衡的控制手稿已提交给 J. Clin. Invest.

Summary of work: The transcription factor C/EBPalpha is a positive modulator of transcription for several adipocyte-specific genes which play a role in energy metabolism. These include the insulin-responsive glucose transporter GLUT4, lipid-synthesizing enzymes and leptin, an hormone that acts centrally to regulate body weight through the control of appetite and energy expenditure. To this date, there is little information available regarding regulation of C/EBPalpha expression by metabolic signals. In this study, we examined the effect of glucose, glucosamine, a product of the hexosamine pathway, and xylitol, an activator of the pentose phosphate pathway, on C/EBPalpha gene expression. Addition of glucose resulted in a dose-dependent inhibition of C/EBPalpha mRNA and protein levels in insulin-treated 3T3-L1 adipocytes while having no significant effect on C/EBPbeta mRNA levels. Increased flux through the hexosamine pathway, either by glucosamine or xylitol, mimicked high glucose?s ability to reduce C/EBPalpha mRNA expression. Activation of the hexosamine pathway is known to increase intracellular levels of substrates for protein glycosylation. We found that the control of C/EBPalpha mRNA expression was independent of protein glycosylation. Using a cell line stably transfected with the C/EBPalpha promoter fused to a reporter gene, we demonstrated the presence of regulatory element(s) within this promoter that is/are influenced by metabolic signals. Of interest, treatment of rats with glucose or glucosamine led to a reduction in C/EBPalpha mRNA levels in epididymal fat, but not in omental adipose tissue. Taken together, these results suggest that metabolic signals modulate C/EBPalpha mRNA levels in part through an effect on the C/EBPalpha promoter. We plan to determine the impact such depot-specific regulation of C/EBPalpha gene will have on the control of regional adiposity and fat distribution, and the overall control of energy homeostasis. A manuscript has been submitted to J. Clin. Invest.