Free fatty acids repress the GLUT4 gene expression in cardiac muscle via novel response elements
Free fatty acids repress the GLUT4 gene expression in cardiac muscle via novel response elements
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DOI：
10.1074/jbc.m502740200
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发表时间：
2005-10-14
影响因子：
4.8
通讯作者：
Karnieli, E
中科院分区：
文献类型：
--
作者：
Armoni, M;Harel, C;Karnieli, E
高脂血症(HL)损害心脏葡萄糖稳态，但其分子机制尚不清楚。我们检测了HL调节的人心肌GLUT4和PPARγ基因的表达。与对照组相比，HL和/或2型糖尿病患者心肌组织中GLUT4蛋白水平降低30%，而GLUT4mRNA水平无明显变化。HL和/或2型糖尿病患者的PPAR-γmRNA水平较正常对照组降低30-50%。在H9C2心肌管中的报道研究表明，在体外，由高水平的花生四烯酸(AA)硬脂酸、亚油酸和油酸(24小时，200 mU M)诱导的HL抑制了GLUT4启动子的转录；AA也抑制了PPARγ1和PPARγ2启动子的转录。共表达的PPARγ2抑制了GLUT4启动子的活性，AA的加入进一步增强了这一作用。5‘-缺失分析显示有三个GLUT4启动子区域与AA介导的作用有关：位于-443/-423bp和-222/-197bp的两个抑制介导性序列，其中一个或两个的缺失导致启动子活性的部分去阻遏，以及在-612/-587bp处的第三个去阻遏介导性序列，它是维持这种去阻抑效应所必需的。电迁移率改变分析进一步表明，AA增强了与心脏核蛋白(S)三个区域中的两个区域的结合，其性质尚不清楚。我们认为，作为一种高水平的游离脂肪酸，HL通过一种复杂的机制来调节心肌中GLUT4基因的表达，其中包括：(A)AA中介蛋白与GLUT4启动子基因上的三个新发现的反应元件结合；(B)AA抑制GLUT4和PPARγ基因的表达。
Hyperlipidemia (HL) impairs cardiac glucose homeostasis, but the molecular mechanisms involved are yet unclear. We examined HL-regulated GLUT4 and peroxisome proliferator-activated receptor (PPAR) gamma gene expression in human cardiac muscle. Compared with control patients, GLUT4 protein levels were 30% lower in human cardiac muscle biopsies from patients with HL and/or type 2 diabetes mellitus, whereas GLUT4 mRNA levels were unchanged. PPAR gamma mRNA levels were 30 - 50% lower in patients with HL and/or diabetes mellitus type 2 than in controls. Reporter studies in H9C2 cardiomyotubes showed that HL in vitro, induced by high levels of arachidonic ( AA) stearic, linoleic, and oleic acids ( 24 h, 200 mu M) repressed transcription from the GLUT4 promoter; AA also repressed transcription from the PPAR gamma 1 and PPAR gamma 2 promoters. Co-expression of PPAR gamma 2 repressed GLUT4 promoter activity, and the addition of AA further enhanced this effect. 5'-Deletion analysis revealed three GLUT4 promoter regions that accounted for AA-mediated effects: two repression-mediating sequences at - 443/ - 423 bp and - 222/ - 197 bp, the deletion of either or both of which led to a partial derepression of promoter activity, and a third derepression-mediating sequence at - 612/ - 587 bp that was required for sustaining this derepression effect. Electromobility shift assay further shows that AA enhanced binding to two of the three regions of cardiac nuclear protein(s), the nature of which is still unknown. We propose that HL, exhibited as a high free fatty acid level, modulates GLUT4 gene expression in cardiac muscle via a complex mechanism that includes: ( a) binding of AA mediator proteins to three newly identified response elements on the GLUT4 promoter gene and (b) repression of GLUT4 and the PPAR gamma genes by AA.