REGULATION OF CARDIAC POTASSIUM CHANNEL GENE EXPRESSION

心脏钾通道基因表达的调控

• 批准号: 6185045
• 负责人: KOICHI TAKIMOTO TAKIMOTO
• 金额: $ 22.8万
• 依托单位: UNIVERSITY OF PITTSBURGH AT PITTSBURGH
• 依托单位国家: 美国
• 财政年份: 1999
• 资助国家: 美国
• 起止时间: 1999-07-15 至 2003-06-30
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/6185045
• 关键词: angiotensin II; cardiac myocytes; gene expression; genetic regulation; heart electrical activity; hormone regulation /control mechanism; laboratory rat; messenger RNA; newborn animals; potassium channel; protein isoforms; protein localization; renal hypertension; tissue /cell culture; transcription factor

Kv4 subfamily genes encode a large portion of transient outward K+ current (Ito) in cardiac myocytes. Differential expression of these genes significantly contributes to differences in action potential waveforms in myocytes located in distinct regions of the heart. For example, in left ventricular wall, action potential duration is shorter in epicardial region than endocardial region, and expression of Kv4.2 mRNA and Ito are well correlated with this difference in action potential waveform. In addition to the differential regional expression, expression of Ito is altered under pathological conditions: a significant reduction in Ito is seen in hypertrophied myocytes produced by various conditions including a chronic increase in blood pressure. Our and others' studies indicate that this decrease in Ito is likely to be due to reductions in Kv4.x channel gene expression. Thus, elucidating the molecular mechanisms controlling expression of Kv4 subfamily genes provide fundamental insights into how regional specification of myocytes is achieved and how pathological conditions produce electrical abnormality. Our preliminary results indicate that Kv4.2 gene transcription starts at distinct sites in different tissues. Specifically, skeletal muscle-type start sites are significant in right ventricle and epicardial region of the left ventricle, whereas brain-type start sites predominate in atria and endocardial region. Furthermore, in vivo experiment revealed that administration of the angiotensin-converting enzyme inhibitor captopril selectively reduces Kv4.2 mRNA in epicardial region, but not in endocardial region. Using neonatal myocyte cultures, we also found that angiotensin II (AngII) produce more dramatic decrease in Kv4.3 mRNA than does the alpha-adrenergic agonist phenylephrine. Moreover, this hormone-induced down-regulation of Kv4.3 mRNA was resistant to inhibition of protein kinase C or calcineurin. These findings suggest that expression of Kv4.x gene expression may be region-selectively controlled by distinct sets of transcription factors and that AngII may mediate hypertension-induced down-regulation of Kv4.x gene expression independently of hypertrophy. Hence, this proposal is to test these possibilities using hypertension animal models and neonatal myocyte cultures.

Kv 4亚家族基因编码心肌细胞瞬时外向钾电流（Ito）的大部分。 这些基因的差异表达显着有助于在不同区域的心脏位于心肌细胞的动作电位波形的差异。 例如，在左心室壁中，心外膜区的动作电位时程比心内膜区短，Kv4.2 mRNA和Ito的表达与这种动作电位波形的差异密切相关。 除了差异性区域表达外，在病理条件下Ito的表达也发生改变：在由各种条件（包括血压慢性升高）产生的肥大肌细胞中，Ito显著减少。 我们和其他人的研究表明，Ito的这种降低可能是由于Kv4.x通道基因表达的减少。 因此，阐明控制Kv 4亚家族基因表达的分子机制提供了对肌细胞如何实现区域特异性以及病理条件如何产生电异常的基本见解。我们的初步结果表明，Kv4.2基因转录开始于不同的组织中的不同位点。 具体而言，骨骼肌型起始部位在右心室和左心室的心外膜区域中是显著的，而脑型起始部位在心房和心内膜区域中占主导地位。 此外，在体内实验表明，血管紧张素转换酶抑制剂卡托普利的管理，选择性地减少Kv4.2的mRNA在心外膜区，但不是在内膜区。 使用新生心肌细胞培养，我们还发现，血管紧张素II（AngII）产生更显着的减少Kv4.3 mRNA比α-肾上腺素能激动剂苯肾上腺素。 此外，这种蛋白激酶C或钙调神经磷酸酶的抑制剂的抑制Kv4.3 mRNA的表达下调。 这些发现表明Kv4.x基因表达可能是由不同转录因子组区域选择性控制的，并且AngII可能介导高血压诱导的Kv4.x基因表达下调，而与肥大无关。 因此，本建议是使用高血压动物模型和新生儿心肌细胞培养来测试这些可能性。