REGULATION OF CARDIAC POTASSIUM CHANNEL GENE EXPRESSION

心脏钾通道基因表达的调控

• 批准号: 6390444
• 负责人: KOICHI TAKIMOTO TAKIMOTO
• 金额: $ 23.41万
• 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/6390444
• 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.

Kv4 亚家族基因编码心肌细胞中大部分瞬时外向 K+ 电流 (Ito)。 这些基因的差异表达显着导致位于心脏不同区域的肌细胞中动作电位波形的差异。 例如，在左心室壁中，心外膜区域的动作电位持续时间比心内膜区域短，并且Kv4.2 mRNA和Ito的表达与动作电位波形的这种差异密切相关。 除了区域表达差异外，Ito 的表达在病理条件下也会发生改变：在各种条件（包括血压慢性升高）产生的肥大肌细胞中观察到 Ito 显着减少。 我们和其他人的研究表明，Ito 的减少可能是由于 Kv4.x 通道基因表达的减少。 因此，阐明控制 Kv4 亚家族基因表达的分子机制为了解如何实现肌细胞的区域规范以及病理条件如何产生电异常提供了基本见解。我们的初步结果表明，Kv4.2 基因转录起始于不同组织的不同位点。 具体而言，骨骼肌型起始位点在右心室和左心室的心外膜区域中显着，而脑型起始位点在心房和心内膜区域中占主导地位。 此外，体内实验表明，给予血管紧张素转换酶抑制剂卡托普利可选择性降低心外膜区域的Kv4.2 mRNA，但不降低心内膜区域的Kv4.2 mRNA。 使用新生儿肌细胞培养物，我们还发现血管紧张素 II (AngII) 比 α-肾上腺素能激动剂去氧肾上腺素更能显着降低 Kv4.3 mRNA。 此外，这种激素诱导的 Kv4.3 mRNA 下调对蛋白激酶 C 或钙调神经磷酸酶的抑制具有抵抗力。 这些发现表明，Kv4.x 基因的表达可能受到不同转录因子组的区域选择性控制，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，该建议是使用高血压动物模型和新生儿肌细胞培养物来测试这些可能性。