Differential expression of cardiac titin isoforms and modulation of cellular stiffness
Differential expression of cardiac titin isoforms and modulation of cellular stiffness
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DOI：
10.1161/01.res.86.1.59
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发表时间：
2000-01-07
影响因子：
20.1
通讯作者：
Granzier, H
中科院分区：
文献类型：
--
作者：
Cazorla, O;Freiburg, A;Granzier, H
肌动蛋白I带节段的延长可产生部分心肌舒张力。以前对人类心脏肌动蛋白转录本的研究表明，在肌动蛋白的I带片段上发生了一系列不同的剪接事件，导致了所谓的N2A和N2B亚型转录本。在这里，我们研究了在蛋白质水平的肌动蛋白在广泛的哺乳动物物种中的表达。结果表明，心肌共表达两种不同的肌动蛋白亚型：一种较小的亚型只含有N2B元件(N2B)，另一种较大的亚型同时含有N2B和N2A元件(N2BA)。大N2BA和小N2BTitin亚型在不同物种中的表达比例有很大差异，例如在左心室中，小鼠的比例约为0.05，猪的比例约为1.5。在心房和心室之间以及不同层的室壁之间也发现了表达比例的差异。异构体特异性抗体的免疫荧光实验表明，这些异构体的共同表达发生在单个心肌细胞水平上。研究了从表达高水平小(大鼠和小鼠)或大(猪)肌动蛋白亚型的不同物种中分离的单个心肌细胞的舒张性。平均而言，猪的肌细胞的硬度明显低于小鼠和大鼠的肌细胞。凝胶分析表明，这一结果不能用小鼠和猪心肌中不同数量的肌动蛋白来解释。相反，猪肌细胞的低硬度可以用其大亚型的高表达水平来解释：这种亚型的较长可伸长区导致对于给定肌节长度的较低的伸展分数，从而导致较低的力。我们的发现对心脏功能的影响也进行了讨论。
Extension of the I-band segment of titin gives rise to part of the diastolic force of cardiac muscle. Previous studies of human cardiac titin transcripts suggested a series of differential splicing events in the I-band segment of titin leading to the so-called N2A and N2B isoform transcripts. Here we investigated titin expression at the protein level in a wide range of mammalian species. Results indicate that the myocardium coexpresses 2 distinct titin isoforms: a smaller isoform containing the N2B element only (N2B titin) and a larger isoform with both the N2B and N2A elements (N2BA titin). The expression ratio of large N2BA to small N2B titin isoforms was found to vary greatly in different species; eg, in the left ventricle the ratio is approximate to 0.05 in mouse and approximate to 1.5 in pig. Differences in the expression ratio were also found between atria and ventricles and between different layers of the ventricular wall. Immunofluorescence experiments with isoform-specific antibodies suggest that coexpression of these isoforms takes place at the single-myocyte level. The diastolic properties of single cardiac myocytes isolated from various species expressing high levels of the small (rat and mouse) or large (pig) titin isoform were studied. On average, pig myocytes are significantly less stiff than mouse and rat myocytes. Gel analysis indicates that this result cannot be explained by varying amounts of titin in mouse and pig myocardium. Rather, low stiffness of pig myocytes can be explained by its high expression level of the large isoform: the longer extensible region of this isoform results in a lower fractional extension for a given sarcomere length and hence a lower force. Implications of our findings to cardiac function are discussed.