Reversing blood flows act through klf2a to ensure normal valvulogenesis in the developing heart.
Reversing blood flows act through klf2a to ensure normal valvulogenesis in the developing heart.
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DOI：
10.1371/journal.pbio.1000246
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发表时间：
2009-11
期刊：
影响因子：
9.8
通讯作者：
Fraser SE
中科院分区：
文献类型：
--
作者：
Vermot J;Forouhar AS;Liebling M;Wu D;Plummer D;Gharib M;Fraser SE
斑马鱼胚胎心脏局部血流的方向性对心脏瓣膜的形成至关重要。心脏瓣膜畸形是最常见的先天性心脏病，但无论是遗传还是表观遗传的力量指导心脏瓣膜的发展是很好的理解。当功能正常时，成熟的心脏瓣膜防止心内逆行血流;在瓣膜发育之前，存在相当大的反流，导致心房和心室之间的反向（或振荡）流动。由于反向流动对培养中的内皮细胞具有特别强的刺激作用，因此一个有吸引力的假设是，心脏瓣膜形成是对通过成熟心脏的逆行血流的发育反应。在这里，我们利用振荡流和心率之间的关系来操纵瓣膜形成之前和期间房室（AV）通道中的逆行流的量，并发现这导致瓣膜生长受阻。使用这种操作，我们确定klf 2a通常在阀门前体中响应于反向流动而表达，并且通过减少这种流动的处理而显著减少。用吗啉反义寡核苷酸（MO）实验性地敲低这种剪切响应基因的表达会导致瓣膜功能障碍。因此，klf 2a表达似乎是正常瓣膜形成所必需的。这与其对心内血流动力学的依赖性一起，使得klf 2a表达成为正确瓣膜发育的早期和可靠的指标。总之，这些结果证明了在瓣膜形成过程中逆转血流的关键作用，并显示了正常血流动力学模式的相对细微的扰动如何导致基因表达的重大改变和严重的瓣膜发育不全。脊椎动物的生长和发育严重依赖于有效的心输出量来驱动血液循环。心脏发育的一个重要步骤是心脏瓣膜的形成，其小叶是通过内皮细胞的一系列复杂的细胞重排制成的。当血液循环时，内皮细胞经历高流动力。此外，当流动力异常时，心脏瓣膜和相关结构可能会畸形，这表明这些流动力实际上是正确瓣膜形成所需的。究竟是血液流动的力量，它的方向性（向前或反向），或者两者都很重要，目前还不清楚。我们研究了瓣膜发育过程中已知参与该过程的关键基因与表观遗传影响（如流动力）之间的相互作用。使用斑马鱼，其光学清晰度允许以高分辨率分析血流模式，我们确定了在瓣膜前体水平上存在的反向流动。通过操纵血流模式，我们表明，反向流动是必不可少的瓣膜形态。具体而言，我们表明，基因klf 2a的表达取决于存在的反向流动，是需要阀门的发展。我们预测，通过影响klf 2a的水平，反向流动构成了一个重要的刺激控制适当的生物反应的内皮细胞在瓣膜形成。
The directionality of local blood flow in the zebrafish embryonic heart is essential for proper heart valve formation. Heart valve anomalies are some of the most common congenital heart defects, yet neither the genetic nor the epigenetic forces guiding heart valve development are well understood. When functioning normally, mature heart valves prevent intracardiac retrograde blood flow; before valves develop, there is considerable regurgitation, resulting in reversing (or oscillatory) flows between the atrium and ventricle. As reversing flows are particularly strong stimuli to endothelial cells in culture, an attractive hypothesis is that heart valves form as a developmental response to retrograde blood flows through the maturing heart. Here, we exploit the relationship between oscillatory flow and heart rate to manipulate the amount of retrograde flow in the atrioventricular (AV) canal before and during valvulogenesis, and find that this leads to arrested valve growth. Using this manipulation, we determined that klf2a is normally expressed in the valve precursors in response to reversing flows, and is dramatically reduced by treatments that decrease such flows. Experimentally knocking down the expression of this shear-responsive gene with morpholine antisense oligonucleotides (MOs) results in dysfunctional valves. Thus, klf2a expression appears to be necessary for normal valve formation. This, together with its dependence on intracardiac hemodynamic forces, makes klf2a expression an early and reliable indicator of proper valve development. Together, these results demonstrate a critical role for reversing flows during valvulogenesis and show how relatively subtle perturbations of normal hemodynamic patterns can lead to both major alterations in gene expression and severe valve dysgenesis. The growth and development of vertebrates are critically dependent on efficient cardiac output to drive blood circulation. An essential step of heart development is the formation of heart valves, whose leaflets are made through a complex set of cellular rearrangements of endothelial cells. Endothelial cells experience high flow forces as blood circulates. Moreover, heart valves and associated structures can be malformed when flow forces are abnormal, suggesting that these flow forces are in fact required for proper valve formation. Whether it is the force of the blood flow, its directionality (forward or reverse), or both that are important is not clear. We studied the interplay during valve development between key genes known to be involved in the process and epigenetic influences such as flow forces. Using zebrafish, whose optical clarity allows analyzing blood flow patterns at high resolution, we identified the presence of reversing flows specifically at the level of valve precursors. By manipulating blood flow patterns, we show that reversing flows are essential for valve morphogenesis. Specifically, we show that the expression of the gene klf2a depends on the presence of reversing flows and is required for valve development. We predict that by influencing levels of klf2a, reversing flows constitute an important stimulus controlling the appropriate biological responses of endothelial cells during valve formation.
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