心脏有能力通过称为机械传导的过程来检测和响应机械负荷的变化。在这项研究中,我们专注于研究心脏特异性N2B元素在Titin弹簧区域内的作用,它被提议用作机械传感器。为了评估其重要性,我们使用N2B敲除(KO)小鼠和野生型(WT)小鼠进行了实验,使它们经受三种不同的条件:1)由横主动脉缩窄(TAC)引起的心脏压力超负荷,2)主动脉腔瘘(ACF)引起的容量超负荷,3)通过游泳运动诱发的肥大。在压力过载(TAC)条件下,两种基因型表现出相似的肥大反应。相比之下,WT小鼠在容量超负荷(ACF)一周后表现出强烈的左心室肥厚,而KO小鼠未能经历肥大并经历了高死亡率。同样,游泳运动诱导的KO小鼠肥大显著减少。RNA-Seq分析显示KO小鼠对容量超负荷的β-肾上腺素能反应异常,以及对异丙肾上腺素诱导的肥大的反应减弱。因为已知N2B元件与四个半LIM结构域1和2(FHL1和FHL2)蛋白相互作用,两者都与机械传导有关,我们评估了这些蛋白质。有趣的是,而容量超负荷导致FHL1蛋白表达水平在KO和WT小鼠之间相当,与WT相比,在KO小鼠中FHL2蛋白水平降低超过90%。这表明,在响应体积过载时,FHL2可能充当N2B元件和下游信号通路之间的信号传递介质。总的来说,我们的研究强调了N2B元素在体积过载期间机械传感中的重要性,在生理和病理环境中。
The heart has the ability to detect and respond to changes in mechanical load through a process called mechanotransduction. In this study, we focused on investigating the role of the cardiac-specific N2B element within the spring region of titin, which has been proposed to function as a mechanosensor. To assess its significance, we conducted experiments using N2B knockout (KO) mice and wildtype (WT) mice, subjecting them to three different conditions: 1) cardiac pressure overload induced by transverse aortic constriction (TAC), 2) volume overload caused by aortocaval fistula (ACF), and 3) exercise-induced hypertrophy through swimming. Under conditions of pressure overload (TAC), both genotypes exhibited similar hypertrophic responses. In contrast, WT mice displayed robust left ventricular hypertrophy after one week of volume overload (ACF), while the KO mice failed to undergo hypertrophy and experienced a high mortality rate. Similarly, swim exercise-induced hypertrophy was significantly reduced in the KO mice. RNA-Seq analysis revealed an abnormal β-adrenergic response to volume overload in the KO mice, as well as a diminished response to isoproterenol-induced hypertrophy. Because it is known that the N2B element interacts with the four-and-a-half LIM domains 1 and 2 (FHL1 and FHL2) proteins, both of which have been associated with mechanotransduction, we evaluated these proteins. Interestingly, while volume-overload resulted in FHL1 protein expression levels that were comparable between KO and WT mice, FHL2 protein levels were reduced by over 90% in the KO mice compared to WT. This suggests that in response to volume overload, FHL2 might act as a signaling mediator between the N2B element and downstream signaling pathways. Overall, our study highlights the importance of the N2B element in
mechanosensing during volume overload, both in physiological and pathological settings.