Department of Systems Biology and Translational Medicine, Texas A&M Health Science Center College of Medicine, College Station, TX 77843, USA.
J Mol Cell Cardiol. 2011 Jan;50(1):203-13. doi: 10.1016/j.yjmcc.2010.10.003. Epub 2010 Oct 16.
The extracellular matrix (ECM) protein-integrin-cytoskeleton axis plays a central role as a mechanotransducing protein assemblage in many cell types. However, how the process of mechanotransduction and the mechanically generated signals arising from this axis affect myofilament function in cardiac muscle are not completely understood. We hypothesize that ECM proteins can regulate cardiac function through integrin binding, and thereby alter the intracellular calcium concentration (Ca(2+)) and/or modulate myofilament activation processes. Force measurements made in mouse papillary muscle demonstrated that in the presence of the soluble form of the ECM protein, fibronectin (FN), active force was increased significantly by 40% at 1 Hz, 54% at 2 Hz, 35% at 5 Hz and 16% at 9 Hz stimulation frequencies. Furthermore, increased active force in the presence of FN was associated with 12-33% increase in Ca(2+) and 20-50% increase in active force per unit Ca(2+). A function blocking antibody for α5 integrin prevented the effects of the FN on the changes in force and Ca(2+), whereas a function blocking α3 integrin antibody did not reverse the effects of FN. The effects of FN were reversed by an L-type Ca(2+) channel blocker, verapamil or PKA inhibitor. Freshly isolated cardiomyocytes exhibited a 39% increase in contraction force and a 36% increase in L-type Ca(2+) current in the presence of FN. Fibers treated with FN showed a significant increase in the phosphorylation of phospholamban; however, the phosphorylation of troponin I was unchanged. These results demonstrate that FN acts via α5β1 integrin to increase force production in myocardium and that this effect is partly mediated by increases in Ca(2+) and Ca(2+) sensitivity, PKA activation and phosphorylation of phospholamban.
细胞外基质（ECM）蛋白-整合素-细胞骨架轴作为一种机械转导蛋白组装体，在许多细胞类型中发挥着核心作用。然而，机械转导过程以及由此产生的机械信号如何影响心肌中的肌丝功能，目前还不完全清楚。我们假设 ECM 蛋白可以通过整合素结合来调节心脏功能，从而改变细胞内钙离子浓度（Ca(2+)）和/或调节肌丝激活过程。在小鼠乳头肌中的力测量表明，在 ECM 蛋白可溶性形式纤连蛋白（FN）存在的情况下，在 1 Hz 刺激频率下，主动力增加了 40%，在 2 Hz 刺激频率下增加了 54%，在 5 Hz 刺激频率下增加了 35%，在 9 Hz 刺激频率下增加了 16%。此外，在 FN 存在的情况下，主动力的增加与Ca(2+)增加 12-33%和单位 Ca(2+)的主动力增加 20-50%相关。α5 整合素功能阻断抗体可阻止 FN 对力和Ca(2+)变化的影响，而α3 整合素功能阻断抗体不能逆转 FN 的作用。FN 的作用可被 L 型钙通道阻断剂维拉帕米或 PKA 抑制剂逆转。在 FN 存在的情况下，新鲜分离的心肌细胞的收缩力增加 39%，L 型钙电流增加 36%。用 FN 处理的纤维显示磷酸化肌浆球蛋白轻链增加；然而，肌钙蛋白 I 的磷酸化没有改变。这些结果表明，FN 通过α5β1 整合素作用于心肌以增加力的产生，而这种作用部分是通过增加Ca(2+)和 Ca(2+)敏感性、PKA 激活和肌浆球蛋白轻链磷酸化来介导的。
