van Kelle Mathieu A J, Khalil Nilam, Foolen Jasper, Loerakker Sandra, Bouten Carlijn V C
Department of Biomedical Engineering, Eindhoven University of Technology, Eindhoven, Netherlands.
Institute for Complex Molecular Systems, Eindhoven University of Technology, Eindhoven, Netherlands.
Front Bioeng Biotechnol. 2019 Mar 12;7:41. doi: 10.3389/fbioe.2019.00041. eCollection 2019.
Prestress is a phenomenon present in many cardiovascular tissues and has profound implications on their functionality. For instance, the mechanical properties are altered by the presence of prestress, and prestress also influences tissue growth and remodeling processes. The development of tissue prestress typically originates from complex growth and remodeling phenomena which yet remain to be elucidated. One particularly interesting mechanism in which prestress develops is by active traction forces generated by cells embedded in the tissue by means of their actin stress fibers. In order to understand how these traction forces influence tissue prestress, many have used microfabricated, high-throughput, micrometer scale setups to culture microtissues which actively generate prestress to specially designed cantilevers. By measuring the displacement of these cantilevers, the prestress response to all kinds of perturbations can be monitored. In the present study, such a microfabricated tissue gauge platform was combined with the commercially available Flexcell system to facilitate dynamic cyclic stretching of microtissues. First, the setup was validated to quantify the dynamic microtissue stretch applied during the experiments. Next, the microtissues were subjected to a dynamic loading regime for 24 h. After this interval, the prestress increased to levels over twice as high compared to static controls. The prestress in these tissues was completely abated when a ROCK-inhibitor was added, showing that the development of this prestress can be completely attributed to the cell-generated traction forces. Finally, after switching the microtissues back to static loading conditions, or when removing the ROCK-inhibitor, prestress magnitudes were restored to original values. These findings show that intrinsic cell-generated prestress is a highly controlled parameter, where the actin stress fibers serve as a mechanostat to regulate this prestress. Since almost all cardiovascular tissues are exposed to a dynamic loading regime, these findings have important implications for the mechanical testing of these tissues, or when designing cardiovascular tissue engineering therapies.
预应力是许多心血管组织中存在的一种现象，对其功能有着深远影响。例如，预应力的存在会改变力学性能，同时也会影响组织生长和重塑过程。组织预应力的形成通常源于复杂的生长和重塑现象，这些现象仍有待阐明。预应力形成的一个特别有趣的机制是，嵌入组织中的细胞通过其肌动蛋白应力纤维产生主动牵引力。为了了解这些牵引力如何影响组织预应力，许多人使用了微加工的、高通量的、微米级的装置来培养能主动产生预应力的微组织，并将其施加到专门设计的悬臂梁上。通过测量这些悬臂梁的位移，可以监测预应力对各种扰动的响应。在本研究中，这样一个微加工组织测量平台与市售的Flexcell系统相结合，以促进微组织的动态循环拉伸。首先，对该装置进行了验证，以量化实验过程中施加的动态微组织拉伸。接下来，对微组织进行24小时的动态加载。在此时间段后，预应力增加到比静态对照高出两倍多的水平。当添加ROCK抑制剂时，这些组织中的预应力完全消除，这表明这种预应力的形成完全归因于细胞产生的牵引力。最后，在将微组织切换回静态加载条件后，或者在去除ROCK抑制剂时，预应力大小恢复到原始值。这些发现表明，细胞内在产生的预应力是一个高度可控的参数，其中肌动蛋白应力纤维作为一种机械调节器来调节这种预应力。由于几乎所有心血管组织都暴露于动态加载状态，这些发现对这些组织的力学测试或设计心血管组织工程疗法具有重要意义。
