Department of Biomedical Engineering, Yale University, New Haven, Connecticut.
Department of Cellular and Molecular Physiology, Yale University, New Haven, Connecticut.
Am J Physiol Heart Circ Physiol. 2020 Jun 1;318(6):H1516-H1524. doi: 10.1152/ajpheart.00055.2020. Epub 2020 May 8.
Engineered heart tissues (EHTs) have emerged as a robust in vitro model to study cardiac physiology. Although biomimetic culture environments have been developed to better approximate in vivo conditions, currently available methods do not permit full recapitulation of the four phases of the cardiac cycle. We have developed a bioreactor which allows EHTs to undergo cyclic loading sequences that mimic in vivo work loops. EHTs cultured under these working conditions exhibited enhanced concentric contractions but similar isometric contractions compared with EHTs cultured isometrically. EHTs that were allowed to shorten cyclically in culture had increased capacity for contractile work when tested acutely. Increased work production was correlated with higher levels of mitochondrial proteins and mitochondrial biogenesis; this effect was eliminated when tissues were cyclically shortened in the presence of a myosin ATPase inhibitor. Leveraging our novel in vitro method to precisely apply mechanical loads in culture, we grew EHTs under two loading regimes prescribing the same work output but with different associated afterloads. These groups showed no difference in mitochondrial protein expression. In loading regimes with the same afterload but different work output, tissues subjected to higher work demand exhibited elevated levels of mitochondrial protein. Our findings suggest that regulation of mitochondrial mass in cultured human EHTs is potently modulated by the mechanical work the tissue is permitted to perform in culture, presumably communicated through ATP demand. Precise application of mechanical loads to engineered heart tissues in culture represents a novel in vitro method for studying physiological and pathological cardiac adaptation. In this work, we present a novel bioreactor that allows for active length control of engineered heart tissues during extended tissue culture. Specific length transients were designed so that engineered heart tissues generated complete cardiac work loops. Chronic culture with various work loops suggests that mitochondrial mass and biogenesis are directly regulated by work output.
工程心脏组织（EHT）已成为研究心脏生理学的强大体外模型。尽管已经开发出仿生培养环境来更好地模拟体内条件，但目前可用的方法并不能完全再现心脏周期的四个阶段。我们开发了一种生物反应器，使 EHT 能够经历模拟体内工作循环的循环加载序列。与在等长条件下培养的 EHT 相比，在这些工作条件下培养的 EHT 表现出增强的同心收缩，但等长收缩相似。在培养过程中允许 EHT 周期性缩短的情况下，当急性测试时，其收缩功的能力增加。工作产量的增加与线粒体蛋白和线粒体生物发生水平的升高相关；当组织在肌球蛋白 ATP 酶抑制剂存在下周期性缩短时，这种作用被消除。利用我们新颖的体外方法在培养中精确施加机械负荷，我们在两种加载方案下培养 EHT，规定相同的功输出，但相关的后负荷不同。这些组在线粒体蛋白表达方面没有差异。在具有相同后负荷但不同功输出的加载方案中，承受更高功需求的组织表现出线粒体蛋白水平升高。我们的发现表明，在培养的人 EHT 中，线粒体质量的调节受到组织在培养中允许执行的机械功的强烈调节，可能通过 ATP 需求来传递。在培养的工程心脏组织中精确施加机械负荷代表了一种研究生理和病理心脏适应的新型体外方法。在这项工作中，我们提出了一种新型生物反应器，该生物反应器允许在延长的组织培养过程中对工程心脏组织进行主动长度控制。设计了特定的长度瞬变，以使工程心脏组织产生完整的心脏工作循环。各种工作循环的慢性培养表明，线粒体质量和生物发生直接受功输出调节。
