Regulatory roles of variable mechanical stimuli in cell function

大多数细胞类型对其物理环境高度敏感，作用于它们的生理力在许多调节细胞功能中起着主导作用。这种机械转导总是使用单调的机械刺激来研究；然而，体内的细胞暴露在不规则变化的刺激下。两个例子包括呼吸和循环。最近，我们发现在肺泡II型上皮细胞中，无论是在培养的还是在体内的，拉伸时的生理变异性的存在从根本上改变了这些细胞的分泌反应。细胞通过黏附分子和细胞骨架(CSK)感知外部机械力。因此，可以假设，通过CSK，即使不是所有的基本细胞功能，也会对机械刺激的可变性敏感。进化力量应该倾向于能够适应和利用现有变异性的结构。因此，我们的中心假设是，机械刺激中正常存在的生理水平的可变性在许多基本细胞功能中具有基本的调节作用。在细胞和组织培养研究中，机械转导的这一方面一直被忽视。因此，一个主要的挑战是确定我们的发现是否针对上皮细胞，或者这种现象是普遍的，代表了机械生物学中的重大范式转变。为了验证这一假设，我们将使用四种不同的体外细胞系统：肺上皮细胞、血管内皮细胞和平滑肌细胞以及皮肤或肺成纤维细胞。我们将在体外测试这些细胞系统的各种结果，同时逐渐改变机械刺激的可变性。具体地说，我们的目标是确定可变拉伸(VS)模式对特定细胞因子、酶和结构ECM蛋白的转录、翻译和分泌的影响。我们还将评估VS对基本细胞功能的影响，如分裂、生长和凋亡，以揭示不同器官系统之间的普遍机制。最后，为了确定VS对代谢的可能影响，我们将评估VS过程中活性氧物种(ROS)的产生。为了阐明VS诱导现象的机制，我们将在VS过程中沿着机械传导通路使用各种抑制剂，同时对CSK的成分和组织进行成像。然后，我们将开发新的CSK网络模型，以更好地了解从粘附点通过CSK到细胞核的机械力传递。如果我们的假设是正确的，那么除了许多基本的细胞功能外，酶、细胞因子和细胞外基质的产生和分泌都将受到VS的影响。此外，VS也可能会影响 ROS在动脉粥样硬化、神经退行性疾病、代谢紊乱、衰老和癌症等几种主要疾病的发病机制中发挥关键作用。因此，我们的项目--第一个应用VS模式来探索细胞功能--对于理解细胞如何在真实的活组织中工作，从而对生物学和医学具有深远的变革意义。因此，这项研究可能会影响包括生物学家、生理学家、物理学家以及临床医生在内的科学家对细胞的看法。

Most cell types are highly sensitive to their physical environment and physiological forces acting on them play a dominating role in many regulatory cell functions. Such mechanotransduction is always studied using monotonous mechanical stimuli; however, cells in the body are exposed to irregularly varying stimuli. Two examples include breathing and circulation. Recently, we found evidence that in alveolar epithelial type II cells, both in culture and in vivo, the presence of physiological variability in stretch fundamentally alters the secretory response of these cells. Cells sense external mechanical forces via adhesion molecules and the cytoskeleton (CSK). It is thus feasible to assume that through the CSK, most if not all basic cell functions would also be sensitive to variability in mechanical stimuli. Evolutionary forces should favor structures that can adapt to and take advantage of existing variability. Accordingly, our central hypothesis is that physiological levels of variability in mechanical stimuli that are normally present in the body have fundamental regulatory roles in many basic cell functions. This aspect of mechanotransduction has been overlooked in cell and tissue culture studies. A major challenge is therefore to establish whether our findings are specific to epithelial cells or the phenomenon is general representing a major paradigm shift in mechanobiology. To test this hypothesis, we will use four different in vitro cell systems: lung epithelial cells, vascular endothelial and smooth muscle cells and skin or lung fibroblasts. We will test various outcomes in these cell systems in vitro while gradually changing variability in mechanical stimuli. Specifically, we aim to determine the effects of variable stretch (VS) pattern on transcription, translation and secretion of specific cytokines, enzymes and structural ECM proteins. We will also assess the effect of VS on basic cell functions such as division, growth and apoptosis to uncover universal mechanisms among different organ systems. Finally, to determine the possible effects of VS on metabolism, we will assess the generation of reactive oxygen species (ROS) during VS. To shed light on the mechanisms of VS-induced phenomena, we will employ various inhibitors along the mechanotransductory pathway during VS while imaging the constituents and organization of the CSK. We will then develop novel network models of the CSK to better understand mechanical force transmission from adhesion sites through the CSK to the nucleus. If our hypothesis is correct, then besides many basic cell functions, the production and secretion of enzymes, cytokines and ECM building blocks will all be affected by VS. Additionally, VS may also influence ROS which play a crucial role in the pathogenesis of several major diseases including atherosclerosis, neuro-degenerative diseases, metabolic disorders, aging and cancer. Thus, our project - the first to apply VS patterns to probe cell functions - could have far reaching transformative implications for the understanding of how cells work in real living tissues and hence for biology and medicine. This research could thus influence the way scientists including biologists, physiologists, physicists as well as clinicians think about the cell.