A Mathematical-Experimental Strategy to Discern the Molecular Basis of "Successful Mucus"

在人体呼吸道中，粘液屏障是防御的第一线，而免疫系统是次要的。“成功的黏液”有效地捕获了侵入性物质（病原体和微粒），并不断地清除从气道到喉部的黏液和物质，在穿透黏液屏障之前将其吞入肠道，并在化学上解除武装，防止接触细胞或血流。许多疾病和病理现在都与“不成功的粘液”有关，从遗传性疾病如囊性纤维化到获得性疾病如慢性阻塞性肺疾病（COPD）。黏液已成为矿工肺部健康的金丝雀。本研究中概述的实验数学项目提出了一种策略，用严谨、稳健的科学指标取代肺部疾病的生活质量指标，该指标将新颖的实验技术与数据分析、模型选择和预测计算的数学相结合。这些进展有望为黏液生物学提供一个新的标准，有可能将临床实践从患者症状转变为对黏液运输特性的预先监测和评估，识别成功和失败的可能来源，并测试治疗的影响和持续时间。在整合生物学、生物物理学、应用数学、统计学和医学的知识和技术方面，对本科生、研究生和博士后学者进行教育和培训，有助于丰富所有学科和领域，并进一步为学术界、公共和私营部门的下一代研究人员和实践者做出贡献。每个器官中的粘液都有一个基线组成（黏液大分子、蛋白质、电解质和水的光谱），可以在细胞培养物中复制，然后是许多“活诱导”的分子物种（病原体和副产物、免疫反应剂、死细胞的DNA以及来自环境和生活方式因素的物质）。这种分子组成向健康粘液传递了阻止物种从纳米到微米扩散的能力，以及被激活（从而清除）到单个纤毛的皮牛顿力的能力。显微镜观察黏液中所有颗粒均呈“非正常”扩散，其扩散统计随颗粒大小和表面化学变化而变化；所有流变学数据都指向非线性粘弹性行为，这取决于肺中推进机制的频率、长度尺度和应力水平。成功黏液的这种惊人的能力，对各种各样的污物以及纤毛和空气阻力对其清除的反应，同时又有不同的反应，这使黏液生物学感到困惑。因此，没有粘液运输特性的评估标准，没有对成功粘液的结论性测试，不了解哪些分子物种或串联物种决定粘液运输特性的成功或失败，也没有严格的基础来测试恢复健康运输特性的潜在补救措施。本项目将探索从分子基础上分解黏液的实验技术，自上而下将临床黏液解构为基线和活诱导成分，自下而上将无菌细胞培养基线与可控活诱导成分叠加重建。将开发数学技术来评估整个黏液样本空间中生理相关的扩散和粘弹性特性，包括解决有关异常扩散和非线性粘弹性的开放数学问题的策略。

In human airways, the mucus barrier is the front line of defense whereas the immune system is secondary.  "Successful mucus" efficiently traps invasive cargo (pathogens and particulates) and continuously clears mucus and cargo from the airways to the larynx where it is swallowed to the gut and chemically disarmed before penetration of the mucus barrier, preventing exposure to cells or the blood stream.  Many diseases and pathologies are now associated with "unsuccessful mucus," from genetic diseases like cystic fibrosis to acquired conditions such as chronic obstructive pulmonary disease (COPD).  Mucus has become the miner's canary of lung health.  The experimental-mathematical projects outlined in this research present a strategy to replace quality-of-life metrics of lung disorders with rigorous, robust scientific metrics that integrate novel experimental technique with the mathematics of data analytics, model selection, and predictive computation.  These advances promise a new standard for mucus biology, with the potential to transform clinical practice from patient symptoms to preemptive monitoring and assessment of mucus transport properties, to identification of likely sources of success and failure, and to test impact and duration of therapeutics.  The education and training of undergraduates, graduate students, and postdoctoral scholars in the integration of knowledge and techniques from biology, biophysics, applied mathematics, statistics, and medicine contributes to the enrichment of all disciplines and fields, and furthermore to the future generation of researchers and practitioners in academia and the public and private sector.    Mucus in every organ has a baseline composition (a spectrum of mucin macromolecules, proteins, electrolytes, and water) that is reproducible in cell cultures, and then a host of "living-induced" molecular species (pathogens and by-products, immune response agents, DNA from dead cells, and substances from environmental and lifestyle factors).  This molecular composition conveys to healthy mucus the ability to impede the diffusion of species from nanometer to micron size, and the ability to be activated (thereby cleared) down to pico-Newton forces of single cilia.  All particles tracked via microscopy in mucus diffuse "non-normally" and the statistics of their diffusion varies with particle size and surface chemistry; all rheology data point to nonlinear viscoelastic behavior that differs depending on the frequency, lengthscale, and stress level of the propulsion mechanisms in the lung.  This striking capacity of successful mucus to respond simultaneously yet differently to the diversity of insults and to its clearance by cilia and air drag has confounded the science of mucus biology.  Consequently, there has been no assessment standard of transport properties for mucus, no conclusive test for successful mucus, no understanding of what molecular species or tandem species determine mucus success or failure in either transport property, and no rigorous basis to test potential remedies to reinstate healthy transport properties.  In this project, experimental techniques will be explored to decompose mucus with respect to its molecular basis, with top-down deconstruction of clinical mucus into baseline and living-induced components, and bottom-up reconstruction from a sterile cell culture baseline superimposed with controlled living-induced components.  Mathematical techniques will be developed to assess diffusive and viscoelastic properties of physiological relevance over this entire mucus sample space, including strategies to resolve open mathematical questions about anomalous diffusion and nonlinear viscoelasticity.