Effects of mechanical forces on lung injury and repair

描述（由申请人提供）：肺部持续处于预先存在的拉伸应力或由经肺压力产生的预应力下，该压力随呼吸周期性变化。这种预应力通过肺泡壁以机械力的形式传递到细胞外基质（ECM）。我们之前的研究表明，这种机械力在肺气肿肺中能够破坏胶原蛋白。由于正常的肺不会因为胶原蛋白的保护而机械衰竭，肺气肿组织的衰竭表明胶原蛋白被重塑了，所以它很容易衰竭。一旦胶原蛋白失效，肺泡壁也会破裂。肺泡衰竭将使附近区域暴露在更高的压力下，更多的肺泡将面临衰竭的风险，这一系列事件与肺气肿的进行性特征一致。也有报道说，在人类晚期肺气肿中，有很强的胶原酶活性。这导致胶原蛋白的重塑，最终导致胶原蛋白衰竭，随后是空域扩大。因此，我们的中心假设是：肺气肿进展过程中肺功能的恶化主要是由机械力如何调节胶原蛋白的重塑和随后的失效决定的。我们将研究机械力如何调节成纤维细胞分泌胶原（I型和III型）的能力，以及成纤维细胞和II型肺泡上皮（II型）细胞分泌胶原重塑酶（如基质金属蛋白酶、MMP-1和MMP-2）的能力。我们将评估机械力是否能加速胶原降解过程中的酶活性，结果将与肺泡结构和器官水平功能相关。我们将利用来自两种啮齿动物肺气肿模型的细胞和组织：弹性酶治疗，与胶原蛋白没有直接关系的标准模型，以及MMP-1转基因小鼠，在没有弹性蛋白或炎症参与的情况下发生肺气肿。我们的具体目标是：1)确定机械力在多大程度上调节成纤维细胞和II型细胞在组织条和细胞培养中表达和分泌胶原和MMPs的能力。2)通过测定酶活性与机械力之间的动态相互作用，评价机械力对损伤进展的影响。3)确定正常和肺气肿小鼠肺的器官水平功能、细胞事件和机械力之间的关系。这一目的将证实目标1和目标2中体外研究的生理相关性。如果这些实验支持我们的假设，其结果对于肺气肿的理解和治疗可能的范式转变是重要的。首先，如果机械转导在肺气肿中起着重要作用，那么未来任何阻止肺气肿发展或停止肺气肿进展的尝试都必须在细胞水平上纳入机械力的影响。其次，药物不可能阻止肺气肿的发展，除非它们也能提供某种形式的保护，防止胶原蛋白的机械失效。项目简介：到2020年，慢性阻塞性肺病将成为世界上第三大常见死因和第五大常见致残原因。目前，尚不清楚这种疾病是如何发展的，也不知道它为什么会发展。这里提出的研究包括研究细胞和结缔组织在呼吸过程中如何在肺中伸展，并可能为理解这种疾病开辟新的方向，并有可能开发新的治疗方法。

DESCRIPTION (provided by applicant): The lung is constantly under a pre-existing tensile stress or prestress generated by transpulmonary pressure which changes cyclically with breathing. This prestress is transmitted through the alveolar walls to the extracellular matrix (ECM) in the form of mechanical force. Our previous studies have shown that such mechanical forces in the emphysematous lung are able to rupture the collagen. Since the normal lung does not fail mechanically due to the protection of collagen, the failure of emphysematous tissue suggests that the collagen is remodeled so that it is prone to failure. Once the collagen fails, the alveolar wall can also rupture. The failure of alveoli will expose nearby regions to higher stresses and more alveoli would be at risk of failure, a sequence of events consistent with the progressive nature of emphysema. It has also been reported that in human late stage emphysema, there is a strong collagenase activity. This results in remodeling of collagen that eventually leads to collagen failure followed by airspace enlargement. Thus, our central hypothesis is that: The functional deterioration of the lung during the progression of emphysema is primarily determined by how mechanical forces modulate the remodeling and subsequent failure of collagen. We will investigate how mechanical forces modulate the ability of fibroblasts to secrete collagens (types I and III) and the ability of both fibroblasts and type II alveolar epithelial (type II) cells to secrete collagen remodeling enzymes such as the matrix metalloproteinases, MMP-1 and MMP-2. We will evaluate whether mechanical forces can accelerate enzyme activity during the degradation of collagens and the results will be correlated with alveolar structure and organ level function. We will utilize cells and tissues from two rodent models of emphysema: elastase-treatment, a standard model not directly related to collagen, and MMP-1 transgenic mice which develop emphysema without the involvement of elastin or inflammation. Our specific aims are to: 1) Determine the extent to which mechanical forces modulate the ability of fibroblasts and type II cells to express and secrete collagens and MMPs in tissue strips and cell culture. 2) Evaluate the effects of mechanical forces on the progression of injury by determining the dynamic interaction between enzyme activity and mechanical forces. 3) Determine the relationship among organ level function, cellular events and mechanical forces in the normal and emphysematous mouse lungs. This aim will confirm the physiological relevance of the in vitro studies in Aims 1 and 2. Should these experiments support our hypothesis, the consequences are important with a possible paradigm shift in the understanding and treatment of emphysema. First, if mechanotransduction plays an important role in emphysema, then any future attempt to prevent the development, or stop the progression of emphysema will have to incorporate the influence of mechanical forces at the cellular level. Second, drugs could not possibly stop the progression of emphysema, unless they also provide some form of protection of collagen from mechanical failure. PROJECT NARRATIVE: By 2020, chronic obstructive pulmonary disease will become the third most common cause of death and the fifth most common cause of disability in the world. Currently, it is not known how this disease develops or why it progresses. The research proposed here involves investigating how cells and connective tissue stretch in the lung during breathing and may open a new direction in understanding the disease with high potential to develop new treatments.