Lean mass dynamics during flight and refueling in migratory birds: causes, consequences, and mechanisms

候鸟在繁殖地和越冬地之间完成了漫长的旅程。这段旅程包括一系列长途不间断飞行，对大多数鸣禽来说，持续时间可能是6-8小时，但对一些滨鸟来说，可能持续数天。在飞行过程中，新陈代谢率非常高，候鸟主要用储存的脂肪为长途飞行提供燃料。然而，在飞行过程中也会发生蛋白质分解，导致器官和肌肉质量急剧减少。这种肌肉和器官质量的急剧减少可能导致器官系统的重大功能损失，但这尚未得到彻底的研究。本项目旨在研究候鸟飞行过程中蛋白质分解的原因、后果和机制。这项研究将进一步加深我们对候鸟独特的飞行代谢的认识，加深我们对候鸟如何在关键器官系统急剧减少的情况下保持体内平衡的理解，并将为肌肉和器官退化和再生的分子和生化机制提供新的见解。此外，该项目将提供一个平台，吸引来自不同背景的本科生和研究生进行综合研究，提供广泛的前沿技术的接触和培训，这些技术将适用于许多STEM领域。这些学生还将为当地低收入学区的中学生制定和实施科学传播和推广计划。在飞行过程中，代谢率比休息时高10倍，水分流失率非常高，这对鸟类管理水和能量预算的能力提出了极高的要求。候鸟主要通过脂肪的氧化为长时间飞行提供燃料，但大量蛋白质也被分解代谢，导致肌肉和器官质量比飞行前减少20% - 40%。然而，飞行过程中瘦质量分解代谢的功能限制和潜在机制尚不清楚。候鸟将在一个气候控制的风洞中长时间飞行，以评估蛋白质分解代谢的原因，而蛋白质分解代谢的后果和机制将通过测量整个动物和组织在关键生理过程中的变化，并通过研究飞行过程中发生的转录差异来评估。这将为在剧烈的器官和肌肉重塑的情况下维持体内平衡的生理机制提供见解，并将进一步加深我们对脊椎动物控制表型灵活性的基本机制的理解。作为该项目的一部分，研究生和本科生将接受许多尖端技术的综合培训，这将广泛适用于许多STEM职业。这项研究将为许多本科生提供真正的研究经验，重点是提供指导和培训，鼓励女性和来自代表性不足群体的学生进一步追求STEM学科的职业生涯。

Migratory birds complete long journeys between the breeding and wintering grounds. This journey is comprised of a series of long-distance non-stop flights that can be 6-8 hours in duration for most songbirds, but could last for days in some shorebirds. During flight, metabolic rate is very high and migratory birds primarily fuel these long flights with stored fat. However, protein breakdown also occurs during flight resulting in dramatic organ and muscle mass reductions. Such dramatic reductions in muscle and organ mass could result in significant functional losses of organ systems but this has not been thoroughly investigated. This project proposes to investigate the causes, consequences, and mechanisms of protein breakdown during flight in migratory birds. This research will further our insight into the unique metabolism of migratory birds in flight, deepen our understanding of how migratory birds maintain homeostasis despite dramatic reductions in critical organ systems, and will provide novel insight into the molecular and biochemical mechanisms involved in muscle and organ degeneration and regeneration. Additionally, this project will provide a platform to engage many undergraduate and graduate students from diverse backgrounds in integrative research, providing exposure and training in a broad range of cutting edge techniques that will be applicable to many STEM fields. These students will also develop and implement science communication and outreach programming for middle school students in a local low-income school district.During flight, metabolic rate is 10-fold higher than at rest and rates of water loss are very high, placing extreme demands on the ability of birds to manage water and energy budgets. Migratory birds fuel long-duration flight primarily by the oxidation of fat, but a large amount of protein is also catabolized, resulting in reductions in muscle and organ mass of 20% - 40% from pre-flight levels. However, the functional limits and underlying mechanisms of lean mass catabolism during flight remain unclear. Migratory birds will be flown in a climatically controlled wind tunnel for extended periods to evaluate hypotheses for the causes of protein catabolism, while the consequences and mechanisms of protein catabolism will be assessed by measuring whole animal and tissue level changes in key physiological processes, and by investigating transcriptional differences that occur during flight. This will provide insight into physiological mechanisms that allow the maintenance of homeostasis despite dramatic organ and muscle remodeling, and will further our understanding of the basic mechanisms controlling phenotypic flexibility in vertebrates. Graduate and undergraduate students will receive integrative training in many cutting-edge techniques as part of this project, which will be broadly applicable to many STEM careers. This research will provide genuine research experiences for many undergraduates with emphasis on providing mentorship and training to encourage women and students from underrepresented groups to further pursue careers in STEM disciplines.