Role of ATII cell senescence in influenza pathogenesis in aging

肺泡II型(ATII)细胞合成、分泌和循环表面活性物质蛋白质和脂类，调节肺泡衬里液体 通过肺泡液清除深度。因为这两个过程都需要大量的能量，ATII细胞包含大量的 主要通过氧化磷酸化(OXPHOS)产生ATP。ATII细胞是 甲型流感病毒(IAV)在远端肺和中央的复制在IAV诱导的ARDS的发病机制中的作用。 重要的是，在与流感相关的死亡中，老年人的比例过高。然而，人们对此的了解有限。 衰老或IAV感染对ATII细胞功能、衰老和能量代谢的影响。ATII细胞的分离 幼龄(2-3月龄)C57BL/6小鼠的肺主要通过OXPHOS产生三磷酸腺苷。相比之下，初步研究表明 衰老(27个月龄)小鼠的ATII细胞发生糖酵解转变并下调OXPHOS，可能是由于 衰老。IAV感染幼鼠引起糖酵解位移和OXPHOS减少，这可被CDP-逆转。 胆碱治疗，导致总三磷酸腺苷产量的净增加，减轻低氧血症，并减少肺 发炎。IAV感染老龄小鼠可引起更严重的低氧血症，并进一步降低OXPHOS而不是 糖酵解的代偿性增加，导致总的ATP产量净减少，尽管能量增加 病毒复制带来的需求。因此，假设流感在老年人中更严重，因为IAV 感染对缺乏固有代谢灵活性的ATII细胞施加了额外的病毒复制能量需求 由于衰老相关的衰老。通过抑制从头合成磷脂，IAV还可引起进一步的线粒体功能障碍。 这些效应共同引发了能量危机，导致ATII细胞不能发挥正常的生理功能 (肺泡液清除和表面活性物质合成)，导致进展为ARDS。现进一步建议，CDP- 胆碱治疗改善ATII细胞中的OXPHOS并增加其功能能力，从而改善流感 结果。这一假设将在两个具体目标上得到检验。目标1将使用健壮、可重现且相关的模型 对21-24月龄C57BL/6和BALB/c小鼠进行IAV诱导的ARDS的研究，以确定衰老、IAV感染和CDP的影响。 胆碱治疗对ATII细胞生理功能(表面活性物质产生和肺泡液清除)、全身的影响 代谢(通过开路量热法)、肺葡萄糖摄取(通过PET/CT)、肺部炎症和病毒复制。目标 2将使用一组全面的流式细胞仪分析和Western印迹来量化ATII的衰老水平 从模拟和IAV感染的幼年和老年小鼠的肺中分离细胞并将分析衰老的影响，IAV 胞外通量分析感染和CDP-胆碱处理对ATII细胞能量的影响。拟议的实验将 为ATII细胞功能障碍和衰老在More的发生中的作用提供了新的机制见解 并将产生与许多肺部疾病相关的基本新信息 老龄化，如慢性阻塞性肺病、肺间质纤维化和非小细胞肺癌。

Alveolar type II (ATII) cells synthesize, secrete, and recycle surfactant proteins and lipids and regulate alveolar lining fluid depth by alveolar fluid clearance. Because both processes require large amounts of energy, ATII cells contain large numbers of mitochondria and mainly generate ATP by oxidative phosphorylation (OXPHOS). ATII cells are the primary site for influenza A virus (IAV) replication in the distal lung and central players in the pathogenesis of IAV-induced ARDS. Importantly, the elderly are over-represented in influenza-related fatalities. However, there is limited understanding of the impact of either aging or IAV infection on ATII cell function, senescence, and energy metabolism. ATII cells isolated from lungs of young (2-3 month-old) C57BL/6 mice primarily generate ATP by OXPHOS. In contrast, preliminary studies show ATII cells from aging (27 month-old) mice undergo a glycolytic shift and downregulate OXPHOS, possibly as a result of senescence. IAV infection of young mice causes a glycolytic shift and a decrease in OXPHOS which is reversed by CDP- choline treatment, resulting in a net increase in total ATP production, attenuated hypoxemia, and reduced pulmonary inflammation. IAV infection of aging mice causes more severe hypoxemia and further reduces OXPHOS without any compensatory increase in glycolysis, resulting in a net decrease in total ATP production despite the increased energy demands imposed by viral replication. Hence, it is hypothesized that influenza is more severe in the elderly because IAV infection imposes additional energetic demands for viral replication on ATII cells that lack inherent metabolic flexibility due to aging-associated senescence. By inhibiting de novo phospholipid synthesis, IAV also induces further mt dysfunction. Together, these effects provoke an energy crisis and render ATII cells unable to perform their normal physiologic functions (alveolar fluid clearance and surfactant synthesis), which results in progression to ARDS. It is further proposed that CDP- choline treatment improves OXPHOS in ATII cells and increases their functional capacity, thereby improving influenza outcomes. This hypothesis will be tested in two Specific Aims. Aim 1 will use a robust, reproducible, and relevant model of IAV-induced ARDS in 21-24 month-old C57BL/6 and BALB/c mice to define effects of aging, IAV infection, and CDP- choline treatment on ATII cell physiologic functions (surfactant production and alveolar fluid clearance), whole body metabolism (by open circuit calorimetry), lung glucose uptake (by PET/CT), lung inflammation, and viral replication. Aim 2 will use a comprehensive battery of flow cytometric assays and Western blot to quantify the level of senescence in ATII cells isolated from the lungs of mock- and IAV-infected young and aging mice and will analyze the impact of aging, IAV infection, and CDP-choline treatment on ATII cell energetics by extracellular flux analysis. Proposed experiments will provide novel mechanistic insights into the contribution of ATII cell dysfunction and senescence to development of more severe influenza in the elderly and will generate fundamental new information relevant to many pulmonary diseases of aging, such as COPD, IPF, and non-small cell lung cancer.