Role of ATII cell senescence in influenza pathogenesis in aging

肺泡II型（ATII）细胞合成、分泌和回收表面活性蛋白和脂质，并调节肺泡衬里液 肺泡液体清除深度。由于这两个过程都需要大量的能量，ATII细胞含有大量的 主要通过氧化磷酸化（OXPHOS）产生ATP。ATII细胞是 甲型流感病毒（IAV）在远端肺中的复制和IAV诱导的ARDS发病机制中的中心参与者。 重要的是，老年人在流感相关死亡中所占比例过高。然而，人们对这一问题的认识有限。 衰老或IAV感染对ATII细胞功能、衰老和能量代谢影响。ATII细胞分离自 年幼（2-3月龄）C57 BL/6小鼠的肺主要通过OXPHOS产生ATP。相反，初步研究表明， 来自衰老（27个月大）小鼠的ATII细胞经历糖酵解转变并下调OXPHOS，这可能是 衰老IAV感染幼鼠引起糖酵解转变和OXPHOS减少，CDP- 胆碱治疗，导致总ATP产生的净增加，减弱低氧血症，并减少肺动脉高压。 炎症老龄小鼠的IAV感染引起更严重的低氧血症，并进一步降低OXPHOS，而没有任何 糖酵解的代偿性增加，导致总ATP产量的净减少，尽管能量增加 病毒复制的需求。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细胞上的病毒复制施加了额外的能量需求 由于衰老相关的衰老。通过抑制从头磷脂合成，IAV还诱导进一步的mt功能障碍。 总之，这些影响引起能量危机，并使ATII细胞无法执行其正常的生理功能 （肺泡液体清除和表面活性剂合成），其导致进展为ARDS。此外，还建议CDP- 胆碱处理改善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中得到检验。目标1将使用一个稳健的、可重复的和相关的模型 在21-24月龄的C57 BL/6和BALB/c小鼠中IAV诱导的ARDS的影响，以确定衰老、IAV感染和CDP- 胆碱治疗对ATII细胞生理功能（表面活性剂产生和肺泡液清除）的影响，全身 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。目的 2将使用一套全面的流式细胞术检测和蛋白质印迹来量化ATII衰老的水平， 从模拟和IAV感染的年轻和衰老小鼠的肺中分离的细胞，并将分析衰老、IAV 感染和CDP-胆碱处理对ATII细胞能量学的影响。拟议的实验将 为ATII细胞功能障碍和衰老对更多细胞发育的贡献提供了新的机制见解。 老年人中的严重流感，并将产生与许多肺部疾病相关的基本新信息， 衰老，如COPD、IPF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.