Functional, transcriptional, and microbial shifts associated with healthy pulmonary aging: insights from rhesus macaques.

Older individuals are at increased risk of developing severe respiratory infections due to age-related changes in the immunological, microbial, and functional landscape of the lung. A more comprehensive understanding of these changes and their implications for antimicrobial function is urgently needed. However, our understanding of the impact of age on the respiratory tract remains limited as samples from healthy humans are challenging to obtain and confounding variables such as smoking and environmental pollutant exposure make it difficult to assess the true impact of aging. On the other hand, studies in rodent models are complicated by their specific pathogen free status. In this study, we utilize a rhesus macaque model of healthy aging to examine the functional, immunological, and microbial consequences of aging in the lunglung using an array of molecular (scRNA-seq, 16S microbiome profiling), immunological (flow cytometry, intra-cellular cytokine staining) and functional (pulmonary fitness testing) assays. Pulmonary function testing in this large (n=34 adult, n=49 aged) cross-sectional study established age and sex differences similar to humans supporting the translational accuracy of this model. Interestingly, the lung microbiome of many animals was dominated by a single microbe, Troperyma spp., the prevalence of which decreased with age. Additionally, an increased abundance of myeloid cells (alveolar and infiltrating macrophages) and a concomitant decrease in T-cells was also observed in aged animals. Single cell RNA sequencing indicated a transcriptional shift in the pulmonary CD8+ T-cell population from GRZMB expressing cells to IFN expressing cells, while frequency of IL-1B expressing alveolar macrophages was significantly reduced. These data provide a comprehensive picture of the functional, microbial and immunological changes of the lung in healthy macaque aging and provide insight into the increased prevalence and severity of respiratory disease in the elderly.

由于肺部免疫、微生物及功能微环境随衰老发生改变，老年人罹患重症呼吸道感染的风险显著升高。当前亟需更全面地阐明此类改变及其对抗菌功能的影响。然而，由于难以获取健康人类受试者的样本，且吸烟、环境污染物暴露等混杂变量干扰了对衰老真实影响的评估，我们对衰老如何影响呼吸道的认知仍十分有限。另一方面，啮齿类动物模型因处于无特定病原体（specific pathogen free, SPF）状态，其相关研究也存在诸多局限。
本研究采用健康衰老恒河猴模型，结合一系列分子层面[单细胞RNA测序（single-cell RNA sequencing, scRNA-seq）、16S微生物组谱分析]、免疫层面[流式细胞术、胞内细胞因子染色]及功能层面[肺功能检测]的实验手段，探究衰老对肺部功能、免疫及微生物组的影响。这项大型横断面研究（共纳入34名成年个体、49名老年个体）的肺功能检测结果显示，恒河猴的年龄与性别差异与人类高度相似，证实了该模型的转化准确性（translational accuracy）。值得注意的是，多数受试动物的肺部微生物组以单一微生物——Troperyma spp.为优势菌群，其检出率随衰老进程逐渐降低。此外，老年动物体内的髓系细胞（肺泡巨噬细胞与浸润性巨噬细胞）丰度显著升高，而T细胞丰度则伴随出现下降。单细胞RNA测序结果显示，肺部CD8+ T细胞群体的转录谱发生显著改变：从表达GRZMB的细胞亚型转向表达干扰素（IFN）的细胞亚型；同时，表达白细胞介素1β（IL-1B）的肺泡巨噬细胞比例显著降低。本研究数据全面阐明了健康恒河猴衰老过程中肺部的功能、微生物组及免疫改变，为理解老年人呼吸道疾病患病率升高与病情加重的机制提供了全新视角。