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.