Abstract
Alveolar macrophages (AM) must perform three seemingly opposing roles including homeostasis, driving inflammation, and facilitating tissue repair. Whilst there is now consensus (supported by a large body of human single cell RNA sequencing (scRNA-seq) data) that the cell subsets that perform these tasks can readily be found based on their transcriptome, their ontogeny has remained unclear. Moreover, there is agreement that in all types of pulmonary fibrosis (PF) there is an expanded population of profibrotic AM that may aberrantly drive PF. From a therapeutic viewpoint, there is great appeal in the notion that the transcriptional program in different AM subsets is not fixed but remains plastic and amenable to pharmacological reprogramming. Accordingly, this study addresses this question by performing scRNA-seq on human AM following treatment with drugs or perturbagens including pioglitazone, trametinib, nintedanib, lipopolysaccharide and the natural compound endiandrin A. Each treatment induced a unique global transcriptional change, driving the cells towards distinct subsets, further supported by trajectory analysis, confirming a high level of plasticity. Confirmatory experiments using qPCR demonstrated that single exposure to a compound induced a relatively stable transcriptome, whereas serial exposure to a different compound allowed the cells to be reprogrammed yet again to a different phenotype. These findings add new insight into the biology of AM and support the development of novel therapies to treat PF.