Expression profiling by high throughput sequencing
Little is known about the relative importance of monocyte and tissue-resident macrophages in the development of lung fibrosis. We show that specific genetic deletion of monocyte-derived alveolar macrophages after their recruitment to the lung ameliorated lung fibrosis, whereas tissue-resident alveolar macrophages did not contribute to fibrosis. Using transcriptomic profiling of flow-sorted cells, we found that monocyte to alveolar macrophage differentiation unfolds continuously over the course of fibrosis and its resolution. During the fibrotic phase, monocyte-derived alveolar macrophages differ significantly from tissue-resident alveolar macrophages in their expression of profibrotic genes. A population of monocyte-derived alveolar macrophages persisted in the lung for one year after the resolution of fibrosis, where they became increasingly similar to tissue-resident alveolar macrophages. Human homologues of profibrotic genes expressed by mouse monocyte-derived alveolar macrophages during fibrosis were up-regulated in human alveolar macrophages from fibrotic compared with normal lungs. Our findings suggest that selectively targeting alveolar macrophage differentiation within the lung may ameliorate fibrosis without the adverse consequences associated with global monocyte or tissue-resident alveolar macrophage depletion.
Monocytes, interstitial macrophages, and alveolar macrophages separated by high or low expression of Siglec F were isolated from Casp8flox/flox at 14 and 19-21 days following bleomycin-induced fibrosis and Siglec F high alveolar macrophages were isolated from naïve mice. The same experiment was repeated for CD11cCreCasp8flox/flox and LysMCreCasp8flox/flox mice and was repeated without naïve mice for CD11cCreCasp8flox/floxRIPK3-/- and LysMCreCasp8flox/floxRIPK3-/- mice. Donor and recipient alveolar macrophages were isolated 10 months following bleomycin injury from bone marrow chimeras. Transcriptome analysis was performed. Experiments were performed with 2-5 replicates.