Diffuse Alveolar Damage (DAD), a severe pathological consequence of acute lung injury triggered by factors like infection or toxins, features intense inflammatory cell infiltration and carries a high mortality rate. Understanding its cellular dynamics is crucial for identifying therapeutic targets to mitigate excessive inflammation and improve outcomes. Interstitial macrophages (IM), key regulators of lung inflammation comprising pro-inflammatory (IM^pi) and anti-inflammatory (IM^ai) subsets, originated partly from monocyte (Mono), but their specific developmental pathways and regulatory factors in DAD remained unclear.
This study employed an integrated multi-omics approach (FCM, CyTOF, scRNA-seq) combined with lineage tracing in a ricin-induced mouse DAD model. It revealed a significant accumulation of pro-inflammatory Mono (Mono^pi) and IM^pi within the DAD lung, accompanied by decreased alveolar macrophages (AM) and anti-inflammatory Mono (Mono^ai). Crucially, scRNA-seq identified a novel proliferative Mono subset (pMono^pi), characterized by high expression of proliferation markers MKI67 and TOP2A, which specifically expanded in the DAD lung. Furthermore, parabiosis and adoptive transfer experiments demonstrated that circulating Mono, particularly Mono^pi, exhibited superior engraftment potential into the DAD lung compared to Mono^ai, which were the primary source of accumulating lung IM.
Trajectory analyses showed that recruited Mono^pi acquired a proliferative state (pMono^pi, expressing Ki67, Ly6C, CCR2) and followed a “Mono^pi-pMono^pi-IM^ai” differentiation pathway contributing to IM^ai generation. Mechanistic investigations identified growth differentiation factor 15 (GDF15), primarily expressed by alveolar type 2 cells and upregulated in DAD, as the key regulator driving pMono^pi formation. Gdf15^-/- mice showed significantly reduced pMono^pi, while recombinant GDF15 administration rescued pMono^pi numbers. scRNA-seq trajectory analysis confirmed that GDF15 deficiency specifically blocked the “Mono^pi-pMono^pi-IM^ai” branch without affecting the direct “Mono^pi-IM^ai” path.
Collectively, this work delineated the dynamic remodeling of the mononuclear phagocyte system in DAD and uncovered the role of GDF15 in driving “Mono^pi-pMono^pi-IM^ai” differentiation, providing a potential therapeutic target for treating lung inflammatory disease. The work entitled “A cell differentiation landscape for monocyte and interstitial macrophage in the lung with diffuse alveolar damage” was published on Protein & Cell (2025 Aug 4:pwaf070. doi: 10.1093/procel/pwaf070. Online ahead of print.).
DOI：10.1093/procel/pwaf070