K. Nakatsutsumi1, N. Kemmerer2, K. Pool1, D. Agarwal2, S. Sayeed2, D. Park1, K. Wahlin2, B. Eliceiri1, T.W. Costantini1 1University Of California – San Diego, Trauma, Surgical Critical Care, Burns, And Acute Care Surgery/Surgery, San Diego, CA, USA 2University Of California – San Diego, San Diego, CA, USA
Introduction: Acute lung injury (ALI) remains a leading cause of morbidity among patients who survive the initial insult after severe trauma. Clarifying the molecular mechanism of the development of ALI after severe trauma is crucial to identify potential therapeutic targets. We hypothesized that trauma activates cellular proliferation genes in alveolar macrophages, which is associated with the development of ALI.
Methods: A polytrauma model was conducted in C57BL/6J mice by causing unilateral lung contusion using a cortical impactor followed by laparotomy with liver crush injury. ALI was characterized by measuring histology, lung permeability, and wet/dry analysis (n=3/group). Bronchoalveolar lavage fluid (BAL) was harvested 24 hours post-injury for single-cell RNA sequencing (scRNAseq) using matched numbers of viable cells from mice subjected to polytrauma (n=2) compared with sham controls (n=2).
Results: Polytrauma increased ALI compared to sham with evidence of histologic lung injury, increased lung vascular permeability and lung edema. scRNAseq of cells harvested from BAL identified a population of cells consisting primarily of macrophages based on the expression of macrophage markers CD68 and LYZ2 and the macrophage scavenger receptor, MARCO. Polytrauma increased a specific cluster of cells expressing these macrophage markers (see arrow in Figure). These clusters demonstrated increased expression of several genes related to the activation of cell cycle like cyclin-dependent kinase (CDK1), cyclin A2 (CCNA2), cell cycle associated protein (Cdca3), and the mitosis spindle regulating Kinesin-like proteins genes (KIF23 and KIFC1). Polytrauma was also associated with increased macrophage expression of the apoptosis inhibitor survivin (Birc5). Together, these increases in macrophage cell cycle support a model in which polytrauma induces a macrophage proliferation response.
Conclusion: Polytrauma promotes macrophage proliferation in the alveolar space by increasing the expression of genes that regulate the cell cycle and prevent apoptosis. Targeted therapies to control lung macrophage proliferation may be a strategy to prevent trauma-induced ALI.