Radiation-induced Lung Injury (RILI) in Non-human Primates (NHPs) Induces Cellular Senescence and Upregulation of Tyrosine Kinase Fgr, which is Detectable in Bronchoalveolar Lavage.

Radiation-induced lung injury (RILI) includes early acute phase radiation pneumonitis (RP), and late chronic phase radiation-induced pulmonary fibrosis (RIPF). There is increasing evidence that ionizing radiation-induced cellular senescence is associated with pulmonary fibrosis. We have recently reported that biomarkers of senescence and, specifically, tyrosine kinase Fgr are induced in mouse RIPF, human idiopathic pulmonary fibrosis (IPF), and in human RIPF. We also reported that treatment with an Fgr inhibitor significantly reduced fibrosis of irradiated mouse lungs. Here, we investigated the association of senescence and tyrosine kinase Fgr in non-human primate (NHP) lung fibrosis and determined whether lung fibrosis can be predicted by analyzing the bronchoalveolar lavage (BAL) cells and fluid at early time points after irradiation. We found that markers of senescence (p16, p21) and expression of Fgr are induced in the lungs of NHP with RILI. That fibrosis can be predicted by analyzing BAL cells prior to the appearance of pulmonary fibrosis. We also induced senescence and expression of Fgr in irradiated normal human primary airway epithelial cells in vitro. In a transwell culture system, we established that senescent human airway epithelial cells induced fibrosis biomarkers collagen1, collagen 3, and alpha-smooth-muscle actin in target human primary lung fibroblasts. Whole-thorax lung irradiated (WTLI) NHPs in this study developed moderate to severe pneumonitis and marked variations in the magnitude of RIPF as measured by trichrome staining. In BAL fluid that was collected from WTLI NHP senescence-associated secretory proteins (SASP) were significantly induced, compared to the BAL fluid collected from control non-irradiated NHPs. Moreover, the levels of Fgr and biomarkers of senescence were significantly higher in NHPs with severely injured lungs compared to those with mildly or moderately injured lungs as indicated by fibrosis. Proinflammatory SASP cytokines increased to levels that correlated with the severity of RILI. The results show that senescent cells with induction of Fgr, and SASP cytokines are detectable in NHPs prior to RIPF and suggest that analysis of these proteins can predict the severity of RIPF prior to fully formed fibrosis.