Figure 3.

Effects of irradiation (IR) on senescence in mouse lung. C57Bl/6NCr mice were exposed to 0 Gy, 5 Gy, or 17.5 Gy thoracic IR. Samples of lung tissue (n = 3 per condition) were collected at intervals after IR and in control mice. A) Hierarchical clustering of samples based on senescence and aging genes. With the exception of the 2-week time point, lung tissue treated to 17.5 Gy clusters with lung from aged, unirradiated mice and aged 5 Gy mice (blue color coding). The remainder of the young mice (5 Gy and control) cluster together (red color coding). B) Representative images of β-galactosidase (β-gal) staining of lung tissue at 4 weeks after IR (left) and graphical representation of β-gal–stained cells per 20× field 4 weeks after IR (right). Scale bar = 16 μm, low power field (LPF). Bars represent mean. Error bars represent standard deviation. Bracket indicates P < .05 by analysis of variance. All statistical tests were two-sided. C) Representative low- (left) and high-power (right) images of costaining for β-gal activity (blue) and pro-surfactant C (pro-SPC) (brown) or p21 (brown) in lung tissue 4 weeks after 17.5 Gy of IR. Scale bar = 16 μm. W = week.