Genetic basis of murine responses to hyperoxia-induced lung injury

Abstract

To evaluate the effect of genetic background on oxygen (O2) toxicity, nine genetically diverse mouse strains (129/SvIm, A/J, BALB/cJ, BTBR+(T)/tf/tf, CAST/Ei, C3H/HeJ, C57BL/6J, DBA/2J, and FVB/NJ) were exposed to more than 99% O2 for 72 h. Immediately following the hyperoxic challenge, the mouse strains demonstrated distinct pathophysiologic responses. The BALB/cJ and CAST/Ei strains, which were the only strains to demonstrate mortality from the hyperoxic challenges, were also the only strains to display significant neutrophil infiltration into their lower respiratory tract. In addition, the O2-challenged BALB/cJ and CAST/Ei mice were among six strains (A/J, BALB/cJ, CAST/Ei, BTBR+(T)/tf/tf, DBA/2J, and C3H/HeJ) that had significantly increased interleukin 6 concentrations in the whole lung lavage fluid and were among all but one strain that had large increases in lung permeability compared with air-exposed controls. In contrast, the DBA/2J strain was the only strain not to have any significant alterations in lung permeability following hyperoxic challenge. The expression of the extracellular matrix proteins, including collagens I, III, and IV, fibronectin I, and tenascin C, also varied markedly among the mouse strains, as did the activities of total superoxide dismutase (SOD) and manganese-SOD (Mn-SOD or SOD2). These data suggest that the response to O2 depends, in part, on the genetic background and that some of the strains analyzed can be used to identify specific loci and genes underlying the response to O2.

Fig. 1

Wet-to-dry ratios of the right lungs from inbred mouse strains that were either exposed to >99% O₂ or room air (control) for 72 hours. The strains were ranked according to the differences of wet-to-dry ratios between the hyperoxic and control mice. The wet-to-dry ratios are used as a marker of pulmonary edema. Data are presented as the mean ± SEM for n = 6 per group. * Significantly different (P ≤ 0.05) from control group (One-way ANOVA).

Fig. 2

The concentration of total protein in the whole-lung lavage fluid from inbred mouse strains that were either exposed to >99% O₂ or room air (control) for 72 hours. An increase in total protein was used as an indicator of lung permeability elicited by hyperoxia. The strains were ranked according to the increase of total protein in the lavage fluid from the hyperoxic mice of each strain. Data are presented as the mean ± SEM for n = 6 per group. * Significantly different (P ≤ 0.05) from control group (One-way ANOVA).

Fig. 3

Number of total cells in the whole-lung lavage fluid from various strains of mice that were either exposed to >99% O₂ or room air (control) for 72 hours. Data are presented as the mean ± SEM for n = 6 per group. * Significantly different (P ≤ 0.05) from control group (One-way ANOVA).

Fig. 4

Number (a) and percentage (b) of neutrophils in the whole-lung lavage fluid from various strains of mice that were exposed to >99% O₂ for 72 hours. The numbers and percentages of neutrophils from the air-exposed (control) mice of each strain were < 50.0 neutrophils/ml and < 2.0 %, respectively. Data are presented as the mean ± SEM for n = 6 per group. * Significantly different (P ≤ 0.05) from control group (One-way ANOVA).

Fig. 5

IL-6 concentrations in the whole-lung lavage of various strains of mice following exposure to >99% O₂ for 72 hours. Data are presented as the mean ± SEM for n = 6 per group. The concentrations of IL-6 for the air-exposed (control) mice of each strain were < 5.0 pg/ml. * Significantly different (P ≤ 0.05) from control group.

Fig. 6

Expression of procollagens I (a), III (b) and IV (c) in the lungs of various strains of mice exposed to >99% O₂ for 72 hours. For each strain, data represent the percent change of expression between a minimum of four hyperoxic-treated and air-exposed (control) mice. * Significantly different (P ≤ 0.05) from control group.

Fig. 7

Expression of Fn I (a) and Ten C (b) in the lungs of various strains of mice exposed to >99% O₂ for 72 hours. For each strain, data represent the percent change of expression between a minimum of four hyperoxic-treated and air-exposed (control) mice. * Significantly different (P ≤ 0.05) from control group.

Fig. 8

Total SOD activity (a) and SOD2 (Mn-SOD) activity (b) in the lungs of various strains of mice exposed to >99% O₂ for 72 hours, and the percent differences between the hyperoxic- and air-exposed (control) mice (n = 6 per group). The % differences of total and SOD2 activity between the hyperoxic and control mice were determined by ((hyperoxic – control/control)* 100). The mouse strains were ranked according to the activity for that group. * Significantly different (P ≤ 0.05) from control group.

Fig. 9

Cosegregation plots for the activity of Total SOD (a) and SOD2 (Mn-SOD) (b) in the lungs of various strains of mice exposed to >99% O₂ for 72 hours versus our ranking of susceptibility of the mouse strains following oxidant injury (Table 2). A low score of susceptibility determined a mouse strain relatively insensitive (i.e. DBA/2J) and a high score determined a mouse strain sensitive (i.e. A/J). Note the scales for the y-axis are different for each Figure. For each strain, total SOD and SOD2 data are presented as the mean values of samples from 6 mice.

Fig. 10

Changes of SOD1 (Cu/Zn SOD) plus SOD3 (EC-SOD) activity (total SOD activity minus the SOD2 activity) between mice exposed to O₂ (hyperoxic) and room air (control) for 72 hours. For each strain, a mean value of samples from at least four hyperoxic and control mice were used to obtain the mean SOD1 + SOD3 activity. Note that the DBA/2J strain, which is the most resistant strain to hyperoxia injury, has the greatest decrease in activity; and the BALB/cJ strain, which is one of the most susceptible, has the greatest increase in activity.