Deficiency in type 1 insulin-like growth factor receptor in mice protects against oxygen-induced lung injury

Abstract

Background: Cellular responses to aging and oxidative stress are regulated by type 1 insulin-like growth factor receptor (IGF-1R). Oxidant injury, which is implicated in the pathophysiology of a number of respiratory diseases, acutely upregulates IGF-1R expression in the lung. This led us to suspect that reduction of IGF-1R levels in lung tissue could prevent deleterious effects of oxygen exposure.

Methods: Since IGF-1R null mutant mice die at birth from respiratory failure, we generated compound heterozygous mice harboring a hypomorphic (Igf-1rneo) and a knockout (Igf-1r-) receptor allele. These IGF-1Rneo/- mice, strongly deficient in IGF-1R, were subjected to hyperoxia and analyzed for survival time, ventilatory control, pulmonary histopathology, morphometry, lung edema and vascular permeability.

Results: Strikingly, after 72 h of exposure to 90% O2, IGF-1Rneo/- mice had a significantly better survival rate during recovery than IGF-1R+/+ mice (77% versus 53%, P < 0.05). The pulmonary injury was consistently, and significantly, milder in IGF-1Rneo/- mice which developed conspicuously less edema and vascular extravasation than controls. Also, hyperoxia-induced abnormal pattern of breathing which precipitated respiratory failure was elicited less frequently in the IGF-1Rneo/- mice.

Conclusion: Together, these data demonstrate that a decrease in IGF-1R signaling in mice protects against oxidant-induced lung injury.

Figure 1

Lung weight and histology under basal conditions. (A) Mean values (×100) of lung-to-body weight ratio (± SD) in IGF-1R^+/+ mice (male: n = 11; female: n = 5) and IGF-1R^neo/- mice (male: n = 7; female: n = 4). (B) Representative histology of hematoxylin-eosin stained lung sections from IGF-1R^+/+ and IGF-1R^neo/- mice. Magnification: 10× objective.

Figure 2

Survival rate following exposure to 90% oxygen. The survival times of IGF-1R^+/+ mice (male: n = 15; female: n = 15) and IGF-1R^neo/- mice (male: n = 16; female: n = 15) were measured following exposure to 90% oxygen. Data are expressed as percentage of mice alive at each time point. The asterisk indicates significant differences between IGF-1R^+/+ and IGF-1R^neo/- mice, as determined by Kaplan-Meier analysis; P < 0.05.

Figure 4

Ventilatory responses before and after hyperoxia, and during recovery. Minute ventilation (V_E) in response to decreasing levels of inspired O₂. In each one of the three conditions, mean values (± SD) of VE in IGF-1R^+/+ and IGF-1R^neo/- mice were recorded under 90% O₂, 21% O₂ and at two levels of hypoxia (12% and 10% O₂). Values with asterisks are significantly different from control values at 90% O₂. Crosses indicate significant differences from normoxic control values, and asterisks indicate significant differences between IGF-1R^+/+ and IGF-1R^neo/- mice; P < 0.05.

Figure 3

Respiratory pattern before and after hyperoxia. Typical respiratory pattern in a control IGF-1R^+/+ mouse (upper traces) and in an IGF-1R^neo/- mouse (lower traces) under basal conditions and following hyperoxia. Expiratory pauses were observed in most control mice but not in IGF-1R^neo/- mice.

Figure 5

Histology following hyperoxic injury. Hematoxylin-eosin stained lung sections of (a) IGF-1R^+/+, and (b) IGF-1R^neo/- mice following 72 h of hyperoxic exposure, illustrating perivascular and peribronchiolar edema as indicated by asterisks. Magnification: 10× objective. Representative histology of lung sections demonstrates (c) focal alveolar hemorrhages (black arrow) and hyaline membrane formation (gray arrow) in IGF-1R^+/+ lungs, and (d) minimal lesions in IGF-1R^neo/- mice. Magnification: 40× objective.

Figure 6

Hyperoxia-induced lung injury, lung edema and vascular permeability. Parameters of lung damage were considered under basal conditions and following hyperoxia. (A) Lung injury scores from IGF-1R^+/+ (n = 4) and IGF-1R^neo/- (n = 4) mice under basal conditions (normoxia) and under hyperoxia. A cumulative score was based on evaluation of hemorrhage and intraalveolar deposition (6 random sections per lung). (B) Quantitated perivascular edema from IGF-1R^+/+ (n = 4) and IGF-1R^neo/- (n = 4) mice under basal conditions (normoxia) and under hyperoxia. Surface of perivascular edema was reported to the surface of the vessel, and noted S_E/S_V (5 selected sections per lung). (C) Lung edema was determined as mean values (± SD) of wet-to-dry lung weight ratio under basal conditions (normoxia) in IGF-1R^+/+ (n = 4) and IGF-1R^neo/- (n = 4) mice, and under hyperoxia in IGF-1R^+/+ (n = 7) and IGF-1R^neo/- (n = 8) mice. (D) Evans Blue dye extravasation was assessed as mean values (± SD) in IGF-1R^+/+ (n = 13) and IGF-1R^neo/- (n = 11) mice. Crosses indicate significant differences between hyperoxic and normoxic values in IGF-1R^+/+ mice, and asterisks indicate significant differences between IGF-1R^+/+ and IGF-1R^neo/- mice under hyperoxic conditions; P < 0.05.