Neutrophil α-Defensins Cause Lung Injury by Disrupting the Capillary–Epithelial Barrier

Abstract

Rationale: The involvement of neutrophil activation in the sentinel, potentially reversible, events in the pathogenesis of acute lung injury (ALI) is only partially understood. a-Defensins are the most abundant proteins secreted by activated human neutrophils, but their contribution to ALI in mouse models is hindered by their absence from murine neutrophils and the inability to study their effects in isolation in other species. Objectives: To study the role of a-defensins in the pathogenesis of ALI in a clinically relevant setting using mice transgenic for polymorphonuclear leukocyte expression of a-defensins. Methods: Transgenic mice expressing polymorphonuclear leukocyte a-defensins were generated. ALI was induced by acid aspiration. Pulmonary vascular permeability was studied in vivo using labeled dextran and fibrin deposition. The role of the low-density lipoproteinrelated receptor (LRP) in permeability was examined. Measurements and Main Results: Acid aspiration induced neutrophil migration and release of a-defensins into lung parenchyma and airways. ALI was more severe in a-defensin-expressing mice than in wild-type mice, as determined by inspection, influx of neutrophils into the interstitial space and airways, histological evidence of epithelial injury, interstitial edema, extravascular fibrin deposition, impaired oxygenation, and reduced survival. Within 4 hours of insult, a-defensinexpressing mice showed greater disruption of capillary-epithelial barrier function and ALI that was attenuated by systemic or intratracheal administration of specific inhibitors of the LRP. Conclusions: a-Defensins mediate ALI through LRP-mediated loss of capillary-epithelial barrier function, suggesting a potential new approach to intervention.

α-Defensins Induce a Post-translational Modification of Low Density Lipoprotein (LDL) That Promotes Atherosclerosis at Normal Levels of Plasma Cholesterol

“…Mice-C57BL/6 mice expressing HNP-1 and HNP-2 in their neutrophils (Def ϩ/ϩ ) have been characterized previously (20,22). Animal care and experimentation were conducted in accordance with protocols approved by the Animal Care Committee of the Hebrew University.…”

“…To examine the role of endogenous ␣-defensins in the metabolism of LDL, we studied transgenic (Def ϩ/ϩ ) mice that express fully processed human ␣-defensins in their PMNs like their human counterparts (20). Levels of ␣-defensins in the plasma of Def ϩ/ϩ mice (74 Ϯ 11 g/liter) are comparable with plasma levels in healthy humans (15,18).…”

“…Therefore, existing mouse models of atherosclerosis do not reflect the complete contribution of inflammation, PMNs, or ␣-defensins to lesion development in humans. To help circumvent this problem, we recently characterized a transgenic mouse that expresses human ␣-defensins in its PMNs (Def ϩ/ϩ ) (20). Def ϩ/ϩ mice, which have a relatively low propensity to develop atherosclerosis even when fed a high fat diet (3,21), were bred onto a C57Bl6 ␣-defensins background (20), enabling us to isolate the contribution of Def Ϫ/Ϫ .…”

“…To help circumvent this problem, we recently characterized a transgenic mouse that expresses human ␣-defensins in its PMNs (Def ϩ/ϩ ) (20). Def ϩ/ϩ mice, which have a relatively low propensity to develop atherosclerosis even when fed a high fat diet (3,21), were bred onto a C57Bl6 ␣-defensins background (20), enabling us to isolate the contribution of Def Ϫ/Ϫ . Our data show that ␣-defensins induce a post-translational modification of LDL that alters its metabolism and disposition in the vasculature.…”

Non-Cardiogenic Pulmonary Edema

“…The EC gaps allow for permeability of fluid, neutrophils and cytokines into the pulmonary parenchymal space (Grommes & Soehnlein, 2011). The neutrophils that infiltrate the lungs and migrate into the airways express proinflammatory cytokines such as TNF-, IL-1 , IL-6 and contribute to both the endothelial and epithelial integrity disruption of the barriers (Bdeir et al, 2010;Grommes & Soehnlein, 2011;Abraham, 2003). It has also been well documented that the percentage of neutrophils correlates directly with the alveolar-arterial PO2 difference in ALI/ARDS pulmonary edema .…”