Neutrophil elastase-induced elastin degradation mediates macrophage influx and lung injury in 60% O₂-exposed neonatal rats

Abstract

Neutrophil (PMNL) influx precedes lung macrophage (LM) influx into the lung following exposure of newborn pups to 60% O2. We hypothesized that PMNL were responsible for the signals leading to LM influx. This was confirmed when inhibition of PMNL influx with a CXC chemokine receptor-2 antagonist, SB-265610, also prevented the 60% O2-dependent LM influx, LM-derived nitrotyrosine formation, and pruning of small arterioles. Exposure to 60% O2 was associated with increased lung contents of neutrophil elastase and α-elastin, a marker of denatured elastin, and a decrease in elastin fiber density. This led us to speculate that neutrophil elastase-induced elastin fragments were the chemokines that led to a LM influx into the 60% O2-exposed lung. Inhibition of neutrophil elastase with sivelestat or elafin attenuated the LM influx. Sivelestat also attenuated the 60% O2-induced decrease in elastin fiber density. Daily injections of pups with an antibody to α-elastin prevented the 60% O2-dependent LM influx, impaired alveologenesis, and impaired small vessel formation. This suggests that neutrophil elastase inhibitors may protect against neonatal lung injury not only by preventing structural elastin degradation, but also by blocking elastin fragment-induced LM influx, thus preventing tissue injury from LM-derived peroxynitrite formation.

The Extracellular Matrix in Bronchopulmonary Dysplasia: Target and Source

“…However, this was not the case with normobaric hyperoxia-based models in mice, where many reports also confirm that Eln mRNA levels were up-regulated by hyperoxia exposure, but there appeared to be a paucity of lung insoluble elastin, when (iso)desmosine was used as a surrogate for mature, insoluble elastin fibers ( 89 , 96 ). However, these observations are complicated by other reports of increased elastin protein in the hyperoxia models, employing either slot–blots ( 98 ) or immunoblots ( 51 , 93 ). This controversy must still be resolved.…”

“…In support of this idea, transgenic over-expression of elafin in the vascular endothelium similarly protected mice against the aberrant alveolarization and perturbed elastin assembly caused by mechanical ventilation ( 101 ). Subsequent exciting work by Keith Tanswell’s group has similarly reported that neutrophil elastase inhibition with sivelestat also improved lung structure and elastin deposition in the hyperoxia-based BPD animal model in mice ( 98 ). In this study, it is also noted that administration of anti-elastin antibodies in the mouse hyperoxia model of BPD prevented inflammatory infiltration into the lungs.…”

Elastase-Induced Parenchymal Disruption and Airway Hyper Responsiveness in Mouse Precision Cut Lung Slices: Toward an Ex vivo COPD Model

“…The effect of elastase on expression levels of alveolar Type I and II markers may be explained via several mechanisms. First, elastase-induced elastin fragments are known chemokines for macrophages in an adult murine model of emphysema, and elastin fragments can impair alveologenesis (Houghton et al, 2006; Masood et al, 2015). Second, mechanical stimuli are well-known to affect proliferation and differentiation of stem cells (Shah et al, 2014).…”

The Role of Neutrophil Proteins on the Amyloid Beta-RAGE Axis

“…Neutrophil elastase and cathepsin G belong to the PA clan, based on their 3D structure (double β barrel fold) and catalytic triad formed by Histidine (His), Asparagine (Asp), and Serine (Ser) residues [ 31 , 32 ]. Substrates cleaved by neutrophil elastase and cathepsin G include proteins involved in maintaining the integrity of the extracellular matrix such as fibronectin, laminin, and proteoglycans [ 33 – 35 ]. Neutrophil elastase also cleaves elastin and collagens [ 35 ].…”