No abstract

Bronchopulmonary dysplasia (BPD) continues to be a major cause of morbidity in premature infants. An imbalance between neutrophil elastase and its inhibitors has been implicated in BPD. Serine protease inhibitor (SERPIN)B1 is an inhibitor of neutrophil proteases, including neutrophil elastase (NE) and cathepsin G (cat G). Recent studies suggest that SERPINB1 could provide protection in the airways by regulating excess protease activity associated with inflammatory lung disorders. In this study, we determined the distribution and ontogeny of SERPINB1 in the baboon lung and characterized the expression of SERPINB1 in baboon models of BPD. SERPINB1 expression was detected in the conducting airway and glandular epithelial cells in addition to neutrophils, macrophages, and mast cells. SERPINB1 mRNA and protein expression increased with advancing gestational age and in the new BPD model. In contrast, SERPINB1 expression levels were decreased in the old BPD model. Furthermore, SERPINB1 was detected as a high-molecular-mass (HMM) complex in lung tissue and bronchoalveolar lavage fluid samples from the BPD group. Analysis of the HMM complex by coimmunoprecipitation showed that these complexes were formed between SERPINB1 and NE or cat G. High-performance liquid chromatography (HPLC) ion trap mass spectrometry verified the presence of SERPINB1 in HMM complexes. Finally, NE activity level was compared between new and old baboon models of BPD and was found to be significantly lower in new BPD. Thus SERPINB1 upregulation in new BPD may be protective by contributing to the regulation of neutrophil proteases NE and cat G.

Rationale: Bronchopulmonary dysplasia (BPD) is a chronic lung disease that adversely affects long-term pulmonary function as well as neurodevelopmental outcomes of preterm infants. Elastolytic proteases have been implicated in the pathogenesis of BPD. Cathepsin S (cat S) is a cysteine protease with potent elastolytic activity. Increased levels and activity of cat S have been detected in a baboon model of BPD. Objectives: To investigate whether deficiency of cat S alters the course of hyperoxia-induced neonatal lung injury in mice. Methods: Newborn wild-type and cat S-deficient mice were exposed to 80% oxygen for 14 days. Histologic and morphometric analysis were performed and bronchoalveolar lavage protein and cells were analyzed. Lung elastin was assessed by real-time polymerase chain reaction, in situ hybridization, desmosine analysis, and Hart's stain. Distribution of myofibroblasts was analyzed by immunofluorescence. Hydroxyproline content of lung tissues was measured. Measurements and Main Results: Hyperoxia-exposed cat S-deficient mice were protected from growth restriction and had improved alveolarization, decreased septal wall thickness, lower number of macrophages, and lower protein concentration in bronchoalveolar lavage fluid. a-Smooth muscle actin-expressing myofibroblasts accounted for at least some of the increased interstitial cellularity in hyperoxia-exposed mouse lungs and were significantly less in cat S-deficient lungs. Lung hydroxyproline content was increased in hyperoxia-exposed wild-type, but not in cat S-deficient lungs. Desmosine content was significantly reduced in both genotypes with hyperoxia. Conclusions: Cathepsin S deficiency improves alveolarization, and attenuates macrophage influx and fibroproliferative changes in hyperoxia-induced neonatal mouse lung injury.Keywords: cathepsin; bronchopulmonary dysplasia; hyperoxia; myofibroblast Advanced perinatal care over the past decade has resulted in improved survival of very-low-birth-weight (VLBW) (birth weight , 1,500 g) infants (1). However, surviving VLBW infants have increased risk of major morbidities, particularly bronchopulmonary dysplasia (BPD). BPD has a negative impact on not only short-term and long-term pulmonary function but also on overall growth and neurodevelopment of VLBW infants (2-4). The major pathologic findings associated with BPD in surfactant-treated lungs are inflammation, disrupted alveolar development, and variable amounts of fibrosis (5). Exposure of the immature lung to hyperoxia, prolonged mechanical ventilation, and antenatal or postnatal infections are primary risk factors for BPD (6, 7). However, the molecular mechanisms that link these factors to disruption of alveolarization are not completely understood and there are currently no evidence-based strategies to prevent or treat BPD.Several studies have shown that alveolar elastin expressed by myofibroblasts is a critical component of alveolar development (8, 9). The impaired alveolar development in BPD is also accompanied by changes in deposition of elas...