John Benjamin - US grants

PROJECT SUMMARY Perinatal inflammation is an established risk factor for bronchopulmonary dysplasia (BPD), a major morbidity of prematurity characterized by abnormal saccular stage lung development. As the airway epithelium is present at the interface of the amniotic sac environment and the fetal lung, it is well positioned to respond to inflammatory stimuli in amniotic fluid. Therefore, we developed a transgenic mouse model to inducibly express the master inflammatory transcription factor NF-?B, in the airway epithelium (IKTA mice). Using this model, we showed that epithelial-derived inflammation results in profound dilation of terminal airspaces during the saccular stage, but does not alter earlier stages of lung development. Airspace dilation in saccular stage IKTA lungs was associated with reduced expression of important elastin assembly components, especially fibulin-5, by interstitial fibroblasts, leading to altered elastic fiber assembly around distal airspaces. In new preliminary data generated to identify epithelial-derived inhibitors of elastin assembly components in fibroblasts, we found that lungs of IKTA mice and tracheal aspirates (TA) from preterm infants exposed to antenatal inflammation had high levels of IL-1 (both IL- 1? and IL-1?). Neutralizing IL-1? or IL-1? restored fibulin-5 expression in fibroblasts exposed to bronchoalveolar lavage fluid (BAL) from IKTA mice or TA from preterm infants. Since IL-1 triggers intracellular signaling via NF- ?B, we tested the direct impact of NF-?B on saccular stage lung fibroblasts and observed that NF-?B signaling inhibited fibulin-5 mRNA expression. Finally, by modifying our transgenic mouse model to enable survival beyond the early postnatal period, we found that inflammation-induced disruption in saccular stage elastin organization results in persistent abnormalities in lung structure. Proposed studies will test the hypothesis that during the saccular stage of lung development, epithelial-derived inflammation propagates down-stream NF-?B activation in fibroblasts through IL-1 signaling, resulting in down-regulation of fibulin-5 and other critical elastin assembly components. Disruption of elastin organization during this critical developmental window impairs lung development, leading to abnormalities in lung structure and function that persist into adulthood. Specific aims are: 1) to define the role of IL-1 signaling in regulation of elastic fiber assembly components, 2) to determine the transcriptional regulation of fibulin-5 in lung fibroblasts during development and in response to inflammation, and 3) to investigate the long-term impact of impaired saccular stage elastin assembly. Together, our studies will determine how inflammation during a critical developmental window can modulate lung structure and function, thus providing new insights into BPD pathogenesis and the long-term consequences of altered saccular stage lung development.

Abstract Emerging data indicate that up to 50% of Chronic Obstructive Pulmonary Disease (COPD) results from failure to attain maximal lung function in early adulthood, rather than accelerated decline in lung function later in life. Because lung function trajectories are established soon after birth, deficits in lung function in infancy may persist and predispose to COPD in adulthood. Many preterm infants are born with lungs in the saccular stage of development. Lung inflammation in these infants can lead to bronchopulmonary dysplasia (BPD), a complication of prematurity characterized by altered development with dilated and fewer airspaces in the distal lung. Along with respiratory morbidity during childhood, patients with BPD are at risk for reduced peak lung function in their adult years and may develop COPD. To understand mechanisms connecting aberrant early lung development to long-term abnormalities in lung growth and function, we developed a transgenic model in which IKK?, an upstream activator of NF-?B, can be expressed in the lungs in a developmental-stage specific manner. Using this model, we found that transient inflammation in the saccular stage (but not the alveolar stage) reduced expression of fibulin-5, a critical elastin assembly component, and resulted in altered elastic fiber organization and dilated terminal airspaces. Remarkably, mice with saccular stage inflammation demonstrated persistent abnormalities in lung elastic fiber organization and developed a COPD-like phenotype with emphysema and loss of alveolar attachments that progressed from 2 to 24 months of age. Neutrophil depletion during the saccular stage rescued the lung phenotype in these mice. Further, we found that neutrophil elastase downregulates fibulin-5 expression by mouse lung fibroblasts and alters saccular stage elastin assembly ex vivo, potentially through activation of epidermal growth factor receptor signaling. These findings support the hypothesis that neutrophil elastase downregulates fibulin-5 expression and alters elastic fiber assembly in the saccular stage lung, thereby predisposing to COPD in adulthood. Specific aims are designed to: 1) delineate the mechanisms by which neutrophils impair elastic fiber assembly in the saccular stage, 2) determine the role and regulation of mesenchymal-derived fibulin-5 in elastic fiber assembly during lung development, and 3) investigate the long-term effects of impaired elastic fiber assembly in the lung. Collectively, proposed studies will determine the impact of inflammation during a critical developmental window on both neonatal and adult lung disease. A mechanistic understanding of the developmental origins of COPD will empower future investigations to prevent and/or treat this debilitating disease.