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Elastin plays a key role in lung mechanodevelopment, and patient data suggests that prematurely born infants who show evidence of elastin remodeling after the first postnatal week are less likely to develop chronic lung disease (bronchopulmonary dysplasia). We seek to understand the mechanisms of elastin remodeling in the developing lung. Total lung elastase activity is highest during the saccular and alveolar stages of lung development and is significantly reduced after alveolarization is complete. By zymography, in situ zymography, and immunofluorescence, we hypothesized that a serine protease named chymotrypsin-like elastase-1 (CELA1) was involved. CELA1 was expressed in vascular cells during embryonic lung development, pulmonary arterial adventitial cells immediately following birth, and in lung fibroblasts during alveolar development. Expression increased throughout development and during lung regeneration. CELA1 was expressed in area of elastin remodeling during lung development. CELA1 expression was higher in mouse models of lung fibrosis.
The pulmonary vasculature is essential for effective gas exchange in the lung. The mechanisms by which it aligns with the growing alveolus are unknown. Angiogenesis is known to occur along elastin strands and elastin degradation products are known to be angiogenic. CELA1 was expressed in vascular cells in the embryonic lung and in a fetal mesenchymal cell line with angiogeneic properties. Elastase inhibition and CELA1 silencing reduced angiogenesis. Transfecting CELA1 into pulmonary fibroblasts imparted an angiogenic phenotype. Our laboratory is currently investigating whether CELA1’s effects are due to its elastolytic properties and determining mechanism of action.
We determined that in mice right pulmonary arterial elastin structure becomes altered 72 hours after left pneumonectomy. We also developed a model of measuring right pulmonary arterial compliance and found it increased following ligature of the left pulmonary artery. We will determine the signaling mechanism and key proteases involved in this remodeling utilizing mRNA sequencing data from right pulmonary arteries and then utilize the above techniques in combination with appropriate activators, inhibitors, or transgenic mice to test this mechanism and develop new therapies for regulating pulmonary vascular compliance and potentially treating pulmonary hypertension.
Click image for caption.
Lung CELA1 mRNA and protein increased throughout lung development and during lung regeneration. CELA1 was expressed in vascular cells in embryonic lung development and was associated with pulmonary arterial elastin remodeling on postnatal day zero. CELA1 was expressed in lung fibroblasts during alveolar development (not shown).
Mouse fetal mesenchymal cells form tubules when cultured in matrigel. Elastase inhibition (top right) largely prevents tubule formation. CELA1 shRNA (middle right) also inhibits tubule formation compared to control shRNA (middle left). Rat fetal lung fibroblasts (bottom left) do not normally form tubules but do when transfected with mouse CELA1 (bottom right).
Confocal imaging of the luminal surface of mouse right pulmonary arteries demonstrates increased size of elastin fenestrae 72 hours after left pneumonectomy.
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