Hyperoxia Decreases Matrix Metalloproteinase-9 and Increases Tissue Inhibitor of Matrix Metalloproteinase-1 Protein in the Newborn Rat Lung: Association with Arrested Alveolarization

Abstract

ABTRACT Matrix metalloproteinases (MMP) are likely effectors of normal lung development, especially branching morphogenesis, angiogenesis, and extracellular matrix degradation. Because hyperoxia exposure (Ͼ95% O 2 ) from d 4 to 14 in newborn rat pups leads to arrest of alveolarization and mimics newborn chronic lung disease, we tested whether hyperoxia altered MMP-2 and -9 mRNA, protein, and enzymatic activity, and the mRNA and protein expression of the endogenous tissue inhibitor of MMP, TIMP-1. No changes due to hyperoxia exposure were observed in MMP-2 mRNA or pro-enzyme (72 kD) protein levels between d 6 and 14, although the overall protein mass and zymographic activity of the active (68 kD) enzyme were diminished (p Ͻ 0.05, ANOVA). However, hyperoxia significantly decreased levels of MMP-9 mRNA and pro-MMP-9 protein and diminished overall MMP-9 pro-enzyme activity.TIMP-1 mRNA was not elevated by hyperoxia until d 14, but protein levels were significantly (p Ͻ 0.001) elevated by hyperoxia from d 9 to 14. To estimate the potential of MMP inhibition to arrest alveolarization, administration of doxycycline (20 mg/ kg, twice daily by gavage), a pan-MMP proteolysis inhibitor, arrested lung alveolarization. We conclude that hyperoxia decreases MMP-9 mRNA, protein, and activity and elevates TIMP-1 protein, and these changes have the potential to contribute to the arrest of normal lung development. Lung alveoli are formed when immature saccules subdivide into functional gas-exchange units through formation of secondary septa (1, 2). The process of septation involves budding from the primary septum (saccular wall), formation of a double-capillary network, elongation of septa, coalescence of vessels to form a single capillary layer, and thinning of the septal walls (1, 2). Exposure of neonatal rats to hyperoxia during alveolarization interferes with the process of septation; alveolar number and internal surface area are decreased and the parenchymal airspace is enlarged (3-5). These parameters persist up to d 40 (6). Hyperoxia during the neonatal period also alters lung connective tissue, alters elastic fiber structure and concentration (7), and causes an inflammatory reaction characterized by interalveolar edema and proteinosis (3,5,8). Chronic inflammation of the neonatal lung leads to fibrosis and thickening of the septa (3, 5).MMP are a group of proteases that exist as pro-enzymes and are cleaved by other MMP to active forms that have several specialized functions, including extracellular matrix turnover. Some of their functions regulate processes associated with development, such as branching morphogenesis and angiogenesis as well as inflammatory processes and wound healing (9). MMP-2 and MMP-9, also called gelatinases-A and -B, respectively, cleave gelatin, type IV and V collagen, and elastin. Types IV, V, and VII collagens are associated with basement membranes (10). MMP-2 and MMP-9 exhibit increased gelatinolytic activities as the lung develops (11), and during the postnatal lung growth stage both MMP-2 and MM...

Fas-Ligand-Induced Apoptosis of Respiratory Epithelial Cells Causes Disruption of Postcanalicular Alveolar Development

“…Whether the lower body weight of Dox-treated pups was the result of indirect effects on the nursing dams or direct effects on growth of the pups remains undetermined. In accordance with previous reports, 83 we further found that Dox negatively affects alveolar development, a phenomenon that has been attributed to its various nonantibiotic activities that include pan-MMP (matrix metalloproteinase) inhibition 83,84 and antiangiogenic and anti-inflammatory effects. 85 Importantly, this study was controlled for Doxrelated effects by comparing Dox-treated double-transgenic CCSP ϩ /FasL ϩ animals with Dox-treated CCSP ϩ / FasL Ϫ littermates.…”

“…Two distinct Dox-related phenotypic effects were identified in the present study. As previously described by others in postnatal rats, 83 we found that Dox treatment during the perinatal period had adverse effects on early postnatal somatic growth. Whether the lower body weight of Dox-treated pups was the result of indirect effects on the nursing dams or direct effects on growth of the pups remains undetermined.…”

Role of matrix metalloprotease-9 in hyperoxic injury in developing lung

“…Our study confirms reports of increased MMP-9 with hyperoxia and further shows that deletion of MMP-9 improves the response to hyperoxia of the developing lung. On the other hand, one study described decreased levels of MMP-9 mRNA and pro-MMP-9 protein and diminished pro-MMP-9 enzyme activity in neonatal rat pups exposed to Ͼ95% oxygen (24). The different findings in that study compared with ours could be related to the fact that the authors of that study measured pro-MMP-9 protein and activity, whereas we focused on mature MMP-9.…”

Determination of the Role of Target Tissue Metabolism in Lung Carcinogenesis Using Conditional Cytochrome P450 Reductase-Null Mice

“…The systemic administration of doxycycline at relatively high doses was found to cause fetoplacental toxicity (45) and alveolar simplification (46). In the present study, doxycycline was given to mice in the diet at f1.9 mg/d/mouse, a dose that was found previously to have no effects on pregnancy or postnatal alveolarization (44).…”