Arginase and α‐smooth muscle actin induction after hyperoxic exposure in a mouse model of bronchopulmonary dysplasia

Abstract

The L-arginine/NO pathway is an important regulator of pulmonary hypertension, the leading cause of mortality in patients with the chronic lung disease of prematurity, bronchopulmonary dysplasia. L-arginine can be metabolized by NO synthase (NOS) to form L-citrulline and NO, a potent vasodilator. Alternatively, L-arginine can be metabolized by arginase to form urea and L-ornithine, a precursor to collagen and proline formation important in vascular remodelling. In the current study, we hypothesized that C3H/HeN mice exposed to prolonged hyperoxia would have increased arginase expression and pulmonary vascular wall cell proliferation. C3H/HeN mice were exposed to 14 days of 85% O or room air and lung homogenates analyzed by western blot for protein levels of arginase I, arginase II, endothelial NOS (eNOS), ornithine decarboxylase (ODC), ornithine aminotransferase (OAT), and α-smooth muscle actin (α-SMA). Hyperoxia did not change arginase I or eNOS protein levels. However, arginase II protein levels were 15-fold greater after hyperoxia exposure than in lungs exposed to room air. Greater protein levels of ODC and OAT were found in lungs following hyperoxic exposure than in room air animals. α-SMA protein levels were found to be 7-fold greater in the hyperoxia exposed lungs than in room air lungs. In the hyperoxia exposed lungs there was evidence of greater pulmonary vascular wall cell proliferation by α-SMA immunohistochemistry than in room air lungs. Taken together, these data are consistent with a more proliferative vascular phenotype, and may explain the propensity of patients with bronchopulmonary dysplasia to develop pulmonary hypertension.

Interleukin-1 Receptor Antagonist Protects Newborn Mice Against Pulmonary Hypertension

“…It is possible that the absence of an increase in arterial α-SMA in hyperoxic pulmonary arteries in our mouse model could explain these discrepancies. However, increased α-SMA associated with vascular smooth muscle thickening in pulmonary arteries of hyperoxic mice was also reported in a study which had applied 85% O 2 (83). We have shown that 85% O 2 represents a more severe model of BPD (19) when compared to the 65% O 2 we applied here; thus, a lower O 2 level could account for the absence of ex vivo vascular reactivity and markers of vascular remodeling in our study.…”

L‐citrulline increases arginase II protein levels and arginase activity in hypoxic piglet pulmonary artery endothelial cells

“…The products of ODC and OAT play an important role in endothelial and smooth muscle cell proliferation and collagen synthesis, respectively, and therefore are thought to contribute to pathologic vascular remodeling in some forms of PH. 19 , 39 Considering our result that L-citrulline increases arginase activity, we expected an increase in ODC and OAT protein abundance due to the likely increase in the shared substrate and product of arginase activity, L-ornithine. However, we found that ODC and OAT protein levels were not increased at any concentration of L-citrulline that we studied, including concentrations that increased arginase activity in hypoxic PAECs ( Fig.…”

Silencing of Long Non-Coding RNA X Inactive Specific Transcript (Xist) Contributes to Suppression of Bronchopulmonary Dysplasia Induced by Hyperoxia in Newborn Mice via microRNA-101-3p and the transforming growth factor-beta 1 (TGF-β1)/Smad3 Axis

“…Collagen I is mainly localized in bronchi, alveolar septa, and blood vessels, and was overexpressed in patients with BPD, resulting in failure of alveolar septation during BPD progression [ 25 ]. According to a recent study, protein levels of α-SMA in lung tissues and blood vessels of BPD mice induced by hyperoxia were far higher than those in normal mice [ 26 ]. These experiments strongly suggest that Xist promotes BPD malignancy.…”