Bronchoalveolar lavage fluid from immature rats with hyperoxia-induced airway remodeling is mitogenic for airway smooth muscle.

Abstract

We previously demonstrated that hyperoxia-exposed immature rats develop airway smooth muscle layer thickening; this remodeling appears partially attributable to smooth muscle hyperplasia. In this study, we tested the hypothesis that excess mitogenic activity for airway smooth muscle cells is present within the lungs of hyperoxia-exposed immature rats. We assessed the proliferative effect of bronchoalveolar lavage (BAL) fluid from air- and O2-exposed animals on cultured rat tracheal smooth muscle cells. BAL fluids from air- or O2-exposed immature rats increased DNA synthesis ([3H]-thymidine incorporation at 24 h of incubation) and cell number (compared with DMEM-treated control cells, at 2 days of incubation), but BAL fluid from O2-exposed animals had significantly greater mitogenic effects. This excess mitogenic activity was lipid inextractable and was ablated by trypsin digestion, indicating that at least one polypeptide growth factor was responsible; molecular sieve fractionation demonstrated a molecular weight of > 10 kD. Because platelet-derived growth factor (PDGF) has been identified in other models of hyperoxia exposure, we tested the further hypothesis that PDGF contributes to the observed excess mitogenic activity. Addition of neutralizing anti-PDGF antibodies to BAL-stimulated smooth muscle cultures did not reduce BAL fluid-induced mitogenesis. These data indicate that the lungs of O2-exposed rats contain excess mitogenic activity for airway smooth muscle, attributable to non-PDGF polypeptide growth factors. It is conceivable that this abnormal mitogenic activity contributes to O2-induced airway smooth muscle remodeling observed in immature rats in vivo.

Prolonged Moderate Hyperoxia Induces Hyperresponsiveness and Airway Inflammation in Newborn Rats

“…A hyperplastic process resulting in airway epithelial and smooth muscle layer thickening induced by high O 2 exposure in immature rats has been demonstrated by cellular DNA synthesis (17). Furthermore, the lungs of O 2 -exposed rats showed excess airway smooth muscle mitogenic activity, attributable to the presence of one or more non-PDGF (plateletderived growth factor) polypeptide growth factor(s) (18). It is possible that this abnormal mitogenic activity is essential to O 2 -induced airway smooth muscle remodeling observed in immature rats in vivo.…”

Endogenous LXR signaling controls pulmonary surfactant homeostasis and prevents lung inflammation

“…Peritoneal macrophages (4x10 5 cells/well) and MLE-12 cells (1.5x10 5 MLE-12 cells/well) were cultured for 24 h on culture chamber slides, precoated with FBS for MLE-12 cells. Subsequently, the cells were incubated with bronchoalveolar lavage uid (BALF) from WT and LXR-DKO mice, according to an adapted version of the previously established [19]. After overnight incubation with BALF, the cells were washed several times with PBS and xed with 4% PFA containing a 1:5000 dilution of Hoechst 33342 dye for 30 minutes.…”

β-Hexosaminidases: Potent Mitogens of Airway Smooth Muscle

“…8 In addition, bronchoalveolar lavage fluid from immature rats with hyperoxia-induced airway remodeling has been shown to stimulate ASMC proliferation. 9 Finally, airway remodeling including ASMC proliferation has been shown to correlate with airway responsiveness. Thus, the pathological ASMC proliferation that is a component of airway remodeling and airway wall thickening may represent a novel target for the development of anti-asthma drugs.…”