High Tidal Volume Ventilation Activates Smad2 and Upregulates Expression of Connective Tissue Growth Factor in Newborn Rat Lung

Abstract

High tidal volume (V T ) ventilation plays a key role in ventilator induced lung injury and bronchopulmonary dysplasia. However, little is known about the effect of high V T on expression of growth factors that are critical to lung development. In a previous study, we demonstrated that connective tissue growth factor (CTGF) inhibits branching morphogenesis. In this study, we investigated the effect of high V T on CTGF expression in newborn rat lungs. Newborn rats were ventilated with normal V T (10 mL/kg) or high V T (25 mL/kg) for 6 h. Nonventilated animals served as controls. We found that high V T upregulated CTGF expression. To identify the potential signaling pathways mediating high V T induction of CTGF, newborn rats were ventilated with high V T for 1 or 3 h. Temporal expression of TGF-␤s, p-Smad2, Smad7, and CTGF was analyzed. High V T ventilation did not change gene expression of TGF-␤s and Smad7 but induced rapid and sustained expression of p-Smad2 that precedes increased CTGF expression. CTGF and p-Smad2 were localized in bronchiolar epithelial cells, alveolar walls and septa. These data suggest that high V T ventilation activates the Smad2 pathway, which may be responsible for downstream induction of CTGF expression in newborn rat lungs. M echanical ventilation is essential for managing prematurely born infants with respiratory failure. However, ventilation with high tidal volume (V T ) can lead to ventilator induced lung injury (VILI) and bronchopulmonary dysplasia (BPD) (1-3). The lung pathology of BPD is characterized by fewer and larger alveoli, dysmorphic and decreased capillary network, and variable interstitial fibrosis, suggesting abnormal lung development and injury repair processes (4,5). Most of the studies in VILI and BPD have been focused on high V T induced lung proinflammatory response (6 -9). Little is known about the effect of high V T on expression of growth factors that are key to lung development and injury repair in neonatal lungs.Connective tissue growth factor (CTGF) belongs to the CCN family of early gene products with a high degree of amino acid sequence homology and 38 conserved cysteine residues (10,11). CTGF promotes fibroblast proliferation, extracellular matrix (ECM) production, myofibroblast differentiation, and cell adhesion and migration (12-16). CTGF is a potent profibrotic cytokine and its mRNA and protein levels have been correlated with the degree of lung fibrosis in bleomycin-treated mice and in human fibrotic lung disorders (17)(18)(19). Previous studies have demonstrated that mechanical stress drastically induces CTGF expression in cultured fibroblasts (20,21). CTGF is closely linked to TGF-␤. Studies have demonstrated that TGF-␤ is a major inducer of CTGF expression in a variety of tissues and organs including the lung (11,(22)(23)(24). Activation of the Smad pathway plays a key role in TGF-␤ induction of CTGF expression (25,26). TGF-␤ stimulation of fibroblast proliferation, collagen synthesis, and myofibroblast differentiation is mediated via a CTG...

Highly conserved transcriptional responses to mechanical ventilation of the lung

“…GPC3, which has not been previously associated with VILI, was repressed in our samples and is repressed by TGF-␤ (66). CTGF was upregulated in our study and is induced by high tidal ventilation in newborn rats (89). GRP was significantly upregulated in the baboon data set and contributes to impaired lung development in premature baboons with mechanical ventilation support (74).…”

Glycogen synthase kinase-3β/β-catenin signaling regulates neonatal lung mesenchymal stromal cell myofibroblastic differentiation

“…Serum levels of CTGF correlate with the extent of pulmonary fibrosis in patients with systemic sclerosis (24). High tidal volume ventilation upregulates CTGF expression in the newborn rat lung (29). CTGF mRNA expression increases within 30 min of mechanical ventilation in preterm lambs (27).…”

Transforming growth factor-β modulates the expression of nitric oxide signaling enzymes in the injured developing lung and in vascular smooth muscle cells

“…For example, studies have documented increased TGF-␤ levels in the pulmonary effluents of premature infants with oxygen-and ventilator-induced lung injury, often followed by the development of bronchopulmonary dysplasia (38,42). TGF-␤ signaling is also increased in models of newborn lung injury (2,13,39,78,83), and overexpression of active TGF-␤ causes pathological changes in the newborn lung that are similar to those observed in premature infants with chronic lung disease (27,76). However, the data supporting the role of TGF-␤ in newborn lung disease are not consistent.…”