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

Popova AP, Bentley JK, Anyanwu AC, Richardson MN, Linn MJ, Lei J, Wong EJ, Goldsmith AM, Pryhuber GS, Hershenson MB. Glycogen synthase kinase-3 beta/beta-catenin signaling regulates neonatal lung mesenchymal stromal cell myofibroblastic differentiation. Am J Physiol Lung Cell Mol Physiol 303: L439-L448, 2012. First published July 6, 2012; doi:10.1152/ajplung.00408.2011.-In bronchopulmonary dysplasia (BPD), alveolar septa are thickened with collagen and alpha-smooth muscle actin-, transforming growth factor (TGF)-beta-positive myofibroblasts. We examined the biochemical mechanisms underlying myofibroblastic differentiation, focusing on the role of glycogen synthase kinase-3 beta (GSK-3 beta)/beta-catenin signaling pathway. In the cytoplasm, beta-catenin is phosphorylated on the NH2 terminus by constitutively active GSK-3 beta, favoring its degradation. Upon TGF-beta stimulation, GSK-3 beta is phosphorylated and inactivated, allowing beta-catenin to translocate to the nucleus, where it activates transcription of genes involved in myofibroblastic differentiation. We examined the role of beta-catenin in TGF-beta 1-induced myofibroblastic differentiation of neonatal lung mesenchymal stromal cells (MSCs) isolated from tracheal aspirates of premature infants with respiratory distress. TGF-beta 1 increased beta-catenin expression and nuclear translocation. Transduction of cells with GSK-3 beta S9A, a nonphosphorylatable, constitutively active mutant that favors beta-catenin degradation, blocked TGF-beta 1-induced myofibroblastic differentiation. Furthermore, transduction of MSCs with Delta N-catenin, a truncation mutant that cannot be phosphorylated on the NH2 terminus by GSK-3 beta and is not degraded, was sufficient for myofibroblastic differentiation. In vivo, hyperoxic exposure of neonatal mice increases expression of beta-catenin in alpha-smooth muscle actin-positive myofibroblasts. Similar changes were found in lungs of infants with BPD. Finally, low-passage unstimulated MSCs from infants developing BPD showed higher phospho-GSK-3 beta, beta-catenin, and alpha-actin content compared with MSCs from infants not developing this disease, and phospho-GSK-3 beta and beta-catenin each correlated with alpha-actin content. We conclude that phospho-GSK-3 beta/beta-catenin signaling regulates alpha-smooth muscle actin expression, a marker of myofibroblast differentiation, in vitro and in vivo. This pathway appears to be activated in lung mesenchymal cells from patients with BPD.