Department of Pediatrics, University of Michigan Medical School, Ann Arbor, Michigan, USA.
Am J Physiol Lung Cell Mol Physiol. 2012 Sep;303(5):L439-48. doi: 10.1152/ajplung.00408.2011. Epub 2012 Jul 6.
In bronchopulmonary dysplasia (BPD), alveolar septa are thickened with collagen and α-smooth muscle actin-, transforming growth factor (TGF)-β-positive myofibroblasts. We examined the biochemical mechanisms underlying myofibroblastic differentiation, focusing on the role of glycogen synthase kinase-3β (GSK-3β)/β-catenin signaling pathway. In the cytoplasm, β-catenin is phosphorylated on the NH(2) terminus by constitutively active GSK-3β, favoring its degradation. Upon TGF-β stimulation, GSK-3β is phosphorylated and inactivated, allowing β-catenin to translocate to the nucleus, where it activates transcription of genes involved in myofibroblastic differentiation. We examined the role of β-catenin in TGF-β1-induced myofibroblastic differentiation of neonatal lung mesenchymal stromal cells (MSCs) isolated from tracheal aspirates of premature infants with respiratory distress. TGF-β1 increased β-catenin expression and nuclear translocation. Transduction of cells with GSK-3β S9A, a nonphosphorylatable, constitutively active mutant that favors β-catenin degradation, blocked TGF-β1-induced myofibroblastic differentiation. Furthermore, transduction of MSCs with ΔN-catenin, a truncation mutant that cannot be phosphorylated on the NH(2) terminus by GSK-3β and is not degraded, was sufficient for myofibroblastic differentiation. In vivo, hyperoxic exposure of neonatal mice increases expression of β-catenin in α-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-3β, β-catenin, and α-actin content compared with MSCs from infants not developing this disease, and phospho-GSK-3β and β-catenin each correlated with α-actin content. We conclude that phospho-GSK-3β/β-catenin signaling regulates α-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.
在支气管肺发育不良（BPD）中，肺泡间隔增厚，伴有胶原蛋白和α-平滑肌肌动蛋白、转化生长因子（TGF）-β阳性肌成纤维细胞。我们研究了肌成纤维细胞分化的生化机制，重点关注糖原合酶激酶-3β（GSK-3β）/β-连环蛋白信号通路的作用。在细胞质中，β-连环蛋白在 NH2 末端被组成性激活的 GSK-3β磷酸化，有利于其降解。在 TGF-β刺激下，GSK-3β被磷酸化失活，允许β-连环蛋白易位到细胞核，在那里它激活参与肌成纤维细胞分化的基因的转录。我们研究了β-连环蛋白在来自有呼吸窘迫早产儿气管抽吸物的肺间充质基质细胞（MSCs）中 TGF-β1 诱导的肌成纤维细胞分化中的作用。TGF-β1 增加了β-连环蛋白的表达和核易位。用 GSK-3β S9A 转导细胞，GSK-3β S9A 是一种非磷酸化的组成性激活突变体，有利于β-连环蛋白降解，可阻断 TGF-β1 诱导的肌成纤维细胞分化。此外，用不能被 GSK-3β 在 NH2 末端磷酸化且不能降解的截断突变体 ΔN-catenin 转导 MSCs 足以诱导肌成纤维细胞分化。在体内，新生小鼠的高氧暴露增加了α-平滑肌肌动蛋白阳性肌成纤维细胞中β-连环蛋白的表达。在 BPD 婴儿的肺中也发现了类似的变化。最后，与未发生这种疾病的婴儿相比，来自发生 BPD 的婴儿的低传代未刺激 MSCs 显示出更高的磷酸化 GSK-3β、β-连环蛋白和α-肌动蛋白含量，并且磷酸化 GSK-3β 和 β-连环蛋白均与α-肌动蛋白含量相关。我们得出结论，磷酸化 GSK-3β/β-连环蛋白信号通路调节体外和体内的α-平滑肌肌动蛋白表达，这是肌成纤维细胞分化的一个标志物。该途径似乎在 BPD 患者的肺间质细胞中被激活。
