CXCR4 regulates migration of lung alveolar epithelial cells through activation of Racl and matrix metalloproteinase-2

摘要

Restoration of the epithelial barrier following acute lung injury is critical for recovery of lung homeostasis. After injury, alveolar type II epithelial (ATII) cells spread and migrate to cover the denuded surface and, eventually, proliferate and differentiate into type I cells. The chemokine CXCL12, also known as stromal cell-derived factor la, has well-recognized roles in organogenesis, hematopoiesis, and immune responses through its binding to the chemokine receptor CXCR4. While CXCL12/CXCR4 signaling is known to be important in immune cell migration, the role of this chemokine-receptor interaction has not been studied in alveolar epithelial repair mechanisms. In this study, we demonstrated that secretion of CXCL12 was increased in the bron-choalveolar lavage of rats ventilated with an injurious tidal volume (25 ml/kg). We also found that CXCL12 secretion was increased by primary rat ATE cells and a mouse alveolar epithelial (MLE12) cell line following scratch wounding and that both types of cells express CXCR4. CXCL12 significantly increased ATI! cell migration in a scratch-wound assay. When we treated cells with a specific antagonist for CXCR4, AMD-3100, cell migration was significantly inhibited. Knockdown of CXCR4 by short hairpin RNA (shRNA) caused decreased cell migration compared with cells expressing a nonspecific shRNA. Treatment with AMD-3100 decreased matrix metalloprotei-nase-14 expression, increased tissue inhibitor of metalloproteinase-3 expression, decreased matrix metalloproteinase-2 activity, and prevented CXCL12-induced Racl activation. Similar results were obtained with shRNA knockdown of CXCR4. These findings may help identify a therapeutic target for augmenting epithelial repair following acute lung injury.