Stromal Cell-Derived Factor-1α/C-X-C Chemokine Receptor Type 4 Axis Promotes Endothelial Cell Barrier Integrity via Phosphoinositide 3-Kinase and Rac1 Activation

Objective-Although stromal cell-derived factor (SDF)-1 alpha is well known to modulate the mobilization of hematopoietic stem cells and endothelial progenitor cells, its effects on some pre-existing vascular functions remain unknown. We have investigated here the role of SDF-1 alpha signaling in endothelial barrier function. Approach and Results-Treatment with SDF-1 alpha elevated transendothelial electrical resistance and inhibited the dextran hyperpermeability elicited by thrombin in bovine aortic endothelial cells, both indicating an increase in endothelial barrier function. SDF-1 alpha binds to 2 receptors, C-X-C chemokine receptor types 4 and 7 (CXCR4 and CXCR7). Pretreatment with a CXCR4 antagonist or CXCR4 gene depletion by small interfering RNA (siRNA) eliminated SDF-1 alpha- induced endothelial barrier enhancement. In contrast, CXCR7 antagonist or CXCR7 gene depletion by siRNA did not influence SDF-1 alpha-induced barrier enhancement. Pretreatment with a Gi-protein inhibitor, a phosphoinositide 3-kinase (PI3K) inhibitor, or PI3K p110 gamma subunit gene depletion by siRNA also inhibited SDF-1 alpha-induced barrier enhancement significantly. Western blot analysis revealed that SDF-1 alpha phosphorylated Akt(Ser473) in endothelial cells, suggesting PI3K activation. Immunostaining showed that treatment with SDF-1 alpha formed a cortical actin rim, which was accompanied by Rac1 activation. In vivo, SDF-1 alpha inhibited croton oil-induced vascular leakage indexed by dye extravasation, which is attenuated by a pretreatment with a CXCR4 antagonist. Conclusions-We have identified SDF-1 alpha as a novel suppressor of endothelial permeability. Specifically, SDF-1 alpha stimulates the CXCR4/PI3K/Rac1 signaling pathway and the subsequent cytoskeletal rearrangement.