Role of angiopoietin-2 in corneal lymphangiogenesis.

PURPOSE Lymphatic research has progressed rapidly in recent years. Lymphatic dysfunction has been found in myriad disorders from cancer metastasis to transplant rejection; however, effective treatment for lymphatic disorders is still limited. This study investigates the role of angiopoietin-2 (Ang-2) in corneal inflammatory lymphangiogenesis (LG) in vivo and in lymphatic endothelial cell (LEC) functions in vitro. METHODS Standard suture placement model was used to study Ang-2 expression in inflamed cornea, and corneal LG and hemangiogenesis (HG) responses in Ang-2 knockout mice. Moreover, human LEC culture system was used to examine the effect of Ang-2 gene knockdown on LEC functions using small interfering RNAs (siRNAs). The effect of siRNA treatment on corneal LG was also assessed in vivo. RESULTS Angiopoietin-2 was expressed on lymphatic vessels and macrophages in inflamed cornea. While corneal LG response was abolished in Ang-2 knockout mice, the HG response was also significantly suppressed with disorganized patterning. Moreover, anti-Ang-2 treatment inhibited LEC proliferation and capillary tube formation in vitro and corneal LG in vivo. CONCLUSIONS Angiopoietin-2 is critically involved in lymphatic processes in vivo and in vitro. Further investigation of the Ang-2 pathway may provide novel insights and therapeutic strategies for lymphatic-related disorders, which occur both inside and outside the eye.