《Arteriosclerosis, Thrombosis, and Vascular Biology》 6:1221-1230 （2014）
Genetic dissection of tie pathway in mouse lymphatic maturation and valve development
Shen, Bin; Shang, Zhi; Wang, Bo; Zhang, Luqing; Zhou, Fei; Li, Taotao; Chu, Man; Jiang, Haijuan; Wang, Ying; Qiao, Tong; Zhang, Jun; Sun, Wei; Kong, Xiangqing; He, Yulong
OBJECTIVE: The genetic program underlying lymphatic development is still incompletely understood. This study aims to dissect the role of receptor tyrosine kinase with immunoglobulin-like and EGF (epidermal growth factor)-like domains 1 (Tie1) and Tie2 in lymphatic formation using genetically modified mouse models. APPROACH AND RESULTS: We generated conditional knockout mouse models targeting Tie1, Tie2, and angiopoietin-2 in this study. Tie1(ΔICD/ΔICD) mice, with its intracellular domain targeted, appeared normal at E10.5 but displayed subcutaneous edema by E13.5. Lymph sac formation occurred in Tie1(ΔICD/ΔICD) mice, but they had defects with the remodeling of primary lymphatic network to form collecting vessels and valvulogenesis. Consistently, induced deletion of Tie1-ICD postnatally using a ubiquitous Cre deleter led to abnormal lymphangiogenesis and valve formation in Tie1-ICD(iUCKO/-) mice. In comparison with the lymphatic phenotype of Tie1 mutants, we found that the diameter of lymphatic capillaries was significantly less in mice deficient of angiopoietin-2, besides the disruption of collecting lymphatic vessel formation as previously reported. There was also no lymphedema observed in Ang2(-/-) mice during embryonic development, which differs from that of Tie1(ΔICD/ΔICD) mice. We further investigated whether Tie1 exerted its function via Tie2 during lymphatic development. To our surprise, genetic deletion of Tie2 (Tie2(iUCKO/-)) in neonate mice did not affect lymphatic vessel growth and maturation. CONCLUSIONS: In contrast to the important role of Tie2 in the regulation of blood vascular development, Tie1 is crucial in the process of lymphatic remodeling and maturation, which is independent of Tie2.