Genetic Dissection of Tie Pathway in Mouse Lymphatic Maturation and Valve Development

Abstract

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 Key Words: knockout mice ◼ lymphatic abnormality ◼ lymphatic vessel ◼ Tie-1 receptor tyrosine kinase ◼ Tie-2 receptor tyrosine kinase ◼ valve

GATA2 is required for lymphatic vessel valve development and maintenance

“…These valve-forming cells reorient themselves with respect to the longitudinal axis of the vessel, extend into the vessel lumen, and form elongated valve leaflets composed of a bilayer of endothelial cells sandwiching an extracellular matrix core composed largely of Fibronectin-EIIIA (FN-EIIIA), laminin-α5, and EMILIN1 (19)(20)(21). Genes identified to be important for lymphatic vessel valve development include the transcription factors FOXC2 and NFATC1 (15,20,22), the transmembrane ligand ephrinB2 (23), integrin-α9 and its ligands FN-EIIIA (19) and Emilin1 (21), gap junction proteins connexin37 (CX37) and connexin43 (CX43) (16,24), NOTCH1 (25), SEMA3A together with receptor components NRP1 and PLEXINA1 (26,27), angiopoietin2 (28,29), TIE1 (30), and BMP-9 (31). Though the signals that initiate valve development are in large part enigmatic, the location of valves predominantly in regions of disturbed flow suggested that mechanical stimuli including shear stress might be important valve-initiating stimuli.…”

Impaired angiopoietin/Tie2 signaling compromises Schlemm’s canal integrity and induces glaucoma

“…These findings led us to generate double Angpt1/Angpt2-deficient (A1:A2 (36,37) or Angpt2 fl/fl (38) mice with the ubiquitin-Cre-ER T2 mouse, depleted Angpt1 or Angpt2 starting at P1 by tamoxifen administration, and analyzed the tamoxifen-treated mice at P14 (Supplemental SCs compared with those of WT (Figure 7, A-G). Moreover, the A1:A2 iΔ/Δ mice had scant GVs, thinned RNFL, and markedly attenuated pSTR and PhNR ( Figure 8, A-H), results similar to those of a previous report (26).…”

Tie2 Expression on Macrophages Is Required for Blood Vessel Reconstruction and Tumor Relapse after Chemotherapy

“…To investigate the effect of Tie2 expression on macrophages after chemotherapy, we generated mice with Tie2 gene knockout in macrophages by the Cre-loxP system, as described before (27). Briefly, Tie2 deletion in the myeloid lineage, mainly neutrophils and monocytes/macrophages, was achieved by crossing the transgenic line with the lysozyme M promoter-driven Cre recombinase (Lyz-Cre) with Tie2…”