Mouse lung contains endothelial progenitors with high capacity to form blood and lymphatic vessels.

BACKGROUND: Postnatal endothelial progenitor cells (EPCs) have been successfully isolated from whole bone marrow, blood and the walls of conduit vessels. They can, therefore, be classified into circulating and resident progenitor cells. The differentiation capacity of resident lung endothelial progenitor cells from mouse has not been evaluated. RESULTS: In an attempt to isolate differentiated mature endothelial cells from mouse lung we found that the lung contains EPCs with a high vasculogenic capacity and capability of de novo vasculogenesis for blood and lymph vessels.Mouse lung microvascular endothelial cells (MLMVECs) were isolated by selection of CD31+ cells. Whereas the majority of the CD31+ cells did not divide, some scattered cells started to proliferate giving rise to large colonies (> 3000 cells/colony). These highly dividing cells possess the capacity to integrate into various types of vessels including blood and lymph vessels unveiling the existence of local microvascular endothelial progenitor cells (LMEPCs) in adult mouse lung. EPCs could be amplified > passage 30 and still expressed panendothelial markers as well as the progenitor cell antigens, but not antigens for immune cells and hematopoietic stem cells. A high percentage of these cells are also positive for Lyve1, Prox1, podoplanin and VEGFR-3 indicating that a considerabe fraction of the cells are committed to develop lymphatic endothelium. Clonogenic highly proliferating cells from limiting dilution assays were also bipotent. Combined in vitro and in vivo spheroid and matrigel assays revealed that these EPCs exhibit vasculogenic capacity by forming functional blood and lymph vessels. CONCLUSION: The lung contains large numbers of EPCs that display commitment for both types of vessels, suggesting that lung blood and lymphatic endothelial cells are derived from a single progenitor cell.

Elevated expression of VEGFR-3 in lymphatic endothelial cells from lymphangiomas.

BACKGROUND: Lymphangiomas are neoplasias of childhood. Their etiology is unknown and a causal therapy does not exist. The recent discovery of highly specific markers for lymphatic endothelial cells (LECs) has permitted their isolation and characterization, but expression levels and stability of molecular markers on LECs from healthy and lymphangioma tissues have not been studied yet. We addressed this problem by profiling LECs from normal dermis and two children suffering from lymphangioma, and also compared them with blood endothelial cells (BECs) from umbilical vein, aorta and myometrial microvessels. METHODS: Lymphangioma tissue samples were obtained from two young patients suffering from lymphangioma in the axillary and upper arm region. Initially isolated with anti-CD31 (PECAM-1) antibodies, the cells were separated by FACS sorting and magnetic beads using anti-podoplanin and/or LYVE-1 antibodies. Characterization was performed by FACS analysis, immunofluorescence staining, ELISA and micro-array gene analysis. RESULTS: LECs from foreskin and lymphangioma had an almost identical pattern of lymphendothelial markers such as podoplanin, Prox1, reelin, cMaf and integrin-alpha1 and -alpha9. However, LYVE-1 was down-regulated and VEGFR-2 and R-3 were up-regulated in lymphangiomas. Prox1 was constantly expressed in LECs but not in any of the BECs. CONCLUSION: LECs from different sources express slightly variable molecular markers, but can always be distinguished from BECs by their Prox1 expression. High levels of VEGFR-3 and -2 seem to contribute to the etiology of lymphangiomas.

Embryonic development and malformation of lymphatic vessels.

In the human, malformations of lymphatic vessels can be observed as lymphangiectasia, lymphangioma and lymphangiomatosis, with a prevalence of 1.2-2.8 per thousand. Their aetiology is unknown and a causal therapy does not exist. We investigated the origin of lymphatic endothelial cells (LECs) in avian and murine embryos, and compared the molecular profile of LECs from normal and malformed lymphatics of children. In avian embryos, Prox1+ lymphangioblasts are located in the confluence of the cranial and caudal cardinal veins, where the jugular lymph sac (JLS) forms. Cell lineage studies show that the JLS is of venous origin. In contrast, the lymphatics of the dermis are derived from mesenchymal lymphangioblasts located in the dermatomes, suggesting a dual origin of LECs in avian embryos. The same may hold true for murine embryos, where Lyve1+ LEC precursors are found in the cardinal veins, and in the mesenchyme. The mesenchymal cells express the pan-leukocyte marker CD45, indicating a cell type with lymphendothelial and leukocyte characteristics. In the human, such cells might give rise to Kaposi's sarcoma. Microarray analyses of LECs from lymphangiomas of children show a large number of regulated genes, such as VEGFR3. Our studies show that lymphvasculogenesis and lymphangiogenesis occur simultaneously in the embryo, and suggest a function for VEGFR3 in lymphangiomas.