Functional differences between two Tie2 ligands, angiopoietin-1 and -2, in regulation of adult bone marrow hematopoietic stem cells.
OBJECTIVE
Angiopoietin-1 (Ang-1) plays a critical role in the maintenance of hematopoietic stem cells (HSCs) in the bone marrow (BM) through its binding to the Tie2 receptor. Ang-2, another Tie2 ligand, is known to be an antagonist of Tie2/Ang-1 signaling in angiogenesis; however, its function in regulation of HSCs remains unclear. Here, we investigated the functional differences between Ang-1 and Ang-2 in the maintenance of HSCs.


METHODS
We treated mouse BM lineage(-)Sca-1(+)c-Kit(+) side population(+) cells with Ang-1 and/or Ang-2, and evaluated angiopoietin function by gene expression analysis, immunocytochemical staining of phosphorylated Akt, a colony-formation assay, and a long-term BM reconstitution assay.


RESULTS
Gene expression analysis and BM transplantation assay revealed that Ang-1 upregulated expression of p57, p18, Itgb1, Alcam, Tie2, Hoxb4, and Bmi1 genes in HSCs, while Ang-2 antagonized the effects of Ang-1. Ang-1 enhanced the phosphorylation of Akt, while Ang-2 again reduced the effect of Ang-1. The colony assay demonstrated that neither Ang-1, nor Ang-2 influenced the colony formation of HSCs. BM transplantation assay, following in vitro cultivation of HSCs with angiopoietins, showed that Ang-1 maintained long-term repopulating activity of HSCs, while the addition of Ang-2 interfered drastically with the effects of Ang-1.


CONCLUSIONS
Gene expression analysis and BM transplantation assay demonstrated that Ang-1 maintained HSC activity in an in vitro culture. In contrast, Ang-2 reversed the effects of Ang-1/Tie2 signaling in the regulation of long-term HSCs. Our data suggest that Ang-1 is a dominant ligand for the Tie2 receptor in long HSCs in BM.
Gomei
Yumiko
Y
Department of Cell Differentiation, The Sakaguchi Laboratory of Developmental Biology, School of Medicine, Keio University, Tokyo, Japan.
Nakamura
Yuka
Y
Yoshihara
Hiroki
H
Hosokawa
Kentaro
K
Iwasaki
Hiroko
H
Suda
Toshio
T
Arai
Fumio
F
D042683:Angiopoietin-1 / Q000037:antagonists & inhibitors / Q000494:pharmacology / Q000502:physiology*; D042702:Angiopoietin-2 / Q000494:pharmacology / Q000502:physiology*; D000818:Animals; D001854:Bone Marrow Cells / Q000166:cytology / Q000378:metabolism; D016026:Bone Marrow Transplantation; D002448:Cell Adhesion / Q000235:genetics; D002455:Cell Division / Q000187:drug effects; D002478:Cells, Cultured; D003114:Colony-Forming Units Assay; D005786:Gene Expression Regulation / Q000187:drug effects; D006412:Hematopoietic Stem Cells / Q000166:cytology / Q000502:physiology*; D051379:Mice; D008807:Mice, Inbred BALB C; D010766:Phosphorylation / Q000187:drug effects; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D042787:Receptor, TIE-2 / Q000378:metabolism*
D042683:Angiopoietin-1; D042702:Angiopoietin-2; D042787:Receptor, TIE-2; D051057:Proto-Oncogene Proteins c-akt