Thromb Haemost 2009; 101(06): 999-1005
DOI: 10.1160/TH08-06-0358
Theme Issue Article
Schattauer GmbH

Maturation of blood vessels by haematopoietic stem cells and progenitor cells: Involvement of apelin/APJ and angiopoietin/Tie2 interactions in vessel caliber size regulation

Nobuyuki Takakura
1   Department of Signal Transduction, Research Institute for Microbial Diseases, Osaka University, Osaka, Japan
,
Hiroyasu Kidoya
1   Department of Signal Transduction, Research Institute for Microbial Diseases, Osaka University, Osaka, Japan
› Author Affiliations

Financial support: This work was partly supported by the Japanese Ministry of Education, Culture, Sports, Science and technology.
Further Information

Publication History

Received: 09 June 2008

Accepted after minor revision: 23 January 2008

Publication Date:
24 November 2017 (online)

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Summary

Apelin is a recently-isolated bioactive peptide from bovine gastric extract. The gene encodes a protein of 77 amino acids, which can generate two active polypeptides, long (42–77) and short (65–77). Both peptides ligate and activate APJ, a G protein-coupled receptor expressed in the cardiovascular and central nervous systems. Although an essential role for the apelin/APJ system in blood vessel formation has been reported in Xenopus, its precise function in mammals is unclear. Blood vessel tube formation is accomplished by two main mechanisms: 1) single cell hollowing, in which a lumen forms within the cytoplasm of a single endothelial cell (EC), and 2) cord hollowing in which a luminal cavity is created de novo between ECs in a thin cylindrical cord. Molecular control of either single cell or cord hollowing has not been precisely determined. Angiopoietin-1 (Ang1) has been reported to induce enlargement of blood vessels. Apelin is produced from ECs upon activation of Tie2, a cognate receptor of Ang1, expressed on ECs. It has been suggested that apelin induces cord hollowing by promoting proliferation and aggregation/assembly of ECs. During angiogenesis, haematopoietic stem cells (HSCs) and progenitor cells (HPCs) are frequently observed in the perivascular region. They produce Ang1 and induce migration of ECs, resulting in a fine vascular network. Moreover, HSCs/HPCs can induce apelin production from ECs. Therefore, this review article posits that HSCs/HPCs regulate caliber size of blood vessels via apelin/APJ and Angiopoietin/Tie2 interactions.