Rat aorta-derived mural precursor cells express the Tie2 receptor and respond directly to stimulation by angiopoietins

Abstract

Recent studies have implicated the Tie2 tyrosine-kinase receptor and its main ligands - angiopoietin-1 (Ang-1) and angiopoietin-2 (Ang-2) - as crucial regulators of mural cell recruitment during angiogenesis. Angiopoietin-mediated activation of Tie2 promotes perivascular mural cell assembly, but the mechanisms regulating this process are poorly understood because differentiated mural cells do not have the Tie2 receptor, which is reportedly expressed only in endothelial cells. There is also no direct evidence that Tie2 activation results in production of mural cell chemoattractants by the endothelium. In the rat aorta model of angiogenesis,developing microvessels recruit mural cells from the intimal/subintimal layers of the aortic wall. Ang-1 and Ang-2 promote angiogenesis in this system,stimulating branching morphogenesis and mural cell assembly. Mural precursor cells (MPCs) isolated with a nonenzymatic method from the intimal aspect of the rat aorta were positive for smooth muscle cell markers (α-smooth muscle actin and calponin) and negative for endothelial markers(factor-VIII-related antigen and CD31). These cells responded chemotactically to Ang-1 and Ang-2, and secreted MMP-2 when treated with these factors. Western-blot analysis, immunocytochemistry and RT-PCR demonstrated that MPCs express the Tie2 receptor. Immunoprecipitation showed phosphorylation of MPC Tie2 on tyrosine residues upon stimulation with Ang-1 or Ang-2. Surface expression of Tie2 was further demonstrated by isolating Tie2+/α-smooth muscle actin+ MPCs from primary aortic outgrowths with anti-Tie2-IgG-coated magnetic beads. Immunostaining of the rat aorta confirmed expression of Tie2 not only in endothelial cells but also in nonendothelial mesenchymal cells located in the aortic intimal/subintimal layers, which are the source of MPCs. These data indicate that the aortic wall contains Tie2+ nonendothelial mesenchymal cells and suggest that Tie2-related recruitment of mural cells during angiogenesis may occur through angiopoietin-mediated direct stimulation of these cells.

Dopamine stabilizes tumor blood vessels by up-regulating angiopoietin 1 expression in pericytes and Krüppel-like factor-2 expression in tumor endothelial cells

“…In addition, these experiments performed in serum-starved HBVP suggested that the effect of DA on Ang1 expression in pericytes is direct and is not the result of its actions on other growth factors. Furthermore, because there are reports indicating that up-regulation of Ang1 in pericytes stimulates migration of these cells (46,47), we examined the action of DA on HBVP migration (SI Results and Fig. S6).…”

Paracrine regulation of angiogenesis by different cell types in the aorta ring model

“…Ang1 promotes the assembly of the vessel wall by directly stimulating mural progenitor cells that express the Ang1 receptor Tie2 (Iurlaro et al, 2003;Howson et al, 2005) or by indirectly stimulating mural cells through the induction in endothelial cells of chemotactic factors such as CCL2 (Aplin et al, 2010). Interestingly, mural cell recruitment is also stimulated by Ang2 (Iurlaro et al, 2003), which was initially reported as an antagonist of Ang1 (Maisonpierre et al, 1997), but later recognized as a potential Tie2 activator whose agonist function was strongly influenced by contextual cues (Teichert-Kuliszewska et al, 2001). The migration and proliferation of mural cells is critically dependent on the p38 MAPK signaling pathway which can be activated by a number of angiogenic regulators including PDGFB and Ang1 (Yamaguchi et al, 2001;.…”

Formation of Stable Vascular Networks in Engineered Tissues

“…By treating the culture with vessel maturation factors, such as Ang-1 and MCP-1, increased MC recruitment was observed in this model. (Aplin et al, 2010;Iurlaro et al, 2003) However, since the model uses an organ part with multiple cell types, many other undefined cell types can also contribute to the network formation. It is difficult to isolate the contribution of each cell type in this model.…”