Abstract 14781: Tie2-expressing Monocytes: An Angiogenic Target In Tissue Ischaemia
Introduction Angiogenic cell therapy using unselected populations of mononuclear cells has been of limited benefit in the revascularisation of critically ischaemic tissue. Monocytes expressing the angiopoietin receptor, Tie2 (CD14+Tie2+, TEMs), are mobilised and migrate to sites of hypoxia in tumours, where they are thought to have a pivotal role in neovascularisation of the tumour. These cells may, therefore, represent an angiogenic target in the development of a novel cell therapy for tissue ischaemia.
Hypothesis TEMs are mobilised in patients with critical limb ischaemia (CLI) and have angiogenic activity.
Results Flow cytometric analysis showed that the proportion of monocytes expressing Tie2 (lineage[CD3, CD56, CD19]-/CD14+/Tie2+ cells) was 10-fold higher in blood from patients with CLI (n=40) than in matched (n=20) and young (n=20) controls (3.52%±0.28 vs 0.39%±0.09 and 0.23%±0.04 respectively, P<0.0001). Immunohistochemical analysis showed that TEMs were present in perivascular spaces in ischaemic, but not normoxic muscle. Removal of the ischaemic stimulus by revascularisation or amputation resulted in a fall in circulating TEMs to control levels (P<0.001). Tie2 mRNA expression in FACS-sorted TEMs was confirmed by RT-PCR. TEMs induced significantly greater in vitro endothelial cell tube formation (Matrigel assay: length P=0.015 and area P=0.012), compared with Tie2- monocytes from the same subjects. Circulating levels of the Tie2 ligand, angiopoietin-2 (Ang-2), were over 2-fold higher (799±128 vs 384±62pg/ml) in CLI patients compared with matched controls (P<0.05). Intracellular flow cytometric assays confirmed angiopoietin-induced phosphorylation of the Tie2 receptor in TEMs, followed by activation of early and late Erk1/2 and Akt downstream signaling pathways. This did not occur in Tie2- monocytes isolated from the same subjects.
Conclusion These data suggest that the Tie2/Ang2 axis in monocytes is an important mechanism in the response to tissue ischaemia, by acting as an endogenous angiogenic drive. These cells may represent a novel therapeutic target that warrants further investigation for the revascularisation of patients with end stage tissue ischaemia.
- © 2011 by American Heart Association, Inc.