Integrin-Linked Kinase, a Hypoxia-Responsive Molecule, Controls Postnatal Vasculogenesis by Recruitment of Endothelial Progenitor Cells to Ischemic Tissue

Abstract

Background-Recruitment and adhesion of endothelial progenitor cells (EPCs) to hypoxic endothelial cells (ECs) isessential for vasculogenesis in ischemic tissue; little is known, however, about the key signals or intracellular signaling pathways involved in orchestrating the expression of adhesion molecules by ECs in response to hypoxia and how this is related to the recruitment of EPCs to the ischemic tissue. Here, we report that endogenous integrin-linked kinase (ILK) is a novel molecule that responds to hypoxia in ECs that regulates the expression of stromal cell-derived factor-1 (SDF-1) and intercellular adhesion molecule-1 (ICAM-1) through nuclear factor-B and hypoxia-inducible factor-1␣ and induces recruitment of EPCs to ischemic areas. Methods and Results-Under hypoxia, both the endogenous amount and kinase activity of ILK were time-dependently upregulated in ECs, which was associated with increased ICAM-1 and SDF-1. This upregulation of ILK was mediated by stabilization of ILK by heat shock protein 90. ILK overexpression in normoxic ECs resulted in ICAM-1 and SDF-1 upregulation through dual control by nuclear factor-B and hypoxia-inducible factor-1␣. Blockade of ILK in hypoxic ECs significantly abrogated the expression of both molecules, which led to decreased EPC incorporation into ECs. A hindlimb ischemia model showed that ILK blockade significantly reduced EPC homing to ischemic limb and consequently led to poor neovascularization. Overexpression of ILK in the Matrigel plug significantly improved neovascularization in vivo, whereas the blockade of ILK resulted in the opposite effect. Conclusions-Endogenous

The SDF-1–CXCR4 signaling pathway: a molecular hub modulating neo-angiogenesis

“…Increased expression of SDF-1 in human and rodent models of infarcted myocardium has been confirmed by several studies [14][15][16][17]. SDF-1 expression was increased as early as 1h after induction of hypoxia in the myocardium or hindlimbs, suggesting a role in the initiation of tissue repair and revascularization [13,18,19]. Taken together, these data suggest that induction of SDF-1 by hypoxia provides an effective means to recruit circulating cells into neo-angiogenic niches.…”

“…Ceradini et al have demonstrated that SDF-1 expression in ischemic sites is directly correlated with the amplitude of hypoxia [12]. Signaling activated by hypoxia leading to SDF-1 upregulation involves the recruitment of integrin-linked kinase and hypoxia-inducible factor-1 (HIF-1) [12,13]. Increased expression of SDF-1 in human and rodent models of infarcted myocardium has been confirmed by several studies [14][15][16][17].…”

Nonproteolytic Properties of Murine Alternatively Spliced Tissue Factor: Implications for Integrin-Mediated Signaling in Murine Models

“…to significantly upregulate SDF1 (Cxcl12) expression in human ECs (33). Because we established that hasTF, and now masTF, ligate integrins, these TF variants could well trigger ILK-dependent signaling in murine ECs.…”

iNOS-Derived Nitric Oxide Induces Integrin-Linked Kinase Endocytic Lysosome-Mediated Degradation in the Vascular Endothelium

“…Other models of neointimal formation have reported similar results, including balloon catheter carotid injury, where a decrease in ILK has been reported at the media layer, and re-expression at the luminal surface may attenuate this process during later stages of the injury response. 13 Additional examples include ablation of ILK in cultured endothelial cells, resulting in defective cell spreading, or progenitor endothelial cells lacking ILK which lead to defective vasculogenesis and embryonic lethality between E8.5 and E12.5, 37 whereas, in the adult, the absence of ILK produced endothelial dysfunction. 6 Despite the relevant role of ILK in the cardiovascular system, the mechanism of ILK stability has not been studied in detail.…”