Emerging evidence demonstrates that proangiogenic cells (PACs) originate from the BM and are capable of being recruited to sites of ischemic injury where they contribute to neovascularization. We previously determined that among hematopoietic progenitor stem cells, common myeloid progenitors (CMPs) and granulocyte-macrophage progenitor cells (GMPs) differentiate into PACs and possess robust angiogenic activity under ischemic conditions. Herein, we report that a TGF-1-responsive Krü ppellike factor, KLF10, is strongly expressed in PACs derived from CMPs and GMPs, ϳ 60-fold higher than in progenitors lacking PAC markers. KLF10 ؊/؊ mice present with marked defects in PAC differentiation, function, TGF- responsiveness, and impaired blood flow recovery after hindlimb ischemia, an effect rescued by wild-type PACs, but not KLF10 ؊/؊ PACs. Overexpression studies revealed that KLF10 could rescue PAC formation from TGF-1 ؉/؊ CMPs and GMPs. Mechanistically, KLF10 targets the VEGFR2 promoter in PACs which may underlie the observed effects. These findings may be clinically relevant because KLF10 expression was also found to be significantly reduced in PACs from patients with peripheral artery disease. Collectively, these observations identify TGF-1 signaling and KLF10 as key regulators of functional PACs derived from CMPs and GMPs and may provide a therapeutic target during cardiovascular ischemic states. (Blood.
2011;118(24):6450-6460) IntroductionAccumulating evidence suggests that in healthy persons, circulating endothelial progenitor cells, broadly defined as proangiogenic cells (PACs), represent a population of BM-derived stem and progenitor cells responsible for repairing injured tissue and initiating neovasculogenesis. 1,2 Potentiation of PAC mobilization, homing, or adhesion has been shown to ameliorate the development of ischemic injury in animal models. 1,2 In addition, blockade of proangiogenic cytokines or their signaling pathways is believed to alter PAC function and to lead to impaired angiogenesis in response to vascular injury and in end-organ ischemia. 1,2 Indeed, reduced levels of circulating PACs and diminished PAC function have been reported and found to correlate with a wide spectrum of atherosclerotic vascular diseases, including peripheral artery disease (PAD). [3][4][5] Several early phase 1/2 trials have been conducted to assess the efficacy of cell-based therapies to treat patients with PAD but have yielded mixed results. 1,2,6-9 Identification of specific PAC subtypes that are endowed with superior capacity to promote neovascularization may represent a particularly efficacious therapeutic strategy. We have demonstrated that among hematopoietic progenitor stem cells, the common myeloid progenitors (CMPs) and granulocytemacrophage progenitors (GMPs) constitute a population of BMderived cells that preferentially differentiate into PACs and possess robust angiogenic activity under ischemic conditions in vivo. 10 However, the signaling pathways and downstream factors that mediate these proangiogenic...