Existence, functional impairment, and lung repair potential of endothelial colony-forming cells in oxygen-induced arrested alveolar growth.

BACKGROUND: Bronchopulmonary dysplasia and emphysema are life-threatening diseases resulting from impaired alveolar development or alveolar destruction. Both conditions lack effective therapies. Angiogenic growth factors promote alveolar growth and contribute to alveolar maintenance. Endothelial colony-forming cells (ECFCs) represent a subset of circulating and resident endothelial cells capable of self-renewal and de novo vessel formation. We hypothesized that resident ECFCs exist in the developing lung, that they are impaired during arrested alveolar growth in experimental bronchopulmonary dysplasia, and that exogenous ECFCs restore disrupted alveolar growth. METHODS AND RESULTS: Human fetal and neonatal rat lungs contain ECFCs with robust proliferative potential, secondary colony formation on replating, and de novo blood vessel formation in vivo when transplanted into immunodeficient mice. In contrast, human fetal lung ECFCs exposed to hyperoxia in vitro and neonatal rat ECFCs isolated from hyperoxic alveolar growth-arrested rat lungs mimicking bronchopulmonary dysplasia proliferated less, showed decreased clonogenic capacity, and formed fewer capillary-like networks. Intrajugular administration of human cord blood-derived ECFCs after established arrested alveolar growth restored lung function, alveolar and lung vascular growth, and attenuated pulmonary hypertension. Lung ECFC colony- and capillary-like network-forming capabilities were also restored. Low ECFC engraftment and the protective effect of cell-free ECFC-derived conditioned media suggest a paracrine effect. Long-term (10 months) assessment of ECFC therapy showed no adverse effects with persistent improvement in lung structure, exercise capacity, and pulmonary hypertension. CONCLUSIONS: Impaired ECFC function may contribute to arrested alveolar growth. Cord blood-derived ECFC therapy may offer new therapeutic options for lung diseases characterized by alveolar damage.

Src family kinase-mediated negative regulation of hematopoietic stem cell mobilization involves both intrinsic and microenvironmental factors.

OBJECTIVE: The intracellular signals that contribute to granulocyte colony-stimulating factor (G-CSF) receptor induced stem cell mobilization are poorly characterized. METHODS: We show enhanced G-CSF induced mobilization of stem cells in mice deficient in expression of Src family kinases (SFK-/-), which is associated with hypersensitivity of SFK-/- bone marrow cells to G-CSF as well as sustained activation of signal transducer and activator of transcription-3. RESULTS: A proteome map of the bone marrow fluid derived from wild-type and SFK-/- mice revealed a significant global reduction in the number of proteins in SFK-/- mice compared to controls, which was associated with elevated matrix metalloproteinase-9 levels, reduced stromal-derived factor-1 expression, and enhanced breakdown of vascular cell adhesion molecule-1. Transplantation of wild-type or SFK-/- stem cells into wild-type mice and treatment with G-CSF recapitulated the G-CSF-induced increase in stem cell mobilization noted in SFK-/- nontransplanted mice; however, the increase was significantly less. G-CSF treatment of SFK-/- mice engrafted with wild-type stem cells also demonstrated a modest increase in stem cell mobilization compared to controls, however, the observed increase was greatest in mice completely devoid of SFKs. CONCLUSIONS: These data suggest an involvement of both hematopoietic intrinsic and microenvironmental factors in Src kinase-mediated mobilization of stem cells and identify Src kinases as potential targets for modulating stem cell mobilization.

Differential mechanisms of x-ray-induced cell death in human endothelial progenitor cells isolated from cord blood and adults.

Endothelial colony-forming cells (ECFCs) are endothelial progenitor cells that circulate at low concentration in human umbilical cord and adult peripheral blood and are largely resident in blood vessels. ECFCs not only appear to be critical for normal vascular homeostasis and repair but may also contribute to tumor angiogenesis and response to therapy. To begin to characterize the potential role of ECFCs during the treatment of tumors in children and adults with radiation, we characterized the X-ray sensitivity of cord and adult blood-derived ECFCs. We found both cord blood and adult ECFCs to be highly radiation sensitive (3 Gy resulted in >90% killing without induction of apoptosis). The X-ray survival curves suggested reduced potential for repair capacity, but X-ray fractionation studies demonstrated that all the ECFCs exhibited repair when the radiation was fractionated. Finally, the mechanisms of X-ray-induced cell death for cord blood and adult ECFCs were different at low and high dose. At low dose, all ECFCs appear to die by mitotic death/catastrophe. However, at high radiation doses (≥ 10 Gy) cord blood ECFCs underwent p53 stabilization and Bax-dependent apoptosis as well as p21-dependent G1 and G2/M cell cycle checkpoints. By contrast, after 10 Gy adult ECFCs undergo only large-scale radiation-induced senescence, which is a cellular phenotype linked to premature development of atherosclerosis and vasculopathies. These data demonstrate that the ECFC response to radiation is dose-dependent and developmentally regulated and may provide potential mechanistic insight into their role in tumor and normal tissue response after ionizing radiation treatment.