Identification of two distinct populations of endothelial progenitor cells differing in size and antigen expression from human umbilical cord blood

Impairment of two types of circulating endothelial progenitor cells in patients with glucocorticoid-induced avascular osteonecrosis of the femoral head

OBJECTIVES

This study examined whether abnormalities of early EPCs and endothelial colony forming cells (ECFCs) are present and compared their functions in glucocorticoid (GC)-induced avascular osteonecrosis of the femoral head (ANFH).

METHODS

Early EPCs and endothelial colony forming cells (ECFCs) were obtained from 33 patients with glucocorticoid-induced ANFH and 33 age- and sex-matched control subjects. Cells were isolated, in vitro cultured and studied by Flow Cytometry and Immunofluorescence. Colony-forming unit counts were observed from 33 patients and 33 healthy controls. Growth kinetics, migratory capacity to multiple chemo-attractants, in vitro tube formation capacity and cytokine (vascular endothelial growth factor and stromal cell-derived factor-1) levels in supernatants of two types of EPCs were assayed in ANFH patients and matched controls (n=4).

RESULTS

Mean numbers of colonies formed by both types of EPCs were decreased in ANFH patients (Early EPCs: 2.42±1.46 versus 4.52±2.00, p<0.05; ECFCs: 0.62±0.55 versus 1.12±0.82, p<0.05). Early EPCs from ANFH patients showed impaired migratory capacity (63.8±11.7 versus 152.3±12.4, p<0.001) and VEGF secretion (50.8±7.2 pg/ml versus 62.8±10.1 pg/ml, p<0.05). ECFCs from ANFH patients showed decreased tube formation capacity (7.1±2.7 versus 23.8±4.3, p<0.001) and proliferation.

DISCUSSION

Early EPCs and ECFCs were impaired in number and function in GC-induced ANFH, and their distinct reduced capacity profiles might reflect different roles they played in endothelial dysfunction of GC-induced ANFH.

CXCR2 mediates the recruitment of endothelial progenitor cells during allergic airways remodeling

Airway remodeling is a central feature of asthma and includes the formation of new peribronchial blood vessels, which is termed angiogenesis. In a number of disease models, bone marrow-derived endothelial progenitor cells (EPCs) have been shown to contribute to the angiogenic response. In this study we set out to determine whether EPCs were recruited into the lungs in a model of allergic airways disease and to identify the factors regulating EPC trafficking in this model. We observed a significant increase in the number of peribronchial blood vessels at day 24, during the acute inflammatory phase of the model. This angiogenic response was associated with an increase in the quantity of EPCs recoverable from the lung. These EPCs formed colonies after 21 days in culture and were shown to express CD31, von Willebrand factor, and vascular endothelial growth factor (VEGF) receptor 2, but were negative for CD45 and CD14. The influx in EPCs was associated with a significant increase in the proangiogenic factors VEGF-A and the CXCR2 ligands, CXCL1 and CXCL2. However, we show directly that, while the CXCL1 and CXCL2 chemokines can recruit EPCs into the lungs of allergen-sensitized mice, VEGF-A was ineffective in this respect. Further, the blockade of CXCR2 significantly reduced EPC numbers in the lungs after allergen exposure and led to a decrease in the numbers of peribronchial blood vessels after allergen challenge with no effect on inflammation. The data presented here provide in vivo evidence that CXCR2 is critical for both EPC recruitment and the angiogenic response in this model of allergic inflammation of the airways.

Nitric oxide production by endothelial cells derived from blood progenitors cultured on NaOH-treated polycaprolactone films: A biofunctionality study

Poly(epsilon-caprolactone) (PCL) is a biodegradable polyester whose biocompatibility has been widely demonstrated both in vivo and in vitro. In the last few years, our group has confirmed that NaOH-treated PCL films can serve as a suitable biomaterial for vascular tissue engineering by supporting the culture of primary vascular cells and, more recently, endothelial-like EC(2) cells derived from endothelial progenitor cells (EPC). In the present study, NO production in basal conditions and after stimulation with different agents has been evaluated and related to the reactive oxygen species (ROS) content and the intracellular calcium levels on EC(2) cells cultured on NaOH-treated PCL films. The results obtained demonstrate that EC(2) seeded on NaOH-treated PCL films enhance the basal NO levels and show a faster, more intense response to physiological stimuli such as VEGF, bradykinin and thrombin than vein endothelial cells (ECv). This result could be indicative of a better capacity of EC(2) cells to maintain their endothelial functionality when seeded on polymers. On the other hand, the culture of both EC(2) and ECv cells on NaOH-treated PCL films induces a significant increase in both ROS content and intracellular calcium that is balanced out through the stimulation of NO production in these cells. In conclusion, these results demonstrate the ability of NaOH-treated PCL films to support endothelial cell production of nitric oxide and reinforce the idea of considering the endothelial-like EC(2) cells derived from blood progenitors as an adequate source of endothelial cells to functionalize vascular grafts. Furthermore, NaOH-treated PCL films could be considered as a promising cellular NO production-inducing biomaterial for vascular tissue engineering applications.

Endothelial progenitor cells and their potential therapeutic applications

Endothelial progenitor cells (EPCs) are derived from the bone marrow (BM) and peripheral blood (PB), contributing to tissue repair in various pathological conditions via the formation of new blood vessels, that is, neovascularization. EPCs can be mobilized into the circulation in response to growth factors and cytokines released following stimuli such as vascular trauma, wounding and cancer. EPCs are involved in vasculogenesis during embryogenesis, but are now recognized to have a significant bearing upon disease outcome through their contribution to neovascularization in a variety of pathological states in adulthood. EPCs exist in very small numbers, especially in circulating blood in adults where they only account for 0.01% of all cells. We discuss the contribution and potential therapeutic applications of EPCs in disease, also noting the prognostic value of PB EPC numbers, especially in heart disease and cancer.