Microvesicles (MVs) which include microparticles (MPs) and exosomes are found in blood circulation in normal physiologic conditions and are increased in a variety of diseases. This study evaluated the effects of MVs on human umbilical vein endothelial cells (HUVEC) by morphologic changes, apoptosis, and thrombogenicty, in vitro. Stimulation of monocyte cell line (THP-1) by starvation or by endotoxin and calcium ionophore A23187 resulted in the release of MVs which express exosome marker Tsg 101, negative phospholipids in their leaflets, monocyte markers (CD18, CD14) and active tissue factor (TF). MVs were found to disrupt EC integrity and rapidly induce membrane blebbing. Brief exposure (2-4 hours) to MVs resulted in EC membrane phospholipids "flip-flop" while longer stimulation (20 hours) led to two contradicting outcomes - tube formation as well as apoptosis, as assessed by nuclear fragmentation. Additionally, MVs exposure resulted in increased cell surface thrombogenicity and perturbation of the endothelial haemostatic balance, which were enhanced during longer exposure time. Activity, antigen level and mRNA expression of the coagulation initiator TF were elevated due to (i) adherence of MVs derived TF to the EC membrane, and (ii) an increase in endothelial TF expression. Furthermore, levels of the anticoagulant tissue factor pathway inhibitor (TFPI) and thrombomodulin (TM) were decreased. These findings demonstrate that monocyte MVs increase endothelial thrombogenicity and apoptosis. In addition, they induce tube formation which may indicate their angiogenic effect. These findings may clarify, in part, the role of MVs in EC dysfunction associated with inflammatory diseases and hypercoagulable states.

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Medication-related osteonecrosis of the jaw (MRONJ) is a serious adverse effect of antiresorptive and antiangiogenic therapies. MRONJ is identified by chronic wounds in the oral mucosa associated with exposed necrotic bone. We hypothesized that zoledronic acid (ZOL) impairs keratinocyte and fibroblast function and reduces soft tissue vascularization; therefore, treating MRONJ with proangiogenic cells may benefit MRONJ patients. The effect of ZOL and dexamethasone (DEX) on gingival fibroblasts and keratinocytes was investigated. In-vitro, ZOL inhibited fibroblast and keratinocyte proliferation, delaying scratch healing. In-vivo, exposed bone was detected at tooth extraction sites, mainly in ZOL(+)/DEX(+) rats; and was associated with significantly decreased soft tissue vascularization, serum-VEGF, and tissue-VEGF. Local injection of early and late endothelial progenitor cells (EPCs) healed 13 of 14 MRONJ lesions compared with 2/7 lesions in the mesenchymal stem cells, and 2/6, in culture-medium group. The EPCs reduced necrotic bone area, increased serum and tissue VEGF levels. EPCs engraftment was minimal, suggesting their paracrine role in MRONJ healing. The EPC-conditioned medium improved scratch healing of keratinocytes and fibroblasts via VEGF pathway and elevated mRNA of VEGFA and collagen1A1. In conclusion, a novel MRONJ treatment with EPCs, increased vascularization and improved epithelial and fibroblast functions as well as cured the lesion.

Vascularization is a prerequisite for bone formation. Endothelial progenitor cells (EPCs) stimulate bone formation by creating a vascular network. Moreover, EPCs secrete various bioactive molecules that may regulate bone formation. The aim of this research was to shed light on the pathways of EPCs in bone formation. In a subcutaneous nude mouse ectopic bone model, the transplantation of human EPCs onto β-TCP scaffold increased angiogenesis (p < 0.001) and mineralization (p < 0.01), compared to human neonatal dermal fibroblasts (HNDF group) and a-cellular scaffold transplantation (β-TCP group). Human EPCs were lining blood vessels lumen; however, the majority of the vessels originated from endogenous mouse endothelial cells at a higher level in the EPC group (p < 01). Ectopic mineralization was mostly found in the EPCs group, and can be attributed to the recruitment of endogenous mesenchymal cells ten days after transplantation (p < 0.0001). Stromal derived factor-1 gene was expressed at high levels in EPCs and controlled the migration of mesenchymal and endothelial cells towards EPC conditioned medium in vitro. Blocking SDF-1 receptors on both cells abolished cell migration. In conclusion, EPCs contribute to osteogenesis mainly by the secretion of SDF-1, that stimulates homing of endothelial and mesenchymal cells. This data may be used to accelerate bone formation in the future.