Abnormal angiogenesis and vascular remodeling contribute to pathogenesis of a number of disorders such as tumor, arthritis, atherosclerosis, restenosis, hypertension, and neurodegeneration. During angiogenesis and vascular remodeling, behaviors of stem/progenitor cells, endothelial cells (ECs), and vascular smooth muscle cells (VSMCs) and its interaction with extracellular matrix (ECM) play a critical role in the processes. Matrix metalloproteinases (MMPs), well-known inflammatory mediators are a family of zinc-dependent proteolytic enzymes that degrade various components of ECM and non-ECM molecules mediating tissue remodeling in both physiological and pathological processes. MMPs including MMP-1, MMP-2, MMP-3, MMP-7, MMP-8, MMP-9, MMP-12, and MT1-MMP, are stimulated and activated by various stimuli in vascular tissues. Once activated, MMPs degrade ECM proteins or other related signal molecules to promote recruitment of stem/progenitor cells and facilitate migration and invasion of ECs and VSMCs. Moreover, vascular cell proliferation and apoptosis can also be regulated by MMPs via proteolytically cleaving and modulating bioactive molecules and relevant signaling pathways. Regarding the importance of vascular cells in abnormal angiogenesis and vascular remodeling, regulation of vascular cell behaviors through modulating expression and activation of MMPs shows therapeutic potential.

Reendothelialization involves endothelial progenitor cell (EPC) homing, proliferation, and differentiation, which may be influenced by fluid shear stress and local flow pattern. This study aims to elucidate the role of laminar flow on embryonic stem (ES) cell differentiation and the underlying mechanism. We demonstrated that laminar flow enhanced ES cell–derived progenitor cell proliferation and differentiation into endothelial cells (ECs). Laminar flow stabilized and activated histone deacetylase 3 (HDAC3) through the Flk-1–PI3K–Akt pathway, which in turn deacetylated p53, leading to p21 activation. A similar signal pathway was detected in vascular endothelial growth factor–induced EC differentiation. HDAC3 and p21 were detected in blood vessels during embryogenesis. Local transfer of ES cell–derived EPC incorporated into injured femoral artery and reduced neointima formation in a mouse model. These data suggest that shear stress is a key regulator for stem cell differentiation into EC, especially in EPC differentiation, which can be used for vascular repair, and that the Flk-1–PI3K–Akt–HDAC3–p53–p21 pathway is crucial in such a process.

IntroductionNumerous studies have demonstrated that endothelial progenitor cells (EPCs) are present among peripheral blood mononuclear cells (PBMNCs) and represent a subset of circulating bone marrow mononuclear cells (BMCs), which have the capacity to differentiate into endothelial cells in vivo. 1 New concepts of stem cell-based therapies for myocardial regeneration resulted in a rapid translation into a clinical context. [2][3][4] Yet, key questions remain unanswered. Importantly, the nomenclature and the phenotype of EPCs are subject to ongoing controversy and there are currently no specific markers that unambiguously identify these cells. 5,6 Thus, a more comprehensive approach is needed to analyze their antigenic profiles.MPs are small membrane vesicles (0.2-1.0 m) that originate from the plasma membrane and are shed from the cell surface after activation and apoptosis. 7 Importantly, MPs retain membrane antigens specific for the parent cell they originate from. Thus, MPs represent an ideal subproteome to clarify the cellular progeny of EPC cultures and mass spectrometry is the instrument of choice for this kind of research. 8 In this study, we used a proteomic approach to identify membrane proteins present on MPs in EPC cultures. Methods EPC cultureThe study was approved by the ethics review board of J. W. Goethe University and King's College London. Peripheral blood was collected from healthy adult volunteers and informed consent was obtained in accordance with the Declaration of Helsinki. EPC cultures were performed as previously described. 9,10 In brief, PBMNCs from healthy volunteers were isolated by Lymphoprep (1.077 g/mL; Axis-Shield PoCAS) density barrier centrifugation. The low-density fraction (Ͻ 1.077 g/mL) was carefully removed from the interface and washed 3 times with PBS (Dulbecco phosphate-buffered saline; Sigma-Aldrich) containing 2% FBS (fetal bovine serum, filtered and heat inactivated; Gibco, Invitrogen). Immediately after isolation, the cells were counted and 8 ϫ 10 6 cells were plated on fibronectin-coated (10 g/mL fibronectin from human plasma; SigmaAldrich) 12-well plates containing 1 mL endothelial basal medium (EBM; Cambrex Bio Science) supplemented with 20% FBS, EGM SingleQuots (10 g/mL epidermal growth factor, 3 g/mL bovine brain extract, 50 g/mL gentamicine, 50 g/mL amphotericin-B, 1 g/mL hydrocortisone; Cambrex Bio Science) and 10 ng/mL human vascular endothelial growth factor 165 (hVEGF 165; R&D Systems). Before use, the medium was passed through a 0.2-m filter. After 3 days in culture, the nonadherent An Inside Blood analysis of this article appears at the front of this issue.The online version of this article contains a data supplement.The publication costs of this article were defrayed in part by page charge payment. Therefore, and solely to indicate this fact, this article is hereby marked ''advertisement'' in accordance with 18 USC section 1734. For personal use only. on May 11, 2018. by guest www.bloodjournal.org From cells were removed and fresh EBM medium was added. T...