Yiqian Zhu

Nanostructured biomaterials have tremendous potential for tissue engineering. However, the performance and integration of the nanomaterials in vivo are not well understood. A challenge in vascular tissue engineering is to develop optimal scaffolds and establish expandable cell sources for the construction of tissue-engineered vascular grafts that are nonthrombogenic and have long-term patency. Here, we used tissue-engineered vascular grafts as a model to demonstrate the potential of combining nanofibrous scaffolds and bone marrow mesenchymal stem cells (MSCs) for vascular tissue engineering. Biodegradable nanofibrous scaffolds with aligned nanofibers were used to mimic native collagen fibrils to guide cell organization in vascular grafts. The results from artery bypass experiments showed that nanofibrous scaffolds allowed efficient infiltration of vascular cells and matrix remodeling. Acellular grafts (without MSCs) resulted in significant intimal thickening, whereas cellular grafts (with MSCs) had excellent long-term patency and exhibited well organized layers of endothelial cells (ECs) and smooth muscle cells (SMCs), as in native arteries. Short-term experiments showed that nanofibrous scaffolds alone induced platelet adhesion and thrombus formation, which was suppressed by MSC seeding. In addition, MSCs, as ECs, resisted platelet adhesion in vitro, which depended on cell-surface heparan sulfate proteoglycans. These data, together with the observation on the short-term engraftment of MSCs, suggest that the long-term patency of cellular grafts may be attributed to the antithrombogenic property of MSCs. These results demonstrate several favorable characteristics of nanofibrous scaffolds, the excellent patency of small-diameter nanofibrous vascular grafts, and the unique antithrombogenic property of MSCs.

Circulating blood endothelial progenitor cells (EPCs) contribute to postnatal vasculogenesis, providing a novel therapeutic target for vascular diseases. However, the molecular mechanism of EPC-induced vasculogenesis is unknown. Interleukin-6 plays multiple functions in angiogenesis and vascular remodeling. Our previous study demonstrated that the polymorphism (174G>C) in IL-6 gene promoter was associated with brain vascular disease. In this study, we investigated if IL-6 receptor is expressed in human EPCs derived from circulating mononuclear cells, and if interleukin-6 (IL-6) stimulates EPC angiogenesis in vitro. First, we isolated and cultured mononuclear cells from adult human circulating blood. We obtained EPC clones that were further cultured and expended for the angiogenesis study. We found that the EPCs possessed human mature endothelial cell phenotypes; however, they proliferated much faster than mature endothelial cells (P<0.05). We then found that IL-6 receptor (gp-80) was expressed in the EPCs, and that administration of IL-6 could activate receptor gp80/gp130 signaling pathways including downstream extracellular signal-regulated kinase 1/2 and STAT3 phosphorylation in EPCs. Furthermore, IL-6 stimulated EPC proliferation, migration, and matrigel tube formation in a dose-dependent manner (P<0.05); anti-IL-6 antibodies or IL-6 receptor could abolish these effects (P<0.05). These results suggest that IL-6 plays a crucial role in the biologic behavior of blood-derived EPCs, which may help clarify the mechanism of IL-6 inflammatory-related diseases.

BACKGROUND AND PURPOSE: Human brain arteriovenous malformation tissue displays increased levels of vascular endothelial growth factor (VEGF) as well as matrix metalloproteinase (MMP)-9, a tissue protease associated with various intracerebral hemorrhage (ICH). We hypothesized that increased MMP-9 was associated with ICH induced by vascular endothelial growth factor hyperstimulation and that this effect could be attenuated by nonspecific MMP inhibition. METHODS: We used a mouse model with adenoviral vector-mediated vascular endothelial growth factor transduction in the brain. The association of MMP-9 expression and the brain tissue hemoglobin levels, an index of ICH, after stereotactic injection of adenoviral vector-mediated vascular endothelial growth factor into caudate putamen was assessed. A dose-response study with adenoviral vector-mediated vascular endothelial growth factor and a time course study at both 24 and 48 hours postinjection were performed. Effects of minocycline, a nonspecific MMP inhibitor, and pyrrolidine dithiocarbamate, an upstream regulator of MMPs, on MMP-9 activity and thereby the degree of ICH were also tested. RESULTS: Adenoviral vector-mediated vascular endothelial growth factor at the higher dose and at 48 hours induced MMP-9 levels 6-fold (n=6, P=0.02) and increased brain tissue hemoglobin (43.4+/-11.5 versus 30.3+/-4.1 mug/mg, n=6, P=0.003) compared with the adenoviral vector control. Immnunostaining was positive for MMP-9 around the cerebral vessels and the hemorrhagic areas. Minocycline and pyrrolidine dithiocarbamate administration suppressed vascular endothelial growth factor-induced MMP-9 activity (n=6, P=0.003 and P=0.01, respectively) and the associated increases in hemoglobin levels (n=5-6, P=0.001 and P=0.02, respectively). CONCLUSIONS: Vascular endothelial growth factor-induced ICH is associated with increased MMP-9 expression. Suppression of MMP-9 by minocycline or pyrrolidine dithiocarbamate attenuated ICH, suggesting the therapeutic potential of MMP inhibitors in cerebral vascular rupture.