Donor-recipient cell interactions are essential for functional engraftment after nonautologous cell transplantation. During this process, transplant engraftment is characterized and defined by interactions between transplanted cells with local and recruited inflammatory cells. The outcome of these interactions determines donor cell fate. Here, we provide evidence that lineage-committed embryonic stem cell (ESC)-derived vascular progenitor cells are the target of major histocompatibility complex (MHC) class I-dependent, natural killer (NK) cell-mediated elimination in vitro and in vivo. Treatment with interferon γ was found to significantly upregulate MHC class I expression on ESC-derived vascular progenitor cells, rendering them less susceptible to syngeneic NK cell-mediated killing in vitro and enhancing their survival and differentiation potential in vivo. Furthermore, in vivo ablation of NK cells led to enhanced progenitor cell survival after transplantation into a syngeneic murine ischemic hindlimb model, providing additional evidence that NK cells mediate ESC-derived progenitor cell transplant rejection. These data highlight the importance of recipient immune-donor cell interactions, and indicate a functional role for MHC-I antigen expression during successful ESC-derived syngeneic transplant engraftment.

Background— In murine embryonic stem cells, the onset of vascular endothelial growth factor receptor 2 (VEGFR-2) expression identifies endothelial precursors. Undifferentiated human embryonic stem cells express VEGFR-2, and VEGFR-2 expression persists on differentiation. The objective of our study was to identify a single population of endothelial precursors with common identifying features from both human and murine embryonic stem cells. Methods and Results— We report that expression of the VEGF coreceptor neuropilin-1 (NRP-1) coincides with expression of Brachyury and VEGFR-2 and identifies endothelial precursors in murine and human embryonic stem cells before CD31 or CD34 expression. When sorted and differentiated, VEGFR-2+NRP-1+ cells form endothelial-like colonies that express CD31 and CD34 7-fold more efficiently than NRP-1 cells. Finally, antagonism of both the VEGF and Semaphorin binding functions of NRP-1 impairs the differentiation of vascular precursors to endothelial cells. Conclusions— The onset of NRP-1 expression identifies endothelial precursors in murine and human stem cells. The findings define the origin of a single population of endothelial precursors from human and murine stem cells to endothelial cells. Additionally, the function of both the VEGF and Semaphorin binding activities of NRP-1 has important roles in the differentiation of stem cells to endothelial cells, providing novel insights into the role of NRP-1 in a model of vasculogenesis.

Inflammation is a key component of arterial injury, with VSMC proliferation and neointimal formation serving as the final outcomes of this process. However, the acute events transpiring immediately after arterial injury that establish the blueprint for this inflammatory program are largely unknown. We therefore studied these events in mice and found that immediately following arterial injury, medial VSMCs upregulated Rantes in an acute manner dependent on Stat3 and NF-kappa B (p65 subunit). This led to early T cell and macrophage recruitment, processes also under the regulation of the cyclin-dependent kinase inhibitor p21(Cip1). Unique to VSMCs, Rantes production was initiated by Tnf-alpha, but not by Il-6/gp130. This Rantes production was dependent on the binding of a p65/Stat3 complex to NF-kappa B-binding sites within the Rantes promoter, with shRNA knockdown of either Stat3 or p65 markedly attenuating Rantes production. In vivo, acute NF-kappa B and Stat3 activation in medial VSMCs was identified, with acute Rantes production after injury substantially reduced in Tnfa(-/-) mice compared with controls. Finally, we generated mice with SMC-specific conditional Stat3 deficiency and confirmed the Stat3 dependence of acute Rantes production by VSMCs. Together, these observations unify inflammatory events after vascular injury, demonstrating that VSMCs orchestrate the arterial inflammatory response program via acute Rantes production and subsequent inflammatory cell recruitment.

Hypoxia-triggered neovascularization occurs in many types of disease. Endothelial cells must be able to cope with hypoxic stress, which in other cell types can induce a DNA repair response and inhibit replication. Matina Economopoulou et al. now show that hypoxia induces the generation of a hallmark of the DNA repair response, phosphorylated histone H2AX, in proliferating endothelial cells and that H2AX function is required for neovascularization under hypoxic or ischemic conditions in vivo pages 491–493 .. H2A histone family member X (H2AX, encoded by H2AFX) and its C-terminal phosphorylation (γ-H2AX) participates in the DNA damage response and mediates DNA repair1,2,3,4,5,6. Hypoxia is a physiological stress that induces a replication-associated DNA damage response7. Moreover, hypoxia is the major driving force for neovascularization8, as the hypoxia-mediated induction of vascular growth factors triggers endothelial cell proliferation8. Here we studied the role of the hypoxia-induced DNA damage response in endothelial cell function and in hypoxia-driven neovascularization in vivo. Hypoxia induced replication-associated generation of γ-H2AX in endothelial cells in vitro and in mice. Both in cultured cells and in mice, endothelial cell proliferation under hypoxic conditions was reduced by H2AX deficiency. Whereas developmental angiogenesis was not affected in H2afx−/− mice, hypoxia-induced neovascularization during pathologic proliferative retinopathy, in response to hind limb ischemia or during tumor angiogenesis was substantially lower in H2afx−/− mice. Moreover, endothelial-specific H2afx deletion resulted in reduced hypoxia-driven retina neovascularization and tumor neovascularization. Our findings establish that H2AX, and hence activation of the DNA repair response, is needed for endothelial cells to maintain their proliferation under hypoxic conditions and is crucial for hypoxia-driven neovascularization.

Relatively little is known regarding the role of mitochondrial metabolism in stem cell biology. Here we demonstrate that mouse embryonic stem cells sorted for low and high resting mitochondrial membrane potential (DeltaPsi(m)L and DeltaPsi(m)H) are indistinguishable morphologically and by the expression of pluripotency markers, whereas markedly differing in metabolic rates. Interestingly, DeltaPsi(m)L cells are highly efficient at in vitro mesodermal differentiation yet fail to efficiently form teratomas in vivo, whereas DeltaPsi(m)H cells behave in the opposite fashion. We further demonstrate that DeltaPsi(m) reflects the degree of overall mammalian target of rapamycin (mTOR) activation and that the mTOR inhibitor rapamycin reduces metabolic rate, augments differentiation, and inhibits tumor formation of the mouse embryonic stem cells with a high metabolic rate. Taken together, our results suggest a coupling between intrinsic metabolic parameters and stem cell fate that might form a basis for novel enrichment strategies and therapeutic options.

Cyclin-dependent kinase inhibitors, including p21Cip1, are implicated in cell turnover and are active players in cardiovascular wound repair. Here, we show that p21Cip1 orchestrates the complex interactions between local vascular and circulating immune cells during vascular wound repair. In response to femoral artery mechanical injury, mice with homozygous deletion of p21Cip1 displayed accelerated proliferation of VSMCs and increased immune cell infiltration. BM transplantation experiments indicated that local p21Cip1 plays a pivotal role in restraining excessive proliferation during vascular wound repair. Increased local vascular stromal cell-derived factor-1 (SDF-1) levels were observed after femoral artery injury in p21+/+ and p21-/- mice, although this was significantly greater in p21-/- animals. In addition, disruption of SDF-1/CXCR4 signaling inhibited the proliferative response during vascular remodeling in both p21+/+ and p21-/- mice. We provide evidence that the JAK/STAT signaling pathway is an important regulator of vascular SDF-1 levels and that p21Cip1 inhibits STAT3 binding to the STAT-binding site within the murine SDF-1 promoter. Collectively, these results suggest that p21Cip1 activity is essential for the regulation of cell proliferation and inflammation after arterial injury in local vascular cells and that the SDF-1/CXCR4 signaling system is a key mediator of vascular proliferation in response to injury.

There is growing interest in collaboration and resource sharing among institutions and organizations. In this paper, we investigate the problems of identity management inherent in distributed subscription-based resource sharing. The paper describes the design, implementation and performance of a system that provides controlled access to subscription-based remote network services through a browser. A third-party authentication protocol is designed and employed to exchange security assertions among involved parties. The web servers use plug-ins to provide an authentication-delegation service and a policy-based authorization service. Users can use a single userID and password to access multiple subscribed resource sites.

There is growing interest in collaboration and resource sharing among institutions and organizations. Identity based security policies are not enough to address access control in such distributed environments. In this paper, we investigate the problems of identity management inherent in distributed subscription-based resource sharing. We extend Role Base Access Control (RBAC) to a distributed environment and implement a distributed role based access control model (DRBAC). We define the concept of subject, role, distributed role, permission and autonomous organization as applicable to the distributed remote resource sharing service. Access is allowed based on the distributed roles, subject to certain constraints. Enforcing distributed role based access control policies allows organizations to ease the administrative overhead in a distributed environment.

eLearning has become an alternative approach to the traditional college and university of education. Experiments have shown that producing of the teaching contents for eLearning is a time-consuming and costly job. This paper introduces a programming-free and easy-to-use multimedia authoring system, T-Cube, designed and has already been used at the University of Trier for eLearning. As a rich-media authoring system, T-cube constructs and presents multimedia contents to students with multi-rate for either offline (CD/DVD/download) or online (in real time or on demand) usage. The rich-media teaching contents, including video, audio and screenshot, are recorded and encoded at the classroom and simultaneously published on Internet. Broadband users can access the lecture in real time as if they were sitting in the classroom. After being compressed and encoded, the teaching contents are also available for narrowband users on demand. Further, the contents on CD/DVD are also available on request. This paper focuses on describing the features, practical experiments and assessments of T-cube system.

eLearning has become an alternative approach to the traditional college and university of education. Experiments have shown that producing of the teaching contents for eLearning is a time-consuming and costly job. This paper introduces a programming-free and easy-to-use multimedia authoring system, T-Cube, designed and has already been used at the University of Trier for eLearning. As a rich-media authoring system, T-cube constructs and presents multimedia contents to students with multi-rate for either offline (CD/DVD/download) or online (in real time or on demand) usage. The rich-media teaching contents, including video, audio and screenshot, are recorded and encoded at the classroom and simultaneously published on Internet. Broadband users can access the lecture in real time as if they were sitting in the classroom. After being compressed and encoded, the teaching contents are also available for narrowband users on demand. Further, the contents on CD/DVD are also available on request. This paper focuses on describing the features, practical experiments and assessments of T-cube system.

Modern information technologies are transforming the way people learn. E-learning provides new possibilities for personalized learning at home or in the workplace, reduces the need for costly classroom training, and enables an optimal balance between traditional and innovative forms of knowledge transfer.But facts have proven that content creation for online courses are time- consuming and costly. Also most of them are not easy to call up. A simple and efficient solution of content creation for online courses is strongly required. Our new system, tele-TASK (2) - Teleteaching Anywhere Solution Kit, paves the way for these requirements. It opens up a new world of learning opportunities to learners, trainers, course authors, companies and educational institutions. With the help of the new developed system tele-TASK a new, drastically simplified entrance technology for on-line lectures has been reached. From his apartment or office each PC user with a suitable Internet connection can follow online lessons comfortably. Not only contents of teaching, which are presented to the students in the lecture-room by either a whiteboard or a video beamer are delivered but also video and audio of the lecturer. For tele-TASK a special hardware (t-Cube) is now available, which permits the creation of Real or Mpeg4 streams in different bandwidth ranges on the fly. Thus a pre- installed standard player can be used.

Reliable, distributed applications based on Internet, such as e-commerce system rely heavily on trust path among involved parties. This article introduces an efficient trust model based trust service, Independent Trust Intermediary Service model using Smart Trust List, for trust management. Fundamentally, Independent Trust Intermediary Service is facilities for distributing certificates of CAs in a manner that ensures their authenticity and integrity.