Single endothelial cells (EC) seeded in suspension culture rapidly undergo apoptosis. Addition of survival factors, such as VEGF and FGF-2, does not prevent apoptosis of suspended EC. However, when cells are allowed to establish cell–cell contacts, they become responsive to the activities of survival factors. These observations have led to the development of a three-dimensional spheroid model of EC differentiation. EC spheroids remodel over time to establish a differentiated surface layer of EC and a center of unorganized EC that subsequently undergo apoptosis. Surface EC become quiescent, establish firm cell–cell contacts, and can be induced to express differentiation antigens (e.g., induction of CD34 expression by VEGF). In contrast, the unorganized center spheroid cells undergo apoptosis if they are not rescued by survival factors. The responsiveness to the survival factor activities of VEGF and FGF-2 was not dependent on cell shape changes since it was retained after cytochalasin D treatment. Taken together, these findings characterize survival factor requirements of unorganized EC and indicate that polarized surface EC differentiate to become independent of exogenous survival factors. Furthermore, they demonstrate that spheroid cell culture systems are useful not just for the study of tumor cells and embryonic stem cells but also for the analysis of differentiated functions of nontransformed cells.

Blood vessel growth in adult organisms involves the following two fundamental processes: angiogenesis, the proliferation and extension of capillary networks; and arteriogenesis, the growth of functional arteries. We provide a protocol for the evaluation of postnatal arteriogenesis and angiogenesis in a mouse model of hind-limb ischemia. Surgical ligation of the femoral artery at a specific site triggers arteriogenesis of small, pre-existing collateral arteries into functional conduit vessels proximally and ischemic angiogenesis distally. The vascular response to hind-limb ischemia can be readily evaluated by laser Doppler-based perfusion measurements, histological quantification of arteriogenesis and angiogenesis or whole-mount visualization of arteries in limb muscles. Depending on the experimental design, the protocol takes between 4 and 29 d to complete; however, the net working time is about 2 d per mouse. The concurrent and specific analysis of postnatal angiogenesis and arteriogenesis in the same animal is a unique feature of the protocol.

Paracrine interactions between endothelial cells (EC) and mural cells act as critical regulators of vessel wall assembly, vessel maturation and define a plasticity window for vascular remodeling. The present study was aimed at studying blood vessel maturation processes in a novel 3-dimensional spheroidal coculture system of EC and smooth muscle cells (SMC). Coculture spheroids differentiate spontaneously in a calcium-dependent manner to organize into a core of SMC and a surface layer of EC, thus mimicking the physiological assembly of blood vessels with surface lining EC and underlying mural cells. Coculture of EC with SMC induces a mature, quiescent EC phenotype as evidenced by 1) a significant increase in the number of junctional complexes of the EC surface layer, 2) a down-regulation of PDGF-B expression by cocultured EC, and 3) an increased resistance of EC to undergo apoptosis. Furthermore, EC cocultured with SMC become refractory to stimulation with VEGF (lack of CD34 expression on VEGF stimulation; inability to form capillary-like sprouts in a VEGF-dependent manner in a 3-dimensional in gel angiogenesis assay). In contrast, costimulation with VEGF and Ang-2 induced sprouting angiogenesis originating from coculture spheroids consistent with a model of Ang-2-mediated vessel destabilization resulting in VEGF responsiveness. Ang-2 on its own was able to stimulate endothelial cells in the absence of Ang-1 producing SMC, inducing lateral sheet migration as well as in gel sprouting angiogenesis. Taken together, the data establish the spheroidal EC/SMC system as a powerful cell culture model to study paracrine interactions in the vessel wall and provide functional evidence for smooth muscle cell-mediated quiescence effects on endothelial cells.

Purpose: In glioma-in contrast to various other cancers-the impact of T-lymphocytes on clinical outcome is not clear. We investigated the clinical relevance and regulation of T-cell infiltration in glioma.Experimental Design: T-cell subpopulations from entire sections of 93 WHO II-IV gliomas were computationally identified using markers CD3, CD8, and Foxp3; survival analysis was then done on primary glioblastomas (pGBM). Endothelial cells expressing cellular adhesion molecules (CAM) were similarly computationally quantified from the same glioma tissues. Influence of prominent cytokines (as measured by ELISA from 53 WHO II-IV glioma lysates) on CAM-expression in GBM-isolated endothelial cells was determined using flow cytometry. The functional relevance of the cytokine-mediated CAM regulation was tested in a transmigration assay using GBM-derived endothelial cells and autologous T-cells.Results: Infiltration of all T-cell subsets increased in high-grade tumors. Most strikingly, within pGBM, elevated numbers of intratumoral effector T cells (T eff , cytotoxic and helper) significantly correlated with a better survival; regulatory T cells were infrequently present and not associated with GBM patient outcome. Interestingly, increased infiltration of T eff cells was related to the expression of ICAM-1 on the vessel surface. Transmigration of autologous T cells in vitro was markedly reduced in the presence of CAM-blocking antibodies. We found that TGF-b molecules impeded transmigration and downregulated CAM-expression on GBM-isolated endothelial cells; blocking TGF-b receptor signaling increased transmigration.Conclusions: This study provides comprehensive and novel insights into occurrence and regulation of T-cell infiltration in glioma. Specifically, targeting TGF-b1 and TGF-b2 might improve intratumoral T-cell infiltration and thus enhance effectiveness of immunotherapeutic approaches. Clin Cancer Res; 17(13); 4296-308. Ó2011 AACR.

Angiogenesis is essential in bone fracture healing for restoring blood flow to the fracture site. Vascular endothelial growth factor (VEGF) and its receptor have been implicated in this process. Despite the importance of angiogenesis for the healing processes of damaged bones, the role of VEGF signaling in modulation of osteogenic differentiation in human mesenchymal stem cells has not been investigated in great detail. We examined the expression of VEGF-A and VEGFR-1 in human adult mesenchymal stem cells derived from trabecular bone (hTBCs). VEGF-A was found to be secreted in a differentiation dependent manner during osteogenesis. Transcripts for VEGF-A were also seen to be elevated during osteogenesis. In addition, transcripts for VEGF-A and the corresponding receptor VEGFR-1 were upregulated under hypoxic conditions in undifferentiated hTBCs. To investigate the signaling of VEGF-A on osteogenesis recombinant hTBCs were generated. High expression of VEGF-A stimulated mineralization, whereas high expression of sFLT-1, an antagonist to VEGF-A, reduced mineralization suggesting that VEGF-A acts as autocrine factor for osteoblast differentiation. In addition, VEGF-A secreted by hTBCs promotes sprouting of endothelial cells (HUVE) demonstrating a paracrine role in blood vessel formation. In summary, an in vitro analysis of transgene effects on cellular behavior can be used to predict an effective ex vivo gene therapy.