Ngs substantiate the stabilizing function of ASCs. To investigate the functionality of vessels supported by different mural cells, an inverse permeability model using a dextran (65 kDa) was applied [43] which is one possibility to examine vessel permeability next to in vivo approaches using fluorescently conjugated lectins [15]. Dextran was added to the bulk tissue to reveal incomplete cell-cell junctions by entering immature vessels lumens. Two weeks after start of the co-culture, less dextran was inside the lumen than after 3 days, likely because of mural cells constructs, which made direct contact with the capillary sprouts. Comparing fibroblasts with ASCs used as supporting mural cells in co-culture with HUVEC, ASCs seemed to mimic the physiology of healthy vasculature better than fibroblasts as evidenced by more controlled permeability, which might have been a result of an increase in EC-EC adherens junctions [43]. The molecular interactions responsible for this development remain to be clarified. Another aspect concerning angiogenesis is the proteolysis of the ECM, which depends on the cell type co-cultured with ECs. Co-culture models of HUVECs with ASCs with inhibition of different protease-families showed that the morphogenesis of blood vessels relied on the plasmin family of proteases for EC elongation and invasion. PubMed ID:https://www.ncbi.nlm.nih.gov/pubmed/12711626 MMPs regulated these parameters to a lesser extent. However, luminal diameter and regulation and possibly vessel stabilization was dependent on these proteinases. Coculturing HUVECs with ASCs resulted in a promotion ofusing the plasmin system for proteolysis in HUVECs, while the level of MMPs was unaffected [51]. These data combined with the upregulation of the proangiogenic factors HGF and tumor necrosis factor alpha (TNF-) within these co-culture systems demonstrated the similarities of molecular communication between co-cultured ASCs or fibroblasts and ECs [51]. On the other hand, a study using OECs instead of HUVECs for a co-culture model with ASCs in a fibrin matrix reported the expression of MMP14 on these ECs [52]. The results were supported by the fact that robust vessels developed even when a low concentration of aprotinin was added to the medium, which is known to prevent premature ROCK-IN-2 fibrin degradation by the plasmin system. According to these findings, OECs form vascular networks supported by ASCs in a fibrin matrix. Furthermore, OECs showed potential PubMed ID:https://www.ncbi.nlm.nih.gov/pubmed/8627573 molecular differences in fibrin degradation compared to HUVECs [52]. In a setting where co-cultures of ASCs with HUVECs in a fibrin clot were compared to co-cultures of ASCs with OECs, OECs were reported to form a mature network earlier than HUVEC, hinting that different ECs show different molecular interactions within co-cultures with ASCs [33]. Another approach to investigate the molecular interactions of ECs and ASCs in co-culture is the evaluation of gene expression levels via RT-qPCR. Experiments showed an increase in CD31 and VE-cadherin after 1 week of co-culture. These molecules are known to be cellular adhesion molecules which help cells in networks to attach to each other. In addition, VEGFR-2, the main receptor for VEGF and vWF, were also increased, in contrast to platelet-derived growth (PDGF) factor and Tie-2. CD31, VE-cadherin, VEGFR-2, and vWF are known to contribute to the prevention of uncontrolled vessel growth. However, PDGF and Tie-2 are mainly involved in vessel stabilization; therefore, their expression levels might have increased after s.