Am19_1_SG), TIMP1 (Mm_TIMP1_1_SG), TIMP2 (Mm_TIMP2_1_SG), TIMP3 (Mm_TIMP3_1_SG). GAPDH was used as reference gene (Mm_Gapdh_3_SG).NaCl). To proceed with the sprouting/proteolytic assay, 500 ml of regular 3D fibrin gels (5 mg/ml) were GNF-7 formed on the bottom of 24well cell culture plates by the addition of 0.2 U/ml thrombin [31]. Then, a second fibrin gel layer including transglutaminase bound (TG-bound) growth factors [TG-BMP2 (1 mg/ml) and TGVEGF121 (100 ng/ml)] or soluble factors [bFGF, Wnt3a and Wnt5a (100 ng/ml)] was used to seed EPIC spheroids on top of the first gel layer. TG-binding of growth factors to the fibrin gel allows for the covalent attachment of these molecules to the matrix. Spheroids were photographed after 3 h, 12, 24, 48 and 72 hours time intervals. The digested and/or sprouting area was calculated using Olympus software and plotted as square micrometers. Quantification of differences in sprouting and proteolysis was performed for each individual clone by compiling the spheroid occupied area/digested area when projected into a 2D image. For zymography assays, cEP4, EPIC and HT1080 cells were cultured in 100 ml fibrinogen gels (0.36106cells/gel) supplemented with 200 ml DMEM (without serum). After 24 hours the medium from each culture was collected, centrifuged to remove cell debris and mixed with 46 loading buffer (0.4 M TrisHCl, pH 6.8; 20 glycerol; 0.03 bromophenolblue). 20 mL samples were loaded in each lane and MMP activity was analyzed using gelatine zymography (48 hours). Briefly, 1.5 mg/ml final concentration of gelatin (AppliChem) was added to a 10 standard Laemmli acrylamide polymerization mixture. 24272870 Human plasmin (FLUCKA) or supernatant from HT1080 cells were loaded as controls. After electrophoresis, gels were incubated twice in 2.5 Triton X-100 (30 min) and then in the zymograpy buffer (50 mMTrisHCl pH 7.5; 200 mM NaCl; 5 mM CaCl2; 0.02 NaN3; 37uC). Gels were stained with Colloidal blue staining solution (Invitrogen) following the instructions of the provider. Proteolytic activity was visualized as white bands against a blue background. An alternative, independent experiment to test the proteolytic activity of cEP4 was performed culturing these cells in 3D fibrin gels (DMEM/12+1 ITS, no serum) and treating experimental groups with the protease inhibitor aprotinin (1 mg/ml).Results Generation and characterization of the EPIC lineAfter 48 hours of culture, E11.5 CAL120 web epicardial embryonic cells grew over the substrate and formed a characteristic halo around the explant (Fig. 1A ). This halo of epicardial cells expressed high levels of cytokeratin (Fig. 1D ). After incubation with methylcholanthrene (MCA) and sustained culture for one month intense proliferation of primary epicardial cells was recorded. Between the first and third passages the majority of these cells had acquired a mesenchymal phenotype, Continuous passage of cells led to the stabilization of the EPIC line, which have been continuously growing in culture for more than three years. EPICs were found to have a morphologically heterogeneous appearance; the majority of the cells displayed a mesenchymal phenotype (Fig. 1F,F9) a result that was partially supported by sqPCR analysis of epicardial mesenchymal markers (Sox9 and Tcf21, Fig. 1G). However, a minor number of EPICs grew closely associated when cultured at low densities thus resembling epithelial cells (Fig. 1H). The epithelial-like nature of these small clones was confirmed by immunohistochemi.Am19_1_SG), TIMP1 (Mm_TIMP1_1_SG), TIMP2 (Mm_TIMP2_1_SG), TIMP3 (Mm_TIMP3_1_SG). GAPDH was used as reference gene (Mm_Gapdh_3_SG).NaCl). To proceed with the sprouting/proteolytic assay, 500 ml of regular 3D fibrin gels (5 mg/ml) were formed on the bottom of 24well cell culture plates by the addition of 0.2 U/ml thrombin [31]. Then, a second fibrin gel layer including transglutaminase bound (TG-bound) growth factors [TG-BMP2 (1 mg/ml) and TGVEGF121 (100 ng/ml)] or soluble factors [bFGF, Wnt3a and Wnt5a (100 ng/ml)] was used to seed EPIC spheroids on top of the first gel layer. TG-binding of growth factors to the fibrin gel allows for the covalent attachment of these molecules to the matrix. Spheroids were photographed after 3 h, 12, 24, 48 and 72 hours time intervals. The digested and/or sprouting area was calculated using Olympus software and plotted as square micrometers. Quantification of differences in sprouting and proteolysis was performed for each individual clone by compiling the spheroid occupied area/digested area when projected into a 2D image. For zymography assays, cEP4, EPIC and HT1080 cells were cultured in 100 ml fibrinogen gels (0.36106cells/gel) supplemented with 200 ml DMEM (without serum). After 24 hours the medium from each culture was collected, centrifuged to remove cell debris and mixed with 46 loading buffer (0.4 M TrisHCl, pH 6.8; 20 glycerol; 0.03 bromophenolblue). 20 mL samples were loaded in each lane and MMP activity was analyzed using gelatine zymography (48 hours). Briefly, 1.5 mg/ml final concentration of gelatin (AppliChem) was added to a 10 standard Laemmli acrylamide polymerization mixture. 24272870 Human plasmin (FLUCKA) or supernatant from HT1080 cells were loaded as controls. After electrophoresis, gels were incubated twice in 2.5 Triton X-100 (30 min) and then in the zymograpy buffer (50 mMTrisHCl pH 7.5; 200 mM NaCl; 5 mM CaCl2; 0.02 NaN3; 37uC). Gels were stained with Colloidal blue staining solution (Invitrogen) following the instructions of the provider. Proteolytic activity was visualized as white bands against a blue background. An alternative, independent experiment to test the proteolytic activity of cEP4 was performed culturing these cells in 3D fibrin gels (DMEM/12+1 ITS, no serum) and treating experimental groups with the protease inhibitor aprotinin (1 mg/ml).Results Generation and characterization of the EPIC lineAfter 48 hours of culture, E11.5 epicardial embryonic cells grew over the substrate and formed a characteristic halo around the explant (Fig. 1A ). This halo of epicardial cells expressed high levels of cytokeratin (Fig. 1D ). After incubation with methylcholanthrene (MCA) and sustained culture for one month intense proliferation of primary epicardial cells was recorded. Between the first and third passages the majority of these cells had acquired a mesenchymal phenotype, Continuous passage of cells led to the stabilization of the EPIC line, which have been continuously growing in culture for more than three years. EPICs were found to have a morphologically heterogeneous appearance; the majority of the cells displayed a mesenchymal phenotype (Fig. 1F,F9) a result that was partially supported by sqPCR analysis of epicardial mesenchymal markers (Sox9 and Tcf21, Fig. 1G). However, a minor number of EPICs grew closely associated when cultured at low densities thus resembling epithelial cells (Fig. 1H). The epithelial-like nature of these small clones was confirmed by immunohistochemi.