(A and B) Experimental outline and tube formation assay of human umbilical vein endothelial cells (HUVECs) that were cultured in conditioned medium received from young (12 weeks) and aged (20 months) cardiac mouse fibroblasts. Accumulated tube length was measured in 5 randomly chosen microscopic fields with a computer-assisted microscope using Axiovision 4.5 (Zeiss) (scale bar: 100 μm; n = 4). (C) Capillary density of random healthy areas of young (12 weeks; n = 6) and old (n = 8) heart sections versus capillary density of fibrotic (n = 8) areas of aged hearts (20 months). Shown is the quantification of the Isolectin B4–positive area versus the total area (%). (D) Expression of Serpine1, Serpine2, and Efemp1 in fibroblasts displayed in log scale in trajectory plots. (E) Secretion of SerpinE1 in isolated young and aged cardiac fibroblasts cultured for 24 hours in serum-free medium. Data were derived using a mouse angiogenesis array (R&D Systems) of culture supernatants of isolated cardiac fibroblasts (n = 4). (F) Tube formation assay of HUVECs that were cultured in conditioned medium received from young (12 weeks) and aged (20 months) cardiac mouse fibroblasts. The aged phenotype was rescued by supplementing the aged fibroblast medium with 4 μg of an anti-Serpin antibody. Accumulated tube length was measured in 5 randomly chosen microscopic fields with a computer-assisted microscope using Axiovision 4.5 (Zeiss) (scale bar: 200 μm; n = 4). (G) RNA expression of IL-6 in HUVECs cultured in conditioned medium received from young (12 weeks) and aged (18 months) cardiac mouse fibroblasts and in the presence and absence of 10 ng/mL TNF-α for 24 hours (n = 5). (H) Quantification of autophagosomes in HUVECs cultured with conditioned medium received from young (12 weeks) and aged (18 months) cardiac mouse fibroblasts. Autophagosomes were detected by immunostainings against p62 and LC3, whereby autophagosomes were considered p62/LC3–double positive (n = 5). Data are shown as mean ± SEM (B, C, E, F, G, and H). After passing Gaussian distribution, statistical analysis was performed using the unpaired, 2-sided t test (C, E, G, and H). For comparisons of more than 2 groups, multiple-group 1-way ANOVA with a post hoc Bonferroni’s test was used (B and F). *P < 0.05; **P < 0.01; ***P < 0.001; ****P < 0.0001.