Activating CD137 Signaling Promotes Sprouting Angiogenesis via Increased VEGFA Secretion and the VEGFR2/Akt/eNOS Pathway

Figure 1

Knocking out/down endothelial CD137 impaired intraplaque angiogenesis. (a) The CD31 expression in ApoE^-/- CD137^-/- mice and ApoE^-/- mice detected by immunohistochemistry in aortic paraffin sections is shown in brown color (black arrows indicate positive cells). (b) CD137 knock-out decreased CD31-positive areas significantly compared with the control. (c) Aortic rings sprouting in CD137^-/- and C57BL/6 J mice ( for each group). (d) CD137 knock-out decreased the sprout number compared with the control aortic ring. (e) The silencing efficiency of CD137 siRNA-1, -2, and -3 (100 nM) detected by western blot. (f) siCD137-1 obviously silenced the expression of the CD137 protein. (g) Endothelial cell tube formation in siCD137 and control HUVECs. (h, i) The number of branch points and total length of tubes were both markedly decreased in CD137-silenced human umbilical vein endothelial cells (HUVECs). (j, l) The EdU-555 proliferation assay and transwell assay were applied to detect the proliferative and migratory ECs. (j) Red and blue fluorescence represents proliferating cells and nuclei, respectively. (l) The violet color represents migrating cells stained with 0.1% crystal violet. (k, m) The numbers of proliferative and migratory ECs extremely decreased in CD137-silenced ECs. After siRNA transfection, ECs were treated with TNFα for 24 h then applied to western blot, proliferation, and migration assay. , (a), (g), and (l) ; (c), (j) , .

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