The importance of LPA₄ in angiogenesis as evaluated by Matrigel plug assay. (A) An H&E-stained section prepared from a Matrigel plug. Erythrocytes are seen in a cavity that traces the shape of the endothelium-lined vessels. Scale bar, 50 μm. (B-C) Matrigel plug sections immunohistochemically stained for PECAM1 (green) and α-SMA (red). Representative staining of Matrigel plug sections obtained from WT (B) and KO (C) mice are shown. KO, LPA₄-deficient. Scale bars, 50 μm. (D) Quantification of mural cell-covered endothelium. Data represent the mean ± SEM (n = 18 from 3 mice in each group). *P < .0001, using Mann-Whitney U test.