ALK1 inhibitor increased Robo4 expression and suppresses LPS-induced vascular permeability in mice. (A) ALK1 expression levels in organs of C57BL/6 mice (n = 4). (B) Robo4 expression levels in lungs and kidneys of wild-type (C57BL/6N) mice treated with or without K02288 (n = 7, *P < 0.05, N.S., not significant by the unpaired t test). (C) Vascular permeability assay using wild-type mice treated with or without K02288. Extravasated Evans blue in lungs and kidneys was quantified. (n = 8, *P < 0.05; N.S., not significant by the unpaired t test). (D) Vascular permeability assay using Robo4−/− mice treated with or without K02288. Extravasated Evans blue in lungs and kidneys was quantified. (n = 5, N.S., not significant by the unpaired t test). Pictures are representative images of the lungs and kidneys. Data are expressed as the mean ± SEM.