Figure 1. ARRB1 is downregulated in human IPAH and loss of ARRB1 in mice results in worsened hypoxia-induced PAH.

(a) Western blot of ARRB1 and 2 expression in lungs from patients with IPAH and controls (n = 5 per group) using an anti-ARRB1/2 antibody (A-1, Santa Cruz). (b) ARRB1, but not ARRB2, expression is significantly decreased in human IPAH. Signal is normalized to GAPDH control. Statistical analysis was performed by two-tailed unpaired t test. (c) Western blot of ARRB1 and 2 expression in pulmonary arterial endothelial cells (PAECs) isolated from patients with IPAH and controls (Control: n = 3; IPAH: n = 8) using an anti-ARRB1/2 antibody (A-1, Santa Cruz). (d) ARRB1 expression is significantly downregulated in PAECs from human IPAH. Signal is normalized to GAPDH control. Statistical analysis was performed by two-tailed unpaired t test. (e) Arrb1 KO male mice develop more severe PAH induced by hypobaric hypoxia compared to WT and Arrb2 KO male mice as assessed by (e) RV hypertrophy and (f) RV systolic pressure at cardiac catheterization (n = 15-20 mice per group). (g) Micro-CT images demonstrate RV enlargement in Arrb1 KO male mice exposed to hypoxia with (h) decreased RV fractional shortening compared to WT and Arrb2 KO male mice (n = 3-6 mice per group). (i) Representative images of immunofluorescence for smooth muscle a-actin (a-SMA, red), von Willebrand’s factor (VWF, green) and nuclei (blue) in lung sections from WT, Arrb1 KO and Arrb2 KO mice exposed to hypoxia (scale bar = 50 μm). (i-j) Arrb1 KO mice demonstrate increased vascular medial thickness and media area/cross-sectional area (CSA) compared to WT and Arrb2 KO mice (n = 5 mice per group). Statistical analysis was performed by one-way ANOVA and Tukey's multiple comparison test. Error bars indicate SEM. *, p < 0.05; #, p < 0.0