(A) Lysates from HASMCs were immunoprecipitated with anti-SLC44A2 antibody followed by mass spectrometry analysis to identify the proteins that interact with SLC44A2. The graph shows the TGF-β signaling–related proteins. iBAQ, intensity-based absolute quantification. (B) HASMCs were treated with Ang II (1 μM). Lysates were immunoprecipitated with anti-SLC44A2 antibody, and blotted with anti-NRP1 and anti-SLC44A2 antibodies. n = 5. (C) HASMCs were treated with Ang II. Lysates were immunoprecipitated with anti-NRP1 antibody, and blotted with anti-SLC44A2 and anti-NRP1 antibodies. n = 4. (D) Apoe^–/– Tagln^Cre/+ mice were intravenously injected with lentivirus containing control vector or Slc44a2. Osmotic pumps were then implanted subcutaneously to infuse saline or Ang II. The interaction of SLC44A2 with NRP1 (red dots marked by arrowheads) in suprarenal abdominal aorta was detected by proximity ligation assay (PLA). Scale bars: 10 μm. n = 5. (E–J) HASMCs were infected with lentivirus containing empty vector or SLC44A2-encoding plasmids with or without siNRP1 transfection, and then treated with Ang II. (E) The TGF-β levels in culture medium was measured by ELISA. n = 5. (F) The levels of p-SMAD2 and p-SMAD3 were detected by Western blotting. n = 4. (G) The levels of VSMC synthetic and contractile markers were detected by Western blotting. n = 5. (H) Contraction of HASMCs grown in collagen discs was assessed and quantified by gel area. Scale bars: 5 mm. n = 5. (I) The activity of MMP2 and MMP9 in culture medium was measured by gel zymography. n = 6. (J) Immunofluorescence images of in situ zymography (DQ gelatin) in HASMCs. MMP activity was quantified by immunofluorescence intensity. Scale bars: 40 μm. n = 5. Differences were analyzed by Welch’s ANOVA followed by Tamhane’s T2 multiple-comparison test (D and I), 1-way ANOVA followed by Tukey’s multiple-comparison test (E, H, and J), or 1-way ANOVA followed by Tukey’s multiple-comparison test or Welch’s ANOVA followed by Tamhane’s T2 multiple-comparison test (G).