Shed syndecan-1 in conditioned medium from HPSE-high cells promotes angiogenesis in an aortic organ culture. (A) Segments of rat aorta were placed within Matrigel and cultured in the presence of medium conditioned by either HPSE-low or HPSE-high CAG cells, with medium from HPSE-low cells with addition of exogenous syndecan-1 (500 ng/mL) or with medium from HPSE-high cells that was immunodepleted of syndecan-1 (exogenous VEGF was added to all wells). Note that more microvessels grow out from the explants treated with conditioned media from HPSE-high cells versus HPSE-low cells. Addition of exogenous syndecan-1 to HPSE-low condition medium enhanced microvessel density, and immunodepletion of syndecan-1 from the conditioned medium of HPSE- high cells reduced the microvessel formation. Bar represents 0.2 mm. (B) Quantitative analysis of endothelial sprouting was performed using images from day 6, and sprout number was quantified using NIH ImageJ software. Data shown are from 2 separate experiments, each of which contained duplicate wells for each condition. *P < .01 vs HPSE-low. **P < .01 vs HPSE-high.