Syndecan-1 is a novel regulator of angiogenesis

Abstract

The cell surface heparan sulfate proteoglycan syndecan-1 (Sdc1) binds to several proangiogenic factors, including bFGF and two VEGF isoforms, under physiological conditions. We used Sdc1 knockout (KO)- and overexpressing mice to study its role in angiogenesis. The interactions of leukocytes and ECs of WT and Sdc1 KO mice were studied in vivo, using a perfusion technique with FITC-coupled ConA and intravital microscopy. Static in vitro adhesion assays were used to study the role of HS in the adhesion process. Angiogenesis was studied in vivo using a cornea angiogenesis assay. Sdc1 KO mice showed dramatically enhanced leukocyte-EC adhesion in the perfusion model (5-fold, p<0.005) and in intravital microscopy (80-fold, TNF-α-stimulation, p<0.001). This effect was leukocyte-dependent, as shown in hematopoietic chimaeras and by in vitro assays measuring adhesion of Sdc1 KO monocytes and PMN's to HUVEC cells. Addition of heparin (10µg/ml) reverted increased adhesion of Sdc1 KO cells to WT levels, suggesting an involvement of the Sdc1 HS chains. However, a HS fingerprint analysis revealed no qualitative differences in the organ-specific disaccharide patterns of HS isolated from Sdc1 KO and wild-type mice. Increased angiogenesis (1.8-fold, p<0.0001) and abnormal blood vessel morphology in the Sdc1 KO mice were demonstrated in the cornea angiogenesis assay. In Syndecan-1-overexpressing mice, we observed abnormally dilated blood vessels in the granulation tissue of healing dermal wounds, accompanied by a reduction of cell proliferation and an increase in the elastolytic activity of wound fluids, which could be attributed to Sdc-1. Using siRNA knockdown technology, we could demonstrate that FGF-2 mediated MAPK signalling was reduced in MCF-7 cells upon treatment with Sdc-1 siRNA. Our data indicate that syndecan-1 acts as a novel regulator of angiogenesis, having implications for several pathologic conditions that involve abnormal angiogenesis, including breast cancer and endometriosis.