Talk abstracts

Talk on Wednesday 04:30-04:45pm submitted by Ning Zhao

Reciprocal regulation of syndecan-2 and Notch in vascular smooth muscle cells

Ning Zhao (Cardiovascular and Pulmonary Research Center, Research Institute at Naionwide Childrens Hospital), Hua Liu (Vascualr Biology Center, Medical College of Georgia), Brenda Lilly (Cardiovascular and Pulmonary Research Center, Research Institute at Naionwide Childrens Hospital)

Abstract:
Purpose: Precise interactions between endothelial and smooth muscle cells are required for proper blood vessel formation. In a quest to investigate the mechanisms that govern this interaction, we focused on Syndecan-2 and Notch3, which were shown to be regulated by the interaction of endothelial cells and smooth muscle cells using a coculture model of angiogenesis.

Methods: Endothelial and smooth muscle cells were cultured alone or together and the regulation of Syndecan-2 expression and Notch signaling were assessed by real-time PCR, Western blotting and luciferase assays. Expression of relevant genes was modulated by siRNA knockdown and overexpression using lenti-virus. Protein-protein interaction was detected by coimmunoprecipitation assays.

Results: We identified Syndecan-2 as one gene that is induced in smooth muscle cells by cocultured endothelial cells. Syndecan-2 is a heparan sulfate proteoglycan that serves as a receptor for extracellular matrix proteins and growth factors, and has been implicated in regulating angiogenesis. Investigations into the mechanism that governs endothelial cell-dependent induction of Syndecan-2, revealed a role for Notch signaling. Treatment with Notch signaling inhibitor DAPT and dominant-negative Mastermind blocked Syndecan-2 upregulation. In addition, silencing of Notch2 and Notch3 by siRNA prevented Syndecan-2 induction, and overexpression of the intracellular domain of either Notch2 and Notch3 drove the expression of Syndecan-2. Our lab previously showed induction of Notch3 by heterotypic cell interaction regulates vessel formation. The activation of Notch signaling is initiated by the binding of ligand to receptor, and this event is a potential target of Syndecan-2, as a transmembrane coreceptor. To test this hypothesis, we silenced Syndecan-2 and found the induction of Notch signaling was attenuated. In addition, coIP assay showed that Syndecan-2 and Notch3 physically ineract with each other to further comfirm our hypothesis.

Conclusion: These finding indicate Syndecan-2 and Notch signaling regulate each other reciprocally, and partially explain the mechanism of autoregulation of Notch3 in mural cells.

Keywords: syndecan-2, Notch, Vascular smooth muscle cell