Abstract 15317: The Transmembrane Protein Thrombospondin, Type I, Domain 1 Play a Vital Role in Angiogenesis by Maintaining Endothelial Integrity
Background: Using a genome-wide microarray analysis of Flk1 positive angioblasts during mouse embryogenesis, we recently identified Thrombospondin, type I, domain 1 (Thsd1) as a new marker of endothelial cells. However, the basic function of Thsd1 in these cells is still fully unknown. In this study, we sought to characterize the function of Thsd1 in endothelial cells in vitro and in vivo.
Method and Results: Whole mount in situ hybridisation on zebrafish larvae validated that the orthologue of Thsd1 was specifically expressed in the developing vascular network. Functional knockdown of Thsd1 by morpholino injection in zebrafish resulted in acute cerebral haemorrhages in an apparently morphologically intact vascular network. In a murine retina model, we found that intra-ocular injection of Thsd1 targeting siRNA also resulted in vascular haemorrhages. Based on its protein domains, Thsd1 may bind to calreticulin and thereby influence the assembly of actin stress fibres that are crucial for normal endothelial cell function and endothelial integrity. This protein-protein interaction was confirmed in vitro by co-immunoprecipitation of THSD1 and calreticulin from cultured human endothelial cells. In addition, we demonstrated by siRNA-mediated silencing of THSD1 that THSD1 is crucial for downstream activation of calreticulin via a FAK/PI3 Kinase signalling pathway, which ultimately shifts the Rac1/RhoA ratio towards actin cytoskeleton relaxation and subsequent preservation of cell-cell junctions.
Conclusion: These findings suggest that by its interaction with calreticulin on the cell surface via Rac1 dependent regulation of the actin cytoskeleton, Thsd1 promotes endothelial integrity.
- © 2011 by American Heart Association, Inc.