Dentin sialoprotein acts as an angiogenic factor through association with the membrane receptor endoglin

Dentin sialophosphoprotein (DSPP) is highly expressed by odontoblasts, the cell type responsible for dentin formation. DSPP therefore has been extensively studied as a regulator of dentinogenesis. Besides defective dentinogenesis in teeth, Dspp-deficient mice also display reduced blood vessels in the transition zone of femurs. However, the exact role and underlying mechanisms of DSPP in the process of blood vessel formation remain enigmatic. Here, we show that dentin sialoprotein (DSP), the NH₂-terminal cleavage product of DSPP, promotes the migration and capillary-like structure formation of human umbilical vein endothelial cells (HUVECs) as well as the migration and endothelial differentiation of human dental pulp stem cells (DPSCs). Further experiments demonstrate that endoglin (ENG), a membrane receptor associated with angiogenesis, can be co-immunoprecipitated by DSP. Flow cytometry assays show that HUVECs and DPSCs, two cell types with endogenous ENG expression, display obvious binding signals of supplemented DSP protein, but human embryonic kidney 293T (HEK293T) cells, a cell type without endogenous ENG expression, do not. Pretreatment with an anti-ENG antibody or knockdown of ENG inhibits the binding of DSP to DPSCs, while ENG overexpression enhances binding signals of DSP to HEK293T cells. Meanwhile, multiple experiments demonstrate that knockdown of ENG impairs DSP-induced migration and endothelial differentiation of DPSCs. Therefore, ENG is essential for the angiogenic effects of DSP. Moreover, Dspp-deficient mice exhibit defective capillary formation in molars, supporting the positive role of DSP in blood vessel development. Collectively, these findings identify that DSP acts as an angiogenic factor through association with ENG.