Thrombospondin‐1‐induced apoptosis of brain microvascular endothelial cells can be mediated by TNF‐R1

Abstract

Thrombospondin‐1 (TSP‐1) treatment of dermal microvascular endothelial cells (MvEC) has been shown to upregulate Fas ligand (FasL) and to induce apoptosis by a mechanism that requires caspase‐8 activity. We have examined the potential anti‐angiogenic effects of TSP‐1 on primary human brain MvEC. The addition of TSP‐1 to primary human brain MvEC cultured as monolayers on type 1 collagen, induced cell death and apoptosis (evidenced by caspase‐3 cleavage) in a dose‐ (5–30 nM) and time‐dependent (maximal at 17 h) manner. TSP‐1 treatment for 17 h induced caspase‐3 cleavage that required caspase‐8 activity and the tumor necrosis factor receptor 1 (TNF‐R1). We did not find a requirement for Fas, or the tumor necrosis‐related apoptosis‐inducing ligand receptors (TRAIL‐R) 1 and 2. We confirmed the findings using caspase inhibitors, blocking antibodies and small interfering RNA (siRNA). Further analysis indicated that the TSP‐1 induction of caspase‐3 cleavage of primary human brain MvEC adherent to collagen required the synthesis of new message and protein, and that TSP‐1 induced the expression of TNFα mRNA and protein. Consistent with these findings, when the primary human brain MvEC were propagated on collagen gels mAb anti‐TNF‐R1 reversed the inhibitory effect, in part, of TSP‐1 on tube formation and branching. These data identify a novel mechanism whereby TSP‐1 can inhibit angiogenesis‐through induction of apoptosis in a process mediated by TNF‐R1. J. Cell. Physiol. 218: 94–103, 2009.