Both TNF receptors are required for direct TNF‐mediated cytotoxicity in microvascular endothelial cells

Abstract

The conditions under which tumor necrosis factor-alpha (TNF) induces apoptosis in primary microvascular endothelial cells (MVEC) were investigated. In the absence of sensitizing agents, TNF induced apoptosis after 3 days of incubation in confluent MVEC. In contrast, upon addition of the transcriptional inhibitor actinomycin D (Act. D), confluence was no longer required and apoptosis occurred already after 16 h. To assess the role of either TNF receptor (TNFR) type in apoptosis, MVEC isolated from mice genetically deficient in TNFR1 (Tnfr1o mice) or TNFR2 (Tnfr2o mice) were incubated with TNF in the presence or absence of Act. D. Under sensitized conditions, Tnfr2o MVEC were lysed like controls, whereas Tnfr1o MVEC were completely resistant, indicating an exclusive role for TNFR1. In contrast, in the absence of Act. D, confluent monolayers of wild-type cells were lysed by TNF, but both Tnfr1o and Tnfr2o MVEC were resistant to TNF-mediated toxicity, indicating a requirement for both TNFR types. Overexpression of the anti-apoptotic protein bcl-xL in MVEC led to a protection against the direct, but not the sensitized cytotoxicity of TNF. In conclusion, in pathophysiologically relevant conditions, both TNFR appear to be required for TNF-induced apoptosis in MVEC.

Pathogenesis of Cerebral Malaria: Recent Experimental Data and Possible Applications for Humans

“…In conclusion, these results indicate that the interaction between membrane TNF and TNFR2 is crucial to the development of the neurological syndrome seen in severe malaria (59). More recently, TNFR2 was shown to be important in endo-thelial cell apoptosis in the absence of sensitizing agents, i.e., under pathophysiologically relevant conditions (58).…”

Role of Caspases in Cytokine-Induced Barrier Breakdown in Human Brain Endothelial Cells

“…Few studies have proposed that cytokines might induce endothelial barrier dysfunction via apoptosis (17,(48)(49)(50)(51). However, one report suggests that primary cultures of human BECs are resistant to cell death mediated by TNF-a (18), although this resistance to apoptosis is not observed in primary cultures of BECs of other species (13,48). These differences in the apoptotic response to cytokines might be associated with cytokine concentrations, time of exposure, cytokine activity, and intrinsic differences among cell types and species.…”

“…TNF receptor 1 (TNFR1) is expressed constitutively on almost every nucleated cell type and tissue, whereas the expression of TNF receptor 2 (TNFR2) is highly regulated with prominent expression in cells of the immune system and endothelium, including BECs (13,14). Increased levels of TNF-a have been reported not only to modulate endothelial TJs and cytoskeleton rearrangement in BECs (15,16) but also to evoke an increase in caspase-3 activation driving BECs into apoptosis (13,17). More recently, a study has proposed that primary cultures of human BECs are resistant to cell death mediated by TNF-a (18).…”

Tumor necrosis factor-α: regulation of renal function and blood pressure

“…Therefore, some have proposed that TNFR2 serves as a "local reservoir" of TNF-␣, both providing readily available TNF-␣ for TNFR1 activation and operating as a "ligand passing" receptor in which TNFR2 captures TNF-␣ and passes it on to TNFR1. In addition, it has been shown that TNFR1 activation requires expression of TNFR2, which can form heterocomplexes with TNFR1 (28,87,107). Although the effects of soluble TNF-␣ may be mediated by either receptor, most of the actions of membrane-bound TNF-␣ are mediated by TNFR2 (47).…”