TRAIL induces death of human oligodendrocytes isolated from adult brain

Tumour necrosis factor-related apoptosis-inducing ligand (TRAIL) has been reported to induce apoptosis in various tumour cell lines and, recently, also in normal cells. TRAIL interacts with four receptors: two signalling receptors (TRAIL-R1 and TRAIL-R2) and two decoy receptors (TRAIL-R3 and TRAIL-R4). We have shown that both signalling receptors are present on the surface of oligodendrocytes isolated from adult human brain (ahOL), whereas the decoy receptors are expressed at a low level on ahOL. TRAIL induces ahOL apoptosis-as characterized by Annexin V staining prior to propidium iodide cell uptake-under conditions of protein synthesis inhibition. However, pre-treatment of ahOL with interferon gamma (IFNgamma) evoked susceptibility to TRAIL-induced death, which did not require inhibition of protein synthesis. A blocking experiment with monoclonal antibodies directed against TRAIL-R1 and TRAIL-R2 revealed that TRAIL-R1 is mainly involved in TRAIL-induced apoptosis of ahOL. In contrast to ahOL, microglial cells were completely resistant to cell death induced by TRAIL. Microglial cells had high surface expression of the decoy receptor TRAIL-R3, suggesting that resistance of these glial cells to TRAIL-induced death depends on the presence of the protective effect of TRAIL-R3. Stimulation of microglia with TRAIL increased further expression of TRAIL-R3, but it had no effect on the expression of TRAIL receptors by ahOL. This result may implicate TRAIL as an effector-immune molecule in selective ahOL demise in inflammatory/demyelinating conditions.