Tumour necrosis factor (TNF)-induced death of oligodendrocytes, the cell type targeted in multiple sclerosis, is mediated by TNF receptor p55 (TNFR-p55). The ligation of TNFR-p55 induces several signal transduction pathways; however, the precise mechanism involved in human oligodendrocyte (hOL) death is unknown. We defined that TNF-induced death of hOLs is non-caspase dependent, as evidenced by lack of generation of caspases 8, 1 and 3 active subunits; lack of cleavage of caspases 1 and 3

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... genic substrates; and lack of hOL death inhibition by the general caspase inhibitor, ZVAD.FMK. Electrophoresis of TNF-exposed hOL DNA revealed large-scale DNA fragmentation characteristic of apoptosis-inducing factor (AIF)-mediated cell death, and co-localization experiments showed that AIF translocation to the nucleus occurred upon exposure to TNF. AIF depletion by an antisense strategy prevented TNF-induced hOL death. These results indicate that TNFinduced death of hOLs is dependent on AIF, information of significance for the design strategies to protect hOLs during immune-mediated demyelination. Abbreviations: AIF = apoptosis-inducing factor; anti-GFAP = anti-glial fibrillary acidic protein; anti-MBP = anti-myelin basic protein; asAIF = antisense AIF; FACS = fluorescence-activated cell sorter; FADD = Fas-associated protein with death domain; hOL = human oligodendrocyte; OL = oligodendrocyte; PI = propidium iodide; TNF = tumour necrosis factor; TNFR-p55 = TNF receptor p55; TPCK = N-tosyl-L-phenylalanine chloromethyl ketone; TRADD = TNF-R1-associated death domain