TRAIL-induced death of human adult oligodendrocytes is mediated by JNK pathway.

Tumor necrosis-related apoptosis-inducing ligand (TRAIL) induces apoptosis of oligodendrocytes, target cells of immune attack in multiple sclerosis (MS). TRAIL-induced human oligodendrocyte (hOL) death depends on TRAIL ligation with its receptor 1 (TRAIL-R1). However, the intracellular signaling initiated with ligation of TRAIL-R1 in hOLs is unknown. We defined that intracellular transduction signaling involved in TRAIL-induced death of hOLs is associated with strong activation of c-jun NH2-terminal kinase (JNK) and a dominant negative mutant of MKK4/SEK1, MAP kinase upstream of JNK, inhibited TRAIL-induced apoptosis of hOLs. The immunoprecipitation experiments showed that JNK3 isoform was predominantly activated upon hOLs exposure to TRAIL and JNK-3 activation occurred before mitochondrial membrane dysfunction. The other mitogen-activated protein kinase p38 and ERK, as well as calpains and serine proteases, were not activated during TRAIL-induced hOL death. Accordingly, the calpain inhibitor, ZLLY.FMK, p38 kinase inhibitor, SB 203580, and serine proteases inhibitor, TPCK, did not protect hOLs from TRAIL-induced apoptosis. These results demonstrate that JNK pathway is critically involved in hOL death induced by TRAIL and might have significant importance in designing new molecules to protect immune-mediated hOLs demise.