| The Fas/Fas Ligand death receptor-ligand system plays an essential role in apoptosis that contributes to secondary damage after spinal cord injury (SCI), but the mechanism regulating the efficiency of Fas/FasL signaling in the central nervous system (CNS) is unknown. Fas/FasL signaling complexes in membrane rafts were investigated in the spinal cord of adult female Fischer rats subjected to moderate cervical SCI and sham operation controls. In sham-operated animals, a portion of FasL, but not Fas was present in membrane rafts. SCI resulted in Fas translocation into membrane raft microdomains where Fas associates with the adaptor proteins Fas-associated death domain (FADD), caspase-8, cellular FLIP long form (cFLIPL), and caspase-3 forming a death-inducing signaling complex (DISC). The formation of the DISC signaling platform leads to rapid activation of initiator caspase-8 and effector caspase-3, and the modification of signaling intermediates such as FADD and cFLIPL. Experiments using FasL neutralizing antibody show that FasL neutralization after SCI blocked an increase in Fas expression and recruitment of Fas into membrane rafts, thus leading to improved functional performance as determined by behavioral tests administered after SCI. The characterization of neuronal membrane protein 35 (NMP35) confirmed the existence of neuronal membrane protein 35 (NMP35), an inhibitor of Fas signaling, in membrane rafts of spinal cord cells in sham-operated animals. SCI induced a rapid translocation of NMP35 out of membrane rafts and altered its association with Fas, suggesting that redistribution of NMP35 out of membrane rafts may contribute to the pathogenesis of cell death after SCI. These results indicate that Fas-mediated signaling after SCI is similar to that of type I Fas-expressing cells, and utilizes membrane rafts to govern diverse signaling responses in the traumatized spinal cord. |
