Fas receptor and neuronal cell death after spinal cord ischemia

Cell death from spinal cord injury is mediated in part by apoptotic mechani sms involving downstream caspases (e.g., caspase-3). Upstream mechanisms ma y involve other caspases such as procaspase-8, a 55 kDa apical caspase, whi ch we found constitutively expressed within spinal cord neurons along with Fas. As early as 1.5 hr after transient ischemia, activated caspase-8 (p18) and caspase-8 mRNA appeared within neurons in intermediate gray matter and in medial ventral horn. We also detected evidence for an increase in death receptor complex by co-immunoprecipitation using Fas and anti-procaspase-8 after ischemia. At early time points, Fas and p18 were co-expressed within individual neurons, as were activated caspase-8 and caspase-3. Moreover, w e detected p18 in cells before procaspase-3 cleavage product (p20), suggest ing sequential activation. The appearance of cytosolic cytochrome c and gel solin cleavage after ischemia was consistent with mitochondrial release and caspase-3 activation, respectively. Numerous terminal deoxynucleotidyl tra nsferase-mediated DNA nick end-labeling-positive neurons contained p18 or p 20 (65 and 80%, respectively), thereby supporting the idea that cells under going cell death contain both processed caspases. Our data are consistent w ith the idea that transient spinal cord ischemia induces the formation of a death-inducing signaling complex, which may participate in caspase-8 activ ation and sequential caspase-3 cleavage. Death receptors as well as downstr eam caspases may be useful therapeutic targets for limiting the death of ce lls in spinal cord.