Platelet‐activating factor induces cell death in cultured astrocytes and oligodendrocytes: Involvement of caspase‐3

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Abstract
The biologically active lipid metabolite, platelet‐activating factor (PAF), is thought to contribute to inflammatory processes and tissue damage in a variety of central nervous system (CNS) injuries. In previous studies, we found that after contusion spinal cord injury, treatment with a PAF antagonist led to significantly increased white matter tissue sparing as well as decreased mRNA levels for pro‐inflammatory cytokines. Some studies suggest that PAF can also have toxic effects on neurons in vitro. Few studies, however, have examined the effects of PAF on glial cells of the CNS. In the present study, the potential for PAF to act as a toxin to cultured astrocytes was examined. Also investigated were the effects of PAF on oligodendrocytes at two different stages of development. Treatment with 0.02–2 μM PAF for 72 h resulted in significant levels of cell death in both cell types (P < 0.05), an effect that was blocked by the PAF receptor antagonists, WEB 2170 and BN 52021. To investigate PAF‐induced glial cell death further, we looked for activation of the enzyme, caspase‐3, which can be indicative of apoptosis. Immunocytochemistry demonstrated that PAF at all concentrations caused activation of caspase‐3 at 24, 48, and 72 h after treatment in both cell types. Caspase‐3‐dependent cell death was further confirmed using knockout mice (−/−) deficient in the caspase‐3 gene. Toxicity was lost when astrocytes (−/−) were exposed to 0.02–2 μM PAF (P < 0.01). Oligodendrocytes (−/−) were not susceptible to toxicity at 2 μM PAF (P < 0.001). The results demonstrate that the pro‐inflammatory molecule, PAF, induces cell death in cultured CNS glial cells and that this effect is, in part, dependent on caspase‐3 activation. GLIA 38:228–239, 2002.