Increased Expression of IL-1β Converting Enzyme in Hippocampus after Ischemia: Selective Localization in Microglia

Abstract

Although the interleukin-1␤ converting enzyme (ICE)/CED-3 family of proteases has been implicated recently in neuronal cell death in vitro and in ovo, the role of specific genes belonging to this family in cell death in the nervous system remains unknown. To address this question, we examined the in vivo expression of one of these genes, Ice, after global forebrain ischemia in gerbils. Using RT-PCR and Western immunoblot techniques, we detected an increase in the mRNA and protein expression of ICE in hippocampus during a period of 4 d after ischemia. Chromatin condensation was observed in CA1 neurons within 2 d after ischemia. Internucleosomal DNA fragmentation and apoptotic bodies were observed between 3 and 4 d after ischemia, a period during which CA1 neuronal death is maximal. In nonischemic brains, ICE-like immunoreactivity was relatively low in CA1 pyramidal neurons but high in scattered hippocampal interneurons. After ischemia, ICE-like immunoreactivity was not altered in these neurons. ICE-like immunoreactivity, however, was observed in microglial cells in the regions adjacent to the CA1 layer as early as 2 d after ischemic insult. The increase in ICE-like immunoreactivity was robust at 4 d after ischemia, a period that correlates with the DNA fragmentation observed in hippocampal homogenates of ischemic brains. These results provide the first evidence for the localization and induction of ICE expression in vivo after ischemia and suggest an indirect role for ICE in ischemic damage through mediation of an inflammatory response.

DNA Fragmentation Follows Delayed Neuronal Death in CA1 Neurons Exposed to Transient Global Ischemia in the Rat

“…Members of the interleukin-converting enzyme gene family and p53 are common apoptosis-driving genes (Yonish-Rovach et aI, 199 1; Miura et aI., 1993;Steller, 1994;Hale et aI, 1994;Sakhi et aI., 1994;Deshmukh et aI, 1996) that have been associated with focal ischemia (Crumrine et aI, 1994;Li et aI, 1994). Their role in global ischemia is less clear as shown by the absence of p53 protein and mRNA in the present study and of interleukin-converting enzyme in an earlier study by Bhat et al (1996). However, their ab sence does not exclude apoptosis because their partici pation is not necessarily required for apoptosis to take place (Hale et aI, 1995;Vasilakos et aI, 1995;Sadoul et aI, 1996).…”

Reduced Ischemic Brain Injury in Interleukin-1β Converting Enzyme—Deficient Mice

“…The exceptions to this pattern are that Fas-mediated killing of thymocytes is reduced in thymocytes isolated from KO mice (Kuida et a!., 1995) as is apoptotic death in dorsal root ganglion cultures after growth factor withdrawal (Friedlander et aI., 1997). In addition, some studies show that ICE is not expressed in neurons (Bhat et a!., 1996;Lynch et aI., 1997), even when the brain is challenged by global forebrain isch emia or lipopolysaccharide and expression is increased in astrocytes and microglia (Vasilakos et aI., 1995). However, it is still unknown whether or not ICE is ex pressed in neurons after a focal ischemic insult.…”

Extended therapeutic window for caspase inhibition and synergy with MK-801 in the treatment of cerebral histotoxic hypoxia

“…macrophages or microglia. Ischemia induces expression of caspase-1 in microglia (Bhat et al, 1996). The preferred substrate for caspase-1 is pro-interleukin-1b that is proteolytically cleaved to its active form.…”