INHIBITORS OF INTERLEUKIN-1 BETA-CONVERTING ENZYME-FAMILY PROTEASES (CASPASES) PREVENT APOPTOSIS WITHOUT AFFECTING DECREASED CELLULAR ABILITY TO REDUCE (4,5-DIMETHYLTHIAZOL-2-YL)-2,5-DIPHENYLTETRAZOLIUM BROMIDE IN CEREBELLAR GRANULE NEURONS

We assessed the possible role of interleukin-1 beta-converting enzyme- family proteases (caspases) in apoptosis in cultured rat cerebellar gr anule neurons. CPP32 (caspase-3)-like protease activity was augmented by low KCl treatment, preceding neuronal cell death. Agents such as br ain-derived neurotrophic factor (BDNF), dibutylyl cAMP, NMDA, actinomy cin D, S-adenosyl-L-methionine, and spermine prevented apoptosis. For various neuroprotective agents, the degree of apoptosis prevention cor related with the prevention of the activation of CPP32-like protease. Furthermore, Z-Asp-2,6-dichlorobenzoyloxy-methylketone (Z-Asp-CH2-DCB) , Boc-Asp-fluoromethylketone (Boc-Asp-FMK), and Z-Val-Ala-Asp-fluorome thylketone (Z-VAD-FMK), which are inhibitors of caspases, also prevent ed apoptosis. in contrast to many other neuroprotective agents, these inhibitors of caspases showed little effect on the decrease of cellula r [4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) red uction activity after low KCl treatment. The neurons rescued by these inhibitors of caspases during low KCl treatment were in a hypoenergic state in their ATP levels and vulnerable to subsequent treatment with medium containing high KCl or glutamate which induce an influx of Ca2, but which are less toxic to normal neurons. These results suggest th at caspase(s) are involved in the apoptosis of cerebellar granule neur ons and that several agents protect neurons from death by blocking the activation of the protease(s). Although several caspase inhibitors ex amined in this study protect neurons from apoptosis, rescued neurons a re vulnerable to subsequent stimuli that induce necrotic cell death. ( C) 1998 Elsevier Science B.V. All rights reserved.