GENETIC AND METABOLIC STATUS OF NGF-DEPRIVED SYMPATHETIC NEURONS SAVED BY AN INHIBITOR OF ICE FAMILY PROTEASES

Sympathetic neurons undergo programmed cell death (PCD) when deprived of NGF. We used an inhibitor to examine the function of interleukin-1 beta-converting enzyme (ICE) family proteases during sympathetic neuro nal death and to assess the metabolic and genetic status of neurons sa ved by such inhibition. Boc-aspartyl(OMe)-fluoromethylketone (BAF), a cell-permeable inhibitor of the ICE family of cysteine proteases, inhi bited ICE and CPP32 (IC50 similar to 4 mu M) in vitro and blocked Fas- mediated apoptosis in thymocytes (EC(50) similar to 10 mu M) At simila r concentrations, BAF also blocked the NGF deprivation-induced death o f rat sympathetic neurons in culture. Compared to NGF-maintained neuro ns, BAF-saved neurons had markedly smaller somas and maintained only b asal levels of protein synthesis; readdition of NGF restored growth an d metabolism. Although BAF blocked apoptosis in sympathetic neurons, i t did not prevent the fall in protein synthesis or the increase in the expression of c-jun, c-fos, and other mRNAs that occur during neurona l PCD, implying that the ICE-family proteases function downstream of t hese events during PCD. NGF and BAF rescued sympathetic neurons with a n identical time course, suggesting that NGF, in addition to inhibitin g metabolic and genetic events associated with neuronal PCD, can act p osttranslationally to abort apoptosis at a time point indistinguishabl e from the activation of cysteine proteases. Both poly-(ADP ribose) po lymerase and pro-ICE and Ced-3 homolog-1 (ICH-1) appear to be cleaved in a BAF-inhibitable manner, although the majority of pro-CPP32 appear s unchanged, suggesting that ICH-1 is activated during neuronal PCD. P otential implications of these findings for anti-apoptotic therapies a re discussed.