Insulin-like growth factor-I analogue prevents apoptosis mediated through an interleukin-1 beta converting enzyme (caspase-1)-like protease of cerebellar external granular layer neurons: developmental stage-specific mechanisms of neuronal cell death.

Using an organotypic slice culture system of neonatal rat cerebellum, we examined developmental stage-specific mechanisms of cell death of granule neurons. This culture system allows a serial process of granule neuron development including their proliferation during the early culture period and the proceeding migration from the external granular layer to the internal granular layer in the presence of a supraphysiological concentration (5 micrograms/ml) of insulin. Insulin deprivation induced apoptosis of granule neurons in external granular layer but not in internal granular layer. A truncated analogue of insulin-like growth factor-I (des (1-3) insulin-like growth factor-I) prevented this apoptosis at a concentration of 65-650 ng/ml. Some apoptotic granule neurons expressed proliferating cell nuclear antigen but not TAG-1, a marker protein of the postmitotic and premigratory granule neurons. Thus, this apoptosis occurred at a specific stage in granule neuron development: at the stage before TAG-1 expression and at least partly at the proliferative state. Ac-YVAD-CHO, an inhibitor of interleukin-1 beta converting enzyme (caspase-1)-like proteases, had a protective effect on this apoptosis. Interleukin-1 beta converting enzyme (caspase-1)-like protease activity increased under the apoptosis-induced condition. High concentration of K+, which is known to prevent granule neuron apoptosis in dissociated cultures, had a partial protective effect on this apoptosis. These findings suggest that (i) cerebellar granule neurons fall into apoptosis at the specific developmental stage unless stimulated by insulin-like growth factor-I (analogue), (ii) this apoptosis is mediated through an interleukin-1 beta converting enzyme-like protease, and (iii) this apoptosis consists of K(+)-sensitive and K(+)-insensitive components.