Caspase‐3 is activated following axotomy of neonatal facial motoneurons and caspase‐3 gene deletion delays axotomy‐induced cell death in rodents

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Abstract
In this report, we examined the possible functions of the cell death protease, caspase‐3, in the axotomy‐induced apoptosis of facial motoneurons in newborn rodents. Using in situ hybridization and Western blot, we found higher levels of caspase‐3 mRNA and pro‐caspase‐3 protein expression in motoneurons of neonatal and 2‐week‐old rats than adult rats. Following facial motoneuron axotomy, caspase‐3 mRNA and protein expression increased in motoneurons of both neonatal and adult rats. However, using an antibody directed to the activated form of the caspase‐3 protease, we found that catalytically active caspase‐3 was present only in axotomized neonatal motoneurons. As motoneurons in neonatal but not adult rodents are susceptible to axotomy‐induced apoptosis, we hypothesized that caspase‐3 may play a role in their demise. To determine the necessity of caspase‐3 activation in axotomy‐induced apoptosis, we counted the number of surviving motoneurons at 4 and 7 days following axotomy in wild type mice and caspase‐3 gene‐deleted mice. There were nearly three times more surviving motoneurons in caspase‐3 gene‐deleted mice than in wild type mice at both 4 days (mean 1074 vs. 464, P < 0.005) and 7 days (mean 469 vs. 190, P < 0.005) following injury, indicating a slower rate of death. Examination of the dying motoneurons using TUNEL staining (for fragmented DNA) and bisbenzimide staining (for nuclear morphology) revealed incomplete nuclear condensation in caspase‐3‐deficient motoneurons. These results demonstrate that caspase‐3 activation plays important roles in the rapid demise of axotomized neonatal motoneurons.

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