Programmed cell death of developing mammalian neurons after genetic deletion of caspases
R W Oppenheim1, R A Flavell, S Vinsant
1Department of Neurobiology and Anatomy and the Neuroscience Program, Wake Forest University School of Medicine, Winston-Salem, North Carolina 27157, USA. roppenhm@wfubmc.edu
Abstract:
An analysis of programmed cell death of several populations of developing postmitotic neurons after genetic deletion of two key members of the caspase family of pro-apoptotic proteases, caspase-3 and caspase-9, indicates that normal neuronal loss occurs. Although the amount of cell death is not altered, the death process may be delayed, and the cells appear to use a nonapoptotic pathway of degeneration. The neuronal populations examined include spinal interneurons and motor, sensory, and autonomic neurons. When examined at both the light and electron microscopic levels, the caspase-deficient neurons exhibit a nonapoptotic morphology in which nuclear changes such as chromatin condensation are absent or reduced; in addition, this morphology is characterized by extensive cytoplasmic vacuolization that is rarely observed in degenerating control neurons. There is also reduced terminal deoxynucleotidyl transferase-mediated biotinylated UTP nick end labeling in dying caspase-deficient neurons. Despite the altered morphology and apparent temporal delay in cell death, the number of neurons that are ultimately lost is indistinguishable from that seen in control animals. In contrast to the striking perturbations in the morphology of the forebrain of caspase-deficient embryos, the spinal cord and brainstem appear normal. These results are consistent with the growing idea that the involvement of specific caspases and the occurrence of caspase-independent programmed cell death may be dependent on brain region, cell type, age, and species or may be the result of specific perturbations or pathology.
Insights
Normal neuronal loss occurs even without caspases (caspase-3 and caspase-9), suggesting alternative cell death pathways in developing neurons. This programmed cell death can be delayed but results in similar cell numbers lost.
Area of Science:
- Neuroscience
- Developmental Biology
- Cell Biology
Background:
- Programmed cell death is crucial for neuronal development.
- Caspases are key proteases in apoptosis, a major form of programmed cell death.
- The role of caspases in neuronal development and potential caspase-independent pathways require further investigation.
Purpose of the Study:
- To investigate the role of caspase-3 and caspase-9 in programmed cell death of developing neurons.
- To determine if the absence of these caspases alters the amount or morphology of neuronal degeneration.
- To explore the mechanisms of neuronal loss in caspase-deficient models.
Main Methods:
- Genetic deletion of caspase-3 and caspase-9 in developing neurons.
- Analysis of neuronal populations including spinal interneurons, motor, sensory, and autonomic neurons.
- Light and electron microscopy to assess cell morphology.
- Terminal deoxynucleotidyl transferase-mediated biotinylated UTP nick end labeling (TUNEL) assay.
Main Results:
- Caspase-deficient neurons exhibited non-apoptotic morphology with reduced chromatin condensation and increased cytoplasmic vacuolization.
- Despite altered morphology and potential delays, the total number of neurons lost was comparable to controls.
- Spinal cord and brainstem appeared normal, contrasting with forebrain perturbations in caspase-deficient embryos.
- Reduced TUNEL labeling in dying caspase-deficient neurons indicated altered cell death pathways.
Conclusions:
- Programmed neuronal loss occurs independently of caspase-3 and caspase-9.
- Neurons can utilize non-caspase-dependent pathways for degeneration.
- The involvement of caspases and caspase-independent cell death is context-dependent, varying by brain region, cell type, age, and species.
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