Oligodendroglial apoptosis occurs along degenerating axons and is associated with FAS and p75 expression following spinal cord injury in the rat

Abstract

Apoptosis or programmed cell death has been reported after CNS trauma. However, the significance of this mechanism in the pathophysiology of spinal cord injury, in particular at the cervical level, requires further investigation. In the present study, we used the extradural clip compression model in the rat to examine the cellular distribution of apoptosis following cervical spinal cord injury, the relationship between glial apoptosis and post-traumatic axonal degeneration and the possible role of apo[apoptosis]-1, CD95 (FAS) and p75 in initiating post-traumatic glial apoptosis. In situ terminal-deoxy-transferase mediated dUTP nick end labeling revealed apoptotic cells, largely oligodendrocytes as identified by cell specific markers, in grey and white matter following spinal cord injury. Apoptotic cell death was confirmed using electron microscopy and by the demonstration of DNA laddering on agarose gel electrophoresis. Beta-amyloid precursor protein was used as a molecular marker of axonal degeneration on western blots and immunohistochemistry. Degeneration of axons was temporally and spatially co-localized with glial apoptosis. FAS and p75 protein expression was seen in astrocytes, oligodendrocytes and microglia, and was also seen in some apoptotic glia after cord injury. Both FAS and p75 increased in expression in a temporal course, which mirrored the development of cellular apoptosis. The downstream caspases 3 and 8, which are linked to FAS and p75, demonstrated activation at times of maximal apoptosis, while FLIP-L an inhibitor of caspase 8, decreased at times of maximal apoptosis. We conclude that axonal degeneration after traumatic spinal cord injury is associated with glial, in particular oligodendroglial, apoptosis. Activation of the FAS and p75 death receptor pathways may be involved in initiating this process.