Autophagy-mediated stress response in motor neuron after transient ischemia in rabbits

ObjectiveSpinal cord injury is considered to be related to a vulnerability of spinal motor neurons to ischemia. However, the mechanisms underlying this vulnerability are not fully understood. We investigated the role of autophagy, which is an intracellular bulk degradation process, at motor neuron as a potential mechanism of neuronal death by immunohistochemical analysis for microtubule-associated protein light chain3 (LC3) and γ-aminobutyric-acid type-A-receptor-associated protein (GABARAP) which are considered as markers of autophagy.MethodsWe used a rabbit spinal cord ischemia model with the use of a balloon catheter. The spinal cord was removed at 8 hours, 1, 2, or 7 days after 15 minutes of transient ischemia, and histologic changes were examined with hematoxylin-eosin staining. Western blot analysis for LC3 and GABARAP, temporal profiles of LC3 and GABARAP immunoreactivity, and double-label fluorescence immunocytochemical studies were performed.ResultsIn the ischemia group, about 85% of motor neurons were preserved until 2 days after reperfusion, but were selectively lost at 7 days (P < .001 compared with sham group). Western blot analysis demonstrated slight immunoreactivity for LC3 and GABARAP in the sham-operated spinal cords. In contrast, the ischemia group LC3 and GABARAP immunoreactivity became apparent at 8 hours after reperfusion. With quantitative analysis we found that ischemia affected expression profiles of LC3-II and GABARAP. At 8 hours after reperfusion, co-labeling of LC3 and GABARAP were observed in the same motor neurons that eventually died.ConclusionThese data suggest that autophagy was induced in motor neurons by transient spinal cord ischemia in rabbits.Clinical RelevancePatients undergoing thoracic aneurysm repair who awake with no neurologic deficit immediately after operation can sometimes eventually develop paraplegia. However, the exact mechanism of this delayed vulnerability is not fully understood. In the present study, we demonstrated that following spinal cord ischemia in rabbits, expression of both LC3 and GABARAP were increased in the same motor neurons which eventually died, suggesting strong induction of autophagy in those cells. Thus, the results of the present study indicate that autophagy may be a potential mechanism of neuronal cell death in this model