Astrocyte mediated toxicity leads to motor neuron death in Spinal Muscular Atrophy (S17.006)

OBJECTIVE: To determine the contribution of non-cell autonomous neuronal death in Spinal Muscular Atrophy (SMA)BACKGROUND: SMA is the leading genetic cause of death in infants and toddlers. In children with SMA, loss of motor neurons in the spinal cord triggers rapidly progressive paralysis, and death in the most severe cases. SMA is caused by a mutation in the Survival of Motor Neuron 1 (SMN1) gene, resulting in diminished production of SMN protein in all cells and tissue. However, the mechanism by which this mutation and reduction in protein causes motor neuron death is unclear. Our previous studies from Amyotrophic Lateral Sclerosis (ALS) have shown the importance of astrocyte mediated neurotoxicity in motor neuron disease, raising the hypothesis that non-neuronal cells may play an important role in SMA related motor neuron degeneration.DESIGN/METHODS: Embryonic spinal cord motor neurons were cultured from SMA Type 1 transgenic mice in the presence or absence of astrocytes. In order to determine the mechanism of cell death observed, we used biochemical inhibitors of individual death pathways, as well as analysis of multiple cell death markers including TUNEL and Ethidium Homodimer (EtHD).RESULTS: We showed that Type 1/SMA motor neurons die in the presence of Type 1/SMA or WT astrocytes, however their survival is unaffected in the absence of astrocytes. Additionally, we observed a pronounced increase in TUNEL and EtHD labeling in SMA motor neurons compared to wild type controls. Interestingly, through western blot analysis, we also found a marked increase of caspase 8 in SMA astrocytes when compared to WT astrocytes. Our findings suggest that inhibition of caspase 8 activity attenuates the MN death seen in our in vitro Type 1 model of SMA.CONCLUSIONS: These data taken together, suggest that astrocytes trigger an apoptosis-like mechanism of motor neuron death in SMA. Disclosure: Dr. Papadimitriou has nothing to disclose. Dr. Phani has nothing to disclose. Dr. Jacquier has nothing to disclose. Dr. LeVerche has nothing to disclose. Dr. Pradhan has nothing to disclose. Dr. Kariya has nothing to disclose. Dr. Monani has nothing to disclose. Dr. Re has nothing to disclose. Dr. Przedborski has nothing to disclose.