Exploration of Target Molecules Related to Pathogenesis and Development of Therapy for Sporadic ALS

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For the elucidation of pathogenesis and therapy development of sporadic ALS, it might be an effective strategy to create disease models by reproduction of early gene expression changes observed in the patients' tissues. Gene expression analysis was performed in ALS and control spinal motor neurons isolated by laser microdissection technique. As a result, we have identified 196 genes in total that revealed motor neuron-specific expression changes in ALS. We have further analyzed expression dynamics of these genes including dynactin 1, early growth response 3, acetyl-CoA transporter, death receptor 5, and cyclin C in relation to pathological markers for motor neuron degeneration (i.e., cytoplasmic accumulation of phosphorylated neurofilament-H (pNF-H) and ubiquitylated protein) and the numbers of residual motor neurons. Through this analysis, we have identified dynactin 1 as one of the genes of which expression changes occurred in the early phase of neurodegeneration in sporadic ALS. We next tried to reproduce gene expression change of dynactin 1 in cultured cell using siRNA technique and analyzed the effect of gene knockdown employing various assay systems.Neuronal cell death was induced by dynactin 1 knockdown and the role of autophagy in this cell death pathway was investigated. As a result, we observed that autophagosome formation was accelerated due to impairment of the autophagosome-lysosome fusion caused by the inefficient function of dynactin 1.Moreover, accumulation of polyubiquitinated protein was suggested in the cells with down-regulated dynactin 1. We suppose that down-regulation of dynactin 1 might lead to accumulation of aberrant proteins unprocessed by autophagic pathway due to its impairment and cause neuronal cell death.Impairment of autophagy was observed also in spinal motor neurons of ALS patients, suggesting that dynactin 1 knockdown cell system might be a good disease model that reflects some part of important pathogenesis of sporadic ALS.