High-throughput quantitative analysis of axonal transport in cultured neurons from SOD1 ALS mice by using a microfluidic device.

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease characterized by selective loss of motor neurons. We have previously shown that autophagosome-like vesicular structures are progressively accumulated in the spinal axons of an ALS mouse model, overexpressing human Cu/Zn superoxide dismutase (SOD1) mutant, prior to the onset of motor symptoms. This suggests that axonal transport perturbation can be an early sign of neuronal dysfunction. However, the exact causal relationship between axonal transport deficits and neurodegeneration is not fully understood. To clarify whether axonal transport of organelles even in neurons at early developmental stages was affected by overexpression of mutant SOD1, we conducted a microfluidic device-based high-throughput quantitative analysis of the axonal transport of acidic vesicles and mitochondria in primary cultured cortical neurons established from SOD1 transgenic mice. Compared to wild-type (WT), a significantly increased number of motile acidic vesicles, i.e., autophagosomes and/or late-endosomes, was observed in the axons of SOD1 neurons. By contrast, mitochondria moving along the axons were significantly decreased in SOD1 compared to WT. Since such phenotypes, where the axonal transport of these organelles is differently affected by mutant SOD1 expression, emerge before axonal degeneration, axonal transport deficits could dysregulate axon homeostasis, thereby ultimately accelerating neurodegeneration.