Title: Role of motor neuron autophagy in a mouse model of Amyotrophic Lateral Sclerosis
Description: Amyotrophic Lateral Sclerosis (ALS) is a neurological disease characterized by the degeneration of upper and lower motor neurons. Genetic studies have revealed that many ALS-associated genes are involved in autophagy, but the role of this pathway in motor neurons remains poorly understood. Here, we use the SOD1G93A mouse model to investigate the role of autophagy in ALS. We find neuronal subtype-specific regulation of autophagy over the course of disease progression. Vulnerable motor neurons form large GABARAPL1-positive autophagosomes that engulf ubiquitinated cargo recognized by the selective autophagy receptor p62. Other motor neurons and interneurons do not engulf cargo within GABARAPL1-positive autophagosomes and instead accumulate somatodendritic aggregates. To investigate whether motor neuron autophagy is protective or detrimental, we generated mice in which the critical autophagy gene Atg7 is specifically disrupted in motor neurons. Phenotypic analysis of these mice revealed that autophagy is dispensable for motor neuron survival but plays a key role in regulating presynaptic structure and function.

By crossing these mice to the SOD1G93A mouse model, we find that autophagy inhibition accelerates early neuromuscular denervation and neurological dysfunction. However, loss of autophagy in motor neurons eventually leads to an extension of lifespan, and this is associated with reduced pathology in interneurons and glial cells. These data suggest that vulnerable motor neurons rely on autophagy to maintain neuromuscular innervation early in disease. However, autophagy eventually acts in a non-cell autonomous manner to promote disease spread and neuroinflammation. Our results reveal counteracting roles for motor neuron autophagy early and late in ALS disease progression.