Increased Axonal Mitochondrial Mobility Does Not Slow Amyotrophic Lateral Sclerosis (ALS)-like Disease in Mutant SOD1 Mice

Abstract

Reduced axonal mitochondrial transport has been observed in major neurodegenerative diseases, including fALS patients and SOD1G93A mice. However, it is unclear whether this defect plays a critical role in axonal degeneration or simply reflects sequelae of general transport alteration. Using genetic mouse models combined with time-lapse imaging of live neurons, we previously discovered that axon-targeted syntaphilin (SNPH) acts as a docking receptor specific for axonal mitochondria. Deletion of the snph gene in mice results in a substantially higher proportion of axonal mitochondria in the mobile state without any effect on the transport of other axonal organelles. Here we address whether increased (rescued) axonal mitochondrial mobility changes the disease course by crossing fALS-linked transgenic SOD1G93A and snph−/− knock-out mice. We found that a 2-fold increase in axonal mitochondrial mobility in SOD1G93A/snph−/− mice did not affect the onset of ALS-like symptoms. Both SOD1G93A and SOD1G93A/snph−/− mice exhibit similar weight loss, deterioration in motor function and motor neuron loss, significant gliosis, and a lifespan of 152–154 days. Thus, for the first time, our study provides genetic and pathological evidence that the impairment of mitochondrial transport seen in SOD1G93A mice plays a minimal role in the rapid-onset of fALS-linked pathology. Reduced axonal mitochondrial transport has been observed in major neurodegenerative diseases, including fALS patients and SOD1G93A mice. However, it is unclear whether this defect plays a critical role in axonal degeneration or simply reflects sequelae of general transport alteration. Using genetic mouse models combined with time-lapse imaging of live neurons, we previously discovered that axon-targeted syntaphilin (SNPH) acts as a docking receptor specific for axonal mitochondria. Deletion of the snph gene in mice results in a substantially higher proportion of axonal mitochondria in the mobile state without any effect on the transport of other axonal organelles. Here we address whether increased (rescued) axonal mitochondrial mobility changes the disease course by crossing fALS-linked transgenic SOD1G93A and snph−/− knock-out mice. We found that a 2-fold increase in axonal mitochondrial mobility in SOD1G93A/snph−/− mice did not affect the onset of ALS-like symptoms. Both SOD1G93A and SOD1G93A/snph−/− mice exhibit similar weight loss, deterioration in motor function and motor neuron loss, significant gliosis, and a lifespan of 152–154 days. Thus, for the first time, our study provides genetic and pathological evidence that the impairment of mitochondrial transport seen in SOD1G93A mice plays a minimal role in the rapid-onset of fALS-linked pathology.