Human Mutant Dynactin Subunit 1 Causes Profound Motor Neuron Disease Consistent with Possible Mechanisms Involving...

Mutations in the gene encoding the p150 subunit of the dynactin complex (DCTN1) are linked to amyotrophic lateral sclerosis, spinal and bulbar muscular atrophy, and Perry syndrome. These neurodegenerative diseases can cause muscle weakness and atrophy, parkinsonian-like symptoms, and paralysis. To examine the evolution of neuropathology caused by a mutation in DCTN1 and cellular mechanisms of disease for therapeutic discovery, we characterized mice expressing either human wildtype or mutant (G59S) DCTN1. Neuron-specific expression of mutant, but not wildtype, DCTN1 caused fatal age-related paralytic disease and motor neuron (MN) degeneration in the spinal cord with axonopathy and chromatolysis without apoptotic morphology. MNs became positive for cleaved caspase-3, cleaved caspase-8, and nitrated Hsp90. Mitochondria accumulated and appeared fragmented and dysmorphic and then were lost. This pathology was accompanied by invasion of CD95- and CD8-positive mononuclear T cells into the ventral horn and accumulation of TNFα and IL9. Administration of the mitochondrial division inhibitor-1 (Mdivi-1) protected MNs and extended the lifespan of G59S-DCTN1 mice. A mitochondrial permeability transition pore inhibitor also extended lifespan. Thus, mutant DCTN1 causes degeneration of MNs associated with axonopathy, mitochondriopathy, nitrative stress, and caspase activation. It appears as retrograde neurodegeneration and inflammatory T-cell-like cytolysis. Mitochondria are possible therapeutic targets in DCTN1-linked neurodegenerative disorders.