Cortical hyperexcitability drives dying forward ALS symptoms and pathology in mice

Abstract

Amyotrophic lateral sclerosis (ALS) is a progressive fatal disorder caused by degeneration of motor neurons in the cortex and spinal cord. The origin of ALS in the central nervous system is unclear, however cortical hyperexcitability appears as an early and intrinsic feature of ALS and has been linked to degeneration of spinal motor neurons via a dying-forward mechanism. Here, we implement chemogenetics to validate the dying forward hypothesis of ALS in mice. We show that chronic hyperexcitability of corticomotoneurons induced by excitatory chemogenetics results in motor symptoms and core neuropathological hallmarks of ALS, including corticomotoneuron loss, corticospinal tract degeneration and reactive gliosis. Importantly, corticomotoneuron loss was sufficient to drive degeneration of spinal motor neurons and neuromuscular junctions (NMJs), associated with cytoplasmic TAR DNA binding protein 43 (TDP-43) pathology. These findings establish a cortical origin of ALS mediated by neuronal hyperexcitability, consistent with a dying forward mechanism of neurodegeneration.