Amyotrophic Lateral Sclerosis Mutations Enhance Replication of a Neurotropic Virus

Abstract

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease affecting motor neurons which causes loss of function in the upper and lower limbs and is invariably fatal. ALS can be familial, due to inherited mutations or Sporadic due to spontaneous uncharacterized mutations. The most common mutation associated with familial ALS is a hexanucleotide repeat (G4C2) expansion found in the C9orf72 gene which can cause a gain of function associated with the expression of abnormal bidirectionally transcribed mRNAs carrying the repeat. Enteroviruses (EV) such as poliovirus have a high tropism for the central nervous system (CNS) and can cause acute flaccid myelitis (AFM). Both ALS and AFM target motor neurons and cause paralysis. Studies found that both ALS and EV infections can disrupt the nuclear pore complex, impair nucleocytoplasmic trafficking, and promote the formation of stress granules leading to impaired function of upper and lower motor neurons. Due to these similarities, we hypothesize that mutations associated with ALS impact viral replication and that viral infection in this setting can exacerbate ALS-associated pathology. To investigate this hypothesis, fibroblasts from familial (C90rf72) and Sporadic ALS patients or healthy individuals were infected with poliovirus. Evaluation by light microscopy revealed that virus-induced cytopathic effects developed more rapidly in fibroblasts from ALS patients compared to controls. Further analysis using plaque assays to monitor poliovirus replication found that fibroblasts from ALS patients produced significantly more virus compared to control fibroblasts. These results reveal that mutations contributing to both familial and Sporadic forms of ALS enhance replication of poliovirus. Analysis of viral RNA in infected ALS patient fibroblasts utilizing qRT-PCR will determine if the increase in viral replication is associated with higher levels of RNA synthesis. Experiments are ongoing to determine if increased viral replication is due to an impaired antiviral response. Similar analyses in patient-derived motor neurons differentiated from iPSC cells will determine if ALS mutations impact viral replication and the antiviral response in clinically relevant cell types. This work reveals a pro-viral effect of mutations associated with ALS and raises the possibility that viral infection may impact the development or progression of this disease in certain individuals.