PROJECT SUMMARY/ABSTRACT
Amyotrophic Lateral Sclerosis (ALS) and Frontotemporal Dementia (FTD), the second most common form of
dementia, comprise a spectrum of fatal neurodegenerative diseases. An intronic GGGGCC (G4C2)
hexanucleotide repeat expansion (HRE) in the C9orf72 gene, have been linked to ALS and FTD, although
clinically two distinct diseases. The C9orf72 HRE is the most common cause of both familial and sporadic ALS
accounting for ~40% and ~8% of patients respectively. Overall, about 10% of ALS cases are familial with the
remaining 90% being sporadic. The molecular mechanisms underlying disease pathogenesis remain poorly
understood. Defects in nucleocytoplasmic transport (NCT) and the nuclear pore complex (NPC) have recently
emerged as a prominent pathomechanism underlying multiple neurodegenerative diseases including C9orf72
ALS/FTD, subsets of sporadic ALS, Alzheimer’s Disease, and Huntington’s Disease. However, little is known
about the nature of the injury to the NPC and its individual nucleoporin components themselves. Using induced
pluripotent stem cell derived spinal neurons (iPSNs) and postmortem human tissue, we have amassed data
that loss of the transmembrane nucleoporin POM121 from NPCs initiates a pathological cascade impacting
NPC composition, function and downstream cellular survival. Notably, loss of POM121 is mediated by
pathologic G4C2 repeat RNA and not dipeptide repeat poly peptides or loss of C9ORF72 protein. Given that
POM121 protein is not mislocalized and POM121 RNA metabolism is unaltered, we hypothesized that
POM121 and subsequently altered nucleoporin proteins are aberrantly degraded in the early stages of C9orf72
ALS/FTD pathogenesis. Recent work in yeast and non-neuronal mammalian cells has shown that nuclear
CHMP7 “activates” ESCRT-III mediated degradation of nuclear pore complexes and nuclear envelope
components during nuclear pore surveillance and homeostasis. Our new preliminary data suggests that the
loss of POM121 from the nucleoplasm and NPCs is initiated by nuclear accumulation of CHMP7.
Mechanistically, increased nuclear CHMP7 appears to be the result of G4C2 repeat RNA mediated impaired
nuclear export. Thus, our data strongly implicate a CHMP7 degradative pathway in disease pathogenesis.
Intriguingly, knockdown of CHMP7 mitigates NPC injury in C9orf72 iPSNs making CHMP7 an attractive
therapeutic target in neurodegeneration. In this proposal we will comprehensively investigate this new pathway
including studies to 1) Determine the degradative pathway by which CHMP7 mediates nucleoporin removal
from NPCs in iPSNs, 2) Investigate the mechanism by which pathologic G4C2 repeat RNA initiates CHMP7
mediated NPC injury. And finally, 3) using a large battery of individual patient iPSN spinal neuron cell lines,
evaluate the ability of CHMP7 antisense oligonucleotides to mitigate C9orf72 ALS/FTD and sporadic ALS
mediated alterations in the nuclear pore complex and nucleocytoplasmic transport and downstream sensitivity
to stressors in iPSNs.