# Modeling C9orf72 neuronal pathogenesis as a function of nucleotide repeat length

> **NIH NIH R21** · THOMAS JEFFERSON UNIVERSITY · 2020 · $429,000

## Abstract

Project Summary
The C9orf72 nucleotide repeat expansion (C9-NRE) mutation has been identified as the most common genetic
mutation link to frontotemporal dementia (FTD) and amyotrophic lateral sclerosis (ALS). Although there has been
significant work investigating the primary pathogenic mechanisms to explain the pathological features found in
patient post-mortem disease tissues, there is still a gap in our assessment of what repeat length leads to disease
pathogenesis. Of these pathogenic mechanisms, the neuro-specific contribution for loss-of-function (LOF) of the
C9orf72 protein is not well described, while two C9-NRE gain-of-function (GOF) mechanisms, RNA toxicity from
the bidirectional transcription of the NRE and/or dipeptide repeat (DPR) toxicity from the non-AUG-dependent
translation of the C9-NRE transcripts, have been shown to contribute to neurotoxic mechanisms. However,
epigenetic modifications to the C9-NRE region can modulate gain-of-function toxicity by reducing the pathogenic
allele transcript levels, which has been proposed to be protective in patients. It is unknown if the LOF or GOF
disease mechanisms and these epigenetic modifications emerge in a C9-NRE track-length-dependent manner.
Therefore, further investigation is crucial to understand the requirements for these pathological and epigenetic
observations identified in patients carrying the C9-NRE and to reconcile the relationship between C9-NRE-linked
disease pathogenesis and C9-NRE track-length in neurons. To this end, we propose (Aim 1) to develop a series
of C9-NRE isogenic iPSC lines with increasing repeat track-lengths that extend from the known non-pathogenic
to the disease pathogenic range. Moreover, these isogenic iPSC lines are derived from a well-characterized
patient with ALS/FTD that carries a C9-NRE mutation, which was corrected to generate the isogenic control.
Additionally, these lines have been engineered to allow direct conversion to cortical or motor neurons using
inducible neuronal-specific transcription factors, called I3Neruons. Utilizing this series of C9-NRE I3Neurons, we
will then (Aim 2) perform a rigorous comprehensive biochemical and cellular assessment to quantitatively
characterize pathological and phenotypic features as well as C9-NRE-specific epigenetic changes, transcript
usage, and repeat instability as a function of C9-NRE track-length in cortical and motor neurons. The
development of this robust series of C9-NRE track-length I3Neuronal models and quantitative characterization
will produce vital disease-modeling resources to be shared with the scientific community; will enhance our
understanding of the C9-NRE disease pathogenesis; and will serve as a prototypical system that can be used to
improve translation of potential therapeutic interventions and diagnostic tools to the clinic.

## Key facts

- **NIH application ID:** 9969881
- **Project number:** 1R21NS116761-01
- **Recipient organization:** THOMAS JEFFERSON UNIVERSITY
- **Principal Investigator:** Aaron Raymond Haeusler
- **Activity code:** R21 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2020
- **Award amount:** $429,000
- **Award type:** 1
- **Project period:** 2020-04-15 → 2023-03-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/9969881

## Citation

> US National Institutes of Health, RePORTER application 9969881, Modeling C9orf72 neuronal pathogenesis as a function of nucleotide repeat length (1R21NS116761-01). Retrieved via AI Analytics 2026-06-08 from https://api.ai-analytics.org/grant/nih/9969881. Licensed CC0.

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