# Defining the altered FUS-PARP-1-DNA Ligase III axis and its implications to nuclear and mitochondrial genome damage response in Amyotrophic Lateral Sclerosis (ALS) and Frontotemporal Dementia (FTD)

> **NIH NIH RF1** · METHODIST HOSPITAL RESEARCH INSTITUTE · 2020 · $2,018,750

## Abstract

Genome damage and defective repair are etiologically linked to Fused in Sarcoma (FUS)-associated
amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). However, the underlying mechanisms
remain enigmatic, which is a roadblock for exploiting genome repair-targeted therapies for ALS/FTD. Our recent
publication (Wang et al, Nature Communications, 2018) identified defects in DNA nick ligation and oxidative
damage repair in a subset of ALS patients, caused by mutations in the RNA/DNA-binding protein FUS. In healthy
neurons, FUS protects the genome by facilitating PARP1-dependent recruitment of XRCC1/DNA Ligase IIIα
(LigIII) to oxidized genome sites and activates LigIII via direct interaction. We discovered that FUS toxicity caused
significantly decreased recruitment of XRCC1/LigIII to DNA strand breaks. DNA ligation defects in ALS patient-derived iPSC lines carrying FUS mutations and in subsequently generated motor neurons were rescued by
CRISPR/Cas9-mediated mutation correction. Moreover, our follow-up studies showed substantially reduced auto
and total PARylation activity of PARP-1 both in vitro and in cell, after loss of FUS or mutant expression, which in
addition to regulating LigIII/XRCC1 recruitment at damage sites, could impact neuronal energy metabolism by
uncoupling NAD+/NADH levels and stress granule dynamics in motor neurons. Collectively these events may
provide a recipe for neurodegeneration. These findings that uncovered a new pathway of defective DNA ligation
and PARP-1 functions in FUS-linked ALS-FTD, raised three key questions that need to be investigated to
understand their implications in neuronal death and to develop a comprehensive strategy of PARylation and
LigIII targeted interventions for ameliorating FUS-associated ALS-FTD. These questions are: (1) How does FUS
affect PARP-1's PARylation activity and what is its impact on genome maintenance and energy metabolism? (2)
What is the effect of FUS-mediated LigIII inhibition on the mitochondrial genome and its functions? This is
important as LigIII is the only DNA ligase for both replication and repair in mitochondria, and both FUS and
PARP-1 localize in mitochondria. (3) What is the effect of FUS pathology on microhomology-mediated alternative
end-joining (MMEJ) pathway of DNA double strand break repair, which involves LigIII, XRCC1 and PARP-1?.
This project, will utilize human patient-derived iPSC lines harboring FUS mutations, their isogenic controls with
mutation correction by CRISPR/Cas9 knock-in strategy, a transgenic FUS-∆NLS mouse model and human ALS,
FTD patient spinal cord/brain tissue, to test our novel hypothesis that FUS pathology-mediated DNA ligation
defects via reduced PARylation inhibits oxidative genome damage repair and promotes
neurodegeneration. We will further show that rescuing Ligase and PARP functions are promising avenues
for neuroprotection. Our studies investigating the previously unexplored link between altered FUS-PARP-1-LigIII axis and ...

## Key facts

- **NIH application ID:** 9980670
- **Project number:** 1RF1NS112719-01A1
- **Recipient organization:** METHODIST HOSPITAL RESEARCH INSTITUTE
- **Principal Investigator:** Muralidhar L Hegde
- **Activity code:** RF1 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2020
- **Award amount:** $2,018,750
- **Award type:** 1
- **Project period:** 2020-04-15 → 2025-08-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/9980670

## Citation

> US National Institutes of Health, RePORTER application 9980670, Defining the altered FUS-PARP-1-DNA Ligase III axis and its implications to nuclear and mitochondrial genome damage response in Amyotrophic Lateral Sclerosis (ALS) and Frontotemporal Dementia (FTD) (1RF1NS112719-01A1). Retrieved via AI Analytics 2026-05-29 from https://api.ai-analytics.org/grant/nih/9980670. Licensed CC0.

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