Amyotrophic Lateral Sclerosis and the DNA Damage Response

Amyotrophic Lateral Sclerosis (ALS) is caused by premature/accelerated degeneration of motor neurones. Whereas some cases of ALS are sporadic and of unknown molecular cause, others are due to hereditary dominant mutations in one of approximately eight genes. It has emerged recently that several of the proteins encoded by these genes are involved in regulating the production of messenger RNA (mRNA); a process known as transcription by which genes are copied into mRNA during gene expression. Two of these proteins are Fused-in-Sarcoma/Translocated-in-Sarcoma (FUS/TLS) and TAR DNA-binding protein 43 (TDP-43). The association of FUS/TLS and TDP-43 with ALS suggests that, in some cases of this disease, neuronal cell death may involve loss-of-function defects in RNA processing. However, the putative roles fulfilled by RNA processing that prevent ALS are unclear. We now present a novel hypothesis and supporting preliminary evidence for how RNA processing might prevent ALS. We show that FUS/TLS and TDP-43 are redistributed in response to DNA damage, with FUS rapidly accumulating at sites of DNA damage and TDP-43 rapidly expelled. We show that this redistribution of FUS/TLS and TDP-43 is an active process that is regulated by proteins with established roles in DNA damage signaling, supporting the idea that RNA processing is a bona fide component of the cellular DNA damage response. Based on these observations, we propose that RNA processing by FUS/TLS and TDP-43 is required to ensure that transcription is properly managed and controlled in the presence of DNA lesions, and that mutation of these and likely other proteins involved in RNA processing results in dysfunctional gene expression and neuronal cell death. In this application, we plan to address this hypothesis directly, using a combination of molecular and cellular approaches. To do this we have divided the proposed work into three specific objectives. We will,

1. Identify the mechanism/s by which FUS/TLS and TDP-43 are redistributed in response to DNA damage.

2. Address the role of FUS/TLS and TDP-43 in DNA damage signaling and/or repair at sites of DNA damage, and how these proteins regulate transcription in the presence of DNA lesions that block this process.

3. Examine the importance of FUS/TLS and TDP-43 for cellular resistance to DNA damage, including motor neurons, and identify additional components of RNA processing during the DNA damage response.

Amyotrophic Lateral Sclerosis (ALS) is caused by premature/accelerated degeneration of motor neurones. Whereas some cases of ALS are sporadic and of unknown molecular cause, others are due to hereditary dominant mutations in one of approximately eight genes. It has emerged recently that several of the proteins encoded by these genes are involved in regulating mRNA transcription, splicing, and stability, including Fused-in-Sarcoma/Translocated-in-Sarcoma (FUS/TLS) and TAR DNA-binding protein 43 (TDP-43). This raises the possibility that, in some cases of ALS, neuronal cell death may involve loss-of-function defects in RNA processing. However, how and why defects in RNA processing might result in the neurodegenerative pathology that typifies ALS is unclear. We now present preliminary evidence suggesting that FUS and TDP-43 are components of the cellular response to oxidative DNA damage, a process known to be important to slow or prevent neurodegeneration. We show that the FUS/TLS and TDP-43 proteins are redistributed in response to DNA damage, with FUS rapidly accumulating at sites of DNA damage and TDP-43 rapidly expelled. We show that this redistribution is an active process that is regulated by established DNA damage signalling proteins, supporting the idea that RNA processing is a bona fide component of the cellular DNA damage response. Based on these observations, we propose that RNA processing by FUS/TLS and TDP-43 is required to ensure that the stability of nascent pre-mRNA and the progression of RNA polymerase is properly managed and controlled during transcription in the presence of DNA lesions, and that mutation of these and likely other RNA processing factors results in dysfunctional gene expression at sites of DNA damage and consequently progressive neuronal cell death. We now plan to address this hypothesis directly, using a combination of molecular and cellular approaches.

Beyond academia and related research fields, the work in this project has the potential to impact, in the long-term, on the health sector and 'quality of life'/'Lifelong Health and Wellbeing'. This is because the project will address the impact of endogenous DNA damage (e.g. that arising during oxidative stress) on RNA processing and cell death/dysfunction in cells harbouring mutant proteins associated with amyotrophic lateral sclerosis/motor neurone disease (ALS/MND). A thorough understanding of the molecular function of proteins associated with ALS is necessary for future design of therapies that will alleviate this disease, and will help inform the health sector in respect to etiological factors that promote this, and related, pathology. This research could thus, in the long-term, inform on environmental and life-style issues relating to 'quality of life' and 'Lifelong Health and Wellbeing'.