Nuclear Phospho-SOD1 Protects DNA from Oxidative Stress Damage in Amyotrophic Lateral Sclerosis.

Matteo Bordoni,Gabriella Tedeschi,Cristina Cereda,Orietta Pansarasa,Stella Gagliardi,Valeria Crippa,Michela Dell’Orco,Daisy Sproviero,Stefano Bernuzzi,Luca Diamanti,Angelo Poletti,Mauro Ceroni

doi:10.3390/jcm8050729

Abstract

We already demonstrated that in peripheral blood mononuclear cells (PBMCs) of sporadic amyotrophic lateral sclerosis (sALS) patients, superoxide dismutase 1 (SOD1) was present in an aggregated form in the cytoplasmic compartment. Here, we investigated the possible effect of soluble SOD1 decrease and its consequent aggregation. We found an increase in DNA damage in patients PBMCs characterized by a high level of aggregated SOD1, while we found no DNA damage in PBMCs with normal soluble SOD1. We found an activation of ataxia-telangiectasia-mutated (ATM)/Chk2 and ATM and Rad3-related (ATR)/Chk1 DNA damage response pathways, which lead to phosphorylation of SOD1. Moreover, data showed that phosphorylation allows SOD1 to shift from the cytoplasm to the nucleus, protecting DNA from oxidative damage. Such pathway was finally confirmed in our cellular model. Our data lead us to suppose that in a sub-group of patients this physiologic pathway is non-functional, leading to an accumulation of DNA damage that causes the death of particularly susceptible cells, like motor neurons. In conclusion, during oxidative stress SOD1 is phosphorylated by Chk2 leading to its translocation in the nuclear compartment, in which SOD1 protects DNA from oxidative damage. This pathway, inefficient in sALS patients, could represent an innovative therapeutic target.

Highlights

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease characterized by progressive loss of cortical and spinal motor neurons, resulting in muscle denervation and paralysis, which lead to death within 3–5 years after diagnosis, normally due to respiratory failure [1,2]
To check DNA damage, we carried out the Comet assay on peripheral blood mononuclear cells (PBMCs) of control and sporadic amyotrophic lateral sclerosis (sALS) patients characterized by high levels of cytoplasmic SOD1aggregates and by normal levels of soluble superoxide dismutase 1 (SOD1)
In PBMCs of sALS patients, we carried out a Comet assay and we clearly demonstrated the lack of DNA damage in the sub-group of sALS patients characterized by high levels of soluble nuclear SOD1, and an extensive DNA damage in sALS patients with high levels of insoluble/aggregate SOD1

Summary

Introduction

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease characterized by progressive loss of cortical and spinal motor neurons, resulting in muscle denervation and paralysis, which lead to death within 3–5 years after diagnosis, normally due to respiratory failure [1,2]. ALS is the most common degenerative disorder affecting motor neurons in adults, with an incidence that ranges from 2 to 5 cases per 100,000 individuals worldwide. The maintenance of genome stability and integrity is fundamental for cellular viability especially in neurons. Neurons are highly susceptible to DNA damage, both single-strand breaks (SSBs) and double-strand breaks (DSBs), because they are post-mitotic cells with a high metabolic rate, and they are vulnerable to oxidative stress, which is one of the sources of DNA damage [6,7]. In post-mitotic neurons, because of their lack of self-renewal and replication, there are lesser choices to repair SSBs compared to proliferating cells. Genome damage and their inadequate repair have been linked to degenerating neurons in ALS patients; the underlying mechanisms remain unknown [8]

Objectives

Methods

Results

Conclusion