Patterns of Mitochondrial DNA Damage in Blood and Brain Tissues of a Transgenic Mouse Model of Machado-Joseph Disease

Abstract

Background: Machado-Joseph disease (MJD) is an autosomal dominant spinocerebellar ataxia caused by a CAG tract expansions in the ATXN3 gene. Patterns of mitochondrial damage associated with pathological findings of brain tissues could provide molecular biomarkers of this disorder. Objective: The potential of mitochondrial DNA (mtDNA) damage as a biomarker of MJD progression was investigated using a transgenic mouse model. Methods: DNA was obtained from affected (pontine nuclei) and nonaffected tissues (hippocampus and blood) of transgenic animals of three distinct age groups: 8 weeks, before onset of the phenotype; 16 weeks, at onset, and 24 weeks, at well-established phenotype. Wild-type littermate mice, serving as controls, were analyzed for the same tissues and age groups. mtDNA damage was studied by fluorescence-based quantitative PCR in 84 transgenic and 93 wild-type samples. Results: A clear pattern of decrease in mtDNA copy number with age and accumulation of 3,867-bp deletions at the initial stages (both being more pronounced in transgenic mice) was observed. Pontine nuclei, the affected tissue in transgenic mice, displayed 1.5 times less copies of mtDNA than nonaffected brain tissue hippocampus (odds ratio = 1.21). Pontine nuclei displayed the highest percentage of mtDNA deletions (6.05% more in transgenic mice). Conclusion: These results suggest that mtDNA damage is related to the initiation of the phenotype in transgenic mice; mtDNA 3,867-bp deletions may be a biomarker of the initial stages of the disease.

Ataxin-3 Protein and RNA Toxicity in Spinocerebellar Ataxia Type 3: Current Insights and Emerging Therapeutic Strategies

“…In accordance with this, a cell model overexpressing mutant ataxin-3 with 78 CAGs showed reduced antioxidant enzyme levels, increased mitochondrial DNA damage, and reduced energy supply, which indicates impaired mitochondrial function [124]. Recently, mitochondrial DNA damage was also seen in SCA3 transgenic mice expressing full-length ataxin-3 with 98 to 104 glutamines [125]. In the disease-affected pontine nuclei of these transgenic SCA3 mice, less mitochondrial DNA copies were seen, as compared to the unaffected hippocampus [125].…”

“…Recently, mitochondrial DNA damage was also seen in SCA3 transgenic mice expressing full-length ataxin-3 with 98 to 104 glutamines [125]. In the disease-affected pontine nuclei of these transgenic SCA3 mice, less mitochondrial DNA copies were seen, as compared to the unaffected hippocampus [125]. Additionally, less mitochondrial DNA copy numbers were observed in the mutant cells and SCA3 patient samples, implying mitochondrial DNA damage due to oxidative stress [124].…”

Overexpression of Cystathionine γ-Lyase Suppresses Detrimental Effects of Spinocerebellar Ataxia Type 3

“…Oxidative stress is associated with the pathogenesis of SCA3 disease (40,41). Previously, it was demonstrated that CSE deficiency is linked to increased levels of oxidative stress (42).…”

Analysis of mtDNA/nDNA Ratio in Mice

“…In humans, defects in mtDNA maintenance generated by mutations in genes involved in mtDNA replication and nucleotide biosynthesis cause mtDNA depletion syndromes (MDS) (El-Hattab and Scaglia, 2013). Such mtDNA depletions are also associated with metabolic diseases, including type 2 diabetes, cancers and neurodegenerative disorders, including Alzheimer’s, Parkinson’s and Machado-Joseph disease (Abolhassani et al, 2016; Kazachkova et al, 2013; Ramos et al, 2015; Sepe et al, 2016). During aging, mtDNA copy number also decreases, probably because it is prone to oxidative damage by reactive oxygen species (ROS) produced in the mitochondrial matrix.…”

“…In this regard, several reports have shown that aging leads to mtDNA damage and dysfunction (Bratic and Larsson, 2013; Gomez-Cabrera et al, 2012; Kennedy et al, 2012; Trifunovic and Larsson, 2008). In such cases, quantification of the mtDNA damage and analysis and quantification of the mtDNA copy number may be a good biomarker for disease progression and development of therapies (Kazachkova et al, 2013). In non-pathological or aging-related conditions, mtDNA quantification is also a good indicator of the mitochondrial mass.…”