Ataxia-Telangiectasia Mutated is located in cardiac mitochondria and impacts oxidative phosphorylation

Marguerite Blignaut,Stanley W Botchway,Barbara Huisamen,Anthony W Parker,Ben Loos

doi:10.1038/s41598-019-41108-1

Abstract

The absence of Ataxia-Telangiectasia mutated protein kinase (ATM) is associated with neurological, metabolic and cardiovascular defects. The protein has been associated with mitochondria and its absence results in mitochondrial dysfunction. Furthermore, it can be activated in the cytosol by mitochondrial oxidative stress and mediates a cellular anti-oxidant response through the pentose phosphate pathway (PPP). However, the precise location and function of ATM within mitochondria and its role in oxidative phosphorylation is still unknown. We show that ATM is found endogenously within cardiac myocyte mitochondria under normoxic conditions and is consistently associated with the inner mitochondrial membrane. Acute ex vivo inhibition of ATM protein kinase significantly decreased mitochondrial electron transfer chain complex I-mediated oxidative phosphorylation rate but did not decrease coupling efficiency or oxygen consumption rate during β-oxidation. Chemical inhibition of ATM in rat cardiomyoblast cells (H9c2) significantly decreased the excited-state autofluorescence lifetime of enzyme-bound reduced NADH and its phosphorylated form, NADPH (NAD(P)H; 2.77 ± 0.26 ns compared to 2.57 ± 0.14 ns in KU60019-treated cells). This suggests an interaction between ATM and the electron transfer chain in the mitochondria, and hence may have an important role in oxidative phosphorylation in terminally differentiated cells such as cardiomyocytes.

Highlights

Ataxia-Telangiectasia (A-T) is a rare, recessive disease characterised by the absence of Ataxia-Telangiectasia Mutated (ATM) protein kinase
This study shows that Ataxia-Telangiectasia mutated protein kinase (ATM) protein kinase is consistently associated with the inner mitochondrial membrane (IMM) of cardiac mitochondria isolated from 12-week old male Wistar rats, and shows that the inhibition of ATM affects complex I-mediated oxidative phosphorylation
ATM was found to be consistently associated with the IMM and expands on previously published work that shows that the absence of ATM is associated with mitochondrial dysfunction in A-T patient derived fibroblasts[20] and ATM−/− mice thymocytes[21]

Summary

Introduction

Ataxia-Telangiectasia (A-T) is a rare, recessive disease characterised by the absence of Ataxia-Telangiectasia Mutated (ATM) protein kinase. Studies have shown that anti-oxidative treatment targeting mitochondria can decrease metabolic syndrome in ATM-null mice[5], and supports the notion that A-T might be a mitochondrial disease[9]. In HeLa cells, ATM localises in the nucleus in response to endogenous mitochondrial oxidative stress, independently of DNA damage response, whilst promoting glucose flux through the pentose phosphate pathway (PPP) and increasing cellular anti-oxidant capacity by increasing glucose-6-phosphate dehydrogenase (G6PD) in bone osteosarcoma cells (U2OS)[11]. Impaired ROS sensing by ATM results in increased glutathione synthesis, possibly due to a decreased flux through the PPP This reduces NADPH availability for glutathione recycling and places ATM, as a redox sensor, at a critical junction of cytosolic carbohydrate metabolism[11]. This study sought to establish where ATM is located within terminally differentiated cardiac cells, and if so, whether there are any mitochondrial respiratory or metabolic implications

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Conclusion