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

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.

Impaired endoplasmic reticulum-mitochondrial signaling in ataxia-telangiectasia

“…ATM activation (ATM pS1981) has also been observed in the nucleus in primary mouse neurons after ATP depletion-induced oxidative stress, where there was no evidence of DNA damage ( Chow et al., 2019 ). Previous results have shown that a fraction of ATM is localized to mitochondria and that mitochondrial damage can directly activate ATM kinase in the absence of DNA damage ( Valentin-Vega et al., 2012 ; Blignaut et al., 2019 ). We thus determined whether ATM was present in mitochondria in this case by depriving cells of glucose rather than using 2DG inhibition.…”

“…These data suggest that ATM is a sensor of reactive oxygen species (ROS) for broader protection of the cell. Although the majority of ATM is present in the nucleus, in most cell types, it is also localized to mitochondria ( Valentin-Vega et al., 2012 ; Blignaut et al., 2019 ), peroxisomes ( Watters et al., 1999 ; Zhang et al., 2015 ) and membrane vesicles ( Lim et al., 1998 ). ATM binds to and phosphorylates PEX5, the peroxisome import receptor, which leads to PEX5 mono-ubiquitination and recognition by the autophagy adaptor protein p62 to induce pexophagy ( Zhang et al., 2015 ).…”

Selective protection of human cardiomyocytes from anthracycline cardiotoxicity by small molecule inhibitors of MAP4K4

“…As a starting point, initial proof-of-concept experiments were undertaken in rat H9c2 cardiomyocytes 20 , a low-cost, tractable model used most typically in toxicology research and early-stage cardiac drug discovery. Notably, this body of work includes more than 300 studies of anthracycline toxicity [21][22][23][24][25][26][27][28][29][30][31][32][33][34] as well as high-throughput, phenotypedriven screens for novel cardioprotective agents 35,36 . Viability as measured by the CellTiter-Glo ATP generation assay was markedly impaired by DOX, with half-maximal effects at 150-250 nM at 24 and 48 h (Fig.…”

“…Despite the widely reported utility of H9c2 cells [21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36] , their applicability as a predictive model in cardiac drug development is compromised by their continuous proliferation, lack of the sodium/calcium exchanger NCX1, lack of beating, and skeletal muscle potential 20,38,39 . Moreover, explicit disparities have been reported in drug effects relating to cardioprotection and cardiotoxicity in this model, compared with human cells 40,41 .…”

ATM Protein Kinase: Old and New Implications in Neuronal Pathways and Brain Circuitry

“…Two years later, Watters et al demonstrated that ATM cytoplasmic fraction associates with peroxisomes and endosomes [ 119 ] and is required for the functioning of these organelles. More recently, it has been shown that ATM also associates with mitochondria, regulating their function and mitophagy [ 120 , 121 , 122 ]. Moreover, the cytoplasmic fraction of ATM does not change in amount or in localization in response to IR [ 118 , 123 ], meaning that the ATM cytoplasmic pool is distinct from the nuclear one and is crucial for cellular and sub-cellular activities far from the function in genome surveillance.…”