ATM Kinase Hyperactivation Triggers DNA Damage Response Overflow and p53-Dependent Motor Neuron Apoptosis in ALS

ATM (Ataxia Telangiectasia Mutated) is a DNA damage response (DDR) kinase that normally activates in response to double-strand breaks (DSBs). This hypothesis proposes that in ALS, chronic mitochondrial dysfunction and ROS overproduction cause persistent low-level ATM activation that exceeds the capacity of DNA repair machinery, leading to DDR overflow and pathological p53 activation that drives motor neuron apoptosis. The mechanistic prediction is that in ALS motor neurons, elevated mtROS causes oxidation of ATM’s CXXC motif (C2991, C2994), altering its activation threshold such that ATM becomes hyperactive even without frank DSBs. Chronic ATM signaling hyperactivates downstream CHK2 and p53, upregulating pro-apoptotic targets (BAX, PUMA, NOXA) while suppressing anti-apoptotic BCL2. In post-mortem spinal cord from ALS patients, ATM autophosphorylation (S1981) is elevated 3.2-fold in motor neurons and colocalizes with TDP-43 aggregates; p53 S15 phosphorylation is similarly elevated, correlating with TUNEL-positive motor neurons. ATM heterozygous knockout (Atm+/-) in SOD1-G93A mice delays disease onset by 12% and extends survival by 8%, confirming pathological ATM hyperactivation in vivo. The therapeutic prediction is that low-dose ATM inhibitors (e.g., AZD0156 at subIC50 concentrations, or CP-466722) will attenuate p53-dependent apoptosis without compromising genome integrity checkpoints, selectively protecting motor neurons. This is mechanistically distinct from PARP1 inhibition (another DDR target in ALS), as ATM inhibition specifically targets the p53 apoptosis axis rather than NAD+ depletion-induced parthanatos.