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The MRE11/RAD50/NBS1 (MRN) complex plays critical roles in cellular responses to DNA double-strand breaks. MRN is involved in end binding and processing, and it also induces cell cycle checkpoints by activating the ataxia-telangiectasia mutated (ATM) protein kinase. Hypomorphic pathogenic variants in the MRE11, RAD50, or NBS1 genes cause autosomal recessive genome instability syndromes featuring variable degrees of dwarfism, neurological defects, anemia, and cancer predisposition. Disease-associated MRN alleles include missense and nonsense variants, and many cause reduced protein levels of the entire MRN complex. However, the dramatic variability in the disease manifestation of MRN pathogenic variants is not understood. We sought to determine if low protein levels are a significant contributor to disease sequelae and therefore generated a transgenic murine model expressing MRE11 at low levels. These mice display dramatic phenotypes including small body size, severe anemia, and impaired DNA repair. We demonstrate that, distinct from ataxia telangiectasia-like disorder caused by MRE11 pathogenic missense or nonsense variants, mice and cultured cells expressing low MRE11 levels do not display the anticipated defects in ATM activation. Our findings indicate that ATM signaling can be supported by very low levels of the MRN complex and imply that defective ATM activation results from perturbation of MRN function caused by specific hypomorphic disease mutations. These distinct phenotypic outcomes underline the importance of understanding the impact of specific pathogenic MRE11 variants, which may help direct appropriate early surveillance for patients with these complicated disorders in a clinical setting., (© The Author(s) 2024. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.)

The ataxia telangiectasia mutated (ATM) protein kinase is best known as a master regulator of the DNA damage response. However, accumulating evidence has unveiled an equally vital function for ATM in sensing oxidative stress and orchestrating cellular antioxidant defenses to maintain redox homeostasis. ATM can be activated through a non-canonical pathway involving intermolecular disulfide crosslinking of the kinase dimers, distinct from its canonical activation by DNA double-strand breaks. Structural studies have elucidated the conformational changes that allow ATM to switch into an active redox-sensing state upon oxidation. Notably, loss of ATM function results in elevated reactive oxygen species (ROS) levels, altered antioxidant profiles, and mitochondrial dysfunction across multiple cell types and tissues. This oxidative stress arising from ATM deficiency has been implicated as a central driver of the neurodegenerative phenotypes in ataxia-telangiectasia (A-T) patients, potentially through mechanisms involving oxidative DNA damage, PARP hyperactivation, and widespread protein aggregation. Moreover, defective ATM oxidation sensing disrupts transcriptional programs and RNA metabolism, with detrimental impacts on neuronal homeostasis. Significantly, antioxidant therapy can ameliorate cellular and organismal abnormalities in various ATM-deficient models. This review synthesizes recent advances illuminating the multifaceted roles of ATM in preserving redox balance and mitigating oxidative insults, providing a unifying paradigm for understanding the complex pathogenesis of A-T disease., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Author(s). Published by Elsevier B.V. All rights reserved.)

Ataxia Telangiectasia (AT) is a rare disorder caused by mutations in the ATM gene and results in progressive neurodegeneration for reasons that remain poorly understood. In addition to its central role in nuclear DNA repair, ATM operates outside the nucleus to regulate metabolism, redox homeostasis and mitochondrial function. However, a systematic investigation into how and when loss of ATM affects these parameters in relevant human neuronal models of AT was lacking. We therefore used cortical neurons and brain organoids from AT-patient iPSC and gene corrected isogenic controls to reveal levels of mitochondrial dysfunction, oxidative stress, and senescence that vary with developmental maturity. Transcriptome analyses identified disruptions in regulatory networks related to mitochondrial function and maintenance, including alterations in the PARP/SIRT signalling axis and dysregulation of key mitophagy and mitochondrial fission-fusion processes. We further show that antioxidants reduce ROS and restore neurite branching in AT neuronal cultures, and ameliorate impaired neuronal activity in AT brain organoids. We conclude that progressive mitochondrial dysfunction and aberrant ROS production are important contributors to neurodegeneration in AT and are strongly linked to ATM's role in mitochondrial homeostasis regulation., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier Inc. All rights reserved.)

Background: Metabolomics, the study of substrates and products of cellular metabolism, offers valuable insights into an organism's state under specific conditions and has the potential to revolutionise preventive healthcare and pharmaceutical research. However, analysing large metabolomics datasets remains challenging, with available methods relying on limited and incompletely annotated metabolic pathways., Methods: This study, inspired by well-established methods in drug discovery, employs machine learning on metabolite fingerprints to explore the relationship of their structure with responses in experimental conditions beyond known pathways, shedding light on metabolic processes. It evaluates fingerprinting effectiveness in representing metabolites, addressing challenges like class imbalance, data sparsity, high dimensionality, duplicate structural encoding, and interpretable features. Feature importance analysis is then applied to reveal key chemical configurations affecting classification, identifying related metabolite groups., Results: The approach is tested on two datasets: one on Ataxia Telangiectasia and another on endothelial cells under low oxygen. Machine learning on molecular fingerprints predicts metabolite responses effectively, and feature importance analysis aligns with known metabolic pathways, unveiling new affected metabolite groups for further study., Conclusion: In conclusion, the presented approach leverages the strengths of drug discovery to address critical issues in metabolomics research and aims to bridge the gap between these two disciplines. This work lays the foundation for future research in this direction, possibly exploring alternative structural encodings and machine learning models., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier B.V. All rights reserved.)

DNA is susceptible to various factors in vitro and in vivo and experience different forms of damage,among which double-strand break(DSB)is a deleterious form.To maintain the stability of genetic information,organisms have developed multiple mechanisms to repair DNA damage.Among these mechanisms,homologous recombination(HR)is praised for the high accuracy.The MRE11-RAD50-NBS1(MRN)complex plays an important role in HR and is conserved across different species.The knowledge on the MRN complex mainly came from the previous studies in Saccharomyces cerevisiae and Caenorhabditis elegans ,while studies in the last decades have revealed the role of mammalian MRN complex in DNA repair of higher animals.In this review,we first introduces the MRN complex regarding the composition,structure,and roles in HR.In addition,we discuss the human diseases such as ataxia-telangiectasia-like disorder,Nijmegen breakage syndrome,and Nijmegen breakage syndrome-like disorder that are caused by dysfunctions in the MRN complex.Furthermore,we summarize the mouse models established to study the clinical phenotypes of the above diseases.

Introduction: Ataxia telangiectasia (A-T) is an autosomal recessive neurodegenerative disease with widespread systemic manifestations and marked variability in clinical phenotypes. In this study, we sought to determine whether transcriptomic profiling of peripheral blood mononuclear cells (PBMCs) defines subsets of individuals with A-T beyond mild and classic phenotypes, enabling identification of novel features for disease classification and treatment response to therapy., Methods: Participants with classic A-T (n = 77), mild A-T (n = 13), and unaffected controls (n = 15) were recruited from two outpatient clinics. PBMCs were isolated and bulk RNAseq was performed. Plasma was also isolated in a subset of individuals. Affected individuals were designated mild or classic based on ATM mutations and clinical and laboratory features., Results: People with classic A-T were more likely to be younger and IgA deficient and to have higher alpha-fetoprotein levels and lower % forced vital capacity compared to individuals with mild A-T. In classic A-T, the expression of genes required for V(D)J recombination was lower, and the expression of genes required for inflammatory activity was higher. We assigned inflammatory scores to study participants and found that inflammatory scores were highly variable among people with classic A-T and that higher scores were associated with lower ATM mRNA levels. Using a cell type deconvolution approach, we inferred that CD4 + T cells and CD8 + T cells were lower in number in people with classic A-T. Finally, we showed that individuals with classic A-T exhibit higher SERPINE1 (PAI-1) mRNA and plasma protein levels, irrespective of age, and higher FLT4 (VEGFR3) and IL6ST (GP130) plasma protein levels compared with mild A-T and controls., Conclusion: Using a transcriptomic approach, we identified novel features and developed an inflammatory score to identify subsets of individuals with different inflammatory phenotypes in A-T. Findings from this study could be used to help direct treatment and to track treatment response to therapy., (© 2024. The Author(s).)

Ataxia Telangiectasia (A-T) is an inherited autosomal recessive disorder characterized by cerebellar neurodegeneration, radiosensitivity, immunodeficiency and a high incidence of lymphomas. A-T is caused by mutations in the ATM gene. While loss of ATM function in DNA repair explains some aspects of A-T pathophysiology such as radiosensitivity and cancer predisposition, other A-T features such as neurodegeneration imply additional roles for ATM outside the nucleus. Emerging evidence suggests that ATM participates in cellular response to oxidative stress, failure of which contributes to the neurodegeneration associated with A-T. Here, we use fibroblasts derived from A-T patients to investigate whether DEAD Box 1 (DDX1), an RNA binding/unwinding protein that functions downstream of ATM in DNA double strand break repair, also plays a role in ATM-dependent cellular response to oxidative stress. Focusing on DDX1 target RNAs that are associated with neurological disorders and oxidative stress response, we show that ATM is required for increased binding of DDX1 to its target RNAs in the presence of arsenite-induced oxidative stress. Our results indicate that DDX1 functions downstream of ATM by protecting specific mRNAs in the cytoplasm of arsenite-treated cells. In keeping with a role for ATM and DDX1 in oxidative stress, levels of reactive oxygen species (ROS) are increased in ATM-deficient as well as DDX1-depleted cells. We propose that reduced levels of cytoplasmic DDX1 RNA targets sensitizes ATM-deficient cells to oxidative stress resulting in increased cell death. This sensitization would be especially detrimental to long-lived highly metabolically active cells such as neurons providing a possible explanation for the neurodegenerative defects associated with A-T., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 The Authors. Published by Elsevier B.V. All rights reserved.)

Background: Clinical observation suggests the atheroprotective effect of chloroquine and its derivatives, while its mechanism remains unclear. This study aimed to observe the protective effect of chloroquine against atherosclerosis and explore the underlying mechanism., Methods: Ataxia telangiectasia mutated (ATM) wild-type or haploinsufficient apolipoprotein-E-knockout (ATM +/+ ApoE -/- or ATM +/- ApoE -/- ) mice were treated with different dosages of chloroquine. Anti-CD25 antibody was used to deplete natural Tregs in ATM +/+ ApoE -/- mice. The atherosclerotic burden in different groups of mice was comprehensively evaluated by H&E staining and Masson staining. The effect of chloroquine on the regulatory T cells (Tregs) was assessed in vivo and in vitro by flow cytometry and immunohistochemical staining. The expression of related proteins was detected by real-time polymerase chain reaction and western blotting., Results: In ATM +/+ ApoE -/- mice, chloroquine alleviated atherosclerotic lesions, stabilized the plaque, and increased Treg counts in the atherosclerotic lesions and spleens. However, in ATM haploinsufficient mice (ATM +/- ApoE -/- ), chloroquine no longer prevented atherosclerosis or impacted Treg counts. Abolishing Treg cells using an anti-CD25 antibody in vivo abrogated the atheroprotective effect of chloroquine. In vitro, chloroquine promoted the differentiation of Tregs from naïve T cells, which was accompanied by enhanced ATM/AMP-activated protein kinase (AMPK) activity and reduced downstream mammalian target of rapamycin (mTOR) activity., Discussion: These findings suggest that chloroquine ameliorates atherosclerosis and stabilizes plaque by modulating Tregs differentiation through the regulation of the ATM/AMPK/mTOR pathway., Competing Interests: The authors declare no conflicts of interest in this work., (Thieme. All rights reserved.)

Cerebellar ataxia is often the first and irreversible outcome in the disease of ataxia-telangiectasia (A-T), as a consequence of selective cerebellar Purkinje neuronal degeneration. A-T is an autosomal recessive disorder resulting from the loss-of-function mutations of the ataxia-telangiectasia-mutated ATM gene. Over years of research, it now becomes clear that functional ATM-a serine/threonine kinase protein product of the ATM gene-plays critical roles in regulating both cellular DNA damage response and central carbon metabolic network in multiple subcellular locations. The key question arises is how cerebellar Purkinje neurons become selectively vulnerable when all other cell types in the brain are suffering from the very same defects in ATM function. This review intended to comprehensively elaborate the unexpected linkages between these two seemingly independent cellular functions and the regulatory roles of ATM involved, their integrated impacts on both physical and functional properties, hence the introduction of selective vulnerability to Purkinje neurons in the disease will be addressed., (© 2023 The Authors. Journal of Neurochemistry published by John Wiley & Sons Ltd on behalf of International Society for Neurochemistry.)

The genetic disorder, ataxia-telangiectasia (A-T), is caused by loss of the homeostatic protein kinase, ATM, and combines genome instability, tissue degeneration, cancer predisposition, and premature aging. Primary fibroblasts from A-T patients exhibit premature senescence when grown at ambient oxygen concentration (21%). Here, we show that reducing oxygen concentration to a physiological level range (3%) dramatically extends the proliferative lifespan of human A-T skin fibroblasts. However, they still undergo senescence earlier than control cells grown under the same conditions and exhibit high genome instability. Comparative RNA-seq analysis of A-T and control fibroblasts cultured at 3% oxygen followed by cluster analysis of differentially expressed genes and functional enrichment analysis, revealed distinct transcriptional dynamics in A-T fibroblasts senescing in physiological oxygen concentration. While some transcriptional patterns were similar to those observed during replicative senescence of control cells, others were unique to the senescing A-T cells. We observed in them a robust activation of interferon-stimulated genes, with undetected expression the interferon genes themselves. This finding suggests an activation of a non-canonical cGAS-STING-mediated pathway, which presumably responds to cytosolic DNA emanating from extranuclear micronuclei detected in these cells. Senescing A-T fibroblasts also exhibited a marked, intriguely complex alteration in the expression of genes associated with extracellular matrix (ECM) remodeling. Notably, many of the induced ECM genes encode senescence-associated secretory phenotype (SASP) factors known for their paracrine pro-fibrotic effects. Our data provide a molecular dimension to the segmental premature aging observed in A-T patients and its associated symptoms, which develop as the patients advance in age., (© 2023 The Authors. Aging Cell published by Anatomical Society and John Wiley & Sons Ltd.)

Introduction: Ataxia telangiectasia (A-T) is a life-limiting autosomal recessive disease characterized by cerebellar degeneration, ocular telangiectasias, and sinopulmonary disease. Since there is no cure for A-T, the standard of care is primarily supportive., Areas Covered: We review clinical trials available in PubMed from 1990 to 2023 focused on lessening A-T disease burden. These approaches include genetic interventions, such as antisense oligonucleotides, designed to ameliorate disease progression in patients with select mutations. These approaches also include pharmacologic treatments that target oxidative stress, inflammation, and mitochondrial exhaustion, to attenuate neurological progression in A-T. Finally, we discuss the use of biological immunotherapies for the treatment of malignancies and granulomatous disease, along with other supportive therapies being used for the treatment of pulmonary disease and metabolic syndrome., Expert Opinion: Barriers to successful genetic and pharmacologic interventions in A-T include the need for personalized treatment approaches based on patient-specific ATM mutations and phenotypes, lack of an animal model for the neurologic phenotype, and extreme rarity of disease making large-scale randomized trials difficult to perform. Ongoing efforts are needed to diagnose patients earlier, discover more effective therapies, and include more individuals in clinical trials, with the goal to lessen disease burden and to find a cure for patients with A-T.

Abstract: Background: Protein kinase ataxia telangiectasia mutated (ATM) regulates the function of endothelial cells and responds quickly to endotoxin. However, the function of ATM in lipopolysaccharide (LPS)-induced blood-brain barrier (BBB) disruption remains unknown. This study aimed to investigate the role and underlying mechanism of ATM in the regulation of the BBB function in sepsis. Methods: We used LPS to induce BBB disruption in vivo and to establish an in vitro model of cerebrovascular endothelial cells. Blood-brain barrier disruption was assessed by measuring Evans blue leakage and expression of vascular permeability regulators. To investigate the role of ATM, its inhibitor AZD1390 and clinically approved doxorubicin, an anthracycline that can activate ATM, were administered as scheduled. To explore the underlying mechanism, protein kinase B (AKT) inhibitor MK-2206 was administered to block the AKT/dynamin-related protein 1 (DRP1) pathway. Results: Lipopolysaccharide challenge induced significant BBB disruption, ATM activation, and mitochondrial translocation. Inhibiting ATM with AZD1390 aggravated BBB permeability as well as the following neuroinflammation and neuronal injury, while activation of ATM by doxorubicin abrogated these defects. Further results obtained in brain microvascular endothelial cells showed that ATM inhibition reduced the phosphorylation of DRP1 at serine (S) 637, promoted excessive mitochondrial fission, and resulted in mitochondrial malfunction. By activating ATM, doxorubicin increased the protein binding between ATM and AKT and promoted the phosphorylated activation of AKT at S473, which could directly phosphorylate DRP1 at S637 to repress excessive mitochondrial fission. Consistently, the protective role of ATM was abolished by the AKT inhibitor MK-2206. Conclusions: Ataxia telangiectasia mutated protects against LPS-induced BBB disruption by regulating mitochondrial homeostasis, at least in part, through the AKT/DRP1 pathway., Competing Interests: The authors report no conflict of interest., (Copyright © 2023 The Author(s). Published by Wolters Kluwer Health, Inc. on behalf of the Shock Society.)

Proliferating cell nuclear antigen (PCNA) is a sliding clamp protein that coordinates DNA replication with various DNA maintenance events that are critical for human health. Recently, a hypomorphic homozygous serine to isoleucine (S228I) substitution in PCNA was described to underlie a rare DNA repair disorder known as PCNA-associated DNA repair disorder (PARD). PARD symptoms range from UV sensitivity, neurodegeneration, telangiectasia, and premature aging. We, and others, previously showed that the S228I variant changes the protein-binding pocket of PCNA to a conformation that impairs interactions with specific partners. Here, we report a second PCNA substitution (C148S) that also causes PARD. Unlike PCNA-S228I, PCNA-C148S has WT-like structure and affinity toward partners. In contrast, both disease-associated variants possess a thermostability defect. Furthermore, patient-derived cells homozygous for the C148S allele exhibit low levels of chromatin-bound PCNA and display temperature-dependent phenotypes. The stability defect of both PARD variants indicates that PCNA levels are likely an important driver of PARD disease. These results significantly advance our understanding of PARD and will likely stimulate additional work focused on clinical, diagnostic, and therapeutic aspects of this severe disease., Competing Interests: Conflict of interest The authors declare that they have no conflicts of interest with the contents of this article., (Copyright © 2023 The Authors. Published by Elsevier Inc. All rights reserved.)

Ataxia telangiectasia mutated (ATM) is a pivotal sensor during the DNA damage response that slows cell passage through the cell cycle checkpoints to facilitate DNA repair, and liver fibrosis is an irreversible pathological consequence of the sustained wound-healing process, However, the effects of ATM on the development of liver fibrosis are still not fully understood. Therefore, the aim of the study was to investigate the effects and potential mechanisms of ATM on the progression of liver fibrosis. Wild-type and ATM-deficient were administered with carbon tetrachloride (CCl 4 , 5 ml/kg, i.p.) for 8 weeks to induce liver fibrosis, and the liver tissues and serum were collected for analysis. KU-55933 (10 μM) was used to investigate the effects of ATM blockage on CCl 4 -induced hepatocyte injury in vitro. The results showed that ATM deficiency aggravated the increased serum transaminase levels and liver MDA, HYP, and 8-OHdG contents compared with the model group (p < 0.05). Sirius red staining showed that ATM deficiency exacerbated liver collagen deposition in vivo, which was associated with the activation of TGF-β1/Smad2 signaling. Furthermore, blocking ATM with KU-55933 exacerbated the production of ROS and DNA damage caused by CCl 4 exposure in HepG2 cells, and KU-55933 treatment also reversed the downregulated expression of CDK1 and CDK2 after CCl 4 exposure in vitro. Moreover, the loss of ATM perturbed the regulation of the hepatic cell ChK2-CDC25A/C-CDK1/2 cascade and apoptosis in vivo, which was accompanied by increased Ki67-positive and TUNEL-positive cells after chronic CCl 4 treatment. In conclusion, our results indicated that ATM might be a critical regulator of liver fibrosis progression, and the underlying mechanisms of exacerbated liver fibrosis development in ATM-deficient mice might be associated with the dysregulation of hepatic cell proliferation and apoptosis., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Inadequate DNA damage response related to ataxia telangiectasia mutated gene restricts hepatic regeneration in acute liver failure. Resolving mechanistic gaps in liver damage and repair requires additional animal models that are unconstrained by ultrarapid and unpredictable mortalities or substantial divergences from human pathology. This study used Fischer 344 rats primed with the antitubercular drug, rifampicin, plus phenobarbitone, and monocrotaline, a DNA adduct-forming alkaloid. Rifampicin and monocrotaline can cause liver failure in people. This regimen resulted in hepatic oxidative stress, necrosis, DNA double-strand breaks, liver test abnormalities, altered serum cytokine expression, and mortality. Healthy donor hepatocytes were transplanted ectopically in the peritoneal cavity to study whether they could supply metabolic support and rebalance inflammatory or protective cytokines affecting liver regeneration events. Hepatocyte transplantation increased candidate cytokine levels (granulocyte colony-stimulating factor, granulocyte-macrophage colony-stimulating factor, interferon-γ, IL-10, and IL-12), leading to Atm, Stat3, and Akt signaling in hepatocytes and nonparenchymal cells, lowering of inflammation, and improvements in intermediary metabolism, DNA repair, and hepatocyte proliferation. Such control of DNA damage and inflammation, along with stimulation of hepatic growth, offers paradigms for cell signaling to restore hepatic homeostasis and regeneration in acute liver failure. Further studies of molecular pathways of high pathobiological impact will advance the knowledge of liver regeneration., (Copyright © 2023 American Society for Investigative Pathology. Published by Elsevier Inc. All rights reserved.)

Ataxia telangiectasia is a rare neurodegenerative disease caused by biallelic mutations in the ataxia telangiectasia mutated gene. No cure is currently available for these patients but positive effects on neurologic features in AT patients have been achieved by dexamethasone administration through autologous erythrocytes (EryDex) in phase II and phase III clinical trials, leading us to explore the molecular mechanisms behind the drug action. During these investigations, new ATM variants, which originated from alternative splicing of ATM messenger, were discovered, and detected in vivo in the blood of AT patients treated with EryDex. Some of the new ATM variants, alongside an in silico designed one, were characterized and examined in AT fibroblast cell lines. ATM variants were capable of rescuing ATM activity in AT cells, particularly in the nuclear role of DNA DSBs recognition and repair, and in the cytoplasmic role of modulating autophagy, antioxidant capacity and mitochondria functionality, all of the features that are compromised in AT but essential for neuron survival. These outcomes are triggered by the kinase and further functional domains of the tested ATM variants, that are useful for restoring cellular functionality. The in silico designed ATM variant eliciting most of the functionality recover may be exploited in gene therapy or gene delivery for the treatment of AT patients., (© 2022. The Author(s).)

Background: Kidney ischemia reperfusion injury (IRI) is characterized by tubular cell death. DNA double-strand breaks is one of the major sources of tubular cell death induced by IRI. 2-Mercaptoethanol (2-ME) is protective against DNA double-strand breaks derived from calf thymus and bovine embryo. Here, we sought to determine whether treatment with 2-ME attenuated DNA double-strand breaks, resulting in reduced kidney dysfunction and structural damage in IRI., Methods: Kidney IRI or sham-operation in mice was carried out. The mice were treated with 2-ME, Ras-selective lethal 3, or vehicle. Kidney function, tubular injury, DNA damage, antioxidant enzyme expression, and DNA damage response (DDR) kinases activation were assessed., Results: Treatment with 2-ME significantly attenuated kidney dysfunction, tubular injury, and DNA double-strand breaks after IRI. Among DDR kinases, IRI induced phosphorylation of ataxia telangiectasia mutated (ATM) and ataxia telangiectasia and Rad3 related (ATR), but IRI reduced phosphorylation of other DDR kinases including ataxia telangiectasia and Rad3 related, checkpoint kinase 1 (Chk1), Chk2, and Chinese hamster cells 1 (XRCC1). Treatment with 2-ME enhanced phosphorylation of ATM and ATM-mediated effector kinases in IRI-subjected kidneys, suggesting that 2-ME activates ATM-mediated DDR signaling pathway. Furthermore, 2-ME dramatically upregulated glutathione peroxidase 4 (GPX4) in IRI-subjected kidneys. Inhibition of GPX4 augmented adverse IRI consequences including kidney dysfunction, tubular injury, DNA double-strand breaks, and inactivation of ATM-mediated DDR signaling pathway after IRI in 2-ME-treated kidneys., Conclusions: We have demonstrated that exogenous 2-ME protects against DNA double-strand breaks after kidney IRI through GPX4 upregulation and ATM activation., (© 2022. The Author(s) under exclusive licence to Maj Institute of Pharmacology Polish Academy of Sciences.)

Effective drug delivery to the brain is critical for the treatment of glioblastoma (GBM), an aggressive and invasive primary brain tumor that has a dismal prognosis. Radiation therapy, the mainstay of brain tumor treatment, works by inducing DNA damage. Therefore, inhibiting DNA damage response (DDR) pathways can sensitize tumor cells to radiation and enhance cytotoxicity. AZD1390 is an inhibitor of ataxia-telangiectasia mutated kinase, a critical regulator of DDR. Our in vivo studies in the mouse indicate that delivery of AZD1390 to the central nervous system (CNS) is restricted due to active efflux by P-glycoprotein (P-gp). The free fraction of AZD1390 in brain and spinal cord were found to be low, thereby reducing the partitioning of free drug to these organs. Coadministration of an efflux inhibitor significantly increased CNS exposure of AZD1390. No differences were observed in distribution of AZD1390 within different anatomic regions of CNS, and the functional activity of P-gp and breast cancer resistance protein also remained the same across brain regions. In an intracranial GBM patient-derived xenograft model, AZD1390 accumulation was higher in the tumor core and rim compared with surrounding brain. Despite this heterogenous delivery within tumor-bearing brain, AZD1390 concentrations in normal brain, tumor rim, and tumor core were above in vitro effective radiosensitizing concentrations. These results indicate that despite being a substrate of efflux in the mouse brain, sufficient AZD1390 exposure is anticipated even in regions of normal brain. SIGNIFICANCE STATEMENT: Given the invasive nature of glioblastoma (GBM), tumor cells are often protected by an intact blood-brain barrier, requiring the development of brain-penetrant molecules for effective treatment. We show that efflux mediated by P-glycoprotein (P-gp) limits central nervous system (CNS) distribution of AZD1390 and that there are no distributional differences within anatomical regions of CNS. Despite efflux by P-gp, concentrations effective for potent radiosensitization are achieved in GBM tumor-bearing mouse brains, indicating that AZD1390 is an attractive molecule for clinical development of brain tumors., (Copyright © 2022 by The American Society for Pharmacology and Experimental Therapeutics.)

Ataxia-telangiectasia (A-T) is caused by absence of the catalytic activity of ATM, a protein kinase that plays a central role in the DNA damage response, many branches of cellular metabolism, redox and mitochondrial homeostasis, and cell cycle regulation. A-T is a complex disorder characterized mainly by progressive cerebellar degeneration, immunodeficiency, radiation sensitivity, genome instability, and predisposition to cancer. It is increasingly recognized that the premature aging component of A-T is an important driver of this disease, and A-T is therefore an attractive model to study the aging process. This review outlines the current state of knowledge pertaining to the molecular and cellular signatures of aging in A-T and proposes how these new insights can guide novel therapeutic approaches for A-T., (Copyright © 2022 The Authors. Published by Elsevier B.V. All rights reserved.)

Children and young adults with mutant forms of ataxia telangiectasia mutated (ATM), a kinase involved in DNA damage signaling and mitochondrial homeostasis, suffer from recurrent respiratory infections, immune deficiencies, and obstructive airways disease associated with disorganized airway epithelium. We previously showed in mice how Atm was required to mount a protective immune memory response to influenza A virus [IAV; Hong Kong/X31 (HKx31), H3N2]. Here, Atm wildtype (WT) and knockout (Atm-null) mice were used to investigate how Atm is required to regenerate the injured airway epithelium following IAV infection. When compared with WT mice, naive Atm-null mice had increased airway resistance and reduced lung compliance that worsened during infection before returning to naïve levels by 56 days postinfection (dpi). Although Atm-null lungs appeared pathologically normal before infection by histology, they developed an abnormal proximal airway epithelium after infection that contained E-cadherin + , Sox2 + , and Cyp2f2 + cells lacking secretoglobin family 1 A member 1 (Scgb1a1) protein expression. Patchy and low expression of Scgb1a1 were eventually observed by 56 dpi. Genetic lineage tracing in HKx31-infected mice revealed club cells require Atm to rapidly and efficiently restore Scgb1a1 expression in proximal airways. Since Scgb1a1 is an immunomodulatory protein that protects the lung against a multitude of respiratory challenges, failure to efficiently restore its expression may contribute to the respiratory diseases seen in individuals with ataxia telangiectasia.

Ataxia-telangiectasia (A-T) is a multisystem autosomal recessive disease caused by mutations in the ATM gene and characterized by cerebellar atrophy, progressive ataxia, immunodeficiency, male and female sterility, radiosensitivity, cancer predisposition, growth retardation, insulin-resistant diabetes, and premature aging. ATM phosphorylates more than 1500 target proteins, which are involved in cell cycle control, DNA repair, apoptosis, modulation of chromatin structure, and other cytoplasmic as well as mitochondrial processes. In our quest to better understand the mechanisms by which ATM deficiency causes cerebellar degeneration, we hypothesized that specific vulnerabilities of cerebellar microglia underlie the etiology of A-T. Our hypothesis is based on the recent finding that dysfunction of glial cells affect a variety of process leading to impaired neuronal functionality (Song et al., 2019). Whereas astrocytes and neurons descend from the neural tube, microglia originate from the hematopoietic system, invade the brain at early embryonic stage, and become the innate immune cells of the central nervous system and important participants in development of synaptic plasticity. Here we demonstrate that microglia derived from Atm -/- mouse cerebellum display accelerated cell migration and are severely impaired in phagocytosis, secretion of neurotrophic factors, and mitochondrial activity, suggestive of apoptotic processes. Interestingly, no microglial impairment was detected in Atm-deficient cerebral cortex, and Atm deficiency had less impact on astroglia than microglia. Collectively, our findings validate the roles of glial cells in cerebellar attrition in A-T., (© 2021 Wiley Periodicals LLC.)

Ataxia-telangiectasia (A-T) is a neurodegenerative and primary immunodeficiency disorder (PID) characterized by cerebellar ataxia, oculocutaneous telangiectasia, immunodeficiency, progressive respiratory failure, and an increased risk of malignancies. It demands specialized care tailored to the individual patient's needs. Besides the classical ataxia-telangiectasia (classical A-T) phenotype, a variant phenotype (variant A-T) exists with partly overlapping but some distinctive disease characteristics. Here we present a case series of 6 patients with classical A-T and variant A-T, which illustrates the phenotypic variability of A-T that can present in childhood with prominent extrapyramidal features, with or without cerebellar ataxia. We report the clinical data, together with a detailed genotype description, immunological analyses, and related expression of the ATM protein. We show that the presence of some residual ATM kinase activity leads to the clinical phenotype variant A-T that differs from the classical A-T. Our data illustrate that the diagnosis of the variant form of A-T can be delayed and difficult, while early recognition of the variant form as well as the classical A-T is a prerequisite for providing a correct prognosis and appropriate rehabilitation and support, including the avoidance of diagnostic X-ray procedures, given the increased risk of malignancies and the higher risk for side effects of subsequent cancer treatment., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Blanchard-Rohner, Peirolo, Coulon, Korff, Horvath, Burkhard, Gumy-Pause, Ranza, Jandus, Dibra, Taylor and Fluss.)

Ataxia telangiectasia mutated (ATM) plays an essential role in DNA damage response and the maintenance of genomic stability. However, the role of ATM in regulating the function of adult neural stem cells (NSCs) remains unclear. Here we report that ATM deficiency led to accumulated DNA damage and decreased DNA damage repair capacity in neural progenitor cells. Moreover, we observed ATM ablation lead to the short-term increase of proliferation of neural progenitor cells, resulting in the depletion of the NSC pool over time, and this loss of NSC quiescence resulted in accelerated cell senescence. We further apply RNA sequencing to unravel that ATM knockout significantly affected Notch signaling pathway, furthermore, notch activation inhibit the abnormal increased proliferation of ATM -/- NSCs. Taken together, these findings indicate that ATM can serve as a key regulator for the normal function of adult NSCs by maintaining their stemness and preventing cellular senescence primarily through Notch signaling pathway., (Copyright © 2021 The Authors. Published by Elsevier B.V. All rights reserved.)

Background: ATM, the protein defective in the human genetic disorder, ataxia-telangiectasia (A-T) plays a central role in response to DNA double-strand breaks (DSBs) and in protecting the cell against oxidative stress. We showed that A-T cells are hypersensitive to metabolic stress which can be accounted for by a failure to exhibit efficient endoplasmic reticulum (ER)-mitochondrial signalling and Ca2 + transfer in response to nutrient deprivation resulting in mitochondrial dysfunction. The objective of the current study is to use an anaplerotic approach using the fatty acid, heptanoate (C7), a metabolic product of the triglyceride, triheptanoin to correct the defect in ER-mitochondrial signalling and enhance cell survival of A-T cells in response to metabolic stress., Methods: We treated control cells and A-T cells with the anaplerotic agent, heptanoate to determine their sensitivity to metabolic stress induced by inhibition of glycolysis with 2- deoxyglucose (2DG) using live-cell imaging to monitor cell survival for 72 h using the Incucyte system. We examined ER-mitochondrial signalling in A-T cells exposed to metabolic stress using a suite of techniques including immunofluorescence staining of Grp75, ER-mitochondrial Ca 2+ channel, the VAPB-PTPIP51 ER-mitochondrial tether complexes as well as proximity ligation assays between Grp75-IP3R1 and VAPB1-PTPIP51 to establish a functional interaction between ER and mitochondria. Finally, we also performed metabolomic analysis using LC-MS/MS assay to determine altered levels of TCA intermediates A-T cells compared to healthy control cells., Results: We demonstrate that heptanoate corrects all aspects of the defective ER-mitochondrial signalling observed in A-T cells. Heptanoate enhances ER-mitochondrial contacts; increases the flow of calcium from the ER to the mitochondrion; restores normal mitochondrial function and mitophagy and increases the resistance of ATM-deficient cells and cells from A-T patients to metabolic stress-induced killing. The defect in mitochondrial function in ATM-deficient cells was accompanied by more reliance on aerobic glycolysis as shown by increased lactate dehydrogenase A (LDHA), accumulation of lactate, and reduced levels of both acetyl CoA and ATP which are all restored by heptanoate., Conclusions: We conclude that heptanoate corrects metabolic stress in A-T cells by restoring ER-mitochondria signalling and mitochondrial function and suggest that the parent compound, triheptanoin, has immense potential as a novel therapeutic agent for patients with A-T., (Copyright © 2021 The Author(s). Published by Elsevier GmbH.. All rights reserved.)

The protein kinase ataxia telangiectasia mutated (ATM) is a master regulator of double-strand DNA break (DSB) signalling and stress responses. For three decades, ATM has been investigated extensively to elucidate its roles in the DNA damage response (DDR) and in the pathogenesis of ataxia telangiectasia (A-T), a human neurodegenerative disease caused by loss of ATM. Although hundreds of proteins have been identified as ATM phosphorylation targets and many important roles for this kinase have been identified, it is still unclear how ATM deficiency leads to the early-onset cerebellar degeneration that is common in all individuals with A-T. Recent studies suggest the existence of links between ATM deficiency and other cerebellum-specific neurological disorders, as well as the existence of broader similarities with more common neurodegenerative disorders. In this Review, we discuss recent structural insights into ATM regulation, and possible aetiologies of A-T phenotypes, including reactive oxygen species, mitochondrial dysfunction, alterations in transcription, R-loop metabolism and alternative splicing, defects in cellular proteostasis and metabolism, and potential pathogenic roles for hyper-poly(ADP-ribosyl)ation., (© 2021. Springer Nature Limited.)

DNA damage occurs constantly in every cell triggered by endogenous processes of replication and metabolism, and external influences such as ionizing radiation and intercalating chemicals. Large sets of proteins are involved in sensing, stabilizing and repairing this damage including control of cell cycle and proliferation. Some of these factors are phosphorylated upon activation and can be used as biomarkers of DNA damage response (DDR) by flow and mass cytometry. Differential survival rates of lymphocyte subsets in response to DNA damage are well established, characterizing NK cells as most resistant and B cells as most sensitive to DNA damage. We investigated DDR to low dose gamma radiation (2Gy) in peripheral blood lymphocytes of 26 healthy donors and 3 patients with ataxia telangiectasia (AT) using mass cytometry. γH2AX, p-CHK2, p-ATM and p53 were analyzed as specific DDR biomarkers for functional readouts of DNA repair efficiency in combination with cell cycle and T, B and NK cell populations characterized by 20 surface markers. We identified significant differences in DDR among lymphocyte populations in healthy individuals. Whereas CD56 + CD16 + NK cells showed a strong γH2AX response to low dose ionizing radiation, a reduced response rate could be observed in CD19 + CD20 + B cells that was associated with reduced survival. Interestingly, γH2AX induction level correlated inversely with ATM-dependent p-CHK2 and p53 responses. Differential DDR could be further noticed in naïve compared to memory T and B cell subsets, characterized by reduced γH2AX, but increased p53 induction in naïve T cells. In contrast, DDR was abrogated in all lymphocyte populations of AT patients. Our results demonstrate differential DDR capacities in lymphocyte subsets that depend on maturation and correlate inversely with DNA damage-related survival. Importantly, DDR analysis of peripheral blood cells for diagnostic purposes should be stratified to lymphocyte subsets., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2021 Felgentreff, Schuetz, Baumann, Klemann, Viemann, Ursu, Jacobsen, Debatin, Schulz, Hoenig and Schwarz.)

Ataxia-telangiectasia (A-T) is a genetic disorder caused by the lack of functional ATM kinase. A-T is characterized by chronic inflammation, neurodegeneration and premature ageing features that are associated with increased genome instability, nuclear shape alterations, micronuclei accumulation, neuronal defects and premature entry into cellular senescence. The causal relationship between the detrimental inflammatory signature and the neurological deficiencies of A-T remains elusive. Here, we utilize human pluripotent stem cell-derived cortical brain organoids to study A-T neuropathology. Mechanistically, we show that the cGAS-STING pathway is required for the recognition of micronuclei and induction of a senescence-associated secretory phenotype (SASP) in A-T olfactory neurosphere-derived cells and brain organoids. We further demonstrate that cGAS and STING inhibition effectively suppresses self-DNA-triggered SASP expression in A-T brain organoids, inhibits astrocyte senescence and neurodegeneration, and ameliorates A-T brain organoid neuropathology. Our study thus reveals that increased cGAS and STING activity is an important contributor to chronic inflammation and premature senescence in the central nervous system of A-T and constitutes a novel therapeutic target for treating neuropathology in A-T patients., (© 2021 The Authors. Aging Cell published by Anatomical Society and John Wiley & Sons Ltd.)

Ataxia-telangiectasia (A-T) is a multisystem disorder caused by biallelic pathogenic variants in the gene encoding A-T mutated (ATM) kinase, a master regulator of the DNA damage response (DDR) pathway. Most A-T patients show cellular and/or humoral immunodeficiency that has been associated with cancer risk and reduced survival, but NK cells have not been thoroughly studied. Here we investigated NK cells of A-T patients with a special focus on the NKG2D receptor that triggers cytotoxicity upon engagement by its ligands (NKG2DLs) commonly induced via the DDR pathway on infected, transformed, and variously stressed cells. Using flow cytometry, we examined the phenotype and function of NK cells in 6 A-T patients as compared with healthy individuals. NKG2D expression was evaluated also by western blotting and RT-qPCR; plasma soluble NKG2DLs (sMICA, sMICB, sULBP1, ULBP2) were measured by ELISA. Results showed that A-T NK cells were skewed towards the CD56 neg anergic phenotype and displayed decreased expression of NKG2D and perforin. NKG2D was reduced at the protein but not at the mRNA level and resulted in impaired NKG2D-mediated cytotoxicity in 4/6 A-T patients. Moreover, in A-T plasma we found 24-fold and 2-fold increase of sMICA and sULBP1, respectively, both inversely correlated with NKG2D expression. Overall, NK cells are disturbed in A-T patients showing reduced NKG2D expression, possibly caused by persistent engagement of its ligands, that may contribute to susceptibility to cancer and infections and represent novel targets for therapeutic interventions., (Copyright © 2021 Elsevier Inc. All rights reserved.)

Mitophagy is defective in several neurodegenerative diseases, including Ataxia Telangiectasia (A-T). However, the molecular mechanism underlying defective mitophagy in A-T is unknown. Literature indicates that damaged mitochondria are transported to the perinuclear region prior to their removal via mitophagy. Our previous work has indicated that conjugation of SUMO2 (Small Ubiquitin-like Modifier 2) to mitofusins (Mfns) may be necessary for congression of mitochondria into SUMO2-/ubiquitin-/LC3-positive compact structures resembling mito-aggresomes at the perinuclear region in CCCP-treated HEK293 cells. Here, we demonstrate that Mfns are SUMOylated, and mitochondria are transported to the perinuclear region; however, mitochondria fail to congress into mito-aggresome-like structures in CCCP-treated A-T cells. Defect in mitochondrial congression is causally related to constitutively elevated ISG15 (Interferon-Stimulated Gene 15), an antagonist of the ubiquitin pathway, in A-T cells. Suppression of the ISG15 pathway restores mitochondrial congression, reduce oxidative stress, and level of unhealthy mitochondria, which is suggestive of restoration of mitophagy in A-T cells. ISG15 is also constitutively elevated and mitophagy is defective in Amytrophic Lateral Sclerosis (ALS). The constitutively elevated ISG15 pathway therefore appears to be a common unifying biochemical mechanism underlying defective mitophagy in neurodegenerative disorders thus, implying the broader significance of our findings, and suggest the potential role of ISG15 inhibitors in their treatment., (Copyright © 2021. Published by Elsevier B.V.)

Ataxia telangiectasia (AT) is a rare genetic neurodegenerative disease. To date, there is no available cure for the illness, but the use of glucocorticoids has been shown to alleviate the neurological symptoms associated with AT. While studying the effects of dexamethasone (dex) in AT fibroblasts, by chance we observed that the nucleoplasmic Lamin A/C was affected by the drug. In addition to the structural roles of A-type lamins, Lamin A/C has been shown to play a role in the regulation of gene expression and cell cycle progression, and alterations in the LMNA gene is cause of human diseases called laminopathies. Dex was found to improve the nucleoplasmic accumulation of soluble Lamin A/C and was capable of managing the large chromatin Lamin A/C scaffolds contained complex, thus regulating epigenetics in treated cells. In addition, dex modified the interactions of Lamin A/C with its direct partners lamin associated polypeptide (LAP) 2a, Retinoblastoma 1 (pRB) and E2F Transcription Factor 1 (E2F1), regulating local gene expression dependent on E2F1. These effects were differentially observed in both AT and wild type (WT) cells. To our knowledge, this is the first reported evidence of the role of dex in Lamin A/C dynamics in AT cells, and may represent a new area of research regarding the effects of glucocorticoids on AT. Moreover, future investigations could also be extended to healthy subjects or to other pathologies such as laminopathies since glucocorticoids may have other important effects in these contexts as well.

Inhibitors of ataxia-telangiectasia mutated (ATM), such as KU-55933 (Ku), represent a promising class of novel anticancer drugs. In addition, the biguanide derivative phenformin exhibits antitumor activity superior to that of the AMPK activator metformin. Herein, we assessed the potential combinatorial therapeutic efficacy of phenformin and Ku when used to inhibit the growth of liver cancer cells, and we assessed the mechanisms underlying such efficacy. The Hep-G2 and SMMC-7721 liver cancer cell lines were treated with phenformin and Ku either alone or in combination, after which the impact of these drugs on cellular proliferation was assessed via 3-(4,5-dimethylthiazol) 2, 5-diphenyltetrazolium and colony formation assays, whereas Transwell assays were used to gauge cell migratory activity. The potential synergy between these two drugs was assessed using the CompuSyn software, while flow cytometry was employed to evaluate cellular apoptosis. In addition, western blotting was utilized to measure p-ATM, p-AMPK, p-mTOR, and p-p70s6k expression, while mitochondrial functionality was monitored via morphological analyses, JC-1 staining, and measurements of ATP levels. Phenformin and Ku synergistically impacted the proliferation, migration, and apoptotic death of liver cancer cells. Together, these compounds were able to enhance AMPK phosphorylation while inhibiting the phosphorylation of mTOR and p70s6k. These data also revealed that phenformin and Ku induced mitochondrial dysfunction as evidenced by impaired ATP synthesis, mitochondrial membrane potential, and abnormal mitochondrial morphology. These findings suggest that combination treatment with phenformin and Ku may be an effective approach to treating liver cancer via damaging mitochondria within these tumor cells., (© 2021 The Authors. FEBS Open Bio published by John Wiley & Sons Ltd on behalf of Federation of European Biochemical Societies.)

Background: The elevated global burden of the breast invasive carcinoma (BRIC) and lack of appropriate biomarkers for its early detection and treatment requires extensive investigation to enhance understanding regarding BRIC associated molecular alterations. Ataxia telangiectasia mutated ( ATM ) is a multifunctional tumor suppressor gene, which participates in the DNA damage response pathway and cellular checkpoint activation. Several studies have reported the reduction of ATM expression as a reliable biomarker of BRIC. However, its role as a clinicopathological feature-specific biomarker still needs to be explored. Aim: The present study was designed to investigate the mutational spectrum and expression variations of ATM in BRIC patients exhibiting various clinicopathological features. Furthermore, we also performed a correlational analysis of clinicopathological feature-specific ATM expression with its promoter methylation, status genetic alterations, copy number variation (CNVs), overall survival (OS), and effectiveness of various anticancerous drugs in BRIC patients. Methods: We utilized multiple online platforms, including UALCN, cBioportal, and CCLE GDSC tool kit. Results: The ATM exhibited decreased expression in the majority of the BRIC patients, and its promoter was hypermethylated compared to healthy controls. Hence, the degree of promoter methylation and ATM expression level were inversely correlated in BRIC. In addition, we also investigated if BRIC patients that had higher ATM expression had lower OS. We found that elevated expression of ATM was found to promoted or decreased the effectiveness of various anticancer drugs. Conclusion: This study revealed the overall and clinicopathological feature-specific role of the ATM , gene, however, these findings need to be validated via larger scale studies.

Senescence phenotypes and mitochondrial dysfunction are implicated in aging and in premature aging diseases, including ataxia telangiectasia (A-T). Loss of mitochondrial function can drive age-related decline in the brain, but little is known about whether improving mitochondrial homeostasis alleviates senescence phenotypes. We demonstrate here that mitochondrial dysfunction and cellular senescence with a senescence-associated secretory phenotype (SASP) occur in A-T patient fibroblasts, and in ATM-deficient cells and mice. Senescence is mediated by stimulator of interferon genes (STING) and involves ectopic cytoplasmic DNA. We further show that boosting intracellular NAD + levels with nicotinamide riboside (NR) prevents senescence and SASP by promoting mitophagy in a PINK1-dependent manner. NR treatment also prevents neurodegeneration, suppresses senescence and neuroinflammation, and improves motor function in Atm -/- mice. Our findings suggest a central role for mitochondrial dysfunction-induced senescence in A-T pathogenesis, and that enhancing mitophagy as a potential therapeutic intervention., (Published 2021. This article is a U.S. Government work and is in the public domain in the USA. Aging Cell published by Anatomical Society and John Wiley & Sons Ltd.)

Mitophagy is a selective process aimed at removing damaged or burned-out mitochondria; it is activated upon different stimuli and plays a fundamental role in preventing overproduction of reactive oxygen species (ROS) that might be generated by dysfunctional mitochondria. From this angle, mitophagy can be considered a fully-fledged antioxidant process. Such a surrogate antioxidant function is recently emerging, being shared among many molecular pathways and players that are usually not included among - and, formally, do not directly act as - antioxidants. ATM (ataxia telangiectasia mutated) is a prototype of this class of "neglected" antioxidants. In spite of its well-known role in DNA damage response, many phenotypes of ataxia telangiectasia (A-T) patients are, indeed, related to chronic oxidative stress, arguing for an additional antioxidant role of ATM. In a recent study, we discovered the mechanism through which ATM exerts antioxidant activity. In particular, we provided evidence that this involves ADH5/GSNOR (alcohol dehydrogenase 5 (class III), chi polypeptide), which, in turn, sustains mitophagy via PARK2 denitrosylation, and protects the cell from detrimental effects due to ROS.

ATM kinase is a tumor suppressor and a master regulator of the DNA damage response. Most cancer-associated alterations to ATM are missense mutations at the PI3-kinase regulatory domain (PRD) or the kinase domain. Expression of kinase-dead (KD) ATM protein solely accelerates lymphomagenesis beyond ATM loss. To understand how PRD suppresses lymphomagenesis, we introduced the cancer-associated PRD mutation R3008H (R3016 in mouse) into mice. R3008H abrogated DNA damage- and oxidative stress-induced activation of ATM without consistently affecting ATM protein stability and recruitment. In contrast to the early embryonic lethality of Atm KD/KD mice, AtmR3016H ( Atm R/R ) mice were viable, immunodeficient, and displayed spontaneous craniofacial abnormalities and delayed lymphomagenesis compared with Atm -/- controls. Mechanistically, R3008H rescued the tardy exchange of ATM-KD at DNA damage foci, indicating that PRD coordinates ATM activation with its exchange at DNA-breaks. Taken together, our results reveal a unique tumorigenesis profile for PRD mutations that is distinct from null or KD mutations. SIGNIFICANT: This study functionally characterizes the most common ATM missense mutation R3008H in cancer and identifies a unique role of PI3-kinase regulatory domain in ATM activation., (©2020 American Association for Cancer Research.)

The three-dimensional structure of chromosomes plays an important role in gene expression regulation and also influences the repair of radiation-induced DNA damage. Genomic aberrations that disrupt chromosome spatial domains can lead to diseases including cancer, but how the 3D genome structure responds to DNA damage is poorly understood. Here, we investigate the impact of DNA damage response and repair on 3D genome folding using Hi-C experiments on wild type cells and ataxia telangiectasia mutated (ATM) patient cells. We irradiate fibroblasts, lymphoblasts, and ATM-deficient fibroblasts with 5 Gy X-rays and perform Hi-C at 30 minutes, 24 hours, or 5 days after irradiation. We observe that 3D genome changes after irradiation are cell type-specific, with lymphoblastoid cells generally showing more contact changes than irradiated fibroblasts. However, all tested repair-proficient cell types exhibit an increased segregation of topologically associating domains (TADs). This TAD boundary strengthening after irradiation is not observed in ATM deficient fibroblasts and may indicate the presence of a mechanism to protect 3D genome structure integrity during DNA damage repair.

Oxidative stress-induced DNA cleavage and apoptosis in pancreatic acinar cells has been implicated in the pathogenesis of acute pancreatitis. Thus, an efficient DNA repair process is key to prevention of apoptotic pancreatic acinar cell death. Ataxia telangiectasia mutated (ATM), a sensor of DNA breaks, functions by recruiting DNA repair proteins to initiate the DNA repair process. In the present study, we investigated whether H 2 O 2 produced by the action of glucose oxidase on α-D-glucose (G/GO) induces apoptosis in pancreatic acinar AR42J cells through an alteration of the level of ATM. As a result, G/GO induced apoptosis by promoting a loss of cell viability, increase in Bax, decrease in Bcl-2, cleavage of poly (ADP-ribose) polymerase (PARP) and fragmentation of DNA. In addition, ATM cleavage along with elevated levels of calpain and caspase-3 activity was induced by G/GO. By using ATM siRNA, we demonstrated that reduction in ATM levels enhanced G/GO-induced apoptosis. Moreover, inhibition of calpain activity by calpeptin or calpastatin, or by inhibition of caspase-3 with z-DEVD, suppressed G/GO-induced apoptosis and ATM cleavage. Collectively, these findings suggest that proteolysis of ATM is the underlying mechanism of apoptosis of pancreatic acinar cells caused by exposure to oxidative stress.

Research on the molecular pathology of genome instability disorders has advanced our understanding of the complex mechanisms that safeguard genome stability and cellular homeostasis at large. Once the culprit genes and their protein products are identified, an ongoing dialogue develops between the research lab and the clinic in an effort to link specific disease symptoms to the functions of the proteins that are missing in the patients. Ataxi A-T elangiectasia (A-T) is a prominent example of this process. A-T's hallmarks are progressive cerebellar degeneration, immunodeficiency, chronic lung disease, cancer predisposition, endocrine abnormalities, segmental premature aging, chromosomal instability and radiation sensitivity. The disease is caused by absence of the powerful protein kinase, ATM, best known as the mobilizer of the broad signaling network induced by double-strand breaks (DSBs) in the DNA. In parallel, ATM also functions in the maintenance of the cellular redox balance, mitochondrial function and turnover and many other metabolic circuits. An ongoing discussion in the A-T field revolves around the question of which ATM function is the one whose absence is responsible for the most debilitating aspect of A-T - the cerebellar degeneration. This review suggests that it is the absence of a comprehensive role of ATM in responding to ongoing DNA damage induced mainly by endogenous agents. It is the ensuing deterioration and eventual loss of cerebellar Purkinje cells, which are very vulnerable to ATM absence due to a unique combination of physiological features, which kindles the cerebellar decay in A-T., (Copyright © 2020 The Author. Published by Elsevier B.V. All rights reserved.)

ATM is a kinase involved in DNA damage response (DDR), regulation of response to oxidative stress, autophagy and mitophagy. Mutations in the ATM gene in humans result in ataxi A-Telangiectasia disease (A-T) characterized by a variety of symptoms with neurodegeneration and premature ageing among them. Since brain is one of the most affected organs in A-T, we have focused on senescence of neural progenitor cells (NPCs) derived from A-T reprogrammed fibroblasts. Accordingly, A-T NPCs obtained through neural differentiation of iPSCs in 5% oxygen possessed some features of senescence including increased activity of SA-β-gal and secretion of IL6 and IL8 in comparison to control NPCs. This phenotype of A-T NPC was accompanied by elevated oxidative stress. A-T NPCs exhibited symptoms of impaired autophagy and mitophagy with lack of response to chloroquine treatment. Additional sources of oxidative stress like increased oxygen concentration (20 %) and H 2 O 2 respectively aggravated the phenotype of senescence and additionally disturbed the process of mitophagy. In both cases only A-T NPCs reacted to the treatment. We conclude that oxidative stress may be responsible for the phenotype of senescence and impairment of autophagy in A-T NPCs. Our results point to senescent A-T cells as a potential therapeutic target in this disease., (Copyright © 2020 The Authors. Published by Elsevier B.V. All rights reserved.)

Ataxia telangiectasia (AT) and Aicardi-Goutières syndrome (AGS) are inherited disorders of immunity with prevalent neurological phenotype. Available treatments are only partially effective, and the prognosis is poor. Induced pluripotent stem cells (iPSCs) are obtained by reprogramming patient somatic cells, preserving the donor individual genetic heritage and creating patient-specific disease models, useful to investigate pathogenesis and drug effects and to develop precision therapies. The aim is to investigate the cytotoxicity of a panel of immunomodulators using iPSCs of patients with AT or different forms of AGS (AGS1, AGS2, and AGS7). iPSCs were obtained by reprogramming AT and AGS patients' cells and, as a control, the BJ normal human fibroblast line, using Sendai virus. Cytotoxic effects of two drugs proposed to treat respectively AT and AGS (dexamethasone and mepacrine) were tested by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay after 72 hours' exposure. Data were obtained also for other immunomodulatory drugs (thioguanine, mercaptopurine, thalidomide, and lenalidomide). Relative expression of genes involved in the tested drug pathways was analyzed. AGS7-derived iPSCs displayed altered viability when treated with a low dose of mepacrine and higher expression of cyclic guanosine monophosphate-adenosine monophosphate synthase, which is the main target for mepacrine action. AGS7-derived iPSCs were also more sensitive to thioguanine, while AGS2 and AT iPSCs were less sensitive to this medication than the BJ-iPSC. All iPSCs were equally sensitive to mercaptopurine and resistant to dexamethasone, thalidomide, and lenalidomide. This work establishes an innovative in vitro model that is useful to investigate the mechanisms of drugs potentially effective in AT and AGS., (© 2020 The Authors Clinical Pharmacology & Therapeutics © 2020 American Society for Clinical Pharmacology and Therapeutics.)

People with ataxia-telangiectasia (A-T) display phenotypic variability with regard to progression of immunodeficiency, sino-pulmonary disease, and neurologic decline. To determine the association between differential gene expression, epigenetic state, and phenotypic variation among people with A-T, we performed transcriptional and genome-wide DNA methylation profiling in patients with mild and classic A-T progression as well as healthy controls. RNA and genomic DNA were isolated from peripheral blood mononuclear cells for transcriptional and DNA methylation profiling with RNA-sequencing and modified reduced representation bisulfite sequencing, respectively. We identified 555 genes that were differentially expressed among the control, mild A-T, and classic A-T groups. Genome-wide DNA methylation profiling revealed differential promoter methylation in cis with 146 of these differentially expressed genes. Functional enrichment analysis identified significant enrichment in immune, growth, and apoptotic pathways among the methylation-regulated genes. Regardless of clinical phenotype, all A-T participants exhibited downregulation of critical genes involved in B cell function (PAX5, CD79A, CD22, and FCRL1) and upregulation of several genes associated with senescence and malignancy, including SERPINE1. These findings indicate that gene expression differences may be associated with phenotypic variability and suggest that DNA methylation regulates expression of critical immune response genes in people with A-T.

We propose a comprehensive mathematical model to study the dynamics of ionizing radiation induced Ataxia-telangiectasia mutated (ATM) activation that consists of ATM activation through dual mechanisms: the initiative activation pathway triggered by the DNA damage-induced local chromatin relaxation and the primary activation pathway consisting of a self-activation loop by interplay with chromatin relaxation. The model is expressed as a series of biochemical reactions, governed by a system of differential equations and analyzed by dynamical systems techniques. Radiation induced double strand breaks (DSBs) cause rapid local chromatin relaxation, which is independent of ATM but initiates ATM activation at damage sites. Key to the model description is how chromatin relaxation follows when active ATM phosphorylates KAP-1, which subsequently spreads throughout the chromatin and induces global chromatin relaxation. Additionally, the model describes how oxidative stress activation of ATM triggers a self-activation loop in which PP2A and ATF2 are released so that ATM can undergo autophosphorylation and acetylation for full activation in relaxed chromatin. In contrast, oxidative stress alone can partially activate ATM because phosphorylated ATM remains as a dimer. The model leads to predictions on ATM mediated responses to DSBs, oxidative stress, or both that can be tested by experiments., Competing Interests: The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.

Ataxia telangiectasia (A-T) is an inherited neurodegenerative disease caused by mutation in the ataxia telangiectasia mutated (ATM) gene, leading to loss of function in the encoded protein ATM. Because ATM functions to reduce oxidative stress by up-regulating antioxidant enzymes, oxidative stress is a prevalent A-T phenotype and a mediator of the inflammation that drives A-T pathology. Reactive oxygen species (ROS) levels and the expression of pro-inflammatory cytokine interleukin-8 (IL-8) were higher in A-T cells than in normal cells. ROS are related to mitochondrial dysfunction and activation of nuclear factor kappa B (NF-κB) to induce IL-8 expression. Alpha-lipoic acid (α-LA), a naturally occurring thiol compound, shows an antioxidant effect in various cells. This study is aimed to determine if α-LA confers protection against NF-κB activation, IL-8 expression, and mitochondrial dysfunction in A-T cells which are exposed to the inflammatory cytokine IL-1β. A-T fibroblasts were treated with or without α-LA. The levels of intracellular and mitochondrial ROS, mRNA and protein levels of IL-8, mitochondrial membrane potential (MMP), ATP levels, and DNA binding activity of NF-κB were determined. As a result, IL-1β increased NF-κB activation, IL-8 expression, intracellular and mitochondrial ROS levels, but decreased MMP and ATP level in A-T cells. Pretreatment of A-T cells with α-LA inhibited IL-1β-induced activation of NF-κB, IL-8 expression, and mitochondrial dysfunction by reducing ROS levels. In conclusion, supplementation with α-LA may be beneficial for reducing the oxidative stress-induced mitochondrial dysfunction and IL-8 production associated with A-T.

Background: Ataxia Telangiectasia (A-T) is an inherited multisystem disorder with cerebellar neurodegeneration. The relationships between imaging metrics of cerebellar health and neurological function across childhood in A-T are unknown, but may be important for determining timing and impact of therapeutic interventions., Purpose: To test the hypothesis that abnormalities of cerebellar structure, physiology and cellular health occur in childhood A-T and correlate with neurological disability, we performed multiparametric cerebellar MRI and establish associations with disease status in childhood A-T., Methods: Prospective cross-sectional observational study. 22 young people (9 females / 13 males, age 6.6-17.8 years) with A-T and 24 matched healthy controls underwent 3-Tesla MRI with volumetric, diffusion and proton spectroscopic acquisitions. Participants with A-T underwent structured neurological assessment, and expression / activity of ataxia-telangiectasia mutated (ATM) kinase were recorded., Results: Ataxia-telangiectasia participants had cerebellar volume loss (fractional total cerebellar volume: 5.3% vs 8.7%, P < 0.0005, fractional 4th ventricular volumes: 0.19% vs 0.13%, P < 0.0005), that progressed with age (fractional cerebellar volumes, r = -0.66, P = 0.001), different from the control group (t = -4.88, P < 0.0005). The relationship between cerebellar volume and age was similar for A-T participants with absent ATM kinase production and those producing non-functioning ATM kinase. Markers of cerebellar white matter injury were elevated in ataxia-telangiectasia vs controls (apparent diffusion coefficient: 0.89 × 10 -3  mm 2  s -1 vs 0.69 × 10 -3  mm 2  s -1 , p < 0.0005) and correlated (age-corrected) with neurometabolite ratios indicating impaired neuronal viability (N-acetylaspartate:creatine r = -0.70, P < 0.001); gliosis (inositol:creatine r = 0.50, P = 0.018; combined glutamine/glutamate:creatine r = -0.55, P = 0.008) and increased myelin turnover (choline:creatine r = 0.68, P < 0.001). Fractional 4th ventricular volume was the only variable retained in the regression model predicting neurological function (adjusted r 2  = 0.29, P = 0.015)., Conclusions: Quantitative MRI demonstrates cerebellar abnormalities in children with A-T, providing non-invasive measures of progressive cerebellar injury and markers reflecting neurological status. These MRI metrics may be of value in determining timing and impact of interventions aimed at altering the natural history of A-T., (Copyright © 2019 The Authors. Published by Elsevier Inc. All rights reserved.)

Ataxia telangiectasia (AT) is a genetic disease caused by mutations in the ATM gene but the mechanisms underlying AT are not completely understood. Key functions of the ATM protein are to sense and regulate cellular redox status and to transduce DNA double-strand break signals to downstream effectors. ATM-deficient cells show increased ROS accumulation, activation of p38 protein kinase, and increased levels of DNA damage. GSE24.2 peptide and a short derivative GSE4 peptide corresponding to an internal domain of Dyskerin have proved to induce telomerase activity, decrease oxidative stress, and protect from DNA damage in dyskeratosis congenita (DC) cells. We have found that expression of GSE24.2 and GSE4 in human AT fibroblast is able to decrease DNA damage, detected by γ-H2A.X and 53BP1 foci. However, GSE24.2/GSE4 expression does not improve double-strand break signaling and repair caused by the lack of ATM activity. In contrast, they cause a decrease in 8-oxoguanine and OGG1-derived lesions, particularly at telomeres and mitochondrial DNA, as well as in reactive oxygen species, in parallel with increased expression of SOD1. These cells also showed lower levels of IL6 and decreased p38 phosphorylation, decreased senescence and increased ability to divide for longer times. Additionally, these cells are more resistant to treatment with H 2 0 2 and the radiomimetic-drug bleomycin. Finally, we found shorter telomere length (TL) in AT cells, lower levels of TERT expression, and telomerase activity that were also partially reverted by GSE4. These observations suggest that GSE4 may be considered as a new therapy for the treatment of AT that counteracts the cellular effects of high ROS levels generated in AT cells and in addition increases telomerase activity contributing to increased cell proliferation.

Introduction and Objectives: Vitamin D plays a role in the immune system, however studies regarding this are scarce. This study aimed to evaluate the nutritional status of vitamin D in patients with Common Variable Immunodeficiency (CVID) or Ataxia-Telangiectasia (A-T) and to relate it to body composition, inflammatory and bone metabolism markers., Patients and Methods: This is a cross-sectional and controlled study involving 24 patients of both sexes (59.3% male), aged 8-56 years, with CVID (n=15) or A-T (n=9). The following variables were evaluated: body mass index (BMI), 25-hydroxyvitamin D (25 (OH) D), hepatic profile, parathormone, calcium, phosphorus, alkaline phosphatase, interleukin 6 and high-sensitivity C-reactive protein., Results: The median age was 26.0 years. A deficiency of 25 (OH) D was found in four A-T patients (44%) and two CVID patients (13%). Nine patients with CVI (60%) and six with A-T (66.7%) were overweight and underweight, respectively. There was a negative correlation between vitamin D and fat mass in the CVID group, and vitamin D and BMI in the A-T group. Vitamin D was negatively associated with the percentage of total fat among the patients (β - 0.842, 95% CI: -1.5-0.17, p=0.015), R 2 =0.21, after adjusting for sex and age., Conclusion: Vitamin D deficiency occurred in a quarter of the patients although there was no difference between the patient and the control group; without association with bone and inflammation biomarkers. The percentage of fat and BMI were negatively associated with the concentrations of 25 (OH) D., (Copyright © 2019 SEICAP. Published by Elsevier España, S.L.U. All rights reserved.)

Oxidative stress has been shown to play a crucial role in the pathophysiology of the neurodegenerative disease Ataxia Telangiectasia. We have recently demonstrated that Dexamethasone treatment is able to counteract the oxidative state by promoting nuclear factor erythroid 2-related factor 2 (NRF2) nuclear accumulation. However, substantial gaps remain in our knowledge of the underlying molecular mechanism(s) according to which Dexamethasone acts as an NRF2 inducer. Herein we investigate the possible effects of the drug on the main NRF2 activation pathways by initially focusing on key kinases known to differently affect NRF2 activation. Neither AKT nor ERK1/2, known to be NRF2-activating kinases, were found to be activated upon Dexamethasone treatment, thus excluding their involvement in the transcription factor nuclear shift. Likewise, GSK3 inactivating kinase was not inhibited, thus ruling out its role in NRF2 activation. On the other hand, p38 MAPK, another NRF2-inhibitory kinase, was indeed switched-off in Ataxia Telangiectasia cells by Dexamethasone-mediated induction of DUSP1 phosphatase, and therefore it appeared that it might account for NRF2 triggering. However, this mechanism was excluded by the use of a selective p38 inhibitor, which failed to cause a significant NRF2 nuclear shift and target gene induction. Finally, dexamethasone effects on the classical oxidative pathway orchestrated by KEAP1 were addressed. Dexamethasone was found to decrease the expression of the inhibitor KEAP1 at both mRNA and protein levels and to induce the shift from the reduced to the oxidized form of KEAP1, thus favouring NRF2 translocation into the nucleus. Furthermore, preliminary data revealed very low levels of the negative regulator Fyn in Ataxia Telangiectasia cells, which might account for the prolonged NRF2-activated gene expression., Competing Interests: The authors have declared that no competing interests exist.

Ataxia telangiectasia is a rare, multi system disease caused by ATM kinase deficiency. Atm -knockout mice recapitulate premature aging, immunodeficiency, cancer predisposition, growth retardation and motor defects, but not cerebellar neurodegeneration and ataxia. We explored whether Atm loss is responsible for skeletal muscle defects by investigating myofiber morphology, oxidative/glycolytic activity, myocyte ultrastructural architecture and neuromuscular junctions. Atm -knockout mice showed reduced muscle and fiber size. Atrophy, protein synthesis impairment and a switch from glycolytic to oxidative fibers were detected, along with an increase of in expression of slow and fast myosin types ( Myh7 , and Myh2 and Myh4 , respectively) in tibialis anterior and solei muscles isolated from Atm -knockout mice. Transmission electron microscopy of tibialis anterior revealed misalignments of Z-lines and sarcomeres and mitochondria abnormalities that were associated with an increase in reactive oxygen species. Moreover, neuromuscular junctions appeared larger and more complex than those in Atm wild-type mice, but with preserved presynaptic terminals. In conclusion, we report for the first time that Atm-knockout mice have clear morphological skeletal muscle defects that will be relevant for the investigation of the oxidative stress response, motor alteration and the interplay with peripheral nervous system in ataxia telangiectasia., Competing Interests: Competing interestsThe authors declare no competing or financial interests., (© 2019. Published by The Company of Biologists Ltd.)

Ataxia-telangiectasia (A-T) is an autosomal recessive disease caused by mutation of the ATM gene and is characterized by loss of cerebellar Purkinje cells, neurons with high physiological activity and dynamic ATP demands. Here, we show that depletion of ATP generates reactive oxygen species that activate ATM. We find that when ATM is activated by oxidative stress, but not by DNA damage, ATM phosphorylates NRF1. This leads to NRF1 dimerization, nuclear translocation, and the up-regulation of nuclear-encoded mitochondrial genes, thus enhancing the capacity of the electron transport chain (ETC) and restoring mitochondrial function. In cells lacking ATM, cells replenish ATP poorly following surges in energy demand, and chronic ATP insufficiency endangers cell survival. We propose that in the absence of ATM, cerebellar Purkinje cells cannot respond adequately to the increase in energy demands of neuronal activity. Our findings identify ATM as a guardian of mitochondrial output, as well as genomic integrity, and suggest that alternative fuel sources may ameliorate A-T disease symptoms., (© 2019 Chow et al.)

Autosomal recessive ataxia telangiectasia (A-T) is characterized by radiosensitivity, immunodeficiency, and cerebellar neurodegeneration. A-T is caused by inactivating mutations in the ataxia telangiectasiamutated (ATM) gene, a serine-threonine protein kinase involved in DNA damage response and excitatory neurotransmission. The selective vulnerability of cerebellar Purkinje neurons (PN) to A-T is not well understood. Employing global proteomic profiling of cerebrospinal fluid from patients at ages around 15 years, we detected reduced calbindin, reelin, cerebellin-1, cerebellin-3, protocadherin fat 2, sempahorin 7A, and increased apolipoprotein B and J peptides. Bioinformatic enrichment was observed for pathways of lipoproteins, endocytosis, extracellular matrix receptor interaction, peptidase activity, adhesion, calcium binding, and complement immunity. This seemed important since secretion of reelin from glutamatergic afferent axons is crucial for PN lipoprotein receptor endocytosis and lipid signaling. Reelin expression is downregulated by irradiation and reelin/ApoB mutations are known causes of ataxia. Validation efforts in 2-month-old Atm-/- mice before onset of motor deficits confirmed cerebellar transcript reductions for reelin receptors Apoer2/Vldlr with increases for their ligands Apoe/Apoh and cholesterol 24-hydroxylase Cyp46a1. Concomitant dysregulations were found for Vglut2/Sema7a as climbing fiber markers, glutamate receptors like Grin2b, and calcium homeostasis factors (Atp2b2, Calb1, Itpr1), while factors involved in DNA damage, oxidative stress, neuroinflammation, and cell adhesion were normal at this stage. Quantitative immunoblots confirmed ApoB and ApoJ increases and VLDLR reduction in cerebellar tissue at the age of 2 months. These findings show that ApoB excess and reelin signaling deficits reflect the neurodegeneration in A-T in a sensitive and specific way. As extracellular factors, apolipoproteins and their cargo such as vitamin E may be useful for neuroprotective interventions.