The team built a diploid yeast strain in which both copies of the SOD1 gene had been deleted, creating a hybrid background containing roughly 50,000 sequence differences between its two parental genomes. This design allowed the researchers to map, with extraordinary resolution, every loss of heterozygosity event that accumulated as cells divided. After subculturing 32 independent isolates for hundreds of generations, whole-genome sequencing revealed a staggering catalogue of damage. Single nucleotide variations accumulated at 13 times the wild-type rate, loss of heterozygosity rose 12-fold, large chromosomal rearrangements increased 4-fold, and aneuploidy—the gain or loss of entire chromosomes—surged an astonishing 48-fold above normal levels.

The scale and diversity of these lesions underscored that Sod1 deficiency does not merely nudge the genome toward instability; it fundamentally rewrites the rules of genome maintenance. The researchers detected 322 interstitial and 134 terminal loss-of-heterozygosity events across their isolates, occurring at rates 15- and 16-fold higher than in wild-type cells, respectively. Gene conversion tracts—the stretches of DNA copied from one homologous chromosome to repair damage on the other—were also markedly longer in the mutant, averaging 10.8 kilobases compared with 5.9 kilobases in healthy cells. Most structural rearrangements were flanked by Ty retrotransposon sequences, pointing to unequal recombination between repetitive elements as a major driver of large-scale chromosome changes.

Perhaps the most striking result came when the researchers repeated the experiment under anaerobic conditions. Deprived of oxygen, the sod1 mutant’s genomic chaos vanished almost entirely: mutation rates fell to wild-type levels and recombination rates dropped dramatically. Supplementing the growth medium with glutathione, a potent cellular antioxidant, similarly cut mutation and recombination frequencies by more than half. Together, these experiments identified reactive oxygen species as the sole executioner behind the genomic storm, confirming that the instability arises from direct chemical attack on DNA rather than from indirect disruption of repair machinery or metabolic collapse.

The mutational fingerprint left by Sod1 loss proved highly distinctive. All six classes of base substitutions increased, but transversions dominated, particularly C:G to A:T changes concentrated within 5′-CCA-3′ sequence motifs. This pattern is the classic signature of 8-oxoguanine, an oxidized form of guanine that mispairs with adenine during replication, producing the characteristic transversion after a second round of DNA copying. The finding directly implicates 8-oxoguanine overproduction as the molecular engine of Sod1-deficient mutagenesis, and it links the enzyme’s antioxidant function to a specific, measurable chemical lesion on DNA.

Dissecting how cells cope with these lesions revealed a sophisticated hierarchy of repair and bypass. The base excision repair glycosylase Ogg1 emerged as the frontline defense: deleting OGG1 alone caused a 19-fold rise in C:G to A:T transversions, and combining OGG1 deletion with SOD1 deletion produced a synergistic 7.5-fold increase over the ogg1 mutant alone. By these calculations, Ogg1-mediated excision corrects roughly 90 percent of the 8-oxoguanine lesions generated in the absence of Sod1. When repair is overwhelmed, translesion synthesis polymerases take over, and here the outcomes diverge sharply. DNA polymerase eta, encoded by RAD30, performs relatively accurate bypass by inserting cytosine opposite the oxidized base, preventing about a third of the characteristic transversions. In contrast, the error-prone polymerase zeta and its partner Rev1 account for approximately two-thirds of all Sod1-induced point mutations, illustrating the costly trade-off between completing replication and preserving sequence fidelity.

Timing analysis of recombination events added another layer of mechanistic insight. Using a colony-sectoring assay on chromosome IV, the team showed that about 65 percent of mitotic crossovers in sod1 mutants were initiated by double-strand breaks arising during the G1 phase of the cell cycle, closely mirroring the pattern in wild-type cells. Fluorescence microscopy of Rad52 repair foci confirmed a four-fold increase in spontaneous DNA breaks. Intriguingly, the distribution of crossover breakpoints was not random: 33 of 35 events on chromosome IV clustered distal to the SSD1 locus, a bias the researchers traced to post-mutational selection rather than intrinsic recombination hotspots. Restoring a functional SSD1 allele, which improved fitness in the sod1 background, redistributed breakpoints uniformly, demonstrating that observed genomic landscapes reflect both where damage occurs and which recombinant cells survive to form colonies.

The study then turned to human disease, testing eight ALS-associated SOD1 variants in the yeast system. Wild-type human SOD1 fully rescued the growth defects and genomic instability of yeast lacking endogenous Sod1, confirming deep functional conservation. But the clinical variants were not created equal. The H48Q mutation, which disrupts a copper-binding residue essential for catalytic activity, shattered genome stability, producing 8- and 10-fold increases in mutation and recombination rates alongside severe growth impairment. The G85R and S133N variants showed moderate effects, while the well-known A4V, G36R, D90A, and G93A variants remained essentially benign in this context. These results suggest that for a subset of ALS patients, loss of genomic protection—driven by failure to quench nuclear reactive oxygen species—may constitute an additional, mutation-specific pathogenic mechanism beyond the prevailing toxic gain-of-function model of protein aggregation.

Notably, the researchers found that human Sod1 is far more tolerant of amino acid substitutions than its yeast counterpart, a difference they attribute to the extraordinary structural robustness of the human enzyme, which remains stable even in metal-deficient states. This resilience likely reflects evolutionary pressure in long-lived organisms to protect the proteome against decades of somatic mutation. The work also carries a cautionary message for cancer therapy: because tumor cells often depend on elevated Sod1 to manage their oxidative burden, pharmacological inhibition of the enzyme, while potentially cytotoxic, risks triggering a mutational burst that could accelerate the emergence of drug-resistant clones. By mapping the full genomic consequences of antioxidant failure—from single nucleotides to whole chromosomes—this study establishes a mechanistic framework for understanding how metabolic defense and genome integrity are inseparably coupled in eukaryotic life.

Subject of Research: The role of superoxide dismutase 1 in protecting eukaryotic genome stability against oxidative DNA damage

Article Title: Decoupling metabolic defense: Mutational and recombinational chaos in Sod1-deficient cells

Article References: Sui, Y., Zheng, D.-Q., Wang, Y., Zhao, S.-S., Li, K.-J., Ye, C., & Zhang, K. (2026). Decoupling metabolic defense: Mutational and recombinational chaos in Sod1-deficient cells. PLOS Genetics, 22(10), e1012326. https://doi.org/10.1371/journal.pgen.1012326

Image Credits: AI Generated

DOI: 10.1371/journal.pgen.1012326

Keywords: Sod1, genome instability, reactive oxygen species, 8-oxoguanine, yeast, loss of heterozygosity, aneuploidy, base excision repair, translesion synthesis, ALS, SOD1 mutations, oxidative stress

Juvenile neuronal ceroid lipofuscinosis, also known as juvenile Batten disease, is caused by mutations in the CLN3 gene and represents a major form of juvenile dementia. Children with the condition typically develop vision loss in early childhood, followed by seizures, motor decline, and progressive cognitive deterioration, usually dying in their late twenties or thirties. The disease belongs to a family of lysosomal storage disorders in which cellular waste-processing machinery fails, leading to the accumulation of fatty waste materials called ceroid lipofuscin inside cells. Despite decades of research into the underlying genetics, effective therapies that slow the relentless neurodegeneration remain painfully out of reach.

The Korean team, led by Hyungkuen Kim, Eunmi Hwang, and Sung-Jo Kim, focused their investigation on parthanatos, a distinctive form of programmed cell death that has been extensively studied in Alzheimer’s disease but never before systematically characterized in JNCL. Parthanatos takes its name from poly(ADP-ribose), or PAR, a polymer produced by the enzyme PARP1. When cells experience excessive DNA damage, PARP1 becomes hyperactivated and floods the nucleus with PAR chains. These polymers eventually trigger the release of apoptosis-inducing factor from mitochondria, which migrates to the nucleus and orchestrates large-scale DNA fragmentation, killing the cell in a way that is distinct from classical apoptosis.

Using patient-derived lymphoblasts, immortalized white blood cells generated from JNCL patients, the researchers employed quantitative immunofluorescence microscopy to compare the disease cells with healthy controls. The results were striking. JNCL cells accumulated significantly higher levels of 8-oxoguanine, a pre-mutagenic DNA lesion produced when reactive oxygen species attack guanine bases, as well as elevated levels of PAR, the molecular signature of parthanatos. The accumulation of 8-oxoguanine is particularly insidious because it impairs DNA repair pathways, creating a vicious cycle in which oxidative damage begets repair failure, which begets further PARP1 overactivation and ultimately cell death.

The mechanistic logic connecting these observations to calcium is central to the study. JNCL is known to exhibit elevated intracellular calcium levels, a disturbance that has been documented in previous work on CLN3-deficient cells. Calcium overload is a well-established activator of PARP1, and studies in cardiomyocytes and other cell types have shown that calcium influx can directly stimulate PAR polymer production. In JNCL, this calcium-PARP1 axis appeared to be running unchecked, pushing vulnerable cells toward the parthanatos threshold. The researchers reasoned that if excess calcium was fueling the PARP1 fire, then dampening calcium entry might extinguish it.

Enter diltiazem. This L-type calcium channel blocker, which has been on pharmacy shelves since the 1970s, works by blocking voltage-gated calcium channels in heart and vascular smooth muscle. When the team treated JNCL patient-derived lymphoblasts with diltiazem, PAR accumulation dropped markedly. Critically, the protective effect persisted even when the cells were simultaneously exposed to a calcium ionophore, a chemical that forcibly floods cells with calcium. This suggested that diltiazem was not merely plugging calcium channels at the membrane but was intervening in the downstream signaling cascade that translates calcium excess into PARP1 activation, suppressing the expression of PARP1 itself and thereby limiting the raw material for parthanatos.

The drug’s benefits did not stop there. Diltiazem also reduced the accumulation of 8-oxoguanine in the JNCL cells, though intriguingly, this effect appeared to be largely independent of its calcium-blocking activity. Subcellular fractionation followed by immunoblotting, a technique that separates cellular compartments and identifies which proteins reside where, revealed that diltiazem enhanced the nuclear recruitment of OGG1, the primary enzyme responsible for excising 8-oxoguanine from DNA, along with its partner proteins. In other words, the drug was not just reducing the damage signal but was actively bolstering the cell’s repair crew, delivering the fix-it enzymes to the nucleus where the oxidative lesions accumulate.

To confirm that OGG1 was genuinely central to the drug’s protective mechanism, the researchers performed knockdown experiments, silencing the OGG1 gene in the treated cells. The results were unambiguous: when OGG1 was removed, diltiazem’s protective effects vanished entirely. This dependency establishes a dual role for the drug, acting simultaneously on calcium signaling to suppress PARP1 expression and on the OGG1-dependent base excision repair pathway to clear oxidative DNA damage. The finding also underscores a broader biological principle that has emerged from studies in Alzheimer’s disease and aging: OGG1-initiated repair is a double-edged sword, essential for genome maintenance but capable of exacerbating parthanatos when repair intermediates overstimulate PARP1.

The therapeutic implications are considerable. Diltiazem is an approved, well-characterized medication with decades of clinical safety data, which means that repurposing it for JNCL could potentially bypass some of the lengthy development timelines that plague novel drug candidates. Previous studies have already hinted at the drug’s relevance to neurodegeneration, with earlier work showing that L-type calcium channel blockers significantly lower intracellular calcium in CLN3-deficient neuroblastoma cells, and animal research demonstrating protective effects of diltiazem in chemically induced dementia models in mice. The new study adds a specific molecular mechanism, parthanatos suppression via PARP1 and OGG1 modulation, to this growing body of evidence.

Significant caveats remain before patients can benefit. The current findings derive from patient-derived lymphoblasts, which are accessible but imperfect proxies for the neurons that actually die in JNCL, and the researchers note that their data identify parthanatos as a novel therapeutic target rather than a validated clinical intervention. Whether diltiazem can cross the blood-brain barrier at sufficient concentrations, whether it will slow neurodegeneration in living organisms, and what dosing regimens would be appropriate for children all require further study. Nevertheless, by pinpointing PAR accumulation as a hallmark of JNCL pathology and demonstrating that an existing cardiovascular drug can interrupt this deadly cascade at two distinct points, the Hoseo University team has given the Batten disease research community something it has long needed: a concrete, pharmacologically tractable target in a disease where hope has been in short supply.

Subject of Research: Parthanatos and DNA repair dysfunction in juvenile neuronal ceroid lipofuscinosis and its modulation by the calcium channel blocker diltiazem

Article Title: The calcium channel blocker diltiazem ameliorates parthanatos in juvenile neuronal ceroid lipofuscinosis

Article References: Kim, H., Hwang, E., & Kim, S.-J. (2026). The calcium channel blocker diltiazem ameliorates parthanatos in juvenile neuronal ceroid lipofuscinosis. Journal of Molecular Medicine, 104(1), Article 118. https://doi.org/10.1007/s00109-026-02726-1

Image Credits: AI Generated

DOI: 10.1007/s00109-026-02726-1

Keywords: juvenile neuronal ceroid lipofuscinosis, Batten disease, CLN3, parthanatos, PARP1, diltiazem, 8-oxoguanine, OGG1, calcium signaling, DNA repair, drug repurposing, neurodegeneration

The review organizes the sprawling literature into five distinct propositions: redox control of telomerase activity, the reverse control of redox metabolism by the telomerase reverse transcriptase TERT, oxidative damage to telomeric DNA itself, redox-associated alternative lengthening of telomeres (ALT), and the therapeutic translation of all of the above. Each proposition is then graded separately for causal strength and molecular directness — two qualities the authors emphasize can vary completely independently. A finding can be causally robust yet mechanistically indirect, resting on a chain of downstream events; or it can be chemically precise yet demonstrated only in a test tube. Recognizing this independence, they contend, is the first step toward cleaning up a literature that has often graded studies on a single, misleading scale.

One of the sharpest methodological criticisms in the review targets a design that appears throughout the redox–telomerase literature: pretreating cells with millimolar concentrations of a thiol antioxidant such as N-acetylcysteine or glutathione before exposing them to a thiol-reactive electrophile. The problem, the authors explain, is one of chemical ambiguity. At those concentrations, the added thiol can simply quench the electrophile directly in the culture medium, a brute-force chemical reaction that has nothing to do with restoring the cell’s own antioxidant capacity. A rescue observed under those conditions cannot distinguish between genuine redox regulation of telomerase and trivial chemical neutralization of the insult. Because so many headline claims about antioxidants modulating telomerase rest on exactly this design, the finding casts a long shadow over a substantial fraction of the field.

What survives the audit? The authors identify the peroxide-driven, Src kinase–dependent phosphorylation of TERT at tyrosine 707, which triggers export of the enzyme from the nucleus via the Ran transport pathway, as among the best-supported redox findings. Hydrogen peroxide activates Src family kinases, phosphorylation at that specific residue promotes nuclear export, and the pathway satisfies necessity tests — blocking the kinase or the export machinery prevents the effect. Similarly well-supported is the glutathione depletion-and-repletion paradigm, in which lowering cellular glutathione alters telomerase activity and restoring it rescues the phenotype. Yet even these strongest findings, the review notes, remain pathway-mediated rather than chemically direct, and several were established in transfected systems or non-cancer cells such as endothelial cells and fibroblasts, leaving open questions about how faithfully they recapitulate events in an intact tumor.

Perhaps the most striking conclusion of the entire appraisal is a negative one. Despite decades of work, the authors identified no study that causally links a residue-resolved oxidative modification of endogenous TERT — a specific cysteine or tyrosine chemically modified by a defined reactive species inside a living cancer cell — to an altered outcome in telomerase assembly, subcellular localization, or catalytic activity. The distinction matters because redox biology has matured into a chemistry-first discipline: modern chemoproteomic tools can now identify which cysteines in a proteome are reactive, which ones get oxidized under defined conditions, and what functional consequences follow. TERT, with its multiple regulatory phosphorylation sites and its dependence on assembly with the telomerase RNA component, dyskerin and other partners, is precisely the kind of protein where such residue-level resolution should be achievable — and has not yet been delivered.

In contrast, the most molecularly direct chemistry in the entire field sits not on the protein but on the telomeric DNA itself. Guanine-rich telomeric repeats are exquisitely vulnerable to oxidation, and the review assembles a compelling body of biochemical work showing that the identity and position of an oxidative lesion govern nearly everything that matters: binding by the shelterin proteins TRF1 and TRF2, folding of the telomeric G-quadruplex structures that regulate telomerase access, recruitment of repair glycosylases such as OGG1 and the NEIL family, and the ability of telomerase to extend the chromosome end. An 8-oxoguanine lesion at one position of a G-quadruplex can destabilize the structure and promote telomerase extension, while the same lesion elsewhere blocks it — a position-dependent logic revealed through single-molecule and biochemical assays.

Even more provocative are recent findings showing that telomeric oxidation can drive dysfunction without any detectable shortening of the telomere. In work highlighted by the review, a single acute burst of targeted 8-oxoguanine damage at telomeres was sufficient to trigger rapid premature senescence, with telomere length remaining essentially unchanged. This decouples telomere dysfunction from the classical model in which telomeres erode gradually with each cell division, suggesting that a discrete oxidative event can flip the shelterin-bound chromosome end into a damage-signaling state essentially overnight. For cancer biology, the implication is double-edged: oxidative stress can push premalignant cells toward senescence, but it can also, under other conditions, push telomeres toward the recombination-based ALT pathway that a subset of tumors uses to elongate their chromosome ends.

On the therapeutic front, the review delivers a sobering translational parallel to its mechanistic gap. Imetelstat, the lipid-conjugated oligonucleotide that directly targets the telomerase RNA template, has now established randomized phase 3 efficacy in lower-risk myelodysplastic syndromes and has earned regulatory approval in the United States and a positive assessment in Europe. Yet the review points out that its redox engagement — whether the drug’s effects intersect with the oxidative stress programs that co-occur in treated tumors — has never been measured, nor have telomere pharmacodynamics been tracked in a way that connects clinical response to telomere biology at the molecular level. The most clinically successful telomerase-targeting agent, in other words, is as much of a black box with respect to redox as endogenous TERT is with respect to residue-level oxidation.

The review also surveys a crowded pipeline of redox-active agents with claimed telomerase effects: disulfiram and its copper diethyldithiocarbamate complex, which has been reported to induce both mitochondrial and telomerase dysfunction in lung cancer models; glutathione synthesis inhibitors such as butionine sulfoximine tested in combination regimens; the nucleoside analog 6-thio-deoxyguanosine, now in a phase 3 trial in non-small cell lung cancer, which recent structural work suggests stalls telomerase in a non-productive complex; and G-quadruplex ligands whose mechanisms have required substantial reevaluation. The authors’ framework provides a way to grade each of these claims, and the grades are frequently humbling: many rest on pharmacological exposures at concentrations far from physiological, in cell lines of uncertain provenance, with telomerase activity measured by the TRAP assay, which is itself known to be vulnerable to artifacts from redox-active compounds in the lysates.

What would close the gaps? The authors set out a concrete measurement agenda. For the protein side, it means deploying residue-resolved chemoproteomics and structural methods such as cryo-electron microscopy to catch endogenous TERT in the act of being oxidatively modified, and then testing causality with precisely engineered non-oxidizable mutants. For the telomere side, it means mapping lesion identity and position in cells, not just in synthetic oligonucleotides, and tracking how those lesions propagate through shelterin binding, repair, and telomerase extension. For the clinic, it means measuring telomere pharmacodynamics and redox biomarkers in imetelstat-treated patients. Until those measurements exist, the review concludes, the field should resist the temptation to narrate a tidy story of oxidants and telomeres — because the honest story, carefully audited, is one of strong chemistry at the chromosome end, plausible but unproven signaling at the enzyme, and a translational success whose deepest mechanisms remain to be written.

Subject of Research: Redox regulation of telomerase and telomeres in cancer

Article Title: Redox regulation of telomerase and telomeres in cancer: a critical appraisal of exposure, causality and molecular directness

Article References: Tatar, M., Khorrami, M., Kazemi, F., Masoumi, M., Babaei, S., & Khorrami, M. (2026). Redox regulation of telomerase and telomeres in cancer: a critical appraisal of exposure, causality and molecular directness. Molecular Biology Reports, 53(1), Article 1638. https://doi.org/10.1007/s11033-026-12826-3

Image Credits: AI Generated

DOI: 10.1007/s11033-026-12826-3

Keywords: telomerase, TERT, telomeres, redox biology, oxidative stress, cancer, 8-oxoguanine, glutathione, ALT, imetelstat, DNA damage, G-quadruplex