Aging is accompanied by a cascade of molecular changes, notably including chronic inflammation, mitochondrial dysfunction, genome instability, and profound epigenetic shifts. Epigenetics refers to chemical modifications superimposed on the genome that regulate gene expression without altering the underlying DNA sequence. Among these modifications, DNA methylation has emerged as a key modulator of neuronal function and aging. The Salk team harnessed state-of-the-art single-cell technologies to chart the epigenetic landscape of eight brain regions, profiling over 200,000 cells through assays mapping DNA methylation and chromatin conformation—a measure of the genome’s 3D folding structure. Complementing this, nearly 900,000 cells were spatially profiled via transcriptomics, providing unprecedented resolution into gene expression patterns while preserving tissue architecture.

This newly published atlas in the journal Cell meticulously catalogs epigenetic changes that distinguish younger from aged mouse brains in a cell type-specific manner. It captures 36 distinct brain cell types, ranging from neuronal subtypes to various glial populations. Intriguingly, the data reveal that age-related DNA methylation changes are considerably more pronounced in non-neuronal cells, such as microglia and astrocytes, lymphocytes of the brain’s immune system. This discovery aligns with emerging evidence pointing to glial cells’ pivotal roles in brain aging and neuroinflammation, broadening therapeutic interest beyond neurons alone.

The atlas also identifies transposable elements—commonly known as jumping genes—as major epigenetic hotspots during aging. These repetitive DNA sequences, which comprise roughly half of mammalian genomes, normally remain epigenetically silenced to maintain genomic stability. However, the research reveals significant demethylation of these elements in aged cells, implicating their reactivation as a contributor to cellular dysfunction. This insight lays vital groundwork for considering how loss of transposable element suppression might drive age-associated neurodegenerative pathology.

Beyond methylation, the study integrates chromatin conformation data, spotlighting the spatial organization of the genome. The architecture is partitioned into topologically associating domains (TADs)—subregions within chromosomes that regulate gene expression through physical proximity in 3D space. Remarkably, the Salk team discovered increased TAD boundary strength and enhanced accessibility of CTCF binding sites—CTCF being a critical architectural protein—as biomarkers of brain aging. These changes point to a rewiring of genomic topology that may destabilize transcriptional programs and accelerate age-related decline.

Capturing nearly one million spatially resolved transcriptomes was a tour de force in scale and resolution, enabling the researchers to dissect regional heterogeneity in aging trajectories. An unexpected revelation is the differential aging rates of identical cell types based on their brain location. For instance, glial cells in posterior brain regions exhibited heightened inflammatory gene expression compared to their anterior counterparts. This spatial variance underscores the intricate interplay of local microenvironments with cellular aging, emphasizing that neurodegeneration does not unfold uniformly across the brain.

The methodological innovation of combining multi-omics with spatial transcriptomics represents a significant leap forward in aging research. The data’s spatial dimension preserves the anatomical context, allowing scientists to link molecular alterations to specific neural circuits and brain functions affected in disease. Moreover, by publicly releasing this extensive dataset through Amazon Web Services and the Gene Expression Omnibus, the researchers have democratized access, enabling a global community to probe these aging-related molecular changes without prohibitive computational infrastructure.

The implications for translational science are profound. Using the atlas, the research team developed deep-learning models that predict the trajectory of gene expression changes based on epigenetic signatures. These virtual models could ultimately simulate brain aging, providing a powerful platform for testing interventions before clinical trials. By elucidating precise molecular targets associated with aging and neurodegeneration, this resource opens new avenues for therapeutic development aiming to halt or even reverse brain aging processes.

Senior investigators Joseph Ecker and Margarita Behrens articulate that this cell type-specific epigenetic map delivers a crucial framework for unraveling how aging reshapes neural circuits at the molecular level. As aging profoundly impairs cognition, memory, motor functions, and emotional regulation, deep molecular insight is required to counteract these effects. This atlas paves the way to decipher the mechanisms underlying age-associated neuronal vulnerability and resilience, potentially transforming our approach to widespread neurodegenerative diseases.

In summary, the Salk Institute’s epigenetic atlas integrates methylation, chromatin architecture, and spatial transcriptomics to produce an unparalleled multi-dimensional portrait of the aging brain. By capturing the complexity at single-cell resolution and mapping longitudinal trajectories across regions and cell types, this work heralds a new era of precision neuroscience. Its open-access availability ensures that these rich datasets will catalyze rapid discovery and innovation, accelerating the global quest to understand and ultimately treat neurodegenerative disorders.

Subject of Research: Aging-related epigenetic changes in the mouse brain and their implications for neurodegenerative diseases

Article Title: Cell-type-specific transposon demethylation and TAD remodeling in aging mouse brain

News Publication Date: 11-Mar-2026

Web References:

• Atlas Data on AWS: https://registry.opendata.aws/salk-aging-mouse-brain-epigeneti/
• Journal Article DOI: http://dx.doi.org/10.1016/j.cell.2026.02.015

Image Credits: Salk Institute

Keywords: Neurodegeneration, aging brain, epigenetics, DNA methylation, chromatin conformation, single-cell atlas, transposable elements, spatial transcriptomics, TAD remodeling, CTCF, mouse model, deep learning

Central to this discovery is the process of active DNA demethylation mediated by TET enzymes, which oxidize 5-methylcytosine into a series of intermediates including 5-hydroxymethylcytosine. This epigenetic reprogramming is followed by base excision repair (BER) mechanisms, where the DNA glycosylase TDG excises the modified bases to restore unmodified cytosine. However, this precise repair process becomes a double-edged sword in the presence of specific cytidine analogues. Cytarabine, a widely used antineoplastic agent, disrupts this repair pathway by interfering with TDG’s function, which in turn leads to the accumulation of DNA double-strand breaks (DSBs) during the demethylation cycle. These breaks pose a serious threat to genomic stability, especially in neurons that are non-dividing and highly sensitive to DNA damage.

Further investigation reveals that the DNA double-strand breaks caused by cytarabine are predominantly converted into more severe chromosomal aberrations such as deletions and translocations through the activity of DNA ligase 4. This ligase is known for its role in non-homologous end joining, an error-prone DSB repair pathway. The formation of these deleterious chromosomal alterations underscores a novel cytotoxic mechanism for cytarabine, connecting epigenetic regulation directly to genome integrity in neurons. This offers an important molecular explanation for the long-recognized, yet previously poorly understood, cerebellar neurotoxicity associated with this drug.

Intriguingly, the neurotoxic effects of cytarabine are not uniform across all neuronal types. In vivo studies have pinpointed Purkinje cells and Golgi neurons within the cerebellum as the primary populations exhibiting elevated DNA damage upon cytarabine exposure. These specialized neurons endure a disproportionate burden of DNA lesions, implicating a unique vulnerability linked to their epigenetic landscape and gene expression profiles. Purkinje cells, in particular, show TET enzyme activity targeted to gene bodies characterized by enhancer-associated histone modifications—epigenetic signatures indicative of active transcription. Many of these genes orchestrate the delicate coordination of movement and motor control, elucidating how cytarabine’s genotoxic stress translates into cerebellar dysfunction and motor deficits.

Another striking facet of this research lies in the differential neurotoxic profiles among various cytidine analogues. While cytarabine induces predominantly double-strand DNA breaks leading to harmful chromosomal mutations, other analogues such as gemcitabine appear to cause mainly single-strand breaks. These less severe lesions are efficiently repaired by DNA ligase 3-mediated pathways, attenuating their toxicity. This divergence not only challenges the traditional view of cytidine analogues as a homogenous group in terms of side effects but also opens avenues for designing safer chemotherapeutics with minimized central nervous system complications.

The elucidation of the interplay between TET-mediated DNA demethylation and base excision repair processes in neurons represents a significant advancement in neuroepigenetics. It establishes a clear mechanistic link connecting DNA methylation dynamics to genomic stability and neuronal health. Such insights could redefine therapeutic strategies, allowing clinicians to weigh the neurotoxic risks of cytidine-based chemotherapies more precisely and tailor treatments accordingly.

Moreover, this research sheds light on the broader theme of neuronal epigenetic regulation and its implications for neurodegeneration and neurotoxicity. Postmitotic neurons rely heavily on robust DNA maintenance mechanisms since their capacity for regeneration is limited. Disruptions in the delicate balance of epigenetic marks and DNA repair not only jeopardize neuronal function but could also underpin the molecular pathology of various neurological disorders where DNA damage accumulates progressively.

From a translational perspective, the findings offer a rational basis for the previously observed selective cerebellar toxicity of cytarabine. By mapping the DNA damage to specific neuronal subtypes and gene regulation contexts, the study provides a blueprint to predict and potentially mitigate adverse neurological outcomes. This could lead to adjunct therapies aimed at preserving DNA repair fidelity or modulating TET enzyme activity during chemotherapy regimens.

At the molecular level, the work emphasizes the centrality of TDG and DNA ligases in safeguarding neuronal genomic integrity during active DNA demethylation. Their roles extend beyond canonical DNA repair, influencing how epigenetic information is rewritten and sustained over the lifespan of neurons. Targeting these enzymes pharmacologically may present novel opportunities to protect the brain from both endogenous and exogenous insults.

In sum, this research redefines our understanding of how chemical modifications of cytosine converge with DNA repair mechanisms to maintain neuronal function or, conversely, precipitate neurodegeneration. It highlights the unique vulnerability of the cerebellum, particularly Purkinje and Golgi cells, to cytarabine-induced DNA damage, tying molecular epigenetics to clinical neurotoxicity. This discovery has the potential to impact drug development, clinical oncology, and neurobiology, marking a milestone in dissecting the molecular intricacies of neuron-specific DNA metabolism.

The implications extend beyond oncology, touching on fundamental questions of how neurons manage and interpret epigenetic signals, and what happens when this delicate balance is disrupted. As the field continues to explore the intersections of epigenetics, DNA repair, and neurobiology, studies like this pave the way for breakthroughs in treating neurotoxic side effects and perhaps even neurodegenerative diseases linked to epigenetic dysregulation.

With the growing spotlight on TET enzymes and base excision repair pathways in neurons, this work urges a careful reconsideration of pharmacological approaches involving nucleoside analogues. It underscores the pressing need for careful mechanistic studies to foresee and circumvent unintended neuronal damage, ultimately striving for therapies that cure without compromising the brain’s intricate genetic and epigenetic architecture.

Subject of Research: Epigenetic DNA modifications and the molecular mechanisms underlying cytarabine-induced neurotoxicity in neurons.

Article Title: Mechanism of cytarabine-induced neurotoxicity

Article References:
Liu, JC., Wang, D., Callen, E. et al. Mechanism of cytarabine-induced neurotoxicity. Nature (2025). https://doi.org/10.1038/s41586-025-09210-9

Image Credits: AI Generated