New Insights Reveal How Our Brain’s Genetic Landscape Transforms as We Age
The human brain, a marvel of biological complexity, is subject to subtle yet profound changes throughout a person’s life. Recently, groundbreaking research employing state-of-the-art single-cell technologies has uncovered how the genetic and transcriptomic architecture within brain cells evolves during ageing. These discoveries shed light on the intricate interplay between somatic mutations—those acquired during life—and gene expression dynamics, providing unprecedented insights into the molecular underpinnings of brain ageing.
Leveraging combined single-nucleus RNA sequencing (snRNA-seq), single-cell whole-genome sequencing (scWGS), and spatial transcriptomics, researchers meticulously mapped both genome-wide mutations and the corresponding transcriptomes of individual brain cells. This multi-faceted approach revealed a striking trend: short, highly expressed housekeeping genes—genes essential for core cellular functions—accumulate significantly more somatic single-nucleotide variants (sSNVs) over time. Intriguingly, this rise in mutation burden correlates strongly with a decrease in the expression levels of these crucial housekeeping genes.
A closer examination offers compelling evidence supporting this novel insight. Firstly, the enriched gene ontology terms related to housekeeping functions predominated among downregulated genes, particularly in neurons, whereas neuron-specific genes maintained relatively stable expression profiles during ageing. This suggests that ageing selectively impacts fundamental cellular maintenance processes rather than cell identity programs. Secondly, the study confirmed that housekeeping genes tend to be both short and robustly expressed, aligning with known genomic properties. Notably, the highest sSNV rates appeared in the shortest, most actively transcribed housekeeping genes.
Further statistical analysis unveiled a nuanced relationship capturing how these variables intersect. A multiple linear regression model demonstrated that elevated gene expression increased the likelihood of transcriptional downregulation with age, whereas longer gene length was associated with either preservation or even upregulation of transcriptional activity during ageing. These findings are particularly illuminating given the longstanding but inconsistent observations about gene length effects in ageing across various tissues. Within neurons, it appears that the transcriptional landscape favors retention of long, identity-defining genes while allowing somatic mutagenesis to erode short housekeeping genes.
The biological mechanisms driving these patterns are multifaceted. One plausible explanation posits that somatic mutations introduce premature stop codons or disrupt splicing fidelity, triggering nonsense-mediated decay pathways that reduce transcript abundance of affected genes. Additionally, faulty or aberrant DNA repair mechanisms implicated in the formation of somatic mutations could result in local epigenetic dysregulation, further influencing gene expression changes during ageing. Another fascinating aspect is the potential differential efficacy of DNA repair machinery between gene classes; short, highly expressed housekeeping genes may bear a higher burden due to their preferential engagement in transcription-coupled DNA repair (TCR).
Recent studies have revealed that single-stranded DNA lesions, often a precursor to mutations, can persist in human cells for extended durations without active repair, raising the possibility that transcription processes themselves may convert DNA damage into fixed, double-stranded mutations. Given that neurons are post-mitotic—non-dividing—and express high levels of topoisomerases that safeguard long genes, this cellular context may amplify the accumulation of mutations selectively in short housekeeping genes rather than the long neuron-specific genes.
Beyond these molecular insights, the research offers a rich portrait of cellular composition changes across the human lifespan. In infant brains, distinct populations of immature neurons and astrocytes were detected, along with an elevated ratio of oligodendrocyte precursor cells relative to their mature counterparts, supporting ongoing postnatal brain development. These developmental insights are complemented by the genomic profiling of somatic mutations in ageing neurons, which captured an increase in sSNVs with mutational spectra reminiscent of COSMIC mutational signatures SBS5 and SBS30, both previously linked to age-related mutagenesis and DNA damage responses.
Delving deeper, two novel mutational signatures designated A1 and A2 emerged from de novo analyses. Signature A1, characterized predominantly by T>C transitions, clustered with the clock-like SBS5 signature and showed enrichment in highly expressed genes, coding regions, and genomic loci marked by open chromatin. In contrast, Signature A2, dominated by C>T transitions and enriched in C>A and T>C variants associated with oxidative DNA damage, resembled the SBS30 signature but exhibited distinct enrichment in non-coding, repressed chromatin domains with repressive epigenetic marks.
The dynamic expression profiles of DNA base excision repair proteins, particularly NTHL1 and OGG1, within neurons across ageing provide tantalizing clues linking cellular repair activity to mutational signatures. While NTHL1’s decreased activity has been connected to SBS30 in other contexts, OGG1 involvement aligns with neuronal C>A mutations. The interplay between these repair pathways and accumulating somatic mutations likely shapes both the mutational landscape and transcriptomic alterations observed during neuronal ageing.
Crucially, the study’s comprehensive single-cell approach sets a new standard for exploring how somatic mutations intertwine with gene expression heterogeneity in distinct brain cell types. As single-cell whole-genome sequencing technologies continue to mature and expand across diverse cell populations, future investigations promise to unravel more intricate connections between somatic genomic alterations and functional consequences in the ageing brain.
This pioneering work not only deepens understanding of fundamental ageing biology but also paves the way for targeted interventions. By revealing vulnerabilities in housekeeping genes stemming from mutation accumulation and transcriptional changes, it opens potential therapeutic avenues aimed at preserving cellular homeostasis and delaying neurodegeneration. Moreover, the differential resilience of neuron identity genes hints at innate protective mechanisms that could be harnessed or augmented.
Altogether, this research exemplifies an integrative multi-omic leap forward in deciphering the genomic and transcriptomic choreography unfolding across human brain lifespan. It paints a detailed molecular narrative where mutation-driven erosion of essential housekeeping genes contrasts with preservation of cell identity programs, offering a refined lens through which to view ageing’s impact on brain health.
As the intersection of genetics, epigenetics, and transcriptomics continues to be illuminated at single-cell resolution, our grasp of brain ageing mechanisms will sharpen, enabling precision medicine strategies attuned to the unique vulnerabilities and strengths of neural circuits. The implication of transcription-coupled repair and mutational signatures further links genome maintenance processes to functional ageing, suggesting new biomarkers and targets for intervention.
Ultimately, this transformative research advances the frontier of neuroscience, calling attention to the silent genomic shifts that accumulate imperceptibly but inexorably within our brain cells, shaping cognition, resilience, and healthspan. Understanding these molecular changes is vital as populations age worldwide and the burden of neurodegenerative diseases rises, highlighting the promise of genomic and transcriptomic studies in the quest for healthier brain ageing.
Subject of Research: Single-cell transcriptomic and genomic changes during human brain ageing.
Article Title: Single-cell transcriptomic and genomic changes in the ageing human brain.
Article References:
Jeffries, A.M., Yu, T., Ziegenfuss, J.S. et al. Single-cell transcriptomic and genomic changes in the ageing human brain. Nature (2025). https://doi.org/10.1038/s41586-025-09435-8
Image Credits: AI Generated
