Cao’s laboratory specializes in refining high-throughput single-cell sequencing methods that capture gene expression and molecular dynamics at an unprecedented scale. These innovative techniques offer the ability to peer deeply into the cellular mechanisms driving aging, mapping in high resolution how individual cells respond and adapt to the passage of time. Previous milestones from Cao’s team have included the identification of rare brain cell types, insights into the molecular mechanisms of brain cell aging, and the characterization of the cells most susceptible to age-related deterioration. This body of work suggests that aging itself may be triggered by specific molecular signals akin to a distinct developmental stage.

The latest contribution from this group introduces two pioneering technologies—IRISeq and EnrichSci—each framing cellular aging through distinct but complementary lenses. IRISeq leverages a novel concept that DNA molecules can serve as molecular barcodes or spatial rulers to record the proximity of molecules without relying on traditional imaging. This approach uses millions of barcoded, microscopic beads embedded within tissue sections. These beads exchange DNA-based signals with neighboring beads, effectively reconstructing the spatial arrangement of cells across large tissue areas without a microscope. This optics-free technique was developed and refined by Abdulraouf Abdul, an M.D.-Ph.D. student, together with research associate Weirong Jiang, and detailed in their recent publication in Nature Neuroscience.

What makes IRISeq particularly transformative is its scalability and resolution. Unlike conventional microscopy-based methods that are expensive and limited in volume, IRISeq provides a cost-effective means to generate high-resolution “maps” of cellular neighborhoods at varying scales—from broad tissue architecture down to microscopic neighborhood interactions. This technique reveals not only which types of cells cluster together but crucially where they do so within the brain’s complex spatial landscape, thus preserving the contextual information essential for understanding intercellular dynamics during aging.

Using IRISeq, Cao’s team uncovered clusters of inflammatory cells—microglia, oligodendrocytes, and astrocytes—in the white matter regions of aged brains. These cellular neighborhoods appear to promote mutual disease-associated states, implicating the white matter as a particularly vulnerable site where inflammatory processes are locally amplified. A striking discovery involved lymphocytes, immune cells found to be highly concentrated near the brain’s ventricular spaces, fluid-filled cavities involved in neuroimmune regulation. This spatially localized immune activity underscores how fine-grained spatial information can reveal previously hidden patterns of cellular aging and inflammation.

Complementing IRISeq, the EnrichSci method hones in on rare but biologically significant cell populations within mixed samples through a targeted enrichment strategy. Published in Cell Genomics, EnrichSci combines single-nucleus RNA sequencing with a pre-enrichment step that increases the fraction of these rare cells, thereby allowing deeper analysis of their molecular states. Applied to aging mouse brains, EnrichSci enriched specific oligodendrocyte subtypes—glial cells integral to insulating neuronal axons and strongly implicated in neurodegenerative diseases—and profiled their gene expression and splicing dynamics.

One of the most intriguing findings from the EnrichSci studies was the identification of changes at the exon level, the segments of genes that encode mature RNA transcripts. These changes involve alternative splicing mechanisms that diversify protein function but are also linked to disease. Unlike conventional analyses focusing solely on overall gene expression, EnrichSci revealed that many genes maintain steady expression levels during aging, yet their exon usage shifts significantly. This post-transcriptional modulation appears to be a critical, previously underappreciated driver of oligodendrocyte aging and possibly neurodegeneration, opening new avenues for therapeutic targeting.

Together, IRISeq and EnrichSci represent powerful additions to the toolkit of aging biology, enabling unprecedented resolution in both spatial context and molecular detail. The ability to map cellular interactions in situ and to dissect post-transcriptional modifications deepens our mechanistic insight into how cellular neighborhoods and RNA regulation contribute to aging phenotypes. Cao envisions these tools as broadly applicable beyond aging research, capable of illuminating cellular behaviors in diverse disease contexts, from cancer immunology to neurological disorders.

Looking forward, efforts are underway to scale IRISeq for large-scale studies probing pharmacological interventions aimed at mitigating age-related decline. By preserving spatial relationships between cells, IRISeq allows researchers to study how tissues function holistically, including how cells communicate and respond collectively to stress and treatment. Meanwhile, advancements to EnrichSci aim to couple RNA and chromatin accessibility profiling, enabling simultaneous capture of gene expression, splicing, and epigenetic states. Such integrative profiling will provide a multidimensional perspective on regulatory mechanisms influencing aging and disease progression.

The implications of this work are profound. By transforming sequencing technologies into novel forms of “biological vision,” Cao’s lab offers a window into the spatial and molecular choreography of cells as they age. This not only refines our fundamental understanding of brain aging but also highlights potential intervention points for slowing or reversing neurodegenerative changes. As the field moves beyond traditional microscopy and gene expression analyses, these innovations may usher in a new era of precision aging research and therapeutic discovery.

The convergence of cutting-edge genomic engineering with high-throughput methodologies signifies a paradigm shift in how we study complex tissues like the brain. More than ever, the realization that cells do not function in isolation but as interdependent communities reinforces the importance of spatially aware technologies. With these tools, researchers can chart the intricate landscapes of aging organisms at a scale and depth previously thought impossible, accelerating the quest to decipher the biological codes that govern longevity and health span.

As these pioneering methods gain wider adoption, they promise to enrich many branches of biomedical research, offering fresh insights into not only aging but also developmental biology, cancer progression, and immune responses. Through creative applications of DNA barcoding and targeted enrichment, Cao’s contributions herald a future where the unseen molecular and spatial dynamics of life’s most fundamental processes are finally within reach.

Subject of Research: Cellular and molecular dynamics of brain aging through high-throughput single-cell genomics.

Article Title: Spatial and molecular profiling of aging brain cells via novel single-cell genomic technologies.

News Publication Date: Not explicitly stated in the provided content.

Web References:

1. IRISeq publication in Nature Neuroscience
2. EnrichSci publication in Cell Genomics

References:

• Abdulraouf Abdul, Weirong Jiang, et al., “Decoding cellular neighborhoods in brain aging using IRISeq,” Nature Neuroscience.
• Andrew Liao, et al., “Post-transcriptional regulation in oligodendrocyte aging uncovered by EnrichSci,” Cell Genomics.

Keywords: Single-cell sequencing, brain aging, spatial transcriptomics, DNA barcoding, post-transcriptional regulation, alternative splicing, oligodendrocytes, neurodegeneration, inflammatory microglia, molecular mapping, spatial genomics, high-throughput sequencing

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

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