Uncovering the signatures of aging and senescence in the human dorsolateral prefrontal cortex.

Gene expression changes characteristic of aged cortical layers were identified in the human dorsolateral prefrontal cortex using spatial transcriptomics.

• Visium spatial transcriptomics (ST) was combined with single-nucleus RNA sequencing (snRNA-seq) on nonpathological human dlPFC tissues.
• The cohort consisted of individuals without pathological brain conditions, enabling isolation of normal aging signatures.
• Spatially resolved gene expression changes were mapped to specific cortical layers.

The cellular composition of the dlPFC changed with age, with increased homeostatic astrocyte abundance and decreased somatostatin (SST) inhibitory neurons.

• Homeostatic astrocyte proportions increased significantly with advancing age.
• Somatostatin (SST)-expressing inhibitory neurons showed decreased abundance with age.
• These compositional shifts were identified through snRNA-seq analysis of the dlPFC cell-type landscape.
• The changes in cellular composition were observed in nonpathological aging tissue.

Nuclei from dlPFC cell types displayed a strong decline in oxidative phosphorylation- and cytoplasmic translation-related genes with age.

• The decline in oxidative phosphorylation-related gene expression was observed broadly across dlPFC cell types.
• Cytoplasmic translation-related genes also showed strong age-associated downregulation.
• These transcriptional changes were identified via snRNA-seq analysis across multiple cell populations.

Oligodendrocytes showed several hallmarks of senescence and a linear increase in CDKN2A expression with age.

• CDKN2A, a canonical senescence marker also known as p16INK4a, exhibited a linear increase in oligodendrocytes across the age range studied.
• Multiple hallmarks of cellular senescence were observed specifically in oligodendrocytes.
• This makes oligodendrocytes a notable candidate cell type for senescence-related dysfunction in the aging dlPFC.

Combined analysis of ST and snRNA-seq datasets revealed astrocyte- and vascular cell-related gene expression programs in the white matter and layer 1 that were strongly enriched with age and for senescence-associated genes.

• The enrichment of senescence-associated gene expression was specifically localized to white matter and cortical layer 1.
• Both astrocyte-related and vascular cell-related gene programs contributed to the senescence-enriched signal in these regions.
• Integration of spatial and single-nucleus data was used to map these programs to specific anatomical locations.
• These spatially restricted programs were among the strongest age-associated signals identified in the study.

The study used a cohort of nonpathological human dorsolateral prefrontal cortex tissues to specifically isolate signatures of normal aging and senescence.

• Tissue samples were selected to exclude pathological conditions, focusing on nonpathological aging.
• Both Visium spatial transcriptomics and single-nucleus RNA sequencing were performed on the same cohort.
• The dlPFC was chosen as the brain region of interest for this aging and senescence profiling study.