Cell-specific RNA isoform remodeling in the aging mouse brain.

Aging is associated with increases in risk of multiple chronic diseases and at the cellular level, with disruptions in RNA homeostasis. Single-cell transcriptomic studies have revealed RNA abundance heterogeneity across brain cell types but the more complex changes in RNA processing such as alternative splicing, isoform usage, transcription start and polyadenylation site selection remain uncharacterized. Here, we combine single-cell analysis with long-read nanopore sequencing to capture full-length RNA isoforms and uncover temporal changes in RNA transcription, processing, and alternative splicing in the aging mouse cortex and hippocampus. By profiling transcriptomes from young adult to very old mice, we identify non-linear, cell-type-specific isoform expression changes and isoform usage shifts, primarily driven by transcription start site selection. These aging-associated isoform changes alter the coding potential and poly(A) site position of genes. Our data also reveal a high proportion of senescence in immune cells, far exceeding that of other cell types. We also identify isoform markers that, when applied to a machine learning model, distinguish senescent from normal immune cells. This study provides a full-length RNA isoform-based atlas of the aging mouse brain, offering insights into RNA metabolism remodeling across brain cell types throughout the lifespan.