Profiling senescent cells in human brains reveals neurons with CDKN2D/p19 and tau neuropathology

Senescent cells contribute to pathology and dysfunction in animal models¹. Their sparse distribution and heterogenous phenotype have presented challenges to their detection in human tissues. We developed a senescence eigengene approach to identify these rare cells within large, diverse populations of postmortem human brain cells. Eigengenes are useful when no single gene reliably captures a phenotype, like senescence. They also help to reduce noise, which is important in large transcriptomic datasets where subtle signals from low-expressing genes can be lost. Each of our eigengenes detected ∼2% senescent cells from a population of ∼140,000 single nuclei derived from 76 postmortem human brains with various levels of Alzheimer’s disease (AD) pathology. More than 97% of the senescent cells were excitatory neurons and overlapped with neurons containing neurofibrillary tangle (NFT) tau pathology. Cyclin-dependent kinase inhibitor 2D (CDKN2D/p19) was predicted as the most significant contributor to the primary senescence eigengene. RNAscope and immunofluorescence confirmed its elevated expression in AD brain tissue. The p19-expressing neuron population had 1.8-fold larger nuclei and significantly more cells with lipofuscin than p19-negative neurons. These hallmark senescence phenotypes were further elevated in the presence of NFTs. Collectively, CDKN2D/p19-expressing neurons with NFTs represent a unique cellular population in human AD with a senescence-like phenotype. The eigengenes developed may be useful in future senescence profiling studies as they identified senescent cells accurately in snRNA-Seq datasets and predicted biomarkers for histological investigation.