Cytoplasmic DNA Sensing Links LINE-1 Expression to Neuronal Senescence in Alzheimer's Disease

Cellular senescence contributes to neurodegeneration in Alzheimers disease (AD), yet brain-penetrant senotherapeutic strategies remain limited. Here, we identify long interspersed nuclear element 1 (LINE-1) retrotransposons as key regulators of neuronal senescence and the senescence-associated-secretory-phenotype (SASP) in AD. Using transdifferentiated induced neurons (iNs) that preserve donor-specific aging-associated molecular signatures, we show that pharmacological inhibition of LINE-1 with nucleoside reverse transcriptase inhibitors (nRTIs) or antisense oligonucleotides reduces p16 expression, suppresses SASP and interferon-stimulated gene programs, and attenuates paracrine induction of reactive astrogliosis. Spatial transcriptomic analysis of human AD brain tissue further supports that senescent neurons with high LINE-1 expression are localized to inflammatory niches in the brain. Although bulk analysis finds no significant differences in LINE-1 expression between AD and control neurons, long-read single-cell RNA sequencing of iNs identifies a subset of neurons with elevated LINE-1 activity which display transcriptional signatures of neurodegeneration, immune activation, and senescence are enriched in AD relative to controls. RNA velocity analysis indicates that LINE-1 activation precedes the induction of canonical senescence markers, supporting a causal rather than consequential role. Mechanistically, LINE-1-derived cytoplasmic DNA activates the cGAS-STING innate immune pathway in post-mitotic neurons, and inhibition of cGAS phenocopies the effects of LINE-1 suppression. Together, these findings establish a LINE-1/cGAS-STING axis as a driver of neuronal senescence in AD and highlight LINE-1 inhibition as a tractable senomorphic strategy for neurodegenerative disease.