Biology subjects

Kelsey, M. M. G.

Publications and source records attributed to Kelsey, M. M. G..

6 recordsLinked to original sources

bioRxiv2026

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.

neuroscience↗

bioRxiv2026

Characterization of Cellular Senescence in Primary Human Astrocytes

Senescent astrocytes have been identified in the brains of patients with neurodegenerative disorders, including Alzheimers disease, yet the molecular characteristics of replicative senescence in human astrocytes remain largely unexplored. Prior work has been hampered by the low proliferative capacity and limited telomere shortening of primary human astrocytes in culture. Here, we describe a culture system in which primary human astrocytes propagated under physiological (3%) oxygen reach canonical telomeric replicative senescence after extensive expansion (up to [~]76 population doublings). Senescence was confirmed through multiple biomarkers, including reduced EdU incorporation, elevated senescence-associated beta-galactosidase (SA-{beta}-gal) activity, persistent DNA damage foci ({gamma}H2AX and 53BP1) predominantly localized to telomeres, and nuclear accumulation of p53. RNA sequencing across a 12-week time course revealed early upregulation of young LINE-1 (L1HS) retrotransposon transcripts, type-I interferon (IFN-I) and senescence-associated secretory phenotype (SASP) pathway genes, alongside downregulation of cell-cycle and DNA repair programs. To resolve L1HS expression at individual locus resolution, we performed Nanopore DNA sequencing to generate a custom reference genome incorporating non-reference LINE-1 insertions. Applying our TE-Seq pipeline, we identified two full-length intergenic L1HS elements consistently upregulated across the replicative senescence time course, one of which, L1HS_9q22.32_2, retained intact ORF1 and ORF2 open reading frames, indicating potential retrotransposition competence. To contextualize the astrocyte replicative senescence program, we compared it to three additional conditions. First, parallel astrocyte cultures maintained under normoxic (20%) oxygen entered senescence earlier and showed stronger SASP upregulation. Second, DNA damage-induced senescence (DDIS) triggered by etoposide treatment produced a stronger pro-inflammatory transcriptional signature than replicative senescence, including elevated IL6, IL1A, and IL1B expression. DDIS also upregulated L1HS_9q22.32_2 as well as a second intact element, L1HS_14q23.2_3, which we have previously identified among the small number of intact L1HS loci activated during replicative senescence in fibroblasts. The convergent activation of these intact elements across cell types and senescence modalities reinforces L1HS-driven IFN-I signaling as a conserved feature of the senescent program. Third, comparison with replicatively senescent fibroblasts revealed cell-type-specific SASP regulation: the pro-inflammatory cytokines IL6 and CCL2 were downregulated in senescent astrocytes relative to proliferating cells, opposite to their behavior in fibroblasts. Together, these data establish the first comprehensive transcriptomic profile of replicative senescence in human astrocytes, offering a resource for understanding brain aging and senescence-associated neurodegeneration.

molecular biology↗

bioRxiv2026

The Translatome of Senescent Cells Revealed by Ribosome Profiling

Cellular senescence drives aging-related tissue dysfunction through the senescence-associated secretory phenotype (SASP), an inflammatory secretome linked to retrotransposable element (RTE) derepression. Transcriptomic and proteomic approaches have extensively characterized the senescence program, but key gaps remain: transcript abundance is a poor proxy for protein output, limited proteomic depth misses low-abundance proteins, and the highly repetitive sequences of RTEs compromise locus-level peptide attribution. To bridge these gaps, we used AHARIBO (AzidoHomoAlanine-mediated RIBOsome isolation), which captures actively translated full-length mRNAs, to profile the translatome of proliferating, senescent, and late-senescent human fibroblasts. Comparing these ribosome-associated transcripts with the total mRNA pool revealed marked post-transcriptional regulation of key senescence programs. Inflammatory SASP components were translationally depleted in senescence, and these transcripts were enriched for AU-rich element-binding protein motifs, including the ZFP36 family, implicating these proteins in post-transcriptional gating of inflammatory signaling. Transcriptome-wide, translational efficiency was associated with 3UTR GC content and specific RNA-binding protein and microRNA (miRNA) motifs. We also observed a striking wobble-position codon bias: a proliferation-specific program favoring A/U-ending codons collapsed in senescence, disproportionately affecting cell-cycle and proliferation gene sets. By pairing AHARIBO with a sample-specific reference genome incorporating non-reference L1 insertions, we resolved translation of individual L1 loci and identified two intact L1HS elements with sustained activation in senescence. One of these, L1HS_14q23.2_3, independently identified in multiple experiments, emerges as a candidate intact L1 locus for producing inflammatory cDNA species. These findings implicate translational control as an important regulatory layer shaping the senescent program.

cell biology↗

bioRxiv2025

Retrotransposon Activation in the Aged and Alzheimer's Disease Brain Examined by Nanopore Long-read DNA Sequencing

BackgroundCellular defenses against retrotransposable elements (RTEs) weaken with age and RTEs have been reported to contribute to Alzheimers disease (AD) pathogenesis by promoting neuroinflammation. The mechanisms implicated include DNA damage promoted by retrotransposition and interferon system activation by RTE-derived cDNA intermediates. LINE-1 (L1) retrotransposons are of particular interest because they are the only autonomously active RTEs in the human genome. ResultsTo investigate L1 activation and retrotransposition in AD, we performed Nanopore long-read DNA sequencing on six late-onset AD (LOAD) and six age-matched control human prefrontal cortex (PFC) samples. We developed and validated a stringent RTE insertion calling pipeline and identified two high-confidence somatic insertions, one AluY and one L1HS. We estimate that [~]1% of cells in the aged PFC have a somatic RTE insertion. AD samples were hypomethylated, and genome-wide analysis of differentially methylated regions (DMRs) supports a process of epigenetic drift in AD. DMR-associated gene sets primarily related to brain function and inflammation. To investigate L1 activation we used CpG methylation as a proxy for L1 expression. We observed decreased methylation at young L1 elements. While most reads overlapping the L1HS promoter were highly methylated (>80% methylated), 7% were <50% methylated, 1% were <25%, and the highly demethylated read fraction increased in AD. L1HS 5 UTR methylation was strongly correlated with RNA expression. ConclusionsCpG methylation-mediated repression of young RTEs is compromised in old age - our findings indicate that this is further exacerbated in AD. Amid these failing defenses, we report somatic retrotransposition events in the aging and demented brain.

genomics↗

bioRxiv2025

Senescence-Associated Chromatin Rewiring Promotes Inflammation and Transposable Element Activation

Cellular senescence is a stable form of cell cycle arrest that contributes to aging and age-associated diseases through the secretion of inflammatory factors collectively known as the senescence-associated secretory phenotype (SASP). While senescence is driven by transcriptional and epigenetic changes, the contribution of higher-order genome organization remains poorly defined. Here, we present the highest-resolution Hi-C maps ([~]3 kb) to date of proliferating, quiescent, and replicative senescent (RS) human fibroblasts, enabling a comprehensive analysis of 3D genome architecture during senescence. Our analyses reveal widespread senescence-associated remodeling of chromatin architecture, including extensive compartment and subcompartment switching toward transcriptionally active states, and a dramatic increase in unique chromatin loops. These structural features correlate with local DNA hypomethylation and are largely independent of canonical CTCF binding. The altered 3D genome landscape supports expression of SASP genes, inflammation-related pathways, and neuronal gene signatures consistent with age-associated epigenetic drift. We further demonstrate that architectural changes at multiple levels, including compartments, subcompartments, and loops, facilitate the derepression of LINE-1 retrotransposons, linking 3D chromatin structure to activation of proinflammatory transposable elements. Interestingly, quiescent cells, commonly used as senescence controls, exhibited substantial overlap in inflammatory gene expression with senescent cells, raising important considerations for experimental design. Structural analysis of cell cycle genes showed distinct chromatin configurations in senescence versus quiescence, despite similar transcriptional repression. Together, our results establish a high-resolution framework for understanding how genome architecture contributes to the senescent state.

genomics↗

bioRxiv2024

TE-Seq: A Transposable Element Annotation and RNA-Seq Pipeline

The recognition that transposable elements (TEs) play important roles in many biological processes has elicited growing interest in analyzing sequencing data derived from this mobile dark genome. The TE-Seq pipeline conducts an end-to-end analysis of RNA-sequencing data, examining both genes and TEs. It implements the most current computational methods tailor-made for TEs, enabling a comprehensive analysis of TE expression at both the individual element level and at the TE clade level. If supplied with long-read DNA sequencing data, it creates a TE-complete genome incorporating non-reference (polymorphic) TE-loci, enabling the functional characterization of the evolutionarily youngest mobile elements in the genome.

bioinformatics↗