Developmental and epigenetic remodeling of inflammation in the aging human innate immune system 2238939

Abstract Introduction Epigenetic alterations and chronic inflammation are hallmarks of aging, shaped by lifelong exposure to environmental, infectious, and psychosocial stressors in humans. Advances in systems biology approaches enable interrogation of these processes directly in humans. We tested the hypothesis that aging reprograms hematopoietic stem cells (HSCs), producing myeloid progeny epigenetically poised for chronic inflammation. Methods In two human cohorts, we assessed inflammation using in vitro stimulation and spectral flow cytometry. In selected individuals, we performed single-cell multiome (ATAC+RNA, scMultiome) sequencing of myeloid cells. Results were validated in publicly available single-cell multiome datasets. Results Myeloid cells from older adults showed a higher pro-inflammatory response to stimulation, which was associated with enhanced chromatin accessibility at AP-1 transcription factor motifs, reproducible across four independent datasets. Enhanced AP-1 accessibility led to transcriptional responses associated with inflammation. Because circulating myeloid cells are short-lived, we examined whether the epigenetic remodeling originates in myeloid precursors. Pseudotime trajectory analysis of scMultiome data supports this model, showing increased AP-1 accessibility in HSCs from older adults, pointing to an inflammatory origin in stem cells. To directly assess lineage output and clonal fitness of AP-1-poised HSCs, we leveraged mitochondrial DNA variants as natural barcodes for lineage tracing in humans. Clonotype analysis revealed a polyclonal increase, without selective expansion of AP-1hi HSCs. Nonetheless, AP-1hi HSCs produced a higher proportion of AP-1hi monocytes, though the effect was modest, suggesting that circulating inflammatory mediators reinforce epigenetic poising. Conclusion Our results reveal a developmental origin of inflammatory poising in aging myeloid cells, with AP-1-remodeling as a molecular driver of innate immune aging, and potential target to treat inflammaging. Funding Source University of Arizona Start-up Funds Topic Categories Immune Response Regulation: Cellular Mechanisms (IRC)