LAUSR

BACKGROUND Aspirin (ASA) is a proven chemoprotective agent for colorectal cancer, though mechanisms underlying these effects are incompletely understood. Human organoids are an ideal system to study genomic and epigenomic host-environment interactions. We utilize human colonic organoids to profile ASAresponses on genome-wide gene expression and chromatin accessibility. METHODS Human colonic organoids from one individual were cultured and treated in triplicate with 3mM ASA or vehicle control (DMSO) for 24 hours. Gene expression and chromatin accessibility were measured using RNA- and ATAC-sequencing, respectively. Differentially expressed genes were analyzed using DESeq2. Top genes were validated by qPCR. Gene set enrichment was performed by SetRank. Differentially accessible peaks were analyzed using DiffBind and EdgeR. Peak annotation and differential transcription factor motifs were determined by HOMER and diffTF. RESULTS The results showed robust transcriptional responses to ASA with significant enrichment for fatty acid oxidation and PPAR signaling that were validated in independent organoid lines. A large number of differentially accessible chromatin regions were found in response to ASA with significant enrichment for Fos, Jun and Hnf transcription factor motifs. Integrated analysis of epigenomic and genomic treatment responses highlighted gene regions that could mediate ASA's specific effects in the colon including those involved in chemoprotection and/or toxicity. CONCLUSIONS Assessment of chromatin accessibility and transcriptional responses to ASAyielded new observations about genome-wide effects in the colon facilitated by application of human colonic organoids. This framework can be applied to study colonic ASA responses between individuals and populations in future studies.