Accute and repeated DSS exposure induce distinct immune responses with differential relevance to human Ulcerative Colitis

Abstract

<h4>Background & aims</h4>Dextran sulfate sodium (DSS)-induced colitis is a widely used model to study ulcerative colitis (UC). However, the extent to which acute vs repeated DSS exposure mimics human disease remains unclear.<h4>Methods</h4>Using histopathology, flow cytometry, single-cell RNA sequencing (scRNA-seq), and 16S rRNA profiling, we compared disease outcomes, immune infiltrate, transcriptional programs, and changes in the microbiome in mice subjected to a single (acute) vs 2 (repeated) DSS cycles. We further evaluated which experimental condition better represents key immune cell subtype states in human disease.<h4>Results</h4>Although disease activity indices were similar between groups, repeated DSS exposure resulted in greater colon shortening, mucosal remodeling, and elevated immune infiltration, particularly by neutrophils (PMNs) in the distal colon. scRNA-seq revealed that PMNs and T cells acquired distinct transcriptional programs in repeated vs acute colitis. Cycle 1 PMNs showed inflammatory and cytotoxic signatures, whereas cycle 2 PMNs were enriched in tissue remodeling and survival pathways. CD4 and CD8 T cells in repeated colitis exhibited migratory, and pathogen-responsive phenotypes, with expanded regulatory T cells and exhausted CD8 subsets. In contrast, macrophage numbers decreased with repeated DSS, though remaining cells exhibited pro-resolution gene expression profiles. Microbiome analysis revealed normalization trends with repeated DSS exposure, including reduced proinflammatory and increased beneficial genera. Cross-species transcriptomic comparisons indicated cycle-specific overlap with human UC, where cycle 2 activated PMNs and alternatively activated macrophages, closer aligned with active human UC.<h4>Conclusions</h4>Collectively, our data indicate that repeated DSS cycles provide a better experimental colitis model for studying immune cells in UC and identifying distinct immune subtypes relevant to UC therapeutics.