Transitional Anal Cells Mediate Colonic Re-epithelialization in Colitis.

BACKGROUND & AIMS: Epithelial wound healing is compromised and represents an unleveraged therapeutic target in inflammatory bowel disease (IBD). Intestinal epithelial cells exhibit plasticity that facilitates dedifferentiation and repair during the response to injury. However, it is not known whether epithelial cells of a neighboring organ can be activated to mediate re-epithelialization in acute colitis. Histological findings of a permanent squamous tissue structure in the distal colon in human IBD could suggest diverse cellular origins of repair-associated epithelium. Here, we tested whether skin-like cells from the anus mediate colonic re-epithelialization in murine colitis. METHODS: We studied dextran sulfate sodium-induced colitis and interleukin 10-deficient colitis in transgenic mice. We performed lineage tracing, 3-dimensional (3D) imaging, single-cell transcriptomics, and biophysical modeling to map squamous cell fates and to identify squamous cell types involved in colonic repair. RESULTS: In acute and chronic colitis, we found a large squamous epithelium, called squamous neo-epithelium of the colon (SNEC), near the anorectal junction. Neighboring squamous cells of the anus rapidly migrate into the ulcerated colon and establish this permanent epithelium of crypt-like morphology. These squamous cells derive from a small unique transition zone, distal to the border of colonic and anal epithelium, that resists colitic injury. The cells of this zone have a pre-loaded program of colonic differentiation and further upregulate key aspects of colonic epithelium during repair. CONCLUSION: Transitional anal cells represent unique reserve cells capable of rebuilding epithelial structures in the colon after colitis. Further study of these cells could reveal novel approaches to direct mucosal healing in inflammation and disease.

Persistence of Lgr5+ colonic epithelial stem cells in mouse models of inflammatory bowel disease.

Intestinal mucosal healing is the primary therapeutic goal of medical treatments for inflammatory bowel disease (IBD). Epithelial stem cells are key players in the healing process. Lgr5+ stem cells maintain cellular turnover during homeostasis in the colonic crypt. However, they are lost and dispensable for repair in a wide variety of injury models, including dextran sulfate sodium (DSS) colitis, radiation, helminth infection, and T-cell activation. The direct loss of Lgr5+ cells activates a plasticity response in the epithelium in which other cell types can serve as stem cells. Whether this paradigm applies to mouse models of IBD remains unknown. In contrast to previously tested models, IBD models involve an inflammatory response rooted in the loss of immunologic tolerance to intestinal luminal contents including the microbiome. Here, we show the persistence of Lgr5+ cells in oxazolone, 2,4,6-trinitrobenzene sulfonic acid (TNBS), and Il10-/-, and Il10-/- Tnfr1-/- IBD models. This contrasts with results obtained from DSS-induced injury. Through high-throughput expression profiling, we find that these colitis models were associated with distinct patterns of cytokine expression. Direct exposure of colonic epithelial organoids to DSS, oxazolone, or TNBS resulted in increased apoptosis and loss of Lgr5+ cells. Targeted ablation of Lgr5+ cells resulted in severe exacerbation of chronic, antibody-induced IL-10-deficient colitis, but had only modest effects in TNBS-induced colitis. These results show that distinct mouse models of IBD-like colitis induce different patterns of Lgr5+ stem cell retention and function.NEW & NOTEWORTHY Acute intestinal injury and epithelial repair are associated with the loss of fast-cycling Lgr5+ stem cells and plasticity in the activation of formerly quiescent cell populations. In contrast, here we show in murine inflammatory bowel disease the persistence of the Lgr5+ stem cell population and its essential role in restricting the severity of chronic colitis. This demonstrates a diversity of stem cell responses to colitis.

Wound-healing plasticity enables clonal expansion of founder progenitor cells in colitis.

Chronic colonic injury and inflammation pose high risks for field cancerization, wherein injury-associated mutations promote stem cell fitness and gradual clonal expansion. However, the long-term stability of some colitis-associated mutational fields could suggest alternate origins. Here, studies of acute murine colitis reveal a punctuated mechanism of massive, neutral clonal expansion during normal wound healing. Through three-dimensional (3D) imaging, quantitative fate mapping, and single-cell transcriptomics, we show that epithelial wound repair begins with the loss of structural constraints on regeneration, forming fused labyrinthine channels containing epithelial cells reprogrammed to a non-proliferative plastic state. A small but highly proliferative set of epithelial founder progenitor cells (FPCs) subsequently emerges and undergoes extensive cell division, enabling fluid-like lineage mixing and spreading across the colonic surface. Crypt budding restores the glandular organization, imprinting the pattern of clonal expansion. The emergence and functions of FPCs within a critical window of plasticity represent regenerative targets with implications for preneoplasia.