Lgr5+ Stem Cells Maintain Apex Position in Cell Hierarchy of the Intestinal Epithelium During Homeostasis and Injury.

The cellular origin of intestinal epithelial homeostasis and regeneration has been a subject of continued debate, with recent models challenging the primacy of WNT-dependent Lgr5+ crypt base columnar (CBC) cells as the central intestinal stem cell population. Here, we revisit this question through quantitative integration of single-cell transcriptomic, chromatin accessibility, spatial, and lineage-tracing analyses across the proximal-to-distal axis of the small intestinal epithelium. Our data show that under homeostatic conditions, Lgr5+ cells exclusively sustain epithelial self-renewal in nearly all crypt-villus units along the entire length of the small intestine, a process for which R-spondin is indispensable. Following irradiation or chemotoxic injury, surviving Lgr5+ cells and their progeny reprogram into transient fetal-like cell states that initiate epithelial repair. Crucially, successful regeneration depends on the reactivation of canonical WNT/β-catenin signaling, as evidenced by increased TCF motif accessibility and upregulation of WNT target genes in newly forming Lgr5+ stem cells. Accordingly, pharmacological inhibition of WNT signaling blocks the reconstitution of Lgr5+ cells and crypt regeneration, leading to epithelial collapse. These findings reconcile prior controversies by demonstrating the central role of Lgr5+ CBC cells in epithelial self-renewal and regeneration following injury.