The Colonic Crypt: Cellular Dynamics and Signaling Pathways in Homeostasis and Cancer.

Abstract

The goal of this review is to expand our understanding of how the cellular organization of the normal colonic crypt is maintained and elucidate how this intricate architecture is disrupted during tumorigenesis. Additionally, it will focus on implications for new therapeutic strategies targeting Epithelial-Mesenchymal Transition (EMT). The colonic crypt is a highly structured epithelial unit that functions in maintaining homeostasis through a complex physiological function of diverse cell types: SCs, transit-amplifying (TA) progenitors, goblet cells, absorptive colonocytes, Paneth-like cells, M cells, tuft cells, and enteroendocrine cells. These cellular subpopulations are spatially organized and regulated by multiple crucial signaling pathways, including WNT, Notch, Bone Morphogenetic Protein (BMP), and Fibroblast Growth Factor (FGF). Specifically, we discuss how these regulatory networks control the precise locations and functions of crypt cell types that are necessary to achieve cellular organization and homeostasis in the normal colon crypt. In addition, we detail how the crypt's hierarchical structure is profoundly perturbed in colorectal cancer (CRC) development. Tumorigenesis appears to be driven by LGR5+ cancer stem cells (CSCs) and the hyperproliferation of TA cells as colonocytes undergo metabolic reprogramming. Goblet cells lose their secretory phenotype, while REG4+ Paneth-like cells foster SC niches. Tumor microenvironment is also disrupted by upregulation of M cells and by tumor-immune crosstalk that is promoted by tuft cell expansion. Moreover, the presence of enteroendocrine cells in CRC has been implicated in treatment resistance due to its contribution to tumor heterogeneity. These cellular changes are caused by the disruption of homeostasis signaling whereby: overactivation of WNT/β-catenin promotes stemness, dysregulation of Notch inhibits differentiation, suppression of BMP promotes hyperproliferation, and imbalance of FGF/WNT/BMP/NOTCH enhances cellular plasticity and invasion. Further discussion of emerging therapies targeting epithelial markers and regulatory factors, emphasizing current development in novel, precision-based approaches in CRC treatment is also included.