Mechanical Regulation of Intestinal Morphology and Function

Abstract

The large absorptive surface area of the small intestine is imparted by finger-like projections called villi. Villi formation is instructed by stromal-derived clusters of cells which induce epithelial bending through actomyosin contraction. Their functions in the elongation of villi have not been studied. Here, we explored the function of mesenchymal contractility at later stages of villar morphogenesis. We induced contractility specifically in the mesenchyme of the developing intestine through inducible overexpression of the RhoA GTPase activator Arhgef11. This resulted in overgrowth of the clusters through a YAP-mediated increase in cell proliferation. While epithelial bending occurred in the presence of contractile clusters, the resulting villi had architectural defects, being shorter and wider than controls. These villi also had defects in epithelial organization and the establishment of nutrient-absorbing enterocytes. While ectopic activation of YAP resulted in similar cluster overgrowth and wider villi, it did not affect villar elongation or enterocyte differentiation, demonstrating roles for contractility in addition to proliferation. We find that the specific contractility-induced effects were dependent upon cluster interaction with the extracellular matrix. As small intestinal villi are highly dynamic structures, we also probed their ability to recover from the architectural abnormalities established in early embryonic stages. Remarkably, we find that villi can return to wildtype architecture in as little as 24 hours after the cessation of transgene expression. Together, these data reveal effects of contractility on villar morphogenesis,distinguish separable roles for proliferation and contractility in controlling intestinal architecture, and demonstrate the robustness of villus architecture in the early postnatal small intestine.Actomyosin contractility can be induced by many physiological and pathological inputs in the adult intestine as well. However, we have little understanding of how contractility impacts the intestinal epithelium on a cellular and tissue level. We probed the effects of contractility in the villar and crypt epithelial compartments, as well as the adult mesenchyme. We found that increased contractility in the villar compartment caused shape changes in the cells that expressed the transgene and their immediate neighbors. While there were no discernable effects on villar architecture or cell polarity, even low levels of transgene induction in the villi caused non-cell autonomous hyperproliferation of the transit amplifying cells in the crypt, driving increased cell flux through the crypt-villar axis. In contrast, induction of increased contractility in the proliferating cells of the crypts resulted in nuclear deformations, DNA damage, and apoptosis. Despite the dramatic effects seen in the epithelium, induction of contractility in the sub-epithelial telocytes of the adult small intestine do not result in any discernable phenotype, suggesting that this environment is highly tolerant do contractile cells. This study reveals the complex and diverse responses of different intestinal compartments to contractility and provides important insight into mechanical regulation of intestinal architecture and function.