GSE134249
Erk1/2 mediated negative feedback regulation is essential for postnatal intestinal development and homeostasis
Objective: Homeostasis of intestinal stem cells (ISCs) is maintained by external niche signals and complicated intrinsic signaling networks. Mitogen-activated protein kinase (MAPK) cascades play pivotal roles in stem cell self-renewal and differentiation, but the functions and underlying molecular mechanisms are not fully understood. Design: We performed studies with mice deletion of Erk1/2 genes in intestinal epithelial cells at embryonic stages or a control mice. Intestinal tissues were collected and analyzed by histology, gene expression profiling, immunohistochemistry, immunfluorescence, western blotting and organoid culture. Organoids were treated with specific inhibitors for Ras or Akt activity. Mice were treated by intraperitoneal injection of rapamycin to inhibit mTOR signaling. Results: We found that deletion of Erk1/2 genes resulted in an unexpected increase in cell proliferation and migration, expansion of ISCs and formation of polyp-like structures, leading to postnatal death. Deficiency of epithelial Erk1/2 strongly impaired secretory cell differentiation and enterocyte maturation with aberrant Wnt signaling activation. Erk1/2 depletion resulted in loss of feedback regulation leading to Ras/Raf cascade activation. Ras then transactivated Akt activity to stimulate mTOR and phosphorylate ß-catenin on Ser552. Suppression of Ras or Akt activity through specific inhibitors significantly repressed Akt downstream signaling and restored cell proliferation and differentiation phenotypes ex vivo. Moreover, inhibition of mTOR signaling by rapamycin partially rescued Erk1/2 depletion-induced intestinal defects and significantly prolonged mutant mouse life span. Conclusions Our study demonstrates an unexplored critical role of ERK/MAPK pathway negative feedback regulation of Akt/mTOR in intestine development and homeostasis, suggesting a complicated regulatory network in ISC function. Overall design: Small intestine mRNA profiles of 14-day old wild type (WT) and Erk1/2 -/- mice were generated by deep sequencing, in triplicate, using HiSeq 2000.